| Nitrous oxide (N2O), an important atmospheric trace gas, has been paid muchattention due to its substantial contribution to global warming and ozone depletion, thetwo severest impacts on the global environment. Although the N2O budget remainspoorly understood at present, fertilized agricultural soils have been believed to be amajor source of annual global N2O emission. Owing to the large spatial and temporalvariabilities in the agricultural practices and environmental factors, it is difficult toprecisely estimate agricultural N2O emission at a large regional scale.China is one of the largest agricultural countries in the world. Huge amount ofsynthetic fertilizer have been applied to maintain high crop yield to feed the increasingpopulation. The impact of Chinese agricultural activities on atmosphere N2O incursincreasing attentions. Moreover, according to the UNFCCC, China is obliged tocompile greenhouse gas inventories in order to make proper policy to reduce theiremissions. The estimation of N2O emission from agricultural fields in China is alreadymore than a scientific topic.The objectives of this study are, 1) to establish empirical models in which theemission factor and background emission for N2O in the IPCC methodology wererectified by key environmental parameters; 2) to simulate long term spatio-temporalcharacteristics of direct N2O emission in China's agriculture by linking the statisticalmodels to spatial datasets via GIS; 3) to predict the response of agricultural N2Oemission to climate change through adopting the output of climate model to drive N2Oestimate models; 4) to examine potential mitigation option of agricultural N2Oemission on regional scale.In this study, we collected direct N2O measurements that were published in peer-reviewed English and Chinese journals between 1982 and 2003. After dataextraction following strict criteria, the employed data set remained of 206measurements from 42 sites. For each data point, we recorded the annual total N2Oemission, the synthetic nitrogen application rate, the precipitation and meantemperature, the location of the measurement and the soil physiochemical parametersincluding soil total N content, soil organic carbon content, and pH. Both nitrogen input(F) and precipitation (P) were found to be largely responsible for temporal and spatialvariabilities in annual N2O fluxes, while no significant correlations were observedbetween N2O emission and other parameters of temperature, pH, organic carbon andnitrogen.Based on the definition of N2O emission factor and its quantification by theIntergovernmental Panel on Climate Change, we established an empirical model forupland (N2O-N=1.49 P+0.0186 P·F), in which both emission factor and backgroundemission for N2O were rectified by precipitation. Fitness analysis suggests that theinclusion of precipitation into regression eqution could improve the predictability, andis more suitable to quantify N2O emissions from agricultural fertilized fields in ChinaConsidering the large paddy rice planting area in China, the cropping-specificemission factors were introduced to estimate fertilizer-induced N2O emissions fromrice paddies, while the precipitation-rectified emission factor to the uplands. Annualfertilizer-induced N2O emissions from China's agricultural fields were simulated bylinking these models to spatial datasets via GIS. During the period 1980 to 2000, themean annual emission was estimated to be 167.22 Gg N2O-N yr-1, equivalent to 1.02%of the national total of synthetic fertilizer N input. Upland was the major source ofannual N2O emission from China's agriculture, contributing about 86% to the total offertilizer-induced N2O emissions from agricultural fields in China.Direct N2O emission from China's agricultural fields occurs essentially with greatspatial and temporal variability. This study showed a significant spatial distributionpattern of direct N2O emission in agricultural fields. The maximum direct N2Oemission occurred in the major district of crop production, where is characterized ashumid climate in China. By contrast, N2O emission rarely exceeded 0.10 kg N2O-Nha-1.yr-1 in the West region, where is generally dominated by dry climate. During thelast two decades in the 20th century, the amount of direct N2O emission from Chineseagricultural fields has increased by about 149 Gg N2O-N yr-1, equivalent to 155% of the initial. The increasing range of N2O emission varied widely with different regions,which is mainly attributed to the quantity of synthetic nitrogen application and climateconditions. In contrast with the IPCC default methodology, this study may providemore insights into the inter-annul variations in N2O emissions.Uncertainty estimate is an essential element of a complete inventory of N2Oemission. The uncertainties of this study were principally originated from the modelsand spatializing process. Similar to the uncertainty estimate in the IPCC methodology,the error propagation equation was adopted to quantify the uncertainties of this study.Results indicated that the combined uncertainty in this study was about 23%.In this paper, we simulated direct N2O emission from Chinese agriculture from2005 to 2050 by linking N2O estimate models with FGOALS's climate changescenario. Results suggest that N2O emission from agricultural fields is sensitive toclimate change. Although the trend of direct N2O emission from Chinese agriculturemay be constant essentially in the future, the inter-annual variations of N2O emissionwill be enhanced. Moreover, the changing spatial distribution pattern of N2O emissionwas predicted, and the high emission centers will move northward.According to the regional variations of direct N2O emission and synthetic nitrogenapplication, we simulated a fertilizer application scenario. Scenario analysis indicatedthat the adjustment to the spatial distribution of fertilizer application in China might bea potential mitigation option of agricultural N2O emission with the premise of insuringcrop production.
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