Harvest Aid Application Timing Affects Wheat and Relay Intercropped Soybean Yield

Abstract

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.