Considerations for Determining Optimal Row Spacing in Soybean Production

Abstract Soybean ( Glycine max L. Merr.) row spacing in the US varies from about 7 to 40 inches, but there has been a widespread shift from wide (≈30 inches) to narrow (≈15 inches) row spacing in the last decades, largely driven by a consensus that narrow rows can yield higher. In this management guide, we explain the general mechanisms driving higher yields in narrow row systems, summarize findings from major US studies evaluating the effect of row spacing on soybean yield, and discuss other considerations that may affect the decision‐making on row spacing. The yield advantage from narrow rows is primarily driven by greater light interception early in the soybean growth cycle, which results from plants being more equidistant. In addition to driving photosynthesis and growth, this increased light interception early in the soybean growth cycle accelerates canopy closure, thus enhancing weed suppression and early‐season water uptake. Overall, the literature indicates that narrow rows outyield wide rows by an average of 7% and about 76% of the time. Narrow rows provide greatest yield advantage over wide rows when early season growth is constrained, like in scenarios of late planting (including double cropping), early maturity cultivars, high competition with weeds, and in low‐yielding environments (less than 45 bushels acre −1 ). In contrast, narrow rows often do not outyield wide rows when severe drought stress happens late in the season, and when inter‐row tillage is critical to alleviate subsoil compaction (e.g., cotton [ Gossypium hirsutum L.]–soybean rotations in southern US).