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

Abstract

A field experiment was conducted to quantify annual nitrous oxide (N2O) fluxes from control and fertilized plots under open-air and greenhouse vegetable cropping systems in southeast China. We compiled the reported global field annual N2O flux measurements to estimate the emission factor of N fertilizer for N2O and its background emissions from vegetable fields. Fluxes of N2O were measured using static chamber-GC techniques over the 2010–2011 annual cycle with multiple cropping seasons. The mean annual N2O fluxes from the controls were 46.1 ± 2.3 μg N2O-N m−2 hr−1 and 68.3 ± 4.1 μg N2O-N m−2 hr−1 in the open-air and greenhouse vegetable systems, respectively. For the plots receiving 900 kg N ha−1, annual N2O emissions averaged 90.6 ± 8.9 μg N2O-N m−2 hr−1 and 106.4 ± 6.6 μg N2O-N m−2 hr−1 in the open-air and greenhouse vegetable systems, respectively. By pooling published field N2O flux measurements taken over or close to a full year, the N2O emission factor for N fertilizer averaged 0.63 ± 0.09 %, with a background emission of 2.67 ± 0.80 kg N2O-N ha−1 in Chinese vegetable fields. Annual N2O emissions from Chinese vegetable systems were estimated to be 84.7 Gg N2O-N yr−1, consisting of 72.5 Gg N2O-N yr−1 and 12.2 Gg N2O-N yr−1 in the open-air and greenhouse vegetable systems, respectively. While N2O 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 N2O 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 N2O emission from Chinese croplands.