Fig. 3. Relationship for the soils of the 5- and 10-cm treatments between the P concentration in 1:2 (w/v) water extracts and (A) phosphorus extractable with a filter paper strip impregnated with iron oxide (FeO-P) and (B) , which was calculated as P_ox/(Al + Fe)_ox [with P_ox and (Al + Fe)_ox in mmol kg^–1]. To guide the eye, lines, fitted to the data using an exponential curve, have been added.