Percepções de Estudantes sobre uma Mostra de Experimentos de Física Realizada em um Evento de Extensão.

Pretendemos avaliar quais as percepções dos participantes sobre uma mostra de experimentos de física bem como quais experimentos os participantes apresentaram facilidade de entendimento. Utilizamos um questionário para coletar os dados. Os participantes consideraram válida a iniciativa dos experimentos e ficaram satisfeitos com as explicações fornecidas pelos professores mediadores. As teorias associadas às experiências do circuito elétrico e motor elétrico obtiveram maior facilidade de entendimento dos participantes, enquanto os mesmos obtiveram dificuldade para compreender a teoria relacionada à atividade proposta no movimento no trilho de ar (colisão) e a prática experimental de difração. Sugestões de experimentos foram fornecidas pelos participantes para a próxima mostra de experimentos; como, por exemplo, experimentos relacionados à geração e transmissão de energia elétrica; bobina de tesla; toróide e experimentos de eletrônica. Como perspectiva futura, pretendemos orientar os participantes na construção de alguns experimentos de física, para que os mesmos possam ser doados para escolas públicas do ensino fundamental e médio, que carecem de laboratório de física

Oxidizable Fractions and Total Organic Carbon in Soil With Application of Biochar and Cultivated With Eucalyptus

Brazil has the largest area of planted forests in the world, about 9 million hectares, mostly composed of eucalyptus and pine. This large plantation area generates a large production of residues, estimated at 10 t ha-1 of eucalyptus bark per cultivation cycle. These residues have been reused for ground cover, heat and electricity production, and production of biochar through pyrolysis. Many characteristics of biochar make it attractive as a soil conditioner, such as its high porosity and specific surface area, associated with aromatic structure and acidic functional groups, which result in the accumulation and persistence of carbon in the soil, formation of electrical charges and nutrient retention and availability. Thus, the objective of this study was to evaluate the influence of the pyrolysis temperature of eucalyptus bark biochar, for periods of 365 and 730 days after the use of doses of biochar in Eucaliptus urograndis plantations, on the total organic carbon (TOC) content and oxidizable carbon fractions in the classes of dry separated soil aggregates. The study was conducted in the experimental area of the Instituto Federal do Espírito Santo (Ifes) Alegre Campus, Alegre, Espírito Santo, Brazil. The soil of the area is classified as Red-Yellow Latosol with medium texture. The experiment was implemented in March 2018, where each treatment, in each block, was composed of a total of six E. urograndis plants, arranged in rows, previously formed in each block. The eucalyptus bark biochar was produced in a pyrolysis reactor (model SPPT V60) and then distributed, prior to planting, in a furrow with depth of 0.30 m and width of 0.40 m. Two slow pyrolysis temperatures (350 °C and 600 °C) were used in the production of biochar, and five doses of biochar (0; 0.25; 0.5; 1 and 2% v v, corresponding to 0; 2.5; 5; 10; 20 t ha-1, respectively). Two soil samplings were performed, at 365 days and 730 days after the start of the experiment, at depths of 0.0-0.10 m and 0.10-0.30 m for the evaluation of TOC content and oxidizable carbon fractions. The effects of treatments and evaluation times were compared by orthogonal contrasts. When contrasting the pyrolysis temperatures for the production of biochar (350 ºC and 600 ºC), it was not possible to observe great differences in the soil attributes evaluated. The exception was in the aggregate class 2.0-0.250 mm, where the biochar produced at 600 ºC produced a significant increase in TOC content (p<0.01) and oxidizable fractions F3 (p<0.05) and F4 (p<0.001) in both years and at both depths sampled. When the two sampling periods were compared, an increase in TOC values (p<0.001) and of the fractions F1 (p<0.001) and F2 (p<0.01), in the first year of the experiment, was observed in the aggregate class <0.250 mm in the two types of biochar studied. The results of this study, after two years of evaluation, show that the incorporation of oxidizable carbon to soil aggregates was relatively low compared to the results of other studies where biochar was as a soil conditioner. These results are related to the lack of adequate time for aggregate formation

Influence of Biochar Doses Applied in Soil Cultivated With Eucalyptus on Oxidizable Fractions and Total Organic Carbon

The pyrolysis of agricultural wastes process in an environment with absence or deficiency of oxygen has drawn much attention for generating products such as biochar with potential to act as soil conditioners. Characteristics of biochar reinforce its performance as soil conditioner, such as high porosity, aromatic structure and presence of acid functional groups, which result in accumulation and persistence of carbon in the soil, generation of electrical charges, and retention and availability of nutrients. Considering that the time of adopting a management system can influence the quantity of total organic carbon (TOC) contents, but this may not indicate differences between the treatments evaluated, some authors have proposed to fractionate TOC according to four decreasing degrees of oxidation, through the use of different concentrations of sulfuric acid. This method, called TOC fractionation by degrees of oxidation, allows the classification of soil carbon into the fractions F1, F2, F3 and F4. Fractions F1 and F2 are more labile and are more related to the availability of nutrients and the formation and stabilization of macroaggregates, while fractions F3 and F4 are related to compounds with greater chemical stability and molecular weight. This work aimed to evaluate the influence of doses of eucalyptus bark biochar on TOC content and oxidizable organic carbon fractions in dry-separated soil aggregate classes. The study conducted in the field consisted of the application at a Eucaliptus urograndis plantation of five doses of eucalyptus bark biochar (0; 0.25; 0.5; 1 and 2% v v, equivalent to 0; 2.5; 5; 10; 20 t ha-1) produced at two pyrolysis temperatures (350 °C and 600 °C). Two soil samples were taken (365 days and 730 days) at depths of 0.0-0.10 m and 0.10-0.30 m. Through regression analysis of the biochar produced at 350 ºC, we observed a linear increase in the content of the fraction F2, in the classes of aggregates 4.00-2.00 mm (p<0.05) and <0.250 mm (p<0.01); F4 in the class of aggregates 4.00-2.00 mm (p<0.1), at depth 0.00-0.10 m; in F1int aggregate class <0.250 mm (p<0.1) and F2 in aggregate class 4.00-2.00 mm (p<0.1), at sampling depth 0.10-0.30 m, in the samples collected at 365 days. At 730 days, quadratic increases were found for F3 in aggregate class 2.00-0.25 mm (p<0.05) and linear increment of F4 fraction in aggregate class <0.250 mm (p<0.1), at depth 0.00-0.10 m. For the depth of 0.10-0.30 m linear increases in TOC contents were found in aggregate class 4.00-2.00 mm (p<0.05) and a quadratic increase in the F3 fraction in aggregate class <0.250 mm (p<0.05). The application of biochar produced at 600 ºC promoted, in the first collection, linear increases in TOC contents in aggregate class 2.00-0.25 mm (p<0.05) and in the F4 fraction in aggregate class 2.00-0.25 mm (p<0.05), at the 0.00-0.10 m depth. At sampling depth of 0.10-0.30 m, an increase occurred in fractions F1 in aggregate class 2.00-0.25 (p<0.1) and F3 in aggregate class 4.00-2.00 mm (p<0.1). For the F4 fraction, in aggregate class 4.00-2.00 mm, there was a quadratic increase (p<0.05). In the second collection (730 days), these effects were noted, in the form of a quadratic equation, for the F3 fraction in aggregate class 4.00-2.00 mm (p<0.05) for the collection performed at 0.00-0.10 m. At depth 0.10-0.30 m, linear increases in TOC were found in aggregate class 2.00-0.25 mm (p<0.05), F2 in aggregate class 4.00-2.00 mm (p<0.1) and F4 in aggregate class <0.250 mm (p<0.1). Few significant results were observed regarding the applied doses of the biochar on TOC contents and organic carbon fractions. We believe the possible causes for not obtaining more significant results from the application of eucalyptus bark biochar in the soil in this experiment were, first, the dosages chosen, which could have been higher, and the texture of the soil studied, which did not have a great need for cementing agents for soil aggregation. Another factor to be observed is the time of the experiment, since the evaluations were performed two years after implementation. We can conclude that according to studies in the area, changes in TOC levels in tropical climate soils are usually noted in the medium and long term after the implementation of new management practices