By Sam Bauer
Sports turf managers are faced with the challenge of maintaining safe and playable turfgrass surfaces while reducing inputs such as fertilizer and water. In particular, water conservation has become a hot topic for all turf managers and will continue to be an important issue as drought events increase in frequency and severity. Reducing water use, resulting in playing conditions that are unsafe for athletes, may negatively impact sports turf performance. Consequently, optimizing water management is key for achieving a balance between conservation and functional and playable sports fields.
Turfgrass water use is impacted by a number of different factors including species and cultivar, management practices, and soil type. For example, low mowing heights will promote increased water use and turf grown in sand-based rootzones requires more frequent irrigation due to a lack of water-holding capacity. Although sand-based rootzones have many beneficial characteristics, managing fields high in sand content can be challenging particularly during dry, hot conditions. Hydrophobicity (the repelling of water) is one of the most common issues of turf grown in sand and can result in ‘hot spots’ that tend to dry out faster compared to other turf areas. Wetting agents are commonly used to manage this situation. Although hydrophobic areas are less common in native soils or rootzones with minimal sand, wetting agents can still aid in water management of these soils.
Wetting agents work by reducing the surface tension of water, allowing greater infiltration into the soil surface and increased percolation through the soil profile. In hydrophobic soils, wetting agents work by restoring the bond between the nonpolar organic coatings on soils and the polar water molecules. In saturated soils, wetting agents can help to increase percolation of water by reducing the attraction of water molecules to themselves; this occurs via the reduction in cohesive forces (aka surface tension) of water molecules. In the case of increasing soil moisture uniformity, a single wetting agent may be effectively making dry areas wetter and wet areas drier. Overall, this could result in decreased water use, improved water conservation and more consistent playing surface.
As a water management tool, wetting agents can also indirectly result in increased rooting depth and density (in turn improving water conservation), reduced disease infection that can impact turf playability (by reducing prolonged leaf wetness duration), and improved moisture holding capacity of infield skins (which can improve playability). In addition, recent research at the University of Minnesota suggests that wetting agents may improve surface firmness and help to reduce winter damage of turf surfaces. Sports turf managers may find it challenging to translate research data supporting these claims because a majority of wetting agent research has been focused on golf course turf; however, recent finding supports the application of wetting agents to entire fields versus only applying to specific, problematic turf areas.
Influence on surface firmness
Over the past 4 years, researchers at the University of Minnesota have been investigating the influence of wetting agent applications on the firmness of sand-based putting greens. As has been shown repeatedly, there is an inverse relationship between the degree of soil wetness and firmness of a turf surface (i.e., more water results in a softer playing surface). Softer playing surfaces on sports fields may manifest several issues including increased susceptibility to damage from athletes and reduced surface stabilization, which can result in athlete injuries. In an ideal sports turf situation, using wetting agents on an entire field would provide a firmer playing surface following a significant rainfall event and help promote uniform wetting of turf surfaces.
Under dry conditions, wetting agents may help with holding moisture at the surface, thereby improving cushioning and player safety. Our research results have demonstrated that wetting agents will impact firmness; some create softer surfaces and some firmer, depending on the chemistry, and some actually do both depending on the moisture status of the soil. Further research is needed to evaluate variations in wetting agent performance associated with environmental and climate factors.
To reduce winter injury
An emerging trend in turf wetting agent use has been making applications later in the season with the goal of improving winter health and spring recovery. In northern climates where irrigation systems are winterized, the strategy has been to apply a wetting just before irrigation blowout, with the anticipation that the wetting agent will be present in the soil throughout the winter months and into the spring. In southern climates, wetting agents are more commonly being applied throughout the winter months to improve soil moisture conditions during this unfavorable growth period for warm season grasses.
Late fall applications in the north
Winter injury of cool-season grasses is an interesting and often puzzling phenomenon. If we analyze the various mechanisms for winter injury, we find that a majority of them are moisture related. Desiccation is the drying of rootzones and turf crowns to the point of death. Crown hydration and ice cover injury occur due to excessive moisture buildup on turf surfaces, and moisture at the surface can also contribute to a greater incidence of snow mold.
If wetting agents influence the moisture status at shallow depths, they have the potential to reduce these winter-related problems. There is no research to support this, however in theory, products geared towards hydration should be used where desiccation is a concern, and infiltration type products will likely benefit with surface moisture issues. In reality, you may find one product that achieves both of these goals, as discussed above.
The question I am often asked regarding late-fall applications is how long will they persist throughout the winter. The breakdown of wetting agents in the soil is influenced by microbial activity, and temperature is the primary driving force for this. In the late-fall and winter when soil temperatures are low, we have found persistence well into May from mid-October applications of various chemistries in Minnesota. We are just beginning to study the impacts of soil temperature on wetting agent breakdown, but when soils are cold, persistence for six months or more is very possible. Research on wetting agent persistence and soil temperature will also help inform turfgrass managers about optimum frequencies for wetting agent applications throughout the growing season.
Late fall and winter apps in the south
One could argue that coming into and out of winter is the most critical time to ensure an adequate moisture status for warm season turfgrasses. Shallow root systems, coupled with slow growth and recovery make moisture management at this time of utmost importance. Could wetting agents at this time be of any benefit? Researchers at the University of Arkansas recently investigated the impacts of wetting agents on winter survivability of bermudagrass, finding that a single late-fall applied wetting agent can dramatically improve spring greenup and survivability of bermudagrass in a sand-based putting green. Unfortunately, these results were not consistent from one year to the next, but no deleterious effects were ever observed from wetting agent applications at this timing. For sports fields, whether overseeded or not, proper selection and application of a late-fall or winter wetting agent will likely provide many benefits for the health and playability of your surfaces.
Wetting agents are not created equal and the most appropriate product for your situation will be based on your experience, trial and error, and data collection. By promoting a healthy turf stand through efficient water use, it may be possible to reduce pesticide and fertility applications while continuing to maintain safe, functional and playable surfaces.
This article intentionally avoided the discussion of specific products because there are simply too many to discuss. Initial studies focused on the impact of wetting agents on surface firmness and applications later into the fall and winter are very promising. Stay tuned as this work progresses and be sure to advocate for this type of research with your local land grant institution. For more information about this and other projects at the University of Minnesota, please visit our blog at turf.umn.edu.
Sam Bauer is Extension Educator-Turfgrass Science, University of Minnesota Extension.