INFLUENCE OF SOIL SOLUTION SALINITY ON BORON ADSORPTION BY SOILS

Boron (B) adsorption on two arid-zone soils from the San Joaquin Valley of California was investigated as a function of equilibrium solution B concentration (0–250 mg Lj1), solution pH (3–12), and electrical conductivity (EC, 0.3 or 7.8 dS mj1). Boron adsorption on both soils increased with increasing pH, reached a maximum near pH 9, and decreased with further increases in pH. Boron adsorption as a function of solution pH was independent of solution salinity from pH 3 to 9. Above pH 9, B adsorption was increased from the solution of higher EC. Boron adsorption for both soils as a function of solution B concentration conformed to the Langmuir adsorption isotherm equa-tion. The B adsorption maxima obtained with the Langmuir equation for both EC were not statistically significantly different at the 95 % level of confidence. The constant capacitance model, a surface complexation model, was able to describe B adsorption as a function of solution B concentration and solution pH. Boron adsorption was predicted usin