Managing moisture
In this article we discuss the technologies and benefits of wetting agents/surfactants and how managing rootzone moisture allows turf managers to have better control over their conditions.
Surfactants
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
- Cohesion - Water will stick to itself
- Adhesion - Water will stick to a solid
- Gravity - Water will move downwards
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.
The Role of Water in Turfgrass
Water is vital for many functions within turf.
- In germination water enables the seed to swell up and supports the chemical reactions required for the growth of the seed embryo
- In photosynthesis water provides the electrons and hydrogen ions required to power the process
- Transpiration provides water for photosynthesis, transporting mineral ions, cooling the leaf and keeping cells turgid to support plant structure
- Water is necessary for transportation of nutrients into the plant through the root system from the soil solution
Aquatrols Mission
Aquatrols is committed to pioneering new methods that advance soil and plant health for turf. We take seriously our responsibility to deliver products that will enhance water use, thereby helping protect the future of our water environment.
Article by Emma Beggs (right)
Wetting agent technologies
Wetting agents should be used in accordance with the desired outcome as not all wetting agent products utilise the same technologies. Similarly, you may not necessarily want to use the same wetting all year round. Wetting agents can be split into two groups, anionic or nonionic. The anionic wetting agents are the original technology developed in the 1950's which are negatively charged. These can cause dispersion within clay particles and have negative impacts in soil.
The nonionic wetting agent group can be further split into two more generic groups. Polyoxyethylene (POE), which also originated around the 1950's and a newer group of block co-polymers developed in the 1990's. Care should be taken when using products that utilise older technologies as issues of phytotoxicity can arise, depending on application rates, grass species and environmental conditions.
Block co-polymers are now commonly used and are safe on fine and sports turf areas. They help to reduce water repellence issues in rootzones and soils, improve soil water content and the amount of plant available water. Within the category of block co-polymer there are; straight block co-polymer to enhance water movement into the rootzone and reverse block co-polymer (retainer) which enhance moisture retention in the rootzone. Blends of both, straight and reverse block co-polymer are now commonplace within the industry, which aim to utilise the benefits of both technologies.
Other products available include those containing Alkyl Polyglucosides which make use of a sugar molecule reacted with a fatty acid to reduce water repellence. These can be mixed with straight block co-polymers and are widely used in the turfgrass industry. Lastly there is the unique modified methyl capped block co-polymer which creates a thin film of water around the soil particle which reduces the ability of the soil to completely dry out, meaning low volumetric water content can be achieved without becoming hydrophobic. Determining what the goal is for your site in relation to water management and distribution is key to deciding which technologies are going to help you achieve it.