Determination of Plant‐available Phosphorus by the Iron Hydroxide‐impregnated Filter Paper (Pi) Soil Test

Abstract

AbstractThe use of iron hydroxide‐impregnated filter paper (Pi) strips as a collector for phosphorus (P) in soil suspension offers a new approach to soil testing for plant‐available P. To correlate the Pi test with crop response, four soils ranging in pH from 4.5 to 8.2 were incubated with three rates of P either as triple superphosphate (TSP) or central Florida phosphate rock (CFPR), and P was measured in these soils by the Pi, Bray 1, Bray 2, double acid, Olsen, water, and resin extraction methods. Two successive crops of maize (Zea mays L.) were grown on these soils in greenhouse pots, and the dry matter yield and P uptake by maize were correlated with the soil test values. The Pi gave highly significant correlation with crop response in all four soils. Across all soils, P source, rates of application and crops, Pi gave the best correlation (0.870) with P uptake and dry matter yield. The next best correlation with dry matter yield was that of Olsen extractable P. The Pi test showed potential as a tool for prediction of P fertilizer requirements in soils.