Preparation of microbial compound element-based fertilizer and application of microbial compound element-based fertilizer in saline-alkali soil treatment

Abstract

The invention discloses preparation of a microbial compound element-based fertilizer and application of the microbial compound element-based fertilizer in saline-alkali soil treatment, and relates to the technical field of saline-alkali soil improvement. The preparation method comprises the following steps: inoculating lactic acid bacteria, rhodopseudomonas, phosphate-solubilizing bacillus, nitrogen-fixing bacillus, halophilic bacillus and halomonas into a composite culture medium in proportion, and carrying out stepped sequential fermentation culture under the conditions that the pH value is 7.5 and the temperature is 28 DEG C until the bacterial count is greater than or equal to 1010 CFU / mL. According to the preparation of the fertilizer based on the microbial compound elements and the application of saline-alkali soil treatment, a synergistic system of the compound functional flora, the chelated mineral substances and the intelligent organic carrier is constructed, so that multi-dimensional improvement of saline-alkali soil is realized, the limitation of a traditional single improvement mode is broken through, the salinity and pH value of the soil are effectively reduced, and the soil quality is improved. The soil fertility and biological activity are remarkably improved, the salt stress resistance of crops is enhanced, the effective period is prolonged, and the preparation cost is low.

Description

Technical Field

[0001] This invention relates to the field of saline-alkali soil improvement technology, specifically to the preparation of microbial compound element fertilizers and their application in saline-alkali land management. Background Technology

[0002] Saline-alkali soils, as an important reserve of arable land in my country, play a crucial role in ensuring agricultural production potential. However, the soil's inherent characteristics—high salinity, high pH, ​​and weak nutrient supply capacity—lead to an imbalance in its physicochemical structure. This not only inhibits crop root development and nutrient absorption but also hinders the sustainable development of agriculture. Currently, how to achieve a synergistic adaptation between saline-alkali soil improvement and crop growth needs through technological means has become a key direction in agricultural technology research and development. Among these, compound fertilizer technology, which integrates microbial functions, mineral nutrients, and organic carriers, is gradually becoming an important area of ​​exploration for solving the problem of saline-alkali land management because it can simultaneously address soil salinity regulation, fertility enhancement, and biological activity improvement.

[0003] Existing technologies for saline-alkali land remediation include various approaches. Chemical amendments can improve the local physicochemical environment by regulating soil ion balance, freshwater leaching can reduce surface soil salt concentration in the short term, single-strain microbial fertilizers can exert specific bioregulatory effects, and ordinary organic fertilizers help replenish soil organic matter. However, these technologies still have certain limitations in practical application: some chemical amendment methods require high resource input, and the stability of soil improvement effects under long-term application needs further improvement; freshwater leaching consumes a large amount of water resources and is difficult to effectively solve the problem of deep soil salinization; single-strain microbial fertilizers are easily subjected to environmental stress in moderate to severe saline-alkali environments, resulting in limited colonization survival rate and functional performance of the strains; and ordinary organic fertilizers have a long decomposition and transformation cycle, which may have a certain impact on the salt ion concentration of the soil solution in the short term. In response, we propose the preparation and application of microbial compound element fertilizers for saline-alkali land remediation. Summary of the Invention

[0004] To address the aforementioned technical challenges, this paper presents a solution for the preparation and application of microbial compound element fertilizers in saline-alkali land management. This solution resolves the problems of high resource input and limited long-term stability of chemical amendments; high water consumption for freshwater leaching, which makes it difficult to address deep soil salinization; low colonization and survival rate of single-strain microbial fertilizers in moderately to severely saline-alkali environments, limiting their functional performance; and long decomposition cycles of ordinary organic fertilizers, which may affect soil salt ion concentration in the short term.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] The preparation of microbial compound element fertilizer includes the following steps:

[0007] The first step, bacterial fermentation, involves inoculating a composite culture medium with *Lactobacillus*, *Rhodopseudomonas*, *Bacillus phosphate-solubilizing*, *Bacillus azotocinus*, *Bacillus halophilus*, and *Halomonas* in a specific ratio. The culture is then carried out using a stepwise sequential fermentation process at pH 7.5 and 28°C until the bacterial count reaches ≥10⁻⁶. 10 CFU / mL;

[0008] The second step is carrier pretreatment, in which straw biochar, amino acids, molasses and chitosan oligosaccharide are mixed evenly in a mass ratio of 60:2:1:1, the moisture content is adjusted to 40-45%, and it is matured at room temperature for 24 hours without the need for high-temperature fermentation activation.

[0009] The third step is compound granulation, in which the high-concentration bacterial solution obtained in the first step is uniformly adsorbed onto the pretreated carrier by spraying, and then mixed evenly with the mineral element mixture, without the need for spray coating.

[0010] The fourth step is low-temperature drying, which uses fluidized bed drying equipment to control the inlet air temperature to <45℃ and the outlet air temperature to <35℃, drying the material to a moisture content of <15%, followed by cooling and sieving to obtain the finished product. The drying time is adjusted in conjunction with the equipment parameters and the actual humidity of the material.

[0011] Preferably, the first step of the bacterial culture fermentation is a stepwise sequential fermentation process: Lactobacillus, Rhodopseudomonas, Bacillus phosphate-solubilizing, Bacillus azotobacter, Bacillus halophilus, and Haloxylon ammodendron are simultaneously inoculated into a composite culture medium at a predetermined ratio. Fermentation is carried out under continuous aeration at pH 7.5 and 28°C. The fermentation cycle is dynamically adjusted by monitoring the bacterial count until the bacterial count in the mixed culture reaches ≥10⁻⁶. 10 CFU / mL.

[0012] Preferably, the complex microbial community in the first-step bacterial fermentation adopts a stepwise sequential fermentation culture, and the final product has a bacterial agent density ≥1×10⁻⁶. 9 CFU / g; Halophilic Bacillus and Halomonas can stably colonize in moderately to severely saline-alkali environments with pH 8.5-10.5 and EC > 4 mS / cm, with a field colonization survival rate > 80%.

[0013] Preferably, in the second step of carrier pretreatment, straw biochar, amino acids, molasses, and chitosan oligosaccharide are mixed in a mass ratio of 60:2:1:1. During mixing, a stirring device is required to ensure that each component is evenly dispersed. The moisture content is controlled at 40-45% during the pretreatment process, and the mixture needs to be matured at room temperature for 24 hours.

[0014] Preferably, the porosity of the straw biochar in the organic slow-release carrier in the second step is >70%, and the particle size is controlled between 0.5-2 mm; the carrier contains straw biochar, amino acids, molasses, and chitosan oligosaccharide, but does not contain brown sugar, and the components are compounded in a mass ratio of 60:2:1:1.

[0015] Preferably, the mineral element mixture in the third step is treated with an amino acid prechelation process, through which amino acids and mineral elements form small molecule organic complexes; the mineral element mixture contains potassium sulfate, borax, zinc sulfate, sodium silicate, and ferrous sulfate, but does not contain ammonium sulfate, and meets the following requirements based on effective elements: effective silicon ≥ 8%, effective zinc ≥ 2%, and effective boron ≥ 1%.

[0016] Preferably, in the third step of compound granulation, the bacterial liquid adsorption operation requires that the high-concentration bacterial liquid from the first step be sprayed evenly onto the pretreated carrier in a spray manner to ensure that the adsorption rate of the carrier to the bacterial liquid is ≥90%. After the bacterial liquid is adsorbed, the carrier and the mineral element mixture are mixed evenly in one go. Finally, the low-temperature drying requires the use of fluidized bed equipment, and the inlet air temperature is strictly controlled to be <45℃ and the outlet air temperature to be <35℃. The drying endpoint is that the material moisture content is <15%. After drying, the material needs to go through cooling and screening steps to remove unqualified particles.

[0017] Preferably, the application rate is 50-80 kg per mu (approximately 0.067 hectares), which can be used as a base fertilizer or applied as a top dressing through a drip irrigation system. When used as a base fertilizer, the fertilizer should be evenly spread on the soil surface and then tilled. When used in conjunction with drip irrigation, the fertilizer should be dissolved and dripped into the crop roots with the water.

[0018] Preferably, through the synergistic effect of the three elements of compound functional microbial community, chelated minerals and intelligent organic carrier, the compound functional microbial community contains salt-alkali tolerant, nitrogen-fixing and phosphorus-solubilizing strains, the chelated minerals are amino acid chelated mineral elements, and the intelligent organic carrier is a straw biochar-based composite carrier.

[0019] The fertilizer can be extended to the fields of desertification soil improvement, degraded black soil protection, facility agriculture soil remediation, and saline-alkali land ecological farm construction.

[0020] The application of microbial compound element fertilizer in saline-alkali land management, used to prepare the aforementioned microbial compound element fertilizer, includes:

[0021] The fertilizer is suitable for moderately to severely saline-alkali land with pH 8.5–10.5 and EC > 4 mS / cm, including coastal saline soil, inland saline-alkali soil and secondary salinized soil;

[0022] The application method is to apply 50-80 kg per mu as a base fertilizer. It can be evenly spread on the soil surface and then tilled, or the fertilizer can be dissolved in the drip irrigation system and applied to the crop roots with water.

[0023] This fertilizer utilizes the synergistic effect of a complex microbial community, a mixture of mineral elements, and an organic slow-release carrier. The complex microbial community contains Lactobacillus, Rhodopseudomonas, Bacillus phosphate-solubilizing, Bacillus azotocinus, Bacillus halophilus, and Haloxylonus. The mineral element mixture is pre-chelated with amino acids and contains potassium sulfate, borax, zinc sulfate, sodium silicate, and ferrous sulfate. The organic slow-release carrier consists of straw biochar, amino acids, molasses, and chitosan oligosaccharides. Applicable crops include rice, corn, cotton, sugar beets, and goji berries.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0025] This invention proposes a method for preparing and applying microbial compound element fertilizers to saline-alkali land management. By constructing a synergistic system of compound functional microbial communities, chelated minerals, and intelligent organic carriers, it achieves multi-dimensional improvement of saline-alkali soils, breaking through the limitations of traditional single-modification models. This method not only effectively reduces soil salinity and pH but also significantly improves soil fertility and biological activity. The compound functional microbial communities exhibit high colonization and survival rates in saline-alkali environments, continuously secreting beneficial substances to promote crop growth. Chelated mineral technology improves nutrient utilization and enhances crops' resistance to salt stress. The intelligent organic carrier enables the slow release of nutrients and microbial agents, extending the fertilizer's effective period. The preparation cost is low, environmentally friendly, and all materials are biodegradable with no chemical residues, effectively promoting the sustainable development of agricultural production. It is widely applicable to various types of saline-alkali land improvement, demonstrating significant economic, social, and ecological benefits. Attached Figure Description

[0026] Figure 1 This is a flowchart illustrating the preparation process of the present invention;

[0027] Figure 2 This is an application diagram of the microbial compound element fertilizer of the present invention. Detailed Implementation

[0028] The following description is intended to disclose the invention and enable those skilled in the art to implement it. The preferred embodiments described below are merely examples, and other obvious variations will occur to those skilled in the art.

[0029] Reference Figure 1 As shown, the preparation of microbial compound element fertilizer includes the following steps: Step 1: Microbial fermentation. Lactobacillus, Rhodopseudomonas, Bacillus phosphate-solubilizing, Bacillus azotocinus, Bacillus halophilus, and Haloxylon ammodendron are inoculated into a compound culture medium in a specific ratio. The mixture is then cultured in a stepwise sequential fermentation process at pH 7.5 and 28℃ until the bacterial count reaches ≥10⁻⁶. 10CFU / mL. The pH and temperature conditions are set based on the optimal growth environment for various functional microorganisms. Lactic acid bacteria and Bacillus typically exhibit the highest proliferation rates within a near-neutral pH range of 28–30°C, while Rhodopseudomonas and Halomonas also adapt to similar conditions, thus ensuring the synergistic growth of the complex microbial community. Stepwise sequential fermentation refers to the simultaneous inoculation of various microbial species at a predetermined ratio, rather than inoculation in stages, thereby simulating the symbiotic relationship of microorganisms in the natural environment, promoting quorum sensing and metabolic complementarity, and avoiding antagonism between species. During aerated fermentation, cell density needs continuous monitoring. The fermentation endpoint is generally determined by combining optical density and plate counts, ensuring that the total viable cell count reaches 10⁻⁶. 10 CFU / mL or higher, this threshold ensures that the bacterial agent density in the final product is not less than 1×10⁻⁶. 9 CFU / g. In addition, the introduction of halophilic Bacillus and Halomonas significantly improved the adaptability of the inoculant under adverse conditions. Both have extremely strong osmotic regulation ability and cell membrane stability, and can maintain metabolic activity in moderately to severely saline-alkali soils with pH 8.5–10.5 and electrical conductivity (EC) greater than 4 mS / cm. Their field colonization survival rate exceeds 80%, which is due to the salt tolerance genes and compatible solute accumulation mechanism of the strains themselves.

[0030] The second step involves carrier pretreatment, where straw biochar, amino acids, molasses, and chitosan oligosaccharides are mixed evenly in a mass ratio of 60:2:1:1, and the moisture content is adjusted to 40–45%. The mixture is then matured at room temperature for 24 hours, without the need for high-temperature fermentation activation. Straw biochar serves as the main carrier, with a porosity exceeding 70% and a particle size controlled between 0.5–2 mm. It possesses a high specific surface area and excellent adsorption capacity, providing habitat for microorganisms and buffering environmental stress. The amino acids selected are plant-derived hydrolyzed amino acids, which, in addition to serving as a nitrogen source, can pre-chelate with minerals added later. Molasses provides a readily available carbon source, while chitosan oligosaccharides act as elicitors to enhance the activity of the microbial community. Brown sugar is not used in this formulation because it easily absorbs moisture and clumps, and may introduce contaminating microorganisms. The combined use of molasses and chitosan oligosaccharides is more beneficial for the stability of the carrier structure and microbial compatibility. Maintaining a moisture content of 40–45% ensures the material is moist but not excessively wet, preventing anaerobic fermentation. Aging at room temperature for 24 hours allows the components to fully integrate. Molasses and chitosan oligosaccharides gradually penetrate into the pores of biochar, and amino acids partially complex with mineral elements to form a preliminary organic-mineral complex. Although this process does not rely on high temperature, a series of physicochemical adsorption and slow-release effects still occur.

[0031] The third step, composite granulation, involves uniformly adsorbing the high-concentration bacterial solution obtained in the first step onto the pretreated carrier via spraying. This is then mixed evenly with the mineral element mixture, without the need for spray coating. The spraying method uses a low-pressure atomizing nozzle to uniformly spray the bacterial solution onto the carrier surface in the form of micron-sized droplets. Continuous stirring is required during the process to ensure an adsorption rate of no less than 90%. The high adsorption rate is attributed to the highly porous structure of straw biochar and the film-forming properties of chitosan oligosaccharides, effectively fixing the bacterial solution inside and on the surface of the carrier. The mineral element mixture contains potassium sulfate, borax, zinc sulfate, sodium silicate, and ferrous sulfate, but does not contain ammonium sulfate to avoid the inhibitory effect of ammonium nitrogen on certain microorganisms. All minerals undergo amino acid pre-chelation treatment, meaning they react with the amino acids in the carrier under appropriate pH and temperature conditions before use to form low-molecular-weight amino acid-metal complexes. Elements such as zinc, iron, and boron form five- or six-membered ring complexes with amino acids, significantly improving element stability and plant bioavailability. Based on available elements, the mixture should contain no less than 8% available silicon, no less than 2% available zinc, and no less than 1% available boron. These contents are designed based on the micronutrient requirements of major crops during their critical growth stages and the general degree of soil deficiency. The mixing process should be completed in one step to avoid damage to the microorganisms or material stratification caused by multiple treatments.

[0032] The fourth step is low-temperature drying, using fluidized bed drying equipment. The inlet air temperature is controlled below 45℃ and the outlet air temperature below 35℃ to dry the material until the moisture content is less than 15%. Afterward, the material is cooled and sieved to obtain the finished product. The drying time is adjusted in conjunction with the equipment parameters and the actual moisture content of the material. The optimal drying curve is usually determined through experiments to avoid excessively high temperatures that could lead to significant microbial inactivation. Fluidized bed drying allows for sufficient contact between hot air and the material, improving drying efficiency while reducing localized overheating. The outlet air temperature is strictly controlled below 35℃ to ensure the bacteria remain in a sub-dormant state and are not damaged by heat. After drying, the material is cooled to room temperature and then sieved to remove excessively large or fine particles, ensuring the product particle size distribution is within the range of 1–4 mm, meeting the requirements for mechanical application and drip irrigation.

[0033] The recommended application rate for this fertilizer is 50–80 kg per acre, with the specific dosage adjusted according to soil fertility and crop type. When used as a base fertilizer, spread it evenly on the soil surface and then till it into the soil, allowing microorganisms and mineral elements to distribute in the crop root zone. When applying as a top dressing using a drip irrigation system, dissolve the fertilizer in the irrigation water beforehand, let it stand for 2–3 hours to activate, and then drip it into the roots with the water, utilizing the high uniformity of the drip irrigation system for precise fertilization. The compound functional microbial community in the fertilizer possesses multiple functions such as salt and alkali tolerance, nitrogen fixation, and phosphorus solubilization. Chelated mineral elements improve its mobility and bioavailability in the soil, while the straw biochar-based composite carrier plays a role in adsorption, slow release, and soil structure improvement. These three elements form a synergistic system, jointly enhancing the fertilizer's resilience and sustainability.

[0034] This fertilizer can also be applied to desertification soil improvement, degraded black soil protection, facility agriculture soil remediation, and saline-alkali land ecological farm construction. In desertification soils, microorganisms promote soil aggregate formation and improve water and fertilizer retention capacity by secreting extracellular polysaccharides and organic acids. In black soil protection, continuous application can alleviate organic matter decline and microbial biodiversity loss. In facility agriculture, it can degrade substances hindering continuous cropping and inhibit soil-borne pathogens. In saline-alkali land ecological farms, salt-tolerant bacteria and the organic-mineral synergistic system can gradually reduce soil pH and electrical conductivity, restoring soil ecological functions. The entire preparation process does not require high-temperature fermentation or complex coating processes, emphasizing low-temperature treatment and organic-inorganic compounding, which improves the product's environmental adaptability and application breadth while ensuring microbial activity.

[0035] Reference Figure 2 As shown, this paper describes the preparation of a microbial compound fertilizer and its application in saline-alkali land management. The aim is to improve the physicochemical properties of moderately to severely saline-alkali soils and enhance crop growth through the synergistic effect of a specific microbial complex system, organic carrier, and mineral elements. This fertilizer is suitable for saline-alkali soil types with a pH between 8.5 and 10.5 and an electrical conductivity (EC) greater than 4 mS / cm, including coastal saline soils, inland saline-alkali soils, and secondary salinization soils caused by improper irrigation in facility agriculture. Its applicability is based on the natural tolerance and regulatory capacity of the specific functional microorganisms and carrier system contained in the fertilizer to high saline-alkali stress.

[0036] Regarding application methods, it is recommended to apply 50 to 80 kg per acre. This can be done as a base fertilizer, evenly spread on the soil surface and then tilled into the soil, or dissolved and applied to the crop root zone with water through a drip irrigation system. This dosage range takes into account the common problems in saline-alkali soils, such as high nutrient fixation rates, low microbial activity, and poor physical structure. Base application and tilling help microorganisms and organic carriers directly contact the rhizosphere soil, promoting the formation of soil aggregates; while drip irrigation and topdressing help to continuously provide active microorganisms and mineral nutrients during the crop's growth period, enhancing salt tolerance and growth promotion effects.

[0037] The core function of the fertilizer relies on a synergistic mechanism involving a complex microbial community, a mixture of mineral elements, and an organic slow-release carrier. The complex microbial community includes *Lactobacillus*, *Rhodopseudomonas*, *Bacillus phosphate-solubilizing*, *Bacillus azotocinus*, *Bacillus halophilus*, and *Haloxylon*. Among them, *Bacillus halophilus* and *Haloxylon* possess extremely strong osmotic regulation capabilities and cell membrane stability, maintaining metabolic activity and stable colonization in high-salt-alkaline environments, with a field survival rate exceeding 80%. *Lactobacillus* and *Rhodopseudomonas* produce organic acids through metabolism, neutralizing soil alkalinity and lowering pH; while *Azotocinus* and *Phosphobilizing* improve nitrogen use efficiency and activate fixed phosphorus, respectively. These strains are inoculated using a tiered synchronous inoculation strategy during fermentation, effectively avoiding inter-species antagonism, promoting quorum sensing and synergistic proliferation, ultimately achieving a bacterial count of 10^6 in the fermentation broth. 10 CFU / mL or higher ensures a high number of viable bacteria in the finished product.

[0038] The mineral element mixture includes potassium sulfate, borax, zinc sulfate, sodium silicate, and ferrous sulfate, and is free of ammonium sulfate to avoid the inhibitory effects of ammonia toxicity on microorganisms and seedlings. All minerals undergo amino acid pre-chelation treatment to form small-molecule organic complexes, such as amino acid-Zn and amino acid-Fe, significantly improving element mobility and crop absorption efficiency in saline-alkali soils. Based on available elements, the mixture contains ≥8% available silicon, ≥2% available zinc, and ≥1% available boron. These proportions are set based on the intermediate elements commonly lacking in crops in saline-alkali soils and the mitigating effect of silicon on salt stress. Silicon can enhance the mechanical strength of cell walls and reduce sodium ion absorption; zinc and boron participate in the activation of various enzymes and reproductive development processes, contributing to crop stress resistance and yield increase.

[0039] The organic slow-release carrier is a compound of straw biochar, amino acids, molasses, and chitosan oligosaccharides in a mass ratio of 60:2:1:1. The straw biochar has a porosity exceeding 70% and a particle size between 0.5 and 2 mm, exhibiting excellent adsorption and microbial shelter capabilities, serving as a habitat for microorganisms and buffering against salt and alkali stress. Molasses and chitosan oligosaccharides provide readily available carbon sources and excitation signaling molecules for microorganisms, while amino acids, in addition to serving as a nitrogen source, participate in mineral chelation processes. This carrier matures at room temperature for 24 hours, achieving component fusion and slow-release function without relying on high-temperature fermentation, effectively maintaining microbial activity and prolonging fertilizer efficacy.

[0040] This fertilizer is suitable for a variety of salt-tolerant or salt-sensitive crops, such as rice, corn, cotton, sugar beets, and goji berries. In different crop systems, it works through multiple pathways, including lowering root zone pH, improving soil microecology, and providing key nutrients, thus contributing to sustainable agricultural production and ecological restoration in saline-alkali land.

[0041] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claimed invention. The scope of protection claimed by the appended claims and their equivalents is defined.

Claims

1. The preparation of microbial compound element fertilizer, characterized in that, Includes the following steps: The first step, bacterial fermentation, involves inoculating a composite culture medium with *Lactobacillus*, *Rhodopseudomonas*, *Bacillus phosphate-solubilizing*, *Bacillus azotocinus*, *Bacillus halophilus*, and *Halomonas* in a specific ratio. The culture is then carried out using a stepwise sequential fermentation process at pH 7.5 and 28°C until the bacterial count reaches ≥10⁻⁶. 10 CFU / mL; The second step is carrier pretreatment, in which straw biochar, amino acids, molasses and chitosan oligosaccharide are mixed evenly in a mass ratio of 60:2:1:1, the moisture content is adjusted to 40-45%, and it is matured at room temperature for 24 hours without the need for high-temperature fermentation activation. The third step is compound granulation, in which the high-concentration bacterial solution obtained in the first step is uniformly adsorbed onto the pretreated carrier by spraying, and then mixed evenly with the mineral element mixture, without the need for spray coating. The fourth step is low-temperature drying, which uses fluidized bed drying equipment to control the inlet air temperature to <45℃ and the outlet air temperature to <35℃, drying the material to a moisture content of <15%, followed by cooling and sieving to obtain the finished product. The drying time is adjusted in conjunction with the equipment parameters and the actual humidity of the material.

2. The preparation of the microbial compound element fertilizer according to claim 1, characterized in that, The first step of the bacterial culture fermentation, a stepwise sequential fermentation, specifically involves simultaneously inoculating a composite culture medium with *Lactobacillus*, *Rhodopseudomonas*, *Bacillus phosphate-solubilizing*, *Bacillus azotocinus*, *Bacillus halophilus*, and *Haloxylon ammodendron* in a predetermined ratio. Fermentation is carried out under continuous aeration at pH 7.5 and 28°C. The fermentation cycle is dynamically adjusted by monitoring the bacterial count until the bacterial count in the mixed culture reaches ≥10⁻⁶. 10 CFU / mL.

3. The preparation of the microbial compound element fertilizer according to claim 1, characterized in that, The complex microbial community in the first-step bacterial fermentation adopts a stepwise sequential fermentation culture, and the final product has a bacterial agent density ≥1×10⁻⁶. 9 CFU / g; Halophilic Bacillus and Halomonas can stably colonize in moderately to severely saline-alkali environments with pH 8.5-10.5 and EC > 4 mS / cm, with a field colonization survival rate > 80%.

4. The preparation of microbial compound element fertilizer according to claim 1, characterized in that, In the second step of carrier pretreatment, straw biochar, amino acids, molasses, and chitosan oligosaccharide are mixed in a mass ratio of 60:2:1:

1. During mixing, a stirring device is required to ensure that each component is evenly dispersed. The moisture content is controlled at 40-45% during the pretreatment process, and the mixture needs to be matured at room temperature for 24 hours.

5. The preparation of the microbial compound element fertilizer according to claim 1, characterized in that, In the second step, the organic slow-release carrier contains straw biochar with a porosity >70% and a particle size controlled between 0.5-2 mm. The carrier contains straw biochar, amino acids, molasses, and chitosan oligosaccharide, but does not contain brown sugar. The components are compounded in a mass ratio of 60:2:1:

1.

6. The preparation of the microbial compound element fertilizer according to claim 1, characterized in that, The mineral element mixture in the third step is treated with an amino acid prechelation process, which forms small molecule organic complexes with the amino acids and mineral elements. The mineral element mixture contains potassium sulfate, borax, zinc sulfate, sodium silicate, and ferrous sulfate, but does not contain ammonium sulfate. It also meets the following requirements based on effective elements: effective silicon ≥ 8%, effective zinc ≥ 2%, and effective boron ≥ 1%.

7. The preparation of the microbial compound element fertilizer according to claim 1, characterized in that, The third step of the compound granulation bacterial liquid adsorption operation requires that the high-concentration bacterial liquid from the first step be sprayed evenly onto the pretreated carrier in a spray manner to ensure that the adsorption rate of the carrier to the bacterial liquid is ≥90%. After the bacterial liquid is adsorbed, the carrier and the mineral element mixture are mixed evenly in one go. Finally, the low-temperature drying requires the use of fluidized bed equipment, and the inlet air temperature must be strictly controlled to be <45℃ and the outlet air temperature to be <35℃. The drying endpoint is that the material moisture content is <15%. After drying, it needs to go through cooling and screening steps to remove unqualified particles.

8. The preparation of the microbial compound element fertilizer according to claim 1, characterized in that, When applying, the dosage is 50-80 kg per mu (approximately 0.067 hectares). It can be used as a base fertilizer or applied top dressing through a drip irrigation system. When used as a base fertilizer, spread the fertilizer evenly on the soil surface and then till the soil. When used in conjunction with drip irrigation, the fertilizer is dissolved and dripped into the crop roots along with the water.

9. The preparation of the microbial compound element fertilizer according to claim 1, characterized in that, Through the synergistic effect of the three elements of compound functional microbial community, chelated minerals and intelligent organic carrier, the compound functional microbial community contains salt-alkali tolerant, nitrogen-fixing and phosphorus-solubilizing strains, the chelated minerals are amino acid chelated mineral elements, and the intelligent organic carrier is a straw biochar-based composite carrier. The fertilizer can be extended to the fields of desertification soil improvement, degraded black soil protection, facility agriculture soil remediation, and saline-alkali land ecological farm construction.

10. The application of microbial compound element fertilizer in saline-alkali land management, characterized in that, The preparation of the microbial compound element fertilizer as described in any one of claims 1-9 includes: The fertilizer is suitable for moderately to severely saline-alkali land with pH 8.5–10.5 and EC > 4 mS / cm, including coastal saline soil, inland saline-alkali soil and secondary salinized soil; The application method is to apply 50-80 kg per mu as a base fertilizer. It can be evenly spread on the soil surface and then tilled, or the fertilizer can be dissolved in the drip irrigation system and applied to the crop roots with water. This fertilizer utilizes the synergistic effect of a complex microbial community, a mixture of mineral elements, and an organic slow-release carrier. The complex microbial community contains Lactobacillus, Rhodopseudomonas, Bacillus phosphate-solubilizing, Bacillus azotocinus, Bacillus halophilus, and Haloxylonus. The mineral element mixture is pre-chelated with amino acids and contains potassium sulfate, borax, zinc sulfate, sodium silicate, and ferrous sulfate. The organic slow-release carrier consists of straw biochar, amino acids, molasses, and chitosan oligosaccharides. Applicable crops include rice, corn, cotton, sugar beets, and goji berries.

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