Research On Soil Carbon Sequestration Potential In Cropland At County Scale In Losses Hilly Region

Taking Zhuanglang county in Gansu province as a represent region, the soil organiccarbon (SOC) changes in the recent30years and its influencing factors in cropland wereexplored at a county scale in the thesis. The carbon sequestration potential in the researchcounty was predicted as well. Basic information database of regional cropland was built basedon the analysis of soil samples in cropland and investigation of input line about croplandorganic matter in the county. Meanwhile, the information of the second national soil survey inthe mid80’s and data about cultivated land quality evaluation recently were also collected andanalyzed. By the method of ‘sampling site in1980s campare to sampling site in2011yr’ and‘type of the patch in1980s compared to the same patch in2011yr’, SOC change in the past30years was calculated. Four different methods for estimating the carbon sequestration potentialof cropland was developed finally. The research can provide scientific basis for evaluation ofregional SOC sequenstation and developing technical measures to reduce emission by thepolicy makers. The results showed that:1) The average content of topsoil organic carbon was8.90g/kg in Zhuanglangcounty in2011, and soil organic carbon density average accounted for2.09kg/m2whilereserve content of SOC arrived in1,288,000t. Soil organic carbon density of different soiltypes was distributed in gray cinnamonic soil> dark loessial soil> alluvial soil> loessial soil>red clay soil, and all of them were less than the average of nationwide dry cropland.2) The changes of SOC mainly trend to increase for nearly30years in Zhuanglangcounty, and SOC express sequestration effect in general. The average contents of topsoilorganic carbon and soil organic carbon density was increased respectively by2.09g/kg and0.49kg/m2for nearly30years, while reserve content of SOC increased by300,000t.Compared the content30years ago, there is approximately an increase of30%. Theincreasing area of SOC accounted for90%of the total area of Zhuanglang County. 3) There was a negative between variation SOC variation and the primary content inZhuanglang county. Besides, there existed a SOC stability level that the variation of SOC waszero. The farther the SOC was from the stability level the more quickly it changed, and thecloser the SOC was from the stability level the slower it changed.4) The SOC variation was affected by the altitude, the primary SOC content and thesoil types significantly. Among which, the altitude had the greatest contribution of about32.6%, the following was primary SOC content, soil types, yield, organic fertilizer and slopeaspect with the contribution of22.5%,17.0%,15.1%,10.1%and2.7%, respectively.5) Significant difference existed among different estimation methods about croplandcarbon sequestration potential in the same region. Take cropland carbon sequestrationpotential in Zhuanglang county for example, theoretical value estimated by maximum valuemethod and classification grading method were1.13Mt and1.02Mt. And the real valueestimated by classification grading method, saturation method, weighting method was0.34Mt,0.32Mt,0.28Mt, respectively, which was1/3of the theoretical value.5) Significant difference existed among different estimation methods about croplandcarbon sequestration potential in the same region. Take cropland carbon sequestrationpotential in Zhuanglang county for example, theoretical value estimated by maximum valuemethod and classification grading method were1.13Mt and1.02Mt. And the real valueestimated by classification grading method, saturation method, weighting method was0.34Mt,0.32Mt,0.28Mt, respectively, which was1/3of the theoretical value.6) SOC density increment estimated by classification grading method, saturationmethod and weighting method was5.54t/hm2,5.21t/hm2,4.56t/hm2respectively, to reachthe real level of carbon sequestration potential. According to topsoil carbon sequestration rateof cropland in Zhuanglang county in the recent30years, it need about30years at least toachieve the real level under the current farming management mode.