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When carbon escapes from soil, it combines with oxygen to form carbon dioxide. Sometimes the loss is gradual, the result of plowing that leaves upturned layers of earth exposed to the elements, or of failure to replant or cover fields after harvest.
Sometimes it happens more suddenly. The thick prairie sod of America’s Great Plains was a rich carbon store until settlers tore it up for farms, leaving hundreds of millions of tons of topsoil to be blown away in the Dust Bowl years. The destruction of millions of acres of carbon-rich Indonesian peatlands for palm oil plantations is helping to drive climate change today.
Low carbon levels leave the ground nutrient-poor, requiring ever-greater amounts of fertilizer to support crops. They also make for thin soil that is vulnerable to erosion and less able to retain water, so yields suffer quickly in times of drought.
To bring levels back up, a set of techniques known as carbon farming, or regenerative farming, encourage and complement the process by which plants draw carbon dioxide from the atmosphere, break it down and sequester carbon into soil. They include refraining from tilling, or turning, the soil; mixing crops together rather than growing large fields of just one type; planting trees and shrubs near or among crops; and leaving stalks and other cuttings on fields to decay.
Mr. Brown keeps his fields planted for as much of the year as possible to minimize nutrient loss. When he mixes clover and oats in the same field, the clover fixes nitrogen into the soil. After the oats are harvested, livestock graze the clover and leave their manure behind.
Such strategies have allowed him to stop using synthetic fertilizers and pesticides, reducing costs. And the rich soil not only yields higher volumes, but the crops are more nutritionally dense than those grown on depleted land, he says.
“Economically, it’s much, much, much more profitable,” he said.
Mr. Brown’s approach is very different from the techniques of industrial-scale farming that have taken hold in the United States and other wealthy countries, where single crops stretch over many acres, and fertilizers and pesticides are used heavily.
Things are worse in poorer nations, where farmers’ desperation often means they are unable to care for the soil, Mr. Lal said. He recalled seeing a Mexican sharecropper carting corn straw away from the fields to sell: “I said, ‘Why don’t you leave it on the land? The land will be better next year.’ And he said, ‘This land will not be mine next year, and I need money now.”’
There is some momentum behind a shift. The French government, which helped broker last year’s landmark Paris Agreement on climate change, is pushing an effort to increase soil carbon stocks by 0.4 percent annually, which it says would halt the rise in atmospheric carbon dioxide levels.
Mr. Lal called the target unrealistic, but said achieving just a quarter of that sequestration would be meaningful. In a generation, he said, agriculture could become carbon neutral, removing all the emissions it creates, for example through the energy used by farm equipment.
Worldwide, 5 percent to 10 percent of growers are using regenerative, climate-friendly techniques, said Louis Bockel, a policy officer at the United Nations’ Food and Agriculture Organization. That number is likely to increase, he said, as multinational institutions and wealthy nations start incorporating carbon sequestration incentives into existing aid to farmers in poor countries.
“More and more additional funding will be available” to encourage such efforts, Mr. Bockel added. “We are moving quite quickly on this.”
Farmers need financing to help them adopt new techniques, though generally only through a two-to-three-year transition period, said Eric Toensmeier, author of “The Carbon Farming Solution.” That money could come through a higher price charged for foods whose cultivation encourages sequestration, via a carbon tax or through trading systems in which polluters buy credits to offset their emissions, he said. Programs known as payment for environmental services, in which governments or others pay farmers for stewardship of land, are another potential avenue.
With that kind of support, the industry could be ready to do things differently, said Ceris Jones, a climate change adviser at the National Farmers Union in Britain.
“People say that farmers are pretty conservative, but actually practice can change quite quickly,” she said.
Another obstacle is the lack of an agreed-upon system for measuring carbon sequestration in soil, which will be required as the basis for any payments, Mr. Toensmeier said.
Technically, though, many elements of carbon farming are ready to be put into practice quickly, he said. Something as simple as planting trees around fields drastically increases the amount of carbon fixed into soil, Mr. Toensmeier said.
“I would love to see a huge, major transformation of agriculture in the industrialized world, but if we started with just adding trees to the system we have, it’s a huge gain,” he said. “We can sort of meet farmers where they are”
It’s not just crops. The earth beneath the world’s grasslands, from America’s Great Plains to the Tibetan Steppe and the Sahel of Africa, holds about a fifth of all soil carbon stocks, the Food and Agriculture Organization estimates. In many places that soil is badly depleted.
“This land is waiting to be filled up again with carbon if we could manage it sustainably,” said Courtney White, author of the book “Grass, Soil, Hope.”
That means moving livestock frequently so each patch of land is grazed just once a year, mimicking the patterns of the native bison that once roamed the American West, he said. The combination of stimulation during animals’ brief presence and long periods of rest encourages plants to lay down more carbon, Mr. White said.
With policies that encourage change, Mr. Toensmeier said, agriculture could benefit the climate rather than harming it. “There do seem to be a remarkable number of win-win opportunities, which is great news,” he said. “You don’t hear a lot of great news about climate change.”
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