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Gas Diffusion as a Factor in Laboratory Incubation Studies on Denitrification¹

ABSTRACT

Lack of nitrogen balance has been frequently observed in laboratory incubation studies on denitrification. Equations were developed for nitrogeneous gas diffusion from incubated soil cores. Calculations using the developed equations indicate that only a fraction of the produced nitrogeneous gases in the soil core diffuses into the incubation container and is measured. The fraction diffusing from the soil core increases as the soil air-filled porosity increases and the adsorption coefficient between the gas and soil decreases. Under saturated soil conditions, only about 30% of the produced N₂O is calculated to be evolved even if adsorption is zero for soil cores 2.5 cm deep. Furthermore, several days are required for produced N₂O to evolve from the core after production ceases under saturated conditions. Similar results are calcualted for N₂. Thus, nitrogen deficits can be explained by diffusion analysis which eliminates the need for a postulated unknown intermediate compound. In a comparison between calculated and measured N₂O evolution, 34% evolution was calculated and 24% was observed for the experimental conditions. The assumptions used in developing the equations lead to a slight overprediction of evolved gases.

Key Words: nitrogen transformation • nitrous oxide • nitrate

¹ Contribution of the Dep. of Soil and Environ. Sci., Univ. of California, Riverside, CA 92521. The research was supported by Grant GI-34733X of RANN of the Natl. Sci. Found.

² Professor of Soil Physics, Associate Professor of Soil Physics, Post Graduate Research Soil Scientist (on leave from the Inst. of Soils and Water, ARO, The Volcani Center, BET, Dagan, Israel), and Staff Research Associate, respectively.

Received for publication April 24, 1978.

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