Title: Estimation of ammonia emissions from two commercial beef cattle feedyards in the southern high plains with process-based models Authors
Submitted to: Meeting Proceedings
Publication Type: Proceedings
Publication Acceptance Date: March 15, 2013
Publication Date: April 3, 2013
Citation: Waldrip, H., Rotz, C.A., Li, C., Todd, R.W., Salas, W.G., Cole, N.A. 2013. Estimation of ammonia emissions from two commercial beef cattle feedyards in the southern high plains with process-based models. Proceedings of the National Conference on Livestock and Poultry Environmental quality; from Waste to Worth:spreading science and solutions. 1:85. 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 71 to 81% 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 66 and 53 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 77 and 61 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 5% to 15% of observations for the two feedyards; whereas, the constant emission factor underestimated annual feedyard emissions by 43% to 64%. 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.