Sérgio da Costa Saab

Characterization of humic acids from a Brazilian Oxisol under different tillage systems by EPR, 13C NMR, FTIR and fluorescence spectroscopy

The importance of soil organic matter functions is well known, but structural information, chemical composition and changes induced by anthropogenic factors such as tillage practices are still being researched. In the present paper were characterized Brazilian humic acids (HAs) from an Oxisol under different treatments: conventional tillage/maize-bare fallow (CT1); conventional tillage/maize rotation with soybean-bare fallow (CT2); no-till/maize-bare fallow (NT1); no-till/maize rotation with soybean-bare fallow (NT2); no-till/maize-cajanus (NT3) and no cultivated soil under natural vegetation (NC). Soil HA samples were analyzed by electron paramagnetic resonance (EPR), solid-state 13C nuclear magnetic resonance (13C NMR), Fourier transform infra-red (FTIR) and UV-Vis fluorescence spectroscopies and elemental analysis (CHNS). The FTIR spectra of the HAs were similar for all treatments. The level of semiquinone-type free radical determined from the EPR spectra was lower for treatments no-till/maize-cajanus (NT3) and noncultivated soil (1.74×1017 and 1.02×1017 spins g−1 HA, respectively), compared with 2.3×1017 spins g−1 HA for other soils under cultivation. The percentage of aromatic carbons determined by 13C NMR also decreases for noncultivated soil to 24%, being around 30% for samples of the other treatments. The solid-state 13C NMR and EPR spectroscopies showed small differences in chemical composition of the HA from soils where incorporation of vegetal residues was higher, showing that organic matter (OM) formed in this cases is less aromatic. The fluorescence intensities were in agreement with the percentage of aromatic carbons, determined by NMR (r=0.97 P<0.01) and with semiquinone content, determined by EPR (r=0.97 P<0.01). No important effect due to tillage system was observed in these areas after 5 years of cultivation. Probably, the studied Oxisol has a high clay content that offers protection to the clay–Fe–OM complex against strong structural alterations.

Tillage and cropping system effects on soil humic acid characteristics as determined by electron spin resonance and fluorescence spectroscopies

Abstract Long-term (5- and 9-year) effects were evaluated of two tillage regimes (conventional tillage: CT; and no-tillage: NT) and two cropping systems (oat/maize: O/M; and oat+vetch/maize+cowpea: O+V/M+C) on characteristics of humic acids (HAs) from surface layer (0 to 25 mm) of a subtropical Brazilian Paleudult soil. Generally, soil HA samples from conservation management systems with no soil disturbance (NT) and high crop residue addition (O+V/M+C) showed lowest humification degree, as demonstrated by lowest concentration of semiquinone-type free radicals, determined by electron spin resonance (ESR), and lowest total fluorescence (TF), which is proportional to area under fluorescence spectrum; however, cropping systems had less effect than tillage regimes on two spectroscopic parameters. Since all HA samples presented a maximum fluorescence emission peak around 518 nm, when excited with blue light, we believe that differences in the fluorescence intensity could be attributed to concentration of similar condensed aromatic moiety. This assumption was consistent with strong correlation with stable semiquinone-type free radicals (r=0.84, P

Determinação da humificação da matéria orgânica de um latossolo e de suas frações organo-minerais.

Laser-induced fluorescence spectroscopy was used to determine the humification degree of the organic matter of a whole soil, that is, soil without any physical or chemical treatment. Particle size was determined in physically separated fractions. The humification of organic matter, the depth of the soil and the planting system can be correlated. On the surface of the soil, no tillage provided the smallest humification in comparison with the conventional tillage and reduced tillage. The fractions of the superficial layer of the soil (0-20 cm) indicated larger humification in the fraction from 20 to 53 µm and the smallest in the fraction of <2 µm.

Studies of semiquinone free radicals by ESR in the whole soil, HA, FA and humin substances

In this work it was studied soil organic matter from a gley soil, using ESR (electron spin resonance spectroscopy). The studied soil samples were collected in Rio de Janeiro, Brazil. Humic and fulvic acid, humin macromolecules, and whole soil samples were analyzed. The results showed that the amount and line width of semiquinone free radical from whole soil samples had good correlation with humin fraction and no correlation with humic and fulvic acids contents.

Mineralogia de um latossolo vermelho distrófico submetido a diferentes manejos por 24 anos

The search for management systems that preserve or improve soil qualities, the mineralogical as well as the organic composition, with a view to higher yields, is becoming more and more intense. The objective this study was to qualitatively verify the mineralogical effects of different management types: conventional , minimum and no-tillage for 24 years on a Red Latosol in Ponta Grossa, PR, Brazil, by the following techniques: X-ray diffraction, X-ray fluorescence and Fourier transform infrared. No significant changes in the mineralogy of the Red Latosol were observed by the techniques applied, as a result of the different management types. It was however possible to qualitatively verify the presence of the following minerals: gibbsite, kaolinite, halloysite, montmorillonite, hematite, rutile, anatase, goethite and quartz.

Characterization by Electron Paramagnetic Resonance of organic matter in whole soil (Gleysoil) and organic-mineral fractions

Electron Paramagnetic Resonance (EPR) spectroscopy was applied in whole soil samples (Gleysoil). The objective of this work was to quantify the degree of humification of the organic matter of the soil, whole soil (Gleysoils) without any chemical treatment, and to compare with its organic-mineral fractions. The signal of semiquinone free radical was detected and quantified showing close relationship with its organic-mineral fractions.

Software Image J to study soil pore distribution

In the soil science, a direct method that allows the study of soil pore distribution is the bi-dimensional (2D) digital image analysis. Such technique provides quantitative results of soil pore shape, number and size. The use of specific softwares for the treatment and processing of images allows a fast and efficient method to quantify the soil porous system. However, due to the high cost of commercial softwares, public ones can be an interesting alternative for soil structure analysis. The objective of this work was to evaluate the quality of data provided by the Image J software (public domain) used to characterize the voids of two soils, characterized as Geric Ferralsol and Rhodic Ferralsol, from the southeast region of Brazil. The pore distribution analysis technique from impregnated soil blocks was utilized for this purpose. The 2D image acquisition was carried out by using a CCD camera coupled to a conventional optical microscope. After acquisition and treatment of images, they were processed and analyzed by the software Noesis Visilog 5.4® (chosen as the reference program) and ImageJ. The parameters chosen to characterize the soil voids were: shape, number and pore size distribution. For both soils, the results obtained for the image total porosity (%), the total number of pores and the pore size distribution showed that the Image J is a suitable software to be applied in the characterization of the soil sample voids impregnated with resin.

pH effect in aquatic fulvic acid from a Brazilian river

Studies of the morphological behavior of fulvic acids were carried out using the Atomic Force Microscopy technique together with zeta Potential techniques and fluorescence spectroscopy. Results showed that the aquatic fulvic acid (AFA) of a Brazilian River changed its morphology when the AFA aqueous solution had its pH changed. In acid pH the morphology is granular forming 10-55 nm high agglomerates. In alkaline pH values were 2.5-4.0 nm, and the morphology forms non granular structures. These results suggest that for pH 3.0 electrostatic interactions are weak and hydrogen bonding is responsible for the aggregates formation; while at pH 9.0 electrostatic interactions are strong due to the increase in phenolic groups ionization and low hydrogen interaction forming open structures. Fluorescence spectroscopy results confirmed the AFM, that is, a change in the AFA in tropical river in alkaline pH compared to the structure in acid pH.

Electron paramagnetic resonance characterization of a humic acid-type polymer model

Humic acid-type polymer models have been shown to be similar to natural humic acids (HA) in terms of chemical properties. Due to the complexity of humic substances (HS), this humic acid-type polymer models, in which the ligand sites are better defined, can be used in the study of metals and for other applications. In this study, a polymer with characteristics analogous to those of humic acids isolated from soil surface cultivated using a no-tillage system for nine years, was obtained by means of synthesis reactions, through oxidative polymerization in an alkaline medium using para-benzoquinone as precursor. An EPR spectroscopy study was made of natural humic acids (HA) and synthetic humic acids (SHA). A semiquinone-type free radical signal was detected in the SHA. The spectra showed similar signals for HA from soil and synthetic HA complexed with Fe3+, Cu2+ and Mn2+ ions.

Use of the EPR technique to determine thermal stability of some humified organic substances found in soil organic-mineral fractions

In this work, using the EPR spectroscopy, we analysed the thermal stability of some organic-mineral compounds found in a Gleysoil from Rio Janeiro. It was observed a complete disappearance of the EPR signal around 600 °C for the < 2 µm fraction and a residual EPR signal of semiquinone free radical for the 2-20 µm and 20-53 µm fractions at the same temperature. Also, the experiments showed that the 2-20 µm fraction had a larger concentration of semiquinone free radical per g of carbon and a smaller line width indicated a larger humification of this fraction. This is an evidence that the soil organic matter of this fraction (2-20 µm) is more stable than the other ones.