Images:

                                                  http://www.shutterstock.com/pic-27926038/stock-photo-green-leaf-border-isolated.html  

                                                  http://www.readysetmom.com/.a/6a00d83451c9bc69e2013488cef2c7970c-pi  

                                                  http://bio1152.nicerweb.com/Locked/media/ch55/phosphorus_cycle.html 

                                                       http://www.hendersonandassociatesre.net/wp-content/uploads/2015/03/1037641-1205160809594954-p.jpg  

                                                 http://parentingpatch.com/wp-content/uploads/2012/02/2012-03-02-Tips-for-Preparing-the-Soil-for-Gardening.jpg 

                                If you want to learn more abou the basics of soil:

                          http://www.eduscapes.com/42explore/dirt.html 

                                  If you want to learn more about soil ecology and soil tests:

                                                  http://www.yukonenvirothon.com/soil-studies.html 

http://www.clemson.edu/extension/hgic/plants/other/soils/hgic1652.html

                                                  http://ucanr.org/sites/intvit/files/24453.pdf 

                                   If you want to learn more about the basics of phosphorus:        

                                                        http://www.esf.edu/pubprog/brochure/soilph/soilph.htm 

                                                ttp://www.hallman.org/plant/soilchem.html 

                                                  http://broome.soil.ncsu.edu/ssc051/Lec8.htm 

                                If you want to learn more about the importance of Phosphorus to plants:

                                                    http://passel.unl.edu/pages/informationmodule.php?idinformationmodule=1130447043&topicorder=2&maxto=15

                                                 http://www.extension.umn.edu/agriculture/nutrient-management/phosphorus/the-nature-of-phosphorus/