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

A climate with high evaporative demand and limited precipitation restr ict yields of winter wheat (Triticum aestivum L.) grown in the semiari d U.S. southern High Plains. Stress effects can be avoided or minimize d by management practices that increase soil water storage at planting or by application of irrigation water We analyzed a 178 crop-year dat abase of irrigated and dryland wheat data from Bushland, TX, to develo p relationships that define the grain yield and water-use efficiency ( WUE) response to a wide range in seasonal evapotranspiration (ET) asso ciated with water deficits and to evaluate yield response to stored so il water at planting. Tile 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 yi elds observed in the combined database were 2.8 and 8.2 Mg ha(-1) for dryland and irrigated wheat, respectively. The Linear regression respo nse of grain yield to soil water stored at planting, 1.57 kg m(-3), wa s significantly higher than the yield response to seasonal ET. Largely similar WUE values occurred over a wide range of seasonal ET within i rrigated and dryland data sets; however, WUE values for irrigated whea t averaged about double the values for dryland wheat. A curvilinear re lationship determined between WUE and yield emphasizes the importance of obtaining high yields for efficient water use.