Quantifying Synergies Among Soil-Based Carbon-Drawdown Approaches

Very large quantities of carbon dioxide (CO₂) will need to be removed from the atmosphere over the course of the next century or two to stabilize Earth’s climate at a safe temperature. A handful of C-drawdown approaches are available to perform this task, three of which involve soils: increasing stocks of soil organic matter (SOM), making biochar (BC) and storing it in soil, and enhanced weathering (EW) of silicate rocks such as basalt that are rich in calcium, magnesium, iron and other trace nutrients. Current evidence suggests that BC can promote SOM formation over the long term, and that BC and crushed-basalt amendments improve soil fertility. However, no work has addressed the combined impacts of BC and SOM on EW rates in soils, of BC and crushed basalt on the rates of EW and compost maturation during the composting process, of soil amendments with co-composted BC and crushed basalt on crop yield and quality, and of hot CO₂-saturated water, prepared during BC production using waste heat and CO₂, on rates of EW of crushed basalt. We hypothesize that these combined impacts will yield significant synergies in terms of crop yield and quality, compost-maturation rate, and total C drawdown by EW. We propose to quantify these synergies by three experiments. We will measure EW rates during BC production using CO₂-saturated water warmed by BC-process heat. We will measure composting efficiency and EW rates during ambient-temperature co-composting experiments with BC, crushed basalt, and their combination. And, we will measure crop yield and quality, and EW rates, in small greenhouse/field trials involving BC, crushed basalt, compost, and the co-composted products. We will determine EW rates by the amount of inorganic C (soluble bicarbonate, solid carbonate) formed during the experiment and estimate total C drawdown of various scenarios by a life cycle analysis. Undergraduates and urban interns from under-represented minorities will perform much of the work. Results will be summarized in a formal report and submitted for publication.