IMPROVEMENT OF NITROGEN-FIXATION IN ACACIA-MANGIUM THROUGH INOCULATION WITH RHIZOBIUM

Acacia mangium, a N-2-fixing tree legume, has become a major plantatio n tree species in the tropical humid and sub-humid zones. In addition to being a major pulp-wood producer, the tree has a good potential to restore soil fertility as a fallow species in agroforestry systems, an d as a fuel species. In this paper, we report an overview of the resul ts from several rhizobium inoculation field trials in different edaphi c and ecological conditions, conducted by the CIRAD-Foret (The Forest Program of Centre de Cooperation Internationale en Recherche Agronomiq ue pour le Developpement) in partnership with national research organi zations of various countries of the humid and sub-humid lowlands of We st Africa and Cook Islands. Rhizobium inoculation had a positive effec t on tree growth up to 39 months after tree planting. Immunological id entification of the Bradyrhizobium strains present in the nodules conf irmed the persistence of the more efficient introduced strains up to 4 2 months after transfer of the inoculated trees to the field. In Cote d'Ivoire, nitrogen derived from atmospheric N-2, fixed symbiotically b y A.,mangium was 50% in the whole trial and up to 90% in plots with le ss fertile soils when the trees were inoculated with an efficient stra in.