ROSCOE, S.D. — Robert Malsam nearly went broke in the 1980s when corn was cheap. So now that prices are high and he can finally make a profit, he’s not about to apologize for ripping up prairieland to plant corn.
Across the Dakotas and Nebraska, more than 1 million acres of the Great Plains are giving way to corn fields as farmers transform the wild expanse that once served as the backdrop for American pioneers.
This expansion of the Corn Belt is fueled in part by America’s green energy policy, which requires oil companies to blend billions of gallons of corn ethanol into their gasoline. In 2010, fuel became the number one use for corn in America, a title it held in 2011 and 2012 and narrowly lost this year. That helps keep prices high.
‘‘It’s not hard to do the math there as to what’s profitable to have,’’ Malsam said. ‘‘I think an ethanol plant is a farmer’s friend.’’
What the green-energy program has made profitable, however, is far from green. A policy intended to reduce global warming is encouraging a farming practice that actually could worsen it.
That’s because plowing into untouched grassland releases carbon dioxide that has been naturally locked in the soil. It also increases erosion and requires farmers to use fertilizers and other industrial chemicals. In turn, that destroys native plants and wipes out wildlife habitats.
It appeared so damaging that scientists warned that America’s corn-for-ethanol policy would fail as strategy to combat global warming if too many farmers plowed over virgin land.
The Obama administration argued that would not happen. But the administration didn’t set up a way to monitor whether it actually happened.
More than 1.2 million acres of grassland have been lost since the federal government required that gasoline be blended with increasing amounts of ethanol, an Associated Press analysis of satellite data found. Plots that were wild grass or pastureland seven years ago are now corn and soybean fields.
In South Dakota, more than 370,000 acres of grassland have been uprooted and farmed since 2006. In Edmunds County, a rural community about two hours north of the capital, Pierre, at least 42,000 acres of grassland have become cropland — one of the largest turnovers in the region.
Malsam runs a 13-square-mile family farm there. He grows corn, soybeans, and wheat, then rents out his grassland for grazing. Each year, the family converts another 160 acres from grass to cropland.
Chemicals kill the grass. Machines remove the rocks. Then tractors plow it three times to break up the sod and prepare it for planting.
Scattered among fields of 7-foot tall corn and thigh-high soybeans, some stretches of grassland still exist. Cattle munch on some grass. And ‘‘prairie potholes’’ — natural ponds ranging from small pools to larger lakes — support a smattering of ducks, geese, pelicans, and herons.
Yet within a mile of Malsam’s farm, federal satellite data show, more than 300 acres of grassland have been converted to soybeans and corn since 2006.
Jeff Lautt, chief executive of Poet, which operates ethanol refineries across the country, including in South Dakota, said it’s up to farmers how to use their land.
‘‘The last I checked, it is still an open market. And farmers that own land are free to farm their land to the extent they think they can make money on it or whatever purpose they need,’’ he said.
Corn prices more than doubled in the years after Congress passed the ethanol mandate in 2007. Now, Malsam said, farmers can make about $500 an acre planting corn.