By Tim Butler
Nowadays, turfgrass managers are faced with the daunting task of providing excellent playing surfaces all year round, in the face of greater usage, wear and exceptionally high user expectations. Coupled with this, there has been mounting pressure from environmental and government bodies regarding nutrient loss through leaching and runoff from playing surfaces. Many feel that highly maintained turfgrass areas are receiving high quantities of fertilisers and chemicals, which may negatively impact upon water quality with problems such as eutrophication. Thus, numerous sportsturf managers are looking for new technologies to reduce inputs, while still maintaining first-rate turfgrass quality. Several products have been developed such as plant biostimulants, which have become for many a critical component in turfgrass management.
What are biostimulants?
Biostimulants are products that contain metabolites, which not only stimulate plant growth, but also are favourable to the health of plants, which is an important factor in soil fertility. Sea kelp, humic acids, plant hormones, sugars, and organic products are common components of biostimulants. Under stress plants produce ''free radicals'' or reactive oxygen molecules (e.g. hydrogen peroxide) and damage plant cells. Antioxidants regulate the plant's responses to environmental and chemical stresses and suppress free radical activity. Applying a biostimulant enhances antioxidant activity, which increases the plants defensive system and may enhance turfgrass resistance to salinity, drought and disease infection. Typically growth stimulation is best after one/two months of treatment, therefore a good biostimulant programme starts in the spring before the summer heat sets in so that the plant is fully conditioned to withstand summer stress. Turfgrass growth can be promoted by biostimulants, by stimulating nutrient uptake of nutrients such as nitrogen, phosphorus and potassium. Many commercially available biostimulant products contain both fertiliser and biostimulants mixed together.
Many important benefits of biostimulants are based on their ability to influence hormonal activity. Hormones in plants (Phytohormones) are chemical messengers regulating normal plant development as well as responses to the environment. Auxins, cytokinins and gibberellins are the principle growth-promoting hormones found in plants and control plant growth and development to one degree or another, depending upon environmental conditions. Changes in ratios of plant hormones within the plant will impact upon plant growth, for instance a higher ratio of cytokinins to auxins will promote tiller initiation and development whereas a higher ratio of auxins to cytokinins will promote adventitious rooting. Certain environmental stresses such as flooding, drought and high temperatures can limit the natural production of plant hormones.
Auxins are present in all higher plants and are of fundamental importance in plant growth and differentiation. Auxins cause several responses in plants including cell elongation, phototropism, geotrophism and root elongation. While cytokinins are considered as hormones, which regulate cell division activities, their role in the plant has gradually been recognised as being so widespread that it includes some aspects of every part of growth. Cytokinins are known to stimulate cell division, morphogenesis and leaf expansion resulting from cell enlargement and enhancement of stomotal opening. Gibberellins are noted as the most powerful of the growth promoters because they affect internode growth. They also promote uniform growth, through cell enlargement.
Kelp, (which is better known as seaweed) has been used as a fertiliser on turf for many years. Seaweed is probably the most universally recognised source of biostimulants and is contained is numerous biostimulant products. Seaweed contains major and minor plant nutrients, trace elements, alginic acid, vitamins, plant hormones and antioxidants. It has also been shown that seaweed extracts stimulate the activities of benign soil microbes. It is important to remember that soil microbes are a critical component to healthy turfgrass swards. They have been shown to increase available rootzone nutrients, enhance plant nutrient uptake, elevate photosynthetic rate and reduce pest and disease problems in turfgrass. It is believed that many newly constructed sand based rootzones have extremely low microbial activity.
Grasses grow by cell division and elongation at their base, therefore the oldest part of a leaf is its tip and the youngest its base. Mowing removes the mature parts of leaves, which, contribute to the energy balance of the plant through photosynthesis, thus leaving stem bases and immature leaves which may have reduced photosynthetic capacities. Seaweed extracts effect chlorophyll production by boosting the photosynthetic process, thereby stimulating plant growth and enhancing the plants ability to tolerate high levels of wear and low mowing heights.
Humic acids are naturally occurring organic materials originating from biological sources. Humic substances enhance the uptake of minerals through the stimulation of microbiological activity. When adequate humic substances are present within the soil, the requirement for nitrogen, phosphorus and potassium fertiliser applications may be reduced. Humic acids actually coat mineral surfaces with a membrane-like layer, which aids in the solubilization of compounds.
Microbial inoculants actually contain spores of beneficial fungi, bacteria or both. These spores are formulated into powder or water-dispersible products that can be applied to soil. Bacteria within the genera Azotobacter, Azospirillum, Enterobacter and Klebsiella are efficient, free-living, nitrogen-fixing organisms, taking nitrogen and converting it to a form that plants can use. Bacteria from the genera Pseudomonas and Azospirillum are well known for their growth-promotive effects. Fungi are also a very important component of microbial inoculants. Mycorrhizal fungi are among the most popular fungi used in inoculants. Mycorrhiza refers to an association between the plant and fungi, where the fungi colonize the plant's root system during times of active plant growth. Several types of mycorrhiza fungi form mycorrhiza with grass plants, with arbuscular mycorrhizae also known as endomycorrhiza being the most common.
As turfgrass managers, you are faced with new biostimulant products every day and I realise that it is very difficult to choose any one product. From my experience, I believe that plant biostimulants are not a wonder tool that will allow you to severely reduce inputs in your particular situation, however, I do feel that incorporating biostimulants into your management strategy will help to improve the performance of your turfgrass sward.
About the author
Tim Butler is currently studying for a doctorate degree in turfgrass nutrition at both University College Dublin, Ireland and Michigan State University, USA.
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