WATER MANAGEMENT FOR PROFIT MAXIMIZATION

Managing irrigation water to replace soil moisture depletion is equiva lent to managing water for yield maximization, and does not constitute efficient resource use. Irrigation water allocation models should be based on profit maximization, which will occur at the same point that maximizes water use efficiency. The objectives of this study were to: (i) optimize water allocation based on profit maximization; and (ii) c ompare curvilinear and linear water production functions for profit ma ximization. Water production functions were developed for four seasona l harvests of alfalfa (Medicago sativa L.) from data collected over a 6-yr field research project conducted at the University of Nevada, Ren o. GAMS/MINOS computer program was used to determine the amount of wat er that should be allocated to individual harvests in order to maximiz e profits. When quadratic production functions were used, water was al located among all four harvests. In fact, water was allocated across a ll harvests at both low and high levels of available water supplies. A n example showed that the net return from applying 21 in. of water acr oss all harvests was $388.76/acre. When 21 in. of water was applied, i n equal amounts, to the first two harvests only, the return was $350.5 7/acre. The results demonstrate the importance of considering profit m aximization for efficient water allocation. The study also showed that when a linear yield function was used in the profit function, all the water was allocated to one harvest, which does not make practical sen se. Finally, the methodology is applicable to any irrigated crop for w hich an empirical water production function has been developed.