After rice, wheat and maize (corn), what is the fourth largest food crop in the world?

Soybeans as a global crop can be traced to the Great Depression, where the severe drought caused the nation's agricultural center to become a veritable "Dust Bowl." Soybeans were discovered to have a strong nitrogen-fixing ability in soil, rendering sterile soil fertile in short time. In addition, soybeans could be processed to create high-protein animal feed, boosting chicken, turkey, and hog growth to unseen heights.

Barley