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Antioxidants (AOX) in soils originate mainly from secondary plant metabolites and are pivotal in many redox processes in environment, maintaining soil quality. Still, little is known about the influence of land uses on their accumulation in soil. The aim of the paper was to determine the content of these redox-active compounds in the extracts of A horizons of abandoned fallows, arable and woodland soils. Total antioxidant capacity (TAC) of soils under various uses and vegetation was evaluated in different soil extracts using Folin-Ciocâlteu method. The contribution of humic acids to TAC was determined and antioxidant profiles estimated using the chromatographic GC-MS method. Forest soils exhibited the highest TAC (15.5 mg g -1 ) and AOX contents (4.34 mg g -1 ), which were positively correlated with soil organic carbon content. It was estimated that humic acids contribute to over 50% of TAC in soils. The main phenolics in woodland A horizons were isovanillic and p-hydroxybenzoic acid (p-HA), while esculetin and p-HA predominated in the abandoned fallows due to the prevalence of herbaceous vegetation. Cultivated soils were the most abundant in p-HA (56.42%). In the studied topsoils, there were considerable amounts of aliphatic organic matter, which role in redox processes should be further evaluated., (© 2024. The Author(s).)

Humic substances, including humin fraction, play a key role in the fate of organic and inorganic xenobiotics contaminating the environment. Humin is an important fraction of humic substances, which has been the least studied to date. This is due to the difficulties connected with its isolation that pose a number of methodological problems. Methods of humin fraction isolation can be divided into following main groups: (1) digestion of mineral soil components with HF/HCl followed by alkali extraction of HA and FA; (2) alkali extraction of HA and FA followed by extraction of humin by different organic solvents; and (3) alkali extraction of HA and FA followed by HF/HCl digestion of mineral soil components. Nevertheless, each of these methods has different limitations. We described in detail a useful procedure of humin isolation, in which this fraction was not extracted, but isolated from the soil by removing its soluble organic and mineral components. A modified method of HA and FA extraction with 0.1 M NaOH, according to the International Humic Substances Society, was used in the first step. Then, the mineral components in the residue were digested with the 10% HF/HCl. Unlike the procedures oriented to increase the concentration of organic matter, samples were treated several times with the HF/HCl mixture until the mineral fraction was almost completely digested. The main assumption of the method modification was to obtain the highest yield with the lowest possible ash content, but without affecting humin chemical structure. The results showed that the proposed procedure is characterized by a high efficiency and recovery and, therefore, it can be used to isolate high amounts of humin from soil., (© 2021. The Author(s).)

The purpose of the research was to determine the molecular properties of humin (HUM) determined by elemental composition, as well as spectroscopic 13C Magic Angle Splitting Cross Polarisation Nuclear Magnetic Resonance (13C MAS CP NMR), Fourier transformed infrared, electron paramagnetic resonance and scanning electron microscope energy‐dispersive x‐ray (SEM–EDX) techniques. Soil samples were isolated from the mollic horizon of Phaeozem and Chernozem arable soils derived from different parent materials in Poland. The HUM was isolated as the fraction that was remined after exhaustive extraction of the humic and fulvic acids by NaOH and was followed by removal of the mineral fraction with HF/HCl treatment. The results obtained indicated that the HUM structures isolated by the adopted method are a chemically heterogeneous conglomerate, composed of a complex of many strongly combined units of organic substances. This fraction indicated a highly condensed structure with a predominance of aromatic components (predominating over chain forms ranging from 7.05% to 10.32%) and hydrophobic reactive moieties. The share of hydrophobic forms ranges from 77.41% to 80.83%. The ash content, ranging from 22.89% to 54.50%, as well as SEM–EDX used indicated that the HUM isolated with the adopted procedure is strongly associated with the mineral components of the soil. The aromatic part of HUM is strongly associated with the mineral components of the soil, what provides their stability in the environment. These observations confirm the high resistance of HUM to decomposition and indicate the great importance of this fraction in carbon sequestration and preventing soil degradation. [ABSTRACT FROM AUTHOR]

The aim of the investigation was to determine the quantitative changes of selected organic compounds during composting of municipal solid wastes (MSWs). The object of the study was a differently matured compost produced according the to open pile/windrow semi-dynamic technology from selectively collected biodegradable municipal solid waste. During the experiment, the temperature and moisture of the composted wastes were monitored. In the collected samples—taken from differently matured compost—the total organic carbon (TOC) and total nitrogen (TN) were determined. The organic matter fractionation method described by Stevenson and Adani et al. was adopted, which allows to determine the carbon content of the following groups of organic compounds: hydrophobic (HSC), hydrophilic (WEOC), acidophilic (CAC), cellulose (CCEL), core-HA (ligno-humic, CALK) and residual carbon (non-hydrolysing, CR). The TOC and TN content, as well as the origin and quality of the starting materials, allow the product tested to be classified for fertiliser purposes. The most intense changes were observed during the thermophilic composting phase. In spite of the optimal technological conditions of the process, the predominance of the CR and CCEL fraction was observed, and the share of humic compounds did not exceed 30% TOC. The investigated compost met legal, ecological and economic criteria for products of biological recycling, thus can be used as a good organic amendment to improve the soil organic matter balance, stimulate the soil biodiversity and carbon sequestration. [ABSTRACT FROM AUTHOR]

Lignite burning is still the main source of energy in many countries, generating huge amounts of alkaline residues deposited in dumping sites, which affects the surrounding environment. There are only a few publications dealing with the effects on pH changes of surface horizons, but there are no reports on the impact on other soil properties. The aim of this paper was to characterize the changes occurring in the soil organic matter (SOM) of ectohumus horizons of Podzols located near the dumping site and at the control site. Conventional one‐dimensional, synchronous, and three‐dimensional fluorescence can provided a new information on differences in the structure of humic substances (HS), which are crucial constituents of SOM. Humic acid (HA) and fulvic acid (FA), originally present in the ectohumus horizon, indicated a lower degree of humification, and were characterized by a looser structure, than HS that were extracted from soils affected by fly‐ash. The neutralization of the soil reaction resulting from the deposition of fly‐ash favored the formation of higher humified HS, characterized by a higher concentration of aromatic rings in the core of the molecule and the presence of double conjugated bonds. The fluorescence technique could be applicable to monitor the chemical modification of soils in regions affected by ashes but also all factors changing soil pH. The conducted research has shown that fluorescence spectroscopy can be successfully used as a sensitive technique to characterize qualitatively structures of different organic substances present in terrestrial and aquatic systems. [ABSTRACT FROM AUTHOR]