Humic substances are naturally occurring compounds derived from decomposed animal and plant matter through microbial activity and geochemical processes, such as composting and lignin degradation. Composing up to 80% of organic soil matter,[1] they play a vital role in promoting plant growth.
Humic acid, a primary component of humic substances, has become a focus of agricultural research for its ability to enhance fertilizer efficiency, improve crop quality and increase yields when combined with mineral fertilizers. Since hydroponics are soilless, supplementing cannabis with humic acid can provide benefits typical of enriched soil.
This blog post explores the components of humic substances and the advantages humic acid may offer to cannabis cultivation.
Humic substances are naturally occurring compounds derived from decomposed animal and plant matter through microbial activity and geochemical processes, such as composting and lignin degradation.
Composing up to 80% of organic soil matter,[1] they play a vital role in promoting plant growth.
Humic acid, a primary component of humic substances, has become a focus of agricultural research for its ability to enhance fertilizer efficiency, improve crop quality and increase yields when combined with mineral fertilizers. Since hydroponics are soilless, supplementing cannabis with humic acid can provide benefits typical of enriched soil.
This blog post explores the components of humic substances and the advantages humic acid may offer to cannabis cultivation.
Components of humic substances
Humic substances consist of three components: humin, fulvic acid and humic acid. These components differ in size and solubility:
- Humin has a high molecular weight and is insoluble.
- Fulvic acid has a low molecular weight and is soluble at all pH levels.
- Humic acid has a larger molecular weight and a more complex structure than fulvic acid, and it is soluble only at a pH above 2.0.[1]
Since humin is non-degradable, hydroponic systems primarily focus on fulvic and humic acids due to their quicker and more direct impact on plant health.
Fulvic and humic acids are classified as acids due to their chemical composition. Acids are compounds that release hydrogen atoms as positively charged ions in solution. Fulvic acid primarily contains carboxyl groups that release hydrogen ions,[2] while humic acid, when insoluble, has hydrogen ions dominating their cation exchange sites.[3]
It’s important to note that fulvic and humic acids are not single molecules but groups of molecules. Their structure and effects vary depending on their source, though their average properties remain consistent.[4]
Thanks to their solubility, humic and fulvic acids are chemically reactive yet resistant to microbial reactions,[5] offering numerous benefits to plants.
Figure 1. Mechanism of action of humic acid on plants. Image source: Bera, Bidyabhusan, Kangujam Bokado, Barka, and Shainika Arambam. 2024. “Effect of Humic Acid on Growth, Yield and Soil Properties in Rice: A Review.” International Journal of Plant & Soil Science 36 (6): 26-35. https://doi.org/10.9734/IJPSS/2024/v36i64603.
Figure 1. Mechanism of action of humic acid on plants. Image source: Bera, Bidyabhusan, Kangujam Bokado, Barka, and Shainika Arambam. 2024. “Effect of Humic Acid on Growth, Yield and Soil Properties in Rice: A Review.” International Journal of Plant & Soil Science 36 (6): 26-35. https://doi.org/10.9734/IJPSS/2024/v36i64603.
Benefits of humic acid in plants
Humic acid works through multiple mechanisms to benefit plants (Figure 1), with improvements in one area often triggering positive effects in another. Its application provides both direct and indirect advantages.
Nutrient availability and uptake
Humic acid attracts positive ions, acting as a chelating agent that prevents micronutrients from precipitating, leaching or oxidizing and providing plants with a slow release of nutrients as needed.[7]
The structure of humic acid, primarily composed of phenolic and carboxylic groups (Figure 2), forms hydrophilic (polar) and hydrophobic (non-polar) parts when dissociated. This structure aids in nutrient chelation and transportation through the root’s plasma membrane.[8]
Humic acid also stimulates uptake of nitrate nitrogen and ammonium nitrogen,[9] the two forms of nitrogen plants can absorb.
When combined with mineral fertilizers, humic acid forms complexes that have a slow-release effect on nutrients and uptake.[10]
Figure 2. Chemical and molecular components of humic acid. Image source: Ampong, Kwame, Malinda S. Thilakaranthna, and Linda Yuya Gorim. 2022. “Understanding the Role of Humic Acids on Crop Performance and Soil Health.” Frontiers in Agronomy 4: 848621. https://doi.org/10.3389/fagro.2022.848621.
Figure 2. Chemical and molecular components of humic acid. Image source: Ampong, Kwame, Malinda S. Thilakaranthna, and Linda Yuya Gorim. 2022. “Understanding the Role of Humic Acids on Crop Performance and Soil Health.” Frontiers in Agronomy 4: 848621. https://doi.org/10.3389/fagro.2022.848621.
Figure 2. Chemical and molecular components of humic acid. Image source: Ampong, Kwame, Malinda S. Thilakaranthna, and Linda Yuya Gorim. 2022. “Understanding the Role of Humic Acids on Crop Performance and Soil Health.” Frontiers in Agronomy 4: 848621. https://doi.org/10.3389/fagro.2022.848621.
Improved hormonal activity and bio-stimulant effects
Humic acid enhances the production and activity of phytohormones like auxin and cytokinin by stimulating plant processes that either boost their production or mimic their effects.[11]
Research shows that humic acid’s hormone-like effects[12] are linked to its chemical structure, especially its non-lignin components. These effects happen through interactions with the roots or shoots. Since auxin and cytokinin also support photosynthesis, increased activity leads to greater photosynthesis, which in turn improves plant height, leaf area index and overall biomass.
As one of the most effective bio-stimulants, humic acid provides an auxin-like effect by elongating lateral root growth and aiding nutrient uptake.[13] For soil-grown plants, it promotes growth by increasing beneficial microbes and reducing harmful ones.[14]
In hydroponic systems, humic acid enhances growth by improving colonization of plant growth-promoting rhizobacteria.
Figure 2. Chemical and molecular components of humic acid. Image source: Ampong, Kwame, Malinda S. Thilakaranthna, and Linda Yuya Gorim. 2022. “Understanding the Role of Humic Acids on Crop Performance and Soil Health.” Frontiers in Agronomy 4: 848621. https://doi.org/10.3389/fagro.2022.848621.
Improved hormonal activity and bio-stimulant effects
Humic acid enhances the production and activity of phytohormones like auxin and cytokinin by stimulating plant processes that either boost their production or mimic their effects.[11]
Research shows that humic acid’s hormone-like effects[12] are linked to its chemical structure, especially its non-lignin components. These effects happen through interactions with the roots or shoots. Since auxin and cytokinin also support photosynthesis, increased activity leads to greater photosynthesis, which in turn improves plant height, leaf area index and overall biomass.
As one of the most effective bio-stimulants, humic acid provides an auxin-like effect by elongating lateral root growth and aiding nutrient uptake.[13] For soil-grown plants, it promotes growth by increasing beneficial microbes and reducing harmful ones.[14] In hydroponic systems, humic acid enhances growth by improving colonization of plant growth-promoting rhizobacteria.
Increased enzyme activity and drought tolerance
Humic acid enhances the activity of enzymes such as nitrate reductase, glutamate dehydrogenase and glutamine synthetase by improving nitrate uptake and assimilation.[15] It also influences enzyme activities involved in the tricarboxylic acid cycle and glycolysis,[16] processes involved in harvesting energy. A study on hydroponically grown maize found that humic acid significantly boosted enzymes involved in nitrogen assimilation and reduction processes.[17]
Increased enzyme activity and drought tolerance
Humic acid enhances the activity of enzymes such as nitrate reductase, glutamate dehydrogenase and glutamine synthetase by improving nitrate uptake and assimilation.[15] It also influences enzyme activities involved in the tricarboxylic acid cycle and glycolysis,[16] processes involved in harvesting energy. A study on hydroponically grown maize found that humic acid significantly boosted enzymes involved in nitrogen assimilation and reduction processes.[17]
These increases in enzyme activity provide additional benefits, particularly under stress conditions. Research shows that humic acid induces antioxidant enzyme activity, helping plants recover from drought. It also promotes plant growth under drought stress by increasing chlorophyll content, antioxidase activity, relative water content and photosynthesis.[18]
Enhanced root development
Humic acid promotes the accumulation of nitric oxide, a molecule essential for root development. Research shows it can increase root thickness, fresh weight and the number of secondary roots. Additionally, humic acid application enhances root hair density and stimulates ground tissue cell proliferation in roots.[19]
Increased secondary metabolite production
Humic acid enhances the production of phenolic compounds and the synthesis of flavonoids.[20] These secondary metabolites not only help plants adapt to stressful situations but are also the chemicals responsible for cannabis’s therapeutic and psychoactive effects.
Higher yields
Studies on various crops show that humic acid increases yields, driven by many of the benefits outlined above.[21] In cannabis, researchers found that humic acid positively impacted canopy uniformity, plant height, chlorophyll content and photosynthetic efficiency. Therefore, they concluded humic acid could be a valuable tool for improving cannabis yield and quality, particularly under stressful conditions.[22]
Higher yields
Studies on various crops show that humic acid increases yields, driven by many of the benefits outlined above.[21] In cannabis, researchers found that humic acid positively impacted canopy uniformity, plant height, chlorophyll content and photosynthetic efficiency. Therefore, they concluded humic acid could be a valuable tool for improving cannabis yield and quality, particularly under stressful conditions.[22]
Benefits of fulvic acid
Fulvic acid’s lower molecular weight and higher solubility compared to humic acid give it the unique ability to pass through the micropores of biological and artificial membranes. It also acts as a natural chelator, mobilizing metal ions such as iron to enhance nutrient availability for plants.[23]
Research shows that applying fulvic acid offers numerous benefits. One study observed improved uptake of nitrogen, phosphorus, potassium, calcium, copper, iron, magnesium and zinc in cucumber plants grown hydroponically in a Hoagland nutrient solution.[24] Another study found increased nitrogen content in wild olive plants thanks to fulvic acid.[25] In maize, fulvic acid enhanced net photosynthesis, transpiration rates and intercellular carbon dioxide concentration—all contributing to improved overall plant growth.[26]
Due to these benefits and its high solubility, fulvic acid is often included in foliar fertilizers.
Conclusion
Due to the absence of soil, hydroponic systems can benefit greatly from the addition of humic substances like humic acid and fulvic acid. Humic acid promotes plant growth by activating enzymes involved in carbon and nitrogen metabolism and encourages positive morphological changes in the root system through increased nitric oxide production. Research shows humic acid is particularly effective under stressful conditions, such as drought, while fulvic acid is a highly effective chelating compound due to its small size. Both bio-stimulants are plant-friendly and non-toxic, even when applied at relatively low concentrations, making them invaluable tools for hydroponic cultivation.
Emerald Harvest Team
[1] Schroeder, Amy. n.d. “Plant Health and Soil Changes with Humic Substance Applications.” Accessed December 16, 2024. https://soils.ifas.ufl.edu/media/soilsifasufledu/sws-main-site/pdf/technical-papers/Schroeder_Amy_Immediate_Release.pdf.
[2] ScienceDirect. n.d. “Humic Substance.” Accessed December 16, 2024. https://www.sciencedirect.com/topics/earth-and-planetary-sciences/humic-substance.
[3] Britannica. n.d. “fulvic acid.” Accessed December 16, 2024. https://www.britannica.com/science/fulvic-acid.
[4] Mikkelsen, R.L. 2005. “Humic Materials for Agriculture.” Better Crops With Plant Food 89 (3): 6-10. http://www.ipni.net/publication/bettercrops.nsf/0/F49FA286830F9CC1852579800081E07E/$FILE/Better%20Crops%202005-3%20p06.pdf.
[5] Grinhut, Tzafrir, Yitzhak Hadar, and Yoda Chen. 2007. “Degradation and transformation of humic substances by saprotrophic fungi: processes and mechanisms.” Fungal Biology Reviews 21 (4): 179-189. https://doi.org/10.1016/j.fbr.2007.09.003.
[6] Ampong, Kwame, Malinda S. Thilakaranthna, and Linda Yuya Gorim. 2022. “Understanding the Role of Humic Acids on Crop Performance and Soil Health.” Frontiers in Agronomy 4: 848621. https://doi.org/10.3389/fagro.2022.848621.
[7] Eshwar, M., M. Srilatha, K. Bhanu Rekha, and S. Harish Kumar Sharma. 2017. “Effect of humic substances (humic, fulvic acid) and chemical fertilizers on nutrient uptake, dry matter production of aerobic rice (Oryza sativa L.).” Journal of Pharmacognosy and Phytochemistry 6 (5): 1063-1066. https://www.phytojournal.com/archives/2017/vol6issue5/PartP/6-5-130-778.pdf.
[8] Ampong, Kwame, Malinda S. Thilakaranthna, and Linda Yuya Gorim. 2022. “Understanding the Role of Humic Acids on Crop Performance and Soil Health.” Frontiers in Agronomy 4: 848621. https://doi.org/10.3389/fagro.2022.848621.
[9] Tavares, Orlando Carlos Huertas, Leandro Azevedo Santos, Osmario Jose Lima de Araujo, et. al. 2019. “Humic acid as a biotechnical alternative to increase N-NO3- or N-NH4+ uptake in rice plants.” Biocatalysis and Agricultural Biotechnology 20: 101226. https://doi.org/10.1016/j/bcab.2019.101225.
[10] Ampong, Kwame, Malinda S. Thilakaranthna, and Linda Yuya Gorim. 2022. “Understanding the Role of Humic Acids on Crop Performance and Soil Health.” Frontiers in Agronomy 4: 848621. https://doi.org/10.3389/fagro.2022.848621.
[11] Ibid.
[12] Primarily auxin-like.
[13] Jindo, Keiji, Fabio Lopes Olivares, Deyse Jacqueline de Paixao Malcher, Miguel Angel Sanchez-Monedero, Corne Kempenaar, and Luciano Pasqualoto Canellas. 2020. “From Lab to Field: Role of Humic Substances Under Open-Field and Greenhouse Conditions as Biostimulant and Biocontrol Agent.” Frontiers in Plant Science 11: 426. https://doi.org/10.3389/fpls.2020.00426.
[14] Li, Yan, Feng Fang, Jianlin Wei, et. al. 2019. “Humic Acid Fertilizer Improved Soil Properties and Soil Microbial Diversity of Continuous Cropping Peanut: A Three-Year Experiment.” Scientific Reports 9: 12014. https://doi.org/10.1038/s41598-019-48620-4.
[15] Jindo, Keiji, Luciano Pasqualoto Canellas, Alfonso Albacete, et. al. 2020. “Interaction between Humic Substances and Plant Hormones for Phosphorus Acquisition.” Agronomy 10 (5): 640. https://doi.org/10.3390/agronomy10050640.
[16] Canellas, Luciano P, and Fabio L Olivares. 2014. “Physiological responses to humic substances as plant growth promoter.” Chemical and Biological Technologies in Agriculture 1: https://doi.org/10.1186/2196-5641-1-3.
[17] Ampong, Kwame, Malinda S. Thilakaranthna, and Linda Yuya Gorim. 2022. “Understanding the Role of Humic Acids on Crop Performance and Soil Health.” Frontiers in Agronomy 4: 848621. https://doi.org/10.3389/fagro.2022.848621.
[18] Shen, Jie, Mei-jun Guo, Yu-guo Wang, et. al. 2020. “Humic acid improves the physiological and photosynthetic characteristics of millet seedlings under drought stress.” Plant Signaling & Behavior 15 (8): 1774212. https://doi.org/10.1080/15592324.2020.1774212.
[19] Canellas, Luciano P, and Fabio L Olivares. 2014. “Physiological responses to humic substances as plant growth promoter.” Chemical and Biological Technologies in Agriculture 1: https://doi.org/10.1186/2196-5641-1-3.
[20] Jindo, Keiji, Fabio Lopes Olivares, Deyse Jacqueline de Paixao Malcher, Miguel Angel Sanchez-Monedero, Corne Kempenaar, and Luciano Pasqualoto Canellas. 2020. “From Lab to Field: Role of Humic Substances Under Open-Field and Greenhouse Conditions as Biostimulant and Biocontrol Agent.” Frontiers in Plant Science 11: 426. https://doi.org/10.3389/fpls.2020.00426.
[21] Ampong, Kwame, Malinda S. Thilakaranthna, and Linda Yuya Gorim. 2022. “Understanding the Role of Humic Acids on Crop Performance and Soil Health.” Frontiers in Agronomy 4: 848621. https://doi.org/10.3389/fagro.2022.848621.
[22] F. Da Cunha Leme Filho, Jose, Bee K. Chim, Cameron Bermand, Andre A. Diatta, and Wade E. Thomason. 2024. “Effect of organic biostimulants on cannabis productivity and soil microbial activity under outdoor conditions.” Journal of Cannabis Research 6: 16. https://doi.org/10.1186/s42238-024-00214-2.
[23] Calvo, Pamela, Louise Nelson, and Joseph W. Kloepper. 2014. “Agricultural Uses of Plant Biostimulants.” Plant and Soil 383: 3-41. https://doi.org/10.1007/s11104-014-2131-8.
[24] Rauthan, B.S., and M. Schnitzer. 1981. “Effects of a soil fulvic acid on the growth and nutrient content of cucumber (Cucumis sativus) plants.” Plant and Soil 63: 491-495. https://doi.org/10.1007/BF02370049.
[25] Murillo, J.M., E. Madejon, P. Madejon, and F. Cabrera. 2005. “The Response of Wild Olive to the Addition of a Fulvic Acid-Rich Amendment to Soils Polluted by Trace Elements (SW Spain).” Journal of Arid Environments 63 (1): 284-303. https://doi.org/10.1016/j.jaridenv.2005.03.022.
[26] Anjum, S. A., L. Wang, M. Farooq, L Xue., and S. Ali. 2011. “Fulvic Acid Application Improves the Maize Performance Under Well-Watered and Drought Conditions.” Journal of Agronomy and Crop Science 197 (6): 409-417. https://doi.org/10.1111/j.1439-037X.2011.00483.x.
