Enhanced weathering of glacial rock flour drives coupled inorganic and organic carbon sequestration in a five-year field experiment

Enhanced rock weathering (ERW) has been proposed as a scalable carbon dioxide removal strategy, yet long-term field-based constraints on weathering rates and associated carbon sequestration remain limited. Here, we present a 5-year field assessment of Greenlandic glacial rock flour (GRF) applied at 50 t ha ⁻¹ to a sandy agricultural soil in Denmark. Using a soil mass balance approach, based on depletion of Mg which provided the most tightly constrained weathering signal, we estimate that at least 56 % of the applied GRF dissolved over 5 years. Initial uptake of CO ₂ via ERW is estimated at 3.2–4.9 t CO ₂  ha ⁻¹ when accounting for carbonate speciation in the acidic soil solution, with the potential for further gains if complete downstream transport of weathering products and subsequent re-equilibration with the more alkaline marine carbonate system is assumed. In addition to inorganic carbon removal, GRF-treated plots exhibited significantly higher soil organic carbon stocks, equivalent to the storage of an additional 18.3 t CO ₂  ha ⁻¹ . These results demonstrate substantial weathering and carbon sequestration over 5 years under field conditions in a temperate climate and suggest that both inorganic and organic carbon dynamics contribute meaningfully to the overall climate impact of ERW of GRF. The findings provide rare multi-year field constraints on ERW performance and underscore the importance of robust measurements for quantifying carbon removal in agricultural systems, representing the first implementation of mass balance methods within the framework of a randomized block design.