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 3.27kgNha^-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 3.73kgNha^-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.