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Nitrous Oxide Evolution from Irrigated Land¹

ABSTRACT

Nitrous oxide (N₂O) fluxes from irrigated land cropped to vegetables in a coastal valley in California ranged from 0.0038 to 1.06 kg N/ha per day. For all sites, maximum fluxes (0.24 to 1.06 kg N/ha per day) were observed during the first post-fertilization irrigation and were followed by a trend to lower values (0.048 to 0.144 kg N/ha per day) towards the end of cropping despite total fertilizer N inputs of 176 to 528 kg N/ha. The N₂O flux showed a pronounced dependence on irrigation events with maximum fluxes associated with soil-moisture contents between 18 and 22% and soil-water suctions between 75 and 150 mbars. The magnitude of N₂O flux during periods of high moisture content appeared to depend primarily upon soil nitrate concentration which declined during the cropping cycle. Data for N₂O flux, soil moisture content, air-filled porosity, and soil-water suction suggested that denitrification rather than nitrification was the major process involved in N₂O production at each field site. Mean N₂O fluxes for each site coupled with soil-water suction data for a 12-month period suggested annual emissions of N₂O ranging from 19.6 to 41.8 kg N/ha.

Key Words: denitriflcation • nitrification • soil nitrate concentration • soil aeration

¹ Contribution from Dep. Soil and Environmental Sciences, Univ. of California, Riverside, CA 92521. Research supported by RANN Div. National Science Foundation, Project AEN 74-11136A01.

² Research Soil Scientist and Associate Professor, respectively. The senior author is now Senior Scientific Officer, The Grassland Research Institute, Hurley, Berkshire, England.

Received for publication January 22, 1980.