The phosphorus cycle. Numbers are 1012 g P or fluxes as 1012 g P per year (data from Schlesinger 199

Phosphorus is slowly released to terrestrial and aquatic ecosystems through the weathering of rocks. As phosphorus is released from mineral deposits, it is absorbed by plants and recycled within ecosystems. However, much phosphorus is washed into rivers and eventually finds its way to the oceans, where it will remain in dissolved form until eventually finding its way to the ocean sediments. It is long-term weathering of the bedrock that results in very low availability of plant-available soil phosphorus in the Canadian Shield and tropical wet forests. In contrast, removal of phosphorus-containing plant biomass, without equal phosphorus inputs, is a major cause of low P levels in agricultural systems.  Ocean sediments will be eventually transformed into phosphate-bearing sedimentary rocks that through geological uplift can form new land. William Schlesinger (1991) points out that the phosphorus released by the weathering of sedimentary rocks has made at least one passage through the global phosphorus cycle.