Recent scientific turfgrass research indicates biostimulants can help plants better survive and recover from stress conditions such as heat, drought and high salinity, as well as improve nutrient uptake.
Biostimulants literally means a group of ingredients that stimulate life. The term usually refers to compounds that promote favorable responses by affecting plant physiology, including primary metabolic processes such as photosynthesis, defense mechanisms and nutrient uptake. Biostimulants also have been described as nonnutritional products best used for turfgrass stress management.
Currently, the three major biostimulant classes are humic substances, amino acid-containing products and hormone-containing products, including those containing auxins and cytokinins. Overlap can occur between these categories. For example, humic substances contain auxins and cytokinins.
Research with humic substances has been extensive because of their use in agriculture. They can improve nutrient uptake from the soil, increase water-holding capacity, improve infertile or sodium/salt dominated soils, and remove toxins such as heavy metals.
Amino acid-containing products provide amino acids that act as chelating agents, which facilitate the most efficient foliar nutrient uptake, in addition to improving turfgrass stress tolerance. These products contain little nutrient value; however, many contain free amino acids, complex polysaccharides and natural phytohormones.
Research shows that when applied as a foliar, amino acid-containing products can improve the heat-stress physiology of perennial ryegrass (Kauffman III et al. 2007). Scientists conducted this research in the controlled environment of a greenhouse with the understanding there may be more variability in the field.
The exact mechanism as to how amino acid-containing substances work to improve stress tolerance remains unknown. One hypothesis contends that supplying plants with free and naturally occurring amino acids allows turfgrasses to conserve energy otherwise used for amino acid production, thereby improving plant metabolism and subsequently stress tolerance.
Hormone-containing products often contain sea kelp (commonly called seaweed or seaplant extract). Both auxins and cytokinins have been identified in seaweed and both improve heat-stress tolerance (Sanderson and Jameson, 1986; Sanderson et al., 1987). Rutgers University research using root-applied (rather than foliar-applied) cytokinins showed improved heat-stress tolerance (root viability) of creeping bentgrass (Liu et al., 2002; Liu and Huang, 2002).
Amino acid and hormone-containing products should be used as part of a sequential and preventive program. Superintendents shouldn’t take this approach if visual observation of turfgrass stress has already occurred. Ideally, it’s best to apply biostimulants four to six weeks before the onset of environmental stress.
Biostimulants don’t cause overt responses like better color, substantial increases in root growth or increased clipping yields. Plant responses to biostimulants are subtle and long lasting. They promote better defense against biotic (i.e. pathogens) and environmental, or abiotic, stress (i.e. drought, heat, salinity) followed by quicker plant recovery.
In other words, biostimulants can improve overall plant health. Turfgrass responses to biostimulants are more difficult to detect than overt responses such as darker turf color; however, promoting overall plant health and implementing the most effective stress management programs, including integrated pest management, remain vitally important. If turfgrasses treated with biostimulants are strong enough to recover following disease pressure, drought conditions, high salinity, and/or heat stress, it’s likely the biostimulants are providing significant benefits. It’s important to be a keen observer of turf performance and vigor during this recovery period. That may be the best way to assess plant health and subsequently the effectiveness of biostimulants.
There’s an additional benefit. Compared to pesticides, biostimulants are applied at low rates to change plant metabolism and are used as part of a plant stress-management program.
Biostimulants are relatively new to the turf marketplace and only recently have scientists accelerated efforts to study and document their potential benefits. Therefore, it’s important always to ask for product research data and make sure those results support claims and marketing materials. GCI
References cited
- Kauffman III, G.L., D.P. Kneival, T.L. Watschke. 2007. Effects of a biostimulant on the heat tolerances associated with photosynthetic capacity, membrane thermostability, and polyphenol production of perennial ryegrass. Crop Sci. 47: 261-267
- Liu X., B. Huang, and G. Banowetz. 2002. Cytokinin effects on creeping bentgrass responses to heat stress: I. Shoot and Root Growth. Crop Sci. 42:457-465.
- Liu X., and B. Huang. 2002. Cytokinin effects on creeping bentgrass response to heat stress II. Leaf senescence and antioxidant metabolism. Crop Sci. 42:466-472.
- Sanderson, K.J., and P.E. Jameson. 1986. The cytokinin in a liquid seaweed extract: Could they be the active ingredients? Acta Hortic. 179:113–116.
- Sanderson, K.J., P.E. Jameson, and J.A. Zabkiewicz. 1987. Auxin in a seaweed extract: Identification and quantification of indole-3-acetic acid by gas chromatography-mass spectrometry. J. Plant Physiol. 129:363–367.
