New estimates of direct N2O emissions from Chinese croplands

Biogeosciences Discussions This discussion paper is/has been under review for the journal Biogeosciences (BG). Please refer to the corresponding final paper in BG if available. Abstract Nitrous oxide (N 2 O) is a long-lived greenhouse gas with a large radiation intensity and it is emitted mainly from agricultural land. Accurate estimates of total direct N 2 O emissions from croplands on a country scale are important for global budgets of an-thropogenic sources of N 2 O emissions and for the development of effective mitigation 5 strategies. The objectives of this study were to re-estimate direct N 2 O emissions using localized emission factors and a database of measurements from Chinese croplands. We obtained N 2 O emission factors for paddy fields (0.41 %) and uplands (1.05 %) from a normalization process through cube root transformation of the original data after comparing the results of normalization from the original values, logarithmic and cube 10 root transformations because the frequency of the original data was not normally distributed. Direct N 2 O emissions from Chinese croplands from 1980 to 2007 were estimated using IPCC (2006) guidelines combined with separate localized emission factors for paddy fields and upland areas. Direct N 2 O emissions from paddy fields showed little change, increasing by 11 % with an annual rate of increase of 0.4 % from 29.8 Gg N 2 O-20 counting for 68.4–88.5 % of total emissions from 1980 to 2007). Synthetic nitrogen fertilizers played a major role in N 2 O emissions from agricultural land, and the magnitude of the contributions to total direct N 2 O emissions made by different amendments was synthetic N fertilizer > manure > straw, representing about 77, 16, and 6.5 % of total direct N 2 O emissions, respectively, between 2000 and 2007. The spatial pattern of 25 total N 2 O emissions in 2007 in China shows that high direct N 2 O emissions occurred mainly in north China and in the Sichuan Basin in the southwest. The provinces with the highest emissions were Henan (32. the lowest (0.6 Gg). High direct N 2 O emissions per unit of arable land occurred mainly on the North China Plain and the southeast coast. The mean value nationally was 2.36 kg N ha −1 , with 17 provinces above this, and with emissions of >4.0 kg N ha −1 in Beijing and in Jiangsu and Henan provinces.