Some Technical and Economic Aspects of the Manufacture, Distribution and Application of Artificial Fertilizers

SOME TECHNICAL AND ECONOMIC ASPECTS OF THE MANUFACTURE, DISTRIBUTION AND APPLICATION OF ARTIFICIAL FERTILIZERS.

Thesis submitted for the degree of Doctor of Philosophy at the University of London in the Faculty of Engineering by Jack G. Helfenstein, B.Sc.,

Dept. of Chemical Engineering, Imperial College of Science and Technology, London, S.W.7. November 1959. -1-

ABSTRACT

This thesis attempts to evaluate some of the economic and technical problems facing the fertilizer industry, both at present and in the future, against the background of the potential demand for fertilizers. The history and growth of the British fertilizer industry is examined. A special study is made of the statistics relating to fertilizer production and consumption since 1945. The economic theory underlying fertilizer use is investigated and extended. An estimate of the potential demand for fertilizers is made and it is concluded that fertilizer consumption could, with advantage, be greatly increased, especially that of nitrogen. The extent to which fertilizer prices and subsidy policy have affected demand are determined and discussed. The results of a survey that was made to determine farmers' attitudes to fertilizer use are given. The relative importance of various factors affecting fertilizer use are assessed. Current methods of distribution and application are compared to alternative methods. It is concluded that the former are in the main satisfactory, though a greater nutrient concentration in fertilizers would lead to significant savings on cost.In view of it's importance to the industry the unit operation of granulation is examined in detail and methods of achieving optimum efficiency suggested. Various fertilizer production processes are assessed for their economic and technical feasibility. It is concluded that the potential demand for nitrogen would be best met by the greater use of ammonium nitrate and the introduction and use of urea. It is further concluded that the present,phosphorus,fertilizer processes are adequate and that certain alternative processes, mainly for the production of water insoluble phosphates, are not economically feasible under British conditions. It is thought that there is little or no scope for the use of liquid fertilizers in the U.K. ACKNOWLEDGEMENTS

The author wishes to thank especially Professor D.M.Newitt,of the Imperial College of Science and Technology, and Professor R.S.Ldwards, of the London School of Economics, for their supervision and continued interest in this work and also for having made possible the writing of a thesis involving both technology and economics. My thanks are also due to Mr.Peston, of the London School of Economics, for his invaluable discussion and critiscism of many of the economic sections of this thesis. I would also like to thank all those individuals and organisations, too numerous to mention separately, who supplied data for this work. Especial thanks are due here to Mr.J.Crosby, of the Cambridgeshire Farmers' Union, whose help in organising the collection of data for Chapter 5 was invaluable. Finally I would like to thank the Department of Scientific and Industrial Research for their maintainence grant during the past three years which enabled me to carry out this work. -iv- CONTENTS Page Title Abstract Acknowledgements iii Contents iv

Chapter 1. The history and organisation of the fertilizer industry. 1 1.1. History of fertilizer use. 1 1.2. Present state of knowledge on fertilizers. 9 1.3. The history of the fertilizer industry in the United Kingdom. 15 1.4. The present organisation and structure of the fertilizer industry. 22 Chapter 2. Consumptionl production and trade in fertilizers. 30 2.1. Sources of statistics. 30 2.2. Consumption of, the major plant nutrients. 32 2.3. Production in the fertilizer industry. 37 2.4. The effect of increased fetilizer consumption on agricultural output. 37 2.5. Nitrogen fertilizers. 40 2.6. Production,consumption and trade in phosphatic fertilizers. 47 2.7. Production,consumption and trade in potassium fertilizers. 55 Appendix, chapter 2. 58 Chapter 3. The potential demand for fertilizers and itIc relation to agricultural policy. 63 3.1. Postwar agricultural policy in the United Kingdom. 63 3.2. Economic condition of the agricultural industry. 68 -v- Contents continued:- Page 3.3. Response of crops to fertilizers 72 3.4. The nature and extent of the potential demand for fertilizers. 84 Appendix, The choice of a response curve for predicting the optimum level of fertilizer application. 103 Chapter 4. The changing structure of fertilizer prices and subsidies and itSc- effect on expenditure and consumption of fertilizers. 115 4.1. Current fertilizer prices. 115 4.2. Level of fertilizer prices, 1946-58. 118 4.3. Fertilizer subsidies. 119 4.4. Expenditure on fertilizers. 124 4.5. Relationship between farm income, fertilizer price and consumption. 125 4.6. Subsidy policy. 127 Appendix, chapter 4. 129 Chapter 5. The attitude of farmers to the use of fertilizers. 132 5.1. Introduction. 132 5.2. Results of preliminary survey. 133 5.3. Survey of farmers in Cambridgeshire. 136 Appendix. Criticism of methods employed and accuracy of results obtained from survey. 146 Chapter 6. Some economic and technical aspects of the fertilizer industry with particular reference to application and distribution. 149 6.1. Properties required of fertilizers. 149 6.2. Granulation in the fertilizer industry. 153 6.3. Distribution of fertilizers. 174 6.4. Application of fertilizers. 181 -vi-

Contents continued:- Page

Chapter 7.Fertilizer manufacturing processes and and the future development of the industry. 185 7.1.Nitrogen fertilizers. 185 7.2.Phosphorus fertilizers. 221 References. 246 -1-

CHAPTER 1

THE HISTORY AND ORGANISATION OF THE FERTILIZER INDUSTRY

1.1 History of fertilizer use

1.1.1, The early history. The use of animal manure on the land stretches back over many thousand years and is presumably as old as settled agriculture itself. It was in Roman times that the first major writings on agriculture appeared and these, besides recommending the use of manure, stated the beneficial effects of marl and limestone on the soil. These may be classified as fertilizers. With the breakup of the Roman Empire conditions in Europe became unsettled and were not condusive to agricultural research. During the succeeding nine or ten centuries the method of restoring fertility to the soil was, in general to allow the land to remain fallow for a season. However from the 16th Century onwards increasing numbers of references to the use of manure and artificial fertilizer? occur.

A fertilizer is here defined as a material which, when added to the soil, increases the yield of a crop grown in that soil i.e. renders it more productive than it would otherwise be. The term 'artificial fertilizer' is here used to denote those materials, other than decayed vegetable matter or animal manure, which are used for this purpose. -2-

In 1563 for example, Bernard Palissy in his work 'Recepte Veritable' (1) recommends the use of marl, lime and wood ashes as fertilizers and suggests that it is the mineral salts in the ashes which are of benefit to the plant. Before the beginning of the 19th Century increasing numbers of substances were found to have an effect on the growth of plants. Glauber, in common with other scientists, found that nitrates increase plant growth and he held that 'saltpeter is the principle of vegetation'. Also it was discovered that bones had a fertilizing action as well as such materials as rags, wool waste, hoofs, horns and blood. However there was no knowledge as to why these were effective. Many experiments were made with different substances to determine their action on plant growth. In 1750, Jethro Tull (2) after a series of experiments summed up the extent of knowledge concerning fertilizers as follows:- 'It is agreed that all of the following materials con- tribute in some manner to the increase of plants, but it is disputed which is that very increase in food. (1) Nitre (2) fire (3) earth (4) water'. It is unfortunate that, although a large number of experiments were made in this period, the lack of a quantitative, scientific approach prevented any rational developments in the restoration and maintenance of soil fertility to be made. It was at the end of the 18th Century that Thomas Malthus wrote his 'Essay on the principle of population as it affects the future improvement of society' (3). Malthus' theory visualised a constant pressure of the population on a food supply limited by the world's available land area and it: gradual declining fertility.. However the latter prediction proved to be incorrect by the knowledge, gained subsequently in the 19th Century, that by the addition of plant nutrients soil fertility could be maintained and even improved. 1.1.2. The growth of knowledge concerning fertilizer use. 1.1.2.1. Early investigations. In 1804 T. de Saussure, as a result of his research, published a book, 'ReCherches chimiques sur la vegetation' (4) which marked the origin of the science of fertilizers. The importance of Saussure's work was that he instituted a.. quantitative method of experimentation in his investigations on plant physiology. He showed conclusively that plants derive their carbon and oxygen from the atmosphere and their nitrogen and mineral matter from the soil. In 1834 J.B. Bou.ssingault (5) laid out a series of field plots and, using Saussure's methods of analysis, confirmed his conclusions concerning the nutrient value of mineral matter on actual crops. He weighed and analysed the quantity of manures applied and the crops obtained and was thus able to relate the increase in growth with the nutrients applied. Although Saussure had pointed to a means by which soil fertility could be increased, the lack of a sufficiently developed chemical industry prevented his theories from being put to any practical use at the time. In addition it is doubtful whether the pressure of population on the nutritional resources of Europe was sufficient to give any impetus to developments in this direction. As a result, in this period, the humus theory, as expounded by A. Thaer in his treatise tGrundsaetze der Rationellen Landwirtschaftt, (6) was accepted. In this theory soil fertility was ascribed to humus or decayed organic matter. The plants were regarded as living on this and the significance of mineral matter was disregarded.

1.1.2.2. The work of Liebig. It was in 1840 that Justus Liebig, in a report (7) to the British Association for the Advancement of Science, questioned and disproved the validity of the humus theory. Liebig examined much of the past experimental work and showed that plants live not on decaying vegetable or animal matter but on the mineral compounds contained therein. He stressed the importance of phosphorus and potassium in plant physiology, as well as other alkali salts. He further observed the beneficial effects of ammonium salts on crop growth. He however drew the erroneous conclusion that plants derived their nitrogen from ammonia assimilated as such by the plant. He gave the sources of this ammonia as the atmosphere, the soil or in the added fertilizers and manures. The great importance of Liebig's work was the advocacy, for the first time, of the addition of mineral compounds as such to the soil in order to enrich it thus giving an impetus for the start of an artificial fertilizer industry. Indeed he went into some detail as to the possible sources of fertilizers. He suggested the use of by-product ammonia from gas works, in the form of ammonium sulphate, and the use of waste products from glue works which had a high phosphorus content. He also advocated the treatment of bones with sulphuric acid to render the phosphorus compounds more soluble and readily available to plants. This treatment had previously been proposed by Escher (8) in 1835, but it had passed unnoticed. It is significant that Liebig's suggestions came at a time when the chemical industry in Europe was rapidly expanding, a fact which enabled them to be implemented. Ammonia was in plentiful supply from gas works and cheap sulphuric acid was coming into the market. Liebig in developing his 'mineral theory', as it became known, postulated two concepts subsequently proved false. In later work he rejected his earlier ideas on the supply of nitrogen to plants and maintained that they derived this nutrient solely from the atmosphere. Alkalis, phosphates and sulphates were the only materials required to promote crop growth. Further he put forward the idea that the extra growth of a plant was directly proportional to the quantity of fertilizer applied. It is now known this growth follows a law of diminishing returns.

1.1.2.3. The work of Lawes and Gilbert. Liebig's mineral theory at the time gained much support. G.B. Lawes and H. Gilbert, who had been conducting field experiments at Rothamsted since about 1840, eventually pointed out the errors contained in it. By 1855 they had completed enough work on the effect of fertilizers on crops to enable them to draw certain conclusions, which have been summarized by Sir E.J. Russell as follows (9):_ (a)Crops require phosphates and the salts of the alkalis but the composition of the ash does not afford reliable information as to the amounts of each constituent needed. e.g. Turnips require large amounts of phosphorus although only a small anount is present in their ash. (b)Non-leguminous crops require a supply of some nitrogen compounds, nitrate or ammonium salts being almost equally good. Without an adequate supply no increases in growth are obtained, even when ash, i.e. mineral, constituents are added. -7-

The amount of ammonia obtainable from the atmosphere is insufficient for the needs of crops. Leguminous crops behave abnormally. (c)Soil fertility may be maintained, for some years at least, by means of artificial fertilizers. (d)The beneficial effect of fallowing lies in the increase in available nitrogen in the soil that occurs. The work of Lawes and Gilbert (10) was extremely important in the development of fertilizer science. Not only did they discover or confirm which nutrients crops require, but also by their quantitative experiments they determined rational levels of fertilizer use.

1.1.2.4. The biological fixation of nitrogen. One problem still remained unsolved. This was the apparently abnormal behaviour of leguminous crops. Boussingault, as early as 1830, had found that the nitrogen in these, and the soil in which they were grown, was apparently greater than the nitrogen added in the fertilizer. This observation was subsequently repeated many times and was probably the reason for Liebig's conclusion that plants derive their nitrogen from the atmosphere. Lawes and Gilbert, in spite of much experimental work, were unable to determine the cause of this increase in nitrogen. It was not until 1886 that the problem was solved. In that year Hellriegal and Wilfarth (11) made the discovery that the symbiotic bacteria, (bacillus radicicola), living on the roots of the legumes, had the power to fix nitrogen in the soil for their own metabolism. This nitrogen then becomes available to the host plant or other roots in the vicinity. The amount of nitrogen that can be fixed by a leguminous crop can be extremely large, ranging in general from 60-90 lbs/acre. Subsequently in 1890, Winogradsky (12) and others discovered the activity of the non-symbiotic bacteria, (azotobacter), which also have the ability to fix soil nitrogen. The nitrogen fixing power of these is less than that of the symbiotic bacteria, being of the order of 5-25 lb/acre. This discovery supplied the reason for the increase in soil nitrogen, which occurs when it is left fallow and for the necessity of maintaining a good, well aerated, soil structure. This knowledge represented the last major advance in the basic theory underlying fertilizer use. Subsequent research, which still continues, has been directed towards obtaining a more detailed and exact knowledge of the use and effect of fertilizers. 1,2. Present state of knowledge on fertilizers.

1.2.1. General. It is recognised that plants require the following elements for the process of growth:-' Carbon, oxygen, hydrogen, nitrogen, phosphorus, potassium, calcium, sulphur, magnesium, iron, zinc manganese, boron and molybdenum. Other elements such as sodium, silicon, aluminium, chlorine and cobalt are found in plant tissues but they have not been shown to be essential for growth. Plant tissue is composed of carbohydrates, fats, proteins and nucleoproteins and the proper functioning of the tissues is maintained by various enzymes. The first three of the essential elements, carbon, oxygen and hydrogen, are obtained from carbon dioxide, oxygen and water found in the atmosphere or the soil. A plant requires large quantities of these elements, they form over 90% of its weight on a dry basis, in the formation of carbohydrates, fats and proteins. These compounds are produced by the process of photo sithesis. These elements are in abundant supply though good methods of cultivation have to be employed to make them freely available to the plant.

1.2.2. The primary nutrients. The group of elements nitrogen, phosphorus and potassium -10. is often referred to as the primary nutrients. Although all three are present in large quantities in the soil, nitrogen is rapidly depleted by intensive cultivation and the other two are often present in forms unavailable to the plant. Additional supplies have therefore to be provided if continuous, intensive cultivation of the land is to be made possible. The function of each of these elements and the form in which it is required by the plant are discussed briefly below. It is important to realise that the performance of each function depends on the presence of adequate supplies of the other nutrients. Substitution between the primary nutrients, i.e. the use of one particular nutrient in preference to or in place of another one, is not possible from an agricultural standpoint. The nutrients are used in a ratio set by the requirements of the plant and the initial amounts available in the soil.

1.2.2.1. Function and supply of nitrogen. Nitrogen is essential to the plant in the formation of proteins though the mechanism of synthesis is latti yet understood. The nitrogen is takeninto the plant by means of the roots, in the form of nitrate or ammonium ions in solution. These are converted, in the plant cells, into amino acids which combine to form proteins. Certain plants -11- can probably utilize both forms of nitrogen equally well (9) though the uptake of nitrate ions is much greater than those of ammonium. This is because the latter are fairly rapidly oxidised to nitrate by the nitrifying bacteria in the soil. Further)the former tend to be in greater concentration round the plant roots and are thus more available. Ammonia under- goes a colloidal reaction with clay or humus and is not present as an ion in solution to the same extent as that of the nitrate ion. Experiment has shown that a large number of materials are suitable as nitrogen fertilizers. Among the more common ones are ammonium sulphate, ammonium nitrate, sodium nitrate, calcium nitrate, calcium cyanamide, urea, ammonia and certain nitrogen carrying organic substances. Most of these commodities are to a large extent interchangeable in their effectiveness as suppliers of nitrogen, though complete substitution of one compound for another is not possible. Some of them exhibit side effects which may render their use un- suitable under certain conditions. Such materials as urea, calcium cyanamide and the organic forms of nitrogen have first to be broken down in the soil to ammonium and nitrate ions before they are of use to the plant. Their action is thus rather more long term and a quick acting nitrogen fertilizer is necessary to get the crop established. -12-

A large number of factors affects the plant response to fertilizer. e.g. 1-ulnfall, soil type and condition, etc. In general these do not vary sufficiently widely in the U.K. to affect the action of different nitrogen fertilizers to any great extent. A high degree of substitution of one compound for another is therefore possible.

1.2.2.2. The function and supply of phosphorus. Phosphorus plays an essential part in cell division and the formation of plant tissue. It is also present in the amino acids which give rise to phosphate bearing protein. It is likely that plants take up this element almost exclusively in the form of the phosphate ion (9), (H2PO4-), in solution. Various materials have been found to be suitable as phosphorus fertilizers. Among the more common are superphosphate, (essentially mono-calcium phosphate), nitrophosphate, (dicalcium phosphate), ammonium phosphate, basic slag, (a calcium silicate and phosphate) rock phosphate, and certain materials of natural origin such as bones. Substitution of one commodity for another is not possible to any great extent with phosphorus fertilizers. Soil conditions may be such that the element may revert from an available form, i.e. one which can be readily assimilated by a plant, to a non-available form. In general, those materials containing the phosphate ion as such, (super- phosph,,,te, ammonium phosphate), are interchangeable as fertilizers. Others, (basic slag, rock phosphate), are only useful in wetter, acid soil areas. Under these conditions phosphate ions' are formed and these materials are then equivalent to others in the group.

1.2.2.3. The function and supply of potassium. Potassium, while essential to plant nutrition, is not a constituent of the plant fabric. Its importance lies in the part it plays in the plant's metabolism. The function of this element is in the processes of protein synthesis and photosynthesis, though the knowledge as to its action is still incomplete. Pldnts take up potassium in the form of the metal ion, (e)7 and any salt containing the latter is suitable as a fertilizer. In actual practice the most common material used is potassium chloride though potassium nitrate or sulphate are also used. Agriculturally these salts are equally effective as fertilizers.

1.2.3. The s.3condary nutrients® The group of elements calcium, sulphur and magnesium is generally referred to as the secondary nutrients. All three are present in the plant structure and play an portant part in its metabolism. Considerable quantities of these lements are required by a plant, calcium and magnesium in the form of the metal ion, sulphur as the sulphate ion. Soils in the U.K. do not on the whole require additions of the secondary nutrients since they are already present in sufficient quantity and in forms readily available to the plant. In practice; however, sulphur and calcium are added in fairly large quantities. The former is applied with the primary nutrients, i.e, as ammonium sulphate or superphosphate. The latter is added during the extensive liming of the soil which is practi/ed in the U.K. Lime is primarily applied as a soil conditioner, e.g. to counter excess acidity, rather than as a plant nutrient.

1.2.4. The trace elements. The remaining essential elements are known as trace elements. -,da.i"e extremely important in the plant metabolism only small amounts of them are required; indeed large doses are often toxic. Their precise function is, in many cases, no' fully understood. Local deficiencies of the trace elements may occur but these are readily made good either by direct addition to the soil or by foliar application. _15_

1.3. The history of the fertilizer industry in the United Kingdom.

1.3.1. The early beginnings. The start of the artificial fertilizer industry in the U.K. dates from about 1840, its development being prompted by the large increase in knowledge concerning fertilizers which occurred at the time. Previously there had been a trade in bones which were ground for use as fertilizers. Their use was particularly prevalent in the U.K. which imported considerable quantities of them and by 1800 demand was exceeding the supply (13). The use of rags, wool waste, hoof, horn and dried blood was also common and there was some trade in these commodities. In 1840, Liebig attempted manufacture of an artificial fertilizer, containing phosphates and potash in order to confirm his theories. Unfortunately the process used rendered both nutrients in a form unavailable to plants. As a result of this failure he abandoned his attempts to develop a commercial fertilizer.

1.3.2. The development of the fertilizer industry. 1.3.2.1. The development of the superphosphate industry. In 1840, G.B. Lawes, probably as a result of Liebig's publications, had begun to treat bones with sulphuric acid in order to make the phosphorus they contained more soluble. He was selling this product before 1843 (14). Lawes had also turned his attention to mineral phosphates as a source of phosphorus for fertilizers. He dissolved coprolites, a low grade, phosphate mineral found in the Cambridgeshire area, in sulphuric acid to make the phosphate water soluble. In 1842 he took out a patent to cover both processes (15). Other people were doing work in this direction, for almost at the same time Sir James Murray took out a similar patent (16) in Scotland. This was subsequently acquired by Lawes. In 1843 Lawes commenced manufacture of superphosphate, as it was known, from coprolites and sulphuric acid in a factory at Deptford. He was almost certainly the first person to do this on a commercial scale. By his action he established superphosphate as the basis of fertilizer manufacture in the U.K., a position it has retained to the present day. Soon after this factory was opened other people also commenced manufacturing superphosphate or dissolved bones. Packard (14) has listed 18 such firms as having begun operating between 1842 and 1870 and has estimated that by 1870 there were some 80 different works. Lawes was unable to establish his patent until 1851 and only by dropping certain of his claims. It appears that he entered into private agreements with certain firms permitting them to manufactui.e superpl!.-Thate. The industry continued to expand up to 1890 and, in addition to domestic sales, a large export trade to Europe was built up. Manufacture tended to be concentrated on the east coast of the U.K. and close to ports, This was done to allow the direct unloading of imported phosphate rock and also to assist export of the product to the continent. Manu- facturers, so as to obtain a more concentrated product, began to import phosphate rock from France, United States and, in 1890, North Africa. Imports from the latter area soon became the principal source of the raw material and have remained so to the present day. Production increased from about 150,000 tons superphosphate in 1862 to about 900,000 tons in 1889 (14). It contained between 12 and 16% of P205.

1.3.2.2. Development of the nitrogen industry. During the growth of the superphosphate industry, two sources of nitrogen were available, sodium nitrate, imported from Chile, and ammonium sulphate obtained as a by-product from gas works d coke ovens. Imports of the former first took place in 1840 and its use as a nitrogen fertilizer was rapidly establi:hed. Ammonium sulphate does not appear to have been used, to any extent, as a fertilizer until 1850. -18-

Consumption of both t'i.ese commodities increased steadily after their introduction and they remained the only major sources of this nutrient until 1920.

1.3,2.3, The development of the potash industry. Although potassium was recognised as an essential plant nutrient, the lack of a cheap source of supply prevented its use on any appreciable scale. In 1856 the extensive Stassfurt deposits of potassium bearing minerals were dis. covered in Germany and in 1861 the first factory for, ex- tracting the salts was established (17). By 1870 the import and use cf potash fertilizers had become widespread in this country,

1.3.2.4. Other phosphorus fertilizers. Guano was imported from 1840 onwards and though a popular fertilizer it was never a serious competitor to superphosphate. In 1879 Thomas and Gilchrist invented the basic process of making steel which produced large quantities of basic slag having a high phosphorus content. It was shown that the slag vas an effective fertilizer under certain conditions and in 1885 it became available on the market. Basic slag soon became a major fertilizer, it being very attractive on account of its low cost. Though it probably took a sector of the market, which would otherwise have gone _19_ to superphosphate; it was noL a real competitor since supplies were limited and del.:endant on production in the steel industry, The various plant nutrients were sold as separate commodities and there does not appear to have been any large scale maaafacture of mixed fertilizers at this time.

1.3.3. The decline of the superphosphate industry. By 1890 the British superphosphate industry was beginning to feel the effects of foreign competition, especially from Be7.gium and France. These countries had a large surplus of sulphuric acid which was used to make superphosphate. This was imported freely into the U,K. and sold at prices below those of British manufacturers. Further there was a surplus of sulphuric acid in Britain itself and the manufacture of superphosphate was the simplest way of disposing of it. This led to severe domestic competition in addition to that faced from abroad. The effect of this was to depress the industry and especially its technology. This condition remained until 1927 and several firms were forced to close down. A short respite was given during the first world war when imports from abroad ceased. -20-

The re-organisition of the superphosphate industry. From 1927 onwards many superphosphate manufacturers amalgamated with a view to limiting domestic competition and rationalising the industry, by closing down small works and building up large units of an economic size. Technological improvements were also initiated, notably in the production of complete mixed fertilizers, granulation and the intro- ductior of continuous methods of production. Vertical integration of the manufacturing stages, i.e. of sulphuric acid, superphosphate, mixing and granulating plants, was practited on a much larger scale than before. In 1934 the industry persuaded the Government to grant a tariff against foreign imports which helped to reduce competition from abroad. These measures led to a steady recovery of prosperity in the superphosphate industry.

1.3.5. The introduction and development of the synthetic nitrogen industry. Methods for fixing atmospheric nitrogen were first developed at the end of the 19th Century, the cyanamide process in 18952 and the electric arc process in 1905. These with their large requirements of electrical energy were not economically feasible in Great Britain. However with the introduction of the Haber-Bosch process, for the production of ammonia, such a method did become available. -21-

The process starts with nitrogen and hydrogen as raw materials which are then di-ectly combined to form ammonia. The latter can then be oxidised to form nitric acid and nitrates. A plant of this type was successfully operated in Germany by 1913. Under the stimulus of the 1914-18 war, with its demand for nitrogen for munitions, the erection of a synthetic nitrogen plant was commenced by the Government at Billingham. Owing t;) technical difficulties it was not operated until 1923. The plant was acquired by Brunner, Mond and Company in 1920 and eventually became part of Imperial Chemical Industries Limited when the latter was formed in 1926. The operation of the synthetic nitrogen process provided iao new fertilizers, ammonium nitrate, sold as nitrochalk and synthetic ammonium sulphate. The latter could be produced more cheaply than the by-product salt and was of better quality. Competition was however eliminated by the formation of the British Sulphate of Ammonia Federation, Ltd., in 1920, which regulated the sale, import, export and storage of ammonium sylphate. Imperial Chemical Industries became closely connected with this organisation and became its sole selling agents in 1930. Further the close association of the company with the various world nitrogen cartels (18), notably the D-E-N, (Deutschland-England-Norway), and the C.I.A., (Convention de VIndustrie de LfAzote), agreements protected -22-

them from foreign competition and gave them a virtual monopoly position in the domestic fertilizer nitrogen market. This period marks the decline of the import and use of sodium nitrate as a fertilizer. The synthetic nitrogen process was integrated with other chemical plants to produce fertilizers as well as a range of other products. The process was vertically integrated with ammonium sulphate, phosphate) mixing and granulating plants to produce high analysis fertilizers based on ammonium phosphate. This re-organisation produced the structure of the fertilizer industry very much as it exists to-day. The technological advances and increased efficiency produced in the industry enabled it to co-operate successfully with the Government in its campaign to increase agricultural productivity during the last war. In spite of severe supply difficulties, fertilizer consumption was able to be almost doubled fol. nitrogen, increased by half for phosphorus and held constant for potassium.

1.4. The Present organisation and structure of the fertilizer indqstry

1.4.1. The structure of the industry, The Britis'.a fertilizer industry can be divided broadly

FIGURE I. I.

DIAGRAM OF STRUCTURE OF FERT 1 LIZ ER INDUSTRY

FERTILIZER MANUFACTURERS

I I M PORTED POTASH PRIMARY k . >_NLTROGEN MATERIAL S SECONDARY MANUFACTURERS -- - - ....b WM 1M 1 SUPERPHOSPHATE I • MAN UFACTURERS I I I I I I

II I II— MID OM OM UM ""' 1 I I I I I I I I MANUFACTURERS PRODUCERS MANUFACTURERS I PRODUCERS MANUFACTURERS 4 AM M ON I UM F I X ED BY-PRODUCT 1 BASIC SLAG AMMONIUM SUPERPHOSPHATE I MANUFACTURERS PROCESSORS GRINDERS PHOSPHATE N ITROGEN SULPHAT E I MIXED FERTILIZERS ORGANIC ROCK I I I I I 1 e I I FERTILIZERS PHOSPHATE I 1 ..n.... — — — — .1 — — — — — — — ^sok. it — • 1 I I I —I — I I i I I I I I r I 1 I \•11/ \l'i T \eli 4/ \i/ I ) I - ... - ..- - - - ...4 - ... . , •ii -1 1.1- r a-- I I \V 4/ MIXED M I XED FERTILIZERS FERTILIZERS -23.. into two main groups g- (Diagram 1.1). a)Primary manufactu:oers b)Secondary manufacturers Th?, first group consists of firms who manufacture fertilizers from basic raw materials, e.g. superphosphate from phosphate rock, fixation of atmospheric nitrogen, etc. The second group comprises those firms who purchase straight fertilizers from the primary manufacturers and then further process them to produce various mixed fertilizers.

1.4.1.1. The primary manufacturers. The primary manufacturers can be further sub-divided into five main groups. 1.4.1.1.1. Manufacturers of superphosphate. There are fifteen firms in the U.K. manufacturing superphosphate (21). By far the largest firm is Fisons Ltd. which probably accounts for over 50% of the current superphosphate production in this country (19). This company, vinich arose from the amalgamation of several superphosphate manufacturers is now, in addition, administratively integrated with several non-fertilizer manufacturing activities. The firms in this group are, in the main, specialist producers of superphosphate. They also make mixed fertilizers but they arc no' producers of the other nutrients required, nitrogen and potash, which they purchase from other -214, manufacturers. Iyo exceptions to this are Fisons Ltd. and West Norfolk Farmers Co-operative Ltd. who produce part of their own nitrogen requirements. These two firms also manufacture both concentrated and ordinary superphosphate whereas the others in this group manufacture only the latter. Scottish Agricultural Industries. Ltd. does, however, manufacture ammonium phosphate in addition to superphosphate.

1.4.1.12.Manufacturers of synthetic (fixed) nitrogen. Until 1959 there were only two companies manufacturing synthetic nitrogen compounds for fertilizers in the U.K. They were Imperial Chemical Industries Ltd. and a firm owned jointly by Fisons Ltd. and the West Norfolk Farmers Co- operative Ltd. The capacity of the latter plant was insufficient to meet the demands of its owners and they were net purchasers of nitrogen from Imperial Chemical Industries Ltd. (20). In 1959 Fisons and the Shell Oil Company commenced manufacture of ammonium nitrate in new plants associated with one of the latter's oil refineries. This has considerably lessened Fisons' dependence on outside purchases of nitrogen compounds. Further the Shell Oil Company now sells a straight nitroLen fertilizer, nitrashell, based on ammonium nitrate. The synthetic nitrogen plants of Imperial Chemical -25-

Industries are integrated with other plants to produce ammonium sulphate; ammonium nitrate, (sold as nitrochalk), and a mixed fertilizer based on ammonium phosphate as well as other non-fertilizer materials.

1,4.1.1.3. The manufacturers of by-product ammonium sulphate. There are a large number of manufacturers of by-product ammonium sulphate, the major sources being the gas industry and coking ovens of iron and steel plants. They are associated, together with Imperial Chemical Industries who manufacture synthetic ammonium sulphate, in the British Sulphate of Ammonia Federation Ltd. This organisation regulates the sales of the product for them and prevents competition between the various manufacturers.

1.4.1.1.4. Producers of basic slag. There are a number of iron and steel firms which pro-. duce basic slag as a by-product. The more important of these have associated together by forming a company, British Basic Slag, Ltd., which handles the sale of the product for them.

1.4.1.1,5. Manufacturers of ammonium phosphate. There are two manufacturers of fertilizer ammonium phosphate in the U.K. They are Imperial Chemical Industries Ltd and Scottish Agricultural Industries Ltd., -26-

which is controlled by the former.

1.4.1.2. Secondary manufacturers. In the group of secondary manufacturers the most important sub.division is those firms which produce various mixed fertilizers based on superphosphate purchased by them from primary manufacturers. There are 28.firms which engage in this activity. Others in this group are those manufacturers who process organic materials, such as bones, hoof, horn, blood, etc., (the primary use for such products is horticultural rather than agricultural), and rock phosphate grinders. Altogether there are about 80 firms in the U.K. which can be classed as fertilizer manufacturers (21).

1.4.2. Source of raw materials for fertilizer industry. The two most important raw materials imported for the fertilizer industry are phosphate rock and potassium salts. British manufacturers obtain their phosphate mainly from North African mines together with some from the Pacific Islands. There is effectively no competition among phosphate rock producers. All rock mined in North Africa is sold through the Comptoir des Phosphates de L'Afrique du Nord, while that from the Pacific is sold by the Phosphate Rock Commission. -.27-

The industry's potash requirements are obtained from various sources including Germany, France, Spain and Israel. The old cartels 1,",dch used to regulate the sales of potassium salts were broken up during the second world war and have never been reformed. There are domestic reserves of potash salts in Yorkshire but their great depth, associated with difficulties of refining, prevent economic exploitation at the present time.

1.4.3, Organisations within the fertilizer'industry. There are a number of organisations within the fertilizer industry of which the following are the most important:_ (a)The Fertilizer Manufacturers' Association (b)The Superphosphate Manufacturers' Association (c)The Basic Slag Producers' Association (d)The British Sulphate of Ammonia Federation Ltd. The first three of these are not concerned with the regulation of the supplies or prices of their members. They exist to gather statistics, promote exchange of technical information and act as the representatives of the industry as a whole (21). The British Sulphate of Ammonia Federation Ltd. does regulate the sales of its members. The primary objects of the Federation are as follows:- (22) 'The Federation acts as an agent for the disposal of -28- all the sulphate of ammonia produced, owned or controlled by its membe-cs. It is a non-profit making concern, returning to its members, as a pooled realisation, all receipts from sales made at home and abroad less the costs of delivery and administration. It seeks to encourage its members to maintain the highest possible standard of the product and to maintain continuous production.' The members of the three Associations and the Federation control about 95% of the production of fertilizers in the U.K. (21).

1.4.4. Competition within the fertilizer market. All sales of fertilizer are made by fertilizer merchants and not directly between manufacturer and the farmer. Competition within the field of nitrogen fertilizers was, until recently, non-existent. This has been due to the position of the British Sulphate of Ammonia Federation Ltd., which in effect controls the ammonium sulphate market and the fact that the remainder of the nitrogen market was virtually in the control of one company which is also the selling agent for the Federation. A degree of competition now exists with the recent, (1959), opening by Fisons Ltd. of a new synthetic nitrogen plant and the entry of the Shell _29_

Oil Company into the field of straight nitrogen fertilizers, their products being designed to compete with those of the Imperial Chemical Industries Ltd. In the case of other straight and mixed fertilizers it is likely that, at the present time, the most important factors in competition are the quality of the product, the type of product and the type of services given by the manufacturers to farmers. There is certainly no competition by price in the case of straight phosphorus and potassium fertilizers. Though there are differences in the cost of mixed fertilizers, when compared on the basis of their plant nutrient content, it would not appear that there is any active competition by manufacturers in each other's markets. Indeed on the basis of various verbal statements made to the author it is likely that it is actively discouraged by them. It is not, however, possible to ascertain whether, in fact, any agreements do exist or to what extent, if any, competition is restricted. The fertilizer industry is currently under investigation by the Monopolies Commission whose report is expected at the end of 1959. -30-

CHAPTER?,

CONSUMPTION, PRODUCTION AND TRADE IN FERTILIZERS

2.1. Sources of statistics

2.1.1. Sources used in this chapter. Three sources of statistics, relating to the production, consumption and trade of the three major plant nutrients in the U.K., have been used. They are:- (a) Publications of the Central Statistical Office, (1,2) (b) Puelications of the 0.E.E.C. (3) (c) Publications of the British Sulphate of Ammonia Federation Ltd.(4). The first source contains monthly and yearly statistics relating to the primary nutrients and also details relating to individual types of phosphorus fertilizer. The figures are based on returns made by the Board of Trade and the Ministry of Agriculture. The second source contains annual statistics relating to the three nutrients and the individual commodities that supply them, in both the U.K. and other member countries of the 0,E.E,C. -31-

The third source contains annual statistics relating to nitrogen fertilizers, especially ammonium sulphate. These figures are collected by the British Sulphate of Ammonia Federation from the producers concerned. Whenever possible the data in the first source has been used as a primary source. The other publications have been used to supplement this data.

2.1.2. Other sources of statistics. Other sources of fertilizer statistics that are available include:- a)International statistics collected by the Food and Agriculture Organisation of the United Nations (5) and published annually by them. b)National sources. A comprehensive bibliography of these is given by Ewald (6) c)Publications of statistics in the press, e.g. Relevant trade journals, daily press, etc. In general it has been found that these contain little that is not published in the sources mentioned previously.

2.1.3. Presentation of statistics. The statistics relating to the production and consumption of fertilizers are expressed in terms of the content -32-

by weight of 11,13205 and K20. This is the system commonly employed in the U.K. at the present time. Unless otherwise stated, all statistics relate to fertilizer years. Such a year covers the period from 1st July of the preee/ding year to 30th June of the given year. Thus fertilizer year 1945 relates to the period from 1st July 1944 to 30th June 1945. All the major and most minor commodities that find use as fertilizers are included in the definitions of fertilizers employed in the sources of statistics used. Details of these definitions are given in the appendix to this chapter.

2.2. Consumption of the major plant nutrients.

2.2,1. The changing levels of consumption. The statistics relating to the consumption of nitrogen, phosphorus and potassium since 1945 are given on graph 2.1. Four distinct phases or trends have occu4d. (a) The postwar period 1945-47. During this period consumption of all three nutrients remained essentially constant. This was a direct result of the continuation of the wartime fertilizer allocation, (rationing), schemes, when supplies were made available by the Government to farmers for use on certain crops, the amount CONSUMPTION OF MAIN TYPES OF FERT ILI Z ER 1945-58

500"-

400 0,4 PHOS PHAT IC 17t 0 POTASSIUM a.'" -300 NITROGENOUS

0 mo 00 2

.1.•• MM. NM 100

(f) 0

II I I I I I I I m o l t 45 46 47 48 49 50 51 52 53 54 55 56 57 58 YEAR -33- depending on the acreage sown. Consumption was therefore directly controlled by the Government. The supply of fertilizer was limited by raw material shortages and lack of manufacturing capacity and not determined by demand on the part of farmers. (b) 1947-50. Subsequent to the removal of fertilizer rationing a steady growth in consumption of all three nutrients was recorded. The use of nitrogen and phosphorus increased by 30% while that of potassium by 120%. This very large increase of the latter can be attributed to the removal of restrictions on supplies from European sources. During the war these had been cut off and potash consumption was limited to a greater extent than was the case with other fertilizers. From 1945 to 1950 fertilizer prices were kept constant by the Government who paid a subsidy directly to the manufacturers. (C) 1950-52. There was a sharp decline in fertilizer use during this period. This was especially marked in the case of phosphorus fertilizers9 consumption of which by 1952 had fallen to well below the 1945-47 level. This situation was undoubtedly brought about by the large increases in fertilizer prices which occurred between 1950 and 1952. -31+-

For example the prices of all types of phosphorus fertilizers more than doubled. These increases were due to the removal of the subsidies coupled with a general rise in prices on the part of manufacturers. The subsidy was withdrawn partially in 1951 and completely in 1952. It was subsequently re- introduced at the end of 1952 for phosphorus fertilizers and made retroactive for purchases made during this year. Under this new scheme the subsidy was paid directly to farmers and not to the manufacturers as previously. Cc') 1952-58. Consumption of nitrogen and potassium increased steadily again during this period to above the previous maximum in 1950, with a specially marked rise in 1956. While the use of phosphorus recovered from the low level of 1952, the trend in recent years would appear to be towards a slightly declining consumption though considerable fluctuations have occurred from year to year. Due to this decline the overall consumption of nutrients is at present not much above that of 1950 but a significant change in the pattern of consumption, i.e. ratio of plant nutrients consumed, has occurred. This is discussed in 2.2.2. below. The increases in consumption which have taken place were coupled with the re-introduction of a nitrogen subsidy in -35-

1953 and the continuation of the phosphorus subsidy. During the succeeding years the value of these payments has been progressively increased. Consumption of fertilizers would appear to be linked with price and subsidy payment. The extent to which there is a correlation is discussed in Chapter 4.

2.2.2. The changing ratio of fertilizer consumption. Table 2.1 shows the ratio N:P205:K20 consumed in fertilizers since 1945, taking the value of N = 1. Two distinct features of the British fertilizer market are shown in the table:- (a)From 1949 onwards the ratio of K20:N has remained substantially constant at about 1:1, i.e. consumption of these two nutrients is directly proportional. (b)Since 1951 the ratio P205:N has declined. Thus before 1951 it was about 2.15 while in 1958 it was 1.18. The emphasis in fertilizer use has been to increase the relative amounts of nitrogen and potassium consumed. This change can be ascribed to two causes:- (a)Farmers are using a greater amount of nitrogen especially for top dressing crops, ioe. a change in demand. (b)Fertilizer manufacturers have been increasing the ratio of N and K20 to P205 in mixed fertilizers. A very high proportion of fertilizers is sold in the U.K. in the mixed form, -36- i.e. all three nutrients together in one fertilizer. In this case the changed ratio has been brought about more by the ac- tions of manufacturers rather than there being a change in demand from farmers. TABLE 2.1. Year Ratio of consumption of nutrients N P2°5 K20 1945 1 2.00 0.67 19+6 1 2.18 0.67 1947 1 2.18 0.65 1948 1 2.11 0.95 1949 1 2.15 1.01 1950 1 2.17 1.10 1951 1 2.03 1.07 1952 1 1.52 0.95 1953 1 1.74 1000 1954 1 1.57 1.04 1955 1 1.38 1.02 1956 1 1.35 1.06 1957 1 1.22 1.05 1958 1 1.18 1.05 INDEX OF PRODUCTION

190

NCHEM ICAL & 180 ALLIED TRADES 170

160 6)

00 150

1 -o 60TOT A L ALL

1945 140 INDUSTR IE S se 1.)

130 ON I C T 120

ODU t R • P 110 • (ii0 FE RT I LIZ ER • 0 • INDUSTRY / 100

90 , ,• 1 • 1 i a a a a a a a a 80 , I 45 46 47 48 49 50 51 52 53 54 55 56 57 58. YEA R -37-

2.3. Production in the fertilizer industry. In order to compare the growth of the fertilizer industry with that of other industries it has been necessary to prepare an index of production for fertilizers. The method used is similar to that employed by the Central Statistical Office in preparing the official index of production (2,7.) and is described in the appendix to this chapter. On graph 2,2. are plotted the indexes for:- (a)Total all industries, (b)Chemical and allied trades, (c)Fertilizer industry, It is apparent from this graph that while the fertilizer industry has expanded, by some 20% since 1948, this growth has not been as great as that of all industries, 38%, &Pe or even comparable to that of the chemical and allied trades, 96%. Indeed between 1954 and 1958 the net overall growth of the industry was negligible. Although production in the nitrogen sector of the industry has increased this has been offset by a decline in the phosphate sector.

2.4. The effect ofncreased fertilizer consumption on agricultural output.

It is of considerable interest to determine what effect -38- the increase in fertilizer consumption has had on agricultural output. One can measure this effect in two ways:- (a)The immediate and long term effects on crop yields. (b)The effect on value of the output of agriculture.

2.4.1. The effect on crop yields. On graph 2.3. are plotted the annual yields of two representative crops, wheat and potatoes, both known to be on average well fertilized, and the total consumption of fertilizers measured in terms of the total 1\1/J205 and K20 contents. (It is assumed that the amount of fertilizer used on a crop is proportional to the total fertilizer consumption in a year.) From the graph it is apparent that there is no immediate, short run correlation between the quantity of fertilizer used and the yield of a crop following that use, i.e. an increased or decreased use of fertilizer does not automatically bring about larger or smaller yields on average. However the trend lines, (calculated by the method of least squares), for both consumption and yields show positive gradients. It is not possible to draw any conclusions from these figures as to the extent to which the trend in increasing yields has been due to the greater use of fertilizer. One of the major difficulties of attempting to relate

TRENDS IN CROP YIELDS AND CONSUMPTION OF R T ILIZ E RS

1000

0 900 CONSUMPTION

FERTILIZERS 0 800 ▪ 9 ars 4 29 700

z x 27 c~ 600 0 ta YIELD POTATOES u 25 N 500

23 400 7 S '

U R E F • 21 300 TOE TREND LINES ON I

19 200 X 1:25.6i + 64.4 POTA YIELD WHEAT 0 -J Xw=071 t 4. 17.9

17 100 CONSUMPT X • :3.12 t .1" 6.8

16 5 45 46 47 48 49 50 S I 52 53 54 55 56 Y EAR

0 i 2 3 4 5 6 7 8 9 10 11 t YEAR -- 1945 GROSS OUTPUT AGRICULTURE 106 £ VALUED AT 1945/46 PRICES

CONSUMPTION OF FERTILIZERS 103 TONS N 4" P2 O5 K20 .... ru A 0 CO 0 0 0 0 O 0 4, 0 0 0 0 ut O 0 I 1 / I / 0 / c 4% / -I a -o t 0 3d c

% 21 -I

t O 11

t F ISNO I

• AGR • IldVV

OD 9113 Z11 v U NO LT 01 No

4. UR G 1f1 E A 11. 81 ND CO 3

t NS UMPTIO

t N O F i FERT I I I LI ZER S a

G - U4 ut

D GROSS OUTPUT OF CROPS PER ACRE CROPLAND m VALUED AT 1945/46 PRICES £ PER ACRE

't*Z HdV):19 0 U) 0 U) U OUTPUT 0 F CROPLA N D 4 .4 VA LUED A T PER ACRE 14 12 10 13 9 RELATION BETWEENVALUEOFCROPSHARVESTEDTO FERTILIZER APPLIEDINGIVENYEAR1945-56 NM 6

FERTILIZER CONSUMPTION 10 X G RAPH2.5. Y

0 72X+6.6 7

N Nos e•

.ar 5 TONS N+P 9

2 O+K 5 10 2 0 X -39- the two quantitieg is that it is not known to what extent fertilizer is used on individual crops, i.e, whether the assumption that fertilizer application to each crop is proportional to the total, overall consumption is in fact true.

2.4.2. The effect on agricultural output. On graph 2.4. are plotted the total, annual consumption of fertilizers, the total, annual, gross output of agriculture and the annual, gross output of crops per acre of crop land. The values of the outputs have been corrected to their values at 1945/46 prices. Further the outputs have been set back one year, since the application of fertilizer in, say, year 1954/55 will affect the output in year 1955/56. Both total gross output and fertilizer consumption have increased but they do not show any instantaneous correlation. (This is not to be expected.) On the other hand consumption and output of crops have not only both increased but also show an apparently quite good instantaneous correlation. The values of these two quantities have therefore been plotted against each other, for each year, on graph 2.5. The points on this graph can be represented by the following equation, (calculated by the method of least squares):- Y = 0.72 x + 6.8 where Y = Gross output of crops per acre crop land valued at 1945/46 prices. per acre. X = Total consumption of fertilizers. 105 tons N,P205 and K20. This equation has a coefficient of correlation of r = 0.756. The probability of this correlation being random is less than 1 in 100 as estimated by Student's ITV! test. (n.b. calculated value of t = 3.7 for r = 0.756 and ten degrees of freedom. Value of Student's t = 3.1 at 1% probability level). Therefore it can be concluded that increased fertilizer use appears to have a significant effect on agricultural output when this is measured in terms of the gross output of crops per acre of crop land.

2.5. Nitrogen fertilizers.

2.5.1. Production, consumption and trade. The statistics relating to the production, consumption and trade in all types of nitrogen fertilizer are given on graph 2.6. (a) Since 1945 there has been a substantial margin of production over consumption, though this has decreased in

GRAPH 2.6.

PRODUCTION CON SUMPT ION 3 TRADE IN NITROGEN FERTILIZERS 1945-58

350

PRODUCT ION V 300

250

/ CONSUMPTION

200

8 150

100 EXPORTS N / INCLUDING

ROGE NON AGRICULTURAL

IT N I TROGEN N 50

I 1,..jI...1 I I I I I 1 I I 0 45 46 47 48 49 50 51 52 , 53 54 55 56 5 7 58 YEAR recent years. (b)Both consumption and production of nitrogen fertilizers have increased steadily over almost the entire period 1945-58. Production in the nitrogen sector of the industry has expanded by almost 50, since 2.948, as compared to an expansion of some 38% for all industries as measured by the official index of production. (c)The surplus production has been disposed of by exports. In recent years these have, on balance, declined as home demand approached the level of production.

2.5.2. Consumption of ammonium sulphate. Ammonium sulphate is the primary source of fertilizer nitrogen in the U.K. The consumption figures are given in table 2,2. below (4). It is apparent that, although the absolute amount of ammonium sulphate consumed has increased, its relative share of the nitrogen fertilizer market has declined slightly in recent years. -42-

TABLE 2.2. Consumption of Ammonium sulphate in U.K.

Year Consumption of nitrogen 103 tons N Percent of total Total As ammonium consumed as sulphate ammonium sulphate 1945 174.5 128.2 73.5 1946 164.5 115.6 70.4 1947 164.1 115.4 70.4 1948 135.4 132.5 71.5 1949 185.1 124.3 67.2 1950 222.5 156.5 70.3 1951 214.6 147.9 68.8 1952 181.0 114.8 63.5 1953 229.5 136.1 59.5 1954 240.8 150.4 62.5 . 1955 248.0 154.5 62.3 1956. 290.5 194.1 66.8 1957 301.5 195.0 64.7

2.5.3 Other types of nitrogen fertilizer. The overall pattern of the nitrogen fertilizer market, in recent years, is given in table 2.3. (a) Sodium nitrate, historically an important fertilizer is now only used in small amounts, (less than 1% of the total). Calcium cyanamide and calcium nitrate, both important

TABLE 2.3. PRODUCTION) CONSUMPTION EXPORTS OF NITROGEN FERTILIZERS SO URGE U.K , 1949-57

UNITS PRODUCTION CONSUMPTION EXPORTS , •N 10 TONS , I. N 52 53 54 55 56 57 49 51 52 53 54 55 56 5 7 52 53 54 55 56 57 1 I p--- 4.

AMMONIUM WEIGHT 209 215 218 2 14 213 230 37 41 33 3 8 151 155 194 200 73 95 62 64 26 11

SULPHATE PERCENT 697 20-7 19.0 18.2 16.6 626 62.5 66.3 65.6 90-1 97.0 99.5 10.0 100 100 OF TOTAL 73.8 70-2 705 71.5 69.8 A A. 4

AMMONIUM WEIGHT 50 66 66 60 65 71 32 41 45 65 63 65 66 77 7 I I X05 - - . . - NITRATE PERCENT 17.7 21.6 21.4 201 21.3 21•5 17.3 19.0 24,9 28.4 26.2 26.2 22.5 25.2 8 1 I. 0 J-5 - - OF TOTAL m -

SODIUM WEIGHT - - - -. - - 6 3 1 2 1 2 3 2 - - - - . . - NITRATE PERCENT ------OF T OTAL - - 3.3 1.4 0 -5 0-9 0.4 O• S 1-0 0 -7 -'- •

CALCIUM WEIGHT ------2 - 4, 05 405 4. 0 5 .. O 5 c.05 4.05 ------

CYANAM IDE PERCENT - _ ------OF TOTAL - - 0 •1 _ ...... -- - -

OTHER WEIGHT 24 25 25 2 5 27 29 I 0 8 130 1 0 2 124 26 26 30 26 I 2 - - - <0.5 r•- COMPLEX PERCENT - - - 8 • 5 8 •2 8 .1 8•4 8.9 8 -8 58-6 60.6 5 6.4 •54.1 10.8 10 .5 10 .2 8•5 1-2 2-0 0 F TOTAL TC

TOTAL WEIGHT 283 306 309 299 305 330 190 215 181 229 241 248 293 305 31 98 63 64 26 II

NOTES

I M PORTS TONS '31("- INCLUDES MIXED FERTILIZERS SODIUM CALCIUM AMMONIUM AMMONIUM NITRATE CYANAMIDE '''SULPHATE NITRATE 195 2 2300 10 0 1953 19 00 10 0 1954 12 0 0 1 00 1955 1700 1 0 0

1956 26 0 0 10 0 80 00

1957 2 20 0 10 0 10 0 890 0 fertilizers elsewhere, are not produced in the U.K. and only a negligible quantity of the former is used. (b)Ammonium sulphate and ammonium nitrate account for over 90% of the total fertilizer nitrogen production. The remainder is made up of complex and other materials, i.e. ammonium phosphate, urea, organic materials, etc. (c)The only nitrogen commodity that is exported is ammonium sulphate, though even this trade has declined in recent years. The export of ammonium nitrate, which was formerly of some importance ceased after 1954 and by 1957 imports of this material were started to meet the growing demand. (d)For the years 1949-53 the consumption figures for other and complex fertilizers included the amount consumed as mixed fertilizers, i.e. those which contain two or more nutrients simultaneously. It can be seen that some 55% of the nitrogen consumption comes under this category. By making an allowance for other and complex fertilizers, it would appear that some 45% of the total nitrogen was consumed in the mixed fertilizer form. It is impossible to determine the figure for more recent years since this method of pre- senting the statistics has been discontinued. However there is no reason to suppose that the position has changed. Indeed from comment, both from the industry and consumer, it is probable that the relative amount of nitrogen consumed in mixed fertilizers has increased compared to use in the straight form, i.e. where nutrient is used separately. (e) By an examination of the statistics for ammonium nitrate in 1952, 1953, it can be seen that production of this commodity equals approximately the sum of consumption plus exports. This means that the bulk of ammonium nitrate was used straight, (in admixtures with calcium carbonate under trade names nitrochalk and nitrashell), and that the greater part of nitrogen used in mixed fertilizers was derived from ammonium sulphate. This situation is known to have continued until 1959 (8). However in this year a new plant, for the production of ammonium nitrate for use in mixed fertilizers, was opened, so that this position is likely to be changed in future years (9).

2.5.4. U.K. nitrogen consumption in relation to Western Europe. It is of interest to compare the British pattern of nitrogen consumption with that of Western Europe and to determine the rank of the U.K. as a fertilizer consumer. The comparative statistics are given in table 2.4. Figures are quoted for the Netherlands, Germany and the average for 0.E.E.C. countries as well as the U.K. In order of consumption in the 0.E.E.C. area, the Netherlands

-45-

ranks first, Germany fifth and the 17'.K. ninth.

Table 2.4. Year 1955. Source 0.E.E.C.

U.K. Germany Netherlands Average 0.E.E.C. Area Consumption as percentage of total consumption

Ammonium sulphate 62.5 12.9 1.9 24.1

Ammonium nitrate 26.6 50.3 75.7 41.1

Sodium nitrate 0.7 1.2 2.8 3.6

Calcium nitrate 4.4 8,3 13.4

Calcium cyanamide 15.7 0.5 7.0

Other and complex 10.2 15.5 10.8 10.8 Consumption per acre agricultural land

Nitrogen used'16.N 1739 25.3 71.6 13.7

There is a striking difference in the quantity'of nitrogen fertilizer that is used per acre of agricultural land between the U.K., the Netherlands and Germany. The Netherlands uses on average four times the amount used in this country This can, in part, be attributed to the very much more intensive pattern of agriculture employed in the former. Even so the corresponding figure for Germany is 50% morel though the U.K. is above the average for the 0.E.E.C. area as a whole. One of the reasons for this disparity is the fact that a far greater proportion of the arable land in 46_ this country is in the form of temporary grassland. It is shown in a subsequent chapter that this land receives only low dressings of fertilizer or none at all. The figures, if they were available, for crop land, as distinct from grassland, would probably show the same order of consumption for both the U.K. and Germany. This does not of course mean that it would not be desirable to increase the use of nitrogen to the levels of other countries. The growth of grass, in particular, responds extremely well to applications of nitrogen and it could only be of benefit to domestic agriculture if better use were made of this resource through larger dressings of fertilizer. In the U.K. ammonium sulphate is the primary source of fertilizer nitrogen with ammonium nitrate as a secondary source. In the rest of Western Europe the position is reversed. The Netherlands obtains the bulk of its nitrogen from ammonium nitrate with calcium nitrate as a secondary source. In Germany the position is similar though both calcium cyanamide and ammonium sulphate are also of importance. In 19537 the last year for which figures were available, this country consumed some 45% of its nitrogen in mixed fertilizers whereas Germany used only 13% and the Netherlands 6% in this way. There is a definite preference in the latter countries to purchase fertilizer nutrients individually rather than in the mixed. form.

2.6. Production, consumption and trade in phosphatic fertilizers.

2.6.1. Source of phosphatic fertilizers. Many phosphatic fertilizers are manufactured from phosphate rock of various types. The raw material is a complex mixture of compounds, known as apatites, of empirical formula Ca5(PO4)3X, where X can be OH,2003901 or F9 associated with calcium fluoride. This country has no deposits of these rocks of a sufficient grade for fertilizer manufacture and the industry has to rely on imported materials. The main source of these are the high grade deposits of North Africa and a smaller amount comes from the Pacific (8). (Nauroo and Ocean Islands.) The rock is imported as mined and is then further processed in this country. The only domestic sources of phosphatic fertilizer are basic slag and some organic materials. The latter find their main use in horticulture and are relatively unimportant. The former, which is of considerable importance, is a by- product of the basic process of steel making. It contains varying amounts of phosphorus, up to 20% P2059 and finds -48-

considerable acceptance as a fertilizer.

2.6.2. Production and consumption of different types of phosphatic fertilizer. The statistics relating to phosphatic fertilizers are given on graphs 2.7 to 2.12. Graph 2.7. Production and consumption of all types of phosphatic fertilizer,1945 - 58. Graphs 2.8., 2.9. The pattern of consumption,1945 - 58. Graphs 2.10., 2.11., 2.12. Production and consumption of individual phosphatic fertilizers)1945 - 58. Further data is given in table 2.5.

2.6.2.1. The general pattern of production and consumption. Until 1952 consumption of phosphatic fertilizers exceeded their production by a margin of the order of 15%, The difference was made up by imports from abroad. Both production and consumption declined sharply in 1951/52. As mentioned previously, (2.2.1.c) this was brought about by the large rise in prices at the time. This rise was especially large in the case of phosphatic fertilizers, for in addition to the removal of the subsidy the cost of sulphuric acid, a major raw material in the industry, also increased during this period. Manufacture and use of phosphorus fertilizers increased

PRODUCT ION & CONSUMPTION ALL TYPES PHOSPHATIC FERTILIZERS 19+5-5e

500

S R ZE RTILI 400 CONSUMPTION

••• C FE

...MM. ram 11•••

OSPHATI °-`1300 H

P UI PRODUCT ION Z 0 < z ("0 0 - 200

z 0 U

100 ON CTI PRODU O 45 46 47 49 49 50 5I 52 53 54 55 56 57 58 YEAR CONSUMPT ION BY TYPE OF PHOSPHORUS FERTILIZER 1945-58

SOO

INI Otn min T TAL 400 a

300— ON I

A.) MPT SUPERPHOSPHATE U CD 200 CONS

BASIC. SLAG

••••••••• 100

— ALL OTHER TYPES GROUND ROCK — — AM. ••••• PHOSPHATE a 0

45 46 47 48 49 50 51 52 53 54 55 56 57 58 YEAR

60 •••• CONSUMPTION BY TYPE AS PERCENTAGE OF TOTAL CONSUMPTION 1945- 511

6-2

SUPERPHOSPHATE

30 pi. BASIC SL AG

0 Fr. .... , ..... eV . .F. 20 ••• •

14. ... ." FM .F., ALL OTHER TYPES ..... oars

AS .6. .0., e

ON I o • "d ...... , mM ...... de MPTI

GROUND ROCK PHOSPHATE ONSU

C I i i I a I I I I I I I O 45 46 47 4B 49 50 51 52 53 54 55 56 57 58 YEAR CONSUMPTION 8 PRODUCTION OF ORDINARY SUPERPHOSPHATE 194 5-58

250 ... CONSUMPTION On acv .4-* in al z ...'"\ 0 .. I- . • el 200 e \ 0 ee \ • .... -,e • • / • PRO DU CT1ON % • ., °- ATE / \ •,...... ' • /

SPH NI 50 N. O I r •

PH \

MD PER SU

100

I I I I I I 0 I I I I I 1 I 45 46 47 48 49 50 51 52 53 54 55 56 57 58 YEAR

CONSUMPTION & PRODUCT ION OF BASIC SLAG 1945—Se

125 WED

CON SUM PT ION

100

ore, •fte. I— — ••#' / 0 75 • I %%% / I % a. % / S. 1 ..,. , • • \I

0 PRODUCT ION

S 0 0

—1 25

In a)

a O 4 5 46 47 48 49 50 51 52 53 54 55 56 57 58 Y EAR

CONSUMPTION 8 PRODUCT ION OF OTHER PHOSPHORUS FERTILIZE RS 1945-58

0 0.cv 100 a OTHER COMPRISES ORGANIC FERTILIZERS,

CONCENTRATED COMPLETE FERTILIZERS, 0 I- MON-AMMONIUM PHOSPHATE, cn 0 80 TREATED PHOSPHATE ROCK CONCENTRATED SUPERPHOSPHATE •••

CONSUMPT ION

.11a. •••• •••••=. MEW NM — — 41/ NO

10. of PRODUCT ION

cC La 20

1 1 1 1 _1 0 1 1 1 1 45 46 47 48 49 50 51 52. 53 54 55 56 57 . 58 YEAR SOURCE 0 .E.E. C. U.K, 1949-57 TABLE 2 • 5 . PRODU-CT ION CONSUMPTION + IMPORTS OF PHOSPHORUS FERTILIZERS

UNITS PRODUCT ION CONSUMPTION IMPORTS

103 TONS

0 52 53 54 55 S6 57 49 51 52 53 54 55 56 57 52 53 54 55 56 57 PZ. 5

- - - - ORDINARY WEIGHT 132 175 177 156 176 176 82 49 70 78 183 167 180 174 15 4

SUPER- PERCENT 50.2 50.5 51 .7 503 49 -I 50•I 19 -6 11.4 25•I 20.1 48.8 500 46.6 46.5 60.0 16.0 •-, - - - PHOSPHATE OF TOTAL

CONCENTRATED WEIGHT 13 25 32 3% 46 42 n -a. v‘ -a.- 8 24 34 38 48 46 - - 2 I I 2

SUPER PERCENT 50 7.2 9.4 12 -3 12-9 12-0 ,‘ .6, y‘.0... 2 • 9 6-2 9-1 11-4 12 -5 12- 3 - 11•1 9.1 5•6 9.5 PHOSPHATE OF TOTAL

I 4 9 70 100 91 74 100 101 10 20 15 8 17 19 BASIC WEIGHT 60 77 71 64 82 83 108

PERCENT SLAG 22.8 22.1 20.8 20.6 22.9 23.6 25.8 34.9 25.1 25.7 24.3 22.1 25.9 27.0 400 80.0 83.3 72'8 94.4 90.5 OF TOT AL

18 2 GROUND WEIGHT 30 4I 34 23 21 17 33 17 15 31 35 24 22. ROCK PERCENT 11.4 11.8 9.9 7.4 5.9 4.9 7.9 4.2 54 8.0 9.3 72 5'7 4.8 - - 9 -1 PH 0 SPHATEOF TOTAL

33 196 212 115 155 32 31 36 35 c05 I 1 OTHER WEIGHT 28 30 28 29 33 -

-1- PERCENT 41.5 400 8.5 9 .3 9.3 9.4 _ COMPLEX 10-6 8.6 8.2 9.4 9.2 9.4 46-7 49.5 40 5.6 OF TOTAL j * * 4re- le'

2 1 263 348 342 310 358 351 419 427 278 388 375 334 386 374 25 25 16 II I8 TOTAL WEIGHT

NOTES

I) EXPORTS NIL INCLUDES MIXED FERTILIZERS 3) n • 0- NOT AVAILABLE -49-

subsequently, (1953), though not to their former levels. Since 1953 the overall trend has been towards a slight decrease in consumption from year to year and by 1958 it was only just above the level maintained after the war: (1945 - 47). The margin between production and consumption is now much smaller. It can be accounted for by the demand for high grade basic slag which has to be imported from the continent, (See 2.6,2.40)

2.6.2.2. The pattern of consumption (Graphs 2.8., 2.9.) Consumption of all the major types of phosphatic fertilizer have followed much the same trend since the war, the most notable feature being the sharp fall in use which occurred in 1951/52. Ordinary superphosphate and basic slag are the two most important phosphate commodities. Some significant changes in the pattern of consumption have occurred between 1945 and 1958. Ordinary superphosphate, whilst still dominating the market, has occupied a decreasing relative share of it. Whereas in 1945/48 it accounted for some 55% of the total, by 1958 this had declined to 42%. Basic slag, the second, most important commodity, has maintained a fairly steady share of the market. (It accounted for between 22 and 28% of the total). Ground rock phosphate use has declined steadily and is now only of minor importance. (Under 5% of total consumption in 1958). In the consumption of 'other types' some significant changes have occurred and their importance has increased in recent years. The reasons for this are discussed in 2.6.2.5.

2.6.2.3, Consumption and production of ordinary superphosphate (Graph 2.10.) Up to 1953 consumption as'a whole exceeded production, though not to any great extent. The difference was made up by imports from the continent. Since 1953 the two have been kept at the same level and imports of ordinary superphosphate have ceased (Table 2.5.).

2.6.2.4. Production and consumption of basic slag (Graph 2.11.) It should be noted that basic slag is obtained as a by-product of the basic process in steel making. Production of this commodity is thus directly related to that in the steel industry. Thus, while it has fluctuated over the period 1945-58, it would appear that the maximum production available is of the order of 80,000 tons P205 per annum. Consumption of basic slag has varied from year to year and it has had to be imported in fairly large quantities in years when demand was high. Basic slag is now almost the only phosphatic fertilizer which is imported. In 1956, 57 -51- it accounted for some 90% of the total imports. In two years, 1952 and 1955, demand fell to below the level of possible maximum production. However imports of basic slag still continuedi though less than in other years. The reason for this is that there is a fairly stable demand for the high grade basic slag produced on the continent. The domestic material contains on average 12-15% P205, whereas the imported slag contains 18% or more of P205 (8).

2.6.2.5. Production and consumption of 'other' types of fertilizer. The term 'other' comprises the P205 content of organic fertilizers, concentrated superphosphates, treated phosphate rock, straight mon-ammonium phosphate and concentrated complete fertilizers. (The latter is a trade name, the P205 is present as mon-ammonium phosphate). Three distinct phases in consumption have occurred within this group of materials. (a)A fall in consumption 1945-49 (b)A period when consumption remained constant 1949-52 (c)A period of rising consumption 1952-58 The reason for these are as follows. During the war quantities of concentrated superphosphate and mon-ammonium phosphate were imported from the U.S.A. and Canada in order that the fertilizer allocation schemes could be implemented. _52-

After the war these imports were stopped and consumption of this group of materials declined to the level of domestic production of other commodities in the group. This position continued until 1952. In this year production of concentrated superphosphate commenced in the U.K. Reference to table 2.5. shows that production and consumption of this commodity accounts for the increases that have occurred within this group of 'other' phosphatic fertilizers. Concentrated superphosphate is now of considerable importance as a fertilizer and it accounts for about 12% of the total consumption of phosphates. Indeed demand is such that small amounts are now imported. It is used almost entirely as a base for making high grade mixed fertilizers. Very little is used for straight application (10). Much of the decline in the use of ordinary superphosphate has been brought about by the introduction and increasing consumption of concentrated superphosphate. The relative share of the market obtained by the two commodities together has Temained constant.

2.6.2.6. Consumption of mixed fertilizers. It was shown that a considerable proportion of the total nitrogen was consumed in the mixed fertilizer form. The position with phosphorus is similar. During the years for which statistics were available some 40-50% of the total was - 53-

used in this way. (Table 2.5.) The major source of phosphorus in mixed fertilizers is siperphosphate, both ordinary and concentrated. Basic slag and ground rock phosphate are used entirely in the straight form for use on grassland. The bulk of phosphorus used on cropland must therefore be applied in the mixed fertilizer form.

2.6.3. U.K. phosphate consumption in relation to Western Europe. The consumption of phosphates in the U.K. is compared with that in the Netherlands, Germany and the average for the O.E.E.C. area in table 2.6. below. In order of consumption of P205 per acre of agricultural land the Netherlands ranks second, Germany fifth and the U.K. ninth in the O.E.E.C. area.

TABLE 2.6. Year 1955. Source O.E.E.C. U.K. Germany Netherlands Average O.E.E.C. Area Consumption as percentage of total consumption Ordinary superphosphate 50.2 13.0 ) ) 34.1 49.8 Concentrated superphosphate 10.9 Basic slag 22.4 65.5 44.9 33.9 Ground rock phosphate 7.3 1.8 0.9 5.6 Other and complex 9.2 19.6 20.6 10.7 Consumption per acre agricultural land Phosphorus used 16.P205 24.0 32.4 41.9 18.7 Both Germany and the Netherlands use more phosphate fertilizer per acre than does the U.K., though domestic consumption is above the average for the 0.E.E.C. area. While this, difference is not as large as is the case with nitrogen fertilizers it is still considerable. The reasons for this are much the same as for the latter nutrient (see 2.5.4.) Basic slag accounts for a much greater proportion of total consumption in other European countries than it does in this country. Germany, for example, obtains about 65% of itl phosphorus fertilizer from this source. The reason for this is that the steel producing countries of Western Europe tend to utilize a larger proportion of high phosphorus bearing iron ores, than does this country, and large quantities of high grade basic slag are produced. Much of the steel in the U.K. is produced by a non-basic process and the slag obtained is of no use as a fertilizer. Basic slag has the advantage that, as a source of phosphorus, it is much cheaper than other commodities. This probably also accounts, to some extent, for the greater use of phosphorus fertilizer in other countries.

2.6.4. The future demand for phosphatic fertilizers. It is unlikely that, given the present structure of prices and subsidies, there will be much change in the -55-

present level of consumption. The current trend would appear to be to increase the proportion of nitrogen and potassium in mixed fertilizers while maintaining the phosphorus content constant (10, 11). It may well be that, once the change in nutrient ratio has been effected, the industry will attempt to bring about an increase in phosphatic fertilizer consumption. A change in the pattern of consumption is however likely. Increasing amounts of concentrated superphosphate will be used at the expense of ordinary superphosphate. Extensions to existing concentrated superphosphate capacity have recently been completed (12). It is also probable that mon-ammonium phosphate will become of increased importance in the future as a phosphorus fertilizer. A new plant for the manufacture of this commodity was opened recently (12). It is used as the basis of concentrated complete fertilizer.

2.7. Production consum•tion and trade in •otassium fertilizers.

2.7.1. Source of potash. The U.K. has to import all the potassium salts used as fertilizer. There are some extensive deposits of potash in Yorkshire, (the geological extension of the Stassfurt deposits), but it has not proved feasible to work them TABLE 2.7. PRODUCT ION CONSUMPTION 1- IMPORTS OF POTASSIUM FERTILIZERS SOURCE O.E.E.0 U.K. 1949-'57

PRODUCTION CONSUMPTION IMPORTS UNITS 4 . A IC? TONS 52 53 54 55 56 57 49 51 . 52 53 54 55 56 57 5,2 511 54 55 56 57 Ke.0 . .. r

2 3 4 - - II 5 3 4 6 6 6 7 6 6 5 5 8 7 POTASS IUM WEIGHT I

PERCENT 2-1 3.5 2.5 1.9 1 . 8 2.4 2.2 SULPHATE 100 100 100 100 - - 5.5 2.2 1.7 1.7 2.4 24 2.0 0 F TOTAL - .

WEIGHT ------38 27 17 24 242 244 298 305 I 160 222 250 261 315 301 POTASSIUM

CHLORIDE PERCENT ------19.6 11.8 9.9 10.4 96.4 96.8 97.4 96V 93.0 92.5 95.4 960 961 956 , >45% KLO OF TOTAL ... 1 POTASSIUM WEIGHT ------10 2 3 2 I I I - 4 9 2 ' I I - CH LORIDE ei PERCENT 20-4 5/0 ------5.1 0.8 1'7 0.9 0.5 0.4 0.3 - 2.3 3.8 0 • 8 0•4 0.3 - KtO OF TOTAL - ;

POT ASS IUM WE I GIST ------2 I I 3 - - 5 5 4 7

CHLORIDE PERCENT • ------0•7 0.4 0.3 1.0 - - 1-9 1.8 l'2 2•2 <20%Kap OF TOTAL - 1 ,

WEIGHT ------136 192 149 201 <0 5 <0 5 <0 5 - 2 3 <05 <05

NOTES:

I) EXPORTS OF ALL TYPES POTASSIUM INCLUDES MIX ED FERTILIZERS

FERTILIZERS ARE NIL - 56- economically. The main sources of British imports are France, Germany and Spain (8). The bulk of such imports is in the form of .•:; high grade potassium chloride salts containing more than 45% K20, (greater than 70% KC1). (See table 2.7.) Some low grade salts are impotted but the high transport costs per unit tend to discourage this.

2.7.2. Consumption of potassium fertilizer. The consumption of potash since 1945 has already been described in 2.2.1. and 2.2.2. The main conclusions reached were:- (a)Consumption has increased steadily. (b)Consumption varies in proportion to that of nitrogen. The major part, some 90%, of potassium fertilizers are consumed in the mixed form.

2.7.3. The U.K. consumption of potash in relation to that of Western Europe. The consumption of potash in the U.K. is compared to that of other 0.E.E.C. countries in table 2.8. below. In order of consumption per acre of agricultural land the Netherlands ranks second, Germany third and the U.K. ninth in the 0.E.E.C. area. -57-

TABLE 2.8. Year 1955. Source 0.E.E.C. U.K. Germany Netherlands Average 0.E.E.C. area Consumption as percentage of total consumption Potassium sulphate 2.1 0.8 1.1 3.2 Potassium ) >45%1C20 96.9 12.2 4.0 41.6 ) )20-45%K20 0.5 62.3 72.1 42.3 ) Chloride )420%K20 0.5 7.0 6.4 4.2 Other and complex - 17.7 16.4 8,7 Consumption per acre agricultural land Potassium used lb.K20 18.2 53.5 56.0 16.7

Both the Netherlands and Germany use about three times the amount of potash that the U.K. does per acre agricultural land. The reason for this are to some extent similar to those outlined for nitrogen and phosphorus fertilizers. An additional factor is the lower price paid for potash in Germany and the Netherlands since the centres of production are located in or near these countries. -58-

APPENDIX CHAPTER 2.

Note on definitions of fertilizers used for statistics given in Chapter 2. The following definitions are used for the statistics relating to the production, consumption and trade in nitrogen, phosphorus and potassium fertilizers given in Graphs 2.1.9 2.6. to 2.12.

Nitrogenous fertilizers. Production figures show the nitrogen content of ammonium sulphate, 'Nitrochalk' and concentrated complete fertilizers. Consumption figures show the nitrogen content of ammonium sulphate, ?Nitro-chalk', concentrated complete fertilizers, Chile nitrates of soda and potash, Trail ammonium phosphate, ammonium nitrate, nitrate of lime and cyanamide. The series for production and home consumption exclude non-agricultural uses; that for total disposals includes exports of ammonium sulphate for all purposes.

Phosphatic fertilizers. The production figures show the P 0 content of the 2 5 phosphatic fertilizers produced, and cover superphosphate, triple superphosphate, ground basic slag (slag ground in the U.K. from home produced raw slag), ground phosphate (phosphate ground in the U.K. from imported phosphate rock), organic fertilizers, treated phosphate and concentrated complete fertilizers. The consumption figures show the P205 content of the following:- Superphosphate, Ground basic slag, (home and imported material), Ground phosphate, (home and imported material and 'other'. (Organic fertilizers, treated phosphate, concentrated complete fertilizers and triple superphosphate).

Potassium fertilizers. Consumption figures show the K20 content of agricultural potash used in manufacture of compound or concentrated complete fertilizers, or delivered for direct application. The above has been quoted from:- Supplement to Monthly Digest of Statistics: Definitions and explanatory notes. H.M.S,O. 1956.

Index of fertilizer production (2.3.). ,The index has been prepared in the same way as the index of industrial production.

-6o-

= XnWi + YnW2 X0141 + YoW2

where I = Index of fertilizer production. Xn = Production of nitrogen fertilizer in year n. Yn = Production of phosphorus fertilizer in year n. X0 = Production of nitrogen fertilizer in base year Yo = Production of phosphorus fertilizer in base year. W1 = weight for nitrogen. W2 = weight for phosphorus.

The weights have been calculated from:-

Wi PNX0 W2 = P pY o X PNXO + PpY o PN o + PpY where PN = average price per ton N in base year Pp = average price per ton P205 in base year.

The average prices have been calculated from:-

PN = PaXa + PbXb , Pp = PcXc + PdXd + PeXe Xa + Xb X0 + Xd + Xe -61- where Pa'= Price, per ton N9 of ammonium sulphate

Pb = Price, per ton N9 of nitro-chalk Xa = Consumption of ammonium sulphate, tons N. Xb = Consumption of nitro-chalk, tons N. Pc = Price, per ton P2052 of ordinary superphosphate. Pd = Price, per ton P205, of basic slag. Pe = Price, per ton P205, of ground rock phosphate. Xc = Consumption of ordinary superphosphate, tons P205. Xd = Consumption of basic slag, tons P205. Xe = Consumption of ground rock phosphate, tons P205. all in base year. Base year taken as 1948. Pa = £48.0, Pb = £64.5, Xa = 132.5 .x'103, Xb = 52.9 x 103 (n.b. Xb = total consumption of nitrogen minus Xa) whence PN = £52.7 per ton N. Pc = £31.0, Pd = £20.8, Pe = £17.1, Xc = 225.5.103, Xd = 82.8.103, Xe = 43.6.103. whence Pp = £26.9 per ton P205 hence W1 = 0.56, W2 = 0.44

All production figures have been taken from Annual Abstract of Statistics. - 62-

The index of production is given in the table below.

Year 1945 1946 1947 1948c 1949 1950 1951 1952 Index 83.5 89.6 88 100.0 107 111 101 100

Year 1953 1954 1955 1956 1957 1958 Index 117 119 111 116 120 120 * Base year. -63-

CHAPTER 3 THE POTENTIAL DEMAND FOR FERTILIZERS AND ITS RELATION TO AGRICULTURAL POLICY

3.1. Postwar agricultural policy in the U.K.

3.1.1. General Objectives of policy. Agriculture in the U.K. before the war was a depressed industry and both income and production were low. However during the war the industry managed to increase production substantially in an endeavour to meet the demand for food that previously had been imported from abroad. After the war, in order to prevent a return to previous conditions, it was decided to give a large measure of support to the industry. The general pattern of agricultural policy was laid down in the Agriculture Act, 1947, introduced by the Labour

Government. Part I, section I of this act gives the general objectives as follows:- 'The following provisions of this part of the Act shall have effect for the purpose of promoting and maintaining, by provision of guaranteed prices and assured markets for the produce mentioned in the 1st Schedule to this Act, a stable and efficient agricultural industry capable of producing such part of the nation's food and other agricultural produce as -64-

in the national interest it is desirable to produce in the United Kingdom and of producing it at minimum prices consistently with proper remuneration and living conditions for farmers and workers in agriculture and an adequate return on capital invested in the industry'. These general objectives were reaffirmed in the Agriculture Act, 19579 introduced by the Conservative Govern- ment. Part I, section 1 of this Act states:- 'The Minister may by order make such provision as appears to him expedient for providing guaranteed prices or assured markets for producers of produce described in the 1st Schedule of this Act'. The produce listed in the 1st Schedule as qualifying for the guarantee is:- 'Part I Crops. Wheat, Rye, Barley, Oats, Potatoes Part II Livestock and livestock products Fat Cattle, Fat Sheep, Fat Pigs, Cow's Milk, Eggs, Wool'. (Sugar Beet which was originally in the list of scheduled products of the 1947 Act is now covered by a separate act2 The Sugar Beet Act2 1957. The provisions of this Act are such as to give also a guaranteed price and market in this commodity.) -65-

The commodities for which guarantees are given, (review commodities), constitute some 80% of the gross output of British Agriculture.

3.1.2 Long term stability of guarantees. The 1957 Act, in addition to giving these guarantees, provides for their long term stability. Section II, part i of the Act states:- 'The price determined for a guarantee period in respect of any produce shall not be less than 96% of the corresponding price determined in the last guarantee period'. A similar clause states further that the total value of the guarantees shall not be less than 9720 of their total value in the preceeding year. These clauses enable the farmer to plan his production policy for the future with a good knowledge of the price he will be able to obtain for his produce.

3.1.3. Determination of guarantees. Section 2 of the 1947 Act requires the appropriate Minister to review annually, in consultation with the representatives of agricultural producers, the economic condition and prospects of the industry. Following these discussions the government reaches a decision on the guarantee prices to -66-

be paid for the review products during the appropriate period. The government is, however, wholly responsible for the guarantees; it only consults with agricultural producerslit does not negotiate with them (1). In fact the latter have often expressed dissatisfaction with the awards.

3.1.4. Cost of guarantees. The cost to the exchequer of these guarantees, together with various production grants, is high, £240 x 106 in 1956/57, £2W+ x 106 in 1957/58 and estimated £250 x 106 in 1958/59. The value of the guarantees in 1956/57 contributed to some 75% of the agricultural net income of £314 x 106 and amounted to some 20% of the gross value of the produce for which they were paid. The agricultural industry is thus substantially supported by the government. It should be remembered however, that, unlike many other industries agriculture is not protected from foreign competition by tariffs or quotas. The guarantees to some extent take the place of such pro- tection and have the effect of enabling the consumer to purchase fool at prevailing world market prices, at the same time preserving a healthy agricultural industry at home.

3.1.5. Specific agricultural objectives. From time to time, generally at the annual review, the government has stated the specific objectives it would like -67- the agricultural industry to attain. Originally these were twofold:- (i) To expand the volume of agricultural net output by 60% above the prewar average. This was to be achieved selectively by setting 'target outputs' for various crops. (ii)To ensure that production becomes more economic by increasing technical efficiency and by decreasing unit costs of production. With the attainment of some of the targets of (i) above and with changing conditions, both in home demand and world supply, the specific objectives have now been somewhat changed. The government still holds (ii) above as of prime importance. However the expansion of output, especially in the production of milk, eggs and pigs, has been achieved by the, substantial use of imported feedstuffs. The government feels that this has had an adverse effect on the balance of payments (2) Under present circumstances, therefore, the government does not require any further expansion of gross output unless this can be achieved. at a substantially lower cost of production and without prejudicing the aim of relieving the taxpayer of the increasingly heavy burden of subsidy cost' (2). Net output can be expanded but should depend in particular on ' the greater sub- -68- stitution of homegrown for imported feeds'(2). The government, with the above in mind, in 1958 has stated the general directions in which the maintenance or expansion of net output should be sought as:- (2) (i)The maintenance of a large arable acreage, of some- thing like the current size, but with more emphasis on feed crops rather than wheat. (ii)Greater reliance on home produced feed for livestock. (iii)Production of more beef and lamb of the quality required by the market. (iv)Production of less milk, pigmeat and eggs. By these changes and diversion of resources it is felt that the industry could make a contribution to the balance of payments as well as preventing a further rise in the subsidy cost paid to it.

3.2. Economic condition of the agricultural industry.

3.2.1. Farm Income. Since the start of the postwar agricultural programme farm net income, as estimated by the Ministry of Agriculture, has been rising steadily. The figures are given in table 3.1. together with the figures corrected to 194-7 levels of prices by use of the index of retail prices. -69-

Net income has risen substantially since 1947. In 1958, when the highest figure since the war was recorded, it was some 85% above that of 1947. In terms of real income the position has also improved. In 1956 it was some 12% above the 1947 level but compared to the period 1949-54 real incomes have somewhat declined in recent years. However in comparison to prewar years the industry is far better off. It's real income since 1948 has averaged between three and four times that of 1938.

TABLE 3,1. Farm Net Income (F.N.I.) 1947-59+ 1938 1947 1948 1949 1950 1951 F.N.I. £106 56 191 223.5 291 305 268.5 F.N.I. at 1947 level of prices £10b 73 191 217 267 272 230 1952 1953 1954 1955 1956 1957195e 1959** F.N.I. £106 323..5 334 332 296 329 319.354.5 327 F.N.I. at 1947 level of prices £10b 241 242 235 204 21 5 202 216 200 Source. Annual Abstract of Statistics +Provisional **Forecast +Years ending 31st May.

3.2.2. Agricultural net output. One of the immediate objectives of government policy was to raise the volume of net output by 60% over the prewar -70- average. Figures for the index of output are given in table 3.2.

TABLE 3.2. Volume of agricultural net output (2) in U.K. Pre-war average = 100

Year 1947 1948 1949 1950 1951 1952 1953 Net output 119 123 138 141 142 147 151

Year 1954 1955 1956 1957 1958* 1959** Net output 155 151 155 160 160 159

Provisional *Forecast. Years ending 31st May. For agricultural holdings over 1 acre. The table shows that this production objective has been met by farmers. Further the increasing trend in production of milk, eggs, pigment and wheat should be reversed in 1959 in accordance with the government's requests (3). In the production of more homegrown feeding stuffs the farmers are, however, not meeting the governments objectives. This is shown in table 3.3. which gives the estimated consumption and purchases of feed stuffs on UuK. farms in recent years. In spite of repeated requests the farming industry has not increased its production of home grown feedstuffs9 in fact in 1958 they even declined. The importance of -71-

improving on this is emphasised by the fact that some 25% of total expenditure by farmers goes on purchasing feedstuffs, mainly imported, and this forms their largest single item of expenditure.

TABLE 3.3. Estimated purchases and consumption of concentrated feeding 6 stuffs on farms in U.K. 10 tons.

Year 1954 1955 1956 1957 1958 1959* Total consumption on farms 11.1 12.3 12.0 12.1 12.3 12.9 Current home crop production 6.1 6.0 6.4 6.6 6.1 6.4 Balance of farmer's purchases to be met mainly 5.0 6.3 5.6 5.5 6.2 6.5 from imported supplies *Fore-cast Years ending 31st May.

3.2.3. Present guarantee policy. In the 1958 review on guarantees the government decided to cut their value to almost the maximum permitted under the 1957 Agriculture Act, The commodities most affected were the three, eggs, milk and pigmeat, the production of which was required to be reduced. This cut was made with the object of:- (a) Keeping down the level of government expenditure on guarantees. It was felt that the industry could take such a cut since its income had increased, -72- accompanied by only a much smaller increase in its costs. (b) It would encourage the diversion of farm resources to the production of those commodities required by the market. The reduced level of the guarantees was maintained in the 1959 review. This decrease was strongly criticized by farmerst representatives who claimed it would have a severe effect on the smaller and marginal producers. A discussion of the merits or otherwise of the reduction in guarantees and of the large support given to agriculture is outside the scope of this thesis. However, if any further reductions in guarantees are made, farmers will have to increase their productivity, if they wish to maintain their present levels of income. It will be shown that a means of doing this would be to use fertilizers on a more extensive scale to raise the yield of crops per acre and decrease the unit costs of production. The government recognises the importance of fertilizers since it pays a considerable subsidy on their use.

3.3. Response of crops to fertilizers.

3.3.1. The theoretical model. From a knowledge of how the yield of a crop responds to treatment with fertilizers it is possible to determine an - 73- optimum level of fertilizer application from purely economic considerations i.e. it is assumed that the optimum level of application is that level at which the maximum profit from using fertilizers is realised. In order to determine this optimum it is necessary to have a knowledge of the response curve of crops to fertilizers i.e. the variation in output of a crop at varying inputs of fertilizer to the soil. For the purposes of theoretical analysis the response curve is considered constant with time and is assumed to be solely a function of the fertilizer input. All other factors that affect the response curve are considered constant. It is generally accepted that in the short run crops respond to fertilizers according to a law of diminishing returns, i.e. increasing equal increments of fertilizer application aftera pointoroduce decreasing increments of crop yield. Experiment has shown that the form of these curves may be of the type shown in Fig. 3.1. Russell (4) suggests that the sigmoid curve represents the response curve, but that the point of inflection is so near the origin that in practice it is often missed and the exponential form of the curve is obtained. At high levels of input a depression of yield is sometimes observed. i.e. the marginal product becomes negative.

SIGMOID EXPONENTIAL

FERTILIZER INPUT w

FIGURE 3.1.

TO TAL PRODUCT MARG I NAL i / TOTAL PRODUCT

FERTILIZER INPUT

FIGURE 3.2. -74-

3.3.2. The theoretical economic model for obtaining optimum levels of fertilizer application. Whichever form of the curve is obtained the analysis for obtaining the optimum input remains the same. From a knowledge of the value of the crop, the cost of the fertilizer and the form of the response curve it is possible to plot the total product and fertilizer input cost curves. The difference between these two gives the net product or profit curve. Similarily the marginal product curve and marginal input cost curve can also be obtained. (Figure 3.2.) From purely economic considerations the optimum level of fertilizer application is the point at which the net product curve is at a maximum or where the marginal cost curve inter- sects the marginal product curve. The net product represents the profit on investing in fertilizers and point A represents the maximum profit that can be obtained. This analysis represents the theoretical model on which all fertilizer economics are based.

3.3.3. The response curve in practice. In practice the prediction of an optimum level of fertilizer application is complicated by the fact that there is not a single response curve, subject only to one variable, but rather a set of response curves subject to several variables. In general the response function can be

-75- represented by the equation:-

Y = F (x19 x29 X3 xn z1, z2, z3 1,001. zn ) 1 where Y is the yield of the crop considered x19 x29 x3...xn are the rates of application of various plant nutrients. In practice only nitrogen, phosphorus and potassium are considered though others may be important. zi,z2,z3...zn represent other variables which may affect the response curve e.g. soil type, plant variety, moisture, weather, etc. Some of these factors are measureable but more often they are intangible and not controllable and taken as random variables with a zero expected value. In practice therefore the obtaining of a yield response function involves determining it as a function of fertilizer input for a given set of zl, z2, z3.....zn. The smoothness of many of such curves f;hat have been obtained has led to attempts to obtain a generalised equation to represent them. Some of these are considered in more detail below.

3.3.3.1. Response function due to Mitscherlich (5). This is the most famous of all attempts to obtain a general equation and is based on a considerable amount of -76-

experimental work carried out in Germany. Mitscherlich assumed that the response curve was exponential and that for large inputs of fertilizer the ftswnp tot;,c response curve becomes accymtopic to some value of the yield Y = A, i.e. no depression of yield at high levels of input. He then postulated that the marginal output of the crop per unit of input of fertilizer is proportional to the difference between the maximum output, i.e. at Y = A, and the output on the point considered on the curve.

i.e. dY A - Y dx

or dY K(A Y) dx where Y is the output (yield) due to input of fertilizer. X is the input of fertilizer (an individual nutrient). A is the maximum level of output. K is a constant. On integrating and as X = Y = 0 is the initial condition, one obtains the general equation Y= A(1- e- KX) Mitscherlich originally maintained that the value of K was a function only of the particular nutrient supplied and independant of all other factors, i.e. x2,x3..xniz1,z2,z3..zn. On the basis of a large amount of experimental data he estimates values of K for nitrogen, phosphorus and potassium. -77-

It should be noted that his method of experiment was to vary one nutrient in the presence of adequate supplies of the other two. He thus recognises the importance of interaction effects between the nutrients. Mitscherlich's equation has been of considerable importance since much of the response data that has been obtained can be made to fit it very well and several workers in this field have used this type of equation. However the constant K is generally regarded as a parameter that depends on the other factors x2x3x4....xn ziz2z3 zn rather than being only a function of the nutrient used.

3.3.3.2. Other mathematical models. Several other models have been suggested to'represent the response curve, of these the more important are the power function Y = AXb, the quadratic Y = AX + BX2, the square root Y = A IR-4- BX and the quadratic square root Y = A VIC+ BX + CX2. In practice much of the data can be made to fit such equations fairly well. All these models make an a priori assumption as to the form of the response curve. An alternative approach is to express the curve by an empirical polynomial equation Y = AX + BX2 + CX3....NXN and estimating sufficient coefficients from experimental data, sufficient to represent the data to the desired degree of accuracy. -78-

So far only single variable response functions have been considered, i.e. no interaction effects between the nutrients is allowed for. In practice interaction between the nutrients is often encountered. Thus the yield obtained at various levels of nitrogen application will depend on the level of phosphorus application employed. This has led to attempts to develop two or three variable functions. Thus the Mitscherlich equation can be written as:- Y = A(1 - e-K1X1)(1 - e - K2X2)(1 _ e -K3X3) where X1,X2,X3 are the levels of input of nitrogen phosphorus and potassium, the power function as:- Y = AX1b1X2b2X3b3 and the polynomial as Y = (A1X1+A2X2+A3X3)+(B1X12+B2X22+B3X32+B4X1X2 +B5X2X3+B6X1X3) + etc. However very little work, especially of an experimental kind, has been done in this direction, though certain results indicate that at high levels of input interaction effects are not very great i.e. the effects are only of importance when one or more nutrients is available at only a low level. If this is in fact the case then the use of a single variable function9 such as that of Mitscherlich9 is valid. -79-

3.3.4. The use of mathematical models in determining the optimum fertilizer application. Given that one can express the crop response to fertilizer by means of equations of the type outlined in 3.3.3., it is possible to derive an expression for the optimum application, that is a function of the value of the crop and the cost of the fertilizer. Consider the function Y = A(1 - e -KX) and let V = value of crop per unit e = cost of fertilizer per unit :.Total product due to fertilizer application = VA(1- e-KX) and total input cost of fertilizer = CX :iNet product (N.P) = VA(1- e-KX) CX for any level of application X. The maximum profit is given by d(N.P.) = 0 dx d(N.P.)= KVA e-KX C = 0' for max dx

whence X optimum = 1 in. :(4 The optimum rate of application will thus vary with the ratio of crop value to fertilizer cost. The above analysis can be refined by allowing, in addition, for cost of applying the fertilizer and for harvesting and selling the extra crop but the resultant equation will still be of the same formo The use of other models give similar results. Thus -80-

b for-the power function Y = AX X 017)tiMUI is given by (bVA)1/1-b and for the quadratic Y = AX + BX2 by C-VA 2VB Thus whichever model is chosen the optimum level remains a function of the ratio V/C. The above analysis can also be extended to a multivariable function. The method is best illustrated by the following example. Response curve is given by Y = A - BN + C +D N/r-ff- EK i.e. interaction effects between use of nitrogen and potassium. N = Level of application of nitrogen K = Level of application of potassium A,B,C,D9 E = Experimentally determined constants. and let V = value of crop per unit cl= cost of nitrogen fertilizer per unit c2= cost of potassium fertilizer per unit. Now net product (N.P.) = BN + C4r-g77-+ EK)

- (c1N c2K) and maximum value of function (N.P.) is given by condition NP) = 0 and -. 11\1P) = 0 ZN now iKRP) = V2AN"4 B + 2 N"2 ) ci = N

-, ,(1\1 P) = VQ-DK7* E+ 2 oN/117 E-7 2 ) =0 K + C,A7N-1 = 2 (c1 + B) (-7 and + C/11K-t = 2 (ai E) whence one can solve for the particular values of N and K which make the function a maximum. For a multivariable function the optimum is thus also a function of the crop value and fertilizer price. An accurate knowledge of the response function is therefore of great importance in making a decision as to what levels of fertilizer application should be employed.

3.3.5. Effect of long run changes on the response curve. So far the response function has been considered as static i.e. there is no shift of the response function with time. In fact, in any progressive agricultural economy, the cultural practices and agricultural techniques employed are continually improving. These improvements will have the general effect of shifting the response curve progressively to the right and of removing limitations on the use of fertilizers. An example of the former is the use of irrigation which will often greatly increase the response of crops to fertilizers (6). An example of the latter is -82-

the introduction of stiff strawed varieties of wheat. The use of nitrogen on wheat was limited in the past by the fact that a high rate of nitrogen application a weak straw was obtained with consequent lodging of the crop. The new varieties have to a great extent removed this limitation. Other factors that can be quoted are the improvements in soil management, leading to a better soil structure, improved methods of cultivation, harvesting and placing of seeds and fertilizers, the introduction of new types of fertilizer, and new high yielding plant varieties and the use of weedkillers, insecticides, soil conditioners and plant growth chemicals. All such long run changes will shift the response function to the right and consequently the optimum level of fertilizer application to the right. Therefore in any progressive agricultural system one would expect the use of fertilizers to become increasingly favourable.

3.3.6. Short run changes in the response curve. A further problem in predicting an optimum level of fertilizer application is that in the short run one is faced not with a single response curve but with a set of response curves. i.e. short run changes due to random variations e.g, weather and long run changes. Thus over a period of years experiment may show that a set of curves as in Figure 3.3. is obtained. The problem is which response curve RESPONSE FIGURE 3.3. FERTILIZER INPUT AVERAGE GOOD BAD -83- should be chosen as the basis for making a decision as to how much fertilizer to apply to obtain the maximum profit, A decision has to be made as to what the expected response curve will be. It is obvious that whatever curve is chosen, the profit that is in fact made, will be less than that which could have been made if perfect knowledge existed as to what the curve would be. This will be true whether expectations as to yield are assumed to be less or greater than the probable expected yield. It is apparent that the 'best' curve to take would in fact be the one that would make the losses due to uncertainty a minimum over a number of years. Common practice, though this has been questioned, has been to take the simple, numerical average of the curves over a number of years as the basis for predicting optimum levels of fertilizer application)though no justification for so doing has been given, It is shown in the appendix to this chapter, that, for a response curve described by a Mitscherlich or quadratic type function, subject to certain limitations, the choice of the average value does in fact minimise the losses due to imperfect knowledge. This is however not true in the case of the power function where the average value is not the best value. This problem is discussed in detail in the appendix to this chapter. - 84-

3.4. The nature and extent of the potential demand for fertilizers.

3.4.1, Response of crops in U.K. to fertilizers. Over the years a certain amount of data has been collected in the U.K. on the response of crops to fertilizers. At the beginning of the last war these results were gathered together by Crowther and Yates (7) in order to formulate a fertilizer policy. The available results of all fertilizer experiments made in the U.K. since 1900 were taken and the average response to fertilizer application calculated, For the purposes of the analysis the U.K. was divided into a number of regions to allow for variations between them. All but a small proportion of the experiments were conducted on ordinary commercial farms. The. results of the analysis were used to obtain a Mitscherlich type response function. The actual form of the equation used was:- Y = d(1-10-KX) where the symbols have their usual meaning d is a constant which is a function of the crop being grown, whereas K is a constant which is a function of the particular nutrient only. The average value of the constant K was found to be:- For nitrogen KN =.1.1 acres/cwt N For phosphorus K2 = 0.8 acres/cwt P205 For potassium KN = 0.8 acres/cwt K20. The values of these constants were of the same order as those calculated from a much larger series of experiments in Sweden and Denmark (7) and those evaluated by Mitscherlich from his experiments in East Prussia. Indeed Crowther and Yates founds that in comparing the average responses in the U.K. to those from a very much larger group of experiments in Europe that there was remarkably close agreement. To a certain extent this must be regarded as fortuitous since there were often large variations between different regional averages in the U.K. From the average response data it is possible to evaluate the optimum rates of fertilizer application by means of the methods outlined previously. Crowther and Yates equation (7) for the optimum is.

xopt. = 0.12 + (log10 V/c) 1.1 For nitrogen x = 0.23 + (log10 V/c ) 0.8 For phosphorus or opt. potassium where

xopt. is the optimum dressing of nutrient cwts/acre. V is the value per acre of the response to a standard dressing of nutrient. - 8 6-

c is the cost per acre of the standard dressing The standard dressings are 0.25 cwt/acre N or 0.50 cwt/acre P205 or K20. The equations and the data on which they are based suffer from several serious limitations. (i)They are based on observations made before 1941. Since this date agricultural techniques have improved and one would expect responses to be somewhat higher now, than they were previously. (ii)They are based on relatively few experiments and their distribution in the U.K. is not uniform, so that the average is probably unfairly weighted to some regions. (iii)The experiments were in the main of a very simple nature often involving only one nutrient level, very few were of a comprehensive nature involving varying levels and com- binations of the three nutrients. In the case of the single level experiments the results were assumed to fit a response function evaluated from more detailed experiments though this may often not have been the case. In spite of such limitations these results represent the only attempt made to gather and correlate all available response data in the U.K. and are the basis on which optimum rates are predicted. Work on responses has continued since and modifications to the basic data suggested. There is 87_ however no attempt made to gather together all such results, in the manner of Crowther and Yates, so as to obtain a more accurate knowledge on response data.

3.4.2. Some typical response data. Using this data the graphical solution for the optimum level of fertilizer application is given for three different crops and fertilizers, Graphs 3.1., 3.2., 3.3. The three examples have been deliberately chosen to illustrate the wide range of financial returns on investment in fertilizers that can be obtained with different crops and fertilizers. To show this, the financial return (profit) per unit of investment has also been plotted. Thus for example, with potatoes, a farmer fertilizing with potassium at the predicted optimum level, whose expectations are realised, will obtain a return of about £9.5 per £ invested in fertilizers, whereas in the case of wheat fertilized with phosphorus the corresponding re-. turn is only about £0.4 per £ invested.

3.4.3. Optimum levels of fertilizer application for major crops in U.K. The calculated optimum levels of fertilizer application, for the more important arable crops are given in table 3.4. (8) The figures are based on the 1953/54 levels of prices for crops and fertilizers. No allowance has been made for the costs of harvesting or selling the extra crop or GRAPH 3.1.

CALCULATION OF OPTIMUM DRESSING OF NITROGEN

FERTILIZER FOR WHEAT

MD ONSE

R TOTAL VALUE OF

IZE CROP RESPONSE RTIL ROP RESP C FE OF

OF NET VA LUE OF

UE CROP RESPONSE OST AL M V C

6 S

ER RETURN ON FERTILIZER

LIZ INVESTMENT TI

R 4 COST OF E FE RTILIZER%.%s N F MENT O T S NT NVE I PE S

N 4 O

RN U PER

IT i a i a I I i a I RET F 0.2 0.4 0.6 0.8 1.0 1.2 RO P

£ RATE OF APPLICATION CWTS/ACRE N

COST OF NITROGEN FERTILIZER £70 .PER TON N (SUBSIDISED)

VALUE OF WHEAT £1-5 PER CWT.

1956 PRICES RE TUR NON INVE ST MENT FERT I LIZ E R £ PER ACRE CALCULATION OFOPTIMUMDRESSINGPHOSPHORUS -0.5 05 2.0 2.5 I'0 1.5 4. ... •• 1956 PRICES VALUE OFWHEAT 41.5PERCWT COST OFPHOSPHORUS FERTILIZER448PERTONP (CENTRAL &NORTHERNREGIONSONLY) 0.2 FERTILIZER FORWHEAT I GRAPH 3.2.

CROP RESPONSE GROSS VALUEOF RETURN ONFERTILIZER INVESTMEN T 04

0.6 FERTILIZER NET VALUEOF se

COST OF CROP RESPONSE 08

1.0 t O s tSUBSIDISED) GRAPH 3.3.

CALCULATION OF OPTIMUM DRESSING OF POTASSIUM

FERTILIZER FOR POTATOES

35 W cc U

GROSS VALUE OF cC ii, CROP RESPONSE a. 30 44 (------rm,

LIZER i:e NET VALUE OF P

RTI CROP RESPONSE RO F FE O OF C E T 20 im OS VALU C

RETURN ON FERTILIZER INVESTMENT

• 15 •

10 ... ENT STM INVE ON

Z CL = COST OF FERTILIZER I- LI., C4

0.4 0.8 12 1.6 2.0 24

RATE OF APPLICATION CWTS/ACRE Ke

COST OF POTASSIUM FERTILIZER 433 PER TON KtO

VALUE OF POT A TOE S k IB PER TON

1956 PRICES _88. applying the fertilizer. The dressings will therefore tend to be somewhat higher than the true optimum values. TABLE 3.4. Crop Most profitable dressing cwts/acre. N(b) P205(a) K20 Cereals 0.8 0.4 0.4 Swedes 0,9 1.4 1.3 Mangolds 0.9 1.0 1.4 S. Beet 0.9 1.0 1.0 Potatoes 1.2 1.6 1.8 notes:- a) For central and northern regions of U.K. only. Add 0.2 cwts/acre P205 for wetter western and northern regions. Subtract 0.2 cwt/acre P205 for drier southern and eastern regions. b) Subtract 0.2-0.4 cwts/acre N for cereals and swedes in wetter western and northern regions.

3.4.4. The nature of the potential demand for fertilizers. The National Agricultural Advisory Service has from time to time conducted surveys of fertilizer practice in various parts of the U.K. (9) They have determined both the actual amounts of fertilizer that are used and the percentage of the acreage that is fertilized. The results of the surveys have been gathered together by Church (10) who discusses them in some detail. From the surveys it is possiblei to draw certain broad conclusions as to the nature of the demand for - 8 9- fertilizers in the U.K. These are given below and are in substantial agreement with those reached by Church. (i) Root crops grown for sale, e.g. sugar beet, potatoes receive on the whole adequate amounts of all three nutrients both with regard to the acreage treated and the level of application used throughout the country. (ii) Cereal crops receive adequate dressings of phosphorus and potassium in most areas, though practice does vary fairly widely. Indeed the former is probably applied at above optimum rates in certain areas. Nitrogen fertilizer use could be increased with profit for a large proportion of the acreage in most areas. (iii) Fodder crops receive, on the whole, inadequate a- mounts of fertilizer. This situation should be remedied for a)It would be profitable for farmers to do this b)The governments agricultural policy is to encourage farmers to rely on home grown feed crops to the greatest extent possible. (iv) Grassland is extremely inadequately fertilized both in the extent to which it is practipd and the actual amounts used. Thus the survey of Boyd and Lessels (11) revealed that in 1951/52 not more than 50% of the temporary grassland and 25% of the permanent grassland received any fertilizer, these - 90-. figures relating to highly farmed arable and dairying areas. In other parts of the country the figures were even lower. Further actual rates of application are low especially with regard to nitrogen. The importance of grassland as an agricultural resource is shown by the fact that some 60% of agricultural land in the U.K. is grassland and that some 60% of the gross output of agriculture is derived from livestock and livestock products, the feeding of which is closely connected to grassland production. Further grass is a crop which responds very readily to the use of fertilizers. It has been shown (12) that grass and grass products form the cheapest source of feedstuff, especially when compared to imported materials. Clark and Bessel (12) in a detailed comparison of some 40 dairy farms practicing intensive grassland management, through the use of fertilizers, to some 280 other grassland farms, showed that the former were able to produce a gross income per acre some 65% greater than that of the latter for only a slight increase in gross charges. The increased cost of the fertilizer was more than offset by the decreased spending on purchased feeding stuffs.

3.4.5. The extent of the potential demand for fertilizers. Having summarized the position with regard to fertilizer -91- use it is desirable to gain some estimate of the extra fertilizer that could be profitably used and to relate this to present production in the fertilizer industry. For the purposes of making such an estimate the data on actual and optimum use of fertilizers assembled by Ohurch(10,14) Crowther and Yates (7), Crowther (15) and Boyd and Lessels (13) will be used.

3.4.5.1. Cash root crops. (potatoes, sugar beet). There is little scope for increased fertilizer use on these crops. Increases in the few areas where improvements could be effected would only lead to negligible increases in the amount of fertilizer used.

3.4.5.2. Cereal crops. 3.4.5.2.1. Nitrogen. The latest surveys show that * of the cereal acreage is receiving no nitrogen fertilizer. Of that acreage receiving fertilizer, average dressings are in the range 0.25-0.35 cwt/acre N. The optimum rate is probably around 0.6 cwt/acre. Calculation Cereal crops not receiving nitrogen to get 0.6 cwt/acre N Cereal crops already receiving nitrogen to get an extra 0.3 cwt/acre N. -92-

Cereal acreage x 106 acres. Extra nitrogen that could be used =(3 x 7.5 x 106) x 0.6 + (3 x 7.5 x 106) x 0.3 tons 20 20 = 150,000 tons N. n.b. For remainder of this section calculations similar to the above are omitted. Only the data used and the result obtained will be stated.

3.4.5.2.2. Phosphorus. About * of cereal acreage is not receiving phosphorus fertilizer. However much of the remaining acreage is receiving dressings at above optimum rates. Therefore a redis- tribution of phosphorus use is required rather than any increase in the total use.

3.4.5.2.3. Potassium. About * of cereal acreage receives potash but dressings are about optimum at 0.3 cwt/acre K20 Assume 50% of cereal acreage to receive 0.3 cwt/acre K20. Extra potassium required = 56,000 tons K,0

3.4.5.3. Fodder Crops. Of the fodder crop acreage probably between * and * is receiving no fertilizer and the remainder is receiving 50% of the optimum amount. -93-

Assume * of acreage to receive optimum rates and remainder to receive extra 50% of optimum rates Optimum rates of application 0.9 cwt/acre N 1.2 cwt/acre P205 1.3 cwt/acre K20 6 Fodder crop acreage --"-1.3 x 10 acres. Extra nitrogen that could be used = 39,000 tons N Extra phosphorus that could be used =52,000 tons P205 Extra potassium that could be used = 569 000 tons K20

3.4.5.9. Grassland. It is difficult to estimate an optimum rate for grassland, since there is no definite market value for grass. Each enterprise involving the use of fertilizer on grassland has to be considered largely on it own merits. Some idea of the vast potential for increased use that does exist can be gained from the following data. Assume that 50% of the temporary and 25% of the permanent grassland is receiving adequate amounts of all three nutrients i.e. All grassland that is at present treated gets optimum amounts of fertilizer. For the remainder assume that adequate dressings would be 0.5 cwt/acre N, 0.25 cwt/acre P205 and 0.25 cwt/acre K20 for temporary grassland and 0.25 cwt/acre N, 0.125 cwt/acre P205 and 0.125 cwt/acre K20 for permanent grassland, -

These rates are conservative. For example Raymohd (16) suggests that 0.6 cwt/acre N could be used on most pastures whereas Hamilton (17) proposes 0.9 cwt/acre N as reasonable for intensive management. Temporary grassland acreage-^- 6 x 106 acres. Permanent grassland acreage 13.5 x 106 acres. On temporary grassland. Extra nitrogen that could be used = 75,000 tons N Extra phosphorus that could be used = 37,500 tons P205 Extra potassium that could be used = 37,500 tons K20 On permanent grassland. Extra nitrogen that could be used = 130,000 tons N Extra phosphorus that could be used = 63,000 tons P205 Extra potassium that could be used = 63,000 tons P205 The estimates are summarized in table 3.5. - 95-

Table 3.5. Estimate of extra fertilizer that could be used in U.K. Extra fertilizer that could be used tons

Crop N P205 K20 Cash roots - - - Cereals 1502 000 - 602 000 Fodder crops 40,000 50,000 60,000 Temporary grass 80,000 40,000 40,000 Permanent grass 130,000 609 000 60,000 Total 4002 000 150,000 220,000

Total for crops other than grass 190,000 50,000 1202000 n.b. All figures to nearest 102 000 tons.

It should be noted that the estimates are based on surveys carried out in 1950/54. Since this time consumption has increased. Table 3.6. give the estimate after allowance has been made for this increase. -96-

Table 3.6. Estimate of extra fertilizer that could be used after allowing for growth in consumption since 1950/54. Fertilizer tons

N P205 K20 Average consumption 1950/54 210,000 390,000 220,000 Consumption 1958 3109 000 370,000 330,000 Growth 1950/54 to 1958 +100,000 -20,000 +100,000 Estimate of extra fertilizer after allowing for growth 300,000 170,000 110,000 Production 1958 340,000 330,000 330,000* Consumption, no production of potash in U.K.

It can be seen that the scope for increasing the production of fertilizers in the U.K. is still very large provided that the agricultural industry can be persuaded to raise its. fertilizer consumption to optimum levels and that the farm crop value/fertilizer price relationship remains as at present. On the basis of the estimates the nitrogen sector of the industry could expand by 1000, the phosphorus sector by 50%, and the potassium sector by 30%. Naturally such an estimate is an extremely approximate one and the results should be treated with caution since the response data on which it is based are very incomplete. If farmers used these optimum levels of application it would bring about a very large increase in the consumption of fertilizers, -97- but it is of interest to note that, even at such levels, the rates of application per acre of agricultural land would still be well below those of the major fertilizer consuming countries in Western Europe. The estimate is based on the approximate 1953/54 levels of fertilizer and farm products prices, but, as table 3.7 shows, the price ratio of the two items has remained fairly steady in recent years.

Table 3.7.' Ratio of prices farm products: fertilizers Price 1952 1953 1954 1955 1956 1957 Farm products (i) A 100 102 101 107 107 104 Fertilizers (ii) B 100 87 83.5 88 88.5 87 ratio A: B 1.00 1.17 1.21 1.21 1.21 1.20 notes (i) Source Annual Abstract of Statistics (ii) Subsidised prices, data given in Chapter 4.

3.4.5.5. Other estimates of optimum levels of consumption. A similar estimate to the one made above was made by the Ministry of Agriculture in 1952 in response to a request by the O.E.E.C. (18). The estimate was based on 1952 levels of prices and is given in table 3.8. - 98-

Table 3.8. Ministry of Agriculture estimate of economic levels of fertilizer consumption in 1952. Nutrient Estimated economic level N 4519000 tons

P205 559,000 tons K20 341,000 tons It can be seen that these estimated levels of consumption are lower than the author's estimate for nitrogen and potassium, though approximately the same for phosphorus. It should be noted, however, that the Ministry of Agriculture estimate is based on 1952 prices, when the structure of prices was less favourable to the use of fertilizers. Further their predicted economic levels for use of nitrogen on cereals and grassland are almost certainly too low as revealed by present knowledge.

3.4.5.6. Conclusions as to the extent of the potential demand. It would appear that the consumption of fertilizers in the U.K. could be increased above present levels since:- (i)There is a substantial acreage not receiving any fertilizer whatsoever. This applies especially to grassland but also, to a lesser extent, to arable crops. (ii)From such response data as is available it would seem that many farmers are not using fertilizer at the economic optimum. -99-

Given the present ratio of farm product prices to fertilizer cost then it would appear that the consumption of nitrogen could be expanded by 100%, of phosphorus by 45%, of potassium by 30%. Even if this ratio becomes more unfavourable to the use of fertilizers, i.e. by removal of the subsidy, there is still scope for increasing consumption if only for the reason given in (i) above, and because in many cases the cost of the fertilizer is small compared to the financial return its use brings i.e. the optimum is shifted only slightly by changes in fertilizer cost in cases where the grass product is large compared to the fertilizer input cost.

3.4.6. The need for more response data. It must be emphasized that the data on which estimates of optima have been based are extremely scanty and relate to a large extent to pre - 1941 experiments. Naturally work on responses has continued since this date but it has not been at all comprehensive and is often not published. Indeed it is surprising that so few experiments are done each year in determining responses of crops to fertilizers since it is only on the basis of such data that a rational system of fertilizing the land can be based. It would be of great use if, each year, a large number of fertilizer experiments could be done on a sample of -100-

ordinary, commercial farms in various parts of the country to determine the form of the response curves. As the information progressively increased so the farmer could be advised, or himself make the decision, as to the economic level of fertilizer application with a greater precision than is possible now. In addition it should become possible to relate other factors to the responses and their importance as the amount of data increased. Such a scheme would have to be under fairly close supervision if the results were to have any validity, The three interested parties would be the Government, the fertilizer manufacturers and the farmers, who would all benefit from such a plan. Therefore it should be possible for the Ministry of Agriculture to operate such a scheme with the co-operation of the National Farmers' Union and the Fertilizer Manufacturer's Association. In addition agricultural research organisations could still carry out or expand their experiments especially those involving all three nutrients at different levels to determineinteraction effects, optimum ratios of nutrients in mixed fertilizers, etc.

3.4.7. The potential demand in relation to agricultural policy. The case for the increased use of fertilizers must, however, be viewed in the context of the government's -101- agricultural policy. It was seen earlier that in certain commodities, (wheat, milk, eggs and pigmeat), increased production was not required whereas in others, (beef, lamb, feedcrops), it was. The government has especially requested farmers to try and:- (i)Lower the unit costs of production (ii)To rely to a greater extent on home grown feeding stuffs in preference to imported ones. The intensive use of fertilizers on wheat crops and on hairy farms to produce grass for feed would raise production in wheat and especially in milk though at a lower unit cost. Therefore some of the land resources devoted to this type of production would have to be utilized for other purposes to avoid overproduction. The obvious use is in the production of more beef cattle, sheep and feedcrops. Greater use of fertilizer could also be made to increase the production of these commodities. Use of more home grown feed, especially grass and grass products, would help to limit or even reduce imports of concentrated feed. The increased use of fertilizers is thus compatible with the government's policy though some forms of control might well have to be used to avoid overproduction in certain commodities. The increased profits and lowered costs of pro. duction resulting from this would make a contribution to -102- holding down or even reducing the substantial government support given to' he agricultural industry. -1u3-

APPENDIX CHAPTER 3

The choice of a response curve for predicting the optimum level of fertilizer application. In the short run one is faced not with a single, unique response curve of a crop to fertilizer input, from which one can predict the optimum level of fertilizer application, but rather with a set of curves due to variations in factors which are not, or cannot be, accounted for in the model. Thus over a period of years a number of curves as in figure (1) may be obtained. If one assumes that the aim is to obtain the maximum possible profits from the use of fertilizers the problem is which curve to choose as a basis for predicting the optimum in any year, It is obvious that whichever curve is, in fact, chosen one will never obtain the maximum profit that could have been obtained, if perfect knowledge as to the form the curve will take had existed, except in the case where expectations as to response are fully realised. However the selection of any particular curve, as a basis for making predictions, will have an important bearing on the profit that is made in relation to that which was expected. Consider figure (ii). Curve 1 is the actual response which is obtained. F IGURE (i)

FERTILIZER INPUT

FIGURE (ii) CT DU O FERTILIZER PR INPUT COST -I e 4 E I- 0 I— X X X

FERTILIZER INPUT Curves 2,3 are bhe responses which might be used as a basis for predicting optimum inputs of fertilizer. X29 X3 are the optimum rates based on the latter and X1 is the true optimum. For the purposes of the analysis it is assumed that past results show that curve 1 is a more probable result than either 2 or 3, i.e. it lies at the mean of the distribution of the curves obtained. Consider the case where curve 3 is used for prediction, i e. in a year when actual results are better than expected. Fertilizer is applied at level x3 in expectation of a profit IX 9 in fact profit 1K is made. With perfect knowledge as to the response curve, level X1 would have been chosen and the maximum profit AC made. Now Ac:*KI so that the loss made due to uncertainty is AC-KI = L1. However although the maximum possible profit has not been made it is still much better, than the expected one. i.e. profit IK as compared to IJ. Now consider the case where curve 2 is used. i.e. in a year when actual results are worse than expected. Fertilizer is applied at level X2 in expectation of profit EH, in fact profit EG is made. As in the previous case, with perfect knowledge level Xi would have been used and the maximum profit AC made. Now AC .-EG so that the loss made due to uncertainty is AC-EG = L2. Over n years one will make a -105-

series of losses due to uncertainty =IL and these are unavoidable. In this particular case however, not only is the maximum possible profit not made, but also the actual profit EG , is less than that which was expected, EH. The difference in the results between the two cases, i.e. whether profit made is greater or less than expected, suggests that it is possible to postulate a reason for the choice of a particular response curve in terms of the farmers attitude to risk taking and the uncertainty concerning the results which will be obtained. Thus a farmer choosing a small response curve as a basis for predicting the optimum might be expected to have a high aversion to risk taking. This is because, by so doing, he is likely at least to obtain his expected profit and in many cases, when the response turns out to be larger than predicted, it will be exceeded. Indeed the lower the expectation of yield that is assumed the greater is the probability that this will be the case. Such a farmer is likely to have a high degree of satisfaction in his results. The farmer, with a low risk aversion, might choose a large response curve as a basis for prediction. Though there is a much greater probability that the profit made will be less than expected, in those cases where the prediction proves correct or is exceeded he will make a bigger profit -106- than the farmer fertilizing at the lower level. Such a position is, in the long run, likely to lead to a low satisfaction concerning the results since the probability of being correct decreases the larger the response assumed. It is not suggested that farmers do in fact consider the response curve in this way but the argument can be summarized in a somewhat simplified form that farmers prefer to use less fertilizer in expectation of a small but certain profit rather than a large amount in the hope of making a bigger but uncertain profit. This would give an explanation for the fertilizer rates of application used by farmers in the U.K. which are generally below what is considered the optimum. By so doing they are more likely to be satisfied by the results though they are not making the maximum profit possible, i.e. their expectation of profit is likely to be realised and there is a good probability of it being exceeded. However any choice of a response curve is justifiable given a farmer's particular attitude to risk and his personal preferences. This is especially true if the latter are not concerned with maximising profits from fertilizer investment. In such a situation any decision can be considered correct given a particular set of preferences and the problem is no longer susceptible to the type of analysis given above. It is suggested that a more preferable course of action -107-

is one which removes the necessity of making such decisions and which leads to the maximum possible profits from fertilizer investment being made. It is apparent that this can be done by using a response curve defined by the condition that the sum of the unavoidable losses due to uncertainty, over a number of years,YLi, is a minimum. Such a curve will lie somewhere in the middle of the set of response curves of figure (i). It's position can, however, only be fixed by assuming that the curve can be represented by a mathematical model and then evaluating the constants of the system from n experimental data such as will maker Li a minimum. This is 0 done below for three of the models already discussed in Chapter 3. 1. Mitscherlich model. This assumes the response curve is represented by Y = A(1-e-KX) Y = response of crop to fertilizer input X, ,A,K are constants. let V = value of crop per unit, c = cost of fertilizer per unit .:Net product (NP) = VA(1- e-KX) - ex -KX •d(NP) = KVAe - c = 0 for maximum dx e-KX = c /KVA or x= 1 ln. KVA = optimum level of fertilizer K c application.

-103-

Assume that one presumes the response curve to be Y = Am(1- e-KmX) and operates at the optimum predicted by the curve, whereas in year i the actual curve is -K 1X Y = Ai(1-e ). Then loss made in year i due to imperfect knowledge as to the response curve is:- Profit that could have been made with perfect knowledge minus profit that is actually made = Li

/ -Ki In /KiVAJA% Now Li Kr c i) c 1 In Ki c / -Ki In /KmVAm\ KmVA1 - [iAi(le .17E k c / c In c Km n ,, Over n years total losses due to uncertainty = Li 0 Assume that variations in the response curve can be represented by changes only in A and that the value of K is constant from year to year. (This assumes a curve of the same shape every year). The value of Am is required that will make the losses a minimum. This will be given by dyLi = 0 dAm Now n d2 L. VAi c Z - c. l= 0 for minimum. 0 o KV A K Am dAm -in (KVAm) = c nab. e KVAm -10)-

...summing over n years _1. 1 2 (A1-1-A2+A3...An)- n c = 0 K Am K.Am .now let Al+A2+A3...An 64, i.e. average measured n value of A over n years. 1 2 oC = c K 'A m KAm Am = Thus taking the average value of the constant A in the response equation, that is used to predict optimum levels of fertilizer application, will make the losses due to uncertainty a minimum. 2. Power function. Assume the response curve is represented by Y = AXb where symbols have their usual meanings, b is a constant. ..Net product (NP) = VAXb - cX b-1 •d(NP) = bVAX - c = 0 for maximum. dx 1 .% X =f c b-1 -= optimum level of fertilizer lbVA) application Now losses due to uncertainty in year i

11/6'k -1 0 iiko., _ 1 1, tiptsi.p.) cite% v A ll [

Ni i.`(1 51..,\/ ATI$.‘1‘"4-1 — c---S------[ n 1:.‘1‘11‘ Total losses due to uncertainty = E Li / 0

-110.

As for Mitscherlich model assume variations can be represented by changes in A 9 b remains constant. Value of Am that will give minimum losses due to uncertainty n is given by dy_Li = 0 dAm

%., vb., ..., u • a t L, _ y- ,c_....1 4.. I . 47.. v.A..(.,by ) .1_ ,-ry. c.A„ — o 1-1 kbv/ I- 6

= 0-for minimum

Let Al + A2 + A3 + A4....An = d i.e, average Ii measured value of A: Summing over n years and dividing by n

6/6_1 26.1 T.7- 14-1 17.-6 ek.V.‘7) . , 1-b by 1-‘

b 10 .4 12VoqL-_,) •••••• 6 V)

b-\ - b . Trt 6V \.12 v

2 .6 -6 An.% ."‘ ,V1

-111- i.e. the value of Am to be taken for predicting optimum levels of fertilizer application, such that losses are minimised, is not the average measured value, but one given by the expression above. Am will be greater or less than depending on the relative magnitude of b, V, C.

3. Quadratic Function. Assume response curve can be represented by Y = AX + BX2 Symbols have usual meaning, B is a constant (negative). Net product (NP) = VAX + VBX2 cX d (NP) = VA + 2vBX - c = 0 for maximum. ' d x X = c-VA = optimum level of fertilizer 2VB application. Loss due to uncertainty in year i

•••

L.. = VAi(c-VAi + VBi(c-VAi2 c c-VAi 2VB. 2VB. 2VB1

•••••••••••1

VA. c-VA7) + VB. c-VA1 c c-V.1 2VBm 2VBm 2VB

-112-

Total losses due to uncertainty over n years = Li Values of Am9 Bm which will make 1E: Li a minimum o n are given by DE:Li = 09 Li = 0 D Am Bm now E Li - VAi - 2V.Bi. (c-VAm). 1 + c = 0 for 0 0 2Em 2VBm 2Bm 2Bm minimum Am

B3 now let Al + A2 A3....An Bl + B2 + ...Bn n n i.e. average value of A9 B over n years.

Summing over n years and dividing by n = V 0( 1" 2V (3 (1)

and 2 nii) 1 - 2VB.(c-VA 1 o Li =.-c-VAVAl m) 2V 2 2V B 3 a Bm Bm m c(c-VAn)1 2V 2 = 0 for minimum. Bm Summing over n years and dividing out by (c - VAm . 2V n (c-VAm) gives value of Am that makes 3E:Li a maximum k 217- o •V 4 + 2V (b (c-VAm) = c (2) 2V13m n i.e. Am9Bm have no unique values which will make E:Li a minimum Any pair of values which will satisfy equation (1) -113- or (2) will minimize the losses.

One such pair of solutions is Am = 0( 9 Bm = i/ let Am = o( V.54 2V(3/c-±( = c k2v13m

2v/5 ) = 2V Bm (c- vat ) Bm = / Thus taking the average, measured value of the constants in the quadratic function, from which the optimum is predicted, will minimize losses due to imperfect knowledge. The use of the quadratic function is the most satisfactory since no limitation has been placed on the constants, in order to obtain a solution, as was the case with the Mitscherlich or power function, i.e. assume K,b fixed and A varying. n.b. Though it is not possible to derive an analytical solution where both constants of the equation vary for these two cases it should be possible to obtain a numerical solution, given the value of the constants in each year. These methods for deriving a response curve for predicting optimum levels of fertilizer application are important, since they remove the element of personal attitudes towards risk and uncertainty. The assumption is made that the maximum profit from investment on fertilizers is required. A model is then used for predicting the optimum level of fertilizer application such that the unavoidable losses, due to imperfect knowledge as to what the response curve will be, are kept at a minimum. The method does however require the measurement of response data from year to year and this is, to a large extent, lacking and the above arguments cannot be treated other than thebretically. It is however of interest to note that the work of Crowther and Yates, on which the estimate of potential fertilizer use in chapter 3 is largely based, does in fact use the average values of the constant. This is justified since the model chosen to represent the response data is in fact of the Mitscherlich type. -115-

CHAPTER 4

THE CHANGING STRUCTURE OF FERTILIZER PRICES AND SUBSIDIES AND ITSr, EFFECT ON EXPENDITURE AND CONSUMPTION OF FERTILIZERS

4.1. Current Fertilizer Prices

Table 4.1. gives the 1959 prices of the more common, straight fertilizers available on the market. The prices have been taken from manufacturers lists which are, for all practical purposes, the same.

Table 4.1. Price of plant nutrients available in various fertilizers (March 1959). Price per ton nutrient Manufacturers Price after price deduction of subsidy Nitrogen Fertilizers £ per ton N Ammonium sulphate 20.8%N 102.90 52.30 Nitrochalk 15.50 119.35 71.75 Nitrochalk 21%N 116.30 68.80 Sodium nitrate 160 170.30 122.80 -116-

Table 4.1. (contd.)

Price per ton nutrient Manufacturers Price after price deduction of subsidy Phosphorus Fertilizers £ per ton P205 Ordinary superphosphate 190205 85.00 47.50 Concentrated superphosphate 470205 82.70 45.20 Basic slag 15% P205 50.40 28.40 Basic slag 20% P205 60.00 38.25

Potassium fertilizers £ per ton K20 Potassium chloride 60% K20 34.10 34,10 Potassium chloride 17% K20 38.95 38.95 Potassium sulphate 50% K20 42.10 42.10

There are differences in the cost of plant nutrients in various fertilizers and these, to some extent, give the reasons for the pattern of consumption described in Chapter 2. Ammonium sulphate is the cheapest source of fertilizer nitrogen available at present. It supplies some 60% of total nitrogen used and almost all that used in mixed fertilizers. Nitrochalk, (ammonium nitrate and chalk), is about £13 - 16 per ton N dearer than ammonium sulphate. Farmers are however willing to pay this premium since this fertilizer -117- is most suitable for certain specialised applications, such as top dressing cereals and high yielding grassland, where a quick crop response to application is required. The supply of nitrogen as sodium nitrate costs approximately 75% more than using ammonium sulphate and consequently this material finds almost no use as an agricultural fertilizer. The two main commodities in the phosphorus fertilizer market are basic slag and superphosphates. Almost the entire possible production of basic slag is taken up for use on grassland, in certain areas of the U.K. where its use is suitable, since it is a very cheap form of phosphorus compared to superphosphate. Indeed demand is such that farmers are prepared to pay a premium on the higher grades of slag imported from the continent. Concentrated superphosphate is slightly cheaper than ordinary superphosphate and is now taking an increasing share of the market at the expense of the latter. 60% potassium chloride is the cheapest form of potassium fertilizer and accounts for almost the entire market in this nutrient. The other two materials find only certain specialised uses. -118-

4.2. Level of fertilizer prices 1946-58

In order to show the changing price levels of fertilizers a price index has been calculated and is given in table 4.2. The method of calculating the index and the sources of data used are given in the appendix to this chapter.

Table 4.2. Fertilizer price index.

Year All Fertilizers N P205 K20 A B A B A B A 1946 100 100 100 100 1947 101 102 102 100 1948 102 102 101 100 1949 104 104 105 100 1950 104 105 104 100 1951 127 124 136 114 1952 195 163 158 263 176 148 1953 187 142 165 136 234 148 143 1954 180 136 165 136 223 137 134 1955 186 143 172 139 230 150 139 1956 200 144 190 136 249 156 143 1957 208 142 201 139 257 141 147 1953 210 134 204 122 265 145 147 _119_

Notes. a) Years ending 30th June b) A series is index based on manufacturers prices B series is index after account has been taken of fertilizer subsidy paid direct to farmers. It is not proposed to discuss the varying price levels in detail. The trends that have occurred are self-evident from the table. Reference to the causes of the trends will be made in the subsequent discussion on subsidies.

4.3. Fertilizer subsidies.

4.3.1. History of subsidies. The fertilizer subsidies arose out of certain wartime measures when, as a matter of national importance, the supply and price of fertilizers were closely controlled by the government. After the war this policy was continued with the effect that, up to 1950, fertilizer prices to farmers were for all practical purposes constant. This stability was achieved by the government paying a subsidy directly to fertilizer manufacturers to cover the difference in their production costs and the fertilizer selling price. Certain restrictions on the amount made available to farmers (until 1947), and the type of fertilizers made, (until 1951) were -120-- also in force. In 1950 the government announced the abolition of the subsidy and the removal of all controls on fertilizer sales, to take place in two stages. The first cut in subsidies dated from July 1st 1950, i.e. start of fertilizer year 1951, and the second a year later. The effect on prices was immediate and is illustrated in table 4.2. The rise in the price of phosphorus fertilizers was magnified due to the fact that subsidy removal occurred at the same time as the world shortage of sulphur. The price of sulphuric acid, a primary raw material in the industry increased at the same time. The effect on consumption of fertilizers was also immediate. Sales of all three nutrients declined rapidly being most marked with phosphorus fertilizers.

4.3.2. Re-introduction of subsidies. The decline in consumption was sufficiently large that Parliament passed the Agriculture (Fertilizers) Act, 1952 which re-introduced subsidies. The relevant parts of the Act are:- 1 (1) ... Contributions out of moneys provided by Parliament may be made, in accordance with a scheme or schemes made by the appropriate Minister with the approval of the Treasury, for relieving occupiers of agricultural land of a part of the expenditure which they would otherwise -121-

incur in respect of fertilizers acquired by them for use for adding to such land to improve the fertility of the soil. 2. ... The provision to be made by a scheme under this act as respects the amounts of the contributions which may be made in accordance with the scheme shall be such as in the opinion of the Minister will secure as far as is practical that the making of contributions in accordance with the scheme in respect of fertilizers of any kind will not relieve occupiers who acquire fertilizer of that kind of more than one half the expenditure which they would have incurred in respect thereof if there had been no provision for the making of those contributions. The Act came into force in July 1952 and made provision for the payment of subsidies on nitrogen and phosphorus fertilizers. In addition it was agreed to pay a subsidy retroactively for phosphorus fertilizers purchased in 1951-52 in order to relieve farmers to some extent of the very large increase in their price. In accordance with the Act the subsidies were paid directly to farmers and not to the manufacturers as previously.

4.3.3• Variations in subsidy 1952-59. Since the re-introduction of subsidies in 1952 the amount paid to farmers, under the various schemes has varied -122- considerably. This is shown in table 4.3. below.

Table 4.3. Variation in fertilizer subsidies 1952-59. Year(e) Value of subsidy paid on fertilizers £ per ton N or P205 Nitrogen Super- Basic slag Ground Phosphate in (a) phosphate 17% P205rock mixed,fertilizers (b) phosphate water water soluble insoluble (d) 1952 27.50 17.70 13.80 32.50 20.00 1953 15.00 27.50 14.40 17.50 32.50 20.00 1954 15.00 27.50 14.40 17.50 32.50 20.00 1955 17.10 25.00 14.70 12,90 28.75 16.25 1956 27.50 28.75 16.90 14.60 32.50 18.75 1957 32.50 37.50 21.45 20.00 37.50 22.50 1958 42.80 37.50 21.45 20.00 37.50 22.50 1959 47.50 37.50 21.45 20.00 37.50 22.50 Notes a)All types of nitrogen fertilizer including mixed. b)Water soluble phosphorus only. c)Payment not pro-rata. Amount depends on concentration. d)Excluding phosphorus from organic sources. e)Years ending 30th June. The value of the subsidy payments has been such that they have maintained fertilizer prices steady at about 40% above the 1946-50 levels. Further they have been used as a -123-

means of encouraging the use of those nutrients which the government thinks would yield most benefit to the agricultural industry. Thus the nitrogen subsidy has been increased greatly in recent years for the express purpose of increasing its use (1). To a great extent, however, price increases have cancelled out the benefits from this increased subsidy so that the effect on consumption has not been as great as was intended. Another example of this policy has been the premium that has been paid in respect to water soluble forms of phosphorus in fertilizers. In this, policy has been sucessfult for almost no water insoluble phosphorus fertilizers are produced, with the exception of basic slag and ground rock phosphate which come under separate schemes. The current level of subsidies, about 45% of the total cost, are close to the maximum permitted under the 1952 Act. To increase them to any great extent on phosphorus and nitrogen fertilizers would require further legislation in Parliament. No subsidies are paid on potassium fertilizers. This is presumably because the price of this nutrient did not increase to the same extent as that of the others. However by encouraging the increased use of nitrogen and phosphorus, an automatic increase in the use of potassium is brought about, since it is largely sold in mixtures with the other two nutrients. -124-

The total cost of these subsidies has been estimated and is given in table 4.4. The method of calculation is given in' the appendix to this chapter.

Table 4.4. Total cost of subsidy schemes. Year (a) 1952 1953 1954 1955 1956 1957 1958 Cost £106 7.5 14.0 14.0 12.5 18.5 21.5 25.0 Note (a) Year ending 30th June.

4.4. Expenditure on fertilizers. Graph 4.1 shows the variation in expenditure on fertilizers since 1947, both actual and that revalued at 1947 fertilizer prices. Expenditure in actual terms has increased greatly though the actual amount spent by farmers, i.e. net of subsidy, curve (ii), graph 4.1., has been far less. Real expenditure by farmers, curve (iii), graph 4.1., has also increased since the low level of 1952 and is now above the previous maximum in 1950. However real expenditure net of the subsidy has not increased nearly as much and farmers are not spending much more on fertilizers than they did in 1947 in real terms. This indicates that the increased real expenditure and hence the consumption of fertilizers has 0 z EXPENDITU RE FERTIL IZ ERS 100 20 40 47 48 495051 52 535455 565758 EXPENDITURE ONFERTILIZERS1947-58 YEAR ov ‘ ACTUALNETOF SUBSIDY t (1) ACTUAL . iii) ACTUALVALUED VALUED AT1947PR ICES (P)ACTUAL NET AT 1947PRICES OF _SUBSIDY 1, - \ Kb U Ln 0 2 i- 2 900 n Z a. i- 0 0 in 100 z z 0 Ne 0 ani

IZER in FERTIL " 1100 800 RELATION SHIPBETWEENFARMINCOME I. FARMNETINCOME 10 PAPER TILI ZERPRICEINDEX PRICES ANDCONSUMPTION 1.6

GRAPH 4.2. 2.0

RATIO Vp/410 24

6 4 2.8 6

) FERTILIZER 3.2 -125-

largely only been brought about by the progressively increased subsidy payments.

4.5. Relationship between farm income, fertilizer price and consumption.

Two factors which might be expectea to affect the level of consumption of fertilizers in any given year are the prices of fertilizers in that year and the net income (profit), of the preceding year. Expressing this mathematically C ID( I/ or C = KI

where C is total consumption of fertilizers I is a measure of farm income in preceding year P is a measure of fertilizer prices. K is a constant. In order to test the validity of such a relationship consumption, measured in tons N + P205 + K20 has been plotted against the ratio I/p on Graph 42. I has been taken as the aggregate net income of the agricultural industry in the U.K. as estimated by the Ministry of Agriculture (1).. P has been taken as the price index for all fertilizers as given in table 4.2. (The subsidised index, B series, has been used with the exception of 1952. In this year the subsidy was only paid retroactively and did not affect actual fertilizer prices). -126-

Up to 1955 a very close relationship between the three quantities appears to have existed but from 1956 onwards the same correlation no longer held. A new trend would appear to be occuring but the data is at present too small for any definite conclusion to be drawn except that, at the present time, the consumption is far less dependant on the ratio I/p than it has been in previous years. The sudden rise in consumption which occurred in 1956 cannot be easily explained in terms of income or price. The farm income in the preceding year, 19552 was lower than it had been for some years and there was no significant change in the subsidised price. A possible explanation is that in 1956 a general all round increase in the subsidies was made. This may have encouraged the disproportionately large increase in consumption even though the benefit from the higher subsidies was almost entirely removed by the parallel increase in fertilizer prices. However, although, very large increases have been made in the nitrogen subsidies since 1956, which have brought about a real decrease in prices, no similar effect to that of 1956 has occurred in consumption. Therefore until further data is obtained it is impossible to draw any conclusions as to the immediate effects of fertilizer price and farm income on fertilizer consumption at the present time. -127--

4.6. Subsidy policy.

The subsidy policy has been such that it has encouraged farmers to utilize more fertilizer. The inreases that have occurred have been due almost, entirely to subsidy payments and not to any real increase in expenditure on the part of farmers. This suggests that any removal of the subsidy would cause a large decrease in consumption, as in fact occurred in 1952 when government support was removed. The subsidy can be justified on the grounds that it brings about increased productivity in farming and hence in the long run reduces the government support that is given to the agricultural industry. However it has been shown in Chapter 3 that fertilizers are most used on the high cash crops e.g. Wheat, Sugar Beet, Potatoes, on which the government has to pay considerable amounts in deficiency payments, whereas fox less fertilizer is used on those crops, where the government feels production ought to be expanded, both in the national interest and that of the agricultural industry, e.g. Feed grains, fodder crops grassland. It is therefore suggested, that in the interest of the agricultural economy as a whole, more benefit would be gained by introducing a system of selective subsidy payments. This would mean the granting of a subsidy on fertilizers used on -128- those crops of which greater production is required. No subsidy or a reduced one would be paid on fertilizers used on other crops. Though such a system would be more complicated to operate than the present one and would require more controls, it would not be unreasonable for the farming industry to accept such a scheme in view of the vary generous support that is already given to it by the government. -129-

APPENDIX CHAPTER 4

(a) Fertilizer price index (Table 4.2.) The price index has been calculated according to the Marshall-Edgeworth formula.

P = 1C D ( 4_ 'n' clo qn) x 100

Po(qo qn) tr where P = Price Index, pn = price in year n9 po = price in base year, qn = quantity in year n qo = quantity in base year. The index has been based on the following fertilizer materials:- Ammonium sulphate, ammonium nitrate, ordinary superphosphate, basic slag, ground rock phosphate, and 60% K20 potassium chloride. These commodities account for some 90% of the total market. Prices have been taken from the Fertilizer and Feeding Stuffs Journal which publishes fortnightly market prices. The quantities of the various materials have been taken from chapter 2. (b)Total cost of subsidy schemes (Table 4.4.) The cost has been estimated from data on consumption of fertilizers in chapter. 2 and on the value of the subsidy -130- payments. The following items have been taken:- Total nitrogen consumption. Total of superphosphate and all 'other' fertilizers (The value of the subsidy has been taken as the rate paid for water soluble P205 in mixed fertilizers). Total basic slag consumption. (The value of the subsidy has been taken at the rate payable on 17% P205 basic slag). Total ground rock phosphate consumption. Specimen calculation for 1953. Material Consumption Value of subsidy Total value x 103 £ per ton N or a x b£ a P205 b Nitrogen 230 tons N 15.00 3.5 x 106 Superphosphate and all 'others' 257 tons P205 32.50 8.4 x 106 Basic slag 101 tons P205 14.40 1.4 x 106 Ground rock phosphate 42 tons P205 17.50 0.7 x 106 Total 14.0 x 106

fertilizer price, P, and farm income of previous year, I. (Graph 4.2.) Total consumption, (ton$N,P205 and K20, has been taken from chapter 2. Fertilizer price has been measured by the price index, B series. -131-

Farm income has been taken as the aggregate net income as estimated by the Ministry of Agriculture and published in the Annual Review and Determination of guarantees. The relevant data' is given below.

Year Income of Fertilizer Total consumption ratio 6 previou9 year Price 103 tonsNI P2054-K20 1/p X 10 £ 10b index I P 1948 191 102 758 1.88 1949 223* 104 809 2.15 1950 291 104 909 2.81 1951 305 127 864 2.40 1952 268* 195 629 1.37 1953 323* 142 861 2.28 1954 333 136 872 2.46 1955 331 143 842 2.32 1956 295 144 983 2.05 1957 329 142 • 989 2.32 1958 319 134 1002 2.39 -132-

CHAPTER 5 .

THE ATTITUDE OF FARMERS TO THE USE OF FERTILIZERS

5.1. Introduction.

In previous chapters it has been shown that farmers, on the wholel do not make use of the optimum levels of fertilizer application as are indicated by such response data as is available. The adoption of a particular level will depend largely on those factors influencing a farmer when making a decision on fertilizer use. Assuming that he wishes to obtain the maximum profit from investment on fertilizers one would expect the economic optimum, as determined by the methods outlined previously, to be used. That this is not the case is apparent from the data in chapter 3. It is possible that many farmers are ignorant of the economic concepts involved and they are likely to be subjected to many external factors, e.g. advice, availability of capital, advertising, etc., which will affect their final decision. It was thought desirable to attempt to determine what these factors are and what effect they may have on fertilizer use. A survey- of farmers attitudes was therefore made. The work was carried out in two sections:- a) A preliminary survey of 12 farmers and 5 County -133--

Advisory Officers of the National Agricultural Advisory Service, (N.A.A.S,). This organisation exists to advise farmers and is therefore in close contact with their views. b) A full scale survey of farmers who are members of the Cambridgeshire Farmers' Union.

5.2. Results of preliminary survey.

This initial work was intended to determine approximately what farmers attitudes were and what factors were likely to be of importance to them in making their decisions on fertilizer use. The work was carried out by personal interview. The farmers were asked:- a) Whether they considered themselves at the optimum usage of fertilizers. b) What factors they considered had most affected their choice of a level of fertilizer application. The N.A.A.S. were also asked to give their views on these questions. From these discussions the following results were obtained,

5.2.1. Optimum use of fertilizers. The farmers interviewed almost invariably considered -13LF- themselves at optimum use on all arable crops. On grassland they thought they were giving reasonably adequate amounts though some improvement might be affected. The N.A.A.S. representatives agreed that this was the farmer's personal attitude in general. Their own estimate of the position was that taking it on an acreage basis, on arable crops farmers were near or even exceeding optimum use of phosphorous fertilizers and they were close to the optimum in the use of potassium, though in some areas a substantial increase could be made. In the case of nitrogen fertilizers a large, all round increase would be of benefit. Generally the high cash crops, cereals, sugar beet and potatoes were well fertilized though nitrogen use was low on cereals. With other root and fodder crops practice was very variable and could often be improved. Grassland was however totally inadequately treated. Potential use on this crop was almost completely undeveloped except by a few progressive farmers. This estimate of the position agrees closely with the conclusions drawn in chapter 3.

5.2.2. Factors affecting fertilizer use. With regard to the factors which determine a farmer's level of fertilizer application almost the only factor the farmers thought significant, not surprisingly, was their own experience and skill. In this 'experience' is undoubtedly -135-

included some estimate of the profitability of each crop and this in turn will affect the amount of fertilizer used. They did not appear to consider whether in fact they were at the economic optimum. A 'good yield' or a 'good looking crop' seemed to be among the major considerations. The N.A.A.S, confirmed that this was the general view among farmers. In addition they thought that some of the following factors '„,ere often of significance:- a)The previous years income b)The value of the subsidy c)N.A.A.S. advice d)Other farmer's practices e)Soil analyses f)Trade advice They were not prepared to commit themselves as to which factors were most important though they were of the opinion that their own advice coupled with the use of soil analyses had a considerable effect. The preliminary survey gave consistent results but being based on a very small, non-random sample could be liable to considerable error and it was therefore decided to extend the work to a very much larger number of farmers. It was found difficult to secure the help, necessary to carry out such a survey, from relevant organisations but eventually the -136-

co-operation of the National Farmers' Union, (N.F.U.), was obtained and through them that of the Cambridgeshire Farmers' Union, (C.F.U.). After discussing the matter with the C.F.U. it was decided that the best approach would be to undertake a postal survey of members of the C.F.U. Several criticisms can be made of the procedure adopted and these are discussed in the appendix to this chapter. The main reasons for limiting this section of the work were lack of time to carry it out and, more important, lack of money to undertake it. The cost of making such surveys is considerable and only sufficient funds were available to carry out the survey described below.

5,3. Survey of farmers in Cambridgeshire

5.3.1. Introduction. A questionnaire was drawn up, based on work carried out in the preliminary survey, the questions being designed to determine what factors, in the farmer's own estimation, had had the most effect in determining the levels of fertilizer application employed by him during the current, (1959) season. A copy of the questionnaire is given at the end of this thesis. The questionnaire was sent to all members, (1700), of the Cambridgeshire Farmers' Union. 571 replies were received of which 525 proved useful. TABLE 5.1. Number of replies classified according to size of farm.

Size range of farm acres +300 150-300 100-150 50-100 0-50 Total number of replies received. 157 113 56 80 119

Number of replies recktved from 156 112 56 80 84 fertilizer users. Total acreage of fertilizer users 102,800 25,200 7,200 5,700 2,400 covered by survey. Total acreage of non—fertilizer users covered by 318 193 0 0 400 survey. TAJ LE 5.2.

Percentage of farmers replyine, to questionnaire, and using; fertilizers, who selected the following listed factors as having played some part in making a decision on the size of fertilizer dressing used in 1959.

Size range of kercentage of replies selecting following factor farm acres 'Factor a b c d e f g h jklm +300 63 35 35 31 1 14 43 13 61 38 10 73 9 150-300 61 40 35 31 1 21 44 11 58 32 12 75 13 100-150 66 36 39 38 2 20 39 21 48 16 11 80 9 50-100 54 29 31 29 8 41 21 51 19 15 76 8 0-50 57 31 24 33 2 12 27 14 32 11 17 66 8

DESIGLATION OF FACTORS a)Price expected for crop. An article on fertilizers seen in farminc b) The cost of the fertilizer. press. c)The value of the fertilizer subsidy. The results of a soil analysis carried ott d)The size of the profit made from the farm on the farm. during the previous season. A practical demonstration of fertilizer use e)?ertilizer manufacturer's advertisement seen seen by farmer. in the press. A neighbouring farmer's results from using f)Advice given to farmer by fertilizer merchant. fertilizer. g) Advice from N.A.A.S. on fertilizer use The results obtained in previous year from use of fertilizer. Advice given to farmer by fertilizer manufacturer's representative. TABLE 5.3. 1UPLIE0 TO QUESTIONS 2,3,4.

Size range Percentage of those replying to question giving following answer of farm acres Question 2 Question 3 Question 4 a b c a b Yes Bo 300+ 23 6 71 8 . 92 58 42 150-300 32 3 65 6 94 51 49 100-150 27 4 69 2 98 61 39 50-100 19 6 75 13 87 53 47 0-50 22 5 73 13 87 54 46

NOTL6:- Question 2 asked whether farmer was using amore, bless, c)the same fertilizer dressings as in previous year.

question 3 asked whether farmer a) limited amount to be spent on fertilizers before deciding level of application or b) whether he decided level without any fixed budget.

Question 4 asked farmer whether he gave preference, whew deciding on fertilizer dressing, to those crops giving biggest cash return per acre. TABLL B.4. a) Inter-relation of factors a,b,c of question 1.

Size range acres +300 150-300 100-150 50-100 0-50 Percentage of farmers replying marking both factors a,b of question 1, together as being of 28 32 30 20 24 importance in determining their level of fertilizer application. Percentage of farmers replying marking factors a,b,c, of. question 1, together as being of 20 24 22 14 11 importance in determining their level of fertilizer application

b) Inter-relation of replies to question'2 and factor c of question 1. Size range acres +300 150-300 100-150 50-100 0-50 Percentage of farmers replying who stated they had increased their fertilizer use in 1959 and who also marked factor c, of question 1, 10 15 11 6 7 (value of subsidy), as being of importance in determining their level of fertilizer application. Expressed as a percentage of those using more fertilizer. 42 50 40 33 33. -137-

The results were analysed according to farm size and are presented in tables 5.1., 5.2., 5.3. and 5.-i-.

5.3.2. Acreage covered by survey and non-users of fertilizer. Reference to table 5.1. shows that the acreage covered by the survey decreased with farm size, However, since the total acreage of large farms is so very much greater than that of small ones, and hence of more importance in determining fertilizer consumption, this bias is not of great importance. The number of non-fertilizer users only becomes significant in the 0-50 acre group and the acreage of farms not using any fertilizer is very small compared to the total acreage. It would appear, in the area surveyed anyway, that most farmers consider the use of some fertilizer essential to farming.

5.3.3. Economic factors. In chapter 3 it was shown that an economic analysis of fertilizer use gives that the primary factors determining a level of fertilizer application are the inter-relation or ratio of the unit value of the crop to the unit cost of the fertilizer. If this economic concept was known and understood by farmers one would expect factors a2 b2 c, or at least factors a2 b2 of question 1, to be selected together as being _13F_ of importance in decision making. Yet only about 30% of those farmers replying in 100+ acre groups, and 20% of those in the 0-100 acre groups, marked both a and b together as having been of importance. (Table 5.4.). An even smaller percentage thought that all three factors were of importance. i.e. 20% in the 100+ acre groups and about 12% in the 0-100 acre groups. The low percentage selecting these factors together suggests that the economic concepts underlying fertilizer use are not widely understood by farmers of all size groups. This result confirms the view formed in the preliminary survey and the information given by the N.A.A.S. on this point.

5.3.4. Individual factors of the greatest importance. Irrespective of farm size, the factors which the farmers thought of most importance in determining their levels of fertilizer application were:- (Table 5.2.) a)The results obtained in the previous year. (Factor b). b)The price they expected to get for the crop. (Factor a). That the former should have been chosen is not unexpected from the results of the preliminary survey since it implies they rely mostly on their own experience and skill. The choice of the value or the price they expect to get for the crop as the second most important factor, especially -139-

the relatively high percentage selecting it independantly of the cost of the fertilizer, suggests that many farmers give a preference to those crops which give a high cash return per acre, e.g. cereals, sugar beet, potatoes, rather than to those on which no immediate value can be set, e.g. feed crops, grassland. This is of course the pattern which does occur with fertilizer application. The former are in the main well fertilized while, with the latter, practice is variable and often poor. Between 50 and 60% of farmers did in fact state that they gave a preference to those crops which gave the biggest cash return per acre. (Table 5.3. question 4). However itelt.‘s now felt that this question)as worded wasambiguous and open to misinterpretation. The results cannot therefore be taken into account.

5.3.5. Cost of fertilizer and farm income as factors of importance. The results of the survey indicated that, while not a major factor, the cost of the fertilizer did play some part in deciding the size of the dressing applied. (30_+0% selected factor b, table 5.2.) Yet shortage of money cannot be a real factor in limiting fertilizer use. Under 10% of farmers in the 100+ acre groups set a limit on their fertilizer expenditure. (Question 3, table 5.3.) If lack of capital -140- was of great importance one would expect the greater proportion of farmers to limit their fertilizer budgets. A slightly higher proportion of farmers in the smaller acreage groups limited the amount spent but even so it was not of great significance. Similarily the value of the subsidy is of some importance though its effect in altering fertilizer use is not as great as one might expect. The subsidy on nitrogen was increased fog the year 1959, yet of those farmers indicating that they were using more fertilizer this year only 40-50% of the 100+ acre groups and 30% of the 0-100 acre groups had indicated that the value of the subsidy was a factor influencing them on the size of fertilizer dressings used. (Table 5.4.). Approximately 30% of the farmers indicated that the size of the profit the3r made in the previous year affected their level of fertilizer application in the following year. (Table 5.2.). This indicates that, while not of major importance, it does play some part in determining the size of dressings used. It was shown in chapter 4 that, in the past, overall consumption of fertilizers was closely related to the ratio farm income to fertilizer price but that in recent years, 1956 onwards, it was no longer so dependant on this ratio.

5.3.6. Other factors affecting fertilizer use. The remaining factors can be classified as external and -141- consist of advice offered to farmers in one form or another. Two such factors are of major importance:- (Table 5.2.). a)Advice given by the N.A.A.S, (Factor g), b)Soil analyses (Factor 1). The general policy of the N.A.A.S, is as far as possible to offer advice on fertilizer application after carrying out a soil analysis, so that the two are largely related. It is of interest to note that the use of this advice is least among the very small farms, the larger farmers relying very much more on such help in planning their fertilizer use. i.e. About 400 of these farmers had nade'use of N.A.A.S. advice and 60% of soil analyses as compared to 30% and 30_50% respectively for the smaller farms. Advice from the fertilizer trade, either from merchants or manufacturers' representatives, is apparently not nearly of the same importance. This is probably due to the fact, this was mentioned in the preliminary survey, that whereas N.A.A.S. advice is impartial that of the trade is not. They are suspected of merely trying to push up fertilizer use in their own rather than the farmers' interests. The other factors, which depend on farmers reading about or seeing the results of fertilizer use, have, with one exception, only minor significance. They are:- (Table 5.2.). a) Seeing practical demonstrations of fertilizer use. -142-

(Factor j). e.g. N.A.A.S. trial plots, demonstration farms, agricultural experimental stations. b)Seeing other farmers results. (Factor k). c)Reading articles about fertilizer use. (Factor h). The smaller farmer takes some notice of (b), though not very much. As farm size increases greater importance is placed on (a) and in the case of very large farms it would appear to be a factor of major importance in influencing fertilizer use especially in view of the much larger, total acreage involved.

5.3.7. Additional factors. The farmers were invited to state any factors which they thought were of importance but which were not on the list in question 1. Approximately 25% did soy but no additional major factor emerged from this information. Mostly it was merely an amplification of their choice of factors in question 1 and especially emphasizing the importance of their own experience and skill as farmers.

5.3.8. Conclusions. It must be emphasized that the conclusions drawn apply properly only to the area surveyed. However since the results are in basic agreement with information given by the N.A.A.S. in other parts of the U.K. it is likely they have a somewhat wider application. From the results of the survey the following pattern emerged as to the farmers' attitude to fertilizer use and his choice of a given level of application. Nearly all farmers consider the use of at least some fertilizer indispensable to farming. It is only on very small farms that any signfficant non-use occurs and the total acreage involved is small. In arriving at a level of fertilizer application farmers apparently rely to the greatest extent on results from previous years. While this practice will take into account some estimate of the profitability of using fertilizers only a small proportion of farmers, about 30%, would appear to understand or take note of the importance of the economic concepts underlying their use.. This attitude will tend to restrict the growth of fertilizer consumption and prevent the best use of different nutrients being made with changing crop value to fertilizer cost relationships. Two examples of this can be cited which occur in the area surveyed. Phosphorus is an historically important nutrient being the first to be applied in any quantity. In recent years the movement of the response curve, crop value and fertilizer cost have produced a situation where only very small dressings of phosphorus can be economically justified for cereals, Farmers however still apply the older, larger rates using money which could be better spent on other nutrients. Secondly, in the past, nitrogen use on cereals had to be restricted to below the optimum rate since lodging of the crop would occur at such levels of application. iee. flattening of the crop due to the excessive growth of straw. New varieties have now been introduced which remove these limitations. The old, low nitrogen dressings are however still in general use even though many farmers have adopted these new varieties. In deciding on fertilizer dressings preference is given to use on cereals sugar beet and potatoes since these crops bring in a relatively large cash return in the short run)i.e. the economic advantage of using fertilizer is immediately apparent. Consequently these crops are generally dressed at near optimum rates. Fertilizer use on other crops, feed and grassland, is to a great extent restricted because there is no immediate cash value for the crop and hence farmers are not so aware of the return that fertilizers can give on this type of enterprise. Farmers, especially in the larger acreage groups, are susceptible to advice especially when it comes from impartial organisations such as the N.A.A.S. rather than from the fertilizer trade. Further seeing demonstrations of fertilizer -145- use is of importance to the larger farmers in making a decision on fertilizer application. In view of the large number of farmers who stated they made use of such advice it is probable that the N.A.A.S. has played a considerable part in increasing fertilizer use. If fertilizer consumption is to be increased, and it has been assumed that this would be of benefit, a greater attempt must be made to educate farmers in the economic concepts underlying its use. When recommended to use a certain level of application as 'best' farmers should be shown, either in the manufacturers' advertising or when they are given advice, how this level is derived, assuming of course that the recom- mendation does in fact have an economic basis. This would at least give a degree of confidence to the farmer that the advice is not merely trying to increase consumption for the manufacturers' benefit. Further they must be shown that the use of fertilizer on crops, where there is no direct, short run, financial return can also be a very profitable enterprise. The best way of doing this would certainly appear to be through an organisation such as N.A.A.S. whose advice would appear to be acceptable to farmers. APPENDIX CHAPTER 5

Critiscism of the methods employed and the accuracy of the results obtained from the survey.

Two major critiscisms can be made of the methods adopted in making the survey:- (a) The survey was carried out in only one area and it is therefore not known if the results are typical of the whole country. An obviously better procedure would have been to make several surveys taking in different types of farming and regions of the U.K. There were three reasons why this could not be done:- (i)Organisational difficulties. It was found extremely difficult to obtain the necessary co-operation from relevant organisations. Considerable trouble was experienced in starting just the one survey in Cambridgeshire. (ii)Time required. The time necessary to send out and then tabulate the results of such surveys is considerable and would have prevented any large scale work. (iii)Cost. The cost of the survey was high and no money was available to carry out any additional work beyond that done in Cambridgeshire. (b) No check was made on the accuracy of the answers obtained. The method which should have been employed to do -14 7_ this would be:- (i)Send a questionnaire to a large sample of farmers in various parts of the U.K. (ii)Check these answers by personal interviews with a sample of those replying to the postal questionnaire. (iii)Repeat this procedure with a different sample in the following year to see how the results agree. This method could not be adopted for the reasons given in (a) above. Therefore one can only accept the results and conclusions drawn as tentative. They do not however appear to contradict what is known of fertilizer practice or the opinions expressed by Advisory Officers of the N.A.A.S. who are in close contact with the views of farmers. Two particular errors might be introduced by farmers into answers given in the questionnaires:- (i)A desire to show knowledge which is not, in fact, acted on. (ii)Unwillingness to give certain replies since they, might feel this would detract from their skill as farmers. Little can be said about the replies to questions 2, 3 and 4 on these points. The answers could only be checked by personal interview or by a much more detailed questionnaire. However on question 1 it is possible to make some estimate of the accuracy of the replies. (i), above, would particularly apply to those farmers selecting factors a, b and c together to show they knew about the economic concepts of fertilizer use while in fact not acting on them. That this was not the case is shown in that so relatively few farmers did in fact select all three factors. (ii) is likely to apply to those factors which come under the heading of advice. Farmers might be unwilling to mark these as being important since they feel this would detract in some way from their own skill. Yet this was not the case since a high proportion did state that N.A.A.S. advice, soil analyses and fertilizer demonstrations had been of importance to them. That a higher percentage of larger, as compared to smaller, farms selected these, fits in with the fact that it is known that the former make much greater use of such advisory services. With regard to the effect of advertising, published articles on fertilizer use and other farmers results it is difficult to know how accurate the replies were without doing further work. It may well be that these are of greater importance than was revealed by the questionnaire. While the survey did not give any quantitative measure of the effect of the various factors it does give an idea of the relative importance of some of them. CHAPTER 6.

SOME ECONOMIC AND TECHNICAL ASPECTS OF THE FERTILIZER INDUSTRY WITH PARTICULAR REFERENCE TO APPLICATION AND DISTRIBUTION.

6.1. Properties required of fertilizers.

In previous chapters the nature and extent of the present and potential demand for fertilizers has been discussed. It is therefore appropriate to examine what properties are required of fertilizers for them to be acceptable to farmers.

6.1.1. Form of fertilizer. At the present time nearly all fertilizers are sold in the form of solids. This position is likely to continue in the future for the following reasons a)Most materials suitable for fertilizer use are solids under normal conditions and in some cases are only sparingly soluble in water. b)Considerable capital has been invested by, the farming industry in application machinery designed to handle solids. There would be considerable resistance to other forms of fertilizer which would entail purchase of new application equipment. c) Farmers are on the whole conservative in their attitude to innovations. They are used to solid fertilizers and benefits, economic and technical, would have to be considerable before they could be persuaded to change. The other form in which fertilizers could be used is as liquids or in solution. At the present time these find little use in the U.K., except horticulturally. The possibility of introducing their use is discussed in a subsequent chapter. For the remainder of this section the discussion of the require-. ments of fertilizers will be restricted to solid forms.

6.1.2. Mixed fertilizers. In the U.K. at the present time a large proportion of fertilizers is sold in the mixed form. i.e. all three primary nutrients are combined in one mixture. Some nitrogen is sold in the straight form for use as a supplementary dressing, once the crop has been established, (top dressing), and also some phosphorus in the form of basic slag on grassland. The big advantage of mixed fertilizers is that the farmer is able to apply all three nutrients in one operation without having to do his own mixing, thereby saving on application costs and his own time. Four this reason they are popular and a large proportion of future production will have to be in this form. The disadvantage of such mixtures is that many farmers will tend to apply them without paying attention to the plant nutrients they contain. It is probably for this reason that, whereas phosphorus is often applied ac above optimum rates for cereals, nitrogen applications are generally too small. Most mixed fertilizers have a P205:N ratio greater than one. An important factor, therefore, is that manufacturers should produce mixtures having appropriate nutrient ratios. One special requirement is for high N:P205 ratio fertilizers.

6.1.3, Ease of application. One of the most important properties required of a fertilizer, from an agricultural standpoint, is that it should be capable of being easily and accurately applied. For this purpose it has to consist of free flowing, uniform, discrete particles. To achieve these properties the industry has largely adopted the granulation process which produces the fertilizer in the form of small, uniform spherical granules. Any new material introduced on to the market would have to be amenable to granqlation or to some process which would produce comparable properties.

6.1.4. Storage quality. Fertilizers should be capable of being stored without caking or setting into a hard mass. . This is of equal importance to both the manufacturer and the farmer. The sale of fertilizer is to a large extent seasonal being concentrated in the January to April period, whereas production extends throughout the year. This necessitates the storage of fertilizers for a considerable length of time either in bulk or in package. It is essential that the product retains those physical properties which lead to ease of handling and application, The process of breaking up fertilizer is difficult, expensive and time consuming. Similarily the farmer requires a product that will retain condition even if stored under adverse conditions for a time on a farm. The method of obtaining this property in fertilizers is associated with the process of granulation,, In view of the importance of this unit operation in the fertilizer industry it is discussed in detail in section 6.2.

6.1.5. Type of nutrients. A further requirement of a fertilizer is that it should contain nutrients available to the plant in both the short and long run. Plant nutrients are required immediately after sowing to get the new plant quickly established. They should then also be available slowly over the entire growing season. Thus it is desirable to have part of the fertilizer in the form of water soluble compounds readily available to the plant, The remainder should if possible be in a less soluble form, or should first have to undergo a reaction in the soil, so that there is a time delay in its availability.

.6.2. Granulation in the fertilizer industry.

6.2.1. The process of granulation. The fertilizer industry has to a great extent adopted the process of granulation to obtain certain desirable physical properties in the finished product (see 6.1.3., 6.1.4.). The process is used to build up granules, (spherical particles of a given uniform size), from a mixture of smaller particles varying in size. Various methods of achieving this exist (1) but one which is widely used in the industry is the one whereby the moistened, raw materials are passed through an inclined rotating drum. The granules so obtained are subsequently, dried to the desired moisture content. A simplified flow sheet of a typical unit is shown in figure 6.1. The raw materials are mixed to give the desired ratio of N:P205:K20 and are fed to the granulator. This consists of a rotating drum through which the fertilizer passes being moistened with water from a suitably located spray. The granules so formed pass to a rotary drier. The required size fraction of the product is removed by screening, oversize and fines are recycled to the granulator. The process ideally FIGURE 6.1.

S I MPLIF IED FLOW SHEET OF FERTILIZER GRANULATION UNIT

RAW MATER IALS

KzO N Pa 06

VEIGHING

MIX ING WATER FOR I GRANULATION OVERSIZE

GRINDING CRUSHED M ILL OVERSIZE TO 1 GRANULATOR

N OFF GAS OVERSIZE c----swTO VENT

HOT GAS

FINES TO GRANULATOR

(OVERSIZE UNDERSIZE SCREEN SCREE N

PRODUCT TO 07AGG ING AND COOLING r1+ produces fertilizer in the form of small, spherical, hard granules which have those physical properties which result in:- a)The granules being easily and accurately applied to the soil. b)The granules being immune to caking. While granulation is widely used in the industry, the mechanisms involved in the formation of granules have not until recently been properly understood and the design and operation of such units has been largely on an empirical basis. It is proposed to discuss some of the work that has been done in this field and to show how this can be applied to the design and operation of granulation plants.

6.2.2. Mechanism of the formation of granules. Initially the mechanisms by which wetted spherical particles can adhere to each other will be considered. The forces of cohesion are due to surface tension effects and their magnitude depends on the size of particles, their arrangement, the quantity of liquid present and its surface tension. Three states of liquid content have been defined for an assembly of spherical particles (2) a) The pendular state, b) the funicular state, c) the capillary state. -155-

6.2.2.1. The pendular state (Figure 6.2.) In this state, with a low liquid content, the liquid collects at the point of contact of the particles and surface tension forces hold the particles together. For systems of spherical particles, regularly packed, the magnitude of the cohesive stress can be calculated (3) and is quite large down to even low liquid contents.

6.2.2.2. The capillary state (Figure 6.3.) In this state the pore spaces are completely filled with liquid and capillary forces are active in the connected pores of the granule. A measure of the forces due to capillary effects is given by the suction potential set up by the curvature of the liquid surfaces in the interstices of the surface layer of particles. The relation between the suction potential and liquid content is shown in figure 6,4. for a bed of uniform, glass spheres and water (4). As moisture is removed from the bed so the water recedes into the surface interstices setting up curvature of the liquid surfaces, with a corresponding increase in the suction potential. At the point A, the pores open up and air is admitted. Thereafter the suction remains almost constant till the pendular state is &pproached. The maximum suction potential at the point A is known as the entry suction potential and gives a measure of the forces holding together a granule in the capillary state. FIGURE 6.2.

PENDULAR STATE

FIGURE 6.3.

CAPILLARY STATE

FIGURE 6.5 .

FUNICULAR STATE SUCTION POTENTIAL MOISTURE RELATION FOR GLASS SPHERES

AFTER HA INES (4)

100 4 1. 1119 1: 80 3

*9 V

ON 6 ATI UR 40 AT S NT

CE 20

PER MO

0 2 4 6 8 10 12 SUCTION POTENTIAL x-r4 -156-

Similar measurements can be made for beds of irregularly shaped particles (49 59 6). The entry suction of such systems can be calculated from the equation:- Pe = xl-e T/r

where Pe = entry suction dynes/cm2 r = mean radius of particless cm. T = surface tension. dyne/cm E = porosity of particles x = dimensionless factor depending on type of packing. In general the cohesive forces in the capillary state are some 3 - + times those in the pendular state.

6.2.2.3. The funicular state (Figure 6.5.) In this state there is insufficient liquid to completely saturate all the pores in the granules. The cohesive forces are intermediate between those of the capillary and pendular states decreasing with decreasing saturation of the granule.

6.2.2.4. Variation in granule strength with liquid content. Assuming the validity of these mechanisms for granule formations one is able to predict the variation in granule strength with liquid content, If, initially, the granule is fally saturated and liquid is progressively removed one would expect the strength to increase to a maximum9 at the point where the entry suction potential is generated i.e. at -157- limiting case of capillary state. Subsequently as more liquid is removed so the funicular state is attained and a progressive lowering of strength is to be expected as the cohesive forces are reduced with decreasing saturation of the granule. Newitt and Conway-Jones (2) have measured the variation in strength of granules of sand bound with water. Their results for fine sand are shown in figure 6.6. and confirm the predicted shape of the curve. Further they show that, within experimental error, the measured strengths are the same as those calculated from suction ,potential measurements.

6.2.2.5. Rate of granule growth. When granules are in the capillary state, with excess surface moisture, two such granules coming together can coalesce to form a larger one (see figure 6.7.(a)). In the pendular state this cannot occur and, in this case, growth can only take place by individual, wetted particles adhering to the surface of the granule. (see figure 6.7.(b)). With such a mechanism one would expect the rate of granule growth to increase with increasing saturation, being slow for low liquid contents but increasing rapidly with the onset of the capillary state. Newitt and Conway-Jones (2) have measured this rate of growth for a sand-water system. The results, (see figure 6,8.), confirm this type of mechanism. -..., L.) 2 0 80 a G TRENG FACTOR cn .

RANULE S TH

VARIATION OFGRANULESTRENGTHWITHMOISTURECONTENT 90 70 50 6 10 0 10 2030 4050 6070 I i i

POROSITY 0.416 FINE SAND MOISTURE CONTENT %VOLUME (AFTER NEWITT&CONWAYJONES2) % I i F IGURE 6.7.

EFFECT OF MOISTURE ON GRANULE GROWTH

(AFTER NEW ITT G CONWAY JONES 2)

A EXCESS SURFACE MOISTURE FORMS FIG. 6.7.4 PERMANENT BOND

B SURFACE DRY GRANULES UNABLE TO

MAKE BOND

C SURFACE DRY GRANULE MAKES PENDULAR

BOND WITH INDIVIDUAL MOIST PARTICLE

F 1G 6,7.E VARIATION OF RATE OF GRANULE GROWTH WITH MOISTURE CONTENT

AFTER N EW 1 T T & CONWAY—JONES (2)

FINE SAND MOISTURE REQUIRED 0.3 TO SATURATE ag 67 % CALCULATED NULE 0.1 GRA OF

La 1 I I i— 0 1 cC 50 60 70 80 MOISTURE CONTENT PERCENT BY VOLUME -158-

The onset of rapid growth of granules occurs at about the moisture content that would be required to saturate them.

6.2.3. Relation of theoretical mechanisms to formation of fertilizer granules. In the operation of fertilizer granulators the criterion of the efficiency of the unit is that a maximum of the granules produced should lie within a given size range. By attaining a high efficiency, the quantity of recycled material, i.e. fines and oversize, is reduced enabling a high throughput to be maintained and also reducing the drying load in the drier. Fertilizer granules are formed by the addition of water and the mechanisms by which they are made will be similar to those described for the theoretical system of spherical particles. The wet granules are then passed to the drier where the moisture is almost entirely evaporated. The granules however maintain and increase their strength due to the presence of soluble salts which are deposited as drying proceeds forming salt bridges between the particles and binding them together. The effects produced in the drier are discussed in a subsequent section. For the present only the formation of wet granules and the means by which maximum efficiency can be attained will be discussed. For a system of particles placed in a granulator the mean size of the granules will increase with the length of time -159- to which they are subjected to granulation. However as the granules rotate in the drum some of them will disintegrate as they impact against each other and the walls of the drum, giving a range of granule sizes. For maximum efficiency the narrowest possible size range is required. One would expect this to occur when the granule strength is at a maximum, since they will then be most resistant to disintegration. Theoretically this occurs when the full entry suction potential is generated and this is confirmed in practice. (see 6.2.3.4.) Newitt and Conway-Jones (2) have investigated the variation in granule size, with length of granulation and moisture content, for sand water systems and the results confirm that the narrowest size ranges occur at approximately the point of maximum strength of the granules. A similar result has been obtained by Hardesty (7) in granulating fertilizers. The results of varying moisture content on granulation efficiency, for two such mixtures, is shown in figure 6.9. (The granulation efficiency was taken as the percentage of granules lying in the size range 6-20 mesh on Tyler screens). The curves clearly show that -blre is an optimum water content for granulation and that thl.s is extremely critical. Once the optimum is exceeded efficiency decreases rapidly. ConfOrmation of this is found in full size plants where only small variations in water flow to the FIGURE 6.9.

VARIATION IN GRANULATION EFFICIENCY WITH MOISTURE

CONTENT FOR TWO FERTILIZERS

(AFTER HARDES TY 7)

T 100

80 RODUC

P o-

z W SH t.) 6 • cc ku a 0 ME

2 4 . 1- x (..7 W2O OF 670 TEMPERA TURE 190-200° F IELD Y 0 2 4 6 8 10 12 14 16 18 20 MOISTURE CONTENT PERCENT MOISTURE-FREE BASIS)

NO. SOURCE OF NITROGEN ANALYSIS N Pa Os 40 I N H3 & NH4.NOls I2 24 I2. 2 N H G (NH4)2.504. 10 20 I2

FIGURE 6.10. EFFECT OF AMMONIUM NITRATE CONTENT ON MOISTURE REQUIRED

FOR OP TIM GRANULATION OF FERTILIZERS.

AFTER HARDESTY 7) et 0 kA. 12

I- z ION tIi.i ce LAT

REMENT u.g a.

I- REQUI GRANU

u_ E RE M

U 3 IST TIMU OP MO 0 2 4 6 a . 10 12 14 UNITS OF AMMONIUM NITRATE AS NITROGEN IN FERTILIZER

NO. RATIO TYPE OF SUPERPHOSPHATE N Pt s KtO I I I 1 ORDINARY 2 I I I CONCENTRATE D

3 1 2 I CONCENTRATED a TEMPERATURE 190-200 F THE EFFECT OF SALTS ON MOISTURE REQUIREMENT FOR OPTIMUM GRANULATION

OF CONCENTRATED AND ORDINARY SUPERPHOSPHATE SALT MIXTURES

(AFTER HARDESTY 7)

20 C ONC. SUPERPHOSPHATE — — -- ORD • SUPERPHOSPHATE e TEMP. 190-200 F 0 I6

.... K CI %... 1:1 ..., , w u.• b---, ...... - cc I2 -...... U. "" •=-, "1...... (NH4VO4 ••••• WI., 0 •••• •••• WI= 0 ftim ...... U.. Ir- - ...... "—.."'" •--KC1 ...... 1.1. I— S cr, 13.."'—(N H4 SO* L

I— ... Z U.1

0 I0 20 30 40 50 60 70

PERCENT SALT IN DRY MIXTURE -160-

granulator produce large changes in its efficiency (8).

6.2.1+. Effect of soluble fertilizer salts on granulation. Fertilizer mixtures contain soluble salts so that in fact the liquid phase in granulation is not water but a solution of the salt. This has some important effects on the process which it is appropriate to consider. Hardesty (7) has found that to increase the proportion of a soluble salt in a fertilizer mixture decreased the quantity of water required for optimum granulation. The main results are reproduced in figures 6.9, 6.10 and 6.11. They can be summarized as follows:- a)By substituting ammonium nitrate for ammonium sulphate in a fertilizer the quantity of water for optimum granulation is greatly reduced (fig. 6.9) b)Increasing the proportion of ammonium nitrate steadily decreases the moisture requirement for optimum granulation (fig. 6.10). c)A similar effect is observed with other soluble salts (fig. 6.11.) It is possible to explain these results largely in terms of the mechanism of granule formation already described and the effects of having a solution present in the liquid phase. These effects are:- a) Change in the surface tension of the liquid phase. -161-

b) Change in the volume of the liquid phase.

6.2.4.1. Effect'of surface tension changes. At the point of optimum granulation one can assume that the granules are in the capillary state with the entry suction potential being generated. A measure of the cohesive forces is given by Pe = x17- -6 T/r (see (:).2.2.2.)

The effect of having a soluble salt present in the liquid phase is that the surface tension is altered and this will change the strength of the granule. The addition of ammonium sulphate or nitrate to water increases the surface tension (Table 6.1). Therefore a greater granule strength is obtained when these salts are present and granulation efficiency is improved. Table 6.1. Surface tension of solutions of ammonium sulphate and ammonium nitrate. Temperature 20°C Concentration of solution grams Surface tension dyne/cm per 100 g.H20 N (NH4)2504 NH4NO3 (NH4)2504 NH4 NO3 0 0 0 72.8 72.8 5 23.6 14.3 74.7 74.5 10 42.2 28.6 80.6 76.1 15 70.6 42.8 84.4 77.5 20 96.3 57.0 88.1 78.0 30 S. 85.6 s. 80.8 40 s. 114.0 S. 82.3 s. = saturated. Source. Int. Crit. Tables. -162-

6.2.4.2. Effect of volume changes in liquid phase. Table 6.2. gives the volumes of solutions containing various amounts of ammonium nitrate and ammonium sulphate.

Table 6.2. Volumes of solutions of ammonium nitrate in water. Concentration Volume of 100 g. water plus dissolved solute, ml. g.NH003/100gH20 25°C '80°C 10 106 109 50 131 135 100 163 168 150 196 202 200 224 229 216 239 300 3o4x 400 373x 5oo 44.3x 580 4.98xs x extrapolated values s saturated solution. -163-

Volume of solutions of ammonium sulphate in water. Concentration Volume of 100 g. water plus g.(NH4)2504/100g.H20 dissolved solute. ml. 20°C 80°C 10 105 108 20 109 112 40 120 123 60 132 135

75.4 141(S) .11•111 8o 147 95.3 156(S) (S) saturated solution Sources Int. Crit, Tables.

The addition of these fertilizer salts to water brings about large increases in the solution volumes and these are large enough to account for the reduction in moisture required for optimum granulation that has been noted by Hardesty (7). The higher solubility of ammonium nitrate giving correspondingly larger solution volumes compared to ammonium sulphate and potassium chloride explains why this effect is greater with the former salt. . The importance of the phenomenon is that in increasing the salt content the moioture requirement for granulation is reduced and this in turn reduces the drying load on the granulator. It has however been reported that with high salt contents granulation is difficult and efficiency is low (8). This can be explained by the fact that as the salt dissolves in the water so the porosity of the granules is increased and their strength is reduced. with a high soluble salt content this increase in porosity will be large and the granule structure readily break down leading to a low efficiency or even making granulation impossible. It is suggested that this could be overcome by using a saturated solution of the salt, instead of water, to bring about granulation of fertilizer mixtures. Such a procedure would not only bring about the reduction in the amount of water required, due to the expansion of the solution volume, but, in addition, the granule structure would be maintained since no further salt could dissolve. This would also enable one to granulate fertilizer mixtures containing very high proportions of soluble salts.

6.2.5. Design of granulation equipment. The criterion of efficiency of a granulator is that a maximum percentage of granules should fall within a given size range. One can apply certain of fhe aspects of granulation, already discussed, to arrive at a design method for a granulator to obtain the optimum efficiency. It can be assumed that the following are known:- a) Composition of the feed material. This will be -165 determined by the ratio and content of plant nutrients required. b)The size distribution of the particles in the feed material. It is desirable to obtain a distribution that will give a low porosity since this will increase the granule strength and hence the efficiency. c)The feed rate of material to the granulator. d)The diameter of the granulator. This will be largely determined by the throughput that is required. e)The speed of rotation of the granulator. The drum speed should be regulated such that the bed of material exhibits a rolling motion. Brook (8) suggests that, for fertilizer materials, 50% of the critical speed, (the speed at which material is completely carried round the drum), gives the best action. Newitt and Conway-Jones (2) suggest that a somewhat lower speed is better. (40% of the critical speed). f)The loading of material in the drum. This will be determined by the rolling characteristics of the fertilizer. Newitt and Conway-Jones (2) have found that a value of 6%2 based on cross-sectional area, was the maximum practical for sand. Brook (8) has stated that loadings of up to 10% can be used with fertilizers. g)The size range of granules required. The size of granules made in fertilizer practice varies but they are -166-

generally between 1 - mm. Given the above, the efficiency and length of the granulator will depend on two factors:- a)The quantity of moisture added. b)The hold-up time of the material in the granulator. Theoretically a) can be determined from porosity measurements. The volume of liquid needed for optimum efficiency will be that required to saturate the pore spaces. i.e. to obtain the limiting case of the capillary state. If a saturated salt solution is used in granulation, this should give a fairly accurate measurement of the liquid required. In those cases where water is used this method will be less accurate since the porosity of the particles will alter as the fertilizer salts dissolve and the resultant solution volume will be increased. Factor b) can only be determined by experimental measurement. It could be determined on a small batch unit, with the speed and loading scaled according to the full sized granulator. A sample of the feed material, with the appropriate moisture content determined from porosity measurements, is placed in the experimental unit and the efficiency is determined for various times of granulation. (The efficiency = weight of granules in desired size range / the weight of -167-

the sample). By plotting the efficiency against the number of revolutions of the drum, the time of granulation required for optimum efficiency can be determined. (In the case where the liquid requirement is not accurately known from porosity measurements, the above method could be modified by repeating it for various moisturA contents of the material° In this way both the granulation time and moisture requirement for optimum granulation would be determined) From these measurements the length of granulator required can be calculated. Let M = throughput of material tons/hr = bulk density of material ton/ft3 dF = diameter of full-size granulator ft.

de = diameter of experimental granulator ft. x = loading of drum based on cross-sectional area. n = speed of rotation of granulating drum revs/hr. N = number of revolutions required to obtain optimum efficiency in experimental unit M = volume of liquid required per unit of feed for optimum granulation.

2 Cross-sectional area of drum = Tr d F/4 ft2 Volume of material ft3/hr. Velocity of material through granulator = 4M (This velocity is obtained by correct inclination of the granulator). In the experimental granulator the distance moved by the rolling particles o. Nde = K1 Nde In the full size granulator the distance 0( ndF = K2ndF

(K1, K2 are constants depending on the speed and loading of the drum. If these have been correctly scaled for the full- size and experimental granulators, K1 = K2). Hold-up time required in granulator = Nde/ndF hr. Length of granulator required, L, is given by L = 4M 2 Nde ft for moisture content x cr dF rdF M. For any changes in the raw material composition or particle sizes the moisture content and hold-up time required for optimum granulation have to be redetermined and the appropriate corrections made. It has been reported that, in practice, there is often a large increase in granule growth in the drier (8). This suggests that the quantity of water being used is too great, i.e. more water is present than that required for the capillary state to be attained, and the first stage of the drying process is continued granulation. The necessity of using such an excc,ss of moisture indicates that the length of the granulator used is too short for optimum conditions to•be obtained. i.e. Larger quantities of water are required to give a high rate -169-

of growth to compensate for the short residence time of material in the granulator. The granules should in fact contain just sufficient moisture for the capillary state to occur and no further growth should take place in the drier.

6.2.6. Drying of fertilizer granules. The drying of fertilizer granules modifies their physical properties in two important respects. a)The strength of the granules is increased. b)The extent to which the granules are dried improves their storage properties.

6.2.6.1. Increase in granule strength on drying. Figure 6.12 shows the effect on the strength of making granules of sand, bound with solutions of ammonium sulphate of varying concentration, followed by drying. For solutions of low concentration the strength/moisture curves closely follow that of pure water until they become saturated and salt begins to be deposited. The strength then increases rapidly and becomes many times the original wet strength as total dryness is approached. With a saturated solution the strength of the granules increases immediately as drying is commenced and the final dry strength is some 50 times the original wet strength. This increase is due to the deposition of ammonium sulphate crystals which bind the individual sand STRENGTH OFGRANULESFINESAND BOUND WITHAMMONIUMSULPHATESOLUTION

STRENGTH 0 20 FIGURE SATURAT ION 40 (AFTER NEWITT&CONWAYJONES2)

2 307,SOLN 3 12%SOLN 5 PUREWATER 4 5%SOLN 175% SOLN(SAID) 6.12. 60 c l 0 SO 100 FIGURE 6.13.

SALT DISTR I BUT ION IN GRANULES

DRIED AT 118° C

(AFTER PAPADOPOULO S 12)

3•

a 0 20 40 60 80 100

PERCENT DISTANCE FROM THE SURFACE -170- particles together. One would expect a similar phenomenon to occur during the drying of fertilizer granules and this is confirmed in practice. Visual observation of dried fertilizer granules (7,10,11) shows that they are composed of an outer shell of a soluble salt with the core containing the more insoluble materials. A similar effect has been observed by Papadopoulos (12) who formed granules of sand, bound with sodium chloride solution, and which were subsequently dried. The salt distribution through the granule is shown in figure 6.13. The bulk of the salt is concentrated in the outer layer. This surface concentration of salts has been explained in terms of the capillary theory of drying (12). The bulk of the drying occurs at the surface of the granule. In the initial stages excess surface moisture is removed. In the second stage liquid, with salts in solution, arrives at the surface from the core of the granule due to capillary action, where it is evaporated and the salts deposited as a surface layer. The strength of such granules, with a hard, outer shell, will be the hoop strength of the shell, with the core con- tributing a lesser amount, depending on the quantity of salt in it. A greater strength can be obtained by having the, soluble salts distributed more uniformly through the whole -171- granule. This is shown in table 6.3.

Table 6.3. Variation of sand granule strength with salt content in the core (13). Average salt content 2.5 g./100 g. sand Experiment A Strength of wet granulos, ozs/sq.in. 13 3 2.5 Strength of dry granules, ozs/sq.in. 7 64 86

Percent salt in core 12 )i)t 56

The case of fertilizer granules is somewhat different since there are usually sufficient soluble salts present in the mixture to saturate the moisture present, so that one would expect to find a greater proportion of salts in the core than is the case where granules of sand are prepared with dilute solutions. The strengths of fertilizer granules, and their density, would be considerably increased if granulation were carried out using saturated salt solutions instead of water. While migration of the salts to the surface would still occur, a much greater proportion would remain in the core since the solid salts would not be dissolved as is the case with pure water.

6.2.6.2. Caking of fertilizers. The layer of soluble salts formed on the fertilizer granules leads to their caking when stored under certain conditions. -172-

The mechanism by which this occurs would appear to be as follows:- Under suitably humid conditions a film of moisture is deposited on the salt crystals at the surface of the granule, ions of the salt then move along this film to the tip of the crystal leading to its outward growth. Where two granules are in contact the crystals can join together forming a bridge and bonding them togetherG When sufficient bonds have been formed a hard, caked mass of fertilizer is produced. Silverberg (11) has investigated the nature of these bonds for a number of fertilizers formed from different materials. For an ammonium nitrate, superphosphate and potassium chloride mixture the bridge is formed by the simultaneous growth of potassium nitrate and ammonium chloride crystals, For fertilizers where the nitrogen is supplied by ammonium sulphate, the bond is formed by ammonium chloridel and with urea by an ammonium chloride-urea crystal. This caking is undesirable since it reduces the free flowing properties of the granules which lead to ease of application and handling. Further the breaking up of caked fertilizer is both costly and time consuming and may involve complete regranulation of the fertilizer. Several methods of reducing caking have been suggested. One such method has been the coating of the surface of the granules with such materials as magnesium oxide, talc, Fuller's -173-

earth, kaolin, bone-meal, etc. None of these additives are successful in eliminating caking, though in some cases they may alleviate it to some extent. The method that appears to be almost completely successful is to dry the fertilizer granules to a very low moisture content, generally under 1%. A salt will pick up moisture when the water vapour pressure in the surrounding air is greater than the equilibrium vapour pressure of a saturated solution of the salt. Raistrick (10) has confirmed that the caking propensity of fertilizers could be related to the water vapour pressure over the granules. The latter will vary with the composition of the fertilizer and its moisture content. He further determined that the safe limit of vapour pressure, below which deposition of moisture cannot occur, was about 30%, expressed as relative humidity at 20°C, for most common fertilizers. For mixtures containing 30-50% of superphosphate this corresponds to a moisture content of 1%. Provided drying is taken to below this limit caking is eliminated. The work of Silverberg (11) clearly shows that, when moisture is reduced to such a low level, the outward growth of salt crystals on the granules is almost entirely eliminated and hence caking cannot occur. The method of drying to low moisture contents to prevent caking has been widely adopted in the fertilizer industry and -174-

would largely appear to have solved this problem. Care still has to be taken that the fertilizers are not stored under such conditions as they can pick up moisture. The use of multiwall paper sacks with a waterproof lining is apparently satisfactory in preventing this.

6.3. Distribution of fertilizers.

The distribution and selling of fertilizers raised certain problems to the industry. a)Distribution of fertilizers is to a great extent seasonal. b)Fertilizers are sold by a relatively small number of manufacturers to a very large number of consumers who purchase only small quantities at one time.

6.3.1. Seasonal distribution of fertilizers. On graph 6.14 is plotted the variation in the sales of .mixed fertilizer through the year 1957-58. From this graph it is apparent that the major sales occur in the January- April period corresponding to the time when fertilizers are most used. (Some 60% of total is sold between these months). The seasonal nature of the sales brings about a considerable problem to the industry. Obviously to minimise costs it is desirable to operate a fertilizer plant continuously throughout SALES OF MIXED FERTILIZERS 1957/58 MONTHLY TOTALS U, 0 1-500 -J 1- 0 et 400

0 300 to tn cc 200 _71

CC u. 100 0 X 0 JULY AUG. SEPT. OCT. NOV. DEC. JAN. FEB. MAR. APR. MAY JUNE MONTH -175- the year at maximum capacity. However in doing this the manufacturer is obliged to store a considerable amount of his output for part of the year. It is probably true to say that it is better for the manufacturer to store the fertilizer rather than the farmer, for a) Storage conditions are likely to be better than on the farm, thereby maintaining the quality of the product. b) The economies of large scale storage are likely to make it cheaper to store in bulk rather than for farmers to make individual provision on the farms. This is discussed more fully in 6.3.3. Seasonal selling however raises the further problem that a great strain is placed on distribution and transport facilities during January to April. This can lead to a position where a farmer who has delayed purchasing is forced either to delay sowing or to go ahead without using fertilizer. For this reason a system of rebates are generally offered to encourage farmers to purchase in the off-peak period so as to relieve this strain on distribution facilities. The scale of rebates offered are shown in table 6.4.1. below. They are for mixed fertilizers and the values are general throughout the industry. Table 6.4.1. Value of rebates off list price offered to farmers purchasing fertilizer during various months 1958. July Aug. Sept. Oct. Nov. Dec. Jan. Value of rebate £ per ton fertilizer 1.5oo 1.50o 1.375 1.25o 1.125 0.625 0.500

In table 6.5, are given the savings ua cost to the farmer taking advantage of the scheme. The cost of a typical mixed fertilizer is taken as £20 per ton, after deducting the subsidy. Interest on the capital required to purchase the fertilizer is taken as 5% up to March when it is assumed the fertilizer is applied. The gross saving equals the rebate minus interest on the cost of the fertilizer.

Table 6.5. Gross saving to farmers from rebate scheme. £ per ton. Month Value of rebate Interest to March Gross saving July 1.500 0.750 0.750 August 1.500 0.646 0.854 September 1.375 0.583 0.792 October 1.250 0.500 0,750 November 1.125 0.416 0.709 December 0.625 0..334 0.291 January 0.500 0.250 0.250 -17V-

It is apparent that the rebate scheme represents a real saving to the farmer even if the capital to purchase the fertilizers has to be borrowed and interest paid. However the majority of farmers still prefer to buy fertilizer near to the time when they use it. The reasons for this would appear to be as follows (1)+). a)Farmers are reluctant to borrow money or obtain long term credit. b) A lack of suitable storage space for fertilizers. c)Farmers feel that the saving from the rebate is insufficient to compensate them for the trouble of storing fertilizers i.e. Their personal estimate of the cost of storage and the 'inconvenience cost' to them. d)Doubts on the keeping quality of fertilizers.

6.3.2. Distribution costs of fertilizers. Fertilizers are sold by a small number of manufacturers to a large number of consumers taking only small quantities and for this purpose they have to be packaged in small amounts. The current and apparently satisfactory method is to use 1 cwt. multiwall paper sacks. These have the advantage of being easily handled manually on the farm and also enable the fertilizer to be stored satisfactorily without construction of any special storage facilities. -.178-

The costs of distribution are as follows:- a)Cost of paper bags. b)Cost of handling and filling bags. c)Cost of loading bags onto transport. d)Cost of transport. Items a, b, c, are fixed per ton of fertilizer while d is variable with the distance transported. The introduction of bulk transport would eliminate a and b. However very few farms have provision for handling supplies in bulk and further it will be shown in 6.3.3, that it would be uneconomic for them to provide facilities except for relatively large quantities. One means by which these costs could be reduced would be to increase the concentration of the fertilizers in terms of plant nutrient content. Most fertilizers currently used contain between 10 and 40% of plant nutrients in terms of N,P205 and K20. By effecting increases in concentration significant savings could be made. Some idea of their magnitude is given below in table 6,6. Table 6.6, Costs of distribution (15) 1958 Shillings per ton fertilizer Bags (20 x 1 cwt.) 25.75 Handling and filling bags 7.00 Loading bags 3.33 GRAPH 6.15.

DISTR I BUT ION COSTS AS FUNCTION OF FERTILIZER CONCENTRATION d

900 a 50 MILES TRANSPORT b 100 M ILE S TRANSPORT c 150 MILES TRANSPORT

8 d 200 MILE S TRANSPORT

W700 1.• cC z 600 1-

-J a. 500 0

;300-

111 In 1'200 •

• L I I I I 10 20 30 40 50 60 70

CONCENTRATION PLANT NUTRIENTS IN FERTILIZER -179-

Transport by road. (This is common practice). The costs will depend on the location and time. A typical scale is as follows (16). Distance, miles 50 100 150 200 Cost /- per ton. 30 -f-0 50 60

From this data the distribution costs per unit of plant nutrient have calculated as a function of concentration using distance as a parameter. The results are plotted on graph 6.15. It is apparent that the economies that can be effected are considerable. Thus, for example, increasing the concentration from 20 to 40% of plant nutrients leads to a saving of 165/- per ton of plant nutrient at 50 miles of transport, and 240/- at 200 miles of transport, on the distribution costs. It will therefore be advantageous to the industry to select those materials, other factors being equal, which have the highest plant nutrient content.

6.3.3. Bulk distribution of fertilizers. One means by which distribution costs could be reduced would be to sell fertilizers in bulk to eliminate the costs of packing. This would however mean the installation of suitable storage facilities on the farm in which fertilizer could be kept without losing quality. i.e. some form of sealed container would be necessary. It is shown below that -180-

this would be uneconomic except for relatively large amounts of fertilizer. It is assumed that the fertilizer is stored in closed cylindrical steel tanks or silos which are vertically mounted. The cost of storage per annum per ton is calculated in table 6.7 and is plotted as a function of capacity on graph 6.16 The saving which would result from handling in bulk would be:- £ per ton Cost of bags 1.29 Cost of handling and filling 0.35 Cost of loading bags O.ly Total 1.81 Less cost of floading in bulk 0.11 1.68 Transport costs are assumed the same in bulk or bags. This is theoretical saving made, the actual allowance given to farmers collecting in bulk is £1.185 per ton (15). Reference to graph 6.16 shows that this only makes bulk storage economic for amounts greater than 100 tons. If the theoretical saving were obtained then the economic quantity would be 50 tons. Even so this represents a quantity of fertilizer greater than the average amount taken. A further factor is COST OF STORING FERTILIZER IN BULK ON FARMS

THEORETICAL SAVING FROM BULK STORAGE \

ACTUAL SAV ING FROM AGE BULK STORAGE OR ST

I 1 1 1 11111 I I III 1_1111 I i kil l, id I I 5 10 50 100 500 1000 TONS FERTILIZE7 --- TABLE 6.7. Cost of storing fertilizers in bulk as function of capacity.

FT3 100 1000 5000 10,000 50,000 100,000 Capacity (a) TONS 2.01 20.1 100.5 201.0 1005.0 2010.0 Capital cost •(e) (17) 220 360 870 1300 3500 5400 Depreciation £ p.a. (b) 14.7 24.0 58.0 86.6 233.0 360.0 Interest £ p.a. (c) 11.0 18.0 43.5 65.0 175.0 270.0 Maintginence £ p.a. (d) 5.5 9.0 21.8 32.5 87.5 135.0 Total costs £ p.a. 31.2 51.0 123.3 184.1 495.5 765.0

Cost of storage 15.5 2.54 1.23 0.916 0.494 0.381 £ p.a. per ton. Notes:- (a)Average bulk density of fertilizers 45 lb/ft3. (b)Assumed life of silo = 15 years. (c)5f, interest charges on capital cost. (d)2.5j maintainence charges on capital cost. (e)Fabricated and erected. -181- that farmers generally take various kinds of fertilizer for different requirements. Each of these would require separate facilities with a correspondingly high cost of storage. Therefore for all except large farms, using relatively large amounts of fertilizer, bulk storage would be uneconomic and the present method of distributing fertilizers in packaged form the most practical.

6.4. Application of fertilizers.

6.4.1. Fertilizer application equipment. It has been shown in the previous section that significant savings could be effected by increasing the concentration of plant nutrients in fertilizers. If such an increase is made then parallel provision must be made for machinery which is capable of applying accurately, both in location and quantity, extremely small amounts of fertilizer. For example 10 cwt/acre of fertilizer applied in rows 6" apart means a delivery rate of only 0.2 ozs per ft. As concentration increases so the quantity of fertilizer used per acre will decrease. Cooke (18) has reviewed the various types of fertilizer application machinery available and made tests to check their accuracy. His results showed that many machines often gave -182- wide fluctuations in the delivery rates and that the latter often bore little relation to the indicated settings of the machine. This was due both to inherent faults in the design of the equipment and to the physical properties of the fertilizer itself. A discussion of such machines is beyond the scope of this work. It is9 howevel9 to be emphasized that increasingly accurate application machinery will be required if the benefits of using more concentrated fertilizers are to be realised. Another aspect of application is that fertilizers need to be accurately placed, in relation to the seed, to obtain maximum efficiency of use. Several workers have shown (199 209 21) that greater yields can be obtained from placement of fertilizers rather than broadcasting the material over the soil. With increased concentration of fertilizers the necessity for accurate placement will become correspondingly greater.

6.4.2. Contract application of fertilizers. As the need for more accurate application machinery grows so the farmer will be required to invest more capital on equipment that is only in use for a short time of the year. It gould therefore seem desirable if the services of outside specialist contractors could be used to undertake fertilizer application. Such a method would be advantageous in that the -183- capital expenditure on equipment would be reduced and the advantages available from bulk delivery could be realised. However the importance of the time factor would prevent large scale adoption of such a service. The peak demand would all be concentrated during the few days during which saving takes place as weather conditions permit. However there are three cases where the advantages of contracting might be realised. a)The small farmer. The smaller farmer is often short of capital and therefore unable to purchase application machinery, thus making a contracting. service especially attractive to him. Such a service could be undertaken by those contractors who spray crops since the sowing period (March), is an off-season for them. b)Top dressing of crops. In this case the time factor is not so important and the use of a contracting service feasible. c)Fertilizer application on grassland. Here again the time factor is not of major importance. Further the use of different types of machinery, from that for other crops, would enhance the desirability of using a contracting service. In view of the importance of using more fertilizer on grassland it would probably be of great benefit to develop such a service. Basic slag and lime are already distributed in this way and -184., there would appear to be little difficulty in extending this practice to other fertilizers. -185- CHAPTER 7

FERTILIZER MANUFACTURING PROCESSES AND THE FUTURE DEVELOPMENT OF THE FERTILIZER INDUSTRY

7.1 Nitrogen Fertilizers.

It has been shown in previous chapters that one of the most important requirements in the use of fertilizers is that the amount of nitrogen consumed should be greatly increased. With the crop value: fertilizer price ratio as at present, nitrogen use could be profitably increased by 100% over present levels. Should this potential demand be realised, even in part, then a very large increase in manufacturing capacity would have to be effected. Nitrogen fertilizers will be required in two forms a) for use straight in the top dressing of crops b) for use in mixed fertilizers. In the case of the latter a highly concentrated nitrogen material is required so as to obtain a high N: P205 ratio. One of the factors at present restrict- ing nitrogen use is that the percentage of the nutrient in mixed fertilizers is generally low. It is also desirable that part of the nitrogen is readily available to crops, i.e. nitrate form, and that some is present in less available forms, i.e. ammoniacal or amide, so that it is available over the -186-

whole growing season. Finally the more concentrated the material, the greater will be the savings in handling, transport and packaging costs. In the following sections those processes currently used in the U.K. for the manufacture of nitrogen fertilizers will be briefly described and certain associated problems discussed. Then possible alternative processes will be described and discussed with reference to the above factors.

7.1.1. Ammonium sulphate. Aftmonium sulphate is the primary source of fertilizer nitrogen in the U.K.,supplying annually some 60-65% of the total consumption. It also supplies the major part of , nitrogen used in mixed fertilizers and in addition, some is used in the straight form for top dressing crops. At the present time, two methods of manufacturing ammonium sulphate are employed in the U.K., a) The by-product pncess,b)The synthetic process.

7.1.1.1. The by-product process. The by-product process is operated in conjunction with plants for the carbonisation of coal in the production of gas or metallurgical coke. In the carbonisation of coal one of the by-products of the process is an aqueous liquor which contains between -187- 1 and 3% by weight of ammonia, depending on the type of process and the coal used in carbonisation. The ammonia is recovered as follows, a full description of the process is given by Key (1). The ammonia, which is present in the liquor in both the free and fixed forms, is recovered by stripping with steam in a column, the fixed ammonia being liberated by the addition of lime or sodium carbonate. The resultant mixture of steam and ammonia is passed to a saturator containing sulphuric acid in which the ammonia is absorbed, crystals of ammonium sulphate separating out. These crystals are then washed, centrifuged and dried to give the finished product. The production of ammonia liquor in the U.K. has been estimated at about 1.5 x 109 gallons, equivalent to about 400,000 tons of ammonium sulphate (2). This in turn corresponds to 80,000 tons of nitrogen. The total, current ammonium sulphate production is of the order of 200,000 tons of nitrogen.

7.1.1.2. The synthetic process. (3,4) This process uses as its raw material ammonia produced by synthesis from nitrogen and hydrogen. Carbon dioxide, a ily-product of the ammoniasynthesis process, is absorbed in aqueous ammonia to give a solution of ammonium carbonate. This solution is then mixed with anhydrite and by double -108- decomposition a solution of ammonium sulphate and a precipitate of calcium carbonate are obtained. The latter is filtered off and the ammonium sulphate is recovered by crystallisation.

7.1.1.3. Comparison of the two processes. When it was first recognised that nitrogen was an essential fertilizer, the recovery of by-prcduct anmonia represented the only domestic source of this nutrient and up to 1930 the process was of considerable profit to those operating it. The introduction of the cheaper synthetic process resulted in a large scale reduction in ammonium sulphate prices and by 1932 the by-product process was, on the whole, uncompetitive with the newer method of production (1). In addition, the latter produced a superior product containing no free acid and consisting of large, free flowing crystals making application to the soil much easier. The by-product process was improved to give a comparable product but whether or not it could have been sold in competition• with the synthetic material is a matter for conjecture. The setting up of the British Sulphate of Ammonia Federation removed competition in the open market and all ammonium sulphate was, and still is,. sold through this organisation at a price fixed by them. -189-

Key (1) has examined in considerable detail the economics of by-product production in the gas industry and means of increasing it's profitability. He concludes that in general the process is either uneconomic or at best marginal except when operated on a large scale, i.e. on large gas works or when manufacture in an area can be centralised at one works. An examination of the process shows, however, that economies of scale likely to be effected by centralisation are small. The figures in table 7.1 are given for the cost of manufacturing ammonium sulphate (1). They represent the costs for a number of typical works, but it should be emphasised that the figures do not represent true average costs but are intended to serve as a guide to the allocation of the costs between the different requirements of the process.

Table 7.1 Manufacture of ammonium sulphate by the by-product process 1953. Process utilizes lime to recover both f'ee and fixed ammonia, Liquor assumed to contain 2.17 g./100 c.c. of ammonia Factor costs Steam 12/- per ton Lime (96% Ca0) 75/6 per ton Sulphuric acid (75% H2SO4) 150/- per ton Bags (2 cwt.) 1/6 each

-190-

Cost per ton of ammonium sulphate Item Cost Percent of total s d cost. Steam 4.16 tons 2 10 0 16.0 Lime 238 lbs 8 0 2.6 Acid 1 ton 7 10 0 48.1 Bags 10 15 0 4.8 Maintenance 1 7 0 8.6 Capital charges 15 0 4.8 Labour, packing, supervision 2 7 0 15.1 Total 15 12 0 100.0 Revenue from sale 16 5 0 Margin 13 0 4.2

From the table it can be seen that the directly v3.riable costs, (items 1-4), form just over 70% of the total. The economies of scale that could be effected are thenfore likely to be small. In addition the cost of transporting liquor is high, per unit of ammonia, since it is of such low strength. Thus, even if economies could be effected by centralisation, they are likely to be offset by costs of transport except where the distances involved are small.

7.1.1.4. Alternative means of disposing of by-product ammonia liquor. In cases where production of ammonium sulphate is -191— uneconomic, the disposal of the ammonia liquor raises considerable difficulties since it cannot be discharged directly as a waste effluent. Four methods of dealing with this problem can be suggested:— (a)To continue to manufacture ammonium sulphate, the loss being subsidised by sales of the commodity from other sources. (b)To continue to manufacture ammonium sulphate and to charge the loss to the manufacture of gas and coke in the main process. (c)To sell the liquor to users of ammonia, who recover it by stripping with steam as in the manufacture of ammonium sulphate. (d)To use the liquor directly as a fertilizer. The first two methods are clearly undesirable for economic reasons, but, if the other processes are not feasible they have to be adopted. The use of the first method a depends on the existence ofkcentral selling organisation or cartel, through which all ammonium sulphate manufacturers are prepared to sell, and that those operating profitable processes are prepared to subsidise those operating at a loss. Method (b) is potentially attractive provided that -192-

there is a requirement for ammonia close to the point of production of the liquor. The economics of the process will depend on (a) the availability of low cost steam for recovering the ammonia, (b) the distance the liquor has to be transported, the cost being high per unit of ammonia. The possible market for liquor for this use is likely, therefore to be small and very much dependent on factors local to the point of production. Method (c) has to be examined for:- (a)The feasibility of using ammonia liquor as a source of nitrogen fertilizer. (b)The cost per unit of nitrogen.

7.1.1.4.1. The practical use of ammonliquor as a fertilVia., Ammonia liquor has been compared to ammonium sulphate and nitrochalk in a series of trials on grassland and other crops from 1953 to 1955 (3). The general conclusions reached were as follows:- (a)On average the liquor was not as effective as other nitrogen fertilizers for all crops. Effectiveness varied between 70 and 100 O. (b)The main objection to the use of the liquor is that it scorches, (burns), a crop if it is not carefully applied. The effect is least marked with grassland which recovers rapidly from any scorch. -193-

(c)Care must be taken to ensure the liquor contains no materials, mainly tarry substances, toxic to plants. This was found to be important only when the liquor had been concentrated before use. (d)The general conclusion reached was that ammonia liquor was most suitable for use on grassland, where it would be as effective as other forms of fertilizer. Lawrence (6) has described the use of such liquor on grassland in the south of England. The application proved successful and few complaints were received. Although the grass was often scorched initially it soon recovered and the growth of the grass was enhanced, though no measurements were made as to the increase obtained. The practice of spraying liquor has grown in recent years and is now quite popular with farmers. Thus-in 1955 the three Southern Area Gas Boards applied some 52 x 106 gallons to grassland.

7.1.1.4.2. The cost of using ammonia liquor as a fertilizer. The ultimate criteria of using ammonia liquor is whether it is cheaper than other forms of fertilizer per unit of nitrogen. In 1956 the following costs applied. Cost of ton of nitrogen as ammonium sulphate = £93.9 Cost of 1000 gallons liquor, delivered and applied to the land, (1.78% N. s.g. = 1.00) = £6.5 -194- .*. 1 ton of nitrogen as liquor costs E81.6. i.e. nitrogen from the latter source is cheaper than that derived from ammonium sulphate. In practice the margin is even larger since no allowance has been made far the additional cost of handling, storing ard applying the ammonium sulphate, whereas this is included in the cost of the liquor. The above comparison of costs assumes the liquor is delivered within a 20 mile radius, the transport costs being equalised within this area. The analysis of costs has been given as follows (2). Cost of liquor E6.10.0. per 1000 gallons, delivered and applied. Of which 40% is due to transport, 40% is due to application, 20% is charges to gas manufacturers - i.e. amount paid for liquor ex works. The cost could therefore be reduced substantially by reducing the radius of delivery, making the use of liquor even more attractive to farmers. The disposal of ammonia liquor by this means appears to be feasible, from both the practical and economic aspects, in those cases where production of ammonium sulphate is either uneconomic or marginal. In areas where this method has been adopted, it's use has been successful (2, 6, 7). -195--

A decision on whether any particular works should adopt this process will depend mainly on factors local to the area. They are:— (a)The existence of sufficient areas of grassland a short distance from the works.(less than 20 miles). (b)The willingness of local farmers to using ammonia liquor. (c)The cost of manufacturing ammonium sulphate on the works. (d)The proximity of other works, making possible joint manufacture of ammonium sulphate to gain economies of scale.

7.1.2. Manufacture of ammonium nitrate. Ammonium nitrate is the secondary source of fertilizer nitrogen in the U.K. The salt is not however used in it's pure form but is sold in admixtures with chalk, under the trade names nitrochalk and nitrashell, containing either 15 or 21% of N, c.f.pure ammonium nitrate 34% N. This fertilizer is especially in demand for top dressing cereals and grass crops. A more recent development (1959 has been the production of ammonium nitrate for use in three nutrient mi::ed fertilizers (8). In 1957 ammonium nitrate supplied some 25% of the fertilizer nitrogen-consumed in the U.K. Ammonium nitrate is manufactured by the neutralisation MANUFACTURE OF AMMONIUM NITRATE TO tVENT AIR

. I WATER HEAT EXCHANGER ....SCRUBS ING DILUTE N Os/H1.0 TOWER SOLUTION

AIR NHS A REACTOR ----01HEATE R 6112.0 B SEPARATOR NH4N 03 - C MOISTURE STRIPPING COLUMN PR I LLING TOWER

TO./T HNO3 • SOLU T101>Nli 8

H N 0 HEAT ER STORAGE HP

Co.001

4— AIR MOLTEN T M IXER N H4N Oj ,PRODUCT -196—

of aqueous nitric acid with ammonia, the former being produced by the catalytic oxidation of the latter. Various processes for this manufacture have been described in the literature (9,10,11,12) and it is not proposed to go into detail on them. They all consist of the neutralisation of the acid with ammonia in a suitable reactor or column and then utilizing the heat of reaction to evaporate the water. In older processes a 90% solution of ammonium nitrate was obtained which then had to be further evaporated to give the pure salt. With newer methods air is used to strip the residual moisture and almost pure ammonium nitrate is obtained. A flow sheet of a typical modern process is given in Figure 7.1. The ammonium nitrate, which is in a molten condition after leaving the separator is then prilled, either in the pure form or in a mixture with chalk to give the nitrochalk type product. This consists of spraying the molten salt down a tower against a current of air, giving a product in the form of small spherical granules. Alternatively the product can be crystallised on cooled, moving belts.

7.1.3 Alternative processes for manufacture of nitrogen fertilizers. Since the potential demand for nitrogen fertilizers is so large, and if it is realised, only in part, a very large -197- increase in manufacturing capacity will have to be made, it is appropriate to consider what nitrogen fertilizer processes and products, alternative to those already described, would be most suitable for use in the U.K. Only three products would appear to be feasible for use under British conditions and these will be considered separately in the following sections. They are:- (a)The use of pure ammonium nitrate both in the straight form and as a constituent of mixed fertilizers. (b)The use of urea both straight and in mixed fertilizers. (c)The use of liquids containing nitrogen derived from ammonia, ammonium nitrate or urea. 94TN There are other nitro materials which might be suitable for use as fertilizers. Some of these are compounds or mixtures which contain both nitrogen and phosphorus e.g. ammomium phosphates, nitrophosphates. Their use is considered in section 7.2. Ammonia is the cheapest source of fixed nitrogen and it is therefore necessary that any potential nitrogen compound be readily manufactured from this material. For this reason and because of the factors mentioned in chapter 6 and at the beginning of this chapter, as to the desirable properties of fertilizers, only ammonium nitrate, urea or ammonium sulphate really come into consideration. -198-

7.1.3.1. The use of pure ammonium nitrate as a fertilizer. The following advantages can be claimed for using pure ammonium nitrate as a fertilizer;- (a)It has a relatively high concentration of nitrogen (34k) which would enable one to obtain those economies of concentration described in 6.4.2., c.f. ammonium sulphate and ammonium nitrate-chalk fertilizers used at present which contain 21% or less of nitroegn. (b)It contains itS.. nitrogen in both the ammoniacal and nitrate forms, thus making it available to some extent in both the short and long term, which is considered advantageous. Against these must be set the following ,disadvantages„:- (a) The pure salt is extremely hygroscopic and has a pronounced tendency to cake into a hard mass making application to the soil impossible. A salt exposed to the air will pick up moisture when the relative humidity is greater than the relative humidity of air in equilibrium with a saturated solution of the salt. The relevent data for ammonium nitrate is given in graph 7.1. (13). Assuming a relative humidityvarying between 60 and 70% and an ambient air temperature of between 15° and 28°C for the U.K. in general, (represented by dotted lines on graph 7.1) it can be seen that conditions readily occur where ammonium GRAPH 7.1.

RELATIVE HUMIDITY OF AIR IN EQUILIBRIUM

WITH SATURATED SOLUTION OF AMMONIUM

NITRATE AT VARIOUS TEMPERATURE S

AMMONIUM NITRATE TAKES UP MOISTURE T 74

MID MO IMMO PERCEN

66 TY DI I M

AMMONIUM NITRATE

VE HU GIVES UP MOISTURE TI A EL

R 50 0 I0 20 30 40 50

TEMPERATURE °C -199- nitrate will take up moisture and then lose it again. It is during the latter process that salt bridges between the crystals are formed and which give a caked mass of fertilizer. (b) There is a considerable explosion hazard involved in the use of ammonium nitrate. Three of the greatest disasters due to explosions have been caused by fertilizer ammonium nitrate (13). These are (a) the explosion at Oppau, Germany, in 1921, as a result of attempting to blast a caked mixture of ammonium sulphate and nitrate, causing 509 deaths; (b) that at Texas City, U.S., in 1947 when a fire in a ship caused the ammonium nitrate cargo to explode causing 400 deaths; (c) that at Brest, France, in 1947, under similar conditions to (b) causing 21 deaths. In addition many other explosions have been reported. However on many occasions reports have been made of ammonium nitrate fires, or blasting has been carried out, in which no explosion took place. No satisfactory explanation has been offered as to why this salt should explode only in certain instances. For British conditions the above disadvantages outweigh the advantages in using pure ammonium nitrate as a source of nitrogen for straight application, especially as such a high premium is set in the U.K. on having non-caking fertilizers which are easy to apply to the land. -200- In the U.S. considerable quantities of this salt are used for straight application. The danger of caking is reduced by adding various materials to the product (14,15), e.g. 1% petrolatum-rosin-paraffin and 4% kaolin or up to 5% of diatomaceous earth, dolomite, chalk or talc. None of these appear to have been entirely successful in practice. It is also claimed that with reasonable precautions ammonium nitrate can be safely handled, with no danger of explosion. The best method for meeting the potential demand for straight nitrogen fertilizers is in the increased production of ammonium nitrate-chalk mixtures rather than of the pure salt. The adaition of chalk renders the product safe to handle and largely non-hygroscopic. These mixtures are extremely satisfactory sources of nitrogen for top dressing crops, for which purpose the bulk of straight nitrogen fertilizers is used, and in addition they supply calcium, a secondary plant nutrient, which also prevents the formation of acidity in the soil as is caused by using straight ammonium nitrate or sulphate. Ammonium nitrate would, however, appear to be very suitable for use in mixed fertilizers and have several advantages over ammonium sulphate which is currently the major source of nitrogen for this purpose. Its high concentration, besides lowering costs of handling, transport and bagging, would give a larger N:P208 ratio than at -201- present which is particularly required. The use of the salt is also advantageous in granulation since it reduces the quantity of moisture required in the process (see 6.3.9). Economically its use would also appear to be justified. One firm which recently introduced mixed fertilizers, incorporating ammonium nitrate, was able to reduce their price by an average of 5% by so doing (16).

7.1.3.2. The use of urea as a fertilizer. Urea is a material which finds considerable use as a fertilizer in many countries, especially in the United States, though virtually none is used in the U.K. for this purpose. The advantages that can be claimed for using urea are:- (a) It has a high nitrogen content, 46%. (b) The nitrogen is an amide form and is therefore available only slowly to the plant and over a longer period of the growing season. (c) It is completely inert and relatively easy to store. It has a hygroscopicity comparable to that of ammonium sulphate which is easily handled. The big disadvantage of using urea is that under certain coLditions during manufacture biuret and other polymerisation products are formed which can be toxic to certain plants. A fuller discussion of this and the means of overcoming it -202-

are given in 7.1.3.2.2.

7.1.3.2.1. Manufacture of urea (17,18,19,20,21,22). Urea is manufactured commercially from ammonia and carbon dioxide, which are reacted under suitable conditions to form ammonium carbamate, the latter dissociates to form urea and water 2N110 + 002 -> NH4C00NH2-----*(NH2)200 + H2O A diagram of the simplified process is given in figure 7.2. The urea plant is generally directly integrated with an ammonia synthesis plant which, in addition to ammonia, produces large quantities of carbon dioxide, which is normally a waste product. The ammonia and carbon dioxide are fed to an autoclave at the requisite temperature and pressure to form a melt of ammonium carbamate, urea and water and unconverted raw materials. This melt then passes through a pressure let-down valve into the carbamate stripper where a solution of urea:and water is formed together with unconverted ammonia and carbon dioxide. The yield of urea is affected by the temperature and pressure in the autoclave. For any given pressure the degree of conversion increases with increasing temperature to a maximum after which it rapidly falls. The point of maximum conversion, of the order of 45)-50% of CO2 MANUFACTURE OF UREA. SIMPLIFIED DIAGRAM

UNCONVERTED * 14H & CO2. 3

AUTOCLAVE CAR BAMA T E

1,..,-----'-----S TRIPPER

PRESSURE LET-DOWN VALVE

AQUEOUS A MM ON IA J *UREA CARBON DIOXIDE SOLUT ION -203- converted, occurs when the dissociation pressure of the ammonium carbamate formed becomes greater than the operating pressure, i.e. when the dissociation pressure becomes greater than the operating pressure then reaction (1) predominates in preference to reaction (2) NH4 COO NH2 2NHa + CO2 (1) 2NH3 + 002---*NH4 COO NH2-->(NH2)2 C(} + H2O (2) Increasing the operating pressure will of course increaoe the degree of conversion. In practice a balance has to be struck between the increased yield due to high temperatures and pressures and the increased operating and capital costs incurred in so doing. With processes operated at present, pressures of the order of 2000-3000 p.s.i. and temperatures between 150 and 200°C are used. Further, an excess of ammonia is used both to increase yields and reduce corrosion. The reaction melt is extremely corrosive and special alloys or liners have to be used for much of the plant. Since only partial conversion is achieved recovery and recycling of the unconverted ammonia is essential if the process is to be economic. The ammonia and carbon dioxide cannot be directly recycled since solid carbamate is deposited in pumps and pipes. Several systems have been devised to achieve recovery. Many of them depend on -204- the separation of the ammonia from the carbon dioxide, the former is recycled to the process and the latter allowed to go to waste. In another process both gases are recycled in the form of carbamate dispersed in mineral oil. Flow sheets of two typical modern processes are given in figures 7.3 and 7.4. American experience indicates that whichever process is used there is little significant difference in manufacturing costs. An alternative method of recovering the ammonia, which would be feasible, though it is apparently not practiced, is to use the off gases to manufacture another fertilizer salt. Thus the ammonia could be utilized to manufacture ammonium nitrate or sulphate by processes outlined previously. Alternatively it could be used to neutralise phosphoric acid to produce ammonium phosphate (see 7.2.1.3). The advantage of doing this is that the considerable capital investment on the recycle plant would be saved and operating costs would be lower. The product leaving the carbamate stripper consists of an aqueous urea solution (75% by weight). This is concentrated by evaporation and the urea recovered by crystallisation or it can be prilled, in a similar manner to ammonium nitrate. The manufacture of urea would appear to be competitive with other forms of fertilizer nitrogen. The current (1959)

MANUFACTURE OF UREA. RECOVERY UNIT. AS USED IN PECHINEY SY TEM (22)

UNCONVERTED AMMONIA A AUTOCLAVE AMMONIUM CARBAMATE- & CARBON DIOXIDE B CARBAMATE STRIPPER OIL SLURRY \ C SALT-OIL REACTOR D OIL-UREA SOLUTION SEPARATOR 1 A 10 ( 11 3 l. e

PRESS UR E ILO I L LETDOWN

D OIL & UREA SOLUTION AQUEOUS VUREA SOLUT ION

r L14--- 1 CARBAMATE OIL n.b. UNCONVERTED NH3 & CO' ARE SLURRY RECIRCULATED AS AMMONIUM CARBAMATE DISPERSED IN MINERAL OIL 4 FIGURE 7.1.

MANOFAC T UM OF UREA

RECOVERY SYSTEM AS USED IN CHEM ICO PROCESS 07)

UNCONVERTED NH3 C, COL

AMMON IUM R BAMAT

PRESSURE LET-DOWN VALVE

UREA * SOLUTION TO COL NH1 COMPRESSOD EVAPORATOR NH 3 COa NH3 NH3 RECYC LE TO WASTE CONDENSER 4:=ZO SOLVENT

M ONO ETHANOLAM INE

A AUTOCLAVE COL SOLUTION AMMON IA SEPARATOR C GARDA MATE ST RIPPER D CO ABSORBER E SOLVENT REGENERATOR -205-

price for plastics grade urea, a purer form than would be required for fertilizer use, is 144.5 per ton or 197 per ton N. This compares to 1103 per ton N for ammonium sulphate or 1106 per ton N for pure ammonium nitrate.

7.1.3.2.2. The use of urea as a fertilizer. The use of urea should be an adequate source of fertilizer nitrogen (23,24), though little work has been done to determine its effectiveness in the U.K. Reports from the U.S., however, state that urea proves uniformly to be an excellent source of fertilizer nitrogen (25). One disadvantage of urea as a fertilizer is that during manufacture compounds are formed which have been reported to be toxic to certain plants (26,27,28). The most common of these is biuret, a condensation product, though cyanic acid and higher polymerisation products of urea are formed. The mechanism appears to be as follows (29): NH200NH2 HN = C = 0 NH2C0 NHCO NH2 -NHa cyanic acid +urea biuret It is claimed that biuret is the toxic compound and certainly many of the commercial ureas in the U.S. contained up to 10% of this material. More recently doubt has been expressed whether in fact biuret is the cause of the toxic effects, or if it is, whether it is as harmful as was thought originally (30). The danger would appear to -206- be mainly to germinating seeds though not all plants are affected (24). The above reaction takes place at temperatures above the melting point of urea, (133°C), the rate of formation of biuret depending on the temperature. Thus at 14000 the rate is 3.30% per hour, at 150°C, 6%, and at 17000, 14% per hour. Under crystallisation conditions the rate of formation is far less, e.g. at 10000, 226 mm Hg, the rate is only 0.115% per hour. Most commercial, crystalline urea contains well below 1% of biuret. It has also proved possible, in the U.S., by careful control of operating conditions, to produce prilled urea which contains less than 1.5% of biuret, at which level it is apparently not toxic. Urea is thus potentially a useful nitrogen fertilizer and its manufacture and use should be considered in any future expansion of the industry.

7.1.3.3. The use of liquids as nitrogen fertilizers. In the United States considerable interest has been shown in the use of liquid fertilizers and a considerable expansion ix). their use has taken place since 1945. This is illustrated in table 7.2 (31,32,33). -207-

Table 7.2. Consumption of liquid fertilizers in U.S.

U.S. Short tons. Years ending June 30th, 1947 1954 1955 Anhydrous ammonia 27,000 350,500 353,500 Nitrogen solutions 7,500 191,500 340,500 Phosphoric acid 6,000 15,000 15,500 Mixed fertilizers 6,500 27,500 not available

Historically the use of anhydrous ammonia was the first to achieve importance with the turning over of ammonia plants, constructed during the war for explosives manufacture, to peace time use. It was found that anhydrous ammonia applied to cotton proved an effective fertilizer and its use spread rapidly to other crops (34,35,36,37). Interest subsequently spread to the use of aqueous nitrogen solutions, (aqueous ammonia and solutions of salts such as ammonium nitrate, urea etc.), for use, both for straight application to the land (37,38,39), and as a means of increasing the nitrogen content of solid mixed fertilizers (40,41,42,43). More recently considerable interest has been shown in the use of liquid fertilizers which coAtain all three plant nutrients in solution (39,44,45), c.f, to solid mixed fertilizers. To some extent, the great increase in the use of liquids in the U.S. can be attributed to a considerable growth in the use -208-

of irrigation which makes application of such fertilizers very easy. In view of the large consumption of liquid fertilizers in the U.S. it is appropriate to consider whether their use would be feasible in the U.K. At present they find virtually no use in this country, with the exception of ammonia liquor on grassland, and in small amounts for horticultural use.

7.1.3.3.1. Anhydrous ammonia. Although anhydrous ammonia would form a relatively cheap source of nitrogen, (88 per ton N compared to KO3 per ton N, for ammonium sulphate, the cheapest source of nitrogen), it is unlikely that its use in the U.K. will become widespread since conditions are generally different from those which encouraged its use in the U.S., i.e. (a) There are no wide row crops grown which are responsive only to nitrogen. (b) There ar6 insufficiently large areas of light, easy working soils to which ammonia is most easily applied. (c) Climatic conditions are such that fertilizer can only be applied at about the same time as the seed is sown, whereas it is preferable to apply ammonia 001310 time before. -209-

It can therefore be concluded that in general the use of this material is not suitable for British conditions. A possible exception to this is that it might have some potential use as a fertilizer for sugar beet. This is a wide row crop, which is grown in a relatively small area of the country and which is highly organised through the British Sugar Corporation (46). In this case it might be possible to organise a contract service, though the farmer would still have to apply phosphorus and potassium fertilizers.

7.1.3.3.2. Aqueous ammonium solutions. These solutions consist of ammonia in water at such a dilution that the vapour pressure is low. The vapour pressure exerted by solutions of ammonia of various strengths is given in table 7.3 (47).

Table 7.3. Total vapour pressure of aqueous solutions of ammonia. Pressure in pounds per sq. in. absolute. Temperature Molal concentrations of ammonia (percent.) °F 0 20 40 60 80 100 60 0.26 3.51 19.30 56.32 86.49 107.6 100 0.95 9.34 44.12 117.17 173.40 211.9 -210- The use of a solution of appropriate dilution, such that vapour pressure is approximately atmospheric, avoids the necessity of the use of pressure equipment, as is the case with anhydrous ammonia, making application both cheaper and easier. With regard to their use one would expect them to have the same effect as the use of gas works ammonia liquor, which is used quite successfully on grassland. It would, however, be of considerable benefit if more work could be done to determine their effectiveness as nitrogen fertilizers, both with regard to the response obtained and the losses that occur due to volatilization from the soil. One use which appears attractive is in conjunction with large scale irrigation of grassland sincethe water applying system can also be used to apply nitrogen fertilizer and in addition scorch effects should be eliminated since the irrigation water will wash the ammonia solutions from the foliage. Aqueous ammonia solutions form the cheapest source of nitrogen available in the U.K. at the present time, the cost being 165.25 per ton of N. delivered, compared to 188 per ton N for anhydrous ammonia and 1103 per ton N for ammonium sulphate.

7.1.3.3.3. Mixed liquid fertilizers. The basic advantages that can be claimed for -211- manufacturing a mixed liquid fertilizer containing the three major nutrients are:- (a) No bagging of the product is required. (b) Application of liquids is simpler and more accurate than that of solid fertilizers. (c) There is no danger of caking or segregation of the fertilizer as is the case with solid fertilizers. (d) Their manufacture is technically much simpler than that of solid mixtures. There is no necessity for granulation or drying plant, all that is required is a simple mixing tank. Against this can be set the disadvantages that:- (a) The liquids are on the whole extremely corrosive making necessary the use of special alloys in mixing and application machinery. (b) The concentration of nutrients that can be attained is limited and is less than that of the more concentrated solid mixtures. (c) Transport costs are relatively high compared to those of solids, due in part to this low concentration, which tends to limit the area, around the point of marufacture, where they can be used. Agronomically there would appear to be little difference between solid and liquid fertilizers though little work has -212-

been published on this (48.49). Luckhardt(38) in a general review of the experience of using liquid fertilizers claims the following advantages for their use:- (a) Greater efficiency when soils are on the dry side and solutioh of solid fertilizers is low. (b) More rapid nitrification in the soil. (c) More rapid availability of phosphates to crops. (d) More lasting benefit from nitrogen under irrigation conditions; ammonia solutions were found to be more lasting than ammonium nitrate either in solution or dry. In the United States mixed liquid fertilizers are manufactured by neutralising phosphoric acid (85% H3PO4) with ammonia (44). This gives..an ammonium phosphate product. The degree to which ammoniation is taken is critical on the solubility of the salt formed. It has been found that a ratio of N/2205 = 0.3 gives the highest solubility (44,50). In practice a ratio of 0.33 is chosen since this gives a pH of 7, i.e. a neutral solution. The nitrogen content can be raised by adding ammonium nitrate or urea and potassiuth can be added by the use of potassium chloride. Various nutrient ratios can be attained though the maximum concentration is of the order of 30% of plant nutrients. This corresponds to the -213-

concentration of many of the solid mixtures at present being used, though mixtures of up to 42% concentration are available. The plant required for manufacture is extremely simple. An open mixing tank and metering equipment for liquids and weighing equipment for solids is all that is required together with storage facilities for raw materials. The degree of ammoniation is readily controlled by pH. Due to corrosion the plant has to be made of stainless steel or aluminium (31). In addition facilities for cooling the reaction mixture have to be provided to prevent overheating during neutralisation with consequent loss of ammonia. The plant can be made to operate on a batch or continuous basis. American practice has evolved to the manufacturer of the liquid fertilizer also applying it in a contract service. Generally the costs of transport limit this service to an area 25 miles in radius. At first sight this process appears extremely attractive and adaptable to British conditions especially in those cases where a contracting service is feasible, i.e. to the smaller farmer and in top dressing crops. In addition it might be attractive to the big farmer who is a large user of fertilizer. The raw materials can be -214-

bought in bulk and readily mixed to give the required nutrient ratios. Unfortunately it is not economically feasible in the U.K. since the cost of the concentrated phosphoric acid required, that derived from the thermal process of manufacture, is too high. The approximate cost of manufacturing the basic liquid fertilizer is compared to the solid form below. Comparative cost of manufacturing a fertilizer containing 8% N and 24% P205 (1959).

As liquid. Raw material costs: 1 ton phosphoric acid (s.g. = 1.7000, 85% H5PO4 1100 1 ton ammonia (industrial quality) 52.5 .°.1 ton P205 as phosphoric acid costs 1163 1 ton ,N as ammonia costs 63.8 To manufacture 1 ton of liquid fertilizer 8% N, 24% P205 Raw material unit cost/ton cost 0.08 ton N 163.3 5.1 0.24 ton P205 1163 38.4 Total 43.5 per ton As solid: 1 ton P205 as super phosphate 82 1 ton N as ammonium sulphate 1103 Approximate cost of mixing andgranulating 1 ton of plant nutrients at 32% concentration (this is based on manufacturers' price lists) 1, 12 -215-

To manufacture 1 ton solid fertilizer 8% N, 24% P205 Raw material unit cost/ton cost 0.08 ton N 1103 8.3 0.24 ton P205 E 82 19.7 Granulation 0.32 tons of 112 3.8 nutrients Total 34.8 per ton

The raw material costs of the wet process are far greater than that of the solid process, even after taking into account the additional costs of granulation, and the process is thus not economically feasible for use in the U.K.

7.1.3.3.4. Liquid fertilizers containing only nitrogen. These solutions are of three main types:- (a) Ammonia-urea-water, (b) Ammonia-ammonium nitrate-water, (c) Urea-ammonium nitrate-water. With systems such as these it is possible to get extremely high concentrations of nitrogen in solution per unit. This is because ammonium nitrate and urea, both highly soluble in water, are even more soluble in aqueous solutions of ammonia as well as increasing their mutual solubilities in water. Table 7.4 gives the maximum solubilities for the three types of system (52,53). -216-

Table 7.4. (a)Solubility of urea in aqueous ammonia, 15°C. Maximum solubility g./100g. water Ammonia 0 20 50 100 150 Urea 94.2 90 103 175 254 0 in solution 22.3 27.5 35.0 43.4 47.7

(b)Solubility of ammonium nitrate in aqueous ammonia, 15°C. Maximum solubility g./100 g. H2O Ammonia 0 20 50 100 150 Ammonium nitrate 175 195 270 435 604 %N in solution. 22.2 '26.9 32.3 37.0 39.2

(c) Solubility of various proportions of urea and ammonium nitrate in water, 30°C. Solubility gms/100 g. water Urea 0 29 74 164 375 719 Ammonium nitrate 242 259 294 381 562 845 %N in solution 24.7 26.8 28.2 32.4 35.6 370

Urea 482 266 204 172 133 Ammonium nitrate 482 178 87 43 . 0 %N in solution 36.7 33.9 31.8 29.9 26.2

NH'Point of maximum mutual solubility. -217-

Solutions of considerable concentration can thus be obtained. The ammonia solution, depending on concentration, may also have a considerable vapour pressure though this is less than the corresponding solution without the added salt. In practice to avoid salting out, i.e. deposition of the salt phase with changing temperature, such solutions axe marketed in the U.S. with ealt concentrations less than those which would give a saturated solution. Typical types of such solutions are given in table 7.5 (31).

Table 7.5. Properties of nitrogen solutions sold in U.S.,

Type of Percent by weight of Saturation Total vapour pressure solution N NH4NO3 (NH2)2C0 NH3 p.s.i.a. NH3/NH4NO3 41 55.4 - 26,2 -25 32 NH3/NH4NO3 41 64.9 - 22.2 21 25 NH3/ (NH2)2C0 33.5 - 11.9 34.0 -31 38 NH3/ (NH2)200 33.5 - 25.3 26.0 18 27 NH4NO3/ (NH2)200 32.0 45.7 34.8 - 32 -

The manufacture of such solutions is technically and economically attractive for the following reasons:- (a) A high proportion of the nitrogen is derived from -218- ammonia, a low cost source of this nutrient. (b) In the manufactureof ammonium nitrate or urea for use in liquids it is not necessary to evaporate water or undertake crystallisation or prilling of the salts thereby reducing the costs of production. (c) The considerable problem of the caking of the salts, due to their hygroscopic nature, is completely avoided. The use of the pressure solutions, i.e. those containing ammonia, would suffer to some extent to the same limitations as apply to using pure ammonia -aqueous solutions of ammonia, e.g. they have to be placed in the soil and covered to avoid ammonia loss and away from the seed to avoid damage. The use of a non-pressure solution of the urea-ammonium nitrate-water type is therefore in many ways more attractive. The solution could for instance be applied to the soil with special equipment, a phosphorus-potassium solid fertilizer being applied simultaneously so that all three nutrients are applied together. Another potential use is for top dressing grassland in those cases where only a nitrogen fertilizer is required, especially if the fertilizer could be applied with irrigation water. The use of nitrogen solutions therefore appears to be feasible in the U.K. They certainly merit close investigation by fertilizer manufacturers to determine the cost of their manufacture and their effectiveness agronomically as fertilizers.

7.1.4. Effect on costs of increased demand for fertilizer nitrogen. Nitrogen fertilizers are almost entirely manufactured from ammonia as a raw material. Since the realisation of the potential demand for these fertilizers would mean a large increase in the demand for ammonia it is appropriate to consider whether this would increase its cost significantly i.e. whether the supply of ammonia is elastic or inelastic. The supply of ammonia should be extremely elastic, though naturally a much larger amount of ammonia manufacturing plant would have to be erected, and the increased demand should have little effect on its cost. Ammonia is manufactured by synthesis from nitrogen and hydrogen. The latter can be manufactured by blowing air or steam into heated beds of coal or coke., Increased demand will therefore mean a greater use of these fuels. They are in plentiful supply and the increase in their use would be small compared to their total consumption in the U.K. Newer processes utilize the gases produced in various oil refining operations as by—products. The increased and projected installation of such plants in -220- the U.K. in recent years should ensure a readily available supply of raw materials for the manufactures of ammonia.

7.1.5. Conclusions. It is probable that a large proportion of the ammonium sulphate manufactured from by-product ammonia liquor is being produced at a loss and is being subsidised by sales of ammonium sulphate from other sources. It is suggested that in those cases where this is so the liquor should be disposed of by an alternative means. One method of doing this would be to use the liquor directly as a fertilizer for grassland. It is likely that ammonium sulphate will continue to remain an important nitrogen fertilizer. However it is thought that in the future more concentrated materials will be required so as to obtain higher N:P205 ratios in mixed fertilizers. The two fertilizers which are economically and technically most suitable for this purpose are ammonium nitrate and urea. The demand for straight nitrogen fertilizer is best met by continued use of ammonium nitrate-chalk mixtures. It is concluded that the scope for the use of liquid fertilizers is small in the U.K. Conditions are in the main not suitable for their use, (anhydrous ammonia)•. -221- or the cost of manufacture is too great compared to solid fertilizers. (Three nutrient mixed liquids). There is possibly some market for aqueous ammonia and solutions of systems of the type NH4NO3-NH2C0NH2741209 especially if irrigation becomes of any major importance in the U.K.

7.2 Phosphorus Fertilizers. In earlier chapters it was concluded that, while there was still scope for the expansion of phosphorus fertilizer use, this was considerably less than was the case with nitrogen fertilizers. With any large change in the crop value:fertilizer price ratio, i.e. such as would be caused by the removal of the subsidy, it is likely that the potential expansion of consumption would be small or non-existent. Indeed in recent years the phosphorus market has shown a slight decline in sales. A recent trend that has occurred in the market has been towards the use of more concentrated materials, e.g. ammonium phosphate and concentrated superphosphate, in substitution for ordinary superphosphate in mixed fertilizers, though the latter is still by far the most important commodity. Basic slag is important in the U.K. as a straight fertilizer for use on grassland, Its main advantage is the low unit cost of the phosphorus it contains. -222-

Production is however directly related to that of the steel industry, of which it is a by-product, therefore and its use can only be expanded with that of the latter. A further factor, in considering phosphorus fertilizer processes of possible interest under British conditions, is that opinion generally favours those materials which contain a high percentage of water soluble forms of phosphorus. With this condition, three manufacturing processes are of potential interest. (a) Manufacture of ordinary superphosphate. (b) Manufacture of concentrated superphosphate. (c) Manufacture of ammonium phosphate. All of these processes are already used in the U.K. and in view of their importance, the economics of each process are discussed in some detail below. Since however the manufacturing details have already been described comprehensively in the literature it is proposed to describe only briefly the manufacturing processes, supplemented by flow sheets where necessary. References to the literature are given at the head of each section.

7.2.1.1. Manufacture of ordinary superphosphates (3,54, 55,56,57,58,59,60,61). This process was the first one ever used to manufacture water soluble, phosphorus fertilizers and its use, with -223- modifications, has continued to the present day. Ground phosphate rock (essentially tricalcium phosphate), is treated with sulphuric acid, the quantity depending on the type of rock and its analysis. Generally a mole ratio of H2SO4:P206 of 2:1 is used. The slurry so formed sets rapidly into a hard mass which is then broken up. The superphosphate has then to be cured for .7 2-4 weeks, to allow the reaction to go to completion before it is ready for use. The material so formed is a mixture of monocalcium phosphate and calcium sulphate. The basic equation for the reaction can be written as:- Ca3(PO4)2 + 2H2SO4 + H20—* 20aSO4 + Oa(H2PO4)2H20 Ordinary superphosphate contains between 16 - 21% of water soluble P206.

7.2.1.2. Manufacture of concentrated superphosphate (56,57,59,62,63,64,65,70). The product of this process is essentially the same as that of ordinary superphosphate in that it contains monocalcilm phosphate but the use of phosphoric acid to attack the phosphate rock gives a more highly concentrated product (46-50% P205 , Sulphuric acid is reacted with phosphate rock to give a solution of phosphoric acid and a precipitate of calcium sulphate which is filtered off. 20a3(PO4)2 + 6H2SO4 + 12H20 + 6CaSO4.2H20 -224- The phosphoric acid is then further reacted with phosphate rock to give the concentrated superphosphate Ca3(PO4)2 + 4H3PO4 + 3H20--> 3Ca(H2PO4)2H20

7.2.1.3. Manufacture of ammonium phosphate (57,59,66, 67,68,69,70). In this process phosphoric acid is manufactured as described above and subsequently neutralised with ammonia. The degree of neutralisation used depends on the product required. In practice this is between that required to give a mono-ammonium or di-ammonium phosphate product. H3PO4 + NH3 = (NH4 )H2PO4 H3PO4 + 2NH3 = (NH4)2HPO4 It is usual for these processes to be integrated with mixing and granulating plants to produce various grades of mixed fertilizers. This is accomplished by adding to the basic product, fertilizer salts, (ammonium sulphate, ammonium nitrate, potassium chloride), the mixture then being granulated. A flow sheet of a typical process for manufacture of concentrated superphosphate or ammonium phosphate based, mixed fertilizers is given in figure 7.5. The three fertilizers so produced ultimately all have the same agricultural value so that the selection of a particular process as a basis of manufacture will largely FIGURE 7.5.

MANUFACTURE OF FERTILIZERS BASED ON AMMONIUM PHOSPHATE OR CONCENTRATED SUPERPHOSPHATE DIAGRAMMATIC FLOW SHEET

PHOSPHATE ROC if WASH TO VACUUM WATER SYSTEM SULPHUR IC WASTE GASES ACID TO SCF UBBER TO VACUUM TO VACUUM . A FILTER ♦ SYSTEM SYSTEM COOLER

-EV• A PORATOR 1 STEAM wir CA SO4 TO WASTE S

• PREMI XERS PHOSPHORIC AC ID -4 RECIRCULATION AG I TATORS7' 4 F ILTER/ FEED SURGE TANK

WASH WATER RECYCLE PHOSPHOR IC AC ID TANK /PHO SPHORIC AC ID

WASTE GASES TO SC UBBER RECYCLE (0) AMMONIA OVERSIZE OR ....CRUSHER

IP' PRO DUCT F1NE$---..

SCREENS REACTORS WASTE GASES TO SCRUBBER POTASSIUM CHLORIDE

& NITROGEN SALT S -225- depend on the economics of its operation. The costs of producing ordinary and concentrated superphosphate and ammonium phosphate are given in 7.2.2. below. The cost estimates that follow in the rest of this chapter have been prepared by the author. They are based on operating data, factor costs and capital costs taken from the literature or,supplied by manufacturers in personal communications. The operating data, i.e. raw material and process requirements have been taken from the literature, in particular references 21, 57, 66, 70, 73 and 95 have been used for this purpose. Factor costs have been collected from trade journals which publish such information or by personal communication from manufacturers. Capital costs have been obtained from manufacturers of such plant.

7.2.2. Costs of producing water soluble phosphorus fertilizers. The following factor costs have been used throughout the calculations, n.b. the costs must of necessity only be approximate, since in many cases, especially for raw materials, they depend on long term contracts which the manufacturers may make and which will vary. They do however represent the current (1959) quoted market rates.

-226- Factor costs. Raw materials. ,Phosphate rock (33% P205) (ground) 110.00. per ton delivered Sulphuric acid 78% H2SO4 7.00

Industrial ammonia 152.50 II n to

Lime 98% CaO 6.00 II II 11

Utilities. Power ltd. per K.Vi.hr. Water 1/- per 1000 gallons Steam 11.20 per ton. Coal 16.00 pel ton.

Miscellaneous. Labour (Chemical industry average) 10.27 per man. hr. Cost of bagging and handling fertilizer. 11.80 per ton. Cost of transporting product. 11.50 per ton per 50 miles. For the purposes of comparison, the costs of operating the various types of process are calculated for a plant of 100 tons/day of P206 capacity.

7.2.2.1. Cost of manufacture of ordinary superphosphate (1959). Product contains 20% P205 of which 19% is water soluble. Plant to produce 100 tons/day P205 (water -227- soluble). This is equivalent to 525• tons/day ordinary superphosphate. Capital cost of plant (a) ;350,000. All requirements are per ton of superphosphate.

Item Quantity Unit Total cost /ton product Sulphuric acid 78% 0.45 tons ; 7.00 3.15 Phosphate rock 33% P205 0.60 tons ;10.00 6.00 Power 9 K.W.hr. 1.5d. 0.06 Labour 0.19 man. ;0.27 0.05 hr. Total operating costs(X) 9.26 .'.Total operating costs per ton water soluble P206 = ;48.8

Capital charges (b) 15%, 350 day year 0.29 Bagging, handling 1 ton ;1.80 1.80 Transport of product (c) 1 ton ;1.50 1.50 Total capital and distribution costs (Y) 3.59 .'.Total manufacturing cost (X Y) 12.85

...Total cost per ton water soluble P206(Z) = ;67.8 n.b. Z = 12.85/0.19. Notes:- (a) Cost of all process equipment only. Does not include buildings for housing plant or for storage, cost of site, -228- raw material handling facilities. (b) Capital charges 71% depreciation, 5% interest, 21% maintenance charges.

7.2.2.2. Manufacture of concentrated superphosphate. Product contains 48% of water soluble P205. Plant to produce 100 ton/day of P205, equivalent to 208 ton/ day concentrated superphosphate. Capital cost of plant 11500,000 (a). Requirements per ton concentrated superphosphate.

Item Quantity Unit Total cost /ton product (i) Manufacture of phosphoric acid (39% P205). Sulphuric acid 78% 1.36 tons 7.00 9.52 Phosphate rock 33% P205 1.20 tons 110.00 12.00 Lime 98% Ca° 0.02 ton 6.00 0.12 Power 56 K.W.hr, 1.5 d. 0.35 Water 8,700 gall. 1/-x10-3 0.44 Steam 0.36 tons 1.20 0.43 Labour 0.48 man.hr.L 0.27 0.13 -229- Item Quantity= Unit Total cost b/ton product (ii) Manufacture of concentrated superphosphate. Phosphate rock 33% P205 0.46 tons 110.00 4.60 Water 1250 gall. 1/- 0.06 Power 60 K.W.hr, 1.5d. 0.37 Coal 0.07 tons 6.00 0.42 Steam 0.09 tons 1.20 0.11 Labour 0.80 man.hr.1 0.27 0.22 Total operating costs (X) 28.77 Total operating costs per ton water soluble P205 = 60.00 Capital charges (b) 15%, 350 day/year 1.03 Bagging, handling '1 ton 1.80 1.80 Transport (c) 1 ton 1.50 1.50 Total capital and distribution costs (Y) 4.33 .°.Total manufacturing costs (X + Y) 33.10 .*.Total cost per ton water soluble P205 (Z) 168.5 n.b. Z = 33.10/0.48. Notes - see 7.2.2.1.

7.2.2.3. Manufacture of ammonium phosphate. Product contains 11% nitrogen, 48% water soluble P205. Plant to produce 100 tons/day P205, equivalent to 208 tons/ day ammonium phosphate. Capital cost of plant = 1500,000 (a). -230- Requirements are per ton ammonium phosphate.

Item Quantity Unit Total cost i/ton product (i) Manufacture of phosphoric acid. Sulphuric acid 78% 1.75 tons 7.00 12.25 Phosphate rock 33% P205 1.56 tons 1100.00 15.60 Lime 98% CaO 0.02 tons 6.00 0.12 Power 72 K.VT.hr. 1.5d. 0.45 Water 11,200 ga11.1/-x10-3 0.56 Steam 0.47 tons 1.20 0.56 Labour 0.65 man.hr.1 0.27 0.18

(ii)Manufacture of ammonium phosphate. Ammonia 0.134 tons 152.50 7.04 Water 120 gall. 1/-x10-3 0.01 Power 52 K.11.hr. 1.5d. 0.33 Coal 0.04 ton 11 6.00 0.24 Labour 0.70 man.hr.1 0.27 0.19 Total 37.53 Less allowance for•0.11 ton N 1100 11.00 Total operating costs (X) 26.53 Total operating costs per ton water soluble P205 = X55.3 -231- Capital charges (b) 1E% 350 day year 1.03 Bagging, handling 1 ton 1.80 1.80 Transport (c) .1 ton K1.50 1.50

Total capital and distribution costs (Y) 4.33 Total manufacturing cost (X + Y) 30.86 ...Total cost per ton water soluble P205 (Z) =X64.1 n.b. Z = 30.86/0.48. Notes - see 7.2.2.1.

It must be emphasized that these costs are only approximate and are intended to determine whether any process shows any significant advantage in production costs. Surh plants are not standard, to any extent, and their capital cost and that of operating them will depend on many variables, e.g. site of plant, what type of raw material handling facilities are required, provision of storage facilities for product, type of fertilizers to be made, integration with other manufacturing processes such as ammonia, sulphuric acid, ammonium nitrate plants, etc. All of these factors will play some part in determining the costs of production and accurate estimates can only be made for any given set of conditions. The foregoing analyses are intended as a guide to the probable order of the costs. -232— None of the processes would appear to offer any significant advantage in total manufacturing and distribution costs when these are compared on a unit basis of the P205 they contain. On operating costs alone ordinary superphosphate is the cheapest process, mainly on account of its simplicity, but also due to the lower process losses of materials. This advantage is however eliminated when costs of distribution are taken into account owing to its low concentration. Indeed if account were taken of administrative costs, cost of storage of product, (fertilizer sales are to a great extent seasonal) and general overheads, it is probable that the ordinary superphosphate process would be more expensive than the other two. It is interesting to note that by far the largest items of cost are those of the two raw materials, phosphate rock and sulphuric acid, which form between 70-85% of the total. The two superphosphate processes have the same acid requirement per mole P205 used, i.e. 2 moIN., whereas the ammonium phosphate process uses 3 moles acid per mole P205, i.e. the raw material costs are greater for the latter. The process is however competitive since ammonia is used as a low cost source of nitrogen which can then be credited to the process at the higher market price for -233- fertilizer nitrogen. This does in fact, with the factor costs used, give the process a slight cost margin in its favour. This is dependent on (a) the price paid for the ammonia, (b) value of fertilizer nitrogen on the market. The relative movement of these will be the determining factor as to whether the process is profitable or not. In conclusion, therefore, it can be stated that none of the processes offers any significant advantage over the others, within the accuracy of the estimates made. A decision on the choice of any process will depend on a particular set of conditions and each case would have to be investigated separately. It is however probable that the advantage will lie with the concentrated superphosphate or ammonium phosphate processes on account of their higher concentration. Further the trend in the market has been to the use of more concentrated fertilizers and it is doubtful whether a manufacturer in future years could market successfully a product based on ordinary superphosphate only, unless he could produce it at a significantly lower cost.

7.2.2. Other phosphorus fertilizers. There is a large group of fertilizers, which find commercial use in many countries, containing their phosphorus in a water insoluble form. The only fertilizer -234- of this type sold in the U.K. is basic slag. In many countries, e.g. France, United States, the availability of the phosphorus is determined by the quantity which is soluble in ammonium citrate solution(71) Itn the U.K. no such test is made and manufacturers are required to state only the total P205 content and the amount soluble in water(72). This regulation has undoubtedly restricted the development of such types of fertilizer in this country. The most important of such fertilizers are the nitrophosphates, where nitric acid is used to make the phosphorus available. Another group of such fertilizers are the thermal phosphates. The nitrophosphates became of interest initially when sulphuric acid was in short supply (1950-53), and alternative processes to superphosphate were sought. They have since become of some importance as fertilizers, both in the U.S. and Europe, but not in the U.K. Thermal phosphates have been used in Germany for many years in considerable quantities. In view of the importance of such processes, it is proposed to examine them in some detail to determine their suitability for British conditions. -235- 7.2.2.1. Agricultural value of non-water soluble phosphate fertilizers. A considerable literature exists on the trials carried out to determine the effectiveness of non-water soluble phosphorus fertilizers both abroad (73,74,75,76,77,78,79, 81,82) and in this country (74,82,83,84,85,86,87,88). The results of some of the trials carried out abrocd indicated that water insoluble phosphorus fertilizerr were as or more effective than water soluble ones. Other results indicated that they were less effective. Similar results have been obtained in the U.K. One general conclusion which would appear is that it is on acid soils that these fertilizers are most effective. On neutral or alkaline soils they are usually not so efficient as fertilizers. It is also claimed that while in the short run they may not be as efficient as water soluble fertilizers their long term efficiency is as great due to their larger residual effects. It has been concluded by Crowther(85), based on work carried out in the U.K. that:- "These results suggest that producers of nitrophosphate or similar fertilizers should not value the phosphate at more than three-quarters of water soluble phosphate .... For farmers and advisers it would appear that the phosphate in nitrophosphate behaves in much the same way as that in -236- high soluble basic slags". With so much contradictory evidence it is difficult to reach any conclusion as to the efficiency of water insoluble phosphorus fertilizers. Indeed it is beyond the scope of this thesis to do so. It is however evident that under certain conditions they are useful fertilizers. It would be of considerable importance if these conditions could be determined by a comprehensive series of trials, thus defining the efficiency of these types of fertilizer.

7.2.2.2. Manufacture of nitrophosphates. Nitrophosphates are manufactured, basically, by treating phosphate rock with nitric acid to give a mixture of monocalcium phosphate (as in superphosphate) and calcium nitrate. Crag (P0,32 + 4HNO3 > Oa(H2PO4)2 + 20a(NO3)2 The product of this reaction has however the following disadvantages:- (a) The presence of the extremely hygroscopic calcium nitrate makes the product readily pick up moisture with consequent danger of caking (89,90). (It has been reported that this can be so severe in humid atmospheres that the fertilizer reduces to a slurry (91)). (h) The reaction product consists of a thixotropic -237- slurry which does not set into a hard mass, as with superphosphates, drying is necessary and the product is difficult to granulate (83). In spite of these difficulties such a process is operated commercially in Switzerland (73), but it does not appear to laave been adopted elsewhere. General opinion states that the process is not suitable for the U.K. (83,89). Tlie first attempt to overcome the problem of calcium nitrate formation was to treat the phosphate rock with an excess of acid and to remove half of the nitrate by cooling./ The remaining solution is ammoniated to precipitate dicalcium phosphate and ammonium nitrate Ca(H2PO4)2 + Ca(NO3)2 + 2NH3----2Cal4PO4 + 2NH4NO3 Dicalcium phosphate is soluble in ammonium citrate but not in water. Such fertilizers, while still hygroscopic, store fairly well and are easy to granulate. The calcium nitrate by-product is sold as a straight nitrogen fertilizer. It is doubtful whether this process is of any commercial interest in the U.K. Not only is the cooling process expensive but it is unlikely that there would be any market for the calcium nitrate. It is of low nitrogen content and extremely hygroscopic. -238- An alternative approach is to ammoniate the reaction mixture as above, but converting the remaining calcium nitrate to calcium sulphate by the addition of ammonium sulphate Ca(H2PO4)2 + Ca(NO3)2 + 2NH3',---20aHPO4 + 2NH4NO3 (1) Ca(NO3)2 + (NH4)2804 CaSO4 + 2NH4NO3 Such fertilizers are satisfactory to granulate and store. They have the particular advantage of having a high N:P205 ratio, (a typical product contains 14% N, 14% P20). This type of process has been operated for a time in the U.K., (up to 1953), on a pilot plant scale.WO A difficulty in ammoniating monocalcium phosphate is that as the pH of the mixtures becomes more alkaline there is a tendency for reversion of the phosphate to non-available tricalciura phosphate. With reaction (1) the degree of ammoniation is insufficient to cause very serious reversion. This problem did however prevent for some time the adoption of another process which in theory has certain advantages. This consists of ammoniating in the presence of carbon dioxide so that the calcium nitrate is converted to calcium carbonate. Ca(H2PO4)2 + 2Ca(NO3)2 + 4N113 + CO2 + H2O 20aHPO4 + 4NH4NO3 + CaCO3 -239- The reaction mixture has to be alkaline in order to fix the carbon dioxide in solution, but this caused reversion of the phosphate. It was not until it was discovered that this reversion at high pH could be prevented by the addition of relatively small amounts of magnesium sulphate that commercial realisation of the process has become possible (92,93,94). It has the advantage that the greater part of the nitrogen is derived from low cost ammonia and not from the more. expensive (per unit of H), ammonium sulphate as in the previous process. All the phosphorus is soluble in ammonium citrate and the presence of calcium carbonate helps to reduce the hygroscopicity of the ammonium nitrate. The plant for manufacture of such fertilizers is extremely simple consisting of two reaction vessels followed by a conventional granulation plant. In the first vessel phosphate rock is dissolved in nitric acid while in the second, the reaction mixture so obtained, is ammoniated in the presence of carbon dioxide and the magnesium sulphate stabilizer. The fertilizer produce can then be granulated. Apart from the agricultural considerations already discussed, the determining factor as to whether such processes are of potential use in the U.K., will be the costs.of production compared to those of water soluble -240- fertilizers. These are given below for the ammonia- carbon dioxide process.

7.2.2.2.1. Manufacture of nitrophosphate by P.E.C. process (93,95). 1959.

Factor costs (see also 7.2.2). Nitric acid 70% HNO3. 132 per ton delivered. Magnesium sulphate. 115 per ton delivered. Product contains 16.2% N, 13.8% P205. To produce 100 tons P205 per day or 725 tons of nitrophosphate. Capital cost of plant = 11,000,000 (a). Requirements per ton fertilizer. Item Amount Unit cost Total /ton Nitric acid 70% HNO3 0.562 tons 132.0 18.00 Phosphate rock 33% P206 0.406 tons 110.0 4.06 Magnesium sulphate 0.025 tons 115.0 4).37 Ammonia 0.100 tons 852.5 5.25 Carbon dioxide 0.075 tons (b) 0.00 Coal 0.075 tons 6.0 0.45 Power 82 K.1 .hr. lid. 0.51 Labour 1.2 man.hr. 0.27 0.32 Total operating costs 28.96 -241- Capital charges 15%, 350 day year 0.59 Bagging, handling 1 ton 1.80 1.80 Transport 1 ton, 50 mls. 1.50 1.50 Total capital distribution charges 3.89 Total manufacturing cost 32.85 Less credit for 0.162 tons N at 1100/ton 16.20

Total 16.65 .'.Total cost per ton of P205 = V121.0

Notes. (a) Cost of plant, granulating equipment, buildings and storage facilities. (b) Carbon dioxide assumed to be obtained as waste product from ammonia synthesis plant.

The cost of producing phosphorus fertilizers by the nitrophosphate process is high and with the factor costs taken it is obviously uncompetitive with the water soluble processes. An examination of the economics shows that this is due to the extremely high cost of the nitric acid used to attack the rock,,i.e. the cost of nitric acid used per ton of phosphate rock is 144.2 as against that of sulphuric acid which is 15.7 for superphosphate and 17.9 for ammonium phosphate, per ton of rock. This extra cost is too large to be recovered by crediting to the -242- process the nitrogen from the ammonia at the fertilizer nitrogen price. (For those nitrophosphate processes which use less ammonia than in the above process the margin will obviously be even greater). Thus the nitrophosphate process under British conditions certainly does not show those advantages in cost which have so often been claimed for it. It must however be stated that the price of nitric acid has been taken at the current market rate which includes a transport charge. Manufacturers of nitrophosphate would probably produce their own nitric acid or locate their own plant close to an acid plant to eliminate the cost of transport. This would probably have a significant effect on its cost. For the nitrophosphate process to be competitive the cost of the nitric acid would have to be X20 per ton 70% HNO3 acid or less. It is probable that with closely integrated ammonia, nitric acid and nitrophosphate plants it would be possible to manufacture at a cost similar to that of water soluble phosphates. In view however of the premium that is placed in the U.K. on the latter form of phosphorus fertilizer it is doubtful whether it is' commercially feasible to produce nitrophosphates in this country. -243- 7.2.2.3. Thermal phosphates. Numerous attempts have been made to produce a fertilizer, containing a high proportion of P205 soluble in ammonium citrate, by fusion with various materials, so as to obtainta product comparable to basic slag (96,97, 98,99). Such materials have included calcium, magnesium or potassium sulphates and olivine. However the only process which has achieved any commercial success is that where the phosphate rock is fused with sodium carbonate and silica to produce a sodium silicophosphate slag. This has been operated in Germany for many years and also on an experimental basis in the U.K. (73,100,102,105) fog a short time. The manufacture consists of fusing the phosphate rock with sodium carbonate and sand in a rotary kiln at 1200-1400°C. In the U.K. a cement kiln was used for this purpose. The product is a material similar to basic slag and contains about 26% of P205 of which 24% is soluble in ammonium citrate. The following is an approximate estimate of the costs of production based on the operating data of a German plant (73).

-244-- Cost of production of a thermal phosphate, 1959.

Factor costs (see 7.2.2). Sodium carbonate 1,14.00 per ton delivered. Sand (silica) 5.00 per ton delivered.

Product contains 26% P205, 24% P205 soluble in ammonium citrate. Capital cost of plant Al0 per ton per year for plant producing 30 tons P205 per day.

Per ton of product. Item Quantiv Unit cost Total f/ton Phosphate rock 33% P205 0.850 tons A10.00 8.50 Sodium carbonate 0.250 tons A14.00 3.50 Silica 0.048 tons A 5.00 0.24 Power 50 K.W.hr. 1.5d. 0.31 Water 100 gall. 1/-x10-3 0.01 Coal 0.16 tons A 6.00 0.96 Labour 1.3 man.hr. A 0.27 0.35

Total operating costs 13.87

Capital charges, 15% 350 day year 1.50

Bagging, handling 1 ton A 1.80 1.80 Transport 1 ton, 50 mls. 1.50 1.50

Total capital and distribution charges 4.80

Total manufacturing and distribution cost 18.67 Total cost per ton P205 = A71.6 -245- The comparable cost for the highest grade basic slag is X59 per ton P205. This type of thermal phosphate is therefore not competitive by price with the former. The cost of production is of the same order as that of water soluble phosphates. It is unlikely that the farmer would be prepared to pay the same price for a fertilizer which contains water insoluble phosphorus as he would for one containing water soluble compounds. The thermal process would therefore appear to be not commercially feasible under British conditions.

7.2.3. Conclusions. An examination of the processes alternative to those producing water soluble phosphates shows that although there are several which are technically feasible, none of them show any economic advantage in their use. The continuation of the manufacture of phosphorus fertilizers based on superphosphates or ammonium phosphate would appear to be the best procedure both in meeting the present and the potential demand. None of the processes for producing water soluble phosphorus fertilizers show any significant economic advantage over the others. The adoption of any particular process will be determined by the particular set of conditions under which manufacture is undertaken. -246- RFFERENCES

Chapter• 1.

1 Quoted in Fertilizers and Manures, D.Hall, 5th Edition 19F5, Nrurray, page 3. 2 Quoted in Soil Conditions end Plant Growth, Sir E.J.Russell, 1937, Longmans, page 6. 3 T.R.Malthus, An essay on the principle of population as it effects the future improvement of society, 1798, J.Johnson, London, (Reprint for The Royal_ Economic Society, 1926, MacMillan.) 4 T.de Saussure, Recherches Chimiques sur la Vegetation Paris, 1804. 5 J.B.Foussingault, Ann.Chim.Phys.,V01.1,series3,18410 p.208. 6 A.T).Thaer, Grundsaetze der Pationellen Landwirtschaft, 4 Volumes, Berlin, 1809-12. 7 J. van LiebiRe, Chemistry in it's application to agriculture and physiology, London, 1840. 8 Ouated in Phosphates and Superphosphates, A.N.Gray, 1943, p. 106. 9 Sir P.J.Fussell, Soil Conditions and Plant Growth, 1937, Longmans. 10 The general results of Lawes' and Gilbert's experiments are sum,larised in The Book of Rothham8ted Experiments, D.Hall, Murray, 1917. 11 H.Tellriegal,H.Wilfarth, Zeitschrift der Ruebenzucker Industrie Peilageheft, Berlin, 1888. 12 S. winogradsky, Ann.Inst.Pasteur, 4,1890, p. 213. 13 A.N.Gray, Phosphates and Superphosphates, London, 1943. 14 w.r.T.T.Dactrard, Proc.Fert.Soc., No. 19, 1952. 15 British Patent, No. 9353. 16 British Patent, No. 9360. 17 i.A.Cowie, Potash, Arnold, 1951. -247- 18 M.Lamer, World Fertilizer Economy,1956, Stanford University Press. 19 Personal communication, Fisons Limited. 20 Sir Clavering Fison, Times Review of Industry, May 1957. 21 Personal comilunication, Fertilizer Manufacturers Assn. 2 Personal communication, British Sulphate of Ammonia u.anufacturerst Association, Ltd.

Chapter 2.

1 W.onthly DiF7est of Statistics, Central Statistical Office. 2 Annual Abstract of Statistics, Central Statistical Office. 3 Fertilizers, Production,consumption and trade in European countries, O.E.E.C., Paris. 4 British Sulphate of Ammonia Federation, Annual Reports, London. Annual review of the world production and consumption of fertilizers, F.A.O., Rome. 6 U.Ewa]d, Pecent developments in the world fertilizer market, Institut fur• Weltwirtschaft, Kie1,1957. 7 The index of industrial production, Studies in official statistics, No. 2, H.M.S.O., 1952. 8 Personal communication, Board of Trade. 9 B.H.S.Pell, Chem. & Ind. No. 24, 1959, p.724. 10 Personal communication, Fisons Limited. 11 Personal communication, Scottish Agricultural Industries ltd. 12 Chairman's Report, 67th Annual General Meeting, Fisons Ltd., Nov. 28th, 1958. 13 Anon. Chem, °- Ind. April 5th, 1958, p.406. -248- Chapter 3. 1 Minister of Agriculture. Hansard, 584,No.77, col 1447. 2 Annual review and determination of guarantees, 1958,cmd.390. 3 ibid, 1959. 4 Sir P.J.Pussell, Soil Conditions and Plant Growth, 7th Fdit., 1937, Longmans. 5 F.A.Mitscherlich, Die Festimmung des Duengerbeduerfnisses des Bodens, Berlin, 1924. 6 W.L.Parks, Economic analysis of fertilizer use data, Iowa State College Press, 1956, p. 113-13C. 7 F.M.Crowther,P.7ates, Fmp.J.Exp.Ag., 9,1941, p.77. 8 E.M.Crowther, Chem. & Ind.,1954, p. 1400. 9 National Agricultural Advisory Service, Surveys of fertilizer practice. 10 P.M.Church, Fmp,J.Fxp.Ag., 20,1952, p. 249. 11 D.A.Poyd, m.J.Lessells, J.Brit.Grassland Soc., 9,No.1,p.7. 12 Grassland Pock, Fisons Limited. 13 J.Clark, J.7.Eessel, Central-Agricultural Control, T.C.I. Ltd., Bulletin No. 7, London,,1956. 14 B.M.Church, J.Sci,Food Agric., 7,1956, p. 711. 15 F.M.Crowther, Path & west & Southern Counties Society Pamphlet No. 13, May 1945. 16 W.F.Raymond, J.Sci.Food Agric., 4,1953, p. 409. 17 R.A.Hamilton, J.Sci.Food Agric., 4,1953, p. 411. 18 Anon., Pert.Feed.Stuffs J., 39,1953, p. 63.

Chapter 4. 1 Annual review and determination of guarantees, 1957, 1958, co-imanda 109,390. -249- Chapter 6. 1 w.C.Peck, Chem. Pc Ind. 1958, p. 1674. 2 D.M.Newitt,J.M.Conway-Jones, Trans.Inst.Chem.Eng., 36,1958, p. 422. 3 R.A.Fisher, J.Agric.Sci., 16,1926, p. 492. 4 w.P.Haines, J.Agric.Sci., 17,1927, p. 264. ibid, 20,1930, p. 95. 5 D.Croney,J.D.Coleman, Foad Res.Tech.Paper, No.24,1952. 6 D.M.Newitt et al., Trans.Inst.Chem.Eng., 27,1949, p. 1. 7 J.O.Hardesty et al., J.Ag.Food Chem., 4,1956, p. 60. 8 A.T.Frook, "Tert.Soc.Proc., No.47, 1957. 9 w.P.mitchell, J.Sci,Food Ag., 5,1954, p. 455. 10 B.Faistrick, Fert,Soc.Proc., No. 38, 1956. 11 J.Silverberg, J.Agric.Food Chem.,6,1958, p. 442. 12 A.L.Papadopou]os, Ph.D. Thesis, London University, 1958. 13 D.M.qewitt,A.L.PaDadopoulos, Proc.Fert.Soc.,No.55, 1959. 14 Personal communication, Ministry of Agriculture and National_ Farmers' Union. 15 Personal communication, Fisons Limited. 16 Personal communication, British Road Services. 18 G.W.Cooke, T.Trit.Ag.Fng., Jan. 1954. 17 Anon., Prit.Chem.Fng„ 4,1959, p. 22. 19 J.W.S.Reith, J.Sci.Food Ag., 5,1954, p. 421. 20 G.W.Cooke, J.Sci.Food Pg., 5,1954, p. 429. 21 G.W.COoke,F.V.widdowson, Field Crop Abstracts, 8,1955,p. 233. -250-

Chapter 7. 1 A. Key, Gas works effluents and ammonia, Inst.Gas Eng., London, 1956. 2 A.Marsden, Ges J., 277,1954, p. 91. 3 A.D.Hall, Fertilizers and Manures, 5th Edit., 1955, London. 4 G.W.Ettle, Pr•oc.Fert.Soc., No.5. 5 H.Tod,K.Simpson, J.Sci,Food Ag., 7,1956, p. 511. 6 H.M.Lawrence, Gas World, 142, p.1671. 7 W.W.Law, Gas J,, 292,1957, p. 363. 8 B.H.J.Bell, Chem. & Ind., No. 24,1959, p. 724. 9 A.J.Hester et al„ Ind.Eng.Chem., 46,1954, p. 622. 10 L.S.Greenslade, Prit.Chem.Fng., 2.1957, p. 664. 11 W.H.Shearon,W.W,Dunwoody, Ind.Eng.Chem., 45,1953, p.496. 12 K.D.Jakob, Fertilizer Technology and Resources,Academic Press,Inc., New York, 1953. 13 G.S.Scott,r.L.Grant, U.S. Bur.Mines Inf.Circ.,No,7463,1948. 14 P.Miller et al., Ind.Eng.Chem., 38,1946, p. 7C9. 15 P.Miller,W.Saeman, Ind.Eng.Chem., 40,1948, p. 154. 16 Fisons Ltd., Advertisement, Times, July 6th, 1959. 17 W.H.Tonn, Chem.Fng., 62,No.10,1955,p. 186. 18 G.F.Chenowith, Chem.Eng.Prog., 54, No.4,1958, p. 55. 19 Anon., Petroleum processing, 11,No.5,1956, p. 127. 20 L.H.Cook, Chem.Fng.ProR., 50,No.7,1954, p. 327. 21 E.B.Frien, Pet.Fng., 26,No.13,1954, p. 46. 22 M.F.Keamy, Heat Engineering, 30,140.2,1955, p, 22. 23 Personal, Dr.G,."r.Cookel Rothamsted Exp. Station. 24 Personal, Dr.J.G.Hunter, Fisons Limited. -251- 25 U.S. Depb,Ag. Circular, No. 697, 1943. 26 W.G.Sandford et al., Science, 120,1954, p, 349. 27 W.W.Jones et al., Citrus Leaves, 35, No.11,1955, p. 12. 28 R.W.Staroska,K.G.Clark, Ag.Chem., 10,1955, p. 49. 29 C.F.Fedeman, Ind.Eng.Chem., 50,1958, p. 633. 30 Personal, Dr.B.Raistrick, Scottish Agricultural Industries Lt 31 I.N.H.Pizer, Proc.Fert.Soc., No. 44, 1957. 32 Y.D.Jakob0 w.Schol1, Commercial Fertilizer Year Book, 1955. 33 U.S.Dept.Ag., A.R.S. Special Report 22-35,1956. 34 W.B.Pndrews et al., Missisippi Agr.Exp.Sta.Bull.,1947, p.448. 35 ibid, 1948, p. 451. 36 W,P.Pnrews, Am.Fertilizer, 9,1947, p. 107. 37 J.G.Hammons, Soil Sci.Am,Proc., 12,1947, p. 266. 38 F.P.Collins, "Nrth.Carolina Ext.Serv.Circ., 369, 1952, 39 R.L.Luckhardt, Ag.Chem., 8,1954, p. 45. 40 H.Haines,T,Lange, Ind.Fng.Chem., 48,1956, p.966. 41 A.B.Phillips et al., J.Agr.Food Chem., 5,1957, p. 834. 42 G.H.Collings, Commercial Fertilizers, 5th Edit. 1955, Mcqraw-Hill 43 K.D.Jakob, Fertilizer Technology and Resources, 1953, Academic Press, New York. 44 A.v.Slack, ,T.Ag. Food Chem., 3,1955, p. 569. 45 P.P.Langguth et al., J.Ag. Food Chem., 3,1955, p. 656. 46 Times Sunip3ement, Home Grown Sugar, Jan. 5th, 1959. 47 J.H.Perry, Chemical Fngineers Handbook. 48 Personal, Pr.q.w.nooke, Pothamsted Exp. Station. 49 Personal, Dr.T."-.7unter, Tisons Limited. -252-

50 J.G.Frosheer,J.F.Anderson, J.Am.Chem.Soc., 68,1946, p. 902. 51 J.L.Hatfield, J.Ag.Food Chem., 6,1958, p. 524. 52 F.A.worthington et al., Ind.Eng.Chem., 44,1952, p. 910. 53 J.O.Hardesty, Ag.Chem., 10,1955, p. 51. 54 P.Parrish,A.Ogilvie, Calcium superphosphate and compound fertilizers: Their manufacture and chemistry, 7utchinsons, London, 1946. 55 W.f3-.M.Packard, Fert.Soc.Proc., No. 19, 1952. 56 T,P.Dee et el., Fert.Soc.Proc., No. 42, 1957. 57 W.waggam9n, Phosphoric scid,phosphates and phosphatic fertilizers, 1052, Rheinhold, New York. 58 A.Gray, phosphates and Superphosphates, London, 1943. 59 K.D.Jakob, Fertilizer Technology and Resources, 1953, Acade,lic Press, New York. 60 R.L.Demmerle,W.J.Sackett, Ind.Eng.Chem., 41,1949, p. 1306. 61 M.Shoeld et al., Ind.Fng.Chem., 41,1949, p. 1314. 62 J.J.Porter,J.Prisken, Fert.Soc.Proc., No.21, 1953. 63 T.V.A. Chem.Png.Peport, No. 5, 1949. 64 G.C.Tniskeep et el., Ind,Fng.Chem., 48,1956, p. 1804. 65 q.L.B.Pridger et al., Ind.Fng.Chem., 39,1947, p. 1265. 66 (1.Purnet, J.Ag.Food. Chem., 5,1957, p. 258. 67 J.Atwell, Ind.Fng.Chem., 41,1949, p. 1314. 68 C.J.Pratt, f-rit.Chem.Fng., 2,1958, p. 300. 69 Anon., Chem_. Ac, Tn9., No. 14,1958, p. 406. 70 Personal communication, Dor*-Oliver Inc. 71 0.E.E.C., Fertilizers: methods of analysis used in 0,F.F.C. countries, Paris, 1953. 72 0.E.E.C., Fertilizers. Trade regulations in 0.E.F.C. countries, Parisi 1951. -253-

73 0.E.E.C. Sulphuric acid and the manufacture of phosphatic fertilizers. Paris, 1953. 74 G.W.Oooke, Proc.Fert.Soc., No. 27, 1954. 75 F. van der Pauw, Landbouwk.Tijd sch., 50,1938, p. 95. 76 F. van der Pauw, Verslag.Landb. Onderzoek, 50,1945, p.207. 77 E.G.Mulder, iroc.Fert.Soc., No. 25, 1953. 78 H.T.Rogers, Agron.J., 43,1951, p. 468. 79 R.W.Starostka, J.Ag.Food Chem., 3,1955, p. 765. 80 D.W.Thorne et al., J.Ag.Food Chem., 3,1955, p. 137. 81 J.Karlovsky, N.Z.J.Sci.Tech., 38A,1957, p.770. 82 Agricultural value of phosphatic fertilizers which economise in sulphuric'acid. Paris, 1956. 83 W.d'Leny, Droc.Fert.Soc., No. 24, 1953. 84 R.Stewart, Bull.Docum.Ass.Int.Fabr.Superph., No.14v 1953, p. 13. 85 E.MiCrowther, Report Rothamsted Exp.Sta., 1953. 86 G.W.Cooke, J.Agr.Sci., 48,1956, p. 74. 87 G.W.Cooke et al., J.Agr.Sci., 50,1958, p. 253. 88 V.1'erampalam, High temperature phosphatic fertilizers, Ph.D. Thesis, London University. 89 T.PDee, Chem. & Ind., 1952, p. 801. 90 M.H.R.J.Plusje, Proc.Pert.Soc., 1951, No. 13. 91 T.PHignett, Chem.-Eng., May 1951, p. 166. 92 L.11'.Andres, Chimie et Industrie, 73,1955, p. 531. 93 L.i.Andres, Chem.Prod., August 1955. 94 French Patents, Nos. 1,031,992,(1951) 1,041,400,(1951) to 'Societe Potasse et Engrais Chimiques.' -254-

95 Personal communication, Humphreys and Glasgow Ltd. 96 G.L.Bridger,D.R.Brylan, Ind.Eng.Chem., 45,1953, p. 646. 97 T.P.Hignett,T.E.Hubbugh; Ind.Eng.Chem., 38,1946, p. 1208. 98 J.H.Walthall,G.L•Bridger, Ind.Eng.Chem., 35,1943, p. 774. 99 B.Schaetzel, Chem.Tech.(Berlin), 3,1951, p. 138. 100 Anon., Zeitschrift fur Angewandte Chemie, Oct. 1922. 101 S.J.Lloyd, Am.Fertilizer, 57,No.13,1922, p.38. 102 Ministry of Supply, Permanent records of research and development, Monograph No. 11, 108,Jan.1951, The production and agricultural value of silico-phosphate slags. Imperial College in association with the CAmbridgeshire Farmers Union. A STUDY IN THE USE OF FERTILIZERS

We would like you to answer the following questionnaire. This questionnaire, which is being sent to all members of the Cambridgeshire Farmers Union, is part of a survey being carried out by Imperial College with the cooperation of the Cambridgeshire Farmers Union and the National Farmers Union. The survey is an attempt to determine what factors are of importance to the farmer in deciding upon a fertilizer dressing. When you have completed the questionnaire would you please return it to Imperial College using the stamped, addressed envelope which is enclosed. Please leave the envelope unsealed. We would like to thank you for your cooperation in assisting with this survey.

Please state:-

Name.

Address..

The total acreage of your farm. acres.

The type or types of soil most common on your farm.

If you are not using any fertilizer this year tick here, BUT please return questionnaire. 4

Question 1. In making the decision on the size of the fertilizer dressing that you are using this season on each of your crops, did any of the factors listed below play any part in making that decision? Please tick those factors which you think played some part in making the decision.

Please tick here

a. The price you expect to get for the crop. b. The cost of the fertilizer. c. The value of the fertilizer subsidy. d. The size of th,-.; profit you made from the farm last season. e. A manufacturer's advertisement that you saw in the press. f. Advice given to you by your fertilizer merchant g. Advice on how much fertilizer to use that you received from a member of the National Agricultural Advisory Service. (N.A.A.S.) h. An article on fertilizers that you saw in the farming press. i. The results of a soil analysis carried out on your farm. j. A practical demonstration of fertilizer use that you have seen. k. The results that a neighbouring farmer to you has obtained by using a given dressing of fertilizer. 1. The results you obtained last year in your use of fertilizers. m. Advice given to you by a fertilizer manufacturer's representative. . . . • „ OOOOOO

(ii) If there are any other factors, not in the above list, but which you think have influenced you when deciding on the fertilizer dressings you would use, would you please state them below. Question 2. On average, is the amount of fertilizer that you are using this year on your various crops a. More than last year? b. Less than last year? c. The same as last year? Please tick either a or b or c.

Question 3. When you were deciding how much fertilizer to use this year did you a. Allocate a fixed budget, i.e. decide how much money you were going to spend on fertilizers, and then determine the individual fertilizer dressings for each crop within the framework of this budget? OR b. Decide first on the fertilizer dressings for each crop individually and then only estimate your expenditure on fertilizers? Please tick either a or b.

Question 4. When deciding on the fertilizer dressing for each crop do you give preference to those crops which give you the biggest cash return per acre? Please answer yes or no.

Date Signed