I believe all the land that will grow food in the southern US is being farmed. With the exception of the forests and there aren’t many of them left.
I know we can grow food more efficiently. But that simply means there are less and less agriculture jobs. A sixteen row plow and a sixteen roll cotton picker can harvest the cotton quicker and more efficiently. But it’s still the same amount of cotton. It can only be grown during the summer months.
Large wheat fields can be harvested in a few days with ten combines going all at once. But it’s the same amount of wheat.
I saw those thrashers rolling by looking more than two lanes wide
https://www.youtube.com/watch?v=t00MXZKbW0M
ducking....
It is beyond simple efficiency in terms of machines; Japan has really gone a long way in finding new methods to increase the amount of farmable land. Even FDR pushed programs that helped farmers use the land more efficiently (terracing and such) that many Third Worlders don’t yet use.
Israel showed how irrigation can turn desert into farmland.