Row‐Spacing and Seeding Rate Effects on Glyphosate‐Resistant Soybean for Mid‐Atlantic Production Systems

Glyphosate [N‐(phosphonomethyl)‐glycine]‐resistant soybean [Glycine max (L.) Merr.] production in the Mid‐Atlantic occurs under full‐season and double‐crop production systems. Row‐spacing and seeding rate manipulation affects the yield of soybean. This study evaluated the effects upon yield caused by reductions in seeding rate from current standards for these two systems. During 2000–2002, row spacing (19 and 38 cm) and seeding rates (current standard, 20 and 40% less, and 20% greater than the standard) were tested using four glyphosate‐resistant cultivars representative of the maturity groups for the region. Tests were conducted for both full‐season and double‐crop systems at two Maryland locations for each per year on coastal plain soils. During the 3 yr, only 1 out of 48 total cultivar × row spacing comparisons for the two production systems had better yield with 38‐cm rows. At best, 38‐cm row spacing produced equivalent to the 19‐cm rows. A 20% seeding rate reduction (345800 seeds ha−1 for full‐season and 444600 seeds ha−1 for double‐crop production) was generally found to not yield significantly different than the standard seeding rates for both systems. A 40% reduction consistently had yield significantly less than the standards in both systems. These results indicate a 20% seeding rate reduction can be a cost‐saving practice for glyphosate‐resistant soybean production in the Mid‐Atlantic. With no yield loss at a 20% reduced seeding rate, additional profit ranging from $14.30 to $27.72 ha−1 can be realized.