I am frequently asked if I can recommend a book on Soils.  And yes, I can. It is Soils: An Introduction by Michael Singer and Donald Munns.  The sixth edition recently came out so there's a lot of older used copies floating around on the wed for under $10.  This book takes a different tack on describing soils.  Instead of tacking the tack of a chapter on Nitrogen another on Calcium etc., it weaves a story of how all the parts are related.