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 L), solution pH (3–12), and electrical conductivity (EC, 0.3 or 7.8 dS m). 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 equation. 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 using the soil chemical properties surface area, organic carbon content, inorganic carbon content, and aluminum oxide content. The predictions are suitable for transport modeling and will be used to describe B movement in large soil columns. Our results are advantageous because they indicate that under agricultural conditions (pH 3–9), B adsorption can be described without consideration of changes in soil solution salinity. (Soil Science 2008;173:368–374)