Contribution and Driving Mechanism of N2O Emission Bursts in a Chinese Vegetable Greenhouse after Manure Application and Irrigation

Abstract

Solar greenhouse vegetable fields have been found to be hotspots of nitrous oxide (N2O) emissions in China, mainly due to excessive manure application and irrigation. Pulses of N2O emissions have been commonly reported by field monitoring works conducted in greenhouse fields, though their significance regarding total N2O emissions and the driving mechanism behind them remain poorly understood. N2O fluxes were monitored in situ using a static opaque chamber method in a typical greenhouse vegetable field. Then, laboratory incubations were conducted under different soil moisture and manure application gradients to monitor nitrous oxide emissions and related soil properties, using a robotized incubation system. Field monitoring showed that the occurrence of clear N2O emission bursts closely followed fertilization and irrigation events, accounting for 76.7% of the annual N2O efflux. The soil N2O flux increased exponentially with the water-filled pore space (WFPS), causing extremely high N2O emissions when the WFPS was higher than 60%. During the lab incubation, emission bursts led to N2O peaks within 40 h, synchronously changing with the transit soil NO2−. An integrated analysis of the variations in the gas emission and soil properties indicated that the denitrification of transit NO2− accumulation was the major explanation for N2O emission bursts in the greenhouse filed. Nitrous oxide emission bursts constituted the major portion of the N2O emissions in the Chinese greenhouse soils. Nitrite (NO2−) denitrification triggered by fertilization and irrigation was responsible for these N2O emission pulses. Our results clarified the significance and biogeochemical mechanisms of N2O burst emissions; this knowledge could help us to devise and enact sounder N2O mitigation measures, which would be conducive to sustainable development in vegetable greenhouse fields.