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Turfgrass Physiology; Diffusion, Transpiration & Osmosis

In nature, it is often said that things will tend towards chaos and this is described by a mechanism known as Entropy. In one of his recent TV programs, Professor Brian Cox demonstrated this using a sand castle as his example. Simply put, Entropy says that due to natural movement by wind and weather, sand is highly unlikely to form itself into a sand castle. However, a sand castle is highly likely to be converted to a pile of sand. This is Entropy in action and it seems to say that nature prefers chaos to order; but, whose description of “order” are we using for this?

What if nature was viewing the sand castle as chaos and was instead trying to make order of it by turning it back into a nondescript (as far as we are concerned) pile of sand?

The fact is, that instead of chaos:

Natural systems will tend towards equilibrium.

A common example of this tendency towards equilibrium is the wind we feel on our faces every day. Wind is caused by uneven warming of the earth’s surface. Where one area is warmed more directly, the air above it will rise. This creates a space for cool air. When that cool air rushes in to fill the void, we feel it as wind.

So, although these processes might look like chaos to us (when our sand castle is ruined), it’s really the opposite to chaos that’s happening:

Natural systems will tend towards equilibrium.

This is the way of nature and it informs and drives a lot of what goes on in and around the grass plants on the bowling green.

Today, we will look at two mechanisms of turfgrass physiology that are active in our grass plants and soil and that follow this tendency towards equilibrium, without which our turf wouldn’t be able to grow and thrive.

Diffusion

The first of these mechanisms is called Diffusion which is a term you will find throughout science. In broad scientific terms Diffusion explains the process through which molecules mix as a result of their energy and random motion.

In more simple terms related directly to the management of bowling greens, we see Diffusion in three distinct plant growth processes. We can think of it as a process that makes molecules move from an area of high concentration to an area of low concentration.

When we looked at the basics of Photosynthesis, we discovered that our grass plants absorb Carbon Dioxide (CO2) from the air through their leaves. Diffusion is responsible for this process; as the CO2 moves from an area of relatively high concentration (the air) to an area of relatively low concentration (the interior of the grass plant leaf). So Diffusion is a very important process in the cycle of food production for the plant.

Diffusion is also the way in which soil borne nutrients are moved towards the roots of our grass plants to enable them to be taken up by the roots. These nutrients are present as ions in the soil. These nutrient ions can spontaneously move from a point of higher concentration to a point of lower concentration by Diffusion. This happens in the soil because the immediate root area, once it is depleted (by the roots sucking them into the plant in the soil water), has a lower concentration of the nutrient ions. In this way, the soil around the roots remains in equilibrium with the greater soil mass.

Transpiration.

Transpiration is the process by which the plant loses water to the air through the leaves. It is essentially a mechanism by which water evaporates out of the plant to the air. This evaporation happens through the leaf stomata, the same tiny holes in the undersides of the grass plant leaves that are used to take in CO2. This is another example of Diffusion in action, as the water vapour moves from an area of relatively high concentration (the interior of the leaf), to an area of low concentration (the air)  

Transpiration is an essential part of the mechanism by which plants continually take up moisture and nutrients from the soil. The combination of the Transpiration Pull (of moisture out of the plant to the air) and the sucking up of water (and nutrients) by the roots from the soil creates the effect of a continuous pump that moves water and nutrients around the plant to where they are needed. In the process, it gives the grass plants some of the functional qualities required to produce a Performance Bowling Surface.

This sucking up of soil nutrients in soil water solution brings us neatly to the second of the mechanisms that keep this natural balance, Osmosis.

Osmosis

Osmosis is the name of the process in plant growth whereby water molecules move from an area of relatively low concentration to an area of relatively high concentration. Osmosis is the mechanism used by the plant to take up most of the water and nutrients it needs.

Direct root interception of nutrients.

Root hairs make direct contact with nutrients in the soil, but can only impact around 3% percent of the soil volume. Symbiotic relationships with Mycorrhizae can increase the soil volume that roots are able to extract nutrients from.

Mass flow

Grass plants, sucking up water through the processes of osmosis and transpiration also move the nutrients that are dissolved in this water up through the plant. Some nutrients are more mobile than others due to the relative weakness of their electrical charge (or polarity of it) and are usually always available in soil solution. The Nitrate form of Nitrogen is quickly available to plants due to this, as are other mobile nutrients like chloride and sulphur. Calcium and magnesium are only loosely held by the soil and are easily brought into the soil water solution. However, some other nutrients are held tightly to what is called the soil colloid and are much less easily accessed by the plants.

Next time we will look at the process that dictates the availability of soil nutrients.

Turfgrass Physiology, Respiration

The breakdown of sugars to release energy in a process that provides the chemical energy source for all cellular activities. Respiration depends on a supply of glucose (from photosynthesis), oxygen and suitable temperature.

Last time I introduced photosynthesis, one of the key processes in turfgrass physiology, used by plants to produce their own food. This happens when the plants use the photosynthesis process to turn carbon dioxide taken in from the air by the leaves into a simple sugar (glucose) product that can then be used to fuel the growth and build tissue in all areas of the plant. We saw how the glucose can be used immediately to fuel the plant’s internal processes, or be stored as starch for later use.

The plant uses a process called Respiration to drive growth and development. In much the same way that we respire, i.e. burning food to grow, develop and keep our bodies healthy, plants burn the food created by photosynthesis to fuel growth and to build and repair all of the component parts of the plant.

A simple way to think of Respiration is that it is almost the opposite reaction to Photosynthesis. Here’s how it looks:

Glucose + Oxygen ——————> Carbon Dioxide + Water + Energy

You will see from the equation above that in addition to the energy developed, there is quite a lot of by product in the form of CO2 and Water. Respiration is quite a wasteful process and a lot of the energy produced is given off as heat into the bargain.

Respiration takes place in all plant cells but can only use one source of fuel and that is the glucose or starch already produced by photosynthesis. This means that Photosynthesis and Respiration are locked into a kind of race. As Respiration fuels growth it is said to assimilate the products of photosynthesis i.e. assimilate the food into plant tissue. This means that for good steady plant growth, photosynthesis must produce more food than respiration requires. The measurement of this is called the Net Assimilation Rate (NAR). We will look at this process in a bit more detail in a later article, but for now it’s enough to know that when photosynthesis can’t keep up with respiration, growth and repair will slow down or even stop.

Respiration operates continually even at night and of course Photosynthesis only happens in sunlight. Both processes require a suitable temperature to work also. This explains the slow down of growth in the cooler, darker months. It also explains the need for different turf management practices where there is shade.

If photosynthesis stops or is even reduced, the plant becomes unable to grow and becomes semi-dormant. With our cool season grasses in the UK, semi-dormancy is usually the full extent of the slow down we see. In a warm winter week, we will usually see a restart of growth and we will probably need to give the green a cut a few times over the winter as growth doesn’t usually stop completely.

However, there are transition zones around the world where it is too hot in summer to use cool season grasses and too cold in winter for warm season grasses, and in these areas the warm season species’ can experience full dormancy where the grass turns completely brown or yellow for the entire winter period.

Dormancy aside, if the plant is to survive, then respiration must continue even in the winter and this is why we see a completely natural receding or shrinking back of the grass plants on our greens even if we leave them mown at a fairly high height of cut at the start of winter. The plants start to use up some of the starch reserves saved in the good days when NAR was low (photosynthesis easily keeping up with respiration) in the roots, stems and crowns of the plants. When this reserve is depleted, the plant must conserve energy by reducing its biomass. Roots will recede and leaf tissue will be sacrificed for the greater good of winter survival.

To wrap up for today, Respiration is the process used by the plant to convert food into plant tissue and is the main driver of growth, repair and reproduction in the grass plant. When photosynthesis (production) is greater than respiration (consumption) then growth will continue unabated. When the opposite happens, then growth slows and semi-dormancy can occur.

Next time we will start to look at the internal mechanisms the plant uses to take in water and nutrients.

Grass Identification

Turfgrass Physiology, an introduction

Over the next few posts we will look at some of the magic that occurs within that green square just outside the clubhouse window. Today I’d like to introduce you to turfgrass physiology

Plant food.

Now, if you’ve been down the garden centre or you’ve been watching the gardening programs on the telly, you will be familiar with the concept of plant food, but what we usually think of as plant food is in fact fertiliser  and plants, including the grass plants on our bowling greens…don’t eat fertiliser. There, I’ve said it!

In my introduction to bowling green ecology (now a free eBook) I explained some of the miraculous things that go on within the turf and soil, but these are but nothing compared to the stuff that goes on within the grass plants themselves.

If not fertiliser, then what do grass plants eat? And if they don’t eat fertiliser, then why do we continue to spend money on it?

The fact is that the grass plants on your bowling green make all of their own food in a process called Photosynthesis.

What is Photosynthesis?

The word Photosynthesis is derived from a combination of two Greek words; Photo, meaning light, and Synthesis, which means to put things together (in this context more precisely it describes the production of chemical compounds by reaction from simpler materials). Photosynthesis is the plant based miracle that guarantees our own existence as well as that of the bowling green.

Each of the grass plants in our green is akin to a little factory where Carbon Dioxide and Water are broken down and converted to a sugar based plant food that can be used immediately to fuel the plant’s growth processes or converted to starch and stored throughout the plant for future use. The energy required for this to take place comes from Sunlight (hence the Photo part of the name) which the plant traps and harnesses in the green tissues. It’s interesting to note that plants get their apparent green colour from the fact that they don’t use the green portion of the light spectrum. instead they reflect it back, giving them their green appearance.

In a fortuitous twist the photosynthetic process creates a waste product called Oxygen, otherwise there could be lots of bowler-less bowling greens:-)

We will look at Photosynthesis in more depth as we go through this short series on plant physiology, but for now here is the basic formula for photosynthesis:

Carbon Dioxide + Water + Light —-> Sugar + Oxygen

Simply put, the plant absorbs Carbon Dioxide gas from the air through the leaf and converts it to a sugar based plant food using Water, which it takes up through the roots, in the presence of sunlight energy.

Why do we use Fertiliser then?

Plants need a series of essential nutrients to fuel a range of metabolic processes and to build specialised tissue. They get these nutrients directly from the soil in the solution they take up through the roots. In a perfectly balanced eco-system there would be no need for us to help out by adding fertiliser to the soil, but since we routinely take away the grass clippings (which would naturally be re-cycled to re-introduce nutrients to the soil) we need to supplement some nutrients, especially Nitrogen which is depleted most rapidly by clipping removal. Later, we’ll investigate these processes further.

Next time we’ll find out what the plant does with all of the food it produces.

Bowling green nutrition, how it works

We are familiar with the concept of our grass plants being composed mostly of water (75-85%), but what else is in a grass plant? The answer is that the dry matter of the plant is made up of a mix of 16 elements, commonly referred to as the essential nutrients. We describe them as essential because the plant can’t exist or complete its life cycle if any of these nutrients are lacking to any great degree. 

Bowling Green Nutrition

Some of these elements are used in bulk by the grass plant. These are Carbon, Hydrogen, Oxygen, Nitrogen (N), Phosphorus (P), Potassium (K), Calcium, Magnesium and Sulphur. Some others like Iron (Fe), Manganese (Mn), Boron, Molybdenum, Copper, Zinc and Chlorine are used in smaller amounts. I’ve added the chemical symbol for the ones we commonly see on fertiliser bags.

A large part of this dry plant matter is made up of the three big elements Carbon, Hydrogen and Oxygen. In my introduction to Photosynthesis we saw that the plant takes Carbon (CO2) and Oxygen directly from the air by absorbing them as gasses through the leaf stomata. Last time we looked at Osmosis, the process used by our grass plants to take up water (H20) from the soil and this is where the Hydrogen (H) comes from as well as more Oxygen. The plants can always find an abundant supply of these three elements and if the day comes when they can’t, then we won’t need to be worried too much about how the bowling green looks!

The remaining 13 essential nutrients are accessed via the soil from 2 main sources, but regardless of the source, the grass plant can only absorb these nutrients once they’ve been dissolved and contained within the soil water, more accurately referred to as the soil solution as it isn’t just water anymore.

One source of nutrition is the process of decomposition that happens when plant tissue dies. This organic (carbon rich) material is broken down by soil organisms and micro-organisms and returned to the soil as readily available plant nutrition in the soil solution. This is why the bowling green needs to be considered as an eco system; nothing happens in isolation.

As we saw, nutrients can only be accessed by the plants if they are able to be taken up by the plant roots in the soil solution, but many of the essential elements needed to complete the grass plant life cycle are securely tied up in the soil minerals. These are made available by the slow weathering of the minerals by rain and wind and are washed into soil solution where they are available to the plants. However, the majority of soil nutrients are bound up and unavailable in what are called insoluble compounds.

To be accessible to the grass plant roots, the mineral and organic nutrients must be broken down to their simplest forms called ions and some of these are negatively charged (anions), while others have a positive electrical charge (cations). The most common form of Nitrogen used by plants is N03 which is an anion due to its negative charge, whereas Calcium is taken up as Ca++ which is a cation due to its positive charge,  notated as two + signs in its chemical symbol.

These plusses and minuses are important in soil chemistry and in the relative success or otherwise of our bowling green maintenance. More + signs in the chemical symbol for any ion means a stronger bond to the soil colloid, the name given to the negatively charged clay and humus particles in the soil which hold on to cations and stop them from leaching through the soil. Incidentally, this is one reason we need to apply Nitrogen frequently as fertiliser; its negative ions are easily leached out of the soil by rain as they aren’t bound to the soil colloid. It also explains why it is futile to double up on fertiliser applications in the hope of a better result.

Before they can be made available to plants as ions in soil solution between 15% to 25% of the essential nutrients need to be dislodged from the soil colloid by an ion exchange and the relative ease or difficulty of this in a soil is called the Cation Exchange Capacity (CEC). The CEC is simply a measure of how many exchange sites exist on the colloid.

Now here is another of those wonders of nature that is difficult to appreciate when you’re looking out the clubhouse window at that square of grass. The root hairs of the grass plants release hydrogen ions (H+) and when these come into contact with the soil colloid, they each take up a place on the colloid, breaking or weakening the colloidal-nutrient bond of one of the other nutrient ions. Each + in a nutrient’s symbol is equivalent to one exchange site, meaning you need 3 H+ Hydrogen ions to knock a Fe+++ Iron ion off the colloid and into soil solution. Once these nutrients are knocked free they become more available to the plants, where they are taken up in soil solution through the root hairs.

Hydrogen ions H+ are at the very heart of another important soil mechanism called pH, but that’s for another day.

Soil Texture part 4, the Soil Texture Triangle.

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:

Soil Texture Triangle

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.

Surprises

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

PSD Testing

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.

Soil Texture 5

Soil Texture 3

Soil Texture 2

Soil Texture 1

Particle Size Distribution (PSD) Soil analysis
Particle Size Distribution (PSD) Soil analysis
Full textural Particle Size Distribution analysis of your green's soil (rootzone) by Sieve and Pipette by Sedimentation method. You will receive a soil sampling kit with instructions for taking and returning (freepost) to the lab for testing. Your results will come back from Bowls Central by email and will include a comprehensive report explaining the test results and what this means for the maintenance of your green. Further advice will be provided as required. This test can determine whether or not your green is too sandy and help with green-keeping programming in terms of fertilisation, aeration and top-dressing.
Price: £85.00
Name, Club name and address please::

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Bowls Green Soil Texture part 3

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.

Clay

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.

Fines

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:

East Coast Links Soil
East Coast Links
USGA Rootzone
USGA Rootzone Mix

 

Links

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.

USGA

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.

Particle Size Distribution

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.

Soil Texture Triangle

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.

Soil Texture Part 4

Soil Texture Part 2

Soil Texture Part 1

Soil Texture part 2

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?

A: No.

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.

Building Sand

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.

Soil Texture Part 3

Soil Texture Part 1

Bowls Green Soil Texture part 1.

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 its physical attributes like structural strength, drainage capability and nutrient and moisture holding capabilities.

50% Nothing

Perfect Soil

 

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.

Soil Fractions

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:

Soil Texture Fractions
The Soil Fractions

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.

Colorado University diagram showing relative sizes of individual particles for each soil fraction. Remember the yellow Coarse Sand particle is just 1mm in diameter.
Colorado University diagram showing relative sizes of individual particles for each soil fraction. Remember the yellow Coarse Sand particle is just 1mm in diameter. Even blown up to this size, Clay is just a tiny speck!

Soil Texture Part 2

Thatch Layer

Fix your bowling green step 2

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.

Read more

stress

Ecology 8. More disturbing news for bowling clubs

Last time, I introduced the subject of Disturbance in bowling green ecology and maintenance. I finished by posing the question; How can we use disturbance theory to our advantage in our quest to create a Performance Bowling Green?

To answer that, let’s look at what might constitute Disturbance in the average bowling green. As greenkeepers we actually have an impressive amount of potential influence we can bring to bear on the turf environment; some good and some bad. We can think of these influences as pressures and by applying them with the right force we can manipulate the bowling green eco system (to some degree) to our advantage.

Last time we also discussed Stress factors, which when compared with physical disturbance from our machinery and bowling, can seem innocuous, but the overall affect of say LDP can easily be more damaging to our turf in the long term than an obvious physical disturbance like hollow tining.

Every day Greenkeeping and bowling can have a high disturbance value and put the very grass we are tending under a lot of stress. Mowing, verti-cutting, wear from bowling, pests, diseases, disorders, aeration, top dressing, water and nutrient availability and soil pH can all cause stress to a greater or lesser degree and this will change depending on grass species, general green condition, weather and soil type/condition.

Well the answer is clear then isn’t it? Maybe if we just do nothing (which is the right thing sometimes) the green will improve on its own. If we had unlimited time and didn’t need the green to be prepared for bowling, then I would say absolutely yes, leave it alone, bar maybe a sheep or two and it would sort itself out easily. There would be no thatch, compaction or LDP either. But we don’t have that luxury so we need to intervene to get our green in the shape we want, especially if our green has been subjected to what has become conventional or traditional greenkeeping.

The transition from a failing green that is deep in the grip of the Circle of Decline to the Nirvana that is a Performance Bowling Green is something that needs a fair deal of skill and a great deal of patience and consistency of approach. Once we are in utopia with a Performance Bowling Green we can start to think of backing off on the heavy, physical maintenance and begin to implement a low disturbance diet.

Once we have reversed the process of decline the bowling green can and will improve quickly, but it’s at this time that we need to exercise caution and stick with the program, avoiding slipping back into the old patterns of maintenance at all costs.

Using Stress to Our Advantage

At that stage we can start to use the stresses of disturbance to our advantage. The plan is to create a healthy, settled green first and then put the thumb screws on the undesirables like annual meadow grass slowly but surely, all the time making sure that the techniques and intensity of maintenance we use don”t put the bent and fescue component of the sward under undue stress.

Disturbance can be used to get the ball rolling on green transition from 100% annual meadow-grass turf with squidgy, thick thatch at the turf base over a claggy clay soil. The first steps would include making sure there is physical drainage to take away excess water.

The program would then move on to the renovation phase which would start with aggressive compaction relief. Then a series of operations to physically remove thatch would follow and this could include, intensive core aeration, deep slotting/scarification and maybe even top dressing with sand (yes you read that correctly) if the conditions demanded it.

When in the grip of the Circle of Decline, greens in this condition usually need a high Nitrogen input just to tease a result out of them for play, so the fertiliser program will definitely need a revisit to reduce this. Watering will usually be too high also so we have to tweak and jiggle the program a little at a time in order to maintain grass cover during this major transition.

Finer surface aeration like verti-cutting will be intensified as will sarrell rollling and it will become increasingly important to keep the mower razor sharp with zero contact blade settings to maintain the health of the turf plants.

The Phases of Recovery

In Performance Bowling Greens I split the recovery and on going delivery of performance into 3 distinct programs of work that may or may not be used in parallel depending on the overall condition of the green in question. These are Baseline Maintenance, Renovation Maintenance and Performance Maintenance, leading to phase known as Continuous Improvement

The process of transition from a predominantly annual meadow grass, thatchy, compact and anaerobic, sickly green to a Performance Bowling Green is detailed in my eBook Performance Bowling Greens below:

Performance Bowling Greens eBook
Performance Bowling Greens eBook
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