Recommendation for book about soil and their food webs
A very good resource can be found here:

http://esdac.jrc.ec.europa.eu/content/global-soil-biodiversity-atlas

If you focus on soil analysis this resource could be helpful:

http://www.geokniga.org/bookfiles/geokniga-handbook-soil-analysis.pdf

I could also recommend the book 
http://www.springer.com/gp/book/9783642309410
with which I worked extensively. It covers the soil chemistry very well.