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

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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
Page 1: BY PAT O'BRIEN and CHRIS HARrWlGER~
Page 5 and 6: THEORYVS. REALITY:CALCULATING SAND

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