OPTIMUM LATERAL SPACING FOR SUBSURFACE DRIP-IRRIGATED CORN

A two-year study was initiated in the spring of 1990 on a Keith silt l oam soil (Aridic Argiustoll) in northwest Kansas to determine the opti mum dripline lateral spacing for irrigated corn (Zea mays L.) using su bsurface driplines installed at a depth of 40-45 cm in a direction par allel to the corn rows. Average corn yields were 13.6, 12.8, and 12.2 Mg/ha for dripline spacings of 1.5, 2.3, and 3.0 m, respectively, for a seasonal-irrigation amount of 462 mm. Yields decreased to 10.8 and 9 .3 Mg/ha when irrigation was reduced by 33 and 50% for the wider 2.3- and 3.0-m dripline spacings, respectively. The wider dripline spacings resulted in nonuniform horizontal distribution of available soil wate r As a result yields decreased with horizontal distance from the dripl ine. The highest yield, highest water use efficiency, and lowest year- to-year variation were obtained with the 1.5 m dripline spacing. An ec onomic analysis indicated that because yield reductions were so great, the wider dripline spacings would be justified only at very high drip line costs and or very low corn grain prices.