ABSTRACT Humic substances (HS) comprise the passive element in soil organic matter (SOM), and represent one of the soil carbon pools which may be altered by different cover crops and weed control methods. This study aimed to assess HS distribution and characteristics in an experimental coffee crop area subjected to cover crops and cultural, mechanical, and chemical weed control. The study was carried out at Londrina, in the state of Paraná, southern Brazil (23°21’30” S; 51°10’17” W). In 2008, seven weed control/cover crops were established in a randomized block design between two coffee rows as the main-plot factor per plot and soil sampling depths (0-10 cm, 10-20 cm, 20-30 cm and 30-40 cm) as a split-plot. HS were extracted through alkaline and acid solutions and analyzed by chromic acid wet oxidation and UV-Vis spectroscopy. Chemical attributes presented variations in the topsoil between the field conditions analyzed. Cover crop cutting and coffee tree pruning residues left on the soil surface may have interfered in nutrient cycling and the humification process. Data showed that humic substances comprised about 50 % of SOM. Although different cover crops and weed control methods did not alter humic and fulvic acid carbon content, a possible incidence of condensed aromatic structures at depth increments in fulvic acids was observed, leading to an average decrease of 53 % in the E4/E6 ratio. Humin carbon content increased 25 % in the topsoil, particularly under crop weed-control methods, probably due to high incorporation of recalcitrant structures from coffee tree pruning residues and cover crops.

O presente trabalho apresenta os resultados das análises de uma investigação realizada ao longo de seis meses com alunos do sexto ano do Ensino Fundamental, com idade entre onze e doze anos, participantes de um projeto de pesquisa. O objetivo principal foi analisar a transferência de significados na perspectiva de David Ausubel, mediante aplicação de atividades investigativas, elaboradas com base na abordagem do National Research Council. Por meio das análises das quatro atividades investigativas, averiguou-se que houve resultados satisfatórios na transferência de significados e manifestação das habilidades cognitivas. Outro aspecto evidenciado é que o desempenho dos estudantes no processo de transferência não dependeu efetivamente do acesso inicial ao conteúdo.

This work presents the analysis results of an investigation over six months with sixth graders of elementary school, the age of eleven and twelve years, participants in a research project. The main objective was to analyze the transfer of meaning from the perspective of David Ausubel, by applying investigative activities, prepared based on the National Research Council approach. Through the analysis of the four investigative activities, examined whether there were satisfactory results in the transfer of meanings and manifestations of cognitive abilities. Another aspect evidenced is that the performance of students in the transfer process did not depend effectively the initial access to the content

El presente trabajo presenta los resultados de los análisis de una investigación realizada a lo largo de seis meses con alumnos del sexto año de la Enseñanza Fundamental, la edad de once y doce años, participantes de un proyecto de pesquisa. El objetivo principal fue analizar la transferencia de significados en la perspectiva de David Ausubel, mediante la aplicación de actividades investigativas, elaboradas con base en los enfoques de National Research Council. A través de los análisis de las cuatro actividades investigativas, se averiguó que hubo resultados satisfactorios en la transferencia de significados y manifestación de las habilidades cognitivas. Otro aspecto evidenciado es que el desempeño de los estudiantes en el proceso de transferencia no dependió efectivamente del acceso inicial al contenido.