IRON OXIDE-IMPREGNATED FILTER-PAPER (P-I TEST) .2. A REVIEW OF ITS APPLICATION

The iron oxide impregnated filter paper test (P-i test) is a recently developed soil test for phosphorus (P) in which the FeO paper acts as an infinite sink for P mobilized in a soil solution. Several papers ha ve been published evaluating the effectiveness of the test for predict ing plant availability of P under different soil conditions. The use o f FeO paper to predict algal availability of P in water bodies and run offs has also been studied. The purpose of this paper is to review stu dies on the use of the P-i test to evaluate plant availability of P in soils, and predict availability of P to algae in an aquatic environme nt. Phosphorus extracted by the FeO paper is primarily physically boun d extractable (resin P) and correlates significantly with Bray I and M ehlich P in acid soils and Olsen P in calcareous soils. Dry-matter yie ld and P uptake by maize (Zea mays L), kidney beans (Phaseolus vulgari s L), and upland rice (Oryza sativa L) grown in acidic soils correlate d well with P-i-P. Likewise, in calcareous soils, P-i-P was as good as Olsen-P in predicting crop response. Field trials have shown that the P-i test is a good predictor of plant yield in soils with wide rangin g properties. Compared to the standard method to measure bioavailable P to algae in waters and agricultural runoffs involving lengthy algal essays culturing selenastrum capricornutum with sediment samples, the P-i method is a faster and easier method to estimate P that may be pot entially available for uptake by algae.