How is the infiltration rate defined?

Infiltration rate is defined as the speed at which water flows into the soil through small pores. This definition captures the essence of the infiltration process, which involves water moving from the surface into the soil layers. It is a critical factor in hydrology and landscape management, as it affects groundwater recharge and surface runoff. Understanding the infiltration rate helps landscape architects design efficient drainage systems and manage water resources effectively.

When considering the other options, while the amount of water absorbed by the soil over time is related to infiltration, it does not specifically convey the rate aspect, which is key to understanding how quickly water enters the soil. The process of water traveling downward through soil does relate to infiltration but does not emphasize the speed aspect as clearly as the correct answer does. Lastly, the measurement of soil's moisture-holding capacity is a different concept altogether, focusing on how much water the soil can retain after it has infiltrated, rather than the rate at which water enters the soil. Thus, the chosen answer accurately represents the definition of infiltration rate by highlighting the speed of water entry into the soil, which is essential for landscape planning and design.