Annual nitrous oxide emissions from open-air and greenhouse vegetable cropping systems in China.

Aims: A field experiment was conducted to quantify annual nitrous oxide (NO) fluxes from control and fertilized plots under open-air and greenhouse vegetable cropping systems in southeast China. We compiled the reported global field annual NO flux measurements to estimate the emission factor of N fertilizer for NO and its background emissions from vegetable fields. Methods: Fluxes of NO were measured using static chamber-GC techniques over the 2010-2011 annual cycle with multiple cropping seasons. Results: The mean annual NO fluxes from the controls were 46.1 ± 2.3 μg NO-N m hr and 68.3 ± 4.1 μg NO-N m hr in the open-air and greenhouse vegetable systems, respectively. For the plots receiving 900 kg N ha, annual NO emissions averaged 90.6 ± 8.9 μg NO-N m hr and 106.4 ± 6.6 μg NO-N m hr in the open-air and greenhouse vegetable systems, respectively. By pooling published field NO flux measurements taken over or close to a full year, the NO emission factor for N fertilizer averaged 0.63 ± 0.09 %, with a background emission of 2.67 ± 0.80 kg NO-N ha in Chinese vegetable fields. Annual NO emissions from Chinese vegetable systems were estimated to be 84.7 Gg NO-N yr, consisting of 72.5 Gg NO-N yr and 12.2 Gg NO-N yr in the open-air and greenhouse vegetable systems, respectively. Conclusions: While NO emissions from the greenhouse vegetable cropping system tended to be slightly higher compared to the open-air system in our experiment, the synthesis of literature data suggests that NO emissions would be greater at low N-rates but smaller at high N-rates in greenhouse systems than in open-air vegetable cropping systems. The estimates of this study suggest that vegetable cropping systems covering 11.4 % in national total cropping area, contributed 21-25 % to the total NO emission from Chinese croplands. [ABSTRACT FROM AUTHOR]