Effect of Temperature on Consecutive Denitrification Reactions in Brookston Clay and Fox Sandy Loam

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Abstract
The kinetics of several steps in the microbial denitrification process in Brookston clay and Fox sandy loam, two soils common to Southwestern Ontario, were studied in the temperature range of 5 to 25°C. The extent of chemical denitrification was also determined in otherwise identical but sterilized soils at temperatures up to 80°C. A gas flow system was used in which soil gases were continuously removed from anaerobic soil columns by argon carrier gas. Net steady-state rates of NO and N 2 O production, rates of loss of NO 3 − , and production and loss of NO 2 − were measured over periods of up to 5 days. Arrhenius activation energies for the zero-order process NO 3 − → NO 2 − were calculated to be 50 ± 9 kJ mol −1 for Brookston clay and 55 ± 13 kJ mol −1 for Fox sandy loam. The overall reaction, NO 2 − → NO (chemodenitrification), in both sterile soils was accurately first order with respect to NO 2 − ; the activation energy was 70 ± 2.8 kJ mol −1 in Brookston clay and 79 ± 1.2 kJ mol −1 in the sandy loam, and the preexponential factors were (2.3 ± 1.2) × 10 9 and (5.7 ± 1.2) × 10 9 min −1 , respectively.