The original aeration device. The latest concept, the Toro Hydro.Iect,

Aeration Takes Rootin Sports TurfSPorts fields, golf greens and park

turf, as simple as they may appear,are complex communities of plants

and organisms living in careful balance.While the vast majority of turf maintenanceis directed at the foliage and thatch aboveground, an equally important portion of theturfgrass community lies below the soilsurface, completely out of sight. Failing tomaintain the subsurface portion of turfover a period of time disrupts the balanceof the turfgrass community and leads to itssteady decline.

There are practical methods availabletoday to maintain "the other half" of turf.They not only improve the overall qualityof turf areas, they also increase the effec-tiveness of surface maintenance methodsand provide the sports turf manager withgreater control.

The most popular of these methods ismechanical aeration. This process makes aseries of holes or slits in the soil. Theseopenings relieve compaction, improvedrainage, permit air and nutrients to pene-trate the root zone, and provide channelsthrough impermeable layers below the sur-face.

In the darkness of the soil, turfgrassesdevelop extensive root systems. Roots sta-bilize the foliage, they explore the porespaces between soil particles for water, airand nutrients, and they store carbohydratesmanufactured in the leaves above. Turfscientists have discovered turfgrass rootsextending more than four feet into the soil.If you consider all the plant functions car-ried out by roots, you quickly realize they

By Dr. John C. Harper

are every bit as important to the turfgrassplant as the leaves.

Leaves have one special task, to manu-facture sugars and starches (carbohy-drates) by a process called photosynthesis.Chlorophyll contained in the leaves cap-tures the energy of the sun to convert waterand carbon dioxide into sugars andstarches. These carbohydrates are then uti-lized by the plant to fuel its growth. Excesscarbohydrates are sent to the roots forstorage.

The roots have the job of obtaining thewater, nutrients and gases for photosynthe-sis, respiration, and growth. A turfgrassplant in full sun without a healthy rootsystem will not perform up to its potential.Therefore, an equal amount of consider-ation should be given to turfgrass roots.

By applying quality fertilizers, sportsturf managers provide most of the nutrientssought by the roots. Irrigation provides thenecessary moisture. Even so, poor drain-age, poor soil, heavy thatch or other barri-ers preventing nutrients and moisture fromentering the root zone greatly reduce theeffectiveness of standard turf maintenancepractices.

These barriers preventing propersoil/atmosphere exchange are oftencaused by compaction of the surface soil.Thousands of impacts caused by foot andvehicle traffic tamp down the top inch ortwo of soil so tightly that neither air orwater can pass through.

The negatives associated with compac-tion have been listed by Dr. J.R. Hall, exten-sion agronomist at Virginia Tech,

Blacksburg, VA. They include destructionof the soil structure, reduced soil drainage,and increased soil-eroding runoff, reducedprotection of the root zone to heat or cold,pesticides are unable to reach and controlinsects in the soil, and there is less storagespace within the soil for water, air, andnutrients, and results in higher mainte-nance costs. Root growth is also stunted bycompacted soil. Shorter and smaller rootsystems render turfgrass more vulnerableto periods of stress.

Thatch, nondecomposed stems, leaves,and roots on the surface of soil, can beharmful to healthy turf if it becomes morethan 1/2-inch thick. Heavy thatch reducesthe effectiveness of some herbicides andinsecticides, harbors insects and diseasesand can disrupt uniform infiltration of irri-gation or natural rainfall. Research hasshown that periodic aeration helps mix soilinto the thatch layer to aid in its decornpo-sition. Some thatch is considered advanta-geous for sports turf since it provides acushion that protects both the player andthe turfgrass from damage upon impact.

Another barrier to healthy turf growthis soil incompatibility, a situation createdwhen sod grown on highly-organic soil isinstalled over a sandy or clay soil. Heavyapplications of organic materials to a turfgrowing in sandy or clay soils can have thesame effect. The organic layer at the surfaceacts like a sponge, keeping the surfaceexcessively damp and preventing surfacewater from draining through the soil as itshould. This environment is destructive to

continued on page 18

July, 1991 17

Holland Aerway fractures subsurface layers of soil.

Aerationcontinued from page 17

organisms living in the turf that assist inthe decomposition of thatch.

Compaction, thatch, and soil incompati-bility are often the real causes of turf failureblamed on poor irrigation practices, dis-eases, insects, or inadequate fertilization.There is enough evidence to support theuse of aerators by sports turf managers toprevent and break up soil barriers.

The earliest documentation of aerationis in a book titled Making A Lawn, writtenin 1912 by LJ. Doogue of the Boston ParksDepartment. Doogue recognized the needto work fertilizer into compacted soils. Hewrites, "Take a round stick about one inchin diameter and three feet long and sharpenone end. At frequent intervals, drive thestick to a depth of two feet about thegrounds. Make many such holes, and intothese ram a mixture of finely-powderedmanure, hardwood ashes and bone meal. Ina short time the good effects of this treat-ment will manifest themselves and duringsubsequent seasons the treatment can beextended to parts not touched before. Itpractically means that the land will be asthoroughly renovated as if it had beenplowed and harrowed."

However, in 1917, the need for aerationwas not recognized in the first comprehen-sive U.S. publication on golf course man-agement, Turf for Golf Courses, by Piperand Oakley. These early agronomistsworked for the United States Departmentof Agriculture and assisted the UnitedStates Golf Association in establishing turfmanagement practices for its members.

18 Golf & sport TURF

Dr. Fred V. Grau, the first extensionturfgrass specialist for Pennsylvania StateUniversity, reported that he had no recol-lection of any type of equipment being usedto improve soil-air relationships or to re-duce soil compaction at the USDA's Arling-ton Turf Gardens in the early 1930s. Graudid remember golf course superintendentsusing potato forks and spading forks toloosen hard spots on putting greens thatresisted water penetration.

In the mid-'30s, a Michigan concern of-fered for sale a three-gang, pull-behindspike disk fairway cultivator, a spike diskgreens cultivator, and a 10-inch-wide homelawn spike disk cultivator. In its advertis-ing, the company stated, "It is an acceptedfact that turf requires aeration and cultiva-tion especially upon turf that receives con-stant play." The tractor-drawn model on themarket today is essentially the same as the1930 version.

During the late '30s and early ,40s,many turfgrass managers developed theirown versions of aerating equipment, rang-ing from devices as simple as large spikesdrive through planks to "Rube Goldberg-type" machines that required several mento push or pull. Soil aeration was a majortopic of "Lawn Schools" given by agricul-tural agent Charles K. Hallowell in Phila-delphia during the period.

In 1945, Grau, then director of theUSGA Green Section, discussed developinga commercial aeration machine with Tomand Tony Mascaro, owners of West PointProducts in West Point, PA. The Mascarobrothers decided to expand their topdress-ing business into equipment manufactur-

ing and designed the West Point Aerifler,This development truly became the begin-ning of a new era for specialized turfgrassmanagement equipment. Hahn purchasedthe manufacturing rights to the "WestPoint Aerifier" in 1970.

The West Point Aerifier had one draw-back. Because the tines entered and exitedthe soil at an angle, they would lift up a lipof turf at the back of the core hole. Golfcourse superintendents were concernedthat these lips would disrupt putting on golfgreens. To provide superintendents with aneater surface following aeration, theGreensaire Aerification Co., of Hopkins,MN, (purchased by Ryan in 1950) inventedan aerator that drove hollow, cylindricaltines vertically into the soil and pulled soilcores straight out. These machines wereconsiderably slower than disc-type or WestPoint aerators.

The first walk-behind aerator for generallawn use was the Motoraire introduced inthe '50s by Soilaire Industries (purchasedby Ryan in 1960). Hollow tines pivoted onsolid metal wheels as they turned. The tinesentered and exited the soil in an almostvertical position providing a neat enoughjob for residential or commercial lawns. Theunit was also as fast as a West Point aerifier,

The Dedoes Co. manufactures a drumaerator which traps the soil cores insideinstead of depositing them on the turf.Screens on both ends of the drums trap thecores until they can be deposited in lowspots or discarded. These are convenientfor smaller jobs where cores could be aproblem, but impractical for large areaswhere the aerator may remove 10 or morecubic yards of cores per acre.

In recent years, several new conceptshave appeared in aerating equipment, in-cluding an oscillating or quaking tine ef-fect. For the most part, the method ofoperation has basically been two-fold. Theso-called punch-type aerators drive hollowor solid tines in and out of the soil verticallywith very little tearing or raising of the sodaround the hole. These machines were de-veloped primarily for golf course greens,grass tennis courts, bowling greens orother c1osely-cut turf areas where minimumdisruption of play is essential.

The second, or rolling-type, machinesare equipped with solid spikes, hollowtines, open-spoon tines, or slitting-slicingtines of varying shapes and sizes. the tinesare mounted on a drum, a series of discs,or directly on an axle that rolls forward withthe machine. The tines enter and exit thesoil at an angle. For this reason, some tines

tend to tear and raise the soil around thelip of the hole.

As previously indicated, there are manydifferent types of tines. Hollow tines andopen-spoon tines remove soil cores whilesolid tines remove little or no soil. Mosttines vary from 1/4 to 3/4 inches in diam-eter. Slicing tines are available in a varietyof shapes, sizes and thicknesses. An earlyaerator known as the Nightcrawler de-signed for greens actually used augers(large drill bits) in place of tines.

The spacing of tines determines thenumber of holes or slices made in a givenarea. A machine equipped with hollow tineson two-inch centers will provide approxi-mately 36,000 holes per 1,000 square feet.A random check of commercial literaturereveals tine spacing of 2, 2.5, 2.75, 3, 3.5,4, 4.5, 5.5, and 6 inches are currently avail-able.

Tine mounting also varies on rolling-type aerators. Most rolling-type, core-re-moving machines have hollow oropen-spoon tines mounted rigidly on thedrum or axle. A few manufacturers of roll-ing-type machines have the tines mountedon hinges. The theory is the tine enters andleaves the soil in an almost straight verticalposition causing less tearing of the sod

around the hole. Generally, spiking, slicingand slitting tines are mounted rigidly.

Speed of operation has been a majorconsideration in the development of aera-tion equipment. Unfortunately, there hasbeen a direct correlation between speedand the quality of the aeration results.Generally, the faster rolling-type machinesdo not have close tine spacing, the cleanentry and exit, or the depth of vertical-coremachines. The outcry for faster equipmentis the result of greatly increased labor costs,down time of the turfgrass area and incon-venience to the player. Some golf courses,where cost is not a limiting factor, havebegun using slow-moving punch-typegreens aerators to cultivate their fairways.Classen, Cushman, Green Care Interna-tional, Jacobsen, Terracare, and Toro havereengineered punch-type aerators for fair-ways and sports fields.

Depth of penetration also has been aconcern. Most machines on the markettoday that pull soil cores penetrate approx-imately two to three inches. One U.S. man-ufacturer provides six inch hollow tines.Slicing or slitting machines may penetrateas deeply as six inches whereas splkersnormally used to break up surface crustsonly penetrate one to two inches.

Some manufacturers offer accessoriesfor their equipment line. Attachments towindrow or pick up soil cores are on themarket today. One manufacturer offers anattachment that picks up the plugs, shattersthem and returns them to the turf astopdressing material. Weight trays andweights for maximum tine penetration areoffered by many suppliers.

A major concern of many turfgrass man-agers is the development of a compactedsoil layer at the point of maximum tinepenetration following frequent aerification.It makes no difference whether the ma-chine is a punch-type or rolling-type.

One possible means of reducing thisproblem may be the development of betterdepth control for existing machines so pen-etration depth can be varied from one aer-ation to the next. Unfortunately, theshallow maximum depth of many machineslimits this approach. A possible alternativewould be to follow a program using severalmachines having different depths of maxi-mum penetration.

The development of the compacted layeris akin to the development of a fragipan orhard pan in a crops soil. Not only is drain-age impeded but roots fail to penetrate the

continued on page 20

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compacted layer. This layer in turf soils maybe more serious than in some crop soilsbecause it develops at such a shallow depth.The resulting shallow roots may lead tosevere stress of the plants during droughtperiods.

Deep aeration devices have been devel-oped in the past few years to break throughsubsurface compacted layers. The Verti-Drain is one example. Holland Co. of On-tario, Canada, has developed a spike-liketine that fractures the soil below the surfacewithout damaging the turf above. YeagerTwose and Olathe have machines that aer-ate by cutting grooves in the soil. TheVertigroove by TurITech removes thin,deep slices of soil instead of cores. Theslices are removed or broken up like coreswould be.

Obviously, tines have the potential todamage irrigation heads and shallow lines.Heads should be marked before aerationand the depth of aeration should be set toprevent tines from hitting irrigation linesor wires.

Tines glazing the sides of core holes orsoil slits is also a concern. Glazed surfaceshave a very thin compacted layer whichreduces the movement of oxygen and waterinto the soil and carbon dioxide out of thesoil. Some manufacturers claim that theaction of their tines shatters the wall of thehole or slit and thus avoids the problem.This may be true for relatively dry soils, butmoist soils do not shatter readily. Further-more, some aerators will not penetrate drysoils well.

Aerator manufacturers have added de-vices to their machines that counteractsome of the tearing and lifting of the sod.Springs attached to each tine compress thesurface as the tine enters the soil andreduces lifting of sod when it exits. Evenvertical core machines have spring-loadedguides that hold the soil around the pointsthe tines enter. Toro has taken a differentapproach to this problem by introducingthe Hydro-Ject which uses jets of waterinstead of tines to create channels in thesoil.

As indicated earlier, speed of aerationis important in some turf operations. Insituations where uninterrupted turf use iscritical, especially from a financial stand-point, sports managers are forced to sacri-fice some quality for speed. Where time isa limiting factor, slicing equipment can beoperated at higher speeds than coring

Aerationcontinued from page 19

equipment although quality may be less.AJ. Turgeon gives a detailed discussion ofthe relative merits of coring as compared toslicing or spiking in his book TurfgrassManagement.

Rapid drying out of the turf can be aproblem if aeration timing is improper. Dur-ing hot weather, especially under windyconditions, desiccation around the core orslit opening can occur quite rapidly. Dryingout potential is greater with coring thanslicing or spiking. During hot, windyweather, it is recommended that a slicingor spiking machine be used rather than acoring unit and that irrigation be available.

On the other hand, soils that are proneto remain wet for long periods benefit fromcoring just prior to expected periods ofprolonged rainfall. When hurricane Agnesstruck the Atlantic Coast in the spring of1972, golf greens that had been core aer-ated that spring withstood flood watersand/or prolonged rainfall much better thanthose that had not been cored. Wet soilscan also be dried out faster by coring pro-viding the equipment used is capable ofpulling cores from wet soil.

Opening up the soil for air, moisture,and nutrients, also opens it up for insectsand weed seeds. Cutworms living in coreholes and feeding near the surface willcause a brown, damaged ring of turf at thetop of the hole. Aerated areas known to beinfested with cutworms or insects of similarhabit, should be treated with an insecticideat the first sign of insect damage.

Aeration can bring viable weed seeds tothe surface that would be too deep togerminate otherwise. Crabgrass seed hasthe ability to lie dormant in the soil formany years and to germinate readily whenbrought to the soil surface. Annual blue-grass seed germination also can be in-creased by aeration.

It's important to note that aeratorsshould not be used during the effectiveperiod of preemergence herbicides. Theseherbicides form a chemical barrier justbelow the surface of the soil which blocksgerminating weeds. Mechanical aerationbreaks through the chemical barrier anddamages the effectiveness of these herbi-cides.

The benefits of aeration far outweighthe problems it creates. The most commonbenefits attributed to aeration are the im-provement of gaseous exchange betweenthe soil and the atmosphere and the reduc-tion of compaction. By removing the cores,the bulk density or hardness of the soildecreases. This softer soil cushions the

impact of players falling on it and a majorfactor in reducing sports injuries.

The effectiveness and efficiency of fertil-izer and liming materials is increased whenthese materials are applied following aera-tion but prior to dragging to break up soilcores on the surface. Experimentally, it hasbeen shown that the amount of phosphorusat the two and three-inch level is increasedapproximately 29 percent if aeration pre-cedes phosphate application. This is espe-cially important in phosphorus-deficientsoils since surface-applied phosphatemoves downward in the soil very slowly.The downward movement of lime is alsoslow and aeration offers a way to amendacid soils more quickly. Control of soil-in-habiting insects and other pests with pesti-cides is markedly improved throughaeration.

Aeration increases water infiltration ifsoils have shallow layers of compacted orincompatible soil within the depth penetra-tion range of the equipment These layersmay consist of sand, organic matter or soilsof totally different composition. This prob-lem most frequently occurs on golf greensor high-maintenance fields where topdress-ing with sand; sand and soil; or sand, soiland organic matter is a standard practice.The problem arises when the type oftopdressing material is changed.

Coring is more effective than slicingwhen layering is a problem. Coring reopensa channel between soil layers, removes partof the problem soil and permits topdressingmaterial is changed.

Thatch layers that develop in sports turfalso impede water movement through thesoil profile, especially if the thatch has driedout. Dry thatch, like dry peat, is highlyhydrophobic (resists wetting). Thatch build-up also prevents lime, fertilizer and pesti-cides from moving downward in the soil.Many insecticides are readily bound bythatch, greatly reducing their efficacy incontrolling insects such as white grubs.

Thatch that becomes saturated tends toremain wet for long periods. This is as mucha problem as dry, hydrophobic thatch.When thatch remains soaked the oxygensupply available to the plant is greatly re-duced and limits the activity of aerobic soilmicroorganisms necessary for nutrient con-version and decomposition of organic ma-terial. Aeration can increase microbialactivity in the soil and assist in the break-down of thatch. By improving oxygen rela-tions in the thatch layer, aerobicdecomposition is increased. Most thatchlayers are highly acidic. The movement of

lime into the thatch through aeration raisesthe Ph of the thatch and stimulates bacte-rial activity.

Examination of turf managed with aregular aeration program will show prolif-eration of new, white and healthy roots inthe core holes or slits. This is the responseof the plants to improved environmentalgrowth conditions, especially oxygen rela-tionships in the soil adjacent to the corehole.

Aeration also provides a means of over-seeding into established turf without de-stroying the existing vegetation.Overseeding with a turf-type disk seeder isthe most effective method of overseeding,But thorough aeration (six to 10 passes)can be quite effective as a means of intro-ducing seed to the soil when a disk-typeseeder is not available. Apply the seed afteraeration but before dragging. Some sports

turf managers prefer to apply one third toone half the seed prior to aeration and theremainder after aeration but prior to drag-ging.

It is impossible to properly maintain anysports turf facility, especially those withheavy use, without a regular aeration pro-gram in combination with other sound ag-ronomic practices.

There is a noticeable difference in aJrpearance between turf that has been aer-ated and turf that hasn't. In some casesresodding can be replaced with aerationand overseeding. But, most importantly,both halves of the turfgrass community willbe properly maintained.Dr. Harper retired last year as extension

agronomist at Pennsylvania State Univer-sity. This article was updated from theoriginal version which appeared in theMarch 1987 issue.

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