Abstract The rise in atmospheric carbon dioxide (CO2) concentrations requires scalable and effective carbon dioxide removal (CDR) strategies. pyrogenic carbon capture and storage relies on the pyrolysis of biomass and the non-oxidative use of biochar, e.g. in soils. Enhanced rock weathering (ERW) captures CO2 by forming dissolved bicarbonate. In addition to CDR, both methods may offer soil improvement as a co-benefit. However, their interaction and combined CDR potential remain largely unexplored. Here, we investigate their individual and combined effects on carbon dynamics in a temperate agricultural soil. Using the process-based LiDELSv2 model calibrated against data from the lysimeter experiment, we simulate 1000 year impacts of applying 4.2 wt% wood biochar, 2 wt% basanite rock powder (RP), their co-application, and co-pyrolyzed material (rock-enhanced biochar, RE-biochar) on soil organic carbon (SOC), net primary production (NPP), net CO2 ecosystem exchange (NEE), and calcium (Ca2+) leaching in a northern German sandy soil. Biochar alone led to the highest increase in SOC and achieved a modeled NEE of −200 g C ha−1yr−1 per ton of biochar throughout 1000 years, acting as a long-term carbon sink. Co-application and RE-biochar increased SOC too, but to a lesser extent. Rock powder alone reduced SOC by 7%. Although RP enhanced Ca2+ leaching, this did not result in net CO2 removal. Ecosystem respiration and NPP remained stable in the long term. Our results suggest that, when accounting for assumed application rates, biochar is the primary driver of long-term soil-based CDR, while ERW provides only minor co-benefits. This highlights the need to tailor interventions to specific soil and climate conditions.
