Seasonal Dynamics of Soil Nitrogen Following Five Years of Pine Straw Harvesting and Fertilization.

In 2002 a study was established in two loblolly pine stands located near Calhoun, Louisiana to determine the impacts of pine straw removal on tree productivity.  Pine straw was harvested annually in three treatment areas but retained in a fourth.  One of the three treatments in which pine straw was harvested received annual additions of inorganic fertilizer (diammonium phosphate + urea) and another received annual additions of poultry litter.  Concentrations of soil carbon and nitrogen as well as potential net nitrogen mineralization and nitrification rates were measured seasonally in 2007.  Seasonal trends in carbon and total nitrogen concentrations were similar across all treatments, with the lowest concentrations occurring in early spring (mid-February) and the highest in late summer (early August).  Since carbon and total nitrogen concentrations varied similarly among seasons, carbon:nitrogen ratios did not vary by season for any treatment.  Except for the treatment which received annual applications of poultry litter, potential net nitrogen mineralization was greatest in late summer and early fall (September to mid-October) and least during the winter (mid-November to early January) and early spring (mid-February to early April).  With the addition of poultry litter, potential net nitrogen mineralization was greatest during the 10-12 week period (mid-May to late July) following litter application in late April.  Application of inorganic fertilizer and pine straw removal did not appear to alter the seasonal nitrogen dynamics in these stands.