LIANE HANSEN, host:
This is WEEKEND EDITION from NPR News. I'm Liane Hansen.
(Soundbite of music)
HANSEN: Greenhouse gases come from many sources - power plants, cars, lawnmowers, dirt. Dirt? Yes, dirt. Farmers release huge amounts of carbon dioxide when they plow their fields. That's the bad news. The good news is that farmers are finding ways to recapture some of that carbon and they may even help slow global warming. As part of our Climate Connection series with National Geographic, NPR's Dan Charles has the story.
DAN CHARLES: So I'm here in the middle of Iowa. Near Story City?
Dr. LEE BURRAS (Professor, Agronomy, Iowa State University): Near Story City.
CHARLES: With Lee Burras, who teaches at Iowa State University. And we are about to do something a little bit disturbing. We are about to slice into some soil that has really not been cut open for how long?
Dr. BURRAS: It's never been cut open. This is part of Doolittle Prairie. Doolittle Prairie is never been plowed. It's been forming like this for the last 8,000 years.
CHARLES: And we're about to disturb it.
Dr. BURRAS: We're about to disturb it.
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CHARLES: Burras is driving a spade into the soil. Cutting through the web of roots, he pulls up a big clump.
Dr. BURRAS: So now we have a piece of Iowa soil - beautiful prairie-derived soil.
CHARLES: And you look at that as a soil scientist, what do you see?
Dr. BURRAS: Well, the first thing I'm noticing is how black it is - beautifully black.
CHARLES: Black like coal, like oil, like charcoal, because this soil is also full of carbon - organic carbon, or humus, Burras calls it. What's left from countless generations of rotting plants.
But now that we've exposed the soil to sun and oxygen, we've started to destroy that legacy. Microbes in the soil are going to work on the humus, eating it and breathing out carbon dioxide, as if they were burning up the soil. This is what happens when farmers till the land.
Dr. BURRAS: The tearing of the soil, introducing more oxygen - that's what tillage is all about. And the history of human civilization is tillage. I believe it was Daniel Webster who said where tillage begins, other arts follow.
CHARLES: But tillage also changes the Earth. Burras walks a hundred feet to the east into a field planted with soybeans. Here, once again, he turns over some soil.
Dr. BURRAS: One of the most striking differences, as we look at this, is the field is a little grayer. It's not quite as black. And that reflects the past century of plowing and such. We've seen the organic carbon content of this field go from maybe five percent organic carbon down to three percent organic carbon.
CHARLES: That means every acre of this field has vented about 50 tons of carbon dioxide into the atmosphere. It's about as much as eight cars pump out in a year. And there are billions of acres of farmland around the globe. Rattan Lal, a soil scientist at Ohio State University, has traveled the world studying those fields, trying to calculate how much carbon farmers have unleashed.
Professor RATTAN LAL (Soil Science, Ohio State University): From time immemorial when the world agriculture began, we have lost roughly 140 billion tons of carbon from trees and soil.
CHARLES: In fact, until the 1950s, plowing had released more carbon dioxide into the air than all the burning of coal and oil. Now this would be just ancient history, except for one thing: a coal mine can't magically suck some of its carbon back into the Earth. The soil, though, can if you treat it right. You could call it farming carbon.
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CHARLES: This Iowa farmer is planting soybeans without plowing up the soil. Sharp steel wheels cut through last year's corn stalks, opening up a narrow slit in the soil. Seeds drop through a tube into the opening, then a wheel comes along and closes it up again. It's called no-till planting because it doesn't stir up the soil. It lets the land keep its stored carbon and even adds some, because those corn stalks on the surface gradually become part of the soil.
In fact by some calculations, each acre of no-till land in Iowa captures about a ton of carbon dioxide from the air each year. At that rate, a seven-acre cornfield inhales about as much of this greenhouse gas as the average American car exhales. But no-till isn't the only way to grow a carbon crop.
Dr. PAUL HEPPERLY (Research and Training Manager, Rodale Institute): So this is finished compost over here that is ready to go on to our fields. You can see that it looks like rich soil.
CHARLES: Paul Hepperly is in charge of research at the Rodale Institute in Kutztown, Pennsylvania. It's a showcase of organic farming methods. There's very little sign of what this compost used to be - tree leaves and cow manure.
Dr. HEPPERLY: It smells just like good rich soil.
CHARLES: Compost is one reason why the fields of the Rodale Institute have been getting richer in carbon year after year. In Searsboro, Iowa, meanwhile, Russell Hughes stopped growing corn or soybeans on part of his farm and turned it into pasture for cattle. Grass and clover covers this ground year-round; the roots grow deep.
Mr. RUSSELL HUGHES (Farmer, Iowa): In a small respect, you're going back to, you know, closer to what the prairie was doing when it was here. I mean, you know, as long as you have roots down there that are holding the soil, you know, you're adding a little all the time.
CHARLES: And if everybody did such things it could add a lot. According to Rattan Lal, from Ohio State, American soil could - at least in theory - capture more than a hundred million tons of carbon a year, enough to offset the emissions from half the cars in the country.
Prof. LAL: If we want to kick the carbon habit, as our president has asked, agriculture is an important part of the solution to rehabilitating our carbon civilization.
CHARLES: Lal says the real beauty of this is no-till farming or growing more grass and hay costs very little. Also farming this way helps the environment in lots of ways; the land becomes more of a sponge for water, less soil and fertilizer washes into nearby streams.
Prof. LAL: It's a truly win, win, win.
CHARLES: But as you can probably imagine, making this happen won't be easy. Farmers grow crops they can see and sell, not something invisible and hard to measure, like carbon in the ground. And scientists are still arguing about how much carbon some of these farming practices actually capture.
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CHARLES: In a small way, though, carbon farming has begun. Under a program run by the Iowa Farm Bureau, almost 2,000 farmers are getting paid a few dollars for every acre of their no-till land or pasture. The money comes from businesses that are trying to balance their greenhouse gas emissions. Right now, those businesses aren't paying a lot, but that could change, if Congress passes strict limits on greenhouse gas emissions. Then, farmers might actually earn some real money capturing carbon.
Dan Charles, NPR News.
HANSEN: And at our Web site, you can see videos of climate science in action from Public Television's Wild Chronicles - go to npr.org/climateconnections.