First of all, the impacts on the global performances of the Grignon farm of two levers for the reduction of nitrogen fluxes in the farming system were modelled. The two levers studied were :
the reduction of nitrogen fertilizer inputs on crops ;
the reduction of the nitrogen content of animals’ diets. Given optimal initial nitrogen inputs, the results obtained show that the levers studied enable to improve effectively environmental performances (assessed through ammonia (NH3) and greenhouse gas emissions and primary energy consumptions). However they affect economic and feeding performances.
Secondly, direct CH4 and NH3 emissions of the Grignon farm were measured by inverse modelling. This method consists in calculating a source of gas emissions based on a model of air flux dispersion and measures of gas concentration around the source. The results obtained are consistent with the actual knowledge on emission processes (correlation with temperature and number of animals, negative effect of covering the slurry pit on NH3 emissions).
