Which soil condition leads to reduced infiltration due to clay dispersion by sodium salts?

• A. Acidic soils
• B. Saline soils
• C. Neutral soils
• D. Sodic soils

Answer: (D)

Sodium-related dispersion of clay is what drives reduced infiltration. In sodic soils, the exchangeable sodium on clay surfaces dominates. When the soil wets, sodium ions weaken the forces that hold clay platelets together, causing deflocculation and dispersion of the clay particles. This breaks up the soil’s stable structure, collapses or seals pore networks at the surface, and forms a crust that water has a hard time penetrating. The result is a sharp drop in infiltration rate.

In contrast, soils with ample calcium and magnesium (typical of saline but not sodic soils) tend to promote flocculation and stable aggregates, which maintain pore continuity and support better infiltration. Acidic or neutral soils don’t inherently create the same sodium-driven dispersion; their infiltration issues arise from other factors, not the dispersion of clays by sodium salts.