NITRATE LOSSES IN SOILS - EFFECT OF TEMPERATURE, MOISTURE AND SUBSTRATE CONCENTRATION

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 N3-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 (Vm) of 36.6-42.2 mg NO-3-N disappeared kg-1soil day-. Half saturation (Kn) values were calculated as 117.1-137.9mgNO-3-N kg- soil. The Vm 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. © 1990.