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.
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:
In 1988, Grime, Hodgson and Hunt published their study called “Comparative Plant Ecology – A functional approach to common British species”, which on the face of it sounds like ideal bed time reading for insomniacs. However, the work these scientists carried out might make you sit up in bed and take notice when you realise how relevant it could be to the performance of your bowling green.
In this work, the authors state that vegetation that develops in a place at a particular time is governed by environmental pressures. These pressures may be categorised as stress, disturbance and competition (S, R and C) and that these vary in their relative intensities. Individual species develop their own growth strategies in order to deal with their own environmental pressures.
In Performance Bowling Greens, I introduced the concept of Disturbance Theory which is simply a way of thinking about and defining the growth strategies of each of the fine grass species we aim to grow on our bowling greens. Furthermore, by relating this Disturbance Theory to our greenkeeping calendar we can develop programs and strategies to help us create the environmental conditions that favour the species we know will produce the finest bowling surface. In the UK these are the bent and fescue grasses, but Disturbance Theory holds up for any environment, including the warm season areas of the world.
In a nutshell, Disturbance Theory encapsulates the main themes of the previous 6 articles (imaginatively labelled Ecology 1 to 6) on bowling green ecology and attempts to become the go to tool for greenkeepers to help them manage their greens in a manner that heeds the importance of ecology in bowling green maintenance. In particular it should help give lay people an understanding of how to manage the bowling green in favour of a dominance of the finer grasses. If allowed to develop, the bent and fescue grasses will provide improved playing qualities and reduced vulnerabilities compared to annual meadow-grass.
To be able to manage your bowling green eco-system correctly it is necessary to understand the nature of the pressures.
■ Stress (S) is defined as the environmental constraints to growth. This may include soil moisture (too much or too little), poor fertility (too low or too high), low temperatures, soil acidity and/or salinity.
■ Disturbance (R) is the physical damage occurring within the environment. This is particularly important for bowling greens due to our reliance on regular mowing as the main route to preparing the green for play. Regular disturbance imposes what ecologists call “selection pressure” on the environment.
■ Competition (C) is the struggle between plants to survive and assume dominance within the environment. Some plants have evolved to naturally assume dominance given the right conditions. The continual removal of leaf tissue by mowing would seem to stack the odds against our fine grasses, but these species have developed naturally in closely grazed environments, like we see on the Machair.
Of course as we’ve increasingly become aware of over this series on ecology, environmental pressures rarely act alone. There is invariably a combination of factors and stresses at work in our greens and this is largely what dictates the nature of the growing environment.
Each species has strengths and weaknesses depending on which environment they evolved to survive in. The bents and fescues are considered to be C-S-R strategists as they do not welcome too much disturbance pressure but will put up with some stresses such as mowing quite well. Poa annua (annual meadowgrass) is considered an R strategist that thrives under disturbance but does not welcome too much stress. It is quick to establish in space but struggles to get a hold in a tight knit turf of finer grass. This gives us a strong indication that what we need to do to ensure our greens favour the finer grasses is to minimise the level of disturbance and use stress as a beneficial selection pressure against the annual meadow-grass.
To set the correct environment we need to be able to play with the pressures.
Next time we will investigate further what the greenkeeper can do to influence the level of environmental pressure on the bowling green and how we can harness the effects of ecology to our benefit.
Soil microorganisms exist in vast numbers in the soil as long as there is a carbon source to provide them with energy.
The microbial population is made up of 6 distinct groups of organisms. In order of average population size (biggest first) there are Bacteria, Actinomycetes, Fungi, Algae, Protozoa and Nematodes.
The actual biomass of each of these organisms can be confusing at first due to the difference in size of the individuals. For example, due to their small size, Bacteria contribute a smaller overall biomass than Actinomycetes, even though these organisms are a factor of 10 times smaller in number. Due to these Actinomycetes being larger as individuals they contribute a similar biomass to the much more abundant Bacteria.
Fungus population numbers tend to be smaller but are usually the dominant presence in the microbial biomass where the soil is left undisturbed. Bacteria, Actinomycetes and Protozoa are hardier making them more able to tolerate disturbance of the soil than fungal populations. Bowling greens are probably a half way house; not being subjected to excessive tillage, but not entirely undisturbed either.
Here’s the really interesting bit:
There are more microbes in a teaspoon of soil than there are people on the earth!
The Circle of Decline is largely predicated on poor soil microbial populations due to inappropriate maintenance practices.
Microbes and plant nutrition
Soil microbes are abundant in the soil and are vital to the recycling of organic matter in the soil to provide nutrition for plants. The smallest and most hardy of these are the Bacteria which can survive under the harshest of conditions and are especially resistant to tillage or the mechanical cultivation of the soil as happens in the top 100-150mm of the bowling green through aeration practices. Fungi are more specialised and need a constant food source meaning that they survive and thrive more readily in uncultivated soils.
Soil organic matter consists of a mix of living microorganisms, dead leaves, shoots and roots (fresh residues), and the older decomposed plant material called humus. Fresh plant or animal material provides an ideal food source for microbes and is composed of easily digested sugars and proteins.
Soil cultivation through aeration (incorporating oxygen) destroys soil organic matter through oxidation and allows bacteria and other microbes to rapidly decompose organic residues. Warmer soil and the presence of moisture speeds up this process by supporting an increased microbial populations in the soil. Organic matter with a low carbon to nitrogen (C:N) ratio (green material) is easily decomposed and nutrients are quickly released (4 to 8 weeks), while organic matter with a high C:N ratio (woody material like roots, rhizomes and stolons) decomposes more slowly and the microbes will tie up soil nitrogen to decompose the residues. Protozoa and nematodes consume other microbes in the soil and release the nitrogen as ammonia, which becomes available to other microorganisms or is absorbed by plant roots.
Bacteria Graphic http://www.soils4teachers.org/
Keeping the bowling green eco-system in balance is important in order to minimise the exposure of our grass plants to a range of environmental stresses. These stresses can be thought of as environmental constraints to growth and regeneration and can come in many guises, such as a shortage of light, water, nutrition or extremes of temperature. Conditions within the soil can induce stress in the grass plant. These include soil acidity/alkalinity (pH), soil fertility and soil salinity (salt levels). Outside factors can also play a part in stressing the desired species within a green. For example shading by trees or inappropriate maintenance such as over/under watering of the turf.
One of the most questioned sections of my book Performance Bowling Greens is the section on disturbance. Disturbance in greenkeeping refers to the partial or total damage/removal of living plant tissue. Although this can be as a result of pathogenic organisms like pests or diseases, it can just as commonly be caused by wind, skinning by heavily delivered bowls and wear from bowling and maintenance traffic. However, the area that raises most questions is the fact that many greenkeeping practices cause disturbance too. Maintenance operations considered essential to the green’s health such as scarification, verti-cutting, aeration and even mowing also contribute to disturbance related stress.
Disturbance theory in bowling green management argues that the more we disturb the surface and the more intensive the maintenance, the more stress we put on plants, which makes aeration practices sound as if they might be counter productive. On completely natural grasslands such as the Machair or meadows this would indeed be a true assumption to make as these are perfectly balanced eco-systems. The majority of bowling greens are not and although it is possible to get to that perfectly balanced state in theory, the future for almost all bowling greens will include disturbance by maintenance.
The trouble with disturbance is that it puts further pressure on the grasses inhabiting the disturbed areas. This means that we must cultivate grasses that are capable of the rapid recovery or regeneration needed to not only tolerate the stress, but to actively exploit regular disturbance. One species that does that already is Poa annua which is quick to capitalise on situations like this, making it a very successful competitor in bowling greens to the extent that it makes up a large proportion of the sward on many greens. Poa annua of course brings with it a lot of trouble as it isn’t ideally suited to the production of a fine, uniform bowling surface, although it can be refined over the longer term through maintenance.
The trick in ecology is never to assume that because something has traditionally been seen as bad for bowling greens, that it needs to be eradicated, as bowling greens are eco-systems like any other. Our understanding of eco-systems and all of the inter-relationships that exist within them is poor to say the least.
An example of where we might be throwing out the baby with the bath water is our use of pesticides. For example, we know that there are many millions of fungi in the soil beneath our greens and that some of these are highly specialised. One specialisation is that some fungi have symbiotic relationships with grass roots, allowing the grass plants to draw nutrients from a much larger volume of soil than they can on their own. It is likely that the use of fungicides has a detrimental effect on these relationships.
Staying on the subject of fungi, the ones that we know most about as greenkeepers are the pathogenic ones like fusarium that can devastate our turf. A flawed assumption is that fusarium somehow turns up at our green to cause this damage at certain times of the year, usually autumn and winter. You will often hear claims that the fungus has been imported to the green by one of many mechanisms such as on a contractor’s machine or in a bag of top-dressing. The fact is that all greens, especially healthy, balanced greens will play host to fusarium to some extent and it’s even possible that it usually plays a beneficial role in the soil. Furthermore, even if we wanted to introduce fusarium to our green, bringing it in from an outside location would be unlikely to result in success for the same reasons that it is very difficult to achieve success when over-seeding bowling greens; the established indigenous organisms will always have an advantage over the imported ones for whom the competition will almost always be too strong to allow them to establish a community.
Ecology is about balance and to achieve this balance there is a constant turmoil as organisms fight to exploit their particular niche within the eco-system. If, by design or bad judgement we make our greens more attractive to fusarium than it is to bent grass we will get a severe outbreak of what we see as fusarium disease. If, on the other hand we keep thatch under control, manage compaction well and ensure that our green provides the ideal environment (which will almost certainly also include a population of fusarium) for bent grass we get what we see as a performance bowling green. Beauty is in the eye of the beholder, it just depends who the beholder is!
Biotic and abiotic factors interact with each other. For example low oxygen levels in turf (abiotic) will affect the health of the turf roots directly when the soil becomes increasingly acidic making it harder for roots to extract nutrients from the soil, and indirectly by reducing the population of beneficial bacteria (biotic factors) which play a role in breaking down organic material to release nutrition.
Some of the key factors that benefit or hinder a species in its quest for dominance are described as Environmental Stresses. It is these stresses that drive the evolutionary process and as such can be used by the bowling greenkeeper to create conditions that are more suitable for the desired species than for others. There are a number of ways for greenkeepers to manipulate the environment artificially, or indeed to take advantage of naturally occurring stresses, in order to alter the balance of the bowling green ecosystem in favour of the desired grass species. An understanding of Competition and Adaptation in eco systems will help you a great deal in developing a sound greenkeeping program for fine, perennial grasses.
However we choose to interact with this bowling green ecosystem (with or against nature) we will be working within a dynamic, constantly changing environment and it is vital that we understand this before stepping off into a new program of maintenance. In other words we need to think of our green as an eco-system. Getting to grips with some universal ecological terms will be useful.
In 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.
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 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 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.
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 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.