WATER-YIELD RELATIONSHIPS FOR IRRIGATED AND DRYLAND WHEAT IN THE US SOUTHERN PLAINS

A climate with high evaporative demand and limited precipitation restrict yields of winter wheat (Triticum aestivum L.) grown in the semiarid U.S. southern High Plains. Stress effects can be avoided or minimized by management practices that increase soil water storage at planting or by application of irrigation water We analyzed a 178 crop-year database of irrigated and dryland wheat data from Bushland, TX, to develop relationships that define the grain yield and water-use efficiency (WUE) response to a wide range in seasonal evapotranspiration (ET) associated with water deficits and to evaluate yield response to stored soil water at planting. The PT-grain yield relationship was determined as Linear, with a regression slope of 1.22 kg grain per m(3) ET above the ET threshold of 208 mm required to initiate grain yield. Marximum yields (>7.0 Mg ha(-1)) required 650 to 800 mm seasonal ET. Maximum yields observed in the combined database were 2.8 and 8.2 Mg ha(-1) for dryland and irrigated wheat, respectively. The Linear regression response of grain yield to soil water stored at planting, 1.57 kg m(-3), was significantly higher than the yield response to seasonal ET. Largely similar WUE values occurred over a wide range of seasonal ET within irrigated and dryland data sets; however, WUE values for irrigated wheat averaged about double the values for dryland wheat. A curvilinear relationship determined between WUE and yield emphasizes the importance of obtaining high yields for efficient water use.