Effects of land-cover type and topography on soil organic carbon storage on Northern Loess Plateau, China

Changes in land cover from cropland to conservation can sequester carbon in soil. On the Loess Plateau of China, vast areas of sloping cropland were converted into forest and grassland to control soil erosion. The northern plateau is a topographically heterogeneous, semi-arid region. A good understanding of the change of soil organic carbon (SOC) storage on the plateau in the process of land-cover change is important for assessing environmental changes and planning future land cover. We selected four land-cover types (cropland, planted grassland, abandoned orchard, and secondary grassland), and two vegetation covers (Stipa bungeana and Caragana korshinskii) on shady and sunny slopes, to analyse the effects of land cover and slope aspect on SOC storage. Soil C in the top 100 cm was significantly (P<0.05) greater in artificial grassland (2.49 kg m−2) and secondary grassland (2.98 kg m−2) than in cropland (1.69 kg m−2). The SOC pool in the surface soil and throughout the 1-m profile followed the order secondary grassland>artificial grassland>abandoned orchards>cropland. Sequestration extended to deep soil (80–100 cm). Slope aspect affected SOC concentration: wind erosion of the shady slope marginally reduced surface SOC relative to the sunny slope. In deep soil, responses of SOC concentration to slope aspect differed between vegetation covers: under C. korshinskii, SOC concentration was significantly greater on the shady slope (P<0.05), but no difference was found under S. bungeana.