This article was produced in partnership with Floodlight

For decades, corn has reigned over American agriculture. It sprawls across 90m acres – about the size of Montana – and goes into everything from livestock feed and processed foods to the ethanol blended into most of the nation’s gasoline.

But a growing body of research reveals that the US’s obsession with corn has a steep price: the fertilizer used to grow it is warming the planet and contaminating water.

Corn is essential to the rural economy and to the world’s food supply, and researchers say the problem isn’t the corn itself. It’s how we grow it.

Corn farmers rely on heavy fertilizer use to sustain today’s high yields. And when the nitrogen in the fertilizer breaks down in the soil, it releases nitrous oxide, a greenhouse gas nearly 300 times more potent than carbon dioxide. Producing nitrogen fertilizer also emits large amounts of carbon dioxide, adding to its climate footprint.

The corn and ethanol industries insist that rapid growth in ethanol – which now consumes 40% of the US corn crop – is a net environmental benefit, and they strongly dispute research suggesting otherwise.

Industry is also pushing for ethanol-based jet fuel and higher-ethanol gasoline blends as growth in electric vehicles threatens long-term gasoline sales.

Agriculture accounts for more than 10% of US greenhouse gas emissions, and corn uses more than two-thirds of all nitrogen fertilizer nationwide – making it the leading driver of agricultural nitrous oxide emissions, studies show.

Since 2000, US corn production has surged almost 50%, further adding to the crop’s climate impact.

The environmental costs of corn rarely make headlines or factor into political debates. Much of the dynamic traces back to federal policy – and to the powerful corn and ethanol lobby that helped shape it.

The Renewable Fuel Standard (RFS), passed in the mid-2000s, required that gasoline be blended with ethanol, a biofuel that in the United States comes almost entirely from corn. That mandate drove up demand and prices for corn, spurring farmers to plant more of it.

Many plant corn year after year on the same land. The practice, called “continuous corn”, demands massive amounts of nitrogen fertilizer and drives especially high nitrous oxide emissions.

At the same time, federal subsidies make it more lucrative to grow corn than to diversify. Taxpayers have covered more than $50bn in corn insurance premiums over the past 30 years, according to federal data compiled by the Environmental Working Group.

Researchers say proven conservation steps – such as planting rows of trees, shrubs and grasses in cornfields – could sharply reduce these emissions. But the Trump administration has eliminated many of the incentives that helped farmers try such practices.

Experts say it all raises a larger question: if the US’s most widely planted crop is worsening climate change, shouldn’t we begin growing it in a different way?

How corn took over the US

In the late 1990s, the US’s corn farmers were in trouble. Prices had cratered amid a global grain glut and the Asian financial crisis. A 1999 report by the Federal Reserve Bank of Minneapolis said crop prices had hit “rock bottom”.

Corn production really took off in the 2000s after federal mandates and incentives helped turn much of the US’s corn crop into ethanol.

In 2001, the US Department of Agriculture launched the bioenergy program, which paid ethanol producers to increase their use of farm commodities for fuel. Then the 2002 farm bill created programs supporting ethanol and other renewable energy.

Corn growers soon mounted an all-out campaign to persuade Congress to require that gasoline be blended with ethanol, arguing it cut greenhouse gasses, reduced oil dependence and revived rural economies.

“I started receiving calls from Capitol Hill saying: ‘Would you have your growers stop calling us? We are with you,’” Jon Doggett, then the industry’s chief lobbyist, said in an article published by the National Corn Growers Association. “I had not seen anything like it before and haven’t seen anything like it since.”

In 2005, Congress created the RFS, which requires adding ethanol to gasoline, and expanded it two years later. The amount of corn used for ethanol domestically has more than tripled in the past 20 years.

When demand for corn spiked as a result of the RFS, it pushed up prices worldwide, said Tim Searchinger, a researcher at Princeton University’s School of Public and International Affairs. The result, Searchinger said, was more land cleared to grow corn. The Global Carbon Project found that nitrous oxide emissions from human activity rose 40% from 1980 to 2020.

In the United States, “king corn” became a political force. Since 2010, national corn and ethanol trade groups have spent more than $55m on lobbying and millions more on political donations to Democrats and Republicans alike, according to campaign finance records analyzed by Floodlight.

In 2024 alone, those trade groups spent twice as much on lobbying as the National Rifle Association. Now the sectors are pushing for the next big prize: expanding higher-ethanol gasoline blends and positioning ethanol-based jet fuel as aviation’s “low-carbon” future.

Research undercuts ethanol’s clean-fuel claims

Corn and ethanol trade groups did not respond to requests for interviews. But they have long promoted corn ethanol as a climate-friendly fuel.

The Renewable Fuels Association cites government and university research that finds burning ethanol reduces greenhouse gas emissions by roughly 40%-50% compared with gasoline. The ethanol industry says the climate critics have it wrong – and that most of the corn used for fuel comes from better yields and smarter farming, not from plowing up new land. The amount of fertilizer required to produce a bushel of corn has dropped sharply in recent decades, they say.

“Ethanol reduces carbon emissions, removing the carbon equivalent of 12 million cars from the road each year,” according to the Renewable Fuels Association.

Growth Energy, a major ethanol trade group, said in a written statement to Floodlight that US farmers and biofuel producers are “constantly finding new ways to make their operations more efficient and more environmentally beneficial”, using things like cover crops to reduce their carbon footprint. “Biofuel producers are making investments today that will make their products net-zero or even net negative in the next two decades,” the statement said.

Some research tells a different story.

A recent Environmental Working Group report finds that the way corn is grown in much of the midwest – with the same fields planted in corn year after year – carries a heavy climate cost.

And research in 2022 by agricultural land use expert Tyler Lark and colleagues links the Renewable Fuel Standard to worsening water pollution and increased emissions, concluding the climate impact is “no less than gasoline and likely at least 24% higher”.

Lark’s research has been disputed by scientists at the Argonne National Laboratory, Purdue University and the University of Illinois, who published a formal rebuttal arguing the study relied on “questionable assumptions” and faulty modeling – a charge Lark’s team has rejected.

One recent study found that solar panels can generate as much energy as corn ethanol on roughly 3% of the land.

“It’s just a terrible use of land,” Searchinger, the Princeton researcher, said of ethanol. “And you can’t solve climate change if you’re going to make such terrible use of land.”

Nitrogen polluting rural drinking water

The nitrogen used to grow corn and other crops is also a key source of drinking water pollution, experts say.

According to a new report by Clean Wisconsin and the Alliance for the Great Lakes, more than 90% of nitrate contamination in Wisconsin’s groundwater is linked to agricultural sources – mostly synthetic fertilizer and manure.

In 2022, Tyler Frye and his wife moved into a new home in the rural village of Casco, Wisconsin, about 20 miles (32km) east of Green Bay. Testing found their well water had nitrate levels more than twice the EPA’s safe limit. “We were pretty shocked,” Frye said.

He installed a reverse-osmosis system in the basement and still buys bottled water for his wife, who is breastfeeding their daughter, born in July.

When he watches manure or fertilizer being spread on nearby fields, he said, one question nags him: “Where does that go?”

What cleaner corn could look like

Reducing corn’s climate footprint is possible – but the farmers trying to do it are swimming against the policy tide.

Recent moves by the Trump administration have stripped out Biden-era incentives for climate-friendly farming practices, which the agriculture secretary Brooke Rollins dismissed as part of the “green new scam”.

Research, however, shows that proven conservation practices – including planting trees, shrubs and hedgerows in corn fields – could make a measurable difference.

In northern Iowa, Wendy Johnson is planting fruit and nut trees, organic grains, shrubs and other plants that need little or no nitrogen fertilizer on 130 of the 1,200 acres (485 hectares) of corn and soybeans she farms with her father. Across the rest of the farm, they enrich the soil by rotating crops and planting cover crops. They’ve also converted less productive parts of the fields into “prairie strips” – bands of prairie grass that store carbon and require no fertilizer.

They were counting on $20,000 a year from the now-cancelled Climate-Smart grant program, but it never came.

“It’s hard to take risks on your own,” Johnson said. “That’s where federal support really helps.”

In south-east Iowa, sixth-generation farmer Levi Lyle mixes organic and conventional methods across 290 acres. He uses a three-year rotation, extensive cover crops and a technique called roller crimping: flattening rye each spring to create a mulch that suppresses weeds, feeds the soil and reduces fertilizer needs.

“The roller crimping of cover crops is a huge, huge opportunity to sequester more carbon, improve soil health, save money on chemicals and still get a similar yield,” Lyle said.

Despite mounting research about corn’s climate costs, industry groups are pushing for legislation to pave the way for ethanol-based jet fuel.

Researchers warn that producing enough ethanol-based aviation fuel could prompt another 114m acres to be converted to corn, or 20% more corn acres than the US plants for all purposes.

“The result,” said University of Iowa professor and natural resources economist Silvia Secchi, “would be essentially to enshrine this dysfunctional system that we created.”

Floodlight is a non-profit newsroom that investigates the powers stalling climate action