Synergistic effects of co-application and co-pyrolysis of biochar and enhanced weathering materials for CO2 removal in an Oxisol

To achieve the 2°C climate goal various carbon dioxide removal (CDR) technologies are being developed. Biochar obtained from biomass pyrolysis contains persistent carbonaceous compounds and offers benefits when applied to soil, including enhanced soil fertility, and improved water retention. Additionally, the application of natural rocks for enhanced rock weathering (ERW) in agricultural soil is gaining attention for its potential to sequester CO₂, while increasing soil pH and providing essential nutrients. Given the promising potential of both biochar and ERW as CDR technologies, their combined application could offer synergistic effects, making it crucial to understand their interaction. However, research on their co-application of biochar and rock powder as well as co-pyrolysis of biomass with rock powder (yielding rock enhanced biochar) remains limited.

This study quantified alkalinity and ion releaseOxisol soil columns after addition of wood and straw biochar, rock-enhanced biochar or co-application of biochar and rock powder. In total 9 treatments were incubated for 27 weeks under elevated CO₂ conditions with 10 leachate sampling events. First results show high initial fluxes of total alkalinity and dissolved inorganic carbon as well as dissolved organic carbon and nutrients, which decrease over time. Notably, pCO₂ has minimal impact on the pyrogenic carbon, while it doubles the total alkalinity flux from ERW. While biochar alone creates a larger carbon sink, co-applying rock powder enhances mineral fertilization and increases the weight of biochar pellets. Soil amendments with biochar further prevent a water logging of the clayey Oxisol, enabling rock weathering and alkalinity fluxes to continue.