COMPARISON OF AVAILABLE SOIL-NITROGEN ASSAYS IN CONTROL AND BURNED FORESTED SITES

The existence of several different methods for measuring net N mineral ization and nitrification rates and indexing N availability has raised questions about the comparability of these methods. We compared in si tu covered cores, in situ buried bags, aerobic laboratory incubations, and tension lysimetry on control and treated plots of a prescribed bu rn experiment in the southern Appalachians. Environmental influences w ere examined with soil moisture and temperature measurements. All meth ods detected significant differences in net N mineralization rates bet ween treated and control plots; P = 0.04, 0.007, 0.001, and 0.07 for c overed cores, buried bags, lab incubations, and lysimeters, respective ly. Mean rates of N mineralization during the growing season were simi lar for the three soil incubation methods. The laboratory incubation o f soil from treated plots produced significantly greater potential nit rification rates than the in situ methods. The four methods were not w ell correlated; this indicates the need for caution when comparing N t ransformation data derived from different methods. We conclude that th e in situ covered core method is superior because it best incorporates site-specific soil temperature and moisture changes into N transforma tion measurements.