This invention pertains to a process for manufacturing an iron-based nutrient composition comprising at least the steps of supplying an iron source and a phosphate source containing at least one polyphosphate, further comprising a mixing step of the iron source with the phosphate source. The iron source and phosphate sources being in their solid phase, the mixing of the two being solid-solid mixing, leading to the obtaining of a water-soluble, iron-based solid nutrient composition.
