Since 1978, 43,000 ha of plantations have been set up on the savannah around Pointe Noire, mainly planted with hybrid clones of Eucalyptus. The stands are monoclonal with a quite good production (20-25 m3/ha/year at 7 years, end of the rotation) on ferralitic, sandy and very desaturated soils. However, little is known about the durability of production concerning the nutrient needs of the plantations, nor about the effect this intensive culture has on the variation in soil fertility. An exhaustive study on the nutrient dynamics in the ecosystem has therefore begun, inspired mainly by the steps followed by the research team of INRA/Champenoux. The description and the quantification of nutrients contents of soil and vegetation compartments are performed as well as the nutrients fluxes through the ecosystem. A lasting field design has been installed in a 5-year-old stand as well as in an adjoining savannah. It has been set up rain gauges to collect rainfall and throughfall, stemflow collars, litterfall bags, lysimeters (up to 4 metres depth) and ceramic cups (up to 6 metres depth). Between 1998-2000, the variation of chemical composition of capillary and gravitational solutions during the planted crop rotation will be studied and the key parameters of the ecosystem behaviour will be estimated. It will be possible to assess, indirectly, mineral balances as the input-output budget : budget = atmospheric inputs + weathering + fertilization nutrient exported through harvesting drainage