The yield potential for crops is easily many times what it is today. Yields for corn have nearly doubled in the last 20 years, wait until genetic engineering starts to be affect yields.
Same for livestock.
I have a friend who grew up on a farm and one day was bemoaning the loss of good farm land to development. I mentioned to him that they don't need as much farm land as they did even decades ago to feed the population. His argument didn't really make sense. If we have enough land to grow crops and feed the population (and obviously we do), why would this suggest to him that developed ex-farm land was a bad thing?
He didn't have an answer for me. He didn't understand that land can be used for more than one thing. But many people, mostly libs, think like he does.