Soil Phosphorus Extracted By Iron‐Aluminum‐Oxide‐Impregnated Filter Paper

The use of Fe‐Al‐oxide‐impregnated paper strips may allow estimation of plant‐available P contents of soils with widely differing properties. Little information is available on the forms of P extracted by paper strips (SP). Relationships between SP and Olsen, Bray I, Mehlich III, and P fractions were investigated for 203 surface soils representing all soil orders. Soils were divided into calcareous, slightly weathered, and highly weathered groups, based on taxonomy and weathering. Amounts of P extracted by paper strips were closely correlated ( r 2 of 0.89 to 0.93, P > 0.001) with soil‐test P (Olsen, Bray I, and Mehlich III), for soils on which use of the test is recommended. It is suggested that the paper strips removed primarily physically bound extractable P from all soils (approximate 1:1 relationship), with little extraction of amorphous Al and Fe or Ca compounds indicated. A potential general applicability of Fe‐Al‐oxide‐impregnated paper strips to estimate plant‐available soil P is suggested.