Double-Crop Soybean Production System in the USA - Literature Review.

Soybean [Glycine max (L.) Merr.] following winter wheat (Triticum aestivum L.) is the most prevalent double cropping system in the United States. Double cropping increases cash flow and profits and ensures global food security by increasing food production. However, double-crop soybean yields 10 to 40% less than full-season production system due to several factors. Maintaining wheat stubble height ≤30-cm during harvesting minimizes any negative effect of wheat residue under no-tillage system. Late planting shortens the soybean growing season, offers less time to develop optimum leaf area, and reduces yield. Harvesting wheat at high moisture (200 g H₂O kg^-1 grain) or using early maturing wheat cultivar with comparable yield potential can allow 7 to 10 d early soybean planting. Planting double-crop soybean in narrow rows at high seeding rates ensures quick attainment of optimum leaf area index (LAI) of 3.5 to 4.0 by R2 to R4 stages to maximize solar radiation intercept and canopy photosynthesis. Small amount of starter N may also help obtain optimum LAI quickly by enhancing early vegetative growth. Double-crop soybean is leaf damage or defoliation than full-season soybean.