This study was conducted to determine the effects of adsorbed Mg on erosion of soils exposed to rain. The effects of adsorbed Mg and Ca on soil erosion and infiltration rate (IR) of two soils (a Calcic Haploxeralf and a Typic Rhodoxeralf) exposed to rainfall, in the absence and presence of adsorbed Na, was studied. A drip-type rainfall simulator and deionized water were used at water-drop kinetic energy of 12.5 kJ m-3. The erosion rate of the soils was higher for the Mg-soils than for the Ca-soils. Both the steady-state IR and the cumulative water depth required to reach a steady-state IR were lower for Mg soils than for Ca soils. Adsorbed Mg by the montmorillonitic soil increased erosion and lowered IR, regardless of CaCO3 content. The Ca aggregates were more stable than Mg aggregates, even in the presence of Na. The specific effect of Mg on soil erosion was explained by the presence of these ions on the external surfaces of the clay tactoids, and the wider hydration shell of the Mg ion, as opposed to that of the Ca ion. It was suggested that the steady-state infiltration and soil erosion rates are the result of two processes that occur in opposite directions: seal formation and soil detachment.
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