Biostimulants 101: Everything Growers Need to Know About Biostimulants

FBN Network

Feb 15, 2024

This guide includes the following sections:

What Are Biostimulants?

The 2018 Farm Bill offered the first legal definition of a biostimulant in the United States: “a substance or microorganism that, when applied to seeds, plants, or the rhizosphere, stimulates natural processes to enhance or benefit nutrient uptake, nutrient efficiency, tolerance to abiotic stress, or crop quality and yield.” While this language may seem vague, it begins to help lay a framework for regulatory oversight of products that may fall under several product classes today, including fertilizers, soil amendments, or inoculants.

Many types of biostimulants are used in crop production, and each has different benefits. Common biostimulant effects on plants include:

  • Increased stress tolerance and recovery

  • Improved plant water and nutrient uptake, translocation, and use 

  • More robust root structure and growth

  • Better disease tolerance

  • Improved plant metabolism for enhanced yield and crop quality

  • Enhanced quality characteristics of produce, including sugar content, color, fruit seeding, etc

While the crop health benefits of biostimulants have been well documented, the mode of action of these products is not always well understood. Generally, biostimulants boost a plant’s vigor, making it more tolerant to abiotic and biotic stress. However, biostimulants do not have a direct mode of action against weeds, diseases, or insects like herbicides, fungicides, and insecticides do. 

Why Do Farmers Use Biostimulants?

Biostimulants are often associated with organic production systems, but in the past decade, their popularity has grown among conventional growers. Research has shown that these products can: 

  • Improve yield potential and crop quality

  • Increase tolerance to stress

  • Optimize root growth

  • Enhance nutrient uptake

Biostimulants may work synergistically with other crop inputs, including fertilizers and pesticides, to improve productivity or increase crop safety. Adding biostimulants to a crop nutrition program may also help fertilizers work harder to improve the return on investment potential of the fertility program.    

Types of Biostimulants

There are many biostimulant classes and formulations that may stimulate various plant responses. A specific product’s efficacy may be affected by its raw ingredients and how it is manufactured, stored, and applied. 

Here are the most common biostimulants used in agricultural production.

Humic and Fulvic Acids

Humic and fulvic acids are the largest segment of the biostimulant market. They are organic acids that occur naturally in soil, resulting from the decomposition of plant, animal, and microbial residues. These acids can also come from soil microbe activity. Humic acids may be derived from non-renewable (mineral deposits like leonardite and soft coal) or renewable (compost or vermicompost) sources. 

Benefits of humic acids in agricultural production include:

  • Improving soil physiochemical properties

  • Increasing root nutrient uptake

  • Expanding lateral root development

Seaweed Extracts and Botanicals

Seaweed extracts are another popular biostimulant class with a long history in agriculture. Farmers have used seaweed extracts to fertilize the soil and improve its structure for hundreds of years. However, the biostimulant effects of seaweed extracts are a relatively new development. 

Brown seaweeds, including species of the genera Ascophyllum, Fucus, and Laminari, are the most commonly used seaweeds in agricultural production. Different extraction processes are used to produce most seaweed biostimulant products and can affect overall product efficacy. 

Seaweed extracts are usually packaged as a soluble powder or liquid formulation. Beneficial polysaccharides account for 30-40% of the dry weight of seaweed extracts and are known to elicit plant defense responses against bacterial and fungal pathogens. 

Other benefits of seaweed extracts include:

  • Improved plant growth and development from phenolic-rich compounds

  • Improved nutrient uptake and utilization

  • Soil conditioning and metal-chelating properties

  • Increased water retention capacity in plants

Other plant extracts are increasingly being studied and used for their biostimulant effects.

Beneficial Bacteria

Plant-growth-promoting bacteria (PGPBs) are well-studied species of beneficial bacteria, including free-living bacteria that inhabit a plant’s root zone, bacteria that colonize the root surface, and bacteria that live within plant roots. 

Bacillus, Rhizobium, Pseudomonas, Azospirillum, and Azotobacter bacteria are popular in the biostimulant market. They offer many plant benefits; the most well-known is rhizobacteria’s nitrogen-fixing capabilities in legume crops. Beneficial bacteria may be inoculated on the seed or applied directly to the soil. 

Other benefits of PGPBs include:

  • Improved water and nutrient uptake

  • Increased nutrient use efficiency

  • Plant hormone stimulation and regulation

  • Resistance to insects and non-beneficial bacterial pathogens

While the modes of action and benefits of PGPBs are well understood and documented, they can be challenging to work with because they are living organisms sensitive to handling and extreme temperatures. PGPB biostimulants may not mix well with other crop protection products and often have limited shelf lives.  

Beneficial Fungi

It’s well-known that mycorrhizal fungi are vital to soil health and crop production. These fungi live symbiotically with plant roots to increase root mass and nutrient and water uptake. 

Other benefits of symbiotic fungi products include:

  • Increased drought stress tolerance

  • Improved phosphorus uptake in phosphorus-deficient soils

  • Beneficial antifungal properties against plant fungal diseases

As living organisms, beneficial fungi are sensitive to crop management practices, including soil tillage, fallow periods, and high rates of fertilizer and fungicides. 

Chitosan & Other Biopolymers

Chitosans are derived from a naturally occurring biological building block, chitin, that supports fungal cell walls and the exoskeletons of insects. Chitosans can induce plant-defense responses, making plants more tolerant to abiotic and biotic stresses. Although these products' exact modes of action have yet to be fully understood, more research is being done to support further product development.

Benefits of chitosans and similar biopolymers include:

  • Antibacterial, antifungal, and antiviral properties

  • Soil amendment characteristics to reduce Fusarium wilt and other soilborne pathogen populations   

Chitosan efficacy can vary greatly depending on how and when it is applied and the quality of raw materials and manufacturing processes.

Inorganic Compounds

Inorganic compounds include minerals such as silica, selenium, cobalt, and others, which promote plant growth, the quality of plant products, and abiotic stress tolerance. 

Some benefits of silicon, specifically, include:

  • Increased plant resistance to diseases

  • Increased photosynthesis efficiency

  • Improved water and nutrient translocation

  • Immobilization of toxic metals in the soil and plant tissues

  • Delayed plant senescence

Protein Hydrolysates

Protein hydrolysates are amino-acid and peptide mixtures obtained by chemical and enzymatic protein hydrolysis from both plant sources and animal wastes. Crop residues and by-products and animal industrial by-products, including leather, collagen and epithelial tissues, are typical sources.

The plant-based peptides, particularly, are the most interesting of the biostimulants due to their multifunctional activity. Protein hydrolysates are known to affect plant hormonal activities and metabolism. 

Benefits of protein hydrolysates may include:

  • Increased soil fertility

  • Improved soil microbial activity

  • Chelating properties to protect against heavy-metal soils

  • Increased micronutrient uptake and translocation

Biostimulant Application Best Practices

Choosing the Right Product

As discussed earlier, you have many options when it comes to choosing a biostimulant. 

The first step in making a decision is to define your goal. Are you looking for a product to enhance root mass or improve soil fertility? With a specific goal in mind, it will be easier to narrow down options. 

Next, consider your current production practices. What equipment and labor resources do you have? Are there product formulations that work better with your current production practices?

For example, some PGPR formulations are manufactured to have a longer shelf life than most products. Paying more for those formulations will buy you more flexibility and peace of mind that products will still work even if your plans are delayed.

Because biostimulants are relatively new, metrics and data are necessary to sort out the reliable technologies from the gimmicks. Biostimulants are lightly regulated. Merchants make many product claims, and all sorts of concoctions are purported to be biostimulants. Ask questions and ensure you receive a scientific explanation and validated data to support product efficacy in your fields.  

When to Apply a Biostimulant

The application timing of a biostimulant will depend on several factors, including:

  • Product class

  • Formulation

  • Agronomic objective

  • Environmental conditions 

  • Crop type

For example, microbial biostimulants, including PGPBs and fungi, are often applied as seed inoculants or directly to the soil at planting to stimulate strong early-season plant growth. Other biostimulants are formulated to work synergistically with fertilizer applications and will be most effective when incorporated into your in-season fertility program. 

Non-microbial biostimulants may be applied repeatedly throughout the season using any of these approaches:

  • Calendar application - Preferable when the crop experiences sub-optimal conditions for most of the growing cycle. This strategy is most common in high-value crops in greenhouse growing environments. 

  • Growth stage application - Multiple biostimulant applications at key growth stages (germination, flowering, grain production) may be more profitable in commodity crops.   

  • Environmental stimulus application - For stress mitigation, biostimulants may be applied several days before the stress event (for example, extreme temperatures) for extra protection and after the event to hasten plant recovery.   

In commercial agriculture, the effects of biostimulants have been most studied on row crops and cereals. The lack of regulation, limited mode of action information, and non-standardized manufacturing processes complicate biostimulant use by farmers. 

While biostimulant science and regulation are advancing rapidly, carefully measuring results is critical to determining what products can create real value for you. 

Buy Biostimulants from FBN Direct®

FBN Direct offers several biostimulant products to maximize crop growth and development and protect against in-season stresses. With 24/7 digital shopping access, direct-to-farm delivery, transparent pricing and savings opportunities, and detailed label information for each product, FBN Direct offers the information and products you need to add biostimulants to your crop management program successfully.

Popular Biostimulants Available from FBN Direct

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FBN Network

Feb 15, 2024