Influence Of Different Vegetation Types On Soil Physical Properties In Changwu Tableland Slope

It is necessary to understand the soil property changes under different vegetation types for the selection of vegetation types and the reasonable spatial layout in Loess Plateau Gully Region.In this paper,three vegetation lands(Pinus tabulaeformis,Hippophae rhamnoides and grassland)and the additional cropland which located in Changwu Tableland Slope were chosen as research objects.The soil basic properties,soil aggregates characteristics,soil macropore characteristics and soil infiltration capacity in the 0~30 cm depth of these research sites were studied to exhibit the influence of different vegetation.The results include as follow:(1)The clay content of the 0~30 cm soil under different vegetation types showed: cropland > Pinus tabulaeformis > grassland > Hippophae rhamnoides;the Silt content showed: grassland > Pinus tabulaeformis >cropland > Hippophae rhamnoides;the sand content showed: Hippophae rhamnoides >grassland > Pinus tabulaeformis > cropland.Soil bulk density and water-stable aggregates showed the same trend: Pinus tabulaeformis >grassland > Hippophae rhamnoides > cropland;soil saturated moisture content and organic matter content showed: Hippophae rhamnoides>grassland > cropland > Pinus tabulaeformis;soil root biomass showed: grassland >Hippophae rhamnoides > Pinus tabulaeformis > cropland.Overall,the soil basic properties of Hippophae rhamnoides and grassland were better than that of Pinus tabulaeformis forestland and cropland.(2)The mean weight diameter(MWD)and geometric mean diameter(GWD)of soil aggregates under different vegetation types in layer of 0~30 cm showed: Pinus tabulaeformis > Hippophae rhamnoides > grassland > cropland;the fractal dimension(D)showed: cropland >Hippophae rhamnoides > grassland > Pinus tabulaeformis;0.25~5 mm aggregates content showed: grassland > Pinus tabulaeformis > Hippophae rhamnoides > cropland.Pinus tabulaeformis owned higher MWD and GWD value because of its higher large aggregate content;Grassland and Hippophae rhamnoides showed higher uniformity of soil aggregate distribution and the soil structure was more reasonable;Cropland owned the least MWD and GWD value,showed poorer aggregate stability and soil antierodibility.Overall,Hippophae rhamnoides and grassland performed better in promoting the soil aggregate than that of Pinus tabulaeformis and cropland.(3)The macroporosity and macropore number showed a decreasing trend with the increase of soil depth under different vegetation types in layer of 0~30 cm.The average macroporosity and macropore number showed: Hippophae rhamnoides > grassland > Pinus tabulaeformis > cropland.Overall,the soil macropore of Hippophae rhamnoides,grassland and Pinus tabulaeformis had a larger degree of improvement than cropland.Soil macropore in Hippophae rhamnoides showed the highest degree of development,and distributed relatively uniform in the depth of 0~30 cm;soil macropore in grassland developed better in the depth of 0~15 cm,while decreased rapidly with the increase of soil depth;though soil macropore in Pinus tabulaeformis forestland performed worse than Hippophae rhamnoides and grassland in the depth of 0~10 cm,it also had a certain degree of development in deeper soil and had no the phenomenon of decreasing rapidly;the development of soil macropore in cropland stay in a low level as a whole.(4)Initial infiltration rate under different vegetation types showed: grassland > cropland > Hippophae rhamnoides > Pinus tabulaeformis;stable infiltration rate showed slight different as: grassland > Hippophae rhamnoides > cropland > Pinus tabulaeformis.Pinus tabulaeformis and cropland showed lower infiltration capacity and not advantaged for rainfall infiltration,so Hippophae rhamnoides and grassland performed better in promoting soil infiltration capacity than that of Pinus tabulaeformis and cropland.The results of our study showed that it was necessary to insist on returning cropland to forestry and grass,and adhere to the way of combination of forestlands,shrublands and grasslands,then design rational distribution of different vegetation types and give full play to soil and water conservation and environment landscaping in the Loess Plateau Gully Region.Shrubland and grassland was of benefit to promote the rainfall infiltration and reduce soil erosion by restoring vegetation and improving the soil basic properties rapidly.Therefore,it is recommended to increase the area of shrubland and grassland moderately in this area.