‘Without oxygen we would not have life as we know it’. That simple statement has been made many times previously and by scientists much more eminent than me. It is a simple truth as also is this statement – ‘Without water we would not have life as we know it’. This is equally true.
When you couple these statements with the knowledge that all the chemistry of the building blocks of living things is based on carbon compounds, then the significance and importance of a very few elements of the Periodic Table becomes extremely clear as far as our life forms are concerned.
If you look through the literature of agriculture/horticulture and turfgrasses you will be sadly disappointed if you are searching for the word ‘oxygen’, for it is rarely mentioned. Even if you look at texts on plant physiology or plant biochemistry, you won’t find a lot of mention of oxygen as such.
Sure, in chemistry you will see the words ‘oxidation’ and ‘redox’ mentioned quite readily and frequently, but you won’t see any development of links back to oxygen.
All living things respire because this is the process which liberates energy to drive the metabolic processes that all living things use to build biological tissues. In the process of respiration we ‘burn’ carbon to produce carbon dioxide (using up oxygen) which then becomes a waste material that reacts with water to form a weak acid, which in turn breaks down rocky minerals to help form soil.
But when too much of it occurs it becomes a pollutant, a greenhouse gas, an invisible thermal blanket, with environmental affects which can be bad when levels in the atmosphere rise too high.
When we talk about fitness we talk about ‘aerobic’ fitness; we don’t talk about oxygen fitness. But if we develop emphysema we don’t give the patient an air cylinder, we give them oxygen. When we talk about soils and healthy soils, we talk about ‘air to water ratios’; we don’t talk about oxygen levels.
When we talk about anaerobic processes we are really talking about processes which occur with exclusion of oxygen.
We only call these anoxic when the lack of oxygen creates processes which are toxic such as the development of black layer in turf, which starts to use sulphur instead of oxygen as its electron transfer carrier producing hydrogen sulphide and eventually sulphuric acid.
We all know that if you try to grow plants in a water-logged situation that, with a few special exceptions such as rice and lotus which are specially adapted to cope, that most plants die from lack of oxygen.
We know that this is because the total pore space of the growing medium becomes filled with water which is not the normal situation. When a growing medium drains after being filled with water, only the capillary pores continue to hold water under the balance of surface tension vs gravity. The larger pores then fill with air.
Over the past eight years there has been ever-increasing attention to using ultra-fine oxygen bubbles (UFOBs) in biological situations where the overall lack of oxygen creates environmental or health problems
If the growing medium has been so compacted or is ageing to the extent that there are very few open pores of the macro variety, then there will be very little air in the growing medium and, to use the usual terminology, it will have a very poor air to water ratio. This then raises the question of whether there is enough dissolved oxygen in a water supply to keep the plants happy. The answer is certainly at least a qualified ‘no’.
It is also the reason why when we try to grow plants hydroponically we keep a continuous supply of air bubbling into the nutrient supply solution. The aim of this exercise is to replace the oxygen taken out of the solution by plant roots on a continuous basis. This type of treatment generally results in about 8 per cent dissolved oxygen in the water supply and this is typically the level found in most town water supplies.
Is this enough to supply the oxygen needs of a plant? The short answer is no because unless there is a continuous exchange of oxygen from the air to supply the depletion from the plant extraction, the supply cannot be kept up. So if the air space is small the exchange is going to be very limited.
All this raises some very interesting questions.
Since Otterbines are a very familiar sight on the water bodies on most golf courses I visit, I can only assume that at last a very big percentage of turf managers are aware of the need to keep the dissolved oxygen level in their water supply at its peak level. Or am I being optimistic and that they are really there to ensure any iron in the water supply is oxidised and precipitated out before it gets to the pump. Or is it simply to keep the algae bloom at bay in nutrient rich effluent supply. It probably doesn’t matter either way because both needs are almost as important as the overall level of oxygen in any case.
Now there are many different sizes and shapes for water storage needs on golf courses; some are narrow and deep, some are broad and shallow and there are plenty of variables from large to small in between. But each shape has its influence on how much oxygen it retains.
The narrower and deeper it is the colder it will be at depth and this helps to hold what oxygen it does have in it at a stable level. But the deeper it is, the less oxygen exchange happens with the surface and the deep level can be as low as 2 per cent on a regular basis.
This will be made even worse if the dam is situated so that it collects a lot of organic debris placing a real strain on its BOD (biological oxygen demand) to deal with the continuous microflora breakdown of this material.
Shallow bodies heat up quickly and once the water temperature goes over 20⁰C the loss of dissolved oxygen becomes exponential. All of these variables play an enormous part in the complexities of managing the consistent delivery of the high quality water supply that producing fine turf surfaces demands.
Historically we have been well aware of these issues at the practical every day level because we have spent more and more time and energy developing ‘aeration’ machines for turf than probably any other implement than mowers. And what have we ended up with at the end of the day? Mostly a lot of well ‘aerated’ core holes but not very well aerated greens. I have written about that issue many times and I will undoubtedly return to it again in the future.
But is there a better way of approaching this problem? The late Dr Bill Daniel of Purdue University in the 1960s developed the PAT (Prescription Athletic Turf) system which included a pump system to pull excess water out and push excess air in. This today is generally referred to as the Motz system and the Sub Air concepts are derivatives of this.
You see these mostly installed on the east coast of the USA in conjunction with large cooling fans (ugly as they are) to try to mitigate the horrid stress of the 40⁰C/95 per cent humidity summer climate where you are trying to grow bentgrass.
The traditional cooling methods of syringe cycling the irrigation system works poorly in these circumstances because every time you put water on you push air out and the end result is almost inevitably black layer.
Perhaps the answer lies in water itself. I previously used the word ‘dissolved’ to describe the oxygen content of water. The technology of very small bubbles developed in liquids by applying a shear force to it in conjunction with a gas has been around for at least 40 years and has been used extensively as ‘micro bubble’ flotation techniques in separation of solids from liquids in the sewage and mining industries for a long time. The micro bubbles float and rise to the surface pushing the solids up with them. They have quite a short shelf life.
In recent years the bubble technology business has developed rapidly to produce a much wider range of bubbles and from our point of view the most important of these are ultra-fine bubbles. These are often wrongly called ‘nano bubbles’ and it has become hard to shake off this terminology, but that needs to happen.
Why ultra-fine bubbles? Because they don’t float, they stay suspended in Brownian motion in the solution. Using this method, the total oxygen content of water can be relatively easily raised to as high as 40 per cent. Does that mean that it is ‘dissolved’ oxygen? Theoretically the answer is no but practically it behaves as if it is.
Over the past eight years there has been ever-increasing attention to using ultra-fine oxygen bubbles (UFOBs) in biological situations where the overall lack of oxygen creates environmental or health problems. The busiest sector has probably been hydroponics where increases of yields of more than 30 per cent in leaf vegetable production have been common place. There have also been a lot of claims made in the cleaning and sanitising areas of food production.