This invention provides a process for the preparation of water insoluble, bio-release iron-manganese fertilizer which comprises, heating phosphoric acid with a mixture of (i) source of iron oxide such as goethite and hematite, (ii) pyrolusite and (iii) one or more basic compound(s) selected from oxide(s) or carbonate(s) of magnesium, calcium, sodium and potassium, (b) neutralisation followed by drying and pulverisation.