Deep ripping and blocked furrow effects on lower 1/3 furrow irrigation infiltration

Methods of primary tillage between annual crops of corn or sorghum on the Southern High Plains commonly includes disking followed by chiseling or occasional deeper loosening by ripping (subsoiling) or moldboard plowing. On slowly permeable clay loams, irrigation water infiltration on the upper 2/3 of graded furrow lengths is usually adequate to wet the rooting depth of about 1.2 m (4 ft). However, reduced infiltration opportunity time on the lower 1/3 can cause inadequate wetting and reduce grain yield unless excessive furrow runoff is allowed. This study was conducted during 1995-1996 on the Southern High Plains at Bushland, Texas, to evaluate the effects of deep ripping the lower 1/3 on irrigation infiltration, soil water storage and distribution, and grain yield along the furrow. Rip treatments were tilled 0.3 m deep and the remainder of the study area was chiseled 0.15 m deep. Treatments included ripping with furrow ends blocked to prevent runoff, ripping with open-end furrows, chiseling with blocked furrow ends, and chiseling with open-end furrows. With blocked-end furrows, irrigation was cut off after about 2 h ponding on the more rapidly advancing furrows to allow water to reach ends of slower furrows. Open-end furrows received 6 to 8 h of runoff during the infiltration phase. Deep ripping increased infiltration during infiltrometer tests in the lower 1/3 furrow interval by 26% to 29% immediately after primary tillage. However, subsequent furrow traffic and soil consolidation from irrigation and rainfall reduced this tillage effect on infiltration to where net irrigation, evapotranspiration, and grain yield were not significantly affected on a field average basis for the complete crop season. Furrow blocking with earlier irrigation cut-off reduced gross application by about 24% and net application by 17% to 20% while the related reduction in grain yield was only 13% in 1995. In 1996, furrow blocking reduced net irrigation by 11% and grain yield by only 3%. Growing season water use efficiency was not significantly affected by any treatment.