How farmland can combat global warming

Field testing reveals carbon stored in soil even in dry climates.

Adding crushed volcanic rock to farmland can play a major role in removing carbon from the air. In a field study, scientists at the University of California, Davis, and Cornell University found that the technology stores carbon in the soil even during extreme drought in California. The study was published in the journal Environmental research communications.

Rain picks up carbon dioxide from the air as it falls and reacts with volcanic rock to trap carbon. This process, called rock weathering, can take millions of years, and is too slow to offset global warming. But by crushing rocks into fine dust, the speed of rock weathering increases. former studies It has been estimated that this “enhanced” rock weathering could store 215 billion tons of carbon dioxide over the next 75 years if spread across farmland globally.

But so far this technology has not been field tested in dry climates.

Researchers from UC Davis found that adding crushed volcanic rock to farmland can remove carbon dioxide from the air. This “enhanced” rock weathering works even in dry climates. Credit: Amy Quinton/UC Davis

“These reactions require water,” said Iris Holzer, lead author, and a doctoral student in soil and biogeochemistry in the Department of Land, Air, and Water Resources at UC Davis. “Because we are interested in the potential of global carbon storage for enhanced weathering, we need to understand whether it can work in these drier climates and whether different measurement methods are effective. We were excited to monitor carbon removal in this environment.”

California drylands: a new frontier for carbon storage

The researchers used crushed rock, both basalt and olivine, on 5 acres of fallow cornfield in the Sacramento Valley. They collected measurements during the winter months of 2020-2021. California was suffering from a severe drought at the time, with rainfall reaching 41% of its historical average.

The study found that plots containing crushed rock stored 0.15 tons of carbon dioxide per hectare (2.47 acres) during the study compared to plots without crushed rock. Although researchers expect different weatherization rates in different environments, if this amount of carbon were removed across all of California’s farmland, it would be equivalent to taking 350,000 cars off the road each year.

A spreader unloads crushed basalt rock into a fallow cornfield in the Central Valley. Credit: Amy Quinton/UC Davis

Implications and future directions

“We definitely see evidence of weathering occurring on short timescales,” Holzer said. “Even the rare heavy rains we get in the west may be enough to enhance rock weathering and remove carbon dioxide.”

Measuring and verifying carbon storage on larger scales and tracking it over time is the next challenge, Holzer said.

Forty-one percent of the Earth’s surface is covered by drylands that are expanding due to climate change. This makes studying enhanced rock weathering in drylands increasingly important, the researchers said.

Lead researcher Benjamin Zee said. “When it comes to bending the global carbon curve, we are in a race against time,” said Holton, dean of Cornell University’s College of Agriculture and Life Sciences. “Our study demonstrates a new way to verify carbon dioxide removal through enhanced weathering, and is a critical leap forward for scaling up this technology on farmland around the world.”

Reference: “Direct Evidence for Removal of Atmospheric Carbon Dioxide through Enhanced Weathering in Farmland Soils” by Iris O. Holzer, Malika A. Nocco, and Benjamin Z. Holton, October 18, 2023, Environmental research communications.
doi: 10.1088/2515-7620/acfd89

Other authors include Malaika Nocco, of the Department of Land, Air and Water Resources at UC Davis.

This research, part of the Center for Working Land Innovation, was funded by the California Strategic Growth Council, the Grantham Foundation, and Roger Sant and Doris Matsui. Aggregates and Mining Company, SGI, a Standard Industries company, donated crushed basalt rock from its site in Ion, California.