Co-Benefits of Wollastonite Weathering in Agriculture: CO ₂ Sequestration and Promoted Plant Growth

Abstract

To lock atmospheric CO ₂ at anthropogenic timescale, fast weathering silicates can be applied to soil to speed up natural CO ₂ sequestration via enhanced weathering. Agricultural lands offer large area for silicate application, but expected weathering rates as a function of soil and crop type, and potential impacts on the crops, are not well known. This study investigated the role of plants on enhanced weathering of wollastonite (CaSiO ₃) in soils. Using rooftop pot experiments with leguminous beans ( Phaseolus vulgaris L.) and nonleguminous corn ( Zea mays L.), CO ₂ sequestration was inferred from total inorganic carbon (TIC) accumulation in the soil and thermogravimetric analysis, and mineral weathering rate was inferred from alkalinity of soil porewater. Soil amendment with wollastonite promoted enhanced plant growth: beans showed a 177% greater dry biomass weight and corn showed a 59% greater plant height and a 90% greater dry biomass weight. Wollastonite-amended soil cultivated with beans showed a higher TIC accumulation of 0.606 ± 0.086%, as compared to that with corn (0.124 ± 0.053%). This demonstrates that using wollastonite as a soil amendment, along with legume cultivation, not only buffers the soil against acidification (due to microbial nitrogen fixation) but also sequesters carbon dioxide (12.04 kg of CO ₂/tonne soil/month, 9 times higher than the soil without wollastonite amendment).