Efeito da inoculação com diferentes estirpes de rizóbio na nodulação, fixação biológica de nitrogênio e na produtividade em feijão-caupi

Abstract

Cowpea is rustic specie, well adapted to different environmental conditions and it is able to associate (nodulate) with nitrogen fixing bacteria of the rhizobium group. The objectives of this study were to select strains of rhizobia and to verify their agronomic efficiency for inoculation on cowpea. The study was conducted in greenhouse and field conditions, at Embrapa Agrobiologia, in Seropédica municipality, Rio de Janeiro State, Brazil. Also, in two farm fields in Santa Luzia do Paruá, Maranhão State, in the pre-Amazon region, and a rural property in Paudalha, Pernambuco State, in the Zona da Mata, respectively. The experimental design in all experiments was completely randomized blocks with six replicates. The treatments in the greenhouse experiment were rhizobium strains: BR 3262, BR 3267; INPA 03-11B, UFLA 03-84 (recommended strains), and the strain BR 3299, plus two controls without inoculation, one with N fertilizer and one without, in interaction with three cultivars of cowpea: IPA 206, BRS Guariba, and BRS Marataoã. In the field experiments the cultivar BRS Guariba was utilized and inoculated with the strains BR 3299, BR 3262, INPA 03-11B, a control without inoculation and fertilizer and another with N fertilizer (80 kg N/ha). In the greenhouse experiment, the nodules number and dry weight, and the dry mass of aerial parts were evaluated 55 days after planting (DAP). Plants in the field experiments were sampled 30 and 50 days after emergence (DAE) for nodule number and mass, shoot dry matter, relative efficiency and accumulation of N in shoot tissue. At 65 DAE the cowpea yield components were evaluated. In the greenhouse experiment, the strain INPA 03-11B promoted the formation of the greatest number of nodules on cultivar BRS Marataoã, compared to the other cultivars. With respect to nodule dry weight the cultivars BRS Marataoã and IPA 206 showed higher values than cultivar BRS Guariba. On the farm field experiments, for both regions, pre-Amazon (Maranhão) and Zona da Mata (Pernambuco), the strains BR 3299 and BR 3262 showed higher nodule number and mass than the other strains at 30 and 50 DAE. With respect to the total dry matter and N accumulation, and the relative efficiency, the strain BR 3299 was superior to all inoculated strains at 30 DAE. All strains promoted increases in grain yield, especially strain BR 3299, where yield was increased by 500, 1087 and 236 % in comparison with the non-inoculated control not fertilized with N, and 1, 17 and 17% compared to the control with N fertilizer (80 kg N/ha). In conclusion, all the trials showed that the inoculation of tested rhizobium strains promoted increases in production of cowpea, and BR 3299 was shown to be an excellent strain to be recommended for the crop.