Christiana Dietzen

Enhanced rock weathering (ERW) has been proposed as a scalable carbon dioxide removal strategy, yet long-term field-based constraints on weathering rates and associated carbon sequestration remain limited. Here, we present a 5-year field assessment of Greenlandic glacial rock flour (GRF) applied at 50 t ha ⁻¹ to a sandy agricultural soil in Denmark. Using a soil mass balance approach, based on depletion of Mg which provided the most tightly constrained weathering signal, we estimate that at least 56 % of the applied GRF dissolved over 5 years. Initial uptake of CO ₂ via ERW is estimated at 3.2–4.9 t CO ₂ ha ⁻¹ when accounting for carbonate speciation in the acidic soil solution, with the potential for further gains if complete downstream transport of weathering products and subsequent re-equilibration with the more alkaline marine carbonate system is assumed. In addition to inorganic carbon removal, GRF-treated plots exhibited significantly higher soil organic carbon stocks, equivalent to the storage of an additional 18.3 t CO ₂ ha ⁻¹ . These results demonstrate substantial weathering and carbon sequestration over 5 years under field conditions in a temperate climate and suggest that both inorganic and organic carbon dynamics contribute meaningfully to the overall climate impact of ERW of GRF. The findings provide rare multi-year field constraints on ERW performance and underscore the importance of robust measurements for quantifying carbon removal in agricultural systems, representing the first implementation of mass balance methods within the framework of a randomized block design.

Enhanced rock weathering (ERW) has been proposed as a scalable carbon dioxide removal strategy, yet long-term field-based constraints on weathering rates and associated carbon sequestration remain limited. Here, we present a five-year field assessment of Greenlandic glacial rock flour (GRF) applied at 50 t ha^-1 to a sandy agricultural soil in Denmark. Using a soil mass balance approach, we estimate that approximately 56% of the applied GRF dissolved over five years. Initial uptake of CO₂ via ERW is estimated at 3.2-4.9 t CO₂ ha^-1 when accounting for carbonate speciation in the acidic soil solution. If downstream transport of weathering products and subsequent re-equilibration with the more alkaline marine carbonate system is assumed, the estimated long-term atmospheric CO₂ removal increases to 6.39 t CO₂ ha^-1. In addition to inorganic carbon removal, GRF-treated plots exhibited a significant increase in soil organic carbon stocks, equivalent to the storage of an additional 18.3 t CO₂ ha^-1, with gains primarily associated with the mineral-associated organic matter fraction. These results demonstrate substantial weathering and carbon sequestration over five years under field conditions in a temperate climate and suggest that both inorganic and organic carbon dynamics contribute meaningfully to the overall climate impact of ERW of GRF. The findings provide rare multi-year field constraints on ERW performance and underscore the importance of robust measurements for quantifying carbon removal in agricultural systems, representing the first implementation of mass balance methods within the framework of a randomized block design.

Enhanced rock weathering (ERW) has been proposed as a scalable carbon dioxide removal strategy, yet long-term field-based constraints on weathering rates and associated carbon sequestration remain limited. Here, we present a five-year field assessment of Greenlandic glacial rock flour (GRF) applied at 50 t ha^-1 to a sandy agricultural soil in Denmark. Using a soil mass balance approach, we estimate that approximately 56% of the applied GRF dissolved over five years. Initial uptake of CO₂ via ERW is estimated at 3.2-4.9 t CO₂ ha^-1 when accounting for carbonate speciation in the acidic soil solution. If downstream transport of weathering products and subsequent re-equilibration with the more alkaline marine carbonate system is assumed, the estimated long-term atmospheric CO₂ removal increases to 6.39 t CO₂ ha^-1. In addition to inorganic carbon removal, GRF-treated plots exhibited a significant increase in soil organic carbon stocks, equivalent to the storage of an additional 18.3 t CO₂ ha^-1, with gains primarily associated with the mineral-associated organic matter fraction. These results demonstrate substantial weathering and carbon sequestration over five years under field conditions in a temperate climate and suggest that both inorganic and organic carbon dynamics contribute meaningfully to the overall climate impact of ERW of GRF. The findings provide rare multi-year field constraints on ERW performance and underscore the importance of robust measurements for quantifying carbon removal in agricultural systems, representing the first implementation of mass balance methods within the framework of a randomized block design.

Enhanced rock weathering (ERW) has been proposed as a scalable carbon dioxide removal strategy, yet long-term field-based constraints on weathering rates and associated carbon sequestration remain limited. Here, we present a five-year field assessment of Greenlandic glacial rock flour (GRF) applied at 50 t ha^-1 to a sandy agricultural soil in Denmark. Using a soil mass balance approach, we estimate that approximately 56% of the applied GRF dissolved over five years. Initial uptake of CO₂ via ERW is estimated at 3.2-4.9 t CO₂ ha^-1 when accounting for carbonate speciation in the acidic soil solution. If downstream transport of weathering products and subsequent re-equilibration with the more alkaline marine carbonate system is assumed, the estimated long-term atmospheric CO₂ removal increases to 6.39 t CO₂ ha^-1. In addition to inorganic carbon removal, GRF-treated plots exhibited a significant increase in soil organic carbon stocks, equivalent to the storage of an additional 18.3 t CO₂ ha^-1, with gains primarily associated with the mineral-associated organic matter fraction. These results demonstrate substantial weathering and carbon sequestration over five years under field conditions in a temperate climate and suggest that both inorganic and organic carbon dynamics contribute meaningfully to the overall climate impact of ERW of GRF. The findings provide rare multi-year field constraints on ERW performance and underscore the importance of robust measurements for quantifying carbon removal in agricultural systems, representing the first implementation of mass balance methods within the framework of a randomized block design.

Enhanced rock weathering (ERW) has been proposed as a scalable carbon dioxide removal strategy, yet long-term field-based constraints on weathering rates and associated carbon sequestration remain limited. Here, we present a five-year field assessment of Greenlandic glacial rock flour (GRF) applied at 50 t ha^-1 to a sandy agricultural soil in Denmark. Using a soil mass balance approach, we estimate that approximately 56% of the applied GRF dissolved over five years. Initial uptake of CO₂ via ERW is estimated at 3.2-4.9 t CO₂ ha^-1 when accounting for carbonate speciation in the acidic soil solution. If downstream transport of weathering products and subsequent re-equilibration with the more alkaline marine carbonate system is assumed, the estimated long-term atmospheric CO₂ removal increases to 6.39 t CO₂ ha^-1. In addition to inorganic carbon removal, GRF-treated plots exhibited a significant increase in soil organic carbon stocks, equivalent to the storage of an additional 18.3 t CO₂ ha^-1, with gains primarily associated with the mineral-associated organic matter fraction. These results demonstrate substantial weathering and carbon sequestration over five years under field conditions in a temperate climate and suggest that both inorganic and organic carbon dynamics contribute meaningfully to the overall climate impact of ERW of GRF. The findings provide rare multi-year field constraints on ERW performance and underscore the importance of robust measurements for quantifying carbon removal in agricultural systems, representing the first implementation of mass balance methods within the framework of a randomized block design.

Enhanced rock weathering (ERW) has been proposed as a scalable carbon dioxide removal strategy, yet long-term field-based constraints on weathering rates and associated carbon sequestration remain limited. Here, we present a five-year field assessment of Greenlandic glacial rock flour (GRF) applied at 50 t ha-1 to a sandy agricultural soil in Denmark. Using a soil mass balance approach, we estimate that approximately 56% of the applied GRF dissolved over five years. Initial uptake of CO2 via ERW is estimated at 3.2-4.9 t CO2 ha-1 when accounting for carbonate speciation in the acidic soil solution. If downstream transport of weathering products and subsequent re-equilibration with the more alkaline marine carbonate system is assumed, the estimated long-term atmospheric CO2 removal increases to 6.39 t CO2 ha-1. In addition to inorganic carbon removal, GRF-treated plots exhibited a significant increase in soil organic carbon stocks, equivalent to the storage of an additional 18.3 t CO2 ha-1, with gains primarily associated with the mineral-associated organic matter fraction. These results demonstrate substantial weathering and carbon sequestration over five years under field conditions in a temperate climate and suggest that both inorganic and organic carbon dynamics contribute meaningfully to the overall climate impact of ERW of GRF. The findings provide rare multi-year field constraints on ERW performance and underscore the importance of robust measurements for quantifying carbon removal in agricultural systems, representing the first implementation of mass balance methods within the framework of a randomized block design.

Enhanced weathering in agriculture is a potential gigatonne-scale carbon dioxide removal (CDR) pathway, but its potential remains difficult to constrain. We used a formal expert elicitation process to estimate CDR potential and efficiency, uncertainties, and key data needs for six feedstocks. Expert opinion of global potential varied by feedstock, with estimates averaging 0.2-0.7 Gt CO2e/yr, but with a wide range (from a source to greater than 5 Gt CO2e/yr removal). When focusing on the American Midwest (pH 5.5-6), carbon dioxide removal efficiency, meaning the fraction of potential ultimately realized, ranged from 27-39%. Key uncertainties included feedstock availability, calcite saturation, and deep soil/freshwater emission pathways. There is a need for empirical data in key stages, with potential to leverage liming data where appropriate. Overall, there appears to be strong potential CDR at broad scales. However, continued research is necessary to build confidence when quantifying that potential and actual removals.

Claire Fyson et al. introduce the Energy and Environmental Science themed reviews issue on CO ₂ reduction.

Greenlandic glacial rock flour (GRF) is a potential source of extremely fine-grained silicate minerals for CO ₂ uptake via enhanced rock weathering. The chemical makeup of this material also indicates that it may be a good source of plant nutrients. GRF was applied at rates of 10 (GRF ₁₀ ) and 50 (GRF ₅₀ ) t ha ⁻¹ to a low-fertility sandy clay loam in Ghana to evaluate its impact on maize production relative to a control over five consecutive growing seasons. Other soil amendments, including N fertilizers, were uniformly applied across all treatments. GRF ₅₀ significantly increased grain and total dry matter yield (TDMY) across all five seasons. Seasonal increases in TDMY with GRF ₅₀ ranged from 28–87% relative to the control, and grain yield increases ranged from 28–77%. In total over the course of the five growing seasons, GRF ₅₀ produced an additional 12.9 t ha⁻ ¹ of TDMY and 7.6 t ha⁻ ¹ of grain relative to the control. GRF ₁₀ had a significant effect on TDMY and grain yield in the first two growing seasons, though the effect of GRF ₁₀ decreased over time and by the fifth growing season TDMY and grain yield were equivalent to the control. Nonetheless, the application of this lower amount of GRF still resulted in an additional 7.4 t ha⁻ ¹ of TDMY and 4.5 t ha⁻ ¹ of grain yield over the course of the experiment. These results suggest that the significant co-benefits of GRF as a fertilizer may incentivize the adoption of enhanced rock weathering in tropical, nutrient-poor environments and could increase food security in such regions.