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 NO_x and NH₃. The two methods used, Bowen ratio and a simplified aerodynamical techniques, agree quite well and quantify NO_x 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.