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.
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 it’s 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; it’s 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.
Next time we will look in more detail at the physical construction of the soil and find out why we need to be more thoughtful when considering top-dressing.
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.
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 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.
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.
The second of these growth processes affected by Diffusion is 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.
The final of our three examples of Diffusion at work is called 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 is the name of the process in plant growth whereby water molecules move from an area of relatively low concentration (of solute nutrients) to an area of relatively high concentration (of solute nutrients). Osmosis then 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.
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.
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 then 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.
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
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.
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.