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Wollastonite, a simple calcium silicate mineral (CaSiO₃), has emerged from relative obscurity to become a critical focus in sustainable agriculture and climate change mitigation. When added to agricultural and forest soils, this mineral object serves as a multi-functional agent, driving enhanced CO2 sequestration, stabilizing organic carbon, and boosting nutrient availability.
CO2 Sequestration: The Carbon Capture Role
At its core, wollastonite is an inorganic carbon sequestering agent. Through geochemical weathering, it reacts with atmospheric CO2 to form stable carbonates. This process accelerates the natural rock weathering cycle, effectively increasing inorganic carbon storage in soils.
The effectiveness of this function is highly dependent on the soil environment:
Optimal Soils: Neutral to alkaline soils are ideal, as they promote the accumulation of stable pedogenic carbonates. Well-aerated agricultural soils with sufficient moisture also show high sequestration rates.
Modifying Factors: Higher pH soils benefit most from stable carbonate formation. Conversely, in acidic soils, the addition can paradoxically increase CO2emissions due to stimulated soil organic carbon (SOC) mineralization, potentially reducing net sequestration.
Mineral-Associated Organic Carbon (MAOC) Stabilization
Beyond inorganic capture, wollastonite significantly interacts with the organic component of soil, markedly increasing stable mineral-associated organic carbon (MAOC).
Recent research confirms wollastonite markedly increases stable mineral-associated organic carbon (MAOC), by up to 170% in forest soils and 250% in farmland soils (Yan et. al., 2025)
The underlying mechanisms differ by ecosystem: in forests, higher pH and available phosphorus enhance microbial carbon use efficiency (CUE), promoting MAOC formation. In farmland, enhanced anabolic microbial processes (biomass-building) increase carbon binding to minerals even without significant changes in CUE.
The forest soil also saw an increase in Ca-associated OC (Ca-OC) and Fe- and Al-associated OC (Fe/Al-OC) likely through ligand exchange, forming strong inner-sphere complexes or co-precipitation as stable organo-metal complexes.
These effects mean more organic carbon is stabilized in soils, where it can persist for decades to centuries.
Soil Nutrient Availability and Trade-offs
Wollastonite also acts as a powerful soil amendment, releasing key nutrients and altering soil chemistry:
Nutrient Boost: It notably raises soil pH, calcium (Ca), and available silicon (Si), and can sometimes increase available nitrogen (N) and dissolved organic carbon.
Agricultural Benefit: The Si supplied by the mineral improves crop yields, enhances root growth, boosts nutrient uptake, and increases resilience to pests and diseases.
However, there is an important trade-off:
Trade-off: The increase in soil pH and changes in chemistry can stimulate soil organic carbon mineralization, especially in acidic soils. This decomposition leads to increased CO2 emissions, which must be weighed against the long-term sequestration gains when calculating the net climate benefit.
Caution: In some farmland applications, the addition of CaSiO3 has been found to significantly decrease available phosphorus (P), a potential negative effect on crop yield that requires careful nutrient management.
In conclusion, the simple mineral wollastonite represents a complex and powerful tool in soil health and climate action. While it strongly supports CO2 sequestration and carbon stabilization, careful management and consideration of soil type, particularly pH, are necessary to maximize benefits and mitigate adverse trade-offs associated with organic matter mineralization.
Reference
Yan, Y., L. Yin, S. Yan, Y. Fang, A. Wang, F. Zhu, Y. Bai, Z. Zhang, and W. Zhang (2025).
Similar mineral-associated organic carbon formation but distinct efficiencies by powdered wollastonite addition between two soils. Soil Biol. Biochem. 211: 109979. https://doi.org/10.1016/j.soilbio.2025.109979.
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