Organic selenium nutrient solution for crops and preparation method thereof

Abstract

The present application relates to an organic selenium nutrient solution for crops and a preparation method thereof. The nutrient solution comprises, by mass percentage, selenomethionine 0.1-0.5%, complex amino acids 2.0-5.0%, potassium humate 1.0-3.0%, plant extracts 0.5-1.0%, EDTA chelated calcium, magnesium and zinc 0.05-0.5%, potassium sorbate 0.05-0.2%, and purified water as the remainder. Preferably, the selenomethionine is L-type selenomethionine with a three-layer coating, the inner layer of which is formed by cross-linking chitosan and citric acid, the middle layer is hydroxypropyl methyl cellulose, and the outer layer is a sodium alginate-gelatin matrix cross-linked by Ca 2+ / Zn 2+ complex ions. The preparation method comprises adding and chelating each component under specific pH conditions, and stabilizing to form a stable multi-component synergistic 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] The present application relates to the technical field of crop nutrient solution, and in particular to an organic selenium nutrient solution for crops and a preparation method thereof. BACKGROUND

[0002] Selenium is an essential trace element for human body, and has important physiological functions in antioxidant and immune regulation. However, the yield of natural selenium-rich agricultural products is limited, which is difficult to meet the daily intake needs of the population. Therefore, improving the selenium accumulation level in crops through exogenous selenium supply has become a key technical path in current agricultural production.

[0003] In the prior art, the selenium supply means mainly includes inorganic selenium fertilizer and organic selenium fertilizer. Inorganic selenium fertilizer such as sodium selenite and sodium selenate is widely used, but its biological utilization rate is low, and it is easy to undergo oxidation-reduction transformation in soil or plant body, resulting in inactivation or increased toxicity of selenium element, and the safety and stability problems are prominent. Compared with inorganic selenium, organic selenium has a molecular structure closer to the biological system, and shows higher utilization efficiency and physiological compatibility in the process of plant absorption and metabolism, and becomes the research focus. Among them, selenium-containing amino acid compounds can be effectively absorbed through the active transport path of plants, and show great application potential.

[0004] In order to improve the absorption efficiency of crops to selenium, some studies attempt to combine the selenium supply system with plant nutrient solution to provide basic nutrients and strengthen the absorption and transport of selenium. However, this kind of technology still faces many challenges in practical application. For example, organic selenium is easily degraded in aqueous solution under the influence of environmental conditions, resulting in loss of activity; in addition, when coexisting with other nutrient components, complexation failure, precipitation and other adverse reactions may occur, affecting the overall system stability and biological availability of selenium. In addition, the absorption capacity of plants to exogenous selenium is jointly regulated by multiple factors such as transport mechanism, physiological state and nutrient environment, and simple addition of selenium supply components cannot significantly improve the migration and enrichment effect of selenium in crops.

[0005] In summary, the current organic selenium supply technology for crops still has obvious deficiencies in the stability, absorbability and coordination with crop nutrition of selenium, and it is urgent to develop a new selenium supply nutrient system that is more efficient, stable and suitable for agricultural application, in order to promote the sustainable development of selenium-rich agriculture. SUMMARY

[0006] In view of the deficiencies in the prior art, the purpose of the present application is to provide an organic selenium nutrient solution for crops and a preparation method thereof.

[0007] An organic selenium nutrient solution for crops, comprising the following components by mass percentage:

[0008] Selenomethionine 0.1-0.5%;

[0009] complex amino acid 2.0-5.0%; The complex amino acid comprises an amino acid mixture mainly composed of soybean protein hydrolysate;

[0010] potassium humate 1.0-3.0%;

[0011] plant extract 0.5-1.0%;

[0012] calcium, magnesium and zinc in EDTA chelate form 0.05-0.5%; The mass ratio of calcium, magnesium and zinc is 1:1:1;

[0013] potassium sorbate 0.05-0.2 wt%;

[0014] purified water in excess.

[0015] Preferably, the selenomethionine is L-type selenomethionine, and the L-type selenomethionine is treated with a three-layer coating, the three-layer coating being formed from an inner layer of chitosan-lactic acid cross-linking, an intermediate layer of hydroxypropyl methyl cellulose coating, and an outer layer of sodium alginate-gelatin coating from inside to outside.

[0016] 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 lactic acid at a molar ratio of 1:2-1:3.

[0017] Preferably, the viscosity of the hydroxypropyl methyl cellulose of the intermediate layer is 60-100 mPa·s.

[0018] Preferably, the outer layer is further cross-linked by complex ions of CaCl2 and ZnCl2, and the mass ratio of Ca 2+ The concentration of Ca 2 + is 5-15%.

[0019] The present application designs a three-layer structure coating strategy from inside to outside for L-type selenomethionine, uses chitosan-lactic acid cross-linking to construct an inner layer network, and by controlling the molecular weight (100-150 kDa) and the degree of deacetylation (75-85%) of chitosan and the cross-linking ratio (molar ratio 1:2-1:3), a colloidal inner core with high compactness and protection can be formed, effectively isolating the external hydrolysis and oxidation environment. The intermediate layer is coated with hydroxypropyl methyl cellulose, and by selecting a cellulose derivative with a viscosity of 60-100 mPa·s to establish a controllable hydration shell, the release curve of its controlled release behavior is stable, and it is suitable for the nutrient absorption rhythm of different crops. The outer layer introduces Ca 2+ and Zn 2+The composite ions are cross-linked to construct a gel outer membrane with an interwoven network structure, and Zn 2+ The concentration of Ca 2+ is set in the range of 5–15%, which helps to adjust the density and mechanical strength of the membrane, and significantly improves the structural integrity and environmental adaptability of the controlled-release particles.

[0020] Preferably, the mass ratio of the three composite amino acids, potassium humate, and plant extracts is 5:2:1.

[0021] Preferably, the plant extract is a compound prepared by mixing loquat leaf extract, honeysuckle extract, and licorice extract in a mass ratio of 1:1:1.

[0022] The loquat leaf extract, honeysuckle extract, and licorice extract can be prepared by conventional water extraction or ethanol extraction. For example:

[0023] (1) Take dried loquat leaf, honeysuckle, and licorice raw materials, crush them through a 40-mesh sieve;

[0024] (2) Add deionized water in a solid-liquid ratio of 1:10–1:20, and extract at 70–80°C for 1–2 h;

[0025] (3) Filter the residue, concentrate under reduced pressure to a solid content of 10–30 wt%, and spray dry or freeze dry to obtain extract powder;

[0026] (4) Mix the three extracts obtained in a mass ratio of 1:1:1 to obtain the plant extract compound.

[0027] Alternatively, 50–70% ethanol solvent can be used for extraction, and the specific conditions can be adjusted according to conventional processes. Those skilled in the art can implement accordingly.

[0028] Preferably, the composite amino acid contains 50–90 wt% of free amino acids, and the total content of glutamic acid and aspartic acid is not less than 30 wt%.

[0029] Preferably, the potassium humate is potassium fulvic acid with a molecular weight of 3000–5000 Da.

[0030] The complex amino acid mainly undertakes the priority chelation of trace elements and the carrier function, the potassium humate improves the rhizosphere soil structure and enhances the water and solute conductivity, and the flavonoids and phenolic compounds in the plant extracts of different sources can induce the expression of plant selenium transport proteins, delay the oxidation and transformation process of Se. Especially by combining the extracts of loquat leaves (signal regulation), honeysuckle (antioxidation) and licorice (selenium stabilization) into a 'plant extract ratio library' with induction characteristics, a multi-site and multi-path physiological activation system is constructed, which helps to improve the migration rate and morphological transformation efficiency of selenium in crops. The overall design shows a synergistic trend in multiple nutrient release, environmental stability and plant absorption mechanism activation.

[0031] A preparation method of an organic selenium nutrient solution for crops, comprising the following steps:

[0032] S1. Dissolve selenium methionine and complex amino acids in purified water in proportion, and adjust the pH to 6.0±0.2;

[0033] S2. Add potassium humate to the above solution, adjust the pH to 5.5±0.2, and stir uniformly;

[0034] S3. Add plant extracts to the above solution, adjust the pH to 5.5±0.2, and stir uniformly;

[0035] S4. Add EDTA chelated calcium, magnesium and zinc to the above solution, and continue to stir uniformly;

[0036] S5. After filtration, add potassium sorbate and stir uniformly.

[0037] The present application introduces a scientific and reasonable component feeding sequence and pH gradient control strategy in the preparation process of the nutrient solution, activates the action window of different components in each stage, and improves the system stability and nutrient efficiency. First, the complex amino acids and mineral elements are mixed at pH 6.0±0.2, so that the carboxyl and amine groups of the amino acids are in a partially dissociated state, thereby forming stable complexes with metal ions, which not only ensures the chelation efficiency of metal ions, but also effectively avoids the precipitation of hydroxides which is prone to occur in alkaline environment, especially for Zn 2+ , which is particularly crucial, providing a good foundation for the subsequent chelation-migration process.

[0038] Then, the potassium humate is introduced when the pH is reduced to 5.5±0.2, at which the phenolic hydroxyl and carboxyl groups reach a better degree of dissociation, which is conducive to the further formation of multi-point complex or spatial cross-linking structure with the existing amino acid-metal complex. This step strengthens the stability of mineral elements, while avoiding the decomposition of selenomethionine in an alkaline environment or irreversible reaction with humic acid. The complexation enhancement at this stage not only helps to control the stability of the liquid phase, but also improves the absorption efficiency of chelated elements by plants.

[0039] Then, plant extracts are added, and the pH of the system is maintained at 5.5±0.2, which fully guarantees that the main active components (such as flavonoids and phenolic acids) can function under stable conditions and avoid oxidation and polymerization inactivation. These components are added as "inducing components" at this stage, which not only help to stabilize the complex system, but also stimulate the expression of plant selenium transport-related proteins, thereby improving the migration and effective absorption capacity of organic selenium from the root.

[0040] Compared with the prior art, the beneficial effects of the present application mainly lie in the following aspects:

[0041] 1. L-selenomethionine is used as an organic selenium source, and its bioavailability is more than 90%, which is significantly better than that of commonly used inorganic selenium (such as sodium selenite) preparations. At the same time, through the three-layer coating technology (chitosan-citric acid crosslinking, hydroxypropyl methyl cellulose coating, and sodium alginate-gelatin outer layer), the release rate is effectively controlled, the degradation in the plant body is delayed, and the migration rate and utilization rate of selenium are improved.

[0042] 2. The complex amino acids in the nutrient solution can form multi-point chelation with calcium, magnesium, and zinc, and the potassium humate further constructs a stable complex network, effectively preventing the precipitation of metal ions; especially under the pH gradient regulation (6.0→5.5), the stability of metal ions and the absorption efficiency of crops are significantly improved.

[0043] 3. The flavonoids and phenolic acids in the plant extracts of loquat leaves, honeysuckle, and licorice are introduced, which activate the expression pathway of plant selenium transport proteins, thereby improving the absorption, transport, and enrichment capacity of plants for selenium from the root.

[0044] 4. Ca 2+ / Zn 2+ are introduced into the outer layer, which regulates the density and strength of the particle membrane, maintains the structural integrity and controlled release stability in complex environments, and is suitable for rice, wheat, vegetables, fruits, and other crops. DETAILED DESCRIPTION

[0045] The present application will be described in detail below with reference to examples. Example 1

[0046] An organic selenium nutrient solution for crops, comprising the following components by mass percentage:

[0047] L-selenomethionine (three-layer coated): 0.3%;

[0048] Complex amino acids (mainly soybean protein hydrolysate): 4.0%;

[0049] Potassium humate: 1.6%;

[0050] Plant extract: 0.8%;

[0051] EDTA chelated calcium, magnesium, and zinc (mass ratio 1:1:1): 0.3%;

[0052] Potassium sorbate: 0.1%;

[0053] Purified water: the balance.

[0054] L-selenomethionine is pre-coated with three layers using the following raw materials and methods:

[0055] Step A: cross-linking of chitosan-lactic acid to form the inner layer

[0056] (1) Prepare a 1% (w / v) chitosan solution (molecular weight 120 kDa, degree of deacetylation 80%) in 0.5% acetic acid solution, and stir magnetically at 40°C until completely dissolved;

[0057] (2) Add L-selenomethionine raw powder and ultrasonically disperse for 10 minutes;

[0058] (3) Add 0.5% (w / v) lactic acid solution dropwise, and allow chitosan and lactic acid to react at a molar ratio of 1:2.5, and stand at room temperature for 30 minutes for cross-linking;

[0059] (4) Collect the preliminary coated particles by centrifugation (5000 rpm, 10 min), and discard the supernatant.

[0060] Step B: middle layer - hydroxypropyl methyl cellulose coating

[0061] (1) Redisperse the above particles in 50 mL of water;

[0062] (2) Add a hydroxypropyl methyl cellulose solution (viscosity of hydroxypropyl methyl cellulose is 100 mPa·s, solution concentration is controlled at 1 wt%, and is dissolved in advance by stirring at 40°C);

[0063] (3) After stirring at low speed for 30 minutes, collect the double-layered particles by centrifugation (5000 rpm, 10 min).

[0064] Step C: outer layer - sodium alginate / gelatin + Ca 2+Zn 2+ complex cross-linking

[0065] (1) Sodium alginate and gelatin were dissolved in a 40°C water bath to prepare a mixed solution at a mass ratio of 1:1;

[0066] (2) The above double-layer particles were dispersed in the mixed solution and uniformly stirred for 10 minutes;

[0067] (3) The pre-configured CaCl2 / ZnCl2 complex cross-linking solution (Ca 2+ with a concentration of 0.2 wt%, Zn 2+ with a concentration of 0.02 wt%) was added dropwise while stirring for 15 minutes;

[0068] (4) The three-layer coated particles were collected by the last centrifugation (5000 rpm, 10 min), rinsed with deionized water twice, and freeze-dried to obtain the finished product.

[0069] The complex amino acid is mainly soy protein hydrolysate, and the complex amino acid contains 80 wt% of free amino acids, of which the content of glutamic acid and aspartic acid accounts for 30 wt%.

[0070] The potassium humate is a potassium fulvic acid with a molecular weight of 4000 Da.

[0071] The plant extract is a complex compound prepared by mixing loquat leaf extract, honeysuckle extract, and licorice extract at a mass ratio of 1:1:1. The loquat leaf extract, honeysuckle extract, and licorice extract are all prepared by conventional water extraction or ethanol extraction method as described in the instruction, or standard commercial raw materials can be used.

[0072] A preparation method of an organic selenium nutrient solution for crops, comprising the following steps:

[0073] Step S1:

[0074] 1.1 Take the three-layer coated L-type selenomethionine, add it to purified water (temperature controlled at 40°C) in proportion, and ultrasonically stir for 5 minutes while stirring to ensure uniform dispersion;

[0075] 1.2 At the same time, take the complex amino acid (mainly soy protein hydrolysate, with free amino acids accounting for 80%, and glutamic acid and aspartic acid accounting for about 30%), and slowly add it to the system;

[0076] 1.3 After constant temperature stirring for 15 minutes, completely dissolve it, and slowly adjust the pH to 6.0±0.2 using 0.1 mol / L NaOH or citric acid.

[0077] Step S2:

[0078] 2.1 Take potassium fulvate with a molecular weight of 4000 Da and add it to the above mixed solution in proportion, continue to stir for 20 minutes, and form a uniform complex system;

[0079] 2.3 Adjust the pH to 5.5 ± 0.2 again using 0.5 mol / L citric acid buffer.

[0080] Step S3:

[0081] 3.1 Take loquat leaf extract, honeysuckle extract, and licorice extract, mix them in a mass ratio of 1:1:1 to prepare a compound solution;

[0082] 3.2 Add the compound solution as a plant extract solution to the system obtained in step S2 in proportion;

[0083] 3.3 Stir for 15 minutes to uniformity, while controlling the system temperature to be 30°C;

[0084] 3.4 Maintain the pH in the range of 5.5 ± 0.2 according to the actual situation. If the pH is lower than 5.3, slowly add neutralizing 0.1 mol / L NaOH solution; if the pH is higher than 5.7, continue to adjust it lower using citric acid or dilute hydrochloric acid.

[0085] Step S4:

[0086] 4.1 Prepare an EDTA chelated calcium, magnesium, and zinc complex solution (in a mass ratio of calcium:magnesium:zinc = 1:1:1);

[0087] 4.2 Add the EDTA chelated calcium, magnesium, and zinc complex solution to the above system in proportion, stir for 40 minutes to ensure that the minerals are fully dispersed and do not precipitate.

[0088] Step S5: Filtration and preservative treatment

[0089] 5.1 Perform primary coarse filtration through a 0.45 μm filter membrane to remove large particle impurities and undissolved substances;

[0090] 5.2 Add potassium sorbate to the filtrate in proportion, then stir for 10 minutes until the potassium sorbate is completely dissolved. Example 2

[0091] An organic selenium nutrient solution for crops, by mass percentage, includes the following components:

[0092] L-type selenomethionine (three-layer coated type): 0.2%;

[0093] Complex amino acids (mainly soybean protein hydrolysate): 2.5%;

[0094] Potassium humate: 1.2%;

[0095] Plant extract: 0.6%;

[0096] EDTA chelated calcium, magnesium, zinc (mass ratio 1:1:1): 0.2%;

[0097] Potassium sorbate: 0.05%;

[0098] Purified water: the balance.

[0099] L-selenomethionine is pre-processed by three-layer coating with the following raw materials and methods:

[0100] Step A: chitosan-lactic acid cross-linking to form the inner layer

[0101] (1) Prepare a 1% (w / v) chitosan solution (molecular weight 120 kDa, degree of deacetylation 80%) (dissolved in 0.5% acetic acid aqueous solution) and stir magnetically at 40°C until completely dissolved;

[0102] (2) Add L-selenomethionine raw powder and ultrasonically disperse for 10 minutes;

[0103] (3) Add 0.5% (w / v) lactic acid solution dropwise, so that chitosan and lactic acid react at a molar ratio of 1:2.5, and stand at room temperature for 30 minutes for cross-linking;

[0104] (4) Collect the preliminary coated particles by centrifugation (5000 rpm, 10 min) and discard the supernatant.

[0105] Step B: middle layer - hydroxypropyl methyl cellulose coating

[0106] (1) Redisperse the above particles in 50 mL of water;

[0107] (2) Add a hydroxypropyl methyl cellulose solution (viscosity of hydroxypropyl methyl cellulose is 100 mPa·s, solution concentration is controlled at 1 wt%, and is dissolved in advance at 40°C with stirring);

[0108] (3) After stirring at low speed for 30 minutes, collect the double-layered particles by centrifugation (5000 rpm, 10 min).

[0109] Step C: outer layer - sodium alginate / gelatin + Ca 2+ / Zn 2+ complex cross-linking

[0110] (1) Dissolve sodium alginate and gelatin in a mass ratio of 1:1 in a 40°C water bath to make a mixed solution;

[0111] (2) Disperse the above double-layered particles in the mixed solution and stir uniformly for 10 minutes;

[0112] (3) Drop the pre-configured CaCl2 / ZnCl2 composite cross-linking solution (Ca2+ concentration is 0.2wt%, Zn2+ is 0.02wt%) slowly, and stir for 15 minutes;

[0113] (4) Collect the three-layer coated particles after the last centrifugation (5000 rpm, 10 min), rinse twice with deionized water, and freeze-dry to obtain the finished product.

[0114] The complex amino acid is mainly soybean protein hydrolysate, and the complex amino acid contains 80wt% free amino acids, wherein the content of glutamic acid and aspartic acid is 30wt%.

[0115] The potassium humate is a potassium fulvic acid with a molecular weight of 4000 Da.

[0116] The plant extract is a complex compound prepared by mixing loquat leaf extract, honeysuckle extract and licorice extract at a mass ratio of 1:1:1. The loquat leaf extract, honeysuckle extract and licorice extract are prepared by conventional water extraction or ethanol extraction method as described in the instruction, or standard commercial raw materials can be used.

[0117] A preparation method of an organic selenium nutrient solution for crops, comprising the following steps:

[0118] Step S1:

[0119] 1.1 Take the three-layer coated L-type selenomethionine, add it to purified water in proportion (temperature control at 40℃), and stir and ultrasonic for 5 minutes to ensure uniform dispersion;

[0120] 1.2 At the same time, take 2.5% of the complex amino acid (mainly soybean protein hydrolysate, free amino acid accounts for 80%, and glutamic acid and aspartic acid accounts for about 30%), and slowly add it to the system;

[0121] 1.3 Constant temperature stirring for 15 minutes, and then use 0.1mol / L NaOH or citric acid to slowly adjust the pH to 6.0±0.2.

[0122] Step S2:

[0123] 2.1 Take the potassium fulvic acid with a molecular weight of 4000 Da and add it to the above mixed solution in proportion, continue to stir for 20 minutes to form a uniform complex system;

[0124] 2.2 Use 0.5mol / L citric acid buffer to adjust the pH to 5.5±0.2 again.

[0125] Step S3:

[0126] 3.1 Take loquat leaf extract, honeysuckle extract and licorice extract, mix them in a mass ratio of 1:1:1 to make a compound solution;

[0127] 3.2 Add the compound solution as a plant extract solution to the system obtained in step S2 in proportion;

[0128] 3.3 Stir for 15 minutes to make it uniform, while controlling the system temperature at 30°C;

[0129] 3.4 According to the actual situation, maintain the pH in the range of 5.5±0.2. If the pH is lower than 5.3, slowly add and neutralize with 0.1 mol / L NaOH solution; if the pH is higher than 5.7, continue to use citric acid or dilute hydrochloric acid to lower it.

[0130] Step S4:

[0131] 4.1 Prepare an EDTA chelated calcium, magnesium and zinc complex solution (in a mass ratio of calcium:magnesium:zinc = 1:1:1);

[0132] 4.2 Add the EDTA chelated calcium, magnesium and zinc complex solution to the above system in proportion, stir for 40 minutes to ensure that the minerals are fully dispersed and do not precipitate.

[0133] Step S5: filtration and preservative treatment

[0134] 5.1 Perform a rough filtration through a 0.45 μm filter membrane to remove large particle impurities and undissolved substances;

[0135] 5.2 Add potassium sorbate to the filtrate in proportion, then stir for 10 minutes until the potassium sorbate is completely dissolved. Example 3

[0136] An organic selenium nutrient solution for crops, by mass percentage, includes the following components:

[0137] L-type selenomethionine (three-layer coated type): 0.5%;

[0138] Complex amino acids (mainly soybean protein hydrolysate): 5.0%;

[0139] Potassium humate: 3.0%;

[0140] Plant extract: 1.0%;

[0141] EDTA chelated calcium, magnesium and zinc (mass ratio 1:1:1): 0.5%;

[0142] Potassium sorbate: 0.2%;

[0143] Purified water: the balance.

[0144] L-selenomethionine was pre-treated by three-layer coating with the following raw materials and methods:

[0145] Step A: inner layer of chitosan-lactic acid cross-linking

[0146] (1) Prepare a 1% (w / v) chitosan solution (molecular weight 120 kDa, degree of deacetylation 80%) (dissolved in 0.5% acetic acid aqueous solution) and stir magnetically at 40°C until completely dissolved;

[0147] (2) Add L-selenomethionine raw powder and ultrasonically disperse for 10 minutes;

[0148] (3) Add 0.5% (w / v) lactic acid solution dropwise, and react chitosan with lactic acid at a molar ratio of 1:2.5, and stand at room temperature for 30 minutes for cross-linking;

[0149] (4) Collect the preliminary coated particles by centrifugation (5000 rpm, 10 min) and discard the supernatant.

[0150] Step B: middle layer - hydroxypropyl methyl cellulose coating

[0151] (1) Redisperse the above particles in 50 mL of water;

[0152] (2) Add a hydroxypropyl methyl cellulose solution (viscosity of hydroxypropyl methyl cellulose is 100 mPa·s, solution concentration is controlled at 1 wt%, and is dissolved in advance at 40°C with stirring);

[0153] (3) After low-speed stirring for 30 minutes, collect the double-layer particles by centrifugation (5000 rpm, 10 min).

[0154] Step C: outer layer - sodium alginate / gelatin + Ca 2+ / Zn 2+ complex cross-linking

[0155] (1) Dissolve sodium alginate and gelatin in a 40°C water bath at a mass ratio of 1:1 to form a mixed solution;

[0156] (2) Disperse the above double-layer particles in the mixed solution and stir uniformly for 10 minutes;

[0157] (3) Add the pre-prepared CaCl2 / ZnCl2 complex cross-linking solution (Ca²⁺ concentration is 0.2 wt%, Zn²⁺ is 0.02 wt%) dropwise while stirring for 15 minutes;

[0158] (4) Collect the three-layer coated particles by the last centrifugation (5000 rpm, 10 min), rinse twice with deionized water, and freeze-dry to obtain the finished product.

[0159] The complex amino acid is mainly soybean protein hydrolysate, and the complex amino acid contains 80 wt% of free amino acids, wherein the content of glutamic acid and aspartic acid is 30 wt% in total.

[0160] The potassium humate is potassium fulvic acid with a molecular weight of 4000 Da.

[0161] The plant extract is a complex prepared by mixing loquat leaf extract, honeysuckle extract and licorice extract at a mass ratio of 1:1:1. The loquat leaf extract, honeysuckle extract and licorice extract are all prepared by the conventional water extraction or ethanol extraction method described in the instruction, and the standardized raw materials on the market can also be used.

[0162] A preparation method of an organic selenium nutrient solution for crops, comprising the following steps:

[0163] Step S1:

[0164] 1.1 Take the three-layer coated L-type selenomethionine, add it into purified water in proportion (the temperature is controlled at 40 DEG C), and ultrasonic for 5 minutes while stirring to ensure uniform dispersion;

[0165] 1.2 At the same time, take 5.0% of the complex amino acid (mainly soybean protein hydrolysate, free amino acid accounts for 80%, and glutamic acid and aspartic acid accounts for about 30% in total), and slowly add it into the system;

[0166] 1.3 After constant temperature stirring for 15 minutes, completely dissolve it, and then slowly adjust the pH to 6.0±0.2 using 0.1 mol / L NaOH or citric acid.

[0167] Step S2:

[0168] 2.1 Take the potassium fulvic acid with a molecular weight of 4000 Da, and add it into the above mixed solution in proportion, and continuously stir for 20 minutes to form a uniform complex system;

[0169] 2.2 Adjust the pH to 5.5±0.2 again using 0.5 mol / L citric acid buffer.

[0170] Step S3:

[0171] 3.1 Take the loquat leaf extract, honeysuckle extract and licorice extract, mix them according to a mass ratio of 1:1:1 to prepare a complex solution;

[0172] 3.2 Add the complex solution as the plant extract solution into the system obtained in step S2 in proportion;

[0173] 3.3 Stir for 15 minutes to be uniform, and control the system temperature to be 30 DEG C at the same time;

[0174] 3.4 According to the actual situation, the pH is maintained in the range of 5.5±0.2. If the pH is lower than 5.3, 0.1 mol / L NaOH solution can be slowly added for neutralization; if the pH is higher than 5.7, citric acid or dilute hydrochloric acid can be used to lower it.

[0175] Step S4:

[0176] 4.1 Prepare EDTA chelated calcium, magnesium and zinc complex solution (mass ratio of calcium: magnesium: zinc = 1: 1: 1);

[0177] 4.2 Add EDTA chelated calcium, magnesium and zinc complex solution to the above system in proportion, stir for 40 minutes, and ensure that the minerals are fully dispersed and do not precipitate.

[0178] Step S5: filtration and preservation treatment

[0179] 5.1 Perform one rough filtration through a 0.45 μm filter membrane to remove large particle impurities and undissolved substances;

[0180] 5.2 Add potassium sorbate to the filtrate in proportion, then stir for 10 minutes until the potassium sorbate is completely dissolved. Example 4

[0181] An organic selenium nutrient solution for crops, comprising the following components by mass percentage:

[0182] L-selenomethionine: 0.3%;

[0183] Complex amino acids (mainly soybean protein hydrolysate): 4.0%;

[0184] Potassium humate: 1.6%;

[0185] Plant extract: 0.8%;

[0186] EDTA chelated calcium, magnesium and zinc (mass ratio 1:1:1): 0.3%;

[0187] Potassium sorbate: 0.1%;

[0188] Purified water: the balance.

[0189] The complex amino acids are mainly soybean protein hydrolysate, and the complex amino acids contain 80 wt% of free amino acids, of which the total content of glutamic acid and aspartic acid is 30 wt%.

[0190] The potassium humate is potassium fulvate with a molecular weight of 4000 Da.

[0191] The plant extract is a complex prepared by mixing loquat leaf extract, honeysuckle extract and licorice extract at a mass ratio of 1:1:1. The loquat leaf extract, honeysuckle extract and licorice extract are all prepared by the conventional water extraction or ethanol extraction method described in the instruction, or the standardized raw materials on the market can be used.

[0192] A preparation method of an organic selenium nutrient solution for crops, comprising the following steps:

[0193] Step S1:

[0194] 1.1 Take L-selenomethionine powder, add it to purified water in proportion (temperature control at 40°C), and ultrasonic for 5 minutes while stirring to ensure uniform dispersion;

[0195] 1.2 At the same time, take 3.0% of the compound amino acid (mainly soybean protein hydrolysate, free amino acid accounting for 80%, and glutamic acid and aspartic acid accounting for about 30%), and slowly add it to the system;

[0196] 1.3 After constant temperature stirring for 15 minutes, completely dissolve it, and slowly adjust the pH to 6.0±0.2 using 0.1 mol / L NaOH or citric acid.

[0197] Step S2:

[0198] 2.1 Take potassium fulvate with a molecular weight of 4000 Da and add it to the above mixed solution in proportion, continue to stir for 20 minutes, and form a uniform complex system;

[0199] 2.3 Use 0.5 mol / L citric acid buffer to fine-tune the pH to 5.5±0.2 again.

[0200] Step S3:

[0201] 3.1 Take loquat leaf extract, honeysuckle extract and licorice extract, mix them according to a mass ratio of 1:1:1 to prepare a complex solution;

[0202] 3.2 Add the complex solution as a plant extract to the system obtained in step S2 in proportion;

[0203] 3.3 Stir for 15 minutes to uniform, and control the system temperature at 30°C at the same time;

[0204] 3.4 According to the actual situation, maintain the pH in the range of 5.5±0.2. If the pH is lower than 5.3, slowly add neutralizing solution of 0.1 mol / L NaOH; if the pH is higher than 5.7, continue to use citric acid or dilute hydrochloric acid to lower it.

[0205] Step S4:

[0206] 4.1 Prepare EDTA chelated calcium, magnesium and zinc complex solution (mass ratio of calcium: magnesium: zinc = 1 : 1 : 1) in proportion;

[0207] 4.2 Drop EDTA chelated calcium, magnesium and zinc complex solution into the above system in proportion, stir for 40 minutes to ensure that the minerals are fully dispersed and do not precipitate.

[0208] Step S5: filtration and preservative treatment

[0209] 5.1 Perform primary coarse filtration through a 0.45 μm filter membrane to remove large particle impurities and undissolved substances;

[0210] 5.2 Add potassium sorbate in proportion to the filtrate, then stir for 10 minutes until the potassium sorbate is completely dissolved. Example 5

[0211] An organic selenium nutrient solution for crops, comprising the following components by mass percentage:

[0212] L-selenomethionine (three-layer coated): 0.3%;

[0213] Complex amino acids (mainly soybean protein hydrolysate): 4.0%;

[0214] Potassium humate: 1.6%;

[0215] Plant extract: 0.8%;

[0216] EDTA chelated calcium, magnesium and zinc (mass ratio 1 : 1 : 1): 0.3%;

[0217] Potassium sorbate: 0.1%;

[0218] Purified water: the balance.

[0219] L-selenomethionine is pre-coated with three layers by the following raw materials and methods:

[0220] Step A: cross-linking of chitosan-citric acid to form the inner layer

[0221] (1) Prepare a 1% (w / v) chitosan solution (molecular weight 120 kDa, degree of deacetylation 80%) (dissolved in 0.5% acetic acid aqueous solution) and stir magnetically at 40°C until completely dissolved;

[0222] (2) Add L-selenomethionine raw powder and ultrasonically disperse for 10 minutes;

[0223] (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 stand at room temperature for 30 minutes for cross-linking;

[0224] (4) Collect the primary enveloped particles by centrifugation (5000 rpm, 10 min) and discard the supernatant.

[0225] Step B: Intermediate layer - hydroxypropyl methylcellulose coating

[0226] (1) Redisperse the above particles in 50 mL of water;

[0227] (2) Add a hydroxypropyl methylcellulose solution (viscosity of hydroxypropyl methylcellulose is 100 mPa s, solution concentration is controlled at 1 wt%, and is dissolved in advance at 40°C with stirring);

[0228] (3) After stirring at low speed for 30 minutes, collect the double-layered particles by centrifugation (5000 rpm, 10 min).

[0229] Step C: Outer layer - sodium alginate / gelatin + Ca 2+ / Zn 2+ Composite cross-linking

[0230] (1) Dissolve sodium alginate and gelatin in a 40°C water bath to form a mixed solution at a mass ratio of 1:1;

[0231] (2) Disperse the above double-layered particles in the mixed solution and uniformly stir for 10 minutes;

[0232] (3) Add the pre-prepared CaCl2 / ZnCl2 composite cross-linking solution (Ca 2+ concentration is 0.2 wt%, and Zn 2+ concentration is 0.02 wt%) dropwise while stirring for 15 minutes;

[0233] (4) Collect the three-layered enveloped particles by the final centrifugation (5000 rpm, 10 min), rinse twice with deionized water, and freeze-dry to obtain the finished product.

[0234] The composite amino acid is mainly soy protein hydrolysate, and the composite amino acid contains 70 wt% of free amino acids, wherein the content of glutamic acid and aspartic acid is 20 wt%.

[0235] The potassium humate is potassium fulvic acid with a molecular weight of 4000 Da.

[0236] The plant extract is a complex prepared by mixing loquat leaf extract, honeysuckle extract, and licorice extract at a mass ratio of 1:1:1. The loquat leaf extract, honeysuckle extract, and licorice extract are all prepared by conventional water extraction or ethanol extraction method as described in the instruction, or standard commercial raw materials can be used.

[0237] A preparation method of an organic selenium nutrient solution for crops, comprising the following steps:

[0238] Step S1:

[0239] 1.1 Take the three-layer coated L-type selenium methionine, add it to purified water in proportion (temperature control at 40°C), and stir while ultrasonic for 5 minutes to ensure uniform dispersion;

[0240] 1.2 At the same time, take 3.0% of the compound amino acid (mainly soybean protein hydrolysate, free amino acid accounting for 80%, and glutamic acid and aspartic acid accounting for about 30%), and slowly add it to the system;

[0241] 1.3 After constant temperature stirring for 15 minutes, completely dissolve it, and slowly adjust the pH to 6.0±0.2 using 0.1 mol / L NaOH or citric acid.

[0242] Step S2:

[0243] 2.1 Take potassium fulvic acid with a molecular weight of 4000 Da and add it to the above mixed solution in proportion, continue to stir for 20 minutes to form a uniform complex system;

[0244] 2.3 Use 0.5 mol / L citric acid buffer to fine-tune the pH to 5.5±0.2 again.

[0245] Step S3:

[0246] 3.1 Take loquat leaf extract, honeysuckle extract and licorice extract, mix them in a mass ratio of 1:1:1 to make a compound solution;

[0247] 3.2 Add the compound solution as a plant extract solution to the system obtained in step S2 in proportion;

[0248] 3.3 Stir for 15 minutes to uniform, while controlling the system temperature to be 30°C;

[0249] 3.4 According to the actual situation, maintain the pH in the range of 5.5±0.2. If the pH is lower than 5.3, slowly add neutralizing solution of 0.1 mol / L NaOH; if the pH is higher than 5.7, continue to use citric acid or dilute hydrochloric acid to lower it.

[0250] Step S4:

[0251] 4.1 Prepare EDTA chelated calcium, magnesium and zinc complex solution (in a mass ratio of calcium:magnesium:zinc=1:1:1);

[0252] 4.2 Add the EDTA chelated calcium, magnesium and zinc complex solution to the above system in proportion, stir for 40 minutes to ensure that the minerals are fully dispersed and do not precipitate.

[0253] Step S5: filtration and preservation treatment

[0254] 5.1 Primary coarse filtration through 0.45 μm filter membrane to remove large particulate impurities and undissolved substances;

[0255] 5.2 Add potassium sorbate to the filtrate in proportion, then stir for 10 minutes until the potassium sorbate is completely dissolved. Comparative Example 1

[0256] This comparative example discloses a selenium nutrient solution for crops, the preparation method of which comprises the following steps:

[0257] (1) Dissolve sodium selenite (selenium content stabilized at 40 mg / L) in purified water in proportion, control the temperature at 40°C, and stir for 10 minutes until completely dissolved;

[0258] (2) Add 4.0 wt% of a compound amino acid (mainly soybean protein hydrolysate, free amino acid content about 80%, glutamic acid and aspartic acid total 30 wt%) to the above solution, continue to stir for 15 minutes, and adjust the pH to 6.0±0.2;

[0259] (3) Add potassium fulvate with a molecular weight of 4000 Da (1.6 wt%), continue to stir for 20 minutes, and adjust the pH to 5.5±0.2;

[0260] (4) Add a 1:1:1 mass ratio of EDTA chelated calcium, magnesium and zinc complex solution (total concentration 0.3 wt%), stir for 40 minutes to ensure uniform complexation;

[0261] (5) Add a compound plant extract solution (total amount 0.8 wt%) formed by mixing loquat leaf extract, honeysuckle extract and licorice extract in a 1:1:1 ratio, and stir for 10 minutes; wherein the loquat leaf extract, honeysuckle extract and licorice extract are all prepared by the conventional water extraction or ethanol extraction method described in the specification, or standard commercial raw materials can be used.

[0262] 6) After filtering out impurities, add potassium sorbate (0.1 wt%) as a preservative, stir until uniform, and obtain the product. Comparative Example 2

[0263] This comparative example discloses an organic selenium nutrient solution for crops, the preparation method of which comprises the following steps:

[0264] (1) Disperse the three-layer coated L-selenomethionine (0.3 wt%) in purified water, keep the temperature at 40°C, and stir and ultrasonically disperse for 5 minutes; the three-layer coated L-selenomethionine used in Comparative Example 2 is the same as that of Example 1, the inner layer is chitosan-citric acid crosslinking (molecular weight 120 kDa, deacetylation degree 80%), the middle layer is hydroxypropyl methyl cellulose with a viscosity of 100 mPa·s, and the outer layer is Ca 2+ / Zn2+ Cross-linked sodium alginate-gelatin.

[0265] (2) Add 4.0 wt% of a complex amino acid, which is artificially synthesized by mixing sodium glutamate, lysine hydrochloride, alanine, etc. in a conventional ratio, with a free amino acid content of only 55%, and glutamic acid and aspartic acid of less than 20%, continue to stir for 15 minutes, and adjust the pH to 6.0±0.2;

[0266] (3) Add potassium fulvic acid with a molecular weight of 4000 Da (1.6 wt%), continue to stir for 20 minutes, and adjust the pH to 5.5±0.2;

[0267] (4) Add a 1:1:1 mass ratio of EDTA chelated calcium, magnesium, and zinc complex solution (total concentration 0.3 wt%), stir for 40 minutes to ensure uniform complexation;

[0268] (5) Add a complex plant extract solution (total amount 0.8 wt%) formed by mixing loquat leaf extract, honeysuckle extract, and licorice extract in a 1:1:1 ratio, 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 method as described in the instruction manual, or standard commercial raw materials can be used.

[0269] (6) After filtering out impurities, add potassium sorbate (0.1 wt%) as a preservative, stir until uniform, and obtain. Comparative Example 3

[0270] This comparative example discloses a selenium nutrient solution for crops, and the preparation method thereof includes the following steps:

[0271] (1) Disperse the three-layer coated L-selenomethionine (0.3 wt%) in purified water, and keep the temperature at 40°C, stir and ultrasonically disperse for 5 minutes; the three-layer coated L-selenomethionine used in Comparative Example 3 is the same as that in Example 1, the inner layer is chitosan-lactic acid cross-linking (molecular weight 120 kDa, deacetylation degree 80%), the middle layer is hydroxypropyl methyl cellulose with a viscosity of 100 mPa·s, and the outer layer is Ca 2+ / Zn 2+ Cross-linked sodium alginate-gelatin.

[0272] (2) Add 4.0 wt% of a complex amino acid (mainly soy protein hydrolysate, with a free amino acid content of about 80%, and glutamic acid and aspartic acid accounting for 30 wt%) to the above solution, continue to stir for 15 minutes, and adjust the pH to 6.0±0.2;

[0273] (3) EDTA chelated calcium, magnesium and zinc complex solution (total concentration 0.3 wt%) in a mass ratio of 1:1:1 was added and stirred for 40 minutes to ensure uniform complexation;

[0274] (5) A compound plant extract solution (total amount 0.8 wt%) formed by mixing loquat leaf extract, honeysuckle flower extract and licorice extract in a ratio of 1:1:1 was added and stirred for 10 minutes; wherein the loquat leaf extract, honeysuckle flower extract and licorice extract were all prepared according to the conventional water extraction or ethanol extraction method described in the specification, and standard commercial raw materials can also be used.

[0275] (6) After filtering out impurities, potassium sorbate (0.1 wt%) was added as a preservative, and stirred evenly to obtain the product. Comparative Example 4

[0276] (1) The three-layer coated L-selenomethionine (0.3 wt%) was dispersed in purified water, and the temperature was kept at 40°C, and stirred and ultrasonically dispersed for 5 minutes; the three-layer coated L-selenomethionine used in Comparative Example 4 was the same as that of Example 1, the inner layer was chitosan-citric acid crosslinking (molecular weight 120 kDa, deacetylation degree 80%), the middle layer was hydroxypropyl methyl cellulose with a viscosity of 100 mPa·s, and the outer layer was Ca 2+ / Zn 2+ complex crosslinked sodium alginate-gelatin.

[0277] (2) 4.0 wt% of a compound amino acid (mainly soybean protein hydrolysate, with a free amino acid content of about 80%, and glutamic acid and aspartic acid accounting for 30 wt%) was added to the above solution and stirred for another 15 minutes;

[0278] (3) Potassium fulvic acid with a molecular weight of 4000 Da (1.6 wt%) was added and stirred for 20 minutes, and the pH was adjusted to 5.5±0.2;

[0279] (4) EDTA chelated calcium, magnesium and zinc complex solution (total concentration 0.3 wt%) in a mass ratio of 1:1:1 was added and stirred for 40 minutes to ensure uniform complexation;

[0280] (5) A compound plant extract solution (total amount 0.8 wt%) formed by mixing loquat leaf extract, honeysuckle flower extract and licorice extract in a ratio of 1:1:1 was added and stirred for 10 minutes; wherein the loquat leaf extract, honeysuckle flower extract and licorice extract were all prepared according to the conventional water extraction or ethanol extraction method described in the specification, and standard commercial raw materials can also be used.

[0281] (6) After filtering out impurities, potassium sorbate (0.1 wt%) was added as a preservative, and stirred evenly to obtain the product. Comparative Example 5

[0282] (1) Disperse the three-layer coated L-selenomethionine (0.3 wt%) in purified water, keep the temperature at 40°C, stir and ultrasonic disperse for 5 minutes; the three-layer coated L-selenomethionine used in Comparative Example 5 is the same as that in Example 1, the inner layer is chitosan-limonene acid cross-linking (molecular weight 120 kDa, deacetylation degree 80%), the middle layer is hydroxypropyl methyl cellulose with viscosity 100 mPa-s, and the outer layer is Ca 2+ / Zn 2+ complex cross-linked sodium alginate-gelatin.

[0283] (2) Add 4.0 wt% of complex amino acids (mainly soy protein hydrolysate, free amino acid content about 80%, glutamic acid and aspartic acid total 30 wt%) to the above solution, continue stirring for 15 minutes, and adjust the pH to 6.0±0.2;

[0284] (3) Add potassium fulvate with molecular weight 4000 Da (1.6 wt%), continue stirring for 20 minutes, and adjust the pH to 5.5±0.2;

[0285] (4) Add 1:1:1 mass ratio of EDTA chelated calcium, magnesium and zinc complex solution (total concentration 0.3 wt%), stir for 40 minutes to ensure uniform complexation;

[0286] (5) After filtering out impurities, add potassium sorbate (0.1 wt%) as a preservative, stir uniformly, and obtain. Comparative Example 6

[0287] The difference between this comparative example and Example 1 is that the L-selenomethionine is pre-coated with three layers by the following raw materials and methods:

[0288] Step A: Form the inner layer of chitosan-limonene acid cross-linking

[0289] (1) Prepare a 1% (w / v) chitosan (molecular weight 120 kDa, deacetylation degree 80%) solution (dissolved in 0.5% acetic acid aqueous solution) and stir magnetically at 40°C until completely dissolved;

[0290] (2) Add L-selenomethionine raw powder and ultrasonic disperse for 10 minutes;

[0291] (3) Add 0.5% (w / v) citric acid solution dropwise to make chitosan react with citric acid at a molar ratio of 1:2.5, and stand at room temperature for 30 minutes for cross-linking;

[0292] (4) Collect the preliminary coated particles by centrifugation (5000 rpm, 10 min) and discard the supernatant.

[0293] Step B: Middle layer - hydroxypropyl methyl cellulose coating

[0294] (1) The above particles were re-dispersed in 50 mL water;

[0295] (2) A hydroxypropyl methylcellulose solution (viscosity of hydroxypropyl methylcellulose was 100 mPa-s, solution concentration was controlled to be 1 wt%, and was dissolved in advance under stirring at 40°C) was added;

[0296] (3) After low-speed stirring for 30 minutes, the double-layer particles were collected by centrifugation (5000 rpm, 10 min).

[0297] Step C: Outer layer-sodium alginate / gelatin+Ca 2+ Crosslinking

[0298] (1) Sodium alginate and gelatin were dissolved in a mass ratio of 1:1 in a 40°C water bath to prepare a mixed solution;

[0299] (2) The above double-layer particles were dispersed in the mixed solution, and uniformly stirred for 10 minutes;

[0300] (3) A pre-prepared CaCl2 crosslinking solution (Ca 2+ concentration was 0.25 wt%) was added dropwise, and stirring was performed during the addition for 15 minutes;

[0301] (4) The triple-layer coated particles were collected by the last centrifugation (5000 rpm, 10 min), washed twice with deionized water, and freeze-dried to obtain the finished product.

[0302] Performance test

[0303] 1. Organic selenium proportion determination

[0304] Method: The nutrient solution of each example and comparative example was used as a sample, and high performance liquid chromatography-inductively coupled plasma mass spectrometry (HPLC-ICP-MS) was used to detect the content proportion of organic selenium forms.

[0305] 2. Particle controlled release performance test

[0306] Method: The sample nutrient solution was placed in a pH=6.5 buffer solution at a constant temperature of 37°C, and samples were taken at regular time intervals (such as 0h, 6h, 12h, 24h, 48h), and the content of released selenomethionine was determined by HPLC.

[0307] T50 (time required for 50% release) and 24h release rate were calculated.

[0308] 3. Plant selenium absorption rate test

[0309] Crop model: Rice seedlings were selected as model crops.

[0310] Treatment: 7 days after spraying with different nutrient solution formulations, the selenium content in the aboveground part of the crops (mg / kg) was determined.

[0311] Detection method: After HNO3-H2O2 microwave digestion, ICP-MS was used to detect selenium.

[0312] Absorption efficiency: Based on the amount of selenium applied, the selenium transfer rate was calculated (selenium content in crops / selenium application amount x 100%).

[0313] 4. Stability test

[0314] Objective: To investigate the physicochemical stability of liquid nutrient solution under storage conditions.

[0315] Conditions: After 30 days of storage at room temperature in the dark, observe the precipitation, pH change and selenium content loss.

[0316] The test results are shown in Tables 1-4 below.

[0317] Table 1 Organic selenium proportion test results

[0318] Sample Organic selenium ratio / % 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

[0319] Due to the different complex protection effects of free amino acids, glutamic acid / aspartic acid ratio, potassium fulvate and plant extracts in the formula, there are certain differences in the organic selenium results of each example. However, samples using selenium methionine all showed >96% organic selenium results, while Comparative Example 1 showed only 2.1% for selenium methionine detection because it used inorganic selenium.

[0320] Table 2 Particle controlled release performance test results

[0321] Sample T50 / h 24 h 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

[0322] According to the test results in Table 2, the three-layer coating (Example 1, Example 2, Example 3, Example 5) using "chitosan-citric acid inner layer + HPMC middle layer + sodium alginate / gelatin-Ca 2+ / Zn 2+ outer layer" can stably achieve a sustained release effect of T50 about 21-22 h and 24 h release rate about 57%-60%; the uncoated sample (Example 4) shows a burst release phenomenon with T50 about 1.6 h and 24 h release rate about 96%; Ca 2+ single crosslinking (Comparative Example 6) has moderate sustained release performance (T50 about 9.4 h), while Comparative Example 4 with loose outer layer structure and optimized pH at S1 stage releases faster (T50 is shortened and 24 h release rate is increased); the difference in amino acid formula (Example 5 vs. Example 1, Comparative Example 2 vs. Example 1) has less effect on the viscoelastic properties of the diffusion interface, and the controlled release performance is generally similar.

[0323] Table 3 Test results of selenium absorption rate of plants

[0324] Sample Above-ground 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

[0325] As can be seen from Table 3, the transference rate of selenium of the seedlings of Example 1 and Example 3 is the highest (≥67%), which is due to the synergistic effect of the slow-release coating combined with high free degree of complex amino acids, potassium fulvic acid and plant extracts, significantly enhancing complexation on the root surface, transmembrane transport and antioxidant protection; Example 2 is slightly lower due to the decrease in the proportion of effective ingredients, but is still better than the uncoated and the control, Example 4 is uncoated, resulting in burst release, environmental loss and decreased absorption efficiency, Comparative Example 1 has the lowest absorption of inorganic selenium (37.6%); Comparative Example 2 has insufficient free amino acid mass and low Glu / Asp ratio, and the transmission and complexation performance is limited, and the transference rate is reduced to about 49%; Comparative Example 3 lacks potassium fulvic acid, and Comparative Example 5 lacks plant extracts, and is slightly lower than Example 1 due to the decrease in complexation sites or the decrease in antioxidant / membrane stability; Comparative Example 6 only has Ca 2+ The cross-linking absorption rate is between Example 5 and Example 2, which is consistent with the moderate burst release, and Comparative Example 4 has insufficient colloidal stability due to the non-optimized pH, and the absorption rate is at a moderate level.

[0326] Table 4

[0327] 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

[0328] As can be seen from the test results in Table 4, the three-layer coating and the Ca 2+ / Zn 2+ The selenium loss of Example 1, Example 2, Example 3 and Example 5 in the potassium fulvic acid-containing system is not more than 2%, which is consistent with the multi-point coordination and ion bridge structure of the outer metal-polypeptide-polysaccharide; Example 4 is uncoated and Comparative Example 6 only has Ca 2+ The cross-linking appears more obvious activity loss and pH drift, and Comparative Example 1, the inorganic selenium sample, has the highest loss due to the easy valence state conversion, yellowing and ligand replacement, and Comparative Examples 2, 3, 4 and 5 have slightly poorer stability than Example 1 due to insufficient ligand mass, lack of potassium fulvic acid, non-optimized pH or lack of plant antioxidant molecules.

[0329] The above is only a preferred embodiment of the present application, and the protection scope of the present application is not limited to the above-mentioned embodiments, and any technical solution falling within the concept of the present application shall fall within the protection scope of the present application. It should be noted that for ordinary technical personnel in the technical field, some improvements and refinements without departing from the principles of the present application shall also be considered as the protection scope of the present application.

Claims

1. An organic selenium nutrient solution for crops, characterized by, by mass percentage, comprising the following components: Selenomethionine 0.1-0.5%; Complex amino acid 2.0-5.0%; The complex amino acid comprises an amino acid mixture mainly composed of soy protein hydrolysate; Potassium humate 1.0-3.0%; Plant extract 0.5-1.0%; EDTA chelated calcium, magnesium and zinc 0.05-0.5%; The mass ratio of calcium, magnesium and zinc is 1:1:1; Potassium sorbate 0.05-0.2 wt%; Purified water in residual amount; The selenomethionine is L-type selenomethionine, and the L-type selenomethionine is treated with three-layer coating, the three-layer coating from inside to outside is an inner layer formed by cross-linking of chitosan-citric acid, an intermediate layer formed by hydroxypropyl methyl cellulose coating, and an outer layer formed by sodium alginate-gelatin coating; The outer layer is further cross-linked by complex ions of CaCl2 and ZnCl2, and Zn 2+ concentration is Ca 2+ 5-15%; The plant extract is a complex prepared by mixing loquat leaf extract, honeysuckle extract and licorice extract at a mass ratio of 1:1:1; The complex amino acid contains 50-90 wt% of free amino acids, wherein the total content of glutamic acid and aspartic acid is not less than 30 wt%; The potassium humate is potassium fulvate with a molecular weight of 3000-5000 Da.

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

3.

3. The organic selenium nutrient solution for crops according to claim 2, characterized by, The viscosity of the hydroxypropyl methyl cellulose of the intermediate layer is 60-100 mPa·s.

4. The organic selenium nutrient solution for crops according to claim 1, characterized by, The mass ratio of the three of the complex amino acid, potassium humate and plant extract is 5:2:

1.

5. A method for preparing the organic selenium nutrient solution for crops according to any one of claims 1 to 4, characterized by, The following steps are included: S1. Mix and dissolve selenomethionine and complex amino acid in purified water in proportion, and adjust the pH to 6.0±0.2; S2. Add potassium humate to the above solution, adjust the pH to 5.5±0.2, and stir uniformly; S3. Add plant extract to the above solution, adjust the pH to 5.5±0.2, and stir uniformly; S4. Add EDTA chelated calcium, magnesium and zinc to the above solution, and continue to stir uniformly; S5. After filtration, add potassium sorbate and stir uniformly.