Direct Measurement of Denitrification Loss from Soils: I. Laboratory Evaluation of Acetylene Inhibition of Nitrous Oxide Reduction1
- J. C. Ryden,
- L. J. Lund and
- D. D. Focht2
The rate and extent of denitrification in soils incubated under helium atmospheres in the presence of acetylene (C2H2) concentrations ranging from 0.1 to 5.0% (vol/vol) was equivalent to that measured in the absence of C2H2. In the absence of C2H2, gaseous nitrogen (N) appeared as a mixture of nitrous oxide (N2O) and dinitrogen (N2), usually dominated by N2, whereas in the presence of C2H2 gaseous N appeared exclusively as N2O. An C2H2 concentration of 1.0% was also sufficient to maintain inhibition of N2O reduction even when the soil nitrate supply had been exhausted. Overall respiration of incubation systems, measured as carbon dioxide evolution, was also unaffected by the presence of C2H2. Similar findings were obtained when soils were incubated under argon-oxygen (4:1) atmospheres containing 1.0% C2H2. The inhibitory effect of C2H2 was virtually instantaneous when a 1.0% C2H2 concentration was established in an actively denitrifying soil. Diffusion of C2H2 into soils packed to their maximum bulk density and held at 5% air-filled porosity was also sufficiently rapid to induce essentially complete inhibition of N2O reduction during incubation in air using a 15N-labeled nitrate addition to the soil. The extent of denitrification varied among soils and ranged from 54 to 154 µg N/g under helium atmospheres, and from 15 to 106 µg N/g under argon-oxygen atmospheres, after 200 hours incubation. Ratios of N2/N2O were essentially the same whether measured directly or calculated from the difference in N2O production in the presence and absence of C2H2. The findings are discussed with respect to the use of the C2H2 inhibition technique for direct infield measurement of denitrification.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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