Soil carbon management and enhanced rock weathering: The separate fates of organic and inorganic carbon

Soil carbon (C) management has been promoted as one of the few readily available strategies to mitigate the rising concentration of atmospheric CO2 and its associated impacts on climate change. One of these carbon management strategies is enhanced rock weathering (ERW) which involves adding crushed silicate rocks to the soil. These rocks weather and remove atmospheric CO2 by converting it into bicarbonate in solution. The approach requires careful interpretation of the differences between soil organic carbon (SOC) and soil inorganic carbon (SIC) and their measurement, with implications for land management and C credit accounting. In this Opinion, we emphasise the distinct nature and fates of SOC and SIC, advocating for their separate management, particularly in C credit schemes. It is imperative that protocols for soil C management explicitly recognise the difference between SOC and SIC to prevent any ambiguity. Farmers should be able to claim credits for increases in SOC alongside and independently of any claim for credits for ERW (i.e. SIC). Despite the potential of ERW for C removal, we emphasise that further research is needed to improve the measurement and monitoring of SIC and to understand ERW's potential implications for SOC turnover and greenhouse gas emissions. Highlights Enhanced Rock Weathering increases dissolved inorganic carbon (bicarbonate). Soil organic carbon (SOC) may be influenced by Enhanced Rock Weathering. Carbon credit via Enhanced Rock Weathering is separate from credit linked to soil organic carbon. Soil organic matter and enhanced rock weathering both have roles to play for carbon credits.