Nitrification in three Alberta soils: Effect of temperature, moisture and substrate concentration

Abstract

The objectives of this study were to determine the effect of temperature on relative rate of nitrification in soils and by comparing it with published results from other climates to see if it supported the hypothesis that temperature relations of nitrification vary with the climate of the region; to determine if the effect of NH + 4-N concentration on nitrification rate in unperfused soil could be represented by an extremely simple model such as a Michaelis-Menten (rectangular hyperbola) expression and if so, calculate the constants; and to determine the effect of soil moisture potential on nitrification in these soils. The optimum temperature for nitrification in soils from central Alberta was 20°C and at 30° activity had almost ceased. An adaptation of soil nitrifiers to soil climatic is indicated. Nitrification in these soils could be represented by a Michaelis-Menten expression with calculated maximum velocities of 9.0–9.9 μg NH + 4-N oxidized g −1 soil day −1. Half saturation ( K n ) values were calculated as 154–186 μg NH + 4-N g −1 soil. This same expression was found to fit only about half the reported results examined. Nitrification was rapid at 200 μg NH + 4-N g −1 but was inhibited at 300μg NH + 4-Ng −1. The depressing influence of NH + 4-N on nitrification in the present soils seems to be the combined effect of low pH and increase in salt content with increased NH + 4-N from 200 to 300 μg N g −1. Results suggested that soil moisture content and temperature in late fall and during winter, under snow cover, in central Alberta or in locations with a similar climate may be high enough to result in nitrification during late fall and winter.