Research Progress of biostimulants (Agricultural field)

Abstract

Biostimulants provide a new technology for the safe and efficient production of agricultural products, and have become an important means to increase fertilizer efficiency and improve crop quality. The definition, main classification and action mechanism of biostimulants were reviewed. The application status and effect of biostimulants in modern agriculture were summarized, and the existing problems were put forward.

In the past few decades, fertilizers and pesticides have played a vital role in agricultural production. A number of technological innovations promote sustainable agricultural production by reducing the use of pesticides and fertilizers. With the growing global population and the aging of the population, agricultural production is facing great challenges, improving the efficiency of resource use while reducing the adverse impact on the ecosystem has been promoting the continuous innovation and development of the agricultural resources industry. Biostimulants for plants is a promising and environmentally friendly innovative research direction. Since the first International Conference on Biostimulants was held in 2012, biostimulants have quickly become popular all over the world. Biostimulants are not traditional fertilizers or pesticides, which improve the physiological state of plants by acting on agricultural crops themselves, improve plant stress resistance, improve the utilization efficiency of pesticides or fertilizers, and thus improve crop yield and quality. At present, the research of biostimulants in Europe and the United States is more advanced, and has the largest biostimulant product market, and has established the European Biostimulant Industry Committee (EBIC) and United States Biostimulants Union (USBC), etc.

The research on biostimulants in China is still shallow, and in recent years, such products have only been introduced and applied in agricultural production. Domestic registration of approved biostimulant related products as fertilizers has hindered the research and application of biostimulants to some extent due to the lack of relevant standards in registration management, production, safety regulations, sales supervision, and other aspects. At present, relevant departments in China are carrying out standardized management of biostimulants related products.

The article summarizes the current definition of biostimulants in the world, elaborates on their main classifications, mechanisms of action, and application methods, analyzes the current application status and effects of such products in modern agriculture.

1. Development of the definition of biostimulants

Biostimulants were first proposed by Spain's Graciem Mining Company in 1974 and did not attract industry attention at that time. In 1997, Zhang and Schmidt from Virginia Tech and State University redefined biostimulants as trace materials that can promote plant growth. After 2012, the research and application of biostimulants in agricultural production has become increasingly widespread. With in-depth research in various countries around the world and the formulation of standards for biostimulants by relevant international organizations, it is believed that the definition of biostimulants will be continuously improved and unified standards will be reached.

At present, the internationally recognized standard is the European Union. At the Fourth International Conference on Biostimulants held in Barcelona in 2019, the European Commission on Biostimulants Industry (EBIC) defined it as a material that contains certain substances or microorganisms and is used in plant plants or their rhizosphere to stimulate natural processes such as improving plant nutrient absorption, nutrient utilization, abiotic stress resistance, and product quality.

2. Types of biological stimulants

The classification of biostimulants has not yet formed a unified standard. The biostimulants for plants reviewed by the author include 9 categories: humic acids, amino acids, seaweed extracts, alginic acid and brown algal oligosaccharides, inorganic salts, microorganisms, chitin and chitosan derivatives, anti-transpirants, and microbial metabolites.

2.1 Humic acids

Humic acid substances belong to natural macromolecular organic matter and are widely present in nature. They are formed by animal and plant residues through long-term physical, chemical, and microbial interactions, and have good physiological activities, mainly including humic acid and fulvic acid. The main function of humic acid substances is to promote the absorption and utilization of nutrients by plants, promote seed germination and root growth and development, improve the rhizosphere ecological environment of crops, increase soil organic matter content, and enhance the ability of crops to resist abiotic stress. China has abundant resources of humic acid, low production costs, and diverse application methods, which have been widely used in agricultural production.

Yang Su et al. investigated the effect of the amount of lignite humic acid on crop growth and nutrient content in the moist soil. The results showed that the application of lignite humic acid can significantly increase maize yield and improve maize nutrient absorption capacity. With the increase of lignite humic acid application, the absorption of nitrogen, phosphorus, and potassium by maize plants shows a trend of first increasing and then decreasing, with the highest absorption rate in the 20 g/kg treatment. Lignite humic acid can significantly increase the organic matter content in soil, reduce the available phosphorus content and pH value. In addition, to explore measures to improve the quality, yield, and economic benefits of pomegranate, Zhao Min et al. used white flower jade seed pomegranate as the experimental object to study the effects of spraying water-soluble fertilizers containing humic acid in the middle and late stages of growth on its yield, bad fruit rate, and quality. The results showed that the yield of pomegranate sprayed with water-soluble fertilizer containing humic acid increased by 10.58%, the cracking rate decreased by 17%, and the economic benefits increased by 10.04% compared to the control, with significant differences; The vitamin C and total sugar content of pomegranate fruit also increased compared to the control.

2.2 Amino acids

Amino acids are the basic unit of protein and essential substances for plant growth. In addition to participating in protein synthesis, they also have a special function of directly regulating plant physiological activities and synthesizing hormones. Amino acids mainly come from animal and plant proteins, microbial hydrolysates, crop residues, etc. They can generally be obtained by hydrolyzing animal collagen at high temperatures or enzymatic hydrolysis of plant proteins at low temperatures. The main function of amino acids is to promote plant photosynthesis, such as glutamic acid and glycine, which can increase chlorophyll biosynthesis and increase crop sugar content; Promote plant growth and development, such as serine, which can directly participate in cell tissue differentiation and promote seed germination; Improving the ability of plants to tolerate various abiotic stresses, such as lysine, can accelerate chlorophyll synthesis, promote photosynthesis, and improve crop drought resistance.

Crops are often affected by various adverse factors such as climate, pests and diseases, as well as unreasonable fertilization and medication. Physiological activities are inhibited, and the synthesis of some amino acids is also inhibited. At this time, it is necessary to supplement the necessary nutrients for plant growth and development by applying exogenous amino acids, thereby regulating the balance of plant physiological and biochemical activities. Chen Wei et al. [6] conducted experiments on red colored strawberries in Wenling City and Jiashan County, respectively. They found that spraying amino acid water-soluble fertilizer can effectively increase strawberry yield. The total yield of strawberries in Jiashan County increased by 12.9% and 9.3% compared to not spraying amino acid water-soluble fertilizer and spraying clean water, respectively, with an increase of nearly 60000 yuan in economic benefits per hectare; The total yield of Wenling City has increased by 9.2% and 5.2% respectively, with an increase of 80000 yuan in economic benefits per hectare. Therefore, spraying amino acid water-soluble fertilizer on the leaves can increase the yield and soluble solid content of strawberries, and extend the shelf life of refrigerated fruits.

In addition, the application of amino acids in horticultural landscapes can increase the aesthetic effect of landscaping, improve plant stress resistance, and prevent freezing damage. Li Xu et al. applied a 5-aminolevulinic acid solution (ALA) with a mass concentration of 50mg/L to 18 garden plants through leaf spraying and root irrigation methods. Research has shown that the application of ALA solution can accelerate chlorophyll synthesis, increase the area and thickness of plant leaves, and enhance the activity of leaf reaction centers. The experiment also found that the application of an appropriate amount of ALA solution can reduce the degree of camphor freezing damage, improve plant cold resistance, and enhance the aesthetic effect of landscaping.

2.3 Seaweed extract

Algae is an important source of organic fertilizers, and large algae substances are often considered as sources of bioactive substances, with extensive antibacterial and disease resistance toxicity. Seaweed extract contains various bioactive substances that contribute to plant growth, such as polysaccharides, auxin, and cytokinin. The main function of seaweed extract is to provide nutrients for plants, improve fertilizer utilization efficiency, and enhance their ability to resist abiotic stress. It has advantages in yield increase, stress resistance, naturalness, and non-toxic side effects. Feng Jingtao used apple seedlings as experimental materials to study the effects of spraying salicylic acid, abscisic acid, and seaweed extract on the growth of apple seedlings under drought stress. The results showed that spraying seaweed extract significantly increased the photosynthetic rate, antioxidant capacity, and organic solute content of apple seedling leaves, thereby alleviating the inhibition of seedling growth under drought stress; Under different degrees of drought stress, the relief effects of seaweed extracts vary. Under moderate and severe drought conditions, seaweed extracts recovered 25.2% and 18.5% in terms of growth (dry mass), respectively. The three substances that alleviated drought stress in apple seedlings were seaweed extract, abscisic acid, and salicylic acid, which alleviated biomass (dry mass) by 20.3%, 13.5%, and 16.9%, respectively. Therefore, seaweed extract had the best alleviating effect.

In order to clarify the effect of seaweed extract on reducing fertilizer application and increasing efficiency in rice fields, Sun Xiao et al. conducted a rice field experiment in Yancheng City, Jiangsu Province in 2018. The results showed that compared with conventional mixed fertilizer treatment, the seaweed mixed fertilizer treatment with equivalent nutrients and the seaweed mixed fertilizer treatment with a 20% reduction in nutrients increased yield by 36.29% and 31.08%, respectively. The effective panicle number, grain number per panicle, and seed setting rate were significantly improved; The seaweed mixed fertilizer treatment with a 20% reduction in nutrients had the best nutrient utilization effect, and compared with the conventional mixed fertilizer treatment, nitrogen fertilizer increased the partial productivity by 61.87%. Research has shown that seaweed extract can significantly increase rice yield and improve fertilizer utilization efficiency, with a significant effect on reducing fertilizer application and increasing efficiency in rice fields.

2.4 Alginic acid and alginic oligosaccharides

Alginic acid is a natural polysaccharide carbohydrate widely present in the cell wall of brown algae, containing various nutrients and active substances, such as amino acids, vitamins, plant hormones, polyphenols, calcium, zinc, etc. The degradation product of alginic acid - alginate oligosaccharides, as a new generation of marine oligosaccharides, has good stability and chelation properties. Currently, they have been widely used in fields such as medicine, food, agriculture, and feed, and have become a research hotspot in recent years.

Alginic acid and alginate oligosaccharides, as natural biostimulants, have shown ideal effects in the agricultural field, with significant improvements in quality, yield, disease resistance, and stress resistance. Gao Yan et al. conducted field experiments to study the effects of different fertilization treatments on maize yield and quality. The results showed that under the same fertilization amount, the treatment of alginic acid compound fertilizer can improve the ability of corn to absorb nutrients, increase ear length, increase grain quality, increase stem diameter, and increase starch and protein content. At the same time, the problem of corn bald tip is reduced, significantly improving corn yield and quality. Research has found that brown algae oligosaccharides have a significant promoting effect on the physiological and biochemical functions of algae. Ma Dongdong et al. measured the effects of applying a concentration of 50mg/L brown algae oligosaccharide solution on the specific growth rate, pigment content, photosynthetic oxygen release, respiratory oxygen consumption rate, and chlorophyll fluorescence parameters of marine Chlorella and Dunaliella salina. The results showed that adding brown algae oligosaccharides under light significantly increased the cell growth rate of both microalgae species. The growth rate of marine Chlorella under co cultivation was 2.4 times that of autotrophic and 2.6 times that of heterotrophic algae; Under co cultivation, the growth rate of Dunaliella salina reached 0.259 d-1, which is 1.9 times that of autotrophic and 1.3 times that of heterotrophic algae. Both types of microalgae can utilize brown algae oligosaccharides for heterotrophic growth, and the growth rate obtained by using brown algae oligosaccharides as organic carbon sources in the dark is similar to autotrophic growth.

Brown algae oligosaccharides can also serve as signaling substances for plants, activate the plant immune system, resist bacterial and viral invasion, and reduce pesticide use; Stimulating the production of phytoalexins, defense enzymes, and osmoregulation substances in plants, enhancing their stress resistance; Promote root development and enhance plant photosynthesis; Brown algae oligosaccharide products have plant "vaccine" efficacy. Research has shown that the principle of growth promoting effect of brown algae oligosaccharides is reflected in: brown algae oligosaccharides can induce the expression of auxin related genes, accelerate the synthesis and transformation of auxin, reduce the activity of auxin enzymes, increase auxin concentration by 37.8%, and thus promote root growth. The principle of enhancing immune resistance is reflected in: brown algae oligosaccharides significantly increase root length and quantity under stress, increase antioxidant enzyme activity, and reduce malondialdehyde content by 37.9%, thereby preventing cell toxicity and damage; It can be used as a super strong immune inducer to induce the expression of immune resistance genes, thereby secreting endogenous resistance hormones, enhancing the plant immune system, and improving disease resistance.

2.5 Inorganic salt

Inorganic fertilizer can generally be directly absorbed by plants, which can promote plant metabolism, activate plant defense response, regulate plant nutrient balance, and improve tolerance to abiotic stress. For example, phosphite has a direct biological stinging effect on plants, and has the effect of increasing production and disease resistance on crops. Ren Shiwei et al. [16] believed that phosphite was conducive to plant growth and development, and improved yield and quality within a certain concentration range. The team's research showed that compared with the control group without phosphite application, when the fertilizer weight ratio of potassium phosphite was 3% to 6%, the seed germination rate was accelerated. The plant height, stem diameter and soluble sugar content in fruit were significantly increased in the middle and late stages of tomato leaves, and the crop disease rate was significantly decreased. When the fertilizer weight ratio of potassium phosphite exceeded 6%, the growth index of tomato gradually decreased.

2.6 Microorganisms

Microorganisms include bacteria, yeast, filamentous fungi, and microalgae, mainly derived from soil, plants, water, compost, and manure. Agricultural microbial agents mainly refer to active biological agents made by fermenting effective bacteria, which are widely used in agricultural production. Their main function is to promote the absorption of trace elements and other nutrients by plants; Promote the effective circulation of substances in the soil; By regulating the hormone status of plants, it promotes the secretion of cytokinins, plant growth factors, etc; Improve tolerance to abiotic stress. Screening excellent strains and researching advanced fermentation processes have become current research hotspots. He Zongjun et al. studied the effects of Bacillus subtilis, Bacillus amyloliquefaciens, Bacillus gelatinosus, and Trichoderma longissimus on the yield and quality of cucumber and rice. The results showed that compared with no application of microbial agents, different microbial agents had a significant increase in yield of cucumber and rice, with an increase in cucumber length and soluble sugar content, as well as the total number of panicles and grains per panicle of rice.

Trichoderma belongs to fungi and is widely present in nature. Currently, commonly used in agricultural production are Trichoderma viride and Trichoderma harzianum, which can effectively promote plant growth. Liu Chang et al. investigated the effects of Trichoderma viride and Trichoderma harzianum alone and in combination on the growth of cucumber seedlings. The study found that compared with the control, the cucumber seedlings treated with mixed Trichoderma had a significant increase in plant height, leaf width, stem diameter, chlorophyll content, maximum photochemical efficiency, peroxidase (POD) activity, etc. This indicates that the mixed liquid of Trichoderma viride and Trichoderma harzianum can significantly promote the growth of cucumber seedlings, with better effects than the application of a single bacterial liquid.

Meanwhile, some microorganisms play a insecticidal role in agriculture. Zhang Zhongrun et al. studied the insecticidal effect of Bacillus thuringiensis (Bt) on the important pests of cashew fruit, the larvae of cashew fruit moth and cashew fruit moth. Research has shown that at a dilution of 500 or 1000 times the concentration, Bt has a strong killing effect on young cashew moth larvae, with a mortality rate of over 70%, and an insecticidal effect on older cashew moth larvae ranging from 20.0% to 52.5%. The experiment also found that under the combined effect of 200 IJs/dish of small roll moth nematodes and 2000 times the concentration of Bt, the insecticidal effect is significantly improved, with a mortality rate of up to 90% after 48 hours. In addition, microbial agents, as biological stimulants, not only provide certain nutrients for crops, but also increase soil microbial diversity, reduce the content of harmful substances in cultivated soil, regulate soil acid-base balance, optimize soil ecological environment, and effectively prevent and control soil borne diseases.

2.7 Chitin and chitosan derivatives

Chitin is a renewable natural polymer substance that is widely present in shrimp, crabs, and crustaceans. Its production in nature is second only to plant fibers. The deacetylation, decalcification, and deproteinization products of chitin are chitosan, among which chitosan derivative - chitosan oligosaccharide - is often used for foliar spraying due to its good water solubility and easy absorption. Chitin and chitosan derivatives, as a type of plant biostimulants, are currently mainly used to regulate soil bacterial balance, improve plant tolerance and immune response to abiotic stress, and improve crop quality. Due to its good degradability, non-toxicity, induced disease resistance, biocompatibility, etc., it has a wide range of applications in agriculture. Liu Jinfeng et al. studied the effect of chitin on the resistance of tomatoes to high temperature and Chinese cabbage to severe cold. The results showed that after treatment with chitin, the content of malondialdehyde and electrolyte permeability significantly decreased, while the content of proline increased, thereby improving the high-temperature resistance of tomatoes and the cold resistance of Chinese cabbage.

Chitooligosaccharide is a degradation product of chitosan, and as a new type of marine biological source inducer, its antibacterial and growth promoting functions will accelerate its development in agricultural applications. At the experimental base of Hainan Academy of Agricultural Sciences, Lei Fei et al. sprayed different concentrations of chitosan oligosaccharides on cherry tomato leaves to study the effects of chitosan oligosaccharides on crop growth and disease resistance. The results showed that compared with the control group without treatment, spraying chitooligosaccharide of appropriate concentration on cherry tomato leaves could promote plant growth, improve leaf photosynthetic rate, increase plant height and significantly reduce leaf incidence rate. In addition, the research results showed that when foliar spraying with a concentration of 450mg/L chitosan oligosaccharide solution, the yield and quality of cherry tomatoes were higher, and the corresponding disease index and growth rate were also lower.

2.8 Anti-transpiration agent

Anti transpiration agent is a special biological stimulant that reduces the transpiration rate of plants while ensuring their normal growth. When crops are under water stress, regulating stomatal movement can reduce water evaporation and improve crop drought resistance. Anti transpiration agents are currently mainly divided into three categories: metabolic anti transpiration agents, reflective anti transpiration agents, and film-forming anti transpiration agents. As biostimulants, they have the functions of regulating photosynthesis and transpiration, improving high-temperature resistance, and reducing sugar and acid levels.

Li Wanping et al. studied the effects of spraying anti transpiration agents on physiological indicators, photosynthetic indicators, and stomatal characteristics of wine grapes. The measurement results showed that spraying anti transpiration agents significantly reduced the content of malondialdehyde and proline in grape plants, as well as the net photosynthetic rate and stomatal conductance. The content of reducing sugars also decreased, delaying the degradation of organic acids and thereby reducing the alcohol content of wine. From an agricultural perspective, spraying anti transpiration agents can reduce water loss and ensure the water required for plant growth and development. To study the effect of anti transpiration agents on greenhouse cucumbers, Chen Yihao et al. conducted experiments using FA type anti transpiration agents. The results showed that the height and leaf area of cucumber plants treated with FA type anti transpiration agents showed a rapid to stable growth pattern; In the experiment, a 0.5% FA type anti transpiration agent solution was sprayed on greenhouse cucumbers under 75% water deficit irrigation. The cucumber yield, chlorophyll content, leaf water content, net photosynthetic rate, and water use efficiency were all improved, while leaf transpiration and stomatal conductance gradually decreased. This proves that appropriate spraying of FA type anti transpiration agent can reduce water loss, promote plant photosynthesis, reduce transpiration, and improve water use efficiency, Achieve water-saving effects.

2.9 Microbial metabolites

Microorganisms affect crop growth through metabolites generated through their own physiological activities, and their metabolites can be converted into various useful products such as amino acids, solvents, antibiotics, enzyme preparations, biological insecticides, etc. In addition, microbial metabolites have a certain impact on soil permeability, soil microbial community, and play an important role in the agricultural field.

In 2019, the new EU standard biostimulant product ZNC was launched. ZNC is a metabolite extracted from functional endophytic bacteria isolated from wild plant roots through deep liquid fermentation and ultrasonic fragmentation. Its physicochemical properties are stable, safe, non-toxic, and cost-effective. Research has shown that ZNC has the function of preventing plant viruses and has a certain therapeutic effect on virus damage. It was also found that ZNC, as an efficient biological stimulator, can induce the biosynthesis of salicylic acid (SA), promote the silencing of ribonucleic acid (RNA), degrade the viral genome, and enhance the plant's ability to resist viruses.

In addition, Y-aminobutyric acid (GABA), as a non protein free amino acid widely present in various biological cells, is also a green, safe, and efficient new type of biostimulant. It is believed to be related to various stress and defense systems in plants and has become a research hotspot in recent years. GABA can promote plant nutrient growth and absorption of key elements; Promote the growth of plant roots, stems, leaves, flowers, and fruits; Regulating plant stress resistance; Promote plant photosynthesis; Simultaneously playing a dual role of metabolism and signaling molecules, it plays a positive role in plant disease resistance. Research has found that the application of GABA can alleviate the impact of high temperature on photosensitivity II by regulating stomata, enhance gene expression of key metabolic enzymes, and effectively alleviate the inhibitory effect of high temperature stress on the growth of ryegrass. The chlorophyll content, carbohydrate content, photosynthetic rate, and transpiration rate of ryegrass are significantly increased.

In addition, GABA can also improve the product's ability to resist low temperature stress, ensuring product quality and freshness. Fang Xiaoqin et al. used exogenous GABA and GABA-T inhibitors (VGB) to treat peach fruit, and compared and analyzed the changes in peach juice yield, soluble sugar content, and sucrose metabolism related enzyme genes. The results showed that the application of exogenous GABA could inhibit the decomposition of sucrose content in peach fruit, increase the juice yield and soluble sugar content of peach fruit; Exogenous GABA combined with VGB treatment enhanced the expression of sucrose synthase genes during late storage, ensuring that peach fruit contains more sucrose, thereby improving the ability of fruit to resist cold damage during low temperature storage.

3. Application of biostimulant products

Research has shown that biostimulants have activities similar to cytokinins and plant auxin within a certain range. They act on the plant itself, indirectly stimulating nutrient absorption and stress resistance processes, while promoting the development of beneficial microorganisms in the soil, improving the soil environment, and promoting plant growth, improving tolerance to abiotic stress, and improving crop quality, The impact on plants mainly depends on the variety of crops, the state of the cultivated soil, and the planting method of the crops.

Humic acid substances, amino acids, seaweed extracts, alginic acid and alginate oligosaccharides, inorganic salts, microorganisms, chitin and chitosan derivatives, anti transpiration agents, and microbial metabolites are 9 types of biostimulants. According to their different mechanisms of action and application methods, they are widely used in agriculture. Humic acid substances are mainly used in rhizome crops, with the most obvious effects in crops with large leaves, wheat, and rice; Amino acids are mainly used in plant leaves, as they can improve crop ecological environment, inhibit pests and diseases, and also act on soil; Seaweed extract has achieved significant results in leaf fertilization, soil, and seed germination; Alginic acid and alginate oligosaccharides, as emerging biostimulants, are currently mainly used in foliar fertilization and flushing fertilization, achieving good results; Inorganic salts are mainly used in soil, which can improve soil pH, inhibit weed growth, and also serve as foliar fertilizers to improve crop quality. In recent years, phosphates have also made breakthroughs in seed germination; Microbial agents contain abundant beneficial bacteria and some fermentation products, mainly used in soil to regulate root environment; Chitin and chitosan derivatives are mainly used on leaves, and there are currently a few applications in seed treatment and soil management; Anti transpiration agents, due to their special mechanism of action, mainly act on the roots, stems, and leaves, promoting water balance in plants; Microbial metabolites are mainly used for soil management and seed germination, and have shown ideal results. Further research is needed for deeper applications. As a new product, biostimulants have significant implications for weight loss and efficiency enhancement. However, biostimulants are not omnipotent and cannot completely replace fertilizers and pesticides. Scientific and reasonable fertilization and medication are still prerequisites for improving crop yield and quality.

4, the relevant system of EU biostimulant products

At present, the EU's standards for biostimulants are leading in the industry. In order to unify and regulate the market for biostimulants, the EU classified biostimulants, mineral fertilizers, organic fertilizers, soil improvement agents, agricultural fertilizer additives, and cultivation substrates into the fertilizer field in 2016. In order to strengthen the regulation of biostimulant products in the European market, it is stipulated that each biostimulant product must submit product registration information to the EU regulatory authority (ECHA or EFSA) in advance, including: ① safety assessment data, including physical and chemical characteristics, toxicity, pathogenicity, infectivity, etc.; ② Risk assessment data, including hazard characteristics, exposure assessment, risk characteristics, etc.; ③ Product characteristic data, including species, ingredients, properties, sources, application scope, etc. ECHA or EFSA receives and verifies the application materials and relevant information, and provides conclusions. Finally, ECHA or EFSA approves the registration of relevant products, and the information materials are archived and saved.

In this way, it is conducive to regulating the relevant market of plant biostimulants and achieving legal compliance; To some extent, it ensures the safety, circulation, and efficacy of biostimulants in the market; At the same time, the process of launching new biostimulants on the market has been standardized, ensuring fair competition between markets, accelerating the application of this product in the market, and indirectly promoting the research and application of biostimulants.

5. Summary and Outlook

The global biostimulant market report shows that the total value of the global biostimulant market exceeded 800 million yuan in 2019, and is expected to reach 1.2 billion yuan in 2026, with a compound annual growth rate of 5.5%. The rise of the biostimulant industry is the trend. Biostimulants, represented by humic acid substances, alginic acid and alginate oligosaccharides, microorganisms, and microbial metabolites, have become a major highlight of new fertilizers in recent years as a new type of agricultural product, with obvious effects and gradually recognized by the market. Biostimulants have been widely promoted and applied, playing an increasingly important role in agricultural production.