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New formulas are proposed for quantitatively assessing irrigation water quality. Except for extremely unsuitable waters, irrigation water quality can be assessed only in the context of the conditions under which the water is to be used. These conditions include the infiltration rate of the soil (I), the evapotranspiration rate (E), the irrigation frequency and duration (tc and ti, respectively) the net downward drainage rate below the root zone (O) and the maximum permissible salinity and chloride concentration for the crop to be grown (ECd and Cld, respectively). When drainage is non-limiting, the potential leaching fraction (LF) is given by: LF = 1 − (Etc/Iti) and when drainage is limiting by: LF = O/(E + O). The maximum permissible EC and Cl concentration of irrigation waters (ECi and Cli, respectively) are calculated from: ECi = LF × ECd and Cli = LF × Cld. Potential leaching fraction calculations will also be useful for estimating CaCO3 precipitation, and the degree to which specific toxic materials will be concentrated as water is evapotranspired.
water quality, irrigation water, salinity, irrigation, soil water, evapotranspiration, soil infiltration, drainage, salt water, plants (organisms)
Plant physiologist, Agricultural Research Service, Riverside, Calif.