That would be the nice thing about an open market: different areas could stay focused on what they're particularly good at. Iowa would definitely stay involved in corn.

But as you sort of alluded to, in a free market some areas could put downward price pressure on corn even if they're not as efficient as Iowa. If they've got land that isn't very well suited for anything else, and it's a choice between making a little money on corn and little or no money at all with their arable land, they'll probably go for it...