Modelling of ammonia emissions from dairy cow houses

Dairy cow husbandry contributes to environmental acidification through the emission of ammonia. In-depth knowledge on the processes and variable factors that play a role in the emission of ammonia from dairy cow houses benefits the production of emission data, the development of low emission housing systems, and evaluation of emission levels in a farming system approach. A mechanistic simulation model for the ammonia emission from dairy cow houses was developed to facilitate this.An ammonia production model, with separate modules for the emission from the slurry pit and the slatted floor, was built and validated against measured data on the ammonia emission. Model improvements followed from this validation and were addressed in experiments on the development of the pH of urine deposited on floors and slurry, and on quantification of air exchange rates through slatted floors. The pH experiments revealed that the urine pH, after the urine was deposited on the floor or the slurry, increased to greater values than originally assumed. Furthermore, the air exchange through the openings of slatted floors was quantified, which made it possible to separately simulate the ammonia emission from the pit and from the floor. These unique theories were used to build a real ammonia emission model, with ammonia mass balances for the slurry pit and the air above the floor. The emission model was successfully validated against emission measurements conducted in a mechanically ventilated and a naturally ventilated cow house. The potential of the model to simulate emission levels (both in terms of emission factors and emission fractions), and measures that reduce ammonia emissions was illustrated using data obtained from an experiment with various dairy cow diets.<strong>Keywords</strong> : cubicle houses, environmental pollution, acidification, emission reduction, validation, simulation