Despite its importance for hydrological and ecological soil functioning, characterizing, and quantifying soil structure in the field remains a challenge. Traditional characterization of soil structure often relies on point measurements, more recently, we advanced the use of minimally invasive geophysical methods that operate at plot-field scales and provide information under natural conditions. In this study, we expand the application using geoelectrical and time-domain reflectometry (TDR) monitoring of soil water dynamics to infer impacts of compaction on soil structure and function. We developed a modeling scheme combining a new pedophysical model of soil electrical conductivity and a soil-structure-informed one-dimensional water flow and heat-transfer model. The model was used to interpret Direct Current (DC)-resistivity and TDR monitoring data in compacted soils at the Soil Structure Observatory (SSO) located in the vicinity of Zürich, Switzerland. We find that (1) soil compaction leads to a persistent decrease in soil electrical resistivity and (2) that compacted soils are typically drier than non-compacted soils during long drying events. The main decrease in electrical resistivity is attributed to decreasing macroporosity and increasing connectivity of soil aggregates due to compaction. Higher water losses in compacted soils are explained in terms of enhanced evaporation. Our work advances characterization of soil structure at the field scale with electrical methods by offering a physically based explanation of the impact of soil compaction on electrical properties and by interpreting DC-resistivity data in terms of soil water dynamics.
