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000061 v 5 There are essentially five alternative strategies for reusing drainage waters for irrigation: i) using the drainage water as a sole supply for irrigation, ii) using a blend of drainage and "fresh" water supplies, iii) using the two water supplies separately and sequentially in the so-called "serial/cyclic" method, iv) using the drainage water directly from the shallow water table by means of deficit irrigation, and v) using the drainage water from the shallow water table by means of a combination subsurface irrigation/drainage &ystem, which controls the water table depth to optimize its use by the crop. Each of these strategies has its own advantages and disadvantages. These strategies are reviewed elsewhere3. The most generally preferred method is the serial/cyclic method. In this strategy, sensitive crops (such as alfalfa, beans, melons, etc.) in the rotation are irrigated with "low salinity" water (usually the developed water supply of the irrigation project), and salt- tolerant crops (such as barley, sugar beets, etc.) are irrigated with the saline water (such as drainage water generated in the project). For the salt-tolerant crops, the switch to saline water is usually made after seedling establishment; preplant and initial irrigations being made with the low-salinity water. The secondary drainage resulting from such reuse is also collected/isolated and used successively (serially) elsewhere for even more salt-tolerant crops (including eventually halophytes). The ultimate unusable drainage water should be disposed of to some non-polluting outlet or treatment plant. The feasibility and utility of this serial/cyclic strategy has been supported by conceptual, modeling and experimental studies. The strategy, along with its advantages and disadvantages, are described more fully elsewhere2. Suffice it to say that better and more sustainable yields can generally be obtained by this strategy than can be obtained by using the saline water either solely for irrigation or after blending with low-salinity water. The next most appealing strategy is that of withholding irrigations in the latter part of the season to promote the extraction of water from the shallow groundwater; early season irrigations are managed to promote deep rooting. Blending is not generally advocated as a means to facilitate the reuse of saline drainage waters because, as compared to the serial/cyclic strategy, it reduces the absolute amount of water that can be consumed in transpiration (hence crop production) and it increases the salinity level in the soil during the most sensitive seedling-establishment period. An important principle to be understood in this matter is the following one: if a drainage (waste) water is too saline to be solely usable for the crop in mind, then no additional consumptive-use benefit can be gained from it by blending it with a low-salinity water. But a loss can occur in the amount of such benefit that could have been achieved from the sole use of the low-salinity water for crop production. 3 J.D.Rhoades.1998. Use of saline and brackish waters for irrigation: implications and role in increasing food production, conserving water. sustaining irrigation and controlling soil and water degradation. pp 261- 308, In R. Ragab and G. Pearce (eds.), Proc. Int I Workshop on Use of Saline and Brackish Water for Irrigation, July 23-24, 1998, Bali, Indonesia.