Reducing N₂O and NO emissions while sustaining crop productivity in a Chinese vegetable-cereal double cropping system

High nitrogen (N) inputs in Chinese vegetable and cereal productions played key roles in increasing crop yields. However, emissions of the potent greenhouse gas nitrous oxide (N₂O) and atmospheric pollutant nitric oxide (NO) increased too. For lowering the environmental costs of crop production, it is essential to optimize N strategies to maintain high crop productivity, while reducing the associated N losses. We performed a 2 year-round field study regarding the effect of different combinations of poultry manure and chemical N fertilizers on crop yields, N use efficiency (NUE) and N₂O and NO fluxes from a Welsh onion-winter wheat system in the North China Plain. Annual N₂O and NO emissions averaged 1.14-3.82 kg N ha^-1 yr^-1 (or 5.54-13.06 g N kg^-1 N uptake) and 0.57-1.87 kg N ha^-1 yr^-1 (or 2.78-6.38 g N kg^-1 N uptake) over all treatments, respectively. Both N₂O and NO emissions increased linearly with increasing total N inputs, and the mean annual direct emission factors (EF_d) were 0.39% for N₂O and 0.19% for NO. Interestingly, the EF_d for chemical N fertilizers (N₂O: 0.42-0.48%; NO: 0.07-0.11%) was significantly lower than for manure N (N₂O: 1.35%; NO: 0.76%). Besides, a negative power relationship between yield-scaled N₂O, NO or N₂O + NO emissions and NUE was observed, suggesting that improving NUE in crop production is crucial for increasing crop yields while decreasing nitrogenous gas release. Compared to the current farmers' fertilization rate, alternative practices with reduced chemical N fertilizers increased NUE and decreased annual N₂O + NO emissions substantially, while crop yields remained unaffected. As a result, annual yield-scaled N₂O + NO emissions were reduced by > 20%. Our study shows that a reduction of current application rates of chemical N fertilizers by 30-50% does not affect crop productivity, while at the same time N₂O and NO emissions would be reduced significantly.