A new study by Christopher Wright and Michael Wimberly of South Dakota State University found that U.S. farmers converted more than 1.3 million acres of grassland into corn and soybean fields from 2006 to 2011, driven by high crop prices and biofuel mandates. In states such as Iowa and South Dakota, about 5 percent of pasture is turning into cropland each year.
The authors concluded that the rates of grassland loss are "comparable to deforestation rates in Brazil, Malaysia, and Indonesia.
For one, farmers are growing crops on increasingly marginal land. In Nebraska and the Dakotas, corn and soy are planted in areas that are especially vulnerable to drought. But farmers take the risk because corn and soy have become so lucrative - and, in part, because the federal government offers subsidized crop insurance in case of failure. (The study also found evidence that many farmers are no longer enticed by federal conservation programs that pay for grassland cover.)
The loss of pasture itself also could have a big environmental impact. Studies have found that grasslands hold carbon in their soil better than cropland does, so there is a climate-change angle.
There is a wildlife angle, too: The Prairie Pothole Region, traversing Minnesota and the Dakotas, is one of the continent's key breeding grounds for ducks and other ground-nesting birds. Tall grasses in the area help sustain a number of species and shield birds from predators. But corn fields are encroaching on the habitat, and bird populations are dropping.
In recent years, some environmental groups have argued that it does not make sense for the federal government to keep subsidizing this push into the prairies. A recent report from the Environmental Working Group (EWG), for instance, argued that Congress should scale back crop insurance for farmers who move into the country's grasslands and wetlands. Farm groups, for their part, say the insurance is vital for their work. Instead, they say, Congress should expand conservation programs.
And what about biofuels? Groups such as EWG have criticized ethanol mandates for pushing up corn and soybean prices and driving the crop boom. There is a lot more hope for next-generation cellulosic biofuels grown from switchgrass or other plants with a much smaller environmental footprint. Or biodiesel made from algae, say. But until those become viable, the crop rush continues.