Development of a farm-scale, quasi-mechanistic model to estimate ammonia emissions from commercial manure-belt layer houses

Poultry production significantly contributes to atmospheric ammonia (NH₃) emissions, causing concerns over their environmental impacts and the effects on human and bird health inside the poultry houses. A model is needed to estimate NH₃ emissions from poultry facilities in order to develop effective mitigation strategies and science-based regulations. The laboratory-scale mechanistic NH₃ emission model developed by Tong, Zhao, Heber, and Ni (2020) requires extensive monitoring and laboratory work for the inputs and therefore cannot be conveniently used by producers or regulatory agencies. Based on this mechanistic model, a farm-scale model was developed for estimating dynamic NH₃ emission rates from commercial manure-belt layer houses. Sub-models were developed to estimate the inputs of the mechanistic model from farm-scale conditions that are commonly known during poultry production. Computational fluid dynamics (CFD) models and analyses of manure characteristics were used to estimate air conditions, manure properties, and NH₃ emission areas inside layer houses. The model estimated daily NH₃ emission from typical commercial manure-belt layer houses for given dates with input data consisting of hen inventory, ambient air temperature, house ventilation mode and rate, and manure management practices. Model performance was evaluated by comparison with NH₃ emission data from four commercial manure-belt layer houses with different ventilation systems. Uncertainties of 26–32% relative to the mechanistic model were obtained based on the uncertainties of individual sub-models along with their corresponding sensitivities. The model had an acceptable performance during ordinary egg production (p-value = 0.10–0.61), but it needs further development for special events such as moulting and introduction of new flocks.