Soil compaction signatures on electromagnetic and DC-current geophysics

Monitoring soil structure is of paramount importance due to its key role in the critical zone as the foundation of terrestrial life. Variations in the arrangement of soil components significantly influence its hydro-mechanical properties, and therefore its impact on the surrounding ecosystem. Soil compaction, resulting from inappropriate agricultural practices, not only affects soil ecological functions by reducing soil porosity and water infiltration, but also decreases the yields spoiling the socio-economic aspect.

In this study, we compared the ability of electrical and electromagnetic geophysical methods, i.e. Electrical Resistivity Tomography and Frequency-domain Electromagnetic Method, to monitor the effects of compaction on agricultural soil. The objective is to highlight the electro-magnetic response caused by plastic deformation of the soil generated by both a super-heavy vehicle and the usual interrows surface compaction generated by tractor traffic for common practices. The survey was conducted both on a small scale, covering an area of 1.5 hectares, and in detail on individual targeted transects. This allowed to capture the 2-D and 3-D spatial heterogeneity that is often difficult to obtain with punctual and invasive traditional methods.

This work aims to contribute to the methodological optimization of agro-geophysical acquisitions and data processing, so as to obtain accurate soil models through non-invasive approach. Results, validated with traditional soil characterization techniques (i.e. penetration resistance, bulk density and volumetric water content on collected samples), show pros & cons of both techniques and how differences in their spatial resolution heavily influence the ability to characterize compacted areas with good confidence.