Dynamics of soil organic carbon in cropland of karst regions in western Guizhou Province during last 30 years: A case study of Puding county, Guizhou Province

Puding, a typical county in the karst region of western Guizhou Province, was selected as the study area. According to the data collected from the second soil survey of Puding county in 1980 and the cropland soil survey of Puding county in 2011, this work calculated the variation in soil organic carbon (SOC) storage and density of cropland topsoil (0 to 20 cm) in Puding county in the past 30 years (from 1980 to 2011). The soil-type classification method and the stepwise regression analysis method were used to analyze the factors affecting the SOC stock change in cropland topsoil of Puding county. The results show that，(1)The SOC stock of cropland topsoil in Puding county increased slightly from 1980 to 2011. Average SOC density for all the cropland topsoil in this area increased by 0.95%, and its average annual variation was 15.31 kg C·hm-2·a-1 from 1981 to 2011. (2)The changes of SOC density and storage in cropland topsoil were larger in soil of different types, where the biggest carbon sequestration was paddy soil, accounting for 28.95%, while the carbon lost was mostly mountain shrub meadow soil, accounting for 70.22%.(3)In general, the spatial distribution of SOC density average annual variation shows an increasing trend in central and southern Puding county and the Sancha river and Yelang lake area, while a decreasing trend in the east and west of the county and most regions of Cape mountain, which was mainly affected by the differences of soil types. (4)The major factors affecting the SOC change in cropland topsoil of Puding county include the initial value of SOC density (1980a), C/N, gravel volume ratio, and available K density. Moreover, C/N and available K density have a positive effect, while the effects of the initial value of SOC density and gravel volume ratio are negative function. In conclusion, the effect of human activities on the SOC stock in cropland topsoil of Puding county is positive in the recent 30 years. Results of this paper identify the dynamic changes and impact factors of cropland topsoil organic carbon pool in Puding county, and the available data would provide a basis for the effective management of cropland topsoil SOC carbon pool in the karst regions of western Guizhou Province.