Modeling Yields from Rainfall and Supplemental Irrigation

Abstract

Frequently, the area of good soils suitable for irrigation far exceeds that for which adequate water is available for maximum crop production. Decisions and/or policies are often required relative to how much land should be irrigated with limited water supplies or the level of deficit irrigation desirable. The use of crop‐yield models provides a tool for determining how best to combine benefits from rainfall and irrigation. Some developments are described that facilitate the modeling of crop yields. A method that requires only temperature measurements for reliable estimates of potential evapotranspiration facilitates modeling at many locations where more complete climatic data are not available. A weather simulation procedure that provides good results without local calibration and requires only monthly climatic input makes it possible to develop a worldwide climatic data base for use with the existing crop‐yield models that otherwise require the availability of daily climatic data. Estimated probable relative yields for rain‐fed agriculture, and with one irrigation and with two irrigations, are calculated with a yield model operated with actual daily data and with data synthesized from a monthly climatic data base. The difference in yields calculated from historical data and synthesized data varies from 0 to 17%.