N₂O and NO emissions from greenhouse vegetable fields and the mitigation efficacy of the optimized fertigation in Beijing

Objectives Quantification of the nitrous oxide (N₂O) and nitric oxide (NO) emissions from greenhouse vegetable fields and clarification of the influencing factors are necessary for assessment of the N₂O and NO emissions of farmland ecosystem.

Methods Using cucumber cultivar of Jinpei98 as the test materials, a field experiment was conducted in a greenhouse located in Doudian Town, southwest suburb of Beijing. The type of soil was calcareous cinnamon soil with loam texture. Four treatments were no nitrogen fertilizer application with flood irrigation (CK), farmer’s fertilizer application with flood irrigation (FP), farmer’s fertilizer application rate with drip irrigation (FPD) and optimized nitrogen fertilizer application with drip irrigation (OPTD). The conventional nitrogen fertilizer application rate was N 1200 kg/hm², and the optimized nitrogen fertilizer application rate was N 920 kg/hm². 70% of nitrogen and potassium fertilizers were top-dressed in 6 stages with drip irrigation. The automatic static chamber-nitrogen oxide analyzer method was used to measure the N₂O and NO emissions during cucumber growing season. The soil temperatures at 5 cm depth and the soil water filled pore space in 0−15 cm soil layer were monitored.

Results Emission peaks were usually observed in 1−2 days after each fertigation for N₂O and 2−4 days for NO, there was no significant emission peaks in CK treatment. The seasonal cumulative emissions of the 4 treatments were 7.32, 28.69, 18.62, 12.16 kg/hm² for N₂O, and 0.32, 0.86, 0.77 and 0.70 kg N/hm² for NO, respectively. The NO emissions of CK, FP, FPD and OPTD treatments accounted for 4.2%, 2.9%, 4.0%, and 5.4% of the total emissions (N₂O + NO), respectively. Compared with FP treatment, the N₂O and NO emissions in FPD treatment were mitigated by 34.4%, 9.0%, while the vegetable yield remain unchanged. When reducing the nitrogen application rates by 40% under the condition of drip irrigation, the cumulative N₂O and NO emissions were further significantly mitigated by 34.7% and 9.1%. The emission factors in FP, FPD and OPTD treatment were 1.78%, 0.94%, 0.53% for N₂O, and 0.08%, 0.06% and 0.09% for NO, respectively.

Conclusions The N₂O emission is strong and NO emission is week in the southwest suburb of Beijing during summer season. Without changing the N fertilization rate, the N₂O and NO emissions can be significantly mitigated by 34.4% and 9.0% only through fertigation, and further mitigated by 34.7% and 9.1% by reducing 40% of the total N input combined with fertigation.