Este trabalho teve como objetivo o estudo fitossociológico da comunidade infestante ao longo do ciclo de desenvolvimento do sorgo sacarino e a determinação do período crítico de prevenção à interferência das plantas daninhas na cultura. O delineamento experimental foi de blocos ao acaso com três repetições. Os tratamentos foram constituídos por períodos crescentes de controle ou convivência das plantas daninhas em diferentes estádios fenológicos da cultura: 0-3 (V3), 0-5 (V5), 0-7 (V7), 0-9 (V9), 0-11(V11) folhas completamente expandidas e 0-R5 (colheita). A comunidade infestante foi avaliada por meio do número de indivíduos e da massa seca acumulada correspondente, para cada população de planta daninha nos diferentes períodos de convivência. O sorgo sacarino foi colhido aos 101 dias após a emergência, quando se avaliaram altura, diâmetro, teor de sólidos solúveis totais (°Brix) em função dos períodos de convivência da cultura com as plantas daninhas, além do rendimento de colmos nos diferentes tratamentos. Commelina benghalensis e Panicum maximum foram as duas espécies de maior importância relativa na área, no momento da colheita. A ausência de controle da comunidade infestante, durante todo o ciclo do sorgo sacarino, ocasionou aumento no teor de sólidos solúveis totais (°Brix) e redução de, respectivamente, 9% e 25% na altura e diâmetro de colmo da cultura, quando comparado com a testemunha capinada durante todo o ciclo. Considerando a tolerância de 5% na redução da produtividade de colmos, observou-se que o período crítico de prevenção a interferência correspondeu ao intervalo do estádio fenológico V3 a V11.

This work aimed to carry out a phytosociological study and to determine the critical period of weed interference on sweet sorghum crop. The experimental design adopted was randomized blocks with three replications. Treatments consisted by increasing periods of control or coexistence of weeds in different phenological stages of crop growth: 0-3 (V3), 0-5 (V5), 0-7 (V7), 0-9 (V9), 0-11(V11) fully expanded leaves and 0-R5 (harvest). The weed community was evaluated based on number the number of individuals and their correspondent dry mass accumulation, for each weed population in different periods of coexistence. Sweet sorghum was harvested at 101 days after emergence, when was measured plant height, culm diameter, total soluble solids (°Brix) in function of coexistence periods between crop and weeds, besides the yield of culms. Commelina benghalensis e Panicum maximum were the two species of higher relative importance at the crop harvested. The lack of weed control, during the crop cycle, caused an increase in total soluble solids (°Brix) and reduction of, respectively, 9 and 25% in plant height and culms diameter when compared with the hoed control during all cycle. Accepting losses of 5% in culm yield, was observed that the critical period of weed interference corresponded to the period of time between the phenological growth stage V3 to V11.

With the purpose of selecting the species of woody Caatinga for mixed plantations with Eucalyptus spp., the allelophatic effects of E. camaldulensis and E. grandis essential oil were studied on the growth activities of Anadenanthera peregrina. The plants were closed in glass chambers in the presence of volatile oil of E. camaldulensis or E. grandis at the concentration of 13 nl.cm-3. The number of leaves, height and diameter at soil lever were compared before, immediately after and after 30 days. Chlorophyll a and b, carotenoids and dry mass were evaluated after the treatment application. There was no inhibitory effect of E. camaldulensis and E. grandis oils on A. peregrina. E. camaldulensis, which was more adapted to semi-arid conditions, was planted in mixture stands with two native legume species, inoculated with Rhizobium and arbuscular mycorrhizal fungi. E. camaldulensis did not inhibit native species growth after two years of cultivation.