Water-Drop Kinetic Energy Effect on Infiltration in Sodium-Calcium-Magnesium Soils
The effect of the complementary adsorbed ion (Ca vs. Mg) in the presence of Na on seal formation and water infiltration in two soils (Calcic Haploxeralf and Typic Rhodoxeralf) at several kinetic energies of water drops was studied using rain simulators. The infiltration rate (IR) of the soils was lower for the Na-Mg soils than for the Na-Ca soils at the studied kinetic energy range of the water drops (3.2–22.9 kJ m−3). The higher the kinetic energy, the steeper the drop in IR. The steady-state IR and the cumulative water depth required to reach steady-state IR were both decreased with increasing kinetic energy of the water drops. Adsorbed Mg on montmorillonitic soils had a specific effect on IR whether or not the soil contained CaCO3. Aggregates with adsorbed Na and Ca ions were more stable than those with adsorbed Na and Mg ions when they were exposed to water drops having a kinetic energy in the range of 8.0 to 12.5 kJ m−3. The specific effect of Mg on IR was explained by the presence of Mg ions on the external surfaces of the clay tactoids and the larger hydration shell of the Mg ion compared to Ca.
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