Nitrous Oxide Concentration Profiles and the Natural Abundance of 15N-N2O in a Paddy Soil During the Wheat Growing Season
Abstract
Soil is an important source of nitrous oxide. Significant temporal and spatial trends exist in the production and emission in paddy fields where upland winter wheat is grown. A multilevel sampling probe (0-5cm, 5-10cm, 10- 15cm, and 15-20 cm) was designed to sample the air in the soil. Changes in N2O gas concentrations in 24 profiles were studied at 10-day intervals during the wheat growing period, for 16 total sampling dates. Surface fluxes were studied simultaneously from 24 field plots (4m x 5m). The natural abundance of 15N2O in eight profiles was measured three times during the wheat season by using a MAT 253 isotope mass chromatograph. Dynamic soil ammonium and nitrate concentrations in the plough layer and profile soil redox potential were also monitored throughout the wheat season. We present the first in situ data of such gradients over time for a paddy field seeded with wheat. Results indicate that N2O was produced at the lower levels of 10cm-15cm and 15-20cm, and that denitrification was the dominant process for N2O production even under the aerobic wheat cropping condition. N2O at 10-15cm depth has the most negative natural abundance of 15N. Profiles with higher concentrations of soil nitrate give more negative values of natural abundance of 15N2O. The lower levels of 10cm-15cm and 15cm-20cm give the highest concentrations during the whole wheat growing season. The maximum concentration of 14.8 mL m-3 and the maximum flux of 126 micro g N m-2 h-1 were found in January and April, respectively. N2O concentrations are significantly correlated between all layers over time. Spatial variations exist in N2O emissions and concentration profiles, but temporal variations are greater. The N2O emission peaks did not always coincide with soil concentration peaks. These results suggest that to understand the underlying processes, we need to measure both surface fluxes and soil concentrations simultaneously. This research was supported by the Office of Science (BER), US Department of Energy, Grant No. DE-FG02- 04ER63913, and the Institute of Soil Sciences, Chinese Academy of Sciences.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2006
- Bibcode:
- 2006AGUFM.B24B..01X
- Keywords:
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- 0402 Agricultural systems;
- 0426 Biosphere/atmosphere interactions (0315);
- 0469 Nitrogen cycling;
- 0490 Trace gases