Any natural or manufactured material that contains at least 5% of one or more of the three primary nutrients - nitrogen (N), phosphorous (P), or potassium (K) - can be considered a fertilizer. Industrially manufactured fertilizers are sometimes referred to as "mineral" fertilizers.

There are several sources of plant nutrients . The two most important are organic manure and mineral fertilizers. When manure and crop residues are used, mineral fertilizers supply the outstanding nutrient balance needed for good crop yields. In most parts of the world, the balance to be supplied by mineral fertilizers is substantial.

Fertilizer production entails gathering raw materials from nature; treating them in order to purify them or increase their concentration; converting them into plant-available forms; and often combining them into products that contain more than one nutrient.

How are fertilizers manufactured?

Nitrogen

78% of the earth's atmosphere is nitrogen. However, the nitrogen we breathe is in a chemically inert form that plants (except legumes) cannot use. Large amounts of energy are required to convert this nitrogen to a form that can be used by plants.The production of ammonia from atmospheric nitrogen was made possible in the first part of the 20^th century by the development of the Haber-Bosch process. It remains the only chemical breakthrough recognized by two Nobel prizes for chemistry , awarded to Fritz Haber in 1918 and Carl Bosch in 1931. The most important nitrogen-based fertilizers are urea and ammonium nitrate.

Phosphate

Phosphorus, in the form of phosphate (a salt of phosphoric acid) is mined from naturally occurring mineral deposits (phosphate rock) that were once sediments at the bottom of ancient seas. Rock phosphate is the raw material used in the manufacture of most commercial phosphate fertilizers. Ground rock phosphate was ounce applied directly to acid soils. However, due to low availability of phosphorous, high transport costs, and low crop responses, very little rock phosphate is currently used in agriculture. Phosphate rock processing consists in the separation of phosphate from the mix of sand, clay and phosphate that makes up the matrix layer.

Potash

The potassium used in fertilizers is found in a salt form called potash. Potash deposits are derived from evaporated sea water. They occur in beds of sediment at only a few places in the world. The largest deposit, in Saskatchewan, Canada is 2.7 to 23.5 metres (9 to 77.6 feet) thick and found at depths of 1000 to 10, 000 metres (3,200 to 10,000 feet). Solution mining methods are used to extract potash at greater depths. Conventional underground dry-shaft mining methods are used in mines as great as 1100 metres (3500 feet.). The ore is extracted from potash deposits by electrically operated mining machines and conveyed to the surface, where it is crushed. Using a flotation process, salt and clay particles are removed, the brine solution is dried, and the potash is sized by screening. The resultant coarse grade product is then ready for distribution. Fine particles remaining from the screening process are compacted into sheets that are crushed and screened to particle sizes suitable for blending.

Sulphur

Most of the sulphur used by the fertilizer industry is a by-product of other industrial processes.

Secondary and micronutrients

Secondary and micronutrients come from mineral deposits.

Common fertilizer products and intermediates

Nitrogen fertilizers

• Ammonia
• Ammonium sulphate (AS)
• Ammonium nitrate (AN)
• Calcium ammonium nitrate (CAN)
• Urea

Phosphate fertilizers

• Single superphosphate (SSP)
• Triple superphosphate (TSP)
• Diammonium phosphate (DAP)
• Monoammonium phosphate (MAP)
• Ground phosphate rock

Potash fertilizers

• Muriate of potash (MOP), also called potassium chloride
• Sulphate of potash
• Sulphate of potash magnesia

Magnesium fertilizers

• Kieserite
• Epsom salts

Complex fertilizers

• NPK fertilizers
• NP fertilizers
• NK fertilizers
• PK fertilizers

Terminology

Manufactured fertilizers are sometimes called "chemical" fertilizers. The nutrients in these fertilizers are all found in nature, but in insufficient quantities to sustain global agricultural production. Because these substances exist in nature, it is not strictly accurate to refer to the fertilizers that contain them as "chemical" or "artificial".

To distinguish its products from manure, legumes and other sources of crop nutrients, the fertilizer industry usually refers to "mineral" fertilizers. Although not very exact with respect to nitrogen (which is a gas), it is generally accepted that this is the most appropriate term.