Lixiviação e sorção de diuron em solos cultivados com citros

Abstract

Understanding the behavior of herbicides in the soil can help determine the doses and the appropriate timing of application for efficient weed control and less environmental impact. The objective of this work was to Evaluate the movement and sorption of the herbicide diuron, in soils of two citrus orchards in the state of Amazonas. Two experiments were installed with the soil samples collected from citrus orchards in the municipalities of Iranduba and Rio Preto da Eva. The experiments were conducted in a greenhouse using the bioassay method with cucumber (Cucumis sativus var. Aodai) as a bioindicator plant. The experimental design was completely randomized with four replicates and five doses of diuron (0, 500, 1000, 2000, 4000 g ha-1 de i.a.) in each soil type. The first experiment consisted of estimating the sorption of the herbicide by the soils at increasing doses of diuron applied to the two soils. In addition to the sorption Evaluation, the same experiment was performed on washed sand with nine doses of diuron (0, 3, 6, 9, 12, 15, 18, 21, 24 g ha-1 de i.a.) to Evaluate the herbicide dose in inert substrate that inhibited 50% of the test plant growth. After herbicide application, the cucumber was sown. At 14 days after sowing, the indicator plant was cut and the dry matter weight and the dose required to cause a 50% reduction in the dry matter of the cucumber seedlings (I50) were determined. From these data, the sorption ratio (SR) of diuron was calculated using the I50 of each soil and the I50 obtained in the washed sand. In the leaching experiment, PVC columns filled with soil were used according to the depth of sampling in the field (0-10, 10-20, 20-30, 30-40 cm). The different doses of diuron were applied to the top of the columns and a rainfall of 150 mm was simulated. After 72 hours, the bioindicator plant was sown to verify the presence of the herbicide in the different soil depths within the column. Phytotoxicity Evaluations were performed at 7 and 14 days after sowing (D.A.S.). The dry matter accumulation of the aerial part of the cucumber was Evaluated at 14 D.A.S. The highest SR value (60,70) was obtained in the soil of Rio Preto da Eva, which was the soil with the highest Cation Exchange Capacity (CEC) and higher organic matter and clay content. diuron promoted phytotoxicity and dry matter reduction in cucumber seedlings to a depth of 40 cm with leaching potential in the soils of both orchards. With increasing doses of diuron, there was a reduction in the dry matter weight of the test plant in both experiments. Therefore, there is a relationship between the physicochemical properties, the dose applied and the sorption and leaching processes in the soils studied.