Assessing double‐crop soybean management practices in central Illinois

Plain Language Summary

Winter wheat–soybean double‐cropping is becoming more common in central Illinois, but soybean planting after wheat often does not occur until late June to early July. Late planting means soybean has less time to grow, which can lead to shorter plants, fewer nodes and pods, and lower yield potential. This study examined three management practices that may improve double‐crop soybean performance in this region; they involve maturity group (MG), seeding rate, and starter fertilizer. Across 2 years, full‐season cultivars (MG 3.6–3.7) yielded 2%–5% (1.4–2.5 bu ac ⁻¹ ) more than early‐maturing cultivars (MG 3.0–3.1) when fall frost risk was low. This suggests that growers can continue to use their adapted full‐season varieties for double cropping in most years. The seeding rate had a greater effect on yield. Full‐season cultivars reached maximum yield at ∼202,000 seeds ac ⁻¹ , while early‐maturing cultivars needed ∼249,000 seeds ac ⁻¹ to maximize yield. Last, applying starter fertilizer containing nitrogen and sulfur did not consistently increase yield. Even after wheat, the small yield increase did not justify the cost. Overall, choosing an adapted MG and using higher seeding rates than for full‐season soybean planted at normal times are practical and profitable strategies for double‐crop soybean in central Illinois.