CONJUNCTIVE USE OF SALINE AND NONSALINE IRRIGATION WATERS IN SEMIARIDREGIONS

In arid and semi-arid regions, effluent from subsurface drainage syste ms is often saline and during the dry season its disposal poses an env ironmental problem. A field experiment was conducted from 1989 to 1992 using saline drainage water (EC = 10.5 - 15.0 dS/m) together with fre sh canal water (EC = 0.4 dS/m) for irrigation during the dry winter se ason. The aim was to find if crop production would still be feasible a nd soil salinity would not be increased unacceptably by this practice. The experimental crops were a winter crop, wheat, and pearl-millet an d sorghum, the rainy season crops, grown on a sandy loam soil. All cro ps were given a pre-plant irrigation with fresh canal water. Subsequen tly, the wheat crop was irrigated four times with different sequences of saline drainage water and canal water. The rainy season crops recei ved no further irrigation as they were rainfed. Taking the wheat yield obtained with fresh canal water as the potential value (100%), the me an relative yield of wheat irrigated with only saline drainage water w as 74%. Substitution of canal water at first post-plant irrigation and applying thereafter only saline drainage water, increased the yield t o 84%. Cyclic irrigations with canal and drainage water in different t reatments resulted in yields of 88% to 94% of the potential. Pearl-mil let and sorghum yields decreased significantly where 3 or 4 post-plant irrigations were applied with saline drainage water to previous wheat crop, but cyclic irrigations did not cause yield reduction. The high salinity and sodicity of the drainage water increased the soil salinit y and sodicity in the soil profile during the winter season, but these hazards were eliminated by the sub-surface drainage system during the ensuing monsoon periods. The results obtained provide a promising opt ion for the use of poor quality drainage water in conjunction with fre sh canal water without undue yield reduction and soil degradation. Thi s will save the scarce canal water, reduce the drainage water disposal needs and associated environmental problems.