The Long Term Soil Productivity (LTSP) experiment is an international effort to determine the effects of organic matter removal, soil compaction, and competition control on forest productivity. Soil NO₃ and NH₄ concentrations have been measured 4 times over 14 years on the Croatan National Forest LTSP site. Studies initiated in the second and fifth growing seasons used the in-situ soil core incubation method to determine N availability from a subset of the treatment plots. These studies found differences in N-mineralization due to soil type, compaction, and vegetation control. During year 10, in-situ measures were compared with laboratory incubations. In-situ measures indicated a significant decrease in total inorganic N with increased soil compaction, while laboratory incubations documented significant decreases in NH₄ in response to increased organic matter removal. Monthly soil samples are currently being taken to determine N availability after 14 growing seasons. Data will be presented and compared to previous results from this site.