Yield-scaled N2O emissions as affected by nitrification inhibitor and overdose fertilization under an intensively managed vegetable field: A three-year field study

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Vegetable fields exhibit contrasting characteristics of high nitrous oxide (N2O) emissions and low nitrogen use efficiency (NUE) compared with other croplands due to intensification. A three-year field experiment consisting of eleven successive vegetable crops was conducted to investigate the effects of wide range of overdose fertilization and chlorinated pyridine (CP, a nitrification inhibitor) on the N2O emissions, agronomic NUE, yield-scaled N2O emissions, marginal yield and marginal N2O emission. Five urea N input rates, combining without (U) or with CP (U-CP), were applied at 0, 587, 880 (the conventional N rate), 1173, and 1760 kg N ha−1 yr−1. Results showed that N2O emission responses to N rate fitted well with cubic models in both the U and U-CP group treatments. Meanwhile, CP addition significantly reduced annual cumulative N2O emissions and the N2O emission factor from 39.1 to 79.7 kg N ha−1 yr−1 and 2.7–3.6% to 31.6–56.2 kg N ha−1 yr−1 and 1.5–2.2%, respectively, in relation to the U treatments at the same N rate. Moreover, CP addition significantly decreased the yield-scaled N2O emissions from 0.30 to 0.52 kg N t−1 to 0.22–0.35 kg N t−1 without obvious influence on vegetable yield. The 587 kg N ha−1 yr−1 was the optimal N rate for both the U and U-CP treatments as indicated by the agronomic NUE and yield-scaled N2O emissions. Thus, one third reduction of the conventional N fertilizer rate combined with CP was recommended to mitigate N2O emissions and maintain the yield for the sustainable development of intensified leafy vegetable production.