Sorção e dessorção do ametryn em Latossolos brasileiros

Abstract

RESUMO -O conhecimento dos processos de retenção de herbicidas em solo é fundamental para se prever o potencial de lixiviação e degradação e a eficiência no controle das plantas daninhas. Objetivou-se com este trabalho avaliar os processos de sorção e dessorção do ametryn em quatro solos brasileiros: Latossolo Vermelho-Amarelo (LVA), Latossolo VermelhoAmarelo húmico (LVAh), Latossolo Vermelho (LV) e Latossolo Amarelo (LA), com diferentes valores de pH. Para isso, utilizou-se o método Batch Equilibrium em condições controladas de laboratório e análise por cromatografia líquida de alta eficiência, com detector UV-Vis a 245 nm. Considerando os valores da constante de Freundlich modificada (K' f ), verificou-se, entre os solos estudados, a ordem crescente de sorção do ametryn: LV pH 6,06 < LV pH 5,00 < LA pH 6,30 < LVA pH 6,11 < LVA pH 5,40 < LVAh pH 6,24 < LVAh pH 4,8. Conclui-se que as características teor de matéria orgânica e pH dos solos estudados afetaram a sorção e a dessorção do ametryn. Verificou-se também que solos com maiores teores de matéria orgânica foram os que apresentaram as maiores taxas de sorção, além das menores porcentagens de dessorção, indicando a ocorrência de histerese.Palavras-chave: herbicida, solo, batch equilibrium, cromatografia líquida, isotermas de Freundlich.ABSTRACT -Knowledge of herbicide retention processes in soil is fundamental to predict leaching potential, degradation, and weed control efficiency. The objective of this study was to evaluate the processes of sorption and desorption of ametryn in four Brazilian soils: Red-Yellow Latosol (LVA), Red-Yellow humic Latosol (LVAh), Red Latosol (LV), and Yellow Latosol (LA), with different pH values. Thus, the method "Batch Equilibrium" was applied under controlled laboratory conditions, and analysis by high performance liquid chromatography using UV-Vis detector at 245 nm. Considering the values of the modified Freundlich constant (K'f), the following increasing sorption order of ametryn was verified: LV pH 6.06 <5.00 LV pH <6.30 LA pH <6.11 pH LVA <LVA 5.40 pH <6.24 pH LVAh <LVAh pH 4.8. It was concluded that the organic matter content characteristics and the pH of the soils affected ametryn sorption and desorption, and that soils with higher organic matter content showed the highest rates of sorption, besides smaller percentages of desorption, indicating the occurrence of hysteresis.

Sorption of Clomazone in Brazilian Soils with Different Physical and Chemical Attributes1

“…Sorption of nonionic molecules such as clomazone is greatly influenced by the percentage of organic matter (Benoit et al, 2008). Studies by various authors (Gunasekara et al, 2009;Silva et al, 2012;Umiljendiae et al, 2013) who worked with different soils prove the contribution of organic matter on clomazone sorption. However, one should not consider only the content of organic matter to estimate the herbicide sorption, as this one is very heterogeneous, and its chemical composition is influenced by several factors, such as parent material and degree of decomposition, which alter the nature and extent of pesticide sorption (Benoit et al, 2008).…”

“…However, these compounds may have some polarity and hence their availability in the soil solution can be altered by pH, clay and mineral complexes and organic matter (Silva et al, 2007). Several authors (Gunasekara et al, 2009;Silva et al, 2012;Umiljendiae et al, 2013) state that the soil attribute that most influences the basic and nonionic compounds sorption is the organic matter. However, the degree of sorption influence of these herbicides by the organic matter depends, in addition to their concentration in the soil, on their chemical composition, which can vary, depending on the parent material and the degree of decomposition (Ðurovic et al, 2009).…”

Ametryn Leaching in Soils from the Sugarcane Region in Northeastern Brazilian

“…According to Liu et al (2010), in soils with low content of organic matter and clay, herbicide percolation may occur with higher intensity, facilitating its availability in soil solution, making it likely to be taken to the water table. Silva et al (2012) verified that the increase in soil pH may decrease the sorption capacity of ametryn, and result in higher leaching of this molecule in soil profile, because when soil pH is close or under the herbicide pKa, this may protone and receive positive charge and be absorbed by the plant as cation. However, when pH becomes higher than the herbicide pKa (which in ametryn's case is 4.1), the quantity of ametryn in its molecular form increases, reducing sorption capacity (Silva et al, 2012).…”

“…This moderate mobility is related to high clay content (Table 2) associated to higher CEC in relation to RQ (Table 1); they help sorption and, consequently, hinder herbicide leaching in the soil profile (Silva et al, 2012). The sorption of basic herbicides to soils increases with CEC increment (Oliveira Jr et al, 1999), which is associated to the clay fraction of soil and to the content of organic matter.…”

“…In these terms, studies have been carried out to better understand the behavior of this herbicide on Brazilian soils (Andrade et al, 2010;Freitas et al, 2012;Silva et al, 2012). These works proved that the dynamic of ametryn depends on the physical and chemical characteristics of soil, with emphasis on organic matter, pH and texture.…”