Amino acid type nano-selenium nutrient and preparation method thereof

Abstract

The present invention relates to an amino acid type nano-selenium nutrient, comprising the following raw materials in parts by mass: 30-40 parts of nano-selenium sol, 10-15 parts of modified chitosan, 12-18 parts of composite amino acids, 3-5 parts of selenoamino acids, 2-3 parts of humic acid, and 200-500 parts of water; the modified chitosan is chitosan modified by thiol and gallic acid. The amino acid type nano-selenium nutrient provided by the present invention uses modified chitosan as a dispersant / protectant to fully protect nano-selenium, can be used in both selenium-rich and selenium-poor areas, and has a wide range of applications for crops, high selenium absorption efficiency of crops, high conversion rate, reliable and stable, and easy to transport and store, and has obvious advantages of practicality and industrialization in agriculture.

Description

Technical Field

[0001] The invention belongs to the technical field of fertilizers, and particularly relates to an amino acid type nano-selenium nutrient and a preparation method thereof. Background Art

[0002] Selenium is one of the essential trace elements for the human body. It has three biological functions: nutrition, anti-oxidation, and detoxification. It can improve human immunity, promote the proliferation of lymphocytes and the production of immunoglobulins IgM and IgG. It has synergistic antioxidant effects with nutrients such as vitamin E, allicin, linoleic acid, germanium, and zinc, and increases antioxidant activity. Literature reports that more than 40 human diseases such as cancer, heart disease, and diabetes are related to selenium deficiency in the body. The selenium element in the human body mainly comes from external intake, so various selenium-rich agricultural products are currently popular on the market. Compared with ordinary agricultural products, organic selenium agricultural products have a significant sales premium. In the early stage, selenium-rich fertilizers were mainly inorganic selenium. After fertilization, crops often cannot absorb and utilize oxide forms. There are problems of insufficient utilization of selenium and serious loss, resulting in a waste of selenium resources. In the later development, organic selenium, especially amino acids containing selenium, are mainly used as effective selenium components, and the absorption and utilization of selenium has been improved. However, there are still defects that crops do not absorb selenium sufficiently and selenium resources in fertilizers cannot be effectively utilized.

[0003] At present, the main types of selenium-enriched fertilizers for agricultural products and products are as follows: inorganic selenium, Na2SeO3 and Na2SeO4 are the most studied, water-soluble selenate is absorbed by the root system of crops, with poor absorption and conversion, easy to accumulate and produce pollution, and a small amount of application cannot achieve the purpose of selenium enrichment, and a large amount of application will cause uneven distribution of selenium in the soil, and will cause selenium poisoning; organic selenium (generally polypeptide selenium or amino acid chelated selenium), dissolved contains unconverted inorganic selenium, and the price is generally expensive; yeast selenium, the current product is suitable for animals, and is rarely involved in the selenium enrichment strategy for agricultural products; mineral selenium powder, poor absorption, can only be used in the roots; nano-selenium (red zero-valent amorphous selenium), can be quickly absorbed, absorbed by the root of the shell or absorbed through the leaf surface, promoting the absorption and conversion of selenium. Nano-selenium is currently a hot spot in the research and development of selenium-enriched fertilizers for agricultural products. Studies have shown that nano-selenium has the ability to regulate the small molecule signal transduction pathways of crop growth hormones, enhance the activity of enzymes such as crop GSH, and has a significant effect on activating crop health compared with inorganic selenium salts.

[0004] CN102391053A discloses a nano-selenium amino acid foliar fertilizer, including composite amino acids, nano-selenium, biodegradable surfactants and trace elements. CN106892755A discloses an amino acid foliar fertilizer containing nano-selenium, which is prepared by mixing selenious acid and platycodon polysaccharide, adding ascorbic acid to prepare a nano-selenium solution, and compounding it with soybean meal composite amino acids and humic acid to obtain a foliar fertilizer. CN108569933A discloses a probiotic foliar fertilizer containing nano-selenium and rare earth elements, including nano-selenium, rare earth elements, and nutrients. CN104058879A discloses a composite amino acid chelated nano-selenium foliar fertilizer, which is obtained by adding sugar alcohol to the enzymatic hydrolyzate of hemoglobin powder, and then adding nano-selenium and nano-titanium dioxide to finally obtain a foliar fertilizer. Although some amino acids in the compound of nano-selenium and amino acids in the above patent have a certain protective and stabilizing effect on nano-selenium, a large part of the nano-selenium is converted into gray or black selenium with low biological activity during transportation and storage, or before being absorbed and utilized by crops after spraying.

[0005] The existing technology also uses bio-friendly surfactants or sugars as stabilizers / stabilizers to protect nano-selenium, but these substances cannot be absorbed and utilized as nutrients for crops. In addition, this type of dispersant / stabilizer system is sensitive to pH, and nano-selenium particles will still aggregate under acidic conditions. The storage conditions are harsh and sensitive, and the thermal stability is poor, which easily loses the special activity of nano-selenium. Summary of the invention

[0006] In order to solve the problem that the red nano-selenium in the selenium-rich fertilizer or nutrient based on nano-selenium in the prior art is unstable and easily converted into other forms of selenium that are difficult to be absorbed and utilized by crops, thereby greatly reducing the absorption of nano-selenium. The present invention proposes an amino acid-type nano-selenium nutrient and a preparation method thereof. By using modified chitosan as a dispersant / protectant, nano-selenium is fully protected and can be used in both selenium-rich and selenium-poor areas. It is also widely applicable to crops, including food crops such as rice, wheat, corn, millet, and soybeans, and fruits and vegetables such as vegetables and potatoes, as well as tea, Panax notoginseng, and other economic or medicinal crops. The nano-amino acid-type selenium-rich nutrient provided by the present invention has high selenium absorption efficiency for crops, high conversion rate, reliable and stable, and is easy to transport and store, and has obvious advantages of practicality and industrialization in agriculture.

[0007] The present invention provides the following technical solutions to solve the above technical problems:

[0008] The first object of the present invention is to provide an amino acid type nano-selenium nutrient, comprising the following raw materials in parts by mass: 30-40 parts of nano-selenium sol, 10-15 parts of modified chitosan, 12-18 parts of complex amino acids, 3-5 parts of selenoamino acids, 2-3 parts of humic acid, and 200-500 parts of water; the modified chitosan is chitosan modified by thiol and gallic acid.

[0009] In the prior art, agricultural nutrients containing nano-selenium are mostly selenites reduced to selenium under the action of reducing agents (such as vitamin C). The main reason is that nano-selenium is unstable, and it is easy to agglomerate into black / grey selenium with low activity when placed for a long time. Its activity is poor and it is difficult to be absorbed and utilized by crops. However, in the nano-selenium system of selenite+reducing agent, nano-selenium only accounts for a very small part of the selenium source, and it cannot be called a real "nano-selenium" nutrient. Moreover, due to different farmlands, the types of crops vary greatly, and the differences in soil acidity / alkalinity, after agricultural irrigation and fertilization of such selenite+reducing agent nutrients, the actual nano-selenium that stannate can be prepared by the reducing agent will vary greatly in different regions, and the scope of application is poor. The present invention directly adopts nano-selenium sol, cooperates with specific raw materials to achieve the best compatibility, and nano-selenium can be stably present after preparing the mother liquor, which is convenient for transportation and storage. Compared with inorganic selenium+reducing agent, the technical solution of the present invention belongs to the second generation of nano-selenium nutrient, which can be quickly and effectively absorbed and utilized by crops, and will not cause adverse effects on the soil, and the absorption and utilization efficiency of selenium is high.

[0010] In the present invention, the nano-selenium exists in the form of nano-selenium sol, wherein the average particle size of the nano-selenium is 20-200nm, preferably 50-100nm, and the concentration of the nano-selenium sol is 2000-5000ppm.

[0011] The modified chitosan is prepared by a preparation method comprising the following steps: chitosan, mercapto carboxylic acid and gallic acid are subjected to condensation reaction in the presence of a condensing agent to prepare the modified chitosan.

[0012] Furthermore, the condensation reaction is carried out in a dilute acid aqueous solution at room temperature and in the dark for 5-10 hours, and the dilute acid is selected from 1-3wt% hydrochloric acid and / or 1-3wt% acetic acid. After the reaction is completed, dialysis is performed, specifically using 5-20mM hydrochloric acid solution, 1-2wt% NaCl solution, and deionized water for 24-48 hours. After the dialysis is completed, freeze drying is performed to obtain modified chitosan. The freeze drying process is not particularly limited and is well known in the art. In a specific embodiment of the present invention, freeze drying is performed in a freeze dryer at -40 to -30°C and 10-100Pa vacuum conditions for 3-5 hours.

[0013] Furthermore, the molecular weight of the chitosan before modification is 500-700 kDa, and the degree of deacetylation is 82-87%. For example, the molecular weight is 600 kDa, and the degree of deacetylation is 86%.

[0014] Furthermore, the mercaptocarboxylic acid is selected from at least one of mercaptoacetic acid, mercaptopropionic acid, mercaptobutyric acid, mercaptosuccinic acid, and mercaptocaproic acid, preferably a composite mercaptocarboxylic acid of mercaptoacetic acid and mercaptosuccinic acid in a molar ratio of 4-7:1; the molar ratio of mercaptocarboxylic acid and gallic acid is 1-2:1-2; the mass ratio of chitosan and the modifier is 100:15-22. The modified chitosan is modified with abundant thiol and polyphenol groups, which play a synergistic role and jointly enhance the protective effect on nano-selenium. The inventors found that when the mass ratio of chitosan and the modifier is the same, only when the chitosan is modified by mercaptocarboxylic acid and gallic acid together, can the best protective effect on nano-selenium be achieved. The use of a single mercaptocarboxylic acid or a single gallic acid cannot achieve the effect of the two being used together, indicating that the modification of chitosan by mercaptocarboxylic acid and gallic acid has a certain synergistic effect.

[0015] The condensing agent is selected from at least one of carbodiimide hydrochloride (EDAC), 1-ethyl-(3-dimethylaminopropyl) carbodiimide (EDC), and N-hydroxysuccinimide (NHS); the amount of the condensing agent is 1.0-1.1 times the total amount of the mercaptocarboxylic acid and gallic acid.

[0016] Further, the composite amino acid is selected from at least one of cysteine, alanine, aspartic acid, threonine, serine, glutamic acid, valine, isoleucine, methionine, glycine, lysine, histidine, tyrosine, arginine and proline, and the content of cysteine ​​accounts for 10-20wt%. Cysteine ​​contains sulfhydryl (-SH) and can better have affinity with nano-selenium. However, the content of cysteine ​​is not easy to be too high, otherwise it can not achieve the best effect of promoting selenium absorption.

[0017] In a preferred technical solution of the present invention, the composite amino acid is a mixed amino acid of glutamic acid, arginine, lysine and cysteine ​​in a mass ratio of 35-50:20-30:20-30:10-20.

[0018] The selenoamino acid is selected from at least one of selenocysteine, selenomethylcysteine ​​and selenomethionine. Preferably, selenocysteine ​​and selenomethionine are compounded in a mass ratio of 1-5:1-5, and more preferably, selenocysteine ​​and selenomethionine are compounded in a mass ratio of 1:2-4. On the one hand, selenoaminoamino acid has the inherent effect of amino acids, and on the other hand, as organic selenium, it is a beneficial supplement to the nano-selenium of the present invention. The combined absorption of nano-selenium and organic selenium by crops significantly promotes the purpose of selenium enrichment of crops.

[0019] The second object of the present invention is to provide a method for preparing the nano-amino acid type selenium-rich nutrient, comprising the following steps: dissolving the modified chitosan in water, slowly adding the nano-selenium sol, stirring and dispersing evenly under ultrasonic conditions, then adding the composite amino acid, selenoamino acid and humic acid, and continuing to stir until a uniform state to obtain a liquid selenium-rich nutrient. If necessary, the liquid selenium-rich nutrient can also be freeze-dried into a freeze-dried powder, and when used, the freeze-dried powder only needs to be dissolved and diluted with an appropriate amount of water.

[0020] Preferably, the modified chitosan is dissolved in water by heating to 50-60° C. and stirring until the system becomes a homogeneous liquid phase.

[0021] The third object of the present invention is to provide the use of the nano-amino acid type selenium-rich nutrient in crop planting, and the crops include but are not limited to rice, wheat, corn, millet, soybean, strawberry, watermelon, pepper, sweet potato, tea, and Panax notoginseng.

[0022] The selenium-rich nutrient is applied to crops by diluting the selenium-rich nutrient to 50-100 times, spraying 50-100 kg of the selenium-rich nutrient dilution per mu of crops, and spraying 1-3 times during the crop growth cycle, such as spraying wheat once in the jointing stage and the filling stage, spraying corn once in the jointing stage and the large trumpet mouth, spraying beans once in the early stage of pod formation, and spraying potatoes twice in the early stage of tuber formation. Spraying the selenium-rich nutrient of the present invention needs to avoid strong winds, dew and noon sun, generally before ten o'clock in the morning or between four and six o'clock in the afternoon.

[0023] The excellent effects of the present invention are:

[0024] 1. The chitosan modified by mercaptocarboxylic acid and gallic acid can provide good protection for nano-selenium, can be stably placed for a long time, and nano-selenium will not agglomerate. The selenium-enriched nutrient of the present invention can exist in the form of liquid reagent and freeze-dried powder. The freeze-dried powder is more conducive to transportation and storage, but if it is prepared locally, it can also be in the form of a liquid nutrient. When used, it is diluted with water to a suitable ratio, or used in combination with other liquid fertilizers.

[0025] Second, the present invention directly uses nano-selenium as a selenium source for crop selenium supplementation, which is essentially different from the prior art that uses inorganic selenate or selenite in a reducing agent state to obtain elemental selenium. This avoids the low conversion efficiency of inorganic selenium salts into nano-selenium in the presence of a reducing agent, and it is difficult to ensure the appropriate reaction conditions for converting selenite into nano-selenium in the field.

[0026] Third, the present invention uses compound amino acids and selenoamino acids to work together, which is beneficial to the absorption of nano-selenium by crops and is also a beneficial supplement of selenium sources, and can achieve the purpose of enriching crops with selenium for a long time. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a photo of the powdered selenium-rich nutrient prepared in Example 1 of the present invention.

[0028] Figure 2 This is a photograph of the powdered selenium-rich nutrient prepared in Example 1 of the present invention diluted 100 times with clean water and stored at room temperature for 1 month.

[0029] Figure 3 This is a photograph of the powdered selenium-rich nutrient prepared in Example 3 diluted 100 times with clean water and stored at room temperature for 1 month. DETAILED DESCRIPTION

[0030] To make the purpose, technical scheme and advantages of the present invention clearer, the technical scheme of the present invention will be described in detail below. The following examples are convenient for better understanding of the present invention, but are not intended to limit the present invention. The experimental methods in the following examples are conventional methods unless otherwise specified.

[0031] The parts described in the embodiments of the present invention, unless otherwise specified, are parts by mass. The "%" described, unless otherwise specified, are percentages by mass.

[0032] Chitosan was purchased from Shandong Yatu Biotechnology, with a molecular weight of approximately 600 kDa and a degree of deacetylation of 86%.

[0033] Nano-selenium sol was purchased from Yantai Jialong Nano Co., Ltd., where the average particle size of nano-selenium was 80 nm and the selenium content was 3000 ppm.

[0034] Preparation Example 1

[0035] 100 parts of chitosan are dissolved in a 1wt% acetic acid solution, 22 parts of a modifier (the modifier is a mixture of mercaptocarboxylic acid and gallic acid in a molar ratio of 1:1, and the mercaptocarboxylic acid is a composite mercaptocarboxylic acid of mercaptoacetic acid and mercaptosuccinic acid in a molar ratio of 4:1), and an appropriate amount of EDAC (the amount of EDAC is 1 times the amount of the total amount of carboxyl groups in the modifier) ​​as a condensing agent are added, and the mixture is reacted at room temperature and in a dark environment for 8 hours. After the reaction is completed, the mixture is dialyzed with 1% acetic acid, 3% NaCl, and deionized water for 24 hours in sequence, and the total dialyzation is 3 days; after the dialysis, the mixture is freeze-dried in a freeze dryer at minus 30° C. and 100 Pa for 5 hours, and the mixture is restored to room temperature to obtain a modified chitosan freeze-dried powder.

[0036] Preparation Example 2

[0037] Other conditions are the same as those in Preparation Example 1, except that the amount of the modifier is 15 parts, and the modifier is a mixture of mercaptocarboxylic acid and gallic acid in a molar ratio of 1:2, and the mercaptocarboxylic acid is a composite mercaptocarboxylic acid of thioglycolic acid and mercaptosuccinic acid in a molar ratio of 7:1.

[0038] Preparation Example 3

[0039] The other conditions were the same as those in Preparation Example 1, except that mercaptosuccinic acid was replaced by an equimolar amount of mercaptobutyric acid.

[0040] Preparation Example 4

[0041] The other conditions are the same as those in Preparation Example 1, except that the mercaptocarboxylic acid is thioglycolic acid.

[0042] Preparation Example 5

[0043] The other conditions are the same as those in Preparation Example 1, except that the mercaptocarboxylic acid is mercaptosuccinic acid.

[0044] Comparative Preparation Example 1

[0045] The other conditions were the same as those in Preparation Example 1, except that the modifier was a composite mercaptocarboxylic acid of thioglycolic acid and mercaptosuccinic acid in a molar ratio of 4:1, that is, gallic acid was not added.

[0046] Comparative Preparation Example 2

[0047] The other conditions were the same as those in Preparation Example 1, except that the modifier was gallic acid, that is, no mercapto-containing carboxylic acid was added.

[0048] Comparative Preparation Example 3

[0049] Chitosan was used directly without modification.

[0050] Effect example

[0051] 15 parts of the modified chitosan freeze-dried powder obtained in the above preparation examples and comparative preparation examples were dissolved in 300 parts of 1% hydrochloric acid aqueous solution, 30 parts of nano-selenium sol were added, and the mixture was uniformly mixed to obtain a nano-selenium-chitosan composite solution system. The system particles were placed under 65±5RH%, 25±2℃ for 60 days, and the Zeta potential of the system particles was tested. The Zeta potential was used to represent the stability of the system nanoparticles. The higher the Zeta potential, the better the stability. The results are shown in Table 1 below.

[0052] Table 1 Zeta potential test

[0053]

[0054]

[0055] Example 1

[0056] Add 15 parts of the modified chitosan freeze-dried powder obtained in Preparation Example 1 to 300 parts of water, raise the temperature to 50°C, and stir until the modified chitosan freeze-dried powder is dissolved in water to form a uniformly mixed liquid phase system, slowly add 30 parts of nano-selenium sol, and add the whole within 1 hour, stir under ultrasonic conditions until the system is uniformly mixed, then add 12 parts of composite amino acids (glutamic acid, arginine, lysine, cysteine ​​in a mass ratio of 40:20:30:10), 5 parts of selenoamino acids (selenocysteine ​​and selenomethionine in a mass ratio of 1:2), and 2 parts of humic acid, continue stirring until the mixture is uniform, and freeze-dry at -40°C, 100Pa for 24 hours to obtain a freeze-dried powder, which is a powdered selenium-rich nutrient product of the present invention.

[0057] Example 2

[0058] The other conditions are the same as those in the operation and Example 1, except that the modified chitosan freeze-dried powder is prepared in Preparation Example 2.

[0059] Example 3

[0060] The other conditions are the same as those in the operation and Example 1, except that the modified chitosan freeze-dried powder is prepared in Preparation Example 3.

[0061] Example 4

[0062] The other conditions are the same as those in the operation and Example 1, except that the modified chitosan freeze-dried powder is prepared in Preparation Example 3.

[0063] Example 5

[0064] The other conditions are the same as those in the operation and Example 1, except that the modified chitosan freeze-dried powder is prepared in Preparation Example 5.

[0065] Example 6

[0066] Other conditions are the same as the operation and Example 1, except that the composite amino acid is a compound of glutamic acid, arginine, lysine, and cysteine ​​in a mass ratio of 40:20:20:20, and the amount of the composite amino acid is 18 parts; the selenoamino acid is a compound of selenocysteine ​​and selenomethionine in a mass ratio of 1:4, and the amount of the selenoamino acid is 3 parts.

[0067] Example 7

[0068] Other conditions are the same as those in the operation and Example 1, except that the composite amino acid is a compound of glutamic acid, arginine, lysine, and cysteine ​​in a mass ratio of 35:20:20:25.

[0069] Example 8

[0070] Other conditions are the same as those in the operation and Example 1, except that the composite amino acid is a compound of glutamic acid, arginine, lysine, and cysteine ​​in a mass ratio of 50:25:20:5.

[0071] Example 9

[0072] Other conditions were the same as those in Example 1, except that the selenoamino acid was a single selenocysteine.

[0073] Example 10

[0074] Other conditions were the same as those in Example 1, except that the selenoamino acid was single selenomethionine.

[0075] Comparative Example 1

[0076] The other conditions are the same as those in the operation and Example 1, except that the modified chitosan freeze-dried powder is prepared in Comparative Preparation Example 1.

[0077] Comparative Example 2

[0078] The other conditions are the same as those in the operation and Example 1, except that the modified chitosan freeze-dried powder is prepared in Comparative Preparation Example 2.

[0079] Comparative Example 3

[0080] The other conditions were the same as those in the operation and Example 1, except that the modified chitosan freeze-dried powder was replaced with commercial chitosan, i.e., the unmodified chitosan in Comparative Preparation Example 3.

[0081] Figure 1 This is a photo of the powdered selenium-rich nutrient prepared in Example 1 of the present invention.

[0082] Figure 2 This is a photograph of the powdered selenium-rich nutrient prepared in Example 1 of the present invention diluted 100 times with clean water and stored at room temperature for 1 month.

[0083] Figure 3 This is a photo of the powdered selenium-rich nutrient prepared in Example 3 diluted 100 times with clean water and stored at room temperature for 1 month. Figure 2 and Figure 3 It can be clearly seen from the comparison that if chitosan is not modified, the diluted nano-selenium solution is not stable enough. There is obvious sedimentation after being stored at room temperature for one month, and the red color of the solution becomes lighter, indicating that part of the red nano-selenium has aggregated and turned into black or gray selenium with low activity, proving that the unmodified chitosan does not have an adequate protective effect on nano-selenium.

[0084] Application Examples

[0085] Test location: farm in Huangfan District, Xihua County, Zhoukou City, soil selenium content 0.14mg / kg. Test wheat variety: Fanmai No. 8.

[0086] Before sowing wheat, apply nitrogen, phosphorus and potassium compound fertilizer as base fertilizer (N: P2O5: K2O mass ratio is 10:5:2.3, 50kg of base fertilizer is applied per mu), the best urea is 8kg / mu in the jointing stage, and 3kg / mu of urea is added in the filling stage. Other operations are carried out according to normal field management. The freeze-dried powder of the selenium-rich nutrient obtained in the above embodiments and comparative examples is dissolved in 100 times water to obtain a dilution, and 50kg of the above selenium-rich nutrient dilution is applied per mu, and sprayed once each in the jointing stage and the filling stage. The control group (CK) replaces the selenium-rich nutrient dilution with clean water. After the wheat matures, it is threshed and dried. The selenium content of the wheat grains is tested by the mixed sampling method in accordance with the GB / 5009.268-2016 standard. The results are shown in Table 2 below:

[0087] Table 2 Selenium content test of wheat grains

[0088]

Claims

1. An amino acid type nano-selenium nutrient, characterized in that: The invention comprises the following raw materials in parts by weight: 30-40 parts of nano-selenium sol, 10-15 parts of modified chitosan, 12-18 parts of complex amino acids, 3-5 parts of selenoamino acids, 2-3 parts of humic acid, and 200-500 parts of water; the modified chitosan is prepared by a preparation method comprising the following steps: chitosan, mercapto carboxylic acid, and gallic acid are subjected to condensation reaction in the presence of a condensing agent to prepare the modified chitosan, wherein the modifier is a mixture of mercapto carboxylic acid and gallic acid; the amount of the condensing agent is the sum of the carboxyl groups of the mercapto carboxylic acid and gallic acid. The present invention relates to a method for preparing the chitosan modified organic compound of claim 10, wherein the amount of the modified organic compound is 1 times the amount of the substance; the thiol carboxylic acid is a composite thiol carboxylic acid of thioglycolic acid and thiosuccinic acid in a molar ratio of 4-7:1; the molar ratio of the thiol carboxylic acid to gallic acid is 1-2:1-2; the mass ratio of chitosan to the modifier is 100:15-22; the condensation reaction is carried out in a dilute acid aqueous solution at room temperature and in the dark for 5-10 hours, the dilute acid is 1-3wt% acetic acid, the reaction is dialyzed after the reaction is completed, and after the dialysis is completed, the modified chitosan is freeze-dried to obtain the modified chitosan; the molecular weight of the chitosan before modification is 500-700 kDa, and the degree of deacetylation is 82-87%; the condensation agent is selected from at least one of carbodiimide hydrochloride (EDAC), 1-ethyl-(3-dimethylaminopropyl) carbodiimide (EDC), and N-hydroxysuccinimide (NHS).

2. The amino acid type nano-selenium nutrient according to claim 1, characterized in that: The average particle size of nano-selenium in the nano-selenium sol is 20-200nm, and the concentration of the nano-selenium sol is 2000-5000ppm.

3. The amino acid type nano-selenium nutrient according to claim 2, characterized in that: The average particle size of nano-selenium in the nano-selenium sol is 50-100nm.

4. The amino acid type nano-selenium nutrient according to claim 1, characterized in that: Dialysis was performed using 1% acetic acid, 3% NaCl, and deionized water in sequence, with a dialysis time of 24-48 hours.

5. The amino acid type nano-selenium nutrient according to claim 1, characterized in that: The composite amino acid is selected from at least one of cysteine, alanine, aspartic acid, threonine, serine, glutamic acid, valine, isoleucine, methionine, glycine, lysine, histidine, tyrosine, arginine and proline, and the content of cysteine ​​is 10-20wt%.

6. The amino acid type nano-selenium nutrient according to claim 5, characterized in that: The composite amino acid is a mixed amino acid of glutamic acid, arginine, lysine and cysteine ​​in a mass ratio of 35-50:20-30:20-30:10-20.

7. The amino acid type nano-selenium nutrient according to claim 1, characterized in that: The selenoamino acid is selected from at least one of selenocysteine, selenomethylcysteine ​​and selenomethionine.

8. The amino acid type nano-selenium nutrient according to claim 7, characterized in that: The selenoamino acid is a compound of selenocysteine ​​and selenomethionine in a mass ratio of 1-5:1-5.

9. The amino acid type nano-selenium nutrient according to claim 7, characterized in that: The selenoamino acid is a compound of selenocysteine ​​and selenomethionine in a mass ratio of 1:2-4.

10. The method for preparing the amino acid type nano-selenium nutrient according to any one of claims 1 to 9, characterized in that: The method comprises the following steps: dissolving modified chitosan in water, slowly adding nano-selenium sol, stirring and evenly dispersing under ultrasonic conditions, then adding composite amino acids, selenoamino acids and humic acid, and continuing to stir until uniform to obtain liquid nano-selenium nutrient.

11. The preparation method according to claim 10, characterized in that: The liquid nano-selenium nutrient is freeze-dried into freeze-dried powder.

12. The preparation method according to claim 10, characterized in that: The modified chitosan is dissolved in water by heating to 50-60° C. and stirring until the system becomes a homogeneous liquid phase.

13. Use of the amino acid-based nano-selenium nutrient according to any one of claims 1 to 9 in crop planting, wherein the crops include rice, wheat, corn, millet, soybean, strawberry, watermelon, pepper, sweet potato, tea, and Panax notoginseng.

14. The use according to claim 13, characterized in that The nano-selenium nutrient is applied to crops by diluting the freeze-dried powder of the nano-selenium nutrient with clean water to 50-100 times, spraying 50-100kg of the diluted nano-selenium nutrient solution per acre of crops, and spraying 1-3 times during the growth cycle of the crops.

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