The receding glaciers of the ice age left behind blocks of ice (think icebergs in the ocean) which, when melted, formed prairie potholes in the Dakotas and MN. These depressions were wet, with the degree of water varying according to the weather from year to year. Dan Morgan writes in the Post that they're now being converted to cropland.
I'd debate the story title [Updated to clarify--Morgan points the finger at subsidized crop insurance, which is valid, but most people, as did I originally and as did all the comments at Volokh.com, will think first of direct payments], but more importantly I wonder about NRCS and the swampbuster provisions (which make people who drain wetlands ineligible for program benefits). If Morgan is right, either I misunderstand the current situation on wetlands or there's something else going on.