While federal ethanol subsidies expired last year, the Obama Administration’s strict clean fuel standards still give farmers across the United States an incentive to plant corn — to the detriment of the environment.

The Associated Press reports that “across the Dakotas and Nebraska, more than one million acres of the Great Plains are giving way to cornfields as farmers transform the wild expanse that once served as the backdrop for American pioneers.”

The physical expansion of the American Midwest, the world’s largest contiguous piece of farmland, is fueled by a green energy policy that requires oil companies to blend billions of gallons of corn ethanol into their gasoline, keeping prices high.

The administration ignored warnings from scientists that its more stringent policy could end up raising emissions if too many farmers plowed over virgin lands — and accelerate aquifer depletion as a result of increased irrigation.

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.

The Associated Press estimates that some 1.2 million acres of grassland have been lost since the Renewable Fuel Standard was introduced.

Nearly half of America’s corn crop is used to produce ethanol. The rising price of corn makes other products, including breakfast cereal, dairy and eggs, more expensive as well.