1908, Russian scholars дпрянишников and зв. ъри. 1927, Germany, France and Germany first decomposed phosphate rock with mixed acid of nitric acid and phosphoric acid, and then added potassium salt to the acidolysis product to obtain a fertilizer containing N, P and K comprehensive nutrients. However, due to the heavy smell of ammonia, the product was discontinued in less than one year. 1928 The Norwegian Oda Smelting Company proposed a method of decomposing phosphate rock with nitric acid. The obtained acidolysis solution was frozen to separate most calcium nitrate, and then processed into fertilizer. 1930 patent was transferred to Norsk Hydro company of Norway, and 1938 began to sell nitrophosphate products. This is the earliest industrial practice of freezing nitrophosphate. At the same time, in 1937, Lonza Company of Switzerland proposed a method of decomposing phosphate rock powder with 70% nitric acid to produce nitrophosphate. The product contains 8% nitrogen and 16% phosphorus pentoxide. Because the product contains hydrated calcium nitrate, which has strong hygroscopicity, low total nutrient content and serious nitrogen dioxide escape in production, it has not been popularized and applied. During the period of 1942- 1945, the production of nitrophosphate in Norsk Hydro company was stopped due to the war, and the raw materials were interrupted. Production resumed after the war. 1950 The output of frozen nitrate is 40,000 tons/year. About 1950, BASF company of Germany, Dutch state-owned mines and some chemical plants in France have successively developed their own frozen mixed acid nitrophosphate technology. Because the technical basis of most companies involves the Aoda process of frozen calcium removal, frozen nitrophosphate is collectively referred to as Aoda process by the fertilizer industry.