Reducing N 2 O 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 (N ₂ O) 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 N ₂ O and NO fluxes from a Welsh onion-winter wheat system in the North China Plain. Annual N ₂ O 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 N ₂ O and NO emissions increased linearly with increasing total N inputs, and the mean annual direct emission factors (EF _d ) were 0.39% for N ₂ O and 0.19% for NO. Interestingly, the EF _d for chemical N fertilizers (N ₂ O: 0.42-0.48%; NO: 0.07-0.11%) was significantly lower than for manure N (N ₂ O: 1.35%; NO: 0.76%). Besides, a negative power relationship between yield-scaled N ₂ O, NO or N ₂ O + 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 N ₂ O + NO emissions substantially, while crop yields remained unaffected. As a result, annual yield-scaled N ₂ O + 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 N ₂ O and NO emissions would be reduced significantly.
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