Fertiliser Types: Phosphorus (P)

Phosphorus never occurs free in nature. It is always combined with some base and forms what is called a phosphate. Phosphorus is quarried from rock. In Ireland our phosphate usually comes from Africa (Morocco). The rock phosphate is shipped to Ireland where it is used in the manufacture of the various phosphate fertilisers.

There are two types of phosphate fertiliser available depending on the degree of chemical processing that has been done on the original rock phosphate - "fast acting" or "slow acting".

 'Fast Acting' means water soluble. Water soluble phosphorus is the most readily available to plants. The phosphorus in "Super Phosphate" is all soluble in water. 'Slow Acting' means the phosphorus needs to be dissolved by some other method, e.g. by soil acids or soil micro organisms.

Superphosphate is produced by treating rock phosphate with acid. Depending on the level of treatment, 8% Super Phosphate or 16% Triple Super Phosphate is produced. It is highly water soluble (over 90%) and is quick acting. It is widely used in compound fertilisers such as 10-10-20 or 18-6-12.