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

Deadline for manuscript submissions: closed (30 April 2021) | Viewed by 38334

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Dr. Maria Roulia

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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
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Special Issue Information

Dear colleagues,

Humic substances (HS) are macromolecular organic materials ubiquitous in both aquatic and terrestrial systems. They are produced from plant material decay and contain highly varying combinations of organic molecules constituting a large reservoir of organic C and N recalcitrant to microbial action.

HS are effective electron shuttling compounds, providing macro- and microelements in organochelate forms and can thus play an important role in determining the mobility and bioavailability of organic/inorganic nutrients and mineral fertilizers. They enhance soil biological life by boosting highly concentrated populations of soil microorganisms. Additionally, HS have long been recognized for their positive effects on plant physiology, root architecture, and soil structure, enabling moisture retention and aeration, and seem to regulate mechanisms involved in plant growth stimulation.

This Special Issue will focus on "Humic Substances: A Novel Ecofriendly Fertilizer". We welcome novel research, reviews, and opinion pieces covering all related topics, including:

Physicochemical properties of HS, derived from different origins, which influence their operational activity;
Interactions/complexation/chelation of HS with chemical compounds affecting HS functionality;
Impact of HS on the environment and living organisms;
Ecofriendly waste management processes, i.e., retention, adsorption, composting, connected to HS fate;
Innovative technologies, concepts, and approaches for application and testing of HS-contained materials in soils and plants.

Dr. Maria Roulia
Guest Editor

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Keywords

humic substances
fertilizers
soil quality
organic/inorganic nutrients
plant growth
waste management
environment

Published Papers (13 papers)

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Editorial

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3 pages, 188 KiB

Open AccessEditorial

Humic Substances: A Novel Eco-Friendly Fertilizer

by Maria Roulia

Agronomy 2022, 12(4), 754; https://doi.org/10.3390/agronomy12040754 - 22 Mar 2022

Cited by 6 | Viewed by 1713

Abstract

Humic substances (HS) are macromolecular organic materials ubiquitous in both aquatic and terrestrial systems, effective electron shuttling compounds providing macro- and microelements in organochelate form, and play an important role in determining the mobility and bioavailability of organic/inorganic nutrients and mineral fertilizers [...] [...] Read more.

(This article belongs to the Special Issue Humic Substances: A Novel Eco-Friendly Fertilizer)

Research

Jump to: Editorial, Review

14 pages, 2784 KiB

Open AccessArticle

Water Purification by Potassium Humate–C.I. Basic Blue 3 Adsorption-Based Interactions

by Maria Roulia and Alexandros A. Vassiliadis

Agronomy 2021, 11(8), 1625; https://doi.org/10.3390/agronomy11081625 - 16 Aug 2021

Cited by 6 | Viewed by 1781

Abstract

Interactions of C.I. Basic Blue 3 with potassium humate in aqueous systems were investigated. Both the humic content and dye removal are of crucial significance in relation to water of a desired quality. Dye retention experiments demonstrated that potassium humate is an exceptionally efficient adsorbent. The effect of both the pH and temperature on the adsorption process was investigated. The temperature proved to only slightly influence the extent of dye sorption; contrarily, under mildly acidic conditions (pH = 4.0), the quantity of dye adsorbed was doubled on standing. At this pH value, interactions between the positively charged dye and the dissociated carboxyl groups of humic substances are encountered. This was also supported by the obedience of the experimental data to the pseudo-second-order kinetic model. Three adsorption models, i.e., Langmuir, Freundlich and BET, were fitted to the experimental data; the equilibrium adsorption conformed to the Langmuir and BET isotherm equations on the basis of electrostatic dye–humics interactions, while the fitting of the Freundlich model referred to the heterogeneities of humic substances attributed to their colloidal behavior. Thermodynamic quantities, i.e., enthalpy, entropy and free energy change in the adsorption, were calculated. The low

Δ H_{a d s}^{θ}

values verify the negligible effect of the temperature on the adsorption;

Δ S_{a d s}^{θ}

denotes a thermodynamically favorable reaction, and

Δ G_{a d s}^{θ}

denotes a spontaneous process. Full article

(This article belongs to the Special Issue Humic Substances: A Novel Eco-Friendly Fertilizer)

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14 pages, 2597 KiB

Open AccessArticle

Comparative Study of Biostimulant Properties of Industrially and Experimentally Produced Humic Substances

by Maris Klavins, Santa Grandovska, Vaira Obuka and Gederts Ievinsh

Agronomy 2021, 11(6), 1250; https://doi.org/10.3390/agronomy11061250 - 20 Jun 2021

Cited by 6 | Viewed by 1962

Abstract

Demand for new biological technologies in agriculture is ever growing, particularly with respect to the need of restoring the soil organic matter and soil fertility. Products of natural origin are developed to stimulate plant growth and productivity. Humic substances (HS) are the decay products of living matter, with high molecular weight and complex structure. Nowadays, HS are industrially produced from various materials like peat, lignin, soil and compost. The objective of this study is to make a comparison of the impact of HS of different origin on plant development. In total, eight different HS were used; four were extracted from various materials and four were commercially available products. To evaluate the stimulating effect, three different species of plants were used (Triticum aestivum, Sinapis alba, Lepidum sativum). The tests were carried out on Phytotestkit plates, germinating the seeds in different solutions of HS in various concentrations in dark, with or without added nutrient solution. Then, the growth parameters were measured. All tested products showed increase in at least some concentrations compared with the control sample. Significant differences in the stimulating effect of HS depending on their origin were found. Full article

(This article belongs to the Special Issue Humic Substances: A Novel Eco-Friendly Fertilizer)

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19 pages, 2081 KiB

Open AccessArticle

One Step Bioremediation of Olive-Oil-Mill Waste by Organoinorganic Catalyst for Humics-Rich Soil Conditioner Production

by Maria Roulia, Evangelia Kontezaki, Nikolaos Kalogeropoulos and Konstantinos Chassapis

Agronomy 2021, 11(6), 1114; https://doi.org/10.3390/agronomy11061114 - 30 May 2021

Cited by 12 | Viewed by 2197

Abstract

A new, simple, and rapid one-step integrated method for the biotechnology treatment of raw olive oil mill waste (OMW) is discussed. The innovations introduced involve primarily the application of microaerobic composting processes for OMW bioremediation plus the addition of both a zeolite and a tailor-made biocatalyst extremely rich in soil microorganisms. The latter operates at a wide pH range and provides, apart from soil microorganisms, nutrients to the compost, enhancement to the bio-oxidative phase and acceleration of biochemical reactions during bioremediation. The basic parameters affecting the bioprocess, i.e., electrical conductivity, pH, C/N ratio, specific weight, ash, organic matter, total organic carbon, total Kjeldahl nitrogen, microorganisms, humic substances, and total polyphenols, were monitored systematically to provide insight into the process and evaluate the product obtained. After a biotreatment of just 60 d, a significant reduction in polyphenols (91.4%) and an increased humic substances content (8%)—both serving as maturation indices—were observed. The OMW compost received is stable, free of toxic compounds and pathogens, affords a richness in cenose and a high humic substances content, both vital for soil fertility. Applications of the OMW product received, both in laboratory-scale and field cultivations, confirm its suitability as a first-class soil conditioner for organic farming. Full article

(This article belongs to the Special Issue Humic Substances: A Novel Eco-Friendly Fertilizer)

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17 pages, 1450 KiB

Open AccessEditor’s ChoiceArticle

Characterization of Soil Organic Matter Individual Fractions (Fulvic Acids, Humic Acids, and Humins) by Spectroscopic and Electrochemical Techniques in Agricultural Soils

by Aleksandra Ukalska-Jaruga, Romualda Bejger, Guillaume Debaene and Bożena Smreczak

Agronomy 2021, 11(6), 1067; https://doi.org/10.3390/agronomy11061067 - 26 May 2021

Cited by 27 | Viewed by 3873

Abstract

The objective of this paper was to investigate the molecular characterization of soil organic matter fractions (humic substances (HS): fulvic acids-FAs, humic acids-HAs, and humins-HNs), which are the most reactive soil components. A wide spectrum of spectroscopic (UV–VIS and VIS–nearIR), as well as electrochemical (zeta potential, particle size diameter, and polydispersity index), methods were applied to find the relevant differences in the behavior, formation, composition, and sorption properties of HS fractions derived from various soils. Soil material (n = 30) used for the study were sampled from the surface layer (0–30 cm) of agricultural soils. FAs and HAs were isolated by sequential extraction in alkaline and acidic solutions, according to the International Humic Substances Society method, while HNs was determined in the soil residue (after FAs and HAs extraction) by mineral fraction digestion using a 0.1M HCL/0.3M HF mixture and DMSO. Our study showed that significant differences in the molecular structures of FAs, Has, and HNs occurred. Optical analysis confirmed the lower molecular weight of FAs with high amount of lignin-like compounds and the higher weighted aliphatic–aromatic structure of HAs. The HNs were characterized by a very pronounced and strong condensed structure associated with the highest molecular weight. HAs and HNs molecules exhibited an abundance of acidic, phenolic, and amine functional groups at the aromatic ring and aliphatic chains, while FAs mainly showed the presence of methyl, methylene, ethenyl, and carboxyl reactive groups. HS was characterized by high polydispersity related with their structure. FAs were characterized by ellipsoidal shape as being associated to the long aliphatic chains, while HAs and HNs revealed a smaller particle diameter and a more spherical shape caused by the higher intermolecular forcing between the particles. The observed trends directly indicate that individual HS fractions differ in behavior, formation, composition, and sorption properties, which reflects their binding potential to other molecules depending on soil properties resulting from their type. The determined properties of individual HS fractions are presented as averaged characteristics over the examined soils with different physico-chemical properties. Full article

(This article belongs to the Special Issue Humic Substances: A Novel Eco-Friendly Fertilizer)

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15 pages, 2490 KiB

Open AccessArticle

Use of the pK Spectroscopy Method in the Study of Protolytic Properties of Humic Substances and Other Soil Polyelectrolytes

by Evgeny Lodygin and Elena Shamrikova

Agronomy 2021, 11(6), 1051; https://doi.org/10.3390/agronomy11061051 - 24 May 2021

Cited by 6 | Viewed by 1595

Abstract

A common technique for the potentiometric analysis of complex protolytic systems is mathematical data processing. This approach allows for transforming the experimental titration curve into a function of the ionogenic group distribution of the titrated object by the values of the pK (−lgKa) acid dissociation. This distribution function is called the pK spectrum, and the approach itself is called pK spectroscopy. In this case, solutions are found not in the form of discrete dissociation constants but as a distribution function of the concentrations of ionogenic groups over a continuous spectrum of dissociation constants. The purpose of this work is to test the possibility of using the pK spectroscopy method for assessing the acid–base properties of humic substances, water-soluble fraction, and soils. The results of testing the pK spectroscopy method showed that this method is expressive and more informative than the traditional method of continuous potentiometric titration. The use of the pK spectroscopy method for studying the protolytic properties of humic substances and other environmental objects is justified. The content and values of pK of ionogenic groups of fulvic acids, water-soluble fraction, and soil suspensions were determined. In the objects, the presence of three to five ionogenic groups with pK values from 3.2 to 9.6 was revealed. Full article

(This article belongs to the Special Issue Humic Substances: A Novel Eco-Friendly Fertilizer)

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17 pages, 1145 KiB

Open AccessArticle

Organo-Mineral Interactions Involved in Herbicide Sorption on Soil Amended with Peats of Different Maturity Degree

by José Dorado and Gonzalo Almendros

Agronomy 2021, 11(5), 869; https://doi.org/10.3390/agronomy11050869 - 28 Apr 2021

Cited by 12 | Viewed by 1890

Abstract

The sorption of three herbicides (alachlor, atrazine and linuron) on samples from six peats of progressive degree of maturity (fibric, hemic or sapric types) and soil samples (dryland agricultural Calcic Luvisol amended with the peats) was determined. The extent of the sorption was examined in terms of peat maturity (up to 220 analytical descriptors of the peat material). In most cases, a sorption enhancement effect was observed in the peat–soil system compared with the sum of the sorption in peat and soil alone, i.e., a positive interaction leading to an increase in soil matrix reactive sites. The analytical characteristics of humic and bitumen peat subfractions were useful in forecasting sorption performance. This was the case for high molecular weight hydrophobic fractions, the extent of the alkyl domain in humic substances and oxygen-containing groups. Correspondence analysis illustrated how different characteristics of the peats played a distinct role in sorption in the herbicide–peat system or in the soil–peat–herbicide system. In the former system, there was a relevant bearing of parameters indicating low peat maturity, whereas in the second the sorption was mainly explained by peat colloidal properties, including the concentration and base saturation of oxygen-containing functional groups. Full article

(This article belongs to the Special Issue Humic Substances: A Novel Eco-Friendly Fertilizer)

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21 pages, 3099 KiB

Open AccessEditor’s ChoiceArticle

The Soil Organic Matter in Connection with Soil Properties and Soil Inputs

by Václav Voltr, Ladislav Menšík, Lukáš Hlisnikovský, Martin Hruška, Eduard Pokorný and Lubica Pospíšilová

Agronomy 2021, 11(4), 779; https://doi.org/10.3390/agronomy11040779 - 15 Apr 2021

Cited by 62 | Viewed by 6302

Abstract

The content of organic matter in the soil, its labile (hot water extractable carbon–HWEC) and stable (soil organic carbon–SOC) form is a fundamental factor affecting soil productivity and health. The current research in soil organic matter (SOM) is focused on individual fragmented approaches and comprehensive evaluation of HWEC and SOC changes. The present state of the soil together with soil’s management practices are usually monitoring today but there has not been any common model for both that has been published. Our approach should help to assess the changes in HWEC and SOC content depending on the physico-chemical properties and soil´s management practices (e.g., digestate application, livestock and mineral fertilisers, post-harvest residues, etc.). The one- and multidimensional linear regressions were used. Data were obtained from the various soil´s climatic conditions (68 localities) of the Czech Republic. The Czech farms in operating conditions were observed during the period 2008–2018. The obtained results of ll monitored experimental sites showed increasing in the SOC content, while the HWEC content has decreased. Furthermore, a decline in pH and soil´s saturation was documented by regression modelling. Mainly digestate application was responsible for this negative consequence across all soils in studied climatic regions. The multivariate linear regression models (MLR) also showed that HWEC content is significantly affected by natural soil fertility (soil type), phosphorus content (−30%), digestate application (+29%), saturation of the soil sorption complex (SEBCT, 21%) and the dose of total nitrogen (N) applied into the soil (−20%). Here we report that the labile forms (HWEC) are affected by the application of digestate (15%), the soil saturation (37%), the application of mineral potassium (−7%), soil pH (−14%) and the overall condition of the soil (−27%). The stable components (SOM) are affected by the content of HWEC (17%), soil texture 0.01–0.001mm (10%), and input of organic matter and nutrients from animal production (10%). Results also showed that the mineral fertilization has a negative effect (−14%), together with the soil depth (−11%), and the soil texture 0.25–2 mm (−21%) on SOM. Using modern statistical procedures (MRLs) it was confirmed that SOM plays an important role in maintaining resp. improving soil physical, biochemical and biological properties, which is particularly important to ensure the productivity of agroecosystems (soil quality and health) and to future food security. Full article

(This article belongs to the Special Issue Humic Substances: A Novel Eco-Friendly Fertilizer)

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19 pages, 2290 KiB

Open AccessArticle

Polarity-Based Sequential Extraction as a Simple Tool to Reveal the Structural Complexity of Humic Acids

by Vojtěch Enev, Petr Sedláček, Leona Kubíková, Šárka Sovová, Leoš Doskočil, Martina Klučáková and Miloslav Pekař

Agronomy 2021, 11(3), 587; https://doi.org/10.3390/agronomy11030587 - 19 Mar 2021

Cited by 8 | Viewed by 3480

Abstract

A sequential chemical extraction with a defined series of eluotropic organic solvents with an increasing polarity (trichloromethane < ethyl acetate < acetone < acetonitrile < n-propanol < methanol) was performed on peat-bog humic acid. Six organic fractions were obtained and subjected to a physicochemical characterization utilizing methods of structural and compositional analysis. Advanced spectroscopic techniques such as Attenuated Total Reflectance (ATR-FTIR), total luminescence, and liquid-state ¹³C NMR spectrometry were combined with elemental analysis of the organic fractions. In total, the procedure extracted about 57% (wt.) of the initial material; the individual fractions amounted from 1.1% to 19.7%. As expected, the apolar solvents preferentially released lipid-like components, while polar solvents provided organic fractions rich in oxygen-containing polar groups with structural parameters closer to the original humic material. The fraction extracted with acetonitrile shows distinct structural features with its lower aromaticity and high content of protein-like structural motifs. The last two—alcohol extracted—fractions show the higher content of carbohydrate residues and their specific (V-type) fluorescence suggests the presence of plant pigment residues. The extraction procedure is suggested for further studies as a simple but effective way to decrease the structural complexity of a humic material enabling its detail and more conclusive compositional characterization. Full article

(This article belongs to the Special Issue Humic Substances: A Novel Eco-Friendly Fertilizer)

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19 pages, 5010 KiB

Open AccessArticle

Modified Humic Substances as Soil Conditioners: Laboratory and Field Trials

by Natalia A. Kulikova, Alexander B. Volikov, Olga I. Filippova, Vladimir A. Kholodov, Nadezhda V. Yaroslavtseva, Yulian R. Farkhodov, Anna V. Yudina, Vitaly A. Roznyatovsky, Yuri K. Grishin, Oral T. Zhilkibayev and Irina V. Perminova

Agronomy 2021, 11(1), 150; https://doi.org/10.3390/agronomy11010150 - 14 Jan 2021

Cited by 9 | Viewed by 2931

Abstract

The paper is devoted to the development and performance testing of a soil conditioner based on leonardite humic substances (LHS) modified with 3-aminopropyltriethoxysilane (APTES). The modified HS were obtained by adding APTES to LHS solution at different mass ratios of LHS and APTES, followed by the investigation of siloxane structures using ³¹Si NMR spectroscopy. The Urbic Technosol was used as a model soil. The size and amount of water-stable soil aggregates were estimated using wet sieving and laser diffraction, respectively. Toxicity was evaluated by monitoring microbial substrate-induced respiration (SIR) and seedling bioassay. Laboratory column experiments demonstrated an increase in water-stability of the 3–5 mm soil aggregates after LHS-APTES application. Field tests showed an increase in the average weighted diameter of micro aggregates (from 59 to 73 μm) and water-stable macroaggregates (from 1.6 to 2.9 mm) due to the LHS-APTES amendment. A substantial increase in SIR from 5 to 9 mg CO₂ (kg h)⁻¹ was detected. Better survival of seedlings was observed. The obtained beneficial results indicate that APTES-modified HS can be successfully used as a soil conditioner. The formation of extended siloxane networks was suggested as the main mechanism of the observed improvement in the structure of the amended soils. Full article

(This article belongs to the Special Issue Humic Substances: A Novel Eco-Friendly Fertilizer)

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15 pages, 2062 KiB

Open AccessArticle

Foliar Application of Humic-Stabilized Nanoferrihydrite Resulted in an Increase in the Content of Iron in Wheat Leaves

by Mariya M. Zimbovskaya, Alexander Yu. Polyakov, Dmitry S. Volkov, Natalia A. Kulikova, Vasily A. Lebedev, Denis A. Pankratov, Andrey I. Konstantinov, Aksana M. Parfenova, Oral T. Zhilkibaev and Irina V. Perminova

Agronomy 2020, 10(12), 1891; https://doi.org/10.3390/agronomy10121891 - 29 Nov 2020

Cited by 14 | Viewed by 3173

Abstract

The objective of this study was to synthesize iron (hydr)oxide nanoparticles (IONPs) stabilized by humic substances, and to estimate the feasibility of their use for foliar application on iron deficient plants. The IONPs were synthesized by rapid hydrolysis of iron(III) nitrate in a solution of potassium humate. The iron speciation and nanoparticle morphologies were characterized using X-ray diffraction, transmission electron microscopy, and Mössbauer spectroscopy. The obtained sample of IONPs was applied at concentrations of 1- and 10-mM Fe, and 0.2% urea was used as an adjuvant. Wheat plants (Triticum aestivum L. cv. L15) were used for the iron uptake test. For both of the concentrations tested, spraying the nanoparticles resulted in a 70–75% higher iron content in wheat leaves compared to ferric ammonium salt of ethylenediaminetetraacetic acid (Fe-EDTA). The synergistic effect of humic substances acting as a surfactant seemed to promote an increase in the iron uptake of the ferrihydrite nanoparticles compared to the aqueous Fe-EDTA solution used in this study. We concluded that humic-stabilized IONPs are much better suited to foliar application as compared to soil amendment when applied as a source of iron for plants. This is because humic substances act as a capping agent for nanoparticles and the surfactants enhance iron penetration into the leaf. Full article

(This article belongs to the Special Issue Humic Substances: A Novel Eco-Friendly Fertilizer)

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14 pages, 1212 KiB

Open AccessArticle

Effectiveness of Humic Substances and Phenolic Compounds in Regulating Plant-Biological Functionality

by Adele Muscolo, Diego Pizzeghello, Ornella Francioso, Santiago Sanchez Cortes and Serenella Nardi

Agronomy 2020, 10(10), 1553; https://doi.org/10.3390/agronomy10101553 - 12 Oct 2020

Cited by 13 | Viewed by 2875

Abstract

Significant benefit of soil organic matter (SOM) to crop productivity is scientifically well documented. The main constituents and active fractions of SOM are humic substances (HS) and phenolic compounds. Since both these two components strongly impact plant–soil relationship, it is importantly from an ecological point of view to discriminate their biological effects and relating them to their composition. In this study we compared the biological effects of HS, and the soil water soluble phenols (SWSP) on growth, antioxidant activities, carbohydrates, proteins, phenols, and vitamins of Pinus laricio callus. Each extract was assessed for the content of low molecular weight organic acids, soluble carbohydrates, fatty acids, and phenolic acids. Moreover, Fourier transform infrared (FT-IR) and surface-enhanced Raman scattering (SERS) spectroscopies were applied to study their molecular structure. The results showed that HS produced better callus growth compared to the control and SWSP. Carbohydrates decreased in presence of HS while proteins, vitamin C and E increased. In contrast, in callus treated with SWSP the amount of glucose and fructose increased as well as all the antioxidant activities. The data evidenced that HS rich in tartaric and fatty acids had beneficial effects on callus growth contrary to soil water-soluble phenols rich in aldehydes, and syringic, ferulic, and benzoic acids. Full article

(This article belongs to the Special Issue Humic Substances: A Novel Eco-Friendly Fertilizer)

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Review

Jump to: Editorial, Research

13 pages, 5451 KiB

Open AccessEditor’s ChoiceReview

Direct and Indirect Detoxification Effects of Humic Substances

by Lydia Bondareva and Nadezhda Kudryasheva

Agronomy 2021, 11(2), 198; https://doi.org/10.3390/agronomy11020198 - 20 Jan 2021

Cited by 20 | Viewed by 2660

Abstract

The review summarizes studies on the detoxification effects of water-soluble humic substances (HS), which are products of the natural transformation of organic substances in soils and bottom sediments that serve as natural detoxifying agents in water solutions. The detoxifying effects of HS on microorganisms are quite complex: HS neutralize free pollutants (indirect bioeffects) and also stimulate the protective response of organisms (direct bioeffects). Prospects and potential problems of bioluminescent bacteria-based assay to monitor toxicity of solutions in the presence of HS are discussed. The main criterion for the bioassay application is versatility and ease of use. The detoxification efficiency of HS in different pollutant solutions was evaluated, and the detoxification mechanisms are discussed. Particular attention was paid to the direct and complex direct + indirect effects of HS. The review focuses on the protective function of HS in solutions of radionuclides and salts of stable metals, with special consideration of the antioxidant properties of HS. Full article

(This article belongs to the Special Issue Humic Substances: A Novel Eco-Friendly Fertilizer)

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