This study describes and evaluates a new ammonia (NH3
) exchange model for grazed fields (GAG_field). GAG_field is able to simulate the main features of the observed NH3
fluxes. A sensitivity analysis for the non-meteorological model parameters showed that the sensitivity of the NH3
fluxes to a parameter varies among urine patches. Moreover, the fluxes modelled with a dynamic soil pH are similar if a constant pH 7.5 is used, suggesting a useful simplification for regional scale model application.