Modelling ammonia volatilization from animal slurry applied with trail hoses to cereals

In Europe ammonia (NH3), volatilization from animal manure is the major source of NH3 in the atmosphere. From March to July 1997, NH3 volatilization from trail hose applied slurry was measured for seven days after application in six experiments. A statistical analysis of data showed that NH3 volatilization rate during the first 4–5 h after slurry application increased significantly (P<5%) with wind speed and soil slurry surface water content. NH3 volatilization in the six measuring periods during the experiments increased significantly (P<5%) with relative water content of the soil slurry surface, global radiation, pH, and decreased with increasing rainfall during each measuring period and rainfall accumulated from onset of each experiment. A mechanistic model of NH3 volatilization was developed. Model inputs are climate variables, soil characteristics and total ammoniacal nitrogen (TAN=ammonium+ammonia) in the soil surface layer. A pH submodel for predicting pH at the surface of the soil slurry liquid was developed. The measured NH3 volatilization was compared with model simulations. The simulated results explained 27% of the variation in measured NH3 volatilization rates during all seven days, but 48% of measured volatilization rates during the first 24 h. Calculations with the model showed that applying slurry in the morning or in the afternoon reduced volatilization by 50% compared with a noon application. Spreading the slurry with trail hoses to a 60 cm high crop reduced losses by 75% compared with a spreading onto bare soil. Ammonia volatilization was 50% lower when the soil had dried out after slurry application compared with a wet slurry surface.