Fig. 4. Relationship for the soils of the 5- and 10-cm treatments between the P concentration in 1:10 (w/v) 0.01 M CaCl₂ extracts and , which was calculated as P_ox/(Al + Fe)_ox [with P_ox and (Al + Fe)_ox in mmol kg^–1]. To guide the eye, a line, fitted to the data using a double exponential curve, has been added.