Three Years of Field Trials Indicate a Sustained Enhanced Rock Weathering Signal with Limited CO2 Removal

Enhanced rock weathering (ERW) is a CO2 removal technology that involves spreading finely ground silicate rock on fields. The chemical weathering of this rock powder removes atmospheric CO2 in the form of bicarbonate ions and secondary carbonates. Despite some promising theoretical simulations and laboratory findings, results from field trials that evaluate the ERW’s impact on soil biogeochemistry and CO2 removal are still scarce. This study investigated the impact of basaltic rock powder applied at the equivalent rate of 20 t per hectare (2 kg m–2) in three temperate vineyard fields in Switzerland over 1000 days. Analyses of soil pore water revealed that most standard ERW monitoring proxies (pH, electrical conductivity, total dissolved inorganic carbon, calcium, and magnesium concentrations) did not increase significantly. By contrast, sodium concentration in soil pore water was on average 3-fold higher in the rock powder-treated plots, indicating active mineral dissolution. Integrating the pore water results with model analyses, we estimated that the average CO2 removal rate was 100 ± 30 kg CO2 ha–1 yr–1, which is 10 to 30 times lower than the upper rates reported in some previous modeling and experimental studies. Future work is now needed to improve our understanding of ERW’s CO2 removal potential and soil contamination under a variety of soils, rock feedstocks, and climate conditions.