Soil Organic Carbon Distribution Under Different Land Uses and Landscape Positions in Two Typical Watersheds of the Loess Plateau, China

Soil organic carbon distribution and its storage were estimated in two classical small watersheds that based on 163 samples under different land uses and landscape positions. Land use conversion may alter land cover, which results in carbon stock changes in biomass as well as in the soil. After the project of Grain for Green, initiated in Loess Plateau, most area has been conducted vegetation restoration same as the comprehensive managed watershed (Shanghuang), with spread vegetation-covered region and lower slope farmland. However, it is not clear that how effective the newly initiated project will be. In this study, we found an original watershed (Sidigou) as the reference, which has not done any ecological restoration projects, and kept primitive cultivated management. The results show that soil organic carbon (SOC) in comprehensive managed watershed (Shanghuang) was higher than the untreated watershed (Sidigou). As the soil depth increases, the SOC content gradually decreases. Soil organic carbon concentration and distribution were significantly influenced by land uses and landscape positions. The SOC of the shrub land and natural grassland were significantly higher than for the other land uses. The SOC of the valley was greater than that for the top of mound crests and mound slope. The total SOC storage of untreated watershed and comprehensively managed watershed were 20099.42 t and 46527.12 t, respectively. The area proportion of land uses is the important reason for income gap of the two study areas. Land use conversion from farmland to shrub land and or artificial grassland was better for loess hilly area. It was found that the projects to restore vegetation, such as Grain for Green would be beneficial for the ecological restoration of Loess Plateau in China.