I am enjoying a book called Teaming with Microbes by Timber Press. It is an excellent argument for organic methods. A bit dense with scientific terms, but if you really want to get the whole picture I don't see how the authors could avoid talking in some detail.
It tells basics of soil composition, all the groups of critters in soil (bacteria, fungi, nematodes , minibeasts) . and what they do. Explains how they all interrelate and how plant roots work with them, beyond mycorhizzae... Well, you just have to read it, I can't do it justice (esp at this time of night 8^P)
Another very good book from Timber Press.