Conventional Ag may have a 20 year time horizon

http://www.getfarming.com.au/pages/farming/articles_view.php?fId=9200020130228130936&cId=1
Apparently, mined sources of phosphate may run out in 20 years.
Small farms working with nature to the rescue.

I have heard about this recently too. Did you read this article?

http://www.motherjones.com/tom-philpott/2012/11/are-we-heading-toward-peak-fertilizer

(Speaking of Phosphorous and Potassium) "These two elements cannot be made, cannot be substituted, are necessary to grow all life forms, and are mined and depleted. It’s a scary set of statements. Former Soviet states and Canada have more than 70% of the potash. Morocco has 85% of all high-grade phosphates. It is the most important quasi-monopoly in economic history.

What happens when these fertilizers run out is a question I can’t get satisfactorily answered and, believe me, I have tried. There seems to be only one conclusion: their use must be drastically reduced in the next 20-40 years or we will begin to starve." Jeremy Grantham

Yet another aspect of the world no one wants to talk about.

No, I don't come across MEN articles much.
Wacky stuff, good thing solutions exist.

BIG new mine coming online in Arizona

http://arizonageology.blogspot.com/