Evapotranspiration of Irrigated Winter Wheat — Southern High Plains

Abstract

Models of water use for irrigation scheduling and for crop growth simulation require validation of the evapotranspiration (ET) submodel. In this study ET was measured for irrigated winter wheat (Triticum aestivum L.) at Bushland, Texas, in the semi-arid Southern High Plains for the 1989-1990, 1991-1992, and 1992-1993 winter wheat cropping seasons using weighing lysimeters that contained undisturbed monoliths 3 3 2.3 m deep of Pullman clay loam soil (Torrertic Paleustolls). Weather data from a nearby station were used to compute daily ET values for a reference alfalfa crop (hypothetical) using the ASCE Manual No. 70 equations based on the Penman-Monteith equation and several other widely used potential or maximum ET models. Linear regressions between ET estimated from widely used equations and the reference alfalfa ET equation indicated that direct comparisons with computed ET values could not be reliably predicted with simple ratios. For the computed reference alfalfa ET base, peak basal crop coefficients (Kcb) varied from 0.88 to 1.00 for the three seasons and were lower than those reported from other locations. Peak mean crop coefficients (Kc) varied from 0.83 to 0.94 for the three seasons. Seasonal ET varied from 791 to 957 mm for the three seasons. Evapotranspiration and crop coefficients for winter wheat varied considerably with season.