Improved net carbon budgets in the US Midwest through direct measured impacts of enhanced weathering

• Published in: Global change biology 2023-12, Vol.29 (24), p.7012-7028
• Main Authors: Kantola, Ilsa B., Blanc‐Betes, Elena, Masters, Michael D., Chang, Elliot, Marklein, Alison, Moore, Caitlin E., Haden, Adam, Bernacchi, Carl J., Wolf, Adam, Epihov, Dimitar Z., Beerling, David J., DeLucia, Evan H.
• Format: Article
• Language: English
• Subjects: Agricultural practices; agriculture; Alkalinity; Atmospheric particulates; Basalt; bioenergy crop; Biofuels; Biomass; Calcium; carbon budget; Carbon capture and storage; Carbon dioxide; Carbon dioxide removal; Carbon sequestration; Cations; Climate change; Corn; Crop rotation; Cropping systems; Crops; Drawdown; Dust; eddy covariance; Energy crops; enhanced weathering; Environmental impact; Inorganic carbon; Magnesium; Major elements; MATERIALS SCIENCE; net ecosystem carbon balance; net primary production; Net Primary Productivity; Perennial crops; Primary production; Rare earth elements; Rocks; Soil; soil respiration; Soil surfaces; Soils; Soybeans; Weathering
• ISSN: 1354-1013; 1365-2486
• DOI: 10.1111/gcb.16903

Terrestrial enhanced weathering (EW) through the application of Mg‐ or Ca‐rich rock dust to soil is a negative emission technology with the potential to address impacts of climate change. The effectiveness of EW was tested over 4 years by spreading ground basalt (50 t ha−1 year−1) on maize/soybean and miscanthus cropping systems in the Midwest US. The major elements of the carbon budget were quantified through measurements of eddy covariance, soil carbon flux, and biomass. The movement of Mg and Ca to deep soil, released by weathering, balanced by a corresponding alkalinity flux, was used to measure the drawdown of CO2, where the release of cations from basalt was measured as the ratio of rare earth elements to base cations in the applied rock dust and in the surface soil. Basalt application stimulated peak biomass and net primary production in both cropping systems and caused a small but significant stimulation of soil respiration. Net ecosystem carbon balance (NECB) was strongly negative for maize/soybean (−199 to −453 g C m−2 year−1) indicating this system was losing carbon to the atmosphere. Average EW (102 g C m−2 year−1) offset carbon loss in the maize/soybean by 23%–42%. NECB of miscanthus was positive (63–129 g C m−2 year−1), indicating carbon gain in the system, and EW greatly increased inorganic carbon storage by an additional 234 g C m−2 year−1. Our analysis indicates a co‐deployment of a perennial biofuel crop (miscanthus) with EW leads to major wins—increased harvested yields of 29%–42% with additional carbon dioxide removal (CDR) of 8.6 t CO2 ha−1 year−1. EW applied to maize/soybean drives a CDR of 3.7 t CO2 ha−1 year−1, which partially offsets well‐established carbon losses from soil from this crop rotation. EW applied in the US Midwest creates measurable improvements to the carbon budgets perennial bioenergy crops and conventional row crops. Enhanced weathering in bioenergy cropping systems reduces carbon loss in annual row crops and increases carbon storage in perennial crops, while increasing grain yields in maize and soybean. A new rare earth element method allows for calculation of weathering rates and carbon capture by ground silicate rock soil amendments. These amendments have the potential to sequester 3.7–8.6 t CO2 ha−1 year−1 in bioenergy crop systems of the US Midwest, altering the carbon balance of one of the largest ecosystems of North America.