Abstract

Soil organic carbon (SOC) plays an important role in preserving soil fertility. Assessing how topographic factors (slope gradient, slope length, slope shape, and slope position) and their interactions influence the SOC dynamics in the surface soil of longitudinal ridges of sloping farmland is very important for Mollisols protection in Northeast China. The SOC contents and variations were quantified within classes of topographic factors. A total of 39 soil samples were collected at the same sampling points in 13 typical Mollisol sloping farmland in 2004 and 2016. The results indicated that the average annual decrease rate of SOC from 2004 to 2016 was 5.64‰. The SOC stocks were significantly affected by slope gradient, slope length, and slope shape, but only affected by the interaction between slope gradient and slope position. In addition, the SOC stocks decreased with increasing slope gradient (p < 0.05). The variation in SOC stocks during 12 years showed a decreasing trend with increasing slope length (p < 0.05). The straight slopes had higher variation in SOC stocks than concave and convex slopes (p > 0.05); the footslope had higher SOC content than the upper and middle slope (p > 0.05), corresponding to the soil erosion and deposition along the slope. Our findings could offer suggestions for future landscape management.