Fertilisers provide mineral ions needed for healthy growth in plants. As plants grow, they absorb mineral ions from the water in the soil through their root hair cells. Over time, the concentration of these ions decreases, so farmers and gardeners add fertilisers to the soil.

Fertilisers are usually sold as solid powders or granules
Fertilisers are usually sold as solid powders or granules

Nitrogen, phosphorus and potassium

Fertilisers may contain nitrogen, phosphorus and potassium compounds to promote plant growth. Fertilisers that supply all three elements are often called NPK fertilisers, after the chemical symbols for these three elements.

Fertiliser compounds must be soluble in water so they can be absorbed by the root hair cells:

  • ammonium ions, NH4+, and nitrate ions, NO3-, are sources of soluble nitrogen
  • phosphate ions, PO43-, are a source of soluble phosphorus
  • all common potassium compounds dissolve in water to produce potassium ions, K+

The table shows some examples of fertilisers, their formulae and the essential elements they provide.

FertiliserFormulaEssential element(s)
Ammonium nitrateNH4NO3Nitrogen
Ammonium sulfate(NH4)2SO4Nitrogen
Ammonium phosphate(NH4)3PO4Nitrogen, phosphorus
Potassium nitrateKNO3Potassium, nitrogen

Urea, (NH2)2CO, is used as a fertiliser. Name the essential element it provides.