A root-leaf coordination based selenium-rich and cadmium-reducing fertilization method and application thereof

Abstract

The application belongs to the technical field of agriculture, and particularly relates to a selenium-rich and cadmium-reducing fertilization method based on root-leaf cooperation and application thereof. The fertilization method comprises the following steps: before flower bud stage, burying soil conditioner; during spring shoot stage and / or flower bud stage, fruit bulking stage and color changing stage, spraying selenium-rich foliar fertilizer; by combining the specific soil conditioner and the selenium-rich foliar fertilizer, the root-leaf cooperation solves the problems of soil acidification and selenium element addition in the process of fruit tree planting, improves fruit quality, increases organic selenium content, and improves total flavonoid content in the fruit. The fertilization method is particularly suitable for the planting of citrus, grapefruit and other fruit trees.

Description

Technical Field

[0001] This invention belongs to the field of agricultural technology, specifically relating to a method for selenium-enriched cadmium-reducing fertilization based on root-leaf synergy and its application. Background Technology

[0002] Soil conditioning is a crucial step in citrus and pomelo cultivation. By adjusting soil pH, increasing the application of organic fertilizers, and planting green manure, the soil environment can be effectively improved, thereby increasing fruit yield and quality.

[0003] The ideal soil pH for citrus and pomelo cultivation is generally between 5.5 and 6.5. Soil acidification can negatively impact root growth and nutrient absorption. Therefore, overcoming soil acidification is a crucial issue to address in citrus and pomelo cultivation.

[0004] In addition, heavy metal pollution in the soil is also an important environmental issue to consider in the cultivation of citrus and grapefruit fruits, which may have adverse effects on plant growth, fruit quality and the ecological environment.

[0005] Selenium is a trace element that is beneficial to the human body. It can improve the nutritional value of citrus fruits and pomelos. Selenium can also promote the accumulation of sugar in fruits, improve their sweetness and flavor, extend their shelf life, and enhance their disease resistance and stress resistance. Therefore, selenium has been widely used in the cultivation of citrus fruits and pomelos in recent years.

[0006] Currently, these methods are mainly achieved by adding various soil conditioners and foliar fertilizers during the planting process. However, the existing common fertilization methods are too simplistic and cannot meet the needs of fruit development and secondary metabolism. Alternatively, the fertilizer components may have limited efficacy, making it difficult to improve the availability of basic nutrients and micronutrients, solve soil acidification problems, passivate heavy metals, and achieve precise regulation of key elements such as selenium and silicon. Summary of the Invention

[0007] In view of the problems existing in the prior art, the present invention provides a method for selenium-enriched cadmium-reducing fertilization based on root-leaf synergy. This method can systematically solve problems such as soil acidification, micronutrient deficiency, organic matter supplementation, efficient supply of selenium and silicon, and introduction of beneficial microorganisms, providing a comprehensive soil and nutrient foundation for high yield, high quality and safety of selenium-enriched citrus and pomelo fruits.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] This invention provides a method for selenium-enriched cadmium-reducing fertilization based on root-leaf synergy, comprising the following steps:

[0010] Apply soil conditioner before the flower bud stage;

[0011] Spray selenium-enriched foliar fertilizer during the spring shoot stage and / or flower bud stage, fruit enlargement stage and color change stage.

[0012] The soil conditioner comprises 60-70 parts by weight of calcined Inner Mongolia calcium magnesium silicate ore powder, 20-30 parts by weight of sterilized and decomposed straw powder, 10-15 parts by weight of modified attapulgite clay, 1-3 parts by weight of humic acid, 3-5 parts by weight of AMF fungal microspheres, and 1-3 parts by weight of freeze-dried bacterial powder. The AMF fungal microspheres have a diameter of 1 mm-2 mm, and the freeze-dried bacterial powder includes nitrogen-fixing bacteria and silica-solubilizing bacteria. The modified attapulgite clay is magnesium-based attapulgite clay modified with a citric acid-ferric chloride composite solution, with a specific surface area ≥120 m². 2 / g;

[0013] The selenium-enriched foliar fertilizer comprises 15-25 parts by weight of a composite selenium source, 10-15 parts by weight of an alkyl polysaccharide APG0810, 10-15 parts by weight of quercetin and salicylic acid, 45-60 parts by weight of mesoporous silica, and 3-5 parts by weight of nano-titanium dioxide. The composite selenium source is composed of sodium selenite and selenomethionine, with a molar ratio of sodium selenite to selenomethionine of 1:1-2.5; the mass ratio of quercetin to salicylic acid is 1:1-1.5; and the mesoporous silica has a pore size of 8 nm-12 nm and a particle size of 30-100 nm.

[0014] This fertilization method involves applying a soil conditioner to the roots of fruit trees and applying a selenium-enriched foliar fertilizer. The soil conditioner combines microorganisms and minerals, with the carrier being calcined calcium magnesium silicate powder from Inner Mongolia, rich in over 60 trace elements and 15 rare earth elements, especially selenium. The composite microorganisms are coated, resulting in a high colonization rate. While improving soil pH and increasing selenium content, it also provides trace elements. Applying it before the flower bud stage provides selenium reserves for fruit trees, activates flavonoid synthase, and promotes later flavonoid synthesis. The selenium-enriched foliar fertilizer uses a composite selenium source of sodium selenite (Na2SeO3) and selenomethionine, replacing ordinary nano-silica with mesoporous silica to increase the loading rate, control the nano-selenium particle size, facilitate selenium absorption, increase fruit peel thickness, enhance the levels of elements in the fruit, promote flavonoid synthesis, and is rich in silicon. Silicon deposition strengthens the fruit peel structure, further enhancing the absorption of more selenium. The fertilization method of this invention promotes synergistic effects between roots and leaves, adjusts soil acidification, efficiently supplies selenium and silicon, improves fruit quality, and increases the selenium content of fruits.

[0015] In some embodiments, the calcined Inner Mongolia calcium-magnesium-silicon ore powder in the soil conditioner is prepared by crushing Inner Mongolia calcium-magnesium-silicon ore, calcining it at 600℃~700℃, and finally ball milling it to a specific surface area ≥20m². 2 / g prepared.

[0016] In some embodiments, the AMF fungal microspheres are obtained by mixing AMF fungal spores with chitosan solution, activating them at 25°C to 28°C for 10 to 15 hours, adding sodium alginate and modified attapulgite clay to encapsulate them into microspheres, and then adding calcium chloride solution to solidify them.

[0017] In some embodiments, the bacterial freeze-dried powder is prepared by centrifuging the nitrogen-fixing bacteria and silica-solubilizing bacteria, mixing them with trehalose, pre-freezing at -35°C to -45°C, and then drying in a cold trap at -50°C to -60°C.

[0018] In some embodiments, the soil conditioner is prepared by first mixing calcined Inner Mongolia calcium magnesium silicate ore powder and sterilized composted straw powder at ≤35°C, then adding modified attapulgite clay at ≤30°C and mixing, followed by adding AMF fungal microspheres at ≤28°C and mixing, then adding freeze-dried bacterial powder at ≤25°C and mixing, and finally spraying with humic acid solution. By strictly controlling the addition temperature, the activity of the carrier and microorganisms can be effectively guaranteed, allowing the components to synergistically release the efficacy of the soil conditioner.

[0019] In some embodiments, the selenium-enriched foliar fertilizer is prepared by the following method.

[0020] S1 Selenium Source Pre-activation: Dissolve the composite selenium source in deionized water at 40℃~50℃, then add alkyl polysaccharide APG0810 and disperse evenly to obtain selenium activation solution;

[0021] S2 Photocontrolled Directional Nucleation: A quercetin-salicylic acid composite solution is added to the selenium activation solution obtained in step S1, and nucleation is carried out for 10-20 minutes under mechanical stirring at 40℃~50℃ and 300rpm~500rpm, during which ultraviolet light irradiation is used; wherein, the quercetin-salicylic acid composite solution is obtained by dispersing quercetin and salicylic acid in deionized water, with pH=4~5;

[0022] S3 Mesoporous silica loading: At 50℃~55℃, mesoporous silica suspension is added to the solution obtained in step S2 in three portions, and the silica is fully dispersed after each addition; the volume ratio of the three additions is 50~60:20~30:10~20. The mesoporous silica suspension is obtained by dispersing mesoporous silica in deionized water, and the concentration is 5wt%~15wt%.

[0023] S4 Functional modification: A protective agent is added to the solution obtained in step S3, and the solution is spray-dried to obtain powder particles. Then, nano-titanium dioxide is coated on the surface of the obtained powder particles; the thickness of the nano-titanium dioxide coating is ≤100nm.

[0024] By activating the nano-selenium fertilizer, nucleating it under ultraviolet light, gradient loading, and then coating it with titanium dioxide, a nano-selenium fertilizer with smaller particle size can be obtained. It also has a high leaf adsorption rate and is resistant to photodegradation.

[0025] In some embodiments, in step S2, the quercetin-salicylic acid composite solution contains 0.05wt% to 0.01wt% quercetin and 0.05wt% to 0.01wt% salicylic acid.

[0026] In some embodiments, in step S2, the ultraviolet irradiation wavelength is 360–370 nm, and the irradiation intensity is ≥30 mW / cm². 2 , the nucleation particle size is small.

[0027] The present invention also provides the application of the fertilization method described herein in the cultivation of citrus or grapefruit.

[0028] In some embodiments, the application rate of the soil conditioner is 200 kg / mu to 250 kg / mu; the application rate of the selenium-enriched foliar fertilizer is 450 mL / mu to 650 mL / mu, diluted with water at a ratio of 150 to 200 times.

[0029] In some embodiments, when used for grapefruit or citrus cultivation, the fertilization method includes:

[0030] Apply the aforementioned soil conditioner 1-2 months before the flower bud stage.

[0031] Apply basic organic fertilizer and phosphate fertilizer during the spring shoot or flower bud stage, and spray the selenium-enriched foliar fertilizer and humic acid.

[0032] During the fruit enlargement period, apply yeast-derived organic fertilizer and water-soluble compound fertilizer to each plant by trenching, and spray the selenium-enriched foliar fertilizer at the same time.

[0033] At the end of the fruit enlargement period or the color-changing period, apply potassium dihydrogen phosphate and the selenium-enriched foliar fertilizer as a foliar spray.

[0034] By combining basic fertilizers, soil conditioners, and selenium-enriched foliar fertilizers, problems such as soil acidification, micronutrient deficiency, organic matter replenishment, efficient selenium and silicon supply (and the introduction of beneficial microorganisms) in the cultivation of citrus or pomelos can be better solved, laying a comprehensive soil and nutrient foundation for high-yield, high-quality, and safe selenium-enriched citrus or pomelos.

[0035] In some embodiments, the basic organic fertilizer is peanut bran, with an application rate of 1.0 kg / plant to 2 kg / plant; the phosphate fertilizer is superphosphate, with an application rate of 0.15 kg / plant to 0.3 kg / plant; the yeast-derived organic fertilizer is applied at a rate of 0.25 kg / plant to 0.3 kg / plant; and the water-soluble compound fertilizer is 13-5-27 compound fertilizer, with an application rate of 0.15 kg / plant to 0.25 kg / plant.

[0036] The beneficial effects of this invention are:

[0037] This invention combines specific soil conditioners with selenium-enriched foliar fertilizers, achieving synergistic effects between roots and leaves. This solves the problems of soil acidification and selenium addition during fruit tree cultivation, improves fruit quality, increases organic selenium content, and enhances the total flavonoid content in the fruit. The fertilization method of this invention is particularly suitable for the cultivation of citrus, grapefruit, and other fruit trees. Detailed Implementation

[0038] This invention provides a root-leaf synergistic method for selenium-enriched and cadmium-reducing fertilization of fruit trees. Before the flower bud stage, a soil conditioner is applied by burying it in the soil. During the spring shoot and / or flower bud stage, fruit enlargement stage, and color-changing stage, selenium-enriched foliar fertilizer is sprayed. This provides selenium reserves for the fruit trees before the flower bud stage, activates flavonoid synthase, and promotes later flavonoid synthesis. The combined application of foliar fertilizer during the spring shoot and / or flower bud stage and the fruiting stage further increases selenium absorption, increases fruit peel thickness, enhances the levels of essential elements in the fruit, promotes flavonoid synthesis, and is rich in silicon. Silicon deposition can strengthen the fruit peel structure. Root-leaf synergy adjusts soil acidification, efficiently supplies selenium and silicon, improves fruit quality, and increases the selenium content of the fruit.

[0039] The soil conditioner used in the fertilization method of this invention includes: 60-70 parts by weight of calcined Inner Mongolia calcium magnesium silicate mineral powder, 20-30 parts by weight of sterilized and decomposed straw powder, 10-15 parts by weight of modified attapulgite clay, 1-3 parts by weight of humic acid, 3-5 parts by weight of AMF fungal microspheres, and 1-3 parts by weight of freeze-dried bacterial powder. The AMF fungal microspheres have a diameter of 1 mm-2 mm, and the freeze-dried bacterial powder includes nitrogen-fixing bacteria and silica-solubilizing bacteria. The modified attapulgite clay is magnesium-based attapulgite clay modified with a citric acid-ferric chloride composite solution, with a specific surface area ≥120 m². 2 / g; among which calcined Inner Mongolia calcium magnesium silicate ore powder can provide alkaline ions (Ca 2+ / Mg 2+ This process neutralizes acidity and releases Si, Se, and rare earth elements; sterilized and composted straw powder replaces manure, providing a carbon source and avoiding the risk of pathogens; modified attapulgite clay can specifically adsorb and passivate Cd; AMF fungal microspheres and freeze-dried bacterial powder can provide microorganisms and activate symbiosis, synergistically improving the selenium activation rate; humic acid can enhance soil aggregate structure; and the components work synergistically with each other. Calcined Inner Mongolia calcium magnesium silicate powder neutralizes acidity, which is conducive to microbial colonization; at the same time, through the adsorption of modified attapulgite clay, silica-degrading bacteria are released simultaneously, and AMF is activated. The combination of these three factors achieves synergistic regulation of heavy metals and selenium through a passivation-activation dual pathway, effectively improving the soil while increasing the available selenium content.

[0040] In a preferred embodiment, the soil conditioner is prepared by first mixing calcined Inner Mongolia calcium magnesium silicate ore powder and sterilized composted straw powder at ≤35℃, then adding modified attapulgite clay at ≤30℃ and mixing, followed by adding AMF fungal microspheres at ≤28℃ and mixing, then adding freeze-dried bacterial powder at ≤25℃ and mixing, and finally spraying with humic acid solution. By strictly controlling the temperature at which each component is added, the activity of the carrier or the survival rate of the microorganisms can be effectively guaranteed, allowing the components to synergistically release the efficacy of the soil conditioner.

[0041] In a preferred embodiment, the calcined Inner Mongolia calcium-magnesium-silicon ore powder in the above-mentioned soil conditioner is produced by crushing Inner Mongolia calcium-magnesium-silicon ore, calcining it at 600℃~700℃, and finally ball milling it to a specific surface area ≥20m². 2 The sample prepared by / g has good adsorption effect and can better release various trace elements and selenium.

[0042] In a preferred embodiment, the AMF fungal microspheres in the above-mentioned soil conditioner are obtained by mixing AMF fungal spores with chitosan solution, activating the mixture at 25℃~28℃ for 10h~15h, then adding sodium alginate and modified attapulgite clay to encapsulate the microspheres, and finally adding calcium chloride solution for solidification. This method better maintains the activity of AMF fungi and facilitates their colonization in acidic soils. Preferably, during encapsulation, the concentration of the chitosan solution is 0.05wt%~0.15wt%, and the mass ratio of AMF fungal spores to chitosan solution is 1:3~5; according to the mass ratio, sodium alginate:modified attapulgite clay = 2~3:1, and the concentration of the calcium chloride solution is 0.1M~0.3M. After encapsulation, the diameter of the AMF fungal microspheres is controlled at 1mm~2mm, which ensures effective release while also facilitating root colonization. If the diameter is <1mm, the AMF spores are released too quickly; if the diameter is >2mm, root colonization is delayed. The modified attapulgite clay used in the AMF fungal microsphere encapsulation process can be the same as the modified attapulgite clay used in the assembly of the aforementioned soil conditioner.

[0043] In a preferred embodiment, the AMF fungus in the soil conditioner is *Rhizophagus irregularis*. *Rhizophagus irregularis* can form mycorrhizal symbionts with most terrestrial plants, increasing the plant's absorption efficiency of mineral nutrients such as phosphorus and nitrogen from the soil, and enhancing the plant's tolerance to abiotic stresses such as drought, salinity, and heavy metals. However, its colonization rate is low in acidic environments; microsphere encapsulation can improve its colonization rate in acidic soils. In a preferred specific embodiment, the AMF fungus is *Rhizophagus irregularis* with accession number CCTCC AF 2018005.

[0044] In a preferred embodiment, the AMF fungal microspheres in the above-mentioned soil conditioner contain ≥8 wt% of the fungal agent.

[0045] In a preferred embodiment, the freeze-dried bacterial powder in the soil conditioner is prepared by centrifuging the nitrogen-fixing bacteria and silica-solubilizing bacteria, mixing them with trehalose, pre-freezing at -35°C to -45°C, and then drying in a cold trap at -50°C to -60°C. This overcomes the problem of microorganisms' difficulty in surviving in acidic soils and improves the colonization rate. Preferably, the concentration of the trehalose solution is 8wt% to 13wt% to better protect bacterial activity. Preferably, the nitrogen-fixing bacteria are *Azotrophus brasiliensis*, and the silica-solubilizing bacteria are *Bacillus circulans*. Preferably, the viable bacteria content in the freeze-dried bacterial powder is ≥1×10⁻⁶. 9 CFU / g. More preferably, the viable counts of *Azotrophus brasiliensis* and *Bacillus circulatoryus* in the lyophilized bacterial powder are both ≥5 × 10⁻⁶. 8 CFU / g, total viable bacteria content ≥1×10 9 CFU / g

[0046] In a preferred embodiment, the silica-degrading bacterium is *Azospirillum brasilense* with accession number CGMCC 1.1767. The nitrogen-fixing bacterium is *Bacillus circulans* with accession number ACCC 01123.

[0047] The fertilization method of this invention uses a selenium-enriched foliar fertilizer comprising: 15-25 parts by weight of a composite selenium source, 10-15 parts by weight of an alkyl polysaccharide APG0810, 10-15 parts by weight of quercetin and salicylic acid, 45-60 parts by weight of mesoporous silica, and 3-5 parts by weight of nano-titanium dioxide. The composite selenium source is composed of sodium selenite and selenomethionine, with a molar ratio of sodium selenite to selenomethionine of 1:1-2.5; the mass ratio of quercetin to salicylic acid is 1:1-1.5; and the mesoporous silica has a pore size of 8 nm-12 nm and a particle size of 30 nm-100 nm. By using mesoporous silica as a carrier and combining it with the composite selenium source, the organic selenium content can be increased. Simultaneously, the addition of alkyl polysaccharides improves surface wettability and enhances adsorption and adhesion rates.

[0048] In a preferred embodiment, the selenium-enriched foliar fertilizer is prepared by the following method:

[0049] S1 Selenium Source Pre-activation: Dissolve the composite selenium source in deionized water at 40℃~50℃, then add alkyl polysaccharide APG0810 and disperse evenly to obtain selenium activation solution;

[0050] S2 Photocontrolled Directional Nucleation: A quercetin-salicylic acid composite solution is added to the selenium activation solution obtained in step S1, and nucleation is carried out for 10-20 minutes under mechanical stirring at 40-50°C and 300-500 rpm, during which ultraviolet irradiation is used; wherein, the quercetin-salicylic acid composite solution is obtained by dispersing quercetin and salicylic acid in deionized water, with a pH of 4-5;

[0051] S3 Mesoporous silica loading: At 50℃~55℃, mesoporous silica suspension is added to the solution obtained in step S2 in three portions, and the silica is fully dispersed after each addition; the volume ratio of the three additions is 50~60:20~30:10~20. The mesoporous silica suspension is obtained by dispersing mesoporous silica in deionized water, and the concentration is 5~15wt%.

[0052] S4 Functional modification: A protective agent is added to the solution obtained in step S3, and the solution is spray-dried to obtain powder particles. Then, nano-titanium dioxide is coated on the surface of the obtained powder particles. The coating thickness of the nano-titanium dioxide is ≤100nm. For example, it can be 20nm, 40nm, 60nm, 80nm, 100nm, etc.

[0053] The selenium-enriched foliar fertilizer prepared by this method has small nano-selenium particle size, is resistant to photodegradation, has good stability, and has a high leaf surface adsorption rate.

[0054] In some embodiments, in step S2, the quercetin-salicylic acid composite solution contains 0.05wt% to 0.01wt% quercetin and 0.05wt% to 0.01wt% salicylic acid.

[0055] In some embodiments, in step S2, the ultraviolet irradiation wavelength is 360–370 nm, and the irradiation intensity is ≥30 mW / cm². 2 The resulting selenium nanoparticles are smaller, which helps to improve leaf surface absorption. For example, the irradiation wavelength can be 360nm, 365nm, 370nm, etc., and the irradiation intensity can be 30mW / cm². 2 40mW / cm 2 50mW / cm 2 wait.

[0056] The fertilization method of the present invention can be used for the planting of fruit trees, especially suitable for the planting of citrus or pomelo.

[0057] In some embodiments, when used for citrus or grapefruit cultivation, the fertilization method includes the steps of:

[0058] Apply the aforementioned soil conditioner 1-2 months before the flower bud stage.

[0059] Apply basic organic fertilizer and phosphate fertilizer during the spring shoot or flower bud stage, and spray the selenium-enriched foliar fertilizer and humic acid.

[0060] During the fruit enlargement period, apply yeast-derived organic fertilizer and water-soluble compound fertilizer to each plant by trenching, and spray the selenium-enriched foliar fertilizer at the same time.

[0061] At the end of the fruit enlargement period or during the color change period, apply potassium dihydrogen phosphate and the selenium-enriched foliar fertilizer as a foliar spray.

[0062] The combined use of basic fertilizer, soil conditioner of this invention, and selenium-enriched foliar fertilizer better solves problems such as soil acidification, micronutrient deficiency, organic matter replenishment, efficient selenium and silicon supply (and introduction of beneficial microorganisms) in the process of citrus or pomelo cultivation, laying a comprehensive soil and nutrient foundation for high yield, high quality, and safety of selenium-enriched citrus or pomelo.

[0063] In some embodiments, the application rate of the soil conditioner is 200 kg / mu to 250 kg / mu; the application rate of the selenium-enriched foliar fertilizer is 450 mL / mu to 650 mL / mu, diluted with water at a ratio of 150 to 200 times.

[0064] In some embodiments, the basic organic fertilizer is peanut bran, with an application rate of 1.0 kg / plant to 2 kg / plant; the phosphate fertilizer is superphosphate, with an application rate of 0.15 kg / plant to 0.3 kg / plant; the yeast-derived organic fertilizer is applied at a rate of 0.25 kg / plant to 0.3 kg / plant; and the water-soluble compound fertilizer is 13-5-27 compound fertilizer, with an application rate of 0.15 kg / plant to 0.25 kg / plant.

[0065] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with specific examples. Obviously, the described embodiments are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0066] Example 1: Preparation of Soil Conditioner

[0067] S1. Raw material preparation:

[0068] 1. Calcination of calcium-magnesium-silicon ore powder: The calcium-magnesium-silicon ore from Inner Mongolia is crushed to particles ≤5mm, then calcined at 600℃ for 3 hours, and ball-milled to a specific surface area of ​​28.2m². 2 / g, to obtain calcined Inner Mongolia calcium magnesium silicate ore powder.

[0069] 2. Sterilization treatment of decomposed straw powder: Sterilize decomposed rice straw by steaming at 121℃ for 30 minutes, then spray with 2% humic acid ethanol solution, and dry at 60℃ until the moisture content is ≤5%.

[0070] 3. AMF fungal embedding:

[0071] Activation: Rhizophagus irregularis spores (preservation number: CCTCC AF 2018005) were mixed with 0.1% chitosan oligosaccharide solution at a ratio of 1:4 (by weight) and activated by shaking at 28°C for 12 h to obtain AMF spore solution;

[0072] Encapsulation: Sodium alginate and modified attapulgite clay were mixed at a mass ratio of 3:1, then added to AMF spore solution to encapsulate spores. Finally, 0.1M calcium chloride was added and solidified for 15 minutes to obtain 1.5 mm AMF fungal microspheres with a fungal agent content of 8 wt%.

[0073] The modified attapulgite clay was prepared by the following method:

[0074] Magnesium-based attapulgite clay (MgO content ≥18%, origin: Xuyi, Jiangsu Province) was crushed to 200 mesh. Then, a 5% citric acid-0.1 mol / L FeCl3 composite solution was added at a solid-liquid ratio of 1:10. The mixture was stirred at 80℃ for 2 hours for modification. Afterward, it was centrifuged and washed until pH neutral, dried at 105℃, and ground to a specific surface area of ​​125 m² / g. 2 / g (determined by BET method). The Cd adsorption capacity of the modified attapulgite clay was 152 mg / kg (measured according to GB / T31290-2014).

[0075] 4. Bacterial freeze-drying:

[0076] Azospirillum brasilense (accession number: CGMCC 1.1767) and Bacillus circulans (accession number: ACCC 01123) were mixed at a 1:1 ratio. The bacterial cells were collected by centrifugation, and then 10 wt% trehalose solution was added as a preservative. The mixture was then pre-frozen at -40°C for 2 hours, followed by drying in a cold trap at -55°C for 48 hours. Finally, the mixture was passed through a 200-mesh sieve to obtain a lyophilized bacterial powder. Plate count analysis showed that the viable cell count in the lyophilized bacterial powder was 1.2 × 10⁻⁶. 9 CFU / g.

[0077] S2 composite assembly:

[0078] At 35°C, 60 parts by weight of calcined Inner Mongolia calcium magnesium silicate ore powder obtained in step S1 and 20 parts by weight of sterilized and decomposed straw powder obtained in step S1 were added to a twin-screw mixer and stirred at 50 rpm. Then, at 30°C, 10 parts by weight of the modified attapulgite clay obtained above were added and stirred. Next, at 28°C, 4 parts by weight of AMF fungal microspheres (containing 8% bacterial agent) obtained in step S1 were added and stirred for 20 min. Then, at 25°C, 2 parts by weight of the freeze-dried bacterial powder obtained in step S1 were added and stirred. Finally, the mixture was conveyed to a fluidized bed and sprayed with 2 wt% humic acid solution, controlling the moisture content to ≤8%, to obtain a mineral microbial soil conditioner.

[0079] Example 2: Preparation of Selenium-Enriched Foliar Fertilizer

[0080] S1 Selenium source pre-activation: Dissolve the composite selenium source consisting of 5 kg (approximately 29 mol) sodium selenite and 12 kg (approximately 58 mol) selenomethionine in 18000 L of 45℃ deionized water, then add 8 kg of alkyl polysaccharide APG0810 and stir at a constant temperature for 15 min to obtain the selenium activation solution.

[0081] S2 Photocontrolled Directional Nucleation: A quercetin-salicylic acid composite solution (pH = 4.5) was added to the selenium activation solution obtained in step S1. The quercetin-salicylic acid composite solution was obtained by dissolving 5 kg of quercetin and 5 kg of salicylic acid in deionized water, wherein the concentration of quercetin was 0.05 wt%. Nucleation was then carried out for 15 minutes under mechanical stirring at 45°C and 400 rpm, during which 370 nm ultraviolet light (irradiation intensity 40 mW / cm²) was used. 2 );

[0082] S3 Mesoporous Silica Loading: At 50°C, a mesoporous silica suspension was added to the solution obtained in step S2 in three separate additions. The silica suspension was obtained by dispersing 60 kg of mesoporous silica in 540 kg of deionized water, wherein the mesoporous silica particle size was 50 nm and the mesopore size was 10 nm. The specific addition method is shown in Table 1 below.

[0083] Table 1. Method of adding mesoporous silica in Example 2

[0084] batch Volume ratio Operating parameters 1 50％ Ultrasound at 50℃ for 7 minutes (40kHz) 2 30％ Ultrasound was performed for 7 minutes (40kHz) after a 2-minute interval. 3 20％ Ultrasound for 12 minutes (40 kHz)

[0085] S4 Functional modification: 0.2 wt% trehalose solution is added to the solution obtained in step S3 as a protective agent, and the solution is spray-dried at 180°C for inlet air and 85°C for outlet air to obtain powder particles. Then, the obtained powder particles are coated with nano titanium dioxide through a fluidized bed, and the finished titanium dioxide coating thickness is 100 nm.

[0086] S5 Finally, the product is passed through a 200-mesh sieve, sealed in a nitrogen-filled aluminum foil bag, and stored away from light (shelf life 24 months).

[0087] Example 3: Root-leaf synergistic fertilization method

[0088] In the following examples, the soil conditioner and selenium-enriched foliar fertilizer prepared in Examples 1 and 2 were used for the cultivation of pomelos.

[0089] Example 3-1 Huazhou Pomelo

[0090] Test location: Red soil area, Shita Village, Pingding Town, Huazhou City, Guangdong Province (GPS: 21.68°N, 110.59°E)

[0091] Trial period: March 2021 (planting) to December 2023 (harvesting)

[0092] Tested variety: 3-year-old Huazhou pomelo (medicinal variety, seedling source: Huazhou Traditional Chinese Medicine Industrial Park)

[0093] Soil composition: pH 5.1, organic matter 18.9 g / kg, available selenium 0.07 mg / kg

[0094] Complete Planting Management Methods (2021-2023)

[0095] The subjects were divided into four groups: T1, T2, T3, and CK (control group). The overall protocol is as follows:

[0096] Table 2. Scheme Design for Each Treatment Group in Example 3-1

[0097] Processing group Soil conditioner Foliar Selenium-Enriched Foliar Fertilizer Solution T1 (combination group) 200kg / mu Flower bud stage + swelling stage + color change T2 (single-leaf group) —— Same as T1 spraying plan T3 (single soil group) 200kg / mu Spray an equal amount of clean water CK (control) —— Spray an equal amount of clean water

[0098] 1. Soil pretreatment (March 2021)

[0099] Deep tillage and acidification: Rotary tillage to a depth of 40cm to remove gravel and weeds.

[0100] 2. Application of soil conditioners:

[0101] Groups T1 / T3: At the end of December 2021, apply 250 kg / mu of the soil conditioner obtained in Example 1, till and mix thoroughly (to a soil layer of 20-30 cm), and then drip irrigate to settle (using 50 m³ of water per mu). 3 ).

[0102] 3. Key procedures during the reproductive period

[0103] The key operations during the growth period of each treatment group are shown in Table 3. The amount of selenium-enriched foliar fertilizer to be sprayed is: diluted with water at a weight ratio of 1:150-200, about 50L / mu. When spraying, spray it evenly on the plants in a "mist" state, so that the leaves and fruits of the whole plant are evenly covered with mist droplets without dripping water.

[0104] Table 3 Key procedures during the reproductive period for each treatment group in Example 3-1

[0105]

[0106] 4. Unified Management:

[0107] Drip irrigation: 21 times throughout the growing season (soil moisture maintained at 60% ± 5%).

[0108] Pest and disease control: 6 times (using imidacloprid + difenoconazole uniformly),

[0109] Effective accumulated temperature: 4820℃ (≥10℃ active accumulated temperature).

[0110] The harvest data was collected in December 2023 and is shown in Tables 4-5 below. After harvesting, the soil samples from each treatment group were tested, as shown in Table 6.

[0111] In the following examples, the method for determining the weight of a single fruit was based on GB / T 8210-2011 "Standard for Grading the Quality of Fresh Fruits"; the measurement of soluble solids was based on NY / T 2637-2014 "Determination of Soluble Solids Content in Fruits and Fruit Products - Refractometer Method"; and the measurement of total selenium and organic selenium content was based on GB 5009.93-2017 "National Food Safety Standard - Determination of Selenium in Food". Flavonoid content was measured using the ultraviolet spectrophotometric AlCl3 complexometric colorimetric method at a detection wavelength of 510 nm.

[0112] Table 4. Data collected from each treatment group in Example 3-1

[0113] index T1 (combination group) T2 (Single-leaf group) T3 (single soil group) CK (control) Yield per mu (kg) 2320 2130 2030 1930 Single fruit weight (g) 140 128 123 118 Peel thickness (mm) 4.4 3.7 3.8 3.1 Total selenium content (mg / kg) 0.83 0.51 0.23 0.09 Organic selenium percentage (%) 81 64 31 29 Flavonoid content (%) 8.0 6.3 5.7 5.6 Fruit cracking rate (%) 3.5 9.2 8.7 24.1

[0114] Table 5. Economic benefit analysis data for each treatment group in Example 3-1

[0115] project T1 (combination group) T2 (Single-leaf group) CK (control) Yield per mu (kg) 2320 2130 1930 Marketable fruit rate (%) 92.5％ 84.3％ 68.7％ Purchase price of high-quality fruit (yuan / kg) 15.0 13.5 12.0 Output value per mu (yuan) 34,800 28,755 23,160 Net income per mu (yuan) 26,20 20,455 15,260

[0116] Table 6 Soil analysis data for each treatment group in Example 3-1 (tested in December 2023)

[0117] index T1 (combination group) T3 (single soil group) CK (control) Soil pH 6.6 6.3 5.1 Available selenium (mg / kg) 0.32 0.15 0.07 Available potassium (mg / kg) 152 138 96

[0118] As can be seen from Table 4-6, the fertilization method of this embodiment has the following effects:

[0119] (1) Yield increase: The T1 group, which uses a combined root and leaf treatment, yielded 390 kg / mu more than the CK (control) group, an increase of about 20.2%, and 190 kg / mu more than the T2 single leaf treatment group, an increase of about 8.9%. Based on the 2023 Huazhou pomelo market price, the premium price of high-quality fruit in the combined treatment group was +25%, and the net income per mu increased by RMB 10,940 compared with the CK.

[0120] (2) Quality Improvement: Peel Thickness: The peel thickness of group T1 was 4.4 mm thicker than that of group CK (control), an increase of approximately 41.9%, and approximately 18.9% thicker than that of group T2 (single leaf group). Flavonoid Enrichment: The flavonoid content of the peel in group T1 was approximately 42.9% higher than that in group CK (control), and approximately 27.0% higher than that in group T1 (single leaf group).

[0121] (3) Selenium fortification significantly increased the total selenium content and the proportion of organic selenium in the fruit. The total selenium content of the T1 treatment group was 0.83 mg / kg, which was 5.5 times the selenium enrichment standard, and the proportion of organic selenium was 81%. In addition, according to Table 6, the available selenium content in the soil of the T1 treatment group was 357% higher than that of the CK (control) group, which proves that the soil conditioner of the present invention continuously releases selenium, increases the selenium content in the soil, and thus increases the selenium content in the fruit.

[0122] (4) The fruit's resistance to adverse conditions was improved. The cracking rate of the T1 group was only 3.5%, and the anthracnose incidence rate was only 4.8%, which were significantly higher than those of other groups.

[0123] Example 3-2 Huazhou Pomelo

[0124] Test location: Red soil area, Shita Village, Pingding Town, Huazhou City, Guangdong Province (GPS: 21.68°N, 110.59°E)

[0125] Experiment period: December 26, 2024 to June 5, 2025 (harvesting)

[0126] Tested variety: 4-year-old Huazhou pomelo (medicinal variety, seedling source: Huazhou Traditional Chinese Medicine Industrial Park)

[0127] Soil composition: pH 5.1, organic matter 18.9 g / kg, available selenium 0.07 mg / kg

[0128] Complete planting management methods

[0129] The plant spacing was 3.5m*4.5m, with about 18 plants per mu (667 square meters). The plants were divided into four groups: T1, T2, T3, and CK (control group). The overall design scheme is shown in Table 7.

[0130] Table 7. Scheme Design for Each Treatment Group in Example 3-2

[0131]

[0132]

[0133] 1. Application of soil conditioner:

[0134] Group T1 / T3: On December 27, 2024, apply 200 kg / mu of the solution obtained in Example 1, till and mix thoroughly (to a soil layer of 20-30 cm), and then drip irrigate to settle the soil (using 50 ml of water per mu). 3).

[0135] 2. Key procedures during the reproductive period:

[0136] The key operations for each treatment group during the growth period are shown in Table 8. Among them, the amount of selenium-enriched foliar fertilizer to be sprayed is: diluted with water at a weight ratio of 1:150-200, about 50L / mu. When spraying, spray it evenly on the plants in a "mist" state, so that the leaves and fruits of the whole plant are evenly covered with mist droplets without dripping water.

[0137] Table 8 Key procedures during the reproductive period for each treatment group in Example 3-2

[0138]

[0139]

[0140] 3. Unified Management:

[0141] Drip irrigation: 12 times throughout the growing season (soil moisture maintained at 60% ± 5%).

[0142] Pest and disease control: 4 times (using imidacloprid + difenoconazole).

[0143] The harvest data collected in June 2025 is shown in Table 9 below.

[0144] Table 9 Harvesting results of each treatment group in Example 3-2

[0145] Group Peel thickness (mm) Total flavonoids (%) Selenium content (mg / kg) Fruit cracking rate (%) T1 4.8 8.8 0.93 3.5 T2 3.4 6.0 0.46 9.2 T3 3.8 5.7 0.23 8.7 CK 2.9 5.4 0.08 24.1

[0146] It can be seen that the fertilization method of the present invention can effectively improve the quality of pomelo fruit and increase the content of selenium and flavonoids. Specifically, compared with the control group, the T1 combined treatment group showed a 40.6% increase in peel thickness, a 41.4% increase in total flavonoid content, a 750% increase in selenium content, and a 10.6% decrease in fruit cracking rate.

[0147] The technical features of the embodiments described above can be combined arbitrarily. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as the combination of these technical features does not contradict each other, it should be considered within the scope of this specification. It should be noted that those skilled in the art can make several modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this patent should be determined by the appended claims.

Claims

1. A root-leaf synergistic method for selenium-enriched cadmium-reducing fertilization, used in the cultivation of citrus fruits, characterized in that, Includes the following steps: Apply soil conditioner before the flower bud stage; Spray selenium-enriched foliar fertilizer during the spring shoot stage and / or flower bud stage, fruit enlargement stage and color change stage. The soil conditioner comprises 60-70 parts by weight of calcined Inner Mongolia calcium magnesium silicate ore powder, 20-30 parts by weight of sterilized and decomposed straw powder, 10-15 parts by weight of modified attapulgite clay, 1-3 parts by weight of humic acid, 3-5 parts by weight of AMF fungal microspheres, and 1-3 parts by weight of freeze-dried bacterial powder. The AMF fungal microspheres have a diameter of 1mm-2mm, and the freeze-dried bacterial powder includes nitrogen-fixing bacteria and silica-solubilizing bacteria. The modified attapulgite clay is magnesium-based attapulgite clay modified with a citric acid-ferric chloride composite solution, with a specific surface area ≥120m². 2 / g; The selenium-enriched foliar fertilizer comprises 15-25 parts by weight of a composite selenium source, 10-15 parts by weight of an alkyl polysaccharide APG0810, 10-15 parts by weight of quercetin and salicylic acid, 45-60 parts by weight of mesoporous silica, and 3-5 parts by weight of nano-titanium dioxide. The composite selenium source is composed of sodium selenite and selenomethionine, with a molar ratio of sodium selenite to selenomethionine of 1:1-2.5; the mass ratio of quercetin to salicylic acid is 1:1-1.5; and the mesoporous silica has a pore size of 8nm-12nm and a particle size of 30nm-100nm.

2. The fertilization method according to claim 1, characterized in that, The soil conditioner is prepared by first mixing and stirring the calcined Inner Mongolia calcium magnesium silicate ore powder and sterilized composted straw powder at ≤ 35℃, then adding the modified attapulgite clay at ≤ 30℃ and mixing, then adding the AMF fungal microspheres at ≤ 28℃ and mixing, then adding the freeze-dried bacterial powder at ≤ 25℃ and mixing, and finally spraying with humic acid solution.

3. The fertilization method according to claim 1, characterized in that, In the soil conditioner The calcined Inner Mongolia calcium-magnesium-silicon ore powder is produced by crushing Inner Mongolia calcium-magnesium-silicon ore, calcining it at 600℃~700℃, and finally ball milling it to a specific surface area ≥20m². 2 / g prepared; The AMF fungal microspheres are obtained by mixing AMF fungal spores with chitosan solution, activating them at 25℃~28℃ for 10h~15h, adding sodium alginate and modified attapulgite clay to encapsulate them into microspheres, and then adding calcium chloride solution to solidify them. The bacterial freeze-dried powder is prepared by centrifuging the nitrogen-fixing bacteria and silica-solubilizing bacteria, mixing them with trehalose, pre-freezing at -35℃ to -45℃, and then drying in a cold trap at -50℃ to -60℃. The AMF fungus is Rhizopus heteromorphus, the nitrogen-fixing bacterium is Azotobacter brasiliensis, and the silica-degrading bacterium is Bacillus circulans.

4. The fertilization method according to claim 1, characterized in that, The selenium-enriched foliar fertilizer is prepared by the following method. S1 Selenium source pre-activation: Dissolve the composite selenium source in deionized water at 40℃~50℃, then add alkyl polysaccharide APG0810 and disperse evenly to obtain a selenium activation solution; S2 Photocontrolled directional nucleation: A quercetin-salicylic acid composite solution is added to the selenium activation solution obtained in step S1, and nucleation is carried out for 10-20 minutes under mechanical stirring at 40℃~50℃ and 300rpm~500rpm, during which ultraviolet irradiation is used; wherein, the quercetin-salicylic acid composite solution is obtained by dispersing quercetin and salicylic acid in deionized water, with pH = 4~5; S3 Mesoporous silica loading: At 50℃~55℃, a mesoporous silica suspension is added to the solution obtained in step S2 in three separate additions, with thorough dispersion after each addition; the volume ratio of the three additions is 50~60:20~30:10~20, and the mesoporous silica suspension is obtained by dispersing the mesoporous silica in deionized water, with a concentration of 5wt%~15wt%; S4 Functional modification: A protective agent is added to the solution obtained in step S3, and the solution is spray-dried to obtain powder particles. Then, the nano-titanium dioxide is coated on the surface of the obtained powder particles; the coating thickness of the nano-titanium dioxide is ≤100nm.

5. The fertilization method according to claim 4, characterized in that, In step S2, the quercetin-salicylic acid composite solution contains 0.05wt% to 0.01wt% quercetin and 0.05wt% to 0.01wt% salicylic acid.

6. The fertilization method according to claim 4, characterized in that, In step S2, the ultraviolet irradiation wavelength is 360nm~370nm, and the irradiation intensity is ≥30mW / cm². 2 .

7. The application of the fertilization method according to any one of claims 1-6 in citrus cultivation.

8. The application according to claim 7, characterized in that, The application rate of the soil conditioner is 200 kg / mu to 250 kg / mu; the application rate of the selenium-enriched foliar fertilizer is 450 mL / mu to 650 mL / mu, diluted with water at a ratio of 150 to 200 times.

9. The application according to claim 7, characterized in that, The fertilization method includes: Apply the aforementioned soil conditioner 1-2 months before the flower bud stage. During the spring shoot or flower bud stage, apply basic organic fertilizer and phosphate fertilizer, and spray the selenium-enriched foliar fertilizer and humic acid. During the fruit enlargement period, each plant should be dredged and bury with yeast-derived organic fertilizer and water-soluble compound fertilizer, while simultaneously spraying with ammonium molybdate and the aforementioned selenium-enriched foliar fertilizer. During the color-changing period or the middle and late stages of fruit enlargement, potassium dihydrogen phosphate and the selenium-enriched foliar fertilizer are sprayed on the leaves.

10. The application according to claim 9, characterized in that, The basic organic fertilizer is peanut bran, with an application rate of 1.0 kg / plant to 2 kg / plant; the phosphate fertilizer is superphosphate, with an application rate of 0.15 kg / plant to 0.3 kg / plant; the yeast-derived organic fertilizer is applied at a rate of 0.25 kg / plant to 0.3 kg / plant; and the water-soluble compound fertilizer is 13-5-27 compound fertilizer, with an application rate of 0.15 kg / plant to 0.25 kg / plant.

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