SORPTION OF PHOSPHORUS BY THE IRON OXIDE-IMPREGNATED FILTER-PAPER (PI SOIL TEST) EMBEDDED IN SOILS

Incubation experiments were carried out to evaluate the feasibility of extracting phosphorus from soil by embedding iron oxide-impregnanted filter paper strips (Pi strips) in soils having a wide range in pH, texture, and extractable-P contents. Under flooded conditions, the amount of P extracted by the Pi strips increased with the period of submergence and embedding time of the Pi strips. Under unsaturated conditions, the Pi strips were found to extract P from soils over a wide range in moisture conditions; however, keeping the soil at moisture level between saturation and field capacity was found to result in maximal sorption of P by the strips. An embedding time of 16 h was found to be adequate. Phosphorus extracted by embedding Pi strips in soil columns for 16 h at field capacity moisture level correlated significantly with P extracted by shaking the soil with 0.01 M CaCl2 solution and a Pi strip for 16 h in the laboratory (r=0.94**). The P extracted by embedding Pi strips correlated best with Bray 1 P in acid soils (r=0.97**) and with Olsen P in alkaline and calcareous soils (r=0.96**). The results of the studies demonstrate the feasibility of developing a nondestructive method of monitoring changes in plant-available P in situ under field conditions. © 1990 Kluwer Academic Publishers.