Nitrous Oxide Emission During Denitrification in a Flooded Field

Abstract

AbstractLittle 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.