Eficiência do manejo com Rhizobium tropici e Methylobacterium symbioticum na cultura do feijoeiro comum

Abstract

Common bean has a high nitrogen requirement and a strong dependence on mineral nitrogen fertilization, which motivates the search for biological inputs able to complement the supply of this nutrient. This study aimed to evaluate the effect of inoculation and co-inoculation of Rhizobium tropici and Methylobacterium symbioticum, applied at different phenological stages of common bean (Phaseolus vulgaris L.) cv. IAC 2153 Cranberry, on growth, grain yield, nitrogen use efficiency (NUE) and the economic viability of the crop. The experiment was carried out under greenhouse conditions, in a randomized complete block design, with seven treatments and five replications. Treatments combined seed inoculation with R. tropici and foliar application of M. symbioticum at the V2 and/or R5 stages. Means were compared by the Scott-Knott test (5%), and an incremental economic return analysis was also performed. The number of pods per plant and grains per pod was not affected by the treatments, so that yield differences resulted essentially from grain mass. A single application of M. symbioticum at the R5 stage, without co-inoculation (T5), provided the highest yield (7.757 g plant⁻¹; 113% higher than the control), the best NUE and the highest economic return (net incremental margin of R$ 6,478.98 ha⁻¹; benefit/cost ratio of 27.8). Co-inoculation with R. tropici reduced yield, indicating antagonism. It is concluded that application timing was more decisive than the number of applications, and that foliar application of M. symbioticum at the R5 stage is a promising strategy to increase yield and nitrogen use efficiency in the crop.