The biostimulant category in the United States remains loosely defined--at least legally. Biostimulants do not fall under the EPA regulatory authority designated by the Federal Insecticide, Fungicide, and Rodenticide Act.
However, it’s important to understand the current landscape for this emerging product class, as well as for other foliar applied crop nutrition products like foliar feeds and Plant Growth Regulators (PGRs). Understanding these different groups will help you determine the best economic returns for your farm.
What is a Biostimulant?
Biostimulants have been defined internationally. Europe, which has the largest biostimulant market, has created the following definition via the European Biostimulants Industry Council:
“Biostimulants contain[ing] substance(s) and/or micro-organisms whose function when applied to plants or the rhizosphere is to stimulate natural processes to enhance/benefit nutrient uptake, nutrient efficiency, tolerance to abiotic stress, and crop quality.”
In the United States, where there is no legal definition, most states require products that fall under the biostimulant category based on academic definitions to be registered as fertilizers.
Foliar Feeds, PGRs and Biostimulants: What’s the Difference?
Foliar applied nutritionals and plant health products fall into one of three main categories:
Foliar Fertilizers - Foliar fertilizer directly provides macronutrients and micronutrients to a plant through the application of liquid fertilizer onto the leaves of crops. Plants are able to absorb essential elements through their leaves. Foliar fertilizers may be complexed and/or chelated to prevent element tie-up and improve nutrient availability.
Plant Growth Regulators (PGRs) - PGRs are regulated by the EPA and defined as "any substance or mixture of substances intended, through physiological action, to accelerate or retard the rate of growth or maturation, or otherwise alter the behavior of plants or their produce. PGRs contain plant hormones such as gibberellic acid and cytokinin. Additionally, plant regulators are characterized by their low rates of application; high application rates of the same compounds often are considered herbicidal.”
There are five general classes of PGRs: auxins, cytokinins, gibberellins, abscisic acid, and ethylene. Each type of growth regulator has a different effect on plants. According to the EPA’s Label Review Manual, whether a product is considered to be a plant growth regulator or not depends on whether the plant response or mode of action being claimed would go beyond what would be expected from simple nutrition. The composition of the product may aid in making the determination.
Biostimulants - Biostimulants do not contain plant hormones--unlike PGRs--and are not considered foliar fertilizers, although some may contain small amounts of nitrogen. Instead, they act as signaling agents to help plants increase the production of their own hormones. They are not to be confused with biopesticides, which are made from natural materials and target specific pests, or biofertilizers, which are microbials that are used to enhance nutrient uptake from soil.
Biostimulants also provide a variety of plant health attributes, including antioxidant properties, increased nitrogen efficiency, improved production of amino acids, and greater resistance to abiotic stress.1 The use of a biostimulant can help crops recover from external stresses, including periods of cold, heat or drought stress.2 Biostimulants represent an interesting frontier in economically beneficial crop production techniques. At some point, simply applying more fertilizer reaches a point of diminishing return. The right biostimulant can improve crop performance past the point at which applying more fertilizer is no longer practical.
It is possible for a farmer to utilize both PGR’s and biostimulants in intensively managed crops. They have different functions and purposes, and contain different substances. Some crop nutrition and plant health products on the market today may in fact contain combinations of PGRs, biostimulants and/or foliar fertilizers.
Most biostimulants are foliar applied. However, new research shows the benefits of applying biostimulants in-furrow. Biostimulants fall into one of several categories:
Protein Hydrolysates - amino acid based biostimulants obtained from animal or vegetable sources. The best ones are extracted from vegetable matter, usually soybeans, by enzymes.
Organic Acids - usually humic or fulvic
Seaweed extracts & botanicals - derived from kelp, algae or terrestrial plants
Chitosan and other biopolymers - often obtained from crustacean shells
Inorganics - minerals such as cobalt or silicon
Beneficial organisms including fungi or bacteria
Understanding this quickly-developing product class along with other classes of foliar fertilizer can help you make powerful purchasing decisions that affect your crops and your bottom line.
1 Van Oosten,, Pepe, De Pascale, Silletti and Maggio, "The Role of Biostimulants and Bioeffectors as Alleviators of Abiotic Stress in Crop Plants". Chemical and Biological Technologies in Agriculture.
2 Du Jardin, P. "The Science of Plant Biostimulants - a Biblographic Analysis." Chemical and Biological Technologies in Agriculture.