Preparation and application method of pig manure carbon-based functional double-coated slow-release organic fertilizer adaptive to growth characteristics of sweet tangelo

Abstract

The invention discloses a preparation method and an application method of a pig manure carbon-based functional double-coated slow-release organic fertilizer adaptive to growth characteristics of sweet tangelo, and belongs to the technical field of agricultural fertilizers. The organic fertilizer is characterized in that decomposed pig manure is used as a core fertilizer particle, modified pig manure biochar, a mineral-trace element composite conditioner and a composite functional microbial agent are coated outside the core fertilizer particle to form a functional layer, and inner and outer slow-release envelopes are arranged on the functional layer. Aiming at the growth characteristics that the sweet tangelo needs nitrogen in a germination period, needs phosphorus in a fruit setting period and needs potassium in a fruit swelling period, and the problems of soil acidification, insufficient organic matters, mismatching of nutrient release and a fertilizer requiring period and the like, release of elements such as nitrogen, phosphorus, potassium, boron, magnesium and the like is accurately matched with nutrient requirements of the sweet tangelo in different growth periods through an internal supply-external control double-layer release regulation mechanism, so that the growth period of the sweet tangelo is shortened, and the yield of the sweet tangelo is increased. The acidified soil can be effectively improved, the organic matter content is increased, the rhizosphere pH is stabilized, and the content of soluble solids and vitamin C of fruits is remarkably increased.

Description

Technical Field

[0001] This invention belongs to the field of agricultural fertilizer technology, and more specifically relates to the preparation and application method of a pig manure carbon-based functional double-coated slow-release organic fertilizer adapted to the growth characteristics of sweet oranges and pomelos. Background Technology

[0002] Sweet citrus fruits exhibit typical stage-specific nutrient requirements throughout their growth cycle: high nitrogen is needed during bud break to promote leaf and branch growth; phosphorus is needed during fruit setting to enhance flower and fruit development; and a large amount of potassium is required during fruit expansion to promote sugar accumulation and fruit quality formation. Simultaneously, sweet citrus fruits are prone to boron and magnesium deficiencies, and their roots prefer slightly acidic soil (pH 5.5-6.5). However, existing sweet citrus orchards generally suffer from the following problems: long-term application of chemical fertilizers leads to soil acidification, causing a decrease in soil pH and directly inhibiting root activity; simultaneously, insufficient soil organic matter content results in a reduction in microbial populations, leading to a gradual decline in soil fertility. Furthermore, the release timing of conventional organic and chemical fertilizers is difficult to match with the crop's nutrient requirements, resulting in a mismatch between nitrogen, phosphorus, and potassium supply and crop demand. These problems collectively cause significant differences in the sugar-acid ratio of fruits in the orchard, uneven quality, and weakened overall disease resistance. Traditional coated fertilizers, mainly single-layer high-molecular-weight fertilizers, have fixed release curves and are unable to meet the multi-stage nutrient requirements of citrus trees. In addition, although conventional biochar has fertilizer retention function, its high surface inertness and uneven micropore distribution limit the efficiency of functional bacteria attachment and trace element release.

[0003] Therefore, there is an urgent need for a new fertilizer system that combines organic matter replenishment, slow-release precision, rhizosphere conditioning, and quality improvement functions to achieve efficient, ecological, and high-quality production of sweet tangerines and pomelos. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing and applying a pig manure-based functional double-coated slow-release organic fertilizer adapted to the growth characteristics of sweet oranges and pomelos, so as to solve the problems existing in the prior art, achieve precise matching of nutrients and growth period, improve fruit quality and improve the soil environment.

[0005] To achieve the above objectives, the present invention provides the following solution:

[0006] One of the technical solutions of this invention is to provide a pig manure-based functional double-coated slow-release organic fertilizer adapted to the growth characteristics of sweet oranges and pomelos, comprising, from the inside out, a core fertilizer granule, a functional layer, and an outer coating; the particle size of the core fertilizer granule is 3-5 mm; the functional layer is fixed to the surface of the core fertilizer granule by the inner coating; the thicknesses of the inner coating, the functional layer, and the outer coating are 0.05-0.1 mm, 0.05-0.1 mm, and 0.1-0.2 mm, respectively.

[0007] The core fertilizer granules are composed of 50-70 parts of well-rotted pig manure;

[0008] The inner coating comprises sodium alginate, oxidized starch, and glycerol in a mass ratio of 3~5:5~7:1;

[0009] The functional layer consists of 15-25 parts of modified pig manure biochar, 10-20 parts of mineral-trace element composite conditioner, and 2-5 parts of composite functional microbial agent;

[0010] The outer coating comprises polylactic acid (PLA), polyhydroxyalkanoate (PHA), and modified nano-diatomaceous earth in a mass ratio of 7~8:2~3:0.5~1.

[0011] Preferably, the preparation steps of the modified pig manure biochar are as follows:

[0012] Step 1: Dry fresh pig manure to a moisture content of ≤10%, crush it, and then pyrolyze it at 500~650℃ for 1~3 hours under nitrogen protection to obtain primary pig manure biochar.

[0013] Step 2: Mix the prepared pig manure biochar with a collagenase solution with a concentration of 2-4 U / mL at a liquid-solid ratio of 1 mL: 8-10 g, stir at 35-40℃ and 120-150 rpm for 24-36 h, filter, and obtain collagenase modified biochar.

[0014] Step 3: Add a citric acid solution with a concentration of 1-2 wt% to the collagenase modified biochar, sonicate for 25-30 min, let stand for 12-16 h, and then dry at 60-70℃ to constant weight to obtain the modified pig manure biochar.

[0015] Preferably, the mineral-trace element composite conditioner is composed of potassium feldspar powder, oyster shell powder, zinc sulfate and manganese sulfate in a mass ratio of 10~15:5~10:1:1.

[0016] Preferably, the compound functional microbial agent is composed of Bacillus subtilis, Bacillus thuringiensis and Trichoderma harzianum in an effective viable count ratio of 1.5~2:1~1.5:1, and the total effective viable count is ≥1 billion / g.

[0017] The second technical solution of the present invention provides a method for preparing the above-mentioned pig manure-based functional double-coated slow-release organic fertilizer adapted to the growth characteristics of sweet tangerines and pomelos, comprising the following steps:

[0018] Well-rotted pig manure is extruded and granulated to obtain core fertilizer particles with a particle size of 3-5 mm.

[0019] Sodium alginate, oxidized starch, and glycerol are dissolved in water to obtain an inner coating solution. The core fertilizer granules are first immersed in the inner coating solution, and then placed in a functional layer mixed powder obtained by mixing modified pig manure biochar, mineral-trace element composite conditioner, and composite functional microbial agent to obtain fertilizer granules with adhesive powder. The fertilizer granules with adhesive powder are then immersed in calcium chloride solution for cross-linking and solidification to obtain single-coated organic fertilizer.

[0020] Polylactic acid, polyhydroxy fatty acid ester, and modified nano-diatomaceous earth are dissolved in water to obtain an outer coating solution; the outer coating solution is sprayed onto the surface of the single-coated organic fertilizer and dried to obtain the pig manure carbon-based functional double-coated slow-release organic fertilizer adapted to the growth characteristics of sweet oranges and pomelos.

[0021] Preferably, the concentration of the inner coating solution is 3-5 wt%; the treatment time in the inner coating solution is 3-5 s; the concentration of the calcium chloride solution is 1-3 wt%; and the curing and crosslinking time is 5-10 min.

[0022] Preferably, the concentration of the outer coating liquid is 5~8wt%; the spraying conditions are: temperature 30~50℃, spraying speed 3~5mL / min.

[0023] Preferably, when preparing the functional layer mixed powder, the composite functional microbial agent and a portion of modified pig manure biochar are first mixed and allowed to stand at 25-30°C for 2-4 hours for adsorption, and then the remaining raw materials are added.

[0024] The third technical solution of this invention is to provide the application of the above-mentioned pig manure carbon-based functional double-coated slow-release organic fertilizer adapted to the growth characteristics of sweet oranges and pomelos in the cultivation of sweet oranges and pomelos.

[0025] The fourth technical solution of this invention provides a method for improving the yield and quality of sweet tangerines and pomelos. The method involves applying the pig manure-based functional double-coated slow-release organic fertilizer, adapted to the growth characteristics of sweet tangerines and pomelos, twice: once before spring budding (late February to early March) and again during the early fruit enlargement stage (June to July). Application method: application is done in holes or trenches at a depth of 20-30 cm, with the application point near the drip line of the tree canopy. Application amount: 200-500 g per tree, depending on tree age. After application, cover with soil and water thoroughly.

[0026] Invention concept:

[0027] This invention addresses three core problems in sweet tangerine and pomelo cultivation: poor soil compatibility, mismatch between nutrient supply and demand, and uneven fruit quality. It focuses on the growth characteristics of sweet tangerines and pomelos, including nitrogen requirements during bud break, potassium requirements during fruit expansion, susceptibility to boron and magnesium deficiencies, and suitability for slightly acidic soils with a pH of 6-6.5. Using a three-dimensional design logic of raw material adaptation, process optimization, and functional targeting, it constructs a targeted pig manure-based functional double-coated slow-release organic fertilizer technology system. The specific concept is as follows:

[0028] (1) Raw material matching: Targeted matching of sweet orange and pomelo needs with soil remediation needs.

[0029] Using well-rotted pig manure as the core fertilizer granule raw material, it not only provides the basic nitrogen, phosphorus nutrients and organic matter required for the growth of sweet oranges and pomelos, but also realizes the resource utilization of agricultural waste and solves the pollution problem of traditional pig manure dumping. The functional layer introduces modified pig manure biochar, which enhances its adsorption and acid-regulating capacity through the process of "drying-nitrogen pyrolysis-collagenase + citric acid modification". It can not only adsorb nutrients and delay their release, but also work synergistically with mineral-trace element compound conditioners (potassium-containing feldspar powder to supplement potassium, oyster shell powder to adjust pH, zinc sulfate / manganese to supplement trace elements) to specifically repair soil acidification and supplement potassium, zinc and manganese elements that are easily lacking in sweet oranges and pomelos. At the same time, through compound functional bacterial agents (gelatinous Bacillus + Bacillus subtilis + Trichoderma harzianum) to inhibit soil-borne pathogens, it achieves synergistic adaptation at the raw material level in terms of nutrient supply, soil remediation and disease control.

[0030] (2) Process optimization: focusing on matching the survival of microbial agents with the slow release cycle of nutrients.

[0031] To address the issue of microbial agents being easily deactivated during fertilizer preparation, a process of "premixing a compound functional microbial agent with modified pig manure biochar (25-30℃ static adsorption for 2-4 hours)" was designed. This process utilizes the porous structure of biochar to immobilize the microbial agent, improving its survival rate and stability, and solving the functional failure problem caused by directly adding microbial agents to existing fertilizers. An innovative double-coating process is employed: the middle layer uses sodium alginate-oxidized starch-glycerol cross-linked and solidified with calcium chloride to achieve initial controlled nutrient release (matching the nutrient demand rhythm during germination); the outer layer uses PLA-PHA-modified nano-diatomaceous earth sprayed through a fluidized bed to form a dense film, achieving long-term slow release. The total slow release period covers the two peak nutrient demand periods for sweet citrus fruits, from pre-germination to early fruit expansion, overcoming the shortcomings of existing single-layer coated fertilizers, such as short slow release periods and inability to match nutrient demand periods. The core fertilizer granules are extruded (3-5mm in diameter), and the functional layers use rolling loading to ensure uniform fertilizer particle size and structural stability of each layer, preventing localized nutrient enrichment or loss.

[0032] (3) Functional targeting: to achieve synergy of "soil improvement - precise nutrient supply - quality improvement".

[0033] To address targeted soil issues, the pH of the rhizosphere soil is stabilized to 6-6.5 (suitable range for sweet tangerines and pomelos) by utilizing the acid-regulating properties of modified pig manure biochar and oyster shell powder. This simultaneously increases organic matter content and inhibits crop pathogens, overcoming the limitation of existing fertilizers that only provide nutrients without repairing the soil. Based on the nutrient requirements of sweet tangerines and pomelos, two applications (20-30cm deep, near the drip line of the canopy) are designed: one before spring budding (late February to early March) and another at the early fruit enlargement stage (June to July). This is combined with a double-coated, stepwise slow-release system to ensure precise nitrogen supply during budding and potassium supply during fruit enlargement, avoiding nutrient waste and supply-demand mismatches. Targeted quality improvement: Through the synergistic effect of soil improvement + precise nutrient application + microbial agents promoting absorption, the soluble solids and vitamin C content of sweet tangerines and pomelos are increased, titratable acidity is reduced, and single fruit weight is increased, addressing the issues of limited quality improvement and uneven fruit size associated with existing fertilizers.

[0034] The core fertilizer granules of this invention consist of 50-70 parts of well-rotted pig manure; the inner coating comprises sodium alginate, oxidized starch, and glycerol in a mass ratio of 3-5:5-7:1; the functional layer comprises 15-25 parts of modified pig manure biochar, 10-20 parts of a mineral-trace element composite conditioner, and 2-5 parts of a composite functional microbial agent; the outer coating comprises polylactic acid (PLA), polyhydroxyalkanoates (PHA), and modified nano-diatomaceous earth in a mass ratio of 7-8:2-3:0.5-1; the mineral-trace element composite conditioner is composed of potassium feldspar powder, oyster shell powder, zinc sulfate, and manganese sulfate in a mass ratio of 10-15:5-10:1:1; the composite functional microbial agent is composed of Bacillus subtilis, Bacillus thuringiensis, and Trichoderma harzianum in an effective viable bacteria ratio of 1.5-2:1-1.5:1, and the total effective viable bacteria count is ≥1 billion / g. The combined use of the above-mentioned raw materials has achieved the effect of improving the yield and quality of sweet tangerines and pomelos, specifically:

[0035] Firstly, the well-rotted pig manure in the core fertilizer granules provides the system with basic organic matter and mineralized nutrients such as nitrogen and phosphorus. It has a homology affinity with the modified pig manure biochar in the functional layer, and the two work together to construct the "nutrient pool" and "carbon skeleton" of the fertilizer granules. With its well-developed porous structure, the modified pig manure biochar adsorbs readily available nutrients such as ammonium nitrogen released from the decomposition of pig manure, effectively preventing excessive local concentrations from stressing the functional microorganisms and roots, and prolonging the fertilizer effect through slow release. On the other hand, it forms an acid-base buffer pair with the oyster shell powder in the mineral-trace element compound conditioner, together stabilizing the pH of the rhizosphere microdomain to the optimal range of 6.0-6.5 for sweet citrus. This environment not only promotes root vitality but also activates the potassium release potential of the potassium feldspar powder in the conditioner and promotes the availability of trace elements such as zinc and manganese.

[0036] Secondly, the introduction and survival of compound functional microbial agents are key to achieving bio-enhancing effects. The combination of *Bacillus spp.*, *Bacillus subtilis*, and *Trichoderma harzianum* creates a complementary effect: *Bacillus spp.* primarily activates insoluble potassium and silicon, *Bacillus subtilis* produces antibacterial substances and promotes phosphorus absorption, while *Trichoderma harzianum* competitively inhibits soil-borne pathogens through root colonization. These microbial agents, pre-adsorbed into the porous structure of modified pig manure biochar, gain physical protection and carbon source replenishment, significantly improving their survival rate and colonization capacity. Their synergistic metabolic activities in the rhizosphere not only directly promote the activation and transformation of nutrients in the mineral-trace element compound conditioner, but the plant hormones they secrete also simultaneously enhance the absorption and translocation efficiency of nutrients in sweet oranges and grapefruits, providing a physiological basis for fruit sugar accumulation and vitamin C synthesis.

[0037] Finally, the inner and outer double-layer coatings constitute a "time-sequence controller" for nutrient release. The inner sodium alginate-oxidized starch film swells rapidly upon contact with water, preferentially releasing some nitrogen sources and active bacterial agents attached to the functional layer during the budding stage, meeting the needs of early tree growth and microbial community establishment; the outer PLA-PHA-nanodiatomite composite film degrades slowly, and its dense structure only begins to be gradually decomposed by microorganisms during the critical period of fruit expansion. At this time, elements such as potassium, zinc, and manganese slowly released from the functional layer can be continuously supplied, precisely matching the high demand for potassium and trace elements during the fruit expansion period of sweet tangerines and pomelos, thereby effectively driving the transport and conversion of sugar to the fruit and significantly optimizing the sugar-acid ratio and single fruit weight.

[0038] The present invention discloses the following technical effects:

[0039] (1) This invention uses modified pig manure biochar and oyster shell powder to synergistically adjust the acidity, which can stably control the pH of the rhizosphere soil at 6~6.5 (the optimal pH range for sweet oranges and pomelos), and increase the organic matter content. At the same time, the compound functional microbial agent significantly inhibits the activity of pathogenic bacteria such as bacterial wilt and Fusarium, achieving a three-in-one soil improvement effect of "adjusting acidity - replenishing organic matter - resisting disease". Furthermore, the adsorption properties of biochar can prolong the duration of the improvement effect, avoiding the problems of incomplete improvement and easy rebound in the existing technology.

[0040] (2) In the existing technology, ordinary organic fertilizers release nutrients quickly, resulting in insufficient nutrient supply during the budding stage of sweet oranges and pomelos and nutrient loss during the fruit expansion stage. The slow-release cycle of single-layer coated fertilizers is mostly around 30 days, which cannot cover the two peak nutrient demand periods of "budding-fruit expansion". Although chemical fertilizers release quickly, they are prone to nutrient loss and soil compaction. The double-coating design of the present invention achieves step-by-step slow release: the inner coating (sodium alginate-oxidized starch-glycerol) controls the initial release of nutrients during the budding stage (February to March), and the outer coating (PLA-PHA-modified nano diatomaceous earth) achieves long-term slow release during the fruit expansion stage (June to July). The total slow-release cycle covers the two key nutrient demand periods, and the potassium, zinc and manganese elements supplemented by the functional layer specifically solve the nutrient deficiency problem of sweet oranges and pomelos, completely solving the defect of mismatch between nutrient supply and nutrient demand period in the existing technology.

[0041] (3) Ordinary pig manure fertilizer has a low effect on increasing the soluble solids and vitamin C content of sweet oranges and pomelos, and the reduction in titratable acidity is not significant; chemical fertilizers easily lead to uneven fruit size and poor taste; general-purpose functional fertilizers have unstable quality improvement effects due to poor nutrient targeting. This invention, through the synergistic effect of "precise nutrient supply + soil microecological improvement", can significantly increase the soluble solids content, significantly reduce the titratable acidity, increase the vitamin C content, and increase the single fruit weight of sweet oranges and pomelos, and significantly improve the uniformity of fruit size. The quality improvement is far greater than that of existing fertilizers. At the same time, due to the stable soil and nutrient conditions, the quality consistency of different batches of fruit is stronger.

[0042] (4) Some coated fertilizers use non-degradable plastic coating materials, which can easily cause soil residue pollution; improper treatment of ordinary pig manure can easily cause environmental problems; some functional fertilizer raw materials rely on external purchases, which are costly. This invention uses "composted pig manure + modified pig manure biochar" as the core raw material to realize the resource utilization of pig manure waste (reducing pollution while reducing raw material costs); the inner coating material (sodium alginate, oxidized starch) and the outer coating material (PLA, PHA) are both biodegradable materials, avoiding the risk of soil residue; at the same time, the pre-adsorption process of microbial agents improves their survival rate, reduces the amount of microbial agents used, reduces production costs, and takes into account both economic efficiency and agricultural sustainability. Attached Figure Description

[0043] Figure 1 The effects of different treatments on the soluble solids and soluble sugar content of sweet orange-grapefruit fruit;

[0044] Figure 2 To investigate the effects of different treatments on the total acid and vitamin C content of sweet orange-grapefruit. Detailed Implementation

[0045] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0046] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0047] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0048] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be readily apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0049] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0050] It should be noted that any aspects not described in detail in this invention are conventional practices in the field and are not the focus of this invention.

[0051] Unless otherwise specified, all methods used in the following embodiments and comparative examples are conventional methods in the art. All parts mentioned in the embodiments and comparative examples are parts by weight.

[0052] The preparation steps of the modified pig manure biochar are as follows:

[0053] Fresh pig manure was dried at 105℃ until the moisture content was ≤10%, then crushed and passed through a 20-mesh sieve. The crushed manure was then placed in a tube furnace and pyrolyzed at 550℃ for 2 hours under nitrogen protection at a heating rate of 10℃ / min. After cooling in the furnace, the manure was removed to obtain primary pig manure biochar. The primary pig manure biochar was then mixed with a collagenase solution at a concentration of 3 U / mL at a liquid-to-solid ratio of 1:9 (mL / g) and stirred in a constant-temperature shaker at 37℃ and 135 rpm for 30 hours. After the reaction, the solid was separated by filtration and washed three times with deionized water to obtain collagenase-modified biochar. A 1.5 wt% citric acid solution (liquid-to-solid ratio of 10:1 (mL / g)) was added to the collagenase-modified biochar, and the mixture was ultrasonically treated at 300W for 28 minutes, followed by standing for 14 hours. Finally, the modified pig manure biochar was dried to constant weight in an oven at 65℃ and then ground through a 100-mesh sieve.

[0054] Collagenase and nano-diatomaceous earth used were purchased from Shanghai Aladdin Biochemical Technology Co., Ltd. The gelatinous Bacillus mucilaginosus, Bacillus subtilis, and Trichoderma harzianum used were purchased from Ningbo Mingzhou Biotechnology Co., Ltd., Shanghai Maclean Biochemical Technology Co., Ltd., and Ningbo Mingzhou Biotechnology Co., Ltd., respectively.

[0055] Example 1

[0056] Preparation of pig manure-based functional double-coated slow-release organic fertilizer adapted to the growth characteristics of sweet tangerines and pomelos:

[0057] 60 portions of well-rotted pig manure (from a farm in Zhejiang Province, with a moisture content of ≤30%) were processed into spherical granules with a particle size of 4 mm using an extrusion granulator, and then dried at 80℃ until the moisture content was <15% to prepare core fertilizer granules for later use.

[0058] Weigh out 12 parts potassium feldspar powder, 8 parts oyster shell powder, 1 part zinc sulfate heptahydrate, and 1 part manganese sulfate monohydrate by mass ratio, mix them evenly, and prepare a mineral-trace element composite conditioner.

[0059] Then, Bacillus subtilis, Bacillus thuringiensis, and Trichoderma harzianum were compounded at an effective viable count ratio of 1.8:1.2:1 to prepare a compound functional bacterial agent with an effective viable count ≥1 billion / g.

[0060] Take 3 parts of the compound functional microbial agent and 10 parts of the prepared modified pig manure biochar, and let them stand at 28℃ for 3 hours for adsorption. Mix the adsorbed mixture with the remaining 10 parts of modified pig manure biochar and 22 parts of mineral-trace element compound conditioner in a V-type mixer to obtain functional layer mixed powder.

[0061] Inner Coating and Functional Layer Loading: Sodium alginate, oxidized starch, and glycerol were dissolved in water at a mass ratio of 4:6:1 to prepare a 5wt% inner coating solution. The core fertilizer granules were immersed in the inner coating solution for 3 seconds and quickly removed, allowing a uniform liquid film to coat their surface. The core fertilizer granules with the liquid film were immediately transferred to the functional layer mixed powder and rolled in a coating pan at 30 rpm for 2 minutes to ensure uniform powder adhesion. The fertilizer granules with the adhered powder were then immersed in a 2wt% calcium chloride solution for cross-linking and curing for 8 minutes. After filtration, they were lightly rinsed with deionized water and air-dried at 50°C to form a stable inner coating, yielding a single-coated organic fertilizer.

[0062] Outer Coating: Polylactic acid (PLA), polyhydroxyalkanoate (PHA), and modified nano-diatomaceous earth were dissolved in dichloromethane at a mass ratio of 7.5:2.5:0.8 to prepare an 8wt% outer coating solution. The prepared single-coated organic fertilizer was then placed in a fluidized bed coating machine, with the material temperature controlled at 40℃. The outer coating solution was sprayed at a rate of 3mL / min. After spraying, the mixture was dried at 50℃ for 2 hours to form a dense outer slow-release membrane, thus obtaining pig manure-based functional double-coated slow-release organic fertilizer (wherein the thicknesses of the inner coating, functional layer, and outer coating are 0.05mm, 0.05mm, and 0.1mm, respectively).

[0063] Comparative Example 1: No outer coating

[0064] The preparation method is basically the same as in Example 1, but the "outer coating" step is omitted, and the resulting product is a single-coated fertilizer with only an inner coating.

[0065] Comparative Example 2: No modified pig manure biochar was used in the functional layer.

[0066] The preparation method is basically the same as in Example 1, but the functional layer uses an equal amount of primary pig manure biochar (i.e., only pyrolyzed, without collagenase and citric acid modification) to replace the modified pig manure biochar.

[0067] Field trials:

[0068] Field trials were conducted on the organic fertilizers prepared in Example 1, Comparative Example 1, and Comparative Example 2 (referred to as Experimental Group 1, Control Group 1, and Control Group 2, respectively). The trials were conducted at a sweet tangerine and pomelo planting base in Zhejiang Province. The initial soil pH was 5.2 and the organic matter content was 1.5 wt%. Sweet tangerine and pomelo trees of the same age and growth were selected. Before spring budding (March 5) and at the early stage of fruit enlargement (June 20), each tree was fertilized with 200 g of fertilizer in holes below the drip line of the canopy. The fertilization depth was 25 cm. After application, the soil was covered and the soil was thoroughly watered.

[0069] The following control group was also set up:

[0070] Control Group 3: Conventional application method: The fertilizer was the same as in Example 1, but the application method was changed to conventional broadcasting followed by shallow swirling (10cm deep), instead of the hole application depth and location specified in Example 1.

[0071] Control group 4: Commercially available slow-release compound fertilizer: Lico (li08) commercially available resin-coated slow-release compound fertilizer (N-P2O5-K2O: 18-9-13) purchased from Hefei Lico Agricultural Co., Ltd. was used. Its nutrient release period is 90 days, and it was applied after being converted according to the equivalent nitrogen content.

[0072] Control group 5 (blank control): No fertilization was performed.

[0073] A total of 60 sweet orange-pomelo plants were selected and divided into 6 groups. Field trials were conducted according to the treatment methods of experimental group 1, control group 1, control group 2, control group 3, control group 4 and control group 5.

[0074] Soil organic matter was determined using the potassium dichromate external heating method: 1. Weigh 0.5000g (±0.0001) of soil sample and add it to a test tube. Add 5mL of potassium dichromate solution and 5mL of sulfuric acid and mix well; (Potassium dichromate solution: 0.8mol / L, 32.2245g, dried at 130℃, and diluted to 1L); 2. Prepare two blanks and place them in an oven at 170℃. 2h; 3. Cool, wash with clean water into a plastic bottle, approximately 60mL; 4. Add 3-4 drops of o-phenanthroline indicator, titrate with ferrous sulfate until brick red; (Ferrous sulfate: 56g ferrous sulfate heptahydrate mixed with 5mL sulfuric acid, diluted to 1L; o-phenanthroline: 1.485g o-phenanthroline mixed with 0.695g ferrous sulfate, diluted to 100mL; Color development: orange-yellow—blue-green—brick red) 5. Calculation: Organic carbon (g / kg) = 0.8 × 5 × (V0 - V) × 3 × 1.1 / V0 × m, where, V0: blank titration volume, V: sample titration volume, m: soil mass. 6. Organic matter = organic carbon × 1.724.

[0075] Effect verification:

[0076] Table 1. Effects of different treatments on the yield of sweet oranges and pomelos

[0077] serial number Single unit weight (kg) Yield per plant (catties) Experimental group 1 1.79±0.09 258.6±4.32 Control group 1 1.22±0.11 243.2±6.24 Control group 2 1.01±0.20 225.5±7.58 Control group 3 1.12±0.14 224.6±6.50 Control group 4 1.34±0.24 239.9±6.30 Control group 5 0.84±0.36 207.0±8.10

[0078] Table 2 Effects of different treatments on soil physicochemical properties

[0079] Group Soil pH (harvest period) Organic matter content (harvest period) Organic matter improvement rate Experimental group 1 6.3 1.78% 18.70% Control group 1 5.9 1.73% 15.10% Control group 2 5.8 1.70% 13.50% Control group 3 5.7 1.67% 11.20% Control group 4 5.1 1.55% 3.30% Control group 5 5 1.50% -

[0080] Figure 1 The effects of different treatments on the soluble solids and soluble sugar content of sweet orange-grapefruit fruit were investigated.

[0081] Figure 2To investigate the effects of different treatments on the total acid and vitamin C content of sweet orange-grapefruit.

[0082] Depend on Figure 1 and Figure 2 It can be seen that the total soluble sugar content of the fruit in Example 1 was as high as 19.37%, significantly better than all control groups, and 68.9% higher than control group 5 (blank control). Meanwhile, its total soluble solids (TTS) content was 13.8%, and its total acid content decreased to 0.6%, the lowest among all groups. Calculations showed that the sugar-acid ratio of Example 1 was as high as 32.3, far higher than other treatments, indicating that its fruit flavor was sweeter and its sweet-acid balance was optimal.

[0083] The total acid content (0.98%) of Comparative Example 1 (without outer coating) was significantly higher than that of Example 1, indicating that the interruption of potassium supply during the fruit expansion period led to insufficient degradation of organic acids. Comparative Example 2 (unmodified biochar) showed only average sugar and acid levels, suggesting that the nutrient slow-release capacity of unmodified biochar is limited. The double-coated, stepped slow-release structure of this invention ensures a stable supply of potassium during the fruit expansion period, which is key to achieving high sugar, low acid, and optimized flavor.

[0084] The vitamin C content of the fruit in Example 1 reached 46.19 mg / 100g, which was 62.9% higher than that of control group 5 (blank control, 28.36 mg / 100g) and 16.0% higher than that of control group 4 (commercially available slow-release fertilizer, 39.83 mg / 100g), reaching the highest level among all treatments.

[0085] The vitamin C content of Comparative Examples 1 and 2 was lower than that of Example 1, at only 38.24 mg / 100g and 32.35 mg / 100g, respectively. This confirms the protective effect of the outer coating on the inoculant and the synergistic importance of biochar modification for the slow release of trace elements. This invention, through a synergistic system of composite functional inoculants and modified biochar, effectively activates trace elements such as zinc and manganese in the soil and promotes metabolic cycles within plants, thereby significantly enhancing the synthesis and accumulation of vitamin C.

[0086] By weighing each harvested fruit during the harvest season to determine the average fruit weight for each group, the average single fruit weight in Example 1 reached 235g, an increase of 6.8% compared to the blank control, and the fruit size was uniform. Control group 3, due to broadcasting instead of the hole application method specified in this invention, failed to accurately deliver fertilizer to the dense root zone, resulting in low nutrient absorption efficiency and uneven fruit size. Control group 4 (commercially available slow-release compound fertilizer) showed significant uneven fruit size and the lowest marketable fruit rate due to a lack of organic matter and comprehensive micronutrient supplementation. This indicates that the specific hole application method proposed in this invention (20-30cm depth, positioned at the tree canopy drip line) ensures that fertilizer is concentrated in the active root area, greatly improving nutrient absorption efficiency and utilization, and is a key agronomic guarantee for achieving balanced fruit enlargement and increasing the marketable fruit rate.

[0087] As shown in Table 1, the yield per plant in Example 1 reached 258.6 kg, which was 24.9% higher than the blank control (207.0 kg) and 10.0% higher than the comparative example 4 (239.9 kg). Due to the lack of technical features in the coating structure, core raw materials or application methods, the yield increase of each control group was significantly lower than that of Example 1.

[0088] In terms of soil improvement, this invention also demonstrates significant effects. The soil pH after treatment in Example 1 steadily increased from an initial 5.2 to 6.3, reaching the optimal range (6-6.5) for sweet tangerine growth; simultaneously, the soil organic matter content increased by 18.70%, far exceeding the expected target. Comparison with the control groups shows that the absence of any technical features, such as the lack of an outer coating (control group 1), the use of unmodified biochar (control group 2), or incorrect application methods (control group 3), all lead to a decrease in soil improvement effects. Control group 4 (commercially available fertilizer) even exacerbated soil acidification, confirming the unique advantages of this invention in soil remediation and maintenance.

[0089] The above results fully demonstrate that the present invention is not a simple superposition of various technical features, but rather a systematic solution to the key limiting factors restricting the quality and yield of sweet tangerines and pomelos through the synergistic effect of soil improvement (acidification and increase of organic matter) - precise nutrient supply (dual membrane slow release) - biological regulation (functional microbial agents), ultimately achieving a simultaneous and significant improvement in quality and yield.

[0090] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0091] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A pig manure-based functional double-coated slow-release organic fertilizer adapted to the growth characteristics of sweet tangerines and pomelos, characterized in that, From the inside out, it includes a core fertilizer granule, a functional layer, and an outer coating; the core fertilizer granule has a particle size of 3-5 mm; the functional layer is fixed to the surface of the core fertilizer granule by the inner coating; the thicknesses of the inner coating, the functional layer, and the outer coating are 0.05-0.1 mm, 0.05-0.1 mm, and 0.1-0.2 mm, respectively. The core fertilizer granules are composed of 50-70 parts of well-rotted pig manure; The inner coating comprises sodium alginate, oxidized starch, and glycerol in a mass ratio of 3~5:5~7:1; The functional layer consists of 15-25 parts of modified pig manure biochar, 10-20 parts of mineral-trace element composite conditioner, and 2-5 parts of composite functional microbial agent; The outer coating comprises polylactic acid, polyhydroxy fatty acid ester, and modified nano-diatomaceous earth in a mass ratio of 7~8:2~3:0.5~1.

2. The pig manure-based functional double-coated slow-release organic fertilizer adapted to the growth characteristics of sweet tangerines and pomelos according to claim 1, characterized in that, The preparation steps of the modified pig manure biochar are as follows: Step 1: Dry fresh pig manure to a moisture content of ≤10%, crush it, and then pyrolyze it at 500~650℃ for 1~3 hours under nitrogen protection to obtain primary pig manure biochar. Step 2: Mix the prepared pig manure biochar with a collagenase solution with a concentration of 2-4 U / mL at a liquid-to-solid mass ratio of 1 mL: 8-10 g, stir at 35-40℃ and 120-150 rpm for 24-36 h, filter, and obtain collagenase modified biochar. Step 3: Add a citric acid solution with a concentration of 1-2 wt% to the collagenase modified biochar, sonicate for 25-30 min, let stand for 12-16 h, and then dry at 60-70℃ to constant weight to obtain the modified pig manure biochar.

3. The pig manure-based functional double-coated slow-release organic fertilizer adapted to the growth characteristics of sweet tangerines and pomelos according to claim 1, characterized in that, The mineral-trace element composite conditioner is composed of potassium feldspar powder, oyster shell powder, zinc sulfate and manganese sulfate in a mass ratio of 10~15:5~10:1:

1.

4. The pig manure-based functional double-coated slow-release organic fertilizer adapted to the growth characteristics of sweet tangerines and pomelos according to claim 1, characterized in that, The compound functional microbial agent is composed of Bacillus subtilis, Bacillus thuringiensis and Trichoderma harzianum in an effective viable count ratio of 1.5~2:1~1.5:1, and the total effective viable count is ≥1 billion / g.

5. The method for preparing the pig manure-based functional double-coated slow-release organic fertilizer adapted to the growth characteristics of sweet tangerines and pomelos according to any one of claims 1 to 4, characterized in that, Includes the following steps: Well-rotted pig manure is extruded and granulated to obtain core fertilizer particles with a particle size of 3-5 mm. Sodium alginate, oxidized starch, and glycerol are dissolved in water to obtain an inner coating solution. The core fertilizer granules are first immersed in the inner coating solution, and then placed in a functional layer mixed powder obtained by mixing modified pig manure biochar, mineral-trace element composite conditioner, and composite functional microbial agent to obtain fertilizer granules with adhesive powder. The fertilizer granules with adhesive powder are then immersed in calcium chloride solution for cross-linking and solidification to obtain single-coated organic fertilizer. Polylactic acid, polyhydroxy fatty acid ester, and modified nano-diatomaceous earth are dissolved in water to obtain an outer coating solution; the outer coating solution is sprayed onto the surface of the single-coated organic fertilizer and dried to obtain the pig manure carbon-based functional double-coated slow-release organic fertilizer adapted to the growth characteristics of sweet oranges and pomelos.

6. The preparation method according to claim 5, characterized in that, The concentration of the inner coating solution is 3-5 wt%; the treatment time in the inner coating solution is 3-5 s; the concentration of the calcium chloride solution is 1-3 wt%; and the curing and crosslinking time is 5-10 min.

7. The preparation method according to claim 5, characterized in that, The concentration of the outer coating solution is 5~8wt%; the spraying conditions are: temperature 30~50℃, spraying speed 3~5mL / min.

8. The preparation method according to claim 5, characterized in that, When preparing the functional layer mixed powder, the composite functional bacterial agent and part of the modified pig manure biochar are first mixed and allowed to stand at 25~30℃ for 2~4 hours for adsorption, and then the remaining raw materials are added.

9. The application of the pig manure carbon-based functional double-coated slow-release organic fertilizer adapted to the growth characteristics of sweet oranges and pomelos, as described in any one of claims 1 to 4, in the cultivation of sweet oranges and pomelos.

10. A method for improving the yield and quality of sweet tangerines and pomelos, characterized in that, Apply the pig manure-based functional double-coated slow-release organic fertilizer, as described in any one of claims 1 to 4, twice, before the sweet tangerines sprout in spring and at the early stage of fruit enlargement. Application method: apply in holes or trenches, with a fertilization depth of 20-30cm, and the fertilization point is located near the drip line of the tree canopy. Application amount: apply 200-500g per tree, cover with soil and water thoroughly after application.

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