A method for applying an agricultural fertilizer to a field through an irrigation system connected to a source of hard water, includes providing a fertilizer composition comprising a mixture of (i) a fertilizer component comprising an ammonium phosphate or an ammonium sulfate, and (ii) an acid comprising one or more of a phosphoric acid, a citric acid, a malic acid, a formic acid, and an oxalic acid; combining the fertilizer composition with hard water from the hard water source and providing the mixture to an irrigation system; and using the irrigation system to apply the mixture of fertilizer composition and hard water to the field.