Soil properties play a crucial role in infiltration, the process of water entering the ground. Texture, structure, and porosity influence how quickly water moves through soil. Understanding these factors helps predict water movement and storage in different soil types.

Soil moisture and hydraulic conductivity also affect infiltration rates. Initially dry soils absorb water faster, but rates decrease as soil saturates. Compaction and surface sealing can significantly reduce infiltration, highlighting the importance of proper soil management practices.

Soil Properties and Infiltration

Key soil properties for infiltration

• Soil texture refers to the relative proportions of sand, silt, and clay particles in a soil
  • Sandy soils have larger pore spaces between particles allowing for faster infiltration (beach sand)
  • Clayey soils have smaller pore spaces resulting in slower infiltration (pottery clay)
• Soil structure is the arrangement of soil particles into aggregates
  • Well-structured soils have more stable aggregates and larger pore spaces facilitating better infiltration (crumbly topsoil)
  • Poorly structured soils have less stable aggregates and smaller pore spaces reducing infiltration rates (compacted subsoil)
• Soil porosity represents the percentage of soil volume occupied by pores or spaces between particles
  • Higher porosity allows for more water storage and faster infiltration (pumice rock)
  • Lower porosity restricts water movement and reduces infiltration rates (granite rock)

Soil moisture and hydraulic conductivity

• Soil moisture content refers to the amount of water present in soil pores
  • Initially dry soils have higher infiltration rates due to capillary forces and available pore space (desert soil after a dry spell)
  • As soil becomes saturated infiltration rates decrease (soil after heavy rainfall)
• Hydraulic conductivity measures a soil's ability to transmit water
  • Depends on soil texture structure and pore size distribution
  • Higher hydraulic conductivity allows for faster water movement and infiltration (gravel)
  • Lower hydraulic conductivity restricts water flow and reduces infiltration rates (clay)

Soil characteristics vs infiltration capacity

• Infiltration capacity is the maximum rate at which soil can absorb water and varies based on soil properties and initial moisture content
• Factors influencing infiltration capacity include:
  • Soil texture: sandy soils generally have higher infiltration capacities than clayey soils (sand dunes vs clay plains)
  • Soil structure: well-structured soils have higher infiltration capacities due to larger pore spaces (healthy grassland vs overgrazed pasture)
  • Soil porosity: higher porosity allows for greater infiltration capacity (volcanic ash vs hard pan layer)
  • Antecedent moisture content: initially dry soils have higher infiltration capacities than wet soils (soil after a dry summer vs soil in the rainy season)
• Infiltration capacity changes over time
  1. Decreases as soil becomes saturated and pore spaces fill with water
  2. Reaches a constant rate when soil is fully saturated

Impact of compaction on infiltration

• Soil compaction is the reduction in soil pore space due to external pressure
  • Caused by heavy machinery livestock or human traffic (construction sites animal feedlots hiking trails)
  • Decreases infiltration rates by reducing pore size and hydraulic conductivity
• Surface sealing is the formation of a thin low-permeability layer on the soil surface
  • Caused by raindrop impact fine particle deposition or chemical dispersion (bare agricultural fields after rainfall)
  • Reduces infiltration rates by limiting water entry into the soil
• Management practices to mitigate compaction and surface sealing include:
  • Minimize soil disturbance and compaction during wet conditions
  • Use conservation tillage or no-till practices to maintain soil structure (cover crops crop residue management)
  • Maintain surface cover to protect soil from raindrop impact (mulch plant litter)
  • Incorporate organic matter to improve soil structure and porosity (compost manure)