A method of producing a fertilizer comprising a micronutrient metal polyphosphate composition, the method comprising: (i) dissolving a metal containing-compound in phosphoric acid to form a reaction mixture containing phosphoric acid and cations other than protons, the cations comprising metal cations of the dissolved metal containing-compound, the amount of phosphoric acid in the reaction mixture being less than the stoichiometric amount required for the complete conversion of the cations to the corresponding dihydrogen phosphate, the metal containing-compound comprising a micronutrient metal selected from the group consisting of chromium, cobalt, copper, iron, manganese, and zinc; (ii) heating the reaction mixture to between 100°C and 160°C; (iii) adding at least about 4 moles water for every mole of micronutrient to the heated reaction mixture; (iv) polymerizing the phosphoric acid and dissolved micronutrient metal cations at a temperature between 90°C and 165°C to form the micronutrient metal polyphosphate composition; and (v) neutralizing the micronutrient metal polyphosphate composition with a neutralizing base, the solubility of the neutralized micronutrient metal polyphosphate composition in water, 2% citric acid and 0.1N HCl being such that: (a) in a 10 minute period and at room temperature, a 50 mg sample of the micronutrient metal polyphosphate composition immersed in 50 ml of water at neutral pH releases no more than 15% of its micronutrient metal content; and (b) in a 1 hour period and at room temperature, a 50 mg sample of the mocronutrient metal polyphosphate composition immersed in 25 ml of 2 wt% citric acid is capable of releasing at least 70% of the amount of the micronutrient metal released by a 50 mg sample of the micronutrient metal polyphosphate composition immersed in 25 ml of 0.1N HCl. (i) dissolving a metal containing-compound in phosphoric acid to form a reaction mixture containing phosphoric acid and cations other than protons, the cations comprising metal cations of the dissolved metal containing-compound, the amount of phosphoric acid in the reaction mixture being less than the stoichiometric amount required for the complete conversion of the cations to the corresponding dihydrogen phosphate, the metal containing-compound comprising a micronutrient metal selected from the group consisting of chromium, cobalt, copper, iron, manganese, and zinc; (ii) heating the reaction mixture to between 100°C and 160°C; (iii) adding at least about 4 moles water for every mole of micronutrient to the heated reaction mixture; (iv) polymerizing the phosphoric acid and dissolved micronutrient metal cations at a temperature between 90°C and 165°C to form the micronutrient metal polyphosphate composition; and (v) neutralizing the micronutrient metal polyphosphate composition with a neutralizing base, the solubility of the neutralized micronutrient metal polyphosphate composition in water, 2% citric acid and 0.1N HCl being such that: (a) in a 10 minute period and at room temperature, a 50 mg sample of the micronutrient metal polyphosphate composition immersed in 50 ml of water at neutral pH releases no more than 15% of its micronutrient metal content; and (b) in a 1 hour period and at room temperature, a 50 mg sample of the mocronutrient metal polyphosphate composition immersed in 25 ml of 2 wt% citric acid is capable of releasing at least 70% of the amount of the micronutrient metal released by a 50 mg sample of the micronutrient metal polyphosphate composition immersed in 25 ml of 0.1N HCl. (a) in a 10 minute period and at room temperature, a 50 mg sample of the micronutrient metal polyphosphate composition immersed in 50 ml of water at neutral pH releases no more than 15% of its micronutrient metal content; and (b) in a 1 hour period and at room temperature, a 50 mg sample of the mocronutrient metal polyphosphate composition immersed in 25 ml of 2 wt% citric acid is capable of releasing at least 70% of the amount of the micronutrient metal released by a 50 mg sample of the micronutrient metal polyphosphate composition immersed in 25 ml of 0.1N HCl.