Spatial distribution characteristics of topsoil organic carbon in farmland and its influencing factors in Yuhang District,Hangzhou City

According to the farmland fertility survey sampling criterion,the spatial distribution of TOC( topsoil organic carbon) density was depicted by GIS based on 2 814 soil samples collected in Yuhang District. Besides,potentially influencing factors TOC density were discussed. It was shown that the highest TOC density was found in the center of Chongxian Town and in the sub-centre of Cangqian Town in Yuhang District,and the spatial distribution of TOC density were radially decreasing from the center. The TOC density in Yuhang District was up to 46. 3 t·hm- 2,which was above the national average. From the perspective of site conditions,the TOC density was decreased as alluvial plain valley plain hilly coastal plain. From the view of topsoil physicochemical properties,the TOC density was gradually increasing with the elevated amount of clay in topsoil. The TOC density increased as sandy loam clay loam clay. The TOC density in near-neutral and neutral soil was higher,while acidic and alkaline soils were not conducive to soil carbon sequestration. Soils with larger CEC( cation exchange capacty) possessed a stronger capacity of soil carbon sequestration. Within a certain range,with the increasing of bulk density,the density of farmland TOC was decreasing. But the relatively high bulk density would also increase TOC density. From the perspective of topsoil nutrients,total nitrogen and available potassium were all positively correlated with TOC density. In terms of land use,TOC density in farmland was slightly higher than those in gardens. From the perspective of soil types,TOC density decreased in the order of paddy soil alluvial soil skeletal soil limestone( rock) soil red soil purple soil yellow soil. Paddy soils exhibited the highest TOC density and the largest organic carbon storage,while the yellow soils showed the lowest TOC density and the smallest organic carbon storage.