Salinity is one of the most damaging agro-environmental problems limiting the growth and development of plants. A large network of canals which is under irrigation use is thought to be responsible for building up salinity. Of the total 22 million hectares of cultivable land, about 6.67 million hectares are salt-affected.

Soil salinity is robbing the country about 25 per cent crop production. Out of this salt-affected land about, 3.64 mha (26 per cent) are moderately saline; 3.08 mha (22 per cent) severe saline; and 2.1 mha (15 per cent) saline-alkali soils. In Sindh, 5.1 mha area is salt-affected, of this 3.23 mha is moderately and 1.87 mha highly saline.

In the country, the gross canal commanded area is 17.04 mha (76 per cent) and 4.5 mha (32 per cent) is highly waterlogged. A total 50 per cent area is affected by water-logging. In Sindh, 3.13 mha area is waterlogged, of this 1.26 mha are moderately and 1.87 mha highly waterlogged.

Pakistan is associated with the region of low rainfall and irrigation water availability is decreasing with the increasing demand for crop to fulfil human needs. Various approaches are formulated to solve the problem, but due to limitations of cost and time, not one is found fruitful.

The plant growing in salinity or water stress may be affected structurally, functionally, qualitatively and quantitatively. Plant may become dwarf with little foliage and may give different physiological and biochemical responses as compared to non-stressed plant.

Plant shows inadequate growth due to water-deficiency, ion toxicity, ion imbalance or a combination of any of these factors. The adverse growth conditions generally affects negatively to plant growth. Generally high evapo-transpiration is the basic cause for salt accumulation on soil surface. The average summer temperature goes up to 40o C and minimum winter temperature remains between 2o C to 5o C. The annual rainfall varies between 100mm to 700mm distributed unevenly throughout the country. The evaporation rate is generally very high and exceeds that of precipitation.

Thus, insufficient rainfall followed by high evaporative demand and shallow groundwater depth enhances the movement of salts towards soil surface. Irrigation water generally increases the amount of salts in the soil. Impermeable soil condition also increases the quantity of salts on the surface. High temperature and low rainfall with shallow ground water causes the formation of saline soils.

In spite of a number of drainage and salinity control schemes under way, the salinity and water-logging problems persist thus tarnishing over million hectares land in the country, while every year about 40,000 hectares of irrigated land is lost to water-logging and salinity. Both phenomena are interlinked problems and co-exist at most of the places.

Our cultivable land is decreasing due to this twin menace. Salt-affected soil reduces the value and productivity of soil. For agricultural practices, such soils are regarded as a class of problem soils that require some special remedial measures and management practices.

At the first step, the scrapping of salt layer, land levelling, deep ploughing, addition of river bed sand, flushing of salts from the root zone by good quality water, drainage and method of irrigation helps in improving the salt-affected soils. The excess water is removed by pumping from the lower part of the soil bed. Permissible depths for groundwater tables vary according to the type of soil being irrigated. A water table should be at least 4.5 to five feet below the surface during most of the crop growing season.

The dwindling source of good quality water is a great concern to a farmer. He is compelled to use saline water. In Pakistan, numerous and diversified methods are used in the fight against salinity according to various soil types. The amending materials improve soil structure and aeration, increases water-holding capacity and availability of water to plants, reduce compaction, improve drainage etc. Consequently a successful yield can be obtained.

The saline–sodic soils have been reclaimed by the use of organic matter, chemical amendments, high salt dilution techniques, and biological methods. Among major practices are the use of organic matter, chemical amendments, especially gypsum, calcium chloride, sulphur, lime sulphur, sugar lime, hydrochloric acid, sulphuric acid, ferrous sulphate, iron pyrites, ferric sulphate, and aluminium sulphate are the most common but the application of acid needs special care due to its corrosive action.

Biological techniques and use of organic matter such as farmyard manure, composts and green manure have long been known to facilitate the reclamation of saline/sodic soils. The beneficial effect of organic matter incorporation followed by leaching is described to the decomposition of organic matter resulting in the evolution of carbon dioxide and organic acids, lowering of soil pH and release of calcium by solubilization of CaCO3 and other minerals thereby increasing the electrical conductivity and replacement of exchangeable sodium by actions like Ca and Mg and thus lowering the ESP.

Organic matter application reduces the compaction of soil created by sodium coming from poor quality tube well water. After decomposition by the soil microbes it becomes humus, which is of lightweight but chemically active. Annual application of organic matter (farmyard manure, crop residue, sugarcane press-mud, etc.,) at the rate of two to four trolleys per acre is recommended. Crop residues include sugarcane trash, wheat-straw, vegetable- market waste etc.

Gypsum is recommended as a calcium source to balance the excess sodium. Gypsum application rate varies with the composition of salt and the soil texture. Application of 1.25 ton per hectare per year to sandy soil, while for a clayey annual application of five ton per hectare is required. It is stated that calcium released from the gypsum mitigates the toxic effect of sodium. Calcium also replaces sodium from exchange sites of the saline soil.

It is necessary that gypsum powder be evenly spread before irrigation and mixed well on the surface soil up to a depth of 15-20 cm. The outcome of this work can improve soil tilt, increased water infiltration, storage, drainage and leaching. The finer the material the greater and quicker is the reaction rate. It has been shown that mixing limited quantities of gypsum in a shallower depth was more beneficial than mixing up to a greater depth. Calcium chloride and calcium carbonate are also good sources for the improvement of saline soils. These salts replace the sodium present in the soils.

Experimentally, a large range of acid materials were tested including sulphur, sulphuric acid, various polysulphides, ferric, ferrous, and aluminium sulphates, pyrites and acid-resin by-products of the oil industry. Among them sulphuric acid is most likely to be considered for reclamation of highly saline/sodic soils which are calcareous and where rapid reclamation is desired. Precaution may be taken to use sulphuric acid and it should be diluted.

Combing either calcium chloride or sulphuric acid with gypsum as an amendment can appreciably improve time and water use efficiency and give quicker and more effective amendment compared to gypsum alone. The acid materials reduce the pH and also decrease the degree of alkalinity of the soil.

Biological technique and use of organic matter such as farmyard manure, composts and green manure have long been known to facilitate the reclamation of saline soils. The beneficial effect of organic materials incorporation followed by leaching is described to the decomposition of organic matter resulting in the evolution of carbon dioxide and organic acids, lowering of soil pH and release OF Ca by solubilization of CaCO3 and other soil minerals, thereby increasing the electrical conductivity and replacement of exchangeable sodium by actions like calcium and magnesium and thus lowering the ESP.

The biological techniques employed in the reclamation of such soils require growing of salt-tolerant plants like kallar grass, junter, berseem and lucerne etc., which are tolerant to saline soils. Saline soils to a depth of 18 inches were successfully reclaimed by growing kallar grass within a period of three years. Studies on the addition of organic matter reveal that considerable amount of sodium can be adsorbed by organic matter.

The greatest constraints in the achievement of optimum results in the field of salt-affected soils is the lack of coordination and communication between the federal and provincial institutes, universities, government departments, researchers and the end-users. Every organization is working in a water-tight compartment without knowing what is happening around. There is no directional policy and each individual is at liberty to adopt whatever course he deems fit.