Biostimulators in crop production
Organic, sustainable and environmentally friendly systems are gaining ground in the practice of agricultural cultivation. An important goal is to reduce or make input material use more efficient without compromising yield or quality.
Few people think that biostimulants are actually the earliest agricultural "inputs" to be mentioned on the same page. It has been recognized that certain organic molecules and compounds activate plant metabolic processes, accelerating plant growth and development. Plant extracts — as common starting materials for biostimulators-contain a number of bioactive compounds, the effect of which is only partially known. Products made from them, usually sprayed on the foliage, improve the nutrient utilization efficiency of the plant. In addition to increasing photosynthetic activity, they increase plant tolerance to abiotic stress factors such as frost, drought, salt, as well as resistance to fungi, bacteria, and viruses.
What substances are biostimulators?
On the side of one of the manufacturers we can read: "the biostimulator is a preparation of natural origin, containing plant extracts, organic substances, vitamins, which aims to increase the condition and improve the quality according to the life cycles of the plant (rooting, flowering). Biostimulators are integrated into the life processes of plants, under their influence the quality of the final product improves."(Source: Malagrow. hu) and indeed, biostimulants are actually extracts from organic substances containing bioactive ingredients. The most common ingredients are mineral elements, occasionally humic acids, vitamins, amino acids, chitin, chitosan, as well as poly — and oligosaccharides, but biostimulants include algae-produced hormones such as cytokinins, auxins, gibberellins or other hormone-like substances. Research on biostimulators has become increasingly intense since the '50s of the last century. For many years, however, little attention has been paid to refining and improving the properties and effectiveness of biostimulator-containing preparations. In recent decades, however, there has been an increase in the number of companies developing and manufacturing biostimulants, which work with partners to carry out intensive research to acquire new bioactive compounds and explore the relationships that shed light on how a given biostimulant can improve the performance and quality of a cultivated crop under different and changing growing conditions.

Today, biostimulants are justified by the fact that while agricultural cultivation practices are developing towards sustainable, environmentally friendly systems, modern agriculture must meet the increasing pressure worldwide to achieve ever higher yields and produce ever higher quality products at reduced costs. We try to meet these aspirations primarily through plant breeding programs, but the goals stated in them can only be realized in a long time. In this "race", organic-based biostimulants developed to improve plant metabolism can be used to improve the performance of cultivated plants, and in a more cost-effective way than traditional and modern means of plant breeding (over a longer period of time). The benefits of this approach are particularly evident in intensive production crops, such as flower or vegetable gardens, where one of the main objectives of production efficiency is to make optimal use of greenhouse capacities.
All this how?
Biostimulants basically help plant growth and development throughout the plant’s life cycle, in the following proven ways:
  • improving the efficiency of plant metabolism to increase yield and improve crop quality;
  • increasing tolerance to abiotic stress factors;
  • accelerating recovery from stress-induced metabolic imbalances;
  • improving the efficiency of nutrient and water utilization;
  • improving the quality parameters of the crop, e.g. increasing the sugar content in fruit crops, promoting fruit colouring or seed setting;
  • enhancing soil fertility, in particular by promoting the growth of beneficial microorganisms in the soil.
What aspects should the producer consider regarding the choice and use of biostimulant preparations?
In addition to a wide range of fertilizers, many growth regulators and biostimulants are now available on the market. The" abundance disorder " the use of the preparation with insufficient care (quenching due to the combined use of several different preparations, the omission of the mixing test) does not help our plant, but can even have a negative impact on the quantitative and qualitative parameters. Therefore, it is important to take a thoughtful, systemic approach when choosing and using biostimulants. Unfortunately, the effect and effectiveness of a biostimulant can not only differ from species to species, but we can also see differences between some varieties. Even for the same Variety, the effectiveness of the product depends on environmental factors, as well as the dose used and the time of application. These" anomalies " often make it impossible to make general statements or judge the effectiveness of substance use when tested on a different culture or in different abiotic stress situations. Therefore, it is worth paying attention to the recommendations of the manufacturers, to listen to their experiences and, if possible, to take a closer look at their experiments set up by the practicing farmers.

Not everyone knows how individual biostimulants work or how they work together. Since biostimulants are typically extracts with a complex composition, it is difficult to assign a specific ingredient to the physiological effect to be achieved. However, the exact ingredients of a biostimulator preparation and the technology behind its production are treated by most manufacturers as a kind of secret. What is certain, however, is that the first step on the thorny path of product development is a thorough and in-depth examination of the plant (s) and ecosystems, followed by a long research work, which (fortunately) leads to the identification of a new bioactive component. Biostimulators are widely used in today’s cultivation practice. They have been used in intensive horticultural crops (mainly vegetable crops) for a long time, and now manufacturers offer biostimulator products for almost all arable crops. It is important to point out that biostimulators do not produce results on their own, but can be a complement to organic and mineral, i.e. artificial preservation, as well as integrated or biological plant protection technologies. Accelerating plant metabolism requires more readily available nutrients, so there are many products available on the market where special mixtures of macro — and micronutrients and biostimulator (s) are formulated. Biostimulators are partially absorbed through the root, and in arable crop production, typically through leaves. Therefore, the photostability and rain resistance of the products being developed is a challenge for manufacturers. Furthermore, the molecules responsible for the effect should not undergo rapid decomposition on the surface of the Leaf. They already belong to the category of industrial secrets of product molding, which manufacturers take care of even just the know-how of the composition of the product. However, it is worth reviewing what are the classic biostimulator groups and what they are characterized by.
What good is what?
Indeed, biostimulants cannot be negotiated into clearly distinguishable categories, as they do not have a clear grouping in legal or regulatory terms. Nevertheless, on the basis of consensus between regulatory authorities and stakeholders, both active substances and micro-organism preparations on the market can be classified into a few main groups.
Preparations containing Humic and fulvic acids:
This includes soil-dwelling microbes resulting from the decomposition of organic soil components (plant, animal and microbial residues) or with active metabolism. These preparations improve the efficiency of Root nutrition through various mechanisms. One is the increased uptake of macro and microelements as a result of the increased cation exchange capacity of the soil, and the other is the improvement of phosphorus uptake due to the effect of these acids on calcium phosphate precipitation.
Protein hydrolysates and other n-containing compounds:
A mixture of amino acids and proteins produced chemically by enzymatic protein hydrolysis from agro-industrial By-Products, plant raw materials (plant residues) and animal waste (e.g. collagen). Other nitrogen-containing molecules include betaines, polyamines, and "non-protein-forming amino acids". Glycine, betaine as amino acid derivatives have well-known antistress properties. Some amino acids (e.g. Proline), protects plants against heavy metals and contributes to the mobility of micronutrients, facilitating their uptake. Their antioxidant effect is also not negligible, since they "capture" free radicals, thereby contributing to the relief of environmental stress.

These substances have been shown to have a complex function in the field of plant growth stimulation. They exert their direct influence on plants through uptake and incorporation of N by regulating these processes by controlling and structural genes. Extracts of seaweed and other plants.

The use of marine algae as a source of organic matter and fertilizer in agriculture has a long history, but their biostimulant effect has only recently been noticed.

These commercially available extracts and purified compounds include polysaccharides, alginate and carrages, as well as their degradation products. Other ingredients contribute to the acceleration of plant growth; these are mainly micro and macronutrients, n — containing compounds and hormones. Truly unique sources of several ingredients are algae, which explains the growing interest in them.

Algae extracts affect both soil and plants and are therefore widely used to treat both soil and vegetation. In the soil, their long-chain sugar molecules cause gel formation, in addition to helping with water retention and soil aerobicity. Their multiple negatively charged compounds may contribute to cation exchange and binding. This is of great importance in heavy metal sequestration and soil remediation. They also have a positive effect on soil microflora by promoting the growth of plant growth-stimulating bacteria and pathogenic antagonists in the soil. Thanks to their nutritive effect in plants, they can be considered as micro — and macroelement sources, but they also have a positive effect on germination and seedling growth. These substances have antistress effect, they can be used as a kind of protective substances as antioxidants. Compared to seaweed, much less is known about the nature and mechanism of action of the ingredients underlying plant extracts as biostimulants. Attention today is mainly focused on the pesticide-like effect of these extracts.
Chitosan and other biopolymers:
Chitosan is a modified form of chitin found in the insect world, which can be naturally derived or industrially produced. Chitosan compounds, for example, can bind to DNA as well as to specific receptors, thus playing a role in activating genes that are important in the defense system of plants. The potential role of chitin and chitosan in stress-induced responses is being intensively researched in defense against fungi that cause infections and in primary and secondary metabolic processes related to quality properties.
Other inorganic ingredients:
These are primarily elements in the chemical sense that promote the growth of certain plant species, but are not considered to be absolutely necessary for all plants in general. Such useful elements include cobalt, sodium, selenium and silicon, which are found in soil and plants in various inorganic salts and in certain plants (e.g. grass) in insoluble form. The beneficial effect of these inorganic compounds on plants is of interest, such as plant-based plants. strengthening cell walls through Silicon deposits, either in defense against pathogen attack or osmotic stress. Beneficial mushroom preparations:

They are based on the complex relationship of mushroom-plant-root interaction, which on the one hand can be characterized by Symbiosis (i.e., when both living organisms form a biome in a direct relationship based on mutual benefits). This kind of coexistence of plants and fungi looks back on a long evolutionary path, just think of the taxonomically different fungal species forming mycorrhiza (fungal thread network), which are symbiontated with more than 90% of plant species. The benefits of mycorrhizal relationships are undeniable in the efficiency of micro-and macroelement feeding (especially phosphorus), as well as in water balance, in eliciting biotic and abiotic stress — induced responses.

Recent research shows that networks of mushroom trees not only connect mushroom and plant partners, but also create and maintain a kind of "communication" link between individual plants within plant communities, exploiting which is one of the great opportunities of organic agricultural production.
Beneficial bacterial preparations:
Bacteria, like fungi, interact with plants in every possible way. This form of coexistence can be any, from parasitism to symbiosis. Bacterial life spaces include a long "chain", including intermediate states such as the root zone, from the occurrence in the soil up to the intra-cellular space. These connections can be temporary or permanent; in the case of some bacteria, one can also speak of "vertical" transmission through seeds. Overall, bacteria have enormous importance in nutrient supply, nutrient utilization efficiency, disease resistance, increased abiotic stress tolerance and plant development.
Environmentally friendly bio-raw material
The use of biostimulants in the practice of agriculture based on innovation and the principles of sustainable growth is increasingly playing a role throughout Europe, contributing to efforts to create a perspective for "bio-based" agriculture. Why is that? Considerable quantities (millions of tonnes) of seaweed are processed annually to extract raw materials for nutrient supplements and biostimulants, which are widely used in agriculture. On the other hand, many raw materials used in the production of biostimulants would otherwise be considered industrial waste (e.g. seaweed and crab carcasses). By converting these substances, valuable biostimulants can be produced, thereby reducing or eliminating the need to remove and destroy waste generated in large quantities. In many cases, the production technology of the biostimulants themselves is also biologically based, for example, micro-organisms are used to produce a specific biostimulant component or micro-organisms are the final product. In addition, the components of biostimulants are largely substances that are very common in nature, such as amino acids, soil microorganisms, or chitin, which is the second most common natural polymer after cellulose.

Stimulants applied to plants, in addition to increasing photosynthetic activity, increase plant tolerance to abiotic stress factors such as frost, drought, salt, as well as resistance to fungi, bacteria and viruses, thus improving yield indicators and ultimately productivity.

The most common misconception about biostimulants is that many people associate their use with organic farming and organic gardening. In fact, biostimulators play an important role in "traditional" agricultural production as a useful complement to plant nutrition and plant protection, as such increasing the safety of agricultural production forced to meet the ever-increasing global challenges of the future.

By Dr. Richard Hoffmann and Dr. Zsolt Ponya University of Kaposvar

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