Potential of combining biochar and enhanced weathering and impacts on soil organic carbon and biomass: PyMiCCS project results

Pyrogenic carbon capture and storage, enhanced weathering (EW), soil organic carbon (SOC) enhancement and biomass carbon capture are terrestrial carbon dioxide removal (CDR) methods that could be implemented on a short timescale. To maximize the CDR potential per area, these methods could be co-deployed and provide complementary co-benefits. This requires a substantial understanding of the ongoing reactions and interactions in the system at different scales, backed up by field data and dynamic models to estimate applicability and scalability of the method combination. Biochar and weathering of silicate rock powder have the potential to provide besides CDR also nutrients, change soil properties and affect plant growth, directly impacting soil organic carbon storage and biomass carbon capture. Nevertheless, the interactions between the amendments and their combined effects in the soil system are sparsely researched.

PyMiCCS as part of CDRterra addresses these knowledge gaps and  estimates the potential of the proposed combination of the different methods. The co-application of various biochars with rock powder as well as the co-pyrolysis of both amendments was realized and products characterized. The co-pyrolysis of biochar and rock powder can modify biochar properties, such as weight, porosity, nutrient content and stability. Furthermore, the application of materials to different soil types with and without crops was tested at various spatio-temporal scales. Biochar additions improved water circulation in clayey soils, while rock powders released nutrients. Furthermore, amendments increased SOC contents, with differences between combinations and single applications. While soil nutrient levels were elevated, no significant plant growth increases were observed in comparison to single applications. In the long-term, simulations for temperate climate and sandy soil suggest that the solo-biochar applications can increase non-biochar SOC by up to 300 kg ha^-1 yr^-1 per ton biochar and result in net ecosystem carbon uptake over 1000 years. Complementing experimental results and process-based modeling, an integrated economic assessment was conducted using a global land-use modelling framework. The analysis shows that the environmental and mitigation outcomes of biochar-based CDR depend on interactions between costs, agronomic yield responses, biochar persistence, application rates, and assumptions about carbon pricing or crediting. 

Overall, the results demonstrate that co-application of biochar and enhanced weathering can enhance soil carbon storage and nutrient dynamics, but side-specific assessments are needed, and amendments do not necessarily translate into increased crop yields. Our results highlight the substantial CDR potential and the importance of tailored evaluations, management strategies, and policy frameworks for their scalable and effective implementation.