The phosphorus cycle is a biogeochemical cycle in which phosphorus moves through the lithosphere, hydrosphere and biosphere. In contrast to other biogeochemical cycles, the atmosphere does not play a significant role in this cycle, because phosphorus and its compounds are mostly solids in the ranges of temperature and pressure found on or near the earth's surface.
The phosphorus cycle is of great importance because phosphorus is an essential nutrient for sustaining life. This element plays central roles in the structure of genetic material, in the transferring of energy within organisms, and in the composition of cell membranes, teeth and bones. There is no substitute for phosphorus.
The phosphorus cycle is a slow process that consists of several basic steps. The first is the extraction of phosphorus compounds from rocks by weathering and their entry into the soil and water. Plants, fungi, and microorganisms are able to absorb phosphorus from the soil and water, and animals absorb it by eating the plants, drinking the water, and eating other animals. When plants and animals die, decomposition results in the return of phosphorus back to the environment via the water or soil.
Humans are having a major effect on the phosphorus cycle, particularly through the large-scale mining of phosphate rock and using it in the production of artificial fertilizers and detergents. The extra phosphorus that is not absorbed by plants or removed in sewage treatment systems eventually enters water bodies and results in their eutrophication, a process in which excessive algae growth occurs and produces toxins that can kill aquatic organisms and thereby reduce biodiversity.