Abstract

In the southeastern United States between 25 and 40% of the soybean [Glycine max (L.) Merr.] hectarage is double-cropped. Information on desirable production practices for double cropping soybeans after small grains, soybeans, or corn (Zea mays L.) is limited. The objectives of this study were to evaluate the effects of late (late June or early July) and ultra-late (late July or early August) planting dates, 51- and 91-cm row widths, irrigated and nonirrigated treatments, and Maturity Group VII determinate ('Bragg') and indeterminate (Ga76-32 and Ga76-18) genotypes on seed yield and other plant traits.The experiment was conducted at Plains, Ga. (32°N Lat 84°W Long) on a Greenville sandy loam (Rhodic Paleudult, clayey, kaolinitic, thermic family) soil in one dry (1978) and two intermediate rainfall seasons (1979 and 1980). Delays in planting from early July to late July resulted in an average yield reduction of 36 kg ha-1 day-1 (1.5%). In the dry season supplemental irrigation increased yield 355% (2,623 kg ha-1) in the late planting and 115% (635 kg ha-1) in the ultra-late planting. In the intermediate rainfall seasons irrigation increased yields 38% (784 kg ha-1) for the late and 15% (190 kg ha-1) for the ultra-late planting. The 51-cm rows averaged 17% (278 kg ha-1) higher seed yield than the 91-cm rows when averaged over years and all other factors. Genotypes did not differ in seed yield. The magnitude of the yield reduction from delays in planting and the high response to irrigation in dry seasons indicate the importance of intensive management to obtain maximum yields in these late-planted environments.