Initial Validation of a Soil-Based Mass-Balance Approach for Empirical Monitoring of Enhanced Rock Weathering Rates

Harnessing Microbes to Weather Native Silicates in Agricultural Soils for Scalable Carbon Dioxide Removal

Anthropogenic carbon emissions contribute significantly to the greenhouse effect, resulting in global warming and climate change. Thus, addressing this critical issue requires innovative and comprehensive solutions. Silicate weathering moderates atmospheric CO2 levels over geological time, but it occurs too slowly to counteract anthropogenic emissions effectively. Here, we show that the microorganism Bacillus subtilis strain MP1 promotes silicate weathering across different experimental setups with various levels of complexity. First, we found that MP1 was able to form a robust biofilm in the presence of feldspar and significantly increased (p < 0.05) silicate dissolution rates, pH, and calcium carbonate formation in culture experiments. Second, in mesocosm experiments, we found that MP1 enhanced the silicate weathering rate in soil by more than six times compared to the untreated control. In addition, soil inorganic carbon increased by 20%, and the concentrations of ions, including calcium, magnesium, and iron, were also elevated under the MP1 treatment. More importantly, when applied as a seed treatment on eight soybean fields, we found that MP1 significantly (p < 0.05) boosted soil inorganic carbon, leading to a gross accrual of 2.02 tonnes of inorganic carbon per hectare annually. Our findings highlight the potential of enhancing native silicate weathering with microorganisms in agricultural fields to increase soil inorganic carbon, contributing to climate change mitigation.

Thermal Ca2+/Mg2+ exchange reactions to synthesize CO2 removal materials

Most current strategies for carbon management require CO2 removal (CDR) from the atmosphere on the multi-hundred gigatonne (Gt) scale by 2100 (refs. 1-5). Mg-rich silicate minerals can remove >105 Gt CO2 and sequester it as stable and innocuous carbonate minerals or dissolved bicarbonate ions3,6,7. However, the reaction rates of these minerals under ambient conditions are far too slow for practical use. Here we show that CaCO3 and CaSO4 react quantitatively with diverse Mg-rich silicates (for example, olivine, serpentine and augite) under thermochemical conditions to form Ca2SiO4 and MgO. On exposure to ambient air under wet conditions, Ca2SiO4 is converted to CaCO3 and silicic acid, and MgO is partially converted into a Mg carbonate within weeks, whereas the input Mg silicate shows no reactivity over 6 months. Alternatively, Ca2SiO4 and MgO can be completely carbonated to CaCO3 and Mg(HCO3)2 under 1 atm CO2 at ambient temperature within hours. Using CaCO3 as the Ca source, this chemistry enables a CDR process in which the output Ca2SiO4/MgO material is used to remove CO2 from air or soil and the CO2 process emissions are sequestered. Analysis of the energy requirements indicates that this process could require less than 1 MWh per tonne CO2 removed, approximately half the energy of CO2 capture with leading direct air capture technologies. The chemistry described here could unlock Mg-rich silicates as a vast resource for safe and permanent CDR.

Exploring the synergy of enhanced weathering and Bacillus subtilis: A promising strategy for sustainable agriculture

Climate change is one of the most urgent environmental challenges that humanity faces. In addition to the reduction of greenhouse gas emissions, safe and robust carbon dioxide removal (CDR) technologies that capture atmospheric CO2 and ensure long-term sequestration are required. Among CDR technologies, enhanced silicate weathering (ESW) has been suggested as a promising option. While ESW has been demonstrated to depend strongly on pH, water, and temperature, recent studies suggest that biota may accelerate mineral weathering rates. Bacillus subtilis is a plant growth-promoting rhizobacterium that can facilitate weathering to obtain mineral nutrients. It is a promising agricultural biofertilizer, as it helps plants acquire nutrients and protects them from environmental stresses. Given that croplands are optimal implementation fields for ESW, any synergy between ESW and B. subtilis can hold great potential for further practice. B. subtilis was reported to enhance weathering under laboratory conditions, but there is a lack of data for soil applications. In a soil-mesocosm experiment, we examined the effect of B. subtilis on basalt weathering. B. subtilis-basalt interaction stimulated basalt weathering and increased soil extractable Fe. The combined application displayed higher CDR potential compared to basalt-only application (3.7 vs. 2.3 tons CO2 ha-1) taking solid and liquid cation pools into account. However, the cumulative CO2 efflux decreased by approximately 2 tons CO2 ha-1 with basalt-only treatment, while the combined application did not affect the CO2 efflux. We found limited mobilization of cations to the liquid phase as most were retained in the soil. Additionally, we found substantial mobilization of basalt-originated Mg, Fe, and Al to oxide- and organic-bound soil fractions. We, therefore, conclude that basalt addition showed relatively low inorganic CDR potential but a high capacity for SOM stabilization. The outcomes indicated the importance of weathering rate-GHG emission integration and the high potential of SOM stabilization in ESW studies.

Iron Chelation in Soil: Scalable Biotechnology for Accelerating Carbon Dioxide Removal by Enhanced Rock Weathering

Enhanced rock weathering (EW) is an emerging atmospheric carbon dioxide removal (CDR) strategy being scaled up by the commercial sector. Here, we combine multiomics analyses of belowground microbiomes, laboratory-based dissolution studies, and incubation investigations of soils from field EW trials to build the case for manipulating iron chelators in soil to increase EW efficiency and lower costs. Microbial siderophores are high-affinity, highly selective iron (Fe) chelators that enhance the uptake of Fe from soil minerals into cells. Applying RNA-seq metatranscriptomics and shotgun metagenomics to soils and basalt grains from EW field trials revealed that microbial communities on basalt grains significantly upregulate siderophore biosynthesis gene expression relative to microbiomes of the surrounding soil. Separate in vitro laboratory incubation studies showed that micromolar solutions of siderophores and high-affinity synthetic chelator (ethylenediamine-N,N'-bis-2-hydroxyphenylacetic acid, EDDHA) accelerate EW to increase CDR rates. Building on these findings, we develop a potential biotechnology pathway for accelerating EW using the synthetic Fe-chelator EDDHA that is commonly used in agronomy to alleviate the Fe deficiency in high pH soils. Incubation of EW field trial soils with potassium-EDDHA solutions increased potential CDR rates by up to 2.5-fold by promoting the abiotic dissolution of basalt and upregulating microbial siderophore production to further accelerate weathering reactions. Moreover, EDDHA may alleviate potential Fe limitation of crops due to rising soil pH with EW over time. Initial cost-benefit analysis suggests potassium-EDDHA could lower EW-CDR costs by up to U.S. $77 t CO2 ha-1 to improve EW's competitiveness relative to other CDR strategies.

A state of the art of review on factors affecting the enhanced weathering in agricultural soil: strategies for carbon sequestration and climate mitigation

As the urgency to address climate change intensifies, the exploration of sustainable negative emission technologies becomes imperative. Enhanced weathering (EW) represents an approach by leveraging the natural process of rock weathering to sequester atmospheric carbon dioxide (CO2) in agricultural lands. This review synthesizes current research on EW, focusing on its mechanisms, influencing factors, and pathways for successful integration into agricultural practices. It evaluates key factors such as material suitability, particle size, application rates, soil properties, and climate, which are crucial for optimizing EW's efficacy. The study highlights the multifaceted benefits of EW, including soil fertility improvement, pH regulation, and enhanced water retention, which collectively contribute to increased agricultural productivity and climate change mitigation. Furthermore, the review introduces Monitoring, Reporting, and Verification (MRV) and Carbon Dioxide Removal (CDR) verification frameworks as essential components for assessing and enhancing EW's effectiveness and credibility. By examining the current state of research and proposing avenues for future investigation, this review aims to deepen the understanding of EW's role in sustainable agriculture and climate change mitigation strategies.

Enhanced weathering in the US Corn Belt delivers carbon removal with agronomic benefits

Terrestrial enhanced weathering (EW) of silicate rocks, such as crushed basalt, on farmlands is a promising scalable atmospheric carbon dioxide removal (CDR) strategy that urgently requires performance assessment with commercial farming practices. We report findings from a large-scale replicated EW field trial across a typical maize-soybean rotation on an experimental farm in the heart of the United Sates Corn Belt over 4 y (2016 to 2020). We show an average combined loss of major cations (Ca2+ and Mg2+) from crushed basalt applied each fall over 4 y (50 t ha-1 y-1) gave a conservative time-integrated cumulative CDR potential of 10.5 ± 3.8 t CO2 ha-1. Maize and soybean yields increased significantly (P < 0.05) by 12 to 16% with EW following improved soil fertility, decreased soil acidification, and upregulation of root nutrient transport genes. Yield enhancements with EW were achieved with significantly (P < 0.05) increased key micro- and macronutrient concentrations (including potassium, magnesium, manganese, phosphorus, and zinc), thus improving or maintaining crop nutritional status. We observed no significant increase in the content of trace metals in grains of maize or soybean or soil exchangeable pools relative to controls. Our findings suggest that widespread adoption of EW across farming sectors has the potential to contribute significantly to net-zero greenhouse gas emissions goals while simultaneously improving food and soil security.