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What lies beneath a bowling green?

In the November 2013 issue, there was an illustration of what lies beneath many bowling greens that were constructed according to the generally accepted practices at the time. It has been included in this issue as well as a point of reference. Materials that are no longer available (ashes and clinker from gas works) are being replaced with graded broken stone to form a raft, with the largest broken stones, 40mm, at the bottom, 100mm deep, on top of which is a further 100mm depth of level layer of stones, 20mm size, and then 50mm depth of pea gravel, 10 – 15mm size, on the top.

We start off with broken stone that has air and water space between them and notice that the spaces, which cannot be dried out because there is no wind and sun down there, will be covered with a thin film of hydroscopic water, because they are touching the water that can move up or down and sideways (capillary water).

The layer of pea shingle is there to prevent the root zone mix, number 9, from moving down into the open spaces between the stones and any disturbance through the turf deeper than that 125mm (5 inches). So with newish greens from the last 25 years, the use of verti-drain equipment must be seriously considered, otherwise these fine materials will get mixed into the stone layers and finish up coming out of the silt traps that are positioned around the drain system.

This can be clearly seen when looking at the outlet covers and this is the first thing I look for when inspecting a green. The cost to rectify once you have penetrated through the root zone can be very, very expensive. So the use of verti-drain equipment must be seriously considered before use.

Still looking at the picture through the section of the green and point number 9 – this root zone is the food cupboard to continually supply the turf with basic materials and nutrients, plus whatever we apply to supplement the need of the grass. It is a very rich supply of elements and is a hive of industry of insects and bacteria breaking down the roots and anything in that area so it is available for recycling within the root zone.

We must realise that we take an awful lot of leaves off the green during the bowling season by using the grasses Fescues and Agrostis, which are summer growing grasses, and only produce leaves from April through to the end of September, after which they are producing roots to store and supply leaf material for the summer season.

So there is much maintenance to be done within that root zone, most of which is done during the winter months when there is lubrication in the soil from the winter rains. This enables roots to press through the soil in the root zone in search of the recycled materials.

I want to stress that through the illustration you can see that there would be a lot of space between the stones at the lower levels because there is this film of moisture attached to all the stones so that gradually the moisture comes back up to the surface where the turf is. The moisture contains a diluted solution of whatever is in the soil, which includes the elements that the roots can select when they need them for growth (turf culture).

The moisture is not lost very easily from the lower levels because there is a connection of water all the way from the surface of the green down into the drains, assuming there has been sufficient spiking to allow the winter rains in and irrigation to prevent the surface drying out. This is another reason why it is necessary to understand turf culture.

Water can move against gravity 31 feet high, so from this illustration, any water that is inside the construction can be drawn and will move upwards to the surface, and that is why when one is kneeling on turf that appears perfectly dry you can get wet knees.

A major reason for understanding that the construction of the green is a well controlled level of stones into which the excess water can escape (number 3) and the rest is inside the construction. So the root zone has to be continually maintained correctly to give us what we require to enable us to bowl as soon as possible after the rain has stopped.

So, if our maintenance is done properly, it can be realised that our job of turf culture is to be practised because we can only change water for air by spiking and chisel tining, equating to as much aeration as possible, allowing water further down into the root zone which can finish up at the lower end of the construction raft and so as it dries it can be sucked up again. That is what we do as greenkeepers – we change air for water and water for air.

There will be more on turf culture construction and maintenance in next month’s edition.