Analysis of the impact to ammonia emissions of covers on slurry/digestate stores near nitrogen-sensitive protected habitats in England

Carnell, E.J. ORCID:; Misselbrook, T.; Tomlinson, S.J. ORCID:; Dragosits, U. ORCID: 2021 Analysis of the impact to ammonia emissions of covers on slurry/digestate stores near nitrogen-sensitive protected habitats in England. Wallingford, UK Centre for Ecology & Hydrology, 33pp. (UKCEH Project no. 06498) (Unpublished)

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This study investigated the potential impact of installing covers on slurry and digestate stores on ammonia emissions in England, both at a country scale and spatially targeting this measure near nitrogen-sensitive designated sites (SACs, SSSIs). The analysis was carried out in three steps: 1) Profiling each holding with cattle and/or pigs present to determine the probability of slurry storage, including store type, on the farm, using assumptions based on average practice by livestock sector (dairy, beef, pig) and herd size. 2) Quantifying emissions from slurry storage for each nitrogen-sensitive designated site, using the holding level probabilities from Step 1, for concentric zones of 1 km, 2 km, 5 km and 10 km. 3) Estimating the potential savings of emissions from covering all slurry stores for England as a whole and the spatial distribution of these potential benefits in relation to the location of sensitive designated sites. Natural crusting of slurry stores reduces ammonia emission by an average of 50%, whereas floating covers can reduce emissions by ca. 60% and rigid covers by ca/ 80%. Installing the most effective covers on all on-farm slurry stores (i.e. impermeable covers on above-ground tanks and permeable covers on lagoons) was estimated to reduce emissions from slurry stores by ~2.5 kt NH3. This would provide a saving of 36% in emissions associated with the storage of slurries in England overall (2019), from a current best estimate of 6.9 kt NH3. The largest savings are associated with the dairy sector (1.5 kt NH3, followed by 0.6 kt for pigs and 0.3 kt for beef cattle). Covering all suitable stores would therefore contribute towards achieving the targets of the NECR and objectives of the CAS and 25 Year Environment Plan, by reducing atmospheric emissions and their subsequent impacts on sensitive habitats and designated sites through elevated ammonia concentration and nitrogen deposition. It has been demonstrated that spatial targeting of ammonia reduction measures near designated sites gives higher returns for investment in mitigation than an even spread of the same effort across the country (e.g. Defra Project AC0109 , and JNCC/Defra project Nitrogen Futures ). The total predicted emission reductions from slurry covers within 1 km of all SACs and SSSIs are relatively small (compared to covering all slurry stores), at 183 t and 418 t NH3, respectively, or 366 t and 884 t NH3, for all suitable stores within 2 km of SACs and SSSIs, respectively. However, mitigation of intensive local “hot spot” point sources such as slurry stores by up to 80% (depending on the system in use) can reduce elevated atmospheric concentrations at nearby designated sites considerably. Therefore, if slurry covers were prioritised close to designated sites, i.e. using a spatially targeted approach, this could make a considerable difference to those sites. It should be noted that emission reductions at the storage stage of manure management result in a higher proportion of valuable nitrogen fertiliser being retained for land spreading to arable crops and grassland. If the slurry is then spread with low-emission techniques such as injection or trailing hose/trailing shoe, using best practice, this can result in savings due to less additional mineral nitrogen fertiliser being needed to achieve the same overall nitrogen input. If slurry stored under covers is spread using splash-plate technology, there is the potential for more ammonia being volatilised. However, this does not offset all savings from the installation of covers. If such measures were supported in, e.g., the Environmental Land Management Scheme under development, it would be important to clearly record the location of the measures (holding ID), the type of store and cover, and the volume and surface area of the store. By making such data available for use in the UK’s agricultural emission inventory, this would then enable crediting measures explicitly and ensuring that progress in emission reductions can be reported accurately. This is not only important for NECR targets, but also for enabling more accurate assessments and reporting of local emissions for quantifying the environmental benefits.

Item Type: Publication - Report (Project Report)
UKCEH and CEH Sections/Science Areas: Atmospheric Chemistry and Effects (Science Area 2017-)
Pollution (Science Area 2017-)
Funders/Sponsors: Defra
Additional Keywords: slurry, digestate
NORA Subject Terms: Atmospheric Sciences
Date made live: 07 Dec 2021 12:04 +0 (UTC)

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