SPATIAL VARIATION IN DENITRIFICATION - DEPENDENCY OF ACTIVITY CENTERS ON THE SOIL ENVIRONMENT

The spatial variation in field denitrification rates was studied in an acid soil where the sole denitrification end product was N2O. The rate of N2O accumulation was measured under a soil cover at 30 fixed sampling locations arranged in a grid. Water and NO3 were added prior to all measurements to provide soil water contents at or above field capacity and excess NO3 for denitrification. No significant differences in N2O production rates were observed in samples incubated with or without C2H2, indicting that nitrification is not a significant source of N2O in this soil. Denitrification was found to occur in "hot spots" in moist soil and throughout the soil volume if the soil was flooded. Denitrification rates followed a skewed frequency distribution when soil water content was at field capacity: most locations had low activity, and a few locations exhibited high activity. The frequency distribution of denitrification rates was less skewed in samples after flooding, following large additions of glucose, or when the vegetation underwent decay in the fall. The intensity of denitrification was much higher after flooding than following glucose addition. A few sample locations occasionally showed outstandingly high denitrification rates when at field capacity, as well as when flooded. The activity in these hot spots approximated the potential denitrification activity of that soil.