Spatial variability of soil organic carbon and related controlling factorsin Renshou County, Sichuan Province

Accurately accessing soil organic carbon (SOC) content at regional scale has been very important in regulating soil carbon and global environmental changes. Spatial distribution characteristics of SOC and the main driving factors (such as soil type, land use and parent materials) in Renshou County, Sichuan Province, were analyzed for a total of 555 topsoil (0 20 cm) samples using variance analysis and regression analysis. The results show that SOC content in the study area was in the range of 3.36?37.10 g kg?1, with an average of 13.46 g kg?1. The coefficient of variation was 48.87%, suggesting that SOC in the study area had moderate variability. The nugget-to-sill ratio value was 66.7%, suggesting that SOC had moderate spatial dependence and that spatial variability of SOC was determined by co-effects of structural and random factors. The content of SOC in the northern area was much higher than that in the southern region. Analysis of variance showed that while the effects of land use and soil type on SOC were significant (P < 0.01), parent materials had no obvious effect on SOC content (P = 0.256). Regression analysis showed that soil type was related with soil classification. Soil group, subgroup and soil family explained respectively 23.7%, 27.0% and 27.1% of SOC spatial variability. Land use type independently explained 53.0% of SOC spatial variability, much larger than that of soil type and suggesting that land use was the main qualitative driving factor of SOC availability. Soil subgroup and family similarly explained spatial variability of SOC, suggesting that soil subgroup was applicable at the lowest level of soil classification in studying spatial patterns of SOC in the study area. Also land use type was the key regulating factor of the spatial variability of SOC in hilly areas of Middle Sichuan Basin.