GRAIN-SORGHUM RESPONSE TO SPRINKLER APPLICATION METHODS AND SYSTEM CAPACITY

The crop yield response of grain sorghum to four sprinkler methods and four irrigation amounts which simulated varying irrigation capacities was evaluated during 1992 and 1993 at Bushland Texas, in the Southern High plains. Irrigation methods were LEPA sock, LEPA bubble, in-canop y spray near ground level, and overhead spray. The application devices were installed on a three-span, hose-fed lateral-move sprinkler syste m. Irrigations were scheduled from neutron soil water measurements in a designated control treatment receiving 100% irrigation by the LEPA s ock method. Soil water in the control plots was maintained above 75% o f the plant available level by simultaneously applying 25-mm irrigatio ns with all four sprinkler methods as the 100% irrigation amount. Defi cit irrigation treatments received 75, 50, and 25% of the control trea tment application on the same date. All furrows were diked to minimize runoff and enhance surface storage from irrigation and rainfall. The 100% irrigation treatments received 250 and 325 mm of irrigation in 19 92 and 1993, respectively, along with 310 and 223 mm, respectively, of rainfall from emergence to the last irrigation. Grain sorghum yields were primarily affected by irrigation amount and to a lesser extent by sprinkler method, especially for the two smaller irrigation amounts. With deficit irrigation, the LEPA bubble and sock methods yielded bett er than the spray methods likely due to reducing evaporation from the crop canopy and soil and thus increasing the amount of water available for transpiration. For example with LEPA in 1992, grain sorghum yield s were reduced only 1 % while the irrigation amount was reduced from 2 50 mm for 100% irrigation to 125 mm for 50% irrigation.