Fractionation of Soil Inorganic Phosphate by a Modification of Chang and Jackson's Procedure

A modified version of the phosphate fractionation procedure of Chang and Jackson (1957) included the determination of “residual inorg. P” and introduced a revised nomenclature for the other fractions. Added phosphate sorbed during the fluoride extraction was usually completely recovered in the succeeding sodium hydroxide extraction; this enabled mutually compensating corrections to be applied to NH 4 F‐P and 1st NaOH‐P values. A second acid treatment increased the amount of Ca‐P extracted. Further modifications simplified the colorimetric determinations of inorganic phosphate in several of the extracts. A measure of the reproducibility of fractionation results was also obtained.