Study On Cropland Soil Carbon Sequestration Rate At County Scale Of The Northwest Semi-humid And Semi-arid Area

This paper take Wugong county Shannxi province and Zhuanglang county Gansuprovince for the main area, study soil organic carbon storage, carbon sequestration rate andinfluencing factors of the farmland in the northwest semi-humid and semi-arid area. Takefarmland type field soil sampling, farmland material input route survey as the basis, establisha repository about the basic situation of the farmland soil in western region. Based on the dataof the second national soil survey and the recent quality of arable land evaluation, through"peer-to-peer"+"face to face" approach, clear soil organic carbon storage, soil organic carbonchanges of the past30years and the past five years of the farmland in western region. Takecertain measures to farmland making it soil carbon pool, and constantly improve theproductivity of land, and also provide some scientific basis for national policy formulation.The main conclusions are as follows:(1)Frequency distribution of SOCSoil organic carbon content in80%of the sampling sites were changed in the range of8.0-12.0g/kg in Wugong county, soil organic carbon content in0-20cm soils presented anormal distribution; Soil organic carbon content in80%of the sampling sites were changedin the range of6.0-11.0g/kg in Zhuanglang county, soil organic carbon content in0-20cmsoils presented a normal distribution.(2)Soil organic carbon distribution characteristics in different landuse-geomorphology-soil typeThe descending order of the organic carbon density of different soil types on the samelandforms in Wugong County: Chao soil>brown soil>loessial; The descending order of theorganic carbon density of different landforms on the same soil type in Wugong County: firstterrace>second terrace>third terrace>valley. The decending order of the organic carbondensity of the different landforms in Zhuanglang county: High mountain area>low hillyarea>hilly gully region; The decending order of the organic carbon density of the differentsoil types: gray cinnamonic soil> dark loessial soils> alluvial soils>loessial>red clay.(3)Soil organic carbon storageIn Wugong county, the farmland soil organic carbon density in0-20cm was26.3t/hm2, the cultivated area is32925.8hm2，Soil organic carbon storage in0-20cm is866.61Gg；InZhuanglang county, the farmland soil organic carbon density in0-20cm was20.58t/hm2, thecultivated area is64200hm2，Soil organic carbon storage in0-20cm is1321.24Gg.(4)Carbon sequestration rateIn2011, the farmland soil organic carbon density in0-20cm in Wugong county was26.3t/hm2. In1980, the soil organic carbon density in0-20cm was24.1t/hm2. Nearly30yearssoil carbon sequestration rate in0-20cm was71.3kg C/(hm2·a). In2006, the soil organiccarbon density in0-20cm was23.9t/hm2. The past five years, carbon sequestration rate was480kg C/(hm2·a). In2011, the farmland soil organic carbon density in0-20cm inZhuanglang county was20.58t/hm2. In1980, the soil organic carbon density in0-20cm was14.99t/hm2. Nearly30years soil carbon sequestration rate in0-20cm was186.3kg C/(hm2·a).In2006, the soil organic carbon density in0-20cm was19.89t/hm2. The past five years,carbon sequestration rate was138kg C/(hm2·a).(5)Influencing factorsIn the semi-humid county scale (Wugong county), soil organic carbon is mainly affectedby soil types, landform types, organic fertilizer. Soil types accounted for30.2%of organiccarbon variability; landform types can explained37.7%; organic fertilizer can explained32.1%. In the county scale in the semi-arid region (Zhuanglang county),50.7%of organiccarbon variability was due to topographic position, organic fertilizer, aspect and soil typecould explain19.6%,18.0%,11.7%of the organic carbon variability.