Quality of Water from Different Sources
Water quality of most the Indian rivers are good with EC values less than 0.7 m mhos /cm except in Krishna (1.4), Hagari (1.6) and Tungbhadra (1.7) rivers. Quality of most the tanks, lakes etc. is good except in those which are fed by stream passing through salt affected areas. Quantity of ground water is affected by and arid regions are generally poor with high salt content.
Irrigation water with poor quality:
In an area where there is no alternative source of good quality irrigation water, it is inevitable to use the available water of poor quality. However, the yield potential of such areas can be increased by adopting proper management practices such as
Improvement of sodium and bicarbonates rich water by gypsum application.
Choice of salt tolerant crops and their varieties.
Optimum fertilizer application and manuring
Proper irrigation management
Breaking any impervious layer by deep ploughing and
Adopting other management practices suitable for area.
A. Gypsum application:
The harmful effect of irrigation water can be minimized to some extent by modifying its ionic composition by adding such chemicals which tend to precipitate the harmful constituents such as bicarbonate and carbonate in the form of less soluble salts or tend to create a favorable catonic Ca : Mg : Na ratio.
Gypsum should be powered up to 0.5 mm size or passed through a 30-mesh sieve. The gypsum requirement of water should be calculated depending upon the relative concentration of sodium, magnesium and calcium 8.6 Q of gypsum of 100 percent purity per hectare meter of water be necessary. Gypsum can directly be mixed in irrigation water.
B. Choice of salt tolerant crops:
Some crops and their varieties are more salt tolerant than others. Hence, salt tolerant crops are to be grown in salt affected areas till the soil are improved by vegetation or other reclamation procedures.
Salt Tolerant Crops: Barly, Dhainacha, Sugar beet, Tobacco, Turnips, Mustard, Cotton, Wheat, Sugarcane, Turnips, Beetroots, Spinach, Date palm coconut etc.
Semi Tolerant Crops: Oats, Rice, Sorghum, Bajara, Maize, Red gram, Green gram, Sunflower, Castor, Sesamum, Linseed, Senji Lucerne, Berseem, Cowpea, Tomato, Cabbage, Cauliflower, Lettuce, Potato, Carrot, Onion, Cucumber, Pumpkins, Bitter ground, Pomegranate, Grape, Guava, Mango, Apple, Orange, Lemon.
Sensitive Crops for Salts: Field beans, Gram, Peas and Guar, etc.
C. Use of Fertilizers:
Generally saline and alkali soils, or irrigated with poor quality waters are low in their fertility status, especially with reference to nitrogen or something phosphorus. Better crop can be grown by raising their fertility status. Nitrogen response to crop better when it is applied to soil along with manures. It has been observed that for wheat, barley, bajara, and maize the usual loses of fertilizers as applied up to an EC value of 6.5 m mhos/ cm and an E.S.P. of about 30. However, excessive fertilization or addition of fertilizers on a highly saline, alkali soil is of no value.
D. Soil Management Practices:
When poor quality water is to be applied, it is important to have the detailed analysis of soil profile for their physical, chemical, and morphological characteristic. Soil analysis should include its structure, texture, pH, lime content, location and amount of gypsum, T.T.S., exchangeable cations, etc Information on water transmission properties on soil and depth of water table should be obtained Data on rainfall, its intensity and distribution and evaporation are obtained. Saline area should be leveled properly for uniform spread of water and its downward movement.
Medium textured soils with Kankar layers pose a problem of sodicity. Such soils are managed by deep ploughing and growing green manuring crop like dhaicha. Application of gypsum under condition of low water table may improve land productivity. Use of optimum fertilizers and manures and improving the surface drainage systems will help in improving productivity.
E. Irrigation management:
Accumulation of salts increase with the fineness of soil texture, it is essential to adopt irrigation practices such that the salinity at the root zone is kept minimum. The quantity of water and the frequency of irrigation are so kept that they could met the leaching requirement of the soil and consumptive sue off the crop grown. Salts often accumulate in the top few centimeters of soil during non-crop period and hence both crop germination and yield can be seriously reduced. A heavy pre-sowing irrigation to leach these surface salts will improve germination and early growth. It is done well in advance to allow cultivation to remove weeds and prepare the seedbed. Sowing the seed in the center of a single row raised bed will place the seed exactly in the area where salts concentrate. Alternate furrow irrigation is often advantageous. Similarly increasing the depth of water in the furrow can also be an aid to improve germination the use of sleeping beds with seeds planted on the sloping sides and the seed row placed just above the water line can help in better salinity control. Large seeded crops like maize planted in water furrows can improve germination.
Effect of salts on plants growth is reflected by increasing the osmotic pressure in the soil solution. Accumulating certain ions toxic concentration in plant tissue and by altering the plants mineral nutritional characteristics resulting in poor stand of crop, stunted growth and yield. It may cause leaf burns in some crops and blue green colour in others. The germination of seed is delayed and retarded. In general, grain yield is affected more than the height of the plants.
F. Salt Tolerance of Crops:
The ability of a plant to tolerate salt in the root zone is known as salt tolerance. Studies are important in selecting it for a particular or its variety to suit the soil conditions and for determining the leaching requirements. The effect of soil salinity on crop growth is negligible when the EC of saturated extract is less than 2 m mhos/ cm. Many crops are affected when EC is in the range of 4 to 8 m mhos/cm. crops with high salt tolerance can grow satisfactorily when EC values are in between 8 to 16 m mhos/cm. Only a few survive at EC beyond 16 m mhos / cm.