Deriving Emission Factors and Estimating Direct Nitrous Oxide Emissions for Crop Cultivation in China

Updating and refining the N2O emission factors (N2O-EFs) are vital to reduce the uncertainty
in estimates of
direct N2O emissions. Based on a database with 1151 field
measurements across China, the N2O-EFs were established
via three approaches including the maximum likelihood method, a linear
regression with an intercept and a linear regression with the intercept
set to 0 using 70% of the observations. The remaining 30% of the observations
were then used to evaluate the predicted N2O-EFs. The third
method had the highest R2 of 0.39 and
the best model efficiency of 0.38 with no significant bias, showing
the best calculation efficiency. The results showed that the N2O-EFs varied with agroregions, crops, and management patterns.
The agroregions of Huang-Huai-Hai and Yangtze River had the higher
N2O-EFs in maize and wheat seasons than other regions,
and the highest N2O-EFs of 0.66–0.92% in the rice
season was found in the South and Southwest agroregions. Both fertilizer
types and water regimes had the remarkable effects on N2O-EFs. Based on the best estimation by the selected method, direct
N2O emissions from China’s crop cultivation were
estimated to be 194 Gg N2O–N with a 95% confidence
interval of 180–208 Gg N2O–N in the year
2016.