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What does the clean-air strategy translate to on British dairy farms?

With ambitious targets for the dairy industry laid out in Defra’s January-launched clean air strategy, farmers were offered some practical tips around what this could mean on-farm. 


Speaking at the recent Royal Association of British Dairy Farmers (RABDF) business and policy conference in Westminster, David Ball of AHDB’s environment and resource management team outlined some of the options and measures farmers may need to consider.


He explained that, in addition to the impact reducing ammonia emissions would have on protecting sensitive habitats and nitrification of various waterways, there was a potential cost-saving to be had from better utilisation of nitrogen within a system.


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Using the example of a large-scale open slurry lagoon giving off 2kg as ammonia per square metre per year, he highlighted that this would equate to £2,500 lost in nitrogen through the year.


It was crucial though, he added, to make sure that nitrogen was efficiently utilised once it had been saved and in addition to reducing exposed surface area via a slurry store or yard, he highlighted reducing airflow across these surfaces, temperature and slurry pH as factors which could potentially impact emission rate.


He outlined a number of practical methods dairy farmers could consider to lower ammonia emissions on their own farms.

1. Efficient feeding strategies

Mr Ball explained that, with the main source of nitrogen obtained by the animal being dietary protein, efficient feeding strategies were a good place to start.


He said: “Cows are not very efficient utilisers of protein and have a low efficiency rate in terms of converting this to milk production, with the rest excreted, so if protein feeding is properly balanced to match requirements, less nitrogen will be excreted and less ammonia will be produced from the slurry.”


In discussing the findings from some AHDB commissioned research, Mr Ball said in nutritionally balanced maize silage-based diets, crude protein levels in milking cow diets can be successfully reduced to 15 per cent with no detrimental effect on milk output or fertility.


2. Housing design and practices

Mr Ball said keeping floors in livestock areas clean would reduce ammonia emissions, and short of an entire building redesign with emission reduction at the helm, offered some tips around practices within existing housing systems which could help.


He said: “Concrete yards and passages contaminated with slurry provide an emitting surface, so frequent cleaning will reduce ammonia emissions.


“Passageways and livestock handling areas should be scraped as regularly as possible, possibly with automatic scrapers or robots, to prevent slurry pooling and minimise fouled floor areas as far as possible which can reduce the amount of ammonia admitted.


“Installing a floor design which drains well is also something to consider when and if this is an option, with examples highlighting a 30 to 50 per cent reduction in emissions as a result.”


3. Slurry storage systems

Having highlighted exposed surface area as a factor which affects emission rate, Mr Ball spoke about methods which could be used to cover manure and slurry storage systems to reduce this and therefore lower the levels of ammonia emissions given off.


He said: “Open lagoons and slurry stores allow ammonia to escape into the atmosphere so it is about creating a wall to stop that process.


“An open lagoon with a floating cover could see a 60 per cent reduction in ammonia emissions given off, with a fixed cover on a tin tank potentially able to achieve up to 80 per cent.

4. Manure application techniques

Utilising slurry efficiently when applying it out in the field was crucial to minimising ammonia losses at the time of spreading, and Mr Ball highlighted a number of pieces of spreading equipment which could help to achieve this.


“Ammonia emissions are increased when slurry comes into contact with the air, especially when conditions are favourable, in warm, windy conditions.


“Using shallow injection, trailing shoe or dribble bar equipment to spread slurry will reduce this, with up to a 30 to 60 per cent reduction possible using a trailing shoe, and 30 to 35 per cent with a dribble bar.


"Shallow injection can reduce ammonia emissions at spreading by up to 70% per cent.”


Slurry acidification: Experience from the pig sector


With some regulation around ammonia emissions already in place within the pig sector, the audience heard an overview of a project one of the UK’s largest pig producers, Elsham Linc, has undertaken to meet these new targets.


The 7,000 sow unit in north Lincolnshire rears all its progeny through to finishing, with about 3,500 pigs finished weekly.


It began its Elsham Linc slurry acidification project at the end of July-2018, following two years of preliminary trial and investigation work, with a deadline for completion of September 2020 in four phases to secure grant funding.


David Alvis, who has been involved as a consultant project manager, explained: “Reducing ammonia emissions is part of licence to operate in order to comply with existing and future legalisation, as well as reducing impact on the environment and focussing on how reductions impact on staff and animal health.


“When completed, the project will see 11 slurry acidification plants retrofitted to 11 slatted system piggeries.


“Formed of infrastructure revolving around a large process tank, slurry is dropped out of every building daily through a valve block where it is treated with sulphuric acid to reduce the pH.


“Slurry is separated at the same time to remove the solids, with part of the acidified slurry pumped back under the slats, which then acts as a buffer for the following material. The rest is pumped into the storage tank.”


As at October 2019, five of the 11 proposed plants have been installed, with the rest on schedule to be completed by the deadline.


Outlining initial observations, Mr Alvis said: “There is a noticeably improved environment inside buildings as soon as the system is switched on.


"Slurry channels under the slats are kept free of solids, which has resulted in a much lower level of fly activity in the summer months as well as the slurry having noticeably less odour.


“Although we have not got enough data to say with certainty yet what the impact has been on growth rates and feed conversion efficiency, it is looking promising.”


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