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l'\) ""-l '"'-I' CD :;,-:,;.:~} (>~ volume needing ultimate disposal out of the project area would be greatly reduced through such reuse of drainage water for irrigat~on within the project. In this case the percent reduction in volume of drainage water ultimately needing to be discharged is 83 (100-17; one can also calculate this value using equation 1, i.e., 1-5.55/32). The secondary saline drainage water of EC=32 dS/m that resulted in this case can not be used again to grow cotton (or sugar beets, etc.), since in a favorable condition for disposal or desalting, i.e., it is in a relatively small volume and at a relatively high salt-concentration. Case 3 The conditions: use of a blend of the "good quality" water of case 1 (EC~0.5 dS/m) and the very saline drainage water IEC=32 dS/m) achieved in case 2 for the irrigation of beans. The blend is made up of 40 units of the "good quality" water and 1 unit of the very saline drainage water; the ECiw of this blend is 1.5 dS/m. It is concluded that this blended water could . theoretically be used to grow beans without yield loss (however a large penalty must be paid in doing so. as will be shown later), since the predicted resulting level of average rootzone salinity can be kept less than the ECe (1.0 dS/m) by irrigating at a very high (though impractical) level of leaching (Lr=0.6, as obtained from Figure 1). This very high level of required leaching makes the use of such water impractical for the irrigation of beans, except in very sandy soils. Even if used in such soils, the process of blending reduces the volume of water in the total supply that can be used by the bean crop (or any other salt-sensitive crop) for evapotranspiration. as shown in the following paragraphs. The relative volume of irrigation water required to meet ET and to achieve Lr in this case is 2.500 units (l/l-Lrl. Of this volume, 1.500 units will pass through the root zone to.become drainage water. (Vdw=Viw - Vetl. Of the 2.500 un~ts of blended 1rrigat~on water, 2.439 units (40/41 x 2.500) consist of the "good quality" water of EC~0.5 dS/m and 0.061 units 11/41 x 2.5001 consist of the very saline drainage water of EC=32 dS/m. Thus, at best, only 0.061 units of the 1.50 units of volume of the drainage water that resulted from irrigating this bean crop with the blended water could possibly have come from the very saline water that was used to make this blend. Therefore, the rest (i.e.. 1.439 units) must have come from the "good-quality" water put into the blend. This amount of drainage water is much higher than that for the case where only the "good quality" water of EC~0.5 dS/m was used to grow the 7 Rhoades