Technical guide for farmers: biostimulants
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What is a biostimulant?
Biostimulants interact with plant signalling pathways. These pathways are like the plant’s communication system, helping it respond to its environment. When something happens like a change in temperature, lack of water or an insect attack the plant receives a “signal”. The signal then triggers a chain reaction inside the plant. These messages tell different parts of the plant how to respond.
Biostimulants can stimulate beneficial microbial communities. Healthy soil is full of helpful microbes, that support plant health and biostimulants can help to provide a good diet for these microbes, giving them the nutrients they need to grow and thrive.
Biostimulants can be natural or synthetic and can help improve plant growth and soil health. They can work by enhancing nutrient uptake, boosting stress tolerance, and improving overall soil structure and biology.
What the science says about biostimulants
A meta-analysis (a review of different scientific studies on the same topic) found an average increase of 17.9% across various crops. The highest benefits were in arid climates and vegetable crops [11] and where soil health was compromised. However, it needs to be kept in mind that results do vary and, as trials have shown, the largest gains are found in vegetable/potato crops and in countries with poorer soils and drier climates. Results in the UK on cereals are less consistent.
Scientific research and trials have evidenced biostimulants may have the ability to offer the following benefits.
- Improved nutrient use efficiency: By enhancing nutrient uptake and utilisation, reducing the need for synthetic fertilisers and improving nutrient use efficiency (NUE) [2, 4, 6].
- Environmental sustainability: By reducing reliance on chemical fertilisers and pesticides, biostimulants could contribute to more sustainable agricultural practices and lower environmental impact [2, 5, 8]
- Soil health and microbial activity: By promoting soil health by enhancing microbial activity and improving soil structure, which in turn supports plant growth [7, 8].
- Enhanced plant growth and yield: Biostimulants can promote plant growth by stimulating natural processes, leading to increased crop yields and improved quality of produce [1, 2, 4, 9].
- Stress tolerance: Biostimulants can help plants withstand abiotic stresses such as drought, salinity, and extreme temperatures by enhancing stress tolerance mechanisms [3, 4, 5, 7].
Whole farm systems
Biostimulants can be part of a whole farm system by reducing chemical dependence on pesticides and artificial fertilisers. Their potential ability to improve soil health alongside increasing stress tolerance and plant health make them a valuable tool on farm.
If you are interested in trialling biostimulants on your farm, the first point to consider is what you would like to achieve from the biostimulant. This might be to:
- improve soil health
- enhance root growth
- increase drought resistance
- boost nutrient uptake
- reduce crop stress
You should also understand which type of bio-stimulant will potentially achieve this:
- Microbial biostimulants: improve root function and soil microbiome.
- Compost teas: encourage beneficial microbes, enhance nutrient availability and reduce stress tolerance
- Humic and fulvic acids: enhance nutrient availability and uptake.
- Amino acids and peptides: support plant metabolism and stress tolerance.
- Seaweed extracts: stimulate growth, boost resistance to pests and diseases.
Another consideration is deciding whether you are going to use an off-the shelf-product or brew your own biostimulant.
Positive outcome areas:
- Soil
- water
- Carbon
- Biodiversity
Biostimulants can be a useful tool as part of a wider whole farm system. However, studies have emphasised the importance of environmental factors and cropping systems in determining the success of biostimulant applications.
Measuring and monitoring
What can be measured to indicate if the applied biostimulant is having an effect?
As with all inputs, having an un-treated control area is essential to ensure that you are seeing a response to the biostimulant applied. In the soil, soil health Indicators can be measured, such as:
- Microbial activity: use soil respiration tests or microbial biomass assessments to see if beneficial microbes are increasing.
- Soil Organic Matter (SOM): higher SOM levels indicate improved soil structure and fertility.
- Nutrient availability: soil tests can measure nitrogen (N), phosphorus (P), and potassium (K) levels to check if nutrient uptake potential is improving.
- Water holding capacity: soil moisture retention can indicate improved soil structure and drought resilience.
- Soil aggregation and structure: better root penetration and reduced compaction suggest positive effects.
Off-the-shelf biostimulants
Pros
- Reliable and consistent: manufactured products have known ingredients and predictable results.
- Easy to use: no need for extra equipment or preparation.
Scientifically tested: backed by research and trials to ensure effectiveness. - Longer shelf life: formulated for storage stability.
- Specific formulations available: tailored products for different crops, soil types, and growth stages.
Cons:
- Higher cost: more expensive per application compared to DIY methods.
- Less control over ingredients: may contain fillers or additives that aren’t needed by the crop or soil or may not provide microbes or nutrients that your crop or
soil requires. - Environmental impact: some products may have a higher carbon footprint due to manufacturing and transport. necessarily.
Brew-your-own biostimulants
Pros:
- Lower cost: can be made from farm waste, compost, or locally sourced materials.
- Customisable: farmers can tailor mixtures to their specific soil and crop needs.
- Supports soil microbiology: fresh brews often contain more active microbes.
- Sustainable and regenerative: reduces reliance on external inputs and supports circular farming.
Cons:
- Inconsistent results: effectiveness depends on brewing conditions and ingredient quality.
- Short shelf life: freshly brewed solutions must be used quickly before they degrade.
- Potential for contamination: risk of harmful bacteria or imbalanced microbial populations if not managed properly.
Time consuming: requires preparation, monitoring, and quality control.
You also need to consider the type of equipment needed for application, where this targets and the amount and timings of applications and if this practically fits into your management system.
- Soil-applied: best for improving soil health and root development.
- Foliar sprays: useful for quick stress recovery and nutrient uptake.
- Seed treatment: enhances early-stage plant growth.
Why should I be doing this?
Biostimulants are not an exact science. Their effectiveness depends on multiple factors such as crop type, existing soil health, application technique and environmental conditions.
Research has shown biostimulants can:
- Enhance crop resilience: Helping plants better cope with drought, heat, and disease.
- Improve nutrient efficiency: Allowing existing and added nutrients work more effectively
- Improve soil health: Encouraging beneficial microbes and improving soil structure.
- Increase yields: Some trials report improved crop quality and yield when biostimulants are used (depending on crop type and conditions) but the evidence is not often independently verified.
For plant growth and resilience, the following indicators can be used:
- Root biomass and depth: digging up sample plants can show if root systems are developing better.
- Leaf chlorophyll levels (SPAD readings): greener, healthier leaves indicate better photosynthesis and nutrient use.
- Plant vigour and growth rate: measure plant height, leaf area, and overall growth.
- Stress tolerance: check for resilience to drought, frost, or disease compared to untreated crops.
- Final yield: compare treated vs. untreated areas for improvements in harvest weight.
- Crop quality: look at grain protein content, sugar levels (Brix test), or fruit/vegetable firmness and size.
- Pest and disease resistance: record any reductions in fungal infections, insect damage, or nutrient deficiencies. Reduction in inputs needed: track if less fertiliser, pesticides, or irrigation is required.
Costs, savings, improvements
For growers, the economic viability of applying any product to a crop is essential. The potential financial benefits of biostimulant use stem from increased yields and improved nutrient use efficiency leading to reduced artificial fertiliser requirements. Alongside enhanced stress tolerance may lower the need for pesticide applications. Cost saving will depend on context of crop type, soil type, environmental conditions and existing soil health.
For example, 36 separate field trials carried out by Biostim on potatoes demonstrated a total percentage increase margin of 9.30%, which, after deducting the cost of the biostimulant equalled £885 per hectare. Trials across onion, potato and turf demonstrated on average a 25% reduction in artificial fertiliser usage.
Download a printable PDF of this biostimulants technical guide
Timescales
The frequency of application depends on the product, some need applying once whilst others multiple times. Therefore, factors such as how often is it difficult to travel on your land after wet weather events and time management need to be taken into consideration.
Improvements in soil health including microbiome and structure is not a quick fix. It will depend on several factors including the type of biostimulant, soil health and management practices. For example, microbial biostimulants can start colonising roots within weeks and improve nutrient uptake within months. Combined with other practices improved soil structure, more efficient nutrient use and reduced disease suppression can be seen. Longer term use can lead to healthier, more resilient soils with increased water holding capacity and organic matter content and reduced reliance on synthetic fertilisers and pesticides as the soil ecology improves.
However, this cannot be done as a standalone practice as it needs to be part of a whole farm approach including practices such as cover crops, mindful cultivation and diverse rotations.
Impact
Improve soil health: Biostimulants can help enhance the biological, chemical, and physical properties of the soil. They can increase microbial activity, improve soil
structure, and enhance nutrient cycling. Which leads to better soil fertility and long-term sustainability.
Enhance root growth: certain biostimulants, such as seaweed extracts and humic acids, promote root development. Stronger, deeper roots allow plants to access more nutrients and water, improving overall plant health and stability.
Increase drought resistance: by improving root systems and water retention in the soil, biostimulants can help plants withstand periods of low rainfall or high temperatures. Some biostimulants also help plants produce stress-related compounds that reduce water loss.
Boost nutrient uptake: biostimulants can make nutrients more available in the soil or help plants absorb them more efficiently. This can reduce reliance on synthetic fertilizers while still ensuring crops get the necessary nutrients to grow.
Reduce crop stress: plants face stress from extreme weather, pests, diseases, and soil imbalances. Biostimulants can help plants produce natural protective compounds, strengthen cell walls, and regulate hormones, making them more resilient against
environmental stressors.