Polymeric phosphorus slow-release compound fertilizer and preparation method thereof

Abstract

The invention discloses a polymeric phosphorus slow-release compound fertilizer and a preparation method thereof, and relates to the technical field of agricultural fertilizers, the polymeric phosphorus slow-release compound fertilizer comprises an inner core and a coating layer, wherein the inner core is prepared from the following components in percentage by weight: 30 to 50 percent of modified ammonium polyphosphate, 15 to 25 percent of urea-formaldehyde slow-release nitrogen, 10 to 20 percent of potassium humate-coated potassium chloride, 2 to 5 percent of amino acid chelated trace elements and 1 to 3 percent of seaweed extract; through the synergistic effect of the citric acid modified ammonium polyphosphate and the three layers of functional envelopes, the phosphorus utilization rate is increased, and the problem that phosphorus is easily fixed by soil is effectively solved. The fertilizer can automatically adapt to different soil environments through the pH responsive coating design, and 30-40% of phosphorus can be quickly released in acid soil to meet the early needs of crops; phosphorus is continuously supplied through activation of the phosphate solubilizing bacteria under a neutral condition; and the fertilizer efficiency is prolonged to 120-150 days by virtue of an outer layer slow release mechanism in an alkaline environment.

Description

Technical Field

[0001] The present invention relates to the technical field of agricultural fertilizers, in particular to a polymeric phosphorus slow-release compound fertilizer and a preparation method thereof. Background Art

[0002] Phosphorus, as an essential nutrient for plant growth, plays an irreplaceable role in agricultural production. However, traditional phosphate fertilizers face severe technical bottlenecks and environmental challenges in practical application. Currently, the phosphate fertilizers available on the market are mainly water-soluble phosphates. These fertilizers have three inherent defects after being applied to the soil: first, phosphorus is easily fixed by cations such as iron, aluminum, and calcium in the soil, forming insoluble compounds, resulting in generally low phosphorus utilization rates for crops in that season and easily causing serious waste of resources; second, the release curve of traditional phosphate fertilizers does not match crop demand, which can easily lead to nutrient excess in the early stage and insufficient supply in the later stage; third, excessive application causes phosphorus to enter water bodies through surface runoff, causing environmental problems such as eutrophication.

[0003] To improve the efficiency of phosphate fertilizers, the industry has explored a variety of technical routes. As a representative of polymeric phosphate fertilizers, ammonium polyphosphate has attracted attention due to its chelation and slow-release properties, but existing technologies still have obvious shortcomings: the hydrolysis rate of unmodified APP in the soil is uncontrollable, making it difficult to match the crop growth cycle; although ordinary polymer-coated fertilizers extend the release period, they generally lack pH response capabilities and are unstable in soils with large differences in pH; more importantly, existing coating materials mostly use non-degradable polymers such as polyethylene and polypropylene, resulting in tens of thousands of tons of plastic micro-pollution each year. In addition, although microbial fertilizers that have emerged in recent years can activate soil phosphorus, the simple mixing of microbial agents and chemical fertilizers results in low survival rates, making it difficult to exert a sustained effect.

[0004] Therefore, we proposed a polymeric phosphorus slow-release compound fertilizer and a preparation method thereof in order to solve the above-mentioned problems.

[0005] The above information disclosed in this background technology is only for enhancing understanding of the background technology of the present invention and therefore it may contain information that does not constitute the prior art that is already known to a person of ordinary skill in the art. Summary of the Invention

[0006] The object of the present invention is to provide a polymeric phosphorus slow-release compound fertilizer and a preparation method thereof, so as to solve the problems raised by the above background technology.

[0007] To achieve the above object, the present invention provides the following technical solutions:

[0008] A polymeric phosphorus slow-release compound fertilizer comprising a core and a coating layer, wherein:

[0009] The core comprises: 30-50 wt% of modified ammonium polyphosphate, 15-25 wt% of urea-formaldehyde slow-release nitrogen, 10-20 wt% of potassium chloride wrapped in potassium humate, 2-5 wt% of amino acid chelated trace elements, and 1-3 wt% of seaweed extract;

[0010] The coating layer has a three-layer structure, the inner layer is pH-responsive chitosan / polylactic acid copolymer with a thickness of 3-5 μm, the middle layer is phosphate-solubilizing bacteria microcapsules with a thickness of 5-8 μm, and the outer layer is hydrophobically modified cellulose with a thickness of 1-2 μm.

[0011] As a further optimization scheme of the present invention, the modified ammonium polyphosphate is citric acid-modified ammonium polyphosphate, and its preparation method includes:

[0012] Ammonium polyphosphate and citric acid were reacted at a molar ratio of 5:1 at 60°C for 2h;

[0013] After spray drying, a modified product with a particle size of 50-100 μm is obtained.

[0014] As a further optimized solution of the present invention, the urea-formaldehyde slow-release nitrogen is a slow-release nitrogen fertilizer formed by condensation of urea and formaldehyde, and its nitrogen release period is 30-90 days.

[0015] As a further optimized solution of the present invention, in the potassium chloride wrapped with potassium humate, the mass ratio of potassium humate to potassium chloride is 1:5-1:10.

[0016] As a further optimized solution of the present invention, the amino acid chelated trace elements are selected from at least two of iron, zinc, manganese, copper and boron, and the chelated amino acid is glutamic acid or aspartic acid.

[0017] As a further optimized solution of the present invention, in the pH-responsive chitosan / polylactic acid copolymer, the mass ratio of chitosan to polylactic acid is 1:2.

[0018] As a further optimized solution of the present invention, the method for preparing the phosphate-solubilizing bacteria microcapsules comprises: mixing the phosphate-solubilizing bacteria with sodium alginate, and preparing microcapsules with a particle size of 10-20 μm by a spray drying method.

[0019] As a further optimized solution of the present invention, the hydrophobically modified cellulose is a product of hydroxypropyl methylcellulose modified with stearic acid.

[0020] The preparation method of the polymerized phosphorus slow-release compound fertilizer comprises the following steps:

[0021] When preparing the modified ammonium polyphosphate, the ammonium polyphosphate is first reacted with citric acid and then spray-dried;

[0022] When performing core granulation, firstly, modified ammonium polyphosphate, urea-formaldehyde slow-release nitrogen, potassium chloride coated with potassium humate, amino acid chelated trace elements, and seaweed extract are mixed and granulated in a fluidized bed to a particle size of 2-4 mm. The temperature of the fluidized bed granulation is 50-60°C and the wind speed is 2-4 m / s.

[0023] Preparation of the coating layer. When spraying the inner layer, a chitosan and polylactic acid copolymer solution is sprayed on the surface of the core to form a pH-responsive layer with a thickness of 3-5 μm. Ethyl acetate is used as the solvent and the spraying pressure is 0.2-0.4 MPa.

[0024] When spraying the middle layer, the phosphate-solubilizing bacteria microcapsule suspension is sprayed to form a biological activation layer with a thickness of 5-8 μm; wherein, the phosphate-solubilizing bacteria are fixed by a sodium alginate-calcium chloride cross-linking method, and after spraying, it is cured by hot air at 40°C for 10 minutes.

[0025] When spraying the outer layer, a hydrophobically modified cellulose solution is sprayed to form a protective layer with a thickness of 1-2 μm; ethanol is used as a solvent, and after spraying, it is dried at 60° C. for 20 minutes.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] This invention utilizes the synergistic effect of citric acid-modified ammonium polyphosphate and a three-layer functional coating to improve phosphorus utilization, effectively addressing the problem of phosphorus being easily fixed in the soil. The pH-responsive coating design allows the fertilizer to automatically adapt to different soil environments, rapidly releasing 30-40% of phosphorus in acidic soils to meet crop early-stage needs. Under neutral conditions, phosphorus is activated by phosphate-solubilizing bacteria to continuously supply phosphorus. In alkaline environments, the outer layer's slow-release mechanism extends the fertilizer's effectiveness to 120-150 days.

[0028] The phosphate-solubilizing bacteria microencapsulation technology in the middle coating of this invention maintains a bacterial survival rate of over 85%, forming a dual-channel phosphorus release mechanism with modified ammonium polyphosphate. The fully biodegradable coating material completely degrades within 120 days, reducing white pollution compared to traditional polymer coatings. Precisely controlled release reduces phosphorus loss by 50-70%, mitigating the risk of water eutrophication. Furthermore, the addition of seaweed extract and amino acid-chelated trace elements increases wheat protein content by 1.2 percentage points and fruit soluble solids by 8-15%.

[0029] The above summary is for illustrative purposes only and is not intended to be limiting in any way. In addition to the illustrative aspects, embodiments and features described above, further aspects, embodiments and features of the present invention will be readily apparent by reference to the accompanying drawings and the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1The present invention is a flowchart of the preparation method of the polymeric phosphorus slow-release compound fertilizer. DETAILED DESCRIPTION

[0031] The following will provide a clear and complete description of the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0032] Example 1

[0033] As attached Figure 1 As shown, the preparation method of the polymeric phosphorus slow-release compound fertilizer comprises the following steps:

[0034] To prepare modified ammonium polyphosphate, 1000 g of ammonium polyphosphate was mixed with 120 g of citric acid, and the mixture was stirred in a water bath at 60°C for 2 hours. The reaction product was spray-dried at an inlet temperature of 180°C and an outlet temperature of 80°C to obtain modified ammonium polyphosphate powder with a particle size of 50-80 μm.

[0035] To prepare the fertilizer core, weigh the following ingredients: 40 kg modified ammonium polyphosphate, 20 kg urea-formaldehyde slow-release nitrogen, 15 kg potassium chloride coated with potassium humate, 3 kg amino acid chelated trace elements, and 2 kg seaweed extract.

[0036] The above raw materials were fully mixed in a mixer for 30 minutes, and granulated using a fluidized bed granulator with an inlet air temperature of 55°C and an atomization pressure of 0.3 MPa to obtain granules with a particle size of 2.5-3.5 mm;

[0037] In the preparation of the three-layer coating, for the inner coating, a 1:2 mixed solution of chitosan with a deacetylation degree of 90% and polylactic acid was prepared, and the solvent was 5% acetic acid; bottom spray fluidized bed spraying was adopted, the spraying amount was 4%, and the hot air temperature was 50°C to form a pH response layer with a thickness of about 4 μm.

[0038] For the middle layer of the membrane, when preparing the phosphate-solubilizing bacteria microcapsules, the bacterial solution concentration is 10 8 CFU / mL, mixed with 2% sodium alginate solution at a ratio of 1:5, and microcapsules with a particle size of 15-20 μm were prepared by electrostatic spraying, wherein the spraying amount was 6% and hot air treatment was performed at 40 °C for 15 minutes to form a bioactive layer with a thickness of about 6 μm.

[0039] For the outer coating, a 5% stearic acid-modified hydroxypropyl methylcellulose ethanol solution was prepared, with a spraying amount of 2%, and the drying condition was hot air at 60°C for 20 minutes to form a hydrophobic protective layer with a thickness of about 1.5 μm.

[0040] Regarding sustained-release performance, according to GB / T 23348-2009 standard, the initial dissolution rate in water is 8.5%, the cumulative release rate after 28 days is 52%, and the peak of the differential release rate occurs on the 45th day.

[0041] The pH response test showed that the 24-hour release rate was 15.2% in pH 5.0 buffer, 8.3% in pH 7.0 buffer, and 5.1% in pH 8.5 buffer after 24 hours.

[0042] Regarding biodegradability, according to ISO 17556 standard, the degradation rate is 78% in 90 days and completely degraded in 120 days.

[0043] Example 2

[0044] The difference between the compound fertilizer and Example 1 is that the modified ammonium polyphosphate is 35 kg, the urea-formaldehyde slow-release nitrogen is 18 kg, and the potassium chloride coated with potassium humate is 25 kg;

[0045] The difference between the preparation method and Example 1 is that 5% of the binder is added during fluidized bed granulation, and the thickness of the outer coating is increased to 2 μm to enhance moisture resistance.

[0046] The initial potassium dissolution rate in 24 hours is 6.8%, which is suitable for crops with high potassium requirements, such as fruit trees.

[0047] Example 3

[0048] The difference from Examples 1 and 2 is that 1 kg of polyglutamic acid is added, the amount of seaweed extract is increased to 3 kg, and 0.5 kg of brown algae oligosaccharide is added.

[0049] In the biological effect test, the wheat pot experiment showed that the root biomass increased by 32% compared with the control, and the soil microbial diversity index increased by 15%.

[0050] Example 4

[0051] The difference from Examples 1, 2, and 3 is that for the preparation of tartaric acid-modified ammonium polyphosphate, ammonium polyphosphate and tartaric acid are reacted in a 1:1 ethanol-water system, the pH is controlled at 4.5-5.0, and the reaction product is spray-dried to obtain a white powder.

[0052] For the preparation of nanocomposite coating, first, nano-SiO2 and KH-550 were ultrasonically treated in ethanol at a ratio of 10:1 for 30 min and dried at 60 °C to obtain hydrophobic modified nanoparticles;

[0053] Prepare 3% stearic acid modified cellulose and 5% pre-treated nano-SiO2, disperse them in tetrahydrofuran at 20,000 rpm for 15 minutes, and use electrostatic spraying with a voltage of 30 kV and a film thickness of 2.5 μm.

[0054] When the pH buffer solution is 8.5, the alkaline resistance test results are shown in the following table:

[0055] index Example 1 Example 4 Phosphorus availability maintenance time (days) 90 150 28-day cumulative release rate 38％ 25％ Coating corrosion weight loss rate 12％ 4％

[0056] As can be seen from the table, the duration of phosphorus effectiveness is increased by 67%, the cumulative release over 28 days is smoother, and the corrosion resistance is increased by 3 times.

[0057] The biological activity test was carried out. The survival rate of phosphate-solubilizing bacteria was 2×10 8 CFU / g, after 60 days, the survival rate in pH8.5 soil was 5.6×10 7 CFU / g, which is 40% higher than that in Example 1.

[0058] Regarding phosphorus activation efficiency, the Olsen-P content in Example 4 is 21.3 mg / kg, which is 18% higher than that in Example 1.

[0059] Example 5

[0060] For industrial-grade ammonium polyphosphate, industrial by-product-grade ammonium polyphosphate with a purity of 85% is used and processed by the following method:

[0061] The raw materials were passed through a 100-mesh sieve to remove impurities and blended with 3% citric acid at 50° C. for 1 hour.

[0062] Sodium lignin sulfonate is used to replace 30% of potassium humate. Sodium lignin sulfonate is pre-mixed with potassium chloride in a ratio of 1:8 to form a porous wrapping structure.

[0063] 38wt% of industrial-grade modified ammonium polyphosphate, 18wt% of urea-formaldehyde slow-release nitrogen, 17wt% of potassium lignin sulfonate complex, 3wt% of amino acid chelated trace elements, and 1.5wt% of seaweed extract.

[0064] In the preparation method, the modified ammonium polyphosphate is activated, 85% pure ammonium polyphosphate is reacted with citric acid at 50° C. in a mixer, 0.5% nano-silicon dioxide is added as a crystallization inhibitor, and the modified product is spray-dried.

[0065] To prepare a composite potassium source, 20% sodium lignin sulfonate solution and potassium chloride powder were mixed at a ratio of 1:8, and granulated in a fluidized bed with an inlet air temperature of 60°C to form 1-2 mm porous particles with a porosity controlled at 35-40%.

[0066] Fertilizer molding method: All raw materials were mixed in a twin-shaft mixer for 15 minutes, and extrusion granulation was performed at a pressure of 8-10 MPa. A composite film of 2% modified starch and 1% paraffin wax was used for coating, with a spraying temperature of 70°C and a film thickness of 8-10 μm. A comparison with Example 1 is shown in the following table:

[0067] Test indicators Example 1 Example 5 Initial dissolution rate (24h) 8.5％ 12％ 28-day cumulative release rate 52％ 45％ Release uniformity index 0.82 0.71

[0068] Corn pot test: phosphorus utilization rate was 58%, biomass difference was -7%, and the available phosphorus content in the soil was 18.5 mg / kg 60 days after application.

[0069] Example 6

[0070] A polymeric phosphorus slow-release compound fertilizer comprising a core and a coating layer, wherein:

[0071] The core comprises: 30 wt% of modified ammonium polyphosphate, 15 wt% of urea-formaldehyde slow-release nitrogen, 10 wt% of potassium chloride wrapped in potassium humate, 2 wt% of amino acid chelated trace elements, and 1 wt% of seaweed extract;

[0072] The coating layer has a three-layer structure, the inner layer is pH-responsive chitosan / polylactic acid copolymer with a thickness of 3 μm, the middle layer is phosphate-solubilizing bacteria microcapsules with a thickness of 5 μm, and the outer layer is hydrophobically modified cellulose with a thickness of 1 μm.

[0073] The modified ammonium polyphosphate is citric acid-modified ammonium polyphosphate, and its preparation method comprises:

[0074] Ammonium polyphosphate and citric acid were reacted at a molar ratio of 5:1 at 60°C for 2h;

[0075] After spray drying, a modified product with a particle size of 50-100 μm is obtained.

[0076] Urea-formaldehyde slow-release nitrogen is a slow-release nitrogen fertilizer formed by the condensation of urea and formaldehyde, and its nitrogen release cycle is 30-90 days.

[0077] In the potassium chloride wrapped with potassium humate, the mass ratio of potassium humate to potassium chloride is 1:5.

[0078] The amino acid chelated trace elements are selected from at least two of iron, zinc, manganese, copper and boron, and the chelated amino acid is glutamic acid.

[0079] In the pH-responsive chitosan / polylactic acid copolymer, the mass ratio of chitosan to polylactic acid is 1:2.

[0080] The preparation method of phosphate-solubilizing bacteria microcapsules comprises the following steps: mixing phosphate-solubilizing bacteria with sodium alginate, and preparing microcapsules with a particle size of 10 μm by a spray drying method.

[0081] The hydrophobically modified cellulose is a product obtained by modifying hydroxypropyl methylcellulose with stearic acid.

[0082] Example 7

[0083] A polymeric phosphorus slow-release compound fertilizer comprising a core and a coating layer, wherein:

[0084] The core comprises: 50 wt% of modified ammonium polyphosphate, 25 wt% of urea-formaldehyde slow-release nitrogen, 20 wt% of potassium chloride wrapped in potassium humate, 5 wt% of amino acid chelated trace elements, and 3 wt% of seaweed extract;

[0085] The coating layer has a three-layer structure, the inner layer is pH-responsive chitosan / polylactic acid copolymer with a thickness of 5 μm, the middle layer is phosphate-solubilizing bacteria microcapsules with a thickness of 8 μm, and the outer layer is hydrophobically modified cellulose with a thickness of 2 μm.

[0086] Example 8

[0087] A polymeric phosphorus slow-release compound fertilizer comprising a core and a coating layer, wherein:

[0088] The core comprises: 40 wt% of modified ammonium polyphosphate, 20 wt% of urea-formaldehyde slow-release nitrogen, 15 wt% of potassium chloride wrapped in potassium humate, 3 wt% of amino acid chelated trace elements, and 2 wt% of seaweed extract;

[0089] The coating layer has a three-layer structure, the inner layer is pH-responsive chitosan / polylactic acid copolymer with a thickness of 4 μm, the middle layer is phosphate-solubilizing bacteria microcapsules with a thickness of 7 μm, and the outer layer is hydrophobically modified cellulose with a thickness of 1.5 μm.

[0090] In summary, industrial-grade ammonium polyphosphate is activated by citric acid, increasing the effective phosphorus content from 85% to 92% purity. Sodium lignin sulfonate serves as both a potassium carrier and a natural binder, reducing the use of additional additives. It is suitable for cost-sensitive areas such as field crops, medium- and low-yield field improvement projects, and integrated solutions for use with organic fertilizers.

[0091] Comparative Example 1

[0092] Commercially available sulfur-coated superphosphate and the product of Example 1 of the present invention were compared under the same conditions. The following table shows the performance comparison:

[0093] Test indicators Embodiment 1 of the present invention Comparative Example 1 (SCP) Initial dissolution rate (24h) 8.5％ 25％ Cumulative release period (days) 60-120 40-80 pH response sensitivity significant none Encapsulation degradation rate (90 days) 78％ Non-degradable Phosphorus utilization rate (%) 68 41 Microbial activity retention rate 85％ 0％

[0094] As can be seen from the table, the release of SCP is hindered in alkaline soil, the coating material causes white pollution, and there is no microbial synergy.

[0095] Comparative Experimental Example 2

[0096] The following table shows the performance comparison of using only a single-layer polyvinyl alcohol coating and the three-layer coating of the present invention:

[0097]

[0098]

[0099] As can be seen from the table, a single-layer coating cannot achieve pH-responsive release, the lack of a microbial protection layer leads to functional loss, and defects in the coating structure make release more likely.

[0100] In summary, the present invention, through the structure of the core and three coating layers, not only achieves the synergistic slow release of phosphorus, nitrogen, potassium and various trace elements, but also improves the nutrient utilization rate and soil adaptability of the fertilizer. Among them, the core adopts a scientific ratio of ingredients such as citric acid-modified ammonium polyphosphate, urea-formaldehyde slow-release nitrogen, and potassium humate-wrapped potassium chloride to ensure long-term fertilizer supply capacity; in the coating layer, the pH-responsive chitosan / polylactic acid copolymer inner layer can intelligently adjust the nutrient release rate according to the soil pH, the phosphate-solubilizing bacteria microcapsule middle layer promotes the conversion of insoluble phosphorus through biological activation, and the hydrophobically modified cellulose outer layer effectively blocks external environmental interference and extends the effective period of the fertilizer.

[0101] In terms of preparation method, the fluidized bed granulation and step-by-step spray coating process are used to achieve uniform compounding and structural stability of each component, and finally obtain a compound fertilizer with moderate particle size and precise and controllable nutrient release.

[0102] In the description of this specification, the reference terms "one embodiment", "some embodiments", "example", "specific example" or "some examples" mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification and features of different embodiments or examples without contradiction.

[0103] In the drawings of the embodiments disclosed in the present invention, only the structures related to the embodiments disclosed in the present invention are involved. Other structures can refer to the general design. In the absence of conflict, the same embodiment and different embodiments of the present invention can be combined with each other.

[0104] Although the embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are illustrative and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention.

Claims

1. A polymeric phosphorus slow-release compound fertilizer, characterized in that: It includes a core and an envelope layer, wherein: The core comprises: 30-50 wt% of modified ammonium polyphosphate, 15-25 wt% of urea-formaldehyde slow-release nitrogen, 10-20 wt% of potassium chloride wrapped in potassium humate, 2-5 wt% of amino acid chelated trace elements, and 1-3 wt% of seaweed extract; The coating layer has a three-layer structure, the inner layer is pH-responsive chitosan / polylactic acid copolymer with a thickness of 3-5 μm, the middle layer is phosphate-solubilizing bacteria microcapsules with a thickness of 5-8 μm, and the outer layer is hydrophobically modified cellulose with a thickness of 1-2 μm.

2. The polymeric phosphorus slow-release compound fertilizer according to claim 1, characterized in that: The modified ammonium polyphosphate is citric acid-modified ammonium polyphosphate, and its preparation method comprises: Ammonium polyphosphate and citric acid were reacted at a molar ratio of 5:1 at 60°C for 2 hours, and a modified product with a particle size of 50-100 μm was obtained after spray drying.

3. The polymeric phosphorus slow-release compound fertilizer according to claim 1, characterized in that: The urea-formaldehyde slow-release nitrogen is a slow-release nitrogen fertilizer formed by the condensation of urea and formaldehyde, and the nitrogen release period is 30-90 days.

4. The polymeric phosphorus slow-release compound fertilizer according to claim 1, characterized in that: In the potassium chloride wrapped with potassium humate, the mass ratio of potassium humate to potassium chloride is 1:5-1:

10.

5. The polymeric phosphorus slow-release compound fertilizer according to claim 1, characterized in that: The amino acid chelated trace elements are selected from at least two of iron, zinc, manganese, copper and boron, and the chelated amino acids are glutamic acid or aspartic acid.

6. The polymeric phosphorus slow-release compound fertilizer according to claim 1, characterized in that: In the pH-responsive chitosan or polylactic acid copolymer, the mass ratio of chitosan to polylactic acid is 1:

2.

7. The polymeric phosphorus slow-release compound fertilizer according to claim 1, characterized in that: The preparation method of the phosphate-solubilizing bacteria microcapsules comprises the following steps: mixing the phosphate-solubilizing bacteria with sodium alginate, and adopting a spray drying method to prepare microcapsules with a particle size of 10-20 μm.

8. The polymeric phosphorus slow-release compound fertilizer according to claim 1, characterized in that: The hydrophobically modified cellulose is a product obtained by modifying hydroxypropyl methylcellulose with stearic acid.

9. A method for preparing a polymeric phosphorus slow-release compound fertilizer, characterized in that: The following steps are involved: When preparing the modified ammonium polyphosphate, the ammonium polyphosphate is first reacted with citric acid and then spray-dried; When performing core granulation, firstly, modified ammonium polyphosphate, urea-formaldehyde slow-release nitrogen, potassium chloride coated with potassium humate, amino acid chelated trace elements, and seaweed extract are mixed and granulated in a fluidized bed to a particle size of 2-4 mm. The temperature of the fluidized bed granulation is 50-60°C and the wind speed is 2-4 m / s. Preparation of the coating layer. When spraying the inner layer, a chitosan and polylactic acid copolymer solution is sprayed on the surface of the core to form a pH-responsive layer with a thickness of 3-5 μm. Ethyl acetate is used as the solvent and the spraying pressure is 0.2-0.4 MPa. When spraying the middle layer, the phosphate-solubilizing bacteria microcapsule suspension is sprayed to form a biological activation layer with a thickness of 5-8 μm; wherein, the phosphate-solubilizing bacteria are fixed by a sodium alginate-calcium chloride cross-linking method, and after spraying, it is cured by hot air at 40°C for 10 minutes. When spraying the outer layer, a hydrophobically modified cellulose solution is sprayed to form a protective layer with a thickness of 1-2 μm; ethanol is used as a solvent, and after spraying, it is dried at 60° C. for 20 minutes.

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