In good years, cargo trains moving west along the flat, sweeping grasslands of North Dakota’s plains are a sign of money rolling in. Today, as tariffs from America’s largest foreign soybean market -- China -- threaten to upend the industry, many trains sit idle. “There are no shuttle trains leaving. There is no nothing,” said Joe Ericson, the 38-year-old president of the North Dakota Soybean Growers Association.