Aeration and Topdressing for the 21st Century - USGA Green ...

BY PAT O'BRIEN and CHRIS HARrWlGER~i;F 7:. #'Putting green aeration and topdressing areliterally and figuratively dirty words. Golfersbegrudgingly accept the fact that to protectthe long-term health of the grass on a puttinggreen, it is necessary to aerate and top dress eachyear. With more sophisticated products and techniques,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 withoutcomparing 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, ~_:t~.- ..,"... _~_'""""'iT __ "._'r_",,"-_ -::'---.-. _ -'_. -'_.. _-Using dry sandand the propertopdressingequipmentworkerimprovesproductivityand helps reducegolfercomplaints.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 physicalproperties in the upperfew inches of the rootzonebegin 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 soilpores (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 problemscan 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 decreases,which can result in puddling and saturationof 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),and trYing to treat them curatively can be expensive.Theyoccur 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 accumulationand 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 disruptionand 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 topdressingapplied 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 proposeanswering 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. Dustingsof 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 recommendationis brief, understanding all its ramifIcationsis more complex, and it should stimulate2 GREEN SECTION RECORD

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 topdressingapplications, we will not need to coreaerate the greens." It is easy to see how this interpretationcould be made, but this strategy is notrecommended. There are agronomic and practicalreasons for not trYing this approach. Therearemerits 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 wouldonly 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.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 portionof theSAMPLE 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 ofMARCH-APRIL 2003 3

Seeing is believing withvolumetricmeasurements.Light, medium,and heavy surfacetopdressingratesare 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 throughtopdressings .light and moderateMany 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 ofOctober 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 remaining16-32 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 likelihoodof 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 accumulation.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.4 GREEN SECTION RECORD

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. Sometimesthe greens are damp or the sand is wet. Thedegree to whichsand is filled into the holes canvary, too. The key point is not whether the suggestedamount is applied to fill the holes, but howmuch sand actually is applied. This information ishelpful when calculating yearly volume and determininghow 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 moderatetopdressings.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 circumstances.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 grownin 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 decomposition.Soil pH much below this level reducesorganic matter decomposition, and more topdressingmay be required.• Turfgrass Species. The 40-50 ft? per 1,000fe recommendation is the minimum requirementfor many bentgrass and/or Paa annua puttinggreens and may need to be adjusted annually.N on-overseeded Tifdwarf or Tifgreen bermudagrassputting greens will have a slightly lowerannual topdressing requirement, somewhere inthe range of35-40 ft? per 1,000 ft? Non-overseededultradwarfgreens 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 cultivars,the "small holes, small spacing" programapplied 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 adjustmentas 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 matterOrganic matteraccumulation in theupper rootzone is theprimary reason whyputting greens sometimesfail over time.Proper aeration andtopdressing programscan prevent excessorganic matteraccumulation.MARCH-APRIL 2003 5

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 structuresto 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 decomposingroot 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-temperaturekill can follow. Field symptoms are a yellowingof 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 macroporechannels and adventitious roots grow nearthe surface. Although live organic matter does notreduce oxygen availability as severely as decomposingorganic 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 decompositiondo not function below 55°F. These conditionsare 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