Fitossociologia e manejo da vegetação natural e sua influência na eficiência agronômica do feijão-caupi na savana de Roraima.

Abstract

The objective of this study was to evaluate the phytosociology, the management of natural vegetation and its influence on the agronomic efficiency of cowpea in the savannah of Roraima. The survey was conducted in the experimental area of the Center for Agricultural Science, Federal University of Roraima-CCA/UFRR, municipality of Boa Vista, Roraima State - Brazil. The experiment was established in tillage with the culture of cowpea, BRS Arace. The experimental design was randomized with four replications and eight treatments, consisting of four methods for managing natural savanna vegetation (natural vegetation, cutting of natural vegetation, fire and application of glyphosate application) and inoculation of seeds (blocks and inoculation). We used a scheme in bands, being evaluated, the plots, the managements of natural vegetation, and the tracks, seed inoculation. The experimental plot consisted of 16 rows of 8.0 m long, spaced 0.20 m between plants and 0.6 m between rows. The group was represented by 8 lines of 8.0 m length in each plot. 0.6 m left-lateral borders of the bands and 0.5 m in front borders. For the seeds that were inoculated, used the Bradyrhizobium strain BR 3262 in peaty vehicle. At 40 days after planting the following variables were evaluated in cowpea: Levels of chlorophyll a and b, leaf area, nodulation, dry weight of shoot and root system and nitrogen contents in leaf and stem, these assessments were made in five selected at random from the first lateral line of floor area plants. Yield components of cowpea were evaluated by three crops of dry pods of floor area, evaluating: pod length; number of grains per pod; index of grain; number of pods per hectare and production of dry beans (productivity - kg ha-1). For the phytosociological study of weed did the assessment as to botany class, family, species, type of propagation, life cycle, growth habit and the total number of species per hectare. The phytosociological parameters were evaluated: frequency, relative frequency, density, relative density, abundance, relative abundance and importance value index. Seeds inoculation of cowpea with strain BR 3262, in the area of first year in the savannah of Roraima, adopted on independently of the natural vegetation management, is conducive to growth and yield of this crop. We observed a drastic reduction in the number of individuals in the species just Axonopus aureus and Trachypogon plumosus after application of managements. The frequencies of the species before applying managements stood out species the Trachypogon plumosus and Axonopus aureus, both with frequency equal to 0.9 and when applied managements observed a reduction in the frequency of these species reaching 0 (zero) in the managements with fire and glyphosate. The species with highest frequency after application of managements was Digitaria insularis (0.75), regardless of inoculation. The species that showed the highest percentage of the index value of importance, before the managements were: Bulbostylis Warei (56.91%), Axonopus aureus (46.83%) and Trachypogon plumosus (42.96%) and after the managements Digitaria insularis were, Trachypogon plumosus and Bulbostylis Warei. The treatment with glyphosate, regardless of seed inoculation of cowpea, was favorable to the emergence of island species Digitaria and Hynchelitrum repens and the disappearance of species Axonopus and Trachypogon plumosus.