Effects of Nitrogen Application on Soil Nitrification and Denitrification Rates and N2O Emissions in Greenhouse

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Nitrous oxide (N2O) has significant impact on global warming and leads to the depletion of ozone in the stratosphere. Agricultural soil is regarded as a major source of N2O emissions. In recent years, greenhouse grown vegetables have rapidly developed in China. Although excessive fertilizer application in greenhouse vegetable production can result in increased N2O emissions, research data on such emissions from greenhouse vegetables, such as cucumber, remains limited. In this study, four nitrogen (N) fertilizer treatments including 1,200 (N1200, traditional N amount), 900 (N900), and 600 kg N ha-1 (N600) and the control (N0) were carried out on cucumber in a greenhouse in the North China Plain. Results showed that N2O emissions mainly occurred in the first five days after topdressing, and accounted for 75.8%-95.2% of total N2O emissions produced in the whole interval (10 days). Significant exponential correlations were observed between N2O flux and nitrification or denitrification rates (P< 0.01). The results also indicated that nitrification dominated and played a more important role in N2O emissions than denitrification under the irrigation conditions of the study (water-filled pore spacewas 40.0 to 66.6%). Cumulative N2O emissions were 0.48-5.01 kg N ha-1 in the cucumber growing season, accounting for 0.28-0.38% of nitrogen input. Compared to N1200, treatment N600 significantly reduced the rate of N2O emissions by 53.4%, and also maintained cucumber yield. Based on this study, 50% of the traditional N fertilizer rate (N600) was considered sustainable for greenhouse cucumber production in the North China Plain.