The Spatial Distribution Of Soil Organic Carbon And Its Influencing Factors In Loess Hilly And Gully Region

The loess hilly and gully area is one of the most fragile zones in the Chinese Loess Plateau region, it is still considered to be one of the most severely eroded areas in the world. Study on the spatial distribution factors of soil organic carbon(SOC), we could calculate soil organic carbon storage much more accurately and provide guidance for vegetation restoration and forest management. To find out the spatial distribution law of this region, we set up 126 sites of topsoil to study on the SOC distribution factors under different land-use types, topography, and 54 soil profiles to a depth of 200 cm (20 cm interval) to study on the vertical distribution factors of SOC and its influencing factors of different soil layer.The results shows that:(1) Land-use types have a significant influence on SOC content of topsoil sites, the SOC content of forestland is significantly higher than shrub and grassland, and shrub and grassland is higher than cropland and orchard.(2) Topography significantly influences SOC content of topsoil sites. The order of SOC content of four kinds of slope angel range is gentle slope angel(<15°)> relatively steep angel (15-25°)> steep angel (25-35°)> urgent slope angel (>35°). The variation of three kinds of slope position is upper slop< middle slope< lower slope. The variation of four kinds of slope aspect is shady slope< half-shady slope< half-sunny slope< sunny slope. When the altitude is increased, the SOC content is decreased.(3) The interaction effect of land-use types and topography has a significant effect on SOC content. In the same land-use type, the SOC content is decreased while the slope angel is increased. At the same slope angel range the order of SOC content of natural mixed forest is the highest and orchard is the lowest. At the same slope aspect the order of SOC content of seven land-use types is orchard and cropland< grassland and shrub< forest; for orchard and grassland the highest SOC content is found at shady aspect; for cropland SOC content at half-sunny aspect is the highest; for shrub and forest the highest SOC content is found at sunny aspect. For all land-use types, SOC content in lowest altitude is the highest; at the same altitude SOC content of orchard is the lowest and natural mixed forest is the highest.(4) The SOC content, density has a negative relationship with soil depth. SOC density in the profile 0-100 cm accounts for 19.09%,64.17% sampled to a depth of 200 cm respectively, while for 100-200cm, SOC density accounts 35.83% in 0-200 cm.(5) The SOC content of topsoil sites has a significant relationship with silt content, clay content, bulk density, soil erodibility, slope angel, slope aspect and altitude. The dominate influencing factors of topsoil sites SOC content are soil erodibility, clay content, silt content, bulk density and slope angel.(6) The main influencing factors are different for soil layers. For all soil profiles, the dominant influencing factors of 0-100 cm are soil properties such as soil erodibility, saturated hydraulic conductivity, clay content, bulk density; For 100-200 cm soil layer, the dominate influencing factors of SOC content are mass of root.