Greenhouse Gases Emissions And Influencing Factors From Typical Greenhouse Vegetable Fields In Beijing Suburbs

Agriculture is one of the important sources of global greenhouse gases （GHGs） emissions. CO₂,CH₄and N₂O emitted from cropland have attracted more and more attentions from the internationalscientists. At present, the studies on GHGs emissions from agricultural ecosystems mainly focus on themain grain crops such as rice, wheat, corn, but only few studies have conducted measurements fromvegetable fields, especially greenhouse vegetable fields. In this study, the emissions of N₂O, CH₄andCO₂from greenhouse vegetable field including tomato and cabbage were separately analyzed using thestatic chamber technique. Four treatments, Control （CK）, farmers’ traditional practice （FP）, decrease ofnitrogen （N） fertilization （OPT）, and the combination of the decrease fertilization and nitrificationinhibitor （OPT+DCD）, were implemented in a typical greenhouse vegetable field in Beijing suburbs totest the impacts of main factors such as fertilization, soil moisture, temperature on N₂O, CH₄and CO₂emissions from the agroecosystem, aiming to provide the scientific basis for searching appropriatemitigation measures. The main results were summarized as follows:The field observation indicated that N₂O emission fluxes from greenhouse vegetable fields showedobvious dynamic variations due to the N fertilizer and irrigation input. The N₂O emission peaks wereshort lived and fluctuated largely and the highest emissions occurred during the4-5day period just afterfertilization and irrigation. The number of peaks and strength during the tomato growth season weregreatly higher than that during the cabbage growth season. The cumulative N₂O emissions calculated bythe method of interpolation in the tomato season (ranging from9.90to21.74kg N hm^-2) were higherthan that in cabbage season (ranging from5.68to7.78kg N hm^-2).The emission factors （EFs） in tomatoseason from different treatments ranged from0.55%to1.15%, of which FP treatment was1.15%higherthan the IPCC default EF, while the EFs from the treatments during cabbage season ranged from0.71%to0.82%, of which the FP treatment was the highest with EF0.82%.The factors such as temperature, moisture, or fertilizer management had great effects on N₂Oemissions for the tested site. The decrease of N fertilizer significantly reduced the cumulative N₂Oemissions while keeping the production. Compared to FP treatment, the OPT treatment significantlyreduced the cumulative N₂O emissions by41.67%in tomato season and23.69%in cabbage season, andthe OPT+DCD treatment significantly reduced the cumulative N₂O emissions by54.46%in tomatoseason and27.05%in cabbage season. Application of nitrification inhibitor can reduce the cumulativeN₂O emissions, but it did not reach the level of significance. Soil temperature and moisture significantlyaffected N₂O emissions in the two vegetables growth season. In cabbage season, N₂O emissionsincreased exponentially with soil temperature and moisture, while in tomato season, there was a highlysignificant positive correlation between N₂O emissions and soil moisture, whereas no significantcorrelation was found between N₂O emissions and soil temperature.CH₄emissions from the tested site showed no obvious dynamic changes. The greenhouse vegetablefields showed a net atmosphere CH₄sink as a whole. The cumulative CH₄absorption in the tomatoseason (ranging from0.56to0.90kg C hm^-2) was higher than that in cabbage season (ranging from0.26 to0.31kg C hm^-2).There was no significant difference in CH₄exchanges among the treatments, andneither the significant correlation was found between CH₄exchanges and soil temperature or moisture.CO₂emissions from the fields showed the same seasonal variation as air temperature in thegreenhouse. The cumulative CO₂emissions in the tomato season (ranging from5.48to10.11t C hm^-2)were higher than that in cabbage season (ranging from1.99to2.65t C hm^-2). The application of organicfertilizer and chemical fertilizer significantly increased CO₂emissions. Soil temperature was the mainenvironmental factors influencing CO₂emissions. There was a significant positive correlation betweenCO₂emissions and soil temperature, whereas no significant correlation was found between CO₂emissions and soil moisture in both tomato and cabbage seasons.Comprehensively considering the fertilizer application rates, N₂O emissions and vegetables yields,the management practices such as decreasing the N fertilizer input combining with the nitrificationinhibitor can effectively reduce the N₂O emissions during greenhouse vegetables growth period, whichhad greater potential in reducing N₂O emissions if further combining with other management practicessuch as irrigation.