As I listen in recent times to people talking about the importance of minding soil, I seldom hear mention of anything other than pH and fertility. While these are both hugely important, they are only part of what makes a soil really tick. Overall soil performance in a high-fertility situation may still be limited where a soil is not inherently healthy.
Why could this be? Surely, having the nutrients present to support growth should be enough to drive it to a maximum.
While soil health is difficult to define it is very important and functional. A healthy effective soil system is dependent on its three primary pillars – the three-legged stool we often refer to – being fully active for any soil to function at its best.
Most will be aware that the growth of any plant will be restricted when the soil around its roots is heavily compacted. And that level of restriction of growth will be far greater when a field is highly fertile but badly compacted. Well, this compaction impacts on one or other of the two soil pillars or stool legs.
If your soil is not in good physical condition – that means compaction, high bulk density, poor aeration, bad structure, low water infiltration capacity, etc – then the roots which support the growth of the plant above may well be limiting growth potential.
The other pillar or leg that is critical to this is the very diverse range of biology in the soil. These guys range from an 18cm earthworm to the billions of bacteria that exist in every cubic centimetre of a healthy soil.
All these guys depend on access to air and water but they also depend on being fed from somewhere. Nature may sustain them but modern agriculture often does nothing to feed them and this is frequently a problem.
Importance of biology
I guess we may never know just how much good active soil biology does in our soils. All these living things together provide the only means by which a damaged soil can be restored to its former self.
Sometimes, aerators or subsoilers may help in extreme situations but they only alleviate a symptom rather than solving a problem. It is the combined efforts of the animal life in a soil that brings about repair by restructuring sand, silt, clay and organic matter.
This is only one of the many tasks undertaken by soil organisms on a daily basis.
Where biology is being “fed’” by organic material – this can be slurry, manures, crop material, compost or straw – they release the component nutrients into the soil or free them up for plant access.
Increasing the number of axles is a good way to spread weight but this can still cause damage to soil.
This process is most visible through the activity of legumes which fix nitrogen and generating a store in the soil for the following crop or land use.
However, in soils that do not have a very active biology this process will be much slower and this slows nutrient availability to plant roots.
But it is also worth noting that the organisms that live in the soil also use the same basic nutrients for growth as they are far more numerous than plant roots. They are frequently nearest to the source and grab nutrients as they are released.
In general, soil organisms are more likely to win this battle for recycled nutrients until their overall number in a soil has reached a level that they have plateaued, ie the soil cannot really support higher numbers.
It is only when this has occurred that soil organic matter levels will increase. At this point, the pace of organic matter production or addition will have a chance of exceeding the rate of breakdown, enabling a faster level of organic matter accumulation.
The three pillars together
The productivity of any soil is very much about having all three of these pillars working in harmony. Having a healthy soil that can support the formation of good structure enables optimum root growth to more effectively forage for the nutrients and water needed to optimise growth.
A well-structured soil will have lower bulk density, increased soil porosity and better water infiltration capacity.
Having good water percolation and filtration ability helps prevent water or other liquid run-off that might make its way to streams and rivers. Having organic matter, air and moisture in the soil helps to facilitate the release of nutrients following the breakdown of vegetation or applied organic matter.
So the biology helps the physical by helping to restructure the soil. It facilitates the chemical through the release of nutrients from mineralisation. It probably also acts to suppress antagonistic species that might suppress root or plant growth in the species present.
And when soil organic matter is increased it provides a buffer of nutrients, increases soil humus level which is useful as a place to store nutrients and is critical for moisture retention on lighter soils.
Meanwhile, good physical structure helps to keep more air in soil and facilitates water percolation. But good structure enables much more root growth because developing root hairs, which are the only part of the root at its tip which can pick up nutrients and water, can grow with less effort to explore more of the total volume of the soil to feed even more growth above.
Roots can limit growth
To a high degree, root growth tends to be proportionate to above-ground growth and root growth levels tend to be the forgotten limiting factor. Then a good soil that supports increased root and top growth should leave more organic material to feed and drive the biological system.
At this point, a well-structured open soil that allows good root growth and biological activity will help to free up additional soil nutrients to feed plant growth. Soil pH is an important part of the system because many of the bugs that do these things for us prefer a high pH – it’s not just about increasing the availability of the nutrients present.
Nutrient use efficiency is never perfect as soil organisms rob some of what we apply but then others die to release nutrients that then become available for plant growth.
Our soil fertiliser recommendations have always been based on a portion of the requirement being supplied as fertiliser and another proportion coming from within the soil. Some of this will come from the clay to go into soil solution and more of it will become available as a result of the mineralisation of various forms of organic matter in the soil.
Our recommendations depend on all these systems working efficiently for the soil and the farmer and when any of them let you down, growth is the thing that suffers.
Management
The principles as to how soil functions are very simple but highly complex and we may never understand them fully.
However, when it is working as it should it is good for the farmer, stock, crop and environment, but mainly to the benefit of the farmer. But sometimes the things we do knock about the health of this system.
Consider two simple measures. When you disturb soil in any way, you should expect to see considerable bird activity as they gather to pick up earthworms and other soil grubs that may become exposed on the surface. Having no birds is a bad sign for the biological activity of your soil.
The second is the speed at which organic materials left on the surface are pulled down into the ground by the biology. Even big volumes of drier substances should be pulled down into the ground a little with three weeks when soil is warm and growthy.
Damage to soil
The most obvious challenge we get to soil nowadays is weight. This is mainly seen as the weight of machines, whether that is during crop establishment or harvest, but animals can also exert substantial pressure on our soils. It is important to remember that soil is more easily damaged when it is wet and difficult to damage when dry. But we do not always have a choice as to when we must travel on the land.
We are all conscious of the huge size and weight of modern farm machinery, such as tractors, combines, forage harvesters, slurry spreaders and trailers.
While weight cannot be hidden, much of this equipment is now travelling on good footwear that is helping to keep the pressure on the ground down below 10psi but it would really need to be much lower to significantly reduce compaction.
While machinery gets all the blame, a 750kg beast on four feet is exerting about 42psi and this increases to 84psi when walking.
When the soil is a bit wet, the impact of this can be quite significant. And this is especially the case at very high paddock stocking density.
Tightening the top of the soil can seriously affect soil porosity and water percolation capacity. If the water can’t get down, then flooding and run-off are inevitable following rain. But this tightening of the soil by machine or animal is also going to have some negative effect on root growth because there are physically more obstacles. There is less air for roots to breathe and less space for water to get away.
The only way one can combat this to a reasonable degree is to always have the land in good physical and biological condition. Such land will damage less easily and repair itself and recover more rapidly. And that means feeding the soil biology – there is no alternative.
In brief
Soil should be a living entity full of organisms that need to eat, drink and breathe.Having your soil well fed helps it perform its physical, biological and chemical functions to its optimum.Achieving a healthy soil is not an instant solution and can take from a few years to many years depending on its condition at the start of the process.Always try to avoid or minimise physical damage to the soil but a healthy soil is likely to recover faster.
As I listen in recent times to people talking about the importance of minding soil, I seldom hear mention of anything other than pH and fertility. While these are both hugely important, they are only part of what makes a soil really tick. Overall soil performance in a high-fertility situation may still be limited where a soil is not inherently healthy.
Why could this be? Surely, having the nutrients present to support growth should be enough to drive it to a maximum.
While soil health is difficult to define it is very important and functional. A healthy effective soil system is dependent on its three primary pillars – the three-legged stool we often refer to – being fully active for any soil to function at its best.
Most will be aware that the growth of any plant will be restricted when the soil around its roots is heavily compacted. And that level of restriction of growth will be far greater when a field is highly fertile but badly compacted. Well, this compaction impacts on one or other of the two soil pillars or stool legs.
If your soil is not in good physical condition – that means compaction, high bulk density, poor aeration, bad structure, low water infiltration capacity, etc – then the roots which support the growth of the plant above may well be limiting growth potential.
The other pillar or leg that is critical to this is the very diverse range of biology in the soil. These guys range from an 18cm earthworm to the billions of bacteria that exist in every cubic centimetre of a healthy soil.
All these guys depend on access to air and water but they also depend on being fed from somewhere. Nature may sustain them but modern agriculture often does nothing to feed them and this is frequently a problem.
Importance of biology
I guess we may never know just how much good active soil biology does in our soils. All these living things together provide the only means by which a damaged soil can be restored to its former self.
Sometimes, aerators or subsoilers may help in extreme situations but they only alleviate a symptom rather than solving a problem. It is the combined efforts of the animal life in a soil that brings about repair by restructuring sand, silt, clay and organic matter.
This is only one of the many tasks undertaken by soil organisms on a daily basis.
Where biology is being “fed’” by organic material – this can be slurry, manures, crop material, compost or straw – they release the component nutrients into the soil or free them up for plant access.
Increasing the number of axles is a good way to spread weight but this can still cause damage to soil.
This process is most visible through the activity of legumes which fix nitrogen and generating a store in the soil for the following crop or land use.
However, in soils that do not have a very active biology this process will be much slower and this slows nutrient availability to plant roots.
But it is also worth noting that the organisms that live in the soil also use the same basic nutrients for growth as they are far more numerous than plant roots. They are frequently nearest to the source and grab nutrients as they are released.
In general, soil organisms are more likely to win this battle for recycled nutrients until their overall number in a soil has reached a level that they have plateaued, ie the soil cannot really support higher numbers.
It is only when this has occurred that soil organic matter levels will increase. At this point, the pace of organic matter production or addition will have a chance of exceeding the rate of breakdown, enabling a faster level of organic matter accumulation.
The three pillars together
The productivity of any soil is very much about having all three of these pillars working in harmony. Having a healthy soil that can support the formation of good structure enables optimum root growth to more effectively forage for the nutrients and water needed to optimise growth.
A well-structured soil will have lower bulk density, increased soil porosity and better water infiltration capacity.
Having good water percolation and filtration ability helps prevent water or other liquid run-off that might make its way to streams and rivers. Having organic matter, air and moisture in the soil helps to facilitate the release of nutrients following the breakdown of vegetation or applied organic matter.
So the biology helps the physical by helping to restructure the soil. It facilitates the chemical through the release of nutrients from mineralisation. It probably also acts to suppress antagonistic species that might suppress root or plant growth in the species present.
And when soil organic matter is increased it provides a buffer of nutrients, increases soil humus level which is useful as a place to store nutrients and is critical for moisture retention on lighter soils.
Meanwhile, good physical structure helps to keep more air in soil and facilitates water percolation. But good structure enables much more root growth because developing root hairs, which are the only part of the root at its tip which can pick up nutrients and water, can grow with less effort to explore more of the total volume of the soil to feed even more growth above.
Roots can limit growth
To a high degree, root growth tends to be proportionate to above-ground growth and root growth levels tend to be the forgotten limiting factor. Then a good soil that supports increased root and top growth should leave more organic material to feed and drive the biological system.
At this point, a well-structured open soil that allows good root growth and biological activity will help to free up additional soil nutrients to feed plant growth. Soil pH is an important part of the system because many of the bugs that do these things for us prefer a high pH – it’s not just about increasing the availability of the nutrients present.
Nutrient use efficiency is never perfect as soil organisms rob some of what we apply but then others die to release nutrients that then become available for plant growth.
Our soil fertiliser recommendations have always been based on a portion of the requirement being supplied as fertiliser and another proportion coming from within the soil. Some of this will come from the clay to go into soil solution and more of it will become available as a result of the mineralisation of various forms of organic matter in the soil.
Our recommendations depend on all these systems working efficiently for the soil and the farmer and when any of them let you down, growth is the thing that suffers.
Management
The principles as to how soil functions are very simple but highly complex and we may never understand them fully.
However, when it is working as it should it is good for the farmer, stock, crop and environment, but mainly to the benefit of the farmer. But sometimes the things we do knock about the health of this system.
Consider two simple measures. When you disturb soil in any way, you should expect to see considerable bird activity as they gather to pick up earthworms and other soil grubs that may become exposed on the surface. Having no birds is a bad sign for the biological activity of your soil.
The second is the speed at which organic materials left on the surface are pulled down into the ground by the biology. Even big volumes of drier substances should be pulled down into the ground a little with three weeks when soil is warm and growthy.
Damage to soil
The most obvious challenge we get to soil nowadays is weight. This is mainly seen as the weight of machines, whether that is during crop establishment or harvest, but animals can also exert substantial pressure on our soils. It is important to remember that soil is more easily damaged when it is wet and difficult to damage when dry. But we do not always have a choice as to when we must travel on the land.
We are all conscious of the huge size and weight of modern farm machinery, such as tractors, combines, forage harvesters, slurry spreaders and trailers.
While weight cannot be hidden, much of this equipment is now travelling on good footwear that is helping to keep the pressure on the ground down below 10psi but it would really need to be much lower to significantly reduce compaction.
While machinery gets all the blame, a 750kg beast on four feet is exerting about 42psi and this increases to 84psi when walking.
When the soil is a bit wet, the impact of this can be quite significant. And this is especially the case at very high paddock stocking density.
Tightening the top of the soil can seriously affect soil porosity and water percolation capacity. If the water can’t get down, then flooding and run-off are inevitable following rain. But this tightening of the soil by machine or animal is also going to have some negative effect on root growth because there are physically more obstacles. There is less air for roots to breathe and less space for water to get away.
The only way one can combat this to a reasonable degree is to always have the land in good physical and biological condition. Such land will damage less easily and repair itself and recover more rapidly. And that means feeding the soil biology – there is no alternative.
In brief
Soil should be a living entity full of organisms that need to eat, drink and breathe.Having your soil well fed helps it perform its physical, biological and chemical functions to its optimum.Achieving a healthy soil is not an instant solution and can take from a few years to many years depending on its condition at the start of the process.Always try to avoid or minimise physical damage to the soil but a healthy soil is likely to recover faster. 
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