Enhanced CO2 removal and improved carbon budget by enhanced rock weathering: a field experiment in Hokkaido, Japan

Climate change affects food production, increasing the need for CO ₂ removal (CDR) strategies. Enhanced rock weathering, which involves the spreading of crushed silicate rock powder on agricultural soil to sequester atmospheric CO ₂ via enhanced natural weathering, shows potential to enrich the agricultural soil. In this study, we evaluated the short-term impacts of basalt powder on CO ₂ emissions in rhizosphere and non-rhizosphere soils and estimated the field carbon budget in an experimental soybean field at Hokkaido University, Japan. Basalt powder application at 150 Mg ha ⁻¹ , with incorporation into the soil to a depth of 15 cm, significantly increased the soil pH and reduced the soil volumetric water content. Regardless of treatment, the carbon budget was negative, indicating the overall carbon loss in field. Basalt powder application reduced this carbon loss from 2.69 ± 0.41 to 1.90 ± 0.73 Mg C ha ⁻¹ , primarily by absorbing CO ₂ that would otherwise have been released into the atmosphere through weathering and sequestering it in the soil, though the difference was not significant. ERW-induced CO ₂ emission reduction rate was 0.81 ± 0.17 Mg C ha ⁻¹ , with approximately 86.4% attributed to rhizosphere soil. In the rhizosphere, basalt application significantly reduced CO ₂ emissions, suggesting that root exudates may promote basalt weathering and increase stabilization of carbon in the rhizosphere through interactions with the rock powder, thereby contributing to the observed emission reduction. These findings indicate that basalt application can significantly reduce CO ₂ emissions from agricultural soils, particularly in the rhizosphere, and could potentially improve the overall farmland carbon balance. However, further research is necessary to explore the long-term effects of ERW on soil carbon dynamics and elucidate the differential responses of soil organic and inorganic carbon pools, especially considering that the applied basalt powder is unlikely to completely weather within a single year, and thus its CO ₂ removal effects may persist over multiple growing seasons.