Efficiency of native rhizobia isolates from Paraíba state on cowpea

Abstract

Cowpea (Vigna unguiculata (L.) Walp.) is a legume present mainly in tropical regions, capable of biological nitrogen fixation in symbiosis with bacteria known as rhizobia. The action of efficient rhizobial inoculants may be limited by the high competitiveness of the native strains. This study aimed to evaluate the efficiency of inoculation of cowpea cv. Sempre-Verde with native rhizobia obtained from soil samples collected in the Agreste region of Paraíba state. In the first experiment, 52 native rhizobia isolated from the soil samples were tested, together with strain BR 3267 and two treatments with presence and absence of mineral N, in Leonard jars. 13 isolates were selected for a second experiment in pots filled with Regolithic Neosoil, and  compared with the recommended strain and the treatments with and without mineral N. The cowpea plants responded to the N addition and to the inoculations. Twelve native isolates promoted aboveground biomass and relative effectiveness that were equivalent to those obtained with the recommended strain or the N fertilization. Aboveground biomass and total N were highly correlated with the relative effectiveness of the isolates.