Application of "four plane model" to the adsorption of K+, NO3-, and SO42- from a mixed solution of KNO3 and K2SO4 on andisols
1996
Kamewada, K. (Tochigi-ken. Agricultural Experiment Station, Utsunomiya (Japan))
To evaluate the interaction between anionic species when they were adsorbed on variable charge soils, we measured the adsorption of NO3(-) and SO4(2-) on an Andisol equilibrated with a mixture of KNO3 and K2SO4 solutions. The amount of No3(-) adsorption declined with the increase in the concentration of SO44(2-). On the other hand, the amount of SO4(2-) adsorption increased with the increase in the concentration of NO3(-). These phenomena can not be explained by the simple "exchange theory" or the "Three-plane model" unless surface complexation is associated with the changes in the electrical potential of the surface. Therefore, in order to explain the phenomena by using the "Four-plane model" with surface complexation, a new equation was derived for the Diffuse Double Layer (DDL) charge from the "main equation of DDL theory" (equation of electrical potential in DDL) symmetric electrolytes but nor for a mixture. By introducing the new equation to the computer program for analyzing the Four-plane model, the interaction between anionic species adsorbed on Andisols could be explained well. It was considered that SO4(2-) acted as a regulator for the ionic concentration, osmotic pressure and pH of the soil solution, and consequently, these factors affected the vertical distribution and mobility of anionic species and also the mobility of counter-ions in Andisols
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