Plant Density and Soybean Maturity in a Soybean-Maize Intercrop

Long, warm seasons that are inadequately filled by sole crops can be more productive when more fully utilized by intercrops. The effect of plant densities and plant maturity on the magnitude of this increased productivity is not well documented. During two seasons of greater than or equal to 190 d at 29 degrees 38' N lat, maize (Zea mays L.) at 12 densities (from 1.0 to 10.0 plants m(-2)) and two soybean (Glycine mar (L.) Merr.] cultivars, representing Maturity Groups VIII (Cobb) and VI (Davis), at three densities (3.0, 8.5 and 24.0 plants m(-2)) were grown in intercrop and sole crop in fan designs. Soybean was planted 56 d (1985) and 31 d(1986) after maize. Soybean density did not affect maize yield (P less than or equal to 0.05). Although predicted sole-crop Cobb and Davis seed yields were not different (P less than or equal to 0.05), averaging 336 g m(-2), the two cultivars were differentially affected by maize density Each unit increase in maize density (plants m(-2)), reduced soybean seed yield 20% for Cobb and 47% for Davis at 3.0 soybean plants m(-2) and 7% for Cobb and 35% for Davis at 24.0 soybean plants m(-2). Cobb had two to three trifoliolates expand after maize removal, while Davis had all leaves fully developed at maize harvest. Land equivalency ratios (LER) were <1.1 for Davis-maize and peaked at 1.4 for Cobb-maize. Area-time equivalency ratios (ATER) were <0.8 for Davis-maize and peaked at 0.9 for Cobb-maize. Davis-maize was not a viable intercrop. The Cobb-maize intercrop at 24 soybean plants m(-2) over a range of maize densities utilized the long growing season more productively (LER = 1.4) than in sole crop; the increased productivity was due to increased season use (ATER < 1.0).