RIDGE-TILLAGE FOR CONTINUOUS GRAIN-SORGHUM PRODUCTION WITH LIMITED IRRIGATION

Improved soil and water conservation are basic goals for crop production systems in the semi-arid southern Great Plains (SGP) of the USA and similar regions, and managing crop residues on the soil surface plays a key role in attaining these goals. Residue production by dryland grain sorghum (Sorghum bicolor (L.) Mocnch) is often too low in semiarid regions to improve soil and water conservation, but much greater amounts are produced by irrigated sorghum. However, irrigation water may be limited, as in the SGP, and a limited-irrigation approach is sometimes used for sorghum, which responds well to timely irrigations. This study, conducted on Pullman clay loam (fine, mixed, thermic Torrertic Paleustoll) from 1986 to 1992, determined effects of residue management treatments involving ridge tillage on continuous production of two grain sorghum hybrids with limited irrigation. Treatments were conventional (ConvT) tillage, which involved stalk shredding, disking, and rebuilding of the ridges soon after sorghum harvest, and two ridge tillage methods (residues shredded early (at harvest) - ConsTE; residues shredded late (at planting) - ConsTL). Soil water storage between crops was greatest with the ConsTL treatment and least with the ConvT treatment. Soil water use by sorghum was greater (66 mm) with ConsTL than with ConvT (51 mm). Mean initial plant populations and panicles harvested were greater with ConvT than with other treatments, but grain yields were less with ConvT (4.21 Mg ha-1) than with ConsTE (4.42 Mg ha-1) and ConsTL (4.52 Mg ha-1). Mean stover yields and seed weight (mg per seed) were not affected by tillage treatments. Although differences were relatively small, mean grain and stover yields were greater for the 'Pioneer' cultivar (4.53 and 5.68 Mg ha-1) than for the 'Funk' cultivar (4.24 and 5.25 Mg ha-1). Mean water use efficiency differences among treatments and between hybrids were small. Ridge tillage was better than conventional tillage for continuous grain sorghum production with limited irrigation in the semi-arid SGP. Ridge tillage that retained residues on the surface until planting increased soil water storage due to reduced evaporation and increased snow trapping, which resulted in the greater yields than where residues were incorporated with soil soon after crop harvest.