Lysimetric Evaluation of Daily Potential Evapotranspiration Models for Grain Sorghum

Evapotranspiration (E t ) information is needed for many applications in agricultural and natural resource management, but commonly used prediction equations have not been adequately tested far the dry, high radiation, windy conditions of the Southern Great Plains. In order to test such equations, two precise weighing lysimeters at Bushland, TX, were used to measure daily E t from wellwatered, irrigated grain sorghum [ Sorghum bicolor L.) Moench] in 1987 and 1988. Forms of the Penman, Penman‐Monteith, Jensen‐Haise, and Priestley‐Taylor models were evaluated for prediction of potential evapotranspiration (E tp ). The Penman‐Monteith model provided the best predictions of E tp and predicted well across the entire range of measured E t . Forms of the Penman model with empirically fit wind functions overpredicted E tp by 20 to 409/0, and aftempts to fit a linear wind function to our data were not satisfactory The Jensen‐Hake model, requiring only daily mean temperature and solar radiation data, overpredicted by 30%, but performed consistently across the range of E t measured. Modification of the Priestley‐Taylor model with vapor pressure deficit or temperature advection terms is recommended. Without such modification, the model overpredicts at low E t rates and underpredicts at high E t rates.