The Spatial Variability Of Soil Infiltration Capacity At Loess Hilly Area

Soil water infiltration is an important part of mutual transformation of precipitation, surface water, soil water and groundwater. Soil water infiltration is also the only way for surface water to be absorbed by Vegetation. It has close ties with the hydrology conversion, soil erosion, irrigation and nutrient transport, etc. I Selected this typical small watershed in Loess Hilly Area-Anjiagou watershed as research object, The spatial variability of soil properties、the spatial variability of macropores under typical vegetation type and the patial variability of soil infiltration capacity at Loess Hilly Area were studied, the results are as follows:(1) By using field soil sampling and laboratory analysis, The spatial variability of soil physical and chemical properties at Anjiagou valley were studied. Results indicated that:(1) In the surface soil (0-20cm), soil bulk density、organic matter、total porosity、capillary porosity and silt content showed a weak variability; non-capillary porosity showed a moderate variability; sand and clay showed a strong variability。(2) There are some differences in soil properties of different slope. Shady soil organic matter、total porosity、capillary porosity and non-capillary porosity are greater than sunny; Shady soil bulk density is greater than sunny; different slope positions of soil properties showed different variation.(3) The biggest soil bulk density was at gully bottom. It was1.354g/cm3. The smallest soil bulk density was at gully central. It was1.132g/cm3. Overall, soil bulk density was exhibited a high-low-high variation from top to ditch. From top to ditch, Organic matter showed a growing trend; total porosity, capillary porosity and non-capillary porosity is showing a low-high-low variation.(2) By using dye tracing method and image analysis technology, the characteristics and distribution of macropores under typical vegetation in Anjiapo catchment of Longxi Loess Plateau and its relationship with plant populations and the properties of soil in study area were studied. the macropore amount differed among6kinds of plant populations, the existence of macropore can accelerate the infiltration depth by2or3times at least; The vertical distribution pattern of soil macropores can be obtained by the variation of dyed area with soil depth; The dye areas of6soils tend to decrease with increasing of soil depth; the dyed areas at second and third dye stained level are bigger, account for29.3%and29.4%of total dyed area on the soil profiles, dyed area on level1and level4are17%and19.8%, respectively, dyed area on level5is the lowest, accounts for45%; The characteristics and distribution of macropores are highly correlated with the organic matter content、bulk density and root length density of vegetation in soil.(3)Method of single-ring was employed to study soil water infiltration characteristics and its influencing factors under typical vegetations in Loss hilly region. Results indicated that:(1) In the topsoil (0-20cm), Differences on soil infiltration capacity among the six kinds of plant populations were significant, Water infiltration characteristics were the same as Robinia pseudoacacia> Primus armeniaca> Pinus tabuliformis> Populus tomentosa> Hippophae rhamnoides> Caragana korshinskii;(2) Both the initial infiltration rates (IIRs) and stable infiltration rates (SIRs) under typical vegetations decreased with soil depths in0-100cm soil profile, the vegetations increased the IIRs and SIRs in surface soil mostly, the influence over IIRs and SIRs by vegetations decreased with soil depths;(3) The correlation analysis showed that the root length density(RLD), the organic matter content and the initial water content were significantly related with water infiltration characteristics. However, the soil bulk density and soil mechanical composition had no significant influence on IIR and SIR in surface soil. Stepwise regression analysis showed that RLD was the main factor affecting the infiltration rate, even played a decisive role on SIR in0-100cm soil profile.(4) Soil infiltration process under typical vegetations was better fitted by Philip infiltration models than by Horton infiltration model and Kostiakov model. Using Philip infiltration model based on Scaling theory, the PTFs of the calibration factor αA and stabilize soil infiltration rate were gained, correlation coefficients were0.776and0.809, it was good for accuracy requirements of the space; Ann Small Watershed calibration factor greater spatial variability, but with a certain regularity. When the initial moisture content was0.1g/g, αA was between0.71to1.05mm/min0.5, at the ditch, the calibration factor value is generally small, the larger part was at top of the velley; When the initial moisture content was O.lg/g, the steady infiltration rate ranged from0.171to0.258mm/min.