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Agricultural liming is a carbon sink in the Mississippi River Basin
Nature
(2026) Cite this article
Application of carbonate minerals to arable lands, known as agricultural liming, is a long-standing practice for counteracting soil acidification1,2,3. 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.
The agricultural sector is responsible for a substantial amount of greenhouse gas (GHG) emissions, with farm-to-fork emissions comprising approximately 30% of total anthropogenic GHG emissions globally6. In the USA, direct agricultural emissions account for about 10% of overall emissions and have increased by approximately 8% since 19907. Global GHG emissions from agriculture are projected to increase by approximately 30–40% by 2050 to meet food demands associated with human population growth6. Agricultural GHG emissions are difficult to mitigate, with the agricultural sector representing a large fraction of residual carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) emissions in net-zero scenarios from integrated assessment modelling8,9. Thus, there is an obvious need to increase crop production without increasing GHG emissions or further degrading soil health.
Acidic agricultural soils are characterized by lower crop yields and lower nutrient use efficiencies10,11. As a result, it is often standard agronomic practice to manage soil pH through the addition of fine-grained limestone (CaCO3) or dolomite (CaMg(CO3)2) to soils1. This practice is termed agricultural liming1. Silicates have also been used as soil amendments to improve soil pH12,13 and have gained recent interest as feedstocks in enhanced weathering for carbon dioxide removal (CDR)14,15. Here we use empirical records and biogeochemical modelling to demonstrate that agricultural liming, beyond demonstrated positive effects on crop yields, can drive carbon removal at the catchment scale.
Dissolution of carbonate minerals at low soil pH values1, the conditions liming is meant to remedy, results in the production of CO2:
This is the conceptual basis for the conventional assumption that agricultural liming represents a net CO2 emissions source1,5,16. For instance, despite some previous evidence to the contrary17, the default Intergovernmental Panel on Climate Change (IPCC) inventory methodology for CO2 emissions from agricultural liming effectively treats the carbonate carbon in applied lime as emitted to the atmosphere5, whereas national GHG accounting in the USA applies a lower emission factor that assumes roughly half of the carbon contained in agricultural lime is emitted to the atmosphere7. This implies a difficult trade-off that requires weighing the potential positive impacts of liming on