Green fingers: seaweed as a biostimulant
Seaweed is a crop with huge potential, but many of its current applications are comparatively low value. Harvested wild seaweed has, for example, long been used in an unprocessed form as a simple fertiliser. Using seaweed as a source for targeted biostimulants can, however, be a better way to extract value.
Gordon McDougall is a Senior Research Scientist and Head of Plant Biochemistry and Food Quality Group at the James Hutton Institute. As he explains, biostimulants and fertilisers have different roles.
Fertilisers are used to provide nutrients a plant needs for growth, typically nitrogen (the most important in terms of bulk), phosphorus and potassium (NPK).
In contrast, biostimulants act in a range of ways to help the plant absorb nutrients more efficiently, or to help it become more resilient in the face of challenges such as disease or drought.
As McDougall puts it: “‘Biostimulant’ is a kind of all-encompassing phrase for something that helps the crop to perform better.”
For example, some biostimulants have been found to strengthen resistance to bacterial or fungal diseases. Another way in which they can be effective is to stimulate early root growth, which in turn means the plant can absorb more nutrients from the soil.
McDougall says: “The nutrient use efficiency of the plant will increase and that’s a really interesting area, because if you can apply less nitrogen and less phosphorus to your crops and get a better effect, then that’s got to be ideal. There’s heavy pressure on a lot of farmers to reduce the amount of fertiliser they use.”
That has not only economic benefits but also environmental benefits.
The Hutton Institute is looking at how to grow crops like barley using less fertiliser, using genetic information to breed a more efficient strain, but also using a variety of biostimulants.
McDougall says: “The best barley tends to be a bit nitrogen hungry, so if you can find some way of making it perform just the same with much less nitrogen being applied, you’re on to a real winner.”
Seaweeds have been found to act as biostimulants – but not all seaweeds are created equal. Their properties vary by species, season and the extractive process applied.
For example, as McDougall explains, the carbohydrate composition of a given crop of seaweed will change massively over the course of a season, and some of these changes may be significant for their effectiveness as a biostimulant.
The Hutton Institute can benchmark the effectiveness of a biostimulant in a number of ways. First, researchers can analyse its chemical composition and compare it against other seaweeds which have known biostimulant effects. They can also run benchmarking trials, from small-scale ones in greenhouses to full-scale field trials, to see how the target crop grows with and without the seaweed extract.
As well as measuring outcomes, understanding the chemical and genetic mechanism by which a biostimulant operates is important to McDougall as a scientist.
He says: “The idea that just spraying a seaweed extract on a plant can make it work better is still very intriguing to me.”
It is also important to note that any biostimulant needs to be appropriate to the target crop – it is not “one size fits all” – and the timing of application can also be crucial. If a biostimulant is applied either too early or too late in the growing cycle, it may not be effective.
Help from kelp
Dale Kingston is a co-founder of Channelled Atlantic, based in the south-west of England. The company processes sugar kelp (Saccharina latissimi) from local seaweed farmers, using fermentation to create a combined biostimulant and fertiliser.
As Kingston explains: “A lot of soils are poor in trace minerals, but our seaweed contains almost all the trace minerals they need.”
In fact, analysis shows that sugar kelp contains 15 out of 16 trace elements needed for plant growth (the other being boron).
Kingston says the fermentation process breaks down large molecules such as the polysaccharide sugars found in kelp into a more easily absorbed form.
The product is targeted at agriculture, especially regenerative and organic agriculture; horticulture; and greenkeeping for estates and sports facilities. It is particularly helpful, Kingston says, for farms making the transition to organic production, where conventional farming methods have led to the soil being depleted of its nutrients. The microbes present with the seaweed can also benefit the soil.
He argues that fermenting seaweed in this way (Channelled Atlantic is one of only two UK companies doing this) makes it more accessible to plants as a biostimulant.
Ascophyllum nodosum, the seaweed most widely harvested wild as a biostimulant, has stress-reinforcing properties to help against challenges such as drought, Kingston says, but sugar kelp has great germination and root growing properties.
Feedback from customers has been good. Kingston says: “We had one farmer say, for example, that yield consistency as well as the health of his crops improved, measured using yield mapping from his combine and BRIX [plant sugars] as a proxy.
“We’ve had sports ground customers telling us: ‘The results have been fantastic on the turf and overall soil health.’”
He concludes: “Seaweed is not a silver bullet, but it is a good ingredient for a ‘farming cocktail’ especially for regenerative agriculture.”
Seaweed as a biostimulant
Biostimulants are substances or microorganisms that, when applied to plants, seeds or soil, stimulate natural processes to improve nutrient uptake, efficiency, tolerance to abiotic stress and crop quality. Unlike fertilisers, which provide nutrients directly, biostimulants enhance the plant’s inherent ability to absorb and utilise nutrients more effectively.
Several types of seaweed are commonly used in biostimulant formulations, each with unique properties and benefits:
• Brown seaweed (Phaeophyceae): Includes species like Ascophyllum nodosum and Ecklonia maxima. Rich in alginates, laminarins and fucoidans, they help in stress tolerance and growth regulation
• Red seaweed (Rhodophyta): Contains carrageenan and other polysaccharides that promote plant cell division and growth
• Green seaweed (Chlorophyta): Known for their high content of chlorophyll and growth-promoting hormones like cytokinins.
Seaweed biostimulants enhance plant growth through multiple mechanisms:
Hormonal Activity: Seaweed extracts are rich in plant growth hormones such as auxins, cytokinins and gibberellins. These hormones regulate various physiological processes including cell division, elongation and differentiation, leading to improved root and shoot growth.
Stress Tolerance: The presence of unique polysaccharides and antioxidants in seaweed helps plants to better withstand abiotic stresses such as drought, salinity and extreme temperatures. These compounds enhance the plant’s defence mechanisms and improve resilience.
Nutrient Uptake: Seaweed contains chelating agents that improve the availability and absorption of essential nutrients like nitrogen, phosphorus and potassium. This leads to more efficient utilisation of fertilisers and reduces the need for chemical inputs.
Soil Health: Seaweed biostimulants improve soil structure and microbial activity. They promote the growth of beneficial soil microorganisms, which in turn enhance nutrient cycling and soil fertility.
Seaweed biostimulants represent a promising solution for enhancing plant growth and resilience in a sustainable manner. By leveraging the unique properties of seaweed, farmers can improve crop yields, reduce reliance on chemical fertilisers and promote environmental health. As research continues to uncover the potential of seaweed extracts, their role in sustainable agriculture is set to expand further, offering a green alternative for future farming practices.
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