Elaine Ingham et al. 2000. Soil Biology Primer. Natural Resources Conservation Service. Available at nrcs.usda.gov/wps/portal/nrcs/main/national/soils/health.
Online version of a Soil Biology Primer that includes chapters, tables and illustrations of Soil Arthropods, Bacteria, Fungi, Nematodes and Protozoa, and the Soil Food Web.