The invention is directed to methods for producing a granular nitrogen fertilizer from an organic material comprising adding a metallic salt to said organic material to form a slurry. Preferably the organic material comprises dewatered biosolids and contains water from a scrubber. Metallic salts that can be used comprise a salt of iron, zinc, or a mixture thereof. Preferred iron salts comprises ferric sulfate or ferric oxide, and preferred zinc salts comprises zinc sulfate or zinc oxide. Preferably, the metallic salt is mixed with an acid such as sulfuric acid to form an acidified metal salt. Slurry pH ranges from approximately 2-2.5. The acidified metal salt is added to the organic material in sufficient quantity to lower viscosity of the slurry such that the resulting fluid does not hinder fluid flow during operation. When the metallic salt comprises acidified ferric sulfate or ferrous sulfate, sufficient iron can be present to produce a fertilizer product with 0.1 weight percent to 10 weight percent iron sulfate calculated on a dry weight basis. The invention is also directed to fertilizer products made by the methods of the invention. Preferred products are granules and the metallic salt increases product hardness. Fertilizer granules preferably contain metal that is bioavailable to a plant when used as a fertilizer. Solubility of the metal of the product in water is enhanced, and the product is low staining.