Corn Belt farming gives a boost to the global carbon cycle

Crops in the Midwest take in and give off so much carbon that the impact can be seen across the northern hemisphere. (Photo courtesy Flickr/USDA NRCS South Dakota)
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January 22, 2015 - 6:45am

Scientists have noticed a change in the atmosphere. Plants are taking in more carbon dioxide during the growing season and giving off more carbon in the fall and winter. What researchers hadn’t considered, until recently, is how farming factors in.

You can find the carbon cycle at work almost anywhere around you. For instance, in the middle of an empty corn field.

On a sunny winter day I walked with Andy Suyker, a micro-meteorologist from the University of Nebraska Lincoln, across a bare, brown field over crunching corn stalks. The field looked like any other until we came to a weather tower covered with buzzing sensors and spinning anemometers.

“We have a carbon dioxide and water vapor sensor, and it’s continuously measuring CO2 concentration [and] water vapor concentration,” Suyker said.

Readings from the research station in eastern Nebraska measure the movement of carbon dioxide, 10 times each second, 24 hours a day, 7 days a week. And it’s been running for the last 15 years.

To the untrained eye, it looks like nothing is happening in a windblown corn field in the dead of winter. But the data tells Suyker otherwise.

Andy Suyker says factors ranging from temperature and rainfall to soil type and crop variety can influence how much carbon is used by plants. (Photo by Grant Gerlock, NET News/Harvest Public Media)

The sensors on this weather station constantly track the carbon cycle, the amount of carbon dioxide being absorbed by plants in the summer and then given off during the winter. (Photo by Grant Gerlock, NET News/Harvest Public Media)

“The ecosystem during the non-growing season period is, in a sense, it’s exhaling carbon dioxide,” Suyker said.

Over the winter, corn stalks and roots break down sending CO2 into the air. Then in the summer when a new crop is growing, it takes up carbon from the atmosphere.

“So that’s like breathing in,” Suyker said. “There’s this constant breathing in, taking up carbon dioxide, and breathing out, releasing carbon dioxide.”

That’s the carbon cycle. It’s different than fossil fuel emissions. This is a give and take with CO2 constantly shifting between plants and the air.

About 20 years ago, scientists realized the peaks and valleys of the carbon cycle are reaching higher - and lower - levels.

“The depth of that breath has gotten bigger,” said Joshua Gray, who studies the carbon cycle at Boston University. “So the CO2 concentrations go down a little bit more in summer than they used to, and they go up a little bit more in the winter than they used to.”

The seasonal concentrations are up to 50 percent higher, or lower, in the northern hemisphere.  

Most of the increase is due to a longer growing season brought on by a warming climate. But in a recent article in the journal Nature, Gray and his colleagues uncovered another human impact on the carbon cycle – farming.

Gray says scientists overlooked farming before. It only covers 6 percent of the land in the area he studied. But he found it accounts for a quarter of the increase to the carbon cycle.

“It’s surprising and not surprising all at the same time,” Gray said. “Surprising to get the result, and then you say, well of course, we have 3 times as much corn as we did 50 years ago. Of course this is going on.”

Farming has made huge strides in northern China, and the U.S. Corn Belt. Farmers use better equipment and plant more productive crop hybrids. They have more effective chemicals to control weeds and they support their crops with more irrigation and fertilizer.

The fact that farming feeds the carbon cycle does not mean it’s making climate change worse. But, when it comes to reversing climate change, Gray says growing wheat or corn does less to sequester carbon than growing a forest or grassland.

“We’re not gaining more long-term carbon in the soil or anything like that by growing more corn like we might with growing more oak trees,” Gray said.

But what if carbon-hungry corn plants did store CO2 underground? The U.S. Department of Agriculture along with conservation groups has been trying to develop methods of carbon farming, ways to use agriculture to remove carbon pollution from the air.

It’s challenging. Scientists disagree on how to measure the impact of different farming techniques. Plus, Gray says, crops weren’t designed for storing carbon.

“Crop breeding has tried to say, ‘If you take a kilogram of carbon out of the air I want as much of that kilogram to go into the thing I want to eat as possible.’ Now, this is at odds with sequestering carbon in the soil where you’d want to put as much carbon as possible in the roots,” Gray said.

Still, there is great potential. UNL’s Andy Suyker explains that corn, the region’s top crop, is a world-class carbon consumer.

“In fact a corn crop, when it’s taking up [its] peak amount of carbon dioxide, it will take up as much CO2 as an Amazon forest,” Suyker said

As research continues, scientists want to find a way to leverage that skill and take more carbon from the atmosphere and put it under the Corn Belt.



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