YIELD AND WATER-USE EFFICIENCY OF CORN IN RESPONSE TO LEPA IRRIGATION

Center-pivot sprinklers are rapidly expanding on the Southern High Pla ins, and LEPA (low energy precision application) application methods a re widely used in this region tb reduce water application losses, to u se the relatively low well yields, and to reduce energy requirements f or pressurization. This study was conducted to evaluate LEPA irrigatio n response of corn (Zea mays L.) on slowly permeable Pullman clay loam (fine, mixed, thermic Torrertic Paleustoll). The effects of irrigatio n amount were investigated in afield study during the 1992 and 1993 cr opping seasons at Bushland, Texas. In 1992, a wetter than normal seaso n, grain yields varied from 0.6 to 1.2 kg/m(2) while in 1993, which wa s a season with slightly less than normal rain, grain yields varied fr om 0.4 to over 1.5 kg/m(2) as irrigations increased from no-post plant irrigations to fully meeting the crop water use. Irrigation amounts f or the full irrigation varied from only 279 mm for the wet year to ove r 640 mm for the more normal year. A significant relationship was foun d between grain yield and water use for the two years described as GY (kg/m(2)) = 0.00169 [WU (mm) - 147] with an r(2) of 0.882 and a S-y/x of 0.10 kg/m(2). Deficit irrigation of corn, even with LEPA, reduced y ields by affecting both seed mass and kernels per ear. Generally, the grain yield was in proportion to dry matter yield. LEPA irrigation was shown to be efficient in terms of partitioning the applied water into crop water use. Irrigation amounts should not exceed 25 mm for altern ate furrows (0.76-m rows) LEPA on the Pullman-type soils with furrow d ike basins.