Microbial compound phosphorus and potassium bacterial fertilizer for promoting nutrient absorption and preparation method thereof

Abstract

This invention relates to the field of microbial fertilizer technology, specifically to a microbial compound phosphorus and potassium fertilizer that promotes nutrient absorption and its preparation method. The preparation method of a microbial compound phosphorus and potassium fertilizer that promotes nutrient absorption includes: preparing sunflower disc extract and Moringa leaf extract; preparing slow-release microcapsules; preparing microspheres loaded with bacteria; and preparing the compound phosphorus and potassium fertilizer. This invention first selectively oxidizes konjac glucomannan using sodium periodate, then crosslinks the oxidized konjac glucomannan with lignin under weakly acidic conditions to form a three-dimensional network crosslinked polymer framework. Urea and dipotassium hydrogen phosphate are encapsulated in the network channels or adsorbed onto the framework during the crosslinking process, forming nutrient-loaded slow-release microcapsules. After the slow-release microcapsules are made into a compound phosphorus and potassium fertilizer and applied, nutrients are gradually released as the crop grows, which helps improve nutrient absorption and utilization, thereby promoting nutrient absorption.

Description

Technical Field

[0001] This invention relates to the field of microbial fertilizer technology, specifically to a microbial compound phosphorus and potassium fertilizer that promotes nutrient absorption and its preparation method. Background Technology

[0002] In agricultural production, phosphorus and potassium are core nutrients that ensure crop growth, development, and yield. Although conventional chemical phosphorus and potassium fertilizers can quickly replenish nutrients, water-soluble phosphorus and potassium are easily fixed by iron, aluminum, calcium, and other ions in the soil and are easily leached away by irrigation and rainfall. This results in low nutrient utilization rates of phosphorus and potassium fertilizers, which can easily lead to fertilizer waste, affect crop nutrient absorption, and cause soil compaction, acidification, and environmental problems such as eutrophication of water bodies when applied in large quantities.

[0003] Microbial fertilizer is a type of fertilizer processed using biotechnology to produce beneficial microbial strains, including various probiotics such as bacteria, fungi, and actinomycetes. These beneficial microbial strains can coexist with plants, not only decomposing organic matter, fixing nitrogen, and dissolving phosphorus, but also increasing soil fertility, improving soil structure, promoting plant growth, and enhancing plant resistance to diseases and pests. However, the microbial cells themselves are fragile and extremely sensitive to external environmental factors such as dryness, high temperature, pH changes, ultraviolet radiation, and soil stress. Direct application of pure microbial agents can easily lead to a large number of inactivations and deaths in a short period of time, making it difficult to maintain the number of live bacteria required to meet the functions of phosphorus and potassium solubilization and growth promotion.

[0004] Sodium alginate hydrogels are widely used as microbial carriers due to their excellent biocompatibility, mild gelling properties, and stable structural characteristics. They provide microorganisms with physical encapsulation space and a moisturizing, buffered microenvironment to resist external stresses such as dryness, acidity, alkali, and ultraviolet radiation. However, sodium alginate relies solely on calcium ions for ionic cross-linking, resulting in a dense and brittle gel network structure with low porosity and specific surface area. This limits the space available for physically accommodating microorganisms, making it difficult to support high concentrations of bacteria. Furthermore, it can only physically embed and fix microorganisms, lacking chemical adsorption sites such as hydrogen bonds and electrostatic interactions that bind to the bacterial surface. As a result, bacteria are easily diffused and lost during gel preparation, washing, and post-processing, leading to low overall loading efficiency.

[0005] Therefore, there is a need to propose a microbial compound phosphorus and potassium fertilizer that can improve nutrient utilization and microbial load rate and promote nutrient absorption, as well as its preparation method. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention aims to provide a microbial compound phosphorus and potassium fertilizer that promotes nutrient absorption and its preparation method.

[0007] This invention provides a method for preparing a microbial compound phosphorus and potassium fertilizer that promotes nutrient absorption, comprising the following steps: S1: Preparation of sunflower disc extract and moringa leaf extract Extracts were extracted from dried sunflower heads and dried moringa leaves to obtain sunflower head extract and moringa leaf extract, respectively. S2: Preparation of sustained-release microcapsules S2.1: Add konjac glucomannan to 95% ethanol solution at a ratio of 1g:(8-10)mL, stir for 10-20min, then filter, and then dry the filter residue at 60℃ for 1-2h to obtain purified konjac glucomannan. S2.2: Add the purified konjac glucomannan above to deionized water at a ratio of 1g:(85-95)mL, heat and stir at 40-45℃ until completely dissolved, then cool to room temperature, and then add sodium periodate aqueous solution dropwise while stirring. After the addition is complete, stir and react in the dark for 4-6 hours, then add ethylene glycol, stir in the dark for 30-40 minutes, terminate the reaction, and obtain the reaction solution; S2.3: While stirring, add 3 times the volume of 95% ethanol solution to the above reaction solution, let it stand for 2-3 hours, then centrifuge to collect the precipitate, wash it twice with anhydrous ethanol and acetone respectively, and then vacuum dry, grind and pass it through an 80-mesh sieve to obtain oxidized konjac glucomannan. S2.4: Add the above oxidized konjac glucomannan and lignin to deionized water at a ratio of (2.8-3.2) g: 1 g: (75-85) mL, heat and stir at 60-65℃ for 30-40 min, then adjust the pH to 4-4.5 with a 1% citric acid aqueous solution, and then add urea and dipotassium hydrogen phosphate trihydrate while stirring. Continue to keep warm and stir for crosslinking for 2-3 h. After cooling, centrifuge to collect the precipitate and vacuum dry to obtain sustained-release microcapsules. S3: Preparation of bacterial-loaded microspheres The compound bacterial agent was activated to prepare a bacterial suspension. Pullulan, sodium alginate and sodium carboxymethyl starch were dissolved to prepare a composite matrix solution. The bacterial suspension and the composite matrix solution were then stirred and mixed, and then added dropwise to calcium chloride solution to prepare bacterial-containing gel microspheres. Finally, the bacterial-containing gel microspheres were added to genipin aqueous solution for cross-linking to obtain bacterial-loaded microspheres. S4: Preparation of compound phosphorus and potassium microbial fertilizer The above-mentioned slow-release microcapsules, above-mentioned bacterial microspheres, above-mentioned sunflower disc extract, above-mentioned Moringa leaf extract and humic acid were stirred and mixed evenly to obtain a compound phosphorus and potassium bacterial fertilizer.

[0008] Furthermore, the mass ratio of sodium periodate to purified konjac glucomannan is 1:(2.7-2.9).

[0009] Furthermore, the concentration of the sodium periodate aqueous solution is 70 g / L, and the molar ratio of ethylene glycol to sodium periodate is (1.5-1.6):1.

[0010] Furthermore, the mass ratio of urea to lignin is (3.5-3.6):1, and the mass ratio of dipotassium hydrogen phosphate trihydrate to lignin is (1.7-1.8):1.

[0011] Furthermore, by mass percentage, the raw material composition of the compound phosphorus and potassium microbial fertilizer is: 45-55% slow-release microcapsules, 15-20% bacterial microspheres, 8-10% sunflower disc extract, 6-8% moringa leaf extract, and the remainder is humic acid.

[0012] Furthermore, S1 includes the following steps: S1.1: Crush the dried sunflower discs, pass them through a 40-60 mesh sieve, add them to distilled water at a ratio of 1g:(15-25)mL, heat and stir at 70-80℃ for 2-3 hours, then filter and centrifuge to collect the supernatant. Then add the precipitate to distilled water again at a ratio of 1g:(10-15)mL, repeat the extraction once, combine the two supernatants, concentrate them by rotary evaporation to a solid content of 20-25%, and then freeze-dry to obtain sunflower disc extract; S1.2: Crush dried Moringa leaves, pass them through a 60-80 mesh sieve, add them to distilled water at a ratio of 1g:(20-30)mL, heat and stir at 60-65℃ for 1.5-2.5h, then filter and centrifuge to collect the supernatant. Then add the precipitate to distilled water at a ratio of 1g:(10-15)mL and repeat the extraction once. Combine the two supernatants, concentrate them by rotary evaporation to a solid content of 20-25%, and then freeze-dry to obtain Moringa leaf extract.

[0013] Furthermore, S3 includes the following steps: S3.1: Add the compound bacterial agent to sterile physiological saline, vortex for 1-2 minutes, then vortex at 37℃ and 180 r / min for 2-3 hours to obtain a concentration of 10. 9 The bacterial suspension of CFU / mL was refrigerated at 4°C for later use. S3.2: Add pullulan, sodium alginate and sodium carboxymethyl starch to deionized water at a ratio of (1-1.1)g:(1-1.2)g:1g:(120-130)mL, and stir thoroughly until completely dissolved to obtain a composite matrix solution; S3.3: While stirring, add the above bacterial suspension to the above composite matrix solution, and then drop it into a 2wt% calcium chloride solution. After the addition is complete, continue stirring for 30-40 minutes, then filter to obtain bacterial gel microspheres. S3.4: Add the above-mentioned bacterial-containing gel microspheres to a 0.3wt% genipin aqueous solution, allow to stand for cross-linking for 1.5-2.5 hours, filter, wash with deionized water 1-2 times, and dry to obtain bacterial-loaded microspheres.

[0014] Furthermore, the compound microbial agent is composed of Bacillus subtilis, Azotobacter chrysophagus, and Pseudomonas fluorescens in a mass ratio of (3-5):(2.4-2.8):1.

[0015] Furthermore, the volume ratio of bacterial suspension, composite matrix solution, calcium chloride solution and genipin aqueous solution is 1:(7.5-8.5):(4.5-5.5):(18-20).

[0016] A microbial compound phosphorus and potassium fertilizer that promotes nutrient absorption is prepared by any one of the above-mentioned methods for preparing a microbial compound phosphorus and potassium fertilizer that promotes nutrient absorption.

[0017] The present invention has the following advantages: 1. In this invention, konjac glucomannan is selectively oxidized using sodium periodate to generate highly active aldehyde groups on the sugar chains, yielding oxidized konjac glucomannan. Then, the oxidized konjac glucomannan is cross-linked with lignin under weakly acidic conditions to form a three-dimensional network cross-linked polymer framework. Urea and dipotassium hydrogen phosphate are encapsulated in the network channels or adsorbed onto the framework during the cross-linking process, forming nutrient-loaded sustained-release microcapsules. Because hydrogen ions easily destroy acetal bonds and other chemical bonds in the sustained-release microcapsules under acidic conditions, the sustained-release microcapsule polymer molecules... Shorter chains reduce the resistance to the diffusion of nutrients such as urea and dipotassium hydrogen phosphate, accelerating nutrient release. Under alkaline conditions, the stability of the slow-release microcapsule membrane increases, further reducing the rate of nutrient diffusion. When slow-release microcapsules are formulated into compound phosphorus and potassium microbial fertilizer and applied, the concentration of organic acids in root exudates increases as crops grow, accelerating the release of nutrients from the microcapsules. This allows nutrients to be released gradually as crops grow, significantly reducing the precipitation of phosphorus and potassium bound to metal ions in the soil, thus improving nutrient absorption and utilization, and ultimately promoting nutrient absorption.

[0018] 2. In this invention, pullulan, sodium alginate, and sodium carboxymethyl starch are first fully dissolved in water to form a composite matrix solution. This solution is then mixed with a bacterial suspension and subsequently added dropwise to a calcium chloride solution. This allows the carboxyl groups in the sodium alginate to undergo a rapid ionic cross-linking reaction with the calcium ions, anchoring pullulan and sodium carboxymethyl starch within the sodium alginate gel network. Simultaneously, the bacteria are physically embedded in situ within the gel channels, forming bacterial-containing gel microspheres within a semi-interpenetrating polymer network. This initial loading and shaping is achieved. The bacterial-containing gel microspheres are then added to a genipin aqueous solution to undergo cross-linking, forming chemical covalent bonds within the gel to further strengthen the gel network structure and prevent... After bacterial cell leakage and the acquisition of microspheres loaded with bacteria, pullulan can fill the gaps between the cross-linked chains of sodium alginate, and sodium carboxymethyl starch can increase the hydrophilic side chains, forming a three-dimensional porous structure with uniform pore size and large specific surface area, which can accommodate more bacteria. Furthermore, sodium carboxymethyl starch carries negatively charged carboxyl groups, which can bind to the functional groups on the surface of bacteria, so that the bacteria are not only physically embedded, but also chemically adsorbed onto the gel backbone. At the same time, pullulan is a non-toxic, highly biocompatible neutral polysaccharide, which can buffer the damage to the bacteria during the cross-linking process, maintain the integrity of the bacterial structure, and significantly increase the countable viable bacteria count, thereby significantly improving the effective loading rate of microbial cells on the microspheres.

[0019] 3. In this invention, sunflower disc extract and moringa leaf extract are added to the compound phosphorus and potassium microbial fertilizer. Sunflower disc extract, rich in water-soluble dietary fiber, pectin polysaccharides, phenolic acids, and flavonoids, can chelate metal ions in the soil, reduce phosphorus and potassium fixation, improve nutrient availability, improve soil aggregate structure, enhance water and fertilizer retention capacity, and provide a stable environment for nutrient release and absorption. Simultaneously, it stimulates the activity of the root tip meristem, promotes taproot elongation and root hair proliferation, and expands the nutrient absorption area. Moringa leaf extract, rich in amino acids, small molecule peptides, microorganisms, saponins, and natural growth regulators, can be directly absorbed and utilized by the crop roots, accelerating metabolism and nutrient transport protein expression, regulating crop physiological state, enhancing root vitality and nutrient affinity, and improving active absorption capacity. The combination of these two extracts can jointly improve the rhizosphere environment, which is beneficial for crop root absorption. It also promotes more developed crop roots, a larger absorption area, and higher absorption efficiency, thereby synergistically enhancing the crop's nutrient absorption capacity. Attached Figure Description

[0020] Figure 1 This is a flowchart illustrating the preparation method of the nutrient-enhancing microbial compound phosphorus and potassium fertilizer used in an embodiment of the present invention. Detailed Implementation

[0021] To enable those skilled in the art to better understand the technical solutions of this invention, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of this invention.

[0022] Example 1: A method for preparing a microbial compound phosphorus and potassium fertilizer that promotes nutrient absorption, such as... Figure 1 As shown, it includes the following steps: S1: Preparation of sunflower disc extract and moringa leaf extract S1.1: Crush the dried sunflower discs, pass them through a 40-mesh sieve, add them to distilled water at a ratio of 1g:15mL, heat and stir at 70℃ for 2 hours, then filter and centrifuge to collect the supernatant. Then add the precipitate to distilled water again at a ratio of 1g:10mL and repeat the extraction once. Combine the two supernatants, concentrate them by rotary evaporation to a solid content of 20%, and then freeze-dry to obtain sunflower disc extract. S1.2: Pulverize dried Moringa leaves, pass through a 60-mesh sieve, add to distilled water at a ratio of 1g:20mL, heat and stir at 60℃ for 1.5h, then filter, centrifuge, collect the supernatant, then add the precipitate to distilled water at a ratio of 1g:10mL, repeat the extraction once, combine the two supernatants, concentrate by rotary evaporation to a solid content of 20%, and then freeze-dry to obtain Moringa leaf extract; S2: Preparation of sustained-release microcapsules S2.1: Add konjac glucomannan to 95% ethanol solution at a ratio of 1g:8mL, stir for 10min, then filter, and then dry the filter residue at 60℃ for 1h to obtain purified konjac glucomannan. S2.2: Add the purified konjac glucomannan to deionized water at a ratio of 1g:85mL, heat and stir at 40℃ until completely dissolved, then cool to room temperature, and then add sodium periodate aqueous solution dropwise while stirring. After the addition is complete, stir and react in the dark for 4 hours, then add ethylene glycol, stir in the dark for 30 minutes, and terminate the reaction to obtain the reaction solution. The mass ratio of sodium periodate to purified konjac glucomannan is 1:2.7, the concentration of sodium periodate aqueous solution is 70g / L, and the molar ratio of ethylene glycol to sodium periodate is 1.5:1. S2.3: While stirring, add 3 times the volume of 95% ethanol solution to the above reaction solution, let it stand for 2 hours, then centrifuge to collect the precipitate, wash it twice with anhydrous ethanol and acetone respectively, and then vacuum dry, grind and pass it through an 80-mesh sieve to obtain oxidized konjac glucomannan. S2.4: Add the above oxidized konjac glucomannan and lignin to deionized water at a ratio of 2.8g:1g:75mL, heat and stir at 60℃ for 30min, then adjust the pH to 4 with a 1% citric acid aqueous solution, and then add urea and dipotassium hydrogen phosphate trihydrate while stirring. Continue to keep warm and stir for crosslinking for 2h. After cooling, collect the precipitate by centrifugation and vacuum dry to obtain sustained-release microcapsules, wherein the mass ratio of urea to lignin is 3.5:1 and the mass ratio of dipotassium hydrogen phosphate trihydrate to lignin is 1.7:1. S3: Preparation of bacterial-loaded microspheres S3.1: Add the compound bacterial agent to sterile physiological saline, vortex for 1 minute, then vortex at 37℃ and 180 r / min for 2 hours to obtain a concentration of 10. 9 The bacterial suspension of CFU / mL was stored at 4°C for later use. The compound bacterial agent was composed of Bacillus subtilis, Azotobacter chrysophagus and Pseudomonas fluorescens in a mass ratio of 3:2.4:1. S3.2: Add pullulan, sodium alginate and sodium carboxymethyl starch to deionized water at a ratio of 1g:1g:1g:120mL, and stir thoroughly until completely dissolved to obtain a composite matrix solution; S3.3: While stirring, add the above bacterial suspension to the above composite matrix solution, and then drop it into a 2wt% calcium chloride solution. After the addition is complete, continue stirring for 30 minutes, then filter to obtain bacterial gel microspheres. S3.4: The above-mentioned bacterial-containing gel microspheres were added to a 0.3wt% genipin aqueous solution, allowed to stand for cross-linking for 1.5 h, filtered, washed once with deionized water, and then dried in a fluidized bed to obtain bacterial-loaded microspheres. The volume ratio of bacterial suspension, composite matrix solution, calcium chloride solution and genipin aqueous solution was 1:7.5:4.5:18. S4: Preparation of compound phosphorus and potassium microbial fertilizer The above-mentioned slow-release microcapsules, above-mentioned bacterial microspheres, above-mentioned sunflower disc extract, above-mentioned moringa leaf extract and humic acid were stirred and mixed evenly to obtain a compound phosphorus and potassium bacterial fertilizer. The raw material composition of the compound phosphorus and potassium bacterial fertilizer by mass percentage is: 45% slow-release microcapsules, 15% bacterial microspheres, 8% sunflower disc extract, 6% moringa leaf extract and 26% humic acid.

[0023] Example 2: A method for preparing a microbial compound phosphorus and potassium fertilizer that promotes nutrient absorption, such as... Figure 1 As shown, it includes the following steps: S1: Preparation of sunflower disc extract and moringa leaf extract S1.1: Crush dried sunflower discs, pass them through a 40-mesh sieve, add them to distilled water at a ratio of 1g:20mL, heat and stir at 75℃ for 2.5h, then filter and centrifuge to collect the supernatant. Then add the precipitate to distilled water again at a ratio of 1g:12.5mL, repeat the extraction once, combine the two supernatants, concentrate by rotary evaporation to a solid content of 22.5%, and then freeze-dry to obtain sunflower disc extract; S1.2: Pulverize dried Moringa leaves, pass through a 60-mesh sieve, add to distilled water at a ratio of 1g:25mL, heat and stir at 62.5℃ for 2 hours, then filter and centrifuge to collect the supernatant. Then add the precipitate to distilled water at a ratio of 1g:12.5mL and repeat the extraction once. Combine the two supernatants, concentrate by rotary evaporation to a solid content of 22.5%, and then freeze-dry to obtain Moringa leaf extract. S2: Preparation of sustained-release microcapsules S2.1: Add konjac glucomannan to 95% ethanol solution at a ratio of 1g:9mL, stir for 15min, then filter, and then dry the filter residue at 60℃ for 1.5h to obtain purified konjac glucomannan. S2.2: Add the purified konjac glucomannan to deionized water at a ratio of 1g:90mL, heat and stir at 42.5℃ until completely dissolved, then cool to room temperature, and then add sodium periodate aqueous solution dropwise while stirring. After the addition is complete, stir and react in the dark for 5 hours, then add ethylene glycol, stir in the dark for 35 minutes, and terminate the reaction to obtain the reaction solution. The mass ratio of sodium periodate to purified konjac glucomannan is 1:2.8, the concentration of sodium periodate aqueous solution is 70g / L, and the molar ratio of ethylene glycol to sodium periodate is 1.55:1. S2.3: While stirring, add 3 times the volume of 95% ethanol solution to the above reaction solution, let it stand for 2.5 hours, then centrifuge to collect the precipitate, wash it twice with anhydrous ethanol and acetone respectively, and then dry it under vacuum at room temperature, grind it and pass it through an 80-mesh sieve to obtain oxidized konjac glucomannan. S2.4: Add the above oxidized konjac glucomannan and lignin to deionized water at a ratio of 3g:1g:80mL, heat and stir at 62.5℃ for 35min, then adjust the pH to 4 with a 1% citric acid aqueous solution, and then add urea and dipotassium hydrogen phosphate trihydrate while stirring. Continue to keep warm and stir for crosslinking for 2.5h. After cooling, collect the precipitate by centrifugation and vacuum dry to obtain sustained-release microcapsules, wherein the mass ratio of urea to lignin is 3.55:1 and the mass ratio of dipotassium hydrogen phosphate trihydrate to lignin is 1.75:1. S3: Preparation of bacterial-loaded microspheres S3.1: Add the compound bacterial agent to sterile physiological saline, vortex for 1.5 min, then vortex at 37℃ and 180 r / min for 2.5 h to obtain a concentration of 10. 9 The bacterial suspension of CFU / mL was stored at 4°C for later use. The compound bacterial agent was composed of Bacillus subtilis, Azotobacter chrysophagus and Pseudomonas fluorescens in a mass ratio of 4:2.6:1. S3.2: Add pullulan, sodium alginate and sodium carboxymethyl starch to deionized water at a ratio of 1.05g:1.1g:1g:125mL, and stir thoroughly until completely dissolved to obtain a composite matrix solution; S3.3: While stirring, add the above bacterial suspension to the above composite matrix solution, and then drop it into a 2wt% calcium chloride solution. After the addition is complete, continue stirring for 35 minutes, then filter to obtain bacterial gel microspheres. S3.4: The above-mentioned bacterial-containing gel microspheres were added to a 0.3wt% genipin aqueous solution, allowed to stand for cross-linking for 2 hours, filtered, washed once with deionized water, and then dried in a fluidized bed to obtain bacterial-loaded microspheres. The volume ratio of bacterial suspension, composite matrix solution, calcium chloride solution and genipin aqueous solution was 1:8:5:19. S4: Preparation of compound phosphorus and potassium microbial fertilizer The above-mentioned slow-release microcapsules, above-mentioned bacterial-carrying microspheres, above-mentioned sunflower disc extract, above-mentioned moringa leaf extract and humic acid were stirred and mixed evenly to obtain a compound phosphorus and potassium bacterial fertilizer. The raw material composition of the compound phosphorus and potassium bacterial fertilizer by mass percentage is: 50% slow-release microcapsules, 17.5% bacterial-carrying microspheres, 9% sunflower disc extract, 7% moringa leaf extract and 16.5% humic acid.

[0024] Example 3: A method for preparing a microbial compound phosphorus and potassium fertilizer that promotes nutrient absorption, such as... Figure 1 As shown, it includes the following steps: S1: Preparation of sunflower disc extract and moringa leaf extract S1.1: Crush the dried sunflower discs, pass them through a 60-mesh sieve, add them to distilled water at a ratio of 1g:25mL, heat and stir at 80℃ for 3 hours, then filter and centrifuge to collect the supernatant. Then add the precipitate to distilled water again at a ratio of 1g:15mL and repeat the extraction once. Combine the two supernatants, concentrate them by rotary evaporation to a solid content of 25%, and then freeze-dry to obtain sunflower disc extract. S1.2: Pulverize dried Moringa leaves, pass through an 80-mesh sieve, add to distilled water at a ratio of 1g:30mL, heat and stir at 65℃ for 2.5h, then filter, centrifuge, collect the supernatant, then add the precipitate to distilled water at a ratio of 1g:15mL, repeat the extraction once, combine the two supernatants, concentrate by rotary evaporation to a solid content of 25%, and then freeze-dry to obtain Moringa leaf extract; S2: Preparation of sustained-release microcapsules S2.1: Add konjac glucomannan to 95% ethanol solution at a ratio of 1g:10mL, stir for 20min, then filter, and then dry the filter residue at 60℃ for 2h to obtain purified konjac glucomannan. S2.2: Add the purified konjac glucomannan to deionized water at a ratio of 1g:95mL, heat and stir at 45℃ until completely dissolved, then cool to room temperature, and then add sodium periodate aqueous solution dropwise while stirring. After the addition is complete, stir and react in the dark for 6 hours, then add ethylene glycol, stir in the dark for 40 minutes, and terminate the reaction to obtain the reaction solution. The mass ratio of sodium periodate to purified konjac glucomannan is 1:2.9, the concentration of sodium periodate aqueous solution is 70g / L, and the molar ratio of ethylene glycol to sodium periodate is 1.6:1. S2.3: While stirring, add 3 times the volume of 95% ethanol solution to the above reaction solution, let it stand for 3 hours, then centrifuge to collect the precipitate, wash it twice with anhydrous ethanol and acetone respectively, and then vacuum dry, grind and pass it through an 80-mesh sieve to obtain oxidized konjac glucomannan. S2.4: Add the above oxidized konjac glucomannan and lignin to deionized water at a ratio of 3.2g:1g:85mL, heat and stir at 65℃ for 40min, then adjust the pH to 4.5 with a 1% citric acid aqueous solution, and then add urea and dipotassium hydrogen phosphate trihydrate while stirring. Continue to keep warm and stir for crosslinking for 3h. After cooling, collect the precipitate by centrifugation and vacuum dry to obtain sustained-release microcapsules, wherein the mass ratio of urea to lignin is 3.6:1 and the mass ratio of dipotassium hydrogen phosphate trihydrate to lignin is 1.8:1. S3: Preparation of bacterial-loaded microspheres S3.1: Add the compound bacterial agent to sterile physiological saline, vortex for 2 minutes, then vortex at 37℃ and 180 r / min for 3 hours to obtain a concentration of 10. 9 The bacterial suspension of CFU / mL was stored at 4°C for later use. The compound bacterial agent was composed of Bacillus subtilis, Azotobacter chrysophagus and Pseudomonas fluorescens in a mass ratio of 5:2.8:1. S3.2: Add pullulan, sodium alginate, and sodium carboxymethyl starch to deionized water at a ratio of 1.1g:1.2g:1g:130mL, and stir thoroughly until completely dissolved to obtain a composite matrix solution; S3.3: While stirring, add the above bacterial suspension to the above composite matrix solution, and then drop it into a 2wt% calcium chloride solution. After the addition is complete, continue stirring for 40 minutes, then filter to obtain bacterial gel microspheres. S3.4: The above-mentioned bacterial-containing gel microspheres were added to a 0.3wt% genipin aqueous solution, allowed to stand for cross-linking for 2.5 h, filtered, washed twice with deionized water, and then dried in a fluidized bed to obtain bacterial-loaded microspheres. The volume ratio of bacterial suspension, composite matrix solution, calcium chloride solution and genipin aqueous solution was 1:8.5:5.5:20. S4: Preparation of compound phosphorus and potassium microbial fertilizer The above-mentioned slow-release microcapsules, above-mentioned bacterial microspheres, above-mentioned sunflower disc extract, above-mentioned moringa leaf extract and humic acid were stirred and mixed evenly to obtain a compound phosphorus and potassium bacterial fertilizer. The raw material composition of the compound phosphorus and potassium bacterial fertilizer by mass percentage is: 55% slow-release microcapsules, 20% bacterial microspheres, 10% sunflower disc extract, 8% moringa leaf extract and 7% humic acid.

[0025] Comparative Example 1 differs from Example 1 in that step S2 is removed and the sustained-release microcapsules in step S4 are replaced with urea and dipotassium hydrogen phosphate trihydrate. The amounts of urea and dipotassium hydrogen phosphate trihydrate used are equal to the amounts of urea and dipotassium hydrogen phosphate trihydrate added in step S2.4 of Example 1.

[0026] Comparative Example 2 differs from Example 1 in that pullulan and sodium carboxymethyl starch in step S3.2 are replaced with an equal amount of sodium alginate.

[0027] Comparative Example 3 differs from Example 1 in that the Moringa leaf extract in step S4 is replaced with an equal amount of sunflower disc extract.

[0028] Comparative Example 4 differs from Example 1 in that the sunflower disc extract in step S4 is replaced with an equal amount of Moringa leaf extract.

[0029] Test example: Test 1: Take 10g of the sustained-release microcapsules prepared in Examples 1-3 in sequence and place them in phosphate buffer solutions with pH=4.5, 6.5 and 8.5 respectively. Incubate at 25℃ with shaking. Then take samples on days 1, 3, 7 and 14 respectively to determine the concentration of phosphorus and potassium in the solution and calculate the cumulative release rate over 14 days. Each treatment is repeated 3 times and the average value is taken. The results are shown in Table 1.

[0030] Table 1: Results of cumulative release rate tests for phosphorus and potassium

[0031] As shown in Table 1, the sustained-release microcapsules prepared in Examples 1-3 showed significantly higher release rates of phosphorus and potassium under acidic conditions than under neutral and alkaline conditions. This indicates that the sustained-release microcapsules are pH-responsive, and the acidic environment can accelerate nutrient release, which is consistent with the characteristics of organic acid secretion in the rhizosphere of crops.

[0032] Test 2: Potted Plant Experiment Experimental Methods: Corn was used as the test crop. Thirty-five potted plants were divided into seven groups: Example 1, Example 2, Example 3, Comparative Example 1, Comparative Example 3, Comparative Example 4, and a control group. Each group consisted of five pots, each containing 5 kg of air-dried soil (basal available phosphorus 8.5 mg / kg, available potassium 46.2 mg / kg, organic matter 12.6 g / kg, pH 7.2). One seedling was planted per pot. After fertilization, each group was planted. Following harvest, the aboveground dry weight of the plants, the cumulative phosphorus and potassium content, and the available phosphorus and potassium in the soil were measured. The average values ​​of the results are shown in Table 2.

[0033] Fertilization: The compound phosphorus and potassium bacterial fertilizer prepared by Examples 1-3, Comparative Example 1, and Comparative Example 3-4 was applied to each pot at a rate of 15g. No fertilizer was applied to the blank group. All fertilizers were applied as a single basal application before sowing. The fertilizer was thoroughly mixed with the potting soil, then filled into the pot, watered thoroughly, and planted the next day. No additional fertilizer or bacterial agent was applied during the entire growth period, and normal watering management was maintained.

[0034] Table 2: Results of Fertilizer Efficacy Test for Compound Phosphorus-Potassium Bacterial F

[0035] As shown in Table 2, when urea and dipotassium hydrogen phosphate trihydrate were directly added to Comparative Example 1, the resulting compound phosphorus and potassium microbial fertilizer resulted in lower aboveground dry weight of harvested corn, lower plant phosphorus accumulation, and lower plant potassium accumulation after application compared to Example 1. This indicates that the nutrient utilization rate of Example 1 was improved. Furthermore, the available phosphorus and potassium in the soil of Comparative Example 1 were also lower than those of Example 1, indicating that the fixation loss of phosphorus and potassium in the soil was reduced in Example 1. Therefore, it can be seen that selective oxidation of konjac glucomannan using sodium periodate to generate highly active aldehyde groups on the sugar chains yields oxidized konjac glucomannan. Then, oxidized konjac glucomannan and lignin are cross-linked under weakly acidic conditions to form a three-dimensional network cross-linked polymer skeleton. Urea and dipotassium hydrogen phosphate are encapsulated in the network channels or adsorbed on the skeleton during the cross-linking process, forming nutrient-loaded slow-release microcapsules. After the slow-release microcapsules are made into compound phosphorus and potassium bacterial fertilizer and applied, as the crop grows, the concentration of organic acids in the root exudates increases, and the release rate of nutrients from the slow-release microcapsules accelerates. This allows nutrients to be released gradually as the crop grows, significantly reducing the binding and precipitation of phosphorus and potassium with metal ions in the soil, which helps to improve nutrient absorption and utilization, and thus promotes nutrient absorption.

[0036] Furthermore, the aboveground dry weight, plant phosphorus accumulation, and plant potassium accumulation of Comparative Examples 3 and 4 were all lower than those of Example 1. This shows that combining sunflower disc extract and Moringa leaf extract can jointly improve the rhizosphere environment, which is beneficial to crop root absorption. At the same time, it can promote more developed crop roots, larger absorption area, and higher absorption efficiency, thereby synergistically improving the crop's nutrient absorption capacity.

[0037] Test 3: 0.1g of the bacterial-loaded microspheres prepared in Examples 1-3 and Comparative Example 2 were placed in 1mL of sterile physiological saline, ground and crushed, and then the number of countable viable bacteria in the bacterial-loaded microspheres was determined by plate count method. The effective loading rate was calculated using the following formula: Effective loading rate = number of viable bacteria in microspheres / number of viable bacteria in the initial bacterial suspension × 100%. The test was repeated 3 times and the average value was taken. The results are shown in Table 3.

[0038] Table 3: Results of Effective Loading Rate Test of Bacterial-Loaded Microspheres

[0039] As shown in Table 3, the effective loading rate of the bacterial-loaded microspheres prepared in Comparative Example 2 without the addition of pullulan and sodium carboxymethyl starch was significantly lower than that in Example 1. This indicates that by first fully dissolving pullulan, sodium alginate, and sodium carboxymethyl starch in water to form a composite matrix solution, then mixing it with the bacterial suspension, and then adding it dropwise into a calcium chloride solution, the carboxyl groups in sodium alginate undergo a rapid ionic cross-linking reaction with calcium ions, anchoring pullulan and sodium carboxymethyl starch in the sodium alginate gel network, and simultaneously physically embedding the bacteria in situ inside the gel channels, forming bacterial-loaded gel microspheres with a semi-interpenetrating polymer network, and then adding the bacterial-loaded gel microspheres to a genipin aqueous solution to undergo cross-linking, thereby forming chemical covalent bonds inside the gel, further strengthening the gel network structure, preventing bacterial leakage, and obtaining bacterial-loaded microspheres, the number of countable viable bacteria can be significantly increased, thus significantly improving the effective loading rate of the bacterial-loaded microspheres for microbial cells.

[0040] It should be understood that those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims. Parts not described in detail in this specification are prior art known to those skilled in the art.

Claims

1. A method for preparing a microbial compound phosphorus and potassium fertilizer that promotes nutrient absorption, characterized in that, Includes the following steps: S1: Preparation of sunflower disc extract and moringa leaf extract Extracts were extracted from dried sunflower heads and dried moringa leaves to obtain sunflower head extract and moringa leaf extract, respectively. S2: Preparation of sustained-release microcapsules S2.1: Add konjac glucomannan to 95% ethanol solution at a ratio of 1g:(8-10)mL, stir for 10-20min, then filter, and then dry the filter residue at 60℃ for 1-2h to obtain purified konjac glucomannan. S2.2: Add the purified konjac glucomannan above to deionized water at a ratio of 1g:(85-95)mL, heat and stir at 40-45℃ until completely dissolved, then cool to room temperature, and then add sodium periodate aqueous solution dropwise while stirring. After the addition is complete, stir and react in the dark for 4-6 hours, then add ethylene glycol, stir in the dark for 30-40 minutes, terminate the reaction, and obtain the reaction solution; S2.3: While stirring, add 3 times the volume of 95% ethanol solution to the above reaction solution, let it stand for 2-3 hours, then centrifuge to collect the precipitate, wash it twice with anhydrous ethanol and acetone respectively, and then vacuum dry, grind and pass it through an 80-mesh sieve to obtain oxidized konjac glucomannan. S2.4: Add the above oxidized konjac glucomannan and lignin to deionized water at a ratio of (2.8-3.2) g: 1 g: (75-85) mL, heat and stir at 60-65℃ for 30-40 min, then adjust the pH to 4-4.5 with a 1% citric acid aqueous solution, and then add urea and dipotassium hydrogen phosphate trihydrate while stirring. Continue to keep warm and stir for crosslinking for 2-3 h. After cooling, centrifuge to collect the precipitate and vacuum dry to obtain sustained-release microcapsules. S3: Preparation of bacterial-loaded microspheres The compound bacterial agent was activated to prepare a bacterial suspension. Pullulan, sodium alginate and sodium carboxymethyl starch were dissolved to prepare a composite matrix solution. The bacterial suspension and the composite matrix solution were then stirred and mixed, and then added dropwise to calcium chloride solution to prepare bacterial-containing gel microspheres. Finally, the bacterial-containing gel microspheres were added to genipin aqueous solution for cross-linking to obtain bacterial-loaded microspheres. S4: Preparation of compound phosphorus and potassium microbial fertilizer The above-mentioned slow-release microcapsules, above-mentioned bacterial microspheres, above-mentioned sunflower disc extract, above-mentioned Moringa leaf extract and humic acid were stirred and mixed evenly to obtain a compound phosphorus and potassium bacterial fertilizer.

2. The method for preparing a microbial compound phosphorus and potassium fertilizer that promotes nutrient absorption according to claim 1, characterized in that, The mass ratio of sodium periodate to purified konjac glucomannan is 1:(2.7-2.9).

3. The method for preparing a microbial compound phosphorus and potassium fertilizer that promotes nutrient absorption according to claim 1, characterized in that, The concentration of the sodium periodate aqueous solution is 70 g / L, and the molar ratio of ethylene glycol to sodium periodate is (1.5-1.6):

1.

4. The method for preparing a microbial compound phosphorus and potassium fertilizer that promotes nutrient absorption according to claim 1, characterized in that, The mass ratio of urea to lignin is (3.5-3.6):1, and the mass ratio of dipotassium hydrogen phosphate trihydrate to lignin is (1.7-1.8):

1.

5. The method for preparing a microbial compound phosphorus and potassium fertilizer that promotes nutrient absorption according to claim 1, characterized in that, By weight percentage, the raw material composition of the compound phosphorus and potassium microbial fertilizer is: 45-55% slow-release microcapsules, 15-20% bacterial microspheres, 8-10% sunflower disc extract, 6-8% moringa leaf extract, and the remainder is humic acid.

6. The method for preparing a microbial compound phosphorus and potassium fertilizer that promotes nutrient absorption according to claim 1, characterized in that, S1 includes the following steps: S1.1: Crush the dried sunflower discs, pass them through a 40-60 mesh sieve, add them to distilled water at a ratio of 1g:(15-25)mL, heat and stir at 70-80℃ for 2-3 hours, then filter and centrifuge to collect the supernatant. Then add the precipitate to distilled water again at a ratio of 1g:(10-15)mL, repeat the extraction once, combine the two supernatants, concentrate them by rotary evaporation to a solid content of 20-25%, and then freeze-dry to obtain sunflower disc extract; S1.2: Crush dried Moringa leaves, pass them through a 60-80 mesh sieve, add them to distilled water at a ratio of 1g:(20-30)mL, heat and stir at 60-65℃ for 1.5-2.5h, then filter and centrifuge to collect the supernatant. Then add the precipitate to distilled water at a ratio of 1g:(10-15)mL and repeat the extraction once. Combine the two supernatants, concentrate them by rotary evaporation to a solid content of 20-25%, and then freeze-dry to obtain Moringa leaf extract.

7. The method for preparing a microbial compound phosphorus and potassium fertilizer that promotes nutrient absorption according to claim 1, characterized in that, S3 includes the following steps: S3.1: Add the compound bacterial agent to sterile physiological saline, vortex for 1-2 minutes, then vortex at 37℃ and 180 r / min for 2-3 hours to obtain a concentration of 10. 9 The bacterial suspension of CFU / mL was refrigerated at 4°C for later use. S3.2: Add pullulan, sodium alginate and sodium carboxymethyl starch to deionized water at a ratio of (1-1.1)g:(1-1.2)g:1g:(120-130)mL, and stir thoroughly until completely dissolved to obtain a composite matrix solution; S3.3: While stirring, add the above bacterial suspension to the above composite matrix solution, and then drop it into a 2wt% calcium chloride solution. After the addition is complete, continue stirring for 30-40 minutes, then filter to obtain bacterial gel microspheres. S3.4: Add the above-mentioned bacterial-containing gel microspheres to a 0.3wt% genipin aqueous solution, allow to stand for cross-linking for 1.5-2.5 hours, filter, wash with deionized water 1-2 times, and dry to obtain bacterial-loaded microspheres.

8. The method for preparing a microbial compound phosphorus and potassium fertilizer that promotes nutrient absorption according to claim 7, characterized in that, The compound microbial agent is composed of Bacillus subtilis, Azotobacter chrysophyte, and Pseudomonas fluorescens in a mass ratio of (3-5):(2.4-2.8):

1.

9. The method for preparing a microbial compound phosphorus and potassium fertilizer that promotes nutrient absorption according to claim 7, characterized in that, The volume ratio of bacterial suspension, composite matrix solution, calcium chloride solution and genipin aqueous solution is 1:(7.5-8.5):(4.5-5.5):(18-20).

10. A microbial compound phosphorus and potassium fertilizer that promotes nutrient absorption, characterized in that, It is prepared by the method for preparing a microbial compound phosphorus and potassium fertilizer that promotes nutrient absorption as described in any one of claims 1-9.

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