Extractability of added phosphorus in short-term equilibration tests of Portuguese soils

As soil phosphorus (P) availability changes with soil type and time after f ertilizer application, use of a P availability index, "F" (fraction of adde d P remaining available after a given lime), was evaluated for as Portugues e soils as a function of soil P extractant (Egner, Fe-oxide strip, Mehlich 3, and Olsen). The F index values, based on a short-term P recovery after a -h and 24-h soil-P equilibration periods, were related to longer term F val ues determined after a 90 day soil-P equilibration of soil and P (r=0.87 to 0.98; P<0.001). Soil sorption was related to F values (r=0.73 to 0.88; P<0 .001). The results suggest that the 2-h and 24-h equilibration procedures c ould be used as a rapid prediction of P fertilizer availability in Portugue se soils widely ranging in P sorptivity.