RESUMO -O estudo da composição da flora de plantas daninhas de uma área ou de uma região agrícola é importante, por identificar a diversidade de espécies e contribuir para recomendação de estratégias de manejo a serem empregadas nos sistemas agrícolas. Palavras-chave: guaranazeiro, fitossociologia, invasoras, freqüência, Amazônia. (Coari, Iranduba, Maués, Presidente Figueiredo and Urucará) ABSTRACT -The study of the floristic composition of weeds of an area or agricultural region is important since it identifies the diversity of species and provides management strategies to be used under various agricultural system conditions. The objective of this work was to identify the floristic composition of weeds occurring in guaraná crops in five counties

O levantamento fitossociológico em pastagens é uma importante ferramenta de suporte às recomendações de manejo. Objetivou-se com este trabalho realizar um levantamento fitossociológico em pastagens de várzea do município de Autazes-AM. O estudo foi realizado em duas áreas de várzea sazonalmente inundadas, localizadas nesse município. No estudo, utilizou-se o método do quadrado, aplicado por meio de um quadrado de 1,0 m², lançado ao acaso 31 vezes em cada área de três hectares. Nas duas áreas foram encontrados 27.706 indivíduos, distribuídos em 12 famílias e 22 espécies. As famílias mais importantes em número de espécies nas duas áreas foram Poaceae (7) e Cyperaceae (4). Brachiaria subquadripara mostrou, nas duas áreas, maiores valores de frequência, densidade, abundância e IVI. As espécies que apresentaram maiores valores de IVI na área 1 foram: B. subquadripara (118,45), Paspalum fasciculatum (51,25), Cynodon dactylon (46,99) e Lindernia crustacea (25,25), e na área 2 foram: B. subquadripara (111,66), C. dactylon (55,44), Acroceras zizanioides (33,70) e L. crustacea (24,91). Em ambas as áreas, a família Poaceae representou mais de 90% do total de indivíduos encontrados, e algumas espécies apresentaram bom potencial forrageiro.

-This study has aimed to carry out a phytosociological survey of weeds in different collection periods, in cassava crops of two varieties grown in two consecutive years. The varieties were Pão, of the sweet class, and Racha-terra, of the bitter class. The weeds surveys were performed at 28, 56, 84, 112, 140, 168, 196, 224, 252, 280 and 308 days after planting in the experimental units of each variety. For weeds sampling, a sampler with an area of 0.25 m 2 released twice at random in the floor area of the treatments was used. The phytosociological survey quantified 5,708 individuals distributed in 17 families, represented by 32 species, of which 25 were dicotyledonous and seven were monocotyledonous. The most representative families in number of species were Euphorbiaceae and Poaceae, followed by Cyperaceae and Fabaceae. The most important species in the two growing seasons were Axonopus affinis, Mimosa pudica, Spermacoce verticillata and Paspalum multicaule. Other important species of the Poaceae family were Axonopus affinis, Axonopus fissifolius and Homolepis aturensis.Keywords: competition, tillage, Manihot esculenta. 28, 56, 84, 112, 140, 168, 196, 224, 252, 280 RESUMO -Este estudo objetivou realizar levantamento fitossociológico de plantas daninhas em diferentes períodos de coleta, em cultivo de duas variedades de mandioca, em dois anos consecutivos. As variedades foram Pão, da classe mansa, e Racha-terra, da classe brava. Os levantamentos das plantas daninhas foram realizados aos

O objetivo deste trabalho foi avaliar o efeito da adubação das plantas matrizes no enraizamento de estacas de guaranazeiro. Utilizou-se o delineamento experimental inteiramente casualizado, em arranjo fatorial 6x2, com cinco cultivares e um genótipo de guaranazeiro, com ou sem adubação. A unidade experimental continha dez estacas com quatro repetições. A adubação foi aplicada após a poda de limpeza (janeiro), após a poda de frutificação (abril) e antes do início da floração (maio). Durante o enraizamento, as estacas foram mantidas em viveiros a 50% de irradiância e sob nebulização intermitente. Após 120 dias no viveiro, foram avaliadas as seguintes características: estacas enraizadas e mortas; comprimento das estacas; e o volume e a massa da matéria seca das raízes. A adubação das plantas matrizes aumentou em 11,15% o percentual de enraizamento e reduziu em 11,05% a mortalidade das estacas. A adubação promoveu maior enraizamento nas cultivares BRS-Maués, BRS-CG882 e no genótipo CMU 381. Independentemente da cultivar, a adubação aumenta o número, o volume e a massa de matéria seca da raiz; porém, não tem influência no comprimento da raiz.

Weeds can occur in cultivated areas, competing with crops and causing considerable losses. Herbicides are the basis of weed control; however, they are questionable due to their possible negative impacts on human health and the environment. An alternative for controlling weeds is using cover plants. This study aimed to determine the floristic composition of weeds in an Amazonian agrosystem with cover plants and to evaluate the production of biomass, the soil cover rate and the weed suppression potential of cover plants. The experimental design was in randomized blocks, in a 4 x 2 factorial scheme. The factors under study were the cover species (Brachiaria ruziziensis, Canavalia ensiformis, Mucuna deeringiana) and the control group that consisted of weeds, evaluated during two agricultural years (2017 and 2018), with four replicates. Digitaria horizontalis was the most important weed species and was completely suppressed by B. ruziziensis. This cover type had a large production of biomass, greater coverage of the soil and high suppression of weeds in the Amazonian agrosystem.

Guarana is a plant native to the Amazon region that produces the fruit known as guarana. Guarana production is carried out by small farmers and is a source of income for thousands of people in rural and urban areas. The interference caused by the competition between weeds and guarana is an important limiting factor of its production. Despite its economic and social importance, there are few studies on the management of weeds in this species. Thus, this research aimed to study the effects of weed interference on guarana yield in different periods. This study was performed in Maués, AM, in the 2014 and 2015 seasons. The experimental design was a randomized block design with eight treatments and four blocks. Treatments consisted of a combination of four different periods of control or coexistence with weeds (March to May, June to August, September to November, and December to February). Weed community was composed of 23 weed species belonging to 12 botanical families, with Paspalum virgatum being the species with the highest importance value index (55.74%). Weed coexistence with guarana from June to August provided the lowest yields (156.16 kg ha-1 of grains) when compared to weed control in the same period (309.05 kg ha-1 of grains). Weed interference from June to August reduced guarana yield by 50%.

Dead cover, or mulch, consisting of plant residues, plays an important role for the success of diverse agricultural crops, working as an insulating layer protecting the soil from daytime temperature variations and maintaining the soil moist and rich in organic matter. Cowpea is a source of proteins, carbohydrates, vitamins and minerals. Its importance in the North, Northeast and Midwest regions of the country is associated with economic and social aspects, since it is an important food for low-income populations, supplying their nutritional needs. This study was carried out under greenhouse conditions in Manaus, state of Amazonas, with the purpose of assessing the effect of different dead covers on the agronomic characteristics of cowpea cultivars. It consisted of a completely randomized design in a 4 × 4 factorial arrangement. The treatments comprised four cowpea cultivars (BRS Caldeirão, BRS Tumucumaque, BRS Guariba and BRS Tracuateua) and three species of cover plants (Brachiaria decumbens, Brachiaria ruziziensis and Mucuna pruriens) and one control treatment, without soil cover, in a total of 16 treatments, with four replications and two plants per experimental unit. Analysis of variance was applied to the data, and the means were compared by the Scott-Knott’s test at 5% probability level. The following characteristics were examined: number of pods per plant, pod length, number of seeds per pod, weight of shoot dry matter, and grain yield. Mulching provided better results for all characteristics assessed in the four cultivars when compared to the control. BRS Caldeirão is the recommended cultivar for the state of Amazonas and the other regions with similar edaphoclimatic characteristics (high air temperature, rainfall, air humidity, and low-fertility tropical soils) because it exhibited the greatest number of pods per plant, number of seeds per pod, shoot dry matter, and the highest average grain yield (Freire Filho et al., 2011; Souza et al., 2016).

The economic potential of guarana relies on the energetic and medicinal properties of its seeds, which can be used to produce soft drinks, sticks, powder, and syrup. Brazil is the only guarana producer on a commercial scale, and the guarana crop system is the main agricultural activity in Maués, Amazonas. Although several types of technology have been developed to reduce costs and increase guarana productivity, the most important optimization of seedling production by cutting still needs to improve the rooting percentage and reduce mortality rates. However, the use of rooting inducers for guarana is still unestablished. Therefore, we evaluated the rooting potential of herbaceous cuttings from three guarana cultivars under different indole-3-butyric acid (IBA) concentrations. We recorded qualitative data from the roots of the cuttings. The IBA doses did not increase the percentage of rooted cuttings; however, they increased the root system quality of the guarana cuttings. We present this rooting method for the guarana plant as the most appropriate and least costly for small producers.