Can dirt clean the climate?

FORBES, Australia — Across 100,000 acres in the vast agricultural heartland of Australia, an unusual approach is taking root to slow down the wrecking ball of climate change. Farmers are trying to tap the superpowers of tiny subterranean tendrils of fungus to pull carbon dioxide out of the air and stash it underground.

It’s part of a big bet that entrepreneurs and investors around the world are making on whether dirt can clean up climate pollution. They are using a variety of technologies on farmland not just to grow food but to eat the excess carbon dioxide produced by more than a century of fossil fuel burning and intensive agriculture.

Why fungus? Because fungi act as nature’s carbon traders. As they sow their crops, farmers are adding a pulverized dust of fungal spores. The fungus latches on to the crop roots, takes carbon that is absorbed by the plants from the air and locks it away in subterranean storage in a form that may keep it underground for much longer than the natural carbon cycle.

The fungal venture, the handiwork of an Australian company called Loam Bio, is among several startups to have mobilized hundreds of millions of dollars in investments in efforts to use soil to remove carbon dioxide from the atmosphere. Like Loam Bio, companies like Andes and Groundworks Bio Ag are also experimenting with microbes. Lithos and Mati offer farmers crushed volcanic rocks that absorb carbon to sprinkle on their fields. Silicate Carbon is milling leftover concrete into a fine powder, while several companies are scorching crop waste into charcoal.

The appeal of the Australian startup is that it doesn’t demand too much of farmers.

“Pretty simple,” is how a fifth-generation Australian farmer named Stuart McDonald described his experience as he sowed a dusting of fungal spores with his wheat and canola seeds on his farm near Canowindra this year. “It’s not asking us to change too much. It’s not a big capital outlay.”

It’s still early days for most of these ventures, and exactly how much excess carbon they can remove and how long they can keep it underground remains contested. But their side-benefits may be equally profound. They are all aimed at restoring the health of soils that have been degraded by decades of intensive agriculture by restoring microbes and minerals that they once contained.

The carbon removal potential of soils is huge. Soils hold three times more carbon than the atmosphere and they can potentially absorb more than 5 gigatons of carbon dioxide per year, or one-seventh of all the carbon dioxide that human activity injects into the atmosphere, according to the Intergovernmental Panel on Climate Change. That makes them the world’s second-largest carbon store, after oceans.

“I think soils will play a key role,” said Rob Jackson, a climate scientist at Stanford University, though he was skeptical about whether the promise of the fungal additives in field tests could have a statistically significant effect on working farms.

“We would need to touch billions of acres to make a real difference,” he said.

Not to mention, agriculture itself creates a climate problem, accounting for a fourth of the world’s greenhouse gas emissions.

Loam Bio’s fungal talcum has been spread on 100,000 acres in Australia this year, with 250,000 acres expected to come online next year. A half-dozen farmers in the United States are trying the product on their soy fields. Field tests are underway in Canada and Brazil.

Loam Bio has attracted $100 million in investments so far, making it among the most well-funded of the many startups looking for ways to store more carbon in the dirt.

Critics are concerned that the new technologies treat the symptom and not the cause of climate change. They “can’t be used as an excuse to continue burning fossil fuels,” Jackson said.

Loam Bio’s co-founder and a sixth-generation farmer, Tegan Nock, agreed.

“This is just one of the things that can buy us time,” she said.

Why Australia?

Not all farmers are doing this out of altruism.

More carbon means better soil health and better yields. But in Australia, farmers have another motive. They hope to reap a harvest of government-issued credits if they can demonstrate they have stored carbon underground.

This is not the first time that farmers in the area have tried to cash in on soil carbon.

Once, McDonald, 52, trucked in solid waste from Sydney’s sewage to fertilize his fields and measured a small uptick in soil carbon. But he has no idea how long it lasted. Some farmers planted trees on a portion of their land and soil carbon increased for a few years, then flattened out.

Critics said carbon credits were awarded not for substantial changes but for seasonal fluctuations in weather: In unusually wet years, carbon accrued in the soil, only to dissipate in dry years. One study warned that the number of carbon credits issued for farming projects was inflated.

Accounting for carbon in soil is complicated by the fact that it comes in different forms. Most soil carbon is in the form of highly volatile organic matter. On farmland, that would be plant residue or manure. It can return to the atmosphere in a matter of years, or a drought or fire can burn it up even faster, releasing carbon dioxide back into the air.

But there are more stable types of soil carbon, including one that attaches itself to minerals in the dirt and remains there for a century or longer. Loam Bio says that its fungal spores can help build that more stable soil carbon. They measure it for their farmer customers, using one-meter deep soil cores.

Fungi do the vital work underground. They take the carbon dioxide that plants pull from the air during photosynthesis, stash it underground, and give back nutrients that plants need.

To Alan Richardson, a soil biologist at the Commonwealth Scientific and Industrial Research Organization, a government agency in Australia, the concept of using fungi to store carbon underground makes sense. But it would work only if farmers applied the fungi year after year, allowing the soil to build carbon over many years.

“The fundamental principle behind it is sound, but whether it translates into practice we don’t know,” he said.

Still, Steve Nicholson, a farmer near the town of Forbes, is so bullish on the prospect that he signed a 25-year contract with Loam. “It’s a gamble,” he said. “But it’s a very, very good gamble.”

Loam’s technicians measured his baseline soil carbon in February, at the peak of the hot, dry season. They will be back next February to find out whether his soil carbon has increased, and to determine how much of it is in the more stable forms.

Nock of Loam Bio tells her customers they can expect to store one to two tons of stable carbon in every hectare, or 2.4 acres.

Australia’s government-run carbon credit agency will have to verify how much carbon Nicholson has added before issuing any credits. Nicholson hopes to cash in by next July.

His earnings will depend on Australia’s carbon price at that time. He is eyeing more than 100 Australian dollars, or about $65, per hectare.

The world’s ravaged soil

Agriculture is increasingly bedeviled by its own environmental toll.

The quest to feed the world has ravaged the land, while emitting vast amounts of greenhouse gases. Clearing forests. Plowing the ground. Applying chemical fertilizers. This activity has altered most of Earth.

The changes are evident on McDonald’s farm.

His ancestors, settlers from England, began tilling the ground in Australia in 1888. They grew acres of wheat, foreign to this continent. They raised cattle and sheep, also foreign. Over the decades, Australia became an agricultural powerhouse.

Also over the decades, as farming intensified, layers of topsoil wore away. Soil carbon levels dropped. The dirt degraded. “Erosion is something everyone accepted,” McDonald said.

Until they no longer could. About 20 years ago, McDonald, like many of his neighbors, stopped tilling. After each harvest, he let the crop stubble decompose naturally. It helped to hold moisture in the soil and slow down erosion, but did little to build soil carbon, according to scientific studies.

Now, climate change poses a new risk. A drier and hotter future threatens to release much more carbon from the soil, according to scientific models.

Australia’s climate targets mean agriculture must change. Its government has set out to reduce its greenhouse gas emissions by 43% by 2030, compared with 1990 levels. Agriculture represents around 14% of those emissions.

Neil Westcott, also a wheat and canola farmer and mayor of a small farming town called Parkes, has his eye on that future. He wants to reduce his farm’s climate effects. Soon, he reckons, he may have to, if the government requires climate pollution cuts or if customers abroad want low-carbon crops.

Westcott, 64, has stopped raising sheep, which produce methane, a potent greenhouse gas, and he has sown about a quarter of his 6,000 acres with the fungus powder. He hopes there will be carbon credits, but he isn’t planning to sell those yet. He wants to hold on to them for when he may have to neutralize his own farm’s carbon emissions.

“I have my own carbon footprint I need to cover,” he said. “I’m sick of just talking about it. I’ve got to do something.”

This article originally appeared in The New York Times.

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