Winter crop effect on soybean production in the Southeast United States

Various winter crops can be produced before soybean [Glycine max (L.) Merr] in the Southeast United States, however the effect of these winter crops on soybean productivity and the optimum maturity group to use following various winter crops remains unknown. This experiment was conducted in five environments across North Carolina in 2019 and 2020 to understand the effect of winter crop and soybean maturity group (MG) on soybean productivity. Winter crops investigated included cereal rye (Secale cereale L.) as cover crop, cereal rye–crimson clover (Trifolium incarnatum L.) as cover crop mixture, May fallow, wheat (Triticum aestivum L.) for grain, rapeseed (Brassica napus L.) for grain, and June fallow. Three soybean cultivars (MGs III, V, and VII) were evaluated following each winter crop. Data collected were cover crop/residue biomass, winter crop grain yields, soybean stand, soil moisture, soil temperature, soybean chlorophyll content, and soybean yield. Across environments, winter crop did not affect soybean yield despite differences in soybean stand, soil moisture, soil temperature, and soybean chlorophyll content following various winter crops. The results indicate that across the environments evaluated in this experiment, factors such as soybean stand, soil moisture, or N availability were not limiting factors for soybean productivity and that soybean yield response is relatively insensitive to previous crops. Across winter crops, greater yields typically were achieved with a MGs V and VII cultivar than with a MG III cultivar. Results from this experiment demonstrate that the insensitivity of soybean yield to the previous crop allows for flexibility incorporating soybean into rotations and that regardless of the previous winter crop, yield is typically optimized with a MG V cultivar or later when standard management practices are employed. Core Ideas Soybean yield was similar among the winter crops highlighting insensitivity to the previous crop. Soybean stand was often reduced following heavier biomass producing winter crops. Soil moisture, soil temperature, and soybean chlorophyll content were affected by winter crop. Maturity groups (MGs) V and VII varieties typically outyielded MG III varieties regardless of winter crop.