Agronomy

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Dear Colleagues,

Humic substances (HSs), the sophisticated and enigmatic dark-colored heterogeneous organic mixtures omnipresent in soils, sediments, and natural waters, are structurally recalcitrant compounds primarily associated with agriculture.

Humic substances are universal amphiphiles and possess unique chelating properties with both organic and inorganic species; they regulate the bioavailability of a wide range of compounds, e.g., nutrients and pollutants; they also ameliorate soils and promote plant growth, displaying auxin-like activity and improving physiological and metabolic performance; they display electron-shuttling behavior and may act as environmental signals. Therefore, HSs have multiple essential functions in water quality improvement, soil chemistry, and sustainable agriculture. However, the elusiveness regarding the molecular structures and the multidisciplinary roles of HSs remains.

In the Special Issue “Humic Substances: Chemistry and Multidimensional Role in Agricultural Systems and Pollution Management” all scientific contributions (e.g., research papers, review articles, communications, short notes, and opinions) that provide innovative insights into the related topics are welcome, and the topics include the following:

The structure and physicochemical properties of HSs;
HS benefits by shifting to more sustainable agriculture;
The impact of HSs and HS-containing materials on soils, waters, plants, crop production, and living organisms (humans, birds, animals, and fishes);
Interactions between HSs and toxic compounds, both organic and inorganic, related to environmental health;
Organic waste management techniques, e.g., composting and adsorption, connected to HSs’ fate.

Dr. Maria Roulia
Guest Editor

Manuscript Submission Information

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Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Agronomy is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

humic substances
humic acid
fulvic acid
humin
soil
water quality
pollutant sequestration
organic/inorganic nutrients
plant growth
waste management

Published Papers (2 papers)

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Research

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16 pages, 4248 KiB

Open AccessArticle

Molecular Composition of Humic Acids of Different Aged Fallow Lands and Soils of Different Types of Use in Northwest of Russia

by Vyacheslav Polyakov, Timur Nizamutdinov and Evgeny Abakumov

Agronomy 2024, 14(5), 996; https://doi.org/10.3390/agronomy14050996 - 9 May 2024

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Abstract

Post-agrogenic transformation of fallow soils leads to changes in soil carbon content, the molecular composition of humic substances, and rates of organic matter stabilization, which can affect climate change on the planet. In this regard, we analyzed the molecular composition of humic acids isolated from natural and fallow soils in the southern Taiga zone of northwest Russia. Different-aged soils on fallow lands represent a model of soil transformation in time, and data on the transformation of soil humic acid molecular composition make a significant contribution to the understanding of soil organic matter stabilization aspect issues. In this case, the molecular structure of humic acids isolated from natural and fallow soils in northwest Russia was analyzed. To study the molecular composition of HAs, the elemental composition was analyzed, and ¹³C (CP/MAS) NMR spectroscopy of HAs isolated from different aged abandoned soils and soils of different types of use was carried out. The obtained data showed that with the increasing age of soils in the fallow state, there is an increase in the carbon content of humic acids as well as a decrease in nitrogen content. As a result of the increasing age of soils in the fallow state, there are dynamics in the content of aromatic structural fragments in humic acids: 34% for 40 years old, 28% for 80 years old, and 31% for 120 years old. This is due to changes in the precursors of humification and the further transformation of plant residues in the soil. Re-involved fallow land soils lead to an increase in the content of aromatic structural fragments in the composition of HA in relation to HA extracted from mature soils. The lowest content of aromatic structural fragments was observed in the humic acids of 130-year-old agricultural soil, which is associated with the long-term application of organic fertilizers. Full article

(This article belongs to the Special Issue Humic Substances: Chemistry and Multidimensional Role in Agricultural Systems and Pollution Management)

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Review

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23 pages, 3853 KiB

Open AccessReview

The Use of Spectroscopic Methods to Study Organic Matter in Virgin and Arable Soils: A Scoping Review

by Evgeny Lodygin and Evgeny Abakumov

Agronomy 2024, 14(5), 1003; https://doi.org/10.3390/agronomy14051003 - 9 May 2024

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Abstract

The use of modern spectroscopic methods of analysis, which provide extensive information on the chemical nature of substances, significantly expands our understanding of the molecular composition and properties of soil organic matter (SOM) and its transformation and stabilization processes in various ecosystems and geochemical conditions. The aim of this review is to identify and analyze studies related to the application of nuclear magnetic resonance (NMR) and electron paramagnetic resonance (EPR) spectroscopy techniques to study the molecular composition and transformation of organic matter in virgin and arable soils. This article is mainly based on three research questions: (1) Which NMR spectroscopy techniques are used to study SOM, and what are their disadvantages and advantages? (2) How is the NMR spectroscopy technique used to study the molecular structure of different pools of SOM? (3) How is ESR spectroscopy used in SOM chemistry, and what are its advantages and limitations? Relevant studies published between 1996 and 2024 were searched in four databases: eLIBRARY, MDPI, ScienceDirect and Springer. We excluded non-English-language articles, review articles, non-peer-reviewed articles and other non-article publications, as well as publications that were not available according to the search protocols. Exclusion criteria for articles were studies that used NMR and EPR techniques to study non-SOM and where these techniques were not the primary methods. Our scoping review found that both solid-state and solution-state NMR spectroscopy are commonly used to study the structure of soil organic matter (SOM). Solution-phase NMR is particularly useful for studying soluble SOM components of a low molecular weight, whereas solid-phase NMR offers advantages such as higher ¹³C atom concentration for stronger signals and faster analysis time. However, solution-phase NMR has limitations including sample insolubility, potential signal aggregation and reduced sensitivity and resolution. Solid-state NMR is better at detecting non-protonated carbon atoms and identifying heterogeneous regions within structures. EPR spectroscopy, on the other hand, offers significant advantages in experimental biochemistry due to its high sensitivity and ability to provide detailed information about substances containing free radicals (FRs), aiding in the assessment of their reactivity and transformations. Understanding the FR structure in biopolymers can help to study the formation and transformation of SOM. The integration of two- and three-dimensional NMR spectroscopy with other analytical methods, such as chromatography, mass spectrometry, etc., provides a more comprehensive approach to deciphering the complex composition of SOM than one-dimensional techniques alone. Full article

(This article belongs to the Special Issue Humic Substances: Chemistry and Multidimensional Role in Agricultural Systems and Pollution Management)

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