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The irrigated arid and semi-arid zones in India face twin problems of overall water scarcity and waterlogging accompanied by salinity. Subsurface drainage has proved successful in the rehabilitation and conservation of waterlogged saline soils. Drainage water from subsurface drainage systems seems to be an important source of water in the next millennium to tide us over the anticipated water scarcity problem in agriculture. However, the drainage waters from subsurface drainage systems are often saline and in the absence of a natural outlet, their disposal creates a problem. Various possible options have been discussed to mitigate the environmental threat posed by low quality drainage waters. Issues relating to potential reuse of low quality drainage waters along with management practices are addressed. Effects of factors influencing the long-term sustainable use of saline drainage waters are presented and it is emphasized that special management practices have to be followed/evolved for sitespecific water quality, soil, crop and climatic conditions. However, the extent of salt leaching and crop establishment will depend on the total amount of monsoon rains and adequate subsurface drainage. It has been concluded that the use of a part of the saline drainage water in the post-reclamation phase will not only augment the water supply but also minimize effluent disposal requirements.

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In arid and semi-arid regions, effluent from subsurface drainage systems is often saline and during the dry season its disposal poses an environmental problem. A field experiment was conducted from 1989 to 1992 using saline drainage water (EC=10.5-15.0dS/m) together with fresh canal water (EC = 0.4 dS/m) for irrigation during the dry winter season. The aim was to find if crop production would still be feasible and soil salinity would not be increased unacceptably by this practice. The experimental crops were a winter crop, wheat, and pearl-millet and sorghum, the rainy season crops, grown on a sandy loam soil. All crops were given a pre-plant irrigation with fresh canal water. Subsequently, the wheat crop was irrigated four times with different sequences of saline drainage water and canal water. The rainy season crops received no further irrigation as they were rainfed. Taking the wheat yield obtained with fresh canal water as the potential value (100%), the mean relative yield of wheat irrigated with only saline drainage water was 74%. Substitution of canal water at first post-plant irrigation and applying thereafter only saline drainage water, increased the yield to 84%. Cyclic irrigations with canal and drainage water in different treatments resulted in yields of 88% to 94% of the potential. Pearl-millet 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 salinity 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 option for the use of poor quality drainage water in conjunction with fresh ca-

SummaryIn a field study at exchangeable sodium percentage (ESP) values of 11 and 32, subjecting a wheat (Triticum aestivum L.) crop to waterlogging for 1, 2, 4 and 6 days at the time of first irrigation (25-day-old plants), significantly reduced tillering and plant height, delayed ear emergence and resulted in 8, 17, 27 and 39% reduction in grain yield, respectively. Waterlogging decreased oxygen diffusion rate (ODR), restricted root growth and reduced ion uptake, especially of N, P, K., Ca, Mg and Zn, and led to higher absorption of Na, Fe and Mn. However, the effects of waterlogging were more pronounced at higher alkalinity values. The results indicated that, to ensure optimum wheat yield in alkaline soils, waterlogging must be avoided.