Soil structure modifier and preparation method thereof

Abstract

The invention provides a soil structure modifier and a preparation method thereof, and belongs to the technical field of soil conditioning materials, the preparation method comprises the steps of preparing biochar, preparing modified biochar, and granulating; the method for preparing the biochar comprises the following steps: soaking fried dough twist-shaped pine barks in a silica gel solution for 6-10 minutes, fishing out, quickly putting into mixed powder of CaCO3, KCl and V2O5, enabling the mixed powder to be uniformly adsorbed on the fried dough twist-shaped pine barks, then putting into a muffle furnace, heating to 750-850 DEG C at a speed of 8-12 DEG C / min in a nitrogen atmosphere, keeping the current temperature for pyrolysis for 2.5-3.5 hours, cooling, taking out, and drying to obtain the biochar. Grinding into powder to obtain biochar; the soil structure modifier can effectively reduce the volume weight of soil and improve the total percentage content of water-stable aggregates larger than 0.25 mm.

Description

Technical Field

[0001] This invention belongs to the field of soil conditioning materials technology, specifically relating to a soil structure modifier and its preparation method. Background Technology

[0002] Soil is the foundation of crop growth, and its structure, fertility, and moisture status directly affect crop growth, development, and yield. However, with changes in agricultural production methods and the excessive use of chemical fertilizers, soil structure has gradually deteriorated, soil fertility has declined, and soil pollution problems have become increasingly serious. Therefore, developing a soil conditioner that can improve soil structure, increase soil fertility, and enhance crop yield is of great significance.

[0003] Currently, there are various types of soil structure modifiers. Among them, natural polymer soil structure modifiers (such as humic acid, lignin, and cellulose) have advantages such as being environmentally friendly and pollution-free, improving soil structure, increasing soil fertility, and being sustainable. Therefore, they are widely used in soil improvement. However, these soil structure modifiers have poor stability in soil. If the amount applied is small, the desired effect cannot be achieved. Increasing the amount applied will increase the cost and may also cause soil acidification and compaction.

[0004] Patent CN107603632A discloses an inorganic-organic composite soil conditioner, which is composed of maifanite, sepiolite, calcium source, iron powder, biochar, humate and calcium magnesium phosphate compound fertilizer. However, the various components of this soil structure improver are simply mixed together in a certain proportion, resulting in poor stability. It is easy to decompose in the soil and is also prone to soil erosion, thus having a poor effect on improving soil structure. Summary of the Invention

[0005] To address the problems existing in the prior art, this invention provides a soil structure improver and its preparation method, achieving the following objectives: reducing soil bulk density and increasing the total percentage content of water-stable aggregates larger than 0.25 mm.

[0006] To solve the above technical problems, the technical solution adopted by the present invention is as follows: A soil structure modifier and its preparation method, comprising the following steps: 1. Preparation of biochar Clean the pine bark thoroughly and dry the surface moisture. Then, cut the pine bark into strips and weave them into a twisted shape. Soak the twisted pine bark in a silica gel solution for 6–10 minutes. After removing it, quickly place it into a mixed powder of CaCO3, KCl, and V2O5, allowing the mixed powder to be evenly adsorbed onto the twisted pine bark. Then, place it in a muffle furnace and, under a nitrogen atmosphere, heat it to 750–850°C at a rate of 8–12°C / min. Maintain the current temperature for pyrolysis for 2.5–3.5 hours. After cooling, remove it and grind it into a powder with a particle size of 0.2–0.6 mm to obtain biochar. The particle size of the CaCO3 powder is 0.005–0.015 mm; The particle size of both the KCl powder and V2O5 powder is 0.01–0.04 mm. The twisted pine bark has a diameter of 3-7 mm and a length of 1-4 cm; The mass ratio of the twisted pine bark to the silica gel solution is 0.8–1.2:6–8; The mass ratio of the twisted pine bark to the mixed powder of CaCO3, KCl, and V2O5 is 0.8–1.2:4–6. The mixed powder of CaCO3, KCl, and V2O5 contains 5-8% KCl powder by mass and 0.1-0.5% V2O5 powder by mass. The mass fraction of sodium silicate in the silica gel solution is 13-14%.

[0007] 2. Preparation of modified biochar Add silane coupling agent KH-550 to an ethanol solution, stir for 20-40 minutes, then add konjac glucomannan to obtain solution A; Biochar and pyridine were added to dichloromethane, and the temperature was maintained at 40-50°C. Acetic anhydride was added dropwise while stirring. After the addition was complete, the temperature was maintained and the reaction continued for 2-3 hours. The mixture was filtered and dried at 40-60°C to constant weight to obtain substance B. Add substance B to solution A and react at 50-80℃ for 4-8 hours. Filter the solution, wash the filter cake with deionized water until neutral, and dry it at 50-70℃ to constant weight to obtain modified biochar. The ethanol solution has a mass fraction of 70-90%. The mass ratio of KH-550, ethanol solution, and konjac glucomannan is 0.8–1.2:12–14:8–10. The mass ratio of biochar, pyridine, dichloromethane, and acetic anhydride is 2.7–3.3: 0.007–0.009: 10–14: 0.5–0.9. The droplet acceleration rate is 15–25 ml / min; The mass ratio of solution A to substance B is 15-17:6-8.

[0008] 3. Granulation Bamboo poles are made into filaments, which are then cut into small segments of 2-6 mm to obtain shredded bamboo. The shredded bamboo, modified biochar, humic acid, and montmorillonite are mixed evenly together and then granulated to obtain 5-8 mm particles, which are the finished soil structure conditioner. The mass ratio of the shredded bamboo, modified biochar, humic acid, and montmorillonite is 0.8–1.2:1–4:10–13:0.5–0.9. The diameter of the shredded bamboo is 0.7 to 1.1 mm.

[0009] Compared with the prior art, the beneficial effects of the present invention are as follows: In the preparation of biochar, CaCO3, KCl, and V2O5 are added. The carbon dioxide produced by the decomposition of CaCO3 creates more pores in the biochar, while the remaining CaO remains on the surface. After the biochar is applied to the soil, the CaO absorbs water to produce Ca(OH)2. Ca(OH)2 effectively inhibits pathogens and harmful microorganisms in the soil. Simultaneously, Ca... 2+ As one of the essential nutrients for plants, the addition of KCl and V2O5 can effectively reduce the pyrolysis temperature of CaCO3, making the biochar formation temperature suitable (750-850℃) and retaining more functional groups.

[0010] The core principle behind using KCl and V2O5 to lower the pyrolysis temperature of CaCO3 is to change the reaction pathway of CaCO3 pyrolysis (lowering the activation energy) and disrupt the stability of the CaCO3 crystal structure, thereby reducing the energy threshold required for CaCO3 decomposition and ultimately lowering the pyrolysis temperature.

[0011] In the preparation of modified biochar, the carboxyl groups present in the biochar are activated into acid anhydrides by acetic anhydride to obtain substance B, which is then added to solution A. In solution A, the silane coupling agent KH-550 is hydrolyzed, the hydroxyl segment is linked to the hydroxyl group of konjac glucomannan, and the amino terminus forms an amide bond with the acid anhydride of substance B. Thus, the biochar and konjac glucomannan are stably linked together to obtain modified biochar.

[0012] Modified biochar is mixed with shredded bamboo, humic acid, and montmorillonite and granulated. After being applied to the soil, the konjac glucomannan on the modified biochar absorbs water and swells, forming a cross-linked three-dimensional network with the humic acid. Combined with the adsorption properties of biochar, this can effectively improve the stability of the aggregates and reduce the soil bulk density.

[0013] The soil structure improver of the present invention can significantly reduce soil bulk density, specifically from 1.65 g / cm³ to 1.44–1.47 g / cm³.

[0014] The soil structure modifier of the present invention can effectively increase the total percentage content of water-stable aggregates larger than 0.25 mm, specifically from 37% to 59-63%. Detailed Implementation

[0015] Example 1 1. Preparation of biochar Clean the pine bark thoroughly and dry its surface moisture. Then, cut the pine bark into strips and weave them into a twisted shape. Soak the twisted pine bark in silica gel solution for 8 minutes. After removing it, quickly place it into a mixed powder of CaCO3, KCl, and V2O5, allowing the mixed powder to be evenly adsorbed onto the twisted pine bark. Then, place it in a muffle furnace and heat it to 800℃ at a rate of 10℃ / min under a nitrogen atmosphere. Maintain the current temperature for pyrolysis for 3 hours. After cooling, remove it and grind it into powder with a particle size of 0.3-0.5 mm to obtain biochar. The particle size of the CaCO3 powder is 0.008–0.012 mm; The particle size of the KCl and V2O5 powders is 0.02–0.03 mm; The twisted pine bark has a diameter of 4–6 mm and a length of 2–3 cm; The mass ratio of the twisted pine bark to the silica gel solution is 1:7; The mass ratio of the twisted pine bark to the mixed powder of CaCO3, KCl, and V2O5 is 1:5. The mixed powder of CaCO3, KCl, and V2O5 contains 6.5% KCl powder by mass and 0.3% V2O5 powder by mass. The mass fraction of sodium silicate in the silica gel solution is 13.5%.

[0016] 2. Preparation of modified biochar Add silane coupling agent KH-550 to an ethanol solution, stir for 30 minutes, then add konjac glucomannan to obtain solution A; Biochar and pyridine were added to dichloromethane, and the temperature was maintained at 45°C. Acetic anhydride was added dropwise while stirring. After the addition was complete, the temperature was maintained and the reaction continued for 2.5 hours. The mixture was filtered and dried at 50°C to constant weight to obtain substance B. Substance B was added to solution A and reacted at 65°C for 6 hours. After filtration, the filter cake was washed with deionized water until neutral and dried at 60°C to constant weight to obtain modified biochar. The ethanol solution has a mass fraction of 80%. The mass ratio of KH-550, ethanol solution, and konjac glucomannan is 1:13:9; The mass ratio of biochar, pyridine, dichloromethane, and acetic anhydride is 3:0.008:12:0.7; The drop rate was 20 ml / min; The mass ratio of solution A to substance B is 16:7.

[0017] 3. Granulation Bamboo poles are made into filaments, then cut into small sections of 3-5 mm to obtain broken bamboo filaments. The broken bamboo filaments, modified biochar, humic acid, and montmorillonite are mixed evenly together and then granulated to obtain 6-7 mm particles, which are the finished soil structure improver. The mass ratio of the shredded bamboo, modified biochar, humic acid, and montmorillonite is 1:3:11:0.7. The diameter of the bamboo shreds is 0.8 to 1 mm.

[0018] Example 2 1. Preparation of biochar Clean the pine bark thoroughly and dry its surface moisture. Then, cut the pine bark into strips and weave them into a twisted shape. Soak the twisted pine bark strips in silica gel solution for 6 minutes. After removing them, quickly place them into a mixed powder of CaCO3, KCl, and V2O5, allowing the mixed powder to be evenly adsorbed onto the twisted pine bark strips. Then, place them in a muffle furnace and heat them to 750°C at a rate of 8°C / min under a nitrogen atmosphere. Maintain the current temperature for pyrolysis for 2.5 hours. After cooling, remove them and grind them into powder with a particle size of 0.2–0.3 mm to obtain biochar. The particle size of the CaCO3 powder is 0.005–0.008 mm; The particle size of both the KCl powder and V2O5 powder is 0.01–0.02 mm. The twisted pine bark has a diameter of 3-4 mm and a length of 1-2 cm; The mass ratio of the twisted pine bark to the silica gel solution is 0.8:6; The mass ratio of the twisted pine bark to the mixed powder of CaCO3, KCl, and V2O5 is 0.8:4. The mixed powder of CaCO3, KCl, and V2O5 contains 5% KCl powder by mass and 0.1% V2O5 powder by mass. The mass fraction of sodium silicate in the silica gel solution is 13%.

[0019] 2. Preparation of modified biochar Add silane coupling agent KH-550 to an ethanol solution, stir for 20 minutes, then add konjac glucomannan to obtain solution A; Biochar and pyridine were added to dichloromethane, and the temperature was maintained at 40°C. Acetic anhydride was added dropwise while stirring. After the addition was complete, the temperature was maintained and the reaction continued for 2 hours. The mixture was filtered and dried at 40°C to constant weight to obtain substance B. Substance B was added to solution A and reacted at 50°C for 4 hours. After filtration, the filter cake was washed with deionized water until neutral and dried at 50°C to constant weight to obtain modified biochar. The ethanol solution has a mass fraction of 70%. The mass ratio of KH-550, ethanol solution, and konjac glucomannan is 0.8:12:8; The mass ratio of biochar, pyridine, dichloromethane, and acetic anhydride is 2.7:0.007:10:0.5. The drop rate is 15 ml / min; The mass ratio of solution A to substance B is 15:6.

[0020] 3. Granulation Bamboo poles are made into filaments, then cut into small sections of 2-3 mm to obtain broken bamboo filaments. The broken bamboo filaments, modified biochar, humic acid, and montmorillonite are mixed evenly together and then granulated to obtain 5-6 mm particles, which are the finished soil structure improver. The mass ratio of the shredded bamboo, modified biochar, humic acid, and montmorillonite is 0.8:1:10:0.5. The diameter of the bamboo shreds is 0.7 to 0.8 mm.

[0021] Example 3 1. Preparation of biochar Clean the pine bark thoroughly and dry the surface moisture. Then, cut the pine bark into strips and weave them into a twisted shape. Soak the twisted pine bark in silica gel solution for 10 minutes. After removing it, quickly place it into a mixed powder of CaCO3, KCl, and V2O5, allowing the mixed powder to be evenly adsorbed onto the twisted pine bark. Then, place it in a muffle furnace and heat it to 850°C at a rate of 12°C / min under a nitrogen atmosphere. Maintain the current temperature for pyrolysis for 3.5 hours. After cooling, remove it and grind it into powder with a particle size of 0.5–0.6 mm to obtain biochar. The particle size of the CaCO3 powder is 0.012–0.015 mm; The particle size of both the KCl powder and V2O5 powder is 0.03–0.04 mm. The twisted pine bark has a diameter of 6-7 mm and a length of 3-4 cm; The mass ratio of the twisted pine bark to the silica gel solution is 1.2:8; The mass ratio of the twisted pine bark to the mixed powder of CaCO3, KCl, and V2O5 is 1.2:6; The mixed powder of CaCO3, KCl, and V2O5 contains 8% KCl powder by mass and 0.5% V2O5 powder by mass. The mass fraction of sodium silicate in the silica gel solution is 14%.

[0022] 2. Preparation of modified biochar Add silane coupling agent KH-550 to an ethanol solution, stir for 40 min, then add konjac glucomannan to obtain solution A; Biochar and pyridine were added to dichloromethane, and the temperature was maintained at 50°C. Acetic anhydride was added dropwise while stirring. After the addition was complete, the temperature was maintained and the reaction continued for 3 hours. The mixture was filtered and dried at 60°C to constant weight to obtain substance B. Substance B was added to solution A and reacted at 80°C for 8 hours. After filtration, the filter cake was washed with deionized water until neutral and dried at 70°C to constant weight to obtain modified biochar. The ethanol solution has a mass fraction of 90%. The mass ratio of KH-550, ethanol solution, and konjac glucomannan is 1.2:14:10; The mass ratio of biochar, pyridine, dichloromethane, and acetic anhydride is 3.3:0.009:14:0.9. The drop rate was 25 ml / min; The mass ratio of solution A to substance B is 17:8.

[0023] 3. Granulation Bamboo poles are made into filaments, then cut into 5-6 mm segments to obtain broken bamboo filaments. The broken bamboo filaments, modified biochar, humic acid, and montmorillonite are mixed evenly together and then granulated to obtain 7-8 mm particles, which are the finished soil structure improver. The mass ratio of the shredded bamboo, modified biochar, humic acid, and modified montmorillonite is 1.2:4:13:0.9. The diameter of the shredded bamboo is 1 to 1.1 mm.

[0024] Comparative Example 1 Based on Example 1, the addition of the mixed powder of CaCO3, KCl, and V2O5 in step 1 is omitted, while the remaining steps are the same. Specifically, step 1 is changed to cleaning the pine bark, drying the surface moisture, cutting the pine bark into filaments, weaving them into a twisted shape, and then placing them in a muffle furnace. Under a nitrogen atmosphere, the temperature is increased to 800°C at a rate of 10°C / min, and then maintained at the current temperature for pyrolysis for 3 hours. After cooling, the pyrolysis is carried out and ground into powder with a particle size of 0.3-0.5 mm to obtain biochar.

[0025] Comparative Example 2 Based on Example 1, the preparation of substance B in step 2 is omitted, and substance B is replaced with biochar. All other steps are the same.

[0026] Test case The experimental field was divided into 5 equal parts, and the soil structure improvers prepared in Examples 1-3 and Comparative Examples 1-2 were applied to the experimental fields respectively. The soil bulk density and the total percentage of water-stable aggregates greater than 0.25 mm were tested at different time periods.

[0027] (1) The specific testing method for soil bulk density is as follows: The soil bulk density of the experimental field was tested at 30, 60, 90 and 120 days using the ring sampler method. For each test, 30 samples were randomly selected and the average value of the test results was taken. The soil bulk density calculation formula is as follows: ρb=m / V In the formula: ρb is the soil bulk density, g / cm³; m is the mass of the soil sample after drying, g; V is the volume of the soil sample before drying, cm³.

[0028] The test results are shown in Table 1.

[0029] Table 1 (Note: The initial soil bulk density of the experimental field was 1.65 g / cm³).

[0030]

[0031] (2) The specific test method for the total percentage content of water-stable aggregates greater than 0.25 mm is as follows: The total percentage content of water-stable aggregates greater than 0.25 mm in the experimental field was tested by wet sieving at 30, 60, 90 and 120 days. For each test, 30 samples were randomly selected and the average value of the test results was taken. The formula for calculating the total percentage content of water-stable aggregates greater than 0.25 mm is as follows:

[0032] In the formula: x i The percentage content of a certain level of water-stable aggregates; m i F represents the dried weight of a certain level of water-stable agglomerates after wet sieving (greater than 0.25 mm); F represents the fractional weight of agglomerates taken from each level of wet sieving (%); W represents the dried weight of the soil sample taken from dry sieving (g); and X represents the total percentage content of water-stable agglomerates greater than 0.25 mm.

[0033] The test results are shown in Table 2.

[0034] Table 2 (Note: The total percentage of water-stable aggregates larger than 0.25 mm in the initial experimental field was 37%)

[0035] The results show that modified biochar can effectively reduce soil bulk density and increase the total percentage of water-stable aggregates larger than 0.25 mm. This indicates that the CO2 produced after the thermal decomposition of CaCO3 powder can effectively increase the porosity of biochar, thereby loosening the soil structure and reducing soil bulk density. The konjac glucomannan on the modified biochar absorbs water and swells, forming a cross-linked three-dimensional network with humic acid. Combined with the adsorption properties of biochar, this can effectively improve the stability of aggregates, thereby continuously increasing the total percentage of water-stable aggregates larger than 0.25 mm in the soil.

Claims

1. A method for preparing a soil structure conditioner, characterized in that: The preparation method includes preparing biochar, preparing modified biochar, and granulation; The method for preparing biochar is as follows: Pine bark in a twisted shape is soaked in silica gel solution for 6–10 minutes, then quickly placed in a mixed powder of CaCO3, KCl, and V2O5 to ensure uniform adsorption of the mixed powder onto the twisted pine bark. The bark is then placed in a muffle furnace and heated to 750–850°C at a rate of 8–12°C / min under a nitrogen atmosphere. The temperature is maintained at this rate for pyrolysis for 2.5–3.5 hours. After cooling, the bark is removed, ground into powder, and the biochar is obtained. The method for preparing modified biochar is as follows: add silane coupling agent KH-550 to an ethanol solution, stir for 20-40 minutes, then add konjac glucomannan to obtain solution A; Biochar and pyridine were added to dichloromethane, and the temperature was maintained at 40-50°C. Acetic anhydride was added dropwise while stirring. After the addition was complete, the temperature was maintained and the reaction continued for 2-3 hours. The mixture was filtered and dried at 40-60°C to constant weight to obtain substance B. Substance B was added to solution A and reacted at 50–80°C for 4–8 hours. After filtration, the filter cake was washed with deionized water until neutral and dried at 50–70°C to constant weight to obtain modified biochar.

2. The method for preparing a soil structure conditioner according to claim 1, characterized in that: In the step of preparing biochar, the mass ratio of the twisted pine bark to the mixed powder of CaCO3, KCl, and V2O5 is 0.8–1.2:4–6. The mixed powder of CaCO3, KCl, and V2O5 contains 5-8% KCl powder by mass, 0.1-0.7% V2O5 powder by mass, CaCO3 powder with a particle size of 0.005-0.015 mm, and KCl and V2O5 powder with a particle size of 0.01-0.04 mm. The silica gel solution contains 13-14% sodium silicate by mass.

3. The method for preparing a soil structure conditioner according to claim 1, characterized in that: In the step of preparing modified biochar, the mass fraction of the ethanol solution is 70-90%. The mass ratio of KH-550, ethanol solution, and konjac glucomannan is 0.8–1.2:12–14:8–10. The mass ratio of biochar, pyridine, dichloromethane, and acetic anhydride is 2.7–3.3: 0.007–0.009: 10–14: 0.5–0.9; The drip rate is 15–25 ml / min; The mass ratio of solution A to substance B is 15–17:6–8.

4. The method for preparing a soil structure conditioner according to claim 1, characterized in that: The granulation method involves making bamboo stalks into filaments, then cutting them into small segments of 2-6 mm to obtain broken bamboo filaments. The broken bamboo filaments, modified biochar, humic acid, and montmorillonite are then mixed evenly together and granulated to obtain particles of 5-8 mm, which are the finished soil structure improver.

5. The method for preparing a soil structure conditioner according to claim 4, characterized in that: In the granulation method, the mass ratio of shredded bamboo fibers, modified biochar, humic acid, and montmorillonite is 0.8–1.2:1–4:10–13:0.5–0.

9. The diameter of the bamboo shreds is 0.7 to 1.1 mm.

6. The soil structure modifier prepared by the method according to any one of claims 1-5.

Images