Abstract: NP- or NPK-containing fertilizers are manufactured from low-grade phosphate ore digested by nitric acid. Substantial problems have been experienced during previous attempts to produce fertilizers from phosphate ore having a high content of magnesium. The problems relate to the solution's viscosity, which becomes extremely high during neutralization with ammonia of the mother liquor, obtained by removal of most of the calcium as calcium nitrate-tetrahydrate from the digested phosphate. The novel process solves the viscosity problems by adjusting the conditions during ammoniation and the subsequent evaporation before prilling or granulation. The adjustment is characterized in that a substantial part of the remaining calcium is kept outside the process itself, at least during the neutralization and evaporation stages.