Organic selenium nutrient solution for crops and preparation method thereof

Abstract

The invention relates to an organic selenium nutrient solution for crops and a preparation method thereof. The nutrient solution is prepared from the following components in percentage by mass: 0.1 to 0.5 percent of selenomethionine, 2.0 to 5.0 percent of compound amino acid, 1.0 to 3.0 percent of potassium humate, 0.5 to 1.0 percent of plant extract, 0.05 to 0.5 percent of EDTA (Ethylene Diamine Tetraacetic Acid) chelated calcium, magnesium and zinc, 0.05 to 0.2 percent of potassium sorbate and the balance of purified water. Preferably, the selenomethionine is three-layer coated L-type selenomethionine, the inner layer of the selenomethionine is formed by crosslinking chitosan and citric acid, the middle layer of the selenomethionine is hydroxypropyl methyl cellulose, and the outer layer of the selenomethionine is formed by crosslinking a sodium alginate-gelatin matrix through Ca < 2 + > / Zn < 2 + > composite ions. The preparation method comprises the following steps: sequentially adding the components under a specific pH condition, chelating and stabilizing to form a multi-component synergistic stable system. The nutrient solution has the advantages of high bioavailability, good controlled release performance, high plant absorption efficiency and strong component stability.

Description

Technical Field

[0001] This invention relates to the technical field of crop nutrient solutions, and in particular to an organic selenium nutrient solution for crops and its preparation method. Background Technology

[0002] Selenium is an essential trace element for the human body, playing important physiological functions such as antioxidation and immune regulation. However, the production of naturally selenium-rich agricultural products is limited, making it difficult to meet the daily intake needs of the population. Therefore, increasing selenium accumulation levels in crops through exogenous selenium supply has become a key technological approach in current agricultural production.

[0003] In existing technologies, selenium supply methods mainly include two categories: inorganic selenium fertilizers and organic selenium fertilizers. Inorganic selenium fertilizers, such as sodium selenite and sodium selenate, are widely used, but their bioavailability is low, and they are prone to redox transformations in soil or plants, leading to selenium inactivation or increased toxicity, highlighting safety and stability issues. In contrast, organic selenium, due to its molecular structure being closer to that of biological systems, exhibits higher utilization efficiency and physiological compatibility during plant absorption and metabolism, making it a key research focus. Among these, selenium-containing amino acid compounds show great application potential because they can be effectively absorbed through the active transport pathways of plants.

[0004] To improve the efficiency of selenium absorption by crops, some studies have attempted to combine selenium supply systems with plant nutrient solutions, enhancing selenium absorption and translocation while providing basic nutrients. However, this technology still faces many challenges in practical applications. For example, organic selenium is easily degraded in aqueous solutions due to environmental conditions, resulting in a loss of activity. Furthermore, when coexisting with other nutrient components, adverse reactions such as complexation failure and precipitation may occur, affecting the overall system stability and the bioavailability of selenium. In addition, the ability of plants to absorb exogenous selenium is jointly regulated by multiple factors, including their translocation mechanisms, physiological state, and nutrient environment; simply adding selenium-supplying components is unlikely to significantly improve the migration and accumulation of selenium within crops.

[0005] In summary, current organic selenium supply technologies for crops still have significant shortcomings in terms of selenium stability, absorbability, and synergy with crop nutrition. There is an urgent need to develop new selenium supply systems that are more efficient, stable, and adaptable to agricultural application requirements in order to promote the sustainable development of selenium-enriched agriculture. Summary of the Invention

[0006] In view of the shortcomings of the existing technology, the purpose of this invention is to provide an organic selenium nutrient solution for crops and its preparation method.

[0007] An organic selenium nutrient solution for crops, comprising the following components by weight percentage: Selenomethionine 0.1-0.5%; The compound amino acids comprise 2.0-5.0%; the compound amino acids consist of a mixture of amino acids, primarily composed of soybean protein hydrolysate. Potassium humate 1.0–3.0%; Plant extracts 0.5-1.0%; The EDTA-chelated calcium, magnesium, and zinc content is 0.05%–0.5%; the mass ratio of calcium, magnesium, and zinc is 1:1:1. Potassium sorbate 0.05–0.2 wt%; The remaining amount of purified water.

[0008] Preferably, the selenomethionine is L-selenomethionine, and the L-selenomethionine undergoes a three-layer coating treatment. The three layers, from the inside out, are an inner layer formed by chitosan-citric acid crosslinking, a middle layer formed by hydroxypropyl methylcellulose coating, and an outer layer formed by sodium alginate-gelatin coating.

[0009] Preferably, the inner layer is formed by cross-linking chitosan with a molecular weight of 100-150 kDa and a degree of deacetylation of 75-85% with citric acid in a molar ratio of 1:2 to 1:3.

[0010] Preferably, the viscosity of the hydroxypropyl methylcellulose in the intermediate layer is 60–100 mPa·s.

[0011] Preferably, the outer layer is further formed by a composite ionic crosslinking of CaCl2 and ZnCl2, and Zn... 2+ Concentration of Ca 2 + 5% to 15%.

[0012] This invention employs a three-layer encapsulation strategy for L-selenomethionine, designed from the inside out. The inner layer network is constructed using chitosan-citric acid crosslinking. By controlling the molecular weight (100–150 kDa), degree of deacetylation (75–85%), and crosslinking ratio (molar ratio 1:2–1:3) of chitosan, a highly dense and protective colloidal core can be formed, effectively isolating the body from external hydrolysis and oxidation. The middle layer is encapsulated with hydroxypropyl methylcellulose. A controllable hydration shell is established by selecting a cellulose derivative with a viscosity of 60–100 mPa·s, exhibiting stable controlled-release behavior and adapting to the nutrient absorption rhythms of different crops. The outer layer introduces Ca... 2+ With Zn 2+ Crosslinking of Zn and Zn can construct a gel outer membrane with an interwoven network structure. 2+ The concentration was set at Ca 2+ Within the range of 5–15%, it helps to regulate the density and mechanical strength of the membrane, significantly improving the structural integrity and environmental adaptability of the controlled-release particles.

[0013] Preferably, the mass ratio of the compound amino acids, potassium humate, and plant extracts is 5:2:1.

[0014] Preferably, the plant extract is a compound composed of loquat leaf extract, honeysuckle extract and licorice extract in a mass ratio of 1:1:1.

[0015] The loquat leaf extract, honeysuckle extract, and licorice extract can be prepared using conventional water extraction or ethanol extraction methods. For example: (1) Take dried loquat leaves, honeysuckle and licorice raw materials, and crush them through a 40-mesh sieve; (2) Add deionized water at a material-to-liquid ratio of 1:10 to 1:20 and extract at 70 to 80°C for 1 to 2 hours; (3) After filtering the residue and concentrating under reduced pressure to a solid content of 10-30 wt%, the extract powder is obtained by spray drying or freeze drying. (4) Mix the three extracts obtained in a mass ratio of 1:1:1 to obtain the plant extract compound.

[0016] Extraction can also be performed using 50-70% ethanol solvent; specific conditions can be adjusted according to conventional processes. Those skilled in the art can implement this method accordingly.

[0017] Preferably, the composite amino acid contains 50–90 wt% free amino acids, wherein the total content of glutamic acid and aspartic acid is not less than 30 wt%.

[0018] Preferably, the potassium humate is potassium fulvate with a molecular weight of 3000–5000 Da.

[0019] Complex amino acids primarily serve as preferential chelators and carriers of micronutrients, while potassium humate improves rhizosphere soil structure and enhances water and solute conductivity. Flavonoids and phenolic compounds from different sources in plant extracts can induce the expression of plant selenium transport proteins and delay the oxidation and transformation of Se. In particular, by directionally combining extracts from loquat leaves (signal regulation), honeysuckle (antioxidant), and licorice (selenium stabilization) into a "plant extract library" with inducible properties, a multi-site, multi-pathway physiological activation system is constructed, which helps improve the migration rate and form transformation efficiency of selenium in crops. The overall design shows a synergistic trend in multiple nutrient release, environmental stability, and activation of plant absorption mechanisms.

[0020] A method for preparing an organic selenium nutrient solution for crops includes the following steps: S1. Selenomethionine and compound amino acids were mixed and dissolved in purified water in a certain proportion, and the pH was adjusted to 6.0±0.2; S2. Add potassium humate to the above solution, adjust the pH to 5.5±0.2, and stir until homogeneous; S3. Add plant extract to the above solution, adjust the pH to 5.5±0.2, and stir well; S4. Add EDTA-chelated calcium, magnesium, and zinc to the above solution and continue stirring until homogeneous; S5. After filtration, add potassium sorbate and stir well.

[0021] This invention introduces a scientifically sound strategy for the order of component addition and pH gradient control during nutrient solution preparation. This activates the activation windows of different components at each stage, improving system stability and nutrient efficiency. Firstly, mixing the composite amino acids and mineral elements at pH 6.0±0.2 allows the carboxyl and amino groups of the amino acids to be partially dissociated, thus forming stable complexes with metal ions. This ensures efficient chelation of metal ions and effectively avoids hydroxide precipitation that easily occurs in alkaline environments, particularly for Zn. 2+ The preservation of these components is particularly crucial, providing a good foundation for subsequent chelation-migration processes.

[0022] Subsequently, potassium humate was introduced at a pH of 5.5 ± 0.2. At this pH, the phenolic hydroxyl and carboxyl groups reached optimal dissociation, which facilitated the further formation of multi-point complexes or spatial cross-linked structures with existing amino acid-metal complexes. This step enhanced the stability of the mineral elements while preventing the decomposition of selenomethionine under alkaline conditions or irreversible reactions with humic acid. The enhanced complexation at this stage not only helped control liquid-phase stability but also improved the subsequent absorption efficiency of chelated elements by plants.

[0023] Next, plant extracts were added, and the pH of the system was maintained at 5.5±0.2 to ensure that the main active components (such as flavonoids and phenolic acids) could function under stable conditions and avoid oxidative polymerization and inactivation. This component was added at this stage as an "inducing component," which not only helps stabilize the complexation system but also enhances the migration and effective absorption of organic selenium from the root by stimulating the expression of selenium transport-related proteins in the plant.

[0024] Compared with the prior art, the beneficial effects of the present invention are mainly reflected in the following aspects: 1. Using L-selenomethionine as the organic selenium source, its bioavailability exceeds 90%, significantly superior to commonly used inorganic selenium (such as sodium selenite) preparations. Simultaneously, a three-layer coating technology (chitosan-citric acid crosslinking, hydroxypropyl methylcellulose coating, and sodium alginate-gelatin outer layer) effectively controls the release rate, delays its degradation in plants, and enhances selenium migration and utilization.

[0025] 2. The compound amino acids in the nutrient solution can form multi-point chelates with calcium, magnesium and zinc, and potassium humate further constructs a stable complex network, effectively preventing the precipitation of metal ions; especially under pH gradient regulation (6.0→5.5), it significantly improves the stability of metal ions and the absorption efficiency of crops.

[0026] 3. By introducing flavonoids and phenolic acids from plant extracts such as loquat leaves, honeysuckle, and licorice, the expression pathway of plant selenium transport proteins is activated, thereby enhancing the plant's ability to absorb, transport, and accumulate selenium from the root.

[0027] 4. Introducing Ca into the outer layer 2+ / Zn 2+ The complex cross-linking mechanism regulates the density and strength of the particle membrane, maintaining structural integrity and controlled-release stability under complex environments, making it suitable for various crops such as rice, wheat, vegetables, and fruits. Detailed Implementation

[0028] The present invention will now be described in detail with reference to the embodiments. Example 1

[0029] An organic selenium nutrient solution for crops, comprising the following components by weight percentage: L-Selenomethionine (triple-coated type): 0.3%; Complex amino acids (mainly composed of soybean protein hydrolysate): 4.0%; Potassium humate: 1.6%; Plant extract: 0.8%; EDTA chelates calcium, magnesium, and zinc (mass ratio 1:1:1): 0.3%; Potassium sorbate: 0.1%; Purified water: Balance.

[0030] L-selenomethionine is pre-treated with a three-layer coating process using the following raw materials and methods: Step A: Chitosan-citric acid cross-linking forms the inner layer. (1) Prepare a 1% (w / v) chitosan (molecular weight 120 kDa, degree of deacetylation 80%) solution (dissolved in 0.5% acetic acid aqueous solution) and stir magnetically at 40°C until completely dissolved; (2) Add L-selenomethionine powder and ultrasonically disperse for 10 minutes; (3) Add 0.5% (w / v) citric acid solution dropwise to react chitosan with citric acid at a molar ratio of 1:2.5, and let it stand at room temperature for 30 minutes to crosslink; (4) Collect the pre-coated particles by centrifugation (5000 rpm, 10 min) and discard the supernatant.

[0031] Step B: Intermediate layer—hydroxypropyl methylcellulose coating (1) Redisperse the above particles in 50 mL of water; (2) Add hydroxypropyl methylcellulose solution (the viscosity of hydroxypropyl methylcellulose is 100 mPa·s, the solution concentration is controlled at 1 wt%, and it is stirred and dissolved at 40°C in advance). (3) Stir at low speed for 30 minutes and then centrifuge (5000 rpm, 10 min) to collect the double-layer particles.

[0032] Step C: Outer layer—sodium alginate / gelatin + Ca 2+ / Zn 2+ Composite crosslinking (1) Dissolve sodium alginate and gelatin in a 1:1 mass ratio in a 40°C water bath to prepare a mixture; (2) Disperse the above-mentioned double-layer particles in the mixture and stir evenly for 10 minutes; (3) Add the pre-prepared CaCl2 / ZnCl2 composite crosslinking solution (CaCl2 / ZnCl2) dropwise. 2+ The concentration is 0.2 wt%, Zn 2+ (0.02wt%), add dropwise while stirring for 15 minutes; (4) After a final centrifugation (5000 rpm, 10 min), the three-layer coated particles are collected, rinsed twice with deionized water, and freeze-dried to obtain the finished product.

[0033] The compound amino acid is mainly composed of soybean protein hydrolysate, and contains 80 wt% free amino acids, of which glutamic acid and aspartic acid together account for 30 wt%.

[0034] Potassium humate is potassium fulvate with a molecular weight of 4000 Da.

[0035] The plant extract is a compound composed of loquat leaf extract, honeysuckle extract, and licorice extract in a mass ratio of 1:1:1. The loquat leaf extract, honeysuckle extract, and licorice extract are prepared according to the conventional water extraction or ethanol extraction methods described in the instructions, or commercially available standardized raw materials may be used.

[0036] A method for preparing an organic selenium nutrient solution for crops includes the following steps: Step S1: 1.1 Take L-selenomethionine with a three-layer coating and add it to purified water (temperature controlled at 40℃) in proportion. Stir and sonicate for 5 minutes to ensure uniform dispersion. 1.2 Simultaneously, take a complex amino acid (mainly soybean protein hydrolysate, with free amino acids accounting for 80%, and glutamic acid and aspartic acid totaling about 30%) and slowly add it to the system; 1.3 Stir at a constant temperature for 15 minutes until completely dissolved, then slowly adjust the pH to 6.0±0.2 using 0.1mol / L NaOH or citric acid.

[0037] Step S2: 2.1 Add potassium humate with a molecular weight of 4000 Da to the above mixed solution in proportion, and stir continuously for 20 minutes to form a homogeneous complex system; 2.3 The pH was fine-tuned again to 5.5 ± 0.2 using 0.5 mol / L citrate buffer.

[0038] Step S3: 3.1 Loquat leaf extract, honeysuckle extract and licorice extract were mixed in a mass ratio of 1:1:1 to prepare a compound solution; 3.2 Add the compound solution as a plant extract to the system obtained in step S2 in a certain proportion; 3.3 Stir for 15 minutes until homogeneous, while controlling the system temperature at 30℃; 3.4 Maintain the pH within the range of 5.5 ± 0.2, depending on the actual situation. If the pH is below 5.3, it can be neutralized by slowly adding 0.1 mol / L NaOH solution; if the pH is above 5.7, continue to lower it using citric acid or dilute hydrochloric acid.

[0039] Step S4: 4.1 Prepare an EDTA-chelated calcium, magnesium, and zinc complex solution (at a mass ratio of calcium:magnesium:zinc = 1:1:1); 4.2 Add the EDTA-chelated calcium, magnesium and zinc composite solution dropwise to the above system according to the proportion, and stir for 40 minutes to ensure that the minerals are fully dispersed and do not precipitate.

[0040] Step S5: Filtration and Corrosion Prevention 5.1 A coarse filtration is performed through a 0.45μm filter membrane to remove large particulate impurities and undissolved matter; 5.2 Add potassium sorbate to the filtrate in proportion, and then stir for 10 minutes until the potassium sorbate is completely dissolved. Example 2

[0041] An organic selenium nutrient solution for crops, comprising the following components by weight percentage: L-Selenomethionine (triple-coated type): 0.2%; Complex amino acids (mainly composed of soybean protein hydrolysate): 2.5%; Potassium humate: 1.2%; Plant extract: 0.6%; EDTA chelates calcium, magnesium, and zinc (mass ratio 1:1:1): 0.2%; Potassium sorbate: 0.05%; Purified water: Balance.

[0042] L-selenomethionine is pre-treated with a three-layer coating process using the following raw materials and methods: Step A: Chitosan-citric acid cross-linking forms the inner layer. (1) Prepare a 1% (w / v) chitosan (molecular weight 120 kDa, degree of deacetylation 80%) solution (dissolved in 0.5% acetic acid aqueous solution) and stir magnetically at 40°C until completely dissolved; (2) Add L-selenomethionine powder and ultrasonically disperse for 10 minutes; (3) Add 0.5% (w / v) citric acid solution dropwise to react chitosan with citric acid at a molar ratio of 1:2.5, and let it stand at room temperature for 30 minutes to crosslink; (4) Collect the pre-coated particles by centrifugation (5000 rpm, 10 min) and discard the supernatant.

[0043] Step B: Intermediate layer—hydroxypropyl methylcellulose coating (1) Redisperse the above particles in 50 mL of water; (2) Add hydroxypropyl methylcellulose solution (the viscosity of hydroxypropyl methylcellulose is 100 mPa·s, the solution concentration is controlled at 1 wt%, and it is stirred and dissolved at 40°C in advance). (3) Stir at low speed for 30 minutes and then centrifuge (5000 rpm, 10 min) to collect the double-layer particles.

[0044] Step C: Outer layer—sodium alginate / gelatin + Ca 2+ / Zn 2+ Composite crosslinking (1) Dissolve sodium alginate and gelatin in a 1:1 mass ratio in a 40°C water bath to prepare a mixture; (2) Disperse the above-mentioned double-layer particles in the mixture and stir evenly for 10 minutes; (3) Add the pre-prepared CaCl2 / ZnCl2 composite crosslinking solution (Ca²⁺ concentration is 0.2wt%, Zn²⁺ is 0.02wt%) dropwise while stirring for 15 minutes; (4) After a final centrifugation (5000 rpm, 10 min), the three-layer coated particles are collected, rinsed twice with deionized water, and freeze-dried to obtain the finished product.

[0045] The compound amino acid is mainly composed of soybean protein hydrolysate, and contains 80 wt% free amino acids, of which glutamic acid and aspartic acid together account for 30 wt%.

[0046] Potassium humate is potassium fulvate with a molecular weight of 4000 Da.

[0047] The plant extract is a compound composed of loquat leaf extract, honeysuckle extract, and licorice extract in a mass ratio of 1:1:1. The loquat leaf extract, honeysuckle extract, and licorice extract are prepared according to the conventional water extraction or ethanol extraction methods described in the instructions, or commercially available standardized raw materials may be used.

[0048] A method for preparing an organic selenium nutrient solution for crops includes the following steps: Step S1: 1.1 Take L-selenomethionine with a three-layer coating and add it to purified water (temperature controlled at 40℃) in proportion. Stir and sonicate for 5 minutes to ensure uniform dispersion. 1.2 Simultaneously, 2.5% of a complex amino acid (mainly from soybean protein hydrolysate, with 80% free amino acids and approximately 30% glutamic acid and aspartic acid combined) was slowly added to the system. 1.3 Stir at a constant temperature for 15 minutes until completely dissolved, then slowly adjust the pH to 6.0±0.2 using 0.1mol / L NaOH or citric acid.

[0049] Step S2: 2.1 Add potassium humate with a molecular weight of 4000 Da to the above mixed solution in proportion, and stir continuously for 20 minutes to form a homogeneous complex system; 2.2 Fine-tune the pH to 5.5 ± 0.2 again using 0.5 mol / L citrate buffer.

[0050] Step S3: 3.1 Loquat leaf extract, honeysuckle extract and licorice extract were mixed in a mass ratio of 1:1:1 to prepare a compound solution; 3.2 Add the compound solution as a plant extract to the system obtained in step S2 in a certain proportion; 3.3 Stir for 15 minutes until homogeneous, while controlling the system temperature at 30℃; 3.4 Maintain the pH within the range of 5.5 ± 0.2, depending on the actual situation. If the pH is below 5.3, it can be neutralized by slowly adding 0.1 mol / L NaOH solution; if the pH is above 5.7, continue to lower it using citric acid or dilute hydrochloric acid.

[0051] Step S4: 4.1 Prepare an EDTA-chelated calcium, magnesium, and zinc complex solution (at a mass ratio of calcium:magnesium:zinc = 1:1:1); 4.2 Add the EDTA-chelated calcium, magnesium and zinc composite solution dropwise to the above system according to the proportion, and stir for 40 minutes to ensure that the minerals are fully dispersed and do not precipitate.

[0052] Step S5: Filtration and Corrosion Prevention 5.1 A coarse filtration is performed through a 0.45μm filter membrane to remove large particulate impurities and undissolved matter; 5.2 Add potassium sorbate to the filtrate in proportion, and then stir for 10 minutes until the potassium sorbate is completely dissolved. Example 3

[0053] An organic selenium nutrient solution for crops, comprising the following components by weight percentage: L-Selenomethionine (triple-coated type): 0.5%; Complex amino acids (mainly composed of soybean protein hydrolysate): 5.0%; Potassium humate: 3.0%; Plant extracts: 1.0%; EDTA chelates calcium, magnesium, and zinc (mass ratio 1:1:1): 0.5%; Potassium sorbate: 0.2%; Purified water: Balance.

[0054] L-selenomethionine is pre-treated with a three-layer coating process using the following raw materials and methods: Step A: Chitosan-citric acid cross-linking forms the inner layer. (1) Prepare a 1% (w / v) chitosan (molecular weight 120 kDa, degree of deacetylation 80%) solution (dissolved in 0.5% acetic acid aqueous solution) and stir magnetically at 40°C until completely dissolved; (2) Add L-selenomethionine powder and ultrasonically disperse for 10 minutes; (3) Add 0.5% (w / v) citric acid solution dropwise to react chitosan with citric acid at a molar ratio of 1:2.5, and let it stand at room temperature for 30 minutes to crosslink; (4) Collect the pre-coated particles by centrifugation (5000 rpm, 10 min) and discard the supernatant.

[0055] Step B: Intermediate layer—hydroxypropyl methylcellulose coating (1) Redisperse the above particles in 50 mL of water; (2) Add hydroxypropyl methylcellulose solution (the viscosity of hydroxypropyl methylcellulose is 100 mPa·s, the solution concentration is controlled at 1 wt%, and it is stirred and dissolved at 40°C in advance). (3) Stir at low speed for 30 minutes and then centrifuge (5000 rpm, 10 min) to collect the double-layer particles.

[0056] Step C: Outer layer—sodium alginate / gelatin + Ca 2+ / Zn 2+ Composite crosslinking (1) Dissolve sodium alginate and gelatin in a 1:1 mass ratio in a 40°C water bath to prepare a mixture; (2) Disperse the above-mentioned double-layer particles in the mixture and stir evenly for 10 minutes; (3) Add the pre-prepared CaCl2 / ZnCl2 composite crosslinking solution (Ca²⁺ concentration is 0.2wt%, Zn²⁺ is 0.02wt%) dropwise while stirring for 15 minutes; (4) After a final centrifugation (5000 rpm, 10 min), the three-layer coated particles are collected, rinsed twice with deionized water, and freeze-dried to obtain the finished product.

[0057] The compound amino acid is mainly composed of soybean protein hydrolysate, and contains 80 wt% free amino acids, of which glutamic acid and aspartic acid together account for 30 wt%.

[0058] Potassium humate is potassium fulvate with a molecular weight of 4000 Da.

[0059] The plant extract is a compound composed of loquat leaf extract, honeysuckle extract, and licorice extract in a mass ratio of 1:1:1. The loquat leaf extract, honeysuckle extract, and licorice extract are prepared according to the conventional water extraction or ethanol extraction methods described in the instructions, or commercially available standardized raw materials may be used.

[0060] A method for preparing an organic selenium nutrient solution for crops includes the following steps: Step S1: 1.1 Take L-selenomethionine with a three-layer coating and add it to purified water (temperature controlled at 40℃) in proportion. Stir and sonicate for 5 minutes to ensure uniform dispersion. 1.2 Simultaneously, 5.0% of a complex amino acid (mainly from soybean protein hydrolysate, with 80% free amino acids and approximately 30% glutamic acid and aspartic acid combined) was slowly added to the system. 1.3 Stir at a constant temperature for 15 minutes until completely dissolved, then slowly adjust the pH to 6.0±0.2 using 0.1mol / L NaOH or citric acid.

[0061] Step S2: 2.1 Add potassium humate with a molecular weight of 4000 Da to the above mixed solution in proportion, and stir continuously for 20 minutes to form a homogeneous complex system; 2.2 Fine-tune the pH to 5.5 ± 0.2 again using 0.5 mol / L citrate buffer.

[0062] Step S3: 3.1 Loquat leaf extract, honeysuckle extract and licorice extract were mixed in a mass ratio of 1:1:1 to prepare a compound solution; 3.2 Add the compound solution as a plant extract to the system obtained in step S2 in a certain proportion; 3.3 Stir for 15 minutes until homogeneous, while controlling the system temperature at 30℃; 3.4 Maintain the pH within the range of 5.5 ± 0.2, depending on the actual situation. If the pH is below 5.3, it can be neutralized by slowly adding 0.1 mol / L NaOH solution; if the pH is above 5.7, continue to lower it using citric acid or dilute hydrochloric acid.

[0063] Step S4: 4.1 Prepare an EDTA-chelated calcium, magnesium, and zinc complex solution (at a mass ratio of calcium:magnesium:zinc = 1:1:1); 4.2 Add the EDTA-chelated calcium, magnesium and zinc composite solution dropwise to the above system according to the proportion, and stir for 40 minutes to ensure that the minerals are fully dispersed and do not precipitate.

[0064] Step S5: Filtration and Corrosion Prevention 5.1 A coarse filtration is performed through a 0.45μm filter membrane to remove large particulate impurities and undissolved matter; 5.2 Add potassium sorbate to the filtrate in proportion, and then stir for 10 minutes until the potassium sorbate is completely dissolved. Example 4

[0065] An organic selenium nutrient solution for crops, comprising the following components by weight percentage: L-Selenomethionine: 0.3%; Complex amino acids (mainly composed of soybean protein hydrolysate): 4.0%; Potassium humate: 1.6%; Plant extract: 0.8%; EDTA chelates calcium, magnesium, and zinc (mass ratio 1:1:1): 0.3%; Potassium sorbate: 0.1%; Purified water: Balance.

[0066] The compound amino acid is mainly composed of soybean protein hydrolysate, and contains 80 wt% free amino acids, of which glutamic acid and aspartic acid together account for 30 wt%.

[0067] Potassium humate is potassium fulvate with a molecular weight of 4000 Da.

[0068] The plant extract is a compound composed of loquat leaf extract, honeysuckle extract, and licorice extract in a mass ratio of 1:1:1. The loquat leaf extract, honeysuckle extract, and licorice extract are prepared according to the conventional water extraction or ethanol extraction methods described in the instructions, or commercially available standardized raw materials may be used.

[0069] A method for preparing an organic selenium nutrient solution for crops includes the following steps: Step S1: 1.1 Take L-selenomethionine powder and add it to purified water (temperature controlled at 40℃) in proportion. Stir and sonicate for 5 minutes to ensure uniform dispersion. 1.2 Simultaneously, 3.0% of a complex amino acid (mainly from soybean protein hydrolysate, with 80% free amino acids and approximately 30% glutamic acid and aspartic acid combined) was slowly added to the system; 1.3 Stir at a constant temperature for 15 minutes until completely dissolved, then slowly adjust the pH to 6.0±0.2 using 0.1mol / L NaOH or citric acid.

[0070] Step S2: 2.1 Add potassium humate with a molecular weight of 4000 Da to the above mixed solution in proportion, and stir continuously for 20 minutes to form a homogeneous complex system; 2.3 The pH was fine-tuned again to 5.5 ± 0.2 using 0.5 mol / L citrate buffer.

[0071] Step S3: 3.1 Loquat leaf extract, honeysuckle extract and licorice extract were mixed in a mass ratio of 1:1:1 to prepare a compound solution; 3.2 Add the compound solution as a plant extract to the system obtained in step S2 in a certain proportion; 3.3 Stir for 15 minutes until homogeneous, while controlling the system temperature at 30℃; 3.4 Maintain the pH within the range of 5.5 ± 0.2, depending on the actual situation. If the pH is below 5.3, it can be neutralized by slowly adding 0.1 mol / L NaOH solution; if the pH is above 5.7, continue to lower it using citric acid or dilute hydrochloric acid.

[0072] Step S4: 4.1 Prepare an EDTA-chelated calcium, magnesium, and zinc complex solution (at a mass ratio of calcium:magnesium:zinc = 1:1:1); 4.2 Add the EDTA-chelated calcium, magnesium and zinc composite solution dropwise to the above system according to the proportion, and stir for 40 minutes to ensure that the minerals are fully dispersed and do not precipitate.

[0073] Step S5: Filtration and Corrosion Prevention 5.1 A coarse filtration is performed through a 0.45μm filter membrane to remove large particulate impurities and undissolved matter; 5.2 Add potassium sorbate to the filtrate in proportion, and then stir for 10 minutes until the potassium sorbate is completely dissolved. Example 5

[0074] An organic selenium nutrient solution for crops, comprising the following components by weight percentage: L-Selenomethionine (triple-coated type): 0.3%; Complex amino acids (mainly composed of soybean protein hydrolysate): 4.0%; Potassium humate: 1.6%; Plant extract: 0.8%; EDTA chelates calcium, magnesium, and zinc (mass ratio 1:1:1): 0.3%; Potassium sorbate: 0.1%; Purified water: Balance.

[0075] L-selenomethionine is pre-treated with a three-layer coating process using the following raw materials and methods: Step A: Chitosan-citric acid cross-linking forms the inner layer. (1) Prepare a 1% (w / v) chitosan (molecular weight 120 kDa, degree of deacetylation 80%) solution (dissolved in 0.5% acetic acid aqueous solution) and stir magnetically at 40°C until completely dissolved; (2) Add L-selenomethionine powder and ultrasonically disperse for 10 minutes; (3) Add 0.5% (w / v) citric acid solution dropwise to react chitosan with citric acid at a molar ratio of 1:2.5, and let it stand at room temperature for 30 minutes to crosslink; (4) Collect the pre-coated particles by centrifugation (5000 rpm, 10 min) and discard the supernatant.

[0076] Step B: Intermediate layer—hydroxypropyl methylcellulose coating (1) Redisperse the above particles in 50 mL of water; (2) Add hydroxypropyl methylcellulose solution (the viscosity of hydroxypropyl methylcellulose is 100 mPa·s, the solution concentration is controlled at 1 wt%, and it is stirred and dissolved at 40°C in advance). (3) Stir at low speed for 30 minutes and then centrifuge (5000 rpm, 10 min) to collect the double-layer particles.

[0077] Step C: Outer layer—sodium alginate / gelatin + Ca 2+ / Zn 2+ Composite crosslinking (1) Dissolve sodium alginate and gelatin in a 1:1 mass ratio in a 40°C water bath to prepare a mixture; (2) Disperse the above-mentioned double-layer particles in the mixture and stir evenly for 10 minutes; (3) Add the pre-prepared CaCl2 / ZnCl2 composite crosslinking solution (CaCl2 / ZnCl2) dropwise. 2+ The concentration is 0.2 wt%, Zn 2+ (0.02wt%), add dropwise while stirring for 15 minutes; (4) After a final centrifugation (5000 rpm, 10 min), the three-layer coated particles are collected, rinsed twice with deionized water, and freeze-dried to obtain the finished product.

[0078] The compound amino acid is mainly composed of soybean protein hydrolysate, and contains 70 wt% free amino acids, of which glutamic acid and aspartic acid together account for 20 wt%.

[0079] Potassium humate is potassium fulvate with a molecular weight of 4000 Da.

[0080] The plant extract is a compound composed of loquat leaf extract, honeysuckle extract, and licorice extract in a mass ratio of 1:1:1. The loquat leaf extract, honeysuckle extract, and licorice extract are prepared according to the conventional water extraction or ethanol extraction methods described in the instructions, or commercially available standardized raw materials may be used.

[0081] A method for preparing an organic selenium nutrient solution for crops includes the following steps: Step S1: 1.1 Take L-selenomethionine with a three-layer coating and add it to purified water (temperature controlled at 40℃) in proportion. Stir and sonicate for 5 minutes to ensure uniform dispersion. 1.2 Simultaneously, 3.0% of a complex amino acid (mainly from soybean protein hydrolysate, with 80% free amino acids and approximately 30% glutamic acid and aspartic acid combined) was slowly added to the system; 1.3 Stir at a constant temperature for 15 minutes until completely dissolved, then slowly adjust the pH to 6.0±0.2 using 0.1mol / L NaOH or citric acid.

[0082] Step S2: 2.1 Add potassium humate with a molecular weight of 4000 Da to the above mixed solution in proportion, and stir continuously for 20 minutes to form a homogeneous complex system; 2.3 The pH was fine-tuned again to 5.5 ± 0.2 using 0.5 mol / L citrate buffer.

[0083] Step S3: 3.1 Loquat leaf extract, honeysuckle extract and licorice extract were mixed in a mass ratio of 1:1:1 to prepare a compound solution; 3.2 Add the compound solution as a plant extract to the system obtained in step S2 in a certain proportion; 3.3 Stir for 15 minutes until homogeneous, while controlling the system temperature at 30℃; 3.4 Maintain the pH within the range of 5.5 ± 0.2, depending on the actual situation. If the pH is below 5.3, it can be neutralized by slowly adding 0.1 mol / L NaOH solution; if the pH is above 5.7, continue to lower it using citric acid or dilute hydrochloric acid.

[0084] Step S4: 4.1 Prepare an EDTA-chelated calcium, magnesium, and zinc complex solution (at a mass ratio of calcium:magnesium:zinc = 1:1:1); 4.2 Add the EDTA-chelated calcium, magnesium and zinc composite solution dropwise to the above system according to the proportion, and stir for 40 minutes to ensure that the minerals are fully dispersed and do not precipitate.

[0085] Step S5: Filtration and Corrosion Prevention 5.1 A coarse filtration is performed through a 0.45μm filter membrane to remove large particulate impurities and undissolved matter; 5.2 Add potassium sorbate to the filtrate in proportion, and then stir for 10 minutes until the potassium sorbate is completely dissolved. Comparative Example 1

[0086] This comparative example discloses a selenium nutrient solution for crops, the preparation method of which includes the following steps: (1) Dissolve sodium selenite (with a selenium content of 40 mg / L) in purified water according to the proportion, control the temperature at 40℃, and stir for 10 minutes until completely dissolved; (2) Add 4.0 wt% of complex amino acids (mainly soybean protein hydrolysate, with a free amino acid content of about 80%, and a total of 30 wt% of glutamic acid and aspartic acid) to the above solution, continue stirring for 15 minutes, and adjust the pH to 6.0±0.2; (3) Add potassium humate (1.6 wt%) with a molecular weight of 4000 Da, stir continuously for 20 minutes, and adjust the pH to 5.5±0.2; (4) Add EDTA chelated calcium, magnesium and zinc complex solution in a 1:1:1 mass ratio (total concentration 0.3 wt%), stir for 40 minutes to ensure uniform complexation; (5) Add the compound plant extract (total 0.8 wt%) formed by mixing loquat leaf, honeysuckle and licorice extract in a ratio of 1:1:1 and stir for 10 minutes; wherein the loquat leaf extract, honeysuckle extract and licorice extract are all prepared by conventional water extraction or ethanol extraction methods as described in the instructions, or commercially available standardized raw materials can be used.

[0087] 6) After filtration to remove impurities, add potassium sorbate (0.1 wt%) as a preservative and stir until homogeneous. Comparative Example 2

[0088] This comparative example discloses an organic selenium nutrient solution for crops, the preparation method of which includes the following steps: (1) The three-layer coated L-selenomethionine (0.3 wt%) was dispersed in purified water, and the temperature was maintained at 40°C. The mixture was stirred and ultrasonically dispersed for 5 minutes. The three-layer coated L-selenomethionine used in Comparative Example 2 was the same as that in Example 1, with the inner layer being chitosan-citric acid crosslinked (molecular weight 120 kDa, degree of deacetylation 80%), the middle layer being hydroxypropyl methylcellulose with a viscosity of 100 mPa·s, and the outer layer being Ca 2+ / Zn 2+ Composite cross-linked sodium alginate-gelatin.

[0089] (2) Add 4.0 wt% of the complex amino acid to the system. The complex amino acid is artificially synthesized and mixed from monosodium glutamate, lysine hydrochloride, alanine and other amino acids in a conventional ratio. The free amino acid content is only 55%, and the content of glutamic acid and aspartic acid is less than 20%. Continue stirring for 15 minutes and adjust the pH to 6.0±0.2. (3) Add potassium humate (1.6 wt%) with a molecular weight of 4000 Da, stir continuously for 20 minutes, and adjust the pH to 5.5±0.2; (4) Add EDTA chelated calcium, magnesium and zinc complex solution in a 1:1:1 mass ratio (total concentration 0.3 wt%), stir for 40 minutes to ensure uniform complexation; (5) Add the compound plant extract (total 0.8 wt%) formed by mixing loquat leaf, honeysuckle and licorice extract in a ratio of 1:1:1 and stir for 10 minutes; wherein the loquat leaf extract, honeysuckle extract and licorice extract are all prepared by conventional water extraction or ethanol extraction methods as described in the instructions, or commercially available standardized raw materials can be used.

[0090] (6) After filtration to remove impurities, add potassium sorbate (0.1 wt%) as a preservative and stir until homogeneous. Comparative Example 3

[0091] This comparative example discloses a selenium nutrient solution for crops, the preparation method of which includes the following steps: (1) The three-layer coated L-selenomethionine (0.3 wt%) was dispersed in purified water, and the temperature was maintained at 40°C. The mixture was stirred and ultrasonically dispersed for 5 minutes. The three-layer coated L-selenomethionine used in Comparative Example 3 was the same as that used in Example 1, with the inner layer being chitosan-citric acid crosslinked (molecular weight 120 kDa, degree of deacetylation 80%), the middle layer being hydroxypropyl methylcellulose with a viscosity of 100 mPa·s, and the outer layer being Ca 2+ / Zn 2+ Composite cross-linked sodium alginate-gelatin.

[0092] (2) Add 4.0 wt% of complex amino acids (mainly soybean protein hydrolysate, with a free amino acid content of about 80%, and a total of 30 wt% of glutamic acid and aspartic acid) to the above solution, continue stirring for 15 minutes, and adjust the pH to 6.0±0.2; (3) Add EDTA chelated calcium, magnesium and zinc complex solution in a 1:1:1 mass ratio (total concentration 0.3 wt%), stir for 40 minutes to ensure uniform complexation; (5) Add the compound plant extract (total 0.8 wt%) formed by mixing loquat leaf, honeysuckle and licorice extract in a ratio of 1:1:1 and stir for 10 minutes; wherein the loquat leaf extract, honeysuckle extract and licorice extract are all prepared by conventional water extraction or ethanol extraction methods as described in the instructions, or commercially available standardized raw materials can be used.

[0093] (6) After filtration to remove impurities, add potassium sorbate (0.1 wt%) as a preservative and stir until homogeneous. Comparative Example 4

[0094] (1) The three-layer coated L-selenomethionine (0.3 wt%) was dispersed in purified water, and the temperature was maintained at 40°C. The mixture was stirred and ultrasonically dispersed for 5 minutes. The three-layer coated L-selenomethionine used in Comparative Example 4 was the same as that used in Example 1, with the inner layer being chitosan-citric acid crosslinked (molecular weight 120 kDa, degree of deacetylation 80%), the middle layer being hydroxypropyl methylcellulose with a viscosity of 100 mPa·s, and the outer layer being Ca 2+ / Zn 2+ Composite cross-linked sodium alginate-gelatin.

[0095] (2) Add 4.0 wt% of compound amino acids (mainly soybean protein hydrolysate, with a free amino acid content of about 80%, and a total of 30 wt% of glutamic acid and aspartic acid) to the above solution and continue stirring for 15 minutes; (3) Add potassium humate (1.6 wt%) with a molecular weight of 4000 Da, stir continuously for 20 minutes, and adjust the pH to 5.5±0.2; (4) Add EDTA chelated calcium, magnesium and zinc complex solution in a 1:1:1 mass ratio (total concentration 0.3 wt%), stir for 40 minutes to ensure uniform complexation; (5) Add the compound plant extract (total 0.8 wt%) formed by mixing loquat leaf, honeysuckle and licorice extract in a ratio of 1:1:1 and stir for 10 minutes; wherein the loquat leaf extract, honeysuckle extract and licorice extract are all prepared by conventional water extraction or ethanol extraction methods as described in the instructions, or commercially available standardized raw materials can be used.

[0096] (6) After filtration to remove impurities, add potassium sorbate (0.1 wt%) as a preservative and stir until homogeneous. Comparative Example 5

[0097] (1) The three-layer coated L-selenomethionine (0.3 wt%) was dispersed in purified water, and the temperature was maintained at 40°C. The mixture was stirred and ultrasonically dispersed for 5 minutes. The three-layer coated L-selenomethionine used in Comparative Example 5 was the same as that in Example 1, with the inner layer being chitosan-citric acid crosslinked (molecular weight 120 kDa, degree of deacetylation 80%), the middle layer being hydroxypropyl methylcellulose with a viscosity of 100 mPa·s, and the outer layer being Ca 2+ / Zn 2+ Composite cross-linked sodium alginate-gelatin.

[0098] (2) Add 4.0 wt% of complex amino acids (mainly soybean protein hydrolysate, with a free amino acid content of about 80%, and a total of 30 wt% of glutamic acid and aspartic acid) to the above solution, continue stirring for 15 minutes, and adjust the pH to 6.0±0.2; (3) Add potassium humate (1.6 wt%) with a molecular weight of 4000 Da, stir continuously for 20 minutes, and adjust the pH to 5.5±0.2; (4) Add EDTA chelated calcium, magnesium and zinc complex solution in a 1:1:1 mass ratio (total concentration 0.3 wt%), stir for 40 minutes to ensure uniform complexation; (5) After filtration to remove impurities, add potassium sorbate (0.1 wt%) as a preservative and stir until homogeneous. Comparative Example 6

[0099] The difference between this comparative example and Example 1 is that L-selenomethionine was pre-treated with a three-layer coating using the following raw materials and methods: Step A: Chitosan-citric acid cross-linking forms the inner layer. (1) Prepare a 1% (w / v) chitosan (molecular weight 120 kDa, degree of deacetylation 80%) solution (dissolved in 0.5% acetic acid aqueous solution) and stir magnetically at 40°C until completely dissolved; (2) Add L-selenomethionine powder and ultrasonically disperse for 10 minutes; (3) Add 0.5% (w / v) citric acid solution dropwise to react chitosan with citric acid at a molar ratio of 1:2.5, and let it stand at room temperature for 30 minutes to crosslink; (4) Collect the pre-coated particles by centrifugation (5000 rpm, 10 min) and discard the supernatant.

[0100] Step B: Intermediate layer—hydroxypropyl methylcellulose coating (1) Redisperse the above particles in 50 mL of water; (2) Add hydroxypropyl methylcellulose solution (the viscosity of hydroxypropyl methylcellulose is 100 mPa·s, the solution concentration is controlled at 1 wt%, and it is stirred and dissolved at 40°C in advance). (3) Stir at low speed for 30 minutes and then centrifuge (5000 rpm, 10 min) to collect the double-layer particles.

[0101] Step C: Outer layer—sodium alginate / gelatin + Ca 2+ Crosslinking (1) Dissolve sodium alginate and gelatin in a 1:1 mass ratio in a 40°C water bath to prepare a mixture; (2) Disperse the above-mentioned double-layer particles in the mixture and stir evenly for 10 minutes; (3) Add the pre-prepared CaCl2 crosslinking solution (Ca 2+ (Concentration 0.25wt%), add dropwise while stirring for 15 minutes; (4) After a final centrifugation (5000 rpm, 10 min), the three-layer coated particles are collected, rinsed twice with deionized water, and freeze-dried to obtain the finished product.

[0102] Performance testing 1. Determination of the proportion of organic selenium Methods: The nutrient solutions of each example and comparative example were used as samples, and the content ratio of organic selenium forms was detected by high performance liquid chromatography-inductively coupled plasma mass spectrometry (HPLC-ICP-MS).

[0103] 2. Granule controlled-release performance test Method: The nutrient solution of the sample was placed in a pH 6.5 buffer solution and kept at a constant temperature of 37℃. Samples were taken at regular intervals (e.g., 0h, 6h, 12h, 24h, 48h) and the content of exogenously released selenomethionine was determined by HPLC.

[0104] Calculate T50 (time required to release 50%) and the 24-hour release rate.

[0105] 3. Plant selenium absorption rate test Crop model: Rice seedlings were selected as the model crop.

[0106] Treatment method: Seven days after spraying with different nutrient solution formulas, samples were taken to determine the selenium content (mg / kg) in the aboveground parts of the crop.

[0107] Detection method: After microwave digestion of HNO3-H2O2, selenium was measured by ICP-MS.

[0108] Absorption efficiency: The selenium transfer rate (crop selenium content / selenium application rate × 100%) is calculated based on the amount of selenium applied.

[0109] 4. Stability Testing Objective: To investigate the physicochemical stability of liquid nutrient solution under storage conditions.

[0110] Conditions: After being placed at room temperature in the dark for 30 days, observe the precipitation, pH changes, and selenium content loss.

[0111] The test results are shown in Table 1-4 below.

[0112] Table 1. Test results of organic selenium content sample Organic selenium percentage / % Example 1 98.6 Example 2 98.2 Example 3 98.7 Example 4 98.4 Example 5 96.9 Comparative Example 1 2.1 Comparative Example 2 97.3 Comparative Example 3 98.1 Comparative Example 4 97.8 Comparative Example 5 98 Comparative Example 6 98 Due to differences in the degree of free amino acids, the ratio of glutamic acid to aspartic acid, the complexing and protective effects of potassium humate and plant extracts in the formulation, the results of organic selenium detection in each example are somewhat different. However, the samples using selenomethionine all showed results of >96% organic selenium, while Comparative Example 1, which used inorganic selenium, showed a detection rate of only 2.1% for selenomethionine.

[0113] Table 2 Results of particle controlled-release performance test sample T50 / h 24-hour release rate / % Example 1 21.8 58.4 Example 2 22.4 56.9 Example 3 20.9 60.2 Example 4 1.6 96.1 Example 5 22 57.6 Comparative Example 2 21.5 59.3 Comparative Example 3 21.7 58.7 Comparative Example 4 16.9 71.5 Comparative Example 5 21.1 60.1 Comparative Example 6 9.4 82.3 According to the test results in Table 2, the combination of "chitosan-citric acid inner layer + HPMC intermediate layer + sodium alginate / gelatin-Ca" is effective. 2+ / Zn 2+ The three-layer coating of the "outer layer" (Examples 1, 2, 3, and 5) can stably achieve a sustained-release effect with a T50 of approximately 21–22 h and a 24-hour release rate of approximately 57%–60%; the uncoated sample (Example 4) exhibits a burst release phenomenon with a T50 of approximately 1.6 h and a 24-hour release rate of approximately 96%, Ca 2+ The single crosslinking (Comparative Example 6) exhibited moderate sustained-release performance (T50 approximately 9.4 h), while Comparative Example 4, which did not optimize pH in the S1 stage, had a loose outer layer structure and accelerated release (shorter T50 and increased 24 h release rate). Differences in amino acid formulations (comparing Example 5 and Example 1, and Comparative Example 2 and Example 1) had little impact on the viscoelastic properties of the diffusion interface, and the overall controlled-release performance was similar.

[0114] Table 3 Results of plant selenium absorption rate test sample Aboveground part Se / (mg·kg⁻¹) Selenium transfer rate / % Example 1 3.41 67.8 Example 2 3.09 62.1 Example 3 3.55 70.2 Example 4 2.31 45.4 Example 5 2.95 59 Comparative Example 1 1.93 37.6 Comparative Example 2 2.49 49.3 Comparative Example 3 2.7 52.4 Comparative Example 4 2.86 55.7 Comparative Example 5 2.78 54.1 Comparative Example 6 3.08 60.5 As shown in Table 3, the seedling selenium transfer rate of Examples 1 and 3 was the highest (≥67%), which was attributed to the synergistic effect of the slow-release coating combined with high-free-degree complex amino acids, potassium humate, and plant extracts, significantly enhancing root surface complexation, transmembrane transport, and antioxidant protection. Example 2 showed a slight decrease due to a lower proportion of active ingredients, but it was still better than the uncoated and control examples. Example 4, without coating, resulted in burst release, environmental loss, and decreased absorption efficiency. Comparative Example 1 showed the lowest inorganic selenium absorption (37.6%). Comparative Example 2 had insufficient free amino acid quality and a low Glu / Asp ratio, limiting transport and complexation performance, and the transfer rate dropped to about 49%. Comparative Example 3 lacked potassium humate, and Comparative Example 5 lacked plant extracts, resulting in slightly lower rates than Example 1 due to reduced complexation sites or weakened antioxidant / membrane stability, respectively. Comparative Example 6 only had Ca 2+ The crosslinking absorption rate was between that of Example 5 and Example 2, consistent with its moderate burst release. Comparative Example 4 had a moderate absorption rate due to insufficient colloidal stability caused by unoptimized pH.

[0115] Table 4 sample precipitation ΔpH Selenium loss / % Example 1 none 0.03 1.2 Example 2 none 0.04 1.4 Example 3 none 0.05 1.5 Example 4 slight 0.08 6.1 Example 5 none 0.05 1.9 Comparative Example 1 Slight (yellowing) 0.11 12.4 Comparative Example 2 slight 0.06 3.8 Comparative Example 3 slight 0.07 3.1 Comparative Example 4 slight 0.09 4.6 Comparative Example 5 slight 0.07 3.5 Comparative Example 6 slight 0.08 5.2 The test results in Table 4 show that using a three-layer coating and Ca... 2+ / Zn 2+ In the composite crosslinked examples 1, 2, 3, and 5, the selenium loss did not exceed 2% in the fulvic acid-containing system, which is consistent with the multi-point coordination and ion bridge structure of the outer metal-peptide-polysaccharide layer; Example 4 was uncoated and Comparative Example 6 only had Ca 2+ Crosslinking resulted in more significant loss of activity and pH drift. The inorganic selenium sample in Comparative Example 1 suffered the highest loss due to its susceptibility to valence state transformation, yellowing, and coordination position switching. Comparative Examples 2, 3, 4, and 5 showed slightly worse stability than Example 1 due to factors such as insufficient ligand quality, lack of fulvic acid, unoptimized pH, or lack of plant antioxidant molecules.

[0116] The above description is merely a preferred embodiment of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. An organic selenium nutrient solution for crops, characterized in that, By mass percentage, it includes the following components: Selenomethionine 0.1-0.5%; The compound amino acids comprise 2.0-5.0%; the compound amino acids consist of a mixture of amino acids, primarily composed of soybean protein hydrolysate. Potassium humate 1.0–3.0%; Plant extracts 0.5-1.0%; The EDTA-chelated calcium, magnesium, and zinc content is 0.05%–0.5%; the mass ratio of calcium, magnesium, and zinc is 1:1:

1. Potassium sorbate 0.05–0.2 wt%; The remaining amount of purified water.

2. The organic selenium nutrient solution for crops according to claim 1, characterized in that, The selenomethionine is L-selenomethionine, and the L-selenomethionine undergoes a three-layer coating treatment. The three layers, from the inside out, are an inner layer formed by chitosan-citric acid crosslinking, a middle layer formed by hydroxypropyl methylcellulose coating, and an outer layer formed by sodium alginate-gelatin coating.

3. The organic selenium nutrient solution for crops according to claim 2, characterized in that, The inner layer is formed by cross-linking chitosan with a molecular weight of 100-150 kDa and a degree of deacetylation of 75-85% with citric acid in a molar ratio of 1:2-1:

3.

4. The organic selenium nutrient solution for crops according to claim 3, characterized in that, The viscosity of the hydroxypropyl methylcellulose in the intermediate layer is 60–100 mPa·s.

5. The organic selenium nutrient solution for crops according to claim 3, characterized in that, The outer layer is formed by cross-linking of CaCl2 and ZnCl2 via composite ions, and Zn... 2+ Concentration of Ca 2+ 5% to 15%.

6. The organic selenium nutrient solution according to claim 1, characterized in that, The mass ratio of the compound amino acids, potassium humate, and plant extracts is 5:2:

1.

7. The organic selenium nutrient solution for crops according to claim 6, characterized in that, The plant extract is a compound made by mixing loquat leaf extract, honeysuckle extract and licorice extract in a mass ratio of 1:1:

1.

8. The organic selenium nutrient solution for crops according to claim 6, characterized in that, The compound amino acid contains 50–90 wt% free amino acids, of which the combined content of glutamic acid and aspartic acid is not less than 30 wt%.

9. The organic selenium nutrient solution for crops according to claim 6, characterized in that, The potassium humate is potassium fulvate with a molecular weight of 3000–5000 Da.

10. A method for preparing an organic selenium nutrient solution for crops according to any one of claims 1 to 9, characterized in that, Includes the following steps: S1. Selenomethionine and compound amino acids were mixed and dissolved in purified water in a certain proportion, and the pH was adjusted to 6.0±0.2; S2. Add potassium humate to the above solution, adjust the pH to 5.5±0.2, and stir until homogeneous; S3. Add plant extract to the above solution, adjust the pH to 5.5±0.2, and stir well; S4. Add EDTA-chelated calcium, magnesium, and zinc to the above solution and continue stirring until homogeneous; S5. After filtration, add potassium sorbate and stir well.