Ammonia deposition in the neighbourhood of an intensive cattle feedlot in Victoria, Australia.

Intensive cattle feedlots are large emission sources of ammonia (NH3), but NH3 deposition to the landscape downwind of feedlots is not well understood. We conducted the first study in Australia to measure NH3 dry deposition within 1 km of a commercial beef cattle feedlot in Victoria. NH3 concentrations and deposition fluxes decreased exponentially with distance away from the feedlot. The mean NH3 concentrations decreased from 419 μg N m(-3) at 50 m to 36 μg N m(-3) at 1 km, while the mean NH3 dry deposition fluxes decreased from 2.38 μg N m(-2) s(-1) at 50 m to 0.20 μg N m(-2) s(-1) at 1 km downwind from the feedlot. These results extrapolate to NH3 deposition of 53.9 tonne N yr(-1) in the area within 1 km from the feedlot, or 67.5 kg N ha(-1) yr(-1) as an area-weighted mean, accounting for 8.1% of the annual NH3-N emissions from the feedlot. Thus NH3 deposition around feedlots is a significant nitrogen input for surrounding ecosystems. Researches need be conducted to evaluate the impacts of NH3 deposition on the surrounding natural or semi-naturals ecosystems and to reduce N fertilizer application rate for the surrounding crops by considering nitrogen input from NH3 deposition.