Vertical dynamics of soil organic carbon across Shaanxi Province, China from 1980s to 2010s

Dynamics of soil organic carbon (SOC) has been paid great emphasis for its linkage to the nutrient cycling as well as the global climate changes. Despite the extensive changes in land use, climate, and field management practices that have profoundly affected SOC in Shaanxi Province, few studies have investigated the vertical dynamics of SOC across different soil depths. In this paper, we investigated vertical (0-100 cm with 20 cm intervals) changes of SOC based on soil surveys conducted in 1980s and 2010s in Shaanxi Province as well as three subregions (LP, GP, and QM) by using Geographic Regression Weighted Kriging (GRWK) method. The results indicated that the first four soil layers received 0.87, 0.79, 0.48, and 0.34 g/kg SOC increments, respectively, while SOC decreased by 0.49 g/kg in 80-100 cm. Spatially, most of study area received slight SOC increment (0-2 g/kg) among all soil layers, significant (>4 g/kg) SOC increments were distributed in the junction area of three subregions, while significant (<-4 g/kg) SOC decrement area was occurred in the western QM. SOC was increased in first four soil layers and decreased in 80-100 cm in LP relating to the implement of revegetation program that many cultivated land changed into grassland and forestland. SOC was increased in first two layers and decreased in last three layers in GP relating to the intensive agricultural activities, and it was decreased in the top layers and increased in sublayers in QM due to decreasing trend of NDVI in the western QM. Even several anthropogenic and environmental variables were highly related to SOC dynamics in Shaanxi, human activities were significantly controlled SOC changes than the natural factors.