Effects of strong ionic polarization in the soil electric field on soil particle transport during rainfall

European Journal of Soil Science

Li, S.Li, H.Hu, F. N.Huang, X. R.Xie, D. T.Ni, J. P.

Specific ion effects are now thought to be important in nature. We studied the specific ion effects on soil particle transport during rainfall simulation (150mmhour(-1), 110minutes) in sodium nitrate (NaNO3), potassium nitrate (KNO3) and caesium nitrate (CsNO3) solutions. The results showed marked differences in the intensity of soil particle transport in Na+, K+ and Cs+ systems. The differences increased sharply with the decrease in electrolyte concentration, which indicated strong specific ion effects on soil transport and suggested that the differences could not be explained by ionic size, hydration effect or dispersion force. The cationic non-classical polarization in a strong electric field increases the Coulomb attractive force between the cation and clay surface, and further adversely decreases the strength of the electric field. With the absolute effective charge coefficients, of Na+ (1.110), K+ (1.699) and Cs+ (2.506), we recalculated the true surface potentials of soil particles in NaNO3, KNO3 and CsNO3 solutions. The true surface potentials decrease sharply with the increase in ionic non-classical polarization, and then the electrostatic repulsive pressure between particles in the soil should decrease sharply. Comparison of fitting the equation for transport intensity in NaNO3 solution with that in KNO3 and CsNO3 solutions showed clearly that the soil electric field controlled the aggregate breakdown and particle transport. The results suggested that the stronger the non-classical polarization for cations in the soil, the weaker is the electrostatic field that forms and the soil erosion at the same solution concentrations.