Avaliação da sorção, dessorção, meia vida e lixiviação do ametryn em Argissolo Vermelho-Amarelo e Latossolo Vermelho-Amarelo

• Autor(a) principal: Andrade, Shisley Ramos Barcelos
• Data de Publicação: 2008
• Tipo de documento: Dissertação
• Idioma: por
• Título da fonte: LOCUS Repositório Institucional da UFV
• Texto Completo: http://locus.ufv.br/handle/123456789/2066
• topic: Herbicida; Comportamento no solo; Cromatografia; Herbicide; Soil behavior; Chromatography; CNPQ::CIENCIAS EXATAS E DA TERRA::QUIMICA::QUIMICA ANALITICA

It was evaluated in this study the sorption, desorption, persistence, half-life (t ½) and the leaching potential of ametryn in soils with different values of pH. For this, it were used three samples of a red-yellow latosol (LVA) with pH 4.4, 4.9 and 5.8 and 2.55 % organic matter content and a red-yellow ultisol (PVA) with pH 5.9 and 1.7% organic matter content. For the sorption studies, it was used the "Batch equilibrium" method, where standard solutions of the herbicide (0.0, 5.0, 10.0, 25.0, 50.0 and 100.0 mg L-1) were prepared in a 0.01 mol L-1 CaCl2 solution and added to 2.00 grams of soil with further agitation for 12 h (predetermined time). After this, the supernatant was filtered and the ametryn was quantified by HPLC. The sorption (Kfa) and desorption (Kfd) coefficients were determined using Freundlich isotherms. The crescent order of the sorption coefficients was: LVA pH 5.8 LVA pH 4.9 LVA pH 4.4 PVA pH 5.9. This fact confirms the influence of soil pH and organic matter content in the sorption of ametryn. It was also observed that the values observed for Kfd were higher than for Kfa, and that the opposite was found for the parameter N, characterizing the phenomenon of Hysteresis (H). The crescent order for the hysteresis rate of ametryn in soils was LVA pH 5.8 LVA pH 4.4 LVA pH 4.9 PVA pH 5.9. To determine the half-life for ametryn, soil samples were previously prepared and placed in plastic pots, coated inside with polyethylene film and sprayed with herbicide. After that, the plastic pots were irrigated and, 12 hours after herbicide contact with the soil, it was made the first Solid Liquid Extraction with Low Temperature Partition (SLE-LTP) and quantification of ametryn by HPLC to determine the amount of ametryn adsorbed at time zero (t = 0). This process was repeated every 5 days, until 90 days after application (t = 90). It was concluded that the degradation of the herbicide followed the first class kinetics (lnC(t) = - kt + lnC(t = 0)) and is strongly influenced by soil pH. It was also found that the t½ for ametryn was 26, 19, 12 and 11 days for LVA pH 4.4, LVA pH 4.9, LVA pH 5.8 and PVA pH 5.9, respectively. For the ametryn leaching study, it were used PVC columns with 10 cm diameter and 50 cm length, filled with soil samples under study, being those irrigated next to field capacity for further herbicide application. Different rains (20, 40 and 80 mm) were simulated on top of the columns. After draining, these columns were placed horizontally in order to collect soil samples and sow the indicator plant (Cucumis sativus) for biological tests. The soil samples collected at different depths of the columns were conducted to a laboratory for extraction and quantification of the herbicide. It was concluded that soil pH and organic matter content influenced the ametryn leaching potential. It was verified that the bioassay method, despite not allowing the ametryn leaching quantification, in a direct way, was more efficient in determining herbicide movement in the soil due to the high sensibility of the indicator plant and, possibly, because sampling has been carried out improperly. It was concluded that ametryn shows low sorption, medium mobility and low persistence in the studied soils.