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Journal of Environmental Quality

Letey, J.; Jury, W.A.; Valoras, N.

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.

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Gas Diffusion as a Factor in Laboratory Incubation Studies on Denitrification
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Letey, J.; Jury, W.A.; Valoras, N.

Gas Diffusion as a Factor in Laboratory Incubation Studies on Denitrification

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.

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