Economic Considerations of Deficit Irrigation

Abstract

The factors related to potential yields of crops are briefly described. The most important are water, fertility, and available energy as measured by the evaporative potential. Mathematical yield models are presented relating crop evapotranspiration and total water available to relative yields. Data relative to irrigation amounts, rainfall, type of irrigation, water costs, costs of applying water, total crop production expenditures, and the range of crop incomes for various California crops are used to determine how various factors relate to the economics of deficit irrigation. The principal considerations in evaluating profit include whether land or water are limiting resources, the value of crop production based on yield and price, the contribution of rainfall to the crop water supply, the costs of irrigation water and its relationship to total crop production costs. Other considerations, such as leaching requirements and the need to promote uniform maturing of a crop, are briefly described. A minimum data set recommended for evaluating crop water requirements consists of rainfall and maximum and minimum temperatures. When water is cheap, rainfall is scarce, and yields and prices are favorable, the farmer should usually irrigate for approximately the maximum possible yield.