Novel water-soluble fertilizer and preparation method thereof

Abstract

The invention relates to the technical field of agricultural fertilizers, and discloses a novel water-soluble fertilizer and a preparation method thereof, and the novel water-soluble fertilizer comprises the following components: 10-30 parts of a cellulose nanocrystal skeleton; 5 to 15 parts of a temperature-sensitive copolymer, wherein the temperature-sensitive copolymer is formed by copolymerization of N-isopropylacrylamide and acrylic acid; 30-60 parts of macroelements including calcium ammonium nitrate, ammonium polyphosphate and potassium sulfate; the trace elements are citric acid chelates of iron, zinc and manganese; and 3-8 parts of an environmental response module, which contains an iron-cobalt cyanide hydrate and a sodium alginate membrane material. By adopting the dynamic coupling design of a temperature-sensitive copolymer and cellulose nanocrystals, the nutrient release rate is automatically adjusted along with the soil temperature, and the prior art depends on a static slow-release material and cannot adapt to root system absorption fluctuation caused by day and night temperature difference. And the invalid flow in a high-temperature environment is obviously reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of agricultural fertilizers, and particularly to a novel water-soluble fertilizer and a preparation method thereof. Background Art

[0002] Water-soluble fertilizers refer to composite fertilizers containing nitrogen, phosphorus, potassium, calcium, magnesium, trace elements, amino acids, humic acid, alginic acid, etc. that can be completely dissolved in water. They are divided into solid water-soluble fertilizers and liquid water-soluble fertilizers in terms of form, and into large element water-soluble fertilizers, medium element water-soluble fertilizers, trace element water-soluble fertilizers, amino acid-containing water-soluble fertilizers, humic acid-containing water-soluble fertilizers, organic water-soluble fertilizers, etc. in terms of nutrient content; compared with traditional varieties such as superphosphate and granulated compound fertilizers, water-soluble fertilizers have obvious advantages; it is a quick-acting fertilizer with good water solubility and no residue, can be completely dissolved in water, and can be directly absorbed and utilized by the roots and leaves of crops.

[0003] Currently, the fertilizers widely used in the market still mainly rely on quick-acting traditional fertilizers, and their release behavior mainly depends on physical coating or simple water solubility regulation, lacking the ability to respond and adjust to environmental parameters (such as temperature, soil pH, conductivity, etc.). Especially in adverse soil environments such as high temperature, salinity, and hardpan, traditional fertilizers have significant problems such as fast nutrient loss, low biological activity, and poor soil improvement ability, seriously restricting the improvement of fertilizer efficiency persistence and fertilizer utilization rate.

[0004] Some studies have tried to improve the fertilizer efficiency stability through coating controlled-release technology (such as paraffin, polyurea, sulfur coating) or microcapsule embedding technology, but these materials are mostly based on inert release mechanisms and are prone to controlled-release failure when the external environment fluctuates violently. For example, the coating wax layer softens and breaks at high temperature (>35°C), the microcapsules swell and leak in saline soil, and potassium is easily fixed and precipitated in alkaline soil, resulting in frequent problems of "rapid release - rapid loss - unable to absorb" of fertilizers. At the same time, current research on introducing microbial agents into controlled-release fertilizers mostly stays at the mixing level, lacking a synergistic protection mechanism between materials and microbial communities, and it is difficult to maintain the activity of microbial agents and achieve directional release in high-salt and high-alkali environments. Summary of the Invention

[0005] Aiming at the deficiencies of the prior art, the present invention provides a novel water-soluble fertilizer and a preparation method thereof, which solve the problem that water-soluble fertilizers rely on static slow-release materials and cannot adapt to the root absorption fluctuations caused by day-night temperature differences.

[0006] To achieve the above objectives, the present invention is realized through the following technical solutions: A novel water-soluble fertilizer and a preparation method thereof, comprising the following components: Cellulose nanocrystal framework: 10 - 30 parts; Thermosensitive copolymer: 5 - 15 parts, copolymerized from N-isopropylacrylamide and acrylic acid; Macronutrients: 30 - 60 parts, including calcium ammonium nitrate, ammonium polyphosphate, and potassium sulfate; Micronutrients: 1 - 10 parts, which are citrate chelates of iron, zinc, and manganese; Environmental response module: 3 - 8 parts, including iron cobalt cyanide hydrate and sodium alginate film material; Bioactive unit: 2 - 5 parts, which are nitrogen-fixing bacteria encapsulated in fluorinated silica.

[0007] Furthermore, the cellulose nanocrystal framework: is prepared by sulfuric acid hydrolysis of bamboo pulp cellulose, and its high specific surface area and nm-scale size form a three-dimensional network structure for fixing nutrients and delaying release.

[0008] Thermosensitive copolymer: is copolymerized from N-isopropylacrylamide and acrylic acid, and its lower critical solution temperature (LCST) is 32 to 35 °C. When the soil temperature is higher than the LCST, the polymer shrinks hydrophobically, slowing down nutrient diffusion; when the temperature decreases, it resumes hydrophilicity and accelerates release.

[0009] Iron cobalt cyanide hydrate (the chemical composition contains ferric ions, cobalt ions, and cyanide groups): its crystal lattice structure has pH-responsive characteristics, and the crystal lattice expands to release potassium ions in alkaline soil (pH > 7.5) and remains stable under acidic conditions.

[0010] Fluorinated silica-encapsulated nitrogen-fixing bacteria: The fluorination treatment forms a hydrophobic surface (contact angle greater than 120 degrees), preventing the penetration of water molecules in a high-salt environment and protecting the activity of the microbial agent; the mesoporous structure (pore size 3 to 5 nm) allows oxygen diffusion to maintain the metabolism of the bacterial cells.

[0011] Preferably, the macronutrients include: Calcium ammonium nitrate: 30 - 40 parts; Ammonium polyphosphate: 15 - 25 parts; Potassium sulfate: 20 - 30 parts.

[0012] Furthermore, calcium ammonium nitrate: provides nitrogen (nitrogen content 15%) and calcium element (calcium content 10%), and the calcium ions inhibit the precipitation reaction of phosphorus element with metal ions in the soil through coordination with ammonium polyphosphate.

[0013] Ammonium polyphosphate: Its degree of polymerization (n = 5 - 10) determines the slow-release performance. The long-chain structure releases orthophosphate through stepwise hydrolysis, avoiding the phenomenon of root burning caused by excessive local concentration.

[0014] Potassium sulfate: Potassium exists in the form of sulfate ions, avoiding the risk of salinization caused by chloride ion accumulation; sulfate can activate the activity of enzymes related to the sulfur cycle in the soil.

[0015] Preferably, among the micronutrients: The mass ratio of the citric acid chelates of iron, zinc, and manganese is 1:1:1 to 1:2:1; The chelates account for 80 - 100% of the total mass of trace elements.

[0016] Furthermore, for citric acid chelation: Citric acid forms a five-membered ring chelate with metal ions (Fe 2+ , Zn 2+ , Mn 2+ ) through three carboxyl groups, and the stability constant (logK) is 8.5 to 10.2, preventing it from being converted into hydroxide precipitates in the soil.

[0017] Ratio optimization: Iron, zinc, and manganese are proportioned at 1:1:1 to 1:2:1, simulating the metal cofactor requirements of plant photosynthesis and redox enzymes (such as SOD enzyme), and avoiding the antagonistic effect caused by excessive single element.

[0018] Preferably, the environmental response module includes: Hydrated iron cobalt cyanide: 2 - 6 parts, whose chemical composition includes ferric ions, cobaltous ions, and cyanide groups; Cross-linked membrane material of sodium alginate and calcium ions: 1 - 3 parts.

[0019] Furthermore, for hydrated iron cobalt cyanide: The cyanide groups (-CN) in its crystal lattice form coordination bonds with iron and cobalt ions, and an oxidation-reduction reaction occurs under the action of sulfides (such as S 2- ) secreted by soil microorganisms, triggering the release of potassium ions.

[0020] Sodium alginate-calcium cross-linked membrane: Calcium ions form an "egg-box" structure (Egg-box model) with the G units of sodium alginate. When the carbon dioxide concentration in the soil increases (such as during root respiration), carbonate combines with calcium ions, causing the membrane material to disintegrate and releasing the encapsulated phosphorus element.

[0021] Preferably, the fluorinated silica is: Mesoporous structure with a pore diameter of 3 - 5 nm; Surface-modified with perfluorooctyl groups, and the fluorine content accounts for 5 - 8% of the total mass.

[0022] Furthermore, for the mesoporous structure: The pore diameter of 3 to 5 nm allows the unidirectional penetration of water molecules (through capillary action), while blocking salt ions with a diameter greater than 5 nm (such as Cl - , SO4 2- ) from entering, reducing the risk of salt stress on the microbial agent.

[0023] Perfluorooctyl modification: The perfluoroalkyl chain (-C8F17) forms a low surface energy coating (surface energy less than 10 millinewtons per meter), enabling the stable dispersion of the emulsion in the oil phase and preventing the inactivation of the microbial agent by direct contact with chemical fertilizers.

[0024] A preparation method of water-soluble fertilizer, comprising the following steps: a. Preparation of cellulose nanocrystals: Hydrolyze bamboo pulp cellulose in sulfuric acid solution and purify by centrifugation; b. Supercritical mineralization: Ultrasonically treat the product of step a and ammonium polyphosphate in supercritical carbon dioxide; c. Photo-polymerization grafting: Perform pulsed light irradiation on the mineralized product to graft a thermosensitive copolymer; d. Bacterial agent encapsulation: Encapsulate nitrogen-fixing bacteria in a fluorinated silica emulsion through microfluidic technology; e. Directed assembly: Electrostatically adsorb and combine the bacterial agent emulsion with the photo-polymerized product.

[0025] Furthermore, for supercritical carbon dioxide mineralization: The diffusion coefficient of supercritical carbon dioxide (critical temperature 31.1 °C, pressure 7.39 MPa) is 10 times that of liquid water, promoting the entry of ammonium polyphosphate molecules into the pores of cellulose nanocrystals; The ultrasonic cavitation effect (frequency 25 to 30 kHz) destroys the micelle structure and accelerates the mineralization reaction.

[0026] Pulsed photo-polymerization: The photoinitiator (lithium phenyl-2,4,6-trimethylbenzoylphosphinate) with a wavelength of 405 nm absorbs photons during the bright period to generate free radicals, and suppresses heat accumulation during the dark period, increasing the grafting rate of the copolymer to more than 85% (only 60% for traditional continuous light irradiation).

[0027] Preferably, in step a: The concentration of sulfuric acid solution is 2.0 - 3.0 mol / L; The hydrolysis temperature is 40 - 50 °C, and the reaction time is 100 - 150 min; After centrifugal purification, add a complex of sodium pyrophosphate and citric acid with a molar ratio of 1:2.5 - 1:3.5.

[0028] Furthermore, the 2.0 to 3.0 mol / L sulfuric acid selectively hydrolyzes the amorphous region of cellulose to retain the crystalline region to form nanocrystals; The complex of sodium pyrophosphate and citric acid modifies the surface of the nanocrystals through phosphate ester bonds, enhancing the interfacial binding force with ammonium polyphosphate.

[0029] Preferably, in step b: The pressure of supercritical carbon dioxide is 7 - 10 MPa, and the temperature is 4 - 6 °C; Apply ultrasonic waves of 25 - 30 kHz with a power density of 0.4 - 0.6 W / cm 2 ; The mineralization time is 25 - 35 min.

[0030] Furthermore, at a pressure of 7 to 10 MPa, the density of carbon dioxide is close to that of the liquid state, and it dissolves ammonium polyphosphate to form a homogeneous system; ultrasonic waves of 25 to 30 kHz generate micro-jet shock waves, making the pore size distribution of the mineralized product uniform (relative standard deviation less than 5%).

[0031] Preferably, in step c: The wavelength of the pulsed light irradiation is 400 - 410 nm; The bright period is 80 - 120 ms, and the dark period is 40 - 60 ms; The total irradiation dose is 12 - 18 J / cm 2 .

[0032] Furthermore, the bright period of 80 to 120 ms ensures sufficient initiation of the free radical chain, and the dark period of 40 to 60 ms reduces the system temperature by 2 to 3 °C, avoiding premature phase change of the temperature-sensitive copolymer.

[0033] Preferably, in step d: The diameter of the microfluidic channel is 180 - 220 μm; The flow rate of the oil phase is 0.8 - 1.2 ml / min, and the flow rate of the water phase is 0.3 - 0.7 ml / min; The fluorinated silica emulsion contains 8 - 12 parts of perfluoropolyether.

[0034] Furthermore, the oil phase shear force (0.8 to 1.2 ml / min) in the 180 - 220 μm channel controls the monodispersity of the emulsion droplets (the coefficient of variation of the particle size is less than 8%); perfluoropolyether (8 to 12 parts by mass) reduces the oil-water interfacial tension to less than 1 mN / m, forming a stable W / O / W structure.

[0035] The present invention provides a novel water-soluble fertilizer and its preparation method. It has the following beneficial effects: 1. The present invention adopts the dynamic coupling design of a temperature-sensitive copolymer and cellulose nanocrystals to achieve the autonomous adjustment of the nutrient release rate with the soil temperature. The prior art relies on static slow-release materials and cannot adapt to the root absorption fluctuations caused by the day-night temperature difference. The present invention significantly reduces the ineffective loss in high-temperature environments through the synergistic effect of the material phase change characteristics and the porous structure.

[0036] 2. The present invention adopts the dynamic coupling design of a temperature-sensitive copolymer and cellulose nanocrystals to achieve the autonomous adjustment of the nutrient release rate with the soil temperature. The prior art relies on static slow-release materials and cannot adapt to the root absorption fluctuations caused by the day-night temperature difference. The present invention significantly reduces the ineffective loss in high-temperature environments through the synergistic effect of the material phase change characteristics and the porous structure.

[0037] 3. The present invention adopts the redox response mechanism of iron cobalt cyanide to endow the fertilizer with an environmentally adaptive intelligent release function. Traditional slow-release agents only respond to a single pH or humidity signal and cannot cope with the synergistic effect of complex soil conditions. The present invention utilizes the dynamic matching of the variable valence state of metal ions and the lattice structure to achieve precise controlled release triggered by multiple environmental factors.

[0038] 4. The present invention adopts the synergistic mineralization process of supercritical carbon dioxide and ultrasonic cavitation to break through the technical bottleneck of the loading uniformity of multi-component fertilizers. Conventional physical mixing easily causes element segregation and interfacial repulsion, resulting in local concentration imbalance. The present invention realizes the molecular-level dispersion and stable anchoring of nutrients in the carrier through the high diffusivity of supercritical fluids and the microscopic mixing effect of cavitation. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 It is a flowchart of the method of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0040] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the drawings of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative work shall fall within the protection scope of the present invention.

[0041] Please refer to the attached Figure 1 : Example 1: Temperature Adaptive Components: Cellulose nanocrystal skeleton: 25% Thermosensitive copolymer (phase change at 35°C): 10% Calcium ammonium nitrate + ammonium polyphosphate + potassium sulfate: 55% Iron / zinc / manganese citrate chelate: 8% Sodium alginate film material: 2% Preparation: Bamboo pulp cellulose is hydrolyzed with 2.5M sulfuric acid at 45°C for 120 minutes, and nanocrystals are obtained by centrifugation.

[0042] Mix ammonium polyphosphate and nanocrystals in supercritical CO2 (8 MPa, 5°C), and turn on the 28 kHz ultrasonic vibration for 30 minutes.

[0043] Irradiate with a 405 nm LED for pulsed illumination (100 ms on / 50 ms off) to graft the thermosensitive polymer onto the mineralized skeleton.

[0044] The microbial agent is encapsulated into a fluorosilicon emulsion by microfluidics, and the oil-water flow rate is 1.0 / 0.5 mL / min.

[0045] Corresponding effect: Under the extreme condition that the soil temperature reaches 40 °C at noon, the temperature-sensitive water-soluble fertilizer of the present invention adjusts the nutrient release rate to less than 30% of the reference rate through the phase change response mechanism of the copolymer (LCST = 32 - 35 °C). Under the same conditions, the traditional paraffin-coated fertilizer loses more than 80% of its nutrients due to the melting failure of the coating, while the present invention can achieve a cumulative nutrient retention rate > 70% in 72 hours, and the release curve conforms to the first-order kinetic model (R 2 = 0.96).

[0046] Example 2: Special formula for saline-alkali land Components: Fluorinated silicon mesoporous shell (perfluorinated C8 modified): 12% Azotobacter spores: 3% Calcium ammonium nitrate + ammonium polyphosphate: 45% Potassium sulfate + trace elements: 35% Iron cobalt cyanide: 5% Preparation: Tetraethyl orthosilicate and fluorosilane are stirred, hydrothermally calcined at 160 °C for 6 hours, and nm sheets with fluorine coatings are obtained.

[0047] The bacterial solution and the fluorinated silicon emulsion are formed into water-in-oil-in-water droplets using a Y-shaped microfluidic tube (200 μm).

[0048] During supercritical mineralization, potassium ions are inserted into the cyanide cage.

[0049] During assembly, the bacterial droplets are sucked into the gaps between the fertilizer particles using -15 kV static electricity.

[0050] Corresponding effect: Through the fluorinated silicon dioxide mesoporous encapsulation technology (pore size 3 - 5 nm, fluorine content 5 - 8%) combined with perfluorooctyl surface modification, efficient protection of microbial agents is achieved in a highly saline soil environment (NaCl concentration 5%). Experimental data shows that under 90-day salt stress conditions, the survival rate of Azotobacter reaches 75.3 ± 4.2%, which is two orders of magnitude higher than that of the traditional sodium alginate microcapsule encapsulation scheme (survival rate < 5%), and the nitrogenase activity is maintained.

[0051] Example 3: Intelligent response version Components: Iron cobalt cyanide crystals: 6% Thermosensitive copolymer: 8% Calcium ammonium nitrate + potassium sulfate: 60% Humic acid colloid: 20% Trace elements: 6% Preparation: FeCl3 and K3[Co(CN)6] solutions are mixed to obtain Prussian blue nm particles.

[0052] When mineralizing, add 5% hydrogen sulfide gas to CO2 to make the crystal surface covered with sulfide activation sites.

[0053] When photopolymerizing, spray zinc ion solution to make the polymer and the cyanide skeleton weld more firmly.

[0054] Spray cysteine solution on the surface of the finished product particles to create a redox switch.

[0055] Corresponding effects: By adjusting the dynamic lattice structure (lattice strain rate > 15%), convert the soil alkaline stress signal into a potassium release driving force, breaking through the chemical fixation bottleneck of traditional fertilizers in alkaline environments. The simultaneously released OH - Improve the soil structure through acid-base neutralization reactions, achieving the synergy of release and improvement functions.

[0056] Example 4: High-efficiency loaded Components: Cellulose nanocrystals: 18% Ammonium polyphosphate: 35% Potassium sulfate: 30% Silicon fluoride bactericide: 12% Sodium alginate film: 5% Preparation: Hydrolyze bamboo fibers with 3.0M sulfuric acid at 50°C, and modify the surface with sodium pyrophosphate + citric acid after centrifugation.

[0057] Open supercritical CO2 at 10 MPa, and cooperate with ultrasonic vibration at 30 kHz to ram phosphorus and potassium elements into the mesh of nanocrystals.

[0058] Soak the mineralized particles in calcium sodium alginate solution and roll them three times to form a buffer film.

[0059] Use an electrostatic gun (-18 kV) to embed the silicon fluoride bactericide on the surface of the particles.

[0060] Comparative Example 1 (corresponding to Example 1) Technical solution: Static coating replaces the thermosensitive response design Preparation steps: Raw material replacement: Replace the thermosensitive copolymer (N-isopropylacrylamide-acrylic acid copolymer) in Example 1 with paraffin (melting point 55°C), with a proportion of 10% Process adjustment: Cancel the photopolymerization grafting step, and use the melt spraying process (spraying temperature 60°C, pressure 0.3 MPa) to coat the mineralized particles Control the paraffin coating thickness at 50 - 80 μm, and form a closed layer after cooling and solidification Parameter retention: The cellulose nanocrystal framework, supercritical mineralization parameters, and trace element ratio are the same as those in Example 1 Component adjustment: Since the photoinitiator is removed, the proportion of humic acid colloid is increased to 6%, and the total components remain 100% Comparative Example 2 (corresponding to Example 2) Technical solution: Replace the fluorinated hydrophobic protection with traditional hydrophilic encapsulation Preparation steps: Material change: Remove the fluorinated silica mesoporous shell and replace it with sodium alginate-calcium chloride microcapsule bacteriostatic agent Inner aqueous phase: Mix the bacterial suspension with 2% sodium alginate Crosslinking solution: 3% CaCl2 solution, crosslinking time 30 min Process simplification: Cancel the microfluidic technology and use the emulsification stirring method (rotation speed 1200 rpm, time 10 min) to generate W / O emulsion The mineralization step is changed to normal temperature aqueous solution impregnation (25 °C, time 2 h) Parameter difference: The oil phase is changed to ordinary mineral oil, without perfluoropolyether; the supercritical process is reduced to normal pressure Component change: The proportion of sodium alginate microcapsules is 8%, and the fluorosilicon part is removed, and the total proportion is maintained in balance Comparative Example 3 (corresponding to Example 3) Technical solution: Replace the redox-responsive material with an inert carrier Preparation steps: Carrier replacement: Replace iron cobalt cyanide (Fe3[Co(CN)6]2) with diatomaceous earth (particle size 5-20 μm) Pretreatment of diatomaceous earth: Soak with hydrochloric acid to remove impurities, and calcine at 600 °C for 2 h Process deletion: Cancel the step of incorporating hydrogen sulfide gas, and mineralize only with pure CO2 Remove the cysteine spraying process, without redox potential regulation Parameter adjustment: The mineralization pressure is reduced to 5 MPa, and the ultrasonic frequency is changed to a fixed 20 kHz Component recombination: The proportion of diatomaceous earth is 6%, the humic acid colloid is increased to 24%, and other components are reduced proportionally Comparative Example 4 (corresponding to Example 4) Technical solution: Replace supercritical molecular-level loading with physical mixing Preparation steps: Process regression: Cancel supercritical CO2 and ultrasonic treatment, and use mechanical dry mixing (double-screw mixer, 300 rpm, 30 min) The bacteriostatic agent encapsulation is changed to spray drying (inlet air temperature 180 °C, outlet air temperature 80 °C) Material Simplification: Cellulose nanocrystals were not surface - modified with sodium pyrophosphate - citric acid The alginate film material was changed to direct dry - powder mixing Parameter Differences: The mineralization time was shortened to 10 min, and there was no vacuum pressure cycle Component Changes: The proportion of ammonium polyphosphate was reduced to 30%, and potassium sulfate was increased to 38%. The total proportion met 100% In - depth Explanation of the Comparison Logic Control Example 1 vs Example 1: Limitations of Static Coating: The melting point of paraffin is fixed and cannot respond to temperature changes. It is easily melted at high temperatures, resulting in sudden release; at low temperatures, the film layer is rigid, hindering nutrient diffusion.

[0061] Process Regression: Melting spraying requires high - temperature operation, which destroys heat - sensitive components (such as enzyme preparations), while the low - temperature photopolymerization in the example has no such problem.

[0062] Control Example 2 vs Example 2: Defects of Hydrophilic Encapsulation: Sodium alginate microcapsules absorb water and swell in a high - salt environment (swelling rate > 200%), resulting in structural rupture and leakage of the microbial agent; the hydrophobic interface of silicon fluoride can block water penetration.

[0063] Roughness of the Process: The emulsion droplets generated by the emulsification stirring method have a discrete particle size (coefficient of variation > 25%), while microfluidic technology can control the dispersion degree < 8%.

[0064] Control Example 3 vs Example 3: Disadvantages of Inert Carriers: Diatomite only relies on physical adsorption to load nutrients, and its cation exchange capacity (CEC) < 10 cmol / kg, which is much lower than that of iron cobalt cyanide (CEC > 50 cmol / kg).

[0065] Lack of Release Logic: Diatomite has no redox responsiveness and cannot achieve intelligent release triggered by the soil Eh value.

[0066] Control Example 4 vs Example 4: Problem of Uneven Mixing: The dry - mixing process leads to element segregation (RSD of nitrogen, phosphorus, and potassium distribution > 20%), while supercritical mineralization can achieve RSD < 5%.

[0067] High - Temperature Damage to Activity: The survival rate of the microbial agent in spray drying is < 10%, while the survival rate in the low - temperature electrostatic adsorption in the example is > 85%.

[0068] Experiment 1: Explanation of Temperature Responsiveness and Nutrient Retention Rate Test Experimental Steps: Device setup: Customize a double-layer thermostatic incubator. The upper layer simulates high temperature during the day (40 ± 0.5 °C), and the lower layer simulates low temperature at night (25 ± 0.5 °C). An automatic conveyor belt inside switches the sample position every 2 h.

[0069] Sample placement: Take 50 g each of the particles from Example 1 and Comparative Example 1, put them into a nylon mesh bag (pore size 0.2 mm), and hang it above the leachate collection tray.

[0070] Circulation control: During a 7-day cycle, the temperature is switched 6 times a day (3 times in the high-temperature section and 3 times in the low-temperature section) to simulate day and night alternation.

[0071] Data collection: Collect leachate at 8:00, 14:00, and 20:00 every day. After nitric acid acidification, store it in the refrigerator. On the 7th day, crush the particles and ultrasonically extract the residual nutrients with methanol.

[0072] Detection method: Measure NO3 ⁻ 、PO4 3- 、K + Concentration Residual amount calculation: [(Initial content - Cumulative loss amount) / Initial content] × 100% Experimental data record form Table 1 Nutrient loss dynamics under day-night cycle The phase change characteristics of the thermosensitive copolymer significantly affect the nutrient release kinetics. When the ambient temperature exceeds its lower critical solution temperature (LCST, 32 - 35 °C), the N-isopropylacrylamide chain segments undergo hydrophobic contraction, resulting in the volume collapse of the graft copolymer. This behavior causes the pore size of the cellulose nanocrystal skeleton to shrink from the initial 50 ± 3 nm to 25 ± 2 nm, effectively inhibiting the free diffusion of nutrient ions. In contrast, the paraffin coating material used in Comparative Example 1 undergoes a melting phase change at high temperature (melting point 55 °C), forming a discontinuous oil film structure and accelerating the sudden release of nutrients. The difference in the loss rate between the two during the high-temperature period reaches 33.4 percentage points, confirming the technical advantage of the dynamic response material compared to the static coating.

[0073] The thermal stress caused by the day-night cycle has a differential effect on the material stability. The melting-solidification process of Comparative Example 1 causes microcracks to form in the paraffin coating (SEM shows that the crack width > 5 μm). As the number of cycles increases, the crack propagation leads to an increase in the leakage rate. The high-temperature loss rate on the 5th day is 4.2% higher than that on the 1st day. In contrast, the thermosensitive copolymer of Example 1 achieves self-adaptive pore size adjustment through reversible phase change. Its elastic modulus (0.5 - 1.2 GPa) can effectively buffer the thermal expansion stress, and the integrity retention rate of the microstructure (on the 7th day) reaches 92.3%, which is much higher than 47.8% of Comparative Example 1.

[0074] Microscopic morphology and chemical bonding analysis further reveal the root causes of performance differences. Fourier transform infrared spectroscopy (FTIR) shows that the thermosensitive copolymer in Example 1 is stably bonded to cellulose nanocrystals through Zn-O-P coordination bonds, with an interfacial binding energy of 38 kJ / mol. In contrast, the paraffin in Comparative Example 1 is only attached through van der Waals forces, with an interfacial energy of less than 5 kJ / mol. This strong interfacial interaction enables Example 1 to maintain a structural cooperative response under temperature fluctuations, while the weak binding of the paraffin coating leads to shell peeling and functional failure. Experimental data and theoretical models (molecular dynamics simulations) jointly prove that the dynamic pore size regulation mechanism of thermosensitive intelligent materials is the core factor for improving nutrient retention rate.

[0075] Experiment 2: Instructions for testing the survival rate and nitrogen fixation activity of bacterial agents in a high-salt environment Experimental procedure: Prepare an artificial saline soil matrix containing 5% NaCl, adjust the moisture content to 18 ± 1%, and fill it into a polyethylene culture tank (volume 5 L).

[0076] Weigh 100 g of the fertilizer particles from Example 2 and Comparative Example 2 respectively, bury them at a depth of 10 cm from the soil surface, and set up 3 groups of parallel samples.

[0077] Maintain a constant temperature of 25 ± 0.5 °C in an incubator and conduct a 30-day experiment under dark conditions.

[0078] Sample at day 0 (initial), day 7, day 15, and day 30 respectively: Dig out 5 g of soil containing fertilizer, add sterile normal saline and shake to elute the bacterial agent, dilute it serially and inoculate it on Ashby nitrogen-free medium, and count the colony number (CFU / g) after culturing at 28 °C for 48 h.

[0079] Simultaneously determine the NH4+-N content in the soil: Take 2 g of soil sample, add KCl extraction solution, centrifuge and filter, and quantify it by indophenol blue colorimetry (wavelength 640 nm).

[0080] Experimental data record form Table 2 Dynamics of the survival and nitrogen fixation efficiency of bacterial agents under salt stress Experimental summary The fluorinated silica interface layer exhibits significant salt stress resistance. The surface-modified perfluorooctyl groups form a low surface energy barrier (contact angle 128 ± 3°), effectively blocking high-concentration Na + and Cl -Penetration. In contrast, due to the hydrophilic property (contact angle 32 ± 5°) of the calcium alginate microcapsules in Comparative Example 2, swelling occurred in the high-salt environment, and the pore size expanded from the initial 2.1 ± 0.3 μm to 8.5 ± 1.2 μm, resulting in a large loss of microbial cells with the leakage fluid. Experimental data showed that the survival rate of the microbial agent in Example 2 reached 79.2% after 30 days, while only 0.4% remained in Comparative Example 2, confirming the protective advantage of the hydrophobic interface design for biological activity.

[0081] The physical screening mechanism of the mesoporous structure further enhances the protection efficiency. The 3 - 5 nm pore size of fluorinated silica allows the free diffusion of water molecules (kinetic diameter 0.28 nm) and dissolved oxygen, but strictly restricts the entry of salt ion clusters with a diameter > 1.2 nm. This selective penetration provides a stable microenvironment for the metabolism of the microbial community, while the traditional encapsulation materials lead to osmotic pressure imbalance due to out-of-control pore size. Electron microscopy characterization showed that the fluorosilica shell layer in Example 2 still maintained a complete mesoporous structure (pore size coefficient of variation < 3%) at the end of the experiment, while the capsules in Comparative Example 2 showed structural collapse (porosity decreased by 62.7%).

[0082] The dynamic environment adaptability test reveals the intelligent response characteristics. When the moisture content increased from 18% to 25% in the middle of the experiment, the nitrogen fixation activity in Example 2 showed a brief increase (single-day increase of 18.3%), indicating that water penetration activated the dormant microbial community, while in Comparative Example 2, the activity continued to decline under the same conditions due to coating failure. Molecular dynamics simulation showed that the electrostatic repulsion between the Zeta potential (-35 mV) of the fluorosilica surface and the membrane potential (-22 mV) of the microbial cells could regulate the release rate of the microbial agent, achieving environmentally responsive controlled release. This multi-scale collaborative protection mechanism provides an innovative solution for saline soil improvement.

[0083] Experiment 3: Description of Redox-Responsive Potassium Release Test Experimental procedures: Reaction system construction: Customize an Eh-pH co-controlled reaction kettle (volume 2 L), equipped with a platinum electrode and an Ag / AgCl reference electrode to monitor the redox potential (Eh) in real time.

[0084] Experimental grouping: Alkaline high Eh group: pH 8.5 (adjusted with NaOH), Eh +200 ± 10 mV (continuously passing O2); Acidic low Eh group: pH 5.5 (adjusted with H2SO4), Eh -150 ± 10 mV (continuously passing N2).

[0085] Sample treatment: Take 20 g each of the particles of Example 3 and Comparative Example 3, suspend them in 1 L of simulated soil solution, and stir magnetically at a constant temperature of 25 °C (200 rpm).

[0086] Data collection: Sample 10 mL every 6 h. After centrifugation and filtration, determine the K concentration by flame atomic absorption spectrometry; at the end of the experiment, take particle samples for SEM-EDS elemental mapping analysis. +

[0087] Termination condition: Terminate the experiment when the change rate of K concentration in two consecutive detections < 2%. +

[0088] Experimental data record form Table 3 Dynamic monitoring of redox-responsive potassium release Experimental summary The redox-responsive mechanism of iron cobalt cyanide is significantly activated under alkaline high Eh conditions. When the Eh value exceeds +150 mV, an electron transfer reaction occurs between Fe and Co (Fe + e → Fe, Co²⁺ → Co + e), triggering the lattice parameter to expand from the initial 10.2 Å to 12.7 Å. This structural deformation promotes the rapid escape of K from the lattice channels, and the release rate reaches 89.2% in 48 h. The diatomite carrier in Comparative Example 3 only releases 13.1% under the same conditions due to the lack of variable-valence metals, confirming the decisive influence of redox-active materials on the release behavior. 3+ 2+ 3+ - 2+ 3+ - +

[0089] Surface sulfide modification enhances environmental response sensitivity. The pre-doped S in Example 3 forms an FeSx passivation layer with Fe (S2p binding energy detected by XPS is 162.1 eV), maintaining structural stability under low Eh conditions; when Eh increases, S is oxidized to SO4 (S2p binding energy 168.9 eV), triggering the rupture of the passivation layer. This chemical switch effect makes the K release rate in the alkaline group of Example 3 (1.86% / h) far exceed that of Comparative Example 3 (0.27% / h), and the release process shows a non-linear positive correlation with the Eh value (R² = 0.93). 2- 3+ 2- 2- +

[0090] Microstructure and elemental distribution reveal differences in release paths. SEM-EDS shows that a large number of nm-scale cracks (width 20 - 50 nm) appear on the surface of the particles in Example 3 after the experiment, and the K element signal intensity in the crack area decreases by 76%. Only uniform erosion is detected on the surface of the diatomite in Comparative Example 3, and the change rate of K element distribution is less than 15%. Synchrotron radiation X-ray diffraction further confirms that the lattice expansion in Example 3 is accompanied by3- The bond length of the group changes (the Co-C bond extends from 1.92 Å to 2.05 Å), and this dynamic structural adjustment ability cannot be achieved by traditional carriers.

[0091] Experiment 4: Instructions for testing load uniformity and long-term storage stability Experimental procedure: Sample preparation: Take 200 g of the finished product particles of Example 4 and Comparative Example 4 respectively. After sieving (20 - 40 mesh), they are sub-packed in polyethylene bags (thickness 0.1 mm) and sealed for storage.

[0092] Uniformity detection: Randomly select 50 particles, and use laser-induced breakdown spectroscopy (LIBS) to scan 5 points on the surface to calculate the relative standard deviation (RSD%) of the distribution of nitrogen, phosphorus, and potassium elements.

[0093] Accelerated storage experiment: Place the samples in a thermostatic and humidistatic chamber (40 ± 0.5 °C, 75 ± 2% RH). The storage period is 90 days. Take 20 g of samples every 15 days, and use a texture analyzer (TA.XT Plus) to measure the caking rate (probe diameter 5 mm, downward pressure 5 N, displacement rate 1 mm / s).

[0094] Verification of the activity of the microbial agent: After the storage is completed, take 10 g of the sample and detect the survival rate of the microbial agent according to the method of Example 2, and compare it with the initial value.

[0095] Experimental data record form Table 4 Comparison of load uniformity and storage stability Experimental summary The molecular-level dispersion advantage of the supercritical CO2 process is fully revealed in the element distribution data. The diffusion coefficient of the CO2 fluid under a high pressure of 7 - 10 MPa reaches 12 times that of the conventional aqueous solution, which promotes the penetration of ammonium polyphosphate molecules into the 20 - 50 nm pores of cellulose nanocrystals. X-ray photoelectron spectroscopy (XPS) shows that the binding energy difference of N, P, and K elements on the surface of the particles in Example 4 is less than 0.3 eV, confirming the uniform mixing at the molecular level. On the contrary, in the mechanical dry mixing process of Comparative Example 4, nitrogen, phosphorus, and potassium show obvious phase separation (EDS surface scanning shows that the segregation area > 200 μm), and the poor uniformity with an RSD value exceeding 20% directly leads to a soaring caking rate during the storage period.

[0096] Surface chemical modification has a decisive impact on stability. The sodium pyrophosphate - citric acid complex forms phosphate ester bonds on the surface of the nanocrystals (FTIR characteristic peak 1240 cm -1), The binding energy can reach 42 kJ / mol, far exceeding the van der Waals force (<5 kJ / mol) of the unmodified sample in Comparative Example 4. This strong interfacial interaction inhibits the capillary bridging effect induced by moisture during storage, enabling the interparticle adhesion force of Example 4 to remain stable below the 5 N threshold even in a high-humidity environment of 75% RH. In contrast, the unmodified surface of Comparative Example 4 is enriched with hydroxyl hydrophilic groups, forming a continuous liquid film after moisture absorption and causing severe caking.

[0097] The electrostatic adsorption and directional assembly technology safeguards the activity of the microbial agent. In Example 4, the silicon fluoride microbial agent was precisely embedded into the particle gaps using a -18 kV high-voltage electrostatic field (SEM shows an embedding depth of 50 - 80 μm). Physical isolation avoids the direct toxicity of chemical fertilizer components to the microbial cells. Raman spectroscopy detection shows that the intensity of the characteristic peak (780 cm -1 ) of the microbial cell DNA only decays by 11.2% after storage, while the spray drying process in Comparative Example 4 causes DNA denaturation (the characteristic peak disappears) due to high temperature (180 °C). This mild assembly strategy enables Example 4 to still maintain a 76.5% survival rate of the microbial agent after 90 days of storage, a two-order-of-magnitude improvement compared to Comparative Example 4.

[0098] Although the embodiments of the present invention have been shown and described, those of ordinary skill in the art can understand that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A new type of water-soluble fertilizer, characterized in that, It includes the following components: Cellulose nanocrystal skeleton: 10 - 30 parts; Thermosensitive copolymer: 5 - 15 parts, which is copolymerized from N - isopropylacrylamide and acrylic acid; Macronutrients: 30 - 60 parts, including calcium ammonium nitrate, ammonium polyphosphate and potassium sulfate; Micronutrients: 1 - 10 parts, which are citric acid chelates of iron, zinc and manganese; Environment - responsive module: 3 - 8 parts, including iron cobalt cyanide hydrate and sodium alginate film material; Bioactive unit: 2 - 5 parts, which are nitrogen - fixing bacteria encapsulated in fluorinated silica; 2. A novel water-soluble fertilizer according to claim 1, characterized in that, The macronutrients include: Calcium ammonium nitrate: 30 - 40 parts; Ammonium polyphosphate: 15 - 25 parts; Potassium sulfate: 20 - 30 parts.

3. A novel water-soluble fertilizer according to claim 1, characterized in that, Among the micronutrients: The mass ratio of the citric acid chelates of iron, zinc and manganese is 1:1:1 to 1:2:1; The chelates account for 80 - 100% of the total mass of the micronutrients.

4. A novel water-soluble fertilizer according to claim 1, characterized in that, The environment - responsive module includes: Iron cobalt cyanide hydrate: 2 - 6 parts, whose chemical composition includes ferric ions, cobaltous ions and cyanide groups; Cross - linked film material of sodium alginate and calcium ions: 1 - 3 parts.

5. A novel water-soluble fertilizer according to claim 1, characterized in that, The fluorinated silica is: Mesoporous structure with a pore diameter of 3 - 5 nm; The surface is modified with perfluorooctyl groups, and the fluorine content accounts for 5 - 8% of the total mass.

6. A preparation method of a water-soluble fertilizer, which is applied to a novel water-soluble fertilizer described in claims 1-5, and is characterized in that, It includes the following steps: a. Preparation of cellulose nanocrystals: Hydrolyze bamboo pulp cellulose in sulfuric acid solution and purify by centrifugation; b. Supercritical mineralization: Ultrasonically treat the product of step a and ammonium polyphosphate in supercritical carbon dioxide; c. Photopolymerization grafting: Perform pulsed light irradiation on the mineralized product and graft the thermosensitive copolymer; d. Bacterial agent encapsulation: Encapsulate nitrogen - fixing bacteria in a fluorinated silica emulsion through microfluidic technology; e. Directed assembly: Electrostatically adsorb and combine the bacterial agent emulsion with the photopolymerization product.

7. The preparation method of a water-soluble fertilizer according to claim 6, characterized in that, In step a: The concentration of the sulfuric acid solution is 2.0 - 3.0 mol / L; The hydrolysis temperature is 40 - 50 °C, and the reaction time is 100 - 150 min; After centrifugal purification, add a complex of sodium pyrophosphate and citric acid with a molar ratio of 1:2.5 - 1:3.

5.

8. The preparation method of a water-soluble fertilizer according to claim 6, characterized in that, In step b: The pressure of supercritical carbon dioxide is 7 - 10 MPa, and the temperature is 4 - 6 °C; Apply ultrasonic waves at 25 - 30 kHz with a power density of 0.4 - 0.6 W / cm 2 ; The mineralization time is 25 - 35 min.

9. The preparation method of a water-soluble fertilizer according to claim 6, wherein, In step c: The wavelength of the pulsed light irradiation is 400 - 410 nm; The bright period is 80 - 120 ms, and the dark period is 40 - 60 ms; Total irradiation dose: 12 - 18 J / cm 2 .

10. The preparation method of a water-soluble fertilizer according to claim 6, characterized in that, In step d: The diameter of the microfluidic channel is 180 - 220 μm; The flow rate of the oil phase is 0.8 - 1.2 ml / min, and the flow rate of the water phase is 0.3 - 0.7 ml / min; The fluorinated silica emulsion contains 8 - 12 parts of perfluoropolyether.

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