ABSTRACT
The degree to which ammonia forms the ammonium ion depends on the pH of the solution. If the pH is low, the equilibrium shifts to the right: more ammonia molecules are converted into ammonium ions. If the pH is high, the equilibrium shifts to the left: the hydroxide ion abstracts a proton from the ammonium ion, generating ammonia. Ammonia emissions are governed by the difference between solution and atmosphere NH3 partial pressure. High NH3 concentrations in the solution and low NH3 concentrations in the surrounding atmosphere increase NH3 emissions. Ammonia emissions associated with livestock housing, manure storage, management and processing result from the degradation of urea by the ubiquitous enzyme urease which results in NH4+ formation. Urea is mainly excreted in the urine and once it is hydrolysed it is much more prone to ammonia losses than organic nitrogen excreted in the faeces. Controlling factors for denitrification have been extensively investigated, mainly under lab conditions.
