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<br />l\) <br />"'-1 <br />"-l <br />ao <br /> <br />In the following case examples, the volumes of Viw <br />were normalized by expressing them relative to Vet' <br />i.e., for the case where Vet is taken to be equal to 1. <br /> <br />Results of case Examples and Discussion <br /> <br />Case 1 <br /> <br />The conditions: use of a good-quality water of ECiw = <br />0.5 ds/m for the irrigation of beans (ECe=1.0 dS/m). <br />This water is similar in salinity level to that of the <br />irrigation water supply of the Wests ide Project in the <br />San Joaquin Valley of California. <br />This water is judged suitable for the irrigation of <br />beans, since the product (ECiw) (Fe) is less than ECe at <br />practical levels of leaching. For example, the <br />predicted level of average salinity within the rootzone <br />resulting from long-term irrigation with this water <br />supply at L=O.15 is only 0.75 dS/m (0.5 dS/m x 1.51; the <br />value 1.51 was obtained from Figure 1). Beans can <br />tolerate a value of ECe=1.0 dS/m without any significant <br />loss in yield using conventional irrigation management <br />(see Maas, 1986). The leaching requirement for this <br />case, as obtained from figure 1, is even lower, i.e., <br />0.09. If beans were irrigated at this latter most- <br />efficient level of leaching, the EC of the drainage <br />water (ECdw) resulting from irrigation would be 5.55 <br />dS/m (ECiw/L, i.e., 0.5/0.091. Obviously one could not <br />use this latter drainage water again to grow beans, <br />since the resulting average root Zone salinity could not <br />be kept within acceptable limits at any reasonable level <br />of L. <br /> <br />I <br /> <br />Case 2 <br /> <br />The conditions: use of the saline drainage water of <br />EC=5.55 dS/m, as obtained in case 1, for the irrigation <br />of cotton (ECe=7.7 dS/m). <br />Water of EC=5.55 dS/m, which was judged unsuitable <br />for growing beans (see case I), is quite acceptable for <br />growing cotton, since the predicted level of average <br />rootzone salinity resulting from it's use for irrigation <br />is less than the ECe of cotton at practical levels of <br />leaching. For example, the average ECe will be less <br />than ECe for any value of L in excess of 0.17 (see <br />figure 1 for the case of FA=7.7/5.5). When irrigated at <br />L=0.17, ECe will be 7.7 dS7m and ECdw will be 32 dS/m <br />(5.5/0.17). <br />Thus it is apparent that the saline drainage water of <br />EC=5.55 dS/m (that resulted from the irrigation of beans <br />with the good quality water) could be used satisfac- <br />torily to grow salt-tolerant crops like cotton, barley, <br />sugar beets, etc. It is also true that the drainage <br /> <br />(1 <br /> <br />Rhoades <br />