Biostimulants: Greater than the sum of the parts

Many misconceptions and misrepresentations exist about biostimulants, but research has started to separate the wheat from the chaff. According to the European Union, biostimulants are defined as products that stimulate plant growth independently from the product’s nutrient composition. The purpose of these products is to help the plant utilise nutrients more efficiently, resist stress better, improve quality and yield, and use plant nutrients in the soil better.

Within this grouping, there are three main categories, namely seaweed extracts, protein and microorganisms. Seaweed extracts are the largest category by far, and various products are registered.

Protein hydrolysates are used less commonly, but trials are being done currently to treat crops with protein extracts from soybeans. Where microorganisms are concerned, there is an overlap with biofertiliser, which I elaborated on in a previous column.


Scientists are not sure about how seaweed extracts can work on plants. What is certain, though, is that it not only stimulates growth but also increases the plant’s resistance to pests and diseases and stimulates soil life.

The uncertainty is because seaweed extracts contain a complex combination of organic compounds, most of which are not found in land-based plants. Consequently, it is difficult to isolate specific components of the extracts. Some cannot even be artificially synthesised after they have been isolated.

There are also differences between the individual seaweed species and the production processes.


South Africa is a world leader in the field of seaweed extracts. It was found as far back as 1975 that the Cape giant kelp (Ecklonia maxima), which does not occur anywhere else in the world, has beneficial effects on plant growth. In 1977 Kelpak developed a ‘cold’ method to extract seaweed extracts using a mechanical pressure differential, ensuring the best possible juice quality.

The first products were manufactured by 1985, and today Kelpak’s products are available in 70 countries.

According to Mr Heino Papenfus, research and development manager at Kelpak, seaweed extracts contain various active ingredients supplemented by natural carbohydrates and carboxylic acids that stimulate growth in plants.

Initially, it was suspected that seaweed extract contains mainly auxin, based on its impact on root development, but research has found that it cannot solely be attributed to that. Seaweed extract has an auxin-like action that can be mainly attributed to polyamines and phlorotannins.

On their own, or in collaboration with each other, these molecules stimulate, among other things, root growth, stress relief, flower development, fruit set, fruit growth and fruit quality. This enables the plant to grow stronger and healthier and subsequently leads to better yields and higher-quality products. Research has also shown that polyamine levels in plants rise when they are under stress because of drought, cold, waterlogging or overplanting. Therefore, plants treated with seaweed extracts are better prepared for such stress conditions. Kelpak has been used with various crops like grapes, fruit, citrus, potatoes and vegetable types. This is mainly thanks to the favourable effect that Kelpak has on the pollen germination and pollen tube growth and the young, developing fruit.

It is also used successfully with tuberous and bulbous crops like potatoes and onions to stimulate root development and cell division.


Seaweed extracts can be used successfully in row crops. According to Papenfus, good results are achieved with treatments centred around the seeds and early leaf spraying.

With maize, they obtained the best results by dripping a 1% solution of Kelpak into the plant furrow. Some trials showed an improved harvest of up to 22% over the control group. Follow-up laboratory research showed that the results could be attributed to the Kelpak solution’s effect on the germinating seed and the impact on soil life.

Kelpak can also be used as a seed treatment for various crops, but more work needs to be done regarding the combination with other seed treatment products.

With maize, seed treatment trials showed a yield increase of between 5% and 9% over the control group at a low Kelpak inclusion. Similar results are achieved when maize is sprayed in combination at the three- to five-leaf phase.

There are still differences between countries about regulating biostimulants, and a lot of research must still be done in the field.

However, the benefits of using it are clear. These benefits also explain why these products grow annually by more than 15%.


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