Surfactants Increase Uniformity of Soil Water Content and Reduce Water Repellency on Sand-Based Golf...

Surfactants Increase Uniformity of Soil Water Contentand Reduce Water Repellency on Sand-Based

Golf Putting GreensDouglas J. Soldat, Birl Lowery, and Wayne R. Kussow

Abstract: Water repellency and related localized dry spots are commonproblems on sand-based root zones often used for golf putting greens.The objective of this study was to quantify the effect of three commonlyused surfactants applied to a sand-based root zone on turfgrass visualquality and drought symptoms, soil water content and uniformity, andsoil water repellency. In 2007 and 2008, a study was conducted inWisconsin on a creeping bentgrass golf putting green with a water-repellent sand soil. Prolonged periods of drought occurred in both years.Treatments included three surfactants and two controls, one irrigated at30% of potential evapotranspiration (ETp) and a second irrigated at100% of ETp. The surfactant treatments were irrigated at 30% of ETp.Soil moisture was measured weekly in each plot on a 5 � 5 30-cm gridpattern, along with visual estimates of area exhibiting drought symptomsand turfgrass visual quality. Soil water repellency was measured beforeand at the conclusion of each growing season. In 2007, the surfactanttreatments maintained visual quality lower than the well-irrigated controltreatment but greater than the reduced-irrigation control treatment. In2008, substantial drought symptoms appeared on all surfactanttreatments, which recovered faster than the reduced-irrigation controltreatment. Soil water contents of surfactant treatments were similar toeach other and the reduced-irrigation control on most testing dates.During periods of drought, surfactant-treated soils had the greatestuniformity of moisture content and lowest water repellency at the end ofeach growing season. These results indicate that use of these surfactantscan reduce water use while improving visual quality compared withuntreated areas, prevent localized dry-spot development, and increasemoisture uniformity in sand-based golf putting green root zones.

Key words: Water repellency, turfgrass, surfactants.

(Soil Sci 2010;175: 111Y117)

I rregular patches of drought-affected turf often appear onturfgrass grown on coarse soils (Wilkinson and Miller, 1978).

These patches are called localized dry spots (LDS) and arecaused by water-repellent soils, which are known to developwhen organic material coats soil particles (Tucker et al., 1990;Piccolo and Mbagwu, 1999; Moody et al., 2009) and soil watercontent decreases to a low level (Dekker and Ritsema, 1994;Dekker et al., 2001). Water-repellent soils have been character-ized as having a high degree of variability in soil water content(Albert and Kohn, 1926; Dekker and Ritsema, 2000) and are

susceptible to development of preferential flow paths (Ritsemaand Dekker, 1996; Nektarios et al., 2003).

Minimizing water use on golf course putting greens isdesirable from an economic, environmental, and functionalperspective. Golfers desire a firm putting surface, which can beachieved by creating root zones from sand and maintaining alimited amount of water in the root zones (USGA Staff, 2009).Increasing water scarcity is forcing golf course superintendentsto reduce use of potable water or switch to alternative sources ofwater for irrigation, both of which are known to lead to increasedlikelihood of soil water repellency (Dekker and Ritsema, 1994;Wallach et al., 2005). Hence, the continued efforts by golf coursesuperintendents to improve playing conditions (irrigating less)and reduce the environmental impact of turf management(reducing water use and using alternative water sources) arelikely to increase the occurrence of LDS.

Surfactants are widely used to decrease the incidence ofwater repellency in soils and associated LDS on coarse soils(e.g., Cisar et al., 2000; Kostka, 2000; Leinauer et al., 2007). Anideal surfactant will prevent development of water-repellent soilconditions and maximize the uniformity of soil water contentwithin the root zone, allowing less irrigation water to be used toachieve similar visual appearance as well-watered turfgrass. Theobjectives of this study were to determine how three surfactantscommonly used on golf turf affect soil water content and spatialdistribution under deficit irrigation regimes and assess thepotential of the surfactants to reduce irrigation requirements onsand putting greens without reducing visual quality.

MATERIALS AND METHODSThe study was conducted during the growing seasons of

2007 and 2008 on a United States Golf Association (USGA)specification sand putting green (USGA Staff, 2004) constructedin 2006 and seeded to FPenncross_ creeping bentgrass (Agrostisstolonifera L.) at the O.J. Noer Turf Research and EducationFacility in Madison, Wisconsin. The putting green was mowed6 days per week at 3 mm during the growing season and fer-tilized with approximately 150 kg N haj1 yearj1 in incrementsof 10 kg N haj1. The plots measured 1.8 � 1.8 m and werearrayed in a completely randomized design with four replica-tions. In 2007, moisture stress was induced on the turfgrass byprogramming the irrigation system to apply water based on afraction of potential evapotranspiration (ETp) as estimated fromdata collected from an on-site weather station. Irrigation wasapplied at 50% of ETp during the month of June and at 30% ofETp from July 2007 through the study conclusion in September2008. In late June 2008, drought symptoms developed on largeportions of the putting green irrespective of treatment. We as-sumed this was caused by low uniformity distribution of irri-gation and decided to individually irrigate plots by hand with ahose equipped with a digital flowmeter (Great Plains Industries,Wichita, KS) for the remainder of the season at 30% ETp. Spa-tial patterns in drought symptoms were not evident in 2007

TECHNICAL ARTICLE

Soil Science & Volume 175, Number 3, March 2010 www.soilsci.com 111

Dept. of Soil Science, University of Wisconsin-Madison, Madison, WI. Dr.Douglas Soldat is corresponding author. E-mail: [email protected] September 29, 2009, and in revised form January 27, 2010.Accepted for publication January 29, 2010.Trade names and company names are included for the benefit of the reader

and do not imply any endorsement or preferential treatment of theproduct listed by the Department of Soil Science, University ofWisconsin-Madison, Madison, WI.

Copyright * 2010 by Lippincott Williams & WilkinsISSN: 0038-075XDOI: 10.1097/SS.0b013e3181d6fa02

Copyright @ 20 Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited.10

and disappeared after hand watering began in 2008. Irrigationwas applied three times per week during both seasons.

The treatments consisted of three surfactants, Aqueduct\,Revolution\, and Primer\ 604 (Aquatrols Corp., Paulsboro, NJ)and two control treatments. The surfactants were applied at1.9 mL mj2 delivered in 81 mL mj2 of water according to labeldirections. The study area was irrigated with 6 mm of waterimmediately after application of the surfactant treatments. Sur-factants were applied monthly for 4 months each year, begin-ning on May 29, 2007, and June 3, 2008. Two untreated controltreatments were included; the first control treatment, hereafterreferred to as reduced-irrigation control, received the same ir-rigation regime as the surfactant treatments, whereas the secondcontrol (well-irrigated control) was irrigated with 100% of ETp

by a metered hose in both years. On August 27, 2008, 50 mm ofirrigation was applied to each plot, and the moisture contentwas evaluated 24 h later.

Turfgrass visual quality was quantified weekly by measur-ing using a 1-to-9 rating scale, where 9 represents the highestquality turf, and 1 represents completely dead or brown turf. Arating of 6 indicates minimally acceptable turf quality. Turfvisual quality integrates many aesthetic properties includingdensity, texture (width of leaf blades), uniformity, color, growthhabit, and smoothness (Turgeon, 2008). Soil moisture was alsomeasured approximately weekly within each plot on a 30 �30Ycm grid pattern, beginning 15 cm from the plot border for atotal of 25 measurements per plot using a portable time domainreflectometer with 5-cm probes (Theta Probe, Delta-T Devices,Cambridge, UK, in 2007; TDR 300, Spectrum Technologies,Inc., Plainfield, IL, in 2008). Readings were averaged and a stan-dard deviation (S.D.) of the mean was calculated. The percent-age of drought-affected turf in each plot was also estimatedvisually on a weekly basis. Soil hydrophobicity was measured atthe beginning and end of the season in 2007 and 2008 using awater drop penetration test. The test was conducted by placing a35-KL droplet of distilled water at 1-cm depth on each of four air-dried soil cores per plot using an electronic pipette. A stopwatchwas used to record the amount of time required for each drop tofully penetrate the soil core.

The study was planned and analyzed as a completelyrandomized design with four replications. Treatments wererandomly assigned to plots in both years. Repeated-measuresanalysis of variance was used to determine statistical signifi-cance at the 0.05 probability level using JMP statistical software(SAS Institute, Cary, NC).

RESULTS AND DISCUSSION

WeatherOnly 50 mm of rainfall occurred between June 22, 2007,

and August 3, 2007, resulting in conditions ideal for the de-velopment of LDS (ETp was 224 mm during this period). FromAugust 3 until the end of the first growing season, rainfall wasfairly consistent and exceeded ETp by 306 mm (Fig. 1). In 2008,conditions were optimum for LDS development from July 13until September 3 (ETp, 265 mm; rainfall, 45 mm; Fig. 2).

Drought Symptoms and Turfgrass QualityThe difference between drought symptoms and LDS was

not distinguished by the visual ratings for lack of a quick reliablemethod. During the prolonged dry period in 2007, more than 45%of the reduced-irrigation control treatment displayed droughtsymptoms, although the other treatments never exceeded 15%(Fig. 3). Drought symptoms were substantially greater for alltreatments in 2008, particularly on August 28 when more than65% of the reduced-irrigation control treatment and between 60%and 80% of surfactant treatments displayed visual drought symp-toms (Fig. 4).

In 2007, significant differences in area affected by droughtoccurred on every observation date beginning with June 12through August 21. On these dates, the reduced-irrigation con-trol had significantly greater drought symptoms compared withthe well-irrigated control (100% ETp replacement) and surfac-tant treatments (30% ETp replacement), which were statisticallysimilar on most dates. The exceptions include July 17, whenPrimer\ 604 had significantly lower drought symptoms thanthose of Aqueduct\, and on July 31, when Revolution\ andPrimer\ 604 had significantly lower drought symptoms com-pared with those of Aqueduct\. In 2007, the drought-affected

FIG. 1. Rainfall and potential evapotranspiration at the researchsite in Madison, Wisconsin, during the 2007 growing season.

FIG. 2. Rainfall and potential evapotranspiration at the researchsite in Madison, Wisconsin, during the 2008 growing season.

Soldat et al. Soil Science & Volume 175, Number 3, March 2010

112 www.soilsci.com * 2010 Lippincott Williams & Wilkins


area of the well-irrigated control was statistically similar to allsurfactants, except on July 17, when Primer\ 604 had fewerdrought symptoms (Fig. 3).

In 2008, significant differences in drought symptomsamong the treatments were detected on the final six ratingdates (Fig. 4). On four of these dates, the well-irrigated controlhad significantly lower drought-affected area than that of atleast one of the surfactant treatments. The surfactants werestatistically similar on all dates except August 13, when Primer\604 had lower drought-affected area than that of Aqueduct\.These findings are consistent with the 2007 observations.

These results demonstrate that the surfactants greatly re-duced drought symptoms in 2007 but did so to a lesser extent in2008. In 2007, surfactant treatments (irrigated to 30% of ETp)had statistically similar drought symptoms to the well-irrigatedcontrol (irrigated to 100% of ETp), indicating that a substantialreduction in irrigation water requirement is possible when usingsurfactants on sand putting greens. In 2008, surfactants seemedto reduce the onset of drought symptoms for at least a week andexpedited the recovery from those symptoms (Fig. 4).

In 2007, differences in turfgrass visual quality were sta-tistically significant for all rating dates except the last (Fig. 5).For much of this period, the well-irrigated control had thegreatest turfgrass quality, the surfactants were intermediate, andthe reduced-irrigation control treatment had the lowest turfgrassquality. On six of the 14 significant rating dates, at least one ofthe surfactants had statistically similar turf quality to the well-irrigated control; and on seven dates, at least one of the surfac-tants had similar turf quality to the reduced-irrigation control.Surfactant treatments had statistically similar turf quality on 11of the 14 dates. On the dates where significant differences weredetected among surfactant treatments, Primer\ 604 had thehighest visual quality.

In 2008, differences in turfgrass quality was only observedon the final six rating dates and on July 2 (Fig. 6). On four ofthese dates, the well-irrigated control treatment had significantly

FIG. 4. Visual assessment of percentage of plot area thatdemonstrated drought symptoms in 2008. Least significantdifferences at the 95%probability level based on repeated-measuresanalysis can be used to compare and contrast treatment differenceswithin and across dates.

FIG. 5. Visual turfgrass quality of treatments in 2007 asdetermined by a 1-to-9 scale, where 9 represents the highestpossible turf quality, and 1 indicated dead or completely brownturf. A rating of 6 is deemed minimally acceptable turfgrassquality. Least significant differences at the 95% probability levelbased on repeated-measures analysis can be used to compare andcontrast treatment differences within and across dates.

FIG. 6. Visual turfgrass quality of treatments in 2008 asdetermined by a 1-to-9 scale, where 9 represents the highestpossible turf quality, and 1 indicated dead or completely brownturf. A rating of 6 is deemed minimally acceptable turfgrassquality. Least significant differences at the 95% probability levelbased on repeated-measures analysis can be used to compare andcontrast treatment differences within and across dates.

FIG. 3. Visual assessment of percentage of plot area thatdemonstrated drought symptoms in 2007. Least significantdifferences at the 95%probability level based on repeated-measuresanalysis can be used to compare and contrast treatment differenceswithin and across dates.

Soil Science & Volume 175, Number 3, March 2010 Surfactants on Golf Putting Greens

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greater turfgrass quality than at least one of the surfactanttreatments; similarly, all surfactant treatments had significantlyhigher turfgrass quality than the reduced-irrigation control onthree dates. On the final rating date, there were no differencesin turf quality among the well-irrigated control and surfactanttreatments, which all had significantly greater turf quality thanthe reduced-irrigation control. This result matches with theobservations on the affect of surfactants on recovery fromdrought in 2008.

During 2007, the well-irrigated control maintained turfquality above or near 6 for much of the year. The surfactanttreatments were between 5 and 6 for much of the year, whereasthe reduced-irrigation control turf quality was between 3.5and 5.5 for much of 2007. In 2008, the surfactant treatmentsmaintained turf quality at or above 6 for all but 3 weeks duringthe intense drought. This is in contrast to the 6 weeks of sub-6turf quality of the reduced-irrigation control treatment. As seenin 2007, the well-irrigated control maintained greater-than-acceptable turf quality for the entire 2008 season. These resultsindicate that surfactants can improve turf quality under deficitirrigation, and although not maintaining turf quality as greatas well-watered grass, the reduction in turf quality was 1 to 1.5units in 2007 and 2 to 5 units in 2008. These decreases in turfquality were associated with 70% lower irrigation requirement.It seems that in some years (i.e., 2007), irrigating at a 30% ETdeficit level can produce only similar drought symptoms andslightly lower turf quality for much less water, whereas in otheryears (i.e., 2008), the quality reduction is much more pro-nounced and may not be acceptable to most golfers.

Soil MoistureIn 2007, statistical differences in volumetric soil water con-

tent were detected on every date except for the first two (June 5and 12). In general, the well-irrigated control had the greatestsoil water content followed by the surfactant treatments, whichwere similar to that of the reduced-irrigation control on five ofthe nine dates with differences (Fig. 7). The Revolution\ treat-ment and the reduced-irrigation control had similar soil watercontents on eight measurement dates. As a group, the surfactanttreatments had statistically similar soil water contents, except onAugust 8 when Aqueduct\ had statistically greater volumetricsoil water content than that of Revolution\.

In 2008, statistical differences in water content in the upper5 cm were detected on all 12 measurement dates (Fig. 8). Thewell-irrigated control had significantly greater soil water contentthan all other treatments on nine of the dates. In contrast to thefindings in 2007, the Aqueduct\ and Primer\ 604 treatmentshad lower soil water content than the reduced-irrigation controlfor the first two rating dates of the season. This phenomenonwas observed during a relatively wet period of the season(Fig. 2), and when the weather became drier, the surfactanttreatments tended to have similar or greater soil water contentthan the reduced-irrigation control. Significant differences in soilwater content among the surfactants were observed on only onedate (July 2), when Primer\ 604 had significantly greater soilwater content than that of Aqueduct\. On August 27, 50 mm ofirrigation was applied to the treatments by hand, and volumetricsoil water content was measured after a 24-h period. After thislarge application, Primer\ 604 and Revolution\ had signifi-cantly greater volumetric soil water contents than that of thereduced-irrigation control. The Aqueduct\ treatment had statis-tically similar soil water content to both the reduced-irrigationcontrol and the other two surfactants.

These results are somewhat different from those of previ-ous researchers. Lyons et al. (2009) found no significant dif-ference among surfactant treatments and control treatments.Leinauer et al. (2001) found that Primer\ increased soil mois-ture content of a sand column in the laboratory compared withthat of an untreated control column. We found that surfactantshad significantly greater volumetric soil water content than thereduced-irrigation control on approximately half of the mea-surement dates, significantly lower water content on two dates,and statistically similar on the remainder. This suggests that theeffect of surfactants on volumetric water content is complex andvaries not only by year (Leinauer et al., 2007), but by intra-annual weather patterns as well. The most important implicationof the effect of surfactants on soil water content may be on howthey affect moisture uniformity rather than moisture content.

Soil Moisture UniformitySoil volumetric water content alone does not fully elucidate

the efficacy of a surfactant. For example, a particular plot mayhave both hydrophobic and hydrophilic soil regions. We hypoth-esized that if irrigation is applied to such a plot, very little of thewater will enter the hydrophobic regions, but will instead moveto the hydrophilic regions via overland flow. This scenario would

FIG. 7. Volumetric soil water content of treatments in 2007 inthe upper 5 cm of soil. Least significant differences at the 95%probability level based on repeated-measures analysis can beused to compare and contrast treatment differences within andacross dates.

FIG. 8. Volumetric soil water content of treatments in 2007in the upper 5 cm of soil. Least significant differences at the 95%probability level based on repeated-measures analysis can beused to compare and contrast treatment differences within andacross dates.




be expected to result in more irrigation infiltrating certain areasthan others, resulting in areas of very high and very low moisturecontents within a single plot. Evidence for this hypothesis wasobserved on the reduced-irrigation control treatment during timesof maximum drought stress. Figure 9 visually compares themoisture distribution between reduced-irrigation control treatmentand surfactant treatments on July 24, 2007, and August 6, 2008.The surfactant treatments had a very uniform moisture contentcompared with the reduced-irrigation control. The degree of soilwater content uniformity is described by S.D. (Figs. 10 and 11).Statistical differences in soil water uniformity were detected on

seven of the 11measurement dates in 2007, and six of the 11 datesin 2008. The reduced-irrigation control treatment had significantlygreater variability in moisture content than most other treatmentsduring the same periods when maximum drought stress wasobserved. As previously noted, in 2008, drought symptoms weresevere on all surfactant treatments and the reduced-irrigationcontrol (Fig. 4). However, the uniformity of water content for thesurfactant treatments was very high (low S.D.) during this period(Fig. 10), indicating that the drought stress was not caused bywater-repellent soils and LDS. This also explains the much morerapid recovery from drought symptoms noticed in the surfactant

FIG. 9. Spatial graphs of plot-scale water content for reduced-irrigation control (A and C) and surfactant treatments (B and D), bothirrigated to replace 30% of ETp. Soil moisture content maps are 1.2 � 1.2 m. Plots (A) and (B) are from July 24, 2007, plots (C) and (D) arefrom August 6, 2008. Actual measurement points are represented by the dots, which are 30 cm apart. Because statistical differencesin moisture uniformity were not detected among the surfactant treatments, unidentified representative examples are shown comparedwith representative examples from the reduced-irrigation control treatment.

FIG. 10. The S.D. of volumetric water content of treatments in2007. Least significant differences at the 95% probability levelbased on repeated-measures analysis can be used to compare andcontrast treatment differences within and across dates.

FIG. 11. The S.D. of volumetric water content of treatments in2008. Least significant differences at the 95% probability levelbased on repeated-measures analysis can be used to compare andcontrast treatment differences within and across dates.




treatments compared with the reduced-irrigation control from endof August to mid-September 2008 (Figs. 4 and 6). The three sur-factants had statistically similar water content uniformities on alldates. The well-irrigated control treatment had statistically similarwater content uniformity to the surfactants in all but two datesduring the 2-year study. Similar increases in moisture uniformityafter applications of surfactants to sand putting greens have beenrecently reported (Aamlid et al., 2008; Kostka et al., 2008).

Soil HydrophobicitySoil hydrophobicity was evaluated before treatment appli-

cation and at the conclusion of the season each year. No sig-nificant differences were observed among the future treatmentlocations before treatment initiation (Table 1), although the soilson the sites of future treatments were considered slightly waterrepellent (5Y60 sec) according to Dekker and Jungerius (1990).At the conclusion of the 2007 growing season, the reduced-irrigation control treatment had substantially greater hydro-phobicity at the 1-cm depth than those of Aqueduct\ andRevolution\ treatments (Table 1). Only the soil from theRevolution\ treatment had significantly lower water repellencythan the well-irrigated control treatment. Before treatment ap-plication in 2008, no significant differences existed in waterrepellency among the treatments. At the end of the growingseason, all surfactant treatments had significantly lower waterrepellency than the reduced-irrigation control treatment. Onlythe Aqueduct\ treatment had significantly lower water repel-lency than the well-irrigated control (Table 1). Similar to theconclusions of Leinauer et al. (2007), these results demonstratethe importance of multiyear or multisite research to better un-derstand how surfactants perform in different soil and weatherconditions.

CONCLUSIONSOn this sand-based putting green in Wisconsin, applying

any of the tested surfactants and restricting irrigation to replace30% of ETp resulted in decreased turfgrass visual quality com-pared with grass irrigated at 100% of ETp but significantly bettervisual quality than grass irrigated at 30% ETp replacement with-out a surfactant in 2007. In 2008, drought symptoms were moresevere, and irrigating to replace 30% coupled with a surfactantwas not adequate to prevent the development of drought symp-toms or maintain turfgrass visual quality comparable to the well-irrigated control. However, the amount of time where turfgrassquality was unacceptable was roughly half of the time as thereduced-irrigation control, and the development of drought symp-toms was delayed. Furthermore, the uniformity of soil volumetric

water content of the surfactant treatments was significantlygreater, and soil water repellency was lower than the reduced-irrigation control treatment. It is likely that drought symptomswere caused by a temporary lack of sufficient plant-availablewaterrather than LDS. Visual assessments of turfgrass quality anddrought symptoms indicated that surfactant treatments were fasterto recover from the drought than reduced-irrigation control, sup-porting the previous hypothesis.

The surfactants had a minimal effect on soil water contentcompared with the reduced-irrigation control under the sameirrigation regime (30% ETp replacement). However, the threesurfactants significantly improved soil moisture uniformity com-pared with the untreated control in both years during droughtconditions. In addition, with the exception of Primer\ 604 in2007, all surfactant treatments led to lower soil water repel-lency than that of the reduced-irrigation control. These resultsindicate that the surfactants evaluated are effective tools for im-proving soil water content uniformity, maintaining good visualappearance, and reducing soil water repellency in sand-basedgolf putting greens under conditions of drought and irrigationrestrictions.

ACKNOWLEDGMENTSThe authors thank B.T. DeBels, J. Dywer, W.C. Kreuser, E.S.

Melby, P. Speth, and P. Wakeman for their extensive assistancewith data collection during the study. Aquatrols Corp. providedpartial funding of this experiment.

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TABLE 1. Time to Penetration of 35 KL of Distilled Water Droplet at 1-cm Depth of Air-Dried Soil Cores

Treatment

May 24, 2007 October 11, 2007‡ May 28, 2008 September 18, 2008‡

Time to Penetration, sec

Reduced-irrigation control 26.9 A† 39.1 A 34.6 A 148 AWell-irrigated control 14.1 A 17.4 AB 36.0 A 52.1 ABAqueduct\ 21.0 A 11.5 B 45.8 A 10.5 CPrimer\ 604 30.9 A 19.6 AB 51.1 A 40.4 BRevolution\ 25.2 A 5.6 C 43.3 A 28.9 B

Cores were taken in May 2007 and 2008 before treatment application.†Column means followed by similar letters are not significantly different according to least significant difference method at > = 0.05.‡Time to penetration values in October 2007 and September 2008 was log transformed for statistical analysis because of unequal variance. For ease

of interpretation, the nontransformed values are reported, but statistics are based on log transformations.




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