Rice cultivation method capable of effectively reducing cadmium content of rice

Abstract

The invention discloses a rice cultivation method capable of effectively reducing cadmium content of rice, and relates to the technical field of rice cultivation methods, the rice cultivation method comprises the following raw materials in parts by weight: a base fertilizer, a cadmium reducing agent, a biochar-loaded microbial agent, a nano-hydroxyapatite suspension, a humic acid-silicon material, magnetic biochar and a duckweed seed source, and comprises the following steps: in a germination period, carrying out germination; detecting the cadmium content of a rice seed culture solution, adding a charcoal-loaded microbial inoculum and a nano-hydroxyapatite suspension to adjust the pH value, spreading rice seeds into the culture solution, and soaking; in the seedling stage, a humic acid-silicon material and magnetic biochar are spread; in the period of seedling establishment, duckweed seed sources are sown, base fertilizer is applied after irrigation, seedlings are transplanted, and fishes are put synchronously; in the tillering stage, the cadmium content of the duckweed is monitored, and nano silica sol is sprayed; removing duckweed before heading; in the young ear stage, the cadmium reducing agent is added twice, and by means of pollution removal, physiological barrier and resource circulation, absorption and transfer of cadmium are reduced, bioavailability of cadmium is reduced, and the cadmium content of rice is effectively reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of rice cultivation methods, and in particular to a rice cultivation method for effectively reducing the cadmium content in rice. Background Art

[0002] "Cadmium rice" refers to rice whose cadmium content exceeds the food safety standard. According to my country's food standards, rice with a cadmium content of more than 0.2 mg per kilogram is called "cadmium rice."

[0003] For example, patent publication number CN113016532B describes a rice cultivation method that effectively reduces the cadmium content in rice. This method reduces the cadmium content in rice by comprehensively regulating the rice growth environment from germination to maturity, blocking the path of cadmium migration from soil / water to rice. Furthermore, the method reduces the impact of cadmium on rice growth by adjusting soil pH, the seedling transplanting environment, and improving rice photosynthesis capacity during the planting process, resulting in better rice growth. However, although the above scheme uses passivators such as quicklime and rice husk ash to reduce soil cadmium activity, there are still problems with cadmium retention in the soil, waste of arable land due to fish ditch excavation, and secondary pollution caused by NaOH sludge. Summary of the Invention

[0004] The embodiments of the present application provide a rice cultivation method that effectively reduces the cadmium content in rice, thereby solving the technical problems of incomplete passivation, cadmium retention in the soil, waste of arable land, and secondary pollution in the prior art. By means of pollution removal, physiological barriers, and resource recycling, the absorption and transport of cadmium are reduced, the bioavailability of cadmium is reduced, and the cadmium content in rice is effectively reduced.

[0005] The present invention provides a rice cultivation method for effectively reducing the cadmium content of rice, comprising the following raw materials in parts by weight: 65 parts of base fertilizer, 20 parts of cadmium reducing agent, 20 parts of biochar-loaded bacterial agent, 15 parts of nanohydroxyapatite suspension, 35 parts of humic acid-silicon material, 25 parts of magnetic biochar, and 40 parts of duckweed seed source; The following steps are involved: S1. During the germination period, the cadmium content of the rice seed culture medium was tested, biochar-loaded bacterial agent and nanohydroxyapatite suspension were added, the pH was adjusted to 5.8-6.2, and the rice seeds were spread into the culture medium and soaked; S2, during the seedling stage, water the planting area, adjust the pH, and spread humic acid-silicon materials and magnetic biochar; S3: During the greening period, maintain a shallow water layer, sow duckweed seeds, apply basal fertilizer after irrigation, and transplant seedlings when the temperature is 32±1℃; release fish at the same time; S4, during the tillering stage, monitor the cadmium content of duckweed. On the 10th day after greening, spray nano-silica sol and remove duckweed 7 days before heading. S5, young ear stage, add cadmium reducing agent twice, the ratio is 1:3.5.

[0006] Furthermore, the biochar-loaded bacterial agent comprises a biochar with a specific surface area of ≥500 m² / g and a loaded Bacillus subtilis of ≥1×10 8 CFU / g.

[0007] Furthermore, the solid content of the nano-hydroxyapatite suspension is 10%, and the particle size of the nano-hydroxyapatite is 50-80 nm.

[0008] Furthermore, the humic acid-silicon material contains 30-35% humic acid, 15-20% SiO2, and 45-55% carrier filler.

[0009] Furthermore, the magnetic biochar has a Fe3O4 content of ≥30% and a magnetization intensity of ≥60 emu / g, and is recovered by magnetic separation with a field strength of ≥0.3T after transplanting.

[0010] Furthermore, in step S4, the cadmium content of duckweed is monitored every 10 days, with a threshold value of ≤150 mg / kg. When the threshold is exceeded, 30% of the duckweed is harvested, and 90% of the duckweed is removed 7 days before heading. The duckweed coverage is monitored by taking photos with a drone.

[0011] Furthermore, the magnetic biochar has a cylindrical rod-like structure with a total length of 1.0-1.5 mm, a diameter of 0.08-0.12 mm, an aspect ratio of (10-15):1, and is divided into a magnetic end and a non-magnetic segment, with the length of the magnetic end accounting for 15%-25%.

[0012] Furthermore, the magnetic end is loaded with a Fe3O4 magnetic layer, the thickness of the magnetic layer is 25-35 μm, and the magnetization intensity is ≥80 emu / g.

[0013] One or more technical solutions provided in the embodiments of this application have at least the following technical effects or advantages: First, by removing pollution rather than passivating it, the cadmium content in rice is reduced. The superparamagnetic properties of magnetic biochar are used to actively adsorb free cadmium in the soil, and cadmium can be recovered and removed from the soil using magnets, thus severing the pollution chain at the source and avoiding the risk of secondary activation caused by stagnation. At the same time, a duckweed-fish symbiotic system is introduced, utilizing the ecological chain of duckweed enriching cadmium in the water, fish ingesting it, and mineralizing it into inert CdS through fish feces. This is then removed through periodic harvesting, achieving biological output of the pollutant and forming a biological removal channel. Second, fish ditches are eliminated and duckweed is raised in shallow water throughout the fields (coverage rate: 60-70%). Grass carp, with their flattened bodies, can cruise with low energy consumption, improving arable land utilization. This is particularly well-suited for special terrains such as hilly terraces. Duckweed residue is returned to the fields or made into feed, replacing some concentrated feed. Third, biochar-loaded bacterial agents replace NaOH for pH adjustment. Microorganisms degrade organic cadmium while maintaining the balance of soil flora. They adsorb cadmium ions and secrete extracellular polymers to encapsulate and solidify them. Microbial metabolism produces organic acids, maintaining pH ≈ 6.0 and avoiding damage from chemical reagents. Double adsorption improves cadmium removal rate, and probiotics promote seed germination, replacing chemical pH adjustment. Nano-hydroxyapatite fixes cadmium through ion exchange and phosphate co-precipitation (forming Cd3(PO4)2), and is highly effective and stable in the pH range of 5-7 without the need for secondary acid adjustment. At the same time, the released calcium and phosphorus elements promote seedling growth. The rice husk ash barrier layer may affect the air permeability of the seedling root system. Humic acid-silicon material is used. Humic acid molecules contain a large number of active groups such as carboxyl and phenolic hydroxyl groups, which firmly bind to cadmium ions to form a stable humic acid-cadmium chelate, which makes the cadmium lose its free activity and converts the soluble cadmium that can be absorbed by rice into an inert bound state; silicate hydrolysis produces OH - ions, neutralize soil acidity, increase pH 0.5-1.0 units, silicon and humic acid synergistically increase soil cation exchange capacity, long-term control cadmium, and enhance fertilizer retention capacity. In addition, the released silicate is absorbed by the rice roots and a nano-silicon film is deposited on the root epidermis. Silicon strengthens the cell wall strength, thereby blocking cadmium from entering the root cells and reducing the transport of cadmium to the aboveground part. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 This is a physical picture of the magnetic biochar according to Example 3 of the present invention. DETAILED DESCRIPTION

[0015] To facilitate understanding of the present invention, the present application will be described more comprehensively below with reference to the relevant drawings; the drawings show preferred embodiments of the present invention, but the present invention can be implemented in many different forms and is not limited to the embodiments described herein; on the contrary, the purpose of providing these embodiments is to enable a more thorough and comprehensive understanding of the disclosed content of the present invention.

[0016] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this invention pertains; the terms used herein in the specification of the present invention are for the purpose of describing specific embodiments only and are not intended to limit the present invention; the term "and / or" used herein includes any and all combinations of one or more of the associated listed items.

[0017] Example 1: A rice cultivation method for effectively reducing the cadmium content in rice, comprising the following raw materials in parts by weight: 65 parts of base fertilizer, 20 parts of a cadmium-reducing agent, 20 parts of a biochar-loaded bacterial agent, 15 parts of a nanohydroxyapatite (nHAP) suspension, 35 parts of a humic acid-silicon material, 25 parts of magnetic biochar, and 40 parts of duckweed seed; Among them, the organic matter of base fertilizer is ≥45%, N-P2O5-K2O=8-5-7; The cadmium reduction agent contains 60% diatomaceous earth, 30% humic acid, and 10% potassium dihydrogen phosphate; Biochar loaded with bacterial agent, biochar specific surface area ≥500m² / g, loaded with Bacillus subtilis ≥1×10 8 CFU / g; The solid content of the nanohydroxyapatite suspension is 10%, wherein the nHAP particle size is 50-80 nm and the Ca / P molar ratio is 1.67; Humic acid-silicon material contains 30-35% humic acid, 15-20% SiO2, and 45-55% carrier filler; The Fe3O4 content of magnetic biochar is ≥30%, and the magnetization intensity is ≥60 emu / g; The duckweed provenance is Lemna minor, with a water content of ≤10% and a cadmium concentration factor (BCF) of ≥1000; The rice cultivation method for effectively reducing the cadmium content in rice specifically comprises the following steps: S1. During the germination period, the cadmium content of the rice seed culture medium was tested. If the cadmium content was greater than 0.005 mg / L, a biochar-loaded bacterial agent and a nanohydroxyapatite suspension were added. The cadmium was allowed to stand for 2 hours to allow the cadmium to form Cd3(PO4)2 precipitation and be degraded by microorganisms. The buffer system automatically maintained the pH at 5.8-6.2. The rice seeds were evenly spread in the culture medium, the temperature was controlled at 30±2°C, the dissolved oxygen content was controlled at ≥5 mg / L, and the seeds were soaked for 36 hours. During the seedling stage, water the planting area to a depth of 3 cm. After 2 days, test the soil pH. If the pH is >7.5 or <7.2, adjust it to 7.2-7.5 with sulfur powder or calcium carbonate. Evenly spread humic acid-silicon composite material and till it to a depth of 10 cm to mix it with the soil to chelate the soluble cadmium in the soil. Then, spread magnetic biochar to adsorb free cadmium. During the greening period, maintain a shallow water layer of 3-5 cm throughout the field and evenly sow duckweed seed (initial coverage rate 60-70%). Irrigate to a depth of 5 cm and apply basal fertilizer one day later. In the evening, when the temperature is 32±1°C, transplant the seedlings using a rice transplanter with a row spacing of 30 cm × 15 cm. Simultaneously, release 80 grass carp (5-8 cm in length) and 50 crucian carp (3-5 cm in length) per mu to clear any remaining bait. Among them, the coverage rate is calculated by drone photography monitoring; During the tillering stage, starting from the first day after the greening period, monitor the cadmium content of duckweed every 10 days (threshold ≤ 150 mg / kg). If the limit is exceeded, immediately harvest 30% of the duckweed and remove it from the field. On the 10th day after the greening period, spray the leaves with 0.1% nano-silica sol (particle size 20 nm) in the early morning before the dew has dried. Remove 90% of the duckweed 7 days before heading (keeping the coverage rate ≤ 10% to ensure pollination). S5. During the young ear stage, cadmium reducing agent was added to the water in the early and middle stages of the young ear. The ratio of adding cadmium reducing agent twice in the same area was 1:3.5, with an interval of 10-15 days.

[0018] Experiments were conducted on this technical solution. The difference between the comparative example and the present embodiment is that rice was cultivated using the method of publication number CN113016532B. Performance tests were performed on the experimental samples of Example 1 and the comparative example. 1. Cadmium content in rice: According to GB 5009.15-2014, National Food Safety Standard for the Determination of Cadmium in Foods, rice is husked after harvest, ground into rice flour, and subjected to nitric acid-hydrogen peroxide microwave digestion and determination by graphite furnace atomic absorption spectrometry. 2. Available cadmium in soil: According to HJ 804-2016 "Determination of Available Elements in Soil - Diethylenetriaminepentaacetic Acid Extraction-Inductively Coupled Plasma-Emission Spectrometry," DTPA extractant (0.005M DTPA + 0.01M CaCl2 + 0.1M TEA, pH 7.3) was used for 2 hours of shaking, followed by centrifugation and filtration. The cadmium concentration in the extract was determined by ICP-MS. The test results are shown in the following table: Group Cadmium content in rice (mg / kg) Available cadmium in soil (mg / kg) Comparative Example 0.15±0.03 1.20±0.15 Example 1 0.04±0.01 0.35±0.05 The technical solutions in the above embodiments of the present application have at least the following technical effects or advantages: By building a "removal-blocking-circulation" system, the cadmium content in rice is reduced by removing pollution rather than passivating it. Specifically, the following methods are used: 1. Removal instead of passivation: Magnetic biochar (Fe3O4 ≥ 30%) uses its superparamagnetic properties (magnetization intensity ≥ 60 emu / g) to actively adsorb free cadmium in the soil. Cadmium in the soil can then be removed through magnets, severing the pollution chain at the source and avoiding the risk of secondary activation caused by stagnation. A duckweed-fish symbiotic system (duckweed BCF ≥ 1000) is also introduced. This involves an ecological chain of duckweed enriching cadmium in the water, fish ingesting it, and mineralizing it into inert CdS through fish feces. This is then removed through periodic harvesting, achieving biological output of the pollutant and forming a biological removal channel. 2. Reuse of spatial resources: Fish ditches are eliminated, and duckweed (coverage rate: 60-70%) is raised in shallow water (3-5 cm) throughout the fields. Grass carp, with their laterally flattened bodies, enable low-energy cruising, improving arable land utilization. This is particularly suitable for special terrains such as hilly terraces. Duckweed residue is returned to the fields or made into feed, replacing some concentrated feed. 3. Ecological compatibility: Biochar-loaded bacterial agents replace NaOH to adjust pH. Microorganisms degrade organic cadmium while maintaining the balance of soil flora. They adsorb cadmium ions and secrete extracellular polymers to encapsulate and solidify them. Microbial metabolism produces organic acids, maintaining pH ≈ 6.0 and avoiding damage from chemical reagents. Double adsorption improves cadmium removal rate. Probiotics promote seed germination and replace chemical pH adjustment. Nano-hydroxyapatite fixes cadmium through ion exchange and phosphate co-precipitation (forming Cd3(PO4)2), and is highly effective and stable in the pH range of 5-7 without the need for secondary acid adjustment. At the same time, the released calcium and phosphorus elements promote seedling growth. The rice husk ash barrier layer may affect the air permeability of the seedling root system. Humic acid-silicon material (humic acid 30%-35% chelates soil cadmium, effective SiO2 15-20% induces root silicon film). Humic acid molecules contain a large number of active groups such as carboxyl and phenolic hydroxyl groups, which firmly bind to cadmium ions to form a stable humic acid-cadmium chelate, making the cadmium lose its free activity and converting the soluble cadmium that can be absorbed by rice into an inert bound state; silicate hydrolysis produces OH - Ions neutralize soil acidity, raising the pH by 0.5-1.0 units. Silicon and humic acid synergistically increase the soil's cation exchange capacity, effectively controlling cadmium and enhancing fertilizer retention. Furthermore, the released silica is absorbed by rice roots, depositing a nano-silicon film on the root epidermis. Silicon strengthens the cell wall, thereby blocking cadmium from entering the root cells and reducing cadmium transport to the aboveground parts. By removing pollution, the cadmium content in rice is reduced, achieving the following effects: 1. Qualitative improvement in food safety: The cadmium content in rice has dropped from 0.15mg / kg to 0.04mg / kg (a decrease of 73.3%), which is below the national standard limit. Furthermore, the silicon deposition layer has increased the hardness of the rice (the chalky grain rate has been reduced by 12%), and the silicon coating of the grains has prevented cadmium accumulation in the later stages. 2. Improved arable land efficiency: The fish-free ditch design frees up 15% of arable land, and combined with duckweed mulch to suppress weeds (reducing weed biomass by 45%), rice yield per mu increased; 3. Improved soil sustainability: Humic acid increases the soil's cation exchange capacity, and after magnetic carbon removal, the soil cadmium desorption rate is less than 5%, avoiding long-term pollution accumulation; 4. Improved economic efficiency: recycling and utilization of magnetic carbon and duckweed feed can reduce costs; Magnetic biochar actively adsorbs free cadmium in the soil through superparamagnetism and efficiently recovers it through permanent magnets, reducing the bioavailability of cadmium at the source. In addition, through magnetic biochar adsorption, duckweed enrichment, silicon membrane barrier and other means, the absorption and transport of cadmium are reduced in multiple ways from the soil, water and plant physiological levels.

[0019] Example 2: The above-mentioned Example 1 solves the technical problems of incomplete passivation, cadmium retention in the soil, waste of arable land, and secondary pollution in the prior art through pollution removal, physiological barrier and resource recycling, reduces the absorption and transport of cadmium, and reduces the bioavailability of cadmium. In order to further reduce the cadmium content in rice, further improvements are made on the basis of Example 1.

[0020] In step S2, the magnetic biochar is subjected to magnetic separation after transplantation to recover the cadmium-loaded magnetic biochar (field strength ≥ 0.3 T), and the recovered biochar is regenerated with 0.1 M HCl and can be recycled for ≥ 5 times; The specific steps of magnetic biochar recovery are: After transplanting, the planting area is moved to the conveyor belt and a permanent magnetic roller (Φ5cm, field strength ≥0.3T) is used to scan and adsorb the seeds 1cm from the bottom of the tray; Among them, the drum speed is 20r / min and the travel speed is 0.2m / s; After the magnetic roller absorbs the carbon powder, it is peeled off by a high-frequency vibrator (50Hz) and sent to the recovery tank; Add an equal amount of clean substrate (humic acid-silicon material: vermiculite = 1:1) to the planting area, and backfill to the same depth as the original substrate; If the transplanting area is not recovered in time, water the dry soil in the planting area to a moisture content of 30-35% to form a semi-fluid slurry; The permanent magnetic roller is placed close to the mud surface (gap ≤ 0.5 cm) and scans at a low speed (0.1 m / s) to absorb the magnetic biochar; After vibrating and stripping the magnetic biochar, the soil was allowed to stand and drain for 10 minutes, and the transplanting area returned to a loose state.

[0021] The technical solutions in the above embodiments of the present application have at least the following technical effects or advantages: The magnetic biochar has an Fe3O4 content of ≥30% and is superparamagnetic (magnetization intensity ≥60 emu / g). It can actively adsorb free cadmium in the soil under the action of a magnetic field. Using a permanent magnetic roller (Φ5cm, field strength ≥0.3T) at a distance of 1cm from the bottom of the plate, the cadmium-loaded magnetic biochar was separated from the soil with a recovery rate of 88%. The recovered cadmium-loaded magnetic biochar was regenerated by 0.1M HCl. + It can undergo ion exchange reaction with cadmium ions adsorbed on magnetic biochar, displacing cadmium ions from magnetic biochar with a desorption rate of >95%, restoring the adsorption capacity of magnetic biochar and enabling recycling. Within 7 days after transplanting, add water to the dry soil in the planting area to a moisture content of 30-35% to form a slurry. In the slurry state, the magnetic biochar is better dispersed and easier to be adsorbed and recovered by the magnetic field. At the same time, the slurry environment is also conducive to the separation of magnetic biochar from other substances in the soil. Through the scanning and adsorption of permanent magnetic rollers and the stripping of high-frequency vibrators (50Hz), cadmium-loaded magnetic biochar can be efficiently separated from the soil in the planting area to avoid cadmium residue in the soil. An equal amount of clean matrix is added to the planting area, and the backfill depth is flush with the original matrix, ensuring the physical structure and fertility of the soil and providing a good environment for rice growth. Through the recovery and regeneration of magnetic biochar, the cadmium content in the soil can be continuously and efficiently reduced, reducing the source of cadmium that rice can absorb from the source, further reducing the cadmium content in rice, and improving the food safety quality of rice. The recovery of magnetic biochar avoids its long-term retention in the soil, reduces the risk of secondary pollution caused by the degradation of magnetic biochar or reaction with other substances, and ensures the sustainability of the soil environment.

[0022] Example 3: The above-mentioned Example 2 recovers magnetic biochar through magnetic separation, which solves the problems of incomplete passivation and cadmium retention in the soil, reduces the cadmium content in the soil, reduces cadmium absorption by rice, improves rice quality, reduces costs, reduces secondary pollution, and ensures soil sustainability. In order to further reduce the cadmium content in rice, further improvements are made on the basis of Example 2.

[0023] like Figure 1 As shown, the magnetic biochar is a cylindrical rod-like structure, wherein the total length of the magnetic biochar in step S2 is 1.0-1.5 mm, the diameter is 0.08-0.12 mm, the aspect ratio is (10-15):1, and it is divided into a magnetic end and a non-magnetic segment, and the length of the magnetic end accounts for 15%-25%; The magnetic end is loaded with a Fe3O4 magnetic layer with a thickness of 25-35 μm and a magnetization intensity of ≥80 emu / g.

[0024] The technical solutions in the above embodiments of the present application have at least the following technical effects or advantages: By designing the structure of magnetic biochar, a rod-shaped single-end magnetized structure is constructed to further improve the adsorption and recovery efficiency of cadmium. The magnetic biochar is designed into a cylindrical rod structure and divided into a magnetic end and a non-magnetic segment. The magnetic end is responsible for magnetic response to facilitate recovery, while the non-magnetic segment is mainly responsible for adsorbing pollutants such as cadmium ions in the soil and forming soil channels, resulting in synergistic optimization and systematic reduction of cadmium content. Once the rod-like structures are inserted into the soil, physical channels are formed based on the shape and size characteristics of the particles, simulating the plant root drainage mechanism. These microchannels actively guide the directional migration of cadmium-containing aqueous solutions through capillary action, increasing the probability of cadmium ions contacting the carbon by 70%. Simultaneously, the channels significantly improve the soil's oxygen diffusion capacity, with a measured increase in oxygen diffusion rate of 20%, effectively alleviating cadmium toxicity stress in rice roots. The formation of microchannels not only promotes the migration and adsorption of cadmium ions, but also improves the air permeability and water permeability of the soil. Air can diffuse into the deep soil layer through the microchannels, increase the activity of aerobic microorganisms, accelerate the mineralization of organic matter, and release PO4 3- / K + Equal nutrients, improve soil fertility; The magnetic end is concentratedly loaded with an Fe3O4 layer, and the magnetic material is concentrated at the end, so that the magnetic field force vector is focused on a single end point. According to the magnetic torque formula τ = m×B (m is the magnetic moment, B is the magnetic field strength), the concentration of the magnetic moment at the end point can increase the magnetic moment, thereby improving the magnetic response force and generating a torque amplification effect. During the magnetic separation process, the particles can automatically rotate until the magnetic end faces the magnetic pole, shortening the migration path and achieving a soil extraction resistance of ≤3N (60% lower than spherical particles). The magnetic separation migration speed is increased (at a field strength of 0.3T) and the recovery energy consumption is reduced, solving the problem of incomplete recovery of magnetic biochar, reducing its residue in the soil, and avoiding secondary pollution. By more efficiently reducing the cadmium content in the soil and reducing the absorption of cadmium by rice, the quality and safety of rice are guaranteed from the source, and the potential risks to human health caused by cadmium pollution are reduced. The improvement in magnetic recovery efficiency reduces the amount of magnetic biochar used, and the preparation cost is relatively controllable. At the same time, the energy consumption of magnetic separation recovery is reduced, and the overall cost of soil remediation is reduced. It effectively solves problems such as incomplete passivation and cadmium retention in the soil, reduces secondary pollution, is conducive to the long-term and stable development of agriculture, and meets the requirements of environmental protection and sustainable development.

[0025] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Various modifications and variations are readily apparent to those skilled in the art. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A rice cultivation method for effectively reducing the cadmium content in rice, characterized in that: The invention comprises the following raw materials in parts by weight: 65 parts of base fertilizer, 20 parts of cadmium reducing agent, 20 parts of biochar-loaded bacterial agent, 15 parts of nano-hydroxyapatite suspension, 35 parts of humic acid-silicon material, 25 parts of magnetic biochar, and 40 parts of duckweed seed source; The following steps are involved: S1. During the germination period, the cadmium content of the rice seed culture medium was tested, biochar-loaded bacterial agent and nanohydroxyapatite suspension were added, the pH was adjusted to 5.8-6.2, and the rice seeds were spread into the culture medium and soaked; S2, during the seedling stage, water the planting area, adjust the pH, and spread humic acid-silicon materials and magnetic biochar; S3: During the greening period, maintain a shallow water layer, sow duckweed seeds, apply basal fertilizer after irrigation, and transplant seedlings when the temperature is 32±1℃; release fish at the same time; S4, during the tillering stage, monitor the cadmium content of duckweed. On the 10th day after greening, spray nano-silica sol and remove duckweed 7 days before heading. S5, young ear stage, add cadmium reducing agent twice, the ratio is 1:3.

5.

2. The rice cultivation method for effectively reducing the cadmium content in rice according to claim 1, characterized in that: The biochar-loaded bacterial agent comprises a biochar with a specific surface area of ≥500 m² / g and a loaded Bacillus subtilis of ≥1×10 8 CFU / g.

3. The rice cultivation method for effectively reducing the cadmium content in rice according to claim 1, characterized in that: The solid content of the nano-hydroxyapatite suspension is 10%, and the particle size of the nano-hydroxyapatite is 50-80 nm.

4. The rice cultivation method for effectively reducing the cadmium content in rice according to claim 1, characterized in that: The humic acid-silicon material contains 30-35% humic acid, 15-20% SiO2, and 45-55% carrier filler.

5. The rice cultivation method for effectively reducing the cadmium content in rice according to claim 1, characterized in that: The magnetic biochar has an Fe3O4 content of ≥30% and a magnetization intensity of ≥60 emu / g, and is recovered after transplanting through a magnetic separation method with a field strength of ≥0.3T.

6. The rice cultivation method for effectively reducing the cadmium content in rice according to claim 1, characterized in that: In step S4, the cadmium content of duckweed is monitored every 10 days, with a threshold value of ≤150 mg / kg. When the cadmium content exceeds the threshold, 30% of the duckweed is harvested, and 90% of the duckweed is removed 7 days before heading. The duckweed coverage is monitored by taking photos with a drone.

7. The rice cultivation method for effectively reducing the cadmium content in rice according to claim 1, characterized in that: The magnetic biochar is a cylindrical rod-shaped structure with a total length of 1.0-1.5 mm, a diameter of 0.08-0.12 mm, an aspect ratio of (10-15):1, and is divided into a magnetic end and a non-magnetic segment, with the length of the magnetic end accounting for 15%-25%.

8. The rice cultivation method for effectively reducing the cadmium content in rice according to claim 7, characterized in that: The magnetic end is loaded with a Fe3O4 magnetic layer, the thickness of the magnetic layer is 25-35 μm, and the magnetization intensity is ≥80 emu / g.

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