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<br />USE OF SALINE DRAINAGE WATER FOR IRRIGATION
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<br />27
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<br />the salinity level (EC) of an irrigation water is about 7.5 dS / m. Shalhevet and
<br />Kamburov (1976) in their worldwide survey of irrigation and salinity found
<br />that waters of up to 6000 mg/L were being used successfully.
<br />Though this number of documented reports on the successful use of brackish
<br />water for irrigation is relatively limited, these examples are sufficient to sup-
<br />port the premise that water more saline than presently termed usable in con-
<br />ventional water classification schemes can be successfully used for irrigation,
<br />Waters having salinities of up to about 8 dS/m EC or 6000 mg/L TDS are ap-
<br />parently usable with conventional management.
<br />Indirect evidence of the potential to use saline drainage waters for irrigation
<br />can be obtained from computer models developed to predict soil water com-
<br />position resulting from irrigation, and models developed to relate crop re-
<br />sponse to soil salinity. The suitability of a saline water for irrigation should be
<br />evaluated by taking into account the specific conditions of use, including the
<br />crop grown, soil properties, irrigation management, cultural practices, and cli-
<br />matic factors. The assessment of suitability should ideally consist of (1) pre-
<br />dicting the composition, osmotic potential and matric potential of the soil water
<br />of the rootzone, both in time and space, resulting under the specific conditions
<br />of management and climate; and (2) interpreting such information in terms
<br />of how suitable the resulting soil conditions are for rooting and how the crop (s)
<br />in question would respond to such soil and climatic conditions (Rhoades, 1972).
<br />A computer model for assessing water suitability for irrigation which em-
<br />ploys the above approach has been developed (Rhoades and Merrill, 1976;
<br />Rhoades, 1984). The accuracy of the predicted soil water salinities, sodicities
<br />and osmotic potentials have been shown to be acceptable (Oster and Rhoades,
<br />1975, 1977), The assumption that crop production is predictable from inte-
<br />grated osmotic and matric potentials or from different indices of soil salinity
<br />dependent on irrigation management has been demonstrated (Ingvalson et a!.,
<br />1976; Letey et aI., 1985; Bresler, 1987; Dinar et a!., 1986). Available crop tol-
<br />erance to salinity data (Maas, 1986) have been shown to be acceptable in such
<br />predictions (Letey et aI., 1985; Bresler, 1987).
<br />When one applies such models to the assessment of the suitability of saline
<br />waters for irrigation, one concludes that tyPical drainage waters can generally
<br />be used for irrigation, of course with crop selectivity being limited to those of
<br />appropriate tolerance (Rhoades, 1977; Dinar et a!., 1986). These predictions
<br />support the empirical results and reports cited above of such feasibility.
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<br />CROP /WATER MANAGEMENT STRATEGY TO FACILITATE THE USE OF SALINE
<br />WATERS FOR IRRIGATION
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<br />Typically farmers will not use brackish water for irrigation if access to water
<br />of lower salinity is available, unless the brackish water can be used without
<br />losses in yield and cropping flexibility, or significant changes in farming prac-
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