Most of the soil wetting agents used inturfgrass management are nonionicsurfactants.

Wetting agents bond both with waterand with the organic coating on thesoil or sand particle, thus allowing the soil or sand particle tobecome wet.

A wetting agent applied to a non-water-repellent soil would mostlikely increase the downward move-ment of water out of the root zone anddecrease the upward capillary move-ment of the water in the soil.

When a wetting agent is applied to anarea with excessive thatch or mat, thatarea dries more slowly than anuntreated area at the same site.

More Info: www.gcsaa.orgKEY points

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84 GCMJune 2004

Wetting agents: What are they, and how do they work?A better understanding of how wetting agents work will lead to their more effective use on the golf course.

Keith J. Karnok, Ph.D.; Kang Xia, Ph.D.; and Kevin A. Tucker

Without question, soil wetting agentshave become an important management toolfor superintendents. The senior author con-ducted a survey of more than 600 superin-tendents that showed 87% use wettingagents as part of their regular maintenanceprogram while another 11% use them in cer-tain situations. According to the survey, wet-ting agents are used for four primarypurposes: relieving localized dry spots (42%),managing water (32%), improving drainage(11%) and improving pesticide movementinto the soil (9%). In addition, superinten-dents use wetting agents for a variety of otherreasons such as reducing dew and frost for-mation, improving seed germination, reduc-ing fairy ring damage, reducing soilcompaction, improving irrigation efficiency,

reducing dust in golf car paths, improvingfirmness of bunker sand, etc. Little researchsupports the use of wetting agents in all thesescenarios. However, when used in the rightsituation, a wetting agent can be can an effec-tive management tool.

Although superintendents commonly usewetting agents, confusion about what wettingagents are and how they work is widespread.In this article we explain the characteristics ofwetting agents and how they work in certainsituations. Perhaps, through a better under-standing of the chemical nature of wettingagents, superintendents will be able to deter-mine whether a wetting agent will be effectivein a given situation.

SurfactantsWetting agents fit into a class of chemical

compounds called surfactants, which arechemicals that cause a physical change at thesurface of liquids. Such changes occur at theinterface between two liquids or between aliquid and a gas or a liquid and a solid.Because they cause changes at the surface,they are known as “SURFace ACTiveAgeNTs.” Surfactants are commonly used inherbicide formulations to enhance the desiredproperties of the formulation and the ulti-mate spray mixture.

Surfactants have many other uses depend-ing on their specific chemical properties. Forexample, other types of surfactants includeemulsifiers, dispersants, spreaders, pene-trants, stickers and detergents. Each type ofsurfactant has one or more characteristics incommon, but all possess the common featureof a water-soluble (hydrophilic) groupattached to a long, oil-soluble (lipophilic)hydrocarbon chain (Figure 1). These twogroups may be linked together or by an inter-vening group. Literally thousands of chemi-

cal combinations are possible.

IonizationSmall differences in the structure of surfac-

tants can significantly affect their behavior.Depending on their ionization or charge, sur-factants are commonly separated into four majorgroups: anionic, cationic, nonionic and ampho-teric. Basically, anionic and cationic surfactantsionize when mixed with water. Their surfaceactive properties are due to their negative charge(anion) and positive charge (cations), respec-tively. Nonionic surfactants do not ionize inaqueous or water solutions, whereas amphotericsurfactants can be either anionic or cationicdepending on the acidity of the solution.

Anionic and cationic surfactants have thedisadvantage of reacting with other ions in thesolution, causing a precipitate or foam to form.Nonionic surfactants do not react with otherions so they are unaffected by hard water. Inother words, they do not form insoluble saltswith calcium, magnesium or ferric ions. Theycan also be used in strong acid solutions andtend to have relatively low toxicity to plants.Most of today’s soil wetting agents used in turf-grass management are nonionic surfactants.

SoapsSuperintendents often ask, “What about

soaps?” Soaps are a type of surfactant; can theybe used as a soil wetting agent? Although soapshave both a polar end and a nonpolar end,they owe their surfactant properties to ananionic portion of the molecule. Therefore,soaps are actually anionic surfactants. Theyhave the disadvantage of forming insolublesalts with magnesium, calcium and ferric ionsin hard water. These salts will precipitate fromsolution and form a scum on the water.Therefore, soap would not be a good substi-tute for a nonionic surfactant or wetting agent.

with oil or grease. Chemical bonds cannot beformed between water and oil. However, if asurfactant, which has both polar and nonpo-lar portions, is added to water, the water is nolonger repelled. The nonpolar portion of thewetting agent bonds with the nonpolar oil,and the polar portion bonds with the water,apparently allowing the two to mix.

Figure 3. A scanning electron micrograph showing a sand particle with a water-repellent organic coating.

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Chemistry of water

PolarityTo understand how a surfactant or wet-

ting agent works in a turfgrass situation, it isimportant to understand the properties ofwater. A water molecule consists of twohydrogen atoms and one oxygen atom. Wateris a dipolar substance, which means it hasboth negative and positive polar ends (Figure2). The unique properties of water are due tothis polarity, which allows it to form bondswith a variety of polar molecules. However,water and other polar molecules will notbond with nonpolar molecules. In fact, waterand other polar substances will be repelled bynonpolar molecules.

An example would be trying to mix water

Surface tensionAnother significant trait of water is sur-

face tension. Surface tension is the tendencyof the surface molecules of a liquid to beattracted toward the center of the liquidbody. Surface tension is why a single waterdroplet on wax paper appears as though ithas a tense, elastic membrane surrounding it.Few liquids have a higher surface tensionthan water. For example, a small sewing nee-dle will float on the surface of pure waterbecause the needle isn’t heavy enough tobreak the surface tension of the water.However, if a wetting agent is added to thewater, the surface tension (that is, theattraction of water molecules to each other)is reduced, and the needle will sink.

Wetting agents and water-repellent soils

It has been well documented that soilwater repellency resulting in localized dryspots is the result of an organic (nonpolar)coating that adheres to the individual soil or— in most cases — sand particle (Figure 3).This organic material is the end product oforganic matter decomposition. The authorshave written about this phenomenon in sev-eral articles in Golf Course Management (seereferences list). The important point to

Figure 1. A typical wetting agent molecule showing a hydrophilicwater-attracting group and a long, oil-soluble (lipophilic) hydro-carbon chain.

Figure 2. Water is a dipolar substance that con-sists of two hydrogen atoms (positive charge)and one oxygen atom (negative charge).

Phot

o co

urte

sy o

f K.K

arno

k

Water-Soluble Group

(HYDROPHILIC/POLAR)

Oil-Soluble Hydrocarbon Chain

(LIPOPHILIC/NONPOLAR)

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86 GCMJune 2004

understand is when this organic coating cov-ers a significant amount of a soil or sand par-ticle, the particle will repel water (Figure 4).

When a wetting agent is added to thewater, the polar portion of the wetting agentbonds with the water while the nonpolar por-tion bonds with the nonpolar organic coat-ing, thus allowing the soil or sand particle towet (Figure 5). As long as there is sufficientwetting agent bonding with the organic coat-ing, the soil or sand particle will not be water-repellent. However, it should be kept in mindthat this alleviation of soil hydrophobicity isonly temporary. As long as the coatingremains on the soil or sand particle, waterrepellency will return when the use of a wet-ting agent is discontinued.

Wetting agents and thatch or matBecause wetting agents are designed to have

an affinity for nonpolar as well as polar sub-stances, then it stands to reason that excessivethatch or mat accumulation will affect wettingagent performance. In other words, a wettingagent will potentially bond with the thatch ormat as readily as it bonds with water-repellentsoil particles. Research at the University ofGeorgia has demonstrated this fact. In a turf-grass site with an excessive accumulation ofthatch, an area that has been treated with a wet-ting agent will dry significantly more slowlythan an untreated area at the same site.

This in part explains the observation somesuperintendents have made that certain wettingagents apparently hold moisture at the soil sur-face. Although this phenomenon could berelated to the chemistry of certain wetting agents,

Figure 5. Diagram of a sand particle with a water-repellent organic coatingafter treatment with a wetting agent.

our research suggests that the amount — andpossibly even the nature — of the thatch or matis at least as important or perhaps a more impor-tant factor. At this point, we are unsure as to howmuch thatch or mat is too much. Research isunder way to better understand the relationshipsamong thatch or mat, organic matter and theperformance of specific wetting agents.

Wetting agents and non-water-repellent soils

Superintendents often ask, “What happenswhen a wetting agent is applied to a non-water-repellent soil or sand?” In agreement with thereasoning discussed above, on a site with littleor no thatch or mat and the absence of water-repellent soil, a wetting agent would have littleeffect on the soil itself. However, a wetting agentwould reduce the surface tension and attractionof water molecules to each other, making water“wetter.” This effect would most likely increasethe downward movement of water out of theroot zone (providing there was subsurfacedrainage) while decreasing the upward capillarymovement of the water in the soil.

ConclusionsMany questions pertaining to wetting

agents remain unanswered, including how,when and under what conditions they shouldbe used on the golf course. We have several studies currently under way to answer many ofthese questions.

References1. Carrow, R.N. 1989. Understanding wetting agents.

Golf Course Management 57(6):18-26.2. Fainerman, V.B., D. Mobius and R. Miller (eds.).

2001. Surfactants: Chemistry, interfacial properties,applications. Elsevier, New York.

3. Karnok, K.J., E.J. Rowland and K.H. Tan. 1993. HighpH treatments and the alleviation of soil hydropho-bicity on golf greens. Agronomy Journal 85:983-986.

4. Karnok, K., and M. Beall. 1995. Localized dry spotscaused by hydrophobic soil:What have we learned?Golf Course Management 63(8):57-59.

5. Karnok, K.J., and K.A.Tucker. 1999. Dry spots returnwith summer. Golf Course Management 67(5):49-52.

6. Karnok, K.J., and K.A.Tucker. 2000. FAQ about LDS.Golf Course Management 68(6):75-78.

7. Karnok, K.J., and K.A. Tucker. 2001. Fight localizeddry spots through the roots. Golf CourseManagement 69(7):58-60.

8. Karnok, K.J., and K.A. Tucker. 2001. Effects of flu-tolanil fungicide and Primer wetting agent on waterrepellent soil. HortTechnology 11(3):437-440.

9. Karnok, K., and K. Tucker. 2002. Water-repellentsoils, Part I. Where are we now? Golf CourseManagement 70(6):59-62.

10. Karnok, K., and K. Tucker. 2002. Water-repellentsoils, Part II. More questions and answers. GolfCourse Management 70(7):49-52.

11. Karnok, K.J., and K.A.Tucker. 2003.Turfgrass stress,water-repellent soils and LDS. Golf CourseManagement 71(6):97-98.

12. Tucker, K.A., K.J. Karnok, D.E. Radcliffe, G. LandryJr., R.W. Roncadori and K.H.Tan. 1990. Localized dryspots as caused by hydrophobic sand on bentgrassgreens. Agronomy Journal 82:549-555.

13. Wilkinson, J.F., and R.H. Miller. 1978. Investigationand treatment of localized dry spots on sand golfgreens. Agronomy Journal 70:299-304.

Keith Karnok, Ph.D. (kkarnok@uga.edu), is a professorof turfgrass science and Kang Xia, Ph.D., is an assis-tant professor of environmental soil science in thedepartment of crop and soil sciences at the Universityof Georgia. Kevin A. Tucker is a research associate inthe department. Karnok will be an instructor at GCSAAeducation seminars in Orlando.

Figure 4. Diagram of a sand particle with a water-repellent organic coating.

Nonpolar End

Will Repel Water

Wetting AgentPolar Head(Attracts Water)

H HO

Water Molecule