Biostimulants are a diverse group of substances or microorganisms applied to plants, seeds, or soil with the intention of enhancing agricultural performance. These products are designed to stimulate natural processes within the plant, improving its ability to function optimally. The primary goals of biostimulant application include improving nutrient use efficiency, boosting tolerance to environmental stresses, and enhancing overall crop quality traits. Biostimulants are defined by their function, acting independently of the product’s actual nutrient content.
How Biostimulants Differ From Fertilizers
The fundamental distinction between biostimulants and fertilizers lies in their mode of action and purpose. Fertilizers are formulated to deliver essential mineral nutrients, such as nitrogen (N), phosphorus (P), and potassium (K), which are necessary for plant structure and metabolic growth. These products directly supply the elements required for photosynthesis, cell division, and other basic physiological processes.
Biostimulants, conversely, are not classified as nutrient products, even though they may contain trace elements. Their mechanism involves modifying the plant’s physiological processes. While fertilizers feed the plant directly by supplying raw materials, biostimulants improve the efficiency and resilience of the plant itself by stimulating natural growth processes, often leading to enhanced root development and improved nutrient uptake efficiency.
Major Categories of Biostimulant Materials
Biostimulant products are derived from a wide variety of sources, leading to several distinct material categories. One major class includes humic substances, which are complex organic molecules resulting from the decomposition of plant, animal, and microbial residues. These substances are commonly extracted from peat or leonardite, and include both humic and fulvic acids, known for their ability to chelate nutrients and interact with root systems.
Another common source is seaweed and algae extracts, frequently derived from brown and red algae species. These extracts contain a rich mixture of compounds, including natural plant hormones like auxins and cytokinins, complex carbohydrates, and amino acids. These components are linked to stimulating cell division and promoting growth.
Amino acids and protein hydrolysates form a significant category, often produced by breaking down plant or animal residues through enzymatic or chemical processes. These products supply the plant with pre-formed building blocks, which the plant can use directly to conserve energy.
The fourth major category consists of microbial biostimulants, which are beneficial bacteria and fungi applied to the soil or plant. These microorganisms form symbiotic relationships with the plant roots, enhancing nutrient availability, solubilizing minerals, and producing growth-promoting substances directly in the root zone.
Other materials also function as biostimulants by triggering specific physiological responses in the plant. These include:
- Inorganic compounds like phosphite or silica.
- Botanical extracts from various plants.
- Specific bacteria (e.g., Bacillus and Azospirillum).
- Fungi (e.g., mycorrhizae and Trichoderma species).
Improving Plant Resilience and Growth
The application of biostimulants leads to several measurable physiological benefits, regardless of the source material. One primary outcome is an enhanced Nutrient Use Efficiency (NUE), which describes the plant’s ability to absorb, assimilate, and utilize existing nutrients more effectively. This improvement is often associated with better root development and architecture, which increases the surface area for nutrient and water uptake from the soil.
Biostimulants are effective at enhancing Abiotic Stress Tolerance, which is the plant’s capacity to withstand environmental hardships. They help plants cope with factors like drought, high salinity, and extreme temperatures by triggering internal defense mechanisms. For instance, certain biostimulants promote osmoregulation, helping the plant maintain cellular water balance under dry conditions, and enhance antioxidant activity to reduce damage from oxidative stress.
The regulation of phytohormone pathways is a common mechanism, where biostimulants adjust the plant’s internal chemical signals to better manage growth and stress responses. Biostimulants also contribute to improved Quality Traits of harvested crops. This can include increasing the sugar content in fruits, improving the color profile, and extending the post-harvest shelf life.