How Rocks Fight Climate Change
By Gavi Welbel
Enhanced rock weathering refers to the practice of adding rock dust to the land as a way to combat climate change. At Zumwalt Acres, we are adding basalt rock, Earth's most abundant bedrock, which we source from Rock Dust Local’s Great Lakes Regional Rock. Adding this crushed silicate rock speeds up a naturally-occurring chemical process, known as weathering. Compounds in the rock dissolve in rainwater and react with carbon dioxide (CO2), pulling CO2 out of the atmosphere and transporting it through surface and groundwater runoff into the ocean. Once in the ocean, the minerals combat ocean acidification and rebuild coral.
Practices that are good for the farmer and good for the Earth are essential in our fight against climate change. Basalt rock has been shown to improve soil quality and crop yield, and decrease the need for other soil amendments, while mitigating climate change (1). It can be easily adopted by conventional farmers using machinery they already own. Moreover, most conventional farmers are accustomed to the practice of adding crushed rock to their land. Limestone, a type of carbonate rock, is often used in agriculture to raise pH and add nutrients to the soil. Basalt can provide the same benefits and may even increase crop yield compared to limestone.
Models of enhanced rock weathering have shown promising results (2), but before farmers can be expected to invest in basalt, we must have data to support it. Field studies will allow us to learn how best to use basalt in the Midwest. It will also provide insight into how basalt can increase crop yields. At Zumwalt Acres, we have divided up our field and perennial nursery to systematically vary the amount of basalt we apply. We have been busy collecting soil samples at depths ranging from one inch to one foot across 12 acres of soy field and our tree nursery to be analyzed for chemical composition, nutrient levels, and total organic carbon. Once basalt is added to the land, we will collect more samples and assess crop yield to track how soil properties change over the course of the year and to determine which application rate is best suited for our soil and crops.
Every mechanism of carbon sequestration comes with financial and environmental trade-offs. In the case of enhanced rock weathering, we must be sure that the rock is sourced in sustainable and carbon-effective ways. Transporting tons of rock across the country or increasing the demand for mined rocks are both carbon-intensive scenarios we want to avoid. Alternatively, using leftover rock from mining or construction operations encourages recycling of otherwise unused waste. Financial and carbon costs may also be offset by replacing limestone and chemical fertilizers with basalt rock, especially if the basalt is sourced locally. Increases in crop yields due to the addition of basalt can also play a role in offsetting costs. Stay tuned for our research outcomes!
(1) Beerling, D.J., Leake, J.R., Long, S.P. et al. Farming with crops and rocks to address global climate, food and soil security. Nature Plants 4, 138–147 (2018). https://doi.org/10.1038/s41477-018-0108-y
(2) Taylor, L., Quirk, J., Thorley, R. et al. Enhanced weathering strategies for stabilizing climate and averting ocean acidification. Nature Clim Change 6, 402–406 (2016). https://doi.org/10.1038/nclimate2882