Serrano Creek Soil Amendments

A very detailed by equally amazing look at the role of fungus in soils and its critical symbiotic relationship for plants.  An amazing fact: 40% of the world's cellulose is recycled each year by fungus.  The science is quite complete, but the effort is worth the understanding.  I'll promise you this, once you finish this one, your gardening habits will be completely changed!

http://www.amazon.com/gp/product/product-description/1405130660/ref=dp_proddesc_0?ie=UTF8&n=283155&s=books

Nyle C. Brady & Ray R. Weil. 14th edition

This is an excellent introduction to the "underworld". The college text covers both the mineral side of soils as well as the microbe. 

http://www.amazon.com/gp/product/product-description/013227938X/ref=dp_proddesc_0?ie=UTF8&n=283155&s=books

This book is part of a 10 volume set that is quite extensive.  The cost is quite pricey, but I was able to obtain a used copy at a significant discount.  You'll really understand the value of building soils with carbon based amendments rather than synthetic fertilizers once you finish.

http://www.amazon.com/Nutrient-Cycling-Terrestrial-Ecosystems-Biology/dp/3540680268/ref=sr_1_fkmr0_1?ie=UTF8&qid=1282256261&sr=8-1-fkmr0

Here's the plant version of the phrase "where the rubber meets the road". A collection of essays, here you get depth over breadth.

 http://www.amazon.com/Roots-Soil-Management-Interactions-Agronomy/dp/0891181598/ref=sr_1_1?s=books&ie=UTF8&qid=1282256937&sr=1-1

Jeff Lowenfels & Wayne

A good primer into the amazing world of soils microbes.  A good introduction to the concept of the Soil Food Web.  It's science based, but not too heavy. 

http://www.amazon.com/Teaming-Microbes-Gardeners-Guide-Soil/product-reviews/0881927775/ref=dp_top_cm_cr_acr_txt?ie=UTF8&showViewpoints=1.