Contribution and driving mechanism of NO2 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 (NO2) emissions in China, mainly due to excessive manure application and irrigation. Pulses of NO2 emissions have been commonly reported by field monitoring works conducted in greenhouse fields, though their significance regarding total NO2 emissions and the driving mechanism behind them remain poorly understood. NO2 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 NO2 emission bursts closely followed fertilization and irrigation events, accounting for 76.7% of the annual NO2 efflux. The soil NO2 flux increased exponentially with the water-filled pore space (WFPS), causing extremely high NO2 emissions when the WFPS was higher than 60%. During the lab incubation, emission bursts led to NO2 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 NO2 emission bursts in the greenhouse filed. Nitrous oxide emission bursts constituted the major portion of the NO2 emissions in the Chinese greenhouse soils. Nitrite (NO2-) denitrification triggered by fertilization and irrigation was responsible for these NO2 emission pulses. Our results clarified the significance and biogeochemical mechanisms of NO2 burst emissions; this knowledge could help us to devise and enact sounder NO2 mitigation measures, which would be conducive to sustainable development in vegetable greenhouse fields.