Improving Hydraulic Conductivity Estimates from Minidisk Infiltrometer Measurements for Soils with Wide Pore-Size Distributions

Disk infiltrometers are established as standard devices for measuring soil surface hydraulic properties. This study explored the validity of a semiempirical approach that is used to obtain estimates of the near-saturated hydraulic conductivity from disk infiltrometer data. The approach was compared with two other estimation expressions. The analysis was based on three-dimensional numerical modeling of the infiltration process, i.e., on synthetic data. The results of the validation procedure showed that the original expression performed best among the compared methods, but still failed for fine-textured soils and the selected Cambisols. This is due to the overwhelming importance of lateral soil water movement by capillarity, which is not adequately addressed by any of the models. The study showed that improved estimates, specifically for fine-textured soils and Cambisols and for small infiltrometer radii (minidisks), can be obtained by extending the original approach. This is achieved primarily (i) by using the modified van Genuchten parameterization of soil hydraulic functions instead of the original one, and (ii) by including a more representative set of soils in the objective function when optimizing the estimation formula.