A series of experiments was carried out in a strongly acidic (with high Al and Fe) and infertile Ultisol to enhance the N inputs derived from biological nitrogen fixation (BNF) through the legume-Rhizobium symbiosis and to draw recommendations on the best agronomic practices needed to intensify sustainable maize production of the subtropical savannahs of Mexico. A large diversity of native Rhizobium strains with variable N fixation capacity exists for use with legume species of agricultural interest in the savannah of Tabasco. Of the black common bean genotypes evaluated, "N. Sahuatoba, DOR 448, TPL 18 and TPL 16" showed the best potential in terms of BNF (% NdfA and fixed N) and they can be recommended for the savannah of Tabasco. Cajanus cajan and Canavalia ensiformis are the multipurpose legumes with greatest potential in terms of BNF and biomass yield, specially when P fertilized, for the acid Ultisols of the Tabasco region. These legumes can be grown in monoculture and in association with maize and they can be recommended as green manures to reduce the need for chemical N fertilizers. The growth, biomass production and recovery of fertilizer N by selected maize genotypes were better when grown as monoculture than in association with legumes. The wild type "Dosmesano" was superior to the other maize genotypes tested. Further studies are needed to increase the N inputs from the Rhizobium-legume symbiosis to contribute to improving productivity and sustainability of the agricultral production on the acid savannah soils of Mexico.
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