Comparing methods for assessing forest soil net nitrogen mineralization and net nitrification

A variety of analytical techniques are used to evaluate rates of nitrogen (N) mineralization and nitrification in soils.. The diversity of methods takes on added significance in forest ecosystem research where high soil heterogeneity and multiple soil horizons can make comparisons over time and space even more complex than in agricultural Ap horizons. This study compares (a) the three most common incubation periods (7, 14, and 28 day) used in potential net N mineralization and nitrification measurements, and (b) three methods of net nitrification assessment (potential net nitrification, in situ net nitrification, and nitrification potential) in the context of a long-term, paired-watershed N manipulation experiment. Results suggest that the 28-day incubation may be most appropriate in these northeastern U.S. forest soils to allow time for patterns of N dynamics to emerge following the disturbance associated with sampling and incubation. All nitrification measurement methods studied showed similar effects of forest type and watershed treatments. Each method could be an appropriate choice depending on objectives. The nitrification potential method should be studied further to determine its sensitivity to detect alterations in N dynamics in forest soils.