Crushed volcanic rock stores carbon in clay, not air
Vienne A, Cox T, Niron H, Guenet B, Poetra R
Soil Health
Basalt rock dust sold at garden centers as a remineralizing soil amendment may do far less for carbon storage than its climate-forward marketing suggests, and mixing it with compost or manure could blunt even that limited effect.
Scientists tested whether spreading crushed volcanic rock on soil could trap carbon and help slow climate change. After more than a year of careful measurements, the carbon mostly ended up stuck in clay particles rather than pulled from the air, which isn't the goal. Adding manure alongside the rock dust actually slowed the rock's breakdown, meaning two amendments often promoted together for soil health can work against each other.
Key Findings
Over 389 days, silicate rock amendments (basalt and dunite) produced no significant increase in dissolved or solid carbon storage compared to unamended controls.
Adding organic matter (manure) reduced basalt's reactive surface area and decreased leached potassium and iron, directly counteracting rock weathering rates.
Geochemical modeling confirmed that released base cations preferentially form secondary clay minerals rather than carbonates, limiting net CO2 removal from the atmosphere.
chevron_right Technical Summary
Adding crushed volcanic rock to soil, a technique called enhanced weathering, doesn't reliably trap carbon dioxide, and mixing it with manure may actually slow the rock's breakdown. A 389-day experiment paired with geochemical modeling found that carbon ended up locked in clay minerals rather than removed from the atmosphere, and that organic amendments reduced basalt's reactive surface area.
Abstract Preview
Original paper
Integrating Experiments and Models To Unravel Interactions between Soil Organic Matter and Enhanced Weathering.
Key uncertainties remain in predicting carbon sequestration through enhanced weathering (EW), particularly regarding secondary mineral formation and interactions with the organic matter. We compare...
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