Corn Fertility

I am just now getting around to reading Michael Pollan's book, The Omnivore's Dilemma.  At one point in the book, Pollan  discusses the growth in yields on a typical farm in Iowa from 20 bushels of corn an acre in 1920 to over 180 bushels an acre today.  He says:

On the day in the 1950s that George Naylor's father spread his first load of ammonium nitrate fertilizer, the ecology of his farm underwent a quiet revolution.  What had been a local, sun-driven cycle of fertility, in which legumes fed the corn which fed the livestock which in turn (with their manure) fed the corn, was now broken.  Now he could plant corn every year and on as much of his acreage as he chose, since he had no need for the legumes or the animal manure.  He could by fertility in a bag, fertility that had originally been produced a billion years ago halfway around the world.  Liberated from the old biologocial constraints, the farm could now be managed on industrial principles.

pp. 44-45 (emphasis added).  As I read these words and his later phrase "synthetic fertility," I couldn't help but wonder whether their are connections - ecological, cultural, psychological, etc. - between our approach to plant fertility (ending the fertility cycle for legumes in Iowa and buying fertility in a bag for corn) and human fertility?  "Liberated from old biological constraints..." 

Any thoughts?