Why should we carry out aeration?

Laurence Gale MScJun 28, 2012in Industry News

I will begin by explaining the reasons why we need to aerate, and then go on to explain the choice of equipment we now have at our disposal, giving examples of how it can be used and on which type of playing surface.

Regular and seasonal aeration is essential to ensure turfgrass quality is maintained throughout the playing seasons of most fine and field turf facilities. The impact and cost of not carrying out these operations can be high, resulting in lost or cancelled fixtures, which will have other impacts for club members and users, often resulting in lost revenue for the facility.

So, why do we need to aerate? The vast majority of turfgrass swards are grown in a medium consisting of a blend of soil and sand (in varying degrees) that provide a suitable environment for plant growth. This growing medium, commonly referred to as the rootzone, is made up of differing proportions of soil solids (mineral and organic material) and soil pores (for water and air).

Maintaining the correct balance of these components is critical for sustaining healthy plant growth. The spaces between the particles of solid material are just as important to the nature of soil, as are the solids themselves. It is in these pore spaces which create the environment for the plant to obtain the necessary nutrients, air and water it requires to respire and grow.

These pore spaces can vary in size and are generally classified into two sizes - macro pores (larger than 0.08mm) and micro pores (less than 0.08mm). Macro pores generally allow movement of air and the drainage of water, and are large enough to accommodate plant roots and micro-organisms found in the soil. The ability to retain a good balance of macro pores in soil structure is essential for maintaining grass plant health. It is when these macro pores are either reduced in size, or filled with water, that we see deterioration in surface playability and resistance to wear.

The main contributing factor that reduces and damages pore spaces in soil is compaction, typically caused by compression forces normally associated with play and use of machinery, particularly during wet weather periods. Over time, these compression forces reduce the pore spaces so that air, water and nutrient flow through the soil profile is restricted, and leads to the many problems associated with compaction.

There are two distinct types of problems on winter games surfaces; one is compaction by treading (30-60mm depth) and the other by smearing and kneading (30mm depth). Compaction has been measured down to depths of 120-150mm on racecourses.

The extent of compaction is also dependent on the soil type. Clay, clay loam, silt and sandy soils will all compact, but the majority of compaction problems are associated with the heavier soils (clay and clay loams). There are a number of methods available to measure soil compaction/hardness and infiltration rates. These include:

Cone penetrometers - devices that are pushed into the ground, measuring the resistance of the soil when inserting
Taking soil samples using density rings to measure soil bulk density
Clegg hammers that measure the impact of a weight dropped from a predetermined height
Changes in visual appearance, performance and physical properties of the soil and surface
Infiltration rings - can be used to measure the infiltration rate of the soils/rootzone profile - decreased water infiltration and reduced hydraulic conductivity through the profile will lead to surface waterlogging, ponding and the possibility of the soil profile remaining in a saturated state until it is able to drain

Having a saturated soil reduces soil strength, which often results in loss of groundcover and can, eventually, lead to a loss of fixtures. Once grass cover is lost, the surface is more susceptible to weed invasion. The most common weeds seen on community winter sports pitches are daisies (bellis perennis), dandelions taraxium officinal) and Greater Plantain (plantago major), the latter being a good early indicator of compaction problems.

Compacted or sealed surfaces can also promote anaerobic soil conditions that, once formed, reduce root growth and restrict microbial activity.

The above conditions will adversely affect a surfaces performance in many ways, such as ball bounce, ball roll, reduced ball speed, player welfare and, in the long term, damage the soil structure, which may lead to expensive reconstruction costs.

How do we aerate?

To alleviate these compacted layers, we need to consider a range of different techniques and equipment that can encompass the different types of playing surfaces (fine turf and field turf facilities). The main aim of aeration is to penetrate the soil profile to create new macro pore space. This is achieved by several methods:

Solid tines - hand forks, pedestrian and tractor mounted vertical punch aerators
Hollow/coring tines that remove soil cores from the soil
Flat/star tines
Disc/blade implements (linear aerators). A number of new machines on the market are designed to open up the ground and back fill with permeable materials
Compressed air and water injection aerator systems
Drill and fill techniques

It is essential to use a variety of aeration techniques to prevent pan layers being created. This usually happens if you continue to use the same aeration technique set at the same depth, resulting in a compacted layer forming at the base of the tine or core depth. Most turfgrass managers will, therefore, vary the methods of aeration by changing the depths, size and diameter of tines.

The variety and choice of implements and devices now available is excellent, providing different tine sizes, operating widths and shattering features that can meet the requirements of any facility and, more importantly, do not disturb the playing surface, allowing play to continue after use.

With the demand for higher quality, all year round playing surfaces, turfgrass managers are always interested in trying out new techniques to keep playing surfaces aerated. In recent years, we have seen the development of high pressure air and water aerators that offer deeper aeration than conventional aerators.

When do we aerate?

Aeration should be carried out on a regular basis, when weather and soil conditions allow. You may contribute to surface deterioration if you aerate during bad weather when the surface is saturated and likely to smear. Timing is the key to successful aeration. Aeration is carried out to complement other seasonal renovation programmes, such as dethatching, topdressing and overseeding, which are usually completed in the spring and autumn.

Hollow coring is generally done annually/biannually, depending on the type of playing surface, and is used to remove thatch and re-introduce new materials to the playing surface. In recent years, this practice has had a resurgence at lower level bowling, cricket (outfields), rugby and football clubs, which cannot afford the high cost of topdressings, and rely on the extracted cores being dragmatted back into the playing surface to help restore levels.

Drill and fill, and sand grooving operations are now a very popular method of restoring good infiltration rates in sealed surfaces, effectively reconnecting the surface back into secondary/primary drains. Ecosol have perfected a deep drilling technique that has become a popular method of rectifying deep seated problems. The drills remove an amount of old soil, which can then be replaced with new materials; it has been particularly effective on golf, bowls and cricket surfaces.

Keith Kennsett has been instrumental in introducing the Graden into the sportsturf market. This is a very popular machine for effective scarification and linear aeration of fine turf surfaces. The Graden has been further developed to offer a backfill operation, injecting kiln dried sand back into the 50mm deep slits. Many golf clubs are now using this method to improve the firmness of their greens whilst, at the same time, reducing the amount of thatch present.

In recent years, we have also seen the advent of quicker, more flexible hollow and solid tine deep aeration, punch action machines, notably those manufactured by the likes of Campey Turf Care, Groundsman Industries, John Deere, Ransomes Jacobsen, RECO, Redexim Charterhouse, Ryetec, Sisis, Toro and Wiedenmann. All

these machines offer a wide range of tine size and types and can be set to operate at various depths from 100mm- 400mm.

Then there are the linear type aerators, such as the Imants Shockwave Blec Ground Breaker and the recently introduced Vert-Quake from Charterhouse Redexim. The Shockwaves are available in a wide range of working widths and depths starting at a 1m working width right through to 2.5m. They are able to penetrate to a depth of between 120mm-530mm, depending on the choice of machine and ground conditions. The Blec Ground Breaker also offers four different specification machines with similar working widths and depths. Like the two other models, the Verti-Quake vastly improves drainage, root development, plus the uptake of moisture and nutrients. Four Verti-Quake models are available, with a working depth up to 380mm. All of the above machines come with various blade options.

Finally, there are compressed air decompactors that are effective at greater depths, being able to penetrate below one metre. Terrain Aeration's machines have been at the forefront of this technology but, in recent years, an Australian interloper, the Gwazae, has entered the marketplace. The technique has been around for a number of years and is tried and tested in many situations both on sports turf and commercial land assets, such as orchards and tree plantations, to help put back air into the soil structure and break up any compacted layers.

Many turf managers say that they would do more aerating 'if time allowed'. Therefore, machinery should be sourced that can take advantage of 'weather windows', collect cores as they go or perform more than one operation.

An example would be the John Deere Aercore 800 which, with the verticutter attachment fitted, will aerate and verticut in one pass. Where speed is important, the Wiedenmann machines should be considered, with some models offering deep aeration at the same speed as shallow aeration,

whilst the PlanetAir from Kensett Sports is able to cover eighteen greens in around four hours.

The Groundsman Flexblade Core Collector was initially developed as an attachment for Groundsman aerators to gather the cores as they are being produced in a one pass operation, but the company have now made it available as a stand alone implement for three point linkage mounting on a compact tractor, or for turf utility vehicle mounting using the tipping body mountings and operating ram.

And, of course, size matters. On fine turf, heavy, tractor mounted machines would be out of the questions. This is where models such as Toro's pedestrian ProCore range, JD's Aercore, the Groundsman 345 and Sisis Dart come into their own on golf and bowls greens, croquet lawns and tennis courts. These pedestrian models are also favoured on football pitches for regular aeration throughout the season.

So, what are the other benefits from carrying out aeration?

Improves soil surface drainage (water infiltration)
Helps to increase soil temperatures
Increases soil pore space - allows gaseous exchanges in the soil (oxygen in, carbon dioxide out) that improves root growth and development
Aids integration of topdressings into the soil profile
Aids the breakdown of thatch/organic matter
Promotes better surface levels that will increase ball roll /speed
Aids surface firmness/dryness, thereby increasing ball bounce and surface grip

Without effective aeration programmes, pitches would return to the quagmires of days gone by. Using a variety of aeration techniques and machines, modern day pitches can remain playable year round.

It goes without saying that aeration plays an important role in the management of natural turf playing surfaces and should be a key operation to aid turf grass performance, but be mindful what technique or machine you choose to use on your playing surface.

It is also important to note that damage can occur to the playing surface if the wrong type of equipment is used or the operation is carried out in the wrong conditions. Dig trial pits or take soil samples to ascertain the type of soil you are dealing with before using a large and fast operating aerator; these powerful machines are capable of doing a lot of damage in the wrong hands.

It's not just a case of 'running over the ground as fast as you can'. There's much to consider when aerating - soil type, speed of the machine, tine spacing, depth of operation and, importantly, what you are trying to achieve, all need to be considered.

Be aware of the health and safety considerations when operating aeration equipment. Do not attempt to adjust the machine when it is working, ensure you switch off the machine and any primary mover when undertaking any adjustment or repairs.

I hope the above has been helpful and portrays the benefits of carrying out aeration practices, and points you in the right direction on choosing the right type of aeration equipment.

The following information highlights some of the aeration machinery and techniques used in the maintenance of specific sports surfaces.

Bowling Greens and Croquet Lawns

Like most fine turf playing surfaces, care has to be taken not to disturb the playing surface, so timing of operations is critical. Most, if not all, of the deeper aeration work is usually completed during the closed season (October-March).

Many surfaces would benefit from a deep aeration into the profile to break up any deep-seated compaction pans. Care should be taken on the choice and size of tines, and be mindful at what speed you run the tines; you do not want to rip the top off your surface. Gradually deepen spiking over time, but avoid damaging any undersoil irrigation pipes, electrical cabling, drainage systems or gravel carpets.

During the playing season, the green will benefit from regular aeration work to keep the surface open. Weekly use of a sarrel roller will also help. Prior to the spring and autumn renovations, the green will benefit from some solid or hollow tine spiking (depending on needs) usually down to 100-150mm depth, providing a key for any newly applied topdressings.

Other regular aeration will involve the use of pencil tines or slit tines, on a monthly basis, to keep the sward free draining and allow gaseous exchange to take place.

Golf Courses

Both tractor mounted and pedestrian aerators are used regularly out on the course.

Greens and tees: The aim is to provide firm, dry and level surfaces with sufficient cover of a tight knit grass sward. When conditions are favourable, windows of opportunity should be taken to achieve this objective by aerating at varying depths and possibly lightly sanding afterwards to maintain a firm and dry surface.

Recent trends have shown that many course managers prefer to carry out solid tining or coring work with 9mm (3/8th) or less tine sizes and then follow-up with micro-coring in April. The larger 13mm (½ inch) coring operation is then left until August, when conditions are usually ideal for such work and a much faster recovery ensues.

Fairways are generally aerated with tractor mounted aerators throughout the winter months (November-March) when the ground is moist enough to penetrate. Operating a deep tine with varying degrees of heave will prove beneficial for removing surface water and to maximise air movement through the soil. If slitting is the desired option, then be aware of cold drying winds opening the surface, particularly on exposed courses on the eastern side of the UK.

Tennis and Cricket

Traditionally, aeration of tennis and cricket facilities was carried out during the winter months, when the clay soil profiles were wet enough and soft enough for penetration. No aeration tended to be carried out after January as they did not want the clay soils cracking open during the playing season.

However, Keith Exton, Head Groundsman at Glamorgan CCC, has now blown this theory away by advocating deep aeration on cricket squares during the playing season, as soon as a pitch has been used. He has perfected the art of deep aerating the square using a very fast acting modified Wiedenmann XF aerator using pencil tines. He now can aerate to below 150mm in depth, thereby aiding the recovery of his wickets after play.

Ecosols Drill 'N' Fill aeration is also a popular end of season renovation at some cricket clubs. A number of wickets have been drilled and filled at Northampton CCC, with head groundsman, Paul Marshall, being very pleased with the results. The drills are used to remove a 300mm depth of old soil, which is replaced with new loam material, which is then backfilled by hand.

Outfields are regularly aerated using a combination of linear and solid tine aerators.

Winter Sports

A wide range of aeration techniques are used on winter sports pitches, using both tractor and pedestrian aerators. However, most topflight stadium venues use pedestrian walk behind spikers, such as the Toro Pro Core 648 and John Deere Aercore 800, to reduce the weight of machinery going onto the pitch; the only time any tractor mounted equipment goes on to the pitch is during the renovation period. The sands used in modern day stadium pitches are susceptible to compaction over time so, to help reduce this, a monthly programme of aerations is the norm, ensuring it done during the right weather conditions and not too close to any fixtures.
The physio at Leicester City regularly assesses the pitch with a Clegg Hammer, before a game, to check its level of hardness, preferring the groundstaff to maintain the pitch at a value around 90 gravities.

For the general soil based community sports pitches, groundsmen tend to use an assortment of tractor mounted aerators, using both the linear and solid tine spikers to aerate their pitches.

Racecourses and Polo Fields

Aeration is a key management tool for the upkeep of racecourses. Adrian Kay at York Racecourse incorporates a robust aeration programme to help decompact, re-level and re-oxygenate the soil profile, with the aim to aerate several times throughout the year. Most of the work is carried out during the summer months when conditions allow. If he has the window of opportunity, aeration will also be carried out during the winter months.

A Charterhouse Verti-Drain is used (2.6m working width) to a depth of between 300-450mm fitted with 25mm diameter solid tines. Depth and heave will vary depending on ground conditions. An additional benefit of this aeration is that it helps to restore surface levels.

Adrian also operates a Toro Procore SR70S deep-tine aerator, using it on the modified sand constructed parts of the track, aerating down to a depth of 125mm using 5mm diameter tines.

Air and liquid injection aeration

Many groundsmen and greenkeepers also use aeration techniques to help incorporate feeding products, wetting agents and fungicides into their rootzones. In recent years, we have also seen the provision of aeration equipment that has the capability to inject water, and air. Machines such as the Sisis Aeraid, GP Air and, more recently, the Liquiject drum spiker that can inject liquid fertilisers.

With an increase in the damage to turf caused by nematodes, particularly in golf and football facilities, the ability to direct products directly into the soil profile using aeration techniques would be advantageous.

Many of the nematode control products are applied as a liquid formulation and, for these products to be affective, they need to get deep down into the soil profile to make contact with the nematodes.

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