METHODS, AMOUNTS, AND TIMING OF SPRINKLER IRRIGATION FOR WINTER WHEAT

The yield response of winter wheat to LEPA double-ended-sock, LEPA bubble and overhead spray sprinkler methods was measured in the Southern High Plains with four irrigation amount and two irrigation timing treatments. Irrigation amount treatments ranged from zero to 100% of soil water replenishment in 33% increments. Irrigation timing treatments were shortening the 100% irrigation season by delaying irrigation until booting or by terminating irrigation during early grain filling. TAM 202 variety wheat was raised on Pullman clay loam soil, and irrigations were applied with a lateral move irrigation system during the 1993-1994 and 1994-95 cropping seasons. Grain yields did not vary significantly among the spray and LEPA sprinkler methods although in 1995 yields with the spray method were generally larger. In 1994, grain yields increased a statistically significant 1 Mg/ha for each 33% increase in irrigation, but significant yield increases occurred only for the first two irrigation increments in 1995. Deficit irrigation with the 33% and 66% irrigation amounts, generally increased the grain yield per unit of irrigation water more than deficit irrigation with the two irrigation timing treatments.