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To outsiders, greenkeeping looks like an easy job; just walking up and down with a mower in the sunshine for an hour or so every other morning in the summertime. Of course, we know it’s much more complex than that. Alongside the mowers in the shed, there are usually one or two other complicated looking machines, and it is here that we get into the next most important consideration in greenkeeping: air!

Importance of aeration

It surprises non-greenkeepers when they find out that half of the volume of a quantity of well-balanced soil will be stuff they recognise as soil and the other half is invisible, it’s just space between the individual clumps and particles of mineral and organic matter. The air space in the soil is vital for retaining enough oxygen in the soil to encourage and support a massive population of aerobic (oxygen loving) fungi, bacteria and other microbes which keep the nitrogen cycle going and perform a huge range of other functions in the soil which are beneficial to our grass plants. Aeration pore space is also critical for good drainage performance. The opposite state to well-draining soil is called compaction which is the name given to soil that has had a lot of the air squeezed out of it either by foot traffic or ironically, the constant weight and pounding of the greenkeeper with the maintenance machinery.

Common Aeration Methods

There are a variety of aeration methods, utilising many different types of steel spikes or tines.

Compaction relief

One of the main aims of sub surface aeration is to relieve built up compaction in the soil. Soil becomes compacted when the structure is damaged due to excessive downward pressure from foot and maintenance traffic. Heavier (high clay and silt content) and wet soil is more susceptible to compaction, but all greens suffer from it to some degree. The edges, heads and walk on/walk off points are particularly affected usually. Symptoms of compaction include poor growth, thinning turf (lack of turf density), annual meadow-grass ingress, moss ingress (due to space created by thinning turf) and yellowing of the grass plant leaves due to poor oxygenation and nutrient starvation. The relief of compaction is essentially a process that re-introduces air to the compacted soil. In the process, we might need to break up hard layers or pans. To relieve built up compaction in the soil, we use a variety of aeration methods depending on the severity of the problem and the time of year.

Solid tining

Solid tining is a useful method of aeration for breaking up compacted layers near the surface and re-introducing air to the soil. The holes created will allow for better water infiltration and facilitate the exchange of built-up sour gasses in the soil for life giving oxygen. This immediately encourages the multiplication of beneficial soil microbes and adds to their ability to break down organic matter in the soil to produce plant available nutrients. No soil or turf is removed during this operation but be vigilant for turf lifting if the green is thatchy. In these circumstances, a condition known as root break can occur where the grass roots donโ€™t penetrate much deeper than the thatch and the turf is susceptible to lifting at this horizon. Solid tines come in a range of sizes, but are always round profile to minimise the chance of old tine holes opening up in dry conditions. Variations include pencil tines, micro tines and mini tines.

Hollow tining

Hollow tining or hollow coring as it is often called is a very popular method of aeration used all over the world by greenkeepers. Hollow tining has three main functions and these are to aerate the soil/turf i.e. to increase the oxygen in the soil, to remove a certain amount of thatch from the turf, and to facilitate soil exchange i.e. to remove some of the native soil to allow replacement with another medium such as sand. As the name suggests, hollow tining utilises hollow metal tines that physically remove a plug of soil/turf from the green. The plugs (cores) removed by hollow tining are essentially miniature profiles of the top 100-125mm of the soil, so you should be able to pick one up and find out quite a lot about your green. At the top, you will see the grass species that dominate an particular area and you should be able to tell if they are growing healthily by their colour and general condition. Below that you will be able to determine how deep and dense the thatch layer is, what the soil texture is like and how deep the roots are getting down into the soil. In addition to the primary functions of hollow tining, other benefits of the operation include opening the surface to allow better entry for water, new seed and fertilisers/soil amendments.

Slit tining

A much overlooked method of aeration that has thankfully started to see a resurgence is called slit tining. This method lost favour, due to new, more effective looking machines coming to the fore over the last few years. However, as a means of dealing with compaction in bowling greens it is one of the most important aeration methods available to the greenkeeper. As the name suggests, slit tining employs long, thin, knife-like tines to penetrate deep into the soil. These are usually fitted to a disc or drum and the whole process is much gentler than that of the punch-like, crank shaft facilitated action preferred when hollow or solid tining. Over the playing season, the pressure from foot and maintenance traffic can result in soil compaction, particularly around the edges of the green and on heads. This can be worse in wet conditions and over the season it builds up. Of course, during the playing season you won’t be popular if you suggest any sort of disruptive aeration operation, so summer aeration tends to be restricted to sarrell rolling and perhaps an occasional pencil or mini tine. This makes it all the more important to compensate for compaction during the close season and deep slit tining is by far the most effective way to do this on a bowling green. The tines get deep into the green without going too deep and disrupting the drainage function of the sub-grade. The effect of deep slit tining is cumulative, with each pass adding to the effect of creating air space in the soil and fissuring hard, compacted areas and layers. You will find that the tines don’t get all the way in on the first few passes, but as time goes on, the green slowly becomes less compacted and the tines go in deeper, until you achieve full depth easily with no extra effort on your part. October to March is the optimum period for this work for de-compaction. It’s not advisable to continue too far into the spring as slit tine marks can dry out and start to open up in hot, dry weather conditions.

Photographed: Hollow tine cores can reveal a lot about the condition of your green