Estimation of Ammonia Emissions from Beef Cattle Feedyards Using the Process-Based Model Manure-DNDC

Abstract

<abstract><title><italic>Abstract.</italic></title> Ammonia (NH₃) emissions from beef cattle feedyards result in loss of agronomically important nitrogen (N) and can have negative environmental consequences. Both empirical and process-based models have been developed to estimate NH₃ emissions from various livestock production systems; however, little work has been conducted to assess their accuracy for large, open-lot feedyards. To validate Manure-DNDC, a process-based biogeochemical model, Manure-DNDC-simulated daily NH₃ fluxes were compared to emission data collected from two commercial feedyards, feedyard A and feedyard E, in the Texas High Plains from 2007 to 2009. Model predictions were in good agreement with observations from both feedyards (p < 0.001) and had high sensitivity to variations in air temperature and dietary crude protein (CP) concentration. Predicted mean daily NH₃ flux densities for the two feedyards had 71% to 78% agreement with observed values. In addition, Manure-DNDC estimates of annual feedyard emissions were within 3% to 15% of observations for the two feedyards, whereas a constant emission factor currently in use by the USEPA underestimated feedyard emissions by as much as 79%. The results from this study indicate that Manure-DNDC can be used to quantify average feedyard NH₃ emissions, assist with NH₃ emissions reporting, provide accurate information for legislators and policy makers, investigate methods to mitigate NH₃ loss, and help evaluate the effects of specific management practices on farm nutrient balances.