A new slow releasing particulate iron humate agricultural nutrient composition exhibiting substantially complete solubility of its iron content in soil solutions as indicated by neutral citrate solubilities, and almost no solubility in water, and a new method for preparing the composition. The method comprises admixing and coreacting iron humate with about equimolar amounts of a divalent metal oxide, an aqueous hydroxide of a monovalent Lewis acid, and a water soluble inorganic phosphate. The iron humate amounts to between 20 and 70 percent of the nutrient particles, and the reaction is carried out at temperatures between 60 and 150 .degree.C for between 4 and 25 minutes.
