Updated April 17, 2012

Last November, University of Wyoming economist Ben Rashford traveled across North Dakota to see the area's famed prairie pothole region, a patchwork of wetlands and grass running from Iowa up through the Dakotas into eastern Montana. He rode with a member of the conservation group Ducks Unlimited, who showed him the potholes "in all their glory. Ducks were everywhere." But Rashford noted a profound transformation taking place: "Every couple miles there would be a big section ... that was being transformed into crops."

Rashford is trying to figure out why, working with conservationists worried that some of America's last remaining native grasslands are falling victim to that historic destroyer of prairie: the plow.

Although some Northern Plains prairie is publicly owned and protected, much of it is private property. Well-managed grazing on this mixed and shortgrass prairie can maintain native plant cover, allowing birds and other wildlife like black-tailed prairie dogs to thrive, says Brian Martin, director of science at The Nature Conservancy's Montana office.

Today, though, ranchers and farmers -- particularly in the Dakotas -- are tearing up their native grassland and planting it row to row. "Some of the conversions maybe started happening as early as 20 years ago, but it's really accelerated the last five years," says Lyle Perlman, a South Dakota farmer. Corn is selling for over $6 a bushel right now, nearly double its 2007 price. The causes of this "corn bubble," which drives all agricultural commodity prices higher, are varied, and include uncontrollable factors like weather and population growth. But federal policies also play a role. As the 2012 Farm Bill debate gears up, conservationists are determined to change the rules and better protect the prairie.

While sodbusting is clearly increasing, no one knows how much native grassland is being broken. The Farm Service Agency, a branch of the U.S. Department of Agriculture, was redirected to track this information after a 2007 Government Accountability Office report highlighted sodbusting as a problem. But the agency has not done so, saying the request lacks both funding and clear instructions. Rashford and his colleagues have thus had to rely on computer models; their modeling of the period from 2006-2011 estimated nearly 1.8 million acres of plowed-up grassland in the prairie pothole region -- and that was based on a slower increase in crop prices than has actually occurred. The Nature Conservancy gauges the annual rate of grassland destruction in this region at 1.1 percent -- higher than the rate of deforestation in the Amazon.

One controversial policy upping corn prices is the renewable fuels standard, which requires a portion of transportation fuel to come from biofuels. This "ethanol mandate" boosted requirements from 4 billion gallons of biofuels a year in 2006 to 15.2 billion gallons in 2012, raising demand for corn.

Subsidized crop insurance, where taxpayers cover 60 percent of farmers' premium costs, also encourages sodbusting. The program is part of the Farm Bill, which authorizes federal funding for a variety of subsidy and conservation programs. Crop insurance is not predicated on disaster; farmers can simply insure at a guaranteed rate of revenue -- $6 per bushel for corn, say -- and if their income dips below around 70 percent of that, they collect. When corn prices are high, the temptation to plow up new land and insure it for that guaranteed revenue grows. In 2008, conservation groups sought a sodsaver provision in the Farm Bill, which would have made newly plowed ground in prairie states ineligible for federal subsidies, including crop insurance, until it had been farmed for five years. At the last minute, this clause was made voluntary, only taking effect if state governors chose to implement it. Not one governor has.

There are other factors involved; aging ranchers, for example, are more likely to turn their grazing land over to crops. "It is real work to run livestock, and historically it has not been as profitable (as crops)," says Perlman. New strains of drought-tolerant, short-season, Roundup-ready corn have more than doubled yields, making corn profitable on the Northern Plains. The increased demand for organic crops also plays a role, since farmers breaking native ground don't have to wait three years to become certified organic.

Countering the tide of plowups is a cadre of hunting groups, conservation groups both small and large, and a few government programs that pay ranchers to keep land in grass or maintain wildlife habitat. In Montana, the federal Natural Resources Conservation Service is working to purchase easements where sodbusting is likely to harm sage grouse habitat. The Nature Conservancy-owned Matador Ranch grass bank lets ranchers graze cattle on its land at a discount, in return for them preserving prairie and undertaking conservation measures on their own property. And groups like Ducks Unlimited, the Isaak Walton Foundation and the National Wildlife Federation are working to get the failed 2008 sodsaver provision implemented in the 2012 Farm Bill, now being discussed in Congress.

But the powerful crop insurance lobby and most farmers' groups strongly oppose tying sodsaver and other conservation measures to eligibility for taxpayer-funded programs like crop insurance. "If they are going to tell us how to farm, then they should probably buy the seed and the fertilizer and everything else," says Rocky Mountain Farmers Union president Kent Peppler.

Yet in the absence of a sodsaver provision, private and government-funded conservation initiatives will likely fail to counter the effects of the corn bubble. "(Government incentives are) still a long way from leveling the playing field," says Perlman, "in terms of getting the profitability of grasslands to a point where people are encouraged to do the right thing."

Correction: Due to a miscalculation in economist Ben Rashford's model, an earlier version of this article included a massive overestimate of the number of acres of grassland converted to cropland in the Dakotas and Montana from 2006 to 2011. The correct number of estimated acres plowed up is 1.8 million, not 30 million as the original article stated; this is still a very significant amount of lost prairie, Rashford says.