Nitrous Oxide Emission During Denitrification in a Flooded Field
1979
Denmead, O. T. (Owen T.) | Freney, J. R. | Simpson, J. R.
Little field information is available on the amounts of nitrous oxide (N₂O) released from soils during denitrification, or the proportion of the denitrification loss attributable to N₂O production. The paper reports studies of N₂O evolution and the simultaneous disappearance of nitrate (NO₃) in a flooded rice field which initially contained 4 g NO₃-N m⁻² in the top 0.08 m of soil. Measurements were made continuously for 18 days after the field was flooded. Nitrous oxide emission was calculated from the rate of increase of N₂O in air circulating in a closed loop between a chamber installed in the field and an infrared gas analyzer. Emission rates as small as 1.8 ng N m⁻² sec⁻¹ could be measured. Nitrate disappearance was measured by chemical analysis of water samples. Nitrous oxide emission showed a diurnal cycle in phase with water temperature. Between the second and nineteenth day of flooding, 2.7 g NO₃-N m⁻² disappeared from the water and 0.038 g N₂O-N m⁻² were produced, only 1.4% of the apparent N loss. In a supplementary, small-bay experiment in which sodium nitrate and glycerol were added to the water, N₂O production accounted for only 0.8% of the NO₃ disappearance. Even allowing for NO₃ removal through other mechanisms, the production of N₂O in both experiments was very much less than the 7% commonly assumed for denitrification in current models of the global N₂O budget.
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