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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.