Process-Based Modeling of Ammonia and Nitrous Oxide Emissions from Open-Lot Beef and Dairy Facilities

Abstract

Abstract. Airborne emissions, such as ammonia (NH3) and nitrous oxide (N2O), vary considerably among open-lot beef and dairy operations as influenced by climate and manure pack conditions. Because of the challenges with direct measurement, process-based modeling is a recommended approach for estimating airborne emissions from animal feeding operations, such as open lots. The Integrated Farm System Model (IFSM), a whole-farm simulation model for crop, dairy, and beef operations, was previously used (ver. 4.0) to simulate NH3 emissions from open lots and performed well in representing emissions for two beef cattle feedyards in Texas. However, the previous model was found to perform poorly in predicting NH3 emissions measured at two open-lot dairies in Idaho, so further work was done to better represent the effects of climate on lot and manure pack conditions and to integrate better models for nitrification and denitrification processes. The revised model (ver. 4.1) appropriately predicted NH3 emissions for the two Texas beef cattle feedyards, with model predictions having 59% and 81% agreement with measured daily emissions at each lot. Compared to the previous version, the revised model performed better in simulating NH3 emissions for the Idaho open-lot dairies, with 56% to 74% agreement between predicted and measured daily NH3 emissions. For an Idaho dairy with a freestall barn and open lot, the revised model simulated NH3 emissions with 92% agreement between predicted and measured values. Based on measurements obtained at two of the Idaho dairies, IFSM also predicted daily N2O emissions with good agreement (64% to 80%) to measured values. Hence, IFSM can be used to estimate open-lot emissions of NH3 and N2O along with other aspects of performance, environmental impact, and economics of cattle feeding operations in different climatic regions. The model provides a tool for evaluating management strategies to mitigate emissions and improve the sustainability of beef and dairy production systems.