It is an asset that is so often taken for granted. It is the asset that generates the yield but it is also the one that takes the abuse when the year is wet.
Soils suffered in 2012, even if they were never touched by a machine or an animal. Frequent heavy rain alone beats down the soil surface, breaking the natural surface soil structure up into its basic components. Bare soil suffers worse as vegetation protects against the momentum of rain drops to some degree. When soil is broken down, the fine particles are easily washed down into the soil where they congregate at the first tight zone which can be either at cultivation or ploughing depth.
This is a natural soil phenomenon and can occur on all soils and soil types regardless of use. In a ploughing scenario, the fine soil that migrates down is turned back up again the following year and so does not appear to be a problem. In min-till this can be a problem over time as a tight dense layer becomes obvious. The reaction is to cultivate deeper but this can just allow the problem to move deeper and, in time, this can become a big problem unless something is done.
The migration of fine particles down the soil profile will, in time, fill the soil pores to decrease the free pore space and increase the bulk density of the soil. A healthy living soil should be a mixture of sand, silt clay, humus, air, water and a myriad of other living organisms that help repair the natural damage that soils endure. Having less air present in the soil is, in itself, a natural limitation to biological activity which, in turn, limits the capacity of a soil to correct the natural wear and tear, not to mention the additional problems that arise in a wet season.
What is soil?
We mainly think of soil as being the solid medium that supports plant growth by providing anchorage for roots and feeding them with water and nutrient. Soil is that and more. It also supports a multiplicity of life forms, from the big ones we know like badgers, rabbits and rodents to the more familiar work horses like earth worms, millipedes, centipedes, down to fungi, bacteria, etc.
All of these have a part to play in the maintenance of a healthy soil but, not surprisingly, they need to be fed to prosper. And they still need conditions in the soil that enable growth and especially enough air and not too much water.
We choose to think of soil as a solid substance on which we can walk and drive. This is far from the full story. Most agricultural soils are a series of small angular crumbs which sit against one another to leave room for air, water percolation and root penetration. The angular crumb structure tends to decrease in time as organic matter levels decrease in worn tillage soils. This would appear to allow the soil to tighten, to go together that bit more, to make it more difficult to break up in cultivation, to slow water percolation and to possibly decrease root penetration.
These are the consequences of a worn soil and if such soil is wet then it is more easily damaged by traffic because a soil full of water is really a suspension liquid and the particles can be pushed together much more easily – resulting in compaction or poaching.
Visible symptoms
With this in mind, we need to think of the problems experience during 2012. Land has been frequently saturated since June with only occasional respite. So everything that went onto land was likely to cause damage and some fields have been building problems over the past few years.
Damage can be seen in many forms. We see dry fields in tillage and grass where ponds have appeared in recent years and these have been getting worse with time. This is most likely a result of fine degraded soil forming in the pond, being filtered down into the profile to clog the pores and, in turn, decreasing water percolation even on traditionally dry land. A feature of this type of damage is that the ponds tend to get bigger every year.
Soil damage can also be seen as tracks in growing crops where tight tracks are growing poorly and are seen as yellowed foliage. More severe damage is seen as tracks or ruts from earlier work, while some of this has been covered over in tillage fields it may still cause a growth problem later in the year.
Tillage fields show all kinds of symptoms, from severe puddling on top following potato harvesting to rutted fields from a combination of field operations. Some very deep ruts are still present in stubbles, while ponds are visible in hollows. In these hollows fine clay and soil tightening are slowing or preventing water percolation, similar to grassland.
We also see ponds appearing at the ins-and-outs on tillage fields where the headlands have been turned into the ditch for a number of consecutive years.
Poaching is another problem where livestock are the sole cause. While this causes problems for the quality of the pasture, it also results in compaction damage beneath the hoof prints. If there is significant compaction in paddocks, reseeding without loosening this compacted layer is likely to significantly shorten the lifespan of a new reseed.
So there are many ways that your soil can be damaged and quite a number of ways that it can show that damage. But damaged soil can all too often result in decreased plant growth which generally means less yield, regardless of the crop.
Soil compression and bulk density
What should you do about the problem or, more importantly, what can you do to prevent the problem from occurring. Many of our modern problems relate to the weight of the machinery now working on our land and that is unlikely to change. But it remains important to be aware of this issue and the type of damage it is causing.
Many land machines are now fitted with bigger tyres, both bigger diameter and wider, to increase the size of the footprint to reduce ground pressure.
But low ground pressure is not a guarantee of no soil damage. These bigger tyres certainly appear to have the potential to reduce compaction but as they carry more weight this force is still transmitted into the ground beneath. So, rather than compaction, the fear is that the weight, transmitted through lower ground pressure, puts a compressive force down into the soil and this is thought to go quite deep into the soil. Researchers estimate that this compression, while not necessarily producing compaction near the surface, acts to tighten the soil down to more than one meter deep.
It is the depth of this influence that is the biggest concern. How do you fix a problem that is over one meter deep? And the extent and depth of the problem is likely to be even greater when the soil is wet during trafficking. The presence of moisture makes it easier for the soil particles to be pushed together to decrease the porosity and percolation capacity of the soil.
So, before you set about attempting to solve a problem on your land, you need to know what and where the problem is. Without this knowledge you run the risk of creating more problems in the future. But any and all remedial action must wait until the ground dries out before there is any chance of longer term success and to avoid doing further damage in the process.
For example, if you pull a subsoiler through a spot that has been a wet saucer you will inevitably enable the water to percolate from the surface downwards. But if the cause of the initial problem is the clogging up of the soil pores with fine soil particles then you may only move your problem downwards. If you move it from, say, eight inches deep to 14 inches deep how will you solve that problem next time, especially if you also have compressed soil where big machines have been used?
Help the soil fix itself
Care is needed when attempting to correct soil problems. The primary focus in all soils must be to restore good biological activity. As stated previously, this means a lot of different types of soil animals and bugs but the most important for the physical condition of the soil is the earthworm.
Earthworms have two major functions in the soil, and probably hundreds of others. They eat and recycle organic materials in the soil and, as part of this process, they consume and reconstitute the particles of fine soil that are always present due to normal soil wear and tear. And, depending on the species present, they move soil and open up movement pores from deep in the soil to the soil surface.
This is about the only way (except for drought) that we can open up the soil profile to that depth and as the machines we use are not likely to get smaller in the coming years, we need to do all we can to have a biologically active soil to enable earthworms to undo the soil compression caused by heavy machinery. Earthworms are important in the generation of humus. This is important for a healthy soil. It is a mixture of the organic matter that was passed through the earthworm, combined with the soil that they ate as they tunnelled through the soil. As I understand it, humus has three very important characteristics.
1. It is a better carrier of moisture than the soil itself in dry conditions (not a recent requirement).
2. It carries plant nutrients in a manner that makes them easier to access by plant roots and this can often help plant growth early in a crop’s life when root mass is limited.
3. Humus is part of the process which reconstitutes soil broken apart by rain, wet, etc to produce the type of crumb structure that is synomonous with good soil structure, ease of cultivation, good percolation, high yields etc.
The key to good soil management in every field is to enhance biological activity. This is normally done by the addition of organic matter to increase earthworm activity. It is my belief, but unconfirmed, that this is best done with coarse materials which can be easily found by moving earthworms. This is what makes straw a good feed for earthworm multiplication, especially when it is chopped.
Dung can be equally as good but full length straw is nearly impossible for an earthworm because it cannot be cut to drag pieces down into the soil for consumption. But if finely ground bits of organic matter are left on the soil surface they can be easily consumed to provide a plentiful food supply to fuel population increase.
In patches where water is standing it is likely that the earthworm population has been destroyed. This may be the cause or the consequence of the current symptoms because they cannot survive in waterlogged soils.
Subsoiling
Many see subsoiling as a cure for compaction – it is not. When you damage a soil to the point of compaction its inherent structure is damaged in the compaction process. All a subsoiler does is burst open the soil to enable water to get down and air to enter. While these are useful benefits, they do not correct the problem of soil structure destruction.
Subsoiled land may only allow the water to sit deeper in the profile, thus holding more water deeper and decreasing trafficability over time. If the following spring is dry, subsoiling will look to have done a good job but if it is wet the original problem could look worse.
To have any potential for benefit, subsoiling should only be done when the soil is quite dry. When it is dry, one expects to get multiple fracturing of the compacted soil allowing air and water through. If this land is then managed to promote root growth into these cracks before any further weight is placed on the soil, the roots can help prevent the soil from going back together again and recompacting.
If properly managed, subsoiling can be useful but if it is done when the land is wet then the soil will not fissure and all you do is make a new problem deeper in the soil.
Where a soil has been tightened due to heavy machinery, even with good big tyres, the damage is likely to be present well below the working depth of the subsoiler. In this case, you only move water from the surface to a greater depth, producing a problem that will be much more difficult to deal with at a later stage.
The initial advice still holds – manage the soil to be healthy and biologically active. Such soils can both better withstand the pressure for damage and also recover faster in the event that damage occurs. Good tyres help prevent or reduce compaction but they may not prevent soil compression further down. When this happens the soil will hold more water, making the risk of further damage more likely.
The only influence we can really have on soil physical properties is via soil biological activity and earthworms in particular. We want them to dig out new pores and channels in the soil to help water percolation and access to nutrients. These initially allow air to move through the soil, followed by water and plant roots. Once roots grow through they act to keep the pores in place because when they die they provide a channel for the next root to grow through.
Recognising compaction
Compacted soils prevent or slow root growth and water percolation. This will mean more run-off and the risk of soil erosion. Getting out the spade is the only way to really examine your soil. The ‘Thinksoils – Soil assessment to avoid erosion and run-off’ book, produced by the Environment Agency in the Britain, provides a terrific picture reference to help farmers recognise soil problems.
Because compacted soils have much lower water percolation they will be more prone to surface run-off. They may also show signs of anaerobic conditions or rust flecking in the soil as water prevents air movement.
Serious compaction will limit crop growth and yield. Compaction can occur at the surface as smearing; it can occur in the top-soil caused by machinery or stock; it can also be in the subsoil caused by heavy machinery compressing the soil, especially during wet soil conditions.
Removing compaction
Alleviating soil damage is not a simple task because there are many different potential problems and causes. Some problems occur on pervious subsoil while others are on impervious subsoil – the former is more easily fixed.
Surface compaction, often found after maize or potato harvesting where the soil is bare on top, can be alleviated by simple shallow cultivation to break the surface cap. It can sometimes be enough to pull a cultivator across a hill to enable surface water to percolate as it flows down the hill.
Machine compaction can often be removed by ploughing, but sometimes subsoiling is necessary. But it is critical to know where the damage is in the soil to target a mechanical solution. Problems resulting from substantial soil compression are much more difficult and can only be targeted through increased earthworm activity. Dryness is a great cure of soil problems but it’s outside of our control. All potential mechanical solutions will only be successful if the soil is dry during the process.
Surface compaction and ponding are dealt with in different ways.
If a problem is purely surface then knifing in dry conditions can be an adequate solution to enable air and water movement. But sometimes deeper loosening can be justified during reseeding for example.
Subsoil tightening resulting from excessive weight is impossible to remove physically.
So care of the soil is essential for repair and to help prevent damage. Perhaps the most important fact to remember is that well structured soils are more resistant to compressive forces and so we must do all we can to support the continuous regeneration of soil structure. This means feeding the soil organisms to encourage soil biological functioning, as this is the primary means of restoring soil structure.
KEY POINTS
Fine soil particles can move down into the soil profile clogging up the pores and slowing water percolation.Compaction can occur in different zones in a soil and its treatment must be properly targeted.Subsoiling is widely misused and can result in more severe soil damage further down the soil profile than the initial problem.Prevention of compaction and subsoil compression must be a target of all farming systems.
It is an asset that is so often taken for granted. It is the asset that generates the yield but it is also the one that takes the abuse when the year is wet.
Soils suffered in 2012, even if they were never touched by a machine or an animal. Frequent heavy rain alone beats down the soil surface, breaking the natural surface soil structure up into its basic components. Bare soil suffers worse as vegetation protects against the momentum of rain drops to some degree. When soil is broken down, the fine particles are easily washed down into the soil where they congregate at the first tight zone which can be either at cultivation or ploughing depth.
This is a natural soil phenomenon and can occur on all soils and soil types regardless of use. In a ploughing scenario, the fine soil that migrates down is turned back up again the following year and so does not appear to be a problem. In min-till this can be a problem over time as a tight dense layer becomes obvious. The reaction is to cultivate deeper but this can just allow the problem to move deeper and, in time, this can become a big problem unless something is done.
The migration of fine particles down the soil profile will, in time, fill the soil pores to decrease the free pore space and increase the bulk density of the soil. A healthy living soil should be a mixture of sand, silt clay, humus, air, water and a myriad of other living organisms that help repair the natural damage that soils endure. Having less air present in the soil is, in itself, a natural limitation to biological activity which, in turn, limits the capacity of a soil to correct the natural wear and tear, not to mention the additional problems that arise in a wet season.
What is soil?
We mainly think of soil as being the solid medium that supports plant growth by providing anchorage for roots and feeding them with water and nutrient. Soil is that and more. It also supports a multiplicity of life forms, from the big ones we know like badgers, rabbits and rodents to the more familiar work horses like earth worms, millipedes, centipedes, down to fungi, bacteria, etc.
All of these have a part to play in the maintenance of a healthy soil but, not surprisingly, they need to be fed to prosper. And they still need conditions in the soil that enable growth and especially enough air and not too much water.
We choose to think of soil as a solid substance on which we can walk and drive. This is far from the full story. Most agricultural soils are a series of small angular crumbs which sit against one another to leave room for air, water percolation and root penetration. The angular crumb structure tends to decrease in time as organic matter levels decrease in worn tillage soils. This would appear to allow the soil to tighten, to go together that bit more, to make it more difficult to break up in cultivation, to slow water percolation and to possibly decrease root penetration.
These are the consequences of a worn soil and if such soil is wet then it is more easily damaged by traffic because a soil full of water is really a suspension liquid and the particles can be pushed together much more easily – resulting in compaction or poaching.
Visible symptoms
With this in mind, we need to think of the problems experience during 2012. Land has been frequently saturated since June with only occasional respite. So everything that went onto land was likely to cause damage and some fields have been building problems over the past few years.
Damage can be seen in many forms. We see dry fields in tillage and grass where ponds have appeared in recent years and these have been getting worse with time. This is most likely a result of fine degraded soil forming in the pond, being filtered down into the profile to clog the pores and, in turn, decreasing water percolation even on traditionally dry land. A feature of this type of damage is that the ponds tend to get bigger every year.
Soil damage can also be seen as tracks in growing crops where tight tracks are growing poorly and are seen as yellowed foliage. More severe damage is seen as tracks or ruts from earlier work, while some of this has been covered over in tillage fields it may still cause a growth problem later in the year.
Tillage fields show all kinds of symptoms, from severe puddling on top following potato harvesting to rutted fields from a combination of field operations. Some very deep ruts are still present in stubbles, while ponds are visible in hollows. In these hollows fine clay and soil tightening are slowing or preventing water percolation, similar to grassland.
We also see ponds appearing at the ins-and-outs on tillage fields where the headlands have been turned into the ditch for a number of consecutive years.
Poaching is another problem where livestock are the sole cause. While this causes problems for the quality of the pasture, it also results in compaction damage beneath the hoof prints. If there is significant compaction in paddocks, reseeding without loosening this compacted layer is likely to significantly shorten the lifespan of a new reseed.
So there are many ways that your soil can be damaged and quite a number of ways that it can show that damage. But damaged soil can all too often result in decreased plant growth which generally means less yield, regardless of the crop.
Soil compression and bulk density
What should you do about the problem or, more importantly, what can you do to prevent the problem from occurring. Many of our modern problems relate to the weight of the machinery now working on our land and that is unlikely to change. But it remains important to be aware of this issue and the type of damage it is causing.
Many land machines are now fitted with bigger tyres, both bigger diameter and wider, to increase the size of the footprint to reduce ground pressure.
But low ground pressure is not a guarantee of no soil damage. These bigger tyres certainly appear to have the potential to reduce compaction but as they carry more weight this force is still transmitted into the ground beneath. So, rather than compaction, the fear is that the weight, transmitted through lower ground pressure, puts a compressive force down into the soil and this is thought to go quite deep into the soil. Researchers estimate that this compression, while not necessarily producing compaction near the surface, acts to tighten the soil down to more than one meter deep.
It is the depth of this influence that is the biggest concern. How do you fix a problem that is over one meter deep? And the extent and depth of the problem is likely to be even greater when the soil is wet during trafficking. The presence of moisture makes it easier for the soil particles to be pushed together to decrease the porosity and percolation capacity of the soil.
So, before you set about attempting to solve a problem on your land, you need to know what and where the problem is. Without this knowledge you run the risk of creating more problems in the future. But any and all remedial action must wait until the ground dries out before there is any chance of longer term success and to avoid doing further damage in the process.
For example, if you pull a subsoiler through a spot that has been a wet saucer you will inevitably enable the water to percolate from the surface downwards. But if the cause of the initial problem is the clogging up of the soil pores with fine soil particles then you may only move your problem downwards. If you move it from, say, eight inches deep to 14 inches deep how will you solve that problem next time, especially if you also have compressed soil where big machines have been used?
Help the soil fix itself
Care is needed when attempting to correct soil problems. The primary focus in all soils must be to restore good biological activity. As stated previously, this means a lot of different types of soil animals and bugs but the most important for the physical condition of the soil is the earthworm.
Earthworms have two major functions in the soil, and probably hundreds of others. They eat and recycle organic materials in the soil and, as part of this process, they consume and reconstitute the particles of fine soil that are always present due to normal soil wear and tear. And, depending on the species present, they move soil and open up movement pores from deep in the soil to the soil surface.
This is about the only way (except for drought) that we can open up the soil profile to that depth and as the machines we use are not likely to get smaller in the coming years, we need to do all we can to have a biologically active soil to enable earthworms to undo the soil compression caused by heavy machinery. Earthworms are important in the generation of humus. This is important for a healthy soil. It is a mixture of the organic matter that was passed through the earthworm, combined with the soil that they ate as they tunnelled through the soil. As I understand it, humus has three very important characteristics.
1. It is a better carrier of moisture than the soil itself in dry conditions (not a recent requirement).
2. It carries plant nutrients in a manner that makes them easier to access by plant roots and this can often help plant growth early in a crop’s life when root mass is limited.
3. Humus is part of the process which reconstitutes soil broken apart by rain, wet, etc to produce the type of crumb structure that is synomonous with good soil structure, ease of cultivation, good percolation, high yields etc.
The key to good soil management in every field is to enhance biological activity. This is normally done by the addition of organic matter to increase earthworm activity. It is my belief, but unconfirmed, that this is best done with coarse materials which can be easily found by moving earthworms. This is what makes straw a good feed for earthworm multiplication, especially when it is chopped.
Dung can be equally as good but full length straw is nearly impossible for an earthworm because it cannot be cut to drag pieces down into the soil for consumption. But if finely ground bits of organic matter are left on the soil surface they can be easily consumed to provide a plentiful food supply to fuel population increase.
In patches where water is standing it is likely that the earthworm population has been destroyed. This may be the cause or the consequence of the current symptoms because they cannot survive in waterlogged soils.
Subsoiling
Many see subsoiling as a cure for compaction – it is not. When you damage a soil to the point of compaction its inherent structure is damaged in the compaction process. All a subsoiler does is burst open the soil to enable water to get down and air to enter. While these are useful benefits, they do not correct the problem of soil structure destruction.
Subsoiled land may only allow the water to sit deeper in the profile, thus holding more water deeper and decreasing trafficability over time. If the following spring is dry, subsoiling will look to have done a good job but if it is wet the original problem could look worse.
To have any potential for benefit, subsoiling should only be done when the soil is quite dry. When it is dry, one expects to get multiple fracturing of the compacted soil allowing air and water through. If this land is then managed to promote root growth into these cracks before any further weight is placed on the soil, the roots can help prevent the soil from going back together again and recompacting.
If properly managed, subsoiling can be useful but if it is done when the land is wet then the soil will not fissure and all you do is make a new problem deeper in the soil.
Where a soil has been tightened due to heavy machinery, even with good big tyres, the damage is likely to be present well below the working depth of the subsoiler. In this case, you only move water from the surface to a greater depth, producing a problem that will be much more difficult to deal with at a later stage.
The initial advice still holds – manage the soil to be healthy and biologically active. Such soils can both better withstand the pressure for damage and also recover faster in the event that damage occurs. Good tyres help prevent or reduce compaction but they may not prevent soil compression further down. When this happens the soil will hold more water, making the risk of further damage more likely.
The only influence we can really have on soil physical properties is via soil biological activity and earthworms in particular. We want them to dig out new pores and channels in the soil to help water percolation and access to nutrients. These initially allow air to move through the soil, followed by water and plant roots. Once roots grow through they act to keep the pores in place because when they die they provide a channel for the next root to grow through.
Recognising compaction
Compacted soils prevent or slow root growth and water percolation. This will mean more run-off and the risk of soil erosion. Getting out the spade is the only way to really examine your soil. The ‘Thinksoils – Soil assessment to avoid erosion and run-off’ book, produced by the Environment Agency in the Britain, provides a terrific picture reference to help farmers recognise soil problems.
Because compacted soils have much lower water percolation they will be more prone to surface run-off. They may also show signs of anaerobic conditions or rust flecking in the soil as water prevents air movement.
Serious compaction will limit crop growth and yield. Compaction can occur at the surface as smearing; it can occur in the top-soil caused by machinery or stock; it can also be in the subsoil caused by heavy machinery compressing the soil, especially during wet soil conditions.
Removing compaction
Alleviating soil damage is not a simple task because there are many different potential problems and causes. Some problems occur on pervious subsoil while others are on impervious subsoil – the former is more easily fixed.
Surface compaction, often found after maize or potato harvesting where the soil is bare on top, can be alleviated by simple shallow cultivation to break the surface cap. It can sometimes be enough to pull a cultivator across a hill to enable surface water to percolate as it flows down the hill.
Machine compaction can often be removed by ploughing, but sometimes subsoiling is necessary. But it is critical to know where the damage is in the soil to target a mechanical solution. Problems resulting from substantial soil compression are much more difficult and can only be targeted through increased earthworm activity. Dryness is a great cure of soil problems but it’s outside of our control. All potential mechanical solutions will only be successful if the soil is dry during the process.
Surface compaction and ponding are dealt with in different ways.
If a problem is purely surface then knifing in dry conditions can be an adequate solution to enable air and water movement. But sometimes deeper loosening can be justified during reseeding for example.
Subsoil tightening resulting from excessive weight is impossible to remove physically.
So care of the soil is essential for repair and to help prevent damage. Perhaps the most important fact to remember is that well structured soils are more resistant to compressive forces and so we must do all we can to support the continuous regeneration of soil structure. This means feeding the soil organisms to encourage soil biological functioning, as this is the primary means of restoring soil structure.
KEY POINTS
Fine soil particles can move down into the soil profile clogging up the pores and slowing water percolation.Compaction can occur in different zones in a soil and its treatment must be properly targeted.Subsoiling is widely misused and can result in more severe soil damage further down the soil profile than the initial problem.Prevention of compaction and subsoil compression must be a target of all farming systems.
This is a subscriber-only article
SHARING OPTIONS: