A new framework to estimate spatio-temporal ammonia emissions due to nitrogen fertilization in France.

In France, agriculture is responsible for 98% of ammonia (NH) emissions with over 50% caused by nitrogen (N) fertilization. The current French national inventory is based on default emission factors (EF) and does not account for the main variables influencing NH emissions. To model the spatio-temporal variability of NH emissions due to mineral and organic N fertilization, we implemented a new method named CADASTRE_NH. The novelty lies in the combined use of two types of resources: the process-based Volt'Air model and geo-referenced and temporally explicit databases for soil properties, meteorological conditions and N fertilization. Simulation units are the Small Agricultural Regions. Several sources of information were combined to obtain N fertilization management: census and surveys of the French Ministry of Agriculture, statistics on commercial fertilizer deliveries, and French expertise on physicochemical properties of organic manure. The practical interest of this new framework was illustrated for France during the crop year 2005/06. Aggregation at crop year level showed a reasonable agreement between estimated values derived from CADASTRE_NH and those from the French inventory method, for N and ammoniacal-N (TAN) application rates, total NH emissions and NH EF. Discrepancies were large for organic manure only; national TAN application rates and NH emissions were 62-63% lower with CADASTRE_NH. This was due to divergences in the representation of cattle farm yard manure and in the TAN:N ratio of solid manure. Annual emissions for fertilization in France were estimated to be 270 Gg NH, 29% lower than the French national inventory estimate. At the regional level, organic manure contributed to 73% of field NH emissions in intensive livestock husbandry areas and to 41% in the other areas. The CADASTRE_NH framework can be seen as a Tier 3 approach able to estimate specific regional EF for different mineral fertilizers and organic manure.