Fixação biológica de nitrogênio do feijão-caupi em diferentes práticas de manejo de plantas daninhas

Abstract

Cowpea presents great importance to the North and Northeast regions of Brazil for showing good adaptability to edaphoclimatic conditions, becoming one of the main sources of low cost food protein for the populations of these regions. Although this legume has a great ability to fix N, this characteristic is attributed to the different ability between cultivar genotypes and rhizobia. However, weeds as well as their practices may interfere with nodulation and consequent production of cowpea. Thus, the objective of this work was to evaluate the biological nitrogen fixation (BNF) under different weed management practices in cowpea [Vigna unguiculata (L.) Walp]. The research was carried out under field conditions, in the experimental area of the State University of Maranhão - UEMA, with five treatments and repetitions in the first year. In 2018, the sounds were constituted by: (T1) total control; (T2) consortium, with maize culture and manual weeding in the period from 8 to 53 days after emergence of the crop; (T3) mulch cover with grass colonium; (T4) chemical control with herbicide and (T5) coexistence with weeds during the whole crop cycle. In the year 2019, the procedures were: (T1) mulch by the addition of shade, (T2), cover with forage grass and mulch, (T3), cover with forage grass, (T4) coexistence with weeds during the entire manual cycle (T5) of weeding throughout the crop cycle. As cultivars of cowpea, the cultivars BR-17 Gurgueia and BRS Guariba were used. The seeds were inoculated with a Bradyrhizobium strain SEMIA 6461. The analyzed variables were at 45 and 35 days, respectively, after emergence of the plants: number (NN) and dry mass of nodules (MSN), dry mass of shoot (MSPA) and dry mass of roots. As for the phytosociological evaluation, densities, frequency, dominance and importance value index were calculated. The survey totaled 934 individuals, distributed in 13 families and 22 genera, represented by 27 species, in which the families that had the highest number of representatives were Poaceae, Asteraceae and Cyperaceae. It was observed that, at 45 DAE, the dry matter mass of the nodules, the total control differed significantly from the other treatments; already for the number of nodules, the chemical control and uncontrolled treatments presented the lowest values. With total control and cover being the best management for this crop, while DAE 35, dry shoot mass, number of nodules and dry mass of nodules, cover plants and clean plants, provided better results. Therefore, legume intercropping with grasses can be a viable alternative for the development and nodulation of cowpea, as well as for the control of invasive plants in this crop