After a season when crops gave up in the summer drought, farmers may be tempted to try a biostimulant to help crops cope better next time.

Some products can deliver valuable benefits in certain situations, but the trick is to avoid wasting money on those that do not deliver on the promises made in the marketing material.

The use of biostimulants has proved to be a frequently asked question to the AHDB, which has prompted knowledge transfer manager Ellie Dearlove to offer advice to farmers who are considering using them. 

See also: Biostimulants – what they are and how farmers can use them

Agronomy issues

To get the best return, first tackle any underlying agronomic issues.

“Before reaching for a product catalogue, it is important to define the problem that you want to solve,” she says.

For example, if compaction, drainage or nutrient deficiencies are an issue, then tackling the causes is likely to provide a better return on investment, rather than pinning hopes on a largely unregulated product.

Ellie says the AHDB’s soil health scorecard as a good place to start, which will help farmers identify soil issues (structure, pH, nutrients, earthworms and organic matter), and address them through tried-and-tested approaches.

“Only once your agronomic foundations are solid, ask: ‘Which crops, under what conditions, might respond to a biostimulant?’”

In many situations, farmers may struggle to see the advantages of biostimulants, especially if growing conditions are good.

The economic evidence of the benefits is weak, says Ellie. Biostimulants are not cheap and a relatively small yield or quality benefit, which may only be seen in certain situations, may not cover cost of the product.

Soil cracks in winter wheat © GNP

Marketing hype

“In farming, it is healthy to have a sceptical approach. Trust nothing, unless the evidence suggests that you should.”

Biostimulants are not subjected to rigorous mandatory testing like other products, such as pesticides and fertilisers, so farmers may need to work harder to uncover the truth, she says.

“It is not helped by the broad claims sometimes made, which are barely backed up by robust trial data.”

Although glossy marketing materials often feature scientific language and data, Ellie says they may not be worth the paper they are printed on.

But she does have some tips to help farmers “sort the science from the sales”:

• Always look for a clear ingredient list – know what is in the product, as it is the first step in understanding what it may do
• Be wary of products that promise to fix multiple issues – make sure the evidence backs up all the claims
• Remember that it is illegal to claim a biostimulant has a pesticidal effect, if it is not authorised as a plant protection product
• Is scientific-sounding jargon – such as “activates plant-signalling pathways” or “enhances microbial synergy” – clearly explained? Does this include how it applies to the product?
• Biostimulants derived from natural products such as seaweed, humic substances and microbes can vary in quantity and quality between batches and brands. Therefore, a lower-cost alternative to a proven product may not deliver the same results
• When products contain added nutrients, be sure that the biostimulant adds value. Look for trial results that compare the biostimulant against a control (based on the added nutrients without the biostimulant, not untreated plots without the added nutrients)
• Look for trials conducted by independent organisations or academic institutions
• Look for claims based on trials over multiple years, which are likely to be the most trustworthy
• Arbuscular mycorrhizal fungi (AMF) may improve yield and quality in cereals, but they are not suitable for use in oilseed rape. That’s because they do not form an association with brassica roots.

Finally, if farmers are still curious, Ellie suggests trialling the product in small area, comparing it against the standard farm approach.

Try to keep all other treatments the same. “Ask the company to give you a small amount to test. If they believe in their product, they may agree.” 

For more on biostimulants, check out the AHDB’s dedicated online hub at ahdb.org.uk/biostimulants