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Surface Organic Matterin Bentgrass GreensResearch reveals the relationship between aeration methodsand surface organic matter on sand-based greens.BY ROBERT N. CARROW, PH.D.

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e USGA golf green recom-mendations were developed tocreate a rootzone medium that

would exhibit good physical propertiesunder continuous traffic, namely waterinfiltration and percolation, oxygenstatus, and resistance to soil compaction.Putting greens, however, are dynamicsystems where the norm is changingover time, especially within the two-inch surface zone. The greatest changesin total organic matter content, thatch/mat status, turfgrass rooting, and eventhe nature of the organic matter oftenoccur during the first two years ofgrow-in, but changes also may continueover future years. All of these factorsmay influence water infiltration andpercolation, as well as soil oxygen status.

Several researchers have documenteddecreases in saturated hydraulic con-ductivity (SHC, the infiltration rateunder saturated profile conditions) asputting greens mature.7,10 Concurrentwith a reduction in SHC has been anincrease in organic matter contentwithin the surface two inches. An upperlimit of 4.5% (by weight) of organicmatter in a sand medium was suggestedby Murphy et al.S because macroporesimportant for rapid SHC are insufficientabove this level. McCoy6 recommendeda maximum of 3.5% organic matter (byweight) based on his work and a reviewof others, since macroporosity starts todecline above this value. The decline inroot growth often observed within twoto three years after establishment has

1I ••, t ~

\ "University of Georgia researchers are investi-gating how various aeration methods can limitorganic matter buildup in newly constructedgreens. This example shows the organic matterbuildup found in an ultradwari bermudagrassgreen after one year if not managed properly.

been attributed to accumulation oforganic matter in the surface.

SUMMER BENTGRASSDECLINE: PATHOLOGICALOR PHYSICAL?The USGA-sponsored project "OrganicMatter Dynamics in the Surface Zoneof a USGA Green: Practices to AlleviateProblems" arose from observations inthe late 1980s of summer bentgrassdecline (SED) on creeping bentgrassgreens in the southern zone of bent-

grass adaptation. From field observationsand a review of the literature, I carne tothe hypothesis that many of the primaryproblems on high-sand bentgrass/ annualbluegrass greens, including SED, weredue to changes in soil physical condi-tions in the surface two inches. Itappeared that either too much organicmatter accumulation or rapid death ofsurface roots could result in reducedwater infiltration and higher water-holding capacity. This resulted indecreased oxygen content within thezone and O2 diffusion across the zone.

Other secondary problems can ariseif the primary problem is organicmatter accumulation and/or change inthe nature of the surface organicmatter. These include more diseaseactivity, severe physiological O2 stress,and further root decline during sum-mer, as well as softer greens. Achieving areduction in these secondary problemsrequires correction of the physical con-ditions within this zone.

TWO TYPES OF SURFACEORGANIC MATTER PROBLEMSThe two common surface organic mat-ter problems are suggested from fieldobservations and the turf grass scienceliterature. The first organic matterproblem is excessive accumulation oforganic matter in the surface zone.USGA specification greens normallycontain less than 3% (by weight) organicmatter throughout the rootzone mix.Research has consistently demonstrated

JANUARY-FEBRUARY 2004 II

Table IFactors favoring rapid organic matter (OM) accumulation.

O.M. accumulation is enhanced by:• Prolonged cool temperatures on cool-season turfgrasses when temperatures are

between 3rF and 55°F,where microbial (especially bacteria) activity declines, and,thereby, OM decomposition declines. Cool, humid temperate climates may have suchconditions most of the year, while in the southern regions of bentgrass adaptationthis climatic condition may be for 5-7 months per year.

• Use of aggressive bentgrass or bermudagrass cultivars that exhibit high rates of OMaccumulation. Many of the newer greens types exhibit this tendency.

• Poor air drainage that allows the surface to remain excessively moist for longperiods. This allows for longer periods of anaerobic conditions and stimulatesproduction of adventitious surface rooting, contributing to more OM load.Theseare often the secluded greens with many trees in the surrounds, little natural airdrainage, and shade on the green surface for a period of time.

• Inadequate integration of sand to sustain a medium where sand is the dominantmatrix rather than OM. Sand must be applied not just by topdressing, but also invertical channels by hollow-tine core aeration that removes plugs of OM and allowslarge quantities of sand to be added.

• Addition of OM to the surface as sod (even washed sod), compost, or OM-contain-ing amendments.

• Acidic pH at < 5.5, which limits bacteria and actinomycete populations and activity.• Maintenance toward rapid growth or thatch buildup such as high N use, frequent

irrigation, high mowing height.• Low earthworm activity.

weather would cause a rapid O2 stressand plant death. It is not the lack ofroots from root dieback that is theproblem, but the creation of an exces-sively moist layer with very low Ozduring hot weather in response to therapid root dieback, resulting in theinability of remaining roots to take upsufficient moisture for transpirationalcooling.

In the late 1990s, Huang et al.4,s pro-vided strong evidence of adverse effectsof the combination of high temperatureand low Oz on bentgrass root viability.Also, the author conducted oxygendiffusion rate (ODR) measurementswithin the surface zone in a study from1992 to 1995 and found numerousperiods when ODR was less than 20 to40 mg O2 cm-Z min-1

, which is con-sidered sufficiently low to limit rootingof grasses.

that as organic matter content in a sandmix increases to above 4% to 5%(by weight), the percent oflarger soilpores (macropores, aeration pores) of>0.08mm diameter between sandparticles decreases due to plugging byorganic matter.6,8 Even with very goodturf grass management, the organic mat-ter content in the surface two inches isoften observed to be more than 3.0%by weight.2,3

Table 1 summarizes the most com-mon conditions that cause excessiveorganic matter accumulation, especiallywhen several of these conditions occursimultaneously. Normally, the extremeinstances of organic matter accumulationoccur in the cool, humid, temperateclimates. However, this is not always thecase. In fact, in climates that stronglyfavor organic matter accumulation, thisis likely the most prevalent problem onhigh-sand greens or atWetic fields.

A second situation suggested to causeproblems occurs when the nature of theorganic matter changes from structuredorganic matter (mainly as live roots)into a gel-like consistency as roots die,plug macropores, and cause Oz stress.This situation is most likely to occur on

12 GR.EEN SECTION RECORD

a cool-season grass during hot, humidweather that induces rapid root death,so this problem would be more com-mon in the warmer regions of bentgrassadaptation.

Root diebackl death occurs everysummer to some extent, but micro-organisms can sufficiently break downthe fresh organic matter to preventexcessive macropore sealing. Underunusually hot, humid weather for oneto two weeks or more, root deathoccurs more rapidly and can inducelow infutration and low aeration. Freshdead roots hold more water and aregel-like, so macropore sealing occurs.The remaining live, Oz-stressed rootscannot obtain enough water uptake fortranspirational cooling. Low soil Oz inthe surface layer where the remaininglive roots are present leads to reducedwater uptake, stomatal closure, anddirect high-temperature kill.This isusually evident by yellowing of the turfand death over one to three days of hot,humid weather when plant andmicrobial oxygen demand is very high.

As organic matter content increasesabove 3% by weight, the more likely amassive root dieback from hot, humid

RESEARCH APPROACHUSED IN THE STUDYThe focus of the research in this studywas on management of the secondproblem: change in nature of the sur-face organic matter during the summermonths. Research was conducted from1996 to 1998 at Griffin, Georgia, on anexperimental golf green with a rootzonemix meeting USGA recommendations.Treatments are summarized in Table 2and consisted of various non-disruptivecultivation techniques, topdressing, wet-ting agent, sand substitute, andcytokinin combinations.

SATURATED HYDRAULICCONDUCTIVITYOne of the most important charac-teristics for bentgrass golf greens in thesummertime is the ability for excessmoisture to infutrate into the surfaceand percolate through the rootzone. Ifsaturated flow (saturated hydraulic con-ductivity) does not occur in a rapidfashion, a saturated surface can occur.

In Table 3, SHC values at 1 to 7 and17 to 26 days after cultivation treatmentare presented as the average SHC valuesof seven summertime measurements

Table 2Research treatments to investigate the change in nature of surface organic matter during the summer months. Exceptfor the core aeration (CA) treatments in March and October, all other cultivation, supplemental topdressing with sand

or Greenschoice sand substitute, wetting agent 0NA), or cytokinin (C) treatments were applied in summer.

Treatmenta

ControlCAHJLHJR

HJR + SandHJR + GreenschoiceHJR +WAHJR + C

HJR + Sand + WAHJR + Sand +WA + CLP + Greenschoice I

Description

No cultivationHollow-tine core aeration, %" diameter, March and OctoberHydroJect Lowered, 3" spacing, Ye" diameter hole, June 1 and every 3 weeksHydroJect Raised, 3Y2" spacing,~" diameter hole,June 1 and every 3 weeks

See HJR.Additional sand topdressing at 0.75 cu. ft per 1,000 sq. ft 5 times per summerSee HJR. Greenschoice as topdressing at 0.75 cu. ft per 1,000 sq. ft. 5 times per summerSee HJR.Wetting agent (Naid) at 3 oz. per 1,000 sq. ft 5 times per summerSee HJR. Cytokinin as CytoGro (0.005% ai) at I oz. per 1,000 sq. ft. 4 times per summer

See previous treatment descriptionsSee previous treatment descriptionsLandPride dry injection of 0.75 cu. ft Greenschoice per 1,000 sq. ft. 5 times per summer

Topdressing per 1,000 sq. ft.Annualb June-Sept.

- - - - - - - cu. ft. - - - - - - -10.7 2.519.0 2.510.7 2.510.7 2.5

14.5 6.314.5 6.310.7 2.510.7 2.5

14.5 6.314.5 6.314.5 2.3

aCA = core aeration, HJL = HydroJect run in lowered position, HJR = HydroJect run in raised position, Greenschoice = fired calcined clay,WA = wetting agent,C = cytokinin

b All plots received 10.7 cu. ft sand topdressing per year with 2.5 cu. ft per 1,000 sq. ft in the summer at 0.5 cu. ft per 1,000 sq. ft every 3 weeks

during 1996-1998.Within 1 to 7 daysafter cultivation, SHC increased at least3.4-fold to more than 20.2 inches perhour for all HydroJect (HJR) treat-ments (HJR = HydroJect operated inthe up position to provide a hole ofapproximately X inch), compared to 5.9inches per hour in the non-cultivatedcontrol.

The plots that were core-aerated inMarch exhibited no difference in SH Ccompared to the control. This illustratesthe effectiveness of spring hollow-tinecultivation as SHC declines with timeas holes refill with root mass, and sug-gests that cultivation methods that arenormally non-disruptive of the surface(i.e., HydroJect or solid quad-tines) maybe necessary to maintain higher SH Cduring the summer periods.

Comparing HJL (HydroJect operatedin the lowered position) to HJR treat-ments at 1-7 days after cultivationdemonstrated that the larger holeformed by the HJR operation wasmore effective in increasing initialSHC. The LandPride device did notresult in any increase in SHC when asand substitute was injected. LandPride

cultivation alone (without amendmentinjection) was not evaluated in thestudy. The same sand substitute amend-ment when applied as topdressing afterHJR cultivation tended to decreaseSHC, especially at 17-26 days aftercultivation.

At 17 to 26 days after cultivation, allHJR treatments exhibited SHC 2.2 to3.6 times greater (10.8-18.0 inches perhour) than the control (5.1 inches perhour).The lowest summertime SHCobserved on the non-cultivated controlwas 0.8 inches per hour versus morethan 3.2 inches per hour for plots thatreceived cultivation in the summer. Thedecline in SHC from 1-7 days to 17-27days after cultivation is expected as thesurface starts to reseal from root massgrowing across the aeration holes orcollapse of the holes themselves.

OXYGEN DIFFUSION RATEOxygen diffusion rate (ODR) readingswere taken in the surface l-inch depthduring the summer months for selectedtreatments and results varied by year(Table 3). In 1996, readings were < 20mg O2 cm-2 min-L most of the time,

regardless of treatment. There wereperiods of limited O2 within the surfacezone in other years. These results, plussimilar ODR findings from a subse-quent study,IOconfirmed that criticallylow O2 levels can occur even undernon-saturated conditions. Low oxygendiffusion rates would be expected morefrequently when rain is frequent ordaily irrigation is practiced, keeping thesurface zone moist.

TURFGRASS QUALITYAND SHOOT DENSITYImproved turfgrass quality and shootdensity were noted for most of theHJR and HJL treatments compared tothe control (Table 4). The reduction inturf quality and shoot density of core-aerated plots occurred in the earlysummer when some residual effectsfrom the spring treatment were stillevident. Generally, when sand or a sandsubstitute was applied immediately afterthe summer cultivation operation,visual quality and shoot density ratingswere not as high as when the topdress-ing was omitted.

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Table 3Treatment effect on summer saturated hydraulic conductivity (SHC): oxygen diffusion at 1.2" depth,

and organic matter content in the 0" to 1.2" zone at 30 months after treatment initiation.

14 84 75

------%------o 100 87

Readings > 0.20pg 02 cm-2 min.1b

1996 1997 1998

Organic Matterat 30 months(0-3 cm)

% (wt.)9.87.3*9.99.1

9.39.38.9

10.3

10.09.19.0

2.2.38

10010029

Treatment Average SHC

and(1996-1998)

LowestContrast 1-70AC 17-260AC SHC

- - - - - - - - inch hr-' - - - - - - - -Control vs. 5.9 5.1 0.8CA 9.3 5.8 3.2HjL 12.9 13.2* 3.2HjR 23.5** 16.0** 7.6

HjR + Sand 24.0** 18.0** 6.2HjR + Greenschoice 20.2** 10.8H 6.4HjR+WA 25.6** 16.2** 5.8HjR + C 23.0** 15.8* 4.0

HjR + Sand + WA 20.2** 14.8* 4.5HjR + Sand + WA + C 21.5** 14.4* 4.3LP + Greenschoice 1 7.9 5.9 3.2

LSD (.05) 9.7 6.9F-test ** **

aCore aeration was in March and October, but SHC readings were in the July-to-September period, so SHC for the CA treatment is not at 1-7 or 7-26 DACbAn ODR rate of> 0.20 to 40 IJgO2 cm-2 min-' is considered as non-limiting for root growth, while below this value root growth is less than optimal<Average of 7 time periods during summers of 1996-1998

Only the hollow-tine core aerationtreated plots received spring core aera-tion with sufficient topdressing to fillthe holes (Table 2). The surface organicmatter accumulation was the least inthis treatment, illustrating the impor-tance of hollow-tine core aeration,which allows for more sand to beincorporated into the surface organicmatter zone than by topdressing alone.All treatments resulted in organicmatter levels greater than the < 4.5%level desired.

IMPLICATIONSFROM THIS STUDYThe immediate increase in SHC fol-lowing cultivation treatment demon-strates that the surface conditions docontrol SHC on high-sand greens andthat creation of temporary macroporesacross this zone results in SH C that aresubstantially higher. One question thatoften arises is whether the field SHCwill be the same as the laboratory SHCfor the rootzone mix without a turf sodon the surface. The answer to this ques-

tion is yes and no, depending on thefollowing circumstances.• If field SH C is taken at severalweeks after cultivation and the holeshave had time to seal, the SH C can beappreciably less than lab SHC.• If field SH C is measured within thetime period when the cultivation holesmay still be partially open, the SHCrate may be intermediate compared toobtaining the SHC rate within a fewdays after cultivation. SHC measuredwithin a few days after cultivation oftenis within the same general range as thelaboratory SH C if the rootzone mixbelow the surface couple of inches hasnot been appreciably altered afterconstruction.

Factors often observed to alter theSHC below the surface two inchesinclude movement of salts that precipi-tate within this zone, movement of finematerials during grow-in into the sub-surface, and a high organic matter layerthat becomes buried. This may includethatch that develops during grow-inthat has not had sufficient sand inte-

grated into it and is buried withsubsequent topdressing.

Some observations from the currentstudy and other cultivation studies thatthe author has conducted over manyyears are:• The holes made by HJR, X-inch solidquad tines, and the Aerway Slicer 100greens cultivation device all initially en-hance SHC, but by about three weekstheir effectiveness starts to decline. TheHJR is least affected, probably because ahole is cut out instead of created bypushing materials to the side.• When hollow-tine core aeration hasbeen conducted with holes filled bytopdressing, the duration of improvedSHC is usually 5-8 weeks for Yz- to %-inch diameter holes on hi.gh-sandgreens.

The responses just noted would sug-gest that non-disruptive cultivationshould be initiated within five to eightweeks after a hollow-tine cultivationoperation and repeated on a three-week schedule to maintain high SHCconditions during the summer months.

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Table 4Summary of treatment effects on bentgrass putting green visual quality and shoot density.

Treatment Visual Shootand Qualitr DensitrContrast < > < >

----------- % -----------Control vs.CA 29 0 29 0HJL 0 19 0 38HJR 0 14 0 24HJR + Sand 0 0 0 0HJR + Greenschoice 10 0 0 10HJR +WA 0 14 0 29HJR + C 0 14 0 14HJR + Sand + WA 5 19 0 24HJR + Sand +WA + C 0 0 0 10LP + Greenschoice I 48 0 33 0aBased on percent of ratings (18) when the treatment was significantly less than «) or greaterthan (» the control

An excellent article by 0 'Brien andHartwiger (USGA Green Section Record,2003,41(2):1-7) reports options forcontrolling the organic matter zone .One question that arises in their article,as well as our study, is, "What is anacceptable level of organic matter in thesurface two-inch zone?"The author'sviews on this question are summarizedas follows:• Regardless of climate zone, greaterthan 4% organic matter content in thesurface two-inch zone becomes a redflag value that indicates the probabilityof developing low O2, excessive surfacewater retention, and reduced SHC.Asorganic matter content increases abovethis value, the greater the potential forthese problems.• In the USGA green constructionmethod, organic matter mixed through-out the rootzone mix is capped atabout 3% (by weight) since above thislevel it is difficult to achieve a mix thatallows sand to be the dominant mediumand maintain a balance between mois-ture retention versus aeration porosity.If the USGA method requires organicmatter levels to be less than 3% for thesake of avoiding problems, then itfollows that organic matter should notgreatly exceed this level after establish-

ment. Who recommends 4-10% byweight of organic matter within high-sand green mixes?• Within the southern zone of bent-grass adaptation, the 4% organic matterlevel is especially critical because theopportunities are greater for low soilO2 to occur in conjunction with hot,humid, wet weather. However, suchhot, humid, wet periods also can occurduring certain years in many coolerreglOllS.• Another reason that organic mattercontent somewhat greater than 4%seems to occur in some situations (oreven at times within a year) at a locationwithout evident problems may be thatmuch of the organic matter is present aslive roots. Live roots have a structure thatallows better air exchange and watermovement compared to when many ofthe roots die and the organic matterbecomes more of a massive, spongynature with macropores less defined.• Maintaining sand as the primary sur-face matrix rather than organic matter(remembering that 1% organic matterby weight equals about 5% organicmatter by volume) is also important tomaintain a firm putting surface as wellas one that will support greens mowerswithout scalping.

It is informative to remember thatsince the very early days of USGAgreens and high-sand greens that pre-ceded the formal USGA recommenda-tions, early agronomists recommendedtwice annual core aeration plus heavytopdressing (15-20 cu. ft. of sand per1,000 sq. ft. per coring operation).Whywould this be the recommended prac-tice except to dilute the ongoing prob-lem of organic matter accumulation inthe surface?

History often has a story to tell ustoday.

LITERATURE CITED1. Carrow, R. N. 1996. Summer decline of bent-grass greens. Golf Course Management 64(6):51-56.

2. Carrow, R. N. 1998. Organic matter dynamicsin the surface zone of a USGA green: practicesto alleviate problems. USGA 1998Turfgrass andEnvironmental Research Summary. USGA, FarHills, NJ.3. Fermanian,TW,]. E. Haley, and R. E. Burns,1985.The effects of sand topdressing on a heavilythatched creeping bentgrass turf ITSR]5:439-448.4. Huang, B., X. Liu, and]. n Fry. 1998. Effectsof high temperature and poor soil aeration onroot growth and viability of creeping bentgrass.Crop Sci. 38(6):1618-1622.

5. Huang, B., X. Liu, and]. n Fry. 1998. Shootphysiological responses of two bentgrass cultivarsto high temperature and poor soil aeration. CropSci.38(5):1219-1224 .

6. McCoy, E. L. 1992. Quantitative physicalassessment of organic materials used in sportsturf rootzone mixes. Agron.J 84:375-381.

7. Murphy,].W, and S.H. Nelson. 1979. Effectsof turf on percolation and water-holding capa-city of three sand mixtures. New Zealand J Exper.Agric.7:245-248.

8. Murphy,].W,TR.o. Field, and M.]. Hickey.1993.Age development in sand-based turf.ITSR] 7:464-468.

9. O'Brien, P, and C. Hartwiger. 2003. Aerationand topdressing for the 21st century. USGAGreen Section Record 41(2):1-7.10.Waddington, nV:,T L. Zimmerman, G.].Shoop, L.T Kardos, and]. M. Duich. 1974.Soilmodification for turfgrass areas. I. Physicalproperties of physically amended soils.Prog.Rept. 337. Penn. State Univ., Univ. Park, Pa.

DR. ROBERT N. CARROW (tuifgrass stressphysiology and soil physical and chemicalstresses) is a researchscientist in the Cropand Soil Science Department} University ifGeorgia} Georgia Experimental Station atGriffin.

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