Nitrous oxide emissions from a wheat field in response to elevated carbon dioxide concentration and open-top chamber enclosure

Soil emissions of nitrous oxide (N2O) were measured using static field cham bers, which were installed in a wheat field. The treatments were: open-top chambers with ambient CO2 concentrations (OTC350), open-top chambers with 7 00 ppm CO2 (OTC700) and ambient air plots without open-top chambers (AA). M easurements of N2O emissions were made weekly starting at anthesis. The mea surements continued for ten weeks, until two weeks after the harvest of the mature crop. During the first eight weeks the N2O emissions were higher in the OTC350 treatment compared to OTC700. At the last two measurements, aft er the plants were harvested, the N2O emissions of the chamber treatments w ere similar to each other and higher than during the preceding period. The accumulation of grain protein per unit area was higher in OTC700 compared w ith OTC350. These results suggest that a competition for soil nitrogen exis ts between plants and the microbial community. The AA plots emitted less N2 O during the green canopy period compared with the chamber treatments. Afte r harvest, the emissions from AA increased up to the same magnitude as the chamber treatments. The lower emissions of the ambient air plots during the pre-harvest period can be explained partly by lower ambient temperatures a nd drier soil.