Sor??o e dessor??o do herbicida pendimetalina em solo e palha de cana-de-a??car

• Autor(a) principal: Oliveira, Gabriella Francisco Pereira Borges de
• Data de Publicação: 2018
• Tipo de documento: Dissertação
• Idioma: por
• Título da fonte: Biblioteca Digital de Teses e Dissertações da UFRRJ
• Texto Completo: https://tede.ufrrj.br/jspui/handle/jspui/5864
• topic: Pr?-emergente; ?leo mineral; ?leo vegetal; Adjuvante; Pre-emergent; Mineral oil; Vegetable oil; Adjuvant; Engenharia Agr?cola

Elimination of pre-harvest burning has brought challenges for management practices in sugarcane production. Despite of environmental and agronomic benefits associated to the permanence of straw in the soil, this production system may negatively affect herbicides efficiency in weed control. It occurs because sugarcane straw may work as a physical barrier and interact with molecules of the herbicides, changing their dynamics in the environment. The sorption corresponds to the main retention mechanism of the herbicides to the straw and can be favored according to the physical-chemical characteristics of the molecules of the herbicides and the chemical composition of the straw. These factors also influence the desorption process, which is associated with the release of the molecules in the soil solution. Pendimethalin is a pre-emergent herbicide used in the cultivation of sugarcane in Brazil to control grasses and some weeds with broad leaves. Due to its hydrophobic characteristics, it has high sorption capacity in soil and straw. Although there is not a common practice, using adjuvants in pre-emergent herbicides may change their dynamics in the environment as well as improve their agronomic efficiency. The objective of this work was to evaluate sorption and desorption, in soil and sugarcane straw, of pendimethalin alone and in mixture with adjuvant. Assay 1 consisted of qualitative and quantitative stability analysis of pendimethalin solutions in emulsifiable concentrate (EC) and capsule suspension (CS) formulations and mixtures with 0.1% (v/v) of vegetable oil (Aureo?), 0.5% (v/v) of mineral oil (Assist?) and 0.1 % (v/v) of acetone. Assay 2 corresponded to the pre-test to determine soil:solution and straw: solution and equilibrium time best suited for the sorption assay. Assay 3 consisted of determining sorption and desorption isotherms. Sorption assay was performed using pendimethalin in the EC formulation alone and in mixture with Aureo? in concentrations between 2.5 and 40 ?g mL-1, because these solutions were considered more stable. Soil was used in the proportion of 1: 2 (w/v) and straw in the proportion of 1:50 (w/v). Systems were in agitation for 12 and 24 hours, respectively. Desorption assay was performed by discarding the supernatant and adding aqueous solution of 0.01 mol L-1 CaCl2 without herbicide. Systems were stirred for 24 hours. Concentration of pendimethalin in the supernatant was determined by high performance liquid chromatography (HPLC). Data were submitted to analysis of variance (p ? 0.05) and ISOFIT software were used to obtain the isotherms parameters of the Freundlich and linear models. Linear model was the most suitable for representing the sorption and desorption isotherms. Sorption coefficient for soil was 18.48 mL g-1 for pendimethalin in the EC formulation alone, while the coefficients for sugarcane straw were 355.52 and 27.24 mL g-1 for the EC formulation alone and for the EC + Aureo? system. In desorption experiment, the Kd values obtained were higher than the sorption values, indicating the herbicide returned to the solution. Therefore, the sorption of pendimethalin in straw for the EC formulation alone is higher when in mixture with Aureo?, indicating the addition of adjuvant may decrease its retention in the straw and, consequently, increase the weed control efficiency