A MODEL OF AMMONIA VOLATILIZATION FROM A GRAZING LIVESTOCK FARM

A dynamic model was developed to predict the ammonia volatilization fr om grazing livestock farms and to allow potential control measures to be evaluated. The relationships within the model were based on the und erlying physical and chemical processes but empirically based factors were used to reduce the demand for input data and where the understand ing of the underlying processes was inadequate, On a daily basis, the model simulates the partitioning of dietary nitrogen into dung and uri ne and its subsequent fate within the pasture or the slurry handling s ystem. The fate of dry matter and water added in dung, urine and from other sources is also predicted. The model illustrates the indirect in teractions between ammonia sources, highlights the influence of slurry management on ammonia losses, stresses the need for integrated, whole farm measurements and demonstrates that assessments of the impact of control measures may be misleading unless considered at the scale of t he whole farm.