Lixiviação e sorção de diuron em solos cultivados com guaranazeiro (Paullinia cupana, var. Sorbilis (Mart.) Ducke) no Amazonas

Abstract

The weeds in the guarana crop directly influence the competition for water, light and nutrients and indirectly, serving as a host of microorganisms, and can thus damage the crop. Therefore, the study of herbicide leaching and sorption processes in the soil helps in the knowledge about the efficiency of weed control. The objective of this work was to evaluate the leaching potential of the herbicide diuron in soils cultivated with guaraná, collected in Maués-AM and Itacoatiara-AM municipalities. This study was carried out under greenhouse conditions and to evaluate the leaching potential, the soil columns were mounted in a PVC pipe 42 cm long and 10 cm in diameter, where the soil samples were conditioned according to each depth, using four depths (0-10, 10-20, 20-30, 30-40 cm). At the top of the columns were applied five doses (0, 200, 400, 800, 1600 g ha-1 i.a.) and made 100 mm rain simulation. Cucumis (Cucumis sativus) var. Aodai was used as a bioindicator. In this experiment, a completely randomized design (DIC) was used in a factorial scheme (2 x 5 x 4) representing (soil location x dose x depth) with four replications. In a parallel study, it was evaluated the sorption of diuron using inert substrate (inert sand), using a 550 ml plastic container containing 3 cucumber seeds, where it was applied nine doses (0, 3, 6, 9, 12, 15, 18 , 21, 24 g ha-1 i.a.) and five replicates using DIC. The evaluated characteristics were leaf area (cm2) and dry weight of the aerial part (g), the values were transformed into a percentage, adopting 100% for the control, where the bioindicator plants were collected at 14 DAS (Days After Sowing). For the soil with a very clayey and sandy clay texture, the herbicide diuron was retained in the first layer of 0-10 cm, more specifically up to 5 cm deep, where it was possible to observe phytotoxicity of bioindicating plants. The I50 of diuron to the soil was 620 g ha-1 i.a. The organic matter and clay content were the factors that most influenced the retention of the herbicide in the studied soils.