A review of double-crop soybean production in comparison to full-season system in the United States

Soybean [Glycine max (L.) Merr.] after winter wheat (Triticum aestivum L.) is the most common double-cropping system in the United States, driven by the desire for increased cash flow and profits and bolstering global food security. Despite its popularity, double-cropping often results in a lower soybean yield compared to full-season systems, attributed to various factors. Maintaining wheat stubble height ≤30 cm during harvesting and planting soybean in between wheat rows minimizes some negative effects of wheat residue. Planting double-crop soybean immediately after wheat harvest is crucial, as late planting is the primary factor of diminished double-crop yield. Late planting results in a shorter soybean growing season, limiting the time available to develop an optimal leaf area index (LAI). Harvesting wheat at high moisture or planting early-maturing wheat cultivars with comparable yield potential can facilitate 7–10 days earlier soybean planting. Employing narrow rows (19 cm) during double-crop soybean planting ensures rapid attainment of optimum LAI (3.5–4.0) by the pod set stage, maximizing solar radiation interception and canopy photosynthesis. A 16 kg ha⁻¹ starter N may enhance early vegetative growth, expediting optimal LAI achievement. Indeterminate soybean may be more appropriate for double-crop due to fewer branching habits, which reduces competition in narrow rows compared to determinate counterparts. Double-crop soybean in narrow rows requires higher seeding rates than full-season to maximize yield by optimizing LAI expeditiously. Additionally, double-crop soybean is more vulnerable to drought and insect–pest infestation or defoliation than full-season system. Therefore, managing double-crop soybean with the same diligence as full-season is imperative to maximize yield and profitability.