A suggested fractionation scheme of inorganic phosphorus in calcareous soils

On the basis of a critical review on conventional fractionation schemes of inorganic phosphate and further study of chemical behaviors of Ca-P and Fe-P in calcareous soils, a systematic scheme for the separation of soil inorganic phosphates in calcareous soils is suggested. In the scheme calcium phosphate is classified into dicalcium phosphate, octacalcium phosphate and apatite types, and Ca₂-P is extracted by NaHCO₃ solution, Ca₈-P by NH₄Ac, Al-P by NH₄F, Fe-P by NaOH-Na₂CO₃, occluded-P by Na₃Cit-Na₂S₂O₄-NaOH, and Ca₁₀-P by H₂SO₄.Synthetic phosphates prepared of which the chemical and physical assay show good consonance with the theoretical value were used in experiment, the recovery rates of the phosphates added into the calcareous soils by specific extractants is at the range of 85–99%.