Soil Losses of Dinitrogen and Nitrous Oxide from Irrigated Crops in Northeastern Colorado

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Abstract
Emissions of nitrous oxide (N20) and dinitrogen (N2) from irrigated fields were monitored during the 1982 and 1983 cropping season to assess the magnitude of N loss by denitrification. Miniplots were established within larger fields of corn (Zea mays L.) in 1982, and barley (Hordeum vulgare) in 1983. Soil inside the miniplots was amended at a rate of 200 kg N ha−1 as 99 atom % 15N ammonium sulfate, and the vertical N20 and N2 fluxes were measured periodically by sampling gases from a soil cover method, and analyzing the N20 by gas chromatography and the N2 by mass spectrometry. Maximum N20 emissions occurred in May for barley and in July for corn, and emissions for both crops increased with increasing soil‐water content. During 1982, total volatile N loss of N20 + N2 from the moderately well‐drained clay loam soil was about 2.5% of the applied fertilizer N, and about 70% of the total was N20. From the barley field in 1983, about 1% of the applied fertilizer N was emitted with about equal amounts of each gas. These data suggest that the role of denitrification as a N loss mechanism has been historically overemphasized for soils in this area.