How fertilizer is made
Synthetic nitrogen fertilizer feeds about half the people on Earth, and it starts with air and natural gas.
- stations
- 7
- things upstream
- 16
- raw sources
- 10
- steps from the ground
- 4
The short version
Fertilizer is made by turning plant nutrients into forms that dissolve in soil water. Ammonia from air and natural gas becomes urea or ammonium nitrate. Phosphate rock is dissolved in sulfuric acid, and potash is mined and washed. The nutrients are blended, formed into granules and bagged.
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Make ammonia from air
Nitrogen is the nutrient plants use most, and the Haber process captures it from the air as ammonia. This is the starting block for most nitrogen fertilizers.
Goes in -
Turn ammonia into solids
Ammonia reacts with carbon dioxide to make urea, or with nitric acid to make ammonium nitrate. Each is concentrated to a hot liquid and then solidified.
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Dissolve the phosphate rock
Phosphate rock is insoluble, so crops cannot use it directly. Sulfuric acid breaks it down into forms that dissolve in water.
Goes in -
Wash and sort the potash
Mined potash ore is crushed, and its potassium salt is separated from clay and common salt by dissolving or floating it. It is then dried and screened.
Goes in -
Blend the nutrients
Nitrogen, phosphorus and potassium ingredients are measured into a mixer in the ratios printed on the bag. A fertilizer for lawns and one for corn use different recipes.
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Form granules or prills
Liquid urea is dropped from a tower and falls as tiny beads, called prills, that harden on the way down. Other plants tumble damp powder in a drum so it grows into granules.
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Dry, coat and bag it
Granules are dried, screened and sometimes coated so they do not cake or dust. They are bagged or shipped loose.
Worth repeating
- Nitrogen fertilizer use rose by 800% between 1961 and 2019.
- Friedrich Wöhler made urea from inorganic starting materials in 1828, which showed that a substance from living things could be made without them.
- In 2021, farmers used 195 million tonnes of nutrients in inorganic fertilizers, and 56% of that was nitrogen.
Back to the ground
Follow every input upstream and fertilizer starts as these 10 raw sources.
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Sources
Cite this page: "How fertilizer is made." Assembly Line, 2026-11-03. https://assemblyline.org/make/fertilizer