Based on the availability of nutrients in them chemical fertilizers are divided into four groups:
- Nitrogenous fertilisers
- Phosphatic fertilisers
- Potassic fertilisers
- Complex fertilisers
Nitrogenous FertilisersFertilisers that contain the macronutrient nitrogen come under this group.
Example: Ammonium sulphate, ammonium nitrate, sodium nitrate, urea.
The fertility of soil can be enhanced by using chemical fertilizers, which provide the essential plant nutrients, potassium, nitrogen and phosphorus.
The most important phosphatic fertilizer is the superphosphate of lime, Ca(H2PO4)2.
This is produced directly from phosphate rock by treatment with concentrated sulphuric acid. In this way the insoluble phosphate rock is rendered soluble in water to improve the release of Phosphorus to the soil for the uptake by the plants.
Phosphatic rock generally contains fluoride, which reacts with H2SO4 to give hydrogen fluoride, which in turn generates other side products. The gaseous side-products are removed by washing with water in a scrubber. Almost 90% of the phosphate rock mined goes into the production of phosphatic fertilizers; the remaining 10% is used for the production of elemental phosphorus.
Treatment of phosphate rock with phosphoric acid yields triple super phosphate, Ca(H2PO4)2.H2O which is free from calcium sulphate and hence contains a greater percentage of Phosphorus: