In the performance evaluation of the bowling green there are visual and functional measurements we can make to ascertain the likely performance of the green. Colour and Smoothness are the last two visual components we need to look at before moving on to the functional attributes we can measure. On the face of it, colour and smoothness seem like fairly innocuous elements to focus on; almost too obvious you might say. Let's see if they are more important or even different to what we previously thought.
So far in this series of articles on the subject of bowling green performance we have used some of the common visual clues to assist in our evaluation of the turf. Today we'll break from that to dig a little deeper into the physiological aspect of the different turf grass species that influence what we see on the surface. Turf Grass Growth Habit can play a big role in the ultimate performance of the bowling green. so let's get started on indentfying the main differences.
In part 4 of our series on the Performance Evaluation of the Bowling Green we move on to examining turf texture. Texture is closely tied in to some of the other aspects of Bowling Green Performance we have looked at so far in this series. Texture is one aspect of turf management that the greenkeeper can influence greatly, but seems so simple that it is often overlooked.
In the performance evaluation of the bowling green, one of the key factors is turf grass density which is important due to its ability to influence other performance factors and in monitoring bowling green and soil health generally.
The Performance Evaluation of the Bowling Green we embarked on last time relies on our ability to appraise a range of factors. Some of these are purely visual, while others are functional and can be quantified more readily. The trick lies in gaining the experience to merge the visual data with likely performance traits. Good old fashioned greenkeeping and the greenkeeper's "feel" for the turf are still as relevant as they've always been. Today we get started on the process of evaluating bowling green performance.
By far the best selling of my eBooks available on this site is Performance Bowling Greens; it out sells all of the others by 10-1. Bowling green performance can seem a bit sketchy and hard to tie down to any sort of measurable parameter, but that's more to do with the lack of a joined up approach to the subject in the industry than it is a lack of measurable components. This article introduces the subject of the Performance Evaluation of the Bowling Green.
Sand Top Dressing - that ubiquitous and apparently simple greenkeeping operation indulged in by most clubs annually is actually a much more complex operation than most give it credit for. In this article John Quinn explains the mechanics of top-dressing. He explains what it can and can't do and why you must understand some soil science before top-dressing is considered.
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 tiniest of particles in the soil, less than 2 thousandths of a millimetre in diameter.
Along with silt particles, which are relative giants at up to 5 hundredths of a millimetre in diameter, clay and the very fine sand fraction (0.05-0.10mm) make up what is known as the Fines in the soil. The fines are very important in any rootzone mix, because they are largely responsible for dictating the soil’s ability to provide water and nutrients to our grass plants. This doesn’t mean, however, that more fines make a better soil, it just means that we need to be very aware of the balance of fines to the other 4 sand fractions. The measure of this spread of particles in any soil or rootzone sample is called the Particle Size Distribution or PSD for short.
High performance rootzones will typically have no more than 10% of the particles in the Fines category. Remember that we are only measuring the mineral element of the soil. For PSD Analysis, all of the organic material is burned off before the dried mineral component is shaken through a series of graded sieves and measured.
Particle Size Distribution (PSD)
In my introduction to this series of articles, I said that an understanding of Bowls Green Soil Texture, was probably the single most important piece of knowledge a greenkeeper can have as it impacts on almost everything else in bowling green maintenance. Well, I can probably refine that statement to simply Greenkeepers must understand PSD. Particle Size Distribution really encapsulates the knowledge of soils that greenkeepers would do well to have in their heads ready for instant recall. This knowledge can help you work out just about anything else that you need to know about the performance of your bowling green. But what is PSD? Have a look at the charts below:
The upper chart shows the PSD for a typical (natural) soil on the links land on the East Coast of Scotland. It’s actually from a very famous golf course. The first thing we notice is that 80% of the particles are in a single fraction, in this case Fine Sand. This is typical of links soils. You will recall from part 2 of this series that beach sand is graded by the wind with the finest particles being blown furthest from the shore. The perfect balance of PSD for the formation of tight knit, dense bent and fescue turf just happens to be found on the Links land that we find around much of the UK. In this example, the mineral element of the Links soil is made up of 80% of the Fine Sand fraction, or sand particles falling between 0.10 and 0.25 mm in diameter. You will also notice the Fines are made up almost entirely of Very Fine Sand, with Clay and Silt barely registering on this graph. Again this is typical of Links soils, as the mineral element is almost entirely made of sand, weathered down from seashells.
In the second graph we can see a typical PSD analysis for a manufactured rootzone material for a USGA (United States Golf Association) Specification golf green. Again you will see a very large percentage of the particles falling in one fraction. This time around 70% of the sample is made up of Medium Sand (0.25-0.5mm). In this case because we are working with a quarried sand material, the fines contain some silt and clay, but the 3 fines combined still make up less than 10% of the rootzone. Incidentally, the reason for specifying Medium Sand in such rootzone materials is to do with Soil Hydraulics (water movement) and the need to build greens economically. The natural links soil might be several feet deep, where as the manufactured green will have no more than 12inches of soil depth. This creates a need for a greater gravitational pull in order to maintain drainage performance. The bigger aeration pores created by Medium Sand means that a 12 inch deep soil can perform as well as a 2 or 3 feet deep soil predominantly made up of Fine Sand.
PSD and Drainage.
The benefit of having a very uniform (70-80% falling in one fraction) sand in the rootzone mix is that it creates a lot of air space in the soil. Remember we talked about the woes of trying to build a sand castle with the ever shifting sand near the dunes? Uniformity in terms of particle size creates air spaces and makes the sand very mobile and resistant to packing down. The air spaces (macro-pores) in the soil are where the oxygen is kept in the soil to help nurture a big population of soil microbes and is also where the drainage occurs. Excess water is pulled through the rootzone by gravity and drained away.
PSD and Moisture Retention
Of course, if we had a rootzone that was too uniform in PSD, then our bowling greens would be very difficult to manage as they wouldn’t even be stable to walk on, let alone support a population of grass plants. This is where the mix of different fractions comes in. We saw in part 2 how Builders sand relies on a wide spread (low uniformity) of particle sizes to enable it to lock down and bind together, well our rootones need a little bit of that ability too, so there will be a spread of particle sizes on either side of the dominant uniform fraction, always remembering that we need to keep the Fines around 10%.
Although soil stability is important, it is the role that the mixture of particle sizes plays in moisture retention that can make or break a bowling green. We saw in part 1 that the variance in soil particle size creates soil porosity; Macro Pores (large spaces between particles) help with soil aeration and drainage and Micro Pores (small spaces between particles) provide moisture retention. It is from these small pore spaces that our grass plant’s roots suck up the soil solution to get at the water and nutrients it needs to grow.
Fines and Nutrients
The weathering of the minerals in the soil actually provides some of the essential plant nutrients, but in part 2 we discovered that, regardless of the type of soil particles we have in our soil, there is no way that our grass plants can access the essential nutrients until they are in solution in the soil water. The smaller micro pore spaces between the finer soil particles are key to the plant’s ability to access these nutrients. As gravity pulls all of the excess moisture out of the soil (macro pores) after rain, plant available water is retained in the micro pores and un-affected by gravity.
The 4 Part Trilogy
Finally for today, the tiny clay particles actually bind many of the nutrients in the soil, preventing them from being flushed out of the rootzone, meaning that the plants can access them over the longer term. We touched on this in part 1 when we discussed Cation Exchange Capacity.
I’ll leave you today with the famous (in the circles I move in ;-( ) Soil Texture Triangle, a tool used by soil
geeks specialists to define soils based on their particle size distribution. It’s a handy tool, but maybe a bit daunting to use at first. I’ll explain it next time.
This started out as a 3 part series, but there’s more to do yet, so in the 4th part of the trilogy :-), we’ll look deeper into the soil texture triangle and start to see where this all links up with soil structure, soil management and bowling green maintenance.
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 it overlooks the need for a firm, fast, true bowling surface, 100% covered with a tight knit turf consisting of the finest of grasses.
The Complexity of Sand and what it tells us about Soil Formation
Before we go deeper on this thorny subject I have a question:
Q: Is all sand the same?
Think about the different places you’ve encountered sand. The most vivid of these memories will be on some golden beach. Did you ever try to build a sand castle on the higher reaches of the beach? Building a sand castle with that stuff is impossible, it just flows right back into a non-descript mess. When you walk in it, it just moves away from you and fills your shoes with gritty particles. Lower down on the beach where the sand is wet, then you have a chance of forming some battlements and maybe even to dig out a moat before the tide comes back in to engulf your handy-work.
Between tides, some of this wet sand will be dried out by the sun and whisked up the beach by the wind to add to the ever changing dune system at the top of the beach. The wind tends to drop the bigger heavier sand particles first whilst the finer, lighter sand particles are carried furthest up the beach to the dunes and beyond. The dunes are sufficiently undisturbed by the tide for pioneer plants to get a hold in the sand. These are hardy species that can withstand the constant wind and spray and have toughened, spiny leaves that resist drying out in the constant wind and bat off the worst of the salt spray to eventually develop into a community of plants. The roots of these plants cause the dune sand to bind together into more stable structures which get higher and wider with each barrage of wind and tide.
Just inland from the dune system is the Links land. Literally the land that links the seashore and the cultivatable land inshore. In Scotland you might also hear of the Machair, a richer, more easily cultivated meadow land beyond the dunes. The Links and the Machair were once the dunes and over time, the continual cycle of life and death of the plants and animals of the area and the addition of wind blown seaweed would gradually lay down more and more organic material, slowly building the once purely Mineral sand into a more complex soil (a mix of mineral and organic material); technically in most cases a Sandy Loam.
The early stage of soil formation is called weathering and the parent rock or mineral material will be eroded and broken down into smaller parts by the rain and wind. In our example the parent material is purely the remaining shells of dead sea creatures like crabs, whelks and oysters. Gradually these shells are broken down into smaller pieces by the wind and tide action.
Sand Particle Shape, Sizes and Distribution
During this process the sand particles are worn from angular shards of shell to more or less spherical particles over a long period of time. When the sand particles eventually become small enough to be blown by the wind they are gradually moved up the beach and this is where a process of grading takes place. As we saw, the smallest (and lightest) sand particles will be carried further up the beach than the larger, heavier ones. This has the effect of grading the sand into bands of the same particle size. The combination of their spherical shape and uniform size makes the particles in the dry upper reaches of the beach very mobile and that is why you sink into the sand near the top of the beach and why it seems to move and flow around you.
Incidentally, this is also what makes sand drain well. Particle Size Distribution (PSD) is a key measurement in the specification of fine turf rootzone mixes.
But, what about building sand?
The other place you’ve probably encountered sand is at the DIY store. The sand you buy to mix concrete or cement or lay slabs is not like the sand you buy for drainage. If it was to behave like the dune sand, your paving would sail away in the first rain storm and your house would fall apart brick by brick!
For a start building sand has a wide spread of different particle sizes and a lot of the particles are angular or semi angular. This sand is typically quarried and not sourced from the beach. This makes it bind together very well and also makes it terrible for drainage. Ironically a lot of it isn’t sand at all. Building sand will contain quite a high percentage of finer silt and clay particles which add to the binding effect.
This should prove once and for all that you shouldn’t listen to the Treasurer when he says he’s found you a supply of sand that is half the price of the usual stuff!
The perfect rootzone.
Next time I’ll introduce the remaining minerals of Silt and Clay and we will look at Soil Texture in terms of its role in bowling green performance. In the process we will discover that the greenkeeper’s knowledge of soil particle shape, size and distribution holds the key to providing the perfect balance of drainage, nutrition and moisture to help us develop the ultimate high performance bowling green that performs like an F1 car but is as predictable and as easy and economical to maintain as the family hatchback! Finally we’ll link this all up and develop an understanding of the folly of continually top-dressing bowling greens every year.