Special fertilizer for fruit and vegetable crops and preparation method thereof

Abstract

The invention discloses a special fertilizer for fruit and vegetable crops and a preparation method thereof in the field of agricultural fertilizers, in the special fertilizer provided by the invention, lignin-chitosan covalent cross-linked zinc-loaded microspheres form a stable structure through covalent cross-linking of lignin and chitosan, and the zinc element is loaded, so that the effectiveness of zinc is improved; according to the biochar-sepiolite composite ammonium nitrate slow-release carrier, the porosity of biochar and the adsorbability of sepiolite are combined with polyethyleneimine, so that the adsorption of ammonium nitrogen is enhanced, and the loss of nitrogen is reduced. The special fertilizer is prepared from conventional fertilizers such as urea, calcium superphosphate and potassium chloride, organic materials such as decomposed chicken manure and the two modified compounds according to a specific proportion, and all the components have a synergistic effect. The preparation method comprises the steps of conventional fertilizer crushing, organic material mixing, adding of two modified compounds for granulation, drying, screening and the like, and the process is simple and easy to implement. The prepared special fertilizer can significantly improve the fertilizer utilization rate, improve the soil structure, and promote the yield increase and quality improvement of fruits and vegetables.

Description

Technical Field

[0001] The present invention relates to the technical field of agricultural fertilizers, and in particular to a special fertilizer for fruit and vegetable crops and a preparation method thereof. Background Art

[0002] In traditional fruit and vegetable cultivation, fertilizers are mainly nitrogen, phosphorus and potassium compound fertilizers. Although they can quickly supplement a large number of elements, long-term use has exposed significant disadvantages: on the one hand, the nutrient release rate of fertilizers is not synchronized with crop needs. Nitrogen is easily lost with rainwater or irrigation leaching, and phosphorus is difficult to be effectively absorbed due to its fixation in the soil, resulting in insufficient fertilizer utilization, which not only wastes resources but also increases planting costs; on the other hand, long-term excessive application of chemical fertilizers will destroy the soil structure, causing compaction and acidification, and the soil organic matter content will continue to decline. Trace elements (such as zinc and boron) are difficult to meet the growth needs of fruits and vegetables due to lack of supplementation, which ultimately manifests as weak plant growth, increased fruit deformity rate, and decreased quality, seriously restricting the sustainable development of the fruit and vegetable industry.

[0003] In recent years, researchers have attempted to improve fertilizer performance through material modification to address the shortcomings of traditional fertilizers. However, existing improvement methods still have significant shortcomings. Some studies have employed simple physical mixing of natural polymers (such as chitosan) or minerals (such as biochar) with fertilizers, attempting to leverage the materials' adsorption properties to achieve slow nutrient release. However, physical mixing has weak binding forces and is susceptible to material decomposition or sudden nutrient release due to environmental changes (such as humidity and temperature fluctuations), making stable controlled release impossible. Another group of studies has attempted chemical modification of minerals (such as acid activation and trace element loading). However, these modified minerals have limited directional adsorption capacity for key nutrients such as ammonium nitrogen, low trace element loading efficiency, and are easily replaced and fixed by other ions in the soil, failing to fundamentally address nutrient loss and soil degradation.

[0004] The present invention focuses on the core pain points of low utilization rate of traditional fertilizers, soil degradation and trace element deficiency, and innovatively designs two new modified compounds: lignin and chitosan are covalently cross-linked to form a stable microsphere structure, which is loaded with zinc. The dynamic covalent bond formed by the phenolic hydroxyl group of lignin and the amino group of chitosan and the ether bond cross-linking of epichlorohydrin are used to significantly improve the stability of the microspheres and extend the effective supply period of zinc. Corn straw biochar is used as the substrate, combining the porous properties of sepiolite with the amino adsorption function of polyethyleneimine to construct an efficient adsorption system for ammonium nitrogen. Through the synergistic effect of the pore interception of biochar, the interlayer ion exchange of sepiolite and the electrostatic adsorption of polyethyleneimine, nitrogen loss is reduced. The two modified compounds are scientifically matched with conventional fertilizers such as urea and superphosphate and organic materials such as decomposed chicken manure to form a multi-functional synergistic mechanism of "slow release-adsorption-soil improvement", which effectively improves fertilizer utilization, improves the soil microenvironment, and provides a new technical path for increasing the yield and improving the quality of fruits and vegetables. Summary of the Invention

[0005] The purpose of the present invention is to provide a special fertilizer for fruit and vegetable crops and a preparation method thereof, which solves the technical problems of easy nutrient loss, soil degradation and insufficient trace elements in existing fruit and vegetable fertilizers.

[0006] The present invention achieves the above-mentioned purpose through the following technical solutions: A special fertilizer for fruit and vegetable crops, the raw materials of which include, by mass percentage: Urea: 18-25%; Superphosphate: 12-18%; Potassium chloride: 8-12%; Magnesium sulfate: 4-6%; Borax: 0.8-1.2%; Zinc sulfate: 0.5-0.8%; Lignin-chitosan covalently cross-linked zinc-loaded microspheres: 6-10%; Biochar-sepiolite composite ammonium nitrate slow-release carrier: 6-10%; Composted chicken manure: balance; The preparation method of the lignin-chitosan covalently cross-linked zinc-loaded microspheres includes the following steps: A1, dissolving alkali lignin in deionized water, adjusting the pH to 10-10.5 with NaOH, adding chitosan, and reacting at 40-42°C with magnetic stirring to form a lignin-chitosan complex solution; adding Zn(NO3)2·6H2O thereto, and ultrasonically dispersing; adding the mixed solution dropwise to a CaCl2 solution at 5-6°C to form a microsphere precursor; A2, subsequently adding epichlorohydrin, adjusting the pH to 5.0-5.2 with glacial acetic acid, and completing the reaction at 24-26°C; and finally washing with deionized water to neutrality, vacuum drying to constant weight, and grinding and sieving.

[0007] In the present invention, the preparation of lignin-chitosan covalently cross-linked zinc-loaded microspheres achieves functional enhancement through multiple cross-linking and coordination. First, after the alkaline lignin is dissolved in water, its phenolic hydroxyl groups are activated under alkaline conditions, showing high reactivity; after the two are mixed, the phenolic hydroxyl groups of lignin and the amino groups of chitosan undergo dynamic covalent bonding (such as ether bonds or imine bonds), forming a preliminary complex network, providing a stable carrier for subsequent components. At this time, zinc nitrate solution is added and ultrasonic dispersion is performed to make Zn 2+ Evenly penetrate into the complex network gap, some Zn 2+ The zinc element is combined with the amino group (-NH2) of chitosan through coordination bonds and partially embedded in the aromatic ring structure of lignin, achieving efficient loading of zinc elements. Calcium chloride solution is then added dropwise. 2+The zinc oxide reacts with the carboxyl groups of chitosan (derived from chitosan hydrolysis) and the phenolic hydroxyl groups of lignin to form crosslinks, further enhancing network density. Under acidic conditions (pH adjusted with glacial acetic acid), epichlorohydrin reacts with the hydroxyl groups to form ether bonds, creating a double crosslinked structure that enhances the mechanical strength of the microspheres and prevents sudden nutrient release. After washing and drying, the microspheres stabilize, with the zinc firmly anchored in the crosslinked network for slow release to meet crop needs.

[0008] According to a preferred embodiment of the present invention, the urea is purchased from Sinofert Holdings Co., Ltd. and is large-particle urea (total nitrogen ≥ 46%).

[0009] According to a preferred embodiment of the present invention, the superphosphate is purchased from Yunnan Yuntianhua Co., Ltd., and the model is ordinary superphosphate (available phosphorus P2O5 ≥ 16%).

[0010] According to a preferred embodiment of the present invention, the potassium chloride is purchased from Qinghai Salt Lake Industry Co., Ltd. and the type is potassium chloride (K2O≥60%).

[0011] According to a preferred embodiment of the present invention, the magnesium sulfate is purchased from Liaoning Jiachen Group and the type is magnesium sulfate heptahydrate (MgSO4·7H2O≥99%).

[0012] According to a preferred embodiment of the present invention, the borax is purchased from Qingdao Mingyue Seaweed Group Co., Ltd. and the type is borax monohydrate (B≥10.8%).

[0013] According to a preferred embodiment of the present invention, the zinc sulfate is purchased from Zhuzhou Smelting Group Co., Ltd. and is zinc sulfate monohydrate (ZnSO4·H2O≥98%).

[0014] According to a preferred embodiment of the present invention, the decomposed chicken manure is purchased from an organic fertilizer production enterprise in Shandong, and the model is commercial decomposed chicken manure (organic matter ≥45%).

[0015] According to a preferred embodiment of the present invention, the alkali lignin is purchased from Shandong Quanlin Paper Co., Ltd. and is of high-purity alkali lignin (phenolic hydroxyl content ≥ 3 mmol / g).

[0016] According to a preferred embodiment of the present invention, the NaOH is purchased from Xinjiang Tianye (Group) Co., Ltd. and the model is ion-exchange membrane caustic soda (NaOH≥45%).

[0017] According to a preferred embodiment of the present invention, the chitosan is purchased from Qingdao Mingyue Seaweed Group Co., Ltd. and is food-grade chitosan (degree of deacetylation ≥ 90%, molecular weight 50,000 Da).

[0018] According to a preferred embodiment of the present invention, the Zn(NO3)2·6H2O was purchased from Shanghai Api Chemical Reagent Co., Ltd. and was of analytical grade (Zn(NO3)2·6H2O≥99%).

[0019] According to a preferred embodiment of the present invention, the CaCl2 solution is purchased from Tangshan Sanyou Chemical Co., Ltd. and is an industrial-grade calcium chloride solution (CaCl2 ≥ 40%).

[0020] According to a preferred embodiment of the present invention, the epichlorohydrin is purchased from Jiangsu Sanmu Group Co., Ltd. and the model is industrial grade epichlorohydrin (epichlorohydrin ≥99%).

[0021] According to a preferred embodiment of the present invention, the glacial acetic acid is purchased from Shanghai Huayi (Group) Company and is industrial-grade glacial acetic acid (glacial acetic acid ≥ 99.5%).

[0022] According to a preferred embodiment of the present invention, in step A1, the magnetic stirring reaction time is 1-2 h, the stirring speed is 50-60 rpm; Zn(NO3)2·6H2O accounts for 4-6% of the mass of the complex solution; the frequency of ultrasonic dispersion is 20-40 kHz, and the time is 30-50 min.

[0023] According to a preferred embodiment of the present invention, in step A2, the reaction time is 2-4 hours at 24-26°C; the vacuum drying temperature is 40-42°C; and the product is ground through a 40-42 mesh sieve.

[0024] According to a preferred embodiment of the present invention, the preparation method of the biochar-sepiolite composite ammonium nitrate slow-release carrier includes: B1, adding corn straw biochar to KOH solution, reflux stirring at 80-82°C, filtering and washing with deionized water to pH=7.0-7.2, and drying at 105-106°C to constant weight to obtain activated biochar; adding the activated biochar to sepiolite suspension, ultrasonically dispersing, adding polyethyleneimine, oscillating reaction at 60-62°C, centrifuging and washing with deionized water; B2, adding the biochar-polyethyleneimine complex and ammonium nitrate to deionized water, adjusting the pH to 9.0-9.2, oscillating and adsorbing at 40-42°C, filtering and vacuum drying to constant weight, grinding and sieving.

[0025] The preparation of the biochar-sepiolite composite ammonium nitrate slow-release carrier in the present invention relies on the synergy of multi-level pore structure and electrostatic adsorption. After the corn straw biochar is activated by potassium hydroxide, the oxygen-containing functional groups (such as hydroxyl and carboxyl groups) on the surface increase, and a large number of micropores and mesopores are formed inside. The specific surface area is significantly increased, providing space for subsequent loading. As a layered silicate mineral, sepiolite naturally has a high specific surface area and ion exchange capacity. The silicon hydroxyl groups (-Si-OH) on its surface can be combined with the oxygen-containing functional groups of biochar through hydrogen bonds to form a "biochar-sepiolite" composite substrate. After the addition of polyethyleneimine, a large number of amino groups (-NH2) on its molecular chain react with the silicon hydroxyl groups of sepiolite, and at the same time form hydrogen bonds with the oxygen-containing groups of biochar, tightly connecting the two; the positive charge characteristics of the amino group make it a "bridge", which not only enhances the structural stability of the composite material, but also creates conditions for the subsequent adsorption of ammonium nitrogen. When mixed with ammonium nitrate solution, the amino group and ammonium ions combine through electrostatic action to transfer NH4 + It is fixed on the surface and pores of the composite material, reducing the risk of loss with water and achieving slow release of ammonium nitrogen.

[0026] According to a preferred embodiment of the present invention, the corn straw biochar was purchased from Henan Jindan Biological New Materials Co., Ltd. and the model was agricultural grade corn straw biochar (particle size 200-220 mesh).

[0027] According to a preferred embodiment of the present invention, the KOH solution is purchased from Qinghai Salt Lake Industry Co., Ltd. and is an industrial-grade potassium hydroxide solution (concentration 10-10.2 mol / L).

[0028] According to a preferred embodiment of the present invention, the deionized water is purchased from Shanghai Pure Water Equipment Manufacturing Co., Ltd. and is industrial-grade deionized water (conductivity ≤ 10 μS / cm).

[0029] According to a preferred embodiment of the present invention, the sepiolite suspension is purchased from Hunan Xiangtan Sepiolite Technology Co., Ltd., and the type is industrial-grade sepiolite suspension (20% w / v).

[0030] According to a preferred embodiment of the present invention, the polyethyleneimine is purchased from Jiangsu Haian Petrochemical Corporation and is industrial-grade polyethyleneimine (molecular weight 10 kDa).

[0031] According to a preferred embodiment of the present invention, the ammonium nitrate is purchased from Yunnan Jiehua Group Co., Ltd. and is industrial-grade ammonium nitrate (total nitrogen ≥ 34%).

[0032] According to a preferred embodiment of the present invention, in step B1, the particle size of the corn straw biochar is 200-220 mesh; the concentration of the KOH solution is 10-10.2 mol / L, the speed of reflux stirring is 80-82 rpm, and the time is 4-6 hours; the frequency of ultrasonic dispersion is 40-60 kHz, and the time is 30-40 minutes; the speed of oscillation reaction is 150-200 rpm, and the time is 6-8 hours; and the number of deionized water washings is 3-4 times.

[0033] According to a preferred embodiment of the present invention, in step B2, the rotation speed of the oscillating adsorption is 150-200 rpm, and the time is 12-14 h; the temperature of the vacuum drying is 60-62° C.; and the product is ground through a 60-62 mesh sieve.

[0034] The present invention also provides a method for preparing the special fertilizer for fruit and vegetable crops, comprising the following steps: S1. Put urea, superphosphate and potassium chloride into a grinder in proportion and grind them; grind magnesium sulfate, borax and zinc sulfate separately, mix them with the crushed basic fertilizer, add decomposed chicken manure and stir; S2. adding lignin-chitosan covalently cross-linked zinc-loaded microspheres and biochar-sepiolite composite ammonium nitrate slow-release carrier to the mixture, adjusting the water content to 35-40%, and granulating using a rotary drum granulator; S3. After granulation, dry in a forced air drying oven until the moisture content is ≤5%, and sieve to remove particles ≤1 mm or >5 mm.

[0035] The synergistic effects of chemical crosslinking, physical adsorption, and ion exchange in each step of this invention ultimately give the specialized fertilizer the multifunctional properties of "slow-release, adsorption, and improvement." Lignin-chitosan microspheres stably load zinc, preventing rapid zinc loss. Combined with organic materials such as decomposed chicken manure, they improve soil structure and replenish organic matter. These mechanisms work together to synchronize fertilizer nutrient release with crop needs, improving utilization efficiency while simultaneously restoring the soil microenvironment and boosting fruit and vegetable yields and quality.

[0036] According to a preferred embodiment of the present invention, in step S1, urea, superphosphate, and potassium chloride are crushed to a particle size of 80-82 mesh; magnesium sulfate, borax, and zinc sulfate are crushed separately and then passed through an 80-82 mesh sieve, the stirring speed is 20-40 rpm; and the stirring time is 15-20 min.

[0037] According to a preferred embodiment of the present invention, in step S2, the diameter of the granules produced by the rotary drum granulator is 3.5-4 mm.

[0038] According to a preferred embodiment of the present invention, in step S3, the drying temperature in the blast drying oven is 50-52°C.

[0039] The beneficial effects of the present invention are: The present invention demonstrates significant benefits in nutrient utilization, soil improvement, and fruit and vegetable quality improvement through the synergistic effect of two novel modified compounds with conventional fertilizers and organic materials. Traditional fertilizers, due to their rapid nutrient release and easy loss, often lead to increased investment with limited effectiveness. In the present invention, the lignin-chitosan covalently cross-linked zinc-loaded microspheres form stable microspheres through a dual cross-linking structure (dynamic covalent bonds between lignin phenolic hydroxyl groups and chitosan amino groups, and ether cross-linking with epichlorohydrin). This effectively delays the release cycle of zinc and prevents sudden nutrient release in the short term. The combined effect of these two compounds allows for the slow release of key nutrients such as nitrogen and zinc from the soil, synchronizing with crop growth needs, significantly improving fertilizer utilization and reducing resource waste.

[0040] Long-term excessive application of chemical fertilizers can easily lead to soil compaction, acidification and loss of organic matter, and the present invention effectively improves this problem through component design. As an organic material, decomposed chicken manure is rich in humus, which can promote the formation of soil aggregate structure and enhance the ability to retain water and fertilizer; the porous structure of biochar can increase soil permeability and absorb excess salt in the soil; the layered chain structure of sepiolite can regulate the charge distribution of the soil and reduce the activity of harmful substances such as heavy metals. The two modified compounds work synergistically with organic materials, not only replenishing soil organic matter, but also regulating the pH value of the soil, promoting the reproduction of beneficial microorganisms, creating a loose and fertile microenvironment for the growth of fruit and vegetable roots, and fundamentally solving the problem of soil degradation.

[0041] The efficient use of nutrients and the improvement of the soil environment are directly reflected in the increase in yield and quality of fruits and vegetables. Experiments have shown that fruit and vegetable plants that have been fertilized with this special fertilizer grow stronger, have darker green leaves, have developed root systems, and significantly enhance their ability to absorb nutrients. Taking tomatoes as an example, plant height and single fruit weight are higher than those treated with traditional compound fertilizers, the fruit deformity rate is lowered, and intrinsic quality indicators such as vitamin C and soluble solids are improved; berry crops such as strawberries have increased sugar content, decreased acidity, and a better taste. At the same time, soil bulk density is reduced and organic matter content rebounds, providing a sustainable fertility foundation for continuous planting and helping to improve the quality and efficiency of the fruit and vegetable industry. DETAILED DESCRIPTION

[0042] The following specific implementation methods are only used to further illustrate the present application and should not be understood as limiting the scope of protection of the present application. Technicians in this field may make some non-essential improvements and adjustments to the present application based on the above application content.

[0043] Example 1

[0044] The raw materials were taken by mass: 20 g urea, 15 g superphosphate, 10 g potassium chloride, 5 g magnesium sulfate, 1 g borax, 0.6 g zinc sulfate, 18 g decomposed chicken manure, 8 g lignin-chitosan covalently cross-linked zinc-loaded microspheres, and 8 g biochar-sepiolite composite ammonium nitrate slow-release carrier.

[0045] The preparation process for lignin-chitosan covalently cross-linked zinc-loaded microspheres is as follows: 5g of alkali lignin was added to a beaker, followed by 50mL of deionized water. Stirring with a glass rod until initially dissolved, 10% sodium hydroxide solution was slowly added to adjust the solution's pH to 10.2 (measured using pH paper). 2g of highly deacetylated chitosan (≥90% deacetylation) was added to the solution. The beaker was placed on a magnetic stirrer at 41°C and 55 rpm, and stirred for 1.5 hours until a uniform lignin-chitosan complex was formed. 0.3g of zinc nitrate crystals (Zn(NO₃)₂·6H₂O, representing 4.6% of the total weight of the complex solution) was added to the complex solution. An ultrasonic cleaner probe was immersed 1cm below the solution surface. Ultrasonic dispersion was performed for 40 minutes at a frequency of 30kHz and a power of 200W to ensure thorough dispersion of the zinc nitrate in the complex solution. The mixed solution was transferred to a constant-pressure dropping funnel and slowly added dropwise (at a rate of approximately 1 mL / minute) to a beaker containing 10 mL of 40% calcium chloride solution. The temperature of the solution in the beaker was maintained at 5.5°C (controlled by an ice-water bath) during the addition. After the addition was complete, the mixture was allowed to stand at 5.5°C for 30 minutes to form microsphere precursors with a diameter of approximately 1-3 mm. 0.1 g of epichlorohydrin was added to the microsphere precursor, and the pH of the solution was adjusted to 5.1 with glacial acetic acid (measured using a pH meter). The beaker was then placed in a 25°C incubator for 3 hours to allow the epichlorohydrin to fully crosslink with the amino groups of the chitosan. After the reaction is completed, the microspheres are transferred to a Buchner funnel and repeatedly rinsed with deionized water until the filtrate is neutral (detected by pH paper). The microspheres are then spread flat on a Petri dish and placed in a vacuum drying oven at 41°C to dry to constant weight (about 6 hours). After being taken out, they are ground and passed through a 42-mesh sieve to obtain lignin-chitosan covalently cross-linked zinc-loaded microspheres.

[0046] The preparation process for the biochar-sepiolite composite ammonium nitrate slow-release carrier is as follows: 10g of corn straw biochar (particle size approximately 200 mesh) was weighed and added to a round-bottom flask. 100mL of 10mol / L potassium hydroxide solution was then poured into the flask. The flask was placed in a constant-temperature water bath at 81°C, connected to a condenser reflux apparatus, and stirred and refluxed at 81 rpm for 5 hours. After reflux, the solution was cooled to room temperature and filtered using a suction filter. The residue was collected and repeatedly washed with deionized water until the filtrate reached a pH of 7.1 (measured using a pH meter). The residue was then transferred to a 105°C vacuum drying oven and dried to constant weight (approximately 4 hours) to obtain the activated biochar. Weigh 5g of activated biochar into a beaker and add it to a 50mL 20% sepiolite suspension (with a 1:4 mass ratio of sepiolite to water). Immerse the ultrasonic cleaner probe 2cm below the surface of the solution, set the ultrasonic frequency to 50kHz and the power to 300W, and perform ultrasonic dispersion for 35 minutes to evenly disperse the sepiolite on the biochar surface. Weigh 1g of 10kDa polyethyleneimine and add it to the dispersion. Place the beaker in a thermostatted oscillator at 61°C and oscillate at 180rpm for 7 hours to allow the amino groups of the polyethyleneimine to fully bond with the silanol groups of the sepiolite. After the reaction is completed, the solution is transferred to a centrifuge tube and centrifuged at 4000 rpm for 10 minutes. The precipitate is collected and washed three times with deionized water (centrifugation and supernatant are discarded after each washing). The precipitate is then spread flat in a Petri dish and placed in a vacuum drying oven at 61°C to dry to constant weight (about 5 hours). The precipitate is then ground and passed through a 61-mesh sieve to obtain a biochar-sepiolite composite ammonium nitrate slow-release carrier.

[0047] The preparation process for a fertilizer specifically formulated for fruit and vegetable crops is as follows: urea, superphosphate, and potassium chloride are each placed in a grinder set to 81 mesh, and the powders are collected. Magnesium sulfate, borax, and zinc sulfate are each ground through an 81-mesh sieve, and the collected powders are then mixed evenly with the three basic fertilizer powders described above. 18 g of decomposed chicken manure (organic matter content ≥ 45%) is added to the mixed powder, and the mixture is stirred at 30 rpm for 18 minutes to achieve preliminary mixing. 8 g of the prepared lignin-chitosan covalently cross-linked zinc-loaded microspheres and 8 g of a biochar-sepiolite composite ammonium nitrate slow-release carrier are added to the mixed powder and stirred for 5 minutes to evenly disperse the microspheres and carrier in the fertilizer. The moisture content of the mixture is adjusted to 38% (so that it can be kneaded by hand to form a clumping mass without disintegrating). The mixture is then transferred to a rotary drum granulator with a granulation diameter set to 3.8 mm and the granulator activated for granulation. After granulation, the granules are transferred to a 51°C forced air drying oven and dried until the moisture content is ≤5% (measured using a moisture meter). After drying, they are sieved through a screen to remove particles ≤1mm or >5mm in size. Particles with a size between 1-5mm are collected to obtain the fertilizer specifically for fruit and vegetable crops.

[0048] Example 2

[0049] The specific implementation method is the same as that of Example 1, except that the raw materials are taken by mass: 22g urea, 16g superphosphate, 11g potassium chloride, 5.5g magnesium sulfate, 1.1g borax, 0.7g zinc sulfate, 19g decomposed chicken manure, 9g lignin-chitosan covalently cross-linked zinc-loaded microspheres, and 9g biochar-sepiolite composite ammonium nitrate slow-release carrier.

[0050] Preparation of lignin-chitosan covalently cross-linked zinc-loaded microspheres: 5.5 g of alkali lignin was dissolved in 55 mL of deionized water, the pH was adjusted to 10.3 with NaOH solution, 2.2 g of chitosan was added, and the mixture was reacted at 42°C with magnetic stirring (58 rpm) for 1.8 h to form a complex solution; 0.33 g of Zn(NO3)2·6H2O (4.8% of the mass of the complex solution) was added, and ultrasonic dispersion was performed (35 kHz, 45 min); 11 mL of 5.8°C CaCl2 solution (40%) was added dropwise to form a microsphere precursor; 0.11 g of epichlorohydrin was added, and the pH was adjusted to 5.2 with glacial acetic acid, and the mixture was reacted at 26°C for 3.5 h; the mixture was washed to neutrality, dried in a vacuum at 42°C to constant weight, and ground through a 42-mesh sieve.

[0051] Preparation of biochar-sepiolite composite ammonium nitrate slow-release carrier: 11 g of corn straw biochar (200 mesh) was added with KOH solution (10.1 mol / L, 110 mL), refluxed at 82°C with stirring (82 rpm) for 5.5 h, filtered and washed to pH = 7.2, and dried at 106°C to constant weight; sepiolite suspension (20% w / v, 55 mL) was added, ultrasonically dispersed (55 kHz, 38 min), and 1.1 g of polyethyleneimine was added. The mixture was shaken at 62°C (190 rpm) for 7.5 h, and centrifuged and washed three times; mixed with 5.5 g of ammonium nitrate (total nitrogen ≥ 34%), adjusted to pH = 9.2, and adsorbed at 42°C with shaking (190 rpm) for 13.5 h. After filtering, the mixture was vacuum-dried at 62°C to constant weight and ground through a 62-mesh sieve.

[0052] Preparation of special fertilizer: crush the raw materials to 82 mesh, add decomposed chicken manure after mixing and stir (35 rpm, 20 min), add microspheres and carriers, adjust the moisture content to 40%, granulate (diameter 4 mm), dry at 52 ° C to moisture ≤ 5%, and sieve.

[0053] Example 3

[0054] The specific implementation method is the same as that of Example 1, except that the raw materials are taken by mass: 24 g of urea, 17 g of superphosphate, 12 g of potassium chloride, 5.8 g of magnesium sulfate, 1.2 g of borax, 0.75 g of zinc sulfate, 17 g of decomposed chicken manure, 9.5 g of lignin-chitosan covalently cross-linked zinc-loaded microspheres, and 9.5 g of biochar-sepiolite composite ammonium nitrate slow-release carrier.

[0055] Preparation of lignin-chitosan covalently cross-linked zinc-loaded microspheres: 5.8 g of alkali lignin was dissolved in 58 mL of deionized water, the pH was adjusted to 10.4 with NaOH solution, 2.4 g of chitosan was added, and the mixture was reacted at 41.5°C with magnetic stirring (56 rpm) for 1.6 h to form a complex solution. 0.35 g of Zn(NO3)2·6H2O (4.7% by mass of the complex solution) was added, and ultrasonic dispersion was performed (32 kHz, 42 min). 10.5 mL of 5.6°C CaCl2 solution (40%) was added dropwise to form a microsphere precursor. 0.105 g of epichlorohydrin was added, and the pH was adjusted to 5.15 with glacial acetic acid. The mixture was reacted at 25.5°C for 3.2 h. The mixture was washed to neutrality, dried under vacuum at 41.5°C to constant weight, and ground through a 41-mesh sieve.

[0056] Preparation of biochar-sepiolite composite ammonium nitrate slow-release carrier: 10.5 g of corn straw biochar (200 mesh) was added with KOH solution (10.05 mol / L, 105 mL), refluxed at 81.5°C with stirring (81.5 rpm) for 5.2 h, filtered, washed to pH = 7.15, and dried at 105.5°C to constant weight; sepiolite suspension (20% w / v, 52 mL) was added, ultrasonically dispersed (52 kHz, 36 min), and 1.05 g of polyethyleneimine was added. The mixture was shaken at 61.5°C (185 rpm) for 7.2 h, and centrifuged and washed three times; mixed with 5.2 g of ammonium nitrate (total nitrogen ≥ 34%), adjusted to pH = 9.15, and adsorbed at 41.5°C with shaking (185 rpm) for 13.2 h. After filtering, the mixture was vacuum-dried at 61.5°C to constant weight and ground through a 61-mesh sieve.

[0057] Preparation of special fertilizer: crush the raw materials to 81.5 mesh, add decomposed chicken manure after mixing and stir (32 rpm, 19 min), add microspheres and carriers, adjust the moisture content to 39%, granulate (diameter 3.9 mm), dry at 51.5℃ to moisture ≤5%, and sieve.

[0058] Comparative Example 1 The specific implementation method is the same as that of Example 1, except that the raw materials, by mass, are: 20g urea, 15g superphosphate, 10g potassium chloride, 5g magnesium sulfate, 1g borax, 0.6g zinc sulfate, 18g decomposed chicken manure, and 8g biochar-sepiolite composite ammonium nitrate sustained-release carrier. Lignin-chitosan covalently cross-linked zinc-loaded microspheres are not added during the preparation method.

[0059] Comparative Example 2 The specific implementation method is the same as that of Example 1, except that the raw materials, by mass, are: 20g urea, 15g superphosphate, 10g potassium chloride, 5g magnesium sulfate, 1g borax, 0.6g zinc sulfate, 18g decomposed chicken manure, and 8g lignin-chitosan covalently cross-linked zinc-loaded microspheres. The biochar-sepiolite composite ammonium nitrate slow-release carrier is not added during the preparation method.

[0060] Comparative Example 3 The specific implementation method is the same as that of Example 1, except that the raw materials, by mass, are: 20g urea, 15g superphosphate, 10g potassium chloride, 5g magnesium sulfate, 1g borax, 3g zinc sulfate (conventional zinc sulfate), and 18g decomposed chicken manure. In the preparation method, zinc sulfate is used instead of the lignin-chitosan covalently cross-linked zinc-loaded microspheres.

[0061] Performance Testing The special fertilizers prepared in Examples 1-3 and Comparative Examples 1-3 were subjected to performance tests according to the following method: 1. Determination of nutrient release rate: Weigh 50 g of special fertilizer sample and place it in a 250 mL Erlenmeyer flask. Add 200 mL of deionized water (pH = 7.0, 25 ° C), seal the flask and place it in a constant temperature oscillator (150 rpm) at 25 ° C. Take 5 mL of supernatant at 1 h, 3 h, 6 h, 12 h, 24 h, 48 h, and 72 h, respectively. Determine the total nitrogen, ammonium nitrogen, and nitrate nitrogen contents by Kjeldahl method (nitrate nitrogen is determined by molybdenum blue colorimetry), the phosphorus content by molybdenum antimony colorimetry, the potassium content by flame photometry, and the zinc content by atomic absorption spectrometry. Calculate the cumulative nutrient release rate at each time point (cumulative release amount / total nutrient content × 100%).

[0062] 2. Determination of soil improvement effect: The soil of the experimental field (initial pH = 5.5-6.0, organic matter content of about 15g / kg) was selected, and the special fertilizers of Examples 1-3 and Comparative Examples 1-3 were applied (dosage 50kg / 667m²), respectively. A blank control (no fertilizer) was set up. After fertilization, the soil was plowed. After 30 days, samples of the 0-20cm soil layer were collected. The soil bulk density was measured by the ring knife method (100cm³ ring knife), and the porosity was measured by the pycnometer method (boiling method) (porosity = 1-bulk density / soil particle density, soil particle density was taken as 2.65g / cm 3 ), the organic matter content was determined by potassium dichromate oxidation method (external heating method), and the pH value was determined by glass electrode method (pH meter).

[0063] 3. Crop yield increase rate determination: Tomato variety 'Pink Crown' was selected as the test material, and 4 replicates were set up (each plot area was 20 m², randomized block arrangement). The special fertilizers of Examples 1-3 and Comparative Examples 1-3 (basal fertilizer, 50 kg / 667 m 2The control group received an equal amount of conventional compound fertilizer (NPK = 15-15-15). Flowers and fruits were thinned during the flowering period (retaining 5-6 ears per plant). Ten fruits were randomly picked from each plot during the maturity period. Fruit weight (electronic scale), sugar content (refractometer, °Bx), and vitamin C content (2,6-dichloroindophenol titration method, mg / 100g) were measured. Average fruit weight, sugar content, vitamin C content, and yield increase were calculated ((treatment group yield - control group yield) / control group yield × 100%).

[0064] 4. Trace Element Utilization Efficiency Determination: During the tomato ripening period, five plants were randomly selected from each plot. Whole-plant samples (aerial parts) were collected, withered at 105°C for 30 minutes, dried at 80°C to constant weight for 48 hours, and then crushed through an 80-mesh sieve. Samples were digested using a microwave digester (HNO₃-HClO₄ mixed acid, 3:1 volume ratio). Zinc content was determined by atomic absorption spectrometry (AAS), and boron content was determined by inductively coupled plasma optical emission spectrometry (ICP-OES). The absorption and utilization efficiencies of zinc and boron were calculated as (plant uptake - soil background value) / total zinc and boron input in the fertilizer × 100%, with soil background value determined using a blank soil sample).

[0065] 5. Performance test results:

[0066]

[0067] As can be seen from Table 1, Examples 1-3 of the present invention, through comparative analysis with Comparative Examples 1-3, significantly demonstrate their effectiveness in addressing core issues such as nutrient loss in fruit and vegetable fertilizers, soil degradation, and trace element deficiencies. In terms of nutrient release rate, the 24-hour cumulative release rates of Examples 1-3 were only 17.8%-18.5% for nitrogen, 11.9%-12.3% for phosphorus, and 7.9%-8.2% for zinc. These rates are significantly lower than those of Comparative Example 1 (without lignin-chitosan microspheres, a nitrogen release rate of 35.6%) and Comparative Example 3 (with traditional zinc sulfate as a substitute, a zinc release rate of 19.8%). This indicates that the microspheres, through the covalent cross-linking structure of lignin-chitosan, effectively delay the initial burst release of nutrients such as nitrogen and zinc, thereby preventing nutrient loss due to leaching or volatilization.

[0068] In terms of soil improvement, the soil bulk density of Examples 1-3 (1.20-1.22 g / cm³) was significantly lower than that of Comparative Example 1 (1.35 g / cm³) and Comparative Example 3 (1.38 g / cm³), the porosity (54.2%-55.1%) was higher than that of Comparative Example 1 (48.6%) and Comparative Example 3 (47.3%), and the organic matter content (22.5-23.1 g / kg) was increased by 21%-28% compared with Comparative Example 1 (18.6 g / kg) and Comparative Example 3 (17.9 g / kg). The pH value was stable at 6.2-6.3 (neutral to slightly acidic), while the pH of the blank control and Comparative Examples 1 and 3 were all lower than 5.9, showing an acidification trend.

[0069] To address trace element deficiencies, Examples 1-3 achieved zinc utilization rates (43.8%-45.2%) and boron utilization rates (37.5%-38.7%) that were 1.6-1.9 times higher than those in Comparative Example 1 (28.6%) and Comparative Example 3 (25.4% and 19.6%), respectively. Lignin-chitosan microspheres immobilize zinc ions through electrostatic interactions and complexation, preventing them from being fixed in the soil or leaching. Silicon hydroxyl groups on the biochar surface combine with borate in borax to form a stable boron-silicon complex, reducing boron fixation. The combined effect of these two factors significantly improves the effectiveness of zinc and boron.

[0070] The improvements further demonstrate the aforementioned improvements: the average single-fruit weight (285-290g) of tomatoes in Examples 1-3 increased by 24%-29% compared to Comparative Examples 1 (230g) and 3 (225g), the sugar content (10.2-10.5°Bx) increased by 19%-23%, and the vitamin C content (18.6-19.2mg / 100g) increased by 27%-29%. This is due to the synergistic effects of slow-release nutrients that match crop growth needs, soil improvement that enhances root absorption capacity, and efficient trace element utilization that promotes fruit quality synthesis, all contributing to increased yield and improved quality.

[0071] In summary, Examples 1-3 effectively solved the problems of rapid nutrient loss, soil degradation, and trace element deficiency in traditional fruit and vegetable fertilizers through the synergistic effect of microspheres and carriers, providing an efficient and sustainable fertilizer solution for fruit and vegetable cultivation.

[0072] The above-described embodiments merely illustrate several implementations of the present invention. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, and all such variations and improvements fall within the scope of protection of the present invention.

Claims

1. A special fertilizer for fruit and vegetable crops, characterized in that: In terms of mass percentage, the raw materials include: Urea: 18-25%; Superphosphate: 12-18%; Potassium chloride: 8-12%; Magnesium sulfate: 4-6%; Borax: 0.8-1.2%; Zinc sulfate: 0.5-0.8%; Lignin-chitosan covalently cross-linked zinc-loaded microspheres: 6-10%; Biochar-sepiolite composite ammonium nitrate slow-release carrier: 6-10%; Composted chicken manure: balance; The preparation method of the lignin-chitosan covalently cross-linked zinc-loaded microspheres includes the following steps: A1, dissolving alkali lignin in deionized water, adjusting the pH to 10-10.5 with NaOH, adding chitosan, and reacting at 40-42°C with magnetic stirring to form a lignin-chitosan complex solution; adding Zn(NO3)2·6H2O thereto, and ultrasonically dispersing; adding the mixed solution dropwise to a CaCl2 solution at 5-6°C to form a microsphere precursor; A2, subsequently adding epichlorohydrin, adjusting the pH to 5.0-5.2 with glacial acetic acid, and completing the reaction at 24-26°C; and finally washing with deionized water to neutrality, vacuum drying to constant weight, and grinding and sieving.

2. The special fertilizer for fruit and vegetable crops according to claim 1, characterized in that In step A1, the magnetic stirring reaction time is 1-2 h, the stirring speed is 50-60 rpm; Zn(NO3)2·6H2O accounts for 4-6% of the mass of the complex solution; the frequency of ultrasonic dispersion is 20-40 kHz, and the time is 30-50 min.

3. The special fertilizer for fruit and vegetable crops according to claim 1, characterized in that: In step A2, the reaction time is 2-4 hours at 24-26° C.; the vacuum drying temperature is 40-42° C.; and the product is ground through a 40-42 mesh sieve.

4. The special fertilizer for fruit and vegetable crops according to claim 1, characterized in that The preparation method of the biochar-sepiolite composite ammonium nitrate slow-release carrier comprises the following steps: B1, adding corn straw biochar to a KOH solution, reflux stirring at 80-82° C., filtering, washing with deionized water to a pH of 7.0-7.2, and drying at 105-106° C. to constant weight to obtain activated biochar; adding the activated biochar to a sepiolite suspension, ultrasonically dispersing the solution, adding polyethyleneimine, oscillating for reaction at 60-62° C., centrifuging, and washing with deionized water; B2, adding the biochar-polyethyleneimine complex and ammonium nitrate to deionized water, adjusting the pH to 9.0-9.2, oscillating for adsorption at 40-42° C., filtering, vacuum drying to a constant weight, and grinding and sieving.

5. The special fertilizer for fruit and vegetable crops according to claim 4, characterized in that: In step B1, the particle size of the corn straw biochar is 200-220 mesh; the concentration of the KOH solution is 10-10.2 mol / L, the reflux stirring speed is 80-82 rpm, and the time is 4-6 hours; the frequency of the ultrasonic dispersion is 40-60 kHz, and the time is 30-40 minutes; the oscillation reaction speed is 150-200 rpm, and the time is 6-8 hours; and the number of deionized water washings is 3-4 times.

6. The special fertilizer for fruit and vegetable crops according to claim 4, characterized in that: In step B2, the rotation speed of the oscillating adsorption is 150-200 rpm, and the time is 12-14 hours; the temperature of the vacuum drying is 60-62° C.; and the product is ground through a 60-62 mesh sieve.

7. A method for preparing a special fertilizer for fruit and vegetable crops according to any one of claims 1 to 6, characterized in that the steps include: S1. Put urea, superphosphate and potassium chloride into a grinder in proportion and grind them; grind magnesium sulfate, borax and zinc sulfate separately, mix them with the crushed basic fertilizer, add decomposed chicken manure and stir; S2. adding lignin-chitosan covalently cross-linked zinc-loaded microspheres and biochar-sepiolite composite ammonium nitrate slow-release carrier to the mixture, adjusting the water content to 35-40%, and granulating using a rotary drum granulator; S3. After granulation, dry in a forced air drying oven until the moisture content is ≤5%, and sieve to remove particles ≤1 mm or >5 mm.

8. The preparation method according to claim 7, characterized in that In step S1, urea, superphosphate, and potassium chloride are crushed to a particle size of 80-82 mesh; magnesium sulfate, borax, and zinc sulfate are crushed separately and then passed through an 80-82 mesh sieve, the stirring speed is 20-40 rpm, and the stirring time is 15-20 minutes.

9. The preparation method according to claim 7, characterized in that In step S2, the diameter of the granules produced by the drum granulator is 3.5-4 mm.

10. The preparation method according to claim 7, characterized in that In step S3, the drying temperature in the blast drying oven is 50-52°C.

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