The phosphorus cycle is one of many mineral nutrient cycles demonstrating the constant cycling of elements through organisms and the environment. The nitrogen cycle and carbon cycle are the two most well known examples of these natural cycles. The phosphorus cycle differs from these other cycles in that it does not have an atmospheric component to the cycle.

Plants are the first link in the phosphorus cycle. The plants obtain their phosphorus directly from the soil. In what form this phosphorus is found in the soil is dependant upon the pH. In alkaline conditions, above pH 7, the phosphorus is encountered as hydrogenphosphate (HPO₄^2-). At more acidic pHs, the phosphorus is encountered as dihydrogenphosphate (H₂PO₄^-). The dihydrogenphosphate is taken up more quickly by plants than the hydrogenphosphate. Once the molecule is in the plant it remains in the form PO₄^3-. In this form...