Cover crop species and termination timing influence corn production in the mid‐Atlantic

Winter cover crops support sustainable agriculture in the US mid‐Atlantic Coastal Plain by addressing challenges related to low soil organic matter and high nitrogen (N) leaching potential. We evaluated the effects of cover crop type (monoculture cereal rye [ Secale cereale L.] vs. rye–legume mixtures) and termination timing (preplant vs. at‐planting) on cover crop performance, soil inorganic N, and corn ( Zea mays L.) production. Experiments were conducted over three growing seasons (2019–2021) at two sites in Delaware, USA. The at‐planting termination maximized cover crop dry matter production (up to 7.02 Mg ha −1 ) and total N accumulation (up to 153 kg N ha −1 ), confirming the ecological benefit of delayed termination. Rye–legume mixtures consistently enhanced residue quality, producing lower C:N ratios (<25:1 for rye–hairy vetch) and accumulating significantly more N than the rye monoculture. However, planting cover crops presented trade‐offs for corn production. Cereal rye terminated at‐planting resulted in the highest C:N ratios (38.8:1 at Middletown in 2020), suggesting a high risk of N immobilization. Furthermore, at‐planting termination consistently led to a reduced final corn stand and resulted in a yield penalty compared to preplant termination in two site‐years at the irrigated Georgetown site. Despite these challenges, no cover crop treatment resulted in significant yield drag in all site‐years. In two of the six site‐year comparisons, cover crop treatments provided a significant yield benefit over the no‐cover crop control. Our results suggest that preplant termination of rye–legume mixtures can help maintain corn yield stability while integrating cover crops in mid‐Atlantic systems.