Early-seeded soybean [ Glycine max (L.) Merr.] relay intercropped into standing wheat ( Triticum aestivum L.) using soybean seed-coat technology may allow profitable wheat production in the Midwest on highly erodible soils. Dry conditions in mid- to late June have reduced relay intercropped soybean stands and yield in some years. We hypothesized that using glyphosate as a wheat harvest aid would reduce the impact of wheat interference on relay intercropped soybean grain yield and increase gross margins. Field research conducted over four site-years in upstate Missouri evaluated timings for application of glyphosate as a harvest aid on wheat and relay intercropped soybean. The cost effectiveness of these cropping systems was compared to full-season soybean, double-cropped wheat-soybean, and wheat-only production systems. Glyphosate applied to wheat 1 wk before harvest, after late dough, in a relay intercrop production system with coated-soybean maintained wheat grain yields similar to nontreated wheat, and increased soybean grain yields 290 to 770 kg ha -1 compared to nontreated wheat relay intercropped or double-cropped with soybean. Earlier glyphosate application timings (2-3 wk before wheat harvest) reduced wheat grain yields 10 to 25% and grain density 3 to 13%, but soybean yield increased 430 to 520 kg ha -1 compared to nontreated wheat in a relay intercrop system. A relay intercrop system with seed coat technology and glyphosate as a harvest aid may allow farmers to maintain wheat in their crop rotation while minimizing risk associated with early fall frost or dry conditions at seeding that may otherwise decrease double-crop soybean yields.
