In the previous articles in this series, we’ve discovered how to evaluate performance by simply looking for visual indicators on the turf and by gauging some of the functional attributes of grass plant communities when they form turf.
Before we move on to the final stage of this series where we will look at some of the latest and most objective techniques for performance measurement, I wanted to stop for a moment to consider what lies beneath the green layer.
All of the functionality and therefore performance of the bowling green depends on healthy turf and turf is of course not just grass plants. Turf is a construct of a healthy grass plant community containing millions of individual plants, growing in a medium that is suited to sustaining healthy growth and reproduction. The medium is, of course the soil our greens are built on; but what is soil?
If you look at the pie chart at the top of the article you will see the proportions of what I think of as the perfect soil.
In the diagram you will see that 45% of the soil is made of Minerals. The mineral component of soil is usually made up of a mixture of 3 main groups and these are Sands, Silts and Clays. A suitable mixture of these is critical to the soil’s performance as they dictate the soil’s ability to provide nutrition and moisture to the grass plants and suitable drainage. The mix of sand, silt and clay defines the soil’s texture.
The organic component will ideally be around 5% and this is made up of living organisms, micro-organisms and dead, decomposing and already decomposed plant tissue (humus). The organic material is added to by the plants themselves as they produce thatch and the soil organisms break this down to release plant nutrients.
Then there’s the remaining 50% of the soil to look for, but if you do, it might cause you some confusion, because in the ideal soil the remaining 50% of its volume will equate to nothing at all. In fact it is 50% space, or soil porosity to give it the correct name.
Ideally half of this space will be made up of small spaces called micro pores and large spaces called macro pores. The micro pores hold the soil solution which is a mix of water and plant available nutrient ions and the macro pores provide air space and this is where all of the drainage occurs after heavy rain. This air space keeps the soil well oxygenated so that it can sustain a huge population of soil microbes; around 1 billion in a teaspoon of soil.
Compaction is of course one of the big issues in bowling green maintenance and people are always looking for ways to prevent or minimise its occurrence.
Compaction happens to a greater or lesser extent depending on soil type. At the two extremes of this are Clay and Sand.
Think of a potter wetting some powdered clay to throw a pot and you can immediately picture the compaction and drainage properties of this soil type; it compacts very well when wet and clay pots don’t allow drainage at all; and when clay soil is wet this is pretty much the case under your green too. Clay is a very good moisture and nutrient retainer.
Now imagine running on to the upper reaches of the beach, up near the dunes and it’s hard to imagine how this highly mobile sand could ever be compacted. Due to the particle shapes which are round, there is a huge amount of air space between particles which doesn’t allow for any level of compaction.
The above examples are, I think, the reasons that clubs have been all too eager to jump on the sand band wagon over the last few decades; more sand seems to equal better drainage and lower compaction.
The best bowling green soil lies somewhere between the two and is a sandy loam as discussed here.
So although individual actions like foot and maintenance traffic can be said to cause compaction, the underlying soil holds the real answer.
It’s essential for strong teeth and bones; I know that much from school, but where does Calcium fit into a bowling green maintenance program?
When we hear discussion of soil nutrients, it is usually in terms of Nitrogen, Phosphorous and Potassium; the famous NPK, that we see written on fertiliser bags.
However, there are another 3 major nutrients; these are Calcium, Magnesium and Sulphur.
However, the most overlooked macro or major nutrient in bowling green maintenance is Calcium. Calcium is needed by plants to grow and maintain health. It is a key constituent of cell walls.
If calcium availability is low or compromised grass plants can experience a range of difficulties
- Once fixed, calcium is not mobile in the plant. It is an important constituent of cell walls and can only be supplied in the xylem sap. Thus, if the plant runs out of a supply of calcium, it cannot remobilise calcium from older tissues.
- If transpiration is reduced for any reason, the calcium supply to growing tissues will rapidly become inadequate.
Calcium plays a very important role in plant growth and nutrition, as well as in cell wall deposition. The primary roles of calcium are:
- As a soil amendment, calcium helps to maintain chemical balance in the soil, reduces soil salinity, and improves water penetration.
- Calcium plays a critical metabolic role in carbohydrate removal in plants.
- Calcium neutralises cell acids.
Therefore the role of calcium in plants must not be overlooked.
In Performance Bowling Greens, a practical guide I go into this in much more detail.