After the introduction of Roundup Ready® technology, there were changes in community composition of weeds in the Southwest of Goiás. In this sense, this study aimed at evaluating weed distribution in different cropping systems in this region. Thus, phytosociological survey was conducted in three different periods. Studies were conducted on thirty-five areas derived from combined soybean crops resistant to glyphosate and conventional soybean, maize, sorghum, millet or fallow in succession. The number of individuals of weeds, dry biomass of soil surface and edaphoclimatic data was obtained in order to describe the variables responses of floristic composition. The factors associated to the total occurrence of species were evaluated and five species difficult to control (Cenchrus echinatus, Alternanthera tenella, Chamaesyce hirta, Euphorbia heterophylla e Glycine max) in regression analysis on tree were selected. A total of 3,219 individuals among 79 species were recorded. Regarding total occurrence of species period desiccation of main crop pre-planting (44.80 pl. 5 m2) and on sites that showed pH> 5,37 (51.20 pl. 5 m2) had higher infestations. Voluntary soybean was found in off-season, preferably with high sand content. Species of hard control, tolerant or resistant to herbicides were diagnosed in areas study.
Key words: Soybean, tolerance, herbicide.
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