Definition
Fertilisers are important as they replace elements that have been taken up by plants. NPK fertilisers contain compounds of nitrogen, phosphorus and potassium which improves agricultural activity. NPK fertilizers are produced in large industrial facilities. NPK fertilisers are formulations of different salts which contain the required elements needed by plants.
Nitrogen
The main compound of nitrogen in NPK fertilisers is ammonium nitrate
Potassium
The potassium in NPK fertilisers comes from potassium chloride or potassium sulfate which both come from mining without processing.
Phosphorous
Phosphate rock has to be chemically processed before being used in fertilisers. Treating Phosphorus Rock
- Treating phosphate rock with nitric acid produces phosphoric acid and calcium nitrate. Phosphoric acid contains phosphorus but this cant be directly added to plants so it must be neutralised with ammonia. This produces ammonium phosphate which can be used.
- Treating phosphate rock with sulfuric acid produces a mixture of calcium phosphate and calcium sulfate. This mixture is called single superphosphate which can be used.
- Treating phosphate rock with phosphoric acid produces triple superphosphate.