Feature

What’s New with Wetting Agents

By Michael Fidanza, Ph.D., Stan Kostka, Ph.D., and Tom Malehorn

Soil surfactants are commonly called “wetting agents” in the turfgrass industry, and there are many, many wetting agent products in today’s turf market. In 2012, the USGA Green Section article — Understanding the different wetting agent chemistries — advanced our understanding of these products in a logical manner. Another good article on wetting agents also appeared in the USGA Green Section — Factors to consider when developing a wetting agent program. Both of those articles and more can be found at: https://tinyurl.com/4f2v8m8r. Recently, wetting agent categories were proposed in a further attempt help the end user understand their chemical properties: https://tinyurl.com/ywyexm4x

Overall, in golf course and sports turf management, wetting agents are employed to improve infiltration, mitigate water repellency (i.e., hydrophobic conditions), and enhance hydration in soils and rootzones. Wetting agents also are useful for enhancing certain soil directed pesticides, improving flushing of excess salts, indirectly helping turf survive the winter, and improving spring green-up and recovery.

Example of a wetting agent field evaluation study on a creeping bentgrass (Agrostis stolonifera ‘L-93’) practice putting green at Mountain Branch Golf Club (Joppatowne, MD). Wetting agent treatments were applied from April through October, 2023. ‘Other’ was applied at 1.5 fl oz/1000 ft2 every 14 days starting in April; Excalibur® was first applied at 4 fl oz/1000 ft2 in April, followed-by 3 fl oz/1000 ft2 every 28 days. From soil evaluations in August, water infiltration into the rootzone profile is indicated by the blue dye. Source: iGin Research.

Retainers versus Penetrants?

The marketing of some wetting agent products can lead one to believe there is precise knowledge of clearly definable modes-of-action, that specific desired outcomes under diverse environmental conditions can prescribe how and when they should be applied, that soil responses can be turned on and off simply by changing what product is applied, or that product “X” can dramatically influence a specific turfgrass surface condition or expectation.

These sorts of questions have only been researched on a handful of products. Researchers at the University of Arkansas, University of Wisconsin, Michigan State University, and the University of Wageningen (Netherlands) have demonstrated that certain wetting agents can increase soil water content under droughty conditions, and lower soil water content during periods of excessive rainfall. Keepin-mind, most of these results come from turf growing on sand or sandy loam rootzones. Does this mean those wetting agents tested are physically “holding onto” (retaining) water in the rootzone, or “pushing” (penetrating) water through the rootzone? Our soil physics colleagues would question that statement. The terms retainer and penetrant are not listed in the soil science terminology, but these terms are used to market wetting agents.

Data remain lacking on the nature and differentiation of products sold as “wetters”, “water retainers”, and “penetrants”. There are many claims based on reports-fromthe-field or on misperceptions or misinterpretations of visual observations. When considering a wetting agent ask for thorough, documented, replicated field research (either from university or industry researchers). A recent article in the USGA Green Section provides further insight into this topic:

O’Brien, D., Fidanza, M., Kostka, S., and Richardson, M. 2023. Penetrants vs. Retainers: Understanding Wetting Agent Clamins and the Science Behind them. USGA Green Section Record. https://www.usga.org/ content/usga/home-page/coursecare/green-section-record/61/issue-10/penetrants-vs--retainers-understanding-wetting-agent-claimsand.html

Over the past two decades, wetting agents have moved from products applied to correct localized dry spots to broader applications in water management, however, marketing claims often outpace the science. Research continues to build upon our understanding of what wetting agents can and cannot do. Understanding the mode-of-action, effects on soil physical phenomena, and effects on soil biology and rhizosphere dynamics are the future. A foundation is being built to support science-based uses of these unique soil amendment compounds.

Conclusion

• Soil surfactants or “wetting agents” lead the way for sustainable water use and water conservation practices on U.S. golf courses.

• Recent research has quantified beneficial effects of using wetting agents, with more work in progress.

• The marketing terms “retainer” and “penetrant” are not soil science terms.

• Ask to see research-based information when considering a wetting agent product.

• Research efforts are underway in the U.S. and Europe that will increase our understanding of how wetting agents affect turf rootzone physical, chemical, and biological properties.

Dr. Mike Fidanza (maf100@psu.edu) is a Professor of Plant and Soil Science at the Berks Campus, Pennsylvania State University, Reading, PA; Dr. Stan Kostka (stan. kostka@gmail.com) is a Visiting Scholar at Penn State Berks Campus; Tom Malehorn (intlturf@gmail.com) is a Penn State turf alum and principal scientist with iGin Research, in Westminster, MD.