Nitrous oxide (N2O) is a long-lived greenhouse gas with a large radiation intensity and it is emitted mainly from agricultural land. Accurate estimates of total direct N2O emissions from croplands on a country scale are important for global budgets of anthropogenic sources of N2O emissions and for the development of effective mitigation strategies. The objectives of this study were to re-estimate direct N2O emissions using localized emission factors and a database of measurements from Chinese croplands. We obtained N2O emission factors for paddy fields (0.41 ± 0.04%) and uplands (1.05 ± 0.02%) 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 root transformations were used because the frequency of the original data was not normally distributed. Direct N2O 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 N2O emissions from paddy fields showed little change, increasing by 10.5% with an annual rate of increase of 0.4% from 32.3 Gg N2O-N in 1980 to 35.7 Gg N2O-N in 2007. In contrast, emissions from uplands changed dramatically, increasing by 308% with an annual rate of 11% from 68.0 Gg N2O-N in 1980 to 278 Gg N2O-N in 2007. Total direct N2O emissions from Chinese croplands increased by 213% with an annual rate of 7.6% from 100 Gg N2O-N in 1980 to 313 Gg N2O-N in 2007, and were determined mainly by upland emissions (accounting for 67.8–88.6% of total emissions from 1980 to 2007). Synthetic N fertilizers played a major role in N2O emissions from agricultural land, and the magnitude of the contributions to total direct N2O emissions made by different amendments was synthetic N fertilizer manure straw, representing about 78, 15, and 6% of total direct N2O emissions, respectively, between 2000 and 2007. The spatial pattern of total N2O emissions in 2007 in China shows that high direct N2O emissions occurred mainly in the north and in the Sichuan Basin in the southwest. The provinces with the highest emissions were Henan (35.4 Gg) and Shandong (31.6 Gg) and Tibet had the lowest (0.65 Gg). High direct N2O emissions per unit of arable land occurred mainly on the North China Plain and the southeast coast. The mean value nationally was 2.52 kg N ha?1, with 18 provinces above this value and with emissions of 4.0 kg N ha?1 in Beijing, Tianjin and in Jiangsu, Shandong, Fujian and Henan provinces.
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