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Media surfactants (wetting agents, penetrants, wetters) describe a group of chemical products which aid in the wetting and movement of water in growing media. These detergent-like products work by lowering the surface tension of water and media particles so that wetting is uniform and effective.

Without uniform wetting, irrigation water tends to move through the larger pores in the media (or the sides of the pot) where it is subject to downward gravitational forces. This in turn leads to increase leaching and reduced irrigation efficiency. By improving penetration, wetting, and water movement, media surfactants can increase the effective wetting area in containers thereby increasing irrigation efficiency. The fact that commercial container media are typically treated with media surfactants is evidence for their value in media performance.

The relative importance of media surfactants in plant production often increases under conditions where media dries out between irrigation applications. When media driesout, organic components (particularly peat and bark) develop hydrophobic or "water-hating" characteristics that become stronger as moisture levels decrease. Media dry-down is most common with low frequency irrigation schedules, non-uniform watering practices (including inadvertent skips or mechanical failures), small pots, and plants at later stages of production. Under these conditions, careful consideration of media surfactant management will likely have its greatest benefits.

Wetting agents, or soil penetrants as they are sometime called, have been studied with field applications of irrigation water where compacted soils may form a dry hydrophobic layer. Some types of golf greens may do this during hot summer months. Even with a small amount of slope, applied sprinkler irrigation water may run off some areas on such golf greens instead of providing uniform wetting. Soil penetrants may be sprayed on golf greens to improve natural rainfall distribution too.

There are situations where use of wetting agents can improve efficiency of irrigation water. If growth media have open channels and are non-polar, uniform wetting is more difficult. Some artificial potting media do tend to have a non-polar surface when they dry out. Added irrigation water may puddle and seek out channels to bypass much of the media instead of providing uniform wetting when applied to such surfaces. Addition of a small amount of wetting agent will prevent this. If nutrients are being applied in irrigation water, uniform wetting is essential for good nutrient distribution throughout the growth media and root zone.

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