1 SURFACE CHARGE AND SOLUTE INTERACTIONS IN SOILS N. S. Bolan 1 , R. Naidu 2 , J.K. Syers 3 , and R.W. Tillman 1 1 Department of Soil Science, Massey University, Palmerston North, New Zealand; 2 CSIRO Land and Water, Glen Osmond, South Australia; 3 Department of Agricultural and Environmental Science, The University, Newcastle upon Tyne, NE1 7RU, UK. I. Introduction II. Types of electrical surface charge III. Development of surface charge A. Isomorphous substitution B. Protonation and deprotonation C. Specific adsorption of anions and cations IV. Components of surface charge V. Solution-surface interface A. Diffuse double layer B. Diffuse double-layer model of variable-charge minerals VI. Concepts of point of zero charge VII. Measurement of surface charge A. Potentiometric titration B. Ion retention C. Electrokinetic techniques VIII. Factors affecting surface charge A. Soil components B. Ionic strength of soil solution C. Soil solution composition