Dicalcium phosphate reaction with soils during 2N ammonium sulfate extraction

The consistent method for fractionation of soil phosphorus has already been recommended by M.L. Jackson et al. (1,2,3) based on the solubility product of different soil phosphates, and being widely applied for soil research and practice. Lately, some criticism of the method arose as to the probability of dissolution in 0.5 M ammonium fluoride solution of freshly formed dicalcium phosphate and other reaction products of fertilizer recently added to soil. Since dicalcium phosphate is of nature soluble in ammonium fluoride, as well as aluminium phosphate, if dicalcium phosphate was contained in appreciable amount in soil, so that the value of aluminum phosphate to be dissolved into ammonium fluoride must become higher beyond the real value. It is, therefore, significant to know the fate of applied phosphate fertilizer and the status of native labile phosphate.