Biological Nitrogen Fixation in Production of Vigna unguiculata (L.) Walp, Family Farming in Piauí, Brazil

Although inoculation of N2-fixing bacteria in cowpea is important, there are no studies on their performance in Itaueira, PI, Brazil. This work aimed to evaluate the symbiotic efficiency of nodulating bacteria strains officially approved by Ministério da Agricultura, Pecuária e Abastecimento, Brazil- MAPA (INPA 3-11B, UFLA 3-84, BR 3267 and BR 3262) and in phase of selection (UFLA 3-164 and UFLA 3-154) in the nodulation and growth of cowpea cultivar BR 17 Gurguéia in Itaueira, PI, Brazil. Experimental design was in randomized blocks with eight treatments and four replications, consisting of six strains cited and two non inoculated controls, one with N mineral (70 kg ha-1 of N) and other without N mineral. Nodulation, growth, yield and accumulation of N, P, K, Ca and Mg in shoots of cowpea beans were evaluated. Strains under test phase (UFLA 3-154 and UFLA 3-164) presented number of nodules, and fresh and dry biomass of nodules similar to strains currently approved as inoculants. Treatments inoculated with INPA 3-11B and BR 3267 strains were more efficient in dry biomass production of shoots. Plants inoculated with strains UFLA 3-164, INPA 3-11B and BR 3267 presented highest concentration of N, P, K, Ca, and Mg in dry biomass of shoots. Strains in selection phase (UFLA 3-164 and UFLA 3-154) presented similar grain yield among themselves, however the strain UFLA 3-154 obtained productivity equivalent to the nitrogen control and all strains evaluated. Inoculation of cowpea with strains BR 3262, BR 326