Abstract/Summary

The effect of dissolved organic P (DOP) (p-nitrophenyl phosphate, sodium myo-inositol hexaphosphate, and β-glycerophosphoric acid) on the ability of Fe-oxide-impregnated filter paper (Pi test) to act as a sink for dissolved inorganic P (DIP) was investigated. The efficiency of DIP recovery from strips equilibrated with DIP plus DOP was also studied. This information is needed to assess the accuracy of the Pi test to estimate bioavailable P (BAP) in soils and agricultural runoff containing high concentrations of DOP (up to 5 mg L−1). Iron-oxide strips removed on average 100% DIP and 99% DOP during a 16-h solution-strip equilibration at 25°C. Thus, none of the DOP compounds affected 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 plus β-glycerophosphoric 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 hydrolyze sodium inositol hexaphosphate and DIP recovery averaged 95%, use of NaOH as strip extractant is recommended for soils and runoff samples containing high DOP concentrations.