Thermal analysis of brazilian tropical soils originating from different sources

As amostras de solos tropicais brasileiros foram analisadas pelas técnicas térmicas termogravimetria (TG) e calorimetria exploratória diferencial (DSC) em atmosferas de ar sintético ou argônio. Nesse processo foi investigado o solo eutrudox Ródico com vegetação de floresta, queimado ou não em plantação de cana de açúcar, e aquele de fase arenosa com vegetação de cerrado. A partir da fração orgânica do solo, foram extraídos ácidos húmicos que se decompõem similarmente ao produto comercial, de acordo com as etapas: i) água adsorvida, desidratação, descarboxilação e perda de moléculas orgânicas, ii) decomposição da fração termolábil, iii) matéria orgânica macromolecular e iv) resíduos acima de 950 o C. As curvas de DSC deram correspondentes picos de perda de água perto de 100 o C e exotérmicos em temperatura maior que 300 o C, atribuídos à combustão de fração de matéria orgânica termolábil. As curvas TG dos solos são mais complexas que os ácidos húmicos, devido aos componentes inorgânicos, caracterizando os estágios: i) desidratação, ii) matéria orgânica termolábil, iii) domínio orgânico macromolecular, e iv) resíduos de óxidos. Essas decomposições correspondem a três picos endotérmicos em DSC e um exotérmico mostrado em atmosfera de ar sintético, atribuído à combustão da fração orgânica macromolecular na região de 300 o C. As curvas de DSC dos solos provenientes de plantação de cana de açúcar mostraram picos endotérmicos mais intensos do que aqueles de solo de floresta. Os resultados térmicos demonstram a influência do material orgânico, que é altamente influenciado pelo componente mineral com alto teor de resíduo, pelo uso na atividade da terra e também pelos processos de queimadas. Brazilian tropical Latosol soil samples were thermally analyzed associating thermogravimetric (TG) and differential scanning calorimetric (DSC) techniques under synthetic air or argon atmospheres. Rhodic eutrudox soils with forest vegetation, from unburnt and burnt cane plantations and that of a sandy phase having cerrado vegetation were investigated. From the organic soil fraction humic acids were extracted that decompose similarly to the commercial product, following the steps: i) adsorbed water, dehydrations, decarboxylations and release of organic molecules, ii) thermolabile decomposition fraction, iii) macromolecular organic matter and iv) residues. The DSC curves gave the corresponding peak for water release near 100 o C and exothermic peaks at temperatures higher than 300 o C, attributed to the combustion of thermolabile organic matter. The TG curves for all soil samples are more complex than those of the humic acids due to the inorganic components, being characterized by stages i) dehydration process, ii) thermolabile organic matter, iii) macromolecular organic domain and iv) oxide residues. These steps of decomposition correspond to three endothermic DSC peaks and one exothermic peak clearly shown under a synthetic air atmosphere, being attributed to the combustion of the macromolecular organic fraction near 300 o C. The DSC curves from burnt and unburnt red Latosol soils from sugar cane cultivation showed more intense endothermic peaks than those of the forest. These thermal results show the influence of both the type and the organic matter contents on curve profiles, which are highly influenced by the soil mineral compositions and land-use activities, as well as the burning processes

Thermal analysis of brazilian tropical soils originating from different sources

Brazilian tropical Latosol soil samples were thermally analyzed associating thermogravimetric (TG) and differential scanning calorimetric (DSC) techniques under synthetic air or argon atmospheres. Rhodic eutrudox soils with forest vegetation, from unburnt and burnt cane plantations and that of a sandy phase having cerrado vegetation were investigated. From the organic soil fraction humic acids were extracted that decompose similarly to the commercial product, following the steps: i) adsorbed water, dehydrations, decarboxylations and release of organic molecules, ii) thermolabile decomposition fraction, iii) macromolecular organic matter and iv) residues. The DSC curves gave the corresponding peak for water release near 100 ºC and exothermic peaks at temperatures higher than 300 ºC, attributed to the combustion of thermolabile organic matter. The TG curves for all soil samples are more complex than those of the humic acids due to the inorganic components, being characterized by stages i) dehydration process, ii) thermolabile organic matter, iii) macromolecular organic domain and iv) oxide residues. These steps of decomposition correspond to three endothermic DSC peaks and one exothermic peak clearly shown under a synthetic air atmosphere, being attributed to the combustion of the macromolecular organic fraction near 300 ºC. The DSC curves from burnt and unburnt red Latosol soils from sugar cane cultivation showed more intense endothermic peaks than those of the forest. These thermal results show the influence of both the type and the organic matter contents on curve profiles, which are highly influenced by the soil mineral compositions and land-use activities, as well as the burning processes.As amostras de solos tropicais brasileiros foram analisadas pelas técnicas térmicas termogravimetria (TG) e calorimetria exploratória diferencial (DSC) em atmosferas de ar sintético ou argônio. Nesse processo foi investigado o solo eutrudox Ródico com vegetação de floresta, queimado ou não em plantação de cana de açúcar, e aquele de fase arenosa com vegetação de cerrado. A partir da fração orgânica do solo, foram extraídos ácidos húmicos que se decompõem similarmente ao produto comercial, de acordo com as etapas: i) água adsorvida, desidratação, descarboxilação e perda de moléculas orgânicas, ii) decomposição da fração termolábil, iii) matéria orgânica macromolecular e iv) resíduos acima de 950 ºC. As curvas de DSC deram correspondentes picos de perda de água perto de 100 ºC e exotérmicos em temperatura maior que 300 ºC, atribuídos à combustão de fração de matéria orgânica termolábil. As curvas TG dos solos são mais complexas que os ácidos húmicos, devido aos componentes inorgânicos, caracterizando os estágios: i) desidratação, ii) matéria orgânica termolábil, iii) domínio orgânico macromolecular, e iv) resíduos de óxidos. Essas decomposições correspondem a três picos endotérmicos em DSC e um exotérmico mostrado em atmosfera de ar sintético, atribuído à combustão da fração orgânica macromolecular na região de 300 ºC. As curvas de DSC dos solos provenientes de plantação de cana de açúcar mostraram picos endotérmicos mais intensos do que aqueles de solo de floresta. Os resultados térmicos demonstram a influência do material orgânico, que é altamente influenciado pelo componente mineral com alto teor de resíduo, pelo uso na atividade da terra e também pelos processos de queimadas.12501258Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq

Enzymatic activity measured by microcalorimetry in soil amended with organic residues

Enzymatic activity is an important property for soil quality evaluation. Two sequences of experiments were carried out in order to evaluate the enzymatic activity in a soil (Rhodic Eutrudox) amended with cattle manure, earthworm casts, or sewage sludges from the municipalities of Barueri and Franca. The activity of commercial enzymes was measured by microcalorimetry in the same soil samples after sterilization. In the first experiment, the enzyme activities of cellulase, protease, and urease were determined in the soil samples during a three month period. In the second sequence of experiments, the thermal effect of the commercial enzymes cellulase, protease, and urease on sterilized soil samples under the same tretaments was monitored for a period of 46 days. The experimental design was randomized and arranged as factorial scheme in five treatments x seven samplings with five replications. The treatment effects were statistically evaluated by one-way analysis of variance. Tukey´s test was used to compare means at p < 0.05. The presence of different sources of organic residues increased the enzymatic activity in the sampling period. Cattle manure induced the highest enzymatic activity, followed by municipal sewage sludge, whereas earthworm casts induced the lowest activity, but differed from control treatment. The thermal effect on the enzyme activity of commercial cellulase, protease, and urease showed a variety of time peaks. These values probably oscillated due to soil physical-chemical factors affecting the enzyme activity on the residues