Country of origin for blended fertilizers is generally determined by where substantial transformation occurs — typically the country where the final granulation or chemical reaction producing the NPK compound takes place. When raw materials from multiple origins are combined, importers should obtain a manufacturer's declaration and consult a licensed customs broker, as origin affects both duty rates and any applicable trade-remedy exposure.

At the SITC level, the heading applies to any product containing all three elements regardless of ratio. However, at the HTS 10-digit level used for US import entry, specific ratios or forms may direct classification to different tariff lines, so the certificate of analysis showing elemental percentages is an essential shipping document.