Response of Gliricidia sepium tree to phosphorus application and inoculations with Glomus aggregatum and rhizobial strains in a sub-Saharian sandy soil

A pot experiment was carried out in a green house at Bel Air station to determine effect of phosphorus on the growth of Gliricidia sepium in presence of rhizobial strains and an arbuscular mycorrhiza fungus. A factorial 3 factors block was designed with arbuscular mycorrhizal fungus Glomus aggregatum, phophorus fertilization as triple super phosphate and rhizobial inoculation strains ISRA 604 and ISRA 605 applied on G. sepium seedlings. A non nitrogen fixing tree (NFT), Cassia siamea was used as reference tree for estimating the nitrogen fixation using the 15N isotope dilution technique. Mycorrhizal infection, nodulation, plant growth, P and N contents, 15N atom % excess (15Nae) and N fixed were determined. The results showed that the rhizobium strain ISRA 604 induced nodulation more than ISRA 605 in G. sepium with an increase of 38.28% for nodules number. Frequency (%F) and intensity (%M) of mycorrhization were highest at 0, 20 and 40 mg P kg-1 soil applied however rhizobial inoculation has influenced frequency of mycorrhization. In the rhizobium- AM fungus interaction, plant shoot total N content increased when trees were inoculated with G. aggregatum whatever the rhizobial strain inoculated. Roots N fixed (Ndfa) increased when plant was inoculated with ISRA 604 and amended with 20 mg P kg-1 soil. The inoculated plants exhibited the highest total nitrogen in whole plant as well as in shoots and roots than in non-inoculated and reference plants. G. sepium growth benefited from selected rhizobia and AM fungus inoculations and P application in a sandy soil.