In contrast to nitrogen, phosphorus can take many forms in the soil-water system; dissolved-P, particle bound-P, organic-P, inorganic-P. The phosphorus form will determine the potential to enter water courses and influence factors such as:

• Solubility in water
• Reaction with surroundings
• Transport mechanism in the environment
• Pathway from soil to water

It is therefore vital for the understanding of the problem of diffuse pollution to have some basic knowledge about these phosphorus forms.

Generally phosphorus exists in inorganic and organic forms, dominated by the inorganic forms in most soils. The inorganic phosphorus is a negative ion when dissolved in water. It is easily adsorbed oxides and hydrous oxides of iron (Fe) and Aluminium (Al) or carbonates of calcium (Ca), which are all commonly found in most soils. These compounds occur as discrete particles or as coatings on other soil particles, especially clay. In addition, amorphous aluminium hydroxy compounds may be present in interlayer locations of expandable aluminium silicates. Orthophosphates is the dissolved form of phosphorus that is readily available to plants and algae.

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External Links
 http://www.nrcs.usda.gov/technical/ECS/nutrient/pindex.html
 http://www.water-research.net/phosphate.htm
 http://pearl.spatial.maine.edu/glossary/misc/lake_class.htm