Biostimulants vs. Biofertilizers vs. Conventional Fertilizers: Understanding Their Roles in Modern Crop Nutritiona

What Are Conventional Fertilizers?

Fertilizers supply nutrients required for plant growth and crop production.

Plants require essential mineral nutrients to build proteins, nucleic acids, cellular structures, enzymes, chlorophyll, membranes, and numerous other compounds.

Among the most commercially important nutrients are:

• Nitrogen (N)
• Phosphorus (P)
• Potassium (K)
• Calcium (Ca)
• Magnesium (Mg)
• Sulfur (S)

Plants also require micronutrients such as:

• Iron (Fe)
• Zinc (Zn)
• Manganese (Mn)
• Copper (Cu)
• Boron (B)
• Molybdenum (Mo)
• Chlorine (Cl)
• Nickel (Ni)

Fertilizers are designed primarily to supply one or more of these nutrients in forms that contribute to crop nutrition.

Common examples include urea, ammonium sulfate, ammonium nitrate, calcium ammonium nitrate, monoammonium phosphate, diammonium phosphate, potassium chloride, potassium sulfate, and compound NPK fertilizers.

Their fundamental role is nutritional.

If a crop requires additional nitrogen, for example, an appropriate nitrogen fertilizer can provide it.

This distinguishes fertilizers from products whose main purpose is to influence plant physiological or biological processes.

How Conventional Fertilizers Work

The function of fertilizer may appear simple—adding nutrients—but the process between fertilizer application and plant uptake is complex.

After application, nutrients can undergo:

• Dissolution
• Mineralization
• Immobilization
• Adsorption
• Desorption
• Precipitation
• Leaching
• Volatilization
• Microbial transformation
• Root uptake

Nitrogen illustrates this complexity particularly well.

Urea applied to soil is hydrolyzed and then undergoes several transformations before much of its nitrogen becomes available to plants, primarily as ammonium or nitrate.

Phosphorus behaves differently.

Applied phosphorus can interact strongly with soil minerals, and its availability depends significantly on soil pH, chemistry, and biological activity.

Potassium has another set of interactions involving soil solution, exchange sites, and mineral reserves.

Effective fertilization, therefore, involves more than simply applying nutrients.

It requires selecting the appropriate:

• Nutrient source
• Application rate
• Placement
• Timing
• Fertilizer formulation
• Irrigation strategy

This is the basis of modern nutrient stewardship.

What Are Biofertilizers?

The term biofertilizer generally refers to products containing living microorganisms that improve plant nutrition by increasing the availability or acquisition of nutrients.

Unlike conventional fertilizers, biofertilizers usually do not supply large quantities of mineral nutrients directly.

Instead, microorganisms influence biological processes associated with nutrient cycling and plant nutrient acquisition.

Depending on the microorganism, these processes may include:

• Biological nitrogen fixation
• Phosphorus solubilization
• Nutrient mobilization
• Root colonization
• Mycorrhizal associations
• Rhizosphere modification

Biofertilizers therefore operate through biological mechanisms.

Their effectiveness depends heavily on the relationship between the microorganism, crop, soil, and environment.

Nitrogen-Fixing Microorganisms

Nitrogen is abundant in Earth's atmosphere as molecular nitrogen, or N₂.

However, most plants cannot directly use atmospheric nitrogen.

Certain microorganisms possess the biological machinery required to convert atmospheric nitrogen into forms that can ultimately contribute to plant nutrition.

The most familiar example is the relationship between Rhizobium bacteria and leguminous crops.

These bacteria form symbiotic associations with plant roots and can fix atmospheric nitrogen within specialized root nodules.

Other nitrogen-fixing microorganisms can interact with plants through different mechanisms.

Biological nitrogen fixation can make an important contribution to crop nitrogen nutrition, particularly in suitable crop-microbe systems.

However, this does not mean every nitrogen-fixing biofertilizer can completely replace conventional nitrogen fertilizer in every crop.

Performance depends on crop species, microbial strain, soil conditions, inoculation quality, environmental conditions, and production objectives.

Phosphate-Solubilizing Microorganisms

Soils may contain significant quantities of phosphorus that are not readily available to plants.

Certain microorganisms can influence phosphorus availability through mechanisms such as the production of organic acids, enzymes, and other compounds.

These microorganisms may help mobilize phosphorus from relatively unavailable pools within the root environment.

This is fundamentally different from applying a phosphorus fertilizer.

A phosphorus fertilizer adds phosphorus to the production system.

A phosphate-solubilizing microorganism primarily attempts to improve access to phosphorus already present in soil or fertilizer-derived pools.

The two approaches can therefore be complementary rather than mutually exclusive.

Mycorrhizal Fungi

Mycorrhizal fungi form associations with plant roots.

The fungal hyphae can extend beyond the immediate root surface and explore soil volumes that roots alone may not access as efficiently.

This expanded network can support the acquisition of nutrients and water.

Phosphorus acquisition is particularly associated with mycorrhizal relationships, although other nutrients may also be affected.

Mycorrhizal effectiveness depends on factors including:

• Crop species
• Fungal species
• Soil phosphorus status
• Soil disturbance
• Moisture
• Temperature
• Fertilizer management
• Agricultural chemicals

High-quality inoculation alone does not guarantee successful colonization.

The surrounding production environment must support the biological relationship.

What Are Plant Biostimulants?

Plant biostimulants represent another category.

Under the European Union Fertilizing Products Regulation, a plant biostimulant is defined as a product that stimulates plant nutrition processes, independent of its nutrient content.

The objective is to improve one or more characteristics, such as:

• Nutrient-use efficiency
• Tolerance to abiotic stress
• Crop-quality traits
• Availability of confined nutrients in soil or the rhizosphere

This definition emphasizes function rather than nutrient concentration.

Plant biostimulants may include products based on or associated with:

• Seaweed extracts
• Humic and fulvic substances
• Protein hydrolysates
• Amino acids and peptides
• Beneficial microorganisms
• Chitosan and related compounds
• Other bioactive materials

Their primary value lies in influencing processes associated with plant nutrition, physiology, roots, rhizosphere interactions, or stress responses.

The Important Overlap Between Biofertilizers and Biostimulants

The terminology can be confusing because biofertilizers and microbial biostimulants overlap.

A microorganism may improve nutrient availability while simultaneously influencing root development or other plant physiological processes.

Different regulatory systems and scientific traditions may therefore classify similar microbial technologies differently.

For example, a microorganism marketed primarily for phosphorus solubilization may commonly be described as a biofertilizer.

A microbial product marketed under a regulatory framework according to demonstrated plant-biostimulant functions may be classified as a microbial plant biostimulant.

The important lesson is that agricultural professionals should not rely only on category names.

Instead, evaluate:

• What organisms does the product contain?
• What function is claimed?
• What scientific evidence supports that function?
• What does the local regulatory framework permit the product to claim?

This function-based approach provides much more useful information than terminology alone.

The Fundamental Difference: Supply, Mobilize, or Stimulate

A practical way to understand the three categories is to focus on their principal functions.

Conventional Fertilizers — Supply

Fertilizers primarily supply essential nutrients.

Examples include:

Urea → nitrogen

MAP → nitrogen + phosphorus

DAP → nitrogen + phosphorus

Potassium chloride → potassium

Ammonium sulfate → nitrogen + sulfur

NPK fertilizers → combinations of nitrogen, phosphorus, and potassium

Biofertilizers — Mobilize Through Biology

Biofertilizers primarily use microorganisms to improve nutrient availability, transformation, or acquisition.

Examples may involve:

Nitrogen fixation

Phosphorus solubilization

Mycorrhizal nutrient acquisition

Rhizosphere nutrient mobilization

Biostimulants — Stimulate

Biostimulants primarily stimulate plant nutrition processes and related physiological responses.

Potential objectives include:

Improved nutrient-use efficiency

Root development

Abiotic-stress tolerance

Crop-quality improvement

Nutrient availability

This creates a useful conceptual model:

Fertilizer = Supply

Biofertilizer = Biological nutrient support

Biostimulant = Physiological or nutritional process stimulation

The boundaries are not always absolute, but the model helps explain the different agronomic roles.

Can Biostimulants Replace Fertilizers?

In most commercial production systems, biostimulants should not be treated as direct replacements for essential crop nutrition.

Consider a crop requiring substantial nitrogen to reach its yield target.

A seaweed extract may influence root development or physiological responses, but it does not normally provide the quantity of nitrogen required to build the crop.

Similarly, a protein hydrolysate may influence nitrogen metabolism, but this does not eliminate the crop's fundamental nitrogen requirement.

The same principle applies to phosphorus, potassium, sulfur, magnesium, calcium, and micronutrients.

A crop cannot physiologically manufacture mineral elements that are absent from its growing environment.

Biostimulants may help plants use available resources more effectively, but those resources must still be present.

Can Biofertilizers Replace Conventional Fertilizers?

The answer depends on the crop, microorganism, nutrient, environment, and production system.

Biological nitrogen fixation can provide substantial nitrogen in appropriate legume systems.

Other microbial technologies may contribute to nutrient availability or acquisition.

However, the performance of biological systems can be less predictable than the direct application of a known quantity of mineral nutrients because microorganisms are sensitive to environmental conditions.

Their activity can be influenced by:

• Soil temperature
• Soil moisture
• pH
• Salinity
• Organic matter
• Existing microbial populations
• Fertilizer concentrations
• Pesticides
• Crop compatibility

The objective should therefore not automatically be "replace fertilizer."

A more scientifically useful objective is:

Determine how biological nutrient technologies can be integrated into fertilizer management to efficiently achieve the required crop performance.

Why Nutrient-Use Efficiency Matters

Not every kilogram of nutrient applied as fertilizer ultimately becomes part of the harvested crop.

Nutrients can be lost, immobilized, transformed, or rendered temporarily unavailable.

Nitrogen may be affected by:

• Ammonia volatilization
• Nitrate leaching
• Denitrification
• Immobilization

Phosphorus may become associated with soil components, reducing its immediate availability to plants.

Other nutrients also undergo chemical and biological transformations.

Improving nutrient-use efficiency (NUE) is therefore an important objective in modern agriculture.

Better nutrient-use efficiency can potentially contribute to:

• Improved crop productivity
• Reduced nutrient losses
• More efficient fertilizer investment
• Lower environmental impact
• More precise nutrient management

Fertilizers, biofertilizers, and biostimulants can potentially contribute to this objective through different mechanisms.

How the Three Categories Can Work Together

The most advanced crop-nutrition programs do not necessarily choose between conventional fertilizers, biofertilizers, and biostimulants.

They may integrate them.

A simplified strategy can follow several stages.

Stage 1 — Diagnose Nutrient Requirements

Use:

• Soil analysis
• Tissue analysis
• Irrigation-water analysis
• Yield targets
• Crop nutrient-removal data
• Historical field performance

The objective is to determine what the crop and soil actually require.

Stage 2 — Build the Nutritional Foundation

Supply essential nutrients using appropriate fertilizer sources, rates, timing, and placement.

This establishes the nutritional foundation required for crop production.

Stage 3 — Evaluate Biological Opportunities

Determine whether microbial technologies could improve nutrient acquisition or rhizosphere function.

Product selection should consider the crop, soil, environment, microbial strain, and compatibility with the existing program.

Stage 4 — Identify Biostimulant Objectives

Determine whether a biostimulant has a specific role.

Possible objectives include:

• Root establishment
• Nutrient-use efficiency
• Drought-stress preparation
• Salinity tolerance
• Transplant recovery
• Crop-quality support

Stage 5 — Measure Performance

Evaluate the integrated program using measurable outcomes.

These can include:

• Yield
• Marketable yield
• Crop quality
• Fertilizer input
• Nutrient-use efficiency
• Root development
• Stress response
• Treatment cost
• Economic return

Example: Nitrogen Management

Consider a crop with significant nitrogen demand.

A conventional nitrogen fertilizer, such as urea, may provide the primary source of nitrogen.

A suitable microbial technology may contribute to nitrogen cycling or biological nitrogen input, depending on the crop and organism.

A biostimulant may be selected to support root development, nutrient-use efficiency, or physiological performance.

These products perform different functions.

The objective of integration is not simply to add more inputs.

The objective is to build a system in which each input has a clearly defined agronomic purpose.

If adding a biological or biostimulant product produces no measurable improvement, its inclusion should be reconsidered.

Example: Phosphorus Management

Phosphorus provides another useful example.

A phosphorus fertilizer, such as MAP or DAP, supplies phosphorus to the crop-production system.

Phosphate-solubilizing microorganisms may potentially improve access to certain phosphorus pools.

Mycorrhizal fungi can extend the effective nutrient-acquisition network associated with plant roots.

Certain biostimulants may influence root architecture or other processes associated with nutrient acquisition.

These mechanisms can potentially complement one another.

However, the correct program depends heavily on soil phosphorus status, pH, crop requirements, soil biology, fertilizer placement, and environmental conditions.

Application and Compatibility Challenges

Integrated programs require careful management because not every product is compatible with every other input.

Potential issues include:

• Extreme solution pH
• High salt concentrations
• Chemical incompatibility
• Precipitation
• Reduced microbial viability
• Incompatible pesticides
• Chlorinated irrigation water
• Unsuitable storage conditions

Living microbial products require particular attention.

A tank mixture that is harmless to a seaweed extract may significantly reduce the viability of a bacterial or fungal inoculant.

Manufacturers should therefore provide clear guidance regarding:

• Tank mixing
• Water quality
• Storage temperature
• Application timing
• Compatible fertilizers
• Compatible pesticides
• Shelf life

Growers should follow product-specific recommendations rather than assuming that all biological products can be mixed together.

Product Quality Is Critical

The quality requirements for each category differ.

Conventional Fertilizers

Important parameters include:

• Nutrient analysis
• Chemical form
• Moisture
• Particle size
• Granule strength
• Solubility
• Contaminants
• Manufacturing consistency

Biofertilizers

Important parameters can include:

• Microbial species and strain
• Viable cell or propagule concentration
• Purity
• Shelf life
• Carrier quality
• Storage conditions
• Contamination control

Biostimulants

Relevant parameters depend on the product category and may include:

• Raw-material source
• Extraction method
• Molecular composition
• Microbial strain
• Peptide profile
• Molecular weight
• Degree of deacetylation
• Formulation stability
• Biological activity

The product name alone is therefore insufficient for professional evaluation.

Avoiding Marketing Confusion

The rapid growth of biological agricultural inputs has led to a proliferation of marketing terminology.

Products may be described as:

"Natural fertilizer"

"Biofertilizer"

"Biological fertilizer"

"Plant enhancer"

"Growth promoter"

"Biostimulant"

"Stress reducer"

"Root activator"

These terms can create confusion when they are not linked to clearly defined functions.

Agricultural buyers should look beyond front-label terminology.

Instead, examine:

• Guaranteed composition
• Microorganism identification
• Nutrient content
• Mode of action
• Regulatory classification
• Scientific trials
• Recommended application
• Crop-specific evidence

The key question remains:

What measurable agronomic function does this product perform?

Regulatory Classification Matters

Product classification can vary between jurisdictions.

The European Union provides a regulatory framework for EU fertilizing products through Regulation (EU) 2019/1009, which includes plant biostimulants among defined product function categories.

Other countries may use different terminology or regulatory structures for fertilizers, microbial inoculants, soil amendments, plant biostimulants, and plant-protection products.

A product considered a biostimulant in one market may require a different classification, registration pathway, or set of permitted claims elsewhere.

Manufacturers and international traders should therefore evaluate regulatory requirements on a market-by-market basis.

This is particularly important when products make claims involving pest or disease control, because such claims may move the product into plant-protection regulatory frameworks.

Which Product Should a Grower Choose?

The correct choice depends on the problem.

If the crop has a documented nitrogen deficiency, the immediate requirement is adequate nitrogen nutrition.

If phosphorus is present in the soil but is limited in availability, fertilizer strategy, soil chemistry, placement, and potentially biological approaches may all need to be evaluated.

If the crop already has adequate nutrition but faces predictable environmental stress, an appropriate biostimulant may be worth considering.

If the objective is to establish a beneficial root-microbe relationship, a suitable microbial inoculant may be appropriate.

This produces a simple decision framework:

Nutrient missing? → Correct the nutrient supply.

Nutrient present but biologically difficult to access? → Investigate soil, root, fertilizer, and microbial strategies.

Is plant nutrition adequate, but physiological efficiency or stress tolerance needs support? → Evaluate an appropriate biostimulant.

Multiple limitations exist. → Build an integrated program.

From Input-Based Agriculture to Systems-Based Nutrition

Historically, crop nutrition was often approached through individual inputs.

A field required nitrogen, so nitrogen fertilizer was applied.

Modern agriculture increasingly requires a systems perspective.

Crop performance emerges from interactions among:

• Genetics
• Soil
• Water
• Mineral nutrition
• Microorganisms
• Root architecture
• Climate
• Crop protection
• Plant physiology
• Management practices

Fertilizers remain essential because plants cannot produce mineral elements themselves.

But understanding the biological and physiological systems surrounding those nutrients can create opportunities to use agricultural inputs more efficiently.

This is where biofertilizers and biostimulants become strategically important.

Their future value is likely to depend less on replacing fertilizers and more on improving the performance of the entire plant-soil-nutrient system.

The Future of Integrated Crop Nutrition

Future fertilizer programs are likely to become increasingly data-driven and biologically informed.

Technologies such as:

• Precision soil mapping
• Plant tissue diagnostics
• Root-zone sensors
• Satellite imagery
• Variable-rate fertilization
• Microbial analysis
• Weather forecasting
• Artificial intelligence
• Crop-growth models

May allow growers to identify when and where different nutritional and biological technologies provide genuine value.

Biological products may also become increasingly specific.

Instead of broad claims such as "improves plant growth," future products may be developed for specific crops, soil conditions, nutrient interactions, or environmental stresses.

The distinction between chemistry and biology in crop nutrition may therefore become less important than understanding how to integrate them intelligently.

Conclusion

Conventional fertilizers, biofertilizers, and plant biostimulants are related components of modern crop nutrition, but they should not be treated as interchangeable products.

Conventional fertilizers primarily supply essential nutrients.

Biofertilizers use beneficial microorganisms to support nutrient availability, transformation, or acquisition.

Plant biostimulants stimulate plant nutritional processes and physiological responses associated with nutrient-use efficiency, abiotic stress tolerance, crop quality, or nutrient availability.

Their functions can overlap, particularly where microbial technologies are involved, but their agronomic purposes remain distinct.

The most effective crop-management strategy, therefore, is not to ask whether biological products should replace conventional fertilizers.

Instead, growers should determine which combination of technologies provides the nutrients, biological support, and physiological efficiency required by the crop.

Successful integration begins with diagnosis, continues with balanced nutrition, and adds biological or biostimulant technologies only when they have a defined purpose and measurable benefit.

As agriculture moves toward higher nutrient-use efficiency and more resilient production systems, the future is likely to involve not fertilizer versus biology, but fertilizer integrated with biology.

References

1. European Parliament and Council (2019). Regulation (EU) 2019/1009 — EU Fertilizing Products Regulation.
2. du Jardin, P. (2015). Plant biostimulants: Definition, concept, main categories, and regulation. Scientia Horticulturae, 196, 3–14.
3. Calvo, P., Nelson, L. & Kloepper, J.W. (2014). Agricultural uses of plant biostimulants. Plant and Soil, 383, 3–41.
4. Vessey, J.K. (2003). Plant growth-promoting rhizobacteria as biofertilizers. Plant and Soil, 255, 571–586.
5. Rouphael, Y. & Colla, G. (2020). Editorial: Biostimulants in Agriculture. Frontiers in Plant Science, 11, 40.
6. Van Oosten, M.J., Pepe, O., De Pascale, S., Silletti, S. & Maggio, A. (2017). The role of biostimulants and bioeffectors in alleviating abiotic stress in crop plants. Chemical and Biological Technologies in Agriculture, 4, 5.
7. Yakhin, O.I., Lubyanov, A.A., Yakhin, I.A. & Brown, P.H. (2017). Biostimulants in Plant Science: A Global Perspective. Frontiers in Plant Science, 7, 2049.