Soil Microsites as a Source of Denitrification Variability

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Abstract
The spatial variability exhibited by soil denitrification rates is high. As is typical for natural denitrification rate measurements, the individual rates of most samples of a given data set are low; however, a few samples often exhibit extremely high rates. Such data are characterized by highly skewed sample frequency distributions. This study was initiated to investigate the underlying mechanisms responsible for these observations. It was found that “hot‐spots” of high specific denitrification activity were associated with particulate organic C material in the soil. The high specific activities of these hot‐spots (incubated under aerobic conditions with no amendments) were similar to the denitrification activity of the bulk soil measured under conditions of anaerobiosis with added glucose and NO3. This observation served as the basis of a computer model that evaluates the influence of the density and dispersion pattern of these high activity sites on the measured rates of denitrification. Histograms generated from computer simulations are very similar to histograms obtained for real data, supporting the concept that the patchy dispersion of particulate organic material in soil is a major factor influencing the variability of natural denitrification rates.