Effect of liming on phosphate sorption by acid soils

SUMMARY The sorption of phosphate (P) by four strongly acid Fijian soils from 0.01 M CaCl 2 decreased with increasing pH up to pH 5.5–6.0 and then increased again. The initial decrease in P sorption with increasing pH appears to result from an interaction between added P, negative charge, and the electrostatic potential in the plane of sorption. The results of a sorption study, involving KCl or CaCl 2 of varying concentrations as the background electrolyte and using Nadroloulou soil incubated with KOH or Ca(OH) 2 , suggested that the increase in P sorption at pH values > 6.0 was caused by the formation of insoluble Ca‐P compounds. For some soils this is consistent with the results of an isotopic‐exchange study in which incubation with lime caused marked reductions in the amounts of exchangeable P at high pH.