An easy read if you would like to know a little more about the soil microbes and the benefits of taking care of them 
Teaming with Microbes by Wayne Lewis

A wonderful book that thoroughly explains how we are repeating the same terrible story over and over again with our poor farming practices
Dirt by David R. Montgomery

A great read if you are new to organic gardening and farming
The Soil Will Save Us by Kristin Ohlson

An awesome read about biodynamics and farmers who practice it religiously.
If you know about Rudolf Steiner, you must read this book!
Secrets of the Soil: New Solutions for Restoring Our Planet by Peter Tompkins