Reduced Seeding Rate for Glyphosate‐Resistant, Drilled Soybean on the Southeastern Coastal Plain

Abstract

Seeding‐rate recommendations for narrow‐row (<76 cm) soybean [Glycine max (L.) Merr.] on the southeastern Coastal Plain are almost double those of more traditional, wider row widths. A 2‐yr field study was conducted on a Dothan loamy sand soil to assess how main‐stem and branch yield fractions of four glyphosate‐resistant cultivars, ranging from maturity group (MG) V through mid‐MG VII, would respond to a lower‐than‐recommended seeding rate for narrow‐row culture. The cultivars Pioneer 95B32 (early MG V), Hartz 6255 (early MG VI), Delta and Pine Land 6880 (late MG VI), and Hartz 7550 (mid‐MG VII) were seeded at 370 000 seeds ha−1 and at the recommended rate of 620 000 seeds ha−1. Total seed yield of all cultivars was usually similar for the two seeding rates. Less seed yield from the main‐stem fraction with the lower seeding rate was usually compensated for by a higher seed yield from the branch fraction, except when insufficient rainfall occurred during critical periods of the growing season. Branch seed yield was more closely correlated with total seed yield at the low seeding rate (r = 0.675) than at the recommended seeding rate (r = 0.453) while the correlation between total seed yield and seed yield from the main‐stem fraction was similar for the two seeding rates (r = 0.579–0.613). In the absence of prolonged periods of drought stress, seeding rates for glyphosate‐resistant soybean grown in full‐season, narrow‐row systems can be reduced below current recommendations, thereby lowering seeding costs without decreasing seed yields.