Martha González-Pérez

Caracterização de fases de cimento Portland por meio das técnicas de difratometria de raios X e espectroscopia de ressonância magnética nuclear de 29Si no estado sólido .

This study on humic acids (HAs) of podzol horizons from the southeastern region of Brazil investigated the accumulation and degradation of soil organic matter (SOM) in warm‐climate podzols. Humic acids from sandy coastal Spodosols (Histic Alaquod and Arenic Alorthod) from Cardoso Island in Sao Paulo State were characterized by pyrolysis in combination with gas chromatography and mass spectrometry (Py‐GC/MS). The soils developed on quartzitics, andy, nutrient‐poor parent materials under restinga forest in a coastal area. The Py‐GC/MS results show that the chemical composition of HAs in B horizons in one out of three profiles was influenced by both dissolved organic C (DOC) and C from in situ decaying roots. Carbon derived from DOC dominated in the deepest part of the B horizons. In the Arenic Alorthod (H9) profile, SOM from the B horizon seemed to be largely derived from roots. The DOC‐derived SOM was characterized by large contributions of phenol, methylphenols, and degraded polysaccharide products, while root contributions were mainly characterized by lignin products. Aliphatics were most abundant in A horizons (E and EB horizons were not analyzed). Both DOC‐derived and lignin‐derived SOM showed distinct degradation patterns. The Py‐GC/MS results corroborate those obtained by ¹³ C variable amplitude cross polarization magic angle spinning nuclear magnetic resonance spectroscopy and Fourier‐transform infrared spectroscopy. Molecular chemistry showed that podzol B horizons are variable in composition, and local influences, such as drainage and vertical or lateral water transport, and SOM decomposition play an important role in podzolization processes in warm climates.

O acúmulo e a estabilidade da matéria orgânica do solo estão relacionados com a declividade de vertentes. Por essa razão, foram avaliadas quantitativamente relações entre a declividade e o grau de humificação de ácidos húmicos, o conteúdo de fragmentos de carvão e suas idades radiocarbônicas. Foram amostrados quatro Latossolos situados nas posições de topo, ombro, meia encosta e sopé de uma toposseqüência com pastagens, de uma área cratônica do Sul de Minas Gerais. Os Latossolos são originados de gnaisses do Complexo Cristalino, da Era Pré-Cambriana, e apresentam regime hídrico údico e regime térmico isotérmico. Foram coletadas amostras de horizontes e sub-horizontes dos quatro perfis, para caracterização química e física, extração de ácidos húmicos e determinação do conteúdo dos radicais livres do tipo semiquinona. Fragmentos de carvão foram coletados nesses mesmos sub-horizontes, para quantificação gravimétrica, avaliação dos teores de C e N e para datações radiocarbônicas. Os resultados deste estudo demonstram que, em toposseqüências de Latossolos do Sul de Minas Gerais, a acumulação e o grau de humificação da matéria orgânica do solo estão fortemente correlacionados com a declividade da vertente, enquanto a quantidade e a idade radiocarbônica de fragmentos de carvão estão relacionadas a processos de gênese dos solos e à posição na vertente.

Fluorescence spectroscopy relies on the fluorescence emitted by rigid conjugated systems and thus can be used to assess the soil organic matter (SOM) humification. This technique is generally applied to solution samples of humic substances, and so far no information exists about its applicability to whole untreated soil samples. The laser‐induced fluorescence (LIF) spectroscopy is proposed as a novel technique to assess the organic matter humification in whole soil samples. We sampled the 0‐ to 2.5‐, 2.5‐ to 5‐, 5‐ to 10‐, 10‐ to 15‐, and 15‐ to 20‐cm layers of three Oxisols of long‐term experiments located in two sites of the Brazilian Cerrado. The humification index based on LIF spectroscopy (H _LIF ) of whole soil samples showed a close correlation with the humification indexes A ₄ /A ₁ , I ₄₆₅ /I ₃₉₉ , and A ₄₆₅ obtained after fluorescence spectroscopy analysis of the dissolved humic acids. The H _LIF in soils under native cerrado or subjected to no‐tillage increased from the top to the deepest layer, which is consistent with the deposition of labile organic matter from plant residues on the soil surface. The soils subjected to conventional tillage, however, showed relatively constant H _LIF along the profile, possibly because homogenization imparted by disturbance of the arable layer. Accordingly, for the two top layers, the soils under no‐tillage showed a lower H _LIF than for conventionally tilled soils. Laser‐induced fluorescence spectroscopy is a promising technique to assess humification in whole soil samples, particularly in Oxisols, which due to high concentration of Fe ³⁺ are not feasible to electron spin resonance (ESR) and Carbon‐13 nuclear magnetic resonance ( ¹³ C NMR) spectroscopy, unless previous treatment is employed.