The Regrarians [0] is another avenue to explore - I find Darren a bit more grounded in science than your average "permie" and appreciate the work he's doing, integrating holistic systems design (see Savory Institute), permaculture, and Yeoman's keyline design work. It seems more of a toolbox approach vs what can feel like "doctrine" at times from permaculture. Perhaps more suitable to larger farming operations than backyard gardens but still worth reading, I think.

[0] http://www.regrarians.org/