Background nitrous oxide emissions from croplands in China in the year 2000

Abstract

It is important to accurately predict annual background nitrous oxide (N2O) emissions (BNE) at a national scale due to the considerable contribution of these emissions to the overall N2O emissions from croplands. We predicted the national background N2O emissions (BNE_n) from croplands in China in the year 2000 within a geographical information system (GIS) framework. The spatial resolution was 10 km× 10 km. The BNE_n was predicted as the sum of two parts. One part was from mineral soils, estimated using four monovariate models based on soil total nitrogen content (TN) and soil organic carbon content (SOC), while the other part was from organic soils, estimated by directly extrapolating the default IPCC (2006) emission factor of 8 kg N ha �1 yr �1 to the area of organic soils, which consisted of less than 0.2% of the total area in national croplands. Our estimates showed that the hectare-based annual background N2O emission rates (BNE_h) 2.0 kg N ha �1 yr �1 occurred in 11-24%, 71- 84%, and 3-5% of national croplands, respectively. A spatial distribution pattern of grid-based background emissions (BNE_g), different from that of BNE_h, was revealed. High BNE_g (>6,000 kg N grid �1 yr �1 ) occurred in the major agricultural regions of North- eastern, Northern, Eastern, and Middle China. The simulation based on soil properties yielded estimates of 99.0-116.9 Gg (1 Gg=10 9 g) N yr �1 for BNE_n, of which organic soils contributed 1.5-1.8%. Among the different models, the model based on TN yielded the smallest uncertainty (ranging from �22% to 30%). We recommend this model for BNE estimation at a national scale. Our estimates of BNE_n accounted for 26-30% of the total N2O emissions from the croplands in China. Methods for improving BNE predictions were proposed for further study.