Chemical Denitrification of Nitrite in Frozen Soils

The effect of low temperature on chemodenitrification of nitrite in several Manitoba soils was investigated using highly enriched N‐15 and a mass spectrometric technique, which distinguished between N 2 formed via a chemical reaction and that formed via the biological reduction of NO ‐ 2 . When a slightly acid soil (pH 6.4) was incubated with NO ‐ 2 concentrations ranging from 25 to 300 µg N/g, the chemical N 2 production rate was approximately first order with respect to initial NO ‐ 2 concentration. When the soil was incubated with NO ‐ 2 under different temperatures (+20 to −20°C), the rate of chemical N 2 production was found to decrease with decreasing temperature up to −1.8°C. Lowering the temperature to −3.5°C resulted in the rate of N 2 production greater than the value observed at 20°C on each concentration. Further decrease in temperature resulted in a gradual decrease in the rate. Similar trends were found with two other slightly acidic soils. The enhancement in the rate of chemodenitrificatoin upon freezing of moist soil was believed to be due to freeze concentration of NO ‐ 2 into an unfrozen layer of soil water near soil colloids. Such an increase in NO ‐ 2 concentration in solution resulted in the rate of denitrification.