ARS | Publication request: Estimation of ammonia emissions from two commercial beef cattle feedyards in the southern high plains with process-based modeling.

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: May 17, 2013
Publication Date: N/A

Technical Abstract: Ammonia emissions from beef cattle feedyards result in loss of nitrogen that could be useful for crop production, and this emission can have negative environmental consequences. Both empirical and process-based models have been developed to estimate ammonia emissions from various livestock production systems; however, little work has been conducted to assess their accuracy for large open-lot feedyards. To validate two process-based models, Manure-DNDC and the Integrated Farm System Model (IFSM), model-simulated ammonia emissions were compared to data collected from two commercial feedyards in the Texas High Plains from 2007 to 2009. Predictions made by Manure-DNDC and IFSM were within 66 to 74% agreement with observed feedyard emissions (p < 0.001), and were sensitive to seasonal variations in air temperature and dietary crude protein concentration. Manure-DNDC predicted mean daily ammonia flux densities for the two feedyards of 43.6 and 55.7 kg ammonia per hectare, and regression analysis showed good agreement with observed data (p < 0.001). With the addition of an open-lot emission routine, IFSM predicted daily per capita emission rates of 72.8 and 60.7 g ammonia per head for the two feedyards, which also agreed well with observations (p < 0.001). Despite differences in the core models, daily Manure-DNDC and IFSM predictions were highly correlated (r = 0.74, p < 0.001). When model predictions for annual feedyard ammonia emissions were compared to predictions made with a constant emission factor that is currently used by the EPA, IFSM and Manure-DNDC estimates were within 19% to 13% of observations, respectively; whereas, the constant emission factor underestimated annual feedyard emissions by 54%. This evaluation indicates that both IFSM and Manure-DNDC are useful tools for predicting ammonia emissions from commercial feedyards, offering accurate information for policy makers and producers and methods for evaluating the effects of specific management practices and mitigation strategies.