Quantification of CO₂ uptake by enhanced weathering of silicate minerals applied to acidic soils

The application of ground silicate minerals to agricultural soils has been proposed as a method for taking up CO₂ by enhancing the weathering rate of these minerals through their exposure to soil acids. Alternatively, glacial rock flour, a finely grained material which is abundantly available without the need for energy-intensive grinding, could be used. However, simple and inexpensive methods for determining the amount of CO₂ taken up as a result of weathering of applied minerals are still needed, and the impact of non-carbonic acids on CO₂ uptake has yet to be accounted for. Here, we present a protocol for correcting estimates of CO₂ uptake due to enhanced mineral weathering to account for weathering by non-carbonic soil acids. We determine that soils with a pH below 6.3 need correction for weathering by other acids than carbonic acid and that, given the impact of non-carbonic acids, soils with a pH below 5.2 may not be ideal candidates for mineral applications aimed at CO₂ uptake, depending on the pCO₂. We report an estimated CO₂ uptake of 728 kg CO₂ ha⁻¹ after the application of 50 tons ha⁻¹ of Greenlandic glacial rock flour to an acidic, sandy soil in Denmark over 3 years.