Soil

Work Package 1

Subsoil geophysical imaging to characterize soil moisture and hydraulic properties where point sensors and optical remote sensing fall short.

Key methods & outputs

Electrical Resistivity Tomography (ERT) and Electromagnetic (EM) mapping at all field sites
Low-cost, open-hardware micro-Ohmpi sensors for permanent field deployment
Partitioning of soil fluxes such as sorption
Training datasets and code converting electrical resistivity into soil hydraulic properties — matric potential (Ψ_soil), saturated hydraulic conductivity (K_s) and fluxes (Q)
Long-term, multi-scale monitoring of key components of the Earth's Critical Zone

This work package addresses the current gap in experimental trials within complex agroecosystems that lack deep subsoil ancillary information by implementing advanced subsoil imaging techniques. WP1 specifically tackles the urgent need to develop a robust scientific basis for time-lapse geophysical soil mapping, overcoming the limitations of point sensors in spatially characterizing soil moisture variability and compensating for periods when optical remote sensing is unavailable due to cloud cover.

At all field sites, Tech4Agro-CSIC will conduct ground geophysics activities using Electrical Resistivity Tomography (ERT) and Electromagnetic (EM) Mapping, both of which allow detailed modeling of subsoil electrical conductivity. Although geophysics has demonstrated its usefulness in diverse contexts, from mountain hydrology to agronomy and ecology, a systematic prospection strategy for complex, layered agroecosystems is still lacking. The recent creation of open-hardware instruments has reduced costs and now enables the permanent deployment of sensors in the field, opening new opportunities for this project.

The figure above is adapted from Dimech et al. (2022), and illustrates (from left to right): a soil elemental unit comprising a soil matrix with air-filled pores and pore tortuosity, from which electrical resistivity is defined according to Ohm's law; a scaled-up view showing subsoil resistivity tomography used in geophysical prospecting; and the temporal component of permanently installed systems for monitoring applications.

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