Taxa de inóculo na habilidade competitiva de rizóbios e eficiência na fixação do N2 em feijão-caupi ( Vigna unguiculata (L.) Walp,).

Abstract

Cowpea (Vigna unguiculata (L.) Walp) in Brazil is grown in the most different climatic conditions. By the adaptability to tropical conditions and recognized as a culture of high socioeconomic value, this legume has an important role for the capitalization of small farmers in the Northeast region. Cowpea may obtain adequate quantities of N by the process of biological nitrogen fixation (FBN) when associated with specific and effective bacteria. However, in Brazil the practice of inoculation is not widely processed due to the low agricultural technology and inconsistent responses using the seed inoculation process. The main goal of this study was to evaluate the effect of different rates of inoculum on effectivity and competitiveness of Bradyrhizobium (strain BR 3267) on cowpea grown in greenhouse conditions. The first experiment was carried out with five different concentration of strain BR 3267 (rhizobia cells/mL of inoculant), N mineral fertilizer treatment without inoculation, and a control without inoculation and N mineral fertilizer. The second experiment conducted in Leonard jars with inoculant produced with BR 3267 strain, 15 native rhizobia (isolated from the used soil), and a control treatment without inoculation and no N mineral fertilizer applied. The application of the low recommended rate increased number and dry biomass of nodules, shoot dry biomass and shoot N total uptake. In the Leonard jars experiment the rhizobia strain BR 3267 was more effective on nitrogen fixation and showed greater competitiveness compared to the native rhizobia isolates. The BRS Pujante cultivar was benefit by the FBN process when inoculated with strain BR 3267 proportional to the inoculum rate.