Under the RFS, crops that are grown on land transformed for farming after 2007 aren't supposed to be converted into part of the nation's fuel supply. The Environmental Protection Agency is even tasked with keeping tabs on newly converted areas to make sure. Using satellite images and government surveys, the authors of this study undertook their own, more-detailed examination of the changes in farmland from 2008-2012 to see if the fields were growing.
They found that US cropland increased by a net 2.98 million acres in those four years. The gross change was an extra 7.34 million acres because 4.36 million acres of existing farmland was removed from production in that time. Around 77 percent of this area used to be grassland, and the center of the country saw much of the transformation.
When the time came to cultivate this converted land, the first choice was corn (which ended up on 26.6 percent of the land), wheat (24.5 percent) and soybeans (20.2 percent). The study didn't investigate to see how these crops were used, but two of them have frequently used to produce ethanol. "Up to 1.9 million acres of new corn plantings and 1.5 million acres of new soy could be ineligible as renewable biomass," as part of the RFS, the authors wrote.
The study suggests that the EPA needs to look at how it determines change in farmland and possibly change it. You can view this study's abstract and download it all to read for yourself, here.