As the year winds down, we here at NPR are looking at a few key numbers that explain the big trends of 2013.
Today's number: 1.6 million.
That's 1.6 million acres — about the area of the state of Delaware.
That's how much land was removed this year from the federal Conservation Reserve Program, or CRP, which pays farmers to keep land covered with native grasses or sometimes trees. Most of that land now will produce crops like corn or wheat.
It's a sign of the shifting economic tides that are transforming America's farming landscape.
If you drive through farm country, especially in the northern plains, you'll see large fields covered with grass.
The federal government is paying for much of that grass. The U.S. Department of Agriculture pays farmers to plant permanent vegetation, usually native grasses, on that land instead of crops. This brings back a little bit of the prairie, which comes with all kinds of environmental benefits.
In 2005, I spent several days touring CRP land in both North Dakota and Kansas. In North Dakota, biologist Ron Reynolds, then with the U.S. Fish and Wildlife Service, led me into a field of tall grass. He pulled back some of the grass and showed me a nest with seven duck eggs. "The eggs are warm," he said. "You can feel the eggs. [The mother duck] is just starting to incubate."
Reynolds was ecstatic about how CRP fields were helping to bring back duck populations.
But ducks are only the start of it.
"Goodness, there's thousands of species that live in grasslands, including several hundred species of higher plants," says Carter Johnson, an ecologist at South Dakota State University in Brookings, S.D. Plus, permanent grass cover keeps soil from washing away.
"With those deeps roots that grasses have, and thick thatch, the water has a hard time getting a hold of the soil," says Johnson.
So more land in CRP means cleaner streams, less fertilizer runoff and more carbon stored in the soil.
Back when Reynolds was showing me those duck eggs, there were 34 million acres enrolled in the CRP — an area roughly the size of the state of New York.
In recent years, though, the conservation reserve has shrunk by more than 25 percent, including those 1.6 million acres that farmers took out of the program this past year.
It's partly because Congress has cut funding for the program. But there's a more important reason: high grain prices.
Farmers have been making a lot of money recently growing corn, soybeans, and wheat. They're bidding up prices for land, and landowners are cashing in.
In southwestern Iowa, near the town of Stanton, the owners of about 60 acres decided to take it out of the CRP. They rented it instead to farmer Mark Peterson. "They felt that it would make more income for them, renting it out, than it would being in the CRP," says Peterson.
Peterson recognizes that "it is fragile ground," so he says he'll be extra careful with that land, which is on a hillside. Some parts are quite steep, and the soil could easily wash away.
He grew soybeans on it this year, but he tried to disturb the soil as little as possible. And he'll plant cover crops in the off season to anchor the soil.
Ecologist Johnson, at South Dakota State University, says the shrinking Conservation Reserve is just one part of a larger trend: Farmers are ripping up other grasslands, too, including native prairie that never was plowed.
"I've seen things that I never thought I'd see here in South Dakota," he says. "With these land prices going up, there actually are people out there with Bobcats and front end loaders, pulling out the rocks in hundreds of acres of land that's been in pasture all these years."
Taking all this land, he says, and planting crops on it, just has to be a bad thing for water quality, soil erosion and wildlife.
The shrinking CRP is a cause for concern, says Jason Weller, who's in charge of the environmental conservation programs at the U.S. Department of Agriculture. "But I think it's important that there's a lot of other approaches that we can take to manage, not just the soil and water, but also these wildlife populations."
His agency, the USDA's Natural Resources Conservation Service, has experts in almost every county, working with farmers. They offer farmers advice on how to reduce soil erosion and provide habitat for wildlife.
For instance, land that's coming out of the CRP doesn't have to go into crops, Weller says. Some farmers may want to use it to graze cattle. "We have assistance we can then provide to them, so we can keep that land in grass," he says.
There's a growing demand for more food and biofuel, Weller says, and farmers are responding to that demand. Most of them also want to protect soil, streams and wildlife, he says.
Yet it can be difficult to do both.