Revisiting Vereecken Pedotransfer Functions: Introducing a Closed-Form Hydraulic Model

We revisited the Vereecken database, which has been used to derive pedotransfer functions (PTFs) to estimate the soil hydraulic parameters of Belgian soils. We developed new PTFs based on the Mualem-van Genuchten model, constraining m = 1 - 1/n and using fewer parameters. The goodness-of-fit was similar to the one originally obtained by Vereecken. We used a one-step procedure that allows direct quantification of the correlation matrix and the uncertainties of the estimated parameter values. The coefficients of the new PTFs were estimated using a global search algorithm and they were validated against independent data. The PTFs have a wider range of applicability since: (i) they allow the use of the closed-form solution of the unsaturated hydraulic conductivity in the Mualem-van Genuchten model; and (ii) they consider the effect of macroporosity. We determined that the hydraulic conductivity measured close to saturation could not be estimated based on the available estimators; however, the hydraulic conductivity in the matrix domain was predicted with high accuracy.