In the first two works (la and lb) we evaluated the interation between selected stumps of Rhizobium (appropiate for the tropical forage legumes Centrosema macrocarpum) and species (Entrophospora colombiana, Acaulospora longula, Glomus manihotis) of vesicular-arbuscular mycorrhiza (MVA), in a sterelize soil fixer of P. The two experiments are different because we used different P sources. For the best production of dry matter, absorption of minerals, nodulation and infection for MVA; rebounded the plants with the inoculation with any of the Rhizobium´s stumps and Glomus manihotis (Experiment la) of Acaulospora longula (Experiment lb). In the third investigation (Experiment II) we evaluated in Centrosema the interaction MVA. Rhizobium and chemical N (levels equivalent to 0,30. 55, 105, O + Rhizobium and 30 + Rhizobium kg N ha-1) and amount of P (O, 20, 40 and 80 kg ha-1). Is advisable to apply small amount (30 kg ha-1) of N fertilizer at the time of sowing the Centrosema and the inoculation with Rhizobium. The plants inoculated with MVA showed a best growing in the amount 40kg Pha -1 80 kg Pha -1 helped in the efficacy of the bacterium and it didn't help in the efficacy of the fungus.