What is the difference between phosphorus and phosphate?

Following on from our question oh phosporous killing plants, we ask the question ‘What is the difference between phosphorus and phosphate?’.

Always handy to know your chemicals if you’re planning to use grey water on your garden and for environmental knowledge, we hope the CHOICE Community can help solve this riddle.

Answer below to enter our competition.


There is no pure phosphorus (in the form of the chemical element) in detergent, fertiliser or any other product you are likely to buy at the supermarket. Elemental phosphorus is toxic and flammable and not useful in the house or garden.

We often use ‘phosphorus’ (or its symbol P) as a shorthand for unspecified phosphorus compounds. Phosphates are a group of compounds that have phosphorus and oxygen in them and are commonly found in fertiliser. You will often see fertiliser described by its NPK content, that is the three macro plant nutrients Nitrogen, Phosphorus and Potassium. As with phosphorus the nitrogen and potassium will be there as compounds not the element.

Strictly phosphorus and phosphate are different things but speaking more loosely the phosphorus in a product is often present in the form of phosphates. Phosphate is very important in agriculture but should be used with care as it is toxic in excess and also runoff water can carry it into waterways causing nutrient pollution. Phosphates are being phased out of detergents worldwide because of this pollution problem.

The world supply of accessible phosphates is limited and being rapidly depleted. As with many finite resources there is no prepared plan from our leadership for what to do when it runs out other than to blame someone else.


@syncretic supplied an excellent answer.

Some might ask though what is Super Phosphate (Superphosphate) then? Simply it is inorganic/mineral Phosphate that has been reacted with an acid to make it a more soluble and available source of Phosphate and therefore Phosphorus § for plant uptake. P is easily fixed by other minerals in soils and can then be hard for plants to obtain it, If you apply too much Phosphate and therefore P it will lock up other minerals such as Calcium, Iron, and Aluminium in the soil.

You can find several types of Super Phosphate for sale. There is Single Superphosphate (SSP) which is 20% Phosphate (7 to 9% P) and has reasonable amounts of Calcium and Sulphur, Double Superphosphate (DSP) (17.1% P) and there is Triple Superphosphate (TSP) which has 48% Phosphate (20.7% P) but has much less Sulphur and Calcium available.

SSP is made by mixing Sulphuric Acid with mineral Phosphate eg Apatite or Bone to make Single Superphosphate, TSP is made by mixing Phosphoric Acid with mineral Phosphate. TSP is usually made in a 2 step process where SSP is made first and Gypsum, a by product of the reaction, is removed leaving Phosphoric Acid and then mixing that acid with mineral Phosphate again. DSP is just a blend of SSP & TSP.

There are also ammonium phosphate compounds available to boost both P and N in soils.

When applying fertilisers to increase the amount of P in the soil it is important to do it at the correct times for best benefit and avoid the fixation issues. When planting it helps increase root growth and early vigour, and when flowering or fruiting it helps them to be bigger in size, Tomatoes & Roses for instance.

P is needed for all growth processes and for the formation of nodes created by rhizobia bacteria as found on legumes such as peas and peanuts and is used in nitrogen fixation. Superphosphate is also often used when Nitrogen (N) is not required to be added to the soil.


Indeed, peak Phosphorus is likely in the next decade or 2, and the misuse and waste of this precious resource borders on insanity, as it is such an essential plant nutrient. Once excessively applied phosphates disappear down the nearest waterway and into the ocean, the Phosphorus becomes impossible to recover (at reasonable cost).

There is also the health issues of heavy metal accumulation in paddocks (-> crops → food) that have had years of application of superphosphate.


Great answers to this burning :fire: question @syncretic, @grahroll, & @gordon.

Compared to their responses, my answer would have been a small pile of guano :poop: .