Multiple-year nitrous oxide emissions from a greenhouse vegetable field in China: Effects of nitrogen management

The greenhouse vegetable (GV) field is an important agricultural system in China. It may also be a hot spot of nitrous oxide (N2O) emissions. However, knowledge on N2O emission from GV fields and its mitigation are limited due to considerable variations of N2O emissions. In this study, we performed a multi-year experiment at a GV field in Beijing, China, using the static opaque chamber method, to quantify N2O emissions from GV fields and evaluated N2O mitigation efficiency of alternative nitrogen (N) managements. The experiment period spanned three rotation periods and included seven vegetable growing seasons. We measured N2O emissions under four treatments, including no N fertilizer use (CK), farmers' conventional fertilizer application (FP), reduced N fertilizer rate (R), and R combined with the nitrification inhibitor "dicyandiamide (DCD)" (R + DCD). The seasonal cumulative N2O emissions ranged between 2.09 and 19.66, 1.13 and 11.33, 0.94 and 9.46, and 0.15 and 3.27 kg N ha(-1) for FP, R, R + DCD, and CK, respectively. The cumulative N2O emissions of three rotational periods varied from 18.71 to 26.58 (FP), 9.58 to 15.96 (R), 7.11 to 13.42 (R + DCD), and 1.66 to 3.73 kg N ha(-1) (CK). The R and R + DCD treatments significantly (P < 0.05) reduced the N2O emissions under FP by 38.1% to 48.8% and 49.5% to 62.0%, across the three rotational periods, although their mitigation efficiencies were highly variable among different vegetable seasons. This study suggests that GV fields associated with intensive N application and frequent flooding irrigation may substantially contribute to the N2O emissions and great N2O mitigations can be achieved through reasonably reducing the N-fertilizer rate and/or applying a nitrification inhibitor. The large variations in the N2O emission and mitigation across different vegetable growing seasons and rotational periods stress the necessity of multi-year observations for reliably quantifying and mitigating N2O emissions for GV systems. (C) 2017 Elsevier B.V. All rights reserved.