By Mike Fidanza, PhD, John Cisar, PhD and Thomas Watschke, PhD
Biostimulants … do they work?
First, what exactly is a biostimulant? From the Latin, “bio” (~life) and “stimulus” (~a thing that evokes a specific functional reaction in an organ or tissue, or a thing that arouses activity or energy in something, or an interesting and exciting quality), these terms don’t seem to tell the whole story. The European Biostimulants Industry Council (www.biostimulants.eu) has this definition: “Agricultural biostimulants include diverse formulations of compounds, substances and other products that are applied to plants or soils to regulate and enhance the crop’s physiological processes, thus making them more efficient. Biostimulants act on plant physiology through different pathways than nutrients to improve crop vigor, yields, quality and post-harvest shelf life/conservation.”
The Association of American Plant Food Control Officials (www.aapfco.org) also includes an addition term “beneficial substances”, which means: “…any substance or compound other than primary (i.e., N, P, K), secondary (i.e., Ca, Mg, S), and microplant nutrients (i.e., Fe), that can be demonstrated by scientific research to be beneficial to one or more plant species when applied exogenously.”
Another version of this definition is that biostimulants are: “…a substance or material, with the exception of nutrients and pesticides, which has the capacity to beneficially modify plant growth.”
Interested in gaining a global perspective on biostimulants? You may want to attend the 2nd World Congress on the Use of Biostimulants in Agriculture, Nov. 12-19, in Florence, Italy (www.biostimulants2015.com). The topics covered include biostimulants and plant nutrition, abiotic stress, plant growth and development, and more.
Biostimulants … what do they do?
Dr. Richard Schmidt, Emeritus Professor of Turfgrass Science at Virginia Tech is considered the pioneer of research on turfgrass biostimulants. He once wrote that: “Biostimulants are organic materials that when applied in small quantities enhance plant growth and development.”
This is still a good definition. Some commonly reported benefits of biostimulants include: increasing plant tolerance and recovery from biotic stresses (i.e., insects pests, weeds, diseases) and abiotic stresses (i.e., heat, drought and other adverse environmental conditions); improved plant nutrient uptake (i.e., nutrient assimilation, translocation and use); improved rooting; reduced nutrient losses to the environment; enhancing soil physiochemical properties to facilitate the growth of beneficial microorganisms in the soil rootzone; and, when used as a soil amendment, the improvement of soil structure and function which translates to positive plant response, and more.
On athletic fields, mowing and traffic are two common and persistent stressors of turf, which leads to visible and detrimental surface wear. Sports turf managers should keep in mind that the turfgrass species used has an optimal range for mowing height, and that going outside that range by lowering the height-of-cut will add more abiotic stress and wear, and overall this makes the plants less tolerant of any stress. Traffic of course is a reality on athletic turf, and field rotation, goal rotation, use-time limits, overseeding and aerification are all part of reducing stress in addition to a sound fertility program which could include biostimulants.
Keep in mind, the exact mode of action of most biostimulants is poorly understood, but their function in plants has been associated with the presence of various plant signaling molecules or molecules that facilitate the transport and efficacy of mineral nutrients. Determining the exact function of biostimulants is difficult since many products contain naturally occurring or commercially added micronutrients, sugars, amino acids and other compounds that may have synergistic, complementary or no plant/soil health effects or may have been added merely for marketing or commercial registration purposes. Thus, separating the effect of one or more ingredients from the others is difficult.
Some sports turf managers have to think about reducing their reliance on synthetic fertilizers due to community pressures or fertilizer laws, and look to biostimulants for help. The difference between biostimulants and traditional fertilizers is that biostimulants operate through different mechanisms than fertilizers, regardless of the presence of nutrients in the products.
Different “types” of biostimulants
Biostimulants are derived from a wide range of materials such as living microbial cultures; extracts from microbial, animal or plant products; soil organic residues (i.e., humic and fulvic acids); industrial by-products and chemicals, synthetic molecules, and others. The Biostimulant Coalition (www.biostimulantcoalition.org) is a non-profit group of various companies that cooperate to “address regulatory and legislative issues involving biological or naturally-derived additives and/or similar products, including but not limited to bacterial or microbial inoculants, biochemical materials, amino acids, humic acids, fulvic acid, seaweed extract and other similar materials.” From their stated purpose, biostimulants are grouped into several categories.
Plant Hormones. Also referred to as phytohormones (phyto = plant), they are considered “chemical messengers.” Abscisic acid (ABA) is involved with water regulation as indicated by an increase in ABA concentrations in plant leaves under drought stress. Auxins are responsible for phototropism (shoots bend toward the light), gravitropism (roots grow downward) and cell enlargement leading to root and shoot elongation. Indoleacetic acid (IAA) is one of the more common auxins used in biostimulant products. Cytokinins promote cell division and delay leaf senescence, and gibberellic acid promotes cell elongation. It has been reported that plant hormones extracted from seaweed can stimulate the production of antioxidants, which scavenge free radicals and thus protect plant cells from damage.
Humic and Fulvic Acids. These substances typically are derived from leonardite or “brown coal,” and were named after A.G. Leonard, the first director of the North Dakota Geological Survey, in recognition of his work in this field. Benefits of these compounds include increased nutrient and water holding capacity of soils (i.e., increased cation exchange capacity), prevention or reduction in leaching of soil nutrients, chelators of organic molecules and minerals thus making them readily available for plant root absorption, increase in enzyme and metabolic activity, and more.
Seaweed Extracts. These naturally occurring products can contain phytohormones, amino acid and vitamins, mineral nutrients and other compounds that may affect plants in many ways. A pioneer in the study of humic acids and seaweed in the US is Dr. T.L. Senn, Emeritus Professor of Horticulture, Clemson University. His work dates back to the 1960s, and he published “Seaweed and Plant Growth” in 1987. Currently, Dr. Erik Ervin at Virginia Tech, and Dr. Roch Gaussoin of the University of Nebraska in Lincoln, have led the way on turf research in biostimulants and plant nutrition. Seaweed extracts, humic acids, amino acids and other products that facilitate a turf benefit either through plant hormone effects or by increase antioxidant levels have been shown in their research.
Amino Acids. Amino acids are the building blocks for proteins and enzymes. Evidently, only the “L” form of these amino acids are assimilated by plants. In plants, these L-amino acids are reported to increase roots mass, activate natural defense mechanisms, and enhance photosynthesis. For example, L-proline is an amino acid that has been shown to improve water-stress tolerance in plants.
Microbial Inoculants. There has been an increased interest with including Bacillus sp. bacteria and other microorganisms in biostimulant products to help with plant disease defense and nutrient availability. For example, mycorrhizae are fungal organisms that form a beneficial relationship with plant roots, essentially increasing the roots’ ability to absorb water and nutrients.
Other Compounds. Vitamins, proteins, various minerals, metabolites and more can be considered as biostimulants. For example, vitamin E, glutathione, beta-carotene and others provide beneficial antioxidant activity in plants. Salicylic acid, which is essentially aspirin, is used to improve plant resistance to diseases and various abiotic stresses. Plant growth regulators, soil surfactants, and perhaps other turfgrass maintenance products also may be considered as biostimulants due to their direct and indirect beneficial effects on plants and the soil rootzone environment.
Back to the question: do biostimulants work for sports turf?
The turf manager has to decide, what is the purpose of using biostimulants? Do you use biostimulants as a component of an overall turf nutrition or plant/soil health program? Do you use biostimulants to prevent and/or alleviate plant stress caused by adverse environmental conditions and excessive turf use and wear? Do you use biostimulants to enhance your current fertility program? Do you use biostimulants to help you sleep at night? Remember, there is no such product as “sunshine in bottle,” at least not yet. Ask the distributor or manufacturer for research to support product claims. Recall that AAPFCO includes “any substance or compound … that can be demonstrated by scientific research to be beneficial” as part of their definition of biostimulants. Remember, some biostimulant products may include N and Fe and other traditional fertilizer components in addition to plant hormones and various other substances. Also, work closely with local cooperative extension and university researchers to see what has been tested that could provide insight on biostimulants and sports turf.
Conventional wisdom says that the use of biostimulants on athletic fields starts with a sound turfgrass fertility program, and to address/correct any soil rootzone issues first. To really know if a biostimulant product, or any product, is working for you, you should leave a “check plot.” For example, place a 4’ x 4’ piece of plywood within the area to be treated. After the product application is made, remove the plywood and observe the site over the next several days and weeks. That way, you can make a visual comparison between the treated and untreated turf and determine if your program produces the benefit you want. Monitor and observe your turf frequently, both above ground turf and below ground roots, especially during heat/drought stress times. Biostimulants can improve plant and soil health, but does this always translate to improved turf surface characteristics (i.e., visual quality and playability)? You may need to include biostimulants as part of an overall, season-long program. Don’t expect to “squirt” once and get instant results. An alternative to treatment large areas would be to apply your chosen product or program to a small test area first and observe.
In conclusion, if you are expecting miracles, then you may be asking a lot from a little bit of product. However, biostimulants may have a place in your turf management program. If you choose to use biostimulants, have a plan. Start with an objective like improved rooting, greater turf density, or healthier turf during heat/drought stress, then develop and turf management program to include a biostimulant product(s) that addresses your objective.
Follow the program and make frequent observations for a period of time, which could be a least several months or a season, and then make evaluation or changes. Did it work or not? Why? What adjustments are needed? If the program works then you have added a valuable tool to your turf management tool box.
Mike Fidanza is Professor of Plant and Soil Sciences, Penn State’s Berks Campus, Reading, PA, firstname.lastname@example.org; John Cisar, Cisar Turfgrass Services, is retired Professor of Turfgrass Science, University of Florida, Ft. Lauderdale, and turfgrass industry consultant, email@example.com. Thomas Watschke, is Emeritus Professor of Turfgrass Science, Penn State, University Park, and currently Director of Research at Floratine Products Group, and turfgrass industry consultant; firstname.lastname@example.org.
Check the label
Some biostimulant products may have certifications on their label and marketing information. The Organic Materials Review Institute, Eugene, OR, www.omni.org) provides manufacturers and suppliers of organic products an independent review based on compliance with their organic standards, and acceptable products are OMRI Listed. The US Department of Agriculture’s BioPreferred program (www.biopreferred.gov) has been reauthorized by the 2014 Farm Bill). Managed by the USDA, the goal of the BioPreferred program is to increase the purchase and use of biobased products, which are derived from plants and other renewable agricultural, marine, and forestry materials. The USDA Certified Biobased Product label assures a consumer that the product contains a verified amount or percent of renewable biological ingredients or “biobased” content.