What happens to infiltration when sodium levels increase?

• A. Infiltration increases
• B. No change
• C. Infiltration becomes erratic
• D. Infiltration decreases

Answer: (D)

When sodium levels rise, soils can become sodic, and the exchangeable sodium on clay surfaces disrupts soil structure. Sodium ions don’t promote the flocculation of clay particles the way calcium and magnesium do; instead, they cause the particles to disperse. This dispersion breaks apart soil aggregates, reduces pore continuity, and often forms a surface crust. With fewer connected pores, water has a harder time infiltrating, so the infiltration rate decreases. The effect is especially strong in fine-textured soils where clays dominate. While it’s possible for infiltration to vary under different moisture conditions, the general outcome of higher sodium is a slower, reduced infiltration.