Proceedings of the

REGIONAL WORKSHOP ON MANAGEMENT OF SALT-AFFECTED SOILS IN THE ARAB GULF STATES

Abu-Dhabi, United Arab Emirates 29 October - 2 November 1995

RE ORGANIZATION OF THE UNITED NATIONS OFFICE FOR THE NEAR EAST . Cairo, 1997 Proceedings of the

REGIONAL WORKSHOP ON MANAGEMENT OF SALT-AFFECTED SOILS INTHE ARAB GULF STATES

Abu-Dhabi, United Arab Emirates 29 October - 2 November 1995

FOOD AND AGRICULTURE ORGANIZATION OF THE UNITED NATIONS· REGIONAL OFFICE FOR THE NEAR EAST Cairo, 1997 TABLE OF CONTENTS

FORWORD ...... III

Summary ofReco=ended Priority Areas for Follow Up ...... IV

I. SALINITY IN THE NEAR EAST: A REGIONAL PERSPECTIVE

1. An Overview of the Salinity Status of the Near East Region, by Ghassan Hamdallah ...... 2 2. Improvement ofItrigation and Drainage Systems for Soil Salinity Control in the Arab Region, by Mustafa AI-Hiba ...... 7

II. MONITORING AND RECLAMATION OF SALT-AFFECTED SOILS

3. Drainage and Salinity Investigation Techniques for the Diagnosis of Land Degradation, by Rami Zurayk ...... 12 4. Pilot Areas for the Reclamation of Salt-Affected and Waterlogged Soils, by Fernando Chanduvi ...... 20 5. A National Plan for the Reclamation ofIrrigated Areas Degraded by The designations employed and the presentation of the material and maps in this Salinity and Waterlogging, by Fernando Chanduvi ...... 24 document do not imply the expression of any opini?n whatsoev~r on the part of the 6. Soil Salinity Assessment: Recent Advances and Findings, Food and Agriculture Organization of the United Nallons concernmg the legal.'~tu~ of by J.D. Rhoades ...... 28 any country, territory, city or area or of its authorities, or concerning the delirnitallon 7. Hydraulic, Chemical, Physical and Biological Techniques for the of its frontiers or boundaries. Reclamation o{Salt-Affected Soils, by Amin Mashali ...... 34 8. Reclamation and Management of Salt-Affected Soils, by Fareed Abdul Nabi ...... 52 9. Measuring and Monitoring Soil Salinity, by J.D. Rhoades ...... 55

ID. TECHNICAL CONSIDERATIONS IN IRRIGATING WITH SALINE WATER

10. Water Management for Salinity Control, by Fernando Chanduvi ...... 64 11. Suitability Assessment of Water Quality for Irrigation, by J.D. Rhoades...... 67 12. Strategies for the Use of Multiple Water Supplies for Itrigation and ~ Crop Production, by J.D. Rhoades...... 80 13. Itrigation Systems, Water Quality and Management in Salt-Affected Soils: Case Study from the UAE, by Mohammad Sakr AI-Asam ...... 89

IV. CROP RESPONSE TO SALINITY

14. Use of Saline and Brackish Waters and the Relationship with Soil Management, by Gilani Abdelgawad, Abdel Nabi Fardous and Z. AI-Shabouni ...... 94 15. Availability of Nutrients, Fertilizer Management and Crop Tolerance Under Saline Conditions, by Amin Mashali ...... 100 16 . Soil-Plant-Water Relationships in Salt-Affected Soils, by Rami Zurayk...... 114 V. COUNTRY PAPERS

1. Crop Management in Irrigated Land Particularly in Salt-Affected Soils of the UAB, by Mohammad Hashim ...... 123 ii. Salinity Problem in the Soils and Water of Bahrain, by Ali Ahmed Nasir ...... 127 Ill. Salt-Affected Soils in Qatar, by Ghanem AI-Ghanem ...... 128 IV. Soil Resources in the UAB, by AhmedAI-Barshamgi...... 129 v. The Use of Salt-Affected Soils and Saline Water in Agriculture in the United Arab Emirates, by Rashid Al Mehrizi ...... 13 0 vi. Salt-Affected Soils in Saudi Arabia, by Ahmed S. AI-Shareef ...... 132 vii. Salt-Affected Soils in Kuwait, by Samir AI-Ghawas...... 133 VU1. Salt-Affected Soils in Oman, by Ishac AI-Gabri...... 134

VI. ANNEXES

Annex l. List of Participants ...... 136 Annex 2. Workshop Programme ...... 140

II FOREWORD

Salinity is a global problem highly affecting 20 to 30 million ha., rendering them unfit for food production. According to FAO, as much as double that area is classified as "less affected" by salinity but remains vulnerable and susceptible to improper irrigation practices, deforestation, overgrazing and other abuses.

In arid and semi-arid areas, such as in the Near East Region, irrigation plays an important role in the overall agriculture sector by producing over 1/3 of the agricultural output. In some countries where rainfall is scanty, irrigated areas are the backbone of their agricultural activity and the main contributors to food security.

In its Continuous efforts to combat hunger, F AO recently launched the "Food For All Campaign. Irrigation was given prime attention in the Campaign's Special Programme for Food Security (SPFS). Soil conservation/rehabilitation, water harvesting and small scale irrigation schemes also figured in prominently in SPFS.

The present volume documents for the "Regional Workshop on Management of Salt-Affected Soils in the Arab Gulf States". The F AO Regional Office sponsored the workshop in response to a request made by the Gulf States themselves.

It is our hope that the review of the latest on monitoring and evaluating the effects of salinity would contribute positively to national activities. Especially in adopting feasible practices to combating soil and water salinization.

ari ADGlRegional Representative for the/Near East

III Regional Workshop on Management of Salt-Affected Soils in the Arab Gulf States

SUMMARY OF RECOMMENDED PRIORITY AREAS

At the Closing Session of the above Regional Workshop, held in Abu Dhabi, the United Arab Emirates (29 October to 2 November 1995), the participants concluded that the issues listed below were deemed priorities and governments, organizations and research institutions in the Region were urged to give them due consideration:

1. Collect and update data and studies concerning salinization of soil and water resources, in order to assess the salinity problem and its impacts on agricultural and environmental aspects.

2. Each state of the Region was encouraged to monitor the irrigation-induced salinity and to evaluate the effect of using different water quality on the soil salinization process, for eventually making the choice of proper irrigation practices and quantities of irrigation water required.

3. The FAO Regional Office for the Near East was requested to prepare studies, hold seminars, expert meetings and training courses, as well as disseminating relevant documents for the purpose of information exchange and training of national cadre in their endeavour to combat soil salinization resulting from the expansion in irrigated agriculture.

4. Urge Governments of the Region to promote the use of non-conventional water resources, such as treated wastewater, with the proper choice of modern irrigation systems; and request FAO and the Regional Office to provide the necessary information and relevant research studies on the subject in order to utilize such "special type" of water with full consideration to public health and the environment.

5. The need to hol~ "specialized courses" for training national cadre on the practical aspects of adopting new technologies available related to modern irrigation systems, as well as new methods for salinity monitoring and assessment.

6. The real necessity to integrate the salinity studies and related research results within the/agricultural extension programmes in order to ensure the exposure of farmers to such information.

7. Urge governments of the Region to draw plans for conducting integrated studies for salinity monitoring and assessment, including all related aspects of soil, water, crops and the environment in order to achieve meaningful and applied results.

IV 1. Salinity in the Near East: a Regional Perspective. An Overview of the Salinity Status ofthe Near East Region

Ghassan Hamdallah Regional Soils Officer FAD Regional Office for the Near East

INTRODUCTION

The Near East is a semi-arid to arid region, where irrigation is necessary for agriculture: irrigated lands cover 34% of the arable land area and account for 75% of crop production. With one of the highest rate of population growth, the region is highly dependant on imported food, mainly from Europe and the US. A quick look at the region's natural resources reveal that the situation is very critical due to the limited arable land and water resources. Therefore, agricultural development plans and policies for land management are required in order to ensure sustainable productivity, better use of land and water resources and to reduce environmental degradation. Soil salinity is an ancient problem in the Near East. The people of Mesopotamia shifted from wheat to barley production in 2500BC because of salinity (Jacobson and Adams 1958). Salinization is initiated by the expansion of irrigated agriculture. Water logging and salinization often follow, if irrigation is poorly managed. Reclamation is economically, socially and environmentally costly.

LAND RESOURCES IN THE NEAR EAST REGION

Arable land constitutes 6.8% of the total land area of the Region. Pastures account for 26% and 7.2% is forest land. Mismanagement of land and water is a major problem. This is often due to insufficient knowledge of these resources and of their management methods. In some cases, agricultural and commercial policies prohibit implementation of good management practices.

Table I: Arable land per capita, irrigated areas, and salt affected soils in the Near East Region

Population Land Area Arable land Arable land Irrigated land Salinlzed area Total COUNTRY in 000 in 000 Ha in 000 Ha per capita in 000 Ha by irrigation Salt-affected COVNlRY 1993 1993 1993 1993 (Aaua~tat) in 000 HA in 000 HA - AFGHANISTAN 17691 65209 7910 0.447 2386 • 3103 AFGHANISTAN ALGERIA 26722 238174 7300 0.273 446 • 3150 ALGERIA BAHRAIN 535 68 1 0.002 3 .. 1 ... 10 BAHRAIN CYPRUS 726 924 110 0.152 40 ... 17 cypRUS EGYPT 60319 99545 2450 0.041 3246 .. 1 210 • 7360 EGYPT IRAN 64 169 163600 16650 0.259 7264 .. 2100 • 27085 IRAN IRAQ 19454 43737 5250 0.270 3525 • 6726 IRAQ JORDAN 4082 8893 315 0.077 64 ... 12 180 JORDAN KUWAIT 1 775 1 782 5 0.003 5 .. 4 209 KUWAIT LEBANON 2806 1023 216 0.077 88 · LEBANON UBYA 5048 175954 1815 0.360 470 • 2457 UBYA MALTA 361 32 12 0.033 1 MALTA MAURITANIA 2161 102522 205 0.095 49 640 MAURITANIA MOROCCO 25945 44 630 9256 0.357 1093 • ·1 148 MOROCCO OMAN 1992 21 246 16 0.008 62 · 290 OMAN PAKISTAN 132941 77 088 20790 0.156 14327 • 4220 • 10456 PAKISTAN QATAR 529 1 100 7 0.013 13 ... 67 QATAR SAUDI ARABIA 17119 214969 3650 0.213 1608 • 6002 SAUDI ARABIA SOMAUA 8954 62734 1000 0.112 50 • 5602 SOMAUA SUDAN 26641 237600 12900 0.4B4 1900 • 4874 SUDAN SYRIA 13696 18378 5120 0.374 1013 .. 60 532 SYRIA TUNISIA 8570 15536 2987 0.349 355 . 200 990 TUNISIA TURKEY 59597 76963 24481 0.411 4070 ... 41 • 1 278 TURKEY UNITED ARAB EM 1816 8360 29 0.016 67 • 1 089 UNITED ARAB EM. YEMEN 13196 52797 1376 0.104 383 YEMEN NEAR EAST., REGION 516845 1 732864 123851 0.240 42528 7848 83 26~ NEAR EAST REGION Sources. Mashali, 1995 .. AQUASTAT,1997 ***Other In high or medium income countries such as in the Gulf countries, Lebanon and It is established that irrigation plays a major role in agricultUre development and food Jordan, agricultUral land is limited. High costs of investment result either from land or water productlOn. On the world scale, the irrigated land area has increased from 94 million ha in unsuitability, or due to climatic limitation. In lower income countries like Sudan, Afghanistan 1950 to 253 million ha in 1985 (Umali, 1993). This area accounts for the production of 1/3 of and Pakistan, the per capita of arable land is much larger, but access to investment is a major the world's crops, although it constitutes only 17% of the land area. hindrance to agricultUre development, in spite of the availability of suitable land. From Table 2 above, irrigated land area in the Region has increased from 27.8 million It is worth noting, in Table 1, that 60% of the agricultUral land of this Region is shared ha in the year 1961 to 42.5 million ha in 1997 (AQUASTAT, 1997). This increase has taken among four countries: Sudan, Turkey, Iran and Pakistan. In the Gulf states, 95% of the place mainly in .Afghanis.tan, Egypt, Iran, Iraq, Libya, Saudi Arabia, Syria and Turkey. It is agricultUral lands belong to Saudi Arabia and 5% is distributed over the other five countries. expected that this area Wlll keep mcreasing at an annual rate of 1.4% in the coming few years m spIte of the "deficiency in water resources. IRRlGATED AREAS AND TIffi PREVAILING METHODS OF IRRIGATION IRRIGATION-INDUCED SALINITY The agricultUral sector is the main consumer of water and accounts for 80-90% of water use in 80% of the countries of the Near East. This figure drops significantly on the .. The inIportance of salinity is increasing world-wide because the inIproper utilization of world's scale, except for Africa (88%) and Asia (86%), compared with 33% for Europe and lITIgated areas, deforestation, overgrazing and other human activities result in the so called 49% for North America. The world average is 69%. The demand on water is expected to "secondary salinization". This be.comes more often in arid and semi-arid regions, mainly in increase by the year 2000 and beyond because of the increased need in all sectors. dev~lopmg countrIes of ASIa, Africa and Latin America regions. By FAO estimates, some 45 Although irrigation leads to an increase in food production, the losses and inefficiency mIllIOn ha are salt-affected in irrigated areas and other 32 million ha in non-irrigated areas. in water use, as well as the mismanagement of water networks cause salinization and land Secondary salinization occured and continues since the irrigation water also contains degradation. It is commonly believed that the quantity of water used in the Gulf area is three salts, which accumulate along with the natUral salts in the soil and are concentrated and times higher than what is required. The adoption of new irrigation practices (sprinkler and drip) redistributed as the result of evapotranspiration cupillary action and water movement through have led to water savings, but also to salinity build-up where washing of the excess salts was the soil profile. Dramage and leaching practices require installation of costly networks that are neglected. Table 2 shows the irrigated areas and the prevailing irrigation methods in the Near beyond the economic and technical capability of many countries. In addition saline East Region countries. It could be noted that in a good number of these countries, the less­ goundwater, when used for irrigation in arid and semi-arid regions, aggravates the situation. efficient surface methods (flood, border, furrow, etc.) are still predominant which are bound to Independent of these problems, the pressure continues for the expansion of agricultUre into use more water, and probably entail waterlogging and salinization. margmal lands to meet the needs of an expanding population. "Bio-Saline Agriculture" could offer an alternative for the use of saline ground and surface waters for agricultUre production, Table 2: Irrigated land area and irrigation method in the Near East part:Icularly for growmg some halophytes of economic potential. This concept, however, needs to be further evaluated f~r establishing that successful cultivation of salt-tolerant plant species Country Irrigated area Irrigation system (OOOha) (% of irrigated area usmg salme water IS feasIble, as well as the sustainability of this approach related to the effects 1997 Surface Sprinkler Drip on soil, water and the environment. Bahrain 3 64 - 36 Kuwait 5 - - - SALINITY AS A GLOBAL PROBLEM Oman 62 94 3 3 Qatar 13 - - - Saudi Arabia 1,608 34 64 2 Soil salinity is a world-wide problem. FAO surveys show that 20-30 million hectares UAB 67 38 17 45 are classified as "highly affected soils" and 60-70 million ha are also affected but to a lesser Egypt 3,246 93 4 3 ext~nt. Two to three million ha are dropped yearly from the production circle due to Syria 1,013 97 3 - sallIDZatIon, and increases to around 7 million ha when other degradation causes are added 3,525 - - - Iraq (some estimates go up to 10 million ha yearly). In the US for example, 28% of the agricultUral Jordan 64 31 9 60 Lebanon 88 - - - land IS salt-affected. Malta 1 - - . In the Near East, the area of salt-affected soils varies geographically according to Cyprus 40 5 - 95 climate, agncultUral practices, irrigation methods and policies related to land management. - Yemen 383 - - Salt-affected soils range between 10-15% in countries such as Algeria to 50% in Iraq (Table Libya 470 - 100 - 3). Tunisia 355 80 18 2 Algeria 446 - - - It should be noted, however, that the presented figures were taken from various Morocco 1,093 90 9 1 references and some of these were not recent citations. The salinity problem is known as a Mauritania 49 - - - dynamic one and the continuous monitoring and assessment is a must for always updating the - - Sudan 1,900 - sal1Illzed areas, as well as, the reclaimed and rehabilitated lands in each country. Somalia 50 - - - Pakistan 14,327 - - - Iran 7,264 99 - - Afghanistan 2,386 - - - Turkey 4,070 95 - - Total 42,528 Source. FAO, AQUASTAT. 1997

2 3 Tbl3Efa e SIma td e areas 0 f Salt - affec t edid' an m s0 me selected countries The Gulf Countries Excluding Saudi Arabia, the arable land in the Gulf region is very Percentage of salt- Percentage of salt small. That is why land management to insure continual prodUctivity is essential. Agriculture is affected land (%) Country affected land (%) Country hindered by several factors such as desertification, urbanisation, a dry climate and the lack of fresh water. The reader is referred to the country papers in this volume for a recent assessment India 11 Algeria 10-15 of salinity in the Gulf countries. Egypt 30-40 Pakistan 21 Sudan 20 Mexico 10 CONCLUSIONS Iran 30 China 23 Jordan 16 Turkmenistan 48 Syria 30-35 USA 28 In the struggle against salinity in the Near East, it is important to implement the Iraq 50 following: Exchange of expertise, information and reports concerning the best land management AN OVERVIEW OF SALINITY STATUS IN THE REGION approaches and irrigation techniques. Continuous documentation and updating ofland and water surveys and statistics following Egypt The cropped land in Egypt is about 3.25 rnillion ha. In spite of the reclamation plans modern methods and progranunes which are readily obtainable from the F AO or from other and projects, the annually reclaimed land area is offset by the area degraded every year, mainly international organisations due to salinity. About one third of the cropped land is situated to the north of the Nile Delta and Operation of a network for the Gulf countries in order to exchange information and AJ-Fayoum. Surface irrigation was prohibited in the Northern desert and replaced by drip and experience. The FAO Regional Office (RNE) in Cairo could be in charge of the co­ sprinkler irrigation-for better water application efficiency. ordination of this network. The use of treated waste-water for agriculture is an old practice. Currently, it is being evaluated in order to supplement the water resources. The drainage of agricultural lands has REFERENCES also received a lot of attention. Statistics show that about 2.9 rnillion ha of agricultural land in Egypt have drainage networks. ESCWAlFAO. 1994. Land and Water Policies in the Near Eastar East. Case Studies on Egypt, Jordan and Pakistan. Report No. ESCWAlAGRl1994/1 0, UN, New York. Iraq The published data describing the situation in Iraq is very contradictory. According to FAO. 1990. Production Yearbook, Rome. Boyadgiev (1989): 1,323,000 ha are affected by low to medium salinity ~d 6,679,000 ha are FAO. 1993. Production Yearbook, Rome. highly saline. FAO. 1993. AGROSTAT, FAO, Rome. FAO. 1994. The State of Food and Agriculture, FAO, Rome. Jordan The cropped land of Jordan is about 310,000 ha of which 66,000 are irrigated. FAO. 1997. AQUASTAT. Irrigation in the Near East Region in Figures. FAO Water Reports Eighteen percent of this land is salt affected and found mostly in the Jordan Valley (95%), nO.9. Rome. where 3000 ha have a salinity of 4-15 dS/m, 5,600 ha have asalinity of 15 dS/m and 3,300 ha Jacobson, T., and R. Adams. 1958. Salt and Silt in Ancient Mesopotamian Agriculture. are considered saline -alkaline. There are also regions with varying salinity on the border with Science 128: 1251 - 1258. Syria and Iraq. Mashali, A. 1995 RNE. 1995. Irrigation with Wastewater in- the Near Eastar East, Cairo. FAO Regional Sudan The arable land in Sudan is about 105 million ha of which 7.6 million ha are cropped. Office for the Near East. Unpublished Data. The salt affected area covers 0.9 million ha found mainly in the largest irrigation project in the Umali, Dina. 1993. Irrigation-Induced Salinity. A growing Problem for Development and the world, "The Jazira Project" and in the state of Khartoum (70% of total area); especially along Environment. The World Bank, Washington, D.C. the White Nile. World Resources Institute. 1987. Basic Books, Inc., New York.

Yemen The cropped land of Yemen is about 1,376,000 ha of which 475,000 ha are irrigated. In the report presented to ESCWA on the national project to stop desertification, 3,830,000 ha in the Northern governates alone were classified as salt-affected. It is obvious that this figure includes all the arable land rather than the cropped land. It was also mentioned that the intrusion of sea water is the major cause of salinization in the coastal regions. The figures mentioned above should be updated and new surveys should be carried out in order to evaluate the real extent of the problem. This is expected to be done when!the land survey project, currently under way and which is aided technically by the FAO, is completed.

Tunisia The arable land in Tunisia is estimated to be around 8.7 million ha, of which 3.9 million ha are cropped and 0.5 million ha are salt-affected(17% of the arable land). This salt affected land is found in the middle and the south of the country and in some northern coastal regions. It is worth mentioning that a large proportion of this land had already been reclaimed.

4 5 Improvement of Irrigation and Drainage Systems Saline soils accumulate sufficient soluble salts to interfere with the growth of most plants. Sodium salts are in relatively low concentration in comparison with calcium and magnesium salts. for Soil Salinity Control in the Arab Region Saline soils are often recognized by the presence of white crusts on the soil, by spotty stands, and by stunted and irregular plant growth. Saline soils are generally flocculated, and the permeability is Mustafa Al-Riba Director Water Resources Management comparable with that of similar non saline soils. Arab Org~ation for Agricultural Development The principal effect of salinity is to reduce the availability of water to the plant. In cases of extremely high salinity, there may be curling and yellowing of the leaves, firing on the margins of INTRODUCTION • the leaves or actual death of the plant. Long before such effects are observed, the general nutrition and growth physiology of the plant will have been altered. Salt-affected soils are a serious constraint for crop production in many parts of the Arab Some crop plants can tolerate relatively large amounts of salt; others are more easily countries which are characterized by arid or semi-arid climate. Salinity problems are mainly due to injured. The tolerance of crops may somewhat vary, depending on the particular variety grown, the inadequa~e irrigation water management. Most of the Arab countries hav~ mobilized tre~endous cultural practices used and the climate. investments for the development of large irrigation schemes to enhance agncultural productlOn ~d In order to keep the salinity under safe limit with regard to the tolerance of different crops, meet their food self-sufficiency. Unfortunately, these projects have not been usually acco~pame? leaching of soluble salts from the root zone is essential in irrigated soils. Leaching is actually the by adequate irrigation water management and appropriate drainage systems for controlling sOli only effective way, when associated with proper crops practices, by which the salts added in the salinity build-up. . . irrigation water can be removed satisfactorily. Sufficient water must be applied to dissolve excess This situatio13. is most serious in the Nile Delta in Egypt, the Euphrates Valley III Iraq and In salts and carry them away by adequate drainage. This means that in addition to frequent irrigation, Syria. The coastal areas of the United Arab Emirates, Kuwait, Morocco and Algeria face similar it is important to envisage in the management of the irrigated schemes the application of excess situations. water to meet the leaching requirements and keep all adequate salt balance in the soil taking into For instance, in Iraq it is estimated that out of the total cultivable area under irrigation (8.0 account the soil permeability, drainage conditions and salt tolerance of the crops under million ha in the middle and south of the country), about 50 to 60% are seriously affected by consideration. salinity and water logging. In the Euphrates Valley in Syria, the introduction of intensi,:,e cu~t~vat~on of cotton under irrigation in the early fifties has resulted in a serious problem of sod sallnlSatlOn Th1PROVEMENT OF IRRIGATION MANAGEMENT AND DRAINAGE TO CONTROL SOIL which, at present, affects about 50% of the total irrigated area. ~ Egypt, sOi.1 salinity. affects about SALINITY 60% of the total irrigated areas. The salt-affected lands are mainly located In the NIle Delta. The remaining 40 to 50% of irrigated lands contain sufficient salt to impair crop growth.. . Control of soil salinity in irrigated schemes can be achieved only if a proper salt balance is This rather gloomy picture of irrigated agriculture in the Arab Region could be 1illproved .If maintained. This involves several factors such as leaching practices, improved irrigation methods, adequate irrigation management and drainage are proper!y introduced wi~~ th~ irrigated schemes. irrigation water quality, drainage conditions, groundwater table, cropping patterns and local The purpose of this paper is to discuss ways for Improvement of 1ITlgatlOn management and climatic conditions. drainage for efficient soil salinity control. . To curb this situation, careful irrigation management is needed in order to provIde Leaching favourable conditions for the leaching of soluble salts accumulated in the irrigated soils. Of equal The leaching of soluble salts from the root zone is essential in irrigated soils. In sub-humid importance is also the design of adequate drainage systems to remove excess irrigation water and region, where irrigation is provided on a supplemental basis, salinity is usually of little concern prevent the rise of the water table in order to control soil salinity build-up. because rainfall is sufficient enough to leach out any accumulated salts. However in the case of arid and semi arid zones, leaching is the only way by which the salts added in the irrigated water can be Occurrence of Soil Salinization in the Irrigated Schemes re!lK)ved satisfactorily. Sufficient water must be applied to dissolve the excess salts and carry them away by proper drainage. Irrigation water, whether from surface streams or groundwater sources, usually contains dissolved salts. When applied to the soil with irrigation water, salts remain in the soil u~ess they Leaching requirements are flushed out by drainage water or removed by the harvested crop. Usually the quantIty of s~t In order to maintain an acceptable .level of salt within the root zone, the leaching removed by crops is so small that it will not make a significant contribution to salt removal: This requirements define the fraction of the irrigation water which must be passed through the root means that with every irrigation a certain amount of salts is added to the soil. !he concentr~tlO~ of zone to keep soil salinity at a specified level. Under conditions of adequate drainage and with no soluble salts in the soil increases as water is removed from the soil by evaporatlOn and transprratlOn. leaching by rainfall or salt removal by the crop, the leaching requirement is defined as Evapotranspiration creates a suction gradient which will produ~e upward flow, especially. i~ the water table is near the soil surface. This is the process by which many soils become salinized. LR=ECjECd Soluble salts increase or decrease in the root zone depending on whether the net downward LR = Leaching requirement movement of salt is less or greater than the net salt input from irrigation water. EC = Electrical conductivity of irrigation water (i) or drainage water (d) If the leaching effect of rain water is of significance, it may be taken into account.

7 6 Improvement of Irrigation Management to Control Soil Salinity Leaching practices Since salt is often more damaging to seedlings and young plants than to mature plants, . Soil salinization in !rrigated area vary more or less depending on the type of irrigation application ofleaching water are often effectively made during a preplant irrigation to reduce salt in tec~qu~s used. Furrow JrngatIon must be practised with considerable care, particularly during the the seed zone as well as to reduce salinity through the soil profile. In some situations excess surface germmatIon stage. Due to the upward movement of water towards the surface of the beds, salinity water is available in the winter time and may be used for leaching, in other situations leaching water may .concentrate on the. seed row. Most crops are particularly sensitive at the germination and may be a part of every irrigation application depending on the level of salinity which may be seedllllg s:ages ar:d specIal care must be taken to avoid salinity build up during these critical stages. tolerated by the cultivated crops. It is very important when defining the leaching requirements to . . WIth slopmg beds .w.her~ salt is transported beyond the seed row, salinity hazards may be envisage'the possibilities to maintain a high level of salinity in the soil during the growing season SIgnificantly reduced. Pre-ImgatIon for leaching the salt under the bed center may be appropriate to particularly during the tolerance stages of the cultivated crops; and keep low salinity levels during allow crops t? overcome damage at this critical early stage. In general less problems are the sensitive period. encountered WIth border irrigation. ' In arid and semi arid zones, as it is the case of the Arab Region where water resources are In Jordan, drip irrigation has provided good results even when using highly saline water. very scarce, leaching should be designed so as to maximize crop production per unit volume of Due to the contInuous. su~ply of water, the high salt concentration build-up is reduced. However, water applied for irrigation and leaching. after the harvest, l~a~hing IS ~equlfed. t~ lower the salt content in the soil before sowing a new crop. It has been shown that, except where salt is concentrated at the bottom of the root zone, .. ~pnnkler ~gatJon m the Jrngated schemes of the Arab countries has affected soil irrigation water is better conserved when leaching is practised periodically rather than by salilllZatl~n. to ~arymg degrees depending on the type of irrigation management. In general, more maintaining a tolerable salt level by regular application of extra water . frequent JrngatJOn and periodic leachings are required in order to lower the salt content in the soil' Salinity undoubtedly causes reduction in yields but the results obtained in some trials in but again there is no single appropriate management method to be applied in all situations. Th~ Morocco, Tunisia, and Jordan have shown that unless an increase in salinity occurs at a time when !ocal ~nVlfonmental conditions should be carefully studied before deciding which appropriate the crops are particularly sensitive, there is no cause for alarm. In the case oflow permeability soils, ImgatJOn management should be adopted. it is advisable whenever possible to delay leaching until after cropping. .. . However the. mo.st se~ous problem associated with sprinkler irrigation is the quality of the :~gatJon water: Sprinkling WIth saline water can cause considerable damage to crops due to salt NEEDS FOR ADEQUATE DRAINAGE TO CONTROL SOIL SALINIZATION lllJUry of the foliage.

With the necessity of using additional water beyond the needs of the cultivated crops to Effect ofIrrigation Water Quality on Soil Salinization provide sufficient leaching, it is imperative that there be adequate drainage for water passing through the root zone. Drainage through the underlying soil may be adequate, otherwise, open or Many i:n~ation schemes in the Arab region, particularly in the Euphrates Valley in Syria tile drains must be provided. In no case should the water table be permitted to rise near the soil and I~aq, are Imgated WIth deep groundwater having high salt content, without application of surface. suffiCIent leaching due to water scarcity and pumping cost. This result in very low net downward Water will rise in the soil above the watertable by capillarity. The height to which water will movement of water through the root zone, and salinization is enhanced. This problem occurs also in rise above a free water surface depends on soil texture, structure and other factors. Water reaching some parts of Jordan, Libya and Morocco. the surface evaporates, leaving a salt deposit. In order to alleviate t~ese problems it is necessary to investigate the possibilities for mixing Some experiments conducted in Egypt with covered drains have resulted in satisfactory the ~umped grou~d water WIth surface water, if any, in such a way as to lower irrigation water control of the watertable. There are actually about 2 million hectares in which covered drains have Sallllty, and proVIde more water supply for leaching purposes. This, of course underscores the been installed. Monitoring this drainage system has shown very significant improvement of crops need for all integrated irrigation management, using surface water and groundwat~r. yield and soil salinity controL The drainage requirement of any irrigated scheme should be determined at the design stage of the irrigated scheme in such a way that the drainage system is properly designed with respect to depth, spacing and drain discharge capacity. Adequate drainage system implies a good hydrogeologic investigations. All alternative solutions which may be available for resolving drainage problems should be carefully studied. It is also important at the preliminary stage to establish pilot plots to test the methods. Experiments should be conducted over at least several seasons. Finally it must be emphasized that successful selection and operation of a particular drainage method in particular area may not be suitable for another area because hydrogeological conditions may vary from one area to another.

8 9 II. Monitoring and Reclamation of Salt-Affected Soils

10 Drainage and Salinity Investigation Techniques for the Diagnosis of Land Degradation

Rami Zurayk, American University of Beirut, Lebanon

WATERLOGGING, SALINITY AND LAND DEGRADATION

Irrigation in arid zones typically entails the hazard of developing a high water-table condition, resulting from the application of water at rates greater than the combined rates of evapotranspiration and of natural groundwater drainage. In situations where the salt load of the irrigation water is high, evapotranspiration will lead to the accumulation of salts in the root zone, requiring the application of extra amounts of water for leaching. This water percolates downwards and tends to augment the water table. Open channel canals are often poorly lined, especially in developing countries. Conveyance losses from poorly lined canals intensify the problem by increasing the amount of seepage water. As the water table rises, accelerated capillary rise coupled with evaporation at the soil surface will result in the precipitation of water-borne salts at the soil surface. The rate of soil salinity accumulation will depend upon irrigation management, salt concentration, depth of the groundwater, soil type and hydraulic conductivity and climatic conditions. It can be seen that the balance between leaching (i.e. removing the excess salts from the root zone) and drainage (preventing water table rise from the leaching water) is critical for maintaining productivity in natural and agroecosystems. Success in balancing these two elements is the key to the prevention of land degradation. Monitoring for optimal management is therefore a key issue in saline agriculture, as well as for the preservation of ecosystem integrity. Methodologies for the diagnosis of drainages' salinity problem have been developed over the past four decades and have now become almost standard. This paper is therefore a compilation of the most commonly used techniques, obtained from the sources that appear in the list of references.

DIAGNOSING DRAINAGE AND SALINITY PROBLEMS

Depending on the scope and intended use, monitoring data can be collected on an agricultural field (or micro) scale or on a basin-wide (macro) scale. National monitoring programs for policy include both approaches (see figure 1).

Data Acquisition: Field Level Methodologies

Field investigations require the collection of information at field or micro basin level, both prior to and during the operation of a project. A salt balance, for instance, is required for the prediction of water table level and soil salinization. In order to achieve proper investigation and monitoring, the following is required: • Current water table level, flow patterns present and past. • Qualitative and quantitative detennination of soil and water salinity with seasonal patterns. • Soil hydraulic and chemo-physical properties, including total soil reserve in the irrigated soil layer and their vertical and horizontal distribution.

11 Sampling for data acquisition • Soil Soil s~linity problems are identified by measurements of soil salinity, soluble salts, and toxic Salt affected soils are highly heterogeneous (Beckett and Webster 1971), and the nature of matenals such as heavy metals and boron. Other types of measurements that can assist in the this variation must be considered in order to ensure that the data collected is representative. The diagnosis and monitoring are water content, water holding capacity of the soil soil texture essential elements of sampling are: soil infiltration rate and hydraulic conductivity. " • Proper site selection. • Water quality • Representative srunples of the total population. • Optimum number of samples and location Measurements made on water samples include salinity, soluble salts, toxic elements, and pH. Other useful measurements for management strategies include flow rates volume and application rates. ' There exists statistical techniques for estimating sample size depending on the variability of the population and the accuracy and confidence level required. These require the knowledge of the standard deviation (SD) and the coefficient of variability (CV), usually unknown at the time of Water table depth and ground water quality sampling. It is suggested that a CV of 35-45% is appropriate for salt affected soils (Blaine and To detennine the effect of a water table on soil salinity, it is necessary to detennine the depth Grattan, 1990). Subsequent samples sizes can then be adjusted as better estimates of the standard and salinity of the ground water. deviation of a specific field are obtained. Although the number of samples has traditionally been perceived as the most significant • Plants factor, other issues affect the reliability of the samples, such as the distance between samples. It is The most important plant parameters to monitor in a saline environment are growth, visual usually assumed that the samples or sub-samples are independent. In reality, observations taken appearance, element concentration in tissues, and crop quality. All these parameters vary in within a limited distance may be auto correlated, (i.e. dependent), and wil not provide entirely new tIme and space, both at field-wide scale and within the plant. info=ation about the desired soil property. This autocorrelation decreases with distance, and sampling intervals must be chosen accordingly. A variogram may be used to determine the optimal Analytical methodologies with special reference to problems and difficulties distance, but studies of field variability have shown that the range falls between 4 and 10m, with the latter being the safest value. The following section, which refers to tandard methodology, has been compiled from Page The next step consists in selecting a sampling strategy. Different approaches exist, and et al (1982), Robbins (1990) and Carter (1993), Rhoades and Miyamoto (1990), Rhoades et al have been thoroughly described (Blaine and Grattan, 1990; Guitjens, 1990). These include: (1992), Ayers and Westcot (1985), and Robbins (1990). judgement sampling, simple random sampling, stratified random sampling, systematic sampling, Once a sampling strategy has been selected, 0.5 to l.0 kg soil samples are taken from each and composite sampling. Each has its specific limitations. d~pth or horizon and chemically analyzed. Larger samples are needed for physical measurements. Due to the problems posed by the spatial and temporal variabilities in salinity, many Fme earth (2= fraction) is then prepared after drying, and placed in durable, labelled containers. researchers and practitioners look at the characterization of salinity and salinity components with Labels should include the date, the upper and lower depth limits, and the site. The approximate descriptive statistics such as mean and variance as inadequate. A whole new set of statistical tools field . ~oisture content, the name of the person who collected the sample, the soil surface is being developed for this purpose like the time series techniques, kriging and co-kriging. The condItIOn: the ~ropls appearance history and yield, the next crop to be grown, and the quality of techniques characterize and estimate temporal and spatial data sets, making use of specialized aVaIlable ImgatlOn water should be noted. Samples should be kept dry and free of contaInination. fo=s of standard statistical parameters, such as correlation, cross correlation, variance, For sampling water used for irrigation, samples should be collected after the pump has run estimation and spectral analysis (Guitjens, 1990). These techniques, which rely on for at least half an hour. This removes standing water from the well casing and the area around interdependence of data for modelling, are still'rarely applied, presumably because of the lack of the well, ensuring a representative sample. Usually, the well water will not ch~ge during the familiarity of the engineers. growmg season, except where sea water intrusion occurs as seasonal demand on water increases. In these cases, periodical sampling during the season are necessary. Water samples of 0.21 to 0.5 I Sampling parameters: what do we sample? are sufficient for analysis. The sample containers should be clean and free of oil salts and other chemical contaIninants. it should be rinsed with the water to be sampled, and closed tightly. The field characteristics that will allow us best to monitors and diagnose salinization and Labels should include the date and time and location of sampling, the approximate water flow, the waterlogging are: soil, water (including water quality and depth to groundwater), and plants, crop to be grown, the irrigation method, and the name of the person con,ecting the sample. The which can give an indication of the distribution of saline patches by looking at species distribution. samples should be refrigerated at about 3°C and analyzed as soon as possible. They should not be frozen.

12 13 1. Chemical analysis The SAR determined in the extracts of low dilution such as the saturation extract is Sodic and salt-affected soils are diagnosed by assessing salinity using the electrical generally more reliable than those determined in the extracts of higher dilution due to dilution conductivity of the saturation extract (BC,), a practical index of total ionized solute concentration. effects as well as to the dissolution of Ca minerals such as calcite and gypsum. In the absence of Sodicity is expressed in terms of the Na+ on the exchanger as the exchangeable sodium percentage mineral dissolution, the SAR decreases in proportion to the square root of the dilution factor. Due (ESP) or the sodium adsorption ratio (SAR). The latter is more conveniently determined. to the soil buffer power, the decrease in SAR in soil systems is less than this estimate. The following sections will briefly list the main procedures for testing soil and water Chloride, sulphate, carbonate and bicarbonate are the most commonly measured anions. salinity and sodicity, while restricting ourselves to soils and waters with a pH of6.5 to 10.0. Many Alkalinity (C03- + HCOn should be determined immediately on fresh extracts. The preferred other research-level procedures exist, but they are inapplicable to data-gathering for the purpose sequence of anion determination, to minimize CaC03 precipitation problems is: alkalinity, then cr of management. ,N03-, and S04-. Finally, B is determined. i) Conductivity of the saturated paste extract 2. Physical analysis This is the lowest soil-to-water ratio that can be extracted easily by vacuum, pressure, or The major soil physical characteristics associated with salinity and sodicity are: depth of centrifugation. This has now become the standardized extraction procedure, on which the c~op water table, aggregate stability, permeability of subsoil layers, infiltration rates and hydraulic tolerance tables are based, as are the procedures for predicting ESP from the SAR. Extractlon conductivity. The interaction between these parameters in saline and sodic soils depends on soil ratios of soil-to-water by weight ex: 1: 1, 1:2, and 1:5 cause errors associated with mineral texture and clay mineralogy. dissolutions, ion hydrolysis, and changes in the exchangeable cations ratio and should be avoided. Soil samples containing gypsum will deviate the most because the calcium and sulp~ate i) Aggregate stability and size distribution concentration remains near-constant with sample dilution, while the concentration of other IOns Aggregate stability is affected by the anture of soil colloids: clay mineralogy, organic decrease with dilution. matter, iron oxides and carbonate coatings, in addition to the concentration and kinds of solutes. The conductivity of aqueous extracts, including that of the saturation extract can be The aggregate stability of one aggregate size fraction rather than aggregate size distribution is related to that of soil solutions (EC,w) at known or given gravimetric soil water contents (wi) often used in order to eliminate sampling variability. Aggregate stability is the fraction of the using the following equation: aggregates of a selected size that does not disintegrate to smaller particles upon wet sieving with EC", = a. (w/wi)EC water of an EC of 0.01 dS/m or less.

where w is the gravimetric soil water content at extraction, and a. the correction factor. ii) Particle size analysis The value for a. depends on ion composition, soil bulk density, and the dissolved salt. It usually Lateral and vertical texture variations, and their relation to salinity patterns, indicate ranges between 0.7 and 1.0. The error increases as w/wf increases and reaches unacceptable processes that cause salt accumulation and may aid in planning reclamation. For textural analysis, values at extractions of 1 : 1. saline and sodic soils should be pre-leached with distilled water until the leachate EC drops below Soil EC can be used to estimate the total salt concentration. One of the relationships used 1.0 dS/m. Organic matter, iron oxides and carbonate coatings must be removed, and the sample is: dispersed by turbulent mixing, in an alkaline dilute solution of sodium polyphosphate. log Tsalt = 0.99 + 1.055 log EC, where T salt= mmolc/l, and EC is dS/m (Dudley 1994) iii) Hydraulic conductivity Knowledge of hydraulic conductivity is neccessary for drainage design and salt balancing. ii) Cations and anions analysis, SAR determination In sodic soils, low hydraulic conductivity at the surface may control water movement throughout The exchangeable sodium percentage, or ESP is cumbersome to determine as it requires the profile. A perched water table may be caused by deep impermeable layer. the determination of the €EC, and is subject to numerous errors. Soil sodicity hazard is now Methods have been developed for the measurement 'Of hydraulic conductivity (HC) in the commonly defined and evaluated in terms of the SARe. The ESP and the SAR are quantitatively field or in the laboratory. The commonly used method for HC determination in saturated soils is related and are nearly the same in value over the range 0 to 30, except in gypsifetous soils where based on the rate of rise of water in a borehole in the watertable, and requires knowledge of the ESP is' usually greater, because the measured soluble Ca and Mg concentrations include Ca and hole depth and the radius. The unsteady drainage flux method for unsaturated soils relies on the Mg ion pairs having no net electric charge. determination of the hydraulic head profile, measured by tensiometers, and the water content profiles, measured by neutron scattering. Vertical flow is assumed. The method, is not suited to The SAR is calculated as SAR = Na/[(Ca+Mg)l2]ll2 soils whose· horizons differ greatly in hydraulic corlductivity, or soils with water tables within where concentrations are in mmolJI about 1.5 ill.

14 15 Hydraulic conductivity can be determined in the laboratory preferably on undisturbed. sO.il cores of 20 mm to 100mm in diameter by 50mm to 250mm length. The recommended test flUid IS Basin-wide Salinity and Drainage Investigations Using Remote Sensing Techniques 5.0 mm CaS04. Clay dispersion is an indirect measurement of hydraulic conductivity impairment. The The costs of operating and processing large scale data are high, so these methods are best Imhoff cone method is commonly used to determine settleable solids during 1 h of settl.rng. ~he sui~ed to gatheri9g data for irrigation districts, river valleys, and other geographic entities of 250 results allow the classification of sodic soils with respect to their potential to undergo dlsperslOn km to 8,000 km . They are more cost-effective when the data is used for multiple purpose and and restrict water movement. several users share the costs. Aerial photography, in which color infrared films are used, produces the most useful data iv) Infiltration rate on plant stress under salinity by showing differently stressed plants in different colors. The The infiltration rate is strongly affecetd by salinity and SAR. These should be considered techniques also allows the differentiation of saline soils. Infrared photographs can be analyzed by together for evaluating the effect of irrigation water on water ~n£ltra~ion rate. .' . . computer to produce clusters of the land into classes of salinity severity. The use of the adjusted SAR which accounts for the dissolutlOn or preclpltatlOn of calclUm Using Infrared Thermometry and Imaging, crop canopy temperatures can be measured and in soil following irrigation is preferable. . correlated with the crop water stress index (CWSI) to monitor the water stress caused by soil SARadj= Na/[(Cax+Mg)I2]II2, where vales are in mmole,/l, and Cax. refers to a m~dified salinity. The technique can also be used to monitor saline seeps, since the temperatures of wet and calcium value based on the salinity of the applied water, the HC03/Ca ratlO and t~e estImated dry soil differ.Infrared thermometers can be hand-held or flown across fields in transects. partial pressure of C02. More details can be found in Ayers and Westcot, 1985 and rn the paper Multispectral Scanners sense in multiple bands or wavelength intervals and can be used to by I. Rhoades describing the Watsuit software in this volume. detect vegetative ground cover affected by salinity. Water-affected bodies can be differenciated by the water-affected bands (I.4 !lm to 2.5 !lm) and can detect dry or wet vegetation and soils. The 3. Water table . thermal bands (5 !lm to 20 !lm) measure the temperature of the plant cover when the growth of When the water table is less than 2m from the soil surface, auger holes or observatJ.on plants varies in response to soil salinity. wells are used for the sampling and monitoring of water depth. Alternatives to observation ,:~lls include piezometer tubes (observation well with an .open botto~ that m~asures the posItIve REFERENCES hydraulic head at a given point and tensiometers. TenslOm~ters, which ar:e plezometer~ closed at the bottom with a porous cup are used to measure hydrauhc head at a gIven depth. PIezometers Ayers, R.S. and D.W. Westcot-. 1985. Water Quality for Agriculture. FAO Irrigation and are more difficult than observation wells to sample for water, and tensiometers cannot be used to Drainage paper # 29. FAO, Rome. obtain water. .. . Beckett, P.H.T. and Webster, R. 1971. Soil variability: a review. Soils and Fertilizers 34: 1-15. The direction of ground water flow and the hydraulic gradient are useful for determrnrng If Blaine, R. H. and Grattan, S. R. 1990. Field sampling of soil, water and plants. In: K. Tangi (ed). an effective drainage system can be installed. They can be mesured with at least four wells or Agricultural Salinity Assessment and Management. American Society of Civil Engineers. piezometers inserted in a rectangular pattern over the area of interest in order to measure the New York. absolute water surface elevation or hydraulic head. Carter, M.R. 1993. Soil sampling and methods of analysis. Lewis publishers, London. Dudley, L. 1994. Salinity in the soil environment. In: Pessarakili, M (ed) Handbook of plant and 4. Instrumental field methods for salinity appraisal crop stress. Dekker, New York. Theoretically, the bulk EC depends on the salinity of the soil solution, soil~water co:"tent, Guitjens, I.e. 1990. Spatial and temporal variabilities in salinity. In: K. Tangi (ed). Agricultural porosity, and type and amount of clay in the soil. Devices that allow rapid field-.":Ide sampling of Salinity Assessment and Management. American Society of Civil Engineers. New York. soil salinity have been developed. They include the f~ur -electrode . saliruty probe, .the Page, AL., Miller, R.H. and D.R. Keeney. 1982. Methods of soil analysis, part 2 (Chemical and electromagnetic conductivity meter, the buried porous electncal conductIvIty se~sors, and tlm~ Microbiological properties). Second edition. American Societt of Agronomy, Inc. Soil domain reflectometry electrode systems. All measure the bulk electrical conductlVlty of the SOlI Science Society of America, Inc, Madison, Wis. USA but not the concentration of individual ions. They are useful for initially mapping large area~, and Rhoades, I.D. and Miyamoto, S. 1990. Testing soils for salinity and sodicity. In: Westerman, R.L. monitoring changes with time. A detailed description of many of these devices can be found rn the (ed). Soil testing and plant analysis. 3rd ed. Soil Science Society of America, Inc, Madison, paper by J. Rhoades in this same volume. Wis. USA Rhoades, J.D.; Kandiah, A and AM. Mashali. 1992. The Use of Saline Waters for Crop Production. FAO Irrigation and Drainage paper # 48.11AO, Rome. Robbins, C.W. 1990. Field and laboratory measurements. In: Tangi (ed) Agriculture Salinity Assessment and Management. American Society of Civil Engineers, New York . . '

16 17 Figure 1:Flow Chart of Investigation Techniques for Diagnosing Salinity and Pilot Areas For The Reclamation Of Salt-Affected And Drainage Problems Waterlogged Soils

Fernando Chanduvi, Technical Officer, AGL FAOlRome

INTRODUCTION

The adverse impacts brought about by irrigation are compelling in many countries in the world: problems of waterlogging and salinization, pollution of ground water with nitrates and toxic substances and intensification of the hazards of vector-borne diseases. All are attributed to irrigation development. It is estimated that of the total 270 million hectares (ha) of irrigated land in the world, some 80 million ha are affected by waterlogging and salinity, while about 20 million ha suffer from severe irrigation-induced salinity problems. Once the irrigated lands are degraded by soil salinity, they are useless for agricultural purposes. Allover the world, technical and economical efforts have been made towards the reclamation of salt-affected soils. In order to gain practical experience and to fully understand all variables in the reclamation of salt-affected areas, several countries have adopted the "pilot area approach" as a first step before undertaking a full scale rehabilitation programme. Pilot areas for the reclamation of waterlogged and salt-affected irrigated lands have been installed in Argentina (Mendoza, San Juan and Santiago del Estero in the late 80s), Brazil (petrolina in the early 90s), Chile (Copiapo in 1990), Jamaica in the 80s, Peru (three in Piura,one in Chiclayo and one in Arequipa in the 70s). Other countries which have used the pilot area approach are Egypt, Pakistan and India.

PILOT AREAS

Pilot areas for the reclamation of salt-affected and waterlogged soils have the following characteristics, they: • are located within the area to be reclaimed, • are of a size of about 20 ha. The size would depend on the number of variables to be evaluated: drain spacing, chemical amendments, crops, depth of water to apply and others, • are representative of the waterlogging conditions, the salinity levels, the soil characteristics, and the presence of impermeable layers in the area, • are used as "test areas" as different known-reclamation techniques will be tried and adapted to local conditions, • are used as "demonstration plots" for farmers, engineers, and managers, • should be monitored for at least two cropping seasons after the reclamation so that crop yield improvements may be determined, • must have irrigation water and drainage facilities to allow the leaching programme to be carried out and the removal of excess water, • are research areas. All works and practices undertaken constitute the applied research works which will provide the tools for the reclamation of a larger area and • should provide all the information to determine the technical and economic feasibility to carry out a land reclamation programme.

18 19 PILOT AREAS FOR THE RECLAMATION OF WATERLOGGED AND SALT-AFFECTED Impermeable layers SOILS IN PERU Soil layers of very low K values with respect to the K values of overlaying layers are considered impenneable for drainage purposes. Shallow (at a depth 00 m) impenneable layers will Background . . . call for closer field drain spacing, making the drainage system more expensive. The selected area Drainage and soil salinity investigations have been carned out ill ~eru sillce. t~e ~arly 6.os. presented a compacted impenneable layer at a variable depth (varying from 6 to 13 m). The Coastal area of Peru bordering the Pacific Ocean, has 52 seasonal nvers providillg ImgatlOn water to approximately 7,320,000 ha. Waterlogging and s~il salinity affected about 34 % of the Drainage irrigated area, deprellsing crop yields and in some cases causillg the aban~onment of.lands. . An open drain which had a drainage pumping station at its lower end provided the In 1970, the first pilot land reclamation/drainage area was deSIgned and ·lIDplemente? ill necessary control of the water table. Peru coverina an area of 17 ha in the Chancay Valley in Lambayeque, some 760 km north of LIma, the ;apital. There are about 7.0,.0.0.0 ha under irrigation in the ~hancay Valley and some 30,.000 ha Soil salinity are affected by waterlogging and soil salinity problems. The mam crops of the Valley ar~ sugar cane The soils were initially extremely saline with an electrical conductivity of the saturation and rice. Sugar cane occupies some 2.0,0.0.0 ha with an average yield of 11.0 to 12.0 metnc tlhalyear. extract (Ee.) of 153 mS/cm and an exchangeable sodium percentage (ESP) of 6.0 for the top 1.0 cm Rice occupies some 24,0.00 ha with an average yield o~ 4.4 tlhalyear: . . of the soil profile. These values dropped to 29 mS/cm (ECe) and 44 (SAR) at the 6.0-8.0 cm depth. The soils in the pilot area were highly saline along WIth high exchangeable sodmm percentages (ESP). Design of the Pilot Area

Research . Land reclamation Three research lines were established as follows: (i) a study of the reclamatlOn process as The following treatments were chosen: (i) Eight water applications spaced every 1.0 days, related to the depth of water applied by establishing a salt and water balance, (i~) to detenn:ne the each one equivalent to 1,250 m3/ha and (ii) four water applications spaced every 20 days, each one effect of the application of chelnical amendments and (iii) to evaluate the operaTI~n of t.he dIfferent equivalent to 2,50.0 m3/ha. pipes (corrugated-perforated plastic and clay) along with different envelop matenals (nce and flax straw, glass wool and gravel). Chemical amendments Chelnical amendments (gypsum and sulphur) at rates of 25 %, 5.0 %, 75 % and 1 00 % of Physical and Chemical Characteristics the total amounts required to bring the ESP values to levels of 15 % were also applied.

Soil profile Drain spacing Drain spacing (Beers, 1965) were calculated taking into consideration the depth to the The soils of the pilot area are of alluvial origin. A layer of clay loam to clay is present from impenneable layer, the depth of the tile drainage (2 m), the drainage requirement (3 mnJday for the surface up to a depth which varies from .0.60 to 1.5.0 m. Below this top layer the soils are rice) and a hydraulic head in the lnid point between drains (0.5 m for other crops than rice and 1.5 generally of the following textures: loam, sandy loam, silty loam and sand. m for rice) and the hydraulic conductivity. The selected drain spacing were 18, 36 and 42 m and the lengths of the drains were long (25.0 to 30.0 m) and short (14.0 to 150 m). The total length oftile Watertable . . drainage installed in the pilot area was 4,35.0 m. The depth to the water table measured in observation wells installed III a gnd pattern was found to vary from 0.9 to 1.2 m from the soil surface. RESULTS

Irrigation water . .. Salts Removal. The selected area for the installation of the pilot area had surface water ngh~s. w~ch The excess salts were effectively removed from the soil profile. The salt removal was higher ensured the cropping and reclamation progranillle. The electrical conductivity of the ImgatlOn in the top 10.0 cm. Further salt leaching was accomplished with the following rice cropping seasons. water was 0.65 mS!cm. Exchangeable Sodium Percentage. Hydraulic conductivity . . . The chelnica! amendments were applied in quantities varying from 4 to 16 tlha of gypsum The Auger hole (Beers, 1963) method was used to measure the hydraulic charactenst:c.1ll and 0.7 to 1.4 tlha of sulphur. Gypsum was applied in three fonus: (i) dissolved in the irrigation several places within the area. This method allows the measurement of the hydraul1c condUCTIVIty water, (ii) broadcasted on the soil surface and (iii) broadcasted on the soil surface and incorporated (K in nJday) of the layers below the water table. Twe~ty eig~t measurements were made (1 test/l.2 in the soil. ha). The geometric average used for design of the dram spaclllg was .0.72 nJday. There was also a reduction of the ESP measured indirectly through the Sodium Adsorption Ratio (SAR) Table 1. Furthennore, it was found out that the application of gypsum dissolved in the irrigation water was not effective as gypsum tends to deposit at the bottom of the canals. Broadcasting on the soil surface was also ineffective because it was blown by the strong winds

21 20 prevalent in the area. The most effective ~ay. to apply ~he che~cal amendments was by broadcasting on the soil surface and incorporatmg it mto the soil by a disk plough. A National Plan for the Reclamation of Irrigated Areas Degraded by Salinity and Waterlogging Tile Drainage and Envelop Materials.. . The different types of pipes and the envelop matenals use~ for the sub.surfac~ dramage w~re Fernando Chanduvi evaluated through the entrance resistance to the flow of water m the zone lIDIDedrate to the pipe Technical Officer, AGL and the amount of sediments found inside the pipe and by the non-alignment or breakage of the FAOlRome line. b" . h ~:"" t I The entrance resistance of clay and plastic pipes in com mation Wit Wlleren e~ve op INTRODUCTION materials in relation to time was evaluated. Taking into consideration that an entrance reSistance value of 0.5 is considered high, the following conclusions were drawn: (i) gravel showed ~he low.est Land Degradation entrance resistance even with time it did not reach a value of 0.5, (ii) rice straw showed mcreasmg Degradation of agricultural lands may be defined as the reduction, in terms of quantity and entrance resistance'values indicating its rotting with time and (iii) entrance resistan~e v"!ues for all quality, of the present or future capacity of the soils for crop production. Land degradation may be envelop materials were higher for plastic pipes than for clay pipes, this .may be explame~ m terms of classified as erosive, caused by wind and water and non-erosive. The most common types of non­ the larger area (pipe joints) for the seepage of ground water for clay pipes and to the pipe diameter erosive land degradation are: compaction, decrease in soil fertility, loss of organic matter, structural (larger for clay pipes). ... . changes, pollution with toxic substances (detergents, pesticides, heavy metals) and wastewater, The capacity of the envelop material to keep the SOlI particles from entenng the pipe was waterlogging and soil salinity. also evaluated. Glass wool was the best envelop material followed by gravel. Waterlogging and Soil Salinity Table 1. Salt Removal by Leaching Up to the Third Cropping Season (EC mS!cm, SAR) About 15 to 20% of the irrigated soils of the world are affected by waterlogging. Soils degraded by waterlogging lose their production potential and hence their capacity to feed a Depth Cumulative deoth of water annlied for leachin~ purposes, in rom growing population. Cern) 0 450 1,667 1,957 3,212 6,800 This is an account of a national plan for the reclamation of waterlogged and salt-affected Initial After first After first Before second After second After third soils carried out in Peru, South America Initial estimates (1965) indicated that about 25% leaching ero ing cronoino CIOPI ino croc ing EC SAR EC EC SAR EC EC SAR EC SAR (250,000 ha) of the irrigated 'area in the Coastal area, which borders the Pacific Ocean, were 0-10 169 90 34 20 25 18 17 13 degraded by waterlogging and soil salinity. 10-20 130 85 45 22 29 20 16 17 12 14 The Peruvian national plan for the reclamation of waterlogged and salt-affected soils 20-40 75 73 54 31 40 24 21 28 16 24 involved various steps which may be summarised as follows: (i) identification of the waterlogging 60-80 33 53 42 36 54 31 29 45 23 35 100-120 26 38 35 35 52 49 27 47 23 46 and salinity problems, (ii) training of national staff, (iii) the detennination of the extent and the 200-240 19 29 21 30 17 30 17 28 causes of the problem in the different irrigated areas (execution of detailed and specific waterlogging and salinity studies), (iv) ensure the political will to carry out a national plan for the reclamation of waterlogged and salt-affected soils within the irrigation districts, (v) the REFERENCES establishment of pilot areas for the reclamation of waterlogged and salt-affected soils, (vi) the creation of a national institution which will be responsible for the execution of the national plan, B W F J van (1963): The auger-hole method. A field measurement of the hydraulic (vii) the preparation of comprehensive technical and economic feasibility studies which should eers'conciu~tivity of soil below the water table. Bull. 1 of the International Institute of Land include the farmers' participation, (viii) secure the budget to carry out the rehabilitation Reclamation and Improvement, Wageningen, The Netherlands. . . progralnme, (ix) execution of the rehabilitation programme, which may be done by the national Beers, W. F. J. van (1965): Some homographs for the calculation of dram spacmg. B~ll. 8 of the institution itself or through national or international contractors (national competitive bidding, International Institute for Land Reclamation and Improvement, Wagenmgen, The NCB, or international competitive bidding, ICB), and (x) monitoring of the results of the Netherlands. programme. ,GENERAL INFORMATION ON TIIE COUNTRY Peru is a South American country with a land surface of 1,285,215 km2 It has three distinctive natural geographic regions: the Coast, the Mountainous region and the Amazon. The Coastal region is a narrow strip which stretches for 2,560 km from north to south and is limited in the West by the Pacific Ocean and in the East by the Andes Mountains. Climate: The arid climate of the Coastal region is dominated by two factors: (i) the cold Humboldt Current which prevents evaporation from the Pacific Ocean and (ii) the Andes Mountains, which prevent arrival of clouds from the Amazon basin. The result is a region with

22 23 very little rainfall (less than 40 rnm/year). The average temperature varies from 26° in the North ~~itution had responsibiliti.es ~or .research, staff training and for the execution of feasibility studies. to 18° in the South. The annual evaporation follows the same trend as the temperature and s stage went from the IDld-slxtles to the early seventies. varies from 1,800 to 1,200 =. • Hydrology: The 52 rivers which cross the Coastal area carry about 40,000 million cubic meters Pilot Land Reclamation Areas annually. The rivers however are seasonal and carry 80% of the water during January, February The NCRLR established five pilot land reclamation areas in different valleys in the Coastal and March. areas ofPero. They were: Chacupe (37.7 ha), La Boya (15.6 ha) Mintearande (500 ha) Curvan (22.0 ha) and Pedregal (16.0 ha). ' 0 ., CAUSES OF WATER WATERLOGGING AND SOIL SALINITY h Investigations carried out in the pilot areas helped to understand the reaching process and t e evaluatIOn of factors related to the determination of drain spacing types f d" d The main causes ofland degradation by waterlogging and soil salinity in irrigation schemes are: envelop (filter) materials. ' 0 ram pipes an • Inefficiency of Irrigation: Inefficiency of irrigation is, among others, the single most important cause of land degradation by waterlogging and soil salinity. A study of the irrigation modules Waterlogging and Soil Salinity Evaluations and scheme supply efficiencies in the Chira-Piura irrigation project in Peru for the period 1980- . Between 1970 and 1974 a detailed evaluation of the waterlogged and salt-affected soils was 1989 shows the following is: (i) the scheme supply efficiency is only 65%, (ii) there are years carned out m the Coastal regIOn of Peru with the following criteria: (Table 1 and 2). (1987 and 1988) when the amount of water flowing out of the area is 25% of the volume of the reservoir located in the upper extreme of the watershed and (iii) that the net crop (cotton) DRAINAGE irrigation requirement is 7,445 m3/ha/six-month season and taking into consideration that the average delivered module is 12,516 m3/ha/six-month season (efficiency of application: 59%), Classification of drainage Depth to the water table during the fallow period,m the overall efficiency of irrigation is about 38%. A large share of all irrigation losses contribute Good >1.5 to 2.0 to waterlogging and soil salinity problems. i~erfect >0.8 to 1.5 Use of Saline Water for Irrigation: There are several irrigation schemes where the irrigation Poor >0.3 to 0.8 water has a high salt content These salt levels, in the absence of proper irrigation management Very poor <0.3 techniques, result in an increase in the soil salinity which hampers both, the soil productive Table 1. Drainage classes, Peru capacity and the crop itself. SOIL SALINITY • Topographical Position: Worldwide experience show that irrigation losses seep from the topographically higher areas to those of lower elevation. In the majority of the alluvial valleys of the Coastal region in Peru, waterlogging and soil salinity exist mainly in the lower D~e of degradation Electrical conductivity of saturation extract mS/cm at 25°C topographical areas which at the same time are close to the sea Taking into consideration that Low 0-4 Slight 4-8 the provision of artificial drainage has a cost, some countries facing these problems take a very Moderate 8-15 close look at the irrigation development of those areas which are located below the 5 meters Strollg 15-30 above sea level limit. Very strong 30-50 • Other Causes: Other causes for the occurrence of land degradation by waterlogging and soil Excessive >50 salinity are: presence of impermeable layers within the soil profile, soils of low hydraulic Table 2. Classification of salt affected soils Peru conductivity, poor maintenance of the irrigation infrastructure, etc. O~t .ofa total area of 775,430 ha, 32.1% (or 248,744 ha) were degraded by waterlogaing and soil AWARENESS OF WATERLOGGING AND SOIL SALINITY PROBLEMS Salillity. 0

Initial Stages NATIONAL PLAN FOR REHABILITATION OF WATERLOGGED AND SALT AFFECTED Artificial drainage for agricultural purposes has been practised in Peru even before the SO~ - sixties, particularly in the private large sugar cane plantations of the Coastal area Clay tiles, covered with rice straw as filter material, were used for drainage purposes. . ~h: national plan .for the. reclamation of waterlogged and salt-affected soils started by It is in this decade that a renewed interest in waterlogging, soil salinity and reclamation estabhs~,:, a separate entity Within the Ministry of Agriculture. called the Special Project for the came about. A preliminary investigation showed that about 25% (250,000 ha) of the irrigated areas RehablhtatlOn of Coastal Lands (SPRCL). in the Coastal area were degraded by waterlogging and soil salinity. . The SPRCL had an Ex~cuti~e Director heading three Executive Directorates: Planning (ad~stratlOn and budget), ~ngrneenng (Studies and Works) and Agricultural Development (land Development of Human Resources gradrng, leaching and extensIOn). Furthermore, the Executive Director was assisted by a legal Several professionals went abroad for specialized training in land reclamation. A national ;ct:on ~d by an E~emal ProgranJIDe of Technical Assistance. The Executive Directorates of institution was created: the National Centre for Drainage and Land Reclamation (NCDLR); this nglI~e.ermg and Agncultural Development were present in each one of the valleys where rehabilitatIOn works were carried out.

24 25 The first stage of the SPRCL (1979-1986) was executed with financing from the Peruvian Soil Salinity Assessment: Recent Advances and Findings d from the Inter-American Bank for Reconstruction and development (World G overnment an . ··1 k· th all f Bank). It comprised the technical and economic feasibility studies and.c~Vl wor s m e v. eys 0 J. D. Rhoades, Director, US Salinity Laboratory, USDA Canete, Pisco, Camand and Tambo. It must be pointed out that th~ ~Ivil. works not only mcluded Riverside, California, USA subsurface drainaae but the improvement and rehabilitation of the ImgatlOn mfrastructure and the soil rehabilitation.'" The most important works carried out in the four valleys (total area 40,867 ha) INTRODUCTION were: o Four heau intake works to derive water from the rivers, A practical methodology for mapping and monitoring soil salinity is a requisite for o Main canals, secondary canals and rehabilitated canals: total 245 kIn, inventorying the extent and magnitude of salt-affected soils, for assessing the effectiveness and o Subsurface field drains: 443 km of plastic drains, appropriateness of irrigation and drainage practices, and for delineating the diffuse areal sources of salt-loading in irrigated lands. o Drainage pumping stations: 3, Mapping and monitoring soil salinity is complicated by its spatially variable and Service areas: 5, and o dynamic nature caused by the effects and interactions of varying edaphic factors (soil o Land grading: 843 ha. . .. permeability, water table depth, salinity of perched groundwater, topography, soil parent The second stage of the SPRCL (1982-1989) was executed with ~anc~g similar to that of material, geohydrology), man-induced processes (irrigation, drainage, tillage, cropping the first stage. Its activities were concentrated in the valleys of Chira and PlUra m the northern part practices), as well as by climate-related factors (rainfall amount and distribution, temperature, of the Coastal regioI}. The most important works in the valley were: relative humidity, wind). Rapid, mobile instrumental techniques for measuring bulk soil electrical conductivity Irrigation Infrastructure. ... 3 .. • (EC,) as a function of spatial position on the landscape have been coupled with procedures for o "Poechos" Reservoir, with a storage capacity of 1,000 million m to regulate lmgatlon inferring salinity from EC" with computer-assisted mapping techniques capable of associating on a total area of 95,200 ha, 3 and analysing spatial databases, and with appropriate spatial statistics to create an integrated Diversion lined canal, 54 km oflength with a capacity m /sec, o of7~ system which now for the first time has the potential of meeting our salinity assessment needs. o Distribution dam with a capacity to operate up to 3,200 m /sec flows, . This paper describes improvements and modifications made in both the system's Main canal (lined), 57.5 km of length with an initial section capable of conveymg 60 o equipment and the methodology used for analysing data. Representative results obtained with 3 m /sec, the systems will be used to illustrate that much of the random spatial variability typically o Secondary and tertiary canals, 73.5 km; and canals at farm level, l38 km. present in field salinity data is not necessarily of a stochastic nature, but rather a result of several interacting edaphic factors and man-induced farming practices that cause systematic Drainage infrastructure. . (deterministic) patterns in soil salinity across the field and within the soil profile. o Main drainage system (open ditches), 454 km. Trapezoidal section With d~pths between 2 5 and 5 m with maintenance roads on both or one side. Number of crossmg structures: MODIFICATIONS IN EQUIPMENT 1:365. Two'main open drains were rehabilitated, one with a length of 66 km and the other of 49 km. The mobile Four-electrode Sensing System o Collectors: 84 km, . . In this system the electrodes are combined into the "heels" of tillage shanks and o Field drains: 421 km of subsurface drains. Perforated-conugated plaSTIC pipes were used mounted on a hydraulically controlled tool-bar attached to a tractor via a conventional three­ as drains. point hitch. The electrodes run at a depth of about 10 cm in the soil as the tractor moves across the field at a speed of 1.0 to 2.5 m/sec. The Global Positioning System (GPS) antenna REFERENCES is positioned above the tractor cab. The conductivity meter, the GPS receiver, their respective power supplies and data loggers are contained in the water-tight, stainless steel box mounted Alva, C. A. et al. 1976. Problemas de Drenaje y Salinidad en la Costa Peruana Bulletin 16. Inti. behind the tool-bar. The tractor operator is provided with a remote monitor displaying time, Inst. for Land Recl. and Improvement (ILRI), Wageningen, The Netherlan~s. . er EC, reading and logging status. The EC, and the GPS signals are sensed at adjustable Alphen, J.G. van. 1975. Some notes on the reclamation ~f salt affec~ed. soils m Peru.. Pap frequencies (as often as every one second) and logged into memory automatically for later presented at the International Conference on Waterloggmg and Salinity m Lahpre, Pakistan· analysis for salinity and spatial (about 2 m absolute accuracy) location. The analysis is carried li Beers, W.FJ. van. 1963. The auger-hole method. A field measurement of th~ hydrau c out at the side of the field in a mobile office equipped with a computer work station and soil conductivity of. soil below the water table. Bulletin 1 of the ILRI' Wagemngen, The testing facilities. Netherlands. . The system was recently modified to increase depth and volume of soil that can be CENDRET. 1970. Area piloto de drenaje, Chacupe, Lambayeque. Dlseno. Informe Tecnico 20. measured by widening the "tool-bar" to acco=odate current (outside to outside) electrode Direccion General de Aguas, Ministerio de Agricultura, Peru. spacing of up to 6 meters, and by modifying the Martek soil conductivity meter to give linear

EC, readings up to 15 dS/m (correspondingly to Eee readings of up to 45 to 100 dS/m depending upon soil texture).

27 26 Using this equipment,EC, readings were collected every second as the tractor moved horizontal position; 3) the EMH reading is made and logged after the selected delay interval in a furrow irrigated, tile-drained alfalfa field in the Imperial Valley of California. The :d 4) the E~~38 sensor is rotated ~ack to the vertical position. This sequence is repeated fo; "minimum" in the EC, readings corresponded to the position of a buried drain-line. The EC, ch Y-Z pOSItIon selected. Depressmg the four-electrode "start" button initiates the followina values increased near the "tail end" of the field, presumably due to reduced application and automated sequence: 1) the scissors apparatus probes to the first depth limit 2) EC ." infiltration of irrigation water. Examples of fields with much greater increases in "tail end" :)easured at the 1-~ arra~ spacing, 3) a delay is provided for data logging at the i-m spacin~: salinity were previously presented (Rhoades, 1992). Salinities on an ECe basis is predicted t~e meter/logger .IS sWlt.ched to the 2-m array, 5) EC, is read after a delay at the 2-m array from the measured data along the transect. The data suggest that much of the variability in spacmg, 6) a delay ~s ~roV1ded for data logging at the 2-m spacing, 7) the probes are inserted average rootzone sa1inity across the field is caused by the effects of the drainage and irrigation to the ~ext depth lImIt (uP. to 5-dept~s are possible), and 8) steps 2-6 are repeated. After systems. completIOn ~f the last loggmg, the sCIssors apparatus lifts the electrodes from the soil and Another example of the effect of subsurface drainage on average rootzone salinity stores them m the travel position. A small printed circuit board provides the necessary time involves a field of silty loam soil in the Coachella Valley of California which has two sets of delay functIons. The ~obile unit then moves to the next measurement site (stop). All buried "tile-lines", one set being about 2.7 m deep and spaced about 90 m apart and another measurements at each sIte can be made in about 30-45 seconds. set being about l.7 m deep and located at one-third and two-third distances between the A belt~driven dis~ance counter attached to the unpowered rear wheel of the vehicle and deeper lines. The data again show a close correlation between the soil electrical conductivity a re~ote momtor were mstalled to: 1) assist in the sitting of measurement locations and 2) to values and the drainage pattern. Soil salinity (ECe) levels of up to 20 dS/m, or more, occurred perrmt the four-electrode measurements to be made at the same locations as the EM at several places in the field between the tile-lines. Concurrently, salinity tended to increase in measurements. The Cartesian coordinates (x,y) of each measurement site are measured and the direction of irrigation, although "tempered" somewhat by the effect of the drainage system. logged by the GPS system. For more engineering details about this apparatus see Carter et al (1993). ' ., The mobile electromagnetic induction/four-electrode sensing system There is typically good agreement between measured salinity levels and those predicted The mobile electromagnetic induction sensor system described previously (Rhoades, from the EM-.38 s~nsor. Results from a furrow irrigated tile-drained alfalfa field in the Imperial 1992) was extensively modified to also incorporate four-electrode arrays as well as new Valley of Callforma, ~SA show that salinity in the center of the seedbed of the fine-textured sensor-positioning, controlling, and recording systems. This system involves an EM-38 sollls not as high as ~ght be expected. A likely reason for this is the presence of an extensive instrument mounted in front of the transport vehicle (a modified spot-spray tractor) within a networka of cracks .w:thin the bed which allows water movement through it, especially in the vinylester pipe as well as two-sets of four-electrode arrays (having 1- and 2-m current later sta",es of the ImgatlOn season. This "inter-flow" likely leaches out salts which othe ise electrode spacing) mounted underneath the vehicle. The EM-38 mounting tube fastens to the ;ould have accumulated by capil1ari~. and ~pward flow, if the bed was completely iso:ed vehicle by sliding over a short section of steel tubing. The EM-38 is secured within the om the furrows. The patterns of salinity WIthin the soil profiles were very similar at various vinylester tube by means of slotted hardwood bulkheads. All hardware within the tube is non­ pomts along the transect; however, in relation to the average profile, salinity increased in the metallic. The tube may be removed and placed in a cradle at the back of the vehicle for long­ upper part of .the p:ofile and decreased in the lower part of the profile with distance towards distance travel. The "EMtube" can be rotated to position the EM-38 in horizontal (EMH) or the downgradlent. SIde of the furrow-irrigated field. The pattern of salinity within the bed and vertical (EMv) configurations by means of a small gearhead DC motor and belt which operates throughou: the SOlI ~ro~e varied systematically in response to the imposed irrigation system. via a non-slip strip applied to the tube. The tube and "rotator" are mounted on a hydraulic . Salimty dls:nbutlOn can. ~s.o be affected by a drainage system. In the Coachella Valley apparatus which elevates the EM-38 sensor sequentially to various heights above ground and field dl~c~ssed ~arlIer lower salimtIes occurred in the soil above the tilelines. The data indicate translates it sequentially in the horizontal direction so as to allow both EMH and EMv that sallmtles WIthin t~e seed bed are related to the mean profile salinity levels, which in tum measurements to be made sequentially at various heights above both the furrow and seedbed. are re~ated :0 the. dramage pattern. The salinity distributions in this silty-loam soil are clearly The four-electrode arrays are mounted on a hydraulically operated scissor-action mechanism two-dlIDenslOnal u: con:ras: to the ~ne-d.imensi.onal profiles observed for the clay textured which includes a sensor and control mechanism to insert the probes sequentially to selected ~penal V ~ley SOlI. 'F~s dIfference m salimty dIstribution is thought to be due to differences depths in the soil and to correspondingly measure EC, at both I-m and 2-m array spacing in m the cracking propertIes of the two soils. both the furrow and seed bed. . . Beside~ irrigation and drainage, another man-induced factor which "emerged" from the An automated control system (including a circuit board) was developed to carry out u:te~slve, spatIally r~ferenced .data .o?tained with our salinity assessment system is that of the sequence of 52 operations involved in the full range of possible sequential "EM-38 and tIlla",e. SystematIc dIfferences m Salilllty patterns of irrigated fields could be associated with four electrode" measurements. The control system is based upon switches and relay logic with the tr~c patt~rns undertake~ with the farm equipment. Tractors typically move through the auxiliary electronic timing. The control system is operated via an interface control panel with fiel~s m a systematIc way as dIctated by the ~vo~ed practices of seed-bed/furrow preparation, enable-buttons for activating EM and four-electrode sensor measurements and a 6-position cultl:,atlOn and tIllage. As a result, tractor weIght IS exerted in some furrows but not in others selection switch for positioning the sensors over (and at various heights above for the EM leadm~ to uneven co~paction among neighbouring furrows. Similarly, till~ge and cultivatio~ sensor) the furrow and seed-bed. When the EM button is enabled, the EM sensor is rotated to operatIOns are often Implemented using equipment with guide/depth wheels which similarly the vertical (EMv) configuration and the carriage moves both the EM and four-electrode lead to oth~r analogous definable. patterns. As a result, some furrows are more compacted than sensors to the selected position (e.g., above the furrow or seed-bed). The EM "start" button others lea~l~g to reduced water-mtake rates, possibly increased lateral water flow and hence then initiates the following automated sequence: 1) the EM reading is made and a selectable higher sallmty levels in both the ~ssoci~ted furrows and beds of trafficed areas com~ared t~ delay (usually l.5 sec) is provided for data logging, 2) the EM-38 sensor is rotated to the nontrafficed areas. The systematIc cyclic pattern in EC (hence soil salinity) mimicked the

29 28 traffic patterns used in the tillage operations. The nature of the cyclic pattern varied depending upon the irrigation system. soil salini~. Cokriging ~or interpolation purpose is used to predict salinity at sites where no While the above "compaction" patterns were determined from EM-38 readings, secondary mformatlOn (I.e. EC, :neasurements) exists. The accuracy of the salinity predictions analogous "tillage" patterns have been observed in our mobile, four-electrode readings. can be mcreased by mcorporatJng the EM-38 and four-electrode data as well as location Markedly abrupt cyclic patterns ofEC, resulted at places where fields had been "ripped" to 0.5 coordmates, mto the MLR equation. m with chisels .. Excavation and detailed examination of the cyclic locations where abrupt . ~ important requisit~ of the MLR approach is that the locations of the soil salinity changes in EC, were mapped revealed deep narrow trenches, or cracks, in the soil callbratlOn SItes must ~e spatJally representative of the entire survey area. This requisite was approximately 2.5 cin wide. An interesting feature of these "cracks" was that they were full of satJsfi.ed by ImplementJng a newl~ developed spatial sampling algorithm. The calibration site dry aggregates of surface soil that had fallen down into them. Such "cracks" potentially selectlOn algont~ ensures that lmear, quadratic and interaction terms in the MLR model can provide preferential flow paths and a means of soil particle translocation by which certain be accurat~ly estimated. The algorithm also provides decision rules for selecting the final MLR pesticides and. other solutes may move to deeper depths in the soil profiles than can be m~del ~anables .. The?ry and t~sts of appropriateness of both the MLR approach and the accounted for by classical solute transport models. calibratlOn samplmg!sltmg algonthm are described in detail elsewhere (Lesch et al 1993 a b) Software for both approaches are available from the U. S. Salinity Laboratory. AdditionallY' Developments of new conversion and mapping theory/software software has be~n developed to process the mobile, four-electrode transect data for th~ Spatially referenced geophysical instrument systems capable of making rapid and purposes ofplottmg transect "profiles" and producing salinity maps. intensive EC, measurements provide a unique tool for field scale soil salinity assessment. Two such systems were described above along with examples showing their practical utility. Several CONCLUSIONS of these examples involved results in terms of soil salinity (ECe). Effective use of the mobile systems requires a rapid method for converting EC, measurements to ECe values. We .This paper described an integrated package of instrumental systems for intensively previously showed (Rhoades et al., 1990, see paper XXX , This volume) that ECe can be measunng EC, ~d x,y coordinates, algorithms for MLR data analysis and site selection and determined from EC, with sufficient accuracy for practical assessment using knowledge, or :ethods for o:tammg ECe, ?:ound-trut~. We believe that the package is unique and repre~ents reasonably accurate estimates, of the clay and water contents in the soil profile at each EC, breakthrouoh m our ability. to :apldly and accurately assess soil salinity in irrigated measurement site. While this method is suitable when EC, measurements are made by hand, it landscapes. Results. refe:r~d to Ill. this paper indicate that much of the apparent chaos in the is impractical for processing the large amounts of data generated with the mobile measurement spatIal pattern of soIl sallmty m lfflgated fields is man-induced and can be explained in terms of systems. For this reason we developed a practical methodology based on multiple linear detefillllllstic processes caused by such management practices as irrigation drainaae regression (MLR) to estimate soil salinity from extensive EC, survey data, limited ground­ cultivatlOn and tillage. The ?alinity patterns and the edaphic and management practices caus~~ truth data, and trend surface parameters. The use ofMLR techniques have been shown to be them can often be ascertamed usmg the new integrated salinity assessment equipment and theoretically equivalent to geostatistical, cokriging techniques, but are more cost-effective and procedures developed at the y. S. Salinity laboratory. The system offers a unique potential for practical (Lesch et al., 1993 a,b). accura~el~ and rapIdly mappmg and monitoring salinity-distributions in the field as well as for dete~mng the c~uses of .salinity, t.he. sources of salt-loading across the landscape and the The typical MLR salinity model takes the form: effectIveness (posslbly effiCIency) oflfflgationldrainage management practices. Since salinity is a tracer ofw~terflow, the mstrumental systems and associated data analysis may have a much broad~r apphcatlOn than s~inity assessment only. For example, the methodology could ?otentlally be used to explaIn or define. t~e un~erl~g processes affecting the transport of where kl, k2, and k3 represent the first three centered and scaled principal components of the m~lV1du.al solutes (I.e. mtrates. or pestJcldes) m Jrrigated fields and to assess irrigation log transformed EC, signal data, x and y represent the cartesian coordinates of the sample umforrmty and degree of leaching. Our findings suggest caution in the adoption of solute­ location, and E is an error term. Different terms in equation (1) can be systematically removed, transport models based on stochastic theory since much of the salinity variability in the field as needed, in order to simplify the model. ~a~ b~ caused by d~te~stic management-related effects. Our results also point out the The MLR technique is an appropriate method when a sufficiently fine grid of hIDltatJons of dete~stlc solute-transport models which do not recognise the interactive secondary data can be acquired quickly and cheaply and where a strong correlation exists ~ffects o.f lmgatlon(drama~e systems, tillage operations, traffic patterns, and seedbed-furrow between the primary and secondary variables. This last requisite involving correlation between mternettmg. These mteractlve effects likely occur in most field situations.

ECe and EC, was previously validated by Rhoades et al., (1989a, 1990). With the assessment system described herein, a series of easily obtained EM, or four-electrode, or both, instrument readings can be acquired across a field using a relatively dense, systematic survey scheme. A limited number of soil samples must be acquired and measured for salinity (the rapid field method of Rhoades et al, 1989b is most practical for this purpose). An MLR equation is subsequently established with the calculated data and tested for residual spatial autocorrelation. If the residuals are independent (or reasonably so), the MLR approach is deemed adequate for salinity assessment involving the prediction, mapping, and monitoring of

30 31 Hydraulic, Chemical, Physical and Biological Techniques for the LITERATURE CITED Reclamation and Management of Salt-affected Soils LIM J D Rhoades and J. H. Chesson. 1993. Mechanization of soil sali~ty C arter, ye ., . . W M' f Am rican Society assessment for mapping. Paper presented at 1993 ater eetmg 0 e Amin Mashali of Agricultural Engineering, Chicago, Illinois, Dec. 12-17, 1?93. .. .' . Technical Officer, AGL Lesch, Scott M., D. J. Strauss and J. D. Rhoades. 1993a. SP.atlal predlc~lO~ of soil sal~mty FAOlRome. usina electromagnetic induction techniques. l. Statistical prediCTIOn models. A com~arison of multiple linear regression and cokridging (In preparaTIo~). . ali' INTRODUCTION tt M D J Strauss and J. D. Rhoades. 1993b. Spatial predictIOn of SOlI s .mty L ecsc,h S co .," . ffi . 'al r algonthm usina electromagnetic induction techniques. H. An e clent spa~ samp mg Shortage of cultivable land resources and growing demand for food and agricultural raw suit:ble for MLR model identification and estimation. (In preparatIOn). .' materials makes the rational utilization of soil and water resources of the world imperative and Phoades, J. D. 1992. Recent advances in the method?!o.gy for measuring and mappmg SOlI urgent. The attainment of self-sufficiency in food remains a difficult objective, even in countries salinity. Proc. Int'l Symp. on Strategies for Utl~g .Salt Affected Lands, Bangkok, with high agricultural potential. Tlailand, Feb. 17-25, 1992. pp. 39-58 estimates. Soil SCI. Soc. Am. J.. 54(1).46-54 ... Recent estimates indicate that the demand for food, fibre and bio-energy products is anteghi P. J. Shouse and W. J. Alves. 1989a. Estlmatmg soil salinity growing at an annual rate of2.5% globally and at 3.7% in developing countries (FAO 1987). In the Rhoa d es, J . D ., N . A . M , , .. .' 53(2)-428-433 from saturated soil-paste electrical conductiVIty. Soil SCI. Soc. Am. J. . . '. Near East Region, agricultural production increased during the period 1981-1986 at an annual rate Rhoades, J. D., N. A. Manteghi, P. J. Shouse, and W. J.. Al~es. 198.9b ..Soll electncal of about 2.1 %, lower than the annual rate of population growth of 3% (F AO 1993). It has been conductivity and soil salinity: New fonnulations and calibratIOns. Soil SCI. Soc. Am. J. estimated that between 1980 and 2000, food production in the region will rise by 2.8% annually, 53(2)-433-439. h 1990 but that the demand for food will increase by 3.2% each year. Historical evidence suggests that a Rhoades, J: D., P. J. Shouse, W. J. Alves, N. A. Man~e.ghi, ~d S. M. Lesc . . global, annual growth in food output of only about 1 % can be expected from area increase at Determining soil salinity from soil electrical conductlVlty usmg different models and global level. In the Near East Region, the arable and pennanent crop land area has increased only estimates. Soil Sci. Soc. Am. J. 54(1):46-54 slightly between 1965 and 1992 (5.0 percent increase in 27 years). It constitutes only 7.6 percent of the total land area (FAO 1994). Hence optimization of the productive potential of the land (including degraded land) will contribute to meeting the increased demand. To meet immediate needs, farmers are forced to strive for maximum production in the short tenn, leading to neglect of long-tenn management needs of the soil and water resources. Such neglect frequently results in decrease of inllerent soil fertility, salinization, or erosion by wind or water. In rainfed areas, fallow periods are declining below safe limits and marginal lands are being put under cultivation in an attempt to meet demands, without adoption of proper and efficient water and soil management practices. On irrigated land, improper water use and poor irrigation management not only prevent the attainment of potentials, but also cause productive land to be withdrawn from cultivation through waterlogging and increasing salinity or sodicity. The net result is physical, chemical and biological degradation ofland on a very large scale. Salinization is one of the major degradation processes leading to desertification because its effect is widespread and has a major impact on land productivity. An increasing awareness of continuing soil salinization and sodication led the United Nations Conference on Desertification (UNCOD), held in Nairobi in 1977,to adopt the following reco=endations: "It is reco=ended that urgent measures be taken to combat desertification by preventing and controlling waterlogging, salinization and sodication, by modifying farming techniques to increase productivity in a regular and sustained way, by developing new irrigation and improvement of the social and economic conditions of people dependent on agriculture".

EXTENT OF SALINIZATION AND SODICATION

Salinization has been identified as a major process of soil degradation. Buringh (1977) calculated from various available data that tlle world as a whole is losing at least 10 ha of arable land each minute: 5 because of soil erosion, 1 because of soil salinity, 1 by other soil degradation processes, and 1 to non-agricultural uses. As a general estimate about 7% of the total soil surface

33 32 of the world is covered by salt affected soils: Australia 38%, Asia 32%, South America 14%, Africa 8.4%, North America 1.7%, Central America 0.5% and Europe 5.4% (Mashali 1989). climates, salts are less concentrated and Na dominates in carbonate and bicarbonate forms hi h enhance the formation of sodic soils. w c There is incomplete information on the extent, distribution and degree of degradation for all soils of countries affected by salinity. In some countries, even the existence of these soils was In .the geography an.d .geo~hemistry of the formation of saline soils, the following salt discovered only through a survey because of the pressing demand for agricultural utilization of a accumulatIOn cycles can be dlstmgulshed. They are not necessarily exclusive (Mashali 1989). region. According to the information derived from the FAOlUnesco Soil Map of the World, the Natural cycles total area - whichjs not necessarily arable - of salt-affected lands in the Near East Region amount to 83.4 million ha. • Marine cycles connected with the accumulation of marine salts in areas lying near the sea or Human-induced salinization is as old as irrigation. The countries affected by human induced salme lake. T~e sea w~ter influences, directly or indirectly, soils and groundwater of these salinization are predominantly located in arid and semi-arid regions and include in the region Egypt, areas, gIVmg nse to salIne sO.ils and groundwater with salt concentrations ranging between 25 Iran, Iraq, Pakistan, Syria, Turkey, Algeria, Tunisia, Sudan and the Gulf States. In Iraq, salinity and and 100 gil. In. coastal aqUIfers freshwater usually overlies a transition zone which in tum waterlogging are problems in more than 50% of the lower Rafadain Plain. In Syria, about 50% of overlIes the salme seawater. The rising watertables of saline aquifers due to increased the irrigated land in the Euphrates Valley is seriously affected by salinity and waterlogging. In recha:ge or the upward leakage from deeper aquifers not only causes land salinization but will Egypt, about 33 % of the irrigated land is affected by varying degrees of salinity and sodicity. In als~ mcre.ase. the seepage of saline groundwater into rivers and water courses and enhance Iran, a combination of salinity, sodicity and waterlogging creates problems in over 15 % of the theIr salinizatIon. area. In Pakistan, out of a total 15 million ha of irrigated land, about 11 million ha are affected by Continental cycles in which salinization results from the migration and redistribution of salt salinity, waterlogging or both to varying degrees. Of the 3 million ha recently surveyed in Algeria, accumulated earlier in s~dimentary salt bearing rocks, or from the deposition of salts during 600,000 ha were classified as salt-affected soils, mainly irrigated land in Oued Chaliff Governorate. the proce~s of weathenng and soil fonnation surface and groundwater. The result is the Salt-affected areas in Tunisia cover about 1.5 million ha, of which 200,000 ha are irrigated. ~ccumulatlOn of ~arbonates: sulphates and chlorides in regions without natural drainage. This In some coastal areas the extraction of groundwater has proceeded to the point where IS more co~on m depreSSIOns and low lying areas than in higher parts of the landscape. intrusion of saline seawater into aquifers has degraded the quality of these resources. Continued I~ nunfed agrIculture, development of saline seeps involves recharge and discharge areas. In irrigation with such low quality groundwater has contributed to the expansion of land salinization. dIscharge areas, groundwater rises to the soil surface creating a seep. As water evaporates Countries with the problem of seawater intrusion include in the Near East Region: Egypt, Iran, from seepage area, s~t accumulates and forms saline soils. The most important factors which Libya, Tunisia and Gulf States (Saudi Arabia, Kuwait, Oman, Qatar, Bahrain and the United Arab may aggrava~e the saline seep problem are the following practices: denudation of vegetation Emirates. by . overgrazmg, drought or fire, replacing native vegetation especially grasses with Globally, more than 77 M ha of land is salt affected by human-induced degradation agncultural fi~lds and. cropping. systems with lower potential evapotranspiration requirements, (Oldeman et at. 1991). (The authors have not distinguished between the extent of salt-affected or ot~er practIces which result m the accumulation of water in the recharge areas. lands in irrigated and non-irrigated areas). Dregne et al. (1991) estimated that about 43 M ha of • ~eslan cycles: If salts migrate with artesian waters through aquifers in, tectonic fault areas irrigated land in the world's dry areas are affected by various processes of degradation, mainly or. m vast, deep contmental depressions, salinity may develop as a result of evaporation under waterlogging, salinization and sodication. However, Ghassemi et al. (1995) estimated that globally and desert conditions. about 20 percent or 45 M ha out of a total 227 M ha of irrigated land are salt affected. Salinity also poses a major management problem in many non irrigated areas where Soil and water mismanagement cycles cropping, relies on limited rainfall. Dryland salinity has been a threat to land and water resources in Anthropo?enic cycles in which man, through poor soil and water management and several parts of the world although only in recent years has the seriousness of the problem become agronomic practIces, aggravates soil salinization and sodication. These practices include the widely known. If it is accepted that 76.6 M ha ofland is affected by human-induced salinization, a following: global total of more than 30 M ha can be attributed to secondary salinization of non-irrigated lands. o Irrigatio~ c~cles ar~ chara~terized by a complex combination of salt movements. In irrigated CAUSES OF SALINIZATION AND SODICATION ar~a~ WIth ms~fficlent dramage, wate: table rises leading to waterlogging, and secondary salinizatIOn. In Imgated areas the followmg can cause soil salinisation: It is necessary to identifY the causes and origin of salinity and sodicity so that the causes and • Insufficient water applications, to the extent that crop water requirements and salt not the symptoms are controlled. leaching requirements are not met· • Irrigation at low efficiency: The efficiency of water use is generally low, less than 30- Salinization 40 pe~cent, due to seepage losses from canals during, conveyance and distribution of In semi-arid and arid areas of the world, the scarcity, variability and unreliabilitly of rainfall ImgatlOn water, and water losses on the farm due to poor irrigation practices. Most and high potential evapotranspiration affect water and salt balance of the soil. Low atmospheric of the water lost finds its way to groundwater, thus gradually raising the water table humidity, high temperature and wind velocity promote the upward movement of the soil solution 1eadmg. to waterlogging and its effects on soil aeration, root penetration and nutrient and the precipitation and concentration of the salts in the surface horizons. In arid regions, various aVaIlabIlIty, and to soil salinization under arid and semi-arid environments Over­ types ofNa, Mg, and Ca salts are concentrated, (mainly chlorides and sulphates). In more humid !rrigatio~ contributes to the high water table, increase in the drainage require~ent and IS a major cause of salinity build-up in many irrigation projects of the world.

34 35 Therefore, a balance between irrigation, leaching, and drainage must be maintained in irrigatio~ wat~r and. :ratertable), and a survey of local conditions including climate, crops order to prevent irrigated lands from becoming excessively waterlogged and salt econOIDlC, SOCIal, pohtlcal ~d cultural environment and existing farming systems. Management of affected (Rhoades, Kandiah and Mashali 1992). salt ~ected lands fo.r agncultural use is largely dependent on the water availability climatic • Irrigation with saline water or marginal quality water: Since good quality water is not condItIOns, crop standing and the availab~ty o.fresources (capital, inputs and time). ' always available, there has been a trend in some countries to use water of marginal fi . Several pract:ces should. be combined Into an integrated system that functions satisfactorily quality for irrigation. Overpumping in the freshwater zone which overlies the saline bor .dlfferent productIOn c~nstra.mts ~d soil types to give higher economic benefit on a sustainable seawater in coastal aquifers and changes in the equilibrium between the fresh and asls. The hydrauhc, ~hyslcal, cheIDlcal, biological and human aspects to improve productivity of saline water, cause the intrusion of seawater in aquifers thus degrading the quality of sal t affected land are dIscussed below. the fresh groundwater zone. Continued irrigation with such -low quality -groundwater has contributed to the expansion of land salinization. Drainage water is mixed with Hydraulic Practices fresh water and used for irrigation in different countries. Using saline water or . . . Leaching and drainage are two basic requirements and prerequisites for agricultural marginal quality water for irrigation without proper soil and water management and utilIzatIOn and successful management of salt affected lands. agronomic practices encourages soil degradation by salinization and sodication. The effect depends on salt concentration and composition, quantity of water, method of irrigation and soil properties. o Poor levelling:. Variations of macro and micro relief also contribute to soil degradation in MANAGEMENT PRACTICES AND HUMAN ASPECTS OF MANAGEMENT RELATED TO USE OF different ways. Small differences in elevation may result in salinization of the lower parts as the SALT AFFECIEn LANDS

water table is closer to the surface and becomes more subjected to evaporation. On the other HYDRAULIC LEACHING (REQUIREMENT, FREQUENCY) hand, changes in the micro relief in the order of 30 cm result in increasing salt content on raised IRRlGATION (SYSTEM, FREQUENCY, QUALITY) spots and better leaching in dips which may explain the spotty nature of salinity observed in DRAINAGE (SYS1EM, DEP1H, SPACINGS, PURPOSE) PHYSICAL poorly levelled but otherwise normal fields. LAND LEVELLING TILLAGE, LAND PREPARATION, DEEP PLOUGHING o Dry-season fallow practices in the presence of shallow water table. SEEDBED SHAPING (pLANTING PROCEDURES) o Misuse of heavy machinery leading to soil compaction and poor drainage conditions. SAND OR MINERAL SOIL MAlERIAL COVER ·SALT SCRAPING CHEMICAL o Excessive leaching during reclamation techniques with insufficient drainage. AMENDMENTS SOIL CONDmONING o Use of improper cropping patterns and rotations. MINERAL FERTILIZATION BIOLOGICAL ORGANIC AND GREEN MANURE Sodication CROP ROTATION AND PATIERN The sodication process involves the presence of soluble sodium salts in the soil solution and MULCHING HUMAN ASPECTS OF MANAGEMENT their adsorption on the exchange complex. The following processes responsible for the formation of ;gi:6~ECONOMIC ASPECTS INCLUDING FARMERS NEEDS AND PREFERENCES

sodic soils in the Near East Region have been given by EI-Gabaly (F AO 1971): ENVIRONMENT desalinization in the absence of enough divalent cations and with insufficient drainage; ORGANIZATION. OPERATION AND MAINTENANCE PQSSIRLE ALTERNATIVE LAND USES evaporation of groundwater rich in NaHC03 and Na2C03 formed under particular geologic FISH FARM:S. HALOPHYIES,MANGROVES, TIMBER AND FUELWOOD, CHEMICALS, ETC. structure in areas having regional faults; • decomposition of sodium alumino silicates which may lead to the formation of NaHC03 and Leaching: Na2C03 and silica; denitrification and sulphate reduction under anaerobic conditions; Methods adopted to remove excess salts from the root zone in saline soils include: • migration and accumulation of sodic salts in arid climates; • use of water with low salinity, in the order of 100-300 ppm, but with dominantly HC03ion5, ~raping:in.s.emi-arid. and arid ~eas the ~dity of the climate characterized by scarcity, variability especially in heavy textured, slowly permeable soils. d u~ehablhty of ramfall and ~g~ potenual evapotranspiration, affects water and salt balance of the sod. Low atmosphenc hUIDldlty, high temperature and wind velocity promote the upward MANAGEMENT PRACTICES movement of the soil solution and salts from shallow salty groundwater to the soil surface ~here salts accu.mulate. Removing these accumulated salts from the soil surface by mechanical means i e Salt affected soils exist under a wide range of hydrological and physiographical conditions, salt scraping has had a limited success, although many farmers have resorted to this soil types, rainfall and irrigation regimes as well as different socioeconomic settings. Therefore, onl~ procedu~e: Although t?is method IDlght temporarily improve crop growth, the ultimate disposal of salts still there is no single technique or agricultural system that will be applicable to all areas. poses a major problem. Management of salt affected lands requires a combination of agronomic and management practices depending on a careful definition of the main production constraints and requirements based on a detailed, comprehensive investigation of soil characteristics, water monitoring (rainfall,

37 36 Flushing: washing away the surface accumulated salts from surface layer to enter through surface same time, salts ne.ar the surface move towards the soil surface where they accumulate The drainage. In arid and semi-arid regions this can be achieved by using irrigation water to desalinize aI~t~nt of~alts which move to the surface depends on the amount of salt present in the ~pper soils having salt crusts. Frequent flushing of salts allows brackish water to enter through the drains. so . ayers om where the water can flow upwards. Thus only a small fraction of salts move u This method is not practical in many cases since the amount of salts that can be flushed is rather dunng evaporatIOn from a SOlI preVIously irrigated by sprinklers. p small. Irrigation practices

Leaching: application of irrigation water in excess of evapotranspiration This allows water to leach in d' It. is . a' important d' to manage water. so as t 0 mamtam.. a re I'atively high. soil moisture content as the salts from the rootzone of soils. This is a very effective procedure to control salinity in salt '1 np rrn".atl.on . unng the croppmg season, and at the same time allow for periodic leaching of affected lands. The leaching requirement (LF) and is defined as the fraction of the applied irrigation s:, .. Good ImgatIOn man~gement allows the achievement of high crop yields with high water use water that must be leached through the root zone to control salinity accumulation at predetermined e clency, and the protectIOn of land from waterlogging and salinization. level. Several aspects should be considered when calculating leaching requirements: . The ~ethods an~ frequency of irrigation and amounts of water applied are of prime Importance . m . controlling salinity . Th ey are d'etermmed by such factors as potential o The recent trend to minimize leaching requirements in order to prevent raising the groundwater ev~potransPlratIOn, root proliferation and depth of root penetration, capacity of the soil to store to minimize the total salt load has to be followed with caution. Its applicability is influenced by an transIIllt water and nature of plant responses to soil moisture stress the salt tolerance of the growing crop, the salt content and composition of irrigation (EC, and relativeISurfa.~e irrigation met~od~ such as border, basin, pond and flood irrigation tend to give SAR); initial ca.ntent, distribution and nature of salts in the soil profile and soil characteristics . . ~ urn orm water applicatIo~ and. downward movement and then relatively uniform salt including exchangeable cations composition (sodicity), texture, clay minerals, soil mineral ?lstn~utIOn and leaching. ~ furrow ImgatIOn, salt distribution is not behind this front. In saline soil weathering, salt dissolution and precipitation and structural stability. It IS dIhfficult to obtam. a satisfactory stand of furrow irrigated crops. However, by doublina the seed o The quantity of salts removed per unit of water leached is increased by intermittent flooding, by rate, t e Yield can be mcreased under furrow irrigation. '" the use of sprinklers and by frequent irrigation, and by small applications of surface water from . Spnnkler irrigation a:IO"\:s a close control of the amount and distribution of water. A high irrigation systems entering the soil at an average rate lower than the infiltration rate of the soil. mOIsture level should be mamt~ned by irrigating more often than would be the practice for similar The slower leaching rate under sprinklers extends the zone of complete leaching more deeply non-saline SOlis. Yadav and Girdhar (1977) found the sprinkler irrigation method better than the into the profile. surface water applicatIOn method because of the ease of applying light and frequent irrigation. o Leaching should preferably be done when the soil moisture is low and watertable is deep. Much . TrIckle or dr:p rrngatIOn results m salt accumulation at the outside edge of the zone of the needed leaching can be achieved during, pre-irrigation between crops and when soil m~lstened by .the. eIIlltters .. Salts should be leached from the planting zone before planting. With permeability is generally at the maximum. Intermittent leaching is more effective than continuous SUitable combmatI~n of SOl~ t~~e, water-quality and discharge rate, roots can function in the leaching. Leaching is easiest in permeable coarse textured soils. The water holding capacity of ~eac~ed zone provIde~ that rrngatIOn period is long enough. Bresler (1977) suggested changing of medium and fine textured soils present no major problems if they have good structure and are . ISC arge. rate. or errutter pOSitIOns to minimize irregular accumulation of salts Trickle or dri underlain by a sand or gravel aquifer. Fine textured, slowly permeable soil is difficult to leach. I~gat~~n IS. SUitable for perennial or seasonal row crops. This method has the adv~tage of keepin~ o The properties of the topsoils (SAR) should be taken into consideration since they limit water t e SOl mOisture ~ontmuously high in the root zone, therefore maintaining a low salt level. The infiltration and are most prone to dispersion (slaking). r~ots of the growmg plants tend to cluster in the high soil moisture zone near the tricklers and t erefore aVOId the salts that accumulate at the wetting front In dn'p and tn' kl . . t' h d o Because sodicity of subsoil horizons or sharp changes in texture and structure with depth may . bl al .. . . c e Imga Ion met 0 s control soil permeability, leaching rates may be limited by the characteristics of such layers. This sal"tapprecia . est t accumulatIOn d . IS likely to occur between the rows d epen di ng on ...Imgatlon water' should be considered in estimating leaching requirements and application rates. lID y, .m er.an mtra row space between the drip points. However heavy irrigation before o Leaching can be timed to precede the criticaJ..growth stages at which stress should be prevented. plantmg IS deSIrable to leach salts that may have accumulated in the soil sdrface . 'i This can be timed through irrigation during dry seasons. o Leaching at times of low evapotranspiration demands is more efficient, for example, at night, Drainage systems during high humidity, in cooler weather or outside the cropping season. The first increments of . When underlying .I~yers are permeable and relief is adequate, artificial drainage is not ~:~~red. ~mce suc.h co~dltIOns are :ar~, a dr~age system will normally be required in salt affected leaching water are more effective than later ones. o Leaching is only effective when salty drainage water is discharged through subsurface drains that .. partlcularl~ m and and seIIll-and condItions. Drainage must remove all precipitation and carry the leached salts out of the areal under reclamation. In general, to reduce the salt content of ImgatIonadj t water m excess d lak of crop demands.. and . any other seepage into the pea or m. t rusIOn . fr om the surface 60 cm of soil to about 20 percent of the original value would require the passage of theace~ seawater.an es .. Under saline conditIOns it regulates both the water and salt balances of about 60 cm water through the soil (a unit depth of water will remove nearly 80 percent of salt soil and subso~l,. e~res a salt free zone and keeps the water table below the depth which may from a unit soil depth). For a more accurate estimation, a leaching curve may be established by Iead to rapid resalinizatIOn. o d The. need for drainage at field level and the required depth and spacing between the drains relating the ratio of actual salt content (ECe) to initial salt content ECeo in the soil (ECeIECe ) to the depth ofleaching water (Dw) per unit depth of soil Ds (DwlDs) (Khosla et al. 1979). ere eter:nmed by the depth of the watertable, irrigation water quality and soil characteristics compactIOn, texture, soil stratification, presence of sodic layer, and mainly the hydraulic o When the soil is subjected to evaporation, water carrying salts moves simultaneously upwards and downwards. Thus some salts continue to move down with the redistributed water and at the

39 38 conductivity of the soil at the drain depth). The capacity of a drainage system should be based on • Mole drains are channels left by a bullet shaped device pulled through the soil. Mole drains are the amount and frequency of water to be removed. .' . generally cheap to install but may last from one to not more than three years, In addition to In a fully developed drainage network the following drainage systems can be dlstmgUlshed being temporary, they are generally shallow (50-60 cm) and have not been used extensively starting at the upstream end: .' where salinity build up from the groundwater table is a major problem, However, they can act as o Field drainage system, which takes up excess water dIrectly from the SOlI. The field drainage a supplementary drainage system and can be connected to the subsurface drainage systems (open channels can be categorized as quaternary channels. or tile) directly in the open system or through hydraulic conjunctions with the tile system and o Collectors (corresponding with tertiary channels): collecting t~e w~ter from a number of field may be ftlled with sand or gravel using specific funnels fixed on the shank to make them last drains and being an intermediate between field dramage and mam dramage system. longer (Mashali 1989), If applicable, mole drainage can reduce the need for deep drainage, i,e. o Main drainage system or disposal system which conveys th.e water from the field drainage increase the spacing between the deep drains. However, in sandy soils mole drains are not stable system to the outlet ofthe.area. It consists of secondary and pnmary channels. or practical, o Outlet where the excess water leaves the area. The outlet may be an open c~annel for .free gravit; flow, or a structure such as a gate or a pumping station. Such a structure IS often built at • Tile drains: these include any type of buried conduit with open joints or perforations that collect the crossing with a protective embankment. and convey excess water from the soil, The conduits may be made from clay, concrete, plastic or other synthetic material, High density polythene (pe) and polyvinylchloride (PVC) are the two Main and secondary drains may be considered as water carriers with n~ interactio~s ~th most common materials for plastic tubes. They are corrugated and flexible, and unlike clay can soil characteristics.. The permissible depth of the watertable in various types of sOlis under rrngal10n deflect vertically when soil is backfilled in the trench, Corrugations in the tubing, provide and drainage varies but it is generally accepted that this depth.ranges between 1.~ to 2.0 m ~~m the sufficient stiffuess to resist the initial soil load, While water enters the clay and concrete tiles at '1 urface The presence of deep sodic layer in the profile will decrease hydra~h~ con~uctlVlty and the butt joints or spaces between adjacent sections, it enters the plastic tubes through sawed slits SOl s . .' Wh laIID1ng this layer and lead to over estimation of the reqUIred field draInage systems. en rec or cut holes spaced unifonnly around and along the tube. For field drains, a diameter of 0,08 m improving hydraulic conductivity the required drainage will be lower. is sufficient in the great majority of cases, Common gradients are in the order of 0,001. In the Various types of drainage systems are used allover the world: surface, subsurface (open, case of pipe collectors, much larger diameters are common (up to some 0.4-0.5 m) at gradients often between 0.0005 and 0.001. For field drains concrete and ceramic pipes have largely tiles and moles) and vertical drainage. become obsolete, For collectors oflarge diameter (over 0.30 m) concrete pipes are widely used. Surface drainage: . h il In surface drainaae ditches are provided so that excess water will run off before It enters t e so . Filter materials are sometimes placed around subsurface drains to prevent the inflow of soil However, the w:t:r intake rates of soils should be kept as .high as possible so that water can be into the drains or to increase the effective drainage diameter and facilitate water inflow. Two types stored and will not be drained off. The capacity of a draInage syste~ should be based on the of materials are generally used: thin sheets of material such as fibre glass or spun nylon etc" or sand amount and frequency of water to be removed, How quickly water runs l,nto dItches depends on the and gravel envelopes or other porous granular materials, rate of leaching water used, land slope and the condition o~ SOli surface mclu~mg the plant cover If Many mathematical equations have been developed to arrive at the optimum depth for any Field ditches used to discharge water into collectlllg dItches should be laId out parall~1 to ~ach spacing offield drains, Computer models that can simulate watertable levels and salt removal under oth~r 20 to 30 m apart and 30 to 50 cm deep depending upon the depth .of the collectlllg dItch. alternative conditions of cropping and water management are available to assess and better design Sharp curves should be avoided to lessen erosion of the banks. ~en leaching IS to be done under the drainage needs of the area. New materials, new methods of installation and the use of larger and especially difficult conditions it is worthwhile to use surface dralllage as a supplementary system to more powerful machinery make construction easier, quicker and more precise than ever before. the subsurface one, Vertical drainage: ;. Vertical drainage by pumping out excess water has given good results in certain soil conditions, i.e. Subsurface drainage: d bl t It may be necessary to install an artificial drainage syst~m for the. control of grou?, water ta e a a when the deep horizons are highly permeable, To detennine if pumping would be effective, specified safe depth. This system may consist of open dItches or tiles perforated pIpes. pumping tests have to be carried out in test wells to detennine the feasibility and area of influence by measuring. water levels in adjacent observation wells or piezometers. Spacing, depth and • Open ditches: open drainage ditches are advantageous for removin~ large volumes of either capacity of the pumped wells and other operational details also need to be evaluated from these surface or subsGil water from land and for use where the water table IS nea: the surface and ~e tests, slope is too slight for proper installation of tile drains or subsurface tile drallls are uneconoID1~al or physically impossible as in many heavy clay soils. Open ditches also serve as, outlets for tde Physical Management drains where their depth is sufficient and other conditions are fav?urable, T~e dIsadvantages of Several mechanical methods have been used to improve inftltration and permeability in the open drains are that they occupy part of the land, obstruct farIDlng, operatIOns, are danger to surface layer and root zone, livestock and more costly to maintain due to growth of weeds, collapse of banks and partIal filling, with soil materials etc" and therefore must be periodically cleaned,

,I ,,I '

! i 41 40

""- Land levelling modified in order to improve leachability and drainability The economics of such measures should be compared with those of less costly alternatives. . Careful levelling of land makes possible a more uniform application of water and hence better salinity control and cropping distribution. Changes in the micro-relief in the order of even Subsoiling less than 30 cm result in increasing salt content on the raised spots and leaching in the dips. thr hS~bsoiling, consists of pullin~ vertical strips of steel or iron called "knives" or "chisels" Repeated land shaping, before cropping would help to level out such differences in elevation. Land ~~~ t e SOI~ to open channels to unprove soil permeability. The shape of the subsoiler's shank levelling that resull s in the formation of shallow profiles or exposure of impervious layers close to an . e ~pace etw~en sh~s depends to a large extent on the depth, thickness hardness an the surface enhances salinization and is not easy to correct. Land that has been irrigated one or two contmuatlOn of the unpervlOus layer (Mashali 1989) Th b fi·al ffi f'. . d persist for only one cropping season. . e ene CI e ects 0 subsOlhng usually years or subjected to heavy rainfall for some years after initia1levelling often needs to be replaned to remove unevenness caused by the settling of fill material. A prior detailed topographic survey could be very helpful to avoid ruining soil properties and in particular removing the surface soil Planting procedures which may be relatively more fertile. For coarse levelling simple scrapers or levellers may be used, Special planting procedures minimizjng salt accumulation around th d h I ful . obtaining bett .. d . e see are e p m while for fine levelling laser controlled precision levelling allows better water distribution and . . er germmatlOr: an seedlmg establishment under saline conditions. Certain smaller water applications, and when combined with automation will lead to higher irrigation modificatIOns of ~lITOW Imgan~n ~et~ods are reco=ended, including planting in single or double efficiency for dead level flooded systems. r~w~. 0: 0; ~opmg beds and m:ganon. of alternate furrows. With either single or double row Land levelling, causes a significant amount of soil compaction due to the weight of the p an ~b' • I S ts are a problem mcreasmg the depth of water in the fuiTo al· gernnnatlOn. w can so unprove heavy equipment ~d it is advisable to follow this operation with subsoiling, chiselling or ploughing, to break up the compaction and restore or improve water infiltration. Annual crops should be Planting in furrows or basins is satisfactory from the standpoint of salinit t lb· often unfavourable for the emer f y con ro ut IS grown after the first levelling so that replanting can be performed before a perennial crop is planted. Pr .. . gence 0 many row crops because of crusting or poor aeration k e-e~:rgenct ~~ganon by sprinkl~r or by special furrows placed close to the seed may be used t~ Land preparation and tillage eep. e so u e salt concentranon low in the seedbed during germination and seedlin establishment. After the seedlings are established, the special furrows may be abandoned and ne! Tillage is another mechanical operation that is usually carried out for seedbed preparation, fu.drrows f.lmade between the rows... or sprinkl· m g may bIde rep ace by fu rrow ...Imgauon. Cultivation on soil permeability improvement, to break up surface crusts and to improve water infiltration. If n ges 0 tOPSOl and furrow culuvatlOn are co=on practices to avoid salt accumulation. tillage is improperly executed it might form a plough layer or bring a salty layer closer to the surface. Sodic soils are especially subject to puddling and crusting; they should be tilled carefully Sanding and wet soil conditions avoided. Heavy machinery traffic should also be avoided. More frequent .. san~~g is. used in some cases to make a fine textured surface soil more permeable by irrigation, especially during the germination and seedling stages, tends to soften surface crusts on llllxmg san mto It,. thus a relatively permanent change in surface soil texture is obtained Wh sodic soils and encourages better stands. pr~p:r~ ~one, s~~~ng results in improved root penetration and better air and water pe~eabili:; w c ac Itat~s mltlal leaching by saline water with high SAR and when surface infiltration limits water penetratIOn. The method can also be used after initial deep ploughing. However certain Deep ploughing Deep ploughing refers to depths of ploughing from about 40 to 150 cm. It is most beneficial proportIOns of sand and clay may give ri.se to a very dense surface (cemented layer). ' on stratified soils having impermeable layers lying between permeable layers. In sodic soil deep . In Egypt some f~ers use this method after irrigating a few years with saline water ploughing should be carried out after removing and reclaiming the sodicity, otherwise it will cause (dramage or well waters) ~o unprove the permeability of the surface layer and facilitate the leaching complete disturbance and collapse of the soil structure. process or as a better media (10-20 cm on,the surface) for plant establishment. Deep ploughing to 60 cm loosens the aggregates, improves the physical condition of dense layers, increases soil-water storage capacity and helps control salt accumulation. Crop yields can be Chemical Management markedly improved by ploughing to this depth every three or four years. In places where sodium­ affected surface or subsoils are underlain by soil containing considerable gypsum, deep ploughing Amendments can bring the gypsum to the surface. This serves to break up the compacted layers and provides a d. In salt affected lands chemical amend men t s are used to neutralize. soli . reaction to react with i more favourable physical matrix for water movement and root penetration while supplying soluble so d~um carbonate and to replace e1changeable sodium by calcium. This decreases the' exchangeable calcium. Soils should not be ploughed when moist, because moving heavy machinery over them so I~m percentage (ESP) and should be followed by leaching for removal of salts derived from the causes compaction. This is a co=on problem in arid areas. (Mashali 1982). :~~c:lOn of ~e :=~ndments with sodic soils. They also decrease the SAR of irrigation water if The selection of the right plough types (shape and spacing between shanks), sequence, h .~ to ~he lmgatlon system. Some work in countries where soils are high in exchanaeable Mg ploughing depth and moisture content at the time of ploughing should provide good soil tilth and d~s I e~t e~ and defined t~e adverse role of high Mg in association with high Na on s;elling and improve soil structure. Special equipment can even invert whole soil profiles or break up substrata IsperslOn 0 some sodlc SOlIs. Generally, these amendments fall into three categories. as deep as 2.5 m that impede deep percolation, so that many adverse physical soil conditions can be

43 42 • Soluble calcium salts such as calcium chloride and gypsum. • Slowly soluble calcium compounds such as limestone (CaC03) and waste lime from sugar mills Amendment Relative guantity (a mixture of alkaline calcium compounds). • Acids or acid forming substances such as sulphuric acid, sulphur iron sulphate, aluminium Gypsum (CaS04- 2H20) 1.00 Calcium chloride (CaCh - 2H 0) 0.85 sulphate, lime sulphur, pyrite, etc. 2 Sulphuric acid (H2 S04.) 0.57 Iron sulphate (peS04 - 7H 0) 1.62 Gypsum (CaS04.2H20) is by far the most common amendment for sodic soil reclamation, 2 particularly when using saline water with a high SAR value for irrigation. Calcium chloride is highly Sulphur (S) 0.19 soluble and would be a satisfactory amendment especiany when added to irrigation water if it were Pyrite (peS2) 30% Sulphur 0.63 not so expensive. Lime is not an effective amendment for improving sodic conditions when used Limestone (CaC03) 0.58 alone. Its solubility in an alkaline medium is very low, therefore it is a very slow acting material. When combined with a large amount of manure, it has a beneficial effect, presumably because of includl.nThteh purity of different amendments to be applied should be considered in the calculation the calcium bicarbonate formed as the manure decomposes and releases carbon dioxide to react g e gypsum. with lime. Sulphur is an inert material until it is oxidized to sulphuric acid by soil micro-organisms. Like other microbial transformations sulphur oxidation requires oxygen and time. The delay in Application method reaction time _ m~nly in very clayey sodic soils - and the strong acidity occurring around sulphur su The effectiveness ?f the amendment dep~nds on the application method. Amendments like particles which may be harmful to plant roots are the principal limitations in the use of sulphur. All r:e d: :eo~oD?allY applied broadcast and then Incorporated with the soil by disking or ploughing. other sulphur containing amendments (sulphuric acid, iron sulphate, aluminium sulphate) are replace~ for s=;a:~o~;~; :re:.:::;;s on the depth up to which excess adsorbed sodium must be effective because of the sulphuric acid they contain originally, or the acid formed upon microbial oxidation or hydrolysis. Reactions leading to oxidation of pyrite are complex and appear to consist ~he bquality of gypsum depends largely on its fineness. The optimum particle size for of chemical as well as biological processes. Press mud is a by-product from the sugar refining to'"gy psumbe for IS the a outreclam 2 mm ti· Howeverf d. ' th~ fi ner th: gypsum partIcles. the more effective they are likely process in some countries such as India, pakistan and Egypt and it can have a quite variable economic considerat~o:n 0 so IC so s. The sIze to which gypsum must be ground is a matter of composition. It may be high in CaC03 and organic matter and, depending on the process being used in the particular refinery, may also contain high sulphur. Press mud may have good local application fi Id B~cause of hazards in h~dling,. the application of sulphuric acid is difficult under ordinary c e con It:ns .. However, ~peclal eqUIpment is now available in some countries that sprays the where it is cheap. Generally, the choice of an amendment for a particular place will depend upon its relative ~:entra~el aCI~ on the SOlI. surface. Amendments are sometimes applied in the irriaation water effectiveness judged from its improvement of soil properties and crop growth, the availability of the . . specla :~Ulpment, partIcularly when using saline irrigation water with a high'"SAR al IIruted solubIlity of gypsum· t (0 25 0 / o. . vue. amendments, the relative costs involved, handling and application difficulties and the time allowed Lthis d h . III wa er. .. /0 at 25 C) IS sometImes cited as the major drawback of and required for an amendment to react in the soil and effectively replace adsorbed sodium. ~en. ment w en rapId reclamatIOn IS desired. When gypsum is mixed in high! sodic soil its SolubJiltYdlllcreases se~eralfold because of the preference of exchange sites for divale:t calcium I·ons compare to sodIUm Ion G . 1 Quantity of amendment: NIL, Cl KCI KH . ypsum partlC ~s are much more soluble in salt solution such as NaCI In sodic soils the calculation of the dosage of amendments required is based on the theory Ca ' , 2P04 than WIth salt solutIOn haVIng common ions with gypsum such as K2 S04 0; of the equivalent of ESP i.e. the dosage of the chemical compound used (gypsum, sulphur, etc.) pa%c~~2. However, pH values, temperatures, form of gypsum or lime affect the suitability of their must be equivalent to the quantity of exchangeable sodium to be removed. This in tum depends on such factors such as the soil texture and mineralogical make up of the clay, extent of ESP value of the soils or SAR of irrigation water, and the crops intended to be grown and accordingly the depth Soil conditioning up to which excess adsorbed sodium must be replaced for satisfactory crop growth. ermeabiliAttempts have been.. made to coagu.a 1 t e SOl·1 partlC. Ies and proVIde . deep aeration and better Because of the presence in some sodic soils of free soda, the actual efficiency is lower. Thus ~m . ty and w~ter infil.tratlOn by chenucal treatment. Treating the soil with dilute bituminous it is recommended that the amount of applied gypsum be increased in accordance with equivalents fi u1s~?ns r;ulted In effectIve ~ggregation, improved aggregate stability and reduced surface crust offree sodium carbonate and bicarbonate. Under field conditions one irrigation prior to application orma IOn. at~~ percolated twIce as fast through bitumen-treated soil. of an amendment would further ensure leaching of soluble carbonate, eliminate the need for a tl P: COn?ltlOn~r based on. ~gni.n sulphate has been shown to improved soil structure and additional quantities of gypsum for neutralizing the free sodium carbonate. Equivalent quantities of =re~ y/mpr~ve sOlI. permeab~lity In the 0-10 cm layer. Soil conditioners can have pr:ctical some chemical amendments commonly used for reclamation of sodic soils are given overleaf: aPP c: IOns In seedh~g est.ablishment when soil is under saline conditions. Stability of soil a ggr.e",ates prevents dlsp~~slOn and formation of crusts and infiltration can be maintained b ::lic~tlOndof small qu~tItIes. of organic polyelectrolytes to the soil surface. They can be effectiv~ ele e~ I~tro uced In the lfTI~atI?n water or when sprayed over the soil surface. Cationic or anionic c 0 ytde~ are most effectIve In the presence of gypsum. Peat has been shown to have a value as a SOl l con ItlOner and compost.

45 44 Factors limiting the use of soil conditioners are high costs, the difficulty of achieving an HUMAN ASPECTS intimate incorporation in the soil and limitation of beneficial effects to a shallow surface layer. Farmers and Extension Services Mineral fertilization . Farmers have over the decades developed their oWl! technologies for crop production under The reader is referred to the paper by the same author in the present v~lume" entitled: different conditions of salt affected land but at subsistence level. With population increase and " Availability of nutrients, fertilizer management and crop tolerance under salme conditIOns . pressure to use marginal land, their production techniques need to be improved to increase and sustain crop yield under such conditions. Therefore, it is necessary as a starting point to understand Biological Practices the local practices of the farmers. These should form a basis for improvement of management techniques practised in salt affected land. To approach the task of improving production under such Organic and green manure . .' . conditions, the following aspects should be considered: Incorporating organic matter into the soil has two ~rmclpal be.n.efic1al effects under saline • First, development of a technological package which consists of individual practices but conditions particularly in sodic soils: improvement of SOli permeability and :elease of c.arbon to be implemented as a package. dioxide ~d certain organic acid during decomposition. This will help in low~rmg the pH m the • An adequate infrastructure and appropriate socioeconomic conditions must be in place release of cations by solubilization of CaC03 and other minerals thereby mcreasmg EC and for the effective application and adoption of proper technologies for salt affected areas. replacement of exchangeable Na+ by Ca++ which lowers the ESP: . . . . • There must be a strong and effective extension service with a strong technical Oroanic m\lIlure also acts as a nutrient source, partlcularly mtrogen, ~t Impr~ves SOli improvement back up. o . b'I' . ul l' d lis and mcreases structure and improves aggregate formatIOn and sta 1 Ity, partlC ar y ill san y so , The technological package available should be field tested under farmers' conditions and the cation exchange capacity of the soil. . . acceptance of newly developed technologies ascertained. This is an essential step towards ensuring Crop residue application is one of the easiest methods to improve water mfiltratl~n, farmer acceptance and its widescale adoption. Management of salt affected land is the resultant of especially for small farmers who do not have the resources to implement more costly correcHve the needs, constraints and potential of a farmer, and therefore the farmer and his environment measures. Unfortunately in many instances, the small farmers use cro? residues for other purposes should be the centrepoint of every management programme. Technology packages by themselves and little if any, is returned to the soil. Crop residues left on the soil surface Will Improve wat~r can hardly make a significant impact on increasing crop yields under such conditions. Other factors, infiltration. Both crop residue left on the soil surfac~ as ~ell as the root .system of the crop hel~ m such as pricing and marketing policies, labour, infrastructure development, intensive training and keepin the sodic soil open. The benefits decline Wlth time until replemshed ~t the next croppmg extension programmes should be considered. o season The incorporation of crop residues to maintain organic matter and nutnent contents should Unless all aspects of soil, water, crop management practices are carried out correctly, the soil deteriorates and crop production declines. Extension officers, project staff and farmers should be encouraoedo in all salt affected soils. . The more fibrous and less easily decomposed crop residues such as those from bru:ley, nce, therefore be fully trained in all aspects of crop tolerance and production. Agriculture is becoming wheat, maize and sorghum have been shoWl! to improve water pe?etration. The best res1d~~s are increasingly mechanized and efficient handling of the machinery, equipment and instruments used those which do not decompose or breakdown rapidly. To be effective,. relatively large quantlHes of should be promoted by training personnel in their use and maintenance. residues are needed - 40 to 400 metric tons per hectare have been apphed.. . . Growino legumes will improve soil structl1re and act as a source of mtro~en m t~e SOli f~r Socio-economic Aspects o . bl . hid' ty particularly ill the next crop. Physical properties of the SOli and nota y ItS .water 0 I~g capaci , A study of the existing farming systems should be carried out in great detail including, a sandy soils, density, structure, and infiltration rate will be lffiprov~d usmg gree~ manure. Green description of actual land use; existing farmers' knowledge; climate and crops; a description of the manure has a similar effect on soil properties and as a source ofnutrlents as orgamc n:anure'l!~der household economy including needs and production in kind and cash; a description of the social, saline conditions green manuring should have a fast growing rate, be resistant to saline conditIOns political and cultural environment (Douglas 1989), as well as farmers' views on the suggested and should decompose rapidly. Green manure cropping probably has a better chance than farm yard management practices. It is now recognized that social and economic factors have a decisive manure (FYM) of being integrated into a reclamation management package. influence on farmer decisions to accept any new technology and therefore have to be fully taken into account Using salt affected soils for crop production calls for increased use of production Mulching . . ali' . inputs including fertilizers, seeds, agrochemicals, machinery, construction of field irrigation and Mulching to reduce evaporation losses will decrease the opportumty for SOli s .mz~tlOn. drainage systems, labour, etc. Farmers often need readily available credit at reasonable interest rates Under saline conditions mulching can considerably help leach salts, reduce ESP and obtam higher to enable them to purchase or implement these inputs. A suitable infrastructure to supply inputs, yields of tolerant crops. facilities and credit is an important factor to increase crop production in salt affected soils. Alternative solutions and management practices for a given situation should be evaluated. Crop choice . l'1 d' Economic, ecological, administrative and social feasibility should be taken as decision criteria The reader will be referred to the paper by the same author ill the p.resent V? .um~. enHt e . (World Bank 1986). "Availability of nutrients, fertilizer management and crop tolerance under saline conditIOns .

47 46 into other value added products such as chemicals, medical products, methane gas or alcohol for Environmental Aspects ~e~ and solvent purposes. Of these plants the Jojoba (Simmondsia chinenis) is an example (as An environmental impact assessment should be undertaken to identifY the possible impacts or~t, ~and. dune fixatIOn, ~ulching, medical products, lighting, in rubber, leather and paper of the proposed activities on the environment (not only the ecological aspects but also the political, pro uctlOn, m alcohol and aCId production, chemicals for paint). engineering, economic, and social aspects). The process of assessment includes understanding the Halophyte.s can. be grown under very saline conditions, for example, Juncus vigidus and J proposed action, understanding the environment in which the suggested activity is taking place and acutus can. crow m salin~ marsh.es or under irrigation with brackish water or even sea water. The projection of the future impacts on the environment, possible alternative course of action to serve culms prOVIde fibre for high quality paper production and the seeds have medicinal value. the main purpose (selection of different areas), a comparison of the effects of the indicated possible ~eptochloa jusca (kallar grass) as forage, green manuring crop compost pul for a er courses of action, and an indication of uncertainties and gaps in available information. It is productIOn and as a solEucalyptus camaldulensls, E. rudis, E. micro theca, E. occidentaiis, Organization, operation and maintenance Gledltsla . triacanthos, Haloxylon aphyllum, Haloxylon persicum, Whether or not to go ahead with the reclamation of a given salt affected area: the decision Parkinsonza aculeata,. Pithecellobium dulca, Populus euphratica Prosopis should be based upon an analysis of costs and benefits in the broadest sense (feasibility study and alba, P. chinensis, P. cineraria, P. tamarogo, Robinia pseudo~cacia and environmental impact assessment) (Cavelaars 1991). Tamanx aphylla (T. articulata). Normally the various aspects of a large reclamation and development scheme (construction of civil engineering works, villages, public facilities, allocation of land to settlers, etc.) would be REFERENCES controlled by various agencies, most likely under the responsibility of different ministries. This might entail the risk of bureaucratic frictions and inefficient performance. A recommendable Bernstein, L., Fireman, ~. and Reeve R. C. 1955. Control of salinity in the Imperial Valley. US alternative is to create a special development authority under the political responsibility of one B . Department of Agnculture, ~gncultural Research Service Bulletin 41 (4). 15 p. minister. urmgh, P. 1977. Food productIOn potential of the world, pp. 477-485. In: The World Food There seems to be a widespread temptation among governmental agencies to divert funds to Problem: Consensus and Conflicts. Radhe Sinha (ed.). Pergamon Press. new reclamation projects rather than to the maintenance of existing ones, which are consequently Bresler, E.· 1977.W Modelsfi of. predicting . the impact of irrigation on soil salinity . Int . SM·ymp. anagmg experiencing a chronic lack of funds with the inevitable probability of a rapid deterioration of the Salme aters or ImgatlOll, Lubbock:, Texas. Proc. 299-315. entire project. A sufficient budget oflocal funds for operation and maintenance should be reserved. Cavelaars, 1. C. 199.1. Water control in reclaimed coastal lands. A paper presented at the Training Also sufficient cooperation and discipline among farmers and other interested parties to respect Course on Agnc~ltural Use of Coastal Reclaimed Land at Collelcoe of Agriculture, Chonnam channels, structures and other works of common interest, and to contribute everyone's assigned D "NatIOnal Uruverslty, ~wang Ju, Re~. of Korea. Oct. 1991. share in common maintenance work, and in the case of irrigation, to respect everyone's allocated ouglas, M. 1989. Integratmg conservatIOn mto the farming, system - Land use planning for small share of water. farmers, concepts and procedures. Dregne, H.~ Ka~sas, M. ~d Razanov, B. 1991. A new assessment of the world status of ALTERNATIVE FORMS OF LAND USE desertIficatIOn. DesertIfication Control Bulletin (United Nations Environment ProgranJIDe) 20:6-18 1 . In some cases, instead of reclaiming salt affected soils to suit the existing crops, some plant El-Gabaly, M.M. 1971. Recl~a.tion and management of salt affected soils. In Salinity Seminar, species could be selected to suit the environment. Introduction of such plant species into the saline Baghdad, pp. 50-79. ImgatlOn and Drainage Paper 7. FAO, Rome. conditions would not only provide green matter for various uses but also improve the land. Such ~ ~O. 1985. Wat.er quality for irrigation. Irrigation and Drainage Paper 29, Rev. 1. FAO, Rome. plants can be introduced on barren saline wasteland where no fresh water is available and ground O. 1987. Agnculture: Toward 2000. Revised version. FAO Conference Twenty-fourth Session water is brackish. The green matter (biomass), or seeds produced on these lands could be used in November 1987. " numerous ways such as forage, manure and for making pulp for paper, and could also be converted FAO. 1993. Country tables, 1993. FAO, Rome.

49 48 FAO. 1994. FAO Production Yearbook, 1993. Vol. 47. FAO, Rome. Reclamation and Management of Salt-Affected Soils · F Jakeman AJ. and Nix H.A 1995. Salinisation ofland and water resources: Human Gh asseIIll , ., " . S d' causes, extent, management and case studies. Centre for Resources and Environment tu les. Fareed Abdul Nabi The Australian National University, Pub. CAB International, Wallingford, Oxon. ., Professor, AI-Ain UniversitY,UAB Khosla, B.K., Gupta, R.K. and Abrol, I.P. 1979. Salt leaching and the effect of gypsum applicatIOn in saline-sodic soil. Agricultural Water Management 2:193-202.. . INTRODUCTION Mashali, AM. 1982. Soil deterioration and the role of the ExecutIOn Authonty ~or land improvement projects, its control. Presented at Panel of Experts on Amel.lOratlOn ~d Increase in food pr?duction is a pressing need due to the increase in population Development of Deteriorated Soils in Egypt, 2-6 May 1982, Carro. Project growth. Natural and envrronmental conditions in addition to human activity have FAOIUNDPIEGY!79/020. re~ulted !n the degradation of a part of the productive land. Degradation resulting from Mashali, AM. 1989. La salinizzazione la de sertification del suolo. Genio Rurale N.11 :5062.Ital~ soil sahmty IS one of the causes of this degradation. Rhoades, J.D., Kandiah, A and Mashal~ AM. 1992. The use of saline waters for crop production. However, to provide food world wide, land reclamation is a must. Salt affected FAO Irrigation and Drainage Paper 48. FAO, Rome. . lands are considered the most difficult and complicated to reclaim as they are usually UNCOD 1977. Desertification, its causes and consequences. Round-up, plan of actIOn and loca~ed m the arid regions of the world. Because of drought, water shortage and poor resolutions. UNCOD, Nairobi, 29 August-9 September 1977. . quality, these lands could be subject to salinity, even after their reclamation. World Bank. 1986.. Land and Water Resources Management Seminar. EconoIIllC Development Continuous management for conservation of productivity is, therefore, necessary. Institute. . Below are some considerations and strategies that should be followed when the Yadav, J.S.P. and Girdhar, I.K. 1977. Salt transl?cation and cr?p growth under spnnkler and reclamation of this land is considered. surface methods of irrigation in sodic soil. Indian J. Agnc. SCI. 47:397-400. Types and Causes of Salinity

The movement of soluble salts and their accumulation following water evaporation is the direct cause of salinity. Salts, usually, originate from sea water, surface and groundwater, artesian wells water and irrigation water. . Water and land of the coastal regions and the land close to lakes are directly and mdrrectly affected by sea water. In deserts, water and soil salinity increase as a result of salt movement and precipitation. . In p~aces where the water table is high, water rises by capillarity and evaporates leavmg behind accumulated salts. Saline water is used for irrigation in areas where water table is high and thus causing secondary salinization.

Reclamation of Salt-Affected Soils

. The success or failure of land reclamation depends mainly on choosing the SUitable reclamation method and'this requires the following prerequisites: * A survey of the accumulated salts including: type, concentration and distribution (vertical and horizontal). * Soil structure and permeability; depth and flow of ground-water. * The availability of irrigation water, its quality and cost. * Infiltration rate of the soil. ; * Local climate. * Land topography * Detailed topographic maps of the area.

Relying on these previous information, the following decisions can be taken: * The size of the land levelling operation. * The water quality required for leaching, irrigation and water distribution. I

I 51 50 * Drainage system design: depth, distance between drains, etc. water has low or no salinity and the evaporation rate is low. This method requires less * The quantity of drained /leached water expected. w~ter . tha.n the contmuous water application technique, but resalinisaton between * The time span for running this operation. ImgatlOn mtervals is possible. The continuous water application is much faster. The quantity of water required for leaching depends on the following factors: To insure the success of this operation, these main goals should be aimed for: * Salt concentration in soil, • Lowering the ESP to less than 10%. * Salt concentration in ground-water, .• Lowering the water table (if high) to an extent far from the critical * Salt species, point to prevent secondary salinization. * SOlI infiltration rate, * Drainage system efficiency (in case of low infiltration and high RECLAMATION USING LEACHING ground-water level), * Depth of soil layer to be desalinised, Reclamation Procedure * Washing procedure (continuous or alternate).

The following is required: There are several ways to calculate the water quantity required for leachino- • Setting a drainage system if the land has a high water table or low infiltration, one of them is Kodva's equation: 0' • Levelling of the land where necessary, y= nl.n2.n3(400x) + 100 • Conoecting irrigation chanoels or networks, where Y = water quantity expressed as water' depth in mm • Final levelling, • Plowing the soil and proceeding with the leaching, nl = infIltration factor, nl = 0.5 for sandy soil, • Monitor the soil salinity and drainage water salinity, = I for loamy soil • When soil salinity permits, proceed with planting of salt tolerant plant species, = 2 for clayey n2 = ground water depth factor, n2 = I for low water table • Shift to other plant species when there is a change in salinity, • Planting salt non-tolerant plants and observing the soil to prevent future . = 2 for high water table n3 = salinity factor 1:3 depending on salt concentration of ground water salinization. X = average soil salinity to a depth of I to 2 m Special attention should be given to dispose of the dissol:ed sal~s removed Cropping During Leaching from the soil profile. When the soil has a low leaching capa~lty, dramage plpe~ should be installed in the early reclamation process and when a high water table eXIsts, t~e Th~ following considerations should be followed when cropping and leaching drainage pipes should be deep enough to prevent depth IS desaliniz~tion. T~s are done simultaneously: influenced by the flow and the salinity of ground water and soIl propertIes such as • Irrigation water application should be higher than the plants needs to satisfY hydraulic conductivity. leaching requirements. • ~lanti~g crops that enhance leaching efficiency such as those that need frequent Leaching Methods ImgatlOn. Adequate quantities of water should be added to dissolve soluble salts and • Over-irrig,ation should be avoided to prevent the rising of the water table. • Preserving the vegetative crop especially during summer so as to minimise move them in the direction of the drains. evaporation. Two methods are usually followed: • Continuous water application, or Reasons for the failure of land reclamation could be summarised as • Alternate application. • Irnrroper land levelling which causes uneven distribution of water and consequently In the first method water is added and kept ponding at a level of 10 cm above the fonnation of saline spots. the surface. This procedure insures a quick removal .of salts ~d ~arly cropping. It can • Inadequate quantity of water. be done when soil infiltration rate is high, evapora1:!on rate IS high and when ground • Unsuitable drainage system. i I • Unsuitable leaching procedure. water is saline. The second method is applied to dissolve salts as a first step and then wash • Application of saline water for leaching without shifting gradually to freshwater. them down. The procedure is repeated to prevent desalinizati?~. It ,,":orks when the ~ ! soil has a high infiltration rate, the water table is below the cntlcal pomt, the ground

.1.

53 52 Measuring and Monitoring Soil Salinity . !his paper describes field methods of salini ". . J.D. Rhoades, Director, US Salinity Laboratory, USDA diagnOSIs, monitoring and mapping usin the mo ty ap~nusal, inclUding tho~e SUited for summarizes the principles of soil electri~al d st ~.odem rnstruments and techniques. It also Riverside, California, USA con measuring it and the means of I' t t· uciltlVlty, the equipment and methods used for " ' n erpre rna so salinity . t f . conductiVity of soil water) and EC (the EC /th .' In erms 0 ECw (the e1ectncal INTRODUCTION e 0 e saturatIOn extract) from EC,. DIAGNOSIS OF SOIL SALINITY USING DIRE The uncertainly of current models for predicting the suitability of brackish and saline ELECTRICAL CONDUCTIVITY IN THE FIELD CT MEASUREMENTS OF BULK SOIL water for irrigation makes it highly advisable to ascertain the initial levels of soil salinity before beginning to irrigate with SUGh water and to monitor changes and trends that result over time. It is Principles of Soil Electrical Conductivity Measurement essential to know the levels of soil salinity within the vicinity of the seeds and young seedling roots during these critical periods in the growth of plants. Subsequently, it is important to know As most soil minerals are ins I t I' . the levels of salinity that exist within the region of the soil profile where the major part of the through the large water-filled ores u a ?rs, e ect~cal co~ductlOn in moist, saline soils is primarily water is extracted by the roots in order to determine water availability to the plant and thus to a relatively small contributionPof e~c;:ch con.tam the e dls~olved ~alts (electrolytes). There is also schedule irrigations. Over the long run it is essential to measure the salinity distribution within the conduction in soils so-called surface ge dcah~ns (Eassoc)lated WIth the solid phase) to electrical · . ' con uctlon C because these I t I soil profile to determine the adequacy of leaching and drainage. The net direction of water flux IlID1ted in their amounts and mobilities Th al '.' e ec ro ytes are more within the soil profile can be deduced by the shape of the salinity depth curve; the relative essentially constant for any given sali~e so~ vE~e ~fEC, ~s a~sume.d, fo~ practical purposes, to be magnitude of leaching can be estimated from the value of soil water salinity occurring at the in the water films associated with the s rei rl: coup e? rn senes With the electrolyte present bottom of the root zone. For more detailed discussion on this subject, see Rhoades and Halvorson bridge adjacent particles to provide a 0 I ;u aces and rn the small water filled pores which (1976) and Rhoades and Corwin (1981). pathway acts in parallel with the rna' 0 secon. ary pathway for current flow in moist soils. This Assessing soil salinity is complicated by its spatial variable nature. Numerous samples relative flow of current in two ath~~' sc~nt1nuous flow pathway (large w~ter-filled pores). The (measurements) are needed to characterize just one field. Furthermore, soil salinity is dynamic in the magnitude ofEC d th p y epe~ds on the solute concentrahon of the soil water , an e contents of water rn the two different categories of pores. ' nature due to the influences of varying management practices, water table depth, soil permeability, evapotranspiration rate, rainfall amount and distribution, salinity of the perched A mathematical description of the above model fl' . .. . groundwater, and geohydrologic situation. Soil salinity information is often quickly out of date as equation I after Rhoades et ai. (1989b): 0 e ectncal current flow In soils IS given in management, water table depth and weather conditions change. When the need for replicate measurements and extensive sampling requirements are met, the expenditure of time and effort to characterize the salinity condition of an area with conventional soil sampling and laboratory analysis procedures becomes prohibitive. [I] It is thus obvious that a practical means of measuring soil salinity directly in the field is advantageous, if not essential, to obtain timely information required for making appropriate Where EC, and EC, are as previously defin dad a e management decisions. Practical procedures are also needed to locate representative monitoring water and solid in the paste; a,", and a = _ e, , an w are the .volu:n fraction of total sites, to delineate sources of salt loading, and to map the distribution and extent of salt-affected the series-coupled pathway (the fin~ ';;ter-~lle Ow,) are the volumetnc SOli wat~r contents in soils. pathway (large water-filled pores) respectively ~~o~~ an~ :~separate contmuous liquid Instrumentation for assessing bulk soil conductivity (EC,) by means offour-electrode and conductivities of the soil water in the tw 'd' an are the specific electrical , The rei t' hi b 0 correspon Ing pathways, respectivey. electromagnetic induction has advanced since 1971 when EC, was first shown applicable to the • a Ions p etween E'" d E'" d EC . \...w, an \...we an e IS, after Rhoades et al. (1989b): determination of soil salinity in the field (Rhoades and Ingvalson, 1971). Theories on the we measurements and interrelationships among the various soil parameters involved have been (EC awe + ECw, Ow,) 1 P b = ECe SP 1100 advanced and subsequently refined, improved instrumentation and circuity have been developed, [2] and commercial units have become available for measuring EC, using both four-electrode and Where Pb is the bulk density of the il F . al electromagnetic induction (EM) methodology. Accurate and simple methods have been assumed that ECwe = ECw, and, therefore ~~ (E' ;:,r pr)a~lc purposes of salinity appraisal, it is developed for calibrating soil salinity and EC,. Applications of the method for measuring, support th al'd' f hi ' Ow - (ECwe awe - EC,., Ow,) Data exist to e v 1 Ity 0 ~ s a~sumption (Rhoades et aI., 1989c; 1989d). . monitoring and mapping field salinity, detecting the presence of a shallow water table, detecting The other relatIOnships used in th fall" saline seeps determining leaching fraction, and scheduling and controlling irrigations have also soil salinity are (after Rhoades et aI., 198~d)ac IC app Icahon ofEC, measurements to appraise been developed and demonstrated. Reviews of some of the above are given elsewhere (Rhoades, 1976, 1984; Rhoades and Oster, 1986; Rhoades and Corwin, 1984, 1989; Rhoades and SP 0.76 (%C) + 27.25 [3] Miyamoto, 1989; Corwin and Rhoades, 1982, 1984, 1989; Rhoades, 1989). Pb 1.73 - 0.0067 (SP) [4] a, Pb 12.65 [5]

54 55 [6] percentage, and b and , are the bulk density of the soil and the density of the aqueous extract, 8wfe SP. Pb /200 [7] respectively. Alternatively, EC, may be obtained from measurements of EC, and reasonable 8 wfe . FC/100 8 w [8] estimates of %C and 8 we. 0.639 8 + 0.011 8w, w [9] 0.019 SP - 0.434 EC, APPRAISAL OF SOll- SALINITY FROM MEASUREMENTS OF EC, UNDER FIELD . d b 'fi I' thods is the estimated CONDITIONS h e %C is cla percentage as estImate Y ee me ,wfee . . W er Y fi Id .ty and FC is the percent water content of the SOli relatIve volumetnc water con~ent at e( C~p~C~y "feel' methods. Use of the above relationships permits The practical use of field measurements of ECa to deteIDline ECe requires that b, " ECs, to that at field capacIty, as es !IDa e ar . . al oses from the 8 w and ew' be estimated, since only EC, is easy to measure in the field. The determination of EC, to be estimated in the field sufficiently accurately for s dlmtb a~t~s ~:1s That such ECe from EC, measurements has been shown to be successful for salinity appraisal purposes in an f EC d the estimates of %C and 8 wfe ma e y ee me 0 . . measurement 0 , an fi. al .d land mineral soils of the Southwestern Umted extensive field test in California where Ph was estimated from soil texture, P s was assumed to procedures are generally adequate or typIC an 3 be 2.65 g/cm , and 8 w, and ECs were calculated from estimates (made by 'feel') of 8 w and clay States has been demonstrated by Rhoades et al. (1989d). . t e I EC from EC Field testing of equation [1] shows that the .ability to deltenruECne;ccur;C ~t 101: 8 is th; percent, respectively, using empirical relationships (Rhoades et aI., 1989a). d Th ·nability to deteIDlIDe accurate y w om, w Additionally, 'sensitivity' analyses have been made of the relationships used in these field decreases as 8 w .e I. urac of measurement ofEC, that is necessary as ec~eases. tests (see Table 1), with respect to the individual effects of the variables EC" EC" 8 w, 8 w" Ph, consequence of the sIgnIficant Illcrease III the acc Y I al f 8 I·t I· s not . I al f 8 At very ow v ues 0 w, P, and %C upon ECe . These analyses establish the magnitude of error in EC due to error in the EC = f(ECw) relatIOn flattens at ow v ues 0 w· e possibl; to deteIDline'ECwfrom EC, (see Rhoades et aI., 1976). each variable (Rhoades et at., 1989b). Ranges were selected to cover typical situations in semi­ 3 arid mineral soils of the Southwestern united States: EC, (0.2 - 10dS/m), Pb (1.2 -1.7 g/cm ), 8 w 3 Assessment of Soil Salinity from Soil Electrical Conductivity (0.1 - 0.4), 8 w, (0.1 - 0.3), , (2.4 - 2.7 g/cm ), %C (5 - 60) and EC, (0.1 - 1.0 dS/m). The sensitivity analysis showed that errors in the estimation of particle density (p ,) of arid land . EC ) fr EC using equation 1 the values of EC" In order to assess soil salimty (ECw or , . om 8' b stimated from bulk density mineral soils have negligible effects, errors in the estimation of soil bulk density (p b) do not 8 8 d 8 must be known or adequately estImate.d ,can e e .. f significantly affect EC in the low salinity range, errors in the estimation of the surface ") ':" an 8:'. /2 65 where 2 65 is a reasonable estimate of the average partIcle denSIty 0 e ( Pb slllce ,- Pb .,. . h fi Id b t be estimated conductance (EC,) are more sensitive to errors made in estimating soil clay content (%C) than to . al ·1 EC and e carmot be directly measured III tee , u can . . differences in clay properties per se, and estimates of 8 wmade by experienced soil scientists using most rmner SOl s. '0 '" soil water content (8 w) using empirical relatI~nships from clay percentage ()foC) and total. means of obtaining these relationships are 'feel' methods should be sufficiently accurate to meet the practical needs of soil salinity appraisal established for representatIve sOIls of the regIOn. The d· th fi Id ing time domain from ECa measurements. For detailed discussion on this the reader is referred to Rhoades et aI., described elsewhere (Rhoades et aI., 1989a). 8 w can be measure III e e us (1989b). reflectometry (TDR) methods or can be estimated by 'feel'. Based on the sensitivity results it was concluded that reliable estimates of soil salinity should be obtainable from measurements of bulk soil electrical conductivity (EC,) and estimates . 1 be solved for EC with the assumption that ECws = ECwe, by arranging it EquatIOn may w, . . . . . of soil water content (8 w) and clay percentage (%C). in the fonn of a quadratic equation and solVlllg for ItS posItIve root. This conclusion and the appropriateness of the model describing electrical current flow in

undisturbed soil were evaluated for purposes of diagnosing and mapping soil salinity (ECe) in an intensive field study (more than 700 sites tested) in the San Joaquin Valley of California. [10] Different methods of measuring bulk soil electrical condutivity (EC,) and different ways of 2a ECw = obtaining the values of the parameters required by the model were also evaluated using three =[(8 +8 )2(ECs)+(8w- 8 m)(8 ws ECs)-(8sEC,)],andc= different sets of data. The reliability of the variously predicted salinities was evaluated by Where a = [(8)(8s w - 8 ws,)] b s ws comparing each against salinities measured with conventional techoiques using linear regression [ 8 w, EC, EC,l analysis, ranking tests and a procedure based on the weighted sums of squared differences IfEC, is desired, it can be obtained from. (Rhoades et aI., 1989c). Measured and predicted (according to Table 1) salinity maps were obtained. Visually, there was a high correspondence between predicted and measured salinity SP Pb) magnitude and distribution within the study area. Where the differences are large, the salinity (EC 8 w) = (ECwe 8 we + ECw, e w,) = (EC, lOa p, w levels are so high as to make them agriculturally unproductive. or rearranging equation 11: Sensitivity analyses and tests have shown that the estimates used in this method are generally adequate for salinity appraisal purposes of typical mineral, arid land soils of the 8w lOa) [-- [12] Southwestern United States (Rhoades et aI., 1989c; 1989d). For organic soils or soil of very EC, = ECw Ph· SP different mineralogy or magnetic properties, these estimates may be inappropriate. For such soils, appropriate estimating procedures will have to be developed using analogous techoiques to those where SP is the gravimetric water content of the saturated soil paste expressed as a used by Rhoades et al. (1989b).

57 56 directly in EC. corrected to 250C. Descri tion of procedure used to predict EC, from measure~ents of ECa and estima~es of the other soil parameters required to solve equatIOns 1, 10 and 12 Electromagnetic Induction Sensors In the EM soil electrical conductivity meter a transmitter coil located in one end of the (after Rhoades et a/., 1988) instrument induces circular eddy current loops in the soil. The magnitude of these loops is directly proportional to the conductivity of the soil in the vicinity of that loop. Each current loop EC.­ Measured by appropriate instrumental method generates a secondary electromagnetic field which is proportional to the value of the current %C­ estimated by 'feel' 1 flowing within the loop. A fraction of the secondary induced electromagnetic field from each _ estimated as SP = 0.76 (%C) + 27.25 SP loop is intercepted by the receiver coil and the sum of these signals is amplified and formed into estimated as P b = 1.73 - 0.0067 (SP) , Pb an output voltage which is linearly related to a depth-weighted soil ECa, ECa *. estimated as e, = P b / P" where P, was assumed to be 2.65 g em e, One of the commercially available EM soil salinity sensors (Geonics EM-38) can be held ewf, estimated as SP p J200' in the vertical (coils) position. This device has an intercoil spacing of 1 metre, operates at a calculated as ew = e wf, FC/lOO' ew freqquency of 13.2 kHz, is powered by a 9-volt battery, and reads EC. * directly. The coil estimated as e~ = 0.639 ew + 0.011 em configuration and intercoil spacing were chosen to permit measurement of ECa * to effective EC,­ estimated as EC, = 0.019 (SP) - 0.434 .' 10] depths of approximately 1 and 2 metres when placed at ground level in a horizontal and vertical - E(' e 100/SP P where ECw was obtamed from equanon [ EC,- calcnlated as EC, - '-'w w b, configuration, respectively. The device contains appropriate circuitry to minimize instrument

response to the magnetic susceptibility of the soil and to maximize response to ECa *. • .... this table have all been desCTIoed previously in Rhoades et The bases of the empirical relanonships, glVen m 'da d cribed in Rhoades et al. (1989c) were used to al. (1989a), with this excepnon. The callbranon ta es Procedure - Large Volume Measurement establish this relationship. Four-electrode Probe wf, is the estimated volumetric water content at field capacity. e To determine soil salinity of entire root zones, or some fraction thereof, it is desirable to FC is the percent of field capacity water content as estimated by the 'feel' method. make the measurement when the current flow is concentrated within the soil depth. This is accomplished with the four -electrode equipment by selecting the appropriate spacing between the MEASUREMENT OF BULK SO~ ELECTRICAL CONDUCTIVITY IN THE FIELD two current (outer) electrodes which are inserted into the soiJ-surface to a depth of about 5 cm. In this arrangement, four electrodes are placed in a straight line. With conventional geophysical resistivity measurements the electrodes are equally spaced in the so-called Wenner array Apparatus (Rhoades and Ingvalsorn, 1971). With the Martek SCT meter each of the inner pair of electrodes is placed inward from its closest outer pair counterpart a distance equal to 10% of the spacing Four Electrode Sensors . d 'stance meter four metal electrodes, and between the outer pair. The inner pair is used to measure the potential while current is passed A combination electnc current source an resl ) , ts The current fi 1 "l lurne (surface array measuremen . between the outer pair. The effective depth of current penetration for either configuration (in the connecting wire. are neede.d or arge so~od tor type or a battery-powered type. Units absence of appreciable soil layering) is equal to about one-third the outer electrode spacing, y, source meter umt may be either a hand-crall e g~nera bros and if used for general soil salinity and the average soil salinity is measured to approximately this depth (Rhoades and Ingvalson, designed for geophysical purposes gener y rea ill 0 , 1971; Halvorson and Rhoades, 1976). Thus, by varying the spacing between current electrodes, measurement, should m~asure from 0.1 to 1O~a~~' stainless steel, copper, brass, or almost any one can measure average soil salinity to different depths and within different volumes of soil. Electrodes used ill surface arrays are d . . t ritical except that the electrode must Another advantage of this method is the relatively large volume of soil measured compared with other corrosion-resistant metal. Array electro e s:ze IS no~. ov~r and to maintain firm contact soil samples. The volume of measurement is about (Xy/st Hence, effects of small-scale be small enough to be easily inserted into the solll' not EtolecltProdes 1 0 to 1 25 cm in diameter by . . h . rt d to a depth of 5 cm or ess. .' variations in field soil salinity on sampling requirements can be minimized by these large-volume WIth the soil w en mse e alth 0 u h smaller electrodes are preferred for measurements. 45 cm long are convenient for most array p(?OS;~, 30 c!) Any flexible well-isulated, multi- F or measurements taken in the Wenner array (electrodes equally spaced) using determination of EC.within shallow depths ess ~ . a electrodes to the meter. geophysical type meters which measure resitance, the soil electrical conductivity is calculated, in . stranded, 12 to 18 gauge wire is suitable for c~nn:~~:~ot::s :a~ be mOlfnted in a board with a dS/m, from: F or surveyor traverse work, the arr Y d uickl for a given inter-electrode ECa = 159.2 t; / aRt handle so that the soil resistance measuremhents can be maa:. spacing of 30 or 60 i~ter-ejectrode where a is the distance between the electrodes in cm, Rt is the measured resitance in obms spacing (Rhoades and Halvorson 1977). T ese purposes, b 't) . (. d· . gs require lengthy cum ersome urn s . at the field temperature t, and t; is a factor to adjust the reading to a reference temperature of cm is adequate and convem~~t WI ~~P~cI~hich the electrod~s are built into the probe (Rhoades 250C. For measurements made with the Martek SCT meter, a factor is supplied in chart form for A four-electrode pro e, ill all il lume measurements. Current source meter sal~ty each spacing of outer electrodes; this factor is dialled into the meter and the correct soil ECa and van Schilfgaarde 1976) IS needed for sm so lvo de salinity probe are much smaller and reading is directly displayed in the meter readout. units specifically designed for use with the four-e ec t ro . . al 't Martek SCT reads more convenient (Austin and Rhoades 1979). One such cornrnerCI urn, '

,i 59 " 58 Electromagnetic Induction Methods Large volumes of soil can also be measured with the electromagnetic induction technique. REFERENCES The volume and depth of measurement can be increased by increasing the spacing between coils, Austin Rs.S.ilansdRsh oadAmeslD. 1979. A compact, low-cost circuit for reading four-electrode salinity sensors by reducing the current frequency, and by varying the orientation of the axes of the coils with o Cl. oc. . 1 43:808-810. . respect to the soil surface plane. The effective depths of measurement of the Geonics EM-38 Corwin ~.Lilian~ Rhoades J.D. 1982. An improved techuique for detenuiuing soil electrical conductivity device are about 1 and 2 metres when it is placed on the ground and the coils are positioned Corwio Dei. ::tl~ from above ground electromagnetic measurements. Soil Sci. Soc. Am. J. 46:517-520. horizontally and verticitlly, respectively. The EM-38 device does not integrate soil EC, linearly . electromagneti~a:d~!~~9;:il s:~aos:=n;. :::2~~~~e1d electrical conductivity profiles using with depth. The 0 to 0.30, 0.30 to 0.61, 0.61 to 0.91, and 0.91 to 1.22 m depth intervals contribute about 43,21, 10 and 6 percent, respectively, to the EC,* reading of the EM unit when COTWln ~.L~ and Rhoa~es J.D. 1989. Establishing soil electrical conductivity - deptb relations from e ec omagnetJc mduc1:!on measurements. Aust. J. Sci. Res. positioned on homogeneous ground in the horizontal position (Rhoades and Corwin, 1981). Halvorson A.D. and Rhoades lD. 1989. Field mapping soil conductivity to delineate dryland saline see s Thus, the weighted bulk soil electrical conductivity read by the EM device in this configuration is Wltb four-electrode techuiqoe. SOlI Sci. Soc. Am. J. 40:571-575 p approximately: Rhoades J.D.. 1976 . Measuring, mappmg. an d momtonng.. field salinity. : and water table depths witb il resistance measurements. Soils Bulletin 31. FAO, Rome. pp. 159-186 so Rhoades J.D. 1976. Inexpensive four-electrode probe for monitoring soil sailTIl''ty EC, = 0.43EC"o-o.3 + 0.21EC"o.3-o.6 + 0.10EC"O.6-0.9 43:817-818. . Soil Sci. Soc. Am. J. + 0.06EC"o.9-1.2 + 0.2ec,,>1.2 Rhoades PJ.D. 1984. Principles and metbods of monitoring soil salini·ty. In: Soil Salinity and Irrigation - rocesses and Management. Springer Verlag Berlin. 5:130-142 where the subscript designates the depth interval in metres. Rhoades pi~tJ D 1989Anai. Detenuiuing so il sal' lTIl 'ty fr'om measurements of electrical. conductivity. Cornm. Soil Sci.

It is desirable to determine soil EC, by depth intervals for calculating soil salinity within Rhoades . J.d. d and . Corwin D.L. ..1981. DeteTInlTIlllg .. SOl'1' electncal conduc1:!Vlty-deptb. . relatlons. using an various parts of the root zone as needed for making assessments and management decision. Since m uctlve electromagnetlc soIl conductivity meter. Soil Sci. Soc. Am. l 45 :255-260 Rhoades J.D. and COTWlnD L 1984 Mom'to' '1 alini" . the proportional contribution of each soil depth interval to EC" as measured by the EM unit, can Rhoade J D ..... nng SOl s ty. J. Soil Water Cons. 39(3):172-175. s s~il's~Cty0TWln D~. 1989. Soil electncal conductivity: Effects of soil properties and application to be varied by raising it above ground to higher heights, it is possible to calculate the EC,-depth apprrus. Aust. J. of SCl. Res. (Submitted) relation from a succession of EM measurement made at various heighs above ground (Rhoades Rhoades J.D. and Halvorson A.D. '1976. Detecting and deli~eating saline seeps witb soil resistance and Corwin, 1981). meastanuremBenullts. . Proc. Saline Seep Control Symposium, Montana State University Bozeman Mon a, etln 1132: 19-34. ' , Rhoades ~,and Halvorson A.D. 1977. Electrical conductivity metbods for detecting and delineating Procedure - Small Volume Measurements s ne seeps and measunng salinity in Nortbem Geat Plains soils ARS W-42 45 Rhoades J.D.'1 Sand . SIngvalson R.D .'1971 D e t enmng . salini" ty m field SOlIs. . witb soil resistance . p. measurements Four-electrode Probe S 01 CI. oc. Am. Proc. 35:54-60. . Sometimes information on salinity distribution within a small, localized volume of the ~oades lD. and Miyrunoto S. 1989. Testing soils for salinity and sorucity Soil Test Plant Anal (In P ) whole root zone is desired, such as that within the seedbed or under the furrows. For such oades J::' and Oster lD. 1986. Solute content. In: Metbods of Soil An~ysis. Part I (2nd ed.) PhYSi~~s~d conditions, the four-electrode salinity probe (Rhoades and van Scbilfgaarde, 1976) and burial type neralogrcal Metbods. A. Klute (ed). Agronomy Monograph 9:985-1006. probe (Rhoades, 1979) are reco=ended. The seedbed probe is designed to be directly inserted Rhoades sJ.Dl'SandAmvan Schilfgaarde 1. 1976. An electrical conductivity probe for detenuiuing soil salinity 01 CI. . J. 40:647-651. . into the soil. In the larger probes four annular rings are moulded in a plastic matrix that is slightly Rhoades J.D., Corwio. .:'D L and Shouse. P J . 1988 . Use of mstrunIental. and computer assisted techui ues to tapered to that it can be inserted into a hole made to the desired depth with a coring tube. In the Rh d a~s;ss SOlI sallTIlty. Proc. Int. Symp. on Solonetz Soils, Osijek, Yugoslavia. pp.50-103. q portable version, the probe is attached to a shaft (handle) through which the electrical leads are oa es .., Raats P.A.C. and Pratber R.J. 1976. Effects of liquid - phase electrical conductivity, water' passed and connected to a meter. In the burial unit, the leads from the probe are brought to the ~~~tent, and surface conduct:lV1ty on bulk soil electrical conductivity. Soil Sci. Soc. Am. J. 40:651- soil surface. The volume of sample under measurement can be varied by changing the spacing Rhoades J.D., Mlanteghi N.A., Sh~use P.J. and Alves W.J. 1989a. Estimating soil salinity from saturated soil- between the current electrodes. The co=ercial unit, Martek SCT, has a spacing of 6.6 cm and Rh paste e ectncal conduc1:!Vlty. SoIl Sci. Soc. Am. J. 53:428-433. 3 measures a soil volume of about 2350 cm . oades J.D.: Manteghi N.A.,. Shouse PJ. and Alves W.J. 1989b. Soil electrical conductivity and soil To determine soil EC with the four-electrode probe, core a hole in the soil to the desired Rho salImty. New formulatlons and calibratlons. Soil Sci. Soc. Am. J. 53:433-439. depth of measurement using a Lord soil sampling tube (or any sampler of similar diameter). ades J.~., Waggoner B.L., ShourseP.J. and Alves W.l 1989c. Determining soil salinity from "soil and Insert the four-electrode probe into the soil and record the resistance, or the displayed value of Rhoades ~o~-p~~e ele~c~OndUCtlVItJes: Sensitivity analysis of models. Soil Sci. Soc. Am. J. (In Press). EC" depending on the meter used. When using meters which display resistance, EC, in dS/m is bill: soilo~se :., ves W.J ..' Manteghi N.a. and Lesch S.M. 1989d., Determining soil salinity from lectncal conduc1:!VIty usmg different calculation models and parruneter estimates Soil Sci calculated as: Soc. Am. J. (In Press). . . EC, =k ['1 Rt US Salinity Laboratory. 1954. Diagnosis and Improvement of Saline and Alkali Soils. Richards LA (ed) US where k is an empirically determined geometry constant (cell constant) for the probe units Dept. of AgrIc. Handbook No. 60. . of 1000 cm, Rt is the resistance in ohms at the field temperature, and ft is a factor to adjust the reading to a reference temperature of250C.

61 60 III. Technical Considerations in Irrigation with Saline Water

62 Water Management For Salinity Control

Fernando Chanduvi Technical Officer, AGL FAO/Rome

INTRODUCTION

Water management for saiinity control means a series of measures or practices undertaken to avoid the continuous accumulation of soluble salts in the soil as a result of irrigation. The application of irrigation water means an input of salts. Irrigation water, even if of excellent quality, is a major source of soluble salts. If soil salinization is to be avoided, these salts have to be leached out of the root zone by water percolating to the subsoil. This percolation of water will cause the water table to rise and has to be drained off because a second source of salinization in irrigated areas is capillary rise from a water table. As groundwater is somehow saline, even a small amount of capillary rise can add greatly to the salinity of the root zone. Drainage, either natural or artificial, is a necessary complement to irrigation.

WATER MANAGEMENT FOR SALINITY CONTROL AT DIFFERENT STAGES OF AN lRRlGATION SCHEME

Different water management options are available at different irrigation scheme development stages:

Planning Stage At this stage, the water management measures for salinity control are the responsibility of design engineers. Alternative irrigation management options should be considered. The analysis of the irrigation management options through the use of mathematical models is a powerful tool which enables project designers to choose the one that will produce the least waterlogging hazard.

Development Stage During this stage, irrigation engineers have an important role to play in the context of properly designing an irrigation systems. Irrigation systems must allow for leaching fractions in order to maintain an appropriate salt balance in the root zone. Land grading in gravity irrigation systems is a prerequisite to ensure high irrigation efficiency . • Operational Stage At this stage, system managers should control the overall irrigation efficiencies of large sections of the system and that of the system as a whole. While Farm operators should make sure that proper irrigation practices are carried out to supply the crop with its water requirements with the appropriate leaching requirements as advised by the extension service. System managers are also responsible for the provision of adequat~ drainage for the irrigation scheme.

TOOLS FOR WATER MANAGEMENT

There is a variety of means available for optimum water management in order to avoid salinization. The following are considered the most important:

63 cost. Large sugar estates in some countries in the Caribbean and in Latin America have found that laser-controlled grading is technically and economically sound. Analysis of Water Management Optio~s .' d orks aimed at the Planning of new irrigation projects should consider studies an w . . I' d salinity problems caused by deep percolanon losses. Such Determination of Crop Water Requirements ~;~~~~n~;e~f~~~;~~ert~:gs~!u:ion of the behaviour of the water table under various ~a:r The crop water requirements should be estimated for each of the crops of the area. The manaaement alternatives with the purpose of determining their effects as a consequence 0 e FAO CROPWAT computer program greatly facilitates these calculations. It provides reference im f(~vement and development of new irrigated areas. .' evapotranspiration, crop water requirements, irrigation requirements and scheme water supply p The simutation is carried out by the use of a mathematical model which :akes mto. acco~nt requirements. The calculation of crop water requirements is done from climatic and crop data, the a oundwater balance. The mathematical model should he calibrated t~ng mto conslderanon while the development of irrigation schedules is based on the soil-water balance for different actu~ data collected from the project area. Long term predictions of changes m the water table may irrigation management conditions. Scheme water supply is calculated for various cropping patterns. be made for one five ten years or other periods for each water management altern~nve. . In addition, FAO has developed a climatic database for CROPWAT, CLIMWAT, which includes The abo~e sU:dies were' carried out in an irrigation project ~total4,750 ha) m Peru m 1992. data from a total of3,262 meteorological stations from 144 countries. In this case the following water management alternatives were considered: • all lands will be irrigated by gravity, ..'d d d Leaching to Keep a Salt Equilibrium in the Root Zone • all lands will be sprinkler irrigated. Artificial horizontal dramage Will be proVI e an Leaching fractions (the amount of water that should be applied with each irrigation in around water will be exploited for irrigation. all t t bl addition to the crop water requirement) should be calculated according to the crop and to the salt F 0 th '4750 ha of the project area, there were 1,300 ha affected by sh ow wa er ~ e content of the irrigation water to be used. Although the amount of salts within the soil profile may rom e , f d th' 1992 The analysis of the water management alternatives change over short periods, the aim of a water management program should be to maintain a non­ levels between 0 and 1 m 0 ep m . fi 11 . showed that in future areas that will have less than one-meter-depth water tables are as 0 ows. harmful salt level over a long term period, say one year. There exist a number of water balance and salt balance equations which when combined with some general assumptions allow for sound water Period of simulation in days Alternative management practices. Observing these practices will contribute to maintain the zero increase salt contents over long term periods. 360 1080 1800

1,704 2,890 3,710 Measurement ofIrrigation Water (i) Irrigation by gravity Water is a precious and scarce resource, particularly where irrigation is practised and (ii)Irrigation by sprinkler, complemented therefore it should be adequately measured and distributed and applied. Where irrigation water is 302 81 49 with subsurface drainage and ground not measured, wastage occurs and this instead builds up water tables from where capillary rise water exploitation. facilitating the accumulation of salts within the soil profile. Irrigation water should be measured at the point of intake along the distribution system and at the delivery point. There are several It was concluded that by following alternative (i) it is estimated that 80% oft~r~je~t ~ea irrigation projects around the world where irrigation water is not measured and therefore irrigation would be affected by less than one-meter-depth water tables.~thin one to five years er I~gat~on efficiency is rather low. starts. The adoption of alternative (ii) would result in the elimin~n?n ~f areas .~ec::d ~l:=e~t: one-meter-depth water tables. It was reco=ended that the Imganon proJe Maintenance of Irrigation Infrastructure and Provision of Drainage selecting the sprinkler method of irrigation. Lack of maintenance of irrigation infrastructure is perhaps the single most important reason why high irrigation water losses occur throughout the system. All these losses will at the end find their way to the water table: FAO has developed a set of computer programs to facilitate the designed. Furrows should and APproP~~:=t~:S!~~t:!!r;~~~!o:e ~~~:l~ h~ve appro~riate slop~s management tasks of irrigation systems as follows: (i) agricultural activities, (ii) crop water ~t.s in ~ombination with maximum non-erosive flows in order to aVOId excessIve water.dosses, lenglll .' . h ld b d in such a way as to avOl long requirements, (iii) seasonal irrigation planning, (iv) irrigation scheduling, (v) water consumption, the same is true for basins. Drip 1ffigatlon sy~tems s ou . e u: 'ty I I within the soil profile. (vi) accounting, (vii) operation and management and (viii)water fees. The program facilitates the term land degradation throu~ the accumulanon o( ~c~tyssl~eil~ :;in l:~: that are drip irrigated. optimum management of irrigation systems and contributes to minimize irrigation water losses. Sprinkler irrigation may proVIde a means to contro s ill u When natural drainage is not enough to remove irrigation losses, artificial drainage must be :t . provided. 1 Land Grading to Improve Irrigation Efficieffinc! f' 'gation labour and energy resources and grading always improves the e clency 0 1m , 1 d d' am L . . . f' f ed a an gra mg progr Monitoring utilization. In some irriga~ion projects where furr~w 1ffiga .~~~ I:::;~/:s in a reduction in irrigation Experience has shown that long term monitoring is necessary to take corrective measures may result in an mcrease m the cropped area and m crop Y1 'd . all . tilled One of the should water table and soil salinity problems arise, particularly in the lower topographical areas of · sh ld be technically an econormc YJUs . water losses. A land grad mg program ou . f 1 t I in land gradina equipment, irrigation schemes. Observation wells should he used to monitor the fluctuation and rise of the ost si nificant advances has been the adaptatIOn 0 aser con ro . 0 • hi h water table. Soil salinity should be monitored, as well. :oweve; in most irrigated agriculture, laser-controlled precision is not practised due to ItS g

65 64 Suitability Assessment of Water Quality for Irrigation each salt is reached. With leaching (achieved with irrigation or rainfall), the degree of accumulation of salts in soil water can be lessened, if not eliminated. Hence, the amount of soil-water salinity J. D. Rhoades, Director, US Salinity Laboratory, USDA, resultmg from the use of an irrigation water is related to its salt content and composition, the Riverside, California, USA composition of the water producing leaching and the amount ofleaching achieved. For this reason any assessment of the suitability of a saline water for irrigation must be made in view of: (a) how much leaching will be achieved; (b) what level of salinity will result in the soil water from the use of INTRODUCTION this irrigation water, and (c) how much salinity the crop can tolerate in the soil water. . . f . t ranging from general N rous' schemes for the classification of water fior Imga IOn eXlS , Since there is approximately a tenfold range in salt tolerance of crops, one might expect a ume . . (US Salinity Laboratory 1954· Ayers and Westcot comparable range in the pennissible salinity of irrigation water, depending on the crop being groWll, schemes designed for average use condItIOns . . . ' me 1951) 1985 EPA 1972) to specific schemes for restricted regronal condItIOns (Thome and Tho h· other factors being equal. Within a crop species, there are varietal and even rootstock variations in Esse~tially all of these are empirical kinds of schemes. That of Aye~s and Westc?t (1985~ ratesa1 e salt tolerance, and tolerances also vary with different stages of growth, including gennination. degree and kind of problem likely to be encountered when usmg water With certam qu ty Climate may modify the responses of plants to salinity. Generally, salinity effects are more drastic under hot, dry conditions than under cool, humid ones. But not all species are equally parameters falling within one of several classes. .. . hi h The substantial experience in using brackish water for Imgatlon ~hows that water. w c affected. ed by Ayers and Westcot (1985) as having a severe restnctIOn for ~se IS, m. ~act, An important consideration in evaluating the salinity hazard of an irrigation water is the ifi wouId b e cI ass Id d . d 1y arymg condItIOns appropriateness of the method used to evaluate salt tolerances of crops. Much of the data on salt being successfully used in numerous places throughout the wor un er WI e v . n· Thi . . t economics and cultural orgamza ons. s tolerances of crops was detemIined under the most favourable conditions, which rarely prevail of soil climate, irrigation technique, croppmg sys em, ... d h the fact shows that the actual suitability of a given wat~r for ImgatIOn depe~ s. veifr muc rr:;ting under field conditions. Further, in most salinity tolerance studies, crop yields were related to specific conditions of use and on the relative econOIll1C bene~t that can be enve om. ·1 average root zone soil-water salinities as measured by electrical conductivity of saturation extracts. with that water compared to others. The conditions of use mclude the crop grown, van~us so~ Under field conditions, soil-water salinity generally ranges from a low level not greatly exceeding . r tic conditions certain management practIces an the salinity of the irrigation water near the soil surface to levels perhaps ten or more times the properties, irrigation management practIces, c Iffia .. .' Thi ill strates the limitation of various other factors related to need and econOIll1C mcentlve. s.u. . irrigation water salinity at the bottom of the root zone. It also varies with time as the water is generalized water-classification schemes and the ne~d for a ~ore quantItatIve means of assessmg consumed by the plant. Results ofunifonn-distribution salt tolerance studies detennined under most water suitability; one that takes into account the specific condinons of use. favourable conditions can only be applied to these nonunifonn salinity distribution field conditions with the assumption that the plant responds to average soil-water salinity irrespective of its CRITERIA AND STANDARDS FOR ASSESSING SUIT ABILITY OF WATER QUALITY distribution in the root zone. While some studies have suggested that such is the case, others have demonstrated the importance of soil-water metric stresses, variations in salinity distribution in the FOR IRRlGATION root zone and method of water application on the responses of crops to salinity. The suitability of water for irrigation should be evaluated on the basis of ~riteria indicative Experimental evidence shows that (a) plants should tolerate higher levels of salinity under . . . h d t p growth or to ammals or humans conditions of low matric stress, and (b) high soil-water salinities occurring in deeper regions of the of its potentials to create SOli condinons azar .ous. ~ cr.o .. f t f al root zone could be largely offset if sufficient low-salinity water is added to the upper profile depths consuming those crops. Relevant criteria for judgmg lIDganon water qUalI;"': te::~ 0 P~:~~ht hazards to cro growth are ( a) salinity, the general effects of salt on crop gro w c ar~ . . fast enough to satisfY the crop's evapotranspiration requirement. Thus, the level of salinity that can be laruel !motic in nature and related to total salt concentration rather t~an to the mdiVIdual be tolerated in the soil water (hence in the irrigation water) may depend not only on the salt to '0 Y . . Th effects are generally eVidenced by retarded tolerance of the crop to be grOWll, but also on the initial content and distribution of salinity in the concentrations of speCIfic salt Co~stltuents. ese 1 . (b) ability/tilth the effect of d cing smaller plants With fewer and sm all er eaves, penne '. soil profile, on the amount and frequency of irrigation, on the extent to which the soil water is growth, pro u f h bl diin the'soil given the electrolyte concentranon of the depleted between irrigations, and on the water content and matric properties of the "'soil. Good an exceSSIve amount 0 exc angea e so um, . d d b .. il bilit soil structure and tilth. The soil effects are eVI ence y irrigation management should therefore check and control pennissible levels of salinity of irrigation infiltratmg water, on so pennea y, . / .. al· bal the fonner water. crusting and by a reduced rate of water intake; and ( c) toxiCIty nutntIOn f lffihi ~ce, d· and For example it has been shoWll that the salinity of water applied by sprinkling (ignoring includes the effects of specific solut~s on plant ~:h, es~e~i~~. t~o:) :~e :e ~~~~r ~~~udes foliar uptake) could be higher than that applied by flood or furrow irrigation with a comparable boron (these effects are generally eVidenced by Ie. urn an eo Ia 0 , degree of cropping success. Further, there is evidence that the techniques of drip or trickle the interference of salts on the uptake of plant nutnents. .. irrigation, in which water is applied at a very high frequency and rate in excess ofET requirements, pennit crops to be groWll more successfully with saline water than otherwise possible (Goldberg CONSIDERATIONS IN ASSESSING SALINITY HAZARDS and Gomat 1971; Gomat et al. 1971). Under most field conditions brackish water rarely contains enough salts to cause i=~diatef . . H ever with time the concentranon 0 .. to cro s other than the most salt-sensItIve ones. ow, ' ... CONSIDERATIONS IN ASSESSING PERMEABILITY AND TILTH HAZARDS :~~le saltsPi~ soils irrigated with saline water increases, because ~ost of.the apPlhed water ~~ . d . f leaving the salt behind WIthout eac hi ng, s In evaluating the suitability of sodic water for irrigation, an important consideration is the removed by evaporatIOn an transprra lOll, ...... til th 1 bility limit of constituents will accumulate in the soil water With succeSSIve ImgatIOns un e so u extent to which the ESP will increase in the soil by adsorption of sodium from the water. ESP is an

67 66 important property of soils which influences soil permeability and tilth. Therefore, any suitable reason such a steady-st~te approach was undertaken, rather than a completely dynamic approach, is evaluation of the potential permeability hazard of a sodic, saline irrigation water must relate some that the mput data r~qUlred for the latter ap?roach are seldom available for real world applications. property of the irrigation water to the ESP that will result in the soil from use of that water. Since Th~ baSIC pnncIples that. govern this model are discussed below. For detailed infonnation the sodium adsorption ratio (SAR) of the soil water is a good estimate of the ESP of soils, it has t h e reader IS referred to FAO SOlis Bulletin 31 (1976). been used advantageously in place of ESP for predicting sodicity build-up. The SAR of the o Increasing irri~ation frequen? can markedly affect crop growth; accordingly, one of the irrigation water (SAR) may be used as a measure of soil sodicity, providing it is relatable to the i'tc mmonly usedfr' practIcal rules of saliruty management IS'." when im'gatm' a Wl'th mo res al'mewater resultant SAR of the equilibrated soil water (SARw). mga e mor~ equently. T~s recommendation implies that crop response is related to the sum of However, 'this is not always true; a lack of 1: 1 correspondence exists because ( a) the osmotIc suctIOn n, and matnc suctIOn Gin the root zone and that, for a given quantity of salt in the concentration of soil water is increased relative to that of applied irrigation water by S?llh, the sum of n and 1:.( $, the total water suction) can be minimized by keeping the water content evapotranspiration processes; (b) this concentration varies with time between irrigations and with hig and mcreasmg the rmgatlOn frequency. depth in the profile; and ( c) the composition of the soil water is affected by cation exchange, salt . Yar~n et al: (.197~), Bresler and Yaron (1972), and Zur and Bresler (1973) have evaluated precipitation and mineral weathering phenomena. It has been shown that higher ESP levels occur in ~he :eractlOns of ImgatlOn regrn:e, level of soil salinity, water and climatic conditions absence of soils than SARiw per se. Recent improvements in modelling have made it possible to predict ESP eac g and. short-tenn use ofva.r:ably s~zed irrigation water on grapefruit and gro~dnut yields values in soils irrigated with water of known SAR. These models take into account the effects of by both statlstlc~ and comp~ter slffiulatlOn .techniques. They concluded that, for non-steady-state, water composition and leaching conditions on the extent of lime precipitation or dissolution ~ho~-tenn conditlO~s and a gIven level of climatic stress, osmotic potential, n, was overwhelmingly processes and silicate mineral weathering processes. o~ant on the fruit YIeld of these crops under conditions of short irrigation intervals (3 days) For such mtervals, the integrated, 1:, was only 10 to 15 percent of the integrated total water potenti~, $. USE OF A SIMPLE INTEGRATED WATER POTENTIAL MODEL TO ASSESS WATER However, 1:, mcreased to about 80 percent of the integrated, $, at longer irrigation intervals (about SUITABILITY FOR IRRIGATION 20t~ 30 days). Fr?m :hese ob~e~ations they concluded that the salt concentration of the soil water eXlstm.g before ImgatlOn .w~s l~tIated mainly determines the value of the time-integrated n under A major point that emerges from the discussion so far is that it is presently impossible to set condItIOns of short-tenn rmgatIon with saline water and absence of leaching. For this reason, they precise general standards of wide applicability for judging irrigation water quality. The suitability of ad,:,~cated u~mg an extra .aIl~tment of water to pre-leach the soil, so as to reduce the level of soil an irrigation water needs to be evaluated on the basis of the specific conditions under which it will salini~ eXlst~ng at ~e ?eg~g of the crop season, rather than using this same amount of water for be used, including crops being grown, soil properties, irrigation management, cultural practices and I eaching dunng the ImgatlOn season. climatic conditions. Because of this, the prevailing procedures for evaluating irrigation water . U~der con~itions ~f long-tenn use of water for irrigation (steady-state conditions) with quality must be taken as rough guidelines at best, to be used in conjunction with a knowledge of leacl~ing, It IS the m.teractlOn between salt concentration of the irrigation water and the leaching local conditions of use. fractI~n that deterrrunes the final level of .soil salinity, as well as the depth-averaged, n, osmotic The ultimate method of assessing the suitability of water for irrigation requires: (a) potemtal of the root. zone soil wa~er. This latter conclusion can be deduced from the equation prediction of the composition and matric potential of the soil water both in time and space that develo?ed by Bernstem and F~ancOls (1973) to describe the mean salt concentration against which result from the interplay of irrigation, rainfall, water table fluctuation and plant growth, and (b) water IS absorbed by a plant, C. interpretation of such information in terms of how soil conditions are affected for crop production and how any crop would respond to such conditions under the prevalent set of environmental variables. It is the lack of such capabilities that has resulted in the use of empirical approaches to (1) evaluate irrigation water quality. Additional research is needed to improve our ability to interpret the interpplay of exchangeable sodium, electrolyfe concentration, and soil properties on field soil permeability and wh~re Viw, V~w,. are. volume of infiltrated and drainage wat'er, respectively, and C;w is the tilth. Knowledge of how plants integrate the effects of osmotic and matric soil water stresses, as concentratIon o.f the rmga~lOn wat~r (one c~ substitute EC for C in this and all of the following well as the effects of individual toxic solutes, and how soil permeability is influenced by solute equatIOns), LF IS the leaching fractIon. EquatIon 1 applies only to the condition of conservation of composition and concentration, cultural practices and soil properties is needed to improve mass, I.e. C;wViw = CdwVdw , where Cdw is the concentration of drain water. It has been shown significantly our present methods of osmotic potential, n, evaluating irrigation water quality. (Raats 1974) that for co?-dition~ ?f ~iston ~isplacement, C is independent of the water uptake Another requisite is the ability to predict what composition, distribution and content of soil water pro~le and frequency oftlme of rmga~n. It IS only the rela\ion between concentration and volume will result from the use of a given set of management conditions. dunng evapotr~spiration that affects C. The degree to which volume is reduced and concentration With the above in mind, a steady-state model was developed for the purpose of assessing IS lllcreased .d~nng the passage of water through the root zone is determined by the leaching water suitability for irrigation (Rhoades and Merrill 1976). This model is a simplification of the fractIOn. and IS mdep~ndent oftime or the extent to which the soil is dried between irrigations. This actual dynamics (levels and trends) of soil water composition and soil water potential that will exist conclUSIOn. agrees WIth :he obse:vational and model findings of Zur and Bresler (1973). Since under real field conditions, in that it only predicts the ultimate (maximum) conditions at steady­ co~centra~lOn and o.smotlc potentIal are closely related, Equation 1 can also be used to calculate n state. These latter conditions are likely to be the worst-case conditions that would result from weIghted m proportIOn to water uptake. irrigation with the water. Thus, it can be used to judge water suitability for irrigation under one significant reference condition, i.e. the worst-case situation that could result from irrigation. The

69 68 Ingvalson et al. (1976) modified Equation 1 to account for the effects of salt precipitation and including hydrogen and hydroxyl concentrations; (iii) equilibrium among carbonate, bicarbonate, dissolution and obtained the relation: hydrogen and hydroxyl ion species with the assigned pCOz; (iv) the solubility products of soil lime, if this option is selected; and (v) the solubility products of soil lime and gypsum, if the appropriate - b c activity products are exceeded. If the input charge concentrations of the cations and anions are not C = a - ---In(LF) +-- (2) (1- LF) (LF) equal, the charge balance constraint results in adjustment in the concentrations of carbonate bicarbonate, hydrogen and hydroxyl ion species. After the equilibrium composition calculation i~ where a, b and c are constants of the second-order polynomial equation describing the finished, the electrical condUCtivity, EC, of the resulting solution composition is calculated by concentration of the water as a function of (1/LF) derived from the chemical model of Oster and method 3 of McNeal et al. (1970), and the sodium adsorption ratio, SAR, is calculated from the Rhoades (1975). Thus, the water uptake weighted n, may be estimated as a function of C, EC, and total concentrations ofNa, Ca and Mg. osmotic potential. The soil water composition (Ca, Mg, Na, C03, HC03, Cl, S04 ), electric conductivity, Ingvalson et al. (1976) correlated alfalfa yield obtained under conditions of non-uniform sodium adsorption ratio, and osmotic potential are calculated for five soil depths - the soil surface, root zone salinity to various indices of salinity including (a)irrigation, water salinities (b) space and 1/4, 1/2,3/4, and full depths of the root zone. The relative water uptake for the four successive averaged, soil profile salinities (c) soil water salinities weighted in accordance with water uptake by root zone intervals from the surface downward is assumed to be 40, 30, 20 and 10 percent of the the crop, and (d) time and space integrated soil wate; salinities. In ~his ~xperiment, ~falfa yield total, respectively. The corresponding depth distribution of pCO, is 0.07 kPa at the soil surface, and correlated best WIth lower root zone depth water EC( r = 0.80) and tlme-mtegrated sOlI water EC 0.5,1.5,2.3 and 3 kPa for each successive root zone interval downward. Leaching fraction choices (r2 = 0.89), although yield also correlated well with average root zone soil sal~ty (r2 = 0.78) and include 0.05, 0.1, 0.2, 0.3 and 0.4; amendment choices include gypsum and SUlphuric acid. The correlated fair with C (r2 = 0.71). The chemistry model used to determine C' in this study was model runs on IBM compatible personal computers. With 16 bit technology the calculation time previously tested with respect to its ability to predict adequ~tely the d~ainage water com?os~tion (of for one leaching fraction is approximately five minutes; with 32 bit technology it is about 30 these same lysimeters) resulting from the use of eight WIdely varymg waters for ImgatlOn and seconds. leaching fractions of 0.1, 0.2 and 0.3 (Oster and Rhoades 1975). The predicted compositions and Table I shows the computer display during data entry. The following choices and entries salt loads agreed very closely with those determined experimentally (Rhoades et al. 1973, 1974 ). are required: (a) are the results to be printed, stored on disk, or displayed on screen?, (b) is the soil lime saturation assumption to be accepted or rejected?; (c) how is the case to be identified?; (d) USE OF A WATSUIT MODEL TO ASSESS WATER SUITABILITY FOR IRRIGATION what is the ionic composition of the water in units ofmm01l1 (=mell)?; (e) which amendments and leaching fractions should be' included? Amendment choices include the following: (i) addition of The steady-state chemistry model discussed above was refined and released under the sulphuric acid to replace 90% of the alkalinity with sulphate; (ii) addition of gypsum to add 1 name Watsuit, by Rhoades (1977, 1987a, 1988a) and Oster and Rhoades (1990). mm01ll of CaS04, simulating water or top dress soil treatment, or add 20 mm01l1 of Ca and S04 to simulate incorporated soil treatment. Both gypsum amendments can be chosen for the same computer run. No amendment is the default condition: it is always run. These amendment routines Description and assumptions ofWatsuit model have less utility for saline water because permeability is less of a problem with it. A brief description ofWatsuit follows. The model assumes that the soil solution begins as irrigation water at the soil surface. With downward movement by piston-flow water uptake by Table 1 TERMINAL DISPLAY DURING W ATSUIT START-UP plants concentrates this solution, and dissolution and precipitation reactions modifY its che~cal Wish to send output to (D)isk or (S)creen composition. Their effects vary with the leaching fraction. Assuming steady state conditIOns To print results in screen mode, hit: control P simplifies calculation of soil solution composition of mixed salt solutions containing Ca, Mg, N a, K., SATURATE WITH CAC03? Y CASEID C03, HC03 Cl, S04. Further simplification is achieved by using annual (or longer) averages of the following ~:mables: irrigation water composition corrected for rainfall, leaching fra~tion, d~pth PORT distribution of plant water uptake, and partial pressure of COz (PCOz). In the soil cheInlstry ENfER DELIMITED BY COMMAS: CA, MG, NA, K, CL, calculations, saturation with respect to soil lime may be assumed to occur, thereby accounting .for ALKand S04 the potential effects of dissolution of soil lime, or soil silicates, or both. For cases where the hme WHICH AMENDMENTS? saturated assumption is invoked, the prograrrune adjusts the concentration of Ca, C0 3, and HC03 (B) H2S04? so that the activity product, ac, • ac03, equals the solubility product of soil lime. Additional (C) I CAS04? assu'mptions include: soil lime equilibrium govern the solution pH; (b) ion activities are a function (D) 20 CASb4? of ionic strength as expressed by the extended form of the Debye-Huckel equation, provided .ion­ WHICH LEACHING FRACTIONS TO ACCEPT? pair formation is taken into account; and (c) the solubility products of gypsum and soil lime are 0.057 2.45 x 10-5 and 6.47 x 10-1°, respectively. The equilibrium solution composition is calculated by 0.1O? successive iterations taking into account ionic strength and (i) ion-pair formation constants for 0.20? sulphate, carbonate and bicarbonate ion~pairs with Na, Ca and Mg. The final composition meets 0.30? 0.407 the following conditions simultaneously: ion-pair equilibrium constants; (ii) charge balance

'\ 70 71 I, The sum of cation and anion charge concentrations entered in response to the fourth request Ca concentrations at the second, third and fourth depths are about the same because gypsum and should be equal. If they are not, Watsuit adjusts the concentrations to m~e them equal.as follows: lime precipitation counteract the concentrating effects of plant water uptake. Consequently the if the sum of the cation concentrations is greater than that for the amons, l.e. the ~I~:re.nce III mass of Ca in the leachate (V*Cc, ; see Table 2, col. 5) decreases with depth in all cases but one. A charge concentrations is positive, the difference is ad?:~ t? the anio~ that has ~ot been ImtlallZed I~ small increase occurs from depth one to two for a leaching fraction of 0.3. The loss of Ca (col. 6) the order CI, S04, ALK (HC03 + C03); if all were Imtlall~ed, the difference IS .added to Cl, and if from the upper portion of the root zone results from soil lime dissolution. Precipitation of soil lime the difference is necrative, the program will subtract the difference from the amon m the order Cl, and gypsum results in a gain of Ca within the lower portions of the root zone. The Ca gains show S04 ALK. If the difference is greater than any single anion concentration, the program stops and a that the amount of solids precipitating in the soil is appreciable for such gypsiferous water, even at mes~age questioning the analysis is displayed. .. . high leaching fractions (LF = 0.3). For each root zone depth interval, the calculation begins by multlplymg the IOn The preceeding data obtained with Watsllit dearly demonstrate that where the drainage concentrations by the value of lILF) appropriate to the leaching fraction at the. bottom boundary of water can be intercepted before returning to surface or groundwater bodies, volume and salt load the root zone. Average EC and SAR are calculated for the top quarter and entire root zone, water- of drainage can be reduced substantially with reduced leaching. uptake weighted EC is also calculated. Use ofWatsuit to assess water suitability for irrigation Table-2 Water and calcium balance within the root zone after irrigation with Pecos River water at leaching fractions of 0.1 and 0.3 calculated using watsuit. Root zone depth Prognoses of water suitability for irrigation are made using predicted soil water is divided into four quarters, with 1 representing the :op quarter and 4 the bottom compositions, salinities, and sodicities obtained from Watsuit. The effect of salinity under . (after Oster and Rhoades, 1990) conditions of frequent irrigation management (i. e. when little matric stress exists) is evaluated from upper profile EC, Corn:. For infrequent irrigation (i.e. conventional management where significant Mass of Calcium gain( +)or Leaching Root zone Volume Calcium matric stress occurs over the irrigation interval), one uses average profile EC (for more discussion concentration calcium in loss( -)within the fraction depth of 3 of the justification for this approach, see earlier discussions or Rhoades and Merrill 1976). To leachate2 depth interval interval leachate in leachate assess toxicity, specific solute concentrations are used in place of EC, C, or n:. To evaluate (mmoll1) (mmoll1) (mmoll1) potential permeabily/crusting problems, one uses soil surface SAR and the EC of the infiltrating 24.5 1740 (-)40 0.1 I 71.1 water and appropriate SAR (or ESP) - EC . threshold relations for the soils of concern (Rhoades 1354 (+)386 iw 2 41.1 33.0 1982a). The benefits of amendments are evaluated from examination of the predicted compositions 698 (+)656 3 21.2 33.1 after treatment. 364 (+)334 4 11.1 32.8 Soil salinity is judged as a likely problem if the predicted root zone salinity exceeds the tolerance of the crops to be grown. Similar assessments are made for boron, chloride and sodium. 2273 (-)90 1 102.9 22.1 The salt and specific ion tolerances for different plant species reported by Maas (1986) are used for 0.3 (-)25 2 73.9 31.5 2298 the assessments. If some yield reduction can be tolerated, a higher salinity (or toxicant (+)534 3 52.9 33.4 1764 (+)324 concentration) tolerance level is used, as appropriate, in place of the threshold levels. Soil 4 42.9 33.7 1440 permeability is judged a problem if the combination of predicted near-surface SAR and irrigation water EC are expected to result in significant aggregate slaking and clay swelling and dispersion. 1 The chemical composition of Pecos River water is as follows: in mmol/l: 11.38 (Na), 0.08 (K), For this purpose the relationship between SAR of topsoil and EC of irrigation water on soil 16.98 (Ca), 9.07 (Mg), 3.11 (RCO,), 12.13 (C1), and 22.39 (S04). The ~C is 3.3 dS/m. permeability reported by Rhoades (l982a) could be used. The benefits of soil and water 2 Mass of Ca infiltrated equalled 1700 and 2186 mmol/l at leaching fractions of 0.2 and 0.3, amendments on water suita~ility are evaluated based on their effects on soil solution composition. respectively. . , The differences in Ca mass entering and leaving the root zone depth mtervals. The potential benefit of treating sodic irrigation water with sulphuric acid is evaluated in Watsuit by simulating a 90 percent reduction in the water's bicarbonate concentration and The data in Table 2 illustrate the use ofWatsuit to predict the effects ofleaching fraction o.n increasing its sulphate concentration by a corresponding amount (equivalent basis). The SAR is the loss, or gain, of Ca in the root zone of a crop irrigated with ~ecoso river water. This :",~ter IS then recalculated. The potential benefit of adding gypsum to .the water can be evaluated by gypsiferous (see Table 2): the Ca concentration, 8.5 mmoll1, IS ~4Yo oof the total m:~molar increasing both the calcium and sulphate concentrations of the water by 1 mmolll and then concentration of cations, and the sulphate concentration, 11.2 mmoll1, IS 43 Yo of the total rmllimolar recalculating the adjusted SAR. This increment of calcium and sulphate is usually as high as is concentration of anions. The volumes ofleachate leaving each quarter depth of the root zone (~ol. practical to obtain with present gypsum water amendment applicators. Soil gypsum application 3) were calculated assuming the following: (a) 100 units ~f plant water uptake; (b) a leaching benefit can be evaluated by increasing both the calcium and sulphate·concentrations of the water by fraction of 0.3 and 0.1 and corresponding total umts of apphed water of 142:9 and 111.1, and .(c) 20 mmolll and then recalculating the adjusted SAR.

th water uptake and pC02 depth distributions described above for WatsUlt. The concentratlng Plant response to salts is thought to be governed primarily by their concentrations in e;ects due to the decreasing leachate volume with depth (i.e. plant wat~r uptake), and to a smaller solution, rather than by the exchangeable cation composition. If a soil is saline, or if the Ca extent the dissolution of soil lime, result in an increased Ca concentrat:on (coL 4) III the leachate concentration exceeds about 2 mmoll1, even a high level of SAR will have little nutritional effect on from the second depth, as compared to that from the first, for both leaching fractIOns. However, the most crops, as distinguishable from that of salinity, and can be ignored. Thus, the major concern,

73 72 with respect to sodium toxicity or calcium nutrition problems, occurs under non-saline, sodic and alkaline pH conditions where Na concentration is high, Ca concentration is low and/or where the However, estimates for t~ese required parameters could be made and dynamic modellino­ Ca/Mg ratio is less than 1. app~aches could be used to predict the results of irrigation with a saline water under the kinds of If the predicted average root zone Ca concentration exceeds 2 mm01l1, calcium deficiency is con tlOns (or ranges) expected to occur for specific situation in mind not anticipated. If this adjusted Ca concentration is less than 2 mmolll, the water is judged For a discussion of this type of modelling see Bresler et al (·1982) . fW (1984) and Letey et al. (1990). ' . or reviews 0 agenet unsuitable for long-term irrigation use with that leaching fraction. In addition, a check should be made to determine whether the resultant average soil water adjusted Ca++ /Mg ++ ratio exceeds the value one. The appropriate value of Mg++ to use is calculated as (Mgj++ )(Fe ) where Fe is the Production function models relative factor appropiate to the leaching fraction, LF (Rhoades 1982a). Amendments to sodic irrigation water that has calcium deficiencies are dealt with in the same fashion described earlier, These models ~e usable under the following conditions: (a) where one wishes to except that the adjusted Ca concentration is calculated rather than SAR. plants at less than full YIeld potential (i.e. where EC > EC' ). (b) wher th ill b d .gro,:", ET and h· I hin· e e , e ere w e a re uctlon m Generally, chloride and sodium toxicities are only of concern with woody plants. The most hni ence ea.c g and dramage volumes will diverge from those predicted by these models and chloride-sensitive plants may be injured when chloride concentration in the soil saturation extract tec ques,. as w!ll the r.esultant level of soil salinity; and ( c) if one wants to calculate irri g ation exceeds 5 or 10 mm01l1, while the most tolerant woody plants are damaged only at a chloride wate:- .reqUlrements, dramage volUllles and resulting soil salinity under less than 0 timum ·eld concentration of about 30 mm01l1 or greater (Bernstein 1974; 1980). This hazard potential is co~ttlOns. The techniques ofLetey et al. (1985 1990), Letey and Dinar (1986) Sol~mon (1~85) assessed by comparing the predicted average root zone chloride concentration in the soil water an mar et al. (1986) can be used for this purpose; all are similar in principle. ' , (diluted to a saturation extract basis) obtained from (Cl;)(Fe), with tolerance levels given in Solomon (1.985) presented the general theory and Letey et al. (1985) developed a s ecial Bernstein (1980) or Rhoades and Bernstein (1971). If the tolerance level is exceeded, a yield case. A ~aslc preIIlls~ of this approach was summarized by Solomon (1985) as follows: "Irri Patin WIth salme water w!ll cause some degree of salinization of the soil Thi . t ill g g reduction will occur. dec . . ld I . . . s, mum, w cause a No procedure is given to evaluate sodium toxicity for field, forage and vegetable crops, in re~se m crop YIe re atlve to Yield under non-saline conditions. This reduced yield ouo-ht to be spite of the fact that sodicity tolerances have conventionally been given for them in terms of assoc:ated With a d~cr~ase in plant size and a decrease in seasonal ET. But as ET o:s down exchangeable sodium percentage (pearson 1960, Bernstein 1974). The crop responses associated e~:ctlve leaching wI~1 mcrease: ~tigating the initial effect of the saline irrigation wat!r. For an; with sodicity levels were probably an artifact of the way the experiments were carried out. An g ~ amount an.d sal~ty of rrngatlon water, there will be some point at which values for yield ET examination of the experimental data (Bernstein and Pearson 1956; Pearson and Bernstein 1958) ~eaChing,. and s~!1 Sall~ty ~l .are .consistent with one another. The yield at this point is the yi:ld t~ shows that the yield reduction ascribed to toxic levels of exchangeable sodium only occurred when e assoclated With a given Imgatlon water quantity and salinity". either Ca was in the deficient range «about 1.2 mmol/l) or the crop's salt tolerance threshold value Letey et al. (1985) combined three relationships· yield and ET meld and t af·ty d . . . , J" average roo zone per se was exceeded. Rhoades (1982a) clearly showed that one cannot increase SAR at low levels s i ~~ ,a~ average root zone salimty. and leaching fraction to develop an equation which relates of salinity without simultaneously reducing Ca concentration to nutritionally inadequate levels, or y e . to t. e amount of seasonal applied water of a given salinity. Combination of these three achieve high values of SAR while keeping Ca nutritionally adequate (>1-2 mm01l1) without also ~e~atlOnShips provides a m~del for pr~~icting yield, drainage volume or EC of the water percolating increasing total salinity to high levels. Sodium toxicity is apparently real for woody plants which do eo,:", the root zo~e for gIVen quantltles of seasonal applied water (AW) of given salinities. The show sodium toxicity symptoms after sufficient accumulation in the plant tissue has occurred. apphed wat.er here mcludes both rainfall and irrigation, but does not include runoff Th dial assumes umform wat r f Th nl . e mo e so Tolerance levels for these crops are given by Bernstein (1974). eva .. er app.I~a IOn. eo y inputs required for the model are: AW, Ep (potential Plants respond primarily to the boron concentration of the soil water rather than to the V rotrans~lratlon) and salinity of !~g~tion water. The results apply to the whole crop season. amount of absorbed B (Hatcher et al. 1959; Bingham et al. 1981). Boron is adsorbed by soil o ume-welghted average water salimty IS used to adjust for rainfalL constituents and an equilibrium exists between the amounts in solution and in the absorbed state. In the long run, boron concentrates in the soil water, just as non-reactive solutes do. Obviously, for Use of.,a simple water and salt balance model to assess water suitability for irrigation some transitional period of time dependent upon soil properties, amount of irrigation water applied, leaching fraction and B concentration of the irrigation water; boron concentration in the soil water suitabiliA very. si.mple, non-~tea~y-state mass balance approach could be used to judge water will be less than that predicted. The time necessary to achieve this steady-state is usually less than 1988 )ty for Imgatlon, whi~h. mcludes water table contributions was developed by Rhoades 10 years. The potential of creating a boron problem upon irrigating is thus assessed by comparing ( a . The water balance WIthin a root zone for a cropping season is: the predicted average boron concentrations (Bi )(Fe), with crop tolerance levels.

OTHER MODELS FOR ASSESSING WATER QUALITY FOR IRRIGATION (3)

Dynamic models where Vi, V, Vd, Vg and V: are the volumes of irrigation water, rainwater, deep percolation, groundwater, and consumptive use (ET), respectively. Equation 3 may be rearranged to give: Dynamic models have indeed been developed to predict soil salinity, concentration of specific ions in soil water and the flux of soil moisture under irrigated condition. Input data for such models are rarely available under practical field conditions thus restricting their application. (4)

74 75 The corresponding salt balance is: REFERENCES.

(5) Ayers R.S. and Westcot D.W. 1985. Water quality for agriculture. Irrigation and Drainage Paper 29, Rev. 1). FAO, Rome. 174 pp. assumIng. tha t an ill' sl'gru'ficant amount of salt is _.removed by the crop and lost by precipitation. or Bernstein L. 1974. Crop growth and salinity. In: Drainage for Agriculture. van Schilfgaarde J. (ed). . h' h CdC are concentration and average concentratIOn, added by IDlneral weat enng, were an .' 1 d Agronomy 17:39-54. ( I These' are all very reasonable assumptions relative to the magmtude of salts illV? ve Bernstein L. 1980. Salt tolerance offruit crops. US Dept. Agr. Info. Bulletin 292. 8 pp. ~:~e~~:e:S'e of brackish and saline irrigation waters. Assuming Cd is equal to Cg, equatIOn 5 Bernstein L. and Francois L.W. 1973. Leaching requirements studies: sensitivity of alfalfa to the simplifies to the following relationship: salinity of irrigation and drainage waters. Soil. Sci. Soc. Amer. Proc 37:931-943. Bernstein L. and Pearson G.A 1956. Influence of exchangeable sodium on the yield and chemical composition of plants. 1. Greenbeans, garden beets, clover, and alfalfa. Soil Sci. 82:247-258. (6) Bingham F.T., Peryea F.J. and Rhoades J.D. 1981. Boron tolerance character of wheat. Proc. of Inter-American Salinity and Water Management Technology, 11-12 December 198C Juarez, Substituting for V . from equation 4 for the average armual condition (or using field capacity as the d Mexico. pp. 208-216. reference condition for soil water content) gives: Bresler E. and Yaron D. 1972. Soil water regime in economic evaluation of salinity in irrigation. Wat. Res. Research 8:791-800. , Bresler E., McNeal B.L. and Carter D.L. 1982. Saline and Sodic Soils: Principles-Dynamics (7) Modelling. Springer Verlag, New York. 236 pp. Dinar A, Knapp KC. and Rhoades J.D. 1986 Production functions for cotton with dated irrigation quantities and qualities. Water Resources Research 22. -1-519 -1525. Expanding LI(C w V w) into its components gives: EPA 1972. Water quality criteria. Envirornnental Protection Agency, Washington DC. 594 pp. FAO. 1976. Prognosis of salinity and alkalinity. Soils Bulletin 31. FAO, Rome. (8) Goldberg D. and Gornat B. 1971. Drip irrigation agricultural development. Presented at the Int. Experts Panel on Irrigation-Drip (Trickle) and Automated Pressure Irrigation. Erzilya-on­ Sea, Israel. 6-13 September 1971. Gornat B. Goldberg D., Rimon D. and Ben Asher 1. 1971. The physiological effect of water on the for the armual case, where LI V w is zero. Dividing by Vc gives: quality and method of application on a number of field crops: II. The effects of sprinkler and (9) trickle irrigation J. Amer. Soc. Hort. Sci. LlECw=[b Ec; + 2EC,Al-b-c)Jld Hatcher J.T., Blair G.Y. and Bower C.A 1959. Response of beans to dissolved and adsorbed boron. Soil Sci. 88:90-100. Ingvalson RD., Rhoades J.D. and Page AL. 1976. Correlation of alfalfa yield with various indices where EC is substituted for C, EC is replaced by the product 2 ECe,d (ECe,d is Valu) d t~e ~f of salinity. Soil Sci. 122:145-153. ECe in the lower quarter of the root zone at the beginning of the year of this calculatIOn, (b IS Letey J. and Dinar A 1986. Simulated crop-water production functions for several crops where VjjVc, (c) is V,Nc, and (d) is VwNc . . • • E = 112EC irrigated with saline waters. Hilgardia 54: 1-32. Equation 9 is used to calculate the increase In soil water EC (or ECo SInce Co w .' . al fV' V V V and (a) The final level ofEew Letey J., Dinar A and Knapp KC.1985. Crop-water function model for saline irrigation waters. over the armual penod USIng appropnate v ues 0 ,,~ g, w' .' Soil Sci. Soc. Amer. J. 49:1005-1009. ( orEC ) at the end of the period is equal to ECwi +LlEC wi· The process is repeated IteratIVely by e Letey J., Knapp K and Solomon K 1990. Crop production functions in: Agricultural Salinity usin the final value of EC was the starting value for the next armual c~c1e. . . Assessment and Management. KK Tanji ASCE, New York (ed). g The value of (b) is determined from the volume of water applied relative to the. ETrn.x , the Maas E.V. 1986. Salt tolerance of plants. Applied Agricultural Research 1(1):12-26. ly value of (c) is determined from the expected (or measured) average yea:- rainfall relatlv~l t~ ETrn'X McNeal B.L., Oster J.D. and Hatcher J.T. 1970. Calculation of electrical conductivity from solution . and the value of (d) is determined from the volume of soil water contamed :"'Ithin the SOl. etween composition data as an aid to in situ estimation of sail salinity. Soil Sci. 110:405-414. ~he soil surface and the water table depth at field capacity (i.e. volumetnc field capacity water Oster J.D. and Rhoades J.D. 1975. Calculated drainage water compositions and salt burdens content (x) depth). ... d th t 1 of resulting from irrigation with river waters in the Western United States. J. Environ. Qual. Whether or not the water of ECw. is acceptable for rrng~tlOn depen s .on e 0 erance 4:73-79.

"t on the llll''tl'allevel of soil salinity on the relative volume-ratIOns b, c and d, and t h e crop to s al1m y, '. . ) Th t's Oster J.D. and Rhoades J.D. 1990. Steady-state root zone salt balance. ASCE Salinity Manual. on the efficiency of leaching (i.e. rainfall intensity and pattern and soil properties. e wa er I Pearson G.A 1960. Tolerance of crops to exchangeable sodium. US Dept. Agric. Info. judged suitable as long as the final level of EC 0 does not exceed the threshold tolerance (as Bull.216.4p. determined form tables).

77 76 Pearson G.A and Bernstein L. 1958. Influence of exchangeable sodium on yield and ch~mic~ composition of plants. II. Wheat, barley, oats, rice, tall fescue, and tall wheatgrass. Soil SCI. Strategies for the Use of Multiple Water Supplies 86254-261. . . P 2 d I t 1 for Irrigation and Crop Production Raats P.A.·C. 1974. Movement of water and salts under high frequency imgatlOn. roc. n. n er. Drip Irrig. Cong., San Diego, CA, 7-14 July. p. 222-227. . .. . J. D. Rhoades, Director, US Salinity Laboratory, USDA, Rhoades J.D. 1977. Potential for using saline agncultural dramage waters for IrngatlOn. Proc. Riverside, California, USA Water Management for Irrigation and Drainage, ASCE, Reno, Nevada. July 1977. pp. 85- INTRODUCTION Rhoa;e~6j.D. 198~a. Reclamation and managen:-ent. of salt-affected soi1~ after drainage. P:oc. 1st Ammal Western Provincial Conf. RationalizatIOn of Water and SOlI Res. and Manaoement. Diversions in excess of crop needs often provide return flows for irrigation downstream and Lethbridge, Alberta. Canada. 29 November -.z December 19~2. pp. 123-197. help modulate the river flows, but such return is the mechanism by which much of the salt loading Rhoades J.D. 1987a. Use of saline water for irrigatIOn. Water Quality Bull~tmJ2.14-20. of rivers occurs which, in tum, limits the kind of crops that can be grown. More significant is the Rhoades J.D. 1988a. Evidence of the potential to use saline water for lrngatlOn. Proc. Symp. Re­ fact that if the water being returned to the river is so saline that it CalIDot be used for crop Use of Low-Quality Water for Irrigation. Water Research Centre, Egypt. pp.l-~1: . production, then dilution with purer water and using the mix for irrigation of crops of the same or Rhoades J.D. 1988b. Final report to FAO on suitability of the water of Lake Xochimih?-Teahuac lesser salt tolerance does not add to the usable water supply. Greater flexibility for crop production for irrigation _ chemical parameters. 9-15 December 1988. Consultant Report Project, FAO, results if the drainage water can be intercepted, isolated and then blended or used separately for irrigation or other uses. Once the drainage is mixed in surface water, these alternatives are lost. Rhoa!~7~. and ~ernstein L. 1971. Chemical, physical and biological characteristics of irrigation A reco=ended strategy for salinity control of surface and groundwater systems is to and soil water. In: Water Pollution Handbook, Ciaccio L.L. (ed), Mar~el Dekker, Ne,,: York. intercept drainage before it is returned to these systems and to use it for irrigation by alternating it Rhoades J.D. and Merrill S.D.1976. Assessing the suitability of.v:ater for lrngatl?n: Theoretical and with the water normally used during certain periods in the growing season of selected crops empirical approaches. In: Prognosis of Salinity and Alkallmty, SOlIs Bulletm 31. F AO, Rome. (Rhoades 1984a; 1984b). When the drainage water quality is such that its potential for reuse is exhausted, it is discharged to evaporation ponds or other appropriate outlets. This strategy will Rh :PJ ~lg in2:Valson R.D. Tucker J.M. and Clark M. 1973. Salts in irrigation drainage waters. conserve water, sustain crop production, and minimize the salt loading of rivers. It will also reduce oa es.. 0 ' • • 1 hin fr t· d t" of year on the salt L Effects of irrigation water compOSItion, eac g ac IOn, an lme the diversion of river water or irrigation. compositions of irrigation drainage waters. Soil Sci. Soc.Amer. Proc. 37:77~- ?7~.. h al The ultimate goal of irrigation management should be to minimize the amount of water Rhoades J.D., Oster J.D., Ingvalson R.D., Tucker 1.M. and Clark M. 1974. Mimrmzmg t est extracted from a good water supply and to maximize the utilization of the extracted water for burdens of irrigation drainage waters. J. Environ. Qual. 3 :311-316. irrigation so that drainage return is minimized before it is discharged to some form of ultimate Solomon K H.1985. Water-salinity-production functions. Trans. AS~ 28(6): 1975-1?80 .. disposal. Towards this goal, to the extent that the drainage water still has value for use by a crop of Suarez D .L.1981. Relationship between pRe and SAR and an alternative method of estlmatmg SAR higher salt tolerance, it should be used again for irrigation. of soil or drainage water. Soil Sci. Soc. Amer. 1. 45:469-475. . This paper describes an integrated strategy of management that will facilitate the successful Thome J.P. and Thome D.W.1951. The irrigation waters of Utah. Agnc. Expt. Sta. BulL346. 64 use of brackish water for irrigation, minimize the harmful off-site effects of drainage discharge and the pollution of water resources and maximize the beneficial use of the total water resources pp .. t f Sal· d Alkali Soils Richards L. US Salinity Laboratory. 1954. DiagnOSIs and Improvemen 0 me an . available in typical irrigated lands and projects. A (ed). USDA Handbook No. 60...... d r Irri ation W t R J 1984 Salt and water movement m the soil profile. In. Soil Sallmty Un e g . DUAL ROTATION STRATEGY TO FACILITATE USING SALINE WATER FOR age~~ainb~rgI. ~d ShalhavetJ. (eds). Springer Verlag, New York. Chap. 4.1. pp. 100-l.14. IRRIGATION · 1 . H Shalhavet J. and Gavish Y1972. Estimation procedures for response Y aron D ., BIe ora! ., . . h . 91-300 functions of crops to soil water content and sallmty. Wat. Res. Resear:c .- 8.2 .. . The feasibility of reusing drainage water for irrigation is facilitated by the 'dual rotation' Zur B and Bresler E.1973. A model for the water and salt economy m lrngated agnculture. In. management strategy, (Rhoades 1984a; 1984b; 1984c), in which sensitive crops (lettuce, alfalfa, Physical Aspects of Soil Water and Salts in Ecosystems. Hadas A,Swartzendruber D., etc.) in the rotation are irrigated with low salinity river water, and salt-tolerant crops (cotton, sugar Rijtema P.E., Fuchs M. and Yaron B. (eds): Springer Verlag, New York. pp. 395-407. beet, wheat, etc.) with drainage water. For the tolerant crops, the switch to drainage water is \ usually made after seedling establishment; replanting and initial irrigations are made with river water. Benefits from this strategy are: (a) a harmful level of soil salinity in the root zone does not occur when drainage water is used only for a fraction of the time; (b) substantial alleviation of salt build-up occurs during the time salt-sensitive crops are irrigated with river water; (c) proper preplant irrigation and careful irrigation management during germination and seedling establishment leach salts out of the seed area and from shallow soil depths. Data obtained in modelling studies

79 78 and in field exptoriments support the credibility of this cyclic reuse strategy (Rhoades 1977; 1988a; 1988b). .... Id b . d Some Experimental Examples of the Strategy There are many situations where the use of dramage water for Im~atIOn c.ou e p~actIse , such as where the source of drainage water or shallow groundwater IS readily acc~ssIble and This strategy has been recently tested in a 20-hectare field experiment, begun on a available for irrigation; water discharged to drainage pipes or canals or presen! m shallo:", commercial farm in the Imperial Valley, California in January 1982, where two cropping patterns oroundwater systems could be intercepted; and where some high quality (non-salme) water IS were tested (Rhoades et al. 1989a; 1989b; 1989c). One was a two-year successive crop rotation of ~vailable for irrigation or sufficient rainfall occurs at certain times of the year to meet crop needs wheat, sugarbeet and cantaloupe melons, in which Colorado River water (900 mg/l TDS) was used periodically and to" leach soluble salts from ~e root z?ne. The dual rotation strategy ?resup~oses for the preplant and early irrigations of wheat and sugarbeet and for all irrigations of the melons. the availability of two water sources: one high qUalIty and th~ other lo~ qualIty (I.e. dramage The remaining irrigations were with the Alamo River (drainage water of 3 500 mg/l TDS). The water), even though they may not be available simu~taneously d~nng tJ:.e .entIre season/year. . other was a four-year block rotation consisting of two years of cotton (a salt-tolerant crop) The most practical siruation where reuse Dllght be consIdered IS m areas .w~ere .high qUalIty followed by wheat (an inte=ediate salt-tolerant crop) and alfalfa (a more salt-sensitive crop) in water is available during the early growing season, but is either costly or too limite.d. m supply to years three and four respectively. meet the entire season's requirements. Where high quality water costs are prohibItI:e, crops of No significant losses in the yields of wheat and sugarbeet occurred from substituting moderate to high salt tolerance could be irrigated with saline drainage. water, especI~ly. at ~ater drainage water in either cycle of the rotation. Also no significant yield loss was observed from growth stages, with economical advantages even if this p~actice re~ulted m some reductIon m YIeld. growing cantaloupe using Colorado River water for irrigation in the land previously salinized from However, long-te= potentially deleterious effects on soil propertIes must be assessed before such the irrigation of wheat and sugarbeet using drainage water. reuse can be advocated. . . There was no loss in lint yield in the first cotton crop (1982) in all three treatments and no The second most practical siruation is in regions where drainage water disposal IS not significant loss in the second cotton crop (1983) from use of Alamo River water for the irrigations possible due to physical, environmental, social and/or political factors ..Since many agncultural given following seedling establishment, which was accomplished using Colorado River (the crops are sensitive to shallow or fluctuating water-tables, a me~s .of l?wermg a shallow water table recommended strategy treatment). But there was a significant and substantial loss oflint yield in. the is essential to sustain crop production. Reuse of the water for ImgatIOn would re?~ce t~e amount second season cotton crop (1983) as expected, where the Alamo River water was used solely for of high quality water required, and decrease the volume of drainage vot~r requmng dISpOSal or irrigation. This loss of yield was caused primarily by a loss of stand that occurred this second year treatment thus reducing the costs associated with treatment and/or dISPOSal. Furthe=ore, a because salinity was excessively high in the seedbed during the establishment period. No loss in reduction' in the drainage volume should also reduce salt loading of rivers and streams. Many yield of wheat grain or alfalfa hay occurred in the block rotation associated with the previous use of Irrowers in the San Joaquin Valley of California are now reusing drainage water at least as a Alamo River water on these lands under these conditions in which they were irrigated with ~emporary solution to their need to reduce drainage volume...... Colorado River water. The long-te= feasibility of using drainage water for Im.gatIon m order to reduce dramage The qualities of all these crops were never inferior, and often superior, when grown using volume would probably be increased if implemented on a regIOnal rather than on a farm scale. the drainage water for irrigation or on the land where it had previously been used (Rhoades et al. Regional management permits reuse while avoiding the successive increase ~n concentratIOn t~at 1988a). would occur where the reuse process operates on the same water supply, as It does when apphed An analysis of the amounts of water applied to each crop and over the entire four-year repeatedly on the same land. Certain areas in the region c0:rId b.e dedica~ed to reuse while others, period was carried out for the successive and block rotations, respectively. The data included all such as upslope areas, continue to be irrigated solely WIth high qUalIty water: The secondary water applied, including that used for preplant irrigations and land preparation purposes. They drainage water from the reuse area could be disch~ged to regional evaporatIOn ponds or :0 showed that substantial amounts of drainage water were substituted for Colorado River water in treatment plants. Regional coordination and cost-sharIng among growers should be undertaken m the irrigation of these crops without yield loss. The results support the credibility of the such a system. . . . recommended cyclic crop and water strategy to facilitate the use of saline water for irrigation. Another but more extreme use of saline waste water IS to al'ply It to specific crops that In another study carried out in the San Joaquin Valley (Ayars and Schoneman 1986: Ayars have the ability'to accumulate large quantities of undesirable constituents. (e.g ..Se, Mo, ~03, B, et al. 1986) drip irrigation was used to apply drainage water EC = 8.0 dS/m) to cotton (after the etc.) in the plants before the subsequent discharge of the secondary dramage mto a saline smk crops were established) for three consecutive years, followed by a wheat crop irrigated with high (evaporation pond, ocean, etc.) or other fo=s of disposal in order to help reduc.e adve~se quality water and then by sugarbeet irrigated with drainage water after stand establishment. ecological effects. Biofiltration, the te= used to describe this process, has been e~ammed usmg Shennan et al. (1987) have tested the dual-rotation strategy on a crop rotation consisting of higher plants by Cervinka et al. (1987) and Wu et al .. (1987). Th~y found that cert~ gr~sses and two years of cotton followed by processing tomatoes in the San Joaquin Valley of California. In native species in California are effective in accumulat~ng substantIal. amounts of Se m theIr shoots. this study saline drainage water (EC of 7.9 dS/m) is applied to the more sensitive crops (processink This alternative management practice is most attractIve where dramage dIsposal pro?lems occur, tomato) to improve fruit quality (e.g. soluble solids). This quality influence was found repeatedly in the bioaccumulator has economic value, and other treatment processes are unaVaIlable or too short-te= studies on tomatoes where drainage water, applied after first flower, supplied over 65 expensive. percent of the irrigation water requirements and did not reduce yields (Grattan et al. 1987). Cotton would be grown after tomatoes for reclamation purposes. Pasternak et al' (1986) also found an increase in soluble solids in the tomato fruit from brackish water (EC = 7.5 dS/m), but yields were reduced 30 percent when saline water was applied after the 4 or 11 leaf stage.

81 80 Reuse of drainage effiuent irrigation) (Shalhevet 1~~4): Another advantage of the cyclic strategy is that a facility for blending waters of different qualities IS not required. Minimizing leaching and deep percolation always minimizes the volume and salt load of the drainage water and usually minimizes pollution of the receiving water (van Schilfgaarde et al. 1974; BLENDING Rhoades et al. 1974; Rhoades and Suarez 1977). For this reason, minimizing leaching and deep percolation should be the goal of irrigation management. For those situations where the water · Th.e second reuse str~tegy is to blend water supplies before or during irrigation (Shalhavet cannot be, or has not been, fully utilized in their first passage through the root zone, the drainage 1984, Mem et al. 1996; ~ns et al. 1987; Rolston et al. 1988). Although cyclic-dual rotation water should be intercepted before its discharge to water supplied of better quality and reused for str~tegy havmg more potentIal and flexibility than the blending strategy some aaricultural enginee irrigation (Rhoades 1984d). The preceeding case examples illustrated the merits of this beheve :he latter is easier to. implement on large farms. Blending ~ay be °more practical a:~ management strategy. While concentrations of salts in drainage water are higher than those of the appropnate, proVldmg the drarnage or shallow groundwater is not too saline per se for the crop to corresponding irrigation water supply, they are often within acceptable limits for growing suitably be grown. salt-tolerant crops (Rhoades 1977). · A study. was conducted . . on an 8 ha site in the Tulare Lake basm' I'n CalifOIlll' a usmg. a crop A reuse strategy that avoids blending has been demonstrated in field projects to be viable rotatIon typICal for this locatIOn (two ye~s o~ cotton followed by one year safflower) (Rains et al. and advantageous in well-managed irrigation projects (Rhoades 1984a; 1984b; 1987; Rhoades et al. ~:~;' r;,.0lston et al. 19.88). Cr.ops were eIther Irrigated continuously with California aqueduct water 1988a; 1988b). The two water supplies (good quality and saline drainage) are kept separate and 1500 mg/] TDS) or With a illlXture of drainage water and aqueduct water that produced water of used without blending. The saline drainage water is intercepted, isolated and substituted for the , 3000, 4500, 6000 and 9000 mg/! IDS. All plots received a preplant irriaation with aqueduct conventional good- water, in suitable locations in the project when irrigating certain salt-tolerant water. The .safflower was not irrigated with either water after the preplant irri~ation. Cotton yields crops grown in the rotation at a suitably salt-tolerant growth stage (after seedling establishment); were not sl~fi~ant]y reduced by any of the drainage water treatments for the first two years. the good water is used at other time. The appropriate timing and amount of substitution of the However, Yield m the subsequent safflower crop (a crop slightly more sensitive than cotton) was saline water will, of course, vary with the quality of the two waters, the cropping pattern, the reduced by almost 40 percent at the highest salinity level. Part of this reduction was due to poor climate, the irrigation system, etc. The maximum soil salinity in the root zone that would result stand establIshment. Wh~n cotton was planted the following year, yield was reduced by the 900 from the sole use of saline water for irrigation will not occur when such water is used for only a mg/l TDS treatment, agam partly due to poor stand establishment. fraction of the time. The levels of salinity will be especially lower during the critical periods of su . If the blending strateill:' is adopted, there must be a controlled means of mixing the water germination and seedling establishment relative to using the saline water solely or in a blend. ppl~es. Shalhevet .(1984~ dIsc~ssed two blending processes: network diluting where water Whatever excessive salt build-up occurs in the root zone from irrigating the tolerant crops in the supphes are blended III the ~gatIOn conveyance system and soil dilution where the soil acts as the rotation with the saline water are alleviated in a subsequent cropping period when a more sensitive medIa for mlxmg water of d~~rent .qualities. Here different water qualities are alternated according crop is grown using the low salinity water for irrigation. to avarlablhty, between or WIthin lITIgation event. Since continuous recycling, in the sense of a closed loop, is not possible, reuse should be Meiri et .al. (1986) conducted a three year study to compare crop performance under designed so that the drainage water intercepted and isolated from the major part of the project area ne:w0.rk and soIl blendlllg systems. A crop rotation of potatoes and groundnuts under drip is redistributed to a designated reuse-area within the project, or sequentially to areas where crops ImgatIOn was tested. They concluded that crop responded to the weighted mean water salinity of lesser to greater salt-tolerance are grown. The resultant minimized volume of drainage from the regardless of the blending method. ' reuse area must eventually be desalted or else disposed of, but not by discharge into good-quality water supplies, unless no other means is practical. LONG-TERM ASPECTS There may be a difficulty adopting the cyclic strategy on small farms where the drainage water produced is too little or does not coincide with peak crop-water demand. In the San Joaquin · The studies that h~ve been discussed thus far have indicated that irrigation water containing Valley in California, farms are large and peak drain water flow occurs from January to June when salts m excess of conv~ntIOnal suitability standards, can be used successfully on nume'ro~s crops for most crops would require high quality water. Use of straight drainage water during the later season at least .seven years .WIthout a .Ioss in yield. The author, however, cautions the overly optimistic may be unfeasible if the flow rate needed to irrigate a field effectively exceeds the flow rate from read~r SIllce un~ertarnty still eXists concerning long-tenn effects of these practices on the physical the drains. To avoid this lack of drainage water availability, a surface storage reservoir could be quality of the soil. constructed to retain drainage water until its use is required. An option is to plug the drains and . The ~rea:est concern with regard to long-term effects of drainage water reuse on soil allow the soil to act as the reservoir. The latter option is more desirable since this would not take physlc.al qual~ty IS that of reduced water infiltration capacity. This is especially important where land out of production. However, regardless of where the drainage water is stored, a drainage reuse IS practIsed on poorly structured soils and if the SAR of the drainage water is > 15. water collection and irrigation system must be constructed in order to implement this strategy. Long-tenn effects on soil salinization must also be considered. Soil salinity under the cyclic The cyclic strategy is unique, however, in that steady-state salinity conditions in the soil strategy Will fl~ctuate ~ore, both spatially and temporally, than under the blending strategy. profile are never reached since the irrigation water can change quality from one irrigation to Therefore, predIctI~g or ~terpreting plant response would be more difficult under the former since another. Consequently, a flexible cropping sequence that includes salt-sensitive crops can be steady-state condItIOns WIll not oc.cu:. Nevertheless, management must be practised that keeps the included. Furthermore, intermittent leaching, which would occur under this strategy, is more average root zone salinity levels WIthin acceptable limits in both strategies. effective at leaching salts than continuous leaching (i.e. imposing a leaching fraction with each

83 82 Much drainage water contains certain elements, such as boron and chloride, that can accumulate in plants to levels that cause foliar injury and a subsequent reduction in yield. In many Criteria that should be considered for selecting crops for a reuse practice (after cases, this may produce more long-term detrimental effects than salinity. In the San Joaquin Valley Grattan and Rhoades 1989) in California, much of the drainage water contains boron in excess of 5 mg/I. Since boron in the soil requires more leaching than salts to remove excessive accumulations, long-term accumulation in the soil must be addressed. Toxic effects may not become evident for several years. Selection criteria Desirable Undesirable Another long-term consideration with regards to reuse of drainage water is the accumulation potential of certain elements (such as Se, Mo, heavy metals) in plants and soils that 1. Economic value/marketability high/marketable low/unmarketable are toxic to consumers of the crops (humans and. animals). In the San Joaquin Valley, drainage 2. Crop salt tolerance tolerant sensitive water in several locations contains unusually high levels of Se 2: 50 ~g /1). Although Se is essential 3. Crop boron/chloride tolerance tolerant sensitive to humans and animals, excessive amounts can cause Se toxicity. In California, melons and 4. Crop potential to accumulate toxic element toxic element processing tomatoes were irrigated with drainage water that contained 250 to 350 ~g Sell (Grattan toxic constituent excluder accumulation et al. 1987). Although the concentrations detected in the fruit (250 to 750 ~g/kg, dry wt.) were not 5. Crop quality improved by unaffected or considered to be a health hazard (Fan and Jackson 1987), they were significantly higher than those saline water adversely affected irrigated with high quality aqueduct water «5 ~g Sell). by saline water Although Se and Mo are of major concern in the drainage water underlying the San Joaquin 6. Crop rotation consideration compatible incompatible Valley in Califorrlla, other specific elements in drainage water could dictate their reuse potential in 7. Management/environmental easy management, requires intensive other regions ofthe world. conditions requirements able to grow management and can only under diverse be grown under specific MANAGE.l\.1ENT CONSIDERATIONS AND GUIDELINES conditions conditions

There are numerous management considerations that must be addressed in order to practise the reuse successfully. The intention of this paper is not to provide a step-by-step process that must . . Economics is. an important selection consideration since it would be senseless to grow a be followed, nor a rigid set of criteria. That approach is impractical since most management high Y1eldmg crop Wlth?u~ a marketable product or a positive cash flow. For example, salt and/or decisions are subjective. The intention, therefore, is to suggest parameters that should be bor?n tolerance o.ften Iun:t the crops usable in a particular location. In the San Joaquin Valley in considered and provide some rough guidelines to help users make rational decisions. Califorrua, there 1S negat1ve correlation between crop tolerance to salinity and eco o· al (Gratt d Rh d ). n IlliC v ue Availability and accessibility of drainage water must be determined. As indicated earlier, the cyclic to s . an an oa es 1990 . It 1S ~nfortunate that there are not many crops that are both tol~rant strategy can have more stringent demands on availability than does the blending strategy. al alinity and h~ve ~ high econOIlliC value. Asparagus is tolerant to salinity and has a reasonable Therefore, if the cyclic strategy is to be adopted, a system of collection and redistribution of the v ue b ut harvestmg 1S labour intensive and costly. drainage water must be developed to avoid the need for storage reservoirs. This is especially ~anagement practices, as well as, soil and climatic conditions dictate the crops that can be important where large areas will be irrigated by furrow or flood. gro~ m a particular region. The most desi.rable crops are those that do not require intensiye A network blending system must be designed and installed if the blending strategy were mana",ement and that can be grown under a Wlde range of environmental conditions . adopted. The theory and design of dilution control junction in irrigation networks is provided by rod ~roper ~an.agement of i~gation water, regardless of its quality, is essential for good crop Sinai et al. (1985,1989). p .uctlOn, d.. but 1t 1S even more lIDportant when saline water l·S used. Managemen t d eC1SlOns.. are In order to evaluate the reuse potential, the quality of shallow groundwater or drainage reqUlre regardmg. st~d .estabhshment, irrigation method selectiQn, blending and timing of drainage water must be determined. This can be done by standard water sampling techniques and analysis water ap~lcat1?n, lITlgauon-scheduling and leaching requirement·s. (Rhoades 1982). Usually the most important water quality parameters to assess are EC, SAR, and . . a . T e 1mg.atlOn. method can have a large influence on crop performance especially wh~n the boron. The water should also be analysed for potentially toxic elements, if suspected in the 1m",a:lOn wateIls salme. Shalhevet (1984) described three factors that should be considered before groundwater. If available, previous records of water quality data at different times of the year sele~t1~g an ImgatlOn me~hod: ~1) t?e salt distribution in the soil, (2) crop sensitivity to foliar should be examined to assess temporal water quality variations. wettm", and (3). the eas~ W1th which high osmotic and matric potentials can be achieved. Perhaps the most important management decision before implementing a reuse practice is b Bernstem an~ FI~eman (1957) showed that salts fccumulate in certain regions of the seed crop selection. A list' of criteria that should be considered for selection of crops when practising ed under furrow ImgatlOn. Information from this early study facilitated improvement in seed bed reuse is presented in Table 1. anda. furrow desum '" to minimize this probl ~m. Suc h seedId p acement an surface ...'.lITlgatlOn strategIes ( e.", .. ~ternatJve furrow, depth of water m furrows) to optimize plant performance under saline cond1tl~ns are ~e.scnbe~ by Oster et al. (1984). Under drip irrigation, the salt content is usually lowest m the soIlllllIDedmtely below and adjacent to ilie emitters and highest in the periphery of the wetted zone. Removal of salt .that ~as. accumulated in the front of the wetting zone must be addressed m ilie long-term. Spnnkler lITIgation can be effective in leaching excessive salinity from

85 84 the top soil and in producing a favourable low-saline environment in the upper soil layer which is necessary for the establishment of salt-sensitive seedlings. However, other problems (such as foliar Rhoades J.D. 1984a. Using saline waters for irrigation. Proc. Intll Workshop on Salt-Affected Soils of Latin Amenca, Maracay, Venezuela, 23-30 October 1983. pp. 22-52. Pnb!. in Scientific Review on Arid Zone injury) are associated with sprinkling of saline water. Research. 1984. Vol. 2:233-264. Many crops have been found to be sensitive to saline water under sprinkler irrigation since Rhoades J:D. 1984b. Reusing saline drainage waters for irrigation: A strategy to reduce salt loading of rivers. In: the foliage absorbs salts upon wetting. Salts can accumulate in leaves by foliar absorption until Sallmty m Watercourses and Reservoirs. French R.H. (ed.). Proc. Int,1 Symp., State-of-the-Art Control of lethal concentrations have been reached. Bernstein and Francois (1973) found that the yield of bell Salimty, Salt Lake City, Utah, 12-15 July 1983. Chap. 43, p. 455-464. peppers were reduced by 59 percent when 4.4 dS/m water was applied through a sprinkler system Rhoades J.D. 1984c. New strategy for using saline waters for irrigation. Proc. ASCE Irrigation and Drainage Spec. Conf., Water-Today and Tomorrow, 24-26 July 1984, Flagstaff; Arizona pp. 231-236. compared to a drip system. Meiri et al. (1982) found similar results for potatoes. Rhoades J.D. I 984d. Principles and methods of monitoring soil salinity. In: Soil Salinity Irrigation _ Processes and Theoretically, plant performance should be optimized by maintaining the average root zone Management. Springer Verlag. Berlin 5:130-142. at the highest possible water potential. Therefore, in regard to irrigation with saline water, irrigation Rhoades J.D. 1987. Use of saline water for irrigation. Water Quality Bulletin 12:14 intervals should be shortened compared to normal conditions. Based on the ease with which a high Rhoades J.D. 1988a. Evidence of the potential to use saline water for irrigation. Proc. Symp. Re-Use of Low Quality soil water potential can be maintained, drip irrigation would be the choice of irrigation method Water for Irrigation. Water Res. Center, Egypt under saline conditions. There is not, however, a substantial amount of evidence in the literature to Rhoades J.D. 1988b. Final report to FAO on snitability of the water of Lake Xochimilo-Tahuac for irrigation chenucal parameters, 9-15 October 1988. COnsultant Rep Project TCPIMEXl6652. support the claim that crop performance can be improved under field conditions by increasing Rhoades J.D., Bingham F.T., Letey J., Dedrick AR., Bean M., HOffman G.J., Alves W. Swain R.V, Pacheco P.G. irrigation frequency with saline water (Shalhevet 1984). Increased irrigation frequency, if exceSSlVe, and LeMert R.D. 1988. Reuse of drainage water for irrigation: results of Imperial Valley Study 1. Hypothesis, can induce problems of poor aeration and increased root disease, that can counterbalance the expenmental procedure and croppmg results; U Soil salinity and water balance. Hilgar 56(5):11-44. benefits of increased water potential. Rhoades J.D., Oster J.D., Ingvalson R.D., Tucker J.M. and Clark M. 1974. Minimizing the salt burdens of irrigation drainage waters. J. Environ. Qual. 3:311-316. Rhoades J.D. and Suarez D.L. 1977. Reducing water quality degradation through minimizing leaching management. REFERENCES Agr. Wtr. Mgrnt. 1(2):127-142. Rhoades ID:, Manteghi N.A, Shouse P.I and Alves W.J. 1989a. Estimating soil salinity from saturated soil-paste Ayars J.E. and Schoneman R.A, 1986. Use of saline water from a shallow water table by cotton. electncal conductivity. Soil Sci. Soc. Am.. J. 53:428-43 Trans. ASAE. 29(6):1674-1678. Rhoades J.D., Manteghi N.A., Shouse P.J. and Alves VJ. 1989b. Soil electrical conductivity a soil salinity: New. Ayars J.E., Hutmacher R.B., Schoneman, R.A, Vail S.S. and Felleke D. 1986. Drip irrigating cotton with saline formulatIOns and calibrations. Soil Sci. Soc. Am. 53:433-439. drainage water. Trans. ASAE. 29(6):1668-1672. RhoadesJ.D.: Vaggone B.L..' Shous~ P.I and Alves VJ. 1989c. Determining soil salinity from soil and soil-paste Bernstein L. and Fireman M. 1957. Laboratory studies on salt distnbution in furrow irrigation soil with special electncal c?nductiVlues: SenSlUVlty analysis of models. Soil Sci. Soc. Am. J. (In Press) reference to pre-emergence period. Soil Sci. 83:249-263. Rolston D.E., Pams D.V., Biggar J.V and Lauchli A 1988. Reuse of saline drain water for irrigation. Paper Bernstein L. and Francois L.E.1973. Comparison of drip, furrow, and sprinkler irrigation Soil Sci. 115 :73-86 presented at UCDIINIFAP Conference. Guadalajara, Mexic, March 1988. Cervinka, V., Finch C., Beyer J. , Menezens F. and Ramirez R. 1987. The agroforestry demonstration program in Shalhevet J. 1984. Management of irrigation with brackish water. In: Shainberg 1. Shalhevet J. (eds.) Soil Salinity the San Joaquin Valley. Progress Report. Calif. Dept. of Food and Agriculture. Agricultural Resources Under Imgauon Processes and Management. Springer Verlag. New York, pp. 298-318. Branch, Sacramento, California. Shennan C., Grattan S., May D., Burau R. and Banson B. 1987. Potential for the long-term cyclic use of saline Fan A M. and Jackson R.J. 1987. Health assessment of human dietary selenium intake from agricultural crops. A dramagewater for the production of vegetable crops. Technical Progress Report, UC SalinitylDrainage Task report of the UC SalinitylDrainage Task Force. Div. of Ag. and Natural Resources. University of California Force, DIV. of Ag. and Natural Resources/UC 22 pp. Sinai G., Jury V.A. and Stolzy L.H. 1985. Application of automated flow and salinity control to dilution of saline Grattan S.R. and Rhoades J.D. 1990. Use of saline groundwater and drainage water for irrigation. ASCE Salinity nngauon water. Irrig. Sci. 6:179-190. Handbook, Chap. 20. (Submitted). Sinai G., Jury V.A and Stolzy L.B. 1989. Methods for automated dilution of saline water sources for irrigation. J. Grattan S.R., Shennan C., May D.M., Mitchell J.P. and Burau R.c. 1987. Use of drainage water for irrigation of Irrig. Drain. Div., ASCE, (In Press). melons and tomatoes. California Agriculture 41(9 and 10):27-28. van Schilfgaarde J., Bernstein L., Rhoades ID. and Ravlins S.L. 1974. Irrigation management for salt control. J. Meiri A, Shalhevet J. , Shinshi D. and Tibor M. 1982. Irrigation of spring potatoes with saline water. Agric. Res. Img. and Drainage Div., ASCE 100(IR3), Proc. Paper 10822, p. 321-338. Org., Volcani Center, Inst. Soil and Water, Bet Dagan, Israel. Annual Report. • Wu L., Burau R. G. and Epstein E. 1987. Study of selenium accumulation and selenium-salinity co-tolerance in turf, Meiri A, Shalhevet J., Stolzy L.B., Sinai G. and Steinhardt R. 1986. Managing multi-source irrigation water of forage, and salt marsh speCIes for crop production in deteriorated soils and water quality improvement in the different salinities for optimum crop production. BARD Technical Report 1-402-81. Volcani Center, Bet San Joaqum Valley. Technical Progress Report. UC SalinitylDrainage Task Force, Div. of Ag. and Natural Dagan, Israel, 172 pp. Resources, University of California. Oster J.D., Hoffman G.J. and Robinson F.E. 1984. Management alternatives: Crop, water and soil. California Agriculture 38(10):29-32. Pasternak D., De-Malach Y. and Borovic J. 1986. Irrigation with brackish water under desert conditions. VII. Effect of time of application of brackish water on production of processing tomatoesj (Lycopersicon esculenturn Mill). Agr. Wtr. Mgrnt. 12:149-158. Rains D.V, Goyal S., Weyranch R. and Lauchli A 1987. Saline drainage water reuse in a cotton rotation system. Califomia Agriculture. 41(9 and 10):24-26. Rhoades J.D. 1977. Potential for using saline agricultural drainage waters for irrigation. Proc. Water Management for Irrigation and Drainage, American Society of Civil Engineers, Reno, Nevada, July 1977, pp. 85-116. Rhoades J.D. 1982. Reclamation and management of salt-affected soils after drainage. Proc. of the First Annual Western Provincial Conf. Rationalization of Water and Soil Res. and Management. Lethbridge, Alberta, Canada, 29 November - 2 December 1982. pp. 123-197.

86 87 Irrigation Systems, Water Quality and Management SOll- TYPES IN THE UAB in Salt-Affected Soils Morphological Characteristics Case Study from the UAB The soil ranges from sandy loam to clay loam, but it is sandy loam in general. Its content of CaC0 is 20-45%. It is dry and does not have any diagnostic horizons. It Mohamad Sakr Al-Asam 3 Director, Water and Soil Department is massive because of its high C03 content, poor in clay and in humus. The water Ministry of Agriculture and Fisheries, The United Arab Emirates holding capacity varies between 10-25% (FC) and 4-12%( PWP). TPS, SAR, ESP and CaS04 values in the irrigated land is more than double those of the virgin soils. INTRODUCTION IRRlGATION METHODS Groundwater is the main water of irrigation water in the UAB. The increase in land cropped with vegetables, forage, palm and fruit trees caused an almost The irrigation methods are numerous and vary from traditional to the most unrecoverable depletion in groundwater, especially with mean precipitation of only 113 modem techniques. In recent years, the irrigated area has increased from 32,000 ha in mm/year. Water qUality has also regressed, and in many places its use may cause soil 1983 to 67,000 ha in 1994 and the area irrigated by modem techniques has increased salinity and degradation. In the absence of alternative water sources, proper from 13.6% to 65%. Different water qualities have been used giving acceptable management of water is an absolute necessity. It is worth noting that the soil of the economical revenue. The water content of Ca++, Mg ++, CaC03 and MgC03 in addition UAB can be'easily reclaimed and cropped provided proper measures are taken along to the physical properties of soil, such as good drainage, the absence of impermeable with the application of modem irrigation technology. layers close to the root zone and the ease of tillage have greatly helped to alleviate the effects of salinity. WATER QUALITY IN UAB The irrigation methods can affect salt accumulation in the following manners: • The irrigation methods which distribute water on all irrigated area (flooding and Water quality varies in the UAB, as it is influenced by the type of soil strata sprinkling) cause homogeneous distribution of salts and are the ideal ways to move through which water flows from the mountainous regions to the plains and by the salts down below the root zone provided that the irrigation interval is short. intrusion of saline water in the aquifers of the coastal area. • The line source irrigation(furrow system, multi-emitters, porous pipes) cause Below are some main characteristics regarding the groundwater: vertical and horizontal salt distribution. The accumulation of salts usually occurs: a) • Water extracted from serpentine reservoirs below gravel layers contain high on the surface between the irrigated patches, b) down in the soil below the soil concentrations of Na+ and cr. profile depending on the leaching efficiency and c) below the water source depending on the length of the irrigation interval and the type of crop. • In rocky valleys, Mg++, HC03',Na+ and cr concentration increase in water that has flowed through serpentine gravel in the direction of the coastal aquifers. • 3-Point source irrigation systems (drip, micro basins, subsurface with widely spaced • Ca++ concentration increases when water flows in calcareous rocks. emitters) cause radial salt distribution under the soil surface. This accumulation could be elliptical or spherical depending on soil type and stratification. • S0 4- concentration increases when water passes through Quaternary gravel. Comparison in general is difficult because salt accumulation is also influenced • The water quality containing Mg and HC03 changes to that containing Na and CI by water application efficiency and frequency. on its way to the coast. • The water quality on the western coast is low due to high salt content. THE INFLUENCE OF IRRlGATION SYSTEMS ON SALT ACCUMULATION IN o The best water qUality is found in the rocky plains al!d the eastern-coastal plains. This water quality has degraded in the recent years due to the drop in the water THE UAB: CASE STUDY table. This study was carried out in Himraniyeh agriculture station in Ras el Khaimeh • The total dissolved salts (TDS) is between 500 and 6000 ppm. between 1983 and 1988 following another study carried out between 1976 and 1978. e NaCl is about 50 to 70% of the total salt, CaS04 and MgS04 is 15 to 20%. It was aimed at applying drip and sprinkler irrigation and improved traditional methods • pH is 7.5 to 8.5 except for some places where it could be higher. to vegetable crops. • The abundance of CaS04 and MgS04 in irrigll>tion water helps in decreasing soil Another objective was applying sprinkler irrigation and comparing it with th6 salinity effects. basin system for trees. The variables were: * crops * seasons * designs * irrigation systems

88 89 * irrigation intervals • ?rip irrigation system: Salt accumulation was lower under the water source and * soil moisture tensions lllcreased to 15 dS/m at the mid-distance between two drippers. The highest rate was at the surface. The following data was obtained: • Sprinkler system: gave a homogeneous salt distribution in the soil profile. Salinity * crop production was 4 dS/m down to a depth of 120 cm. * quantity of water added * salt distribution and accumulation in the soil The results could be summarised as follows: • The bubbler system gave the least salt accumulation and the best homogeneous The soil where these tests were carried out had the following properties: deep, distribution in the root zone. poorly developed profile, sandy loam to loamy sand, calcareous, poor in organic • The drip irrigation system gave the highest accumulation rates accompanied by matter. Its structure is conglomerates on the surface with a layer of gravel (30-50 cm acute lllJUry symptoms and caused also leaf drop. thick) at a depth of 90 to 100 cm which gives it a high drainage capacity and • The sprinkler system ~ave a steady low concentration to a depth of 120 cm, but infiltration. Water holding capacity was low: FC = 10-20% and PWP: 5-8%. The EC cause? NaCI absorptlOn by leaves which caused injury in the first year of of the water applied was 2.3 dS/m. The initial soil ECe was 2.4 dS/m. expenmentatlOn. In the first experiment, drip and furrow irrigation was used to irrigate • Ba~in system: salt accum?lation was low in the soil profile but was high on basins' vegetables: two seasons of squash followed by two seasons of cabbage. Water was penphenes and on the SOli surface between basins. added when the soil water potential reached -15 bars. Salt accumulation was higher in the dry seasons than in other seasons indicating that rainfall had helped in soil leaching. The experimental blocks were distributed over four other seasons to measure the accumulation rate over a longer period of time.

• First season: An important decline in soil salinity took place in the upper layer (0- 30 cm) and in the next layer (30-60 cm). This is attributed to salt redistribution due to both irrigation and rainfall (83 mm). • Second season: An increase in salinity was observed at depths of 15-60 cm. However it was not a major increase due to the high rainfall in that season (200 mm). • Third and Fourth season: An increase in salt accumulation in the upper layer occurred (0-30 cm) • Fifth season: Salt accumulation increased in the furrows to reach a range of 6-16 dS/m. Soil EC was similar to that of the irrigation water till 120 cm depth. With drip irrigation, soil EC, was 3-8 dS/m on the surface and close to water salinity below surface till a depth of 120 cm. e Sixth season: A decrease in salt accumulation was observed due to the good leaching by rainfP,ll.

One can conclude from this study that salt accumulation is higher in the furrow system than that in the drip irrigation. However, it was the same where salt distribution along crop lines is concerned. In the experiment with basin, bubbler and sprinkler systems on orange trees, the trees were p!anted on 18/2177 and the study continued till 2/6/80 and was repeated from 1980 to 1983. It gave the following results: • Basin system: the EC, of the root zone down to 120 cm was 2-3.5 dS/m. It was much higher on the basins' edges. • Bubbler system: Soil EC, was steady up to a depth of 120 cm and was 2-3 dS/m. High accumulation occurred on the peripheries.

90 91 IV. Crop Response to Salinity

92 Use of Saline and Brackish Waters and The Relationship With Soil Management

Gilani Abdelgawad - The Arab Center for the Studies of Arid Zones and Dry Lands (ACSAD) Damascus-Syria Abdel Nabi Fardous - National Center for Agricultural Research and Technologies (NCARTT)- Jordan Z. Al-Shabouni - Rural and Agricultural Engineering Research Center-Tunisia

INTRODUCTION

Irrigated agriculture depends on adequate water supplies of usable quality. The question of water quality has often been neglected because good quality water supplies have been plentiful and readily available. This situation is now changing in many areas of the world. The intensive use of nearly all good quality water supplies means that new irrigation projects as well as those seeking new or supplemental supplies must rely on lower quality and less desirable sources. Sound planning is necessary to avoid problems in using these poorer quality supplies and to ensure that the water available is put to the best use. During agricultural expansion, planners tend to use good quality water for irrigation in development projects while neglecting or ignoring the potential of lower quality water. In order to maximize the use of good quality water without exposing it to deterioration, it is important to mix its use with saline water. Intensive use of good quality water leads to falling water levels and a deterioration in quality. Information on using water of high salinity has been gained from experience and detailed study of the problems that may arise (Abdelgawad et at, 1981). Saline water is currently used for irrigation in several areas of the world, but careful management is necessary to cope with the potential problems. In some areas, this water is the only supply available and while crop yields may not be at the maximum, they provide an economic return. The use of saline and highly saline water in irrigation is discussed in various research papers, (Hoffinan et at. 1983a, Mass and Hoffinan 1983, ACSAD 1986-1987, Rhoades 1984-1986-1990. Abdelgawad, 1993). There is a growing demand for fresh water for domestic, agricultural and industrial purposes. In the Arab world, this situation increases the need to use saline water for agriculture, bearing in mind that only 43 million hectares, or 32.6 per cent, of the 132 million hectares of available agricultural land are being cultivated (Juma 1991 ). This low percentage results mainly from a shortage of water and a decline in water quality. Eight years ago, ACSAD initiated a programme for using saline water and salt-affected soils for agriculture. The studies were carried out in both Qatar and Tunisia. The potential use of saline water and salt-affected soils has been discussed in several ACSAD papers (1986,1987 ). These studies focused on the use of water with salinity levels up to 2,000 mg/l or electrical conductivity (EC) values of 3 .13 dS/m. The present paper will discuss : • The use for irrigation of highly saline water obtained from agricultural drainage water and from mixing different ratios of agriculture drainage water and good quality water. • The yields of alfalfa, barley, cotton, onion and sugar beet irrigated with these water mixtures, using different leaching fractions. • The validity of computer predictions of increases in soil salinity when water of different salt levels is used for irrigation.

93 The total amount of water used in the 30% LF was large and resulted in the salinity of soil MATERIALS AND l'vIETHODS water and in a decrease in yield. The yield for the 0, 15 and 30% leaching fractions were 21.38, 22.43 and 19.35t/ha respectively. This research was carried out in the ACSAD experimental station at Der EI Zoor, Syria The alfalfa grown using a mixed water ratio (E:D) of 50:50 and 15 % leaching fraction between 1991 and 1994 for alfalfa, between 1991 and 1995 for barley and between 1991 and 1994 yielded 25.20 t/ha-more than for the same mixed water ratio of (E:D) 50:50 and the zero and 30 for cotton. Barley was evaluated in Tunisia in 1993-1994 and 1994-1995. !n Jordan, barley percent leaching fractions (22.35 and 23.46 tons/ha, respectively). It is 83 percent of the yield from experiments were conducted between 1992 and 1995, and for sugar beet and omon between 1993 100 percent fresh river water treatments with a zero percent leaching fraction ( 30.48 t/ha). This yield is 81 percent of the yield from alfalfa grown using a mixed water ratio (E:D) of 100.0 with a and 1995. . . t (D) 'th In Syria the water used for irrigation was drawn from agricultural dram~ge wa er WI 15 percent leaching fraction (31.23 t/ha). The amount of fresh water used is 18,645 m3/ha 3 an avera"e electrical conductivity (ECdw) of 13.57 dS/m mixed with Euphrates nver water C:E) from compared with 37,290 m /ha, ie, it is only 57.50 percent of the total fresh water requirement for the irrigatio: canals with average EC values of 1.55 dS/m. The ratios of mixing used for this s~udy alfalfa grown with a 15% leaching fraction. were, E:D, 100:0, 70:30,50:50, 30:70, 20:80, 0:100. The waters from both sources were Illixed For the ratio of mixed water (E:D) of 50:50 with a 15 percent leaching fraction, the amount 3 in water tanks and then used to irrigate alfalfa, barley and cotton. . of agricultural drainage water used is 2,070 m /ha or 57.50 percent of the fresh water requirement The amounts of water used in irrigation were based on previous ACSAD studIes of crop of the barley crops as grown by farmers irrigating just with fresh river water and zero percent water requirements for these crops. A leaching r:acti~n of.O%, 15% and 30% was ad~ed. The leaching fraction (3600 m3/ha). design of the experiments was randomized block With SIX replic~tes and a plot. SIZe ~f 55. m. . The yield of barley grain was highest with the 15 percent leaching fraction for all water In Tunisia the design of the experiments was by randolllised bl~ck deSIgn With SIX replIcates mixtures. Even using 70 percent agricultural drainage water, with zero or 15 or 30 percent leaching and a plot size of 1000 m2 The water salinity ~reatments wa~ MaJarda nver water (2.7) dS/m, fraction the yield was more than the average of 2.50 tons/ha produced by state farms using 100 (50:50) Majarda river water and agricultural dramage water With EC 4.51 dS/m and .agncultu:al percent Euphrates river water. drainage water with EC 6.31 dS/m. The amount of irrigation v.:ater was based. on preVIOUS studIes The data on barley straw shows no significant difference in the yields for the 0 and 15 on crop water requirement. In Jordan, the design of the expenments was s~lit plot ~~ the fresh leaching fractions, but a yield reduction for the 30 percent leaching fraction. Since straw has great water with EC 0.78dS/m was mixed with saline ground water resource to Yield a salinity level of value for animal nutrition in the area, experiments are underway on alternative barley species for 456 dS/m and 6.56 and 7.2 dS/m. . . hay production. . The experimental areas were irrigated using the flood irrigation system. The soIl~ In the The amounts of water used for the irrigation of cotton using 0, 15 and 30 percent leaching experimental area in Syria were torrifluvents, loamy in texture, with soil pH of ?5 soil water fractions are 9,455, 10,872 and 12,291 m3/ha, with ECiw values for water mixtures ranging from 1.6 saturation extract salinity (ECe) of 2 dS/Ill, and containing 15-25 percent calCIUm carbonate to 14.0 dS/m. . d . 'fl ·th H f7 8 and 35 % The mean cotton yield was 2,023; 2,203 and 1,542 kg/ha for the 0, 15 and 30 percent (CaC03). The soil in Sheriffs area were clayey ffilXe xenc tom uvent WI a po. CaC0 . In Jordan, the soil of AIKhaldialI station was clay loam, had a pH of7.7, 36.5 CaC03, EC leaching fractions, respectively. There was a drastic decrease in yield for the 30 percent leaching 3 5.4 dS/m and with CEC of28 meq/l00 gram. . fraction. This is possibly due to the leaching of nutrients, especially nitrogen from root zones. The Piezometers were placed in each experimental area to morutor wat~r .tabl.e dept~ and the soil analyses during the growing seasons confirmed this assumption. electrical conductivity of soil water (EC",) every 48 hours and we~kly, after ImgatIOn. SOlI samples were collected periodically and the following analyses were carned out: EC, pH, soluble catIOns Salinity Monitoring at the Experimental Plots and anions, CaC03 and gypsum (CaS04) content, an~ available nitrogen (N), phosphorus (P) and potassium (K). The analyses were c~ed out accordmg to .Pa~e (1982) and ACSAD (1987). The Salinity monitoring was carried out in two ways: Watsuit model was used for the predICtIOn of salt accumulatIon m SOIL • by placing 48 piezometers on the experimental plots, and measuring water table depth and the salinity of drainage water (ECdw) which is equal to the salinity of soil water (EG.w). RESULTS AND DISCUSSION • by collecting soil samples at various soil depths during the growing seasons of the tested crops.

In the piezometer study, water table depth and the salinity of soil water (EC,w) was Syria 0 I hin fr ( d . The alfalfa grown using a mixed water ratio (E:D) of50:50 and a 15Yo eac g ac IOn ~se measured every 48 hours and weekly; after irrigation. There was little increase in the salinity of the 5747 o/c of the fresh water used to irrigate the crop grown using 100 per cent EUPFates nver soil water saturation extract (ECe) on the experimental plots irrigated with saline water compared • 0 .' ( 430 3/h) Thi' ving of 13 785 m /ha offresh water and a zero percent leaching fractIOn 32, m a.. s IS a sa '0 with the ECe of the plots before irrigation. water or 42.5 percent. With a mixing ratio of30:70 the savmgs of fresh water was 80.5 Yo. . The salinity of soil water (EC,w) measurements were found to be below the assumed values The alfalfa crown using a mixed water ratIO (E:D) of 30:70 and a 15 percent leaching of EC,w = 3 ECiw. For example, the salinity (ECiw) of the mixed water ratio (E:D) of 50:50 is 7.50 fraction used 26 103 m3/h~ of agricultural drainage water. This is 80.5 % of the total amount. of dS/m. Consequently, it was assumed that the salinity of soil water (EC,w) would be 3 x 7.50 dS/m water used to ~row alfalfa using 100 percent Euphrates river water and a 0 percent leaching or 22.50 dS/m whereas the average reading were 4.01, 5.86 and 4.83 dS/m for the 0, 15 and 30 3 fraction (32,430 m /ha). percent leaching fractions, respectively. These surprising results can only be explained by the dilution of ECsw from surrounding fields, winter rainfall (about 150 mm ) and the precipitation of gypsum and lime which lower soil water salinity. The leaching fraction had a moderate effect on the

95 94 leaching of salts, especially for the mixed water. This is due to the large amounts ofdraina~e wa~er used, and gypsum and lime precipitation, as will be shown by the results of the detaIled soli studIes Non saline aIld saline water with three salinity levels (0.78, 4.0, 6.36 dS/m) was used for and the prediction of salt precipitation by computer model. . irrigating sugar beet crops for the 1993/1994-199411995 growing seasons. Leaching fractions of 15 The data from the barley and cotton plots followed a pattern similar to that of alfalfa In the and 30 % caused a yield increase especially in the non saline water treatment. The saline water (EC relationship between EC;w and EC,w for the mixed water ratios (E:D) of 50:50. and 20:80. The 6.56 dS/m) caused all increase in sugar beet roots growth. Generally, sugar % increased with all leaching fraction had a clear effect on the leaching of salts. The water table depth IS shallower than increase in the salinity of irrigation water. This is due to osmotic adjustment. The average root yield that of the alfalfa experimental plots. The salinity of soil water (EC,w) values for the cotton fields at O.78dS/m, 4 dS/m aIld 6.56 dS/m was 71.5 tlha, 50.4 t/ha artd 57 t /ha respectively (LSD=7.34), were generally lcrwer than those for barley and alfalfa. The Watsuit model was used to predIct the while the sugar content was 16.8%, 19.2% and 19.0%. (LSD=1.07). There was no significaIlt chemistry of soil water from that of irrigation water. ..' . differences in sugar %, vegetative growth aIld weight of roots between leaching treatments and According to the model, the predicted mean salinity of SOli water (E.C,:,,) for a :ruxed water amount of water applied. ratio (E:D) of 20:80 and a 0.05 percent leaching fraction is 31.59 dS/m. This IS very hi~h for ?lant The experiments of the 1994-195 season confirmed the response to leaching fraction and growth and, if correct, then no yield can be expected. However, the actual alfalfa YIeld. uSing a salinity, however, yields were lower nearly by 50%. The use of saline aIld non saline water mixed water ratio (E:D) of 20:80 and a zero percent leaching fraction was 11.00 tlha. This means (6.56dS/m and O.78dS/m) caused a significaIlt difference in yield in both 199311994 aIld 1994/1995 that the model predicted the worst condition of salinity accumu!ation (Rhoades 1990) . . seasons. The average sodium adsorption ratio (SAR) for the ffi1Xed water ratIO soil crust. The model predicted the precipitation of gypsum and lime. The rate of preCIpItatiOn. of amount of water added for both non saline aIld saline water aIld with an average 73.5% and 46 % these substances is a function of the percentage of drainage water used(+) and the leaching respectively. fraction(-). . . d' all The same experiments were repeated in the growing season 94/95. Yield was 13.1 tlha aIld Soil salinity was monitored by collecting soil samples and an~yslng them peno IC y. 9.0 t/ha for non saline and saline water treatment respectively aIld without significaIlt treatment Generally there was a little increase in the salinity of soil water saturatIOn extract (ECe) on the between 75 and 100 % water treatments ( 2458 and 3111 m3/ha) respectively. The yield of onion experimental plots irrigation with saline water compared with the ECe of the plots before such increased with the amount of water applied whether the applied water was saline or non saline. The data confirms the results of 93/94 growing season aIld the superiority of the 75 % evaporation paIl ~~ . The model predicted higher EC.w than the actual ~easurements. .The measured ratios of water treatment. calcium to magnesium were always greater than one, unlike those predIcted by the model and, In Tunisia, the experiments reported here were conducted during the 199411995 season at generally, in both cases there was an increase in gypsum content. .The measured SAR decreased the Shershif agricultural stations. The Majarda river water (EC=3.7 dS/m) was mixed with of with the increase in leaching fraction and increased with the mcrease In ~he percentage r agricultural drainage water (EC=9.25 dS/m) to give mixed water (EC=7.2 dS/m).These constituted agricultural drainage water. The sodium absorption rate at ~he soil surface was higher ~an at lower the three water quality treatments aIld were used to irrigate barley with two leaching fractions: 0 surfaces. This explains the fonnation of soil surface crusts m the lower Euphrates agncultural area aIld 15%. The plots also received 221.3 mm of rainfall which contributed to the dilution of the salts. of Syria. Generally the yield was 4.6, 4.3, 4.5 tlha for Majarda river water, mixed aIld agricultural drainage water respectively, without significaIlt differences between them. The EC of the irrigation water Jordan was adjusted to account for the precipitation. The grain yield of barley "ACSAD variety 176" for the growing seasons 92!fJ3.-93/94- The adjusted EC value was below the EC that can affect the growth of barley. The EC of 94/95 irricrated with non saline (0.78 dS/m) and saline water (7.2 dS/m) was not slgmficantly the soil extract was also below the EC of the soil that can cause a reduction in the yield of barley differ~nt. The water applied was 0, 500, 1000, 1500, 2000 m3/ha. Rainfall in 199211993 was. 68 aIld it was found to be very close to the Ee of irrigated water due to the precipitation of gypsum. mm. The average yield for the non saline water and saline treatme~ts for the 1992-1~93 growmg season was 2.76 and 2.79 tlha, aIld increased to 4.23 aIld 4.74 tlha In 19931199~. GraIll aIld .straw yields increased with the qUaIltity of water added, aIld th~ highest yield was obtaIlled by additIOn of 2000 m31 ha whether for non saline or saline. The straw Yield was 19.39 t/ha aIld 19.35 tlha for non saline aIld saline water, respectively.

97 96 CONCLUSION Availability of Nutrients, Fertilizer Management and This paper has considered the use of saline water f~~ irrigati~g alfalfa, barley, cotton, Crop Tolerance under Saline Conditions suaarbeet and onion in three countries: Syria, Jordan and TurnSla. The yIeld performance of these Amin Mashali was discussed with regard to levels of salinity and leaching fractions. In Syria for example 83 cr~ps Technical Officer, AGL percent yield of alfalfa (100 percent is the yield using 100 percent Euphrates nver water and no FAOlRome. leaching fraction) was obtained using a lnixture of 43 percent ~uphrates nver water ~d 57 percent INTRODUCTION agricultural drail1age water. If the same yield is compared WIth the crop gr~wn usmg only fresh river water and a 15% leaching fraction (30.48 tlha) this represents a savmg of 57 percent of Plants growing in the presence of excessive concentrations' of salts suffer nutritional Euphrates river water. . . . . imbalances even though the concentrations of the nutrient elements in the soil may seem to be ater The yield of barley grown in the AI-Khalidia area in Jordan Imgated W1~ s~llle v: . for adequate from a standard chelnical analysis. In saline soils fertility is generally poor, deficiency three years averaged yield of 5.35 tlha without a harmful effect of salt a.c~umulatlOn III the lffigated symptoms of most plant nutrients, particularly, nitrogen, phosphorus and in many cases plots. This was due to the addition of leaching fraction, r~all and. precl~ltat1On of gypsum .. lnicronutrients, are expected. In sodic soils, major effects on plants occur through the deVelopment In Tunisia barley grew in the Sherifs area irrigated Wlth MaJarda ~1Ver wa.ter and agncultural of adverse physical properties in the soil. The high soil pH results in the formation of relatively drainage water gave an average yield of 4.45 and 4.25 t/~a, resp:ctIvely WIthout ~armful. salt insoluble carbonates ofCa and Mg from the more soluble Na carbonates causing plant deficiency of accumulation in soils irrigated with these waters, due to leaching fractIons practIces, wIllter rainfall Ca or Mg. Solubility and therefore availability ofP, Fe, Mn and Zn also decrease while Na, Mo and and precipitation"of gypsum. ..' . B may become increasingly available and toxic to plants. As a general rule, the gypsum content in the soil pr~files Illcre~sed, p.~lcu~arly ~ear the SOli It is therefore important to conduct systematic soil testing which leads to identifYing the surface as the percentage of agricultural drainage water Illcreased III the Imgat.lOn lllxture .. The deficiency of nutrients. When the level of available nutrient elements in the soil is too low to satisfY calcium to magnesium ratio decreased with an in:rease in the percentage of agncultural dramage plant needs, plant growth is impaired. Consequently, crop yield and its quality will suffer. water. This could have a harmful effect on the nutnent status and uptake by crops. . Fertilization under these conditions prevents nutrient deficiencies. However, to develop specific The SAR of the surface soil increased with the percentage of agricultural dramage w~ter, fertilizer reco=endations for any soil-crop system, soil-water-nutrient interaction should be the precipitation of calcium as calcium carbonate and gypsum, and the leaching o~ excess calclUm studied. and magnesium from the surface to subsurface soils. This is thought to explam surface crust formation in the soils of the Euphrates area. SOIL-WATER-NUTRIENT INTERACTION

REFERENCES: Some understanding of the physical and chelnical properties of the soils is essential before mineral fertilization is undertaken. Soil texture, colloidal composition, pH and exchangeable ions ACSAD. 1986. Use of saline water for irrigation offorage crops in Qatar, No.3. Division of Soil 198511987, pp 1- should be detennined in order to assess the best fertilizer management prograrrnne. Soil physical and chelnical properties have an effect on retaining nutrients within the area of maximum uptake. ACS~\ 987. Use of slightly saline water for irrigation of olive trees in Tunisia. ACSAD Publications No. 78, Availability of nutrients vary according to soil texture and infiltration rate which control the Division of Soils, pp. 1-34. ACSAD. 1987. Methods of soil water and plant analyses. ACSAD, pp 1- 98. .., . . movement and leaching of nutrients. Application of fertilizer in heavy clay soils must be done in a Abdelgawad, G. 1993. Rationalization of the use of water of

98 99 concentrations are inter-related since uptake rate by plants is the integral of the flux multiplied by Salinity affected fertilizer behaviour in experiments reported by Balba (1980) who found the root surface area or root length, in a given soil sub-volume, over the total number of sub- that increasing NaCI and CaCh concentrations enhanced the immobilization ofP (superphosphate) volumes in the soil profile. applied to Egyptian soils due to increased solubility of soil CaC03 in the presence of the cr, If the estimated uptake and Q(t) do not match, a correction measure (e.g. enhanced or providing more Ca++ ions and thus precipitating more fertilizer P as calcium phosphate. reduced fertilizer rate from concerned nutrient) must be imposed, subject to an econOffilC optimization procedure. . . . Effects on Nutrient Losses Expanded soil root volumes have a high buffer capaCIty for water an~ nutne~ts, thus Evidence that salinity or alkalinity can increase nutrient losses from the soil-plant system is avoiding possible stresses in case of disrupted .supply, but. they cannot be rapIdly en.r:rched or available from several sources. The N balance for cotton on five different soils showed that N was depleted of nutrients and thus accommodate rapId changes In uptake accor~Ing to s?ecific pl~t lost in every case (EI-Shakweer and Ghaffar 1972). The deficit ranged from 8 to 297 kg/ha N (10 needs. Optimal nutrient additions as fertilizer must be established from empmcal fu~ctIons .relatIng to 31 % of soil plus applied N) and was greatest from the sodic and least from the saline soils. nutrient addition to uptake rates by whole plants. These functions are specific to a given SOli group Leaching of a sodic soil in laboratory columns caused substantial P losses and up to 60 ppm and crop. in the leachate (Chhabra et al. 1980). The loss was reduced by mixing adequate amount of gypsum with the soil. The magnitude of the loss was attributed to the reaction ofNazC03, the dominant salt FACTORS AFFECTING NUTRIENT A V AlLABILITY in the soil, with soil CaP04 and the formation of highly soluble phosphate which is readily leached during the reclamation process. Salt accumulation, alkalinity and sodicity within the root zone of salt affected soils m:ect Leaching ofK may increase with the salinity of irrigation water. Irrigation with sodic water plant nutrient content and availability for plants in o~e or more o~ the follOWIng .ways: by changu:g results in displacement ofK+ from the soil colloids by Na+ and decreases plant uptake ofK the form in which the nutrients are present in the SOli; by enhancIng loss of nutnents from the soil, through cation and anion interaction effects, through the effects of non nutnent (c?~plementary) Ion competition ions on nutrient uptake and by adverse interaction between the salt present and fertIlIzers, thereby It is well established that the uptake of a cation species is influenced by the concentration of decreasing fertilizer use efficiency. other cations in the soil solution. Fink (1977) found that wheat plants grown on slightly to moderately saline soils in southern Italy suffered from nutritional stress, while those growing on Effects on Soil Nutrient Forms . soils high in Na and Mg contained a harmful excess ofNa, but not ofMg and became deficient in Salinity, alkalinity and sodicity have a complex ~ffect .on the availability ofpl~t nutnents. For Ca and K with increasing salt content of the soil. example, incubating a soil for 15 days after moistemng With 2 mell Na2C03 solutIOn re~uced the The relative effects ofNaCI, NaZS04, CaCh and MgCh on K, Ca and Mg contents of the availability and thus the extractable contents ofP, Ca, Fe, Mn and Zn (Table 1); all o~,:,hich can be whole broad bean plants Vicia jaba (L) reported by Balba and El- Etriby (1980) is shown in Table explained by the effect of Na2C03 on changing the form of the nutnent due to r~sIng sorI pH. 2. For K, the depressing effect ofNaCl on uptake was almost double that ofMgCh Irrio-ation with Na2C03 solution resulted in reducing the uptake of Fe and Mn by maIze plants and The relationship between Na, K and Zn uptake by maize was studied by Shukla and Muhi in dOecreasing the proportion of these nutrients translocated to the shoot. (1980) who found that increasing the concentration of each of them in the growth medium depressed uptake of the other two. They attributed the adverse effect ofNa on plant growth to its TABLE I: Effect of incubation with Na2CO, on Soil P, Ca, Fe, Mn andZn antagonistic relationship with Ca, K and Zn within the plant, as well as to the effects of increased

Incubated with: 2meq/l salinity and sodicity in the soil. Fraction or extract Water Nutrient Na2CO, solution 2.4 TABLE 2 Relative effects of NaC!, Na2S0" CaCh and MgCh on K, Ca and Mg &, uptake and concentration in bean Na2CO, 12.4 P(ppm) plants (Vieia jab a, L.) Water soluble 1.32 0.42 K Ca Mg Ca(meq/l) 12.1 Exchangeable 17.4 Sal! type Concentration Uptake Concentration Uptake Concentration Uptake NaCI' 1 1 1 1 1 1 6.7 NaEDTA 11.0 Na2S0, 0.97 0.87 1.15 1.05 0.61 0.84 Fe(ppm) 5.2 NR,OAc 10.0 CaCh 0.26 0.60 0.61 0.84 MgCb 0.15 0.52 1.26 1.23 14.0 Easily reducible 20.0 , Effect ofNaCI relative to non-saline control taken as unity Mn(ppm) 1.0 NR,OAc ,. 1.5 Source: Balba and EI-Etriby (1980) 0.5 0.38 Zn(ppm) NR,OAc Source: AdaptedJrom El Khatib(1977) Anion competition is an important factor in some circumstances. Chloride retarded P uptake Paliwal and Maliwal (1971) found that soil organic matter cont~nt an~ availa~il.ity ofP are and sulphate inhibited uptake and accumulation ofP by barley and sunflower (Zhukovskaya 1973). decreased by increasing soil or water salinity beyond 6 dS/m and by IncreaSIng SOdiCIty to mo:e Excess cr in the growth media restricted N03- uptake leading to N deficiency. than an ESP of 32. At EC values of 13 dS/m or an ESP of 50, available P increased and more so In soils in which N a+ was the dominant cation than where Ca++ was dominant.

101 100 Many forms of N have been used for the fertilization of salt affected soils such as urea, Complementary Ion Effects .... calcium nitrate, sodium nitrate, anhydrous an1ll1onia and an1ll1onium nitrate. Calcium nitrate is more It has been recognized for many years that absorptlOn of amons and catlO?S by plants IS a suitable than sodium nitrate in salt affected soils because its Ca++ content strengthens competition linked process. Many investigations on excised roots and intact plants have proVIded data on the with N a+ present in these soils. With an1ll1onia nitrate fertilizer, the main factor is that of anion effect of cation on uptake of anions and vice-versa and have shown that the effect of greater uptake competition, i. e. with cr under saline conditions. of anion might be to retard or enhance uptake of another of the opposite charge. Phosphorus NUTRIENT DEFICIENCY AND FERTILIZER RECOMMENDATIONS Adequate application of P fertilizers is needed in alkaline conditions because at high pH, P tends to be immobilized. However, excess levels of P can have an unfavourable interaction with Nutrient status in the soils affects fertilizer recommendation for different ~oil types. ~d salinity, especially in sodic conditions. When P fertilizer is broadcast on the soil surface, it will not conditions. Therefore it is always recommended that relevant alterations in ordmary fertilizer normally move more than 2 to 5 cm into the soil. Most of the P remains on the surface and is not manao-ement be made only if supported by valid specific information. accessible to plant roots. There is greater movement in coarse textured than in fine textured soils. '" Phosphorus fertilizer includes two main groups: those containing water insoluble phosphate Nitrogen . . . d . al" . f and those containing phosphate in water soluble form. The former is not recommended for saline In salt affected areas, available N supplies tend to be liIDlted by rest?cte mmer IzatlOn 0 conditions and, more particularly for sodic soils, since dissolution of its P is very slow at pH higher oro-anic N and by the loss of mineral N by leaching. Frankenberger and Bmgham (1982) showed than 7.0. The water soluble group (single and triple superphosphate, an1ll1onium phosphate) are th:t the activity of 1'2 soil enzymes was affected, but that of dehydrogenase was most affected .. T~e more effective but are generally used less efficiently in saline conditions than in normal conditions inhibitino- effect of salt was in the following order: NaCl > CaCh > Na2S04. The range of sal1ll1ty because: tested w~s 3-22 dS/m with maximum reduction of enzyme activity above ~O dS/m. .. • The presence of Ca++, which may exist in the soil solution leads to precipitation as calcium Leaching is a common practice in reclamation of salt affected soils. Frequent lea.ching will phosphate. involve losses of available N through nitrate movement below the crop root zone. N IS leached • Uptake of H2 P04- ions is inhibited by the presence of high concentrations of other anions, more rapidly from the surface than K and both more than P. Therefore lesser amounts of more mainly cr. frequent applications ofN may promote greater uptake an~ decr~se N leaching los.ses. ._ .d Organic matter content is low m salt affected so~s, ~artl~ularly under and and s~IDl.an Potassium d· tions and in most sandy soils. N fertilizer applicatIOn IS therefore generally J~stified Many salt affected soils are well supplied with K, but when the K status is low, competition ;~~ularl~ in sandy soil with low fertility status, but its efficiency is often low because of dIfferent with high levels of exchangeable Na or Na+ in soil solution may call for increased K fertilizer use. K pathways ofN losses. ... . application resulted in a lower increase in soil salinity in relation to N fertilizers but higher in Waterlogged soils and impermeable conditions ar~ affecte~ by derutnficatlOn losses ofN. comparison with phosphorus fertilizer as it introduces neither changes in pH (as in NE4+ -containing Under such conditions "anaerobic" microbial process turnlllg N03 to NzO or ~2 ~as takes pla~e, fertilizers) nor production of insoluble substances in the soil. particularly in the presence of ample available organic carbon. Available data llldlcate very high The main K fertilizers are KCI and K2 S04. Fink (1977) suggested that potassium sulphate level ofN losses through denitrification, with an average of25%. . . is more suitable for saline conditions because it avoids the increase in soil cr content implicit in the Volatilization of NH3 from the soil can be very significant. Re~ent data llldlcate that losses use of KCI. Potassium nitrate may be preferable to both KCl or K2S04 since it avoids the from urea may be better related to soil texture and CEC than t? SOli pH (Mat~ns and Bre~er application of any unwanted anions being a source ofK and N. 1989). However, as pH rises the potential loss increases exponentially due to the mcreasmg partIal pressure of volatile NH3 gas equilibrium with NE4+. Losses due to this mechamsm are often a Calcium and Magnesium problem in flooded rice where floodwater pH increases dunng daylIght hours due to algeal and Magnesium is rarely limiting in salt affected land but Ca is usually used in the form of cyanobacter photosynthesis...... gypsum as a soil improver. However, saline soils' are usually rich in calcium, magnesium and ,,= + and NO - may be inhibited by competltlOn WIth other catIOns and amons, sulphur, and application of these nutrients is seldom necessary although Ca and S are applied U p tak e 0 f iU.L4 3 . fi ili h respectively. Therefore, there may be a small advantage from using ~oruum_ .ert zer suc as incidentally in fertilizers such as calcium nitrate and superphosphate. The level of Ca in the soil ammonium nitrate or phosphate which do not contain complementary S04 or Cl IOns that tend to solution should be at least 2 mel! (Ayers and Westcot 1985). As Ca deficiency is associated with accentuate the anion competition problem. sodicity conditions and influenced by plant water status, the addition of Ca directly to soil solution or through foliar application or as amendment in irrigation management may be useful to prevent Another important soil process affected by sali~ty i~ biological N fixat~o? The. reason f?r damage to crops (Feigin 1985). the effect of salinity is either osmotic or that high salts Impair the metabolIc act!V1ty taking place m nodule cortical cells. . .. A· f Micronutrients Salinity and sodicity generally reduce the efficiency and utIlIzatIOn of N. sen~s? Crops under saline or sodic conditions tend to suffer from micronutrient deficiencies due to experiments carried out on rice and wheat on sodic soils have led to the general ~ecommendatlOn.lll immobilizaton by the high pH or to ion antagonisms, When pH is above 7.0 then Fe, Zn, and Cu India that these crops when grown on sodic soils should have 25 % extra N applIed compared WIth become less available, usually due to precipitation. Also, available Fe, Mn, and Zn are depressed in the rates recommended for sodic conditions. non-saline sodic conditions with high pH and Na2C03 accumulation. Because of the rapid

103 102 i=obilization of soluble inorganic forms of these nutrients, they are best applied in the form of .Damage often occurs at relatively low ion concentrations for sensitive crops It is usually chelates. Molybdenum deficiency is sometimes observed due to competition between molybdate fi rst eVIdenced.. by margm' alleafburn an d mtervem. . al chl oro SIS.. If the accumulation is great. enough anions and the chlorides or sulphate present under saline conditions. Boron status is generally ~~~u~ Yle~s WIll re~ult. The more tole.rant .armual crops are not sensitive at low concentration~ adequate, or often excessive. Manganese has been applied as manganese sulphate, boron as Borox h ost crops will ?e. damaged or killed if concentrations are sufficiently high. Damage results and boric acid, zinc as zinc sulphate or in chelated form, iron and copper in a chelated form. w en the potentIally.toXlc IOns are absorbed in significant amounts with the water taken up by the Micronutrients can always be combined as complex fertilizer. In India, for applications of Zn to be ~~ots. The absorbe~ IOns are transported to the leaves where they accumulate. The ions accumulate effective, they should be applied within 15 days of transplanting rice and up to 30 days for wheat A a greate:- extent ~ the. areas. where the water loss is greatest, usually the leaf tips and leaf edges without any substantial yield loss. If applied after 50 days there is a large yield loss. If a basal ccumulatlOn resultmg m toXIC concentrations takes time and visual damage is often slow to b . application is missed or if Zn deficiency symptom appears it may be corrected by 3 to 4 foliar inotIced . The degree . . . of d amage d epen ds upon.' t h e duratIOn . . of. exposure, concentrations of the toxice sprays of 0.5 % ZnS04. .on, crop SenSltIV!~, and the volume of water transpired by the crop. In a hot climate, accumulation IS more rapId than if the same crop was grown in a cooler climate. FERTILIZER MANAGEMENT PLANT PHYSIOLOGICAL CONSTRAINTS Improved fertilizer management in salt affected soils can be of significance because it ensures balanced plant nutrition which prevents deficient or excessive application of fertilizers. Effect of Osmotic Pressure Efficient fertilizer management consists of suitable chemicals, applied in appropriate levels Increasing the soil salt content raises the osmotic pressure of the soil solution and makes it of nutrients. Therefore, proper fertilization should be based on detailed information on plant and :tre dIfficult for plant roots to adsorb water. If the soil solution contains salt, more energy per unit soil properties. Standard methods used to control fertilizer management consist of plant and soil I w.ater must .be expended by the. pl~t to adsorb relatively salt-free water from a soil-water analysis and with the recent addition of appropriate computer modelling. so utlOn. As saliru.tY ll~creases, reductIOn m water available to the crop increases. Timing, frequency of nutrient application, and placement of fertilizers are important and As the SOli dnes, .the plant is also exposed to a continually changino- water availability in unless properly applied they may contribute to, or aggravate, a salinity problem if placed too close each ~ortlOn of the rootmg depth since the soil water content and soil :ater salinity are both to the germinating seedling or to the growing plant. Seedlings are sensitive to salt and require little changIng as the plant uses water between irrigations or rainfalls. fertilization. A small amount of fertilizer can be applied at or before planting and the remainder in ad The plant takes. up water from wherever it is most readily available (the least resistance to one or more applications after crop emergence but before the main growth period (Gascho and so~tlOn). Usually this IS the upper root zone, the area most frequently replenished by irrigation Mashali 1991). A fertilizer with a lower solubility can be considered. The higher the solubility of ;:d r~nfal1. !f water becomes unavailable in this upper zone, the plant must meet its water demand the fertilizer, the more danger there is of salt burn and damage to seedlings or young plants. · om mcreasmgly greater depth. When the upper rooting depth is well supplied with water salinity Additional fertilizer may be needed to compensate for leaching and other losses. Such m t h e lower root zone becomes less important. ' compensation is always needed where leaching is continuously used or under waterlogged Not all crops are equally affected at the same soil salinity. Some are more able than others to extract water from a. salty soil and are, there fiore, more toIf' erant 0 saliruty. . The increased osmotic conditions. Generally, the type of fertilizer used in salt affected soils should preferably be acid, p~essure tends to re~tnct water uptake, but in addition, when plants take up the constituent ions of particularly in sodic soils. It may also be necessary to take account of the complementary ion t e sall~e soIl solutIOn they may accumulate toxic amounts of a particular ion, or through an ion present in the fertilizer. a~ta:orusm may not take up enough of an essential nutrient. Plants can raise the osmotic pressure When reco=ending mineral fertilizer, the crop should be considered and even crop o t elr cell sa? and m these circumstances decreased water uptake and transpiration is not due varieties must be taken into account, i.e. fertilizer management should be adjusted to specific crop SImply to the higher osmotIc pressure of the soil solution. situations. Environmental conditions, especially humidity, temperature and evapotranspiration The effects on plant growth of the increased osmotic pressure of cell sap can be attributed potential should also be considered. However, crop response to fertilizer in salt affected lands is to: complex since it is influenced by many soil, crop and environmental factors, particularly by nutrient • the extra energy expended by the plant on increasing and maintaining the higher osmotic status of the soil before fertilizer application. Certain nutrients are also provided by irrigation water pressure of the cell sap; or by addition through manures or other agrochemicals. • the inability of some organelles such as plastids and mitochondria to adapt to the osmotic pressure; CROP SALT TOLERANCE • the possibility that the higher concentration of some elements associated with the increased ~ osmotIc pressure can affect enzymes and enzyme activity. A judicious selection of crops is required that can produce satisfactorily under saline conditions and particular attention should be given to the salt tolerance of the crop during seedling Effect of Salinity on Transpiration development because low yields frequently result from failure to obtain a satisfactory stand. · . Evapotranspiration ~T) is a complex process influenced by soil, plant and climatic factors Toxicity problems occur if certain constituents (ions) in the soil or water are taken up by the plant mcludmg temperature, relatIve hUIDIdity, wind velocity, sunshine and solar radiation. ' and accumulate in concentrations high enough to cause crop damage or reduce yields. The degree lITO It ha~ been shown by s:veral workers that ET decreases with increasing salinity level in the of damage depends on salt uptake and on crop sensitivity. '" ~ medIUm due to the difficulty plants have in absorbing water from a salt solution with osmotIc pressure higher than that of cell sap.

105 104 Salinity of the growth medium reduces water uptake for two reasons: ~he greater difficulty plants have in adsorbing water from a soil solution with elevated osmotic pressure and t~e Carbonate ions reduction in root system growth caused by the elevated salt concentration. The l~af surface area IS High concentrations of carbonate (CO/- ) or bicarbonate (HC03") ions depress crop also reduced and leaves retain more water. The overall result is a reduction In ET and In the growth. HC03- and CO/- are usually considered to have similar effects, since the former is readily efficiency of water use, accompanied by decreased plan~ growth and yield. . converted to the latter. Elevated CO/- and/or HC03 concentration in the soil solution or irrigation The salt tolerance of most agricultural crops IS known well enough to g.lve gen~ral salt water causes Ca++ and Mg ++ to be precipitated. Deficiency of both these nutrients is therefore a tolerance guidelines. However, such estimations c~ot pr~vide accurate Informa~lOn on feature of strongly alkaline soils and the resulting cation imbalance accentuates Na toxicity. 2 quantitative crop 'Yield losses from salinity for e:ery sltuatlO.n, since ~ctual ~esponse varle~ With Elevated HC03- or C03 - concentrations may lead to loss of availability of other nutrients including other conditions of growth including salt composItion, climatiC and soil condltlOn,agrono1lllc and Fe and Mn. irrigation management, crop variety, stage of growth, r.oot stock in the case ~f.frult trees, etc. While the values are not precise, since they incorporate interactIOns between sal1ill~, sodlclty and Sodium other factors· these data can be used to predict how one crop might perform relative to another Sodium toxicity is not as easily diagnosed as chloride toxicity, but clear cases of the former under similar' conditions. The tolerance of many common field, vegetable, forage and tree crops as have been recorded. Typical toxicity sy!llptoms are leaf burn, scorch and dead tissue along the influenced by irrigation water salinity or soil salinity, can be found in Maas (1984} and Maas (~986) outside edges of leaves in contrast to symptoms of chloride toxicity which normally occur initially and in Ayers and Westcot, (1983). However, if there are few crops In an area, It may be deSirable at the extreme leaf tip. An extended period of time (many days or weeks) is normally required to prepare separate guidelines for each specific crop or group. of crops rather th~ use the broad before accumulation reaches toxic concentrations. Sy!llptoms appear first on the older leaves, QUidelines. Guiddines for an individual crop can be more speCific and are better mds to managers starting at the outer edges and, as the severity increases, move progressively inward between the :::nd cultivators for evaluating the suitability of the soil for different crops. veins towards the leaf centre. Sensitive crops include deciduous fruits, nuts, citrus, avocados and beans, but there are many others. For tree crops, sodium in the leaf tissue in excess of 0.25 to 0.50 Specific Ion Effects and Toxicities ...... percent (dry weight basis) is often associated with sodium toxicity. Sodium toxicity is often A toxicity problem is different from salinity or sodlclty problems In that It occursw~thin the modified or reduced if sufficient calcium is available in the soil. plant itself and is not caused by a water shortage. Toxicity normally resu~ts :vhen certain IOns are Particular care in assessment of a potential toxicity due to SAR or sodium is needed with taken up with the soil-water and accumulate in the leaves dunng transpiratIOn to an e~ent that high SAR water because apparent toxic effects of sodium may be due to or complicated by poor results in da!llage to the plant. The degree of da!llage depends upo~ time, concentratIOn, crop water infiltration. Only the more sensitive perennial crops have yield losses due to sodium if the sensitivity and crop water use; and if da!llage is severe enough, crop YIeld IS reduced. Da!llage can physical condition of the soil remains good enough to allow adequate infiltration. Several of the be caused by each ion, individually or a combination. . . crops listed as more tolerant do show fair growth when soil structure is maintained and in general, Not all crops are equally sensitive to these toxic ions. Most armu~ crops are not senSItive. at these crops can withstand higher ESP levels if the soil structure and aeration can be maintained, as medium concentrations but the majority of tree crops and woody perenmal-type plants are. TOXlC:ty in coarse textured soils. symptoms, however, can appear on ~o~t any .crop if. concentrations are hig.h enough. TOXlClty often accompanies or complicates a sallmty or infiltratIOn problem although It may appear ~ven Boron when salinity is low. Many trace elements, in addition to sodium, chlonde and boron, are toXiC to Boron, unlike sodium, is an essential element for plant growth. (Chloride is also essential plants at very low concentrations. but in such small quantities that it is frequently classified as non-essential). Boron is needed in relatively small a!llounts, however, and if present in a!llounts appreciably greater than needed, it Chloride . . ak becomes toxic. For some crops, if 0.2 mg/I boron in water is essential, 1 to 2 mg/l may be toxic. Chloride is not adsorbed by soils. Therefore it moves readily with the SOlI-water, IS t en .up Surface water rarely contains enough boron to be toxic but well water or springs occasionally by the crop moves in the transpiration strea!ll, and accumulates in the leaves. If the chlonde contain toxic a!llounts, especially near geothermal areas and earthquake faults. Boron problems concentratio~ in the leaves exceeds the tolerance of the crop, injury sy!llptoms develop such as le~ originating from the water are probably more frequent than those originating in soil. Boron toxicity burn or drying of the leaf tissue. Normally, plant injury occurs first at the leaf tipS (which .IS can affect nearly all crops but, like salinity, there is a wide range of tolerance a!llong crops. common for chloride toxicity) and progresses from the tip back along the edges as sev~nty Boron toxicity sy!llptorns normally show first on older leaves as a yellowing, spotting, or increases. Excessive necrosis (dead tissue) is often accompanied by early leaf drop or defoliatIOn. drying of leaf tissue at the tips and edges. Drying and chlorosis often progress toward the centre With sensitive crops, these sy!llptoms occur when leaves accumulate from 0.3 to 1.0 per,cent between the veins (interveinal) as more and more boron accumulates with time. On seriously chloride on a dry weight basis, but sensitivity varies amonglthese crops. Many tree-crops ~or affected trees, such as almonds and other tree crops which do not show typical leaf sy!llptoms,' a eXa!llple beain to show injury above 0.3 percent chloride (dry weight). Crop tolerance to chlonde gum or exudate on limbs or trunks is often noticeable. is not n~arl; so well documented as crop tolerance to salinity. The kno~ tolerances of several Most crop toxicity sy!llptoms occur after boron concentrations in leaf blades exceed 250- crops to chloride in the saturation extract or the applied water can be found In Maas (1984). These 300 mg/kg (dry weight) but not all sensitive crops accumulate boron in leaf blades. For eXa!llple, values may need to be changed where local experience indicates that different levels cause da!llage. stone fruits (peaches, plums, almonds, etc.), and pome fruits (apples, pears and others) are easily da!llaged by boron but they do not accumulate sufficient boron in the leaf tissue for leaf analysis to be a reliable diagnostic test. With these crops, boron excess must be confirmed from soil and water analyses, tree symptoms and growth characteristics.

106 107 of little direct benefit to the farmer because it bears little relationship to yield reductions within SALT TOLERANCE CRITERIA commercially acceptable limits. The model described above describes the response of many herbaceous species and also There are different ways to describe plant tolerance to salinity which have different values describes very well, certain growth parameters of woody perennials, e.g. lateral growth, leaf area for agronomists and plant breeders. First, and of most ~alue.to agronomists, is the relative YIeld or development (West 1986). However, woody species also respond to specific ion toxicities which relative growth under saline conditions compared WIth YIeld or growth under non-salin~, but will cause leaf damage, die back and eventual death. otherwise similar growing conditions. This is the criterion most widely used because expresslOn of This treatment of salt tolerance using a relative yield decline model has produced lists of the yield on a relative basis allows comparison of different species. The usefulness of this me~sure of type presented by Maas and Hoffman (1977). These lists must be treated with caution because they salt tolerance depends upon the degree to which environmental and management factors mteract can be misleading unless the person using them is aware of a number of underlying assumptions and with the plant and the degree to which these interactions are recogniz~d ar:d understood by the conditions that have gone into their deVelopment. They may be misleading because they are mostly agronomist. The expression of relative salt tolerance is most commonly gwen m the form: developed for plants growing under otherwise optimum conditions which have been established Relative Yield = 100 - B (ECe - A) under non saline conditions and they do not take account of several plant and environmental factors that affect sensitivity to salt stress. As developed by Maas and Hoffman (1977) and very widely used. It describes a model in which there is initially no loss of yield as soil salinity increases until it reach~s a cri.tical "threshold FACTORS AFFECTING CROP TOLERANCE value" which is then followed by a phase of more-or-less linear decline as SOlI salirnty contmues to increase beyond the threshold value. With this expression, knowledge of two parameters can be Tolerance of plants is not a fixed characteristic of each species or variety, but may vary with used to compare different species or cultivars, namely: the environmental conditions. The tolerance also varies with the stage of crop growth of the same • the threshold salinity at which yield loss commences, and .. . species as mentioned earlier. The factors that affect tolerance of plants are as follows: • the rate of yield decline for each unit increase in root zone salinity after the threshold sallrnty IS exceeded. Stage ofgrowth Species or cultivars may differ in either one or both the above parameters. The val~e ofEC, Tolerance during the germination and early seedling stage is different from late seedling is the averaae saturation extract electrical conductivity (dS/m) of the root zone. This model stage to maturity. In general, if, the soil salinity in the surface soil (seedling area) is greater than 4 idealizes the "'response of the plant to soil salinity but in its simple form it still qu~te ad~quately dS/Ill, it may inhibit or delay" germination and early seedling growth. Tbis slowed germination may describes the response of a great many herbaceous species to salinity. The followmg pomts are delay emergence, allowing soil crusting and disease problems to reduce crop stand. relevant to this model of salinity response: . . • It is generally unwise to extrapolate the relationship too far, e.g. beyond 50% YIeld decline Several cereal crops such as barley, maize and wheat are more sensitive during emergence where the response often becomes non linear. ..' and early seedling growth than at later stages, while sugar beet and safflower are most sensitive • With respect to relative yield vs. absolute yield, it may be misleadin~ sometimes m agronoIlllc during germination. The tolerance of soybean could either increase or decrease between terms to rely totally upon relative yield responses for cases where It would clear~y b~ much germination and maturity depending on the crop variety. Rice can tolerate a high concentration of better to have a plant with a high absolute yield and low salt tolerance than a plant WIth high salt salts at germination (up to 30 dS/m), but it is sensitive to salinity in the early growth stage and the tolerance and low absolute yield. A small reduction in a very low yield may be worth less for the tolerance increases with age during the tillering phase of growth. The tolerance of rice, however, farmer than the return from a larger reduction on a very large yield potential. decreases from panicle formation stage to flowering stage so that salinity stress at this stage invariably results in reduced grain yield. There is clear evidence of differences in sensitivity through An alternative form of the above expression is sometimes used. This is: development stages of many crops. These differences are important where it is under, the control of ~~~ . Y = 100 (EC - ECe) / ECo- EClOo . o If the farmer has irrigation water available and can vary salinity of the water or that of the where EC is the salinity threshold value and ECo is the salinity at zero yield where Yield has been lOO root zone to match different crop sensitivity to salinity; then it is possible that good quality water linearly extrapolated to zero. can be saved for critical periods and poorer quality water be used at less critical periods. Many legumes germinate well under so die conditions but their subsequent growth is Ofless interest to the agronomist, but valuable to the plant breeder, is the ability ofthe plant arrested due to low tolerance. Similarly, in many small seeded crops germination failures are largely to survive at a particular salinity. This abilitl provides a way for plant breeder to select v.al~able t~e responsible for poor or uneven crop stands. Cotton, a crop considered tolerarit of saline conditions, for salt tolerance in plants by imposing a high external salinity on a population to cause death of ~e is only moderately tolerant of sodic conditions and relatively sensitive to sodicity at the germination a high proportion of the population. If the salinity stress is correc~y selected, the remammg small stage. For rice, sodicity tolerance increases with age in the initial growth stage, and it is beneficial proportion of the plant population will be to a higher salt tolerance than those e~pected h.a~e to transplant somewhat older rice seedlings (35 to 40 days of age) instead of the usually members of the population which did not SUfVlve. The survwmg plants may be damaged by the salt recommended 30 days old seedlings in sodic soils. stress but since salt injury in many species is reversible with removal of the external stress, t~e surviving plants may be recovered and used in a breeding prograrrnne. Survival in a farmer's field IS

108 109 Rootstock and plant size Soil fertility Most fruit crops are more sensitive to salinity than are field, forage or veg~tabl~ crops. Salt Interaction between soil fertility and salinity may affect apparent tolerance in many crops. tolerance of tree and bush crops such as avocado, citrus, many stone fruits and vl.nes IS related to Crops grown on infertile soil may seem more salt tolerant than those grown with adequate fertility, the ability of the root stock to exclude salt, especially the toxic so?ium and chlonde Ions. With a because fertility is the primary factor limiting growth. If fertility is a limiting factor, proper reduction in the amount absorbed, accumulation is reduced. Bernstem (1965) attnbuted the d~age fertilization will increase yields, but if fertilization is not limiting, additional fertilizer will not to the plants in many fruit crops to the concentration of specific ions i. e. chloride or sodIUm III the improve salt tolerance. soil solution and/or plant leaves rather than to the total soil salinity. For this reas.an, c.lasslficatlOn of fruit crops with respect to specific salinity according to vari~ties and. ro~tstocks IS Of.lID~ortance. Salinity and waterlogging interactions There are also effects of plant size with respect to IOn localIZatIOn and dlstnbutlOn that are Another of the external factors which affects salinity tolerance response is the interaction important in fruit, timber and forage trees, in addition to the e~ects that ~ccur with herbaceous between salinity and rootzone waterlogging. For a wide range of species the coincident stresses of species. Some fruit trees have the ability to accumulate Na or Cl III woody tissues of roots, trunks salinity and low root zone oxygen concentration reduces growth or gennination and/or drastically and major branches. . increases the transport of Na+ and cr to the shoots with an increase in the chance of damage Another area of considerable physiological interest for fruit and other trees species related occurring. to plant size is the carry over of salinity effects from season ~o season. Berstein. et al. (195~) Waterlogging occurs naturally with salinity in agricultural situations in poorly structured reported effects of salinity to be worse in the second year of Sallllity treatment for fruit trees than III soils (e.g. alkali soils), from irrigation with saline water, or as saline seepage waterlogging. In all the first year. Bernstein and Francois (1973) have also shown the s~e effect for the woody these conditions some degree of root zone anoxia will occur at least occasionally. perennial forage species - lucerne (alfalfa). Storage and ~arry-over of sallmty effects from s~ason to For some sensitive plants to waterlogging (barley, wheat, bean, tomato, tobacco, season are involved in the observations cited above WIth respect to second year effects III stone sunflower), waterlogging at high external salinity greatly increased concentrations ofNa+ and cr in fruits. the shoots or leaves. The increases in concentration were not due to reductions in growth. With low external salinity the plants must be exposed to lower O2 concentrations to have Crop varieties . . adverse effects; while at high external salinities, damage occurs in the presence of some O2 (West Varietal differences also exist among cultivars of annual crops. The greatest differences III and Taylor 1980). Drew and Lauchli (1985) showed an increase in Na transport to shoots of maize

tolerance appear to be among selections from cultivars of the more salt tolerant crops. Alth~ugh when solution O2 concentration fell from 21 % to 15 %. there have been several studies aimed at identifYing genotypes and breedlllg new crop vanetles Adaptation of many species to waterlogging depends upon the presence of parenchyma tolerant of salinity conditions, there appears only limited effort in this direction with .regard to tissue in the roots or ability to develop adventitious roots at the waterlogging surface. These are sodicity. However, any new varieties developed and having greater tolerance should be Judged on capable of providing an alternative pathway for the supply of oxygen to the submerged root tips. their own merits. A number of years (5-15 or more) may be needed before even a. few new, more Sunflower (Kriedemann and Sands 1984) is able to adapt to waterlogging by developing salt tolerant crops are commercially available and competitive in yield and quality WIth present aerenchyma tissue plus adventitious roots. They were not able to do so when exposed to saline varieties. waterlogging. Rice, which normally has aerenchyma tissue in roots, has a lower transport of Na+ and cr to the shoots with saline waterlogging (John et al. 1974). Climatic conditions Plant response to salinity is influenced by temperature and relative hu~dity. In general, REFERENCES crops grown in cooler climates or during cooler times of the year will have a higher tolerar:ce to salinity than similar crops grown during warmer drier perio~s ..~ince crop de~and .for water IS. ~ess Ayers, R.S. and Westcot, D.W. 1983. Water quality for agriculture. Irrigation and Drainage Paper during the cooler periods, the' effect of reduced water availability due to sallmty IS not so cntlcal 24, Rev.!. FAO, Rome. • and a greater proportion of applied water may be available to leach accu:nulated salts. In contrast, Balba, A.M. 1980. Minimum management programme to combat world desertification. UNDP in dry, hot conditions, and because of the high ET ~emand, wat~r absorption by the plant roots may Consultancy Report. Adv. Soil Water Res., Alexandria. not be sufficient due to both rapid depletion of soil water and Illcreased salt concentratIOn around Balba, AM., EI-Etriby, F. 1980. The quantitative expression of the effect of water salinity on plant the roots. Climate appears to affect salt sensitive crops to a much greater extent than salt tolerant growth and nutrient adsorption. Soil Sci. Symp., Kamal, India. Proc. 451-456. ones. . Bernstein, L. 1965. Salt tolerance offruit crops. USDA Agriculture Information. s Rice crops grown under submerged cond~tions t~l~ra:e ~gher s~dicity levels III wet yea: Bernstein, L., Brown, J.W., and Hayward, H.E. 1956. Prhc. Am. Soc. Hort. Sci. 68:86-95 when the rainfall is well distributed and atlnosphenc hUillldlty IS high dunng the crop season than III Bernstein, L. and Francois, L.E. 1973. Comparisons of drip, furrow and sprinkler irrigation. Soil the dry years when the atmospheric evaporative de:nar:d is high. This is attri~uted to .the Scl.115 :73-86. accumulation of sodium in toxic quantities when the ET IS high. For crops other than nce, there IS a Chhabra, R., Abrol, I.P., Singh, M. 1980. Leaching losses of phosphorus in sodic soils. Int. Symp. strong interaction between exchangeable sodium level of the soil and wa~er supply to plants, on o~e Salt-affected Soils, New Delhi. Proe. 418-422. hand, and the evaporative demand on the other. The adverse effect of high ES.P on plant growth IS Drew, M.C. and Lauchli, A 1985. Plant Physio!. 79:171-176. likely to be accentuated under conditions of high evaporative demands and this would make water EI-Khatib, S.A 1977. Manganese and zinc relationships of soils and plants. M.Sc. Thesis. Dept. of management for crops more critical. Soil and Water Sciences, University of Alexandria.

110 111 EI-Shakweer, M.H. Ghaffar, SA 1972. N-balance studies for some salt-affected soils cropped with Soil-Plant-Water Relationships in Salt-affected Soils cotton. Int. Symp. Salt-affected Soils, Cairo, Proc. 909-920. Feigin, A 1985. Fertilizer management of crops irrigated with s~e wate~. P!. Soil 82:2852~9 .. Rami Zurayk Fink, A 1977. Soil salinity and plant nutritional status. ManagIng SalIne Water for IrrigatlOn, American University of Beirut, Lebanon Lubbock Texas. Proc. 199-210. Frankenberger:W.T. and Bingham, F.T. 1982. Influence of salinity and soil enzyme activities. Soil INTRODUCTION Sci. Soc. AmJ. 46:1172-1177. Gascho, G.J. and Mashali, AM. 1991. Soil-water-nutrient interaction. Proceedings Consultation on The earliest and most easily discernible response of a crop plant to salinity is a slowing FertigationiChemigation, 8-11 September 1991, Cairo. AGLIMISCI1991. down of vegetative growth (e.g. beans and sorghum, Kawasaki et aI, 1983). At low salt levels, John, e.D., Limpinuntana, v., and Greenway, H. 1974. Aust. J. Plant Physio!. 1:513-520. root growth may be unaffected, or even enhanced, while shoot growth will be reduced (Munns Kriedemarm, P.E. and Sands, R. 1984. Aust. J. PlantPhysioI1l:287-301. and Termaat, 1986). Typical salt damage shows first on the older leaves of a plant (Flowers and Mass, E. 1984. Salt tolerance of plants. In The Handbook of Plant Science in Agriculture. B. R. Yeo, 1986), usually in the form of browning and necrosis of the leaf tips. This is often followed by Christie (ed). C.R.e. Press, Boca Raton, Florida. general chlorosis, and ultimately, by the death of the leaf. Growth reduction in plants can be Mass E. V. 1986. Salt tolerance of plants. Applied Agricultural Research 1 (1). observed after short exposures to salt (one or two days), even before ion accumulation in the Mass: E.V. and Hoffman, G.J. 1976. Crop salt tolerance: Evaluation of existing data. In Proc. Int. leaves has reached high levels. Long term exposure (weeks or months) causes high levels of salt Salinity Conference, Lubbock. Texas, August 1976. pp. 187-198. . build-up in the leaves (up to 90% of total plant sodium, Pitman, 1984), and is usually thought to Matens, D.A and Brenmer, J.M. 1989. Soil properties affecting volatilization of ammoma from bring about the death of the plants. Specific ion toxicity, stress due to ion imbalance, and water soils treated with urea. Co=un. in Soil Sci. and Plant Anal. 20:1645-1657. stress due to low osmotic potentials (physiological drought) are thought to be the main factors Paliwal, K.W., Mallwal C.L. 1971. Effect of fertilizers and manure on the mineralization and behind the growth limiting effect of salinity on the growth of plants (Wyn Jones, 1987), The availability of N to barley irrigated with different quality waters. Int. Symp. Salt-affected extent to which growth reduction is really due to these factors has been critically questioned by Soils Cairo. Proc. 709-718. Munns and Termaat (1986) and Cheeseman (1988). Shukla, D.C. and Muhi, A.K. 1980. The amelioration role of Zinc on the growth of maize (Zea mays L.) in salt-affected soils. Int. Syrup. Salt-affected Soils Proceed. 36~-3~8, New D~lhi: Factors Underlying the Differential Responses of Plants to Salinity Threadgill, E.D., Eisenhauer, D.E., Young, and Bar-Yosef, B. 1991. ChemlgatlOn. In Imgatlon Systems. (ed) G. Hoffman. Am. Soc. Agr. Eng. Monograph (in press). Crop plants vary widely in their resistance to salinity, There is evidence that the extent of West,D.W. 1986. Acta Hort. 175:321-332. this resistance is genetically determined (Epstein, 1976 ; Zurayk et al, 1993). Other factors have West, D.W. and Taylor, J.A 1980. Ann. Bot. 46:51-60...... been outlined by Meiri (1984). These include crop factors, such as growth stage, and soil factors Zhukovskaya, N.V. 1973. Uptake and accumulation of phosphate by plants In salimzed soils. SOlIs such as the type of salinity (salt species), temporal and spatial variability in salinity. Additionally, and Fertilizers 36:241. the response of otherwise similar plants can depend on enviromnental factors. Of these, factors causing changes in evapotranspiration, and subsequently in the water relation of the plant are of special interest. This is understandable in view of the strong interaction between water uptake and ionic uptake, which would determine the amount of salt taken up and, subsequently the degree of salt injury, Hence, a study of soil-plant-water relationship under salinity must look closely at the interaction between enviromnent, water uptake and salt stress.

ENVTRONMENTALFACTORS

The Effect of the Aerial Environment on Plant Response to Salinity

Enviromnental factors can significantly affect the response of plants to salinity. Tolerance of most crops has been shown to be improved by cool and humid weather. It was reported that cool temperatures and high relative humidity more than doubled the salt tolerance of kidney beans. A similar effect was recently demonstrated in greenhouse cucumber grown in the United Arab Emirates. The water salinity level which produced a 50% decrease in the total biomass during the su=er failed to cause any significant reduction in the winter crop (Mujaess 1995).

112 113 The most straightforward explanation relies on the increase in transp~ration caused by ~gh osmotic potential. Thus, the extent of the allowable water depletion for a crop will depend on the temperature and low relative humidity. This, in turn, affects the specific salt Injury as high maximum acceptable salt concentration. Yields start to be reduced if water is depleted beyond this transpiration rates have been linked with increased Na and Cl uptake. lirnit, and salts concentrate in the soil. Therefore, irrigation frequency needs to be higher in salt affected soils, in order to minimize evapoconcentration. Interactions between water relations and salt stress. Plants can establish a zonal response to salinity, with most water extraction taking place The relationship between salt uptake and water uptake, and the apparently resulting from the zone of minimal salinity. In case of frequent irrigations, this zone corresponds to the damaO'e to the plant seems to depend on both uptake path of the ion involved and on the plant upper root zone. Poor drainage-salinity interactions can severely reduce the yield of crops. In itself '" There is evidence that, as a result of low transpiration rates the growth of some plant poorly drained soil, anoxic conditions can worsen salt injuries, and reduce the salt tolerance level. species in saline conditions can be improved ifhigh ambient humidity is maintained (Hoffinan and Differences in water distribution in different irrigation methods indirectly affect the crop Jobes 1978). A tentative explanation is that a low water uptake rate can ease the effects of salt response. In flooded soils, water and salt movement is one-dimensional, essentially downwards. In induced water deficit (yVyn Jones 1987). furrow irrigated soils flow is two-dimensional, both downwards and lateral. In drip systems, flow Aside from its direct effect on transpiration rate, high ambient humidity has been shown to is three-dimensional, and water and salt move radially from the source, causing salts to cause an increase in the fresh-to-dry weight ratio of some plant species. The result was less severe accumulate at the fringes of the wetted area. This can cause problems when winter rainfall washes salt injuries, due probably to a reduction in the concentration of electrolytes. in th~ shoot (e.g. salts back into the root zone. bean and cotton, Niemen and Poulsen 1967). Conversely, factors caUSIng high rates of transpiration, such as high radiation level, low relative humidity ~d high temperature have been Implications for Crop Tolerance Models shown to intensifY- salt damage, usually by facilitating solute entry mto the root (Gale 1975a). . Salinity will usually result in a depression of the transpiration rate and of th~ cumulatl~e One can deduce from this rapid review that a large number of factors, affect the response water uptake (Gale 1975a; Hanks et aI, 1978 (maize); Hoffinan .~d Jobes. 1978 (malZe); Schleiff of plants to salinity. In these conditions, two general approaches may be used to predict the yield 1986), although some conflicting results have been reported (Mem an~ ~oIJakoff-~ayber 1970). in saline environments: (1) modelling the effects, including possible interactions of all the factors The causes underlying the depression in transpiration caused by sallmty are stIll unclear. Gale affecting the results, and (2) normalization of the results to isolate the effects of the experimental (1975b) suggests the following hypotheses: variables. The most common approach has been the second one, as extensive reviews of the * Physiological drought literature in general found that crop tolerates increases in salinity up to a threshold level, above * Osmotic or ionic imbalance which yields show an approXimate linear decrease as salt concentrations continues to increase. * Reduction in the hydraulic permeability of the root The basic model that follows this approach is that ofMaas and Hoffman (1977), which relates the * Partial stomatal closure possibly due to loss of turgor. yield decline of a given crop to the EC, (saturation extract of the soil) or the ECw of the irrigation It is also possible, as noted by Gorham et al (1985), that the commonly observed water, using this linear response model, reduction in transpiration could simply be due to the reduction in plant size and leaf area Y = 100 - b(EC,-a) associated with salinity. where As a result, it appears that transpiration can increase ion uptake by the whole plant .(e.g. Y= relative crop yield (%) Broyer and Hoagland (1943); Greenway and Klepper (1968) at high external salt c.oncentratlOn~. EC,= salinity of the soil saturation extract (dS/m) Pitman (1984) proposed that ion movement could be coupled to water flow durmg symplastlc a = salinity threshold value passage across the root; or, at high concentration, that ions could be moved by water along an b = yield loss per unit increase in salinity apoplastic pathway. Using this model, the FAO has calculated and tabulated the values for the tolerance of 71 There appears, therefore, to be a highly interactive relationship between ~he fac:ors of different crops. salinity, salt uptake, transpiration rate, and plant growth. Defining this rel.atlOnship reqUires an The model has 'been updated and improved, (van Genuchten and Hoffman 1984) but in exact knowledge of the mechanisms involved in the response of plants to sallmty. This knowledge view of the specificity of response under various environmental conditions; it can only serve as a is not yet completely available. guide to the relative tolerance among crops. The model also assumes a steady state condition and no spatial or temporal variability. Soil-Water Effects: Water Application and Water Flow Absolute tolerances vary depending on soil, climate, cultural practices, cultivar and growth stage. In poor irrigated gypsiferous soils, plants will tolerate about 2 dS/m higher EC, The avoidance of soil water stress is a primary concern of saline agriculture. Plant water than predicted ~y the model (Ayers & Westcot, 1985). The optimization of saline agriculture stress is caused by a reduction of the total water potential, which includes matric and osmotic would require a model which can account for the different variables that can be encountered. potential. In salt affected soils, the osmotic potential can contribute significantly to the tot~ water Such a model has yet to be completed, and it is possible to foresee that it would include a number potential. Allowing the soil to dry will increase the salt concentratIOn, hence decreaSIng the of related sub models, each accounting for a specific variable. In the next section, an attempt will

114 115 be made to develop sub-models that can offer the option of refining ~e rr:an.agement of salt Diffusion and mass-flow are the mechanisms by which ions move in a soil root system. affected soils, by specifically addressing the complex soil-plant-water relatIOnship Issues. They do not, however, always occur concurrently with the same relative significance. When the value of mass-flow in a system is large, due to a high transpiration rate, the significance of APPROACHES TO A WATER-SALINITY-YIELD MODEL diffusion in moving nutrients towards the root can be very reduced. Under low transpiration, mass-flow will have a small value, and very little solute will be convectively transferred to the Perhaps the most famous model relating water and salinity stress to yield was developed roots. Diffusion, in this case, will often be the main mechanism of ionic movement. by Hanks (1974). The model is based on the following relationship: Mass-flow will usually bring appreciable quantities of ions to the root surface. Root YlY'm= T/Tm absorption will usually increase to adjust to the new external concentration. When large amounts where of ions are transported, the increase in uptake cannot prevent the excess ions from accumulating Y m = maximum yield at the root surface. Tm = transpiration when here is no limit imposed by water or salt stress. Thus, concentration gradients between the root surface and the surrounding soil will be Thus, any factor which depresses transpiration will depress yield. Predictions also require established when the replenishment of the absorbed ion is not synchronized with its uptake by the the determination of potential soil evaporation Em. The model handles salt and water flow by root. It is not difficult to anticipate that a natural system such as the plant-soil system will rarely considering basic soil properties. The water flow equation also includes a ~e~ for water be in phase. In fact, concentration gradients have been theoretically predicted (Nye and Spiers extraction by roots, which includes an osmotic component to account for sal~ty. The pl~t 1964; Nye and Marriott 1969) and experimentally observed for different plants under different factors (such as root growth) are otherwise minimally represented, and salt flow mto the plant IS environmental conditions (Barber, 1962; Barber and Ozanne 1970; Dunham 1971). also considered ta be absent, thus salt can be concentrated by root uptake of pu~e water. Chemical transformations of salts (dissolution, precipitation, exchange) are also not consIdered. Experimental Demonstration of Salt Accumulation Near Plant Roots in Saline The model was tested under various conditions, and agreement between the computed and Environments measured soil water was good over a year. The model was also successful in predicting ET (hence yield) when salinity was low, but agreement between I?-easured .and predicted value was poor in A number of researchers (Riley and Barber (1970), Sinha and Singh (1974, 1976b), high saJinities. This was attributed to the fact that cheffilcal reactIOns were not accounted for, and Schleiff (1982» have shown experimentally that sodium and chloride accumulation close to the that the salt effect was assumed to be only osmotic. root surface could occur. Riley and Barber (1970) measured the increase in concentration of the This approach was used to predict yields on a multi-year basis. The simulations were used rhizocylinder to be 5 to 15 'times that of the bulk soil. These results have, however, been as a basis for economical analysis of the cost oflimiting salt outflow m dramage water. questioned by Greenway and Munns (1983) on physiological grounds, stating that a rapid mass Based on Hank's work, a more realistic and more complicated model which accounts for flow, the prerequisite for accumulation to occur, was impossible due to plant injury. Sinha and chemical transformations was developed by Robbins et al (1980). Agreement betwee~ .measu~ed Singh (1974) further developed Riley and Barber's (1970) technique. They measured increases in and simulated yield and salt build up were poor, due to parameters, such as boron tOXlClty, which concentration ofNa and CI in the soil "close to the root" (0 to 2 =) of pot grown maize. were unaccounted for. Since salt concentration at the root surface will directly affect plant performance, it would In conclusion, models which describe the combined water and salt effect on the plants are be interesting to be able to predict the magnitude of the accumulation or depletion and the extent currently available, and can be used to simulate field condition reasonably ~ell. However, they are of the ionic gradient in the root vicinity. still limited by the difficulty of representing processes which occur at the ffilcro-scale, such as root The processes involved, namely plant uptake of ions, mass-flow and diffusion, can be water uptake, chemical transformation, and spatial and temporal variability. joined into a coherent mass-balance equation, representative, to a large extent, of the nature of the changes occurring with time and distance, in the soil. Interaction Between Soil-Water-Plant Parameters in the Root Environment Modelling Salinity at the Root-Soil Interface. In this section, an attempt to understand and model the soil-plant-water relationship.s ~t micro-scale level will be presented. The approach is based on developing a clear, m~charustlc The mathematical equations representing diffusion and mass-flow can be joined together in analysis of the processes involved in salt movement and uptake in salt affected SOlIs, under what is known as the continuity equation, and used to concentration of nutrients near the roots. different transpiration regimes. The final product would complement the mode~s .presented a?ove. Nye and Spiers (1964) provide a convenient mathematical model in the form of a differential Solute concentration in the soil is rarely, if ever, homogeneous. L~V1ng plants ~nd~ce equation relating the concentration of a substance moving by simultaneous diffusion and chan".es and movement in the ionic environment of their roots. Ions moving Wlth the transpIratIOn mass-flow to its distance from the root surface and the absorption time. Their equation: stre~ will move in what is termed mass-flow or convective transfer. Plants taking up ions fr?m the root surface cause a depletion which trigger diffusive transport caused by concentratIOn gradients.

116 117 C/ t = lIr [(D r dCLldr + a Fa CL)/ r] REFERENCES where: C is the concentration of substance in soil Ayers, R.S. and Westcot, D.W. (1985). Water quality for agriculture. Publication 29. FAO, Rome. CL is the concentration of substance in the soil solution Barber, SA (1962). A diffusion and mass flow concept of soil nutrient availability. Soil Science 93, 39-49. D is the apparent diffusion coefficient Barber, S.A and Ozanne, P. (1970). Autoradiographic evidence for the differential effect of four plant species in a is the radius at absorbing surface altering the calcium content of the rhizosphere soil. Soil Science Society of America Proceedings 34, 635- 637. Fa i;; the flux of water at the root surface . Broyer, T.C. and Hoagland, D.R (1943). Metabolic activities of roots and their bearing on the relation of upward is the fundamental equation for simultaneous diffusion and mass-flow to plant roots ill a movement of salts and water in plants. American Joninal of Botany :3 0, 261-273 cylindrical system. . . Cheeseman, J. (1988). Mechanisms of salt tolerance in plants. Plant Physiology 87, 547-550. . A model which simulates solute movement in the soil-root system in cases of saliruty was Dunham, RJ. (1971). The influence of soil water content on the movement of plant nutrients to roots. D.Phil developed based on Nye and Spiers's approach and tested .. ~he different pl~t uptake param~ters Thesis, University of Oxford. required by the model under different environmental c~ndItIOn~ were expefillle~t.ally dete~ed. Epstein, E. (1976). Genetic potential for solving problems of salt mineral stress. Adaptation of crops to salinity. In: The model was used to predict the expected concentratIon gradIents under of high "Proceedings of Workshop on Plant Adaptation to Mineral Stress in Problem Soils". Wright, M.1. (Editor). con~ItIOn.s ~d Cornell University, Ithaca, New York. 73-82. low water flux (transpiration). The model is applicable to chloride, and to sodIUm ill the speCIal Flowers, T.J. and Yeo, AR (1986). Ion relations of plants under drought and salinity. Australian Journal of Plant case of negligible exchange in the soil matrix. This would be the case in soils of very low CEC, Physiology 13, 75-91. such as some sandy desert soils. . Gale, J. (1975a). The combined effect of environmental factors and salinity on plant growth. In: Plants in Saline The simulations showed that under normal field conditions and practices, apprecIable Environments. Ecological Studies 15. Gale, 1. and Poljakoff-Mayber, A (editors). Springer Verlag, Berlin. concentration increases of chloride at the root surface were unlikely to occur. It appears that a 169-185. Gale, J. (1975b). Water balance and gas exchange of plants under saline conditions. In: Plants in Saline rise in concentration at the root surface will be counteracted by diffusion-mediated back transport Environments. Ecological Studies 15. Gale, 1. and Poljakoff-Mayber, A (editors). Springer Verlag, Berlin. during the night, except when the soil becomes very dry. In this case, it is doubtful wh~the~ the 186-192. plant processes leading to the establishment of the gradients (water and solute uptake) WIll still be Gorham, 1., Wyn Jones, R G. and Mc Donnell, E. (1985). Some mechanisms of salt tolerance in crop plants. Plant active. and Soil 89, 15-40. It is possible that a soil with different physical properties could produce a significantly Greenway, H and Klepper, B. (1968). Phosphorus transport to the xylem and its regulation by water flow. Planta 83, 119-136. different impedance factor and cause larger accumulation than that predicted for the pres~nt data. Greenway, H. and Munns, R (1980). Mechanisms of salt tolerance in non-halophytes. Annual Review of Plant The difference in the value of the impedance factor will, however, have to be very large ill order Physiology 31, 149-190. for the difference in accumulation to be appreciable. This is unlikely to be the case in agricultural Hanks, R.I. (1974). Model for predicting plant growth as influenced by evapotranspiration and soil water. soils, unless significant water gradients are established at the root surface. There is not yet enough Agronomy Journal 66 (5) 660-665 evidence to confirm that. Hanks, RJ., Ashcroft, G.L., Rasmussen, v.P., and Wilson, G.D. (1978). Com production as influenced by irrigation and salinity- Utah Studies. Irrigation Science 1, 47-59. Hoffman, G.T. and Jobes, J.A (1978). Growth and water relations of cereal crops as influenced by salinity and CONCLUSION relative humidity. Agronomy Journal 70, 765-769. Kawasaki, T., Akiba, T, and Moritsuga, M. (1983). Effect of high concentration of sodium and chloride and The modelling approaches presented in this paper underscore the necessity to understand polyethylene glycol on the growth and ion absorption in plants. I-Water culture experiments in a the physical, chemical and biological dimensions of plant responses to salinity. Prediction of the greenhouse. Plant and Soil 75,75-85. processes in the soil-water-plant continuum is a key step for the development of management Maas, E.V. and Hoffman, G.J. (1977). Crop salt tolerance-Current assessment. ASCE Journal of the Irrigation and Drainage Division 103, 115-134. systems that will allow the sustainable utilization of all available resources. Mem, A and Poljakoff-Mayber, A (1970). Effect of various salinity regimes on growth, leaf expansion and transpiration rate of bean plants. Soil Science 109, 26-34. Mujaess, Nehrneh. 1995. Salinity Management for optimal cucumber production. MSc thesis, American University of Beirut. Munns, R and Terrnaat, A (1986). Whole plant responses to salinity. Australian Journal of Plant Physiology 13, 143-160. Nieman, RB. and Poulsen, L.L. (1967). Interactive effects of salinity and athrnospheric humidity on the growth of bean and cotton plants. Botanical Gazette 128, 69-73. Nye, P.H. and Marriott, F.H.C. (1969). A theoretical study of the distribution of substances around roots resulting from simultaneous diffusion and mass flow. Plant and Soil 30, (3)459-472. Nye, P.B. and Spiers, J.A. (1964). Simultaneous diffusion and mass flow to plant roots. Transactions of the International Congress of Soil Science. Bucharest 1964 11, 535-542.

118 119 Nye, P.H. and Tinker, P.B. (1977). Solute Movement in the Soil-Root System. Blackwell, Oxford. Pitman, M.G. (1984) Transport across the root and shoot/root interactions. In: Salinity Tolerance in Plants: Strategies For Crop Improvement. Staples, R.C. and ToenIJiessan, G.H. (editors). Wiley Interscience, New V. Regional Experience: Country Reports York. 93-123. Riley, D. and Barber, SA (1970). Salt accumulation at the soyabean (Glycine max (L.) Merr.) root-soil interface. Soil Science Society of America Proceedings 34, 154-155. Robins, C.W., Wagenet, R1. and Jurinak, 1.1. (1980) A combined salt transport-chemical equilibrium model for calcareous and gypsiferous soils. Soil Science Society of America Proceedings. 29:597-601. Schleiff, U. (1986). Wasseraufnalune junger zuckerruben in beziehung zur salzkonzentration der wurzelnahen bodenlosung. Zeitschrift fur Pflanzenernahrung und Bodenkunde 145, 436-447. Sinha,B.K. and Singh, N.T. (1974). Effect of transpiration rate on salt accumulation around corn roots in a saline soiL Agronomy Journal 66, 557-560. Sinha, B.K. and Singh, N.T. (1976). Root uptake coefficient for Cl ions in com as affected by transpiration rates and solution concentration. Plant and Soil 44, 521-525. van Genuchten, M.Th. and Hoffman, GJ. (1984). Analysis of crop salt tolerance data. In: Shainberg, 1. and 1. Shalhevet (eds) Soil Salinity under Irrigation-Process and Management. Ecological Stndies 51, Springer­ Verlag, New York. Wyn Jones, R.G. (1981). Salt tolerance. In: "Physiological Processes Limiting Plant Productivity". Johnson, C.B. (editor). Butterworth, London. 271-292. Zurayk, R., M. Nimah, and M. Hamze. 1993. The Salt Tolerance Potential of Local Cultivars of Eggplant (Solanum melongena L.). Biological Agriculture and Horticulture. 9:317-324.

120 121 Crop Management in Irrigated Land Particularly in Salt-affected Soils of the United Arab Emirates

Mohamad Haslrim Department of Research and Production Ministry of Agriculture and Fisheries, UAB

INTRODUCTION

Fresh water is a scarce natural resource of crucial and economic importance to most Arab Nations. Large investments have been made in water resource development, particularly in the agricultural sector, the largest consumer of fresh water. The exploitation of arid and semi-arid lands which constitute 40% of the world's land surface, is necessary. A number of institutions around the world haVe been developing technologies to make use of such resources which have been neglected. For example, the use of salt-tolerant species of crops and the application of suitable methods of irrigation for control of the salts in the soil solution allow the utilization of saline water. Sandy soils, where the water percolates down rapidly and does not stagnate in the plant root zone are suitable for saline agriculture. One approach to the exploitation of these regions which otherwise are suitable for crop production is the improvement of the salt tolerance of cultivated species. The ability of a plant to tolerate salt can be measured as the relative reduction in yield with the increase of soil salinity.

PROBLEMS TO BE ADDRESSED

About 87% of the total area of the Arab Region is predominantly desert, arid or cold mountainous land. In the region, the use of brackish and saline water for irrigation has been limited. New technologies suggest that saline water could now be used for irrigation, and this led to rising hopes for converting the non-productive deserts into productive land. However, there are innumerable technical and management problems in bios aline agriculture including the quantity of water, soil characteristics, plants tolerance, lack of adequate information base and often management difficulties. A major challenge will be the screening of potential salt tolerant germplasm of food crops, shrubs, and forage plants that can withstand different levels of salinity for use in crop breeding and production programs. Management issues include selection and adaptation of: * irrigation technology * crop manage'inent * farm management * information management * expertise in the field of bios aline agriculture.

THE ROLE OF RESEARCH PROGRAMME FOR THE SALINITY PROBLEM UNDER THE UAE CONDITIbNS

In the UAE, one can say that the water salinity increases in the sandy and coastal regions as follows: Northern Region: between 1500 and 3500 ppm. Southern Region: between 1500 and 3500 ppm. Central Region: between 500 and 4800 ppm.

122

------~--~---- Woody Species Eastern Region : between 500 and SOOO ppm. There are a number offorage and field crop evaluation programs underway in the UAB including: . The range o~ crops which can be grown in a lowland station in the UAB is limited by the climate. The most llllportant factor is the number of hours below rc Celsius dun'ncr WI'nt I ( f h h ' '" er. nspeclOn 0 t e weat er d.ata from Al Ain station suggests that only deciduous species with very Forage Crops The main forage grass grown in the most saline areas is Rhodes Grass (Chloris gayana). low chillrng reqUIrements will be adequate. The crops most likely to be grown include: Trials involve variety evaluations, fertilizer rates and vegetation management. The Australian * CItruS cultivar, Pioneer, is the most commonly grown cultivar in the region. This cultivar has been shown * Guava as the most productive salt-tolerant forage on saline lands in the sub-tropical environment of * Mango Queensland, Australia. In the UAB, there are extensive areas of Rhodes grass being grown on "The * Pomegranate State Forage Farms in Abu Dhabi" using irrigation water at salinities ranging from 4,000 ppm to * Deciduous trees with low chilling requirements over 10,000 ppm. * Grapes In these areas, production of Rhodes grass involves cutting every two months or so and Deciduous species (pistachio, peach, apple, apricot almond pear and cherry) * illw ' , then top dressing with a combined IS: 18: 18 compound fertilizer. Stands can last up to six or seven * years but in high salinity situations (around 8,000 ppm or more) stands are renewed every four years. At Al-Sale and Al-Chasm areas, 15 cm of sand from the surrounding desert is carted in to Vegetables: The range of species which are possible under saline conditions include: top dress the paddocks which have accumulated salts. * Tomato In the areas with lower salinity of irrigation water, alfalfa (A1edico sativa) is also grown. * Eggplant Research on irrigation and cutting intervals is being undertaken in the northern agricultural region * Cabbage and cauliflower at the Al Hamraniyah Research Station. There is also a research program with irrigation of A triplex * Cucurbits of various kinds species. * Onion Two experiments are underway involving native grasses. These are production studies on * Okra local grasses Esman, Panicum turgidum and Sabat Cenchrus ciliaris and yield comparison of two * Various melons local grasses identified as "Alaf Al Fil" and "Mosiblo". Efforts to improv~ yield capability under salinity stress within the moderate salinity range can. be expected to be fruItful for some of these species. Gains in water use efficiency could also be Field Crops achieved rn the lower salinity range. The UAB field crop experimental program is based in the Northern region and involves As the salinity of ~e soil and! or irrigation water increases to the point where reclamation wheat, barley and sorghum, consisting of: for conve~tlOnal cropprng IS no longer feasible, the only prospect is to remove the involved fields Wheat and Barley: A number of introduced cultivars of wheat and barley are being assessed for from ~ultlvatlOn. If. suitabl~ halophytic crops were available to replace the relatively salt-tolerant their productivity under irrigation at different sowing dates. crops rn such SItuatIOns, this would extend the time, may be indefinitely, for continued uses of that • Millet and Sorghum: Introduction studies on a small number of cultivars of these two crops. land as long as the soil conditions still pennit the use of the brackish water. The department of Agriculture in Al Ain has 2,000 ha field of irrigated cereal crops in Abu Dhabi on two State Cereal Farms. One is using low salinity irrigation water of 1,000 ppm and Areas that Need to be Pursued Further the other uses moderate to high salinity water of 4,000 to 5,000 ppm. Grain production on the low salinity site is 4 to 5 tones per hectare, but only half of this yield is obtained on the high Atriplex as a fodder salinity site. Atri?lex species are. distribute~ in many coastal and inland desert regions of the world, and Other agronomic species: Forage legumes: both annual and perennial species including: occupy a WIde range o~ saline to alkalrne habitats. The forage value of these herbaceous to woody Trifolium spp such as alexandrinum, balansa, vesiculosum, resupinatum and fragiferum spp. flan~s has been. re~ogmzed for years as ~any of the perennial shrubs are important grazing species • Grass Species: Puccinellia, Festuca, Agropyron and Okoeleria sp. n and an? seIDl-and ran~eland COlllI::J.Urntles. Atriplex could be an alternative forage source in areas where salrne water supphes are relatively abundant for irrigation. Horticultural Crops S~me experiments aimed at evaluating Atriplex as forage crops under irrigation are Most horticultural crops are technically classified as having low salinity tolerances (below currently rn progress at the AL Hamraniya Research Station in the UAB. 2,000 ppm). However, the salinity limits should be taken more as guides than as absolutely fixed standards. This is because the level of management of soil moisture and rootzone salinity can have a . Halophytes as grain or oil seed crops very great influence on the response of the plants to any water salinity level. In addition, the . A particularly pro~sing halophyte is the oilseed crop Salicomia bigelovii Torr. which chemical composition of the water is important. For example sulphate-rich waters will be less Yields up to ISt/ha of dry bIOmass under sea water irrigation in the United Arab Emirates. The oil hazardous than chloride-rich waters. Woody (fruit tree) species are sensitive to both chloride and seeds are used for production of edible oil and the crop residue can be used as forage for livestock. boron.

123 124 Halophytes asfuel crops Salinity Problem in The Soil and Water of Bahrain The possibility of using halophytes, such as mangroves, for fuel crops has been suggested and in fact, mangroves have been used as a source of charcoal. There are other woody halophytes Ali Ahmed Nasir that might also be considered and that might be more feasible for use under a wider range of Agricultural Projects Management environmental and soil conditions. Ministry of Labor and Agriculture, Bahrain

Multiple Use of Irrigation Water The land of Bahrain is arid and the annual precipitation does not exceed 73 There IS an increasing interest in the multiple use of irrigation water as a way of increasing rnn;t. The temperature ranges between 35° and 45°C in su=er and 8-20° in winter. efficiency of water use. This involves irrigating a crop, then using the drain water, or irrigation This has led to the accumulation of salts in the soil and to scarcity of natural return water to irrigate asecond crop and possibly more, before discarding the water. The intent is vegetatIon. to minimize the amount of waste water from irrigation use, and the ultimate goal would be to The soil of t~e surface layer is Sandy-loam in texture and ranges from loamy­ return none to the source. To fully realize these objectives, it requires a series of crops with sand. to sandy-!oam III the lower strata. It is generally light with low water and nutrient increasing salinity tolerance. hold~g c~paclty. The water table is high and ranges between 0.5 and 3m depth espeCIally III the coastal regions. THE POTENTIAL OF SEAWATER IN IRRIGATION The production capacity of the land is as follows: On the basis of long term field trials it appears that some species of halophytes irrigated Snitability with sea water produce yields of biomass and seed equivalent to high yielding agronomic crops. area ilia) % of total areas A major problem with using sea water for irrigation is the amount that must be used Good 1055 1.78 Medium compared with fresh water irrigation. The optimum salinity for the growth of even the most 350 0.58 Medium(subject to salinity) 3100 tolerant halophytes is 1/3 the level of the salts in sea water and the relative growth rates of 5.22 Medium to low 6250 10.51 halophytes growing on full strength sea water is typically 30-50% of the maximum growth rates Low 17540 29.53 achieved on lower salinities. A second major constraint to halophyte farming is the need to adapt Not snitable for Agriculture 22473 37.83 conventional agronomic practices to the new crops. Other USes 9634 14.54 One of the most likely uses for halophyte is as a forage or folder crop. The most productive halophytes yield the equivalent of 8-17 t of dry matter per 00. This compares well with a . The soil fertility is low in general, nd the organic matter is less than 1% because conventional forage crop such as alfalfa, which yields 5-20 t of dry matter per ha annually. when of ~hmatic conditions which enhance its oxidation. Dissolved N is I-Sppm and the irrigated with fresh water. av~lable P rang~s betw~en ~-SOppm. However, the soils contain 100 to 200ppm of Even though Atriplex can tolerate soil salinities and levels of trace elements significantly available K and IS poor III IDIcro elements. The Soil EC averages 8 dS/m in irrigated higher than those suitable for irrigated field crops, the long term effect of continuous irrigation with areas. saline water on the productivity and forage quality would need to be determined. The salinity of the irrigation water ranges between 2500 to 6000ppm with NaCl The soil/water management practices to provide adequate drainage and other soil related as the most abundant salt. aspects are critical factors in using saline water for irrigating halophytes. Establishing salt tolerance . Al~ough agriculture is practiced on a small scale in Bahrain, it faces a number data for the difference species and developing guidelines for irrigation, drainage and cultural of difficultIes, mostly related to water. Although the irrigated land does not exceed management practices are required before introducing Atriplex or other halophytes to irrigated 3500 ~a, It uses about 142 million cubic meters, with low efficiency. This is causing the farming on a larger scale. ~ depletIOn of the water resources. Although there are exceptions, salt tolerance of most halophytic plants at germination does Ninety percent of the water used is underground water, 9% originates from not appear to be any higher than that of conventional crops, thus requiring careful management for treated waste water and. 1.% fro~ ~he drainage of agricultural land. Surface irrigation establishment. Under ordinary leaching fractions (less than 0.25) irrigated production of halophytic and the lack of water pnclllg poliCIes have resulted in a water use of 220 MCM which fodder plants appear to be optimum at irrigation water salinity ofless than 13-15 dS/m. ~ore than twice of the annual recharge of groundwater. The water salinity has Other management strategies, such as growing halophytic plants in strips with limited Illcreased also from 2000 to 3000ppm in many places. irrigation, can utilize saline water from the shallow water table and can remove dissolved salts at a . . The government has already initiated desalinisation projects for potable and rate of 5 to 10t/ha/yr. The projected costs of sea water farms are similar to conventional irrigated muruclpal. water .use. It has alS? built an intensive drainage system in all the cropped farms. But high rates of return per unit of land area are needed to repay the capital and operating land. BeSIdes, pilot water projects for water preservation and treatment have been expenses of irrigated agriCUlture. Continued searching and screening are necessary to find the best already executed. possible candidates for use as crop plants, but the major limitations are soil-related problems. There is need for much research before halophytes occupy a significant role in irrigated agriculture. Some scientists believe that it is inevitable that they will. It is important though that such a role is neither prematurely expected nor promised.

125 126 Salt-Affected Soils in Qatar Soil Resources in the UAB

Ghanem A. Al- Ghanem Ahmed Al Barshamgi Ministry of Municipal Affairs and Agriculture, Qatar Central Lab., Al-Ain, Ministry of Agriculture and Fisheries, U AE The land of Qatar is classified as arid. The precipitation is minimal, 20- 160rnrn/year, whereas the evaporation rate in open water bodies is 2,191 to 2,526= The land suitable for agriculture in the UAE covers 50,000-60,000 ha and the per year. Tlie high content of soluble salts in the cropped ~o~s ~d the abu~dance ?f pasture areas cover 300,000 ha, of which 35,000 ha have already been forested. gypsum and other Ca compounds in hard strata add to the llIDltatlOns of agnculture ill Mountains constitute nearly 34% of the total area, 53% is a sandy desert, saline Qatar. plains are about 10% and flat plains constitute 13 % of the total area. This is where agricultural land is found. This land includes: Batiniia fertile plain, Jiri, Thaid, Gharif Trees and grasses are found in "oasis", valleys and plains. Some of these plant and Madam. varieties are salt-tolerant. The agricultural land is scattered all over the country, where The climate is semi arid to arid with temperature differences between day and vegetables and fruits are cropped. night are wide. Precipitation is about 110rnrn/year and humidity is usually high in the su=er. Following is a =ary of the land distribution in Qatar: The only natural water resource is the ground water, the salinity of which • Gardens CAl Roudat) lands :this makes up about 2.44% of the total area. The soil is ranges between 400 and 3500ppm. formed from recent sedimentation eroded from the nearby, elevated land. The average soil depth is 30-180cm. It includes 90% of the farm land and found mainly The main chemical soil properties in the UAE are: in the middle and north parts of the country. • pH: the soil is alkaline with pH varies between 7.5 and 8.5. This leads to poor • Sandy land is about 3.17% of the total area. It includes about 10% of the farming availability of soil nutrients such as P, Zn, and Fe. land and is found mainly in the south of the country. • CaC03 : the carbonate content is very high (35-40%) and could reach up to 90% in • Subkhat (salt flats): about 6% of the land, highly saline and found on the coastal some areas (Jad). Consequently, fertilization problems arise such as the fixation of region. The use of this land is very limited due to high reclamation costs. P and micro elements. Surface cracking also takes place and therefore short interval • Rocky areas occupying about 80% of the total area and is unsuitable for agricultural irrigation is reco=ended. High Ca++ concentration can also prevent K+ from reaching the soil exchange sites. use. • Soil organic matter content is very low (less than 1%) due to the high temperature Some of the irrigated land has been affected by salinity. Water varies in quality and rapid decomposition. and its salinity ranges from 1500 to 5000ppm. This water may not be suitable for • CEC is low also and ranges between 6-13 m.eg/lOOgr of soil. irrigating all kinds of crops. • Soil texture: sand is dominant over silt and clay. Soils in some places lack silt completely and the major element is coarse sand. The saline soils in Qatar can be divided into two groups: • Salinity in irrigation water varies according to regions.

1. Soils in which salinity is caused by irrigation, which exist in: Regions with high water salinity are usually those affected by the sea, while o low to medium saline soil found in the middle of the country, far from the inland soils have low salinity. coastal regions with soil EC ranges between 0.4 to 16 dS/m. • Salinization is induced by the use ofland for irrigated crop production in places o medium to high saline soil found close to the coast with soil. EC between 8 where water is saline. High temperature, the lack of drainage, the high water table and and 16 dS/m. Reclamation is possible. high alkalinity can intensify the problem. Highly alkaline soils cover the largest part of the UAE. This is due to the high 2. Soils in which salinity is due to sea water. They cover 7% of the land, and are exchangeable N a whereas saline-alkaline soil existence is minimal. extremely expensive to reclaim, for it would take a huge quan~ty of fresh water for Saline soil management in arid and irrigated semi-arid land is complicated and leaching, as well as requiring a drainage system. requires advanced techniques. Therefore, preventive methods are the best solutions.

127 128 • Leaching was the most successful and popular method. The main issue is to The Use of Salt-Affected Soils and Saline Water determine the quantity of water needed to get rid of salts and reach optimal in Agriculture in the UAB conditions. The major problem in arid regions is therefore the water-salt balance in the root zone. Rashid Al-Mehrizi Central Lab. Al-All. UAB The Ministry of Agriculture and Fisheries has shown great enthusiasm and Salt accumulates naturally in soil formed from mineral rocks having a high salt already executed several projects in order to back up farmers, through: . content. Hov.:ever it increases in soil due to other factors such as: • Providing adequate quantities of water by building darns, reservoirs, by diverting • Using irrigation water with considerable salt content, salt is liable to' accumulation if the water of the plains and by improving the ground water reserves and their the drainage system is inefficient and if the quantity of water applied is not sufficient qUality. This is in addition to testing the irrigation water, providing guidance on the for leaching. introducing of salt tolerant plants and insisting on the use of modem irrigation • High water table causing poor drainage and capillary rise of water loaded with salt techniques. that stays on the soil surface when water evaporates. • Providing farmers with fertilisers and instructions on their use. • Instructing farmers on how to preserve the top soil by building wind breaks and by • The high content of C03 and HCOl in water leads to increase in soil alkalinity as they bind/precipitate Ca and Mg and consequently increasing the ESP. planting forage crops to prevent soil erosion. The quality of water is affected by the presence of micro elements such as • Land surveying and soil testing to prepare complete reports according to which boron which can be toxic to plants at high concentration. reclamation plans are set. • Working on plans to combat desertification by: The Effect of Soil and Water Salinity on Plants: o proper social, economical and environmental planning to develop water resources, Soil and water salinization cause poor seed germination, root tissue decay and o improving irrigation and drainage systems and executing new projects. the death of most plant species. This is due to the following reasons: o improving cropping systems to keep up the high productivity. .. An increase in osmotic pressure of the soil solution and consequently the plants fail o applying a complete program to develop the social and economical conditions of to absorb water. the farmers. .. The specific damage caused by the increase in Na+ and cr ions. .. Working on controlling salinisation by advising farmers to monitor their farmland .. The imbalance in nutritional elements in the soil solution and the appearance of and to report any problem. The ministry sends experts to analyse problems on the spot, take samples and carry out lab tests and provide the necessary advice. The deficiencies. ministry also encourages the protected farming for production of vegetables from .. The changes caused by these salts in the soil physical and chemical properties. fully-controlled greenhouses. Sandy and calcareous soils are very co=on in the UAE. These soils are poorly developed, have very little nutritive elements, high pH, and high Ca and gypsum content which affect the availability of P and other elements. Humus content is low and so is the cation exchange capacity which affect the soil capability to hold nutrients. In addition, the existence of impermeable layers or shallow top soil limits the root growth. •

The expansion policy in land reclamation which took place in the last decade was an unavoidable and very necessary step that increased the productivity of the country on more scientific and modem basis. If this policy continues, it will only be a land expansion to previously cropped land with all its problems. Several reclamation methods were appUed in the past: • Biological: where plants were used to absorb salts from the soil. However, it proved to be a very slow process which requires many years. • Mechanical treatment was applied in several places and gave good results, for it was used when salt crusts were found on the surface only and the rest of the soil was salt-free. • Surface leaching was applied but proved to be inefficient.

129 130 Salt-Affected Soils in Saudi Arabia Salt-Affected Soils in Kuwait

Ahmed Suleiman Al-Shareef Samir Al-Ghawas Technical Director, NAWRC Associate Research Scientist Riyadh, Saudi Arabia KISR, Kuwait

The arable land in Saudi Arabia is about 28 million ha, however, the planted area is only 0.5 million ha. Saudi Arabia falls within the arid to semi-arid region, as the annual precipitation is less than evaporation. Hence, all land used for agriculture is . The land of Kuwait is classified as arid because of high average temperature irrigated, with sprinkler irrigation as the most co=on method. The water quality and and high evaporatIOn rates compared with little precipitation of 115mmJyear. This has quantity differs according to locations. Salinity ranges between 200 ppm and 9000 led to continuous increase in salinity. The soils are generally sandy, poor in organic ppm. Ca+" Na+, Mg++ are the most co=on cations found in water, in addition to S04- matter, calcareous and comparatively saline. - and cr anions. Soils in Saudi Arabia are generally described as calcareous, light textured, of low water holding capacity, low humus content and a low CEC with a pH In 1969, FAO classified the soils of Kuwait into 4 groups: between 7.5 and 8.5. It requires a lot of fertilization as it is generally poor in nutrients. The arable land is divided into five classes according to the standards of the • Desert soils: covers 3/4 of the land, with a very low water holding capacity and American Land Reclamation Board. The first class is expected to give an excellent generally saline. economical return, can be planted with a variety of crops and has no production • Desert-Regos'ol Intergrades: about 14% of the total area. Slightly saline with low limiting factors. Only a few small and scattered land patches of class I exist in the water holding capacity and used for irrigated agriculture when water is available. country. The fifth class is unsuitable for irrigated agriculture. The second and third However salinity rate is increasing due to water shortages or mismanagement. classes combined make up the biggest irrigated area in Saudi Arabia, whereas the • Lithosol: On very slopy land, 1% of the total area. fourth and the fifth class constitute the pasture land. The water available for irrigation, • Alluvial Soils: formed from marine sedimentation on the coastal regions. These mainly underground is limited and should therefore be very well-managed in order to constitute about 7% of the total area, mostly in the North of Kuwait. Variable prevent salt accumulation and soil degradation, as well as water resources depletion. texture which could be sandy or clayey with high salt accumulation accompanied by The factors that influence soil salinity relate to both water quantity and quality. poor drainage and a high water table. Salinity increases when saline water is used for irrigation and when water for leaching is unavailable, when impermeable layers cause waterlogging and when improper types It is clear that salinity is a real problem in Kuwait, however the causes differ and quantities of fertilizers are used. Considering the climatic, soil and water from one place to the other. In some regions, the reason is geological or morphological conditions mentioned above, management appears to be the "axis" around which all an? in others it is the result of agricultural practices and the lack of good quality factors leading to ideal crop production rotates. Unfortunately, the agricultural rrngatIon water. expansion in Saudi Arabia was not accompanied by sufficient studies to evaluate the changes in soil salinity. Recent attempts have been made to evaluate the economics of land reclamation The following reco=ended practices resulted from a recent study on the and the use of halophytes in agriculture, as well as the use of treated waste water for relationship between irrigation system, fertilization and soil salinization: irrigation. • Developing land according to water availability to prevent land degradation, • Farms should keep updated dala on salt accumulation, • The necessity of relating optimal water requirements to fertilizer balance, • The importance of applying a balanced agriculture system, where crop rotation is practised and mono cultures are abandoned. There is a possibility of solving soil salinity problem according to one of the following management systems: • The Traditional Manag'ement system based on the classical reclamation of irrigated land by drainage, leaching and the usage oflow salt content organic fertilizers, • The Integrated Management system where the traditional system is integrated into the technical management by using remote sensing data. For instance, several experiments have shown that the usage of sprinklers result in uneven water distribution followed by yield reduction in the insufficiently irrigated spots, and washing down and depletion of fertilizers exist in the over-irrigated areas. Water logging, where impermeable soil layers exist, is also a problem. Remote sensing could detect this problem and assist in finding solutions and optimize land use.

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