Mass. Gen. Laws ch. 128 § 65
The total phosphoric acid and the degree of fineness of unacidulated mineral phosphatic materials and basic slag, bone, tankage, and other organic phosphate materials may be guaranteed. Guarantees for plant nutrients other than nitrogen, phosphorus and potassium may be permitted or required by regulation of the commissioner. The guarantees for such other nutrients shall be expressed in the form of the element.
The sources of other nutrients may be required to be stated on the application for registration and may be included as a parenthetical statement on the label.
Other beneficial substances or compounds, determinable by laboratory methods also may be guaranteed by permission of the commissioner with the advice of the director of the agricultural experiment station.
When any plant nutrients or other substances or compounds are guaranteed, they shall be subject to inspection and analysis in accord with the methods and regulations prescribed by the commissioner.
Potential basicity or acidity expressed in terms of calcium carbonate equivalent in multiples of one hundred pounds per ton shall be guaranteed when required by regulations.
Mass. Gen. Laws ch. 128, § 65