EFFECT OF CONTINUOUS IRRIGATION WITH SODIC AND SALINE-SODIC WATERS ON SOIL PROPERTIES AND CROP YIELDS UNDER COTTON-WHEAT ROTATION IN NORTHWESTERN INDIA

A field experiment was conducted for 8 years ( 1983-1991 ) on a well-drained sandy loam Typic Ustochrept soil involving sodic (NaHCO3) and saline-sodic (NaHCO3+NaCl) irrigation waters under cotton-wheat rotation. Soil pH and exchangeable sodium percentage (ESP) increased with increase in residual sodium carbonate (RSC) and SAR of the irrigation water. The build up of salts and ESP was considerably higher under saline-sodic irrigation treatments. From amongst the empirical equations used for predicting the sodicity hazards of irrigation waters, the Rhoades equation could fairly accurately predict the build up of ESP for sodic waters containing mainly NaHCO3. The modified Ayers and Westcot equation predicted the ESP for all the sodic waters and also for the saline-sodic waters with high RSC values. For the waters with high SAR values due to a high NaCl concentration and low RSC values, none of the models could predict the build up of ESP. Under the cotton-wheat rotation, irrigation waters with high RSC values decreased the crop yields considerably more than irrigation waters with low RSC and high SAR values. The decrements in the yields of both wheat and cotton crops were almost similar under increasing levels of RSC in irrigation water.