A Boon for Soil, and for the Environment

Since people began farming, the world’s cultivated soils have lost 50 percent to 70 percent of their natural carbon, said Rattan Lal, a professor of soil science at the Ohio State University.  That number is even higher in parts of south Asia, sub-Saharan Africa and the Caribbean, he added.

Globally, those depleted soils could reabsorb 80 billion to 100 billion metric tons of carbon, reducing atmospheric carbon dioxide by 38 to 50 parts per million, Mr. Lal said.  That does not include the carbon that could be simultaneously sequestered into vegetation, but the numbers are significant on their own, equaling up to 40 percent of the increase in concentrations since pre-industrial times.  Last year, atmospheric carbon dioxide for the first time hit a monthly average of 400 parts per million, a symbolic threshold but one that many experts say could indicate that warming will soon spiral beyond control.

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 peat lands 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.
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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.

Read more at A Boon for Soil, and for the Environment