Can Dirt Really Save Us From Global Warming?
A farmer plants soybeans in an untilled field. - A farmer plants soybeans in an untilled field. No-till farming, in which crops are planted into last year's field stubble without plowing, has gained acceptance in the past two decades as a way to build organic matter, reduce erosion and control pesticides and fertilizers. (J.D. Pooley / AP)
This month the Senate is set to take up the climate and energy bill that Congress began work on last spring. One provision will likely set up a system to pay farmers for something called "no-till farming."
The concept: When crops are planted without tilling, the soil holds more carbon, which means less goes up into the atmosphere.
But scientists aren't sure no-till really sequesters carbon any better than conventional farming.
(J.D. Pooley / AP)
Soil scientist Michel Cavigelli of the U.S. Department of Agriculture agrees that no-till fields, like the one he studies in rural Maryland, can hold more carbon than plowed fields.
In part that's because the Maryland field has more organic matter — dead vegetation (mostly the residue from the previous crop), microorganisms, manure or compost.
"The percentage of organic matter in this soil is two percent," Cavigelli says of a no-till field of corn, "twice as much in some of the tilled systems, at the very surface."
But that is only at the surface. Researchers have discovered that when you dig down three feet or so, plowed fields hold just as much — if not more — carbon than no-till.
This is important because the energy bill would allow farmers to earn "offsets" if they practice no-till.
No-Till Offsets: A Fair Trade?
Offsets are like "get out of jail free" cards in Monopoly. If you do something that reduces carbon in the atmosphere, you earn an offset that you can sell to a company that would have to limit its carbon emissions if the bill becomes law. Each offset a company buys allows that company to emit more carbon at its own facilities.
But no-till only stores carbon as long as it isn't tilled. "If you till it, you can lose almost all the carbon you gained in the previous five years say with one tillage, even," says Cavigelli. "So one of the challenges is to maintain your no-till fields forever in essence to really gain the benefits of carbon sequestration."
Rattan Lal, a soil scientist at Ohio State University, says that's not what a lot of American farmers do. "The farmer plows one year and does no-till the next year."
But if it isn't tilled, Lal says, the no-till field can store more carbon than a plowed field if the conditions are just right — the right kind of soil, moisture, and soil temperature, for example.
The Question Of Residue
There's a possible conflict brewing here, though. Federal law and the energy bill encourage farmers to remove crop residue — the remains of the previous season's crop — to make ethanol.
"That's a no-no," Lal says. "The moment you take the crop residue away the benefit of no-till farming on erosion control, water conservation and on carbon sequestration will not be realized."
Nonetheless, Lal supports no-till for carbon offsets, mostly because when you don't plow, you use less fossil fuel to run equipment and make fertilizer.
These savings mean that no-till has a smaller "carbon footprint" than plowing.
Farm interests are eager to win offsets. They say the energy bill will raise their fuel costs across the board. The final list of what will be allowed in the bill could help swing votes when the Senate votes on the measure.
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RENEE MONTAGNE, host:
This is MORNING EDITION from NPR News. I'm Renee Montagne.
ARI SHAPIRO, host:
And I'm Ari Shapiro.
Here's one way to cut carbon emissions: bury the stuff in farm fields. The Senate is considering a plan that would pay farmers to do just that as part of a climate and energy bill. The bill would essentially raise the cost of any fuel that emits carbon dioxide, the main contributor to climate change. As a result, farmers would see higher prices for their fuel and fertilizer. The payments for burying the carbon on their land would soften the blow, as NPR's Christopher Joyce reports.
CHRISTOPHER JOYCE: The American Clean Energy and Security Act aims to make companies reduce the amount of carbon dioxide they emit or be penalized. Reducing emissions can be hard and expensive, so the bill creates something called an offset. It's kind of like a get out of jail card in Monopoly.
A company could offset its emissions by paying someone else to get rid of carbon instead. Someone who can do it more cheaply. Secretary of Agriculture Tom Vilsack recently told Congress that farmers would be delighted to get paid to store some of that carbon.
Secretary TOM VILSACK (Department of Agriculture): They'll be able through the use of land, through cover crops, through altering how they use fertilizer to how they raise livestock to what they do what they do with their land. I mean, there are a series of steps that can be taken and will be taken that will generate opportunities for offsets.
JOYCE: A good place to store carbon is in dirt, something farmers have a lot of. Dirt is full of organic matter, plant residue, microorganisms, earthworms. It's chock full of carbon. And theoretically, if you don't till the field more of the carbon stays put. Guided by that belief, members of Congress want to allow farmers to sell offsets earned by no-till farming. Does it work? Scientists say maybe.
Dr. MICHEL CAVIGELLI (Soil scientist, United States Department of Agriculture): My name is Michel Cavigelli. I'm a soil scientist with the U.S.D.A. in Beltsville, Maryland.
JOYCE: Cavigelli shows me a no-till plot.
Dr. CAVIGELLI: We have a corn crop on our left and we have a soybean crop on our right. We might want to go inside the field a little bit. Ok. So I'm digging up the soil. You'll notice that when I break it apart it breaks apart relatively easily. It's not a hard block like a brick.
JOYCE: Compared to a plowed field, this one has lots of dead vegetation in and on top of the dirt.
Dr. CAVIGELLI: The percentage of organic matter in this soil, for example, is two percent, twice as much as in some of the tilled systems, at the very surface.
JOYCE: At the surface and down to about four inches or so. And the carbon will stay put if it isn't plowed. Plowing exposes the soil's organic matter to the air. It breaks down and the carbon goes up into the atmosphere.
Dr. CAVIGELLI: If you till it, you can lose almost all the carbon you gained in the previous five years say with one tillage, even. So one of the challenges is to maintain your no-till fields forever, in essence, to really gain the benefits of carbon sequestration.
JOYCE: But that doesn't fit in with the kind of no-till that most American farmers practice.
Dr. RATTAN LAL (Soil scientist, Ohio State University): The reason is farmers plow one year and does no-till the next year.
JOYCE: That's Rattan Lal, a soil scientist at Ohio State University. Moreover, Lal says research finds that no-till fields actually don't store any more carbon than plowed fields if you look deeper - say three feet down.
So do no-till fields really qualify as carbon offsets? Lal says they can store more carbon than a plowed field if the conditions are just right — the right kind of soil and soil temperature, for example.
There's a possible conflict brewing here, though. Federal law and the energy bill encourage farmers to remove crop residue to make ethanol. And, says Lal…
Dr. LAL: That's a no-no. The moment you take the crop residue away the benefit of no-till farming on erosion control, water conservation, on carbon sequestration - will not be realized.
JOYCE: Nonetheless, Lal supports no-till for carbon offsets, mostly because of how no-till fields are planted. When you don't plow, you use less fossil fuel to run equipment and make fertilizer.
Dr. LAL: Saving in diesel, saving in labor, saving in fertilizer consumption, saving in time.
JOYCE: These savings mean that no-till has a smaller carbon footprint than plowing.
Farm interests are eager to win offsets for farmers. In part, because they say the energy bill will raise their fuel costs across the board. The final list of what will be allowed in the bill could help win supporters when the Senate on the measure.
Christopher Joyce, NPR News. Transcript provided by NPR, Copyright National Public Radio.
