A large-scale enhanced weathering experiment to quantify soil percolation fluxes

Despite growing interest in enhanced weathering (EW)—the application of silicate rock powders to croplands—substantial uncertainty remains regarding its actual CO₂ removal potential. From a data perspective, small-scale laboratory experiments often indicate limited carbon uptake, but their representativeness of field conditions remains unclear. By contrast, field experiments yield highly variable results, but they face the challenge of quantifying percolation fluxes in open, heterogeneous, dynamic systems.

Here, we present a novel hybrid approach: a large-scale yet controlled laboratory experiment designed to quantify all soil percolation fluxes and EW-driven CO₂ removal. The experiment is conducted in an approximately 200 m² garden at the Politecnico di Torino (Italy), subdivided into three hydraulically isolated plots with different basalt applications: a control plot (no basalt), 3 kg m⁻², and 6 kg m⁻². Beneath the 50 cm soil profile, all percolating fluxes are collected, enabling direct measurement of drainage outflows and dissolved-ion fluxes. Combined with soil measurements, this setup can constrain the mass balance of the weathering products and their associated CO₂ removal potential.

Preliminary results from the first year of experiment show a small but statistically significant increase (≈ 50 µS/cm) in the electrical conductivity of percolating water in both high and intermediate application plots. This is accompanied by moderate increases in major cation and dissolved inorganic carbon concentrations. Changes in hydrological response and percolating dissolved nitrogen are also observed. Overall, this study aims to provide process-based evidence of EW performance at the plot scale, thereby improving the assessment and modelling of soil-based carbon dioxide removal strategies.