Field studies were conducted from 1999 through 2004 in southeastern Kansas to evaluate the influence of tillage method [conventional (CT) and no-till (NT)], row spacing-population system (7.5-, 15-, and 30-inch rows planted at 225,000, 175,000, and 125,000 seeds/acre, respectively), and glyphosate application timing on soybean [ Glycine max (L.) Merr.] yield, weed control, and net economic returns. Herbicide treatments were: (i) preplant residual (pendimethalin) followed by glyphosate at 3 weeks after planting (WAP); (ii) glyphosate at 3 WAP; (iii) sequential glyphosate at 3 and 5 WAP; and (iv) glyphosate at 8 WAP. Soybean followed grain sorghum [ Sorghum bicolor (L.) Moench] in a 2-year rotation. Tillage method influenced yield very little. Narrower row spacing (7.5- and 15-inch) increased soybean yields 2 to 4 bu/acre in high-yielding environments compared to 30-inch rows and also provided greater weed control. Glyphosate applied sequentially (3 and 5 WAP) provided the highest weed control, but a single glyphosate application 3 WAP often produced the greatest net return, regardless of tillage or row spacing system. The results suggest that the adoption of NT planting will likely increase soybean net returns to a greater extent than reducing row spacing in the eastern Great Plains.
