Introduction
Faced with the current challenges in agriculture—increasing yields, climate adaptation, reducing inputs—biostimulants appear to be strategic levers.
Their effectiveness is based on the stimulation of key physiological processes such as root growth, hormonal regulation,optimization of mineral nutrition, and tolerance to abiotic stress (Du Jardin, 1991).
Unlike fertilizers, which directly supply nutrients, or plant protection products, which target pests, biostimulants do not act directly. Their purpose isto optimize plant physiology in order to improve overall performance (Calvo et al., 2014).
Origin and definition of biostimulants
The beginnings of the concept (1990–2010)
The term "biostimulant" appeared in the 1990s. As early as 1991, they were described as substances capable of stimulating the biological functions of plants at low doses, promoting the absorption of water and nutrients ( Du Jardin, 1991).
In 2006, at the Biostimolanti in agricoltura conference in Italy, they were defined as "non-fertilizing substances applied in small quantities and capable of improving plant growth"(Biostimolanti, 2006).
In 2012, Patrick Du Jardin proposed a definition that has become the standard: biostimulants are substances or microorganisms that, without directly providing nutrients, improve nutrition, quality, and tolerance to abiotic stress (Du Jardin, 2012).
Regulatory recognition (since 2019)
Since 2019, the European Union has adopted an official definition in Regulation (EU) 2019/1009, which classifies them in the PFC6 category of fertilizing products. A biostimulant is described as a product that stimulates the nutritional processes of the plant "regardless of its nutrient content, "with the aim of improving:
- Nutrient use efficiency,
- Tolerance to abiotic stress,
- The qualitative characteristics of crops,
- The availability of nutrients in the rhizosphere (EU Regulation 2019/1009).
This regulatory framework has legitimized their use and enabled CE marking for compliant products.
A complementary tool, not a substitute
To fully understand the specific nature of biostimulants, they must be considered in relation to the other two pillars of modern agronomy:
- Fertilizers directly provide nutrients (nitrogen, phosphorus, potassium, etc.).
- Plant protection products protect crops against pests (diseases, pests, weeds).
- Biostimulants, on the other hand, work differently: they do not provide nutrients or destroy pests, but optimize the plant's internal functioning so that it makes better use of available resources and responds more effectively to environmental stresses.
This logic makes them valuable allies in reducing dependence on chemical inputs without compromising productivity.
Why use biostimulants in agriculture?
Strengthening tolerance to abiotic stress
Abiotic stresses (drought, heat, salinity, frost) currently account for more than 50% of agricultural yield losses worldwide (FAO, 2022).
Biostimulants activate natural defense mechanisms: production of heat shock proteins (HSP), stimulation of antioxidant enzymes such as superoxide dismutase and catalase, and accumulation of osmolytes (proline, glycine-betaine) (Hayat et al., 2010).
Algae extracts, rich in bioactive compounds, are being studied in particular. They stimulate stomatal regulation and strengthen antioxidant mechanisms, increasing tolerance to drought and salinity (Frontiers in Plant Science, 2021; Journal of Applied Phycology, 2019).
Optimization of Nutrient Absorption
Biostimulants influence both root morphology and microbial activity in the rhizosphere. Humic and fulvic acids, for example, facilitate the transport of trace elements and improve the bioavailability of phosphorus (Soil Science Society of America Journal, 2020).
Some microorganisms used as biostimulants also promote the secretion of root exudates, which mobilize poorly soluble nutrients (Calvo et al., 2014). This results in more efficient mineral nutrition, particularly in soils poor in organic matter.
Reducing the use of chemical inputs
By strengthening plants' adaptive capacities, biostimulants make it possible to reduce the use of fertilizers and protective products while maintaining agronomic performance (Du Jardin, 2015). Their role is not to replace conventional inputs, but to optimize them in a spirit of sustainability.
When and how should biostimulants be used?
The effectiveness of a biostimulant does not depend solely on its composition: it also depends on its positioning in the crop cycle and the chosen method of application. When used correctly, they become powerful strategic tools, capable of securing yield potential at different stages.
- At start-up: certain biostimulants applied at sowing or transplanting stimulate rooting and biological activity in the soil. They promote rapid and uniform establishment, reducing losses due to early stress.
- During active growth: plant extracts or protein hydrolysates support leaf vigor and improve nutrient use efficiency. They support the plant during its development phase and optimize the use of fertilizers.
- During sensitive stages (flowering, fruit set, fruit growth): preventive application helps the plant to better tolerate hazards such as drought, heat, or salinity by activating internal regulatory mechanisms.
- Before or after a stressful event: certain biostimulants applied to the foliage or via fertigation promote resilience and/or the resumption of photosynthesis and growth, limiting losses in yield and quality.
These effects vary depending on the type of product (seaweed extract, humic acids, microorganisms, etc.), but also on the method of application (seed coating, fertigation, foliar spraying). The challenge is therefore not to follow a universal schedule, butto adapt the strategy to the context: type of crop, physiological stage, and local climatic conditions.
Conclusion
Biostimulants are now a third pillar of modern agronomy, complementing fertilizers and protective products. Their value lies in their ability to:
- Increasing crop resilience to climate stress,
- Improve nutrient and water use efficiency,
- And actively contribute to the sustainability of agricultural systems.
By harnessing the natural physiological mechanisms of plants, they pave the way for agriculture that can reconcile performance, adaptation, and respect for resources. More than just an innovation, they represent a strategic lever for preparing agriculture for the challenges of tomorrow.
In the next article, we will take a more scientific and detailed approach, exploring the different families of biostimulants —organic and microbial—and analyzing their specific modes of action. This technical dive will provide a better understanding of how these solutions actually work within the plant and its rhizosphere.
References
- Calvo, P., Nelson, L., Kloepper, J. (2014). Agricultural uses of plant biostimulants. Plant and Soil.
- Du Jardin, P. (1991). Biostimulants and their role in sustainable agriculture. Journal of Agricultural and Food Chemistry.
- Du Jardin, P. (2012). Biostimulants: Definition and Applications. Biostimulants in Modern Agriculture, Conference Proceedings.
- Du Jardin, P. (2015). Plant biostimulants: Definition, concept, categories, and regulation. Scientia Horticulturae.
- FAO (2022). The State of Food and Agriculture.
- Frontiers in Plant Science (2021). Seaweed extracts in agriculture.
- Hayat, S., et al. (2010). Environmental and Experimental Botany – Role of salicylic acid under abiotic stress.
- Journal of Applied Phycology (2019). Seaweed extracts in agriculture.
- Soil Science Society of America Journal (2020). Biostimulants and nutrient use efficiency.
- Rouphael, Y., Colla, G. (2020). Biostimulants and crop quality improvement. Frontiers in Plant Science.
- European Regulation (EU) 2019/1009. Official definition of biostimulants.
Disclaimer
The aim of this series is to share practical information on biostimulants. Each month, a new topic will be covered, based on our expertise and research.
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