Development and Evaluation of Evapotranspiration Muueis for Irrigation Scheduling

VAPOTRANSPIRATION (ET) data for irri- 1.7.1 gated crops in southern Idaho were used to de- velop relationships for estimating net radiation and potential ET for the USDA-ARS Computerized Irri- gation Scheduling Program. ET estimated with the initial relationships compared well with recent mea- surements obtained with two sensitive weighing lysim- eters. 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 mea- sured as a test of its performance. The standard devia- tion of the difference between predicted and measured was about 0.95 mm/day from planting until harvest. The results also demonstrated the importance of ob- taining -representative meteorological data for irrigation scheduling.