LEPA irrigation of grain sorghum with varying water supplies

Research was conducted on the Texas Southern High Plains to determine optimum water management practices for low energy precision application (LEPA) irrigation of grain sorghum. Irrigation quantity treatments ranged from 0.4, 0.7, 1.0, and 1.3 BI (BI=ET-rain) and were applied both alternate and every furrow at intervals of 3.5, 7, 10.5 and 14 days during the growing season from 1992 through 1994. The experiment was conducted at Halfway, Texas on an Olton loam soil with moderately slow permeability. Highest average grain sorghum yields were obtained with the 3.5-day irrigation intervals (7.57 Mg ha(-1)) which was significantly different (P less than or equal to 0.05) from 7, 10.5, and 14-day intervals when averaged across all years and quantities. These treatments yielded 7.37, 7.33, and 7.33 Mg ha(-1) respectively. Grain yield was significantly different between preplant only, 0.4 BI and 0.7 BI water quantities. However there were no yield differences between 0.7, 1.0, and 1.3 BI water quantity treatments (7.51, 7.62, and 7.55 Mg ha(-1), respectively) which resulted in seasonal irrigation water use efficiency (IWUE) for the 0.7 BI treatment of almost double that of the 1.3 BI treatment (1.16 kg m(-3) vs. 0.63 kg m(-3)). Total seasonal water use efficiency [WUE=yield/(irrigation+rainfall+soil water depletion)] varied with irrigation quantity and frequency. Values were 1.69, 1.56, 1.36, and 1.19 kg m(-3) for the 0.4, 0.7, 1.0, and 1.3 BI treatments respectively. WUE for preplant only irrigation was 1.52 and was equal to the 0.7 BI irrigation treatment. The three year average 3.5-day irrigation interval resulted in a significantly higher WUE than the 14-day interval (1.47 vs. 1.43 kg m(-3), respectively). There were no significant responses in yield, IWUE or WUE due to applicator location (alternate vs. every furrow). Tests show that deficit seasonal LEPA irrigation (approximately 0.7 BI) of medium maturity grain sorghum varieties on the Southern High Plains can be employed without significant yield loss if adequate preplant soil water is available. Frequent irrigation intervals added only slightly to yield but are desirable in order to decrease surface relocation of water from high intensity LEPA application.