Comparison of Available Soil Nitrogen Assays in Control and Burned Forested Sites
The existence of several different methods for measuring net Nmineralization and nitrilkation rates and indexing N availability has raised questions about the comparability of these methods. We compared in situ covered cores, in situ buried bags, aerobic laboratory incubations, and tension lysimetry on control and treated plots of a prescribed burn experiment in the southern Appalachians. Environmental influences were examined with soil moisture and temperature measurements. All methods detected significant differences in net N mineralization rates between treated and control plots; P = 0.04, 0.007,0.001, and 0.07 for covered cores, buried bags, lab incubations, and lysimeters, respectively. Mean rates of N mineralization during the growing season were similar for the three soil incubation methods. The laboratory incubation of soil from treated plots produced significantly greater potential nitrification rates than the in situ methods. The four methods were not well correlated; this indicates the need for caution when comparing N transformation data derived from different methods. We conclude that the in situ covered core method is superior because it best incorporates site-specific soil temperature and moisture changes into N transformation measurements. 1990; Hart and Firestone, 1989; Hill and Shackleton, 1989). However, these comparisons were limited by the number of methods tested or by the sites on which they were tested.