Biostimulant
- Also known as
- plant biostimulant
A biostimulant is a substance or microorganism that, when applied to seeds, plants or the root zone, stimulates the plant's natural processes to improve nutrient uptake, nutrient use efficiency, tolerance to abiotic stress, or crop quality and yield, independent of any nutrients it contains.
What is a biostimulant?
A biostimulant is a crop input that works by prompting the plant, or the microbial activity around its roots, to perform better, rather than by supplying nutrients directly or by killing pests. The benefits it is meant to deliver are improved nutrient uptake and nutrient use efficiency, better tolerance of abiotic stress such as heat, drought or salinity, and better crop quality and yield.
Biostimulants are one category of agricultural biological, although some biostimulants are not biological in origin.
Legal definitions
In the United States, the Agriculture Improvement Act of 2018 (the 2018 Farm Bill) defined a plant biostimulant as a substance or microorganism that, when applied to seeds, plants or the rhizosphere, stimulates natural processes to enhance or benefit nutrient uptake, nutrient efficiency, tolerance to abiotic stress, or crop quality and yield. That definition does not by itself create a federal registration system; biostimulants are regulated largely at the state level, often under fertilizer and soil amendment laws.
The European Union’s Fertilising Products Regulation, (EU) 2019/1009, defines a plant biostimulant as a product that stimulates plant nutrition processes independently of its nutrient content, with the aim of improving nutrient use efficiency, tolerance to abiotic stress, quality traits, or the availability of nutrients confined in the soil or rhizosphere.
Both definitions draw the same line. A biostimulant is judged by its effect on the plant’s own processes, not by the nutrients it contains, and it is distinct from a pesticide: a product that claims to control pests or disease is regulated as a pesticide instead.
Main categories
Reviews of the field commonly group biostimulants into these categories:
- Humic and fulvic substances
- Protein hydrolysates and other nitrogen-containing compounds
- Seaweed and other botanical extracts
- Chitosan and other biopolymers
- Beneficial inorganic compounds, such as silicon
- Beneficial fungi, including mycorrhizae and Trichoderma
- Beneficial bacteria, including plant growth-promoting rhizobacteria
Microbial products appear in more than one regulatory category. A strain sold to improve nutrient availability may be treated as a biostimulant or a biofertilizer, and one sold to suppress disease as a biopesticide.
How biostimulants work
Mechanisms vary with the product. Some change root architecture, helping roots explore more soil; some influence plant hormone signaling; some protect cell function under stress; some increase microbial activity in the root zone, or make soil nutrients more available. Many products act through several of these at once, and for complex extracts the exact mechanism is often not fully known.
Using biostimulants
Biostimulants are applied as seed treatments, in furrow, through irrigation, or as a foliar application. Timing matters: products aimed at stress tolerance or reproductive growth are usually applied before or during the crop stage they are meant to protect. Because responses vary with crop, soil, weather and management, growers generally evaluate biostimulants in replicated field trials or on-farm comparisons rather than relying on a single result.
Biostimulants at Locus
Locus’s Bombigro is a foliar-applied biological that Locus describes as supporting photosynthetic activity, stress tolerance and crop development at key growth stages.
Frequently asked questions
A fertilizer supplies nutrients. A biostimulant improves the plant’s ability to take up and use nutrients, or to cope with stress, and its effect does not depend on the nutrients it contains. Some products contain both.
A biofertilizer contains living microorganisms that increase the supply or availability of nutrients, for example by fixing nitrogen or releasing phosphorus. A biostimulant is defined by its effect on plant processes and may be microbial or non-microbial. The categories overlap, and the label a product carries often reflects its regulatory route.
There is a federal definition from the 2018 Farm Bill but no dedicated federal registration system. Most biostimulants are regulated by states, usually through fertilizer or soil amendment laws. A product making pest control claims is regulated as a pesticide by the Environmental Protection Agency.
Sources
- Plant biostimulant definition, Agriculture Improvement Act of 2018, U.S. Congress
- Regulation (EU) 2019/1009 on EU fertilising products, European Parliament and Council
- Plant biostimulants: definition, concept, main categories and regulation, P. du Jardin, Scientia Horticulturae, 2015