Tim Jesper Suhrhoff

China faces the converging challenges of farmland soil acidification, securing food security, and meeting carbon neutrality goals. Enhanced weathering (EW) offers a promising scalable carbon dioxide removal (CDR) pathway that can also deliver valuable agronomic benefits, but its potential for soil pH management, crop yield increases, and CDR in Chinese croplands is poorly constrained. Here, we develop a modeling framework to simulate co-benefits of basalt-based EW in acidic rice fields in China and conduct a spatially explicit national assessment. Focusing on the expected benefits from soil deacidification based on previous empirical data, EW can enhance relative rice yield by 4.61 ± 2.45% to 6.34 ± 3.98% by increasing mean soil pH by 0.68–1.02 units, resulting in a preliminary economic gain of USD 3.56 billion annually. This process also has the potential to simultaneously sequester 204.39 Mt CO2 over 35 years based on strategic applications of an additional 50 t basalt ha-1 every ten years for fields where soil pH remains below 6.5. We find that the yield benefits alone would provide a gross agricultural revenue of USD 609 per tonne of gross CO2 sequestered. Jiangxi, Hunan, Guangxi, and Guangdong persistently show the greatest co-benefits and should be prioritized as areas of early deployment. Our findings identify targeted EW deployment in China’s acidic rice fields as a promising strategy to improve soil quality and support rice production, while potentially contributing to national CDR targets.

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.

Application of carbonate minerals to arable lands, known as agricultural liming, is a long-standing practice for counteracting soil acidification^1,2,3. Although liming boosts crop yields⁴, it is also considered a source of agricultural carbon dioxide (CO₂) emissions⁵. Here we show, using century-scale records of agricultural liming and anthropogenic acidity inputs for the Mississippi River Basin, that agricultural liming has acted as a net carbon sink over the past century. Records of river alkalinity fluxes suggest that approximately 90% of the ideal CO₂ removal potential of agricultural lime added since 1900 (approximately 0.44 GtCO₂) has been realized at the catchment scale, with a decadal-scale time lag owing to soil cation exchange and solute transport. These results are consistent with reactive transport modelling of soil cation throughput, which indicates that net CO₂ removal emerges after an initial emissions pulse associated with neutralization of soil acidity pools. Current accounting frameworks implicitly apply an incomplete counterfactual, attributing CO₂ emissions to lime addition rather than to the anthropogenic acidity inputs that drive CO₂ release. Evaluated against the counterfactual of anthropogenic acidity inputs, agricultural liming represents a net carbon sink in the Mississippi River Basin on decade-to-century timescales. These results suggest that optimized soil pH management can reduce agricultural greenhouse gas emissions while simultaneously improving crop yields and soil health.

Biochar production from biomass may be a scalable and cost-effective means of atmospheric carbon dioxide removal. Current accounting frameworks, however, focus primarily on persistent organic carbon and overlook how pyrolysis alters the return of biomass-derived ions to soils and waters. Here, we quantify a first-order alkalinity-related adjustment to biochar CDR by comparing the inorganic carbon cycling implications of biochar production with a biomass-decay counterfactual. During plant growth, net cation uptake generates soil acidity, which can consume bicarbonate alkalinity and shift the carbonate system toward dissolved CO2, causing CO2 emissions upon re-equilibration with the atmosphere. Biomass decay can eventually reverse this acid-base perturbation by returning cations to the biogeochemical cycle. Biochar formation delays or prevents part of this return flux by retaining cations and anions within the biochar matrix, making permanent or prolonging what would otherwise have been a temporary CO2 source. We estimate the resulting change in inorganic carbon cycling from the cation–anion charge equivalent imbalance associated with the retained elemental inventory relative to recalcitrant organic-carbon storage. Across observations reporting complete Ca, Mg, K, Na, N, and S data (n = 85), the mean alkalinity-related reduction in effective CDR is 3.2% when the retained elemental inventory is assumed to be released in proportion to biochar degradation. If cations and anions are instead retained preferentially as organic carbon is lost, the mean reduction increases to 3.9% and 5.1% when 82% and 63% of organic carbon persists, respectively. The fraction of observations showing a reduction in effective CDR of ≥5% similarly increases from 18.8% under proportional release to 21.2% and 22.4% under the two complete element retention scenarios. Individual biochars span a wide range of compositions and durabilities through time, including cases in which the inorganic carbon effect instead increases estimated net CDR.

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.

Per- and polyfluoroalkyl substances (PFAS) are persistent synthetic compounds that have contaminated millions of hectares of agricultural land through decades of biosolids application. Conventional remediation approaches, such as thermal destruction or excavation, are prohibitively expensive, carbon intensive, and leave affected farmland unfit for agriculture. Here, we present a potential scalable remediation strategy that combines phytoremediation, biochar production, and enhanced weathering to simultaneously remove PFAS from soil, immobilize residual contamination, and achieve durable carbon dioxide removal (CDR). Using stochastic modeling constrained by experimental data, we show that soil pH management through alkaline rock amendment can accelerate PFOS removal, shortening remediation timelines by more than a decade under typical contamination levels. Pyrolysis of harvested biomass effectively destroys PFAS and produces biochar, which, when reapplied to soil, substantially reduces leaching to groundwater and the surrounding environment. National-scale simulations across the estimated one million hectares of PFAS-impacted cropland indicate a combined CDR potential of approximately 11 Mt CO ₂ y ^–1 , equivalent to 4 to 6% of the US 2050 carbon removal target. We estimate a median remediation cost of $1,460 USD ha ^–1 y ^–1 —more than an order of magnitude lower than current technologies, with costs substantially reduced through carbon removal revenues valued near the social cost of carbon. This integrated thermal and phytoremediation framework provides a viable pathway to restore contaminated farmland, mitigate PFAS exposure risks, and contribute meaningfully to national climate mitigation goals.