Chitosan oligosaccharide liquid fertilizer, and preparation method and application thereof

Abstract

The application relates to the technical field of fertilizers, and particularly discloses a chitosan oligosaccharide liquid fertilizer as well as a preparation method and application thereof. The chitosan oligosaccharide liquid fertilizer is prepared from the following raw materials in parts by weight: modified chitosan oligosaccharide 5-20 parts, macroelement nutrient 10-40 parts, microelement nutrient 2-10 parts, organic acid chelating agent 1-5 parts, polyaspartic acid 0.5-3 parts, nano silicon dioxide 0.1-1 part, alkyl polyglycoside surfactant 0.3-2 parts, xanthan gum 0.05-0.5 part, preservative 0.05-0.5 part, defoaming agent 0.05-0.5 part and water 20-80 parts. The modified chitosan oligosaccharide is a copolymer prepared from starch and chitosan oligosaccharide under the action of an initiator. The chitosan oligosaccharide liquid fertilizer can significantly improve the leaf surface adhesion rate and water retention and efficiency, solves the defects of conventional chitosan oligosaccharide liquid fertilizer, such as easy rolling, easy washing and fast evaporation, has high fertilizer utilization rate, good system stability, simple preparation process and is suitable for large-scale production and application.

Description

Technical Field

[0001] This application relates to the field of fertilizer technology, and more specifically, to a chitosan oligosaccharide liquid fertilizer, its preparation method, and its application. Background Technology

[0002] Liquid fertilizers are fluid fertilizers prepared by dissolving all or part of their nutrients in water. They are suitable for various application modes such as drip irrigation, fertigation, foliar spraying, and aerial plant protection. They possess significant advantages, including rapid nutrient dissolution, quick crop absorption, precise nutrient ratio control, high application uniformity, and strong adaptability to mechanized operations. They have become the mainstream top dressing for improving the quality and yield of facility agriculture and cash crops. Conventional inorganic liquid fertilizers can quickly replenish nitrogen, phosphorus, potassium, and micronutrients, while organic liquid fertilizers also have additional benefits such as improving soil microecology, stimulating crop growth, and enhancing stress resistance. Their application rate continues to increase in the large-scale promotion of green agriculture.

[0003] Chitosan oligosaccharides, as natural biostimulants, possess multiple functions, including inducing crop disease and stress resistance, promoting root growth, activating beneficial soil microorganisms, and improving fertilizer absorption and utilization. The formulation of chitosan oligosaccharide liquid fertilizers has become a hot research topic in the industry. Existing patent CN105218262A discloses a water-soluble fertilizer containing chitosan oligosaccharide and amino acids, and its preparation method. This fertilizer uses chitosan oligosaccharides, amino acids, and trace element salts as core raw materials, supplemented with chelating agents and organosilicon. Utilizing the bioactivity of chitosan oligosaccharides combined with amino acid nutrition, it can be applied as a foliar spray to supplement foliar nutrition or as a root drenching agent to improve the rhizosphere environment. Compared to ordinary inorganic liquid fertilizers, it can reduce the amount of chemical fertilizer used, alleviate soil compaction, and achieve improved quality and efficiency.

[0004] However, in practical use, due to the lack of long-lasting adhesive components and hydrophilic water-locking structures in this type of conventional chitosan oligosaccharide liquid fertilizer system, the surface tension of the fertilizer concentrate is relatively high. After spraying, the droplets are difficult to fully spread and wet the waxy leaf surface of the crop, and are very easy to aggregate into spheres and roll off. In light rain, nutrients are even more easily washed away. At the same time, the fertilizer solution evaporates quickly, and the leaf surface is wetted for a short time. Nutrients do not fully penetrate into the leaf tissue before crystallization and precipitation, resulting in a low overall leaf retention rate and insufficient wetting effect. Therefore, there are defects in poor leaf adhesion and water retention, which directly leads to low fertilizer nutrient utilization. Frequent topdressing is required, increasing labor and fertilizer costs, and restricting the full realization of the quality and efficiency improvement advantages of chitosan oligosaccharide liquid fertilizer. Summary of the Invention

[0005] In view of this, the present invention proposes a chitosan oligosaccharide liquid fertilizer, its preparation method and application to solve the above problems.

[0006] The technical solution of this invention is implemented as follows:

[0007] A chitosan oligosaccharide liquid fertilizer comprises the following raw materials in parts by weight:

[0008] Modified chitosan oligosaccharide 5-20 parts;

[0009] 10-40 servings of macronutrients;

[0010] 2-10 portions of trace elements;

[0011] 1-5 parts of organic acid chelating agent;

[0012] Polyaspartic acid 0.5-3 parts;

[0013] 0.1-1 part of nano-silica;

[0014] Alkyl glycoside surfactant, 0.3-2 parts;

[0015] Xanthan gum 0.05-0.5 parts;

[0016] Preservative: 0.05-0.5 parts;

[0017] Defoamer 0.05-0.5 parts;

[0018] 20-80 parts water;

[0019] Furthermore, the modified chitosan oligosaccharide is a copolymer of starch and chitosan oligosaccharide obtained under the action of an initiator.

[0020] By adopting the above technical solution, and addressing the technical shortcomings of conventional chitosan oligosaccharide liquid fertilizers in terms of insufficient leaf adhesion and water retention, a foliar sustained-effect system integrating "wetting-spreading-anchoring-water locking" was constructed by introducing modified chitosan oligosaccharide as the core functional component and coordinating it with polyaspartic acid, nano-silica, alkyl glycoside surfactants and xanthan gum, etc.

[0021] Firstly, at the wetting and spreading level, alkyl glycoside surfactants, as green nonionic surfactants, can significantly reduce the solid-liquid interfacial tension between the fertilizer solution and the waxy leaf surface of the crop. After spraying, the contact angle of the fertilizer solution droplets on the leaf surface is greatly reduced, changing from the original aggregated spherical shape to a fully spread thin layer, effectively preventing the droplets from rolling off due to excessive surface tension, thus physically ensuring the initial adhesion area of ​​the fertilizer solution on the leaf surface.

[0022] Secondly, modified chitosan oligosaccharides play a crucial role in adhesion and anchoring. This copolymer uses starch molecular chains as its backbone, with chitosan oligosaccharides covalently linked to the starch backbone through graft copolymerization. The copolymer molecular chains are distributed with numerous polar groups such as hydroxyl and amino groups, which can form hydrogen bonds and intermolecular van der Waals forces with components such as waxes and cuticles in the crop leaf epidermis, generating strong interfacial interactions. Simultaneously, the introduction of nano-silica further enhances this anchoring effect—nanoscale silica particles deposited on the leaf surface form microscopic physical anchoring points, increasing the mechanical interlocking effect between the fertilizer solution and the leaf surface. The synergistic effect of the dual anchoring mechanisms of chemical adsorption and physical anchoring makes the liquid film less prone to being washed away or detached even in light rain or wind disturbances.

[0023] Furthermore, in terms of water retention, the modified chitosan oligosaccharide starch backbone can form a physically entangled network in aqueous solution, and the grafted chitosan oligosaccharide side chains retain a large number of hydrophilic groups; the dense carboxyl and amide groups on the polyaspartic acid molecular chains have extremely strong hydrophilicity and can capture a large number of water molecules through hydrogen bonds; xanthan gum can form a gel system with a three-dimensional network structure in water. The three work synergistically to form a multi-layered water-retention barrier on the leaf surface: "modified chitosan oligosaccharide backbone provides network support → chitosan oligosaccharide side chains and polyaspartic acid lock in water through hydrogen bonds → xanthan gum gel network retains water," which significantly reduces the rate of water evaporation and prolongs the duration of leaf wetting.

[0024] In summary, this application, through the synergistic formulation of the aforementioned multi-components, systematically solves the technical problems of poor leaf adhesion and water retention of conventional chitosan oligosaccharide liquid fertilizers from three dimensions: reducing surface tension to promote spreading, enhancing chemical and physical dual anchoring to improve erosion resistance, and constructing a multi-layered water-retaining network to delay water evaporation. This allows fertilizer nutrients to obtain sufficient time for penetration and absorption, thereby improving fertilizer utilization, reducing the number of re-spraying applications, and lowering fertilizer and labor costs.

[0025] Furthermore, the modified chitosan oligosaccharide described above was prepared using the following method:

[0026] (1) Dissolve starch in deionized water to obtain starch milk, stir and gelatinize at 90-95℃ for 30-40 min, then place it in an ice water bath to cool to 55-60℃, add chitosan oligosaccharide, stir until completely dissolved, and obtain starch-chitosan oligosaccharide mixed solution.

[0027] (2) Add an initiator to the starch-chitosan oligosaccharide mixed solution and stir the reaction at 64-66℃ for 3.0-3.5h under nitrogen protection. After the reaction is completed, cool to room temperature, add anhydrous ethanol to precipitate the precipitate, filter and collect the precipitate, wash it repeatedly with anhydrous ethanol 2-4 times, freeze dry to obtain modified chitosan oligosaccharide.

[0028] Further, in step (1), the starch is waxy corn starch, and the mass ratio of starch to deionized water is (1.3-1.7):20; the molecular weight of the chitosan oligosaccharide is 800-3000 Da, and the mass ratio of starch to chitosan oligosaccharide is 1:(0.6-0.8).

[0029] Furthermore, in step (2), the initiator is selected from ammonium persulfate and potassium persulfate. The amount of initiator added is 0.5%-1.0% of the total mass of starch and chitosan oligosaccharide. The initiator is prepared as an aqueous solution with a mass fraction of 5%-10% before being added. It is added in two portions, with an interval of 30 minutes between each addition.

[0030] By employing the above-mentioned technical solution, this preparation method utilizes a free radical graft copolymerization strategy. The free radicals generated by the thermal decomposition of the initiator serve as active centers, capturing hydrogen atoms from the hydroxyl groups of glucose units on the starch molecular chain to form active sites. This initiates the grafting reaction of chitosan oligosaccharides, allowing them to be stably covalently linked to the starch molecular chain. This covalent linkage ensures that the modified chitosan oligosaccharides do not undergo phase separation during fertilizer storage and dilution, exhibiting system stability far superior to physical mixing methods. Gelatinization treatment disrupts the starch crystalline structure, fully extends the molecular chains, and exposes the active hydroxyl groups; ethanol precipitation and repeated washing effectively remove unreacted chitosan oligosaccharides and small molecule impurities, ensuring the purity of the product.

[0031] Furthermore, the macronutrients include a nitrogen source, a phosphorus source, and a potassium source. The nitrogen source is selected from urea, ammonium nitrate, and potassium nitrate. The phosphorus source is selected from potassium dihydrogen phosphate and dipotassium hydrogen phosphate. The potassium source is selected from potassium dihydrogen phosphate, potassium nitrate, and potassium sulfate.

[0032] By adopting the above technical solution, the nitrogen source is selected from urea, ammonium nitrate, potassium nitrate, etc.; the phosphorus source is selected from potassium dihydrogen phosphate, dipotassium hydrogen phosphate, etc.; and the potassium source is selected from potassium dihydrogen phosphate, potassium nitrate, potassium sulfate, etc. These raw materials are all water-soluble inorganic salts that can quickly dissolve in water to form a uniform fertilizer solution. They have good compatibility with organic functional components (modified chitosan oligosaccharide, polyaspartic acid, etc.) and will not produce precipitation or stratification, ensuring the uniformity and stability of the fertilizer system. At the same time, it also ensures that crops can quickly obtain core nutrients such as nitrogen, phosphorus, and potassium.

[0033] Furthermore, the trace element nutrients include a calcium source, a zinc source, and a boron source. The calcium source is selected from calcium nitrate and calcium chloride, the zinc source is selected from zinc sulfate and EDTA-zinc, and the boron source is selected from boric acid and borax.

[0034] By employing the aforementioned technical solutions, all three are essential micronutrients for crop growth and development. However, calcium and zinc ions readily form insoluble precipitates with phosphate and sulfate ions in conventional fertilizer systems, leading to nutrient inactivation. This application pre-chelates micronutrients using organic acid chelating agents, ensuring that calcium, zinc, and boron exist stably in a chelated state within the fertilizer system. This avoids precipitation formation and improves the efficiency of micronutrient absorption by crop leaves.

[0035] Furthermore, the organic acid chelating agent is selected from any one of citric acid, malic acid, and tartaric acid.

[0036] Furthermore, the alkyl glycoside surfactant is selected from any one of octyl glucoside, decyl glucoside, and lauryl glucoside.

[0037] By employing the above technical solution, alkyl glycosides are nonionic surfactants synthesized from natural glucose and fatty alcohols, exhibiting excellent biodegradability and low toxicity. Their molecular structure combines a hydrophilic sugar ring head with a hydrophobic alkyl chain tail, effectively reducing the surface tension of the fertilizer solution. After spraying, alkyl glycoside molecules align at the solid-liquid interface—the hydrophobic alkyl chain faces the waxy layer of the leaf, and the hydrophilic sugar ring faces the fertilizer solution. This molecular alignment not only promotes rapid droplet spreading but also enhances the affinity between the fertilizer solution and the leaf surface through hydrophobic interactions.

[0038] This application also provides a method for preparing chitosan oligosaccharide liquid fertilizer, which adopts the following technical solution:

[0039] A method for preparing a chitosan oligosaccharide liquid fertilizer includes the following steps:

[0040] S1. Dissolve the organic acid chelating agent in 30%-50% of the total amount of water, stir until completely dissolved, adjust the pH to 4.0-6.0 with citric acid or potassium hydroxide, add trace element nutrients, and stir the chelation reaction at 40-60℃ for 30-60 minutes to obtain the trace element solution.

[0041] S2. Add macronutrients, modified chitosan oligosaccharide, polyaspartic acid, nano silica, alkyl glycoside surfactants, xanthan gum, preservatives and defoamers to the remaining water, stir at 25-40℃ until completely dissolved, then slowly add the trace element solution obtained in step S1, and continue stirring for 10-20 minutes until uniform to obtain chitosan oligosaccharide liquid fertilizer.

[0042] This application also provides an application of chitosan oligosaccharide liquid fertilizer, employing the following technical solution:

[0043] The application of a chitosan oligosaccharide liquid fertilizer in promoting crop growth, improving foliar fertilizer adhesion rate and water retention capacity, wherein the chitosan oligosaccharide liquid fertilizer is diluted 300-800 times before use.

[0044] Compared with the prior art, the beneficial effects of the present invention are:

[0045] 1. This application uses modified chitosan oligosaccharide, obtained by graft copolymerization of waxy corn starch and chitosan oligosaccharide under the action of an initiator, as the core functional component. Since the copolymer has starch molecular chains as the backbone and chitosan oligosaccharide as the side chains, the two are stably connected by covalent bonds. The molecular chains have a large number of polar groups such as hydroxyl and amino groups, which can form hydrogen bonds and intermolecular van der Waals forces with the waxy layer of crop leaves, resulting in a strong interfacial adhesion effect. At the same time, the starch backbone can form a physical entanglement network in aqueous solution, and the grafted chitosan oligosaccharide side chains retain a large number of hydrophilic groups, which can effectively capture and retain water molecules. Thus, while enhancing the adhesion to the leaf surface, it significantly improves the water retention capacity of the fertilizer solution, fundamentally solving the problem of low leaf retention rate and insufficient wetting effect caused by the lack of long-term adhesion and hydrophilic water-locking structure in conventional chitosan oligosaccharide liquid fertilizers.

[0046] 2. In this application, alkyl glycoside surfactants and nano-silica are preferred as synergistic components. Since alkyl glycoside surfactants have both hydrophilic sugar ring heads and hydrophobic alkyl chain tails, they can significantly reduce the surface tension of the fertilizer solution. After spraying, the droplets spread fully on the leaf surface, increasing the effective contact area between the fertilizer solution and the leaf surface. After being deposited on the leaf surface, nano-silica forms microscopic physical pinning points, which increases the mechanical interlocking effect between the fertilizer solution and the leaf surface. The dual anchoring mechanism of chemical adsorption and physical pinning works synergistically, making the liquid film less likely to fall off even when it is washed away by rain or wind disturbance. This greatly improves the fertilizer's resistance to erosion and retention stability on the leaf surface, overcoming the application defect of conventional products that are washed away by light rain.

[0047] 3. This application constructs a multi-layered water-retaining network through the synergistic construction of polyaspartic acid and xanthan gum. Due to the strong hydrophilicity of the dense carboxyl and amide groups on the polyaspartic acid molecular chain, it can capture a large number of water molecules through hydrogen bonds. Xanthan gum can form a gel system with a three-dimensional network structure in water. The two and the modified chitosan oligosaccharide physically entangled network interpenetrate and synergistically form a multi-layered water-retaining barrier on the leaf surface, consisting of "chitosan oligosaccharide side chains and polyaspartic acid hydrogen bonds locking water - xanthan gum gel network holding water - starch skeleton network support". This significantly slows down the water evaporation rate, prolongs the leaf surface wetting effect time, and allows nutrients to obtain sufficient penetration and absorption windows, thereby effectively improving fertilizer utilization, reducing the labor and fertilizer costs caused by frequent topdressing, and fully leveraging the quality improvement and efficiency enhancement advantages of chitosan oligosaccharide liquid fertilizer. Detailed Implementation

[0048] To better understand the technical content of this invention, specific embodiments are provided below to further illustrate the invention.

[0049] Unless otherwise specified, the experimental methods used in the embodiments of this invention are all conventional methods.

[0050] Unless otherwise specified, all materials and reagents used in the embodiments of this invention are commercially available.

[0051] Preparation example of modified chitosan oligosaccharide

[0052] Preparation Example 1

[0053] Modified chitosan oligosaccharide was prepared using the following method:

[0054] (1) Weigh 13 kg of corn starch and add it to 200 kg of deionized water. Stir evenly to obtain starch milk. Heat the starch milk to 90°C and stir to gelatinize for 40 min. Then place it in an ice water bath to cool to 55°C. Add 7.8 kg of chitosan oligosaccharide with a molecular weight of 800 Da to the gelatinized liquid and continue stirring until the chitosan oligosaccharide is completely dissolved to obtain a starch-chitosan oligosaccharide mixed solution.

[0055] (2) Nitrogen gas was introduced into the above mixed solution for 10 min to remove oxygen. 0.104 kg of ammonium persulfate initiator (the amount added was 0.5% of the total mass of starch and chitosan oligosaccharide) was added. The initiator was prepared as a 5% aqueous solution before addition. It was added in two portions with an interval of 30 min between each addition. The reaction was carried out under a nitrogen protective atmosphere and stirred at 64 °C for 3.5 h. After the reaction was completed, the system was cooled to room temperature. Three times the volume of anhydrous ethanol was added to the reaction solution to precipitate the precipitate. The precipitate was collected by filtration and washed three times with anhydrous ethanol. The precipitate was then dried in a freeze dryer at -50 °C for 24 h to obtain modified chitosan oligosaccharide.

[0056] Preparation Example 2

[0057] Modified chitosan oligosaccharide was prepared using the following method:

[0058] (1) Weigh 15kg of corn starch and add it to 200kg of deionized water. Stir evenly to obtain starch milk. Heat the starch milk to 92℃ and stir to gelatinize for 35min. Then place it in an ice water bath to cool to 58℃. Add 10.5kg of chitosan oligosaccharide with a molecular weight of 1800Da to the gelatinized liquid and continue stirring until the chitosan oligosaccharide is completely dissolved to obtain a starch-chitosan oligosaccharide mixed solution.

[0059] (2) Nitrogen gas was introduced into the above mixed solution for 10 min to remove oxygen. 0.191 kg of ammonium persulfate initiator (the amount added was 0.75% of the total mass of starch and chitosan oligosaccharide) was added. The initiator was prepared as an 8% aqueous solution before addition. It was added in two portions with an interval of 30 min between each addition. The reaction was carried out under a nitrogen protective atmosphere and stirred at 65℃ for 3.2 h. After the reaction was completed, the system was cooled to room temperature. Three times the volume of anhydrous ethanol was added to the reaction solution to precipitate the precipitate. The precipitate was collected by filtration and washed three times with anhydrous ethanol. The precipitate was then dried in a freeze dryer at -50℃ for 24 h to obtain modified chitosan oligosaccharide.

[0060] Preparation Example 3

[0061] Modified chitosan oligosaccharide was prepared using the following method:

[0062] (1) Weigh 17 kg of corn starch and add it to 200 kg of deionized water. Stir well to obtain starch milk. Heat the starch milk to 95°C and stir to gelatinize for 30 min. Then place it in an ice water bath to cool to 60°C. Add 13.6 kg of chitosan oligosaccharide with a molecular weight of 3000 Da to the gelatinized liquid and continue stirring until the chitosan oligosaccharide is completely dissolved to obtain a starch-chitosan oligosaccharide mixed solution.

[0063] (2) Nitrogen gas was introduced into the above mixed solution for 10 min to remove oxygen. 0.306 kg of potassium persulfate initiator (the amount added was 1.0% of the total mass of starch and chitosan oligosaccharide) was added. The initiator was prepared as a 10% aqueous solution before being added. It was added in two portions with an interval of 30 min between each addition. The reaction was carried out under a nitrogen protective atmosphere and stirred at 66℃ for 3 h. After the reaction was completed, the system was cooled to room temperature. Three times the volume of anhydrous ethanol was added to the reaction solution to precipitate the precipitate. The precipitate was collected by filtration and washed three times with anhydrous ethanol. The precipitate was then dried in a freeze dryer at -50℃ for 24 h to obtain modified chitosan oligosaccharide.

[0064] Preparation Example 4

[0065] The modified chitosan oligosaccharide differs from that in Example 3 in that potato starch is used instead of waxy corn starch in this example.

[0066] Example

[0067] Example 1

[0068] A chitosan oligosaccharide liquid fertilizer, the raw material components and formulation of which are shown in Table 1, wherein the modified chitosan oligosaccharide is the modified chitosan oligosaccharide prepared in Preparation Example 1; the macronutrients include 5 kg of urea, 3 kg of potassium dihydrogen phosphate, and 2 kg of potassium nitrate; the micronutrients include 1.2 kg of calcium nitrate tetrahydrate, 0.5 kg of zinc sulfate heptahydrate, and 0.3 kg of boric acid; the organic acid chelating agent is citric acid; the alkyl glycoside surfactant is octyl glucoside; the preservative is potassium sorbate; and the defoamer is a polyether defoamer.

[0069] A method for preparing a chitosan oligosaccharide liquid fertilizer, comprising the following steps:

[0070] S1. Dissolve the organic acid chelating agent in 30% of the total amount of water, stir until completely dissolved, adjust the pH to 4.0 with citric acid or potassium hydroxide, add trace element nutrients, and stir the chelation reaction at 40℃ for 30 minutes to obtain trace element solution.

[0071] S2. Add macronutrients, modified chitosan oligosaccharide, polyaspartic acid, nano silica, alkyl glycoside surfactants, xanthan gum, preservatives and defoamers to the remaining water, stir at 25°C until completely dissolved, then slowly add the trace element solution obtained in step S1, and continue stirring for 10 minutes until uniform to obtain chitosan oligosaccharide liquid fertilizer.

[0072] Example 2

[0073] A chitosan oligosaccharide liquid fertilizer, the raw material components and formulation of which are shown in Table 1, wherein the modified chitosan oligosaccharide is the modified chitosan oligosaccharide prepared in Preparation Example 2; the macronutrients include 12 kg of ammonium nitrate, 8 kg of dipotassium hydrogen phosphate, and 5 kg of potassium dihydrogen phosphate; the micronutrients include 3.5 kg of calcium chloride, 1.5 kg of EDTA-zinc, and 1 kg of borax; the organic acid chelating agent is malic acid; the alkyl glycoside surfactant is decyl glucoside; the preservative is potassium sorbate; and the defoamer is a polyether defoamer.

[0074] A method for preparing a chitosan oligosaccharide liquid fertilizer, comprising the following steps:

[0075] S1. Dissolve the organic acid chelating agent in 40% of the total amount of water, stir until completely dissolved, adjust the pH to 5.0 with citric acid or potassium hydroxide, add trace element nutrients, and stir the chelation reaction at 50℃ for 45 minutes to obtain a trace element solution.

[0076] S2. Add macronutrients, modified chitosan oligosaccharide, polyaspartic acid, nano silica, alkyl glycoside surfactants, xanthan gum, preservatives and defoamers to the remaining water, stir at 35°C until completely dissolved, then slowly add the trace element solution obtained in step S1, and continue stirring for 15 minutes until uniform to obtain chitosan oligosaccharide liquid fertilizer.

[0077] Example 3

[0078] A chitosan oligosaccharide liquid fertilizer, the raw material components and formulation of which are shown in Table 1, wherein the modified chitosan oligosaccharide is the modified chitosan oligosaccharide prepared in Preparation Example 3; the macronutrients include 18 kg of potassium nitrate, 12 kg of dipotassium hydrogen phosphate, and 10 kg of potassium sulfate; the micronutrients include 5 kg of calcium chloride, 3 kg of EDTA-zinc, and 2 kg of borax; the organic acid chelating agent is tartaric acid; the alkyl glycoside surfactant is lauryl glucoside; the preservative is potassium sorbate; and the defoamer is a polyether defoamer.

[0079] A method for preparing a chitosan oligosaccharide liquid fertilizer, comprising the following steps:

[0080] S1. Dissolve the organic acid chelating agent in 50% of the total amount of water, stir until completely dissolved, adjust the pH to 6.0 with citric acid or potassium hydroxide, add trace element nutrients, and stir the chelation reaction at 50℃ for 60 min to obtain trace element solution.

[0081] S2. Add macronutrients, modified chitosan oligosaccharide, polyaspartic acid, nano silica, alkyl glycoside surfactants, xanthan gum, preservatives and defoamers to the remaining water, stir at 40°C until completely dissolved, then slowly add the trace element solution obtained in step S1, and continue stirring for 20 minutes until uniform to obtain chitosan oligosaccharide liquid fertilizer.

[0082] Table 1. Raw material components and proportions (kg) of the liquid fertilizers in Examples 1-3

[0083]

[0084] Example 4

[0085] A chitosan oligosaccharide liquid fertilizer differs from Example 2 in that the modified chitosan oligosaccharide used in this example is the modified chitosan oligosaccharide prepared in Preparation Example 3.

[0086] Example 5

[0087] A chitosan oligosaccharide liquid fertilizer differs from Example 2 in that the modified chitosan oligosaccharide used in this example is the modified chitosan oligosaccharide prepared in Preparation Example 1.

[0088] Example 6

[0089] A chitosan oligosaccharide liquid fertilizer differs from Example 2 in that the macronutrients in this example include 10 kg of urea, 10 kg of dipotassium hydrogen phosphate, and 5 kg of potassium sulfate.

[0090] Example 7

[0091] A chitosan oligosaccharide liquid fertilizer differs from Example 2 in that: in this example, the alkyl glycoside surfactant is selected as octyl glucoside.

[0092] Example 8

[0093] A chitosan oligosaccharide liquid fertilizer differs from Example 2 in that: in this example, tartaric acid is used as the organic acid chelating agent.

[0094] Comparative Example

[0095] Comparative Example 1

[0096] A chitosan oligosaccharide liquid fertilizer was prepared according to Example 1 in the patent application document with publication number CN105218262A entitled "A Chitosan Oligosaccharide Amino Acid Water-soluble Fertilizer and Its Preparation Method".

[0097] Comparative Example 2

[0098] A chitosan oligosaccharide liquid fertilizer differs from Example 2 in that: in this comparative example, an equal amount of unmodified chitosan oligosaccharide is used instead of modified chitosan oligosaccharide.

[0099] Comparative Example 3

[0100] A chitosan oligosaccharide liquid fertilizer differs from Example 2 in that no alkyl glycoside surfactants were added in this comparative example.

[0101] Comparative Example 4

[0102] A chitosan oligosaccharide liquid fertilizer differs from Example 2 in that: no nano-silica was added in this comparative example.

[0103] Comparative Example 5

[0104] A chitosan oligosaccharide liquid fertilizer differs from Example 2 in that xanthan gum was not added in this comparative example.

[0105] Performance testing

[0106] 1. Test sample

[0107] Test samples: Chitosan oligosaccharide liquid fertilizers prepared in Examples 1-8;

[0108] Control sample: Chitosan oligosaccharide liquid fertilizer prepared in Comparative Examples 1-5.

[0109] 2. Testing Items and Operating Procedures

[0110] (1) Leaf retention rate

[0111] The detached leaf immersion and weighing method was adopted: mature cabbage leaves with typical waxy layers and uniform growth were selected, and leaf discs with a diameter of 2 cm were prepared using a punch. The initial mass of each leaf disc was accurately weighed by an electronic balance and recorded as m0. The leaf discs were completely immersed in the test fertilizer solution diluted 500 times with deionized water. After standing for 5 seconds, they were taken out vertically with tweezers at a uniform speed and suspended on a support to drain naturally. When no liquid dripped from the leaf edge (about 30 seconds), the mass of the leaf disc was immediately weighed and recorded as m1. Five parallel samples were set up for each sample, and the average value was used to calculate the leaf retention rate.

[0112] Calculation formula:

[0113]

[0114] The higher the value, the stronger the fertilizer solution's ability to adhere to the leaf surface.

[0115] (2) Complete drying time of liquid film

[0116] The test was conducted under constant temperature and humidity conditions (temperature 25℃±1℃, relative humidity 60%±2%). A clean, dry glass slide was used. 0.2 mL of the fertilizer solution diluted 500 times was accurately transferred using a pipette and evenly added to the center of the slide to form a continuous liquid film. Timing was started simultaneously. The state of the liquid film was visually observed until it completely lost its luster and no visible liquid water remained. The time required for complete drying was recorded. Three parallel samples were prepared for each sample, and the average value was taken.

[0117] The longer the drying time, the better the water retention of the fertilizer solution and the longer the leaf surface moisture retention lasts.

[0118] (3) Water-insoluble matter content

[0119] (4) The method for determining water-insoluble matter in GB / T17420-2020 "Trace Elements Foliar Fertilizers" shall be followed.

[0120] Accurately weigh 10.000g of the mixed fertilizer sample to be tested, add 100mL of deionized water, and stir until fully dissolved; filter using a G4 glass frit crucible that has been dried to constant weight at 105℃, and wash the residue three times with hot deionized water; place the crucible with residue in an oven at 105℃ and dry to constant weight, then weigh the residue after cooling.

[0121] The lower the value, the better the fertilizer solubility and the less likely it is to clog drip irrigation and spraying pipelines.

[0122] 3. Test results: The test results for each performance item are shown in Table 2 below.

[0123] Table 2 Performance test results of each sample

[0124]

[0125] As shown in Table 2, the chitosan oligosaccharide liquid fertilizers prepared in Examples 1-8 of this application are significantly superior to the existing technology products of Comparative Example 1 in terms of both leaf retention rate and liquid film complete drying time. At the same time, the water-insoluble content remains at a low level, indicating that this solution effectively solves the technical defects of conventional chitosan oligosaccharide liquid fertilizers, such as poor leaf adhesion rate and insufficient water retention, without sacrificing the basic solubility and storage stability of liquid fertilizers. The performance improvement effect is obvious.

[0126] In terms of leaf adhesion performance, the leaf retention rates of Examples 1-3 were 35.2%-48.1%, an increase of 88%-157% compared to 18.7% in Comparative Example 1, demonstrating a significant improvement in adhesion ability. Comparing Comparative Example 2 with Example 2, it can be seen that after replacing with an equal amount of unmodified chitosan oligosaccharide, the leaf retention rate decreased from 42.6% to 26.3%, indicating that the starch-grafted modified chitosan oligosaccharide forms hydrogen bonds and van der Waals forces with the leaf wax layer through the hydroxyl and amino groups on the molecular chain, which is the core factor in improving interfacial adhesion strength. In Comparative Example 3, the retention rate decreased to 22.4% after the absence of alkyl glycoside surfactants, confirming the role of alkyl glycosides in reducing droplet surface tension and promoting full droplet spreading, which is crucial for ensuring the initial adhesion area. In Comparative Example 4, without the addition of nano-silica, the retention rate decreased to 34.7%, demonstrating the microscopic physical pinning and mechanical interlocking effect formed by nanoparticles, which can further enhance the liquid film's resistance to erosion and shedding. The "spreading and wetting-chemical anchoring-physical pinning" system, constructed through the synergy of these three components, has significantly improved leaf surface adhesion performance.

[0127] In terms of water retention and longevity, the complete drying time of the liquid film in Examples 1-3 reached 165-255 min, which is 1.2-2.4 times longer than the 75 min in Comparative Example 1, significantly increasing the duration of leaf wetting. Comparing Comparative Example 2 with Example 2, it can be seen that the unmodified chitosan oligosaccharide cannot form a stable molecular entanglement network, and the drying time is shortened to 110 min, indicating that the starch skeleton network of the modified chitosan oligosaccharide is the structural support of the water retention system. In Comparative Example 5, after the absence of xanthan gum, the drying time decreased to 130 min, verifying the physical retention effect of the xanthan gum three-dimensional gel network on water molecules. The hydrophilic side chains of the modified chitosan oligosaccharide and the high-density carboxyl groups of polyaspartic acid capture water molecules through hydrogen bonds. Combined with the water-holding gel network of xanthan gum, the multi-layered water-retention barrier formed by these three elements can effectively delay water evaporation and prevent rapid nutrient crystallization, providing a sufficient time window for leaf nutrient absorption.

[0128] Regarding the stability of basic applications, the water-insoluble matter content of all embodiments remained at 1.2-1.8 g / L, which is far superior to the general quality requirements for foliar fertilizers, and there was no significant deterioration compared with the comparative examples. This indicates that the functional components introduced in this application, such as modified chitosan oligosaccharide, nano silica, and xanthan gum, have good compatibility with the basic fertilizer system, and no stability problems such as flocculation and precipitation have occurred. They will not clog drip irrigation and spraying pipelines, and can be adapted to various application scenarios, taking into account both functional improvement and practical application feasibility.

[0129] Overall, the changing patterns of various indicators are highly consistent with the mechanism of action of the technical solution. The core functional components are not simply superimposed, but rather take modified chitosan oligosaccharide as the core and work together with multiple components to form an integrated system of "wetting-spreading-anchoring-locking water". This systemically improves the defects of conventional chitosan oligosaccharide liquid fertilizers for foliar application, effectively reduces the number of re-sprayings, improves fertilizer utilization, and achieves the application effect of improving quality and reducing costs.

[0130] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A chitosan oligosaccharide liquid fertilizer, characterized in that, The raw materials include the following parts by weight: Modified chitosan oligosaccharide 5-20 parts; 10-40 servings of macronutrients; 2-10 portions of trace elements; 1-5 parts of organic acid chelating agent; Polyaspartic acid 0.5-3 parts; 0.1-1 part of nano-silica; Alkyl glycoside surfactant, 0.3-2 parts; Xanthan gum 0.05-0.5 parts; Preservative: 0.05-0.5 parts; Defoamer 0.05-0.5 parts; 20-80 parts water; The modified chitosan oligosaccharide is a copolymer of starch and chitosan oligosaccharide obtained under the action of an initiator.

2. The chitosan oligosaccharide liquid fertilizer according to claim 1, characterized in that, The modified chitosan oligosaccharide was prepared using the following method: (1) Dissolve starch in deionized water to obtain starch milk, stir and gelatinize at 90-95℃ for 30-40 min, then place it in an ice water bath to cool to 55-60℃, add chitosan oligosaccharide, stir until completely dissolved, and obtain starch-chitosan oligosaccharide mixed solution. (2) Add an initiator to the starch-chitosan oligosaccharide mixed solution and stir the reaction at 64-66℃ for 3.0-3.5h under nitrogen protection. After the reaction is completed, cool to room temperature, add anhydrous ethanol to precipitate the precipitate, filter and collect the precipitate, wash it repeatedly with anhydrous ethanol 2-4 times, freeze dry to obtain modified chitosan oligosaccharide.

3. The chitosan oligosaccharide liquid fertilizer according to claim 1, characterized in that, In step (1), the starch is waxy corn starch, and the mass ratio of starch to deionized water is (1.3-1.7):20; the molecular weight of the chitosan oligosaccharide is 800-3000 Da, and the mass ratio of starch to chitosan oligosaccharide is 1:(0.6-0.8).

4. The chitosan oligosaccharide liquid fertilizer according to claim 1, characterized in that, In step (2), the initiator is selected from ammonium persulfate and potassium persulfate. The amount of initiator added is 0.5%-1.0% of the total mass of starch and chitosan oligosaccharide. The initiator is prepared as an aqueous solution with a mass fraction of 5%-10% before being added. It is added in two portions, with an interval of 30 minutes between each addition.

5. The chitosan oligosaccharide liquid fertilizer according to claim 1, characterized in that, The macronutrients include a nitrogen source, a phosphorus source, and a potassium source. The nitrogen source is selected from urea, ammonium nitrate, and potassium nitrate. The phosphorus source is selected from potassium dihydrogen phosphate and dipotassium hydrogen phosphate. The potassium source is selected from potassium dihydrogen phosphate, potassium nitrate, and potassium sulfate.

6. The chitosan oligosaccharide liquid fertilizer according to claim 1, characterized in that, The micronutrients include calcium, zinc and boron sources. The calcium source is selected from calcium nitrate and calcium chloride. The zinc source is selected from zinc sulfate and EDTA-zinc. The boron source is selected from boric acid and borax.

7. The chitosan oligosaccharide liquid fertilizer according to claim 1, characterized in that, The organic acid chelating agent is selected from any one of citric acid, malic acid, and tartaric acid.

8. A chitosan oligosaccharide liquid fertilizer according to claim 1, characterized in that... The alkyl glycoside surfactant is selected from any one of octyl glucoside, decyl glucoside, and lauryl glucoside.

9. A method for preparing a chitosan oligosaccharide liquid fertilizer according to any one of claims 1-8, characterized in that, Includes the following steps: S1. Dissolve the organic acid chelating agent in 30%-50% of the total amount of water, stir until completely dissolved, adjust the pH to 4.0-6.0 with citric acid or potassium hydroxide, add trace element nutrients, and stir the chelation reaction at 40-60℃ for 30-60 minutes to obtain the trace element solution. S2. Add macronutrients, modified chitosan oligosaccharide, polyaspartic acid, nano silica, alkyl glycoside surfactants, xanthan gum, preservatives and defoamers to the remaining water, stir at 25-40℃ until completely dissolved, then slowly add the trace element solution obtained in step S1, and continue stirring for 10-20 minutes until uniform to obtain chitosan oligosaccharide liquid fertilizer.

10. The application of the chitosan oligosaccharide liquid fertilizer as described in any one of claims 1-8 in promoting crop growth, improving foliar fertilizer adhesion rate and water retention capacity, characterized in that, The chitosan oligosaccharide liquid fertilizer should be diluted 300-800 times before use.

Images