Method for enriching iron membrane on root surface with selenium and producing selenium-rich rice and application thereof

Abstract

The present application relates to the field of agricultural planting technology, and particularly relates to a method for strengthening root surface iron membrane Se and producing Se-rich rice, wherein a sulfur-selenium composite functional fertilizer compounded by elemental sulfur, sodium selenite and an iron-based MOF carrier is applied in soil preparation; peroxide urea is applied once at the tillering peak period to the jointing period, and nano-selenium aqueous solution is applied at the jointing period and the booting period of rice, respectively; a stable reduction environment is created by continuous flooding from the tillering end period to the initial milk filling period, and conventional wet management is restored in the later period, and the whole process is combined with standard field management, so that the rice is stably enriched in selenium and the heavy metal passivation effect is improved. Thus, the problems of insufficient iron membrane selenium regulation and utilization, non-systematic measures, mismatched selenium supply timing, and non-optimized nano-selenium particle size in the prior art are solved.

Description

Technical Field

[0001] This invention relates to the field of agricultural planting technology, specifically to a method and application for strengthening the root surface iron film to enrich Se and producing Se-rich rice. Background Technology

[0003] Rice is a typical wetland plant. In long-term flooded environments, the root aerenchyma releases oxygen, and Fe is oxidized on the root surface. 2+ An iron film is formed, a reddish-brown gel composed of iron oxides / hydroxides. Studies have shown that the iron film has a large specific surface area and abundant surface functional groups, exhibiting a strong adsorption capacity for selenite ions. The proportion of selenium in the iron film reaches as high as 73.63% of the total selenium during the seedling stage. Throughout the entire growth period, the iron film acts as a "buffer" for selenium, accumulating selenium in the early stages and slowly releasing it for absorption by the rice plants in the later stages.

[0004] In recent years, significant progress has been made in research on the regulation of iron film and selenium absorption in rice. Studies by Yang Xujian et al. have shown that applying urea peroxide can significantly increase the content of non-crystalline iron film on the root surface of rice by 41.9%–111.0%, with a maximum increase at 90 kg / hm². 2 The iron film content in the urea peroxide treatment increased by 128.89% compared to the control, and the grain selenium content increased by 25.92%. Regarding water management, the iron film content and grain selenium content in the continuous flooding treatment were significantly higher than those in the alternating wet and dry treatment. Orthogonal experimental results showed that a phosphorus-iron ratio of 1:1 and an urea peroxide concentration of 90 kg / hm² were optimal. 2 The combined treatment of continuous flooding resulted in the highest selenium content in the grains, reaching 0.34 mg / kg. Furthermore, the selenium content in the grains treated with seaweed polysaccharide nano-selenium under optimized conditions was 0.37 mg / kg, significantly higher than that treated with sodium selenate and sodium selenite.

[0005] Recent studies have shown significant differences in selenium absorption in rice due to variations in nano-selenium particles of different sizes. A 2019 study found that the translocation coefficient of 50nm nano-selenium in rice was significantly higher than that of 100nm and 150nm nano-selenium treatments. A 2025 study published in Environmental Science: Nano further revealed that 30nm small-particle-size nano-selenium overstimulates root oxygen secretion, leading to excessive iron film deposition, which fixes selenium on the root surface and inhibits translocation. In contrast, the grain selenium content of 110nm nano-selenium was 85.3% higher than that of 30nm nano-selenium.

[0006] However, the existing selenium-enriched rice cultivation technology system still has many technical shortcomings, specifically in the following aspects: (1) Existing technologies have not fully explored and utilized the selenium enrichment-slow release regulation mechanism of iron film on rice root surface, and have failed to rely on the natural adsorption characteristics of iron film to achieve efficient selenium enrichment. The adsorption carrying capacity of iron film for selenium cannot reach the theoretical extreme value, resulting in low selenium resource utilization rate, which restricts the improvement of selenium enrichment effect of rice. (2) Existing studies only focus on single regulatory measures such as urea peroxide application and field water management, lacking systematic research and supporting technology on the coupling and synergy of multiple measures. As a result, an integrated regulatory system adapted to the growth of selenium-enriched rice cannot be formed, and the overall regulatory effect is limited. (3) Currently, most selenium fertilizers are applied as a single basal application or foliar spraying. They do not build a selenium supply system based on the core mechanism of root surface iron film enrichment-slow release, which is difficult to achieve a precise time-series match between the selenium release pattern during the key growth period of rice and the plant's absorption needs. This can easily lead to problems such as selenium waste in the early stage and insufficient selenium supply in the later stage, resulting in poor selenium enrichment stability. (4) Existing nano-selenium application technologies have not been precisely adapted and optimized for particle size parameters, and have not fully utilized the dual technical advantages of 110nm nano-selenium inducing iron film formation and improving selenium transport efficiency. The growth-promoting and selenium-enriching potential of nano-selenium has not been maximized. Summary of the Invention

[0007] This application provides a method and application for enhancing the iron film on the root surface to enrich Se and producing Se-rich rice, in order to solve the problems of insufficient selenium regulation and utilization in the iron film in the prior art, unsystematic measures, mismatched selenium supply timing, and unoptimized nano-selenium particle size.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows: The present invention provides a method for strengthening the root surface iron film for Se enrichment and producing Se-rich rice, comprising the following steps: (1) Basal application of sulfur-selenium compound functional fertilizer: When preparing the land, mix elemental sulfur, sodium selenite and carrier evenly and then spread the mixture and plow it into the soil. The carrier is an iron-based metal-organic framework material. (2) Application of urea peroxide: Apply urea peroxide once during the tillering stage to the jointing stage; (3) Targeted selenium supplementation during key growth periods: Apply nano-selenium aqueous solution with a particle size of 80-150nm at the jointing stage and the booting stage of rice, respectively; (4) Continuous flood irrigation: From the end of tillering to the beginning of grain filling, maintain continuous flooding with a water depth of 3-5cm; (5) Routine field management and harvesting: Restore normal shallow water irrigation and keep the field moist until it dries naturally 7-10 days before harvest; pest and disease control, weed control and topdressing are carried out according to the conventional high-quality rice cultivation techniques; harvest and dry the rice after it matures.

[0009] Furthermore, the iron-based metal-organic framework material is amino-modified MIL-53(Fe)-NH2.

[0010] Furthermore, the amino-modified MIL-53(Fe)-NH2 is prepared by a solvothermal method using iron salt and 2-aminoterephthalic acid.

[0011] Furthermore, the solvothermal method includes the following steps: (a) FeCl3·6H2O and 2-aminoterephthalic acid were dissolved in N,N-dimethylformamide at a molar ratio of (1:0.5)–(1:1.5) and reacted solvothermically at 120–160 °C for 12–48 h. After cooling, centrifugation, washing and drying, MIL-53(Fe)-NH2 was obtained. (b) The product of step (a) was immersed in an aqueous solution of sodium selenite and adsorbed at 20–40 °C for 2–12 h. After filtration and drying, a selenium-loaded amino-modified iron-based MOF was obtained. (c) The selenium-loaded amino-modified iron-based MOF obtained in step (b) is mixed evenly with elemental sulfur and sodium selenite to obtain sulfur-selenium compound functional fertilizer.

[0012] Further, the concentration of the sodium selenite aqueous solution in step (b) is 10–20 g / L, and the selenium loading is 0.5–5 wt%.

[0013] Further, in step (1), the amount of elemental sulfur used is 20-50 kg / mu, the amount of sodium selenite used is 15-30 gSe / mu, and the amount of iron-based metal-organic framework material used is 0.1-0.3 kg / mu.

[0014] Furthermore, the particle size of the elemental sulfur in step (1) is 200-325 mesh; the particle size of the nano-selenium in step (3) is 110±20 nm.

[0015] Furthermore, the jointing period mentioned in step (3) is 40-50 days after transplanting, and the booting period is 60-70 days after transplanting; the amount of nano-selenium applied each time is 7.5-15gSe / mu.

[0016] Furthermore, the amount of urea peroxide used in step (2) is 90 kg / hm. 2 Furthermore, the application time is 3-10 days after the start of the peak tillering period.

[0017] This invention also provides applications for producing selenium-enriched rice in acidic paddy soil, neutral paddy soil, or cadmium-selenium contaminated paddy soil.

[0018] The beneficial effects achieved by using the present invention described above are as follows: 1. This invention utilizes amino-modified MIL-53(Fe)-NH2 as a selenium slow-release carrier in rice cultivation. This material possesses a regular microporous structure and a large specific surface area, with a well-developed pore structure, enabling efficient loading of selenium components and controllable slow release. Sodium selenite is loaded into the material's pores using an impregnation adsorption method, with the selenium loading controlled at 0.5-5 wt%, constructing a MOF-loaded selenium slow-release system. Under basal application conditions, the sodium selenite loaded within the MOF pores releases selenite ions through diffusion and partial degradation of the framework, forming a slow-release component. Free sodium selenite in the system serves as the fast-acting component, and the coupling of these two components constructs a fast-acting-slow-release synergistic selenium supply mode. The slow-release component can extend the effective selenium supply period and adapt to the dynamic buffering characteristics of the root surface iron film, which accumulates in the early stage and releases in the later stage; the fast-acting component can quickly supply selenium after application, meeting the selenium demand of rice during the tillering stage and the selenium accumulation demand of the root surface iron film during the seedling stage, thereby achieving a stable selenium supply throughout the entire growth period of rice and avoiding the technical defects of selenium loss and insufficient selenium supply during key growth periods caused by one-time basal application. 2. This invention employs a synergistic effect of four regulatory mechanisms: elemental sulfur supplying iron, urea peroxide promoting oxidation, 110nm nano-selenium promoting root oxygen secretion, and continuous flooding creating a reducing environment. This constructs a positive feedback loop of iron supply, film formation, and selenium enrichment. Under anaerobic conditions of flooding, elemental sulfur is reduced by microorganisms to generate sulfur ions, reducing ferric iron in the soil to ferrous iron, increasing the content of free ferrous iron in the soil, and continuously supplying iron sources for film formation. Urea peroxide hydrolysis produces hydrogen peroxide and urea, constructing a local oxidizing microenvironment, promoting the oxidation of ferrous iron to ferric iron, and driving the deposition of iron hydroxide on the rice root surface. 110nm nano-selenium can moderately induce the development of root aerenchyma, promote radial oxygen secretion from roots, drive iron film deposition, and avoid the adverse effects of excessive oxygen secretion caused by small-particle-size nano-selenium (below 30nm), resulting in abnormal thickening of the iron film and selenium fixation on the root surface. Continuous flooding maintains an anaerobic reducing environment, ensuring the microbial reduction process of elemental sulfur and the continuous accumulation of ferrous iron. 3. Based on the selenium absorption pattern of rice, this invention selects two key selenium absorption windows—the jointing stage and the booting stage—for targeted selenium supplementation. A 110nm nano-selenium aqueous solution is applied during these growth stages. The nano-selenium applied during the jointing stage can be efficiently adsorbed and enriched by the iron film on the root surface, and can be slowly released along with the iron film during the grain-filling and ripening stage, precisely matching the physiological needs for selenium accumulation in the grains. The nano-selenium applied during the booting stage effectively ensures selenium supply during the grain-filling stage, directly meeting the growth requirements for selenium accumulation in the grains. This invention, relying on the enrichment-slow-release characteristics of the root surface iron film and combined with the targeted selenium supplementation regulation method during key growth stages, overcomes the shortcomings of traditional technologies where the timing of selenium supply does not match the physiological absorption needs of rice. It achieves precise regulation of the entire chain of selenium accumulation within the iron film, slow release, and absorption and utilization by the plant. 4. This invention uses selenium nanoparticles with a particle size of 110±20nm for application, which can moderately stimulate the development of root aerenchyma and radial oxygen secretion in rice roots, induce the formation of a root surface iron film of suitable thickness, and provide sufficient selenium adsorption sites. Simultaneously, it overcomes the technical drawbacks of small-particle-size selenium nanoparticles (below 30nm), which can excessively stimulate root oxygen secretion, causing abnormal thickening of the iron film, resulting in a large amount of selenium remaining on the root surface and inhibiting selenium translocation to the aboveground parts and grains. The 110±20nm particle size selenium nanoparticles achieve an optimal balance between the supply of iron film adsorption sites and long-distance selenium translocation. 5. The multi-regulation system of this invention achieves selenium enrichment in rice while simultaneously reducing the accumulation of heavy metals such as cadmium through multiple synergistic mechanisms. The thickened root surface iron film, through adsorption and co-precipitation effects, fixes cadmium ions, lead ions, arsenate ions, etc., forming a physical barrier that hinders the transport of heavy metals to the aboveground parts of the plant. The amino-modified MIL-53(Fe)-NH2, relying on its pore structure and surface amino functional groups, adsorbs heavy metal ions from the soil through coordination and ion exchange. Sulfide ions generated by the reduction of elemental sulfur can react with cadmium ions and other heavy metals to form insoluble sulfide precipitates, reducing the bioavailability of heavy metals. These multiple passivation mechanisms work synergistically to reduce the heavy metal content in rice, simultaneously achieving selenium enrichment and safe production. 6. The raw materials used in this invention are readily available, and the base fertilizer and top dressing fertilizer can be prepared in batches. The management process, such as field irrigation and pest and disease control, is compatible with conventional rice cultivation technology. No special equipment or strict implementation conditions are required. It can be adapted to various soil types such as acidic paddy soil, neutral paddy soil, and cadmium-selenium compound polluted paddy soil, and is suitable for large-scale field production of selenium-enriched rice.

[0019] This solves the problems of insufficient selenium regulation and utilization in existing technologies, unsystematic measures, mismatched selenium supply timing, and unoptimized nano-selenium particle size, and achieves the synergistic goal of root surface iron film-enhanced selenium enrichment and safe rice production.

[0020] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application. Detailed Implementation

[0021] The technical solution of the present invention is illustrated below through specific examples. It should be understood that the one or more method steps mentioned in the present invention do not preclude the existence of other method steps before or after the combined steps, or the insertion of other method steps between these explicitly mentioned steps; it should also be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the present invention. Furthermore, unless otherwise stated, the numbering of each method step is merely a convenient tool for identifying each method step, and not for limiting the order of the method steps or defining the scope of the present invention. Changes or adjustments to their relative relationships, without substantially altering the technical content, should also be considered within the scope of the present invention.

[0022] To better understand the above technical solutions, exemplary embodiments of the present invention are described in more detail below. While exemplary embodiments of the present invention are shown, it should be understood that the present invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided to enable a more thorough understanding of the present invention and to fully convey the scope of the invention to those skilled in the art.

[0023] The conventional chemical reagents used in this invention (FeCl3·6H2O, 2-aminoterephthalic acid, N,N-dimethylformamide, sodium selenite, etc.) were all analytical grade and purchased from Sinopharm Chemical Reagent Co., Ltd. The nano-selenium aqueous solution was prepared in the laboratory using a chemical reduction method; the elemental sulfur was industrial-grade sublimed sulfur, pulverized and passed through a 200-325 mesh sieve before use; the urea peroxide was industrial-grade with an effective content ≥95%. The rice variety used in the experiment was conventional indica rice, and the seeds were purchased from a local seed company.

[0024] Example 1 This embodiment provides a method for enhancing the iron film on the root surface to enrich Se and producing Se-rich rice, including the following steps: (I) Preparation of amino-modified MIL-53(Fe)-NH2 FeCl3·6H2O (1.0 mmol, 0.27 g) and 2-aminoterephthalic acid (1.0 mmol, 0.18 g) were dissolved in 30 mL of N,N-dimethylformamide and ultrasonically dispersed for 15 min until completely dissolved. The mixed solution was transferred to a 100 mL polytetrafluoroethylene-lined stainless steel reactor and reacted at a constant temperature of 150 °C for 24 h. After the reaction was completed, the mixture was allowed to cool naturally to room temperature, and the yellow precipitate was collected by centrifugation (8000 rpm, 10 min). The precipitate was washed three times alternately with N,N-dimethylformamide and anhydrous ethanol, and then dried under vacuum at 70 °C for 12 h to obtain amino-modified MIL-53(Fe)-NH2.

[0025] (II) Preparation of selenium-loaded amino-modified iron-based MOFs The MIL-53(Fe)-NH2 (10g) obtained in step (I) was immersed in a 15g / L sodium selenite aqueous solution (100mL) and adsorbed at a constant temperature of 30℃ with shaking for 6h (150rpm). After adsorption, the mixture was filtered, the solid product was collected, washed three times with deionized water, and dried under vacuum at 50℃ for 12h to obtain a selenium-loaded amino-modified iron-based MOF. The selenium loading in this example was determined to be 3.5wt%.

[0026] (III) Preparation of sulfur-selenium compound functional fertilizer The selenium-loaded amino-modified iron-based MOF obtained in step (II) (0.1 kg / mu) is mixed evenly with elemental sulfur (200 mesh, 35 kg / mu) and sodium selenite (total amount 22.5 g Se / mu) to obtain the sulfur-selenium compound functional fertilizer. The selenium-loaded MOF has a selenium loading of 3.5 wt%, equivalent to a selenium contribution of 3.5 g Se / mu, with the remaining 19 g Se / mu existing as free sodium selenite.

[0027] (iv) Apply sulfur-selenium compound functional fertilizer as basal fertilizer The tested variety was conventional indica rice (Huanghuazhan), and the tested soil was typical acidic paddy soil in southern China (pH 6.2, organic matter content 28.5 g / kg, total selenium content 0.18 mg / kg, total cadmium content 0.45 mg / kg). During land preparation, the sulfur-selenium compound functional fertilizer obtained in step (III) was evenly spread on the field surface, then plowed into the soil (depth 0-20 cm), and leveled.

[0028] (v) Application of urea peroxide Apply urea peroxide once, at a rate of 90 kg / hm², on the 5th day after the peak tillering stage of rice (approximately 25 days after transplanting). 2 .

[0029] (vi) Targeted selenium supplementation during critical reproductive periods Apply 110nm nano-selenium aqueous solution as top dressing at the jointing stage (45 days after transplanting) and the booting stage (65 days after transplanting), with a dosage of 10gSe / mu each time. Dilute with water and apply evenly to the root area of ​​the rice.

[0030] (vii) Continuous flood irrigation From the late tillering stage (about 40 days after transplanting) to the early grain-filling stage (about 85 days after transplanting), keep the field continuously flooded, with a water depth of 3-5 cm.

[0031] (viii) Routine field management and harvesting After the initial grain-filling stage, resume normal shallow irrigation and keep the field moist until it dries naturally 10 days before harvest. During the growing season, field management, including disease and pest control and weed control, should be carried out according to conventional high-quality rice cultivation techniques. Harvest and dry the rice in a timely manner after it matures.

[0032] Example 2 This embodiment provides a method for enhancing the iron film on the root surface to enrich Se and producing Se-rich rice, which differs from Embodiment 1 in that: In step (ii), the sodium selenite aqueous solution has a concentration of 20 g / L and a selenium loading of 5.0 wt%. In step (3), the amount of elemental sulfur used is 50 kg / mu, the total amount of sodium selenite used is 30 g Se / mu, and the amount of selenium-loaded MOF used is 0.2 kg / mu (the selenium loading is 5.0 wt%, which is equivalent to contributing 10 g Se / mu, and the remaining 20 g Se / mu exists in the free state). The remaining steps and parameters are the same as in Example 1.

[0033] Example 3 This embodiment provides a method for enhancing the iron film on the root surface to enrich Se and producing Se-rich rice, which differs from Embodiment 1 in that: In step (3), the amount of elemental sulfur used is 25 kg / mu, the total amount of sodium selenite used is 18 g Se / mu, and the amount of selenium-loaded MOF used is 0.15 kg / mu (the selenium loading is 3.0 wt%, which is equivalent to contributing 4.5 g Se / mu, and the remaining 13.5 g Se / mu exists in the free state). In step (5), the dosage of urea peroxide is 60 kg / hm. 2 The application time is the third day after the start of the peak tillering period; The remaining steps and parameters are the same as in Example 1.

[0034] Example 4 This embodiment provides a method for enhancing the iron film on the root surface to enrich Se and producing Se-rich rice, which differs from Embodiment 1 in that: The tested soil was neutral paddy soil (pH 7.0, organic matter content 30.2 g / kg, total selenium content 0.15 mg / kg, total cadmium content 0.38 mg / kg).

[0035] The remaining steps and parameters are the same as in Example 1.

[0036] Example 5 This embodiment provides a method for enhancing the iron film on the root surface to enrich Se and producing Se-rich rice, applied in field production of paddy soil contaminated with cadmium and selenium. The difference from Embodiment 1 is: The tested soil was cadmium-selenium contaminated paddy soil (pH 6.0, total selenium content 1.80 mg / kg, total cadmium content 0.92 mg / kg). In step (iii), the amount of elemental sulfur is increased to 50 kg / mu to enhance the fixation effect of Fe-S coprecipitation on cadmium. In step (III), the total amount of sodium selenite used is adjusted to 15gSe / mu, and the amount of selenium-loaded MOF is 0.1kg / mu (the selenium loading is 3.5wt%, which is equivalent to contributing 3.5gSe / mu, and the remaining 11.5gSe / mu exists in the free state).

[0037] The remaining steps and parameters are the same as in Example 1.

[0038] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is as follows: (1) No iron-based metal-organic framework material carrier is added, and sodium selenite is applied in a free state (22.5gSe / mu). (2) No elemental sulfur is added; (3) No additional nano-selenium aqueous solution is applied in step (vi).

[0039] The remaining steps and parameters are the same as in Example 1.

[0040] Comparative Example 2 The difference between Comparative Example 2 and Example 1 is as follows: In step (vi), 30nm nano-selenium is applied instead of 110nm nano-selenium. The 30nm particle size is not within the 80-150nm range defined in the claims of this invention. This is used to verify the effect of particle size on selenium absorption and iron film deposition.

[0041] The remaining steps and parameters are the same as in Example 1.

[0042] Comparative Example 3 The difference between Comparative Example 3 and Example 1 is as follows: In step (six), the jointing stage and the booting stage are not distinguished. On the 30th day after transplanting, 20gSe / mu of nano selenium is applied once (the amount is the same as the total amount of two applications in Example 1).

[0043] The remaining steps and parameters are the same as in Example 1.

[0044] Performance testing The selenium content, cadmium content, and root surface iron film content of rice in Examples 1-5 and Comparative Examples 1-3 were tested. The detection methods and results of each indicator are as follows.

[0045] I. Detection Methods Determination of root surface iron film content: The DCB (sodium dithionite-sodium citrate-sodium bicarbonate) extraction method was used. Rice root samples were washed with deionized water, cut into 1cm segments, and placed in 50mL centrifuge tubes. 40mL of DCB extraction buffer (0.3mol / L sodium citrate + 0.125mol / L sodium dithionite + 0.5mol / L sodium bicarbonate, pH 7.3) was added, and extraction was carried out at 25℃ with shaking for 1h (200rpm). After extraction, the samples were filtered, and the root segments were rinsed three times with deionized water. The filtrates were combined, and the iron content in the extract was determined by inductively coupled plasma atomic emission spectrometry (ICP-AES). The root surface iron film content (mg / gDM, dry matter) was calculated.

[0046] Selenium content determination in rice: Harvested rice was hulled, crushed, and sieved through a 100-mesh sieve. 0.5g of rice flour sample was weighed, and 5mL of nitric acid and 1mL of hydrogen peroxide were added. The mixture was then digested using a microwave digester. After complete digestion, the acid was removed and the volume was adjusted to 25mL. The selenium content in the digest was determined using atomic fluorescence spectrometry.

[0047] Determination of cadmium content in brown rice: Weigh 0.5g of brown rice flour sample, add 5mL of nitric acid, and digest using a microwave digester. After complete digestion, remove the acid and bring the volume to 25mL. Determine the cadmium content in the digestion solution using inductively coupled plasma mass spectrometry.

[0048] The test results of each embodiment and comparative example are shown in Table 1.

[0049] Table 1 Test Results

[0050] As shown in Table 1, the selenium content of rice in Examples 1-5 ranged from 0.31 to 0.40 mg / kg, all meeting the national standard for selenium-enriched rice (≥0.15 mg / kg); the cadmium content of brown rice ranged from 0.11 to 0.18 mg / kg, both conforming to the GB2762-2022 cadmium limit standard (≤0.2 mg / kg). In Comparative Example 1, the selenium content of rice was 0.18 mg / kg, and the cadmium content of brown rice was 0.28 mg / kg (exceeding the standard). This indicates that without the addition of iron-based MOF carriers, elemental sulfur, and topdressing with nano-selenium, the selenium enrichment effect of rice was poor, and the cadmium content exceeded the standard. The root surface iron film content of Comparative Example 2 was 412.5 mg / g DM, higher than that of Example 1 (386.2 mg / g DM), but its rice selenium content was only 0.26 mg / kg, significantly lower than that of Example 1 (0.35 mg / kg). This indicates that although 30 nm nano-selenium stimulated the formation of more iron films, its excessive stimulation of root oxygen secretion led to abnormal thickening of the iron film, fixing a large amount of selenium on the root surface and inhibiting the translocation of selenium to the grains. This verifies the technical rationality of using 110±20 nm nano-selenium in this invention. The rice selenium content of Comparative Example 3 was 0.24 mg / kg, lower than that of Example 1 (0.35 mg / kg). This indicates that applying nano-selenium once on the 30th day after transplanting could not match the temporal characteristics of "early enrichment and later release" of the iron film. This verifies the technical rationality of applying nano-selenium in stages during the jointing and booting stages in this invention.

[0051] In Example 5, the root surface iron film content was 398.7 mg / g DM, and the rice selenium content was 0.40 mg / kg, both the highest among Examples 1-5. The brown rice cadmium content was 0.18 mg / kg, still meeting national standards in cadmium-selenium co-contaminated soil. This indicates that the present invention has a significant synergistic effect in achieving selenium enrichment and cadmium reduction in cadmium-selenium co-contaminated soil. In Comparative Example 1, the rice selenium content (0.18 mg / kg) was significantly lower than all examples, and the brown rice cadmium content (0.28 mg / kg) was the highest among all treatments and exceeded the standard. This demonstrates that the technical solution of the present invention, consisting of the MOF-loaded selenium slow-release system, elemental sulfur for iron supply, and nano-selenium targeted selenium supplementation, possesses an irreplaceable overall synergistic effect. Furthermore, in Example 3, the urea peroxide dosage was 60 kg / hm². 2 (Lower limit of the dosage range in claim 1) The selenium content of rice is still 0.31 mg / kg, and the cadmium content of brown rice is 0.14 mg / kg, both of which are superior to all comparative examples. This shows that the present invention can still achieve stable selenium enrichment and cadmium reduction effects at a low dosage of urea peroxide, verifying the 60-90 kg / hm² dosage in claim 1. 2 The rationality of the dosage range.

[0052] In summary, this invention, through the synergistic regulation of MOF-loaded selenium slow-release system with free sodium selenite (rapid-release synergistic selenium supply), elemental sulfur for iron supply, urea peroxide for oxidation promotion, 110nm nano-selenium targeted selenium supplementation, and continuous flooding irrigation, can significantly increase the selenium content of rice and reduce the cadmium content of brown rice. It exhibits good applicability and stability of effects under different parameter conditions and soil types.

[0053] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for enhancing the iron film on the root surface to enrich Se and producing Se-rich rice, characterized in that, Includes the following steps: (1) Basal application of sulfur-selenium compound functional fertilizer: When preparing the land, mix elemental sulfur, sodium selenite and carrier evenly and then spread the mixture and plow it into the soil. The carrier is an iron-based metal-organic framework material. (2) Application of urea peroxide: Apply urea peroxide once during the tillering stage to the jointing stage; (3) Targeted selenium supplementation during key growth periods: Apply nano-selenium aqueous solution with a particle size of 80-150nm at the jointing stage and the booting stage of rice, respectively; (4) Continuous flood irrigation: From the end of tillering to the beginning of grain filling, maintain continuous flooding with a water depth of 3-5cm; (5) Routine field management and harvesting: Restore normal shallow water irrigation and keep the field moist until it dries naturally 7-10 days before harvest; pest and disease control, weed control and topdressing are carried out according to the conventional high-quality rice cultivation techniques; harvest and dry the rice after it matures.

2. The method according to claim 1, characterized in that, The iron-based metal-organic framework material is amino-modified MIL-53(Fe)-NH2.

3. The method according to claim 2, characterized in that, The amino-modified MIL-53(Fe)-NH2 was prepared by a solvothermal method using iron salt and 2-aminoterephthalic acid.

4. The method according to claim 3, characterized in that, The solvothermal method includes the following steps: (a) FeCl3·6H2O and 2-aminoterephthalic acid were dissolved in N,N-dimethylformamide at a molar ratio of (1:0.5)–(1:1.5) and reacted solvothermically at 120–160 °C for 12–48 h. After cooling, centrifugation, washing and drying, MIL-53(Fe)-NH2 was obtained. (b) The product from step (a) was immersed in an aqueous sodium selenite solution and adsorbed at 20–40 °C for 2–12 h. After filtration and drying, a selenium-loaded amino-modified iron-based MOF was obtained. (c) The selenium-loaded amino-modified iron-based MOF obtained in step (b) is mixed evenly with elemental sulfur and sodium selenite to obtain sulfur-selenium compound functional fertilizer.

5. The method according to claim 4, characterized in that, The concentration of the sodium selenite aqueous solution in step (b) is 10–20 g / L and the selenium loading is 0.5–5 wt%.

6. The method according to claim 1, characterized in that, The amount of elemental sulfur used in step (1) is 20-50 kg / mu, the amount of sodium selenite used is 15-30 gSe / mu, and the amount of iron-based metal-organic framework material used is 0.1-0.3 kg / mu.

7. The method according to claim 1, characterized in that, The particle size of elemental sulfur in step (1) is 200-325 mesh; the particle size of nano-selenium in step (3) is 110±20nm.

8. The method according to claim 1, characterized in that, The jointing period mentioned in step (3) is 40-50 days after transplanting, and the booting period is 60-70 days after transplanting; the amount of nano selenium applied each time is 7.5-15gSe / mu.

9. The method according to claim 1, characterized in that, The amount of urea peroxide used in step (2) is 90 kg / hm. 2 Furthermore, the application time is 3-10 days after the start of the peak tillering period.

10. The application of the method according to any one of claims 1-9 in the production of selenium-enriched rice in acidic paddy soil, neutral paddy soil or cadmium-selenium contaminated paddy soil.

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