Water Deficits—Irrigation Design and Programming

Irrigation system design and economic analysis of proposed irrigation schemes require quantitative prediction of relationships between crop production and water use. In keeping with recent irrigation design practice, a comprehensive table is presented to update and add to earlier information defining the limits of allowable soil water depletion prior to irrigation of various crops for avoidance of yield reducing water deficits. Table values of soil water suction (bars) and available soil water depletion (percent) are given. A continuing research program on preseason irrigation programming techniques and development of water production functions for principle crops, relating yield reductions to water deficits are presented. Within this context, the importance of detailed knowledge of the capabilities of annual crops to utilize stored soil water via root system expansion is emphasized. An example of this type of information and its implications for irrigation design is presented from results of USBR funded research with corn at UC.