Crop biostimulants: Cutting through the marketing hype

Ellie Dearlove investigates whether biostimulants can really support crop growth and how to make sense of marketing materials.

Water-stressed crops are giving up on the season, with a very early harvest on the cards for many. The extremely dry weather, especially during spring, has negatively impacted crop condition.

With extreme events increasing (not limited to drought), we need to increase crop resilience, to help crops weather the inevitable storm.

Against this backdrop, it is not surprising to see one question popping up time and time again in our research ideas letterbox: “Do biostimulants work and are they cost-effective?”

Biostimulants are marketed as part of the solution, but the array of product types makes it difficult to sort those that may make a difference, from those likely to disappoint (and drain the wallet).

Biostimulants contain substances and/or microorganisms that potentially stimulate natural processes to benefit crops.

For instance, some are marketed as increasing tolerance to abiotic stresses, including extreme temperatures, drought conditions and nutrient deficiencies.

They gained traction in the 2010s, with AHDB Cereals & Oilseeds reviewing biostimulant products about a decade ago, which provided a foundation for our biostimulants web pages.

Defra also published a review (2022) that considered UK-relevant studies on plant biostimulants, which concluded that:

• There is some evidence that some biostimulants benefit growth and/or yield of arable crops
• There is limited evidence that biostimulants improve nutrient uptake and quality
• There is little evidence that biostimulants improve nutrient use efficiency and abiotic-stress tolerance
• Results are variable (depending on crop type, conditions and product usage)
• Some studies show no benefit at all

So, biostimulants work, in some situations – but we need to know which biostimulants work in specific situations.

Because of product diversity, variable efficacy mechanisms, their biological nature, system complexities (e.g. soil types) and seasonal influences, it is costly to fund robust biostimulant trials.

But there is some low-hanging fruit. Biostimulants deliver the most noticeable benefits when plants are stressed. To get the best return, it is important to tackle any underlying agronomic issues first.

We can learn lessons from cover crops, where a wide range of options also sprang up, leaving farmers bewildered by choice.

Before reaching for a product catalogue (cover crop or biostimulant), it is important define the problem you want to solve.

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

Our soil health scorecard is a good place to start, which will help you identify soil issues (structure, pH, nutrients, earthworms and organic matter) and address them, via tried-and-tested approaches.

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

Let’s cut to the chase. In many situations, you may struggle to see benefits from biostimulants, especially if growing conditions are good. Certainly, the economic evidence of the benefits of biostimulants is weak.

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. Are there better ways to invest, say, £20/ha?

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 you may need to work harder to uncover the truth.

It is not helped by the broad claims sometimes made, which are barely backed up by robust trial data (if at all).

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

• 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 (including how it applies to the product)?
• Biostimulants derived from natural products (seaweed, humic substances and microbes) can vary in quantity and quality between batches (and brands) – 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 (as they do not form an association with brassica roots)

Biostimulants offer promise, but the evidence is patchy, regulation is lacking and the economic return is often unclear.

If you are curious, trial the product in small area, comparing it against your standard approach (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).