Frações da matéria orgânica e composição molecular de substâncias húmicas de solos sob cultivo de eucalipto em biomas distintos

• Ano de defesa: 2009
• Autor(a) principal: Soares, Emanuelle Mercês Barros
• Orientador(a): Silva, Ivo Ribeiro da
• Banca de defesa: Neves, Júlio César Lima , Dieckow, Jeferson , Fernandes, Sergio Antônio
• Tipo de documento: Tese
• Tipo de acesso: Acesso aberto
• Idioma: por
• Instituição de defesa: Universidade Federal de Viçosa
• Programa de Pós-Graduação: Doutorado em Solos e Nutrição de Plantas
• Departamento: Fertilidade do solo e nutrição de plantas; Gênese, Morfologia e Classificação, Mineralogia, Química,
• País: BR
• Palavras-chave em Português: Carbono; 13C - NMR; Nitrogênio
• Palavras-chave em Inglês: Carbon; 13C - NMR; Nitrogen
• Área do conhecimento CNPq: CNPQ::CIENCIAS AGRARIAS::AGRONOMIA::CIENCIA DO SOLO
• Link de acesso: http://locus.ufv.br/handle/123456789/1602

The eucalypt is a fast growing forest species. During its growth cycle and after its harvest contributes to the soil a large amount of biomass, which can contribute to formation of soil organic matter (SOM). The present thesis has as general goals: i) to evaluate the impact of eucalypt cultivation on C and N in fractions of SOM in soils of different texture in Rio Grande do Sul State; ii) to evaluate the alterations in the stocks of C and N in SOM fractions under influence of the rotation duration, and time after harvest and new planting of eucalypt plantations and; iii) to carry out characterization of molecular composition of fulvic acids (FA) and humic acids (HA) from soils under eucalypt cultivation in different biome in Brazil through 13C Nuclear Magnetic Resonance (NMR) spectroscopy. In the first study it was verified that the clayey soil under eucalypt cultivation (second rotation) presented smaller stocks of C-HA, C associated to humin (C-HU) and the microbial biomass (C-MB), and similar total organic C stock (TOC), C associated to the light organic matter (C-LOM) and C-FA in comparison to the soil under native forest. In the sandy soil with eucalypts plantations in the second rotation there were larger stocks of TOC, C-LOM, C-HA and C-FA than in the forest soil. The clayey soil under eucalypt plantation stored more TOC and humic substances (HS) than the sandy soil. On the other hand, the stocks of C-LOM and C-MB were larger in sandy soil under eucalypt. The clayey soil presented larger capacity to store SOM and HS, because of greater clay content. In the second study a decrease was verified in the TOC, C-HU and C-LOM stocks after 10 years of eucalypt cultivation in a soil previously under native grassland. However, recovery of the stocks of C-MB and C-FA was observed in this period. In the 13 year old eucalypt increases were observed in TOC, C-FA, C-HA, C-LOM (0-100 cm) and C-MB (0-60 cm) stocks. However C stocks in the HU increased only after 22 years of eucalypt cultivation. When the 13 year old plantations were harvested and a new planting was performed, increases in TOC, C-FA, C-HA, C-HU and N-HU along with reductions in LOM and MB were verified after year (0- 100 cm). After four years of the new planting, decreases were observed in C-LOM stocks and SOM mummified fractions. Eucalypt plantation management with short rotations and more frequent reforms seems not to provide enough time for the recovery of SOM. In the third study 13C NMR associated with advanced procedures of DP/MAS (Direct Polarization/Magic Angle Spinning), CP/TOSS (Cross Polarization/Total Suppression of Sidebands), and CSA (Chemical Shift Anisotropy) allowed obtaining more quantitative estimates of the degree of HS aromaticity. According to the results DP-based aromaticity was greater than the CP-based aromaticity. The major NMR-identifiable components in these HS were primarily: aromatics, COO groups, peptides, lignins, carbohydrate and nonpolar aliphatics. The replacement of native vegetation by eucalypt plantations increases the relative contribution of nonpolar aliphatic groups in HA from soils previously under Atlantic Forest (Sooretama and Montanha sites), grassland and the Cerrado (Curvelo site only) biomes. The same trend was observed for FA. There is evidence of substantial contribution of lignin-derived C for HA and FA, especially in sites planted with Brachiaria sp pastures. In all biomes the dipolar dephasing technique confirmed the presence of condensed C in the aromatic regions, possibly inherited from charred materials derived from natural and anthropic fires in the region. The ratio of alkyl to O alkyl (A/O-A ratio) decreased from HA to FA, revealing a more advanced humification degree of HA.