MINNEAPOLIS — Minnesota converted more wetlands into farmland than any other state when crop prices spiked between 2008 and 2012, according to a new study by University of Wisconsin-Madison researchers.

About 250,000 acres, or nearly 400 square miles, were converted to row crops, according to Minnesota Public Radio News reports. Most was grassland, but 25,000 acres were wetlands — more than any other state.

“In the Midwest we saw a lot of croplands expanding outside the traditional corn belt area, and Minnesota in particular was a key hot spot of land conversion,” said Tyler Lark, a university graduate student and the study’s lead author. “Much of the conversion came at the cost of natural ecosystems.”

Also, 13,000 acres of forests were converted — the second largest forest conversion in the country.

The study, which used satellite data from three different sources to analyze land conversion, was published Thursday in the journal Environmental Research Letters.

The study estimated that 7.3 million acres were converted nationwide. According to the study, the increased carbon emissions from the additional corn and soybean crops alone would be equal to a year’s emissions from 34 coal-fired power plants.

The high corn and soybean prices came after the federal Renewable Fuel Standard took effect. The standard calls for a certain amount of ethanol and other renewable fuels to be added to gasoline. Part of the policy’s goal was to reduce greenhouse gas emissions, but some environmental groups have argued the standard is coming up short in that regard because of the consequences of land conversion.

The study also found that converted land was often considered “marginal.”

“This marginal land is often characterized by increased risks for erosion, flooding or drought, and as such can have much greater consequences of cultivating new croplands as opposed to preexisting cropland area,” Lark said.

Corn and soybean prices have dropped since the study period, so Lark said it will be interesting to see what effect that has on land conversion.

The new federal Farm Bill limits the number of acres where farmers can earn money for keeping land as grasslands, wetlands or forests.