Nitrate losses in soils: Effect of temperature, moisture and substrate concentration

Abstract

Our objectives were to determine the effect of temperature on relative rates of NO − 3-N losses in three north-central Alberta soils and to compare them with published results from warmer climates; to determine if the effect of NO − 3-N concentration on rates of NO − 3-N losses in un-perfused soil could be represented by a Michaelis-Menten (rectangular hyperbola) expression and if so, calculate constants; and to determine the effect of soil moisture potential on NO − 3-N loss in these soils. The rate of NO − 3-N loss increased rapidly upward from − 4°C, with the greatest response between 4 and 10°C. The rate of NO − 3-N loss continued to increase to 40°C but raising the temperature to 60°C brought a decrease in two out of the three soils studied. It appears that soil denitrifiers adapted to soil climate. The optimum temperature of <60°C for N 3-N loss in soils in the present study was lower than in soils from warmer areas. The rate of loss of NO − 3-N increased with increasing concentration of NO − 3-N from 50 to 500mgkg − 3. The NO − 3-N losses in these soils appeared to follow a Michaelis-Menten expression with calculated maximum velocities ( V m) of 36.6–42.2 mg NO − 3-N disappeared kg −1soil day −. Half saturation ( K n) values were calculated as 117.1–137.9mgNO − 3-N kg − soil. The V m appeared to increase slightly with increasing clay and organic C content. The NO − 3-N loss was most rapid under flooded conditions, but measurable NO − 3-N appeared to be lost even at −1500 kPa soil moisture potential. The NOv-N loss was greater in a fine-textured soil high in organic C (5.8%) than coase-textured soil low in organic C (1.1%). These results suggest that soil moisture and temperature in early spring after snow melt in north-central Alberta may be high enough to result in substantial NO − 3-N losses in early spring.