Development and Evaluation of Evapotranspiration Models for Irrigation Scheduling

EVAPOTRANSPIRATION (ET) data for irrigated crops in southern Idaho were used to develop relationships for estimating net radiation and potential ET for the USDA-ARS Computerized Irrigation Scheduling Program. ET estimated with the initial relationships compared well with recent measurements obtained with two sensitive weighing lysimeters. The:average daily measured Et for alfalfa for 128 days when there was full cover was 7.23 mm, while the average daily estimated ET was 7.15 mm. Crop curve relationships were developed from the ET results for snap beans (Phaseolus vulgaris L). The depletion of soil water was predicted for two years of irrigated beans with the scheduling program using the improved crop curves and compared with the measured as a test of its performance. The standard deviation of the difference between predicted and measured was about 0.95 mm/day from planting until harvest. The results also demonstrated the importance of obtaining representative meteorological data for irrigation scheduling