Many agricultural workers continue seeking ways to balance crop input and output economics without contributing to climate change. Global warming has dealt undeniable damage to the agricultural sector, despite some positive effects. The increased CO2 concentration in the atmosphere may have increased crop productivity, but the adverse effects from rising temperature, such as reduced crop quantity and quality, outweigh the positives.
Regardless of the scale of the agricultural business, growers face issues affecting plant growth and crop yields. This constant problem prompts farmers to adopt new technology as the world changes. Farmers must keep up with the developing agricultural landscape to stay relevant. Some farmers have turned to biostimulants as advanced horticultural technology to help solve their plant growth and crop production problems.
Biostimulants are a new type of agricultural additive product that many European experts have observed to improve plant growth and crop yields. Experts claim that biostimulants reduce the need for plant inputs, like fertilizers and pesticides, while maintaining an ideal quality and quantity of crop output. With less input and a constant or possibly higher output, any grower would naturally assess their options to improve their farming productivity.
The experts that make such claims practice mainly in Europe because biostimulants remain new agricultural additives that require further studies before the American agricultural sector can confidently adopt and distribute the technology. The European experts who engage in biostimulant experiments tend to agree that these products have great potential for making positive changes to the existing agricultural landscape.
Existing studies have highlighted the different positive effects that biostimulants offer to agricultural products. The current data may support calls for further investigations into biostimulants’ effects, which currently place the product as a potential answer to the problems growers face regarding farm sustainability. To understand these new products better, we gathered the existing data on biostimulants and their effects on the agricultural sector.
What Are Biostimulants in Agriculture?
Biostimulants are a new product class designed to increase agricultural crop yield. However, there is no legal definition for the products because they require further studies before the product class can have its official description. Longitudinal studies into new products may require years of close experiments, so we may not see a standard definition any time soon.
European Experts who explore new ways to improve farm sustainability have established the current definition of biostimulants. Among these experts is Professor Patrick du Jardin, the Director of the Botanic Garden at the University of Liège in Gembloux, Belgium. He says that biostimulants are “defined by what they do” instead of what the products are. In essence, biostimulants alter microbial content in the soil. This chemical alteration promotes plant growth, making the products be potential initiatives that contribute to sustainable agriculture.
Meanwhile, the European Biostimulants Industry Council (EBIC) defines plant biostimulants as materials containing stimulating substances and microorganisms. These substances and microorganisms stimulate the natural processes that plants undergo to enhance nutrient uptake, nutrient efficiency, abiotic stress tolerance, and crop quality regardless of its nutrient content. In other words, biostimulants have contents that benefit the natural plant processes without necessarily providing additional nutrients for a plant.
How Biostimulant Products Work
Farmers would apply biostimulants to a plant’s rhizosphere or the soil region around a plant’s roots. This area involves microbiology and chemistry that influences a plant’s growth, respiration, and nutrient exchange. These qualities make biostimulants seem comparable to fertilizers.
The United States Environmental Protection Agency (EPA) even classifies some fertilizers as plant growth regulators (PGRs) because they include chemicals that improve a plant’s growth. PGR chemicals contain hormones that may increase plant branching, suppress shoot growth, boost crop yield, remove excess fruit, and alter fruit maturity.
These effects are direct results of PGRs. The fact that they directly influence a plant’s growth is a critical differentiating factor between traditional fertilizers and biostimulants. The EBIC also differentiates biostimulants from conventional fertilizers by agreeing with the product’s role in improving plant growth.
Biostimulants and Nutrient Content
Biostimulants affect a plant’s growth rate independently of the product’s nutrient content. In addition, biostimulant products may not necessarily contain supplementary nutrients that help a plant grow more efficiently, which is the premise behind fertilizers and PGRs. Traditional fertilizers improve the soil’s chemical composition by adding more nutrients for better plant growth.
In contrast, the premise behind biostimulants is that they target the existing nutrients in the soil to help with plant growth. Biostimulants may improve plant growth by stimulating or boosting the microbial activity that naturally occurs in the rhizosphere by supplementing the existing bacteria with substances or microorganisms. In other words, the supplementary substances that biostimulants offer indirectly improve plant growth because they target the existing nutrients in the soil.
Biostimulants and Plant Vigor
Enhancing the natural microbial makeup in the soil where a plant grows affects the plant’s vigor. A plant’s vigor is another critical factor that the EBIC cites as a differentiator between biostimulants and fertilizers. We can also compare the enhancement of a plant’s vigor to the way pesticides work. Like fertilizers, pesticides are input products that directly affect plants.
Since biostimulants are soil additives that only target the existing microorganisms in a particular area, the stimulated microorganisms will trigger a plant’s natural processes that involve those microorganisms. This trigger may result in a plant’s boosted resistance against natural stresses without needing extra chemicals to enhance its protection against those stresses.
Plant stressors include abiotic stresses like excess or deficient water levels and high- or low-temperature levels. These stressors may degrade a plant’s condition, making them more susceptible to diseases. Plants are also prone to biotic stresses like insects and pests, which usually call for pesticides.
Unlike pesticides that require chemicals to ward off pests and protect them from insect-borne diseases, biostimulants only strengthen a plant by improving the microbial content in the soil. When biostimulants enhance a plant’s vigor or hardiness by stimulating the naturally existing microorganisms in the rhizosphere, the plant indirectly becomes more susceptible to diseases and pests.
“Biostimulants” That Directly Affect Plants
We have established that the European definition of biostimulants is the current standard when we talk about this product class. Biostimulants must be products containing rhizobacteria that indirectly improve plant growth. However, some agricultural experiments use alleged biostimulant products that require a direct application.
This confusion lends itself to the fact that biostimulant products need further studies before having an official definition. Biostimulant products that directly affect a plant’s growth without intervention through the rhizosphere, but contain elements of the usual biostimulant products, such as rhizobacteria, make biostimulant classification difficult.
Regardless of this inconsistent definition, bacteria and microorganisms remain constant among the different classes of biostimulant products. A farmer can either add the product to the soil to improve natural processes through the roots or directly add the substances to certain plant parts to stimulate growth. These substances and microorganisms are the main factors that influence plant growth, which require more longitudinal studies to assess their actual efficacy.
Section Recap: What We Know About Biostimulants in Agriculture
Biostimulants are new products that improve plant growth by enhancing natural microbial processes in the rhizosphere. This rhizosphere is the soil layer around a plant’s roots that influence plant growth.
Biostimulants, as new products, have no legal or official definition apart from the EBIC’s classification. This council recognizes biostimulants as products that contain substances or microorganisms that enhance a plant’s natural processes involving nutrient uptake.
Biostimulants provide natural stimulation, which affects plant growth and may increase plant yield. This effect makes experts deem the product a potential answer to the growing need for modern technology to improve farm sustainability.
Biostimulants are different products from fertilizers and pesticides. While all three types of products are inputs, they affect a plant’s growth and potential yield increase through other mechanisms.
Fertilizers and pesticides directly affect a plant upon application. Meanwhile, biostimulants indirectly affect a plant by targeting the microorganisms that affect plant growth. Biostimulants contain substances and microorganisms that interact with soil nutrients and root secretions in the rhizosphere. However, some biostimulant experiments involve direct product application for plant growth.
This inconsistency contributes to the confusion of classifying biostimulants as a unique product type altogether. We need more studies to establish this product as a unique type before confidently giving biostimulants an official definition.
Regardless of the direct and indirect plant growth that biostimulants offer, rhizobacteria is a constant in these products. These microorganisms stimulate the existing microbes in the rhizosphere. When the microbes in the soil have more activity, plants grow through biostimulation.
What Is Biostimulation?
Biostimulation is an environmental modification process involving the encouragement of indigenous bacteria and microorganisms in a particular area to perform bioremediation. The process usually involves adding limiting nutrients and electron acceptors. These elements are oxidizing agents such as carbon, nitrogen, oxygen, and phosphorus. Adding these nutrients to a particular area will stimulate the existing microorganisms through natural processes.
Organic substrates or electron donors are other input materials that may help remediate halogenated contaminants in an anaerobic environment. In other words, an environment that lacks oxygen may have halogen contamination, which is pollution due to fluorine, chlorine, bromine, or iodine. Electron donors are reducing agents that donate electrons to an area for similar natural processes that electron acceptors offer.
Typical delivery techniques of anaerobic bioremediation for biostimulation purposes include injection wells, circulation systems, direct injection, borehole backfill, trenching, excavation, and biosparging wells. These methods depend on the type of substrate needed for delivery to the subsurface. Typical substrates for anaerobic bioremediation purposes include soluble substrates, slow-release substrates, solid substrates, and miscellaneous substrates.
Relatedly, it is notable that injection well technology is still an emerging method for biostimulation. As such, using this method to deliver organic substrates to the subsurface to stimulate anaerobic biodegradation may not be the best solution for bioremediation. In addition, the subsurface may contain enough nutrients that sustain the microbial population, which makes the addition of substrates to the area potentially create a demand for the additional nutrients.
Significance of Biostimulation
Regardless of the need for more research into certain organic substrate delivery methods, bioremediation for biostimulation purposes remains an EPA-approved method for certain environmental contamination issues. The significance behind the process is to reverse the environmentally debilitating effects of gas and oil spills.
The biostimulation process would encourage local bacteria and indigenous microorganisms in an affected environment by adding organic substrates. The existing microorganisms are already suited to an affected environment. Thus, stimulating the local microbes capable of bioremediation helps clear the contaminants in an affected area by speeding up the natural biodegradation processes that microorganisms perform.
Experts mostly associate biostimulation with the removal of hydrocarbons, which explains why the process is a standard method for reversing environmental contamination cases from oil spills. Hydrocarbons naturally occur in crude oils such as petroleum and natural gas. These substances are the usual contaminants in groundwater and the subsurface due to oil spills.
An existing study by Matt Radermacher on using bioremediation for marine oil spills highlights the method as an ideal approach for cleaning contaminated areas. Radermacher discussed how oil contains different toxic compounds that endanger the natural habitats involved in a spill.
However, the native microorganisms in an affected area can decompose toxic compounds and thrive on such materials. Thus, bioremediation in marine oil spills aims to utilize natural processes for cleanup efforts.
The bioremediation process in a marine oil spill would involve adding organisms capable of degrading hydrocarbons to an affected site. The input material enhances the biodegradation process by encouraging the native microorganisms to speed up their natural capability to consume and degrade hydrocarbons present in an oil spill site.
This concept applies to agriculture. Instead of improving the natural degradation processes in a marine oil spill, biostimulation in agriculture improves the biological processes that local bacteria undergo in the rhizosphere, affecting a plant’s overall growth and development.
Advantages of Biostimulation
The existing study on bioremediation for marine oil spills highlighted several advantages biostimulation has over traditional methods of cleaning up oil spills. The author cited financial advantages as the most significant edge biostimulation offers.
Proper bioremediation procedures may cost less than traditional oil spill cleanup procedures. Traditional processes include physical and chemical cleanup methods.
Physical cleanup may involve booms, which are floating barriers made of plastic or metal to contain an oil spill within a manageable area. Washing coastal areas is another physical method involving hot or cold water, high or low pressure, and absorbent materials to remove oil from coastal areas. Cleaners may also need to physically transport oil to another site, which costs extra funds and human resources.
Meanwhile, chemical cleanup methods may involve dispersants containing compounds that help disperse oil from the water surface. Other chemicals include demulsifiers, solidifiers, and surface film chemicals that help make physical cleanup easier. The U.S. has been hesitant to use chemical cleanup methods to avoid the risk of introducing toxic compounds to the natural environment.
The study cited the Exxon Valdez oil spill in 1989 as evidence for biostimulation being a cheaper alternative to traditional cleanup methods. The Exxon Valdez oil spill cleaners utilized bioremediation methods to clean 120 km of shoreline, which cost less than the price they paid to wash the shore for one day physically.
The fact that bioremediation procedures require fewer labor costs also contributes to the procedure’s financial advantage over traditional cleanup methods. With bioremediation saving time, experts can spend labor time conducting more research into bioremediation as a sustainable method.
Biostimulation is also a natural cleanup method, making it an environmentally friendly approach than the chemical alternative and less invasive than the physical approach. Biostimulation does not introduce foreign materials to an ecosystem, which may disrupt natural habitats.
The bioremediation process only adds materials to encourage local bacteria to perform their natural processes. The natural processes would degrade hydrocarbons into simpler compounds that pose no threat to the contaminated area, thus eliminating the need to transport the oil to another site physically.
These financial advantages may translate to the agricultural sector by reducing the need for input materials like fertilizers and pesticides. Biostimulation in agriculture involves the improvement of local bacteria and microorganisms for plant growth.
Fertilizers and pesticides are also foreign materials that risk contaminating the local environment. By adopting inputs that target the naturally occurring bacteria in the rhizosphere, farmers can save on fertilizers for direct plant improvement.
Potential of Biostimulation
Besides cleaning marine oil spills and subsurface contamination, biostimulation could potentially treat contaminations in the agricultural sector. Pesticide and herbicide contaminant spills in farmlands are especially common. The same principle of introducing additives that speed up the biodegradation process would operate in these types of contaminations.
Apart from being ideal cleanup methods, the idea behind biostimulation of utilizing the existing microbes in a particular area has the potential to improve the natural processes that influence plant growth. European biostimulant experts already harness this potential with their biostimulant products. Such products contain substances and microorganisms that may work together with indigenous microbes to improve the natural processes that occur in the rhizosphere.
Section Recap: What Is Biostimulation?
The idea behind biostimulation is environmental modification. It is a process that involves adding substances or microorganisms to a particular area to assist the existing microbes in performing their natural processes. The microorganisms in an area that are capable of bioremediation are the main targets for biostimulation.
Bioremediation is a process that involves microorganisms and bacteria in removing pollutants, contaminants, and toxins from an affected area, whether it is in water or soil. These microorganisms that are capable of bioremediation already exist in affected areas. The existing bacteria are responsible for the natural biodegradation process. Biostimulation aims to speed up that natural degradation process to break down contaminants into safer compounds to save an affected area.
This procedure has advantages and disadvantages. The primary advantage of biostimulation is that it can save a lot of time and effort during a cleanup. A study on marine oil spills highlighted that the bioremediation procedures that cleaners conducted cost much less than what it cost them to clean the affected shoreline physically. Bioremediation saves time by reducing the need for extra labor hours. So, researchers can spend the extra time developing the existing bioremediation procedures.
Meanwhile, the primary disadvantage of biostimulation for cleanup purposes is its unpredictability as a cleaning method. There is no telling how the local bacteria and microorganisms in an affected area will react to biostimulant substances. Bioremediation remains in its early development stages, making longitudinal research extremely necessary to establish procedural standards.
At the same time, conducting field research on bioremediation can be difficult because of the factors that vary from case to case. Some affected sites may have certain local microorganisms that do not occur in other locations. In other words, numerous uncontrollable variables make field tests challenging. Researchers have more control in laboratory tests, although they must find ways to apply their lab results to real-world situations at a certain point.
In the agricultural sector, biostimulation can potentially benefit plants by adopting the concept of utilizing the existing microorganisms in a particular area to improve naturally occurring plant processes. Microorganisms and bacteria in the rhizosphere naturally affect plant processes, so stimulating these microbes with additives would enhance plant activities. European biostimulant experts already utilize this concept with the biostimulant products they use.
Benefits of Biostimulants in Agriculture
In an agricultural context, biostimulants mainly benefit plants by boosting their nutrient efficiency, providing more effective and efficient plant growth and development. Biostimulant plant growth and development owe to biostimulants' design and formulation to target the local bacteria in a given area.
The microorganisms undergo natural processes associated with increasing plant tolerance to abiotic stresses such as fluctuations in water intake, changes in temperature, high salinity levels in the soil, and ultraviolet radiation. When plants have better tolerance against these stressors, they are likely to grow better and yield more crops.
Biostimulant products may provide a cheaper alternative and more profitable option for farmers seeking to improve their harvestable yields. Biostimulants offer the potential to enhance farm sustainability by reducing the need for foreign input products like fertilizer and pesticides. High-quality and carefully researched biostimulant products may provide similar results that traditional input products offer. As such, growers may get the chance to save on extra input products while maintaining an ideal crop output.
Although biostimulants and fertilizers work toward similar goals of improving a grower’s land and overall yield, we must reiterate that biostimulants and plant growth regulators are different product classes. Biostimulants’ potential to reduce the need for fertilizers and pesticides owe to the products’ ability to target indigenous microorganisms existing in the soil, which perform the natural processes that affect plant growth.
Traditional fertilizers and pesticides are direct input products that farmers would add to their plants to impact growth and development. Biostimulants target growth and development indirectly by enhancing the plants’ nutrient intake through the microorganisms existing in the soil. These products activate the natural micro-bacterial activities instead of providing foreign nutrients for plant growth, development, and protection against pests.
Reducing fertilizer and pesticide use also reduces the risk of chemical runoffs. While natural fertilizers and pesticide products exist, these additives may contain traces of chemical components that traditional input products use.
Farmers who would reduce their dependence on such products for agricultural practices would likewise reduce the chances of foreign chemicals leaching into their immediate environment. Similarly, using plant biostimulants decreases nutrient leaching, or the loss of water-soluble plant nutrients, which would otherwise be detrimental to plant growth and crop yield.
Other benefits of plant biostimulants include biofortification improvements. Biofortification is the process of improving nutritional crop quality through agronomic practices, which aim to enhance soil quality and enhance water usage while limiting environmental impact. Biofortification also involves conventional plant breeding, consisting of crossbreeding plants with ideal characteristics to produce offspring with particular and desirable traits.
The biofortification improvements that biostimulants offer involves modern biotechnology. The substances and microorganisms that biostimulant products contain potentially improves food crop quality by enhancing the sugar and protein content.
The Role of Biostimulants in Plants
European experts have established their definition of plant biostimulants, aiming to improve plant growth, development, and yield. These products contain extracts and compounds that indirectly enhance plant activity through the bacteria and microorganisms in the rhizosphere.
These capabilities make biostimulants an exciting breakthrough in the agricultural sector’s constant search for modern practices that enhance farm sustainability. However, the lack of official definitions and standard licensing in America may leave many farmers wary of biostimulants’ purported benefits.
Skeptical growers may get insight from existing studies highlighting the role of biostimulants in plants. One peer-reviewed chapter explores biostimulants and their role in improving plant growth under abiotic stresses. This paper gathers different studies on how effective plant biostimulant products are in improving plant resistance against environmental stressors, particularly water, salt, and temperature.
Water Stress Protection
Water stress in plants may involve either too much or too little water. Water deficiency is a more prevalent abiotic stress for plants in the U.S., considering that drought conditions persist, worsen, and dramatically expand as climate change affects vast portions of the country.
Plants that experience drought stress suffer on a molecular, biochemical, ecological, morphological, and physiological level. In general, the adverse effects of water deficiency hinder the quality of a plant’s growth, thus affecting the quantity of its crop yield.
The peer-reviewed chapter cited a study where researchers found that some plants in their early development stages had demonstrated accelerated recovery rates when they introduced biostimulants in the mix. The plants in the study exhibited quicker growth rates despite water deficiency and generally unfavorable conditions.
The study highlighted organic biostimulants as the type of product that showed more favorable effects on plant productivity and resistance against low water availability. The study featured soybean plants under water stress, which have shown an increase in dry mass and leaf area once the researchers applied biostimulant products.
In addition, the experimental plants’ total chlorophyll index has increased. This development suggests a greater photosynthetic efficiency, so the plants become more capable of converting light energy into chemical energy. Thus, the plants are more active and have more resources to grow.
The study also featured sugarcane and maize plants under water stress to see how well biostimulants work across different plant species. The findings under the sugarcane experiments included a higher productivity and profitability index. These results suggest that biostimulants for sugarcane under water stress may be a practical economic solution during a drought crisis.
Meanwhile, the experiments with biostimulants for maize plants under water stress found that the plants contained a higher relative water content in their leaves. Other results included lower temperatures in leaves and surrounding air, suggesting that maize plants with biostimulants become more resilient despite water deficit conditions.
Salt Stress Protection
Salinity as abiotic stress in plants may lead to stunted growth, which would affect production rates. Stunted plant growth occurs because the high salinity levels in soil inhibit a plant’s water absorption rates. Furthermore, plants risk absorbing the salt from the soil with excessive salinity levels. Plants that absorb too much salt from their growing environment would risk injuring their leaf cells, further affecting the plant’s growth rate.
Researchers studied the effects of biostimulants on plants under salt stress using humic biostimulants. This category of biostimulant products comes from decomposed materials and has shown a promising impact in protecting plants against salt stress.
Adding humic biostimulants to soil with high salinity levels has improved the affected area’s physical and chemical properties, resulting in soil with better conditions for plant growth. Relatedly, humic substance-based biostimulant products have shown potential in improving a plant’s water absorption rate despite growing under salt-stressed conditions.
The study used common beans and rice as the experimental plants under salt stress to determine how effective humic biostimulants are. The study mentioned how humic acids could increase endogenous proline (amino acid) levels and reduce plant membrane leakage in common beans under high-salinity stress.
Plants with boosted amino acid levels and reduced membrane leakage are well-adapted to high salinity environments. The study suggested the effects that humic acids bring to common beans may exist in humic substance-based biostimulants. Thus, biostimulants formulated with humic substances may improve plant resistance against high salinity environments.
Other biostimulants that have the potential to improve plant resistance against salt stress are those based on algae and arbuscular mycorrhizal fungi (AMF). Turfgrass experiments featuring Kentucky bluegrass had shown improvement in grass growth despite salt stress when researchers applied algal extracts. Meanwhile, researchers who conducted tomato plant experiments found potential protective qualities against salt stress in AMF.
Temperature Stress Protection
Plants under temperature stress, which classify as either high, chilling, or freezing, will have a reduced ability to photosynthesize. This disability leads to reduced germination rates and delayed plant growth. As such, plant yield would decrease.
Biostimulants target a plant’s natural processes to cope with temperature stress. Plants have biological processes that involve molecular mechanisms. These processes use natural protectants such as antioxidants, membrane lipids, metabolites, and proteins.
The study discussed how melon plants under high-temperature conditions showed promising effects when researchers introduced biostimulants in the mix. Researchers conducted a controlled experiment featuring melon plants and subjecting them to 25°C and 40°C (77°F and 104°C) temperatures.
In both cases, melon plants appeared to improve their germination and initial growth rates when researchers added biostimulants as a temperature stress reliever. The findings suggest that biostimulant products have the potential to enhance plant growth and development in high-temperature areas, which may prove helpful in regions that experience rising temperature levels.
Meanwhile, studies on low-temperature stress involved strawberry plants and porcine hemoglobin hydrolysate (PHH). PHH are proteins derived from pig sources and have undergone water treatments or hydrolysis for extraction. Researchers observed that the strawberry plants in their experiments experienced an increase in plant biomass when the researchers used PHH as biostimulants.
The researchers subjected strawberry plants to cold-temperature experiments, which included chilling and freezing temperature categories. The strawberry plants exhibited early flowering when the researchers applied PHH biostimulants. This effect suggests the potential of PHH biostimulants in improving crop yields during winter.
Although biostimulants have no official categories yet, experts in the biostimulant movement widely recognize some major categories. Scientists, regulators, and stakeholders typically categorize biostimulant products based on the substances and microorganisms that potentially affect plant growth and development. In particular, the scientific journal Scientia Horticulturae highlights seven categories of biostimulants in the journal’s 196’th volume released in 2015:
Humic and Fulvic Acids
Humic substances (HS) are organic compounds, and fulvic acids are a group of chemicals. These substances come from plant, animal, and microbial decomposition. HS may form when soil microbes metabolize the residue from decomposing matter. Meanwhile, fulvic acids form when organic animal and plant matter decomposes.
HS is a standard contributor to soil fertility. Experts have observed the compounds’ ability to affect soil’s physical, chemical, and biological properties. So, HS-based biostimulants mainly operate similarly to increase a plant’s macro and micronutrient uptake.
Protein Hydrolysates and Other N-Containing Compounds
Biostimulants under this category contain plant and animal amino acids that undergo hydrolysis. Alternatively, these products may contain other compounds with nitrogen molecules such as polyamines and betaines.
This category of biostimulants has demonstrated positive effects in modulating a plant’s nitrogen uptake and assimilation. These effects affect a plant’s growth rate, which may offer significant improvements in crop yield.
Seaweed Extracts and Botanicals
This up-and-coming category of biostimulants utilizes seaweed extracts, which have a history of being the main ingredients in fertilizers. Agricultural reports using seaweed-based biostimulants suggest the substance’s potential to improve a plant’s tolerance against abiotic stress.
Chitosan and Other Biopolymers
Biostimulants based on chitosan have demonstrated improvements in a plant’s resistance against environmental stress. Chitosan is a chitin derivative that undergoes deacetylation. Chitin is a biopolymer or fibrous substance forming fungal cell walls and arthropod exoskeletons.
Meanwhile, deacetylation is a process that substitutes chitin acetyl groups with reactive amino acids. The process improves a plant’s stress responses against fungal pathogens. The increased stress resistance induces significant physiological changes in the plants.
Biostimulants based on inorganic compounds improve plant tolerance against abiotic stress. Experts have also observed how these products improve nutrient efficiency to promote plant growth. Inorganic compounds such as cobalt, silica, and selenium are traditional fungicides, which may explain the effects in improving stress resistance.
Biostimulants containing beneficial fungi may promote crop yield by affecting the microbial activity in the rhizosphere. This process should classify these products as biostimulants. However, some experts classify these products as biopesticides, which contributes to the fact that categorizing biostimulant products remains an ongoing effort.
Biostimulants with beneficial bacteria closely resemble rhizospheric PGPRs (plant growth-promoting rhizobacteria), which fall under a different product class. Distinguishing both product types from each other remains challenging for experts, similar to the dilemma with biostimulants containing beneficial fungi. Regardless of their definitions, both types of products target rhizobacteria to improve a plant’s nutrient efficiency, disease resistance, and stress tolerance.
What Are Biostimulants?
Biostimulants are new products meant for improving plant growth and boosting crop yield. These products contain substances or microorganisms that will enhance a plant’s nutrition efficiency and natural traits, and boost its tolerance against stressful environments regardless of the product’s nutritional content.
In other words, a biostimulant product does not necessarily contain additional nutrients that improve plant performance. The substances that these products contain help enhance plant growth and crop yield by supplying rhizobacteria around a plant’s roots to boost natural processes associated with improved plant performance.
What Is Biostimulation?
Biostimulation is a process involving environmental modification by encouraging indigenous bacteria and native microorganisms in an area. These microbes are capable of bioremediation, meaning they perform natural processes that can help a site recover from contaminants.
Experts typically associate bioremediation for biostimulation purposes with remedying oil spills. Crude oils contain hydrocarbons, which are compounds that some naturally occurring bacteria and microorganisms thrive upon and are capable of degrading. Thus, supplying affected areas with substances that improve the natural activities that these organisms perform helps clean up oil spills.
Are Biostimulants and Fertilizers the Same?
No, biostimulants and fertilizers are different kinds of products. These horticultural products may be comparable with each other because they share similar goals of enhancing farm sustainability.
Additionally, both biostimulants and fertilizers may count as input products because farmers would have to add the substances to their plants. However, each product class improves plant growth and crop yield in different ways.
How Do Biostimulants Work?
Biostimulants affect the microorganisms in the rhizosphere. The rhizosphere is the area around a plant’s roots where root secretions and soil nutrients interact with local bacteria, thus affecting a plant’s growth.
Biostimulant products stimulate the natural micro-bacterial activity occurring in the soil by providing nutrients that encourage the existing bacteria to perform their biological processes. Thus, the idea behind biostimulants is that the products make the indigenous microorganisms work double-time to boost natural plant processes.
The increased activity of plant processes leads to improved plant growth and development, further leading to boosted crop yields. Likewise, plant hardiness improves due to the enabled natural processes. Plant hardiness determines how well a plant performs under abiotic stresses such as low or high temperature or water levels.
Meanwhile, some biostimulant products work on plants without affecting the rhizosphere. These products may still contain rhizobacteria that affect plant activity, but the products are for direct application on plants. This inconsistency makes it difficult to classify biostimulants.
Can Biostimulants Help Increase Plant Growth Rate?
Yes, biostimulants can increase plant growth rate. These products improve plant growth by affecting the natural processes that influence plant development. Biostimulants contain substances or microorganisms that are vital to a plant’s biological processes associated with growth.
Applying biostimulants to plant seeds, shoots, and the surrounding soil from where the plant grows will affect the naturally occurring bacteria in the ground. The substances and microorganisms in biostimulant products encourage the local bacteria to perform their natural processes, which promote plant growth.
Thus, biostimulants indirectly help increase plant growth by affecting the microorganisms that influence plant growth. These products do not directly improve plant growth by supplying plants with extra nutrients as fertilizers do.
Can Biostimulants Help With Yield Increase in Plants?
Yes, biostimulants can help increase plant yields. These products may indirectly affect plant yields by improving the natural processes associated with plant growth and hardiness.
Applying biostimulants to crops through the rhizosphere boosts the natural activities that local bacteria perform. Promoting plant activity by improving the biological processes associated with plant development will stimulate plant growth and mitigate plant stress due to abiotic factors.
As plants become hardier due to the improved natural processes, plants are likely to grow regularly despite abiotic stresses like inconsistent water and temperature levels. Thus, crop yield is likely to increase.
Are Biostimulants Natural Products?
Biostimulants can either be natural or synthetic products. Generally, these products contain substances or microorganisms that help improve a plant’s physiological processes. The products may contain plant hormones or their precursors (amino acids, isoprenoid compounds, or lipids) that will enhance natural processes in the soil that improve plant development. These hormones may come from natural or synthetic sources, as long as they contain the necessary compounds associated with plant growth and development.
Conclusion: Biostimulants in Agriculture
Biostimulants in agriculture are a new technology that may contribute to the sector’s need for more sustainable farming practices. Biostimulants have no official definition and categories in America. However, biostimulant experts in Europe have established a description based on the products’ function.
The European Biostimulants Industry Council defines biostimulants as products that contain substances or microorganisms that incite natural plant processes. Inciting plant processes would enhance a plant’s nutrient uptake, nutrient efficiency, abiotic stress resistance, and overall crop quality. In addition, biostimulants achieve this overall plant enhancement regardless of the product’s nutrient content.
Regarding nutrient content, biostimulants may not necessarily contain extra nutrients that benefit plants. These products contain substances that benefit the local bacteria and microorganisms in an area. These microbes have roles in plant growth and development. So, biostimulants help plants grow indirectly through the bacteria that contribute to their growth.
The fact that these products are indirect plant-growing substances is the main factor differentiating biostimulants from traditional fertilizers. Although both product types are inputs or additives, fertilizers directly influence plant growth.
Relatedly, some biostimulant products designed for direct plant application complicate the product’s classification even further. Although these direct-application biostimulants contain rhizobacteria, they go against the EBIC’s definition of products meant for soil application. Still, these products utilize biostimulation to help plants grow and remain potential solutions for sustainable agriculture.
The concept behind biostimulation is the utilization of the indigenous microorganisms in an area to speed up natural processes. Existing cases of biostimulation involve bioremediation, which is an EPA-approved process for reversing the effects of subsurface or marine oil spills. Biostimulation introduces substances to affected areas to encourage the local bacteria to perform their biodegradation process.
Despite the potential of biostimulants in improving agricultural sustainability, experts continue conducting longitudinal studies into the products’ underlying mechanisms. Although several accepted categories of biostimulants exist, we still know little about each of their specific actions on specific plant species. Some experts are concerned about possible adverse effects on certain species. This possibility suggests that biostimulants may not be an ideal product for enhanced plant growth and development.
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