But this year, the Chinese have all but stopped buying. The largest market for one of America’s largest exports has shut its doors. The Chinese government imposed a tariff on American soybeans in response to the Trump administration’s tariffs on Chinese goods. The latest federal data, through mid-October, shows American soybean sales to China have declined by 94 percent from last year’s harvest.Mr. Karel, the general manager of the Arthur Companies, which operates six grain elevators in eastern North Dakota, has started to pile one million bushels of soybeans on a clear patch of ground behind some of his grain silos. The big mound of yellowish-white beans, already one of the taller hills in this flat part of the world, will then be covered with tarps.The hope is that prices will rise before the beans rot.“We’re sitting on the edge of our seat,” Mr. Karel said.President Trump sees tariffs as a tool to force changes in America’s economic relationships with China and other major trading partners. His tough approach, he says, will revive American industries like steel and auto manufacturing that have lost ground to foreign rivals. But that is coming at a steep cost for some industries, like farming, that have thrived in the era of globalization by exporting goods to foreign markets.