The forms of phosphate extracted from soils by various methods were established by calculation according to the law of solubility product. Ammonium carbonate solution may extract water soluble phosphates, CaHPO₄·2H₂O, CaHPO₄, Ca₄H(PO₄)₃·3H₂O,aluminum and iron phosphates, a little organic phosphorus and probably a little Ca₃(PO₄)₂, and Ca₅(PO₄)₃OH,similarly sodium carbonate solution may extract the same phosphates except those in organic forms. Sodium citrate solution extracts water soluble phosphates, CaHPO₄·2H₂O, CaHPO₄, aluminum and iron phosphates, and a little organic phosphorus. Lactate solution and Burriel-Hernando's extractant extract all forms of calcium phosphates in soils, but not aluminum and iron phosphates as well as organic phosphorus. Ammonium oxalate solution extracts all the above forms of phosphate from soils.Recovery test made on CaHPO₄, Ca₃(PO₄)₂ and FePO₄·4H₂O confirmed the results from calculation.The difference in the degree of correlation between the available phosphorus content as determined by the various methods and the response of crops to phosphorus fertilization was explained by the forms of phosphate extracted and the present knowledge of their availability.