With the massive efficiency of corn its actually kinda hard to do that to the level you expect. Corn is very effective at turning space into starch.

What massive efficiency? You're feeding it to animals. 80% of the calories are immediately pooped out.

Which is why you could just feed it to people instead - or grow something else.

Solar panels destroy corn in terms of converting solar power to energy. Ethanol is geopolitical and special interests, definitely not efficient.