ORGANIC PHOSPHORUS EFFECTS ON SINK CHARACTERISTICS OF IRON-OXIDE-IMPREGNATED FILTER-PAPER

The effect of dissolved organic P (DOP) (p-nitrophenyl phosphate, sodi um myo-inositol hexaphosphate. and beta-glycerophosphoric acid) on the ability of Fe-oxide-impregnated filter paper (Pi test) to act as a si nk for dissolved inorganic P (DIP) was investigated. The efficiency of DIP recovery from strips equilibrated with DIP plus DOP was also stud ied. This information is needed to assess the accuracy of the Pi te.st to estimate bioavailable P (BAP) in soils and agricultural runoff con taining high concentrations of DOP (up to 5 mg L-1). Iron-oxide strips removed on average 100% DIP and ''% DOP during a 16-h solution-strip equilibration at 25-degrees-C. Thus, none of the DOP compounds affecte d the P-sink characteristics of the Fe-oxide strip. Recoveries of DIP by 0.1 M H2SO4 and 0.5 M NaOH, from strips equilibrated with DIP plus p-nitrophenyl phosphate. averaged 95%; with DIP pius beta-glycerophosp horic acid, recoveries averaged 97%. However, amounts of DIP recovered by 0.1 M H2SO4 from strips equilibrated with DIP plus sodium inositol hexaphosphate were greater than those added. As 0.5 M NaOH did not hy drolyze sodium inositol hexaphosphate and DIP recovery averaged 95%, u se of NaOH as strip extractant is recommended for soils and runoff sam ples containing high DOP concentrations.