Corn farmers could see growing pressure from the companies that buy their golden kernels to adopt sustainable practices, according to a new report that warns of price swings, risk of groundwater depletion and nitrogen runoff contributing to the Gulf of Mexico’s dead zone.

U.S. farmers produced almost 14 billion bushels of corn in 2013 worth $67 billion. The annual harvest is essential to a wide variety of industries and products from sweeteners and plastics to meat and ethanol.

But there are threats to that bounty, according to the report by Ceres, a Boston-based nonprofit known for bringing together large business interests to address environmental and social issues.

The Nebraska corn and ethanol boards criticized the 71-page report as inaccurate and misleading.

It warns of looming dangers to corn supplies from climate change, unsustainable water use and inefficient fertilizer practices. It encourages corn buyers, through corporate policies and buying practices, to pressure farmers to adopt environmentally friendly practices.

“Despite a bumper U.S. harvest in 2013 and lower corn prices in 2014, many of the drivers of high corn prices, price volatility and overall risk are likely to worsen, in large part due to climate change,” the report says.

“Severe droughts, floods and heat waves at key moments in the growing season are becoming increasingly common, causing dramatic year-to-year supply shocks.”

Nebraska is the nation’s No. 1 producer of irrigated corn, with 70 percent of the crop getting water from irrigation at some point during the growing season. That compares with 14 percent of corn nationally.

Kelly Brunkhorst, the Nebraska Corn Board’s director of research, said the state’s corn production already is sustainable. He also was disappointed Ceres didn’t consult any of the land grant universities that work hand-in-hand with farmers.

Nebraska is on the cutting edge of irrigation efficiency, he said, thanks to research and expertise at the University of Nebraska and technology like watermark sensors and other moisture-measuring instruments that let farmers know when and how much water to put on a field.

“I think it is fair to say we in the industry, we are getting pressure from the retail sector to prove our sustainability,” Brunkhorst said. “We can continue to increase efficiencies, but we believe at this point in time we continue to be sustainable.”

The report says 87 percent of irrigated corn is grown in areas with limited water that can expect worsening shortages because of climate change, including Nebraska, Kansas, California, Colorado and Texas.

The report also says there are a dozen ethanol plants with production capacity worth nearly $1.7 billion a year operating in areas where aquifer water levels are dropping.

Ethanol Board Administrator Todd Sneller said the report’s claims that 35 percent of all corn produced goes to make ethanol is inflated. He said supplies of corn change each year, as does the percent used by ethanol producers.

Sneller said ethanol helps stabilize corn prices by providing a local market and that with more profit, farmers can afford new irrigation technology.

“Ethanol producers have also faced the same pressures and … water management innovation and new processes have significantly reduced the amount of water used in ethanol production,” he said.

Distillers grain, a fermented byproduct of making ethanol, is a high-quality feed for livestock and part of the “golden triangle” of corn, ethanol and animals that is an important driver of the state’s economy.

The study singled out five counties, four of which are in Nebraska, as ones that produce more than $150 million worth of corn each that is at risk from groundwater depletion. The counties are Yuma in Colorado and York, Hamilton, Adams and Fillmore in Nebraska.

Natural resources districts in those Nebraska counties have implemented water management plans for decades. Water levels often wax and wane from year to year depending on precipitation.