N₂O Emission From Agricultural Ecosystem In Middle-Lower Reaches Of The Yangtze River Region

Climate change is a current global environmental issue, one of the main reasons is the constant increasing of greenhouse gases concentrations in atmosphere. CO₂, CH4 and N₂O are considered as the most important greenhouse gases. Nitrous oxide plays an important role in the process of the global warming enhancement and atmospheric ozone (O₃) layer destruction (IPCC, 2001, 2007). The atmospheric N₂O concentration was 319×10^-9 LL^-1 in 2005, while in the past few decades, it increasing at the rate about 0.8×10^-9 LL^-1 linearly.The source of N₂O emission can divide into nature sources (including oceans, forests, grass lands) and artificial sources (including agricultural fertilizer, animal waste disposal systems, fossil fuel combustion, biomass combustion, adipic acid and N-fertilizer production, etc.). Agricultural production is an important source of N₂O in atmospheric, N₂O emissions from agricultural land affected by many factors. Therefore, the study of the agro-ecological N₂O emission in time and space under climate change scenarios, can help us make the future climate predict more reasonably, to deal with the effect of climate change, ozone depletion on the global environment and human beings.At present, the estimates study of N₂O emission of agro-ecosystem in China (including direct indirect emissions from agricultural land), activity levels only accurate to the provincial and municipal levels. In order to gain a better understanding of different agricultural land types N₂O emissions and its changes year by year of the county-level administrative units in the middle and lower reaches of Yangtze River region (including one municipality, Shanghai and six provinces , Jiangsu, Zhejiang, Anhui, Jiangxi, Hubei and Hunan), the agro-ecosystem N₂O emission sources of the middle and lower reaches of the Yangtze River region during 1990-2004 were estimated based on the level of county-level data and regional nitrogen cycle model of IAP-N methods ,and the temporal and spatial distribution were analyzed by the application of ArcGIS.The results showed that the temporal change and the distribution of arable land and nitrogen fertilizer application in the middle and lower reaches of the Yangtze River region determine direct and indirect N₂O emissions of farmland and the direct emissions flux change yearly and regional distribution of agricultural land .The average agro-ecosystem N₂O emissions in the middle-lower Yangtze River basin area from 1990-1994, 1995-1999, 2000-2004 were 13.32,16.02,15.77×10⁴t/a respectively. The overall agro-ecosystem N₂O emission followed the trend that increased rapidly at first and then fell back. The changes of the age of inter-municipal N₂O emissions from agro-ecosystem in the middle-lower Yangtze River basin region were different, and the regional distribution was different. The main emission regions are Jiangsu, Anhui, Hubei and Hunan. The main emission regions in Jiangsu Province are the north and eastern areas, in Anhui Province are the northern part of the central and western areas, in Hubei Province are central regions and in Hunan Province are central and north-east.The direct N₂O emissions from agricultural land of the middle-lower Yangtze River basin area from 1990-1994, 1995-1999, 2000-2004 were 10.37 (2.64-23.02), 12.53 (3.54-27.57), 12.17 (3.11-26.77)×10⁴ t/a respectively. The overall agro-ecosystem directly N₂O emission followed the trend that increased rapidly at first and then fell back. The changes of the age of inter-municipal N₂O emissions from agro-ecosystem in the middle and lower Yangtze River basin region were different, and the regional distribution were different too. The main emission regions are Jiangsu, Anhui and Hubei. The main emission regions in Jiangsu Province are the north and eastern areas, in Anhui Province are the central and western areas and in Hubei Province are central regions. The agricultural N₂O emission flux in the middle-lower Yangtze River basin area from 1990-1994, 1995-1999 and 2000-2004 were 5.87,6.88and 6.90kg/(ha·a) respectively. The overall agro-ecosystem N₂O emission followed the trend that increased rapidly at first and then slowly to nearly standstill. Emission intensity is highest in Shanghai, followed by Jiangsu Province.For the type of farming systems and agricultural lands, flood and crop rotation is the most important N₂O emission source of the Yangtze River area farmland, which accounted for 46.82% of the direct N₂O emissions in the region. Non-vegetable dry land is also a great contribution in direct N₂O emissions of the area amounting to 23.24%. The structure of the direct N₂O emissions sources of the middle and lower Yangtze River basin area farmland is more stable, the main change is that the proportion of vegetable land emission has increased. The Provinces and cities direct emissions structures in this region were different and the results in different year in same provinces and cities were also different.The results of the study can provide a scientific basis for policy-makers to make rational use of fertilizers, plan the development of farming and rational manner and make the Yangtze River region agro-ecosystem greenhouse gas emission reduction measures.