A critical assessment of methods for determining organic phosphorus in savanna soils

Two newly introduced extraction techniques for determining total organic P (P-o) were compared with the standard high-temperature ignition method in s elected savanna soils of Nigeria. The two extraction techniques were: (1) c oncentrated H2SO4 and dilute base sequential extraction (18 N H2SO4 and 0.5 N NaOH) and (2) basic EDTA method (0.25 M NaOH plus 0.05 M Na(2)EDTA). The concentrated H2SO4 and dilute base method extracted significantly higher t otal P-o than the high-temperature ignition method and the basic EDTA extra ction. The high-temperature ignition and the basic EDTA extraction gave sim ilar total P-o values (mean = 91 mg kg(-1) for ignition and 90 mg kg(-1) fo r basic EDTA). The precision of the methods, determined by coefficients of variation (CV, %) associated with each P-o determination method in the soil s, was better for the concentrated H2SO4 and dilute base extraction method (CV = 13%) than the ignition method (CV = 18%) and the basic EDTA method (C V = 15%). The high C:P-o ratios determined for the high-temperature ignitio n and basic EDTA extraction indicated that the two methods underestimated t otal P-o in the soils. The concentrated H2SO4 and dilute base sequential ex traction appears to be suitable for the rapid determination of P-o in savan na soils because the method can be simplified to a single-step analysis.