The Mechanisms of High N2O Emissions from Greenhouse Vegetable Field Soils

Vegetable cultivation in China is characterized by high N application rate, multiple cropping, and frequent irrigation, which may have caused high N2O emission. However, the N2O emission characteristics and the underlying mechanisms responsible for N2O emission under high N application rate in the greenhouse vegetable field soils remains largely unknown. Thus, we conducted a field experiment to monitor N2O emissions using static chamber and gas chromatography techniques. Meanwhile, an incubation experiment was carried out to quantify soil gross N transformation rates and N2O emissions pathways via N-15 tracing and N2O source partitioning methods, respectively. The experiment involved three treatments: conventional farmland cultivated with soybean (CF), greenhouse vegetable field receiving only chemical N fertilizer (CGV), and greenhouse vegetable field receiving both organic manure and chemical N fertilizer (OGV). Our results showed that soil N2O emissions in the greenhouse vegetable fields, especially in OGV treatment, were significantly higher than those in CF treatment. Heterotrophic nitrification was the dominant pathway for N2O emissions accounting for up to 84.0% of the total N2O flux. The gross heterotrophic nitrification rate was 19.52 mg N kg (-1) per day (accounting for 81% of the total nitrification rate) in OGV treatment, which was significantly higher than in CGV and CF treatment. As a consequence, the application of nitrification inhibitors might not be an effective mitigation options of N2O emissions from the greenhouse vegetable fields in China.