PARENT SESSION
Oral Session #35: Nitrogen cycling: Response to inputs, variation in time and space. Presiding: M. Fenn.
Tuesday, August 7, 2001. 1:00 PM to 5:00 PM. Hall of Ideas G.
Spatial variability in soil nitrogen (N) dynamics in N-treated and untreated watersheds of Fernow Experimental Forest, WV.
Gilliam, Frank1, Lyttle, Nikki1, Somerville, Charles1, Adams, Mary Beth2, 1 2
ABSTRACT- Several watersheds of the Fernow Experimental Forest (FEF), West Virginia, exhibit symptoms of nitrogen (N) saturation. Many of these watersheds, however, display a high degree of spatial variability in soil N processing. This study examined the effects of temperature on net nitrification in N-saturated soils from FEF, and how these effects varied between high N-processing versus low N-processing soils collected from two watersheds, WS3 (N-treated) and WS4 (untreated). Samples of mineral soil were taken from three sub-plots within each of the four plots (treated/high N, treated/low N, untreated/high N, untreated/low N). Subsamples were extracted immediately with 1N KCl and analyzed for ammonium and nitrate to determine pre-incubation levels. Remaining soil was incubated at three temperatures: 10, 20, and 30 C. Subsamples of soil were taken at 3, 7, 14, 21, 28, and 90 d. Net nitrification was essentially 100% of net N mineralization for all samples combined, supporting field data. By Day 28, nitrification rates from incubations at all temperatures supported earlier observations based on in situ field incubations. At 30 C, rates from treated/high N were 3X those of treated/low N. Highest rates were found for untreated/high N (>2X those of treated/high N), whereas untreated/low N exhibited no net nitrification. By Day 90, untreated/low N unexpectedly showed substantial net nitrification. Results support the hypothesis that N additions to WS3 have decreased spatial variability in N processing in mineral soil.
KEY WORDS: nitrogen saturation, soil nitrogen, central Appalachian hardwood forests