Food and livestock companies may have a new way to address one of their most vexing sustainability problems — corn.

University of Minnesota scientists have identified which counties nationwide use the most — and least — water and fertilizer to grow the crop, and tracked the corn to where it ends up, whether in a cow, a corn dog or ethanol in a car.

And it turns out that, compared to other parts of the country, Minnesota’s corn has a much smaller environmental impact than corn grown in some other places.

The detailed analysis published last week provides one of the first looks into what has been a black box of environmental information about corn — a commodity that consumes huge amounts of water and fertilizer and produces significant amounts of carbon. It’s designed to help companies like General Mills, Hormel and Cargill figure out how to reduce all three, up and down their supply chains, as they face growing pressure from consumers and investors to be better stewards of the environment.

“If you are Walmart, you can’t just do it with light bulbs,” said Timothy Smith, a professor of engineering and sustainable systems management at the University of Minnesota, and author of the study, which was published in the Proceedings of the National Academy of Science. “They have to look at the corn … that feeds the animals and ends up in their facilities.”

Smith said the model he used could be replicated for other commodities such as soybeans or even plastic and steel. Like corn, those products are notoriously difficult to track because they all merge into one giant global supply stream, and their place of origin is lost.

“You can’t track a kernel of corn from Joe’s farm,” said Jennifer Schmitt, lead scientist for the NorthStar Initiative for Sustainable Enterprise at the U and co-author of the study. “For the majority of U.S. corn, we don’t know where it’s going.”

Yet for many corporations, especially food companies, knowing just that information is increasingly important to their stock price, said Brooke Barton, senior program director for food and water at Ceres, a Boston-based nonprofit that works with industry and large investment groups on environmental sustainability.

In recent years, corporate stock valuation has been driven more and more by “intangibles” like consumer perceptions of corporate behavior, values and brand, she said. “Consumers are a lot more attuned to where their food is coming from and how it’s grown,” she said.

Ceres this week released its second corporate scorecard for how responsibly 42 of the largest food corporations use water. General Mills scored high and Hormel was on the lower end of the range, though it said in an e-mail that it’s on track to reduce its water usage with a new comprehensive water stewardship policy for the company and its suppliers.

The U’s corn sourcing report is another useful tool for companies to achieve such goals, said Barton. The nation’s fertilizer hot spots and high-irrigation regions are well known, she said. “But until now companies [have used] lack of traceability as a shield.”

The researchers conducted the project at the urging of the Environmental Defense Fund, a nonprofit that works with food companies and farm organizations on environmental problems, because the opacity of commodity industries has stalled progress in sustainability.

That’s not true for all companies. General Mills has determined that two-thirds of its overall greenhouse gas emissions come from its agricultural supply chain rather than its own operations, said Kevin O’Donnell, the company’s global responsible sourcing director.

It’s making a major effort to reduce that, including sourcing its corn from regions and farmers who follow rigorous environmental practices. So far, the company has succeeded with about a third of its corn, and expects to reach 100 percent of its supply by 2020, O’Donnell said.

Big influence with farmers

The researchers created the corn supply-chain model by compiling county-specific data for water and fertilizer use. Not surprisingly, they found water use highest in the dry states such as Kansas and Nebraska. Fertilizer use, which drives 70 percent of the greenhouse gas emissions related to corn, is much higher in the eastern part of the United States because of poorer soils.

In contrast, Minnesota-grown corn has lower impacts because the soils are rich and water plentiful, Smith said.

They tracked where the corn went by assuming the most basic economic equation of all, that buyers would acquire corn that was closest and least expensive. “The assumption says that corn finds its least-cost home,” Smith said.

From that, they were able to estimate the amounts of carbon and irrigated water used by some of the nation’s largest companies, including Cargill, ADM, Hormel and National Beef.

The tool is not perfect, Smith said. But Smithfield Foods, the nation’s largest pork producer, tested it on its operations and found it to be pretty accurate, said Kraig Westerbeek, the company’s vice president of environmental support services. Now, Smithfield is working with U researchers to map its grain supply chain specifically, he said.

The ultimate goal, Smith said, is not to encourage companies to buy their corn from low-impact regions of the country. That wouldn’t alter the overall environmental picture because someone would simply step in and buy the other corn.

But it does allow corporations to use their influence to change how farmers farm — to encourage more efficient irrigation and farming systems — on an extremely large scale.

“If you are trying to motivate a Cargill to engage at a scale that leads to real difference,” he said.