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.

Cassava production in Amazonas state deserves to be highlighted due to its great historical, social, and economic importance. Weed competition severely constrains cassava production in Amazonas. The use of cover crops is safe and very efficient at eliminating weeds while keeping the soil covered. The objective of this study was to evaluate physical properties of soil and glyphosate residues in storage roots as a function of the weed management in cassava. The experiment was carried out in a randomized complete block design with five treatments and five repetitions. The treatments were biological control with two species of cover plants (Brachiaria ruziziensis and Mucuna pruriens), chemical control, mechanical control, and treatment with no weed control. The cover crops characteristics evaluated were dry weight, the percentage of cover, and rate of decomposition of plant residues. In the soil, the bulk density and total porosity were determined. The contamination of the storage roots was evaluated based on the analysis of glyphosate residue. Brachiaria ruziziensis presented more dry weight and higher percentage of cover compared with M. pruriens, and both cover crops showed very similar decomposition rates. The physical properties of soil were unaffected by any treatment evaluated. There was no detection of glyphosate and its metabolite, aminomethylphosphonic acid (AMPA), in any treatment evaluated. Chemical control with glyphosate is not able to contaminate cassava storage roots.

Guarana (Paullinia cupana var. Sorbilis (Mart.) Ducke) is a species native from Amazon which has high caffeine concentration. The interactions between guarana and microorganisms in Amazonian soils need to be investigated, especially in relation to the seedling production process, due to its beneficial relationships such as biosynthesis and the supply of stimulating substances, which may result in shortening of the nursery garden or increased productivity. Thus, this research had the objective of evaluating the potential of growth caused by rhizobacteria (Burkholderia ambifaria and Bacillus sp.) in rooting of guarana seedlings. The root length, volume, dry matter of the aerial part, height, number of leaves, leaf area and dry matter of shoot were evaluated at 180 days after planting emergence. Were also determined the carbohydrate and proline content of the aerial part. The rhizobacteria did not influence the growth of the seedlings, however, the carbohydrate contents were higher when the inoculation of the rhizobacteria was carried out with the Burkholderia ambifaria bacteria in the cultivar BRS-Amazonas, with the best results. The proline levels were higher in the control treatment of the two cultivars.

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.

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