CHAPTER 31 · LEGAL NOTES
Chapter 31
The 30 legal notes below govern classification under Chapter 31. They are part of the official Harmonized Tariff Schedule and are cited verbatim in CBP rulings.
As of June 9, 2026
Chapter notes
Note 1
Chapter Note 1: This chapter does not cover: (a) Animal blood of heading 0511; (b) Separate chemically defined compounds (other than those answering to the descriptions in note 2(a), 3(a), 4(a) or 5, below); or (c) Cultured potassium chloride crystals (other than optical elements) weighing not less than 2.5 g each, of heading 3824; optical elements of potassium chloride (heading 9001).
Note 2
Chapter Note 2: Heading 3102 applies only to the following goods, provided that they are not put up in the forms or packages described in heading 3105: (a) Goods which answer to one or other of the descriptions given below: (i) Sodium nitrate, whether or not pure; (ii) Ammonium nitrate, whether or not pure; (iii) Double salts (whether or not pure) of ammonium sulfate and ammonium nitrate; (iv) Ammonium sulfate, whether or not pure; (v) Double salts (whether or not pure) or mixtures of calcium nitrate and ammonium nitrate; (vi) Double salts (whether or not pure) or mixtures of calcium nitrate and magnesium nitrate; (vii) Calcium cyanamide, whether or not pure or treated with oil; (viii) Urea, whether or not pure. (b) Fertilizers consisting of any of the goods described in (a) above mixed together. (c) Fertilizers consisting of ammonium chloride or of any of the goods described in (a) or (b) above mixed with chalk, gypsum or other inorganic nonfertilizing substances.
Note 3
Chapter Note 3: Heading 3103 applies only to the following goods, provided that they are not put up in the forms or packages described in heading 3105: (a) Goods which answer to one or other of the descriptions given below: (i) Basic slag; (ii) Natural phosphates of heading 2510, calcined or further heat-treated than for the removal of impurities; (iii) Superphosphates (single, double or triple); (iv) Calcium hydrogenorthophosphate containing not less than 0.2 percent by weight of fluorine calculated on the dry anhydrous product. (b) Fertilizers consisting of any of the goods described in (a) above, mixed together, but with no account being taken of the fluorine content limit. (c) Fertilizers consisting of any of the goods described in (a) or (b) above, but with no account being taken of the fluorine content limit, mixed with chalk, gypsum or other inorganic nonfertilizing substances.
Note 4
Chapter Note 4: Heading 3104 applies only to the following goods, provided that they are not put up in the forms or packages described in heading 3105: (a) Goods which answer to one or other of the descriptions given below: (i) Crude natural potassium salts (for example, carnallite, kainite and sylvite); (ii) Potassium chloride, whether or not pure, except as provided in note 1(c) above; (iii) Potassium sulfate, whether or not pure; (iv) Magnesium potassium sulfate, whether or not pure. (b) Fertilizers consisting of any of the goods described in (a) above mixed together.
Note 5
Chapter Note 5: Ammonium dihydrogenorthophosphate (monoammonium phosphate) and diammonium hydrogenorthophosphate (diammonium phosphate), whether or not pure, and intermediates thereof, are to be classified in heading 3105.
Note 6
Chapter Note 6: For the purposes of heading 3105, the term "other fertilizers" applies only to products of a kind used as fertilizers and containing, as an essential constituent, at least one of the fertilizing elements nitrogen, phosphorus or potassium. Unit Rates of Duty of Quantity Article Description Stat. Suffix Heading/ Subheading 1 2 General Special Animal or vegetable fertilizers, whether or not mixed together or chemically treated; fertilizers produced by the mixing or
footnote
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Classify under Chapter 31 with confidence
TariffLens applies the legal notes above automatically when classifying — citing the relevant note in every GRI reasoning chain.