Soil Humic Acids Research Articles

Biochar Application Alleviated Rice Salt Stress via Modifying Soil Properties and Regulating Soil Bacterial Abundance and Community Structure

Increased soil salinity significantly inhibits crop production worldwide, and biochar may alleviate salt stress. In the present study, the application of biochar significantly increased the biomass of rice under salt stress treatment. The analysis of soil properties demonstrated that biochar application significantly decreased electrical conductivity and soluble Na+ and Cl− contents in the soil under salt stress. In addition, biochar application increased the soil cation exchange capacity, soil organic matter, humic acid, total nitrogen, and total phosphorus contents in the soil, suggesting that biochar improved the soil nutrient conditions. The application of biochar further increased the abundance of soil bacteria and changed the bacterial community structure under salt stress. Proteobacteria, Chloroflexi, and Acidobacteria were the top three phyla in bacterial abundance. Biochar increased Proteobacteria abundance and decreased Chloroflexi abundance, which were considered to be eutrophic bacteria and oligotrophic bacteria, respectively. Redundancy analysis showed that soil bacterial communities were mainly affected by soil pH and EC (p < 0.05). In conclusion, the application of biochar alleviated salt stress in rice via modifying soil properties and regulating the bacterial abundance and community structure.

Mechanisms of the effects of humic acid on antibiotic resistance genes and microbial communities in Cd-contaminated soils

Humic acid (HA) is an organic macromolecular compound that widely exists in nature, but its effect on antibiotic resistance genes (ARGs) in Cd-contaminated soil is unknown. This study investigated the effects of Cadmium (Cd) and HA in soil on ARGs, mobile genetic elements (MGEs), and bacterial communities. The relative abundance of ARGs and MGEs increased 0.89-fold and 1.12-fold after the addition of 2 mg kg−1 Cd to the soil, and 1.06-fold and 1.68-fold after the addition of 8 mg kg−1 Cd. Redundancy analysis further revealed that among environmental factors, available Cd was the dominant factor influencing ARGs. In Cd-contaminated conditions, the addition of high concentrations of HA suppressed the expression of ARGs and MGEs. The abundance of ARGs and MGEs decreased by 0.12-fold and 0.44-fold after the addition of HA (50 mg kg−1) to the soil at a Cd concentration of 2 mg kg−1, and by 0.18-fold and 0.41-fold at a Cd concentration of 8 mg kg−1. IntI1 was significantly associated with all ARGs (sul1, sul2, tetG, tetW), and intI2 was significantly correlated with most ARGs (sul2, tetG, tetW). Network analysis illustrated that Proteobacteria were the main host bacteria causing changes in the abundance of ARGs and MGEs. HA has an important role in agricultural production. To reduce the enrichment of ARGs in Cd-contaminated soil, the addition of higher concentrations of humic acid can be considered to mitigate the environmental and biological hazards.

Humic Acid Alleviates Fe Chlorosis in Graminaceous Plants Through Coordinated Fe-Dependent and Fe-Independent Mechanisms.

Many studies have shown the close relationship between the beneficial action of soil and sedimentary humic acids on the growth of plants cultivated in calcareous soils and their ability to improve Fe plant nutrition. These results have been ascribed to the humic acid (HA) capability to improve Fe solubility and bioavailability. However, other effects more related to a humic acid action on the specific mechanisms activated in roots of plants under Fe deficiency cannot be ruled out. Although this question has been studied in dicotyledonous plants, in graminaceous plants there are no specific studies. Here we investigate the ability of a humic acid extracted from peat (HA) to improve Fe nutrition in wheat plants cultivated under Fe deficient and sufficient conditions. The results show that HA can improve the physiological status of Fe deficient wheat plants by alleviating some of the deleterious consequences of Fe deficiency on plant development and increasing the plant ability to secrete phytosiderophores to the nutrient solution. This action of HA is associated with increases in the Fe-active pool in leaves that might be related to the mobilization of the Fe complexed by HA resulting from the interaction of HA with the phytosiderophores in the nutrient solution. The Fe translocation from the root to the shoot may be favored by the action of trans-Zeatin Riboside (tZR) since the leaf concentration of this phytohormone was enhanced by HA in Fe deficient plants.

Assessing Factors Controlling Structural Changes of Humic Acids in Soils Amended with Organic Materials to Improve Soil Functionality

Humic acids (HAs) regulate soil chemical reactivity and improve many soil functions. The amendment of soil with organic materials increases soil organic matter (SOM) content and promotes the formation of HAs. However, the effect of the type, frequency and duration of amendment, and pedoclimatic conditions on SOM transformation and HA structural changes remains unclear. Herein, four experimental field sites (S1–4) with short-to-long-term organic fertilisation schemes were used to assess the effects of such factors, i.e., S1: loamy sand amended once with farmyard manure (FYM), brown coal waste (BCW), and biochar (BIO) for 0.5 and 1.5 years; S2: silt loam amended once with BIO for 8 years; S3: loamy sand amended every 5 years with FYM for 94 years; and S4: clayey silt amended every 2 years with FYM for 116 years. All HAs were extracted and analysed for structural differences by elemental analysis (EA), attenuated total reflectance–Fourier transform infrared spectroscopy (ATR-FTIR), solid-state cross polarisation magic angle spinning nuclear magnetic resonance spectroscopy (CP/MAS 13C-NMR), and differential scanning calorimetry (DSC). Results from EA, FTIR, and NMR showed that the long-term samples from S3 (treatments, T9–T10) and S4 (T11–T12) had the greatest aromatic characteristics, which increased with FYM amendment (T10 and T12). These agreed with DSC data, which indicated lower aliphatic contents compared with other samples. Samples from S2 (T7–T8), with receded amendment effects, had less aromatic and greater aliphatic characteristics compared with the short-term samples, S1 (T1–T6). In S1, structural changes were limited, but aromaticity increased with BIO (T3 and T6) compared with corresponding FYM (T1 and T4) and BCW (T2 and T5) amendments due to inherently high aromatic groups in the former. Overall, the results showed that the site (due to differences in pedoclimatic conditions), field age of OM, and amendment frequency were the main factors that influenced HA structure, and hence SOM transformation. Regular, long-term organic amendment increases the aromatic characteristics of HAs, which can improve soil functionality, but short-term structural improvements are achievable only when amending material is rich in aromatic compounds.

Self-aggregation of soil humic acids with respect to their structural characteristics

The main goal of this work was to estimate the influence of carboxyl and phenolic groups, as well as aromatic, aliphatic and polysaccharide components, on the soil humic acids (HA) self-aggregation process. Soil HAs (leptosol and regosol) were separated using base resin getting fractions with different functional group contents. Blocking of carboxyl groups was performed using the esterification procedure to estimate the participation of each functional group in the HA aggregation. The presence of HA structural components was evaluated by potentiometric titration and ATR-FTIR. The aggregation was monitored at pH 3 using dynamic light scattering. Results indicated that the higher group content, the HA aggregation is less pronounced. A significant positive correlation of aliphatic C and aggregate size revealed their dominant influence in the HA self-aggregation. A lower abundance of aliphatic C in HA fractions could be considered as not sufficient to start the process. An increase of aromatic C in esters likely pointed out to its participation in hydrophobic bonding and, consequently, more pronounced aggregation. The relation of HA self-aggregate size with carboxyl and phenolic group, as well as aliphatic C, at low pH, could be considered universal regardless of the structural characteristics of the original or modified HA forms.

Soil Humic Acid and Arsenite Binding by Isothermal Titration Calorimetry and Dynamic Light Scattering: Thermodynamics and Aggregation

Soil Humic Acid and Arsenite Binding by Isothermal Titration Calorimetry and Dynamic Light Scattering: Thermodynamics and Aggregation

Influence of humic acid on morpho-physiology and yield of rice

A pot experiment was conducted to investigate the influence of soil organic amendments-cow dung and humic acid on morphology and yield of rice under drought stress at the net-house, Agricultural Botany Department at Sher-e-Bangla Agricultural University, during the period from July 2018 to November 2018. This single factorial experiment pots where arranged in a randomized complete block design with four replications. Four different levels of soil organic amendments viz. SM1 = Soil + inorganic fertilizer (control), SM2 = Soil + cow dung + inorganic fertilizer, SM3 = Soil + inorganic fertilizer + humic acid and SM4 = Soil + inorganic fertilizer + cow dung + humic acid. The results showed that morphological characters and yield of rice significantly increased with addition of cow dung and humic acid into the soil. In terms of morpho-physiology, the highest plant height 112.90 cm and number of tillers plant-1 11.25 were achieved from the treatment SM4 (Soil + inorganic fertilizer + cow dung + humic acid). In terms of the variables that contribute to the yield, the highest days to 1st flowering (72.75) and days to 1st maturity (122.05 days) were found from control treatment SM4 (Soil + inorganic fertilizer + humic acid + cow dung). Similarly, the highest panicle length (24.94 cm), number of filled grain panicle-1 (221.40), number of unfilled grain panicle-1 (42.25), root length (17.93 cm), number of grains panicle-1 (247.40), grain weight hill-1 (25.17 g), straw weight hill-1 (33.26 g) and harvest index (42.93%) were achieved from SM4 (Soil + inorganic fertilizer + cow dung + humic acid) . The highest soil moisture content (17.23 and 16.17% at 55 and 70 DAT, respectively) was also achieved from SM4 (Soil + inorganic fertilizer + cow dung + humic acid). This experimental results highlighted that together use of cow dung and humic acid increased the grain weight plants-1 more than 150% compared to controlled condition. Finally, it concluded that application of cow dung and humic acid as soil organic amendments increases the yield of aman rice.

E4/E6 ratio and total acidity of soil Humic and Fulvic acids from different land use patterns

Humic substances, the major fractions (nearly 85%) of organic matter, constituting humic (HA) and fulvic acid (FA) extracted from soils of different land use patterns viz., agriculture, forest, fallow, pasture, salt affected, horticulture and agroforestry land under varied agroclimatic zones of western Maharashtra (India) were evaluated for their individuality and properties through E4/E6 ratio and total acidity. Higher degree of aromaticity of HA was evidenced by lower E4/E6 ratio than FA in all the LUP. Soils from fallow land showed lower total acidity than forest. The distinctiveness of humic substances was influenced by land use management and climatic parameters (temperature and rainfall).

Water movement in sodic soils explained through hands‐on demonstrations

AbstractMillions of ha of sodic soils exist around the world and the movement of water through these soils is most directly dictated by the concentration of Na and overall electrical conductivity of the soil, and minerology of the clay. Helping farmers, land managers, crop advisors, and students better understand why water moves or does not move in these soils is necessary so that proper management strategies for these soils can occur. The purpose of this article is to provide educators and extension specialists with demonstrations that help describe water movement through sodic and non‐sodic soils. The first demonstration links water movement through sodic soils and how altering the concentration of Na and soluble salts influences water movement. The second demonstration allows audiences to link the movement of water through soil horizons having varying concentrations of Na, soluble salts, and clay. These demonstrations may be useful educational tools on how and why amendments are used for improving water movement within sodic soils and also to show restrictions in water movement through naturally‐occurring natric or clay‐enriched horizons.

Трансформація гумусових речовин дерново-підзолистого ґрунту за тривалого внесення добрив

The article reflects the results of a study of the regularities of the transformation of humic substances at different levels of structural organization during long-term fertilization against the background of liming of podzolic sandy loamy soil in a field experiment in Western Polissya of Ukraine. It was found that the low content of chemically active organic substances in the humus composition of podzolic soils, caused by the zonal features of humus formation, can be positively corrected by applying fertilizers. Long-term use of organic and mineral fertilizers intensifies the process of new formation of humic acids and the formation of their mobile forms – the ratio of Cha-1 / Cfa-1 is 0.28 in the control without fertilizers and 0.33–0.88 in the variants of fertilization against the background of liming. With an organo-mineral fertilizer system, the most favorable conditions are formed for the humification of organic substances however, the type of humus remained fulvate – the Cha / Cfa ratio is 0.93 in the control variant and 0.41 – against the background of liming. Also, the application of fertilizers had an effect on the redistribution of the polydispersity of humic acids, which was characterized by a decrease in the heterogeneity of the composition of hydrophobic molecular aggregates. In a wide range of 1800 cm-1 to 2500 cm-1, a change in the direction of the line of the integral spectrum of soil humic acids under the application of CaCO3 from left to right was found, which is associated with a change in molecular parameters. Based on the results of chromatographic analysis, it was established that the profiles of the molecular distribution of humic acids podzolic soil correspond to the humus substances class. The first fraction is characterized by the formation of ion associates of larger molecules of polar composition. The recovery of humic acids occurred mainly due to high-molecular structures, which is the most sensitive to the application of fertilizers.

Impacts of earthworm casts on atrazine catabolism and bacterial community structure in laterite soil

Atrazine accumulation in agricultural soil is prone to cause serious environmental problems and pose risks to human health. Vermicomposting is an eco-friendly approach to accelerating atrazine biodegradation, but the roles of earthworm cast in the accelerated atrazine removal remains unclear. This work aimed to investigate the roles of earthworm cast in promoting atrazine degradation performance by comprehensively exploring the change in atrazine metabolites and bacterial communities. Our results showed that earthworm cast amendment significantly increased soil pH, organic matters, humic acid, fulvic acid and humin, and achieved a significantly higher atrazine removal efficiency. Earthworm cast addition also remarkably changed soil microbial communities by enriching potential soil atrazine degraders (Pseudomonadaceae, Streptomycetaceae, and Thermomonosporaceae) and introducing cast microbial degraders (Saccharimonadaceae). Particularly, earthworm casts increased the production of metabolites deethylatrazine and deisopropylatrazine, but not hydroxyatrazine. Some bacterial taxa (Gaiellaceaea and Micromonosporaceae) and humus (humic acid, fulvic acid and humin) were strongly correlated with atrazine metabolism into deisopropylatrazine and deethylatrazine, whereas hydroxyatrazine production was benefited by higher pH. Our findings verified the accelerated atrazine degradation with earthworm cast supplement, providing new insights into the influential factors on atrazine bioremediation in vermicomposting.

Stability of humic acid carbon under conservation agriculture practices

Recently conservation agriculture (CA) using the principles of zero tillage, crop residue management and suitable crop rotation has gained the momentum and quite popular among the farmers. Researchers throughout the globe have shown the potential of CA in enriching soil organic carbon storage in various soil types and cropping systems. But there is very limited study on the effect of CA on soil humic acid content and their stability and abundance of functional groups. An experiment was conducted in an Alfisols with four scenarios (designated as Sc) namely conventional farmers practice (Sc1) of transplanted rice (TPR) followed by conventional tilled broadcasted wheat (CT- wheat) with residue removal, transplanted rice (TPR) followed by zero tillage (ZT) wheat and mung bean with partial residue retention (Sc2), direct seeded rice (DSR) followed by ZT- wheat and mung bean with full residue retention (Sc3), ZT-maize followed by ZT-wheat and mung bean (Sc4) at the research farm of ICAR-Central Soil Salinity Research Institute, Karnal, Haryana, India. The objectives of this study were to assess the humic acid (HA) content and stability of soil carbon through desorption study and to characterize the functional groups of HA by Fourier Transform Infrared (FTIR) spectroscopy under different scenarios. HA was extracted from soil samples collected from 0 to 15 and 15–30 cm depth after rice harvesting in 2018 after nine years of the experiment. Results showed that Sc4 recorded significantly highest HA content at 0–15 depth (4.23 g/kg) and 15–30 cm soil depth (2.08 g/kg). Lower E4/E6 ratio revealed higher stability and humification of humic acid carbon under CA based scenarios. Lowest desorption rate constant (0.20/day) was observed under Sc4 indicating higher organic carbon stability in soil. Higher labile carbon and nitrogen was observed in soils under Sc3 as revealed through desorption study. FTIR spectroscopy results confirmed the prevalence of higher number of functional groups (OCO, CO or CHO) in HA under CA based scenarios with an order of Sc4 >Sc3 >Sc2 >Sc1. Therefore, CA is not only efficient in enriching the organic carbon in soil but also in more stable complex of HA with soil particles having long term implications in soil carbon sequestration for future posterity.

Enhanced adsorption of humic/fulvic acids onto urea-derived graphitic carbon nitride

Since humic substances (HSs) can cause environmental problems, their elimination has been attracting more and more concerns. In this study, we investigated HSs adsorption onto urea-derived graphitic carbon nitride (CNU) and elucidated adsorption mechanisms (i.e. heterogeneity, interface rearrangement, and multiple interactions). The adsorption capacity of CNUs was enhanced as increasing calcination temperature and time. Among CNUs, CNU-575–3 showed the highest adsorption capacity; the maximum adsorption capacities for humic acid (HA) and fulvic acid (FA) were 164.06 mg C/g, 14.61 L/cm·g, 91.12 mg C/g, and 5.34 L/cm·g, respectively. The adsorption affinity of CNUs mainly correlated with the amount of amino groups, and that of HSs components was dependent on aromaticity due to π-π interactions. More specifically, terrestrial humic-like and fulvic-like components within HA and FA showed the greatest adsorption affinity, respectively. HSs adsorption was remarkably affected by pH, alkali metals, and alkali earth metals via electrostatic interactions, H-bonding, cation bridge, and configurational effect. In addition, the adsorption of Elliott soil HA (ESHA) and the landfill leachate concentrate by CNUs was also highly efficient. This study shows the great promise of CNUs for HSs adsorption in waters and wastewaters.

Influence of humic acid application on onion growth characteristics under water deficit conditions

In this study, effect of water shortage on onion growth and quality was evaluated under soil humic acid (HA) application. Three levels of irrigation namely: a1; 80%, a2; 70% and a3; 60% of field capacity (FC) were supplied to plants in combination with two levels of HA namely: b1; 0 and b2; 100 mg/kg soil, in a factorial and completely randomized design with four replications. The interaction of irrigation and HA was significant on leaf dry weight, vitamin C, calcium, total chlorophyll and bulb flavonoids, while the onion fresh yield was not affected by treatments. Many plant growth traits showed a reducing trend with deficit irrigation levels. The leaf biomass as well as the leaf concentrations of potassium, calcium and zinc were significantly decreased under highest water deficit treatment (60% FC; a3b1 and a3b2) compared to control (a1b1) treatment. Leaf vitamin C and calcium concentration showed almost a similar response in which their highest levels were observed in a1b2 treatment, while the lowest amounts were recorded under higher water shortage (a3b1), and application of HA (a3b2) significantly increased these traits under higher water shortage. The amounts of bulb flavonoids and phenols were increased by deficit irrigation and application of HA further increased their content under highest deficit irrigation. The results indicate that water deficit particularly at highest level reduced onion plant growth, while soil application of HA significantly increased the growth and quality traits including leaf biomass, vitamin C, and minerals like Ca, as well as bulb flavonoids under water deficit conditions.

Changes in Soil Humic Acid Composition after Nine Years of Repeated Application of Organic Wastes in Black Soil: a Study Using Solid-State FT-IR and (13C-NMR) Analysis

Changes in Soil Humic Acid Composition after Nine Years of Repeated Application of Organic Wastes in Black Soil: a Study Using Solid-State FT-IR and (¹³C-NMR) Analysis

Improving Phytoremediation Efficiency of Copper-spiked Calcareous Soils by Humic Acid Applications

In current study, the enhanced efficiency of copper (Cu) phytoremediation potential of Calendula officinalis L. was investigated in a Cu-spiked calcareous soil, using foliar and soil application of humic acid. For this purpose, in a greenhouse experiment, seedlings of C. officinalis were transferred to Cu-spiked soils (0, 250 and 500 mg/kg) and treated separately with soil (soil drench) and foliar (spraying plant leaves) humic acid applications at different levels (0, 10, 20 μM). The humic acid treatments were applied 2 weeks after transferring plant, and eventually the various biochemical-physiological traits and phytoremediation indices of Cu in C. officinalis were measured at (specific) time points. According to the results, C. officinalis grew normally without any toxicity signs in Cu-spiked soils, however with increasing the Cu levels, the dry weight biomass decreased and antioxidant enzymes activities increased. Both foliar and soil humic acid application in Cu-spiked soils increased dry weight biomass, photosynthetic pigment contents, Cu concentration, and bioconcentration factor (BCF). Furthermore, the application of this organic substance, obviously moderated the Cu stress since the antioxidant enzymes activities reduced compared to the control. Based on the results, the obtained translocation factor (TF) and BCF values of Cu, which were >1, indicated that this plant is a Cu-hyperaccumulator, which could extract Cu via phytoextraction mechanism. Generally, the results of this study showed that, among the humic acid treatments, application of 20 μM (especially soil drench application) had the best effect on increasing Cu phytoremediation efficiency in the studied soil and it recommended to enhance the efficiency of Cu phytoremediation in calcareous soils.

Interaction of soil humic acids with gold ions and pathfinder elements

The study aims at experimental modeling of interaction of gold, arsenic, copper and lead ions with humic acids. The relevance and choice of the research objects are attributed to the poor coverage of characteristics of the mentioned ions with regard to their sorption interaction with humic acids. Arsenic, copper and lead are, on the one hand, common pollutants accumulated in soils exposed to anthropogenic impact and, on the other hand, are pathfinder elements for gold, which serve as indicators of gold mineralization in geochemical prospecting in secondary halos. The experiment has been carried out with the solution concentration ranging from 5 to 100 μg/cm3 at the temperature of 298 K. The adsorption isotherms obtained experimentally are described through the empirical Freundlich adsorption isotherm equation and the Langmuir adsorption model. A model experiment has been conducted on the effect of iron (III) ions on gold ion sorption, which is essential for determining the forms of gold in loose deposits in the presence of iron oxides and hydroxides. It has been shown that an increase in the iron concentration has practically no effect on the amount of sorbed gold ions in the concentration range under study.

English

In arid and semi-arid lands, water salinity often restricts plant growth, degrades soils, and even causes irrigation systems to fail, especially in hot climates. Worldwide, it is a “major cause” of the irrigation-induced salinization that had already affected 76 million ha of soil in 1991. Our novel and inexpensive irrigation technique addresses these issues, thus potentially improving the food security of affected farmers and pastoralists who often are amongst the world’s poorest. Saline or brackish water is dispensed inside plastic bottles that are modified so as to feed only vapour to the soil, where roots and moisture-retaining materials can capture it. We tested this method in the field in Turkana County (Kenya) with Dual-Purpose Sorghum. Five treatments in five replicates were applied with different moisture-retaining material: biochar; organic mulch; plastic sheeting; Super Absorbent Polymer); and none (Control). Effectiveness of the treatment was appraised by comparing the average heights of plants. At 64 cm after 30 days, the Super Absorbent Polymer treatment performed best (34% better than the control, p=0.05), followed by organic mulch (18% better than the control, p=0.05). Super Absorbent Polymer and organic mulch also retained the most moisture in the soil (37 and 32% better than the control, respectively; p=0.05). Key words: Irrigation, pitcher irrigation, condensation irrigation, superabsorbent polymer, mulch, salinity, brackish water, saline water, soil salinization.

Reductive Transformation of 3-Nitro-1,2,4-triazol-5-one (NTO) by Leonardite Humic Acid and Anthraquinone-2,6-disulfonate (AQDS).

3-Nitro-1,2,4-triazol-5-one (NTO) is a major and the most water-soluble constituent in the insensitive munition formulations IMX-101 and IMX-104. While NTO is known to undergo redox reactions in soils, its reaction with soil humic acid has not been evaluated. We studied NTO reduction by anthraquinone-2,6-disulfonate (AQDS) and Leonardite humic acid (LHA) reduced with dithionite. Both LHA and AQDS reduced NTO to 3-amino-1,2,4-triazol-5-one (ATO), stoichiometrically at alkaline pH and partially (50-60%) at pH ≤ 6.5. Due to NTO and hydroquinone speciation, the pseudo-first-order rate constants (kObs) varied by 3 orders of magnitude from pH 1.5 to 12.5 but remained constant from pH 4 to 10. This distinct pH dependency of kObs suggests that NTO reactivity decreases upon deprotonation and offsets the increasing AQDS reactivity with pH. The reduction of NTO by LHA deviated continuously from first-order behavior for >600 h. The extent of reduction increased with pH and LHA electron content, likely due to greater reactivity of and/or accessibility to hydroquinone groups. Only a fraction of the electrons stored in LHA was utilized for NTO reduction. Electron balance analysis and LHA redox potential profile suggest that the physical conformation of LHA kinetically limited NTO access to hydroquinone groups. This study demonstrates the importance of carbonaceous materials in controlling the environmental fate of NTO.

HUMIC ACIDS COMPOSITION OF ARABLE SOD-PODZOLIC SOIL AFTER LONG-TERM APPLICATION OF TRADITIONAL AND UNCONVENTIONAL ORGANIC FERTILIZERS

The elemental composition and structure of humic acids (HA) of arable sodpodzolic soil (Eutric Albic Retisols (Abruptic, Loamic, Cutanic) was studied inPerm Agricultural Research Institute – division of PFRC. Application of traditional and unconventional organic fertilizers was fulfilled in long-term stationary experiment. The carbon content in HA of sod-podzolic soil varied from 30.7 to 34.6; hydrogen – 28.9-35.5, oxygen – 21.1-27.9, nitrogen – 1.9-2.2%. The Н/С ratio for all treatments was >1, the structure of the supramolecular associations of humic acids is predominantly aliphatic. Long-term use of manure, sewage sludge (SS) and their combination with mineral fertilizers led to the enrichment of humic acids with nitrogen. The maximum degree of HA oxidation was observed with the use of cattle manure. The FTIR spectra of humic acids had absorption bands of carboxyl, hydroxyl, methyl, methylene, methoxyl and other groups in a wide wavelength range. At 1720 cm-1, an absorption band was recorded, which had a high intensity in the control variant and was due to oscillations of the >C=O group of carboxylic acids. With an increase in the load of the anthropogenic factor on the soil (application of organic and mineral fertilizers), a decrease in its intensity is observed. The structure of supramolecular HA aggregates of the control variant, with the introduction of NPK and unconventional organic fertilizer – SS, is characterized by a higher content of aromatic fragments, as evidenced by a clear existence of the absorption band at 1628 cm–1. Cattle manure application promoted the formation of humic acids with a branched aliphatic structure.