Study on Soil Organic Carbon Pool of Topsoil in Farmland in a Typical Area of Southwestern Chongqing

Jiangjin District,a typical area in Southwestern Chongqing,was selected as the study area in the paper.Based on an analysis of field-collected soil samples and an investigation of historical data,the distribution of soil organic carbon density and organic carbon storage of the local topsoil of farmland were estimated with the help of geographic information system(GIS)technology.The results showed that the soil organic carbon content of the topsoil of farmland in Jiangjin District was lower than the averages of Chongqing and of China,varying from 1.14g/kg to 52.3g/kg and averaging 9.47g/kg.Its soil organic carbon density was 2.54kg/m2 on average.Spatially,soil organic carbon density of the topsoil was shown to be inhomogeneously distributed,with the high distribution areas scattered along the rivers and their surrounding areas and the low distribution areas extending from the central area to the southeastern areas. The soil organic carbon storage of farmland totaled 3 668.9×109 g,and that of the paddy soil and purple soil accounted for 96.14%of the total.The index of soil organic abundance of topsoil ranged from 0.80to 1.33,and that of the alluvial soil being the highest and that of the purple soil being the lowest.Therefore, paddy soil and purple soil are the key in the management of soil organic carbon pool of farmland in the study area,and whether their soil organic carbon storage can be stabilized and increased is of great significance to the formulation of its management patterns and implementation of the soil organic carbon-increasing measures.