Agro-environmental applications of humic substances: A critical review (original) (raw)

Humic and fulvic acids as biostimulants in horticulture.pdf

Maintaining food production for a growing world population without compromising natural resources for future generations represents one of the greatest challenges for agricultural science, even compared with the green revolution in the 20th century. The intensification of agriculture has now reached a critical point whereby the negative impacts derived from this activity are now resulting in irreversible global climate change and loss in many ecosystem services. New approaches to help promote sustainable intensification are therefore required. One potential solution to help in this transition is the use of plant biostimulants based on humic substances. In this review we define humic substances in a horticultural context. Their effects on nutrient uptake and plant metabolism are then discussed and a general schematic model of plant-humic responses is presented. The review also highlights the relationship between the chemical properties of humified matter and its bioactivity with specific reference to the promotion of lateral root growth. Finally, we summarize and critically evaluate experimental data related to the overall effect of humic substances applied to horticultural crops. Current evidence suggests that the biostimulant effects of humic substances are characterized by both structural and physiological changes in roots and shoots related to nutrient uptake, assimilation and distribution (nutrient use efficiency traits). In addition, they can induce shifts in plant primary and secondary metabolism related to abiotic stress tolerance which collectively modulate plant growth as well as promoting fitness. In conclusion, the exogenous application of humic substances within agronomic systems can be used to aid the development of sustainable intensification. As most humic substances used in agriculture are currently derived from non-renewable resources like coal and peat, the promotion of this technology also requires the development of new sustainable sources of humic products (e.g. organic wastes).

Application of Humic Substances Results in Consistent Increases in Crop Yield and Nutrient Uptake

Journal of Plant Nutrition, 2009

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Properties of Humic Acid Substances and Their Effect in Soil Quality and Plant Health

Humus and Humic Substances - Recent Advances

During aerobic and anaerobic decomposition of plant and animal reside a complex aggregate of brown to dark coloured amorphous substances is obtained which is called as Humus. It includes humic substances and resynthesizes products of microorganisms. These products are stable and a part of the soil. Humus is categorised according to their molecular weights and solubility into humus, humic acids and fulvic acids. Humic substances are the organic material naturally present in soil. Humic substances positively effect’s soil quality and fertility by increasing its water holding capacity, stabilisation of soil structure, soil microbial activity, plant physiology. It also influence nutrient uptake and root architecture act like phytohormones for phosphorus acquisition, and improving plant adaptation to saline condition. Humus is the primary microhabitat for microorganism such as dictyostelids, myxomycetes, some species of protostelids, members of the genus Copromyxella etc. Other than that...

Review : Humic and Fulvic Acids . A Practical Approach

FERTASA Symposium, 2015

INDEX 1. General description and basic chemistry of humic and fulvic acids 2. Methods of extraction of humic and fulvic acids. 3. Sources and characteristics of products from different sources. 4. Chemical characteristics 5. Physical characteristics 6. Biological characteristics and soil biological activity 7. Product claims and facts 8. Dosage response and optimal dosages 9. Registration requirements and registration 10. Practical guidelines for farmers 11. What questions should farmers ask 12. Conclusion 13. References 1 GENERAL DESCRIPTION AND BASIC CHEMISTRY Waksman defined humus as "a complex aggregate of brown to dark colored amorphous substances, which have originated during the decomposition of plant and animal residues by microorganisms, under aerobic and anaerobic conditions, usually in soils, composts, peat bogs, and water basins". Soil Organic Matter or humic substances (HS) which are the largest constituent of soil organic matter (∼60%) and are considered as a...

Biochemically active humic substances in contrasting agricultural managements

Spanish Journal of Agricultural Research, 2016

ing (IEF) on the basis of the isoelectric point of the humic substances. IEF did not modify either the enzyme activity or the molecular structure of the complexes (Benítez et al., 2000; Ceccanti et al., 2008). Beta-glucosidase activity has been proposed as a good indicator for soil functions because its critical role on soil-carbon cycle (Nannipieri et al., 2012). The importance of extracellular β-glucosidase lies in the capacity of the soil to hydrolyse C substrates too large or insoluble for direct absorption by microbial cells. The characterization of stable humic-β-glucosidase compounds could assess the ability to fulfil essential Short communication oPEn accESS

Humic Extract as a Biostimulant in Crops Subjected to Abiotic Stress

Agrociencia, 2023

Because abiotic stresses pose significant challenges to the growth and productivity of crops, the development of plants with greater survival and growth when exposed to unfavorable situations is an objective of several research groups. Biostimulants are substances or microorganisms that, when applied to crops through the foliar or root pathways, serve to enhance various processes related to growth and development. These processes include nutrient absorption, tolerance to environmental stress, and overall harvest quality. Interestingly, biostimulants can achieve these effects even when they possess a low concentration of nutrient elements in their composition. Among the main and most often used biostimulants are plant hormones, algae extract, mycorrhizal fungi, protein hydrolysates, and humic substances (humic and fulvic acids). This review sheds light on the biostimulant effects of applying humic substances to plants experiencing hydric stress conditions and low rainfed cultivation. Additionally, it aims to identify gaps in the current research and highlights areas that require further investigation. Furthermore, the review provides a concise overview of the origin and progression of research on humic substances (HS), including their extraction and obtaining process, as well as their structural characteristics and the relationship between structure, properties, and functions. The review also presents the research findings that support the potential of humic substances influencing crops affected by abiotic stress. These findings highlight the beneficial effects of humic substances in enhancing the resilience and performance of crops facing challenges such as drought, salinity, temperature extremes, and other non-biological stressors. The evidence underscores the significance of humic substances as a valuable tool in mitigating the detrimental impacts of abiotic stress on crop productivity and overall plant health.

Understanding the Role of Humic Acids on Crop Performance and Soil Health

Frontiers in agronomy, 2022

Humic acids (HA) are organic molecules that play essential roles in improving soil properties, plant growth, and agronomic parameters. The sources of HA include coal, lignite, soils, and organic materials. Humic acid-based products have been used in crop production in recent years to ensure the sustainability of agriculture production. Reviewed literature shows that HA can positively affect soil physical, chemical, and biological characteristics, including texture, structure, water holding capacity, cation exchange capacity, pH, soil carbon, enzymes, nitrogen cycling, and nutrient availability. This review highlights the relevance of HA on crop growth, plant hormone production, nutrient uptake and assimilation, yield, and protein synthesis. The effect of HA on soil properties and crops is influenced by the HA type, HA application rate, HA application mode, soil type, solubility, molecular size, and functional group. This review also identifies some knowledge gaps in HA studies. HA and its application rate have not been tested in field experiments under different crops in rotation, nitrogen fertilizer forms, sites and climatic conditions. Furthermore, HA chemical and molecular structures, their water and alkaline soluble fractions have not been tested under field experiments to evaluate their effects on crop yield, quality, and soil health. The relationship between soil-plant nutrient availability and plant nutrient uptake following HA application should also be further studied.

Influence of humic acid on increase yield of plants and soil properties

2014

Humic acids are heterogeneous, which include in the same macromolecule, hydrophilic acidic functional groups and hydrophobic groups. A distinction on the effects of HAs should be made between indirect and direct effects on plants growth. Under water stress, foliar fertilization with humic molecules increased leaf water retention and the photosynthetic and antioxidant metabolism. Several studies showed that humic acid increase root length, root number and root branching. Stimulation of root growth is generally more apparent than shoot growth (Nardi, 2002).