In many countries, wetting agents are not subjected to the rigorous registration process that is used for pesticides, making it difficult for the ill-informed to really distinguish between the various products. Sportsfields.Magazine provides a short introduction.
Organic matter like thatch can disturb the water infiltration of a surface and even make it become water repellent. In a social media post from 2020, Dr Jonathan Knowles, the Head of Sports Turf Academy at Leicester City Football Club, pointed out that, “Soils that repel water may cause a weakening in the sward that may not affect play ability in the short term, but potentially contribute to moss, disease and pest susceptibility that may compromise future turf quality.”
Since the 1950s, the industry has been offering surfactants or wetting agents as a solution.
Wetting agents are designed to lower the surface tension of water by altering the surface of a liquid. They can be applied to prevent localized dry spot (LDS), improve moisture uniformity, increase water infiltration, prolong rootzone moisture retention, reduce winter injury, and enhance the efficacy of fertilisers and pesticides, to name a few.
Because they are not subject to the same registration process or labelling requirements as pesticides, wetting agents arrive in the marketplace accompanied by far less data about what they are and how they work. In addition to the chemistry of the product, the weather and cultural management also play a part in the performance of a wetting agent.
Like all other surfactants, wetting agents have a hydrophilic portion that will interact with the water, and a hydrophobic portion that will interact with the soil. By adjusting the ratio of hydrophile to hydrophobe, suppliers emphasise one of these interactions over the other.
Penetrant vs retainer
Penetrants supposedly reduce surface water tension to assist the downward flow of water. A water droplet holds its shape, as water molecules are highly attracted to each other. A wetting agent disturbs this cohesion of water molecules and makes the droplets spread out into a film, thus increasing the contact area. Presumably, this enables the water to penetrate the ground more easily.
Retainers supposedly emphasise interactions between the hydrophobe and the soil. Organic material that has built up in the top layer of the field releases a waxy substance that can coat the surface and prevent the water from penetrating into the soil. A hydrophobic part of the wetting agent connects with hydrophobic coatings on sand particles. This allows the hydrophile to hold onto water in the rootzone.
In their article “Penetrants vs. Retainers: Understanding wetting agent claims and the science behind them,” scientists from Penn State University and the University of Arkansas point out that “penetrant” and “retainer” are marketing terms. In the absence of established standards, it is up to the manufacturers to decide what they want to call a penetrant or a retainer. The authors advise that greenkeepers and groundsmen should take a more open-minded approach and observe how water behaves differently in the rootzone as a result of applying a particular product. “How much a wetting agent improves infiltration, retention and uniformity of rootzone moisture, regardless of any penetrant or retainer designation, is what’s most important,” they argue.[pms-restrict subscription_plans=”7998, 10994″]
Anionic, nonionic and cationic
The abovementioned social media post by Dr Knowles explains that there are three different classifications of surfactants that are relevant: anionic, nonionic and cationic.
Anionic surfactants are negatively charged agents that can be fast-acting but short-term as they move quickly through the profile. Knowles warns that, “While these types of wetting agents give great results, there is potential for phytotoxicity using anionic surfactants,” which is why they should be used with guidance and care.
Nonionic surfactants, he says, are excellent non-phytotoxic, re-wetting agents and adhere well to soil particles for greater longevity.
Cationic surfactants are not commonly applied, as they may cause hydrophobicity in clays and potentially have a biocidal fate in the soil.
Summer vs winter agent
Summer wetting agents are primarily used for water conservation and to prevent hydrophobic dry patches developing. Winter wetting agents are supposed to improve water movement, particularly infiltration and downward penetration.
Granules vs liquid
Wetting agents are available as granules as well as in liquid form. They both have advantages and disadvantages. In terms of activation, liquid wetting agents will act much quicker than granules. They can provide instant relief. However, granules remain effective over a much longer period of time. They do not have to be applied so frequently. Granules are also easier to apply where liquid wetting agents often require specialised equipment. Having said that, liquid wetting agents can be applied more uniformly compared to granular products.
Preventative, curative, soil penetrant, and retentive
Despite the numerous products available, there is no one-fits-all solution. Most products are designed to be used preventively on a monthly basis, and in general, their effect is cumulative. Exactly which wetting agent should be used to deal with a problem depends on the local circumstances, the time of the year and the point within the process: do you want to use it preventatively, curatively, retentively or to disperse moisture from the upper profile? To answer this, one has to know what grass species are present and their rooting depth, establish the current hydrophobic conditions of the root zone and establish whether thatch is present.
[/pms-restrict]