Corydon - The hills of southern Iowa bear the scars of America's push for green energy: The brown gashes where rain has washed away the soil. The polluted streams that dump fertiliser into the water supply.Even the cemetery that disappeared like an apparition into a cornfield.It wasn't supposed to be this way.With the Iowa political caucuses on the horizon in 2007, presidential candidate Barack Obama made home-grown corn a centrepiece of his plan to slow global warming. When President George W Bush signed a law that year requiring oil companies to add billions of gallons of ethanol to their gasoline each year, Bush predicted it would make the country "stronger, cleaner and more secure".But the ethanol era has proven far more damaging to the environment than politicians promised and much worse than the government admits today.As farmers rushed to find new places to plant corn, they wiped out millions of acres of conservation land, destroyed habitat and contaminated water supplies, an Associated Press investigation found.Two million hectares of land set aside for conservation - more than Yellowstone, Everglades and Yosemite National Parks combined - have been converted on Obama's watch.Landowners filled in wetlands. They ploughed into pristine prairies, releasing carbon dioxide that had been locked in the soil.Sprayers pumped out billions of pounds of fertiliser, some of which seeped into drinking water, polluted rivers and worsened the huge dead zone in the Gulf of Mexico where marine life can't survive.‘Raping the land’The consequences are so severe that environmentalists and many scientists have now rejected corn-based ethanol as bad environmental policy. But the Obama administration stands by it, highlighting its benefits to the farming industry rather than any negative consequences.All energy comes at a cost. The environmental consequences of drilling for oil and natural gas are well documented and severe. But in the president's push to reduce greenhouse gases and curtail global warming, his administration has allowed so-called green energy to do not-so-green things.In some cases, such as the decision to allow wind farms that sometimes kill eagles, the administration accepts environmental costs because they pale in comparison to the havoc global warming could ultimately cause.In the case of ethanol, the administration believes it must encourage the development of next-generation biofuels that will someday be cleaner and greener than today's."That is what you give up if you don't recognise that renewable fuels have some place here," EPA administrator Gina McCarthy said. "All renewable fuels are not corn ethanol."But next-generation biofuels haven't been living up to expectations. And the government's predictions on ethanol have proven so inaccurate that independent scientists question whether it will ever achieve its central environmental goal: reducing greenhouse gases.That makes the hidden costs even more significant."They're raping the land," said Bill Alley, a Democratic member of the board of supervisors in Wayne County, Iowa, which now bears little resemblance to the rolling cow pastures shown in postcards sold at a Corydon town pharmacy.Billion pound increaseThe numbers behind the ethanol mandate have become so unworkable that, for the first time, the EPA is soon expected to reduce the amount of ethanol required to be added to the gasoline supply. An unusual coalition of big oil companies, environmental groups and food companies is pushing the government to go even further and reconsider the entire ethanol programme.But the Obama administration stands by the mandate and rarely acknowledges that green energy requires any trade-offs."There is no question air quality, water quality is benefiting from this industry," Agriculture Secretary Tom Vilsack told ethanol lobbyists recently.But the administration has never conducted studies to determine whether that's true.Fertiliser, for instance, can make drinking water toxic. Children are especially susceptible to nitrate poisoning, which causes "blue baby" syndrome and can be deadly.Between 2005 and 2010, corn farmers increased their use of nitrogen fertiliser by more than a billion pounds. More recent data isn't available from the Agriculture Department, but conservative projections suggest another billion-pound increase since then.In the Midwest, where corn is the dominant crop, some are sounding alarms.The Des Moines Water Works has faced high nitrate levels for many years in the Des Moines and Raccoon rivers, which supply drinking water to 500 000 people. Typically, when pollution is too high in one river, workers draw from the other."This year, unfortunately the nitrate levels in both rivers were so high that it created an impossibility for us," said Bill Stowe, the utility's general manager.For three months this summer, huge purifiers churned around the clock to meet demand for safe, clean water.Dubious policyObama's support for ethanol dates to his time as a senator from Illinois, the nation's second-largest corn producer."If we're going to get serious about investing in our energy future, we must give our family farmers and local ethanol producers a fair shot at success," Obama said in 2007.From the beginning of his presidential administration, however, Obama's environmental team saw corn ethanol as a dubious policy. Corn demands fertiliser, which is made using natural gas. What's worse, ethanol factories typically burn coal or gas, both of which release carbon dioxide.Then there's the land conversion, the most controversial and difficult-to-predict outcome.Digging up grassland releases greenhouse gases, so environmentalists are sceptical of anything that encourages planting more corn."I don't remember anybody having great passion for this," said Bob Sussman, who served on Obama's transition team and recently retired as the Environmental Protection Agency's senior policy counsel. "I don't have a lot of personal enthusiasm for the programme."There was plenty enthusiasm at the White House and at the Department of Agriculture, where officials argued to the EPA that ethanol was cleaner than it thought. The EPA ultimately agreed.The policy hinged on assumptions that corn prices would not go too high and farms would get more efficient. That way, there wouldn't be much incentive to plow untouched areas and destroy conservation land.But corn prices climbed to more than $7 a bushel, about twice the administration's long-term prediction. Suddenly, setting aside land for conservation was bad economics for many farmers."I'm coming to the point where financially, it's not feasible," said Leroy Perkins, a farmer in Wayne County who set aside 37ha years ago and let it grow into high grass.Losing millions of conservation acres was bad. Ploughing over untouched prairies was worse.Still cleaner than oilUsing satellite data - the best tool available - The Associated Press identified at least 490 000ha of virgin land in Nebraska and the Dakotas that have been converted to corn and soybean fields since 2006."The last five years, we've become financially solvent," said Robert Malsam, a farmer in Edmunds County, South Dakota, who like others in the Dakotas has ploughed wild grassland to expand his corn crop.The government could change the mandate or demand more safeguards. But that would pick a fight with agricultural lobbyists and would put the administration on the side of oil companies, which despise the ethanol requirement.Bob Dinneen, president of the Renewable Fuels Association, the ethanol lobbying group, said there's no reason to change anything. Ethanol is still cleaner than oil, he said.These days, when administration officials discuss ethanol, they often frame it as an economic programme for rural America, not an environmental policy.When Obama gave a major speech in June on reducing greenhouse gas, biofuels received only a passing reference.With the government's predictions so far off from reality, scientists say it's hard to argue for ethanol as global warming policy."I'd have to think really hard to come up with a scenario where it's a net positive," said Silvia Secchi, a Southern Illinois University agriculture economist.She paused, then added: "I'm stumped."