According to Horton's equation, what soil property most directly influences the initial rate of infiltration capacity (f₀) at the start of a rainfall event?

According to Horton's equation, the initial rate of infiltration capacity (f₀) represents the maximum rate at which water can enter the soil surface at the very beginning of a rainfall event, typically when the soil is dry and its pores are largely air-filled. This f₀ value is most directly influenced by the soil's structure. Soil structure refers to the arrangement of individual soil particles (sand, silt, and clay) into larger, stable units called aggregates. A well-developed soil structure, characterized by numerous and stable aggregates, creates a network of large, interconnected pores known as macropores. These macropores, which include spaces between aggregates, old root channels, and wormholes, provide low-resistance pathways that allow water to quickly penetrate the soil surface when rainfall begins. This rapid initial entry capability leads to a high initial infiltration capacity (f₀). Conversely, a poor soil structure, such as that found in compacted soils where aggregates are crushed or poorly formed, significantly reduces the number and connectivity of these macropores. This restriction on initial water entry results in a lower f₀. Therefore, while soil texture (the proportion of sand, silt, and clay) provides the fundamental building blocks, it is the soil structure that most directly dictates the effective pore network and thus the initial rate at which water can infiltrate.