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Water infiltration

Also known as
infiltration rate, soil infiltration

Water infiltration is the process by which water on the ground surface, from rain or irrigation, enters the soil. The infiltration rate is how fast that happens, usually in inches or millimeters per hour. Poor infiltration leads to runoff, ponding and erosion.

What is water infiltration?

When rain falls or irrigation is applied, water either soaks into the soil or runs off the surface. Infiltration is the soaking in. The infiltration rate measures how quickly the soil accepts water. If water arrives faster than the soil can take it in, the excess ponds or runs off, carrying soil and nutrients with it and leaving less water stored for the crop.

Infiltration is the entry of water at the surface. Once inside, the movement of water down through the soil is often called percolation or drainage.

What controls infiltration

  • Soil texture. Sandy soils generally infiltrate faster than clay soils.
  • Soil structure. Stable aggregates and continuous pores, including old root channels and earthworm burrows, let water in quickly.
  • Surface crusting. Raindrops break down aggregates on bare soil, forming a crust that seals the surface.
  • Soil compaction, which reduces large pores.
  • Soil water repellency, which makes some soils resist wetting.
  • Existing moisture. Dry soils often take in water quickly at first; saturated soils cannot take in more.
  • Cover. Residue and living plants protect the surface from crusting and slow runoff.

How infiltration is measured

A common field method, used in the USDA Natural Resources Conservation Service soil quality test kit, drives a ring into the soil, adds a set volume of water, and times how long it takes to soak in. Results are compared across fields or over time.

Improving infiltration

  • Keeping soil covered with residue and cover crops.
  • Reducing tillage to preserve structure and pore networks.
  • Building soil organic matter.
  • Avoiding traffic on wet soils to prevent compaction.
  • Using gypsum on some sodic and crusting soils.
  • Using soil surfactants where water repellency or poor wetting limits water entry.

Better infiltration is one of the most visible benefits of improved soil health.

Water infiltration at Locus

Locus’s Unpac biosurfactant soil conditioner is positioned to improve water infiltration and moisture distribution in compacted or drainage-limited soils.

Frequently asked questions

It depends on soil texture and use. The practical goal is an infiltration rate high enough that typical rainfall and irrigation soak in without ponding or runoff.

Infiltration is water entering the soil at the surface. Percolation is water moving downward through the soil below the surface.

  • Soil compaction

    Soil compaction is the pressing together of soil particles, which reduces the pore space between them. Compacted soil holds less air, lets water in more slowly and physically resists root growth, which can reduce crop yield.

  • Soil surfactant

    A soil surfactant, also called a soil wetting agent, is a surfactant applied to soil or growing media to help water enter, spread and move through it more evenly. Soil surfactants are used to overcome water repellency in turf, horticultural media and some agricultural soils.

  • Soil water repellency

    Soil water repellency is a condition in which soil resists wetting, so water beads on the surface or flows through narrow paths instead of soaking in evenly. It is caused by water-repellent organic coatings on soil particles and is most common in dry, sandy soils.

  • Soil health

    Soil health is the continued capacity of a soil to function as a living ecosystem that sustains plants, animals and people. A healthy soil holds and supplies water and nutrients, supports roots and soil life, cycles organic matter and resists erosion.

Sources

  1. Soil quality indicators: infiltration, USDA Natural Resources Conservation Service
  2. Soil Quality Test Kit Guide, USDA Natural Resources Conservation Service