Annual Straw Harvesting and Fertilizer Source Modify Nitrogen and Carbon Dynamics in a Loblolly Pine Plantation in the Mid-South USA.

Harvesting of fallen needles (straw) in the abundant southern pine forests of the southeastern United States for use as mulch is conducted to improve profitability of plantation management by providing a substantial mid-rotation source of income, but this practice and the fertilization practices that accompany it can have profound impacts on soil carbon, nitrogen, and microbial dynamics.  The objective of this study was to determine the effects of annual straw harvesting, fertilization, and fertilizer source on:  (1) annual soil nitrogen mineralization, ammonification, and nitrification, (2) total nitrogen, (3) total carbon, (4) labile soil C, (5) potential turnover rate of labile C, (6) microbial biomass C, and (4) microbial dehydrogenase activity.  In 2002 a study was initiated in two loblolly stands located in north central Louisiana.  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.   Fertilizing in annually raked soil with inorganic fertilizer was associated with the lowest microbial biomass C, activity, total N concentrations and the highest potential labile C turnover rates among all treatments.   Annually raked soil fertilized with poultry litter had the highest N mineralization, nitrification, total N, and labile C concentrations among all treatments.