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Cross-Polarisation Magic Angle Spinning Carbon-13 Nuclear Magnetic Resonance spectroscopy (CPMAS 13 C-NMR) represents one of the most powerful tools to investigate soil organic matter (SOM) mainly because of its inherent capacity to provide a semi-quantitative evaluation of carbon distribution. A critical parameter during acquisition of CPMAS 13 C-NMR spectra is the contact...
We compared the quantitative responses of liquid-state (LS) and solid-state (CPMAS) 13 C-NMR spectroscopy of four different soil humic substances. The intensities of signals for the alkyl carbons (0-40 ppm) were significantly larger in CPMAS than in LS spectra. This difference is in agreement with the pseudo-micellar model of the conformational nature of humic substances. By this view,...
The effects of humidity and metal ions in the determination of humic organic free radicals concentration (HOFRC) were studied by electron paramagnetic resonance (EPR). Increasing the sample humidity caused a decrease in both HOFRC, probably due to free radicals recombination, and in the derivative peak-to-peak line width (ΔH), probably due to a higher spin-spin relaxation time (T 2 ) as the...
In Vertisols, organic matter contributes to soil colour by formation of organo-mineral complexes and affects morphological, physico-chemical, biological and biochemical properties. Turbation may affect the chemical and structural composition of the most stabilised fractions of soil organic matter (SOM), i.e., humic substances (HS). The objectives of this study were to: (1) characterise SOM in two...
Soil organic matter plays an important role in soil properties and influences ecosystem cycles of C, N, Al, Fe, and other major and trace elements. We examined spatial variations in the structure and chemistry of soil organic matter at the Hubbard Brook Experimental Forest in New Hampshire, USA. Humic substances were extracted and isolated chromatographically into humic acid, fulvic acid, and polysaccharide...
Humic acids were extracted from the different horizons of three soil profiles sampled in the volcanic apparatus of Vico, Italy, above vitreous parent material. Two soils developed andic properties in a udic environment with a short dry season under a beech forest, whereas the third soil resulted in a well-structured Bw horizon in a xeric pedo-environment under an oak forest. The structural characteristics...
This work consisted of determining the degree of humification of humic substances (HS) extracted from six different Amazonian soils collected from flooded and unflooded regions at different depths (0–10, 10–20, 20–40, and 60 cm). The humic substances were extracted according to procedures recommended by the International Humic Substances Society and characterized using elemental analysis, electron...
The content and fractional composition of humus in soil exposed to conventional, shallow and minimum tillage for 40 years was investigated on Cambisols. Humus status depended on tillage methods and depth. In cultivated soil, conventional annual tillage can be replaced by shallow or minimum tillage, since this significantly increased soil humus content in the 0–10 and 10–20 cm soil layers. In both...
Titration curves were determined for soil from horizon samples of a clayey and a sandy loam Oxisol by (a) adding NaOH to soil suspensions and (b) incubating moist soils with Ca(OH) 2 . The organic fraction was primarily responsible for buffering in both soils. Humic acids were more important than fulvic acids in buffering against NaOH additions. With Ca(OH) 2 ,greater buffer capacities...
The dynamics of the stable fractions of soil organic matter (SOM), the humic substances, has been rarely studied in tropical soils. We evaluated extraction yields, elemental composition, isotopic δ 13 C abundance and solid-state 13 C NMR spectra of humic fractions isolated from five forested and cultivated soils in Ethiopia in order to assess the influence of deforestation and subsequent...
The combined application of organic residue and inorganic phosphate fertilizer has been suggested as a means of increasing the availability and solubility of applied phosphate (PO 4 ) in weathered soil. We studied the impact of dung manure on the solubility and retention of applied PO 4 in a tropical semi-arid soil under laboratory conditions. Surface and subsurface samples, collected...
There is currently no agreement to what extent humic substances may compete with arsenate and other anions for oxide adsorption sites in soils, and how to model this interaction. In this study, batch experiments were made in which the competition between fulvic acid and arsenate was studied in a spodic Bs horizon. Additional experiments were performed in which the pH and concentration dependence of...
Cultivation is known to strongly affect not only soil structure but also organic substances responsible for aggregation. This research was conducted to study the effect of cultivation on the distribution of soil macro- and microaggregates as related to changes in soil organic matter content in a Typic Haplustoll, located in central Cordoba, the principal peanut (Arachis hypogaea L.) growing area of...
The role of terrestrial humic substances as electron shuttles in bioreduction processes has gained broad acceptance as recognition has grown that the ability to transfer electrons to humic materials is distributed widely among microorganisms in nature. A fundamental property of humic substances pertinent to their mediation of reductive transformations is the maximum moles of electron charge they can...
A Andisol humic acid (HA) was fractioned by preparative size exclusion chromatography and polyacrylamide gel electrophoresis in the presence of denaturising agent (SEC-PAGE setup). Three fractions exhibiting high, medium and low molecular size (MS) and showing well-defined and distinct electrophoretic mobility were obtained. These fractions were analysed by UV–visible, FTIR and 3-D fluorescence spectroscopies...
Most models of soil humic substances include a substantial component of aromatic C either as the backbone of humic heteropolymers or as a significant component of supramolecular aggregates of degraded biopolymers. We physically separated coarse (0.2–2.0 μm e.s.d.), medium (0.02–0.2 μm e.s.d.), and fine (>0.02 μm e.s.d.) clay subfractions from three Midwestern soils and characterized the organic...
Soils are complex mixtures of solids from millimeter to nanometer in particle size, which may contain moisture. It is now possible to understand these structures using techniques developed for nanotechnology such as Transmission Electron Microscopy and Atomic Force Microscopy. These techniques illustrate the organisation of colloidal material in soils such as phyllosilicates, and humic acids and the...
Predictions of global warming render studies of organic matter stored in permanently frozen sediments of northernmost areas particularly topical. This paper offers results of fluorescence spectroscopy applied to the study of humic and/or humic-like fractions gained from polygenetic syncryogenic sediments in northern Yakutia in comparison with humic substances (HS) from recent soil and the Nordic (NOM)...
Open-air composting evolution of domestic solid wastes (DSW) collected during 150 days from a neighborhood of Santiago del Estero, Argentina, was investigated using several standard methods of compost analysis, in combination with steady-state UV–Vis absorption and fluorescence measurements of their extracted total humic substance-like (HSL), fulvic acid-like (FAL), and humic acid-like (HAL) molecules...
Use of a single factor for converting soil organic carbon to soil organic matter is challenged. The basis for this challenge arises from four sources: the original papers published in the nineteenth century, empirical studies published throughout the twentieth century, theoretical considerations of organic matter composition, and a consideration of what led to the popularity and general acceptance...
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