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.

Turfgrass Physiology, an introduction

Grass Identification

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.

done for you greenkeeping schedules

ring binder report

Done for you greenkeeping schedules. Instead of relying on guesswork, hearsay and myth, wise clubs are putting their faith in science and proven agronomic expertise to help them draw up the correct greenkeeping schedule for their greens. In this article we explain how you can easily tap into John's Master Greenkeeper expertise and have a "done for you' greenkeeping schedule for your green.

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How to painlessly transform greens from Poa annua to bent/fescue

Transitioning your green from Poa annua to bent/fescue is not only critical to achieving a Performance Bowling Green, but is actually a realistic goal. The spongy, soft turf associated with annual meadow grass is less than ideal for bowls. Common wisdom says that this can't be done without major disruption and that even after it is achieved it wont last. This article explains in detail how to undertake the transition of your green from Poa annua to bent/fescue turf and dispels the myths about stressing Poa. This is the way to change your green permanently and without fuss. It will also save your club money on maintenance, so what's not to like?

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The perfect soil. Performance Evaluation of the Bowling Green Part 12

Green Performance Explained

In the previous articles in this series, we’ve discovered how to evaluate performance by simply looking for visual indicators on the turf and by gauging some of the functional attributes of grass plant communities when they form turf.

Before we move on to the final stage of this series where we will look at some of the latest and most objective techniques for performance measurement, I wanted to stop for a moment to consider what lies beneath the green layer.

All of the functionality and therefore performance of the bowling green depends on healthy turf and turf is of course not just grass plants. Turf is a construct of a healthy grass plant community containing millions of individual plants, growing in a medium that is suited to sustaining healthy growth and reproduction. The medium is, of course the soil our greens are built on; but what is soil?

If you look at the pie chart at the top of the article you will see the proportions of what I think of as the perfect soil.

Mineral Component

In the diagram you will see that 45% of the soil is made of Minerals. The mineral component of soil is usually made up of a mixture of 3 main groups and these are Sands, Silts and Clays. A suitable mixture of these is critical to the soil’s performance as they dictate the soil’s ability to provide nutrition and moisture to the grass  plants and suitable drainage. The mix of sand, silt and clay defines the soil’s texture.

Organic Component

The organic component will ideally be around 5% and this is made up of living organisms, micro-organisms and dead, decomposing and already decomposed plant tissue (humus). The organic material is added to by the plants themselves as they produce thatch and the soil organisms break this down to release plant nutrients.

50% Nothing

Then there’s the remaining 50% of the soil to look for, but if you do, it might cause you some confusion, because in the ideal soil the remaining 50% of its volume will equate to nothing at all. In fact it is 50% space, or soil porosity to give it the correct name.

Ideally half of this space will be made up of small spaces called micro pores and large spaces called macro pores. The micro pores hold the soil solution which is a mix of water and plant available nutrient ions and the macro pores provide air space and this is where all of the drainage occurs after heavy rain. This air space keeps the soil well oxygenated so that it can sustain a huge population of soil microbes; around 1 billion in a teaspoon of soil.

The Green Stuff. Performance Evaluation of the Bowling Green Part 11.

Verdure

Sometimes the things we see every day become so familiar that we stop noticing them and this can be the case with the most obvious of performance signals on the bowling green. We can learn a lot from just being a bit more observant of the every day activities we get involved in as greenkeepers.

There are two aspects of green maintenance that sound so obvious that they are easy to dismiss:

  1. How much grass comes off when you mow? This is called Yield
  2. And how much grass is left after you mow? Which is called Verdure

It might sound ridiculous to make up special words like Yield and Verdure for fundamental factors like this, but they are important and give us much more information than we might first realise.

Yield

This is the measure of how much material comes off when we mow the green. Of course we aren’t interested in the yield in the same way a farmer would be. Our job isn’t to grow as much grass as possible; our job is to grow dense healthy turf that supports the preparation of the green surface to a high performance level, consistently throughout the season. Turf scientists might take the clippings, dry them and weigh the remaining dry tissue matter to come up with an accurate measure of Yield in kg/Ha, but my old boss at my first greenkeeping job had a much more straightforward and instant way of monitoring this. When I returned to the maintenance shed after cutting 18 golf greens in the morning he would simply ask; “did you get much grass?”

Unscientific as that may sound, it’s as good a measure as any to an experienced greenkeeper who treads the same piece of ground every day in life. The subtle nuances of Yield Fluctuation (the increase or decrease in boxes of grass removed to you and me) can tell you a lot about your green’s condition.

Assuming that everything else such as mowing height, sharpness of mower, weather conditions and timing of cut are roughly the same, we can make a judgement of the condition of the green relative to previous cuts we’ve made, whether that was yesterday or last year at the same time. But what can we ascertain from this?

Nutrition

Increasing yield is common after Nitrogen fertiliser has been applied. Fertiliser applications, particularly when using granular fertilisers tend to have a distinct life span pattern and the green will go through a growth pattern after application. For example a few days after application of fertiliser like this it will be common for the yield to increase steadily day after day. At some point after the first flush of growth, yield will level off and stay roughly the same for several weeks. Then it is likely that yield will steadily reduce until a new application of Nitrogen is made and the pattern will repeat. Being able to judge when the next application needs to be made is a skill picked up by greenkeepers over time and relies a lot on watching the grass box filling up. By having this feel for what’s happening in terms of growth patterns, you can form a better understanding of the right fertiliser program, application rates and frequency of application for your green at any given time.

Moisture

Another key contributor to yield will be the level of plant available moisture in the soil at any given time. Yield will decrease as this dips below optimum and will increase as you get closer to field capacity. There’s a close connection with nutrition here too as fertiliser needs a good amount of soil water for the nutrient ions to be able to get into the soil solution where they can be taken up by the plant roots.

Cultural Practices

The other non-mowing cultural practices you carry out on your green will also influence yield. Jobs such as scarifying and aeration of any kind will have the effect of introducing oxygen to the soil which will increase microbial activity, releasing nutrients which might increase yield.

Of course, the object is to try to create a steady growth pattern that allows the green to recover from the rigours of play and maintenance and to exhibit all of the other key components of performance we have looked at over the previous  9 articles. Measuring yield even by just counting the boxes of grass collected every day is a great starting point in getting a feel for your green’s performance and the effect that your work has on it over time.

Verdure

This is a measure of the green plant material that is left after mowing. Oh come on John, I just call that grass, I hear you say, but Verdure is just a little more complex (and useful) than that.

For example in any turf grass species, turf resiliency and rigidity will increase when you leave more tissue on the plant i.e. raise the blades. This will generally increase wear resistance too. Grass will generally be healthier and more robust at higher mowing heights and that is why I recommend raising the height during drought conditions and of course in winter.

Turf Resiliency. Performance Evaluation of the Bowling Green Part 10.

Turf Resiliency

Turf resiliency is one of the major factors determining bowling green performance and as such warrants close attention by the greenkeeper. Up to this point in our series on the evaluation of bowling green performance we have been dealing with attributes of grass, turf and soil that depend a lot on the greenkeeper's experience and "feel" for the turf. With resiliency we are getting closer to making more objective measurements.

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