What is a wetting agent and how does it affect water infiltration in compacted soils?

• A. A wetting agent reduces water repellency and improves infiltration
• B. It increases water repellency
• C. It séals off the soil
• D. It removes organic matter

Answer: (A)

Wetting agents are surfactants added to soil to counteract water repellency and improve infiltration. In compacted or hydrophobic soils, water tends to bead up on surfaces or fail to move through pore spaces because a coating of organic matter or soil particles repels water. A wetting agent lowers the surface tension of water and changes how water interacts with soil particles, effectively reducing the soil–water contact angle. This lets water spread more easily over and into the soil, breaking up air-filled pathways and allowing it to move through the pore network more readily.

So, the primary effect is to reduce water repellency, which directly enhances infiltration in soils where dryness or compaction hinder water entry. It’s not about sealing the soil, increasing repellency, or removing organic matter; those ideas don’t align with how wetting agents work.