Fertilizers are soil amendments applied to promote plant growth; the main nutrients present in fertilizer are nitrogen, phosphorus, and potassium (the ‘macronutrients’) and other nutrients (‘micronutrients’) are added in smaller amounts. Fertilizers are usually directly applied to soil, and also sprayed on leaves (‘foliar feeding’).
Fertilizers are roughly broken up between organic and inorganic fertilizer, with the main difference between the two being sourcing, and not necessarily differences in nutrient content.
Organic fertilizers and some mined inorganic fertilizers have been used for centuries, whereas chemically-synthesized inorganic fertilizers were only widely developed during the industrial revolution. Increased understanding and use of fertilizers were important parts of the pre-industrial British Agricultural Revolution and the industrial green revolution of the 20th century.