Fractionation of the Residual Phosphorus Compounds in Black and Red Soils Treated with Phosphatic Fertilizers

Inorganic P fractions were determined in black and red soils after treating them separately with ammonium phosphate and superphosphate at three levels of P. In both soils, Fe-P was more than the other forms. Al-P was found only in soils treated with superphosphate. The liberation of strong acid as a result of the reaction of superphosphate with soil water might have caused the dissolution of Fe and Al from clay which precipitated Fe- and Al-phosphates.