Effects of silvicultural treatments on soil microbial biomass, functional diversity, and nitrogen availability

This study was conducted on two sites, One was located on a Lower Coastal Plain, in Craven County, North Carolina. The other is located in the Sandhills, Scotland County, North Carolina. The objective of study on the Lower Coastal Plain was to assess the effects of soil type and silvicultural treatments on (1) soil environmental conditions (temperature and moisture), (2) soil nitrogen dynamics (net N mineralization and available N), and (3) soil microbial properties (microbial biomass and functional diversity). The objective of study on the Sandhills site was to assess the effects of irrigation and fertilization on soil microbial biomass and functional diversity. For the study on the Lower Coast plain site, three levels of organic matter removal (stem only, complete tree, and complete tree plus forest floor), three levels of compaction (none, medium, and severe) and two levels of vegetation control (none and total vegetation control) were combined.; Soil N dynamics at year 2 and year 5, including net N mineralization and available N, were measured from December 1992 to December 1993 (Wilson 1994) and from March 1996 to December 1996. Soil microbial properties, including soil microbial biomass and functional diversity were assessed from May 1997 to September 1997.; Across all treatments, the Goldsboro soil had a higher soil temperature, lower soil moisture, lower soil available nitrogen pool, and lower nitrogen mineralization than the Lynchburg soil in the second and the fifth year following plantation establishment. In the fifth year, vegetation control increased soil temperature, soil available nitrogen pool (extractable NH4 +-N and NO3--N), and net nitrogen mineralization, but decreased soil moisture. Organic matter removal increased soil temperature, decreased soil moisture, but did not influence soil available nitrogen pool and net nitrogen mineralization. Compaction did not influence soil temperature and soil available nitrogen pool, but increased soil moisture and decreased net nitrogen mineralization. At year 5, soil temperature was 5.2°C less, soil available nitrogen pool was 90% less, and net nitrogen mineralization was 87% less than at year 2.; Soil microbial C and N were positively related with soil total C and N respectively. Soil microbial C, N, and C:N ratio on the Lynchburg soil were higher than those of the Goldsboro soil. Organic matter removal, compaction, and vegetation control influenced soil microbial C and N. Soil type and silvicultural treatments may have changed soil microbial species, or changed soil microbial preferences for carbon compounds on the BIOLOG GN plate. However, soil type and silvicultural treatments did not change numbers of carbon compounds utilized by soil microbes on the BIOLOG GN plate. Soil microbial properties varied more due to the natural soil difference as compared with silvicultural treatment induced differences suggesting that silvicultural treatments may not have significant impacts on long-term soil productivity. (Abstract shortened by UMI.)...