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 (NO) emissions. However, knowledge on NO emission from GV fields and its mitigation are limited due to considerable variations of NO 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 NO emissions from GV fields and evaluated NO mitigation efficiency of alternative nitrogen (N) managements. The experiment period spanned three rotation periods and included seven vegetable growing seasons. We measured NO 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 NO emissions ranged between 2.09 and 19.66, 1.13 and 11.33, 0.94 and 9.46, and 0.15 and 3.27kgNha for FP, R, R+DCD, and CK, respectively. The cumulative NO 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 3.73kgNha (CK). The R and R+DCD treatments significantly (P<0.05) reduced the NO 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 NO emissions and great NO mitigations can be achieved through reasonably reducing the N-fertilizer rate and/or applying a nitrification inhibitor. The large variations in the NO emission and mitigation across different vegetable growing seasons and rotational periods stress the necessity of multi-year observations for reliably quantifying and mitigating NO emissions for GV systems.