Links
[1] https://hootsgo.org/?q=node/6372
[2] http://en.wikipedia.org/wiki/Phosphorus_cycle
[3] http://en.wikipedia.org/wiki/Nitrogen_cycle
[4] http://www.swanrivertrust.wa.gov.au/docs/fact-sheets/river-science-issue-4-nitrogen-and-phosphorus-cycles.pdf
[5] http://www.envirothon.org/pdf/CG/nutrient_cycles.pdf
[6] http://www.answers.com/Q/What_is_the_difference_between_nitrogen_cycle_and_phosphorus_cycle
[7] http://phosphoruscycleboy.blogspot.in/2012/10/what-is-different-about-phosphorus.html