Preparation method and application of rice seedling raising substrate based on quick fermentation of reed sludge

Abstract

The present application relates to rice seedling raising substrate preparation technical field, especially to a kind of based on reed mud rapid fermentation rice seedling raising substrate preparation method and application, by weight fraction, including the following components: reed residue 35-50 parts, cow dung 15-22 parts, carbonized rice husk 8-15 parts, grass carbon 10-20 parts, modified bacteria-loaded vermiculite 13-22 parts and nutrient composition 3-8 parts, the modified bacteria-loaded vermiculite includes nitrogen-fixing bacteria and the vermiculite carrier modified by function.The active substances such as humic acid produced in composting fermentation process of reed residue and cow dung can chelate metal ions in nutrient composition, improve its biological availability, carbonized rice husk, grass carbon and bacteria-loaded vermiculite construct a composite substrate system with excellent physical properties and strong biological function, realize the organic unity of nutrition supply, physical support and biological regulation, provide ideal growth medium for cultivating suitable machine insertion healthy rice seedling.

Description

Technical Field

[0001] This invention relates to the field of rice seedling substrate preparation technology, and in particular to a method for preparing and applying a rice seedling substrate based on rapid fermentation of reed foam. Background Technology

[0002] With the rapid development of mechanized rice transplanting technology, the quality requirements for seedling substrates are increasingly stringent. While traditional soil-based seedling raising is lower in cost, it suffers from numerous problems, including large soil consumption, difficulty in soil sourcing, severe vegetation damage, slow thawing in spring, inability to raise seedlings at the appropriate time, poor soil quality, weak seedlings, susceptibility to diseases and pesticide damage, and high labor intensity in land preparation and soil sourcing. Organic waste-based substrate seedling raising can fully utilize agricultural waste resources, significantly improve seedling quality, better meet the requirements of mechanized transplanting, and is of great significance for developing a circular economy and improving rice production efficiency. However, current single-substrate seedling raising generally suffers from incomplete nutrient composition and poor water absorption and retention capacity, often resulting in water shortages in the early stages of seedling raising. This necessitates increased watering volume and frequency, easily leading to lower bed surface temperatures, resulting in decreased rice emergence rates, sluggish growth, and uneven seedling development.

[0003] Existing patent CN202010450411.6 discloses a method for preparing an organic microbial seedling substrate resistant to rice damping-off. This technology uses a compound microbial agent prepared by combining *Actinomyces malathioides*, *Bacillus methyltrophicus*, and *Lactobacillus plantarum*, and combines it with organic materials such as fermented straw, well-rotted cow manure, and well-rotted mushroom residue to prepare the seedling substrate. However, this technology has the following shortcomings: First, the preparation process is complex, requiring the three strains to be fermented and cultured separately, then the compound microbial agent is prepared, and then the microbial fertilizer is fermented, with the entire production cycle lasting more than 4 weeks, resulting in low production efficiency; second, the production cost is high, requiring the use of cash crops such as corn flour, wheat bran, and soybean cake as carriers for the microbial agent, increasing raw material costs; third, using agricultural waste such as straw as the main raw material results in scattered sources, low standardization, and difficulty in ensuring quality stability; finally, this technology mainly relies on general beneficial bacteria to exert its effects, lacking targeted biological nitrogen fixation function, and has limited effect on improving the nitrogen nutrition of the substrate. Summary of the Invention

[0004] In view of this, the present invention proposes a method for preparing rice seedling substrate based on rapid fermentation of reed foam and its application, in order to solve the technical problems of complex preparation process, long production cycle, unstable raw material quality and lack of efficient nitrogen fixation function in the prior art.

[0005] The technical solution of the present invention is implemented as follows: The present invention provides a rice seedling substrate based on rapid fermentation of reed foam, which, by weight, includes the following components: 35-50 parts of reed residue, 15-22 parts of cow dung, 8-15 parts of carbonized rice husk, 10-20 parts of peat moss, 13-22 parts of modified bacterial-carrying vermiculite, and 3-8 parts of nutrient composition, wherein the modified bacterial-carrying vermiculite includes nitrogen-fixing bacteria and a functionalized vermiculite carrier.

[0006] Specifically, reed residue, as the main component, is characterized by its uniform texture, moderate fiber content, and ease of composting. Its rich organic matter provides a long-term nutrient source for rice seedlings, while its porous structure improves the substrate's aeration and water retention. Cow manure, as a high-quality organic fertilizer raw material, contains abundant nitrogen, phosphorus, potassium, and other nutrients, as well as a large number of beneficial microorganisms. During composting, it not only provides ample nitrogen but also promotes the rapid decomposition of reed residue. Its colloidal properties help improve the substrate's aggregate structure and water and fertilizer retention capacity. Carbonized rice husks are lightweight, porous, and chemically stable, significantly improving the substrate's physical properties, enhancing aeration and drainage, and preventing substrate compaction. Its siliceous surface layer also enhances the seedlings' resistance to adverse conditions. Peat moss, as a high-quality organic substrate material, has excellent water and fertilizer retention properties and suitable pH levels, regulating the substrate's pH and providing a stable root growth environment. Its highly decomposed organic matter provides excellent nutritional conditions for seedling root development. Modified vermiculite with bacterial support, through polydopamine-functionalized vermiculite carrier, specifically loads magnesium and molybdenum ions as key trace elements for nitrogenase catalysis. A sodium alginate-calcium chloride crosslinking system is used to encapsulate nitrogen-fixing bacteria, achieving stable loading and slow release of highly efficient nitrogen-fixing bacteria. The nutrient composition provides rice seedlings with comprehensive and balanced trace element nutrition, ensuring an adequate supply of various mineral elements required for robust seedling growth. A good synergistic effect is formed among the components. Active substances such as humic acid produced during the composting fermentation of reed residue and cow manure can chelate metal ions in the nutrient composition, improving its bioavailability. The physical structure of carbonized rice husks and peat moss, combined with the bioactivity of the bacterial-supported vermiculite, constructs a composite matrix system with excellent physical properties and strong biological functions, achieving an organic unity of nutrient supply, physical support, and biological regulation, providing an ideal growth medium for cultivating robust rice seedlings suitable for machine transplanting.

[0007] Based on the above technical solutions, preferably, the preparation method of the modified bacterial-loaded vermiculite includes: S1. Vermiculite is calcined at high temperature to obtain expanded vermiculite; the expanded vermiculite is added to a Tris-HCl buffer solution of dopamine hydrochloride and stirred at room temperature for 12-24 hours to obtain supported polydopamine vermiculite. S2. The polydopamine-loaded vermiculite was placed in a mixed solution of MgSO4 and ammonium molybdate and impregnated and adsorbed at room temperature for 8-12 hours to obtain composite vermiculite. S3. Mix the composite vermiculite with nitrogen-fixing bacteria at room temperature for 2-4 hours, filter and separate, and dry to obtain bacteria-loaded vermiculite; S4. Add the bacterial-loaded vermiculite to the sodium alginate solution, add calcium chloride as a crosslinking agent, and stir at room temperature for 1-2 hours to obtain modified bacterial-loaded vermiculite.

[0008] Specifically, in step S1, vermiculite is calcined at high temperature to form an expanded vermiculite support with abundant microporous structure and a large specific surface area, providing sufficient reaction sites for subsequent functionalization modification. Dopamine hydrochloride undergoes spontaneous oxidative polymerization in a weakly alkaline environment of Tris-HCl buffer solution to form a polydopamine polymer with catechol and o-quinone structures. This polymer forms a uniform and stable coating on the vermiculite surface through hydrogen bonding, π-π stacking, and electrostatic interactions. In step S2, utilizing the chelating ability of the active groups such as hydroxyl, amino, and carboxyl groups of the polydopamine coating with metal ions, magnesium ions and molybdate ions are fixed on the support surface through coordination bonds and electrostatic interactions, forming a stable metal-polydopamine complex structure. Magnesium ions, as important cofactors of nitrogenase, participate in the assembly of the nitrogenase complex and the ATP hydrolysis process, while molybdenum ions directly participate in the reduction reaction of nitrogen molecules. The pre-loading of these two ions on the carrier surface provides essential trace element reserves for the subsequent efficient nitrogen-fixing activity of nitrogen-fixing bacteria, avoiding the decrease in nitrogen-fixing efficiency caused by trace element deficiency. In step S3, the nitrogen-fixing bacteria are thoroughly mixed with the composite vermiculite carrier. Utilizing the adhesive properties of the polydopamine coating and the trace element reserves on the carrier surface, uniform distribution and stable immobilization of the nitrogen-fixing bacteria are achieved on the carrier surface. The hydroxyl and amino groups of the polydopamine coating can form hydrogen bonds and electrostatic interactions with biomolecules such as polysaccharides and proteins on the cell wall of nitrogen-fixing bacteria, promoting effective adsorption and immobilization of the bacteria. The magnesium and molybdenum ions pre-loaded on the carrier surface can be gradually utilized by the microorganisms during the immobilization process, providing essential cofactors for the nitrogenase system and ensuring that the nitrogen-fixing bacteria maintain high biological activity on the carrier. In step S4, sodium alginate, as a natural polysaccharide polymer, undergoes an ionic cross-linking reaction between its carboxyl groups and calcium ions provided by calcium chloride, forming a three-dimensional gel network. This network structure not only possesses excellent biocompatibility and biodegradability but also provides an additional protective barrier for the carrier loaded with nitrogen-fixing bacteria. The semi-permeable membrane properties of the calcium alginate gel allow the free diffusion of nutrients and metabolites while preventing the entry of macromolecules and harmful factors, creating an ideal microenvironment for the nitrogen-fixing bacteria on the carrier. The porous structure of the gel network can also regulate the oxygen diffusion rate, maintaining the microaerobic environment required by the nitrogen-fixing bacteria and ensuring that nitrogenase activity is not completely inhibited by oxygen. Simultaneously, the coating effect of the gel further enhances the mechanical strength and environmental stability of the bacterial-loaded vermiculite.

[0009] Based on the above technical solutions, preferably, in step S1, the high-temperature calcination temperature is 800-900℃, the high-temperature calcination time is 2-4h; the concentration of the Tris-HCl buffer solution of dopamine hydrochloride is 2-4mg / ml; and the mass-volume ratio of expanded vermiculite to the Tris-HCl buffer solution of dopamine hydrochloride is 1g:10-20ml.

[0010] Based on the above technical solution, preferably, in step S2, the concentration of MgSO4 solution is 0.1-0.5 mol / L, the concentration of ammonium molybdate solution is 0.05-0.2 mol / L, and the mass-to-volume ratio of the loaded polydopamine vermiculite to the mixed solution of MgSO4 and ammonium molybdate is 1 g: 15-25 ml.

[0011] Based on the above technical solution, preferably, in step S3, the mass-to-volume ratio of the composite vermiculite to the nitrogen-fixing bacteria solution is 1g:2-4ml, and the concentration of the nitrogen-fixing bacteria is 10. 8 -10 9 CFU / ml.

[0012] Based on the above technical solutions, preferably, the nitrogen-fixing bacteria include *Azotomyces brasiliensis* and *Bacillus polymyxa*, with a mass ratio of 1:(1-2):1.

[0013] Azospirillum brasiliensis has a high efficiency in biological nitrogen fixation and good environmental adaptability, while Bacillus polymyxa has the ability to promote plant growth and disease resistance. The synergistic effect of the two strains not only improves nitrogen fixation efficiency, but also enhances the comprehensive biological activity of the bacterial vermiculite.

[0014] Based on the above technical solutions, preferably, the concentration of sodium alginate solution is 1%-3%, the concentration of calcium chloride solution is 2%-5%, and the mass-volume ratio of bacterial vermiculite, sodium alginate solution and calcium chloride solution is 1g:8-12ml:2-4ml.

[0015] Based on the above technical solutions, preferably, the nutritional composition is one or more of calcium sulfate, potassium dihydrogen phosphate, ferric sulfate, zinc sulfate, manganese sulfate, boric acid, and copper sulfate.

[0016] The various nutrients in the nutrient composition form a good nutritional balance and synergistic effect. With the help of the biological nitrogen fixation function of the bacterial vermiculite, it provides rice seedlings with a complete nutritional supply system of macronutrients such as nitrogen, phosphorus, and potassium, medium-quantity elements such as calcium, magnesium, and sulfur, and micronutrients such as iron, zinc, manganese, boron, and copper. This ensures that the seedlings can obtain sufficient and balanced mineral nutrition at each growth stage, so as to achieve the goal of robust growth and high-quality cultivation.

[0017] This invention also provides a method for preparing a rice seedling substrate based on rapid fermentation of reed foam, the preparation method comprising the following steps: (1) Mix cow dung, reed residue and carbonized rice husks in a weight ratio to obtain a mixture, adjust the moisture content to 55%-65%, adjust the carbon-nitrogen ratio to (25-35):1, add fermentation microbial agent and mix, the amount of fermentation microbial agent added is 4%-5% of the mass of the mixture, and carry out composting fermentation for 15-20 days. Composting fermentation can be carried out using trough fermentation process combined with mechanized turning operation. The fermentation temperature is controlled at 55-65℃, and the pile is turned once every 2-4 days to obtain a compound fermented product; the fermentation microbial agent includes Bacillus subtilis, Bacillus thermophilus licheniformis and Trichoderma, and the mass ratio of Bacillus subtilis, Bacillus thermophilus licheniformis and Trichoderma is 1:(1.0-1.2):(0.8-1); (2) After sterilizing the compound fermentation product and peat, the nutrient composition is then formulated, and finally the bacteria-carrying vermiculite is added and mixed evenly. By ensuring that the nutrients are evenly mixed with the mixture, the influence of the nutrients on the effective bacteria in the bacteria-carrying vermiculite is prevented. The mixture is then passed through a 5-10 mesh sieve to obtain a rice seedling substrate based on rapid fermentation of reed foam.

[0018] Specifically, the fermentation microbial agent significantly improves the decomposition efficiency of organic materials such as reed residue through the synergistic effect of three functional strains. Among them, Bacillus subtilis secretes a variety of extracellular enzymes such as cellulase, hemicellulase and pectinase, which rapidly decompose the cellulose and hemicellulose components in reed residue; Bacillus thermophilus has excellent high temperature resistance, which can further promote the decomposition of recalcitrant components in lignocellulose complex and promote the rapid maturation of organic materials; Trichoderma can effectively break down the complex structure of lignin in reed residue and release the encapsulated cellulose and hemicellulose.

[0019] The present invention also provides an application of a rice seedling substrate based on rapid fermentation of reed foam, the substrate being used for rice seedling cultivation, including dry seedling cultivation, wet seedling cultivation, or water seedling cultivation.

[0020] The method for preparing and applying a rice seedling substrate based on rapid fermentation of reed foam of the present invention has the following advantages over the prior art: (1) This invention uses reed residue as the main substrate raw material, combined with a scientific ratio of organic components such as cow dung, carbonized rice husks, and peat moss, making full use of the abundant reed residue resources in the Dongting Lake area. Compared with traditional straw, reed residue has the technical advantages of uniform texture, moderate fiber structure, and easy composting. Its porous structure and suitable carbon-nitrogen ratio enable rapid fermentation, and the fermentation efficiency is significantly better than that of traditional substrate preparation processes. The standardized supply and stable physicochemical properties of reed residue solve the problems of dispersed raw material sources and large quality fluctuations in the existing technology. At the same time, its rich cellulose and hemicellulose provide a continuous carbon source for beneficial microorganisms, promoting substrate maturation and granular structure formation. The final substrate has good water retention and air permeability and suitable bulk density, meeting the strict requirements of machine-transplanted rice seedlings for substrate physical properties.

[0021] (2) The bacterial-loaded vermiculite was modified with polydopamine functionalization technology. Through the self-polymerization reaction of dopamine under weakly alkaline conditions, a coating with abundant active groups was formed on the surface of the vermiculite, which significantly improved the carrier's ability to bind metal ions and microorganisms. The magnesium ions and molybdate ions preloaded on the carrier surface provided essential cofactors for nitrogenase. The three-dimensional gel network constructed by the sodium alginate-calcium chloride crosslinking system not only provided an ideal micro-aerobic environment for nitrogen-fixing bacteria, but also achieved a slow-release effect of the bacteria, enabling the nitrogen-fixing bacteria in the modified bacterial-loaded vermiculite to maintain a high level of activity in the matrix for a long time.

[0022] (3) By combining *Azotomyces brasiliensis* and *Bacillus polymyxa*, a significant synergistic nitrogen-fixing effect was observed. *Azotomyces brasiliensis* can efficiently catalyze the reduction of nitrogen to ammonia under microaerobic conditions, providing a biologically effective nitrogen source for the substrate. *Bacillus polymyxa*, on the other hand, promotes seedling root development and inhibits pathogen growth by secreting plant hormones and antibacterial substances. The synergistic effect of the two strains ensured sufficient nitrogen-fixing capacity and exerted a comprehensive effect of promoting growth and resisting disease, significantly increasing the soluble nitrogen content in the substrate, significantly enhancing seedling root vitality, and greatly reducing the incidence of damping-off disease. The combined bacterial strain and the magnesium and molybdenum ions pre-loaded on the carrier formed a complete biological nitrogen-fixing system, continuously supplementing nitrogen nutrition during substrate use, reducing dependence on chemical nitrogen fertilizers, and realizing the biological supply of substrate nutrition and environmentally friendly production. Detailed Implementation

[0023] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0024] It should be noted that *Azotospira brasiliensis* was purchased from Shanghai Yushao Biotechnology Co., Ltd. (product number YS-JZ12008); *Bacillus polymyxa* (strain number HZB114245) was purchased from Zhengzhou Fangjue Biotechnology Co., Ltd.; *Bacillus subtilis* (product number BMZ135811) was purchased from Mingzhou Biotechnology; *Bacillus thermophilus* (product number B80844) was purchased from Mingzhou Biotechnology; and *Trichoderma* (product number BMZ073081) was purchased from Mingzhou Biotechnology.

[0025] Example 1 This embodiment provides a rice seedling substrate based on rapid fermentation of reed foam and its preparation method. By weight, the rice seedling substrate includes the following components: 45 parts of reed residue, 18 parts of cow dung, 12 parts of carbonized rice husk, 15 parts of peat moss, 18 parts of modified bacterial-carrying vermiculite, and 5 parts of a nutrient composition. The nutrient composition includes 30 parts of calcium sulfate, 25 parts of potassium dihydrogen phosphate, 15 parts of ferric sulfate, 10 parts of zinc sulfate, 8 parts of manganese sulfate, 7 parts of boric acid, and 5 parts of copper sulfate.

[0026] The preparation method of modified bacterial-loaded vermiculite is as follows: S1. 100g of vermiculite was calcined at 850℃ for 3h to obtain expanded vermiculite; 100g of expanded vermiculite was added to 1500ml of Tris-HCl buffer solution of dopamine hydrochloride (concentration of 3mg / ml), stirred at room temperature for 18h, and washed with deionized water until neutral to obtain supported polydopamine vermiculite; S2. Place 100g of polydopamine-loaded vermiculite in 2000ml of a mixed solution of MgSO4 and ammonium molybdate, wherein the concentration of MgSO4 solution is 0.3mol / L and the concentration of ammonium molybdate solution is 0.1mol / L. Impregnate and adsorb at room temperature for 10h, stirring once every 2h. After filtration, wash lightly once with deionized water to obtain composite vermiculite. S3. Prepare a nitrogen-fixing bacterial suspension by mixing *Azotobacter brasiliensis* and *Bacillus polymyxa* at a mass ratio of 1.5:1, and adjust the bacterial suspension concentration to 5 × 10⁻⁶. 8 CFU / ml, mix 100g of compound vermiculite with 300ml of nitrogen-fixing bacteria solution, mix slowly at room temperature for 3 hours, filter and separate, place in a ventilated place to air dry naturally until the moisture content is 10%-15%, avoid direct sunlight, and obtain bacteria-loaded vermiculite; S4. Add 100g of bacterial-loaded vermiculite to 1000ml of sodium alginate solution (concentration of 2%), add 300ml of calcium chloride solution (concentration of 3.5%) as a crosslinking agent, stir at room temperature for 1.5h, and let stand for 30min to obtain modified bacterial-loaded vermiculite.

[0027] The preparation method of rice seedling substrate is as follows: (1) After crushing the reed residue to 2-5mm, mix the cow dung, reed residue and carbonized rice husks evenly according to the weight ratio, adjust the moisture content to 60%, adjust the carbon-nitrogen ratio to 30:1, add fermentation microbial agent (the amount of agent is 4.5% of the mass of the mixture, of which the mass ratio of Bacillus subtilis: Bacillus thermophilus: Trichoderma is 1:1.1:0.9), mix thoroughly, and pile it into a trapezoidal pile 1.3m high in a standardized fermentation tank, cover it with a breathable film, and carry out composting fermentation for 18 days. The fermentation temperature is controlled at 60℃. Turn the pile every 3 days. Check the moisture content and the decomposition effect when turning the pile. After complete decomposition, the compound fermented product is obtained. (2) After mixing the compound fermentation material with peat, sterilize it at high temperature and normal pressure at a temperature of 80-100℃ for about 20-30 minutes to kill pathogenic bacteria and pathogenic fungi and evaporate most of the moisture in the material, making the material more fluffy. After sterilization, mix it thoroughly with the nutrient composition, add modified bacterial vermiculite, mix thoroughly and evenly, and pass it through a 10-mesh sieve to obtain rice seedling substrate.

[0028] Example 2 This embodiment provides a rice seedling substrate based on rapid fermentation of reed foam and its preparation method. By weight, the rice seedling substrate includes the following components: 35 parts of reed residue, 15 parts of cow dung, 8 parts of carbonized rice husk, 10 parts of peat moss, 13 parts of modified bacterial-carrying vermiculite, and 3 parts of a nutrient composition, which includes 30 parts of calcium sulfate, 25 parts of potassium dihydrogen phosphate, and 15 parts of ferric sulfate.

[0029] The preparation method of modified bacterial-loaded vermiculite is as follows: S1. 100g of vermiculite was calcined at 800℃ for 4h to obtain expanded vermiculite; 100g of expanded vermiculite was added to 1000ml of Tris-HCl buffer solution of dopamine hydrochloride (concentration of 2mg / ml), stirred at room temperature for 12h, and washed with deionized water until neutral to obtain loaded polydopamine vermiculite; S2. Place 100g of polydopamine-loaded vermiculite in 1500ml of a mixed solution of MgSO4 and ammonium molybdate, wherein the concentration of MgSO4 solution is 0.5mol / L and the concentration of ammonium molybdate solution is 0.2mol / L. Impregnate and adsorb at room temperature for 8h, stirring once every 2h. After filtration, wash lightly once with deionized water to obtain composite vermiculite. S3. Prepare a nitrogen-fixing bacteria culture by mixing *Azotoxinus brasiliensis* and *Bacillus polymyxa* at a mass ratio of 1:1, and adjust the concentration of the culture to 1×10⁻⁶. 9 CFU / ml, mix 100g of compound vermiculite with 200ml of nitrogen-fixing bacteria solution, mix slowly at room temperature for 2 hours, filter and separate, place in a ventilated place to air dry naturally until the moisture content is 10%-15%, avoid direct sunlight, and obtain bacteria-loaded vermiculite; S4. Add 100g of bacterial-loaded vermiculite to 800ml of sodium alginate solution (concentration of 3%), add 200ml of calcium chloride solution (concentration of 5%) as a crosslinking agent, stir at room temperature for 1h, and let stand for 30min to obtain modified bacterial-loaded vermiculite.

[0030] The preparation method of rice seedling substrate is as follows: (1) After crushing the reed residue to 2-5mm, mix the cow dung, reed residue and carbonized rice husks evenly according to the weight ratio, adjust the moisture content to 55%, adjust the carbon-nitrogen ratio to 25:1, add fermentation microbial agent (the amount of agent is 4.5% of the mass of the mixture, of which the mass ratio of Bacillus subtilis: Bacillus thermophilus: Trichoderma is 1:1.1:0.9), mix thoroughly, and pile it into a trapezoidal pile 1.2m high in a standardized fermentation tank, cover it with a breathable film, and carry out composting fermentation for 20 days. The fermentation temperature is controlled at 65℃. Turn the pile every 2 days. When turning the pile, check the moisture content and the decomposition effect. After complete decomposition, the compound fermented product is obtained. (2) After mixing the compound fermentation material with peat, sterilize it at high temperature and normal pressure at a temperature of 80-100℃ for about 20-30 minutes. After sterilization, mix it thoroughly with the nutrient composition, add modified bacterial vermiculite, mix thoroughly and evenly, and pass it through a 5-mesh sieve to obtain rice seedling substrate.

[0031] Example 3 This embodiment provides a rice seedling substrate based on rapid fermentation of reed foam and its preparation method. By weight, the rice seedling substrate includes the following components: 50 parts of reed residue, 22 parts of cow dung, 15 parts of carbonized rice husk, 20 parts of peat moss, 22 parts of modified bacterial-carrying vermiculite, and 8 parts of a nutrient composition, which includes 30 parts of calcium sulfate, 25 parts of potassium dihydrogen phosphate, 10 parts of zinc sulfate, and 7 parts of boric acid.

[0032] The preparation method of modified bacterial-loaded vermiculite is as follows: S1. 100g of vermiculite was calcined at 900℃ for 2h to obtain expanded vermiculite; 100g of expanded vermiculite was added to 2000ml of Tris-HCl buffer solution of dopamine hydrochloride (concentration of 4mg / ml), stirred at room temperature for 24h, and washed with deionized water until neutral to obtain loaded polydopamine vermiculite; S2. Place 100g of polydopamine-loaded vermiculite in 2500ml of a mixed solution of MgSO4 and ammonium molybdate, wherein the concentration of MgSO4 solution is 0.1mol / L and the concentration of ammonium molybdate solution is 0.05mol / L. Impregnate and adsorb at room temperature for 12h, stirring once every 2h. After filtration, wash lightly once with deionized water to obtain composite vermiculite. S3. Prepare a nitrogen-fixing bacteria solution by mixing *Azotoxinus brasiliensis* and *Bacillus polymyxa* at a mass ratio of 2:1, and adjust the concentration of the solution to 1×10⁻⁶. 8 CFU / ml, mix 100g of compound vermiculite with 400ml of nitrogen-fixing bacteria solution, mix slowly at room temperature for 4 hours, filter and separate, place in a ventilated place to air dry naturally until the moisture content is 10%-15%, avoid direct sunlight, and obtain bacteria-loaded vermiculite; S4. Add 100g of bacterial-loaded vermiculite to 1200ml of sodium alginate solution (concentration of 1%), add 400ml of calcium chloride solution (concentration of 2%) as a crosslinking agent, stir at room temperature for 2h, and let stand for 30min to obtain modified bacterial-loaded vermiculite. The preparation method of rice seedling substrate is as follows: (1) After crushing the reed residue to 2-5mm, mix the cow dung, reed residue and carbonized rice husks evenly according to the weight ratio, adjust the moisture content to 65%, adjust the carbon-nitrogen ratio to 35:1, add fermentation microbial agent (the amount of agent is 4.5% of the mass of the mixture, of which the mass ratio of Bacillus subtilis: Bacillus thermophilus: Trichoderma is 1:1.1:0.9), mix thoroughly, and pile it into a trapezoidal pile 1.5m high in a standardized fermentation tank, cover it with a breathable film, and carry out composting fermentation for 25 days. The fermentation temperature is controlled at 55℃. Turn the pile every 4 days. When turning the pile, check the moisture content and the decomposition effect. After complete decomposition, the compound fermented product is obtained. (2) After mixing the compound fermentation material with peat, sterilize it at high temperature and normal pressure at a temperature of 80-100℃ for 20-30 minutes. After sterilization, mix it thoroughly with the nutrient composition, add modified bacterial vermiculite, mix thoroughly and evenly, and pass it through a 10-mesh sieve to obtain rice seedling substrate.

[0033] Comparative Example 1 This comparative example provides a rice seedling substrate based on rapid fermentation of reed foam and its preparation method. By weight, the rice seedling substrate comprises the following components: 45 parts reed residue, 18 parts cow dung, 12 parts carbonized rice husks, 15 parts peat moss, 18 parts modified bacterial-loaded vermiculite, and 5 parts a nutrient composition. The nutrient composition includes 30 parts calcium sulfate, 25 parts potassium dihydrogen phosphate, 15 parts ferric sulfate, 10 parts zinc sulfate, 8 parts manganese sulfate, 7 parts boric acid, and 5 parts copper sulfate. The preparation method is the same as in Example 1, except that the modified bacterial-loaded vermiculite is not loaded with polydopamine. Specifically, The preparation method of modified bacterial-loaded vermiculite is as follows: S1. 100g of vermiculite is calcined at 850℃ for 3 hours to obtain expanded vermiculite; S2. Place 100g of expanded vermiculite in a 2000ml mixed solution of MgSO4 and ammonium molybdate, wherein the concentration of MgSO4 solution is 0.3mol / L and the concentration of ammonium molybdate solution is 0.1mol / L. Impregnate and adsorb at room temperature for 10h, stirring once every 2h. After filtration, wash lightly once with deionized water to obtain composite vermiculite. Steps S3-S4 are the same as in Example 1.

[0034] Comparative Example 2 This comparative example provides a rice seedling substrate based on rapid fermentation of reed foam and its preparation method. By weight, the rice seedling substrate comprises the following components: 45 parts reed residue, 18 parts cow dung, 12 parts carbonized rice husks, 15 parts peat moss, 18 parts modified bacterial-loaded vermiculite, and 5 parts a nutrient composition. The nutrient composition includes 30 parts calcium sulfate, 25 parts potassium dihydrogen phosphate, 15 parts ferric sulfate, 10 parts zinc sulfate, 8 parts manganese sulfate, 7 parts boric acid, and 5 parts copper sulfate. The preparation method is the same as in Example 1, except that the modified bacterial-loaded vermiculite is not loaded with ammonium molybdate. Specifically, The preparation method of modified bacterial-loaded vermiculite is as follows: Step S1 is the same as in Example 1; S2. Place 100g of polydopamine-loaded vermiculite in 2000ml of MgSO4 solution with a concentration of 0.3mol / L and impregnate at room temperature for 10h, stirring once every 2h. After filtration, wash lightly once with deionized water to obtain composite vermiculite. S3-S4 are the same as in Example 1.

[0035] Comparative Example 3 This comparative example provides a rice seedling substrate based on rapid fermentation of reed foam and its preparation method. By weight, the rice seedling substrate comprises the following components: 45 parts reed residue, 18 parts cow dung, 12 parts carbonized rice husks, 15 parts peat moss, 18 parts modified bacterial-carrying vermiculite, and 5 parts a nutrient composition. The nutrient composition includes 30 parts calcium sulfate, 25 parts potassium dihydrogen phosphate, 15 parts ferric sulfate, 10 parts zinc sulfate, 8 parts manganese sulfate, 7 parts boric acid, and 5 parts copper sulfate. The preparation method is the same as in Example 1, except that the modified bacterial-carrying vermiculite is not loaded with Bacillus polymyxa. Specifically, The preparation method of modified bacterial-loaded vermiculite is as follows: Steps S1-S2 are the same as in Example 1; S3. Adjust the concentration of *Azotomyces brasiliensis* bacterial solution to 5 × 10⁻⁶. 8 CFU / ml, mix 100g of compound vermiculite with 300ml of Brazilian nitrogen-fixing spirochete solution, mix slowly at room temperature for 3 hours, filter and separate, place in a ventilated place to air dry naturally until the moisture content is 10%-15%, avoid direct sunlight, and obtain bacteria-loaded vermiculite; S4 is the same as in Example 1.

[0036] Comparative Example 4 This comparative example provides a rice seedling substrate based on rapid fermentation of reed foam and its preparation method. By weight, the rice seedling substrate comprises the following components: 45 parts reed residue, 18 parts cow dung, 12 parts carbonized rice husks, 15 parts peat moss, 18 parts modified bacterial-carrying vermiculite, and 5 parts a nutrient composition. The nutrient composition includes 30 parts calcium sulfate, 25 parts potassium dihydrogen phosphate, 15 parts ferric sulfate, 10 parts zinc sulfate, 8 parts manganese sulfate, 7 parts boric acid, and 5 parts copper sulfate. The preparation method is the same as in Example 1, except that the modified bacterial-carrying vermiculite is not loaded with *Azotocinobacter brasiliensis*. Specifically, The preparation method of modified bacterial-loaded vermiculite is as follows: Steps S1-S2 are the same as in Example 1; S3. Adjust the concentration of Bacillus polymyxa bacterial culture to 5×10⁻⁶. 8 CFU / ml, mix 100g of compound vermiculite with 300ml of Bacillus polymyxa bacterial solution, mix slowly at room temperature for 3 hours, filter and separate, place in a ventilated place to air dry naturally until the moisture content is 10%-15%, avoid direct sunlight, and obtain bacterial-loaded vermiculite; S4 is the same as in Example 1.

[0037] Performance testing The seedling substrates prepared in the examples and comparative examples were spread in the seedling trays to a thickness of 1.8-2.0 cm, and the seeds were sown evenly with a sowing amount of 180g per tray. Finally, another layer of the corresponding substrate was spread on each tray, and the trays were placed in the greenhouse for seedling cultivation. The trays were watered and managed normally every day.

[0038] Agronomic traits of rice seedlings were tested: at the 3-leaf stage, 30 seedlings were taken from each pot to measure seedling height, stem base width, number of adventitious roots per seedling (number of adventitious roots longer than 5mm), length of the longest adventitious root, and area of ​​the largest single leaf (length × width × 0.7746). The chlorophyll content of the seedlings was measured using a SPAD instrument. The dry weight of the aboveground and underground parts of the seedlings was measured (after washing the roots, the roots and stems were cut apart at the base and placed separately). The test results are shown in Table 1.

[0039] Table 1 Agronomic traits of rice seedlings Rice root cohesion test: A portion of the substrate (28 cm × 15 cm) was cut from the seedling tray and placed on a flat wooden board. Both ends were clamped with a clip, one end fixed, and the other end was pulled with a spring scale until the seedling block broke. The tensile force displayed on the spring scale is the root cohesion force of the seedling block. Rice seedling root development test: At the 3-leaf stage, 20 seedlings were taken from each pot, and all roots were cut off. The seedlings were placed in plastic cups filled with distilled water and cultured in an intelligent light incubator (temperature 25℃, relative humidity 94%, 12 hours of light and 12 hours of darkness), with distilled water added to maintain moisture. After 7 days, the seedlings were removed, and the root length and number were measured. The test results are shown in Table 2.

[0040] Table 2. Root system of rice seedlings Total nitrogen, phosphorus, and potassium (TP) content determination: At the 2-leaf-1-heart stage, three trays were randomly selected from each treatment. A certain amount of whole seedling samples were randomly taken from each tray. The substrate on the plant roots was washed off, and the seedlings were placed in an oven at 105℃ for blanching, followed by drying at 60℃ to constant weight. The TP content of the seedlings was then determined by crushing. Total nitrogen was determined using the Kjeldahl method, total phosphorus using the vanadium-molybdic acid colorimetric method, and total potassium using the flame photometry method. The results are shown in Table 3.

[0041] Table 3 Results of Total Nitrogen, Phosphorus and Potassium Detection As shown in Tables 1-3, the rice seedling substrate prepared by the technical solution of this invention exhibits excellent comprehensive performance: In terms of agronomic traits, the seedling height, stem diameter, SPAD value, and seedling dry weight of Examples 1-3 are all optimal; in terms of root development, the root dry weight, root length, number of adventitious roots, and root cohesion force show strong root structure and excellent cohesion characteristics; in terms of nutritional quality, the total nitrogen, total phosphorus, and total potassium contents all show a good nutritional balance. However, the rice seedling substrates of Comparative Examples 1-4 show varying degrees of decline in all indicators. Comparative Example 1, due to the lack of polydopamine loading, shows the largest decline in all indicators, especially a significant reduction in root cohesion force and total nitrogen content. The lack of polydopamine functionalization modification leads to a significant decrease in the carrier's ability to bind with metal ions and microorganisms, directly affecting the maintenance of nitrogen-fixing bacteria activity and the stable supply of nutrients; Comparative Example 2, due to the lack of ammonium molybdate loading, shows a significant decline in nitrogen-fixing related indicators. The lack of molybdenum ions causes a sharp decrease in nitrogenase catalytic efficiency, resulting in severe damage to biological nitrogen fixation function and nitrogen content. Insufficient nutrient supply; Comparative Example 3, without Bacillus polymyxa, although the decrease was relatively small, was still significantly lower than Example 1. Although Bacillus polymyxa has limited nitrogen fixation capacity, its secreted plant hormones and antibacterial substances play an important role in promoting seedling growth and disease resistance, forming an important synergistic effect with Azotobacter brasiliensis; Comparative Example 4, without Azotobacter brasiliensis, also showed severe nitrogen nutrient deficiency. Azotobacter brasiliensis is the main nitrogen-fixing functional bacterium, undertaking the core nitrogen reduction task. Its absence directly leads to the loss of substrate nitrogen fixation capacity, affecting the nitrogen nutrition status of seedlings.

[0042] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A rice seedling substrate based on rapid fermentation of reed foam, characterized in that, By weight, it comprises the following components: 35-50 parts of reed residue, 15-22 parts of cow dung, 8-15 parts of carbonized rice husk, 10-20 parts of peat moss, 13-22 parts of modified bacterial-carrying vermiculite, and 3-8 parts of a nutrient composition, wherein the modified bacterial-carrying vermiculite includes nitrogen-fixing bacteria and a functionalized vermiculite carrier. The preparation method of the modified bacterial-loaded vermiculite includes: S1. Vermiculite is calcined at high temperature to obtain expanded vermiculite; Expanded vermiculite was added to a Tris-HCl buffer solution of dopamine hydrochloride and stirred at room temperature for 12-24 h to obtain supported polydopamine vermiculite. S2. The polydopamine-loaded vermiculite was placed in a mixed solution of MgSO4 and ammonium molybdate and impregnated and adsorbed at room temperature for 8-12 hours to obtain composite vermiculite. S3. Mix the composite vermiculite with nitrogen-fixing bacteria at room temperature for 2-4 hours, filter and separate, and dry to obtain bacteria-loaded vermiculite. The nitrogen-fixing bacteria include Azotobacter brasiliensis and Bacillus polymyxa. The mass ratio of Azotobacter brasiliensis to Bacillus polymyxa is (1-2):

1. S4. Add the bacterial-loaded vermiculite to the sodium alginate solution, add calcium chloride as a crosslinking agent, and stir at room temperature for 1-2 hours to obtain modified bacterial-loaded vermiculite; In step S1, the high-temperature calcination temperature is 800-900℃, and the high-temperature calcination time is 2-4h; the concentration of the Tris-HCl buffer solution of dopamine hydrochloride is 2-4mg / ml; and the mass-volume ratio of expanded vermiculite to the Tris-HCl buffer solution of dopamine hydrochloride is 1g:10-20ml. In step S2, the concentration of MgSO4 solution is 0.1-0.5 mol / L, the concentration of ammonium molybdate solution is 0.05-0.2 mol / L, and the mass-to-volume ratio of the loaded polydopamine vermiculite to the mixed solution of MgSO4 and ammonium molybdate is 1 g: 15-25 ml.

2. The rice seedling substrate based on rapid fermentation of reed foam as described in claim 1, characterized in that: In step S3, the mass-to-volume ratio of the composite vermiculite to the nitrogen-fixing bacteria solution is 1g:2-4ml, and the concentration of the nitrogen-fixing bacteria is 10. 8 -10 9 CFU / ml.

3. The rice seedling substrate based on rapid fermentation of reed foam as described in claim 1, characterized in that: In step S4, the concentration of sodium alginate solution is 1%-3%, the concentration of calcium chloride solution is 2%-5%, and the mass-volume ratio of bacterial vermiculite, sodium alginate solution and calcium chloride solution is 1g:8-12ml:2-4ml.

4. The rice seedling substrate based on rapid fermentation of reed foam as described in claim 1, characterized in that: The nutrient composition comprises any four or more of potassium dihydrogen phosphate, ferric sulfate, calcium sulfate, zinc sulfate, manganese sulfate, boric acid, and copper sulfate.

5. A method for preparing a rice seedling substrate based on rapid fermentation of reed foam as described in any one of claims 1-4, characterized in that: The preparation method includes the following steps: (1) Mix cow dung, reed residue and carbonized rice husks by weight, adjust the moisture content to 55%-65%, adjust the carbon-nitrogen ratio to (25-35):1, add fermentation microbial agent and mix, compost for 15-20 days, control the fermentation temperature at 55-65℃, turn the pile every 2-4 days to obtain compound fermented product; (2) After sterilizing the compound fermentation material and peat, the nutrient composition is then formulated, and finally the bacteria-carrying vermiculite is added and mixed evenly. The mixture is then passed through a 5-10 mesh sieve to obtain a rice seedling substrate based on rapid fermentation of reed foam.

6. The application of a rice seedling substrate based on rapid fermentation of reed foam as described in any one of claims 1-4, characterized in that: The substrate is used for rice seedling cultivation, including dry seedling cultivation, wet seedling cultivation, or water seedling cultivation.

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