Fertilizer production ranges from backyard composting to massive industrial operations that convert raw minerals and atmospheric gases into plant-ready nutrients. The three primary nutrients in commercial fertilizer are nitrogen, phosphorus, and potassium, and each one requires a fundamentally different manufacturing process. Global output is enormous: in 2024, the world produced roughly 190 million metric tons of ammonia, 88 million metric tons of phosphoric acid, and 73.5 million metric tons of potash.
Nitrogen Fertilizer Starts With Air
Nitrogen makes up about 78% of the atmosphere, but plants can’t use it in gas form. The Haber-Bosch process, developed in the early 1900s, solved this by combining atmospheric nitrogen with hydrogen gas under extreme heat and pressure in the presence of an iron catalyst. The result is ammonia, the building block of nearly all nitrogen fertilizers.
That ammonia can be applied directly as a fertilizer (anhydrous ammonia) or processed further into urea, ammonium nitrate, or ammonium sulfate. Urea is by far the most common form. Global urea production hit a record 199.7 million metric tons in 2024. To make urea, ammonia is reacted with carbon dioxide under pressure, forming a solid that contains about 46% nitrogen by weight, the highest concentration of any common solid nitrogen fertilizer.
The hydrogen needed for the Haber-Bosch process typically comes from natural gas through a process called steam methane reforming, which is why nitrogen fertilizer prices track closely with natural gas prices. This also makes nitrogen fertilizer production one of the most energy-intensive manufacturing processes in the world, consuming roughly 1-2% of global energy.
Phosphorus Fertilizer Comes From Rock
Phosphorus fertilizer begins as phosphate rock, a mineral mined primarily in Morocco, China, and the United States. The rock itself is not soluble enough for plants to absorb, so it must be chemically processed.
The dominant method is called the wet process. Phosphate rock is dissolved in a mixture of sulfuric acid and phosphoric acid inside large reactors at temperatures between 70 and 100°C. This produces phosphoric acid, the key intermediate for nearly all phosphorus fertilizers, along with a calcium sulfate byproduct (essentially a form of gypsum) that gets filtered out. The phosphoric acid is then combined with ammonia to create the finished products most farmers use: monoammonium phosphate (MAP) or diammonium phosphate (DAP). Combined production of these two products reached about 66.8 million metric tons in 2024.
A simpler, older method involves reacting phosphate rock directly with sulfuric acid to create single superphosphate, which contains both phosphorus and sulfur. This product has a lower phosphorus concentration but requires less processing infrastructure.
Potassium Fertilizer Is Mined and Refined
Potassium fertilizer, commonly called potash, is the most straightforward of the three to produce because the raw material already contains the nutrient in a usable form. Potash ore, primarily potassium chloride mixed with sodium chloride and clay, is mined from underground deposits in Canada, Russia, and Belarus.
After mining, the ore is crushed and the potassium chloride is separated from impurities. The most common separation methods are flotation (using reagents that selectively attach to potassium chloride crystals, floating them to the surface) and dissolution-recrystallization (dissolving the ore in hot water and then cooling it so the potassium chloride crystallizes out). More advanced techniques like anti-solvent crystallization, which uses organic solvents such as acetone to force potassium chloride out of solution, can produce product purities above 99.9%. Global potash production recovered by 5% in 2024 to reach 73.5 million metric tons.
Turning Raw Chemicals Into Granules
Raw fertilizer chemicals are powders, liquids, or crystals. To make them practical for spreading on fields, manufacturers turn them into uniform granules through a process called granulation. The two most common machines for this are disc granulators and rotary drum granulators.
A disc granulator uses a large, tilted rotating disc. Raw material is fed onto the disc, where gravity and centrifugal force cause small particles to roll toward the lower edge, picking up fine powder as they go and gradually forming spherical pellets. Once granules reach the target size, they overflow the disc’s edge and are collected. This setup works well for smaller production volumes and gives operators good visual control over the process.
Rotary drum granulators handle larger volumes. Material enters a long, slowly rotating cylinder, where it tumbles and gradually forms round particles. Steam heating inside the drum helps bind the material, and a rubber lining prevents sticking. The granules that exit the drum are then dried further to harden them for storage and transport. Most large-scale fertilizer plants use drum granulation for its higher throughput.
After granulation, the pellets typically pass through screens to sort them by size, a dryer to remove excess moisture, and a cooler. Many products also receive a coating to prevent caking during storage.
Blending Compound Fertilizers
Many farmers need fertilizers that contain specific ratios of nitrogen, phosphorus, and potassium (the familiar N-P-K numbers on a bag). These are produced either by chemically reacting the components together during granulation (compound fertilizers) or by physically mixing pre-made granules of each nutrient (blended fertilizers).
Liquid fertilizers follow a specific mixing sequence to prevent chemical reactions that could cause clumping or precipitation. The tank is first filled halfway with clean water. If the water is hard, ammonium sulfate goes in next to prevent minerals from interfering. Water-dispersible powders are added after that, pre-mixed into a slurry before being poured in. Liquid concentrates follow. Surfactants, which help the fertilizer spread evenly on plant surfaces, always go in last.
Composting: Producing Organic Fertilizer
Organic fertilizer production relies on biological decomposition rather than chemical synthesis. The most accessible method is aerobic composting, which converts plant waste, manure, and food scraps into a nutrient-rich soil amendment.
The critical factor in composting is the carbon-to-nitrogen ratio of your starting materials. The ideal ratio is about 30 parts carbon to 1 part nitrogen by weight. Carbon-rich “brown” materials include dried leaves, straw, and wood chips. Nitrogen-rich “green” materials include fresh grass clippings, food scraps, and manure. If you add too much nitrogen (a ratio below 30:1), the excess escapes as ammonia gas, creating strong odors. Too much carbon (above 30:1) starves the microbes of nitrogen, keeping the pile cool and slowing decomposition to a crawl.
A well-balanced compost pile heats up to 55-65°C within days as microbes rapidly consume the organic matter. Turning the pile regularly introduces oxygen, which keeps the aerobic bacteria active and prevents the pile from going anaerobic (which produces foul smells). Over weeks to months, the C:N ratio drops from 30:1 to around 10-15:1 in the finished compost, meaning the nutrients have become concentrated and stable enough for plants to use.
Microbial Inoculants as Bio-Fertilizers
Bio-fertilizers take a completely different approach. Instead of supplying nutrients directly, they contain living microorganisms that help plants access nutrients already in the soil. Nitrogen-fixing bacteria, for example, convert atmospheric nitrogen into forms plant roots can absorb.
Production starts with isolating effective microbial strains, then mass-culturing them through either liquid fermentation (growing bacteria in nutrient broth) or solid-state fermentation. The cultured microbes are then combined with a carrier material to keep them alive during storage and application. Solid carriers include peat, charcoal, vermiculite, and talc, formulated into powders or granules. Liquid formulations use water, mineral oils, or organic oils as the base. The first commercial microbial inoculant, called “Nitragin,” was introduced in the United States in 1896 using gelatin as a carrier for nitrogen-fixing bacteria.
The European Union currently permits marketing of bio-fertilizers containing four types of microorganisms: Rhizobium, Azotobacter, Azospirillum, and mycorrhizal fungi. Each serves a different role. Rhizobium and Azotobacter fix nitrogen, Azospirillum stimulates root growth, and mycorrhizal fungi extend the root network to access phosphorus and water in a wider area of soil.
Controlled-Release Coatings
One of the biggest problems with conventional fertilizer is that nutrients dissolve quickly and wash away in rain before plants can use them. Controlled-release fertilizers address this by coating granules in materials that slow nutrient release over weeks or months.
The earliest coatings used sulfur, which gradually breaks down in soil. Modern versions use synthetic polymer shells that control how quickly water penetrates to the fertilizer core. The thickness and composition of the coating determine the release timeline, which manufacturers can tune to match a crop’s growing season. Newer research focuses on replacing synthetic coatings with biological polymers like cellulose, chitin, and lignin, which break down naturally in soil without leaving plastic residue. These bio-based coatings also help retain moisture around the granule, improving nutrient uptake in dry conditions.
Safety Considerations for Stored Fertilizer
Most fertilizers are stable and safe to handle with basic precautions, but ammonium nitrate is a notable exception. This nitrogen fertilizer is also a powerful oxidizer, and improper storage has caused catastrophic explosions. OSHA guidelines require that ammonium nitrate never be heated above 170°C in a confined space, never be contaminated with organic materials like wood chips, diesel fuel, or oils, and never be exposed to shock. Storage bins must be constructed of non-combustible materials, kept padlocked when not being loaded or unloaded, and posted with reflective warning signs visible to emergency responders. Quantities above 2,000 pounds trigger additional security requirements due to theft-diversion risk. Smoking and open flames are prohibited in any storage area.