Wetting agents (sometimes referred to as surfactants) are packaged in a variety of formulations — liquids, wettable powders, granules — and can be applied to the turf surface and soil. Wetting agents are anionic (negatively charged), cationic (positively charged) or nonionic (having neither a positive or negative charge). Surfactants are used every day in the form of detergents and fabric softeners. Nonionic surfactants are the most commonly used in turfgrass management.
Wetting agents are not to be confused with adjuvants or stickers, which help a chemical application “stick” to the turf plant surface. There are many types of wetting agents on the market, some recommended as soil penetrants, and others used to maximize the efficacy of pesticides. Some are more viscous than others and require specific spray application equipment. Because they are soil applied, the turf manager must also have the right spray nozzles and spray volume.
Label rates, timing and frequency will change among products, and turfgrass phytotoxicity is also a consideration. Furthermore, research has suggested that the behavior of a wetting agent can depend upon location and soil type, so a field manager should do some investigation and talk to their chemical rep about which one(s) best fit their situation and why.
There are a number of claimed uses for wetting agents within the turfgrass industry, including water retention, water removal, better efficacy of applied pesticides, reduced irrigation input, management of fairy rings, alleviating isolated dry spots, and removal of dew. Most recently, they have also been evaluated for their effectiveness on synthetic turf surfaces.
Almost all of the research on wetting agent use has been funded by the Golf Course Superintendents Association of America (GCSAA), the United States Golf Association (USGA) and other golf-related groups, which means that most of the information on wetting agents relates to a USGA golf green rootzone or sand system. It would be reasonable to assume though that a sand athletic field rootzone would respond to wetting agents somewhat similar to a sand golf green rootzone.
A standard test for soil hydrophobicity is the water drop penetration time (WDPT) test. Apply droplets of water to the sand and time how long it takes for the water to disappear. If the water does not absorb into the sand, or runs off (as in this picture), it is an indicator of water repellency.
PHOTOS COURTESY OF PAM SHERRATT.
The most common use for wetting agents in sports turf management is on sand-based sports fields that have problems with localized dry spot (LSD) or hydrophobic (water-repelling) tendencies in the thatch or underlying soil surface. LDS and hydrophobicity on sand-based fields is a phenomenon that occurs when the thatch and/or sand particles in the top 1 to 2 inches of rootzone become very dry and repel water.
The cause of hydrophobicity within the sand rootzone is an organic component (wax) that coats the sand particles and repels water. The formation and removal of this organic coating has been the subject of many years of research that suggests the coatings are formed from waxy leaf cuticle deposits, root exudates and/or fungal pathogens.
While the exact nature of the coating may not be known, research has shown that wetting agents can help reduce its negative effect by binding to the organic coating and/or removing the organic coating thereby allowing water to adhere to the soil particles and offer more uniform soil wetting. In this type of situation, a wetting agent can help increase volumetric moisture within the sand rootzone and prevent LDS, which can ultimately lead to turf decline.
In addition to uniform rootzone wetting and increased volumetric moisture in hydrophobic sand rootzones by wetting agents, research undertaken by Dr. John Cisar, a former turfgrass professor at the University of Florida, has shown that irrigation input can be reduced by 50 to 70 percent if wetting agents are used as a preventative measure prior to the onset of drought stress. Research has shown that the quality of turf and its ability to survive during drought is comparable to an irrigated sports field if a wetting agent has been applied as soon as stress is noticed. Like all good IPM programs though, reduction in irrigation and the management of hydrophobic sands should not be reliant upon the use of a wetting agent alone. Sound cultural practices like well-timed compaction relief and topdressing, dethatching and hand watering/syringing all contribute to the turf’s ability to handle heat and drought stress.
Advances in more efficient irrigation systems and stress monitoring tools like volumetric soil moisture sensors can also be used to develop a preventative approach to LDS and hydrophobicity, rather than reacting to the problem.
In summary, wetting agents can play a role in the management of sand-based fields during summer drought stress, and they can help reduce irrigation costs during those times.
The role wetting agents have to play on native soils fields is not extensively researched, since hydrophobicity on soil sports fields has not presented itself as a major problem. Given that native soil fields typically have earthworms and other organisms that control thatch and improve soil structure, and since the topsoil is so rich in organic material, the formation of hydrophobic conditions is more of a concern on sand fields. Nevertheless, the use of wetting agents on soil fields, and in particular the effect of wetting agents on irrigation conservation are two areas of study that need to be looked at.
There has been some work on using wetting agents under wet ground conditions, which concluded that the wetting agent lowered soil volumetric moisture under wet conditions on a rootzone with low organic matter content. They did not see a reduction in soil volumetric moisture under wet conditions with high organic matter content.
Another, perhaps little known, use for surfactants on sports fields is to prevent dew formation. In situations where a game is due to take place in the morning or early evening when dew is forming, it is possible to apply a surfactant the day before to reduce the surface tension and, therefore, prevent the dew from forming on the leaf tissue.
This can be helpful in preventing a wet playing surface for games like rugby and football (soccer players like a wet surface, and, in fact, many MLS field managers are asked to wet fields down prior to games to enhance the roll and performance of the ball). Once applied, the surfactant prevents dew formation for no longer than about 48 hours, and it is applied at a very low volume.
Wetting agents and synthetic turf
Dr. Andrew McNitt, Penn State, has done some preliminary studies looking at the use of surfactants for reducing static electricity on synthetic fields, particularly in the first few years when the fields are new. The static causes rubber granules to cling to the top of the synthetic fibers so that they create black shadows in areas of play or where the marching band has been.
Surfactants such as fabric softeners (cationic) showed promise, with many field managers using them as standard practice prior to games to reduce static. Some field managers will apply them several days prior to the game to eliminate any chance of an athlete slipping.
Another possible use of surfactants on synthetic fields is to manage hydrophobic conditions once the field is a few years old. The infill material may become hydrophobic and prevent water infiltration, causing runoff and surface puddling. It is suggested that adding a wetting agent program to the annual care of a synthetic field should maintain permeability over time.