Erwin Beltman was the head groundsman for stadium De Kuip in the Netherlands between 2013 and 2022. In that period, the field was elected 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 the aerating, dressing and fertilizing of a field.
With the temperatures rising, aeration, fertilising and dressing will now be dominating the agenda of most groundsmen and greenkeepers. As fields are coming out bumpy or uneven after the winter break, this work is crucial at this time of the season. The bumpiness or unevenness is mainly caused by the different types of grass that are now dominating the surface. In addition to the desirable sports field grasses that were selected at the time of sowing or overseeding, unwanted grasses have used the period of relative rest in terms of usage and the less favourable growing conditions for sports grasses in particular, to develop and multiply. Cutting the grass back will help, but that requires mowing multiple times during the week. Especially for fields at grassroots level, this is a luxury that few clubs or municipalities can afford – perhaps only those that use a robot to mow the field. However, these come with consequences too, that I will highlight in the future. The easiest thing to do is to use the land roller to flatten the bumps, but the flip side of that is that you also compact the soil. Unless you aerate the field, you’ll pay the price when it starts raining. Therefore, I advise to roll the field and then aerate and sand it.
Air brings life
Now that the grass is coming out of its relative hibernation, it will take full advantage of the arrival of spring and the improving conditions. More air in the top layer will be important. Good turf requires the top 60 cm of the soil to be easily rootable. Grass is very strong, but it needs to be tickled every now and then to stimulate the growth of new roots. How this can be achieved is addressed in this article.
There are various ways to introduce oxygen into the soil. One of the solutions is the well-known Vertidrain. Another one is the Pro Core. Both machines break the soil open. They can do so up to a depth of 40 cm. A shaker aerator can even go to as far as 50 cm deep. Where the Vertidrain pens hit the ground, the vibrating aerator cuts the top layer with rotating blades. When the blades do not go higher than the first few centimetres, we call it slitting. I recommend subjecting a field at least twice a year to a beating, depending on the conditions.
Aerating a field comes almost automatically with dressing it. This fills the resulting slots of holes through which water can drain into the bottom. Roots often use the space to grow. In addition, the surface becomes atrophied, while a sanded field is less slippery. The size of the sand particle is key when selecting the sand. The ideal top layer for sports is 15 to 20 cm thick with an M50 grade of 180-250, a loam content of <10% and containing about 3% organic matter. If you are going to sand, it is advisable to use a sand with an M50 rating of 180-230, a loam content of <5% and an organic matter content of less than 1%. In addition to these technical specifications, it is also important to determine the source of the sand. I’ve seen sand that still had bits of shells in it. I can tell you: using that will hand players something to complain about on a silver platter. Irrespective, players are very sensitive to maintenance work anyway. They don’t like seeing the holes made by the aeration for fear that their studs will get caught in there. My advice is to plan the dressing a few days prior to the game.
Firm thanks to fertilising
Particularly after such a slow start to the year that we are currently experiencing, the grass could do with some help by fertilising it. Planning for doing so will be a delicate exercise, as the flip side to it is that, when it kicks in and is followed by some favourable weather conditions, you’ll end up with having to mow it regularly to avoid the grass getting too long to play on. To fertilise or not to fertilise is a tricky question. For professional sports, this is obvious, as the results in the coming weeks can be vital or detrimental to a season. Without taking anything away from the competitiveness at grassroots level, you’ll have to ask yourself what the added value will be when many fields will literally be removed in just over a month’s time, when they’ll undergo major renovation.
The most well-known fertiliser contains a mixture of nitrogen, phosphate and potassium. These three main elements ensure strong and healthy growth and that the grass will thrive. Nitrogen fertilisation is especially important, but the grass will be sensitive to the quantity given: it should not be too high or too low. If this is the case, it will inhibit root growth. The need for nitrogen depends on the availability in the soil as well as the weather conditions. Both are difficult to estimate, which means that you have to assess the growth as well as have experience with the particular turf.
Phosphate supply also needs careful consideration. Most of the phosphate the grass takes in, it will get from the soil itself. An extra dose will inhibit root growth instead of stimulating it. Phosphate moves slowly through the soil, so roots will have to grow towards it.
Potassium ions that are in the grass ensure a better moisture balance and metabolic process. A dose of potassium will therefore stimulate the growth and quality of the grass.
Now that the number of hours of sunshine and the intensity of the sun are increasing, irrigation will certainly become necessary. If you don’t irrigate, it is likely that your turf will burn, especially when you have fertilised it. Grass is robust, but the combination of an excess of fertilisers and a shortage of water is something it cannot handle.
The question remains whether much additional irrigation is necessary. With the first quarter of this year going down in the books as one of the wettest on record, I assume most fields now have enough moisture in the soil to subsist. That is why it is now important that we retain that moisture as much as possible in the coming period.
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.
In May I will discuss the stress that groundsmen and greenkeepers experience at this time of year and how best to deal with it.