Ammonia levels in the air are high in NI. These high levels can have wide-
ranging negative environ-mental effects on sensitive habitats, human health and climate change. International targets have
been set for the reduction of ammonia emissions, and the UK must achieve a reduction of 16 per cent by 2030, in comparison to 2005 levels.
This article is the sixth in a series of articles from AFBI looking at the ammonia issue. In a previous article, the impact of a suite of ammonia abatement strategies adopted Province-wide was shown to reduce ammonia emissions across NI by 25 per cent. Last week’s article demonstrated that the adoption of proven ammonia reduction technologies, many of them with a low cost, can reduce emissions on typical dairy farms by over 43 per cent and on typical beef farms by 34-42 per cent.
As part of the same research programme, AFBI, working in collaboration with Rothamsted Research, has also been modelling ammonia emissions for typical Northern Ireland pig and poultry enterprises using the UK inventory model (NARSES). A number of proven and practical ammonia reduction measures have been applied to these baseline scenarios to evaluate the overall effect on the ammonia emissions from typical pig and poultry farms to demonstrate the reductions achievable on individual farms.
Pig System Scenarios
The two systems investigated here generally represent a large proportion of NI pig producers. These are:
1) Sows and litter (to 40kg) and
2) Finishing pigs (40 to 115kg).
Table 1 outlines the key parameters adopted as a ‘baseline’ for each of these systems.
Ammonia Reduction Strategies
Various ammonia reduction strat-egies were applied to both pig systems to generate ‘mitigation scenarios’.
These included: (see chart). A fifth measure, pH adjustment of slurry in house (acidification), was applied to a duplicate of scenario 2.
As shown in Figure 1, in the sows and litter scenario (1) total ammonia emission are reduced by 45 per cent. The majority of these reductions are achieved in housing due to the modelled genetic improvement of the animal and the frequent removal of slurry to a covered outdoor store.
A move to covered slurry stores achieves proportionally higher emission reductions in the pig sector than in the cattle sector due to the higher ammoniacal nitrogen content of pig slurry compared with cattle slurry, and the fact that pig slurry does not crust as readily as cattle slurry. Crusting creates a natural barrier and helps to reduce some of the ammonia emissions from slurry storage. Finally, land spreading emissions are reduced by approximately 60 per cent with the move from splash plate to trailing shoe.
In the finishing pig scenario (2) a total ammonia reduction of 55 per cent is achieved with the additional reduction above the previous scenario largely due to the reduction in the dietary crude protein (CP) to an optimal level. When an pH adjustment to slurry in-house (acidification) was added to this scenario (3) total farm ammonia was reduced by 79 per cent. This is a very significant additional reduction, however the effects on soil health of long-term application of pH adjusted (acidified) slurry to land requires further research.
Poultry System Scenarios
A range of typical NI poultry systems were modelled, but the two being shown here represent 1) a standard broiler system and, 2) a multi-tier free-range layer system. Table 2 outlines the key parameters used in each of the systems as a ‘baseline’.
Ammonia Reduction Strategies
Three ammonia reduction mea-sures were applied to each poultry system (see chart).
Both scenarios achieved a 24 per cent reduction in total ammonia emissions when the abatement measures were applied (Figure 2). The majority of reductions are achieved in housing, due to the modelled genetic improvement of the birds, the optimised CP diet and increased litter dry matter. However, these measures also reduce emissions at land spreading as lower nitrogen excretion leads to manure with a lower ammoniacal nitrogen content.
Manure land spreading emissions are a significant proportion of total emissions from a poultry system (as assumed here).
However, in Northern Ireland a large proportion of poultry manure is exported off-farm, so land spreading emissions may not be a component of the local system.
If we omit land spreading emissions from the calculations, ammonia emission reductions of 35 per cent are achievable across both scenarios.
Ammonia reductions during poultry litter land spreading to grassland are inherently difficult to achieve. Incorporation of poultry manure into tilled land within 24 hours of application will give significant emission reductions over broadcast spreading on grassland, but this was not modelled on this occasion.
Another reduction option would be to spread only under favourable weather conditions, ie, cool temp-eratures, or to treat litter in house or storage with alum, which has gained popularity in the US and can achieve emission reductions of up to 70 per cent through acidification.
However, similar to the acid-ification of pig slurry, the effects on soil health of long-term application of acidified manure to land requires further research.
Air scrubbers also offer significant emission reduction potential (up to 90 per cent reduction of housing emissions) for both pig and poultry facilities. But this measure was not modelled as it is seen as a relatively expensive ‘end of pipe’ solution.
Scrubbers are most effective in mechanically ventilated accom-modation and not as effective in free-range systems.
Overall, significant reductions in ammonia emissions are achievable across the pig and poultry scenarios modelled using existing and proven ammonia reduction strategies which are technically feasible and could be adopted within a 5-10 year timeframe.
Genetic improvement is some-thing that will continue to develop through selecting for feed efficiency.
Optimised crude protein diets are a cost-effective method to reduce nitrogen excretion and subsequently ammonia emissions.
Changes to manure management, such as covering slurry stores, drying litter and spreading slurry by trailing shoe, will require more significant capital investment on
farms, but are important if significant reductions in emissions from the sectors are to be made.
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