Title: Estimation of ammonia emissions from beef cattle feedyards using process-based model manure-dndc Authors
Submitted to: Transactions of the ASABE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 17, 2013
Publication Date: July 1, 2013
Citation: Waldrip, H., Todd, R.W., Cole, N.A., Li, C., Salas, W. 2013. Estimation of ammonia emissions from beef cattle feedyards using process-based model manure-dndc. Transactions of the ASABE. 56(3):1103-1114. Interpretive Summary: Ammonia loss from beef cattle feedyards results in manure with a lower fertilizer value and can also cause environmental pollution. Both process-based and mathematical models have been developed that estimate ammonia loss from different types of livestock production systems. However, we do not know if these models can predict ammonia loss from beef cattle feedyards. We tested Manure-DNDC, a process-based model, by comparing model predictions to real ammonia loss measurements taken from two feedyards in Texas. The model predictions agreed well with measurements from both feedyards, and the model was sensitive to air temperature and the amount of protein in the animal diet. This shows that Manure-DNDC can help figure out how much ammonia is lost from commercial feedyards and provide true information for legislators and policy makers. Manure-DNDC can also be used to test methods to reduce ammonia loss and show how different feedyard management practices can influence farm nutrient balances.
Technical Abstract: Ammonia 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 ammonia 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 ammonia fluxes were compared to emission data collected from two commercial feedyards in the Texas High Plains from 2007 to 2009. Model predictions were in good agreement with observations from both feedyards (p < 0.001), and showed high sensitivity to variations in air temperature and dietary crude protein (CP) concentration. Predicted mean daily ammonia flux densities for the two feedyards were 42.4 and 55.7 kg ammonia-N per hectare, compared to observed values of 41.3 and 48.3 and kg ammonia-N per hectare. This indicates that Manure-DNDC can assist with ammonia emissions reporting for commercial feedyards, provide accurate information for legislators and policy makers, investigate methods to mitigate ammonia flux, and help evaluate the effects of specific management practices on farm nutrient balances.