Phosphorus is essential for photosynthesis – the process by which plants trap the sun’s energy. It also plays a part in the healthy working of the plant cell necleus and in control processes. It stimulates root development and is important in energy storage.

Phosphorus occurs naturally. In soil it is mainly in mineral form, but it can also be found in organic matter. Some rock formations contain large concentrations of phosphorus that is mined for use in various mineral fertilisers. The simplest of these is ground phosphate rock that is insoluble in water and therefore releases phosphate slowly. A more soluble and more readily available phosphate fertiliser is made by treating the rock with a mineral acid such as sulphuric or nitric acid and then neutralising with ammonia.

Generally soil phosphorus bonds strongly to soil minerals. This has two benefits. Levels in the soil can be built up for use by future crops. Very little soil phosphorus dissolves in soil water at any one time, therefore it is not easily washed out.

The concerns about phosphorus:

Loss of phosphorus

It is fortunate that phosphorus is not easily lost to water because increasing levels can cause eutrophication and excessive growth of algae. The concern with phosphorus is that only a small increase can cause problems. Care is therefore needed to prevent even small phosphorus losses especially from light sandy soils which do not hold on to phosphorus as well as clay soils. Also, if heavy rain falls just after phosphate fertiliser has been applied, there may not have been enough time for it to bond properly to the soil.

There is a limit to the amount of phosphorus the soil can hold. Therefore, at very high concentrations dissolved phosphate may be lost in water draining from the soil but the biggest cause of phosphorus loss from soil is erosion, which occurs when soil particles are washed off after heavy rainfall.

There are no health concerns associated with phosphorus.

* Fact!

The components of mineral fertilisers occur naturally in the soil.

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