Colloidal biochar and its preparation method and application

Abstract

The present invention discloses colloidal biochar, its preparation method, and application. The colloidal biochar of the present invention has a particle size of 400 to 1000 nm. The colloidal biochar is prepared by mixing and stirring biochar and water, and then heating and emulsifying the mixture to obtain the colloidal biochar. A soil conditioner comprises the colloidal biochar and fertilizer. The soil conditioner of the present invention is applied to grasslands. The colloidal biochar of the present invention has a colloidal-grade particle size, reduces the amount used by more than 50% compared to large-particle biochar, and has a more significant fertilizer effect.

Description

Technical Field

[0001] The present invention belongs to the field of agricultural ecological technology, and specifically relates to colloidal biochar and a preparation method and application thereof. Background Art

[0002] Biochar-based fertilizer is a fertilizer made from biochar as the main raw material. It has attracted widespread attention due to its good soil improvement and crop yield-increasing effects in the soil. However, there are several problems in the current process of applying biochar-based fertilizer to improve soil: (1) Fertilization method: Traditional biochar-based fertilizers are applied on the surface and then mixed into the soil by plowing. This method is not only time-consuming and labor-intensive, but also increases water loss during plowing under drought conditions. In areas with soil erosion or wind erosion, the soil after plowing is in a loose state, which is prone to water erosion or wind erosion. At the same time, since grasslands and woodlands cannot usually be plowed, biochar-based fertilizers have poor fertilizer efficiency after being applied to grasslands and woodlands, and are prone to loss. (2) Texture problem: Traditional biochar-based fertilizers are light in texture. After being applied on the soil surface, they are easily blown away by the wind or runoff with water, resulting in certain losses, thus affecting the application effect. (3) Application amount and cost problem: Traditional biochar-based fertilizers are applied in large amounts, mostly 1%-3% of the soil mass, and the cost is relatively high. Taking grassland as an example, biochar is often applied to grassland soil by surface broadcasting to avoid damaging the grass root system. However, because grasslands lack shelter, traditional biochar-based fertilizers are easily blown away by the wind and fail to reach the underlying soil, resulting in low utilization efficiency. Therefore, biochar needs to be improved.

[0003] Colloidal biochar is obtained by decomposing, crushing or precipitating large biochar particles. The particle size is at the colloidal level and has unique physical and chemical properties, including high porosity, high specific surface area and cation exchange capacity. Due to its small particles and more negative charge, colloidal biochar has good migration ability in the soil. When colloidal biochar is applied to the surface soil, it can migrate to the lower soil layer with water under the influence of precipitation, irrigation, etc. to exert its effect. Based on these advantages, colloidal biochar particles are expected to become a very promising soil conditioner, which can provide innovative solutions for agricultural production and environmental protection.

[0004] Currently, colloidal biochar is mostly used in research on its environmental benefits, but rarely is it combined with other nutrients for use as a fertilizer or soil conditioner, and applied to soils such as farmland and grassland. Therefore, producing colloidal biochar through a simple, rapid, and large-scale preparation method, combined with other nutrients according to soil needs, provides a new fertilization approach for soil nutrient supply, improvement, and management. Summary of the Invention

[0005] The present invention aims to provide a colloidal biochar that promotes growth and improves quality with low additive dosage, as well as its preparation method and application. The colloidal biochar of the present invention has a wide range of raw materials and is low-cost. The preparation method is simple to operate and can be widely produced and promoted. No pollutants are generated during the preparation process.

[0006] The present invention provides a colloidal biochar having a particle size of 400-1000 nm.

[0007] In the present invention, the pH of the colloidal biochar is 9.94 and the conductivity is 2.55 mS / cm.

[0008] In the colloidal biochar mentioned above, the colloidal biochar is prepared by the following method: mixing biochar and water, stirring, heating and emulsifying, thereby obtaining the colloidal biochar.

[0009] In the colloidal biochar mentioned above, the raw material of the biochar is selected from at least one of wheat straw, corn straw, rice straw, sawdust, branches and leaves, and bark;

[0010] The mass ratio of the biochar of the colloidal biochar to the water may be 1:5-40;

[0011] The temperature of the heating emulsification can be 85-95° C., and the time can be 30-120 min.

[0012] In the present invention, the stirring is carried out in an electrically heated emulsifying stirring tank.

[0013] The present invention also provides a method for preparing the colloidal biochar, comprising the following steps: mixing biochar and water, stirring, and heating and emulsifying to obtain the colloidal biochar;

[0014] In the above method, the mass ratio of the biochar to the water may be 1:5-40;

[0015] The temperature of the heating emulsification can be 85-95° C., and the time can be 30-120 min.

[0016] In addition, the preparation method of the biochar in the present invention is as follows: collecting biochar raw materials, drying the raw materials, and then oxygen-limited cracking at 450° C. for 1 hour, and after cooling, crushing and sieving the biochar with a grinder to obtain the biochar.

[0017] The present invention also provides a soil conditioner comprising the colloidal biochar and fertilizer.

[0018] The soil conditioner comprises the following components in parts by mass: 2 parts of colloidal biochar; 0.03-0.08 parts of diammonium phosphate fertilizer; and 0.03-0.08 parts of urea fertilizer.

[0019] In the present invention, the soil conditioner is specifically composed of the following components by mass: 2 parts of colloidal biochar; 0.066 parts of diammonium phosphate fertilizer; 0.066 parts of urea fertilizer

[0020] The present invention further provides application of the above-mentioned soil conditioner in grassland.

[0021] In the above application, the grassland is soil for growing alfalfa.

[0022] In the above application, the total application amount of the soil conditioner is 2-5 g per kilogram of grassland soil.

[0023] In the above application, the application amount of the soil conditioner per kilogram of grassland soil is specifically 2 g of colloidal biochar; 0.066 g of diammonium phosphate fertilizer; and 0.066 g of urea fertilizer.

[0024] The present invention has the following advantages:

[0025] 1. The colloidal biochar of the present invention has a colloidal particle size that, when applied, is distributed on the soil surface with water and is not easily blown away by wind. Furthermore, it does not need to be incorporated into the soil through tillage, but can be migrated to the lower soil layers with rainfall or irrigation water.

[0026] 2. Due to its high specific surface area, the colloidal biochar of the present invention can more effectively absorb nutrients and reduce nutrient loss. When used in combination with inorganic fertilizers, it can significantly increase the fresh and dry weight of the above-ground and underground parts of the plant, as well as the nitrogen and phosphorus content in the plant.

[0027] 3. The colloidal biochar of the present invention reduces the amount of biochar used by more than 50% compared with large-particle biochar, and has a more significant fertilizer effect.

[0028] 4. After being applied to the soil surface, the colloidal biochar of the present invention can penetrate into the soil, helping to activate the available phosphorus in the soil, providing good nutrient conditions for plant growth, and promoting carbon fixation in deep soil (30-40 cm).

[0029] 5. The colloidal biochar preparation method of the present invention is simple to operate, saves time and labor, and its raw materials are easy to obtain and the usage is low, which significantly reduces the production cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 is the particle size distribution range of colloidal biochar at different preparation times.

[0031] Figure 2 The effect of colloidal biochar and large particle biochar on NH4 + -N adsorption capacity comparison.

[0032] Figure 3The growth of alfalfa seedlings in sand under different treatments.

[0033] Figure 4 Germination rate and relative chlorophyll content of alfalfa seedlings under different treatments.

[0034] Figure 5 are the fresh weight and dry weight of the aboveground and underground parts of alfalfa seedlings under different treatments.

[0035] Figure 6 The stem length and root length of alfalfa seedlings under different treatments.

[0036] Figure 7 Schematic diagram of alfalfa growth status under different treatments.

[0037] Figure 8 is the fresh weight and dry weight of the aboveground and underground parts of alfalfa under different treatments.

[0038] Figure 9 Plant height and total root length of alfalfa under different treatments.

[0039] Figure 10 The nitrogen and phosphorus contents in the aboveground and underground parts of alfalfa under different treatments.

[0040] Figure 11 is the available phosphorus content in soil under different treatments.

[0041] Figure 12 Schematic diagram of alfalfa growth status under different treatments.

[0042] Figure 13 is the fresh weight and dry weight of the aboveground part of alfalfa under different treatments.

[0043] Figure 14 is the content of total organic carbon and soluble organic carbon in soil profiles under different treatments. DETAILED DESCRIPTION

[0044] Unless otherwise specified, the experimental methods used in the following examples are conventional methods.

[0045] Unless otherwise specified, the materials and reagents used in the following examples can be obtained from commercial sources.

[0046] The present invention provides a method for preparing colloidal biochar, which has the advantages of simple preparation, small amount of biochar used, and low price, and comprises the following preparation steps:

[0047] 1) Collect the biochar raw materials, wash and dry them, and then pyrolyze them at 450℃ for 1 hour under limited oxygen. After cooling, use a grinder to crush the biochar and pass it through a 2 mm sieve to obtain large-particle biochar.

[0048] 2) The prepared biochar and water were mixed at a ratio of 1:20 (w / w) and poured into an electric heating emulsification stirring tank (Wenzhou Qiangzhong Machinery Technology, Zhejiang). The mixture was heated and emulsified at 90°C for 30 min to obtain colloidal biochar with a particle size of 400–1000 nm.

[0049] In the following examples, large particle biochar and colloidal biochar were prepared by the above method.

[0050] Example 1

[0051] Biochar raw material (wheat straw) was pyrolyzed under limited oxygen at 450°C for 1 h and then passed through a 2 mm sieve to produce large biochar particles. Biochar and water were mixed at a ratio of 1:20 (w / w) and poured into an electrically heated emulsifying mixing tank (Wenzhou Qiangzhong Machinery Technology, Zhejiang Province). Emulsification was performed at 90°C for 30–120 min to produce colloidal biochar.

[0052] Adsorption isotherm determination: The concentration of colloidal biochar and biochar was 1000 mg / L, and different concentration gradients of NH4 + -N (0.07-562 mg / L), after mixing, constant temperature shaking at 25 ° C and 180 r / min for 24 hours, and then filtered and the NH4 content of the solution was determined by flow analyzer + The Langmuir model was used to fit the data.

[0053] like Figure 1 As shown, the preparation time in the electrically heated emulsified mixing tank had little effect on the particle size of the colloidal biochar. Within a preparation time of 30 to 120 minutes, the particle size distribution of the colloidal biochar ranged from 400 to 1000 nm, with an average particle size of approximately 600 to 700 nm. Compared with larger biochar particles (<2 mm), the smaller particle size of the colloidal biochar facilitates its mobility in the soil.

[0054] Figure 2 The results show that the colloidal biochar and large particle biochar have a great influence on the NH4 + -N adsorption capacity comparison, Table 1 lists the two biochars for NH4 + The results show that the Langmuir model can better fit the experimental data. With the increase of the equilibrium concentration of the solution, the adsorption of NH4 + -N adsorption gradually increased and then stabilized. + The adsorption capacity of -N was 49.51% higher than that of large-particle biochar, which indicates that colloidal biochar has a stronger adsorption effect on nutrients, can reduce the loss and migration of nutrients in the soil, and can play a role in slow-release nutrients, thereby better maintaining soil fertility.

[0055] Compared to large-particle biochar, the colloidal biochar of this invention carries a more negative charge and a more negative zeta potential (Table 1). This is due to the larger surface area and more exposed charge sites of the colloidal biochar. The higher negative charge of the colloidal biochar helps it absorb more nutrients and migrate downward through the soil, thereby affecting deeper soil layers.

[0056] Table 1 Zeta potential of colloidal biochar and large particle biochar and their NH4 + Fitting parameters of -N adsorption

[0057]

[0058] Example 2

[0059] Sand column test: 150 g of sand was weighed and placed in a transparent plastic cup. Fertilizer was applied according to the mass of the sand. The colloidal biochar prepared in Example 1 of the present invention was added at a rate of 2 g / kg, diammonium phosphate was used at a rate of 0.066 g / kg, and urea was used at a rate of 0.066 g / kg. The specific treatments are shown in Table 2. Alfalfa seeds with plump, uniform grains were selected for sowing. The moisture content was adjusted within a certain range. The seeds were observed for germination and harvested on the 10th day.

[0060] The experiments of Comparative Examples 1-3 were carried out according to the conditions in Example 2 of the present invention, except that the fertilizers in the experimental treatments were replaced with the fertilizers shown in Table 2.

[0061] Table 2 Experimental treatments

[0062]

[0063] Figure 3 The growth of alfalfa seedlings in sand under different treatments is demonstrated. Compared with the control groups T1-3, the growth of alfalfa seedlings under the treatment of Example 2 (T02) was more significant, 1.19 times higher than that of T1 (Comparative Example 1). This may be attributed to the strong adsorption capacity of colloidal biochar for nutrients, which reduces the rapid migration of nutrients to the bottom with water, thereby achieving a slow-release effect of nutrients. At the same time, the nutrients in the colloidal biochar itself can be quickly released into the environment for absorption and utilization by the seedlings. Compared with the large-particle biochar in the control group T3, the colloidal biochar in Example 2 (T02) is easier to migrate downward, avoiding the biochar from acting only on the surface. The results of the sand column test provide technical support for the potential of colloidal biochar in soil applications.

[0064] Example 3

[0065] Grassland soil was collected from the Saibei Pasture in the Saibei Management District, Guyuan County, Zhangjiakou City, Hebei Province (115°51′29″E, 41°52′57″N). The soil was air-dried and then passed through a 2 mm sieve to remove impurities such as stones and plant roots. The soil had a pH of 7.71 and an electrical conductivity of 78.3 µS / cm, indicating a loamy texture.

[0066] The test plant was alfalfa, the variety of which was Zhongmu No. 1, purchased from Jiuquan Daye Seed Co., Ltd.

[0067] The experimental steps are as follows: weigh 50 g of soil and put it into a culture dish, and fertilize according to the quality of the soil. The amount of colloidal biochar prepared in Example 1 of the present invention is 2 g / kg, and the amount of diammonium phosphate and urea is 0.066 g / kg. Each treatment has 3 replicates, and the specific treatments are shown in Table 3. The soil moisture content is adjusted to 60-70% of the field water holding capacity. After one day of pre-cultivation, alfalfa seeds with full grains and uniform size are selected, disinfected with 10% hydrogen peroxide for 5 minutes, and then rinsed with distilled water several times. The seeds are sown in the soil using a hole sowing method, and 16 seeds are sown in each culture dish to ensure that there is a uniform spacing between each seed to ensure good contact with the soil and sufficient growth space.

[0068] During the germination period, add an equal amount of water every day, record the germination of seeds, and calculate the germination rate. Germination rate (%) = (number of germinated seeds / number of test seeds) × 100%

[0069] After 14 days of culture, five alfalfa seedlings of uniform growth were selected from each culture dish. Their aboveground and underground fresh and dry weights, stem length, and root length were measured. Chlorophyll content in the leaves was also measured using a chlorophyll meter (SPAD-502Plus).

[0070] The experiments of Comparative Examples 4-6 were carried out according to the conditions in Example 3 of the present invention, except that the fertilizers in the experimental treatments were replaced with the fertilizers shown in Table 3.

[0071] Table 3 Experimental treatments

[0072]

[0073] Figure 4The germination rate and relative chlorophyll content of alfalfa seedlings under different treatments were shown. The results showed that under the T4 (Comparative Example 4) treatment, the germination rate and leaf chlorophyll content of alfalfa seedlings were the lowest. Compared with T5 (Comparative Example 5), the T6 (Comparative Example 6) and T03 (Example 3) treatments increased the germination rate and leaf SPAD value of alfalfa seedlings. This shows that the addition of biochar promoted the germination rate of alfalfa and the relative content of leaf chlorophyll. In particular, compared with T6 (Comparative Example 6), the application amount of biochar in T03 (Example 3) was lower, but the effect of promoting the germination rate of alfalfa seedlings and the leaf chlorophyll content was better, increasing by 2.17% and 29.10%, respectively.

[0074] Figure 5 The fresh weight and dry weight of the aboveground and underground parts of alfalfa seedlings are shown. Compared with the T4 (Comparative Example 4) treatment, the T5 (Comparative Example 5), T6 (Comparative Example 6), and T03 (Example 3) treatments all significantly increased the fresh weight and dry weight of the aboveground and underground parts. The overall trend was T03 > T6 > T5 > T4, with the T03 (Example 3) treatment having the most significant yield-increasing effect. Specifically, the T03 treatment increased the fresh weight of the aboveground and underground parts by 10.77% and 34.74%, respectively, compared to T6 (Comparative Example 6), and the dry weight of the aboveground and underground parts by 11.82% and 5.33%, respectively. This demonstrates that the colloidal biochar prepared by the present invention can significantly increase the fresh weight and dry weight of alfalfa seedlings while reducing the amount of biochar used.

[0075] Figure 6 The results show the stem and root lengths of alfalfa seedlings. Compared to treatment T4 (Comparative Example 4), stem lengths of treatments T5 (Comparative Example 5), T6 (Comparative Example 6), and T03 (Example 3) increased by 60.50%, 81.51%, and 107.08%, respectively, while root lengths increased by 127.93%, 162.16%, and 170.27%, respectively. Treatment T03 (Example 3) had the most significant effect on increasing stem and root lengths of alfalfa seedlings.

[0076] Overall, the combination of the colloidal biochar prepared in this invention and inorganic fertilizer significantly promoted the growth of alfalfa seedlings. Compared with the application of large-particle biochar, the colloidal biochar significantly increased the chlorophyll content, fresh weight, dry weight, and stem and root length of the seedlings while reducing the application amount.

[0077] Example 4

[0078] The test soil was the same as that in Example 3.

[0079] Alfalfa (Nongmu 803) was selected as the test plant. 500 g of soil was placed in a flowerpot (13 cm in diameter, 11 cm in height), and fertilization was performed according to soil quality. The amount of colloidal biochar prepared in Example 1 of the present invention added was 2 g / kg, the amount of diammonium phosphate used was 0.066 g / kg, and the amount of urea used was 0.066 g / kg. Each treatment was replicated five times, and the specific treatment scheme is shown in Table 4. Alfalfa seeds of uniform size and full grains were selected, and seven seeds were sown per pot at a sowing depth of approximately 1-2 cm. When the alfalfa seedlings reached the three-leaf stage, thinning was performed, retaining four seedlings with consistent growth potential per pot. During pot cultivation, the soil moisture content was maintained at 60-70% of the field water holding capacity. After three months of cultivation, the fresh and dry weights of the aboveground and underground parts of the alfalfa, plant height and total root length, as well as the total nitrogen and total phosphorus contents were measured. Since the colloidal biochar of the present invention is applied on the soil surface, soil is sampled in layers to determine the available phosphorus content in the soil. The depths of the soil layers are 0-3.5 cm and 3.5-7 cm, respectively.

[0080] The experiments of Comparative Examples 7-9 were carried out according to the conditions in Example 4 of the present invention, and the fertilizers in the experimental treatments were replaced with the fertilizers shown in Table 4.

[0081] Table 4 Experimental treatments

[0082]

[0083] Figure 7 The growth status of alfalfa after cultivation is shown. From the appearance, compared with the comparative examples T7, T8 and T9, the growth of example T04 is significantly better, and the aboveground plants are significantly taller.

[0084] Figure 8 The fresh weight and dry weight data of the aboveground and underground parts of alfalfa are shown. The results show that the growth-promoting effect of Example T04 is the best. Compared with the comparative example T7, the fresh weight of the aboveground parts processed by T8, T9 and T04 increased by 21.41%, 24.37% and 36.81% respectively, and the fresh weight of the underground parts increased by 17.51%, 20.87% and 42.44% respectively. The changing trend of the alfalfa dry weight is similar to that of the fresh weight. Compared with the comparative example T7, the dry weight of the aboveground parts processed by T8, T9 and T04 increased by 18.56%, 21.65% and 37.63% respectively, and the dry weight of the underground parts increased by 22.54%, 30.48% and 41.90% respectively. These results show that the colloidal biochar prepared by the present invention significantly increases the fresh weight and dry weight of the aboveground and underground parts of alfalfa plants, helping to increase plant yield.

[0085] Figure 9Data on plant height and total root length of alfalfa are presented. The results indicate that Example T04 exhibits a significant growth-promoting effect. Under the different treatments, the average plant height of alfalfa reached 18.13 cm (T7), 19.32 cm (T8), 21.81 cm (T9), and 23.26 cm (T04), respectively, representing increases of 6.56%, 20.30%, and 28.30% compared to the control treatments T7, T8, T9, and T04, respectively. Furthermore, the average total root length per alfalfa plant under the different treatments was 72.07 cm (T7), 76.58 cm (T8), 79.53 cm (T9), and 88.61 cm (T04), respectively, representing increases of 6.26%, 10.35%, and 22.95% compared to the control treatments T7, T8, T9, and T04, respectively. These results demonstrate that the colloidal biochar prepared in this invention exhibits a significant growth-promoting effect on both the stems and roots of alfalfa.

[0086] Figure 10 The nitrogen and phosphorus contents in the aboveground and underground parts of alfalfa are shown. The results show that the nitrogen content in the aboveground and underground parts of the plants treated with comparative example T7 is the lowest, while the nitrogen content under other treatments increases to varying degrees. The nitrogen content in the aboveground and underground parts follows the trend of T04 (Example 4) > T9 > T8 > T7. This shows that T04 (Example 4) significantly promotes the utilization of nitrogen in the soil by the aboveground and underground parts of the plants. In terms of phosphorus utilization, the phosphorus content in the aboveground and underground parts follows the trend of T04 (Example 4) > T9 > T8 > T7. T04 (Example 4) also increases the absorption of phosphorus by the aboveground and underground parts of the plants. Overall, the colloidal biochar prepared by the present invention significantly improves the nutrient content and quality of alfalfa plants.

[0087] Figure 11 The results show that the content of available phosphorus in the 0-3.5 cm and 3.5-7 cm soil layers after the potted plants have grown is 127.50%. In the 3.5-7 cm soil layer, the T8 treatment reduced the available phosphorus content by 17.19% compared with the comparative example T7, while the T9 and T04 treatments increased it by 3.39% and 12.82%, respectively. In particular, the T04 treatment significantly increased the available phosphorus content in the 3.5-7 cm soil layer. Overall, the colloidal biochar prepared by the present invention helps to activate available phosphorus in the soil, thereby promoting the absorption and utilization of phosphorus by plants.

[0088] Overall, compared to other treatments, the colloidal biochar-inorganic fertilizer treatment prepared in this invention significantly increased the fresh and dry weight of both above- and below-ground plant parts, as well as stem and root growth. This treatment helps activate available phosphorus in the soil, providing sufficient nutrients for plant growth and promoting plant absorption of nitrogen and phosphorus.

[0089] Example 5

[0090] The test soil and test plants were the same as those in Example 4.

[0091] A PVC tube (44 cm long, 11.4 cm radius) was used and filled with soil that had passed a 2 mm sieve according to the actual field soil bulk density. Fertilizer was applied to the soil surface along with water according to the requirements in Table 5. The amount of colloidal biochar prepared in Example 1 of the present invention added was 2 g / kg, the amount of diammonium phosphate used was 0.066 g / kg, and the amount of urea used was 0.066 g / kg. Inorganic fertilizer and colloidal biochar were added based on the mass of the 0-20 cm soil layer. The moisture content of the potted plants was maintained at 70% of the field capacity. After the soil column equilibrated for 7 days, sowing was performed, with 10 seeds per pot. Three months after planting, the fresh and dry weights of the aboveground parts of the plants were measured, and the total organic carbon (SOC) and soluble organic carbon (DOC) contents in the soil (0-10 cm, 10-20 cm, 20-30 cm, and 30-40 cm) were determined.

[0092] The experiments of Comparative Examples 10-12 were carried out according to the conditions in Example 5 of the present invention, and the fertilizers in the experimental treatments were replaced with the fertilizers shown in Table 5.

[0093] Table 5 Experimental treatments

[0094]

[0095] Figure 12 The aboveground and underground growth conditions of alfalfa are shown. Compared with comparative examples 10-12 (T10-12), the aboveground growth condition of Example 5 (T05) is better, and the fibrous roots below the root system are more vigorous.

[0096] Figure 13The fresh and dry weights of the aboveground parts of alfalfa are shown three months after planting. Under the T05 (Example 5) treatment, alfalfa growth was optimal, with the overall fresh weight showing a trend of T05 (Example 5) > T11 > T12 > T10, while the dry weight showed a trend of T05 (Example 5) > T12 > T11 > T10. Compared with the control examples T10-12, the fresh weight under the T05 (Example 5) treatment increased by 26.05%, 13.17%, and 21.85%, respectively, and the dry weight increased by 48.95%, 30.65%, and 13.02%, respectively. The colloidal biochar prepared by the present invention significantly increased aboveground yield.

[0097] Figure 14 The data show the total organic carbon (TOC) and soluble organic carbon (SOC) contents in different soil layers under different treatments. Compared to Comparative Examples T10 and T11, both T12 (Comparative Example 12) and T05 (Example 5) increased TOC content in different soil layers, demonstrating that biochar addition can increase organic carbon content within the soil profile. In particular, T05 (Example 5) increased TOC content by 3.14% in the 30-40 cm soil layer compared to T12 (Comparative Example 12). This suggests that colloidal biochar is more beneficial for carbon sequestration in deep soil layers (30-40 cm) than large-particle biochar. This may be due to the mobility of the colloidal biochar itself or its enhanced migration of soluble organic matter to the 30-40 cm soil layer.

[0098] In general, the T05 (Example 5) treatment can significantly increase the fresh weight and dry weight of the aboveground part of the plant, promote the growth of fibrous roots, and is beneficial to carbon sequestration in deep soil (30-40 cm).

[0099] The colloidal biochar produced by this method not only enhances nutrient adsorption and reduces nutrient loss, but also, when used in combination with inorganic fertilizers, improves alfalfa yield and quality, aids in activating available nutrients in the soil, and helps fix carbon in deep soil layers (30-40 cm). Furthermore, the fertilizer is simple to prepare, saving time and effort. The colloidal biochar's raw materials are readily available and require low dosage, reducing production costs. This provides a new approach and technical preparation method for improving degraded grasslands.

[0100] The embodiments described above are some, but not all, of the embodiments of the present invention. The detailed description of the embodiments of the present invention is not intended to limit the scope of the invention as claimed, but rather merely represents selected embodiments of the present invention. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without inventive effort are also within the scope of protection of the present invention.

Claims

1. A colloidal biochar, characterized in that: The particle size of the colloidal biochar is 400-1000 nm, and the average particle size is 600-700 nm; The colloidal biochar is prepared by the following method: mixing biochar and water, stirring, heating and emulsifying, thereby obtaining the colloidal biochar; The mass ratio of the biochar to the water is 1:5-40; the temperature of the heating and emulsification is 85-95° C., and the time is 30-120 min.

2. The colloidal biochar according to claim 1, characterized in that The raw material of the biochar is selected from at least one of wheat straw, corn straw, rice straw, wood chips, branches and leaves, and bark.

3. The method for preparing the colloidal biochar according to claim 1 or 2, comprising the steps of: mixing biochar and water, stirring, heating and emulsifying, thereby obtaining the colloidal biochar.

4. The method according to claim 3, characterized in that The mass ratio of the biochar to the water is 1:5-40; the temperature of the heating and emulsification is 85-95° C., and the time is 30-120 min.

5. A soil conditioner for grassland, characterized in that: The soil conditioner comprises the colloidal biochar and fertilizer according to claim 1 or 2; the soil conditioner comprises the following components in parts by mass: 2 parts of colloidal biochar; 0.03-0.08 parts of diammonium phosphate fertilizer; and 0.03-0.08 parts of urea fertilizer.

6. Use of the soil conditioner according to claim 5 in grassland.

7. The use according to claim 6, characterized in that The grassland is soil for growing alfalfa.

8. The use according to claim 6 or 7, characterized in that The total amount of the soil conditioner applied is 2-5 g per kilogram of grassland soil.

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