toxic to plants, such as ferrous sulphide and ethylene. The associated build up of carbon dioxide in anaerobic conditions can occur as a result of excessive watering, soil compaction (reduced porosity and increased bulk density) and increased levels of microbial activity.icrobial activity. In the atmosphere oxygen, carbon dioxide and nitrogen comprise in the region of 21%, 0.03% and 79% respectively. In the soil these percentages can differ drastically, with oxygen being less than 20%, up to 10-100 times more carbon dioxide and about the same amount of nitrogen. High carbon dioxide levels result in root die back. The amount of air present in a soil is
directly influenced by soil texture. In sandy soils it is of the order of 25% or more, in loamy soils it is between 15 and 20% and, in clayey soils that tend to retain the most water, it can fall below 10% of the total soil volume. In fine textured soils structure also plays a significant role. Strongly aggregated soils, with macroaggregates of the order of 5mm or more in diameter, generally have a considerable volume of macroscopic (interaggregate) pores which drain very quickly and remain air filled practically all of the time. Hence, such soils exhibit an air capacity of 20-30%. As the aggregates are dispersed or broken down by mechanical forces these pores tend to disappear so that a strongly compacted soil can have less than 5% air by volume.
A comparison of the amount of oxygen
present in the soil with existing respiration rates reveals that there is not a very great reserve of oxygen in the soil. In the top one metre of a soil profile there is around a 3-4 day supply of oxygen contained in soil pore space. Therefore, in order to sustain respiratory
small gusts entering the soil. Because it is localised and short term, it is really localised in significance and importance being restricted to the top 2-3 centimetres.
The solubility of oxygen in water is 0.028cm3
of oxygen in a cm3 of water.
This may be important in stimulating a flush of activity, but it is generally a negligible contribution to the transport process.
which oxygen moves into the soil are the same as carbon dioxide moves out
The processes by
processes oxygen must be replenished and waste products removed. The processes by which oxygen moves into the soil are the same as carbon dioxide etc. move out. The oxygen moves from the bulk atmosphere into the soil and can move by mass flow, diffusion or in water. The rate by which soil oxygen exchanges with atmospheric oxygen is the oxygen diffusion rate (ODR) and this directly influences the levels of carbon dioxide present. A low ODR results in increasing levels of carbon dioxide.
Mass flow occurs when a pressure gradient exists and involves the bulk flow of gas in a particular direction. This process can account for 5-10% of oxygen consumed in the soil. Gusting of wind can lead to sudden pressure increases at the soil surface and, in turn, lead to
TWENTYQuestions
Kiel Barrett - appears to be a big fan of peri-peri chicken, pigeons and cheerleaders!
Who are you? Kiel Barrett, assistant groundman at Headingley Carnegie Stadium.
Family status? Single, girlfriends cost money!
Who’s your hero and why? Jonny Hepworth (Leeds Carnegie) and Wayne Godwin (Bradford Bulls), because they have both taken me under their wings and always help me out when I am struggling with things.
What is your dream holiday? Somewhere where you can relax on a warm beach through the day then, at night, party away.
What annoys you the most? Paying tax.
What would you change about yourself? Nothing, I am happy the way I am.
Who wouldn’t you like to be? Gordon Brown.
Favourite record, and why? Day and Night by Kid Cudi, it reminds me of BCM in Magaluf.
Who would you choose to spend a romantic evening with? The Leeds Rhinos
cheerleaders.
If you won the lottery, what is the first thing you would do? I would buy a Bentley, then enter the Gumball 3000 rally.
If you were to describe yourself as a musical instrument, what would you be and why? The drums, because I am always loud when I am talking.
What’s the best advice you have ever been given? Don’t try to run before you can walk.
What’s your favourite smell? Grass being cut.
What do you do in your spare time? When I do get any spare time you can normally find me in Nandos restaurant or down at the gun club shooting a few clays.
What’s the daftest work related question you have ever been asked? Well, it’s me that normally asks those questions!
What’s your favourite piece of kit? The vertidrain, because it saves me from hand forking.
What three words would you use to describe yourself? Passionate, Hardworking, Polite.
What talent would you like to have? To be able to play golf better.
What makes you angry? Paying the tax man!
What law/legislation would you like to see introduced? Free car insurance for young drivers.
By far the greatest movement occurs by way of diffusion involving a concentration gradient, and it is this process that enables oxygen to get down to depth. Given that a concentration difference exists and the thermal motion of gas molecules, there is a tendency for gas molecules to move from high to low concentrations. Therefore, it can be seen that soil aeration is extremely important in order to optimise the growth of plants and that often poor growth is an indirect result of compaction and its effects on gaseous exchange, nutrient availability and drainage. With zinc and manganese, if these are low in the soil, so what? You are generally aiming to correct discrepancies found in the leaf tissue, and so this should be the focus of any management philosophy. Applying these to the soil seldom guarantees addressing any issues that may exist, and is a pretty inefficient means of achieving this. Besides, so what if zinc and manganese are low in the soil? What does this mean? Bearing in mind fungicides based on mancozeb are based on manganese and zinc, on every occasion I have carried out tissue testing, following an application of this, I have seen a spike in plant tissue levels References available upon request
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