Which term refers to water moving from the surface into the soil?

• A. Infiltration
• B. Evaporation
• C. Runoff
• D. Transpiration

Answer: (A)

Infiltration is the process by which water moves from the surface into the soil. When precipitation or irrigation supplies water to the ground, it begins to soak down through the soil pores, driven by gravity and aided or hindered by the soil’s texture, structure, and moisture level. The rate at which this happens is called the infiltration rate and can vary widely: sandy soils with larger pores often absorb water quickly, while clayey soils with tiny pores may absorb it slowly and may even become saturated, leading to runoff if rainfall is heavy. This downward movement helps recharge moisture in the soil profile and, in some cases, groundwater. By contrast, evaporation is water turning into vapor from surfaces, transpiration is water vapor released from plant leaves, and runoff is water that flows over the surface instead of soaking in.