There's more than cattle feed left after the ethanol is made from the corn...and many farmers like to hunt too, so they'll maintain habitat that they can make use of after the harvest.
Actually, the new plant being planned in SW Kansas, will burn feedlot manure for the heat required, thus eliminating that problem, the residue of the manure will be returned to the feedlots to pave the pens. The grain will have the alcohol removed from the carbohydrates, and the remaining high protein mash will then be returned to the feedyards as feed. It is hard to beat a system like that, and it also blows holes in the nay-sayers whining about energy requirements needed to produce ethanol.
Yeah, and it makes the cows sick and increases the amount of saturated fat in the meat. The corn lobby doesn't just make us waste money on highly inefficient energy source; it also creates incentives for farmers to raise unhealthy beef.