Take a drive down country roads in the Corn Belt, and you don't need a USDA report to tell you farmers have been harvesting bumper crops and investing in grain storage.

For instance, Illinois on-farm corn stocks have almost tripled from September 2014 to September 2015, and on-farm storage of soybeans is up a staggering 520%.

The situation is similar in other corn- and soybean-producing states