Developing Economically Optimal Irrigation for Soybean Production in East Central Mississippi.

Water stress is one of crucial limiting factors for soybean production in east central Mississippi. A large number of research have stud ied the effect of irrigation on soybean yield. But most of them are targeting on the maximization of grain yield, while profitability of irrigation is usually more of a concern from producers’ perspective. Depending on the irrigation system installation costs, water price, and soybean price, the yield-maximizing irrigation water amount can be far from profit-maximizing. However, in the current literature, studies that directly address the profit-maximizing irrigation water amount are still relatively rare.

This study builds upon the existing research of irrigation’s effect on soybean productivity, and incorporates prices and cost information to further develop the economically optimal irrigation management for soybean producers. The objective was achieved through three steps: (1) use the APEX model to simulate soybean yields under various conditions,; (2) use a multiple regression model to estimate the continuous response of yield to water stress level, especially how the response interacts with different soil, weather and location conditions; (3) incorporate the price and cost information to the estimated yield-water response relationship, and set up the profitability maximization problem with various constraints (budget, water capacity, etc.), and solve for it using mathematic programming techniques.

The results showed that the economically optimal supplementary irrigation water amount varies substantially across locations, soil types, rainfall conditions, water costs and soybean market prices. In most cases, the profit-maximizing irrigation amount differs greatly from the yield-maximizing irrigation amount, with also a considerably different profit gap. Those results can serve as guidelines of building budget tables for soybean irrigation to assist producers for improving profitability under different conditions and price scenarios.