What is Phosphate?
In agriculture and horticulture phosphate is the common term for nutrient forms of the element phosphorus (P). Phosphorus is predominantly taken up by plants as the primary orthophosphate ion (H2PO4–) an in the UK is declared in the phosphate form P2O5.
Phosphate in Nature
Phosphates are found in nature in many organic mineral compounds known as phosphate rock or ore. Phosphate rock was formed millions of years ago by the accumulation of organic matter on the ocean floor, which contains the apatite minerals. The main deposits around the world are in the USA, Africa the Middle East and Oceania but the world’s largest are in Morocco.
Phosphate based fertilisers are made by treating this phosphate rock with acid (typically sulphuric acid) to produce phosphoric acid.
Functions of Phosphate
Phosphate plays a vital role in almost every plant process that involves energy transfer, as part of ATP, the plant’s energy source. The cell processes in which phosphate is involved include photosynthesis, respiration, biosynthesis, stomatal opening, and the transfer of organic solutes across membranes. Soil reserves are an essential requirement for adequate nutrient supply of phosphate to plants.
Human Needs
Most of the phosphorous in the human body is in the bones, teeth, blood, and soft tissues. Foods that are rich in protein are also excellent sources of phosphorus including meat and poultry, fish, dairy products, eggs, legumes and nuts. A normal blood phosphorus level is 2.5-4.5 milligrams per deciliter (mg/dL). Adults require approximately 0.7g P per day.
Phosphate in Plants & the Environment
To ensure healthy and nutritious plant growth, adequate supplies of phosphate must be maintained in the soil by judicious use of fertilisers and manures. However, excess phosphate can be harmful to the environment, through run-off or erosion, carrying phosphate into watercourses. This can stimulate excess growth of algae leading to low dissolved oxygen levels, harmful algal toxins and the blockage of sunlight needed by organisms and plants in the water. This process is called eutrophication and is the primary reason for the increased scrutiny on phosphate applications.