Salt-affected soils exist under a wide range of hydrological, physiographical conditions, soil types, rainfall and irrigation regimes and different socio-economic settings. Therefore, there is no single technique or agricultural system that will be applicable to all areas and conditions.

Management of salt-affected soils requires a combination of agronomic and management practices, depending on careful definition of the main production constraints and requirements based on a detailed, comprehensive investigation of soil characteristics, water monitoring (rainfall, irrigation water and watertable), and a survey of local conditions including climate, crops, economic, social, political and cultural environment and existing farming systems. Management of salt-affected lands for agricultural use is largely dependent on the water availability, climatic conditions, crop standing and the availability of resources (capital, inputs and time)

Several practices should be combined into an integrated system that functions satisfactorily for different production constraints and soil types to give higher economic benefit on a sustainable basis. Summaries of the hydraulic, physical, chemical, biological and human aspects to improve productivity of salt-affected land are discussed below. The mentioned management technologies are only those practised within the FAO collaborative projects with the national institutes participating in the Network.

Drainage
When underlying layers are permeable and relief is adequate, natural drainage may function well. Since such conditions are rare in areas where saline and sodic soils occur, a drainage system will usually be required. Various types of drainage are used all over the world: surface drainage in which ditches are provided so that excess water will runoff before it enters the soil; subsurface drainage for the control of the ground water table at a specified safe depth, consisting of open ditches or tile drains or perforated plastic pipes; mole drainage where shallow channels left by a bullet shaped device pulled through the soil can act as a supplementary drainage system connected to the main drainage system (open or closed); and vertical drainage by pumping out excess water from tubewells when the deep horizons have an adequate hydraulic conductivity. The depth and spacings of the drainage system should be based on soil type (soil permeability, the existence of hardpans, or impermeable layer, etc.) and the local economic consideration.

Several mechanical methods have been used to improve infiltration and permeability in the surface and root zone and thus to control saline and sodic conditions, including land levelling, deep ploughing and tillage, subsoiling and planting procedures.

Land levelling to achieve a more uniform application of water for better leaching and salinity control.

Tillage for seedbed preparation and soil permeability improvement.

Deep ploughing is most beneficial on stratified soils having an impermeable layer. It loosens the soil aggregates, improves the physical condition of this layer and increases air space and hydraulic conductivity.

Planting procedures Special planting procedures that minimize salt accumulation around the seed such as planting on sloping beds or raised furrows in single or double rows are helpful in getting better stands under saline conditions.

These include using chemical amendments and mineral fertilizer. Using chemical amendments neutralizes sodic soil conditions (exchangeable Na and any Na carbonate), followed by leaching for removal of salts derived from the reaction of the amendments with sodic soils. Gypsum, sulphur and sulphuric acid are commonly used. Since the benefits expected from reclamation of salt-affected soils would not be obtained unless adequate plant nutrients are supplied as fertilizer, the proper types and balanced amounts of mineral fertilizers should be used.

The biological practices include using organic matter, farm manure, growing legumes, mulching, crop residue and selection of salt-tolerant crops:

Organic manure incorporated in the soil. This has two principal beneficial effects on saline and sodic soils: improvement of soil permeability and release of carbon dioxide and certain organic acids during composition. It also acts as a source of nutrients.

Mulching to reduce evaporation losses and thus decrease or prevent soil salinization.

Crop residue application. This is one of the easiest methods to improve water infiltration, especially for small farmers who do not have the resources to implement more costly corrective measures.

Salt-tolerant crops. Judicious selection of crops that can produce satisfactorily under moderately saline or sodic conditions has merit in some cases. Barley, wheat, sugar beet, millet, rice, salt-tolerant forage and grasses for animal production are examples.

Farmers should become active participants in the development of appropriate management systems and should become the main originators of technical solutions to their environmental problems. Any management option considered available should be field-tested under farmers' conditions and acceptance of newly developed technologies ascertained.

Management of salt-affected soils requires a combination of agronomic and management practices depending on a careful definition of the main production constraints and requirements. Therefore, the integrated management approach, as a package of the required management techniques should be always implemented.

Management and Rehabilitation Technologies practised in Participatig Countries

Countries with FAO Collaborative Projects

Africa 

Ghana: The Accra-Ho-Keta Plains have diverse agricultural practices as a result of the different soils types. Large-scale irrigation project are located at Dawhenya, Weija, Ashaiman, Akuse and Okyereko producing mainly rice and vegetables. Large scale commercial production of pineapple for export is practised on salt-free soils west of Accra. Cassava, maize, sweet potatoes and curcubits production is confined to well drained non-saline upland soils.

Two major breakthrough or successes in the use of salt-affected soils in the Plains are recorded. These have been the large-scale production of vegetables on the sodium saturated soils of Agawtaw series. The second has been the large-scale production of shallots on beach sands. In both cases the salt contents are flushed out with fresh water and plots fertilized.

• Large tracts of land of sparse grass vegetation with salt-affected soils especially Agawtaw series are being used. Beds are raised about 30 cm high and watered regularly with fresh water to flush out the salts. Seedlings are then transplanted on to the beds. Organic matter especially poultry manure and cowdung is applied before the transplanting of the seedlings. The beds are heavily mulched. Minor quantities of inorganic fertilizers especially 15:15:15 may be applied. The vegetables produced are mainly peppers, onions, cabbages, lettuce, cauliflower, okro and watermelons. Maize and cassava may be produced on old beds.
• Large-scale commercial production of shallots (Allium aecalonicum) has long being the main agricultural activity of the communities of the Keta District of Volta Region. The sandy soils are flushed with fresh water regularly to remove the salts. Long and wide beds are made about 50 cm high and watered almost daily with fresh water from shallow wells dug in between the beds. The sandy soils are fertilized with organic manures from bat droppings, cowdung, poultry manure and small fishes (onchoris). These are used in combination with low rates of inorganic fertilizers, mostly urea and 15:15:15. Halfway through the growing period of three months, the crop may be intersown with garden eggs, tomatoes, pepper and maize which benefit from the residual effects of the applied manure.

Kenya: Although there some attempts directed toward reclamation and increasing productivity of salt-affected soils through drainage systems, the available information is still insufficient to recommend appropriate integrated management techniques. Leaching soils to remove soluble salts is the most effective method known to reclaim these soils. In Kenya about 75 percent of the agriculture lands receives less than 500 mm of rainfall annually, coupled with potential evapotranspiration rate at least 1500 mm. Therefore, salinity problems cannot be solved by rainfall leaching. As such, application of irrigation water is the only possible method of leaching excessive salts. This requires good irrigation water and good permeability of the soils. Leaching in some cases might cause permeability to decrease and pH to increase particularly in saline-sodic soils as the soil changes to sodic soil.

Special planting procedures are used in management of salt-affected soils to minimize accumulation of the salts around the seed and the rootzone. Use of organic manure resulted in improvement of soil permeability and act as source of nutrients. Improvement of salt-affected soils in Kenya through installation of drainage systems have proved to be an expensive venture due to cost involved. Also, maintenance of these drainage canals requires a lot of effort and unless there is good coordination between the farmers, the probability of their failure to operate is very high.

Nigeria: Management of salt-affected soils in Nigeria concentrates on leaching and planting procedures for increasing productivity. Farmers also use organic manures as available.

Tanzania: Reclamation of salt-affected soils in Tanzania is an area, which has not received adequate attention. Commercial crop estates have conducted most reclamation efforts perhaps due to the economic loss they suffer under such soils. In areas where saline soils were forming due to improper drainage like the sugar estates, adequate drainage has reclaimed most of the soils with considerable success. For the sodic and saline sodic soils, efforts in utilizing chemical amendments for their reclamation have been hampered by the high costs of such amendments. Despite the fact that Tanzania has an abundant local gypsum resource at Makanya in Kilimanjaro region, its use has been confined to the manufacturing of cement. Similarly pyrite is available in Geita close to Lake Victoria but it has so far not been mined.

In a sugarcane plantation, just outside Moshi town in northern Tanzania, use of the locally available gypsum (Makanya gypsum) and various combinations with sugarcane filtermud, lime, sulfur and magnesium carbonate were used at small-scale and gave high yield of sugarcane growing under sodic conditions. In practice however, many chemical amendments like gypsum, sulfuric acid, and iron pyrite have been used for reclamation of sodic soils with good results. The choice of chemical amendment to be used for sodic soil reclamation depends on many factors like, the type of soil, the time available for reclamation, the amount of water available for leaching, adequate soil drainage, the extent of reclamation, economic considerations, etc. The primary disadvantage is high cost involved in using these amendments.

Gypsum and pyrites were used more effectively when combined with organic materials like farmyard manure, green manure, compost etc. Green manuring of sodic soil with Sesbania aculeta and Leptochloa fusca resulted in reduced sodicity in an experimental farm.

There are adequate amounts and types of organic materials in Tanzania that can be tested in combination with the gypsum and the pyrite provided there is motivation to do so.

Establishment of alternative salt-tolerant crops in the affected soils is an area which if pursued may hold a lot of potential in Tanzania. Literature is rich with a variety of crops which grow on salt-affected soils. Most of these crops are not found in Tanzania. It would be interesting to introduce some of these crops in Tanzania and monitor their performance as well as educate the general population in their potential in providing food, fodder, timber and fruits.

Bangladesh: Increasing agricultural productivity of the coastal saline soils has been one of the major national agricultural development concerns in Bangladesh. Since salinity is the main productivity constraint in the coastal zone, the Government, through the Bangladesh Water Development Board, started construction of coastal embankments in the mid-1970s to prevent the intrusion of saline waters into agricultural lands. Until now, 3 700 km of embankments with 900 sluice gates have been constructed at different points of the coastal zone. This project has been partially successful in reducing soil salinity in areas within the embankments. However, thousands of ha of land still remain saline.

• The development of salt-tolerant rice varieties has been one of the major research thrusts of the Bangladesh Rice Research Institute (BRRI) during the last few years and two varieties, BRRI Dhan 40 and BRRI Dhan 41, have been very recently released for growing in the coastal region during the wet season. These varieties have the potential of giving about 2.0 ton/ha higher yield than the local traditionally cultivated varieties under moderately saline conditions (soil EC_e around 6 dS/m) in the wet season. The Bangladesh Agricultural Research Institute (BARI) is working on several profitable cropping patterns for the different areas.
• There are also a few HYV rices developed earlier by BRRI which have shown tolerance of moderate soil salinity although these were not bred for salt tolerance. These varieties, BR22, BR23 and BRRI Dhan 32, are grown by some farmers in moderate saline areas in the wet season.
• There are some non-rice crops which have quite a good degree of salt tolerance. These crops are grown in the Rabi season, especially in the eastern coastal region (Chittagong-Noakhali -Feni region) taking advantage of the residual soil moisture and relatively low soil salinity following T. Aman rice (main crop). The Rabi crops could be vegetables like sugar beet, spinach, chili, grass pea, mustard, sesame etc. In fact, although at a slow pace, the farmers are trying to increase the cropping intensity.
• Farmers use fertilizer doses as advised by the local extension workers who, in turn, recommend the doses from the National Fertilizer Guide Book. There is, however, a great scope of improving crop performance using site-specific soil test based fertilizer doses as observed by BRRI researchers. However, integrated nutrient management packages for the different coastal locations have not yet been developed. Research in this field is urgently needed.

China: Main solutions and technologies applied in China for combating salinization and for using salt-affected soils include:

1. Construction of drainage-irrigation systems: In saline areas complete and rational drainage-irrigation systems are essential in improving water-salt regime, controlling water-salt movement in soil, preventing volume accumulation of salts in the surface soils and accelerating steady desalinization of the soil.
2. Drainage and rice-planting: Drainage and rice planting is one of the traditional practices of ameliorating and utilizing saline land. This practice usually does not need special leaching. The land thus becomes suitable for paddy-upland rotation. Research results show that in coastal areas, 3-5 years of drainage-and-rice-planting lowered the salt content of the groundwater to 1-3g/L, increased the thickness of the fresh water layer to 1.5 m or more and reduced soil salt content to 0.1 percent or so. In sodic soils, application of organic manure and chemical amendments such as gypsum, phosphogypsum, etc., helped to achieve better results.
3. Combination of wells, ditches and canals and comprehensive amelioration of saline land: According to China's experience over the last 2 decades, in saline areas, developing pump wells (20-60 m deep) to make use of groundwater resources for irrigation and setting up irrigation-drainage engineering systems with various forms of combinations of wells-ditches-and-canals have contributed greatly to the management of soil salinization. For example Renming Shengli (People's victory) Canal Irrigation Region, using water diverted from the Huanghe River, in Henan Province, China. The construction of the combination of well-canal irrigation got underway in 1964.
4. Addition of organic manure to improve soil fertility: Organic matter available for use includes crop stems and straws, green manure, barnyard manure, compost, etc. Growing of green manure is promoted in light of the local conditions. Besides growing green manure solely in the field, rotation, inter-planting and intercropping of grain crops or cotton with green manure of different varieties can also be adopted to expand green manure sources, which can ameliorate soil, improve soil fertility and inhibit salt accumulation.
5. Application of techniques of water saving agriculture: In practice, application of low-quota irrigation, pipe-transferring of irrigation water and other integrated water-saving agricultural measures have successfully increased efficiency of water resources with selection and planting of water-saving crops.
6. Regulation of regional water resources: Clearing drainage ditch and canal, improving regional river water system are helpful in enhancing drainage capacity. Rational planning and construction of drainage water pumping /irrigation station, increasing pumping capacity has shown good results.
7. Proper management of brackish water irrigation: Irrigation with saline water shows some successful experience. Main approaches include a) direct irrigation with brackish water during certain crop growth stages; b) alternative irrigation with fresh water and brackish water; c) mixed irrigation with fresh water and brackish water. In some area with large saline groundwater, improving groundwater quality by pumping saline groundwater and replacing it with fresh water is a good way. Results of experiments and extension of such approach in Hebei province show significant increased in area of non-saline groundwater.
8. Integrated biological-agronomic management. In the coastal area of China, development of aquaculture by setting large scale fresh fish pond or shrimp pond is a good practice on use of coastal salt-affected land, and is also practical on leaching salt and desalting water bodies (including groundwater). Such kind of so-called "step-up utilization" strategy is successful in Jiangsu and Zhejiang. Building up of coastal forestry band is also a good way to improve agro-ecological condition in salt-affected regions. Other agronomic management measures, such as soil surface covering with plastic films or crop straw, can also effectively prevent strong soil evaporation and salt surface accumulation. Crop yield could be greatly increased by such simple means applied in wheat and cotton planting.
9. Introducing and application of salt-tolerant crops. Selecting various salt-tolerant varieties of crops to fit different saline ecological environments and tapping the inherent tolerance of the varieties are important measures to improve the efficiency of the reclamation, amelioration and utilization of salt-affected soils.

Indonesia: The reclamation of swamp land for agriculture is usually carried out by constructing drainage canals. Basically three system are used in Indonesia: a traditional system, well known as "parit kongsi" in Riau or "handi" in south Kalimantan; a fork system designed by the University of Gajah Mada and a perpendicular drainage system, practised in south Sumatera. Modification of the specifications and a combination of the last two systems have been carried out in several places. Primary drainage canals are directed to the sea with flapgates, that prevent the entrance of seawater and direct the drain water out of the scheme.

Overdraining made the pyrites oxidize in acid sulphate soils, because the groundwater fell down below the pyritic layer. In the wet season of 1994/1995, the seedlings in the nurseries died, especially those in the lower part of the area. The groundwater brought up all toxic substances produced by the oxidation process of pyrites. Water surface should be kept high enough in the drainage canals by constructing overflow dams at the mouth of secondary and even of primary canals. An intensive shallow drainage system is recommended for these acid sulphate soils. The spacing of the shallow drains is 6 to 9 m depending on the intensity of the salinity or acidity problems. A rice-fish system is usually recommended in the system.

A polder system was also used to control the water and its salinity in order to develop the Pulau Nyiur, Riau Island to extend and intensify rice and "palawiji", especially maize and soyabean. Rain water is kept as much as possible inside the polder by closing all outflows from the island through constructing dykes along the coast and overflow structures at the mouth of every creek and canal. There are separate canals for irrigation and for drainage. To run the system, pumps are required, either to irrigate or to drain.

Good management of salt-affected soils should include the application of high amounts of N, P and K fertilizers and strict control.

In Indramayu, farmers make beds 1.2-1.6 m wide and about 0.5 m apart separated by furrows of 0.5- 0.6 m depth. The furrows are filled with about 0.15- 0.20 m depth water so that the top soil of the bed will not become saline. The same system is practised by farmers at Sei Kakap. They plant sweet potato on dykes 1.5-2.0 m apart. Farmers also plant horticultural crops on the dykes. Before planting the rice all dykes are dug, levelled and all weeds and plant residues are buried. Farmers are planting the rice without harrowing or puddling the soil.

Pakistan: Approaches tried in Pakistan to control and arrest the problems are: (a) commissioning of Government-sponsored large salinity control and reclamation projects (drainage projects over about 8 million ha); (b) leaching of salts by applying increased irrigation water and chemical amendments, organic wastes and plants (small local level interventions); and (c) promoting saline agriculture bioreclamation techniques using tolerant crops, bushes and trees, and fodder grasses. The sustainability of the first approach used since the early 1960s is becoming highly questionable

The Philippines: The application of the Balanced Fertilization Strategy (BFS) includes seven formulae of mixed organic and inorganic fertilizers to provide the required nutrients for specific areas affected by nutrient deficiencies and soil salinity. The BFS emphasizes the need to recycle crop residues and farm wastes along with a balanced combination of organic and inorganic fertilizers. For saline soils, the recommended BFS is NPK rates at 95-20-15, in addition to 5 kg zinc sulfate, five bags of commercial organic fertilizer and one bag of chemical ameliorant. Studies reveal positive results on the use of this technology.

In 1997, PhilRice, in collaboration with the Bicol Integrated Agricultural Research Center, officially released by the Philippine Seed Board two salt-tolerant varieties (PSBRC 48 and PSBRC 50) which were jointly developed. However, these varieties were not widely adopted by the rice-growing farmers in salt-affected coastal soils. Up to 1998, IRRI has screened more than 55 000 rice varieties and breeding lines for salinity tolerance. Tolerance donors have been used successfully as parents in hybridization activities at IRRI and within national programmes.

Thailand: The preventive method is being practised on both inland and coastal salt-affected areas. In inland areas, biological measures are being used to prevent soil salinization caused by saline groundwater interaction. Certain salt-tolerant plant species including Acacia ampliceps and, Azadirachta indica, are used to lower the groundwater level through water consumption. In the coastal areas, dykes or bunds are constructed to prevent salinization by seawater intrusion.

Concerning improvement and reclamation of salt-affected soils in slightly saline and moderately saline soils, planting of green manure crops such as Sesbania rostrata, cultivation of salt-tolerant varieties and addition of organic matter are recommended methods to improve saline soil conditions and to increase yield. Reclamation of salt-affected soils which includes leaching of salts and drainage systems to lower the groundwater level is mostly practiced in the high or very high salinity areas. The farmers in the coastal areas have used indigenous technologies to reclaim their lands. The lands are improved by ridging and growing coconut or other salt-tolerant crops on the ridges. The width of the ridges is usually 6 to 7 meters. Continued leaching, use of salt-tolerant crops, amendments such as gypsum and organic matter are recommended to assist in this process.

The slightly to moderately salt-affected lands are generally used for rice cultivation. Some other crops such as vegetables and peanut are also grown. The agronomic package programme has been recommended to farmers through demonstration and training programmes for increasing rice production. It comprises land levelling, leaching, application of organic amendments and use of salt-tolerant varieties of older seedlings and at higher seed rates. Split applications of fertilizer, mulching and green manuring are also recommended.

Reforestation in the potential salt source areas is recognized as one of the land management practices for minimizing groundwater recharge. In Northeast Thailand, it is suggested that neem, eucalyptus, tamarind, manila tamarind should be grown in the recharge area as farmers’ choice. While the highly salt-tolerant tree Acacia ampliceps is planted in the discharge area with halophytes or highly salt-tolerant grasses. Positive effects in lowering groundwater level in the recharge and discharge area are found after one year's planting. And in the 8^th National Economic and Social Development Plan (1997-2001), the Land Development Department plans to plant forests in 800,000 ha in the northeast to control salinization through groundwater movement.

The severely salt-affected land which covers about 1.5 percent of the northeast region, is regarded as waste lands. Some selected salt-tolerant tree species and halophytes could be grown in these soils. Halophytes are introduced as forage crops. Plants from USA and Australia are screened with some native species. The promising species are Sporobolus virginicus and Distichlis spicata.

Viet Nam: Management practices include:

1. A strategic plan for water resource exploitation and protection has been worked out for long-term and short-term irrigation development on large rivers and key areas.
2. Improvement of drainage-irrigation systems: irrigation is essential to leach out salts, thus, a rational drainage-irrigation system to strengthen drainage capacity and control ground water table is a must to control salinity development.
3. Improving soil fertility by applying organic manures, including rice straws, crop residues, green manures, farmyard manures, compost, etc.
4. Protect coastal mangrove forests with aquaculture resources.
5. Rhizophora apiculata forest planting combined with shrimp farming (Penaeus indicus, Panaeus mergriensis). Eighty percent of the shrimp and fish rearing area was planted with mangrove forests.
6. Normally cropping patterns on coastal saline soils are as follows:

7. Making dykes to prevent seawater intrusion. In the Red river delta, where population density is high, typhoons and floods often happen. People have to make large and long dykes surrounding the seashore to reclaim the new land. These dykes are 10 m wide and cover an area about 10 000 ha. Along these dykes, deep channel digging is necessary for preventing the penetration of the seawater into the newly reclaimed area. In these newly reclaimed areas, highly salt resistant plants can be grown during the first three years. Then local rice varieties can be grown. There is only one rice crop in the rainy season but if fresh water is available in the dry season, another rice crop can be added. Incorporation of organic fertilizer, rice straw, rice husk and soluble silicate is highly effective in increasing rice yields up to 5 to 7 ton/ha/year.

Hungary: The radical amelioration of salt-affected soils includes i) control of saline/alkaline groundwaters by the construction of proper drainage systems, ii) application of soluble Ca-containing amendments, iii) improvement of the vertical drainage of soils and horizontal drainage conditions by using organic manures and crop residues, iv) leaching the accumulated salts and draining them from the area. These complex measures are expensive and at present, not economic. However, for sustainable use of salt-affected soils the following practices are applied:

• rational land use and cropping pattern;
• adequate agrotechnics for surface water management and soil moisture control;
• reduction of ecological constrains and practising rational plant nutrition only in the slightly or moderately salt-affected areas
• proper infrastructure for extensive (low input) farming and/or wetland management in the strongly saline/sodic regions

In the case of solonetz soils, the leaching out of salt and drainage are unavoidable, parallel with the use of chemical amendments. Application of gypsum as well as deep ploughing and subsoil loosening is useful. In all cases, the types and utilization of salt-affected soils must be carefully adjusted to local conditions. In the case of soils containing sodium carbonate, the application of acid chemical amendements as one factor of reclamation is nearly always necessary.

Romania: The main management practices used are drainage; land levelling and modelling for leaching; gypum is used as a chemical amendment (in Romania: phospho-gypsum, wastes from phosphorus fertilizer factories); leaching; chiselling;fertilization; salinity or sodicity tolerant crops; proper crop rotations; monitoring of salinty develoment and improvement; etc. To obtain good results, these measures are always applied in an integrated approach.

The drainage system recommended is in accordance with the permissible critical limit of watertable depth and salinity as follows: steppe zone (2.5-3.3 m and 1.5-3.0 g/l, respectively); forest steppe zone (1.8-2.4 m and 0.5-1.5 g/l, respectively); and for forest zone (less than 1 m and 0.5-0.8 g/l, respectively). Drainage should accomplish the discharge of salt leaching waters; desalinization of the plant root zone, and desalinization of watertable to the limits mentioned. Under the conditions of a deep drainage system (2.5-3.5 m deep and 300-500 m apart), it is recommended to add a shallower drainage system (0.6-1.4 m deep and 40-70 m apart). At the same time the drainage system is supplemented with mole drainage, 8 and 12 cm diameter and with a slope of 1-3 per cent.

In soils with high exchangeable sodium content, phospho-gypsum is used as a chemical amendment (such as used in a moderately sodic alluvial soils in Traianu - Valea Encii). Under the drainage and amendment conditions, leaching is applied which represents the basic treatment for salt-affected soils improvement. The leaching of salts may be of several types according to the way of land development or the water application: leaching by flooding the crops as in the case of paddy cropping; leaching by flooding following the crop harvesting on the levelled lands; leaching by furrows or strips during the cropping season on specially prepared lands; continuous leaching maintaining a certain water stratum at the soil surface according to the leaching rate; intermittent leaching consisting of application of the total leaching rate step by step at certain intervals, without permitting the soil re-salinization; prophylactic leaching by applying water from time to time when some soil re-salinization tendency is noticed.

Within the framework of salt-affected soils improvement, particular attention is paid to cropping plants tolerant to salinity according to the improvement stage. In the first improvement stages, use of the most salt-tolerant plants and in the last improvement stages, when soils become more fertile and with lower salt contents, growing crops more sensitive to salinity such as rape, soybean, corn, etc

Within the national programme for reclamation of salt-affected soils, rice cropping was one of the most profitable farming systems. Thus since 1980, the rice cultivated area increased from 19 800 ha to 49 000 ha in 1989. Unfortunately, it then decreased to only 4 000 ha in 1997. As Romania faces a severe economic crisis, investments for land reclamation decreased significantly. The issue of salt-affected soils reclamation is focused on those areas where very important socio-economic problems arise.

Turkey: Main management practices applied in Turkey in an integrated approach include: construction of appropriate drainage systems in connection with irrigation systems when starting any irrigation project; applying proper management practices (organic manures, fertilizers, salt-tolerant crop varieties, minimum tillage practices); use of high quality water for irrigation; selectinng better irrigation methods (sprinkler, drip etc.) for improved water management and applying new advanced technologies such as GIS, RS, and computer modelling for monitoring and management of salt-affected soils.

Reclamation also includes use of leaching water requirement to reduce soil salt content to 4 dS/m and the amount of amendment (gypsum) according to the requirements, as applied in Great Konya Basin., Aydın-Söke Plain, Denizli-Acıpayam Plain and Burdur-Yarıköy Plain.

In Turkey, studies are focused on:

1. Assessment of the full extent of salt-affected soils suitable for reclamation: some successful project examples are: Iğdır, Konya-Ereğli, Aksaray, Gediz, Lower Seyhan, Menemen, Bafra, Söke, Salihli, Kayseri-Karasaz, Eskişehir-Alpu, Denizli-Acıpayam plains and Çankırı Kızılırmak Basin.
2. Hydrologic and drainage response to drain excess water.
3. Development and calibration of computer-based models (DRAINMOD, SALTMOD, Gypsum and Leaching Water Requirement).
4. Characterization of the properties of waste and drainage waters for re-use and its impacts.
5. Diagnosis and predicting of soil salinity and alkalinity, applied research and modelling for salinity development and management using GIS and RS techniques.
6. Ecology of halophytic vegetation in salt-affected lands.

Argentina: The soils of the Lower Valley of the Colorado River (LVCR) in south-central semi-arid Argentina have been irrigated for about 90 years with waters obtained from the near-by river using "flooding" irrigation after levelling of the land. The area has been cultivated to mixed pastures (Medicago sativa, Agropyrum elongatum. Festuca spp. etc.) for either seed production or grazing, and to horticultural crops, mainly onion (Allium cepa), garlic (Allium sativum), tomato (Lycapersicum esculentum), several varieties of melon (Cucumis melo), watermelon (Citrullus vulgaris), apple (Malus sylvestris), etc. Now the salt- affected areas developed in the basin of the LVCR are being reclaimed using the construction of effective and active drainage system (this is the basic and key point of the whole rehabilitation process); rainfall leaching in humid and/or wet years; leaching with the water from the Colorado river, cropping to barley and using it as a green manure; surface soil application and disking in the soil of gypsum or sulphur. The barley-vetch green manure production showed also that the crop (barley) is very effective in reclaiming salt-affected soils.

Crop production in the central Pampean region has been impaired due to the development of salt-affected soils (cropping pattern in the region includes wheat/soybean-corn and wheat/corn–soybean). The programme to reclaim the salt-affected soils in the Region include leaching under supplementary irrigation system, use of straw cover as mulching (2 to 10 tons soybean residues/ha) and gypsum requirements (1 to 3 tons/ha)

In some reclamation projects in the basin of LVCR, reclamation of salt-affected soils included construction of shallow drainage ditches, leaching with low-salinity river waters and use of green manure (barley crop grown close to maturity and then ploughed-in the soil as a source of organic matter). The cropping pattern during the reclamation period included barley accompanied by a legume (Lotus corniculatus and/or Medicago sativa).

In irrigated areas in Argentina, the more important cultivated crops are wheat, barley, fruticulture, including grape production. Cash and horticultural crops cover almost 50 percent of the irrigated crop; sugar cane occupies close to 15 percent; alfalfa and other forage crops cover 11 percent of the producing irrigated areas.

Brazil: The main technology used in Northeast Brazil to reclaim saline soils is sub-surface drainage, and for sodic soils it is the use of gypsum followed by subsurface drainage. The results obtained up to now are highly positive.

Cuba: The policy of reclamation of salt-affected soils in Cuba has been directed fundamentally toward those soils with moderate salt content, where leaching, the drainage system establishment, and some cultural methods can be beneficial; or in those where serious reason exists for the introduction of intensive production systems, as is the case of soils devoted to rice production.

Main solutions and technologies applied in Cuba for combating salinization and for using salt-affected soils include:

• Establishment of drainage-irrigation systems: main drainage canals and field drainage systems are the fundamental conditions for ameliorating and utilizing salt-affected soils. The irrigation has two functions, one is to meet the water demand of crops and the other is to leach salts out of the soil using calculated excess water leaching requirements.
• Drainage and rice planting: this is one of the traditional practices of reclaiming and utilizing saline land in Cuba. This practice usually does not need special leaching. After flooding the field with diverted water, rice can be planted and yield 4-5 ton/ha/year. During the rice growing period the field is often flooded, thus accelerating soil desalinization. After rice cultivation the land can be cultivated for rice- pasture legumes cropping system.
  Application of organic manure and chemical amendments such as gypsum, sulfuric acid, etc. helped to achieve better results.
• Combination of wells, ditches and canals and amelioration of salt-affected soils. In Cuba, in the last ten years, development of pump wells (30-70 m deep) to make use of groundwater resources for irrigation and setting up irrigation-drainage engineering systems with several combination forms of wells-ditches and canals have contributed greatly to the management of salt-affected lands. This situation is common in Cauto and Guantanamo Valleys.
• Organic matter application to improve soil fertility: also using green manure plants solely in the field or in rotation, inter-planting and intercropping of pasture legumes can also be adopted to increase soil fertility and reduce salt accumulation, as well as to promote combination of agriculture with animal husbandry.
• Use of salt-tolerant crops: even planting or protecting natural halophyte vegetation contributes to controlling further salinization of the soil. Salt-tolerant plants can be used as forage for animals. The reclamation effect of growing salt-tolerant rice varieties in saline and sodic soils is well know in Cuba.
• In the sugar cane cropping project in Guantánamo Valley, with the hydrotechnical practices (leaching and buried drainage), combined with the sloth application (100 ton/ha) and deep subsoiling, it was possible to obtain yields between 152 and 218 tons of cane per ha and between 21 and 31 tons/ha of sucrose content.
• In the Cayama zone, salt-affected soils were improved using granulometric light composition of the sloth with leaching application (13 168 m³/ha); and surface drainage.
• Another example of technology applied in Cuba, is the establishment of a package for the rehabilitation and management of salt-affected soils devoted to rice cropping, that includes the optimum drainage parameters (drain spacings of 150-200 m with a 1.2 and 2.5 m depth); subsoiling (distance between chisels 5 m at 40-60 cm depth), with an irrigation norm (15 000 m³ of water/ha) permitting the leaching of 50-100 ppm of total soluble salt in the first irrigation (1 to 3) and avoiding puddle and lagoon formation in the field. Also organic amendments were applied (sloth and manure at the rate of 60 ton/ha) chemicals (calcium sulphate at 20 ton/ha) and a new NPK fertilization formulation (161-100-50 ton/ha). The joint application of the package has permitted rice yields to increase from 1.5 to 3.5 ton/ha (more than 10 000 ha in the state and private sector).

Mexico: Remote sensing was found to be a more efficient and cost effective technique for soil salinity assessment, compared to the traditional one (extensive soil sampling), as long as extensively planted crops are dominant in the study area. Satellite imagery has been utilized as the basic diagnosis tool to assess salt-affected areas in the 233 000 ha in Rio Yaqui ID, the 97 000 ha in Rio Mayo ID and the 228 000 ha in Rio Fuerte ID, all of them in the northwest, using four reference crops (maize, wheat, sorghum and cotton).

Open drain systems for flood control are quite common in the southeastern part of the country, where precipitation is high (> 1 500 mm). However, subsurface drainage for salinity control in the northern arid and semi-arid regions in Mexico, is an open field for research and technology transference. Before the 1990s, only some IDs in the northwest had a few areas with installed subsurface drainage. The Rio Yaqui, Rio Fuerte and Valle del Carrizo IDs had a few 10-50 ha fields installed with subsurface drainage, some of them deficiently designed.

Unfortunately, other kind of associated practices to reclaim salt-affected soils, like soil fertility management and organic matter application (incorporation of crop residues, green manures, animal manures), are not well known by the farmers. It is important to promote these practices among farmers through permanent extension programmes wherever soil salinity exists, and generate new technological alternatives in research centres and universities.

The private sector is not really involved in these kinds of problems, except some companies that manufacture, sell and install drainage pipes. Mainly government institutions are aware of the magnitude of the problem, led by the Water National Commission (CNA), which is promoting and investing in extensive soil reclamation projects.

Egypt: The reclamation of saline soils in Egypt (depending on salinity level, the extent of the problem and many other factors) includes the constructional stage during which all constructional work including land levelling, construction of irrigation and drainage systems, roads, buildings, are completed; the leaching stage during which the excess salts are leached to a level and depth that permits the start of cropping; the leaching-cropping stage during which the growth of crops combined with leaching affect further reclamation (during this stage the input from the land is less than the output); the normal cropping stage during which a variety of crops can be grown with outputs from land exceeding inputs. If the leaching is achieved before the month of November a salt-tolerant winter crop such as barley, rye grass, berseem clover, can be cropped. If the leaching is completed before the month of May, a summer crop such as nuseila (Echinochloa stagnina) and rice can be grown.

Management practices during the combined leaching cropping stage include use of excess irrigation water according to leaching requirements; cropping in rotation which ensures effective leaching of accumulated salts; keeping a plant cover to protect soil surface from evaporation during the summer as much as possible; ploughing deep enough before leaching; subsoiling and deep ploughing with proper fertilization is essential; for row crops planting on the slope of a furrow below the zone of salt accumulation and re-levelling very carefully following the removal of each crop to ensure uniform distribution of water.

Incorporating organic matter into the soil has been applied in Egypt, particularly in sodic soils for improvement of soil permeability and release of carbon dioxide and certain organic acid during decomposition. and to act as a nutrient source. Crop residue application is one of the easiest methods to improve water infiltration. Growing legumes has improved soil structure and acted as a source of nitrogen in the soil for the next crop. Green manure has a similar effect on soil properties and as a source of nutrients as organic manure.

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.

Additional fertilizer may be needed to compensate for leaching and other losses. Such compensation is always needed where leaching is continuously used or under waterlogged conditions.

Sprinkler irrigation is considered in Egypt as an ideal irrigation method for frequent irrigation and with small quantities of water at a time. Salt leaching can be accomplished under this system with a uniform water application. Trickle or drip irrigation has been found particularly useful when irrigating with water of high salinity. In Egypt, it is expected that drainage water will be a source of over 7 000 million m³ of water for agriculture in the year 2000, while it was 4 500 million m³ in 1990. The Egyptian Law No. 48 identified the maximum limits of the re-used water in terms of its content of salt and other elements.

Iran: During the past decade balanced fertilization was applied to various crops cultivated on the salt-affected soils, irrigated with saline water. The preliminary results demonstrated that in saline soils split application of N-fertilizers (mostly ammonium sulphate), in a higher rate than that conventionally applied gives better yield. This was also the case when relatively higher amounts of potassium sulphate were applied. In Qom region application of the fertilizer rate N₂₂₅ K₁₂₀, result in wheat-grain yields going up to 5 600 kg/ha.

Recently reclamation of saline and sodic soils has been carried out by acidification through application of sulphuric acid and sulphur powder enriched by Thiobacillus bacteria.

The first scientific investigations on salinity problems in Iran started about 30 years ago. These investigations were confined to some leaching tests and the effects of salinity on crop yields. Most of these studies were carried out in Khuzestan, Fars and Esfahan provinces. In later years other research programmes such as the use of soil amendments for improving soil physical properties were conducted in the same locations and some other parts of the country. In this respect, a lot of work was done on the use of sulphur for improving infiltration rates of sodic soils.

During the last three decades leaching practices using leaching required values were applied in 13 provinces. Also, use of some salt-tolerant crops such as Kalar grass in the first stage of salt-affected soil reclamation are being used.

Management plans have been prepared to overcome the problems of salinity and waterlogging. Development of modern irrigation and drainage networks accompanied by leaching has reduced soil salinity in many parts. Management has also changed the spatial distribution of the salt-affected soils. Examples are found in the Moghan plain, and after construction of the Drudzan dam near Shiraz, the capital city of Fars Province, in 1972. Using these techniques, beneficial effects on the reduction of soil salinity and alkalinity in the two regions were obtained.

Syria: Management practices on salt-affected soils include establishing sufficient tile drainage network that meets fields requirements; maintenance of irrigation and drainage networks periodically to avoid watertable rise and to stop seepage from channels and use of salt-tolerant crops.

Salinization process are found in the whole Syrian portion of the Euphrates River. Therefore it can be admitted that the ecological situation in the Euphrates river basin (lower Euphrates basin) is in danger. Salinity development has led to a reduction in the productivity and deterioration of the population situation in terms of income, unemployment and labour migration from rural areas to towns.

Tunisia: Because of the necessity of maximizing national utilization of soil and water resources, the country programme is to define appropriate integrated management techniques to improve the productivity of small farmers' fields in salt-affected areas. The management practices include use of subsurface drainage, leaching requirements, appropriate tillage system, addition of gypsum, organic matter, mulching and applying crop residues, special planting procedures and selecting tolerant crops (alfalfa, barley, date palm, vegetables such as lettuce, carrot and onion).

Associate Members

Options for mitigating salinity effects on agriculture fall into the following two broad categories.

Dry Land Salinity:

• Changes in current land management systems and practices – usually to restrict the entry of rainfall into the groundwater systems. These usually involve attempts to change crop types on recharge areas to achieve use of a higher proportion of rainfall, thereby reducing the amounts of water entering the groundwater. More recently, the accepted theory that selection of agricultural plants with higher community water use than existing crop plants can have a significant positive effect on groundwater systems is being questioned. Apart from differences between annual and perennial communities, the difference in water use within these groups under naturally occurring, water-limited, field conditions use is constant, so changes are unlikely to be significant in effect on groundwater recharge.
• Seeking new uses for salt-affected soils. The saline agriculture approach uses plants that are already adapted to high salinity in management systems that do not require reclamation of the salt-affected soils as a first step before any worthwhile production is obtained. Farmers will gain some economic returns as the land is slowly reclaimed. In dryland areas, these systems involve the establishment and utilization of halophytic grasses, shrubs and trees. In this regard there are two approaches to saltland pastures: "Natural Saltland Pastures" (many areas of primary saltland in Australia already support natural "pastures" of halophyte shrubs and grasses. These can be managed for light grazing by animals according to the seasonal production); and "Sown Saltland Pastures" (land that is of high salinity growing poor cover of annual salt-tolerant grasses is sown with halophytic shrub species at densities of 1000 to 2000 plants per ha. After establishment some leaching can take place from winter rainfall and other species with lower salt tolerance but higher forage value have been used). Species favoured for saltland pastures include Atriplex amnicola, Atriplex undulata, Atriplex nummularia, Atriplex cinerea, Maireana brevifolia, Puccinellia ciliata, Thinopyrum elongatum and Trifolium michelianum.

Irrigation Salinity:

Some work has been done in Australia on irrigation of the shrub species in relation to a Serial Biological Concentration System approach to disposal of saline groundwater in irrigation areas. Productivity under saline irrigation can be increased more than 10 times compared with dryland conditions. No use is made in Australia of organic amendments e.g. organic matter, crop residues animal manure, specifically targeted at remediation of conditions of high salinity.

Because of the higher value of irrigated agriculture (land and production) a wider range of technologies is applied to salinity problems. At lower salinities, information from various sources on the relative salt tolerance of a wide range of crop and forage plants is used to assist in selecting plants suited to the particular salinity category. Limited plant breeding and selection research is also funded to develop varieties of particular plants with improved salt tolerance for irrigation areas. Engineering works (shallow tubewell pumping, tile and surface drainage, local evaporation basins) are important in irrigation areas to control shallow saline watertables and waterlogging. Generally there is not sole reliance on engineering solutions to solve salinity problems, where they are used it is always in combination with various on-farm land and water management measures to control rootzone watertable levels. These include better matching of irrigation applications to crop water use requirements and patterns, laser levelling of irrigated soils to improve efficiency of water applications and surface drainage of irrigated land.

Canada: Management of salt-affected soils include:

• Preventing and retarding the accumulation of water and salts at near surface. Agronomically, a balance between water needs and supply for vegetation is sought. This includes: growing crops which use water before it moves below the rootzones such as alfalfa hay crops upstream of the saline sites; drain any surface water such as ponds and ditches which contribute to subsurface accumulations; mulch soil surfaces to deter evaporation; form seed-beds so as to present salt accumulation far from crops; keep irrigation leaching fraction at a minimum; increase infiltration rate, install wind shelterbelts to reduce evaporation.
• Lowering ground water tables and potentiometric heads to reduce salinization rates. This includes pumping of groundwater from upper aquifers; growing deep-rooted plants; practising favourable cropping strategies (minimizing summerfallow) and engineering surface and subsurface drainage.
• Removing salts from the rootzone. This includes removing salts with harvested halophytes and leaching salts from rootzone.
• Effective leaching can be promoted by improving infiltration and transmission of water including cultivating and ploughing; surface mulching; adding amendments for soil conditioning; organic and green manuring and when appropriate fallowing. Leaching is best accomplished by irrigating sufficiently with designed leaching fractions. Even under dryland cultivation some additional water for leaching can be obtained by snow management.
• Living with the problem. This may be necessary, especially in the short term, until more permanent controls can be developed. Growing plant crops which tolerate or avoid salinity exemplifies this approach. The usual sequence followed by prairie farmers as their salinity problem persists is to convert wheat to barely, barley to alfalfa, alfalfa to bromegrass and brome to tall wheatgrass.

Colombia: Successful rehabilitation of salt-affected soils includes effective drainage systems; non-saline good quality water for salt leaching; use of chemical amendments (gypsum, sulphur, etc.); use of biological systems (barley and its straw as amendment) and deep ploughing to alleviate soil compaction.

India: Reclamation techniques for the two distinct categories of salt-affected soils in India, namely, alkaline and saline have been developed and applied in the field. Three approaches for reclamation of alkaline soils have been developed for different situations including reclamation for maximizing crop production (agrochemical technology); reclamation based on cultivation of salt-tolerant crops with reduced dose of amendment or no amendment (bioreclamation) and reclamation for planting trees and grasses (alternative land use). Package of practices for the first two technologies have been developed. The agrochemical technology (the agrochemical package includes recommendations on pre-reclamation management, amendments use, choice of crops and cropping sequences, nutrient management, water management and agronomic management) has been implemented on a large scale in the states of Haryana, Punjab, for reclaiming 0.7 million ha of land. Bioreclamation for crop production is being extended in resource scarce areas of Uttar Pradesh. Salt-tolerant trees and grasses have been grown mostly on community and forestlands. Technology for reclamation of waterlogged saline lands concentrates on the use of subsurface drainage. Drainage design criterion for monsoon climates has been established and tested on a pilot scale. Also, the methodology for re-use of drainage effluents has been extensively tested and refined. Large-scale pilot projects are being implemented adopting this technology. Tecno-economic analysis shows that the technology is highly profitable but it requires community participation on a large scale.

Italy: Long-term field experiments are one way to develop suitable irrigation strategies but these are expensive, site specific and time consuming. An alternative solution is application of computer simulation models to be used to examine some different possible combinations of existing field conditions (soil, climate and water) and to provide accurate and quick estimate of crop growth, water and salt balance. Several studies were carried out in this regard to show a) the relevant influence that reductions in hydraulic conductivity due to increasing sodicity (ESP) play in water transport in the soil crop system; b) possibility for predicting the hazard of salinization/sodication due to irrigation with saline/sodic waters.

Spain: A National Plan for river transfers from different Spanish regions although very controversial, is now under political discussion for remedial of the scarcity of water in the Comunidad Valenciana. In parallel, a modernization of the irrigation systems from furrow to sprinkler and mainly to drip irrigation, as well as amelioration of the water transport infrastructure to avoid water losses by evaporation and spills, and even some initiatives to desalinize water are making more rational use of water resources.

Traditionally orange trees are irrigated by flooding or by furrow, but the high income for farmers having this crop as well as the increasing scarcity of water and worsening of its quality have moved the farmers to introduce drip irrigation facilities, with fertirrigation. This saves water and allows control of the fertilization rate according to the needs of the tree along its cycle.

Sudan: The management practices include expansion of wheat, legume production to the irrigated areas including using salt-tolerant varieties, chemical amendments (gypsum) and organic (FYM) and wheat straw, irrigation intervals and chemical fertilizers.

Uzbekistan: The works at Lake Sudoche would test wetland restoration by re-use of drainage water. Thus these activities will demonstrate a means of wetlands restoration which will be applicable to further projects in the Aral Sea Basin.

Uzbekistan Drainage Project and Environmental Assessment of Irrigation and Drainage Project in the Amu-Darya Basin was started in 1996. Three scenarios of water-related sector at various intensities of political, agricultural reforms and investments in the future have been carried out: diversion and management of drainage flow, decreasing salt mobilization and an abandonment of highly saline soils, leaching practices improvement and other technical solutions and their environmental assessment were worked out by the projects.

Existing practices of irrigation and leaching do not provide adequate desalinization of moderate and highly saline lands. Economic changes, restructuring and privatization in the agriculture of Uzbekistan demand new methods and technologies to combat salinization and environmental rehabilitation of land use and water management, having a real benefit and attraction for farmers and water users' associations.

At the present, projects of inter-farm water use and management in agriculture have started in Uzbekistan and other Aral Sea states.

WUFMAS Project (TACIS ЕС) on test plots in 10 farms of the Republic-Bukhara, Khorezm, Surhandarya, Karakalpakistan and others began in 1996. The project includes a systematic measure of production factor and output, agronomic and soil observations, monitoring of water quality and drainage and other investigations.

Inter-farm Irrigation and Management Project (EC) aims to demonstrate the possibility of improvement of on-farm irrigation and management of agriculture on hardly meliorated lands of the Hungry Steppe in Uzbekistan. Farm restructuring, rehabilitation of irrigation infrastructure and soil management will be developing by means of improvement fertility management, salinity control, and irrigation efficiency and leaching practices.

There are new applied technologies to combat each type of salinization which include:

1. Rehabilitation of degraded saline soils on the basis of effective ways of leaching soils by furrows with consequent seeding of salt-tolerant crops and fodder crops and introducing of fertilizers and soil treatment. The advantage of this way, in comparison with leaching on basin check method, is water saving in 1.4-1.5 times and high efficiency of soil desalinization, significant reduction of before sowing works and efficiency of land use and others. Cotton yield increased from 0.6 to 1.25 ton/ha.
2. In developing irrigation of saline lands in Uzbekistan, biological drainage technologies have been started. One of the advantages of the technology is biological desalinization of drainage waters and creation of additional biomass (fodder, domestic fuel, etc.) with minimal investment. The positive results of biological drainage use are received in the Hungry Steppe

Different management techniques are practised including leaching requirements, applying special planting procedures, drainage systems and chemical amendments (gypsum) and balanced fertilizers.