We carried out a series of numerical simulations to evaluate the changes in ionic activity ratios, (Ca2+)/(K+)2, (Ca2+)/(Na+)2, (Mg2+)/(K+)2, and (Mg2+)/(Na+)2, associated with the changes of water content. We considered cation exchange reaction, complexation with sulfate, and gypsum precipitation as factors affecting the soil solution composition. All the ionic activity ratios decreased as water content decreased to a significant extent depending on the values of effective cation exchange capacity (ECEC), and cation exchange selectivity. Smaller ECEC values and lower selectivity for potassium resulted in a larger magnitude of change. Formation of calcium and magnesium sulfate complexes and gypsum precipitation exerted a small effect on the changes in the activity ratios. Based on the simulation, we concluded that these activity ratios should not be regarded as constants and are not reliable tools to predict the changes in cationic composition of soil solution at different water contents.
All Science Journal Classification (ASJC) codes
- Soil Science
- Plant Science