A buyer may choose to ship the Illinois corn a long distance, even overseas. Most grain around the world either goes right into the mouths of the farm family or becomes cash grain. Think of rice in the Far East, millet in Africa, rye in Poland. Actually it is wasteful to allow animals to consume grain and then for humans to consume animal products, wasteful in terms of grain and water for the stock to drink. Soybeans are almost exclusively a cash grain, though meal made from beans in factories goes to feed livestock.
Rotation means corn one year in a field and beans the next.
In terms of return on investment of labor and capital, grain for cash is a better use of the land in these areas than would be other uses, like grain for hogs or pasture for dairy cattle. The relatively flat land with its high fertility lends itself to big machinery operating in big fields on endless acres of crops for cash. Little marginal land means little need for livestock to utilize. Seed corn is another form of corn for cash sale. I had the opportunity one summer, soon after I came here, to work as a seed field inspector for Funk Seeds.