How adding rock dust to soil could help drag carbon into the soil

This story was produced in collaboration by the Food and Environment Reporting Network and Yale Environment 360. It is reproduced here with permission.

On a hot and humid August day near Geneva, New York, Garrett Boudinot stands in a hemp field, green stems protruding a foot or more from his 6-foot-4 frame. Today, Cornell University’s mustached research assistant will harvest six acres of the crop, weigh it in red plastic bins, and continue to analyze the hundreds of water samples taken with measuring devices called lysimeters. who have been buried in the field in the past three months. .

Boudinot, a member of a research team at Cornell University, will sweat over the next two days of fieldwork to see if an unusual component added to the soil earlier in the year helped increase yields and to sequester carbon. This soil amendment “we just affectionately call” rock dust “, which is not very descriptive,” says Boudinot. “But these really are silicate rocks that have been ground into a fine powder.”

The hemp field trial is just a project led by Ben Houlton, dean of the Cornell College of Agriculture and Life Sciences. Over the past two years, he and his colleagues at Work land innovation center, a research consortium based at the University of California at Davis, tested various soil amendments that capture carbon from the air and trap it underground. They have tested the biochar, manure, and rock dust used on New York land and California farm plots, and so far the most effective soil treatment has been basalt pulverized to dust.

“As far as I know,” Houlton says, “ours is the larger-scale project of its kind, using this type of intensive scientific approach.”

Researchers are spreading basalt on corn fields in Illinois, on sugarcane in Australia and on soybean fields in Canada.

Hemp field experiments go beyond testing amendments that increase yields and sequester carbon and look at how much rock dust to apply for best results. Some sections received 20 tons of rock dust per acre, while others received 40, allowing researchers to get a more accurate picture of the relationship between dust, soil and crops. The research adds to a growing body of scientific work showing the potential of these soil amendments to become one of the many measures needed to help solve our climate crisis.

Agriculture accounts for nearly a quarter of global carbon dioxide emissions, making the agricultural sector an important part of efforts to reach net zero by 2050 and limit global warming to 1.5 degrees Celsius, an increase according to scientists, whom the world should not overtake if we are to avoid some of the most drastic consequences of climate change. To help reduce carbon in the atmosphere, scientists once suggested seeding the oceans with iron. This tactic was criticized as damaging to the environment and ineffective and has not been widely accepted. But seeding soils with carbon-capturing rock dust could do just that.

In addition to Houlton, scientists from the UK in Canada are testing various soil amendments on farmland, assessing how much carbon they sequester through a process called enhanced weathering. As Houlton researchers apply basalt to hemp in New York City and alfalfa and olive trees in California, scientists working with the University of Sheffield Leverhulme Center for Climate Change Mitigation in the UK spread basalt on cornfields in Illinois and on sugarcane in Australia. In Ontario, Canada, researchers are application of wollastonite from a nearby mine on soybean and alfalfa fields.

According to the UN Intergovernmental Panel on Climate Change (IPCC), rocks remove naturally 1 billion tonnes of carbon dioxide per year from the atmosphere (a number that has changed over time). Adding rock dust to farmland speeds up chemical reactions that trap carbon – for thousands of years – in the soil. Applied to cropland around the world, rock dust could theoretically help suck around 2-4 billion tonnes of carbon dioxide from the air each year, or between 34% and 68% of global greenhouse gas emissions. greenhouse produced by agriculture every year. While treating so much land may be unrealistic, the process has the potential to spread quickly as rock dust is not uncommon and farmers don’t need to buy new equipment to apply it: they already have fertilizer application equipment in their barns.

“It’s an incredibly exciting technology that has a lot of payoff for the company and quite frankly we could deploy it very quickly,” Houlton said.

Basalt, the additive used in the Cornell Project, is a by-product of mining and manufacturing operations and is found all over the world. Some estimates show enough stored basalt rock dust to treat the world’s cropland for several years.

“Rock mining is one of the biggest things we do as a species,” says Phil Renforth, an engineer at Heriot-Watt University in Edinburgh, who works on carbon capture. “In droves, we mine more than twice as much rock as we produce food.”

clod of earth (right) containing rock dust.  (Credit: Sophie Nasrallah)

Basalt contains magnesium, calcium and silica, among other components. When rock is pulverized and applied to soils, magnesium and calcium are released from the silica and dissolve in water as it moves through the soil. Minerals in the soil react with water and carbon that would otherwise return to the atmosphere, forming bicarbonates, which can stay in the water for thousands of years, eventually making their way to the oceans where they can. precipitate as limestone and remain on the seabed for millions of years.

Different amendments cause slightly different chemical reactions in soils, and soils provide different conditions, such as different pHs. Some amendments, such as wollastonite, may sequester carbon better but are not as abundant. Others may contain heavy metals, which can damage crops and groundwater. “There is rock chemistry; there is the availability of rock; and then there are the benefits of the material’s carbon, as well as the potential for what I would call “negative consequences,” Houlton explains.

The varied lands on which crops are grown require a number of field trials to assess how much carbon remains in the soil, but the results are encouraging. On plots in California, the first results show a doubling of carbon absorption. This is surprising, Houlton says, given that the crops have been grown under the driest conditions in the state’s history.

If a carbon market ever does materialize, farmers could be paid for the amount of carbon they sequester.

Leverhulme Center director David Beerling, after five years of ten-year efforts to study improved weathering of cropland, published an article last year Nature who demonstrated the potential of the method. He and his colleagues found that if China, India and the United States applied rock dust to all of their farmland, 1 billion tonnes of carbon dioxide could be removed from the atmosphere.

The research results so far are significant enough that the IPCC mentions increased spoilage in his last report, listing the method of spreading crushed rock on soils as a means of capturing more carbon and boosting cropland productivity.

But scientists are still weighing the costs and benefits of such applications, including the cost of transporting the material and better calculating the benefits of carbon storage and crop yields. Researchers may soon have more data to rely on: Results from much larger trials by Houlton and Beerling could be published as early as next year.

Rock dust applications could benefit far more than the climate – they could help farmers too. Field tests on corn and alfalfa show increased crop yields thanks to rock dust, which releases other essential nutrients such as phosphorus and potassium. In some cases, yields are 30 percent higher, results that could prompt farmers seeking to reduce inputs while increasing the harvest. Initial weight measurements also show potentially higher yields in hemp fields in New York City.

Scientists are evaluating the costs and benefits of these ground applications, including the cost of transporting the material.

Rock dust can also affect the nitrogen cycle, Beerling points out, ultimately allowing farmers to apply less nitrogen fertilizer. This could lead to fewer nutrient pollution problems, especially in the Corn Belt states where runoff flows into the Mississippi watershed and the Gulf of Mexico. Beerling and researchers are working on a map of available basalt and the crops it could be applied to in 13 states in the Midwest.

Reducing atmospheric carbon does not yet provide a source of income for farmers, although the Biden administration has launched a “carbon farming” incentive. Houlton and Beerling seek to quantify exactly how much carbon a crop can capture so that if a market does materialize, farmers could be paid for the amount of carbon they sequester.

To do this, Boudinot examines the soil water chemistry of hemp fields to see how much bicarbonate has formed a foot below the surface. These data, along with information from experimental plots in California and the results of the first five years of research conducted by the Leverhulme Center, could provide vital evidence for the farming community.

“What do you think of a carbon dioxide removal technology that reuses waste rock dust, captures carbon, improves soils, restores soils and improves yields? Beerling asks. “It’s obvious, at least in the short term, if you have this material and the evidence accumulates. Why wouldn’t you do it? “

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