DAP and MAP have specific chemical identities (diammonium hydrogenorthophosphate and ammonium dihydrogenorthophosphate, respectively). Products that are blends, solutions, or chemically distinct ammonium phosphate compounds that do not meet those precise definitions — but still supply both nitrogen and phosphorus — fall into the N.E.S. category. A detailed certificate of analysis is essential to support the classification decision.

Liquid ammonium polyphosphate solutions and other liquid NP fertilizers used in drip or pivot fertigation systems often fall under this heading when they do not correspond to the pure DAP or MAP chemical definitions. The physical form (liquid vs. granular) does not itself determine classification, but the chemical composition and the presence or absence of potassium are decisive factors.