Effect of liming and added phosphate on charge characteristics of acid soils

SUMMARY The effects of liming‐induced pH changes on surface charge were studied with four acid Fijian soils. All the soils possessed both positive and negative charge. Much of this charge was pH‐dependent, but some negative charge was present at pH values as low as 4.0 and small quantities of positive charge were detected at pH values as high as 8.2. Adsorption of phosphate (P) reduced positive charge at low pH and increased negative charge at high pH. The net amount of surface charge per unit of P adsorbed varied with pH and appeared to depend on the mineralogy of the soil.