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.