... ARRGH. I see this point made in every single discussion of peak resources. And it completely ignores that industrial agriculture has a resource consumption of near zero. Have you ever been on a farm? Industrial farming needs, in order:

1. Land.
   
2. Steel.
   
3. Ammonia. (for fertilizers, and for fuel. Yes, you can run tractors and combines on ammonia. People do so already.)

.. and thats it. And none of it is going to run out before the sun enters its red gigant phase and swallows the earth. Enough ammonia to keep the agricultural sector fueled and fertilized can be made with the output of extremely modest hydro electric facilities, never mind types of renewables less than a century old.

grumble Doomers. Stop fantasizing about the apocalypse, pay a tiny bit of attention to what the actual constraints and possible/probable substitutes of our industrial ecology are, because all you are currently doing is destroying your own credibility. Which, to be honest.. go ahead, the less influence you have, the better for the planet.