Agricultural N₂O Direct Emissions, Spatial Distribution And Trends In China

Nitrous oxide (N2O) is an important greenhouse gas. China is the largest N2Oemissions country in the world; agriculture is an important source of N2O emissions,which accounting for60%of total agricultural N2O emissions from human activitiesin the world. The rate of emissions from Chinese agricultural fields is higher than thefigure, reaching to89%(IPCC2007c).Studies were limited to using emission factorsrecommended by IPCC or adopting provincial activity data to calculate N2Oemissions. However, high-resolution emission inventories based on local conditionshave not yet been established; Moreover, Studies mainly focused on chemicalfertilizer or fertilizer in paddy; additionally, Long time series emissions of farmlandwere rarely found.Accordingly, this paper is based on the county scale of activity data,differential emission factors and parameters, using GIS technology in the aim ofre-evaluating the structure, spatial distribution and trends of china’s agriculture directN2O emissions from1978to2008. The emissions in this article primarily contain fouremissions ways: fertilizer, including synthetic nitrogen fertilizer and organic fertilizercrop residues, pasture and manure management. Comparing with other studies likeIPCC and EDGAR to illustrate the study in this article is reasonable and reliability.What the results show as follows:1) The total quantity of nitrous oxide emitted directly from farmland is1072.4Gg.with fertilize, manure management, pasture, crop residues as the most importantsource (52.8%,28.7%,15.8%,2.6%, respectively). Emissions from fertilize areconsist of two parts: synthetic nitrogen fertilizers and organic fertilizers, whichrespectively accounted for41.7%and11.1%of this total counterparts.2) In terms of space, The average emissions intensity in the eastern region on thewhole is much higher than the western region. N2O emissions from cropland of Chinaare mainly concentrated in the North China Plain, northeast of the Song-Liao Plain,Sichuan Basin, the Yangtze River Basin, Pearl River Delta, Leizhou Peninsula, and the west side of Taiwan mountains. Specifically, The distribution is in province ofJilin (107.6Gg), Sichuan (74.6Gg), Henan (62.2Gg), Hunan (62.1Gg), Shandong(59.6Gg), Guangdong (58.4Gg), Jiangsu (57.4Gg) and Heilongjiang (53.6Gg),which totally accounting for one fifth of the china’s total land area andcontributing more than half (53.9%) of the total emissions. In the view of county,The largest emissions in counties are Jiutai, Nong’an, Yuzhou, Dehui,, in Jilinprovince, Mianzhu, in Sichuan province, Urumqi, Harbin and Guangzhou.They areemitted25.1Gg (2.4%),21.0Gg (1.9%),7.0Gg (0.66%),5.5Gg (0.52%),3.3Gg(0.3%),7.4Gg (0.69%),4.9Gg (0.46%),4.3Gg (0.4%) and3.3Gg（0.3%）,respectively.3) From the view of the change in30years, Total agricultural emissions fromcropland has significantly increased from593.6Gg from1978to2008, with anaverage annual rate of2.8%. Emissions from fertilizers, crop residue, pasture andmanure management were increased from1978to2008and the average annualgrowth rate was3.1%、2.3%、4.3%、2.7%, respectively.4) Comparing emissions on spatial variation between1978and2008, we find thatthe total N2O emissions in30years ranged from0to12.8Gg. Overall, The differencchange in east region is bigger than west region. Different distributions are similar tototal emissions. Change mainly distribute in the North China Plain, northeast of theSongliao Plain, Sichuan Basin, South China’s Yangtze River Basin and the Pearl RivDelta, Leizhou Peninsula, the mountains on the west side of Taiwan.5) Emissions calculated using IPCC’s emission factors and parameters are975.1Gg,which is lower than my study (9%). However, there has a big difference indifferent source. Emissions from crop residues are overestimated0.1Gg.Whileemissions from fertilizer, pasture and livestock management were underestimated59.6Gg,13.7Gg and24.2Gg. Cumulative frequency at30%contains173counties,which is more than this article (44). In contrast, The number exceed this paper onagricultural fertilizers, crop residues, pasture excretion, livestock management, was48,49,22,6. The spatial pattern of total agricultural emissions undervalued in theeastern regions and overvalued in western. The area which was overvalued was distribute in Xinjiang province, the western of Inner Mongolia, Shandong and Henanregions; The part underrated mainly in the east side of Daxinganlinge, Anhui,Jiangsu, Hunan, Hubei, Sichuan Basin and Taiwan Province.6) Compared with EDGAR, Emissions from agriculture is approximately18%higher than this study; Emissions from grassland in1978to1990was in line with thisarticle. And it became lower between1997and2007. In2008the results were higherthan the results of this paper (30Gg). Emissions from livestock management haveapparently underestimated since1997(almost twice times). On the whole, EDGAR isrelatively consistent from this study at1978to1995, but the gap was graduallyincreased.7) comparison with other domestic scholars, Emissions based on local emissionfactors and parameters or IPCC emission factors which has been modified wereconsistent with this article. On the contrary, Emissions from farmland via IPCC’semission factor tend to overestimate.