1. Juma, Noorallah, The Pedosphere and its Dynamics, Salman Productions, 1990.
2. Pipkin, Bernard W. and Trent, D.D., Geology and the Environment, Brooks/Cole Publishing, 2001.
3. Black, Jacquelyn G., Microbiology: Principles and Explorations, Simon and Schuster Publications, 1999.
4. www.nrsc.usda.gov
5. www.statlab.iastate.gov
6. http://www.silsoe.cranfield.ac.uk/sslrc/soilinfo/level7.htm
(Note: Updated URL: http://www.silsoe.cranfield.ac.uk/nsri/
Verbal resources:
1. Reed, William R., B.S. M.S. Soil Scientist with the NRCS-USDA.
2. Metcalf, Robert L. Ph.D. Professor of microbiology at California State University, Sacramento.