I've been having excellent results in the home garden using the hugelkultur approach. Just bury logs and vegetative waste beneath a foot or two of topsoil. Adding some fungi spawn to the organic matter speeds up the process. The rotting organic matter acts like a big sponge to keep soil moisture high. Mycelia act to swap plant sugars from above, with nutrients from below. From a small plot, I was able to donate about 250 pounds of gourmet blue potatoes to local food banks this year.

Other than a little cow manure added to help feed the fungi and plant roots, no other fertilization was required. There are so many great low-tech approaches to get great yields of delicious produce, but it takes some extra initial labor inputs. Maybe when the AIpocolypse hits the labor market, this approach will be economical on larger scales.

Only 16% of agricultural land today is used directly for food, providing 83% of calorie supply, while 80% is used for livestock, providing 17% of calorie supply [0].

Not all land used for livestock is usable for food crop agriculture. Though I suspect it still gives us plenty of margin.

If the population stays constant, we could probably deal with a 50-75% yield reduction without using more land overall, but gradually switching to a more plant-based diet. So, good news, we're not fucked yet.

There are many other solutions other than vegetarianism. Changing the ways we do agriculture, switching away from industrial processes, could greatly increase yield. Education in general about soil and plant ecology would probably help a lot globally.

[0]https://ourworldindata.org/global-land-for-agriculture