Slow-release compound microbial fertilizer and preparation method thereof

Abstract

The invention belongs to the field of agricultural biology, and particularly discloses a slow-release compound microbial fertilizer and a preparation method thereof. The temperature response phase change microcapsule sequentially comprises co-immobilized microspheres, a pentadecanoic acid-titanium dioxide composite phase change material, a carboxymethyl chitosan-magnesium slag composite pH sensitive layer and a PLA-PCL copolymer controlled release film from inside to outside, a nutrient slow release unit; the three-dimensional fiber network carrier comprises polylactic acid and a chitosan nanofiber net; through collaborative design of the temperature response phase change microcapsules, the nutrient slow release unit and the three-dimensional fiber network carrier, accurate matched release of microorganisms and nutrients is achieved, the survival rate of the microorganisms in soil is increased through a multi-level protection structure, meanwhile, temperature response triggers microorganism release, and the survival rate of the microorganisms is increased. The nutrient release period is highly synchronous with the nutrient release period controlled by humic acid-attapulgite gel, and the nutrient release behavior is dynamically adjusted according to soil conditions.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of agricultural biology, and particularly relates to a slow-release compound microbial fertilizer and a preparation method thereof. BACKGROUND

[0002] The compound microbial fertilizer is a new type of fertilizer taking specific functional microbial flora as the core and supplemented with nitrogen, phosphorus, potassium and other nutrient elements, and promoting soil fertility and crop growth through the metabolic activity of microorganisms and the synergistic effect of nutrients. The core principle is to convert the nutrients in the soil that are difficult for crops to absorb into effective forms by using the life activities of microorganisms (such as nitrogen fixation, phosphorus solubilization and growth hormone secretion), thereby reducing the excessive use of chemical fertilizers and agricultural non-point source pollution, and thus becoming an important technical means for realizing green and sustainable development of agriculture.

[0003] Traditional compound microbial fertilizers mostly use single embedding materials (such as sodium alginate and starch) to fix microorganisms, but such materials are easily decomposed by microorganisms or rapidly swelled by humidity in the soil, have a short release period, a large amount of nutrient loss, and cause the embedded microorganisms to be exposed to a complex environment in a short time after being applied to the soil. Factors such as competition of pathogenic bacteria in the soil, ultraviolet radiation and extreme pH (such as the pH of red soil in the south is usually lower than 5.5) will cause a large number of microorganisms to die, and thus the nitrogen utilization rate and the survival rate of microorganisms are generally reduced.

[0004] Secondly, the fluctuation of soil environmental factors (temperature, pH and salinity) will significantly affect the activity of microorganisms and the release of nutrients. For example, the increase of soil temperature in summer (more than 30℃) will accelerate the volatilization of nutrients and inhibit the metabolism of microorganisms; the acid soil (pH<6.0) will damage the cell membrane structure of microorganisms and cause them to be inactivated. SUMMARY

[0005] The purpose of the present application is to provide a slow-release compound microbial fertilizer and a preparation method thereof, so as to solve the problems of the traditional slow-release compound microbial fertilizer that cannot dynamically adjust the nutrient release behavior according to the soil conditions, has poor stability in complex soil environment and has low survival rate of microorganisms.

[0006] To achieve the above purpose, the present application provides the following technical scheme:

[0007] A slow-release compound microbial fertilizer, comprising:

[0008] The temperature-responsive phase change microcapsule sequentially comprises a co-immobilized microsphere, a pentadecanoic acid-titanium dioxide composite phase change material, a carboxymethyl chitosan-magnesium slag composite pH-sensitive layer and a PLA-PCL copolymer controlled-release film from inside to outside.

[0009] The nutrient slow-release unit has a core of magnesium ammonium phosphate nanoparticles and an outer layer of humic acid-attapulgite clay composite gel.

[0010] The three-dimensional fiber network carrier comprises polylactic acid and chitosan nanofiber network and is embedded with temperature-responsive phase change microcapsules and nutrient slow-release units.

[0011] The slow-release composite microbial fertilizer realizes precise release through the synergistic structure of "temperature-responsive phase change microcapsules-nutrient slow-release units-three-dimensional fiber network carrier".

[0012] The temperature-responsive phase change microcapsule serves as a microbial core carrier, the inner layer of which co-immobilizes functional bacterial groups, the middle layer of which is a pentadecanoic acid-titanium dioxide composite phase change material that undergoes phase change with the change of soil temperature (26-30℃), triggering the release of the microorganisms, the outer layer of which is a carboxymethyl chitosan-magnesium slag composite layer that swells in response to soil pH (5.5-6.5) to synchronously regulate the acid-base degree of the microenvironment, and the outermost layer of which is a PLA-PCL copolymer film that controls the release rate.

[0013] The nutrient slow-release unit slowly releases magnesium ammonium phosphate nutrients through the adsorption of the humic acid-attapulgite gel, which matches the metabolic needs of the microorganisms, specifically, the magnesium ammonium phosphate nanoparticles are wrapped by the humic acid-attapulgite gel and slowly diffuse through the gel pores, the chelation of humic acid reduces nitrogen loss, and the porous structure of attapulgite adsorbs potassium and phosphorus ions, achieving long-acting supply of nutrients.

[0014] The three-dimensional fiber network carrier provides space for microbial colonization and simultaneously fixes the microcapsules and nutrient units, forming a stable slow-release system, specifically, the polylactic acid-chitosan nanofiber network (diameter 200-500 nm, porosity ≥ 85%) forms a three-dimensional scaffold, reducing the loss of microorganisms due to soil erosion, and the degradation products of the fibers provide carbon sources for the microorganisms.

[0015] Preferably, the co-immobilized microspheres are formed by azotobacter, phosphorus-solubilizing bacteria, endophytic bacteria and ectomycorrhizal fungi at a mass ratio of 2:1:1:0.5, the concentration of the azotobacter is 10 9 CFU / mL, and the concentration of the phosphorus-solubilizing bacteria is 10 9 CFU / mL.

[0016] The azotobacter (10 9 CFU / mL) in the co-immobilized microspheres can convert nitrogen in the air into a plant-available state, the phosphorus-solubilizing bacteria (10 9 CFU / mL) decompose insoluble phosphorus in the soil, the endophytic bacteria promote root development, and the ectomycorrhizal fungi expand the nutrient absorption area, and the four types of bacteria interact through metabolic products (such as auxins and organic acids) to improve nutrient utilization rate.

[0017] Preferably, in the carboxymethyl chitosan-magnesium slag composite pH-sensitive layer, the mass ratio of carboxymethyl chitosan to magnesium slag is 3:1, which is used for swelling in the pH range of 5.5-6.5.

[0018] In acidic soil (pH 5.5-6.5), the carboxymethyl chitosan-magnesium slag layer swells, and the magnesium slag releases Ca 2 + neutralize the acidity, at the same time provide alkaline protection microenvironment for microorganisms, and improve the survival rate.

[0019] Preferably, the block ratio of the PLA-PCL copolymer controlled-release film is lactic acid:caprolactone = 65%-75%:25%-35%, and the thickness is 50-100 nm.

[0020] Preferably, the fiber diameter of the nanofiber network is 200-500 nm, and the porosity is ≥85%.

[0021] Preferably, the melting point of the pentadecanoic acid-titanium dioxide composite phase change material is 26-30℃.

[0022] When the soil temperature reaches 26-30℃, the pentadecanoic acid-titanium dioxide phase change material changes from solid to liquid, increasing the internal pore size of the microcapsule and accelerating the release of microorganisms, matching the growth needs of crops in the high temperature period, and realizing the temperature response effect.

[0023] A preparation method of a slow-release type composite microbial fertilizer, comprising:

[0024] S1, the nitrogen-fixing bacteria, phosphorus-solubilizing bacteria, endophytic bacteria and ectomycorrhizal fungi are mixed in a ratio of 2:1:1:0.5 to obtain a microbial mixture;

[0025] S2, the microbial mixture is mixed with a carboxymethyl chitosan solution with a mass concentration of 2% at a volume ratio of 1:3, and is dropped into a 0.3M CaCl2 solution to form a co-immobilized microsphere;

[0026] S3, the molten pentadecanoic acid and titanium dioxide nanoparticles are mixed in a mass ratio of 19:1, and are sprayed and cooled to 10℃ to form solid particles;

[0027] S4, the co-immobilized microspheres are adsorbed in the pores of the solid particles to form a preliminary structure of the co-immobilized microspheres;

[0028] S5, carboxymethyl chitosan and magnesium slag are mixed in a mass ratio of 3:1, water is added to form a carboxymethyl chitosan-magnesium slag composite solution with a solid-liquid ratio of 1:0.5, and the carboxymethyl chitosan-magnesium slag composite solution is sprayed on the surface of the preliminary structure by electrostatic spraying to form a carboxymethyl chitosan-magnesium slag composite pH-sensitive layer;

[0029] S6, coating the PLA-PCL copolymer solution on the surface of the co-immobilized microspheres with the carboxymethyl chitosan-magnesium slag composite pH-sensitive layer by a fluidized bed to form a PLA-PCL copolymer controlled-release film, and obtaining temperature-responsive phase change microcapsules;

[0030] S7, mixing the magnesium ammonium phosphate nanoparticles and the humic acid-attapulgite clay composite gel at a mass ratio of 1:2 to obtain a nutrient slow-release unit;

[0031] S8, dispersing the temperature-responsive phase change microcapsules and the nutrient slow-release unit in a polylactic acid and chitosan blended spinning solution at a mass ratio of 1:2, and performing electrospinning under the conditions of a voltage of 14-16 kV, a receiving distance of 14-16 cm, and a humidity of ≤30% to form a nanofiber network embedded with the temperature-responsive phase change microcapsules and the nutrient slow-release unit, and obtaining a compound fertilizer carrier;

[0032] S9, performing liquid nitrogen cryogenic treatment on the compound fertilizer carrier at-196℃ for 8-12 minutes, then vacuum freeze-drying, and cutting into granular finished products to obtain a slow-release compound microbial fertilizer.

[0033] Preferably, the particle size of the TiO2 nanoparticles is ≤50 nm.

[0034] Preferably, the particle size of the magnesium ammonium phosphate nanoparticles is ≤100 nm, and the porosity of the humic acid-attapulgite clay composite gel is ≥80%.

[0035] Preferably, the concentration of the polylactic acid and chitosan blended spinning solution is 15 wt%, and the solvent is hexafluoroisopropanol.

[0036] Compared with the prior art, the beneficial effects of the present application are:

[0037] The present application realizes the precise matching release of microorganisms and nutrients through the synergistic design of temperature-responsive phase change microcapsules, nutrient slow-release units and three-dimensional fiber network carriers, the multi-level protection structure improves the survival rate of microorganisms in the soil, and the temperature-responsive trigger microorganism release is highly synchronized with the nutrient release period controlled by the humic acid-attapulgite gel, so as to dynamically adjust the nutrient release behavior according to the soil conditions, effectively avoid the problems of early release of nutrients and late activation of microorganisms, and improve the effect stability of the fertilizer in complex soil environments.

[0038] The carboxymethyl chitosan-magnesium slag composite layer can swell in the pH range of 5.5-6.5 and release Ca 2+ neutralize soil acidity, improve the pH of acidic soil, and create a suitable microenvironment for microorganisms; the PLA-PCL copolymer film can still maintain controllable degradation in soil with a salt concentration of 0.3%-0.5%, avoiding the inhibition of high salt environments on microorganisms, so that the present application can stably play a role in complex soils such as acidification and salinization.

[0039] The present application reduces ammonia volatilization loss by adsorbing free nitrogen through the porous structure of the three-dimensional fiber network carrier; and significantly reduces the risk of water eutrophication caused by nutrient loss by extending the phosphorus release period through the chelation of humic acid-attapulgite gel to phosphorus.

[0040] The present application can secrete growth hormones, organic acids and other substances through the synergistic metabolic activity of microbial flora, promote crop root development and nutrient absorption; and synchronously released nutrients meet the needs of crops at each growth stage, realizing the dual improvement of yield and quality. BRIEF DESCRIPTION OF DRAWINGS

[0041] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings needed in the embodiment description will be briefly introduced as follows. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor. Among them:

[0042] Figure 1 The method steps of the present application are shown in the figure. DETAILED DESCRIPTION

[0043] In order to make the above-mentioned purposes, features and advantages of the present application more apparent and easy to understand, the specific embodiments of the present application will be described in detail below with reference to the drawings of the specification.

[0044] In the following description, many specific details are set forth in order to provide a thorough understanding of the present application, but the present application can also be implemented in other ways different from those described herein, and those skilled in the art can make similar generalizations without departing from the connotation of the present application, therefore the present application is not limited by the specific embodiments disclosed below.

[0045] Secondly, the "one embodiment" or "embodiment" referred to herein means that the specific features, structures or characteristics can be included in at least one implementation of the present application. In this specification, "in one embodiment" does not mean the same embodiment, nor is it an independent or alternative embodiment that excludes other embodiments.

[0046] As shown in the accompanying Figure 1 As shown in the accompanying

[0047] Embodiment one: the present embodiment provides a slow-release type composite microbial fertilizer, comprising:

[0048] Material:

[0049] Azotobacter vinelandii, Pseudomonas fluorescens, Ensifer CS, Glomus mosseae are all strains reported in public literature and can be legally obtained from the national strain preservation agency. Their concentrations are all adjusted to 10 9 CFU / mL when used.

[0050] Carboxymethyl chitosan (molecular weight 50 kDa, degree of deacetylation ≥90%) was purchased from Shandong Aokang Biological Technology Co., Ltd.

[0051] Magnesium slag (particle size ≤100 μm, CaO content 35%) was from Tangshan Iron and Steel Group Waste Slag Treatment Plant.

[0052] Pentadecanoic acid (purity ≥98%) and titanium dioxide nanoparticles (particle size 30 nm) were purchased from Aladdin Reagent Co., Ltd.

[0053] PLA-PCL copolymer (LA:CL=70:30) was purchased from Sigma-Aldrich Company, USA.

[0054] Magnesium ammonium phosphate (particle size 80 nm) and humic acid (purity ≥85%) were purchased from National Pharmaceutical Group Chemical Reagent Co., Ltd.

[0055] Palygorskite clay (specific surface area 300 m 2 / g) was purchased from Gansu Linze Fjun Mining Palygorskite Co., Ltd.

[0056] Polylactic acid (molecular weight 100 kDa) and chitosan (molecular weight 80 kDa) were purchased from Shanghai Maikelin Biological Technology Co., Ltd.

[0057] Equipment:

[0058] Constant temperature shaker (THZ-300, Shanghai Boxun Industry Co., Ltd.);

[0059] Electrostatic spraying machine (SP-100, Beijing Saiderui Technology Co., Ltd.);

[0060] Fluidized bed coating machine (LBF-5, Changzhou Limar Drying Engineering Co., Ltd.);

[0061] Electrospinning machine (ET-2535H, Beijing Yongkangleye Technology Development Co., Ltd.);

[0062] Liquid nitrogen deep cooling equipment (YD-10, Chengdu Kelais Low Temperature Equipment Co., Ltd.);

[0063] Vacuum freeze dryer (FD-1A-50, Beijing Boyikang Experimental Instrument Co., Ltd.).

[0064] The slow-release compound microbial fertilizer is prepared by a method for preparing the slow-release compound microbial fertilizer, comprising:

[0065] S1, mixing nitrogen-fixing bacteria, phosphate-solubilizing bacteria, endophytes and ectomycorrhizal fungi in a ratio of 2:1:1:0.5 to obtain a microbial mixture;

[0066] S2, mixing the microbial mixture with a 2% carboxymethyl chitosan solution at a volume ratio of 1:3, and dripping it into a 0.3M CaCl2 solution to form co-immobilized microspheres;

[0067] S3, mixing molten pentadecanoic acid and titanium dioxide nanoparticles in a mass ratio of 19:1, spray cooling to 10° C., to form solid microparticles;

[0068] S4, adsorbing the co-immobilized microspheres into the pores of the solid microparticles to form a preliminary structure of the co-immobilized microspheres;

[0069] S5, mixing carboxymethyl chitosan and magnesium slag in a mass ratio of 3:1, adding water to form a carboxymethyl chitosan-magnesium slag composite solution with a solid-liquid ratio of 1:0.5, and spraying it on the surface of the preliminary structure by electrostatic spraying to form a carboxymethyl chitosan-magnesium slag composite pH sensitive layer;

[0070] S6. Coating the PLA-PCL copolymer solution on the surface of the co-immobilized microspheres with the carboxymethyl chitosan-magnesium slag composite pH sensitive layer by a fluidized bed to form a PLA-PCL copolymer controlled-release membrane to obtain temperature-responsive phase-change microcapsules;

[0071] S7, mixing magnesium ammonium phosphate nanoparticles and humic acid-attapulgite clay composite gel in a mass ratio of 1:2 to obtain a nutrient slow-release unit;

[0072] S8, dispersing the temperature-responsive phase-change microcapsules and the nutrient slow-release units in a polylactic acid and chitosan blend spinning solution in a mass ratio of 1:2, and performing electrospinning at a voltage of 15 kV, a receiving distance of 15 cm, and a humidity of ≤30% to form a nanofiber network embedded with the temperature-responsive phase-change microcapsules and the nutrient slow-release units, thereby obtaining a composite fertilizer carrier;

[0073] S9. The compound fertilizer carrier is subjected to a liquid nitrogen cryogenic treatment at -196° C. for 10 minutes, and then freeze-dried in a vacuum, and cut into granular finished products to obtain a slow-release compound microbial fertilizer.

[0074] Detection:

[0075] Microbial survival rate: The plate count method (GB / T 38577-2020) was used with a colony counter (JJ-2, Changzhou Zhongjie Experimental Instrument Co., Ltd.);

[0076] Result: The survival rate of microorganisms was 82.3% after 90 days.

[0077] Nitrogen utilization rate: Kjeldahl method (NY / T 1116-2014) was used, and automatic nitrogen determination instrument (K9840, Jinan Haineng Instrument Co., Ltd.) was used.

[0078] Result: The nitrogen utilization rate was 68.7%.

[0079] Phosphorus release period: Inductively coupled plasma mass spectrometry (ICP-MS, Agilent 7900) was used to detect the concentration of phosphorus in soil leachate.

[0080] Result: The phosphorus release period was 58 days.

[0081] pH adjustment effect: pH meter (PHS-3C, Shanghai Ray Meter Factory) was used to measure the pH of the soil.

[0082] Result: The pH of the acidic soil (initial pH 5.2) was increased to 6.3 after treatment.

[0083] Example 2: The present example provides a slow-release type of composite microbial fertilizer, which comprises:

[0084] Materials:

[0085] Azotobacter vinelandii, Pseudomonas fluorescens, Ensifer CS, and Glomus mosseae are strains that have been reported in public literature and can be legally obtained from national strain preservation agencies. Their concentrations were adjusted to 10 9 CFU / mL when used.

[0086] Carboxymethyl chitosan (molecular weight 80 kDa, degree of deacetylation ≥90%) was purchased from Shandong Aokang Biological Technology Co., Ltd.

[0087] Magnesium slag (particle size ≤100 μm, CaO content 30%) was obtained from Tangshan Iron and Steel Group Waste Residue Treatment Plant.

[0088] Pentadecanoic acid-titanium dioxide composite phase change material (melting point 28℃) was purchased from Jiangsu Chengguang High Polymer Material Co., Ltd.

[0089] PLA-PCL copolymer (LA:CL=70:30) was purchased from Sigma-Aldrich Company, USA.

[0090] Ammonium magnesium phosphate (particle size 80 nm), humic acid (purity ≥85%) were purchased from National Pharmaceutical Group Chemical Reagent Co., Ltd.

[0091] Attapulgite clay (specific surface area 300 m 2 Attapulgite clay (specific surface area 300 m

[0092] PLA (molecular weight 100 kDa), chitosan (molecular weight 80 kDa) were purchased from Shanghai Maikelin Biotechnology Co., Ltd.

[0093] Equipment:

[0094] Constant temperature shaker (THZ-300, Shanghai Boxun Industry Co., Ltd.);

[0095] Electrostatic spraying machine (SP-100, Beijing Saide Li Technology Co., Ltd.);

[0096] Fluidized bed coating machine (LBF-5, Changzhou Limar Drying Engineering Co., Ltd.);

[0097] Electrospinning machine (ET-2535H, Beijing Yongkangleye Technology Development Co., Ltd.);

[0098] Liquid nitrogen deep cooling equipment (YD-10, Chengdu Kelais Low Temperature Equipment Co., Ltd.);

[0099] Vacuum freeze dryer (FD-1A-50, Beijing Boyikang Experimental Instrument Co., Ltd.).

[0100] The preparation method of a slow-release compound microbial fertilizer is used to prepare the slow-release compound microbial fertilizer, comprising the following steps:

[0101] S1, the nitrogen-fixing bacteria, phosphorus solubilizing bacteria, endophytic bacteria and ectomycorrhizal fungi are mixed in a ratio of 2:1:1:0.5 to obtain a microbial mixture;

[0102] S2, the microbial mixture is mixed with a carboxymethyl chitosan solution with a mass concentration of 2% at a volume ratio of 1:3, and is dropped into a 0.3M CaCl2 solution to form a co-immobilized microsphere;

[0103] S3, the molten pentadecanoic acid and titanium dioxide nanoparticles are mixed in a mass ratio of 19:1, and are sprayed and cooled to 10℃ to form solid particles;

[0104] S4, the co-immobilized microspheres are adsorbed in the pores of the solid particles to form a preliminary structure of the co-immobilized microspheres;

[0105] S5, the carboxymethyl chitosan and magnesium slag are mixed in a mass ratio of 3:1, water is added to form a carboxymethyl chitosan-magnesium slag composite solution with a solid-liquid ratio of 1:0.5, and the carboxymethyl chitosan-magnesium slag composite solution is sprayed on the surface of the preliminary structure by electrostatic spraying to form a carboxymethyl chitosan-magnesium slag composite pH sensitive layer;

[0106] S6, coating the PLA-PCL copolymer solution on the surface of the co-immobilized microspheres with the carboxymethyl chitosan-magnesium slag composite pH-sensitive layer by a fluidized bed to form a PLA-PCL copolymer controlled-release film, and obtaining temperature-responsive phase change microcapsules;

[0107] S7, mixing the magnesium ammonium phosphate nanoparticles and the humic acid-attapulgite clay composite gel at a mass ratio of 1:2 to obtain a nutrient slow-release unit;

[0108] S8, dispersing the temperature-responsive phase change microcapsules and the nutrient slow-release unit in a poly-lactic acid and chitosan blended spinning solution at a mass ratio of 1:2, and performing electrospinning under the conditions of a voltage of 16 kV, a receiving distance of 14 cm, and a humidity of ≤30% to form a nanofiber network embedded with the temperature-responsive phase change microcapsules and the nutrient slow-release unit, and obtaining a compound fertilizer carrier;

[0109] S9, performing liquid nitrogen cryogenic treatment on the compound fertilizer carrier at -196℃ for 8 minutes, then vacuum freeze-drying, and cutting into granular finished products to obtain a slow-release compound microbial fertilizer.

[0110] Detection:

[0111] Microbial survival rate: plate count method (GB / T 38577-2020) was used, and a colony counter (JJ-2, Changzhou Zhijie Experimental Instrument Co., Ltd.) was used;

[0112] Results: The 90-day survival rate of microorganisms was 79.5%.

[0113] Nitrogen utilization rate: Kjeldahl nitrogen determination method (NY / T 1116-2014) was used, and an automatic nitrogen determination instrument (K9840, Jinan Haineng Instrument Co., Ltd.) was used;

[0114] Results: The nitrogen utilization rate was 65.2%.

[0115] Phosphorus release period: inductively coupled plasma mass spectrometry (ICP-MS, Agilent 7900) was used to detect the phosphorus concentration in soil leachate;

[0116] Results: The phosphorus release period was 52 days.

[0117] pH adjustment effect: a pH meter (PHS-3C, Shanghai Raymeter Instrument Factory) was used to measure the soil pH;

[0118] Results: The pH of the acidic soil (initial pH 5.2) was increased to 6.1 after treatment.

[0119] The comparative analysis of Example 1 and Example 2 is shown in the following table:

[0120]

[0121] Both embodiments verify the technical effects of the present application, wherein the parameter combination of embodiment one is more optimal, and the overall performance is more outstanding, indicating that the fertilizer effect can be further optimized by adjusting the process parameters and material specifications.

[0122] It should be appreciated that during the development of any actual implementation, as in any engineering or design project, numerous implementation-specific decisions can be made. Such development efforts might be complex and time-consuming, but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure, without undue experimentation.

[0123] It should be noted that the above examples are only used to illustrate the technical solutions of the present application but not limit the present application, and although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application can be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present application, and all should be covered in the scope of the claims of the present application.

Claims

1. A slow-release compound microbial fertilizer, characterized in that: include: Temperature-responsive phase-change microcapsules, which are composed of, from inside to outside, co-immobilized microspheres, a pentadecanoic acid-titanium dioxide composite phase-change material, a carboxymethyl chitosan-magnesium slag composite pH-sensitive layer, and a PLA-PCL copolymer controlled-release membrane; A nutrient slow-release unit, wherein the core of the nutrient slow-release unit is magnesium ammonium phosphate nanoparticles and the outer layer is a humic acid-attapulgite clay composite gel; The three-dimensional fiber network carrier includes a polylactic acid and chitosan nanofiber network, and is embedded with temperature-responsive phase-change microcapsules and nutrient slow-release units.

2. The slow-release compound microbial fertilizer according to claim 1, characterized in that: The co-immobilized microspheres are formed by nitrogen-fixing bacteria, phosphate-solubilizing bacteria, endophytes and ectomycorrhizal fungi in a mass ratio of 2:1:1:0.5, and the concentration of the nitrogen-fixing bacteria is 10 9 CFU / mL, the concentration of phosphate-solubilizing bacteria was 10 9 CFU / mL.

3. The slow-release compound microbial fertilizer according to claim 1, characterized in that: In the carboxymethyl chitosan-magnesium slag composite pH sensitive layer, the mass ratio of carboxymethyl chitosan to magnesium slag is 3:1, and is configured to swell within a pH range of 5.5-6.

5.

4. The slow-release compound microbial fertilizer according to claim 1, characterized in that: The block ratio of the PLA-PCL copolymer controlled-release membrane is lactic acid:caprolactone=65%-75%:25%-35%, and the thickness is 50-100 nm.

5. The slow-release compound microbial fertilizer according to claim 1, characterized in that: The fiber diameter of the nanofiber web is 200-500 nm, and the porosity is ≥85%.

6. The slow-release compound microbial fertilizer according to claim 1, characterized in that: The melting point of the pentadecanoic acid-titanium dioxide composite phase change material is 26-30°C.

7. The method for preparing a slow-release compound microbial fertilizer according to any one of claims 1 to 6, characterized in that: include: S1, mixing nitrogen-fixing bacteria, phosphate-solubilizing bacteria, endophytes and ectomycorrhizal fungi in a ratio of 2:1:1:0.5 to obtain a microbial mixture; S2, mixing the microbial mixture with a 2% carboxymethyl chitosan solution at a volume ratio of 1:3, and dripping it into a 0.3M CaCl2 solution to form co-immobilized microspheres; S3, mixing molten pentadecanoic acid and titanium dioxide nanoparticles in a mass ratio of 19:1, spray cooling to 10° C., to form solid microparticles; S4, adsorbing the co-immobilized microspheres into the pores of the solid microparticles to form a preliminary structure of the co-immobilized microspheres; S5, mixing carboxymethyl chitosan and magnesium slag in a mass ratio of 3:1, adding water to form a carboxymethyl chitosan-magnesium slag composite solution with a solid-liquid ratio of 1:0.5, and spraying it on the surface of the preliminary structure by electrostatic spraying to form a carboxymethyl chitosan-magnesium slag composite pH sensitive layer; S6. Coating the PLA-PCL copolymer solution on the surface of the co-immobilized microspheres with the carboxymethyl chitosan-magnesium slag composite pH sensitive layer by a fluidized bed to form a PLA-PCL copolymer controlled-release membrane to obtain temperature-responsive phase-change microcapsules; S7, mixing magnesium ammonium phosphate nanoparticles and humic acid-attapulgite clay composite gel in a mass ratio of 1:2 to obtain a nutrient slow-release unit; S8, dispersing the temperature-responsive phase-change microcapsules and the nutrient slow-release units in a polylactic acid and chitosan blend spinning solution in a mass ratio of 1:2, and performing electrospinning at a voltage of 14-16 kV, a receiving distance of 14-16 cm, and a humidity of ≤30% to form a nanofiber network embedded with the temperature-responsive phase-change microcapsules and the nutrient slow-release units, thereby obtaining a composite fertilizer carrier; S9. The compound fertilizer carrier is subjected to a liquid nitrogen cryogenic treatment at -196° C. for 8-12 minutes, and then freeze-dried in a vacuum, and cut into granular finished products to obtain a slow-release compound microbial fertilizer.

8. The method for preparing a slow-release compound microbial fertilizer according to claim 7, characterized in that: The particle size of the TiO2 nanoparticles is ≤50nm.

9. The method for preparing a slow-release compound microbial fertilizer according to claim 7, characterized in that: The particle size of the magnesium ammonium phosphate nanoparticles is less than or equal to 100 nm, and the porosity of the humic acid-attapulgite clay composite gel is greater than or equal to 80%.

10. The method for preparing a slow-release compound microbial fertilizer according to claim 7, characterized in that: The concentration of the polylactic acid and chitosan blended spinning solution is 15 wt%, and the solvent is hexafluoroisopropanol.

Images