Mark my words...I am calling it first!
I just realized....FC5 is going to be MASSIVE and EXPANSIVE. The reason for the wheat fields is an area for the planes to land!
Other wise the open fields would be big open areas with no cover, and a waste of space. They are basically the games runways! Which means there will be a lot of them, in key areas, for the planes. To incorporate these, the map has to be HUGE, much larger than past FC maps, otherwise, the map would be a bunch of emptiness. Probably the only thing in the fields will be a lone NPC farmer driving a combine or tractor kicking up dust.
There will probably be barns with crop dusters at every field area, and you can spray enemies with the chemicals...mark my words I am calling it first!