Which soil properties control how quickly rainwater can infiltrate the ground?

In hydrologic sciences, the rate at which rainwater infiltrates the ground is primarily controlled by the soil's physical structure and composition. Key factors include:

• Soil Texture and Pore Size: Soil texture—the relative proportions of sand, silt, and clay—determines the size of the spaces between particles. While finer-textured soils (clay-rich) have higher total porosity, they possess smaller pores, which significantly reduces permeability and slows water movement compared to coarser, sandy soils.1
• Aggregate Structure: The presence of humus and biological activity, such as plant roots, helps bind soil particles into aggregates. This creates a network of larger pores, or macropores, that facilitate rapid water infiltration.1
• Surface Conditions: Rainfall impact can cause compaction and the formation of a surface crust, which restricts water entry. Furthermore, as rain continues, infiltration rates often decrease due to the clogging of pores by fine particles and the swelling of colloidal clay particles as they absorb water.23
• Saturation: Infiltration capacity is also influenced by the initial moisture state of the soil; soils that are already waterlogged have limited capacity to accept additional water, leading to increased surface runoff.32