Effectiveness of cowpea rhizobia selected strains on cowpea grown in a soil of the semiarid region of Paraiba State - Brazil

Abstract

A field experiment was carried out in randomized block design, with four replicates, to evaluate the effectiveness of rhizobial inoculation on cowpea [Vigna unguiculata (L.) Walp.] grown in a soil of the semiarid region of Paraíba state in northeast Brazil. Two native isolates from the soil, three recommended strains (BR 3267, INPA 3-11B e UFLA 3-84), and one strain selected for cowpea grown in acid soils at the UFRPE (NFB 700) were inoculated on cowpea (cv. CNCx 409-11F). Two control treatments were also used, one being with mineral nitrogen, and other without mineral nitrogen applied, both uninoculated. Nodulation (nodule number and dry biomass), shoot dry biomass, N content and total N and relative effectiveness at 17, 38, 52 and 67 days after emergence (DAE) were analyzed. There were significant effects of treatments, plant age and plant age x treatment interactions for nodule number and dry biomass. For the remaining variables there were no significant differences. Results indicate that the rhizobial population native from the soil was very effective on cowpea
nitrogen fixation. Inoculation of cowpea (cv. CNCx 409-11F) with selected strains or isolates from the used soil, as well as nitrogen fertilizer were unnecessary for cowpea in the experimental conditions tested.