The Big Mac might be an American icon, but it wouldn’t exist without Canadian potash. 

More than 500 million of these hamburgers are sold in the U.S. each year, requiring huge quantities of wheat, corn, soy and other crops to feed the machine. Some of these ingredients make the Big Mac’s bun, while others feed the cattle that become the beef patties. And almost none of this would exist without Canadian potash fertilizers.

America’s potash dependency runs much deeper than the Big Mac, though. A trade war between the U.S. and Canada would slap a 25 per cent tariff on Canadian potash, which could in turn undermine the entire American agriculture sector and throw the food supply chain into chaos.

The U.S. imported 79 per cent of its potash from Canada between 2020 and 2023, United States Census Bureau data shows. There aren’t many alternatives, either. Canada is the world’s largest producer of potash and refined 21.9 million tonnes—32 per cent of the world’s supply—from its mines in 2023 alone. After Canada, the world’s biggest potash producers are Russia, Belarus, China, and Israel, according to data from the Canadian government.

Canada has vast deposits of potash, a group of minerals that can be converted into potassium-based fertilizers through a purification process. Potash is one of the most common forms of agricultural fertilizer after nitrogen-based varieties, which are derived from natural gas.

In the case of the Big Mac, tariffs on potash would raise the cost of producing wheat, which would have a “cascading effect” through the mill and push up the price of the bun, said Gary Schnitkey, a professor of farm management at University of Illinois . Similarly, potash is applied to pastures, and used to grow corn or soybeans which are processed into feed for cows. 

“That 25 per cent tariff would impact the feed costs, which would then impact the beef, which would then go up the chain,” Schnitkey said. 

What’s bad for the chain is bad for farmers. And in Iowa, farmer Lance Lillibridge is not pleased. His 1,300-acre farm near Cedar Rapids needs potash to grow corn, which is later processed into feed for cattle, ethanol, paper and hard candies. If the price of potash increases, Lillibridge said he’d cut output or pass along the cost to buyers.

“Tariffs is a word that none of us like,” Lillibridge said. “We don’t much care for them, and it would definitely impact our costs.” 

In the past, Lillibridge used around 100 pounds of potash per acre on his farm, but faced with the possibility of costs increasing, he’s going to use it more sparingly this year, he said. “Margins are almost non-existent in agriculture right at the moment,” he added. 

A report from the University of Illinois published on Feb. 4 estimated that, if the price of potash is around US$450 per imperial ton, a 25 per cent tariff would increase costs by over US$100 per ton from Canada. Average potash prices were around US$456 per ton as of last Friday, according to the biweekly Illinois Farm Production Cost Report.

Around 80 to 86 per cent of potash is already in place for this harvest, said Schnitkey. If tariffs were imposed they would hit hard next year, squeezing the agriculture industry and driving up prices from farm to fork. The price of equipment and cars for farmers could also increase with the tariffs in place, further affecting the farming supply chain, according to Schnitkey.

Tariffs on potash imports from Canada would “just about wipe out the savings” amassed from the slightly lower potash prices this year, said Mark Mueller, a fourth generation Iowa farmer who grows soybeans, grains and corn—much of which becomes livestock feed. Mueller buys potash from local co-operatives and a multinational company, and said he has “little doubt” the big players set the prices. 

“Few farmers have debt-free operations and fewer still seem to have a handle on their costs of production,” he said. “I will have to reduce my input costs by a significant amount if I hope to avoid red ink in 2025.”

Potash in Canada is almost entirely produced by just four companies: Nutrien, The Mosaic Company, Compass Minerals and K+S Potash Canada. Lillibridge said this was “kind of irritating” and, tariffs or not, left him with little choice as to who he could buy from. 

K+S Potash, which operates in Canada but is a German company, said it has the “flexibility” to shift exports to other countries quickly should tariffs be imposed. “The impact on our own business remains relatively small,” spokesperson Michael Wudonig said.

Saskatoon-based Nutrien, Canada’s largest potash producer and one of the country’s biggest companies following a US$36-billion merger in 2017, said U.S. farmers would foot the bill for any added costs resulting from tariffs. “We intend to pass through the tariff costs to customers,” Nutrien spokesperson Shawn Churchill said. 

McDonald’s did not respond to requests for comment.

Tariffs would “threaten food production” for farmers in both the U.S. and Canada, said Kayla FitzPatrick, spokesperson for Fertilizer Canada, an industry association.

“Imposing U.S. tariffs on Canadian fertilizer imports will distort the U.S. market in favour of countries such as Russia and China, who do not operate under the same environmental, human rights and trade practices, undermining the critical trade goals of each of our countries,” FitzPatrick said.

With files from Jesse Snyder.

Correction: Canada produced 21.9 million tonnes of potash in 2023. This story has been updated.