Soybean futures prices have pushed higher during the past few weeks thanks to dry weather in South America. But with a growing stockpile and Chinese purchases down sharply from a year ago, it will be tough for soybeans to sustain any long-term rallies, according to Todd Hultman, lead analyst at DTN.

“If we go another year of piling up soybean surpluses related to China’s lack of purchases, it’s going to be a big strain on...