The future is rock dust

Maia Welbel

What if we discovered that by sprinkling rock dust on farms across the U.S., we could capture massive volumes of global carbon emissions and increase crop yields? A team of researchers at Yale University working with midwestern farmers are pretty sure they’ve done just that. Welcome to the age of basalt.

Measuring healthy soil

Farmers use all sorts of soil enhancement techniques to maximize crop yields. In regions like the Corn Belt, where single crop species are grown on the same land repeatedly (also known as monoculture), soil eventually gets degraded to the point where it will no longer support growth.

While there are many factors involved in soil health and vitality, soil pH is a crucial variable that industrial farming practices tend to rapidly disturb. When soil is too acidic, it becomes a toxic environment for crops. Farmers address this is by spreading pulverized limestone onto the fields because it contains minerals that alkalize the soil to bring it back to an optimal pH for cultivation.

What exactly is basalt?

At Zumwalt Acres, a regenerative farm in Central Illinois, a team of farmers, scientists, and environmental activists are trying out a new approach. Basalt, which is a calcium- and magnesium-rich silicate rock, has an alkalizing effect similar to lime and can be spread onto fields using the same infrastructure that corn and soybean farmers in the area already use for lime and fertilizers. But basalt also happens to have a very high carbon sequestration potential, meaning it can capture and store large volumes of carbon dioxide from the atmosphere. Zumwalt Acres is one of just a few research sites currently conducting field trials with basalt, but early results indicate incredible possibilities for its role in global climate change mitigation.

“We need solutions right now, and this is one of them,” says Gavi Welbel, one of the researchers at the farm.

The process of spreading finely ground silicate rock to accelerate carbon drawdown is knows as enhanced rock weathering (ERW). ERW is a truly “natural” carbon solution in that it just speeds up a naturally occuring process. When silicate rocks (the most abundant type on earth) are exposed to water, heat, or acidity and begin to break down, a chemical reaction occurs which removes carbon dioxide from the atmosphere and stores it as carbonate minerals. By grinding down basalt into fine particles, distributing it into a warm soil environment, and optimizing for which types of rock work best, carbon drawdown potential increases exponentially.

Last year, the team at Zumwalt Acres applied basalt to 20 acres of corn and hay fields. Working with the Yale Center for Natural Carbon Capture, they determined that their tests led to significant increase in crop yields. This is great news because it indicates that farmers would be incentivized to adopt the practice regardless of its climate impact (though farmer education should also be an important part of the transition). Furthermore, they used only machinery that farmers in the region already deploy, kept all other inputs the same, and found no issues with crop quality or lifecycle.

During the upcoming farming season, Zumwalt Acres will become one of the largest ERW trial sites in the world by applying basalt to over 200 acres of farmland, aiming to glean a better understanding of how it can best play in to global climate solutions from both a scientific and logistical perspective.

“I think it’s really exciting that we are on the ground working with farmers, so we’re thinking about a lot of the practical questions that universities and traditional research sites might be less interested in,” Welbel says.

Another company investing in enhanced weathering is The Future Forest Company. Focused on spreading rock dust through forested areas, FFC is trialing large-scale rapid testing to accelerate carbon sequestration. As the technology for rock weathering is adopted more companies can lead reforestation efforts in tandem.

What does basalt mean for climate mitigation?

Eventually, employing ERW as a heavy-duty climate solution could mean the U.S. government subsidizing farmers to swap out lime for basalt nationally. Unlike other carbon capture technologies that might disrupt managed land or require its own parcel, this strategy minimally disturbs, and often could benefit land owners and managers. Additionally, silicate rock dust doesn’t have to be applied to agricultural soil for it to store carbon — other research groups are looking at how it could be put to use in a variety of environments, from golf courses to wastewater treatment plants. Since there is no shortage of basalt on this planet, there’s endless potential for exploration.

As with all climate mitigation strategies, farming with basalt is not a silver bullet solution. It’s one piece of a broader effort toward making agriculture a more sustainable industry. ERW implementation in the cornbelt and beyond has to occur in tandem with other regenerative methods including, but not limited to, cover cropping, agroforestry, water conservation, and crop diversity. Ancillary carbon emissions and other resource use must also be taken into account, as mining, grinding, and shipping basalt comes at its own environmental cost. Sourcing locally, using sustainable transport methods, and prioritizing already mined sources of basalt (such as that leftover from industrial and construction projects), will be crucial to ensuring a net positive impact for the climate.

“Everyone working at the farm is optimistic that basalt is the future,” Welbel says. The Zumwalt Acres and Yale research crew is looking at potential carbon capture at the gigaton scale if their trials continue to show promise for worldwide adoption.