"Sales have already been lower this crop year because of the existing tariffs. If we went all the way to no China exports whatsoever, that would, of course, result in an even larger market and price impacts," Pat Westhoff, director of the Food and Agricultural Policy Research Institute at the University of Missouri, told CNBC. "Cutting China completely out of the market would be a very big deal."

Even before China officially said it would stop buying US agricultural products, the US Department of Agriculture's (USDA) weekly export sales data shows US corn exports plunged to a 19-month low in June and could be depressed even further in July as elevated spot prices and increased foreign competition continued to weaken exports, reported Reuters.