16 November 2023

Crushed volcanic rock helps soil capture carbon


A new study highlights the effectiveness of rock dust in aiding the process. Even under severe drought conditions

by Matteo Cavallito


Adding crushed volcanic rock to cropland could promote carbon sequestration from the atmosphere, a study by the University of California Davis (UC Davis) and Cornell University suggests. The investigation, the results of which were published in the journal Environmental Research Communications, found that by using this system, carbon could be stored in the soil even during a period of extreme drought.

Rock dust is a valuable resource

The principle behind the study is known as weathering and occurs when rain, which falls captures carbon dioxide from the air, reacts with volcanic rock to lock in carbon. This process turns out to be effective but takes geological timescales of millions of years. The mechanism, in other words, is too slow to compensate for global warming.

Rock crushing, however, allows the process to be greatly accelerated. Provided there is sufficient water availability.

Indeed: the experiment, conducted during a particularly dry period characterized by a shortage of rainfall, demonstrated the effectiveness of the mechanism even under problematic starting conditions. “Even the infrequent heavy rains we get in the West might be enough to drive enhanced rock weathering and remove carbon dioxide,” Iris Holzer, a UC Davis doctoral student and lead author of the study, said in a note released by the California university.

Carbon sequestration increases in treated soils

The researchers applied crushed metabasalt rock and olivine to 5 acres in a fallow wheat field in the Sacramento Valley and took measurements during the winter months of 2020-2021. That period, they point out, had been characterized by extreme drought, with rainfall 41 percent of California’s historical average.

The study found that plots with crushed rock stored 0.15 tons more carbon dioxide per hectare when compared with untreated soils.

If this process could take place in all California cropland, the researchers point out, it would result in carbon removal that could offset the annual emissions of 350 thousand cars.

Rock dust may help sequester 4 billion tons of CO2

The research takes on particular significance in the context of climate change. Forty-one percent of the Earth’s surface, the note recalls, is covered by drylands that are expanding due to global warming. “Our findings support the hypothesis that enhanced weathering removes CO2 in real-world settings, while simultaneously illustrating challenges in quantification under weather extremes,” the study states.

The results, in particular, “suggest we may expand the margins of where enhanced weathering technology might operate into global arid lands.”

According to the U.N.’s Intergovernmental Panel on Climate Change, as reported by Yale Environment magazine, “If applied to croplands globally, rock dust could theoretically help suck an estimated 2 to 4 billion tons of carbon dioxide from the air every year.” That is “between 34 and 68 percent of the global greenhouse gas emissions produced by agriculture annually.”