Using Seaweed Extracts as Biostimulants
For several years, algae extracts have been available for sale as biostimulants[1].
Description
Algae have long been used in coastal regions as soil fertilizers. This type of amendment is called seaweed. In France, algae deposits are abundant on the Atlantic coasts.
Originally used whole, as an organic amendment, algae are now increasingly used in the form of liquid extracts[2], sometimes marketed as mixtures with mineral elements, amino acids, and humic acids. Most formulations come from the brown alga Ascophyllum nodosum. This knotted rope-shaped brown alga grows in dense colonies and has been the subject of research as a biostimulant for several years.
Extraction techniques vary. Depending on the chosen method and solvent, the active ingredients preserved in the algae-based biostimulant are not the same. Thus, each commercial formulation is unique and has different effects and modes of action.[1]
Currently, the mechanisms of action of these extracts are not fully known or understood. Regardless of their origin or preparation method, these extracts are very complex and contain many mineral elements and organic constituents. Today, it is accepted that marine algae contain four types of particularly interesting components[2]:
- Colloids,
- Amino acids and mineral elements,
- Complex sugars such as alginate. Alginate acts as a chelating agent, meaning it facilitates the absorption of mineral elements present in soils.
- Phytohormones: auxin, cytokinin.
Mode of action
Although the mode of action of algae extracts is not fully elucidated, research has highlighted certain roles of algae constituents[2]:
- Phytohormones present in small quantities (mainly cytokinins) would act at the level of organ development.
- Polysaccharides would be involved in the stimulation of natural defense reactions of plants (elicitors).
- The presence of complex sugars such as mannitol and alginate would also contribute to the absorption and translocation of mineral elements thanks to their chelating properties.
- Mineral elements present in algae extracts would contribute only insignificantly to the needs of the treated plant, given the small amount of product applied.
The elicitor function of algae thus plays a role in plant protection.
Depending on the manufacturing process (action of different temperatures, alkaline medium, varying pressures) and the species of algae used, the resulting product favors one or another of the 4 main components, both in quantity and quality. But that is not all; the same product can have a different effect depending on the plant on which it is applied and the developmental stage of the plant at the time of application[2].
Algae extracts under development as biostimulants in Europe
- Ascophyllum nodosum
- Dictyota dichotoma
- Ecklonia maxima
- Laminaria sp.
- Phymatolithon (Lithothamnium) calcareum
- Macrocystis pyrifera
- Sargassum plagiophyllum
- Ulva lactuca
Properties of algae
The influences of algae on plant and soil fertility are diverse:
- Growth stimulation.
- Improvement of tolerance to water stress and cold : experiments have shown that only extracts rich in Zinc and Magnesium were effective in improving this tolerance in maize. In this case, the antioxidant properties of algae would allow the plant to better manage oxidative stress caused by ROS (Reactive Oxygen Species) in cells and thus better resist nutrient deficiency induced by cold[3][4].
- Enhancement of foliage coloration.
- Reduction of transplant shock during sowing and improvement of rooting.
- Acceleration of organic matter decomposition thanks to alginic acids[5].
- Increase in soil bacterial population[5].
- Improvement of soil water retention capacity: alginate molecules contained in algae extracts can promote the formation of a granular and aerated soil structure ideal for cultivated soils.
Characteristics to consider
- Rapid biodegradation of growth hormones
- Presence of hormones not guaranteed in most products on the market
- Use in small doses but frequently
- Often a low fertilizer formulation is associated with algae extracts
La technique est complémentaire des techniques suivantes
- ↑ 1.0 1.1 Académie des Biostimulants, online, ORGANIC BIOSTIMULANTS: The example of algae extracts
- ↑ 2.0 2.1 2.2 2.3 Louvieaux J., 2004, Measuring the effectiveness of algae extracts on grapevine (Vitis vinifera L.), under controlled conditions and in the vineyard, validated by measuring photosynthetic activity and chemical analyses, Université Libre de Bruxelles (ULB)
- ↑ Bradáčová K, W. N.-T. (2016). Micronutrients (Zn/Mn), seaweed extracts, and plant growth-promoting bacteria as cold-stress protectants in maize. Chemical Biological Technologies in Agriculture, 19.
- ↑ Jeannin I, L. J.-G. (1991). The effects of aqueous seaweed spray on the growth of maize. Botanica Marina, 469-473.
- ↑ 5.0 5.1 Thivy, F. (1964). Seaweeds manure for perfect soil and smiling fields. Salt Res. Indust., 1-4.
