Below- and above-ground growth of Eucalyptus nitens in a young plantation I. Biomass

The relative distribution of below- and above-ground biomass in an Eucalyptus nitens plantation was studied under a set of five fertilizer regimes. In addition to a control (unfertilized) treatment, N and P fertilizers were applied at a ratio of 2:1 with rates of N at 75, 150, 300 and 600 kg ha-1 at 2 and 26 months after planting. There was a small response in stem diameter to fertilization by 34 months. Biomass of fine and medium roots was influenced by spatial variation in soil properties arising from cultivation as well as fertilization, but the effects of fertilization on root biomass was inconsistent. Biomass of coarse roots increased with the size of tree, and fertilizer treatments did not influence the relationship between coarse-root weight and tree-size. There was a significant decrease in the amount of below-ground production per unit above-ground production of biomass with increasing rates of fertilization. This change in distribution of biomass was mainly due to an increased contribution of coarse roots and a reduced contribution of branches to total biomass in fertilized trees. Thus, application of fertilizers to ameliorate even a modest nutrient limitation in plantations can change relative distribution of biomass in below- and above-ground components of trees.