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Enhanced weathering (EW) is a promising modification to current agricultural practices that uses crushed silicate rocks to drive carbon dioxide removal (CDR). If widely adopted on farmlands, it could help achieve net-zero or negative emissions by 2050. We report detailed state-level analysis indicating EW deployed on agricultural land could sequester 0.23-0.38 Gt CO$_2$ yr$^{-1}$ and meet 36-60 % of U.S. technological CDR goals. Average CDR costs vary between state, being highest in the first decades before declining to a range of $\sim\$$100-150 tCO$_2{}^{-1}$ by 2050, including for three states (Iowa, Illinois, and Indiana) that contribute most to total national CDR. We identify multiple electoral swing states as being essential for scaling EW that are also key beneficiaries of the practice, indicating the need for strong bipartisan support of this technology. Assessment the geochemical capacity of rivers and oceans to carry dissolved EW products from soil drainage suggests EW provides secure long-term CO$_2$ removal on intergenerational time scales. We additionally forecast mitigation of ground-level ozone increases expected with future climate change, as an indirect benefit of EW, and consequent avoidance of yield reductions. Our assessment supports EW as a practical innovation for leveraging agriculture to enable positive action on climate change with adherence to federal environmental justice priorities. However, implementing a stage-gating framework as upscaling proceeds to safeguard against environmental and biodiversity concerns will be essential.

Enhanced weathering (EW) with crushed basalt on farmlands is a promising scalable atmospheric carbon dioxide removal strategy that urgently requires performance assessment with commercial farming practices. Our large-scale replicated EW field trial in the heart of the U.S. Corn Belt shows cumulative time-integrated carbon sequestration of 15.4 +/- 4.1 t CO2 ha-1 over four years, with additional emissions mitigation of ~0.1 - 0.4 t CO2,e ha-1 yr-1 for soil nitrous oxide, a potent long-lived greenhouse gas. Maize and soybean yields increased 12-16% with EW following improved soil fertility, decreased soil acidification, and upregulation of root nutrient transport genes. Our findings suggest that widespread adoption of EW across farming sectors has the potential to contribute significantly to net-zero greenhouse gas emissions goals and global food and soil security.

Enhanced Rock Weathering (ERW) is a promising scalable and cost-effective Carbon Dioxide Removal (CDR) strategy with significant environmental and agronomic co-benefits. A major barrier to large-scale implementation of ERW is a robust Monitoring, Reporting, and Verification (MRV) framework. To successfully quantify the amount of carbon dioxide removed by ERW, MRV must be accurate, precise, and cost-effective. Here, we outline a mass-balance-based method where analysis of the chemical composition of soil samples is used to track in-situ silicate rock weathering. We show that signal-to-noise issues of in-situ soil analysis can be mitigated by using isotope-dilution mass spectrometry to reduce analytical error. We implement a proof-of-concept experiment demonstrating the method in controlled mesocosms. In our experiment, basalt rock feedstock is added to soil columns containing the cereal crop Sorghum bicolor at a rate equivalent to 50 t ha$^{-1}$. Using our approach, we calculate rock weathering corresponding to an average initial CDR value of 1.44 +/- 0.27 tCO$_2$eq ha$^{-1}$ from our experiments after 235 days, within error of an independent estimate calculated using conventional elemental budgeting of reaction products. Our method provides a robust time-integrated estimate of initial CDR, to feed into models that track and validate large-scale carbon removal through ERW., Comment: Environmental Science & Technology (2023)