Slowdown of N2O emissions from China’s croplands

Background/Question/Methods: To feed the increasing population, China has experienced a rapid agricultural development over past decades, accompanied by increased fertilizer consumptions in croplands, but the magnitude, trend, and causes of the associated nitrous oxide (N₂O) emissions has remain unclear. The primary sources of this uncertainty are conflicting estimates of fertilizer consumption and emission factors, the latter being uncertain because of very few regional representativeness of the N_rate-flux relationships in China. Here we re-estimate China’s N2O emissions from croplands using three different methods: flux upscaling technique, process-based models and atmospheric inversion, and also analyze the corresponding drivers using an attribution approach.  

Results/Conclusions: The three methods produce similar estimates of N2O emissions in the range of 0.67 ± 0.08 to 0.62± 0.11 Tg nitrogen per year, which is 29% larger than the estimates by the Emission Database for Global Atmospheric Research (EDGAR) that is adopted by Intergovernmental Panel on Climate Change (IPCC) as the emission baseline and 80% larger than the latest Chinese national report submitted to the United Nations Framework Convention on Climate Change., but the revised trend slows down after 2005. Fertilizer N application per area is the dominant factor driving the increase in N2O emissions across most cropping regions from 1990 to 2004, but climate-induced change of emission factors has also controlled N2O flux from 2005 onwards. Our findings suggest that, as precipitation would increase in North China but decline in the South in future, EF will increasingly control China’s agri. soil emissions of N₂O, unless offset by larger reductions of fertilizer consumptions. It also implies that national reports including N₂O annual emissions submitted to UNFCCC needs to be updated by improving the accuracy of both EF and agricultural management, which is much important for design the quota of cumulative future carbon emissions among nations.