AbstractIn open beef feedlot systems, more than 50% of dietary nitrogen (N) is lost as ammonia (NH₃). Here we report an effective and economically-viable method to mitigate NH₃ emissions by the application of lignite. We constructed two cattle pens (20 × 20 m) to determine the effectiveness of lignite in reducing NH₃ emissions. Twenty-four steers were fed identical commercial rations in each pen. The treatment pen surface was dressed with 4.5 kg m⁻² lignite dry mass while no lignite was applied in the control pen. We measured volatilised NH₃ concentrations using Ecotech EC9842 NH₃ analysers in conjunction with a mass balance method to calculate NH₃ fluxes. Application of lignite decreased NH₃ loss from the pen by approximately 66%. The cumulative NH₃ losses were 6.26 and 2.13 kg N head⁻¹ in the control and lignite treatment, respectively. In addition to the environmental benefits of reduced NH₃ losses, the value of retained N nutrient in the lignite treated manure is more than $37 AUD head⁻¹ yr⁻¹, based on the current fertiliser cost and estimated cost of lignite application. We show that lignite application is a cost-effective method to reduce NH₃ loss from cattle feedlots.