By Laurence Gale
Regular and seasonal aeration maintenance operations are essential to ensure turfgrass quality is maintained throughout the playing seasons of most fine natural turf 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 the club members / users, often resulting in lost revenue.
Why do we need to Aerate?
All grass swards are grown on soil / sand profiles that provide the appropriate environment structure for plant growth. This growing medium, commonly known as soil, is made up of proportions of soil solids (mineral and organic material) and soil pores (water and air).
An example of the volume composition of a loam soil is represented in Figure 1
Figure 1 Loam soil
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 (Brady & Weil 2002). It is in these pore spaces that air and water circulate, and help provide the plant with the necessary nutrients and 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 by compaction or filled with water that we see deterioration in pitch playability and resistance to wear.
However, the main contributing factor that reduces and damages pore spaces in soil, is compaction, 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 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) when playing in the rain and bare soil surfaces (Adams & Gibbs 2000). Compaction has been measured down to depths of 120-150mm on horse racing courses.
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:
Cone penetrometers are 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 measures the impact of a weight dropped from a predetermined height.
Other indicators of compaction are changes in visual appearance, performance and physical properties of the soil and surface:
Plantain weeds (Plantago major) seen in the surface generally indicate compaction problems.
- An anaerobic soil condition is formed that reduces root growth and restricts micro organism activity.
- Decreased water infiltration and reduced hydraulic conductivity that leads to surface water logging and ponding.
- Saturated soils have reduced soil strength, which often results in loss of ground cover.
The above conditions will adversely affect pitch playability in many ways, reduced ball speed, ball bounce, ball roll, player safety and, in the long term, damage the surface 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:
- Using solid tines (Hand forks, Pedestrian and tractor mounted)
- using hollow / coring tines (that remove soil cores from the soil)
- Using flat / star tines
- Disc / blade implements (linear aerators)
- Compressed Air and water systems
It is essential to include a variety of aeration techniques to prevent pan layers being created. This usually happens if you continue to use the same aeration tine / corer set at the same depth, and will result in a compacted layer forming at the base of tine / core depth. Most turfgrass managers try and vary methods of aeration, 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 and allow 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 pressure air and water aerators that offer deeper aeration than conventional aerators. The following picture demonstrates the use of air penetration on a golf green.
When do we aerate?
Aeration should be carried out on 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, de- thatching, and topdressing and over seeding 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.
- Improves soil surface drainage (water infiltration).
- Helps to increase soil temperatures
- Increases soil pore space.
- Allows gaseous exchanges in the soil (oxygen, carbon dioxide) that improves root depth (growth and development).
- Aids integration of top dressings into soil profile
- Aids the breakdown of thatch /organic matter
- An aid to promoting better surface levels that will increase ball roll /speed
- Aids surface firmness / dryness thus increasing ball bounce and surface grip
The table below depicts some of the aeration machinery used in the turfgrass profession. There are many more makes and types of equipment available, including hand held tines, forks, pedestrian aerators, and large tractor mounted aerators.
Bowling greens / Croquet / Golf greens
Coring machine Sarrel rollers
Golf greens / Tees
Solid tine Compact Vertidrain Verticore machine
Football / Rugby / Golf fairways /Horse racing and polo fields
Vertidrain Linear Aerator
|Without effective aeration programmes we are likely to see pitches turning into quagmires and unplayable surfaces.||Using a variety of aeration techniques and machines we should see pitches playable all year round.|
Adams, W. A. and Gibbs, R.J.(2001) Natural Turf for sport and Amenity; CAB International.
Brady, N. C. and Weil, R.R. (2000) The Nature and Properties of Soils; (thirteenth edition); Prentice Hall.