The fertilizer elements are present in various compounds (e.g., urea, ammonium nitrate, phosphoric acid, calcium phosphate, potassium chloride). The composition by percentage of each of the ‘big 3’ elements present in the fertilizer must be stated on the bag and is referred to as the fertilizer guarantee, which expresses each of elemental N, phosphate, and potash as a percentage of the contents. For example, suppose your fertilizer has the numbers 10-5-8 (an unconventional fertilizer but useful as an example). This fertilizer contains 10% (1st number) elemental nitrogen, 5% (2nd number) available phosphate (P2O5) and 8% (3rd number) water soluble potash (K2O). The remainder of
the material is comprised of the other elements in the compounds and filler. The filler may be ground limestone to offset the acid potential of the fertilizer, along with some inert material. The filler facilitates spreading of small amounts of nutrients over a large area.
