Optimum Crop Water Application as Affected by Uniformity of Water Infiltration 1

Economic analyses of irrigated agriculture stress that yield levels which maximize profits can be attained with less water than maximum yields. A premise of such analyses is that irrigated soils have perfectly uniform rates of infiltration. A general method for evaluating the effects of nonuniform infiltration rates on optimal levels of water application is developed. Empirical analyses of the implications of non‐uniform infiltration rates on optimal levels of applied water, yields, and profits are reported for corn ( Zea mays L.) and cotton ( Gossypium hirsutum L.). The results are critically influenced by the nature of the water yield relationships postulated for these crops. For corn, where excessive water applications apparently have no effect on yield, nonuniform conditions reduce yield and profit. These outcomes can be offset by increasing water applications and optimal levels of applied water increase as the degree of uniformity declines. For cotton, nonuniformity leads to decreases in yields and profits that cannot be offset by increased water applications. This is attributable to the apparent sensitivity of cotton yields to excessive applications of water. For both crops, increases in the price of water provide little incentive to improve the uniformity of infiltration. The results demonstrate that conventional economic analyses which ignore infiltration uniformities, underestimate optimal levels of applied water, often substantially.