Fenologia de leguminosas graníferas e efeito de ácido húmico na produtividade de leguminosas inoculadas com Bradyrhizobium no Maranhão

Abstract

Cowpea (Vigna unguiculata L. Walp) is an important legume for low-income populations in Northeast Brazil. Just like cowpea, mungbean green (Vigna radiata), azuki bean (Vigna angularis) and rice bean (Vigna umbellata) can be alternatives to diversify food and income, but they are little known by Maranhão farmers. The objective was to evaluate i) the phenology and field productivity of cowpea, adzuki bean, rice bean and green mung bean, and ii) the effects of humic acid (HA) on the growth and productivity of rice bean, cowpea and green mung bean with and without inoculation of Bradyrhizobium spp, in the humid tropics of Maranhão. In 2019, two field experiments, with four grain leguminous species: cowpea, adzuki beans, rice beans and green mung beans. In 2021 an experiment was carried out in the field. The 3×2×2 factorial arrangement was used: bean species (cowpea, rice bean and green mung bean), application of HA (with and without) and inoculation with Bradyrhizobium spp (with and without). The design was in randomized blocks, with four repetitions (2019) and three repetitions (2021). In 2019, the life cycle of species ranged from 56 to 70 days. Adzuki beans, rice beans and green mung beans had cycles of lifespan shorter than that of cowpea. None of the three species showed potential higher productivity than cowpea. Rice beans were the only species that had productivity close to that of cowpea. In 2021, with Bradyrhizobium, the AH increased the productivity of rice beans by 39% and cowpeas by 79.5% in regarding the non-application of HA. HA did not influence green mungbean productivity with Bradyrhizobium. Without Bradyrhizobium, HA increased plant productivity rice beans by 63%, cowpeas by 27.5% and green mung beans by 23% in in relation to the absence of HA. Our results suggest that rice beans can be considered promising for cultivation in the humid tropics of Maranhão. Furthermore, the HA application increases the productivity of rice beans, cowpeas and mungbeans green regardless of seed inoculation with Bradyrhizobium