What is it?
The soil profile is penetrated usually by physical means, such as a fork or similar type of implement, and this results in soil air being replaced by air from the atmosphere.
Why aerate?
There are a number of reasons for carrying out aeration on turf areas :
- To improve surface and subsurface drainage. This can have a significant effect on the soil temperature by encouraging the soil to warm up quicker in the spring, consequently encouraging earlier growth.
- To relieve compaction. This temporarily increases the pore space in part of the rootzone subject to the aeration work, allowing roots to grow in to that pore space.
- To improve the oxygen - carbon dioxide exchange around the grass roots, promoting healthy growth and enabling undesirable soil gases to be removed from the soil.
- To aid the incorporation of top-dressings, fertilisers, seeds and irrigation.
- To reduce the potential for disease incidence. Roots grown in poorly aerated soils have an increased diameter and contain more and larger air spaces than roots adequately supplied with oxygen. This may make roots more susceptible to fungal attack, especially Take-All Patch disease.
- To aid in the breakdown of thatch and organic matter. (Oxygen is required by aerobic bacteria that decompose the organic matter ).
- To encourage the deeper rooting of grasses, which will aid drought resistance and plant health.
- To achieve optimum growth and improve the visual appearance of the sward.
- To improve surface traction and grip.
- To increase ball (or bowl) speed and performance by the production of drier and firmer surfaces.
Aeration should be carried out during the main rooting and growth periods, when oxygen requirements of grass roots and micro-organisms are relatively high, and particularly when the rootzone material is in a relatively dry state.
Compaction by foot traffic is mainly caused within the top 75-100mm of the turf surface, so this is where regular aeration needs to take place to relieve the compaction caused.
It is important, however, to vary the depth of penetration of the tines to reduce the chance of root breaks and (aeration) pans developing.
Types of aeration tine
(a) Solid tines
These tines are used on a regular basis, particularly during the summer period when the soil is relatively dry and with the added benefit of the tine holes not gaping in dry weather, unlike the slit tine holes which dry out at the edges and increase in size. Solid tines are especially suitable for use on compacted soils.
It is beneficial to use solid tines prior to the application of fertilisers, seed, top-dressings and irrigation.
During the summer period, when it can be too dry for effective solid tining without causing surface disturbance, narrow tine rollers with typically 25 - 37mm spike tines can be used to good effect, by maintaining surface aeration as well as permitting irrigation water to readily penetrate the surface layer.
(b) Hollow tines
These tines are used on an occasional (yearly to every three years for example) basis, because over use will result in a surface that is soft and easily worn.
Their use helps in the gradual reduction of thatch layers, reduction of surface compaction and particularly for soil exchange where part of the existing rootzone is replaced with a more desirable rootzone material.
A typical size of hollow-tine for fine turf areas is 12.5 or 19 mm diameter, being used at 50mm spacings. Micro-hollow tines of 6mm diameter can also be used, typically with a spacing of 25mm, however, they can be prone to clogging up due to the narrow bore of the tine.
Football and larger turf areas would typically use hollow-tines with a diameter of 19 or 25mm.
Problems with hollow-tines
The exposed area caused by the hollow-tine can be an ideal environment for colonisation by Poa annua and weed seeds, particularly when the area is top-dressed afterwards producing an ideal seed bed.
It is essential that suitable grasses can incorporate this exposed area as soon as possible by ensuring that the work is carried out when the grasses are growing actively.
Where top-dressing is not applied, and the operation is carried out in the autumn, the tine holes are sometimes left open over the winter to improve drainage and oxygen circulation in the rootzone, however, the area will be prone to slight sinkage due to the non-replacement of material.
(c) Slit / Chisel tines
These form the backbone of any aeration programme and are used on a regular basis, throughout the year, with the exception of the summer period when tine holes are prone to 'gaping' when dry weather occurs.
Specialist Aeration Equipment
Other forms of more specialised aeration equipment are available and many of these are ideal in reducing the effects of deeper seated compaction and can be used in conjunction with traditional aeration methods.
Note : When using any deep penetrating implements it is important to ensure there are no cables or pipework beneath the ground that could be damaged or cause harm to the operator.
(a) Vertidrain
This is mainly used for deep seated compaction and on sandy soils it can generally be used at any time of the year, however, the use of this equipment generally corresponds with renovation time - spring or autumn.
Heavy soils are usually only suitable for vertidraining in the autumn, when the soil is moist enough for good penetration and allows for adequate shattering of the subsoil. If it is left until the winter, the soil will be too wet resulting in no shattering in the soil profile as well as soil smearing where the tines have entered the soil.
The vertidrain commonly used on fine turf areas has 300mm length tines which penetrate to a depth of 250mm. The tines used are either 18 no. x 12mm, or 12 no. x 18mm diameter, with either solid or hollow tines.
The vertidrain commonly used on football and general turf areas has 400mm length tines which penetrate to a depth of 300-350mm. The tines used are typically 12 no. x 25mm diameter; with either solid or hollow tines.
The surface disturbance is variable depending upon the level of lift used, typically varying from 12mm to 67mm and the experience of the operator.
(b) Drill
This is a very slow operation, but can be suitable for relatively small areas that are heavily compacted or are prone to drying out, particularly when a poorly developed root system is present. The equipment typically penetrates to 250mm depth (using 300mm long drills) at 100mm spacings with 12 drills forming the operating unit, e.g. Sisis 'Powadrill'.
(c) Compressed air
A hollow probe ( c. 30mm diameter ) which is hammered into the soil and penetrating up to 0.75m depth, e.g. 'Terralift'. It is sensible to ensure the air holes in the probe are no nearer than some 250mm from the surface, otherwise surface disturbance can occur due to the pressure of the compressed air blasting itself back to the surface.
Solid or hollow tine aeration prior to the use of compressed air can act as a 'pressure release valve' and reduce the chance of major surface disturbances occurring. Soil conditioners, nutrients or fungicides to treat fairy rings might also be applied using this method.
(d) Water injection
e.g. ' 'Toro Hydroject' - Fine jets of water are forced into the soil profile. The entry holes from the water jet are about 3mm in diameter, whilst the depth of penetration is said to be 100 - 200mm using the standard nozzles.
Water injection can be suitable for use on areas that are prone to drying out, especially with a poorly developed root system and as part of a summer aeration programme, particularly due to the minimal surface disturbance caused. Any disturbance, if it did occur, would invariably be evened out by the roller that is positioned behind the nozzles and by any follow up mowing which may take place.
Concern has been reported over the possibility of the injected water forcing fine particles to migrate to lower levels producing a fine layer or pan and also about the overall effectiveness of relieving compaction, especially on soil based greens. However, as part of an integrated approach to turf aeration this operation provides opportunities not available from mechanical penetration of the soil profile.