Friday, August 10, 2007 - 9:00 AM

COS 149-4: The influences of forest floor management and soil mixing on N availability and microbial biomass

Jose L. Zerpa1, H. Lee Allen1, Jennifer Phelan1, and Robert G. Campbell2. (1) North Carolina State University, (2) Weyerhaeuser, Co.

A study was conducted to determine the influence of different level of forest floor retention and soil mixing on soil nitrogen dynamics in a clear cut loblolly pine plantation in the coastal plain of North Carolina. The treatments were imposed in a full 3x2 factorial combination of three levels of forest floor retention (removed, control, and doubled forest floor) and two levels of soil tillage (mixed and non-mixed). Soil samples were collected before harvest and at 1, 3, and 4 months after treatment imposition to gain an understanding of nitrogen dynamics following harvesting. Soil samples were analyzed for KCl extractable nitrogen and microbial biomass carbon. After one month, tillage affected both extractable nitrogen and microbial biomass carbon, with the mixing treatment resulting in 110% more extractable nitrogen and 43% more microbial biomass carbon than the non-mixed treatment. After four months, treatment influences changed, with the non-mixed treatment showing a 62% increase in extractable nitrogen over the mixed treatment. Although there were no forest floor influences after one month, in all subsequent sampling times the double forest floor had significantly higher extractable nitrogen and microbial biomass carbon. These results demonstrate that during the four months following harvest the tillage effect was very transient, while the influence of forest floor retention was more consistent; greater amounts of forest floor were equated with higher levels of available nitrogen and larger microbial biomass.