Headings 3102, 3103, and 3104 each cover fertilizers whose fertilizing value comes from a single element (nitrogen, phosphorus, or potassium, respectively). Once a product is formulated to supply two or three of those elements in commercially meaningful proportions, it moves to heading 3105. The declared nutrient analysis (N-P-K percentages on the label or certificate of analysis) is the primary classification evidence.

Antidumping and countervailing duty orders have been imposed on DAP and MAP from certain countries. The scope of each order is defined by Commerce Department scope rulings tied to specific HTS lines and country of origin. Importers should review current CBP and Commerce Department records for active orders and request scope rulings when the product or origin is borderline, since duty deposits on covered entries can be substantial.