A biostimulant is any compound or microorganism that is applied to plants in order to stimulate growth, enhance nutrition efficiency, and/or improve stress tolerance or crop quality. Often, the term biostimulant is used to describe those plant supplements that are neither fertilizer nor pesticide and encompasses natural substances that can be either mixtures of compounds or single entity products. Biostimulants may be classified using many different systems, but all exert their unique effects by influencing hormone levels within the plants they are applied to.

Humic and Fulvic Acids

Humic and fulvic acids are natural components of soil that are produced from the breakdown of microbial, plant and animal material. These compounds are vital contributors to soil fertility and work in the soil to enhance growth and development of plants. The major mechanism of growth promotion from humic and fulvic acid is they have the ability to enhance a plant’s uptake of micro and macronutrients and also work in the soil to increase the availability of phosphorus. Some evidence also suggests humic and fulvic acids play a role in protecting plants from certain environmental stresses like drought or cold temperatures.

Protein Hydrolysates and Betaine

Protein hydrolysates include amino acids and peptide mixtures; glycine betaine is an amino acid derivative. These nitrogenous compounds are traditionally used to provide nitrogen to growing plants. In addition to this nutritional advantage, protein hydrolysate and betaine play many roles as biostimulants. Betaine, for example, is a unique amino acid derivative that has documented anti-stress properties and may be used to enhance environmental stress tolerance. Protein hydrolysates may also contribute to soil fertility and both compounds have been shown to enhance nutrient acquisition by roots of treated plants.

Seaweed Extract and Botanicals

Seaweed is a unique substance as it may be classified as a fertilizer and as a biostimulant. As a fertilizer, seaweed and its extract provide nutrition directly to crops. As a biostimulant it may act in soils to enhance water retention, aeration, and protect against heavy metal stress. In plants, seaweed and botanicals have shown to enhance seed germination, plant establishment and growth via hormonal changes. Finally, certain protective components are found in seaweed, which suggests a potential role in environmental stress protection.

Chitosan and Other Biopolymers

Chitin or chitosan is a natural compound that makes up the cell walls of fungi. It may also be collected from seafood shells and other structural exoskeletons in the animal kingdom. As a biostimulant, chitosan exerts profound protection against environmental stresses including drought, salinity and cold temperatures, as well as protection from fungal pathogens. Other roles have been suggested, including the use of chitosan to improve quality traits of treated plants.

Inorganic Compounds

There are five main elements that work as biostimulants – aluminum (Al), cobalt (Co), sodium (Na), selenium (Se) and silicon (Si). These elements are found naturally in soil and each play a specific role in enhancing crop growth, quality, and tolerance to stress. These elements may also improve tolerance to heavy metal stress through their various mechanisms of action. The 5 essential elements act on the cell wall, osmoregulation, transpiration, thermal regulation, and uptake of nutrients and contain antioxidant properties in order to provide their many benefits.