Spreading crushed stone across farm fields could inexpensively pull CO2 from the air while also increasing yields. But it would require a mo
Excerpt from this story from Scientific American:
The scene that unfolded on a cold November day in central Illinois might seem commonplace, but it was part of a bold plan to pull billions of tons of carbon dioxide from the atmosphere and stuff it into the ocean.
A few miles south of Urbana a dump truck trundled past bare fields of dirt before turning into an adjacent lot. It deposited a cottage-size mound of grayish-blue sand—190 metric tons of a crushed volcanic rock called basalt. Farmers spread the pulverized basalt across several fields that they sowed with corn months later. This was the fourth year of an ambitious study to test whether the world’s farmlands can be harnessed to simultaneously address three global crises: the ever rising concentration of planet-warming CO2 in the atmosphere, the acidification of the oceans and the shortfall in humanity’s food supply.
The trial results, published in February 2024, were stunning. David Beerling, a biogeochemist at the University of Sheffield in England, and Evan DeLucia, a plant physiologist at the University of Illinois Urbana-Champaign, led the study. They found that over four years, fields treated with crushed basalt and planted with alternating crops of corn and soy pulled 10 metric tons more CO2 per hectare out of the air than untreated plots. And crop yields were 12 to 16 percent higher. In other research, they found that adding crushed basalts to soils improved the harvest of miscanthus, a tall grass that is used to make biofuels, by 29 to 42 percent, and the fields captured an estimated 8.6 metric tons of CO2 per hectare of land each year, compared with untreated fields. “It was exciting,” Beerling says. “We were pleasantly surprised.”
Their findings added to positive results elsewhere. In 2020 researchers in Canada reported that adding the mineral wollastonite to fields growing lettuce, kale, potatoes and soy sequestered CO2 in the soil at rates as high as two metric tons per hectare per year. And last spring Kirstine Skov, a natural geographer at the start-up company UNDO Carbon in London, showed that crushed basalts improved the yields of spring oats by 9 to 20 percent while reducing soil acidity in several fields in England.
The basalt in Illinois came from a quarry in southern Pennsylvania, where it is mined for roofing and building materials. Basalt is the most abundant rock in Earth’s crust. As it naturally weathers—gradually dissolving in soil water—it captures CO2, converting it into bicarbonate ions in the water, which cannot easily reenter the atmosphere. The reaction also releases into the soil nutrients that are important for plant health, including calcium, magnesium and silicon. Grinding and spreading basalt—an approach known as enhanced rock weathering (ERW)—speeds up those processes greatly. It could help cash-strapped farmers around the world by increasing crop yields, reducing fertilizer use and potentially allowing them to sell carbon credits.
