Soil conditioner for promoting flue-cured tobacco root development and preparation method thereof

Abstract

The invention relates to the technical field of soil improvement, in particular to a soil conditioner for promoting flue-cured tobacco root development and a preparation method thereof, and the soil conditioner is mainly composed of struvite modified biochar, a microbial agent, a microbial protective agent, a carboxyl functionalized polyacrylamide solution and the like. The preparation method comprises the following steps: preparing struvite modified biochar through oxygen-controlled cracking, citric acid activation and chemical reaction, combining the struvite modified biochar with a microbial agent, loading the struvite modified biochar on the surface of the biochar, then mixing the microbial-loaded biochar with a carboxyl-functionalized polyacrylamide solution, adding chitosan, wormcast, humic acid, sodium alginate and plant ash, and granulating and drying to obtain the modifier. The modifier prepared by the invention can significantly improve the physical and chemical properties of soil, provide long-acting nitrogen and phosphorus sources, enhance the water retention capacity of soil, and promote the healthy development of flue-cured tobacco roots.

Description

Technical Field

[0001] The present invention relates to the technical field of soil improvement, and particularly to a soil conditioner and a preparation method thereof. Background Art

[0002] Flue-cured tobacco is one of the important cash crops in China, and its planting area and output rank among the top in the world. The growth of flue-cured tobacco has relatively high requirements for soil conditions. A good soil environment can significantly promote the root development of flue-cured tobacco, thereby increasing its yield and quality. The healthy development of the roots of flue-cured tobacco is the key to its growth. Healthy roots can better absorb nutrients and water in the soil, enhance the stress resistance of plants, and thus improve the economic benefits of flue-cured tobacco.

[0003] A soil conditioner is a substance used to improve the physical, chemical and biological properties of soil, with the aim of increasing soil fertility, enhancing soil water retention performance, and promoting plant growth. Common soil conditioners include organic fertilizers, microbial inoculants, humic acids, sodium alginate, etc.

[0004] Traditional improvement methods often have many limitations. For example, although conventional chemical fertilizers can quickly provide nutrients, they are easily inactivated quickly due to soil adsorption, fixation or leaching, resulting in low nutrient utilization rate, and may also have a negative impact on soil structure and ecological environment. In addition, insufficient water retention performance of the soil is also one of the important factors affecting the root development of flue-cured tobacco. Especially in arid or semi-arid regions, the rapid loss of soil moisture will limit the growth of flue-cured tobacco. Therefore, there is an urgent need for a new type of soil conditioner that can improve nutrient utilization rate, improve soil structure and enhance water retention performance to promote the healthy development of the roots of flue-cured tobacco and increase the yield and quality of flue-cured tobacco. Summary of the Invention

[0005] Aiming at the deficiencies of the prior art, the present invention provides a soil conditioner for promoting the root development of flue-cured tobacco and a preparation method thereof, so as to provide a new type of soil conditioner that can improve nutrient utilization rate, improve soil structure and enhance water retention performance, so as to promote the healthy development of the roots of flue-cured tobacco and increase the yield and quality of flue-cured tobacco.

[0006] To achieve the above object, the present invention is realized through the following technical solutions: A preparation method of a soil conditioner for promoting the root development of flue-cured tobacco, comprising the following preparation steps: S1: Crush the corn straw and place it into an oxygen-controlled pyrolysis furnace. Pyrolyze it at 200°C - 300°C for 30 - 40 min, and then rapidly heat it to 550°C - 600°C at a heating rate of 10°C / min - 15°C / min for 10 - 15 min to form a porous structure. Extend the pyrolysis time by 20 min at 600°C to obtain the pyrolysis product. Immerse the pyrolysis product in a citric acid solution at a solid-liquid ratio of 1:10 for activation for 3 - 5 h. Add the activated pyrolysis product to a 0.06 mol / L KH₂PO₄ solution at a solid-liquid ratio of 1:5, and stir intermittently. Stir for 30 min and then let it stand for 10 min, stir for 2.5 h - 4 h, add NH₄Cl solution, MgCl₂·6H₂O solution, and FeCl₃·6H₂O solution, adjust the pH value to 8.5 - 9, stir at room temperature for 3 - 4 h, and filter and wash to obtain struvite-modified biochar; S2: Mix the microbial inoculant and the microbial protectant, add water and stir evenly to obtain a microbial inoculant suspension. Add the struvite-modified biochar prepared in S1 to the microbial inoculant suspension, apply a vacuum negative pressure of -0.08 MPa, stir at a speed of 30 - 100 rpm, and stir for 3 - 5 h to obtain the modified biochar loaded with the microbial inoculant; S3: Dissolve anionic polyacrylamide in deionized water, add succinic anhydride, and react at 60°C - 70°C for 1 - 2 h to obtain a carboxyl-functionalized polyacrylamide solution. Add the modified biochar loaded with the microbial inoculant prepared in S2 to the carboxyl-functionalized polyacrylamide solution, heat up to 40°C - 50°C, stir for 2 - 3 h, add chitosan, earthworm manure, humic acid, sodium alginate, and plant ash, mix evenly, granulate, and dry to obtain a soil conditioner for promoting the root development of flue-cured tobacco.

[0007] Preferably, the concentration of the NH₄Cl solution in the reaction solution is 0.06 mol / L, the concentration of the MgCl₂ solution is 0.06 mol / L, and the concentration of the FeCl₃·6H₂O solution is 0.01 mol / L.

[0008] Preferably, the volume ratio of the KH₂PO₄ solution, NH₄Cl solution, MgCl₂·6H₂O solution, and FeCl₃·6H₂O solution is 1:1:1:0.02.

[0009] Preferably, the microbial inoculant is EM inoculant.

[0010] Preferably, the microbial protectant is composed of trehalose and arabic gum, and the mass ratio of trehalose to arabic gum is 1:1 - 2.

[0011] Preferably, the preparation method of the carboxyl-functionalized polyacrylamide solution: Dissolve anionic polyacrylamide in deionized water, add succinic anhydride, and react at 60°C - 70°C for 1 - 2 h to obtain a carboxyl-functionalized polyacrylamide solution.

[0012] Preferably, the mass ratio of the anionic polyacrylamide, deionized water, and succinic anhydride is 100: 1000 - 1300: 50 - 80.

[0013] Preferably, the mass parts of the struvite-modified biochar, microbial inoculant, microbial protectant, carboxyl-functionalized polyacrylamide solution, chitosan, earthworm manure, humic acid, sodium alginate, and plant ash are 1000 - 1300 parts of struvite-modified biochar, 10 - 15 parts of microbial inoculant, 20 - 30 parts of microbial protectant, 7000 - 8000 parts of water, 1100 - 1450 parts of carboxyl-functionalized polyacrylamide solution, 300 - 500 parts of chitosan, 500 - 800 parts of earthworm manure, 300 - 550 parts of humic acid, 500 - 800 parts of sodium alginate, and 400 - 600 parts of plant ash.

[0014] Advantages of the present invention: The soil conditioner of the present invention can significantly improve the physical and chemical properties of the soil by adding various components such as struvite-modified biochar, humic acid, and sodium alginate. The struvite in the conditioner is a slow-release fertilizer that slowly dissolves in the soil and can continuously release NH4 + and PO4 3- , providing a long-term nitrogen source and phosphorus source for flue-cured tobacco. This slow-release characteristic avoids the problem of rapid inactivation of traditional phosphate fertilizers due to soil adsorption, fixation, or leaching after application.

[0015] The introduction of carboxyl-functionalized acrylamide endows the soil conditioner of the present application with remarkable water retention performance. The hydrophilic group carboxyl in the carboxyl-functionalized acrylamide in the conditioner can combine with water molecules to form hydrogen bonds, thereby improving the water retention capacity of the soil. In addition, the porous structure of the struvite-modified biochar can also adsorb and store a large amount of water, reducing the evaporation and loss of soil water. Specific embodiments

[0016] To make the objectives, technical solutions, and advantages of the present invention clearer and more understandable, the following further elaborates on the present invention in conjunction with specific embodiments. Embodiment

[0017] A preparation method of a soil conditioner for promoting the root development of flue-cured tobacco includes the following preparation steps: S1: Crush the corn straw and place it into an oxygen-controlled pyrolysis furnace. Keep it at 260 °C for 33 min, then rapidly heat it up to 580 °C at a heating rate of 14 °C / min for pyrolysis for 12 min to form a porous structure. Extend the time to 20 min at 600 °C to obtain the pyrolysis product. Immerse the pyrolysis product in a citric acid solution at a solid-liquid ratio of 1:10 for activation for 4.5 h. Add the activated pyrolysis product to a 0.07 mol / L KH2PO4 solution at a solid-liquid ratio of 1:5, and stir intermittently. Let it stand for 10 min every 30 min of stirring. Stir for 3.5 h, add a 0.06 mol / L NH4Cl solution, a 0.06 mol / L MgCl2·6H2O solution, and a 0.01 mol / L FeCl3·6H2O solution, adjust the pH value to 8.5, stir at room temperature for 4 h, and filter and wash to obtain struvite-modified biochar; S2: Mix trehalose and arabic gum at a mass ratio of 1:2 to obtain a microbial protectant; mix 12 g of EM bacterial agent with 24 g of the microbial protectant, add 7500 mL of water and stir evenly to obtain a microbial agent suspension. Add 1100 g of the struvite-modified biochar prepared in S1 to the microbial agent suspension, apply a vacuum negative pressure of -0.08 MPa, and stir at a speed of 70 rpm for 4.5 h to obtain the modified biochar loaded with microbial agents; S3: Dissolve 100 g of anionic polyacrylamide in 1200 mL of deionized water, add 70 g of succinic anhydride, and react at 67 °C for 1.6 h to obtain 1330 mL of a carboxyl-functionalized polyacrylamide solution. Add the modified biochar loaded with microbial agents prepared in S2 to 1330 mL of the carboxyl-functionalized polyacrylamide solution, heat up to 42 °C, stir for 3 h, add 360 g of chitosan, 670 g of earthworm manure, 350 g of humic acid, 500 g of sodium alginate, and 450 g of plant ash, mix evenly, granulate, and dry to obtain a soil conditioner for promoting the root development of flue-cured tobacco. Example

[0018] A preparation method of a soil conditioner for promoting the root development of flue-cured tobacco, comprising the following preparation steps: S1: Crush the corn straw and put it into an oxygen-controlled pyrolysis furnace at 200 °C for 40 min. Then, rapidly heat it to 600 °C at a heating rate of 10 °C / min and pyrolyze for 10 min to form a porous structure. Extend the pyrolysis time at 600 °C by 20 min to obtain the pyrolysis product. Immerse the pyrolysis product in a citric acid solution at a solid-liquid ratio of 1:10 for activation for 4.5 h. Add the activated pyrolysis product to a 0.06 mol / L KH2PO4 solution at a solid-liquid ratio of 1:5, and stir intermittently. Stir for 30 min and then let it stand for 10 min, and stir for 2.5 h. Add a 0.06 mol / L NH4Cl solution, a 0.06 mol / L MgCl2·6H2O solution, and a 0.01 mol / L FeCl3·6H2O solution, adjust the pH value to 8.5, stir at room temperature for 3 h, and filter and wash to obtain struvite-modified biochar; S2: Mix trehalose and arabic gum in a mass ratio of 1:1 to obtain a microbial protectant; mix 10 g of EM bacterial agent with 20 g of the microbial protectant, add 7000 mL of water and stir evenly to obtain a microbial agent suspension. Add 1000 g of the struvite-modified biochar prepared in S1 to the microbial agent suspension, apply a vacuum negative pressure of -0.08 MPa, stir at a speed of 30 rpm for 3 h to obtain the modified biochar loaded with microbial agents; S3: Dissolve 100 g of anionic polyacrylamide in 1050 mL of deionized water, add 50 g of succinic anhydride, and react at 60 °C for 1 h to obtain 1260 mL of a carboxyl-functionalized polyacrylamide solution. Add the modified biochar loaded with microbial agents prepared in S2 to 1260 mL of the carboxyl-functionalized polyacrylamide solution, heat to 40 °C, stir for 2 h, add 300 g of chitosan, 500 g of earthworm manure, 300 g of humic acid, 500 g of sodium alginate, and 410 g of plant ash, mix evenly, granulate, and dry to obtain a soil conditioner for promoting the root development of flue-cured tobacco. Example

[0019] A preparation method of a soil conditioner for promoting the root development of flue-cured tobacco, comprising the following preparation steps: S1: Crush corn straws and place them into an oxygen-controlled pyrolysis furnace. Pyrolyze at 245°C for 36 min, then rapidly heat up to 600°C at a heating rate of 15°C / min and pyrolyze for 10 min to form a porous structure. Extend the pyrolysis time at 600°C by 20 min to obtain the pyrolysis product. Immerse the pyrolysis product in a citric acid solution at a solid-liquid ratio of 1:10 for activation for 4.5 h. Add the activated pyrolysis product to a 0.07 mol / L KH2PO4 solution at a solid-liquid ratio of 1:5, and stir intermittently. Stir for 30 min and then let it stand for 10 min. Stir for 3 h, add a 0.06 mol / L NH4Cl solution, a 0.06 mol / L MgCl2·6H2O solution, and a 0.01 mol / L FeCl3·6H2O solution, adjust the pH value to 8.5, stir at room temperature for 3.5 h, filter and wash to obtain struvite-modified biochar; S2: Mix trehalose and arabic gum in a mass ratio of 2:3 to obtain a microbial protectant; mix 13 g of EM bacterial agent with 25 g of the microbial protectant, add 7500 mL of water and stir evenly to obtain a microbial agent suspension. Add 1200 g of the struvite-modified biochar prepared in S1 to the microbial agent suspension, apply a vacuum negative pressure of -0.08 MPa, and stir at a speed of 80 rpm for 3 h to obtain the modified biochar loaded with microbial agents; S3: Dissolve 100 g of anionic polyacrylamide in 1150 mL of deionized water, add 65 g of succinic anhydride, and react at 70°C for 2 h to obtain 1290 mL of a carboxyl-functionalized polyacrylamide solution. Add the modified biochar loaded with microbial agents prepared in S2 to 1290 mL of the carboxyl-functionalized polyacrylamide solution, heat up to 45°C, stir for 2.4 h, add 400 g of chitosan, 680 g of earthworm manure, 450 g of humic acid, 650 g of sodium alginate, and 500 g of plant ash, mix evenly, granulate, and dry to obtain a soil conditioner for promoting the root development of flue-cured tobacco. Example

[0020] A preparation method of a soil conditioner for promoting the root development of flue-cured tobacco, comprising the following preparation steps: S1: Crush corn straw and place it into an oxygen-controlled pyrolysis furnace. Keep it at 300 °C for 40 min, then rapidly heat it up to 550 °C at a heating rate of 15 °C / min for pyrolysis for 15 min to form a porous structure. Extend the time to 20 min at 600 °C to obtain the pyrolysis product. Immerse the pyrolysis product in a citric acid solution for activation for 4.5 h according to a solid-liquid ratio of 1:10. Add the activated pyrolysis product to a 0.08 mol / L KH2PO4 solution according to a solid-liquid ratio of 1:5, and stir intermittently. Let it stand for 10 min every 30 min of stirring. Stir for 4 h, add a 0.06 mol / L NH4Cl solution, a 0.06 mol / L MgCl2·6H2O solution, and a 0.01 mol / L FeCl3·6H2O solution, adjust the pH value to 9, stir at room temperature for 4 h, filter and wash to obtain struvite-modified biochar; S2: Mix trehalose and arabic gum in a mass ratio of 1:2 to obtain a microbial protectant; mix 15 g of EM bacterial agent with 30 g of the microbial protectant, add 8000 mL of water and stir evenly to obtain a microbial agent suspension. Add 1300 g of the struvite-modified biochar prepared in S1 to the microbial agent suspension, apply a vacuum negative pressure of -0.08 MPa, and stir at a speed of 100 rpm for 3 h to obtain modified biochar loaded with microbial agents; S3: Dissolve 100 g of anionic polyacrylamide in 1300 mL of deionized water, add 80 g of succinic anhydride, and react at 70 °C for 2 h to obtain 1440 mL of a carboxyl-functionalized polyacrylamide solution. Add the modified biochar loaded with microbial agents prepared in S2 to 1440 mL of the carboxyl-functionalized polyacrylamide solution, heat up to 50 °C, stir for 3 h, add 500 g of chitosan, 800 g of earthworm manure, 550 g of humic acid, 800 g of sodium alginate, and 600 g of plant ash, mix evenly, granulate, and dry to obtain a soil conditioner for promoting the root development of flue-cured tobacco.

[0021] Comparative Example 1: A preparation method of a soil conditioner for promoting the root development of flue-cured tobacco, comprising the following preparation steps: S1: Crush corn straw and place it into an oxygen-controlled pyrolysis furnace. Keep it at 260 °C for 33 min, then rapidly heat it up to 580 °C at a heating rate of 14 °C / min for pyrolysis for 12 min to form a porous structure. Extend the time to 20 min at 600 °C to obtain the pyrolysis product. Immerse the pyrolysis product in a citric acid solution for activation for 4.5 h according to a solid-liquid ratio of 1:10. Add the activated pyrolysis product to a 0.07 mol / L KH2PO4 solution according to a solid-liquid ratio of 1:5, and stir intermittently. Let it stand for 10 min every 30 min of stirring. Stir for 3.5 h to obtain phosphorus-fixed biochar; S2: Mix trehalose and gum arabic at a mass ratio of 1:2 to obtain a microbial protectant; mix 12 g of EM microbial agent with 24 g of the microbial protectant, add 7500 mL of water and stir evenly to obtain a suspension of the microbial agent. Add 1100 g of the phosphorus-fixed biochar prepared in S1 to the suspension of the microbial agent, apply a vacuum negative pressure of -0.08 MPa, stir at a speed of 70 rpm for 4.5 h to obtain a modified biochar loaded with the microbial agent. S3: Dissolve 100 g of anionic polyacrylamide in 1200 mL of deionized water, add 70 g of succinic anhydride, and react at 67 °C for 1.6 h to obtain 1330 mL of a carboxyl-functionalized polyacrylamide solution. Add the modified biochar loaded with the microbial agent prepared in S2 to 1330 mL of the carboxyl-functionalized polyacrylamide solution, heat up to 42 °C, stir for 3 h, add 360 g of chitosan, 670 g of earthworm manure, 350 g of humic acid, 500 g of sodium alginate, and 450 g of plant ash, mix evenly, granulate, and dry to obtain a soil conditioner for promoting the root development of flue-cured tobacco.

[0022] Comparative Example 2: Compared with Example 1, in the preparation process of S3 of this comparative example, "1330 mL of carboxyl-functionalized polyacrylamide solution" was not replaced with "100 g of anionic polyacrylamide dissolved in 1230 mL of deionized water to obtain 1330 mL of anionic polyacrylamide solution", and the rest of the steps and parameters were the same. This comparative example will not be repeated here. Finally, a soil conditioner for promoting the root development of flue-cured tobacco was obtained.

[0023] Determination and method of soil indicators: Test soil: The soil type is mountain red soil, and its basic physical and chemical properties are as follows: pH value 5.21, available nitrogen content 112.5 mg / kg, available phosphorus content 59 mg / kg, available potassium content 157.3 mg / kg.

[0024] Test crop: The variety of the test crop is Yunyan.

[0025] Test soil conditioner: The test soil conditioner is the soil conditioner for promoting the root development of flue-cured tobacco prepared in Examples 1-4 and Comparative Examples 1-2.

[0026] Experimental design: A total of 4 treatments were set up in the experiment, namely the conventional group (CK) without applying any soil amendments, the test group 1 (T1) applying the soil amendment prepared in Example 1, the test group 2 (T2) applying the soil amendment prepared in Comparative Example 1, and the test group 3 (T3) applying the soil amendment prepared in Example 3. The experiment adopted a completely randomized block design, with 3 replicates, a total of 12 plots, a plant spacing of 0.5 m, a row spacing of 1.2 m, and protective rows were set up around the tobacco field. Compound fertilizers (N∶P2O5∶K2O = 15∶15∶15), cake fertilizers (N∶P2O5∶K2O = 6.34∶1.17∶1.34), potassium sulfate (K2O is 50%), and potassium nitrate (N∶K2O = 13∶46) were applied to the tobacco fields of each treatment. The compound fertilizer was 1150 kg·hm -2 , and the nitrogen, phosphorus, and potassium ratio was 1∶1.5∶3. 375 kg·hm of cake fertilizer was applied -2 . Among them, the compound fertilizer and cake fertilizer were applied by hole application before transplanting, and potassium sulfate and potassium nitrate were used for topdressing; the soil amendments applied in T1, T2, and T3 were 600 kg·hm -2 .

[0027] Soil determination items and methods: At 30 days, 60 days, and 101 days after transplanting of tobacco plants, sample points were determined by the five-point sampling method, rhizosphere soil was collected by the soil shaking method, and the soil pH was measured by the potentiometer method; the available nitrogen content in the soil was measured by the alkali diffusion method; the available phosphorus content in the soil was measured by the NaHCO3 antimony anti-colorimetric method; the available potassium content in the soil was measured by the NH4 + molybdate OAc extraction - flame photometry method, and the detailed results are shown in Table 1; the soil moisture content of soil layers 0 - 10 cm, 10 - 20 cm, and 20 - 40 cm was measured by the drying method, and the detailed results are shown in Table 2.

[0028] Root development determination and methods: Starting from 30 days after transplanting, the root growth of tobacco plants was measured every 15 days, including the dry weight, root length, and root volume of the roots. Each time, 3 flue-cured tobacco plants were selected, a cross-section was cut in the vertical direction (0 - 10 cm, 10 - 20 cm, 20 - 40 cm from the base of the main stem), the roots were taken out, washed clean with water, and the dry weight, root length, and root volume of the roots in different groups were measured. The detailed results are shown in Table 3.

[0029] Table 1

[0030] Table 2

[0031] Table 3

[0032] Data analysis: As can be seen from Table 1, the pH value of Group T1 was 6.33 on the 101st day after transplanting, significantly higher than 5.44 of the CK group and 5.47 of the T2 group; the available phosphorus in Group T1 was 96.23 mg·kg −1 on the 101st day, significantly higher than 60.01 mg·kg −1 of the CK group and 75.11 mg·kg −1 of the T2 group; the available potassium in Group T1 was 177.5 mg·kg −1 on the 101st day, higher than 152.35 mg·kg −1 of the CK group, indicating that through impregnation with KH2PO4 solution, phosphate radicals are adsorbed on the surface of biochar, and then struvite (MgNH4PO4·6H2O) is generated in the presence of Mg 2+ and Fe 3+ to achieve chemical fixation of phosphorus. Struvite slowly dissolves in the soil, releasing NH4 + and PO4 3- , providing a long-term phosphorus source and nitrogen source, avoiding the rapid loss of traditional phosphate fertilizers. The NH4 + produced by the decomposition of struvite can be absorbed by plants, and at the same time, OH - ions are released to neutralize acidic soil and improve the absorption of nutrients by flue-cured tobacco roots. In addition, the potassium supplementation of plant ash and the adsorption effect of biochar together improve potassium availability.

[0033] As can be seen from Table 2, the deep water content of Group T1 at 20 - 40 cm was 16.7% on the 60th day, significantly higher than 10.2% of the CK group and higher than 15.4% of the T3 group. The introduction of a hydrophilic group carboxyl into carboxyl-functionalized acrylamide can improve the hydrophilicity of acrylamide by binding with water molecules through hydrogen bonds. The struvite-modified biochar contains a large number of hydroxyl groups, and these hydroxyl groups can combine with the carboxyl groups in carboxyl-functionalized acrylamide to achieve the fixation of carboxyl-functionalized acrylamide as a water-retaining agent. Moreover, the struvite-modified biochar has a rich microporous and mesoporous structure, and the binding effect of carboxyl-functionalized acrylamide promotes particle forming. The porous structure of biochar and carboxyl-functionalized acrylamide as a water-retaining agent synergistically optimize soil air permeability and promote root expansion.

[0034] Those of ordinary skill in the art should understand that the discussion of any above embodiment is only exemplary and is not intended to imply that the scope of the present invention is limited to these examples; under the idea of the present invention, the technical features in the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations in different aspects of the present invention as described above, which are not provided in detail for the sake of brevity.

[0035] The present invention aims to cover all such substitutions, modifications and variations that fall within the broad scope of the appended claims. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A soil conditioner for promoting the root development of flue-cured tobacco, characterized in that, The soil conditioner is prepared from the following raw materials in parts by mass: 1000-1300 parts of struvite-modified biochar, 10-15 parts of microbial agent, 20-30 parts of microbial protective agent, 7000-8000 parts of water, 1100-1450 parts of carboxyl functionalized polyacrylamide solution, 300-500 parts of chitosan, 500-800 parts of earthworm castings, 300-550 parts of humic acid, 500-800 parts of sodium alginate and 400-600 parts of wood ash.

2. The soil conditioner for promoting the root development of flue-cured tobacco according to claim 1, characterized in that The struvite-modified biochar preparation method comprises the following steps: crushing corn stalks and placing them in an oxygen-controlled cracking furnace, heating them at 200°C-300°C for 30-40 minutes, rapidly heating them to 550°C-600°C for cracking for 10-15 minutes to form a porous structure, and heating them at 600°C for 20 minutes to obtain a cracking product, activating the cracking product with 3% citric acid and adding it to a KH2PO4 solution, stirring for 2.5 hours to 4 hours, adding an NH4Cl solution, a MgCl2·6H2O solution, and a FeCl3·6H2O solution, adjusting the pH value to 8.5-9, stirring at room temperature for 3-4 hours, and filtering and washing to obtain the struvite-modified biochar.

3. The soil conditioner for promoting the root development of flue-cured tobacco according to claim 2, characterized in that: The concentration of the KH2PO4 solution is 0.06-0.08 mol / L.

4. The soil conditioner for promoting the root development of flue-cured tobacco according to claim 2, wherein: The concentration of the NH4Cl solution is 0.06 mol / L, the concentration of the MgCl2 solution is 0.06 mol / L, and the concentration of the FeCl3·6H2O solution is 0.01 mol / L.

5. The soil conditioner for promoting the root development of flue-cured tobacco according to claim 1, wherein: The microbial agent is an EM agent.

6. The soil conditioner for promoting the root development of flue-cured tobacco according to claim 1, wherein: The microorganism protective agent consists of trehalose and gum arabic, and the mass ratio of trehalose to gum arabic is 1:1-2.

7. The soil conditioner for promoting the root development of flue-cured tobacco according to claim 1, wherein: The preparation method of the carboxyl functionalized polyacrylamide solution comprises the following steps: dissolving anionic polyacrylamide in deionized water, adding succinic anhydride, and reacting at 60° C.-70° C. for 1-2 hours to obtain the carboxyl functionalized polyacrylamide solution.

8. The soil conditioner for promoting the root development of flue-cured tobacco according to claim 7, wherein: The mass ratio of the anionic polyacrylamide, deionized water and succinic anhydride is 100:1000-1300:50-80.

9. A method for preparing a soil conditioner for promoting the root development of flue-cured tobacco according to any one of claims 1-8, characterized in that, The method comprises the following preparation steps: The microbial agent and the microbial protective agent are mixed, water is added and stirred evenly to obtain a microbial agent suspension, struvite-modified biochar is added to the microbial agent suspension under vacuum negative pressure at a stirring speed of 30-100 rpm and stirred for 3-5 hours to obtain modified biochar loaded with microbial agents, the modified biochar loaded with microbial agents is added to a carboxyl functionalized polyacrylamide solution, the temperature is raised to 40°C-50°C, and stirred for 2-3 hours, chitosan, earthworm castings, humic acid, sodium alginate and wood ash are added, mixed evenly, and then granulated and dried to obtain a soil conditioner for promoting the development of flue-cured tobacco roots.

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