Which statement describes the effect of increasing sodium on infiltration?

• A. Infiltration decreases
• B. Infiltration increases
• C. No change
• D. Infiltration depends on moisture

Answer: (A)

Increasing sodium in the soil water disrupts soil structure by dispersing clay particles and forming a surface seal. When exchange sites become dominated by sodium, clays repulse each other, aggregates break down, and a crust can develop at the surface. This seals pores and reduces the continuity of macropores that normally carry water downward, so infiltration slows and overall infiltration rate decreases. While moisture conditions can influence infiltration in other ways, the direct effect of higher sodium is to degrade pore structure and lower infiltration, which is why this option is the best choice.