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

Abstract Emissions of nitrous oxide (N 2 0) and dinitrogen (N 2 ) 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 % 15 N ammonium sulfate, and the vertical N 2 0 and N 2 fluxes were measured periodically by sampling gases from a soil cover method, and analyzing the N 2 0 by gas chromatography and the N 2 by mass spectrometry. Maximum N 2 0 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 N 2 0 + N 2 from the moderately well‐drained clay loam soil was about 2.5% of the applied fertilizer N, and about 70% of the total was N 2 0. 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.