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Use of Humic Substances and Biostimulants for Environmentally Sustainable Agriculture

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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: 30 September 2024 | Viewed by 10701

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Dr. Diego Pizzeghello

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Department of Agronomy, Food, Natural Resources, Animals and Environment (DAFNAE), Padova University, 35020 Legnaro, Padova, Italy
Interests: effect of humic substances on plant growth; biostimulants; soil organic matter; soil phosphorus forms

Special Issue Information

Dear Colleagues,

Humic substances are natural biostimulants with very high biological activity and they have always been considered key elements in soil fertility. They affect many physical, chemical, and biological properties (e.g., structure, water retention, nutrient leaching, redox conditions, nutrient storage, and availability). The current understanding of the molecular and biochemical mechanisms involved in the beneficial effects of humic substances on plant development is partial and fragmented. These mechanisms involve the coordinated actions of signaling pathways that are regulated by major plant regulators such as auxin, ethylene, nitric oxide, gibberellins, and cytokinins, and secondary messengers such as reactive oxygen species and Ca²⁺. The result is an overall increase in the uptake of nutrients and the stimulation of the primary and secondary metabolism, and at the end, growth increments.

Biostimulants are gaining prominence in agricultural systems because of their high potential for improving plant nutrient use efficiency, tolerance to abiotic stress such as drought and salinity, soil remediation, and crop health. In addition to humic substances, bio-stimulants include amino acids, protein hydrolysates, chitosan, algae extracts, mycorrhizal fungi, and the plant growth-promoting rhizobacteria of strains belonging to the genera Azospirillum, Azotobacter, and Rhizobium spp., and silicon. Bio-stimulants typically act at low or very low concentrations and can activate the responses induced by humic substances.

This Special Issue will focus on the “Use of Humic Substances and Biostimulants for Environmentally Sustainable Agriculture”. Original research articles, review articles, communications, letters, and opinions are welcome, providing innovative insights into all related topics of interest that include bio-stimulants action in either small-scale or agronomic field trials. The valorization of agro-wastes to develop a new generation of bio-stimulants will be of great interest, leading to substantial social and economic advantages and environmental preservation—likely in the form of the circular economy. A particular welcome will also be offered to those studies and techniques that might unravel the complex relationships between molecular structure and mode of action.

Dr. Diego Pizzeghello
Guest Editor

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Keywords

humic substances
humic acids
bio-stimulants
agro-wastes
compost
hormone-like
molecular structure
mode of action
plant nutrition and metabolism
plant growth
abiotic and biotic stress
crop health
soil remediation

Published Papers (8 papers)

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Research

20 pages, 5714 KiB

Open AccessArticle

Thymol Deploys Multiple Antioxidative Systems to Suppress ROS Accumulation in Chinese Cabbage Seedlings under Saline Stress

by Changwei Sun, Jian Chen, Lanlan Wang, Jiajun Li, Zhiqi Shi, Lifei Yang and Xiangyang Yu

Agronomy 2024, 14(5), 1059; https://doi.org/10.3390/agronomy14051059 - 16 May 2024

Viewed by 310

Abstract

Developing biostimulants is a promising approach for sustainable agriculture under a saline environment. Thymol is a plant-derived compound with a potential antioxidative capacity. However, little is known about whether and how the antioxidative property of thymol plays a role in inducing plant tolerance against abiotic stresses. Here, we find that thymol induces saline tolerance in Chinese cabbage seedlings via enhancing the antioxidative capacity. Treatment with NaCl (100 mM) decreased the seedling fresh weight by 59.9% as compared to a control. Thymol at 20 μM showed the greatest effect on promoting seedling growth under saline stress, with the seedling fresh weight being increased by 71.0% as compared to NaCl treatment. Thymol remarkably decreased the overaccumulation of ROS (hydrogen peroxide and a superoxide radical); cell membrane damage (evaluated by lipid oxidation, membrane integrity, and relative conductivity); and cell death in seedlings under saline stress. Thymol induced three antioxidative systems to lower the ROS level in salt-treated seedlings. First, thymol remarkably activated a set of antioxidative enzymes, such as SOD (superoxide dismutase), APX (ascorbate peroxidase), CAT (catalase), and POD (peroxidase). Second, thymol balanced the cellular redox status by increasing the ratio of AsA/DHA (ascorbic acid/dehydroascorbic acid) and GSH/GSSG (glutathione/oxidized glutathione). Third, thymol significantly enhanced the level-two kinds of antioxidants (total phenol and flavonoid). All of these physiological responses were observed in both the shoots and the roots. In sum, thymol deploys multiple antioxidative systems to help Chinese cabbage seedlings against saline stress. Such findings suggest that thymol has great potential to be developed as a novel biostimulant enhancing crop tolerance against saline stress. Full article

(This article belongs to the Special Issue Use of Humic Substances and Biostimulants for Environmentally Sustainable Agriculture)

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18 pages, 9350 KiB

Open AccessArticle

Waste-Derived Fertilizer Acts as Biostimulant, Boosting Tomato Quality and Aroma

by Mariateresa Russo, Rosa Di Sanzo, Federica Marra, Sonia Carabetta, Angela Maffia, Carmelo Mallamaci and Adele Muscolo

Agronomy 2023, 13(12), 2854; https://doi.org/10.3390/agronomy13122854 - 21 Nov 2023

Viewed by 977

Abstract

Tomato quality is intricately regulated by a combination of factors, including the presence of bioactive compounds referred to as secondary metabolites and various organoleptic characteristics. These attributes are notably influenced and harmonized by the specific growing conditions, with a particular emphasis on the type of fertilization employed. Traditionally, chemical fertilizers have been favored in crop cultivation due to their cost-effectiveness and ability to accelerate crop growth. However, in pursuit of sustainable and intelligent agricultural practices, there is a growing need for alternative fertilizers. In this context, the present study aimed to assess the impact of fertilizers derived from waste materials, specifically sulfur bentonite and orange residue (referred to as SB), on tomato quality. This assessment extended to examining qualitative and quantitative alterations in aroma-related volatile compounds and the antioxidant systems of tomatoes, in comparison to the conventional use of fertilizers such as horse manure (HM) and nitrogen, phosphorus, and potassium (NPK). The results obtained revealed distinct effects of different fertilizers on tomato quality. Notably, parameters such as TPRO (total protein), TCARB (total carbohydrate), LIC (lycopene content), TCAR (total carotenoid content), total phenols (TPHE), total flavonoids (TFLA), and aroma profiling exhibited significantly superior values in the group treated with sulfur bentonite (SB) fertilizer. These findings strongly suggest that the novel fertilizer functioned as a biostimulant, enhancing the nutraceutical and sensory attributes of tomatoes, with a pronounced impact on the synthesis of secondary metabolites and the aroma profile of the fruits. Full article

(This article belongs to the Special Issue Use of Humic Substances and Biostimulants for Environmentally Sustainable Agriculture)

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17 pages, 2419 KiB

Open AccessArticle

Effect of Metal Cations with Different Valences on the Humus Composition of Dark-Brown Soil Mixed with Tilia Wood Shavings

by Nan Wang, Zhijiang Liu, Chengxin Bai, Ren Li, Min Li, Ying Wang, Wenting Yu, Pingxin Liu, Ruisi Yin and Shuai Wang

Agronomy 2023, 13(11), 2681; https://doi.org/10.3390/agronomy13112681 - 25 Oct 2023

Viewed by 817

Abstract

To clarify the contribution of the bridging effect from three metal cations (K⁺, Mn²⁺, and Fe³⁺) on the humification of lignin-rich Tilia wood shavings and further enrich the theory of lignin humification, an indoor incubation method with constant temperature and humidity was adopted. K⁺, Mn²⁺, and Fe³⁺ served as additives, with CK as the control for studying the differential influence of metal cations with different valences on the humus composition of dark-brown soil mixed with Tilia wood shavings. The change in the C contents of water-soluble substance (C_WSS), humic-extracted acid (C_HE) and humin (C_Hu), ∆logK value of HE, atomic ratio and FTIR spectra of humic acid (HA), and the ratio of C content of humic acid to fulvic acid (C_HA/C_FA) of dark-brown soil mixed with Tilia wood shavings were analyzed after 0, 30, 80, and 150 days of incubation, and the following conclusions were reached: (1) The addition of metal cations, regardless of their valence, could effectively improve the microbial utilization and consumption of WSS, and the effect was as follows: Fe³⁺ > Mn²⁺ > K⁺. The addition of three metal cations could effectively inhibit mineralization and reduce the loss of TOC, and the effect could be seen as follows: Fe³⁺ > Mn²⁺ > K⁺. (2) Although the C_HE content first decreased and then increased with incubation, the addition of Fe³⁺ and Mn²⁺ ions increased the C_HE content, showing that Fe³⁺ > Mn²⁺, and K⁺ ions had no significant effect. Throughout the incubation, the structure of HE molecules changed first via a complex process and then through a simple process. Comparing the change before and after the incubation, the overall structure of HE molecules tended to be simpler with the CK control, and HE became more complicated with the addition of Fe³⁺ and Mn²⁺; however, the addition of K⁺ had little effect on the structure of HE molecules. (3) At the end of the incubation, the addition of Fe³⁺, Mn²⁺, and K⁺ ions strengthened the molecular condensation of HA and its aromatization degree, while the CK control without any added metal cations caused HA molecules to decompose and obtain a greater aliphatic degree. In addition, the number of O-containing functional groups and N-containing compounds in HA molecules increased to varying degrees regardless of which metal cation was added. The decomposition of Tilia wood chips led to a partial entry of the decomposition products into the HA component, which was then reconsumed by continuous mineralization. After incubation, the polysaccharides in HA molecules were consumed only with the addition of Mn²⁺ ions. Fe³⁺ and Mn²⁺ ions had greater advantages in increasing the C_HA/C_FA ratio and improving the humus quality than K⁺ ions. (4) The addition of metal cations could effectively inhibit the mineralization and decomposition of the Hu component, among which Fe³⁺ ions had the most significant effect, followed by Mn²⁺ ions. Compared to monovalent cations (K⁺), polyvalent cations (Fe³⁺ and Mn²⁺) had the advantage of a bridging effect, and their addition promoted the microbial utilization of WSS, effectively reduced the loss of TOC, increased the C_HE content, complicated its molecular structure, improved the humus quality, and inhibited the decomposition of Hu. Regardless of which metal cation was added, the degree of molecular polycondensation and aromatization of HA was enhanced, and the number of O-functional groups and N-containing compounds in HA molecules increased. Full article

(This article belongs to the Special Issue Use of Humic Substances and Biostimulants for Environmentally Sustainable Agriculture)

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12 pages, 1339 KiB

Open AccessArticle

Co-Inoculation with Bradyrhizobium and Humic Substances Combined with Herbaspirillum seropedicae Promotes Soybean Vegetative Growth and Nodulation

by Luciano Pasqualoto Canellas, Rakiely Martins Silva, Lucas José da Silva Barbosa, Fernando Soares Sales, Rafael Chaves Ribeiro, Gabriela Petroceli Mota and Fábio Lopes Olivares

Agronomy 2023, 13(10), 2660; https://doi.org/10.3390/agronomy13102660 - 23 Oct 2023

Cited by 1 | Viewed by 983

Abstract

The effect of humic substances (HSs) in combination with or without plant-growth-promoting bacteria on soybean vegetative growth and root nodulation was examined in this study. Seeds were inoculated with Bradyrhizobium japonicum SEMIA 5079 in the presence of HSs from leonardite and Herbaspirillum seropedicae HRC54. Additional HSs and H. seropedicae application at the substrate surface was conducted at the V3 stage. The experiment was carried out in a greenhouse using pots filled with a top layer of an Oxisol soil, and plants were harvested at the R1 stage. The HS and H. seropedicae treatments significantly promoted plant shoot and root growth. The number and weight of soybean nodules were higher in the treated plants when compared to a control. The plant nodulation process was affected by the treatments that included activities of malate dehydrogenase (MDH), nitrate reductase (NR) and plasma membrane H⁺-ATPase (MHA). At low concentrations, the HSs and H. seropedicae increased the nodule quantity, size and weight, favoring plant growth. Combining humic substances and plant-growth-promoting bacteria (PGPB) could be a promising approach to promoting soybean nodulation and increasing crop production. Full article

(This article belongs to the Special Issue Use of Humic Substances and Biostimulants for Environmentally Sustainable Agriculture)

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16 pages, 2263 KiB

Open AccessArticle

Humic Acid and Selenium Supplementation Modulate the Growth and Antioxidant Potential of Chili under Cadmium Stress

by Muhammad Zohaib, Kamran Ashraf, Komal Fatima, Khawar Sultan, Abdel-Rhman Z. Gaafar, Mohamed S. Hodhod and Qamar uz Zaman

Agronomy 2023, 13(10), 2554; https://doi.org/10.3390/agronomy13102554 - 4 Oct 2023

Viewed by 1068

Abstract

Maximizing food production under adverse conditions is a major challenge to food security and sustainability in the face of population growth and climatic change. The use of amendments applied as a supplement under adverse conditions may play a significant role in the mitigation of biotic and abiotic stress. This study aimed to explore the morpho-physio-biochemical changes in chili in response to cadmium (Cd) stress. The present study investigated the effects of foliar-applied selenium (Na₂SeO₄) (3 µM) and soil-applied humic acid (250 mg kg⁻¹ w/w soil) in the sole and synergistic form under varying levels of cadmium stress (0, 2, and 4 mM using CdCl₂) in chili. Results revealed that a linear decrease was noticed in the growth, biomass, and phenological attributes of chili plants by increasing the Cd stress. More reduction was noticed at the higher levels of Cd stress as compared to control due lowering plant dry weight (18.15 and 39.67%), relative water content (RWC) (10.73 and 24.17%), total chlorophyll concentrations (16.01 and 31.44%) and increased electrolyte leakage (49.44 and 129.35%) and malonaldehyde contents (MDA) (68.41 and 104.04%). Dry biomass significantly increased with humic acid and selenium treatments, regardless of cadmium level. The reduced enzymatic activities associated with reactive oxygen species (ROS) detoxification, underscores the pivotal role of Se and humic acid in maintaining redox homeostasis. The combined effect of selenium and humic acid proved better results as compared to the sole application in minimizing Cd uptake in roots and fruit. This study demonstrates that the application of humic acid and selenium activates physio-biochemical defense responses against cadmium stress in chili plants and provides significant pavement for the cultivation of chili in cadmium-containing soils with a target of high-yielding and quality. Full article

(This article belongs to the Special Issue Use of Humic Substances and Biostimulants for Environmentally Sustainable Agriculture)

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23 pages, 4232 KiB

Open AccessArticle

Chernozem Land Use Differentiation by Temperature-Dependent IR Spectra

by Mikhail A. Proskurnin, Dmitry S. Volkov, Yaroslav V. Timofeev, Dmitry S. Fomin and Olga B. Rogova

Agronomy 2023, 13(8), 1967; https://doi.org/10.3390/agronomy13081967 - 26 Jul 2023

Cited by 1 | Viewed by 1079

Abstract

Granulometric aggregate fractions (20 µm–2 mm) of chernozem soils with different agriculture-use histories (native steppe, permanent bare fallow, arable land, and shelterbelt) were investigated in mid-IR and far IR regions (4000–100 cm⁻¹) by heating in the air from 25 to 215 °C, using ATR FTIR and linear discriminant analysis to differentiate the land-use samples without chemical perturbation. The temperature dependences of the band maxima significantly differed for bands of silicate matrix and bands with the contribution of soil organic matter and were more stable to experimental conditions compared to the absolute positions. The thermal behavior of the integral intensities of the IR bands at 790–750 cm⁻¹ and 440–420 cm⁻¹ that was different compared to pure quartz, may be attributed to –C–H bending of alkanes and (poly)aromatic structures and skeletal bending, and could be used to distinguish intact soils from agriculturally used samples. The different temperature behaviors of the bands for fractions of soils with different land use are shown, with the maximum difference in fractions below 20–50 µm and medium fractions (50–200 µm). Changes in the band-maximum frequencies and the integral intensities of the bands were reversible for a heating–cooling cycle. The linear discriminant analysis of the spectra obtained for granulometric fractions of chernozem soils made it possible to separate the samples of native steppe, arable land, bare fallow, and shelterbelt with a high probability based on the type of vegetation and agrogenic load, mainly on the basis of the spectral ranges associated with biogenic forms of quartz and phytoliths. Full article

(This article belongs to the Special Issue Use of Humic Substances and Biostimulants for Environmentally Sustainable Agriculture)

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18 pages, 3994 KiB

Open AccessArticle

Two-Dimensional Correlation IR Spectroscopy of Humic Substances of Chernozem Size Fractions of Different Land Use

by Mikhail A. Proskurnin, Dmitry S. Volkov and Olga B. Rogova

Agronomy 2023, 13(7), 1696; https://doi.org/10.3390/agronomy13071696 - 25 Jun 2023

Cited by 4 | Viewed by 1070

Abstract

Diffuse reflectance FTIR measurements with two-dimensional correlation spectroscopy (2D-COS) are used for accurate band identification of chernozem comprising soil organic matter (SOM), including humic substances and mineral silicate matrix. Samples of different land use (native steppe, shelterbelt, bare fallow, and arable land) of a long-term field experiment were compared. Homospectral 2D-COS maps for size fractions obtained by wet fractionation were built, and the fraction size was used as a correlation-building variable (external perturbation) of 2D-COS. Synchronous 2D-COS maps are characterized by main correlation regions at 4000–3600 (hydrogen bonds), 1800–1150 (SOM), and 1100–200 cm⁻¹ (quartz matrix). SOM range can be used as a signature of the samples distinguishing two pairs, native steppe–bare fallow and arable land–shelterbelt, by correlations at 1340–1320 cm⁻¹ (CH₂) and 1670 cm⁻¹ (aromatic –C=C–). Asynchronous 2D-COS maps show bands at 3690–3620, 2930–2830, in the range of 1640–1250 (8 bands), 1160, 1070, 797, 697, 505, and 400 cm⁻¹, the latter 5 indicate the increasing proportion of silicate to quartz in small fractions. The manifestation of asynchronous correlation bands at 1650, 1580–1560, 1444, 1340, and 1250 cm⁻¹, which have no major contribution from inorganic soil components, are due to carbonyl, carboxylate, and aromatic C–C; their appearance order (accumulation of corresponding substances in larger factions) is different for each land use. The proposed approach provides the identifying SOM components with enough reliability for SOM IR bands that are weaker compared to mineral matrix bands in original IR spectra. Full article

(This article belongs to the Special Issue Use of Humic Substances and Biostimulants for Environmentally Sustainable Agriculture)

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15 pages, 1435 KiB

Open AccessArticle

Biostimulants Using Humic Substances and Plant-Growth-Promoting Bacteria: Effects on Cassava (Manihot esculentus) and Okra (Abelmoschus esculentus) Yield

by Luciano P. Canellas, Natália O. A. Canellas, Rakiely M. da Silva, Riccardo Spaccini, Gabriela Petroceli Mota and Fábio L. Olivares

Agronomy 2023, 13(1), 80; https://doi.org/10.3390/agronomy13010080 - 26 Dec 2022

Cited by 11 | Viewed by 2777

Abstract

Traditional agriculture represents the most-extensive food-producing segment in the world. However, these agroecosystems are widely and closely associated with rural poverty, reflecting the dualism between the subsistence and the commodity-producing sector in the peripheric countries. Therefore, socially adapted technologies may be a reliable and helpful methodology to enhance subsistence crop production. Humic substances are natural organic biostimulants extractable as water suspensions from renewable sources such as agricultural biomass and farming residues. These easy-to-handle extracts may be mixed with plant-growth-promoting bacteria (PGPB) and used as biostimulants within a low-cost technological application in the circular economy strategy. Few investigations have been focused on the use of biostimulant practices on marginal or subsistence crops. Cassava (Manihot esculenta Crantz) and okra (Abelmoschus esculentus) are two essential foods for poor communities of rural territories in tropical and subtropical countries. The aim of this study was to evaluate the effect of the foliar application of a humic/PGPB mixed biostimulant on cassava and okra crops grown in an agricultural soil with very low natural fertility. In pot trials, the applied biostimulant improved the plant development with a 200% increase of the root weight in cassava, while the preservation of active diazotrophic bacteria was improved by 10- and 100-times in cassava and okra in the mixed formulation with humic acid. In real field systems, the plant treatment increased the yield of cassava and okra by 70% and 50%, respectively thereby allowing a simultaneous nitrogen savings with the best yield performance obtained at the lower N fertilization rate. The use of biostimulants can play a role in the transition process, helping the food security and the autonomy of impoverished farmers. Combining the elements of traditional knowledge and modern science is essential to create innovative technologies enabling the sustainable management of agroecosystems. Full article

(This article belongs to the Special Issue Use of Humic Substances and Biostimulants for Environmentally Sustainable Agriculture)

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