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This article in SSSAJ

  1. Vol. 43 No. 1, p. 110-118
    Received: Apr 10, 1978
    Accepted: Aug 22, 1978

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Direct Measurement of Denitrification Loss from Soils: II. Development and Application of Field Methods1

  1. J. C. Ryden,
  2. L. J. Lund,
  3. J. Letey and
  4. D. D. Focht2



A method was developed for the direct measurement of denitrification N loss from field soils. The method was based on the observation that in the presence of acetylene (C2H2) concentrations of 0.1 to 5.0% (vol/vol) the sole product of denitrification in soils was nitrous oxide (N2O). Sustained C2H2 concentrations of approximately 0.4 to 1.6% were induced in the atmosphere of a field soil by supplying C2H2 through probes inserted into the soil to a depth of 1 m. The time required to establish these C2H2 concentrations ranged from 15 to 30 min. The concentrations could be maintained for at least 17 hours during which C2H2 was supplied at 2.8 liters/hour. Essentially, no increase in 30N2 concentration was detected under closed soil covers installed at C2H2-treated field locations which had received 15N-NO3. At locations without C2H2 treatment an average 30N2 enrichment of 14.2% relative to air was observed. Production of 15N-labeled N2O and N2 at locations with and without C2H2 treatment was very similar, and essentially 100% of the 15N evolved at C2H2-treated locations appeared as N2O. Direct measurements of N2O fluxes from an irrigated, fertilized Haploxeroll at locations with and without C2H2 treatment were made using a previously established method. Net denitrification N fluxes, measured as N2O flux from C2H2-treated locations ranged from 0.5 to 80 g N/ha per hour. Peak N fluxes were between 30 and 80 g N/ha per hour and usually occurred 30 to 60 hours after irrigation had ceased. Total denitrification loss during 123 days was 51.2 kg N/ha with the total fertilizer application being 335 kg N/ha. Dinitrogen/nitrous oxide ratios, determined from the difference in N2O evolution at sites with and without C2H2 treatment, ranged from 0 to 1 during the first 12 to 24 hours of each denitrification cycle after which the ratio gradually increased to values of 10 to 20 towards the end of each cycle. The average value was between 5.6 and 7.4. The methodology provides a technique for direct monitoring of denitrification N loss in situ.

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