Turf aerators have long given grounds managers and golf-course superintendents the "punch" needed-literally-to promote strong, healthy turf. With advances in equipment technology and soil and turfgrass research, equipment manufacturers now offer you a variety of choices when selecting a turf-aeration system.

Webster's Collegiate Dictionary defines the word "aerate" as: "1) To expose to the action of air or to cause air to circulate through. 2) To change or treat with air or gas." Although one of the primary results of turf aeration is to open channels in the soil for air movement and gas exchange in the root zone, our expectations for grounds-maintenance aeration are much greater.In most instances, traditional turf aeration involves the process of punching holes in the soil and removing a portion of the soil/thatch layer via a coring or spooning action. Other common practices included solid-tine spiking, slicing and-to an extent-deep vertical mowing. All of these processes create openings in the root zone that allow for air and gas exchange. However, turf aeration has a much greater impact on the development and maintenance of quality turfgrass (see boxed information, page 35, "Advantages of aeration").

Aeration processes The most common and traditional method of core aeration involves using equipment containing hollow steel tines or open spoons.

* Hollow tines. These units use a vertical action to remove cores of soil. They force the tines to penetrate or "punch" holes in the soil surface to a depth of 3 to 6 inches. Larger units-often called deep-tine aerators-often offer optional cutting or spiking tools that can penetrate to greater depths, usually up to 12 inches.

In many cases, smaller units are self-powered, either walk-along or riding units. Others receive power from PTO systems from a tractor or other powered maintenance equipment. Larger units can be pull-behind or three-point-hitch implements.

* Open spoons. Spoons are mounted to a roller, disc or barrel-type of equipment. You then pull or push the unit across the area to be aerated. To avoid extreme surface damage, many of these units are equipped with spring-loaded, swivel or pivot assemblies on which the tines are attached to compensate for the rolling/pulling force as the tine enters and leaves the soil. Many of these units also have the capability of adapting to surface undulations over these large areas to achieve successful results.

Some units rely on gravity and the addition of heavy weights on the aerator to force the tines or spoons to penetrate the soil. Others use hydraulics to force down-pressure on the aeration unit to penetrate soil efficiently via a rolling action. Again, based on the type of cutting tool you use and the size of the aerator, soil penetration depth is typically between 3 and 12 inches.

One of the major drawbacks of the traditional coring systems is the amount of surface damage encountered during the aeration process. Other potential problems include core-hole glazing and the creation of a hardpan layer. Glazing is the smoothing of the sidewall of the core hole that commonly occurs from aerating during wet soil conditions. When this happens, it actually seals off the plant root zone and causes more harm than good. Hardpan layers occur over time through repeated aeration applications with the same equipment at the same depth, creating a compacted soil layer just below the aerated level.

Aerators that do not remove the cores, such as solid-tine spiking and slicing, are similar in to traditional coring and spooning equipment. In fact, it is becoming more common for manufacturers to offer equipment that allows for quick-and-easy interchanging of a variety of cutting or spiking tools. Other companies offer specialized equipment that perform a specific soil-cultivation task.

Alternative techniques are recent trend A few of the more recent developments in turf aeration include deep-tine coring, spiking or drilling; water-injection systems; and soil-shattering units.

* Deep-tine aerators. Deep-tine coring, spiking or drilling has gained great popularity over the past few decades. By penetrating deeper into the soil profile, you encourage the benefits gained from traditional aeration but at a greater depth. Certain equipment offer options for soil penetration up to 24 inches. You do need to take special care when using deep-tine equipment to avoid damaging underground utilities, drainage and irrigation systems. Some of the more positive results from deep-tine aeration include the breaking up of soil layering caused by inconsistent topdressing practices, as well as breaking through hardpan layers created by traditional 4-inch coring. In addition, some units offer the process of fracturing thecore sidewalls to avoid core-hole glazing. Deep-tine aeration also is beneficial in managing the black layer. Deep-soil penetration allows the release of phytotoxic gases, improves soil-water drainage and improves surface-water and nutrient infiltration.

* Water-injection systems. These units, the newest option to turf aeration, also are becoming quite popular. They force small streams of water through a high-pressure system to deeply penetrate the soil and break up compaction or treat localized dry spots without disrupting the surface area. You also can use them to incorporate certain liquid soil amendments, such as wetting agents or fertilizers. The greatest advantage of water-injection systems is that you can use them throughout the season during heat or dry stress periods when traditional aerators would cause severe turf damage.

Some of the limitations of water-injection systems include the lack of soil/thatch removal and not effectively gauging the depth of water penetration into the soil profile. Although these units are versatile and you can use them for many turf applications, they seem to have found a permanent home on golf courses and athletic-field complexes, where it is vital to limit disruption of play and field availability.

* Soil-shattering units. Soil-shattering units use a unique design where solid tines are forged using a combination of angles at various points on the tines. Then the tines are mounted onto a barrel-type frame and used as a pull-behind or 3-point-hitch unit. When in use, these units penetrate to about 7 inches deep and create a twisting action that shatters the soil in a sideways and downward direction. Turf surfaces experience very little damage, and you can accomplish cleanup by performing a couple of mowings in opposite directions. These units are designed specifically for use on golf-course fairways, roughs, parks and sports complexes.

Purchasing considerations Before purchasing a new-or even a used-turf-aerator system, it is important that you evaluate your operation and match the equipment to your budget and needs. For example, aerating a home lawn may not demand the precision in core spacing or depth that a golf-course putting green requires. In fact, equipment companies actually offer turf aerators that are primarily designed for use on putting greens. Some are walk-behind units, some are riders, and you can mount some on small tractors. Many offer a range of choices for tine or spike diameters from 0.25 to 0.75 inch. Other features include various cutting-tool depths and applications and adjustable core spacing.

A few manufacturers have designed models for commercial use by lawn-care companies with golf-course-type features. These units can withstand the demands of home-lawn or grounds-maintenance use. However, these units do not provide the precision of hole-spacing and quality that is demanded for a golf-course putting green. Even though somewhat heavier and built to withstand hitting rocks and tree roots-not typically found on a putting green-these aeration units have fewer moving parts and contain less manufacturing and engineering costs. Thus, they typically cost much less than the golf-course models.

Sizing an aerator unit is important to consider before purchasing. Keep in mind whether your needs may require an aerator for use in small areas with obstacles such as trees, sidewalks and landscaped beds. Thus, you need to match equipment to fit those needs. You also must be able to maneuver the unit in a safe and efficient manner while achieving your aeration goals.

At the opposite spectrum, if you aerate large turf areas-such as golf-course fairways or athletic fields-you may need a larger unit that will cover the area in a shorter time. Some of these units also are capable of maneuvering around obstacles while also operating in a more open area.

Still, another factor to consider is that lawn-care companies use aerator units more often and in more types of locations than a user such as a sports-field manager, who is responsible for only one location. If you operate a lawn-care company, then, you may need to purchase more than one unit. Even on single sites such as golf courses, however, it has become popular to purchase multiple units to complete the aeration task on putting greens and tees in a shorter time to limit the disruption of play.

In numerous cases, grounds professionals use a combination of aerating systems. In some instances, for example, superintendents practice traditional aeration as many as two to three times per season. They then may supplement this technique with deep-tine or water-injection aeration to achieve desired results. Costs involved in deep-tining or water injection are somewhat greater, and the jobs themselves also are more complicated. In certain cases, you may want to consider contracting these operations out to a qualified contractor.

Another option that is gaining popularity toward offsetting the expense of purchasing a deep-tine or water-injection system is the co-op method. Many site managers share the cost of the equipment purchasing and maintenance so that all can benefit from its use.

Finally, try out the equipment at your site. Compare various types of aeration systems in a side-by-side setting. Allow crew members to operate and evaluate the equipment. After all, ease of operation and handling is as important as any other aspect.

David A. Willoughby is assistant professor and coordinator of the Turfgrass Management Program at The Ohio State University Agricultural Technical Institute (Wooster, Ohio).

Grounds Maintenance readers spoke out strongly when asked what aeration techniques they prefer. Of the choices-solid-tine/shatter-core, hollow-tine (closed-tine), spoon-type (open-tine), water-injection and slicing/spiking-nearly half (47 percent) of the respondents supported the hollow-/closed-tine technique. When asked why, comments varied from a simple "It works" to more complicated explanations:

* "Better reduction of compaction and penetration of water and fertilizer."-Landscape supervisor, apartment complex (Phoenix, Ariz.) * "We have small parcels, and pulling plugs works good with overseeding."-Lead gardener (Federal Way, Wash.) * "Does not further compact soil. With cam device, hole is straight in, straight out."-Owner, lawn-care service company (Minot, N.D.) * "To me, it serves my customers best, and it produces the best results to the lawns I take care of in my area."-Owner, landscape contractor (Decatur, Ga.) * "[I get] longer soil plugs, more holes per yard. In spring of '98, I was pulling 1.75- to 2-inch-long plugs. This is with a walk-behind unit."-Owner/operator, lawn-care company (Wahoo, Neb.) * "Permits topdressing to fill in holes, speeds soil-texture modification, infiltration."-Landscape manager, airport (St. Louis) * "Hollow tine opens up soil more to accept fertilizer and water while bringing up soil to topdress. I also use slicing on turf such as St. Augustine to cut wild runners."-Owner, lawn-care company (Tallahassee, Fla.) * "Removes core without compacting surrounding soil and at times helps bring soil types from below the surface to the surface."-Manager, horticulture department, government site (Columbia, S.C.)

Aside from two readers (one who used a dedicated riding aerator and the other who used an out-front riding-mower attachment), all other respondents were split evenly between using dedicated walk-behind aerators or pull-behind attachments. The majority of respondents (57 percent) who said they use techniques that pull cores answered that they left the cores on the turf. A smaller group (30 percent) said they dragged an attachment over the cores to break them up. The last 13 percent said they collected the cores.

As for other comments concerning aerator use, readers offered advice and explanations: * "Big plus prior to overseeding an established lawn. It creates not only fresh oxygen for existing grass plants but makes a home for your seed to germinate in."-Owner/operator, lawn-care service (Rock Hill, S.C.) * "I use spoon-type only. Other [techniques] are a waste of time....Aerate and topdress are two crucial elements to superior turf."-Owner, lawn-care service (Laguna Beach, Calif.) * "I have a spoon aerator, which is now in permanent storage....I am just getting into aeration with organics, but it really makes sense. You want the soil to have 25 percent air, so how do you get this with the spacing of mechanical aerators? You don't. You use organics."-Owner/operator, lawn-service company (Odessa, Texas) * "We encourage fall aeration, but many people think 'turf' only in the spring, so we end up doing a lot of both. We tell people that if they only plan to do one thing for their lawn this year, it's aeration."-Owner, lawn-care service (Minot, N.D.) * "Open-tine aeration is more or less a given for residential accounts in our area."-Owner, lawn-care company (Cincinnati) * "I have found over the past 10 years [that] if I core aerate at least once a year the turf is much stronger and is less likely to die due to the heat."-Owner, landscape contractor (Decatur, Ga.) * "The slicing/spiking method affords us to aerate four to six times a year. The time saved by using this method gives us the opportunity to concentrate on other areas of grounds maintenance. It also allows our sports teams to continue play/practice with no delay."-Athletic director, sports complex (Nashville, Tenn.) * "Today's heavy mowers create need for aeration."-Owner, lawn-service company (Tallahassee, Fla.)

* Relieves soil compaction * Modifies layered soil conditions * Removes a limited amount of thatch * Allows for better gas/air exchange in the root zone * Promotes efficient water percolation * Improves fertilizer and pesticide penetration and effectiveness * Limits the disruption of grounds use, play on golf courses, etc. * Improves plant-root development * Helps prepare soil for overseeding * Improves surface drainage.

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