Evaluation of Methods for Assessing Soil Water Repellency via a Single Tension Infiltrometer Experiment

Soil water repellency is a spatially and temporally variable phenomenon known to enhance runoff and erosion and impede infiltration, particularly following fire. Attempts to measure soil water repellency have been hindered by methodological constraints and environmental complexities, including scale-dependencies, prolonged measurement durations, and esoteric methodologies. Our study evaluated commonly used methods of assessing soil water repellency via a single tension infiltrometer experiment (minidisk infiltrometer, METER Group). Experiments (n=89) were conducted throughout three pinyon-juniper woodlands with multiple land management treatments (control, burned, tree thinning, and tree mastication). We assessed the efficacy of each analysis method with four criteria: agreement with paired water drop penetration time (WDPT) measurements, required duration of experiment, tractability, and robustness. Our preliminary results suggest several analysis methods are quite robust and track well with the WDPT. However, they require occasionally long-duration (several hours) experiments and advanced understanding of hydraulic properties. In contrast, cumulative infiltration over the first minute of a tension infiltrometer experiment provides a short-duration and tractable relative measure of soil water repellency, which may not be comparable across soil types with differing saturated hydraulic conductivities. Since numerous replications at each study site are typically desirable, there appears to be a tradeoff between increased sampling density at a single site, and the ability to make inter-site comparisons of soil water repellency. Our study highlights the need for a robust short-duration test of soil water repellency, which allows for inter-site comparisons and rapid deployment.