Applying minerals to soil to draw down atmospheric carbon dioxide through synergistic organic and inorganic pathways

Minerals in soil can sequester atmospheric carbon dioxide through natural organic and inorganic processes. Here we consider three soil- and mineral-based methods for carbon dioxide removal: (1) grinding and spreading of calcium- and magnesium-rich silicate rocks for enhanced rock weathering and subsequent inorganic carbon formation, (2) mineral doping of biomass prior to conversion into biochar for enhanced biochar carbon yield and stability, and (3) strategic application of minerals to soil to increase soil organic carbon accrual and stability. We argue that there are powerful synergies between these approaches for carbon dioxide removal through organic and inorganic pathways. We find that primary silicates, as contained in basalt, can benefit both enhanced weathering and soil organic carbon formation, while phyllosilicates and other reactive secondary minerals may have positive synergies for biochar and soil organic carbon. Optimising such synergies may substantially enhance economic and environmental benefits, yet these synergies require accurate quantification.