A rhizosphere fertilizer composition for fruit tree cultivation and a method for preparing the same

Abstract

The present application relates to the technical field of fertilizer, in particular to a rhizosphere fertilizer composition for fruit tree cultivation and a preparation method thereof, which comprises a water-retaining agent, a slow-release compound fertilizer, humic acid, a medium element chelate, a trace element chelate and a bentonite carrier. Modified polyacrylamide forms connected channels after absorbing water. The microcapsule wall material gradually relaxes in structure after absorbing water, CaO2 in the core material reacts with water to generate Ca(OH)2 and an intermediate product H2O2, H2O2 is then catalytically decomposed into water and O2 in situ by MnO2 to achieve slow and continuous release of oxygen. The shell layer has a protective effect on the slow release of the microcapsule and maintains the overall water retention stability of the water-retaining agent.

Description

Technical Field

[0001] This invention belongs to the field of fertilizer technology, specifically a rhizosphere fertilizer composition for fruit tree cultivation and its preparation method. Background Technology

[0002] Polyacrylamide-based water-retaining agents are widely used in orchards and greenhouse fruit cultivation in arid regions due to their excellent water absorption and retention properties. However, existing water-retaining agents have the following technical drawbacks: after absorbing water and swelling, they form a dense gel layer in the rhizosphere. The oxygen diffusion coefficient of this gel layer is significantly lower than that of pure water, making it difficult to replenish the oxygen consumed by the fibrous roots of fruit trees in a timely manner. This is especially true for shallow-rooted fruit trees such as peaches and grapes, whose fine roots have active metabolism and high oxygen demand, making them extremely sensitive to a decrease in rhizosphere oxygen partial pressure. The gel layer not only causes localized micro-oxygen deficiency but also physically hinders the penetration and extension of new roots, easily inducing root rot in orchards with heavy soil texture or poor drainage during the rainy season. Summary of the Invention

[0003] (1) Technical problems to be solved The purpose of this invention is to provide a rhizosphere fertilizer composition for fruit tree cultivation and its preparation method, aiming to solve the problem that existing water-retaining agents cannot simultaneously meet the dual needs of fruit tree rhizosphere for water retention and oxygen supply.

[0004] (2) Technical solution To achieve the above objectives, a rhizosphere fertilizer composition for fruit tree cultivation comprises the following components in parts by weight: 15-20 parts water-retaining agent, 40-50 parts slow-release compound fertilizer, 5-10 parts humic acid, 2-3 parts medium-element chelate, 0.5-1 parts micro-element chelate, and 10-16 parts bentonite carrier. The water-retaining agent consists of a water-retaining matrix and an outer shell layer from the inside out. The water-retaining matrix is ​​modified polyacrylamide, whose pores anchor the slow-release oxygen-enriching microcapsules. The modified polyacrylamide was modified with vinyl-modified nanocellulose whiskers and hydrophobic groups were introduced. The sustained-release oxygen-enriching microcapsules use CaO2 / MnO2 composite material as the core material and glutaraldehyde-crosslinked chitosan as the wall material. The outer shell layer is composed of L-glutamic acid-modified carboxymethyl chitosan and Ca2+-modified... 2+ It is composed of ionically cross-linked sodium alginate.

[0005] Furthermore, the preparation method of the modified polyacrylamide includes the following steps: S11. Disperse nanocellulose whiskers in deionized water, sonicate, add anhydrous ethanol, add KH-570 dropwise while stirring, adjust the pH of the system to 4.0 with glacial acetic acid, heat to 60℃, and magnetically stir the reaction. After the reaction is complete, centrifuge with deionized water, wash with anhydrous ethanol, vacuum dry, and grind into powder to obtain vinyl-modified nanocellulose whiskers. S12. Dissolve N-dodecylacrylamide in deionized water containing sodium dodecyl sulfate, stir to form a transparent micelle solution, purge with high-purity nitrogen to remove oxygen, add acrylamide, acrylic acid, vinyltrimethoxysilane, and vinyl-modified nanocellulose whiskers in sequence, stir and heat to 50°C and keep warm for 30 min, add ammonium persulfate and sodium bisulfite, react at a constant temperature, cut the resulting gel into small pieces, precipitate with anhydrous ethanol, wash, vacuum dry, and pulverize through an 80-mesh sieve to obtain modified polyacrylamide.

[0006] Furthermore, the preparation method of the sustained-release oxygen-enriching microcapsules includes the following steps: S21. Potassium permanganate solution and manganese sulfate solution were mixed and stirred in a water bath. The resulting precipitate was centrifuged, repeatedly washed with deionized water, ultrasonically exfoliated, and vacuum dried to obtain MnO2 nanosheets. S22. Dissolve anhydrous calcium chloride in deionized water, add H2O2 solution and NaOH solution dropwise under ice bath conditions, maintain the pH of the system at 11~12, add MnO2 nanosheets simultaneously during the dropwise addition, stir the reaction, filter the precipitate, wash it with anhydrous ethanol and acetone in sequence, and dry it under vacuum to obtain CaO2 / MnO2 composite core material. S23. Dissolve chitosan in acetic acid solution, stir until completely dissolved, cool in an ice bath, slowly adjust the pH of the system to 5.0~5.5 with NaOH solution, add polyethylene glycol, stir and mix evenly to obtain chitosan film-forming base solution; separately take glutaraldehyde crosslinking agent, and prepare crosslinking agent solution with acetic acid-sodium acetate buffer solution at pH=5.5; S24. The CaO2 / MnO2 composite core material is dispersed in a chitosan film-forming base solution to obtain a dispersion; the dispersion is then added dropwise to liquid paraffin containing surfactant Span-80, and emulsified by high-speed shearing to form an emulsion. The pH of the system is maintained at 5.0~5.5, and glutaraldehyde crosslinking agent solution is slowly added. The reaction is carried out in a water bath. After the reaction is completed, the emulsion is broken, the mixture is centrifuged, washed successively with n-hexane and anhydrous ethanol, and dried under vacuum to obtain sustained-release oxygen-enriched microcapsules.

[0007] Furthermore, the preparation method of the water-retaining agent includes the following steps: S31. The modified polyacrylamide was dispersed in MES buffer, EDC and NHS were added, the mixture was activated at room temperature, hexamethylenediamine was added dropwise, the mixture was stirred at room temperature in the dark, and the mixture was thoroughly dialyzed with deionized water and dried under vacuum to obtain surface-aminated modified polyacrylamide. S32. The sustained-release oxygen-enriching microcapsules were immersed in a chloroacetic acid / NaOH system, reacted, washed, and collected to obtain surface carboxylated microcapsules; the surface-aminated modified polyacrylamide and the surface carboxylated microcapsules were co-dispersed in a MES buffer / anhydrous ethanol mixed solvent, EDC and NHS were added, and the reaction was stirred at room temperature in the dark. After the reaction was completed, the microcapsules were washed alternately with deionized water and anhydrous ethanol, and then dried under vacuum to obtain the first compound. S33. Dissolve carboxymethyl chitosan and sodium alginate in deionized water, stir until dissolved, add to MES buffer, then add L-glutamic acid, EDC, and NHS, stir at room temperature in the dark, after the reaction is complete, dialyze to purify again, freeze dry to obtain shell powder. S34. Prepare a 6% (w / v) aqueous solution of the shell powder, and spray it evenly onto the surface of the first compound particles. During the spraying process, add 2% (w / v) CaCl2 solution dropwise, and dry to form a film to obtain a water-retaining agent.

[0008] Furthermore, the mass ratio of the modified polyacrylamide, the sustained-release oxygen-enriching microcapsules, and the shell powder is 12~17:1~4:1~3.

[0009] On the other hand, based on the same inventive concept, the present invention also provides a method for preparing a rhizosphere fertilizer composition for fruit tree cultivation, which is applied to the aforementioned rhizosphere fertilizer composition for fruit tree cultivation, including the following steps: weighing water-retaining agent, slow-release compound fertilizer, humic acid, medium-element chelate, micro-element chelate, and bentonite carrier according to the formula amount, mixing and stirring at room temperature until uniform, granulating using a rotary granulator, drying the granules in a forced-air drying oven, and sieving to obtain the finished rhizosphere fertilizer composition.

[0010] Furthermore, the moisture content of the rhizosphere fertilizer composition is <10%.

[0011] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are: 1. Through the synergistic effect of CaO2 / MnO2 composite core material and MnO2 in-situ catalytic decomposition of H2O2 intermediate products, the risk of toxicity caused by the accumulation of H2O2 in the rhizosphere is avoided while achieving slow-release oxygenation.

[0012] 2. The rigid framework constructed by vinyl-modified nanocellulose whiskers / silane is combined with the covalent anchoring of microcapsules, which improves the pore connectivity of the water-retaining agent during water absorption and expansion, and makes the microcapsules less likely to fall off and be lost, thus achieving the dual functions of long-term water retention and continuous oxygen supply.

[0013] 3. The outer shell layer protects the sustained release of the microcapsules and maintains the overall water-holding stability of the water-retaining agent. Detailed Implementation

[0014] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0015] Example 1: This example discloses a rhizosphere fertilizer composition for fruit tree cultivation, comprising the following components by weight: 20 parts water-retaining agent, 50 parts slow-release compound fertilizer, 10 parts humic acid, 3 parts medium-element chelate, 1 part trace element chelate, and 16 parts bentonite carrier. The water-retaining agent consists of a water-retaining matrix and an outer shell layer from the inside out. The water-retaining matrix is ​​modified polyacrylamide, whose pores anchor the slow-release oxygen-enriching microcapsules. The modified polyacrylamide was modified with vinyl-modified nanocellulose whiskers and hydrophobic groups were introduced. The sustained-release oxygen-enriching microcapsules use CaO2 / MnO2 composite material as the core material and glutaraldehyde-crosslinked chitosan as the wall material. The outer shell layer is composed of L-glutamic acid-modified carboxymethyl chitosan and Ca2+-modified... 2+ It is composed of ionically cross-linked sodium alginate.

[0016] The preparation method of the modified polyacrylamide includes the following steps: S11. Disperse 3.0g of nanocellulose whiskers in 100mL of deionized water and sonicate for 30min. Add 100mL of anhydrous ethanol and add 1.5g of KH-570 dropwise while stirring. Adjust the pH of the system to 4.0 with glacial acetic acid. Heat to 60℃ and stir magnetically for 4h. After the reaction is complete, centrifuge with deionized water, wash with anhydrous ethanol, vacuum dry at 40℃, and grind into powder to obtain vinyl-modified nanocellulose whiskers. S12. Dissolve 6.0 g of N-dodecylacrylamide in deionized water containing sodium dodecyl sulfate, stir to form a transparent micelle solution, purge with high-purity nitrogen for 30 min to remove oxygen, then add 42.6 g of acrylamide, 14.4 g of acrylic acid, 3.0 g of vinyltrimethoxysilane, and vinyl-modified nanocellulose whiskers in sequence, stir and heat to 50 °C and keep warm for 30 min, then add 0.3 g of ammonium persulfate and 0.15 g of sodium bisulfite, react at 50 °C for 4 h, cut the resulting gel into small pieces, precipitate with anhydrous ethanol, wash, vacuum dry at 40 °C for 24 h, pulverize and pass through an 80-mesh sieve to obtain modified polyacrylamide.

[0017] The preparation method of the sustained-release oxygen-enriching microcapsules includes the following steps: S21. Mix 0.1 mol / L potassium permanganate solution with 0.15 mol / L manganese sulfate solution and stir in a 65℃ water bath for 2 h. The resulting precipitate is centrifuged, washed repeatedly with deionized water until neutral, ultrasonically exfoliated for 30 min, and vacuum dried at 40℃ to obtain MnO2 nanosheets. S22. Dissolve 22.2g of anhydrous calcium chloride in 150mL of deionized water. Under ice bath conditions, add 45.4g of 30% H2O2 solution and 200mL of 2mol / L NaOH solution dropwise, maintaining the pH of the system at 11~12. During the dropwise addition, add 0.15g of MnO2 nanosheets (pre-dispersed ultrasonically in 10mL of deionized water). Stir the reaction for 1h, filter the precipitate, wash it successively with anhydrous ethanol and acetone, and vacuum dry it at 40℃ for 12h to obtain CaO2 / MnO2 composite core material. S23. Dissolve 3.0g of chitosan (degree of deacetylation ≥90%) in 150mL of 1% acetic acid solution. After stirring until completely dissolved, cool in an ice bath. Slowly adjust the pH of the system to 5.0~5.5 with 1mol / L NaOH solution. Add 1.5g of polyethylene glycol (PEG-400) and stir to mix evenly to obtain chitosan film-forming base solution. Separately, prepare a 25% (v / v) crosslinking agent solution using glutaraldehyde crosslinking agent and acetic acid-sodium acetate buffer solution at pH=5.5. S24. Disperse 5.0g of CaO2 / MnO2 composite core material in chitosan film-forming base liquid to obtain a dispersion; then add the dispersion dropwise to liquid paraffin containing surfactant Span-80 (oil phase), emulsify by high-speed shearing to form an emulsion, maintain the pH of the system at 5.0~5.5, slowly add glutaraldehyde crosslinking agent solution, react in a water bath at 40℃, after the reaction is completed, demulsify, centrifuge, wash successively with n-hexane and anhydrous ethanol, and vacuum dry to obtain sustained-release oxygen-enriched microcapsules.

[0018] The preparation method of the water-retaining agent includes the following steps: S31. The modified polyacrylamide was dispersed in 100 mL of MES buffer solution with pH 5.5~6.0, 1.0 g of EDC and 0.6 g of NHS were added, and after activation at room temperature for 30 min, 2.0 g of excess hexamethylenediamine (dissolved in 10 mL of deionized water) was added dropwise. The mixture was stirred at room temperature in the dark for 4 h, dialyzed thoroughly with deionized water for 48 h, and dried under vacuum at 40 °C to obtain surface-aminated modified polyacrylamide. S32. The sustained-release oxygen-enriching microcapsules were immersed in a chloroacetic acid / NaOH system and reacted at 60°C for 2 h. After washing, the microcapsules were collected to obtain surface-carboxylated microcapsules. The surface-aminated modified polyacrylamide and the surface-carboxylated microcapsules were co-dispersed in a mixed solvent of MES buffer / anhydrous ethanol (volume ratio 4:1). 1.5 g of EDC and 0.9 g of NHS were added, and the mixture was stirred at room temperature in the dark for 6 h (during which the pH was maintained constant with 0.1 mol / L NaOH). After the reaction was completed, the mixture was washed alternately with deionized water and anhydrous ethanol and dried under vacuum at 40°C to obtain the first compound. S33. Dissolve 10.0g of carboxymethyl chitosan and 3.0g of sodium alginate in 150mL of deionized water, stir until dissolved, add to MES buffer (pH 5.5), then add 1.7g of L-glutamic acid, 2.2g of EDC and 1.3g of NHS, stir at room temperature in the dark for 6h, after the reaction is completed, dialyze to purify again, freeze dry to obtain shell powder; S34. Prepare a 6% (w / v) aqueous solution of the shell powder, and spray it evenly onto the surface of the first compound particles. During the spraying process, add 2% (w / v) CaCl2 solution dropwise. Dry the mixture at 40°C to form a film and obtain a water-retaining agent.

[0019] The mass ratio of the modified polyacrylamide, sustained-release oxygen-enriching microcapsules, and shell powder is 17:4:3.

[0020] The preparation method of the rhizosphere fertilizer composition includes the following steps: Weigh 200g of the water-retaining agent, 500g of the slow-release compound fertilizer, 100g of humic acid, 30g of the medium-element chelate, 10g of the trace element chelate, and 160g of the bentonite carrier according to the formula amount, mix and stir at room temperature for 30 minutes until uniform, granulate using a rotary granulator, control the particle size to 2~5mm, place the granules in a 45℃ forced-air drying oven to dry to a moisture content of less than 10%, and sieve to obtain the rhizosphere fertilizer composition.

[0021] Example 2: This example is based on Example 1, but differs from Example 1 in that it discloses a rhizosphere fertilizer composition for fruit tree cultivation, comprising the following components by weight: 17.5 parts water-retaining agent, 45 parts slow-release compound fertilizer, 7.5 parts humic acid, 2.5 parts medium-element chelate, 0.75 parts trace element chelate, and 13 parts bentonite carrier.

[0022] The other components and preparation methods are the same as in Example 1.

[0023] Example 3: This example is based on Example 1, but differs from Example 1 in that it discloses a rhizosphere fertilizer composition for fruit tree cultivation, comprising the following components by weight: 15 parts water-retaining agent, 40 parts slow-release compound fertilizer, 5 parts humic acid, 2 parts medium-element chelate, 0.5 parts trace element chelate, and 10 parts bentonite carrier.

[0024] The other components and preparation methods are the same as in Example 1.

[0025] Example 4: This example is based on Example 1, but differs from Example 1 in that the mass ratio of modified polyacrylamide, sustained-release oxygen-enriching microcapsules, and shell powder in this example is 12:1:1.

[0026] The other components and preparation methods are the same as in Example 1.

[0027] Comparative Example 1: This comparative example is based on Example 1, but differs from Example 1 in that vinyl-modified nanocellulose whiskers are not added in step S12 of this comparative example.

[0028] The other components and preparation methods are the same as in Example 1.

[0029] Comparative Example 2: This comparative example is based on Example 1, but unlike Example 1, no hydrophobic groups are introduced in step S12 of this comparative example.

[0030] The other components and preparation methods are the same as in Example 1.

[0031] Comparative Example 3: This comparative example is based on Example 1, but differs from Example 1 in that MnO2 nanosheets are not added in step S21 of this comparative example, that is, the core material of the slow-release oxygen-enriching microcapsule is only CaO2.

[0032] The other components and preparation methods are the same as in Example 1.

[0033] Comparative Example 4: This comparative example is based on Example 1, but unlike Example 1, this comparative example does not add sustained-release oxygen-enriching microcapsules.

[0034] The other components and preparation methods are the same as in Example 1.

[0035] Comparative Example 5: This comparative example is based on Example 1, but unlike Example 1, L-glutamic acid is not added in step S33 of this comparative example.

[0036] The other components and preparation methods are the same as in Example 1.

[0037] Comparative Example 6: This comparative example is based on Example 1, but differs from Example 1 in that the surface of the water-retaining agent particles in this comparative example is not covered with an outer shell layer.

[0038] The other components and preparation methods are the same as in Example 1.

[0039] Comparative Example 7: This comparative example is based on Example 1, but differs from Example 1 in that the water-retaining agent in this comparative example is not chemically assembled, but rather the modified polyacrylamide, slow-release oxygen-enriching microcapsules, and shell powder are physically mixed.

[0040] The other components and preparation methods are the same as in Example 1.

[0041] Comparative Example 8: This comparative example is based on Example 1, but differs from Example 1 in that the water-retaining agent in this comparative example is replaced entirely with an equal amount of commercially available unmodified polyacrylamide water-retaining agent.

[0042] The other components and preparation methods are the same as in Example 1.

[0043] Experimental verification: Experiment 1: (1) Mix the water-retaining agent and the cultivation substrate (river sand: peat moss = 1:1, volume ratio, sieved and mixed) thoroughly according to the ratio of 2g water-retaining agent / L substrate. Put the mixture into an organic glass simulated root box (6cm inner diameter, 15cm high, with a fiber optic dissolved oxygen probe sleeve embedded in the central axis). Pour deionized water into the box once until the substrate is saturated with water (based on slight seepage at the bottom). Place the root box in a 25℃, light-proof constant temperature incubator for static culture. Insert the dissolved oxygen probe into the sleeve at 12, 24, 48, and 72h respectively. After standing for 3min and the reading stabilizes, record the dissolved oxygen concentration (mg / L) at the center point. Repeat each group 5 times.

[0044] Table 1. Dissolved oxygen concentration (DO, mg / L) at the center point of the simulated root chamber (2) Weigh 1.0g of each group of water-retaining agent and place it in a 100mL sealed reaction bottle. Add 50mL of simulated rhizosphere acidification solution, seal quickly and connect the water displacement and gas collection device, and let it stand in a 25℃ constant temperature water bath for reaction. Record the cumulative oxygen release volume (mL) and net oxygen release per unit mass of water-retaining agent sample (mL O2 / g) every 12h. At each time point, take 1mL of reaction solution and immediately use the H2O2 detection kit to determine the hydrogen peroxide concentration (mmol / L) in the system. Monitor continuously for 72h. Set up 3 parallel samples for each group.

[0045] (3) Weigh 0.5000g of each group of desiccant sample m1, place it in a beaker, add excess distilled water (≥200mL), let it stand at room temperature for 24h until the water absorption is completely balanced, transfer the swollen gel to a 100-mesh nylon filter, let it drain the surface free water naturally for 15min, weigh m2, and calculate the water absorption ratio Q (g / g): Each group has 3 parallel samples.

[0046] (4) Take the gel sample after water absorption equilibrium and place it in a constant temperature and humidity chamber at 35℃ and 40% relative humidity. Weigh it every 24 hours, record the mass change, calculate the water loss rate, and record the time (d) required for the gel to lose 50% of its water (relative to the water absorption equilibrium mass) as the water retention time index. Set up 3 parallel samples for each group.

[0047] Table 2. Cumulative oxygen release of water-retaining agent, peak H2O2 concentration of system, water absorption ratio and water retention time: As shown in Tables 1 and 2, the dissolved oxygen concentration and cumulative oxygen release of Example 1 were significantly higher than all comparative examples, with H2O2 remaining at extremely low levels. Furthermore, the water absorption ratio and water retention time remained at high levels, indicating that the water-retaining agent introduced in this invention simultaneously met the dual needs of fruit tree rhizosphere for water retention and oxygen supply. Although the core oxygen release chemical system was retained in Comparative Examples 1 and 2, the increase in dissolved oxygen concentration was lower than in the examples, demonstrating that the rigid framework and hydrophobic groups of the vinyl-modified nanocellulose whiskers physically enhanced pore connectivity and gas diffusion flux. Comparative Example 6 exhibited a trend of "sudden release at 12h and rapid decay at 72h." Although the initial DO was even slightly higher than in the examples, the water retention time plummeted to 3-4 days, proving that the outer shell layer plays a crucial role in the slow-release protection of the microcapsules and the overall water-holding stability of the water-retaining agent.

[0048] Experiment 2: Experimental materials: One-year-old peach tree cuttings with uniform growth, with a ground diameter of 0.8-1.0 cm and a plant height of 40-50 cm; cultivation containers were flower pots with a diameter of 30 cm and a height of 35 cm; the cultivation substrate was heavy clay loam (simulating poorly drained orchard conditions).

[0049] Experimental groups: Examples 1-4, Comparative Examples 1-8, and blank control CK (no fertilizer composition of the present invention was applied, only conventional compound fertilizer with equal nitrogen, phosphorus and potassium content was applied), a total of 13 groups, 20 plants in each group, arranged in randomized block design, with 3 replicates.

[0050] Experimental steps: M1. Planting and fertilization: Before planting seedlings, apply the corresponding group fertilizer composition evenly to the root distribution layer around the planting hole at a ratio of 150g per plant (planting in the hole + covering with soil). The CK group is treated with conventional compound fertilizer with the same nutrient content. M2. Cultivation and Management: All groups are watered uniformly (maintaining 70%~80% of field water holding capacity to simulate the high humidity conditions with poor drainage in the early and middle stages of the rainy season), and are subject to uniform light, temperature (22~28℃) and pest and disease control management. No additional growth regulators are applied. M3. Regular observation: Observe the plant growth every 15 days after transplanting for 60 days; M4. Destructive sampling assay (60 days): (1) Root rot rate: 10 plants were randomly selected from each group, the whole plant was lifted up, the roots were rinsed, and the proportion of blackened and soft rotten root segments to the total root length was counted (%). (2) Survival rate: The percentage of surviving plants in the group of 20 plants was counted (%). The mortality standard was that the above-ground parts were completely dried. (3) Number of new roots: Count the number of new white roots with a diameter > 1 mm per plant (roots / plant); (4) Root activity: The TTC (triphenyltetrazolium chloride) method was used. 0.5g of fresh fine roots were reacted with TTC solution under dark conditions, extracted with acetone and color developed. The amount of tetrazolium reduction was determined by spectrophotometry (485nm) and expressed as μg TTF / g·h. Table 3. Growth and root system indicators of peach seedlings in each group: As shown in Table 3, Examples 1-4 were superior to the comparative example and the control group in all four core indicators: survival rate, root rot rate, number of new roots, and root vitality. Among them, Example 1 showed the best results. The root vitality of Comparative Example 4 was low, close to the level of the control group, indicating that under the stress conditions of simulated "poor drainage" in heavy clay loam and high water content, without a continuous oxygenation mechanism, the water-retaining agent itself exacerbated local hypoxia due to the densification of the gel layer.

[0051] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, and improvements made by those skilled in the art within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A rhizosphere fertilizer composition for fruit tree cultivation, characterized in that, It includes the following components by weight: 15-20 parts water-retaining agent, 40-50 parts slow-release compound fertilizer, 5-10 parts humic acid, 2-3 parts medium-element chelate, 0.5-1 part trace element chelate, and 10-16 parts bentonite carrier. The water-retaining agent consists of a water-retaining matrix and an outer shell layer from the inside out. The water-retaining matrix is ​​modified polyacrylamide, whose pores anchor the slow-release oxygen-enriching microcapsules. The modified polyacrylamide was modified with vinyl-modified nanocellulose whiskers and hydrophobic groups were introduced. The sustained-release oxygen-enriching microcapsules use CaO2 / MnO2 composite material as the core material and glutaraldehyde-crosslinked chitosan as the wall material. The outer shell layer is composed of L-glutamic acid-modified carboxymethyl chitosan and Ca2+-modified... 2+ It is composed of ionically cross-linked sodium alginate.

2. The rhizosphere fertilizer composition for fruit tree cultivation according to claim 1, characterized in that, The preparation method of the modified polyacrylamide includes the following steps: S11. Disperse nanocellulose whiskers in deionized water, sonicate, add anhydrous ethanol, add KH-570 dropwise while stirring, adjust the pH of the system to 4.0 with glacial acetic acid, heat to 60℃, stir magnetically to react, after the reaction is completed, centrifuge with deionized water, wash with anhydrous ethanol, vacuum dry, grind into powder to obtain vinyl-modified nanocellulose whiskers. S12. Dissolve N-dodecylacrylamide in deionized water containing sodium dodecyl sulfate, stir to form a transparent micelle solution, purge with high-purity nitrogen to remove oxygen, add acrylamide, acrylic acid, vinyltrimethoxysilane, and vinyl-modified nanocellulose whiskers in sequence, stir and heat to 50°C and keep warm for 30 min, add ammonium persulfate and sodium bisulfite, react at a constant temperature, cut the resulting gel into small pieces, precipitate with anhydrous ethanol, wash, vacuum dry, and pulverize through an 80-mesh sieve to obtain modified polyacrylamide.

3. The rhizosphere fertilizer composition for fruit tree cultivation according to claim 1, characterized in that, The preparation method of the sustained-release oxygen-enriching microcapsules includes the following steps: S21. Potassium permanganate solution and manganese sulfate solution were mixed and stirred in a water bath. The resulting precipitate was centrifuged, repeatedly washed with deionized water, ultrasonically exfoliated, and vacuum dried to obtain MnO2 nanosheets. S22. Dissolve anhydrous calcium chloride in deionized water, add H2O2 solution and NaOH solution dropwise under ice bath conditions, maintain the pH of the system at 11-12, add MnO2 nanosheets simultaneously during the dropwise addition, stir the reaction, filter the precipitate, wash it with anhydrous ethanol and acetone in sequence, and dry it under vacuum to obtain CaO2 / MnO2 composite core material. S23. Dissolve chitosan in acetic acid solution, stir until completely dissolved, cool in an ice bath, slowly adjust the pH of the system to 5.0~5.5 with NaOH solution, add polyethylene glycol, stir and mix evenly to obtain chitosan film-forming base solution; separately take glutaraldehyde crosslinking agent, and prepare crosslinking agent solution with acetic acid-sodium acetate buffer solution at pH=5.5; S24. The CaO2 / MnO2 composite core material is dispersed in a chitosan film-forming base solution to obtain a dispersion; the dispersion is then added dropwise to liquid paraffin containing surfactant Span-80, and emulsified by high-speed shearing to form an emulsion. The pH of the system is maintained at 5.0~5.5, and glutaraldehyde crosslinking agent solution is slowly added. The reaction is carried out in a water bath. After the reaction is completed, the emulsion is broken, the mixture is centrifuged, washed successively with n-hexane and anhydrous ethanol, and dried under vacuum to obtain sustained-release oxygen-enriched microcapsules.

4. The rhizosphere fertilizer composition for fruit tree cultivation according to claim 1, characterized in that, The preparation method of the water-retaining agent includes the following steps: S31. The modified polyacrylamide was dispersed in MES buffer, EDC and NHS were added, and the mixture was activated at room temperature. Hexamethylenediamine was added dropwise, and the mixture was stirred at room temperature in the dark. The mixture was then thoroughly dialyzed with deionized water and dried under vacuum to obtain surface-aminated modified polyacrylamide. S32. The sustained-release oxygen-enriching microcapsules were immersed in a chloroacetic acid / NaOH system, reacted, washed, and collected to obtain surface carboxylated microcapsules; the surface-aminated modified polyacrylamide and the surface carboxylated microcapsules were co-dispersed in a MES buffer / anhydrous ethanol mixed solvent, EDC and NHS were added, and the reaction was stirred at room temperature in the dark. After the reaction was completed, the microcapsules were washed alternately with deionized water and anhydrous ethanol, and then dried under vacuum to obtain the first compound. S33. Dissolve carboxymethyl chitosan and sodium alginate in deionized water, stir until dissolved, add to MES buffer, then add L-glutamic acid, EDC, and NHS, stir at room temperature in the dark, after the reaction is complete, dialyze to purify again, freeze dry to obtain shell powder. S34. Prepare a 6% (w / v) aqueous solution of the shell powder, and spray it evenly onto the surface of the first compound particles. During the spraying process, add 2% (w / v) CaCl2 solution dropwise, and dry to form a film to obtain a water-retaining agent.

5. A rhizosphere fertilizer composition for fruit tree cultivation according to claim 4, characterized in that, The mass ratio of the modified polyacrylamide, sustained-release oxygen-enriching microcapsules, and shell powder is 12~17:1~4:1~3.

6. A method for preparing a rhizosphere fertilizer composition for fruit tree cultivation, applied to the preparation of a rhizosphere fertilizer composition for fruit tree cultivation as described in any one of claims 1 to 5, characterized in that, The method includes the following steps: weighing water-retaining agent, slow-release compound fertilizer, humic acid, medium-element chelate, trace element chelate, and bentonite carrier according to the formula, mixing and stirring at room temperature until uniform, granulating using a rotary granulator, drying the granules in a forced-air drying oven, and sieving to obtain the finished rhizosphere fertilizer composition.

7. The method for preparing a rhizosphere fertilizer composition for fruit tree cultivation according to claim 6, characterized in that, The moisture content of the rhizosphere fertilizer composition is <10%.

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