DEVELOPMENT OF ROOT BIOMASS IN AN EUCALYPTUS-GLOBULUS PLANTATION UNDER DIFFERENT WATER AND NUTRIENT REGIMES

The distribution along the soil profile of Eucalyptus globulus root bi omass was followed in a plantation in central Portugal at 1, 2 and 6 y ears after planting, using an excavation technique. The experimental d esign consisted of a control (C) and 3 treatments: application of soli d fertilizers twice a year (F), irrigation without the application of fertilizers (I) and irrigation combined with liquid fertilizers (IL). Below- and above-ground biomass decreased as follows: IL>I>F>C. So, wa ter stress limited growth more severely than nutrient stress. The root s rapidly colonized the top soil volume (0-20 cm depth) during the fir st year after planting. Fine root biomass 6 years after planting was 2 .2, 1.8 and 1.6 times higher in IL treatment than it was respectively in control, and in F and I treatments. The distribution of fine roots along the soil profile 6 years after planting was more even in IL comp ared to the other treatments. However, line roots in the top soil were more concentrated along the tree rows in the irrigated treatments tha n in the others. The proportion of below-ground biomass relative to th e total tree biomass and the root/shoot ratio were higher in C than in the treatments at early growth stages. This pattern was not so clear 6 years after planting, due to the increased proportion of the tap roo t relative to total biomass, especially in the IL treatment.