Abstract While cover crop adoption in the United States has increased, limited research exists on the impact of cover crop mixtures on soybean ( Glycine max (L.) Merr.) production. This study evaluated the effects of cereal rye ( Secale cereale L.), cereal rye + hairy vetch ( Vicia villosa ) mixture (rye + vetch), and cereal rye + crimson clover ( Trifolium incarnatum ) mixture (rye + clover), along with pre‐plant and at planting termination timings, on total aboveground biomass, nitrogen (N) accumulation, C:N ratio, soil inorganic N, and soybean yield. A 3‐year study at two Delaware locations revealed that at planting terminated rye + clover produced the highest biomass, reaching 17.56 Mg ha − 1 in 2020, exceeding regional averages. Grass + legume mixtures generally outperformed monoculture rye in biomass and N content, except in 1 year at Middletown. The C:N ratio of mixtures (9:1–43:1) was consistently lower than monoculture rye (17:1–68:1). Soybean yield was influenced by cover crops only in 2018 with rye + vetch increasing yield by 0.45 Mg ha − 1 at Georgetown, but no differences were observed between rye + clover, rye, and control. The results suggest that rye + legume mixture (with low rye seed rate) can enhance biomass production, reduce C:N ratios, and potentially supply N through more rapid decomposition to high‐yielding soybeans, particularly under irrigated conditions. This study highlights the benefits of grass + legume cover crop mixtures for improving biomass and N dynamics without compromising soybean yield.
Pokhrel et al. (Thu,) studied this question.