Quantification of N-losses as NH3, NO, and N2O and N2 from fertilized maize fields in southwestern France

Emissions of nitrogen compounds (NO, NH3, N2O and N2) from heavily fertilized (280 kg(N) ha-1) and irrigated maize fields were studied over an annual cultivation cycle in southwestern France. NO and N2O emissions were measured by chamber techniques throughout the year. During fertilization and maize growth periods, chamber measurements were intensified and complemented by flux-gradient micrometeorological measurements of NOx and NH3. The two methods used, Bowen ratio and a simplified aerodynamical techniques, agree quite well and quantify NOx and NH3 flux variations during the period of intense emission which followed fertilizer application. Over a yearly cycle, nitrogen loss in the form of NH3, NO and N2O were calculated using micrometeorological flux measurements and emission algorithms calibrated with field data (chambers). The soil denitrification potential represented by the ratio N2O/(N2O+N2) was measured in the laboratory to calculate potential total gaseous nitrogen loss. Taking into account all uncertainties, the total N loss into the atmosphere represents 30 to 110 kg(N) ha-1 with about less than 1% as NH3, 40% as NO, 14% as N2O and 46% as N2. This is in agreement with the agronomic nitrogen budget based on the N fertilizer input and soil furniture and, on the N-output by crops and crop residues, which displays a net imbalance of 50 to 100 kg(N) ha-1.