Selenium fertilizer formula and application method thereof

Abstract

The invention provides a selenium fertilizer formula and an application method, the formula comprises selenite, citric acid, nano silica gel, humic acid-chitosan and other components, and stable loading and pH response release of selenium element are realized through a three-stage chelating system. The citric acid and Se < 4 + > form a [SeO3.C6H5O7] < 3-> complex, the nano silica gel (with the aperture of 3 nm) is used for physical adsorption, and the humic acid-chitosan film is swelled and released when the pH value is 6.5. Polyglutamic acid inhibits selenium-iron antagonism, and ammonium molybdate activates selenite reductase. Soil basal application and foliage spraying are combined, so that the selenium absorption rate of rice is increased to 78.3%, the selenium methionine proportion of tomatoes is 67.2%, and the selenium distribution uniformity (CV value is 12.3%) of citrus is improved. Proportionally, the invention verifies the significant advantages in stability, bio-availability and slow release characteristic.

Description

Technical Field

[0001] The present invention relates to the technical field of agricultural fertilizers, and specifically relates to a selenium fertilizer formula and its usage method. Background Art

[0002] Traditional selenium fertilizers have problems such as low conversion efficiency of selenium elements, poor stability, element antagonism, mismatch between the slow-release period and the selenium demand period of crops, and single application method. Although the prior art has proposed improvements, there are still problems such as serious selenium fixation due to the lack of a synergistic chelation mechanism, the pH-responsive release problem not being solved despite the improvement of the slow-release property, and too high an effective selenium loss rate due to photosensitivity. Therefore, there is an urgent need to develop a selenium fertilizer system that takes into account stability, biological effectiveness, and environmental adaptability. Summary of the Invention

[0003] The purpose of this part is to outline some aspects of the embodiments of the present invention and briefly introduce some preferred embodiments. Some simplifications or omissions may be made in this part, as well as in the abstract and title of the present application, to avoid obscuring the purpose of this part, the abstract, and the title. However, such simplifications or omissions cannot be used to limit the scope of the present invention.

[0004] In view of the problems existing in the above-mentioned prior art, the inventors of the present invention have proposed the present invention.

[0005] Therefore, the purpose of the present invention is to overcome the deficiencies in the prior art and provide a selenium fertilizer formula and its usage method.

[0006] To solve the above technical problems, the present invention provides the following technical solutions: A selenium fertilizer formula, comprising:

[0007] By mass percentage, it contains 15 - 25% of selenite, 8 - 12% of citric acid chelating agent, 10 - 18% of nano-porous silica gel carrier, 5 - 8% of humic acid-chitosan composite film material, 3 - 5% of polyglutamic acid, 0.5 - 1.5% of ammonium molybdate, 0.1 - 0.3% of vitamin B1, and the balance is a plant-derived amino acid mixture.

[0008] As a preferred scheme of the selenium fertilizer formula of the present invention, wherein: the pore diameter of the nano-porous silica gel carrier is 2 - 5 nm, and the specific surface area ≥ 300 m 2 / g.

[0009] As a preferred scheme of the selenium fertilizer formula of the present invention, wherein: the mass ratio of humic acid to chitosan in the humic acid-chitosan composite film material is 1:2.

[0010] To solve the above technical problems, the present invention also provides the following technical solutions: A method for preparing a selenium fertilizer, comprising the following steps:

[0011] (a) Chelate selenite with citric acid at pH 4.5 - 5.5 and 60 °C for 30 min;

[0012] (b) Load the complex obtained in step (a) onto a nano-silica carrier under a vacuum impregnation pressure of 0.08 MPa;

[0013] (c) Coating the loaded material with a humic acid - chitosan mixture, and the outlet temperature of spray drying is 70 °C.

[0014] To solve the above technical problems, the present invention also provides the following technical solutions: A method for using selenium fertilizer, including: When applying it as a soil base fertilizer, mix it with the base fertilizer at 2 - 3 kg / mu and deeply plow the soil by 20 cm.

[0015] As a preferred embodiment of the method for using selenium fertilizer described in the present invention, when spraying on the leaf surface, dilute it 500 times, the spraying amount is 30 L / mu, and spray it 2 times at an interval of 7 days.

[0016] As an application of the selenium fertilizer described in the present invention in cereal planting, the cereals include rice and wheat.

[0017] As an application of the selenium fertilizer described in the present invention in fruit and vegetable planting, the fruits and vegetables include tomatoes and citrus.

[0018] As a preferred embodiment of the selenium fertilizer formula described in the present invention, in the plant - derived amino acid mixture, the mass ratio of glutamic acid to proline is 3:1.

[0019] As a preferred embodiment of the selenium fertilizer formula described in the present invention, the coating rate of the humic acid - chitosan composite film material is ≥90%, and the film - forming thickness is 50 - 100 nm.

[0020] The beneficial effects of the present invention: Based on the dynamic chelation of citric acid and selenite, a pH - responsive complex is formed, which stably exists in the soil and can controllably release active selenium with the change of the plant internal environment, solving the problem that it is difficult to balance the stability and activity of traditional selenium fertilizers; through the physical adsorption of the nano - silica carrier and the slow - release synergy of the humic acid - chitosan coating, a multi - level loading structure is constructed to achieve the precise supply of selenium elements during the crop growth period; introducing polyglutamic acid to selectively chelate metal ions, effectively inhibiting the antagonistic precipitation of selenium with elements such as iron and zinc, and ensuring the biological availability of selenium; combining the activation effect of ammonium molybdate on selenium - metabolizing enzymes and the promotion of vitamin B1 on the synthesis of seleno - amino acids, significantly improving the organic conversion efficiency of selenium in plants, and finally forming a selenium nutrition fortification system integrating stability, efficient absorption and targeted conversion. Detailed implementation manners

[0021] To make the above - mentioned objects, features and advantages of the present invention more obvious and understandable, the following detailed description of the specific implementation manners of the present invention will be given in conjunction with the embodiments of the specification.

[0022] In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. However, the present invention may be practiced in other ways different from those described herein. Those skilled in the art can make similar generalizations without departing from the spirit of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed below.

[0023] Secondly, the so-called "one embodiment" or "embodiment" refers to specific features, structures, or characteristics that may be included in at least one implementation manner of the present invention. The appearances of "in one embodiment" in different places in this specification do not all refer to the same embodiment, nor are they separate or selectively exclusive embodiments from other embodiments.

[0024] Example 1

[0025] This embodiment provides a selenium fertilizer formula and its usage method. Specifically, it is a selenium fertilizer specialized for rice.

[0026] Formula: Sodium selenite 22%, citric acid 10%, nano-silica gel (pore size 3nm) 15%, humic acid-chitosan (1:2) 6%, polyglutamic acid 4%, ammonium molybdate 1.2%, vitamin B1 0.15%, glutamic acid-proline (3:1) the balance.

[0027] Preparation:

[0028] Stir and chelate sodium selenite and citric acid at pH 5.0 and 60°C for 30 minutes to form a light yellow complex;

[0029] Mix the complex with nano-silica gel, with a vacuum impregnation pressure of 0.08 MPa, and the loading rate is detected to be 92.3%;

[0030] Coat with a humic acid-chitosan solution (solid content 8%), with a spray drying outlet temperature of 70°C and a coating rate of 91.5%.

[0031] Application effect:

[0032] Selenium content in rice: 0.32 mg / kg (control group 0.05 mg / kg);

[0033] Glutathione peroxidase activity: increased by 280% (detected by ELISA);

[0034] Selenium volatilization loss rate: 5.7% (traditional formula 32%, determined by gas chromatography).

[0035] Furthermore, conduct an in-depth analysis of the principle:

[0036] Citric acid-Se chelation mechanism:

[0037] FT-IR analysis shows that after chelation of sodium selenite and citric acid at pH 5.0, the Se-O vibration peak shifts from 830 cm -1 / to 780 cm -1 / , indicating the formation of [SeO3·C6H5O7] 3- complex. This complex is stable at soil pH 4.5 - 5.5 and dissociates to release Se as the cell sap pH increases (pH 7.2) after entering the root system 4+ .

[0038] Silica gel carrier adsorption kinetics:

[0039] The nitrogen adsorption - desorption isotherm shows that the pore size of the nano - silica gel carrier is concentrated at 3.2 nm (calculated by the BJH method), which matches the molecular size of the citric acid - Se complex (2.8 nm), and a loading rate of 92.3% is achieved through capillary action

[0040] Chitosan membrane pH responsiveness:

[0041] Dynamic light scattering (DLS) detection shows that the swelling rate of the humic acid - chitosan coating suddenly increases to 120% at pH 6.5 (simulating the leaf surface stoma environment), resulting in membrane rupture and realizing the on - demand release of selenium on the leaf surface

[0042] Furthermore, when ammonium molybdate is removed, the activity of selenite reductase (SIR) in rice roots decreases to 8.7 U / mg (35.2 U / mg in the complete formula); when vitamin B1 is removed, the proportion of selenocysteine in grains decreases from 58% to 22%

[0043] Furthermore, 3 comparative examples were also designed, and the comparison results are as follows:

[0044] Group Formulation difference Comparison of key data Comparative example 1 Without citric acid, replaced with EDTA Selenium absorption rate decreased by 42%, soil fixation rate increased by 68% Comparative example 2 Without nano-silica gel, replaced with bentonite Selenium retention rate decreased by 35%, release peak delayed by 12 days Comparative example 3 Humic acid-chitosan ratio 1:1 Foliar selenium release rate is too fast, photolysis loss increased by 21%

[0045] Specifically, in Comparative Example 1 (without citric acid, using EDTA instead), the selenium absorption rate decreases from 78.3% to 45.2%, and the soil fixation rate increases from 7.2% to 68%

[0046] Specifically, although EDTA is a strong chelating agent (binding constant logK = 16.5), the hexadentate chelate ([Se - EDTA] 2- ) formed by it and selenite (SeO3 2- ) has extremely strong stability (FT - IR shows that the Se - O bond is fixed at 720 cm -1 / ). This structure is difficult to dissociate in plants, resulting in selenium not being released as the active form (Se 4+ or Se 2- ). While the present invention adopts the tridentate chelation of citric acid ([SeO3·C6H5O7] 3-) When the pH of the root cell sap increases (7.0 - 7.5), the complex dissociates due to the deprotonation of the carboxyl group (-COOH) of citric acid (characteristic peak at 780 cm -1 / disappears), thereby releasing selenium for plant absorption. Excessive chelation by EDTA instead hinders the biological availability of selenium, verifying the necessity of the dynamic chelation system.

[0047] In Comparative Example 2 (without nano-silica gel, using bentonite instead), the selenium retention rate decreased from 86.7% to 63.8%, and the release peak was delayed by 12 days.

[0048] This is because the average pore size of the layered structure of bentonite is 12 nm, which is much larger than the molecular size of the selenium complex (2.8 nm), resulting in low physical adsorption efficiency (loading rate only 41%). The mesoporous structure of nano-silica gel (3 nm) realizes molecular-level encapsulation through van der Waals forces and capillary action (loading rate 92.3%), and its surface hydroxyl groups (-OH) form a hydrogen bond network with the carboxyl groups of the humic acid-chitosan film, enhancing the carrier-envelope interface binding force (contact angle 105°). Due to the mismatch of pore size and weak interface binding force of bentonite, selenium is easily washed away by rain (leaching rate 37% vs 13% of the present invention).

[0049] In Comparative Example 3 (humic acid-chitosan ratio 1:1), the photolysis loss rate of foliar selenium increased from 6.2% to 27.3%.

[0050] This is because when the ratio of humic acid to chitosan is imbalanced (1:1), the amino groups (-NH2) of chitosan are over-crosslinked to form a rigid membrane structure (DSC shows that the glass transition temperature Tg increases from 70 °C to 95 °C), losing pH responsiveness. Under the ratio of 1:2 in the present invention, the phenolic hydroxyl groups (-OH) of humic acid form dynamic hydrogen bonds with the amino groups of chitosan, and at the leaf surface stomata (pH 6.5), the hydrogen bonds break, triggering membrane swelling (swelling rate 120%), and synchronously releasing selenium. In addition, the quinone groups (C=O) in humic acid absorb ultraviolet light (absorbance at 280 nm in UV-Vis detection is 0.85), and cooperate with the ultraviolet shielding effect of chitosan to reduce photolysis loss.

[0051] Example 2

[0052] This example provides a selenium fertilizer formula and its usage method. Specifically, a drip irrigation selenium fertilizer for tomatoes.

[0053] Formula adjustment: Sodium selenite 18%, citric acid 12%, nano-silica gel 12%, humic acid-chitosan 7%, polyglutamic acid 5%, ammonium molybdate 1.0%, vitamin B1 0.2%.

[0054] Application parameters:

[0055] Drip irrigation concentration: 0.1 g / L, once a week from flowering stage to fruit setting stage;

[0056] Selenium speciation transformation: The proportion of Se(IV) in the soil decreased from 58% to 22%, and the proportion of SeMet (selenomethionine) increased to 67% (detected by HPLC-MS).

[0057] Effect:

[0058] Selenium content in fruits: 0.15 mg / kg;

[0059] Fruit cracking rate: decreased by 42% (the traditional selenium fertilizer group decreased by 18%).

[0060] Furthermore, the mechanism of selenium speciation transformation is described as follows:

[0061] Antagonistic effect of polyglutamic acid:

[0062] X-ray diffraction showed that after adding polyglutamic acid, the intensity of the characteristic diffraction peak of Fe 3+ and SeO3 2- at 2θ = 28.3° decreased by 92%, proving that it inhibits the precipitation of Fe-Se through competitive chelation.

[0063] Verification of the molybdenum-selenium metabolic pathway:

[0064] Real-time fluorescence quantitative PCR (qRT-PCR) detection showed that the expression level of the SIR gene in the tomato roots of the present invention group increased by 4.3 times, while that of the control group (without ammonium molybdate) only increased by 1.2 times.

[0065] Design of the control group:

[0066] Group Formulation difference Comparison of key data Comparative example 4 Without polyglutamic acid Fruit selenium content decreased by 37%, fruit cracking rate increased by 24% Comparative example 5 Without humic acid-chitosan coating Selenium leaching amount increased by 58%, utilization rate decreased by 41% Comparative example 6 Using ordinary silica gel (pore size 10nm) Carrier adsorption rate decreased by 63%, release fluctuation increased by 29%

[0067] Specifically, in Control Group 4 (without polyglutamic acid), the selenium content in fruits decreased from 0.15 mg / kg to 0.09 mg / kg, and the fruit cracking rate increased from 6% to 18%.

[0068] This is because the carboxyl group (-COOH) of polyglutamic acid preferentially chelates Fe 3+ (binding constant logK = 8.3), inhibiting the formation of insoluble FeSeO3 by Fe 3+ and SeO3 2- . In the absence of polyglutamic acid, Fe 3+ combines with selenium to precipitate (XRD shows a significant intensity of the FeSeO3 peak), reducing the available selenium. In addition, polyglutamic acid reduces fruit cracking caused by water imbalance in fruits by regulating the cell osmotic pressure (the conductivity decreased by 42%).

[0069] In Control Group 5 (without humic acid-chitosan coating), the selenium leaching loss increased from 15% to 58%, and the utilization rate decreased from 68% to 41%.

[0070] After the absence of the coating, the selenium complex is directly exposed to the soil solution. Although nano-silica can adsorb part of the selenium, it cannot resist the competitive adsorption of Ca 2+ , Mg 2+ (the ion exchange capacity decreases from 1.8 meq / g to 0.5 meq / g). The hydrophobic layer of the humic acid-chitosan membrane (water contact angle 105°) blocks the penetration of cations, and its carboxyl group (-COOH) selectively adsorbs SeO3 2- (adsorption capacity 18.7 mg / g vs 6.2 mg / g in the membrane-free group), and controls the selenium release rate through slow release.

[0071] For Comparative Example 6 (ordinary silica gel, pore size 10 nm), the carrier adsorption rate decreases from 92.3% to 34%, and the release volatility increases from 3% to 29%.

[0072] Silica gel with a pore size of 10 nm has too large a pore size (> the size of the selenium complex 2.8 nm) and cannot form effective capillary adsorption (BJH pore volume 0.25 cm 3 / g vs 0.68 cm 3 / g), resulting in easy desorption of the selenium complex. In addition, the binding force between the large-pore carrier and the coating is weak (SEM shows an increase in interface cracks), and soil moisture fluctuations cause uncontrolled selenium release (standard deviation of release rate 0.12 vs 0.03).

[0073] Example 3

[0074] This example provides a selenium fertilizer formulation and its usage method. Specifically, a slow-release selenium fertilizer for citrus.

[0075] Formulation: Sodium selenite 20%, citric acid 9%, nano-silica 17%, humic acid-chitosan 8%, polyglutamic acid 3.5%, ammonium molybdate 1.5%.

[0076] Field experiment:

[0077] 3-year data: The selenium content in the fruit is stable at 0.12 - 0.14 mg / kg (inter-annual coefficient of variation < 8%);

[0078] Selenium distribution: peel: pulp = 1:3.2 (LA-ICP-MS imaging).

[0079] Comparative example (commercially available slow-release selenium fertilizer).

[0080] Long-term effect comparison:

[0081] Index This invention group Comparative example Fruit selenium content (mg / kg) 0.14±0.01 0.07±0.02 Selenium distribution uniformity (CV value) 12.3％ 38.7％ Soil selenium residue (%) 82.4 45.6

[0082] Furthermore, the differences in the adsorption and slow-release properties of the carrier materials:

[0083] As determined by the BET method in the present invention, the pore size of the nano-silica gel is 3.2 nm, which highly matches the molecular size (2.8 nm) of the citric acid-Se complex, and a loading rate of 92.3% is achieved through capillary action.

[0084] The hydroxyl groups (-OH) on the surface of the silica gel form hydrogen bond networks with the carboxyl groups of the humic acid-chitosan film, resisting the competitive adsorption of Ca 2+ and Mg 2+ in the soil.

[0085] The pore sizes of commercially available products do not match. The pore size between the swelling soil layers is >10 nm, and the selenium complex cannot be effectively adsorbed, resulting in the easy leaching of selenium by rainwater.

[0086] The interfacial binding force is weak. The bentonite and the coating material (polyvinyl alcohol) are combined only by physical mixing, and the fluctuation of soil moisture causes the sudden release of selenium.

[0087] Meanwhile, there are differences in the environmental responsiveness of the coating technology:

[0088] The swelling rate of the coating of the present invention is 25% in the rhizosphere acidic environment (pH 5.2) and suddenly increases to 120% during the fruit swelling period (pH 6.5), triggering the release of selenium.

[0089] The chitinase secreted by soil microorganisms can degrade chitosan (enzymolysis rate 0.12 mg / day), achieving bio-triggered slow release.

[0090] The quinone group (C=O) of humic acid absorbs ultraviolet light (absorbance at 280 nm detected by UV-Vis is 0.85), reducing the photolysis loss of selenium (6.2% vs 24.5% of commercially available products).

[0091] The commercially available polyvinyl alcohol film releases selenium depending on water diffusion, which cannot match the selenium requirement cycle of crops. The photolysis is serious, and there is a lack of ultraviolet shielding components. After foliar spraying, the selenium photolysis loss rate >25%.

[0092] Furthermore, the lack of metabolic activation components:

[0093] In the present invention, molybdenum (MoO4 2- ) acts as a cofactor of selenite reductase (SIR), stabilizes the enzyme active center through molecular docking (binding energy -9.2 kcal / mol), and catalyzes Se 4+ →Se 2- (the proportion of Se 2- detected by HPLC is 68%).

[0094] Glutamic acid-proline (3:1) regulates the cell membrane permeability (the conductivity is reduced by 42%) and promotes the transport of selenium to the pulp by upregulating the expression level of selenium transporter (such as NIP2;1) (2.3 times shown by qRT-PCR).

[0095] The selenium metabolism of commercially available products is blocked. The lack of molybdenum results in an SIR enzyme activity of only 8.7 U / mg, and Se 4+ cannot be effectively reduced, and the proportion of passive absorption is >80%.

[0096] The selenium distribution is unbalanced. The unoptimized amino acid ratio causes selenium to accumulate in the pericarp with low metabolic activity.

[0097] Differences in selenium forms and bioavailability:

[0098] The proportion of organic selenium in the present invention is high. HPLC-MS detection shows that the proportion of selenomethionine (SeMet) in the fruit is 67.2%, selenocysteine (SeCys) is 25.3%, and inorganic selenium (Se 4+ / Se 2- ) is only 7.5%.

[0099] High human absorption rate: The simulated digestion experiment shows that the bioavailability of SeMet reaches 81.3% (49.7% for commercially available products).

[0100] Due to the lack of metabolic regulation in commercially available products, the proportion of inorganic selenium is >60% (Se 4+ 58.7%, Se 2- 1.3%), and its bioavailability is only 1 / 3 of that of organic selenium.

[0101] Furthermore, the mechanism analysis:

[0102] LA-ICP-MS imaging: In the present invention group, selenium is evenly distributed in the pulp (gradient difference <15%), and in the comparative example 4, selenium accumulates in the pericarp (pericarp:pulp = 3:1);

[0103] In summary, citric acid forms a pH-sensitive complex with selenite ([SeO3·C6H5O7] 3- , verified by FT-IR), remains stable in the acidic soil environment (pH 4.5 - 5.5), and dissociates and releases active Se 4+ as the pH of the cell sap increases (7.0 - 7.5) after entering the plant roots, avoiding the oxidation loss of traditional selenite in the soil (the absorption rate of the comparative example 1 is only 28.5%).

[0104] The nano-silica carrier (pore size 2 - 5 nm, specific surface area ≥300 m 2 / g) fixes the selenium complex in the mesoporous structure through physical adsorption (verified by the BET method), combined with the hydrophobic barrier of the humic acid-chitosan coating (contact angle 105°), reducing the selenium leaching caused by rainwater scouring.

[0105] Polyglutamic acid preferentially chelates Fe3+ through carboxyl (-COOH) +(Combined with the constant logK = 8.3, DFT calculation), competitive inhibition of Fe 3+ and SeO3 2- forms insoluble FeSeO3 (no characteristic peaks detected by XRD), while the selenium-iron binding rate in the traditional formula is as high as 89.4%.

[0106] The pH-responsive property of humic acid-chitosan coating (the swelling rate is 120% at pH 6.5 shown by DLS) is synchronized with the pH change during the crop growth period. For example, during the booting stage of rice, organic acids secreted by the roots reduce the rhizosphere pH to 5.2, triggering selenium release (the peak of the release rate detected by HPLC deviates from the selenium-required period by < 2 days).

[0107] Ammonium molybdate provides MoO4 2- as a cofactor to activate selenite reductase (the SIR enzyme activity is increased by 3.8 times), reducing Se 4+ to Se 2- for plants to synthesize SeMet; vitamin B1 promotes the expression of thioredoxin and enhances the efficiency of selenocysteine integration (when there is no ammonium molybdate in Comparative Example 3, SeMet is only 42.1%).

[0108] The ultraviolet shielding effect of chitosan coating (the absorbance at 280 nm detected by UV-Vis is 0.85) and the antioxidant property of humic acid (the DPPH scavenging rate is 91%) synergistically protect selenium compounds from photodegradation, while the photolysis loss of traditional foliar fertilizers reaches 25.8%.

[0109] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not restrictive. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the spirit and scope of the technical solutions of the present invention, and they should all be covered within the scope of the claims of the present invention.

Claims

1. A selenium fertilizer formulation, characterized in that: By mass percentage, it contains 15 - 25% of selenite, 8 - 12% of citric acid chelating agent, 10 - 18% of nano-porous silica gel carrier, 5 - 8% of humic acid-chitosan composite film material, 3 - 5% of polyglutamic acid, 0.5 - 1.5% of ammonium molybdate, 0.1 - 0.3% of vitamin B1, and the balance is a plant-derived amino acid mixture.

2. The selenium fertilizer formulation according to claim 1, wherein: The pore diameter of the nano-porous silica carrier is 2-5 nm, and the specific surface area is ≥ 300 m 2 / g.

3. A selenium fertilizer formulation according to claim 1, characterized in that: In the humic acid-chitosan composite film material, the mass ratio of humic acid to chitosan is 1:

2.

4. The method for preparing selenium fertilizer according to claim 1, characterized in that: It includes the following steps: (a) Chelate selenite with citric acid at pH 4.5 - 5.5 and 60 °C for 30 min; (b) Load the complex obtained in step (a) onto the nano-silica gel carrier, with a vacuum impregnation pressure of 0.08 MPa; (c) Coating the loaded material with a humic acid-chitosan mixture, and the outlet temperature of spray drying is 70 °C.

5. The method for using selenium fertilizer according to claim 1, wherein: When applying to the soil as base fertilizer, mix it with the base fertilizer at 2 - 3 kg / mu and deep plow 20 cm.

6. The method for using selenium fertilizer according to claim 5, characterized in that: When spraying on the leaves, dilute it 500 times, with a spraying amount of 30 L / mu, and spray 2 times at an interval of 7 days.

7. The application of a selenium fertilizer as described in claim 1 in cereal cultivation, wherein the cereals include rice and wheat.

8. The application of a selenium fertilizer as described in claim 1 in fruit and vegetable cultivation, wherein the fruits and vegetables include tomatoes and citrus fruits.

9. The selenium fertilizer formulation according to claim 1, wherein: In the plant-derived amino acid mixture, the mass ratio of glutamic acid to proline is 3:

1.

10. A selenium fertilizer formulation according to claim 1, characterized in that: The coating rate of the humic acid-chitosan composite film material is ≥90%, and the film-forming thickness is 50 - 100 nm.