A seismic shift for soil health monitoring: scalable, non-invasive seismology at the decimetre scale.

Soil is a complex ecosystem at the heart of survival for all life on land. Harbouring more carbon than the atmosphere and vegetation combined, it is home to more than 60% of Earth's species and delivers 99% of calories for the human food system. Despite growing demands, more than 70% of global arable land is classified as degraded. Monitoring soils and thereby improving soil health at scale is difficult due to their multiscale heterogeneity, limited accessibility of remote sensing techniques, and destructive, labour-intensive nature of soil coring, on the other hand. Geophysical techniques offer a tangible alternative. To date, active seismics have scarcely been considered for the living topsoil, a layer mere 10-50 cm below our feet.

We show how seismology with ultrahigh frequency wavefields above 500 Hz generated by hammer strikes and recorded by cheap, bespoke geophones should allow us to infer on a variety of crucial soil health parameters, such as bulk density, soil moisture, topsoil depth, soil carbon, and more, which collectively give rise to determining soil function and health. We present consistently high data quality up to 1500 Hz collected across three continents in more than 10 ecosystems and crop types, showcase a pathway for automated data processing and inference, introduce novel low-cost MEMS sensors, and highlight emerging AI engines.

Our non-profit organisation, Earth Rover Program, is tasked with implementing the vision towards a global soil health assessment of unprecedented resolution and coverage. This, in turn, can eventually equip farmers with spatially explicit, local knowledge of their soils’ state and suggest remedial measures based on this novel data, with the potential to reduce environmental pressures and agricultural costs while increasing long-term yields.