Search

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.

The interactions of tropical aquatic fulvic acids (AFA) with chlorine and formation of trihalomethanes were characterized by fluorescence spectroscopy. The aquatic humic substances (AHS) were isolated from a dark-brown stream (located in a environmental protection area near Cubatão city in São Paulo State, Brazil) by means of the collector XAD 8 according the procedure recommended by the International Humic Substances Society. The photoluminescence measurements were made by using a Perkin Elmer spectrometer; AHS, aquatic humic acids (AHA) and AFA samples were assayed. The interactions of AFA and chlorine were characterized by using different reaction times (1, 24, 48, 72 and 168 h) and chlorine concentrations (2.5, 5.0, 10.0 and 20.0 mg L-1). The relative fluorescence intensity for AFA was significantly decreased with the increasing of chlorine concentration and reaction time. The reduction of fluorescence intensity in the region of longer wavelength was interpreted as an indicative of interaction between condensed aromatic groups of AFA and chlorine.

Sewage sludge from wastewater treatment contains organic matter and plant nutrients that can play an important role in agricultural production and the maintenance of soil fertility. The present study has aimed to evaluate the degree of humification following sewage sludge application of soil organic matter by laser-induced fluorescence and humic acids using ultraviolet-visible fluorescence, and including comparison with Fourier-transform infrared spectroscopy and elemental analysis. Sewage sludge applications to the soil caused a decrease in the degree of humification of the soil organic matter and humic acids for both a Typic Eutrorthox (clayey) soil and a Typic Haplorthox (sandy) soil of around 14 and 27%, respectively. This effect is probably due to incorporation of newly formed humic substances from the sewage sludge into the characteristics of less humified material, and to the indigenous soil humic substances. The minor alterations observed in the clay soil probably occurred due to both the greater mineral association, which better stabilized the indigenous soil organic matter, and the higher microbial activity in this soil, which accelerated sewage sludge mineralization. Sewage sludge applications increased the C content for the clay and sandy soils by 7.4 and 15.4 g [kg.sup.-1], respectively, suggesting a positive effect on these two soils. Abbreviations: FTIR, Fourier-transform infrared; HA, humic acid; LIE laser-induced fluorescence; SOM, soil organic matter; TOC, total organic carbon. doi:10.2136/sssaj2008.0176

Fluorescence spectroscopy relies on the fluorescence emitted by rigid conjugated systems and thus can be used to assess the soil organic mailer (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.sub.LIF]) of whole soil samples showed a close correlation with the humification indexes [A.sub.4]/[A.sub.1], [I.sub.465]/[I.sub.399], and [A.sub.465] obtained after fluorescence spectroscopy analysis of the dissolved humic acids. The [H.sub.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 mailer from plant residues on the soil surface. The soils subjected to conventional tillage, however, showed relatively constant [H.sub.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.sub.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.sup.3+] are not feasible to electron spin resonance (ESR) and Carbon-13 nuclear magnetic resonance ([sup.13]C NMR) spectroscopy, unless previous treatment is employed.

Soil organic matter (SOM) plays an essential role in agronomic systems and is of great importance to environmental sustainability and carbon sequestration. This study evaluates the accumulation of carbon in soils from integrated agricultural systems (S) that include crop (C), livestock (L), and forest (F) components (in different combinations: CLFS, LFS and CLS) and an undisturbed native forest (NF) as a reference area. The study sites are part of the Embrapa Pecuária Sudeste research station located in the southeast of Brazil in a region of dystrophic Red‐Yellow Latosol soils. Stable carbon isotopic analysis (δ13C) and solid‐state 13C nuclear magnetic resonance (13C NMR) spectroscopy were used to evaluate the chemical characteristics of humic acid (HA) extracts of soils from different soil horizons. The findings were discussed in the context of laser‐induced fluorescence spectroscopy (LIFS) measurements on the whole soils and carbon content on both the whole soils and HA extracts. With increasing depth of the soil horizons, bulk SOM (in the whole soil) and a more recalcitrant humic fraction (the HA) became enriched in carbon, indicative of accumulation. Isotopic analysis revealed that SOM in the crop‐livestock‐forest system exhibited δ13C signatures corresponding to C4 plants (grass and corn). The native forest exhibited a uniform δ13C signature characteristic of C3 plants (native trees). Benzenepolycarboxylic acids (BPCA) quantification on limited samples revealed condensed aromatic structures in both crop‐livestock‐forest system and native forest. The absence of burning suggests that these compounds come from the humification of lignin. Based on structural characterization, carbon is sequestered as recalcitrant and long‐lived oxidized ligninaceous structures and condensed aromatic groups. The current research demonstrates the feasibility of novel agricultural approaches such as using crop‐livestock‐forest systems. Such pastureland management enhances higher agricultural productivity and sustainability, thus avoiding new deforestation of native areas. Highlights: Integrated agricultural systems enhance carbon enrichment in soil organic matter and humic acids.Carbon stabilized in oxidized ligninaceous and condensed molecules promotes long‐term carbon storage.Extended root systems are likely to play a critical role in carbon sequestration.Integrated agricultural systems can be effective alternatives for reducing greenhouse gases. [ABSTRACT FROM AUTHOR]

The spin-label probe 5-SASL (stearic acid spin-label with nitroxide free radical in position 5 of hydrocarbon chain), which is detectable by electron spin resonance, is identified as an alternative means of studying the pH dependence of hydrophobic interactions in humic acid.