Avaliação da produção de biomassa vegetal e grãos por cultivares de feijão-caupi

Abstract

The ability to establish effective symbiosis with diazotrophic bacteria represents a considerable increase in the rate of Biological Nitrogen Fixation (BNF), productivity and development of the cowpea plant. The objective of this study was to evaluate, under field conditions, the applicability of cowpea cultivars (Vigna unguiculata (L.) Walp), for simultaneous grain and plant biomass production, after inoculation with strains of Bradyrhizobium sp., which are recommended for the cowpea crop. Field experiments were implemented at three different planting times with a randomized block design with four replications and a factorial 2x5. Treatments consisted in inoculation of cultivars IPA 206 and Maua with strains BR3262 (SEMIA = 6464) and BR3267 (SEMIA = 6462), a consortium of strains (BR3267, BR3262, INPA 03-11B (SEMIA = 6463) UFLA 3-84 (SEMIA = 6461) and BR3299), nitrogen control (50 kg ha-1 N) and absolute control (free of inoculation and fertilization). Plants were collected at 35 and 65 days after emergence (DAE) and the following variables were analyzed: mass of nodules (MNS), shoot tissue dry weight (SDW), yield of green pods and dry grains, N accumulation in shoot tissue and N content in green beans. At the first planting time, concerning MNS, SDW and N content, the Maua cultivar presented higher values than the IPA 206 at 35 DAE. With respect to the third planting time, inoculation with strain BR 3267 lead to an increment in MNS and SDW at 40 DAE for cultivar IPA 206. Highest concentrations of total accumulated N and shoot tissue dry mass were found in Maua associated with BR 3267 collection at 35 DAE. For the second planting time, MNS of the cultivar Maua showed a higher average than the cultivar IPA 206, but no significant effect (p> 0.01) among treatments was observed for the other variables studied in both cultivars. The inoculated strains provide good nodulation, dry matter yield and N accumulation in shoot tissue compared to the absolute control and nitrogen control. The crops from March-May and from September-December were more favorable for the planting of cowpea cultivars, presenting similar responses in the production of green pods and dry grains.