New Horizons for Seaweed Extracts in Sportsturf Maintenance

Dr Henry Lyons, B.Sc,Ph.D, C.Chem.FICI,FRSC

 

A common factor in many of my meetings and discussions with turf professionals over the years is the confusion that surrounds the science behind seaweeds - much of this confusion is generated by commercial claims that are given poetic licence by marketing and sales personnel. Hereunder are some of the more common themes for debate that have been put to me during the course of my career.

 

Q. All seaweeds are the same?

A. No, not at all. There are as many seaplants as land plants and the variety and diversity is just as complex. The Algabase seaweed database lists over 123,000 different seaweeds. They are classified into families much the same as plants and animals. The three main classifications are by colour - red, green and brown.

Within these classifications there can be major differences, e.g. brown seaweeds that are constantly immersed in water (sub-tidal) and those that are under water part of the time and exposed to the elements on the shoreline for the rest of the time (inter-tidal).

Ascophyllum nodosum

 



Q. Seaweed is a nuisance with minimal commercial value?

A. Quite the opposite in fact. The seaweed industry is estimated to be worth over £6 billion annually with more than 80% of this coming from the food industry. Common everyday products such as ice-cream, beer and toothpaste may contain seaweed derived ingredients.

 

 

Q. Seaweed is a muck and magic product with little scientific basis?

A. Research on the use of seaweeds in plant care has been ongoing for more than fifty years. Several universities became very well known for the volume and depth of research with significant centres being Trondheim in Norway, Portsmouth in the UK, Clemson and Virginia in the USA.

Several industry led projects on bioactives from seaweed are currently underway in Ireland, UK and EU with funding coming from both national and international research agencies. It is expected to fill in the gaps in existing knowledge and produce sound scientific data in three years' time on which future applications can be based. Seaweed is a complex natural storehouse of biomolecules and unlike synthetic chemicals the activity is frequently due to a combination of effects and this makes it particularly difficult to identify and explain.

 

 

Q. Why is Ascophyllum nodosum promoted so strongly?

A. Ascophyllum nodosum is the species which has been used most extensively for the past sixty years and which has been the subject of several hundred research papers and reports based on trials carried out in universities and research institutes. This brown seaweed is only found in the temperate waters of the North Atlantic but the extracts have been widely used in all continents. In more recent years commercial extracts from some other brown seaweeds such as Ecklonia maxima and Macrocystis have come on the market and have been the subject of scientific trials and reports.

All seaweeds are continuously exposed to stress but intertidal species such as Ascophyllum have to grow and survive in conditions fluctuating between immersion in temperate salt water and exposure to blistering sunshine or deep frost on bare rocks in dry surroundings for several hours each day. This is the driving force behind the production and accumulation of an arsenal of stress resistant substances which can also come to the assistance of terrestrial plants such as turf grass in stressful situations ranging from frost to intense solar radiation and from very wet to drought conditions as well other stresses such as those arising from high salt levels in the soil.

 

 

Q. Hot processes destroy the beneficial growth hormones?

A. An intriguing question and the on that results in the main from the claims and counter claims of commercial companies eager to differentiate their product and claim supremacy in the quest of sales.

There is a variety of ways of liquidising seaweeds ranging from cold, physical mechanical processes to

enzymatic and high temperature hydrolysis. It would be outside the scope of this brief general article to describe each method in detail - in fact there is much scope for variation within these processes e.g. pH, temperature, pressure etc.

It should be noted that all processing methods have some effects on the plant components ranging from high shear mechanical stress in milling and shredding to high temperature in hot processes. The effects are not always negative ones as there are several examples of heat conversion of inactive substances into active forms especially in the food industry.

Cold processes are basically cell disrupting techniques commonly used for land plants for the release of components of interest to be used in food and drinks. In the case of seaweed extracts it sometimes claimed that plant growth hormones are deactivated by high temperature extraction but I have never seen scientific evidence of this.

On the contrary an M.Sc project at the University of Limerick in 2006 showed no change in concentration levels of IAA, adenine, kinetin and Gibberellic acid on autoclaving in aqueous media for prolonged periods, under the same conditions used in industrial high high temperature extraction processes. So, even if these were the real active components, the use of elevated temperature would have little or no effect on their stability.

In general low temperature extraction is more energy efficient and eco-friendly but this may be outweighed by the lower solids content and suitability for spraying through fine nozzles of the extract obtained.

The ultimate test is the benefits observed when used and I have yet to hear of a process that yields a product that does not work.

 

 

Q. What are the relative merits of the various methods of obtaining Seaweed extracts?

A. There have been claims and counterclaims concerning the merits of these processes. Up to recent times it was difficult to refute the arguments of the low temperature supporters that their methods were superior as the mild conditions did not cause degradation of heat sensitive biologically active molecules although I have never seen any scientific research reports to back up this claim. Now that oligosaccharides, humic acids and amino acids are gaining favour as the real active ingredients in biostimulant cocktails the pendulum has swung back in favour of liquids obtained by high temperature processes. Take Ascophyllum nodosum for example as it is the seaweed species most commonly used and also the most researched species. It contains approx 50% carbohydrate (mainly alginate, a long chain polysaccharide), 7% protein and 9% polyphenols as well as minerals and small amounts of other organic molecules. Mild alkaline hydrolysis of this seaweed at high temperature converts the polyphenols to humic acids and the long chain carbohydrates are broken down to form short chain sugars i.e. oligosaccharides. These biostimulants are then present at high levels (per cent) in comparison to the traditional plant growth hormones which ,if they survive, would be measured in ppm (parts per million) or ppb (parts per billion). It is thought that these oligosaccharides act as 'elicitors' i.e. they elicit the plant to produce its own natural plant hormones.

In spite of what salesmen and brochures may claim it is a fact that irrespective of the process used you will see a "seaweed effect" particularly if the extract is derived from Ascophyllum nodosum, the most researched seaweed in the world.

 

 

Q. Are seaweed extracts of any use in nematodes control?

A. Yes, nematode infestation is a problem in some golf courses. Trials have shown that liquid seaweed extracts have a beneficial effect against several types of nematodes including the root knot nematodes. The majority of the published research carried out to date used alkaline Ascophyllum nodosum extracts and there are no scientific reports of comparisons with other extracts in the literature.Seaweed extract on its own will rarely lead to acceptable levels of control for any nematode problem.

It should be borne in mind that liquid seaweed extracts are not nematicides, their effects are probably due to the stimulation of antagonists to the nematodes in the soil and maybe the physical blocking of the sensory apparatus of the nematodes. They will also have direct effects on the plant, stimulating the natural defence systems against nematode attack as well as stimulating early plant growth, especially root growth.

For optimum results against the nematodes the levels of Seaweed Extract required in the top 15 cm of soil would be rather high and uneconomical in most cases.(it would be much higher than the level recommended for biostimulation /growth benefits). In practice a balance should be struck, say 2-3 litres per hectare of Seaweed Extract each week. To summarise, they have a beneficial effect but are not regarded as nematicides.