Fertilizers generally contain in varying compositions one or more of the three primary crop nutrients -- nitrogen(N), phosphorus(P) and potassium(K).

Each nutrient has a particular role in supporting the growth of plant life and needs to be in the right proportion to the other primary nutrients. It is not possible to use one primary nutrient as a substitute for any other.

Fertilizer producers obtain phosphorus only from phosphate rock. There are no substitute sources. (Fertilizer manufacturers obtain the potassium from potash and produce the nitrogen used in fertilizers using a process that is heavily reliant on natural gas.)

Primary Nutrients in Fertilizers*