Soil-compaction imaging using geoelectrical methods in a grassland field of Buenos Aires, Argentina.

The soil is an essential natural resource that supports agriculture and forestry, and plays a crucial role in global hydrological processes. Traditional methods used to study soil properties are commonly based on laboratory measurements on core samples, sporadic field measurements on soil profiles or visual evaluation of soil traits. These methods provide detailed information of soil physical properties, yet they offer limited capabilities to quantify and monitor spatial and temporal variations about soil physical properties. Geoelectrical methods, due to their non-invasive nature, sensitivity to soil physical properties and robustness in their application, are increasingly used to complement traditional observations and fill spatial and temporal gaps of information on soil properties. 

In this work, we present a case study of using geoelectric methods to investigate soil compaction. We measured Electrical Resistivity Tomography (ERT) data before and after an experimental soil compaction event and for two different levels of compaction (ten passages of a five-ton tractor and 4 passages of a ten-ton vehicle) in an agricultural field. The field of study was a grassland, that had remain unmanaged for approximately four decades, located in the  Santa Escolástica agricultural site, in San Antonio de Areco, Buenos Aires, Argentina. We collected two (7.75m long and 0.25m electrode spacing) ERT transects (before and after the compaction event) along the wheel tracks, and a third similar transect perpendicular to the wheel tracks (only after compaction). In addition, a soil pit was dug to conduct a visual analysis of the soil layering.

The ERT transects were independently inverted using the res2dinv software to obtain an image of the electrical resistivity of the three soil profiles. Results indicate a reduction in soil electrical resistivity of up to 25% in the top soil after the 4 passages of the 10 ton vehicle and 20% for the 10 passages of the 5 ton tractor. Correspondingly, in the upper subsoil layer at a depth of 0.55 m, we estimated a reduction of up to 10% for the first compaction case and negligible reduction for the second compaction treatment. Ongoing and future work will focus on enhancing the inversion results by incorporating geometrical constrains and simultaneously collected ground penetrating radar data.