AN ECONOMIC ANALYSIS OF ALTERNATIVE IRRIGATION SCHEDULING METHODS

Four irrigation scheduling methods for corn were analyzed over a fifteen year historical weather pattern to determine how each of the methods perform in terms of returns over variable production costs. The four methods were: a continuous method, where water is applied on a continuous rotation across a field; a soil depletion method, where irrigation water is applied to refill the soil profile when soil moisture is depleted to one-half the holding capacity; a soil depletion method, where a one inch irrigation is applied when soil moisture is depleted to one-half the holding capacity; and, a frequency method in which enough water is applied to refill the soil profile at fixed time intervals. Each scheduling method was analyzed under two systems--sprinkler and gravity--, and three pumping capacities--5, 7 and 10 gallons per minute per acre. The corn yields for each situation and year were estimated using a physiological corn growth simulation model. The resulting corn yields were used along with estimated variable costs to calculate returns over variable production costs as a basis for selecting the most economic scheduling method for each situation. In addition to variable production costs, a user cost for water was estimated to reflect varying degrees of water scarcity. Finally, an analysis was conducted to assess the impact of a higher energy price on pumping costs and thus the selection of a scheduling method. Surprisingly there was very little difference in the economic performance of each scheduling method, except for the continuous method. The continuous method was the most inefficient in the use of water (as much as 30 acre inches for high pumping capacity situations compared to about 11 acre inches for the other methods, with little difference in yields). In the limited water and high energy cost situations, the more frugal water using scheduling methods were especially attractive. Thus the most economic choice was either the soil moisture depletion method, which restricts irrigation to one inch per application or the frequency method, depending on the irrigation system type or pumping capacity