High-resolution non-invasive mapping of vertical heterogeneity in sandy soils of the Oak Openings Region, Ohio, USA, using electromagnetic induction and ground penetrating radar methods

Geophysical methods provide a non-invasive approach to rapidly characterize soil physicochemical properties distribution. Currently, gaps exist in the systematic application and validation of non-contact-based geophysical methods, such as ground penetrating radar (GPR) and electromagnetic induction (EMI), for characterizing the vertical variation of soil properties and quantitatively linking geophysical responses to independently measured soil parameters. This study assesses the use of EMI and GPR for quantifying the vertical variation of soil moisture content (SMC), soil organic matter (SOM), and soil texture. Co-located EMI and GPR surveys were conducted at the Stranahan Arboretum research site in Toledo, which is within the Oak Openings Region in the state of Ohio, USA. Soil samples collected from nine locations along the transects were analysed for SMC, SOM, and soil texture. Apparent electrical conductivity ( σₐ σ a ) datasets from EMI survey were inverted to obtain lateral and vertical variations of soil electrical conductivity ( σ σ ), which captures three major lithostratigraphic units—sandy, silt loam, and silt soils—found in soil cores within the top 2.0 m. Soil electrical conductivity correlates with measured soil properties (SMC, SOM and soil texture), with coefficient of determination ( R 2 ) ranging from 0.6 and 0.9. The GPR radargrams show structural boundaries, with reflectors consistent in delineating sandy unit but unable to distinguish between the silt loam and silt. These results validate the effectiveness of combining EMI with GPR to delineate vertical variation of soil properties and characterize stratigraphic heterogeneity, expanding the possibilities for non-invasive three-dimensional soil properties mapping.