Efficient fertilizer for crops and preparation method thereof

Abstract

The invention relates to the technical field of organic fertilizers, in particular to a high-efficiency fertilizer for crops and a preparation method of the high-efficiency fertilizer. The method comprises the following steps: on the basis of semi-hydrated gypsum and attapulgite, sequentially constructing a calcium-based inner core, a calcium-magnesium-based inner core and a composite shell through multi-step layered granulation, and synergistically introducing fulvic acid, high-molecular / low-molecular-weight poly-L-sodium glutamate, livestock and poultry manure compost, magnesite, NH4 < + > pre-loaded 4A zeolite and other organic-inorganic components. An inner core forms a crystal-organic micro-network with both toughness and compactness, an initial diffusion channel is effectively passivated, and an outer layer inhibits an instantaneous ion peak value and guarantees stable release under a dry-wet cycle through a hydrophilic dynamic diffusion membrane and a proper amount of exchangeable ion sites. According to the structure, the crack resistance and the forming integrity of the fertilizer particles are improved, the controllability and the stability of the nutrient release process are ensured, the requirement for continuous growth of saline-alkali soil crops is very met, and the field practicability and the industrial preparation feasibility are both achieved.

Description

Technical Field

[0001] This invention relates to the field of organic fertilizer technology, and in particular to a high-efficiency fertilizer for crops and its preparation method. Background Technology

[0002] Saline-alkali soils, due to the coupled effects of high pH and high exchangeable sodium, often exhibit fragile aggregate structures, poor permeability, and an imbalanced rhizosphere ion environment. In such environments, applied nutrient formulations are easily affected by two key factors: first, early burst release and nutrient loss caused by the high-permeability environment and strong ion competition; and second, shell cracking and flux decay caused by alternating wet and dry conditions and mineral dissolution-redeposition. Traditional controlled-release technologies mainly control release by thickening the coating or increasing the crosslinking density, but thick films often lead to insufficient flux in the middle and later stages, and release decay is more pronounced in saline-alkali environments due to membrane embrittlement or pore closure. If a loose membrane is used to increase flux, there is a lack of effective constraint in the early stages, which easily leads to ion peaks, causing seedling burn and low efficiency.

[0003] From a materials science perspective, neither a single organic membrane nor a single inorganic framework can effectively balance low initial release and stable flux in saline-alkali soils. Pure organic membranes are prone to chain extension and phase separation in solutions with high alkalinity and ionic strength, resulting in uneven pore distribution and flux fluctuations. While pure inorganic shells are rigid, they are brittle, crack propagate rapidly, and are more likely to form through-hole defects after wet-dry cycles, inducing burst release. Furthermore, the high Na content in saline-alkali soils... + The background competes with exchangeable sites in the shell for key soil-modifying ions. If the exchangeable sites are not distributed properly or are "occupied" in advance, the regulation of the release interface will be weakened, causing the release trajectory to deviate from the design target.

[0004] To address the initial burst release issue, one approach attempts to provide rapid acidification using strongly acidic components, promoting the gradual release of ions. However, this strong acidification leads to excessively low local pH, disrupting shell stability and easily triggering rapid mineral dissolution and recrystallization, resulting in a non-uniform microstructure that exacerbates burst release and subsequent flux decay. Another approach enhances complexation and water retention by increasing the macromolecular content, but excessive complexation reduces effective diffusion and causes uneven swelling during rewetting, leading to stress concentration and membrane delamination. Therefore, controlled release under saline-alkali conditions cannot be solved by a single parameter (membrane thickness, degree of crosslinking) but requires a comprehensive synergy of structural, chemical, and temporal factors.

[0005] Therefore, the core contradiction in saline-alkali soil conditions can be summarized as follows: on the one hand, it is necessary to establish an effective diffusion buffer in the early stage of application to prevent ion peaks; on the other hand, it is essential to maintain a stable and predictable flux in the middle and later stages to meet the continuous absorption needs of crops. Simply relying on thick films or strong acidification is insufficient to address both of these issues. Summary of the Invention

[0006] In view of this, the purpose of this invention is to provide a high-efficiency fertilizer for crops and its preparation method, so as to simultaneously suppress the initial burst release and maintain a stable flux in the middle and late stages in saline-alkali soil.

[0007] To achieve the above objectives, the present invention provides a method for preparing a high-efficiency fertilizer for crops, comprising the following steps: S1: Hemihydrate gypsum powder and attapulgite are dry-mixed in a granulator for 1-3 minutes, then fulvic acid solution is sprayed in and mixed for 10-20 minutes. Then, high molecular weight poly-L-glutamate sodium salt solution and saturated calcium sulfate solution are sprayed in simultaneously and mixed for 20-30 minutes to obtain a calcium-based core. S2: Based on the calcium-based core, add livestock and poultry manure compost and magnesite powder to the granulator, turn and toss for 3-8 minutes, then spray in fulvic acid solution, mix for 10-20 minutes, then add potassium humate powder, spray in deionized water, mix for 20-30 minutes to obtain the calcium-magnesium-based core. S3: Based on the calcium-magnesium-based core, NH3 is added to the granulator. 4+ Preload 4A zeolite, turn and toss for 3-8 minutes, then spray in low molecular weight poly-L-glutamate sodium salt solution, mix for 10-20 minutes, then simultaneously spray in fulvic acid solution and saturated calcium sulfate solution, and finally spray in deionized water, continuously roll into balls for 10-20 minutes, sieve to retain particles with a diameter of 2-4 mm, dry with hot air until the moisture content is below 10%, cool at room temperature, and obtain high-efficiency fertilizer for crops.

[0008] Preferably, in step S1, the hemihydrate gypsum powder has a mesh size of 100-300 mesh, and the attapulgite has a mesh size of 100-300 mesh.

[0009] Preferably, in step S1, the granulator is a disc granulator with a disc diameter of 1-1.5m and an inclination angle of 45°, and is equipped with a coaxial dual-fluid nozzle with a nozzle diameter of 1-1.5mm and an atomizing air pressure of 0.18-0.22MPa.

[0010] Preferably, the fulvic acid solution is prepared by mixing fulvic acid and deionized water in a weight ratio of 1-3:5-11.

[0011] Preferably, the high molecular weight poly-L-glutamate sodium salt solution is prepared by high molecular weight poly-L-glutamate sodium salt and deionized water in a weight ratio of 0.8-1.6:3.2-6.4.

[0012] Preferably, the low molecular weight poly-L-glutamate sodium salt solution is prepared by low molecular weight poly-L-glutamate sodium salt and deionized water in a weight ratio of 0.6-1:3.2-6.

[0013] Preferably, the high molecular weight poly-L-glutamate sodium salt has a weight-average molecular weight of 100,000.

[0014] Preferably, the weight-average molecular weight of the low molecular weight poly-L-glutamate sodium salt is 10,000.

[0015] Preferably, the organic matter content of the livestock and poultry manure compost in step S2 is 45% or more.

[0016] Preferably, the magnesite powder in step S2 has a mesh size of 100-300 mesh.

[0017] Preferably, in step S3, NH 4+ The pre-loaded 4A zeolite was obtained by ion exchange of 4A zeolite in an ammonium sulfate solution with a concentration of 0.8-1.2 mol / L at a solid-liquid weight ratio of 1:8-12.

[0018] Preferably, the 4A zeolite has a mesh size of 200.

[0019] Preferably, the hemihydrate gypsum powder, attapulgite, fulvic acid solution, high molecular weight poly-L-glutamate sodium salt solution, saturated calcium sulfate solution, livestock and poultry manure compost, magnesite powder, potassium humate powder, deionized water, and NH4+ are used. 4+ The weight ratio of preloaded 4A zeolite and low molecular weight poly-L-glutamate sodium salt is 15-25:2-4:6-14:4-8:1.3-2.8:40-70:5-10:2.5-5.5:3.5-6.5:4-6:4-7.

[0020] Preferably, the weight ratio of the fulvic acid solution in steps S1, S2 and S3 is 2-4:2-5:2-5.

[0021] Preferably, the weight ratio of the saturated calcium sulfate solution in steps S1 and S3 is 1-2:0.3-0.8.

[0022] Preferably, the weight ratio of deionized water in steps S2 and S3 is 2-4:1.5-2.5.

[0023] The beneficial effects of this invention are: This technology achieves precise control of the release process in saline-alkali environments through multi-scale structural synergy, effectively constraining early burst release while maintaining stable flux in the middle and later stages. Firstly, a layered construction concept is adopted, with the inner and outer layers each playing a distinct role in terms of function and timing: the inner layer, with its directionally hydrated crystalline framework interpenetrating with crosslinkable organic matter, generates a continuous and resilient micronetwork, effectively passivating early diffusion channels and avoiding osmotic stress and nutrient waste caused by short-term ion peaks; the outer layer constructs a dynamic diffusion membrane with a hydrophilic and tunable polymer interface, maintaining channel continuity under humidity changes and supporting uniform release in the middle and later stages, thus covering the needs of the crop during its critical growth stages. This structure remains stable under alternating wet and dry conditions and high pH backgrounds, reducing burst release and membrane delamination caused by shell defects.

[0024] Secondly, the coupling design of ion exchange sites and complexation buffers significantly improves the directionality and anti-interference ability of the release. The exchangeable material is rationally arranged in the outer layer, enabling preferential exchange with sodium ions in the soil and mitigating the disturbance of the diffusion gradient by the high-salt environment. Simultaneously, weakly acidic small molecules and multi-carboxyl polymers provide a mild proton supply and complexation regulation within the micro-regions, avoiding the blocking effect caused by excessive acidification or strong complexation, ensuring that the dissolution-diffusion-re-complexation process is reversible and controllable. This combination maintains smooth ion migration under saline-alkali conditions, reduces the uncertainty of initial release, and prevents subsequent release from decaying too rapidly due to shell hardening.

[0025] Furthermore, the particles exhibit good structural integrity and crack resistance during forming and use. The organic-inorganic composite framework endows the shell with toughness and moderate density, resisting micro-cracks caused by mechanical application, soil compaction, and rewetting expansion; simultaneously, the water-bearing window of the core is expanded, and the particles maintain geometric stability between water absorption expansion and water loss shrinkage, reducing interfacial separation caused by volume changes. As a result, the long-term release curve is closer to the design trajectory, and the impact of field environmental fluctuations on the release flux is significantly weakened.

[0026] Finally, in terms of process, in-situ crosslinking and localized hydration are achieved through coaxial spraying and time-series control, reducing the damage to the shell integrity caused by secondary processing steps; particle size control and gentle drying ensure that the outer microporous structure does not collapse, preserving the necessary diffusion channels. In summary, this technology achieves the synergistic goal of "suppressing initial burst release and maintaining mid-to-late-stage flux" without relying on thick films or strong acidification, taking into account both field applicability and preparation feasibility, and is suitable for the steady-state fertilizer supply needs in saline-alkali soil environments. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments.

[0028] Example 1: (1) Add 1 kg of fulvic acid to 5 kg of deionized water and stir at 35°C for 40 min to obtain a fulvic acid solution; then add 0.8 kg of high molecular weight poly-L-glutamate sodium salt (weight average molecular weight 100,000) to 3.2 kg of deionized water and stir at 40°C for 1.5 h to obtain a high molecular weight poly-L-glutamate sodium salt solution; then add 0.6 kg of low molecular weight poly-L-glutamate sodium salt (weight average molecular weight 10,000) to 3.2 kg of deionized water and stir at 35°C for 0.5 h to obtain a low molecular weight poly-L-glutamate sodium salt solution.

[0029] (2) 4A zeolite (200 mesh) was dried at 100℃ for 3h, and then added to a 0.8mol / L ammonium sulfate solution at a solid-liquid weight ratio of 1:8. Ion exchange was carried out by stirring at room temperature for 20h. After centrifugation, the solution was washed three times with deionized water and dried to obtain NH4+. 4+ Preloaded with 4A zeolite; (3) A disc granulator (disc diameter 1.2m, inclination angle 45°) is used, equipped with a coaxial dual-fluid nozzle (nozzle diameter 1.2mm, atomizing air pressure 0.2MPa). The material disc temperature is maintained at room temperature. 15kg of hemihydrate gypsum powder (200 mesh) and 2kg of attapulgite (200 mesh) are put into the disc granulator and dry-mixed at 15rpm for 1min to make it evenly dispersed. Then, 2kg of fulvic acid solution is sprayed in with nozzle I within 2min and mixed at 15rpm for 10min to make hemihydrate gypsum begin to directionally hydrate in the weak acid environment of fulvic acid. Then, 4kg of high molecular weight poly-L-glutamate sodium salt solution is sprayed in with nozzle II within 4min. At the same time, 1kg of saturated calcium sulfate solution (room temperature) is sprayed in with nozzle I and mixed at 15rpm for 20min to obtain a calcium-based core. (4) Based on the above calcium-based core, add 40 kg of livestock and poultry manure compost (dry basis, organic matter content of 49.2%) and 5 kg of magnesite powder (200 mesh), mix and turn at 20 rpm for 3 min, spray 2 kg of fulvic acid solution in 1 min with nozzle I, mix at 15 rpm for 10 min, then directly add 2.5 kg of potassium humate powder, and spray 2 kg of deionized water with nozzle II, mix at 15 rpm for 20 min to obtain the calcium-magnesium-based core; (5) On the basis of calcium-magnesium-based core, add 4 kg of NH 4+Preload 4A zeolite and mix and tumble at 20 rpm for 3 minutes to ensure even distribution on the outer layer of the particles. Then, spray 4 kg of low molecular weight poly-L-glutamate sodium salt solution into the mixture through nozzle II within 2 minutes and mix at 15 rpm for 10 minutes. Next, spray 2 kg of fulvic acid solution into the mixture through nozzle I, while simultaneously spraying 0.3 kg of saturated calcium sulfate solution (at room temperature) through nozzle II. Finally, spray 1.5 kg of deionized water through nozzle I and continuously roll the mixture into balls for 10 minutes. Sieve the balls to retain 2 mm particles and dry them with hot air at 60℃ until the moisture content reaches 7.8%. Cool the mixture at room temperature to obtain a high-efficiency fertilizer for crops.

[0030] Example 2: (1) Add 2 kg of fulvic acid to 8 kg of deionized water and stir at 40 °C for 45 min to obtain a fulvic acid solution; then add 1.2 kg of high molecular weight poly-L-glutamate sodium salt (weight average molecular weight 100,000) to 4.8 kg of deionized water and stir at 45 °C for 2 h to obtain a high molecular weight poly-L-glutamate sodium salt solution; then add 0.8 kg of low molecular weight poly-L-glutamate sodium salt (weight average molecular weight 10,000) to 4.5 kg of deionized water and stir at 40 °C for 1 h to obtain a low molecular weight poly-L-glutamate sodium salt solution.

[0031] (2) 4A zeolite (200 mesh) was dried at 105℃ for 4 h, and then added to a 1 mol / L ammonium sulfate solution at a solid-liquid weight ratio of 1:10. Ion exchange was carried out by stirring at room temperature for 24 h. After centrifugation, the solution was washed three times with deionized water and dried to obtain NH4+. 4+ Preloaded with 4A zeolite; (3) A disc granulator (disc diameter 1.2m, inclination angle 45°) is used, equipped with a coaxial dual-fluid nozzle (nozzle diameter 1.2mm, atomizing air pressure 0.2MPa). The material disc temperature is maintained at room temperature. 20kg of hemihydrate gypsum powder (200 mesh) and 3kg of attapulgite (200 mesh) are put into the disc granulator and dry-mixed at 18rpm for 2min to make it evenly dispersed. Then, 3kg of fulvic acid solution is sprayed in with nozzle I within 3min and mixed at 18rpm for 15min to make hemihydrate gypsum begin to directionally hydrate in the weak acid environment of fulvic acid. Then, 6kg of high molecular weight poly-L-glutamate sodium salt solution is sprayed in with nozzle II within 5min. At the same time, 1.5kg of saturated calcium sulfate solution (room temperature) is sprayed in with nozzle I and mixed at 18rpm for 25min to obtain calcium-based core. (4) Based on the above calcium-based core, add 56 kg of livestock and poultry manure compost (dry basis, organic matter content of 49.2%) and 8 kg of magnesite powder (200 mesh), mix and turn at 30 rpm for 5 min, spray 3.5 kg of fulvic acid solution with nozzle I within 2 min, mix at 18 rpm for 15 min, then directly add 4 kg of potassium humate powder, and spray 3 kg of deionized water with nozzle II, mix at 18 rpm for 25 min to obtain the calcium-magnesium-based core; (5) On the basis of calcium-magnesium-based core, add 5 kg of NH 4+ Preload 4A zeolite and mix and tumble at 30 rpm for 5 minutes to ensure even distribution on the outer layer of the particles. Then, spray 5.3 kg of low molecular weight poly-L-glutamate sodium salt solution through nozzle II over 3 minutes and mix at 18 rpm for 15 minutes. Next, spray 3.5 kg of fulvic acid solution through nozzle I, while simultaneously spraying 0.5 kg of saturated calcium sulfate solution (at room temperature) through nozzle II. Finally, spray 2 kg of deionized water through nozzle I and continuously roll into balls for 15 minutes. Sieve to retain particles with a diameter of 2-4 mm, dry with hot air at 55℃ to a moisture content of 8.1%, and cool at room temperature to obtain a high-efficiency fertilizer for crops.

[0032] Example 3: (1) Add 3 kg of fulvic acid to 11 kg of deionized water and stir at 45 °C for 50 min to obtain a fulvic acid solution; then add 1.6 kg of high molecular weight poly-L-glutamate sodium salt (weight average molecular weight 100,000) to 6.4 kg of deionized water and stir at 50 °C for 2.5 h to obtain a high molecular weight poly-L-glutamate sodium salt solution; then add 1 kg of low molecular weight poly-L-glutamate sodium salt (weight average molecular weight 10,000) to 6 kg of deionized water and stir at 45 °C for 1.5 h to obtain a low molecular weight poly-L-glutamate sodium salt solution.

[0033] (2) 4A zeolite (200 mesh) was dried at 110℃ for 5 h, and then added to a 1.2 mol / L ammonium sulfate solution at a solid-liquid weight ratio of 1:12. Ion exchange was carried out by stirring at room temperature for 28 h. After centrifugation, the solution was washed three times with deionized water and dried to obtain NH4+. 4+ Preloaded with 4A zeolite; (3) A disc granulator (disc diameter 1.2m, inclination angle 45°) is used, equipped with a coaxial dual-fluid nozzle (nozzle diameter 1.2mm, atomizing air pressure 0.2MPa). The material disc temperature is maintained at room temperature. 25kg of hemihydrate gypsum powder (200 mesh) and 4kg of attapulgite (200 mesh) are put into the disc granulator and dry-mixed at 20rpm for 3min to make it evenly dispersed. Then, 4kg of fulvic acid solution is sprayed in with nozzle I within 4min and mixed at 20rpm for 20min to make hemihydrate gypsum begin to directionally hydrate in the weak acid environment of fulvic acid. Then, 8kg of high molecular weight poly-L-glutamate sodium salt solution is sprayed in with nozzle II within 6min. At the same time, 2kg of saturated calcium sulfate solution (room temperature) is sprayed in with nozzle I and mixed at 20rpm for 30min to obtain calcium-based core. (4) Based on the above calcium-based core, add 70 kg of livestock and poultry manure compost (dry basis, organic matter content of 49.2%) and 10 kg of magnesite powder (200 mesh), mix and turn at 40 rpm for 8 min, spray 5 kg of fulvic acid solution in 3 min with nozzle I, mix at 20 rpm for 20 min, then directly add 5.5 kg of potassium humate powder, and spray 4 kg of deionized water with nozzle II, mix at 20 rpm for 30 min to obtain the calcium-magnesium-based core; (5) On the basis of calcium-magnesium-based core, add 6 kg of NH4+. 4+ Preload 4A zeolite and mix and tumble at 40 rpm for 8 minutes to ensure even distribution on the outer layer of the particles. Then, spray 7 kg of low molecular weight poly-L-glutamate sodium salt solution through nozzle II within 4 minutes and mix at 20 rpm for 20 minutes. Next, spray 5 kg of fulvic acid solution through nozzle I, while simultaneously spraying 0.8 kg of saturated calcium sulfate solution (at room temperature) through nozzle II. Finally, spray 2.5 kg of deionized water through nozzle I, and continuously roll and press into balls for 20 minutes. Sieve to retain particles with a diameter of 2-4 mm, dry with hot air at 50℃ to a moisture content of 8.5%, and cool at room temperature to obtain a high-efficiency fertilizer for crops.

[0034] Comparative Example 1: The difference between Comparative Example 1 and Example 2 is that the high molecular weight poly-L-glutamate sodium salt solution in step (3) and the low molecular weight poly-L-glutamate sodium salt solution in step (5) are interchanged.

[0035] Comparative Example 2: The difference between Comparative Example 2 and Example 2 is that the NH in step (5) is... 4+ The pre-loaded 4A zeolite was replaced with dried 4A zeolite.

[0036] Comparative Example 3: The difference between Comparative Example 3 and Example 2 is that the fulvic acid solution was completely replaced with a humic acid solution of equal concentration.

[0037] Comparative Example 4: The difference between Comparative Example 4 and Example 2 is that a magnesium-based core was prepared first, followed by a magnesium-calcium-based core.

[0038] The specific steps are as follows: (1) Add 2 kg of fulvic acid to 8 kg of deionized water and stir at 40 °C for 45 min to obtain a fulvic acid solution; then add 1.2 kg of high molecular weight poly-L-glutamate sodium salt (weight average molecular weight 100,000) to 4.8 kg of deionized water and stir at 45 °C for 2 h to obtain a high molecular weight poly-L-glutamate sodium salt solution; then add 0.8 kg of low molecular weight poly-L-glutamate sodium salt (weight average molecular weight 10,000) to 4.5 kg of deionized water and stir at 40 °C for 1 h to obtain a low molecular weight poly-L-glutamate sodium salt solution.

[0039] (2) 4A zeolite (200 mesh) was dried at 105℃ for 4 h, and then added to a 1 mol / L ammonium sulfate solution at a solid-liquid weight ratio of 1:10. Ion exchange was carried out by stirring at room temperature for 24 h. After centrifugation, the solution was washed three times with deionized water and dried to obtain NH4+. 4+ Preloaded with 4A zeolite; (3) A disc granulator (disc diameter 1.2m, inclination angle 45°) was used, equipped with a coaxial dual-fluid nozzle (nozzle diameter 1.2mm, atomizing air pressure 0.2MPa). The temperature of the material disc was maintained at room temperature. 56kg of livestock and poultry manure compost (dry basis, organic matter content of 49.2%) and 8kg of magnesite powder (200 mesh) were put into the disc granulator and mixed and turned at a speed of 30rpm for 5min. 3.5kg of fulvic acid solution was sprayed in with nozzle I within 2min and mixed at a speed of 18rpm for 15min. Then 4kg of potassium humate powder was added directly and 3kg of deionized water was sprayed in with nozzle II and mixed at a speed of 18rpm for 25min to obtain the magnesium-based core. (4) Based on the above magnesium-based core, 20 kg of hemihydrate gypsum powder (200 mesh) and 3 kg of attapulgite (200 mesh) are added to a disc granulator and dry-mixed at 18 rpm for 2 min to make it evenly dispersed. Then, 3 kg of fulvic acid solution is sprayed in with nozzle I within 3 min and mixed at 18 rpm for 15 min to allow the hemihydrate gypsum to begin directional hydration in the weakly acidic environment of fulvic acid. Then, 6 kg of high molecular weight poly-L-glutamic acid sodium salt solution is sprayed in with nozzle II within 5 min. At the same time, 1.5 kg of saturated calcium sulfate solution (room temperature) is sprayed in with nozzle I and mixed at 18 rpm for 25 min to obtain the magnesium-calcium-based core. (5) On the basis of the magnesium-calcium-based core, add 5 kg of NH4+. 4+Preload 4A zeolite and mix and tumble it at 30 rpm for 5 minutes to ensure it is evenly distributed on the outer layer of the particles. Then, spray 5.3 kg of low molecular weight poly-L-glutamate sodium salt solution into the mixture through nozzle II within 3 minutes and mix at 18 rpm for 15 minutes. Next, spray 3.5 kg of fulvic acid solution into the mixture through nozzle I, while simultaneously spraying 0.5 kg of saturated calcium sulfate solution (at room temperature) through nozzle II. Finally, spray 2 kg of deionized water through nozzle I and continuously roll the mixture into balls for 15 minutes. Sieve the balls to retain particles with a diameter of 2-4 mm, dry them with hot air at 55℃ until the moisture content is 8.1%, and cool them at room temperature to obtain the fertilizer.

[0040] Comparative Example 5: The difference between Comparative Example 5 and Example 2 is that the attapulgite from step (3) and the NH4+ from step (5) are used in the same way. 4+ Pre-loaded 4A zeolite is interchangeable.

[0041] Performance testing: Nutrient slow-release performance test: Following the method for determining the water dissolution rate in GB / T 23348-2009 "Slow-Release Fertilizers", 100g of fertilizer granules prepared in the examples and comparative examples were placed in 1000mL of deionized water and shaken at 100rpm in a constant temperature shaker at 25℃. 10mL samples were taken at 1 day, 28 days, and 56 days, and the Ca2+ content was determined using an atomic absorption spectrophotometer. 2+ The concentration of Mg was determined using inductively coupled plasma atomic emission spectrometry. 2+ The concentration of NH was determined by Nessler's reagent spectrophotometry. 4+ -N concentration, after each sampling, an equal amount of deionized water was added to maintain a constant total volume, and the cumulative release rate at each time point was calculated. The initial release rate (1d) reflects the fertilizer's rapid effect, the 28d release rate reflects the medium-term fertilizer supply capacity, and the 56d release rate reflects the long-term effect. The results are shown in Table 1.

[0042] Test on the effect of saline-alkali soil improvement: Referencing GB / T 17296-2009 "Soil Conditioners" and LY / T 1228-2015 "Determination of Cation Exchange Capacity of Forest Soils," simulated saline-alkali soil was prepared. 1000g of soil sample (pH=8.5, ESP=25%) was taken, and 20g of each of the example and comparative fertilizers was added at a 2% application rate. After thorough mixing, deionized water was added to adjust the moisture content to 60% of field capacity. The sample was then incubated at 25℃. Samples were taken for analysis after 14 days, and soil ESP (exchangeable sodium percentage) and pH were calculated. The results are shown in Table 1.

[0043] Particle structure stability test: According to the compressive strength test method in GB / T 8576-2010 "Compound Fertilizer", the compressive strength of the particles was measured using a physical property tester. Fifty particles were randomly selected and placed one by one under a pressure sensor. They were uniaxially compressed at a loading speed of 10 mm / min until the particles broke. The maximum load at the time of breakage was recorded and the average compressive strength was calculated. The results are shown in Table 1.

[0044] Water absorption and retention performance test: Accurately weigh 10g of each sample particle, immerse it in deionized water until it is saturated with water, drain the surface water and weigh it. Calculate the water absorption rate = (saturated weight - initial weight) / initial weight × 100%. Then place the water-saturated sample in an environment of 25℃ and 60% relative humidity to lose water naturally. Weigh it after 24 hours and calculate the water retention rate = (weight after 24 hours - initial dry weight) / (saturated weight - initial dry weight) × 100%. The results are shown in Table 1.

[0045] Table 1 Performance Test Results

[0046] Data Analysis: As can be seen from the data in Examples 1-3 in Table 1, the particles prepared by this invention exhibit both controlled initial release and continuous mid-to-late-stage supply, and show synergistic improvement in salinity and pH under short-term culture conditions, while maintaining high mechanical stability and favorable water absorption-release behavior. This is mainly due to the layer-by-layer crosslinking of dimolecular-weight poly-L-glutamic acid forming a gradient diffusion film on the particle surface. The inner layer, together with the microcrystalline network generated by the directional hydration of hemihydrate gypsum, jointly suppresses the early ion peak, while the outer layer maintains hydrophilic channels and complexation buffers under the action of fulvic acid, thereby achieving stable release. External NH4+ 4+ Preloading 4A zeolite as an ion-grafted shell may provide exchangeable sites and cation pools, enabling better directionality in the migration and exchange of calcium, magnesium, and ammonium in the rhizosphere. Controlled water volume and temperature windows, combined with coaxial dual-spray in-situ crosslinking, help form a dense rather than brittle shell, thus achieving high compressive strength and structural integrity without sacrificing flux release.

[0047] As can be seen from the data in Table 1 for Example 2 and Comparative Example 1, Example 2 exhibits a more balanced release trajectory and a more stable particle structure. It is speculated that the difference mainly stems from the rational division of labor between high-molecular-weight and low-molecular-weight γ-PGA at the layer level: high-molecular-weight γ-PGA preferentially enters the inner layer, forming a spatial network through in-situ cross-linking with the calcium source, thus anchoring the calcium source generated by the conversion of hemihydrate gypsum and reducing early extravasation; low-molecular-weight γ-PGA is distributed in the outer layer, forming an adjustable diffusion interface and working with fulvic acid to regulate hydration microregions, avoiding the formation of excessively dense or discontinuous barrier layers. This rational arrangement of high-molecular-weight and low-molecular-weight poly-L-glutamic acid at the layer level is a key technological point for achieving a balance between rapid and slow release, and between strength and flux.

[0048] As can be seen from the data in Table 1 for Example 2 and Comparative Example 2, Example 2 achieves a better balance between improvement indicators and nutrient availability, which is presumably related to the outer NH4+ layer. 4+ Preloading of 4A zeolite is closely related. The trends shown in the data indicate that pre-occupation of zeolite exchange sites with ammonium ions may avoid non-selective capture of free calcium and magnesium during wet granulation, ensuring that the immediate cross-linking of the outer shell is not interfered with by competing ions, resulting in a more complete and controllable outer network. Simultaneously, preloading allows the outer shell to participate more directly in Na+ in the soil-water system. + Replacement reduces the hysteresis effect of "adsorption-release" and improves the effective driving force of ion exchange.

[0049] As can be seen from the data in Table 1 for Example 2 and Comparative Example 3, Example 2 exhibits a more coordinated response in terms of release process and soil chemical indicators. This suggests that fulvic acid plays a dual role in this system, involving both localized weak acidification and complexation regulation. Compared to the case where only humic acid is substituted, the data trend indicates that fulvic acid is more likely to enter the outer micropores and interfaces of particles under limited moisture conditions, thus providing a mild and continuous proton source for magnesite. Furthermore, it stabilizes Mg through synergy with low molecular weight poly-L-glutamic acid. 2+ The phased release of fulvic acid prevents the overall pH from dropping excessively. Furthermore, the strong small-molecule diffusivity of fulvic acid facilitates the formation of hydrophilic channels and a uniform cross-linked microenvironment.

[0050] As can be seen from the data in Table 1 for Example 2 and Comparative Example 4, Example 2 shows greater consistency in initial release stability and particle mechanics maintenance. This difference may be related to the "calcium first, then magnesium" core construction sequence and its interface timing. The data suggests that when a calcium-based core is constructed first and the in-situ crosslinking of the inner layer of high molecular weight poly-L-glutamic acid with a dilute calcium source is completed, followed by localized weak acidification and buffered complexation of magnesite, the directional hydration of hemihydrate gypsum to dihydrate gypsum onto the surface can proceed in a controlled environment, forming an interpenetrating crystal-gel framework. If the order is reversed, the added calcium source is more likely to rapidly deposit and crystallize unevenly on the existing magnesium-based surface, inducing microcracks in the shell and localized burst release, and reducing the efficiency of dense shell formation during the rolling film stage. Therefore, it is reasonable to conclude that the sequence of calcium first constructing the framework and then magnesium undergoing controlled activation is a key factor in achieving a synergistic effect of low burst release, high integrity, and soil improvement efficiency.

[0051] As can be seen from the data in Table 1 for Example 2 and Comparative Example 5, Example 2 exhibits a more favorable combination effect in terms of exchange site accessibility and granular structure organization, which may be related to the morphological coupling of attapulgite and 4A in the stratigraphic layer. Data trends show that placing rod-shaped attapulgite in the core provides heterogeneous nucleation and a water-holding platform, promoting the orderly growth of the gypsum phase and increasing the critical water-bearing window; placing cubic 4A in the outer layer maximizes the exposure of its exchangeable surface, allowing Na... + Selective exchange and the slow release of ammonium occur directly at the shell / soil interface. Conversely, when the two exchange layers, although the water retention of the outer layer may be improved, the effective exchange sites are masked, and it is difficult to simultaneously optimize the driving force of ion replacement and the compactness of the structure.

[0052] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the invention is limited to these examples; within the framework of the invention, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations of the different aspects of the invention as described above, which are not provided in detail for the sake of brevity.

Claims

1. A method for preparing a high-efficiency fertilizer for crops, characterized in that, Includes the following steps: S1: Hemihydrate gypsum powder and attapulgite are dry-mixed in a granulator for 1-3 minutes, then fulvic acid solution is sprayed in and mixed for 10-20 minutes. Then, high molecular weight poly-L-glutamate sodium salt solution and saturated calcium sulfate solution are sprayed in simultaneously and mixed for 20-30 minutes to obtain a calcium-based core. S2: Based on the calcium-based core, add livestock and poultry manure compost and magnesite powder to the granulator, turn and toss for 3-8 minutes, then spray in fulvic acid solution, mix for 10-20 minutes, then add potassium humate powder, spray in deionized water, mix for 20-30 minutes to obtain the calcium-magnesium-based core. S3: Based on the calcium-magnesium-based core, NH3 is added to the granulator. 4+ Preload 4A zeolite, turn and toss for 3-8 minutes, then spray in low molecular weight poly-L-glutamate sodium salt solution, mix for 10-20 minutes, then simultaneously spray in fulvic acid solution and saturated calcium sulfate solution, and finally spray in deionized water, continuously roll into balls for 10-20 minutes, sieve to retain particles with a diameter of 2-4 mm, dry with hot air until the moisture content is below 10%, cool at room temperature, and obtain high-efficiency fertilizer for crops.

2. The method for preparing high-efficiency fertilizer for crops according to claim 1, characterized in that, In step S1, the granulator is a disc granulator with a disc diameter of 1-1.5m and an inclination angle of 45°. It is equipped with a coaxial dual-fluid nozzle with a nozzle diameter of 1-1.5mm and an atomizing air pressure of 0.18-0.22MPa.

3. The method for preparing high-efficiency fertilizer for crops according to claim 1, characterized in that, The fulvic acid solution is prepared by fulvic acid and deionized water at a weight ratio of 1-3:5-11; the high molecular weight poly-L-glutamate sodium salt solution is prepared by high molecular weight poly-L-glutamate sodium salt and deionized water at a weight ratio of 0.8-1.6:3.2-6.4; and the low molecular weight poly-L-glutamate sodium salt solution is prepared by low molecular weight poly-L-glutamate sodium salt and deionized water at a weight ratio of 0.6-1:3.2-6.

4. The method for preparing high-efficiency fertilizer for crops according to claim 1, characterized in that, The high molecular weight poly-L-glutamate sodium salt has a weight-average molecular weight of 100,000; the low molecular weight poly-L-glutamate sodium salt has a weight-average molecular weight of 10,000.

5. The method for preparing high-efficiency fertilizer for crops according to claim 1, characterized in that, In step S3, NH 4 + The pre-loaded 4A zeolite was obtained by ion exchange of 4A zeolite in an ammonium sulfate solution with a concentration of 0.8-1.2 mol / L at a solid-liquid weight ratio of 1:8-12.

6. The method for preparing high-efficiency fertilizer for crops according to claim 1, characterized in that, The hemihydrate gypsum powder, attapulgite, fulvic acid solution, high molecular weight poly-L-glutamate sodium salt solution, saturated calcium sulfate solution, livestock and poultry manure compost, magnesite powder, potassium humate powder, deionized water, and NH4+ are mentioned. 4+ The weight ratio of preloaded 4A zeolite and low molecular weight poly-L-glutamate sodium salt is 15-25:2-4:6-14:4-8:1.3-2.8:40-70:5-10:2.5-5.5:3.5-6.5:4-6:4-7.

7. The method for preparing high-efficiency fertilizer for crops according to claim 1, characterized in that, The weight ratio of the fulvic acid solution in steps S1, S2 and S3 is 2-4:2-5:2-5.

8. The method for preparing high-efficiency fertilizer for crops according to claim 1, characterized in that, The weight ratio of the saturated calcium sulfate solution in steps S1 and S3 is 1-2:0.3-0.

8.

9. The method for preparing high-efficiency fertilizer for crops according to claim 1, characterized in that, The weight ratio of deionized water in steps S2 and S3 is 2-4:1.5-2.

5.

10. A high-efficiency fertilizer for crops, characterized in that, It is obtained by the method for preparing high-efficiency fertilizer for crops according to any one of claims 1-9.

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