Factors Controlling Soil Organic Carbon and Total Nitrogen Densities in the Upstream Watershed of Miyun Reservoir, North China
密云水库上游流域土壤有机碳和全氮密度影响因素研究

Effects of climate (temperature and precipitation), topography (elevation and slope), soil properties (soil bulk density, pH, water and clay contents) and land use on soil organic carbon (SOC) and total nitrogen (TN) densities were investigated in the study to identify dominant factors controlling SOC and TN densities in the upstream watershed of Miyun Reservoir of North China by soil sampling, laboratory analysis and statistical analysis. Results showed that SOC and TN densities in the 0-20 cm soil layer were 4.77 kg·m-2and 0.41 kg·m-2 in forestland, 6.79 kg·m-2 and 0.69 kg·m-2 in grassland, 2.90 kg·m-2 and 0.30 kg·m-2 in cropland, respectively. Significant differences in SOC and TN densities were observed among the three land uses. Soil water content, land use, slope, soil pH and clay content were the most significant factors controlling SOC density, while land use, soil clay and water contents were the most significant determinants of TN density. Climate, topography and soil properties jointly explained 63.6% and 53.4% of SOC and TN densities variability, respectively, while environmental factors and land use together explained 67.6% and 57.8% of variations in SOC and TN densities, respectively. Clearly, environmental variables were more important for SOC and TN densities variability than land use in the study area. Therefore, establishing a high-spatial-resolution database of environmental factors is a key to more accurate assessments of SOC and TN stocks on a regional scale.