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Soil surfactant

Also known as
soil wetting agent, soil penetrant, turf wetting agent

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.

What is a soil surfactant?

Water does not always soak evenly into soil. Some soils and growing media repel water, and compacted or crusted soils let it in slowly, so rain or irrigation runs off, ponds, or funnels down narrow paths while nearby soil stays dry. A soil surfactant is a surfactant formulated to reduce these problems. It lowers the surface tension of water and improves how water wets soil particles, so that water enters and spreads more uniformly.

Where soil surfactants are used

  • Turfgrass, especially golf greens and sports fields, to treat localized dry spots caused by soil water repellency.
  • Greenhouse and nursery production, because peat-based growing media become hard to rewet once they dry out.
  • Agriculture, to improve water infiltration and water distribution in the root zone, reduce runoff, and improve the efficiency of irrigation and fertigation.

Types of soil surfactants

In the turf industry, products are often described by their effect on water movement:

  • Penetrants help water move quickly down through the soil profile.
  • Retainers, or humectant-type products, help the root zone hold more water.
  • Blends combine both behaviors.

Most are nonionic surfactants, often block copolymers or blends with other surface-active ingredients, chosen to be safe for plants at use rates.

What soil surfactants do not do

Soil surfactants improve how water interacts with soil. They do not by themselves loosen physically compacted soil or add nutrients. Where compaction is the underlying problem, they work best alongside practices that address soil compaction and improve soil health.

Soil surfactants at Locus

Locus’s Unpac is a biosurfactant soil conditioner that Locus describes as lowering the surface tension between soil particles and water to improve infiltration and moisture distribution in compacted or drainage-limited soils.

Frequently asked questions

A soil surfactant changes how water interacts with soil particles. A soil conditioner is any material used to improve soil physical properties, such as structure, aeration or water movement. Some soil conditioners are surfactant-based.

At labeled rates, soil surfactants are formulated to be safe for plants. Overapplication, or use of surfactants not intended for soil, can injure roots, so product selection and rates matter.

  • 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.

  • Water 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.

  • Surface tension

    Surface tension is the energy per unit area, or force per unit length, at the surface of a liquid where it meets a gas such as air. It arises because molecules at the surface have fewer like neighbors to attract them than molecules inside the liquid.

  • Wetting

    Wetting is the ability of a liquid to spread over and stay in contact with a solid surface. It depends on the balance between the liquid's attraction to the surface and to itself, and it is usually measured by the contact angle a droplet makes with the surface.

  • Soil conditioner

    A soil conditioner is a material added to soil to improve its physical properties, such as structure, aeration, water infiltration and water-holding capacity, rather than to supply nutrients. Examples include compost, gypsum, polymers and soil surfactants.

Sources

  1. Soil water repellency: its causes, characteristics and hydro-geomorphological significance, S. H. Doerr, R. A. Shakesby and R. P. D. Walsh, Earth-Science Reviews, 2000
  2. Soil wetting agents for turfgrass, Land-grant university turfgrass extension