| Global warming has become a worldwide environmental problem, which is caused by the increasing concentration of greenhouse gases (GHGs) in the atmosphere. Nitrous oxide (N2O) is one of the most potent greenhouse gases contributing to global warming. Agriculture is a major source of global atmospheric N2O, which constitutes 60% of its total anthropogenic sources. Over the past several decades, N2O emissions from croplands have been given more attention for its large source strength. At present, many studies concentrated on N2O emissions from the major crops such as rice, wheat or corn, while little is known concerning N2O emissions in the vegetable especially greenhouse vegetable cropping systems in southeast China.This study was conducted in a typical greenhouse vegetable cropping system in the suburbs of Nanjing in China. Three treatments were involved consisting of the plots with no fertilizer application as control, the plots with conventional urea application (F) and the plots with urea-formaldehyde application (UF). The static chamber-GC method was used to simultaneously in-situ measure N2O fluxes in the greenhouse vegetable cropping system for a whole year. We aim to give an insight into the seasonal or annual dynamics and intensity of N2O emission in facility vegetable cropping systems as affected by slow-release nitrogen fertilization; to examine the impacts of soil temperature or moisture, as well as soil mineral N availability on N2O emissions from greenhouse vegetable systems; and finally to evaluate the N2O mitigation potential with slow-release nitrogen fertilizer application under the greenhouse vegetable cropping practice.The main results of this study listed as follows:The N2O fluxes from greenhouse vegetable fields present obvious seasonal variation. The emission intensity of N2O was higher with increased temperature during the cropping season. The emission intensity during green pepper season was significantly lower than that in eggplant season. Seasonal total of N2O emissions in green pepper season ranged from 0.05 kg N hm-2 to 5.10 kg N hm-2, and that in eggplant season differed from 1.33 kg N hm-2 to 9.78 kg N hm-2. Field managements contributed a lot to seasonal N2O emissions. Seasonal N2O peaks occurred within a week following the initial soil tillage although with low intensity; The N2O peaks were also captured within the first 5 days following N fertilizer or irrigation but only sustained a short period.Fertilizer application significantly increased seasonal or annual N2O emissions in facility vegetable cropping systems. The annual fertilizer N-induced N2O emission factor averaged 2.18% and 1.51% for plots with urea and urea-formaldehyde application, respectively, which are substantially higher than the IPCC default value (1%).Urea-formaldehyde application significantly decreased N2O emissions but without reducing the vegetable yield. Annual cumulative N2O emissions totaled 14.88 kg N hm-2 and 10.90 kg N hm-2 for the urea and urea-formaldehyde applied plots, respectively. Under the identical annual N input level, the plots with urea-formaldehyde decreased annual N2O emissions by 26.74% relative to plots with urea.Additionally, N2O emissions significantly correlated with soil water content and temperature during the vegetable cropping cycle, which presented to be the key factors driving N2O production in facility vegetable cropping systems.In conclusion:By comparing seasonal or annual total N2O emissions and vegetables yields among different fertilizer treatments, low N2O emissions and high vegetable yields would be simultaneously achieved by optimizing field managements together with slow-release N fertilizer application in greenhouse vegetable cropping systems. |
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