Soybeans are legumes, plants that can have a symbiotic relationship with nitrogen-fixing bacteria — rhizobia — and therefore do not need additional nitrogen fertilizer. Each type of legume — peas, beans, lentils, alfalfa — have their own rhizobia.

“Soybeans are from Asia and so there were originally no nitrogen-fixing bacteria that would colonize soybeans in U.S. soils,” said Consuelo De Moraes, associate professor of entomology. “The rhizobia had to be transferred here.”