The research greens are constructed from 4-foot by 24-foot wooden boxes. The support legs are blocked for slope adjustment, rain simulators are located overhead, and tipping bucket rain gauges are attached to the drainage outflow lines to allow for the measurement of water output. Subsurface Drainage of Modern Putting Greens There's a lot going on below the surface. by GUY PRETIYMAN and ED McCOY, Ph.D. S UBSURFACE drainage involves both intensity and capacity attri- butes. Intensity of subsurface drainage refers to how rapidly a root zone drains. Capacity, on the other hand, refers to the extent of excess (gravitational) water removal from the root zone. Consequently, discussions of putting green drainage often be- come confused since the expression improved drainage can imply im- proved drainage intensity, improved drainage capacity, or both. This con- fusion most often occurs with modem high sand content greens where sub~ surface drainage performance is em- phasized. The two most prevalent modem putting green construction methods are the California Method (Davis et aI., 1990) and the USGA (USGA Green Section staff, 1993)green construction technique. The principal differencesbe- tween these two construction methods are a higher recommended root zone permeability in a California (CA)green (relative to a USGA green) and the presence of a gravel blanket in a USGA green. With all other factors being equal, a higher root zone permeability should lead to higher drainage rates, and for most sandy root zones, a drier soil profile. Correspondingly, the gravel blanket should help drainage water move rapidly to drain pipes, but it also is shown to increase water retention in the root zone (reviewed by Hummel, 1993; Taylor, 1993). The key to com- paring subsurface drainage in CA and USGA greens is understanding the interaction between root zone perme- ability and the presence of a gravel blanket. Also, the natural contours or slopes that exist on putting greens may influ- ence both the intensity and capacity of subsurface drainage. Even though these slopes are typically slight, they do represent a driving force for lateral, downslope water movement within the greens profile. The supposition here is that soil water retained in the profile after initial drainage may mi- grate downslope to yield spatially non- uniform soil moistures across a green. To our knowledge, however, no previ- ously reported research on greens drainage has examined green slope effects. This article reports research findings to address modem putting green drain- age issues. The green construction methods under investigation are the USGA and California specifications. Other factors investigated include the effect of green slope on water drainage and redistribution. The Research Approach This study employed four green con- struction approaches consisting of: 1. A CA-style soil profile containing a 9:1 sand:sphagnum root zone. 2. A CA-style profile containing a 6:2:2 sand:biosolids composttopsoil root zone. 3. A USGA layered profile (no inter- mediate layer) containing the 9:1 sand: sphagnum mix. 4. A USGA layered profile (no inter- mediate layer) containing the 6:2:2 sand:composttopsoil mix. Based upon independent testing by an accredited laboratory, both root zone mixes met the particle size and performance criteria for a USGA root zone. Additionally, the sand:sphagnum mix, although not entirely pure sand, met the recently proposed performance criteria of a CA root zone (Hummel, 1998). The sand:sphagnum root zone had a permeability of 20.8 in. hr.-!and is referred to as the high-permeability mix, while the sand:composttopsoil blend had a permeability of 12.6 in. hr:! and is referred to as the low-per- meability mix. Gravel selection for the drainage blanket of the USGA profiles and for the drain line trenches of the CA profiles were based on the particle sizes of the respective root zones cor- responding to USGA specifications for two-tier greens construction (USGA Green Section staff, 1993). The four treatments were replicated three times for a total of 12 experimental greens. At the time of the study, the greens contained a 15-month-old Penncross creeping bentgrass turf maintained at a mowing height of 0/16 inch. The greens were built above ground in 4 ft. by 24 ft. wooden boxes sup- ported by a legged, metal framework. Six-inch-wide by 8-inch-deep drain line trenches extended below the pro- files, with each containing an outlet. The drain line trenches (perpendicular to the long axis) were constructed into each green at 2 ft., 12 ft., 17 ft., and 22 ft. from the downslope end. PVC pipes were connected to the outlet of each 12 USGA GREEN SECfION RECORD
Transcript
The research greens are constructed from 4-foot by 24-foot wooden boxes. The supportlegs are blocked for slope adjustment, rain simulators are located overhead, andtipping bucket rain gauges are attached to the drainage outflow lines to allow for themeasurement of water output.
Subsurface Drainage ofModern Putting GreensThere's a lot going on below the surface.by GUY PRETIYMAN and ED McCOY, Ph.D.
SUBSURFACE drainage involvesboth intensity and capacity attri-butes. Intensity of subsurface
drainage refers to how rapidly a rootzone drains. Capacity, on the otherhand, refers to the extent of excess(gravitational) water removal from theroot zone. Consequently, discussionsof putting green drainage often be-come confused since the expressionimproved drainage can imply im-proved drainage intensity, improveddrainage capacity, or both. This con-fusion most often occurs with modemhigh sand content greens where sub~surface drainage performance is em-phasized.
The two most prevalent modemputting green construction methods arethe California Method (Davis et aI.,1990) and the USGA (USGA GreenSection staff, 1993)green constructiontechnique. The principal differencesbe-tween these two construction methodsare a higher recommended root zonepermeability in a California (CA)green(relative to a USGA green) and thepresence of a gravelblanket in a USGA
green. With all other factors beingequal, a higher root zone permeabilityshould lead to higher drainage rates,and for most sandy root zones, a driersoil profile. Correspondingly, the gravelblanket should help drainage watermove rapidly to drain pipes, but it alsois shown to increase water retention inthe root zone (reviewed by Hummel,1993; Taylor, 1993). The key to com-paring subsurface drainage in CA andUSGA greens is understanding theinteraction between root zone perme-ability and the presence of a gravelblanket.
Also, the natural contours or slopesthat exist on putting greens may influ-ence both the intensity and capacityof subsurface drainage. Even thoughthese slopes are typically slight, theydo represent a driving force for lateral,downslope water movement withinthe greens profile. The suppositionhere is that soil water retained in theprofile after initial drainage may mi-grate downslope to yield spatially non-uniform soil moistures across a green.To our knowledge, however, no previ-
ously reported research on greensdrainage has examined green slopeeffects.
This article reports research findingsto address modem putting green drain-age issues. The green constructionmethods under investigation are theUSGA and California specifications.Other factors investigated include theeffect of green slope on water drainageand redistribution.
The Research ApproachThis study employed four green con-
struction approaches consisting of:1. A CA-style soil profile containing
a 9:1 sand:sphagnum root zone.2. A CA-style profile containing a
6:2:2 sand:biosolids composttopsoilroot zone.
3. A USGA layered profile (no inter-mediate layer) containing the 9:1 sand:sphagnum mix.
4. A USGA layered profile (no inter-mediate layer) containing the 6:2:2sand:composttopsoil mix.
Based upon independent testing byan accredited laboratory, both rootzone mixes met the particle size andperformance criteria for a USGA rootzone. Additionally, the sand:sphagnummix, although not entirely pure sand,met the recently proposed performancecriteria of a CA root zone (Hummel,1998). The sand:sphagnum root zonehad a permeability of 20.8 in. hr.-!andis referred to as the high-permeabilitymix, while the sand:composttopsoilblend had a permeability of 12.6 in.hr:! and is referred to as the low-per-meability mix. Gravel selection for thedrainage blanket of the USGA profilesand for the drain line trenches of theCA profiles were based on the particlesizes of the respective root zones cor-responding to USGA specifications fortwo-tier greens construction (USGAGreen Section staff, 1993). The fourtreatments were replicated three timesfor a total of 12 experimental greens.At the time of the study, the greenscontained a 15-month-old Penncrosscreeping bentgrass turf maintained ata mowing height of 0/16 inch.
The greens were built above groundin 4 ft. by 24 ft. wooden boxes sup-ported by a legged, metal framework.Six-inch-wide by 8-inch-deep drainline trenches extended below the pro-files, with each containing an outlet.The drain line trenches (perpendicularto the long axis) were constructed intoeach green at 2 ft., 12 ft., 17 ft., and 22ft. from the downslope end. PVC pipeswere connected to the outlet of each
12 USGA GREEN SECfION RECORD
Drainage rates between the two rootzone profiles differed significantly. The USGAprofile greens (right) had a higher drainage rate than the California greens (left).
drain line trench, with each fitted witha valve for selective closure. Thepresent study was conducted with onlythe 2 ft. and 17 ft. drain lines open,effectivelyyieldinga drain spacing of 15ft. The 12 research greens were placedin a randomized complete block designon an 80 ft. by 28 ft. concrete pad. Thisallowed adjustment of the green slopeby jacking and blocking the metal legs.Green slopes used in this study were0%,2%, and 4%.
The root zones of each experimentalgreen were instrumented with soilmoisture probes at three depths (3 in.,6 in., and 9 in.) and five locations (2ft., 7 ft., 12ft., 17ft., and 22 ft. from thedownslope end of the green) for a totalof 15 positions per green. The probeswere connected to a measurementsystem that allowed frequent monitor-ing of soil moistures. Additionally, tip-ping bucket rain gauges were con-nected to the drainage outflow pipe ofthe furthest downslope drain line tomonitor drainage outflow rate.
This experimental setup was used tomonitor water drainage and redistribu-tion within the root zone as influencedby green construction method, greenslope, and rainfall rate. The overallstudy was conducted as a series of 18experimental runs. During an experi-mental run, individual greens wereconfigured to a predetermined slopeof 0%,2%, or 4%. Additionally, eachgreen received rainfall from an over-head rain simulator set to deliver eithera high (ca. 4.4 in. hr.-') or low (ca. 1.9in. hr.-') rainfall rate. Rainfall wasapplied for 3 hours to ensure a constantdrainage rate. At the end of the rainfallperiod, the rain device was turned off.
Drainage outflow was measuredevery 5 minutes for both the 3-hourrainfall period and for a 48-hour drain-age period. Soil water contents weremeasured every 20 minutes for the 3-hour rainfall period and for the first24 hours of the drainage period. Soilmoisture levels were measured hourlyfor the remaining 24 hours. This re-sulted in about 44,000 total drainageoutflow measurements and 113,000total soil moisture measurements forthe full 18 runs of the study. Data col-lection began on 6 August 1997 andended on 30 October 1997.
ResultsDue to space limitations, only a
portion of the data collected in thestudy will be presented in this article.Specifically, we will present only thehigh rainfall rate data since, after the
first two hours of the drainage period,rainfall rate had little effect on theexperimental results.
During rainfall, drainage rates fromthe research greens exhibited a signifi-cant interaction between profile design(either with or without a gravel blan-ket) and root zone permeability. TheUSGA profile greens, containing thegravel blanket, had higher drainagerates than the CA profile greens. Addi-tionally, drainage rates from the USGAgreens were essentially the same re-gardless of root zone permeability.Thisresult differed from that of the CAgreens, where the drainage rate duringrainfall was substantially reduced forthe low-permeability root zone com-pared to the high-permeability rootzone. Finally, drainage rates in theUSGA greens consistently increasedwith increasing green slope, while thiswas not the case for the CA greens.
Although drainage rates were muchlower after 27 hours without rainfall,outflow was still observed from allresearch greens. The CA style greenshad higher overall drainage rates thanthe USGA greens, due principally todifferences between the high-perme-ability root zone treatments. Also, re-versed from that observed duringrainfall was the effect of green slope,where drainage rates of the CA greensexhibited a larger increase with in-creasing slope than the USGA greens.
Just as drainage rates showed aninteraction between profile design androot zone permeability, the pattern ofsoil moistures through a cross-sectionofthe root zone yielded a similar inter-action. This pattern is illustrated by
Figures 1 and 2, where isobands of soilmoisture are shown as a function ofdistance upslope and root ZOnedepthfor each of the profile design:root zonepermeability combinations. Also, theindividual figures correspond to greenslopes of 0%,2%, and 4%.
After 48 hours drainage at 0% slope,both CA profiles showed an effect dueto drain spacing. Lower soil moistureswere observed over the drain lines at2 ft. and 17 ft., and higher moistureswere observed between the drains.This contrasts with the USGA profileswhere soil water contents were moreuniform laterally across the soil profile.As expected, root zone permeabilityyielded higher soil moisture levels forthe low-permeability root zone for bothprofiles. It was interesting, however,that the levels of near-surface soilmoistures were similar in the CA high-permeability and the USGA low-per-meability greens.
All research greens exhibited in-creased water contents with root zonedepth. In both permeability rates in theCA profiles, water contents increasedby about 15% to 20% from the 2 in. tothe 10 in. depths. The USGA low-permeability greens yielded about a10% increase and, while not readilyapparent from the figures, the USGAhigh-permeability greens had a 4%increase in water content with depth.
The patterns of soil moisture forgreens sloped at 2% were somewhatsimilar to those observed at 0% slope.This small slope applied to the greens,however, generated some downslopeaccumulation of soil moisture for allsystems. Consequently, the soil mois-
Figure 1. These contour plots demonstrate the soil moisture (% by volume) after 48 hours of drainage for research greens slopedat 0%. Individual plots show results for the California profile with a high permeability root zone, the California profile with a lowpermeability root zone, the USGA profile with a high permeability root zone, and the USGA profile with a low permeability rootzone. Each plot shows moistures in a cross-section of the root zone with the horizontal axis given as distance upslope (feet) and thevertical axis given as root zone depth (inch). The plots are shown with the vertical axis expanded 16.7 times true scale.
_21r=J 25r=J 298iJ 33_37~41_45_ above
48 Hours Drainage, 4% Slope-2 -2-4 -4
-6 -6- -8 -8.c0c;:. -10 -10.ca. 4 8 12 16 20 4 8 12 16 20Q) CA Profile, High Perm. CA Profile, Low Perm.0 -2 -2Q)c:0 -4 -4N15fi -6 -6
Figure 2. Contour plots of soil moisture (% by volume) after 48 hours of drainage for research greens sloped at 4% demonstrate thedifferences in drainage characteristics between California and USGA profile greens.
14 USGA GREEN SECflON RECORD
Table 1Mean drainage rates during rainfall application and after
27-hour drainage for the experimental putting greens.
exhibited higher soil moistures mid-way between the drain lines. Both ofthese soil moisture features result fromthe need for water to move laterallythrough the root zone in a CA greenbefore reaching a drain line. This ratherslow route for water to exit the rootzone, as compared with flow into andthrough the gravel of a USGA green,resulted in wetter soil conditions evenafter 48 hours of drainage. Again, formore complete drainage, a CA greenappears to need a higher root zonepermeability than a USGA green.
This research also illustrates that weneed to consider how a putting green,either a CA or USGA constructionmethod, fits into the landscape; that is,the green slope and direction. Greenslope clearly had an effect on waterredistribution following rainfall, anddid so for both putting green construc-tion methods. Within each profile de-sign, however, the lower permeabilityroot zone yielded enhanced downslopeaccumulation simply because there wasmore moisture retained and accessiblefor migration in this root zone. Inter-estingly, increasing slope in the CAprofiles resulted in higher drainagerates at 27 hours and slightly drier rootzones after 48 hours. Thus, green slopemay be beneficial for continued drain-age of a CA green.
On the other hand, the slope-in-duced, lateral differences in soil mois-ture observed for both the CA andUSGA greens appears to be analogous
Root ZonePermeability
ture pattern due to drain spacing in theCA profile greens was skewed in thedownslope direction, and downslopewater accumulation, particularly atdepth, was observed in the USGAgreens. This downslope soil wateraccumulation was accentuated in allgreens after 48 hours at 4 % slope.Drain spacing effects disappeared forthe CA greens and evidence of waterperching in the USGA greens wasabsent near the upslope end. Finally,the 4 % slope had the greatest influenceon near-surface soil moistures in theCA low-permeability greens, wherewater contents ranged from 37% to25% within a distance of about 18 ft.
It is important to point out thatwhereas results of Figures 1 and 2 are for48 hours of drainage, similar soil mois-ture patterns were observed at earliersampling times. The exception wasthat overall water contents were higherat earlier sampling times and slopeeffects did not become apparent untilabout 12 hours after rainfall stopped.
ImplicationsThis research illustrates that when it
comes to greens drainage, we need togo beyond considering just the rootzone permeability or the profile designand consider the interaction of thesetwo factors. Given equal root zonepermeability, the USGA profile yieldedmore rapid drainage. Indeed, evenrainfall rates of about 4.4 in. hr.-l failedto overwhelm drainage of the USGAprofiles as evidenced by equivalentdrainage rates for both the low- andhigh-permeability root zones. Conse-quently, it appears that CA profilesneed a root zone permeability about 20in. hr:l greater than USGA profiles toyield similar drainage rates. Of course,greens built to CA specifications maybe reasonably expected to have thesehigher permeabilities since the rootzones frequently contain pure sand.
Drainage rate represents an intensityattribute. The capacity attribute ofsubsurface drainage, in the context ofthe present study, is the completenessof excess water removal from the re-spective root zones. Here, it is com-monly thought that formation of aperched water table in a USGA greenwould result in a less completelydrained root zone than a CA green.Our results show that for equal rootzone permeabilities the experimentalUSGA greens are drier after 48 hours(interpreted as having an increaseddrainage capacity) than the experi-mental CA greens. Also, the CA greens
GreenProfile
California
USGA
LSD (0.05)
High
Low
High
Low
GreenSlope
%
o24o24
o24o24
Drainage RateDuring Rainfall 27 HoQl'S
_______n_ gal. hr:' ----------
59 0.2267 0.5152 0.5210 0.086 0.223 0.46
82 0.13130 0.21140 0.2481 0.1798 0.29
146 0.30
11 0.14
to spatially non-uniform soil moisturesobserved within greens on golf courses.This spatial non-uniformity may resultin the formation of localized drying or"hot spots" at upslope locations andexcessive soil wetness in downslopelocations. Both green constructionmethods apparently face this dilemma.ReferencesDavis, W B., J. L. Paul, and D. Bowman.1990. The sand putting green: constructionand management. Publication No. 21448.University of California Division of Agri-culture and Natural Resources.Hummel, N. W, Jr. 1993. Rationale forthe revisions of the USGA green construc-tion specifications. USGA Green SectionRecord. 32(2):7-21.Hummel, N. W, Jr. 1998. Which root-zonerecipe makes the best green? Golf CourseManagement. 66(12):49-51.Taylor, D. H., S. D. Nelson, and C. F.Williams. 1993. Sub-root zone layeringeffects on water retention in sports turf soilprofiles. Agron. J. 85:626-630.US Golf Association Green Section Staff.1993. The 1993 revision, USGA recom-mendations for a method of putting greenconstruction. USGA Green Section Record.32(2):1-3.
GUY PRETIYMAN is a graduate studentpursuing his master's degree in soilscience. DR. ED McCOY is an associateprofessor of soil science at Ohio StateUniversity. The authors wish to acknowl-edge the USGA and the GCSAA for theirsupport of this research project.
