Is that a problem or a good thing. We currently suffer from deforistation due to agriculture. If those feilds could be reforested that would be a good thing. Of course pure capitalism doesn't allow for that, but with a little government intervention (aka, buy up the unneeded feilds) or economic decay (feilds become abandoned due to their lack of value ;) ) then reforestation could occure.

Or there could be solar panels put there, or the corn could end up producing the input to the vat. Or hemp could be grown there which could be used as a construction material, or ...