Land-use types and slope topography affect the soil labile carbon fractions in the Loess hilly-gully area of Shaanxi, China

This study evaluated the effects of vegetation restoration on soil organic carbon (SOC) and its fractions, by exploring the SOC, particulate organic C (POC), mineralizable organic C (MOC), and light fraction organic C (LFOC) of three sloping land-use types (sloping farmland, forestland and grassland) and at four locations along each hillslope (30, 60, 90 and 120 m from the hilltop). Soil Cs-137 was measured to calculate the soil erosion rate. The SOC, POC, MOC, and LFOC were significantly higher (p < 0.05) in the forestland and grassland than the sloping farmland. The SOC, LFOC, MOC, and POC of the grassland and forestland were higher in the lower than in the upper parts of the hillslope. The Cs-137 activity was associated with soil loss rate and related to the redistribution of soil carbon fractions along the hillslope. The distribution of the soil carbon fractions and soil erosion in the forestland and grassland showed opposing trends. The soil labile organic carbon distribution and erosion of sloping farmland displayed a consistent distribution trend. Land-use changes and erosion were the most important factors that governed soil labile organic carbon: accounting for 21.7% and 25.7% of the observed variances, respectively.