Improving sustainability of common bean production systems by co-inoculating rhizobia and azospirilla

Common bean is likely the most important grain legume on population feeding for developing countries worldwide. With a natural ability to establish symbiosis with rhizobia, the inoculation technology is poorly exploited, especially in co-inoculation with others plant growth promoting rhizobacteria. This work aimed to determine the agronomical performance of common bean co-inoculated with Rhizobium tropici and Azospirillum brasiliense. A set of seven field experiments were carried out for three consecutive years in experimental areas and, majorly in commercial farms. Treatments consisted of non-inoculated control (NI), N-fertilizer treatment (NfT), single inoculation of R. tropici (Rt), R. tropici + one dose of A. brasiliense on seed (Rt+Ab1s), R. tropici + two doses of A. brasiliense on seed (Rt+Ab2s), R. tropici + two doses of A. brasiliense sprayed on plants (Rt+Ab2p) and R. tropici + three doses of A. brasiliense sprayed on plants (Rt+Ab3p). Evaluations were based on the nodule number (NN), nodule dry weight (NDW), root dry weight (RDW), shoot dry weight (MSPA), grain yield (GY), relative grain yield to NfT treatment (RGY:NfT) and relative grain yield to Rt treatment. The average of seven field experiments showed an increase of about 9%, 25%, 35% and 31% in NN, NDW, RDW and SDW, respectively as compared to Rt treatment. These increases over nodulation and plant growth resulted in a GY about 3200 kg ha−1, representing an increase in GY of about 5% and 26% as compared to NfT and Rt treatments, respectively. The results indicate the feasibility of using rhizobia and azospirilla co-inoculation in commercial farms as an efficient technology in replacing N-fertilizers, helping to save expenses and preventing environmental risks.