Interestingly farm land prices are stable and rising slightly (in Iowa, 2017 numbers)
http://dreamdirt.com/blog/iowa-farm-land-land-values-up-2-in...
http://dreamdirt.com/blog/iowa-farm-land-land-values-up-2-in...
the need for farming hasn't dropped, it's the desire/ability/money to do it that is. Small farmers are going away and corporate farming is taking over.
Who buys them? Maybe big agro? Or maybe convert it into building-approved land? Report doesn't exactly say as far as I can tell.