Water and energy conservation through irrigation scheduling. Rept. for 1 July 1983-30 September 1984

Over the past five years, irrigated areas have increased substantially in Michigan and in other midwestern states. Existing water-balance models used for irrigation scheduling have been largely developed for application in the arid to semi-arid west. The procedures in these models for estimating evapotranspiration (ET) using crop coefficients, effective rainfall, and deep-percolation estimates were inadequate for application to areas with significant growing season rainfall. The overall goal of this research was to develop improved methods for scheduling the timing and amount of water used for irrigation in the more-humid areas of the midwest. To address the need for improved crop coefficients, a technique for using a portable chamber to measure actual ET in the field was developed and compared to ET measured by a weighing lysimeter. In addition, an interactive microcomputer program was developed that includes historic rainfall probabilities in irrigation-scheduling forecasts.