N2O Budget Research Articles

Nitrous oxide emissions from fertilized and unfertilized soils in a subtropical region (Andalusia, Spain)

Field measurements of N2O emission rates were carried out from August until October 1982 in a subtropical region in Europe, i.e. in Andalusia, Spain. The measurements were performed by using an automatic sampling and analysis technique allowing the semi-continuous determination of N2O emission rates. The N2O emission rates were positively correlated to the soil surface temperature and exhibited a diurnal rhythm with maximum rates in the afternoon and minimum rates in the early morning with average values of 1 μg N2O−N/m2/h for the grass lawn and 15 μg N2O−N/m2/h for cultivated land. Application of urea and ammonium nitrate resulted in elevated N2O emission rates when compared to the unfertilized control. The loss of fertilizer-nitrogen as N2O was 0.18% for urea and 0.04% for NH4NO3 which compares very well with data obtained in a temperate climate (Germany). The total source strength of fertilizer-derived N2O is estimated to be 0.01–2.2 Tg N2O−N per year. The N2O flux from unfertilized natural soils may be as high as 4.5 Tg N2O−N, indicating that the N2O emission from soils contributes significantly to the global N2O budget.

Nitrous Oxide Emission During Denitrification in a Flooded Field

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.

Sources and sinks for atmospheric N2O

Observations of the temporal and spatial distribution of N2O in solution are not yet sufficient to permit quantitative assessment of the role of the ocean in the budget of atmospheric N2O. Consideration of the global nitrogen cycle suggests that the land should be the primary source of N2O. The gas is removed in the atmosphere by photolysis and by reaction with O(¹D), and there may be additional sinks in the ocean.

Absence of N2O photolysis in the troposphere

We have demonstrated experimentally that the photolysis rate of tropospheric N2O by ambient sunlight occurs with a rate of <1×10−11 s−1. This is in agreement with a recent revision of the absorption cross section of N2O. The effects of this finding on the global N2O budget are discussed.

Upper limits on atmospheric ozone reductions following increased application of fixed nitrogen to the soil

Our understanding of the marine and terrestrial nitrogen budgets is severely limited. For instance, atmospheric data indicate a residence time of N2O in the atmosphere of about 10 years and consequently sources and sinks of atmospheric N2O of the order of 130×106 ton N/year. Such large sources and especially sinks for atmospheric N2O have not been satisfactorily identified and it may not be excluded, a priori, that not only the N2O source, but also its sink is affected by man. The limited knowledge about the earth's N2O budget so far obtained is in favor of the view that there is no imminent danger of large ozone reductions following the predicted increase in the input of fixed nitrogen in the soil by the year 2000. However, it seems likely that, with unchanged agricultural practices, there will develop serious long term problems, certainly in a world of exponential growth, and, for best action, it is essential that a well balanced, interdisciplinary research effort now be designed to increase our knowledge of all aspects of the earth's nutrient cycles.