At the ITLUS conference on organic manures and soil in early December, Dr Patrick Forrestal of Teagasc emphasised that soil health is not a conventional versus organic issue.
Care for our soils continues to be of paramount importance to all farmers but not all farmers exercise this requirement.
Soil degrades naturally and degraded soil can be easily lost from a field. But soil that is lost takes generations to replace.
Soil is most easily lost where soil organic matter is low.
Soil is most commonly degraded by rainfall (especially on bare soil) and temperature (not our problem) and damage is likely to be worse where soil organic matter levels are low.
Patrick reminded us that soil is generally lost in one of two ways.
The heavier the rain the greater the level of damage
It can blow away with the wind, as was the case in the dustbowls in the US, or it can wash away in moving water.
This latter pathway is most familiar to us with gullies sometimes seen where water runs down hills.
Both issues arise when soil has been damaged and lacks structure, either as a result of excessive organic matter degradation (generally as a result of high temperatures and so this is most prevalent in hot climates) or where soil particles are degraded to their components of sand, silt and clay by exposure to frequent heavy rain.
And the heavier the rain the greater the level of damage.
It is important to remember that brown water, or water that contains soil, contains the very best components of your soil – the clay fraction.
Clay is the smallest of soil particles and it is the clay that carries the nutrients within its electrical charges.
So soil going out the gate by any natural means is a permanent and long term loss.
Organic matter is key to soil stability through the creation of an interlocking crumb structure which should be constantly produced within a diverse biological population in the soil.
Patrick reminded us that soil systems need to have an active combination of physical (structure), chemical (fertility) and biological (from earthworms to microorganisms) activity to be sustainable – a three-legged stool effect.
For many years, the biological element was largely ignored and this is now hindering soil productivity. Soil can only be at its peak productivity when there is an adequate focus on all three of these elements.
Soil biology
We sometimes see organisms that live in the soil as being problems for us.
When we think of pests such as leather-jackets, slugs and other plant eating bugs or diseases such as fusarium, rhizoctonia, take-all or eyespot, then this is true.
But these are only a small proportion of the total life in the soil and the more life we have, the more difficult it can be for the pest species to proliferate.
It is generally accepted that many different species live in a soil and we possibly know less than 2% of them.
There can be a lot of life in the soil and it may become more important to us in the future as we have fewer chemical tools to control our problems
These are a combination of both macro- and micro-organisms. And they can be hugely numerous, from the earthworms at the top of the food chain right down to the tiniest of the microorganisms.
Have you ever wondered what part any of these might play in preventing a pest species from causing a problem? Did you even wonder if the presence of fungi or biting insects in the soil might help to reduce the numbers of weed seeds faster?
There can be a lot of life in the soil and it may become more important to us in the future as we have fewer chemical tools to control our problems.
Scientists continue to attempt to learn about these as they try to identify the ones that can be regarded as being beneficial to either crop growth or pest reduction. But it’s a “needle in a haystack” issue.
Patrick commended that on the basis that an average person can count up to 150 in 30 seconds (and that’s fair going), it would take 6.5 years to count the multiplicity of organisms present in just one teaspoon full of healthy soil. That’s a heck of a number by any standards.
‘Organics’
One of the big talking points around the modern climate change debate is carbon. It is not just about carbon but this is the biggest element involved.
Carbon is the main building block for plant growth and so it is essential. “But where does carbon come from?” Patrick asked.
The quick answer is that it is all recycled and soil organisms play their part in this recycling process.
The bugs need carbon too and this opens the question as to where they get theirs.
We know that many macro- and micro-organisms benefit plant growth but these may not be there if we do not feed them in our soil.
Biological activity in the soil is a type of catalyst which helps to make things happen more effectively for plant growth.
This means it can also help to decrease the cost of production.
By now, it should be apparent that we need to put carbon into our soils to help make/keep them healthy.
You don’t see “carbon” listed as a constituent of inorganic fertilisers such as 10:10:20 or 18:6:12, it can only be supplied as organic matter.
Any kind of organic matter can work but some will be much faster than others depending on the amount of lignin present and the carbon-to-nitrogen ratio.
When using products such as cattle slurry we tend to put a lot of emphasis on valuing the nutrients that we purchase normally like N, P and K.
As well as being part of the nutrient recycling process, soil organisms also act to improve the structure of soils where they are used
But by far the biggest element is carbon, which is seven or eight times greater than the level of K present. It also contains a lot of K and calcium, which are important for microbes.
Patrick stated that experiments had regularly shown that if we act to reduce or decrease the level of active biology in a soil, so too do we decrease the amount of nutrient which is released by nature to support plant growth and this can be a penalty on productivity .
As well as being part of the nutrient recycling process, soil organisms also act to improve the structure of soils where they are used.
Patrick reported on an AFBI experiment which showed that the long-term use of slurries visibly improve the structure of treated soils.
Earthworms are a very important macro-organisms in our soils.
In general, they are helped by reduced tillage, either through min-till, no-till or reduced ploughing depth. But they are also helped by the addition of organic matter, which can further help any tillage system.
The importance on keeping ploughing depth to a minimum was also emphasised in terms of the cost of cultivation.
Microorganisms do not have teeth or jaws to help break up organic matter but they do use enzymes, which Patrick described as the jaws of degradation. They are critical for life and they tend to fulfil very specific functions.
For example, nitrogenase is the enzyme that helps convert atmospheric nitrogen to forms that can be utilised by the plant.
Urease converts urea to ammonia to make it a usable source of nitrogen for plants.
Benefit
Enzyme activity denotes life taking place and Patrick pointed out the great benefit of having fresh organic matter in the soil to enhance this activity.
And the more easily degradable a source of organic matter is the more life that it encourages.
So every form of organic matter that is added to the soil will help to improve it, regardless of the abundance of nutrients it contains. Organics supply carbon as well as plant nutrients.
Degradable
Patrick pointed out that it is important to remember that the more degradable an organic source is, the more short-term its benefit can be.
In this regard, it is useful to alternate organic matter sources between ones that are highly degradable, like organic manures, and ones that are much less degradable, like straw.
As well as helping the microbes, organic matter also helps the macro-organisms and numbers respond to food availability.
This is especially important as these also help to re-establish good soil structure with the help of the exudates from both plant roots and microbial activity.
Huge variability in nutrient content of manure sources
It is common to place a lot of emphasis on the nutrient content of manure sources to justify the cost and inconvenience of organic matter application.
While the previous comments from Patrick Forrestal indicate that organic additives bring many benefits to a soil, their nutrient content is still important.
For this reason, the analysis of manures and slurries might be considered to help guide actual nutrient supply as book values can deviate considerably in individual samples.
That said, even if we take the trouble of taking good representative samples and getting them analysed, these results cannot be used as the actual nutrient content of the product applied for official nutrient management purposes.
And given the huge variability that is indicated in this article, it is perhaps understandable why some farmers may choose to do nothing.
The exact nutrient content of organic manures has long been a cause for concern.
Farmers are very aware that slurries and even manures can be very variable but how variable? NRM is a big agronomic and waste analysis provider in Britain and in recent years the company produced a report outlining the variability in the organic manure samples it received for analysis.
The nutrient value of manures
Duncan Rose of NRM Laboratories talked about this report at the ITLUS meeting. Speaking on manures initially, he stated that they had found a strong correlation between dry matter and total nitrogen in manure.
He suggested that management and storage practices were likely to have had a big impact on the nutrient values and that the ammoniacal N content was even more variable.
The phosphorous levels were also very variable, ranging from 44% to 74% in the different sources.
Potassium levels were somewhat less variable but there was still big variation between samples.
Duncan said that this is a very mobile nutrient and that it is easily leached if not maintained properly.
For this reason, he said that it is important that samples for analysis be taken close to application timing.
He went on to say that pig and cattle FYM had the highest variation in dry matter content.
This had significant effect on the content of other nutrients also.
Values in slurry
The nutrient consistency in cattle and pig slurry was also quite variable but less so than with manures.
As a general rule, the report found that relatively little variability in the total nitrogen content of cattle slurry as long as the dry solids level was below 10%, but above that there was significant variation.
Pig slurry was good too but only up to 4% solids. Above that, the report found that the book values could be very misleading.
Testing of ammonia nitrogen showed much more variability in result levels, with little or no relationship to the solids level.
On the phosphorous content of cattle and pig slurry, Duncan said that the variability increased considerably in both in samples above 4% solids.
But he also commented that the actual value in cattle slurry could be double the book value in samples at 10% solids and higher.
That may well fit situations where cattle are being finished on largely concentrate diets, leaving the possibility of much higher nutrient content.
On potassium, the report concluded that book values determined by dry solids content should not be used to assess K content.
The tests found very poor correlations between K and the dry solids values for both cattle and pig slurry.
Money value
Duncan presented a few application scenarios based on the available nutrient value in different scenarios.
An application rate of 8t or 8m3/ha of pig FYM represented a financial value of application for potatoes of €63/ha.
And using pig slurry at 30t/ha for winter wheat, his estimated value depended on the level of solids with 2% equating to €81/ha, 4% equating to €114/ha and 6% equating to €147/ha. In theory, the 6% value should be treble the 2% value but the observed nutrient content did not follow suit.
A healthy soil requires a balanced approach to the maintenance of its chemical, physical and biological requirements.Organic manures bring more to a soil than nutrients and so have a higher net value.Nutrient content of any sample could be higher or lower than its book value making it a more questionable input for just nutrients alone.
At the ITLUS conference on organic manures and soil in early December, Dr Patrick Forrestal of Teagasc emphasised that soil health is not a conventional versus organic issue.
Care for our soils continues to be of paramount importance to all farmers but not all farmers exercise this requirement.
Soil degrades naturally and degraded soil can be easily lost from a field. But soil that is lost takes generations to replace.
Soil is most easily lost where soil organic matter is low.
Soil is most commonly degraded by rainfall (especially on bare soil) and temperature (not our problem) and damage is likely to be worse where soil organic matter levels are low.
Patrick reminded us that soil is generally lost in one of two ways.
The heavier the rain the greater the level of damage
It can blow away with the wind, as was the case in the dustbowls in the US, or it can wash away in moving water.
This latter pathway is most familiar to us with gullies sometimes seen where water runs down hills.
Both issues arise when soil has been damaged and lacks structure, either as a result of excessive organic matter degradation (generally as a result of high temperatures and so this is most prevalent in hot climates) or where soil particles are degraded to their components of sand, silt and clay by exposure to frequent heavy rain.
And the heavier the rain the greater the level of damage.
It is important to remember that brown water, or water that contains soil, contains the very best components of your soil – the clay fraction.
Clay is the smallest of soil particles and it is the clay that carries the nutrients within its electrical charges.
So soil going out the gate by any natural means is a permanent and long term loss.
Organic matter is key to soil stability through the creation of an interlocking crumb structure which should be constantly produced within a diverse biological population in the soil.
Patrick reminded us that soil systems need to have an active combination of physical (structure), chemical (fertility) and biological (from earthworms to microorganisms) activity to be sustainable – a three-legged stool effect.
For many years, the biological element was largely ignored and this is now hindering soil productivity. Soil can only be at its peak productivity when there is an adequate focus on all three of these elements.
Soil biology
We sometimes see organisms that live in the soil as being problems for us.
When we think of pests such as leather-jackets, slugs and other plant eating bugs or diseases such as fusarium, rhizoctonia, take-all or eyespot, then this is true.
But these are only a small proportion of the total life in the soil and the more life we have, the more difficult it can be for the pest species to proliferate.
It is generally accepted that many different species live in a soil and we possibly know less than 2% of them.
There can be a lot of life in the soil and it may become more important to us in the future as we have fewer chemical tools to control our problems
These are a combination of both macro- and micro-organisms. And they can be hugely numerous, from the earthworms at the top of the food chain right down to the tiniest of the microorganisms.
Have you ever wondered what part any of these might play in preventing a pest species from causing a problem? Did you even wonder if the presence of fungi or biting insects in the soil might help to reduce the numbers of weed seeds faster?
There can be a lot of life in the soil and it may become more important to us in the future as we have fewer chemical tools to control our problems.
Scientists continue to attempt to learn about these as they try to identify the ones that can be regarded as being beneficial to either crop growth or pest reduction. But it’s a “needle in a haystack” issue.
Patrick commended that on the basis that an average person can count up to 150 in 30 seconds (and that’s fair going), it would take 6.5 years to count the multiplicity of organisms present in just one teaspoon full of healthy soil. That’s a heck of a number by any standards.
‘Organics’
One of the big talking points around the modern climate change debate is carbon. It is not just about carbon but this is the biggest element involved.
Carbon is the main building block for plant growth and so it is essential. “But where does carbon come from?” Patrick asked.
The quick answer is that it is all recycled and soil organisms play their part in this recycling process.
The bugs need carbon too and this opens the question as to where they get theirs.
We know that many macro- and micro-organisms benefit plant growth but these may not be there if we do not feed them in our soil.
Biological activity in the soil is a type of catalyst which helps to make things happen more effectively for plant growth.
This means it can also help to decrease the cost of production.
By now, it should be apparent that we need to put carbon into our soils to help make/keep them healthy.
You don’t see “carbon” listed as a constituent of inorganic fertilisers such as 10:10:20 or 18:6:12, it can only be supplied as organic matter.
Any kind of organic matter can work but some will be much faster than others depending on the amount of lignin present and the carbon-to-nitrogen ratio.
When using products such as cattle slurry we tend to put a lot of emphasis on valuing the nutrients that we purchase normally like N, P and K.
As well as being part of the nutrient recycling process, soil organisms also act to improve the structure of soils where they are used
But by far the biggest element is carbon, which is seven or eight times greater than the level of K present. It also contains a lot of K and calcium, which are important for microbes.
Patrick stated that experiments had regularly shown that if we act to reduce or decrease the level of active biology in a soil, so too do we decrease the amount of nutrient which is released by nature to support plant growth and this can be a penalty on productivity .
As well as being part of the nutrient recycling process, soil organisms also act to improve the structure of soils where they are used.
Patrick reported on an AFBI experiment which showed that the long-term use of slurries visibly improve the structure of treated soils.
Earthworms are a very important macro-organisms in our soils.
In general, they are helped by reduced tillage, either through min-till, no-till or reduced ploughing depth. But they are also helped by the addition of organic matter, which can further help any tillage system.
The importance on keeping ploughing depth to a minimum was also emphasised in terms of the cost of cultivation.
Microorganisms do not have teeth or jaws to help break up organic matter but they do use enzymes, which Patrick described as the jaws of degradation. They are critical for life and they tend to fulfil very specific functions.
For example, nitrogenase is the enzyme that helps convert atmospheric nitrogen to forms that can be utilised by the plant.
Urease converts urea to ammonia to make it a usable source of nitrogen for plants.
Benefit
Enzyme activity denotes life taking place and Patrick pointed out the great benefit of having fresh organic matter in the soil to enhance this activity.
And the more easily degradable a source of organic matter is the more life that it encourages.
So every form of organic matter that is added to the soil will help to improve it, regardless of the abundance of nutrients it contains. Organics supply carbon as well as plant nutrients.
Degradable
Patrick pointed out that it is important to remember that the more degradable an organic source is, the more short-term its benefit can be.
In this regard, it is useful to alternate organic matter sources between ones that are highly degradable, like organic manures, and ones that are much less degradable, like straw.
As well as helping the microbes, organic matter also helps the macro-organisms and numbers respond to food availability.
This is especially important as these also help to re-establish good soil structure with the help of the exudates from both plant roots and microbial activity.
Huge variability in nutrient content of manure sources
It is common to place a lot of emphasis on the nutrient content of manure sources to justify the cost and inconvenience of organic matter application.
While the previous comments from Patrick Forrestal indicate that organic additives bring many benefits to a soil, their nutrient content is still important.
For this reason, the analysis of manures and slurries might be considered to help guide actual nutrient supply as book values can deviate considerably in individual samples.
That said, even if we take the trouble of taking good representative samples and getting them analysed, these results cannot be used as the actual nutrient content of the product applied for official nutrient management purposes.
And given the huge variability that is indicated in this article, it is perhaps understandable why some farmers may choose to do nothing.
The exact nutrient content of organic manures has long been a cause for concern.
Farmers are very aware that slurries and even manures can be very variable but how variable? NRM is a big agronomic and waste analysis provider in Britain and in recent years the company produced a report outlining the variability in the organic manure samples it received for analysis.
The nutrient value of manures
Duncan Rose of NRM Laboratories talked about this report at the ITLUS meeting. Speaking on manures initially, he stated that they had found a strong correlation between dry matter and total nitrogen in manure.
He suggested that management and storage practices were likely to have had a big impact on the nutrient values and that the ammoniacal N content was even more variable.
The phosphorous levels were also very variable, ranging from 44% to 74% in the different sources.
Potassium levels were somewhat less variable but there was still big variation between samples.
Duncan said that this is a very mobile nutrient and that it is easily leached if not maintained properly.
For this reason, he said that it is important that samples for analysis be taken close to application timing.
He went on to say that pig and cattle FYM had the highest variation in dry matter content.
This had significant effect on the content of other nutrients also.
Values in slurry
The nutrient consistency in cattle and pig slurry was also quite variable but less so than with manures.
As a general rule, the report found that relatively little variability in the total nitrogen content of cattle slurry as long as the dry solids level was below 10%, but above that there was significant variation.
Pig slurry was good too but only up to 4% solids. Above that, the report found that the book values could be very misleading.
Testing of ammonia nitrogen showed much more variability in result levels, with little or no relationship to the solids level.
On the phosphorous content of cattle and pig slurry, Duncan said that the variability increased considerably in both in samples above 4% solids.
But he also commented that the actual value in cattle slurry could be double the book value in samples at 10% solids and higher.
That may well fit situations where cattle are being finished on largely concentrate diets, leaving the possibility of much higher nutrient content.
On potassium, the report concluded that book values determined by dry solids content should not be used to assess K content.
The tests found very poor correlations between K and the dry solids values for both cattle and pig slurry.
Money value
Duncan presented a few application scenarios based on the available nutrient value in different scenarios.
An application rate of 8t or 8m3/ha of pig FYM represented a financial value of application for potatoes of €63/ha.
And using pig slurry at 30t/ha for winter wheat, his estimated value depended on the level of solids with 2% equating to €81/ha, 4% equating to €114/ha and 6% equating to €147/ha. In theory, the 6% value should be treble the 2% value but the observed nutrient content did not follow suit.
A healthy soil requires a balanced approach to the maintenance of its chemical, physical and biological requirements.Organic manures bring more to a soil than nutrients and so have a higher net value.Nutrient content of any sample could be higher or lower than its book value making it a more questionable input for just nutrients alone. 
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