Effect Of Vegetation Restoration On Soil Hydrological Properties And Soil Infiltration In Loess Hilly Region

The Loess Plateau is located in the arid and semi-arid region of Northwest China,with serious soil erosion and fragile ecological environment.In recent decades,to curb soil erosion problems,a large-scale construction of returning the sloping farmland to forest and grass lands has been implemented in the Loess Plateau,which has significantly increased the vegetation coverage and effectively alleviated the slope soil erosion.Meanwhile,vegetation restoration changes the soil hydrological and physical properties,and has a significant impact on the process,capacity and mode of soil water movement.Soil moisture is the main limiting factor for plant growth and restoration in this region.Improving the storage and utilization efficiency of precipitation is of great significance for the ecological construction of the Loess Plateau.In this study,we analyzed the soil hydrological characteristics and infiltration characteristics of forest,shrubland,grassland and cropland in the Zhifanggou watershed and their relationship with soil physicochemical properties through in situ field experiments combined with indoor analysis.The findings could provide a reference for understanding the effect of vegetation restoration on soil hydrology in the loess hilly region.The main conclusions are as follows:(1)Vegetation restoration in the loess hilly area has an important impact on soil hydrophysical properties.Vegetation restoration generally reduces soil bulk density,sand content,p H and soil moisture,increases soil porosity(total porosity,capillary porosity,non-capillary porosity and macroporosity),clay,silt and organic matter,and improves saturated water content,field capacity and saturated hydraulic conductivity(K_s).Across the Loess Plateau,the K_s of forest and shrubland was greater than that of grassland and cropland,and the K_s of the surface layer was higher than that of the subsurface layer.(2)Vegetation restoration affects soil hydrological properties by changing soil physicochemical properties.The three soil hydrological properties(saturated water content,field capacity and K_s)were significantly negatively correlated with bulk density and p H,but significantly positively correlated with total porosity,capillary porosity,non-capillary porosity and organic matter.The correlation between soil particle composition and soil hydrological properties is low and more complex.Soil porosity(total porosity,capillary porosity and non-capillary porosity)and bulk density,soil chemical properties(organic matter and p H),and soil particle composition(clay,silt and sand)explain 93.8%,59.2%and 13.4%of the variation of soil hydrological properties,respectively.Soil porosity and bulk density contributed the most to K_svariation(53.3%),followed by soil particle composition(38.6%)and soil chemical properties(38.3%).Soil porosity and bulk density are the dominant factors affecting the changes of soil hydrological characteristics.The established pedotransfer function(PTF)of K_s using BD,clay and silt content has a better performance than two existing PTFs.In the entire Loess Plateau,the Ks of woodland and shrub land was greater than that of grassland and agricultural land,and the saturated hydraulic conductivity of the surface layer was higher than that of the subsurface layer.(3)The processes of soil infiltration at different sites go through“transient-leakage-stable”stages,but the timing of each stage varies somewhat.Three infiltration models were used to estimate soil infiltration processes in this study,and the performances of three models decrease in the following order:Philip model,Kostiakov model and Horton model.Vegetation restoration generally improves the soil infiltration capacity,which is mainly reflected in the increase of stable infiltration rate and saturated hydraulic conductivity(K_s).The infiltration capacity is ranked from high to low:shrubland,forest,grassland and cropland.The increase of soil moisture and bulk density reduces the soil infiltration capacity,while the increase of total porosity,macroporosity and organic matter improves the soil infiltration capacity.Soil moisture and total porosity explains more about soil infiltration capacity than other soil physical and chemical properties.(4)Vegetation restoration generally promotes the occurrence and development of soil preferential flow and improves the role of preferential flow in the soil hydrological process in the region.The development degree of preferential flow from high to low is shrubland,forest,grassland and cropland.The increase of soil moisture and bulk density reduces the development degree of soil preferential flow,while the increase of total porosity,macroporosity and organic matter improves the development degree of soil preferential flow.Macroporosity explains more about soil infiltration capacity than other soil physical and chemical properties.(5)There are differences in soil water retention curve and dynamic change characteristics of soil moisture content of different land use types under numerical simulation rainfall conditions.Both simulated soil saturated water content and measured saturated water content show that vegetation restoration can effectively improve soil water holding capacity,and the water holding capacity of shallow soil is higher than that of deep soil.