Erwin Beltman was the head groundsman for stadium De Kuip in the Netherlands between 2013 and 2022. In that period, the field was voted the best stadium field in the Dutch Eredivisie eight times in a row. These days, he works as a consultant and shares his experiences about achieving good turf pitches on Sportsfields.info. Today he discusses aerating a turf surface.
Healthy turf requires sufficient light, water, temperature, and nutrients but also oxygen, hence the regular aerating of a surface is important. Oxygen in the soil nourishes the roots but also helps break down the organic matter present. As a rule of thumb, a percentage oxygen level of 10 to 12% is preferred. If the percentage drops below this number, the grass root will die from a lack of oxygen, which ultimately results in insufficient moisture and nutrients being absorbed. Furthermore, a lack of oxygen will hamper the decomposition of organic substances. As a result, unwanted substances can form and grants sponge felt the opportunity to thrive in the surface.
However, aerating a field also helps to remove the gases that form during the process of decomposition of organic substances. In principle, this occurs via capillary rise from the groundwater, and it works its way out through the pores of the turf. But, given this year’s abundant precipitation, those pores will now be largely filled with water. This hinders the removal of gases from the subsurface. At the same time, the (frequent) treading on the turf will close many of those pores, especially under the pressure of heavy-duty maintenance vehicles. The type of soil, the groundwater level and the degree of compaction determine the extent to which the pores fill with water. Aeration is therefore a delicate activity and one whose timing must be carefully planned.
The chosen method of aeration can also help to simultaneously loosen the soil, combat thatch, improve water permeability and achieve greater effectiveness of dressing and overseeding. It can also stimulate good root penetration and better rooting depth for the sports grass, so that it can compete better with annual meadow grass. That is precisely the point of departure for pesticide-free or integrated turf management (ITM).
Viewed over an entire year, the best effect is achieved by varying the approach method. This prevents the formation of a disturbing layer that negatively affects the natural water drainage. This variation in approach also requires an investment in different types of solutions and associated equipment. Although modern technology can be a great help, it can quickly become expensive. This means that many clubs are dependent on the municipalities, the maintenance company or a contractor. However, I advise the club to ensure that a certain quality is strived for rather than the work being carried out at predetermined times or at a predetermined frequency. A good healthy turf can only be achieved by a tailor-made approach.
The most basic activity is cutting rolling or slitting. This activity works the top 10 cm of the top layer. Depending on the solution chosen, this is done with knives, chisels or pens. The activity is best carried out every 14 days in dry conditions and is most effective when the direction of travel is varied continuously, as this will strengthen the turf.
If you want to achieve an effect at greater depths, you can consider deep aeration. This can be done with a vertidrain or with a vibrating cutter. Both machines can work the soil to a depth of more than 50 cm and both also pry off the top layer. The downside, however, is that they both require a somewhat heavier tractor. In addition to the significant investment, incorrect use can contribute to compaction.
While the vibrating cultivator has knives rotating on an axle that shake as they move through the soil and thus pry, tear or break open the soil, the vertidrain uses pins. They make a prying or breaking movement, while the pins are drilled into the ground.
Different pens and knives
There are different types of pins for pin rollers and vertidrains. For example, there are solid pins for machining at greater depths. The downside of these pins is that they can lead to some compaction around the hole. Especially in clay and loam soil, rooting or water permeability will be negatively affected.
Hollow pins help bring up some soil to level the field. These pins are also suitable for introducing material into the soil to improve the soil.
Processing with both solid and hollow pins increases the chance that annual meadow grass will grow in a good turf, especially in the spring when sand or dressing soil is dragged in.
Knives or chisels cause the least disruption. They also create a larger surface area for air exchange. Cutting the sod promotes the sprouting of the turf. However, the effectiveness of those blades depends on how they are driven. In addition, it is the least accurate method.
Points to note
Aeration is best done under dry conditions and when the soil is sufficiently dry. A frequency of twice a month is recommended, but ultimately, the soil type, intensity of use and weather conditions are decisive. Before you start aerating, first determine the location of the irrigation and drainage to avoid puncturing or causing a leak. Also keep in mind that the optical end result will not please everyone. Aerating a field will certainly make it look a lot less attractive. It is the irony of our profession that we continually cultivate beautiful turf to guarantee that quality in the long term. Only the latter is what matters to the layman. However, there is no other activity whose optical result initially suggests otherwise. Having a good conversation with the management, technical staff and players prior to commencing, prevents them from venting wildly once the job is done.
Erwin Beltman is a former groundsman of Stadium De Kuip in Rotterdam. Between 2013 and 2022, the stadium field was voted the best stadium field in the Dutch Eredivisie eight times in a row. Today, he is director of Master in Grass and consults and advises fellow groundsmen.
The views or information he shares in his articles are not necessarily the views of the publisher
Next month I will discuss the various options and consequences of choosing a hybrid turf system.