ET for Full and Deficit Irrigated Sorghum Under Drought Conditions.

USDA-ARS scientists at Bushland, Texas compared crop response of late- and early-maturing hybrids of grain sorghum irrigated under a center pivot system at four different irrigation treatment levels and two irrigation methods during the exceptional drought of 2011. One irrigation method was based on a soil water balance using weekly soil water readings from a field-calibrated neutron probe and the watering amount was 80%, 50%, 30% and 0% replenishment of soil water depletion to field capacity. Irrigation timing for the second method was based on plant feedback using thermal stress index thresholds derived from proximal canopy temperature measurements. Watering amounts were based on percentages of average peak daily water use for grain sorghum in the Texas High Plains region. For the late-maturing hybrid, overall, mean dry grain yields were similar between irrigation methods and mean ET was significantly less for the plant feedback method. For the early-maturing hybrid, overall mean dry grain yields were similar,however, mean seasonal ET was significantly greater for the plant feedback method. The reduction of ET in the more deficit irrigation treatments, regardless of irrigation method, negatively impacted grain yields. The water balance method also indicated that in 2011, mean seasonal ET levels were 18 to 29% greater than, and mean dry grain yields were 25% less than historical levels of seasonal ET and dry grain yields, respectively, for grain sorghum grown in this region between 1980 and 2013.