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Agronomy
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Humic Substances: Chemistry and Multidimensional Role in Agricultural Systems and...
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Humic Substances: Chemistry and Multidimensional Role in Agricultural Systems and Pollution Management

A special issue of Agronomy (ISSN 2073-4395). This special issue belongs to the section "Soil and Plant Nutrition".

Deadline for manuscript submissions: 31 January 2025 | Viewed by 6155

Special Issue Editor

Dr. Maria Roulia

E-Mail Website
Guest Editor
Department of Chemistry, Inorganic Chemistry Laboratory, National and Kapodistrian University of Athens, Panepistimiopolis, 157 71 Athens, Greece
Interests: humic substances; aluminosilicate materials; fertilizers; adsorption; soil quality; clays and clay minerals; waste management; perlites
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

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

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

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

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Published Papers (5 papers)

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Research

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20 pages, 2640 KiB  
Article
Humic Substances from Waste-Based Fertilizers for Improved Soil Fertility
by Angela Maffia, Federica Marra, Francesco Canino, Santo Battaglia, Carmelo Mallamaci, Mariateresa Oliva and Adele Muscolo
Agronomy 2024, 14(11), 2657; https://doi.org/10.3390/agronomy14112657 - 11 Nov 2024
Viewed by 616
Abstract
This research explores how different organic waste transformation methods influence the production of humic substances (HSs) and their impact on soil quality. Using olive and orange wastes as substrates, the study compares vermicomposting, composting, and anaerobic digestion processes to determine which method produces [...] Read more.
This research explores how different organic waste transformation methods influence the production of humic substances (HSs) and their impact on soil quality. Using olive and orange wastes as substrates, the study compares vermicomposting, composting, and anaerobic digestion processes to determine which method produces the most humic-substance-rich products. The characterization of HSs in each product included analyses of total organic carbon (TOC), humic and fulvic acid content, humification rate, humification degree, and E4/E6 ratio, with HSs extracted using potassium hydroxide (KOH) and analyzed via Diffuse Reflectance Infrared Fourier-Transform (DRIFT) spectroscopy to assess structural complexity. The results revealed that the chemical composition of the input materials significantly influenced the transformation dynamics, with orange by-products exhibiting a higher humification rate and degree. Vermicomposting emerged as the most efficient process, producing fertilizers with superior humic content, greater microbial biodiversity, and enhanced cation exchange capacity, thus markedly improving soil quality. Composting also contributed to the stabilization of organic matter, albeit less effectively than vermicomposting. Anaerobic digestion, by contrast, resulted in products with lower levels of HSs and reduced nutrient content. Aerobic processes, particularly vermicomposting, demonstrated the most rapid and effective transformation, producing structurally complex, stable humus-like substances with pronounced benefits for soil health. These findings underscore vermicomposting as the most sustainable and efficacious approach for generating HS-rich organic fertilizers, presenting a powerful alternative to synthetic fertilizers. Furthermore, this study highlights the potential of organic waste valorization to mitigate environmental pollution and foster circular economy practices in sustainable agriculture. 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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18 pages, 2764 KiB  
Article
Effect of Vermicompost Application on the Soil Microbial Community Structure and Fruit Quality in Melon (Cucumis melo)
by Mei Tian, Rong Yu, Song Guo, Wanbang Yang, Shengfeng Liu, Huiying Du, Jinjin Liang and Xingxu Zhang
Agronomy 2024, 14(11), 2536; https://doi.org/10.3390/agronomy14112536 - 28 Oct 2024
Viewed by 797
Abstract
Melon (Cucumas melon) is widely cultivated and popular because of its quality value and unique flavor. However, the continuous cropping of melons in greenhouses has various negative effects on the soil environment, melon growth, and quality. Recently, farmers have utilized organic [...] Read more.
Melon (Cucumas melon) is widely cultivated and popular because of its quality value and unique flavor. However, the continuous cropping of melons in greenhouses has various negative effects on the soil environment, melon growth, and quality. Recently, farmers have utilized organic fertilization, especially vermicompost, for melons to resist the harmful effects of continuous cropping. A field experiment was conducted to explore the effects of vermicompost on soil microbes and melon fruit quality via high throughput sequencing and chemical sequencing methods. The results showed that the application of vermicompost decreased (p < 0.05) soil pH and increased organic matter, available phosphorus, biomass, urease, catalase, peroxidase, and alkaline phosphatase. A total of 3447 bacterial and 718 fungal operational taxonomic units were identified in all soil samples. Application of vermicompost decreased (p < 0.05) the relative abundances of Acidobacteriota, Gemmatimonadota, Actinobacteriota, and unclassified and increased the relative abundance of Planctomycetota. Compared with the control soil, vermicompost application resulted in significantly higher bacterial Chao indices and a significantly lower Chao index under vermicompost of 60 t ha−1 based on farmers’ normal fertilizer and significantly lower diversity under vermicompost of 90 t ha−1. Otherwise, vermicompost application increased the photosynthetic rate and chlorophyll content of melon leaves and increased the total sugar, soluble solids, vitamin C, soluble protein, and organic acid contents of melon. The results of redundancy analysis indicated that Proteobacteria exhibited a positive correlation with soil ammonium nitrogen (AN) and pH, while showing a negative association with soil available phosphorus and organic matter. Spearman’s correlation analysis revealed that both total sugar content and central soluble solid content in melon had a significant positive correlation (p < 0.05) with Patescibacteria. This study demonstrates that the application of vermicompost alters the microbial community structure in melon cultivation, enhancing fruit quality; this not only promotes a healthier soil ecosystem but also contributes to sustainable and productive practices in melon farming. 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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20 pages, 1350 KiB  
Article
The Role of Organic Matter in Phosphorus Retention in Eutrophic and Dystrophic Terrestrial Ecosystems
by Magdalena Debicka
Agronomy 2024, 14(8), 1688; https://doi.org/10.3390/agronomy14081688 - 31 Jul 2024
Viewed by 779
Abstract
Phosphorus (P) retention in soils in the presence of organic matter (OM) has been, for years, a topic with no clear conclusions. Considering the important ecological functions of peatlands, the objective of this study is to examine the role of OM transformation in [...] Read more.
Phosphorus (P) retention in soils in the presence of organic matter (OM) has been, for years, a topic with no clear conclusions. Considering the important ecological functions of peatlands, the objective of this study is to examine the role of OM transformation in relation to P status in Histosols in the Oder Valley (Poland). Basic physical and chemical properties and the following P forms were determined in the organic horizons of 5 soil profiles from two habitats (eutrophic and dystrophic): total (Pt) and organic P (Po), available P (PM3), easily soluble P (PCaCl2), water-soluble P (PW), and fraction of Po in humic (Po_HA) and fulvic (Po_FA) acids after extraction with 0.5 mol L−1 NaOH. The results were statistically verified in both examined habitat groups separately. The higher values of mobile P forms were found in the upper organic horizons released from OM constituents as a result of their decomposition. The role of OM in P retention was strongly related to the activity of humic substances (HS): a higher Po percentage (6.9–99.4% of Po) was observed in dystrophic, whereas a lower (9.3–28.6% of Po) was observed in eutrophic Histosols. Humic acids played a dominant role in P retention compared to fulvic acids in most peat horizons, especially at pH < 5. The role of HA and FA in P retention was clearly dependent on forms found only in eutrophic Histosols. The important role of FA in P retention during OM transformation was confirmed by negative correlations between Po_FA and macronutrient ratios in both soil groups. The results confirm the variable role of OM in P retention, depending on soil environmental conditions and OM type (peat and moorsh). This may have important applications not only in areas of natural importance, for which the release of mobile P forms may be a threat, but also in agricultural areas where, for a change, we struggle to increase P availability. 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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16 pages, 4248 KiB  
Article
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
Viewed by 778
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 [...] Read more.
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  
Review
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
Cited by 2 | Viewed by 1501
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 [...] Read more.
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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