Farming With Rocks Could Help Pull Carbon Dioxide From the Atmosphere

Carbon dioxide mixes with rainwater to create carbonic acid, which breaks down rocks. Sprinkling rocks across croplands could boost the conversion of carbon dioxide.

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Sprinkling basalt and similar crushed rocks on croplands could remove carbon dioxide from the atmosphere and fight climate change, according to researchers.

The approach would speed up the natural chemical processes that erode rocks every day, the researchers wrote in a study published in the journalNature Plants.

On a daily basis, carbon dioxide in the air mixes with rainwater to create carbonic acid, which breaks down rocks. The acid then recombines with elements in the rocks to form bicarbonate, a key ingredient in baking soda and other chemical compounds that include minerals.

“Bicarbonate is stable and washes out of the system…pumping that CO2 from the atmosphere through this circuitous weathering process into the depths of the ocean,” Evan DeLucia, a professor of plant biology at the University of Illinois at Urbana-Champaign, said in an interview with Seeker.

Under normal circumstances, carbonic acid only breaks down the outside of rocks, said DeLucia, limiting the amount of carbon that helps form bicarbonate. Sprinkling crushed rocks on farm fields would expose more of the rocks’ surface to the acid and convert more carbon from the air into bicarbonate.

“That’s the natural process of geologic weathering of silicate rocks like basalt that’s been happening forever and forever,” said DeLucia. ““Can we accelerate that weathering process?”

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Farms are ideal places to sprinkle the crushed rocks because magnesium and other byproducts from rock weathering act as fertilizers. Farmers already pour limestone on their fields to reduce acidity from fertilizers, too, so they have the infrastructure and habit of pouring crushed rocks on their land. Limestone, however, is not as effective as basalt and other volcanic rocks at removing carbon from the air.

The researchers conclude that spreading enough basalt on two-thirds of the world’s arable land could remove more than 4.4 billion tons of carbon from the air annually by 2100. Since bicarbonate is alkaline, it would reduce acidification in the oceans, too.

DeLucia is now determining whether sprinkling crushed basalt on 20 acres of corn field in Illinois would reduce carbon dioxide. He didn’t know the result of those tests yet, but it appeared as if levels of another potent greenhouse gas that often originates in fertilizers — nitrous oxide — were decreasing from the field, he said.

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The study notes that “mining, grinding, and spreading the ground rock” as well as transporting it would also require energy that would emit carbon, potentially offsetting the carbon losses by as much as 30 percent. The costs associated with obtaining, processing and transporting the rock could also undercut the researchers’ plans, they wrote.

Using crushed rocks in agriculture to reduce carbon in the atmosphere might not work everywhere, but that was beside the point, note DeLucia. If farmers in parts of the globe where rock was easily found and processed could more easily extract carbon in the air, they would be contributing to the multitudes of measures humankind needs to tackle climate change, he said.

“This is kind of in the ‘desperate times require desperate measures’ mode,” said DeLucia. “How are we going to dramatically decrease CO2 in the atmosphere in the next 20 years? To do that, we are going to require some active measures.”