ERT and EMI Characterization of the Spatiotemporal Variability of Agricultural and Forest Soils: Some Common Methodological Issues

The interplay between water dynamics and soil characteristics underpins the functioning and resilience of the soil-plant-atmosphere continuum, but also leads to complex spatiotemporal variability. This variability challenges mapping and monitoring methodologies, ultimately hindering the definition of more effective management practices. Hence, informing the development of effective management practices has become a multidisciplinary and multi-methodological effort. Among geophysical methods, electrical resistivity tomography (ERT) and electromagnetic induction (EMI) have been increasingly used for their sensitivity to water and soil texture changes, as well as for their capability to provide spatially extensive information and noninvasive monitoring. We present some common ERT and EMI survey designs in hydrological and agricultural applications, reviewing their potential and highlighting some key limitations. We first consider the use of ERT time-lapse measurements during irrigation tests, which allows the decoupling of static soil properties and water dynamics, but also requires a careful survey design to achieve the right trade-off of spatial and temporal resolutions and guarantee reliable results. We then present the use of EMI to map the irrigation and evapotranspiration dynamics in orchards, where the strong spatial variability and anisotropy challenge EMI high-resolution surveys and quantitative interpretations. This study reviews how the characteristics of the methods are reflected in their common usage, but also possible pitfalls.