Spatial Distribution Characteristics Of Soil Hydraulic Parameters Under Irrigation-Drainage Unit Based On Pedo-Transfer Functions

Soil hydraulic parameters are important parameters for studying soil moisture and solute motion process.It is of guiding significance to analyze their spatial variation characteristics,and explore the effects of cultivation practices on soil water utilization and solute transport.However,the determination of these parameters is often time-consuming and soil hydraulics parameters have strong spatial heterogeneity.Pedo-transfer functions based on soil basic physicochemical properties is an effective method to estimate soil hydraulic parameters.In this study,30 typical samples were selected in the Jianghan Plain,and their soil physical properties were obtained by laboratory measurement.By using statistical methods such as correlation analysis and stepwise multiple linear regression,pedo-transfer functions suitable for Jianghan plain was constructed.Taking Irrigation-Drainage unit of Jianghan Plain as the research object,based on the measured value of Irrigation-Drainage unit and pedo-transfer functions,the soil hydraulic parameters are inversed.Combined with the statistical methods,analysis of the spatial variation characteristics of soil hydraulic parameters of Irrigation-Drainage unit,and further explore the effects of different farmland farming measures on soil hydraulic parameters.The results are as follows:(1)There was a significant correlation between the soil hydraulics properties and basic physicochemical properties,and Pearson correlation analysis showed that soil saturated hydraulic conductivity was extremely significantly positively correlated with organic matter content(P<0.01),which was significantly negatively correlated with the bulk density(P<0.05).The parameter θs of van Genuchten model was significantly or very significantly positively correlated with organic matter content,the soil particle composition and soil porosity,but was very significantly negatively related to the clay content,sand content and bulk density.The θr was very significantly correlated with the soil particle composition.α was extremely significantly positively correlated with organic matter content and soil porosity,but was very significantly negatively correlated with the bulk density.n was significantly or very significantly relevant to organic matter content,the soil particle composition and soil porosity.(2)The soil particle composition,bulk density and soil porosity are important input variables for constructing pedo-transfer functions,and organic matter content has no significant effect on its functions.The results of each assessment and verification index showed that except soil saturated hydraulic conductivity,the predicted values of other pedo-transfer functions were better,and the determination coefficient R2 ranged from 0.51 to 0.70,which had high accuracy.Compared with three commonly pedo-transfer functions,in addition to soil saturated hydraulic conductivity,the accuracy of pedo-transfer functions built by other parameters were higher,which were obviously superior to other commonly pedo-transfer functions,and were more suitable for the soil in Jianghan Plain.(3)There is a large difference in the spatial variation characteristics of soil hydraulic parameters in Irrigation-Drainage unit.The saturated hydraulic conductivity varied from 11.14 to 39.18 cm·d-1,and showed a vertical distribution pattern with the soil depth decreasing firstly and then increasing.In horizontal space,it had a strong spatial autocorrelation.The θs decreased firstly and then increased with the depth of the soil layer,except for the medium-level space autocorrelation in 40-60 cm,the spatial autocorrelation in other soil layers were strong spatial autocorrelation.The θr gradually increased to stable,and then increased with the depth of the soil layer.The vertical distribution of the a was similar to the trend of the θs,and n fluctuated with depth.In horizontal space,θr,α and n were strong spatial autocorrelations.In vertical direction,total water storage Wt firstly increased,and then decreased with depth of soil layer,other types of water storage fluctuated with depth.In horizontal space,except for 0-40 cm,Wt had medium-level spatial autocorrelation,the spatial autocorrelation in other soil layers were strong space autocorrelation,other types of water storage in all soil had strong spatial autocorrelations.(4)The difference in cultivation practices such as land use and cultivation history of rice fields were affected soil texture and structure,which in turn affected soil hydraulic parameters.The soil saturated hydraulic conductivity of the dryland was higher than the paddy field,but there was no significant difference(P>0.05).The water retention capacity was stronger in paddy field than in dryland,and the soil water storage of paddy field was higher than that of dryland,except for flood water storage.With the increase of paddy field cultivation history,the saturated hydraulic conductivity of paddy soil decreased,but the water retention capacity increased significantly,total and available water storage of soil increased,and the flood water storage decreased,while other types of water storage showed no obvious change trend.In addition,the land use type of paddy field before conversion also significantly affected soil hydraulics parameters.