LONG-TERM MEASUREMENTS OF N2O EMISSIONS

Nitrous oxide (N2O) emission was measured weekly over a period of one year (1994) on a grassland, a maize field and a permanent pasture. The refore, the closed box method was used. To estimate the total (N2O+N-2 ) loss, also soil cores were taken for incubation in the presence of a cetylene. N2O fluxes were highest in the grazed grassland (11.9 kg N.( -1).435 day(-1)) because of the high nitrogen input (fertilization, de position of urine and dung by cattle), a higher soil compaction and re latively high moisture content. N2O losses out of the temporary grassl and (3.35 kg N.ha(-1).312 day(-1)) and maize field (2.7 kg N.ha(-1).31 2 days(-1)) were significantly lower. This is attributed to a lower N input and the fact that these 2 fields were very well managed (control led fertilization, good drainage system, lower compaction,...). From a n agronomic point of view, N-losses as N2O are small and not important to take into consideration. Besides, these small N2O fluxes can have a negative influence on the environment.