Water-soluble microbial compound fertilizer and preparation method thereof

Abstract

This invention provides a water-soluble microbial compound fertilizer and its preparation method, belonging to the field of fertilizer technology. The water-soluble microbial compound fertilizer includes compound fertilizer granules. The compound fertilizer granules are provided with a slow-dissolving core, a quick-dissolving layer, a microbial coating layer, and a protective film from the inside out. The mass ratio of the slow-dissolving core, the quick-dissolving layer, the microbial coating layer, and the protective film is (55-65):(15-25):(3-8):(2-5). The protective film is used to awaken the dormant microorganisms in the microbial coating layer after dissolution. The quick-dissolving layer is used to induce the accumulation of intracellular compatible solutes by microorganisms during dissolution, so as to build the resistance of microorganisms to changes in osmotic pressure. The slow-dissolving core is used to gradually release nutrients during dissolution, ensuring a steady increase in osmotic pressure. This allows the microorganisms to undergo the process of activation, adaptation, and steady-state osmotic pressure changes in sequence, avoiding dehydration, rupture, or even death of a large number of microbial cells.

Description

Technical Field

[0001] This invention relates to the field of fertilizer technology, and in particular to a water-soluble microbial compound fertilizer and its preparation method. Background Technology

[0002] Water-soluble fertilizers have advantages such as high nutrient content, good solubility, rapid absorption, and convenient application, and are increasingly widely used in integrated water and fertilizer technologies such as drip irrigation and sprinkler irrigation. Combining functional microorganisms with water-soluble fertilizers to achieve "water, fertilizer, and microorganism integration" is an important way to improve fertilizer utilization efficiency, increase crop yield, and reduce chemical fertilizer usage.

[0003] However, water-soluble microbial compound fertilizers face a core technical challenge in application—osmotic pressure shock. Water-soluble fertilizers contain high concentrations of readily available nutrients such as nitrogen, phosphorus, and potassium. After dissolving, they rapidly create a high osmotic pressure environment, causing a fatal osmotic pressure shock to the functional microorganisms. This leads to the dehydration, rupture, and even death of a large number of microbial cells, thereby reducing the actual efficacy of the water-soluble microbial compound fertilizer. Summary of the Invention

[0004] In view of this, it is necessary to provide a water-soluble microbial compound fertilizer to alleviate the impact of osmotic pressure on microorganisms and improve the actual efficacy of water-soluble microbial compound fertilizer. It is also necessary to provide a method for preparing water-soluble microbial compound fertilizer.

[0005] In a first aspect, the present invention provides a water-soluble microbial compound fertilizer, comprising compound fertilizer granules, wherein the compound fertilizer granules are provided with a slow-dissolving inner core, a quick-dissolving layer, a microbial coating layer and a protective film from the inside out, and the mass ratio of the slow-dissolving inner core, the quick-dissolving layer, the microbial coating layer and the protective film is (55-65):(15-25):(3-8):(2-5). The protective film is used to awaken the dormant microorganisms in the microbial coating layer after dissolution. The quick-dissolving layer is used to induce the accumulation of intracellular compatible solutes by microorganisms during dissolution, so as to build the resistance of microorganisms to changes in osmotic pressure in a timely manner. The slow-dissolving inner core is used to gradually release nutrients during dissolution to ensure a steady increase in osmotic pressure.

[0006] Preferably, the microbial coating layer comprises a compound bacterial powder, trehalose, betaine, proline, potassium humate, polyglutamic acid, and glycerol, and the mass ratio of the compound bacterial powder, trehalose, betaine, proline, potassium humate, polyglutamic acid, and glycerol is 100:(5-15):(3-10):(2-6):(10-25):(5-15):(2-8).

[0007] Preferably, both the slow-dissolving core and the quick-dissolving layer comprise the following raw materials in parts by weight: 32-38 parts urea, 24-28 parts potassium dihydrogen phosphate, 18-24 parts potassium nitrate, 10-14 parts potassium humate, 2-3 parts alginate oligosaccharide, 2-3 parts betaine, and 1-2 parts choline chloride; in addition, the slow-dissolving core also comprises 7-9 parts hydroxypropyl methylcellulose.

[0008] Preferably, the protective film comprises polyvinyl alcohol and hydroxypropyl methylcellulose, and the mass ratio of the polyvinyl alcohol to the hydroxypropyl methylcellulose is (1-3):1.

[0009] On the other hand, the present invention provides a method for preparing a water-soluble microbial compound fertilizer, comprising the following steps: Step 1: Mix urea, potassium dihydrogen phosphate, potassium nitrate, potassium humate, alginate oligosaccharide, betaine, and choline chloride according to the specified ratio and then pulverize them to obtain the first mixture. Mix urea, potassium dihydrogen phosphate, potassium nitrate, potassium humate, alginate oligosaccharide, betaine, choline chloride, and hydroxypropyl methylcellulose according to the specified ratio and then pulverize them to obtain the second mixture. Step 2: Granulate the second mixture to obtain a slow-dissolving inner core; Step 3: Coat the first mixture onto the slow-dissolving core to form a slow-dissolving core containing a fast-dissolving layer; Step 4: Mix the compound bacterial powder with the first protective liquid to maintain the activity of the microorganisms in the compound bacterial powder during storage, and obtain premixed bacterial powder; Step 5: Spray the premixed bacterial powder and the second protective liquid onto the surface of the slow-dissolving inner core containing the fast-dissolving layer, which is in a fluidized state, to form a slow-dissolving inner core containing a microbial coating layer. Step 6: The film-forming liquid is sprayed onto the surface of the slow-dissolving inner core containing the microbial coating layer, which is in a fluidized state, and then dried at low temperature to form a protective film, thereby obtaining compound fertilizer granules. The film-forming liquid is an aqueous solution of polyvinyl alcohol and hydroxypropyl methylcellulose. The mass ratio of the slow-dissolving inner core, the quick-dissolving layer, the microbial coating layer and the protective film is (55-65):(15-25):(3-8):(2-5).

[0010] Preferably, in step 1, the mass ratio of urea, potassium dihydrogen phosphate, potassium nitrate, potassium humate, alginate oligosaccharide, betaine, and choline chloride in the first mixture is (32-38):(24-28):(18-24):(10-14):(2-3):(1-2), and the mass ratio of urea, potassium dihydrogen phosphate, potassium nitrate, potassium humate, alginate oligosaccharide, betaine, choline chloride, and hydroxypropyl methylcellulose in the second mixture is (32-38):(24-28):(18-24):(10-14):(2-3):(1-2):(7-9).

[0011] Preferably, step 3 specifically involves: feeding the slow-dissolving core into a rotary drum granulator and introducing steam to wet the surface of the slow-dissolving core particles, then sprinkling in the first mixture to utilize the wetting effect of the steam to roll the first mixture onto the surface of the slow-dissolving core, forming a slow-dissolving core containing a quick-dissolving layer, wherein the mass ratio of the slow-dissolving core to the first mixture is (55-65):(15-25).

[0012] Preferably, step 4 specifically includes: S41: Dissolve trehalose, betaine and proline in sterile water to prepare a first protective solution with a mass concentration of 8-10%, and adjust the pH to 6.8-7.2, wherein the mass ratio of trehalose, betaine and proline is (3-5):(2-4):(1-2). S42: A compound bacterial powder is obtained by mixing Azotobacter chrysophagus, Bacillus megaterium, Bacillus mucilaginosus and Bacillus subtilis in a mass ratio of 1:1:1:(1-2). S43: Mix the compound bacterial powder with the first protective liquid at a mass ratio of 1:(2-5) to obtain premixed bacterial powder.

[0013] Preferably, step 5 specifically comprises: S51: Dissolve potassium humate, polyglutamic acid and glycerol in sterile water to prepare a second protective solution with a mass concentration of 8-10%, and adjust the pH to 6.8-7.2, wherein the mass ratio of potassium humate, polyglutamic acid and glycerol is (4-6):(2-3):(1-2). S52: The slow-dissolving core containing the quick-dissolving layer is placed in a fluidized bed coating machine, and the premixed bacterial powder and the second protective liquid are alternately sprayed onto the surface of the slow-dissolving core containing the quick-dissolving layer. The slow-dissolving core containing a microbial coating layer is formed in a fluidized state at 35-45°C. The amount of the second protective liquid sprayed is 4%-10% of the mass of the slow-dissolving core containing the quick-dissolving layer, and the amount of the premixed bacterial powder sprayed is 3%-8% of the mass of the slow-dissolving core containing the quick-dissolving layer.

[0014] Preferably, step 6 specifically includes: S61: Polyvinyl alcohol and hydroxypropyl methylcellulose are dissolved in deionized water to prepare a film-forming solution with a mass concentration of 1%-3%, wherein the mass ratio of polyvinyl alcohol to hydroxypropyl methylcellulose is (1-3):1. S62: After the premixed bacterial powder and the second protective liquid are sprayed, the film-forming liquid is continued to be sprayed onto the surface of the slow-dissolving core containing the microbial coating layer in the fluidized bed coating machine. The amount of film-forming liquid sprayed is 2%-5% of the mass of the slow-dissolving core containing the fast-dissolving layer. S63: After completing S62, the granules are dried at low temperature until the moisture content is less than 5% to form a protective film, and then compound fertilizer granules are obtained.

[0015] Therefore, the water-soluble microbial compound fertilizer and its preparation method provided by the present invention include compound fertilizer granules. The compound fertilizer granules are provided with a slow-dissolving core, a quick-dissolving layer, a microbial coating layer and a protective film from the inside out. The mass ratio of the slow-dissolving core, the quick-dissolving layer, the microbial coating layer and the protective film is (55-65):(15-25):(3-8):(2-5). The protective film is used to awaken the dormant microorganisms in the microbial coating layer after it is dissolved. The quick-dissolving layer is used to induce the accumulation of intracellular compatible solutes by microorganisms during dissolution, so as to build the resistance of microorganisms to changes in osmotic pressure in a timely manner. The slow-dissolving core is used to gradually release nutrients during dissolution to ensure a steady increase in osmotic pressure.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: When the compound fertilizer granules provided by the present invention come into contact with water, the protective film first dissolves rapidly, exposing the dormant microorganisms in the microbial coating layer to a low osmotic pressure environment. The microorganisms absorb water and revive, initiating metabolic activities. At the same time, the trehalose, betaine, and proline in the microbial coating layer also dissolve, forming a microenvironment rich in protective substances around the microorganisms, preparing physiologically and materially for subsequent changes in osmotic pressure. Subsequently, the quick-dissolving layer dissolves, releasing some readily available nutrients, causing a gentle increase in the osmotic pressure around the microorganisms. This change in osmotic pressure induces the microorganisms to actively take up and accumulate the surrounding compatible solutes betaine and proline into their cells. To balance the osmotic pressure inside and outside the cell, the microorganisms are able to build up their resistance to changes in osmotic pressure in a timely manner. This initial protective mechanism enables the microorganisms to effectively resist the subsequent continuous increase in osmotic pressure, avoiding cell membrane rupture or functional damage caused by sudden changes in osmotic pressure. Finally, the slow-dissolving core gradually releases the main nutrients, achieving a steady increase in osmotic pressure. This process matches the microorganisms' adaptation speed to osmotic pressure, allowing the microorganisms to successively experience the process of activation, adaptation, and steady-state osmotic pressure changes. This effectively mitigates the high osmotic pressure shock that may occur when the fast-acting nutrients dissolve instantly, preventing a large number of microbial cells from dehydrating, rupturing, or even dying, and significantly improving the actual efficacy of water-soluble microbial compound fertilizer. Detailed Implementation

[0017] To further understand the present invention, preferred embodiments of the present invention are described below in conjunction with examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, and not for limiting the scope of the claims of the present invention.

[0018] In a first aspect, the present invention provides a water-soluble microbial compound fertilizer, comprising compound fertilizer granules, wherein the compound fertilizer granules are provided with a slow-dissolving inner core, a quick-dissolving layer, a microbial coating layer and a protective film from the inside out, and the mass ratio of the slow-dissolving inner core, the quick-dissolving layer, the microbial coating layer and the protective film is (55-65):(15-25):(3-8):(2-5). The protective film is used to awaken the dormant microorganisms in the microbial coating layer after dissolution. The quick-dissolving layer is used to induce the accumulation of intracellular compatible solutes by microorganisms during dissolution, so as to build the resistance of microorganisms to changes in osmotic pressure in a timely manner. The slow-dissolving inner core is used to gradually release nutrients during dissolution to ensure a steady increase in osmotic pressure.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows: When the compound fertilizer granules provided by the present invention come into contact with water, the protective film first dissolves rapidly, exposing the dormant microorganisms in the microbial coating layer to a low osmotic pressure environment. The microorganisms absorb water and revive, initiating metabolic activities. At the same time, the trehalose, betaine, and proline in the microbial coating layer also dissolve, forming a microenvironment rich in protective substances around the microorganisms, preparing physiologically and materially for subsequent changes in osmotic pressure. Subsequently, the quick-dissolving layer dissolves, releasing some readily available nutrients, causing a gentle increase in the osmotic pressure around the microorganisms. This change in osmotic pressure induces the microorganisms to actively take up and accumulate the surrounding compatible solutes betaine and proline into their cells. To balance the osmotic pressure inside and outside the cell, the microorganisms are able to build up their resistance to changes in osmotic pressure in a timely manner. This initial protective mechanism enables the microorganisms to effectively resist the subsequent continuous increase in osmotic pressure, avoiding cell membrane rupture or functional damage caused by sudden changes in osmotic pressure. Finally, the slow-dissolving core gradually releases the main nutrients, achieving a steady increase in osmotic pressure. This process matches the microorganisms' adaptation speed to osmotic pressure, allowing the microorganisms to successively experience the process of activation, adaptation, and steady-state osmotic pressure changes. This effectively mitigates the high osmotic pressure shock that may occur when the fast-acting nutrients dissolve instantly, preventing a large number of microbial cells from dehydrating, rupturing, or even dying, and significantly improving the actual efficacy of water-soluble microbial compound fertilizer.

[0020] Furthermore, the microbial coating layer comprises a compound bacterial powder, trehalose, betaine, proline, potassium humate, polyglutamic acid, and glycerol, and the mass ratio of the compound bacterial powder, trehalose, betaine, proline, potassium humate, polyglutamic acid, and glycerol is 100:(5-15):(3-10):(2-6):(10-25):(5-15):(2-8). Trehalose, betaine, and proline can serve as the first protective component to ensure the stability of the microbial cells during storage, while potassium humate, polyglutamic acid, and glycerol can... As a second protective component, the microbial coating layer buffers osmotic pressure shocks during dissolution. Specifically, betaine and proline act as protectants to stabilize the cell structure during storage and are actively taken up by the microorganisms as compatible solutes during dissolution for intracellular osmotic pressure regulation. Potassium humate can adsorb salt ions and reduce the osmotic pressure of the microenvironment, while polyglutamic acid can form a hydration protective layer. The two work together to construct a low-salt microenvironment, effectively blocking the impact of high external osmotic pressure. Glycerol enters the cell and directly balances the intracellular osmotic pressure, further enhancing the microorganisms' resistance to stress.

[0021] Furthermore, both the slow-dissolving core and the quick-dissolving layer comprise the following raw materials in parts by weight: 32-38 parts urea, 24-28 parts potassium dihydrogen phosphate, 18-24 parts potassium nitrate, 10-14 parts potassium humate, 2-3 parts alginate oligosaccharide, 2-3 parts betaine, and 1-2 parts choline chloride. Additionally, the slow-dissolving core also comprises 7-9 parts hydroxypropyl methylcellulose. The synergistic effect of potassium humate, betaine, and choline chloride effectively reduces the initial osmotic pressure peak during fertilizer dissolution, providing initial osmotic pressure protection for microorganisms. The hydroxypropyl methylcellulose in the slow-dissolving core, encapsulated by various raw materials, forms a gel barrier upon contact with water, delaying water penetration and significantly slowing the dissolution rate of the slow-dissolving core. This allows for the gradual and stable release of the main nutrients, achieving a stable increase in osmotic pressure during fertilizer dissolution, matching the osmotic pressure adaptability of microorganisms.

[0022] Furthermore, the protective membrane comprises polyvinyl alcohol and hydroxypropyl methylcellulose, and the mass ratio of polyvinyl alcohol to hydroxypropyl methylcellulose is (1-3):1. Polyvinyl alcohol can impart good flexibility and mechanical strength to the protective membrane, and can form effective physical protection for the microorganisms in the microbial coating layer during storage, preventing the microbial powder from falling off. Since the hydroxypropyl methylcellulose in the protective membrane is directly exposed to water, it will swell rapidly after absorbing water, increasing the internal stress of the membrane layer, which leads to rapid rupture and dissolution of the membrane layer. This allows the dormant microorganisms in the microbial coating layer to be exposed to a low osmotic pressure environment in a timely manner, thereby absorbing water, reviving, and initiating metabolic activities.

[0023] On the other hand, the present invention provides a method for preparing a water-soluble microbial compound fertilizer, comprising the following steps: Step 1: Mix urea, potassium dihydrogen phosphate, potassium nitrate, potassium humate, alginate oligosaccharide, betaine, and choline chloride according to the specified ratio and then pulverize them to obtain the first mixture. Mix urea, potassium dihydrogen phosphate, potassium nitrate, potassium humate, alginate oligosaccharide, betaine, choline chloride, and hydroxypropyl methylcellulose according to the specified ratio and then pulverize them to obtain the second mixture. Step 2: Granulate the second mixture to obtain a slow-dissolving core. Specifically, the granulation process can be carried out by extrusion granulation or spray granulation in the prior art. Step 3: Coat the first mixture onto the slow-dissolving core to form a slow-dissolving core containing a fast-dissolving layer; Step 4: Mix the compound bacterial powder with the first protective liquid to maintain the activity of the microorganisms in the compound bacterial powder during storage, and obtain premixed bacterial powder; Step 5: Spray the premixed bacterial powder and the second protective liquid onto the surface of the slow-dissolving inner core containing the fast-dissolving layer, which is in a fluidized state, to form a slow-dissolving inner core containing a microbial coating layer. Step 6: The film-forming liquid is sprayed onto the surface of the slow-dissolving inner core containing the microbial coating layer, which is in a fluidized state, and then dried at low temperature to form a protective film, thereby obtaining compound fertilizer granules. The film-forming liquid is an aqueous solution of polyvinyl alcohol and hydroxypropyl methylcellulose. The mass ratio of the slow-dissolving inner core, the quick-dissolving layer, the microbial coating layer and the protective film is (55-65):(15-25):(3-8):(2-5).

[0024] Furthermore, in step 1, the mass ratio of urea, potassium dihydrogen phosphate, potassium nitrate, potassium humate, alginate oligosaccharide, betaine, and choline chloride in the first mixture is (32-38):(24-28):(18-24):(10-14):(2-3):(1-2), and the mass ratio of urea, potassium dihydrogen phosphate, potassium nitrate, potassium humate, alginate oligosaccharide, betaine, choline chloride, and hydroxypropyl methylcellulose in the second mixture is (32-38):(24-28):(18-24):(10-14):(2-3):(1-2):(7-9).

[0025] Further, step 3 specifically involves: feeding the slow-dissolving core into a rotary drum granulator, and introducing steam as a binding medium to wet the surface of the slow-dissolving core particles. Then, the first mixture is sprinkled in, so that the first mixture is rolled onto the surface of the slow-dissolving core using the wetting effect of steam. At the same time, the particles are rolled to ensure the uniformity of the thickness of the quick-dissolving layer, so that the dissolution rate of each part of the quick-dissolving layer on each particle is consistent, forming a slow-dissolving core containing a quick-dissolving layer. The mass ratio of the slow-dissolving core to the first mixture is (55-65):(15-25).

[0026] Furthermore, step 4 specifically involves: S41: Dissolve trehalose, betaine and proline in sterile water to prepare a first protective solution with a mass concentration of 8-10%, and adjust the pH to 6.8-7.2, wherein the mass ratio of trehalose, betaine and proline is (3-5):(2-4):(1-2). S42: A compound bacterial powder is obtained by mixing Azotobacter chrysophagus, Bacillus megaterium, Bacillus mucilaginosus and Bacillus subtilis in a mass ratio of 1:1:1:(1-2). S43: Mix the compound bacterial powder with the first protective liquid at a mass ratio of 1:(2-5) to obtain premixed bacterial powder.

[0027] Furthermore, step 5 specifically includes: S51: Dissolve potassium humate, polyglutamic acid and glycerol in sterile water to prepare a second protective solution with a mass concentration of 8-10%, and adjust the pH to 6.8-7.2, wherein the mass ratio of potassium humate, polyglutamic acid and glycerol is (4-6):(2-3):(1-2). S52: The slow-dissolving core containing the quick-dissolving layer is placed in a fluidized bed coating machine. The premixed bacterial powder and the second protective liquid are alternately sprayed onto the surface of the slow-dissolving core containing the quick-dissolving layer. Specifically, alternating spraying is used, where the second protective liquid is sprayed first to wet the surface, and then the premixed bacterial powder is sprayed, thereby reducing the premixed bacterial powder from flying away. A slow-dissolving core containing a microbial coating layer is formed in a fluidized state at 35-45°C. The amount of the second protective liquid sprayed is 4%-10% of the mass of the slow-dissolving core containing the quick-dissolving layer, and the amount of the premixed bacterial powder sprayed is 3%-8% of the mass of the slow-dissolving core containing the quick-dissolving layer.

[0028] Furthermore, step 6 specifically includes: S61: Polyvinyl alcohol and hydroxypropyl methylcellulose are dissolved in deionized water to prepare a film-forming solution with a mass concentration of 1%-3%, wherein the mass ratio of polyvinyl alcohol to hydroxypropyl methylcellulose is (1-3):1. S62: After the premixed bacterial powder and the second protective liquid are sprayed, the film-forming liquid is continued to be sprayed onto the surface of the slow-dissolving core containing the microbial coating layer in the fluidized bed coating machine. The amount of film-forming liquid sprayed is 2%-5% of the mass of the slow-dissolving core containing the fast-dissolving layer. S63: After completing S62, the granules are dried at low temperature until the moisture content is less than 5% to form a protective film, and then compound fertilizer granules are obtained. Specifically, the low-temperature drying can be carried out using a fluidized bed dryer with an inlet air temperature of 40-60℃ to ensure drying efficiency while avoiding thermal damage to microorganisms caused by high temperature. The outlet air temperature does not exceed 45℃ to ensure that the microorganisms are within a safe temperature range. Fluidized drying is carried out for 15-30 minutes.

[0029] To further understand the present invention, the following examples and comparative examples of the present invention demonstrate water-soluble microbial compound fertilizer and its preparation method.

[0030] Example 1 Step 1: Weigh the raw materials according to the following mass ratio. First mixture: 35 parts urea, 26 parts potassium dihydrogen phosphate, 21 parts potassium nitrate, 12 parts potassium humate, 2.5 parts alginate oligosaccharide, 2.5 parts betaine, and 1.5 parts choline chloride. Mix the above ingredients evenly and pulverize to 300 mesh. Second mixture: 35 parts urea, 26 parts potassium dihydrogen phosphate, 21 parts potassium nitrate, 12 parts potassium humate, 2.5 parts alginate oligosaccharide, 2.5 parts betaine, 1.5 parts choline chloride, and 8 parts hydroxypropyl methylcellulose. Mix the above raw materials evenly and pulverize them to 300 mesh. Step 2: The second mixture is fed into an extrusion granulator. A die with an aperture of 0.9-1.5 mm is selected. Extrusion granulation is carried out at room temperature, and the extrusion pressure is controlled at 5-15 MPa. After the second mixture passes through the die, it forms strip-shaped particles. These are then cut into short columnar particles with a length of 2-4 mm by a cutter. The short columnar particles are fed into a fluidized bed dryer. The inlet air temperature is controlled at 60-80℃, and the outlet air temperature is controlled at 45-55℃. Fluidized drying is carried out for 15-30 minutes until the particle moisture content is less than 3%. The dried particles are then graded and screened by a double-layer vibrating screen: the upper screen has an aperture of 1.6 mm, and the lower screen has an aperture of 0.8 mm. Particles with a particle size between 0.8-1.6 mm are selected as the slow-dissolving core. Step 3: Put the slow-dissolving core into the rotary drum granulator, adjust the speed to 18 r / min, introduce saturated steam to wet the surface of the granules, and then evenly sprinkle the first mixture. Use the wetting effect of the steam to roll the first mixture onto the surface of the slow-dissolving core, and at the same time roll the granules into rounds. The mass ratio of the slow-dissolving core to the first mixture is 60:20. After drying, a slow-dissolving core containing a fast-dissolving layer is obtained. Step 4: S41: Dissolve trehalose, betaine, and proline in sterile water at a mass ratio of 4:3:1 to prepare a first protective solution with a mass concentration of 9%, and adjust the pH to 7.0. S42: Mix commercially available azotobacter chrysophagus powder, Bacillus megaterium powder, Bacillus mucilaginosus powder, and Bacillus subtilis powder in a mass ratio of 1:1:1:1.2 to obtain a compound bacterial powder with a total viable count greater than 2.9 × 10⁻⁶. 9 CFU / g; S43: Mix the compound bacterial powder and the first protective liquid at a mass ratio of 1:3 and stir evenly to obtain the premixed bacterial powder; Step 5: S51: Dissolve potassium humate, polyglutamic acid, and glycerol in sterile water at a mass ratio of 5:4:1 to prepare a second protective solution with a mass concentration of 9%, and adjust the pH to 7.0. S52: Place the slow-dissolving core containing the quick-dissolving layer in a fluidized bed coating machine, set the inlet air temperature to 40℃, the outlet air temperature to 32℃, and the atomization pressure to 0.25MPa, and adopt an alternating spraying method: first spray the second protective liquid to wet the surface, then spray the premixed bacterial powder, and repeat the cycle; the amount of the second protective liquid sprayed is 6% of the mass of the slow-dissolving core containing the quick-dissolving layer, and the amount of the premixed bacterial powder sprayed is 5% of the mass of the slow-dissolving core containing the quick-dissolving layer, forming a slow-dissolving core containing a microbial coating layer under fluidized conditions at 40℃; Step 6: S61: Dissolve polyvinyl alcohol and hydroxypropyl methylcellulose in deionized water at a mass ratio of 2:1 to prepare a film-forming solution with a mass concentration of 2%. S62: After step 5 is completed, continue to spray the film-forming liquid in the fluidized bed coating machine. The amount of spraying is 3% of the mass of the slow-dissolving core containing the fast-dissolving layer.

[0031] S63: Place the coated granules in a fluidized bed dryer with an inlet air temperature of 55℃ and an outlet air temperature of ≤45℃. Fluidize and dry for 20 minutes until the moisture content is ≤5% to obtain compound fertilizer granules. The mass ratio of the slow-dissolving inner core, the quick-dissolving layer, the microbial coating layer, and the protective film in the obtained compound fertilizer granules is 60:20:5:3.

[0032] Example 2 Compared with Example 1, the difference in this example is that: in step 1, the ratio of the first mixture and the second mixture is 32 parts urea, 24 parts potassium dihydrogen phosphate, 18 parts potassium nitrate, 10 parts potassium humate, 2 parts alginate oligosaccharide, 2 parts betaine, and 1 part choline chloride. The second mixture is additionally supplemented with 9 parts hydroxypropyl methylcellulose. In step 2, the particle size of the slow-dissolving core is 1.0-1.4 mm; In step 3, the mass ratio of the slow-dissolving inner core to the first mixture is 55:15; In S41, the concentration of the first protective solution is changed to 8%, and the mass ratio of trehalose, betaine, and proline is 3:2:1. The mass ratio of compound bacterial powder to the first protective liquid in S43 is 1:4; The concentration of the second protective solution in S51 is 10%, and the mass ratio of potassium humate, polyglutamic acid, and glycerol is 4:2:1. In S52, the amount of the second protective liquid sprayed is 8%, and the amount of the premixed bacterial powder sprayed is 6%. The concentration of the film-forming solution in S61 is 1.5%, and the mass ratio of polyvinyl alcohol to hydroxypropyl methylcellulose is 1:1. The film-forming liquid spraying amount in S62 is 4%; In the obtained compound fertilizer granules, the mass ratio of the slow-dissolving inner core, the quick-dissolving layer, the microbial coating layer, and the protective film is 55:15:6:4, and the other components and conditions are the same as in Example 1.

[0033] Example 3 Compared with Example 1, the difference in this example is that: in step 1, the ratio of the first mixture and the second mixture is 38 parts urea, 28 parts potassium dihydrogen phosphate, 24 parts potassium nitrate, 14 parts potassium humate, 3 parts alginate oligosaccharide, 3 parts betaine, and 2 parts choline chloride; the second mixture is additionally supplemented with 7 parts hydroxypropyl methylcellulose. In step 2, the particle size of the slow-dissolving core is 0.9-1.2 mm.

[0034] In step 3, the mass ratio of the slow-dissolving inner core to the first mixture is 65:25.

[0035] The concentration of the first protective solution in S41 is 10%, and the mass ratio of trehalose, betaine, and proline is 5:4:2.

[0036] The compound bacterial powder ratio in S42 is 1:1:1:2.

[0037] The mass ratio of compound bacterial powder to the first protective liquid in S43 is 1:2.

[0038] The concentration of the second protective solution in S51 is 8%, and the mass ratio of potassium humate, polyglutamic acid, and glycerol is 6:3:2.

[0039] In S52, the amount of the second protective liquid sprayed is 10%, and the amount of the premixed bacterial powder sprayed is 8%.

[0040] The film-forming solution concentration in S61 is 3%, and the mass ratio of polyvinyl alcohol to hydroxypropyl methylcellulose is 3:1.

[0041] The amount of film-forming liquid sprayed in S62 is 2%.

[0042] In the obtained compound fertilizer granules, the mass ratio of the slow-dissolving inner core, the quick-dissolving layer, the microbial coating layer, and the protective film is 65:25:8:2, and the other components and conditions are the same as in Example 1.

[0043] Comparative Example 1 Compared with Example 1, the difference in this comparative example is that S61 and S62 are deleted, that is, no film-forming liquid is sprayed and no protective film is set in this comparative example, while the other components and conditions are the same as in Example 1.

[0044] Comparative Example 2 Compared with Example 1, the difference in this comparative example is that: a slow-dissolving inner core is prepared first, then premixed bacterial powder and a second protective liquid are sprayed to form a microbial coating layer, followed by coating with a first mixture to form a quick-dissolving layer, and finally spraying with a film-forming liquid. That is, the resulting compound fertilizer granule structure, from the inside out, consists of a slow-dissolving inner core, a microbial coating layer, a quick-dissolving layer, and a protective film, while other components and conditions are the same as in Example 1.

[0045] Comparative Example 3 Compared with Example 1, the difference in this comparative example is that in step 5, sterile water is used instead of the second protective solution, while the other components and conditions are the same as in Example 1.

[0046] Effect verification and experimental results 1. Experiment to determine the survival rate of microorganisms after dissolving water-soluble microbial compound fertilizer: The water-soluble microbial compound fertilizer samples obtained in Examples 1-3 and Comparative Examples 1-3 were diluted 800 times and dissolved in tap water at 25℃. Samples were taken at 5 min, 30 min, 2 h, and 4 h after dissolution. The total viable bacteria count in the bacterial solution was determined by plate count method, and the survival rate relative to the initial value (0 h) was calculated. Each sample was repeated 3 times, and the average value was taken. The results are shown in Table 1.

[0047] 2. Water solubility test: Take 10g of each of the water-soluble microbial compound fertilizer samples obtained in Examples 1-3 and Comparative Examples 1-3, place them in 200mL of tap water at 25℃, stir until completely dissolved, filter through a 100-mesh (0.15mm pore size) filter, weigh the residue on the filter screen, and calculate the insoluble content (%). Simultaneously observe the appearance of the solution. The results are shown in Table 2.

[0048] 3. Osmotic pressure change measurement experiment: The water-soluble microbial compound fertilizer samples obtained in Examples 1-3 and Comparative Examples 1-3 were diluted 800 times and dissolved. Samples were taken at 30, 60, 120, and 160 seconds after dissolution, and the osmotic pressure (mPa) of the solution was measured using a freezing point osmometer. Each sample was repeated 3 times, and the average value was taken. The measurement results are shown in Table 3.

[0049] Table 1. Results of experimental determination of microbial survival rate after dissolution of water-soluble microbial compound fertilizer Analysis of the data in Table 1 shows that the water-soluble microbial compound fertilizers prepared in Examples 1-3 of this invention exhibit excellent microbial activity retention after dissolution. Five minutes after dissolution, the microbial survival rate of Examples 1-3 reached over 95% (95.8%-97.2%), while the survival rate of the comparative examples was only 65.5%-82.5%. As the time extended to 4 hours, the survival rate of Examples 1-3 remained at a high level of 83.5%-85.5%, while the survival rate of Comparative Examples 1-3 had decreased to 45.2%-55.5%. This result fully demonstrates that the four-layer gradient dissolution structure of this invention—comprising a slow-dissolving carrier layer, a fast-dissolving carrier layer, a microbial coating layer, and an outer fast-dissolving membrane—combined with a dual protection system of a first protective liquid and a second protective liquid, can provide full osmotic pressure buffer protection for microorganisms from the initial to the later stages of dissolution, significantly improving the actual efficacy of the water-soluble microbial compound fertilizer.

[0050] Table 2. Results of water-soluble microbial compound fertilizer water solubility test As can be seen from the data analysis in Table 2, the insoluble content of each sample of water-soluble microbial compound fertilizer obtained in Examples 1-3 and Comparative Examples 1-3 is between 0.09% and 0.14%, which is lower than the upper limit of 0.2% required for drip irrigation. This indicates that all samples can meet the requirements of drip irrigation for water-insoluble matter and will not cause blockage of the dripper.

[0051] Table 3. Results of osmotic pressure changes (mPa) after dissolution of water-soluble microbial compound fertilizer Analysis of the data in Table 3 shows that in the initial dissolution phase (30 seconds) of Examples 1-3, the osmotic pressure was only 0.22-0.28 mPa, significantly lower than that of Comparative Example 1. This is because the protective membrane dissolves rapidly (5-15 seconds) to form a low-concentration solution, and the rapidly dissolving layer has not yet released a large amount of nutrients, providing a low-osmotic-pressure activation environment for microorganisms. In the middle dissolution phase (60-120 seconds), the osmotic pressure gradually increases from 0.58-0.72 mPa to 1.18-1.32 mPa, with a gradual increase rate (approximately 0.005-0.010 mPa / s). At this time, the rapidly dissolving layer releases some readily available nutrients, inducing microorganisms to accumulate compatible solutes. The hydroxypropyl methylcellulose in the slowly dissolving core forms a gel barrier, delaying the release of the main nutrients. In the later dissolution phase (160 seconds), the osmotic pressure stabilizes at 1.20-1.35 mPa without a sudden increase. Throughout the process, the microorganisms sequentially experience osmotic pressure changes of activation, adaptation, and steady state, effectively avoiding high osmotic pressure shocks. In contrast, Comparative Example 1... In the initial dissolution phase (30 seconds), the osmotic pressure rises to 0.58 mPa. This high osmotic pressure environment activates microorganisms, easily causing dehydration, rupture, or even death of microbial cells. In Comparative Example 2, because the microbial coating layer is located between the slow-dissolving core and the rapid-dissolving layer, the coating layer is exposed to a high-salt environment during the mid-dissolution phase (60-120 seconds). This prevents the microorganisms from inducing intracellular compatibility solute accumulation through the rapid-dissolving layer carrier, resulting in a lack of adaptation phase. As shown in Table 1, the microbial activity was only 65.5% after 5 minutes of dissolution. The osmotic pressure at each time point in Comparative Example 3 was significantly higher than in the Example 1. This is because the lack of potassium humate, polyglutamic acid, and glycerol in the second protective solution prevents effective adsorption of salt ions and formation of a hydration protective layer, leading to a rapid increase in osmotic pressure after nutrient release. As shown in Table 1, this is directly related to the 75.5% survival rate of microorganisms at 5 minutes in Comparative Example 3, demonstrating that the second protective solution plays a crucial buffering role against osmotic pressure shocks during dissolution.

[0052] The above-disclosed embodiments are merely preferred embodiments of the present invention and should not be construed as limiting the scope of the invention. Those skilled in the art will understand that all or part of the processes for implementing the above embodiments, and equivalent variations made in accordance with the claims of the present invention, are still covered by the invention.

Claims

1. A water-soluble microbial compound fertilizer, characterized by, The compound fertilizer granules are provided with a slow-dissolving inner core, a quick-dissolving layer, a microbial coating layer, and a protective film arranged sequentially from the inside out. The mass ratio of the slow-dissolving inner core, the quick-dissolving layer, the microbial coating layer, and the protective film is (55-65):(15-25):(3-8):(2-5). The protective film is used to awaken the dormant microorganisms in the microbial coating layer after dissolution. The quick-dissolving layer is used to induce the accumulation of intracellular compatible solutes by microorganisms during dissolution, so as to build the resistance of microorganisms to changes in osmotic pressure. The slow-dissolving inner core is used to gradually release nutrients during dissolution to ensure a steady increase in osmotic pressure.

2. The water-soluble microbial compound fertilizer according to claim 1, characterized in that, The microbial coating layer comprises compound bacterial powder, trehalose, betaine, proline, potassium humate, polyglutamic acid, and glycerol, and the mass ratio of the compound bacterial powder, trehalose, betaine, proline, potassium humate, polyglutamic acid, and glycerol is 100:(5-15):(3-10):(2-6):(10-25):(5-15):(2-8).

3. The water-soluble microbial compound fertilizer according to claim 1, characterized in that, Both the slow-dissolving core and the quick-dissolving layer comprise the following raw materials in parts by weight: 32-38 parts urea, 24-28 parts potassium dihydrogen phosphate, 18-24 parts potassium nitrate, 10-14 parts potassium humate, 2-3 parts alginate oligosaccharide, 2-3 parts betaine, and 1-2 parts choline chloride; in addition, the slow-dissolving core also comprises 7-9 parts hydroxypropyl methylcellulose.

4. The water-soluble microbial compound fertilizer according to claim 1, characterized in that, The protective film comprises polyvinyl alcohol and hydroxypropyl methylcellulose, and the mass ratio of polyvinyl alcohol to hydroxypropyl methylcellulose is (1-3):

1.

5. A method for preparing a water-soluble microbial compound fertilizer, characterized by, Includes the following steps: Step 1: Mix urea, potassium dihydrogen phosphate, potassium nitrate, potassium humate, alginate oligosaccharide, betaine, and choline chloride according to the specified ratio and then pulverize them to obtain the first mixture. Mix urea, potassium dihydrogen phosphate, potassium nitrate, potassium humate, alginate oligosaccharide, betaine, choline chloride, and hydroxypropyl methylcellulose according to the specified ratio and then pulverize them to obtain the second mixture. Step 2: Granulate the second mixture to obtain a slow-dissolving inner core; Step 3: Coat the first mixture onto the slow-dissolving core to form a slow-dissolving core containing a fast-dissolving layer; Step 4: Mix the compound bacterial powder with the first protective liquid to maintain the activity of the microorganisms in the compound bacterial powder during storage, and obtain premixed bacterial powder; Step 5: Spray the premixed bacterial powder and the second protective liquid onto the surface of the slow-dissolving inner core containing the fast-dissolving layer, which is in a fluidized state, to form a slow-dissolving inner core containing a microbial coating layer. Step 6: The film-forming liquid is sprayed onto the surface of the slow-dissolving inner core containing the microbial coating layer, which is in a fluidized state, and then dried at low temperature to form a protective film, thereby obtaining compound fertilizer granules. The film-forming liquid is an aqueous solution of polyvinyl alcohol and hydroxypropyl methylcellulose. The mass ratio of the slow-dissolving inner core, the quick-dissolving layer, the microbial coating layer and the protective film is (55-65):(15-25):(3-8):(2-5).

6. The method of claim 5, wherein the water-soluble microbial compound fertilizer is prepared by the steps of: mixing the microorganism and the inorganic substance; and drying the mixture. In step 1, the mass ratio of urea, potassium dihydrogen phosphate, potassium nitrate, potassium humate, alginate oligosaccharide, betaine, and choline chloride in the first mixture is (32-38):(24-28):(18-24):(10-14):(2-3):(1-2), and the mass ratio of urea, potassium dihydrogen phosphate, potassium nitrate, potassium humate, alginate oligosaccharide, betaine, choline chloride, and hydroxypropyl methylcellulose in the second mixture is (32-38):(24-28):(18-24):(10-14):(2-3):(1-2):(7-9).

7. The method for preparing the water-soluble microbial compound fertilizer as described in claim 5, characterized in that, Step 3 specifically involves: feeding the slow-dissolving core into a rotary drum granulator and introducing steam to wet the surface of the slow-dissolving core particles; then sprinkling the first mixture onto the surface of the slow-dissolving core using the wetting effect of the steam, forming a slow-dissolving core containing a quick-dissolving layer; wherein the mass ratio of the slow-dissolving core to the first mixture is (55-65):(15-25).

8. The method of claim 5, wherein the water-soluble microbial compound fertilizer is prepared by the steps of: mixing the microorganism and the inorganic substance; and drying the mixture. Step 4 specifically involves: S41: Dissolve trehalose, betaine and proline in sterile water to prepare a first protective solution with a mass concentration of 8-10%, and adjust the pH to 6.8-7.2, wherein the mass ratio of trehalose, betaine and proline is (3-5):(2-4):(1-2). S42: A compound bacterial powder is obtained by mixing Azotobacter chrysophagus, Bacillus megaterium, Bacillus mucilaginosus and Bacillus subtilis in a mass ratio of 1:1:1:(1-2). S43: Mix the compound bacterial powder with the first protective liquid at a mass ratio of 1:(2-5) to obtain premixed bacterial powder.

9. The method for preparing the water-soluble microbial compound fertilizer as described in claim 5, characterized in that, Step 5 specifically involves: S51: Dissolve potassium humate, polyglutamic acid and glycerol in sterile water to prepare a second protective solution with a mass concentration of 8-10%, and adjust the pH to 6.8-7.2, wherein the mass ratio of potassium humate, polyglutamic acid and glycerol is (4-6):(2-3):(1-2). S52: The slow-dissolving core containing the quick-dissolving layer is placed in a fluidized bed coating machine, and the premixed bacterial powder and the second protective liquid are alternately sprayed onto the surface of the slow-dissolving core containing the quick-dissolving layer. The slow-dissolving core containing a microbial coating layer is formed in a fluidized state at 35-45°C. The amount of the second protective liquid sprayed is 4%-10% of the mass of the slow-dissolving core containing the quick-dissolving layer, and the amount of the premixed bacterial powder sprayed is 3%-8% of the mass of the slow-dissolving core containing the quick-dissolving layer.

10. The method for preparing the water-soluble microbial compound fertilizer as described in claim 9, characterized in that, Step 6 specifically involves: S61: Polyvinyl alcohol and hydroxypropyl methylcellulose are dissolved in deionized water to prepare a film-forming solution with a mass concentration of 1%-3%, wherein the mass ratio of polyvinyl alcohol to hydroxypropyl methylcellulose is (1-3):

1. S62: After the premixed bacterial powder and the second protective liquid are sprayed, the film-forming liquid is continued to be sprayed onto the surface of the slow-dissolving core containing the microbial coating layer in the fluidized bed coating machine. The amount of film-forming liquid sprayed is 2%-5% of the mass of the slow-dissolving core containing the fast-dissolving layer. S63: After completing S62, the granules are dried at low temperature until the moisture content is less than 5% to form a protective film, and then compound fertilizer granules are obtained.

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