Determinate- and Indeterminate-Type Soybean Cultivar Responses to Pattern, Density, and Planting Date

Soybean [Glycine max (L.) Merr.] seed yield is influenced by planting date, pattern, and density of seeding, but cultivars differing in growth habit may vary in response to cultural treatments. Narrow-row compared to conventional wide-row plantings have consistently produced higher seed yields in the northern USA, where early maturity groups (MG) and indeterminate (INDT) types are commonly used. Positive responses to narrow rows have been less consistent in the southern USA, where late MG and determinate (DT) cultivars are common. Therefore, we hypothesize that this disparity in seed yield response to narrow-row culture between the two areas is due to inherent differences in DT- and INDT-type canopies resulting from their growth habits. This study, conducted in Gainesville, FL (29 ° 38′N) in 1984 and 1985, employed ‘Duocrop’ (INDT) and ‘Kirby’ (DT), May and July planting dates, 0.91-, 0.61-, and 0.30-m interrow spacings, and 0.18- and 0.08-m intrarow spacings in a Randomized Complete Block (RCB) design. Node and pod numbers, leaf area index (LAI), crop growth rate (CGR), total biomass, and seed yields were significantly increased (per unit land area) with increasing plant population density (PPD) up to a certain PPD, depending on spatial arrangement. The greatest seed yield of both INDT and DT types was from the May planting, narrow-row culture (0.30 m), and high PPD, but response to PPD was confounded with squareness (ratio of intra- to interrow distance among plants) of planting pattern. High PPD (18 to 42 plants m⁻² and high squareness values gave higher seed yields than combinations of lower PPDs and lower squareness values. We conclude that seed yield of both DT and INDT soybean in subtropical latitudes is optimized by May seeding, high PPD (40 plants m⁻²), and use of square planting patterns as approximated by narrow-row culture. Florida Agric. Exp. Stn. Journal Series no. 8098.