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Nitrous Oxide Emission During Denitrification in a Flooded Field¹

ABSTRACT

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.

¹ Contribution from CSIRO, Australia.

² Senior Principal Research Scientists, CSIRO Division of Environ. Mech., P.O. Box 821, Canberra City and CSIRO Division of Plant Industry, P.O. Box 1600, Canberra City, A.C.T. 2601, Australia, respectively.

Received for publication October 24, 1978. Accepted for publication February 16, 1979.