Fertilizer shortages caused by the Iran war will have a “dramatic” impact on food prices globally next year, and have already driven up costs for U.K. farmers by as much as 70%, according to one of the U.K.’s most powerful property and farming companies.

The Guardian reports that Mark Preston, executive trustee of the 349-year-old Grosvenor Group, which is controlled by the Duke of Westminster, said fertilizer “was already quite expensive” before the 50% to 70% surge in prices after the war began.

The effective closure of the strait of Hormuz has throttled global supplies of fertilizer, as well as oil. So far, the effect on consumers has been mostly felt as high prices at the gas pump, but global food supply chains, from seed to grocery shelf, tend to have longer lags. On May 7, John Denton, Secretary General of the International Chamber of Commerce warned during an interview with Forbes TV that the fertilizer shortage could cause deadly food scarcity and price hikes.

In April, a statement by the American Farm Bureau Federation said that around 70% of U.S. farmers report being unable to afford all the fertilizer they need. The AFBF’s Fertilizer Availability Survey of nearly 6,000 farmers and ranchers across the country also found that nearly six in 10 U.S. farmers report worsening finances, because of rising fertilizer and fuel costs during spring planting.

U.S. farmers face additional pressures from increased tariffs on imported materials and equipment, plus the U.S. administration’s recent crackdown on laborers working illegally in the country. According to U.S. Department of Agriculture (USDA) figures, roughly half of hired crop farmworkers lack legal immigration status. A letter to the House and Senate Committees for Agriculture from a bipartisan group of commodity organization chiefs, farm leaders and former USDA Officials in April stated, “The policies of this Administration have caused tremendous harm to U.S. agriculture.”

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In the U.K., the Grosvenor executive said, crops were unlikely to be affected this year as most fertilizer had already been used. But the effects from the current shortage could kick in next year. “Farmers are not buying that fertilizer, they’re sitting on their hands and hoping things will improve, which they probably won’t,” he told the Guardian. “It’s going to be a very, very dramatic problem for the world, not just the U.K. in terms of food, just because so much fertilizer comes through those straits.” 

His remarks came a few days after the head of the world’s largest fertilizer company Yara International warned that the war in the Middle East could cause food shortages and price rises in some of Africa’s poorest and most vulnerable communities.

“Developments in the Middle East put significant pressure on the global food system, with knock on effects across the value chain and growing challenges for farmer affordability. This volatility highlights how fragile the food system is,” said Yara in an April 24 statement.