ponsored

Research YCJU Can Use

Rootzone Depth AffectsPutting Green PerformanceResearch at Michigan State University demonstrates how varyingputting green rootzone depth affectsmoisture retention.BY KEVIN W. FRANK, B. E. LEACH, J. R. CRUM, P. E. RIEKE,B. R. LEINAUER, T. A. NIKOLAI, AND R. N. CALHOUN

The United States Golf Association(USGA) introduced putting greenconstruction guidelines 45 years

ago, and since then the USGA greenhas become the standard for golf courseputting greens. The concept behind theUSGA guidelines is to build a greenthat provides a measure of resistance tocompaction in the rootzone and drainsquickly to an optimum soil moistureleveP Specifications for a USGA putt-ing green require that the sandy root-zone mixture be placed at a uniformdepth of 12 inches, plus or minus oneinch, across the entire surface of thegreen. If greens lacked slopes, there islittle doubt that most, if not all, USGAgreens would perform well. However,with the severe slopes present on someputting greens today, USGA greens donot always perform ideally.

Putting greens constructed to USGAspecifications function very well on arelatively level surface4

; however, whenthe green has undulating areas, moistureextremes in the rootzone can lead toturf grass decline? Two conditions associ-ated with moisture extremes in therootzone are localized dry spot (LDS)and black layer. Both impair turfgrassgrowth and can be problematic onundulating sand-based putting greens.

Moisture variability problems onUSGA putting greens could be attrib-uted to the uniform depth of the root-zone layer. In theory, on a level surface,there is minimal lateral flow of waterwithin the rootzone and the putting

green drains at a uniform rate. However,Nektarios et aP have shown that drain-age in the rootzone is not always uni-form. In an unsaturated putting greenrootzone, water does not drain from therootzone into the gravel layer, therebyallowing water to move laterally alongthe rootzonel gravel layer interface tolower elevations in the green. Theresultant problems associated with thisdown-slope water movement are par-ticularly evident at the higher elevationsof the green, where hand watering isoften necessary to prevent turf decline.

Research was initiated to investigateif altering the rootzone depth, decreas-ing it in high areas and increasing it inlow areas, would increase the watercontent near the soil surface in highareas and decrease the water contentnear the soil surface in low areas. Ourresearch objective was to determine ifmodifying the rootzone depth increasessoil moisture uniformity across theslope of an undulating sand-basedputting green.

MATERIALSAND METHODSA sloped USGA putting green wasconstructed at the Hancock TurfgrassResearch Center on the campus ofMichigan State University in 1998. Theputting green was designed for moni-toring the down-slope movement ofwater in the rootzone. Time domainreflectometry (TDR) instrumentationwas installed in the green to monitorsoil volumetric water content (VWC).

The putting green was constructedwith a summit 1.2 feet in height, withtwo downhill slopes of different magni-tude. The peak of the summit wasconstructed 26 feet from the northernedge of the green and 55 feet from thesouthern edge. The putting green has a7% north slope and a gradual 3% southslope. These slope gradients werechosen to represent average andextreme slopes that occur on modernUSGA-recommendation puttinggreens.

The putting green was divided into12 plots, 8 feet wide and 80 feet long.Six test plots were built to USGAspecifications consisting of a uniformdepth rootzone (12 inches). The remain-ing six test plots were built with a vari-able depth rootzone: 8 inches at thesummit and gradually increasing indepth to 16 inches at the base of theslopes (toe slopes, Figure 1).Three root-zone mixes were used in the construc-tion of both the USGA (uniformdepth) and variable depth plots: sand,85:15 sandlpeat (reed-sedge), and 85:15sandi soil. A polyvinyl cWoride linerwas placed between adjacent plots toprevent the lateral movement of waterbetween plots.

Prior to construction, rootzonematerials were tested for particle sizedistribution, organic content, and soilphysical properties following USGAguidelines~ The sandi peat rootzone mixconformed to USGA specifications, butthe sandi soil and sand rootzone mixes

NOVEMBER-DECEMBER 2005 21

Figure ICross section view of the standard USGA and variable-depth construction

methods. Mean percent volumetric water content for the 0- to 4-inch depthlevel is presented for day 3 of the dry-down period (2000-2002).

did not conform (Table 1).The sandisoil rootzone did not conform to

specifications because of particle sizedistribution. The sand rootzone mix did

not conform to USGA specificationsfor hydraulic conductivity and percentcapillarity.

Mter the construction of the puttinggreen was completed, 108 TDR probesOocally manufactured by B. R. Leinauer)were buried in the soil to measurevolumetric soil moisture at four loca-

tions within each test plot: probe loca-tion 1 at the base of the north slope,probe location 2 at the summit, probelocation 3 at the base of the south

slope, and probe location 4 in themiddle of the south toe slope (Figure1). The TDR probes were positioned inthe soil at a 45-degree angle to measureVWC at depths of 4-8,8-12, and 12-16inches. A hand-held TDR was used torecord VWC at the four locations of

the surface (0-4 inches).Mter installation of the TDR probes

in the summer of 1998, the puttinggreen was seeded with L-93 creepingbentgrass. To evaluate soil moisture rela-tionships, the putting green was sub-jected to "dry-down" cyles, with fourcycles in each year from 2000 through2002. Dry-down cycles were scheduledduring dry periods without rainfall, andno irrigation was applied to the puttinggreen. During each cycle, VWC wasmonitored daily with the TDR probesat the four locations in each plot.VWCwas recorded at each location at depthsof 0-4 inches and 4-8 inches. At the

locations where depths were present,VWC was recorded at 8-12- and

12-16-inch depths.Each dry-down cycle began with

uniform, healthy turf across the entireputting surface. To establish near fieldcapacity soil moisture content, irrigation(1 inch) was applied the night beforeeach cycle, and the morning of "day 0"(0.5 inch). Mter the morning irrigation,TDR readings were taken at the fourlocations on each individual plot. TheTDR readings were taken at 24-hourintervals for the length of the cycle.

RootzoneMix

RootzoneMix

16 in. 16 in.12% VWC 11% VWC

Variable-Depth Rootzone Green

16 in.II%VWC

12 in.17%VWC

Table IRootzone mix physical properties and particle size distribution.

Rootzone MixUSGA

Physical Properties Recommendation* Sand Sand/Peat Sand/Soil

Organic Matter (%) 1-5 1.20 3.20 2.00Hydraulic Conductivity (em hr") Minimum 15 86.20 27.90 15.70Bulk Density (g cm'3) N/A 1.75 1.57 1.74Particle Density (g cm'3) N/A 2.64 2.35 2.66Porosity:

Total (%) 35-55 35.20 42.80 36.00Capillary at 40cm tension (%) 15-25 8.90 16.70 15.80Air Filledat 40cm tension (%) 15-30 27.30 26.10 20.20

Particle Size (mm) %

2.0 - 3.4t Maximum 0.1 0.1 0.81.0 - 2.0 10 7.6 7.3 12.00.5 - 1.0 Minimum 26.0 25.4 24.6

0.25 - 0.50 60 45.4 46.6 36.80.15 - 0.25 Maximum 20 19.1 18.3 16.6

0.05 - 0.15+ Maximum 5 0.6 1.1 1.3

0.002 - 0.05+ Maximum 51.2 1.2 7.9

<0.002+ Maximum 3

*The USGA Green Section Staff,2004tMaximum of 3%,preferably none+Maximum of 10%total between the three categories

22 G R E ENS E C T [ 0 N R E COR D

\Table 2Mean percent volumetric water content for the different rootzone types.

0-4 Inches Depth Sand Sand/Soil Sand/Peat

--- - - -- -- - - - - - -- - % --- - - - - - -- - - - - -- - --Aug. 23, 2000 IsBt 2sA 27AAug. 24, 2000 14C 21B 24AAug. 25, 2000 13C ISB 23AAug. 26, 2000 12C ISB 23AJuly 23,2002 ISC 2sA 27AJuly 24,2002 17B 23A 27AJuly 25,2002 14B 20A 21AJuly 26, 2002 12B ISA 21ASept. 2S, 2002 20B 27A 29ASept. 29, 2002 16B 22A 2sASept. 30, 2002 ISB 24A 2sAOct. 1,2002 13C 21B 24A

4-8 Inches DepthJuly I0, 2002 17B 20A 22AJuly II, 2002 IsB 19A 20AJuly 12,2002 14B ISA 20ASept. 2S, 2002 1St 20 31Sept. 29, 2002 IsB 19AB 22ASept. 30, 2002 16 19 21Oct. 1,2002 IsB 17AB 21A

peat rootzone had the lower Cv. Forthe variable-depth rootzones, therewere either no differences in CVamong the rootzones or the sandrootzone had the highest Cv.

Differences in Construction rypeComparisons between the two con-struction types reveal that uniform-depth sand greens had a higher CV thanvariable-depth sand greens on almost alldates. For the sandlsoil greens, therewere no differences between the con-struction types in 2000, but in 2002,the variable-depth rootzones had alower CV on three of four dates. Thesandi peat rootzones did not have adifferent Cv, regardless of constructiontype. The CV data support our hypoth-esis that by altering the rootzone depth,the variability of VWC across the slopeof the green, especially for the sandrootzone greens, can be greatly reduced.

tMeans in a row followed by the same letter are not significantlydifferent according to t-test(p=O.Os)

tData not followed by letters are not significantlydifferent

Each dry-down cycle was ended aftereither 3 or 4 days, at which time therewere visible signs of severe turfgrassmoisture stress on the sand rootzoneplots at the peak of the summit.

Statistical analysis was conductedindependently for each day and for themeasurement depths 0-4 and 4-8inches, as these were the only depthspresent at each location within each testplot. Coefficient of variation (CV) wascalculated for VWC data in each plotand analyzed for treatment differences.The CV is a relative measure of varia-tion in the data, and it was used to assessthe variability of VWC across the slopeof the putting green.

RESULTSDifferences in Rootzone rypeVWC for rootzone type, when averagedacross the two construction types, wassignificantly different throughout thedry-down cycles in 2000 and 2002. Forthe 0-4-inch depth, for the majority of

sampling days, there were no differencesin VWC among the sandi soil andsandi peat rootzones (Table 2). The sandrootzone consistently had the lowestVWC. For the 4-8-inch depth, theresults were similar. There were noVWC differences between the sandi soiland sandi peat rootzones, and the sandrootzone had the lowest VWC. Theresults indicate that regardless of con-struction type, the water-holdingcapacity of the rootzone mixes con-taining soil or peat is higher than thesand rootzone. Sand rootzones withpeat or soil added should not see theextremes in VW C that are oftenencountered in 100% sand rootzones.

Among USGA greens, the sandrootzone had the highest Cv, indicatingthat the sand rootzone green had thegreatest variation in VWC across theslope of the green. Generally, for theUSGA greens, there were either nodifferences in CV among the sandi soiland sandi peat rootzones, or the sandi

Mean VWC:Construction rype and SoilrypeOn day zero, the greatest difference inVWC among sampling locations for allrootzone mixes with variable depthswas 4%. On day three, the greatestdifference among sampling locationswas still only 4%.

Differences in VWC among locationsremained consistent as the green drieddown. In contrast, for USGA greens(with uniform rootzone depths), thegreatest difference in VWC amonglocations on day zero was 6% and forday three was 11%. The differencesbetween USGA (uniform depth root-zone) and variable-depth rootzoneconstruction types on day zero wassmall (2%), but by day 3 was large (7%).These data further support our con-clusions that for variable-depth root-zones,VWC was more uniform acrossthe green.

Also, the difference in VWC amongthe sampling locations explains the highCV of the standard-depth greens. Forthe uniform-depth sand greens on day3, the range in VWC included a low of7% at location 2 (summit of slope) and

N 0 V E M B E R - 0 E C E M B E R 2005 23

Table 3Coefficient of variation for volumetric water content for

construction and rootzone type, 0-4 inches rootzone depth.

Construction Type Sand Sand/Soil Sand/Peat

2000 - - - - - - - Coefficient of Variation - - - - - - -

Aug. 23: Day 0 Standard 31 12 9Modified 12 II 9

Aug. 24: Day I Standard 44Ata:j: ISBa 20BaModified 20Ab 18Aa 16Aa

Aug. 25: Day 2 Standard 381f 16 13Modified 29 16 25

Aug. 26: Day 3 Standard 43Aa 19Ba 16BaModified IIAb 17Aa 15Aa

2002

July 23: Day 0 Standard 24Aa 24Aa 8BaModified 14Aa 10Ab 14Aa

July 24: Day I Standard 30 21 10Modified 10 12 12

July 25: Day 2 Standard 45Aa 35Ba 15CaModified 32Ab 19Bb 19Ba

July 26: Day 3 Standard 42Aa 32Ba 22CaModified 22Ab 13Bb 16ABa

tMeans in a row followed by the same upper-case letter are not significantlydifferent accordingto t-test (p=O.1 0)

:j:Means in a column, for each date, followed by the same lower-case letter are not significantlydifferent according to t-test (p=O.1 0).

1fData not followed by letters are not significantlydifferent

Table 4Mean percent volumetric water content for the 0- to 4-inch depth,2000-2002.

Location I Location 2 Location 3 Location 4

Day 0USGA Sand 21 15 21 20USGA Sand/Peat 30 26 28 27USGA Sand/Soil 29 23 27 25Modified Sand 16 17 18 17Modified Sand/Peat 26 28 24 24Modified Sand/Soil 24 26 22 22Day 3USGA Sand 17 7 18 18USGA Sand/Peat 27 20 26 25USGA Sand/Soil 27 16 24 21Modified Sand II II 12 IIModified Sand/Peat 21 22 18 19Modified Sand/Soil 18 19 16 15

24 GREEN SECTION RECORD

a high of 18% at locations 3 and 4(Figure 1). In contrast, for the variable-depth sand greens, there was only a1% difference in VWC among thelocations.

CONCLUSIONSThe USGA specifications for puttinggreen construction, first published in1960, were designed to improve thequality of putting greens. Although theUSGA has published several revisions,most recently in 2004, the recommen-dation for a uniform 12-inch rootzonelayer has remained unchanged. Thelayering of a sand-based rootzone mixover a gravel layer maintains optimummoisture across the putting green on arelatively level putting surface; however,in areas of undulation the uniformrootzone depth can result in moistureextremes at the different elevations.

Our research confirmed that theaddition of peat and/or soil to therootzone mix increased water-holdingcapacity. Modifying the depth of thesand rootzone improved the uniformityof VWC across the surface of anundulating putting green. When soil orpeat was added to the sand rootzone,extremes in soil moisture contentbetween the high and low elevations ofthe green were reduced, regardless ofconstruction type. For greens con-structed with a 100% sand rootzone, itwould be beneficial to modify thedepth of the rootzone (i.e., shallower inhigh areas and deeper in low areas) tomaintain uniform soil moisture contentacross the surface of the putting green.Although varying the rootzone depthin this way helps even out rootzonewater content, constructing greens inthis way may be too impractical and isnot currently part of USGA puttinggreen recommendations.

Even if greens are not constructedwith a variable-depth rootzone, thisresearch reveals the importance ofclosely following rootzone depthspecifications during construction.Special attention should be given tofollowing rootzone depth specifications

Researchers at Michigan State University investigated the hypothesis that reducing rootzone depth in higher-elevation areas and increasingdepth of the rootzone in lower-elevation areas of contoured putting greens may result in more even moisture distribution across the entireputting green.

during construction and not makingalterations based on aesthetics. In cer-tain situations, rootzone material unfor-tunately is excavated from lower areasand moved to other regions of thegreen to increase elevation changes. Theresult is that the green would have ashallower rootzone depth in low areasand rootzone depths in excess of 12inches in hig~er areas, a worst-casescenario. At a minimum, this researchemphasizes the importance of closelymonitoring construction activities toensure that higher points in contouredputting greens do not have rootzonedepths greater than 12 inches, whichwould cause "hot spots," and low pointsdo not have rootzone depths that aretoo shallow, which could createexcessive moisture conditions.

LITERATURE CITED

1. Hummel, N. W 1993. Laboratory methods forevaluation of putting green rootzone mixes.USGA Green Section Record. 31(2):23-33.

2. Nektarios, P. A., T. S. Steenhuis, A. M. Petrovic,andJ.-Y Parlange. 1999. Fingered flow inlaboratory golf putting greens.] if Tuif. Mgt.3(1):53-67.

3. Prettyman, G., and E. McCoy. 1999. Sub-surface drainage of modern putting greens.USGA Green Section Record. 37(4):12-15.

4.Taylor, D. H., S.D. Nelson, and C. F. Williams.1993. Sub-root layering effects on water reten-tion in sports turf soil profiles. Agron.]85:626-630.

5. U.S. Golf Association Green Section Staff.2004. USGA Recommendations for a Methodof Putting Green Construction. USGA WorldWide Web Site. http://www.usga.org/turf/-course construction/green articles/puttinggreen guidelines.html.

Editor's Note: A more completeresearch report on this study may befound at: http://usgatero.msu.edu/ -v04/n11.pdf

KEVIN W FRANK, PH.D., AssistantPrifessor;BRIAN E. LEACH,former M. S.student;JIM R. CRUM, PH.D., Prifessor;PAUL E. RIEKE, PH.D., Prifesso~ Plantand Soil SciencesDepartment, MichiganState University, East Lansing; BERND R.LEINAUER, PH.D., Assistant Prifesso~Extension Plant Sciences,University oj NewMexico, Las Cruces;THOMAS A. NIKOLAI,PH.D., Academic Specialist; and RONALDN. CALHOUN, PH.D., Environmental Tuif-grass Specialist, Plant and Soil SciencesDepartment, Michigan State University,East Lansing.

N 0 V E M B E R - DEe E M B E R 2 0 0 5 25