Study On Soil Infiltration Parameters Simulation And Remote Sensing Inversion In Semi-arid Steppe Basin

In this paper,Xilin River Basin,semi-arid continental sandy meadow grassland basin,was set as subject for the study.From the surface layers of the soils(0-50 cm),soil samples were collected,a total of 1050 by ring knife and ziplock bag in 42 sampling sites,for analysis of particle size composition,bulk density,organic matter content,saturated hydraulic conductivity(Ks)and some other physical and chemical properties.Then four saturated soil hydraulic conductivity pedo-transfer functions(PTFs)were used for fitting of Ks in soil layers,10cm each,within the 0~30 cm soil layers of the 32 sampling sites for modeling.Based on the PTFs and backscattering of quadrupolarized RADARSAT-2,Synthetic Aperture Radar(SAR),the surface soil Ks was predicted in a large-scale.After the analysis of the difference of the saturated hydraulic conductivity and the actual soil infiltration situation,190 double ring infiltration experiments were carried out at 38 sites in the study area to simulate the surface soil unsaturated infiltration process and the inner-ring scale effect of the double ring infiltrometer.The main conclusions were as follows:(1)The PTFs can better fit the relationship between Ks and soil parameters.Saxton model has the best simulation effect in the study area,with the multiple regression model and the Weston model followed,and the Cosby model worst.The number of PTF's parameters and the soil properties it contains have a great correlation with the accuracy of the simulation.Generally speaking,the more comprehensive the soil properties are included,the better the model simulation effect is.(2)In the grassland with sparse vegetation,SAR technology can describe the physical and chemical parameters of surface soil in a finer way.The soil properties such as particle size composition and bulk density of surface soil can be established by surface roughness and quadrupole data and their combinations.Multivariate linear regression model inversion,through the soil parameters of remote sensing inversion combined with soil transfer function,can predict the Ks of surface soil in large area.(3)The surface soil Ks in the study area is relatively fast,between 2 and 8 m/d.The particle size and lack of vegetation are the main reasons for the rapid soil water infiltration,and human activities have a greater impact on it.After the agricultural or urbanization transformation,the water conductivity of the surface soil can be greatly reduced.The distribution regulation of the surface Ks of the study area is:mountainous bare land>dune sand land>inter-wet wetland>village and town construction land>drip irrigation area.(4)The double-ring infiltration test will be affected by the scale effect of the infiltrometer.The increase of the inner-ring diameter within a certain range will obviously reduce the influence of the scale effect on the soil water infiltration process,but the designed infiltrometer of 40cm inner-ring diameter with a buffer index of 0.33 is not sufficient to completely overcome the scale effect.(5)The Hydrus-1D software can perform the infiltration test process of the study design,the hydraulic characteristics of 0-50 cm per 10 cm soil layer,and the change of the observation point indenter,soil moisture content and flux including the soil surface and the bottom of each soil layer.Although the validation results using the measured soil moisture content after the end of the infiltration is ordinary effective in a few soil types,the measured and simulated soil moisture content are between the field water holding capacity and the saturated water content,indicating that the vertical infiltration is under the unsaturated soil conditions.(6)The study area is extremely high in soil sand content,almost nil in clay content and low in organic matter content and the parameters do not vary much with soil depth from layer to layer.The final infiltration rate and time calculated by Horton model can be divided into three categories by using K-means clustering,and the infiltration process is mainly affected by two kinds of factors:the soil physical properties related to soil compaction and pore distribution and the external environmental components related to the kinetic energy potential of infiltrating liquid.(7)The soil type can not represent the infiltration process.The study area was divided into three areas based on the soil infiltration:Valley Wetland,Pastoral Grassland and Desertification Sandy Land.Besides,the validation results of three infiltration zones by using infiltration model are improved compared with soil type zones.The infiltration rate of the soil in the Valley Wetland is relatively slow.The Pastoral Grassland is affected by the animal husbandry and human activities.The water-holding capacity of the surface soil tends to decrease and more reasonable policies and regulations for animal husbandry should be formulated to reduce vegetation damage.Vegetation in Desertification Sandy Land is sparse,sand content is high,and ecological degradation is serious.Appropriate physical measures can be taken to improve soil water retention capacity.The remapped infiltration zone and its impact can provide a theoretical basis for future ecological and soil remediation.