Caracter?sticas Estruturais da Mat?ria Org?nica em Organossolos H?plicos

Autor: Ebeling, Adierson Gilvani
Jazyk: portugalština
Rok vydání: 2010
Předmět:
Zdroj: Biblioteca Digital de Teses e Dissertações da UFRRJUniversidade Federal Rural do Rio de JaneiroUFRRJ.
Druh dokumentu: Doctoral Thesis
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Conselho Nacional de Desenvolvimento Cient?fico e Tecnol?gico, CNPq, Brasil.
The Histosols have a small geographic extension in the Brazilian territory; however, they are intensively used in family agriculture systems and have a great environmental importance. The drainage of Histosols leads to the subsidence process and other changes in the soil organic matter (SOM), with consequences in their characteristics and potential. The nature of humic substances (HSs) is determinant in the alterations of the Histosols. The characterization of the HSs allows the understanding of processes of SOM transformation in the Histosols, and their environmental impact. The objectives of this study were: to characterize Histosols from different environments and land usage intensity; and to evaluate alterations in humic fractions of SOM, by using elemental composition analyses, spectroscopic, thermal degradation, and nuclear magnetic resonance (NMR) techniques. The study was developed in eight Histosols, from the States of Rio de Janeiro, Maranh?o and Paran?, in Brazil. Their chemical properties: total organic carbon (TOC), pH, sum of bases (SB), H+, Al3+, cation exchange capacity (CEC), and V%; and physical properties: bulk density (BD), MR, MM, and OMD, were evaluated. Also, the quantitative fractionating of the HSs: fulvic acid (C-FAF), humic acid (CHAF), and humin (C-HUM), and C-FAH/C-FAF relations, C-EA/C-HUM (C-EA = C-FAF + C-FAH). The humic acids were extracted using the method of the International Humic Substances Society (IHSS), and evaluated by different techniques. The chemical attributes varied with the intensity of burning and agricultural usage. Though, in general, the Histosols presented low natural fertility, and it was related to the humic acid fraction (high ratio CFAH/ C-FAF). Amongst the SOM fractions the HUM predominated, with an average value of 59.98% of total carbon determined by the CHN; followed by the FAH. The C-FAH/C-FAF ratio diminished with the increase of agriculture usage intensity. The results of the TGI (Thermal Gravimetric Index) suggested strong resistance to thermal degradation of majority of the organic horizons. The elemental composition (%C, %H, %N, %O) of the humic acids showed large amplitude of variation between the horizons, but no pattern was observed between the Histosols. The increase of carbon content, the high values of TGI, and the reduction of oxygen content in the humic acids (HA) might explain the high thermal decomposition resistance found in the HA extracted form the Histosols. A correlation between H/C and TGI was observed, where the lower values of H/C were related to the highest resistance of the humic acids to thermal degradation. The spectroscopic and NMR techniques allowed characterizing compounds and groups of substances in the HA, showing the great potential of these tools in studies of HS from Histosols. The multivariate methods allowed a combined analysis of techniques applied in the study, showing a group of labile and recalcitrance materials in the soils. The results, in general, indicated the fragility of the Histosols areas, in terms of agricultural management and the formation environment. Their importance for the environment should be priority in comparison to agricultural usage, mainly due to their relevant part in the aquifers preservation.
Os Organossolos t?m pequena representatividade geogr?fica no Brasil, entretanto, s?o utilizados intensamente em modelos de agricultura familiar e t?m grande import?ncia ambiental. Por?m, a sua drenagem conduz ao processo de subsid?ncia e outras modifica??es na mat?ria org?nica do solo (MOS), com implica??es nas caracter?sticas dos Organossolos e em sua potencialidade. A natureza das subst?ncias h?micas (SHs) ? determinante nessas altera??es nos Organossolos. A caracteriza??o das SHs permite a compreens?o dos processos de transforma??o da MOS nos Organossolos e seu impacto no ambiente. Os objetivos deste trabalho foram: caracterizar Organossolos em v?rios ambientes e intensidade de uso agr?cola e avaliar altera??es nas fra??es humificadas da MO, atrav?s de t?cnicas de an?lise da composi??o elementar, espectrosc?picas, termodegradativas e de resson?ncia magn?tica nuclear (RMN). Foram estudados oito perfis de solos, nos Estados do Rio de Janeiro, Maranh?o e Paran?. Foram avaliadas as suas propriedades qu?micas: carbono org?nico total (COT), pH, soma de bases (SB), H+, Al3+, CTC e V%; e propriedades f?sicas: densidade do solo (Ds), RM, MM e DMO. Al?m do fracionamento quantitativo das SHs: ?cidos f?lvicos (C-FAF), ?cidos h?micos (C-FAH) e humina (C-HUM), e rela??es C-FAH/C-FAF, C-EA/CHUM (C-EA = C-FAF + C-FAH). Os ?cidos h?micos (AH) foram extra?dos pelo m?todo da Sociedade Internacional de Subst?ncias H?micas (IHSS) e avaliados por distintas t?cnicas. Os atributos qu?micos variaram com o efeito das queimadas e da intensidade de uso agr?cola; por?m, em geral, os Organossolos apresentaram baixa fertilidade natural, a qual, em geral, esteve relacionada ? fra??o ?cido h?mico (maior raz?o C-FAH/C-FAF). Dentre as fra??es da MO, a HUM predominou, com valor m?dio de 59,98% do carbono total determinado pelo CHN, seguida da FAH. A rela??o C-FAH/C-FAF diminuiu a medida que o uso agr?cola ? intensificado. Os dados do ITG (?ndice Termogravim?trico) sugeriram forte resist?ncia ? termodegrada??o para a maioria dos horizontes org?nicos. A composi??o elementar (%C, %H, %N, %O) dos ?cidos h?micos apresentou grande amplitude entre os horizontes, por?m sem padr?o diferenciado entre os Organossolos. O aumento do conte?do de carbono, os altos valores de ITG e a diminui??o do conte?do de oxig?nio nos ?cidos h?micos podem explicar a maior resist?ncia a termodecomposi??o dos AH extra?dos dos Organossolos. Foi observada correla??o entre a raz?o H/C e o ITG, onde os menores valores de H/C estiveram relacionados a maior resist?ncia dos AH ? termodegrada??o. As t?cnicas espectrosc?picas e de RMN permitiram caracterizar compostos e grupamentos nos AH, demonstrando o potencial dessas ferramentas nos estudos de SHs provenientes de Organossolos. Os m?todos de an?lise multivariada permitiram uma avalia??o conjunta das t?cnicas utilizadas, mostrando um grupo de amostras l?beis e recalcitrantes nos solos. Os resultados encontrados, em geral, indicam a fragilidade das ?reas de Organossolos, em fun??o do manejo para agricultura e do seu ambiente de forma??o. A sua import?ncia em termos ambientais deveria ser priorizada em rela??o ao uso agr?cola, principalmente pelo papel relevante na preserva??o de aqu?feros.
Databáze: Networked Digital Library of Theses & Dissertations
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