Managing moisture

Surfactants can be found everywhere. You will find them in everything from detergents and shampoos to toothpaste, cosmetics, shaving foams and even fabric conditioners. Why are they used? Their role is to increase the wetting properties of a liquid. Surfactants are compounds that affect the surface tension between a liquid and a liquid, a liquid and a solid, or a liquid and a gas. Surfactants have a hydrophobic (water-hating) tail and a hydrophilic (water-loving) head. They lower the surface tension of a liquid and allow for increased spreadability.

For household products, these chemistries allow compounds to better penetrate dirt and oils, dissolving stubborn residues and removing them from surfaces. In the case of soil surfactants, these products alter the behaviour between water and soil and can be used to develop optimum conditions for turf surface performance.

In the case of dry, water repellent soils, the use of a curative soil surfactant such as Aquatrols Aqueduct sees the hydrophobic tail attach to dry soil particles and the hydrophilic head attach to water molecules – acting as a bridge to uniformly re-wet the soil profile. Alternatively, similar chemistries are used in surfactants designed for regular turfgrass programmes to better manage the relationship between the water and the soil profile through depth, improving moisture retention within the upper profile or speeding up movement of surface water to depth.

Changing the behaviour of water

The formula for water is H2O, and this tells us that one molecule of water comprises two atoms of hydrogen and one atom of oxygen bonded together. The water molecule has 10 protons – positively charged and 10 electrons negatively charged. Therefore, a molecule of water is neutral, meaning it has a net charge of zero. However, it is a strongly polar molecule, meaning it carries a partial positive charge near the Hydrogens, and a partially negative charge at the Oxygen. As a result, the water molecule is attracted to itself.

Cohesion is the force which pulls water molecules into a droplet, creating surface tension. When cohesive forces are strong, water forms droplets on a surface. A soil surfactant will reduce these cohesive forces, reducing surface tension.

The other force at work is the adhesive force influencing the behaviour of water molecules on a surface. When adhesive forces are strong, water tends to spread across a surface. A soil surfactant will increase the adhesive force, increasing the spreading of water over a surface.

Surface Tension - Water will bead

Most widely used turfgrass soil surfactant chemistries

Proven, reliable turfgrass products will usually consist of either one of these chemistries or a blend of these different chemistry types. For example, Aquatrols Fifty90 is a straight block co-polymer, Revolution is a modified block co-polymer, whilst Dispatch Sprayable is a straight block co-polymer and APG blend.

Not only do you have these different types of chemistries, but within the chemistries there are various chain lengths; these have a dramatic effect on how long the chemistries remain viable in the rootzone.

The amount of molecular chemistry within the finished product is also important. More chemistry = more active ingredient = better cost effectiveness. It can be difficult to identify what chemistry is in a soil surfactant from product literature or labels, however the Safety Data Sheet (SDS) can be an excellent source of additional information.

Polyoxyethylene - 1954