Corn on corn is not sustainable even in the short run.  Pest (nematodes, corn borer, Cargill, ADM, & so on :-) populations explode and the land becomes too sick to support a viable crop.  Even the old corn-beans duo-crop rotation required massive and expensive pesticide, herbicide, and fungicide applications.  And the "expensive" didn't include the external cost of turning the Iowa, Des Moines, & etc rivers into toxic chemical soups or the rise in cancers among farmers, naming only two.

A doo run-run-run, a doo run-run