Impact of soybean planting date and row width on weed suppression and yield

Variable weather patterns and extended growing seasons over the last couple of decades have prompted growers to plant soybean [ Glycine max (L.) Merr.] earlier than the historical standard. Field experiments were conducted in Michigan over three site‐years to evaluate soybean planting date, row width, and herbicide program on weed suppression and soybean yield. Planting date had minimal impact on soybean stand, except at one site‐year where soil crusting reduced stand 44%–52% in early (April 12–21) compared with the typical planting date (May 11–23). Weed densities and biomass for the untreated controls were substantially higher in early compared with the typical planting in all site‐years. Soybean planted in 19 cm rows (370,500 and 494,000 seeds ha −1 ) reduced weed biomass 29%–47% compared with 76 cm rows (370,500 seeds ha −1 ) in two of three site‐years when weeds were not controlled; however, the effects of row width were not observed when a PRE herbicide was applied. Similarly, narrow row widths (<76 cm) resulted in quicker canopy closure compared with 76 cm rows in two of three site‐years. Regardless of row width, a PRE followed by a POST herbicide program provided the most consistent weed control. Soybean yield was 7% greater for 19 cm rows at 494,000 seeds ha −1 compared with 76 cm rows in two of three site‐years. However, planting date did not affect soybean yield when weed control was good in all site‐years. Overall, combining narrow row widths with a complete herbicide program is equally beneficial for soybean planted early and at typical planting dates.