A SUGGESTED FRACTIONATION SCHEME OF INORGANIC PHOSPHORUS IN CALCAREOUS SOILS
Jiang Baifan Gu Yichu (Institute of Soil Science, Academia Sinica, Nanjing)
A new soil inorganic-P fractionation scheme is presented in this paper, in which calcium phosphate is classified into three groups; dicalcium phosphate-type, octocalcium phosphate-type and apatite-typs, and Fe-P is extracted with NaOH-Na_2CO_3. The recovery rates of synthetic phosphates in calcareous soils are at the range of 85-99%.Compared with Chang and Jackson's scheme, it shows no remarkable difference in the amount between the total of three groups of calcium phosphates in this scheme and the total of NH_4Cl-soluble and H_2SO_4 -soluble phosphate in Chang and Jackson's scheme; and so does the total of unoccluded Fe-P and occluded-phosphate between two schemes. But in Chang and Jackson's scheme all the calcium phosphates are in one group of H_2SO_4 extractant, and the extracted amount of unoccluded Fe-P is only a trace. But in this scheme, the three groups of calcium phosphates and much unoccluded Fe-P can be extracted. There may be of significance on further study of the relationship between the transformation of phosphorus form in calcareous soil and plant phosphorus nutrition.