Cláudio A. Spadotto

Acetamiprid, carbendazim, diuron and thiamethoxam sorption in two Brazilian tropical soils

Sorption of acetamiprid ((E)-N1-[(6-chloro-3-pyridyl)methyl]-N2-cyano-N1-methylacetamidine), carbendazim (methyl benzimidazol-2-ylcarbamate), diuron (N-(3,4-dichlorophenyl)-N, N-dimethyl urea) and thiamethoxam (3-(2-chloro-thiazol-5-ylmethyl)-5-methyl-[1,3,5]oxadiazinan-4-ylidene-N-nitroamine) was evaluated in two Brazilian tropical soils, Oxisol and Entisol, from Primavera do Leste region, Mato Grosso State, Brazil. To describe the sorption process, batch experiments were carried out. Linear and Freundlich isotherm models were used to calculate the K d and K f coefficients from experimental data. The K d values were utilized to calculate the partition coefficient normalized to soil organic carbon (K oc ). For the pesticides acetamiprid, carbendazim, diuron and thiamenthoxan the K oc (mL g− 1) values ranged in both soils from 98 – 3235, 1024 – 2644, 145 – 2631 and 104 – 2877, respectively. From the studied pesticides, only carbendazim presented correlation (r2 = 0.82 and p < 0.01) with soil organic carbon (OC) content. Acetamiprid and thiamethoxam showed low sorption coefficients, representing a high risk of surface and ground water contamination.

Sorption, Degradation, and Leaching of Tebuthiuron and Diuron in Soil Columns

Abstract A study in small outdoor lysimeters was carried out to determine the leaching of the herbicides tebuthiuron and diuron in different soil types, using undisturbed soil columns. Soil sorption and degradation for both herbicides were also studied in the laboratory. The multi-layered AF (Attenuation Factor) model was evaluated for predicting the herbicides leaching in undisturbed soil columns. Tebuthiuron leached in greater amounts than diuron in both soils. Sorption was well represented by linear and Freundlich equations, however parameters from the linear equations were used in the AF model. In general, both herbicides presented very low sorption, with diuron presenting lower values of sorption coefficient than tebuthiuron in the two soils. Chromatographic data indicated rapid late degradation of diuron and tebuthiuron in both soil types at two different depths. Simple exponential equation was not able to represent degradation, thus a bi-exponential equation was used, and some model adjusting was needed. Average measured amounts of each herbicide were compared with amounts predicted by the multi-layered-soil AF model. The AF model was able to predict leaching amounts in the sandy soil, especially for diuron, however it did not perform well in the clayey soil.A study in small outdoor lysimeters was carried out to determine the leaching of the herbicides tebuthiuron and diuron in different soil types, using undisturbed soil columns. Soil sorption and degradation for both herbicides were also studied in the laboratory. The multi-layered AF (Attenuation Factor) model was evaluated for predicting the herbicides leaching in undisturbed soil columns. Tebuthiuron leached in greater amounts than diuron in both soils. Sorption was well represented by linear and Freundlich equations, however parameters from the linear equations were used in the AF model. In general, both herbicides presented very low sorption, with diuron presenting lower values of sorption coefficient than tebuthiuron in the two soils. Chromatographic data indicated rapid late degradation of diuron and tebuthiuron in both soil types at two different depths. Simple exponential equation was not able to represent degradation, thus a bi-exponential equation was used, and some model adjusting was needed. Average measured amounts of each herbicide were compared with amounts predicted by the multi-layered-soil AF model. The AF model was able to predict leaching amounts in the sandy soil, especially for diuron, however it did not perform well in the clayey soil.

Determinação do período crítico para prevenção da interferência de plantas daninhas na cultura de soja: uso do modelo "broken-stick"

Visando a fornecer subsidios para programas de manejo de plantas daninhas em culturas agricolas, foi conduzido um experimento de campo em Botucatu, SP. O objetivo foi determinar, atraves do procedimento estatistico de analise de regressao, o periodo critico para prevencao da interferencia (PCPI) de plantas daninhas de folha larga na produtividade da cultura de soja. Foi utilizado o delineamento experimental em blocos casualizados, com 3 repeticoes. A cultura foi mantida na presenca das plantas daninhas de folha larga por diferentes periodos. O periodo critico determinado foi de 21 a 30 dias apos a emergencia da cultura, segundo ajuste dos dados de produtividade ao modelo Broken-Stick. No entanto, o periodo critico determinado indica que o controle das plantas daninhas pode ser realizado, uma unica vez, atraves do uso de metodo momentâneo, sem efeito residual.

Sorption and Leaching Potential of Acidic Herbicides in Brazilian Soils

Abstract Leaching of acidic herbicides (2,4-D, flumetsulam, and sulfentrazone) in soils was estimated by comparing the original and modified AF (Attenuation Factor) models for multi-layered soils (AFi). The original AFi model was modified to include the concept of pH-dependence for K d (sorption coefficient) based on pesticide dissociation and changes in the accessibility of soil organic functional groups able to interact with the pesticide. The original and modified models, considering soil and herbicide properties, were applied to assess the leaching potential of selected herbicides in three Brazilian soils. The pH-dependent K d values estimated for all three herbicides were observed to be always higher than pH-independent K d values calculated using average K oc data, and therefore the original AFi model overestimated the overall leaching potential for the soils studied.Leaching of acidic herbicides (2,4-D, flumetsulam, and sulfentrazone) in soils was estimated by comparing the original and modified AF (Attenuation Factor) models for multi-layered soils (AFi). The original AFi model was modified to include the concept of pH-dependence for Kd (sorption coefficient) based on pesticide dissociation and changes in the accessibility of soil organic functional groups able to interact with the pesticide. The original and modified models, considering soil and herbicide properties, were applied to assess the leaching potential of selected herbicides in three Brazilian soils. The pH-dependent Kd values estimated for all three herbicides were observed to be always higher than pH-independent Kd values calculated using average Koc data, and therefore the original AFi model overestimated the overall leaching potential for the soils studied.

Avaliação de parâmetros para o monitoramento da interferência de plantas daninhas na cultura de soja (Glycine max L.)

O presente estudo visa fornecer subsidios para o processo de tomada de decisao de controle das plantas daninhas baseado em nivel de dano na produtividade de culturas agricolas. Com o objetivo de avaliar o aproveitamento de parâmetros das plantas e daninhas e das plantas de soja no monitoramento da interferencia das plantas daninhas, foi realizado, em Botucatu (SP), um experimento sob condicoes de campo, com delineamento em blocos casualizados. A cultura foi mantida na presenca ou ausencia da comunidade vegetal infestante por diferentes periodos . O monitoramento da interferencia das plantas daninhas na cultura da soja pode se dar atraves do acumulo total de materia seca da comunidade vegetal infestante e dos seguintes parâmetros de crescimento das plantas de soja: numero de folhas trifolioladas, area da lâmina foliar, acumulo de materia seca de folhas e total. O acumulo de materia seca de cada especie de planta daninha isoladamente, nao foi parâmetros eficiente para determinar-se interferencia (competicao) na cultura da soja.

Environmental Behavior of Chlorpyrifos and Endosulfan in a Tropical Soil in Central Brazil

The environmental behavior of chlorpyrifos and endosulfan in soil was studied in the central-western region of Brazil by means of a field experiment. Sorption was evaluated in laboratory batch experiments. Chlorpyrifos and endosulfan were applied to experimental plots on uncultivated soil and the following processes were studied: leaching, runoff, and dissipation in top soil. Field dissipation of chlorpyrifos and endosulfan was more rapid than reported in temperate climates. Despite the high Koc of the studied pesticides, the two endosulfan isomers and endosulfan sulfate as well as chlorpyrifos were detected in percolated water. In runoff water and sediment, both endosulfan isomers and endosulfan sulfate were detected throughout the period of study. Observed losses of endosulfan by leaching (below a depth of 50 cm) and runoff were 0.0013 and 1.04% of the applied amount, whereas chlorpyrifos losses were 0.003 and 0.032%, respectively. Leaching of these highly adsorbed pesticides was attributed to preferential flow.

Movimento do herbicida tebutiuron em dois solos representativos das áreas de recarga do aqüífero Guarani

O movimento do herbicida tebutiuron foi analisado em um Latossolo Vermelho Distrofico psamitico (LVdq) e um Neossolo Quartzarenico Ortico tipico (RQo), representativos das areas de recarga do aquifero Guarani no Brasil, tendo como fatores influenciadores, a condutividade hidraulica (K), o teor de carbono orgânico (CO) e o teor de argila (TAr). O presente estudo foi realizado em colunas de solos indeformados, com aplicacao do produto comercial contendo o herbicida em discussao. Esses parâmetros evidenciam certa influencia na movimentacao vertical do herbicida tebutiuron, particularmente no RQo, uma vez que esse herbicida e quimicamente neutro. Observou-se, por exemplo, uma diferenca significativa entre os valores K dos dois solos, sendo superior no RQo. Alem de uma relacao inversa entre teores de CO e de TAr e os valores de K dos dois solos, indicando serem aqueles parâmetros inibidores do deslocamento do tebutiuron no perfil do solo. Os resultados aqui obtidos neste trabalho visam subsidiar estudos de avaliacao de risco ambiental, sobretudo agua subterrânea, a partir de areas de recarga de aquiferos naturalmente frageis, com enfase para o aquifero Guarani.

Priorização de regiões do Cerrado brasileiro para o monitoramento de Helicoverpa armigera (Lepidoptera: Noctuidae)

The objective of this work was to detect priority regions of the Brazilian Cerrado for monitoring of Helicoverpa armigera (Lepidoptera: Noctuidae). Municipalities with high production of cotton, soybean, corn, tomato, beans, coffee, orange, pine, and eucalyptus, based on data from the Brazilian Institute of Geography and Statistics, were considered in 2012. This information was spatialized and crossed with the occurrence of Cerrado areas, using ArcGIS 10.3. One hundred forty‑one municipalities located in eight states and in the Federal District were prioritized. The crops evaluated and found in these sites should be under constant monitoring, even when out of action range, because they are potentially subject to the migration of moths.