The three numbers separated by hyphens on a fertilizer bag indicate the percentage of nitrogen, phosphate, and potash, respectively, that is available to the plants. The remaining materials in the bag are typically micronutrients and filler material, according to The Fertilizer Institute.
Nitrogen comes from the air, which contains about 78 percent nitrogen, but few plants can make direct use of nitrogen in the air. To make it available to plants, it is converted into nitrogen fertilizer. This is done by capturing nitrogen from the air and combining it with hydrogen from natural gas under heat and pressure to form anhydrous ammonia.
Ammonia can be applied directly to crops as a fertilizer or can be used to make other fertilizers such as urea, ammonium nitrate, ammonium sulfate, and water-based liquid nitrogen fertilizers.
Ammonia (82-0-0): Used as a fertilizer or building block for other fertilizers.
Urea (46-0-0): A solid nitrogen fertilizer usually applied in granular form. It can be combined with ammonium nitrate and water to make a liquid fertilizer known as urea ammonium nitrate.
Ammonium nitrate (34-0-0): A solid nitrogen fertilizer applied in granular form.
Ammonium sulfate (21-0-0): A solid byproduct of coke ovens, where sulfuric acid is used to remove ammonia evolved from the coal.
Nitrogen solutions: Usually a combination of urea and ammonium nitrate dissolved in water.
Phosphorus fertilizer is derived from the fossilized remains of ancient marine life found in rock deposits in North America, North Africa, and China. It is made by combining phosphate rock with sulfuric acid.
Triple superphosphate (0-46-0) is a highly concentrated form of phosphorus.
Monoammonium phosphate (11-52-0) and diammonium phosphate (18-46-0) are called ammoniated phosphates, because phosphoric acid is treated with ammonia to form these products, which also contain nitrogen.
Fertilizer producers mine potassium, or potash, from ore deposits that were formed when seas and oceans evaporated, many of which are covered with several thousands of feet of earth. After ore is brought to the surface, unwanted minerals are removed, and the product is granulated.