A grass–legume cover crop maintains nitrogen inputs and nitrous oxide fluxes from an organic agroecosystem

Legume cover crops are central to an ecological nutrient management approach that can reduce nitrogen (N) losses from agriculture. Diversifying cropping systems with a legume–grass crop mixture could further N by increasing soil assimilation and synchronizing mineralization uptake the following crop. We established four winter treatments (crimson clover, cereal rye, clover–rye mixture, weedy fallow control) in organic grain agroecosystem had been managed for 30 years legume as only external source. hypothesized would provide similar inputs of biologically fixed N2 compared sole legume, while reducing N2O emissions during decomposition tillage. measured aboveground biomass C:N clover fixation, inorganic fluxes throughout corn growing season tillage, at harvest. Even reduced seeding rate inputs, litter C:N, no differences cumulative emissions. During first peak flux, were 2–5 times higher relative rye fallow, between mixture. There treatment second peak, which followed major rain event. contextualized these findings calculating 6-year partial mass balance this agroecosystem, was slightly negative (?6.8 ± 0.8 kg ha?1 year?1) when accounting historical mean annual nitrate leaching. Overall, harvested exports approximately legume-based rotation, suggesting legacy has promoted efficient cycling. However, results our field experiment indicate short-term flux rates incorporation be high even Additional strategies disturbance therefore needed tighten cycling agroecosystems.