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

摘要

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 mu g N2O-N m(-2) hr(-1) and 68.3 +/- 4.1 mu g 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 mu g N2O-N m(-2) hr(-1) and 106.4 +/- 6.6 mu g 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.