Soil Infiltration Characteristics And Influencing Factors Of Different Vegetation Restoration Types In Loess Hilly Region

Loess hilly area is a key area for vegetation restoration and construction in Loess Plateau,and the vegetation restoration improves the infiltration performance of soil and slows down soil erosion.In this study,field surveys and experimental measurements of agricultural land,grassland,and four typical tree and shrub vegetation types（buckthorn,lemon,acacia,and loblolly poplar）were conducted in three areas of Wuqi,Zhidan,and Dingbian counties,and the herbaceous vegetation diversity and root characteristics,soil physical and chemical properties,and soil infiltration characteristics were analyzed under different vegetation types.The factors influencing soil infiltration characteristics were determined based on path analysis,in order to provide a theoretical basis for understanding the response of soil hydrological characteristics to vegetation restoration.The main conclusions are as follows:（1）The vegetation restoration improved the species diversity and enhanced the root system’s soil fixation capacity.A total of 107 species of herbaceous plants,belonging to 33families and 83 genera,were recorded in the vegetation survey of this study.Among them,Asteraceae,Gramineae and Leguminosae dominated the area.The vegetation restoration improved the species diversity index,richness index and evenness index.The root system was more densely distributed in the 0～20 cm soil layer,and its root biomass accounted for54%～64%of the total root biomass in the 0～40 cm soil profile.（2）The vegetation restoration process significantly improved soil physicochemical properties.There was a significant increase of>0.25 mm grain size agglomerates in each vegetation type in the 0～40 cm soil layer compared to the agricultural land,and the stability of the agglomerates was enhanced.In the soil profile,agglomerate stability decreased with increasing soil depth.In the 0～40 cm soil layer,the MWD,GMD,and R_0.25 values of water-stable agglomerates of poplar soil were significantly higher（P<0.05）and D and K were significantly lower（P<0.05）than those of agricultural land.The soil bulk density decreased and porosity increased after restoration of different vegetation types.Soil bulk density tended to increase with soil layer,while soil porosity and water content did the opposite.The organic matter content of shrub and tree forests as a whole was higher than that of agricultural land and grassland.（3）Soil infiltration capacity increased after vegetation restoration.The initial infiltration rate,saturated hydraulic conductivity and cumulative infiltration volume of soils of different vegetation restoration types increased compared with agricultural land.0～20 cm soil layer,the initial infiltration rate of each vegetation type increased by 42.31%～189.82%compared with agricultural land,and the saturated hydraulic conductivity and cumulative infiltration volume were 1.42～2.38 and 1.50～2.58 times higher than agricultural land,respectively.Overall,the initial infiltration rate,saturated hydraulic conductivity,and cumulative infiltration of soils of different vegetation types decreased with increasing soil layers.The infiltration performance of agricultural soils was at a low level.The infiltration performance of soil is better than that of lemongrass,and the infiltration performance of buckthorn among shrubs is better than that of lemongrass.The main infiltration changes of soils of different vegetation types occurred within the first 6 h.（4）Soil infiltration characteristics are influenced by several factors.Saturated hydraulic conductivity was negatively correlated with bulk density（P<0.01）,with silt content and soil water content（P<0.05）,and with total porosity and large aggregates content（P<0.01）.The flux path analysis showed that the most influential factor on soil initial infiltration rate was bulk density,and the most influential factor on soil saturation hydraulic conductivity was large aggregates content.The difference in soil structure due to vegetation restoration was the key factor affecting soil infiltration characteristics.In summary,understanding the changes of soil infiltration characteristics of different vegetation types in the area and their influencing factors can provide reference for regional vegetation restoration and ecological environment construction.