AbstractIntensive 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.