Not All Biologicals Are Created Equal. Here’s How to Tell the Difference.

By Dr. Lee Opdahl, Research and Development Manager

Picture credit: AgWeb

Every crop has a yield ceiling set by the plant breeder. How close it gets to that ceiling depends on how well abiotic stress is managed through the season. Biological products have become one of the most talked-about tools for doing exactly that, and for good reason.

However, the category has grown fast, and with it comes a lot of noise. Not all biologicals work the same way, and not all of them will deliver results in every system.

Understanding what’s inside the jug and how it actually functions is the difference between a smart investment and an expensive experiment.

What Are Biologicals?

Agricultural biologicals are broadly defined as crop production and protection products derived from living organisms, natural materials or naturally occurring processes. Most fall into one of two buckets.

Biostimulants are defined by the USDA (United States Department of Agriculture) as substances or microorganisms that, when applied to seeds, plants or the root zone, stimulate natural processes to enhance nutrient uptake, nutrient efficiency, tolerance to environmental stress or crop quality and yield. (1) Because there isn’t unified federal regulation for biostimulants, registration and compliance requirements vary from state to state.

Biopesticides are regulated by the EPA (Environmental Protection Agency) and include naturally occurring substances that control pests, microorganisms that control pests and pesticidal substances produced by plants containing added genetic material. (2)

Compared to biopesticides, biostimulants aren’t as well-defined and tend to be less understood. And within biostimulants, there’s significant variation in how each category works and where they actually fit in an operation.

Four Ways Biostimulants Work

Grouping plant biostimulants by function is the most practical way for retailers and growers to evaluate what belongs in a program. The four groups below generally describe the biostimulant categories.

1. Live Microbes and Enzymes

These products introduce living microorganisms such as bacteria and fungi, or specific enzymes like phosphatases and cellulases, into the soil system. The agronomic intent is a targeted biological function like nitrogen fixation, nutrient cycling, solubilization or abiotic stress tolerance.

The practical challenge with this group is consistency. Performance is heavily influenced by soil temperature, moisture, chemistry and the competitive pressure from the native microbial populations already present. Shelf stability, handling requirements and tank-mix compatibility also tend to be more limiting with live organisms than with other categories.

For example, a nitrogen-fixing bacteria product may perform well in warm, moist soils with low native bacterial pressure but struggle to establish in a field that's cold, dry or already teeming with competing microbes. That variability is the defining challenge of this entire category.

In short, getting live microbe products to perform requires several conditions to line up at the right time, and that doesn’t always happen.

2. Carbon and Nitrogen Nutrition

This group includes sugars, organic acids, amino acids and protein hydrolysates. These inputs primarily supply carbon and nitrogen sources to native soil microbes and plants without introducing organisms or directing a specific biochemical pathway (like nitrogen fixation). They provide readily available food sources that stimulate microbial growth and activity.

Applied to soil, they can support microbial populations and nutrient cycling. Applied foliar, they can supply energy-saving carbon and nitrogen for plant nutrition.

The tradeoff is that these effects are often short-lived, and the total fertility delivered in a foliar pass is modest next to conventional fertilizer rates. Think of it as a snack for your soil biology rather than a full meal.

3. Natural Signaling Compounds

Seaweed extracts, chitosan, certain organic acids, peptides and amino acids fall into this group.  These are naturally derived chemical messengers intended to prompt physiological responses in the plant rather than to function as fertilizers. In other words, they don’t feed the plant directly, they tell it to do something.

A number of compounds used this way, including seaweed extracts, laminarin, jasmonates and harpin proteins, appear on EPAs list of active ingredients found in registered plant regulator products. (3) That’s worth knowing because it affects how these products are labeled and sold. If you’re evaluating a natural signaling product, look for an EPA registration number on the label. Its absence is a question worth asking about.

The agronomic tradeoff in this group is timing. Signaling compounds prompt a plant response whether or not the plant is actually under the stress being prepared for. The plant doesn't know the difference, so it spends energy responding either way. Research results in this category have also been inconsistent when products are applied under low-stress conditions, which makes application timing critical.

4. Nonessential Beneficial Minerals Silicon and selenium are the most common examples. These elements aren’t required for a plant to complete its life cycle, and they’re not recognized plant nutrients. Silicon is formally classified by AAPFCO (Association of American Plant Food Control Officials) as a plant beneficial substance rather than a micronutrient. (2) Where they show value is under stress conditions, through contributions to water use efficiency and abiotic stress tolerance. Think of them as a backup system that kicks in when conditions get hard.

This category shouldn’t be confused with recognized micronutrients. Cobalt, zinc, manganese, copper, boron, iron, molybdenum, nickel, chlorine and sodium are recognized plant nutrients under AAPFCO's micronutrient definition and are regulated as fertilizer, not as beneficial substances or biostimulants. (2)

The caveat on beneficial nonessential elements is that they tend to show their clearest response  when a plant is under stress. In optimal growing conditions, the response may be minimal.

Two distinctions worth noting. Humic and fulvic substances aren’t included in this framework because their contribution is largely nutrient binding and water retention, which places them closer to the soil amendment category. And some inputs span more than one group. Certain organic acids and amino acids act as signaling molecules while also supplying carbon and nitrogen. Across all four groups, results depend on environmental conditions, application timing and following label directions

So How Do You Choose?

No single type of plant biostimulant is right for every situation. Each has a role and each has limits. The best programs match the tool to the need, whether that’s feeding soil biology, prompting  a physiological response or correcting a nutrient limitation when the crop needs it most.

The more useful question isn’t which of the four boxes a product sits in. It’s whether the product actually delivers measurable results under real field conditions.

Where Microbial Catalyst Fits, and Where it Doesn't

Agnition’s Microbial Catalyst technology isn’t a biostimulant and it’s not a biopesticide. It’s a patented trace mineral technology that delivers highly soluble nutrients directly where the plant and soil biology need them most.

This technology is made up of trace minerals engineered for solubility and plant availability. Because it’s a stable chemistry rather than a living organism, it carries fewer storage restrictions, strong shelf stability and broad tank-mix compatibility, and there isn’t an establishment period to wait through before the nutrients are available.

Applied to soil, it supplies micronutrients that are readily available by plants and supports the native microbial populations to increase enzymatic activity that mineralize nutrients already present in soil and applied fertilizer. Applied foliar, it’s readily taken up through leaf tissue, which matters most in mid-season when dry soil limits root uptake and a micronutrient shortfall is hardest to correct through the soil.

What the Science Shows

Micronutrients aren’t optional. They function as cofactors in the enzyme systems plants and soil microbes rely on to build proteins, cycle nutrients and manage the byproducts of stress. When a required micronutrient is short, the systems that depend on it can’t run at full capacity, and the shortfall shows up as lost yield well before it shows up as a visible symptom.

Cobalt is a good example. It’s a recognized micronutrient under AAPFCO’s definition, but it’s not one most crop programs account for. Multiple peer-reviewed studies have examined cobalt nutrition in crops grown under drought and salinity, with results indicating that cobalt supply is a meaningful variable in crop performance under those conditions. (4, 5, 6) Meaning, it’s a nutrient your crop may already need more of, especially when the season gets stressful.

Here’s why it matters at the cellular level. When a crop is under drought or salinity stress, it produces reactive oxygen species inside its cells as a byproduct. Essentially, cellular damage that builds up faster than the plant can manage. The enzyme systems responsible for neutralizing that damage run on micronutrients. Without enough of them, those systems slow down at exactly the moment the plant needs them most. Supplying micronutrients in a soluble, plant-available form closes that gap before it costs yield.

That’s exactly the gap Microbial Catalyst technology was built to close. Agnition products combine this technology with precise micronutrient formulations to overcome solubility and availability, so the crop gets what it needs in a form it can actually use when it matters most.

Overall, the biological products category is going to keep growing and so is the noise around it. The best way to cut through it is simple. Ask what a product guarantees and what the data shows under real field conditions. The answers will tell you everything.

Want to learn more about crop nutrition and biologicals? Talk to an Agnition representative at 1-855-832-0613.

References

1. Agriculture Improvement Act of 2018, Sec. 10111. Plant biostimulant definition for purposes of the USDA report to Congress. https://www.congress.gov/bill/115th-congress/house-bill/2

2. Association of American Plant Food Control Officials, Uniform Beneficial Substances Bill and Official Publication. https://www.aapfco.org/biostimulants.html

3. U.S. Environmental Protection Agency, Draft Guidance for Plant Regulator Products and Claims, Including Plant Biostimulants. https://www.epa.gov/pesticides/draft-guidance-plant-regulators-and-claims-including-plant-biostimulants

4. Sami, A., et al. (2024). Cobalt and crop production under stress. https://pmc.ncbi.nlm.nih.gov/articles/PMC11020780/

5. El-Saadony, M.T., et al. (2023). Cobalt application and plant stress tolerance. South African Journal of Botany. https://www.sciencedirect.com/science/article/pii/S0254629923002946

6. Al-Selwey, W.A., et al. (2025). Cobalt and drought/salt stress in crops. BMC Plant Biology. https://link.springer.com/article/10.1186/s12870-025-06596-6