PARENT SESSION
Oral Session #76: Plant Ecology: Nutrient Uptake, Movement, Use. Presiding: J. Schade.
Friday, August 10, 2001. 8:00 AM to 11:45 AM. Hall of Ideas G.
Litter layer nitrogen release in fertilized and unfertilized Pinus taeda L. stands in southeastern Georgia.
MEASON, DEAN1, WILL, RODNEY1, MARKEWITZ, DANIEL1, 1
ABSTRACT- Net nitrogen flux from the litter layer in fertilized and unfertilized Pinus taeda L. stands was measured to understand the impact of nutrient addition on nitrogen cycling. Annual nitrogen fertilization was applied to stands established in 1987, 1989 and 1993. Throughfall and litter leachate samples were collected for one year beginning in April 2000. The first collection from fertilized plots had very high nitrate and ammonium release (404, 372 g N ha-1 day-1) due to fertilizer application. The following results exclude the first collection. The fertilized plots either released significantly more or retained significantly less nitrogen than the unfertilized plots (p<0.05). Overall fluxes of nitrate and ammonium were -1.8 and 5.0 kg N ha-1 yr-1 for the fertilized plots and -2.9 and 0.4 kg N ha-1 yr-1 for the unfertilized plots. At age 14, the unfertilized plots had an overall net retention of plant available nitrogen of -3.2 kg N ha-1 yr-1 while the fertilized plots had an overall net release of plant available nitrogen at 1.4 kg N ha-1 yr-1. The litter layer in unfertilized P. taeda stands acted as a nitrogen sink at all ages while annual fertilization changed the litter layer to a nitrogen source. Thus, released nitrogen from the litter layer in fertilized stands can increase the total pool of plant available nitrogen to the forest ecosystem.
KEY WORDS: Nitrogen, Litter layer, Fertilizer, Pinus taeda