-The increasing use of glyphosate in Brazil has increased the selection pressure on species of weeds tolerant and resistant to this herbicide. This study aimed to evaluate the influence of glyphosate use pattern in the population dynamics of weeds in soybeans in thirty-five sampling areas of different properties. These areas were classified as to the number of applications and equivalent amount of glyphosate acid. We used the square-inventory method in thirty-five sampling areas in the 2012/2013 harvest. The structural parameters relative frequency, abundance and value indicator of individuals number and dry weight of shoot were calculated. The graphical representation of the differences of the floristic composition was performed by the non-metric multidimensional scaling technique, with distances of Sorensen. The multi response permutation procedures test was used to test hypotheses of differences in floristic composition. The occurrence of typical species of each treatment was evaluated by the indicator value using the Monte Carlo test (p<0,05). The floristic composition of the number of plants differ between areas using average standards of glyphosate (six applications or 6001 to 8000 g ha -1 of acid equivalent) compared to very low standard areas (four or five applications or 2000 to 4000 g ha -1 of a.i.). The Gnaphalium coarctatum, Eugenia sp., Rumex acetosella and Spermacoce latifolia, Digitaria horizontalis, Urochloa decumbens, Panicum maximum, Gossypum hirsutum and Indigofera hirsuta species showed significant indicator value of environments with different levels of use of glyphosate. Different glyphosate usage patterns exerted influence on the floristic composition of weeds in soybean areas evaluated.

ABSTRACT. Roundup Ready ® technology adoption and the cultivation of a second crop have changed chemical control methods and weed management in the southwest region of Goiás State, Brazil. Considering these changes, this study aimed to perform a phytosociological survey in areas with glyphosate resistant soybeans and conventional soybeans as the main harvest and sorghum, maize, millet or fallow in succession as the second harvest. A multivariate matrix of the floristic composition was constructed, and the indicator values of the individual number and dry biomass of species were measured. Based on the number of individuals, the species Chamaesyce hirta, Bidens subalternans, and Cissampelos ovolifolia were typical of areas cultivated with glyphosate-resistant soybean, while Euphorbia heterophyla presented indicator values of areas with conventional soybean cultivation. During the second harvest period, significant indicator values were observed for Crotalaria spectabilis in maize areas, Cenchrus echinatus in sorghum, and Commelina benghalensis, Sida glaziovii, Ipomoea grandifolia, Sida rhombifolia, and Ipomoea cordifolia in areas with millet. The species Conyza bonariensis was typical in the period before the herbicide application at post-emergence in harvest. Volunteer soybean presented as typical for the period before the herbicide application at postemergence in the second harvest. Weeds that were difficult to control or were tolerant and resistant to the herbicide applications were recorded in the areas studied.Keywords: soybean, second crop, crop succession, resistance, herbicide. Fitossociologia de plantas daninhas na região sudoeste de Goiás RESUMO.A adoção da tecnologia Roundup Ready ® e o cultivo de segunda safra alteraram os métodos de controle químico e o manejo das plantas daninhas na região sudoeste do Estado de Goiás, Brasil. Tendo em vista estas alterações, este estudo teve o objetivo de realizar um levantamento fitossociológico em áreas de soja resistente ao glyphosate e soja convencional na safra principal e sorgo, milho, milheto ou pousio em sucessão na segunda safra. Foi constituída uma matriz multivariada da composição florística e calculado o valor indicador do número de indivíduos e biomassa seca das espécies. Com base no número de indivíduos as espécies Chamaesyce hirta, Bidens subalternans e Cissampelos ovolifolia foram típicas de áreas de cultivo com soja resistente ao glyphosate, enquanto que Euphorbia heterophyla apresentou valor indicador para áreas de cultivo de soja convencional. Na safrinha, os valores indicadores significativos foram observados para: Crotalaria spectabilis, nas áreas de milho; Cenchrus echinatus no sorgo; e Commelina benghalensis, Sida glaziovii, Ipomoea grandifolia, Sida rhombifolia e Ipomoea cordifolia, nas áreas com milheto. A espécie Conyza bonariensis foi típica do período que antecede a aplicação de herbicidas em pós-emergência na safra. A soja voluntária apresentou-se como típica para o período que antecede a aplicação de herbicidas em pós-emergência na safri...

Resumo: As áreas de reservas legais exercem importantes funções ecológicas em regiões onde predominam os agroecossistemas. Nosso objetivo foi realizar o levantamento da composição florística e da estrutura da comunidade vegetal lenhosa de um fragmento de floresta estacional semidecidual mantida como área de reserva legal no município de Rio Verde, Goiás. As espécies registradas foram avaliadas quanto ao seu status de conservação. Para os levantamentos de campo, foram alocadas 20 parcelas de 10 x 10 metros (100 m 2). Foram inventariados 338 indivíduos distribuídos em 48 espécies, 43 gêneros e 22 famílias botânicas. A densidade total de indivíduos obtida foi de 1.690 ind ha-1. O índice de diversidade de Shannon registrado foi de 3,16 nats ind-1 e a equabilidade, de 0,80. As espécies que se destacaram em importância foram: Bocageopsis matogrossensis, Erioteca gracilipes, Psidium sartorianum, Ocotea sp., Cabralea canjerana, Miconia calvescens, Myrcia fenzliana, Calyptranthes concinna, Xylopia sericeae e Amaioua guianensis. A reserva legal apresentou bom estado de conservação. Não foram registradas espécies vegetais vulneráveis ou ameaçadas de extinção.

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 m 2 ) and on sites that showed pH> 5,37 (51.20 pl. 5 m 2 ) 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.

The appropriate arrangement of sorghum plants combined with the supply of nutrients increases grain yield. In this context, the objective was to evaluate the agronomic performance of grain sorghum grown under different plant arrangements and nitrogen fertilization levels. Experiments were carried out in Rio Verde and Montividiu in a 3 x 2 factorial randomized completely block design with six replications, with three spacing between rows (reduced, traditional and double row) and the use or not of 90 kg ha-1 topdressing nitrogen. There was a beneficial effect of topdressing nitrogen fertilization on grain yield when sorghum was grown in double rows in both locations, and for the reduced arrangement in Montividiu. However, the effect of topdressing nitrogen fertilization on grain yield in the traditional arrangement was not found. The dry shoot biomass of sorghum plants increased with nitrogen fertilization in Montividiu. The arrangement or topdressing nitrogen fertilization did not influence the thousand-grain weight of Sorghum.

O conhecimento das espécies de plantas daninhas nas lavouras é fundamental para o planejamento dos métodos de controle. Diante disto, objetivou-se realizar um levantamento florístico e fitossociológico de uma área de sucessão entre as culturas de soja e arroz no sudoeste do Tocantins. As plantas daninhas foram inventariadas pelo método do quadrado vazado. Foram calculados os descritores estruturais e os índices de diversidade e similaridade. No total, foram registradas 63 espécies, 50 gêneros e 26 famílias. No cultivo da soja, as espécies que se destacaram, em ordem decrescente, do índice de valor de importância foram: Physalis angulata, Senna obtusifolia, Caperonia sp., Oryza sativa e Cyperus esculentus. No cultivo de arroz, a tiririca (Cyperus esculentus) se destacou em importância. A composição e estrutura da comunidade de plantas daninhas no cultivo de arroz e soja foram diferentes quanto a diversidade e similaridade de espécies.

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