A Simplified Model of Nitrogen Flows from Manure Management

This report describes a model to simulate release processes of trace gases from manure into the atmosphere. This "manure handling model" (MHM) provides a mass-consistent scheme to follow nitrogen and carbon compounds along the typical stages of manure treatment in animal husbandry. In each of the model compartments, which reflect the respective stages, conversion between reactive and unreactive nitrogen or carbon species is possible, as well as the release of gaseous compounds from the reactive species. We use total ammoniacal nitrogen (TAN) as the reactive nitrogen species, and degradable volatile solid (VSd) as the reactive carbon species. Conversion parameters, either derived from specific information, e.g. national data, or as default values, allow assessing transformation rates. As a result, the model generates emission factors for the release of nitrogen components (gaseous NH3, N2O, NOx, N2 and NO3 -- in runoff and the associated N2O emission) and CH4 for use in IIASA's integrated assessment model GAINS. Results of MHM have been compared with the German emission model GAS-EM for dairy cattle on liquid manure to demonstrate that the simplified model is able to reflect complex national information. With identical input parameters, the simplified model reproduces results of the more complex models within 1% difference for the emission of all N components and emission of CH4. MHM was also used with default input (excretion rates, emission coefficients and removal factors) to generate emission factors for all possible combinations of animals and control strategies for all European countries. However, a comparison with current GAINS emission factors reveals substantial differences due to country-specific information that is available in GAINS.