Open access peer-reviewed chapter

The Contribution of Humic Substances in Improving Agriculture and Livestock Sector in African Great Lakes Region: A Review

Written By

Daniel Nsengumuremyi, Sylvestre Havugimana and Nadezhda V. Barakova

Submitted: 08 August 2022 Reviewed: 31 August 2022 Published: 11 October 2022

DOI: 10.5772/intechopen.107526

From the Edited Volume

Humus and Humic Substances - Recent Advances

Edited by Abdelhadi Makan

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Abstract

The economy of the Great lakes region (GLR) depends on livestock and agricultural production. Although the region boasts massive diverse natural resources, such as humic substances (HSs), it is yet to benefit from this valuable natural resource. The current review sought to establish the contribution of HSs in improving the agriculture and livestock sector in the GLR. The outcome of the review establishes a positive relationship between the use of HSs and the improvement of the agriculture and livestock sector in the GLR. These substances stimulate the growth of plants, enhance soil fertility, and increase the availability of nutrients to plants. Conversely, HSs are vital components in controlling mycotoxins in animal feed. While the GLR is reputable for its massive agricultural production, this review affirms that the region has yet to fully explore HS’s benefits. Further research is necessary to specifically explore ways to maximize the use of HSs in boosting agricultural and livestock production in the GLR.

Keywords

  • humic substances
  • great lakes region (GLR)
  • agriculture
  • and livestock sector

1. Introduction

According to MacArthur Foundation, the African Great Lakes (Swahili: Maziwa Makuu, Kinyarwanda: Ibiyaga Bigari) region encompasses eleven countries: Burundi, Democratic Republic of Congo (DRC), Ethiopia, Kenya, Malawi, Mozambique, Rwanda, South Sudan, Tanzania, Uganda, and Zambia [1]. Burundi, Rwanda, Malawi, and Uganda are fully covered, while the other seven countries are partially covered. There are varied definitions of the GLR based on the different geographical locations [2].

The GLR encompasses regions with some of the world’s largest freshwater systems, comprising diverse ecosystems. Also, the region is rich in a significant quantity of natural resources such as land (peatland), water (lakes and rivers), and others rich in organic matter [3]. Humic substances are essential components of organic matter, widely distributed in surface soils, sediments (Sapropel, peat, charcoal), rivers, lakes, and marine waters [4]. Previous research has highlighted the application of HS in both agriculture and livestock rearing. Some sources report that farmers use this component to improve rhizome growth and speed up seed germination [5]. HS facilitates the transport of oxygen and nutrient utilization by plants and accelerates respiration. These findings have motivated scientists to evaluate the characteristics of HS and their potential use in improving the well-being of animals and plants [5].

A similar study by Yasar et al. [6] established a positive correlation between increased use of humic acid and significant weight gain in rats. On the other hand, Islam et al. [7] concluded that HS can improve how animals utilize nutrients in their feed. Notably, HS can achieve this by forming a protective layer on the gastrointestinal tract, which protects the host against toxins and infections.

Stakeholders in the agricultural sector have extensively utilized HS to spur growth and production. The benefits attributed to the use of HS on agricultural soils are enormous, mainly in areas with limited organic matter. HS form an integral part of global ecosystems and are valuable in cycling both carbon and nutrients [8].

Although GLR has abundant humic substance sources, these organic compounds are not exploited and utilized. According to FAO [9], agriculture is the principal economic sector in the Great Lakes region of Africa. This sector represents a significant source of income for rural populations in Burundi, the Democratic Republic of Congo (DRC), Rwanda, and Uganda [9].

Therefore, the application of HSs may play a vital role in improving agriculture and livestock. This review seeks to highlight the role of humic substances from sediments (Sapropel and peat), waters, and surface soil in improving the agricultural land and livestock sector in African GLR (great lakes countries). The paper also covers the primary sources of HSs in the GLR and explains the extraction methods of HSs from different sediments, soil, and water.

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2. Definition and primary sources of humic substances in GLR

In the environmental chemistry book, humic substances were defined as “a general category of naturally occurring, biogenic, heterogeneous organic substances that can generally be characterized as being yellow to black in color, of high molecular weight and refractory” [10].

HSs comprise a combination of heterogeneous organic compounds of biotic origin that have been transformed since plants first produced them. They are heterogeneous refractory since they resist decomposition and breakdown [11]. They have attracted widespread interest due to their applications in different sectors and have long been studied. Many famous scientists from the 18th century until now are involved in researching soil humic substances. Humic substances can originate from terrestrial or marine (e.g., phytoplankton) [12].

2.1 Sapropel

Sapropel is a resource of organic origin characteristic of limnetic areas of eutrophic freshwater bodies. The term “sapropel” means “decayed sludge.” The first work referring to “gyttja” was published in 1862 by a Swedish scientist Hampus von Post who accurately described it as a decomposed mass consisting of mineral particles with inclusions of plankton remains mollusk shells, chitin from the exoskeletons of insects, pollen, and spores [13, 14].

Sapropels are notable sources of humic acid. These are natural organo-mineral formations formed from dead plant and animal organisms, minerals of biochemical and chemical origin, and mineral components. Sapropel humic acids possess the properties of biogenic stimulants, stimulate the macrophage defense reaction, and promote tissue repair [15].

Lake Kivu is one of the African Great Lakes. It lies on the border between the Democratic Republic of the Congo and Rwanda [16]. The sapropel deposits in Kivu lake of the rare mineral monohydrocalcite interlaid with diatoms. Under these deposits, there are sapropelic sediments with high pyrite content [16]. The layer of sapropelic deposits in Lake Kivu contained organic matter from primarily algal sources [16].

The group composition of the organic matter of sapropel is represented by bitumoids, humic substances, easily hydrolyzable (carbohydrate complex) and difficult to hydrolyze (cellulose and lignin components) substances, and non-hydrolyzable residue [17]. Various nitrogenous and hormone-like compounds, enzymes, pigments, organic acids, alcohols, and others make up the pool of the biologically active component of sapropel [14]. The mineral component of sapropel contains silicon dioxide, calcium oxide, and compounds of iron, magnesium, potassium, aluminum, sulfur, phosphorus, and other macro-and microelements [14, 17]. In small doses, it was revealed that sapropels contain such substances as crude protein, digestible protein, quickly hydrolyzable carbohydrates, and vitamin A [18].

An essential feature of the organic part of sapropel is the high content (up to 50%) of humic compounds, which largely determine the attributes and nature of silts. The humic acids included in the composition of sapropel have a different degree of chemical activity, and the bactericidal effect of sapropel depends on it [14]. Humic acids of silica sapropels have a more pronounced antimicrobial effect [18].

Using sapropel as a feed additive increases the number of microorganisms in the rumen of lactating cows, resulting in the optimal acidity of the contents being established more than in the control variants [19]. In comparison with the control group increases by 8.2%, the number of protozoa in the experimental variant increases by 20.3% and is 647 thousand/ml. The high content of microorganisms in the rumen promotes better digestion of plant material [19].

Currently, the volumes and range of use of various humic fertilizers are constantly increasing. A comparison of different humic fertilizers showed their high efficiency in growing potatoes. The most significant increase in yield was provided by the use of stimulated fertilizer, the increase in yield over 3 years of research varied within the range of 14.6−27.3% [4, 20]. An increase in the starch content in potato tubers and a decrease in the accumulation of nitrates in plants were found [21].

2.2 Peat

The great lakes region hosts million and millions of tons of peat deposits. The first study on the peatlands of Rwanda and Burundi was carried out between 1958 and 1964 [22]. It was estimated around 14,000 ha of peatlands along the valley of the Akanyaru river, which lies between Rwanda and Burundi.

For instance, Rwanda hosts millions of tons of peat deposits, and the western province is important as it is close to Kivu Lake (which lies between DRC and Rwanda). About 77% of peat reserves are near the Akanyaru river (which lies between Rwanda Burundi), the Nyabarongo river, and the Rwabusoro Plains [23].

According to Pfadenhauer [24], 7% of Uganda (14,350 km2) is covered with peatlands. They are located around lakes and rivers to cite Kego, Albert, and Victoria lakes and the Nile, Victoria, and Okok rivers [25].

In DRC, peat deposits are located in different areas (Table 1). For instance, the mountainous area of Bukavu in the eastern province, west of Lake Kivu. The peatland area is around 0.5 to 10km2. Table 1 shows the peatlands area in DRC.

AreaExtent (in km2)
Upemba8500 (W),
4500 (D)
Kamulondo depression11,800 (W)
7040 (D)
Tumba767
Chesi41
Maji Ndombe2294
Kifukula depression1502
Mweru (Luapula River)4580
Middle Congo swamps40,550
Malebo Poolca. 300
Ruzizi River?
Semliki delta?

Table 1.

Potential peatland areas in the Democratic Republic of Congo (Howard-Wiliams and Thompson 1985). W = extent during wet season and D = extent during dry season (= permanent).

Peat is an accumulation of decayed plant material over thousands of years. It is generally found in wetland areas, and the type of decayed plants determines the type of peat (grasses or heathers) and the location (inland or maritime). Peat is composed of water (88–92%), carbon (50–60%), hydrogen (5–7%), nitrogen (2–3%), phosphorus (< 0.2%), oxygen, and mineral nutritional elements [26]. Besides elemental composition, peat has four groups of organic compounds. The first group is bitumen, a natural compound found in peat. The second group consists of water-soluble matter, easily hydrolyzed matter, and cellulose. The third group is humus or humic substances, which includes humic acid, fulvic acid, and humin; and the fourth is a mixture of lignin, lignin-like matter, cutin, suberin, etc. [27].

According to Lehtonen et al. [28], HSs are common organic constituents in soils and peats. HSs in peat comprise multiple structures derived from plants. The formation of these substances occurs during organic matter’s chemical, physical, and microbial degradation.

2.3 Aquatic humic substances

Aquatic HSs are water-derived organic acids that are colored and polyelectrolytic. They constitute between 40 and 60 percent of dissolved organic carbon and make up a significant amount of aquatic natural organic matter.

Aquatic HS has multiple functional groups, including carboxylic acids, phenolic hydroxyl, carbonyl, and hydroxyl groups. Aquatic humic substances are comprised of two components; humic and fulvic acids. Humic acid component precipitates at pH 2.0 or less, while fulvic acid remains in solution at pH 2.0 or less [29].

The differences in functional and elemental groups and average molecular weights among other characteristics mark the distinction between aquatic fulvic acids and humic acids. Also, there is a significant difference.

Aquatic humic and fulvic acids also differ from their corresponding soil counterparts. The typical average molecular weights of aquatic fulvic acids are 800−1000 daltons, and those of aquatic humic acids are 2000−3000 daltons. In contrast, Suffet and MacCarthy [30] postulate that the molecular weight of soil humic acids can measure several hundred thousand Daltons.

2.4 Surface soils

Humic substances are the main organic compounds of soil, and they are the markers of healthy soil. HSs are considered a vital component of the terrestrial ecosystem, responsible for many complex chemical reactions in soil [12].

Typical surface soils have up to 30% organic matter (OM), of which HSs can amount to 50−60%. The sources of soil humic substances are lignin and lignin-like materials; leaf polyphenols; cellulose and other polysaccharides; lipids; and proteins and amino acids.

Dead biomass mixed in and on top of soil consists of 50−60% cellulose and other polysaccharides, 15−20% lignin, and 15−20% fatty lipid molecules. Depending on the water, oxygen supply, temperature, and other environmental factors, up to 80% of the carbon in the biomass is converted to CO2 and returned to the air within a year. But with the aid of fungi, the remaining carbon is converted into humus (humified) and protected, resulting in some HSs that are thousands of years old! Eventually, however, these HSs form CO2 by reacting with oxygen. Such a respiration process prevents the HS soup from covering the earth’s surface. Also, it is crucial in completing the carbon cycle. Notably, the long-lived HS occurs after the loss of most of the CO2 during the respiration process highlighted above [31].

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3. Composition, structure, and properties of humic substances

Humic substances contain carbon, hydrogen, oxygen, and nitrogen with a small amount of sulfur and phosphorus. These elements are always present regardless of their origin and country [32, 33, 34].

Humic substances are made of humic acids (HA), fulvic acids (FA), and humins (HM). Humic acids are a fraction of humic substances, readily soluble in alkali and less aggregately stable than the other humic fraction and fulvic acids. Humic and fulvic acids also differ in molecular weight and degree of aromaticity: fulvic acids contain more aromatic structures with a molecular weight of two orders of magnitude [35]. The difference between humic acids and fulvic acids is present in Table 2. The degree of polymerization of fulvic acids by hydrogen bonds, cation bridges, and other methods may be lower due to the relatively low ability of the benzene nucleus to enter into chemical reactions. Humins are insoluble components, and their insolubility and intractable nature have made them difficult to study [42]. Research on humins depicts similarities between the substance and humic acids. However, humins are generally insoluble components because they bind firmly to metals and clays, rendering them insoluble components [43].

Humic acids (HA)Fulvic acids (FA)
HAs are dark (carbon rings and chains) [36]FAs are tight yellow to golden yellow [37]
HAs are not soluble in acidic conditions, and they are soluble in alkaline conditions[36]FA are soluble in acidic and alkaline conditions [36]
HAs unlock nutrients and bind to them, thereby making them available for uptake by plants [36]FAs bind to nutrients and transfer them to plants [37]
HAs have a higher molecular weight (1500−5000 Daltons in streams and from 50,000−500,000 Daltons in soils) [38]FAs are characterized by relatively low molecular weight [39]
HAs contain oxygen, nitrogen, hydrogen, and phosphorus [33]FAs are more biologically active: the oxygen is twice that of Humic acids [37]
HAs have aromatic rings in a molecule [40]FAs have many functional groups (hydroxyl and carbonyl groups) [37]
They are less polar and more hydrophobic than fulvic acids [40]These groups make FA polar [40]
The physical shapes of HAs molecules are determined by pH value, ionic strength of a solution and metal ions. HAs are negatively charged [41]FAs are negatively charged. They are the most effective carbon-containing compound known due to their small molecular size and electric charge [37]
HA molecules are susceptible to photodegradation (abiotic) [41]FA are resistant to microbiological degradation [37]

Table 2.

The comparison between humic acids and fulvic acids.

Different studies have shown that humic substances vary in their composition. The difference in the composition depends on the source, location, and mode of their extraction. However, the similarities are higher than the differences [44]. The above chapter discussed the source of humic substances, while the following section of the review will discuss the extraction mode.

In 2014, Hou and his colleagues analyzed the humic substances in sediments separately in different fractions: humins (HM), humic acid (HA), and fulvic acid (FA). The results of the study revealed that the concentrations of HM, HA, and FA in sediments were detected in the range of 6.40–58.16 g kg − 1, 0.27–3.50 g kg − 1, and 0.27–4.26 g kg − 1, respectively. HM was the dominant form and accounted for 74–94% of total organic compounds (TOC) and 80–90% of humus [27].

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4. Extraction and quantification of humic substances

Humic substances can be extracted from the soils, sapropel, peat, and other sediments with alkaline solutions [45]. After their extraction, they can be operationally fractionated into humic acids and fulvic acids based on their different water solubility, [46].

The IHSS method for humic substance extraction from soils has been developed by the International Humic Substances Society (IHSS). The advantage of this method is that high yields are obtained and this method is the applicable gold standard in making lab-based comparisons. The use of an adsorbent resin in the purification process is the main feature of this method [47].

The second method is the NAGOYA method developed in Japan at the University of Nagoya. This method is different from the IHSS method. Among the differences, we can highlight the volume of 0.1 N NaOH used for both methods. The IHSS method uses a 0.1 N NaOH solution with 10 times the volume of the soil weight (g) to extract the humic substances while the NAGOYA method used the same solution with 300 times the volume of the carbon content (g) in soil. The second difference is the Fulvic acids (FA) purification process. According to Kuwatsuka et al. [48], Fulvic Acids fractions contain brown polymeric materials designated as humic substances and other organic substances such as carbohydrates, peptides, and lipids, designated as non-humic substances. IHSS considers and designates only humic substances in the FA fractions as “FAs.” In the IHSS method, the polymeric-colored materials are collected from FA fractions using the hydrophobic adsorption resin XAD-8. However, NAGOYA considered that those FAs consist of humic and non-humic substances. Also, it is challenging to distinguish between humic substances and non-humic substances in the FA fractions. In the NAGOYA method, FAs do not exclude non-adsorbed materials on resins such as XAD. Those materials are also important constituents of FAs in their quantity and role in the soil environment [48, 49].

The third method to discuss is ultrasound-assisted extraction with 0.1 N KOH solutions. At RAS Limnology Institute (Russia), Mityukov and others have developed a new way of extracting ultra-disperse humic sapropel suspensions (UDHSS). The latter was extracted with alkaline extraction and ultrasound treatment of air-dry sapropels from the Seryodka deposit (Pskov region, Russia). UDHSS was derived from the hot method extraction at 40°C (104°F) and the cold method at 20°C. In his dissertation, Nsengumuremyi used the IHSS method to extract and quantify humic acids from UDHSS [50].

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5. Application of humic substances

Humic substances in agriculture are primarily due to their environmental safety, physiological activity, immunomodulatory properties, and ability to bind toxic compounds.

A promising direction for using humic substances is the reclamation of contaminated environments. Composition of carboxyl, hydroxyl, and carbonyl groups in a complex with aromatic structures promotes the formation of ionic and donor-acceptor interactions and active participation in sorption processes. The binding of toxicants leads to a decrease in the concentration of their free form and, consequently, a reduction in toxicity. Therefore, humic substances act as natural detoxifying substances [51].

According to Stevenson et al. [46], approximately 60% of soil organic matter is humic substance (HS). HSs are critical components of the terrestrial ecosystem, responsible for many complex chemical reactions in the soil. Research shows that humic substances enhance root, leaf, and shoot growth and stimulate the germination of various crop species.

The interaction between HSs on one hand and metabolic and physiological processes on the other underpins the positive effects of sapropels. There is a positive relationship between humic substance and soil fertility. Such a positive impact implies that increased HS content in the soil is likely to increase the level of nutrient availability to plants. In other cases, HS can act on certain physiological targets to hasten the signaling pathways and metabolic processes in plant development [12, 46].

The positive physiologic effects of humic acid make them viable for the cultivation of low-lose plants. They have effects on plant physiology, including the promotion of root growth. Humic acids induce the plasma membrane proton (H+)-ATPase activity in root cells in the same way that growth is induced by exogenous auxin [52].

HSs are valuable components in plant physiology. They improve the structure and fertility of soil and influence nutrient uptake and root architecture.

Due to the presence of oxygen-, nitrogen- and sulfur-containing functional groups in the structure of humic substances, the latter can form stable complexes with metal micronutrients [20]. However, according to [53], the stability of metal-HS is lower than the complexes between iron and synthetic chelating agents (such as EDTA, EDDHA) or organic compounds of biological origin (such as organic acids, siderophores, and phenols).

Molar ratio and pH between micronutrients affect HS stability and solubility of the complexes. High stability may be favored when the pH range is 5–9 and by low metal: HS ratio [54]. Therefore, plants growing in calcareous soils with limited iron availability could benefit from the formation of stable and soluble iron-HS complexes and insoluble complexes with high molecular weight HS [20].

Sapropel humic acids cannot only remove ecotoxins from the body but also introduce the necessary biogenic metals into it in an easily accessible complex form, which makes it possible to consider them as a biologically active food additive.

In studies carried out by Ismatova with colleagues, it was found that humic substances isolated from peat and sapropel have anti-inflammatory activity, which in some cases is comparable with the effect of diclofenac (a nonsteroidal anti-inflammatory drug with an analgesic effect). The object of the study was purified sodium humate.

The antimicrobial activity was assessed on test cultures of museum strains Proteus mirabilis N 132, Citrobacter diversus N 244, Klebsiella pneumoniae N 251, Staphylococcus aureus ATCC 25923, Pseudomonas aeruginosa ATCC 27853., wild yeast [55].

The bactericidal effect of humic substances is based on the action of active groups included in humic acids and is comparable to the action of synthetic antibiotics [56]. Biological testing of various sapropel preparations was tested for Staphylococcus Aureus, Escherichia Coli, Corynebacterium diphtheriae gravis, and wild Candida yeast to establish a significant bactericidal effect of sapropel preparations comparable to that of synthetic antibiotics [13, 57].

The bactericidal properties of sapropel preparations can ensure stability during the storage of grain, used for preparing food products (flour, bread, cereals, etc.) or feeding animals [58].

Fulvic acids are a group of humic acids with a more pronounced peripheral part and a less pronounced aromatic core. FAs dissolve well in alkaline solutions, acids, and water. The humification process begins with forming fulvic acids [59]. The concentration of fulvic acid can be determined by the spectrophotometric method [31].

Fulvic acid also affects enzyme activity during grain germination. The chemical composition of fulvic acid (FA) with a molecular weight below 500 (FA-500) has been analyzed and its activity in promoting the germination of wheat seeds has been studied in that article [60]. FA-500 was obtained using membrane separation technology and analyzed qualitatively and quantitatively using gas chromatography–mass spectrometry coupled with the retention index. The best concentration was 0.5%, and an inhibitory effect appeared with increasing concentration. During seed germination, FA-500 can influence seed growth by affecting the activity of amylase, associated with respiration [60].

Humin (non-hydrolyzable residue) is a combination of humic and fulvic acid compounds; currently, sapropels are used to produce ceramic products and chipboards, in drilling, and manufacture fabrics in the foundry. Based on sapropels, preparations were obtained that can bind heavy metals and remove them from soil and water. Sapropels are used in medicine and veterinary medicine. Sapropels are essential in agriculture as plant growth activators (fertilizers) and in animal husbandry as animal growth stimulators and immunomodulators (biological active feed additives). Doctors have established that the humic complex from sapropel is for the body and has a wide spectrum of action; the harmless complex has antimicrobial properties. Sapropel peloids (medicinal mud) have antiseptic properties [14].

Purifying sapropel is fairly cheaper than other sorbents because it is a natural substance. Besides, the substance has a characteristic high efficiency in absorption compared to other absorbents in the contemporary market, including clays or activated carbons.

The specific properties of humic acids make it possible to use them in industry, agriculture, ecology, and biomedicine [61].

It is important to conduct research on the use of extracts obtained from sapropel in the food industry; to expand the field of application of sapropel [17, 62].

Humic substances have shown a strong affinity for binding various substances, including various mutagenic, herbicides, heavy metals, Bacillus subtilis bacteria, and other substances [63].

Experimentally, Santos, et al. [64] proved the ability of polymers of humic acids to adsorb mycotoxins such as oсhratoxin A and zearalenone. Humic acid polymers have also been found to be able to absorb more than 96% of both mycotoxins at pH 3.0.

In the study by Van Rensburg et al. (2006), oxygumate (pure, high-quality humic acids from bituminous coal) proved to be much more effective in attenuating aflatoxicosis in broilers. Oxygumate showed a high affinity for aflatoxin B1 in vitro.

Humic substances are present in all-natural environments, including river water and lakes, soil, peat, coal, and sapropel. The complex composition of humic substances is caused by the absence of a unique dependence on the properties of the composition [65, 66]. Despite the known inhomogeneity of the chemical composition, the use of modern Physico-chemical methods of research has confirmed the independence of humic substances as a special class of natural organic high-molecular heterogeneous nitrogen-containing compounds [67].

Humic substances also can increase the yield of grain and fodder crops, stimulating photosynthesis and the respiration of plants. They are involved in plant lipid metabolism and in nonspecific plant responses to stress to restore membrane structure damage due to membrane ruptures and lipid peroxidation [68].

The antibacterial properties of humic compounds are due to their influence on the metabolism of proteins and carbohydrates of bacteria. Acting as catalysts, they accelerate the direct destruction of bacteria or viruses, thereby reducing antibiotics and the cost of treating animals [69, 70, 71].

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6. Conclusion

Humic substances are essential organic compounds found in surface soils and aquatic environments. These degraded substances benefit agriculture in several ways. The current study sought to establish the contribution of humic substances in improving the agriculture and livestock sector in the Great Lakes Region. This study establishes a positive correlation between HSs and improvement in livestock and agricultural production. In agriculture, HSs significantly decrease the toxicity as detoxifying agents, stimulating the root growth and germination of various crop species, soil fertility, and increasing nutrient availability for plants. Whereas in livestock, they are used against mycotoxins in animal feed. While the GLR is reputable for its massive agricultural production, this review affirms that the region has yet to fully explore HS’s benefits.

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Authors’ contribution

Writing–Original Draft Preparation, DN, NVB and SH Writing–Review & Editing, DN and SH; Supervision, NVB.

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Competing interests

“The authors declare that they have no competing interests”.

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ATPaseAdenosine Tri-Phosphatas
CO2Carbon Dioxide
EDDHAEthylenediamine-N,Nʹ-bis(2-hydroxyphenylacetic acid)
EDTAEthylenediaminetetraacetic acid
FAsFulvic acids
H+Hydrogen ion
HAsHumic acids
HMHumin
HSsHumic Substances
IHSSInternational Humic Substances Society
KOHPotassium Hydroxide
NNormality
NaOHSodium Hydroxide
°CDegree Celcius
°FDegree Fahrenheit
pHPotential Hydrogen
RAS limnology instituteRussian Academy of Sciences limnology institute
UDHSSultradisperse humic sapropel suspensions
XAD & XAD-8Resin & Resin category

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Written By

Daniel Nsengumuremyi, Sylvestre Havugimana and Nadezhda V. Barakova

Submitted: 08 August 2022 Reviewed: 31 August 2022 Published: 11 October 2022