Simulation of field NH3 and N2O emissions from slurry spreading

Land application of manures and slurries are a major source of pollution such as water contamination by nitrates and greenhouse gas emissions. NH3 and N2O emissions can be lowered by suitable spreading techniques. However, a comprehensive review of the impact of slurry spreading techniques is lacking. For that we developed a model, named OSEEP, that simulates the effect of slurry incorporation, slurry spatial distribution, and soil compaction on NH3 and N2O emissions. OSEEP integrates a soil compaction model, a hydraulic pedotransfer function, a NH3 volatilization model, and a crop model. We ran OSEEP for five sites in France for 7 years. Four techniques were simulated: broadcast spreading, band spreading, incorporation after surface spreading, and injection. We tested various sizes of slurry tankers and tractors. We calculated NH3 and N2O relative emissions from various spreading techniques with respect to band spreading. Results show good agreement between model calculation and published field data. We found that slurry applied by a self-propelled 15-m3 tanker with extra large tires led to an increase of 20 % in N2O emission, by comparison with a 15-m3 tanker trailed by a tractor. Hence, we show that soil compaction should be taken into account to optimize trade-offs between NH3 and N2O emissions.