Deep tillage and crop rotation effects on cotton, soybean, and grain sorghum on clayey soils

Deep tillage (subsoiling) of clayey soils in the fall when the profile is dry is a new concept that results in increased yields and net returns from soybean [Glycine mar (L). Merr.] grown without irrigation. Crop rotation may also result in increased crop yields. Field studies mere conducted on Tunica clay (clayey over loamy, smectitic, nonacid, thermic, Vertic Haplaquept) near Stoneville, MS (33 degrees 26' N lat) to determine the individual and combined effects of fall deep tillage and crop rotations on crop yields and net returns. Treatments included monocrop cotton [Gossypium hirsutum (L.)], soybean, and grain sorghum [Sorghum bicolor (L.) Moench], and biennial rotations of cotton with grain sorghum and soybean with grain sorghum grown without irrigation and in either a conventional-till (CT) or deep-till (DT) production system. Yields from all cotton and soybean crop sequences grown in the DT respectively averaged 541 kg ha(-1) and 525 kg ha(-1) greater than comparable cotton (2184 kg ha(-1)) and soybean (2983 kg ha(-1)) crop sequences grown in the CT. Net returns from monocrop cotton ($552 ha(-1)) and soybean ($462 ha(-1)) in the DT respectively averaged $392 ha(-1) and $121 ha(-1) more than similar crop sequences in the CT. Rotations increased cotton and soybean yields but not net returns because of the low value of the grain sorghum component. These data indicate that fall deep tillage should be incorporated into monocrop cotton and soybean crop sequences to maximize and stabilize net returns from these crops on Tunica clay.