An economic study on the optimum input mix for irrigated pastures

Abstract

The purpose of this study was to maximize the returns to labor and fixed assets from feeder steers utilizing forage produced on irrigated orchardgrass pasture. A linear programming model was designed to analyze the economic alternatives of various application rates of irrigation water and nitrogen on the irrigated pasture. Irrigation water and nitrogen were not limited and were constrained only by their respective costs. Later, the quantities of irrigation water, nitrogen, and capital were sequentially varied and the effect on the returns noted. A model was also developed which analyzed the effect on returns to labor and fixed assets when marginal cost of water was varied from $4 per acre foot to $0 per acre foot of water. The results of this study indicate that as the marginal cost of irrigation water goes to zero, the optimal application rate of irrigation water approaches a rate which keeps the soil at field moisture capacity at all time. As the marginal cost of irrigation water increased above about $1.50 per acre foot, the optimal application rate of irrigation water approached that application rate which just keeps the soil moisture above the wilting point for orchardgrass; approximately one-third the amount of water used when the marginal cost approached zero. The optimal application of nitrogen was a direct function of the amount of water used, as the amount of water varied, the amount of nitrogen varied in about a 1:1 relationship. In general, the returns to labor and fixed assets were adversely affected more by rates of nitrogen which were in excess to the optimal amount than by application rates which were less than the optimal amount.