Constructing pedo-transfer functions based on grey relational and nonlinear programming to estimate hydraulic parameters in black soil

Abstract: Soil water characteristic curve and saturated hydraulic conductivity are important parameters for constructing soil moisture and solute transport models, both of which are affected by soil texture, bulk density, organic matter content, porosity, etc. In order to simply and accurately obtain the 2 parameters above, a total of 136 soil sampling points in the southern part of the black soil area in the Songnen Plain were designed, and the soil samples in 2 layers of these sampling points were collected to measure the soil water characteristic curve, saturated hydraulic conductivity and soil physical and chemical properties, the grey correlation analysis was used to determine the main soil physical and chemical properties affecting soil hydraulic parameters.The results showed: 1) in 0-20 cm soil layer, the residual moisture content of van Genuchten model had the higher correlation with fractal dimension, dry bulk density and organic matter content, and the correlation between parameter pore distribution index and fractal dimension, dry bulk density and clay content was the highest. The parameter of reciprocal soil air influx had the higher correlation with sand content, dry bulk density and fractal dimension. In soil layer from 20 to 40 cm, the parameter of residual moisture content of van Genuchten model had the higher correlation with sand content, dry bulk density and organic matter content; the parameter pore distribution index and fractal dimensions had the highest correlation; The correlation between fractal dimension, organic matter content and silt content and parameter pore distribution index was the highest, and the correlation between parameter reciprocal soil air influx and sand content, fractal dimension and organic matter content was the highest. 2) The correlation between soil saturated hydraulic conductivity and soil organic matter, dry bulk density and fractal dimension in 0-40 cm soil layer was higher. 3) The pedo-transfer functions of the soil water characteristic curve and the saturated hydraulic conductivity based on soil fractal dimension, organic matter, dry bulk density and soil particle composition were established by using the nonlinear optimal programming method. The accuracy of the pedo-transfer functions established in the study was verified by comparing with the existing common pedo-transfer functions. The results showed that soil fractal dimension was one of the primary parameters in constructing soil pedo-transfer functions to predict soil water characteristic curve and saturated hydraulic conductivity. In addition, soil dry bulk density and organic matter content also played an important role in pedo-transfer functions of different soil layers. Based on the verification analysis, the mean absolute errors of the estimated soil hydraulic parameters in different soil layers were all close to 0, and the root mean square error values of the predicted soil hydraulic parameters in different soil layers were also small. Specially, the root mean square errors of soil moisture content estimated by pedo-transfer functions established in the study were 0.022 and 0.017 cm3/cm3 in different soil layers, respectively. On the basis of comparing with the other existing common pedo-transfer functions of soil water characteristic curve and saturated hydraulic conductivity, the pedo-transfer functions of soil hydraulic parameters established in the study had high estimation accuracy, the root mean square error values were small; the determination coefficient values were all above 0.66, which was better than the other existing common pedo-transfer functions. In summary, the pedo-transfer functions of the soil water characteristic curve and saturated water conductivity established in the study can be used to estimate the soil hydraulic parameters in the black soil area of the Songnen Plain, and also provide technical support for acquisition of regional soil hydraulic properties.