GROWTH HABIT, PLANTING DATE, AND ROW-SPACING EFFECTS ON LATE-PLANTED SOYBEAN

When soybean [Glycine max (L.) Merr.] is double-cropped with small grains, as is often done in the southeastern USA, it yields less than full-season soybean. Incorporation of indeterminate growth habit into adapted germplasm has been suggested as a means of reducing the yield loss associated with delayed planting of determinate soybean (the predominant plant type grown in the Southeast). Little is known about management of indeterminate soybean in late-planted systems. Our objective was to compare response of determinate and indeterminate growth habit to row spacings and planting dates within a late-planted, narrow-row copping system. Determinate 'Braxton' [maturity group (MG) VII] and 'Kirby' and indeterminate experimental genotypes G82-8468 and G84-9006 (MG VIII) were compared in 0.60- and 0.30-m row spacings, and in June and July plantings for 4 yr in Alabama (32-degrees30' N lat). Determinates yielded more than indeterminates, but indeterminates had less yield loss caused by delayed planting. Indeterminate plant height was reduced more by later planting, but was greater than determinates in both plantings. Seed-filling period was reduced in the later planting in both determinate and indeterminate genotypes. Indeterminates had more mainstem pods and nodes per plant than determinates. Plants in 0.30-m rows had fewer days to canopy closure, mainstem nodes, number of branches, pods per branch, and pods per plant than plants in 0.60-m rows, but yields were not different. We concluded that row spacings < 0.60 m between rows provide no advantage for late-planted soybean, and neither growth habit has any advantage for yield in late-planted, narrow-row cropping systems.