Diammonium phosphate refers to the standard product containing N18%, P2O548%, the crystal shape is flat oblique prism, the solubility in 25C water is 71%, and the pH of its saturated solution reaches 8, which is much higher than that of monoammonium phosphate. The phosphate rock powder is reacted under the condition of excessive NH, F solution, pH 6~7, and temperature of 100 degrees: to obtain diammonium phosphate. However, the general factory adopts the process developed by the Tennessee Valley Authority (TVA) of the United States, that is, , Since the saturated solution of diammonium phosphate is alkaline, applying it on acidic soil can reduce the fixation of iron and aluminum on phosphorus, so that phosphorus can maintain a high effectiveness, so it is recommended to use diammonium phosphate on acidic soil.