1. Scherer, H.W., Mengel, K., Dittmar, H., Drach, M., Vosskamp, R., Trenkel, M.E., Gutser, R., Steffens, G., Czikkely, V., Niedermaier, T., Hähndel, R., Prün, H., Ullrich, K.‐H., Mühlfeld, H., Werner, W., Kluge, G., Kuhlmann, F., Steinhauser, H., Brändlein, W. and Kummer, K.‐F. 2006. “Fertilizers I: Ullmann's Encyclopedia of Industrial Chemistry”. Berlin: Wiley‐VCH.
2. International Fertilizer Industry Association (IFA). “Phosphate fertilizer nutrient consumption, 1996–2008”. Available athttp://www.fertilizer.org/ifa/statistics/indicators/tablep.asp(viewed May 2008)
3. Steen, I. “Phosphate recovery. Phosphorus availability in the 21st century. Management of a non‐renewable resource. Phosphorus & Potassium, 217”. 25–31. Available athttp://www.nhm.ac.uk/research-curation/projects/phosphate-recovery/p&k217/steen.htm(Accessed May 2008)
4. European Fertilizer Manufacturers Association (EFMA). “Phosphorus an essential element for food production”. Available athttp://cms.efma.org/EPUB/easnet.dll/ExecReq/Page?eas:template_im=000BC2&eas:dat_im=000C23(Accessed November 2008)