Influence of Reduced N Diets on Ammonia Emissions from Cattle Feedlot Pens

Nitrogen (N) loss from cattle feedlots on Colorado’s Front Range is contributing to nitrogen enrichment and measureable ecological changes in Colorado’s pristine alpine environments. Though agriculture is one of many N sources, mitigation of N losses is critical to reverse ecological changes and address widespread concern among the public, and State and Federal agencies tasked with addressing the problem. We collected intact soil core samples (n=36 per treatment) of feedlot pen surfaces to measure ammonia volatilization from 12 pens (4 per treatment) under a reduced (11.62% crude protein), oscillating (13.5% crude protein 4 days/wk and 11.62% crude protein 3 days/wk) and a control diet (13.5% crude protein). Intact soil/manure cores were loaded into a 12 chamber flow-through laboratory ammonia flux system and ammonia was trapped for a period of 7 days in acid bubblers that were switched out every 24 hours. Samples were decanted, diluted and analyzed using a Flow Injection Analyzer. We observed significantly lower ammonia emissions (25 to 40%) from the reduced N treatment compared to the control diet. Cattle on different diet treatments showed no significant differences in their average daily gains through 120 days of the feeding trial.