Sustainable wheat production method based on alkaline arsenic-cadmium combined polluted soil improvement

Abstract

The invention discloses a sustainable wheat production method based on alkaline arsenic-cadmium combined polluted soil improvement, and belongs to the technical field of soil remediation, and the method comprises the following steps: before wheat sowing, mixing an iron-based modified biochar composite material and a functional microbial microsphere solution, and applying the mixture into soil; sowing wheat after soil preparation; spraying the silicon-selenium nano composite sol on leaf surfaces in a wheat jointing stage; harvesting and recovering the iron-based modified biochar in the soil after the wheat is mature. A synergistic system of iron-based modified biochar and functional microorganisms is innovatively provided, A / Cd is synchronously fixed by a nano zero-valent iron-humic acid compound through a reduction-adsorption dual mechanism, the surface of a passivated material is activated by a metabolite of the functional microorganisms, and the repair period is prolonged; and meanwhile, a staged strategy is combined with soil passivation and leaf surface obstruction, the limitation of an alkaline environment on the remediation efficiency is broken through, and the method has both economical efficiency and sustainability.

Description

Technical Field

[0001] The invention belongs to the technical field of soil remediation, and specifically is a sustainable wheat production method based on improving alkaline arsenic-cadmium composite polluted soil. Background Art

[0002] The problem of combined arsenic and cadmium pollution in alkaline soils is becoming increasingly serious. Under high pH conditions, arsenic exists stably in the form of As(V), while cadmium easily combines with carbonates to form insoluble CdCO 3 , traditional passivators (such as lime and phosphate fertilizer) are difficult to fix two heavy metals simultaneously. In existing technologies, the adsorption efficiency of biochar on As is limited by the high pH environment, and single microbial remediation is easily affected by the alkaline environment of the soil and inactivated. In addition, foliar barrier technology mostly relies on single components of silicon or selenium and lacks a synergistic inhibition mechanism. Summary of the invention

[0003] In order to solve the problem in the prior art that it is difficult to simultaneously repair soil contaminated by two heavy metals, arsenic and cadmium, the present invention provides a sustainable wheat production method based on the improvement of alkaline arsenic-cadmium composite contaminated soil. The method can complete the repair of arsenic-cadmium contaminated soil under the premise of ensuring the safe production of wheat, and the repair effect is significant, achieving the purpose of repairing while producing.

[0004] This invention innovatively proposes a synergistic system of iron-based modified biochar and functional microorganisms: nZVI (nano zero-valent iron)-humic acid complex simultaneously fixes As / Cd through a dual mechanism of reduction-adsorption, and the functional microbial metabolites activate the surface of the passivation material to extend the repair cycle. At the same time, a phased strategy is adopted to combine soil passivation and leaf barrier to break through the limitation of alkaline environment on repair efficiency, which is both economical and sustainable.

[0005] The sustainable wheat production method based on improving alkaline arsenic-cadmium composite contaminated soil provided by the present invention comprises the following steps: Step 1: Before sowing wheat, mix the iron-based modified biochar composite material with functional microbial microspheres and apply them to the soil; The iron-based modified biochar composite material is biochar modified by nano zero-valent iron and humic acid; The functional microbial microsphere solution is prepared from arsenic-reducing bacteria and cadmium-resistant plant growth-promoting bacteria. Shewanella sp. strain PV-4 ) was purchased from Ningbo Mingzhou Biotechnology Co., Ltd., and cadmium-resistant plant growth-promoting bacteria (Enterobacter ludwigii, Enterobacter ludwigii , strain number S15) was purchased from China General Microbiological Culture Collection Center with the collection number CGMCC NO.29744.

[0006] Step 2: Sow wheat after land preparation; Step 3: spraying silicon-selenium nanocomposite sol on the leaves during the jointing stage of wheat; Step 4: harvest the wheat after it matures and recover the iron-based modified biochar in the soil.

[0007] Furthermore, in step one, a rotary tiller is used to till the iron-based modified biochar composite material and the functional microbial microspheres to a depth of 20-30 cm.

[0008] Furthermore, in step 2, the wheat selected is a low-accumulation wheat variety, and the sowing rate is 12-15 kg / mu. When sowing low-accumulation wheat varieties, the base fertilizer is a compound fertilizer with a mass ratio of N:P:K of 16:16:8, and the application rate is 40 kg / mu; 20 kg / mu of urea is applied during the tillering stage.

[0009] Furthermore, in step 1, the method for preparing the iron-based modified biochar composite material comprises: (a) pyrolyzing rice husk at 500-600°C under anoxic conditions for 2-4 hours and crushing to 100 mesh to obtain biochar with high specific surface area; (b) using a chemical reduction method to load nano-zero-valent iron (nZVI) and humic acid into the pores of biochar, the mass ratio of nZVI to humic acid is 1:2-1:5; and the total mass ratio of nZVI and humic acid to biochar is 1:10; (c) The loaded biochar was calcined under nitrogen protection (350°C, 1h) to enhance the stability of the material.

[0010] Furthermore, in step 1, the method for preparing the functional microbial microspheres comprises: (A) Arsenic-reducing bacteria ( Shewanella sp. strain PV-4 ) and cadmium-resistant plant growth-promoting bacteria (Enterobacter ludwigii, strain number S15) were mixed in a volume ratio of 1:1. Before mixing, the bacterial liquid concentrations of arsenic-reducing bacteria and cadmium-resistant plant growth-promoting bacteria were both 1×10 7 -1×10 8 CFU / mL; (B) The mixed bacterial solution and the sodium alginate solution were mixed in a volume ratio of 1:1 to obtain a mixed solution, wherein the concentration of sodium alginate in the sodium alginate solution was 2% w / v; then biochar powder was added to the mixed solution, and the amount of biochar powder added was 5% of the mass of the mixed solution; finally, 5 times the volume of CaCl 2 Solidified in solution, CaCl 2 CaCl in solution 2 The concentration is 2% w / v; a functional microbial microsphere solution is obtained.

[0011] Furthermore, in step 1, the application amount of the iron-based modified biochar composite material is 2-5% of the soil mass; the application amount of the microbial microsphere solution is 1×10 7 -1×10 8 CFU / g soil, that is, the number of colonies in the microbial microsphere solution applied per gram of soil is 1×10 7 -1×10 8 CFU; of which: When As≤50 mg / kg and Cd≤2 mg / kg in the soil, it is slightly polluted and the application rate of iron-based modified biochar is 2-3%; When the As content in the soil is 50-100 mg / kg and the Cd content is 2-5 mg / kg, it is moderately polluted and the application rate of iron-based modified biochar is 3-5%.

[0012] Furthermore, in step 3, the preparation method of the silicon-selenium nanocomposite sol is: Mesoporous silica nanoparticles (particle size 50-100 nm, pore size 5-10 nm) were prepared by sol-gel method; Sodium selenite (Na 2 SeO 3 ) solution and silica particles according to Se / SiO 2 The mixture was mixed at a mass ratio of 1:100, ultrasonically dispersed for 30 minutes, and freeze-dried to obtain a nanocomposite powder loaded with selenium. The nanocomposite powder was dispersed in water to obtain a silicon-selenium nanocomposite sol. When used, the powder was dispersed in water in proportion, and the selenium concentration was adjusted to 0.1-0.3 mg / L and the silicon concentration to 50-100 mg / L.

[0013] Furthermore, in step 3, the method of spraying the silicon-selenium nanocomposite sol on the leaf surface is: Use a backpack electric sprayer (droplet diameter ≤ 100 μm), spray pressure 0.3-0.5 MPa, spray volume 30-50 L / mu, selenium concentration 0.1-0.3 mg / L, silicon concentration 50-100 mg / L.

[0014] Furthermore, in step four, the iron-based modified biochar is recovered by magnetic separation.

[0015] Compared with the prior art, the present invention has the following beneficial effects: (1) In the preparation method of the iron-based modified biochar composite material of the present invention, the iron-based modified biochar nZVI and humic acid are co-loaded at a mass ratio of 1:2-1:5 to achieve simultaneous fixation of As / Cd. Humic acid at this ratio can not only buffer the pH of alkaline soil to prevent the oxidative inactivation of nZVI, but also enhance the fixation of Cd through chelation. The step of calcining at 350°C for 1 hour under nitrogen protection can significantly improve the stability of the material, avoid the rapid oxidation of nZVI in alkaline soil, and effectively extend the repair cycle.

[0016] (2) In the preparation method of the functional microbial microspheres of the present invention, by introducing 5% biochar powder as a filler into the microspheres, the mechanical strength of the microspheres is enhanced, the degradation of sodium alginate in an alkaline environment is delayed, the slow release effect of the functional microorganisms is ensured, and the synergistic effect is utilized to achieve the simultaneous repair of arsenic and cadmium. The arsenic-reducing bacteria reduce As(V) to As(III) and adsorb it on the biochar, and the cadmium-resistant bacteria secrete organic acid to dissolve CdCO 3 , inducing wheat roots to secrete metallothionein to chelate Cd²⁺.

[0017] (3) The sustainable wheat production method based on the improvement of alkaline arsenic-cadmium complex contaminated soil of the present invention adopts a phased remediation strategy: first, soil passivation is carried out before sowing (step one) to reduce the effective heavy metal content in the soil; second, silicon-selenium nanosol is sprayed on the leaves during the jointing stage (step three) when the wheat stems are growing rapidly, rather than the traditional tillering stage. The wheat leaf absorption efficiency is highest during the jointing stage, and silicon-selenium synergistically inhibits the transport of As / Cd to the grains, forming a "soil-plant" double barrier.

[0018] (4) In the sustainable wheat production method based on the improvement of alkaline arsenic-cadmium complex contaminated soil of the present invention, a recovery mechanism is also integrated: iron-based biochar is recovered by magnetic separation (recovery rate ≥ 90%), which not only improves the remediation efficiency but also takes into account the material recyclability and farmland applicability to ensure technical and economic feasibility. On the one hand, it guarantees the safe production of wheat grains in food agriculture, and on the other hand, it realizes the remediation of farmland soil slightly contaminated by arsenic and cadmium. DETAILED DESCRIPTION

[0019] The technical solution of the present invention is described in detail below through embodiments, but the protection scope of the present invention is not limited to the embodiments.

[0020] Example 1: Effect of iron-based modified biochar on As / Cd fixation A farmland contaminated by heavy metals in a certain city was used as the experimental field (mildly contaminated). The soil pH was 8.2, the organic matter content was 1.5%, and the available As (using 0.5 M NaHCO 3The content of Cd in situ (determined by DTPA extraction-atomic fluorescence spectrometry) is 45 mg / kg, and the content of effective Cd (determined by DTPA extraction-graphite furnace atomic absorption spectrometry) is 1.8 mg / kg.

[0021] The biochar material was applied to the soil and tilled to a depth of 20-30 cm using a rotary tiller. The experimental group prepared an iron-based modified biochar composite material at a ratio of nZVI: humic acid = 1:3, and the application amount was 3% of the soil mass (mild pollution gradient). The control group included unmodified biochar (As fixation rate 35%, Cd fixation rate 40%) and nZVI-loaded biochar alone (As fixation rate 60%, Cd fixation rate 50%). The experimental group reduced the available As in the soil by 78% (to 9.9 mg / kg) and Cd by 82% (to 0.32 mg / kg), which was significantly better than the control group (p<0.05).

[0022] Among them, the preparation methods of iron-based modified biochar composite materials, unmodified biochar, and single nZVI-loaded biochar are as follows: Specific preparation method of iron-based modified biochar composite material: (a) 1 kg of dried rice husk was pyrolyzed at 600 °C under anoxic conditions for 3 h and crushed to 100 mesh to obtain biochar with high specific surface area; (b) Loading nZVI and humic acid by chemical reduction method: 0.5 g nano zero-valent iron (nZVI) and 1.5 g humic acid (mass ratio 1:3) were dissolved in 200 mL deionized water and ultrasonically dispersed for 30 min; 20 g biochar was added, stirred (500 rpm) for 4 h, and allowed to stand for 12 h; Nano-zero-valent iron and humic acid were co-loaded into the pores of biochar, the mass ratio of nano-zero-valent iron to humic acid was 1:3, and the mass ratio of the total mass of nZVI and humic acid to the mass of biochar was 1:10.

[0023] (c) The loaded biochar was calcined under nitrogen protection (350°C, 1h) to enhance the stability of the material.

[0024] 2) Preparation method of unmodified biochar: The dried rice husk was pyrolyzed in a tube furnace at 600°C under anoxic conditions for 3 h and crushed through a 100-mesh sieve to obtain unmodified biochar.

[0025] 3) Preparation method of nZVI loaded biochar alone: (a) 1 kg of dry rice husk was pyrolyzed in a tube furnace at 600 °C under anoxic conditions for 3 h and crushed to pass through a 100-mesh sieve; (b) 2.0 g of nano-zero-valent iron (nZVI) was dissolved in 200 mL of deionized water and dispersed by ultrasonication for 30 min. (c) Add 100 g of biochar, stir (500 rpm) for 4 h, and let stand for 12 h; (d) The loaded biochar was calcined at 350 °C for 1 h under nitrogen protection, cooled, sieved through a 100-mesh sieve, and sealed for storage.

[0026] Example 2: Sustained release effect of functional microbial microspheres Laboratory conditions simulated alkaline soil (pH 8.5), temperature 25±2℃, humidity 60%. Two treatments were set up. The experimental group was a functional microbial microsphere solution containing 5% biochar, and the ratio of arsenic-reducing bacteria and cadmium-resistant plant growth-promoting bacteria was 1:1. The control group was a pure sodium alginate microsphere (no biochar) solution. After 30 days, the bacterial survival rate of the experimental group was >80%, while the bacterial survival rate of the control group was only 30%.

[0027] The arsenic-reducing bacteria ( Shewanella sp. strain PV-4 ) was purchased from Ningbo Mingzhou Biotechnology Co., Ltd., and cadmium-resistant plant growth-promoting bacteria (Enterobacter ludwigii, Enterobacter ludwigii, The strain number S15 was purchased from China General Microbiological Culture Collection Center with the collection number CGMCC NO.29744.

[0028] The preparation methods of the functional microbial microsphere solution containing 5% biochar and the pure sodium alginate microsphere solution are as follows: (1) Preparation method of functional microbial microsphere solution containing 5% biochar: (a) The bacterial solutions of arsenic-reducing bacteria and cadmium-resistant plant growth-promoting bacteria were mixed in a volume ratio of 1:1; before mixing, the concentrations of the bacterial solutions of arsenic-reducing bacteria and cadmium-resistant plant growth-promoting bacteria were both 1×10 8 CFU / mL.

[0029] (b) The mixed bacterial solution and the sodium alginate solution were mixed in a volume ratio of 1:1 to obtain a mixed solution, wherein the concentration of sodium alginate in the sodium alginate solution was 2% w / v; then biochar powder was added to the mixed solution, and the amount of biochar powder added was 5% of the mass of the mixed solution. Finally, 5 times the volume of CaCl 2 Solution to obtain functional microbial microsphere solution. CaCl 2 The concentration of the solution was 2% w / v and the diameter of the formed microspheres was 2-3 mm.

[0030] (2) Preparation method of pure sodium alginate microspheres (without biochar) solution: (a) The bacterial solutions of arsenic-reducing bacteria and cadmium-resistant plant growth-promoting bacteria were mixed in a volume ratio of 1:1; before mixing, the concentrations of the bacterial solutions of arsenic-reducing bacteria and cadmium-resistant plant growth-promoting bacteria were both 1×10 8 CFU / mL.

[0031] (b) The mixed bacterial solution and the sodium alginate solution were mixed in a volume ratio of 1:1 to obtain a mixed solution, wherein the concentration of sodium alginate in the sodium alginate solution was 2% w / v; 5 times the volume of 2% w / v CaCl 2 Pure sodium alginate microsphere solution was obtained by solidification in the solution without adding biochar powder.

[0032] Example 3: Synergistic Effects of Phased Strategy 1. Experimental site and soil physical and chemical properties A field experiment was conducted in a cadmium-contaminated farmland in a certain city (mildly contaminated). The soil pH was 8.3, the total arsenic (As) was 85 mg / kg, and the total cadmium (Cd) was 4.8 mg / kg. The available As (using 0.5M NaHCO 3 Extraction-atomic fluorescence spectrometry) 38 mg / kg, effective Cd (DTPA extraction-graphite furnace atomic absorption spectrometry) 2.5 mg / kg.

[0033] 2. Experimental plan Experimental group (phased remediation strategy): application of iron-based modified biochar and functional microbial microspheres for foliar spraying; the specific steps are as follows: Step 1: Soil passivation and coordination with functional microorganisms: 15 days before wheat sowing, iron-based modified biochar composite materials (nZVI: humic acid = 1:3, application rate is 3% of soil mass), functional microbial microspheres (application rate is 1×10 7 -1×10 8 CFU / g soil) solution was evenly spread on the ground and tilled to a depth of 20-30 cm using a rotary tiller; Step 2: Sow wheat after land preparation; choose Jimai 22 wheat, and sow at a rate of 15 kg / mu. When sowing, base fertilizer is compound fertilizer with a mass ratio of N:P:K of 16:16:8, and the application rate is 40 kg / mu; 20 kg / mu of urea is applied during the tillering stage.

[0034] Step 3: Spraying silicon-selenium sol on leaves: During the wheat jointing period, choose a clear and windless day (temperature 15-20°C) and use a backpack electric sprayer (spraying pressure 0.4 MPa) to spray silicon-selenium nanocomposite sol (Se / SiO 2 mass ratio 1:100, selenium concentration 0.2 mg / L, silicon concentration 80 mg / L), no rainfall within 6 hours after spraying, and even coverage on both sides of the leaves.

[0035] Control group 1 (soil passivation only): only iron-based modified biochar was applied, no microbial microsphere solution was added in step 1, and no foliar spraying was performed in step 3. The parameters were the same as those of the experimental group.

[0036] Control group 2 (leaf barrier only): Spray silica-selenium sol only at the jointing stage, do not perform step 1, and perform steps 2 and 3, with the same parameters as the experimental group.

[0037] Control group 3 (conventional planting without any restoration measures): Steps 1 and 3 were not performed, and the parameters were the same as those of the experimental group.

[0038] Control group 4 (soil passivation only + foliar spraying): In step 1, only iron-based modified biochar was applied without adding microbial microsphere solution, and steps 2 and 3 were performed with the same parameters as the experimental group.

[0039] In the above experimental group and control group, the preparation method of the iron-based modified biochar is the same as in Example 1, and the preparation method of the functional microbial microspheres is the same as in Example 2. Preparation method of silicon-selenium nanocomposite sol: (a) Mesoporous silica nanoparticles (particle size 50-100 nm, pore size 5-10 nm) were prepared by sol-gel method. 1.0 g of CTAB (hexadecyltrimethylammonium bromide) was dissolved in a mixed solution of 200 mL of deionized water and 50 mL of anhydrous ethanol, and 5 mL of ammonia water (25%) was added after stirring to dissolve; 4 mL of TEOS (tetraethyl orthosilicate, drop rate 0.5 mL / min) was added dropwise, and the mixture was stirred and reacted at 25°C for 6 hours; the mixture was centrifuged and washed, dried, and calcined at 550°C for 4 hours to obtain mesoporous silica nanoparticles (particle size 80±20 nm, pore size 7±3 nm).

[0040] (b) Sodium selenite (Na 2 SeO 3 ) solution and silica nanoparticles, according to Se / SiO 2 The mixture was mixed at a mass ratio of 1:100, ultrasonically dispersed for 30 minutes, and freeze-dried to obtain a selenium-loaded nanocomposite powder; the powder was dispersed in water, and the selenium concentration was adjusted to 0.2 mg / L and the silicon concentration to 80 mg / L.

[0041] 3. Data Collection and Analysis (1) Soil remediation effect The test indicators include soil available As (using 0.5M NaHCO 3 extraction-atomic fluorescence spectrometry), effective Cd (DTPA extraction-content measured by graphite furnace atomic absorption spectrometry).

[0042] Experimental group: Available As dropped to 8.7 mg / kg (a decrease of 77.1%), and available Cd dropped to 0.45 mg / kg (a decrease of 82.0%).

[0043] Control group 1: effective As 15.2 mg / kg (60.0% decrease), Cd 0.82 mg / kg (67.2% decrease).

[0044] Control group 2: The decrease in As / Cd was less than 10%.

[0045] Control group 3: effective As 38 mg / kg (0% decrease), effective Cd 2.5 mg / kg (0% decrease).

[0046] Control group 4: effective As 12.5 mg / kg (67.1% decrease), effective Cd 0.68 mg / kg (72.8% decrease).

[0047] (2) Wheat growth and heavy metal accumulation: Biomass: The grain yield of the experimental group was 482 kg / mu, which was 17.6% higher than that of the control group 3 (410 kg / mu); Control group 1: grain yield 455 kg / mu; Control group 2: grain yield 418 kg / mu; Control group 4: grain yield 460 kg / mu.

[0048] The As and Cd contents in wheat tissues in the experimental and control groups are shown in Table 1: Table 1

[0049] Example 4: Recovery and recycling of iron-based biochar When wheat (Jimai 22) was planted each season, the application rate of iron-based modified biochar composite material was 3% of the soil mass, and the cumulative application rate for three consecutive seasons was 9%.

[0050] The iron-based biochar was recycled by a permanent magnetic drum magnetic separator (magnetic field strength 1.0 T, treatment time 40 min), with a recovery rate of 92%. After recycling, it was acid-washed and regenerated (0.1M HCl, oscillation rate 150 rpm, time 2 h). The oxidation rate of the iron-based modified biochar composite material was <10%. After three consecutive wheat planting seasons, the soil available As / Cd was still reduced by more than 70% when the recycled material was applied again.

[0051] As described above, although the present invention has been shown and described with reference to specific preferred embodiments, it should not be construed as limiting the present invention itself. Various changes may be made to the form and details without departing from the spirit and scope of the present invention.

Claims

1. A sustainable wheat production method based on the improvement of alkaline arsenic-cadmium composite contaminated soil, characterized in that: The following steps are involved: Step 1: Before sowing wheat, mix the iron-based modified biochar composite material with the functional microbial microsphere solution and apply it to the soil; The iron-based modified biochar composite material is biochar modified by nano zero-valent iron and humic acid; The functional microbial microsphere solution is prepared from arsenic-reducing bacteria and cadmium-resistant plant growth-promoting bacteria; Step 2: Sow wheat after land preparation; Step 3: spraying silicon-selenium nanocomposite sol on the leaves during the jointing stage of wheat; Step 4: harvest the wheat after it matures and recover the iron-based modified biochar composite material in the soil.

2. The method according to claim 1, characterized in that In step 1, the arsenic-reducing bacteria is Shewanella sp. strain PV-4, The cadmium-resistant plant growth-promoting bacteria are Enterobacter ludwigii S15.

3. The method according to claim 1, characterized in that: In step 1, the preparation method of the iron-based modified biochar composite material is as follows: (a) pyrolyzing rice husk at 500-600°C under anoxic conditions for 2-4 hours and crushing to 100 mesh to obtain biochar with high specific surface area; (b) Using chemical reduction method to load nano-zero-valent iron and humic acid into the pores of biochar: the mass ratio of nano-zero-valent iron to humic acid is 1:2-1:5, and the mass ratio of the sum of the mass of nano-zero-valent iron and humic acid to biochar is 1:10; (c) The loaded biochar was calcined at 350 °C for 1 h under nitrogen protection.

4. The method according to claim 1, characterized in that: In step 1, the preparation method of the functional microbial microsphere solution is as follows: (A) The bacterial solutions of arsenic-reducing bacteria and cadmium-resistant plant growth-promoting bacteria were mixed in a volume ratio of 1:1; before mixing, the concentrations of the two bacterial solutions were both 1×10 7 -1×10 8 CFU / mL; (B) The mixed bacterial solution and the sodium alginate solution were mixed in a volume ratio of 1:1 to obtain a mixed solution, and then biochar powder was added; finally, the mixed solution was dropped into a CaCl2 solution for solidification; Among them, the addition amount of biochar powder is 5% of the mass of the mixed solution; the volume ratio of the mixed solution to the CaCl2 solution is 1:5; the concentration of sodium alginate solution is 2% w / v; the concentration of CaCl2 solution is 2% w / v.

5. The method according to claim 1, characterized in that In step 1, the application amount of the iron-based modified biochar composite material is 2-5% of the soil mass; the application amount of the microbial microsphere solution is: the number of colonies in the microbial microsphere solution applied per gram of soil is 1×10 7 -1×10 8 CFU.

6. The method according to claim 1, characterized in that The preparation method of the silicon-selenium nanocomposite sol is as follows: Mesoporous silica nanoparticles are prepared by a sol-gel method, wherein the particle size of the silica nanoparticles is 50-100 nm and the pore size is 5-10 nm; The sodium selenite solution and the silicon dioxide particles are mixed in a mass ratio of Se to SiO2 of 1:100, and then ultrasonically dispersed and freeze-dried to obtain a selenium-loaded nanocomposite powder; the nanocomposite powder is dispersed in water to obtain a silicon-selenium nanocomposite sol.

7. The method according to claim 1, characterized in that The spraying amount of the silicon-selenium nanocomposite sol is 30-50 L / mu; in the silicon-selenium nanocomposite sol, the selenium concentration is 0.1-0.3 mg / L, and the silicon concentration is 50-100 mg / L.

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