Fig. 3. Soil P adsorption isotherms: (a) surface soil layer (A, Ap) and (b) subsoil (Bw, B/E horizon). Inserted figures depict the whole range of values. Symbols represent the average of three replicates. Lines are fitted Langmuir isotherms for Arkport (lower) and Genesee (upper); fitted lines for other soils fell between those shown.