Biotic and abiotic factors interact with each other. For example low oxygen levels in turf (abiotic) will affect the health of the turf roots directly when the soil becomes increasingly acidic making it harder for roots to extract nutrients from the soil, and indirectly by reducing the population of beneficial bacteria (biotic factors) which play a role in breaking down organic material to release nutrition.
Some of the key factors that benefit or hinder a species in its quest for dominance are described as Environmental Stresses. It is these stresses that drive the evolutionary process and as such can be used by the bowling greenkeeper to create conditions that are more suitable for the desired species than for others. There are a number of ways for greenkeepers to manipulate the environment artificially, or indeed to take advantage of naturally occurring stresses, in order to alter the balance of the bowling green ecosystem in favour of the desired grass species. An understanding of Competition and Adaptation in eco systems will help you a great deal in developing a sound greenkeeping program for fine, perennial grasses.
However we choose to interact with this bowling green ecosystem (with or against nature) we will be working within a dynamic, constantly changing environment and it is vital that we understand this before stepping off into a new program of maintenance. In other words we need to think of our green as an eco-system. Getting to grips with some universal ecological terms will be useful.
In this article we take the soil samples you removed in Fix your bowling green Step1 and look more closely at them to discover what's going on under your green. This is one of the most valuable practices that any greenkeeper can undertake as it can reveal a wealth of information about the condition of your green that you could previously only guess at.
I once commented that there are only ever two real problems in bowling greenkeeping; compaction and thatch, with the rest of the myriad problems we come across being merely symptoms of these Big Two. Lately, I've revised that thinking, as the more I see of ill treated bowling greens the more I realise that, although they are important, even thatch and compaction are only symptoms too. The trouble we face in greenkeeping is that the industry wants us to treat symptoms. If we treated the root cause after all, we wouldn't need to buy half as much stuff! But before we get too carried away, let's have a recap on what bowls green compaction actually means.
The plant available water in bowling greens is determined by the physical characteristics of the soil. Most importantly the soil texture dictates the relative percentages of Macro, Meso and Micro pore space in the soil. This soil porosity also dictates the rate at which the green will drain. The balance between drainage and plant available water is one of the most critical components of a performance bowling green maintenance program. Here then is the very crux of all those arguments about top-dressing!
So far on our investigation into soil texture we’ve discussed the problems of building sand castles, why you shouldn’t let the Treasurer buy sand for you and a few other less important details like the complexity of sand, soil formation, particle size distribution, macro and micro soil porosity and we finished last time by looking at the famous Soil Texture Triangle. Here it is again:
The Soil Texture Triangle can look a bit off putting at first, but if you stick with me for a minute I’ll try to explain it.
The Soil Texture Triangle is a tool we can use to help define what type of soil we have. The ideal bowling green soil (rootzone) I described in part 1 of this series falls into the category Sandy Loam. Let’s see how that would look on the Texture Triangle.
The triangle gives names to various combinations of clay, sand, and silt. First of all, look at each of the 3 sides of the triangle. There’s one side to represent Sand (base of the triangle) and one side each for Silt and Clay, so we’ve covered the 3 mineral components of all soils. Now look at the numbers that are arranged symmetrically around the perimeter of the triangle. These correspond with the percentages of Clay (left), Silt (right) and Sand (base).
Now look for the arrow beside each mineral element. You will notice that each arrow points in a particular direction and that there are hatched lines within the triangle which run in the direction of the arrow.
When you have the percentages (by weight) of each mineral component of your soil sample, you can find the percentage for each component on the relevant side of the triangle and trace these into the interior following the direction of each of the arrows. To classify a soil sample, you find the intersection of the three lines that correspond with the proportions of your soil components. The triangle is divided up into eleven soil texture types by thick blue lines, making it easy to define your soil type.
The Soil Texture Triangle throws up a few surprises. Firstly, a soil with just 21% Clay is basically still classified as a Sandy Clay Loam indicating that it is very clayey. Even if it contains upwards of 50% sand.
A soil with just 75% sand and 15% clay is a Loamy Sand, meaning that it is predominantly sandy in nature.
Regardless of the final 10%, a soil with 90% sand is considered just Sand. Many bowling clubs have added so much sand over the years through top-dressing that they are now trying to manage a rootzone that is classified as sand
These surprises crop up for one main reason; samples are classified by percentage in terms of weight and not volume. In a later article I will go into a bit more detail on this…it’s important!
Particle Size Distribution tests are carried out in a soil lab using expensive, but really quite simple equipment. I have often set up make shift soil labs on golf course construction projects in order to monitor the quality of sands and rootzone materials being delivered to the site before they are used in the construction process.
PSD testing involves taking a small sample of a soil, drying it out completely and then shaking it through a series of graduate sieves before weighing the results from each sieve. The results can be easily converted to a percentage by weight which can then be translated into a PSD chart and the soil located on the Triangle we looked at above.
Here’s a video that shows the process:
The Sand Craze
In relatively recent times, say from the 1970’s onwards, greenkeepers, bowls clubs and golf clubs have become more than a little obsessed with sand. It’s true that some of the best greens are very sandy in their construction, but their success is due to more than just sandy-ness. As mentioned, the ideal rootzone of a bowling green is a Sandy Loam and the Triangle reminds us that the sand content of this could be anywhere between 55 and 85%. A suitable smooth, fast and consistent green can certainly be achieved with a maximum of 70% sand in the original mix. Please remember that we are only talking about the Mineral component of the soil at this stage and that sand varies widely.
The trouble with the promotion of high sand rootzones comes when people get it into their heads that if sand is good, then more sand must be better. A very high proportion of the greens built in the UK over the last 200 years would have started with 150-200mm (6-8inch) deep rootzones made up of local soil, rocks n all. The approach to improving these greens would quite rightly have included regular top-dressing with a sandy top-dressing. In recent times (1970’s onwards) we have seen a huge increase in the sand applied to greens in an attempt to improve them. Once a workable rootzone has been achieved, the relentless adding of sand every year must stop and for a very large number of clubs in the UK and further afield that time passed many years ago. Every ounce of sand added now is taking these greens further towards the extreme left side of the Soil Texture Triangle and is making greens unmanageable. They are inert, lacking soil microlife and stuffed full of hydrophobic sand that restricts moisture and nutrient availability.
The end of the 4 part trilogy?
This was supposed to be a trilogy, but now that it’s reached 4 parts, why not go the whole hog and add a 5th? In this series we’ve looked at a subject that is at the very core of good greenkeeping and the key to a Performance Bowling Green; Soil Texture. In the 5th and final part of this trilogy we’ll look at Sand Top Dressing.
Please leave a comment and/or questions below:
In the first part of this series we discovered that the ideal bowling green soil (or rootzone) will be 50% space, 5% organic matter, with the remainder (45%) being made up of mineral matter, namely Sand, Silt and Clay. These are the 3 universal mineral components of soil. Part 1 finished with an explanation of the soil fractions, 5 of which were sands of varying sizes.
In part 2 we found out a little bit more about sand and it’s behaviour as a drainage medium and we discovered a little more about how soils are formed. We finished by looking at the importance of sand particle shape and size in bowling green rootzones.
We are all familiar with clay as a substance in many different aspects of our lives. It’s used to make bricks, pottery and for modelling. If you’ve ever moved to a newly built house you will doubtless have encountered the problem of trying to make a decent garden out of the heavy clay soil that builders seem to carry around for the purpose of making your life difficult; or is it that all new houses are built in areas where there is heavy clay soil? Regardless of the solution to that conundrum, we often think of clay as big, chunky, unmanageable clods of red earth. The fact is though, that those whopping clods are actually made up of the Read more
Last time we saw how the perfect bowling green’s soil volume will be 50% space called porosity. We discovered that half of that pore space (25% of the soil volume) should ideally be filled with air (macro pores) and that the other half (again 25% of the soil volume) is for water (micro pores). We finished last time by discovering that the mineral part of the soil is actually made up of a lot of different sized soil particles called the Soil Fractions.
Today we’ll try to get a better handle on Soil Texture and discover how some of the soil fractions come about. In particular we will look at the complexity of sand, before getting a better understanding of how soils are formed in the first place. This will help us to understand the importance of sand in bowling green maintenance, but hopefully also to understand more fully, its limitations.
Soil Texture; the Mineral Fractions
In bowling green Nirvana, out of the remaining 50% of the soil volume, 45% would be Mineral and 5% would be Organic Matter. Today I want to concentrate on the 45% Mineral matter as this is where we can really influence the performance of our greens.
Now, if fast drainage was our only concern, then this would be a no brainer; it would seem logical to use just sand wouldn’t it? Well, that is the deeply rutted road that much of the fine turf industry has been heading down for a few decades now and I can tell you it is fundamentally wrong. Wrong because Read more
This subject is so important to the future performance of bowling greens that I would say it is essential for greenkeepers to understand this subject over any other.
The physical condition of the soil in the bowling green is the most important aspect of bowling green maintenance because it impacts every other aspect of green management. The physical properties of your soil dictate everything from drainage, nutrient availability and pH right up to green speed, green smoothness, consistency and ultimately whether or not the green performs to a high standard.
But what do I mean when I say Soil Physical Properties? This is primarily about 2 distinct qualities of the soil, Texture and Structure. Soil Structure relates to the way the soil holds together and there can be no doubt that soil structure plays a big role in green performance. However, soil structure is largely dictated by Soil Texture and for that reason I believe that the Soil Texture is the single most important aspect of green maintenance for greenkeepers to understand. Unfortunately, in my experience it very rarely is understood sufficiently to give the greenkeeper enough confidence in creating a program of work that majors on getting this right. But what do I mean by Soil Texture?
Animal, Vegetable or Mineral?
No, this isn’t just the question you ask your daughter about the spotty youth she has brought home for tea; it’s also the phrase that describes the make up of all soils. More accurately, soils are made of a base Mineral material mixed with Organic (dead animal and vegetable) material . The mix of the two dictates the soil’s performance in terms of it’s physical attributes like structural strength, drainage capability and nutrient and moisture holding capabilities.
In art and design, it’s often said that the white space around the images and text is often more important than the objects themselves, and a similar rule applies to good soil. In fact the perfect bowling green’s soil will be 50% nothing! By that, I mean that there should be lots of space in the soil between the soil particles. We call this nothingness, Pore Space or Porosity. Some of these pores are big (macro) and some are small (micro) pores. Micro pores are actually classified into two sub groups, but these basic groupings will be fine for now. The Mineral and Organic materials, might make up the structure of the soil, but it’s within the soil porosity that all of the action happens!
Last time we saw how the grass plants extract the 16 essential nutrients from the soil solution. The soil solution contains plant usable forms of the essential elements called ions and although these originate in the organic and mineral components of the soil, the plant can’t access them until they are in solution in the spaces between soil particles. That soil solution exists within the micro-pore space. The macro-pore space contains air and is essential for the supply of oxygen to support a healthy soil microbe population as well as for good drainage and resistance to compaction.
But what do I mean by soil particles?
The Mineral element of all soils is made up of a mix of 3 basic structural components called Sand, Silt and Clay. These are the basic soil fractions. The sand part varies greatly in particle size so we categorise it into 5 sub fractions for the purposes of soil texture classification. Here are the soil fraction classifications:
Stop to look at those sizes for just a minute, because they are quite mind boggling, especially at the lower end where the silt and clay is. Coarse sand has a maximum size of just 1mm, so imagine how very tiny a clay particle is at less than 2 thousandths of a millimetre! Well, that minuscule size hides a big secret and I introduced the intricacies of it when we looked at Cation Exchange Capacity last time. The tiny clay particles are where a lot of the nutrient ions are held within the soil, meaning they can be used by the grass plants later. Clay also plays a role in moisture retention which is critical for the health of the bowling green.
To finish today, I will leave you with a very useful visual representation of the relative sizes of these soil particles courtesy of the University of Colorado and next time we will move on to the importance of getting soil texture right in your bowling green.