BY PAT O'BRIEN and CHRIS HARrWlGER~i;F 7:. #'

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Putting green aeration and topdressing areliterally and figuratively dirty words. Golfersbegrudgingly accept the fact that to protect

the long-term health of the grass on a puttinggreen, it is necessary to aerate and top dress eachyear.With more sophisticated products and tech-niques, gone are the days when putting greenswere aerated in the spring and fall and buried in ablanket of sand. But lost in the changes to theseprograms may be an incomplete understanding ofhow much aeration and topdressing are needed toprotect the long-term health of the greens.

The long-term health of putting greensdepends on maintaining sand as the primarymedium. If organic matter accumulates beyond areasonable degree, the physical benefits of sand arediminished and putting green physical propertiesdecline along with the health of the turf. For toolong golf courses have been making changes intheir aeration and topdressing programs without

comparing these changes to a standard or targetlevel. A previous Green Section Record article titled"Core Aeration by the Numbers" detailed howtine size and spacing affects the amount of surfacearea impacted by an aeration treatment and madea recommendation to impact 15-20% of thesurface each year (O'Brien and Hartwiger, 2001).This recommendation did not go far enoughbecause it did not include surface topdressingapplications, which go hand in hand with coreaeration in diluting organic matter accumulation.This article expands upon these concepts andlinks core aeration and sand topdressing.

THE SIGNIFICANCE OF COREAERATION AND SAND TOPDRESSINGAccording to University of Georgia turfgrassresearcher Dr. Bob Carrow, the number-oneproblem experienced on sand-based puttinggreens is the excessive accumulation of organic

Using dry sandand the propertopdressingequipment improvesworker productivityand helps reducegolfer complaints.

MARCH-APRIL 2003

matter in the upper portion of the soil profIle(Carrow et al., 2002). Core aeration and sandtopdressing are the two most effective means tocontrol the content and distribution of organicmatter in this zone. The scientifIc literature is fullof references to the benefIts of core aeration andsand topdressing. Unfortunately, details on howmuch aeration and topdressing are needed arelacking.

The moment any type of grass is planted ona putting green rootzone mix, the soil physical

properties in the upperfew inches of the root-zone begin to change(Habeck and Christians,2000; Curtis, 2001).In a new putting greenthe cycle of rootgrowth, decline, andnew growth is repeatedyear after year. Rootsgrow down throughthe soil in the large soil

pores (macropores) and provide the plant withneeded water, oxygen, and nutrients. When aroot is no longer viable, it begins to plug up soilmacropores and can hinder the ability of livingplants to function.

Dr. Carrow conducted extensive research(Carrow, 1998) in the mid-1990s on the organicmatter dynamics in the rootzone of sand-basedputting greens. He concluded as organic matter ina sand-based putting green reaches 3-4% byweight, the percentage of soil macropores beginsto decrease. The reduction of pore space has threedistinct implications, and a host of primary prob-lems can be expected: 1) The diffUsion of oxygeninto the rootzone begins to decline. Oxygen isvital for plant growth as well as soil microorganismbalance and function. 2) Water infiltration de-creases, which can result in puddling and satura-tion of the surface. 3) Moisture content in theupper rootzone increases, which can make thesurface less fIrm. The decrease in macropores(aeration pores) is accompanied by an increase incapillary or water-holding pores.

If organic matter accumulation begins toexceed 3-4% by weight, putting greens becomevulnerable to a host of secondary problems suchas disease, wet wilt, soft surfaces, poor root growth,black layer, and more frequent high-temperatureinjury. These secondary problems are often calledsummer bentgrass decline (Carrow et al., 2002),

2 GREEN SECTION RECORD

and trYing to treat them curatively can be expen-sive.They occur often at courses that have notadequately aerated and topdressed the greens.Many of these courses are doomed to many yearsof frustration because they are not willing tomake the effort to do the additional aeration andtopdressing needed to prevent the situation.

Dr. Carrow's research shows that core aerationand applYing sand can help dilute organic accumu-lation and create new macropores. The remainderof this article will be devoted to developing anaeration and topdressing program that keepsorganic matter levels below 3-4% by weight. Thisproactive approach ultimately will cause less dis-ruption and be less expensive than trYing toalleviate primary and secondary problems througha curative approach.

The organic matter dilution program is a catch-allterm that includes core aeration accompanied bysand topdressing to fill the holes and sand top-dressing applied directly to the surface. Referencesto core aeration refer only to hollow-tine aerationat a standard depth of 3 inches. Aeration depthcan vary signifIcantly based upon machine andtype of tine used. Deep-tine aeration or similarpractices designed to correct deep rootzone issuesare not considered. Suiface topdressing refers to sandapplied directly to the turf grass canopy. Light,medium, and heavy topdressing applications areapproximately 0.50 ft: per 1,000 ft?, 2.0 ft: per1,000 fe, and 4.0 fe per 1,000 ft?, respectively.

AERATION AND TOPDRESSINGRECOMMENDATIONSThe case has been made for the importance ofusing core aeration and sand topdressing to dilutethe accumulation of organic matter. The questionis, How much of each needs to be done? We pro-pose answering this question in a slightly differentway. The answer requires linking the topics ofaeration and topdressing together. We link thetwo together because they are the key elements inan organic matter dilution program. Core aerationremoves organic matter. Filling the holes withsand makes sure those columns stay open. Dust-ings of sand applied directly to the surface alsohelp manage organic matter accumulation.

ApplYing at least 40-50 ft: of sand per 1,000 ft?per year is recommended to keep organic mattercontent below 3-4% by weight in the upperportion of the rootzone. Although this recom-mendation is brief, understanding all its ramifIca-tions is more complex, and it should stimulate

many questions that will be addressed in thefollowing sections.

UNDERSTANDING SAND VOLUMESRates of sand topdressing can be difficult toconceptualize. Table 1 shows quantities of sandexpressed in different units and yields someinteresting comparisons. Conveniently, it turnsout that 100 pounds of dry sand is equivalent to1.0 ft~ of sand. Wet sand is approximately 6-10%heavier for an equivalent volume. Finally, the sandquantities are expressed in inches, which are easierto conceptualize for large quantities of sand.

TO CORE OR NOT TO CORE,THAT IS NOTTHE QUESTIONBy now, many readers will have looked at therecommendation and said, "Aha. If we apply 40-50 ft~ of sand per 1,000 ft; through regular top-dressing applications, we will not need to coreaerate the greens." It is easy to see how this inter-pretation could be made, but this strategy is notrecommended. There are agronomic and practicalreasons for not trYing this approach. There aremerits to removing organic matter through coreaeration and packing these vertical columns thatcut through the high organic matter zone withsand. Applying 50 ft~ of sand per 1,000 ft?through surface topdressing would only requireapproximately 25 applications of2.0 ft~ per 1,000ft;, or one application every two weeks. Thiswould be far too stressful during the summerand would be difficult to work into the canopyduring periods of slow winter growth. Invariably,interference with play and weather make thisprogram impractical.

Similarly, do not try to meet the topdressingrequirement with only core aeration and fillingthe holes with sand. This method could result inlayering. All applied sand is not worked into theholes; some falls between the holes. This excesssand would only be mixed into the canopy twiceper year if the greens are aerated twice per year.Additionally, it would be difficult to keep sand asthe primary component of the rootzone matrixnear the surface without regular surfacetopdressing applications.

SAMPLE PROGRAMSThe best program is one that includes a certainamount of core aeration along with regular sandtopdressings. When considering tine sizes, select asize that allows easy and complete backfilling of

the aeration holes. Based upon field observations,the smallest hole that can be reliably filled withsand is created by a tine of just less than Yz in.Holes of % in. diameter are not easily filled, evenwith the driest sand. Outlined below are a fewsample programs to stimulate thought. There is nosingle program that is right for everybody, butwith an overall goal of total topdressing applied, aplan that meets the needs of any course can bedeveloped.• Program 1: Big Holes, Big Spacing. Thisapproach uses traditional aeration equipment with% in. tines on a 2 in. X 2 in. spacing. The greensare aerated once in the spring and once in thefall. A total of 36 ft: per 1,000 ft? (3,600 lbs. per1,000 ft?) is applied for the two core aerations.See Table 2 to see sand volumes required to fillaeration holes for other tine sizes and spacingpatterns.

The remaining 14 ft~ of sand necessary per1,000 ft? to meet the 50 fe goal is applied vialight to moderate topdressings throughout theyear. A light to moderate topdressing is consideredto be anywhere from 0.5 ft~to 2.0 ft: per 1,000ft? This is rougWy equivalent to 50 to 200 lbs. ofsand per 1,000 ft;• Program 2: Dethatching. This program isfor new construction only or for a putting greenthat has met the topdressing requirement. Adethatching machine is used to physically removeorganic matter from the upper portion of the

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Seeing is believing withvolumetric measure-ments. Light, medium,and heavy surfacetopdressing ratesare approximately0.50 ft! per 1,000 ft?-,2.0 ft! per 1,000 ft?-, and4.0 ft! per 1,000 ft?-,respectively.

profile. Spring and fall dethatching treatments areperformed. Less disruption to play is the primaryadvantage. This program is not recommended as acurative approach on greens with excessiveorganic matter. It is too difficult to incorporatesand into the channels made by the dethatchingequipment, especially when the grooves are cutgreater than 0.25 in. deep.

The amount of sand incorporated into thecanopy following dethatching is much lower thanwith core aeration. As channel depth increases,sand incorporation decreases because the channelscollapse and seal off. This may be considered adisadvantage because much more time must bespent applying light and moderate topdressingsthroughout the year. For example, assumethe greens are dethatched with %4 in. blades.Approximately 14% of the surface area isimpacted, but only 1-3 ft? per 1,000 fe of sandis applied. This amount is highly variable anddepends on how well the dethatching channelsstay open. This leaves 40-44 ft? per 1,000 fe leftto be applied through light and moderatetopdressings .

Many courses that use a dethatching machineuse it in combination with an aerator. Somedethatch and aerate at the same time, while othersde thatch and aerate on separate dates.

The moderate topdressings (2.0 ft? per 1,000ft?) should be applied at a time of year whenorganic accumulation is most rapid. On bentgrassputting greens in the South, the period of

October through April is the most prolific periodof organic matter production. Bermudagrassgreens generate the most organic matter in thesummer months. Light topdressings can beapplied at any time of the year.• Small Holes, Small Spacing. A sampleprogram using this approach might include thefollowing: super quad tines with an outside tinediameter of 0.420 on a 1 in. X 1Ysin. spacing. Thegreens are aerated twice in the spring and once ortwice in the fall. The total amount of sandrequired to fill the holes after each aeration isapproximately 6.15 ft? per 1,000 fe or 18-24 ft?per 1,000 fe per year. The remaining 16-32 ft?per 1,000 fe can be applied through light ormoderate topdressings throughout the year.

This approach relies on smaller tine diametersand a tighter spacing pattern. The advantage ofthis program is reduced healing time becausesmaller diameter holes require less time to healthan larger holes. The disadvantages are the needfor special equipment and more difficulty fillingthe aeration holes. As hole size decreases, the like-lihood of sand particles bridging over the surfaceof the hole increases. The super quad tine onlygoes 1.75 in. into the rootzone, which could be aconcern with a thick layer of organic accumula-tion. An aerator with variable spacing and a tractorwith a creeper gear are necessary to duplicate thisprogram. For best results, take the time to makesure the holes are open and clean, and try to usethe driest sand possible.

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THEORYVS. REALITY:CALCULATING SAND VOLUMEEvery golf course is faced with a unique set ofcircumstances. Determining the total amount oftopdressing applied can be challenging. Table 2shows the approximate amount of sand necessaryto fill aeration holes with sand for common tinesizes and spacing.

When recommended topdressing amounts arein hand, the turf grass manager must adjust thetopdressing applied if it is determined that thesand is not working easily into the holes. Some-times the greens are damp or the sand is wet. Thedegree to which sand is filled into the holes canvary, too. The key point is not whether the sug-gested amount is applied to fill the holes, but howmuch sand actually is applied. This information ishelpful when calculating yearly volume and deter-mining how much sand must be added throughlight or moderate topdressing applications.

When calculating sand volume applied, anotherconsideration is estimating how much sand isthrown onto areas other than the putting green.This is an issue when spinner top dressers are usedto apply light or moderate topdressings.

MEETING THE RECOMMENDATION:IS MORE OR LESSNEEDED?The beauty of coupling aeration and topdressingtogether and making an annual topdressingrecommendation as a target value is its simplicityand flexibility. It may need to be adjusted upwardor downward, depending on individual circum-stances. The Atlanta, Georgia, climate was selectedfor this recommendation. Other areas may requirea higher topdressing or lower requirement basedupon some of the factors listed below.• Nitrogen Levels. Nitrogen is directly relatedto organic matter production. Higher nitrogenprograms may be required on putting greens withextremely high traffic levels or on greens thatmust be grown in from some type of seasonaldamage. More topdressing may be required.Greens managed under low nitrogen programsmay require somewhat less sand .• Soil pH. A soil pH > 5.5 is optimal forbacterial activity and organic matter decompo-sition. Soil pH much below this level reducesorganic matter decomposition, and more top-dressing may be required.• Turfgrass Species. The 40-50 ft? per 1,000fe recommendation is the minimum requirementfor many bentgrass and/or Paa annua putting

greens and may need to be adjusted annually.N on-overseeded Tifdwarf or Tifgreen bermuda-grass putting greens will have a slightly lowerannual topdressing requirement, somewhere inthe range of35-40 ft? per 1,000 ft? Non-over-seeded ultradwarf greens may require 40-50 ft?per 1,000 ft? Overseeded Tifdwarf or Tifgreenbermudagrass putting greens will require 40-50ft? per 1,000 ft?, but with newer ultradwarfcultivars that tend to accumulate organic matterin the surface 1-2 in., a somewhat higher amountmay be necessary. For newer bermudagrass culti-vars, the "small holes, small spacing" program

applied at more than two times per year is a goodoption. High annual topdressing sand rates areimportant for the newer bentgrass cultivars thattend to accumulate organic matter in the surfaceor in climates where organic matter accumulationis favored. In these situations, the "small holes,small spacing" program is worth trying.

UNUSUAL FIELD CONDITIONSTwo common field conditions exist that mayrequire a higher sand requirement or an adjust-ment as to when sand should be applied.• Rapid Root Dieback. This condition ischaracterized by the rapid death of a bentgrassroot system caused by high temperatures in thesummer months. When bentgrass roots die backsuddenly, the nature of some of the organic matter

Organic matteraccumulation in theupper rootzone is theprimary reason whyputting greens some-times fail over time.Proper aeration andtopdressing programscan prevent excessorganic matteraccumulation.

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Rapid root dieback onbentgrass putting greensin the summer producesa gel-like layer in theupper rootzone and lowsoil oxygen levels. Turfloss can occur within 24to 72 hours, and extraaeration (!.nd topdressingwill be needed topromote recovery.

changes from live root structures to decomposingorganic matter with a gel-like consistency. Dr.Carrow states, "It is not the lack of roots fromroot dieback that is the problem, but the creationof an excessively moist layer from the decompos-ing root tissues with very low oxygen during hotweather in response to the rapid root dieback"(Carrow et al., 2002). The remaining roots areunder low oxygen stress and cannot take upenough water for transpirational cooling. Reducedwater uptake, stomatal closure, and high-tempera-ture kill can follow. Field symptoms are a yellow-ing of the turf and death over a one- to three-dayperiod of hot, humid weather. This scenario canoccur at organic matter levels of 3-5% by weightin the top 1 in. of the rootzone, but it is muchmore likely when organic matter is greater than5% by weight (Carrow et al., 2002). Mter thehot weather has ended, it will be necessary tocontinue diluting this rapid accumulation oforganic matter created from the dead roots as wellas organic matter arising from new root initiation.The topdressing requirement will increase andshould be met through a combination of surfacetopdressing and filling aeration holes.• Cool-Weather Organic Accumulation.Root growth can be rapid during periods of coolweather. Roots grow down through the macro-pore channels and adventitious roots grow nearthe surface. Although live organic matter does not

reduce oxygen availability as severely as decom-posing organic matter, oxygen infIltration andwater infiltration can decrease as the roots fillmany of the macropores. This is commonlyobserved in the winter to early spring monthswhen greens begin to puddle more substantiallyafter a rain. The problem is more severe in coolerclimates with prolonged soil temperatures above32°F, but less than 55°F. Bentgrass/ Paa annuawill grow in temperatures above 32°F, but soilmicrobes necessary for organic matter decompo-sition do not function below 55°F. These condi-tions are more common in northern climatesand, particularly, coastal northeastern and coastalnorthwestern climates. Other than a reductionin water infiltration, surface symptoms are notobserved, but suboptimal oxygen levels can reducethe rate of deeper rooting. Mter spring aeration,adequate oxygen will be available for maximumroot growth.

PROGRESS REPORTTurf managers who have embarked on an organicmatter dilution program will be curious abouthow the program is working. There are threeways to assess the program's effectiveness.

The fIrst is to send a core sample of the top1-2 in. of the rootzone profile to a physical soiltesting laboratory. Request a test to determineorganic matter by weight.

6 GREEN SECTION RECORD

A result of less than 3% organic matter byweight is good news and indicates that organicaccumulation has been well diluted with sand. Aresult of 3-5% organic matter by weight is border-line, and problems caused by plugged macroporescould occur. Pay careful attention to the organicmatter dilution program over the next fewseasons. A result of 5% or more is cause for con-cern. A serious effort must be made to reduceorganic matter buildup. Place more emphasis oncore aeration and topdressing to fill the holes.Some superintendents may sample and findorganic matter contents greater than 5% withoutany apparent sYmptoms at the time of sampling,but the chances for future problems are muchgreater.

In the cooler regions of bent grass adaptation,organic matter content can be above the 5% limitwithout immediate concern. The reason is thatthese climates have fewer hot periods in thesummer. When periods of high heat do occur,bentgrass can decline rapidly. Also, in theseclimates organic matter can continue to increaseto a point where decline occurs from oxygenstress, regardless of the temperature.

Cases of seasonal organic matter accumulationfluctuations occur on bentgrass during the winterin the southern transition zone and on overseededbermudagrass greens in the late spring. Rootgrowth during cool periods may increase organicmatter 1-2% from the fall level due to live rootscontributing to the overall organic matter content.The seasonal changes suggest that sampling fororganic matter for both bentgrass and bermuda-grass should be in May and late summer. Thehighest organic matter content will occur duringMay, especially on overseeded bermudagrassgreens, and late summer should be the time of theyear with the lowest organic matter content.

A second method to assess the program's effec-tiveness is to take field observations of the soilprofile. I£layering is present, as evidenced by adistinct sand or organic matter layer(s), it is likelythat topdressing applications are being made toofar apart or that light applications betweenmoderate applications are too light. Also, look forthe columns of sand created by aeration and top-dressing. Checking this right after aeration allowsthe turf manager to see if the holes are beingcompletely filled with sand.

A final assessment method involves the use of adouble ring infiltrometer to take seasonal infiltra-tion readings. Readings taken in conjunction with

organic matter sampling can be especially useful.By taking an infiltration measurement at the sameplace on a green a few times a season, the super-intendent can obtain several important pieces ofinformation. First, the changes in infiltration byseason will be apparent. Second, after takingreadings for a few years, the superintendent cansee if infiltration rates are increasing, decreasing,or staying the same in response to the organicmatter dilution program.

CONCLUSION"More sand, laddie;' is a quote attributed to OldTom Morris. Although Old Tom probably neverimagined that the science and art of putting greenmaintenance would ever reach today's qualitylevels attained on a daily basis, his emphasis onsand still rings true. The information presented inthis article has the scientific backing to confirmwhat most in the industry know - that aerationand topdressing are the foundation for successfulputting greens.

ACKNOWLEDGEMENTSA special thank-you to Dr. Bob Carrow,University of Georgia, and Mike Pilo, golf coursesuperintendent, Charlotte Country Club (Georgia).

REFERENCESBeard,]. B. 2002. Tuif Management for Golf Courses, 2nd ed.Ann Arbor Press, Chelsea, Mich.

Carrow, R. 1996. Summer decline of bent grass greens. GolfCourse Management. 64(6):51-56.

Carrow, R. 1998. Organic matter dynamics in the surfacezone of a USGA green: practices to alleviate problems. TheUSGA 1998 Tuifgrass and Environmental Research Summary.Golf House, Far Hills, N.J.

Carrow, R., P. O'Brien, and C. Hartwiger. 2002.WhyPutting Greens Sometimes Fail. Unpublished manuscript.

Curtis, A. 2001. Evolution of a sand-based rootzone. GolfCourse Management. 69(3). www.gcsaa.org/gcmI2001/-marOl/03evolution.html.

Habeck,]., and N. Christians. 2000.Time alters greens' keycharacteristics. Golf Course Management. 68(5). www.gcsaa.-org/ gcm12000/ mayOO/oftime.html.

Hartwiger, C. 1997.A shower a day fills the holes ok. USGAGreen Section Record. 35(3):18.

O'Brien, P., and C. Hartwiger. 2001. Core aeration by thenumbers. USGA Green Section Record. 39(4):8-9.

PAT O'BRIEN, director,and CHRIS HARTWIGER,

agronomist, run the Green Section's Southeast Region.

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