Fallow and Fertile

It is my habit to listen to NPR when I am traveling. This week I caught part of an interview by Terry Gross of Fresh Air with Bruce Feiler. The point of the interview was Feiler's book The Council of Dads but during the interview the subject of rest came up.

It used to be the practice of farmers to let their fields lie fallow every seventh year. This year of rest would regenerate the land and allow it to be more fertile. Today, many farmers supplement the land with chemicals and nutrients to maintain productivity. This artificial fertility allows production to go on uninterrupted by rest.

If the land needs to be fallow to be fertile how much more do we need rest to be productive?