Transition from Extensive to Intensive Agriculture with Fertilizers

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Tran itio1fo Exensive to intensive

ithvr~tio.a1 _Potash Ihstiut 1969 Transition from Extensive to Intensive Agriculture with Fertilizers

Proceedings of the VIIth Colloquium of the International Potash Institute held in Israel 1969 Contents

Opening Session

Dr. R. HAEBERLI Opening Address I I

Prof. Dr. 1.ARNON Transition from Extensive to Intensive Agri- culture in Israel with Fertilizers 13

1st Working Session: Attaining Maximum Yield

Prof. Dr. K. MENGEL Factors Limiting Maximum Yield 27

Dr. J. WARREN WILSON Maximum Yield Potential 34

Dr. M.THIELEBEIN Plant Breeding for Increased Efficiency Dr. W. M.TAHIT in Fertilizer Use 57

Discussion, Session No. I 69

Dr. G.W.COOKE Co-ordination Lecture for Session No. 1 71

2nd Working Session: Irrigation and Nutrient Uptake

Dr. G.W. COOKE Plant Nutrient Cycles 75

G. DROUINEAU Influence of Irrigation on the Distribution of Fertilizer Elements in the Soil Profile 96

Discussion, Session No. 2 106

A. DAM KOFOED Co-ordination Lecture for Session No. 2 107

3rd Working Session: Interaction between Nutrition and other Factors of Plant Growth

Dr.D.SH[MSHI Interaction between Irrigation and Plant Nu- trition III 5 R. BLANCHET Some Interactions of Cation Nutrition and M. Bosc the Water Supply of Plants 121 C. MAERTENS

Dr. ELOY MATEO-SAGASTA The Interaction between Irrigation and Plant AZPEiTiA Diseases 132

D.LACHOVER Iron Deficiency Problems in Peanuts under ADELINA EBERCON Irrigation 138

Prof. G.C.CHISC( Interaction between Irrigation and Fertiliza- tion in Mediterranean Grassland 144

Dr. A. BAR AKIVA Methods of Diagnosing Nutrient Deficiencies in Citrus 160

Discussion, Session No. 3 168

G. DROUINEAU Co-ordination Lecture for Session No. 3 171

4th Working Session: Economics and Planning of Fertilizer Use

Prof. Dr. H. RUTHENBERG The Economics of Introducing Fertilizer 175

Prof. J.HAGN Problems of Fertilizer Requirement Predic- tion in Intensive Agriculture 185

L.AUDIDIER New Trends in the Use of Fertilizers, New Products and New Techniques of Application 190

M. HASEGAWA Changes in Agriculture and Fertilizer Use in Japan 197

Prof. E.YALAN The Place of the Second Generation in Rural Space 208

Discussion, Session No. 4 222

Prof. Dr. H.LAUDELOUT Co-ordination Lecture for Session No. 4 225

5th Working Session: Educating the Farmer for the Transition from Extensive to Intensive Agriculture

G. FRADKIN Training of Agricultural Extension Officers 229 6 T. GANS The Impact of Courses for Fertilizer Techni- cians 234

Dr. J. Noy Irrigation and Fertilizer Extension 237

Discussion, Session No. 5 241

Dr. Th.WALSH Co-ordination Lecture for Session No. 5 243

Lectures held during technical Agricultural Research and Fertilizer Use excursions in Israel

Dr. M. GISKIN Problems of Plant Nutrition and Fertilizer A. MAJDAN Use on Huleh Muck Soils 249

Dr. Z. KARCHI Nitrogen Fertilization of Wheat in Israel 253

SH. H. DAJANI Short Outline on Agriculture in the West Bank 262

Dr. D.SHIMSHI Irrigation of Wheat in the Northern Negev 265

Dr. SH. FELDMAN Transition from Extensive to Intensive Agri- culture with Fertilizers in the B'sor Area Israel 267

D.SADAN Soil Tests for Fertilizer Recommendations D. MACHOL under Extensive Conditions 277 Dr. U.KAFKAF

Dr. R. HAEBERLI Closing Address 281

7 Opening Session

Chairman of the Colloquium: Prof. Dr.i.Arnon, Honorary Director of the Volcani Institute of Agricultural Research (N.U.I.A.) Israel; Member of the Scientific Board of the Inter- national Potash Institute Opening Address

Dr. R_ HAEBERLI, Member of the Board of Administrators of the International Potash Institute

Before the meeting starts, my first duty is to convey to you thebest wishes ofDr. Gallay, President of the Scientific and Administrative Boards of IPI and to excuse him for not being there. Dr. Gallay having not recovered from a severe illness has unfortunately not been allowed by his medical doctor to attend the Colloquium. Giving me the honour of speaking in his name as Swiss member of the Board of Administrators of the International Potash Institute, he entrusted me to express his deep regrets, the more so as he was particularly interested in the subject of the Colloquium and also as he would have greatly appreciated this opportunity of visiting again Israel. The theme adopted for the Colloquium Transitionfrom Extensive to Intensive Agri- culture with Fertilizerscould not suit better another country than Israel. Israel, within a few years in often unhealthy and difficult conditions has been able through a prodi- gious amount of undiscouraged efforts, and clever and hard work to transform her agriculture into a modern agriculture supplying the major part of the food requirements of her people and also exporting in increasing quantities to distant countries top quality products, results of a high level of intensification. International Conferences and Congresses organized recently have been dealing already with the general aspects of the transition from traditional to modem agriculture, trying to point out the technical, social, and economical obstacles to the evolution of agriculture. None of them however have been considering in details the role played by fertilization, factor of production, which is regarded with right as a good criterium of agricultural intensification. In adopting as theme of a Colloquium the Role of Fertilizers in the Transition from Extensive to Intensive Agriculture, the International Potash Institute will, I trust, open new ways. The sessions and the excursions foreseen by the programme, will give the opportunity to recall the rapid evolution undergone by the agriculture of Israel as example of a mediterranean country, and to study how fertilization together with the other factors of production can still contribute to further the intensification. But I would blame myself of insisting too much on these aspects, that those who have been in charge of preparing the programme know much better than I do. Before expressing them my gratitude I should like to say to Mr.Maas representing the Minister of Agriculture of Israel, how we are honoured to be able to open the Col- loquium in his presence. I dare say that we find there a mark of interest of the Officials of Israel for our Collo- quium. I should like also to compliment you on the beautiful Auditorium and campus in which our opening session takes place. It shows in itself how well balanced have been the efforts made in intensifying your agriculture, since this campus is one II of the main educational center for the research and extension officers engaged in agriculture. I should like to express my gratitude to Prof. Arnon, Honorary Director of the Vol- cani Research Institute of Agriculture who kindly accepted to be chairman of this Colloquium whose main features were suggested by him on occasion of one of the last meetings of the Scientific Board of the International Potash Institute. My best thanks have to be extended to all the members of the Scientific Board of the International Potash Institute but first of all to Dr. Cooke, Deputy Director and Head of the Chemistry Department of Rothamsted Experimental Station (U. K.) and to Mr. Drouineau, Inspecteur Gdndral de la Recherche Agronomiqu (France), who have always been ready to give their valuable assistance in preparing this programme. I wish to address my warm welcome to all the participants of this colloquium and especially to the lecturers and authors of communications who in spite of many other com- mitments have agreed to contribute to this meeting and to introduce the results of their research, to the coordinators of the sessions, and to all the scientists attending these sessions. It is perhapsjustified before the opening of the sessions to recall briefly the main activities of the International Potash Institute. Today, we observe two very clear tendencies which are increasing all the time. The one is the growing complexity of agronomic problems, which leads research workers to specia- lise more and more. The other is the ever more pressing economic requirement which compels the farmers to use fertilizers in the way that will give them the maximum benefit. The International Potash Institute in its particular field tries to fill the gap between these tendencies and without dissociating the potassium from the other plant nutrients aims at collecting and spreading to all those concerned with increasing agricultural yields by the proper use of fertilizers, the most recent results of scientific research. The activities of the International Potash Institute may be classed in two groups, i. e., internal and external activities. The first comprise, notably the collection of a copious scientific literature (technical publications and original works), its study and classifica- tion and the making of card indexes covering the various problems relating to potassium. The list of external activities is very varied. The chief ones are the editing and publication of a monthly Review = The Potash Review, of a Press-Bulletin = International Fertilizer Correspondent, the organisation of Congresses and Colloquia, the sending of missions abroad. Such a wide set of activities could not be completed without a regular cooperation with a Scientific Board, consisting of 15 research workers who are in the first rank in the domain of Agronomy in their own countries and have established international reputation. It is this Scientific Board, which chooses the themes of the Congresses and Colloquia, de- fines their frame and suggests the countries where they should take place, as well as the names of the speakers to be solicited. Further to a cycle of meetings dedicated to the vast and complex problem of the influence of potash and other nutrients on the quality of food crops, a new cycle has been started in 1967, on the Role of Fertilization in the Intensification of the Agricultural Pro- duction. The first Colloquium belonging to this cycle was devoted to Forest Fertiliza- tion, Colloquium ofJyvgskyli, Finland; the second studied the Fertilization of Protected Crops, Colloquium of Florence, Italy 1968. Today opensa third Ccllcquium on an interesting question of the moment to the success of which I formulate my best wishes. 12 Transition from Extensive to Intensive Agriculture in Israel with Fertilizers

Prof. Dr. I. ARNON, The Volcani Institute of Agricultural Research (N.U.I.A.) Bet Dagan (Israel)

1. Background

1.1 Available land and water resources

Israel is a small country of 21,000 km'. About 20% of the area is cultivable, the rest being too steep, rocky or shallow for cultivation. Nearly all the land suitable for agricultural use without special reclamation works is already under cultivation. The main and essential development of recent years was therefore an increase in the irrigated area. The total water resources of the country available to agriculture annually are estimated 3 at 1035 million m [3], which are already almost entirely exploited. This amount irri- gates an area of 165,000 ha [2]. Water is therefore the limiting factor in further development. As all the available conventional and relatively cheap water resources are already being used, future development will have to rely on far more costly means, derived from floodwater control, reclaimed sewage, salt water conversion, etc.

1.2 Ecological conditions

In the northern part of the country, the climate is typically Mediterranean. Aridity increases with decreasing latitudes, and the southern half of the country is desert. Where winter rainfall exceeds 350-400 mm, a single crop can be grown annually, either during the cool rainy season, or during the rainless summer on soil-stored moisture. In areas with less than 300 mm average rainfall, production of winter cereals is sporadic with frequent crop failures. The low-rainfall areas are mainly used by Bedouins for grazing flocks of sheep, goats and camels.

1.3 Mineral and energy resources

The country has few mineral resources, which consist mainly of potassium, phosphorus and a small amount of copper. Energy resources are still more limited: there are no by- dro-electric sources and the local output of oil and natural gas accounts for only about 10 Y of the present requirements.

13 1.4 Politicalbackground

The hostile political environment in the Middle East has economic implications in Is- rael: normal commercial relations with neighbouring countries are nonexistent; communication lines are lengthened and more expensive; an enormous proportion of the GN. P. is devoted to defense; and production is hampered by frequent military call-ups.

1.5 Agrarian population

Approximately 110,000 persons, out of a total population of over 2,600,000, are employed in agriculture; i.e., 12.4 % of the total labour force. This figure includes 68,000 independent farmers and members of collective agricultural settlements, and 42,000 wage earners [2]. Ifefficient production was the only motive, their number could be reduced, mainly by increasing the size of the farm unit. Other considerations, however, are opposed to such a trend: security needs which require a relatively large and dispersed agricultural population; and social trends favouring family-sized farms and opposed to the establishment of large managerial farms - whether private or government-owned.

2. Patterns of change and development

2.1 The evolution of Israel's Agriculture

2.1.1 The first phase (before the establishment of Israel)

The earliest agricultural settlements were established in those parts of the country where rainfall was sufficient to produce one crop a year. The first attempts at farming, based on Arab traditional-type farming, showed clearly that an acceptable standard of living could not be expected without drastic changes in production methods and commodities. Diversified farms, based on the integration of animal husbandry and arable cropping, were therefore established. Such diversification made possible a balanced labour schedule throughout the year, based entirely on family labour; improved management practices led to increased yields.

2.1.2. The second phase: Irrigation

The erratic and relatively low rainfall of Israel leaves very little scope for diversification or for intensification of production. The choice of crops adapted to these conditions is limited, and yield levels are as erratic as the rainfall. After the establishment of the State of Israel high priority was therefore given to the development of the water resources of the country. Irrigated areas increased five-fold, at an average rate of 8000 ha per year [2]. Settlements were established in the drier areas, and the density of settlement in the higher rainfall areas, was increased by re-allocation of the land. Cropping became more diverse and industrial crops (cotton, sugar beets) and fruit production increased rapidly. 14 2.1.3 The third phase Israel now produces most of the food and fibres she needs, excepting a few relatively low- cost commodities. With the factors of production available to them, Israel's farmers are capable ofproduc- ing far in excess of the capacity of the local market. Further agricultural expansion must be for export, using advanced methods and taking advantage of Israel's mild, sunny winter. Export crops are of two kinds: sub-tropical fruits, such as citrus, avocado, mango, etc.; and vegetables and flowers that can be grown for the European markets under relatively inexpensive protection, when production in Europe is low or nonexistent. Producing for the export market requires a high degree of professional skill, large investments, and a highly organised system of transport, marketing and quality control. The periods during which prices are sufficiently high tojustify the efforts and investments involved are very short, quality requirements are very stringent, and competition from other countries is great. Export of agricultural commodities increased from S17 million in 1950 (mostly citrus) to $122 million in 1966 [2].

2.2 Changes in objectives andstrategy In a dynamic agriculture a constant reappraisal of objectives and strategy is essential.

2.2.1 Yields At first, the shortage of all commodities made it imperative to increaseyieldsper unit area as rapidly as possible. A considerable research effort, and rapid translation of research results into farming practices have achieved very high yield levels in all commodities produced. Analysing the average annual increase in agricultural production in 48 countries, a recent FAO report found that in only five countries: Greece, Israel, Japan, Mexico and Yugoslavia had production increases exceeded population growth by an average of 4-6 each Y year. Of these countries only two, Israel and Mexico, have had population increases that have been more than fairly moderate. At this point, it may be appropriate to indicate the role fertilizers played in increasing production at every phase of agricultural development. In dryland agriculture, it was found that an improved crop rotation, including a leguminous crop for forage, was the first essential to increased production, and provided the basic framework within which other factors of production, such as improved varieties, new crops and improved tillage methods could be effective in increasing productivity. However, the backbone of these rotations, the legumes, were absolutely dependent on fertilizers without which they produced negligeable yields. Even cereals, within the improved crop rotation, were not able to reach high yield levels without appropriate fertilizer applications. Since the introduction of dwarf wheats, yield levels of 4000 to 5000 kg of grain per hectare have become commonplace. The introduction of irrigation made it essential for the farmer to break away from the fairly cautious habits of fertilizer use that are normal in rain-fed agriculture, where risks

15 of drought are relatively great and where excessive or inappropriate fertilizer applications may accentuate the harmful effects of moisture deficiencies. The need for adapting farming practice to the needs and potentialities of irrigation farming can be best illustrated by the changes that have occurred in the use of fertilizers. One has been of the most striking innovations in agricultural practice in Israel in recent years experi- the high rates of application of fertilizers used in irrigated areas. During early those mental work with irrigated crops, rates that were 25, 50 or 100% greater than these which were customary for dryland crops were tested. The responses obtained from additional amounts were generally so unspectacular that they created the impression was only that further increases from fertilizer application were not to be expected. It the po- when rates of application were increased three- and fourfold and even more, that use tentialities of fertilizer application as a means of increasing the efficiency of water limited the were fully realised. It is true that, for certain crops, factors other than yield to avoid amounts of fertilizer that could properly be used: with cotton it was necessary me- excessive vegetative growth, as this increased the costs of handpicking and made af- chanical picking impracticable; with sugar beet, excessive N fertilization adversely ability to fected sugar content; the wheat varieties available did not yet have the genetic make full use of high fertility levels, and responded by lodging and increased incidenceof of fertili- disease. For these crops the development of varieties adapted to the high levels In the case of ty which are possible with irrigation, is a major challenge to plant breeders. irrigated pas- other crops, such as maize for grain or forage production, fodder beets, achieved by tures, and many vegetable crops, really astonishing yield increases were heavy fertilizer dressings. The most consistently spectacular responses were obtained from nitrogenous fertilizers. for ir- Rates of up to 200 kg N/ha for maize, 300 kg for stock beets, and 500 kg and more costs involved rigated pastures, have given economic returns. Indeed, in view of the high in fact afford in irrigation farming, high yields are an economic necessity and one cannot not to apply fertilizer at these high rates. in the rate The heavy dosage of nitrogen used almost automatically called for an increase in this ele- of application of phosphate fertilizers. Most of the soils of the region are poor on the ment. However, response to phosphates is often erratic, and largely dependent proportion fertilizers applied to previous crops in the rotation. Only a relatively small However, (5-10 Y) of the phosphatic fertilizer is used by the crop to which it is applied. phosphate in the the excess is not lost but contributes to the building up of reserves of at the rate soil. It is therefore not surprising that, after several consecutive applications to further applications of phosphate of 150-200 kg P2O5 per ha, the response of crops of phosphatic tends to become erratic. Thus it can be argued quite logically that the rates but to those fertilizers should be adjusted, not to the requirements of the individual crops of the crop rotation as a whole. in potash. Most of the soils of the Mediterranean region are known to be relatively rich cropping, lib- With the relatively low yields usually obtained once a year under dry-land with the removal eration of available K from the soil has usually been able to keep pace of this element by crops. is usually When irrigation is first practised on these soils, response to K fertilizers static. meagre. However, it has been found that this situation is not necessarily improved The high yields levels made possible by the combination of heavy fertilization, pro- varieties, better cultural operations and systematic crop protection and continuous rate. We al- duction are exhausting the potassium reserves of the soil at an increasing 16 ready observe typical potassium deficiency symptoms in fields of cotton, lucerne an other crops; symptoms we formerly knew only from text-books or from visits to European farms. In citrus and deciduous fruit trees, potassium deficiencies are also becoming increasingly evident. With the advent of crop production under protection, the approach to fertilizer use has again changed radically. The differences are both quantitative and qualitative. In the field, fertilizer costs constitute about 10-15 % of the costs of production, whilst in fully protected crops with controlled environment they may fall as low as 0.5-1 %, so that economic considerations that apply in the field are not relevant to greenhouse production. The plants growing in greenhouses are characterised by a very high foliage: root ratio, and they have to take up enormous amounts of nutrients with a very small root system. Therefore, fertilizers are applied at rates used farabovethose normallyused inotherenvi- ronments, and non-conventional methods of fertilizer application are indicated. The development of semi-automatic and automatic irrigation makes it practical to apply water and nutrients frequently, at very close intervals, and the soil as a source of nutrients becomes of secondary importance.

2.2.2 Costs of production

As long as the main problem was to obtain an assured supply of essential commodities, costs ofproduction were not of primordial importance. The main item was the high cost of labour, and labour was relatively abundant in the early stages of development. However, the point was eventually reached at which economic considerations became of major concern. Costs of production in Israel are generally high, compared with international standards, because of the small size of average holdings, high labour costs due to the government policy of not discriminating in wage levels against rural labour, and the extremely high cost of water (see below).

2.2.3 Efficiency of production

Labour was not only costly, but output, expecially in operations requiring manual labour, was very low, because many of the new immigrants were not accustomed to manual farm work and their physique was very poor. The rapid expansion of industry, building, and services, also resulted in a shortage of labour available to agriculture, so that the next important objective was to reduce the labour component of production, by mechanisation and increased efficiency inproduction. Between 1950 and 1965, labour efficiency increased at an average annual rate of approximately II Y [5]. Mechanisation also advanced rapidly; e.g., the number of tractors increased from630 in 1948 to 12,300 in 1966. Efficiency in production is not dependent on mechanisation alone. Biological methods, such as chemical weep control, the use of monogerm seed of sugar beets, the breeding of varieties that require less labour and the adoption of cultural practices reducing labour requirements, all contributed to increased labour efficiency. For example, in ten years, the number of work days involved in the production of peanuts decreased from 80 to 30 per ha, in sugar beets from 60 to 20 per ha, and in cotton from 120 to 17 per ha.

2 17 2.2.4 Water requirements

After the more conventional and least expensive sources of water had been fully developed it was quite clear that water would be expensive, and that the total amount available would not suffice for the area that could be irrigated. The cost of irrigation water to the farmer is extremely high, 2-3c per m 3, which is equivalent to $120-190 per hectare (6000 m 3/ha). In most countries, $35 to $50 per ha would be considered prohibitive and seldom used for irrigation. The cost of water is high in Israel, because of the great expense involved in water development and transportation; the altitude to which it must be pumped, the cost of power generated from imported fuel, and high depreciation costs of imported equipment. Therefore a major research effort was devoted to increasing the efficiency of water use mainly by improving techniques of water application, economizing on the quantity of water per unit area, in particular during the less-critical periods of growth, and increasing yields by heavy fertilization and other improved cultural practices. In the period 1959 to 1964, the water requirements per hectare were reduced by 150/,, whilst yields per unit area increased [4].

2.2.5 Quality

At present, with the emphasis on export crops, increasing efforts are devoted to improving quality - by improved techniques of handling, processing, storing and marketing agricultural produce.

2.3 Change and development

The patterns of change and development of agriculture in Israel cannot be understood without an awareness that different groups of farmers have been involved, with basic differences in tradition, cultural and economic levels and social organisation. Hence, agricultural change in Israel actually relates to a number of concurrent 'case histories', of different groups whose development has evolved on different lines and proceeded at different speeds, within the overall framework of agricultural change described above.

2.3.1 The early settlers

There are three main groups of Jewish farmers: a) The small 'first wave' immigrated at the end of the nineteenth century, mainly from Russia. They had the ideal of rebuilding Israel and many of them were highly educated, but had no social ideology and knew nothing of agriculture. They founded a few villages in the centre and north of the country, where they owned their lands, and employed hired labour. Their first attempts with unirrigated production of almonds and vineyards failed, because yields and prices were low. In the north, with its abundant rainfall, they became cereal farmers like the fellaheen and made no progress. In the coastal plain, where groundwater is relatively abundant they developed citrus plantations and irrigated vineyards. 18 The villages 'Moshavot' became similar in organisation, outlook and structure to villages in the developed regions in the world. A number of them have since evolved into small provincial towns. b) The 'Second wave'. These immigrants came mainly from Russia and Poland in the years up to the First World War. They were educated, middle class people who worked to establish a new social order, as well as to rebuild a Jewish national home. They established novel agricultural settlements, based on national ownership of the land, and on communal or cooperative communities: the Kibbutz and the Moshav ovdim. The kibbutz is a collective agricultural settlement grouping families in a community in which all resources are owned jointly, all able-bodied adults form a single labour force, and no salaries are paid. All the economic activities of the settlement are planned by an elected management, and the members work according to directives of the management. The education of the kibbutz farmers, their eagerness to adopt new techniques and develop new branches of production, their social organisation which enables the training of specialists in all branches, have made possible the high productivity and efficiency achieved in agriculture. The moshav ovdimn is a village consisting of individual family farms, of equal size(3-5 ha) and productivity. No labour is hired, but mutual aid is the rule in periods of peak labour requirements. A cooperative framework embraces most of the economic activities of the village, including purchase of equipment and consumer goods, sales of farm produce, and joint enterprises such as village tractor station, credit, provident funds, educational and social facilities, etc. The farms were originally 'mixed', producing a little of everything, mainly for their own consumption. Now the trend is towards specialisation: a number of farm types have evolved, based respectively on dairy production, citrus-and-vegetables, field crops, poultry-and-vegetables, and vegetables-and-orchards. These specialised farms are not monocultural but emphasize one or two branches of production, according to regional conditions. Because these family farms are small they cannot take full advantage of modern methods, particularly large-scale mechanisation. To overcome these problems of scale they have consolidated areas of crops, such as cereals and industrial crops, so that they can work them with machinery from a cooperative pool, and they have encouraged labour intensive, high value crops such as flowers, strawberries and vegetables under protection, in which the family farm has an advantage and in which economies of scale are not of overriding importance. Whatever the solution adopted, the family farm remains handicapped in its ability to ad- just to modern technology. It is, however, the only form adapted to the outlook and wishes of a large proportion of the farming community.

2.3.2 Immigration after the establishment of the State of Israel

After 1947, more than half of the settlers who arrived came from the underdeveloped countries of North Africa and Asia. They were destitute and uneducated. They were not motivated by ideals; and though they were directed into agriculture they had neither the ability nor the physique to become farmers. Self-government and cooperation were entirely alien to their mentalities. The transition from town to village life was a traumatic shock in most cases. Work morale and output in manual labour were very low. Population turnover has been considerable; in some vil- 19 lages not more than one out of three of the original families remained after a few years. It was clear from the outset that the family-farm was the only form suitable for absorbing these immigrants into agriculture, and that it would be a long and difficult process to get them accustomed to cooperative procedures. After much trial the following procedure was finally adopted: When new immigrants were established in a village, the lands were first administered as a kind of state farm. The villagers built their permanent homes, planted orchards, and grew industrial and vegetable crops, etc. After they had acquired sufficient experience and self-reliance, each villager received his allocation of land, loans of equipment and materials, and began to run his farm independently. By this time, the orchards already ensured some income. During the training period he was considered an occupant, later he became the owner of his farm. After this, the development of the villages followed the pattern of the older moshavim.

2.3.3 Arab agriculture

The Arab fellaheen of Israel are industrious and intelligent and have a great deal of traditional knowledge of crop production in the difficult environment. They are generally very conservative in their agricultural practices. Characteristic of traditional agriculture in the MiddleEast is the almostcomplete separa- tion of arable farming and animal husbandry: arable farming, mainly devoted to cereal production in the high rainfall zones, pastoralism in the drier parts of the region. In the hills, olives, vines and other fruits are grown, mostly on natural rainfall. Equipment has practically not changed since biblical times. Since the establishment of Israel, the Arab villages have evolved far more slowly than Jewish agriculture. As agriculture, industry and building expanded, work was provided for the underemployed of the Arab villages. 40 years ago, work outside the villages was practically unknown. Today, up to 60 % of the men work outside. They continue to live in their villages; and the high wages outside the village became an important source of cash income. The market prices for agricultural produce, in line with government policy, were high - so that income from farming also increased steeply. The reduced labour supply in the village and the higher incomes caused a change-over from animal power and manual labour to mechanisation. The first step by government to foster a change in the traditional patterns of agriculture was by supplying drinking and irrigation water to the villages, which made cooperatives necessary to buy and develop water and distribute it amongst their members. This was the first step towards cooperation in a highly individualistic society. It was followed by a break from traditional subsistence agriculture when Arab farmers began to produce high-value vegetables and fruit crops for the market, instead of wheat and barley. To meet the greatercosts of production and to exploit the potential for high yields, the farmers began to use fertilizers and improved seeds, and to employ disease and pest control measures. Young Arabs were trained for extension work. After experiencing the advantages of high yields and high income resulting from the abandonment of traditional practices, the Arab farmer was prepared to undertake even more sophisticated developments, including the growing of strawberries under plastic covers for export, as well as out-of-season melons, cucumbers squashes, etc., for the local market. Rainfed Arab farming has also undergone a transformation. Previously the plots were 20 small and scattered, tillage consisted in scratching the soil surface with a 'nail-plough' drawn by oxen, asses or camels. Many of the cultivators took up outside work, whilst a minority leased the vacated land. The consolidated holdings were too large for farming with drought-animals so that tractors and mechanical equipment had to be purchased. The higher costs of mechanical farming and labour could only bejustified if yields were increased. The application of fertilizers, chemical weed control and pesticides became 0 routine. Fertilizers alone account for 5 /c of production costs. Because of the higher expenses involved in production, the owners of the land no longer received half the produce as rent, but'only' one third. However, one third of a yield of 3000 kg/ha is more than one-half of a yield of 600 kg/ha, so that both owners and lessees profited. Wheat production was partially replced by semi-intensive raingrown crops: onions and lettuce for export, sugar beets and cotton, so that a further increase in income resulted. For example, by growing onion, instead of wheat, net income per hectare is more than doubled. The transition from a subsistence to a marketing economy made cooperation essential, so that cooperatives have been set up in the unirrigated regions too.

3. Some aspects of the infrastructure of agriculture

3.1 Planning

Since 1952, an Agricultural Planning Centre has been responsible for national and regional planning as well as individual farm planning. High priority was given to agriculture, over other forms of development, for ideological and security reasons, but as output has increased economic considerations have become more important. The basic policies on which agricultural planning was based are: a) The farmer's income should be similar to that of a skilled urban worker or entrepre- neur. b) Prices of agricultural commodities may not be so high, that they raise thecost of living excessively. c) For security reasons, the country cannot depend entirely on farm imports, even for products which it cannot produce competitively.

3.1.1 Changes in planning methods [51

During thefirst years (1949-195 1) about 250 settlements were established throughout the country. Planning was rudimentary, and the settlements were frequently founded without a preliminary soil survey and without a sound economic basis. The sites were frequently chosen mainly for security reasons. During 1952-1954 settlement planning improved. Though some were still isolated, most settlements (each of 80-100 farm units) were established in clusters of three to five, shar- ing a common service centre (school, marketing facilities, tractor station, etc.). Learning from the experience and failures of the previous periods, it became clear that the planning of agricultural production alone was not sufficient. Since 1954 a comprehensive regional approach to planning has been adopted. 21 First, a survey of all the resources and characteristics of the region to be settled are sur- veyed and the best types of agriculture determined. Plans are produced at three levels: a) the individual farms of a settlement; b) a rural centre serving a cluster of settlements; and c) an urban centre providing services, processing industries and marketing facilities. In regional planning complex social problems arising from the diverse backgrounds of the settlers were met. The planning process itself is greatly facilitated by the fact that land and water are na- tionally owned, so that land reform is not an essential preliminary to rational planning, as in many other countries.

3.2 Controlanddirection ofproduction

The inducements by which government directs planned production include: a) Pricepolicy: The government guarantees minimum prices for certain commodities if produced according to plan. b) Subsidies are given to decrease the cost of inputs like fertilizers, foodstuffs, protection chemicals and water. c) Quotas: are allocated for certain commodities; production over these quotas is not entitled to subsidies, either direct or indirect. d) Loans are made on easy terms to farmers who wish to producefavoured newcommod- ities, such as export crops, or to increase efficiency of production in established crops. The official agricultural production plan is translated into practice by Marketing Boards for each of the principal commodities: citrus, vegetables, fruits other than citrus, poultry, dairy products, etc. Each Board consists of representatives of the producers, thecon- sumers and the Ministry of Agriculture. The boards establish regional and individual quotas, determine guaranteed minimum prices and regulate market supplies. Agricultur- al exports are organised by the Citrus Marketing Board and by Agrexco.

3.3 Administration of water resources

Ownership and administration of all water resources is vested in the public domain by a comprehensive Water Law. A public company - Tahal - is responsible for planning of water resource and use; another public company - Mekorot - is in charge of construction and operation of water resources. Water allocations are planned by the Agricultural Planning Centre and ad- ministrated by a Water Commissioner, directly responsible to the Ministry of Agricul- ture.

3.4 Research, extension and education

3.4.1 Research

A central research Institute, affiliated to the Ministry of Agriculture, is responsible for most of the agricultural research in the country, it employs some 350 research workers 22 and maintains a number of regional experiment stations. Agricultural research is also carried out by the Faculty of Agriculture of the Hebrew University, and the Faculty of Agricultural Engineering of the Technion-Israel Institute of Technology. Pressure from farmers ensures that research findings are rapidly applied to agricultural practice.

3.4.2 Extension

In the villages for new immigrants, there are three or four resident instructors: one who trains the villagers in all matters pertaining to administration, purchase and sales; one in home economics; and one or two agricultural extension workers. When the village has developed sufficiently the extension work is taken over by the Ministry's extension service, which has a number of regional bureaux in different parts of the country, and employs 400 instructors.

3.4.3. Education

The first agricultural school was founded at Miqwe Israel in 1870, when the very first Jewish village was established. There are now 30 agricultural schools at secondary school level in Israel, with over 5000 students. The Faculty of Agriculture has graduated over 700 agronomists since its founding in 1942.

4. Discussion and Conclusions

The physical and ecological environment in which Israel's agricultural development has taken place is typical of most of the Mediterranean region: a variety of soils, depleted by centuries of exhaustive cropping and scarred by erosion; in part of the country a limited and erratic precipitation, concentrated in a relatively short season and desert in.the remainder. In addition, Israel has a few less general characteristics: a dearth of water and mineral resources and an absence of energy resources. It is also a very small country, isolated among hostile neighbours. Agriculture is still underdeveloped in most of the Mediterranean region, even in those parts of highly developed industrial countries, such as France and Italy, which belong to our region. The recent history of Israeli agriculture shows that even under the physical and ecological limitations of the arid Mediterranean environment, a modern agricultural technology, when established on a sound economic and social basis, can transform the traditional agriculture of the region. As yield and output increase, rising living standards provide a foundation for local industries; increased efficiency and mechanisation release the labour required for industrial production. Two factors are essential for this transformation: financial aid, and a farming community motivated by a desire for progress. The first can, and frequently must, come from outside sources; the latter depends entirely on the country concerned. During the period under review the total population in Israel increased more than three- fold: from 800,000 in 1947 to 2,700,000 in 1967. Total agricultural production at con- 23 stant prices increased more than six-fold, from IL 275,000 to IL 1423 million in 1966 [2], through increased yield per unit area, per animal and per unit of water in existing farms; the establishment of new settlements and the expansion of irrigation. Israel's agriculture can produce most of its own food and fibre requirements (except for certain low-value commodities such as grain cereals), and contributes substantially to exports. Of the various social frameworks within which agricultural development has taken place in Israel, it is doubtful whether the «kibbutz ), or even the older type of «moshav ) can serve as models to be transposed elsewhere. They were based on an elite group whose educational, national and social motivation and ideals made up for their lack of experience in agriculture. Farming was to be a way of life that would rehabilitate the Jewish people after centuries of exile. The new (post-independence) moshavim and the experience of the Arab villages, can provide useful guides for agricultural development elsewhere. Both the new moshav settlers, with no previous experience in agriculture, and the Arab traditional farmers, have changed and adjusted to the requirements of modern agriculture, as evidenced by their important contribution to the overall agricultural production. Agricultural production has developed on lines dictated by the ecological environment and can therefore be related only to countries with a similar environment, i.e., those in the Mediterranean region, but the organisational forms and planning methods that have proven themselves, are of wider adaptation.

Literature cited

I. Ben-David J.: Agricultural planning and village community in Israel. UNESCO, Arid Zone Research 23,9-11 (1964). 2. CentralBureauofStatistics: Statistical Abstract of Israel. Government Press, Jerusa- lem (1967). 3. Ministire de 'Agriculture d'lsratl:Elements du Plan Quinquennal pour le Dve- loppement de ]'Agriculture. HaQirya, Tel Aviv (1967). 4. Shmueli E.: The contribution of research to the efficient use of water for Peace. Washington D. C. (1967). 5. Weitz R. and Rokach A.: Agricultural Development: Planning and Implementation (Israel Case Study). Dordrecht, ed. D. Reidel Pub]. Company. Holland. (1968).

24 I" Working Session: Attaining Maximum Yield

Coordinator of the Session: Dr. G. W. Cooke, Head of the Chemi- stry Department, Rothamsted Experi- mental Station, Harpenden, Herts/Unit- ed Kingdom: Member of the Scientific Board of the International Potash Institute.

25 Factors Limiting Maximum Yield

Prof. Dr. K. MENGEL, Head of the Biintehof Agricultural Research Station, Hannover (Federal Repu- blic of Germany)

The yield of whole plants and of individual plant parts directly depends on the genetic potential of the plant species and variety and on the climatic and nutritional factors which bring about this genetic potential. According to Liebig's law, the factor being in the minimum will limit the yield and numerous experiments have shown that an apparent deficiency of one growth factor (i.e. water, temperature, mineral nutrients) results in a considerable yield depression. These facts are well known and, therefore, will not be discussed here in detail. But even under the conditions of a highly intensified agricultural or horticultural management, we cannot be sure that an optimum nutrient supply during the whole vegetation period is maintained. In practice, the genetic potential ofcrop production is onlyex- hausted to about 50-60%. Under the climatic conditions of Central Europe, the average grain yield of cereals amounts to about 3.5 t/ha, but maximum yields of 8-9 t/ha are at- tainable and, with methods of excellent farming, mean yields of 6.0 t/ha grain of winter wheat have been obtained by modern farmers during recent years. There are many reasons for the fluctuations of the yield level between the different years, and there is no doubt that these differences must be attributed to the weather conditions prevailing in those years. The weather during the growing season does not only affect the yield by climatic factors, such as water, light intensity and temperature, but it has also a remarkable influence on the nutrient supply and nutrient availability in the soil. In warm and humid periods, the decomposition of organic material is promoted which may result in a high N mineralization. Under these conditions, the N supply of the soil is favourable and the mobilization and transportation of inorganic nutrients are enhanced. Thus, growth and organic matter production reach the optimum provided that light intensity is satisfactory. In dry and warm periods with bright weather, light intensity and temperature are most favourable for organic matter production. If there are no extreme conditions, the water supply from the deeper layers of the soil may still be sufficient for optimum growth, but the availability of plant nutrients in the upper layerof the soil (0-25cm) is limited. Under these circumstances, the decomposition of organic material and also the diffusion of K + and phosphate to the plant roots is restricted. As in most cases only the upper soil layer is rich in organic N and exchangeable K and phosphate, in dry and warm periods the nutrient supply may thus be the limiting factor of plant production although an adequate fertilization with inorganic plant nutrients has been provided. Garwood and Williams (1967) in a model experiment proved that it was not the water supply but deficiency of nutrients, especially of N, which was the limiting factor of herbage production with insufficient moisture (water deficit) in the upper layer. By injection of N, phosphate and potash into greater depths (46 cm), the nutrient availa- 27 bility became satisfactory thus resulting in a significant yield increase (Table I). For practical farming, this means that the chance to overcome a limited nutrient availability during dry seasons will be the better the greater the depth in which the soil is enriched with nutrients. Thus, especially dry periods which provide optimum climatic conditions can be utilized for increased production of organic matter.

Table 1. The influence of an NPK injection into the deeper layer of the soil on herbage production, with sufficient and insufficient water supply of the upper soil layer (Data from an experiment by Gar- wood and Williams 1967)

Water deficit 33 mm 91 mm Yield (kg dry matter/ha) NPK surface appl. (control) ...... 1630 590 NPK injection into 46 cm depth ...... 1460 1330

On the other hand, an interruption in plant nutrition, even for a rather short period, has a negative effect on the yield (Achinich 1955, Heyland 1961, Noguchi and Sugawara 1966). In most cases, such an interruption in the nutrient supplycannot be corrected by a later nutrient application (Mengel and Forster 1968). With cereals, a discontinuation in the K nutrition during the vegetative phase of the growth period is particularly detrimental. As can be seen in Table 2, an interruption of the K supply during and after the tillering stage resulted in a decrease of grain yield, a smaller mumber of heads per plant and a lower 1000-grain weight. Table 2. The effect of a 16-day interruption in K nutrition after the tillering stage on yield factors and grain yield of barley Control Interruption

G rain yield (g/pot) ...... 87.9 51.7... Number of grains/ear ...... 16.1 14.9* Number of ears/plant ...... 6.28 5.28-: 1000-grain weight ...... 31.9 24.0-* Percentage of grains > 2.8 mm ...... 38.4 8.8... Percentage of grains < 2.2 mm ...... 7.8 28.7* Significant at 5 % level. * Significant at 1.0% level. ***Significant at 0.1 % level.

With increased intensification of agriculture, more information is needed about the specific nutrient requirements during the various growth phases of the plant. Cereals need, particularly during the development of grains, an additional supply of N and phosphate whereas the K supply at this growth stage is of minor importance. Table 3 shows the influence of an interruption in K nutrition at different growth stages on grain yield. The K requirements are particularly high at the shooting stage during which, within a short period of 2-3 weeks, about 100 kg K 2O/ha must be translocated from the soil into the plant. This high potash demand can only be met if the K potential of the soil and the actual availability of K is sufficiently high (Mengel et aL 1969). A K supply below the optimum during this stage which causes a hidden K deficiency, without any symptoms becoming visible in the plant, results in a lower yield (Mengel and Helal 1968, Helal and Mengel 1968) and may also have a negative effect on the quality of the grain (Primost 1968). 28 I N-application ------0 N kg/ha 70 N kg/ha 7°i A .7o----1 N kg/ha

= I o* I l,/\

z 35-

15-

di,... I, a± wi/ ,,I of I n Ionih'

O N D J F M A M J J A S0 N O months

sages-,. Illtarinig practice. this adjustmrent ncunteCrs whuh1.lliCUlt ICs. 1i s holds eCp,- craik trtle for nitrogen bczause tihe concentration of soluble nitrogen1 in tle soil till- degoe drasticchanges within the coLrse ofone "Car. In temperatc climate, there is a steep1 1neremen Lip [O 11maximu of soluble N during the summnier ascan be seen in ItIl- ure 2/(iauu 1 9 f lhi peak depends on stil temoerniure and soil andoistured may shill to tle light or left (see I'w, 21 tinder NMl in xveathcr conditions. For these reia- sonvs. theqlrtv ol'N-Lipplied te organicmatrofthesoinlOf ma diltterconriderahlk from year roe v l'ot the mensie alid clae s rn t [Tu1/I %5. Tlbl< 4). Particu- larl\ in sand' soils ,ith a Io\ capacit< of Incorlptrtion and liberation if inorganic iI- trogen, the nitrogen dressing Ill the spring ma' inrclebae the content of OlublC nitrogen considerabl\ It the beginrvng or the season, bt phnil uptake and sometilso leaching Ina> decrease he cncen tttion of soluble N 'ry )Iuch \w ithin a fe\ x eekx, his can be seen in Itaui3. based on data ofa pot exlei ent with spring %Nheat Vt,h l 1 9671.

u IrthtI 4. ii iaCke tfvtttl N [bysi1!;iir beer't to iticre ni ']cfin.A ~tn ironyl (tysirtyce r c\"Krliycnlr

Iiberalion 01 N k 1i) I "601 I W0 Soil UIigh No m iI rahitii ra tlwa1

i ...... ! [o c - ...... 84 I15

1NInI I41 ...... 2 ...... l 0 04t~) Sr) ke:It N ;ut? I ~i~ln 1i)1 12l0i ( (a h N 1IaiCa t11wn

30 60 \

-= 0.3g NO3-.

40 1,2gNH 3 a z

0.6g NH3 c, 20 E

0.3g NH-3

00 -22,4 35 125 ' 24.5 harvest4 8 N- fertilisation

..ivi,it3 5t. N, ttzl-Nm , Z, 1 t >d 1, rel .atio t h, N-.upl .rtfttce/ O196

At the end of the shooting sage, the sOILhIe n itrogen reser Cs were nearly exhatisled re- suiting ina rather low yield level. Such conditions are often found in agriculturnal practice. fT overcome this di;llnItl ,modern f:armlers Iherefore a ppl nitrogen 3 4 times dU- ing one season on the sandv soils n North (.ermany.With high rates of potuish and phosphate given] n addition, itwill thus he possible to produce high grain yields on soils which formerly were known as very infrrile and stinsnitable for agiriciurIal use. The availability and supply of phosphate and especiall of K is not sO nmuch influenced by soil microorganism activity as this is the ca,e with N I-or the phosphate and K supply the physical and chemical soil properties play an important pari. The estension of the root system of most allnual crops is limiled and the root volune in the upper layer of the soil covers hardly I ...of the soil volunme ( Neni/ - al. 969). T hus, the qalllit of nuttients Which can be reached by root orowrth often meets the reqtuiremeni, oftthe plants to a limited extent only. tinder notrluJI conditions, cereals by root grow illcan only reach about 10 ",,Of the total K and 25 ",of the total phosphate needed folsatisfactory groW th (awher et al. 1963. l/amlict 1965). Therefore, the tran port of K and phosphate to the plant roots plays a predominant role in the nulrient suppl' duiring the growing season. It is well known that in dr', seasons lhe actual a'ailabilitv of K and phosphate is reduced (I il/whI,, 1955, Lou and Pipe, 1960) T hi, is mainly idueto the restricted diflusion and mass flow ofn utrients to the plant root,. The rate of diffusion or mass fltiWs i rectly influenced by the nutrient concentration in the soil sohition. This may differ "idel> depending on soil moistnre, sol texture and the contents of scolUble and exchangeable nutrient,. In the water-saturated estract, Riothard' 19411) f about 60 ditferent ,oil sample, from North Germany, the concent rations ditife red x it hi The flIoi ing ran ci> 31 Ni, ..* , mc I K. ,1 3.0 mieI

K .. 01' 0 me P 0.0 15 0l file I ]here isis a siginilicant,d corrlation l etseeti rhc (a _eci!inCentrat in tIe saLLt-

tion estirict and the C\ch'lIg'ealec('o and Mg, rcspectively(%{ 'fth,/ a/ 1969). iu silt thal on1 the K colleenttliji1t depclded to it ereatet Cecll Oil tie content of clt 111 tle theexchangeafle K, Soils rich I n ctI ' Ind silt 'L ferilly hac a low K concenlilao i) soil solutioi and, Ih etcl orc, hav-e it KoiK iranspo-liftaion i-aie. This rnim lead to in,iaslf ticicnt K -upply particulril nder unast ()LcMie conditions ofldiltu-itln and mrss flow This rcsticted K supplN only arci lead' tu a visi ble K deficiency Finthe plaWnis hut growth is rentardcd and the namimum Sicld potential cannot be cx hauisted. F nic 4 11hmus-uch ait pica I hidden K deficiency in ripe I Bh a itvmpts). lhc ptnt- on the left (pos Nos. I517 and 1519) received the lowest K diesin, the plants on the flght (pots Nos. 1 125 and 1527) the highesi dose The planti ifthe pots 1521 and 15 receed an intermediate K supply. The plants Nkere grown in heavy loam, so' I. There %fee remairkable d itlecnces in gro l i rate, as caln be seen Ii Filure 4. bitt there were no %',sibc K-delt - cienc s%mptoms it all. Thereore, it isof great imporIance to detect and identifI such L, Ie hidden tntrient deiciency itan early stage because this often red fice' the ieId ci in highly intensified agriculture.

I BEE

157 1519 1521 1531525 1527

>ifl',i 4 Crosth o ripe IT, rc 1L0nIthe supply of K. 32 Summary

I. In most cases, the genetic potential of crop plants for maximum yields is only exhausted to a limited extent. 2. The nutritional factors largely depend on the weather conditions. In many cases, limiting nutritional factors, influenced by weather conditions, are responsible for lower yields. 3. In order to approach the maximum yield level, the nutrient supply must be adjusted to the specific requirements of the plants during the various growth stages. 4. Therefore, it is not only necessary to supply the soil with sufficient quantities of nutrients. Care must also be taken that these nutrients are available to the plant roots in sufficient amounts during the growing period. 5. Only when the nutritional demands are fully satisfied at each phase of the growing period, the climatic factors can largely be utilized for organic matter production and the yield will approach the optimum level.

References to literature

Achmich W.: Der Einfluss zeitlich variierter Nfihrstoffgaben auf den Ertrag bei Gerste und Hafer. Z. Acker- und Pflanzenbau 99, 273-293 (1955). Barber S. A., Walker J. M. and Vasey E. H.: Mechanisms for the movement of plant nutrients from the soil and fertilizer to the plant root. Agricultural and Food Chemistry 11,204-207 (1963). Blancher R.: Quelques aspects r~cents des tudes relatives A l'alimentation minrale des plantes dans le sol. Sci. do Sol 2, 109-119 (1965). Garwood E.A. and Williams T.E.: Growth, water use and nutrient uptake from the subsoil by grass swards. J. agric. Sci ., Camb. 69, 125-130 (1967). Harmsen G. W.: Waskann uns die Bestimmung des Gehaltes l6slichen Stickstoffs im Boden lehren ? Z. Pflanzenern~thr. Dung. Bodenk. 84, 98-102 (1959). Helal M. and Mengel K.: Der Einfluss einer variierten N- und K-Ernihrung auf den Gehalt an l6slichen Aminover bindungen und auf die Ertragsbildung bei Sommerweizen. Z. Pflanzenern1hr. Bodenk. 120, 89-98(1968). HeylandK. U.: Ober die Bedeutung der Ernhrung in verschiedenen Entwicklungsstadien for den Er- trag der Sommergerste. Z. Acker- u. Pflanzenbau 113, 41-65 (1961). Low A.J. and PiperF.J.: The influence of water supply on the growth and phosphorus uptake of Ital- ian ryegrass and white clover in pot culture. Plant and Soil 13, 242-250 (1960). Mengel K.: Moderne Gesichtspunkte in der Pflanzenernahrung und Duingung. Ergebnisse landw. Forschung an der Justus-Liebig-Universitgt, IX, 73-82 (1967). Mengel K. and Forster H.: Der Einfluss einer zeitlich variierten, unterbrochenen K-Ern~hrung auf Ertrags- and Qualitgtsmerkmale von Gerste. Z. Acker- u. Pflanzenbau 127, 317-32 6 (1968). Mengel K. and Helal M.: Der Einfluss einer variierten N- und K-Ernahrung auf den Gehalt an ldslichen Aminoverbindungen in der oberirdischen Pflanzenmasse von Hafer. Z. Pflanzenernahr. Bodenk. 120, 12-20 (1968). Mengel K., Grimme H. and Nemeth K.: Potentielle und effektive Verfogbarkeit von Pflanzen- nfhrstoffen im Boden. Landw. Forschg. 23. Sonderheft, 79-91 (1969). Nemeth K., Mengel K. and Grimme H.: The concentration of K, Ca and Mg in the saturation extract in relation to exchangeable K, Ca and Mg. Soil Sci. 100, 179-185 (1970) Noguchi Y. and Sugawara T.: Potassium and Japonica rice. Intern. Potash Inst., Berne (1966). Primost E.: Der Einfluss von Duingungsmassnahmen auf die Qualitalt von Weizen. Landw. Forschg., 22. Sonderheft, 149-157 (1968). Richards L.A.: A pressure membrane extraction apparatus for soil solution. Soil Sci. 51, 377-386 (1941). Vlmel A.: Der Versuch einer Nahrstoffbilanz am Beispiel verschiedener Lysimeterbdden. 1. Mittei- lung: Wassersickerung und Nahrstoffhaushalt. Z. Acker- u. Pflanzenbau 123, 155-188 (1965/66). Wilhelm A.F.: Zur Diagnose von Ngthrstoffmangelerscheinungen bei Reben. Weinberg u. Keller 2. 297-304 (1955).

33 Maximum Yield Potential

Dr. J. WARREN WILSON, Head of the Plant Physiology Department, Glasshouse Crops Research In- stitute, Littlehampton (United Kingdom)

1. Introduction

This paper suggests a strategy for maximizing crop yield. The principles proposed are, briefly: a) to ensure optimal supply of those environmental factors, such as soil water and mineral nutrients, which it is practicable to modify; b) so far as possible, to select sites where those climatic factors which it is not practicable to modify, such as light and temperature, are favourable; c) to recognize that the basic environmental limitation to yield is then imposed through restriction of photosynthesis by light and CO 2 ; d) to select genotypes with leaf characteristics that allow the most efficient use of CO 2 and intercepted light; e) to ensure that genotype characteristics and management practices (sowing dates, spacings, etc.) provide a canopy of leaves which intercepts and uses as efficiently as possible the light available throughout the year for photosynthesis; f) to optimize partitioning of photosynthate between the several vegetative organs and harvestable parts, and to minimize loss of photosynthate by inadequate sink strength, by death, or by retention in non-harvestable parti. These aims are implicit in agronomic studies generally, but it may be useful to examine explicitly the procedures that can be used, and to compare the theoretical maximum yields with present actual yields. This examination is concerned not with immediate practical limitations by labour or finance, but with ultimate biological and climatic limitations.

1.1 Accumulation of matter by crops

Crops grow by accumulating matter from their environment by three processes. Water accumulation accounts for some 60-80% of total weight; of the remaining dry matter, about nine-tenths is derived by photosynthesis and about one-tenth by mineral uptake. Water and mineral uptake occur by transfer across the soil-root interface, but for photosynthesis only 7 % enters as hydrogen in water across the root surface while 93 % enters as CO, diffusing across the air-leaf interface. Plants vary in composition, but the three processes that together comprise crop growth contribute roughly as follows: W ater accum ulation ...... 70 % Photosynthesis ...... 27% M ineral uptake ...... 3 34 Quantitatively photosynthesis is thus not the main contribution to growth. However, for crops supplied with adequate water and mineral nutrients, photosynthesis is the limiting process, on which accumulation of water and minerals depends. Photosynthetic transfer of CO2 from air to leaf is therefore the basic rate-determining process for advanced systems of crop production.

2. Photosynthetic capacity of leaves

2.1 Determination ofphotosynthetic rate by characteristics of leafandenvironment; theory

The photosynthetic rate of a leaf is determined by interactions between leaf characteristics and the climate to which the leaf is exposed, which can be summarised by the equation Pg=bI/[l +(bT/rC)] (I)

where Pg is the rate of gross photosynthesis as CO . uptake per unit leaf area; b and r are constants for the particular leaf, representing respectively the efficiency of the photochemical process and the efficiency of CO, uptake by diffusion and carboxylation processes; and I and C are the light in the plane of the leaf and the ambient CO 2 concentration. (Light is measured throughout this paper as the flux density of radiation in the pho- tosynthetically active wavelengths between 0.4 and 0.7 [Lm. In calculations it is assumed that 45 % of solar radiation lies between these wavelengths, and that I ft-c corresponds to approximately 0.045 J m- 2s-1. SI units are used for all quantities). Equation (1), based on studies by Rabinowitch[50], has been adopted by several authors [14, 16,42]. For any particular CO2 concentration, equation (I) reduces to Pg=b/(I +al) (2) where a is a constant (=b/rC). Similarly, for any particular flux density equation (I) simplifies to Pg = +kC)±Cl (3) where k is a constant ( = T/bI). Equations (2) and (3) are the response curves of photosynthesis to light and CO2 ; the former has been widely used, but the latter less often [25]. These hyperbolic curves have the following characteristics:

Light response CO, response (equation 2) (equation 3)

Initial slope ...... b T Asymptote ...... b/a (= rC) r/k ( =bl)

For the light response curve, the initial slope represents the maximum efficiency of the photochemical process (light limiting, CO, saturating), and the asymptote represents the maximum photosynthetic rate (light saturating, CO2 limiting). Gross photosynthesis has in the past been estimated as net photosynthesis plus dark respiration. However, it is now known that in many species this procedure is not valid be-

35 Table 1. Photosynthetic characteristics of leaves of four species

Species b - 6 rt 2 2 - Cc (X 106 g COe J-1) (X 10- g CO 2 M- S-1 ppm-) (JM- s l) (ppm) Acer saccharuma (maple) ...... 20.2 0.8 4.1 50 Trifollum pratense (red clover) . 10.2 3.3 5.7 38 Zea mays (maize) ...... 9.8 6.0 10.7 0 Amaranthus edulis (grain amaranth) ...... 23.0 5.7 6.0 0

Differences in P, of the order shown in figure 2 affectcrop productivity powerfully, and it is important to understand how these high photosynthetic capacities can be achieved.

2.3 Leafcharacteristics for maximum photosynthesis

The interaction between the four leaf characteristics (b, r, I, Cc) that determine the photosynthetic response is defined by equation (4); nevertheless it may be helpful to indicate roughly what changes in these characteristics increase Pa at normal CO2 concentrations: a) At values of Jclose to the compensation point, P. rises with decrease in Ic but is little affected by b, r, or Cc. b) At low and moderate values of I, Pa rises with increase in b, and to some extent with increase in r and decrease in Ic and Cc. c) At high /, P. rises with increase in r and to some extent with increase in b and decrease in Cc, but is little affected by lc. Thus altough Pa tends to rise with increase in b and r and decrease in Ic and Cc, the influence of each characteristic varies with the light climate. Shade plants may be expected to benefit especially from low lc and high b, but to gain less from low Cc and high r (see maple in table I). Leaves of crop plants that receive moderate or strong light will photo- synthesize most rapidly if they have high b and r, and low Cc (grain amaranth, table 1). Variation among species is greater for r than for b. The range of b, in 18 species exam- -6 1 ined, is about three-fold (7.4-23.0 x 10 g CO2 J- ) whereas the range in r is over tenfold [25, 43]. Genotypic differences among varieties also occur both in b [7] and in r [7, 13,58]. Since r represents the reciprocal of resistance to CO 2 transfer (see Durandin discussion to [14]), differences in leaf anatomy, stomatal properties and physiological state affect its value. Within a genotype, the environmental history of a plant or leaf can have a lasting effect on r. It has been found to fall as a result of low temperature, low light, water stress, and potassium deficiency [7. 27.48]. An initial step in maximizing yield is thus to select a genotype with leaf characteristics that allow high rates of CO2 transfer, and to grow the crop in conditions that enhance rather than suppress these desirable characteristics.

3. Light interception andphotosynthesis by the crop canopy

The previous section considered photosynthesis of isolated leaves. However, in a crop the leaves are not isolated but are arranged in a canopy, within which the climate is modified in a way that depends on the canopy structure: shading depresses 1, and photosyn- 38 thesis lowers C. The interaction of these two effects on canopy photosynthesis is complex [14], and in this account the effect of only I, and not C, will be considered. This simplification is adopted because, first, I varies greatly with time of day, weather, season and region whereas C is comparatively uniform; and secondly, reduction of f near the base of a mature canopy often exceeds 90% whereas reduction of Cseldom exceeds 15 %. Consequently C is of only secondary importance as a source of differences in productivity in field crops. Since productivity depends ultimately (through photosynthesis) on light receipt, it is essential that light should be intercepted and used as efficiently as possible.

3.1 Effect of canopy structure on liht interception

The proportion of incident light that is intercepted by the canopy depends not only on the leaf area index (leaf area per unit area of ground, L) but also on the extinction coefficient (K), which is a measure of the light-intercepting efficiency of the leaf area. Kfalls as leaves become more erect, or grouped in clumps, or as their scattering coefficient increases; all of these features reduce efficiency of interception. The influence of L and K on interception can be expressed quantitatively by a relation based on Beer's law: 1'=o exp (-KL) (7) where 1o is the light flux density above the canopy and ' is the light beneath a canopy of leaf area index L (both measured as downward fluxes through horizontal planes); hence the intercepted light I is given by

I =o-I' = 1o[I -exp (-KL)] (8) Although there are reasons to expect departures from this simple relation, it has been found to fit satisfactorily data for many crop canopies [41]. The interaction of L and Kon light interception is shown in figure 3. Table 2 lists typical values of K for several crop species, but values vary somewhat with variety, growing conditions, and light climate.

1-0

0)2

044

Figure 3. Effect of L (leaf area index) and K (extinction coefficient) on I/1o (proportion of incident light intercepted by canopy). 39 Table 2. Extinction coefficients Species Extinction Reference coefficient Zea mays (maize) ...... 0.38 [68] Oryza sativa (rice) ...... 0.53 [44] Lolium perenne (ryegrass) ...... 0.70 [38] Helianthus annuus (sunflower) ...... 0.90 [29] Trifolium repens (clover) ...... 1.03 [67] Gossypium hirsuum (cotton) ...... 1.06 [40] iiefficient interception of light is a major source of losses in annual yield. Table 3 shows rough estimates of the proportions of total available light that are intercepted during the year by five crops. Almost complete interception is achieved by perennial crops that maintain a sufficient L throughout the year, but light is wasted if L is low (e. g. saltbush) or the growing season is restricted (cotton, tulip). Efficient interception can be promoted by minimizing losses due to slow development of the canopy, unfavourable defoliation tystems, orearly senescence. Suitable choice of cultivars, sowing dates, spacings and cul- sural treatments can all assist.

Table 3. Leaf area index and annual interception of light flux density for various crops

Species Site -°X . x e

Trifolium subterraneum Adelaide, 1.0 66 55 (subterranean clover) Australia 1.0 66 55 35 296 .7 [S[8

Elaeis(oiI palm) guineensis Benin, Nigeria 10 . . .3 21 .7 [1

Gossypim hirsutum Kimberley, 05 . . (cotton) Australia 05 .. .3 17 .6 [7 Tulipa gesneriana Liulehampton.4 (tulip) England 04 . . .7 05 .6 [2 Atriplex vesicaria Deniliquin, 10 . . (saltbush) Australia 10 . . .5 04 .3 [5

3.2 Canopy photosynthesis

When L is low, a high Kis advantageous in maximizing interception. On the other hand, a low K becomes beneficial when L is sufficiently high to ensure nevertheless that most light is intercepted. This is because photosynthetic efficiency of light utilization is greatest in relatively weak light (in fact, at the light flux density at which a line from the origin is tangential to the light response curve of net photosynthesis: at this flx density the efficiency of light utilization approaches b). At high L, a lower Ke[sures that the total light available is dispersed over a greater area of leaves but at a proportionately lower flux density. These relations can be analysed by relating the ef o tic response to light (equation 5) to the light profile with depth in the canopy (equation 7). First, however, a-

40 5 5 L=8 K= 05 Kz10

L=4

K00 C4

x8 -1 -e bd2'o2

lt (Jnv s'

Figure 4. Effect of L (Ieaf area index) andJo (Iight flux density)on Pn (net photosynthetic rate per unit ground area) for canopies of leaves with photosynthetic characteristics as stated in text and with K (extinction coefficient) = 0.5 (left) or 1.0 (right). lowance must be made for the fact that the light flux density f in the plane of a leaf in the canopy is not equal to the flux density I' in the horizontal plane at the same depth, except in the special case of a horizontal leaf. For inclined leaves I is lower, being given by I exp (-KL)/(-I --- ) - -K (9) where mnis the transmission coefficient of the leaf. Approximations in this relationship are discussed by [54] and [1], and will not be pursued here. By substituting equation (9) into equation (5) and integrating with respect to L, an expression is obtained that relates the rate of net photosynthesis of the canopy per unit ground area (Pi) to a) the light climate (term Io); b) the canopy structure and opticalioncefcetoh[hr(stetrnms properties (termsleaf. Apoia L, K, mn); i -nthi (eat0)hi c) the photosynthetic characteristics of the leaf (terms a, bn g): b l ( -m)(--a c)+a oK ] blL ( 0 IKaO -K-c)In ( -,,L- m)xp -L)J (9)-a)

In figure4 this equation has been used to examine theeffects ofL and oon P for acano- py o idealleaves having characteristics roughly corresponding to those of the most efficient leaves in table I 1 a=0.0 m s t (equivalent tor = about6 IAgCO2 s' ppm at

normal CO. concentrations) b=20x 10-6g CO, J-1 c= 6 J m- s-l rn =0.1 41 Graphs for K=0.5 and K= 1.0 indicate that to achieve maximum Pa, Io should be as high as possible, K should be low, and the optimum value of L depends on In and K. Equation (10) can be used to examine the interacting effects on P,, of the seven parameters in the equation; and the analysis can be extended, by applying the equation to successive layers in the canopy, to consider effects of changes in leaf characteristics with depth. However, these interactions are too complex to be discussed in the space available here. It is nevertheless of interest to compare (Table 4) P. for a canopy of 'ideal' leaves at L - 4 and 1. = 400 J M- 2 s- 1 with maximum values of Poobserved in actual canopies at roughly similar L and In.

Table 4. Maximum ratesof net photosynthesis per unit ground area bycrop canopies Species L Jo Pn Pallo Reference (J M-2 s- 1) (x 10-' g CO. m- 2 s-1)(x 10-' g COl J-1)

'Ideal' leaves (K=0.5); see text ...... 4.0 400 3.46 8.65 'Ideal* leaves (K = 1.0); see text ...... 4.0 400 3.03 7.58 Zea mays (corn) ...... 4.4 440 2.78 6.32 [28] Glycine max (soybean) ..... 6.0 314 2.60 8.28 [55] Hordeurn vulgare (barley) ... 11.7 342 2.35 6.87 [47] Gossypium hirsutum (cotton) 3.0 412 2.00 4.85 [3] Medicago sativa (alfalfa) .... &0 450 1.86 4.14 [67] Hordeum vulgare (barley) ... 4.9 430 1.50 3.49 [43] Gossypium hirsutum (cotton) 5.7 367 1.50 4.09 [2] Beta vulgaris (sugar beet) ... 5.0 430 1.14 2.65 [43] iponioea batatas (sweet pota- to) ...... 3.5 283 1.11 3.92 [59] Oryza sativa (rice) ...... 3.8 204 1.06 5.20 [72] Trifoliun repens (clover) .... 3.0 405 0.83 2.05 [67]

Observed P, for corn is not much lower than Pn calculated for'ideal' leaves. Indeed, a P of 3.70 x 10-3 g CO, m-2 s-' has been recorded for corn [35], but this was estimated by micrometeorological methods which have also given maximum P,, of 1.70 X 10-3 g CO. m 2 s- 1 for corn [71]; estimates by these methods must for the present be treated with reserve. For other species, observed values of Pa fall short of the 'ideal' P,, to various extents. This is due in part to lower photosynthetic efficiency of individual leaves. For example, the leaf characteristics quoted for clover in tables I and 2 give (using equation 10 and 2 -3 2 - taking L = 3 and/o -J400 J M- s-) a Pa of 1.47x 10 g CO 2 m- s 1, well below the 'ideal' Pn and nearer to the observed Pn for clover in table 4. A second cause of lowered P, lies in interception of light by stems and petioles and by leaves that are to young or old for efficient photosynthesis. Thirdly, P,, is reduced by respiration of very young, actively growing leaves and non-photosynthetic organs. Values of Philo listed in table 4 show that efficienciesof light utilization by photosynthes- - is of these canopies lie in the range 2-8 x 10 6 g CO 2 J-1, i.e. about one-third of the efficiencies of the basic photochemical process (given by b) which was quoted earlier as - 6 7-23 x 10 g CO 2 J-1. However, Pn/lo varies with 1. and in the case explored in figure 4 2 - 1 . reaches a maximum of about I IX 10-g COJ2 P at about 100J M- s 42 3.3 Photosyntheticproduction over long periods

The gasometric methods which have provided the data on CO 2 uptake quoted above are used for measurements over periods of minutes or hours. To estimate photosynthetic production over many days or weeks, other methods must be used. First, it is possible to calculate P. or P, over long periods from long-term records of for Io, assuming that relations between photosynthetic rate and light flux density observed over short periods remain applicable. Several authors have used such computation techniques [19,53, 70]. A second course is to re:ognize that long-term production is measured more appropriately not by CO 2 uptake but by dry-matter gain. Data from the two measurement methods can be related by assuming that the dry matter takes the form of (for instance) CH 20, whence the ratio of weights CO 2 : CH 2O is 44:30 - 1.47. For many actively growing crops, the long-term rate of dry-matter production per unit area of ground ('crop growth rate') is found to be almost directly proportional to the intercepted light, so that from equation (8) crop growth rate =1o [I -exp (-KL)]e (11) where eis the efficiency of use of intercepted light in dry-matter production. This direct proportionality is not expected from figure 4, where the relation of P,, to Io departs from the origin and from linearity. However, the lower is peak 1o the less is the departure from linearity; and there are other reasons for expecting a more linear relationship, as discussed in an earlier review [64], where values of Eare tabulated for various crops. In table 5 these values of Ebased on data on dry-matter production have been converted to CO, uptake by multiplying by 1.47. If KL exceeds 3, as in many mature canopies, [l-exp (-KL)] exceeds 0.95; and e expressed in terms of CO 2 is roughly the equivalent of Pn/Ilo.

Toble 5. Efficiencies of light utilization in production by crop canopies: estimated from dry-matter gain but expressed as rate of CO 2 uptake per unit ground area per unit light flux density

Species (=P,,/1l) (c 10-6 g CO2 J-1) Oryza sativa (rice) ...... 6.1 Zea mays (corn) . 5.0 Ipomoea batatas (sweet potato) ...... 4.5 Brassica oleracea (kale) ...... 3.9 Helianthus annu s (sunflower) ...... 3.8 Goss, pium hirsutum (cotton) ...... 3.7 Trifolium subterraneum (clover) ...... 2.4 Glycine max (soybean) ...... 1.9

Values of Pn/Io in table 5 are fairly close to those of Pn/10 in table 4, except for soybean. This correspondence may be due partly to compensating discrepancies; for example, mineral uptake and certain respiratory losses are included in data of table 5 but not table 4, and may contribute roughly 10 % discrepancies in opposite directions. Nevertheless, the degree of correspondence gives some confidence in attempts to relate short-term photosynthesis to long-term dry-matter gain, and suggests that for actively photosynthesising crop canopies the efficiencies of light utilization over long periods may be not widely different from those expected from short-term studies of CO2 uptake. 43 4. Utilization of photosynthate

4.1 The components of utilization:structural growth, storage and respiration

Whether the photosynthate formed in the leaves is retained in them or translocated elsewhere in the plant, it is utilized in one or other of three ways: a) structural growth, i. e. increase in the essential fabric of the plant; b) storage, i.e. increase in material held in reserve and which may be used later in structural growth or respiration; c) respiration. The strengths of these three sinks for photosynthate vary with environmental conditions, with the type of plant, and with its stage of development as crudely suggested in table 6.

Table 6. Typical rates of utilization of dry matter by three types of sink, relative to total dry weight (g g- d-), at three stages of development Stage Structural Storage Respira- growth tion Germ inating seedling ...... 0.20 0.05. 0.10 Young vegetative plant ...... 0.15 0.05 0.08 Mature plant with storage organ ...... 0.05 0.10 0.04 * Assumes that seed reserves are not part of embryo; otherwise a negative value arises here.

During germination and establishment the plant needs growth of first a root system and soon afterwards a leaf system, to provide rapidly a large interface with soil and air for uptake of water, minerals and CO2. This growth utilizes at first stored photosynthate from the seed, and subsequently current photosynthate. Rapid increase in size is of critical importance-especially where there is competition-and this is achieved by relatively great accumulation of water, which may amount to ten times the weight of dry matter. Both root extension and leaf expansion depend closely on water uptake [11]. These processes achieve surface areas for environment-plant interchange of nearly I m2 g-1 dry matter, when root hair surfaces and internal airspace surfaces of leaves are taken into account. Storage may be relatively small during this stage of vegetative growth. Subsequently, however, in those crops in which the harvested part is a storage organ, structural growth becomes subordinate to storage as a sink for photosynthate. Respiratory utilization tends to be most important in young plants, and when structural growth predominates over storage. Efficient use of photosynthate in obtaining maximum yields depends on achieving optimal relations between these three sinks for photosynthate.

4.2 Balance between formation and utilization ofphotosynthate

Whereas the rateof photosynthesis increases strongly with light and is not greatlyaffected by temperature over a considerable range, the rates of structural growth and respiration increase strongly with temperature and are not much affected by light (except indirectly). Consequently, the ratio of formation of photosynthate to its utilization by growth and respiration tends to be low in warm dim climates, with the result that stored photo- 44 synthates may fall to a level at which they limit structural growth. By contrast, in cool bright climates the rates of growth and respiration are relatively slow, and photosynthates may accumulate to a level at which they limit photosynthesis [45]. For maximum production, these unbalanced conditions should be avoided. The ultimate limitation is set by efficient use of the prevailing light by the canopy; this determines the maximum rate of formation of photosynthates. The size and activity of sinks should be sufficient to utilize these photosynthates without undue storage; at the same time there is no advantage in excessive potential for growth, so that potential rates are never allowed by the supply of photosynthate. At present there is little evidence as to theextent to which the rates of formation and utilization of photosynthates limit each other in normal field crops. For extreme climates the position is clear: in the arctic summer, the rate of utilization limits the rate of photosynthesis [61], and in a dense crop in a warm but dull climate photosynthesis limits structural growth [29]. For a range of intermediate climates, however, neither limitation is clearly dominant. Indirect evidence has been taken to suggest that grain growth in wheat in England may be limited about equally by rates of formation and utilization of photosynthate [66]. Some indication of the balance between formation and utilization in growth and respiration is given by the leaf area/leaf weight ratio (specific leaf area, S). If leaf expansion depends on structural growth, increase in formation of photosynthate relative to its utilization in structural growth will lead to accumulation of storage products and so to a fall in S. On this argument, S should be inversely proportional to the rate of dry matter formation per unit leaf area (net assimilation rate, E), provided factors affecting the structural growth rate- such as temperature - are constant. In fact this relation has been found experimentally [32] (Figure 5) but not hitherto accounted for. Undoubtedly this interpretation is an oversimplification. Nevertheless, S tends to rise with treatments that increase structural growth (higher temperature, water status, or nutrition), and to fall with treatments that increase formation of photosynthate (higher light or CO, concentration). S seems to provide some guide to the balance between formation and utilization of photosynthates.

010

008

006 E 004

0.02

E (g m I d ) Figure 5. Relation between E (rate of net dry-matter gain per unit leaf area) and S (leaf area/leaf weight) for plants of Impatiens parvifora. Line is reciprocal relation fitted to data of Hughes and Evans [32] for field and controlled-environment plants; circles are data of Warren Wilson (unpublished) for controlled-environment plants grown at 140 C. 45 Thus, a low S implies that the photosynthetic source could support a greater number or activity of sinks for structural growth. In glasshouse crops, sink strength can be increased by raising the temperature. In field crops, it can be increased by closer spacing, or by selecting genotypes with more sinks (e.g. more tillers, more fruit primordia) or sinks that are more active. Genetic differences of this type are known: dark respiration rates under standard conditions tend to be higher in species from colder climates [60]:

Respiration rate (T 1s" g CO, M-2 s-) Tropical species ...... 14 Tem perate species ...... 35 A rctic species ...... 64 and in species from more strongly lit climates [24]:

Respiration rate (X 10- gg-s-1) Shade-tolerant species ...... 0.52 Shade-intolerant species ...... 1.23 Crop and arable weed species ...... 1.46 and higher relative growth rates are associated with these differences [24].

4.3 Respiration

The proportion of gross photosynthate that is used in respiration varies widely with the crop and environment but is often substantial; it may be useful to recognize three components of total respiration, even though they are not fully distinct: a) Constructive respiration. Structural growth requires respiratory energy to drive the synthetic processes. A close relationship between relative growth rate and respiration rate has been shown in, for example, sunflower plants [49] and sweet potato tubers [59]. Scattered estimates suggest that for each gram of tissue synthesised, about half a gram of substrate is respired to provide energy; i.e. that the efficiency of growth is about two-thirds (Table 7).

Table 7. Efficiency of growth (dry weight of synthesised tissue/dry weight of substrate utilized) Species Substrate Efficiency Source Hordeun distichum (barley) (Seedling) ...... Endosperm 0.64 [5] Helianthus tuberosus (Jerusalem artichoke) ...... Photosynthate 0.70 [30] Helianthus annuus (sunflower) ...... Photosynthate 0.71 [49] Ipornoea batatas (sweet potato) (Tuber) ...... Photosynthate 0.84 [59] b) Maintenance respiration. Even in mature organs where there is no growth, respiration is required to maintain existing organisation; for example, to maintain concentration of mineral salts within tissue. c) Substrate-induced respiration. Both constructive and maintenance respiration utilize photosynthate in ways that are of value to the plant. By contrast, respiration that is not 46 coupled to productive metabolic processes may also occur. This is suggested by the increased respiration rates of potatoes when sugar levels have been raised by low temperature [4], and by the increased rates in mature leaves that are associated with fall in S [67] or with increase in photosynthesis and sugar concentration [59, 73]. The implication for maximising productivity is that the crop should have, in the prevailing environment, rates of growth that are sufficiently high to utilize fully the available photosynthate, with minimal uncoupled respiratory 'wastage'.

4.4 Partitioningof dry matter between organs

Partitioning between organs varies with species, environment, and plant size. For example, the proportion of total dry matter incorporated in the leaves is greater for smaller plants and stronger light, especially in certain species [37]. For widely-spaced plants, increase in the relative size of theleaves greatly enhances accumulation of dry matter. Forexample, consider thecase of two plants of similar initial dry weight (0.1 g) and E(10 g m- 2 d-1) but with different leaf area/plant weight ratios (0.010 and 0.015 m 2 g-). This 50 Y increase in leaf area relative to plant weight results in an increase of over 700 % in plant weight after 40 days' growth (Table 8).

Table 8. Calculated effect of a difference in leaf area/plant weight on dry matter accumulation Time (days) Dry weight of plant (g) for leaf area/ plant weight of 0.010 m2 g' 0.015 m 2 g-1 0 ...... 0.10 0.10 10 ...... 0.27 0.45 20 ...... 0.74 2.0 1 30 ...... 2.0 1 9.00 40 ...... 5.46 40.35

Leaf expansion (and probably root extension too) are determined not only by dry- matter partitioning. Accumulation of water, as affected by cell wall plasticity and turgor pressure, is probably also an important determinant. Although more research is needed in this field, it seems clear that freedom from water stress must be ensured in order to achieve the high rates of surface area extension that are essential in vegetative establishment. On the other hand, surface area increase is less important than dry weight increase where the harvested part is concerned, since dry weight is more closely related to food value (ornamental crops excepted). It is therefore important that, once the harvestable part has been initiated - such as the wheat grain or the potato tuber - all dry matter that is surplus to the minimum needed to maintain an efficient photosynthetic source should be partitioned to the harvestable part. Also, there should be as much remobilisation of material as possible from non-harvestable parts to the harvested organ during the later stages of maturation. There is wide variation among crops in the ratio of harvestable to total dry weight, as the following approximate values show: Potato (tuber) ...... 0.82 [10] Sweet potato (tuber) ...... 0.65 [59] 47 Sugar beet (root) ...... 0.50 [23] Chrysanthemum (flower) ...... 0.46 [17] Cotton (boll) ...... 0.33 [57] French bean (pod) ...... 0.25 [36] Tulip (flower) ...... 0.20 [52]

Unfortunately, increase in harvestable yield in terms of dry matter sometimes brings a loss of quality. For example, a higher level of soil nitrogen increases the weight yield of sugar beet roots, but reduces the sugar yield [39]; restriction of the number of fruits on the tomato truss increases their sugar concentration and quality [69].

5. Optimizing the crop environment

For field crops, artificial modification of the climate is impracticable, except marginally as by windbreaks. On the other hand, within glasshouses it is possible (at a heavy cost) to modify CO, concentration, temperature, and other factors.

5.1 Glasshouse climates

At present, CO, enrichment is used during only those seasons when light is weak; during summer, the ventilation of glasshouses that is needed to prevent excessive temperature makes enrichment impracticable. Raising the CO 2 concentration three-fold, to about 1000 ppm, increases dry-matter production and fruit yields by about 30 % [15,33]. This increase is useful, but in magnitude it does little more than compensate for the reduction associated with the 30% loss of light caused by the glasshouse structure. Equation (4) and figure 1 suggest that CO 2 enrichment would be far more effective during periods of strong light. Experiments show [34] that enrichment to 1000 ppm raises

* I i xcJ..

2 010x0'4 'a

C (pot

Figure 6. Effect of 14 (light flux density) and C (CO 2 concentration) on relative growth rate of Beta vulgaris plants [34]. 48 the relative growth rate of Beta vulgaris plants by only about 0.003 g g-' d-1 in winter glasshouse light, but by over 0.02 g g'I d-I in summer light (Figure 6). Moreover, the increased response to CO2 in strong light should make it worthwhile enriching to higher concentrations, with increases in relative growth rate of perhapsO.04 g g- d-1. Such advances await the development of glasshouses cooled by refrigeration instead of ventilation and, preferably, constructed of self-supporting transparent plastics which transmit more light.

5.2 Field crop environments

Although climatic control is impracticable for field crops, it is possible at least to select regions or localities where the climate is relatively favourable, and to choose crops and growing systems suitable for the prevailing conditions. Earlier sections have shown that a high light receipt is of first importance for maximising productivity. Temperatures must also be reasonably high, particularly in order for sink activity to be sufficient to accommodate the photosynthate; however, temperature is perhaps less critical, both because high light receipts usually result in warm conditions, and because increased density and the breeding of appropriate cultivars can help to provide adequate sink strength. The close dependence of productivity on the light climate is made clear in figure 7 by data on rates of dry-matter production per unit leaf area (E) for young, widely-spaced sunflower plants grown with non-limiting nutrient and water supply. Measurements on various occasions during the growing season show E to be almost directly proportional to light flux density, with similar slopes for two different climatic regions. More detailed analyses reveal that temperature also affects E (this is responsible for some of the scatter of data in figure 7); however, its effect is of secondary importance during the growing season. In aclimate that has a cold season, temperature of course becomes a major limitation to annual productivity. Multiple regression analyses of Eon light flux density and temperature [63], coupled with meteorological records, allow prediction of seasonal trends in E; examples for four

•Oxt d F,land 20 2

" 1. (W 0Jm.'d ) Figure 7. Effect of 4 (light flux density) on E (rate of net dry-matter gain per unit leaf area) for He- lianthus annuus plants; data from [9] and [63].

4 49 'a-Ml d dMd

WtrS,*tmr Winter Figure 8. Seasonal changes in E (rate of net dry-matter gain per unit leafr area) for Helianthus annuus plants, predicted from multiple regression on light and temperature, for four climates. climatic regions are shown in figure 8. In the arctic climate, low temperature seriously limits both the length of the growing season and the value of Eduring the brief summer. In the temperate climate, restriction by temperature is less severe, and during the warmer part of the year light becomes the main limiting factor. In the tropical climate, limitation is by light rather than temperature throughout the year; the seasonal cycle is small. For the arid climate, seasonality is marked but Eduring the summer is very high and the total annual production not less than that in the tropical climate. For these four particular examples, predicted annual dry-matter production by widely-spaced sunflower plants, with non-limiting nutrient and water supply, is as follows (expressed on a leaf-area basis):

-2 - Arctic (Resolute, N.W.T., Canada) ...... 670 g m yr ' 2 - Temperate (Kew, England) ...... 2170 g M- yr ' 2 -1 Tropical (Benin City, Nigeria) ...... 5110g m- yr 2 1 Arid (Deniliquin, N.S.W -, Australia) ...... 5522 g m- yr-

There is an apparent conflict between the direct proportionality between Eand 1 in figure 7, and the hyperbolic relation between Pu and I in figure 2. The same contrast has been found in other, comparable data. Possible contributing factors are that, since data of the type in figure 7 are based on long-term field observations, (i) the tendency in natural climates for temperatures to increase with light may enhance the rise in E with increase in 1o, (ii) there is time for leaf structure and physiology to become modified in relation to increased I, in ways that allow more efficient use of the strong light [7,27]. Whether or not these interpretations are correct, it is certain that the leaves of some species do not become light-saturated in the field as readily as might be expected from laboratory studies on leaves grown under moderate or low light. As a result, extremely high values of Ehave been found to occur [62] in plants growing in the arid zones around latitudes 300 in summer, when clear skies, fairly long days, and a sun rising high in the sky combine to give more light than in any other climate. Indeed, provided adequate soil nutrients and water are provided, it seems that these arid zones can support the greatest annual crop production. This is because, as shown in table 50 Table 9. Variation in annual light flux density with latitude, for conditions of mean cloudiness [31. 56] Latitude Light flux density 1) (x 10 J rn-2 yr- 0- 100 ...... 3.16 10-20 ' ...... 3.28 20-30o ...... 3.32 30-40 ' ...... 2.9 1 40-50...... 2.3 1 50-60 ' ...... 1.79 60-70...... 1.37 70-80' ...... 1.10

9, the mean annual light receipt in the 20-30 latitudinal zone is higher by a small margin than that for any other latitude. The sites of highest light receipt occur in certain regions only within this zone, where it crosses the continents. The natural vegetation of these arid lands is unproductive, owing to drought. Only if sufficient water and mineral nutrients are provided can the high potential productivity be achieved. For two reasons, it may be preferable to supply water and nutrients by a water culture system. First, water and nutrients supplied in containers are used far more economically than if they are added to the ground (which in these regions is infertile). Se- condly, even with fertile soils it may be impossible to ensure adequate supplies at the root surface owing to the very high rates of water demand. Figure 9 shows that Efor plants in fertile soil is equal to Efor plants in water culture when under moderate light, but falls below Efor plants in water culture under conditions of intense light characteristic of the arid summer. Many soils have physical properties such that appreciable water potentials may arise close to the roots under conditions of intense water demand [18]. Local gradients in mineral nutrients within the rhizosphere are also to be expected [46], and may well be unfavourable in some cases. Water culture systems avoid these limitations associated with soils.

100

0 5i 0 ~ I (51. J I,; d') Figure 9. Effect ofil (light flux density) on E(rate of net dry-matter gain per unit leaf area) for He- lianthus annuns plants grown on soil (open circles) or water culture (closed circles). 51 6. Maximum yield potential

6.1 Estimatedpotential

An estimate of the highest yields that can be expected when crops grow efficiently in a favourable environment can be arrived at by stages as follows, using relations discussed in preceding sections: a) Yield is ultimately limited by the light climate, and for the present purpose a light flux density of 3.30X 109 J m- 2 yr -' is assumed. This is typical for latitudes 10-300, though appreciably higher values occur in some arid regions within this latitudinal zone. b) A perennial crop is likely to intercept more of this light than an annual crop; even for a perennial, however, the canopy is incomplete during establishment. If it is assumed that the fraction of the year for which the canopy is complete is 0.9, the available light is 0.9 X 3.30 = 2.97 x 109 J m-2 yr-. c) It is assumed that the proportion of light intercepted by the established canopy is 0.9. This fraction would be intercepted by, for example, L=5 and K=0.46, or by other combinations of L and K as shown in figure 3. Hence intercepted light is 2 0.9 X 2.97 = 2.67 X 109 J m- yr1. d) Section 2.3 noted that estimates of the maximum efficiency of the photochemical - 6 process (b) vary between 7.4-23.0 x l0 g CO 2 J-1 Assuming an efficient system, with b = 20 x 10" g CO . J 1, then if gross photosynthesis is operating at maximum efficiency the rate of CO, uptake per unit area of ground is (20 X 10-6) x (2.67

2 Tropical g m- yr-' Crops, perennial ...... 8000 Reedswamp ...... 6000 Rain forest ...... 3500 Crops, annual ...... 3000 Temperate Crops, perennial ...... 3000 Crops, annual ...... 2000 Grassland ...... 2000 Forest, deciduous ...... 1500 52 It is concluded from this theoretical analysis that it should be possible, by careful application of agronomic techniques to suitable crops grown in favourable climatic regions, to achieve maximum yields about 30 % greater than the highest now obtained.

6.2 Suggestedproceduresfor achieving maxinnm yieldpo tential

The following practical procedures are indicated by the arguments above: (i) Regions of high light receipt are potentially the most productive. Many of these regions are arid and semi-arid, and extension ofcropping into these zones may be most efficiently achieved by water culture techniques. (ii) Canopies capable of intercepting most of the incident light must be maintained for most or all of the year. This is best achieved with perennial crops. If annuals are to be grown, special cultural practices may be worth exploring, e.g. sequential sowing dates, or the adjustment of spacing of plants during growth in water culture. (iii) Genotypes with high photosynthetic efficiency (b preferably exceeding 20 x 10-6 g CO., J-1) should 1e selected. (iv) To minimize respiratory losses, genotypes are required which have high efficiencies of growth (Table 7), adequate but not excessive sink strengths for the prevailing conditions, and low values of C,. (v) To minimize depression of P/In belowb, it is desirable to have leaves with high r; this can be promoted both by selection of genotypes and by appropriate cultural techniques. CO, enrichment can achieve the same end. (vi) Selection of cultivars and growing systems should ensure that Kand L are optimal in relation to 1o. (vii) Crops should be so selected and grown as to give maximum ratios of harvestable to total dry matter (section 4.4).

Definitions of symbols used a constant in photosynthesis equation (=b/TC) ...... m 2 s J-I b maximum efficiency of photochemical process in photosyn-

thesis ...... g C O 2 J-1 C CO , concentration ...... ppm C, CO 2 ccncentration at compensation point ...... ppm E net assim ilation rate ...... g 2d-1 I light flux density in plane of leaf ...... J M-2 s- lk light flux density in plane of leaf at compensation point ...... J m-2 s- 1 o light flux density in horizontal plane above canopy ...... J m-2 s- ' light flux density in horizontal plane beneath leaf area index L J M- 2 s- 1 2 - I light flux density intercepted by leaf area index L ...... J M- s 1 K extinction coefficient of canopy k constant in photosynthesis equation ( = rbI) L leaf area index In transmission coefficient of leaf Pg gross photosynthetic rate per unit leaf area ...... g CO M-2 S-1 -2 - Pn net photosynthetic rate per unit leaf area ...... g CO 2 M S 1 2 - Pn net photosynthetic rate of canopy per unit ground area ...... g C0 2 M- s 1

53 2 S leaf area/leaf weight ...... m g-1 e efficiencyof light utilization incrop dry-matter production ... g J- efficiency of CO diffusion process in photosynthes- r maximum 2 2 - 1 is ...... g CO , rM- s ppm-' Units m metre s second ppm parts per million, by g gram d day volume J joule yr year

Summary

For field crops provided with adequate water and mineral nutrients, the ultimate limitation to yield is set by the amount of light intercepted by the crop canopy and by the efficiency with which this light is used in photosynthesis. Equation (10), on page 41, describes how six basic physiological and structural characteristics of the leaf canopy interact with the light climate in determining the photosynthetic rate of the crop. The equation shows how dry-matter production can be maximized by optimizing these characteristics through selection and crop management, and it allows prediction of the potential rate for any given light climate. The greatest potential productivity is to be expected in arid climates, owing to their high light receipts. In theseclimates, soil may fail to transport adequate water supplies to the root surface, and it may be necessary to adopt water culture to achieve maximum potentials. g yr-' is predicted for total dry matter in arid climates, A potential production of about 11,000 m-2 - 2 1 and a crop dry-matter yield of about 8000 g M yr- . Such yields, which are some 30% higher than those attained hitherlo, can be achieved only by crops in which high efficiency of formation of photosynthate is balanced by efficient utilization of photosynthate in respiration and the synthesis of new tissues.

Acknowledgements

I am grateful to Mr. R. C. Hoare for deriving equation (10) from equations (5) and (9), and to Mr. J.Tunny and Mr. S. J. Rance for assistance with experiments on Helianthus annuis and Impatiensparviflora respectively.

Bibliography

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Dr. M. THIFLEBEIN, Chief, Field Crops Branch, Plant Production and Protection Division, Food and Agriculture Organization of the United Nations, Rome (Italy) Dr. W. M.TAMT, Cereal Improvement and Production Officer, FieldCrops Branch, Plant Production and Protection Division, Food and Agriculture Organization of the United Nations, Rome (Italy)

1. Introduction

'Combined variety/fertilizer trials have already proved that individual varieties show great differences in their nutritional requirements. It hasalso been theparticularendeav- our of plant breeders in recent decades to produce as many good fertilizer-users as possible, i.e. varieties able to withstand and repay interest on improved soil productivity through more perfect cultural techniques and fertilization.' This is a translation of the introductory part of a paper published 40years ago by J. Wei- gert and F. First [56], and is put at the beginning of this paper to show that the subject to be treated here is by no means new. It was first considered at least a century ago when in parts of Europe soil productivity was suddenly increased by the introduction of leguminous and root and tuber crops in the rotation cycle to replace the fallow and thus provide high amounts of stable and green manure to thesoil and at the same time by the start of mineral fertilization. It was then that contemporary agriculturists reported the decreasing yields of cereals due to lodging and to the increasing incidence of cereal diseases [35]. From that time up to the present plant breeders have been in a steady race with the increasing utilization of chemical fertilizers to provide varieties which give economic returns to the increasing soil fertility. Thus, average yields of wheat have increased from a little over I ton/ha in the middle of the last century to the present 3 tons/ha in most European countries, and to more than 4 tons/ha in Belgium, Denmark, Germany, Netherlands, New Zealand an the United Kingdom. With regard to rice, the advances in temperate climates have been even more spectacular with average yields of nearly 7 tons/ha in Australia, over 6 tons/ha in Spain and over 5 tons/ha in Italy and Japan [60]. However the world average yield for wheat is still about 1.5 tons/ha and for rice about 2 tons/ha, mainly because developing countries in the tropical and subtropical zones of the world have been excluded from this steady year by year increase in yields of the food crops and particularly of cereals. This has lead to a critical food situation in many of thesecountries, sincecereals are still the staple food, by direct and indirect consumption, for the majority of people. The hopes that, with the arrival of chemical fertilizers in developing countries over the past two decades there would be a change for the better by raising the fertility of the soil which had been exhausted by thousands of harvests without nutrient replacement, have not materialized. Cereals yields are still below I ton/ha in most of these areas due to the same phenomenon which developed countries experienced a century ago - most tradi- 57 tional crop varieties, particularly cereals, did not respond adequately to additional nutrients. It is only in the past 3 to 4 years that, due to the unique breakthrough in cereal breeding in Mexico and the Philippines, with the assistance of the Rockefeller and Ford Founda- tions, in providing varieties of wheat and rice with high yielding potential and economic response to fertilizers and other inputs in tropical and subtropical areas, a real hope exists for a much more rapid improvement in the world food situation than has hitherto been possible. A rise in cereal crop production in developing countries similar to that in developed countries can now be expected, but instead of requiring a century it could be done in a quick motion tempo with all the production means at hand and the experience of developed countries in mind. It is with this background that the following summary of work already done and still being done in breeding forefficient fertilizer use is restricted to cereals.

2. Breeding for sturdiness

It was in fact the demand progressive farmers made for cereal varieties capable of using increased soil fertility more efficiently that marked the beginning of practical plant breeding in the middle of the last century. Better and deeper tillage for the newly introduced root and tuber crops into the rotation, the cultivation of leguminous foddercrops, such as clover and lucerne, on arable land, the useof the drill and hoe in cereal husbandry, heavier manuring resulting from increased livestock, and the application of mineral fertilizers, increased the soil fertility to such an extent that the traditional land races of cereals with their weak straw and poor root system went down from lodging and decreased in yield instead of giving higher yields expected from the improved environmental conditions. The first problem to be tackled therefore was to look for varieties with lodging resistance. This was found in the English 'Square-head'wheat, avarietywhich spread over the continent and was widely grown in Germany, despite its weakness in winter hardiness, and it was only after the re-discovery of the Mendelian laws and with the beginning of systematic cross breeding that the production began of new winter hardy, lodging resistant varieties in all cereal species. Despite early recognition that the lack of sturdiness is one of the main limiting factors for the productivity of cereals as well as for the efficient utilization of fertilizers, one will find that breeding has always been behind demands arising from the increasing application of fertilizers, particularly nitrogen. This was mainly due to the fact that on the one hand farmers were interested until recently in obtaining adequate straw yields for litter and fodder, and on the other lodging was dependent on many inherent and environmental factors. A comprehensive literature dealing with the causes of lodging as well as with inherentence of lodging resistance extends, therefore, from 1905 when C. Kraus first dealt with the formation and mechanical capacity of the stalk [24] until up to the present, when K. Koch and H. Kuehn [20] reported on the influence of potash on stalk stability and lodging tendency of spring and winter wheat. Some literature for easy reference to readers interested in the subject has been cited in the bibliographical data [ l, 2,4, 1l,12,15,18,21,22,24,25,26,27,31,34,36,42,44,45,51,55]. The general conclusions from this literature are as follows. 58 The tendency to lodging is correlated to the length of culms (r >0.6); radial diameter of vascular bundles and number of vascular bundles in the Parenchyma region are greater in stiff straw varieties; the mechanical resistance of the stalk increases with shorter and stronger basal internodes; linear correlation-coefficients exist between varietal differences in lodging and the spreading angle of roots. However, there is no strict relationship between resistance to lodging and any specific morphological character - consequently any determination of straw stiffness founded on morphological characters has to include several ones. The comparative analysis has to include: 1) plant length and internode length; 2) in basal internode: total cross-section area, culm-wall and anatomic details such as vascular bundles, diameter and composition of sclerenchymatic tissus; 3) root system as far as possible. What might be of particular interest here is the fact that potassium has been shown to have very important role in determining strength of straw. Thus Purvis [38] found that in the absence of potassium, culms of Dactylisglonerata loose their capacity to stand erect and concluded that it was not so much by inducing anatomical changes as by influencing physiological character of chemical composition of the cell wall that K played its part. Also Pfaffenberger [35] reported on an increasing stability of the stalk by potassium application. Tubs [52] in wheat and barley, and Raniah [41] in rice also reported that K was essential for straw length. Ekstein [9] found increasing strengthening of the straw with increasing potassium doses in wheat and barley fertilization trials. Krants and Chandler [23] found that lodging in maize decreased and yield increased by the application of K in potash-deficient soil, but it did not effect lodging or yield in potash-rich soils. Furthermore, lodging increased with higher plant populations despite the fact that potash uptake, as reflected by leaf composition of all samplings, went up with application of potash. Koch and Kuehn [20] very recently reported that an optimal potash nutrition of plants had a positive effect on culm length of spring and winter wheat. Plants sufficiently provided with K had been shortened by CCC much more in both relative and absolute terms, than plants badly nursed with K. The diameter of culm in the zone between root and first node had not been changed significantly either through potash or through CCC, but that of the first and second internodes had been enlarged. A significant increase in the diameter had been provided by K. However the biggest enlargement of the diameter of the culm as well as that of the first and second internodes was found by optimal potash application andco-incident CCC applications. Theelasticityof theculms had not been changed by potash. Plants provided with an optimal dose of K withstand wind pressure better than badly nourished plants. All past research, of course, was based on relatively tall cereal varieties which, even when bred for short and stiff straw, went down in densely grown crops due to the etiolation effect on basal internodes caused by insufficient light resulting from the largecanopy. Application of phosphatic and potassium fertilizers alone even at larger doses had little or no effect while nitrogenous fertilizers only further aggravated the situation. How far the tallness of cereals has been responsible for limiting the plant population and use of fertilizers has been clearly indicated by two recent developments. Researches carried out on growth regulators in Europe during the last few years have shown that the problem of lodging in cereals can be solved by shortening and strengthening the straw of plants through an application of CCC (2-chlorethyl, tri-methyl-ammonium chloride). Humphries[17], who has reviewed the present knowledge on the use of CCC has quoted reports from Austria, Belgium, Finland, France, Hungary, Italy, Netherlands, Roma- nia, Sweden, Switzerland, Germany and the United Kingdom, which indicate that the 59 application'of CCC on winter wheat prevented lodging in wet weather and substantially increased grain yield. Humphries concluded that the ability of CCC-treated cereals to withstand lodgingdepended partlyon itsreduced height and partly on changes in theanat- omy of basal internodes by increasing their cell thickness, size of parenchyma cells and number of vascular bundles. There were also reports that CCC enlarged the root system and sometimes leaves were shorter, broader and more erect. However, as these varieties were inherently tall and were not bred specifically for higher fertilizer consumption, CCC application did not show positive interaction with nitrogen beyond optimum levels and in fact the greater the amount of nitrogen supplied the less was the effect of CCC in reducing stem length. A dawn to the reconstruction of the morphology of the wheat plant had broken when in Japan genes were discovered in the Norm wheat variety which conferred a dwarf and non-lodging plant habit. Several dwarfing genes had been known for long in wheat, such as the S or C genes which govern the spherococcum and compactum characteristics respectively, but these genes produced coincidentally short, very dense and compact ears. Roemer, one of the preachers of lodging resistance, in his Handbuch der Pflanzenziichtung [47J feared that breeding for short straw would be limited by these undesirable compactum factors and also by shortening of root lengths. The first variety which appears to have had the desired combination of short plant height, lodging resistance and good ear characters was Norm 10. This variety was one of a collection of Japanese wheats brought to the U. S. A. by Dr. S. C. Sabnon in 1946. This was followed by two other sources of dwarfing genes, namely 'Olesen dwarfing' and 'Tom Thumb'. Three recessive genes for dwarfing with additive effect have so far been identified in this material. Using the Norin dwarfing genes the semi-dwarf winter wheat variety' Gaines' was developed by Dr. 0. A. Vogel in Washington State, U. S. A. in 1961. In 1954, Dr. N. Borlaugand co-workers started making crosses between improved Mexi- can varieties and two of Dr. Vos'el's selections, e. g. Norm 10 x Baart and Norm 10 X Brevov. The selections from these crosses containing Norin recessive gene for shortness resulted in a whole new set of varieties which have become world famous for theiradapt- ability to sub-tropical zones and their high fertilizer response [6]. Latest news from Eu- rope indicates that its plant breeders are now on the way to following the example given by the U. S. A. breeders.

3. Disease and pest resistance

A second main limiting factor to effective utilization of increased soil fertility had been the heavier incidence of diseases and insect pests. With the improved growing conditions for the cultivated plants the conditions for the parasites also changed for the better. They even are often more favoured by the changed micro-climate and by faulty one-sided fertilization than the crop itself. Until the beginning of systematic plant breeding combat- ting the parasite and healing the disease, similar to human and veterinary medicine, had been regarded the only possible way of control in plant pathology. Only when it became clear that the basic relationship between host and parasite is genetically fixed and that this genetical base is constant, that breeding for disease resistance started on a broad frontier. Breeding methods established at that time are still valid today and are widely used. Complete bibliographical data up to 1937 have been given by Roemer, Fuchs and Isenbeck [46]. It has to be understood, however, that in contrast to other genetically de- 60 termined plant characters the breeding for disease and insect pest resistance is a continuous process because the two living systems are interacting and new races of diseases and strains of insectscontinue to appear. New approaches have to be developed through fundamental breeding research with regard to identifying the sources of resistance genes. After Flor [10] first formulated in 1946 the gene hypothesis of host parasite interaction to explain the relation of pathogenecity genes in Melampsora lini (Ehrenb) to reaction genes in flax stating that each gene conditioning the action of the host corresponds to a specific gene conditioning pathogenecity of the parasite, a new field of fundamental research has been opened which could help augment the parental material in breeding for disease resistance.

4. Relationship ofyield toplant characters

Richardson and Gurney [43] observed that the number of ears at harvest was almost directly related to yield in winter wheat in Australia. Locke et al. [30] reported that correlation between yield and number of kernels per unit area was the highest (r= 0.98) and was unaffected by seasons or treatments, and this was followed by heads per unit area (r= +0.77 to 0.86) and by kernels per head (r - 0.63). In these tallvarieties the relationship of yield with plant height was high (r = 0.74), while that with plants per unit area was almost non-existent (r = - 0.14). Mean kernel weight (r = 0.20), head length (r =0.38), and spikelets per head (r -0.29) were relatively unimportant. Fromthemultiple correlations they concluded that selection for higher yield should be based on the highest number of heads per unit area and the number of kernels per head, which would result in a higher number of kernels per unit area. A similar relationship was found by Tahir [50] in maize. Gregory [13] found in pot experiments on barley that in N deficiency photosynthesis was normal but leaf area was reduced partly due to smaller leaf size but mainly due to the reduced number of tillers, and this adversely affected the total grain yield. In P deficiency, reduced tillering and lower assimilation and smaller and earlier aged leaves all contributed to lower yields. Thus tillering is an important character for selecting high yielding small grains cereal varieties. However, the tillers which contribute to yield are those which are formed in the beginning of the growth period as the tillers formed later die off without producing ears [16]. A significant feature of high yielding dwarf wheat varieties is their ability to produce a large number of fertile tillers. A well developed and efficient root system increases the feeding power of plants, and the plant breeder may be able to produce strains which increase the uptake of nutrients from the soil. There are also indications [59] that at low nitrogen levels and wide spacing, the open tiller types yield better, but with a heavy nitrogen application and at close spacing the upright tiller types produce a higher grain yield.

5. Yield andplant type

When a crop is supplied with adequate water and nutrients and is kept free from disease, the maximum rates of water use and dry matter production are determined primarily by the receipt and use of radiant energy. Therefore plant breeders should strive to select varieties which will make the most efficient use of solar radiation in a given climate. Bessel Kok [3], after considering the spectral composition of sunlight, arrived at an optimal en- 61 ergy conversion factor in plant growth of some 20% of absolute radiation which was about tenfold higher than attained in customary methods of plant cultivation. It was concluded that the great difference between potential and achievement indicated the scope of further research aimed at improving the low yields obtained in field crops resulting from sub-optimal conditions of light intensity and absorption, temperature, supply of carbon dioxide, water and nutrients. Therefore the most effective breeding techniques would be those based on understanding and careful evaluation of physiological efficiency of plants in the segregating generations of crosses. However, such techniques have not been put into wider practice and some of the basic data are lacking on which research workers could proceed to evaluate'physiological breeding' methods. McCloudet al.[31] reported that the measurements of net photosynthesis by successive layers of leafage at different light intensities showed that photosynthesis (and hence the total dry matter production) was related to light interception leaf area and leaf angle. Monteith [32] stated that the transmission of radiation through the canopy of a field crop could be expressed as a function of the leaf area index (ratio of leaf surface area to the area of underlying ground), and a parameter that depended on the distribution and orientation of leaves. The suggestion implicit in his findings was that with better orientation of leaves, a higher leaf surface area per unit of land could be supported without mutual shading by intercepting a higher fraction of incident radiation. This interpretation is also supported by Williams et al.[57], who related parameters of canopy architecture of maize at population densities ranging between 17,500 and 125,000 plants per hectare to light interception and productivity, and concluded that, with nutrients and soil moisture non-limiting, the amount of solar radiation intercepted by the foliage canopy was a major determinant of crop growth at the vegetative stage and that leaf arrangements with a majority of errect leaves, occurring just before tasseling, allowed the deepest penetration of light into the foliage canopy and gave the highest crop growth rates. Since the grain yield is the function of dry matter production after flowering, and adequate leaf area index is one of the requisites for dry matter production, it is important to breed for plant and leaf characters which will maximize the leaf area index at the initiation of the repro- ductive phase without the debilitating effect of mutual shading. Leaf area index (LAI) is the product of tiller number per unit area, leaf number per tiller, and average leaf size. Studies on physiology of types of rice plant at the International Rice Research Institute [59] have shown that the increase in LAI in high nitrogen-responsive and dwarf variety Tainan 3 was dominantly controlled by an increase in tiller number, and to a limited extent by leaf size, especially in the early stages of growth. Fur- thermore, if increases in LAI of a variety occurred mainly as a result of an increase in leaf size, plants suffered from mutual shading and leaves tended to be long, open, thin and droopy and there was a less amount of nitrogen and a lower photosynthetic rate per unit leaf area. It was concluded that varieties with leaves that were short, erect, thick and rich in nitrogen, and with moderate tillering capacity, were desirable for increasing the re- spcnse to fertilizers. Leaf erectness is a particularly important leaf character because it permits light penetration to lower leaves of the leaf canopy which are enabled to make a positive contribution to assimilation. In a study on relationship of growth duration to yielding ability and nitrogen response, the Institute[59] reported that at high nitrogen levels (100 kg/ha) the photosynthetic rate at flowering increased as the growth duration (from sowing to flowering) increased up to 90 days due to an increase of LAI, without mutual shading becoming serious, but if the growth duration exceeded 90 days the photosynthetic and assimila- 62 tion rates declined markedly due to increased and prolonged mutual shading and higher respiratory rates, and there was also an indication of a declining grain-straw ratio with increased growth duration. Thus there is an optimum growth duration for obtaining the highest grain yield under a given set of conditions, and the optimum is shorter under high than under low nitrogen levels. Moreover, nitrogen response tends to be larger with shorter than longer duration varieties of cereals. The relationship between growth duration, fertilizer response and high yield is only applicable to varieties without photoperiodic sensitivity, as the varieties which are season- bound give consistent but lowyields underdifferent treatments. Thesevarieties have self- adjusting mechanisms which allow them to have more or less the same tiller number and LAI at flowering time irrespective of differential fertilizer, weeding, spacing, dates of planting, etc., treatments. Burton [5] has pointed out that whereas short-day photoperiod sensitivity (to have a longer vegetative period), late maturity, and leafiness are desirable characters in forage varieties of pearl millet, in varieties to be used for grain, 7 or 8 short, stiff, erect leaves per culm, photoperiod intensitivity, short maturity, dwarfness to permit the application of fertilizer, irrigation, and other practices to maximize grain yield, the ability to develop fertile and lodging-resistant tillers, are the most desirable characters. The varieties of wheat or rice wich have recently made a break-through in yield levels and responses to fertilizers are those which are insensitive to photoperiodism and are therefore adapted to a wide range of latitudes. 'Norin 1 ', released in 1930 in the Hokuriku District of Japan, was the first semi-dwarf variety of Japonica rice bred especially for early maturity, high yield and quality, resistance to diseases and responsiveness to heavy application of fertilizer [58], and this has been followed by even more efficient fertilizer-consuming varieties with the result that consumption in Japan of N, PO, and K 20 in rice between 1950 and 1960 increased by 30, 100 and 400 percent respectively. Short statured and highly fertilizer-responsive varieties of Indica rice were first developed in China (Taiwan), and these have been used in the hybridization programme of the International Rice Research Institute in the Philip- pines to produce a range of varieties which have short stature (about 100 cm), stiff and non-lodging straw, short and upright dark green leaves, resistance to a number of important diseases and insect pests, reasonable seed dormancy at harvest time, moderately firm threshing ability, medium maturation period, and are responsive to very high doses of fertilizers (e. g. N = 120 kg/ha) and give yields which were unthinkable in the past in these zones. Because of their photoperiod insensitivity, new types are adapted to a wide range of latitudes. Although still far from perfect, these varieties have not only introduced in the rice growing areas of the tropics a plant type best suited to make economic use of modern technology in farm management, but also incited local breeders to search for this type in their material. It has also been demonstrated in the field that the efficient utilization of available sunlight by reducing mutual shading to the minimum is essential for high yields. Vogel and his colleagues [53, 54] placed considerable emphasis on the development of short stature in wheat varieties. Widespread use has been made of the semi-dwarfing trait found in the beginning in the Japanese selection 'Norin 10' and later in another variety called 'Tom Thumb'. Studies have indicated that there are one or two major semi- warfing recessive genes which, in combination with several modifying factors, produce a wide range of culm lengths. Recent releases of semi-dwarf spring (Mexican) and winter (U.S.A.) varieties with remarkable yield potential have stimulated much interest in breeding for this character. A reduction in plant height generally reduces lodging and 63 mutual shading, increases the grain-straw ratio, permits higher plant density and heavy fertilization as well as irrigation, and results in potentially higher grain yields. The development of the semi-dwarf spring varieties by the International Maize and Wheat Im- provement Center in Mexico has revolutionized wheat production in many developing countries (e.g. Mexico, India, Pakistan). The Center's reports [62] point out that in transferring dwarf character from Norm 10 to Mexican varieties apparently additional genes for potential yields were incorporated in newvarieties which,when properly fertilized and irrigated, enables them to produce more fertile tillers per plant and fertile florets per spike. Semi-dwarf Mexican varieties have a yield potential ranging between 5and 7tons/ha at high levels of fertilizers, and have a wide adaptation because of their insensitivity to daylength, and a broad spectrum of resistance to stem and leab rusts. Al- though developed especially for conditions in irrigated areas, they rank among the top yielders under assured rainfall conditions. Varieties so far developed are either 'single dwarfs' (semi-dwarfs) or 'double dwarfs' (dwarfs), which can utilize 90-100 and 120-140 kg/ha of nitrogen respectively without lodging. By using new sources of dwarfing genes derived from the Rhodesian dwarf variety' Mazoe'attempts are being made to develop a suitable'triple dwarf' to further reduce plant height so that even higher doses of fertilizers can be used to increase yields. Dwarfing genes from bread wheat have also been introduced in durum wheat, resulting in dwarf and photoperiod insensitive lines which give over 40 % more yield, reduced straw-grain ratio and can consume 140 kg/ha nitrogen without lodging, compared with 80-100 % lodging in the tall varieties [62]. In millet the dwarfing genes from cytoplasmic male sterile line 'Tift 23A', which tillers profusely and uniformly, has better standing ability, is leafy, remains green at maturity, in combination with other desirable lines with largeearheads and photoperiodic insensitivity, have produced pearl millet hybrids which give double the yield of local varieties and make efficient use of fertilizers. A high tiller number is a significant character in increasing yields of hybrid millets [14]. Stringfield[48] has raised the question whether hybrid maize yield performance has attained a plateau in the U.S.A. because the present hybrids are generally susceptible to lodging at higher plant densities (over 60,000 plants/ha) which are now possible as a result of new researches in fertilization, soil and water conservation etc. He has stressed that high tolerance to crowding is an essential requirement for efficient exploitation of the increasingly high levels of soil fertility. There is ample evidence that resistance to lodging can be increased by selection, and methods to identify resistance genotypes and make rapid progress in breeding for lodging resistance in maize have been developed. These include rind thickness of lower internode and weight of a 5 cm cylindrical section of stalk [63]. Results indicate that plant and ear height can be appreciably reduced by recurrent selection in a broadly based maize germplasm without adversely affecting plant yield [62]. The dwarf mutant 'brachytic-2' has also been successfully bred into normal maize in several countries with promising results. Once the plant height has been reduced, multi-ear character can be safely transferred to semi-dwarf plant without fear of lodging. Thus lodging-resistant, multi-eared, semi-dwarf hybrids or synthetic varieties would permit higher population densities and heavier fertilization application and establish new records of yields.

64 • Yield and Heterosis

Although active interest in hybrid vigour in artificial plant hybrids had started since the rediscovery of Mendel's laws in 1900, the commercial exploitation of heterosis in field crops until the mid-fifties was mainly confined to maize. Although hybrid maize is now used extensively in the U. S. A., Europe and some othercountries, a simple genetic explanation of hybrid vigour has still not been provided. The more generally accepted explanation of heterosis is the interaction of dominant favourable genes. According to Leng [28, 29] heterotic effects are largely concentrated on the number of grains per row (ear length) and mean grain weight, indicating greater storing capacity in hybrids. There is also an increase in growth rate and total size of plant. There is general agreement that hybrids or synthetic varieties based on good combining ability of parental lines of diverse origin give better response to fertilizers than unselected open-pollinated varieties. Dogett [7, 8] has given a comprehensive review of the history and potentials of hybrid sorghum which, since the commercial exploitation of the cytoplasmic male sterility factor found in combine Kafir 60, has resulted in substantial increases in sorghum yields in many countries, including the U.S.A., India, Rhodesia, and South and East Africa. Sorghum hybrids were first issued in 1956 in the U. S. A. and by 1962-1964, when 95 % of the area was under hybrids, the yield had increased to 2750 kg/ha from 1280 kg/ha during 1954-1956. Dogett [8] pointed out that sorghum hybrids and varieties showed similar responses to changing environment, with constant relative yield increases from the hybrids over a wide range of conditions, due almost entirely to more florets and grains per plant and per hectare. Kirby and Atkins [19] reported that in 24f, hybrid populations ofgrain sorghum the greatest heterotic responsewas observed forgrain yieldand individual hybrids ranged between 106 and 147 % of mid-parent values. The inter-character correlations among hybrids indicated that seeds per head was the character most highly associated with grain yield. Quinby [39] concluded that the increase in grain production due to heterosis in the two highest yielding sorghum hybrids, with twice the yield of parents, came from greater tillering and a large increase in the number of seeds per plant. The hybrids that showed the least hybrid vigour in grain production showed the least manifestation of ieterosis in time of blooming, height, tillering, stalk diameter and leaf and head size. Thus the development of hybrids of sorghum and pearl millet through the use of cytoplasmically-sterile lines has appreciably raised the potential yields. As a consequence the fertilizer requirements have been more than doubled during the last decade. There is considerable scope for further improving the productivity and adaptability of hybrids. The discovery of stable cytoplasmic male sterile lines in a hexaploid wheat in 1962 in a crossing and back crossing programme between hexaploid (T. aestivum) and tetraploid (T. tinophaevi)wheats and finding of genes capable of restoring complete fertility have given a hope of commercial production of wheat hybrids. In experimental hybrids yield increases up to 43 % over the higher yielding parent have been obtained in Mexico [62]. However, much research remains to be done, not only concerning the feasibility of production of hybrid wheat on a commercial scale, but also on the problems of tallness, lodging, shattering, etc. Similar problems will still have to be solved with Triticale (wheat-rye hybrids) - avery promising cereal of the future.

5 65 7. Conclusions

An endeavour has been made in this brief review to show that susceptibility to lodging in cereals is a major obstacle to fertilizer responsiveness and to high grain yield. Therefore, before either of these objectives can be fully realized varietal types will have to be modified to best respond to improved crop husbandry techniques. Straw strength must be vastly improved and height of the plant considerably reduced in order to overcome the tendency of the crop to fall over under high doses of nitrogen and population densities, and also to improve the ratio of grain to straw. Plant diseases and insect pests reducecrop yields, amongother things, by interfering with physiological processes of translocation, photosynthesis and assimilation and by generally weakening the plant, and this adversely affects crop response to applied nutrients. Higher plant populations and N application necessary to obtain optimum yields provide an environment for rapid increase and spread of diseases and insect pests within the crop. Therefore it is vital that a broad resistance to serious disease and pests should be built into highly fertilizer responsive varieties andcontinuous research should be carried out to find out sources of resistance to new physiologic races of diseases and strains of harmful insects. Early maturity and insensitivity to photo- and thermo-periods not only increase response to fertilizer but also, by allowing the development of multiple cropping systems, increase the net return on investment in land, irrigation and equipment, provide more employment opportunities throughout the year, and improve labour productivity. Thus more efficient use of resources helps the farmer to increase his annual income and the country's economy. Plant types need to be developed with relatively short, erect, narrow, thick, dark green leaves, which permit the penetration and efficient utilization of sunlight. Reasonable grain dormancy at the time of harvest will reduce losses from sprouting on the panicles maturing during the rainy period and moderately firm thresh- ability will help reduce losses from shattering. The development of hybrids of sorghum and pearl millet, based on cytoplasmic male sterility factors, has dramatically changed during the last decade the prospects of these crops from the ones grown on poor soil by subsistence farmers to those of potential high yielding commercial crops suited to high fertility. The search for material suited to different environmental conditions needs to be intensified and should be extended to other crops, especially those which are partially or fully cross fertilized. Although maize hybrid production is now a well established practice in the developed countries, present hybrids are based on a narrow range of inbreds ind this limits the scope of further progress to increase yield. Efforts are already being made by some institutes to create multi-variety composites which will broaden the genetic background of future hybrids and open- pollinated synthetics. There is also need for genetic research to find out the factors which contribute to heterosis in field crops so that breeding programmes for hybrid production can be rationalized. There is no doubt that we are still at the beginning and not at the end of efficiently utilizing solar radiation through our cultivated plants. However, it is only by joint efforts of geneticists, plant physiologists, biochemists, plant pathologists and plant breeders that varieties with an optimal utilization of solar energy as well as fertilizers will be produced. It will be then that a progress, similar to that achieved in systematic breeding for higher yields and input responsiveness since the beginning of the century, can be expected.

66 Summary

Increasing soil fertility - as experienced in the 19th century in European countries - by improved preparation of the land, introduction of new crops and cultural techniques, heavier manuring and fertilization, decreased the yields of cereals instead of increasing them- The main reasons for this phenomenon were the susceptibility of the tall land races to lodging and their heavy infestation with diseases through the changing micro-climatic conditions and one-sided fertilizer application. The efforts of plant breeding to produce sturdy and disease resistant varieties are reviewed. The relationship between yield and plant character as well as between yield and plant type have been handled, in more detail, based on recent literature. The interaction between photosynthesis and nutrient uptake has been particularly stressed in this context. A comprehensive review of the newdevel- opments in breeding high-yielding wheat and rice varieties suited to subtropical and tropical regions and an evaluation of their success is given. The achievements and future possibilities of the utilization of the heterotic effect through hybrid varieties in maize, sorghum and millet are indicated and faster progress in breeding for intensified fertilizer use concludes the paper.

Literature cited

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68 Discussion, Session No. 1

Prof. Dr.S.L.Jansson (Uppsala/Sweden):

Dr. Thielebein gave some figures on the delivery of soil nitrogen to wheat crops (in Germany) which may look astonishing. This supply was said to have increased from about 30 kg N/ha around 1800 to 50 kg around 1900 and 80 kg around 1970. Normally it is assumed that cultivation decreases the organic matter content of our soils and, consequently, their ability to provide nitrogen to the crops. From this point of view the figures of the paper by Dr. Thielebein ought to decrease with time, not to increase. In spite of this I think that the figures are correct. Soil organic matter has decreased but the nitrogen-supplying power of the soils has increased. The cause of this apparent discrepancy will be the residual effects of the fertilizer nitrogen. This effect is often overlooked. Wheat growing under normal West-European conditions normally means that about two thirds of the fertilizer nitrogen will remain in the soil or turn back to the soil as crop residues, farmyard manure, etc. A stock of organically bound residual fertilizer nitrogen will be built up. Compared with the commercial fertilizer nitrogen itself this organic nitrogen has a very long-term effect but compared with native soil organic matter nitrogen its effect is fairly rapid. According to isotopic• work the effect of one single nitrogen application can be traced for decades. However, this residual effect of fertilizer nitrogen cannot be responsible for the increased supply of nitrogen during the ninteenth century. No fertilizers were used at that time. Instead we have a similar long-term effect of legume growing, especially the growing of clover. During the nineteenth century grass-clover leys became important crops on our arable soils. During the twentieth century this type of crop has decreased. Its residual nitrogen effect has been taken over by the commercial nitrogen fertilizers.

Mr. J. Warren-Wilson (Lit tlehampton/United Kingdom):

I should like to refer to the relevance of computer simulation in problems where the number of variables is too great to allow intuitive appreciation of their interactions. Equation (10) in my paper describes the relations between seven variables in determining net photosynthesis of the crop canopy. Dr. Shirnshi has referred to the important effects of stomatal resistance on photosynthesis. It can be shown that stomatal resistance is included in the term in equation (10), which can be resolved into = (ra + r, + r.) - 1 where ra, r, and rm are the boundary layer, stomata and mesophyll resi- 69 stances to CO2 diffusion. In the same way, each of these resistance terms can be resolved into more detailed components. Dr. Thielebein asks why the yield from barley and wheat should differ by five-fold, where in both cases the productive system is similar in consisting of a flag leaf acting as a photosynthetic source and an ear forming the sink. In such a system we can list many determining factors: flag leaf area, attitude, and photosynthetic efficiency; limitations by the capacity of the translocation system or its effectiveness in partitioning the maximum fraction of photosynthate to the ear: the rate and duration of photosynthesis by the ear itself; and the sink strength of the ear as affected by the number of grains and their potential for growth and storage. All these parameters can be measured and compared among genotypes grown in any specified environment. In such cases where many variables interact (and this applies to most crop processes in the final analysis) the complexity of the interactions need be no deterrent to quantitative study, now that computers are readily available. Computer simulation of biological systems seems likely to become increasingly important as a method of examining the effects on yield that result from altered values of plant or environmental parameters.

Prof. Dr. H. Heymann (Kirjat Bialik/Israel):

Losses of yield caused by nocturnal respiration are considerably intensified by the intrusion of sodium into the soil-plant system. Such action of sodium is typical for arid, semi-arid hot regions, but also for certain coastal regions of the humid, tropical climate. Potassium supply seems to be able to restrict the sodium uptake by the plants. This could mean a new function of potassium not only of nutritive character, but also as an environment conditioning agent. In Israel sugarbeet seems to be a typical case of respiration losses caused by sodium.

Dr. M. Thielebein: FAO (Rome/Italy): Dr. Thielebein considers that the adsorption capacity of the root systems of various plant species is not enough known to the plant breeders.

70 Co-ordination Lecture for Session No. 1

Dr. G. W. COOKE, Head of the Chemistry Department, Rothamsted Experimental Station, Har- penden, Hers. (United Kingdom); Member of the Scientific Board ofthe I mernational Potash Institute

When an agricultural system is to be intensified we must know what yields to aim for; the paper on maximum yield potential shows how climate determines yield and sets production targets. If actual yields are less, research is needed to discover what limiting factors have not been corrected. These are immediate and practical aims, but such work is also useful to crop physiologists and plant breeders. In future plants will be bred to make best use of the environment, to be more efficient in intercepting the sun's energy, and in conducting and converting CO2 into yield. Calculations based on weather data also indicate how potential yields vary in different seasons. Another practical development from basic work on crop physiology has been in ad- ding carbon-dioxide to the air in glasshouses. Legumes seem to have small efficiency in using both CO2 and incident light; is this why recent improvements in yield have been more striking from non-leguminous plants than from legumes? In intensifying farming we must have plants that fit the new agricultural systems, we must use the land fully by having crops there to grow whenever temperature, radiation and water are enough for photosynthesis. So we may have to develop new types of plants for new systems of husbandry, or else handle existing plants in different ways. Varieties are needed that use fertilizers more efficiently, either because they are basi- cally more productive, or resist diseases better. Both methods of dealing with disease problems - resistant varieties and chemical control - must be investigated. It is unsafe to rely solely on breeding for resistance, for this may breakdown quite suddenly. We have all been thrilled by the development of the new dwarf wheats, bred from Japanese material, which have revolutionised the potential for wheat growing in Western USA and Mexico. They respond to large amounts of N-fertilizers and do not lodge. These new wheats may have great potential in countries like India if local diseases do not damage them. Another example of large gains from breeding crops that respond better to fertilizer is the recent success with new varieties of Indica rice developed at the InternationalRice Research Institute. When we aim for maximum yields from a new agricultural system we must be sure that crop growth will not be limited by inadequate nutrition; new developments in other sciences tend to make our knowledge about using fertilizers out-of-date. We used to use the Mitscherlich curve to express fertilizer responses; but with the larger fertilizer dressings now commonly used the relationship is not assymptotic (as in the Mitscherlich-curve) but parabolic, too much fertilizer often decreases yields. On the 71 other hand factors that raise potential yield interact with nutrition so that more fertilizer can be used with profit. In intensive farming N-fertilizer is used to achieve maximum yield; the nutrients that are not easily leached from soils, mainly P and K, are balanced to the farming system used. The larger crops grown in intensified agricultural systems demand larger supplies of all nutrients; magnesium and sulphur deficiencies become more common, micronutrient supplies that were enough for the older agriculture are not enough for more productive systems of farming. Soil scientists have the responsibility of ensuring that crop yields are never limited by nutrient deficiency, only then can new developments in plant breeding, crop physiology, and crop protection be fully used in building larger yields.

72 2nd Working Session: Irrigation and Nutrient Uptake

Coordinator of the Session: A. Dam Kofoed, Director of the Agri- cultural Research Station, Askov pr. Vejen/Denmark; Member of the Scienti- fic Board of the International Potash Institute.

73 Plant Nutrient Cycles

Dr. G.W.COOK., Head of the Chemistry Department, Rothamsted Experimental Station, Harpen- den, Herts. (United Kingdom)

Intensified agriculture produces larger yields which need extra plant nutrients. In early improvements fertilizers are used simply for their immediate effects; but, to make a new system stable, account must be taken of residual effects of fertilizers and crops and of the cycle of nutrients between crop, soil, air and rain. Amounts of nutrients in crop, soil, rain, animal excreta, leaf fall and crop residues must be known. How the yield is used determines whether nutrients used to produce the crop remain, or are lost to the system. Nutrient balance sheets may be made for a country or region, a whole farm, or a single field or plantation. Calculations for a whole region aid planning. Balance sheets for a forest or perennial plantation help to understand nutrition where fertilizer experiments cannot be done, or take too long. For a whole farm they take account of sources of nutrients other than fertilizers, and of the nutrients lost in produce sold. Calculations of nutrient balance for single fields supplement the results of field experiments and soil analyses in advisory work and reveal weakness in manuring systems. Large amounts of fertilizer-N are needed to make large yields. But the nitrogen cycle involving the soil is very important in the nutrition of natural communities and in understanding the effects of previous use of land and cropping. Intensifying agriculture usually involves increasing the stock of soil P and cycles involving this nutrient have little practical value. Calculating the K removed and added to soils is important because crops take up such large amounts and can easily exhaust reserves. Except in calcareous soils, calcium balance is important but is usually indicated by measuring reaction; changes in pH reflect losses and gains of Ca. Direct calculations involve measuring Ca in drainage water and this may not be possible. Nutrient balance sheets are particularly useful for assessing the need to supply nutrients which are not generally applied as fertilizers because they are provided by traditional organic manures, soil and rain. Sulphur, magnesium, sodium and micro-nutrients are the best examples. The use of plant nutrient cycles was recognised by early writers. John Morton in his book,' On the nature and property of soils...' published in 1838, wrote: 'The process of the growth and decay of vegetable matter goes on in a continual succession, and the decay of one crop becomes the nourishment of the next.'(The decay was brought about by 'insensible fermentation'.) Very little later, in 1840, Liebig showed that he understood how an increase of nutrients in the cycle could increase productivity. In his 'Organic Chemistry in its application to Agriculture and Physiology' he wrote: 'It is the greatest possible mistake to suppose that temporary diminution of fertility in a soil is due to loss of humus: it is the mere 75 consequence of the exhaustion of the alkalis. The manurial action of solid excrements is due to their mineral constituents: human faeces supply phosphates of lime and magnesia, horse dung supplies phosphate of magnesia and silicate of potash. Straw supplies silicate of potash and phosphates. We could keep our fields in a constant state of fertility by replacing every year as much as we remove from them in the form of produce; but an increase in fertility and consequent increase in crop, can only be obtained when we add more to them than we take away.'

1. Nutrient cycles in regions

Gains and losses of all the nutrients involved in producing crops in a few countries have been published. Tables I and 2 give examples for United Kingdom in 1956 [4] and U. S. A. in 1963 [8]. The British calculation shows that fertilizers and feeding stuffs together supplied nearly half the N and 40 % of the K used to produce crops, but 140 % of the P; the nutrients supplied more than replaced the losses in produce sold and in using grass. The comparison for U. S. A. is simply of nutrients in harvested crops with those in fertilizers (which supplied two-thirds of the N and half of the K, but 20% more P than the crops contained).

Table/. Estimated gains and losses of plant nutrients on U.K. farms in 1956 together with estimates of the nutrients present in crops and grass (from Cooke [4]). All data are approximate

N P K thousands of tons Nutrients in crops and grass ...... 940 140 760 Additions Fertilizers ...... 290 170 250 Feeding stuffs (imported) ...... 160 50 50 Total additions ...... 450 220 300 Losses Crops, milk and stock sold ...... 200 40 75 G rassland utilization ...... 210 20 150 Total losses ...... 410 60 225 Balance: additions minus losses ...... +40 + 160 +75

Table 2. Amounts of plant foods in crops harvested in U.S.A. in 1963 and amounts replaced by fertilizers (from Garman and White [8]).

N P K Total in harvested crops millions of (short) tons Including legum es ...... 8.2 1.1 3.9 Excluding some legumes ...... 5.6* -- Supplied by fertilizers A m ount ...... 3.9 1.4 2.1 Percentage ...... 70* 118 54 -Excluding the N in soybeans, peanuts and half that in hay.

In contrast with U. K. and U. S. A., Australia uses much P but little N or K and Donald [6] calculated that fertilizers have added P to the stocks in Australian soils. These are common features of all nutrient balance sheets for countries with developed agriculture which use much fertilizer. Although N and K supplied may be much less than crops contain, the P supplied is more and the surplus accumulates and benefits later crops. All 76 long-term fertilizer programmes must take account of phosphate residues that accumulate in soil and use soil analyses to assess them. In contrast many countries with less developed agriculture supply much less N, K and P than their crops contain. For example in India, Rao [221 estimated that the nutrients in farmyard manure (FYM), other organic manures, and fertilizer, together supplied only about a fifth of the N, P and K in crops.

2. Nutrient cycles on farms

Calculations of nutrient balances in a whole country are inevitably imprecise because the amounts in total yields and soils, and in produce removed are guesses. They are, however, useful to people responsible for national planning. Calculations for a whole farm can be more accurate and take account of nutrients in: total yields, crops that are sold, purchased manures or fertilizers, and purchased animal foods used on the farm.

An example of the large change in nutrient balance that occurs when traditional agriculture is changed to modern cash cropping is in Table 3. The data arecalculationsof losses in 4 years of cropping in Eastern England 100 years ago and now. In the nineteenth century the common four-year rotation was swedes, clover, wheat and barley. Swedes and clover fed animals on the farm, some feeding stuffs were bought and the straw was used to make FYM used on the farm. The only products sold were meat and wheat and barley grain. In some areas this kind of farming has been displaced by systems where all produce, including straw, is sold andTable 3 illustrates losses in a modem rotation of potatoes, barley, peas and wheat.

Table 3. Losses of plant foods in old and modern farming systems (from Cooke [43) Losses (in kgfha) over 4 years of N P K Norfolk four-course feeding rotation ...... 64 9 7 Modern cash cropping rotation ...... 437 63 405

Although much more of all nutrients are needed to maintain the modem system the largest change is in the K needed. Older systems where little produce was sold, and animals were kept, conserved K so that practically none was lost. But when all crops are sold much K is removed. Such changes in farming systems, and in the yields required, have made potassium a very important fertilizer in almost all countries with intensive arable agriculture. In 1906 the world used 0.4 million tons of K, in 1964 8.5 million tons.

3. The components of nutrient cycles

Nutrient balance calculations for an individual plantation or field depend on knowing the contribution of these components: 77 Gains of nutrients are from: 1) Rain 2) Organic manures or crop residues 3) Fertilizers 4) Weathering of soil minerals 5) Fixation of N by symbiotic and non-symbiotic processes

Losses of nutrientsare from: I) Yield removed 2) Plants a) by volatilization b) by leaching 3) Soil a) by leaching b) by erosion

3.1 Gains of nutrients

3.1.1 Rain

Rain provides a little of many nutrients which are important for forests, natural vegetation and for crops that need little nutrients. In North-Western Europe rain supplies 1-8 kg N, 1-8 kg K, 1-20 kg Mg, 3-20 kg Ca and 3-100 kg S/hectare/year but practically no P. Estimates for other parts of the world differ much; examples of larger amounts of nutrients supplied by rain were made for Malaya byShorrocks[24, 25] and of very small amounts in Northern Australia by Wetselaar and Hutton [35].

3.1.2 Manures and crop residues

The nutrients in organic manures and fertilizers should be known precisely. It is more difficult to estimate nutrient returns in crop residues, and more difficult still when grazing animals use the crop. Nitrogen in excreta may be lost to the air or by leaching. All nutrients in excreta from livestock on grassland fall in patches which make the soil locally irregular.

3.1.3 Weathering

Soils containing weatherable minerals continually release cations but there are few measurements of the amounts. Estimates of the K released/year in long-tern: British experiments range from 20-100 kg/ha, varying with kind of crop and type of clay. An average release from soils ranging from loam to clay under grass in Britain is 45 kg of K/ha. But many clays release much more than this; 100 kg K/ha have been released each year in an experiment continued for 70 years at Saxmundham [5]. 78 3.1.4 Fixation of nitrogen

Legumes add much nitrogen to agricultural systems. Symbiotic fixation ranges from 50-150 kg N/acre fixed by annual arable legumes, or clovers growing with grasses in dry areas. 200-300 kg N/ha are fixed by tap-rooted clovers and lucerne in Europe; 600 kg N/ha has been fixed by clover growing in New Zealand pastures (Henzell and Norris fOU).

3.2 Losses ofnutrients

3.2.1 Yield

The crop and the way it is used determine the nutrients removed. In a forest little is lost until the timber is removed. In artificial plantations losses are small where only a little of the annual growth is harvested (as with rubber trees), but may be very large if fruit is removed (oil palm). Nutrients removed in annual arable crops may be relatively little. Ce- real grain removes only moderate amounts of N, P and K; the straw contains more nutrients and the way it is used determines whether they are lost. Root crops (e. g. sugar beet and potatoes) often remove five times as much nutrients as cereals grown on the same land. Ploughing in sugar beet tops conserves nutrients, using the tops for food removes N, P and K. Large yields of grass deplete nutrient reserves; 12 tons/ha of dry grass often contain 300 kg N, 50 kg P, 250 kg K/ha. These nutrients are completely removed if the grass is used for hay, silage or feeding green, but most are returned if livestock graze the herbage.

3.2.2 Losses from plants

Leaching. All nutrients are leached from growing plants by rain and when washed into soil may be used again. These nutrients are important in forests and in perennial plantations, like the examples in Table 4. Recycling of nutrients may be important for agricultural crops. Much of the cations may be lost from ripening cereals, Chambers [2] found a third of the K in wheat at Rothamst- ed was lost in 6 summer weeks together with some calcium. In a similar period Knowles and Watkin [ 13] found wheat lost half its K and much CI and Ca, but no N or P.

Table 4. Nutrients in rain in Malaya and in rain and in leaf-drip (in kg/ha) from hard beech forest in New Zealand (from Shorrocks [24, 25] and Miller [17])

Malaya New Zealand 250 cm In 76 cm of In 135 cm of of rain leaf-drip rainfall N ...... 20 - - Ca ...... 38 13 7.3 M g ...... 3 13 It K ...... 12 31 6.6 Na ...... - 74 63 P ...... 0.2 0.6 0.2 S ...... - l0 8.4 Cl ...... - 160 117

79 Volatilization. Nitrogen is lost from growing plants, from exposed but dead plant material (such as cut grass) and from organic manures that are not ploughed in. These losses are of gaseous forms of N which is lost to the system. Tanaka and Navasero [26] found rice fertilized with 120 kg N/ha lost 30% of the N taken up during later growth, rice receiving no fertilizer lost no N. Ammonia (with much K) was found in the dew on the fertilized plants. In old German experiments nutrients were lost from cereals between earing and harvest, but potatoes lost none. Before harvesting, spring-sown cereals lost a third to a half of the Na and K they had contained in mid-June, up to a quarter of the N was lost in the same time [37]. In recent work at Rothamsted wheat given 182 kg N/ha as fertilizer contained 187 kg N/ha at earing but only 137 kg/ha at harvest. Such large losses of N from growing plants only occur when much fertilizer-N is applied; but, as large dressings are now common practice, the losses are important by diminishing fertilizer efficiency and complicat- ing nutrient balance sheets. Fertilizer scorch. When fertilizer applied to growing crops 'scorches' the leaves, the nutrients in damaged tissues are lost. Cations and P may return to the soil, but the N is liable to volatilize. Scorch often happens when liquid fertilizers are used.

3.2.3 Losses from soil

Leaching. Most published work shows that only small amounts of nutrients are leached from soils under forests or unfertilized plantations but large amounts are when the trees are cleared. Leaching losses depend on the amount of water passing through the soil (this must be assessed for each season of a year by calculating the excess of rainfall over evapotranspiration), and are serious in wet areas growing annual crops which receive much fertilizer. Few measurements have been made of leaching losses from fertilized agricultural crops, most published accounts are for relatively artificial conditions in lysimeters. There are no modern lysimeter results published in Britain. Hendrick [10] gave the values in Table 5 for crops on lysimeters inScotland in 1921-1926; the manuring was typical good practice before British agriculture was intensified during the 1939-1945 War. Table 5. Gains and losses of nutrients in six years of cropping at Craibstone in Scotland (from Henid- rick [10]) N P K Ca kilograms/hectare Added in manures ...... 219 128 173 247 Brought in by rain ...... 21 0 0 0 Total ...... 240 128 173 247 Removed by crops ...... 627 114 544 278 Lost in drainage ...... 43 0 55 377 Total ...... 670 114 599 655

Average rainfall was 85 cm, drainage 45 cm; turnips, oats and grass (for hay) were grown. The turnips had 30 tons/ha FYM plus 700 kg/ha of superphosphate; oats and hay each received 125 kg/ha of ammonium sulphate. Annual losses by leaching were about 7 kg of N, 9 kg of K and 60 kg of Ca; no P was lost. The fertilizers and manures applied in 6 years in this system supplied no more nutrients than might now be used in one year for a single root crop, or for grass. 80 Leaching may cause large losses from modern fertilizer dressings. Both old [14] and modern [39] analysesof drainage water show that much rain falling in spring causes serious losses of N fertilizers; 3 cm of drainage water passing through soil in 24 hours in April/May after spring manuring has been done may remove 20-30 kg/ha of N [39]. Even with modern manuring P is rarely leached except from the coarsest sand soils, but residues from regular large dressings may move into subsoils. Potassium is more mobile and, when annual dressings are much larger than crops take up, some K may be leached into subsoil and part may be lost: At Woburn [31] light sandy loam soil that received 75 tons/ha FYM annually contained, after 20 years, as much soluble K (320-350 ppm) 60 cm deep as the topsoil; nearby fertilizer-treated plots receiving only 50 kg K/ha annually had 80 ppm soluble K in topsoil but only 50 ppm 60cm deep. Potassium has also been leached from the clay-loam topsoil of the Broadbalk wheat experiment receiving 100 kg K/ha each year. Coarse sandy soils with only I % clay at Wareham in Dorset retain little nutrients. N is quickly leached by spring and summer rain and 70 % of the K applied has been leached. Even water-soluble phosphates are leached from this soil; only 10 % of Papplied over 4 years as superphosphate was retained in topsoil, but 80% of that given as rock phosphate. These results for phosphate are unusual, for such light soils are not commonly used in agriculture. Calcium and magneshun are leached in amounts depending on rainfall, soil texture, supplies of Ca and Mg in soil, and on other fertilizers used. There is no' fixation'mechanism to hold non-exchangeable but potentially useful reserves of Ca and Mg such as hold K reserves in soil. Heavy clay soils may have several thousand kg/ha of exchangeable Ca; in addition all calcareous soils contain further reserves as CaCO3 . In southern and eastern England where drainage averages 25 cm/year losses range from about 50 kg Ca/ha from light acid soils (like that at Woburn) to 300 kg/ha of Ca from slightly-calcareous clay-loam soils (like those at Rothamsted). An average loss of about 150 kg/ha/year of Ca seems inevitable in the kinds of intensive agriculture now common in north-western Europe. Losses of magnesium are much less, estimates for agricultural soils range from 5 to 30 kg Mg/ha/year. Losses of cations are largest from soils with the most reserves. Walker [29] described an experiment on light soil in Shropshire which needed 5 tons/ha CaCO, to make it neutral. The losses of calcium from 3rates of CaCO 3 (in Table 6) were greatly increased by giving more than was needed. Losses of Ca and Mg are accelerated by fertilizers supplying anions not taken up by crops but leached. Ammonium sulphate and chloride cause most loss because cations accompany the sulphate and chloride when these are leached; chloride in potassium chloride acts similarly. All ammonium salts, urea, and anhydrous or aqueous ammonia, increase loss of calcium and magnesium if the nitrate formed from them is leached. Erosion causes serious loss of plant nutrients in many countries, but most can be prevented by better cultivations, drainage and control of surface water. In Southern Illinois Moe et al. [19] found both freshly applied fertilizer-N and Ncombined with soil organic matter were lost; the loss of soil-N was the larger. 12.5 cm of rain caused the following runoff and loss of N where NH4 NO, supplying 225 kg N/ha had been applied: Total runoff Total mineral-N lost cm kg/ha Fallow land ...... 7.2 14 G rassland ...... 6.8 33 6 81 Table 6. Losses of lime (as calcium carbonate) from sandy soil (after Walker [29]) Amount added (tons/ha) Amount lost (tons/ha) Annual rate in first 5 years Total in 15 years 3.14 ...... 0.38 3.1 6.3 0.63 5.3 12.6 ...... 1.00 8.8

3.3 The soil

Nutrient reserves in soils depend on parent material, soil-forming processes, and history of the land. Changes that take place when farming is intensified are the net result of many processes including those described in previous sections.

3.3.1 Nitrogen

Inorganic nitrogen in soils is ephemeral; growing crops take it up quickly; any not used by plants is likely to be leached or denitrified. The large and long-lasting reserves of N in soils are all combined with organic matter. A part of the organic matter in most soils is very ancient, but part is derived from recently-added crop residues or organic manures. A small part of the old organic matter is decomposed to release a few kg of N each year. Turn-over of the more recent organic matter is much quicker and soils containing residues of leguminous crops, grassland, or organic manures may release 100 kg N/ha/year, or even more. The total supplyof organic matter in a soil cannot be altered quickly. Reserves of organically-combined N increase where organic manures are regularly used and when land is sown to grass; they diminish after grassland is ploughed or arable land is cultivated more often. Fertilizers have little effect, the extra crop residues grown with large manuring seem to compensate for the increased oxidation caused by more intensive cultivation.

Table 7. Change in per cent N in soil with age of grassland (after Richardson [23]) Age of grassland (years) Per cent N in soil 0 (A rable) ...... 0.12 10 ...... 0.15 20 ...... 0.16 38 ...... 0.20 200 (O ld Park) ...... 0.25

Richardson[23] found percent total N in soil changed as in Table 7 when arable land was converted to grass. Two experiments on ley and arable farming at Rothamsted give an interesting contrast. One began on old grassland with 3.6 % organic carbon, the other on old arable land with 1.4% carbon. On both fields plots were ploughed, reseeded with grass and clover and then cut and grazed, on other plots arable crops were taken. The carbon in the soils after 12 years is shown in Table 8. 12years of arable cropping on the old grassfield removed one-third of the stock of organic matter, even a single ploughing with immediate reseeding allowed some loss. Growing grass for half of the 12 years hard- lychecked the loss. On theold arable field organic matterchanged little with arable cropping, growing leys for half of the time increased it by only about 10 Y. Under sown grasses organic matter increased quickly and was nearly 50 % greater after 12 years. 82 Table 8. Amounts of organic carbon in the surface 30cm layer of soils of the Rothamsted ley-arable experiments after 12 years of cropping (from Warren, Johnston and d'Arifat [32]) Highfield Fosters Carbon per Loss (relative Carbon per Gain (relative cent to permanent cent to arable) grass) Continuous treatment with permanent grass ...... 3.57 - - - reseeded grass ...... 3.26 0.31 2.05 0.70 all-arable rotation ...... 2.13 1.44 1.35 - Ley-arable rotations: 3 years of arable crops after 3 years of lucerne ...... 2.22 1.35 1.33 -0.02 grazed ley ...... 2.38 1.19 1.48 0.13 cut grass ...... 2.29 1.28 1.44 0.09

All change in soil organic matter that occurs when land use is changed is accompanied by change in nitrogen reserves. The 12-year change(shown in Table 8)caused by ploughing grassland removed more than I % of organic carbon. Assuming a usual carbon: nitrogen ratio in the soil (10: 1) means that 0.1 %of total N was mineralised,equivalent to 2000 kg N/ha in the top 22 cm layer of soil. Crops grown on this land ploughed from grass did not respond to N-fertilizers for many years, whereas there were large responses to N in the parallel experiment made on old arable land. To decide the fertilizer needed in Icy and arable cropping systems, the N released by leys of different lengths must be known. Low, Piper and Roberts [15] ploughed leys at Jealott's Hill that had lasted for 1, 2 or 3 years and grew kale followed by wheat. The per cent N in the arable soil did not change during 12years. The N released is shown in TabIe 9. The 3-year ley fixed 450 kg N/ha that became available for following arable crops, as well as the N needed for its own growth. Table 9. Nitrogen released for use by crops in 0-15 cm layers of soil after ploughing leys in Jealott's Hill experiments (from Low, Piper and Roberts [15]) Year of Icy First test year (from ploughing Second test year (from harvest- Total in two years the ley to harvesting kale) ing kale to harvest of wheat) kg of N/ha 3 290 160 450 2 160 130 290 I 100 100 200 0 90 10 100

Other published results show how cropping systems determine per cent N in soil. Fon any system of cropping, manuring and cultivation there is an equilibrium value for pe cent N in soil that depends on climate. When land is used differently, slow changes beg ij and per cent total N tends towards the equilibrium value for the new conditions. In the Morrow Plots in Illinois [12], begun in 1876, three rotations were tested: i) Continuous maize (M); ii) Maize and oats, with catch crops in the oats (MO); iii) Maize, oats, red clover (MOCI). (Before 1900 catch crops were not taken in the MO rotation, and the' MOCI' rotation was two crops of maize, one of oats, followed by 3 years of pasture.) The manuring tested against none) was: a) FYM once/rotation to supply as much dry weight as the crops removed, b) five dressings of lime since 1904, 83 c) phosphate totalling 6.6 (short) tons/acre of rock phosphate from 1876-1925 with none since. Some results are summarised in Table 10. Table 10. Amounts of organic matter and nitrogen in soils of the Morrow Plots (from Illinois University [12J) Manuring Manuring None FYM+lime+P None FYM+lime+P Organic "tatter in soil (tons/hectare) 1904 1953 M ...... 90 85 54 70 MO ...... 96 99 74 99 M OCI ...... 112 114 90 110 Nitrogen it soil (kg/ha) M ...... 4700 4500 2700 3500 M O ...... 4500 4600 3400 4600 MOCI ...... 5200 5500 3900 5200

Where fertilizer, lime and FYM have been used the MOCI rotation has maintained per cent nitrogen in the soil near its original value whereas under continuous maize without manuring, it has been roughly halved. A few experiments have shown how per cent soil N may be affected by inorganic fertilizers. An example from India in Table I I shows changes in 20years in atea-manuring experiment at Tocklai. Calculated equilibrium values for per cent N in soil depended on manuring, and suggested that soil under unmanured tea would ultimately lose 41% of the N originally in the topsoil when theexperiment began. With 135 kg N/ha/year only a quarterof the original N was likelyto be lost. Table 11. Changes in percentages of nitrogen in soils under tea at Tocklai (from Gokhate [9])

Manuring Nitrogen in soil in Calculated equilibrium value for N P K 1937 1940 1956 per cent N in soil kg/ha percentage 0 0 0 0.094 0.088 0.074 0.068 45 10 19 0.096 0.091 0.082 0.075 90 20 37 0.101 0.094 0.083 0.079 135 29 56 0.104 0.098 0.087 0.085

3.3.2 Phosphorus and potassium

In contrast to the complexities of nitrogen relationships in soil, P and K behave simply. If more P and K are supplied than crops take up the surpluses accumulate in soil to increase the stock of potentially soluble P and K. We believe the whole residue may ultimately be available to crops. The effects of long-continued manuring on soluble Pand K in experiments where all the produce was removed are shown in Figures I and 2.

4. Examples of nutrient cycles

This section shows examples of nutrient balances for conditions ranging from natural forest to glasshouse cropping. 84 Soluble P (pprn) 140- 1 Hoosfield I t ornfield J (OPGars) 120 0 Pork Gross o AgdeII J too SMdRototon I B S.R2=Rotation II 80

40- SR2 Figure 1. Relationships between P solu- 20 SRI ble in 0.05MNaHCO3 extracts ofRo- A thamsted and Saxmundham soils and the P annually applied as fertilizer in long-term experiments. 0 It 22 33 P applied per year (Kg P/ho) .4 140 00 + BROADEALK 0~120- 1843- 1943 0 e00-

+~80 -a

,460

.L +400 ~

0 +20

On 0 10 200 300400 500 600 oExchangea1ble K (ppm) -20 /O Figure 2. Relationships between gains of K from fertilizers and losses in crops / with exchangeable K in the soils of / Broadbalk at Rothamsted. -40

4.1 Forests

Forests appear to be suited to poor soils, but, if supplied with enough, they take up as much or more nutrients than agricultural crops. Forest trees use poor soils well because they match growth to nutrient supply. Because nutrients are recycled, and the canopy and litter layer catch all nutrients from air and rain, forests make very efficient use of small additions. 85 4.1.1 Hard beech

Miller [17] produced the annual balance sheet in Table 12 for a hard beech (Nothofagus truncata) forest in New Zealand. The forest contained 300 tons/ha of dry matter and had accumulated approximately 1100kg of Ca, 120 kg of Mg, 450 kg of K, 22kg of Na, 400 kg of N, and 80 kg of P per hectare. Each year the trees immobilized 10kg of Ca, 3-4 kg of N and K and about 1 kg each of P and Mg per hectare. The fresh and decomposed litter held a considerable stock of nutrients: kg/ha kg/ha C a ...... 215 N a ...... 8 M g ...... 26 N ...... 126 K ...... 15 P ...... 8 Table 12. Annual balance sheet for a hard beech forest site in New Zealand (from Miller [17]) Amounts of elements in kg/ha Ca Mg K Na P N S Cl Gains from atmosphere ...... 10 13 10 74 0.3 3 10 160 Losses Immobilised in trees ...... 10 I 4 0.2 0.7 3 I 0.4 Lost by drainage ...... 34 17 17 80 0.03 2 17 160 Total losses ...... 44 18 21 80 0.7 5 18 160 Losses minus gains ...... 34 5 11 6 0.4 2 8 -

4.1.2 Conifers

Cole and Gessel [3] measured the nutrients in organic and ionic forms in a 35-year old plantation of Douglas fir in Washington State(U. S. A.). These are shown in Table 13, together with the amounts of N in the same fractions of the system of a Corsican pine plantation in Scotland. N in the two forest systems was distributed similarly. The Douglas fir forest retained nutrientswell, Table 14 shows only 0.02 % of total N, 0.4 % of exchangeable K and 0.5 % of exchangeable Ca was leached deeper than 90 cm in a year. Figure 3 shows the nitrogen components of the tree-litter-soil system. TREE

310 Returned 14 Uptke FOREST 28 > FLOOR Leached5

Figure 3. Cycling of nitrogen in a Dou- Leached glas-fir ecosystem (kg/ha). 087 86 Table 13. Distribution of nutrient stocks, in organic and ionic forms, in forest ecosystems. 35-year- old Douglas-fir plantation, Barneston soil series (after Cole and Gessel [3]) and Corsican pine on dune sand in Scotland (after Miller [16]) (all data are in kg/ha) Douglas fir Corsican pine Nitrogen Calcium Potassium Nitrogen Forest ...... 324 333 220 287 Subvegetation ...... 4 3 3 9 Forest floor ...... 175 137 32 361 Soil...... 2809 741 234 1542 *Soil was 60 cm deep under Douglas fir, 100 cm of dune sand under Corsican pine.

Table 14. Annual movement of elements through the soil under forest in Washington State (after Cole and Gessel [3]) Soil depth (cm) 2.5 90 Nitrogen In leachates kg/ha ...... 4.8 0.6 In overlying soil' kg/ha ...... 179 2989 Leached from overlying soil (%) ...... 3 0.02 Potassium In leachates kg/ha ...... 10 1.0 In overlying soil' kg/ha ...... 36 271 Leached from overlying soil (%) ...... 27 0.4 Calcium In leachates kg/ha ...... 17 4.5 In overlying soil' kg/ha ...... 141 882 Leached from overlying soil (%) ...... 12 0.5 - Total N in soil and exchangeable K and Ca.

4.2 Tree crops

Some tree crops need very large nutrient supplies, whereas others produce tolerable yields with no more nutrients than a forest receives to produce acceptable growth.

4.2.1 Rubber

Rubber is an extreme example of small nutrient loss in the harvest; latex contains very little nutrients. Bolton [1] found the follow,;ing nutrients were needed to replace losses in latex and to grow the trees: N P K Mg Ca kg/ha/year In 1120 kg dry rubber ...... 7 1.3 4.7 1.1 0.04 In annual tree growth ...... 78 II 34 17 22 The nutrients needed for tree growth are similar to those used by some temperate crops, but most are immobilized in trunk and branches. Watson [33] gave some components of the nutrient cycle in a rubber plantation in Malaya (Table 15). The trees of the mature plantation contained more calcium and nearly as much K and Mg as was exchangeable in the soil. In early years the trees take up nutrients rapidly and must be fertilized to grow well. Less nutrients are needed later in the plantation's life and recycling in dead litter and by rainwash from the trees provides much of the nutrients needed each year.

87 4.2.2 Oil palm

The harvested fruit of oil palm contains more nutrients per hectare than do most temperate crops. Tinker and Stnilde [27] gavethe figures in Table 16 for a 20-year-old plantation (148 palms/ha) in Nigeria. Before harvest the N, P and K in fruit were more than half of the total amounts on the site. Much K is removed in fruit and K-deficiency soon devel- ops inoil palm in Nigeria. Comparisons ofTables 15 and 16 show very different fertilizer treatments are needed for these two tropical tree crops. Manuring young rubber with similar fertilizers to those used for cereals in Europe (much N, moderate P and K) seems reasonable. Oil palm needs fertilizers rich in N and K, resembling those used for such crops as potatoes in Europe.

Table 15. Some components of the nutrient cycle in a rubber plantation (from IVatson [33]) K Ca Mg N P In leguninous covers(2yearsold) 110 114 34 284 25 In rubber trees aged 2 years ...... 42 35 15 72 7 4 years ...... 187 168 63 351 - 30 8 years ...... 290 415 85 558 49 33 years ...... 1051 1798 324 1603 228 Annual return in dead liuer by 31-year-old trees ...... 15 58 7 78 3 Insoil Total Exch. Total Exch. Total Exch. Top 107 cm 4 years after clearing from jungle ...... 1222 330 650 409 359 126 - -

Table 16. Nutrient contents of oil palm in Nigeria (from Tinker and Smilde [27]) N P K Ca Mg kg/ha Tree ...... 390 55 250 220 230 Roots ...... 70 5 90 14 30 Fruit ...... 430 90 500 76 65 Total ...... 890 150 840 310 325

4.3 Sequences of annual agricultural crops

Nutrient cycle balance sheets are of little use in planning to use N- and P-fertilizers on sequences of annual arable crops. Enough N must be applied to produce the yield required, allowances being made for supplies from soil and crop residues, and for season. Dressings of P recommended when agriculture is being intensified always supply more than crops remove, so reserves accumulate. But modern K-manuring does not necessarily increase the amount in soil; a balance of soil potassium must be calculated so that 'optimum' recommendations will supply enough K to maintain reserves in the soil. Many arable crops, potatoes and wheat are examples, respond to fresh dressings of K-fertiliser more than grasses do. So when grass and arable crops are grown alternately, the potassium applied must replace that removed in the (unresponsive) grass so that following crops, which are more responsive, do not suffer. Soils with good reserves of K often give larger yields than poorer soils dressed liberally with fresh K-fertilizers. Replen- ishing soil K should not be left until reserves are exhausted as the soil may not then give maximum yields, however much fresh K-fertilizer is applied. The components of a potassium cycle vary greatly. Herbage and fodder crops, potatoes and sugar beet remove much K. Cereal grain removes relatively little K and the straw 88 contains about as much as the grain. But, as was shown earlier, cereals at earing often contain twice as much K as at harvest, and thegreen crop may have taken up as much as potatoes do. Grazing animals return much K, often 200 kg/ha. 40tons/ha of rich FYM may supply 300-400 kg K/ha. These examples emphasize the need to use enough K; but it is easy to use too much and the surplus may be taken up (as 'luxury') without extra yield, or it may be leached from light soils. In the early years of Ley-Arable experiments at Rothamsted and Woburn nutrients were not balanced to allow for different amounts of K removed in different farming systems. All rotations received 250 kg K/ha for 6 years of cropping. This was sufficient to replace K removed in arablecrops or in grazed Icy (where sheep returned in excreta most oftheK taken up). But grass that was cut removed 600 kg K/ha in 3 years. The serious K-deficiency that resulted diminished yields of both wheat and potatoes where these followed grass that was cut and removed. A balance sheet was calculated and extra K was applied where most was being removed. Since then wheat and potatoes have yielded similarly in the contrasted rotations. There is always a danger that too little K may be used when crop sequences include many crops that have a reputation for needing little K-fertilizer because they are unresponsive. Table 17 shows calculations for a Rothamsted experiment. Kale, barley, ryegrass and wheat were grown. All of these are considered to need much N but relatively little P and K and'high-nitrogen' compound fertilizers are commonly used. Using the standard fer- ilrizer 20-4.4-8.3 supplied enough N and rather more P than the crops used. But the crops removed nearly 200 kg K/ha more than was supplied. To balance the nutrients removed a compound fertilizer with nearly equal percentages of N and Kwas required. Al- ternatively a large dressing of FYM to the kale, or feeding off the grass and kale on the field, would restore the potassium balance.

Table 17. Gains and losses of plant nutrients in a four-course rotation N P K kg/ha Removed in 4 crops ...... 437 58 348 Added by fertilizer* with 20 %N 5 4.4%8.3% KP I ...... 359 81 151 10O%N 4.4% PK ...... 3615305.%P.64 347 30 56 34 168 AddedThe amounts by farmyard of compound manure ...... fertilizer being adjusted to supply roughly the same amount of N.

The nutrient cycle for sugar beet in Figure4 shows the vast contrast between nutrition of a forest(Figure 3 andTables 13 and 14)and an arable crop. Annual uptake and removal bysugar beet is very much larger, much N is lost by leaching. When tops and roots are removed, all the nutrients in thecrop are lost.

4.4 Grassland

Where grass-clover associations grow well (as in New Zealand), large yields of 20 tons/ ha of dry matter or more are possible without using N fertilizer. In other regions, including most of North-Western Europe, nitrogen fertilizers must be used to obtain max- 89 140 N Roots 12 P Tops & Roots 00 1 30K 280N r 24P 260K 1 0 ? Tops

Uptakel Tops? 140N12P A/ 130K Soil • SNlON 100 P Fertilizer 25 P Figure4. Nutrient cycle in a sugarbeet 100K crop. (All nutrienles are in kg/ha, soil I is soluble in 0.5 M NaHCO solu- I Leached 50 tion, soil K is exchangeable.) imum yields from grassland. Grassland that has enough water and 300-400 kg N/ha/ year can produce 12-14 tons/ha of dry matter in one season in England; tropical grasses (e.g. southern U. S.A. or Puerto Rico [28] can yield two or three times as much. Very large yields of grass need much fertilizer to produce them and maintain the sward. A 12 ton/ha crop of grass may contain 300 kg of N and K and 60 kg of P and these are' at risk' when the glass is used. Where grass is cut and removed continuously, fertilizers must be used to replace the P and K, if reserves of soluble P and K in soils are to be maintained. Where the grass is grazed continuously, the situation is more complicated. Most of the P, Ca and Mg, and nearly all the K in the grass eaten, are returned in excreta. But because they are returned in patches the nutrients are distributed irregularly making it difficult to plan the P and K manuring needed to maintain the sward; no simple solution of this problem has been obtained in England. Experience suggests that once a good stock of P and K has accumulated, only a little extra as fertilizer will maintain the crop. Nitrogen is even more difficult. Not only is the return irregular but ammonia may be lost when urea in urine decomposes and some of the large amounts of nitrate formed may be lost by leaching. Although nitrogen accumulates in grazed swards, and some of it may be used more than once in a season, much N is lost by volatilization and leaching besides the amount retained to make protein by the grazing animals. Many experiments have shown that soil under grazed grass accumulates more N than soil under cut grass; yield is increased because the N that is retained is used again. Table I8 gives an example by Walker [30] for New Zealand grassland. Clover contributed very much nitrogen, and 130 kg/ha of extra nitrogen was available to the system in a grazing as compared with a cutting regime. An English example by Wolfon[41] is shown in FigureS. As the total nitrogen available to the sward is increased, yield is linearly related to N supplied in cutting systems, with grazing the effect of the N available progressively increases as dressings increases. 90 Grazed grass 168

112

S56

M andFigure grazed S. Comparisons herbage showing of the Neffect in cutof N recycled by excreta of grazing ani. 0 Irals. m (After Wolton 41). 112 224 Total N from fertilizer &clover Kglha Table 18 Yields of nitrogen in herbage in one year in New Zealand (after Walker [30)) Grass plus clovers N in grass N in grass N in clovers Total N in grown alone sward kg/ha Cut and removed ...... 56 211 388 599 Grazed ...... 84 425 304 729

4.5 Glasshouse crops Intensive glasshouse cropping has more nutrients in circulation than any of the systems discussed above, the soils receiving and losing large amounts. W~ebber et al [34] gave the nutrient balance in Table 19 from an experiment with tomatoes where additions and losses were measured for 3 seasons. Much more IN, K and Mg was used than was needed. The glasshouses were flooded in winter and 80L90 % of the water applied drained away. Each I110,0001itres/ha (equivalent, roughly, to I cm of water) removed 7-10kgof N,6-7 kg of K, 33-38 kg of Ca and 4-6 kg of Mg/ha. In the growing season only nitrogen losses were serious (about 70 kg/ha). Table 19 suggests that the manuring used wastes much N and allows unnecessarily large amounts of K and Mg to accumulate. To use fertilizers more efficiently in glasshouse cropping, the balance of nutrients in crop, fertilizer and drainage must be calculated. Winsor [40] also discussed the large losses caused by leaching in glasshouse cropping. He estimated glasshouse tomatoes removed 620 kg K/ha in fruit, whereas 250 kg K/ha was lost in summer drainage and 460 kg K/ha through winter flooding. This work at Cheshunt, originally described by O wen [20], lead to 1340 kg K/ha being recommended for tomatoes and, of this amount, over half was intended to allow for waste ! 91 Table 19. Difference between nutrients added and lost in glasshouse cropping from Spring 1957 to Autumn 1959 (from Webber et al [34]) Added Lost Difference kg/ha N itrogen ...... 1652 569 + 1083 Potassium ...... 3392 322 + 3070 Calcium ...... 1720 1911 - 191 Magnesium ...... 1263 201 +1062

4.6 Balance sheets for individual nutrients

Calculations of nutrient cycles are particularly important for those elements not normally supplied by fertilizers.

4.6.1 Sulphur Crops need roughly as much S as P, but it tends to be forgotten because supplies come in rain and in subsidiary components of fertilizers. Experiments suggest there is an increasing risk of sulphur-deficiency and wherever agriculture is intensified the components of the sulphur cycle should be measured. Whitehead[36] has discussed gains and losses of sulphur. Leaching removes unused sulphate, Freney, Barrow and Spencer [7] consider that average leaching losses are 14 kg S/ha/year in Europe and North America, 4 kg S/ha/year in South America and less than I kg in parts of Australia. Crops vary in S uptake. Cereals, potatoes, grasses and cotton may remove 10-20 kg/ha, legumes and sugar beet 20-30 kg, and cruciferous crops 40-50 kg S/ha/year. The obsolete fertilizers ammonium sulphate and ordinary superphosphate contain 24 and 12% S respectively and, at normal rates (500-600 kg/ha), supply more S than crops need. Where S containing fertilizers are not used, and soils contain no reserves of calcium sulphate or weatherable minerals, supplies must come from rain which provides from 1 kg S/ha/year in parts of the southern hemisphere to 100 + kg/ha near to industrial towns. Freney et al. [7] state the average supply of sulphur in rain in Western Europe is about 13 to 14 kg/ha, but in parts of Scandinavia precipitation supplies only 3 kg and S-fertilizers must be used. Whitehead[36] considers that where rain supplies 10-12 kg S/ha/ year, deficiencies in crops are unlikely.

4.6.2. Magnesium Until magnesium deficiency is diagnosed most farmers do not consider this nutrient, they rely on unknown supplies in soil, the rain, organic manures and other fertilizers. Growing larger crops, or different crops needing more Mg, increases the risk of magnesium deficiency. Most soils contain some reserve of exchangeable and non-exchangeable Mg. Leaching losses are normally small, 20-30 kg/ha, but they are increased by large dressings of chloride, sulphate or nitrate. One example of losses of Mg being increased by intensive farming was for an irrigated U.S.A. citrus orchard [21] where the leaching loss each year without fertilizers, 16 kg of Mg/ha, was increased to 75 kg by using much fertilizer. FYM is an important source of Mg, 25 tons/ha will usually supply at least 20-30 kg Mg. Low-grade K-fertilizers like kainit often supply Mg as do some kinds of basic slag. Lim- 92 ing material also supply some magnesium. Rain supplies magnesium, estimates for Swe- den range from 1-hO kg Mg/ha. In industrial areas of U.S.A. 30-35 kg have been found in a year's rain. Most crops take up rather little Mg (5-7 kg Mg/ha for most crops at Rothamsted, 3 kg for potatoes, 12 kg for sugar beet, and legumes even more). Under many conditions these small amounts will be supplied by the sources discussed but the componen ts of the Mg cycle must be assessed when changing the cropping in an area.

4.6.3. Micronutrients

Mitchell [18] showed that the top 22 cm of normal soil contains many times more micronutrients, in easily-soluble form, than a crop requires and that there are great reserves in «fixed forms. Williamsetal. [38]ccmparedthe amounts of micronutrients removed by 5 successivecrops with total reserves at Rothamsted (Table 20).

Table 20. Comparisons of micronutrients in soil with amounts removed by crops (from Williams el al. [38]) Total amounts present Approximate amounts removed by crops in soil grown with FYM+NPK fertilizers kg/ha Cu ...... 58 0.3 Mn ...... 3100 2.5 M o ...... 2.7 0.01 Zn ...... 250 1.8

Table 21. Amounts of micronutrients supplied by fertilizers and FYM (from Williams etal. [38]) Cu Mn Mo Zn grams/hectare FYM (38 tons/hectare) ...... 560 3360 I1 1120 «Nitro-Chalk' (560 kg/ha) ...... I I 11 0.5 11 Superphosphate (450 kg/ha) ...... 22 5 0.8 67 Potassium sulphate (220 kg/ha) ...... 2 2 0.02 2

The reserves were proportionately least with zinc and most with manganese. Such balance sheets are only useful if the reserves of micronutrients become soluble at similar rates but they may give advance warning of deficiencies. Because crops remove such small amounts of micronutrients, traces of these elements in manures, fertilizers and the atmosphere may be important. Table 21 shows that the amounts of micronutrients supplied by an average dressing of FYM are about enough for a sequence of four agricultural crops, but the amounts supplied by the ordinary N-, P- and K-fertilizers tested were very much less and would make no worthwhile contribution to reserves.

5. The use of nutrient cycles in intensive agriculture

Calculations of nutrient cycles are essential for understanding the economy both of low- yielding natural vegetation or simple farming and of the large-producing cropping systems that replace them. Nutrient balance sheets alone may be useful in early stages of quick intensification when agriculture is dramatically changed in areas where fertilizer 93 experiments have not been done. When intensive systems are well established nutrient balance sheets remain important, but other scientific information to help in manuring should then be available from field experiments and soil and plant tissue analyses. In constructing and using a nutrient cycle the components involved in gross gains and losses and in internal recycling within the system must be identified and measured. When calculations are done two decisions must be made before using the nutrient cycle to advise farmers: i) The size of yield required - this determines how much nutrients must be injected into the system to produce extra crop. ii) Whether the amounts of each nutrient in the soil are to be depleted, maintained or increased. For example in soils that release much K continuously it is reasonable to lessen the stock and save money on K-fertilizer. Most soils that are to be intensified contain too little P for large yields and generally much more fertilizer P will be applied in early years than thecrops remove. If nitrogen reserves in soil have to be increased organic manures should be produced and used, or well-manured grass should be grown. Decisions on manuring should be reviewed continually so that allowance can be made for changes in nutrient reserves in soils (measured by analysis) and for changes in yield or management that alter components of the nutrient cycle.

Summary

Plant nutrients cycles are discussed for countries and regions, for individual farms and for single fields or plantations. The components of nutrient cycles should be identified and measured for existing systems and for the more intensive systems that replace them. Balance sheets show how much extra nutrients must be injected into a system to intensify production; they supplement field experiments with fertilizers and are essential for interpreting the results of repeated soil analyses. They may be the only means of assessing nutrient needs for crops where experiments have not been done, or are too difficult, or take too long. For major nutrients, calculations of nutrient balances are least useful with phosphorus (which normally accumulates in soils manured at modern rates) and most useful with the cations K, Ca, Mg, reserves of which are easily depleted by intensive farming. Losses of nitrogen are almost inevitable with present methods of intensive agriculture but measurements on the nitrogen cycle show how to use N-fertilizers more efficiently. When changing an agricultural system it is essential to estimate supplies and losses of these elements wich, normally are not deliberately applied as ordinary fertilizers - sulphur, magnesium and micronutrients.

Literature cited

I. BoltonJ.:ThemanuringandcultivationofHeveabrasiliensis.J. Sci. Fd Agric. 15, 1-8 (1964). 2. Chambers W.E.: Nutrient composition of the produce of the Broadbalk continuous wheat experiment. 11. Changes occuring during one season's growth. J. agric. Sci. Camb. 43, 479-484 (1953). 3. Cole D. W. and Gessel S-P.: Cedar river research. Forest resources monograph, March 1968. University of Washington. 4. Cooke G. W.: The Nation's plant food larder. J. Sci. Fd Agric. 9, 761-772 (1958). 5. Cooke G. W., Mattingly G.E.G. and Williams R.J.B.: Changes in the soil of a long-continued field experiment at Saxmundham, Suffolk. J.Soil Sci. 9, 298-305 (1958). 6. Donald C.M.: Phosphorus in Australian agriculture. J. aust. Inst. agric. Sci. 30. 75-105 (1964). 7. Freney J. R.. Barrow N.J.and Spencer K.: A reviewof certain aspects of sulphur as a soil consti- tuent and plant nutrient. P1. Soil 17, 295-308 (1962). 8. Gman IV. H. and White V. C.: Crop removal of plant nutrients balance sheet. Pl. Fd Rev. 10 (No. 4), 4-16 (1964). 9. Gokhale N.G.: Soil nitrogen status under continuous cropping and with manuring in the case of unshaded tea. Soil Sci. 87. 331-333 (1959). 10. Hendrick J.: A soil balance sheet for a rotation. Results obtained from the Craibstone drain- gauges. Trans. R. Highld agric. Soc. Scotland 42, 1-27 (1930). 94 11. Henzell E. F. and Norris D.O.: A review of nitrogen in the tropics with particular reference to pastures. Commonwealth Bureau of Pastures and Field Crops Bull. 46, 1-18 (1962). 12. Illinois University (College of Agriculture): The Morrow Plots. Circ. Ill. agric. Exp. Sin, No. 777 (1960). 13. Knowles F. and Watkin J. E.: The assimilation and translocation of plant nutrients in wheat during growth. J. agric. Sci. Camb. 21. 612-637 (1931). 14. Lawes JR., Gilbert J.H. and Waringlon R.: On the amount and composition of the rain and drainage water collected at Rothamsted. J1 R. agric. Soc. 18, 1-71 (1882). 15. Low A.J., Piper F.J. and Roberts P.: Soil changes in ley-arable experiments.J. agric. Sci. Camb. 60, 229-238 (1963). 16. Miller H.G.: Current research into the nitrogen nutrition of Corsican pine. In Physiology in Forestry. Supplement to Forestry 38. 70-77 (1966). 17. MillerR. B.: Plant nutrients in hard beech. N. Z. JI Sci. 6,365-377,378-387 and 388-413 (1963). 18. Mitchell R.L.: Soil aspects of trace element problems in plants and animals. J1R. agric. Soc. 124, 75-86 (1963). 19. Moe P.G., Mannering J. V. and Johnson C.B.: Loss of fertilizer nitrogen in surface run-off water. Soil Sci. 104, 389-394 (1957). 20. Owen 0.: Tomato nutrition. Scient. Hort. 9, 45-49 (1949). 21. Pratt P.F. and Harding R. B.: Decreases in exchangeable magnesium in an irrigated soil during 28 years of differential fertilization. Agron. J. 49.419-421 (1957). 22. Rao D.M.: Indiansoilsarebecoming poorereveryyear. Fertilit6, No.4,15-18(1958). 23. Richardson H.L.:The nitrogen cycle in grassland soils: with especial reference to the Rothamst- ed Park Grass Experiment. J. agric. Sci. Camb 28, 73-121 (1938). 24. Shorrocks V. M.: Mineral nutrition, growth and nutrient cycle of Hevea brasiliensis. 1. Growth and nutrient content. J. Rubb. Res. Inst. Malaya 19, 32-47 (1965). 25. Shorrocks V.M.: Mineral nutrition, growth and nutrient cycle of Hevea brasiliensis. 11. Nu- trient cycle and fertilizer recommendations. J. Rubb. Res. Inst. Malaya 19, 48-61 (1965). 26. Tanaka A. and Navasero S.A.: Loss of nitrogen from the rice plant through rain or dew. Soil Sci. PI. Nutr. 10, 36-39 (1964). 27. Tinker P. B. H. and Smilde K. W.: Dry matter production and nutrient content of plantation oil palms in Nigeria. 11. Nutrient content. Pl. Soil 19, 350-363 (1963). 28. Vicente-Chander J., Caro-Costas R., Pearson R. W.. Abruna F Figarella J. and Silva S.: The intensive management of tropical forages in Puerto Rico. Bull. Puerto Rico agric. Exp. Stn: No. 187 (1964)" 29. Walker T. W.: The estimation of the lime requirements of soils. J. Soil Sci. 3, 261-276 (1952). 30. Walker T. W.: The nitrogen cycle id grassland soils. J. Sci. Fd Agric. 7, 66-72 (1956). 31. Warren R. G., Johnston A.E.: The accumulation and loss of soil potassium in long-term experiments, Rothamsted and Woburn. Proc. Fertil. Soc., No. 72 (1962). 32. Warren R.G., Johnston A.E. and d'Arifat J.M.: Organic manures and soil organic matter. Rep. Rothamsted exp. Stn, for 1964, pp.40-47 (1965). 33. Watson G.A.: Maintenance of soil fertility in the permanent cultivation of Hevea brasiliensis in Malaya. Outl. Agric. 4, 103-109 (1964). 34. Webber J., Herbert R.F., Rothwell J.B. and Jones D. A. G.: Losses of nutrients in drainage from glasshouse soils. Expl. Hart. No. 8, 19-26 (1963). 35. Wetselaar R. and Hutton J.J.: The ionic composition of rainwater at Katherine, N.T. and its part in the cycling of plant nutrients. Aust. J. agric. Res. 14, 319-329 (1963). 36. Whitehead D.C.: Soil and plant nutrition aspects of the sulphur cycle. Soils Fertil. 27, 1-8 (1964). 37. Wilfarth H., Rnier H. and Wimmer G.: Ober die N'dhrstoffaufnahme der Pflanzen in verschiedenen Zeiten ihres Wachstums. Landw. Ver. Sta. 63, 1-70(1906). 38. Williams R.J.B., Stojkovska A., Cooke G. W. and Widdowson F.V.: Effects of fertilizers and farmyard manure on the copper, manganese, molybdenum and zinc removed by arable crops at Rothamsted. J. Sci. Fd Agric. 11,570-575 (1960). 39. Williams R.J. B. and Cooke G. W.: The composition of rain and drainage water. The efficiency of nitrogen fertilizers. Rep. Rothamsted exp. Stn for 1967, pp.244-2 48 (1968). 40. Winsor G. W.: The nutrition of glasshouse and other horticultural crops. Proc. Fertil. Soc.. No. 103 (1968). 41. Walton K.M.: Techniques in grassland experimentation. Bull. Docum. Ass. int. Fabr. Super- phos., No.41, 1-13 (1965).

95 Influence of Irrigation on the Distribution of Fertilizer Elements in the Soil Profile

G. DROuINEAU, Inspecteur C,~ndral de I'lnstitut National de Ia Recherche Agronomique (I.N.R.A.), Paris (France)

1.Introduction

A knowledge of ion behaviour in moist soil acquired during the past half century is relevant to this question. It is known that rainfall or irrigation may result in leaching, but leaching behaviour is not the same for all elements. Migration is rapid in the case of anions like nitrates which are not adsorbed, slow and usually insignificant for anions and cations which are adsorbed, fixed or which produce insoluble salts in the soil. The movement of fertilizer elements under natural conditions in soils has been under study for a long time and this applies more particularly to percolation studies which have been pursued by soil scientists in long-term experiments. Re- sults for irrigated soils are less numerous as would be expected [14], and difficult to interpret as they are often incomplete, though the general soil conditions may be adequately described, the amounts of water lost through infiltration and evaporation during the experiments are not accurately known. We shall first of all examine the principal factors which can influence the distribution in the soil profile of the most mobile nutrient, nitrate nitrogen.

2. Changes in nitrate nitrogen in the soilprofile during a dry period

When the soil surface dries, even in the absence of a shallow water table, anions not adsorbed by the soil complex tend to ascend. This phenomenon is well known in saline soils with reference to chlorides and sulphates. In normal soils the same occurs with nitrates within a relatively short pei iod. During dry periods nitrates formed by microbial activity at shallow depth move upwards and accumulate in the surface layer at approximately 10 centimetres depth until there is rain or irrigation. This phenomenon has been carefully studied in the field and laboratory [3, 4, 16]. Nitrates accumulated in this way in the surface behave thereafter in the same way as those applied superficially as nitrate fertilizers (Figure 1).

3. Influence of rain and irrigation

Ion movements are dependent on the extent of percolation. For nitrates, under average soil physical conditions,we consider that 3 mm of rain will cause a descent of one cen- 96 PLOT 15 CONTROL 1 26O 22 20 16 16 14 12 10 8 6 4 2 2 4 6 8 10 12 14 16 1B 20 22 24 26 28 30 38 Mrnera N tm010g dry soil 2 Moi6sture "%dry soil 59 E 22 6A 4 2 2// 13 1 // 132 6 /7 F4 A42 o 93 /7 09 0.0225 Jos

PLOT 14 MII3ON

0 26 24 22 20 1816 14 12 10 8 6 4 2 0 2 4 68 121416120 22 24 26 28 3D 2 Moisture % dry soil Ia1. nral N nrl10Og dry soil

E 156 21

PLOT 4 FARMYARD 0 26 2422 20 11614 1210 8 64 2 0 24 6 012 14 11 202 24 2 83

2 Moisture 1. dry sodi r 18 VIA s 1163 t1298 --

t4t46 81 Miteral N ericriy siw 6 51 23

u ISO 21 ,G-12 r -14 16 8-2 15

Figure 1. Moisture and mineral N content in the surface layer of the soil (September 1951. J1. E. Grasse, Arrangement No. 35).

timetre(l 1). Differences in rapidity of movement as affected by soil texture were reviewed by Webster and Gasser [15]. We see that the amount of water applied influences the distribution of nutrients in the profile and frequency of application can influence upward movement. These considerations must be of importance in fruit culture. Numerous authors have stated, as a result of profile studies or from research in lysimeters, that nitrates move like a sheet. As a general rule and for reasons of water economy, irrigation need is calculated in such a way as to avoid causing nitrates to move into the deeper soil layers out of range of the root system. Table I gives an example of what can happen when varying quantities of water are applied under different soil moisture-retaining capacities.

7 97 Table . Hydric characteristics of the soils

Soils Reserve of water Reserve of water Quantity of water utilisable utilisable at the which might be re- per metre time of irrigation tained (l/, R. u.) ('/.JR. u.) Sandy gravel ...... 50 mm 33 mm 17 mm Coarse sand ...... 100 mm 67 mm 33 mm Loam or clay ...... 200mm 134mm 66mm

Table 2. Leaching of nitrates Water applied 50 mm 100 mm 150 mm 200mm

Soils Water Lowering Water Lowering Water Lowering Water Lowering loss of nitrate loss of nitrate loss of nitrate loss of nitrate mm level mm level mm level mom level cm cm cm cm Sandy gravel ...... 33 11 83 28 133 44 183 61 Coarse sand ...... 17 6 66 22 117 39 166 55 Loam or clay ...... 0 0 33 11 83 28 133 45 After Blancher. Puech and Maeriens (personal communication).

In soils of poor macro-structure (loam or clay) a small proportion of total porosity is concerned with drainage (30-40 % of porosity). The movement of nitrates is restricted as a result. One may conclude from the preceding that when irrigation is well managed and on soils which are not excessively free-draining movement of nitrates beyond the rooting system is avoided in practice. It is quite otherwise when water is applied deliberately in excess, which is the case with saline waters. If it is wished to avoid salt accumulation, continuous percolation is arranged. We shall now examine factors which are concerned with the spatial distribution of irrigation water. While natural rainfall results in even distribution of water in the field, one cannot obtain the same results with artificial irrigation except with the most perfect arrangement of sprinklers and under windless conditions. Though sprinkler irrigation has been developed for various technical, economic and social reasons, very large areas are still irrigated by traditional methods with furrows and with lev~es. These two methods obviously cause heterogeneity in the distribution of fertilizer elements [5, 6, 7]. In the raised ground between the furrows, one finds nitrate accumulation [3]. Thus in a long term experimental plot at Grasse the following amounts of mineral nitrogen were found immediately following an irrigated maizecrop:

N mg per cent of dry soil Furrow Between furrows M ineral fertilizer plots ...... 0.9 3.13 Organic manure plots ...... 1.5 4.50

In the cultivation of egg plants which is carried on in long narrow basins called <> en Provence, the vertical distribution of mineral nitrogen is found (Figure 2). In the basin the maximum concentration of mineral nitrogen is found between 15 and 30 cm depth. Irrigation has been well managed and this depth corresponds to the zone of 98 Basin 18 16 14 12 10 4 2 - .0-

17.2 26 6- 139S 0 144 G2 0- 136 417 12 - 114 07 15- 9.6 31 20-

H 2,625 -

30-

35-

Mcsture . air dried soil M., N Per100 drysol

Ridge 16 14 1210 8 6 4 2 0 1 2 3 4 5 6 7 8 9 10 11 -2 1.66. -4 37V// -6 3 6.9 - .//// -45 -12 8633 5£ 42

-20 z63 -IsN651 3 -25/ /

-233

5 3 3 -35 /

Moisture 'A air dred Soil Mn N ,rOOQ dy s Figure2. Influence ofsurface irrigation o on distribution of mineral nitrogen. 99 maximum root activity. On the ridge mineral nitrogen accumulates in the top 8cm. In regions and in years where winter rains do not cause significant leaching cultivation with irrigation by furrow itcan cause differences which are evident in the followingyear. We have had occasion to observe this with cereal crops following melons in the South of France. If there is autumn rain this can affect the crop [13]. Furrow irrigation can result in variations in the intensity of percolation along the furrow on account of difficulty in the setting up of a regulargradient in accordancewith permeability and of deciding optimum length in relation to these factors and to the rate of delivery of water at the head of the furrow. Very often the bottom end of the furrow obtains more watercausing greater leaching at that point.

Concerning other forms of nitrogen, disregarding losses in gaseous form, NH4 does not move so long as it remains in this form except in pure sands. On the other hand, NH 4 rapidly nitrifies and the resulting NO 3 behaves as described previously. It is quite otherwise for urea which is scarcely retained at all so long as it is not hydrolized. Although hydro- lysis is normally rapid, it is possible in very free-draining soils to encounter leaching of urea below the superficial layeis. With crops havingvery shallow rootingsystem (gladiolus)with abundant irrigation, poor results have been obtained with urea due to its percolation in the irrigation water. On the other hand, the use of urea with plentiful irrigation can be a means of bringing ammonia- cal nitrogen to depth in the soil without subsequent losses, and this can be an advantage with fruit trees [4]. It is scarcely necessary to speak of organic nitrogen which does not move. Nevertheless, movement of soluble humic material can occur in rice soils under alkaline conditions.

4. Phosphate andpotassium

In some very old investigations we showed that with roses under irrigation phosphoric acid applied to the surface in the form of superphosphate on a calcareous clay did not move over a period of 18 years; the greatest part was recovered in the top 20cm [2]. Fig- ure 3 shows phosphate distribution in the profile of a calcareous clay which received heavy applications of phosphates for 18 years and which was irrigated for roses at An- tibes. Phosphoric acid content was measured by various methods in current use during that time. One sees clearly that the P2 0 has been retained in the surface and that this retention is demonstrated by all the methods of analysis used. This is quite a classic example [9]. We have used the example of these old results because similar profile analyses obtained on irrigated soils over a long period are not very frequent in the literature. Re- sults in vitro also show the minor importance of phosphate movement [12]. Exchangeable potassium was determined on the same profile (Table 3). It can be seen that during the long period under consideration potassium has penetrated to depth and is found to be well distributed down the profile. Maximum exchangeable potassium content is found in the level between 10 and 30cm. The following results are part of recent work by Mr. Bouat now being prepared for publication andsummarising the results ofthreeexperiments, two on sand from the Landes and one on calcareous alluvium. The object was to examine the movement of potassium applied to the surface of a bare irrigated soil (frequency of irrigation accoiding to evapotranspiration measurements). 100 40 ;50 0- iS1 ~t~i.O. 10 30

20-3C /a / Ith... METHOG 304 f ... IXCKE%,I ME T KESI4H WWIC 4------h15,NGTIO0

SA-=-TURATEDO UTON S0. j" Depth Figure 3. Phosphate distribution in the profile of a calcareous soil (under irrigation) after heavy P-applications (-/o. of fine earth)

Fertilizer treatments were 0, 200,400 and 600 units K0 per hectare per year and were re- plicated eight times. In each plot mean contents resulting from 16 individual analyses were determined at intervals of 10 cm in depth down to 50 cm. Determinations were made twice a year before and after the irrigation period. The mean results obtained were as follows: Sandy soil (Landes) (80% sand, uniform profile) In irrigated sandy soil the movement of potassium is very rapid and significant differences between treatments are found after afive months interval. In one of thetwo experiments winter drainage was good, though the other was deliberately placed on a site where the water table was near the surface. There is rapid movement on the well-drained site, though on the other there is a levelling off of potassium content in the profile in winter (Table 4).

Table 3 Layer Exchangeable KO per 1000 0-10 cm ...... 1.000 10-20 cm ...... 1.020 20-30 cm ...... 1.025 30-40 cm ...... 0.980 40-50 cm ...... 0.800 50-60 cm ...... 0.630

Table 4. Exchangeable K.0 %

Plots K 0 K 200 K 400 K 600 Sampling April Sept. April Sept. April Sept. April Sept. Depth cm 0-10 0.04 0.05 0.04 0.09 0.04 0.13 0.05 0.15 10-20 0.04 0.05 0.05 0.08 0.04 0.12 0.05 0.14 20-30 0.05 0.06 0.05 0.07 0.05 0.10 0.05 0.11 30-40 0.04 0.05 0.04 0.06 0.04 0.07 0.04 0.08 40-50 0.03 0.04 0.04 0.05 0.04 0.06 0.04 0.06

101 Alluvial soils (Montpellier-Lavalette, Domaine INRA-ENSAM) Homogenous soil from the physical point of view with lime content rising with depth (66% at the surface, 77% at 50 cm depth). Clay content about 15 % at all depths: - No noticeable difference between the treatments in the first year. - After two years of irrigation significant differences are found in the top 30 cm between different plots. - After three years of irrigation the effect is more marked. Statistical examination of the results leads to the conclusion that there has been movement of potassium to about 30 cm under treatment K 200, to 40 cm in K 400 and 50 cm under the treatment K 600. Figures 4, 5 and 6 giving differences in exch. K content between treatment and control (KO) at varying depths show up well the phenomenon of migration resulting from irrigation (and of the cumulative effect of fertilizers). These two phenomena have been separated for further study for two years (Table 5).

Table 5. Exchangeable K20, 0/00 after 3 years irrigation Plots K 0 K 200 K 400 K 600 Depth (cm) 0-10 0.13 0.21 0.31 0.39 10-20 0.13 0.21 0.28 0.38 20-30 0.13 0.18 0.22 0.27 30-40 0.09 0.11 0.12 0.17 40-50 0.07 0.07 0.08 0.10

0-10 0KO $ (10 20 tZSO K 20 exch=(K200-Ko)

$+ PLOT K 2

10-20+

. . st Year 2 0. .. ..2n d Ye a r

+*... 3rd Year

3D-40 (

40-80 DEPTH" Figure 4. Differences in content of exchangeable K between treatment and control (= K 0) at varying depths. 102 KO 0.10 0,20 0130 A K 20 exch=(K 400- Ko) 0-10

I XIIVPLOT K 400 I

10-20 It / / /~ ~ ...... - 1t.Year

/ .. 2nd Year /.... rd. Year 20-30 / ,A' 3 / /I / 0 30-40 It

40-50 DEPTHI Figiire5. Differences in content of exchangeableK between treatment and control (=KO) at varying depths. 0-10 K 0.10 0.0 Q0 A, K20exch=(KG00-KO)

+ + + 10-20 {

/ x / KI"..... l~tYear

20-30 / -- "dvear /./ .,...' rdyear // / / // / 30-40

40-50 DEPTH t Figure 6. Differences in content of exchangeable K~between treatment and control (=K 0) at varying depths. 103 Exchange Surface -0 110 220 330 440 550 660 770 ameol1a) Depth\\\\\\\-,\ \>\\\ 13.0 $~\ \\\'~ \\ 12.5 30 10.0 45 9.5

Depth 60 Loamy sand in cm 4550 kglha K20 7.5 75 90 f applied in 9 years 8.5

90 9.5 105

120 7.5 135

150

Exchange Capacity ) -0 220 330,10 (meg/lOO Surface r~n\\\Q- 15 -Depth K 0. 10.0 30- 7.0 45- Depth 60 Loamy Sand 5 in cm 2.370kg/ha K20 k5 75 applied in 5 years 4.0 90 3.5 105 3.5

135 3.0 2.5 150

Figure 7. Analysis of soil potassium (exchangeable K in kg/ha), (Overdahl C.J. and Munson R. D.) 104 Overdahl and Munson have studied the distribution of potassium in loamy sands used for potatoes grown under irrigation (750 mm rain and 250-300 mm irrigation). There was, for all practical purposes, no migration of potassium below 45 cm (Figure 7). We have not touched on the problems of distribution of secondary and trace elements which, particulary in the case of the former, await further investigation into the composition of irrigation waters. So far as boron is concerned, we can only say that its distribution must eventually be of importance in poor soils irrigated with water which does not contain it. The application of fertilizers in the irrigation water can influence the distribution of nutrient elements in the profile, more particularly of nitrogen [II]. When the nutrient solutions are evenly applied, the distribution of nitrate nitrogen in the profile is favourable: that of potassium and of phosphate is not improved. The superficial distribution of irrigation water containing nutrients must be carefully arranged. This, of course, depends on the efficiency of the sprinklers and the conditions of use.

5. Conclusion

The distribution of fertilizer elements in the profiles of irrigated soils does not present problems any different from those which are well understood in soil science. Move- ment is related to the degree of percolation and to the behaviour of the ions as related to conditions of fixation and adsorption, functions of the individual ions and of the nature of the environment. As a general rule there is little movement of phosphate and potassium, so one can say that losses will not be very marked except under particular exchange conditions and on shallower soils. On the other hand, irrigation arrangements are of prime importance in deteimining the movement and eventual loss of nitrogen, particularly nitrate nitrogen, and this necessitates great precision in determining the quantities of water to be applied in relation to climatic conditions, though special considerations apply to the management of saline soils.

Literature cited

I. Drouineau G.: C. R. Acad. Agric., 1007-1011 (1938). 2. Drouineou G.: Ann. Agron. Inst. Nat. Rech. Agron., 245-255 (1940). 3. Drouineon G., Lefevre G. and Blanc-Aicard D.: Ann. Agron. Inst. Nat. Rech. Agron., 245-256 (1953). 4. Gadet R., Soubies L. and FourcassidF.: C. R. Acad. Agric., 897-912 (1961). 5. Nelson C. E. and Wheeting L. C.: J. Amer. Soc. Agron., 105-114 (1941). 6. Nelson C. E.: Agron. J., 154-157 (1963). 7. Nelson C. E.: Washington Agr. Exp. Sta. Circ. 380 (1961). 8. Nielson R. F. and Banks L. A.: Utah Farm Home Sci. 21. 2-3. (1960). 9. Pratt W. W.J. and Chapman H. D.: Soil Sci. 82, 295-306 (1956). 10. Premier Colloque sur l'irrigation fertilisante: Bull. Tech. Inf. Min Agric. No. 211 (1966). II. Sotbi s L. and Gadet R.: Ann. Agron. Inst. Nat. Rech. Agron., 365-383 (1952). 12. Spencer K. and tVlasow A.: Irrig. Res. Sta. Techn. Paper No. 4, C.S.I.R.O., Australia (1960) 13. Stout M.: J. Amer. Soc. Sugar Beet Techn., 388-398 (1961). 14. Viers F. G., Jr., Humbert R. P. and Nelson C. E.: Amer. Soc. Agron. No. 11. 1009-1023 (1967). 15. Webster R. and Gasser J. K. R.: J. Sci. of Food and Agric., 584-588 (1959). 16. Welselaar R.: Plant and Soil, 110-133 (1961).

105 Discussion, Session No. 2

Mr. Y.Araten (Haifa/Israel): Regarding irrigation and distribution of fertilizers, Mr. Drouineausays that irrigation is causing heterogeneity of distribution of fertilizers. 1 drew the attention to 'drip-irrigation' developed by Prof.Goldberg in Rehovot/lsrael whereby each individual plant gets exactly the same amount of water and the same amount of fertilizers. In addition 'drip-irrigation' saves water and fertilizers because in row-crops the soil between one plant and the other plant remains dry.

Dr. G. W. Cooke (Harpenden/United Kingdom): I commented that: 1) The amount of leaching depends on the water-holding capacity of the soil. Light sandy soils may only have I cm of available water in 10 cm depth and a heavy rain may move nitrate below the root zone. 2) Even in heavy soils regular applications of K-fertilizer may saturate the exchange capacity for K so that K moves down the profile. In long-term Rothamsted experiments K has proved I metre deep. 3) There can be a large loss of nitrate from systems where no N-fertilizer is used; vigorous clover-grass associations lose nitrate in leaching when roots die in winter and the amounts of nitrate in drainage water may be as large as when fertilizers are used.

Prof. Dr. S. L. Jansson (Uppsala/Sweden): A comment upon the problem of water pollution. Of course, the use of fertilizers has indirectly caused much of the severe water pollution we have today. This by increasing the food supply and thereby making possible the growth of the large urban areas which dispose their sewage into the water systems. However, agriculture is often blamed for a direct water pollution caused by the leaching of fertilizer nutrients from the soils into the waters. This water pollution is normally exaggerated. Considerable amounts of fertilizer nitrogen and potassium may reach the water systems by leaching but they will not be too decisive for the plant production in these systems. They are not representing the limiting growth factor in the waters. It is phosphorus which is the critical nutrient element in the waters. Since only small amounts of fertilizer phosphorus are leached from the soils, the leaching of fertilizer nutrients is only a minor factor in water pollution. The main problem will be to remove the phosphorus from the sewage water of our urban areas and thereby stop this supply of phosphorus to the water systems.

106 Co-ordination Lecture for Session No. 2

A. DAM KOrOED, Director of the Agricultural Research Station, Askov/Vejen (Denmark)

The problems concerning irrigation and uptake of nutrient and plant nutrient cycles are very important and Dr. Cooke has presented them to us in a very clear and inspir- ing way. As it was put in the introduction Dr. Cooke said: 'In early improvements fertilizers are used simply for their immediate effects, but, to make a new system stable, account must be taken of residual effects of fertilizers and crops and of the cycle of nutrients.' It seems to me we are all of us more or less working to make new systems stable, in different planes perhaps, but the higher the fertilizing plane, the bigger the problems. The old rule: 'You must bring back to the soil the same amount of nutrients as you took away, if you wish to keep up the productivity of that soil', may still be valid, as far as you correct your fertilizer rates to the nutrients supplied from soil and air. In case of high fertilizing rates of N and K, problems may be bigger than will be overcome by help of annually balance sheets. I am here thinking of the luxury consumption of N and K in grass cut for silage or hay. We have seen, that the consumption of N has increased very much, but P and K have not followed. Are the consump- tions of P and K too low, in relation to this increasing trend for N. What is the right ratio or balance of NPK for barley, for example? When supplying the calculated years consumption at one application in the spring, the grass may consume more than needed before first cut leaving the following cuts to starve. In this case it may be necessary to have a balance sheet for every cut of grass. Much work is needed before it will be possible to built up balance sheets for all, but the reward for better balanced fertilizing lies in better quality of crops. With higher NPK consumption it becomes more and more important to use a balanced amount. It is one of the major important problems in fertilizing research to day. Your contribution, Dr. Cooke, has given us a very interesting statement of grea t est value.

107 3 rd Working Session: Interaction between Nutrition and other Factors of Plant Growth

Coordinator of the Session: G.Drouineau, Inspecteur Gn6ral de l'lnstitut National de la Recherche Agronomique (I. N. R. A.), Paris (Fran- ce); Membre du Conseil Scientifique de li'nstitut International de Ia Potasse

109 Interaction between Irrigation and Plant Nutrition

Dr. D. SnimsHI, Department of Soils and Water, The Volcani Institute of Agricultural Research, Rehovot (Israel). Contribution from the Volcani Institute of Agricultural Research, Bet Dagan (Israel). No. 1457-E.

1. Introduction

Irrigation and fertilization are two major factors in agricultural intensification; it has long been noted that a strong interaction exists between the effects of soil moisture regime and nutrient level on most crop species. Numerous studies have shown that the nature of crop response to fertilization is markedly modified by the soil moisture regime and vice versa. Nevertheless, many projects in agricultural intensification have tended to rely on one particular factor to the exclusion of the other, often with rather disappoint- ing results. The subject of irrigation-fertilization interaction may be considered from several aspects. One is the analysis of response functions to the combination of the two factors; an other is the study of the combined effect of these factors on some processes of plant life. The present paper, while dealing mainly with an example pertaining to the former aspect, refers also to the latter.

2. Irrigation-fertilizationexperiment on maize

Maize (Zea mays L.) is a crop known to respond strongly to both irrigation andfertiliza- tion. A factorial experiment was carried out at the Gilat Experiment Station (Negev, Is- rael) in which combinations of 5 irrigation treatments and 5 nitrogen-fertilization treatments were applied to maize. The treatments are described in Table 1; the number of replications was four. Maize was planted on an initially moist soil, and the irrigation treatments were started 35 days after planting. Frequent soil moisture samplings were made,

Table 1. Details on the fertilization and irrigation treatments Fertilization Irrigation

Treatment (NH 4) 2SO4 Nitrogen Treatment Number of Time of irrigation (days (kg/ha) (kg/ha) irrigations after planting) A 0 0 1 2 35, 70 B 250 52.5 2 3 35,63.91 C 500 105 3 4 35, 53.72, 91 D 1000 210 4 5 35.49. 63, 77, 91 E 2000 420 5 9 35, 42, 49, 56, 63. 70, 77, 84.91 IlI on the basis of which the amount of the individual irrigations (aimed at replenishing the moisture deficit to field capacity in the main root zone) could be determined and the evapotranspiration calculated. The various fertilizer treatments were applied before planting. During the growth season, plant matet ial was analysed for nitrogen content, and the total nitrogen uptake in the above-ground parts of thecrop was calculated. At the end of the season, the grain was harvested and weighed. It was realized that any particular irrigation treatment might not necessarily result in identical soil moisture regimes at the various fertilizer levels, because of differences in rates of moisture extraction; therefore, at the end of the experiment, the soil moisture data for the entire growth season were pro- cessed in conjunction with the soil moisture retention functions (water tension curves) of the soil, and the integrated moisture stress ( MS) (Taylor 1952) was calculated. This I MS served to characterize the soil moisture regime of each combination of irrigation and fertilization, and it was correlated to the yield of each such combination. Another index of soil moisture regime to which yields were related was the seasonal evapotranspiration. A comparison was made between the amount of nitrogen taken up by the crops and the water evapotranspired; this comparison was expressed as the ratio of nitrogen uptake to evapotranspiration. Table 2 summarizes the values determined for evapotranspiration, soil moisture stress, grain yields, nitrogen content, nitrogen uptake and the ratio of nitrogen uptake to evapotranspiration. In each fertilization treatment, increase in irrigation frequency caused, as expected, an increase in evapotranspiration and a drop in I MS; in this case, it may be reasoned that the lower IMS in the wet treatments caused greater evapotranspiration. On the other hand, at each irrigation frequency, nitrogen deficiency lowered the rate of moisture depletion, and the soil moisture stress did not rise at the end of each irrigation cycle in the less- as in the well-fertilized plots, resulting in a lower I MS. Statistical analysis of grain yields brings out clearly the strong interaction between irrigation and nitrogen fertilization. However, whereas any fertilization treatment is represented by a definite numerical expression (rate of fertilization), each irrigation treatment is represented by varying numerical values of soil moisture regime (evapotranspiration or IMS) as conditioned by fertilization, and therefore these values cannot be used directly for the construction of a response surface. The nitrogen content of the plants increases predictably with increase in fertilizer application. At each fertilization rate, there is a slight but consistent increase of nitrogen content as the soil moisture regime becomes drier. The absolute amount of nitrogen incorporated in the crop at any given fertilization rate increases as the soil moisture regime becomes wetter; this is evident even in the unfertilized plots, suggesting that high moisture stress reduced the availability of whatever little nitrogen there was in the unfertilized soil. Comparison of nitrogen uptake with the amount applied in the fertilizer (see table I) indicates that the utilization of nitrogen was almost complete in the wet treatments, except at the highest fertilization rate; here, a somewhat lower utilization rate (about 60%) may be attributed to early loss of nitrogen through volatilization. As the soil moisture stress increases, a lower proportion of the applied nitrogen is taken up by the crop; this tendency begins at lower soil moisture stiess in the heavily fertilized plots, and is less pronounced in the nitrogen-deficient plots. At any given fertilization rate, the ratio between nitrogen uptake and evapotranspir- 112 Table 2. The effect of five irrigation treatments and five nitrogen fertilization treatments on evapotranspiration, mean integrated moisture stress, grain yields, nitrogen content of dry matter, nitrogen uptake and the ratio nitrogen uptake/evapotranspiration in maize

No. of Nitrogen Seasonal Mean inte- Grain yield N content N uptake Ratio irriga- applied evapotran- grated moi- (kg/ha) in dry mat- (kg/ha) N uptake tion (kg/ha) spiration sture stress ter (%) 1lO2 (mm) (atm.) evapotranspiration 2 0 342 1.62 1,513 1.03 32 9.4 52.5 378 - 1.95 2,058 1.30 66 17.4 105 391 2.23 2,520 1.38 114 29.2 210 394 2.26 2,502 1.50 147 37.4 420 381 2.16 2,027 1.52 120 31.5 3 0 349 1.47 1,734 0.83 32 9.2 52.5 394 1.57 2,466 1.02 73 18.5 105 407 1.59 3,141 1.15 122 30.0 210 462 1.60 3,920 1.38 170 36.8 420 479 1.60 3,862 1.54 216 45.1 4 0 388 0.81 1,860 0.76 35 9.0 52.5 472 1.08 3,391 0.96 82 17.3 105 516 1.24 4,625 0.99 152 29.4 210 526 1.20 5,038 1.23 184 35.0 420 559 1.19 5,401 1.39 270 48.2 5 0 476 0.42 2,309 0.66 40 8.4 52.5 532 0.57 3,981 0.76 89 16.7 105 602 0.66 5,734 0.96 162 26.9 210 644 0.61 7,637 1.20 224 34.8 420 675 0.67 8,317 1.32 275 40.7 9 0 693 0.19 2,417 0.64 42 6.1 52.5 786 0.21 4,103 0.71 84 10.7 105 827 0.20 6,217 0.92 150 19.1 210 830 0.23 9,049 1.11 218 26.2 420 817 0.23 10,101 1.21 274 33.6 Statistical analysis' S.E. main plots (irrigation) 19.2 139 0.14 S. E. sub plots (fertilization) 13.9 108 0.08 Significance of effects: Irrigation Xx xx xx Fertilization xx xx xx Replications n.s. n.s. n.s. Irrig. x Fertil. x xx n.s. * The statistical analysis refers to primary data only (evapotranspiration, grain yields and N con tent) and not to the other data which were derived by calculations. The following designations o significance are used: n.s. = not significant; x = 0.05> p> 0.01; xx = 0.01 > p. ation is remarkably constant in all the irrigation treatments, except in the wettest one (No. 5), for which the ratio tends to be lower. Since, unlike the irrigation treatments, each fertilization treatment could be expressed by a definite numerical term (rate of fertilization), it was possible to correlate the IMS data with the yields for each fertilization treatment. Thus five linear regressions, each based on five points, were calculated, and their correlation coefficients were found significant (Table3). Thegeneral form of these regression was y = a-bS, where y = yield,in kg/ha; S = IMS, in atm.: a, b = two parameters. The parameters a, b, changed with the fertilizer rate; this change was represented by an ascending, upward-convex curve, which could befitted reliably to thefollowing quadratic functions: a =2422 +47.3F

8 113 Table 3. Effect of mean integrated moisture stress S on yield y at five fertilizer rates Fertilizer rate Regression equation* Correlation coeffieent (kg N/ha) y = a-bS 0 y= 2,504- 597S -0.968x (y= 2,422- 524S) 52.5 y= 4,547-1276S -0.976- (y= 4,731 -1349S) 105 y= 6,788-1978S -0.978 xx (y= 6,685-2070S) 210 y = 9,528-3305S -0.988- (y= 9,529-3205S) 420 y = 10,964-4243S -0.996u (y = 10,963-4212S)

* y = yields, in kg/ha. The numbers in parentheses are the corrected regressions; those without, are the original regressions.

-0.0643 F 2 and b=524+ 16.7 F-0.0187 F2 , where F isthe nitrogen application in kg/ha. These two functions were used to calculate the corrected values of a and b for each fertilizer treatment; the corrected regressions are presented (in parentheses) below the originally calculated regressions in Table3. The response surface is therefore a linear- quadratic one, represented by the equation YS,F = 2422 + 47.3F-0.0643F 2 -(524 + 16.7 F-0.0187 F 2)S. The yields estimated from this response surface deviated (25 points) from the actual yields by ± 297 kg/ha. This response surface can be considered from three viewpoints: 1. A series of linear descending functions relating yields to IMS at five fertilization rates (Figure 1).

N Yield applied kglha kg/ha

iaooo 420

8.000 210

6000 105

4.000 525

20 0

05 1.0 1.5 20

Mean moisture stressatn. Figure 1. The effect of mean integrated moisture stress on maize yields at five rates of nitrogen fertilization. 114 2. A series of quadratic parabolas relating yields to fertilization rates at several arbitrary values of IMS (Figure 2). The general form of the curves is y = i +jF-kFt (Table4). These curves have maxima; the estimate of the maximum yield is given by y(max) = i ±j 2 /4K, and of thenitrogen application producing the maximum yield, F(max) =j/2k. Both values decrease when moisture stress increases. 3. A series of isoyield lines, in which the fertilizer rate and the IMS form the grid coordi- nates (Figure 3). Yield Satm. kglha

1Q0000---02 0.5

------I- to

.02.0

2000 l4 I I i I

0 100 200 300 400

Nitrogen applied, kg/ha Figure 2. The effect of nitrogen fertilization on maize yields at five given levels of mean integrated moisture stress. (Horizontal lines denote maximum yields, and vertical lines denote fertilizer rates which produce maximum yields.)

Mean moisture stress atm

2000 2.015 40000

0 100 200 300 400

Nitrogen applied, kgIha Figure 3. lsoyield diagram ror a combination of nitrogen fertilizer rate and mean integrated moisture stress. 115 Table 4. Effect of fertilizer rate F on yield y at five given values of S

Moisture stress Fertilizer -yield equation* y(max) F(max) S (atm.) y = i + jF-kF

0.2 y=2317+ 44.0 F-0.0605 F2 10,322 363 0.5 y=2160+ 39.0 F-0.0549 F 2 9,070 355 1.0 y- 1898+ 30.6 F-0.0455 F2 7,041 336 1.5 y= 1636+ 22.2 F-0.0362 F2 5,061 307 2.0 y= 1374+ 13.9 F-0.0268 F 2 3,178 258

SF= nitrogen application in kg N/ha; y= yield in kg/ha.

An analysis of the response curve reveals that the specific damage to yield per increment of moisture stress (the negative slope of the linear regressions) is greater at high fertilization rates. Moreover, the ratio b/a is not constant, but increases with fertilization; this causes the regression line of treatment E to intersect the regression lines of treatments C, D at high moisture stress, so that in dry treatments, heavy fertilization actually lowers yields. This can also be seen from the series of parabolas (Figure 2) where maximum yields are seen to occur at progressively lower fertilizer rates as moisture stress increases. The steep negative slope of the moisture stress -yield function at high fertilization rate, and the diminishing value of optimal fertilizer rates at high moistures stress probably reflect the detrimental effect of the osmotic potential of the soil solution as conditioned by the high fertilizer application and the lack of dilution by frequent irrigation. One well known function, used to describe the response of crop yields to fertilizer application, is that of Mitscherlich (1930): log (A-y)= log A- C (B + X) where y = yield; A = potential maximum yield at an infinite nutrient level; B = initial amount of nutrient in the soil; X = amount of nutrient applied and C = response coefficient. The constancy of the coefficient C for any nutrient element, which is one of the postulates of Mitscherlich's yield law, has been disputed (Rinno, 1959). The regressions presented in table 3 make it possible to estimate the yield at any arbitrary I MS. The estimated yields in the five fertilizer treatments were calculated at five values of IMS (0.2, 0.5, 1.0, 1.5 and 2.0 atm.), using the original (uncorrected) regressions. Thus it was possible to calculate the Mitscherlich equations, each based on five points, for the above valuesof 1MS. An exception to this was the2.Oatm. IMS: the estimated yield at fertilizer treatment E is lower than that at treatment D, and since the Mitscherlich equation has no maximum point, this equation was based on four points only (treatments A, B, C and D). The five equations are presented in Table 5.

Table 5. Mitscherlich equations, calculated for five given values of S

Moisture Mitscherlich equation- stress log (A-y)= log A-C (B + F) S (atm.) 0.2 ...... log (10,840- y)= log 10,840- 0.00270 (37.2 + F) 0.5 ...... log (9,620- y)= log 9,620- 0.00267 (39.5 + F) 1.0 ...... log (6,800- y)= log 6,800- 0.00371(37.2+ F) 1.5 ...... log (4,680- y)= log 4,680- 000570(31.9 + F) 2.0 ...... log (2,980- y)=log 2,980- 0.00779 (24.7 + F) OF= nitrogen application in kg N/ha; y =yield in kg/ha. 116 The changes in the parameters A, Band Care noteworthy. The values of A, representing the maximum potential yields at any given IMS, are very close to the maximum yields calculated from the quadratic equations. The values of B, representing the available nitrogen reserves in the soil prior to fertilization, tend to decrease at high IMS; they agree well with the nitrogen uptake in the unfertilized treatment (A). Both the nitrogen uptake data and the Mitscherlich equation indicate that nitrogen availability may decrease at high soil moisture stress, although the actual nitrogen content of the unfertilized soil was probably the same in all the plots. The values of C increase markedly as the IMS rises above 0.5 atm.; thus it seems that one of Mitscherlich's postulates, namely, the constancy of the coefficient C for any nutrient element, regardless of other growth factors, does not necessarily hold true when the crop is subjected to high moisture stress. In figure 4, the five Mitscherlich equations are plotted with a common point of origin (that is, as functions of the combined nitrogen supply in the soil and the fertilizer). The slopes of the curves near the origin for the 0.5, 1.0, 1.5 and 2.0 atm. I MS are practically equal (23-25 kg of yield per kg of nitrogen). This series of curves, therefore, approaches a limiting-factor type of interaction, according to the postulates of Liebig or Blackman, rather than those of Mitscherlich. When yields are plotted against evapotranspiration (Figure 5) the limiting-factor type of interaction is very evident. The yield-evapotranspiration function at the highest level of fertilization is linear, its regression being y = 5282 + 19.3 ET (r = 0.972xx). The functions for lower fertilization levels start at this same line, but branch out horizontally at progressively lower values of yield and evapotranspiration. De Wit (1958) states that as long as water limits plant growth, the relationship between production and transpiration is linear. When water does not limit plant growth, crop yields will be determined by other growth factors specific to the location, such as soil characteristics, fertilizer supply, etc. Figure 5 may therefore be interpreted as follows: at the highest level of nitrogen fertilization, practicallythe entire range of response represents water-limiting conditicns; at lower levels of nitrogen, a horizontal break from linearity occurs as the nitrogen supply gradually becomes the limiting factor. The fact that the regression line does not pass through the origin, but intersects the evapotranspiration axis at about 260 mm, may be attributed to two causes: I) direct evaporation from the soil before the formation of full leaf canopy; and 2) transpiration by maize during the later stages of grain maturation, when there is no appreciable net production of dry matter. The data on the ratio between nitrogen uptake and transpiration seem to suggest that nitrogen is carried from the soil into the plant in direct proportion to the water flux; this raises thequestion of the role of transpiration in supplying the plant with nutrients from the soil solution. It is well recognized that the uptake of ions by plant roots is effected mainly through an active, metabolically-dependent process (Sutcliffe 1962). However, when this active absorption momentarily depletes the root-soil interface of any particular nutrient ion, renewal of the nutrient supply depends mainly on the movement of the ion with the massflow of water from the soil bulk to the root;diffusional movement of ions in the soil solution is probably slower by several orders of magnitude. Theoretical- ly, a reduction in transpiration rates could, at relatively low nitrate concentrations in the soil solution, cause nitrogen deficiency, which would not occur at the same nitrate concentrations if transpiration were more intensive. This phenomenon does not usually occur, since the most common cause of reduction in transpiration is high soil moisture stress; this very stress also reduces crop growth to an extent that nitrogen supply is no more limiting. On the other hand, conditions of high atmospheric humidity may lower 117 Yield kg/ha Satm.

10000 _I2

8000 8,00015

S4000

2011

180 200 300 4O

Nitrogen (initialIapplied ), kg/ha

Figure 4. Calculated Mitscherlich curves for five given levels of mean integrated moisture stress. Horizontal lines denote maximum potential yields.)

etd kg N iha kglha -420

10000 o- 210 8000 0 0 A 105

6000. L o

A 4000 o4 e, -- 52.5

2000

0 300 400 500 600 700 800

Evapotranspiration, mm

Figure 5. The relation between seasonal evapotranspiration and maize yields at five rates of nitrogen fertilization. 118 transpiration without reducing potential growth; in such cases, nutritional deficiencies could develop at critically low nitrate concentrations in the soil, because of the lower rates of mass flow to the roots. It is well known that grain crops growing in arid regions have a higher nitrogen content than those growing in humid ones. One possible explanation is that in arid climates, crops have higher ratios of transpiration to dry-matter production and, consequently, mote nitrates are carried to the absorbing sites on the root surface. If the irrigation-fertilization interaction is of the limiting factor type, it is interesting to consider the possibility of using one factor to replace the other for the attainment of higher yields. Whenever one factor is at a low level which limits plant growth to the exclusion of the other factor, mutual replaceability is inefficient: The yield of a moisture- stiessed crop cannot be raised by applications of fertilizer. At intermediate levels, both factors may be mutually replaceable, the feasibility of such a substitution being a question of the relative cost per unit of each factor and the yield increment per such unit. Whenever any one factor approaches the flattening-off of its response function, the efficiency of the other factor in raising yields increases; finally, the combined effect of both factors may reach a peak, and at this range mutual replaceability is economically irrele- vant.

3. The effect of nutrient supply on plant water relationships

From the data on evapotranspiration presented in Table 2, it appears that for a given irrigation frequency, unfertilized maize tended to extract less water from the soil. The possible effect of fertilization on water consumption has been reviewed by Viets (1962) and Black (1967). In general, it was found that fertilization may cause an increase in water consumption but this is more than offset by the increase in yield, so that fertilization almost invariably results in a higher yield/transpiration ratio. Two main explanations have been offered for the increased rates of transpiration following the application of fertilizers: 1) Fertilizers encourage vegetative growth of transpiring surfaces which may cause an increase in transpih ation, especially in arid climates or where advective vapor transfer is intensive; and, 2) Fertilizers may encourage deeper root development, resulting in the extraction of moisture from otherwise untapped soil layers. However, some recent studies have indicated that nutrient deficiencies impair the proper functioning of the stomatal mechanism, so that the stomata of nutrient-deficient plants fail to open widely under conditions which otherwise are conductive to stomatal opening; this has been observed wtih potassium- (Peaslee and Moss 1966), and nitrogen- and iron- (Shimshi 1967) deficiencies. Thus a third explanation may be offered for the effect of fertilization on transpiration, namely that nutrient deficiencies may cause an increase in the diffusive resistance to water vapor through their effect on the stomata. The action of nutrient supply on the stomatal mechanism is not understood. Those nutrient deficiencies characterized by leaf chlorosis (nitrogen, iron), may affect stomatal behaviour through their effect on chlorophyll content, just as albinism, etiolation and variegation may result in a partial or complete inability of the stomata to open. How- ever, potassium deficiency was found to reduce stomatal opening before the appearance of leaf chlorosis(Peasleeand Moss 1966). 119 There is some evidence that nitrogen deficiency not only causes smaller stomatal aper- tures under conditions which encourage stomata to open (ample light and soil moisture), but under conditions of progressive water deficit, it prevents stomata from closing tight- ly. This is apparently related to some impairment of the osmoregulative functions in the epidermal cells surrounding the guard cells (Shimshi, 1970) It is well known that nutrient-deficient plants may fail to exhibit typical symptoms of wilting under soil or atmospheric conditions which would normally induce wilting. This is probably caused by the greater rigidity of leaf tissues in nutrient-deficient plants; these plants usually have a higher proportion of cell-wall materials than do normal plants, which may explain the lack of wilting symptoms.

Sunnary

Some aspects of the interaction between irrigation and fertilization are discussed and exemplified by means of a bifactorial experiment on maize, in which 5 irrigation treatments and 5 rates of nitrogen were applied. It was found that nitrogen fertilization strongly modifies the parameters of response function to calculated integrated moisture stress, and conversely, soil moisture stress has a marked effect on the response function to nitrogen, which is reflected in changes of the parameters of the quadratic function and the locations of yield maxima. When the Mitscherlich equation was fitted to the predicted yields at five arbitrary values of soil moisture stress, it was found that the value of C in the Mitscherlich equation increases with increasing moisture stress, and that the series of functions approach a limiting factor type of interaction. Such a type of interaction was also found when yields were related to seasonal evapotranspiration at five nitrogen application rates. At each nitrogen application rate, the ratio between nitrogen uptake and seasonal evapotranspiration was constant except in the wettest treatment, where this ratio was lower. The possible relationships between plant nutrition and stomatal behaviour are discussed.

Literature cited

Black C.A.: Crop yields in relation to water supply and soil fertility. In: Plant environment and efficient water use. Pierre W. H., Kirkham, D.. Pesek J. and Show R. eds. Am. Soc. Agron. and Soil Sci. Soc. Am. Madison, Wis., 177 (1966). De Wit C. T.: Transpiration and crop yields. Versi. Landbouw Onderz. Wageningen, No. 64-6, 88 (1958). Mitscherlich E.A.: Die Bestimmung des Diingerbediirfnisses des Bodens. Paul Parey, Berlin (1930). Peaslee D.E. and Moss D.N.: Photosynthesis in K- and Mg-deficient maize (Zea mays L.) leaves. Proc. Soil Sci. Soc. Am. 30. 320 (1966). Rino G.: Ober die Schwankung des Wirkungswertes eines Nfihrstoffes in und ihre Auswirkung auf die Bestimmung des Dfingerbedarfs des Bodens. Albrecht- Thaer-Arch.3, 87 (1959). Shis/hi D.: Leaf chlorosis and stomatal aperture. New Phytol. 66, 455 (1967). Shimshi D.: The effect of nitrogen supply on some indices of plant-water relations of beans (Phaseolus vulgaris L.). New Phytol. 69,413 (1970) Sutcliffe J.F.: Mineral salt absorption in plants. International Series on Pure and Applied Biology. Pergamon Press, New York (1962). Taylor S.A.: Use of mean soil moisture tension to evaluate the effect of soil moisture on crop yields. Soil Sci. 74, 217 (1952). Viets F.J. Jr.: Fertilizers and the efficient use of water. Advan. Agron. 14, 223 (1962).

120 Some Interactions of Cation Nutrition and the Water Supply of Plants

R. BLANCHET, M. Bosc and C. MAERTENS, I.N.R.A., Station d'Agronomiede Toulouse (France)

The past few decades have seen a significant increase in agricultural yield, occasioned by progress in plant breeding, pest and disease control, soil science and in the whole range of cultural techniques. The use of fertilizers has played a significant role in this improvement. Nowadays it is very often the water supply that is the principal factor limiting plant growth and production. Irrigation is ever more widely used in a diversity of climatic conditions and its use brings newproblems in agricultural intensification in both theoretical and applied fields (Robelin [14]). While not belittling the part played by other techniques, one can safely say that irrigation and the use of fertilizers are essential prerequisites for intensive agriculture. Be- tween these two, water and nutrients, thereare many interactions affecting the basic physiological and physico-chemical processus in the plant, and having far-reaching agricultural consequences. In a very general way, irrigation by increasing growth increases the crop demand for nutrients and at the same time adequate fertilizer application is essential if the full benefits of irrigation are to be realised. The cost of irrigation is one of the major components in the total cost of production. Water moving in the soil transports the nutrient ions in the rooting zone and facilitates their movement towards the roots and their absorption into the plant. Various interactions are found in the rhizosphere. In the sub-aerial parts of the plant transpiration results in water loss. The rate of transpiration depends upon osmotic processes and, to the extent that mineral nutrition can influence the osmotic pressure of plant tissue, transpiration can be modified. We shall examine several aspects of these diverse interactions, briefly quoting results obtained in the simultaneous study of nutrient cation and water supply. From the experimental results obtained we shall put forward ideas.which lead to a better understanding of the mechanisms involved.

I. Mineral nutrition of irrigated crops (fieldexperiments)

1967 was a particularly dry year in S.W. France when the water deficit (Potential Evapo- transpiration-Rainfall) attained 700 mm over the period Ist May to 30th September. Table I details results obtained in that year from an irrigation experiment with maize and sorghum in which irrigation resulted in large yield increases. The crops were well 121 manured by generally accepted standards though possibly at a rate somewhat below their maximum requirements. 150 kg/ha of each N, P20 5 and K 20 were applied. The soils were rather poor in P and K. The greater amounts of dry matter produced under irrigation resulted often, despite the generous manuring, in a diminution in mineral content of various parts of the plants. This was a classical dilution effect seen here particularly in regard to nitrogen and phosphate. Total quantities absorbed were much greater under irrigation but the concentrations of the elements expressed as percentage of dry matter were often diminished, particularly in the case of maize. Such a result could incidentally be particularly important in respect of grain composition since the feeding value could thereby be reduced as a result of irrigation if manuring were not sufficiently generous. Behaviour was not entirely straightforward as far as cations were concerned. In the case of K+ we observed both a dilution effect and the converse, particularly evident in sor-

Table 1. Dry matter yields and mineral nutrition of irrigation crops

Maize Maize Sorghum Pioneer 320 Iowa 4417 NK 120 dry irrigated dry irrigated irrigated dry irrigated 295 mm 355 mm 472 mn 300 mm

Yield Dry matter qfha Stems + leaves ...... 27 66.6 55.3 70.5 83.5 35.5 65.5 Grain ...... 26 110 7.0 80.0 93.5 25.0 66.5 Total ...... 53 176.6 62.3 150.5 177 60.5 132 Nitrogen Per cent of D. M. Stems+ leaves ..... 1.22 0.81 1.60 - 0.86 1.03 0.94 1.06 Grain ...... 1.64 1.43 2,12 1.56 1.59 2.23 1.91 Total absorption kg/ha 80 221 105 187 235 89 161 Removed in grain kg/ha 43 157 15 125 149 56 127 Phosphorus Per cent of D. M. Stems+ leaves ..... 0.12 0.06 0.20 0.07 0.07 0.06 0.10 Grain ...... 0.23 0.25 0.38 0.31 0.31 0.23 .0.32 Total absorption kg/ha 9.6 32.2 3.6 29.9 34.8 7.9 24.6 Removed in grain kg/ha 6.0 27.5 2.6 25.0 29.0 5.8 21.3 Potassium Per cent of D. M. Stems + leaves ..... 1.30 0.98 1.57 2.00 2.44 1.19 1.38 Grain ...... 0.33 0.36 0.41 0.35 0.33 0.38 0.45 Total absorption kg/ha 46 119 80 169 235 52 75 Removed in grain kg/ha 8.5 40 3 28 31 9.5 30 Calcium Per cent or D. M. Stems + leaves ..... 0.44 0.54 - - - 0.70 0.88 Grain ...... - 0.01 - - - 0.01 0.01 Total absorption kg/ha - 37 - - - 25 58 Removed in grain kg/ha - 1.1 - - - 0.2 0.6 Magnesiani Per cent of D. M. Stems + leaves ..... 0.24 0.28 - - - 0.28 0.55 Grain ...... 0.09 0.10 - - - 0.14 0.17 Total absorption kg/ha 9 29.5 - - - 13.3 40 Removed in grain kg/ha 2.3 11 - - - 3.5 4.2

122 ghum, where, though yield is greatly increased, irrigation increased the percentage K content. (A similar effect was found with P in this experiment.) Two opposing actions seemed to be involved simultaneously in the influence of water supply-on the one hand a tendency towards dilution of potassium as a result of greatly increased plant production, and on the other hand an improvement in the plant's ability to take up potassium when water supply was adequate which resulted, in certain cases (sorghum and sometimes maize), in theKcontent of partsof theplant being increased. Data for Ca + + and Mg+ + were not so complete but it appeared that there was a similar increase in the concentrations in dry matter of those two ions, that is to say, uptake was facilitated by irrigation. While irrigation greatly increases the plant's requirement for nutrients it also facilitates their absorption, particularly so that of the cations. We shall now try to explain the latter effect by detailed examination of the cationic environment of the root and of the effect of water on cations movement in this environment.

2. Cationic environment of the root and the influence of water on cation movement

2.1 Diffusion

Various authors (Tepe and Leidenfrost [16], Blancher and Chaminade [6], Nye [12j) have shown that diffusion of cations in the soil is relatively slow and limited. It follows from this that soil particles in the immediate neighbourhood of the roots becomeimpover- ished in exchangeable cations when these are not overabundant. This effect is particularly marked in thecaseof potassium, the more so if the root system is not well developed and does not fully explore the soil at its disposal. Table 2 shows an example of the variation in soil K observed in a pot experiment with maize having root systems more or less well developed (Blanchet and Chaninade [6]). Generally, soil desiccation reduces root range, notably on account of increased mechanical resistance to penetration (Maertens [lO.) Root penetration is, however, an important precondition for the utilisation of water and nutrient reserves. In addition the diffusion of K+ ions is much slowed down when the soil dries out. This was demonstrated experimentally as follows: Pairs of artificial (Montmorillonite mixed with ground quartz,

Table 2. Exchangeable potassium content of soils variously exploited by maize roots in pot culture Pot with one plant poorly developed root system Pot with one plant well developed root system Roots Final exchangeable Roots Final exchangeable mg/g soil K ppm in soil mg/g soil K ppm in soil 3.2 30 12.9 80 1.3 48 2.8 80 1.2 43 2.4 75 0.8 53 1.7 88 0.5 55 1.5 94 0.5 78 1.3 80 0.3 78 0.9 79 0.3 83 0.8 78 0.2 95 0.7 80

Initial exchangeable K 107 ppm 150 ppm

123 - lniti content i2 2 hours yp a,

E Water utit-abke by crs Free water (non saturated) (saturated)

------nitial content Ft LiudLimit

Figure 1. Variation in exchangeable potassium content of two soil discs, 1,6 mm. thick and placed in close contact, as a function of water content ofthe soil. in which no fixation or release of K would occur) soil plates 1.6 mm thick, one of each pair containing initially 80 ppm K, the other 800 ppm, were placed in contact under varying moisture conditions. The exchangeable K contents of the plates were measured after various elapsed times. Figure I indicates how the migration of K + ions from one to the other plate was affected by moisture content. It is clear that the diffusion of K + was greatly accelerated as moisture content increased. We have seen how increased moisture improves potassium nutrition in two ways: by improved root growth and through accelerated ion diffusion.

2.2 Mass-flow It is not only K+ ions which are involved in the soil: they are found in association with Ca + +and Mg+ + notably in the soil solution, which flows under theinfluence of transpiration by plants. The ensuing movement of cations by mass flow can be estimated from their concentrations in the liquid phase, with the results shown in table 3. It is difficult to know how the cation concentrations in the soil solution are affected by irrigation. This is essentially a function of the quantity of anions present, among which bicarbonate formed in the decay of organic matter is the most important. Biological activi-

Table 3.Order of importance of transport ofdifferent mineral elements by water movement in soil Cation Concentration Amount ofelement transported kg/ha in Quantity in in soil solution relation to per per crop require- mg/litre per1000 tons 2500 tons 5000 tons me water water water K 10 10 25 50 Insufficient Ca 200 200 500 1000 Great excess Mg 25 25 63 125 Excess

124 ty being more intense in humid than in dry soil, one may think that cation concentration in the soil solution will vary little in the course of a season and that the transport of cations to the root zone will be largely proportional to the amount of water transpired. The transport of K+ by mass flowis doubtless insufficient to meet crop requirements except in soil particularly rich in this element. But massflow will result in supplies of Ca + + and Mg+ + at the root in excess of requirements, and this explains the increases in plant content of these nutrients shown in Table 1. Because of cation movements, the soil of the rooting zone will differ in composition from the rest of the soil body. This can be verified experimentally by analysis of small samples of soil from the immediate neighbourhood of the roots and comparing with samples further removed. In comparison with the original (uncropped) soil, soil from the rhizosphere shows a reduction in potassium content and an increase in calcium. The Ca/K ratio thus varies widely, though its magnitude does not appear greatly to affect the uptake of potassium (Blanchet et al. [4]).

2.3 Cation exchange

A further problem is raised by the transport of cations in water flow; the rhizosphere is impoverished in K+ butone mayask towhatextent thepredominance of Ca+ + ions in the liquid phase, acting as exchangers, can facilitate the desorption of exchangeable K+ ions and thus contribute to restoring the balance of the medium. To test this hypothesis we used a model root made from silica gel, to cause a water flux (Puech [13]) accompanied by acation exchange resin incorporated in cellulose fibres ( Vaidyanathan and Nye [17]). This model root was placed in contact with an artificial soil disc, a flow of water or saline solution comparable to that found in the soil was established, and the quantities of K extracted by the model were measured.

Table 4. Exchangeable potassium and calcium contents of samples of sandy soil variously explored by wheat roots (pot culture over one month) Sample Exchangeable K Exchangeable Ca Ca/K ratio ppm in soil ppm in soil Original soil ...... 124 520 4.2 Rhizosphere ...... 48 696 14.5 Soil less explored by roots ...... 65 356 5.5

Table 5. Amounts of potassium extracted by a model root under various treatments from a soil section 1.5 mm thick having initial potassium content of 300 ppm Applied treatment Potassium extracted (Y equiv.) I. No resin paper: Solution movement 8.25 ml H-O 0.5

Solution movement 7.3 ml CaCI1 4.8 N Solution movement 16.9 ml -Tj CaCI, 7.2 2. Resin paper: Solution movement Nil 7.5 Solution movement 19ml H1O 9.3 N Solution movement 16 ml T CaCI, 12.8

125 The results, Table 5, show that the flow of pure water involved only traces of potassium, while the substitution for water of 0.01 N CaCI 2 was efficient in bringing about the movement of appreciable amounts of potassium. These findings merit further exploration but weconsider that water movement caused by transpiration of crops is an important factor in K + enrichment of the rhizosphere on account of the Ca++ions transported in the liquid phase. There are then a whole range of complex interactions which influence, according to the moisture status of the soil, the cation nutrition and watereconomy of the plant. In general the maintenance of the soil in a moist condition, and the resulting water flow to which it is the key, favour the desired diffusion of cations and thus the supply of nutrient to the roots. It is therefore not surprising that we often experience in the field improved nutrient status of the plant as a result of irrigat'ion, even though this does so markedly increase the need of the plant for mineral nutrients. Naturally this statement is only true when nutrient reserves of the soil, and manuring, are adequate. Following this examination of water-cation interactions in the soil, we may now ask how nutrient supply affects the water economy within the plant.

3. Influence ofpotassium supply on water metabolism in theplant

This problem has focussed the attention of several authors (Hudson [9], Achitov [1]). It is a complex problem and remains incompletely understood, having as it does so many aspects. Black [2] distinguishes these as follows: - specific influence of potassium on water metabolism, notably transpiration; - general influence of potassium (or other nutrient elements) on the volume of water required for production of a given mass of dry matter, which Black calls 'general growth effect'. This aspect has lost much of its interest since the notion of potential evapotranspiration attracted the attention of most research workers; - interaction between potassium nutrition and water supply in the production of dry matter; - salt effects raising the osmotic pressure of certain alkaline soils very rich in potassium and thus capable of interfering with water uptake by the plant. The specific mechanisms brought into play by potassium seem to be principally those connected with osmosis: thus, we have shown (Blanchet [3]) that improved potassium nutrition of the plant can result in appreciable increases in osmotic pressure of its organs, a more important result than just the raising of the K content of the cells: this increase in osmotic pressure can reduce transpiration and promote water absorption from thesoil. In quoting results we have observed in pot experiments we have attempted to ascertain the importance of these phenomena and their possible repercussions on dry matter production.

3.1 Pot experiments (Blanchet et al. [5I)

In these experiments Italian ryegrass, red clover and lucerne were grown in soils initially very poor in K and to which increasing dressings of potassium had been applied. After a preliminary cut, carried out at flowering, the soils were maintained on three different wa- 126 ter regimes representing 60, 80 and 100% field capacity. Daily transpiration was measured by weighing the pots. Table 6 and 7 give examples of the results obtained with lucerne and Italian ryegrass in the course of two periods with contrasting weather conditions, the data describing which, measured in the plant house, were:

21-25 August 26-30 August M inimum temperature ...... 15.00 C 16.50 C M aximum temperature ...... 27.2 35.0 Evaporation (Piche's evaporimeter) ...... 3.2 mm/day 5.3 mm/day

3.1.1 Reduction of transpiration

Lucerne. Table 6 shows how total transpiration increased with improved plant development, that is, with improved potassium supply (at constant soil moisture). Reducing water supply resulted in a large reduction of transpiration and of dry matter production. Relating transpiration to dry matter production (columns 5 and 6) placed a different emphasis on the results; the coefficient of transpiration decreased both with increase of dry matter production and with increase in potassium content of the plants. We shall exam-

Table 6. Influence of potassium nutrition of lucerne on transpiration and water utilization during two periods of contrasting climate No. Soil Meq. K D.M. K % Transpiration Total transpiration moisture per kg produced in D.M. gfg D. M. g/pot/day soil gfpot 21-25/8 26-30/8 21-25/8 26-30/8 I 2 3 4 5 6 7 8

I Optimum 2.5 9 0.72 - 92.8 - 835 2 Optimum 5 18.9 1.02 28.5 56.3 538 1064 3 Optimum 10 27.75 2.4 27.5 44.5 765 1236 4 Optimum 20 28.3 3.6 25.8 45.3 730 1282 5 80% 2.5 10.75 0.72 41 71.7 441 772 6 80% 5 14.45 0.99 34 56.5 494 816 7 80% 10 20.1 2.7 27.7 44.6 557 898 8 80% 20 22.35 3.63 26.7 41.4 597 925 9 60% 2.5 8.45 0.84 37 63.7 313 538 10 60% 5 10.6 1.38 32.7 55.6 347 591 11 60% 10 13 3.15 29.2 49.6 380 646 12 60% 20 13.8 3.96 24.4 42 336 579

Table 7. Influence of potassium nutrition of Italian ryegrass on transpiration and water utilization during two periods of contrasting climate

No. Soil Meq. K D.M. K % Transpiration Total transpiration moisture per kg produced in D. M. g/g D. M. g/pot/day soil g/pot 21-25/8 26-30/8 21-25/8 26-30/8 I 2 3 4 5 6 7 8 I Optimum 2.5 9.15 0.42 42 70 386 641 2 Optimum 5 11.2 0.51 39 65 437 728 3 Optimum 10 12.75 0.66 35.8 61 456 778 4 Optimum 20 12.55 2.22 37.2 59.5 467 747 5 80% 2.5 8.5 0.44 34 55 289 469 6 80% 5 10.35 0.62 33.1 56.7 343 587 7 80% 10 11.6 0.84 33.1 55.5 384 644 8 80% 20 13.8 2.4 31.9 50 441 692

127 ine this latter point which appears to be a specific effect of potassium. Consider, for example, plants 6, 11 and 12 which produced comparable yields but had increasing potassium contents. Wefind, as a function of increasing potassium supply, a diminution in the coefficient of transpiration (columns 5 and 6) evident in both hot and less sunny weather. Comparison of I I and 12 is particularly interesting -total transpiration was less in No. 12 although its yield was somewhat higher. Similarly, comparing 5 and 10 which gave similar yields, a large reduction in transpiration coefficient followed potassium enrichment of the plant. Thus we estimate that the transpiration coefficient of lucerne can be reduced by about 20% through imprQved potassium supply, quite apart from the general effect on growth. Climatic conditions determine the general level of transpiration, but the physiological factor in which potassium has an influence is capable of modifying this general level wether the potential evapotranspiration is great or small. Italian Ryegrass. As table 7 shows, the effect in this crop was much less marked. The plant pairs 3 and 4, or 7 and 8, gave comparable yields with very different K contents, which did not result in marked differences in transpiration coefficients. From the physiological point of view ryegrass appears better adapted than lucerne to drought resistance when equal volumes of soil are at their disposal, and the intensity of transpiration depends essentially on climatic factors. Chaussat [8] has observed similar behaviour in wheat. Red clover exhibits behaviour intermediate between that of lucerne and ryegrass.

3.1.2 Utilization of soil H 20 reserves

Water utilization was directly reflected in the total quantities of water transpired (columns 7 and 8 of tables 6 and 7). Water supplywas a factor limiting growth in the media maintained at 80% and 60% of optimum moisture content. Total transpiration was greatly increased by Kequally on hot and less sunny days. With lucerne it was difficult to distinguish the specific role of K from the general effect on growth, which manifested itself in the development of a better root system and thus in better exploration of the soil. There was less uncertainty with ryegrass (Table 7). Plants deficient in K in dry soil (Nos. 5 and 6) absorbed much less water than the corresponding plants well supplied with K (Nos. 7 and 8) although their production of dry matter was not much different. Thus, the favourable effect of potassium in the reduction of transpiration and the improvement in utilization of soil water reserves is demonstrated. It is always difficult to distinguish this effect of potassium from the general effect on growth, and the effect varies according to plant species. We shall now discuss the extent to which these findings can be reproduced in the field.

3.2 Field experiments (Studer and Blanchet [15])

We attempted to carry out a comparable experiment in the field on a rendzine soil equally well suited to ryegrass and lucerne. Lucerne establishment was adversely affected by drought and results are available only for ryegrass. The soil, 30cm in depth, contained 40 % clay and had a mean exchangeable K content of 180 ppm. Dressings of 0,250 and 1000 kg/K 20 were applied. There were five water re- 128 gimes, ranging from no irrigation to almost complete satisfaction of potential evapotranspiration. During the period referred to in Fig. 2, rain supplied about 25 % of water requirement and the respective irrigation treatments brough total water supply up to 42 %,60 %,77 Y and 94% of full requirements. Without irrigation the yields at all rates of potassium were to all intents and purposes identical: water supply was limiting to the extent that fertilizer potassium had no effect. When water was applied the three potassium treatments behaved differently: - Without potassium yield reached a plateau when total water supply attained 60 % of potential evapotranspiration. Further water had no effect and potassium supply was seen to be the principal limiting factor. -At 250 kg/ha KO the maximum yields was greatly increased, but to achieve this a generous water supply was needed (94 % of requirement). - Thesame high yield was reached with a lesser water supply (60 % of requirement) when the potassium supply wasincreased to 1000 kg/ha K 20. Under this treatmentwater utilization was improved, a fact which wasevident from the yield attained at 42 Y water supply; 5 tons dry matter compared with only 3 tons when K supply was reduced to 250 kg or less. Generous K manuring thus greatly improved the efficiency of water utilization. This result can be explained in terms of the two mechanisms with which we have dealt above: reduction of transpiration, more rapid and more thorough utilization of water reserves of the soil, presumably through the agency of osmotic processes.

4. Conclusion

Interactions between water supply and cationic nutrition have many aspects which are of importance throughout the relations between the plant and the growing medium.

6- 5-

' 4 -

-C

0d 2 "5 . m mrappliedl 3I-I (irrigation rain) o 5P 190 150 200 25 42 550 77 94 . potential Evapotranspiration Figure 2. Dry matter production by Italian ryegrass as a function of water applied at three levels of potassium (3rd cut; 18/6-23/7). 9 129 In the soil the maintenance of a humid condition favours diffusion of K+ ions as well as root exploration which in turn permit improved utilization of potassium reserves and of water reserves. Concurrently water flow brought about by transpiration helps in replacing cation supply in the rhizosphere both by simple transport in the liquid phase and by the exchange reactions which ensue. We have outlined the importance of these phenomena by showing that K content of certain irrigated crops was not less than similarcrops without irrigation, which were far less productive (Table 1). We find a more precise illustration in table 8 showing the amounts of K absorbed by the lucerne in the pot experiment described above: the varying moisture content of the soil and the amounts of water transpired have greatly affected potassium nutrition without greatly altering potassium content of dry matter (Table 6). On the other hand, this influence is much less marked with ryegrass whose fibrous roots explore the soil more minutely. Table 8. Potassium absorbed by lucerne (mg/pot) as affected by potassium status of soil and water supply Meq. K per kg soil Soil moisture Optimum 80% 60% 2.5 ...... 65 77 7 1 5 ...... * ...... * ..... 193 143 146 10 ...... 663 540 410 20 ...... 10 10 8 10 550

All these interactions bring into play subtle and complex mechanisms which are difficult to analyse. Potassium supply has an equally important influence above the ground where varying climatic and physiological factors are involved. Apart from general growth effects attributable to all nutrient elements, potassium plays a specific role with regard to better water utilization and sometimes in bringing about a reduction in transpiration. At least under certain conditions this element greatly increases the efficiency of water consumed by the crop. Intensification of agriculture requires precise control of water and nutrient supply in order to reap the benefits made possible by fertilizers and irrigation.

Summary

Interactions between water supply and nutrient supply are discussed in the light of results of field experiments on the nutrition of irrigated and non-irrigated crops. The interactions occur at different levels: 1) Below ground. The maintenance of soil in a moist condition promotes cation diffusion notably of K+ ions. The rhizosphere becomes depleted in this element in comparison to the general soil mass; moisturesupply isthen animportant faclorin restoringthebalance(K+ level). It improves soil exploration by the root system. Water flow brought about in the soil by transpiration carries to the roots some potassium but principallyCa+ + and Mg++. Ca++ thustransported released K+-which is then at the disposal of the plant. The result is that calionic nutrient supply is improved in irrigated as compared with dry soil; nutrient requirements are frequently higher. Complementary to this, improved K supply results in better and more rapid water utilization. 2) Above ground, plants well supplied with K transpire less water per unit weight of dry matter produced than do deficient plants; this effect, apparently specific to K, is distinct from a 'general growth effect' common to all nutrient elements, and varies according to crop type: very important in lucerne, it is less so with red clover and negligible with ryegrass. This complex of interactions is of great practical importance. It points the need in intensive agriculture for even more precise control of water and nutrient supply. 130 Literature cited

1. Achitov M.: Revue de Ia littrature relative A ['interaction entre le potassium ct I'eau dans les plantes. Revue dc Ia Potasse (Communications mensuelles de linslitut International de ]a Po- tasse, Berne), Section 3, 15- suite, 1-16 (1961). 2. Black C.A.: Soil-Plant relationships, p. 309-311. Wiley, New York (1957). 3. Blanche: R.: Energie d'absorption des ions mindraux par les colloldes du sol et nutrition mindrale des plantes. Thdse doctorat no 4033, p. 131-132, Paris (1958). 4. Blancher R., Studer R., Chaumont C.: Propriitdsphysico-chimiquesdes sols et alimentation potassique des plantes. Ann. Agron. 13. 175-201 (1962). 5. Blancher R., Studer R., Chaumont C.: Interactions entre l'alimentation potassique et l'alimentation hydrique des plantes. Ann. Agron. 13, 93-110 (1962). 6. Blanche: R., Chaminade R.: Quelques aspects des interactions entre I'alimentation mindrale des plantes et les propridtds physico-chimiques des sols. 8th Intern. Congress of Soil Science, Bucha- rest, Vol.117, 645-657 (1964). 7. Blancher R.. Bose M.: Etude des principaux facteurs ddterminant les mouvements d'ions potassium du sol vets un moddle de racine. C. R. Acad. Sc. Paris 265. 1970-1973 (1967). 8. Chaunel R.: Variations du coefficient de transpiration en conditions climatiques contr6ldes. Ann. Agron. 8, 147-160 (1966). 9. Hudson J. P.: General effect of potassium onthewatereconomyofplants, in Potassium Sympo- 10. sium, 95-108, International Potash Institute, Berne (1958). Maertens C.: La resistance mdcanique des sols A Ia pdntration: sos facteurs et son influence sur l'enracinement. Ann. Agron. 15, 539-554 (1964). sur le ddveloppement radiculaire et 11. Maertens C.: Influence des propridtds physiques des sols 0 consequences sur l'alimentation hydrique et azotde des cultures. Science du Sol, n 2, 1-11 (1964). 12. Nye P. H.: Processes in the root environment. J. Soil Sci 19,205-215(1968). 13. Paeh J.: Modalits de [a dessiccation des sols par le gel de silice. C. R. Acad. Sci. Paris, 0, 263, 645-648(1966). 14. Robelin M.: Eau et nutrition mindrale. Bull. Technique d'Information. oFertilisation>) (Paris), no 231, 541-548 (1968). 15. Studer R., Blanche: R.: Irrigations en rgion tempre a l'influence ocanique et interactions en- Ire I'alimontation potassique et l'alimentation hydrique des plantes. C. R. Ac. Agric. France 49, 339-348 (1963). 16. Tepe W., Leiden-Frost E.: Ein Vergleich zwischen pflanzenphysiologischen, kinetischen and sta- tischen Bodenuntersuchungs-Werten. Landw. Forsch. 11,217-230 (1958). 17. Vaidyanathan L. V., Nye P. H.: The measurement and mechanism or ion diffusion in soils; 2. an exchange resin paper method for measurement of the diffusive flux and diffusion coefficient of nutrient ions in soils. J. Soil Sci. 17, 175-183 (1966).

131 The Interaction between Irrigation and Plant Diseases

Dr. ELoy MATEO-SAGASTA AZPEITIA, Instituto Nactional de Investigaciones Agrondmicas, Estaci6n de Fitopatologia Agricola, Madrid (Spain)

A brief review will be given here of the chief problems arising from irrigation, in so far as the common pests and diseases of plants are influenced by an enhanced supply of moisture and the associated nutritional changes. The subject is such a wide one that in at- tempting to treat it briefly, the main difficulty is to know where to start. However, the problems encountered will first be examined in a general way, and then some illustrative examples will be taken in more detail. One may distinguish between two situations in which the problems are quite different; there are, the 'classical' or well-established irrigated areas, and those that have only recently come under irrigation.

1. The classical irrigated areas

In these zones the human factor does not in general constitute any problem. The grower is used to handling water, and exploiting the soil in an intensive fashion. Problems only arise when a new kind of cultivated plant is introduced, unfamiliar to the local farmers. These farmers are quite used to the requirements of irrigated crops, so different in nearly all respects from those of non-irrigated ones. They are accustomed to giving the heavy fertilizer dressings that are normally called for an irrigated land, they know the requirements of the standard crops, and on new lands they are not unprepared for the appearance of the numerous diseases characteristic of the plant species and the environmental conditions. Consequently, plant protective treatments are much more frequently practised on irrigated land than on non-irrigated land. Where irrigation has been established for a considerable time, the growers arecompletely familiar with these techniques. If a new crop is introduced they are on the look out for the appearance of characteristic symptoms and are prepared to treat the trouble as soon as it begins.

2. Newly established irrigated areas

In newly irrigated areas the adaptability of the grower himself is perhaps the most important of all the factors that condition the success of the enterprise. All the factors mentioned above are absent, at the outset. Thus, thefarmers will probably be reluctant to use 132 the amounts of fertilizer needed in practice in irrigated country. Moreover they are likely to be surprised by the way in which diseases proliferate, and sometimes slow to adapt the prescribed treatments or cultural practices that can control these troubles.

3. Moisture, the decisive factor in the spread of infection

The introduction of water creates the humidity (90% R. H.) needed for all parasitic fungi to flourish. The other limiting environmental factor is temperature. In the countries round the Mediterranean the spring and summer temperatures are generally favourable to the development of diseases. At these times of year the rainfall is very low, and it is only on irrigated land that the humidity becomes high enough for the organisms of disease to flourish. The presence of various plant species in the rotation of crops also conditions the appearance of different kinds of pathogens. A technician in a newly irrigated zone will have these facts available as a guide to what may occur. But only experience, which brings all the factors together, is capable of providing a firm basis for predicting the likely outbreaks of disease. Several examples could be cited in confirmation of these general principles. We have chosen one which is, perhaps, of special instructional value since it relates to one of the best known diseases of the entire Mediterranean basin, namely Leaf Spot (Tavelure), Venturia (Fusicladin) sp. In France, there are agricultural stations (Stations d'aver- tissement) that undertake to warn growers when it is time to apply plant-protective treatment, and in the case of apple and pear leaf spot the general practice is to issue an announcement 6when ascospores are liberated from hibernation at times favourable to the development of the disease. As soon as these ascospores are detected, by specially installed apparatus, it is announced that treatment ought to be undertaken, so that the germination of these first ascospores and the subsequent massive production of conidia will find the fruit trees well protected, and the damage due to the disease will be kept within economically tolerable limits. If however, it were desired to apply this technique in Spain then it would be likely to fail completely. Formation of ascospores by this parasite is in fact conditioned by the fall of temperature in winter, and the necessary low levels are not at all commonly attained in the fruit growing areas of Spain. Furthermore the conidia of the fungus have a very adequate capacity to resist the winter temperatures of Spain, and so they are able to hibernate and to complete the developmental cycle of the parasite, albeit in an imperfect facies, without the necessity of going through the ascospore stage. Although one cannot be absolutely certain of it beyond possible exception, it is nevertheless quite likely that the ascospore phase of the fungi of the genus Venturia does not exist at all in Spain. Personally, the author has not come across a single perithe- ca in thecourse ofeleven years' experience in the Laboratoryof Agricultural Phytopathol- ogy, Madrid, (chiefly in the section dealing with growers' specimens), during which he has examined thousands of leaves. He has also studied sites of attack on the wood by this fungus and these also showed the conidial facies. One may conclude that, even though there is no complete guarantee that the ascospore phase does not exist, if it ever appears it does so only occasionally or over such a restricted range that it cannot be regarded as the usual source of initial leaf-spot infection in our apple and pear orchards. We have here a classical case of climatic influence. The climate of Spain implies that techniques of' plant protection alert' intended for use there would have to be radically 133 different from those employed in the French system. The areas of incidence of the disease in Spain are in the irrigated zones, and it is the water brought in that enables the humidity to rise to the values necessary for the parasite to develop. One must bear in mind the fact that most of the unirrigated land in Spain has an annual rainfall of less than 400 mm (16 in.). One may say that our moister, unirrigated lands in the north experience natural climatic conditions similar to what is generally created by bringing irrigation into our areas of more difficult climate and lower rainfall. The putting to use of the newly irrigated zones has, on the plane of plant nutrition, the benefit of more effective, more scientifically precise aids than it has on the plane of precautions against diseases, for which local experience is the only certain pointer to the correct lines of action. Soil analysis gives a very clear idea of the fertilizer requirements for the growing of each plant species intended to occupy a newly irrigated area.

4. The chief types of diseases to he considered; risks of diseases in intensive plant production under irrigation

From what may be termed the classical epidemiological standpoint, there areconsidered to be two types of diseases: 1. That in which the intensity of the disease depends only on the amount of infective agent present when the crop is commencing its cycle of growth. 2. That in which plants infected by an infective agent pre-existing on the land, or arriving there, become in their turn new sources of infection for the rest of the plants in course of the same cycle of growth. This basic distinction is assumed in the graphs currently used to represent the course of epidemics, but it is not exact or absolute, since naturally any infected material turns into a source of re-infection eventually, even if slowly. The important point is that the intensity of damage can be mainly due, either to the amount of infective agent present initially, or else to the fructifications derived from the primary inoculant, which may have been so sparse as to beeasily overlooked. Consequently, when a diseaseofthefirst type is encountered,and if it be supposed that the terrain harbours enough of the infective agent to produce a serious outbreak, the external limiting factors for the biological development of the parasite will be the only ones that will influence the greater or lesser incidence of the disease. On irrigated land, high relative humidity so necessary for the development of nearly all cryptogams, is a factor inherent in the irrigation itself, and only temperature remains to act as a limiting factor in this case. This is typically the case with soil fungi, which extend their radius of action rather like oil spreading on water, so that whole plots are often completely invaded. The intensity of their attack very often becomes the limiting factor for the success of thecrop, since in many places where the type of climate (warmth) suits both the crop and the parasite, the irrigations necessary to secure a good harvest are also adequate for the strong development of its enemy. When the population of theinfective agent is high enough, attacks of this kind can scarcely be arrested since no known fungicide will fully control these parasites under practical conditions. As a general rule, the diseases of the second type cover the great majority of the fungi that attack leaves or other green parts of plants. Environmental moisture enters into the likelihood of spread of these diseases in two fundamental ways. The necessity of moisture 134 for the germination of fungal spores has been fully established in many instances. An example is provided by Gloeosporium olivarun, a well-known fungal pest of the olive plantations in the Mediterranean basin. Once the spores have germinated and the first myce- lial tubes have penetrated inside the fruits or other infected structures, the ambient humidity is no longer critical for the further development of this endoparasitic organism, until in due course the life cycle begins to repeat itself with the production of new spores, and the need for a high ambient relative humidity, attaining values above 90% again makes itself felt. It may be pointed out in this connexion that atmospheric humidities recorded by the standard methods as used in weather stations are often wholly misleading for the study of development of disease organisms. In practice where there is a low-growing crop, or indeed even a tall one, the plants themselves, whether watered from ground level or by spraying, constitute a sort of cloche, almost like a real' humidity chamber' as used in laboratories. The humidity inside, i.e. close to the plant, thus has little to do with the external humidity as measured by a hygrometer, being always much higher than the latter. These conditions are very favourable to the induction of attack by fungal parasites, both at the implantation stage, since the moist conditions allow the spores to germi- nate, and at the fruiting stage, the formation of the spores by which the disease is passed on. These brief remarks will have demonstrated that irrigated land offers ideal conditions for the development of either of the two types of fungal disease, by maintaining local conditions of atmospheric humidity almost continuously within the limits required for the development of the infective organism. The creation of moist conditions favourable to the progress of diseases is by no means the only consequence of irrigation that has a bearing on plant pathology. By their very nature, irrigated crops are a way of exploiting the soil more intensively. Harvests follow one another at shorter intervals and the plant residues left when crops have been lifted are still (when their successors have begun to grow) in a form utilisable by a multitude of disease organisms, which can thus survive to infect the ground, with a virulence unknown on non-irrigated land. One may deduce the highly important consequences that follow from this, both for the agricultural technician and for the economist. From this point of view of agricultural technique the desired rotation of crops on the irrigated land may have to be changed abruptly because the dangerously high population of infective agents in the soil exposes susceptible species to unacceptable risks. To avoid losses it is often necessary to bring plants resistant to these pathogens into the rotation. A classical example is that of invasion by Fusarium and other soil fungi, making it obligatory to bring cereals into the rotation. They generally give a lower yield than the crops they replace but are more resistant to Fusarium. A further consideration is the recent or less recent introduction of the irrigation system. If this has been long established the likelihood of the presence of these infections on the land is high. On the other hand in newly irrigated areas these problems are much less serious to begin with although they may show themselves increasingly as time goes on. The massive uptake of plant nutrients from the soil by plants grown under irrigated conditions, in amounts farexceeding the uptake from unirrigated soils, clearly demands res- titution through relatively heavy fertilizer use. The gathering of the crop always leaves behind plant residues which in time decompose and become part of the organic matter of the soil itself, but offer in the meantime an excellent substrate for the maintenance of fa- cultatively parasitic fungi. These problems are of a much lesser order where the land is not irrigated. 135 5. Problems arisingfrom the utilisation of water and rate of watering

The amount of water supplied to the crops influences the rate of growth, the vegetative development attained, and flowering and fruiting. In many instances the desire for rapid development, for example to obtain early fruit that will command a high market price, occasions use of irrigation water beyond the normal needs of the plant. This prodigality with water has immediate consequences which have a bearing on the nutrition of the plants and their susceptibility to diseases. In the first place the excess of water washes out of the soil some of the nutrients that the plant ought to be taking up rapidly, and in the second place it maintains conditions of continuous ampness in the rooting zone, conditions immensely favourable to the implantation of all kinds of parasites. Important among these are the genera Fusarium, Rhizoctonia and Pythium, but there are many others contributing to the biocomplex which normally attacks plants on irrigated ground in the above circumstances. Also arising from theexcessive provision of water, especially to the young plant, are physiological consequences that become apparent later. These are worthy of discussion in somewhat greater detail. During the first phase of growth of a plant it is normal for the aerial part to develop strongly whilst at the same time the roots tend to bury themselves further and further into the soil, maintaining a balance between the aerial part and the root system. If however the plants are continually watered the roots have no need to penetrate deeply in search of the necessary moisture since they can find it all the time at the surface. It is then quite usual for all the roots of young plants to remain in the upper- most soil layers instead of going downwards. This produces an imbalance between the development of the aerial part and the root system. The ill effects are not obvious at first because the amount of water that the roots can supply is ample for the needs of the plant. It may also be remarked that transpiration will not be too intense during these young stages of the plant (early in the season), since temperatures will not be excessive. Later on, temperatures will rise higher, and with them the transpiration rate of the plant. It may well turn out that the plant will suffer from the physiological imbalance between the moisture loss from a large, leafy aerial part and the limited uptake through a puny and shallow root system. This leads in turn to imbalances of growth, deficiency of flowers, failure to set fruit and so on. The true condition is often masked after a time by the presence of the facultative pathogens that are almost certain to make their appearance on any sickly plant. Hence it is not unusual to make a false diagnosis of the troubles, ascrib- ing the poor state of the plants to the parasites when it is really the misuse of water that has impaired their vigour in the first place and left them open to subsequent infection. These troubles are increased if root penetration is hindered by a clay layer a little below the surface, or if the water table is high. The water table can be even more objectionable, even though it is comparatively deep down, if trees or bushes are being grown and their roots encounter it after a few years' growth. Study of the external appearance (habit) of the plant can in such cases help one to arriveat a true diagnosis regardless of the presence and location of any kind of parasite. The roots in fact show a tendency to run horizontally and to avoid plunging into thesoil. Root volume and root lenght is disproportionately small as compared with the size of the aerial parts and in many instances by the time the symptoms are clearly visible, the plant is trying to compensate for its lack of an adequate water supply system by putting out adventitious roots from zones that normally do not have any, and even from the stem above ground, the first ones being clearly visible.

136 6. The influence of manuring on resistance to certain diseases

As a general rule equally as true for irrigated land as for anywhere else, it can be said that any plant grown under the conditions that permit proper vegetative development has a better resistance to any kind of external parasites than a plant grown under poor conditions. It follows from this, agains as a quite general principle, that a complete fertilizer dressing on any soil, adjusted according to the findings of a preliminary soil analysis, helps to defend the crop against disease. In confirmation of this there are in the literature of plant pathology many reports in full detail, whilst many further instances find briefer mention. For example, Berkley found that symptoms of Mosaic as seen in the field on strawberry and tobacco plants are less severe in the plants grown on well fertilized soils. Rolandobserved that an increase in nitrogen content reduced the severity of symptoms produced by Virus Yellows of the sugar beet. Dalton reported the same finding for the Potato Leaf Roll virus. Increased resistance on the part of French bean plants to Colletotrichum lindenuthianuan has been found to result from potassium fertilization, even at low rates. Potassium has the same effect on rice, in relation to the parasite Piricularia oryzae, although it is without effect towards Hehninthosporiunz oryzae. Potassium dressings reduce the intensity of attack by Alternaria spp. on tobacco. In some instances an enhanced resistance of a crop to certain diseases, obtained by adjusting the manurial treatment, is secured at the expense of structural changes that impair the product commercially. This happens to rice excessively manured with nitrogen and potassium. Its resistance to Helninthosporiunoryzae is enhanced but the commercial quality of the grain is lowered by granulations appearing on the plasma. In contrast to the above findings, it seems that plant nutrient dressings can sometimes sensitize plants to attack by certain pathogens. Wilson for example found that increasing the nitrogen content of the soil increased the adverse effects of 'Dwarf' disease on onions. Applying excessive amounts of fertilizers to the soil often brings serious trouble, causing damage to the plants. Ornamental plants are particularly susceptible to over-manuring, the appearances produced by excess of nitrogen being fairly general. The symptoms are necroses, bounded by the veins, on the leaf blades, with a quite characteristic appearance in many plants, examples being begonias and Cissusantarctica. In some other instances there is secondary attack by parasites following on after initial direct damage. Thus, heavy nitrogen dressings on wheat can induce lodging, and subsequent attacks of abnormal severity, by Septoria tritici. There is thus considerable evidence, albeit still fragmentary, that manuring can increase either sensitivity to disease or resistance to disease in certain instances.

137 Iron Deficiency Problems in Peanuts under Irrigation

D. LACHOVER and ADELINA EriERCON, Division of Agricultural Chemistry, The Volcani Institute of Agricultural Research, Bet Dagan (Israel)

1. Introduction

The peanut, although a relative 'newcomer' to Israel, has become an important cash crop, thanks to intensive research. On the basis of various investigations that have been carried out on the production of peanuts under irrigation, mainly at the Volcani Insti- tute of Agricultural Research; Israel has succeeded in obtaining one of the highest yields in the world [3]. Under adequate and uniform moisture supply, efficient Rhizobium inoculation [6], phosphorus and sometimes potassium application, peanuts have proved to be a potentially high-yielding crop. Although the peanut for years was mostly cultivated under irrigation in sandy and red sandy loarns of the Coastal Plain it was established that it can grow with not a lesser success in medium heavy soils. The light soils are in general deficient or poor in CaCO3 with a pH ranging from 6.8 to 7.3. With the development of the country, while being a good cash crop, peanut has been introduced in new regions, between them in southern more arid parts of Israel - the North- ern Negev, where soils are relatively rich in lime. Approximately 25 % of the total production is now centered in this region [3]. In the Coastal Plain and some parts of the Esdralon Valley, plants close to harvest were sometimes pale green in color; there are no estimates of a possible subsequent reduction in yield. This phenomenon, when occurring in these regions, is attributed to excessive growth of the foliage or to senescence. In the southern part of Israel since the introduction of the peanut crop into the Negev, the young plants exhibit often incidences of yellowing more striking and early after emergence. Consequently there were relatively lower yields in such fields. In general, when slight yellowing occurs, the primary symptoms were similar to those of nitrogen deficiency although the roots of plants were well nodu- lated. In one of the relatively new settlements in the Negev, Ze'elim, whet e peanuts were sown for the first time, plants exhibited striking yellowing symptoms 3 weeks after emergence. With time, the more acute the disappearance of chlorophyll, the more striking were the associated morphological changes. Some parts of the field were characterized by slick- spots in scattered areas, differing in size, where severe chlorosis was widespread, causing with time a complete loss of yield. Pathological examination did not show any disease infection. It occurred to us that the cause of these early yellowing and more striking nutrition disorders might be due to iron deficiency for the following reasons: 138 a) Plants without available iron are unable to manufacture chlorophyll and lose their natural green color [2,5]. b) The disorders caused by iron deficiency is particularly prev- alent on calcareous soils, where it is difficult to keep the iron in formswhich are available to plants [2,4]. c) Iron deficiency had been detected earlier in fruit trees, growing in the same Negev areas, where peanuts have been affected. d) In preliminary tests conducted on affected peanut fields in which quick acting nitrogen fertilizers were applied, no improvement was observed in the plants. e) Also leaf analysis did not reveal any marked difference in the nitrogen level between the yellow affected and green normal plants.

2. Experimental

2.1 Field tests

Preliminary treatments to moderately chlorotic plants in different localities in the Ne- gev, either by nitrogen soil dressing with ammonium nitrate or by foliar application with I % urea solution did not improve the situation. Fui thermore, a comparative analysis of leaflets taken from the same morphologically homologic position, revealed only negligible differences between the nitrogen content of the affected plants and that usually found in normal green plants. A rather surprising result was obtained in measurements to determine the activity of the enzyme peroxydase as an indicator of the iron requirement (according to Bar Akiva's method of analysis) [I]; it was found, that in green leaflets of relative normal plants in the Negev, the activity values of the enzyme reached 4 units, while in leaves from severe affected yellow plants an average low value of only 0.9 units were recorded. Supplementary tests were carried out in a markedly affected (yellow) field in the Negev on small plots, using the iron chelate Sequestrene 138. On all treated plants the leaves started to turn green and the plants grew well after approximately 10 days.

2.2 Potexperiment

To confirm these preliminary observations, in the following season an experiment was carried out under controlled conditions in large containers holding 60 kg of soil. This basic study was confined to two objectives: a) to determine whether the characteristic yellowing observed at Ze'elim, when it appears early and is followed sometimes by more severe physiological disorders, is caused by iron deficiency; b) to compare the effectiveness of different iron treatments with respect to their speed in curing chlorosis, and their effect on yield. In order to guarantee the appearance of yellowing and to study other striking symptoms in the experimental plants, similar to that observed in the severe affected field, soil was brought from the same extreme scattered areas in which the symptoms had appeared. The soil was a loess-like type, sandy-loam in texture, showed no salinity, but had a relatively high pH of 7.9, a relatively high amount of lime - 11.3 % CaCO3, and was very low in organic matter. The containers received uniform fertilization, equivalent to 1000 kg/ha ammonium sulfate, 600 kg/ha superphosphate and 250 kg/ha potassium sulfate. Four seeds were planted in each container in April 1968. After the plants became well established they were thinned to one per container. 139 Visual observations. Six days after emergence the seedlings in the containers showed symptoms of mild chlorosis, exhibited in the youngest leaves, while the oldest were normal green in appearance. As soon as this phenomenon was visible in all containers, ten days after emergence, the differential iron treatments were started.

Treatments. The experiment involved II treatments, including the control (no iron added). Five forms of commercial iron products available on the local market were compared, four of them were chelates. The products were: I) Sequestrene 138 (containing Fe-EDDHA); 2) Plant Green Iron (containing (Fe-EDTA-OH); 3) Rayplex (containing FePF); 4) Iron Polyflavonoid (containing Fe-PF); 5) Wuchsal nutrient solution (containing macro elements and iron salt). Sequestrene 138 and Plant Green Iron, in solid form were dissolved in water and injected as a side-dressing to a depth of 5 cm; Rayplex, granulated and insoluble, was broadcast and cultivated; Iron Polyflavonoid, dissolved in water, and Wuchsal nutrient solution were applied as sprays. Details concerning methods of application, amounts, number of dressings are presented in Table 1.

3. Results

3.1 Visual observations

The visual observations have proved beyond doubt that deficiency symptoms detected in the plants, resulted from an iron shortage. On the other hand it was shown that the different iron chemicals vary in their suitability for correction of iron deficiency in thecrop. Peanuts grown without iron, or treated with the chelates granulated Rayplex, Plant Green Iron or the nutrient solution Wuchsal, and which were mildly affected before treatment, continued to show abnormal growth and with time exhibited more severe characteristic symptoms of deficiency. These anomalies led to the gradual development of a typical, more acute pattern; the intervenal areas became deep yellow while the veins, remained light green. Subsequently the entire surface turned yellow, then whitish, often mottled with some brown spots, or necrosis appeared on the lamina. Figures 1-5 illustrate some typical examples of the chlorotic peanut plants.

A striking and pronounced effect of iron treatment was observed when Sequestrene 138 was used in any amount and number of dressings. The response was exhibited in a change of color of the leaves which became green only a few days after treatment, followed by a stimulation of growth. The best results, consisting of visibly much more persistent improvement in color and growth, were obtained when 15 or 10 kg/ha Sequest- rene was applied in two dressings (10 and 46 days after emergence). Another favorable iron treatment was that with Iron Polyflavonoid, applied as a spray on leaves. At first, two sprays wereapplied with aO.2%solution, onlya very slight and temporary improvement was noted. However, when two more sprays (at the age of 46 and 67 days) with a higher concentration (2 % solution) were used, there was amarked improvement in color and plants started to grow. 140 7,!/ , ] ticcfl'c ot'tii :rco i t nt itCa¢[/t On] T}hypod and (tar ticlds< Of pr.'anlats c({tti ttrCkontat-

i rc'ittntcts Nlc'Whod I quialcn Nicld pitr p"lat of apphi- amonts \it ber ol pod \\ eight otlhat .

h'eoforA i pr alrOwic is par Cant of O n "I I c it o t. ..onro ..noi~n. 0 it of . toni i Contri.,fna ~ Cotntrio)lO Seq.t,I!Cne 13A I .... .I q I5 Ike fa f2e 5A 545 W ! p55 Sequcstrcn -. .0 k10ha (2i '4 4so5 6 53 Sc I1uc'trcnr8 . . 1 q 1 kit ha f & 40 s08 63 1 329 Scuocstrcn I S Fr . Pq 5 kit h 0) 32 8 32 45A 238 Iron Spr )lvilI.22'', 4 320 320 39.7 207 Ra tfcv,-fe SI 15 k ha I 115 26.1 3f Rap .-I a St I5 kg ha 12, 5 0 S) 1I. -I Pla t (rec lion I q 10 kit haI A I1k8 118 27.4 I43 Plant Olccn Iron ...... i 30 ki ha 3) 68 68 II 6I \ iuithif ... p' nL 0.4' 4)I 10.5 10o5 24 ; 12' S I 4A ft 4

I S I) (p fto51 97 21 Itq ity f f Inr Sit "pratoe on iani: SI sold wiQ rlnsn Oild cotalnng [all dwrlte, and nttge pods" IhcI!leItres tn parcftitc'cs ttrldiWtc ih nrtlhcr of applicatons into "hirl, tl total anoolti "as dO- ided. (2) 10and 3 , tf"lt crngcncc (A f10.36 and 44dasdtwccr enrgnice: 4) 10. 36.44 ad 66day a ftic it itn ac n'cr'

32. } /ch

The esu Its of pod and hay yiels presented in fable Icont in the vs tal Obs'V Iton I that the characelisicssymptons of nutrition disorders are due to iron chkrosi. The yields of pods and ty differed ma kedly in their response to treatment with a close relation existing between the aspect of the plants and their yields. Sequestrene 138 in all a mounts and number of dressings, gave high lields. The ophimal teatment was 15 or 10 kgh a divided in two dressings. INon Polvflavonoid gave a reatively normal yield, whereas nearly total crop failu resulted in the control containers and in these treated with Rayle\ Plant Green ronand Wuchsal. The resuhs demonstrate clearly the inportance of including iron treatments itie F rt i- li/er progran for peanuts, where synipItns s uggest its need.

Lit, orof/Y''c' r

I - Bvi-ArtvN V. und I svvos R. Peroxsd ist as an indtc2rok'iron , rteduirccn citrus plan ts. is ncI J acrc.R nit 145 153I1968). 2. B u ,ij I roto, orsis in plant' Ad \gron It 329 36f 1961 i 3. (il tIE.and Htis-Ilzoos A.Grou dnt rulahtation in Ihrael. World Qrops, 1, I. 40966j 4. UaR~Rs I. and Ill" R.W :Phstology and tmerat nutrition. Inn Ih Peoanut teUnpr- dilale Lguomc, p89 21 1he National FertlerAssocaton. Wash. D (' t]95t 5. RtI, P II. and 'trsir, E..:t fler oafnutrtent deficohntnes ot growth and k'riting claraictstics 01 peanut, in i sand rultures Agron J 0al(63 6- (19oik , 6. S, n FttA'N andl A P,RIN Y.: Inoculatin ot"prf not' b applicatlon of Ilthizobiunlupcnti o into the planting urrows. I pl,Agic 4 _I'-- 6(lsf)-.

141 t >,, I, rad t tjI

in sovorOl 01foc td

nti,n ilthct i ing

(1w Ol pl antmonth. charl /Cil>>!l H> mark cd lowo Ito uitt i tat.2c

Durk gr I m

clo, jwcp Hn"

dsoll I orSt um oe ,, Iic ulpt',!c , C, cha ra i c r,tvd. t,1o- o color. ct.pL in til

>010> 010)ot cmlamod gPn Righi

[ \ HOill c ,gc nlalor m ')"in¢."CtKI d - ,cl,,p,,[ , ,l] On" .,I vo]l I.. Ill oi>> o1 1010

1491 discolor io i of ilic

142 I.rntritIccl. (\ge: 78 dfis Ltcr ncrg2ncc S'rc iro(,jj ...... ,ni,f< >Ite uppQ, I s [hse-llo mnotled flItmha aletra tiebrownsh red sIom

V mmtrealted A'ge: 88¢di necro'm ct edges of sev1r afLeted" tLaves t t0e mopof

143 Interaction between Irrigation and Fertilization in Mediterranean Grassland

. Ih'l "d tion

It is icII kno~k n that c hnges in botanical conposition ofa mi\ed swar- are hastened h the Lire ot ir igat ic n andlit li/cr lreatmntts, This is e ,entia lh a problem i plant ecolo- ge>.btu I henIIIett ItmIent applied skiperticiall to a srs ard ha, an immediate effte.i upon bolallii composition, this in tln I, reoflcted in theOutptlofherbage 10 . I he 'e 'ional patterll of grass giowth in temperate climates shows a sharp peak in the spi inglie asen. lo< cd by a fall in mid-sumner. Another peak, less marked than in the sp1g, IllaN foilo in autumn at the Waven latitudes, while a more or less long period of Iest is nomma] during the winter seascn Stich seasonal pattern of the gilass gr wth seems to depend, besides the incidence oh man ot her iirow th factor,. upon' the interaction between tem peratires and photoperiod 29,42 . It follow s that Ihe length oft he periods of'opltial growth depends on the latitude: passing from cold temperate climate to mild temperate clmate, the t pical seasonal pattern of the ctIve of gn ass grow th becomes nore manifest. In faci descending to looer latitudes the optimal growth period shoxs a tendency ito conceni rate in the spring and au itn i seasons. Il the summer, the cornbination of high tell pera lIres a ld relatively short day diration results in a lowering of the vegeta live po- tentia.l of the grasses, tntii growt h ceases wthen the critical tentmperature tI gras' gnowth is it ained. Ilowever, descending to lower latitudes the optimal coilditions of temlpra- ture and photopet iod for grass gromth start eat ier in spring and are prolonged toward \ Inter. Eenllllit lI legumes show somaewhat dillierent -eqtilretlielll fron grasses, bet itg mole resistanti to hilg temperattre, while less influenced by the phooperiod, bween the range of optimal tenllperaIlres ftor vegetative growth. MNeover, the legumes utili/e ohe increase of davliglt intensilv better than the graSS,,s. (otlsequetitly, the legCtumles Of a 11ied sard. in the given environilentai conditions. start their grow Itn sping later than do the grasses, but the growth period persists more toward the sirmmer. When the ntoisture reginLe of the soil and other growth factors are not i miting. the growth season of the legues with important differences hetween species and ecct pes) extends throuIghout the sumnIet seiaSon., It follows front the above that in thetemperate /one apart from the large variation of species and ecotvpes represented in natural swards a consistent variation is observed in the grass legume ratio throughout the vegetative season. The ratio is more fa- 144 vourable to the grasses in spring and autumn, and to the legumes in late spring and summer. Such seasonal pattern due to climatic variation is generally observed in both natural and artificial mixed swards of the mediterranean area, with a tendency to become mol eevi- dent from the humid to temperate and finally to subarid mediterranean climate. In the former climate, a sufficient summer rainfall favours the legume's vegetative growth. Passing to the latter climate, the decrease in summer rainfall involves an increasing stress on legume vegetative growth, until growth completely ceases due to water deficiency in thesoil. The pattern of summer rainfall from higher to lower latitudes, within the mediterranean area, would obviously interact with the otherclimatic factors determining changes in the grass/legume ratio in natural as well as in artificial mixed swards. In fact, while the grasses find adequate moisture in the soil in the seasons suitable to their growth (spring and autumn), the legumes encounter a low moisture content in the soil in the late spring and summer. In other words, the seasonal pattern of rainfall of the dry mediterranean area results in competitive dominance of the grass component in the sward. This situation would be reversed by a better moisture regime in the soil. by the distribution of irrigation water in the late spring-summer period (Table 1).

Table 1. Potential yield (q/ha) and botanical composition (%) of natural grassland under different natural and artificial water regimes.

a) Humid mediterranean climate Temperate mediterranean climate April-September April-September April-September 800mm of rain - 400 m of rain 150-200 mm of rain with without with without with without irrigation irrigation irrigation irrigation irrigation irrigation

Hay ...... 124 115 1M0 104 200 20 Legumes .... 34 33 40 28 50 5 Grasses ..... 63 63 35 46 30 50 Other species 3 4 25 26 20 45

The data of table I show, too, that irrigation would normally increase the output of the legumes, depending on the pattern of natural rainfall in the spring-autumn period. Some experimental data on the irrigation of two-year-old lucerne meadows obtained in several locations extending from humid to subarid mediterranean area, show clearly that the yield of irrigated lucerne in comparison with unirrigated increases greatly passing from the former to the latter climatic condition (Figure 1). The comparative increase of the yield of grasses and clovers due to irrigation is also illustrated in figures 2 and3. The summer yield of clovers is consistently increased by irrigation, while the grasses cannot benefit from irrigation to the same extent. The above supports the hypothesis that in the mediterranean area the increase of forage output of a mixed sward, due to application of irrigation water, depends mainly on the legume component. The examination of the ecological behaviour of the main botanicalcomponents seems to be useful in clarifying some aspects of mineral fertilization in mediterranean grassland under irrigation.

10 145 90 180

80 TORINO with iriolion 160 70 wilhout irrigtin 140 60 fl120 50 F ]H100. N40 Xi ii8 so~ 30 600 20 I I 40 10 JJ [20 0 - 0 J F M A M j A S o N D J

90 -180 80 MATERA -160 70 140 60 withirrigtion 120 wihoutirrigotion

4020 40 20 - 'o"40 fll! 20 H 20

3 F M A M J J A S 0 4 J

90 I80

80 SICILIA - wilt irtigon -160 70 bo#'- -- wilthouoirrigotion 14 60" -120 60 f I82 ~40 so80 - 30 H H 20 40 10 20

0 0 j F M A J j A S o N J Figure 1. Response of two year old luccrne to irrigation at different latitudes within the mediterra- neon area. 146 I:.

o i. ~ .. -- 0 .

Figure 2. Potenti yieldofsoeurssfces and gmseswith and without irrigation in Po Valley.

SA47 2. Generalfeatures of N-fertilization

In cold temperate climates the grass component of the sward exerts a consistent yield potential, being able to produce large amounts of herbage throughout the vegetative season, when N-fertilizer use is generous. In such conditions a well-managed pure grass sward, treated with much N, would produce more dry matter than a mixed grass/clover sward [21, 30]. In the mediterranean area, especially when water is available for irrigation, the situation is quite different. The legume component, favoured by the environment, is capable of a higher yield potential than the grass component of a mixed sward [11]. The above is clearly seen from some yields of the main botanical components of a mixed grass/legume sward under irrigation, in the Po Valley (Figure 4). The higher potential yield of the legumes, in comparison with the grasses, during the late spring-summer period emphasizes the importance of a programme of manuring to maintain a consistent percentage of legumes in the sward, aiming either to increase the total yield of herbage or to favour the nitrogen nutrition of the grasses. Moreover, it has been ascertained that a mixed sward of grasses and legumes has a higher potential productivity than either a pure grass or a pure legume sward in the given conditions [16,31]. In fact, the legume component of a mixed sward expresses the maximum potential yield in late spring-summer, and the grasses in early spring and autumn. Consequently, a balance between these main components would increase the total herbage output of the mixed sward troughout the vegetative season [8,9, 11].

100 a.Test only compost b N (compost+150 Kg! c.P (compost-240 Kg/ d. K (compost+250 Kg 95 manuring) / ha N at the end of ha PsO o the end of ha K2O at the end of 90 winter) winter) winter) 85 i 80 --. Total mixture 75 -Legumes 70 Grasses 65- 60 1t Other species

a55 50- 45 -I 30 \/*"-\

25- " " 20

10 •

M J J A S ON M J J A SON MJ J A SON M J J A S 0N

Figure 4. Potential yield of total herbage and botanical components of permanent grassland under irrigation treated with different fertilizers in Po Valley. 148 To this purpose, careful consideration is required in the use of N-fertilizers. In fact, many experiments have shown that the excessive use of N-fertilizer on swardswith more than 30% of legumes may reduce the total output of herbage [8,9, 11, 17, 18, 19,31,32, 33]. The above would be the result when large doses of N-fertilizer are applied at the beginning of the vegetative season (Figure 4b). While the yield of the grasses is enhanced at the first cut, the yield of the legu res is consistently reduced either at the first or at the following cuts. If nitrogen is applied after the cuts, the depressive effect on the legume yield in late spring and summer is reduced [9, 10] especially by applying fertilizer N when the regrowth of herbage has already started [52]. This aspect of N-fertilization is clarified by the results of an experiment carried out in the Po Valley on permanent grassland irrigated with 8000 mc/ha of water (frequency of 15 days). With constant PK-fertilization (120 kg/ha P20; 100 kg/ha K 2O) 50 kg/ha of N were applied in early spring or split after the first and second cut. The N applied in early spring increased the yield of the grasses in spring but reduced the yield of legumes in summer, while the split N did not reduce the yield of the legumes in the summer season (Figure 5). The total forage output is not significantly different with the two systems of N-application, but we must consider that the amount of N applied is quite low. From other experiments it is known that, if a higher rate of N is given in early spring, the reduction of yield of the legumes in the summer period may be greater than the increase of the grass yield in spring (Figures 4a and b). The differences of forage output, particularly of the grasses in spring and legumes in summer, due to the time of application of fertilizer N, are probably correlated with competition - for nutrient uptake as well as for other growth factors - between the botanical components of the sward. While the fertilizer N applied in early spring would affect the yield of the legumes by the competition exerted (directly and indirectly) by the early- growing grasses, towards the late-growing legumes, when the N is applied after the cuts, the grasses are limited in their potential growth by the ecological factors previously discussed. Therefore the negative influence of N on the legumes output would be lessened. The data of the same experiment confirm this interpretation, when the results of different mowing systems are compared. The competition effect of the grasses on the legumes in spring, when N is applied, seems stronger when the first cut is made later in the season (infrequent mowing: 4 cuts in the season) and becomes weaker the earlier the first cut is made (normal mowing: 6 cuts in the season; frequent mowing: 8 cuts in the season). The statement that seasonal distribution of forage output of a mixed sward under irrigation can be largely modified by the application of N-fertilizers is well supported by these data as well as by other references [30,34,35,55,56]. Another important point in the N-fertilization of a mixed sward under irrigation concerns the interaction between the system of exploitation and the optimal dose of Nsuit- able for application (Figure 6). Increasing amounts of N-fertilizer applied to the sward appear to decrease the total output when the herbage is infrequently mown. On the other hand, frequent mowing seems to enhance the efficiency of increasing doses of N applied to the sward. The comparative yields of the main botanical components are also widely affected by the increasing N application. Generally, legume yield is reduced while grass yield is progressively enhanced. Nevertheless, the patterns of the relative curves show different inclination with increasing frequency of mowing. The fall of thecurve of the legume yield and the corresponding increase in the curve of the grass yield are more marked in the sward frequently mown. 149 q/h. ho, frequent(8 cuts) mowing 2P 4P 69 89 OP 120 110 1§0 1 0 2q0 240 Totolmixtre

" /I II II ,/1!111tllt1!1/11@ A /B [7Z1 GrossesLegumes --..... I C// M Other sp.

- 50 40 A B C 30 • / ""\.,, .. 20

* .. .,_-- ...... - : '. A M

q/h hoy normal mowing 2 10 io 6. 8P l10 i l6?0 l10 20 20 Total mixtu. e

07/3/7/ 1A ZZ Legumes .....-- /B E/Grosses = = I = =-7/ z// 122(77 // i//14C C::) Othersp, ...... 60 A B C 2F 50

\ 20 ------, -og ..-.. \-

.. .,. . A t 3 AS O 4k J J kspt htJJA SON

q/ho hoy unfre uent mowing

2O 40 40 80 IlQ 120 14' I I10 200 20 Toto[ mixture-m M A Z Legumes ...... /B // MGrsses /22gz~~r/ / C : Other sp...... 60 A B C

30 -- '- . , 0 ,,, ,......

...... A MJ J A S 0 N A N A M J J A S N Figure 5. Effect of methods of fertilizer N application on the seasonal yield of total herbage and botanical components in combination with different frequencies of cutting. (A = control: compost only; B = compost + 120 kg/ha PO + 100 kg/ha KO + 50 kg/ha N at end ofwinter; C - compost + 120 kg/ha PO + 100 kg/ha K 2 O + 50 kg/ha N splitted at first and second cut). 150 250 Total mixture/ (a) 240

230 b)

220 P = 240 Kg/ho K = 200 Kg/ho 2 210 = 200

180 170 " - c

160 idO 260 310 Kg/ho N 140 Legumes

130

120

o 110 (b) 100 P = 240 Kg/ha aK = 200 Kg/ho 90

80 (c) 0 70 Id0 2do 360 Kg/ha N 140 Grasses 130

120 P = 240 Kg/ho 110 K = 200 Kg/ho 100

- 90 = (b) 80 070 ()

60 00 200 300 Kg/hoN

Figure 6. Interaction between increasing rates of fertilizer N and frequency of mowing of permanent grassland under irrigation in Po Valley. a) = frequent mowing: 8 cuts; b) = normal mowing: 6 cuts; c) = infrequent mowing: 4 cuts. 151 The observation that such patterns of the curves correspond to higher total output of herbage by the sward shows that with more frequent defoliation - as in grazing - the increase of grass yield may more than compensate for the decrease of legume yield, when a large amount of N is applied to the sward. In other words, more N-fertilizer may with advantage be applied to grassland when grazed and irrigated in the mediterranean area.

3. Generalfeaturesof P-fertilization

The P-fertilization of mixed permanent swards is in many ways less difficult than N-fertilization. P-nutrition of an herbaceous plant, in competitive association, seems mainly governed by the P status in the soil. Thedistribution of fertilizer P-in soils providedwithan average content of phosphorus - would favour the stability of the existing botanical composition of the sward, particularly its grass/legume ratio [36]. The percentage of legumes in the sward will be maintained but not increased by the top-dressing of P-fertilizer in soils with an average content of available P [1]. Nevertheless, an adequate supply of P is fundamental to increase the persistence of legumes in the sward [51]. The increase in the legume fraction of a sward depends on the PK-intcraction. If available P is at a low level in the given soil, while the level of exchangeable K is sufficiently good, the application of fertilizer P would increase the percentage of legumes as well as their individual output in the sward [31, 33,44,50]. In many instances, well-balanced P-fertilization is a sine qua non for maximum exploitation of the potential yield either of the grasses [21] or of the legumes of a mixed sward [3. 27, 51]. Efficiency of P-fertilization depends, primarily, either on the level of P in the soil or on the factors governing its availability to the plants throughout the vegetative season. The rate of P uptake per unit of dry matter appears quite uniform throughout the vegetative season in a sward under irrigation. Such uptakes are consistently enhanced when P-fertilizers are applied (Table 2). Top-dressing of P on permanent grassland, continued for many years, increases progressively the level of total and available P in the soil (Table 3), from which a relative decrease of efficiency of P-fertilization may occur [31]. As for the best method of application of P-fertilizers, many experimental results have pointed out that a certain latitude could be allowed, depending on the mechanism of absorption and release of P ions in the soil. In fact, the efficiency of P-fertilization does not change markedly with the time of distribution. The increase of the available P in the soil under a fertilized sward is rather superficial, as stated by Plat and Chavane [46], Roscoe and Brockmann [49] and many others. The recovery of P by the plants isvery seldom over 25 %of the applied fertilizer P, while the residue is concentrated in a thin layer of soil. Micaleffand Bonat [41] have observed that the splitting of P-fertilizer in several dressings may improve the available P level in the soil more than a single dressing of the same total amount in early spring. Gasparini[26] has reported that the application of P-fertilizers in autumn may be suitable in thetemperate Mediterranean area, as P uptake by plants continues during thewin- ter season. Reserves accumulate in the plant and better spring growth results. 152 Table 2. P1O5 per cent of dry matter in successive cuts of a permanent grassland under irrigation. Date Control N K P PK NPK 15/5 0.25 0.25 0.25 0.30 0.27 0.35 18/6 0.30 0.32 0.32 0.35 0.42 0.31 20/7 0.31 0.30 0.30 0.34 0.38 0.37 30/8 0.37 0.34 0.34 0.41 0.39 0.43 15110 0.30 0.30 0.30 0.36 0.36 0.36

Table3. Available P 0/00 in the soil of irrigated meadows treated with and without P-fertilizers. Treatments Available PO/.. Lombardy Montpellier C ontrol ...... 0.18 0.13 P...... 0.25 0.18

* Rateof POs applied in three years: Lombardy kg/ha 640 Montpellier kg/ha 600

The application of fertilizer Pat the beginning of the vegetative season (end of winter) is the usual method. There are no valid reasons - based on sound experimental evidence - to modify this practice. The yield of herbage would be increased not only at the spring cuts but also - thanks to absorption and slow release of fertilizer P by the soil system - at the later cuts [31]. However, it may be sound in certain circumstances to give some fertilizer P after the first and second cut, to increase the yield of ladino clover in irrigated grassland characterized by an explosive regrowth. In fact, there is a critical period for Puptake in late spring and at the beginning of summer [9, 31, 45]. P-application after the cuts did not prove efficient on the irrigated grass/lucerne leys [ 14, 41].

4. Generalfeaturesof K-fertilization

K-top-dressing should be extensively used on mixed swards under irrigation in the mediterranean region, not only to raise the exchangeable K-level in the soil but also to smooth the competition in space and time for K-uptake between different botanical components of the sward. It is well known that, in this area, irrigation greatly increases K-uptake from the soil by the herbage [ 13.25,33,41]. Such withdrawal may reduce the exchangeable K in the soil in few years, both when fertilizer K is not used and, to a lesser degree, when the balance of K-input and output is in deficit [41]. However, it has been recognised that K-fertilization of grassland is complicated by the competition for K-uptake between botanical componentsof the sward. The K-fertilization of a mixed sward under irrigation is one of the most important factors for the realisation of the maximum potential yield of the legume component [2,3.4, 5,27,28,36,43,51]. Lowe [38] has reported that K-fertilization of a mixed sward influences indirectly the N-nutrition of the grasses by increase of legume N. This aspect is particularly important in the humid cold areas, where the total output of a mixed sward is mainly governed by the N available to grass [ 15]. 153 Grasses are more efficient extractors of K from the soil than legumes, but the amount of K-fertilizer required by the legumes to reach the maximum potential yield is conversely higher than for the grasses. Moreover, when fertilizer K is supplied to a mixed sward, the total K-uptake by the legume component increases more than proportionately in comparison with the grass component. It follows, as pointed out by Drake et al. [23] and McNaught [40], that, if exchangeable K in the soil is low, the grasses are able to secure their requirements of K better than the legumes, in spite of the comparatively higher requirements of the latter. In the mediterranean area, where the optimum growth of legumes occurs in late spring and early summer, optimum herbage output is assisted by K-fertilizer applied to raise soil K during this period. Such application will assure the K-requirements of the different components of the sward throughout the season [7, 6, 12: 31, 33]. Experiments on irrigated permanent grassland in the Po Valley confirm this statement (Figure 4d). Applica- tion of fertilizer K in early spring increases the yield of the legumes during the summer season, thus increasing the total output of herbage by the sward. The size and method of application of the K-fertilizer are, to some extent, governed by the competition for K-ions either in space (soil) or in time (season) between grasses and legumes [3, 43, 47]. Drouineau [24], Jain [37], Malquori [39], Smith and Wallace [53] and others have found that the exchange capacity of the roots is higher for the legumes than for grasses. Therefore, the legumes show a preferential uptake for bivalent ions (e. g. Ca) and the grasses for monovalent ions (e.g. K). This may explain the experimental observation that in spring the grasses can take up as much as three times the original quantity of exchangeable K in the soil [23]. This withdrawal is bound to result in a fall in exchangeable K in late spring and summer, causing a nutritional gap for the legumes. In such a situation, even in a soil apparently well provided with total K, a top-dressing of K-fertilizer would be necessary to maintain a sufficiently high yield of the legumes [6, 7, 9, 10, 31, 33]. Early spring application of K causes a problem through the uptake by the grasses of K well above their physiological requirements (luxury consumption). However, K-manuring reduces the shortage of K for legume nutrition in late spring and summer, as appears from data on the seasonal pattern of K-contents of herbage dry matter under different manuring treatments (Table 4).

Table 4. K20 per cent dry matter in successive cuts of permanent grassland under irrigation Date Control N K P PK NPK 15/5 2.49 2.51 2.68 2.37 2.68 3.37 18/6 2.39 2.40 2.69 2.19 3.41 2.83 20/7 1.78 1.68 2.08 1.74 2.02 2.36 30/8 1.71 1.55 2.08 1.86 1.90 2.10 15/10 2.05 1.81 2.18 2.43 2.09 2.44

On the time of application of K-fertilizer, many authors have reported contrasting results, probably due to different environmental, botanical and soil conditions [4, 7, 9, 10, 22, 31, 48]. Nevertheless, even though the splitting of the K-fertilizers at the beginning of the vegetative season and after the cuts maynot increase forage output in comparison with one single dressing (in early spring), the splitting system probably reduces luxury consumption.

154 5. Some results on NPK-fertilization

In a general way, many results have shown that NPK-top-dressing of a mixed sward under irrigation is a very important factor to obtain the largest possible output of herbage. In the Po Valley, on permanent grassland receiving 8000 mc/ha of water (frequency of 15 days), several fertilizer treatments of increasing doses of PK, with and without N, were compared. The sward on which the trial was performed was well manured for the past 20 years and received as much as 50 ton/ha of compost ('% soil and 2/, FYM), 150 kg/ha P20, 150 kg/ha K 20 and 40-50 kg/ha N annually. The mean responses to the mineral fertilizers in the last fewyears, are plotted in figure 7a. From the data it is clearly seen that the yield of herbage is higher under frequent mowing than under infrequent mowing. The shape of the curves is always quadratic, reducing the relative increments with increasing doses of PK mineral fertilizers. The use of N increases the efficiency of the following doses of mineral PK, mainly under frequent mowing, while under infrequent mowing the N application seems to produce a reduction of yield with increasing levels of PK. The removal of K by the crop has been calculated at about 350-400 kg/ha/year, which considering the annual input of K in compost indicates only a very small recourse to soil reserves, when an annual input of 150 kg/ha K 20 is provided by mineral fertilizer. This dose seems to be - examining the reported data - sufficient on the given sward. Moreover, the exchangeable K-level in the soil of the plot treated with fertilizer K, in comparison with plots without K, did not show any substantial difference after three years. PK fertilization increases mainly the yield of the legume component of the sward (Figure 7 b). Nevertheless, when the rate of PK is enhanced, mineral N increases the yield of the legume component also by a small amount. The importance of mineral N-fertilization is more evident for the grasses, particularly under frequent mowing (Figure 7c). Figure 8 shows the relative increases of yield, both of total herbage or of the main botanical components, in the fertilized plots (compost + PK or NPK) in comparison with the test (compost only). The data show an interesting interaction between mineral fertilizers and the system of exploitation. Passing from infrequent mowing to frequent mowing, the mineral N increases consistently the total herbage yield, as has already been reported. PK-fertilization is particularly favourable to the output of the legume component of the sward, the increase of yield being more consistent with increasing frequency of mowing. The application of mineral N decreases generally the output of the legumes. Howev- er, the fall would be lessened with a moderate frequency of mowing. The favourable effect of mineral N on the grasses output in comparison with the un- treated plots ariseswith the frequency of mowing, so that the increase of grasses yield in the fertilized plot more than compensates for the fall in the yield of legumes when the more frequent mowing system is applied. These experimental data answer, under many aspects, to the general pattern previously described, explaining the influence of the single mineral fertilizers on the output of herbage in permanent grassland of the irrigated mediterranean area. A relevant difference, nevertheless, arises in case of the application of a frequent mowing system of exploitation (simulated grazing). At least in the humid mediterranean area, the potential grassland output under irrigation may be positively affected by generous use of mineral N after defoliation, in the spring and in the autumn seasons. 155 230 TOTAL MIXTURE without N with N 220 -

210 * .

$200 '

190 -I

180 *

170 A .4--

160 1

12240' 2 120 240 0 100 200 K20 100 200

140 LEGUMES without N with N

120 . 4cuts

120 . .8cuts

100 a 90

70 I - 60 0 120 240 P 0 120 240 0 100 200 K202 5 100 200

100 GRASSES without N with N 90

$80 ~70-

60 -

50 120 246 P205 120 240 0 100 200 K 2 0 100 200

Figure 7. Interaction between increasing rates of PK-fertilizers, with and without N-fertilizer, and frequencyof mowing of permanent grassland under irrigation in Po Valley.

156 unfrequent mowing +60 PIK N 2PK - N PK -- fsoII 1 2 440

+30

>- 20 f 10

*10 -20 -30 -40 6 0 -- P K 0 2normal N I Pmowing K tN 2P K - .- E -'T o ta l mW ,ur e .450 j ELegumes -'40 30: Grosses

420 Other species 0 o +10

- 10 -20 30 -40 frequent mowing +80 PK I PK N2 PK +70 460 I

+40

>- +30 +10I 0

-10 -20 *30 -40

Figure 8. Increases or decreases of the yields of total herbage and botanical components of fertilized plots in comparison with control plots. (PK = 240kg/ha PO,+ 200kg/ha K.0; NPK = asPK + 100kg/ha N ['1at theend ofwinter + after each of the first two cuts); NPK = as N1 PK + 25 kg/ha N after third and following cuts). 157 The point requires wider testing, especially at lower latitudes, to ascertain the optimal level of mineral N to be applied on grazed swards; those exploited for hay seem to need much less nitrogen, providing that the legumes contribute substantially to the yield.

Literature cited

I. Agerberg L. S.: Vasetnringsaumnenas inverkan pd skdrdeprodikternas kwalitet 1. Slittervallar - Sta. Jakdbr. Fdrsbk, Uppsala, p. 32 , 1959. 2. Brown J.M. and Rouse R.D.: Fertilizer effects on botanical and chemical composition of white clover. Agr. Jour., 45, 7, p.279- 2 82 (1953). 3. Brown B.A. and Mansell R. L: Clover in permanent grassland as influenced by fertilization. Bull. 309 Connecticut Agr. Exp. Sta., 35 (1956). 4. Brown B. A.: Potassium fertilization of ladino clover. Agr. Jour. 49,9, 477-480 (1957). 5. Chiasson T. C.: The effects of various increments of N, P and K on the yield and botanical composition of permanent pastures. Canad. Jour. P1.Sci. 51, 2, 235-247 (1960). 6. Chisci G. C.: La concimazione dei prati stabili irrigui. L'Inf. Agr., 2 (1957). 7. Chisei G.C and Haussmann G.: Primi risultati agronomici dell'impiego dei concimi complessi sulle colture foraggere. Concimi e Concimazioni 4-5 (1959). 8. Chisel G. C. and Ferrari A.: Variazioni di composizione floristica e di ritmo produttivo di un prato polifito irriguo per l'azione dominante di alcuni elementi nutritivi fondamentali in una formula di concimazione completa. Ann. Sper. Agr., n. s. XV, 3-4. p. 717-750 (1961). 9. Chisel G.C.: Influenza della concimazione frazionata sui prati poliennali nel corso della vegeta- zione. Ann. Fac. Agr. Univ. Cat. del S. Cuore, I1, 473-509 (a) (1962). 10. ChisciG.C.:Top-dressing by mineral fertilizers on irrigated mixed sward in Po Valley. Zemijiste i Biljca, Xl, 1-3, 564-571 (b) (1962). I1. Chisci G. C.: Mineral fertilization of permanent grassland under irrigation in the Mediterranean area. Proc. 9th Inter. Grass. Congr., 1145-1152 (1965). 12. Chisel G. C.: Prove di concimazione minerale della marcita Lombarda. IL Effetti degli elementi nutritivi fondamentali N, P. e K sulla produzione di foraggio verde, sostanza secca, proteina greggia, grassi greggi, fibra grezza, estrattivi inazotati, ceneri e unitiA foraggere. Ann. Fac. Agr. Univ. Calt. del S. Cuore, V, 1, 25-66 (1965). 13. Chisci G. C.: Prove di concimazione minerale della marcita lombarda. V. Effetti delle concimazioni con fertilizzanti a base di N, Pc K sulle asportazioni di alcuni elementi minerali ad opera dei raccolti. Ann. Fac. Agr. Univ. Calt. del S. Cuore, V, IL 267-309 (1965). 14. Chisel G. C.: Risultati di una prova di concimazione fosfopotassica al medicaio. L'Agricultura Italiana, Set.-Ott., 247-273 (1966). 15. Cooke G. W.: General principles governing the potassium manuring of Grassland. Potassium in relation to grassland production. Int. Potash Institute, 71-82 (1963). 16. Crescini G. and Francescheti G.: Per lincremento della praticoltura italiana. La grafica Moder- na, Torino, 1942. 17. Crocioni A.: Rapporti fra concimazion azotata e consociazione di due specie dei prati polifiti (Loliam italicum e Trifolitam repens). Ann. Sper. Agr. 9, 6, 1485-1501 (1955). 18. Crocioni A.: Progresso Agricolo 2. 5(1956). 19. Crocioni A.: Ann. Sper. Agr. n.s. 8, 5, 1575-1607 (1964). 20. Davies W.:The use and misuse of grassland. Potassium Symposium, 41-54 (1957). 21. Davies W. and Williams T.E.: Fertilizers and grassland. Fert. Soec.Grass. Res. Inst., 1958. 22. De Vries, P. and De Wit C. T.: The effect of potash fertilization on dry matter production of permanent pasture throughout the season. Neth. Jour. Agr. Sci. 6, 2, 124-130 (1958). 23. Drake M., Vengris J. and Colby W.: Cation-exchange capacity of plant roots, Soil Sci. 72, 2, 139-147 (1951). 24. Droaineau G.: La fumure potassique des herbages dans [a r6gion mtditerrandenne. Potassium Symposium, 223-239 (1957). 25. Fabris A.: Lentiti delle asportazioni potassiche in alcune foraggere irrigue dell'Italia meridio- nale. Potassium Symposium, 503-510 (1955). 26. Gasparini M.: II contributo della sperimentazione al problema della praticoltura artificiale della Montagna appenninica. Atti Acc. dei Georgofili, VII. 5,3-4 (1958). 27. Gervais P.: Productivity and chemical composition of ladino clover (Trifoliamrepens L.) grown alone and in mixture with grasses as influenced by height and frequency of cutting and fertilizer levels. Diss. Abstr. 19, 8 (1959). 28. Gerwing J. L. and Ahigren G. If.: The effect of different fertility levels on yield, persistence, and chemical composition of alfalfa. Agr. Jour. 50, 6, 291-294 (1958). 29. Grant S.A.: Temperatures and light as factors limiting the growth of hill-pasture species. Sym- posium on Hill-Land productivity, Aberdeen, 1968. 158 30. Green J.0. and Cowling D. W.: The nitrogen nutrition of grassland. Proc. 8th Inter. Grass. Congr., 126-129 (1960). 31. Haussmann G. et aL: Relazioni sulrattivitA della Stazione Sperimentale di Praticoltura di Lodi, 1948-1964 (annual series). 32. Haussmann G.: Foraggi e Concimi. Bull. dellrAgr. 26 (1956). 33. Haussmann G.: La fumure potassique dans les prairies irrigu6es de culture intensive. Potassium Symposium, 241-271 (1957). 34. Ho/tes W.: The intensive production of herbage for crop-drying. Ill. The effect of continued application of nitrogen with and without phosphate and potash on the yield of grassland herbage. Jour. Agr. Sci. 41, 64-69 (a) 1951. 35. Holmes W.: The intensive production of herbage for crop-drying IV. The effect of continued massive application of nitrogen with and without phosphate and potash on the yield of grassland herbage. Jour. Agr. Sci. 41, p. 70-79(b) (1951). 36. Hughes P. et al.: Etude d'une prairie de fauche irrigu~e en Crau. Evolution de ]a flore et variation du rendement sous rinfluence de diverses fumures mindrales. Ann. Ist. Nat. Rech. Agr., Sez. B, Ann. des Pl. 2, 4, 539-643 (1953). 37. Jain S. P.: Cation-exchange capacity of plant roots. Curr. Sci. 28, 71 (1959). 38. Lowe J.: Output and grass/clover ratio of swards as influenced by potassium in conjunction with other treatments. Potassium in relation to grassland production. Int. Potash. Inst., 137-143 (1963). 39. MalquoriA.:Scambioioniconeivegetai. Atti Acc. dei Georgofili, VI, 7(1960). 40. MeNaught K.J.: Potassium deficiency in pastures. 1. Potassium content in legumes and grasses. N.Z. Jour. Agr. Res. 1, 2,148-181(1958). 41. Micaleff P. and Bouat M.: Essai de fractionnement des fumures phosphatic et potassique sur prairie temporaire irrigue. Fourrag~s 28, 16-40 (1966). 42. Mitchell K.J. and Lunanus R.: Growth of pasture species under controlled environment. Ill. Growth at various levels of constant temperature with 8 and 16 hours of uniform light per day. N.Z. Jour. Agr. Res. 5. 135-14 (1962). 43. Mouat M.C. and Walker T. W.: Competition for nutrients between grasses and white clover. 2. Effect of root cation - exchange capacity and rate of emergence of associated species. Plant and Soil 11, 1,41-52 (1959). 44. Nelson W. W.: The effect of rate, ratio, and time of fertilizer application on the yield, composition and longevity of alfalfa - Diss. Abstr.' 16, 10 (1956). 45. Norman M.J.T.: Frequency of superphosphate dressings on permanent pasture. Agr. Canad. 62, 8,377-379 (1955). 46. Plat J. and Chavance A.: Essai de fumure azotde progressive de longue dur6e sur prairie perma- nente. Fourrag~s 28, 41-58. (1966). 47. Rebischung J.: The influence of potassium levels in soil on the growth of various pasture species. Potassium in relation to grassland production, Int. Potash Inst., 35-42 (1963). 48. ReithJ. W.S. et aL: Jour. Agr. Sci. 56. 17 (1961). 49. Roscoe B. and Brockmano J.S.: The availability of phosphate reserves in permanent grassland. Proc. 8th Inter. Grass. Congr., 249-251 (1960). 50. Rouse R.D.: Behaviour of potassium in soil. 3. The effect of mineral plant nutrients on the maintenance of clover in pasture on Black Belt soils. Alabama Agr. Exp. Sta. (1953/54) Rep. (Abstract) Bett. Crops 41, 4, p.42 (1957). 51. Sachs E.: Kleegrasgemische und DOngung. Bayer. Landw. Jahrb. 33, 3,319-333 (1956). 52. Sasso G.: Sulrepoca di distribuzione dci concimi minerali azotati al prato polifita. Ann. Sper. Agr. n.s. 11, 2, 505-515 (1957). 53. Smith R.L. and Wallace A.: Influence of nitrogen fertilization, cation concentration, and root cation-exchange capacity on calcium and potassium uptake by plants. Soil Sci. 82 (1956). 54. Stanford G. et al.: Effectiveness of recovery of initial and subsequent fertilizer application on oats and the succeeding meadow. Agr. Jour. 47, 1, 25-31 (1955). 55. Walker T. W. et al.: The use of fertilizers on herbage cut for conservation. Pt. 3. The effect of rates, methods of application and forms of fertilizer nitrogen on the yield of dry matter and nitrogen of grasses and clover in a rye-grass and white clover sward, cut at different stages of growth. Jour. Brit. Grass. Soc. 8, 4,281-299 (1953). 56. Walker T. W.: Nitrogen and herbage production. Proc. 7th intern. Grass. Congr., 13 (1956).

159 Methods of Diagnosing Nutrient Deficiencies in Citrus*

Dr. A. BAR AIKIVA, Division of Citriculture, The Volcani Institute of Agricultural Research, Bet Dagan (Israel)

1. Introduction

Citrds is one of the best examples for demonstrating the meaning and importance of plant nutrition from the practical and horticultural points of view. Almost all of the known 'essential' elements for plant growth have been found indispensable for satisfactory growth and functioning of citrus trees under field conditions, and they are supplied in various forms and rates of application in addition to what is found, naturally, in the soil. In consequence, and due to the world-wide economic importance of the citrus crop, the nutrition of citrus is the subject of intensive and large-scale investigations aimed at the evaluation of its mineral requirements and the establishment of a practical guide for determining its current nutritional needs. The status of the different methods used for this purpose, such as visible symptoms, soil and leaf analyses were reviewed recently by various authors [14, 18]. In this communication we present a critical examination of these methods, and some data from preliminary trials on the further development of leaf analysis as a diagnostic tool.

2. Visible symptoms

The most common and practical means of determining mineral deficiencies, especially those of micronutrients, is the use of specific and typical symptoms which usually appear in various forms of chlorosis in the leaves or, in the minority of cases, in distorted forms of fruits. With some elements, like Zn and Mg, the symptoms are typical, and their characteristics are easily recognized by most citriculturists. However, in some cases an exact and reliable definition of the cause of certain visible symptoms will present problems even to those people who possess comprehensive knowledge of the subject. The problems and uncertainties encountered in making such a diagnosis may be summarized as follows:

2.1 Overlapping symptomns

which occasionally occur in thecase of Fe, Mn and Zn deficiencies /1, 12], and in certain excesses [14].

* Contribution from the Volcani Institute of Agricultural Research, Bet Dagan, Israel. 1969 Series No. 1465 E 160 2.2 Vt, 'i/wal ...... Itx-, Ym )1 fmo ti/ toFr cut144o- et t ft ff5tors

as apparently occurIsIth Mo dcficiencs s,hich exhibits different types of visible symptoms under field coditions 24 and in greenhouse cultures 3, 25: and with Mn defi- ctenc , %hich exhibits I hr-ce different kinds of symptom' under greenhouse conditions I , but usually only one n the orchard. Mg deficiency symptoms of Eureka lemon lea'e n the greenhouse wcre also found to differ from those occurring in the orchards - .A'si,,s I aml2>.

2. 3 AIrod iicartont/s i mptoms,dhic to Iatiationin 'usl ate ri ipoition

K deficiency sv mpions appear different against a background ofvery high (a nUtition as compared to against lov Ca or Mg 20 .But supposing at least foi the 'ake of discussion that the isiblc s.ymptom-, see ca' the -,ole guide for diagnosing deficiencies

I - MgW11e iccrick iipromptonI i rurcika lemon ]caves fhom coTIIIIO l Orehi ra-

is si .6.T .,I uck, 1calor c rs m a r,,nho., r 161 then this diagio i' til be somewhat ate, ince he apearance of exlernal Inptots ino- dicate , thMal a stae of distorted etiabolic ptnceess's aleady exiss in the plant cel Al- ho ugh there are indication, that the presncn e of sIght deliciency s mptoms will not affect ield 14 .they may allct the resistance OCthecLtrIus tree undercindita n ostress duc to frost I/9 and pi...IN) also to CIe e iron mental factobs. 1hence, le obteetiv e of diagnosing the plants nitrtient requiremnt[ is; primnarily to preetl escalition It, tihe s;tage ola real deticiency, In searching for suich a method, chemists and platnt phm-siolo- gists have tr ied different aj..preaches., antlg w hich the mIost intportant aie soil tanalvsis and Woiar analysis which have been used complementarilv or alternati' ely

3. Yoi andas,

Since it was discovered that the soil, in addition to giving mechanical suppoit to the groing plant and providing il Water supply. servel als o as general store for vatiou, mteral nutrients, there has beetn a tendency to devlop he cotiception of storagt and "totzeg-balianc and to apply it to estimating uiltlrien requirements. According to t its concept ion. once the chenlical composi ion of a certain plant is established, t is neces'ar nly to detelmmine whether the so il possesses these eletnent, ii an available totm and in stich quantities as to ensure optinal growth of the lant Such chemical analsis for aaiahble soil nutrients is based on the assump tion that pllait toots will extract niu- triets fi rI the soil in a inatnee comparable to chemical soil extractiotis and that there exist, a relationhip between the extractable ions in the soil and their uptake by the plants. Ihe ever, this is not always the case. and even if it were so, lhe 'atues obtained in one orchard are hardly comparable ,with thocc obtained in different type, of soil, due to the relativ h ounding powers of xarmius soil colloid s, the effect of complementary ions. etc. Table I presents data to available soil P in a fertili/er expenriment with graiefr uit trees 2 A thlogh iWe phosphate and chicken manutre-treated plots show somewhat higher amounts of plic sphate t hall the no- Pplots, they are not able to demonstaes enif- icant differences as is possible with leafanalysi. N\IoeCr. these soil P values, accord- mg to values esta hIihed for bicarbonate-extracted soil 1, still fall it the category to Shelm a responuse shht d be expected to '-ferintiliat ion J1 Froni this point of view, the method of measring the soiIs potential to supply so-me ii tentas lhe ."-value 26 , wh ick apparentl is independent of soil type, appears to be mo reprmisg 7 (Ta- ble 2l. I lo neer,even the best chemical or phlsico-chetticaI method fot deletining the available nmurient will tit be able to forecast the nutrient-absorbintg capacity of a certain tree in aceingrterv because offtheaefectsnothetsol atid plant conditions such as aeration. tettiperature. wte r satturatioti, effct of cotipleniettlary is. , inlltaIgonisflt. etc. Due to the uvnantic nature of biological and chemical processes in the soil, the time las humt the satipling until the practical use of the possible diagnosis also COlnsittCs a problem.

4. Leaf anat'si

The great adva ntage or leaf anal sis over soil analysis lies in the fact that the forner mttethod shos te aticu ns t Ifnutrient which are ateady absorbed by the roots and dis- tinibuted among the arieus organs atnd tissues of the pant. There is evidence to show 162 Table 1. Effect of phosphorus and chicken manure treatments on the sodium bicarbonate-extracted soil phosphorus, leaf P content and yield of grapefruit trees (after three years of differential fertilization)

Treatment Soil P Leaf P Yield. kg/ha/year in ppm in ppm in kg/tree N, 80 N 2.22 0.064a* 148.6a1 N. 160 N 2.80 0.070- 128.3- N; 240 N 2.70 0.066- 224.8b NP, 160 N + 16P 3.09 0.087 b 358.6e NP, 100 N + 8m' chicken manure 3.35 0.093b 333.4e Significance-- N.S. C.V. (%) 10.6 8.3 21.5 * Mean values followed by different superscript letters are statistically different at the I %, or at the 5 % level. - N.S. = Non-significant. * Significant at 0.1 %.

Table 2. Effect of potassium fertilization on the soil AF values * and the leaf K composition of Shamouti orange leaves 7 (after four years of differential fertilization) (>) Treatment K in leaves A F value- % in dry matter K0 control ...... 0.57 - 3280 K,-- as KCI ...... 0.69 - 2600 Ka as KCI ...... 0.79 - 2010 K, as KSO ...... 0.68 - 2520 K, as KSO...... 1.06 - 2190 o * AF = free energychange in cal/mol C of the process of Ca/K ion exchange in thesoil; average of 3 layers 0-30, 30-60 and 60-90 cm. - 2500 to - 3000 indicates optimal amount of available K. - 2000 or less indicates excessive amount of available K. - 3500 to - 4000 indicates deficiency amount of available K. K, = 250 g K/tree/year; Ka = 750 g K/tree/year. that citrus trees under normal circumstances utilize, for the flush and blooming seasons, their previously built-up reserves [16] and apparently the leaves serve as the principal organ for the storage of these reserves, at least for certain elements [15]. The hundreds of publications which have appeared and continue to appear in the literature and the wide-scale commercial use of leaf analysis services as a fertilizer guide in many citrus- growing centers, such as the U. S. A., South Africa, Israel, etc., are perhaps the best evidence of the tremendous success of this method and its contribution to evaluating the fertilizer needs of citrus trees. Leaf analysis, in practice, refers to the well-known 'standard values' which have been developed with corresponding data on yield and fruit quality as a result of years of experimentation under field conditions. The standard values are tabulated in five ranges [13, 21] such as deficient, low, optimal, high and excess, and these valuesserve, along with a thorough knowledge of the orchard in question, as a basis for the fertilizer recommendations. However, in some cases, these standard values appear to be rather arbitrary. The tabulation of five ranges of nutrient status, which is perhaps most useful as an 'alarm system', is itself arbitrary, actually, the three-range tabulation [1I] - deficient, normal and excess - is closer to the prevailing situation in the trees [2]. The deficient and excess ranges, which are generally associated with visible symptoms, are considered to be the most well-defined ranges of the leaf standards curve. However, even within the deficient range, the deficiency itself- in causing a generally unbalanced condition in the plant cell

163 may complicate the picture by altering the levels of other elements too, towards either the deficiency side [1] or the excessive side (Table 3) [2]. Table 3. Effect of phosphorus deficiency and its application on yield and on some macronutrients in grapefruit leaves (2) Treatment kg/ha/year Yield kg/tree N P K Ca 80 N 258.3- * 2.62b 0.062- 0.57 4.55- 160 N 274.6a 3.00b 0.063- 0.51 4.43- 240 N 312.6- 2.60b 0.071&b 0.48 4.78 b 160 N + 16P 433.3c 1.94 0.076ab 0.39 5.54b 100 N + 8 m3 chicken 371.3 b 1.74a 0.080b 0.32 6.08b manure Significance-- N.S. C.V. (M) 13.7 17.6 9.9 30.7 11.8 I) Mean values followed by different superscript letters are statistically different at the I% or at the 5 % level. 2) N.S. = Non-significant * = Significant at 1% and 0.1%, respectively

In phosphorus-deficient grapefruits tree leaves, the low P-values are not only associated with abnormally high N-levels, but also induce a chain of interactions in increasing K- and decreasing Ca-concentrations. Apparently, this chain of interaction works in both directions, since P-application restores the situation rather quickly to normal. Figure 3 also demonstrates the interaction or antagonistic effects between the different ions which constitutes one of the main difficulties in the interpretation of leaf analysis data. As increasing applications of N had almost no influence on the N-level, but affected considerably the P- and K-levels in the corresponding tree leaves even within the range which is regarded as normal nutrient status. Another problem which the interpretation of leaf analysis has to face is the extent capacity of the plants to adapt themselves to various nutrient levels, which apparently fall within the normal range, without that this change of the level should affect yield, growth or plant performance. Consequently, the assump-

N I N2 N3 120

DecN 0 z 0 0 l-K W. 100 0

I~90

W 80

Figure 3. Effect of gradually increasing levels of nitrogen fertilization in the relative N, P- and K-contents of Shamouti orange leaves (unfertilized control = 100). 164 tion that for every point in the standard curve there exists also a point in the plant performance, will not hold. If this is so, then also the positive relation between the leaf content and production, which forms actually the physiological background of the leaf analysis method and which should enable its use, in forecasting plant response for a certain nutrient application, would hardly exist.

5. The biochemical approach

It is now rather generally recognized that further development of the leaf analysis method lies in a better understanding of the function of the various elements in the plant cell [20]. Actually, the mode of action and function of various elements in plants are studied by producing the specific deficiencies artificially in solution cultures [17]. It is assumed that also the visible symptoms of the deficiency are in some way an expression of the dis- turbed metabolic processes in plant cells. The disturbances can cause either the accumulation of some metabolic products or the failure to produce others. Similarly, the dis- turbed metabolic patterns may explain the visual similarity of symptoms, while differences may be used for differentiating between them. This approach has been used for diagnosing apparent mixed Fe and Mn deficiencies; it has been found that free xylose accumulation, low chlorophyll a/b ratio and high peroxidase activity are specific for Mn deficiency [ 1,3] (Figure 4). Low peroxidase activity was found to be associated with iron deficiency even prior to the appearance of visible symptoms, indicating that it might be used not only for diagnosing external symptoms but also for a general appraisal of the iron nutrition status. Indeed, a preliminary experiment using peroxidase activity for this purpose has been successful [4]. Similarly, we have tested several other enzyme systems as indicators for the determi-

Penloe Peroxido. Chlorophyl /Tb

500

UMn 400 - -cu [E] -F,

300- -Zn

US.E. 200

0- Figure 4. Pentose accumulation, peroxidase activity and chlorophyll a/b ratio in leaves of Eureka lemon grown in micronutrient deficient cultures (percent of values obtained from nondeficient culture). 165 nation of mineral nutrient requirements, such as nitrate reductase for N [9] and Mo [22], ascorbic a cid oxidase for Cu [6], and carbonic anhydrase for Zn [5]. The enzyme systems, due to their protein nature, are very sensitive, and apparently they are among the first to suffer from mineral deficiency; but they are also very quick to re- cover when the eficient element is supplied. In table 4 it is shown that the citrus leaf fragments deficient or low in Mo, reacted to Mo supply with an increase in enzyme activity, whereas the control and high-Mo-levels did not. Thus, the increase, or actually the rate of increase in enzyme activity as a result of Mo introduction into these tissues, can demonstrate the assimilation capacity of the tested leaves and corresponding trees forthe element in question. In other words, this characteristic of the enzyme maybe used as a tool for measuring the degree of deficiency orthe potential of response of the tested plant to the nutrient supp!y.

Table 4. Effect of molybdenum supply in the incubation solution on the NaRl)-activity of Mo-deficient and control citrus leaf fragments [22].

Treatment NaR-activity** Mo in Mo, ppm Rate or response nutrient solution indrymaterial* After Mo-supply to Mo-supply*** /'g/I Initial 00 0.020 44 536 12.18 00.1 0.050 144 578 4.01 00.2 0.080 256 440 1.72 00.4 0.080 560 792 1.26 30 (control) 0.140 792 780 1.01

') NaR = Nitrate reductase * Determined by chemical analysis. ** m iM NO 2 formed per 120 minutes per I g fresh material. after Mo-supply .. NaR initial

The introduction of this approach promises solutions for several problems of the conventional leaf analysis. Firstly it does not measure the nutrient itself butrather some metabolic system and it therefore distinguishes between the active, and apparently, inactive part of the element. The lack of activity of certain parts of the element may be of metabolic origin, as occurs with nitrogen in the case of P-deficiency [8]; or, as occours after foliar application o f a nutrient, a part of it is absorbed physically on the leaf surface and cannot be removed by washingand rinsing procedures [23]. Secondly, in measuring the apparent potential response of the tested plant to nutrient supply, the way is opened for the use of these tests in forecasting plant response to fertilizer application. Since the proposed test measures response, or, in other words, the difference in the activity of certain enzyme systems before and after the addition of the tested element in each case, it is likely that the proposed test would not require standard values, asdoes the conventional leaf analysis.

166 Literature cited

I. Bar Akiva A.: Visible symptoms and chemical analysis vs. biochemical indicators as a means of diagnosing iron and manganese deficiencies in citrus plants. In: Plant Analysis and Fertilizer Problems. Vol. 4, 9-24 (1964). Editors: C. Bould, P. Prevot and J. R. Magness. Amer. Soc.Hort. Sci. Michigan 2. Bar Akin, A., Hiller V. and Part J.: Effect of phosphorus and chicken manure application on yield, fruit quality and leaf composition of grapefruit trees. Proc. Amer. Soc. hort. Sci 93, 145-152 (1968). 3. BarAkivaA. and Lavon Ruth: Visible symptoms and some metabolic patterns in micronutrient- deficient Eureka lemon leaves. Israel . agric. Res. 17. 7-16 (1967). 4. Bar Akina A. and Lavon Ruth: Peroxidase activity as an indicator of the iron requirement of citrus trees. Israel J. agric. Res. 18 (4), 144-153 (1968). 5. Bar Akina A. and Lavan Ruth: Carbonic anhydrase activity as an indicator of zinc deficiency in citrus leaves. J.hort. Science. (1969) 44 (4) 359-362. 6. Bar Akiva A.. Lawn Ruth and Sagiv J.: Ascorbic acid oxidase activity as a measure of the copper nutrition requirement of citrus trees. Agrochimica. 14:49-54 (1970). 7. Bar Akiva A., Porath A. and Feigenbaum S.: Leaf and soil analysis studies for the evaluation of potassium requirement of citrus trees. International Potassium Symposium, Athens (1962) Edi- tors: International Potash Institute, Berne/Switzerland. 8. Bar Akina A., Shaked A. and Sagiv J.: The use ofnitrate reductase activity for the appraisal of nitrogen status and productivity of grapefruit orchard trees. Hort Sci. 2 (2), 51-53 (1967). 9. Bar Akiva A. and Sternbaum J.: Possible use of the nitrate reductase activity as a measure on the nitrogen requirement of citrus trees. PI. Cell Physiol. 6, 575-577 (1965). 10. Bingham F. T.: Phosphorus. In: Diagnostic criteria for Plants and Soils. Div. of Agric. Sciences, Univ. of California, Riverside, pp. 324-261 (1966). I1. Chapman H.D.: Citrus leaf analysis. Calif. Agric. 3 (11), 10, 12, 14 (1949). 12. Chapman H. D.: Nutrient deficiencies of citrus. Citrus leaves 25 (3), 1-7 (1954). 13. Chapman H. D.:Leafand soil analysisincitrusorchards. Manual25 Div. ofAgric. Sciences, Uni- versity of California Riverside (1960). 14. Chapman H.D.: The status of present criteria for the diagnosis of nutrient conditions in citrus. In: Plant Analysis and Fertilizer Problems. Vol. 111, 75-106. Ed. W. Reuther. Amer. Inst. of Bio- logical Sciences, Washington. D.C. (1961). 15. Chapman H.D. and Kelley W.P.: The mineral nutrition of citrus. In: TheCitrus Industry.Vol. I, Chap. 7. University of California Press (1948). 16. Chapman H.D., Wallihan E.F., Rayner D.S. and HarrietannJ.: Citrus trees in water culture. Calif. Agric. 12 (3), 3-4 (1958). 17. Hewitt E.J.: Sand and water culture methods used in the studyof plant nutrition. Tech. Com- mun. Commonw. Bur. Plantn Crops. No.22 (Revised 2nd ed.) (1966). 18. Jones W. W. and Smith P.F.: Nutrient deficiencies in citrus. In: Hunger Signs in Crops. Ed. H. B. Sprague, 359-414. 3rd ed. David McKay Co., New York (1964). 19. Lawless W. W.: Effect of freeze damage on citrus trees and fruit in relation to grove practices. Proc. Fla St.hort. Soc. 54, 67-74 (1947). 20. Reuther W.: Limitations of plant analysis as a research and diagnostic tool. In: Plant Analysis and Fertilizer Problems. p. 453. American Institute of Biological Science, Washington, 6, D.C. (1961). 21. Reuther W., Jones W. IV., Embleton T. Br. and Labanauskas C. K.: Leaf analysis as a guide for orange nutrition. Bett. Crops 46 (3). 44-49 (1962). 22. Shaked A. and Bar-Aki a A.: Nitrate reductase activity as an indication of molybdenum level and requirement of citrus plants. Phytochemistry 6, 347-350 (1967). 23. Smith P.F.: Effect of Zineb sprays on zinc concentration of orange leaves. Hort Sci. 1, 101-102 (1966). 24. Stewart L and Leonard C. D.: Molybdenum deficiency in Florida citrus. Nature 170, 714-715 (1952). 25. Vanselow A. P. and Datta N. P. Molybdenum deficiency of the citrus plant. Soil Sci. 67, 363-375 (1949). 26. WoodruTC. H.: The energy of replacement ofcalcium by potassium in soils. Proc. Soil Sci. Soc. Am. 19, 167-169 (1958).

167 Discussion, Session No. 3

Dr. D. Shinshi (Doar Na Negev/lsrael): 1) Mr. Lachover - is there any effect of soil moisture on the appearance of Fe chlorosis? The impression is that chlorosis is more severe following irrigation or waterlog- ging. 2) Could a comment be given on the effect of methods of irrigation on plant diseases? It is expected that leaf diseases would predominate under sprinkling and soil-borne infection - in flood or furrow irrigation.

Mr. D. Lachover (Bet Dagan/Israel): The phenomenon mentioned by Mr. Shinmshi can be due to the following causes: 1) Lack of air after irrigation. 2) High rates of bicarbonates formed by a prolonged contact of lime with water (CaCO + H2O + CO2 4 Ca(HCO) 2). As suggested bicarbonates supplied to roots, decreased iron translocation to leaves. 3) Calcium as bicarbonate in soil solution can decrease the absorption of iron by plants.

Dr. G. W. Cooke (Harpenden/United Kingdom): 1) Commented that the constant C in the Mitscherlich equation varies with crops and with local conditions and with the amounts of other nutrients. There was nothing of a law about the Mitscherlich equation: it was a convenient way of dealing with data. 2) Asked whether Dr.Shimshi had looked at his response curves to see if the standard errors showed a significant departure from a linear relationship. A linear relationship was easy to use, and should be used unless the experiment showed, significantly, that the curve was non-linear. 3) Commented that irrigation affects soil-borne diseases. For example potato scab would be controlled by careful watering. The damage done by migratory nematodes varied with moisture content of soil.

Dr. Y.Noy (Emek Hefer/israel): Nitrate pollution of ground water has been found in the south of Israel where pumped irrigation water may contain up to 80 ppm of nitrate, in extreme cases. The use of this kind of water may throw off results of irrigation and fertilizer experiments. In peat soils in the Huleh the decomposition of peat contributes much nitrate to the leaching water. Nitrates could not be found however in the Galilea sea to which the 168 nitrates should drain. They must have been assimilated or denitrified on the way. In mineral soils, however, the pollution by nitrates of the ground water should be of concern.

Dr. Th. Walsh (Dublin/Ireland): The subject of chlorosis caused by iron deficiency referred to by Mr. Vaadia is a most complicated one. He especially mentioned factors external to the plant involved in the inducement of this deficiency. Our experiences that mobility of iron within the plant is especially important with a number of factors apparently influencing such mobility. On one occasion I was able to cure an iron chlorosis with an injection of potassium. On our peat soils we get a chlorosis in cereals and grasses where again both external and internal factors seem to be involved.

Prof. Dr. H. Heimann (Kirjat Bialik/Israel): Under saline conditions at least there are some limitations to the validity of the results of foliar diagnosis. I wish to exemplify that on citrus trees. A tree may most severely suffer from sodium intrusion into its tissues. But due to barriers on the way from the root to the top the sodium will not at all arrive at the leaves, except the case saline water is applied by overhead sprinkling. The tree may be fatally affected by the sodium entered by the roots without its actual presence in the leaves. If feasible a root analysis (radical diagnosis) could complement foliar diagnosis. Under the conditions of irrigated agriculture one has to replace the narrow concept of mineral fertilization by the broader one of mineral environment. The amount of minerals introduced by water into the soil-plant system may surpass those put into it with the mineral fertilizers by a factor of 10. Therefore, in the evaluation of fertilizer experiments under the conditions of irrigated farming, it seems compulsory to inte- grate the whole input of mineral elements.

Prof. G. Chisci (Lodi/Italy): I agree widely with Prof. Arnon on the large variation of ecological environmental conditions between humid to temperate, sub-arid mediterranean zone. The use of tropical perennial grasses in permanent grassland that seems possible in the African and Oriental zone of the mediterranean basin, becomes precarious as far as Sicily latitude, due to the lack of winter hardiness of such species. We have found that a possibility to get a very large potential yield of dry matter from gramineous plants, using consistent amount of nitrogen mineral fertilizers, on the place of legumes nitrogen accumulation, would be reached by using a tropical gramineous plant, i.e. Sudangrass during the summer, and Italian Raygrass during the winter. But this rotation through the year asks for large application of chemical means, which must be evaluated carefully by an economical point of view in comparison with the cheaper way of permanent grassland dry matter production and utilization for animal feeding. It appears to me that this model would explain very well the finding of Cunningham and many others of the variation of the A/C-ratio in grasses with increasing amounts of nutrients and particularly of nitrogen. Things seem quite different with legumes, Bear and Wallace having found that there is a consistent tendency to a constant value 169 of the anion/cation ratio in spite of a large variation of nutrient in the soil solution. I would like to ask Prof. Vaadia if there is some explanation of such different findings on the base of the model he has presented here.

Dr. D. Shinshi (Doar Na Negev/lsrael): I meant to add my observations to those which disprove the constancy of the coefficient C in Mitscherlich function. The moisture stress-yield functions were linear by any statistical criterion. The fertilizer-yield functions were significantly curvilinear. When breeding crop varieties for desirable geometry of leaves, which would lead to more efficient photosynthesis, we should be on the lookout for anatomic characteristics which may control the rate of photosynthesis. A point to this case is stomatal behaviour. There is a controversy to what extent stomatal aperture controls photosynthesis rate. We have accidentally found that two wheat varieties have different patterns of stomatal behaviour under conditions that are conducive to stomatal opening (ample moisture and high light intensity). At the stage of heading, when presumably photosynthesis is at its peak, a tall variety opens the stomata until about 9-10 a.m., and then gradually closes the stomata; a dwarf variety keeps the stomata wide open until sunset. It may be incidental, but the dwarf variety yields about 40Y more than the tall variety even when there is no lodging.

Dr. G. W. Cooke (Harpenden/United Kingdom): In South-east England of an average of 600 mm of rain, often 340 mm falls in winter and cannot be used. 260 mm falls in summer when in each month transpiration is greater than rainfall and irrigation increases yields in 9 years out of 10.

170 Co-ordination Lecture for Session No. 3

G. DROUINEAU. Inspecleur Gnral I. N. R.A., Paris (France). Member of the Scientific Board of the International Potash Institute

First of all I would emphasize the great interest of the two first papers; they are at the heart of our subject of this morning session and as it has been said before their complementary is striking. Dr. Shirnshi has choiced to give us a single example but a wonderful one: The strong interaction between irrigation and nitrogen fertilization on corn. We have much appreciated the refinements on collection of data and in interpretation of this work. It looks like a model of fertilization experiments with irrigation. After responses considerations Dr. Shimshi gives a physiological approach of the problem of interrelations of nitrogen fertilization with water economy in the plant. Men of industry would be pleased to know the increase of productivity of one pound of nitrogen fertilizers, and may be it is the same thing for water buyers and sellers. Dr.Blanchet has studied the problem of interaction between cations, mainly potassium, and water availability with field experiments, laboratory work on diffusion of potassium, considerations on mass flow, pot experiments and examination of root system. Dr. Blanchet gives us an enlarged view of what we need for the approach of this problem. His physiological approach, with transpiration measurements, gives us interesting data on change in water economy with potassium fertilization. With the communication of Prof. Chisci we reach a new problem of interaction between irrigation and fertilization in grassland. The change of equilibrium and competition beetween families during the year. The ecological behaviour of the main botanical components became a dominant phenomenon and must be associated to the effect of water, fertilizers and system of exploitation for the study of interaction. The relative depression of grasses during summer in hot conditions of mediterranean regions seems to be more important. Complicated studies of the effect of fertilizers, mainly N and K and of the method of dressing are the consequence of this fact. Dr. Sagasta pointed out the differences between newly irrigated areas and the old ones, and the impact of irrigation on the development of diseases. But the ecological conditions are proeminent and the experience in a given country is not valuable in another one. It would be a matter of discussion in a plant pathology colloquium in Mediterranean area and precisely it is subject of the next congress of the InternationalPotash Institute in the South of France in September 1970. The examples given by Dr.Sagasta tell us the risks and different ways of fighting, mainly the importance of rotation, and plant residues.

171 It seems that it remains a lot of work to be donebetween agronomists, plant physiologists and plant pathologists, mainly in the field of soil fungi, if vascular and root problems are of increasing importance in irrigated areas as Dr. Sagasta clearly has shown US. Dr. Lachover has shown with an example the necessity of control of minor elements deficiencies and the experience with commercial iron compounds on peanuts. Diagnosis of the conditions of nutrition of a crop by plant analysis is the goal of all agronomists, and as you know there is specialized symposium on this matter and international group working on foliar diagnosis. Till now, I was thinking that scientists working on citrus were the most fortunate and since Chapmans work there was no problem about the nitrogen level need in citrus leaves. We have learned from Dr.BarAkiva that for the citrus, too, a better approach, more 'physiological' is better. From a practical point of view difficulties may arise with enzyme activity determinations but with nitrate reductase, it is possible to predict the response to nitrogen.

172 t 4 h Working Session: Economics and Planningof FertilizerUse

Coordinator of the Session : Prof. H. Laudelout, Universit6 Catholi- que de Louvain, Institut des Sciences de la Terre, Laboratoire de Physico-Chimie Biologique, Heverlee-Louvain, Belgium; Member of the Scientific Board of the International Potash Institute.

173 The Economics of Introducing Fertilizer*

Prof. Dr. H. RUTHENBERG, Director of the Institut fCr Ausldndische Landwirtschaft, University of Hohenheim, Stuttgart/Hohenheim (Federal Republic of Germany)

1. The economic properties of mineralfertilizer

It is generally agreed today that mineral fertilizers are one of the most effective means for raising agricultural production. In wide areas of the tropics and subtropics, however, mineral fertilizer is still an innovation which has to be introduced. The technical problems are relatively easy to solve. Virtually everywhere we have established fertilizer rec- ipes. In addition I would argue, that there are very few irrational aspects as to fertilizer use, even among illiterate people. The chief problem of spreading the use of fertilizer are economic and organisational ones. Both again are interrelated with the paramount problem of proper husbandry. Mineral fertilizers are having definite socio-economic properties. First of all we may say, that they are yield increasing innovations and not labor saving ones, which fits into the general situation of underemployment in low income countries. In addition, I would list several other properties of mineral fertilizers: - Mineral fertilizer is a complement not a substitute for other inputs. The input-output ratio of additional labour, irrigation investments, new varieties, tractors, depends, more- often than not, on adequate fertilizer application, and vice versa. Looking at it from the standpoint of tactics of farm development, we may say that the application of mineral fertilizer puts the farmers on an expansion path of their farming system, where they usually cannot escape, taking one step after the other towards higher intensity. - There is no large unit as with tractors, grade cattle, etc. Mineral fertilizer may be purchased in small units. Risks are comparatively low. Large and small holdings can apply fertilizer with the same degree of efficiency, which is usually not the case with farm equipment. - The time lag between investment and return is very short; frequently not more than a few months or even weeks. - Most mineral fertilizers are easy to transport and to store. With adequate storage facilities, they may be stored almost indefinitely. They are clean and usually not poisonous. - The techniques of fertilizer application are not difficult to learn, in particular where adequate mixture of nutrients are available. * This paper mainly relies on research in East Africa. See: Ruthenberg, H.. ed.: Smallholder Farm- ing and Smallholder Development in Tansania. Afrika-Studien, Nr.24, tfo-[nstitut Mflnchen 1968; dito: African Agricultural Production Development Policy in Kenya, 1952-1965. Afrika-Studien No. 10, lfo-Institut Munchen 1966. 175 - Manures usually require additional inputs: Carts, field roads, and traction power for transports, ploughs and traction power to work the manure into the soil, etc. Mineral fertilizers are not depending on additional investments, except on those which improve plant development. - Because of the ease in application timing is no major farm management problem as with organic manure. - An important disadvantage of mineral fertilizer is, that it has to be paid for in cash. However the provision of finance is comparatively easy whereever a major cash crop is marketed. Cooperative or licenced traders may organize delivery on a credit basis. The dues can be deducted from crop sales. Because of these properties, mineral fertilizers, jointly with new crops, new varieties and irrigation are the most important'icebreakers'of the transition from extensive to intensive agriculture. Worthwhile fertilizer schemes, however, have to be economic, in terms of the farmer and in terms of the national economy. Let us first look at the farm economic situation and keep in mind that we deal with the initial stage of introducing fertilizer only.

2. The determinants for the introduction of mineral fertilizer at the farm level

2.1 The relevance of input-output ratios

The propensity to innovate, to invest additional capital and labour and to carry the additional risk obviously depends on a great number of cultural and social factors. There seems to be, however, a common basis, verified by substantial field work, that farmers all over the world are - on the long run - rational in pursueing their numerous objectives. I would secondly argue, that additional cash income, is a major objective of a rapidly increasing number of smallholders. The introduction of mineral fertilizer consequently depends largely on favorable input-output ratios. It is important in this connection that profitability in terms of an industrialized agriculture, is not sufficient from the standpoint of traditional cultivators. They have learnt from experience and their forefathers that it might be dangerous to innovate. They do not overlook the consequences of each move, which leads away from traditional farming pattern. They therefore require rather favorable input-output ratios. Certain threshold values, apparently, have to be surpassed before smallholders in greater numbers react*. In this connection a rule of thumb is useful: The value of the additional output at the farm level has to be at least two times or three times as much as the value of the purchased fertilizer for fertilizer programmes to catch on, i.e. we need a return on investment of about 200 to 300 Y. Fertilizer schemes with lower returns at the farm level, are rarely finding an active response. The threshold value is, of course, not the same under all circumstances. A ratio of 1:2 seems to be the lower floor. The poorer thefarmers are, the lower the degree of so far in- volvement with market economy, the lower the standards of information, the more favorable the ratio has to be. While Taiwanese farmers are likely to jump ahead at a ratio of I : 2, we may need 1 : 3 oreven 1:4 in Central Africa, to get going on a slow rate of expansion.

- See also: Kemmler G.: D~ingemittelprogramm der FAO fur Entwicklungslnder, in: Landwirt im Ausland, Heft 4, 1968. 176 2.2 The intportance offavorable price ratios

Input-output ratios in fertilizer use, depend on price relations and the physical production function. Let us turn to price relations first. Again and again it is argued, that smallholders in low income countries are target workers, that they are not interested in improving their economic conditions or -in more precise economic terms- that we have to reckon with backward sloping supply curves in case prices improve or innovations are introduced. This argument is not valid. Thei e is overwhelming evidence from almost everywhere in the tropics and subtropics, that the more fertilizer is used the more favorable the price relations are. The reactions to changes in prices are perhaps slower and less pronounced than in highly industrialized countries but they are completely normal. Price ratios are obviously important determinants for smallholders propensity to innovate. One of the major reasons why mineral fertilizers have not yet been introduced in wide parts of the world or why consumption remains at a low level is the low and unsecure price for the produce.

2.3 Husbandry and the production function

The other crucial factor influencing the input-output ratio is the physical production function, which depends not only on soil and climate, but also on husbandry and husbandry again is influenced by the economic, social, cultural and even political setting. First of all we have to consider that practical farming, even with optimum husbandry, cannot attain the yield level of field experiments under similar conditions. The physical production function of practical farming in comparison to field experiments may be about 25 % lower with commercial farmers and perhaps about 50 % with cultivators in remote areas, where husbandry is a problem. Traditional cultivators, particularly in fallow systems, are highly knowledgeable as to soils, microclimate and plants. They usually know much better than experts where to plant and what to plant. They are however poor in maintenance of fields and plants and this may be desastrous for the economic return of mineral fertilizer. We may well assume, that traditional farming was built on experience and intelligence and that traditional farming systems - in economic terms - used to be optimum solutions under traditional circumstances, but circumstances changed. Traditional farming pattern do not fit to modern inputs like fertilizers. Late planting, late weeding, obsolete plant densities, lack of pruning are some of the most important husbandry problems. It is not easy to explain, why most of the smallholders stick to obsolete techniques and why husbandry, even at their own standards, is generally poor. There is probably some relevance to the hypothesis, that adaptation to modern techniques takes time, that we face a 'cultural lag', because of very high rates of change. Even more important seem to me simple bot- tlenecks in the labour economy. Cash cropping brings unaccustomed peaks in labour demand. Regular working days of 8 or even 10 hours per day are customary in Asia but not in Africa south of the Sahara, where 5-6 hours even in the busy season are considered to exhaust labor capacity. An even more important drawback is the low efficiency per hour of work.

12 177 2.4 Risks and uncertainty

Finally risks and uncertainty have to be taken into consideration. The average input- output ratio is of little relevance to a cultivator, who has not the means to pay cash for fertilizer in case of a crop failure. Input-output ratios from plots with controlled irrigation are of little relevance for a cultivator with uncontrolled irrigation. This is particularly important for wet rice production. In addition cultivators face uncertain markets and frequently hesitate because of short run price fluctuations to introduce intensive techniques.

2.5 Interactionsbetween price relations,husbandry and risks

We arrive at the heart of the problem if we look at the interactions between several factors. In wide areas where technically and economically fertilizer application would be worthwhile the situation looks as follows: Because of poor prices husbandry is poor and because of poor husbandry the quality and thus the price of the produce is low. Low prices and poor husbandry result again in rather low input-output ratios, which, includ. ing the risks of production and the uncertainty of the market, do not surpass the threshold value of the farming community. In other words: in order to introduce mineral fertilizer, we have to look for the better situations, as to price relations at the farm-level, as to the potential physical production function and as to husbandry. Better husbandry again, i. e. the reduction of the discrepancy between the realized and potential production function, so the experience goes, depends on the following conditions: - there either has to be a very strong incentive in the form of a high cash return per hout of work, - or there has to be a maximum, long-term land shortage, which leaves no choice but to take care of plants, soils and animals, - or there has to be production under close supervision.

3. Outline of a strategyfor introducing mineralfertilizer

While the farmer is looking at the input-output ratio in terms of fertilizer input and additional value of production, the planners of fertilizer schemes are asked to maximize the ratio between public inputs and national objectives, in terms of marketed produce, value added or additional tax revenues. In order to attain the best possible input-output ratio in national terms it is advisable not to work according to models of production derived from field experiments of model holdings, but from the experience which has been established by' trial and error'. Iwould summarize the experience as follows:

3.1 Choice of location andfarmingsystem

It is detrimental to development, and thus to the fight against poverty, by moving in poor, remote, or the most traditional areas first. In introducing mineral fertilizer, we have to ask for the location and for the farming system, where the input-output ratios in 178 terms of the cultivator and the national objectives are the most favorable ones. This frequently implies that we have to start development efforts in areas with more evolved farming systems, which already show a somewhat higher income level. The appendix of this paper contains a summary outline of the most important manuring and fertilizing practices in the main types of farming. Shifting systems are difficult to improve by fertilizers for numerous reasons which are inherently tied to essential features of the system. Similar problems are encountered in short term fallow systems, except where leading cash crops are properly husbanded. In permanent farming systems and particularly in irrigation farming with controlled irrigation and in farming systems with tree crops, we have technically good starting points for intensive fertilizer application, provided markets and prices are adequate.

3.2 Choice of crops

I n the initial phase of agricultural development it is usually not advisable to recommend fertilizers for all crops, but to concentrate on the most profitable one. In this respect the following principles are useful: - Cash crops come before subsistence crops, for the simple reasons, that you need cash to pay for fertilizer and that the governments, in order to support fertilizer schemes, rely on additional revenues levied directly or indirectly on additional marketed produce. Propagating fertilizers for subsistence crops belongs into an advanced stage of agricultural development. - Food crops come before feed crops, because innovations in plant production are more readily accepted than those in animal production. There seems to be a typical sequence in some parts of the world which runs as follows: The first step is the introduction of a new cash crop. The second involves the purchasing of additional inputs like fertilizer. In a third stage, savings out of cash cropping are invested in modern animal activities and increased fodder production. - New crops come before traditional crops, because new crops are usually better husbanded than traditional ones. Usually it is easier to introduce better husbandry with something new, than with something one is for generations accustomed to. It is obvious that the phrase 'fertilizers should first go to crops with the highest input- output ratio' implies that we have to look for the market. Estimates about deficits in calories and protein are no sufficient criteria for fertilizer programs. The planner or development worker may have many objectives, but to the producer - who is expected to risk his money - nothing but effective demand is relevant. Consequently we have to concentrate on those crops with favorable markets and on produce with a high elasticity of demand.

3.3 Choice of cultivators

There is much evidence available that in order to introduce innovations, it is in the initial phase not advisable to approach the community as such, to try to get peasant masses moving, or to work on co-operative lines, except in settlements under close supervision. One of the most conspicuous properties of smallholder farming in low income countries is a wide variation in performance. On-farm managerial ability is one of the major fac- 179 tors differentiating progressive producers from others. Even under almost identical conditions of production, performance is far from being uniform. Smallholders differ widely as to their physical efforts, their drive and their knowledge, and this differientiation is probably more pronounced than in industrialized countries. As a rule of thumb we may say, that one-third of the cultivators receive two-thirds and more of the total income. Empirical evidence shows that in order to maximize the return of fertilizer schemes in terms of national economic objectives we have to approach this third.

3.4 Choice of technique

The most important aspect as to thechoiceof techniques is to put mineral fertilizer into a bundle of innovations and to sell the whole lot as one unit. Thus the introduction of a new crop might involve the introduction of row cultivation, weeders, new plant distances, fertilizers, terracing, etc. In wet rice production, the bundling of new varieties, fertilizers, improved nursery-techniques, water control and insecticides is usually required. There are several advantages connected with the' bundle approach'. First of all we have the complementary effect of the various inputs, resulting in much more favorable input-output ratios for the total, than it would be possible with each innovation taken for itself. Secondly it is possible to combine conspicuous innovations, like new seeds, nitrogen or trace elements with less conspicuous ones which are essential for the long run success as for instance terracing or proper plant distances. The nature of the bundle has, of course, to he adapted to the circumstances. In settlements under close supervision, we may jump ad hc into a modern farm technology. In extension work we will have to limit the bundle to those items, which are likely to catch on, and which can be dealt with by the limited staff.

3.5 Choice of the procedure

Mineral fertilizer.may be introduced [1] by obligatory means, [2] with the help of certain 'tie-systems' and [3] on the basis of persistent persuasion of cultivators who are entirely free to innovate as they want to. There is no general answer as to which procedure is the best one. The choice depends on the conditions of production.

3.5.1 Obligatory application of fertilizer, may have the advantage of an immediatejump from traditional farming to optimum inputs of modern means of production. Compul- sion of this kind, however, is difficult to support for any length of time. More often than not it leads to a waste of labor and capital because cultivators, who have been compelled, tend to drop the practice a]ltogether -even in cases where it is highly profitable to ferti- lize - as soon as the pressure is reduced. Obligatory application is thus only advisable in settlements under long term close supervision, where fertilizer is highly profitable, where it is applied on a large scale basis by the scheme management and where costs are automatically deducted, as it is the case for instance with cotton in the Gezira, Sudan. Under no circumstances a procedure is advisable, where growers have to buy fertilizer. There are cases, where cultivators receive fertilizer without asking for it and the costs are deducted from their sales,which has to take place via a co-operative, and this in spite 180 of the fact, that fertilizer application at local levels of husbandry is hardly economic. It is obvious, that this peasantry will consider mineral fertilizer as an instrument of pression and exploitation and that the way for proper innovations is barred for a long time. Soon- er or later procedures of this nature will also lead to a black market for mineral fertilizer.

3.5.2 While obligatory application of mineral fertilizer is advisable under very specific conditions only, the use of 'tie systems' in the initial stage of agricultural development has brought striking success. In Kenya for example, smallholders may be allowed to grow tea. They have to ask for a license and granting of the license is' tied'to certain cultivation techniques, one of them being the application of fertilizer. The delivery of improved seeds, for instance hybrid maize, may be tied to the purchase of mineral fertilizer on a credit basis or - in the case of tobacco - the granting of loans for the payment of seasonal labourers may be tied to proper husbanding of the crop, part of it is the application of prescribed amounts of fertilizers. The principle of tying popular items with necessary supplements has wide application. In cases where nitrogen is asked for, because of its conspicuous effect, but where other nutrients are necessary supplements on the long run, it might be worthwhile to sell a ready mixture and to grant credits only to those who ask for it.

3.5.3 Persistent persuasion, with no conditions attached, the classical approach of extension work, is also the most economic approach in more advanced areas of developing countries with partly commercialized smallholdings. It should not be overlooked, however, that in those areas, where fertilizers are newly introduced, we face the danger of poor results, because of inadequate husbandry. It may take a long time before persistent persuasion and the example of some better farmers is changing husbandry practices in such a way as to make fertilizer application fully profitable. Wherever feasible, I would prefer therefore, to tie an innovation like fertilizer, together with some instruments of direct or indirect pressure, which induce improved husbandry.

3.6 Choice of organisation

It is no use propagating mineral fertilizers unless sufficient supplies are available in time and unless the produce can be marketed at prices sufficiently favorable to make fertilizer application worthwhile. In addition we need credit facilities, because without them it takes usually a very long time before smallholders are willing to risk their own savings which are usually available, but which - in the initial stage of development - are rarely invested into purchased means of production. Credit schemes, however, are likely to end up in enormous arrears unless we organize some kind of one-channel marketing. The usual and proven procedure runs as follows: The scheme is concentrating on one major cash crop. Fertilizer is delivered to those who ask for it and who fullfill certain standards of husbandry. The produce can only be marketed through licensed traders or co-operatives, who also organize fertilizer supply. The costs of the fertilizer including interests are deducted from the receipts. In order to tie the smallholders to the supplier of credits, we have to have either crops like cotton or coffee, which cannot be sold elsewhere, or we have to offer some advantages, as for instance a lower fertilizer price at the licensed trader.

181 Summary

Because of its socio-economic properties, mineral fertilizers, jointly with other innovations are one of the most important 'icebreakers' of agricultural development. The introduction and increased application of mineral fertilizers depends primarily on the input-output ratio in terms of the cultivator and thus on the price ratios and the production functions. As a rule of thumb we may say, that the value of the additional output at the farm level has to be at least two to three times as much as the value of the purchased fertilizer for fertilizer programmes to catch on. In planning fertilizer schemes it is - as a rule - advisable - to choose the farming system with the most favorable input-output ratio which is usually not the one with the lowest incomes; - to prefer cash crops before subsistence crops, food crops before feed crops and new crops before traditional crops; - not to approach rural masses, but selectively the more active cultivators; - to introduce fertilizers together with a bundle of other innovations; - to tie fertilizer credits on proper husbandry and - to organize fertilizer schemes with credit schemes and 'one channel marketing' or licensed trade.

Appendix: Some notes about the fertilizer economy in various types of arable farming

1. Shifting cultivation systems (long term fallow systems)

Long term fallows are the main instrument of shifting cultivator to regenerate soil fertility with no costs and no labour involved. In addition we find here and there the following practices of manuring: - Systematic use of household ashes, etc. - Systematic change of the hut site. The old hut site may be considered as a heavily fertilized plot. - Green manuring with fallow vegetation and weeds. Ridge- and mound cultivation as well as the' pit systems'usually involve some kind of green manuring. - Use of ashes (Chiteme system in East- and Central Africa). Branches and pieces of wood are transported to the cleared plot, where burning takes place. The ashes serve as fertilizer. - The application of mineral fertilizer is of little importance in shifting systems. An important exception are commercial tobacco growers.

2. Semi-permanent cultivation systems (short term fallow systems)

Short-term grass and bush fallow which prevail in savannas and tropical highlands, are used by more stationary cultivators to regenerate soil fertility, with no costs and no labour involved. In addition we find a more evolved fertilizer economy. - Although farming is stationary, we still find, as in shifting systems, a systematic change of hut sites. The rebuilding moves are generally short, often not more than a few yards. Moving of hute sites leads to a kind of human folding. - The direct application of boma kraal manure is rare. We usually find a systematic moving of boma sites. With increasing land shortage boma sites change more frequently. In somecases (Senegal, Ethiopia) proper folding systems have developed. - Cash cropping with cotton and groundnuts, which are important activities in the Afri- can savannas, is increasingly practised with mineral fertilizer.

182 3. Dry-farming systems in the subtropics

Traditional dry farming in the subtropics is usually practised without manuring. The available manure is either used as fuel, or applied to irrigated gardens. The yield potential of dry farming has significantly been improved in recent time, mainly due to new varieties, tractor ploughing and mineral fertilizer. The introduction of mineral fertilizer in dry farming systems is a rather straightforward proposition, compared with most other farming systems. It mainly depends on proper ploughing and timing of planting and thus on the use of tractors. Already Marcus Cato wrote: 'What means to cultivate the field properly? Good ploughing! What is the second? Good ploughing! What is the third? Fertilizer application!' (p. 93)*.

4. Permanent cultivation systems on rainfed land in the tropics

In the tropics the shortening of the period of fallow and thechange to permanent cultivation alltogether, would usually lead to a drastic decline of yields. Most permanent farming systems on rainfed land, therefore rely on soil mining or have arrived at the stagna- tion of yields at a very low level. Intensive types of manuring and moderately high yield levels are attained only in those areas with a long tradition of extreme land shortage and here manuring is very labour intensive. This is typical for the chinese intensive land use systems, which relies on heavy manuring. Justus von Liebig, in comparing nineteenth- century German agriculture with Chinese farming, viewed the former as a procedure of a child compared to that of a mature and experienced man". In intensive traditional permanent cropping systems the following practices to reduce the export and waste of nutrients and organic matter may be found: - Production of compost, including household ashes, crop residues, hut site soil, etc. - Production of stable manure, mainly pig manure. - Cultivation of green manure crops. - Use of night soil. In addition we find traditional practices of importing nutrients and organic matter. - Grazing on communal land combined with stabling of the animals leads to the import of nutrients into the holding. - The search for fuel has stripped extensive bush areas near intensively cropped land. The ashes serve as fertilizers, either directly or as a component of compost. - Purchase of various fertilizing agents: oil cakes, shrimp powder (Singapor), night soil, etc. It is obvious that the introduction of mineral fertilizers in these farming systems, which are preconditioned for further intensification, would lead to a rapid increase in demand, provided the price relations are sufficiently attractive. One of the main advantages of mineral fertilizer under these conditions is the low demand on additional labour.

* Thietscher P.: Des Marcus Cato Belehrungen iber die Landwirtschaft. Berlin, Duncker& Humblo, Berlin (1963). ** Liebig .v.: Chemische Briefe, Leipzig-Heidelberg, C. F. Winter'sche Verlagshandlung(1878). He writes: <(Diese Mitteilungen ... (about chinese methods of manuring, H.R.) diirften gendgen, um dem deutschen Landwirt die Oberzeugung beizubringen, dass seine Praxis gegen die des ltesten ackerbautreibenden Volkes in der Welt sich verhalt wie die eines Kindes zu der eines gereiften und erfahrenen Mannes... (p.4 53). 183 5. Systems with irrigation farming

High yields, multiple cropping, and consequently high rates of export of nutrients and increased leaching put particularly high demands for the fertilizer economy of irrigation systems. Traditionally, however, intensive manuring is rare in irrigation farming, except in East Asia. This is partly due to certain advantages of wet rice, the most important irrigated crop. A slower rate of decomposition of organic matter and a greater availability of several nutrients in water logged soils may favor the maintenance of fertility in wet rice fields. Irrigation farming lends itself to intensive manuring and high rates of fertilizer application, particularly in systems with controlled irrigation. This is clearly shown by the speed of the evolution of the fertilizer economy in Japan, which showed the following phases*: Phase I: Up to 1890 night soil and composts were the main fertilizers. They were supplemented by grasses from forest land, etc. Phase 2: With increasing urbanisation and improved transport facilities night soils and soybean and fish cakes gained in importance while green manuring with forest grasses faded away. Green manure crops were, however, increasingly cultivated. This phase lasted up to 1930. Phase 3: The third phase is characterized by the introduction of ammonium sulphate and superphosphate. In a few years mineral fertilizer became the most important purchased input item. In addition an increase in compost production, partly induced by higher plant production due to mineral fertilizer, could be observed. Phase 4: Since 1950 the fertilizer economy of wet rice producers in Japan became a more diversified one. In addition to nitrogen and phosphate more potash and trace elements are applied. Night soil lost in relative importance. Green manuring was partly replaced by multiple cropping. Phase 5: The most recent move is the introduction of intensive animal activities in the farm economy, largely based on purchased concentrates. The import of nutrients via concentrates and additional stable manure is of increasing importance for the fertilizer economy.

We may take from the agricultural development of Japan and - in more recent time of Taiwan - certain rules of thumb which are important for introducing fertilizer and increasing its application. 1) The more intensive the farming system and the traditional manuring systems, the easier and the more effective is the introduction of mineral fertilizer. 2) Input-output ratios of fertilizers depend on complementary inputs. Improved varieties and improved water control may be more important for increasing for fertilizer, than information about fertilizer as such. 3) One of the great attractions of mineral fertilizer in these farming systems is the low demand on labour for its application. 4) It is much more interesting to increase the application per hectare on the better land with regular water supplies, than to try to introduce mineral fertilizer on land marginal as to water control.

* Ogura T.: Agricultural development in modern Japan. Tokyo Fuji Publishing Co. Ltd. (1966). 184 Problems of Fertilizer Requirement Prediction in Intensive Agriculture

Prof. J. HAGIN, Technion - Israel Institute of Technology, Haifa (Israel)

The title is rather comprehensive, but it should he stated at the outset that most of the material is based on experience gained in Israel under its special conditions. The problem of fertilizer requirement prediction was raised in Israel in the process of intensification of agriculture. Large areas of extensive crop land were brought under irrigation, and high yields were obtained as a result. Assuming that higher yields use up more mineral nutrients, the amounts of fertilizers were increased, but in reality no reliable information was available as to the actual requirements in nutritive elements. Ferti- lizer trials were concentrated at a few experimental farms, which were unable to furnish information permitting reliable prediction of fertilizer requirements for individual farmer's fields, differing in management history and scattered over a variety of soil types. Nothing like the systems of field trials undertaken by extension service officers in some West European countries was available. In these circumstances the shortest path to rationalized fertilizer application seemed to be through adaptation or development of soil- testing methods. Fertilizer recommendations for irrigated field crops were high and ranged from 100 to of var- 200 kg P,20/ha, with about the same amounts of N. Adaptation and calibration ious soil-testing methods were accompanied by numerous experiments ou commercial fields. In most cases these field experiments showed that the response to fertilizers was nil or very low, and this finding was associated with very high levels of extractable or ' available' nutrients found, prior to fertilization, in the soils from the experimental sites. Some results obtained by Hagin and Schmueli [4J for tomatoes in the Jordan Valley are given as examples (Table I). (The amounts of fertilizer used were up to 320 kg N/ha.)

Table 1. Yield of tomatoes in field experiments with N-, P-, K-fertilizers and 'available' nitrogen in soil samples from same plots (Hagin and Schmueli [4])

Field No. Average yields in t/ha in plots NO,. ppm accumulated in soil incubation without N-addition with N-addition samples during

1 54.8 53.9 142 2 42.0 46.2' 98 3 52.3 55.0 114 4 50.0 50.0 164 5 41.0 43.9 120 6 40.8 41.8 130

185 Similarly, table 2 presents results drawn from a report [5 on field trials with phosphorus fertilization carried out in conjunction with soil tests. In this case up to 96 kg P/ha were used. Both tables demonstrate the low response to fertilization in field experiments, and show the high level of 'available' nutrients in the experimental soils. Accor- ding to Hanway and Dumenil [7J, about 100 ppm of NO3 obtained upon incubation of soil samples represents a high level of available nitrogen in the soil. Binglham [1, 2] cites 2.5 ppm of P in water extract as a high level of available P. The'available' nitrogen and phosphorus data in tables I and 2 may thus be evaluated as high, or even very high.

Table 2. Yield of vetch (green matter, oven dried) in field experiments and 'available' phosphorus in soil samples from same plots (Hagin and Hillinger [51)

Field No. Average yields in t/ha in plots P ppm without P-addition with P-addition in water extract 96 kg P/ha

1 4.2 4.2 8.1 2 7.4 8.2 8.7 3 5.5 5.6 5.7 4 4.4 5.5 7.6 5 5.0 5.4 2.1 6 5.4 5.4 8.0 7 4.8 5.6 4.9

The above results obviously indicate the high residual effect of fertilizers used freely during the last two decades or so. It is worthwhile noting that both nitrogen and phosphorus are preserved in available forms. Examples of yield responses to potassium fertilization are not included here, but the situation is similar to that for nitrogen and phosphorus, namely none in most cases. For further illustration of the relationship between fertilizer application and yield response, some results from a long-term study ('Permanent-plots experiment' [10]) are quoted. The plots received, from the year 1960 onwards, the same relative fertilizer amounts at several fertilizer levels for each nutrient, namely five each for nitrogen and phosphorus and three for potassium. The experimental layout permitted calculation ol the direct effects of each nutrient and of their interactions. Data cover a period of six years, with eight crops. No yield response to potassium was observed over the reported period; although potassium fertilization resulted in a slight increase in the amount of potassium extractable in a CaCI 2 solution [11]. An average of 4.0 ppm K was found in soil samples from the 0-20 cm soil layer taken in April 1966, five years after the start of the experiment, in plots that did not receive any potassium; as against 7.5 ppm in plots fertilized with approximately 1.5 t/ha. This slight increase, which definitely does not reflect the total amount applied, shows either strong K-fixation or inadequacy of the extraction method. In any case, yield results indicate high available potassium reserves in the soil. Response to nitrogen fertilization is noticeable from the third crop on (Table 3), indicating that the residual effect of nitrogen as demonstrated in one-year trials and illustrated in Table I above may be of rather short-term character. The response to phosphate fertilization of some crops in the permanent-plots experiment is shown in table 4. The figures quoted represent a small fraction of the findings and do not reflect possible interactions with nitrogen and potassium fertilization. The response is already noticeable in the third crop, indicating that the residual effect of phos- 186 Table 3. Nitrogen fertilization effect on some crops in Permanent Plots Experiment [10]. Yields in t/ha N-fertilizer Chickpeas Sugarbeets Vetch Wheat level grain yield of sugar green matter grain June 1962 June 1963 March 1964 June 1966 N, 6.1 11.6 22.4 0.78 N, 5.8 15.3 25.4 1.35 N, 5.4 17.3 24.9 1.76 N, 5.4 18.3 25.8 1.75 N 4 5.0 17.9 26.0 1.73 S.E. 0.2 0.5 0.8 0.04 phorus as shown in table 2 is also rather short-term. On the other hand, no response is seen in the sixth-crop for cotton, but is significant in later crops, as seen in the results for wheat. Sodium-bicarbonate extraction of phosphates (Table 4) [9] differentiates well between the low and high phosphate levels, but there is no correlation with yield results at the five levels of P-application. As regards the cotton crop, the correlation fails completely. Apparently, phosphate extraction as used in these experiments is not sensitive enough for fertilizer requirement determination. Table 4. Phosphorus fertilization effect on some crops and available P found in soil samples from same plots from Permanent Plots Experiment [1O]. Yields in t/ha P-fertilizer Chickpeas Sugarbeets Vetch Cotton Wheat level grain Yield of sugar green matter raw cotton grain June 1962 June 1963 March 1964 October 1964 June 1966

P0 5.6 13.6 21.4 4.7 1.47 P1 5.4 16.7 24.6 4.9 1.72 P2 5.6 16.6 26.0 5.0 1.70 P, 5.5 16.3 25.8 4.7 1.89 P4 5.4 17.2 26.8 5.0 1.89 S.E. 0.2 0.8 1.0 0.1 0.04 P-fertilizer P-extract in NaHCO, ppm/soil level July 1963 March 1964 April 1966 PO 4.7 3.5 4.1 P1 5.6 5.8 6.4 P. 7.6 9.3 6.1 P, 8.3 13.7 10.2 P, 11.8 16.6 18.4 S.E. 0.5 0.5 1.2

Further illustration of the relationship between soil testing values and crop response to fertilizers is provided by the results of another relatively long-term experiment [6] which consisted in application of different levels of superphosphate to three consecutive crops on large field plots, on two sites. After the third crop the large plots were divided into four subplots, on which different levels at a constant ratio were applied to subsequent crops. Results shown in table 5 are for the fifth crop, i.e. the second after subdivision. I t is seen that up to the fifth crop, with no phosphate fertilizer added, the level of extractable phosphorus was still relatively high. Bingham [2] cites values of about I I ppm P as high for corn, whereas in the present case the lowest figure is 12.0 ppm. Yield response to fertilization was only slight and statistically non-significant. The extractable phosphate clearly reflects the accumulated phosphate in the first, build-up, stage of the experiment, and shows very high residual available phosphate levels. Apparently, soil testing differentiates well between low - and high - phosphated soils, but is of little use in predicting exact fertilizer requirements under the prevailing conditions. 187 Table 5. Yield response to phosphorus fertilization in long-term field experiment and corresponding values of'available' phosphorus (Hagin et al. [6j)

Previous P-application P-addition to 5th crop NaHCOa so]. - P prior Yield of corn (5th to main plots P kg/ha to fertilization, ppm P crop) green matter oven-dried t/ha None 0 12.5 2.5 13 12.0 2.9 26 14.5 2.9 52 15.0 2.8 Low 0 15.8 2.7 13 15.3 3.2 26 14.9 3.5 52 19.8 3.0 Medium 0 28.3 3.1 13 27.2 2.8 26 29.5 3.2 52 28.5 3.1 High 0 43.0 3.2 13 49.0 3.0 26 47.8 3.3 52 48.0 3.3 S. E. 0.2

The experimental data and practical experience gained in recent years indicate a general trend toward high levels of available phosphorus, potassium and nitrogen in soil. Fur- ther these high levels are, apparently, rather slowly depleted in respect of potassium and somewhat faster in respect of phosphorus. Nitrogen, believed to be a mobile nutrient with a low residual value in more humid climates, shows considerable residual values under local conditions. In seeking a suitable procedure for predicting fertilizer requirements, there is no doubt that the first steps, consisting in adoption and correlation of known testing methods, was important and certainly an advance over the earlier stages, where fertilizer recommendations were based on trials confined to a small number of experimental farms often with different soil and crop-rotation characteristics compared with the commercial fields. To- day, the value of soil testing in determining fertilizer requirements under intensive crop rotation is questioned, and certainly yields, for an intensive irrigated system, less information than had been hoped for. Still, it may point out exceptional cases. Cooke [3] states, for conditions in the U. K.:' The profit made by using soil analysis to decide manuring was compared with the profit made from a uniform dressing to all fields using the same total amount of P- or K-fertilizer. Using any of the methods was more profitable than uniform manuring and would have helped farmers as a whole to save money by decreasing dressings on soils that were high in soluble phosphorus'. This statement probably applies to local conditions as well. Continued soil testing is also advocated mainly asa means forcost reduction in intensive agriculture. In fact, arguments against soil testing in highly-intensive irrigated agriculture are also largely economic. The main point is that, in irrigated agriculture, fertilizer is a minor item in the total production cost, and although soil testing may influence the quantity of fertilizer used, it would make little difference economically. However, several points may be raised to show that soil testing still has its place even in an intensive system. From the economic viewpoint, it is well known that a slight saving in expenses, or a slight increase in yield, may have a considerable effect on marginal profit. From the agronomical viewpoint, there are certain aspects in which soil testing is important. Agri- culture is sometimes accused of being a source of water pollution through the nitrates 188 and phosphates in water drained from intensively cultivated fields. This polluting may be controlled, or even prevented, by propercontrol of nitrogen and phosphorus fertilization. Moreover, a proper balance between available mineral nutrients is often important in timing the flowering or ripening of fruits, in controlling the development of a special part of the plant or in influencing the quality or storability of products. Furthermore, intensive agriculture is becoming more refined and industrialized, which calls for control at all stages of production. Undoubtedly the control of inorganic plant nutrition is a very important aspect of the whole plant production. In any case, the present state of soil testing may best be summed up in the following quo- tation from Nye [8]:'The future of soil testing will consist in an endless series of fertilizer trials designed for correlation with an ever increasing number of hit or miss extractions.'... Apparently, the known methods of soil testing, both the 'classical' and the newer ones allowing for capacity, intensity and other parameters, are rather crude measuring tools in a developed, intensive and high-yield agricultural system. It may be concluded that soil testing for mineral nutrition of plants has reached the flat part of the growth and development curve and further progress on a steeper path calls for an entirely new approach.

Summary

In an extensive agricultural system, the amounts of fertilizers used are as a rule not very high. Con- ventional soil testing provides sufficiently reliable information on fertilization practices. With the intensification of agriculture, increasing amounts of fertilizers are used; they are applied more frequently, and there is a build-up of available nutrients in the soil. In such a system, although fertilizer additions are still necessary for long-range yield maintenance, no immediate response can often be measured, and conventional soil testing fails to yield information on fertilizer requirements. To illustrate this argument, data from field and greenhouse experiments in Israel are presented, showing the trend of response to fertilizer application in intensive agriculture and the relationship between soil testing and the prediction of fertilizer requirements and yield responses. Possible approaches to the determination of fertilizer requirements in intensive agriculture are ana- lyzed. It is shown that, although soil testing may differentiate well between soils high and low in available nutrients, the methods used do not provide an accurate criterion for fertilizer requirements in an intensive agriculture.

Literature cited

I. Bingham F. T.: Soil test for phosphate. Calif. Agr. 3 (8), II, 14(1949). 2. Bingiant F. T.: Chemical soil tests for available phosphorus. Soil Sci. 94, 87-95 (1962). 3. Cooke G. W.: The control of soil fertility. Crosby Lockwood and Son Ltd., London (1967). 4. Hagin J. and Schmueli E.: Determination of available nutrients and fertilizer requirements of winter tomatoes in the Jordan Valley. Ktavim 10.43-52 (1960). 5. Hagit J. and Hillinger J.: The availability of fertilizer phosphorus in the soils of the main agricultural areas in Israel. Research Report to the Batsheva de Rotschild Foundation for Advance- ment of Science (1963). 6. Hagin J. et al.: Basic and applied research into the efficiency of phosphate fertilization. Report to USDA Project No.A 10-SWC-22 (1968). 7. Hanway J. and Dumenil L.: Predicting nitrogen fertilizer needs of Iowa soils. Ill. Use of nitrate production together with other information as a basis for making nitrogen fertilizer recommendation for corn in Iowa soils. Soil Sci. Soc. Amer. Proc./9, 77-80 (1955). 8. Nye P. H.: Processes in root environment. Journal of Soil Sci. 19, 205-215 (1968). 9. Olsen S. R. et a.: Estimation of available phosphorus in soils by extraction with sodium bicar- bornate. U.S. Dep. Agr. Circular 939 (1954). 10. The Permanent Plots Team: The permanent plots experiment. The Volcani Institute of Agricul- tural Research (mimeographed report) (1968). II. Woodruff C.M. and McIntosh J.L.: Testing for soil potassium. Trans. 7th Int. Congr. Soil Sci. Soc. 3, 80-85 (1960). 189 New Trends in the Use of Fertilizers, New Products and New Techniques of Application

L. AUDIDIER, Ing. gin. hon. de l'Agric., Membre de I'Acad. d'Agric., Paris (France)

1. Introduction

If one has to follow the advice of Mr. Mansholt, Vice-President of the Economic Euro- pean Community, half of the European farmers and doubtless the major part in other countries should disappear; half of the surfaces presently under cultivation should be converted into forests, parks or sport grounds. In this respect, prospects for fertilizers would be limited, but personnally, I believe the contrary, even, if one day, the Mansholt plan comes into being. The surfaces which will be devoted to agriculture shall be, more than ever, intensively cultivated calling upon more and more fertilizers. But those fertilizers shall no the necessarily the same as the ones of the past generation nor even those which are presently the most used and the techniques of application will evolve there as well. The object of this report is to find out what are the present trends of the evolution now in progress as regards fertilizer usage. To begin with, it must be emphasized that to days' civilisation is characterised by the quest for efficiency. To attain this goal, it needs more particularly, to reduce the non productive expenses such as transport costs and bagging as well as working hours and labour expenses.

2. Incidence of labour problems

Agriculture as a whole isentirely dominated by the main fact i. e. that labour is becoming more and more costly and more and more scarce and accepts no more certain painful jobs. Therefore powdered fertilizers belong to the past generation. Fertilizers are no more sold on the market in 2-cwt. bags. They are too heavy to handle whereas liquid fertilizers are expanding; for it is easier to work a pump than haul a bag. All the fertilizers tomorrow will be granulated or in liquid form. Nevertheless to reduce labour expenses, mixed and complete fertilizers, although generally more expensive per unit of plant food'have supplanted straights; taking the total of fertilizers consumed, they amount to more than 60 % in U. S. A., 78 % in U. K. and 55% in France.

Compoundsorrnixed fertilizers will develop in the countries where they are still in little use. 190 3. Advantages of chemically pure products

The traditionalists draw the attention to the fact that the impurities, the fillers, which occur in many fertilizers, had the advantage to supply micronutrients, but this argument is worthless, because it is easier to supply under a small volume, that is to say with lower transport and spreading costs, the amounts of nutrients required for each type of soil and crop. I will add that the supply of micronutrients through the fillers and impurities of fertilizers conduces to some risks with intensive manuring which leads to the use of big quantities of fertilizer materials supplying excessive amounts of micronutrients through the impurities they contain. One knows that for many of these micronutrients, boron for instance, its toxicity levels are veryclose to those of its efficiency. In intensive cultivation, useless salts supplied by fertilizers may accumulate in the soil, they are not always leached out sufficiently early enough by the drainage waters thus preventing their detrimental effect on plants. This is all the more noticeable when the soils are not sufficiently pervious and the rainfall too low at certain seasons. Salinity increases, the phenomenon, unluckily, has too often been observed in intensive glasshouse crops in Belgium, Holland as well as in intensive vegetable and flower crops in the dry southern countries. These phenomena of soil toxicity, for instance, is a question which, up to now, has been insufficiently investigated and fortunately the agronomists of all countries are beginning to give their attention to this matter; it explains why, in spite of very high prices, certain types of fertilizers without chlorine are more and more demanded. Potassium sulphate, potassium nitrate are expanding at the expense of Muriate for several intensive crops and for certain soils having a high salinity level. It is undeniable that smaller yields occur insidiously long before the toxic symptoms appear just as a rheumatic pain reduces the work of a labourer a long time before he is affected with paralysis. Among the fertilizers which do not bring in any detrimental element and which are all taken up by the plants, one must quote urea, potassium nitrate, ammonium phosphate, the metaphosphates and triple super which supply a very limited amount of useless anions.

The fertilizers of to morrow shall be pure products and because of their high concentration will add to their advantage of not holding anything detrimental.

4. Good quality crops are matter of necessity

Farmers have been rightly charged of not applying sufficiently their thoughts not only to markets which could be offered to them but also to special qualities which facilitate the transport and preservation of their products. The customers' taste must be more and more taken into account. To day, the farmer who does not want to surrender must bear in mind these problems of quality and marketing. He will have to grow wheat sufficiently rich in gluten and will have to be on the look out not only for suitable varieties butalso as to late applications of certain forms of nitrogenous fertilizers and calling upon certain methods of applying fertilizers unharmful to crops (for instance, urea applied by plane or by helicopter). Potato growers should, more than they have done up to now, give their attention to the 191 water content of their potatoes and take more into account the quality of these tubers, there again it is not only a matter of variety which has to be dealt with, but also a question of manuring: potassium sulphate or potassium nitrate replacing the muriate for instance in order to obtain good quality potatoes bearing less water. Chlorides, as one knows, enhances water fixation in the living structures of animals and plants. As for vine, whether a matter of growing good quality table grapes fit for transport or fine wines which are more and more appreciated by the customers, there too, potassium sulphate or potassium nitrate shall be recommended. The ammoniacals and the urea forms, because of their extending effect, may run the risk of supplying an excess of nitrogen detrimental to their good maturity or promote grape-rot which would arise if they are applied late at a time when the plant needs practically no more nitrogen. As regards tobacco, for which Muriate and certain forms of ammoniacals have been ruled out; in certain countries like the U. S. A., the only form of potash recommended for its growth is potassium nitrate which compared to the other potash fertilizers has the advantage to increase the burning quality of the leaf. The ammonium or ammonium nitrate fertilizers have a well-deserved success because their cost of production is cheaper than that of nitrate fertilizers, but we must not forget that plants absorb also a fraction of the NH 4-N supplied to the soil before this one is entirely nitrified. On the other hand it has been shown that the ammonium ion was not much favourable to the synthesis of higher proteins. NH 4 is involved also in the saturation of anions at the expense of other cations needed by the plants like K, Mg or Ca. For obtention of products of quality, nitrate fertilizers ought to retain more often the attention of farmers and agronomists, though being of a higher cost per unit. To conclude, we state thatfertilizers to come will be selected, more than in the past, in relation to their specific action on the quality of crops. About the new nitrogenous fertilizers, we must report the recent manufacture of slow release N-fertilizers in concurrence with urea formaldehyde: so is produced crotenylidene diurea (CDU) in Germany and isobutylidene diurea in Japan. These new fertilizers are of interest because of their sustained action, but the rate of application must not exceed a certain amount, not always well determined, if crops are not to suffer of toxicity from dressings of these new chemical fertilizers.

6. Techniques of application

6.1 Normal application

For thereasons mentioned above, hand broadcasting ought to disappear completely in a near future, so that fertilizers will exist only under granular form or liquids.

6.1.1 Distributors on soil with large working output

Granular fertilizers are applied today with various types of distributors, whose differences are in the width of spread and regularity of distribution. Granular fertilizers may be applied with usual distributors (endless floor, chain, plates..., width of spread limited to 3 or 4 m) and centrifugal distributors, spreading up to 10-12 m and even 18 m, but whose work though more rapid is often less regular. 192 We do not hesitate to say that to morrow only will be used the distributors of the simplest type and the cheapest to buy and upkeep which can work rapidly on large areas. It will be alleged that the simplest distributors do not spread regularly. I answer that it has not much importance because the fertilizers before being absorbed by the plants must be dissolved in the soil solutions and if the first year of application these solutions are not uniform, quickly they become such when fertilizers are applied regularly each year as it is thecase with all good farmers. For phosphate and potash regular dressings lead to the build-up of the well known reserves which can be used appropriately by the plants. For the application of nitrogenous fertilizers, it is also easy to remedy to the imperfection of distributors by judicious crossing of the dressings; the homogeneity of the granulation has moreover a favourable effect on the regularity of distribution.

6.1.2 Application by aircraft

We think also that to morrow the aircraft will be used more than presently by farmers for the application of fertilizers. In countries where labour is scarce and expensive (U. S. A., New-Zealand, Australia) it is a current practice: more than 5000 airplanes and 100 helicopters are used currently in U.S.A., nearly 300 in New-Zealand apply fertilizers on millions of hectares, more than 200 in Australia operate on nearly 3 million ha. The present changes of structure concerning the too small farms in Europe, theconstitu- tion of groups for pooling equipment and the development ofcooperatives in spite of the strong individualism of the farmers, will permit to have sufficiently large areas for a good output of the airplanes or helicopters, whose cost price decrease furthermore as manufacture techniques develop.

6.1.3 Bulk-blending

We think that another form of use of fertilizers on soils will develop as mixtures of plant food made on demand from elements supplied in bulk: that is the bulk blending as Americans call it. Moreover, the fertilizers salesmen, either from a cooperative or a dealer, should have technical knowledge and if they want to succeed, they must become real farm advisers. They may play this role in using, for example, the techniques of bulk blending, the development of which has been explosive, since it was tried, for the first time in 1947 in U. S. A. and involves to day more than 15 % of the total fertilizers sold. This system tends to eliminate one link of thecommercial distribution, hence to decrease the costs. Effectively the producer supplies directly the retailer, who is in close contact with the consumer. The production, at competitive prices, of pure fertilizers of high grade and containing several elements like ammonium phosphate, potassium phosphate, potassium nitrate (fertilizer of the future, of which we have already spoken for other reasons) will encourage the development of bulk-blending. Moreover, the homogeneousness of the fertilizer granules in form and density will facilitate very much the extension of simple mixing plants, which will not include expensive

13 193 equipment but a single shed with 3 or 4 compartments for stocking, one loader elevator, a weighing machine and a mixer. One important advantage of this technique of dry-mixing is that formulation may be made locally according to the specific requirements of the crops and soils of the area, while formulae of fertilizers manufactured in the huge plants can not be multiplied without increasing considerably their cost price.

6.1.4 Fluidified fertilizers

Under this denomination we think of anhydrous ammonia, the most concentrated of nitrogenous fertilizers, since it holds 82 units of N in 100 kg, however, as its density is only 0,6, the volume concentiation does not exceed 70%. gaseous, in or- It is well known that under atmospheric pressure anhydrous ammonia is 3 der to be more easily transportable and storeable, it gets compressed to 10-13 kg/cm and, under this pressure, it becomes liquid; it returns to the gaseous state when emerging from the nozzles in the soil, so that these nozzles must be buried 12-15 cm deep into a well loosened and broken-up soil. Anhydrous ammonia gives the cheapest nitrogenous fertilizer unit, but its delicate handling requires somewhat sophisticated, therefore rather costly apparatus and specially trained labour, which is not always available on the farm. In the United States, the use of anhydrous ammonia developed at a quicker pace than elsewhere. The French prefer solutions containing 36 kg N per litre.

6.1.5 Fluid fertilizers stricto sensu

Fluid fertilizers may be applied with sprayers fitted with non-corrosive equipment, offered by all manufacturers to their customers, and which work with booms extending in length from 10 to about 20 m. These fluid fertilizers may also be driven into the soil or 'placed' by the use of special implements mounted on the frame of a Canadian cultivator, but in this case the working breadth is much diminished. Fluid fertilizers have the advantage of being easily handled: with pumps, but their storage raises a first problem. There is a need for rather large tanks, that resist corrosion and are coated with a special paint carefully applied after thorough sand-blasting. Rein- forced polyester tanks and also vast, tight, flexible plastic bags on a platform are also in use. If the pump is the typical centrifugal one, it has to resist corrosion (stainless steel, plastic, etc.), and must be thoroughly cleaned after use, if clogging accidents are to be prevented. Unfortunately, very high concentrations cannot be attained in fluid fertilizers, otherwise they salt out when temperature falls. Under European climates, the concentrations of NP-fertilizers reach 17-17-0 per 100 litres, i.e. 14-14-0 per 100 kg. With complete NPK-fertilizers, the elements are little soluble and the solutions are not much concentrated. At the 1-1-1 ratio, there are 1 -11-1l per 100 litres solutions on the market, but these correspond to 9-9-9 per 100 kg only. Another use of fluid fertilizers consists in the fertilizing of intensive crops grown in greenhouses on more or less inert media: sand, peat often mixed with porous plastic material, schist, vermiculite etc. 194 Dissolved nutrients may be applied to these protected crops either by spraying them through a system of pipes fitted with fixed jet-nozzles or by driving them into the soil with small injector tubes. A border-line case is that of hydroponic crops grown on no other medium than the nutrient solution itself. This technique makes it possible to grow strawberries, tomatoes and vegetables out of season or in particularly cold or arid regions, but they are of so particular a nature that they are profitable only under certain conditions. On the other hand fertilization by nutrient solutions on wholly or partly inert media is of economic interest for flower crops, selections and nurseries at the first stage; for these, it can only progress.

6.1.6 Suspensions

In order to delay settling and salting out, there is presently a tendency towards fertilizer suspensions, in which certain types of clay are added to the solutions, which delay precipitation and make possible the ciruclation in the premises, pump and distribution equipment of higher grade NPK-suspensions. Concentrations in the range of 15- 5-15 may thus be obtained without too great difficulties but the distribution circuits and pump have to be specially worked out if settlings are to be avoided.

6.1.7 Foliar sprays

Foliar sprays may be linked up to fluid fertilizers although they are only used forcomple- mentary manuring. Plants do take up their nutrients through their roots and only accessorily can fertilizing solutions sprayed on leaves and fruits penetrate into the tissues, either by traversing the cuticle which covers the parenchyma, or through the stomates. With this techniques, only complementary dressings are possible, at moments when plants have high physiological requirements, but these complementary dressings are extremely valuables in order to get maximum yields and to better the desired qualities. The spraying of urea on wheat some time before maturity has been shown by Core to increase the protein percentage (gluten of wheat corn) and to better the baking strength to - a large extent. When a deficiency is to be corrected, the spraying of trace elements leads quickly to a satisfactory result, as is well known. The same applies to deficiencies in potassium, which sometimes disappear only after many years, and which may be rapidly corrected by spraying potassium sulphate, or still better nitrate, at I %. Non-corrosive liquid fertilizers applied on leaves (o. g. potassium nitrate) are acting extremely rapidly, as was demonstrated in 1950 by an ancient colleague of mine, M.Lecat. If it is applied on leaves of vines before ripeness with K 42, radio-active potassium may be detected in the grapes two days after the spray, it being well understood that the grapes have been previously bagged for protection against the spray. Potassium nitrate has the advantage of being mixable with most pesticides, so that two birds can be killed with one stone if I kg potassium nitrate is added to 100 litres of the an- tiparasitic mixture. 195 It has been shown that this same potassium nitrate can be used with great advantage as foliar sprays on tomatoes and on potatoes, certain varieties of which have leaves supporting concentrations of 5 to 6 %, as well as on citrus, where solutions of 7-8 % KNO, better the yield, the quality and thecolour of the fruits. The grade of the solution has naturally to be checked foreach variety and according to local environment.

7. Special dressing techniques: Placement, (

Both these methods are known to give good results on poor soils, or on newly reclaimed land where continuous fertilizer dressings have not yet brought the soil to a well-balanced satisfactory level of fertility. Even there, if these techniques have to be applied to their full advantage, it will be indispensable to use only products which will not increase soil salinity, such as triple superphosphate, dicalcium phosphate, ammonium phosphate, potassium sulphate, potassium nitrateetc., but none containing chlorides. The very short survey of the problem I was confronted with leads us to the conclusion that, tomorrow still more than today, industry will have to produce fertilizers of as high a grade as possible, uniformly granular if in solid form, and with granules small enough to ensure a rapid solubilisation and working of the nutrients. We noted certain new typesof fertilizers, such as urea-formaldehyde, potassium phosphates and polyphosphates; their cost per fertility unit is higher than of the usual fertilizers, but the development of the techniques of chemistry gives us hope that the production costs will be lowered. The high grades of some of them may make their use profitable in thecase of transport to distant localities, and others have special qualities (e. g. progressive release of nitrogen) which may give an extra advantage to them. We remain therefore confident that they will go on developing in the future.

Fortunately we are today in Israel, where the well-known dynamism of our hosts makes it possible to work out chemical and technical processes of great interest, particularly as concerns potassium nitrate, now produced by a new method, and which is cheap enough to have a price per nitrogen unit probably comparable to that of other nitrogenous fertilizers, and a price per potassium unit of the order of that of potassium sulphate. This example enables me to be optimistic about the other forms of fertilizers, all for the good of world agriculture, which should not be hampered by a menace of over-production, at a time when so many underfed populations imperatively claim for the food to which they are entitled, and which world agriculture is able to offer them, especially through a larger use of modern fertilizers, discerningly applied and with the most appropriate techniques.

196 Changes in Agriculture and Fertilizer Use in Japan

M. HASEGAWA, Kali Kenkyu Kai, Tokyo (Japan)

1. Introduction

Japan, which belongs to the humid temperate region for the most part, was a country depending entirely on rice. Ever since its introduction about 2000 years ago [1], rice has been the most important food, and it would not be too much to say that up to quite recently the history of rice cultivation in Japan had represented the history of the country. It would be, therefore, impossible to understand fully the Japan of today without considering rice cultivation in general. Japan at present holds the first place in the production and consumption of fertilizers among rice countries, and ranks high among various countries of the world in the fertilizer use per unit area. It may, therefore, be interesting to analyze the reasons for the early introduction of fertilizer into the Japanese agriculture and the comparatively rapid increase in its use.

2. Characteristics of rice and rice cultivation

As staple food, rice has advantages over other crops as given below, though Westerners may not always approve. a) Serious decrease in soil fertility is not caused even by repeated cultivation of several thousand years. b) The yield is high and stable. c) Growth of weeds is a less serious problem. d) Storage is easy, and cooking is simple. e) Not much subsidiary food is needed, etc. The agriculture in rice-eating countries including Japan is indeed still in the traditional phase [2]with a population density far higher than inWestern countries (figures 1,2) and people living there are patient, conservative and obstinate. In other words, many of the problems in agriculture now Japan and other rice countries are facing have derived from the fact that rice was too superb a food crop, and the very stability offered by rice often makes a westernization of agriculture very difficult. The advance in science and industry in Western countries has made the globe small. It inevitably expedited the interchange in culture and science between countries and areas far 197 Canada U.S.S.R. 31 Europe 38 Korea

Fi 3r1.283 Japan U.S. A. 1 386 44 Cn 0

3 A267a34 €422 Taiwan132

4 Philippines 289 1 29

New Zealand

Figure 1. Distribution of the World's Population.

4 2,000

India0 0 26 0 -i Fertilizerinput 1,000

Fiue2.Dmn an upyoicutepo J" duce and 500ferultili n pl~aault ran '

Demand of • an,.produce

" ' ' 200 .= "A r. productionl

100), 100

domestic supply of 90 90

80 80 T,

Figure 2. Demand and supply of agriculture produce and fertilizer input. 198 apart, and by westernizing rice countries, it is lowering the relative position of rice. It is said that 'there is no nationality in the medical art', and the infiltration of medicine in rice countries produced a rapid increase of population. But the application of Occidental technology to agriculture at present is by no means satisfactory, and hunger is a serious problem in some parts of rice-eating countries. Production of fertilizer alone can not largely solve this problem. Rice growing farmers in Asia with a history of thousands of years have their own measures of value, and it has proved to be a very difficult task to change it for a new measure, perhaps far more difficult than to change the yard-pound system for the metric system. It will be theoretically correct to consider that the additional production of so much tons of fertilizer is needed to settle the world food shortage expected in future. There is no doubt that the necessary quantities of fertilizer can be produced. But the real question is how could that much fertilizer be utilized effectively for production increase of food, who could create such environmental conditions that permit farmers to use fertilizers, and how.

3. Background of agriculture with heavy fertilization in Japan

3.1 Historical observation

It will be difficult to understand and explain the present situation without a short look into the historical background. The very rugged topography of Japan set an early limit to the available land suitable for rice cultivation. Growing communities on topographi- cally separated and limited land areas made the creation of a local organized power for a better use of water and for military protection against neighbouring communities a necessity. Thus a number of well-organized, independent countries were created, which later on, when the whole country was unified under a central rule, provided the structure for a local government. Thus professional differentiation started early in Japan and this differentiation was enhanced by a climate that made food storage, clothing, housing fuel, etc., a necessity. This means that the non-agricultural population in Japan was comparatively large since early days. The wealth and the power of the 'daimyo' (feudal lords) depended on the number of samurai (retainers) he could maintain and this again depended on how much rice was available. For centuries, rice played the role of currency. Since early times more than 50% of the rice has been dealt as a commodity [3], though farmers themselves had very little to do with its commercialization. But for survival, farmers always had to produce far more than they would need for subsistence. (This is in sharp contrast to the conditions in tropical Asia.) As a result, considerable attention had been paid to improve cultivation techniques and to maintain and improve soil fertility. The importance of manuring was referred to already in a document in the twelfth century, and dried fish and oil cakes were marketed as fertilizer in the seventeenth century [4]. Toward the end of the seventeenth century (1696), a complete book on agriculture was published, in which methods of manuring by crops and by kind of fertilizers had been explained in detail together with the necessity of top dressing application [5]. It was therefore not surprising that the use of chemical fertilizer spread widely after its first introduction in 1880's (see figure 2) [6]. In the early days, individual farmers gained very little from the use of fertilizers. It was the landlords who showed the most active in- 199 kg/ha 300

N, N=O, kg (N PNO,+K,0)/ha planted

or KO Mill. I20 200

.0 ......

.4 100

.2 -

1951 1956 1961 1966 FigureS3. Change in fertilizer consumption in Japan after World War 11.

terest in the use of fertilIizer in order to increase their income. In this effort, they joined hands with the authority then in power, who was also interested in an increased income from agriculture to finance industrialization [7]. While rice cultivation required a great deal Of manpower, it could feed a large population on limited land. Therefore, rice was the most advantageous crop for the man in power to exploit. The situation changed drastically after the farmland reform of 1946 which tufned all ten- ant farmers into owners. Though the size of the average farming unit did not expand by this reform, high food prices, initially caused by the serious food shortage after the war and later supported by the rapid economic recovery, greatly improved the financial situation of the farmers. This fact together with the introduction of a more materialistic approach to life induced farmers to cultivate crops for reasons of profit (rather than to sustain life as before), and it resulted in a very rapid increase in fertilizer consumption which in turn improved the purchasing power of the farmers themselves (figure 3) [8]. The policy of the government to promote land productivity by all possible means in order to cut down rice imports supported the trend to heavy fertilizer use and high rice yields. With industrialization progressing at ever faster rates, outflow of labor from rural areas increased rapidly. This resulted in an increasing number of part-time farmers (80 Y of all farm families were part-time farmers in 1967) posing various problems such as aged and feminized labor force in agriculture, difficulties in securing successors in farming, etc. To keep agriculture alive under such conditions, the Government adopted a high rice price policy where the producer gets more for his rice than the consumer has to pay. This 200 Price index 1960=100

160 160

Agr. products 140 140

/ N.-- -' Fertilizers 120 120

------100

1951 53 55 57 59 61 63 1965

Figure 4. Change in prices of agriculture products and fertilizers. greatly encouraged farmers to adopt every means to produce more r ice, and average fertilizer input now stands at 96 kg N/ha, 89 kg P2Os/ha and 81 kg K 20/ha [9] with ex- tremes going as high as 250 kg N, 200 kg PO, and 250 kg K2O. This policy has been so Isuccessful' that overproduction of rice now poses a serious problem to government fi- nances. Whereas rice prices went up year after year, fertilizer prices remained constant or even declined, thus remarkably reducing the burden of fertilizer expenses for farmers (see figure 4) [8]. With changing prices and a changing labor situation, there was a rapid change from straight fertilizer to compounds and high-grade compounds. Though compounds are about 15-20% higher in price than straight materials (plant nutrient base) compounds presently account for over 70% of all fertilizer consumed. The number of different brands and grades of compounds on sale in Japan exceeds 10,000, reflecting partly the complexity in climate, topography, soils, diversity of crops and cultivation techniques, 201 Paddy rice N Wheat barley Sw. Potato Wh.Potato [ Misc cereals Pulses Eil Vegetables Planted area Orchards Fertilizer consumption

Industrial crops Tea

Mulberry Tobacco Forage crops

Others

Total

(mill. ha) 8 7 6 5 4 3 2 1 0 100 200 300 400 500 600 700 (1000 t0 Figure .. Estimated cropwise consumption of fertilizer 1965. Compiled by M.A. F., based on reports from Pref. Gov'ts. and also reflecting partly the existence of too many small-scale fertilizer producers. There are now trends to consolidate fertilizer production in order to strengthen the competitive power of a reduced number of producers.

3.2 Patterns offertilizer use

With rapidly progressing westernization of urban life and with the expansion of international trade, the diet of Japanese people has undergone considerable changes and the relative importance of rice is on the decline. Yet supported by the long-term policy ofguar- anteeing a high rice price - as if to compensate farmers for the past exploitation for industrial development - rice still holds its position as the most important, profitable, and stable crop. As seen from figure 5, fertilizer consumption for rice is still by far the largest among various crops. 202 In recent years, a rather interesting differentiation in the pattern of fertilizer use has developed as a result of the action of following factors: a) Very small farming units (average farm size in Japan is about I ha) are posing great difficulties in introducing labor-saving methods (mechanization). b) Increasing labor shortage in agriculture and increasing possibilities for side income from non-agricultural occupation. c) The highly commercialized mind of the young rural generation. d) Very high prices for agricultural quality products (rice, vegetables, fruits, animal products). e) Comparatively low prices for other agricultural products (small grains, pulses, sweet potato, etc.).

As a result of this situation, the area under vegetables, fruits,and grassland is increasing whereas the area under small grains, pulses, and sweet potatoes is decreasing at a rather rapid rate (in spite of the fact that the prices for small grains in Japan are still very high by world market standards). As the decrease in the acreage of the low price product group is larger than the increase in the acreage of the high price product group, the total planted acreage in Japan shows a steady decline. Generally it is observed that the fertilizer application rates for small grains, pulses and sweet potatoes are usually below the recommended rates, whereas the fertilizer application for high priced crops often far exceeds the recommendation. In extreme cases, the actual application may be two- to three times higher than the recommendation. This is particularly true for fruits and vegetables.

Recommendation Actual application-

(kg/ha) N P2 05 K.0 N P0 K20 Satsuma Orange ...... 200-300 150-250 150-250 500-600 400-500 400-500 Cucumber ...... 350-500 250-400 300-500 1000-1400 800-1000 700-800

* Extreme case.

In spite of a substantialdecrease in the planted acreage, total fertilizer consumption is still increasing steadily, which means that for the crops mentioned under' d)', fertilizer use is increasing inspite of the very high rates already used. But thesituation is somewhat different with each of these crops.

3.2.1 Rice

An old proverb, 'grow barley with manure: grow rice with care', indicates that a stabilized yield of rice can be obtained without specific manuring. If, however, a high yield is aimed at, heavy use of fertilizer becomes a necessity. Breeding of high yielding, fertilizer responsive varieties has greatly contributed to ever increasing rates of fertilizer (seefig- ure 6) [10]. The increase in fertilizer consumption for rice is thoroughly attributable to a rise in the application level per unit area, and the planted area of rice as a whole is quite stabilized though there is some decrease or increase in it locally (see table below andfigure 7) [1.12]. 203 Yield grown rice I/ha .-

6 0

2 C- 0 Z-

- N

50 100 N kg/ha

Figure6. Increase in yield and N application with change in variety.

Japan Thailand Mill. ton - Production Fertilizer Yield Mill. ha- plannedarea (kg/ha) (t/ a)

15Production/

300 6

10 Yield N 5k/h A2 F e6Ica 00 Production 4 i PlneM FPtinzertiieil 3ra00 6

Yieldeld M ha p e r (Planled area 1

Fertilizer

1942 47 52 57 62 67 42 47 52 57 62

Figure 7. Comparison of Rice Production Increase between Japan and Thailand. 204 Changes in fertilizer application to rice [8,9] (kg/ha) 1957 1962 1965 1966 1967

N 80.0 85.3 85.3 91.8 96.1 P'%5 56.4 67.8 74.5 80.8 88.6 80.9 K2O 67.7 73.1 72.1 78.3

3.2.2 Vegetables

Vegetables have been receiving very high rates of fertilizer for many years. The present increase in fertilizer consumption is mainly due to a shift from vegetables requiring comparatively little fertilizer (radish, carrot, etc.) to fruit and leaf vegetables having a higher fertilizer requirement. Another factor is an increase in the acreage of intensively managed vegetables under plastic covers.

3.2.3 Fruits

The increase in fertilizer consumption for fruits is mainly attributable to the increase in the total planted acreage and to the increase in the number of fruit bearing trees. Fertiliz- er application rates for fruits have presently reached levels where further increases can hardly be expected.

(kg/ha) N P 2 0 KeO Satsurna Orange ...... 250-500 200-450 200-450 Apple ...... 200-400 100-300 200-400 Pear ...... 200-450 200-300 200-400

In case where rice and vegetables are cultivated by the same grower, the crop that has more weight in the farm management receives more intensified care, and the other less importantcrops areoften neglected. Where vegetables, forexample, becomethecenter of management, both capital and labor are concentrated on them, even if otherwise rice is considered to be a very profitable crop. Rice in such case is only considered as a means to make more intensified cultivation of vegetables possible. With heavy fertilizer application to several rotation of short-term vegetable crops, the accumulation of harmful substances and salts becomes a problem. In such cases, rice is introduced into the rotation mainly to wash out those harmful substances and it often happens that no fertilizer is applied to rice at all. As mentioned before, the actual fertilizer application to vegetables and fruits often far exceeds recommended rates. This is partly because the quantities recommended by the experiment station is for average farmers, and is naturally lower than the application level of skilled farmers who obtain much higher yields. But with vegetables, it is not only the yield, but also the quality and the proper timing of marketing that decides the profit. Farmers now tend to pay increasing attention to quality of fertilizers and timing of application to suit changing market conditions. Therefore, it is very difficult for the stations to give any valid recommendations. 205 4. Futureprospects offertilizer consumption

It is extremely difficult to forecast the future of fertilizer consumption, and reliability of any given figures would be low. Therefore, only the expected trend will be discussed. Some of the factors which might concern with fertilizer consumption will be mentioned below. a) The cultivated area in Japan is about 6 million ha, and there has been no marked change in it in recent years. b) The total planted area of crops is yearly decreasing, and the planted area of such crops as wheat, feed grains, etc., which can be imported at low prices will decrease further. c) The farming population is decreasing at a yearly rate of 3-4% , but the decrease in the number of farm households is comparatively small. The expansion in the size of farm management is, therefore, slow and tardy, and it is assumed that the number of households with farming as only side-line will further increase. d) With the expansion in international trade, the rate of dependence on domestic agriculture is yearly decreasing. In order to increase the volume of exports of industrial products, Japan will have to import more agricultural products. e) Vegetables, fruits, and livestock products are the agricultural products for which the demand is expected to increase and which must be chiefly produced within the country. Japanese economy will be able to maintain a high demand and high prices for them for some time to come. f) The fertilizer industry in Japan will try to cut down the cost by production rationalization and by increased exports. For this purpose, the expansion of production scale and the increase in domestic consumption are considered indispensable. g) The value of land and cost of labor will get still higher. Land and labor productivity, especially the latter, will assume more importance, and mechanization and collectivization of work will advance. However, the improvement of labor productivity at the cost of land productivity would be infeasible in Japan in the near future. h) Farmer's organizations will remain powerful, or will be further strengthened. Japa- nese farmers know very well about fertilizers, and the production of crops on commercial bases with liberal application of fertilizers will increase steadily. i) The Government will take various measures - including the improvement of land productivity - to increase farm household income, trying to avoid drastic changes and protect farmers as much as possible. j) With such circumstances as given above as the background, the possibility of further improvement in land productivity together with the effective utilization of waste land will be explored through experiments and researches. It can be easily considered from the above that the relative prices of fertilizers will be maintained low, or will be lowered still, further lessening the burden of fertilizer expenses on farmers, and therefore, the fertilizer application level per unit area will continue to increase so long as crops are to be cultivated. On the other hand, it is extremely difficult to estimate the total demand forfertilizers because various influencing factors are complicatedly involved in it. If these factors would develope as expected at present, the demand for fertilizer will continue to increase at the yearly rate of about 4-5 % for some time to come. However, this estimate is based on the following presupposition: the high rice price policy is maintained; the demand for 206 vegetables and fruits increases; the Government gives positive assistance and takes measures to encourage milk and meat production; and the decline in land productivity caused by the abandoning of cultivation of wheat, barleys, miscellaneous cereals, and feed grains which cannot compete in price with foreign produce can be checked to some extent by collectivization, mechanized cultivation on commission, and other measures.

Acknowledgements

The author is deeply indebted to Dr. H. R. v. Uexkull, Director of Kali Kenkyu Kai, for his encouragement in preparing this article and for his valuable suggestions in many ways.

Literature cited

1. Ando K.: Ancient History of Rice Cultivation in Japan, Chikyu Publishing Co., Tokyo (1951). 2. F.A.O.: Production Yearbook, Vol. 19 (1965). 3. Araki M.: Agricultural Encyclopedia, Vol.6, pp. 39, Agricultural Administration Research Commitee, Tokyo (1967). 4: Furushima K.: Agricultural Encyclopedia, Vol.6, pp. 5 4 , 55, Agricultural Administration Re- search Committee, Tokyo (1967). 5. Miyazaki Y.: Nogyo Zensho (Agriculture Encyclopedia), 1697, revised publication by Daibos- atsu Toge Publishing Association (1941). 6. Ogura T.: Agricultural Development in Modern Japan, Fuji Publishing Co., Tokyo (1963). 7. Fukushima Y.: Rice, Iwanami Publishing Co., Tokyo (1955). 8. Fertilizer Sec., M.A. F.: Recent Fertilizer Status (1968). 9. Fertilizer Sec., M.A.F.: Monthly Fertilizer Bulletin, September/October (1968). 10. Tanaka M.: Rice Cultivation Techniques in Aomori - Techniques and Management in Future Rice Cultivation, M. A. F. (1966). 11. Motooka T.: Agricultural Development in Southeast Asia, Kyoto University (1968). 12. MA.F.: Statistical Pocketbook on Agriculture, Forestry and Fisheries (1968). Statistical Yearbook on Agriculture, Forestry and Fisheries (1966/67).

207 The Place of the Second Generation in Rural Space

Prof. E. YALAN, Rural Building Research Centre, 25 Derech Hayam, Mount Carmel, Haifa (Israel)

1. Introduction

On the subject of regional planning and urbanisation so much has been said and written that it has become practically impossible to distinguish in this maze the clear outlines of its predominant separate components. We shall try to throw some light on this problem by defining the influence of the diverse patterns of Agricultural Settlements upon Rural Regional Structure. Certain trends in Regional Development in Israel in the field of Regional Extension of Local Agricultural Producer Cooperatives serve us as a beacon pointing towards the probable pattern of future Regional Structure. It is generally accepted that modernization of farming leads to de-ruralization. In Israel, however, certain already existing patterns of Rural Regional Services and organization have made possible the promotion of farming in a manner which may lead to a balanced development of urban and rural rationalization, as opposed to the sole domination of urbanization within the entire process of human settlement.

2. The Family Farm

The family is predominantly recognized as the basic element of organized society throughout the world. The family is the only environment in which man is less exposed to loneliness; it serves asa deterrent to his destructive genius. Community development tends to strengthen the family nucleus and provides a 'Fami- ly-Substitute' for the lone individual. In urban community development it is the self-contained neighbourhood units that promote the family nucleus. Life-stream (LS) is composed of three functional components, namely:

H = Habitat R = Recreation W = Work In an 'Amorphous Urban Organism' all three components are separate and of disrup- tive character: 208 Amorphus Urban LS = H + R ±W.

In a' Neighbourhood Units Urban Organism', Habitat and recreation are interconnect- ed thus: Neighbourhood Urban LS = H R + W.

In this case only Work is disconnected from H R. The Work of men, and increasingly also of women, becomes isolated from the stream of family life causing a conflict of loy- alties. The ever-increasing time available to urban man for his leisure and his instinctive lean- ing towards contact with nature changes this 'Week-day Industrial Worker' into a 'Week-end Fisherman - Hunter - Farmer', this divergence of leanings bringing about a splitting of personality. In 'Agricultural Settlement* Organism', Habitat, Recreation and Work are interwoven: Agricultural Settlement LS = HRW, thus farming becomes a mode of life and not merely a profession. Successful farming requires close contact with and profound understanding of nature and its varying moods, making farming and related activities a unique environmentally integrated mode of life which may be described as' Rurality'. The partnership of urban and rural societies may result in reciprocal influence benefiting human society as a whole. To enable this, however, the technology of Family Farming in its local and regional manifestations must be brought up to date. Rational up-to-date farming has proved to be possible only on big farms, i.e. both private and cooperative.

3. Private Big Farms

Private Big Farms employ hired labour and lead towards urbanisation and de-ruralisation :

pBF -- * De-ruralization - Urbanisation total pBF ) World City = 'Ecumenopolis'**

Private Big Farms are undergoing changes, which we shall describe in their past, present and predicted future forms: 1.' Past' Region of Big Private Farms*** can be described by means of the following figurative description, which is based on a principle of arbitrary figurative abbreviation and is not to be regarded as a mathematical formula. n (fI1 H Y P) + uC

* Agricultural Settlement is a 'community location' in which mainly agriculturalists and persons engaged in related production and services live and work. .* See enclosed bibliography p. 16 'Ekistics'. ** See: Yalan E.: 'Land Planning of the Agricultural Cooperative Village - 1963'. Yalan E.: 'The influence of Farming Rationalization on Village Planning in Scattered and Gathered Settlements - 1964.' 14 209 where: n represents a number of... f farmer ff farmers I labourer II labourers H Habitat Y " Farm Yard P " Agricultural Plot uC Regional Services Centre

The above figurative description therefore reads:

A number of 'farms', each consisting of farmer's and labourers' habitat attached to farmyard with single plot of agricultural land. These'farms' are scattered around a distant service centre, attached to or of an urban nature.

II.' Present' Region of Big Private Farms is described as follows: n(fHYP) +IIHuC where: symbols as above. in which labourers' habitat (11H) moved to Regional Centre.

Ill. Predicted Future Region of Big Private Farms is described as follows: n(YP) +ffllHuC where: symbols as above, in which both farmers' and labourers' habitat (f11 H) move to Regional Urban Centre (uC). This is how the gradual urbanisation of a rural region takes place.

4. Co-operative Big Farms

Cooperative Big Farms based on self-work family-farm-units lead towards Rural Ra- tionalization: cpBF -- Rural Rationalization Total cpBF I Integrated Rural Urban Coordination = 'RURACORDIA' where: cpBF represents Cooperative Big Farm. Although at present Private Big Farms are the most successful up-to-date farming pattern, we foresee future ever-increasing socio-economic difficulties, as they depend on hired labour. There are 3 types of cpBF in Israel, and each of them is composed of Habitat compactly encircling their local service centre. These three patterns of cpBF in their regional structure are grouped around distant Regional Service Centres. These centres lately tend to be of a non-urban character and are known as the Non-inhabited Regional Centres (rC). 210 I. Old Moshav* is described as follows: n(f H YP) C where: Crepresents Service Centre. Remainder of symbols as above.

New Multi-Unit Moshav** reads: n,(fHYP +n 2 bP) mC where: n, n, represent different numbers of... bP represents Agr. Plot within Block of Plots. mC represents Mult-Unit settlement Service Centre.

11. Moshav Shitufi*** reads: n(fH) +cYcP C where: cY represents Communal Farm Yard. cP represents Communal plot.

1ll. Kibbutz**** reads: n(cfH) +cYcP C where: cf H represents Communal Farmers Habitat. A number of such co-operative Big Farms grouped around a distant co-operative Re- gional Centre can be described as follows: n (cpBF) + rC Where the co-operative Big Farm (cpBF)may be any of the above described, Moshav, Kibbutz or Moshav Shitufi, in anycomposition. If a region has several such diverse co-operative Big Farms, it can be described as follows:

Sn, (f H Y P) [n,(fH)+cYcP) n(cfH)+cYcP]\ +n, I +n 5 +rC \,,n ------' ± n C, .C [ C 3 ])

These co-operative Big Farms (cpBF) with their gathered farming population around their services are the local expression of agricultural co-operative production, whereas the regional non-inhabited centres (rC) are the expression of regional extension of these agricultural producer co-operatives. * 'Moshav' isacooperative Family Farms Agricultural Settlement; see: Edited by E. Yalan, 'Private and Cooperative Agricultural Settlement Physical Planning', 1961. * In Old Moshav each Farmer has all his agricultural land attached to his Habitat. In New Multi Unit Moshav the Settlement is composed of several neighbourhood units grouped around its Service Centre. Each Farmer has a small Agricultural plot attached to Habitat and rest of Agricultural parcels located in several Blocks of homogenous cultivation. . 'Moshav Shitufl' is a collective farming, Multiple Family Agricultural Settlement. 'Kibbutz' is a collective farming and habitat Multiple Family Agricultural Settlement. 211 5. Some Aspects of the Socio-Economic Structure of Various Patterns of Settlement in Israel

1. In the Initial Type of Moshav, the economic and social structure is relatively egalita- rian in character. Farmers cultivate privately on a self-work basis, and co-operate chiefly in regard to equipment and trade (Figure 1). II. In the Present-day Type of Moshav, the socio-economic structure is influenced by a measure of co-operative regimentation, and maintains only economic relative egalitarianism. Production is composed of co-ordinated individual and community activities (Figure 2). l1. In the Moshav Shitufi and the Kibbutz, the Collective Settlements,complete social organisational regimentation takes place, alongside of economic egalitarianism (Figure 3).

Hp Farmersn

Figure 1. Socio-economic structure in Old Mosbav.

Manager

Farmers In, (Hyp+nb'p)

R* The block plot necessitates regimentation

Figure 2. Socio-economic structure of New Moshav.

Manager

Instructors

o000 qo q Farmers I n (cH+cYbP)

Figure 3. Socio-economic structure in Collective Settlements. 212 IV. The Industrial-Urban Socio-Economic structure is that of a complete pyramid, with no social or economic egalitarianism (Figure 4).

Manager

Supervisors

Works

Figure 4. Socto-cconomic urban structure.

6. Regional Service Centres

In gathered settlements, habitat is grouped compactly around the community service centre. The services are of a local and limited nature, within the means of a small agricultural community, such as initial education, some religious, cultural and recreational activities, and some group consumer-producer services. Intersettlement Rural Service Centres cater for a number of agricultural communities, and provide services of a higher order on a regional scale. There exist in Israel different types of'Rural' intersettlement Centres serving a varying number of settlements, which have been meant by the planners to be inhabited, thus actually forming the initial stages of the Urban hierarchy*. During the last few years, through the initiative of the collective and co-operative settlements and with the encouragement of settling authorities, non-inhabited Rural Service Centres (rC) came into being" and these belong to the Rural hierarchy***. Diverse Rural Service Centres are usually of geographic significance, and can best be represented schematically in the form of an inter-connected grid made up of the different types ofcentres, with their satellites (see figure 5). But Rural Service Centres develop and may change, assuming functions of a lower or higher category than that which was intended. Thus functional and not geographic character aquires predominant significance. The interdependence of the farmer and the various local and regional services is more of functional than of geographic significance. The prosperity of the individual farmer, especially in the case of co-operative family farming, depends to a great extent on the quality and scope of services available to him, whereas the standard of these services in turn depends on the measure of initiative and organisational ability of the body of farmers.

* Settlement Study Centre Rehovot: 'Regional Co-operation in Israel', Publication No. 1. The Agricultural Extension Service: 'Rural Regional Development in Israel', 1965. Idem. Priori Dr. L: 'The Israel Trend of Inter-Settlement Cooperation', Settlement Study Centre, Re- hovot 1965. 213 jiag

Key: Farmers 0 Village service centre * Sub-regional service centre Regional service centre

Inter-Regional service centre

Figure 5. Geographic relationship between individual farmer and local and regional services.

214 A I High Local and regional ab senvices: * Social services Aeducation, culture, 3 /religion, recreation SA3. health -Technical services B Medium agrotechnic, zootechnic, 3 Csupply, distribution. // "marketing, administration, .processing, extension, mechanical, maintenance

Farmer Level olservices

Figure 6a. Rationality of services resulting from the relationship between level of services and scope of activities.

Intet-conamunal. A

Scope of activities Communal /-

Individua[

Farming initiative and cooperative Restricted D1 attitude

Average D2

Extensive D3 Degree of initiative and attitude

Figure 6b. Degree of farm development resulting from the relationship between rationality of services and farming initiative and cooperative attitude. Fig. 6a and 6b. Functional inter-relationship between individual farmerand local and regional services. 215 The individual farmer is simultaneously in contact with local, regional and inter-regional services, the degree of contact changing with the flow of developments in the course of time. The geographic dependence of the farmer on the location of the various levels of services no longer, as was once thought, depicts their true interrelationship. One must take into consideration the fourth dimension, time, and the dynamic functional rather than the static geographic nature of this relationship. The functional interrelationship between Farmer and Local and Regional Services is influenced by three factors: I. Level of services; 11. sphere of activity - viz.: individual, community and intercommunity; ll. the degree of integrated farming initiative plus cooperative attitude; all these resulting in the degree of Farm Development (see figures 6 a and 6 b).

Organizational and Industrial Regional Services should be related chiefly to Agricul- tural Production and Processing, employing only rural manpower. General industrial manufacture should be theecological prerogative of Urban Areas (see figure 7).

Urban contres Urban Rare( industrial agdcultural products products

Fanty @ 1 Rural area mnanpower

Figure 7. Rural-urban activities inter-relationship. The population of CooperativeSettlements, (Moshavim)and Collective Settlemenls(Kibbutzim),are composed of: Farming Families, Local Services families, and Regional Services families. Under 'Services' are meant all social and economic activities related to the needs of Rural Space. Thus in addition to the son who gradually takes over the farm, the other sons or marrieddaughters remain in (heir accustomed environment working in processing of agricultural raw material, Market. ing, Banking, Cooperative Organization, Education, Culture, Health, etc. 216 I

future posiblv6C

*'¢ Ho'elland {W ld,,)z tl' , V)k I uro1pC I S

2S. 'I .... i.,

FWA Q

, ?'h p , 1 1,tI r e [ 1......

21 '1 t / ff¢rl $7 [¢r ' t c I I~I[UcI t ~b F[I tA 1h rI~a 7. Schematic Comparison of Urbanisation with Urban-RuralCoordination

The shrinking of agricultural population proceeds not only because of the economic opportunities of urban industrial employment capacity and the rationalisation of farming, but very often because of better urban services and the'glamour' of the city. This process manifests itself in theU. S.A. where today peopleengaged in farming constitute only approx. 7 % of the total population (see figure 8 b). The fact that farmers who remain in rural areas feel left behind expedites this urbanisation even further. The surplus rural manpower immigrates to urban areas in their own countries, or even crosses frontiers to foreign lands, with social instability caused by this uprooting. The size of the exodus depends, amongst other factors, on the type of farming e.g. the small private family farm gradually disappears due to competitive inadequacy. What is more, the private family farm is liable to disappeareven in carefully planned regional developments, such as in the polders of Holland (see figure 8a). The habitat of agricultural hired labour is situated in neighbourhood units, attached to Urban Regional Cen- tres (uC) with the workers commuting daily. The very high development cost of the scattered settlement pattern of the polders and the tendency towards ever-increasing size of private farms because of rationalization (whereas the polder-farms were in the past approximately 12 hectares, they have lately been allotted 40 hectares, and there is a tendency to increase them further still to 60 hectares) lead the authorities concerned to consider the possibility of in future discontinuing to site the farmer's habitat on his lands, but instead to place it within special neighbourhood units again attached to the Urban Re- gional Centre (see figure 8a)*. Thus we would find the farmer commuting to his lands, instead of he and his family travelling regularly to the Regional Centre. So we see that even on fairly big private farms the process of urbanisation is still advanc- ing. The present approximately 7 % of agricultural population in U. S. A. is actually a very artificial figure, representing not those whose source of income is farming, but those whose habitat is near their fields. This trend of de-ruralisation brings about the creation of a single demographic centre of gravity - a single urban hierarchy of towns of different categories which ultimately may result in total urbanisation, and may well take the form of a World City, the 'Ecumenopolis'(see figure 8 d), as previously mentioned". We believe that this total urbanisation, the creation of a sole pattern of amorphous human settlement is not desirable and not inevitable. In Israel, the Regional Planners promoted the establishment of different categories of Service Centres: lntersettlement-' Rural' Service Centres, serving 4-6 settlements Intersettlement-Regional Service Centres, serving 10-20 settlements Interregional Service Centres (Country town) serving 30-50 settlements*** These existing centres strengthened the rural economy, elevated the standard of life of the farmer, and improved rural amenities, but have not fundamentally changed the existing trend of urbanisation, as these diverse service centres, with their inhabitants are in themselves the initial stage of the Urban hierarchy. - Yalan E.: 'Influence of Farming Rationalisation on Village Planning in Scattered and Gathered Settlements.' Rural Building Research Centre 1964, p. 7 . Mumford Lewis:'A New Regional Plan to Arrest Megalopolis.' Ekistics September 1965, p. 1' 7 . Prion Dr. L: ( Proposal for the location of Regional Centres>, Tel-Aviv, 1965. 219 The creation in its time of the Agricultural Producer Co-operatives and Collectives was not a result of Technological Planning, but that of a social movement - that of a philosophy of life*. Recently in Israel a number of non-inhabited co-operative Regional Centres were established (see figure 8c) chiefly on the initiative of the farmers themselves. The Non-inhabited Regional Service Centre is the manifestation of the regional extension of the local Agricultural Producer Co-operative. This promotion of self-sufficiency of 'rurality' brings about the creation of two demographic centres of gravity and a partnership between rural and urban economies, creat- ing two parallel development hierarchies.

It is estimated that in time in Israel:

Farming Population will constitute 121/ Y of the total population; Service Population will constitute 121/ %of the total population; Thus Rural Population will constitute 25 % of the total population".

The ultimate form of this comprehensive Rural-Urban Co-ordinated Development, 'Ruracordia', will take the shape of scattered, separate cities with their own environmental characteristics within open spaces composed of cultivated areas with their Rural Settlement Elements (see figure 8 c), forests, lakes, mountains, etc. Man's environmentally integrated life-stream aquires individuality and character.

8. Conclusions

The influence of local and regional manifestation of co-operative farming upon urbanisation has been defined and described on preceding pages, bearing in mind certain existing developments in Israel. We have tried to predict possible future trends. Local co-operation, in the form of community activities, obviates undue enlargement of farms seeking rationalisation. Rural regional co-operation brings about basic improvement in cultural, educational, social and economic services, bringing them to a level comparable with those of urban development. The self-sufficient Rural Regional Community which has been created achieves the following objectives: a) Employment capacity to absorb the young generations of rural population, as well as aging farmers. b) An opportunity has been created for urban population desiring to enjoy urban amenities within a rural environment to move from urban to rural areas and occupa- tions. c) The creation of a complementary rural-urban economy. d) Rationalisation of population distribution, important to all nations, but vital to Is- rael.

* Published jointly by: Ministry of Agriculture, Jewish Agency Settlement Dept., Agriculture, and Settlement Planning and Development Centre. ,Rural Regional Development in Israel.> 1965. Articles by: Weitz Dr. R.. p. 7; Landau Y. H., M. Sc., p. 21. IWelt: Dr. R.: 'Anticipated Form of Settlements in Israel', Oct. 1963. 220 The Israeli co-operative expericnce has so far withstood the test of time, but currently there appear to be certain reservations concerning the nature and scale of co-operation. There is a growing movement among farmers in the Moshavim, opposing Organisation- al co-operative regimentation. In Collective Settlements, on the other hand, there is a growing opposition to regional and even local industrialisation, promoting diversification of social strata, viz. managers and those who are managed, which in farming is less apparent than in industrial production. In spite of the reservations which have lately manifested themselves in Israel, there are indications that constructive methods of solving the problems will be evolved, bringing about the lasting establishment of local and regional co-operative farming, safeguarding rurality.

Literature cited

Ekistics: Doxiadis C. A.: Ecumenopolis- Toward a Universal City, Jan. 1962. Doxiadis C. A.: The Future of Copenhagen, Apr. 1963. Doxiadis C.A.: The Forces that will Shape Ecumenopolis, May 1963. Mead Margaret:The Underdeveloped and the Overdeveloped, Feb. 1963. The City of the Future, etc., July 1965. The Human Community, 83-113, August 1965. Munmford Lewis: A New Regional Plan to Arrest Megalopolis, 117, Sept. 1965. Ministry of Agriculture, Jewish Agency Settlement Dept., Agriculture and Settlement Planning and Development Centre. 'Rural Regional Development in Israel', 1965. Articles by Weitz Dr. R., p.7;Landau Y.H., M.Sc., p.2 1. Prion Dr. L: 'The Israel Trend of Inter-Settlement-Cooperation', Settlement Study Centre, Rehovot 1965. Prion Dr. L: 'Proposal for the Location of Regional Centres', Tel-Aviv 1965. Settlement Study Centre, Rehovot - 'Regional Cooperation in Israel', Publication No. 1. Yalan E. in collaboration with Maos ]. and Kam L.: 'Land planning of the Agricultural Co-operative Village', Dept. for International Cooperation of the Ministry for Foreign Affairs, Centre for Technical Services of Ministry of Agriculture, and the Settlement and Technical Depts. of the J.A.1. 25 p. Yalan E., Maos J.. Kam L.: 'Influence of Farming rationalization on Village Planning in Scattered and Gathered Settlements', The Israel Rural Building Research Centre. Yalan E.: Private and Cooperative Agricultural Settlement Physical Planning', pub. by the Interna- tional Seminar on Rural Planning. October-November 1961. • Weitz Dr. R.: Anticipated Form of Settlements in Israel', Oct. 1963.

221 Discussion, Session No. 4

Prof. Dr. H. HEIMANN (Kirjat Bialik/Israel): I would like to give further strength to two points brought for in Mr. Audidier's lecture: t) In orchards of oranges and deciduous fruits the potash put into the soil is easily fixed in its top layers where it remains without getting to the roots. Therefore the importance of tools for the application of potassium in depth. The now lacking response to this element may then come into appearance. - 2) There is some good evidence that by foliar application of potassium to sugar beet during the last months of growth, the decline of sugar content due to soil and water salinity can be efficiently counteracted. These experiments should be followed-up with more intensity in Israel and all the many countries confronted with the same problem.

Mr. T. Gans (Tel-Aviv/lsrael): I) To the lecture of Prof.Ruihenberg I feel that the discount rate of 50% for experimental data compared to farmers practices in developing countries is much too low. In actual fact in many cases there is a complete lack of communication between the agricultural research worker and the farmer. Thus it is very dangerous to use the above discount rate for planning. The fault of the lack of communication is more the fault of the research workers than the farmers. 2) Every fertilizer introduction program has to be planned. In order to delete faulty statistics in developing countries for planning, we teach the collection of key data by the planners themselves in order to make the first plan as realistic as possible. These of course should be elastic and prove to change according with the feed back data.

Prof. Dr. H. Ruthenberg (Stuttgart/Hohenheim/Federal Republic of Germany): Of course, careful scheme planning is necessary, but it should not be rigid. Planning for the feed-back of experience is necessary. The lack of the application of research results is usually due to - the innovation is not sufficiently worthwile from the standpoint of the cultivator; - the scheme is badly designed; - there is no proper extension work; - the political situation is not in coordination to economic activity. 222 Mr. Y.Araten (Haifa/Israel): Concerning Prof. Ruthenberg's paper: He did not mention that for the introduction of fertilizers in underdeveloped countries extension workers are most essential. A number of years ago a team visiting India found that in certain areas the cultivator did not use fertilizers, even if received in certain cases free of charge, because he never hea.rd of the function of fertilizers.

Mr. M.Bazelet (Beersheba/Israel): Speaking about problems of correlation between soil analysis, fertilization and response of plants as it was given by Prof.Hagin, one must not forget that many times, in intensive agriculture, the soils are above the critical level with the different nutrients and this is the reason of not getting response to fertilization although we are able to see increase in soil analysis. Therefore, in order to decide if a method is good or not, we have to find empirically the critical level in poor fields or even in pot experiments.

Prof. J. Hagin (Haifa/Israel): The response of crops to fertilizers and correlation with testing methods was performed over the whole yield range. Soil testing by conventional methods is good in relatively primitive agriculture; it differentiates well between low and high availability, but it is not enough to help in fertilization rates determinations in a very intensive highly fertilized and high yielding agricultural system. In such a system we cannot rely only on soil testing as done today. We have to develop a more accurate and integrating measuring method.

Dr. G. W. Cooke (Harpenden/United Kingdom): Stated that the true value of soil analysis was not as bad as Prof. Hagin suggested. We have 2 good methods - Olsen method for P and exchangeable K which give a true picture of the soluble P and K (not available - «available>> prejudges the issue). The Olsen method is a great advance. All investigations show it to be reliable in all the countries where it has been tested in most comparisons it is the best among other methods. The values that separate dow>> and «medium ) in soil P are similar for the same crops in countries in Europe, America, Africa, India, Australia and New Zea- land. This gives us considerable confidence. The failure of soil analyses to correlate with fertilizer responses in annualfield experiments, when good methods are used is because the crop performance varies from place to place and year to year. In long-term experiments at Rothamsted, response on the same soil varies greatly year by year, from zero to large amounts, on the same soil. The remedy in intensive developed agriculture, is to settle from long-term experiments the soil analysis values that determine whether crops may be likely to give responses. Above this figure only maintenance fertilization is needed. In areas where extensive agriculture is being changed by starting to use fertilizers, the economist must, when he proves in like agronomist, have a soil chemist with him and as soon as a development scheme starts, long-term field experiments of simple pattern must be started. They must test amounts of fertilizers up to those needed in developed countries 223 for large production, not only the small dressings that may be judged economically. (Failure to test large dressings in East Africa in recent work meant that responses were not discovered).

Dr. Th. Walsh (Dublin/Ireland): I would in congratulating Prof. Ruthenberg on a very interesting paper like to raise briefly the need for research workers to synthezise and test arable systems for different enterprises before expecting farmers to use research results to the best advantage. In the past I feel that farmers were expected too often to fit bits and pieces of information into their systems by trial and error methods with, I am afraid, too much of the error. Farmers in business will require more than this in the package deal is resulting, even farmers will come to expect - a package based on market possibilities with its production, economic and marketing components integrated.

Prof. Dr. H. Ruthenberg (Stuttgart/Hohenheim/Federal Republic of Germany): Risks and uncertainty have to be taken into account in judging the worthwileness of fertilizer inputs. When risks are very high, large scale farming - with liquid assets - should be pre- ferred to small scale farming. Government minimum garanties (crop insurance schemes) are to be recommended.

224 Co-ordination Lecture for Session No. 4

Prof. D,. H. LAUDELOUT. Directeur du Laboratoire de Physico-Chimie Biologique, Universit6 Catholique de Louvain, Heverl'e-Louvain (Belgium); Membre du Conseil Scientifique de I'Institut International de la Potasse

Les aspects 6conomiques de I'introduction des engrais mindraux dans un syst~me agricole o6 its faisaient encore ddfaut sont infiniment moins simples qu'on ne pourrait le supposer au premier abord. La condition sine qua non de l'intensification de I'agriculture sur br61is ou shifting cultivation est dvidemment l'introduction des engrais mindraux et I'abandon de ]a technique qui consiste A les produire sur place par incindration de la v6gdtation naturelle. Outre le fait que cette technique est spdciale- ment peu efficace en ce qui concerne l'utilisation des sols, elle exclut A peu pros toute forme d'intensification telle que l'emploi du machinisme agricole. II est donc tr~s dif- ficile d'isoler l'effet 6conomique de l'introduction des engrais mindraux au stadc initial de l'intensification de l'agriculture. II n'en reste pas moins vrai que cette intensification n'est pas d'embl6e gdndrale et que dans beaucoup de rdgions des tropiques hu- mides le transport et ]a distribution des engrais mindraux se font suivant des techniques trds primitives. C'est la raison pour laquelle l'utilisation des engrais A tr~s haute concentration en lments fertilisants tel que par exemple le m6taphosphate d'ammonium est A examiner de prds. II semble certain que les sites o6 ]'introduction d'engrais minraux a le plus de chance de succds A long terme sont ceux o6t Ia productivitd naturelle est ddjA dlevde, puisque c'est IA que [ensemble des investissements d'intensification se rdvdlera plus rentable A long terme. La tentation est souvent forte de faire porter ]'effort d'introduction des engrais sur les sols pauvres ob I'accroissement relatif du rendement sera le plus 6levd. Toutefois le potentiel de ces sols est limit6 et leretour 6conomique de l'intensification y est souvent probl]matique. Ce dernier point est li au probldme tr~s gdndral de Ia prddiction du besoin en engrais mindral d'un sol donn6. II est 6vident que I'apport d'engrais doit atre limitd aux 6Idments dont I'effet est marqu6 tant pour des raisons psychologiques que pour des raisons dconomiques et les doses appliqu&s ne peuvent pas ddpasser le seuil des rendements ddcroissants ce qui impose une prediction non seulement quantitative mais aussi qualitative du besoin en engrais. II s'agit IA d'un probkme quasi insoluble dans [Itat actuel de nos connaissances en science du sol, une fois le stade initial de l'intensification ddpassd le problme se simplifie considdra- blement. Toutefois I'analyse pddologique doit s'inspirer de nouveaux concepts pour sortir des limitations sdvdres qui sont encore les siennes jusqu'A prdsent meme dans les cas les plus favorables.

15 225 5Lh Working Session: Educating the Farmer for theTransition from Extensive to Intensive Agriculture

Coordinator of the Session: Dr. T. Walsh, Director of the Agricul- tural InstituteDublin/Ireland ; Member of the Scientific Board of the Interna- tional Potash Institute

227 Training of Agricultural Extension Officers

6, I I5 ,f..Dircctor. f ore r *jrIna, i ), p tnr t, ,t'cnoon c,, iSc!. ] ] \'t' i, II

The need forI increased and diversified agricUlt ural production in dCeClopig CoLntries is too ,,ell knos n to need documeniation. This paper wili concern itself %viththe training of vidlage extension otficer s as a step towards the solition of this problem. fhe traimngi of extension officefs ciearlv depends upon the setling in which they %%iII weork and .1pe01 the goal which itis hoped they "'il achieve. In the short run the extension officer is expected to effct change in agricultural practice lfoa limited nu m her of crops. butin tihe Ong run it I hoped that the extension officer wilt be successful in chaig- ing the tr mer s'ati ude tokards change itel f.th us prcpa ing the ground for the over-all introduction of technological and social innovation in the rural pattern. Clearly, for these changce to be effective on a pernianet basis and to result iii genuiri improvemelt litthe total situation. purely technical changes are not stifficient. 'Fle extension otficer must generally bring about changes in the rural leadership patterns. In the light of this iew of the extension officer's role, a training program otght to be aimed at the fol loting additional broad, non-agricultural objectives: a) To prepare the prospective officer to be an effective link in ihe total process which binds the farnrnr and his problenms on the one hand to the source of information and problem solutions on the other. b) ]lo change the attitude of the prospective extenion officer toward the farmer in order that he may be moe effecti e in his at tempts to change the farmers atltiltLdes toward change itself c) To develop the leadership qualities of the prospective extension oflicer so that his training effor ts will IheInore proCIuctive.

In addition to the foregoirg non-tgricut It u rII objec iies, the trainig program for exten- yen officers described ln this paper I, based on the following lati ely ion-contro- ermal aslsumption' I Anv change, to he introduced must require minimal expenditures of money. This means that on the technological side. only inexpensie changes in practice can be recommended for the fanmiv farm it the initial stages. On the admitistrati ye side, the extension officer m st spend a maximum amount of time in the ield and a minimum amount of time in the office. 2. Existing agricultural practice in developing countries is, in the mai, very incificient. For example, sugar beet yield in a des eloping countr, may be of the order of4 tons or less per acre. sshile in a deseloped countr the %jeld may be in excess of 20 tons per 229 acre. sit h the sate pe cent of sigar. SiIIilaI yor cotton, a developi ng COLtrIy maN produce 250 kilograms per acre while tIe ie Id in a deelo ped country ma be Ii e- ce's of" 1200 ki Igra ins pCI acre. . De, pI te the general preaiing inelcnieaCes. sound agrr LituraI knowledge and some elficient falling Ilopi no couo r'. These so LrIFCCof knowIv- edgcce Ihich the extension officer may draw ipont are: a) the successful \i lage faimer Ii) the large corilcial faim rI ranch: c) the experiment station or model fai'n d) lie regional expe i, uskiallY attached to the ninistrv oragrliClLire: el tle Foreign expert. 4, Faimcrs in develiping coLiltics are relaive[N unwojphisicaetd and must see a sub- 'tantial increawse in their output as a result of an innovation if they ate to be persuadI that an Innovation is w orthxilc. I i vie\ of the assunilption of relalivC unsophistica- 'tin. ile recomirended changes n1.ust be sinple both in technique and in tie psycho- logica demands thex make. inder tie gi\en conditions the extension officer must select an innovatin in agricultural practice which is sound on technical grounds. noit demanding ofcaplital, reqluiring oLI n,Ilil al ps)Chological adaptation on the palt of the faier and one which will Mke possible a large increase in Otput. A sirIiplc examiple osLIch an innoation is the use of ross ',ceding in p lace off broadcasting. Ini order to maximize his chances olf UCCess, leI extension officer is to concen rate his efforts on a iied number of such eligible innovations. on a limited number nfcrops. and in a limited area. Onlv if successful, does he attempt to carry these changes to a ss ider area, toialcrease the nTLmber ot crops and the nILIr her of in novations. Israel has developed a training program for extension officers based tipo t heforeigo- ing des cription ofihe setting and of the role of the extension officer. Th is prograim has its roots it an Cxtlensic pCriod of rural settlement and extension work, during which 230 time e.xpcienced fariers,. not trained as extension officers, were used to alsist the ne se ttlers. ]]owNcxer. in 1956. a formal program for training extension officers ,a, set up. drawking upon the rich e perience wAhich had accuImIlated over ma' ears of agricultural dcvelopient. Graduaes of this training program hae supplied nearly allof the demand for nt ructr(ts in Israel mertthe last IO ears,. While Israel's program for ireining ete-in otlice rs from a broad which now includes It) year, ofeperience and oser I50 course-s. necessari h, had to take into account ie difTrences n backero iind betseen the Israeli extension officer-in-training and the student from abroad, the basic approach to training has remained relative un- changed. Briefly, the progriam aims to teach the student h ow to transfer knoMedecto others, to change the trainee' attitudes loward manual labor and tokard the eli- tionship , between hirmself and the village farmer, and to prepare the studentIs for leadership roles. In addition to the trainig of Israeli and foreign jIllage extension of- liccrs in I rae I. the progr am has been cart ried otil i n CtLt isC a' ' idcr spread ats Zamnia, Mexico. I ganda. ITan. Scnega. Thailand. and Brazil. That portion of tie ptogram dealing wkith the Itranfler of technica l knowledge is perhaps the most easily accomplished, and it may suflice io acquaint th e trainee with the ICC In i,Irce- tofinformation pre uly mentioned. ( ha i ge, involving psychclogia If ac- tI,. such a, the attitude tosard Manual labor and social status, are clearl molt difficult to bring about and require a period of apprenticeship in the field. Wotkig aloneside farmer s who ale also educated and cultured people helps to ovetruomt the negaive attitude towkard phssical efifit and social distance. as does the obctlvatilol , that tilestudent' Islaeli instructor is not ab.e dirtying his hatid, when inttlti'g B 0 rk ing in the held wilh a good extension officer, the trainee isable to experitnce the tangible changes which the instructor is able to bring about on his o n initiatiy in a village and thus tis acquire a more favorable attitude toward the role of etcenion officerand toward the responsibilities inherent in it. To ache' e the obiectiv es of the progr an. the trainig is d i ided into four mail part'. not seq nts tial in time, but interwoven. These are: a) learningihespecial probilcnsoftheffamnis farm: h) some theoy to support Ia) c) practical work in e.'tenion, aiccopan} ing anr experienced instructor oi his daily routines: d! prepaiationi fa plan for the trainee in advanice of his returLn to his owkn coun try

In part a) the trainee obtains a picture of the agricultural famil) unit as if is inteutated , X lthin the xvhole of the' illage and the uir uding region. le then Clearl ho to 'ep- arate the vatriol factor, of agricultural product ion from one anot her, so that a progra is , Ichange can be itnitated. lte is at all ties madeamarc that thefirst steps should be mod - est Ones. using Ihe factors e,t to Change, fionihoth the economic and psycho-social point, of %tew. The theory referred to itpar( b is consposed of to parts technical and ps cho-social In the latter categorv, the sLudent becomes acquainted vith simple sociological and pri>- cho logical ideas. SLlicien t for him to undersiand basic human motivations and TIe problems inherent in the attempt to change inchl idual and ' iflage beha' mar. Ii the tcch- sicaf part the trainee is introduced to mate ial dealing x%itlh basic probletitof agricti IT L I prodtiction and special crop, 231 IThe practical wko.rk of part c)conists of. o phases, in the Iirs t olwich the student li'es with a f*amily in a cooperative farming village, IIere he becomes acquainted > ith the filI , IagcC of, vIllage acte itie and problcns. frontn Ohe functioning ofa locaI cooperative society to the relatiotns of the' ilage toall ieagencies serving the ,illage. [is in this phase Ihat IIhe ai nce has Iirst hand exlerience in (he role of the farmer" " horm he %ill later have to serve. III the second phase. le iaine is assigned to an experienced extension officer and accoli pan1ies him as hie goes thLrough his dadv rouline In addition, th[ht Iince si- , tie the c\teniol officers wveek I}and m nthlT pograms. T%picall the trainee will ha an Opportunoity tO obsCr' the extensiOll OtfieCl %ot king Nith inetri in' illaces in 'C' cra I stages, ofde ellment -frotfullI establi'hgd to iambeginners. In parlt d) the student is reqiteld to Caluate tilesituation in iM , 11 1rlregion. kkith a viewNli'I Iowa rds finding those factors which he hin ill be able I chancc. %kithno teat financial sLppOrt and with cotnitions s the alrycidc c s. An exat iple ofsuLch a riecon mendati on i I he Lil Uip t"ll Ne' to Codairy catle so a tol increas milk yield', h r ic nt pract ice in Ih is region is to stpp I' w iter twice weekly.) Nol-agricultUral rcolllmeltilatiolls arc also made in this part of the training pirogiam: ftr example: the encouragemet of iHagers to bil Ida touth center for social and ed ucational activilies, using freel' available local materials> ith the exception of nails, which wte to be otight fol town 1 the instIUCtoF 232 By the time the student has finished the preparation of his plan he has come to realize the importance of the correct allotment of his time, most of which should be spent out in the field working with the farmers, relatively little being spent in the office. He has also come to realize that it is far better to be responsible for a smaller area, e.g. 3-4 villages, rather than 30-40, with the opportunity to actually implement plans for improvements. He also knows how important it is to work with the local leaders of the respective villages. A student's recommended project is presented to the trainees and staff for evaluation in the light of the basic assumptions upon which the training program is based and upon an appraisal of his local situation. The basic points of analysis are: I. Are the proposed changes simple? 2. Are the proposed changes feasible? 3. Are the proposed changes inexpensive? 4. Do the proposed changes represent a modest start? 5. Do the proposed changes lead to significant changes in income? Beyond the basic points outlined, the evaluation of the recommended project includes an analysisof the implementation of the project by means of a detailed work plan for the trainee. This work plan should include details of the implementation on a weekly, monthly, and yearly basis. In conclusion, it cannot be emphasized too strongly that even the best possible training program for village extension officers will not be effective at the village level if proper support from higher policy makers is lacking. The agricultural complex, consisting of farm youth, farmers and their wives, extension officers, regional directors, and staff on the national level, may be compared to a chain which is no stronger than its weakest link. When lines of communication are open,it becomes possible to obtain the teamwork and cooperation so vitally necessary for the struggle to improve living standards in the rural community.

233 The Impact of Courses for Fertilizer Technicians

T. GANS, Executive Director, Fertilizer and Chemical Development Council, Tcl-Aviv (Israel)

Since 1963 eight courses have been given to a total of 178 students from 37 countries of Asia, Africa and Latin America. The courses were sponsored by the Ministries of For- eign Affairs, Development and Agriculture and the Israel Fertilizer Industry. They were organized by The Foreign Training Department of the Ministry of Agriculture and the Fertilizer Development Council. The objective of the courses was to teach the students how to convince farmers to use fertilizers. The aim was that the graduates could formulate fertilizer recommendations under local conditions and could plan fertilizer promotion projects for groups of farmers and local technicians in country districts. The program of the course has been reviewed from one course to the next. During the lecture we shall demonstrate graphically how the program has been changed from a standard theoretical course in fertilizer use and extension methods, to a practical course with a limited objective of preparing the graduates to undertake the tasks mentioned above. The main subjects covered in the later courses were: I. Formulating theobjective of the fertilizer project. 2. Collecting the most relevant data in order to analyse the problems and find solutions. 3. Collecting information from research and other information services to help solve the problems. 4. Choosing the farmers for demonstrations. 5. Planning and laying out of the demonstrations. 6. Analysing and utilizing the demonstration in order to convince the farmers to use fertilizers. The various steps in the program are illustrated and studied both theoretically and practically. For instance the background to data collection includes the principles of soil science, the principles of nuttient uptake and fertilizer use, collection and analysis of economic data. We also teach extension methods and the theory underlying extension principles. The cultivation of crops which are grown in the country and can be seen in the field are studied. The forms of study include lectures, laboratories, field days, demonstrations,joint meetings with agricultural committees and planning a program that can be applied in their own country. The main benefits the students take home with them can be summarized as follows: 1. The will to work. The example of giving a hand in carrying out the project by the teachers and technicians in the field, brings participants from mere talkers to doers. 234 2. The confidence that they can plan and carry out a small project on their own initiative. 3. Where to look for the information they need in their own country. 4. The benefit of cooperation with their fellow workers and other institutions working in similar lines. 5. A reference file and books about all the subjects covered. Full transcripts of lectures are given to all students. In addition valuable literature on the subject is contributed by the various fertilizer associations. 6. A plan of operation for a fertilizer extension program which they can adapt to their own conditions. 7. The organization of an efficient fertilizer field service, that exists in this country and that can serve as an ultimate example for organizing a fertilizer extension service. 8. The making of friends with colleagues from other developing countries and learning how they go about solving similar problems. 9. Reporting to their own authorities about what they have learnt and the making of recommendations to fit their local conditions.

The impact of the courses is limited by the difficulties the graduates encounter on their return home. Quite a number of them see the farmer for the first time and are faced with a man with whom it is difficult to find acommon language. The supervisors of the graduates quite often dampen the enthusiasm of the returning student by not letting him use his initiative or not assisting him to find the tools he needs. In other cases the mere fact that the student has participated in a course in a foreign country propels him into a higher position, where he does not have the direct contacts with the farmers and without having had a chance to adapt and practise what he has learnt. In some cases they can not obtain the cooperation of the allied institutions or even the other branches in their own organizations to put through a fertilizer project. The main impact of the courses can be measured by the number of students who have carried out their own projects. All the graduates working in the field plan their projects in such a way that the information reaches the farmers. A number of the students are putting on demonstrations to large and small groups of farmers and some of those working in the research stations have organized successful field days around fertilizer experiments. We are in contact with about two thirds of the students who have attended the courses. We can safely say that they all work. In many cases the confidence they have gained here puts them in leading positions. A number of graduates use our offices as a clearing house for their technical problems. We have sent a lot of technical information on specific subjects, which has been collected to a large extent from other institutions, both local and foreign who cooperate with us. We have sent improved seeds and requested our contacts in their own countries to contribute fertilizers, pesticides and simple tools, so that the graduates could lay out their demonstrations. We have supplied the students with advice on subjects outside our field; for example the design for a sprinkler irrigation system and the organization of small soil laboratories, etc. All graduates are being supplied with the publications issued by The Frtilizer Council, the Ministry of Agriculture and the Foreign Fertilizer Association. 235 Conclusions

I. We have trained individuals and quite a number of them have made an impact in their own way in their immediate surroundings. 2. Wedid not make a visual contribution to the expansion of thefertilizer market in anyone of the countries. This was mainlycaused by selecting two or three students from every country instead of taking 25 students from one country. 3. As far as extension and fertilizer use is concerned the best results were received by those students working in the frame of a fertilizer project or by the F.A.O., The F. F. H. C., Local Soil Institutes, extension services of private firms. 4. The students coming from agricultural research stations have found a new purpose for their work. They are actually seeing to it that the results reach the farmers and at times they even translate the results into a language understandable to the farmers. 5. We started the courses in 1963 for field technicians and we found that, eventhough we succeeded to do something for the individuals who participated in the course, we did not receive an echo in their own country. In latercourses we limited the participation to university graduates, who hold super- visory positions, in order to spread the knowledge and the experience that the participants take home. Through this latter group the impact has become greater. 6. We have passed on our knowledge to a small number of people in every one of the 37 countries. The largest group is concentrated in han where 22 graduates are working. The smallest groups are two graduates per country. In all of these countries we have formed nuclei on which we can build a practical course in fertilizer extension in their own countries. In those countries where a framework for fertilizer extension exists, we could make the greatest impact with short, on t he spot courses for field technicians. The program would include adapting our extension methods to the local conditions. In these courses the graduates from the courses held here in Israel would participate actively.

236 Irrigation and Fertilizer Extension

Dr. JOSEF Noy, Rupin Institute, Central Lab. Emek Hefer (Israel)

1. The needfor prudent application of agriculturalinputs

Farmers are obtaining increasingly higher yields through the integrated use of selected seeds, irrigation water, chemical fertilizers, pesticides and other materials. Application of these means of production, or inputs in the language of the economists, requires prior investment by the farmer in agricultural machinery and irrigation systems and a flow of working capital for input purchases. On the other hand, indiscriminate application of these inputs will not bring in the optimum economic yield or even the highest yield and hence input mixes must be rationalized if the farmer is to obtain the full return for his investment. Moreover, exaggerated use of water or fertilizers may have an adverse effect on plant growth, may cause a deterioration in soil structure, evidenced by poor aeration and low permeability. Salts that cannot be effectively leached may accumulate, and even assuming that the soil is responsive to amelioration practices, additional costs will be in- curred for leaching and chemical amendments. These hazards are likely to occur, in particular, in the finer textured soils. Maintenance of a satisfactory soil-plant environment is therefore dependent on prudent employment of production inputs. However, the farmer can no longer rely, as in the old days, solely on his own experience, since the dynamic nature of agriculture, thecomplex- ity of modern farming and the numerous fields of activity calling for expert knowledge, require that the farmer be guided in applying newly developed practices or inputs to his own particular conditions in order that the selected seed of higher potential or greater resistance to disease, the more efficient fertilizers, or the improved irrigation methods be used to the fullest advantage.

2. The functions of agriculturalextension services

This guidance is generally provided through governmental or public agricultural extension services, structured and staffed to offer advice in all the required fields of agriculture, such as soil cultivation and seed bed preparation, choice of seeds, irrigation practices and methods, fertilizers and plant protection materials. The extension set up must also provide laboratory facilities forsoil, plant and water analysis to determine optimum irrigation and fertilizer practices, and to detect the presence of salts or toxic elements and mineral deficiencies in the soil. Further, it must provide personnel capable of interpret- 237 ing the results of these analyses to the farmer, since this interpretation will often be beyond the farmer's comprehension, and translating these results into recommendations for fertilizer and other soil management practices. True, these services are at times offered by commercial laboratories, though here a warning must be uttered that the recommendations put out by such laboratories are generally of a standardized nature and hence are not ielated to the individual farmer's plot. Performance of such analyses by governmental agencies and the drafting of recommendations translating these results into the quantitative terms of agricultural inputs is therefore preferable. For the reasons given above, trained extension service personnel to disseminate information to the farmers is required. These persons must themselves undergo periodic re- fresher courses to bring them up to date in recent advances, and must be guided in their day to day activities by the senior staff members of the Service. The latter also serve as in- termediaries between the research station and the field, translating research conclusions into everyday practice and instructing the extension service personnel in the findings of the experimental stations.

3. The Soil and Irrigation Field Service in Israel

The Soil and Irrigation Field Service, a unit of the Extension Services of the Ministry of Agriculture of Israel, provides guidance to the farmers in soils and soil amelioration, carries out tests to determine the suitability of soils for orchard plantings, advises on fertilizer requirements, follows up irrigation practices, methods and equipment, and puts forward recommendations for the irrigation of field crops, vegetables, forage crops and orchards. The service is organized on a regional basis, each region with its own staff and laboratory. Seventeen such regional services and laboratories exist at present, but it is likely that a number of laboratories will be combined in the near future to reduce the number to ten. The annual budget for the operation of this service is contributed jointly by the regional councils (who tax the farmers accordingly) and by the Ministry of Agri- culture. The regional laboratories areequipped to carry out all the required physical and chemical analyses of soils, plants and water. In 1967 the laboratories reached a total output of 340,000 analyses. The personnel of the service maintain direct contact with the farmers in each region and offer the services described in the following:

3.1 Irrigation,nethods and systems

Advise on irrigation system design, method of operation and improvements to the existing system. This advice is offered on the basis of equipment tests and recommendations issued by the Service on various items of equipment.

3.2 Irrigationpractices

The amount of water to apply at each irrigation and the frequency of irrigation, have been determined for all the important crops grown in Israel for a wide range of conditions under experiments or field trials and observations carried out with the participation of Extension Service personnel. In the trials or observations, soil moisture stress or 238 moisture content is determined by neutron scatterers or by gravimetric methods. These experiments or trials are then followed up in commercial sized fields. Soil samples are measured for moisture content in the regional laboratory and recommendations issued as to when and how much to irrigate.

3.3 Soilorchardcriteria

Soil profiles are examined in the field and soil properties in the laboratory for plots in which it is planned to raise orchards such as citrus, deciduous fruits and avocados. Spe- cial attention is given in these surveys to the properties of the subsoil since these often prove to be a limiting factor in productivity in the mature years of tree life when the roots reach their full length. Horticultural and soil specialists have set up criteria for orchard soils and areas sampled for prospective sampling are either approved or rejected on the basis of these criteria.

3.4 Soil management

Soils are often found to be of limited use owing to the presence of a hardpan which reduces soil permeability and increases hazards of inadequate drainage. This situation may be aggravated still further by poor soil management practices with the result that the salt build-up in the root zone may become serious. Extension service personnel have amassed considerable experience in assessing soil structure, permeability and salinity on the basis of field surveys and laboratory observations, and issue recommendations to the amelioration measures required, such as leaching and the addition of chemical amendments.

3.5 Fertilizerrecommendations

The Service has formulated recommendations for fertilizer applications on the basis of research studies carried out in other countries and on the basis of results obtained in local trials. Soil and plant analyses are employed to regulate applications according to current fertility levels. The demand for soil and plant analyses has been increasing in the last four years. Soil tests are carried out to assess N-P-K-levels for unirrigated wheat and irrigated cotton, peanuts, bananas, tomatoes and of late - greenhouse crops, especially roses. Fertilizer applications are recommended by regional advisers according to criteria set by a professional committee consisting of Extension Service specialists and research workers. In many cases, salinity levels are also determined and irrigation applications modified if necessary. Leaf analyses are employed in such as apple, avocado and citrus orchards and also in vineyards. Leaf samples are collected once a year, in the season for which the content of minerals is known. Both the sampling of leaves and the formulated fertilizer recommendations are done by regional advisers. All information iscollected on deficiencies and fertilizers applied, as well as other information on soils and water of the orchard. This information is recorded and analysed by computer to determine the relationships between the nutrient levels in the leaves and the various crop and environmental conditions. 239 4. Professional coordination

Specialists in the various disciplines mentioned function at the professional centre of the Field Service, collecting the available information and directing regional advisers. A central laboratory operates at this centre; its functions are to introduce new analytical methods and laboratory equipment, to standardize the methods employed in the regional laboratories and to supervise their performance. Some of the samples are transferred from the regional to the central laboratory after proper preparation, since better equipment such as an auto-analyser and an atomic absorption flame photometer are available at this laboratory. The Specialists of the Service also maintain close contact with the various departments of the Volcani Institute of Agricultural Research and take part in experiments, surveys and observations performed in the field by the regional advisers in conjunction with scientists of the Volcani Institute. The purpose of these experiments is to obtain additional data on irrigation and fertilizer regimes. One special study is at present being made, also using a computer, namely to assess the effect of salinity on irrigated citt us, avocado and deciduous fruit trees. Computer services are also employed in leaf analyses for fertilizer recommendations in citrus, avocado and apple orchards.

5. Conclusion

It is difficult to assess the benefit of the Soil and Irrigation Field Service. One indicator is the economy of water use achieved as evidenced by the following. With the aid of close follow up in cotton fields, use of soil moisture tests and phenological observations, it has been possible to reduce water application in thisciop from 5000 to 6000 m 3/ha to 3000 to 3500 m3/ha in the period of i 956 to 1965, while at the same time reducing the number of irrigations per season from 6-8 to 3 or 4. This was achieved without any loss in yield. Rather the opposite is true, the yield of coton continued to climb in the period of 1956 to 1965 reaching an average of 1280 kg lint per hectare.

240 Discussion, Session No. 5

Mr. T. Gans (Tel Aviv/Israel): Concerning Dr. Walsh's remarks that our extension activities have to be based more on profitability and analysed business-wise, I should like to point out that we are teaching the participants in our courses the elements of economic analysis. The graduates have to be in a position to calculate the production expenses and the profitability of any results the farmer attains from a technological change. We also teach them to use this tool in planning extension projects.

Mr. P. Martin-Prdvel (Paris/France): I would like to cite an example of a particular case of extension. In Ivory Coast, a pineapple cannery has stopped its own planting program (stabilized at 17,000 metric tons a year) and developed an increasing program of production by a lot of small African farmers (actually about 45,000 metric tons a year, projected 100,000 tons). These hundreds of little farms are scattered until 100 km (60 miles) around the factory, which has set in place its own network of extension officers, each one visiting continuously the sector to which he is devoted. This mention-worth case of close association between European modem capitalism and African traditional farming is successful owing to two reasons: 1) People of the Research Station do not always wait for the visit of the cannery's agronomists, but go and visit them several times in the year, doing themselves the first step of extension. 2) Association between farmers and factory includes together advices and furniture of planting material and fertilizers, whose price is not paid in advance by the owners but retained on the sale price of the harvest.

Dr. G. Kemmnier (Hannover/Federal Republic of Germany): Concerning extensionwork: In addition to the example of pineapple cultivators in the Ivory Coast I should like to mention what I have observed in Japan. As Mr. Hase- gawa will confirm, in Japan there are about 6 million farmers, served by some 10,000 local advisors. These extension workers are trained in schools located at the local experiment stations. But when they start to work they have first to get in touch with high-class farmers in order to learn the latest practical advances and to coordinate

16 241 them with the theoretical knowledge obtained during the training course. Only when they are able to combine the theoretical with the practical aspect, they will be really successful extension workers. Also in the course of their further activity they are continuing close contact with the village study groups of advanced farmers in order to convey their results to the less advanced cultivators who are actually in need of advice.

242 Co-ordination Lecture for Session No. 5

Dr. TH. WALSH, Director of The Agricultural Institute, Dublin (Ireland)

Taking into account the subject matter of this Colloquium, the contributions at this Session concerning the education of the farmer for the transition from extensive to intensive agriculture, had a special significance. In the opening address of the meeting, Prof.Arnon drew attention to the manner in which Israeli agriculture had developed. We saw that against the background of an age old subsistence agricultural environment, settlers had been introduced. Many of these were either ill equipped or not equipped at all with agricultural know-how and certainly not with modern techniques. Through the use of knowledge from research, through systematic training and development, using all possible resources, a modern efficient agriculture had resulted. On our tours, we saw ample evidence of this. Most of theother sessionsofthis meeting were primarily concerned with research. We had here a session which was mainly concerned with seeing how this research could best be translated into practice, a subject which under any system of agriculture must increasingly occupy the attention of everyone. It is not proposed to discuss at length the subject matter of the different papers and other contributions presented. Director Fradkin in his paper on the training of agricultural extension officers touched the kernel of the whole subject of training when he stressed that in the long run, it was hoped that one of the primary functions of the extension officer, would be to change the farmers' attitude towards change itself. The role of the extension officer in bringing about changes in rural leadership patterns was also stressed. Indeed it emerged from Director Fradkin's concept that what might loosely be termed non-agricultural objectives in training, are at least of equal if not of more importance than training in technology. Anyone who has been confronted by this problem will certainly agree with him. Likewise his contention that there are few countries which have not important sources or knowledge available whether it be the successful farmer, the experimental farm or the agricultural adviser, is readily acceptable as is also his view that new techniques must be simple, understandable and must have an economic significance while meeting social goals. Dr.Zuckerman's paper setting out the teaching and communication methods used at the Rupin Instute is well worth study by all concerned in this field. Here, the behavioural sciences, an understanding of how to change attitudes and, the socio-psycho- logical approach are shown to be the tools of modern communication technology. There is little doubt that we are fast approaching the time when human behavioural factors can be more and more quantified and in these circumstances the computer, as 243 stressed by the speaker, will play an important role. We see the spectrum of development as outlined, beginning with awareness coming from technical knowledge, interest created by problems and needs through a continuum of evaluation and trial to the process of adoption where attitudinal factors are all important.

The content of the paper presented by Director Gans becomes of very immediate interest to those concerned with fertilizer use in countries in course of development. Here, however, we see again re-echoed the principles which were set out by the two first speakers, the creation of motivation, the role of change agents themselves, e.g., advisers, followed by the development and use of specific extension plans. There is little doubt that the programme of training outlined will play a very important part in the future overall development of agriculture in these developing countries.

Dr. Noy showed were the more scientific inputs of knowledge fit into the extension pattern and rightly stressed the services and technical knowledge which must be available. It was obvious from his lecture that many major gaps remain, not necessarily in the strictly research field itself but in the developmental and extension research fields to which attention must be given if the overall programme is to be effective. There is scarcely anyone who will disagree with Dr. Noy's contention that extension services must be adequately supported by highly trained specialists and sophisticated laboratory techniques, that indeed it is difficult to distinguish between research, development and extension and that the more these different activities are integrated organisa- tionally, the more successful will be the process of transfer of research results from the laboratory to the farmer in the field. In the various additional contributions at this session, these principles were reiterated by other speakers. It was shown that there is little doubt that the various matters raised during the session provide food for thought on the part of all those engaged in the research field. In an environment where research is being increasingly accepted as a basic tool in economic and social development, the question of attitudes to change especially dominated the thinking of those present. The implications of the changes which are required when in transition from a subsistence type 'market surplus' eco- ncmy to a 'market oriented' one in relation to the production processes were clearly shown. The question as to how to effect required changes in the most efficient manner becomes of special importance under such circumstances. In the first place, there must obviously be a realisation, and this was clear from the discussions, that change agents, - and there are a great many of these - from the good farmer to the research worker and the different ccmmunications media, must in their work concentrate on those factors which can be changed. This has not always been so in the past. These factors must of course be systematically identified and if possible quantified. It also clearly emerged that research in the behavioural sciences must increasingly be the concern of agricultural research organisations, demanding equal if not more concentration of effort as the conventional subjects, if the products of research are to reach and meet the needs of those concerned with the complex of agricultural industries, farmer, manufacturer, processor, sales agent, merchandiser and others. All these users involve the use of different communication techniques. It is clear that modern communication, information and extension media have a vital role to play. Increas- ingly, change must be based on facts produced by systematic mission-oriented research. 244 It also emerged from this session that in the future, the users of research will require that the different research components be synthesized into usable systems before application either on the farm or in the processing plant. Finally, both at this session and throughout the meeting as a whole, the great social implications of research and extension and the way in which these tools were being used to develop the rural areas of Israel, could not but impress all those who participated in this meeting.

245 Agricultural Research and Fertilizer Use in Israel

Lectures held during technical excursions

247 Problems of Plant Nutrition and Fertilizer Use on Huleh Muck Soils

Dr. M. GISKIN, Soil Science Laboratory, Technion Research and Development Foundation, Haifa (Israel) A. MAJDAN, Faculty of Agricultural Engineering, Technion, Haifa (Israel)

1. Introduction

The largest part of the organic soils of Israel are found in the Hulch Valley. Until 1956 these soils were under water and the region was a breeding place for malaria. The lake and adjoining swamp area was formed due to the narrowing, by volcanic activity, of the natural outlet for the Jordan waters. By widening the natural outlet and by subsequent drainage of the swamp and part of Lake Huleh, approximately 4000 hectares of organic soils weje available for agricultural purposes. The soils are classified as low moor. The pH is generally about 7-7.5, but in some areas it is found to be 5.5-6.0. The organic matter content ranges roughly between 20 and 80 % with increases in the inorganic fraction as one goes from thecenterof the old lake and swamp area toward their perimeter. Regardless of the variability in organic matter contents two specific problems are common to all the soils. These are:

I. A high CaSO 4.2H 2O content of the soil solution. 2. A high rate of decomposition of the organic matter. Plant nutrition considerations and fertilizer practices will be governed by these two factors.

2. The soil solution

Crop yields on these soils have not been up to expectation. Soil analyses revealed that a salinity problem exists. Electrical conductivity measurements on the soil solution range between 3 and 20 mmohs/cm. The principle causes for these values are the high CaSO4 and NO; contents of the soil solution. The latter is due to the high rate of decomposition of the organic matter. In order to increase crop yields it is necessary to lower the salt content of the soil solution. Field and laboratory studies have shown that the NO; can be removed by normal leaching practices. These soils contain up to 45 g/kg soil of CaSO4. 2H20. Because of the low solubility of gypsum (2.4 g/l), its removal necessitates high amounts of water (at least ten times that required to remove NO). This is not economical. In addition, such removal results in short range benefits because of the supplement cf new salts through de- 249 composition. Therefore, we are compelled to apply fertilizers to a soil solution saturated with respect to CaSO 4.2H 20.

3. Decomposition of organic matter

Subsidence is a phenomenon generally occurring on organic soils; including those of the Huleh Valley. The rate of subsidence measured was found to average approximately 10 cm/year [J0]. It was found, in our laboratory, that this was due primarily to the decomposition of the muck [1). The rate of decomposition is dependent on temperature and water content and under laboratory conditions nitrate formation was between 7and 19 ppm NO/day. These results concurr with field results which showed that nitrates may accumulate, in the upper 10 cm of soil, up to 4500 ppm NO; per year. During the decomposition study, the rate of release of potassium was followed for eight weeks and no detectable quantity was found. This supports the findings of Karfnel[7].

4. Problems of N-, P-, K-fertilization

Let us discuss N-, P- or K-fertilization individually in light of the special problems involved.

4.1 Nitrogen

Nitrogen fertilization of the Hutch muck is superfluous because its high rate of decomposition results in an adequate supply of NO. A greenhouse experiment, in which Huleh muck had been leached with 500 m '/hectare prior to potting, showed no response to applied N and N-applications even led to yield decrease [4]. Other investigators have also reported no response to applied N [5].

4.2 Phosphorus

The response of organic soils to phosphatic fertilization is a well known fact. Even soils showing no deficiency in phosphate will require an addition of phosphate at planting time [9]. The relatively high pH and high calcium content of the Huleh muck soils decrease the availability of phosphates. Accordingly, response to phosphatic fertilization was found both in field and greenhouse studies. The test crops were tomato, alfalfa and millet [4]. Field observations have shown that responses to applied phosphate increase as the lag time between leaching and the seeding of crops decreases. This may indicate that irrigation waters leach phosphates. Such effects have already been reported [6]. Decomposi- tion of the Huleh soils does not release phosphates [7] whereas decomposition of organic soils increases the soluble iron and aluminium contents [3]. Larsen [8] found that phosphate availability is related to the sesquioxide content of organic soils. Therefore, it is possible that a part of the applied phosphates may become unavailable for plant growth due to the high rate of decomposition of the Huleh muck soils. It is feasible that 250 during the growth period there is competition for available phosphates between the plant and the sesquioxides formed through decomposition. Until the amount of phosphates and sesquioxides released are quantitatively determined, it'is difficult to establish whether the phosphates are leached, fixed or both.

4.3 Potassium

Analyses of the Hulch muck soils frequently show a deficiency in available potassium. This fact is explainable on the basis of cation exchange between calcium and potassium. The calcium concentration of the soil solution is at least 1.4 X l- 2N (normality of saturated CaSO4 . 2H 20) and as divalent cations are adsorbed more than univalent ones; the molar fraction of exchangeable potassium is negligible. Because of these facts added potassium remains mainly in the soil solution and is subject to movement by water. Results of an experiment carried out in our laboratory with soil columns showed that distilled water is incapable of leaching potassium whereas a saturated solution of CaSO4 . 2H 20 removes all applied potassium [2]. No specific fixation of potassium was observed. Potassium deficiencies observed on Huleh soils are a result of the applied potassium being easily leached and this prevents the soil from building up a reserve supply. As decomposition of muck does not increase the potassium content of the solution, the only way to maintain an adequate potassium level for plant growth is by several small applications through-out the growing season. Several years ago fertilizer experiments with cotton resulted in only occasional responses to applied potassium although soil tests had been low. Sometimes the application of 1500 kg KCI per hectare did not increase yields and the plants showed the typical signs of potash deficiency. These observations are explainable today if we remember that the usual practice was to apply the potassium prior to the winter rains. Field and greenhouse experiments, with both controlled fertilizer application and irrigation, have shown responses to potassium [4].

5. Soil testing

The standards for fertilizer recommendations are based, in general, on the correlation between yield and soil tests. Whereas, this may hold for inorganic soils, one should be wary in applying these same standards to organic soils. Organic soils are highly dynamic and soil tests for inorganic soils do not take into account the products of decomposition that are continually being formed. The hydraulic conductivity of muck soils exaggerates the effects of leaching and results in ions in solution beingextremely mobile. Under our conditions, the high calcium concentration of the solution creates a situation in which the reserves of potassium and other cations are small. Soil tests which indicate the situation at any given time can not indicate the amounts of nutrients available to the plant throughout its growth period. Another point to consider is that present soil tests may be invalid due to the interaction between the chemicals used and the organic matter. The established procedures for phosphate determinations may therefore be unacceptable on organic soils. Our present soil tests also do not account for excesses of othercompounds being present such as NO; and CaSO,. 2H O. 251 The interpretation of results obtained by the Woodruff test, when the soil solution is CaSO4 . 2H 2O saturated, is doubtful. This test for potassium does not give us a basis for recommendations on the muck soils of the Huleh.

Literature cited

I. Avnimelech Y. et al.: Accumulation of nitrates in Huleh peat (in Hebrew). Report of the Fertiliz- er Development and Soil Fertility Laboratory, Technion (1968). 2. Avnimelech Y. et al: Management of potassium in peat soils (in Hebrew). Hasadeh, Vol. 48. 1346-1347(1968). 3. Dawson i.E.: Advances in Agronomy, Vol. 8, 337-402. Academic Press, Inc. N.Y. (1956). 4. Giskin M.: Fertilizer experiments on peat soils in the Hutch Valley (in Hebrew). Report of the Fertilizer Development and Soil Fertility Laboratory, Technion (1968). 5. Guzman V.L. et al.: Sweet corn production on the organic and sandy soils of South Florida. Bull. 714, Instit. Food-Agric. Sci. Univ. of Florida (1967). 6. Haveraaen 0. and Steenberg K.: Leaching of nutrients from peat soil. Some results by use of ra- dioactive isotopes. Scientific Report Agric. Coll. Norway, Vol. 46, 1-25 (1967). 7. Karmel L.: The value of Hulch muck as an organic manure (in Hebrew)- Hasadeh, Vol. 29. (1949). 8. Larsen J.E. et al.: Studies on the leaching of applied labeled phosphorus in organic soils. Soil Sci. Soc. Amer. Proc. 20. 522-526 (1958). 9. Shickluna J. C. and Lucas R.E_: The pH, phosphorus, potassium, calcium and magnesium status of organic soils in Michigan. Quart. Bull. Mich. Agric. Exper. Sta. Vol. 45.417-425 (1963). 10. Shoham D. and Levine I.: Subsidence in the reclaimed swamp area of Israel. Israel Jour. Agric. Res. Vol. 18.15-18 (1967).

252 Nitrogen Fertilization of Wheat in Israel*

Dr. Z. KARCn, Volcani Institute of Agricullural Research, Newe Ya'ar Experiment Station (Israel)

The main cereal crop in Israel is wheat, of which about 90,000 hectares are sown annually. The crop iscomposed mainly of spring wheat varieties, grown during the rainy winter season. The usual seeding time is during November, germination usually takes place from early to mid-December, and the crop is harvested in May. Although the rainy season lasts from November to March or even April, precipitation is concentrated during theperiod from late December through February. Divergence in the amount of rainfall in different parts of thecountry is quite large. (Table 1). Average annual rainfall in the southern part of the country, which comprises about 75 % of the area planted to wheat, ranges from 200 to 350 mm compared to 400 to 650 mm in the northern region. Regardless of the growing region, the post anthesis period (end of March through April) is relatively devoid of rain. The amount of annual rainfall and the pattern of its monthly distribution (Table 1) points out that moisture is the main limiting factor in small grain culture in Israel. Therefore, moisture deserves prime consideration when designing the nitrogen fertilization practices under the semi-arid conditions of Israel.

Table 1. Annual rainfall and its monthly distribution in several wheat-growing regions in Israel (Av- erage for 1959-1968)

Region September October November December January Days mm Days mm Days mm Days mm Days mm

Central Negev ...... 0.3 0.4 1.5 9.0 3.5 23.0 4.7 37.8 6.0 51.3 Eastern Negev ...... 0.6 0.8 2.5 13.9 4.5 26.6 6.4 49.2 7.5 77.7 Jerusalem foothills ...... 0.1 0.2 2.8 18.1 5.7 51.3 8.5 135.0 10.5 116.2 Western Jezrcel valley ...... 0.5 2.3 3.4 27.3 5.4 69.7 11.4 157.3 11.9 137.7 Eastern Galilee ...... 2.5 5.5 4.0 14.7 6.2 56.5 10.0 118.0 10.6 101.3 Region February March April May Total Days mm Days mm Days mm Days mm Days mm Central Negev ...... 5.7 20.4 4.4 21.5 1.2 10.4 0.3 0.2 27.6 174.1 Eastern Negev ...... 8.0 57.0 6.5 39.6 1.4 9.4 1.2 3.7 38.6 277.9 Jerusalem foothills ...... 8.9 81.4 7.1 57.4 3.1 14.6 1.0 6.0 47.7 480.2 Western Jezreel valley ...... 13.0 113.0 9.0 62.3 3.5 23.5 1.8 12.1 60.4 608.5 Eastern Galilee ...... 10.3 95.2 7.8 59.0 4.2 16.7 3.1 24.3 58.7 491.2

Contribution from the Volcani Institute of Agricultural Research, Israel. Series No. 1462-E 1969. 253 I. General considerations of nitrogen fertilization In the present marketing situation in Israel, there is no premium paid for quality or protein content of the grain, apart from external kernel characteristics such as color or size. Consequently, it pays the Israeli farmer to produce as much grain per hectare as possible. The eventual amount of grain harvested is determined by the number of ears per unit area and by ear weight. The latter factor is determined by the number of kernels per ear and by kernel weight. Number of ears per unit area depends on the number of plants and their ability to produce tillers. An average crop of wheat is traditionally seeded at a population ranging between 2,000,000 and 3,000,000 plants/hectare. The amount of tillering in this crop can be promoted by a generous early dressing of nitrogen, especially, when plant population is thin. Nitrogen dressing promoting tillering, with a consequent adequate number of ears per unit area, is effective probably during the 30 to 40 days following germination (Table 2). The number of spikelets per ear, i.e., the number of grains per ear, is likewise determined at a relatively early stage of growth. Field observations based on extensive longi- tudinal sectioning of wheat culms revealed that ear primordials initiated about 50-60 days following germination, depending mostly on prevailing temperatures. Nitrogen deficiency at this stage of growth might depress ear length and reduce the number of kernels. Kernel size depends on plant longevity during the post anthesis period. Generally, however, plant longevity under semi-arid conditions depends on available moisture resources rather than on amount of nitrogen. Methods of nitrogen dressing can exert a profound effect on the amount of moisture conserved for grain formation. Excessive nitrogen dressing prior to seeding or as an early top dressing results in a luxurious vegetative development which, in addition to lodging, can cause an excessive depletion of the moisture resources, resulting in shrivelled kernels. Needed, then, is a method of dressing with a controlled promotion of tillering and photosynthesizing leaf area and which still relinquishes enough soil moisture for grain formation and maturation. Table 2. Various stages of development in the life cycle of wheat in Israel, and their corresponding dates of occurrence Growth stage Date of occurrence Germination 20 November to 15 December Tillering 15 December to 10 January Ear initiation 15 January to 10 February Flowering 10 March to 20 March Physiological maturation 25 April to 15 May

2. Materials and Methods. With this as the goal, a series of experiments was carried out during 1961-1964. Trials included five nitrogen dressing methods, as follows: A. Basic dressing The entire seasonal ration was applied prior to seeding. B. 1/ Basic + 1/2 Top I Half of the seasonal ration was applied prior to seeding, and the remainder at tillering. Karchi Z., Rudich Y., Solomon D., and Y-Saa-Shalom (1964). Nitrogen Fertilization of Spring Wheat. Hassadeh, 44:541-547; 683-687 (In Hebrew). 254 C. 1/2 Basic + 1/2 Top 11 Half of the seasonal ration was applied prior to seeding, and the remainder at ear initiation. D. 1/ Top I + 2 Top II Half of the seasonal ration was applied at tillering, and the remainder at ear initiation (no nitrogen was applied prior to seeding). E. '/3 Basic + 1/3 One third of the seasonal ration was applied prior to Top I + '/, Top II seeding, one third at tillering, and one third at ear initiation. Each of the five dressing methods was tested at three rates of nitrogen: 63.0, 94.0 and 126.0 kg/hectare. All trials were randomized blocks with four replications, conducted in commercial fields in the central and northern regions of the country. Trials were cou- ducted under the two prevailing rotation systems commonly used under dryland conditions: in the first, wheat follows a leguminous crop usually cut for hay, and in the second, wheat follows a grain sorghum crop. To eliminate varietal differences the same tester, Florence Aurore 8193, a variety grown commercially throughout the country, was used in all trials. Throughout this paper, the various dressing methods will be referred to by their alphabetical designations.

2.1 Rates of nitrogen dressing

The data in Table 3 demonstrate that under semi-arid conditions, the rate of fertilization above a certain minimal level is not a factor in yield increase. Regardless of the preceding crop, legume or sorghum, there was a slight yield increase above the rate of 63.0kg N/ha. However, the results do point out that yield response is determined by crop sequence. When grown under dryland conditions, a sorghum crop is considered to be hard on the soil for several reasons: as a deep-rooted summer crop it causes an almost complete exhaustion of soil moisture reserves; its root remnants are high in carbohydrate content; and a large proportion of the stubble is left in the ground at harvest and incorporated into the soil. Under dryland conditions, wheat follows sorghum mainly in the northern, wetter part of the wheat-growing area. The average yield of the control plots for the seven experiments conducted on sorghum, was 2654 kg/ha. The range of control yields of the individual experiments was 1710 to 4040 kg/ha, depending primarily on the amount and distribution of the annual rainfall, but also on the inherent fertility of the field. The highest average yields of the control plots, 3610 and 4040 kg/ha, were obtained in 1963/64 in locations characterized by having more than 50% of the total rainfall in the latter part of the season, from February through April. Under sorghum rotation, rates of nitrogen application ranging from 63.to 126.0 kg/ha brought about a corresponding insignificant yield increase of 22.1 to 26.5 % over the control yield. Table 3. Effect of three rates of nitrogen on the yield of wheat under two systems of rotation (average of nine experiments on legume and seven experiments on sorghum) Rotation Yield LSD Control In % of control (P=0.05) (in kg/ha 63.0 94.0 126.0 kg N/ha

Following legumes ...... 3012.0 104.9 105.2 104.9 3.0% Following sorghum ...... 2654.0 122.1 126.5 126.2 16.5%

255 A leguminous hay crop promotes different soil conditions: I) The crop is grown during the winter and cut to hay relatively early in the spring, leaving a sizeable moisture reserve in the soil. 2) The green part of the crop is completely removed from the soil by modern farm equipment. 3) Roots enrich the soil nitrogen content. 4) Residual soil moisture has a favorable effect, under the prevailing high summer temperatures, on continuous biological activity, resulting in a probable increase of soil fertility. Following the leguminous crop, yields of non-fertilized plots averaged, for nine experiments, 3012 kg/ha (Table 3). The range in yield was from 2160 to 5120 kg/ha, depending mostly on the amount and distribution of the annual rainfall. Yield increased by only 104.9 to 105.2y over the non-fertilized treatment as a result of nitrogen dressings ranging from 63.0 to 126.0 kg/ha.

2.2 Methods of dressing

The data in Table 4 point out that the method of nitrogen dressing is probably a major factor in bringing about yield increase. Under both the legume and sorghum rotations, lowest yield increases, 101.2 and 118.6%, respectively, were achieved by applying the total seasonal nitrogen ration prior to seeding. However, the yield response, as compared to control, was highest under legume and sorghum rotations, 110.5 and 130.6%, respectively, when the seasonal ration was split equally between early and late topdressings, without any basic nitrogen application. There is a striking similarity between legume and sorghum rotations in the relative yield response to the dressing methods over the range of nitrogen rates tested (Figures I and2). The application of nitrogen in equal amounts as early and late top dressings (method D) resulted in the highest yield returns regardless of the nitrogen rate or type of rotation.

Table 4. Effect of five methods of nitrogen dressing on the yield of wheat under two systems of rotation (average from nine experiments on legume a-nd seven on sorghum)

Method of Yield (in %of Control)- Dressing Legume Sorghum A 101.2 118.6 B 104.2 119.8 C 104.5 128.3 D 110.5 130.6 E 104.6 127.3 LSD P = 0.05 3.0% 16.5%

* Yield ofcontrol (in kg/ha): following legumes, 3012; following sorghum, 2654.

On the other hand, a pre-seeding application of the whole nitrogen ration (method A) resulted in the lowest yield response regardless of nitrogen rate or type of rotation. The effects of the remaining dressing methods on yield increase were related to the proportion of nitrogen applied at early or late season, especially under sorghum rotation. Thus, method C, with 50 % of the ration given as a late top dressing, exceeded method E in its effect on yield increase, especially at the highest nitrogen rate (Figure 2). 256 E 115.0 --

zD -* Do"*.....o-o C-° ZG110.0 - o- .. -o--C 8 -......

aA c-o _105.0 o.>.-. .----... -o C o. .... LSD O.05

100.0 3012.0 Kg/ha

63-0 94J 126.0 Rote of N in Kg/ho Figure 1. Yield response to five dressing methods at three nitrogen rates of a wheat crop under legume rotation (as percentage of non-fertilized treatment; average from nine experiments, 1962-1964).

135.0

130 .0 - . . . ..

.125.0 - Z o-,

- 120.0

a 115.0

5- 110.0 - LSD 0.05

105.0 -

100.0 2654.0 Kg/ha I I I 63.0 94.0 126.0 Rote of N in Kg/ha Figure 2. Yield response to five dressing methods at three nitrogen rates of a wheat crop under sorghum rotation (as percentage of non-fertilized treatment; average from seven experiments, 1961-1964). 17 257 Where inherent soil fertility was high, under legume rotation, method D, was the only dressing method resulting in an appreciable yield increase (Figure 1). Data on the influence of nitrogen dressing on yield components provided at least a partial explanation for the differential response of the dressing methods (Table 5). Differ- ences among dressing methodsin numberofears per plant were not significant. Method D, however, increased ear weight by 3.4 and 14.2% over the non-fertilized treatment under the legume and sorghum rotations, respectively (Table 5).

Table 5. Effect of five dressing methods on the number of ears per plant, ear weight, and tillers- to-ears ratio of wheat, under legume and sorghum rotations (data expressed as percent of control; average from nine legume and seven sorghum rotation experiments)

Method of Ears per plant Ear weight Tillers: Ears Ratio Dressing Legume Sorghum Legume Sorghum Legume Sorghum A 108.3 124.6 98.3 108.3 96.1 99.3 B 108.3 128.5 97.4 105.0 94.8 94.8 C 107.3 126.8 98.3 111.7 94.1 91.5 D 106.4 129.6 103.4 114.2 92.2 91.5 E 107.3 126.3 96.6 106.7 92.2 92.8 Control 2.0 1.8 1.17g 1.20g 1.54 1.55

Compared to the effect of early and late top dressing on car weight, the remaining methods influenced ear weight to a lesser extent under sorghum, and even depressed it under legume rotation. These differences point out that, under a regime of early and late top dressing, more moisture reserves are available during the post anthesis period. The split top dressing method was highly efficient in reducing the amount of tillering without significantly reducing ear formation, as manifested by the lowest tiller-to-ear ratios (Table 5). The rate of tillering reduction was probably determined by the lower amount of available nitrogen at tillering. The split top-dressing method had a favorable effect on lodging. Plots treated with this method invariably had a more erect stand compared to other dressing methods. Thus, the top dressings method (D) provides, under semi-arid conditions, an essential measure of control over excessive early vegetative development and growth, which probably resulted in additional moisture at the post anthesis period.

2.3 Yield efficiency pcr unit of nitrogen

In this series of experiments, ammonium sulfate was used solely at pre-seeding, whereas calcium ammonium nitrate was used as a top-dressing fertilizer. To avoid nitrogen loss, immediate incorporation was ensured by applying the fertilizer during rainfall or when the soil surface was still wet. The pattern of yield response, under both rotations, is marked by the high efficiency of theearly and late top dressing method (D). Therefore, it is safe to assume that the method of top dressing ensured immediate availability of the nitrogen. Moreso, it points out that, under the prevailing winter temperatures in Israel, the root system was developing actively and was capable of absorbing the N fertilizer. Generally, the highest yield returns per unit of N were obtained at the lowest fertilizer rate and decreased with increasing the nitrogen rate. The method of top dressing (D) 258 proved to be highly efficient, yielding, at the low nitrogen rate, 5.5 and 11.1 kg of grain per unit of nitrogen under legume and sorghum rotations, respectively (Figures 3 and 4). In comparison, the respective values under the pre-seeding fertilization were -0.76 and 6.4 kg of grain per unit of nitrogen. Other dressing methods were intermediate in yield returns. The efficiency rate of the dressing methods decreased, under both rotations, in proportion to. the fertilizer applied at preseeding and at early top dressing. Thus, when two thirds of the seasonal ration was applied during the pre-tillering period (method E), yield returns were lower as compared to method C- in which only half of the fertilizer was applied during the same period (Figures 3 and 4). Compared to sorghum (Figure 4), nitrogen response under legume rotation (Figure 3) is suggestive of a sizeable reserve of soil mineral nitrogen. This reserve is of practical value in designing nitrogen fertilization procedures. Yield response curves (Figures I and 2) and nitrogen response curves (Figures 3 and 4) indicate that the optimal N fertilization rate approaches 63.0 kg N/ha under legume (or fertile) rotation, and is closer to 94.0 kg N/ha under sorghum (or nitrogen-depleted) rotation. On the local market the price of a unit of N corresponds to 1.3 kg of wheat grain. Consequently, under legume rotation it is economically feasible to apply 63.0 kg N/ha only by using the method of early and late top dressing (D). Under sorghum rotation practically all the methods tested are economical at the low nitrogen rate. The split top dressing method (D), however, reaches its highest economy at the low nitrogen level, and is the only dressing method approaching economical feasibility at the 94.0 kg N/ha.

3. Literature Review

Yield response of wheat to nitrogen fertilization is subject to wide variation from site to site and from year to year, especially under arid and semi-arid conditions. Nitrogen fertilization under these conditions is characterized by a low mean yield response to basic dressing; mean response values ranging from 5.1 to 8.7 lb. of grain for each lb. of N at rates ranging from 11.5 to 46.0 lb. of N per acre respectively were reported by Russell [5]. Yield response to nitrogen fertilization is associated with rainfall distribution, especially during preheading, and with climatic variables of which mean spring temperature, and evapotranspiration are of importance [5,6,13].These climatic variables accounted for more than 25 % of the variance of grain yield and 67 % for grain and straw yield [6]. The importance of stored soil moisture to 120 cm prior to seeding was pointed out [2, 13]. It seems that as stored available soil moisture at seeding increases,lesser amounts of rainfall are required to produce profitable response to N [2]. The pattern of nitrogen uptake is marked by a rapid N absorption from the 4-5 leaf stage until the end of jointing phase then the rate decreases, but uptake continues until flowering [3,8]. Generally and even under the better rainfall conditions, mineral-nitrogen and nitrate-nitrogen in the surface 12-30" is the main source of N to the plant under arable soil conditions [8]. There is some evidence that wheat will absorb nitrogen in excess of its requirement and subsequently lose the surplus depending on the availability of moisture [1, 9]. Grain production appeared to be more dependant on transfer of nutrient from other plant parts rather than upon the absorption from the soil during the post anthesis period [3]. Increase in grain protein on the other hand is associated with nitrogen released by mineralization or nitrogen applied to the soil in the post flowering period [8]. 259 z 166.C0 0

E40 N 0 o2 c.._.0.. .,. 2D -

- 0 • 3012.0 Kg/ha - b- . -2o I II 63.0 94.0 126.0 Rate of N in Kg/ho

Figure 3. Nitrogen response to five dressing methods of a wheat crop under legume rotation (kg grain/kg N; average from nine experiments, 1962-1964).

12.0 -

10-0 10.0 - '. .

,6.0 - 4.0- .

5"2.0

0 I I 2654.0 Kg/ha 63.0 94.0 126.0 Rote of N in Kg/ha Figure 4. Nitrogen response to five dressing methods of a wheat crop under sorghum rotation (kg grain/kg N; average from seven experiments, 1961-1964). 260 In general, moisture stresses influenced those plants parts that were actively developing when the stress occurred [8, 9]. Nitrogen increases the potential yield of wheat, but an oversupply of N could cause this potential to exceed the capacity of the supporting environment and result in loss of yield [10]. Dry matter response to N at jointing was associated with an increase in tiller number and a decrease in mean tiller weight. Under these conditions moisture stresses induce a high rate of tiller mortality resulting in fewer ears [1,10]. Flowerdevelopment andconsequently grain number is influencedby available N and moisture during jointing-anthesis period [10, 11]. Spikelets per ear increased but flower survival may be depressed by N, due to a tiller competition for moisture. As a result grain number per ear is depressed [11]. On the whole N fertilization can reduce grain yield but, unless under extreme drought, no significant depression in grain + straw yield is expected. Harvest index is usually lowered by additional N fertilization [5]. The lower values are usually associated with excessive vegetative growth early in the season followed by moisture deficits later in the season. On the whole variety x yield/N interaction in field experiments have not been marked [1, 7, 12]. However differences between semi-dwarf and tall varieties were noted [12], probably due to the longer period of grain growth of the semi-dwarfs [12]. Variation in sowing time of the same variety may also result in higher grain yield due to earlier flowering and longer duration of grain growth [4].

Literature cited

1. Barry K.P. and Naido N.A.: The performance of three Australian wheat varieties at high levels of nitrogen supply. Aust. J. Exp. Agric. and Anim. Husb. 4,29 (1964). 2. Bauer A., Young R. A. and O-bun J. L.: Effects of moisture and fertilizer on yield of spring wheat and barley. Agron. J. 57, 354 (1965). 3. Boatwright G. 0. and Hatas H.J.: Development and composition of spring wheat as influenced by nitrogen and phosphorus fertilization. Agron. J. 53, 33 (1961). 4. Fischer R.A. and Kohn G.D.: The relationship of grain yield to vegetative growth and post-flowering leaf-area in the wheat crop under conditions of limited soil moisture. Aust. 1. of Agric. Res. 17, 281 (1966). 5. Russel J.S.: Nitrogen fertilizer and wheat in semi-arid environment I. Effect on yield. Aust. J. Exp. Agric. and Anim. Husb. 7,453 (1967). 6. Russeli.S.: Nitrogen fertilizerand wheat in semi-arid environment 2.Climatic factorsaffecting response. Aust. J. of Exp. Agric. and Anim. Husb. 8, 223 (1968). 7. Stickler F. C. and Pauli A. W.: Response of four winter wheat varieties to nitrogen fertilization. Agron. J. 56, 470 (1964). 8. Storrier R.R.: The availability of mineral nitrogen in a wheat soil from Southern New South Wales. Aust. J. Exp. Agric. and Anim. Hush. 2,185 (1962). 9. Storrier R. R.: The influence of water on wheat yield, plant nitrogen uptake and soil mineral nitrogen concentration. Aust. J. Exp. Agric. and Anim. Hush. 5,310 (1965). 10. StorrierR. R.: Excess soil nitrogen and the yield and uptake of nitrogenby wheatin Southern New South Wales. Aust. J. Exp. Agric. and Anim. Husb. 5, 317 (1965). II. Storrier R. R.: The leaching of N and its uptake by wheat in a soil from Southern New South Wales. Aust. J. Exp. Agric. and Anim. Hush. 5. 323 (1965). 12. Syme J. R.: Growth and yield of irrigated wheat varieties at several rates of nitrogen fertilizer. Aust. J. Exp. Agric. and Anim. Hush. 7, 337 (1967). 13. Young R.A.. Ozbun J. L.. Bauer A. and Vasey E. I.: Yield response of spring wheat and barley to nitrogen fertilizer in relation to soil and climatic factors. S. S. S. of Amer. Proc. 31,407 (1967).

261 Short Outline on Agriculture in the West Bank

SH. H. DAJANI, Director, Agriculture Research and Extension, Ramallah (West Bank)

Introduction

The West Bank of the Jordan River have an area of 5500 square kilometers and a population at present of approximately 600,000 people. Nearly 70% of the people are involved in agriculture. The estimated arable area is around 2 million donoms* of which less than 5 % is under irrigation while the majorcultivated crops depends largely on rainfall which varies from 700 mm in the upland down to 100 mm in the eastern slopes and the Jordan Valley. Tree plantations cover an area less than one million donoms which includes olives, .grapes, decidous trees and citrus. Cereal grains also covers around 650,000 donoms. Vegetable crops which constitute an important factor in the agriculture pattern covers nearly 250,000 donoms. Livestock which mostly include sheep and goats totalling around 200,000 heads are mostly reared by nomads on poor ranges which have been deteriorated along the years as a result of over grazing. Limited number of Freisian cows totalling around 3500 are raised by limited number of small farmers nearby the main cities. On the other hand there are 26,000 Baladi or local cows, a small dual purpose animal that are still considered popular in the upland villages. Farming practices in the West Bank depends mainly on old family farmers of small land ownership applying a mixed type of farming. The West Bank can be generally divided into four Agricultural regions:

1. Seti-coastalregion

Lies in the North West of the West Bank and forms the final stretch of the Mediterra- nean Coastal Plains. It enjoys good annual rains that ranges between 350-700 mm. Rela- tively small area lies under irrigation mainly in the south carrying citrus plantations and summer vegetables. Such irrigation is totally supplied from drilled wells. A mixed type of farming is being practised with cereal crops covering most of the cultivated area in winter followed by decidous plantations and vegetables. Tobacco growing and curing is particularly limited to this area and the yield is largely marketed to the local cigarette factory. * One donom - 1000 square meters. 262 1I. The Central Uplands

It covers the larger portion of the West Bank extending from extreme north to south. Most of the region is mountainous and rocky with alluvial type of soil. The area depends totally on rainfall which varies between 300-600 mm a year and in most cases the distribution of rainfall is the limiting factor for obtaining any yield. Olive plantation is the apparent crop to this area which covers over half a million donoms. It constitutes an important factor in the agricultural economy of the West Bank. The annual production varied from oneyear to the other and usually good yields are obtained every other year which reaches up to 20,000 tons of which 70% goes for export. While in bad years production may drop below 50%. Cereal growing which is scattered over the region in small patches covers a similar area as olives. It produces between 200-300 kilograms per donom. Grapes are mostly grown in the south covering an area of 130,000 donoms. Most of the yield is exported and a small percentage goes for local industry. Along with grapes decidous trees as apples and plums are also important crops in the south.

I/. The eastern slopes

Extends from the central uplands towards the Rift Valley. This area hasvery low precipitation that does not exceed 300 mm. It is largely considered for grazing of sheep and goats with scattered patches of winter barely on the narrow and somewhat discontin- uous strip valley terraces. Cereal crops are usually subject to drought and are not considered a safe crops to grow. The natural vegetation however has undergone severe damage during the years because of two main factors: first, the over grazing, and secondly, the ploughing up of land for cultivation, thus causing erosion and forced a drop in animal population.

IV. The Jordan Valley

Constitute the major agriculture region in the West Bank. The area totally lies under sea-level (200-300 meters below sea-level). There are approximately 150,000 donoms under intensive cultivation. Nevertheless, only 60% of this area is presently utilized. The Jordan Valley enjoys warm winters and hot summers with very low rainfall averag- ing less than 150 mm. Therefore all the cultivated area is irrigated by the limited water supply derived from springs, wells or water drawn from the Jordan River. Off-season crops are the main feature in the Jordan Valley. Citrus, bananas, and winter vegetables constitute the main cropping pattern and have been for years an important export crops. Tomatoes, eggplants, cabbages, cauliflowers and pepper are popularly grown.

Agricultural production The agriculture produce of the West Bank has been estimated at 14 million pounds ster- ling in 1966. A good portion of the product is exported to neighbouring countries as well as for local industry. 263 Major crop production in the West Bank during 1968/1969 Crop Tons Per cent exported W heat ...... 50,000 Barley ...... 20,000 Sesam e ...... 1,500 50% Chick-peas ...... 2,000 50% Tobacco ...... 350 35% Tom atoes ...... 55,000 25% M elons ...... 30,000 30% O ranges ...... 35,000 40% G rapes ...... 36,000 30% O lives ...... 50,000 50%

Agricultural industries

There are a number of agricultural industries in the West Bank that are built on the local agriculture produce and constitute important export lines. Of these are mainly the popular local soap industry from pure olive oil, hydrogenation oil plant and match factory located at Nablus, in the north. The fruit and vegetable canning factory, fruit drying and leather industry at Hebron in the south. The noted hand carving works from live wood in Bethlehem and cigarette factory in East Jerusalem. A good number of advanced olive presses are gradually replacing the several hundred olive presses existing in the central uplands.

Department of Agriculture

The Departement of Agriculture in the West Bank have been promoting advance agris culture practices and offering services for adapting better farming through its various sections which include: Extension, Veterinary, Research and Forestry. There are three main provinces and each province or district is divided into a number of subdistricts which represent certain agriculture features. Extension activities in these district cover over 350 villages and a good number of demonstrational work on various crops and field practices are continuously carried. There exist four experimental farms of which one is in the north for field crops, two station in the Jordan Valley for vegetable, citrus and subtropical fruits and the fourth station in the south for decidous trees. There are three forest nurseries producing over 1.5 million seedlings annualy for affor- estation purposes. The present forest areas covers only 2 %/ofthe cultivated area. The veterinary Department with itsefficient field activitiesare in goodcontrol of the animal and poultry diseases and similarly stimulating improved livestock managements.

264 Irrigation of Wheat in the Northern Negev

Dr.D.SHIMSHI, Department of Soils and Water, Volcani Institute of Agricultural Research, Rehovot (Israel)

Although wheat is grown without irrigation in the rainier regions of Israel, where winter precipitation is usually sufficient for a satisfactory yield, there has been lately a tendency to grow wheat under supplemental irrigation in the more arid regions of the country. The aim is to make Israel self-sufficient in bread-grains; several years ago most of the wheat consumed was imported, mainly from the U. S. and Canada. During the last two years local production of wheat supplied about two-thirds of the needs, and this proportion will continue to increase. The present experiment at Gilat is part of a series of wheat irrigation experiments that have been going on for several years; this is the main experiment, other supplementary experiments being conducted at 3 settlements in the Negev, I experiment farm at the Lachish region and I settlement in the Bet-Shean Valley. The aim of the experiment is to test several irrigation treatments on two varieties of wheat (one tall, one dwarf), and in conjunction with a CCC-treatment on the tall variety. The six irrigation treatments are: I. No irrigation. 2. One irrigation after planting (end of November). 3. One irrigation after planting (end of November) + one irrigation at heading (beginning of March). 4. One irrigation in mid-January. 5. One irrigation in mid-January + one irrigation after heading (mid-March). 6. One irrigation at heading (beginning of March). The present winter had a rainy period in November-December (80 mm), little rain in January (55 mm), no rain in February, and some rain in the last third of March (36 mm). Due to the lack of rains during 7 weeks, the unirrigated wheat is already severely damaged over the entire Negev region. The soil moisture status under the various treatments is followed by frequent measurements with a neutron moisture probe. During the growth season, observations are made on the wheat plants for some indices of moisture stress, particularly stomatal behaviour; this is done by means of a porometer. At harvest time, several components of yield (number of ears per unit area, number of spikelets and kernels per ear, 1000-weight of kernels) will be determined. As rainfall conditions fluctuate from year to year, the optimal treatments will vary accordingly. However, even on relatively rainy years (total winter rainfall of over 350 mm), 265 it was found that at least one irrigation resulted in considerable yield increases. On a drought year, a 150 mm irrigation could spell the difference between complete failure (320 kg/ha) and a satisfactory and profitable yield (3910 kg/ha). A subsidiary experiment is carried out, where the interaction of 4 irrigation treatments and 3 rates of nitrogen fertilizer is studied on two wheat varieties. The aim is to find the nitrogen-supply regime best suited to any particular irrigation regime. In another experiment, an extensive study of stomatal behaviour of 10 different wheat varieties is carried out under a moist and a dryregime. In previous experiments it was accidentally found that wheat varieties exhibit drastic differences in the daily course of stomatal opening under any given water-stress level; the experiment is aimed at clarifying the role of these varietal differences of stomatal behaviour in controlling transpiration, photosynthesis, and yield. A rapid field method has been developed for the determination of photosynthesis based on the useof labelled CO 2.

266 Transition from Extensive to Intensive Agriculture with Fertilizers in the B'sor Area Israel

Dr. SH. FELDMAN, Mivtachim Experimental Farm, Beer Sheva (Israel)

The B'sor area is located in the southwestern part of the Negev region. This area includes the following kibbutzim: Nir Oz, Magen, Nir Yitzchak, Kerem Shalom, Gvulot, Tzei'lim, and Revivim; also the following moshavim: Ami-Oz, Mivtahim and Yesha. The Agricultural Settlement of the Jewish Agency is now in the processes of building three new moshavim, to be settled in the near future. There are 275,000dunams available of agricultural settlement in the B'sor area. Before 1957 the settlers in the moshavim were working in the vineyards of the area for their living, as they did not do any farming at all on their own lands. The lack ofagricul- tural production was due to the settlers not knowing which crops to plant, when, and a lack of knowledge on fertilizer applications. The situation in the kibbutzim was somewhat different compared to the moshavim. Aside from their vilneyards, the members of the kibbutzim were growing barley and wheat planted in November and harvested in June. During the spring sorghum was planted. Due to the kibbutzim having dairy herds, alfalfa and Berseem clover was grown as a sourceof green feed and a haycrop. Some attempts were made to produce vegetables in the kibbutzim, but extremely low yields were obtained. Due to the low rainfall in the area the field crops were fully irrigated in order ot obtain yields resulting in a high cost of production. The B'sor area is an arid region and its climate is typical of a desert area. The rainfall comes during the winter season from the end of November to the third week in March. The average precipitation is 125 mm per year. During the months of February and September many windy days can be expected, though these desert winds can also occur any other time of the year. The average summer temperatures are 290 to 320 C during the day and may drop to 20 to 220 C during the night. The day temperatures during the winter season fluctuate between 12- to 18 C and fall to 30 C during the early morning, about 4-5 o'clock. The area may suffer a freezing spell every three to four years, so precautions to overcome it must be taken everyyear. The soil of this area is a fine sandy loam, though there are some places where the subsoil may have a higher percentage of loess soil (typical of the northern Negev). This comes from the transition of a loess to a fine sandy loam as the B'sor area borders the northern Negev. 267 Due to its sandy texture the soil is well drained, areated and easily tilled. There are no specific cultivation problems.though it is easier to work the soil when it is irrigated as compared to a dry condition. Soil moisture properties are of importance in determining its use for an irrigation program. The average field capacity of the B'sor soils is 9 and its wilting coefficient 2. There are 27 mm of available soil moisture per 30 cm of depth soil. More frequent irrigations are required for shallow rooted crops as potatoes and peppers. The infiltration rates are very high, but seldom will an irrigation of more than 100 mm at one time be applied. Only for pre-irrigation will large amounts of water be applied at one time. Soils formed under desert conditions are usually fertile but may respond well to applications of organic matter due to its effect on soil structure and nitrogen and phosphorus fertilizers. The organic matter content of the B'sor soils are extremely low, less than 0.02 %, and in some cases there is absolutely no organic matter. The nitrogen supplying power of the soil is not enough to obtain profitable yields without the application of nitrogen fertilizers. Under present conditions phosphorus fertilizers are used, but no positive results were obtained in field trials, as seen later on in this paper. A zinc deficiency was observed on field corn ten years ago, but with the use of zinc fungi- cides in the area a zinc deficiency has not been observed or reported. All the other essential macro- and micro-elements for crop production appear available in sufficient quantities to obtain high yields. The pH-range of the soils is 7.8 to 8.4, and the salt content is low though there are some boron spots known to exist in the area. The development of an area from an extensive agricultural system to one that is intensive -raising crops that require many work days per dunam, fully irrigated and fertilized heavily - should be seriously questioned from the beginning, especially under the present conditions where the local market is limited in its ability to absorb inore produce and irrigation water is limited and expensive. With this in mind, all the field experiments were carried out on crops that were able to be exported and supply the local market during the off-season. Field trials were begun in 1957 upon request of the Agricultural Settlement Department (Negev Region) of the Jewish Agency because of settlers' complaints that crop yields were extremely low and they were not succeeding with field or vegetable crops. The studies were made on a short-term basis, due to the urgent requests for answers of those crops best adapted to sandy soils. The field trials include the effect of organic and chemical fertilizers on crop yields. The experimental results are presented according to crops. The field trials were carried out under ordinary farming conditions. At times it was even difficult to carry out the experiments under the best of conditions due to a lack of equipment or not getting the equipment on time. Aside from the fertilizer trials it was necessary to investigate certain cultural practices in the area as there was no previous experience and the climatic and edaphic conditions were different compared to other areas in the country. With the increase of an intensive system of agricultural production, the control of diseases and insects became a must. Groundnuts are well adapted to a sandy loam soil since the hulls produced in it are light colored and free from staining, in compliance with the world market demand. Due to its high demand on the world market it was decided to begin the initial fertilizer trial on 268 Table I. Yield response of groundnuts to nitrogen and phosphorus at Nir Yitzchak

Treatments (kg/du) Yields (kg/dunam)

Ammonium sulfate Superphosphate 10% 30 days after 60 days after planting planting (applied before planting)

1. Control 136 2. 80 145 3. 40 80 350 4. 80 80 403 5. 120 80 400 6. 40 80 40 445 7. 60 80 60 406 8. 40 80 20 20 437

Table 2. Mechanical analysis and pH of the Nir Yitzschak soil Depth pH Coarse Fine Silt Clay (cm) sand sand % % % % 0- 30 8.4 13.6 78.4 3.6 4.4 30- 60 8.2 15.8 74.0 4.0 6.0 60- 90 8.4 14.8 71.2 5.6 8.6 90-120 8.4 10.2 71.4 8.2 10.2 groundnuts the summer of 1957. Nitrogen is the only fertilizer element that produced yield responses in groundnuts in the sandy soils of the B'sor area [2, 3]. The response of groundnuts to nitrogen and phosphorus is shown in table 1. The soil analysis of the fertilizer trial is presented in table 2. Yields were significantly increased by the application of nitrogen. Maximum yields were obtained by the split application of 80 kg ammonium sulfate per dunam. There was no advantage in splitting the side application, while much lower yields were obtained by applying all the nitrogen at planting. This may have been due to the low

Table 3. The uptake of N, P, K in Virginia Bunch groundnuts in the B'sor area (kg/dunam) N P K Yield

5500 plants/du ...... 38.2 4.4 17.3 400

percentage of clay in the soil and to the field being irrigated throughout the season ret suiting in a drainage of the available nitrates. Under the conditions of this experimen- the nitrogen-fixing bacteria, if at all present in the soil, were not effective as seen by the low yield obtained without application of nitrogen. Phosphorus and potash have been ineffective as fertilizers, for groundnuts [4] but in time to come this situation may change. Poultry manure applied in the form as a side application did not increase groundnut yields [1]. This was probably due to the late application of the poultry manure. The nutrient uptake of N, P, K was studied on Virginia Bunch groundnuts as reported in table 3 [10].

is 269 From the above figures it can be seen that the groundnut crop must be grown on a fertile soil and fertilized heavily in order to obtain a high yield. Since the introduction of groundnut inoculation in Israel, this crop is successfully in- oculated the past three years in the B'sor area, resulting in a much lower cost of production as compared to the application of nitrogen fertilizer. In field experiments the effect of gypsum, applied after flowering as a source of calcium, zinc spray and gibberillum were found to have no effect on yield or grade of groundnuts [4]. At present there are two varieties of groundnuts grown for export in the B'sor area - Virginia Bunch, 145 days, and X-30 (a local variety) 135 days. The crop is planted in April as soon as the soil is 18- C warm. The general recommendation for planting distances is rows 60 to 70 cm wide and one seed every 30 to 35 cm in the row [4]. Field experiments are carried out on introduction and breeding of new varieties. The control of soil-borne diseases and leaf diseases, the control of Verticillium by the introduction of a resistant variety, crop rotation studies in relation to disease control, and the effect of planting populations on increasing yield and grade of groundnuts for export from the B'sor area. Potatoes are well adapted to a fertile fine sandy loam. Upon investigation of potato production in the B'sor area it was found that the settler was fortunate to receive his seed crop back upon harvesting the crop. It may not have been realized that in order to receive high crop yields under desert conditions large amounts of nitrogen must be supplied and at the correct stage of plant growth. In Nir Yitzchak the potato crop was receiving a total of 40 kg ammonium sulfate and this amount was applied in four to five applications. The initial potato fertilizer trial was carried out in Nir Yitzchak in 1957 on spring potatoes of the variety Up-To-Date [6]. The fertilizer treatments are given in table 4.

Table 4. The effect of nitrogen and phosphorus on spring potato yields

Treatments Application before planting (kg/dunam) Side applica- Yields (tons/ tion (kg/dun- dunam) am) Ammonium Superphosphate Ammonium sulfate sulfate (16%)

1. Control 1.69 2. 80 3.29 3. 80 1.89 4. 80 80 3.22 5. 120 80 2.96 6. 40 80 20+ 20 3.44 7. 40 80 40 4.07 8. 60 80 30+ 30 3.86 9. 60 80 60 3.74 L.S.D. 5% 0.53

Nitrogen is the fertilizer element that significantly increased potato yields and the data indicates that when the ammonium sulfate was applied in two applications, one at planting and the second as side dressing resulted in the highest yields. Splitting the side application does not result in higher yields. This may be due to the need of applying the correct amount of nitrogen at the right time according to crop requirement 270 Table S. The effect of nitrogen and phosphorus on fall potato yields Treatments Application before planting (kgfdunam) Side application Yields (tons/ (kg/dunaml" dunam) Ammonium Superphosphate Ammonium sulfate (16%) sulfate 1. 1.177 2. 40 -* 3. 80 1.186 4. 40 80 5. 120 80 1.208 6. 40 80 20+ 20 2.053 7. 40 80 40 2.164 8. 60 80 30+ 30 2.044 9. 60 80 60 2.186 L.S. D. 5% 0.320 - Treatments 2 and 4 were not weighed due to a technical mistake in the field.

for nitrogen. There was no plant response to phosphorus as reported on the ground nut fertilizer trials. The effect of nitrogen and phosphorus on fall potatoes was carried out in 1957 [6]. The treatments and yields are outlined in table 5. The yields in table 5 show that applying the nitrogen applications one half at planting and one half as a side application results in obtaining the highest yields. Though not all the treatment yields were obtained, phosphorus is not a limiting factor in obtaining high yields. Since there is a fair amount of poultry manure available in the settlements it was decided to study its effects on potato yield and grade with nitrogen and phosphorus. The field trial was carried out on spring potatoes in 1958 [7]. The experimental treatments were as follows:

I. No Po Check 2. N80 P100 80 kg ammonium sulfate plus 100 kg superphosphate (16y) per dunam at planting. 3. N40+40 40 kg ammonium sulfate plus 100 kg superphosphate (16y) at PI00 planting plus 40 kg ammonium sulfate per dunam side application (after complete germination). 4. N120 P100 One hundred and twenty kilo ammonium sulfate plus 100 kg superphosphate (16 %) per dunam at planting. 5. N60 +60 60 kg ammonium sulfate plus 100 kg superphosphate (16%) per P100 dunam at planting plus 60 kg ammonium sulfate side application (after complete germination). 6. N80 Same as treatment 2 plus 1000 kg poultry manure per dunam at P100+M planting. 7. M40 + 40 Same as treatment 3 plus poultry manure. P100+ M 8. N120 Same as treatment 4 plus poultry manure. P100-+ M 9. N60 + 60 Same as treatment 5 plus poultry manure. PI00+M 10. NO P100 One hundred kilograms superphosphate (16%) per dunam applied at planting. 271 Table 6. Summary of the effects of nitrogen, phosphorus, poultry manure on the total and grade A yield of spring potatoes at Nir Yitzchak Treatments Total yield Grade A yield arranged in order of magnitude (kg/dunam) (kg/dunam)

7 ...... 4181 3022 9 ...... 4136- 2761 8 ...... 3920 2750 6 ...... 3738 2488 3 ...... 3113 1738 5 ...... 2965 1727 4 ...... 2159 875 2 ...... 1954 761 10 ...... 1011 193 1 ...... 875 x 102

S.S.D. at P = 0.05 111 483 * The lines indicate a significant difference between subsequent treatments.

The results are summarized in table 6. Poultry manure applied with single of split applications of nitrogen resulted in the highest total and grade A yields compared to the nitrogen treatments without poultry manure. Throughout the growing season those treatments include manure had a better top growth, as size is considered, and were much greener in color compared to the treatments without poultry manure. The manure may have supplied nitrates to the potato crop during a longer portion of the growing season than where fertilizer is applied and growth factors may be present in chicken manure, other than its available nitrogen which may encourage higher yields as compared to those treatments which received only ammonium sulfate as its source of nitrogen. As in the previous fertilizer trials, split applications of ammonium sulfate resulted in a more efficient use of the nitrogen compared to single applications of ammonium also with and without poultry manure. Phosphorus alone, while increasing the total yield, did not have any effect on the yield of grade A potatoes. During the season of 1957/58 a field observation was madetoobservethe effect of poultry manure on yields of winter potatoes [5]. Before planting the crop received 50 kg ammonium sulfate and 100 kg superphosphate (16%) per dunam plus 50 kg ammonium sulfate per dunam applied as a side dressing after complete germination. The field was 10 dunams and one half of the field also received an application of 600 kg poultry manure per dunam plus the above mentioned treatments. The results are summarized in table 7. The yields are significantly high though date of planting was late (which was not known at that time) and the settlers in the area obtaining less than 900 kilo per dunam

Table 7. The effect of nitrogen and poultry manure on winter potato yields Yield (kgfdunam)

N 50 + 50 Pl00 ...... 1300 N50+ 50 PIOO+ M anure ...... 1700

272 only with nitrogen and phosphorus during the same period planting. Upon investigation of the low yields it was discovered that the settlers were applying the ammonium sulfate in three to five applications. It was not fully realized that the winter potato crop, which is harvested approximately 90 days after planting, cannot utilize the late nitrogen applications as was practical. Upon reporting the yields of the poultry manure experiments the settlers in the area immediately accepted these results and not only applied manure to the potato crops but whatever crop they planted. So much so, that the B'sor area is one of the best customers of poultry manure in the country. The control of plant diseases is an important factor in a successful potato producing area. The relation between the ratio of yield to foliage on the incidence of early blight, Alternaria solani, in potato was investigated [121. In potatoes grown in natural field conditions, low yield-to-foliage weight ratio was associated with reduced incidence of Altemaria blight. Artificial lowering of the yield-to-foliage ratio in Up-To- Date potatoes by partial removal of stolons was similarly associated with reduced infection. The development of infection was found to be influenced to a greater extent by yield- to-foliage rations than by postinoculation temperatures. The winter potato crop in the B'sor area are grown for export to Europe and Eng- land. During the winter of 1966/67 the crop was infected with Verticillium wilt. A field trial was conducted the winter of 1967/68 to investigate the effects of nitrogen side applications of ammonium sulfate and urea foliar applications on Verticillium wilt, yield, and grade of winter potatoes [9]. Winter potatoes are planted from the beginning of October to the end of October and harvested within 90 days after planting: While the tubers are fresh and the skin peels easily and they are shipped in moss to keep the tubers fresh. Though increased amounts and times of nitrogen side dressings did not have a significant effect upon the percentage of Verticillium wilt, there was a tendency for higher potato yields up to two nitrogen side dressings. It may be that increased amounts of nitrogen applications applied before planting and the first and second side applications must be investigated. The winter potato crop cannot utilize more than two side dressings due to the short growing period and the length of day and temperature decreasing each successive day. Tomatoes are now grown successfully during the off-season in the B'sor area. The main purpose of tomato production in this area is for export. After the successful production of groundnuts and potatoes, tomatoes were commercially planted on a large scale the fall of 1958, without any previous cultural or fertilizer data (field trials in the B'sor area). The crop resulted in a dismal failure. Upon investigation it was found out that the tomatoes were field seeded the middle of August. The yield was nil and the plants showed a high percentage of virus and early blight. The Settlement Department of the Jewish Agency allotted a field and budgets to investigate how to produce off-season tomatoes in the B'sor area for export. Another area in Israel, Emek HaYarden, is able to produce field tomatoes until the beginning of March. Af- terwards there are no tomatoes in the land until the spring crop begins yielding- about May 20th. During the season of 1959/60 a field experiment was carried out testing the effect of fungicide sprays to control Altemari solani [11]. Early blight was significantly controlled by Waneb fungicide. There was no trouble with virus due to the experimental field being planted in September. Tomatoes planted in September are affected by virus, 273 and if planted after September 15th the yield is obtained late, due to the plant not des- veloping during the winter season. The variety planted for export is Moneymaker, and is planted from September 1 to September 15. The yield is obtained from Janu- ary to April. At present yields of 6 to 8 tons per dunam are obtained. The relation between the ratio of yield-to-foliage and the incidence of early blight in Moneymaker tomatoes has been investigated [12]. A low yield-to-foliage weight ration was associated with reduced incidence of Alternaria blight. Artificial lowering of the yield-to-foliage ratio in Moneymaker tomatoes by partial removal of flowers was similarly associated with reduced infection. The development of infection was found to be influenced to a greater extent by yield-to-foliage ratios than by post inoculation temperatures. In warm winters, favoring plant growth, and in which there was a high incidence of Alternaria blight, blossoming of up to four early trusses brought about a marked increase in the resistance of winter tomatoes to infection. The variety Moneymaker tomato grown for export is susceptible to puffiness. This is a condition when air pockets are found between the parenchymatic tissue of the pla- centa and the inner walls of the pericarp, thus the popular name 'puffiness'. Aside from genetical susceptibility, climate and soil conditions are known to affect this condition. The effect of nitrogen and potash on the percent puffiness in Moneymaker tomato was investigated [13]. A decrease in the amount of nitrogen and an increase of potash applied reduced the per-cent puffiness but total yields were reduced.

Table 8. The effect of nitrogen source and amount of side applications on field beets Treatments Yield (kg/dunam)

1. 30 ke Ammonium sulfate + 30 kg Ammonium sulfate/dunan 23,295 2. 30 kg Kalkamon + 30 kg Kalkamon/dunam 17,159 3. 60 kg Ammonium sulfate/dunam 20,455 4. No side application 5,306

L.S.D. 5% 4,594

Two tomato varieties studied, Benner Beste and Potantate, were found to be highly resistant to puffiness in the B'sor area [13]. Field beets are well adapted to light soils and have been grown in the area as a source of green feed for dairy cattle. A field trial was carried out investigating the effect of nitrogen side applications and source of nitrogen [8]. The treatments and yields are summarized in table 8. The data shows there isn't any significant difference in applying the ammonium sulfate in one or two applications though there is a rise in yields with two applications. Some settlers are convinced of the advantage of kalkamon due to the presence of nitrates in this fertilizer, but with the pH of the soil 8.4 there is the distinct advantage of applying ammonium sulfate due to its acidifying effect, though it may only be brief due to the high buffering capacity in the B'sor soils. Aside from the fertilizer field trials, experiments on introduction of varieties, dates of planting, seeding rates and the control of diseases have been carried out with various vegetable crops for export. The process of changing from an extensive system of agriculture to an intensive one is not a simple one. Much knowledge and information must be gathered for the crops to be produced successfully. Aside from the information reported field and laboratory work is presently being carried out on ground- 274 nuts, winter potatoes, tomatoes, onions, garlic, strawberries, egg plants, marrows, peppers, carrots and snap beans. From the crop yields reported it is seen when the B'sor soils are irrigated a nitrogen deficiency will probably be the main limiting factor in obtaining high yields. Most of the crops require 80 to 120 kg ammonium sulfate per dunam and half of this amount must be applied as side application. A long season crop as tomatoes may require a total of 250 kg ammonium sulfate per dunam. Poultry manure should be applied to all crops, if at all available. The results with this organic fertilizer has been out of the ordinary in the B'sor area in obtaining high yields. Though increased yields with phosphorus fertilizers have not been obtained it is suggested that a general recommendation of 20 kg superphosphate (triple) be applied to all crops, only for maintenance purpose. For the present there is no need for potash fertilizers, but this situation will surely not be a permanent one under an intensive system of agricultural production. From the field trials reported and with the existing intensive agriculture in the B'sor area it is observed that this area can be successfully developed as an agricultural area with its main purpose to export its produce. For the insurance of this maintenance of the agricultural system, further fertilizer trials must be carried out in conjunction with a laboratory testing program and in relation to a crop rotation program. Re- search work must be carried out on introduction of varieties, dates of planting, seeding rates, and investigate land management practices. A thorough research program must be maintained in relation to the diseases already present and diseases that may show up in time. A lack of irrigation water in the country is one of the main problems limiting agricultural production. Due to the success of the settlers with the irrigated crops a shortage of irrigation water is a chronic problem in this area. An important phase of the research program should be to investigate the irrigation requirements of the crops and in relation to fertilizer use in order to obtain an efficient use of the fertilizer applied and water use. The future research program must be flexible in order to handle problems that may arise in the future with the increased agricultural progress in the B'sor area.

Literature cited

I. Feldman S.: The Effect of Poultry Manure Side Application in Groundnut Yields in the Southwestern Negev. Report to the Settlement Dept., Jewish Agency (Negev Region) (1958). Hebrew. 2. Feldman S.: Groundnut Fertilization at Nir Yitzchak. Israel Agric. Dept. Pub.26 (1960). He- brew. 3. Feldman S.: Groundnuts. Israel Fertilizer Development Council Crop Fertilization Series (1962). 4. Feldman S.: Progress Report on Groundnut Experiments at the Mivtahim Experimental Farm. Israel Agric. Dept. Pub.45 (1962). Hebrew. 5. Feldman S.: Field Observation on the Effect of Nitrogen and Poultry Manure on Winter Pota- to Yields at Nir Yitzchak. Report to the Settlement Dept. (Negev Region), Jewish Agency (May 1958). Hebrew. 6. Feldman S.: The Effect of Nitrogen and Phosphorus on the Yields of Spring and Fall Potatoes. Vegetable Growers' Association Bul. 5 (September 1958). Hebrew. 7. Feldman S.: The Effect of Nitrogen, Phosphorus and Poultry Manure on the Yield and Grade of Spring Potatoes. Vegetable Growers' Association, Bul. I (Dec. 1958). Hebrew. 275 8. Feldman S. and Singer A.: The Effect of Nitrogen on Field Beet Yields. Hassadeh (November 1958). Hebrew. 9. Krlkun J. and Feldman S.: The Effects of Ammonium Sulfate and Urea on Verticillium Wilt, Yield, and Grade of Winter Potatoes. Report to the Settlement Dept. (Negev Region) Jewish Agency (June 1968). Hebrew and English. 10. Lachover D.: Nutrient Consumption of Groundnuts. Israel Agric. Res. Sta. Pub. (1961). He- brew. II. Rotetn J.: Fungicidal Spraying Experiments for the Control of Alternaria solani of Winter To- matoes in the Southwestern Negev 1959/60. Israel Agric. Experiment Station Bul.300 (July 1960). Hebrew. 12. Rotem J. and Feldman S.: The Relation Between the Ratio of Yield to Foliage and the Inci- dence of Early Blight in Potato and Tomato. The Israel Journal of Agric. Res. Vol. 15 (July 1965). 13. Palevirch D.: Studies on the Puffiness of Tomato Fruits (Lyscopersicon esculentum Mill). The- sis submitted for the degree Doctor of Philosophy to the Hebrew University of Jerusalem (Feb. 1966). Hebrew, summary in English.

276 Soil Tests for Fertilizer Recommendations under Extensive Conditions*

D. SADAN, D. MAC,.OL, Israel Ministry of Agriculture, Extension Service, Negev (Israel) Dr. U. KAFKAFI, The Volcani Institute of Agricultural Research, Bet Dagan (Israel)

'Soil testing is to the art of crop production what the thermometer is to the medical profession' [6]. Under the extensive farming conditions in Israel it was shown that a relationship exists between yields and precipitation [1]. In a specific climatic region such as the Ne- gev, where the annual rainfall is 250 + 100 mm, and no supplementary irrigation is provided, the grain yield is generally limited by water supply. Two basic questions in applying the routine soil testing procedure led to the present work: a) Do soil test analysis values and their interpretation predict the chances of a response in the field to additions of phosphatic fertilizers; and b) how much fertilizer must be applied in order to obtain a predetermined soil test value. In the Negev area, application of 250 kg/ha of 22% P205 superphosphate accounts for 15-20% of the total production costs. Soil tests can serve as a means to prevent a situation whereby a nutrient deficiency will be a limiting factor for yield, and to prevent accumulations of unprofitable surpluses of fertilizer in the soil. Growing crops under dry-farming conditions is almost an art, requiting much skill. All the variables being the same, one farmer can succeed where his neighbor may fail.

I. Materials and methods

The main work was along two lines:

1.1 Response of small grains to superphosphate

Yield measurement followed by a soil test, in which a) two levels of P were tested in 4-5 replicates in the same field; and b) 'observations' were made in plots where two levels of P, 0 and 200 kg/ha 22% POs superphosphate, were tested in one replicate in each of seven fields in the Negev. In each plot, 350 m 2 was harvested.

2.1 Calibration of a soil test

Soil test calibrations were done in order to assess the amount of fertilizer needed to raise the soil test value to a predetermined level [3]. The survey was begun in 1965

* Publication of the Agricultural Research Institute, Bet Dagan, No. 1478 E (1969). 277 and continued for four years in the fields of ten kibbutzim (cooperative settlements), and of 'Moshavei HaNegev' (a cooperative company). Two hundred and fifty fields were sampled annually, to evaluate the effect of the fertilization practice on the soil test for phosphate. Forty subsamples of soil were taken for a composite sample in each field, to a depth of 20 cm. Phosphate was determined by the bicarbonate method [4]. In 1967/68, when prospects of supplementary irrigation were envisaged in the Negev, a single split-block experiment was laid out to study the effect of supplementary irrigation and levels of nitrogen and phosphate on wheat yields, and to provide a further check of the soil test values. Two levels of water (natural rainfall and 80 mm supplementary irrigation on 11/111/68); two levels of phosphorus (4.4 and 7.5 ppm bicarbonate-soluble P); and two levels of nitrogen (70 and 120 kg/ha, given as ammonium sulfate and urea), were examined in four replications. Since all the fields consist of loess-derived soils, and are situated in areas with the same climatic conditions, a comparison among them is justified.

2. Results and discussion

The 'observation' fields in 1965 had an average of over 6 ppm of bicarbonate-soluble P in the soil extract (Table 1). During 1965, the yields were rather high for the region.

Table 1. Bicarbonate-soluble P and wheat yield (kg/ha) of 'observation' field tests (1965)

Location. Nirim Nirim Shoval Kefar Nahal Nirarn Dvir I 2 Azza Oz Bicarbonate-soluble P (ppm) ...... 6.4 8.8 8.0 5.4 5.6 8.2 7.6 Wheat yield (kg/ha) Control ...... 2810 4180 3050 3430 2660 2590 3240 200 kg/ha superphosphate ...... 2920 4330 3030 4040 2810 2460 3360

The average yield from four replications in three fields, and the decline in soil test values after harvest, are shown in table 2. No clear response to addition of superphosphate was obtained, nor did the yield of control plots show any relationship to the extractable soil phosphorus value.

Table 2. Yields of wheat and barley (kg/ha) as affected by soil test values and superphosphate application (averages of four replications)

Year: 1966 1966 1967 Crop: Wheat Wheat Barley Site: Netivot Be'eri Tidhar

Control plots P before seeding (ppm) 8.0 8.0 6.2 Control plots P after harvest (ppm) 4.8 6.0 3.2 Yield (kg/ha) Superphosphate 0 kg/ha 2600 1320 4100 200 kg/ha 2500 1440 4100

The data on bicarbonate-soluble P, obtained in the soil test survey, are presented in table 3. The results showthe effect of introducing a soil test service on fertilization 278 Table 3. Results of soil sampling in two types of fields in the Negev Per cent of Per cent of samples, grouped according to bicarbo- total area nate-soluble P sampled <6 ppm 6-8 ppm > 8 ppm

July 1965 Kibbutzim ...... 80 19 17 64 Co'op. company ...... 40 16- 27 57 July 1966 (after drought) Kibbutzim ...... 95 14 12 74 Co'op company ...... 90 6 15 79 July 1967, accepted by Kib. Kibbutzim ...... 95 45 25 30 Co'op company ...... 90 29 19 52 July 1968, accepted by Co'op. Kibbutzim ...... 95 44 16 40 Co'op company ...... 90 52 27 21

* Of that group, 50% were between 5 and 6 ppm. practices and decision derivations to two distinctly different types of agricultural associations. In 1965 most of the tested fields were rich in phosphate, due to prior practice. No recommendations were issued in 1966 and, combined with low yields due to drought, the percentage of fields with over 8 ppm even increased. On the basis of these factors, and responses to fertilizers (tables I and 2, and data not presented here), it was suggested that no superphosphate be given to fields having over 6 ppm bicarbonate-soluble P. The ten kibbutzim adopted this recommendation, while the cooperative company did not. This is reflected in the data from 1967, in which almost 50% of the kibbutz fields had a value below 6 ppm. In 1968, the recommendation based on soil tests was also accepted by the cooperative company. The extraction values from 48 fields throughout the country, which were sampled about 2 weeks after fertilizer application, gave a calibration value of practical importance: an increase of I ppm bicarbonate-soluble P, which corresponds to I I kg/ha to rec- (± 20%) P2O5 supplied as superphosphate. Knowing this value, it is possible ommend the amount of fertilizer needed to raise the extraction value of a field to a predetermined desired value. The main problem is to find the desired value, under conditions of limited water supply. The results of the supplementary irrigation experiment on wheat are presented in table 4. In the analysis of variance the irrigation effect was very significant, and the interactions of nitrogen X irrigation and nitrogen N irrigation X phosphate were also significant. The significance of the interaction is rooted in the fact that, at low levels of P, N has a positive effect (though not significant) on both rainfall and irrigation treatments, while at a higher level of P, the N-effect is positive on rainfall (5% significant) and negative (non-significant) on irrigation. The effect of irrigation on yield increase shows that water was the limiting factor, while the efficiency of water usage by the crop was identical with and without irrigation. The control plots gave average yields of 2800 kg/ha grain, which is equivalent to about 7420 kg/ha dry matter production; with 360 mm rain, and with supplementary 279 Table 4. Yield of Florence Aurore wheat (kg/ha) as affected by supplementary irrigation, soil phosphate and nitrogen fertilizer. Bicarbonate-soluble P (ppm) N (kg/ha) '4.4 7.5 360 mm rainfall Rainfall + 80 mm 360 mm rainfall Rainfall + 80 mm only irrigation only irrigation 70 2810 3310 2400 3520 120 3020 3420 2980 3360 irrigation totalling 440 mm, 9000 kg/ha dry matter were produced. Assuming that all the water was used by the plants, 465-490 kg water was used per 1 kg dry matter of wheat produced. This value is within the ranges reported earlier, and close to the average value (500) found in the U.S.A. [2]. Increasing the amount of bicarbonate-soluble P over 4.5-5 ppm had no dramatic effect on yields when there was less than 440 mm of water. When rainfall totaled 330 mm, it was found in a field experiment on 450 plots that wheat yield leveled off at 6-10 ppm bicarbonate-soluble P [5]. Since the average annual rainfall in the Negev is about 300 mm, a soil test value of 6 ppm bicarbonate-soluble P is taken as a safe level for wheat production.

Literature cited

I. Azrikan M.: Economic consideration of dry farming crop rotation. (In Hebrew.) Hassadeh 46, (5), 395-398 (1966). 2. Barber S.A., Walker.J.M.. Vasey E.N.: Mechanisms for the movement of plant nutrients from the soil and fertilizer to the plant root. J. Agric. Fd Chem. 11, 204-207 (1963). 3. BondorfK.A.: The evaluation of soil analysis. Trans. Int. Soc. Soil Sci. Dublin 1952 1, 290-295 (1953). 4. Olsen S.R.. Cole C. V., Watenabe F.S., Dean L.A.: Estimation of available phosphorus in soils by extraction with sodium bicarbonate. Circ. U.S. Dep. Agric. 939 (1954). 5. Permanett Plot Team: The permanent plot experiment. Methods and results, 1961-1966, pp. 155-162. Volcani Inst. Agric. Res., Bet Dagan, Israel (1968). 6. Tisdale S. L.: Problems and opportunities in soil testing and plant analysis, part I. Soil Sci. Soc. Am. Spec. Publ. Ser. No.2, 1-12, Madison, Wisc. (1967).

280 Closing Address

Dr. R. HAERERLI, Member of the Board of Administrators of the International Potash Institute

The 7th Colloquium of the International Potash Institute has now come to an end, after five working sessions and two days and a half of excursions of an exceptional interest. The theme selected: Transition from extensive to intensive agriculture with fertilizers was challenging and the fact that the numerous questions raised appear to require further investigations or studies is the mark of a fruitful meeting. It is not my privilege to review point by point the scientific conclusions of the Collo- quium and I should certainly not like to repeat the excellent comments given by Prof. Ar- non and the Coordinators of the sessions. I may berhaps be justified in making two general observations which may well apply to many other disciplines, but which are certainly appropriate to the intensification of agriculture through fertilization. To balance the ever increasing specialization due to the growing complexity of research it is of primary necessity for those working in related fields to exchange information on the results of their work. Economics of fertilizer use, new developments in their technology, extension, as well as soil science, plant physiology and plant breeding are equally involved in the intensification of agriculture through fertilization. The rapidly changing conditions of agricultural production require also a continuous re- vision of the techniques and methods used by agronomists. It was most encouraging for the future to hear, that intensified agriculture in semi-arid regions even in Israel, which offers many examples ofhigh intensification, isfrom a plant physiological point of view far from having reached its maximum potential. I should like to stress also in my opinion as a journalist that the lectures, communications and discussions offer not only to the agronomist and the scientist but also to a very large audience a source of useful information. Many people are interested for instance to know more about the effect of fertilizers on the quality of food, the evolution of the rural structure in a changing agriculture ... and the International Potash Institute may have to play also an important role in that field. We have been most fortunate to have had the opportunity to hold the 7th Colloquium of the International Potash Institute in this country of striking contrast, meeting place of orient and occident, old and new, religious and secular. Again in the name of the Administrative Board I should like to express my deep gratitude to the excellent chairman of the Colloquium, Prof. Arnon, to the Coordinators Dr. Cooke, Mr. Drouineau, Mr. Dam Kofoed, Prof. Laudelout, Dr. Walsh, to the lecturers and authors of communications responsible for the value of the meeting, and the 281 Scientific Secretaries of the International Potash Institute, Mr. de Tarragon and Prof. Mengel. The succes of this colloquium did not happen by chance, and I should like to convey again my thanks to those who have contributed in its very careful preparation and in Israel especially to Mr. Gans and his collaborators who helped very efficiently for various arrangements of the meeting. Now I declare closed the 7th Colloquium of the International Potash Institute and wish to all participants a good return back to their respective countries.

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