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

The yield response of winter wheat to LEPA double-ended-sock, LEPA bub ble and overhead spray sprinkler methods was measured in the Southern High Plains with four irrigation amount and two irrigation timing trea tments. Irrigation amount treatments ranged from zero to 100% of soil water replenishment in 33% increments. Irrigation timing treatments we re shortening the 100% irrigation season by delaying irrigation until booting or by terminating irrigation during early grain Filing. TAM 20 2 variety wheat was raised on Pullman clay loam soil, and irrigations were applied with a lateral move irrigation system during the 1993-199 4 and 1994-95 cropping seasons. Grain yields did not vary significantl y among the spray and LEPA sprinkler methods although in 1995 yields w ith the spray method were generally larger In 1994, grain yields incre ased a statistically significant 1 Mg/ha for each 33% increase in irri gation, bur significant yield increases occurred only for the first tw o irrigation increments in 1995. Deficit irrigation with the 33% and 6 6% irrigation amounts, generally increased the grain yield per unit of irrigation water more than deficit irrigation with the Two irrigation timing treatments.