Bioscience Journal | 2021 | vol. 37, e37012 | ISSN 1981-3163 1 Marco Aurélio CASTRO 1 , Sebastião Ferreira de LIMA 2 , Germison Vital TOMQUELSKI 3 , Maria Gabriela de Oliveira ANDRADE 4 , Jordana Dias MARTINS 2 1 Postgraduate Program in Agronomy, Federal University of Mato Grosso do Sul, Chapadão do Sul, MS, Brazil. 2 Department of Agronomy, Federal University of Mato Grosso do Sul, Chapadão do Sul, MS, Brazil. 3 Private Practice, Chapadão do Sul, MS, Brazil. 4 Postgraduate Program in Agronomy, São Paulo State University, Botucatu, SP, Brazil. Corresponding author: Sebastião Ferreira de Lima Email: sebastiao.lima@ufms.br How to cite: CASTRO, M.A., et al. Crop management and its effects on weed occurrence. Bioscience Journal. 2021, 37, e37012. https://doi.org/10.14393/BJ-v37n0a2021-48271 Abstract The objective was to evaluate weed phytosociology and similarities between crop management systems in the Chapadões region. The experiment was conducted at in agricultural area located in the municipality of Chapadão do Sul, MS, during the 2016/17 harvest. Three crop managements strategies were used: (1) cotton/soybean/Urochloa, (2) millet/soybean/millet and (3) millet/soybean/crotalaria. A phytosociological survey of weeds was carried out during soybean cultivation and cover crops growth, in succession. The evaluation area for each management strategy was 0.5 ha. Soybean surveys were carried out in October and January, while the cover crop surveys were performed in February and May. The relative frequency (RF), relative density (RD), relative abundance (AR), and relative importance (RI) of weeds, Venn diagram, and Jaccard and Sorenson similarity indices were evaluated. The management area represented by the cotton/soybean/Urochloa rotation had fewer weed species than others. The species Cenchrus echinatus, Digitaria insularis, Digitaria sanguinalis, Eleusine indica and Commelina benghalensis had the highest phytosociological indeces among the monocotyledons. Attention is required for managing the dicotyledons Amaranthus deflexus, Conyza canadensis and Senna obtusifolia despite their low indices because of herbicide resistant cases. The highest indeces of similarity were found between managements areas 2 and 3, which did not rely on cotton cultivation prior to soybeans. Keywords: Germination Flow. Monocotyledons. Phytosociology. Seed Bank. 1. Introduction Competition with weeds affects crop development by reducing access to resources such as water, light, and nutrients (Brighenti 2010), thereby resulting in decreased crop productivity (Braz et al. 2010) and consequently, economic losses (Vendruscolo et al. 2017). Identifying species as well as understanding their cycles, propagation methods, and growth habits within conventional or direct sowing systems enables the adoption of management strategies, thus minimizing losses (Adegas et al. 2010; Santos et al. 2015), which can range from 23%–70% of grain productivity (Vidal and Merotto Júnior 2001). In cultivated areas with different cultures, monocot and dicot weed species have been observed to be predominantly from the families Poaceae and Asteraceae, respectively (Silva et al. 2019; Ávila et al. 2020; Machado et al., 2020; Santos et al. 2015; Schmidt et al. 2020). CROP MANAGEMENT AND ITS EFFECTS ON WEED OCCURRENCE