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Salinity is a serious problem affecting irrigated agriculture




  •  Salinity is a serious problem affecting irrigated agriculture. Improper irrigation practices and lack of drainage have generally led to accumulation of salts in the soil in concentrations, which are harmful to crops

    Muhammad Mohsin Raza1,Malik Muhammad yousaf1,Samiullah2,Mumtaz Hussain 1,Muhammad zeshan1, jhangir shah1,Qazi Bashir Ahamad1, Usman Ali 1,Hammad Fayyaz1,Hafiz Muhammad Bilal3,Ahsan Raza Asif3.

    1.Arid Zone research Institute(PARC) Bahawallpur

    1. Department of Agronomy University of agriculture Faisalabad
    2. Institute of soil and environmental sciences university of agriculture Faisalabad

    There is a major imbalance in the amount of salt entering and leaving the soil. Each year about 120 million tons of salt is added to the land from canal water and brackish underground water. Only about 1/5th of this salt finds its way to the sea. The remainder accumulates in the soil and continues to reduce the growth and survival of crops.

    The soils with electrical conductivity of less than four dSm-1 are generally considered as salt-free, where almost all crops can be grown. As the salt concentration increases, the choice becomes limited and one has to go for tolerant plants suited for specific conditions.

    Over 2.5 million hectares of irrigated land is affected with severe surface salinity with 18 per cent affecting lands in Sindh, three per cent in the Punjab and two per cent in NWFP. The moderately affected areas are 10 per cent in Sindh, four per cent in the Punjab and two per cent in the NWFP.

    Saline agriculture involves some compromise on yields as even a very salt tolerant species is bound to suffer some crop losses under the adverse conditions.

    Leaching

    is the process in which extra water is added to a field and allowed to soak through the soil and drain away underground. A common method of leaching is to pond the water in basins over the entire field. Sometimes the excess water is removed by pumping from wells. Permissible depths for ground-water tables vary according to the type of soil being irrigated.

    The amount of leaching water that enters the soil by surface flooding determines how much salt is removed from the soil. When water is leached through the soil, a surface depth of six inches of water for every foot of plant root will leach out 50 per cent of the salt. One foot of water for every foot of root zone leaches out 80 per cent of the salt. Two feet of water per foot root zone leaches out 90 per cent of the salt.

    Chemical

    Most saline soils need chemical amendments to restore their productivity. Of the many suitable available amendments, gypsum, sulphur and sulphuric acid are the most common, but application of acid needs special care due to its corrosive action. Application of acid is effective in reclaiming saline soils by lowering ESP (exchangeable sodium percentage), SAR (sodium adsorption ratio), and pH.

    Scrapping of salt layer, land levelling, deep ploughing, sub-soiling, sanding (i.e. adding sand), flushing with good quality and enough quantity of water and drainage also help in improving soil condition.

    For better results in cultivating saline soils, higher seed rate for higher plant population, crop rotation, proper choice of crops and sufficient amount of NPK fertilisers, avoiding urea and using ammonium sulphate as an N source, is advised.

    Green manuring

    through leguminous crops and application of farm yard manure not only provide organic matter and other nutrient, but also make the soil porous for aeration and moisture absorption and enhance soil microorganisms, thus improving the overall condition of the soil. Similarly replacement of sodium-ions by calcium, using gypsum helps in mitigating the adverse conditions.

    Lands, specially the saline ones, should never be left fallow for extended periods, because in uncultivated lands, there is a constant upward flux of water, which keeps evaporating and leaves behind the salts on the surface. Presence of vegetation of any kind helps to minimise this development.

    Halophytes

    Modern research has identified more than 1,500 plant species that have high levels of tolerance to saline soils; these are called halophytes. Some of these are able to withstand salt concentrations in excess of those found in sea-water. These plants (trees, shrubs and salt tolerant grasses and herbs) are a major resource that can be used in the development of agricultural systems for salt affected soils. In addition, there are opportunities to increase the salt tolerance of existing crops using conventional plant breeding and molecular biological approaches.

    The research conducted over the last decade shows that there is a wide range of plant species with varying levels of salt tolerance that can be used in saline agriculture. Furthermore, at least some of these plants are able to lower local water-tables, improving the condition of the land, and acting as `biological pumps`.

    Saline agriculture can be a profitable and practical venture under proper management and by observing suitable precautionary measures. Initial establishment is crucial for subsequent plant growth and hence stress should be minimised as far as possible at this stage. Saline agriculture is an economical and effective approach to use unproductive lands for growing various plant and food crops.

    If the plant survives the shock at seeding/ transplanting stage, the chances of its subsequent survival and growth are likely to be increased. Several salt-tolerant grain, fruit and fodder species have been identified for practising saline agriculture.

    This approach, if prudently adapted, can help to reduce the imports of agricultural commodities to a great extent. Leaching with only good quality water or by rain reduces shock and improves growth. Use of mulch to conserve moisture, planting on ridges, light but more frequent irrigation often helps under such conditions.

    Out of about 5,000 crops that are cultivated throughout the world, a few can survive with water that contains more than one per cent salt. The world food base can be vastly expanded if the currently cultivated crops can be grown by maintaining proper soil management. It is also necessary that government should encourage the local agencies by supplying all sorts of facilities for the betterment and reclaiming of salt affected lands.

     

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