Spatial distribution of soil organic carbon and its influencing factors under the condition of ecological construction in a hilly-gully watershed of the Loess Plateau, China

- The SOC concentrations showed a downward trend with increasing soil depth.
- SOC decreased in the following order: grassland > forest > terrace > sloped cropland > dammed field.
- Land use type is the most important factor influencing soil organic carbon stocks.
- SOC stocks in the 0-100 cm soil layers was 113.16 Mg hm− 2 in Wangmaogou Watershed.

Carbon is an essential element for plants and plays an important role in terrestrial ecosystem functions by affecting soil properties and quality. A large percentage of organic carbon is stored in soils, and even small changes in soil carbon can significantly alter CO2 concentrations in the atmosphere and contribute to global climate change. Soil organic carbon (SOC) is one of the hot spots in soil nutrient research. In this study, SOC concentration and its correlations with environmental factors were studied in the Wangmaogou Watershed of Wuding River, China. To enhance the understanding of the spatial patterns of SOC and its dominant influencing factors, 216 sites were sampled by field sampling in a 100 × 100 m grid from a soil profile of 100 cm (thickness of each layer is 20 cm). This study included five land use types and 216 sites: terrace (18), grassland (114), forestland (48), sloped cropland (20) and dammed field (16). Mean SOC concentrations showed a downward trend with increasing soil depth. One-way ANOVA revealed that SOC concentrations differed significantly among the five soil layers (P < 0.01). The SOC concentration of A1 (0-20 cm) soil layers showed a significant difference (P < 0.05) with type of land use. The mean SOC concentrations in the five land use types were in the following decreasing order: grassland > forestland > terrace > sloped cropland > dammed field and SOC content in five soil layers (0-100 cm) was 115.00, 120.80, 116.70, 111.20 and 102.10 Mg hm− 2, respectively. SOC stock in the 0-100 cm soil layers was 113.16 Mg hm− 2 in Wangmaogou Watershed. In conclusion, land use type was the main important factor influencing SOC concentration in Wangmaogou Watershed. The promotion of the soil and water conservation measures for increasing SOC had a constructive significance in the river basin of Loess plateau.