Improvement of nitrogen fixation in Acacia mangium through inoculation with rhizobium

Acacia mangium, a N-2-fixing tree legume, has become a major plantation 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, and as a fuel species. In this paper, we report an overview of the results from several rhizobium inoculation field trials in different edaphic and ecological conditions, conducted by the CIRAD-Foret (The Forest Program of Centre de Cooperation Internationale en Recherche Agronomique pour le Developpement) in partnership with national research organizations of various countries of the humid and sub-humid lowlands of West Africa and Cook Islands. Rhizobium inoculation had a positive effect on tree growth up to 39 months after tree planting. Immunological identification of the Bradyrhizobium strains present in the nodules confirmed the persistence of the more efficient introduced strains up to 42 months after transfer of the inoculated trees to the field. In Cote d'Ivoire, nitrogen derived from atmospheric N-2, fixed symbiotically by A.,mangium was 50% in the whole trial and up to 90% in plots with less fertile soils when the trees were inoculated with an efficient strain.