Elizabeth Severson, Rachel Perry and Ajay Nair
Department of Horticulture, Iowa State University
Biostimulants are a fast-growing class of agricultural additives that may increase nutrient and water uptake, tolerance to stress, and improve root growth by supporting a variety of biological processes. These substances give a boost to a plant’s natural processes, growth, and defense mechanisms to help the plant more effectively use what is already present in its environment. These effects may, in turn, help enhance the growth and yield of crops, although research results are limited and often mixed.
Biostimulants have especially caught the attention of organic farmers and those interested in sustainable food production as a substitute for more conventional synthetic fertilizers, but many conventional farmers utilize biostimulants for their beneficial properties. From using salicylic acid to increase quality and essential oils in herbs, to applying biostimulants to potatoes late in the season to reduce shrinkage and increase skin quality, biostimulants are a wide range of products with a wide range of applications. Biostimulants products often fall into one or more of these categories below:
Humic and fulvic acids in the form of compost or vermicompost are used to increase soil organic matter which improves soil structure and function. This allows for more efficient nutrient uptake and lateral root development, mostly by increasing the soil's cation exchange capacity.
Seaweed biostimulants are well known for their promotion of plant growth. Typically made out of brown seaweeds and sold as a soluble powder or liquid, this biostimulant class is known to improve soil structure and increase the activity of beneficial bacteria, allowing plants to efficiently absorb nutrients. Seaweed can also create hydrogel networks within plants, increasing their water retention capacity.
Symbiotic bacteria species have a variety of beneficial effects on crops. While nitrogen-fixing bacteria are among the most well-known beneficial bacteria, some bacteria species can also produce compounds that increase resistance to insects and reduce the growth of soil pathogens. Additionally, some strains have been found to produce plant hormones such as auxins and cytokinins which trigger plant growth.
Arbuscular mycorrhizal fungi are a type of symbiotic fungi known for increasing nutrient uptake, especially of phosphorus, and increasing plant available water. These fungi create a large, interconnected web of plant and fungi roots by penetrating plant roots, thereby increasing both organisms' surface area for water and nutrient uptake. However, these webs are easily disturbed by tillage and fungicides.
Protein hydrolysates, or peptides and amino acids derived from animal and plant products, may increase soil fertility as well as beneficial bacteria activity. These biostimulants are often made using industrial byproducts, such as crustacean shells, collagen, and epithelial tissue.
For growers considering the use of biostimulants in their growing operation, keep in mind that the regulation and research of biostimulants is a rapidly evolving field. Currently, there is very little regulation in the United States as to what evidence a company must provide to back up the claims they make about their products. Identify biostimulants that have been researched by an accredited university or independent research facility to back up the claims the company is making. You may want to consider products that have been verified in the European Union as their regulations are much tighter and require each claim to be backed up by clear evidence.
Additionally, consider biostimulants that have been used in a set up that is similar to your own growing operation. Currently, much of the research on biostimulants is on herbs, vegetables, and other horticultural crops within greenhouses rather than row crops such as corn and soybeans. Prior biostimulants research has revealed that many products have highly variable effects depending on the crops it is used on, the timing of application, and environmental conditions. Consider working with a local extension office to perform a field trial of the biostimulants to verify that the product will be beneficial to your crops in the specific conditions they will be grown in.
Agriculture and Horticulture Development Board: https://ahdb.org.uk/biostimulants
Biological Products Industry Alliance: https://www.bpia.org/solutions-provided-by-biological-products-biostimulants/
University of Florida Extension: https://swfrec.ifas.ufl.edu/docs/pdf/plant-physiology/2019-05-Albrecht-EDIS-H1330.pdf
University of Minnesota Extension: https://blog-crop-news.extension.umn.edu/2018/12/biostimulants-what-are-they-and-do-they.html
Frontiers in Plant Science: https://www.frontiersin.org/articles/10.3389/fpls.2019.00494/full