| Pingluo County farmland ecosystem of Ningxia in the northwest arid areas and theYellow River Irrigation District was selected as the research object in this study. Choosetypical sample area farmland, field investigation, sampling and laboratory analysis.Chemical method was adapted to soil organic carbon and vegetation organic carbon. Thecarbon footprint of Pingluo County was calculated based on the IPCC method and theparameters of carbon emission. The dynamic variation and its impact factors of carbonsource and sink of Pingluo County farmland ecosystem were analyzed. The relationbetween straw returning and soil organic carbon was analyzed based on the situation ofstraw returning and the variation of soil organic carbon in the period from1981to2010.The main achievements of this study are listed as follows:1. The carbon footprint of three main crops in Pingluo County was calculated basedon the investigated data of farmland production in the county by using basic theories andresearch approaches of carbon footprint. The carbon footprints of corn, rice and wheatwere931.03±142.90,1487.56±164.59and809.75±144.99kg Ce/hm~2·a, the carbon costswere0.08±0.02,0.17±0.05and0.12±0.03kg Ce/kg, respectively. The carbon footprint themain crops in Pingluo County was exceeding the research result domestic and overseas.Therefore, the potential of emission reduction in Pingluo County farmland ecosystem wastremendous.2. In the composition of carbon footprint of rice, corn and wheat, chemical fertilizercarbon footprint of them were677.94±142.09,594.37±107.56and537.95±144.99kgCe/hm~2·a, occupied75%、40%and66%in total carbon footprint, respectively. N fertilizercarbon footprint of crops occupied more than96%in chemical fertilizer carbon footprint.Therefore, increase the use ratio of chemical fertilizer was the key to reduce the farmlandcarbon footprint. 3. The carbon fixed ability of difficult crops was different. In the all kinds of crops,the yield proportion and the carbon fixed ability of grain crops was more than economiccrops and fruits-vegetables crops. The carbon fixed ability of corn was notable especiallyin grain crops. The carbon efficiency of corn (12.070.02kg/kg Ce) was larger than rice(8.490.03kg/kg Ce) and wheat (5.940.05kg/kg Ce), mean that the yields of corn wasthe largest under the same carbon emission. So the significant way to increase the carbonsinks of Pingluo County farmland ecosystem was appropriately expanding sown area ofcorn.4. The dynamic variation of carbon source and sink of Pingluo County farmlandecosystem was divided into three stages during the last10years. The first stage was from1991to1995, the amounts of carbon absorption and emission were increased. The formerwas larger than the latter, so the amounts of carbon sink was increased in this stage. Thesecond stage was from1996to2003, the amount of carbon emission was stable relatively.The amount of carbon absorption was reduced as the reason of crop failure, so the amountsof carbon sink was reduced slowly. The third stage was from2004to2010, the amount ofcarbon absorption was increased due to the cultivation of fine crops. The amount of carbonemission was reduced slowly owing to the use of advanced agro-technology. So theamount of carbon sink was increased substantially. The result indicated that, PingluoCounty farmland ecosystem has carbon sink function, and the ability of carbon sink wasenhancing gradually.5. The amount of crop straw land-returning of Pingluo County farmland ecosystemwas increased by degrees from1981to2010. The amount of crop straw land-returning was136.01t/ha accumulative total, the average amount of carbon land-returning was66.46t/ha.The average increased rage of soil organic carbon was37.41%, and the increment of soilcarbon density was6.18t/ha. The ratio of the increment of soil carbon density and theaverage amount of carbon land-returning was9.29%. It considered that crop strawland-returning gave the important play to carbon sink function Pingluo County farmlandecosystem. |
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