The recently launched Teagasc marginal abatement cost curve (MACC) for ammonia emissions provides a framework to help the industry on the island address this serious challenge. It is primarily an issue for the livestock sector, but ammonia loss can also occur from any soil system that is heavily loaded with nitrogen.
The ultimate objective of a MACC analysis is to quantify the extent and costs associated with measures to help meet future ammonia emissions targets. These have been negotiated as part of the amended clean air policy package.
Loss of ammonia via emissions is important, both in terms of compliance with the national emissions ceilings directive and as a source of nitrogen loss from agriculture.
Improving nitrogen use efficiency is a key focus for improving farm efficiency and sustainability. It is also important in terms of reducing the ammonia, nitrate and greenhouse gas (GHG) footprint of agriculture.
The direction of policy evolution is evident, regardless of jurisdiction, and agriculture will have to play its part in reducing these emissions.
Major causes
In its report, Teagasc logged total annual ammonia emissions over the years and attributed them across the major causes, which are predominantly livestock-based plus the contribution from inorganic nitrogen fertiliser (especially urea) and sewage sludge applied to soils.
In recent years (since 2011), ammonia emissions have been increasing, with a particular spike from 2016.
At that point, the expansion in dairy farming saw higher livestock numbers, but also the movement of land out of relatively low-emission tillage cropping into dairy operations with higher emissions.
Nearly all ammonia emissions on this island come from agricultural activities (99.2% in the Republic and 96% in Northern Ireland).
And in the south, 89.4% of the total originates from animal manures. However, it is important to state that emissions are estimated based on livestock numbers, rather than physically measured.
Loss of ammonia can occur at different points in production systems and from all types of livestock – bovines, pigs, and poultry. They can occur in a grazing system, during slurry or manure spreading, from housing and from manure storage.
Losses can also occur directly or indirectly from the loading of nitrogen in soil systems, which is affected by nitrogen fertiliser use, manure or slurry usage, legumes and the crude protein levels used in animal feeds.
The higher the nitrogen loading in a soil, the greater the risk of ammonia loss through natural soil-based processes. Many of the measures proposed to reduce emissions seek to optimise the use of all N sources without necessarily affecting production.
Addressing the loss pathways is not simple. For example, measures to reduce ammonia losses during slurry storage mean more of the nitrogen is retained and this can lead to losses elsewhere in the system if it is not properly accounted for.
However, if ammonia loss is minimised throughout the manure management chain, and if the overall N levels in the diet can be reduced, this can improve the nutrient use efficiency of organic manures and lead to fertiliser N reductions.
This, in turn, would lower the overall emissions associated with synthetic fertiliser use.
Pollution swopping
The report points out that measures to reduce ammonia loss, such as low-emission spreading or injection, can do that successfully, but they can also result in increased losses of other nitrogenous compounds such as N2O (nitrous oxide). So, all measures must be weighed up against the range of mitigation possibilities.
One mitigation measure involves the switch from standard urea to protected urea. This is an obvious measure on grassland, as urea is a very high ammonia risk product, particularly when temperatures rise a little in spring.
A second element of fertiliser mitigation involves a switch from CAN to protected urea. As CAN carries the lowest risk of ammonia emissions, the switch from it to protected urea will result in some increase in ammonia emissions alongside a significant reduction in N2O emissions (which is a GHG).
However, if the overall N loading in a soil is reduced, it can benefit all emissions. It is important to remember that nitrate, and all other nitrogen molecules, can be transformed to different N compounds in the soil and high N loadings in themselves will result in ammonia production and loss. These antagonistic relationships between emission reduction measures must be considered within an integrated analytic framework.
The problem with ammonia loss
A simple justification to address this problem is that ammonia emission represents a loss of nitrogen. Nitrogen is a cost to farming, as fertiliser, slurry handling, clover inclusion in swards, protein in diets, etc.
The better use we can make of this resource, the more efficient farming will be.
We must also comply with the legislative requirement, which sees ammonia as an air pollutant. Ammonia is a soluble gas. When it leaves our fields it can be blown in the wind and fall elsewhere in rain.
If it only fell on agricultural fields that might be considered a bonus. But it is not so obliging and N-containing rain also falls in places which are very sensitive to additional nitrogen.
This concern for ecosystems and heritage items is increasingly evident everywhere, but it has already become a driver of decisions in Northern Ireland, where there are many more intensive livestock systems.
Teagasc identified 13 different measures in its MACC to address ammonia emissions.
These include increased use of protected urea, liming, increased use of clover, low-emission slurry or manure spreading, adding amendments to slurry or manure, covering slurry stores, a reduction in crude protein for dairy cows and pigs, and the drying of poultry manure.
All MACC tables rank mitigation measures (in this case on the basis of €/t of ammonia abated) from the most cost-beneficial measures (ie measures that not only reduce ammonia emissions, but also save farmers money) to the cost prohibitive measures (those that save ammonia emissions but which are relatively expensive). On the chart (Figure 1), measures that sit below the X-axis on the left-hand side of the graph have a cost benefit while those above the X-axis (the zero line), to the right of the graph represent a cost to farming.
The MACC also indicates the magnitude of the abatement potential of each measure in kilo tonnes (‘000) of ammonia. So, it shows the relative cost and potential benefit of different measures, with the height of the bar indicative of the cost and the width indicative of the abatement potential.
The Teagasc report analysed three different scenarios (S1, S2 & S3) relating to future farming activity and policy, which are summarised in Table 1.
The main activity consequences are summarised as follows:
S1: In this scenario, dairy cow numbers would continue to increase, with suckler numbers falling to 2030 to leave a slight decrease in total cattle numbers. Overall nitrogen use would increase out to 2030.
S2: In this scenario dairy cow numbers would increase to about 2027 and then decline slightly. Suckler numbers would show the same decrease as in S1, leaving total cattle number falling from 2020. In this case, there would only be a very modest increase in overall N use.
S3: In this case, dairy cow numbers would continue to increase significantly out to 2030 and there would be a much smaller reduction in suckler cow numbers to leave total cattle numbers increasing out to about 2027 and then levelling out. Achieving this would see a significant increase in nitrogen usage.
The outcomes
If there is no mitigation employed, all three scenarios would considerably exceed our 2030 emissions target, with S1 being worst and S2 being best.
If we do the maximum possible mitigation, ammonia emission under both S1 and S2 would be below the target level in 2030.
The maximum mitigation assumes:
That all the urea would revert to protected urea, as well as 50% of the CAN-based fertilisers. A high level of low-emission spreading by 2030.The use of slurry or manure amendments to decrease ammonia loss. All open slurry stores to be covered by 2030. Reduced crude protein level in dairy and pig rations.All poultry manure to be dried. LESS only part of the solution for NI
With an agricultural sector dominated by livestock production, it is perhaps inevitable that Northern Ireland (NI) has higher ammonia emissions per square kilometre of area than the Republic of Ireland (ROI) or any of the UK nations.
Figures produced by Rothamsted Research in England estimate emissions in NI at over 2t per square kilometre, compared with 1.5t in ROI, just over 1t in England and Wales and less than 0.5t in Scotland.
The main issue in NI is the impact that these ammonia emissions are having on internationally designated sites and protected habitats.
Excess nitrogen (N) from ammonia in these areas results in plants that are adapted to low-N concentrations being outcompeted by more N-tolerant plants, leading to biodiversity loss.
Most designated sites and priority sites in NI are significantly above their critical load for N.
To meet international obligations and to improve the situation at designated sites, scientists and policy-makers in NI estimate that by 2030 ammonia emissions need to fall by at least 25%. That is an extremely challenging target and, in the coming weeks, NI’s Minister for Agriculture Edwin Poots is expected to publish a draft ammonia action plan, which will set the policy direction for the years to come.
The switch to LESS
At the forefront of that plan will be a switch to low-emission slurry spreading (LESS) technology. Already, new rules will require slurry contractors to use LESS equipment from 1 February 2021 and, in the following year, all large farms with more than 200 livestock units will be required to follow suit.
But a recent report by an expert group, led by Devenish Agriculture director Dr John Gilliland, went further than that and recommended that slurry spreading using splash plates be banned from 2025.
So what impact will this have on NI emissions? Research at the Agri-food and Biosciences Institute (AFBI) in NI suggests that where splash plates are used, 80% to 100% of the available N is lost as ammonia.
Compared with the traditional splash plate, a trailing hose (dribble bar) system reduces these ammonia losses by 30% and a trailing shoe system by 60%.
Knock-on benefits
That has knock-on benefits for grass growth and in an AFBI trial looking at second-cut silage yields, respective increases of 19% and 21% were noted for trailing hose and trailing shoe systems, when compared with a splash plate.
But investing in LESS equipment is a significant cost and previous work in NI has suggested that it is only cost effective in herds of at least 300 cows. Grant funding is crucial if farmers are to make the switch.
Even if all slurry in NI was spread using LESS, it only goes part of the way to meeting the 25% reduction target. Recent estimates presented by Dr John McIlroy from AFBI indicated that a switch to 50% trailing shoe and 50% trailing hose for all NI slurry would only cut agricultural emissions by 10%.
As a result, other interventions are required if NI is to meet its 25% reduction target.
Ten steps to meeting
the target
In the early 2000s, the UK developed a model to predict ammonia emissions from agriculture.
Known as the national ammonia reduction strategy evaluation system (NARSES) model, it is recognised by the European Environment Agency as a best-practice approach to monitoring and evaluating flows of nitrogen within agriculture.
A lead UK researcher in this area is Professor Tom Misselbrook from Rothamsted Research in Devon. He has used the NARSES model to predict ammonia emissions from NI agriculture and the potential impact of various mitigation measures.
At an online event earlier this autumn, Misselbrook set out 10 potential mitigation scenarios to be applied over the next five to 10 years that would cut ammonia emissions by the targeted 25% in NI.
Unsurprisingly, that list includes a complete switch to low-emission slurry spreading and from using straight to using protected urea.
But while the other eight measures are considered by researchers to be feasible and practical to implement by farmers, they would require significant changes within the industry.
Included is a new focus on lowering the crude protein of diets and linking specific diets to the production potential of dairy and beef cattle, pigs and poultry. That would reduce nitrogen loss as urine and, ultimately, ammonia emissions. Uptake is assumed at 75%. Other measures include continued genetic gains in pigs and poultry to improve feed efficiency and also reducing emissions in a proportion of pig and poultry housing by various technologies such as frequent belt removal of manure.
The remaining measures required to achieve the 25% reduction are mostly targeted at the cattle sector.
Extending the grazing season by two weeks for all NI cattle sounds feasible, but it would be a challenge. The model also assumes that 25% of beef cattle and 35% of dairy cattle are kept in “low-emission cattle housing” with slat mats and regularly scraped floors; 15% of dairy collection yards are roofed, slatted and have a scraping system; 30% of slurry stores are covered; and there is a limited uptake of acid treatment of slurry at both storage and spreading.
In short
Losses of ammonia are most associated with livestock systems, but also with the spreading of urea.A higher proportion of housed intensive livestock adds to the risk of loss.The use of low emission slurry spreading systems and a move to protected urea will be key measures to achieve reductions, north and south.It is likely that additional measures with be required in Northern Ireland where the overall problem is even more severe.
The recently launched Teagasc marginal abatement cost curve (MACC) for ammonia emissions provides a framework to help the industry on the island address this serious challenge. It is primarily an issue for the livestock sector, but ammonia loss can also occur from any soil system that is heavily loaded with nitrogen.
The ultimate objective of a MACC analysis is to quantify the extent and costs associated with measures to help meet future ammonia emissions targets. These have been negotiated as part of the amended clean air policy package.
Loss of ammonia via emissions is important, both in terms of compliance with the national emissions ceilings directive and as a source of nitrogen loss from agriculture.
Improving nitrogen use efficiency is a key focus for improving farm efficiency and sustainability. It is also important in terms of reducing the ammonia, nitrate and greenhouse gas (GHG) footprint of agriculture.
The direction of policy evolution is evident, regardless of jurisdiction, and agriculture will have to play its part in reducing these emissions.
Major causes
In its report, Teagasc logged total annual ammonia emissions over the years and attributed them across the major causes, which are predominantly livestock-based plus the contribution from inorganic nitrogen fertiliser (especially urea) and sewage sludge applied to soils.
In recent years (since 2011), ammonia emissions have been increasing, with a particular spike from 2016.
At that point, the expansion in dairy farming saw higher livestock numbers, but also the movement of land out of relatively low-emission tillage cropping into dairy operations with higher emissions.
Nearly all ammonia emissions on this island come from agricultural activities (99.2% in the Republic and 96% in Northern Ireland).
And in the south, 89.4% of the total originates from animal manures. However, it is important to state that emissions are estimated based on livestock numbers, rather than physically measured.
Loss of ammonia can occur at different points in production systems and from all types of livestock – bovines, pigs, and poultry. They can occur in a grazing system, during slurry or manure spreading, from housing and from manure storage.
Losses can also occur directly or indirectly from the loading of nitrogen in soil systems, which is affected by nitrogen fertiliser use, manure or slurry usage, legumes and the crude protein levels used in animal feeds.
The higher the nitrogen loading in a soil, the greater the risk of ammonia loss through natural soil-based processes. Many of the measures proposed to reduce emissions seek to optimise the use of all N sources without necessarily affecting production.
Addressing the loss pathways is not simple. For example, measures to reduce ammonia losses during slurry storage mean more of the nitrogen is retained and this can lead to losses elsewhere in the system if it is not properly accounted for.
However, if ammonia loss is minimised throughout the manure management chain, and if the overall N levels in the diet can be reduced, this can improve the nutrient use efficiency of organic manures and lead to fertiliser N reductions.
This, in turn, would lower the overall emissions associated with synthetic fertiliser use.
Pollution swopping
The report points out that measures to reduce ammonia loss, such as low-emission spreading or injection, can do that successfully, but they can also result in increased losses of other nitrogenous compounds such as N2O (nitrous oxide). So, all measures must be weighed up against the range of mitigation possibilities.
One mitigation measure involves the switch from standard urea to protected urea. This is an obvious measure on grassland, as urea is a very high ammonia risk product, particularly when temperatures rise a little in spring.
A second element of fertiliser mitigation involves a switch from CAN to protected urea. As CAN carries the lowest risk of ammonia emissions, the switch from it to protected urea will result in some increase in ammonia emissions alongside a significant reduction in N2O emissions (which is a GHG).
However, if the overall N loading in a soil is reduced, it can benefit all emissions. It is important to remember that nitrate, and all other nitrogen molecules, can be transformed to different N compounds in the soil and high N loadings in themselves will result in ammonia production and loss. These antagonistic relationships between emission reduction measures must be considered within an integrated analytic framework.
The problem with ammonia loss
A simple justification to address this problem is that ammonia emission represents a loss of nitrogen. Nitrogen is a cost to farming, as fertiliser, slurry handling, clover inclusion in swards, protein in diets, etc.
The better use we can make of this resource, the more efficient farming will be.
We must also comply with the legislative requirement, which sees ammonia as an air pollutant. Ammonia is a soluble gas. When it leaves our fields it can be blown in the wind and fall elsewhere in rain.
If it only fell on agricultural fields that might be considered a bonus. But it is not so obliging and N-containing rain also falls in places which are very sensitive to additional nitrogen.
This concern for ecosystems and heritage items is increasingly evident everywhere, but it has already become a driver of decisions in Northern Ireland, where there are many more intensive livestock systems.
Teagasc identified 13 different measures in its MACC to address ammonia emissions.
These include increased use of protected urea, liming, increased use of clover, low-emission slurry or manure spreading, adding amendments to slurry or manure, covering slurry stores, a reduction in crude protein for dairy cows and pigs, and the drying of poultry manure.
All MACC tables rank mitigation measures (in this case on the basis of €/t of ammonia abated) from the most cost-beneficial measures (ie measures that not only reduce ammonia emissions, but also save farmers money) to the cost prohibitive measures (those that save ammonia emissions but which are relatively expensive). On the chart (Figure 1), measures that sit below the X-axis on the left-hand side of the graph have a cost benefit while those above the X-axis (the zero line), to the right of the graph represent a cost to farming.
The MACC also indicates the magnitude of the abatement potential of each measure in kilo tonnes (‘000) of ammonia. So, it shows the relative cost and potential benefit of different measures, with the height of the bar indicative of the cost and the width indicative of the abatement potential.
The Teagasc report analysed three different scenarios (S1, S2 & S3) relating to future farming activity and policy, which are summarised in Table 1.
The main activity consequences are summarised as follows:
S1: In this scenario, dairy cow numbers would continue to increase, with suckler numbers falling to 2030 to leave a slight decrease in total cattle numbers. Overall nitrogen use would increase out to 2030.
S2: In this scenario dairy cow numbers would increase to about 2027 and then decline slightly. Suckler numbers would show the same decrease as in S1, leaving total cattle number falling from 2020. In this case, there would only be a very modest increase in overall N use.
S3: In this case, dairy cow numbers would continue to increase significantly out to 2030 and there would be a much smaller reduction in suckler cow numbers to leave total cattle numbers increasing out to about 2027 and then levelling out. Achieving this would see a significant increase in nitrogen usage.
The outcomes
If there is no mitigation employed, all three scenarios would considerably exceed our 2030 emissions target, with S1 being worst and S2 being best.
If we do the maximum possible mitigation, ammonia emission under both S1 and S2 would be below the target level in 2030.
The maximum mitigation assumes:
That all the urea would revert to protected urea, as well as 50% of the CAN-based fertilisers. A high level of low-emission spreading by 2030.The use of slurry or manure amendments to decrease ammonia loss. All open slurry stores to be covered by 2030. Reduced crude protein level in dairy and pig rations.All poultry manure to be dried. LESS only part of the solution for NI
With an agricultural sector dominated by livestock production, it is perhaps inevitable that Northern Ireland (NI) has higher ammonia emissions per square kilometre of area than the Republic of Ireland (ROI) or any of the UK nations.
Figures produced by Rothamsted Research in England estimate emissions in NI at over 2t per square kilometre, compared with 1.5t in ROI, just over 1t in England and Wales and less than 0.5t in Scotland.
The main issue in NI is the impact that these ammonia emissions are having on internationally designated sites and protected habitats.
Excess nitrogen (N) from ammonia in these areas results in plants that are adapted to low-N concentrations being outcompeted by more N-tolerant plants, leading to biodiversity loss.
Most designated sites and priority sites in NI are significantly above their critical load for N.
To meet international obligations and to improve the situation at designated sites, scientists and policy-makers in NI estimate that by 2030 ammonia emissions need to fall by at least 25%. That is an extremely challenging target and, in the coming weeks, NI’s Minister for Agriculture Edwin Poots is expected to publish a draft ammonia action plan, which will set the policy direction for the years to come.
The switch to LESS
At the forefront of that plan will be a switch to low-emission slurry spreading (LESS) technology. Already, new rules will require slurry contractors to use LESS equipment from 1 February 2021 and, in the following year, all large farms with more than 200 livestock units will be required to follow suit.
But a recent report by an expert group, led by Devenish Agriculture director Dr John Gilliland, went further than that and recommended that slurry spreading using splash plates be banned from 2025.
So what impact will this have on NI emissions? Research at the Agri-food and Biosciences Institute (AFBI) in NI suggests that where splash plates are used, 80% to 100% of the available N is lost as ammonia.
Compared with the traditional splash plate, a trailing hose (dribble bar) system reduces these ammonia losses by 30% and a trailing shoe system by 60%.
Knock-on benefits
That has knock-on benefits for grass growth and in an AFBI trial looking at second-cut silage yields, respective increases of 19% and 21% were noted for trailing hose and trailing shoe systems, when compared with a splash plate.
But investing in LESS equipment is a significant cost and previous work in NI has suggested that it is only cost effective in herds of at least 300 cows. Grant funding is crucial if farmers are to make the switch.
Even if all slurry in NI was spread using LESS, it only goes part of the way to meeting the 25% reduction target. Recent estimates presented by Dr John McIlroy from AFBI indicated that a switch to 50% trailing shoe and 50% trailing hose for all NI slurry would only cut agricultural emissions by 10%.
As a result, other interventions are required if NI is to meet its 25% reduction target.
Ten steps to meeting
the target
In the early 2000s, the UK developed a model to predict ammonia emissions from agriculture.
Known as the national ammonia reduction strategy evaluation system (NARSES) model, it is recognised by the European Environment Agency as a best-practice approach to monitoring and evaluating flows of nitrogen within agriculture.
A lead UK researcher in this area is Professor Tom Misselbrook from Rothamsted Research in Devon. He has used the NARSES model to predict ammonia emissions from NI agriculture and the potential impact of various mitigation measures.
At an online event earlier this autumn, Misselbrook set out 10 potential mitigation scenarios to be applied over the next five to 10 years that would cut ammonia emissions by the targeted 25% in NI.
Unsurprisingly, that list includes a complete switch to low-emission slurry spreading and from using straight to using protected urea.
But while the other eight measures are considered by researchers to be feasible and practical to implement by farmers, they would require significant changes within the industry.
Included is a new focus on lowering the crude protein of diets and linking specific diets to the production potential of dairy and beef cattle, pigs and poultry. That would reduce nitrogen loss as urine and, ultimately, ammonia emissions. Uptake is assumed at 75%. Other measures include continued genetic gains in pigs and poultry to improve feed efficiency and also reducing emissions in a proportion of pig and poultry housing by various technologies such as frequent belt removal of manure.
The remaining measures required to achieve the 25% reduction are mostly targeted at the cattle sector.
Extending the grazing season by two weeks for all NI cattle sounds feasible, but it would be a challenge. The model also assumes that 25% of beef cattle and 35% of dairy cattle are kept in “low-emission cattle housing” with slat mats and regularly scraped floors; 15% of dairy collection yards are roofed, slatted and have a scraping system; 30% of slurry stores are covered; and there is a limited uptake of acid treatment of slurry at both storage and spreading.
In short
Losses of ammonia are most associated with livestock systems, but also with the spreading of urea.A higher proportion of housed intensive livestock adds to the risk of loss.The use of low emission slurry spreading systems and a move to protected urea will be key measures to achieve reductions, north and south.It is likely that additional measures with be required in Northern Ireland where the overall problem is even more severe. 
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