(Above) Kyle Waters, turf manager for the Home Depot Center in California, displays root growth 30 days after biostimulants were applied.
The word biostimulants can mean a lot of things depending on who you are talking to and what you are talking about. In the Green Industry, or when we are specifically dealing with turfgrass stands, a biostimulant is an organic compound that aids in stimulating turfgrass growth. Another description could be that it is the opposite of a plant growth regulator. Within the turfgrass plant there are natural biostimulants that are called plant growth hormones and they have been around since the beginning of time.
What are biostimulants?
There are several that exist as we know it and it is certain that more will be identified as we progress into the future. While biostimulant technology is loosely used in our industry, there is a most definite difference in what truly makes a biostimulant and what makes one more effective than another.
Not only does the presence or absence of these hormones have a direct impact on whether a plant grows or not or even how it grows, the balance of one hormone to the rest is of most importance. For instance, the hormone ethylene is a compound readily produced in turfgrass stands. It is necessary to slow the production of other hormones that may otherwise grow a plant to death. When a root system reaches a limiting factor in the soil such as anaerobic (no oxygen) conditions or physical barriers, the production of ethylene rises. As this level rises, the levels of other hormones necessary for cell division such as cytokinins and auxins proportionately declines. With slowed cell division, we get slowed growth. Since most cell division occurs in the root system with nearly 18,000 cells being potentially divided each twenty-four hour period in a turfgrass stand, this will make a huge impact on essential growth necessary for key compounds to be formed within the plant. These compounds will be used for energy storage, growth, production of anti-stress compounds that will fight off disease and pest invasions, and many other beneficial and necessary reactions that will allow a turfgrass stand to meet or exceed the demands of our industry.
While any product that contains these growth hormones in one form or another is called a biostimulant, only the product that dials in the relationship of several key hormones to each other will truly allow us to help the plant achieve what it needs to achieve while meeting our demands. For instance, as we mow turf regularly (every day on putting greens) and at heights of cut well below what the plant would grow to in a natural unhindered environment, we throw these growth compounds out of whack so to speak. Gibberellic Acid (GA) for instance is a key growth stimulating hormone that is produced in the leaf tips. As we let a plant grow in a natural state its level is kept in balance with Cytokinins and Auxins which are mostly produced in the root tips and plant crown respectively. However, as we mow the leaf tips off the level of GA is reduced and the natural response in the plant is to reduce the levels of Cytokinins and Auxins as well. When this happens, we simply get a reduction in root mass. There is always a direct relationship between top growth and root growth as they want to maintain a somewhat proportional relationship. But we want to have a low height of cut with extensive roots as the roots serve as a means for taking in water and nutrients from the soil, providing stability and storing many types of sugar-based compounds that will be called on when the plant needs them.
To achieve our objective, properly utilizing the correct biostimulant compound that has the desired growth hormonal products in the proper ratios to meet our needs is vital to producing the turfgrass stand we desire. Many pesticides include growth stimulating hormonal compounds in their chemistry to aid the turf in recovery processes. However, much research now exists to show that we can greatly improve the plant’s natural defense against pests by improving its growth efficiency which is certainly possible when utilizing proper biostimulant technology. Another example would be when we consider a cool season (C3) turfgrass stand such as Creeping bentgrass or Poa annua as the turf is preparing for dormancy. Certain sugar storage compounds are produced just prior to the plant entering dormancy. If we maximize this growth and natural compound production through extensive root and lateral stem growth, we better the chances for the turf as it wakes from dormancy the following spring. The same can apply to warm season (C4) grasses such as Bermudagrass, Zoysiagrass and Seashore paspalum. As these grasses come out of dormancy, research now shows a direct correlation between the plant’s ability to utilize these storage sugars and whether or not it declines in growth just after dormancy break. In other words, as the storage energy is utilized and the energy needs are not met just when the plant needs it most (a lot of internal growth and reactions take place just out of dormancy), the plant can literally run out of reserves to meet its needs for growth to take place. We can maximize the energy built up in the plant and meet those maintenance needs by stimulating site specific growth through the proper use of biostimulants.
In a final note we can consider how the plant reacts to a nitrogen input. Many apply nitrogen and see a nice green color response followed by some growth. This growth is typically in the form of leaf growth or top growth. Just as internal compounds dictate growth, this flush of top growth will occur from nitrogen inputs at the expense of root growth. This is quite the opposite of what we truly want to occur when managing turfgrass stands for golf and sports. We need nitrogen but we want it to be utilized most effectively. With proper nitrogen utilization and the use of specific biostimulants, we can target this energy to go where we most need it which is a balance of top growth with an abundance of root growth. There is no doubt that much nutritional research in the coming years will be targeted toward maximizing what many have seen in the field already through experience…desired growth through the proper use of biostimulants.
Carmen Magro, CGCS, is Senior Agronomist, Floratine Products Group.