Compound microbial fertilizer suitable for cotton in saline-alkali soil and preparation method thereof

Abstract

The application belongs to the field of fertilizers, and particularly relates to a compound microbial fertilizer suitable for cotton in saline-alkali soil and a preparation method thereof. The compound microbial fertilizer comprises core microbial agents: 1-3 parts; modified load carriers: 70-85 parts; slow-release coating layers: 10-20 parts; and co-precipitation complexes: 0.5-1.5 parts. The modified load carrier is attapulgite clay activated by citric acid and treated by iron loading. The slow-release coating layer is composed of gel material formed by compounding sodium lignosulfonate and calcium alginate. The co-precipitation complex is a co-precipitation product generated by the reaction of salicylic acid and gamma-aminobutyric acid. The preparation method comprises the following steps: carrier premixing, granulation forming, coating wrapping and post-treatment. The application solves the technical problems of low survival rate of microorganisms, high risk of drip irrigation system blockage and insufficient physiological response of cotton to salt in cotton planting in saline-alkali soil.

Description

Technical Field

[0001] This invention belongs to the field of fertilizer technology, specifically relating to a compound microbial fertilizer suitable for cotton in saline-alkali land and its preparation method. Background Technology

[0002] Cotton is an important economic fiber crop in my country. The high osmotic pressure, ion toxicity, and poor physical structure of saline-alkali soils severely inhibit cotton seed germination, root development, and nutrient absorption. Taking some cotton-growing areas in Xinjiang as an example, when the electrical conductivity of the topsoil exceeds 4 dS / m, the cotton emergence rate can plummet by more than 50%, and stunted seedlings and premature aging in the middle and late stages are common, leading to yield losses of 30%-50%, severely dampening cotton farmers' enthusiasm for planting.

[0003] To address the salinity problem, various measures have been adopted in agricultural production. Traditionally, flood irrigation is used to suppress salt, but this exacerbates the water crisis in arid regions and its effects are short-lived. Chemical soil conditioners such as desulfurized gypsum and phosphogypsum are also applied, which can reduce soil alkalinity and sodium ion content to some extent, but long-term, large-scale use carries risks of high costs, potential introduction of new pollutants, and soil compaction.

[0004] In recent years, microbial fertilizers have received much attention as a green and sustainable solution. There are already many general-purpose or stress-resistant microbial fertilizer products on the market, whose bacterial strains are mostly common plant rhizosphere growth-promoting bacteria such as Bacillus subtilis and Bacillus mucilaginosus, and are often mixed with humic acid, organic matter, etc.

[0005] However, when these general-purpose microbial fertilizers are directly applied to cotton cultivation in saline-alkali land, several specific and acute technical shortcomings have been exposed in actual production. In 2023, a biotechnology company conducted a trial in saline-alkali cotton fields in the Yellow River Delta and found that the performance of microbial fertilizer products using Bacillus subtilis and Bacillus megaterium in the field was far inferior to the laboratory results. One of the core problems is the extremely low survival rate of the microbial agents in the field. The high salinity, high pH, ​​and drastic alternation of dry and wet conditions in saline-alkali land pose a fatal stress to microorganisms that have not undergone special acclimatization or protection. The activity of functional microbial communities rapidly declines after application to the soil, making it difficult to establish a stable population of beneficial microorganisms.

[0006] Another more common and troublesome problem for farmers is the compatibility of formulations with modern agricultural facilities. Currently, intensive cotton fields commonly use integrated water and fertilizer drip irrigation systems, but most microbial fertilizer products are powders or easily disintegrating granules, presenting two major challenges during application: First, uncoated microbial fertilizer granules may rapidly dissolve their binder and disperse their carrier material upon contact with the drip irrigation solution or water. This immediately generates a large amount of extremely fine powder, sticky substances, and free microorganisms. These tiny substances easily deposit in pipe bends and filter meshes, adhering like sludge to the surface of the dripper's flow channels, gradually accumulating and causing blockages. Second, the microbial agent settles and flocculates in the fertilizer solution, leading to uneven delivery and microbial death. Some have attempted to dissolve commercially available branded microbial fertilizers in drip irrigation tanks, resulting in a large amount of viscous sediment forming at the bottom of the tank, which is difficult to clean and causes localized blockages in the drip irrigation tape.

[0007] In summary, existing solutions mostly involve simple mixing of microbial strains with ordinary carriers, failing to integrate the design from a systems engineering perspective of "protection-delivery-activation." Specific technical bottlenecks can be summarized as follows: First, there is a lack of a dedicated carrier material that can adapt to environments with high salinity and high fertilizer ion intensity, firmly support microorganisms, control their slow release, and possess soil-improving functions; second, there is a lack of a coating technology that can encapsulate microbial fertilizer particles, preventing premature disintegration and pulverization in drip irrigation solutions, while also enabling intelligent degradation upon contact with wet soil; third, there is a lack of an active signaling substance that can synergistically enhance functional microbial communities, actively stimulating the cotton's salt-resistance physiological response, rather than merely providing nutrients.

[0008] Therefore, it is necessary to design a compound microbial fertilizer suitable for cotton in saline-alkali land and its preparation method. Summary of the Invention

[0009] To overcome the shortcomings of existing technologies, a compound microbial fertilizer suitable for cotton in saline-alkali land and its preparation method are provided.

[0010] To achieve the above objectives, the present invention provides the following technical solution:

[0011] A compound microbial fertilizer suitable for cotton in saline-alkali soil is made from the following raw materials in parts by weight:

[0012] Core microbial agent: 1-3 parts;

[0013] Modified load carrier: 70-85 parts;

[0014] Sustained-release coating layer: 10-20 parts;

[0015] Coprecipitated complex: 0.5-1.5 parts;

[0016] The core bacterial agent is composed of microbial preparations of Bacillus subtilis, Bacillus colloidis, and Bacillus licheniformis; the modified loading carrier is attapulgite clay activated with citric acid and treated with iron loading; the slow-release coating layer is composed of a gel material composed of sodium lignosulfonate and calcium alginate; and the coprecipitation complex is a coprecipitation product generated by the reaction of salicylic acid and γ-aminobutyric acid.

[0017] In the core microbial agent, the effective viable count ratio of Bacillus subtilis, Bacillus mucilaginosa, and Bacillus licheniformis is (5.0-7.0):(3.0-4.5):(2.0-3.0).

[0018] The modified load carrier is prepared by the following method:

[0019] a. Acid activation treatment: Attapulgite clay powder and citric acid solution are stirred and reacted at 75-85℃ for 3-5 hours;

[0020] b. Iron-loaded aging: Cool the slurry obtained in step a to room temperature, adjust the pH value to 4.5-5.5 with alkali solution, add ferrous sulfate solution, and age at 45-55℃ for 10-14 hours;

[0021] c. Washing and drying: After aging in step b, filter the material and wash it with water until no white precipitate is produced when the filtrate is tested with barium chloride solution. Then dry it at 100-110℃ to constant weight and pulverize it to pass through a 300-mesh sieve to obtain the modified support carrier.

[0022] In step a, the citric acid solution has a mass percentage concentration of 6%-10%, and the attapulgite clay powder is mixed with the citric acid solution at a solid-liquid mass ratio of 1:(8-12); in step b, a ferrous sulfate solution with a concentration of 0.4-0.6 mol / L is added, so that the mass ratio of the added iron element to the dry basis of the attapulgite clay is (2-4):100.

[0023] In the practical application of cotton cultivation in saline-alkali soils, a key obstacle is the difficulty for exogenous beneficial microorganisms to effectively colonize and survive in adverse soil conditions. Current technologies typically involve directly mixing common bacteria such as Bacillus subtilis with simple carriers. These carriers primarily function to adsorb and dilute the microorganisms, but lack specific physicochemical protective designs. When these products are applied to saline-alkali soils, the microorganisms are rapidly exposed to severe adverse conditions, causing their activity to decline quickly and failing to form a sufficient effective population to continuously act on the cotton roots. This is a major reason for the unstable field effects of many microbial fertilizers.

[0024] To address the aforementioned problem of microbial survival, this application modifies the design of the loading carrier. The selected substrate material is attapulgite clay, which possesses a natural porous structure, but its protective capacity is limited when used directly. Therefore, we first perform thermal activation treatment on it using citric acid solution. The purpose of this step is primarily to utilize the acidity of citric acid to dissolve some impurities at the edges of the clay minerals, thereby clearing and expanding the original pore structure, increasing its specific surface area and adsorption capacity, and creating space for subsequently loading more microorganisms and their nutrients.

[0025] The subsequent iron-loaded aging process is a crucial step, involving the binding of iron ions from ferrous sulfate to the activated clay surface under specific acidity conditions. The introduction of iron ions is not arbitrary. On one hand, iron is a trace element essential for microbial growth, providing a readily available nutrient source for the microorganisms attached to it. On the other hand, and more importantly, these iron ions may precipitate or bind on the clay surface and in pores in forms such as ferric hydroxide. They can partially capture or fix harmful ions such as sodium ions in the soil solution through ion exchange or specific adsorption. When the microbial fertilizer granules are applied to the soil, this modified carrier is not merely a passive physical adsorbent, but rather a miniature "ion buffer unit." It physically shields microorganisms through its increased surface area, while the iron and other active sites on its surface can regulate the micro-ionic environment around the bacterial attachment points to a certain extent, mitigating the direct impact of salt ions on microbial cells. This provides a longer window of opportunity for the functional microbial community to overcome the environmental stresses of the initial colonization stage, helping to improve its survival rate and colonization success rate in the rhizosphere.

[0026] The powder raw material for the sustained-release coating layer is prepared by the following method:

[0027] <1> Gel synthesis: Sodium lignosulfonate was dissolved in hot water at 60-70℃ to prepare solution A; sodium alginate was dissolved in deionized water at room temperature to prepare solution B; under stirring conditions, solution A and solution B were mixed at a volume ratio of 1:1 to obtain mixture C.

[0028] <2> Cross-linking and curing: While stirring continuously, add calcium chloride solution dropwise to mixture C. After the addition is complete, continue stirring for 30-60 minutes to form a uniform viscous gel.

[0029] <3> Dehydration and pulverization: [The process involves...] <2> The resulting gel is dried in a vacuum drying oven at 60-70°C until the water content is less than 5%, and then mechanically pulverized and passed through a 200-mesh sieve to obtain the powder raw material of the sustained-release coating layer.

[0030] In the steps <1> In the process, the mass percentage concentration of solution A is 12%-18%, and the mass percentage concentration of solution B is 3%-5%; in step <2> In this process, the mass percentage concentration of the calcium chloride solution is 8%-12%, and the amount of calcium chloride solution added is such that the molar ratio of calcium ions to carboxyl groups in sodium alginate is (0.8-1.2):1.

[0031] After initially solving the problem of microbial survival, another obstacle that becomes prominent when moving from the laboratory to the field, especially when integrating with modern agricultural fertigation models, is the physical compatibility of the formulation. Drip irrigation systems are widely used in cotton-growing areas of saline-alkali soil to save water and fertilizer, which requires the input fertilizer products to maintain a certain level of physical stability in the irrigation water. Existing microbial fertilizer formulations often face the challenge of rapid disintegration and dispersion when in contact with high-ionic-strength fertilizer solutions or irrigation water. The dissolution of binders and the pulverization of carriers produce a large number of fine particles. These particles and the released microorganisms are highly susceptible to deposition and flocculation in delivery pipes, filter screens, and dripper channels, forming sludge-like blockages that hinder the practical application of many theoretically effective microbial products.

[0032] To address this, this application incorporates a sustained-release coating layer outside the core particles. The coating layer is a composite of sodium lignosulfonate and calcium alginate, formed through an ionic cross-linking reaction between the carboxyl groups in sodium alginate and calcium ions, resulting in a water-insoluble calcium alginate gel network. The addition of sodium lignosulfonate, acting as a natural polymeric dispersant and modifier, allows it to permeate the gel network, adjusting its structural density and water molecule permeation rate.

[0033] In the preparation process, the coating material is formulated into a suspension and then coated onto the inner layer particles in a fluidized bed to form a uniform coating film. The mechanism of this coating film mainly lies in its regulation of water response behavior. When the coated particles are transported with the water flow in the drip irrigation pipeline, the short-term water contact causes the surface of the coating film to hydrate, forming a lubricating interface. However, the slow-dissolving properties of sodium lignosulfonate and the toughness of the cross-linked gel network ensure that the film itself remains intact under fluid shear force, thereby preventing premature disintegration and pulverization of the inner layer particles.

[0034] This allows the granules to pass through the filtration system and drippers in their intact physical form, significantly reducing the risk of clogging caused by the release of fine particles. Once the coated granules successfully reach the moist soil environment, the situation changes. Soil water infiltration is a relatively slow and continuous process, and root exudates or soil microbial activity may produce substances such as organic acids. Under these conditions, the coating layer begins to gradually dissolve and biodegrade from the surface inwards. At this point, its designed function shifts from "protective delivery" to "controlled release," and the internally loaded functional microbial agents are gently released into the rhizosphere soil as the coating layer degrades. This release mode avoids the loss of active ingredients during transport and may allow its release profile to better match the needs of the crop.

[0035] The coprecipitated complex was prepared by the following method:

[0036] (I). Dissolution: Dissolve salicylic acid and γ-aminobutyric acid together in ethanol, and stir in a water bath at 65-75℃ until completely dissolved to obtain a clear solution;

[0037] (II). Coprecipitation: The clear solution obtained in step (I) is cooled to 0-4°C at a rate of 0.5-1.5°C per minute and kept at this temperature for 1.5-2.5 hours to allow the coprecipitated complex to be fully precipitated.

[0038] (III). Separation and drying: Filter the system obtained in step (II), wash the obtained solid with pre-cooled anhydrous ethanol 2-3 times, and then dry it in a vacuum drying oven at 40-50℃ for 4-6 hours to obtain a powdered coprecipitated complex.

[0039] The molar ratio of salicylic acid to γ-aminobutyric acid is 1:(0.9-1.1), and the concentration of salicylic acid in ethanol is 0.08-0.12 g / mL.

[0040] After improving the environmental adaptability of microorganisms and the practicality of formulations through carrier modification and coating design, we further considered how to enhance the crop's resistance to saline-alkali stress from the perspective of the crop itself. The damage of saline-alkali stress to crops is systemic. Traditional growth-promoting microbial fertilizers mainly provide nutrients or stimulate growth through microbial activity. However, for plants already under stress, if their internal physiological disorders are not alleviated, the external growth-promoting effect may be greatly reduced.

[0041] Therefore, this application introduces a coprecipitation complex as a physiological regulatory component, prepared from salicylic acid and γ-aminobutyric acid (GABA) via a coprecipitation process. Salicylic acid is a known endogenous substance in plants associated with disease resistance and stress signal transduction, while GABA is a metabolite that accumulates rapidly under stress conditions, participating in nitrogen metabolism, carbon balance, and maintaining cell osmotic pressure. Applying these two components as a coprecipitation complex leverages intermolecular interactions to enhance the stability of the complex and produce a synergistic effect.

[0042] This coprecipitation complex is designed to attach to the outermost layer of the coated particles, contacting the roots or entering the rhizosphere as the coating degrades in the soil. Salicylic acid mimics and enhances systemic acquired resistance signals within the plant, regulating the expression of a series of stress-related genes. Gamma-aminobutyric acid (GABA), as a compatible solute precursor or direct signaling molecule, helps regulate cellular osmotic balance and redox state. When cotton roots sense these signaling substances, they can trigger their intrinsic defense and adaptation programs, promoting the activity of antioxidant enzyme systems to scavenge excess reactive oxygen species, regulating stomatal opening and closing to reduce water loss, or adjusting the distribution of photosynthetic products to maintain a balance between growth and stress resistance. This regulation, starting from the plant's internal physiological state, forms a synergistic effect with the growth-promoting, phosphorus-solubilizing, and nitrogen-fixing functions of external microorganisms. Microbial activity improves rhizosphere nutrition and microenvironment for plants, while the co-precipitation complex enhances the overall physiological state and stress tolerance of plants, and provides healthier microecological sites and root exudates for rhizosphere microorganisms, thus forming a more positive and stable interactive cycle, which together improves the growth performance and yield potential of cotton in saline-alkali land.

[0043] A method for preparing a compound microbial fertilizer suitable for cotton in saline-alkali soil, the method comprising the following steps:

[0044] Step 1, carrier premixing: Place the modified load carrier in a high-speed mixer, spray in the core bacterial agent while stirring, mix for 15-25 minutes to obtain a uniformly loaded premix.

[0045] Step 2, Granulation and molding: Atomized polyvinyl alcohol adhesive solution is sprayed into the premix obtained in Step 1, and then the resulting wet material is fed into an extrusion granulator to prepare wet granule preforms under a molding pressure of 0.8-1.2 MPa.

[0046] Step 3, Coating: The wet granule blank obtained in Step 2 is transferred to a fluidized bed. The powder raw material for the slow-release coating layer is prepared into an aqueous suspension with a mass fraction of 6%-10% as a coating agent. The particles are coated by bottom spraying process to obtain coated particles.

[0047] Step 4, post-processing: The coated granules obtained in Step 3 and the co-precipitation complex are put into a three-dimensional motion mixer and mixed for 20-40 minutes to allow the co-precipitation complex powder to adhere to the surface of the coated granules. Finally, the granules are treated in a ventilated drying equipment at 35-40℃ for 2-4 hours to reduce the final moisture content to less than 10%, thus obtaining the compound microbial fertilizer product.

[0048] In step two, the mass percentage concentration of the polyvinyl alcohol adhesive solution is 1%-3%, and after the atomized polyvinyl alcohol adhesive solution is sprayed in, the total water content of the material reaches 18%-22%.

[0049] In step three, the amount of coating agent used is such that the dry weight of the slow-release coating layer accounts for 10%-20% of the dry weight of the particle preform. During the coating process, the inlet air temperature of the fluidized bed is maintained at 40-45℃, and the material bed temperature is maintained at 32-38℃.

[0050] Compared with the prior art, the advantages and beneficial effects of the present invention are as follows:

[0051] 1. The core microbial agent of this compound microbial fertilizer consists of Bacillus subtilis, Bacillus mucilaginosus, and Bacillus licheniformis. These microorganisms are common commercially available strains with cost advantages. By combining them with a modified loading carrier and a slow-release coating layer, their application effect is specifically enhanced. The core microbial agent is loaded onto attapulgite clay that has been activated with citric acid and treated with iron loading. The modification process of the modified loading carrier not only removes impurities and increases the specific surface area, but also introduces iron ions into the carrier surface and pores, providing more attachment sites for microorganisms. The presence of iron ions also creates a relatively stable microenvironment. When the microbial fertilizer is applied to saline-alkali soil, the carrier can buffer the impact of high salinity and alkalinity to a certain extent, reduce the direct damage of harmful ions to microbial cells, and thus help prolong the survival time of functional microorganisms in the rhizosphere, providing a window of opportunity for the microorganisms to colonize and exert their effects.

[0052] 2. The slow-release coating layer of this invention is composed of a gel material made of sodium lignosulfonate and calcium alginate, which solves the compatibility problem between microbial fertilizer and drip irrigation systems. This coating layer is formed by encapsulating an aqueous suspension on the particle surface in a fluidized bed. The calcium alginate in the coating material forms a gel upon contact with water, but the introduction of sodium lignosulfonate regulates its hydration and disintegration rate. When the microbial fertilizer particles pass through the drip irrigation system, the slow-release coating layer maintains the physical integrity of the particles during delivery, transporting them as complete, smooth, and non-fragmented units. This prevents premature dispersion of particles within the pipeline, forming easily clogging fine particles or sticky substances, thus reducing the risk of drip irrigation system blockage. Simultaneously, it ensures that the functional components are effectively delivered to the rhizosphere soil before release. When the coated particles reach the soil with water, the coating layer gradually and controllably dissolves and degrades under the action of soil capillary water and root exudates, thereby releasing the core microbial agent loaded inside. This design not only meets the physical requirements of drip irrigation delivery, but also enables the slow release of the microbial agent at the target location.

[0053] 3. The coprecipitation complex introduced in this invention, namely the coprecipitation complex formed by the reaction of salicylic acid and γ-aminobutyric acid (GABA), does not directly provide nutrients, but rather acts as a signaling substance to regulate the physiological metabolism of cotton. The form of the coprecipitation complex improves the stability and synergy of the two active ingredients. Under saline-alkali stress, cotton plants undergo a series of physiological reactions such as osmotic imbalance and oxidative stress. This coprecipitation complex is designed to be on the outer layer of the microbial fertilizer granules, allowing it to contact the roots or enter the rhizosphere as the coating layer dissolves. After being absorbed by the plant, salicylic acid and GABA participate in activating stress-related metabolic pathways within the plant, helping to regulate stomatal behavior to reduce water loss and promoting the synthesis of antioxidants to alleviate oxidative damage. This enhances the cotton's own tolerance at a physiological level, forming a functional complement with the growth-promoting effect of microorganisms, helping cotton cope with saline-alkali environments from different perspectives. Detailed Implementation

[0054] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0055] The technical solution of this application is as follows:

[0056] A compound microbial fertilizer suitable for cotton in saline-alkali soil is made from the following raw materials in parts by weight:

[0057] Core microbial agent: 1-3 parts;

[0058] Modified load carrier: 70-85 parts;

[0059] Sustained-release coating layer: 10-20 parts;

[0060] Coprecipitated complex: 0.5-1.5 parts;

[0061] The core bacterial agent is composed of microbial preparations of Bacillus subtilis, Bacillus colloidis, and Bacillus licheniformis; the modified loading carrier is attapulgite clay activated with citric acid and treated with iron loading; the slow-release coating layer is composed of a gel material composed of sodium lignosulfonate and calcium alginate; and the coprecipitation complex is a coprecipitation complex generated by the reaction of salicylic acid and γ-aminobutyric acid.

[0062] In the core microbial agent, the effective viable count ratio of Bacillus subtilis, Bacillus mucilaginosa, and Bacillus licheniformis is (5.0-7.0):(3.0-4.5):(2.0-3.0).

[0063] The modified load carrier is prepared by the following method:

[0064] a. Acid activation treatment: Attapulgite clay powder and citric acid solution are stirred and reacted at 75-85℃ for 3-5 hours;

[0065] b. Iron-loaded aging: Cool the slurry obtained in step a to room temperature, adjust the pH value to 4.5-5.5 with alkali solution, add ferrous sulfate solution, and age at 45-55℃ for 10-14 hours;

[0066] c. Washing and drying: After aging in step b, filter the material and wash it with water until no white precipitate is produced when the filtrate is tested with barium chloride solution. Then dry it at 100-110℃ to constant weight and pulverize it to pass through a 300-mesh sieve to obtain the modified support carrier.

[0067] In step a, the citric acid solution has a mass percentage concentration of 6%-10%, and the attapulgite clay powder is mixed with the citric acid solution at a solid-liquid mass ratio of 1:(8-12).

[0068] In step b, a ferrous sulfate solution with a concentration of 0.4-0.6 mol / L is added, so that the mass ratio of the added iron element to the dry basis of attapulgite clay is (2-4):100.

[0069] The powder raw material for the sustained-release coating layer is prepared by the following method:

[0070] <1> Gel synthesis: Sodium lignosulfonate was dissolved in hot water at 60-70℃ to prepare solution A; sodium alginate was dissolved in deionized water at room temperature to prepare solution B; under stirring conditions, solution A and solution B were mixed at a volume ratio of 1:1 to obtain mixture C.

[0071] <2> Cross-linking and curing: While stirring continuously, add calcium chloride solution dropwise to mixture C. After the addition is complete, continue stirring for 30-60 minutes to form a uniform viscous gel.

[0072] <3> Dehydration and pulverization: [The process involves...] <2> The resulting gel is dried in a vacuum drying oven at 60-70°C until the water content is less than 5%, and then mechanically pulverized and passed through a 200-mesh sieve to obtain the powder raw material of the sustained-release coating layer.

[0073] In the steps <1> In this process, the mass percentage concentration of solution A is 12%-18%, and the mass percentage concentration of solution B is 3%-5%.

[0074] In the steps <2> In this process, the mass percentage concentration of the calcium chloride solution is 8%-12%, and the amount of calcium chloride solution added is such that the molar ratio of calcium ions to carboxyl groups in sodium alginate is (0.8-1.2):1.

[0075] The coprecipitated complex was prepared by the following method:

[0076] (I). Dissolution: Dissolve salicylic acid and γ-aminobutyric acid together in ethanol, and stir in a water bath at 65-75℃ until completely dissolved to obtain a clear solution;

[0077] (II). Coprecipitation: The clear solution obtained in step (I) is cooled to 0-4°C at a rate of 0.5-1.5°C per minute and kept at this temperature for 1.5-2.5 hours to allow the coprecipitated complex to be fully precipitated.

[0078] (III). Separation and drying: Filter the system obtained in step (II), wash the obtained solid with pre-cooled anhydrous ethanol 2-3 times, and then dry it in a vacuum drying oven at 40-50℃ for 4-6 hours to obtain a powdered coprecipitated complex.

[0079] The molar ratio of salicylic acid to γ-aminobutyric acid is 1:(0.9-1.1), and the concentration of salicylic acid in ethanol is 0.08-0.12 g / mL.

[0080] A method for preparing a compound microbial fertilizer suitable for cotton in saline-alkali soil, the method comprising the following steps:

[0081] Step 1, carrier premixing: Place the modified load carrier in a high-speed mixer, spray in the core bacterial agent while stirring, mix for 15-25 minutes to obtain a uniformly loaded premix.

[0082] Step 2, Granulation and molding: Atomized polyvinyl alcohol adhesive solution is sprayed into the premix obtained in Step 1, and then the resulting wet material is fed into an extrusion granulator to prepare wet granule preforms under a molding pressure of 0.8-1.2 MPa.

[0083] Step 3, Coating: The wet granule blank obtained in Step 2 is transferred to a fluidized bed. The powder raw material for the slow-release coating layer is prepared into an aqueous suspension with a mass fraction of 6%-10% as a coating agent. The particles are coated by bottom spraying process to obtain coated particles.

[0084] Step 4, post-processing: The coated granules obtained in Step 3 and the co-precipitation complex are put into a three-dimensional motion mixer and mixed for 20-40 minutes to allow the co-precipitation complex powder to adhere to the surface of the coated granules. Finally, the granules are treated in a ventilated drying equipment at 35-40℃ for 2-4 hours to reduce the final moisture content to less than 10%, thus obtaining the compound microbial fertilizer product.

[0085] In step two, the mass percentage concentration of the polyvinyl alcohol adhesive solution is 1%-3%, and after the atomized polyvinyl alcohol adhesive solution is sprayed in, the total water content of the material reaches 18%-22%.

[0086] In step three, the amount of coating agent used is such that the dry weight of the slow-release coating layer accounts for 10%-20% of the dry weight of the particle preform. During the coating process, the inlet air temperature of the fluidized bed is maintained at 40-45℃, and the material bed temperature is maintained at 32-38℃.

[0087] The present invention will be described in detail below through examples and comparative examples, but the scope of protection of the present invention is not limited to these examples. Unless otherwise specified, the chemical reagents and raw materials used in the following examples and comparative examples are all conventional commercially available products.

[0088] Example 1

[0089] The raw materials were prepared according to the following proportions by weight: 3 parts core bacterial agent, 70 parts modified support carrier, 20 parts slow-release coating layer, and 0.5 parts co-precipitated complex. The core bacterial agent consisted of commercially available Bacillus subtilis, Bacillus licheniformis, and Bacillus licheniformis microbial preparations, physically mixed at an effective viable count ratio of 7.0:3.0:2.0.

[0090] Preparation of modified support: Attapulgite clay powder was mixed with 10% citric acid solution at a solid-liquid mass ratio of 1:8 and stirred at 85℃ for 3 hours. After the reaction, the slurry was cooled to room temperature, and the pH was adjusted to 4.5 with sodium hydroxide solution. Then, 0.4 mol / L ferrous sulfate solution was added, controlling the mass ratio of iron to dry clay at 2:100. The mixture was aged at 55℃ for 10 hours. After aging, the material was filtered, washed with deionized water until no precipitate was found in the filtrate when tested with barium chloride solution, dried at 110℃ to constant weight, and pulverized through a 300-mesh sieve to obtain the modified support.

[0091] Preparation of the sustained-release coating powder raw material: Sodium lignosulfonate was dissolved in hot water at 70℃ to prepare a 12% (w / w) solution A. Sodium alginate was dissolved in deionized water at room temperature to prepare a 5% (w / w) solution B. Solutions A and B were mixed at a volume ratio of 1:1 to obtain a mixture C. An 8% (w / w) calcium chloride solution was added dropwise to mixture C while stirring, controlling the molar ratio of calcium ions to sodium alginate carboxyl groups to be 1.2:1. After the addition was complete, stirring was continued for 30 minutes to form a gel. This gel was vacuum dried at 70℃ until the moisture content was below 5%, then pulverized through a 200-mesh sieve to obtain the coating powder.

[0092] Preparation of the coprecipitated complex: Salicylic acid and γ-aminobutyric acid were dissolved in anhydrous ethanol at a molar ratio of 1:0.9, with the salicylic acid concentration controlled at 0.08 g / mL. The solution was stirred and dissolved in a water bath at 75°C. The resulting clear solution was cooled to 4°C at a rate of 0.5°C per minute and held at this temperature for 1.5 hours. The precipitate was collected by filtration, washed twice with pre-cooled anhydrous ethanol, and dried under vacuum at 50°C for 4 hours to obtain a white powder.

[0093] Preparation of compound microbial fertilizer: 70 parts of the above modified loading carrier were placed in a high-speed mixer, and 3 parts of core microbial agent were sprayed in under stirring. The mixture was mixed for 25 minutes to obtain a premix. Atomized polyvinyl alcohol solution with a mass percentage concentration of 1% was sprayed into the premix to control the total moisture content of the material to 22%. The wet material was fed into an extrusion granulator to produce wet granule green bodies with a diameter of 1.0 mm under a pressure of 1.2 MPa. The green bodies were transferred to a fluidized bed and coated with a 6% mass fraction aqueous suspension of the above coating powder. The dry weight of the coating layer was controlled to account for 20% of the dry weight of the green body. The inlet air temperature during the coating process was 45℃, and the bed temperature was 32℃. The coated granules were mixed with 0.5 parts of coprecipitated compound powder in a three-dimensional motion mixer for 40 minutes, and then dried at 40℃ for 2 hours until the moisture content was less than 10% to obtain the final product.

[0094] Example 2

[0095] In this embodiment, the similarities to those in Embodiment 1 will not be repeated, and the differences are as follows:

[0096] Prepare the raw materials according to the following proportions by weight: 1 part core bacterial agent, 85 parts modified support carrier, 10 parts sustained-release coating layer, and 1.5 parts co-precipitation complex. The effective viable count ratio of the three bacteria in the core bacterial agent is 5.0: 4.5: 3.0.

[0097] Preparation of modified support: Clay powder and 6% citric acid solution were mixed at a solid-liquid mass ratio of 1:12 and reacted at 75℃ for 5 hours. The pH of the slurry was adjusted to 5.5, and 0.6 mol / L ferrous sulfate solution was added, with an iron to clay dry basis mass ratio of 4:100. The mixture was aged at 45℃ for 14 hours. After washing, it was dried at 100℃, pulverized, and sieved.

[0098] Preparation of sustained-release coating powder raw material: Prepare a 18% (w / w) sodium lignosulfonate solution A and a 3% (w / w) sodium alginate solution B. After mixing, add a 12% (w / w) calcium chloride solution dropwise, with a calcium ion to carboxyl group molar ratio of 0.8:1, and stir for 60 minutes to form a gel. Then, vacuum dry at 60℃ and pulverize.

[0099] Preparation of the coprecipitated complex: Salicylic acid and γ-aminobutyric acid were dissolved in anhydrous ethanol at a molar ratio of 1:1.1 to achieve a salicylic acid concentration of 0.12 g / mL, and the solution was dissolved at 65 °C. The solution was then cooled to 0 °C at a rate of 1.5 °C per minute and maintained at this temperature for 2.5 hours to precipitate. After filtration and washing, the precipitate was dried at 40 °C for 6 hours.

[0100] Preparation of compound microbial fertilizer: Mix 85 parts of carrier with 1 part of core microbial agent for 15 minutes. Spray in a 3% (w / w) polyvinyl alcohol solution to achieve a moisture content of 18%. Granulate at 0.8 MPa to obtain a 1.2 mm diameter green body. Coat with a 10% (w / w) coating agent suspension, with the coating layer dry weight accounting for 10%, at an inlet air temperature of 40℃ and a bed temperature of 38℃. Mix the coated granules with 1.5 parts of co-precipitated compound powder for 20 minutes and dry at 35℃ for 4 hours to the required moisture content.

[0101] Example 3

[0102] In this embodiment, the similarities to those in Embodiment 1 will not be repeated, and the differences are as follows:

[0103] The raw materials were prepared according to the following proportions by weight: 2 parts core bacterial agent, 77.5 parts modified support carrier, 15 parts sustained-release coating layer, and 1.0 part co-precipitation complex. The effective viable count ratio of the three bacteria in the core bacterial agent was 6.0: 3.75: 2.5.

[0104] Preparation of modified support: Clay powder and 8% citric acid solution were mixed at a solid-liquid mass ratio of 1:10 and reacted at 80℃ for 4 hours. The pH of the slurry was adjusted to 5.0, and 0.5 mol / L ferrous sulfate solution was added, with an iron to clay dry basis mass ratio of 3:100. The mixture was aged at 50℃ for 12 hours. After washing, it was dried at 105℃, pulverized, and sieved.

[0105] Preparation of sustained-release coating powder raw material: Prepare a 15% (w / w) sodium lignosulfonate solution A and a 4% (w / w) sodium alginate solution B. After mixing, add a 10% (w / w) calcium chloride solution dropwise, with a calcium ion to carboxyl group molar ratio of 1:1, and stir for 45 minutes to form a gel. Dry under vacuum at 65℃ and then pulverize.

[0106] Preparation of the coprecipitated complex: Salicylic acid and γ-aminobutyric acid (GABA) were dissolved in anhydrous ethanol at a molar ratio of 1:1 to achieve a salicylic acid concentration of 0.10 g / mL, and the solution was dissolved at 70 °C. The solution was then cooled to 2 °C at a rate of 1.0 °C per minute and maintained at this temperature for 2.0 h to precipitate. After filtration and washing, the precipitate was dried at 45 °C for 5 h.

[0107] Preparation of compound microbial fertilizer: Mix 77.5 parts of carrier with 2 parts of core microbial agent for 20 minutes. Spray in a 2% (w / w) polyvinyl alcohol solution to achieve a moisture content of 20%. Granulate under 1.0 MPa pressure to obtain a 1.1 mm diameter green body. Coat with an 8% (w / w) coating agent suspension, with the coating layer dry weight accounting for 15%, at an inlet air temperature of 42℃ and a bed temperature of 35℃. Mix the coated granules with 1.0 part of co-precipitated composite powder for 30 minutes and dry at 38℃ for 3 hours to the required moisture content.

[0108] Example 4

[0109] In this embodiment, the similarities to those in Embodiment 1 will not be repeated, and the differences are as follows:

[0110] This embodiment aims to demonstrate an implementation scheme with a set of preferred parameters. The raw material mass parts are: 2 parts core bacterial agent, 75 parts modified support carrier, 15 parts sustained-release coating layer, and 1.0 part co-precipitated complex. The effective viable count ratio of the three bacteria in the core bacterial agent is 6.0: 4.0: 2.5.

[0111] Preparation of modified support: An 8% (w / w) citric acid solution was used at a solid-liquid ratio of 1:10. The reaction temperature was 80℃ for 4 hours. After adjusting the pH to 5.0, a 0.5 mol / L ferrous sulfate solution was added at an iron-to-clay ratio of 3:100. The mixture was then aged at 50℃ for 12 hours. After drying at 105℃, the material was pulverized and passed through a 300-mesh sieve.

[0112] Preparation of sustained-release coating powder raw materials: Equal volumes of sodium lignosulfonate solution (15%) and sodium alginate solution (4%) were mixed. Crosslinking was performed using a 10% calcium chloride solution, with a calcium ion to carboxyl group molar ratio of 1:1, and stirring for 45 minutes. After vacuum drying at 65℃, the powder was pulverized and passed through a 200-mesh sieve.

[0113] Preparation of the coprecipitated complex: Salicylic acid and γ-aminobutyric acid (GABA) were dissolved in anhydrous ethanol at a molar ratio of 1:1 to achieve a salicylic acid concentration of 0.10 g / mL, and dissolved at 70 °C. The solution was cooled to 0 °C at a rate of 1.0 °C per minute and maintained at this temperature for 2.0 h to precipitate. The precipitate was filtered, washed with cold ethanol, and dried under vacuum at 45 °C for 5 h.

[0114] Preparation of compound microbial fertilizer: 75 parts carrier and 2 parts core microbial agent were mixed for 20 minutes. A 2% polyvinyl alcohol solution was sprayed in to achieve a moisture content of 20%. Granulation was carried out at 1.0 MPa to obtain particles with a diameter of 1.1 mm. The particles were coated with an 8% coating agent suspension, with the coating layer dry weight accounting for 15%. The fluidized bed air inlet temperature was 42℃, and the bed temperature was 35℃. The coated particles were mixed with 1.0 part co-precipitated complex powder for 30 minutes and dried at 38℃ for 3 hours.

[0115] To verify the necessity and synergistic effect of the various technical features of this invention, the following comparative examples were set up for comparison. Comparative Examples 1 to 3 simulate common forms of microbial fertilizers in the prior art. Comparative Examples 4 to 7, based on Example 4 of this invention, sequentially omitted or replaced a key component to examine the specific contribution of that component. Comparative Example 8 examines situations where the component proportion exceeds the scope of this invention.

[0116] Comparative Example 1

[0117] Ordinary compound microbial agent. It contains only a mixture of Bacillus subtilis, Bacillus licheniformis, and Bacillus spore powders in the same proportions and viable counts as in Example 4, but does not contain the modified support carrier, sustained-release coating layer, or co-precipitation complex.

[0118] Comparative Example 2

[0119] A mixture of microbial agent and common carrier. It contains the same core microbial agent in the same proportions as in Example 4, and an equal mass of unmodified raw attapulgite clay powder (passed through a 300-mesh sieve). The two are simply physically mixed without granulation, coating, or the addition of co-precipitation complexes.

[0120] Comparative Example 3

[0121] Ordinary granular fertilizer containing bacteria. It contains the same core bacterial agent and raw attapulgite clay in the same proportions as in Example 4, and is granulated by spraying with a 2% polyvinyl alcohol solution (process as in Example 4), but the resulting granules are not coated and no co-precipitation complex is added.

[0122] Comparative Example 4

[0123] Based on Example 4, but replacing the modified load carrier with an equal mass of unmodified raw attapulgite clay powder, the acid activation and iron loading steps are omitted in the preparation process, and the remaining raw materials and steps are exactly the same as in Example 4.

[0124] Comparative Example 5

[0125] Based on Example 4, but omitting the sustained-release coating layer. That is, in the preparation process, the wet granule preform obtained by granulation does not undergo the fluidized bed coating step, but is directly mixed with the coprecipitated complex powder and then dried. The remaining raw materials and steps are exactly the same as in Example 4.

[0126] Comparative Example 6

[0127] Based on Example 4, but omitting the coprecipitation complex. That is, the salicylic acid and γ-aminobutyric acid coprecipitation complex powder is not added in the final compounding step, and the remaining raw materials and steps are exactly the same as in Example 4.

[0128] Comparative Example 7

[0129] Based on Example 4, but only Bacillus subtilis is retained in the core bacterial agent, and its total number of effective viable bacteria is the same as the sum of the three bacteria in Example 4. It is missing Bacillus licheniformis and Bacillus licheniformis. The other raw materials and steps are exactly the same as in Example 4.

[0130] Comparative Example 8

[0131] Based on Example 4, but with adjustments to the key proportions, the raw material mass parts were changed to: 5 parts core bacterial agent, 60 parts modified support carrier, 5 parts sustained-release coating layer, and 0.2 parts co-precipitated complex. The preparation process parameters were the same as in Example 4.

[0132] Performance Test Results and Analysis

[0133] To comprehensively evaluate the performance of the compound microbial fertilizer of this invention, the following three sets of tests were designed to test the products of the examples and comparative examples respectively.

[0134] Test 1: Survival and Colonization Capacity of Bacterial Agents under Salt-Alkali Tolerance: 10.0 g of samples from each example and comparative example were weighed and uniformly mixed into 1.0 kg of sterilized simulated saline-alkali soil (soil conductivity 4.5 dS / m, pH 8.5). The soil was placed in a 25℃ constant temperature incubator to maintain a soil moisture content of 60% of field capacity. Samples were taken on days 1, 7, and 30 after mixing. The total viable count of Bacillus subtilis, Bacillus mucilaginosa, and Bacillus licheniformis in the soil was determined using the dilution plating method, and their survival rate relative to the initial addition amount was calculated.

[0135] Test 2: Drip Irrigation System Compatibility Test: Referring to common operating conditions in agricultural drip irrigation fertilization, a stock solution containing macro-elements (nitrogen, phosphorus, and potassium) was prepared. 10.0 g of each example and comparative sample was weighed and added to 1.0 L of the above stock solution. The solution was stirred at 150 rpm for 10 minutes to simulate the dissolution process. Subsequently, the suspension was allowed to stand for 30 minutes, and the sedimentation and flocculation were observed and recorded. Afterward, the suspension was passed through a standard 200-mesh filter (simulating a drip irrigation system filter), the filtration time was recorded, and the residue on the filter screen was checked. Finally, the filtrate was collected and passed through a new dripper at a constant flow rate (2 L / h) for 2 hours. After the test, the dripper was disassembled, its internal blockage was checked, and it was rated.

[0136] Test 3: Effect on Promoting Cotton Growth in Saline-Alkali Soil: A pot experiment was conducted. Each pot was filled with 1.5 kg of the simulated saline-alkali soil described above. The cotton variety used was a local conventional medium-sized cotton variety. Five seeds were sown per pot, and seedlings were thinned to two plants per pot after emergence. A blank control group was set up without any microbial fertilizer. At sowing, the experimental groups received a base fertilizer of 2.5 kg per mu (approximately 0.067 hectares) mixed with the soil from each example and comparative sample. Uniform management was implemented during the growth period. Plant height, stem diameter, and above-ground dry weight were measured at the seedling stage (30 days after sowing). The number of bolls per plant and the weight of each boll were measured at harvest, and the seed cotton yield was calculated.

[0137] The results of Test 1 are shown in Table 1, which demonstrates the survival dynamics of the microbial agent in saline-alkali soil.

[0138] As shown in Table 1, the survival rate of the microbial agents in all four examples remained at a high level within 30 days. This contrasts sharply with Comparative Example 1 (pure microbial agent), where the bacterial population declined significantly by day seven, and the survival rate was less than 10% by day 30, demonstrating that microorganisms without protection struggle to survive in saline-alkali soils. While the survival rates of Comparative Example 2 (simple mixture of microbial agent and original carrier) and Comparative Example 3 (ordinary granules containing bacteria) were higher than those of Comparative Example 1, they were still significantly lower than those of the examples, indicating that the protection provided by the original carrier and ordinary granules was limited.

[0139] Comparative Example 4, using the unmodified carrier, showed a significantly weaker protective effect than the examples using the modified carrier, verifying the positive effects of citric acid activation and iron loading treatment on enhancing the carrier's bacterial retention and buffering capacity. Comparative Example 5 (without coating) had a similar survival rate to the examples in the early stages (days 1 and 7), but showed a significant decrease on day 30, indicating that the coating layer plays a crucial role in the long-term slow release and protection of the bacterial agent in the soil.

[0140] The survival rate of Comparative Example 6 (without coprecipitation complex) was close to that of Example 4, indicating that the coprecipitation complex did not have a significant direct impact on the survival rate of soil microorganisms. The survival rate of Comparative Example 7 (single species) was lower than that of the multi-species combination examples, suggesting that a reasonable combination of species may enhance community stability through micro-ecological interactions. The protective effect of Comparative Example 8 (imbalanced ratio) was also poor, indicating that the mass ratio of each component needs to be controlled within a reasonable range.

[0141] Table 1. Survival rate (%) of microbial agents in simulated saline-alkali soil

[0142] Group Day 1 Day 7 Day 30 Example 1 95.2 82.1 65.3 Example 2 93.8 80.5 63.8 Example 3 96.5 84.7 68.9 Example 4 97.1 86.3 70.5 Comparative Example 1 85.4 45.2 8.7 Comparative Example 2 90.1 60.3 20.5 Comparative Example 3 92.5 70.8 35.4 Comparative Example 4 91.8 68.4 32.1 Comparative Example 5 93.0 78.5 52.7 Comparative Example 6 92.8 79.1 60.0 Comparative Example 7 92.3 76.2 48.9 Comparative Example 8 88.9 58.6 25.3

[0143] The results of Test 2 are shown in Table 2, which comprehensively evaluates the physical compatibility of the samples. Table 2 shows that all examples exhibited good dispersion stability in the fertilizer solution, with minimal precipitation, smooth filtration, and low risk of dripper clogging. Examples 3 and 4, in particular, showed the best results. This contrasts sharply with Comparative Example 1 (pure bacterial powder), which rapidly flocculated in the fertilizer solution and clogged the filter and drippers, making it completely unusable through the drip irrigation system. Comparative Example 3 (uncoated ordinary granules) and Comparative Example 5 (uncoated variant of Example 4) showed significantly more severe clogging than the examples, directly demonstrating the irreplaceable role of the slow-release coating layer in maintaining the integrity of the granules during liquid transport and preventing premature disintegration and blockage. Comparative Examples 2 and 4 (using the original carrier or unmodified carrier) also produced significant precipitation, indicating that the modified carrier itself may have better water dispersibility. Comparative Examples 6 (without coprecipitation complex) and 7 (single bacterial species) showed little difference from the examples in the compatibility test, indicating that these two primarily affected biological functions rather than physical properties. Comparative Example 8, however, suffered from decreased compatibility due to improper formulation.

[0144] Table 2. Compatibility Test Results of Drip Irrigation System

[0145] Group Sedimentation / flocculation after standing 200-mesh filtration time (s) Drip head clogging level rating* (1-5 levels) Example 1 Slight precipitation, no flocculation 58 Level 2 (Slight Adhesion) Example 2 Slight precipitation, no flocculation 62 Level 2 Example 3 Very slight precipitation 52 Level 1 (Basic Cleaning) Example 4 Very slight precipitation 50 Level 1 Comparative Example 1 Severe flocculation 180 (not fully filtered) Level 5 (Severe Congestion) Comparative Example 2 Severe precipitation 150 Level 4 Comparative Example 3 Obvious sedimentation, partial flocculation 95 Level 3 (Moderate congestion) Comparative Example 4 Obvious sedimentation 88 Level 3 Comparative Example 5 Obvious sedimentation, partial flocculation 92 Level 3 Comparative Example 6 Very slight precipitation 63 Level 2 Comparative Example 7 Slight precipitation, no flocculation 60 Level 2 Comparative Example 8 Obvious sedimentation 105 Level 3

[0146] *Drip head clogging level rating: Level 1 indicates virtually no visible blockage, while Level 5 indicates complete blockage of the flow channel.

[0147] The results of Test 3 are shown in Table 3, demonstrating the actual promoting effect of microbial fertilizer on cotton growth. Table 3 shows that all four examples significantly outperformed the control group in promoting cotton growth and increasing yield, with Example 4 showing the best effect. Comparative Example 1 (pure microbial agent) showed a weak effect, indicating that unprotected microbial agents are difficult to function effectively in saline-alkali soil. Comparative Examples 2, 3, and 4 were all better than Comparative Example 1, but not as good as any example, indicating that modified carrier, granulation, and coating are crucial for improving the final effect, and their combined action ensures the effective delivery and survival of functional microorganisms. Comparative Example 5 (uncoated) showed similar growth indicators to the examples during the seedling stage, but a difference in final yield, possibly related to the fact that the slow-release mode of the microbial agent controlled by the coating layer affected the fertilizer efficiency in the mid-to-late stages. The yield of Comparative Example 6 (without coprecipitation complex) was also slightly lower than that of the corresponding Example 4, indicating that salicylic acid and γ-aminobutyric acid, as a coprecipitation complex, make a positive contribution to the reproductive growth and yield increase of cotton under saline-alkali stress. The decreased effect of Comparative Example 7 (single strain) indicates that the combination of Bacillus subtilis, Bacillus mucilaginosa, and Bacillus licheniformis has a synergistic growth-promoting effect. The poor effect of Comparative Example 8 further emphasizes the importance of the specified formulation range in this invention.

[0148] Table 3. Growth and yield indicators of potted cotton in saline-alkali land

[0149] Group Seedling height (cm) Aboveground dry weight of seedlings (g / plant) Number of bolls per plant Seed cotton yield (g / pot) Increase in production (%) compared to the control group Blank group* 15.2 1.05 6.8 32.1 - Example 1 18.8 1.58 9.2 45.7 42.4 Example 2 18.5 1.52 9.0 44.9 39.9 Example 3 19.5 1.65 9.7 48.3 50.5 Example 4 19.8 1.68 9.8 49.0 52.6 Comparative Example 1 16.5 1.18 7.5 35.2 9.7 Comparative Example 2 17.2 1.32 8.1 38.4 19.6 Comparative Example 3 18.0 1.45 8.6 41.0 27.7 Comparative Example 4 17.8 1.42 8.5 40.5 26.2 Comparative Example 5 18.3 1.60 9.1 44.0 37.1 Comparative Example 6 18.2 1.55 8.9 43.2 34.6 Comparative Example 7 18.2 1.48 8.4 40.8 27.1 Comparative Example 8 17.0 1.28 7.9 37.1 15.6

[0150] *The blank group is a control group that receives no microbial fertilizer or other exogenous additives and only undergoes the same basic environmental and management conditions.

[0151] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A compound microbial fertilizer suitable for cotton in saline-alkali soil, characterized in that, Made from the following parts by weight of raw materials: Core microbial agent: 1-3 parts; Modified load carrier: 70-85 parts; Sustained-release coating layer: 10-20 parts; Coprecipitated complex: 0.5-1.5 parts; The core bacterial agent is composed of microbial preparations of Bacillus subtilis, Bacillus colloidis, and Bacillus licheniformis; the modified loading carrier is attapulgite clay activated with citric acid and treated with iron loading; the slow-release coating layer is composed of a gel material composed of sodium lignosulfonate and calcium alginate; and the coprecipitation complex is a coprecipitation product generated by the reaction of salicylic acid and γ-aminobutyric acid.

2. The compound microbial fertilizer suitable for cotton in saline-alkali soil according to claim 1, characterized in that, In the core microbial agent, the effective viable count ratio of Bacillus subtilis, Bacillus mucilaginosa, and Bacillus licheniformis is (5.0-7.0):(3.0-4.5):(2.0-3.0).

3. The compound microbial fertilizer suitable for cotton in saline-alkali soil according to claim 1, characterized in that, The modified load carrier is prepared by the following method: a. Acid activation treatment: Attapulgite clay powder and citric acid solution are stirred and reacted at 75-85℃ for 3-5 hours; b. Iron-loaded aging: Cool the slurry obtained in step a to room temperature, adjust the pH value to 4.5-5.5 with alkali solution, add ferrous sulfate solution, and age at 45-55℃ for 10-14 hours; c. Washing and drying: After aging in step b, filter the material and wash it with water until no white precipitate is produced when the filtrate is tested with barium chloride solution. Then dry it at 100-110℃ to constant weight and pulverize it to pass through a 300-mesh sieve to obtain the modified support carrier.

4. The compound microbial fertilizer suitable for cotton in saline-alkali soil according to claim 3, characterized in that, In step a, the citric acid solution has a mass percentage concentration of 6%-10%, and the attapulgite clay powder is mixed with the citric acid solution at a solid-liquid mass ratio of 1:(8-12). In step b, a ferrous sulfate solution with a concentration of 0.4-0.6 mol / L is added, so that the mass ratio of the added iron element to the dry basis of attapulgite clay is (2-4):

100.

5. A compound microbial fertilizer suitable for cotton in saline-alkali soil according to claim 1, characterized in that, The powder raw material for the sustained-release coating layer is prepared by the following method: <1> Gel synthesis: Sodium lignosulfonate was dissolved in hot water at 60-70℃ to prepare solution A; sodium alginate was dissolved in deionized water at room temperature to prepare solution B; under stirring conditions, solution A and solution B were mixed at a volume ratio of 1:1 to obtain mixture C. <2> Cross-linking and curing: While stirring continuously, add calcium chloride solution dropwise to mixture C. After the addition is complete, continue stirring for 30-60 minutes to form a uniform viscous gel. <3> Dehydration and pulverization: [The process involves...] <2> The resulting gel is dried in a vacuum drying oven at 60-70°C until the water content is less than 5%, and then mechanically pulverized and passed through a 200-mesh sieve to obtain the powder raw material of the sustained-release coating layer.

6. A compound microbial fertilizer suitable for cotton in saline-alkali soil according to claim 5, characterized in that, In the steps <1> In this process, the mass percentage concentration of solution A is 12%-18%, and the mass percentage concentration of solution B is 3%-5%. In the steps <2> In this process, the mass percentage concentration of the calcium chloride solution is 8%-12%, and the amount of calcium chloride solution added is such that the molar ratio of calcium ions to carboxyl groups in sodium alginate is (0.8-1.2):

1.

7. The compound microbial fertilizer suitable for cotton in saline-alkali soil according to claim 1, characterized in that, The coprecipitated complex was prepared by the following method: (I). Dissolution: Dissolve salicylic acid and γ-aminobutyric acid together in ethanol, and stir in a water bath at 65-75℃ until completely dissolved to obtain a clear solution; (II). Coprecipitation: The clear solution obtained in step (I) is cooled to 0-4°C at a rate of 0.5-1.5°C per minute and kept at this temperature for 1.5-2.5 hours to allow the coprecipitated complex to be fully precipitated. (III). Separation and drying: Filter the system obtained in step (II), wash the obtained solid with pre-cooled anhydrous ethanol 2-3 times, and then dry it in a vacuum drying oven at 40-50℃ for 4-6 hours to obtain a powdered coprecipitated complex.

8. A compound microbial fertilizer suitable for cotton in saline-alkali soil according to claim 7, characterized in that, The molar ratio of salicylic acid to γ-aminobutyric acid is 1:(0.9-1.1), and the concentration of salicylic acid in ethanol is 0.08-0.12 g / mL.

9. A method for preparing a compound microbial fertilizer suitable for cotton in saline-alkali soil as described in any one of claims 1-8, characterized in that, The method includes the following steps: Step 1, carrier premixing: Place the modified load carrier in a high-speed mixer, spray in the core bacterial agent while stirring, mix for 15-25 minutes to obtain a uniformly loaded premix. Step 2, Granulation and molding: Atomized polyvinyl alcohol adhesive solution is sprayed into the premix obtained in Step 1, and then the resulting wet material is fed into an extrusion granulator to prepare wet granule preforms under a molding pressure of 0.8-1.2 MPa. Step 3, Coating: The wet granule blank obtained in Step 2 is transferred to a fluidized bed. The powder raw material for the slow-release coating layer is prepared into an aqueous suspension with a mass fraction of 6%-10% as a coating agent. The particles are coated by bottom spraying process to obtain coated particles. Step 4, post-processing: The coated granules obtained in Step 3 and the co-precipitation complex are put into a three-dimensional motion mixer and mixed for 20-40 minutes to allow the co-precipitation complex powder to adhere to the surface of the coated granules. Finally, the granules are treated in a ventilated drying equipment at 35-40℃ for 2-4 hours to reduce the final moisture content to less than 10%, thus obtaining the compound microbial fertilizer product.

10. A method for preparing a compound microbial fertilizer suitable for cotton in saline-alkali land according to claim 9, characterized in that, In step two, the mass percentage concentration of the polyvinyl alcohol adhesive solution is 1%-3%, and after the atomized polyvinyl alcohol adhesive solution is sprayed in, the total water content of the material reaches 18%-22%. In step three, the amount of coating agent used is such that the dry weight of the slow-release coating layer accounts for 10%-20% of the dry weight of the particle preform. During the coating process, the inlet air temperature of the fluidized bed is maintained at 40-45℃, and the material bed temperature is maintained at 32-38℃.