7 Pa. Code § 73.1
The following words and terms, when used in this chapter, have the following meanings, unless the context clearly indicates otherwise:
Act—The Pennsylvania Fertilizer, Soil Conditioner and Plant Growth Substance Law (3 P. S. § § 68.1—68.23).
Primary plant nutrient—A fertilizer component consisting of nitrogen, phosphorus and potassium compounds.
Secondary plant nutrient—A fertilizer nutrient component other than primary plant nutrients.
The provisions of this § 73.1 adopted July 28, 1972, effective July 29, 1972, 2 Pa.B. 1435.