How are fertilizers manufactured

Nitrogen :Nitrogen N
Nitrogen is the motor of plant growth. It is taken up from the soil in the form of nitrates or ammonium. As the essential constituent of proteins, nitrogen is involved in all the major processes of plant development and yield formation.
78% of the earth's atmosphere is nitrogen. However, the nitrogen we breathe is in an  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 20th 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 P
Phosphorous performs a key role in the transfer of energy. It is essential for photosynthesis and other chemico-physiological. Phosphorous is indispensable for cell differentiation, as well as for the development of the tissues that form a plant's growing points. Most natural and agricultural soils are phosphorus deficient. When there are problems with phosphorous fixation, this also limits its availability.
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 : Potassium K
Potassium activates more than 60 enzymes, (the chemical substances that govern life and play a vital part in carbohydrate and protein synthesis). It improves a plant's water regime and increases tolerance to drought, frost and salinity. Plants that are well supplied with potassium are less affected by disease.
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.