RESPONSE TO NUTRIENTS IN EUCALYPTUS-GRANDIS .2. NITROGEN ACCUMULATION

Fertilizer and irrigation treatments (with and without) were applied in factorial combination for 3 years to Eucalyptus grandis (four seedlots) planted near Gympie, Queensland. Timing and quantity of fertilizer applications aimed to ensure that nutrient availability did not limit growth during this period. Tree growth in both height and basal area was significantly increased by fertilizer treatment but was not affected by irrigation. Nitrogen contents of above-ground components were estimated in one of the four seedlots. Foliage was the major sink for nitrogen accumulation during the first 3 years in both unfertilized and fertilized trees, but the importance of foliage declined as tree size increased. Annual net rate of nitrogen accumulation in fertilized plots was highest during the first year (150 kg ha-1) and was an order of magnitude greater than in unfertilized plots. The net rate of nitrogen accumulation in fertilized plots decreased rapidly after the first year whereas only minor differences occurred in unfertilized plots. Tree growth in unfertilized plots was severely limited by poor nutrient availability over all 3 years studied. Net primary production was directly related to mean canopy nitrogen content. In this experiment, each kilogram of nitrogen in foliage was associated with a production of 220 kg of above-ground dry matter each year, regardless of fertilizer treatment.