Trees can help mitigate ammonia emissions from farming

Pig with piglets in a sty

11 December 2018 by Sarah McDaid

A new online calculator and guidance has been developed to help farmers and others to design woodlands to capture airborne ammonia, and so reduce air pollution.

Scientists from the Centre for Ecology & Hydrology (CEH) worked with Forest Research to develop the free online tool and guidance for users, as part of research funded by the Scottish Environment Protection Agency.

Agriculture is the main source of ammonia emissions in the UK, with the majority coming from animal manure and fertilisers. Ammonia can lead to excess reactive nitrogen levels in sensitive habitats, causing a decline in the biodiversity of lichens, mosses and other flora. It can also lead to acidification of soils, and combines with other pollutants to produce particulate matter pollution, which is harmful to human health.

By following the advice in the guidance, farmers, regulators and planning authorities can optimise tree planting to recapture ammonia around animal housing, which is a key source of ammonia emissions. The calculator estimates the percentage of ammonia that will be recaptured by different planting options, over a set time period - up to 50 years.

Diagram of effect of woodlands to capture airborne ammonia reducing air pollution

Trees can have a beneficial effect as landscape structures to mitigate ammonia (NH3) air pollution

Upwind trees provide sheltering of ammonia sources (eg slurry pit, animal housing), reducing emissions.

Downwind trees recapture ammonia from the air and recapture from livestock under the trees.

Further downwind, beyond the trees, increased mixing of the air increases dispersion.

Enhancing local recapture and dispersion reducing nitrogen deposition to sensitive habitats further downwind.

The guidance advises which tree species will thrive in different parts of the UK, what distance to plant trees from animal housing, and in what configuration. There is also information to help with the incorporation and use of existing woodlands.

Dr Bill Bealey, an ecologist at CEH, said:

Trees are particularly effective scavengers of air pollutants like ammonia. They recapture the pollutant in the tree canopy and on to the leaves, and they also help disperse the ammonia plume which reduces impacts of nitrogen pollution on nearby sensitive habitats.

Farmers who use trees to mitigate ammonia can look to a long-term range of benefits. New canopies can improve animal welfare by providing animals with shade and protection from aerial predators. They can also provide screening around animal housing units, to soften the look of buildings and minimise visibility impacts on the landscape.

Dr Elena Vanguelova, a soil sustainability expert from Forest Research, said:

Tree shelters are an agroforestry technique that have benefits for farmers and society as a whole. The capture of carbon and nitrogen by additional planting will play a role in helping the UK achieve its greenhouse gas emission reduction targets.

Our calculator and guidance provide farmers and landowners with the information they need to use nature's best nitrogen mops to mitigate the ammonia produced by animal housing units while protecting soils, waters and the wider environment.

The calculator is available for free online on the Tree Shelter Belts for Ammonia Mitigation website - external link -.