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Special Issue "Natural Organic Matter as Plant Growth Promoter: Research Activities and Technology Applications"

A special issue of Molecules (ISSN 1420-3049). This special issue belongs to the section "Bioorganic Chemistry".

Deadline for manuscript submissions: 20 April 2022.

Special Issue Editor

Prof. Dr. Riccardo Spaccini
E-Mail Website
Guest Editor
Department of Agriculture, NMR Research Centre CERMANU, University of Napoli Federico II, Naples, Italy
Interests: Soil Organic Matter (SOM) dynamics in agro and forestry ecosystems; SOM molecular characterization; SOC cycling and stabilization mechanisms; Biomass recycling; SOM-plant-microbial interaction and structural-bioactivity relationship; Soil remediation technologies
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Organic matter is the keystone soil component of agro and forestry ecosystems. It is well acknowledged that various pools of native organic materials closely affect the physical, chemical and biological soil equilibria. In the current scenario of fast evolving conditions determined by the climate change, the maintenance of soil organic matter is increasingly regarded as basic reference to counteract the economic and environmental side effects related with the decline of soil fertility and to improve the resilience capacity of either soil or cultivated and natural plants. As highlighted by the FAO organization, the organic matter inputs are crucial to soil health, fertility and ecosystem services, including food production – making its preservation and restoration essential for sustainable development.

In respect to plant growth, besides the traditional indirect functionalities exerted by SOM (water retention, nutrient availability, etc.) the research activities in the recent years have clearly outlined the occurrence of direct beneficial effects promoted by natural organic molecules on plant development. It has been claimed that the higher plants have evolved by establishing a cross-talking interaction with the main soil organic fraction represented by so-called humic substances which are currently assimilated to hormone-like substances able to promote the stimulation of biochemical pathways and physiological processes. Different natural organic matter components, with variable origin also beyond the humic molecules, with specific molecular characteristics and conformational properties have hence been tested with positive responses on plant biostimulation. The outputs encompass a large array of bioactivity effects on either overall plant growth such as root elongation/branching and shoot developments as well as on specific metabolic processes: enhanced nutrient use efficiency, improvement of carbon, nitrogen, phosphorous metabolisms and secondary metabolic pathways, induction of plant tolerance to either abiotic and biotic stresses with an effective suppressive potential against plant pathogens. Moreover, bioactive organic molecules have been shown to play an important role as mediating agents in the interaction between plant and beneficial microorganisms (e.g., arbuscular mycorrhizal fungi, plant growth promoting bacteria).

Although this has already become a well-defined research field, there are still scientific gaps or margins left to improve the comprehensive understanding of structural-activity relationships and for a potential "tailoring application" of different organic materials for specific objectives. In fact, this research is considered an important issue for the development of circular economy in the agro-industrial sector. A topical challenge of modern agriculture is to guarantee adequate crop yields and productivity, while concomitantly matching the stringent environmental regulations devised for the preservation of ecosystems. An increasing amount of attention is devoted to sustainable approaches based on the technological use of recycled organic biomasses as plant growth promoting substrates with potential application on agricultural, nutraceutical, and pharmaceutical sectors. Various research activities are conducted on the utilization as biostimulants of residual biomasses and wastes from agricultural and agro-industrial sectors based on either bulk material (compost, vermicompost, digestates, bio- and hydro-chars, biorefinery by-products) or derived molecular components (humic and humic-like molecules, compost teas, etc.). Additionally, innovative technological developments of bioactive products are conceived (e.g., microemulsion, hydrogels) as eco-friendly agro-chemicals to effectively convey on plant tissues both bioactive organic molecules and beneficial microorganisms as standardized methodologies for field utilization.

This Special Issue aims to cover recent progress and trends in the investigation of the molecular mechanisms and the structural-activity relationships underpinning the bioactive properties of NOM as well as to elucidate the advances of the technological applications streamed from the scientific outputs. Submissions are welcome but not limited to the topics listed below. Types of contributions to this Special Issue can be full research articles, short communications, and reviews focusing on the utilization of natural organic materials and derived products as plant growth promoting materials.

Prof. Dr. Riccardo Spaccini
Guest Editor

Manuscript Submission Information

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Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2300 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

  • Natural organic matter
  • Plant growth promoter
  • Biostimulation
  • Molecular characteristics/molecular mechanisms
  • Structural activity relationship
  • Biomasse recycling
  • Eco-compatible agrochemicals

Published Papers (11 papers)

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Research

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Article
Expressed Soybean Leghemoglobin: Effect on Escherichia coli at Oxidative and Nitrosative Stress
Molecules 2021, 26(23), 7207; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules26237207 - 28 Nov 2021
Viewed by 441
Abstract
Leghemoglobin (Lb) is an oxygen-binding plant hemoglobin of legume nodules, which participates in the symbiotic nitrogen fixation process. Another way to obtain Lb is its expression in bacteria, yeasts, or other organisms. This is promising for both obtaining Lb in the necessary quantity [...] Read more.
Leghemoglobin (Lb) is an oxygen-binding plant hemoglobin of legume nodules, which participates in the symbiotic nitrogen fixation process. Another way to obtain Lb is its expression in bacteria, yeasts, or other organisms. This is promising for both obtaining Lb in the necessary quantity and scrutinizing it in model systems, e.g., its interaction with reactive oxygen (ROS) and nitrogen (RNS) species. The main goal of the work was to study how Lb expression affected the ability of Escherichia coli cells to tolerate oxidative and nitrosative stress. The bacterium E. coli with the embedded gene of soybean leghemoglobin a contains this protein in an active oxygenated state. The interaction of the expressed Lb with oxidative and nitrosative stress inducers (nitrosoglutathione, tert-butyl hydroperoxide, and benzylviologen) was studied by enzymatic methods and spectrophotometry. Lb formed NO complexes with heme-nitrosylLb or nonheme iron-dinitrosyl iron complexes (DNICs). The formation of Lb-bound DNICs was also detected by low-temperature electron paramagnetic resonance spectroscopy. Lb displayed peroxidase activity and catalyzed the reduction of organic peroxides. Despite this, E. coli-synthesized Lb were more sensitive to stress inducers. This might be due to the energy demand required by the Lb synthesis, as an alien protein consumes bacterial resources and thereby decreases adaptive potential of E. coli. Full article
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Article
Chemical Transformation of Humic Acid Molecules under the Influence of Mineral, Fungal and Bacterial Fertilization in the Context of the Agricultural Use of Degraded Soils
Molecules 2021, 26(16), 4921; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules26164921 - 13 Aug 2021
Viewed by 624
Abstract
The main goal of this work was to study the structural transformation of humic acids (HAs) under the influence of selected strains of fungi (Aspergillus niger and Paecilomyces lilacinus) and bacteria (Bacillus sp., Paenibacillus polymyxa and Bacillus amyloliquefaciens) with/without [...] Read more.
The main goal of this work was to study the structural transformation of humic acids (HAs) under the influence of selected strains of fungi (Aspergillus niger and Paecilomyces lilacinus) and bacteria (Bacillus sp., Paenibacillus polymyxa and Bacillus amyloliquefaciens) with/without the presence of NPK fertilizers. Two-year experiments were conducted on two different soils and HAs isolated from these soils were examined for structure, humification degree, and quantity using fluorescence and UV-Vis spectroscopy, elemental analysis, and extraction methods. Results showed that the applied additives contributed to the beneficial transformation of HAs, but effects differed for various soils. HAs from silty soil with higher organic carbon content showed simplification of their structure, and decreases in humification, molecular weight, and aromaticity under the influence of fungi and bacteria without NPK, and with NPK alone. With both fungi and NPK, increases in O/H and O/C atomic ratios indicated an increase in the number of O-containing functional groups. HAs from sandy soil did not show as many significant changes as did those from silty soil. Sandy soil exhibited a strong decline in HA content in the second year that was reduced/neutralized by the presence of fungi, bacteria, and NPK. Periodically observed fluorescence at ~300 nm/450 nm reflected formation of low-molecular HAs originating from the activity of microorganisms. Full article
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Article
Humic Acid Improves Zn Fertilization in Oxisols Successively Cultivated with Maize–Brachiaria
Molecules 2021, 26(15), 4588; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules26154588 - 29 Jul 2021
Viewed by 666
Abstract
Zinc (Zn) is an essential micronutrient for plant growth, and Zn deficiency is a global issue, especially in tropical soils. This study aimed to investigate the effects of humic acid (HA) and the Zn addition (Zn sulfate + HA) on the growth of [...] Read more.
Zinc (Zn) is an essential micronutrient for plant growth, and Zn deficiency is a global issue, especially in tropical soils. This study aimed to investigate the effects of humic acid (HA) and the Zn addition (Zn sulfate + HA) on the growth of maize and brachiaria in two contrasting Oxisols. The potential complexation of Zn sulfate by HA was evaluated by Fourier-transform infrared (FTIR) spectroscopy analysis. Zinc content and its availability in solution and the shoot and root biomass of maize and brachiaria were determined. FTIR spectroscopy revealed the complexation of Zn sulfate by HA through its S and C functional groups. In both Oxisols, solution Zn increased due to the combined use of Zn and HA. In a soil type-dependent manner, maize biomass and Zn in its shoots were affected only by the exclusive use of Zn fertilization. In the Yellow Oxisol, brachiaria growth and Zn accumulated in its shoot were positively affected by the combined use of Zn fertilization with HA. In the Oxisol with lower organic matter content, HA can assure adequate supplying of residual Zn, while increasing growth of brachiaria cultivated in sequence to maize. Full article
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Article
Calcium Phosphate Particles Coated with Humic Substances: A Potential Plant Biostimulant from Circular Economy
Molecules 2021, 26(9), 2810; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules26092810 - 10 May 2021
Cited by 4 | Viewed by 860
Abstract
Nowadays, the use of biostimulants to reduce agrochemical input is a major trend in agriculture. In this work, we report on calcium phosphate particles (CaP) recovered from the circular economy, combined with natural humic substances (HSs), to produce a plant biostimulant. CaPs were [...] Read more.
Nowadays, the use of biostimulants to reduce agrochemical input is a major trend in agriculture. In this work, we report on calcium phosphate particles (CaP) recovered from the circular economy, combined with natural humic substances (HSs), to produce a plant biostimulant. CaPs were obtained by the thermal treatment of Salmo salar bones and were subsequently functionalized with HSs by soaking in a HS water solution. The obtained materials were characterized, showing that the functionalization with HS did not sort any effect on the bulk physicochemical properties of CaP, with the exception of the surface charge that was found to get more negative. Finally, the effect of the materials on nutrient uptake and translocation in the early stages of development (up to 20 days) of two model species of interest for horticulture, Valerianella locusta and Diplotaxis tenuifolia, was assessed. Both species exhibited a similar tendency to accumulate Ca and P in hypogeal tissues, but showed different reactions to the treatments in terms of translocation to the leaves. CaP and CaP–HS treatments lead to an increase of P accumulation in the leaves of D. tenuifolia, while the treatment with HS was found to increase only the concentration of Ca in V. locusta leaves. A low biostimulating effect on both plants’ growth was observed, and was mainly scribed to the low concentration of HS in the tested materials. In the end, the obtained material showed promising results in virtue of its potential to elicit phosphorous uptake and foliar translocation by plants. Full article
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Article
Assessment of Aqueous Extraction Methods on Extractable Organic Matter and Hydrophobic/Hydrophilic Fractions of Virgin Forest Soils
Molecules 2021, 26(9), 2480; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules26092480 - 23 Apr 2021
Viewed by 784
Abstract
The assessment of water-extractable organic matter using an autoclave can provide useful information on physical, chemical, and biological changes within the soil. The present study used virgin forest soils from Chini Forest Reserve, Langkawi Island, and Kenyir Forest Reserve (Malaysia), extracted using different [...] Read more.
The assessment of water-extractable organic matter using an autoclave can provide useful information on physical, chemical, and biological changes within the soil. The present study used virgin forest soils from Chini Forest Reserve, Langkawi Island, and Kenyir Forest Reserve (Malaysia), extracted using different extraction methods. The dissolved organic carbon (DOC), total dissolved nitrogen (TDN), total dissolved phosphorus (TDP), and ammonium-nitrate content were higher in the autoclave treatments, up to 3.0, 1.3, 1.2, and 1.4 times more than by natural extraction (extracted for 24 h at room temperature). Overall, the highest extractable DOC, TDN, TDP, ammonium and nitrate could be seen under autoclaved conditions 121 °C 2×, up to 146.74 mg C/L, 8.97 mg N/L, 0.23 mg P/L, 5.43 mg N mg/L and 3.47 N mg/L, respectively. The soil extracts became slightly acidic with a higher temperature and longer duration. Similar trends were observed in the humic and nonhumic substances, where different types of soil extract treatments influenced the concentrations of the fractions. Different soil extraction methods can provide further details, thus widening the application of soil extracts, especially in microbes. Full article
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Article
Insights on Molecular Characteristics of Hydrochars by 13C-NMR and Off-Line TMAH-GC/MS and Assessment of Their Potential Use as Plant Growth Promoters
Molecules 2021, 26(4), 1026; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules26041026 - 15 Feb 2021
Cited by 1 | Viewed by 821
Abstract
Hydrochar is a carbon-based material that can be used as soil amendment. Since the physical-chemical properties of hydrochar are mainly assigned to process parameters, we aimed at evaluating the organic fraction of different hydrochars through 13C-NMR and off-line TMAH-GC/MS. Four hydrochars produced [...] Read more.
Hydrochar is a carbon-based material that can be used as soil amendment. Since the physical-chemical properties of hydrochar are mainly assigned to process parameters, we aimed at evaluating the organic fraction of different hydrochars through 13C-NMR and off-line TMAH-GC/MS. Four hydrochars produced with sugarcane bagasse, vinasse and sulfuric or phosphoric acids were analyzed to elucidate the main molecular features. Germination and initial growth of maize seedlings were assessed using hydrochar water-soluble fraction to evaluate their potential use as growth promoters. The hydrochars prepared with phosphoric acid showed larger amounts of bioavailable lignin-derived structures. Although no differences were shown about the percentage of maize seeds germination, the hydrochar produced with phosphoric acid promoted a better seedling growth. For this sample, the greatest relative percentage of benzene derivatives and phenolic compounds were associated to hormone-like effects, responsible for stimulating shoot and root elongation. The reactions parameters proved to be determinant for the organic composition of hydrochar, exerting a strict influence on molecular features and plant growth response. Full article
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Article
Transcriptome Changes Reveal the Molecular Mechanisms of Humic Acid-Induced Salt Stress Tolerance in Arabidopsis
Molecules 2021, 26(4), 782; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules26040782 - 03 Feb 2021
Cited by 1 | Viewed by 952
Abstract
Humic acid (HA) is a principal component of humic substances, which make up the complex organic matter that broadly exists in soil environments. HA promotes plant development as well as stress tolerance, however the precise molecular mechanism for these is little known. Here [...] Read more.
Humic acid (HA) is a principal component of humic substances, which make up the complex organic matter that broadly exists in soil environments. HA promotes plant development as well as stress tolerance, however the precise molecular mechanism for these is little known. Here we conducted transcriptome analysis to elucidate the molecular mechanisms by which HA enhances salt stress tolerance. Gene Ontology Enrichment Analysis pointed to the involvement of diverse abiotic stress-related genes encoding HEAT-SHOCK PROTEINs and redox proteins, which were up-regulated by HA regardless of salt stress. Genes related to biotic stress and secondary metabolic process were mainly down-regulated by HA. In addition, HA up-regulated genes encoding transcription factors (TFs) involved in plant development as well as abiotic stress tolerance, and down-regulated TF genes involved in secondary metabolic processes. Our transcriptome information provided here provides molecular evidences and improves our understanding of how HA confers tolerance to salinity stress in plants. Full article
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Article
Kinetics Growth and Recovery of Valuable Nutrients from Selangor Peat Swamp and Pristine Forest Soils Using Different Extraction Methods as Potential Microalgae Growth Enhancers
Molecules 2021, 26(3), 653; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules26030653 - 27 Jan 2021
Cited by 3 | Viewed by 815
Abstract
Soil extracts are useful nutrients to enhance the growth of microalgae. Therefore, the present study attempts for the use of virgin soils from Peninsular Malaysia as growth enhancer. Soils collected from Raja Musa Forest Reserve (RMFR) and Ayer Hitam Forest Reserve (AHFR) were [...] Read more.
Soil extracts are useful nutrients to enhance the growth of microalgae. Therefore, the present study attempts for the use of virgin soils from Peninsular Malaysia as growth enhancer. Soils collected from Raja Musa Forest Reserve (RMFR) and Ayer Hitam Forest Reserve (AHFR) were treated using different extraction methods. The total dissolved nitrogen (TDN), total dissolved phosphorus (TDP), and dissolved organic carbon (DOC) concentrations in the autoclave methods were relatively higher than natural extraction with up to 132.0 mg N/L, 10.7 mg P/L, and 2629 mg C/L, respectively for RMFR. The results of TDN, TDP, and DOC suggested that the best extraction methods are autoclaved at 121 °C twice with increasing 87%, 84%, and 95%, respectively. Chlorella vulgaris TRG 4C dominated the growth at 121 °C twice extraction method in the RMRF and AHRF samples, with increasing 54.3% and 14%, respectively. The specific growth rate (µ) of both microalgae were relatively higher, 0.23 d−1 in the Ayer Hitam Soil. This extract served well as a microalgal growth promoter, reducing the cost and the needs for synthetic medium. Mass production of microalgae as aquatic feed will be attempted eventually. The high recovery rate of nutrients has a huge potential to serve as a growth promoter for microalgae. Full article
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Article
The Singular Molecular Conformation of Humic Acids in Solution Influences Their Ability to Enhance Root Hydraulic Conductivity and Plant Growth
Molecules 2021, 26(1), 3; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules26010003 - 22 Dec 2020
Cited by 2 | Viewed by 810
Abstract
Some studies have reported that the capacity of humic substances to improve plant growth is dependent on their ability to increase root hydraulic conductivity. It was proposed that this effect is directly related to the structural conformation in solution of these substances. To [...] Read more.
Some studies have reported that the capacity of humic substances to improve plant growth is dependent on their ability to increase root hydraulic conductivity. It was proposed that this effect is directly related to the structural conformation in solution of these substances. To study this hypothesis, the effects on root hydraulic conductivity and growth of cucumber plants of a sedimentary humic acid and two polymers—polyacrylic acid and polyethylene glycol—presenting a molecular conformation in water solution different from that of the humic acid have been studied. The results show that whereas the humic acid caused an increase in root hydraulic conductivity and plant growth, both the polyacrylic acid and the polyethylene glycol did not modify plant growth and caused a decrease in root hydraulic conductivity. These results can be explained by the different molecular conformation in water solution of the three molecular systems. The relationships between these biological effects and the molecular conformation of the three molecular systems in water solution are discussed. Full article
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Review

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Review
Chemical Structure and Biological Activity of Humic Substances Define Their Role as Plant Growth Promoters
Molecules 2021, 26(8), 2256; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules26082256 - 13 Apr 2021
Cited by 9 | Viewed by 858
Abstract
Humic substances (HS) are dominant components of soil organic matter and are recognized as natural, effective growth promoters to be used in sustainable agriculture. In recent years, many efforts have been made to get insights on the relationship between HS chemical structure and [...] Read more.
Humic substances (HS) are dominant components of soil organic matter and are recognized as natural, effective growth promoters to be used in sustainable agriculture. In recent years, many efforts have been made to get insights on the relationship between HS chemical structure and their biological activity in plants using combinatory approaches. Relevant results highlight the existence of key functional groups in HS that might trigger positive local and systemic physiological responses via a complex network of hormone-like signaling pathways. The biological activity of HS finely relies on their dosage, origin, molecular size, degree of hydrophobicity and aromaticity, and spatial distribution of hydrophilic and hydrophobic domains. The molecular size of HS also impacts their mode of action in plants, as low molecular size HS can enter the root cells and directly elicit intracellular signals, while high molecular size HS bind to external cell receptors to induce molecular responses. Main targets of HS in plants are nutrient transporters, plasma membrane H+-ATPases, hormone routes, genes/enzymes involved in nitrogen assimilation, cell division, and development. This review aims to give a detailed survey of the mechanisms associated to the growth regulatory functions of HS in view of their use in sustainable technologies. Full article
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Other

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Opinion
Which Traits of Humic Substances Are Investigated to Improve Their Agronomical Value?
Molecules 2021, 26(3), 760; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules26030760 - 02 Feb 2021
Cited by 2 | Viewed by 1316
Abstract
Humic substances (HSs) are chromogenic organic assemblies that are widespread in the environment, including soils, oceans, rivers, and coal-related resources. HSs are known to directly and indirectly stimulate plants based on their versatile organic structures. Their beneficial activities have led to the rapid [...] Read more.
Humic substances (HSs) are chromogenic organic assemblies that are widespread in the environment, including soils, oceans, rivers, and coal-related resources. HSs are known to directly and indirectly stimulate plants based on their versatile organic structures. Their beneficial activities have led to the rapid market growth of agronomical HSs. However, there are still several technical issues and concerns to be addressed to advance sustainable agronomical practices for HSs and allow growers to use HSs reliably. First, it is necessary to elucidate the evident structure (component)–function relationship of HSs. Specifically, the core structural features of HSs corresponding to crop species, treatment method (i.e., soil, foliar, or immersion applications), and soil type-dependent plant stimulatory actions as well as specific plant responses (e.g., root genesis and stress resistance) should be detailed to identify practical crop treatment methodologies. These trials must then be accompanied by means to upgrade crop marketability to help the growers. Second, structural differences of HSs depending on extraction sources should be compared to develop quality control and assurance measures for agronomical uses of HSs. In particular, coal-related HSs obtainable in bulk amounts for large farmland applications should be structurally and functionally distinguishable from other natural HSs. The diversity of organic structures and components in coal-based HSs must thus be examined thoroughly to provide practical information to growers. Overall, there is a consensus amongst researchers that HSs have the potential to enhance soil quality and crop productivity, but appropriate research directions should be explored for growers’ needs and farmland applications. Full article
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Planned Papers

The below list represents only planned manuscripts. Some of these manuscripts have not been received by the Editorial Office yet. Papers submitted to MDPI journals are subject to peer-review.

1.Type of the paper: Full article
Tentative title:Calcium phosphate particles coated with humic acid: a potential biostimulant for plant cultivation from circular economy.
Author names: Francesca Carella1, Momy Seck2, Hamet Diadiou2, Anita Maienza3, Silvia Baronti3, Patrizio Vignaroli3 Michele Iafisco1, Alessio Adamiano1

Affiliations:

1 Institute of Science and Technology for Ceramics (ISTEC), National Research Council (CNR), Via Granarolo 64, 48018 Faenza (RA), Italy

2 Department of Agri-Food, Animal and Environmental Sciences, University of Udine, via delle Scienze 206, 33100 Udine, Italy

3 Institute of Nanotechnology (NANOTEC), National Research Council (CNR), Campus Ecoteckne, Via Monteroni, 73100 Lecce, Italy

4 Department of Agricultural Chemistry and Food Science & Technology and IALS, Gyeongsang National University, Jinju 52828, Republic of Korea
Abstract
Maintaining food production for a growing world population without compromising natural resources for future generations represents one of the greatest challenges for agricultural science. The intensification of
agriculture has now reached a critical point whereby the negative impacts derived from this activity are now resulting in irreversible global climate change and loss in many ecosystem services. Moreover, the nutrient use efficiency in intensive agriculture is decreasing year by year, making of intensive cultivation progressively unviable both from the environmental and the economical point of view. New approaches to help promote sustainable intensification are therefore required, such as the use of smart materials developed accordingly to circular economy principles. In this work, we report on calcium phosphate particles extracted from an abundant food by-product, i.e. fish bone, modified with natural humic substances to increase their biostimulating action. The obtained materials were characterized from the chemical-physical point of view, and their ability to boost the germination of seeds and plant growth on the two model species Valerianella locusta and Diplotaxis tenuifolia was assessed.

2. Title: Insights on hydrochars organic matter composition by13C NMR and Off-line TMAH-GC/MS and assessment of their potential use as plant growth promoters 

Authors: Laís G. Fregolentea,b, João Vitor dos Santosa, Giovanni Vincib, Alessandro Piccolob, Altair B. Moreiraa, Odair P. Ferreirac, Márcia C. Bisinotia, Riccardo Spaccinib*

Abstract: Hydrochar is a carbon-based material derived from the by-products of sugarcane industry that can be used as soil amendment. As the physical-chemistry properties of hydrochar are mainly assigned to process parameters, we aimed at evaluating the organic fraction of different hydrochars through 13C NMR and off-line TMAH-Thermochemolysis. Four hydrochars produced with sugarcane bagasse, vinasse and sulfuric or phosphoric acids were evaluated, as well as the humic-like acids extracted from them. Germination and initial growth of maize were assessed using hydrochar water-soluble fraction to evaluate their potential as growth promoters. For hydrochars prepared with sulfuric acid the amount of C-Alkyl/O-Alkyl and aromatic moieties were respectively higher. The hydrochars prepared with phosphoric acid showed greater amounts of lignin-derived structures. For all humic-like acids, the relative percentage of benzene derivatives decreased and the aliphatic esters increased compared to hydrochars. Although no differences were signed to percentage of maize seeds germination, the hydrochar produced with phosphoric acid promoted a better seedling growth. For this sample, the greatest relative percentage of benzene derivatives and phenolic compounds were identified, to which was attributed to a hormone-like effect, responsible for stimulating shoot and root elongation. The reactions parameters proved to be determinant to hydrochar organic composition, exerting great influence on plant growth response.

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