Compound fertiliser

A compound fertiliser contains at least two major nutrients — nitrogen, phosphorus or potassium — within a single granule or a homogeneous blend. The abbreviations NP, NK, PK and NPK denote the possible combinations, with nutrient contents expressed in the N-P-K formula sequence^[1]. The sum of fertiliser units (N + P₂O₅ + K₂O) typically ranges from 30% to 60%^[1].

Manufacturing follows two distinct chemical routes: the mixed-acid route and the Odda process, the latter being installed at five plants across Europe^[1]; alternatively, fertilisers may be produced by mechanically blending straight fertilisers without chemical reaction^[2]. The European regulation on fertilising products sets minimum solubility requirements for phosphorus and mandates the declaration of nitrogen forms^[3].