To ensure best results from aerification and topdressing operations, the topdressingmust be thoroughly brushed into the aerification holes.

AERATION:Needed More Today Than Ever Beforeby ROBERT C. VAVREK, JR.Agronomist, Great Lakes Region, USGA Green Section

TRADITIONAL hollow-tine aera-tion is probably the most un-popular maintenance practice

performed on the golf course. From thecrew's point of view this operationranks near repairing an irrigation leakon a bone-chilling morning or re-distributing wet sand to the slopes ofwashed-out bunker faces. From thegolfer's point of view, well ..."expletives deleted."

However, as the amount of playincreases at most golf courses, so doesthe need to address the detrimentaleffects of wear and compaction caused

by concentrated foot traffic, motorizedgolf cart use, and maintenance equip-ment. The combination of these factorsand the often unreasonable expecta-tions for flawless day-to-day playingconditions exact a toll on the turf andthe superintendent. Golfers view superbplaying conditions on television eachweekend but fail to realize that it hastaken months and sometimes years toprepare a course for these events. Thenumber of rounds played at mostcourses is unlikely to decrease, so thebest chance for maintaining a high-quality stand of turf is to provide

optimal growing conditions - which iswhy a sound aeration program is soimportant.

The ideal growing medium for turf isconsidered to be 50% mineral matter,25% air, and 25% water by volume. Theamount of large pores should roughlyequal the amount of small pores. Largepores, called macropores, drain quicklyand ensure the movement of air andwater through the soil profile. Smallpores, called micropores, hold wateragainst gravity, through capillaryaction. Most of the water in microporesis available to plant roots.

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The key to "good greens" is matching the rate and frequency of topdressing application tothe growth of the turf Less-intensive aeration operations are necessary on greens built toUSGA recommended specifications when the inputs of fertilizer, topdressing, irrigation,etc. are carefully managed.

Traffic compresses the soil and re-duces the percentage of macropores,while the percentage of micropores re-mains unchanged or is slightly in-creased. The shift in the distribution ofpore space limits the infiltration ofwater into the playing surface and slowsthe movement of water through the soil.Since air is "pulled" into macropores aswater drains through the soil profile, theloss of large pores indirectly affects rootgrowth by limiting the amount ofoxygen available for root respiration.

The physical resistance of tight soilsto root penetration alters rootingpatterns to a point where most rootgrowth occurs close to the surface andis exposed to environmental extremes.Compacted, poorly drained soils warmmore slowly than dry soils duringspring, another factor that further limitsroot growth. When the turfgrass rootsystem is compromised, sooner or laterthe effects are seen on the surface asreduced quality or a limited ability torecover from stress.

Once a significant amount of soilcompaction has occurred, the onlypractical way to reestablish morefavorable growing conditions on anestablished stand of turf is to aerate. Forthe record, though, there is little scien-tific evidence that aeration increases theamount of oxygen in the soil betweenthe holes. Therefore, the only portionsof the soil that are actually "aerated" arethe sidewalls and bottom of the emptyholes. A more appropriate term for"aeration" would be hollow-tine, solid-tine, water, drill, etc., cultivation.

There are, however, many well-documented benefits of aeration. Theholes and channels accelerate themovement of rain or irrigation waterinto the soil. The timely removal ofexcess moisture from the surfaceequates to fewer delays of play andmore consistent playing conditions. Thephysical removal of cores lowers thebulk density - a measurement directlyrelated to the degree of soil compaction.

The prolific amount of rooting thatoccurs in aeration holes is apparentwhen the cups are changed. A densemass of white, healthy roots often canbe seen in aeration holes even during thepeak stress periods of midsummer.

The benefits of aeration are notlimited to improving the soil's physicalproperties. Hollow-tine aeration is themost effective way to minimize theundesirable effects of excess thatchaccumulation - short of stripping thesod. One pass with a "punch-type"aerifier equipped with 11" diameter

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hollow tines on a 2" x 2" spacingremoves about 5% of the surface areawhen the cores are broken up and thesoil worked back into the playingsurface with a brush or dragmat. Asdone on most tees and fairways, mostof the organic material remains on thesurface and is easily blown away orcollected with the clippings.

The incorporation of broken coresinto a thatchy playing surface modifiesthe physical properties of this layer andintroduces soil microorganisms re-sponsible for organic matter decay. Weare in the era of biostimulants, com-posted microbes, natural extracts, etc.,and some manufacturers have claimedor suggested thatch control. Untilresearch proves otherwise, though, thebest chance of enhancing the degrada-tion of organic matter is to improve theconditions for the native microbesalready present in or under the thatchas described above - and it doesn't costa cent.

Not too long ago the choices weresimple: a pull-behind drum aerifier forthe fairways/ tees and a punch-typemachine for the putting surface. Todaythere are many choices, and some unitshave more specific applications thanothers.

Splicer / Spiker

A slicer utilizes triangular or rec-tangular knives mounted on a drum oraxle. These units are simple to use andcause very little disruption to theplaying surface. This operation is usefulfor breaking up a surface crust andpromoting more rapid infiltration ofwater into the soil. The severing ofstolons or rhizomes can improve turfdensity as well. Slicers, though, do notbring soil to the surface and have alimited depth of penetration on com-pacted sites.

Hollow Tines

Hollow-tine aeration is the standardagainst which all other forms ofaeration are compared. There are twotypes of hollow-tine aerifiers: those withtines mounted on a drum, and the"punch-type" units that utilize verticallyoperated tines.

Drum aerifiers are simple to use, havefew moving parts to wear out or breakdown, and can cover considerable acre-age in a relatively short time. Unfortu-nately, the depth of penetration is highlydependent on the degree of soil com-paction and the moisture content of the

On the other hand. aeration is needed when greens become severely layered due to anexcessive accumulation of organic matter that can occur during the "grow in"period orwhen the greens are topdressed infrequently. Note the "black layer" and the deeppenetration of roots through the aeration hole.

soil, and close spacing is sacrificed forspeed. If soil conditions are not ideal,these units tend to ride over compactedsites, producing the least effect wherepenetration is needed the most. Theholes can be quite ragged, which limitsthe use of most drum units on greens.This type of equipment will continue toperform an important task on manylow- to moderate-budget courses.

The vertically operated hollow-tineunits are the most versatile aerators onthe market. They cause much lesssurface disruption than the drum oropen-spoon type designs, making themwell suited for use on greens. There isno better way to overcome the effects ofcompaction, increase the infiltrationrate of water into the soil, encouragedeep root growth, and minimizeexcessive thatch accumulation in oneoperation.

The price of versatility is a consider-able amount of surface disruption -much less than the old designs, but stillenough to aggravate golfers, especiallyon greens. Core removal or breakup hastraditionally been a time-consuming,labor-intensive task, but with special-ized equipment such as core harvesters,core pulverizers, and highly efficientsweepers, this operation has been

greatly simplified. The slow groundspeed of punch-type aerators oncelimited their use on the golf course, butnow fairway units have been developedthat can remove deep, closely spacedcores at a rate of up to an acre per hour.

The optimal time to aerify is a subjectfor debate. After hearing all the argu-ments from superintendents and golfers,it seems that there is no "best" time.They say not to aerify in early springbecause soil temperatures are low, turfis not actively growing, and the holeswill take a long time to heal. Some don'taerify in late spring because Poa annuais germinating and they believe the openholes invite encroachment of this weed.Others can't aerify during summerbecause the open holes will cause severewilting. Early fall is out, because oftournaments, and late fall to winter isimpossible because of a limited laborforce and little chance to dry the coresbefore breakup or collection.

All might be valid arguments, but theoverall benefits of aeration, especiallyon heavily compacted areas, far out-weigh the disadvantages. For example,some Poa annua may germinate in theholes during spring, but by relievingcompaction and improving drainagethe more desirable species have a better

chance of competing with and crowdingout the Poa annua. The potential lossof turf from severe wilt followingaeration during midsummer is a con-cern, especially on a hot, windy daywith low relative humidity. Timelyirrigation or syringing, though, canprevent serious drought stress.

A variation of hollow-tine aerationnot utilized to its full potential on golfcourses is "quadra-tine" aeration.Quadra-tines are 14" diameter tines thatpenetrate up to 112" deep on a 1" xl"spacing. Due to the close spacing, theamount of surface area removed afterone pass is only slightly less than theamount removed following 12" diameteraeration on a 2" x 2" spacing. A primaryadvantage is little surface disruptionand fewer golfer complaints.

The close spacing of holes greatlyincreases the amount of exposed surfacearea, which accelerates the evaporationof excess moisture from poorly drained,shaded sites. This operation also canrelieve surface compaction duringperiods of heavy play and be a beneficialpre-treatment to the application ofwetting agents to relieve localized dryspots.

Several superintendents have hadgood success overseeding into quadra-tine aeration holes. This is a practicalway to introduce new, improved bent-grass cultivars into a green. The depthof penetration can be adjusted to about12': and a mixture of seed, topdressing,and a little fertilizer can be worked intothe holes with a brush or upside-downpiece of carpet. The numerous, shallowholes are an ideal place for germinationand development of seedlings.

Solid Tine

There are no cores to collect fol-lowing solid-tine aeration, and this isperhaps the only advantage to thisoperation. The use of solid tines issometimes called "shatter-core" aera-tion because the jarring effect ofinserting blunt tines into the soil, intheory, loosens the soil and relievescompaction. The benefits tend to beshort-lived, though, and the operationhas little beneficial effect on compac-tion when the soil is moist. In fact, thereis a greater potential to develop acompaction pan when solid tines areused because soil is not removed fromthe hole. The pros and cons of hollow-versus solid-tine aeration are furtherdiscussed in the September/October1990 issue of the GREEN SECTIONRECORD.

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The ever-increasing amount of play at most golf courses necessitates the use of aeration ona wider scale.

Verti-Drain

Routine use of hollow-tine aerationcan create a layer of compaction calleda cultivation pan located just beyondthe depth of tine penetration. Evidenceof a cultivation pan is a soil core thatbreaks apart about 4" deep when cupsare changed. A cultivation pan slowsthe movement of water through thegreen and restricts root penetration. Aneffective way to minimize the effects ofthis kind of compaction is by deep-tineaeration.

A Verti-Drain deep-tine aeratorutilizes ~" to I" diameter solid or hol-low tines that penetrate up to 12"deep.When fully inserted, a "kicking action"

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is imparted on the tines which fracturesthe surrounding soil profile. The depthof penetration and amount of kick areadjustable to minimize surface dis-ruption. The kick has more effect whenthe soil is a little on the dry side becausedry soil fractures more readily than wetsoil - not too dry, though, because thetines then lift and tear the sod.

Many superintendents hire contrac-tors to perform deep-tine aeration be-cause the contractors have experiencedoperators and because a Verti-Drain isexpensive and requires the use of a high-powered tractor. Usually, only greensand perhaps tees are aerated to keeprental costs to a minimum. Those for-tunate enough to own the equipment

have found that this operation is effec-tive on fairway soils and cart-traffickedrough areas as well.

Never assume that the least amountof disruption will occur when the small-est diameter tines are used. Arrange ademonstration using several tine sizeson the practice green before making adecision. You may be surprised to findthat the use of ~" diameter solid tinesmay be less disruptive than ~" tinesbecause there is less chance of bendingor bowing the heavier tines in rocky orheavily compacted soil. Furthermore,the large holes are more easily filledwith topdressing than small holes.Taking the time to fill holes with sandor a suitable mix prolongs the beneficial

effects of this operation by preservingthe integrity of the holes. A similarargument can be made for removing thecores and filling the holes withtopdressing after hollow-tine aerationon greens and tees. More material isrequired, but the long-term benefits areusually worth the added cost.

Floyd-McKay Deep Drill

The deep drill also is capable ofreaching beyond the depth of standardaeration tines. It is a self-propelled unitthat utilizes two sets of carbide-tippeddrills to bore holes up to 10inches deep.The operation deposits a small amountof soil on the playing surface, andcleanup is usually required on greens.There is no kicking action, so the bene-ficial effect on subsurface compaction isprobably less than that achieved withdeep-tine aeration. Similar to deep tine,deep-drill aeration provides the mostbenefit where permeable soil existsbelow the layer of compaction.

Relatively few problems have beenobserved in the field with either opera-tion. As mentioned above, a notableexception is a lifting or tearing of shal-low-rooted turf when these operationsare performed under dry soil condi-tions. This effect also is observed whenstandard aeration is performed undersimilar conditions.

This study is a promising indicationthat water injection is an operation wellsuited to relieve compaction on fair-ways and tees. It provides the uniqueopportunity to relieve compaction andimprove drainage during midsummerwithout disrupting play. Current re-search is investigating the potentialbenefits of mixing additives such asphosphorus or wetting agents with theinjection water.

Its effect on high-sand-content greensbuilt to USGA recommended specifi-cations is not well understood. Neitheris the effect on old native-soil greenswhich have been topdressed with sandfor a number of years.

Many greens have received waterinjection treatments this season withpositive results - deeper root pene-tration, improved drainage, etc. A fewproblems have occurred on greenshaving a substantial accumulation ofsandy topdressing above the originalconstruction mix of coarse sand, peat,and soil. Contamination of the top-dressing with back-washed silt and clayand the deposition of fine gravel on theputting surface have been observed ona few greens.

Whether or not these isolated casesare cause for concern has yet to be de-termined. As superintendents becomemore familiar with water injection, theappropriate uses will become evident.The prudent course of action is to

proceed slowly with any new equip-ment until the more common problemsare discovered and addressed.

Summary

The key to success with aeration is todetermine the problem and then choosethe most appropriate equipment andmethod of aeration. There is no need topurchase a $100,000 subhydro-verti-mole deep-drill shatterslicer to break upa surface crust of algae on the greens.Combinations of techniques are morelikely to produce better results than asingle unit. For example, an early springdeep-tine aeration, supplemented byquadra-tine or Hydroject aerationduring the summer, topped off with astandard hollow-tine aeration duringthe fall could produce great results withlimited disruption to the playingsurface.

There is no shortage of reasons topostpone aeration, and before youknow it, it has not been performed atall. The potential benefits of aerationare usually well worth the trouble.

Finally, keep the golfers well in-formed about when and, more impor-tant, why aeration is being performed.Make the extra effort to communicatewith golfers and you might be surprisedhow much support there is for yourprograms.

Water Injection

Water injection is an innovativemethod of aerating, and is in its firstseason of use on most golf courses.High-pressure jets of water are utilizedto produce deep, irregular channels intothe soil. The primary benefits are thevariable depth of penetration and theabsence of surface disruption undermost conditions.

Initial research was performed atMichigan State University on a sandyloam soil where water injection wascompared to hollow-tine aeration.Various soil physical properties, such asbulk density, porosity, and saturatedhydraulic conductivity (percolationrate) were measured, as were rooting,clipping yield, and turf quality. Waterinjection generally performed as well orbetter than standard aeration, and theresults were similar on either bentgrassor Kentucky bluegrass turf. Onlyhollow-tine aeration, though, limitedthatch accumulation, because waterinjection neither removes thatch nor isit supposed to bring soil to the playingsurface.

Quadra-tine aeration is an excellent way to improve drainage and "dry out" the turfin a moist, shaded site.

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