Fertilizer is made from three primary raw materials: nitrogen pulled from the air, phosphorus mined from rock, and potassium extracted from underground salt deposits. These three nutrients, often listed on packaging as N-P-K, form the backbone of nearly every commercial fertilizer. How they’re sourced, processed, and combined varies widely depending on whether the end product is synthetic or organic, liquid or granular.
Nitrogen: Pulled From Thin Air
About 78% of Earth’s atmosphere is nitrogen gas, but plants can’t use it in that form. To make it available, manufacturers rely on a century-old industrial process that converts atmospheric nitrogen into ammonia, the starting point for virtually all nitrogen fertilizer.
The process works by combining hydrogen (usually stripped from natural gas through steam reforming) with nitrogen separated from air. These two gases are forced together at extreme conditions: temperatures between 370 and 540°C and pressures above 2,000 psi, in the presence of an iron-based catalyst. The result is ammonia. In countries without cheap natural gas, like China, coal gasification provides the hydrogen instead. Newer catalysts made from ruthenium on graphite can run at lower pressures (around 1,300 psi), cutting equipment costs.
That ammonia is then the building block for other nitrogen fertilizers. It can be applied directly as anhydrous ammonia, converted into urea, or combined with other chemicals to produce ammonium nitrate or ammonium sulfate. This single industrial reaction consumes roughly 1 to 2% of the world’s total energy supply, making nitrogen fertilizer production one of the most energy-intensive manufacturing processes on the planet.
Phosphorus: Mined From Ancient Rock
Phosphorus fertilizer starts as phosphate rock, a sedimentary mineral mined in large open pits. The rock is dried, crushed, and then treated with sulfuric acid in what’s called the wet process. This chemical reaction dissolves the phosphorus out of the rock and produces two things: phosphoric acid (the useful part) and calcium sulfate, better known as gypsum (the waste byproduct).
The raw phosphoric acid that comes out of this reaction contains about 26 to 30% phosphorus pentoxide, which isn’t concentrated enough for most fertilizers. It gets run through vacuum evaporators two or three times to bring the concentration up to 40 to 55%. From there, manufacturers can combine it with ammonia to produce common fertilizers like monoammonium phosphate (MAP) or diammonium phosphate (DAP), which deliver both nitrogen and phosphorus in a single product.
Potassium: Harvested From Salt Deposits
Potassium for fertilizer, commonly called potash, comes from ancient underground salt deposits or from mineral-rich brines and seawater. Canada, Russia, Belarus, Germany, Israel, and Jordan are the world’s leading producers, largely because of their abundant salt deposits.
Two main extraction methods dominate. Shaft mining works like traditional mining: digging down to reach buried layers of potassium-bearing salts like sylvite and carnallite. Solution mining takes a different approach, pumping water underground to dissolve the salts, then bringing the brine back to the surface for processing. In coastal regions, potash can also be recovered from seawater through chemical precipitation or membrane separation. The extracted potassium is refined into potassium chloride, the most common form used in fertilizer blends.
How NPK Numbers Work on the Label
Every bag of fertilizer carries a three-number code like 10-10-10 or 15-30-15. The first number is the percentage of nitrogen by weight. The second is the percentage of phosphorus (expressed as phosphorus pentoxide). The third is potassium (expressed as potassium oxide). So a 50-pound bag of 10-10-10 contains 5 pounds each of nitrogen, phosphorus pentoxide, and potassium oxide.
Labeling conventions vary by country. Australia uses elemental percentages and adds a fourth number for sulfur (N-P-K-S). The U.K. allows elemental phosphorus and potassium values in parentheses after the standard numbers. Some European fertilizers tack on additional numbers for calcium and sulfur. Regardless of the system, the core idea is the same: giving you a quick ratio of the three nutrients plants need most.
Secondary and Trace Nutrients
Beyond the big three, plants need calcium, magnesium, and sulfur in moderate amounts. These secondary nutrients are sometimes included in blended fertilizers or applied separately through materials like limestone (for calcium) or Epsom salt (for magnesium).
Then there are micronutrients, required in only tiny quantities but still essential for healthy growth. These include iron, zinc, manganese, boron, copper, and molybdenum, among others. Specialty fertilizer blends may contain one or several of these, particularly for crops or soils known to be deficient. A soil test is the most reliable way to know which of these your soil actually needs.
What Organic Fertilizers Are Made From
Organic fertilizers skip the industrial chemistry and rely on plant, animal, or mineral sources instead. They tend to have lower nutrient concentrations than synthetics, but they deliver a wider range of nutrients and feed soil biology over time.
For nitrogen, the most concentrated organic options are blood meal (roughly 12.5% nitrogen) and feather meal (about 12% nitrogen). Blood meal releases its nitrogen slowly over two to six weeks, while feather meal breaks down somewhat faster.
Phosphorus-rich organic materials include rock phosphate (20 to 33% phosphorus), bone meal (15 to 27%), and colloidal phosphate (17 to 25%). These release phosphorus more gradually than synthetic phosphoric acid products, which can be an advantage in preventing runoff but means results take longer.
For potassium, organic growers turn to kelp meal (4 to 13% potassium), wood ash (3 to 7%), greensand (about 5%), and granite meal (3 to 6%). Compost and well-aged manure supply modest amounts of all three major nutrients along with secondary nutrients and micronutrients, making them a broad-spectrum soil amendment rather than a targeted fertilizer.
Granular vs. Liquid Formulations
The same nutrients can be delivered in granular or liquid form, and the manufacturing difference matters for how they perform. Granular fertilizers are made by combining raw materials into solid particles, either through chemical reaction (reactive granulation) or by coating a core material with nutrient layers. They’re easier to store because they don’t settle out or crystallize in cold weather the way liquids can.
Liquid fertilizers dissolve nutrients in water or suspend them in solution. Their key advantage is uniformity: every drop contains exactly the same nutrient ratio, while individual granules in a bag may each contain different nutrient components. Liquids are also more mobile in soil water, meaning they reach plant roots faster. The tradeoff is that they’re more prone to leaching through the soil before plants can absorb them.
Controlled-Release Coatings
Standard fertilizers dissolve quickly when they get wet, releasing all their nutrients at once. Controlled-release fertilizers solve this by wrapping each granule in a coating that breaks down gradually. The coating materials fall into two broad categories. Inorganic coatings include sulfur, bentonite clay, and phosphogypsum. Organic polymer coatings can be synthetic (polyurethane, polyethylene, alkyd resin) or derived from natural materials like starch, chitosan, and cellulose. Some newer formulations use biochar or plant-derived compounds like rosin and polyphenol.
The thickness and composition of the coating determine how fast nutrients escape. Thicker coatings or less permeable polymers slow the release, letting a single application feed plants for weeks or months instead of days. This reduces the number of applications you need and cuts down on nutrient loss to runoff and groundwater.