Row spacing effects on soybean production in North Carolina

Abstract

North Carolina soybean [Glycine max (L.) Merr.] growers use a diverse range of row spacings, commonly between 7.5 and 38 inches. Research findings regarding the effect of row spacing on soybean yield have been inconsistent and influenced by factors such as planting date and environmental conditions. Although small-plot data from North Carolina often indicates that narrower row spacings lead to higher yields, growers have raised concerns about the potential benefits of wide rows when ripping is employed in environments exhibiting symptoms of subsurface compaction. Research was conducted over 2 years (2021–2022) in the Coastal Plain region to evaluate the effects of wide row ripped spacing (36 or 38 inches) compared to un-ripped narrower spacing (15 inches) on plant population, canopy cover, soil compaction, and yield across four environments. One of the environments included an additional treatment with an un-ripped drilled row spacing of 7.5 inches. Although seeding rates were calibrated similarly, the ripped wide-row spacing treatments led to lower achieved plant population, predominantly due to adverse seed bed conditions resulting in lower germination caused by the inline ripper. The un-ripped narrow row spacings (7.5 and 15 inches) consistently demonstrated 7–25% greater canopy cover than ripped wider spacings (36 and 38 inches) by the flowering stage (R1). Soil penetration resistance varied by row spacing in only two environments, with differences generally lacking agronomic significance (i.e., penetration resistance <2 MPa). Yield results indicated no significant effect of row spacing in three out of four environments; in the fourth environment, the un-ripped 15-inch row spacing yielded significantly more than both the un-ripped drilled and ripped wide-row soybeans. In the environments in this study, wide-row ripped treatments offered no agronomical advantage over narrow row un-ripped treatments.