SALINITY AND UNIFORMITY OF WATER INFILTRATION AS FACTORS IN YIELD AND ECONOMICALLY OPTIMAL WATER APPLICATION.

The effects of irrigation water salinity and uniformity of infiltered water on average crop yields, economically optimal water applications, and profits are analyzed for steady-state and transient salinity conditions. Input data specific for corn (Zea mays L. ) are used in the analysis to illustrate results. Except at very low water application levels, decreasing uniformity of infiltered water results in decreasing yield at a given water application rate and at all levels of water salinity under both steady-state and transient conditions. Profit-maximizing water applications increase under conditions of increased irrigation water salinity, decreased uniformity of infiltered water, and decreased water price; whereas profits decrease with increased salt concentrations and decreased infiltered water uniformity. Economically optimal water applications and profit can vary by factors of three or more depending on water prices, salt concentrations, and uniformity of infiltered water. Therefore accurate determination of these variables is important for decision making at the farm level.