Influence of Soil Solution Salinity on Boron Adsorption by Soils.

Boron 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^-1), solution pH (3-12), and electrical conductivity (EC = 0.3 or 7.8 dS m^-1).  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 ECs 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, as they indicate that under agricultural conditions (pH 3-9), B adsorption can be described without consideration of changes in soil solution salinity.