NPK fertilizers are properly selected, multicomponent mixtures different substances containing the most basic elements essential for proper growth and evolution of plants: nitrogen (N), phosphorus (P) and potassium (K). Everyone of them is assimilated by plants in different forms:
- nitrogen - as nitrates or ammonia salts,
- phosphorus - as phosfates,
- potassium - generally as potassium chloride.

The composition of NPK fertilizers are showed in (generally) three number that states after NPK name. Theese numbers determinates percentage participation of individual componets. Share of theese somponets is given for:
- nitrogen - calculated on free element,
- phosphorus - calculated on oxide P2O5,
- potassium - calculated on oxide K2O.

Beside mentioned macronutrients, NPK fertilizers might contain also other elements, which enrich the soil and have selective effect on the crops properties. We rank here: calcium (Ca), magnesium (Mg), sulphur (S), boron (B) and often many other additional micronutrients.