Adjusting Management Practices Using Glyphosate‐Resistant Soybean Cultivars

Glyphosate [ N ‐(phosphonomethyl)glycine]‐resistant soybean [ Glycine max (L.) Merr.] cultivars have increased drastically in usage and acceptance. Little information exists to see how glyphosate‐resistant soybean cultivars should be managed. The objective of this study was to evaluate different row‐spacing and plant population systems using three weed management systems. A field study was conducted from 1997 through 1999 at six locations in Wisconsin. Soybean was planted in 19‐, 38‐, and 76‐cm rows at a recommended (optimum), low, and high plant population for each row‐spacing system with three weed management systems [glyphosate‐resistant soybean cultivars with glyphosate (GRS/G), glyphosate‐resistant soybean cultivars with conventional herbicides (GRS/CN), and conventional soybean cultivars with conventional herbicides (CN/CN)]. In northern Wisconsin, soybean yield in a GRS/G system did not respond to plant population while GRS/CN and CN/CN systems yielded 6% more in high than in low plant population. Additionally, soybean yield responded positively to plant population in 76‐cm row CN/CN and GRS/CN systems in northern Wisconsin. In southern Wisconsin, GRS/G and GRS/CN systems yielded 6% less than the CN/CN system. No differences were observed among weed management systems in central and northern Wisconsin. Averaged across weed management systems and plant population, 19‐ and 38‐cm rows yielded 7, 9, and 10% more than 76‐cm rows in southern, central, and northern Wisconsin, respectively. No yield differences were observed between optimum and high plant population across Wisconsin, averaging 4% greater yield than the low plant population. The results demonstrated that it might be beneficial to alter management practices when using glyphosate‐resistant soybean in some production environments in Wisconsin.