Preparation method of humic acid biochar saline-alkali soil conditioner

Abstract

The invention belongs to the technical field of soil improvement, and discloses a preparation method of a humic acid biochar saline-alkali soil conditioner. The preparation method comprises the following steps: by taking waste edible fungus chaff as a raw material, activating the waste edible fungus chaff with a KOH solution, pyrolyzing the waste edible fungus chaff under a limited oxygen condition to obtain fungus chaff-based biochar with a porous structure, mixing the fungus chaff-based biochar with humic acid, a sodion replacement material (desulfurized gypsum powder and / or calcium chloride) and purified water according to a certain mass ratio, and drying and fixing at medium temperature to obtain the modifier. According to the modifier, the porous adsorption performance of the biochar, the pH adjustment and agglomeration improvement functions of the humic acid and the sodium ion replacement capacity of the calcium source material are comprehensively exerted, the sodium ion content in the saline-alkali soil is synergistically reduced, and the soil agglomeration structure and the water and fertilizer retention capacity are improved. The prepared modifier is especially suitable for soil treatment of moderate and severe saline-alkali soil in which the ratio of sodium ions to exchangeable cations exceeds 10%, and has agricultural waste resource utilization and ecological restoration values.

Description

Technical Field

[0001] This invention belongs to the field of soil improvement technology, specifically relating to a method for preparing a humic acid biochar soil conditioner for saline-alkali land. Background Technology

[0002] Saline-alkali land is an important reserve of arable land with high potential for agricultural development. However, due to the enrichment of salt, increased alkalinity, and excessive sodium ion content in the soil, saline-alkali soils generally suffer from structural damage, poor permeability, insufficient nutrient supply, and difficulty in normal crop growth, severely restricting agricultural production efficiency and the sustainable use of soil resources. Among these issues, excessive accumulation of sodium ions is one of the key factors inducing soil alkalization, easily leading to the dispersion of soil colloids, destruction of aggregate structure, and subsequently triggering a series of vicious cycles such as soil compaction, poor aeration, and decreased water retention capacity.

[0003] Currently, soil improvement in saline-alkali land mainly relies on methods such as the application of calcium and magnesium minerals, organic matter supplementation, and the addition of chemical conditioners. Although organic fertilizers are widely available as soil conditioners, their degree of decomposition and the instability of resource acquisition often affect the improvement effect. In recent years, biochar has been increasingly used for soil improvement due to its rich pore structure, high cation exchange capacity, and environmental friendliness. Specifically, by loading calcium-source materials such as gypsum onto the surface of biochar, effective exchange of sodium ions in the soil can be achieved, improving ion balance and nutrient environment. For example, CN120209843A discloses a method for preparing a composite soil conditioner of titanium slag-coconut shell charcoal-desulfurized gypsum and its application, but it is mainly for acidic soil improvement and not suitable for alkaline saline-alkali soils; moreover, the organic matter in its conditioner comes from a single source, only coconut shell charcoal, lacking diversity and hindering the utilization and reproduction of soil microorganisms. Humic acid is a type of natural organic additive widely used for alkaline soil improvement, possessing good metal ion chelation and acid buffering capacity, which helps regulate soil pH, increase organic matter content, and promote microbial growth. For example, CN120229982A discloses a soil conditioner based on ultra-fine particle energy-concentrating humic acid, but this technology does not involve the addition of sodium ion replacement materials, making it difficult to effectively treat moderately to severely saline-alkali land with high sodium ion concentrations.

[0004] Therefore, there is an urgent need to develop a new type of composite soil conditioner that uses waste resources as raw materials and has both high sodium ion exchange capacity and slow-release conditioning function. This conditioner can not only effectively improve the physical and chemical properties of soil and reduce sodium salt hazards, but also promote the resource utilization of agricultural waste and achieve the coordinated development of ecological restoration of saline-alkali land and increased agricultural production. Summary of the Invention

[0005] This invention aims to solve at least one of the technical problems existing in the prior art. This invention proposes a method for preparing humic acid biochar as a soil conditioner for saline-alkali land. Using agricultural waste as raw material, high specific surface area biochar is obtained through KOH activation and carbonization at 500–700℃. Combined with humic acid and sodium ion exchange materials, this method can effectively reduce the sodium adsorption ratio (SAR) of saline-alkali soil, improving soil structure and the crop growth environment.

[0006] To achieve the above objectives, the present invention provides the following technical solution: In a first aspect, the present invention provides a method for preparing a humic acid biochar soil conditioner for saline-alkali land, comprising the following steps: 1) Pretreatment of mushroom residue: Take waste mushroom residue from edible fungi, and wash, dry and crush it in sequence to obtain pretreated mushroom residue; 2) Activation of bacterial residue: The pretreated bacterial residue was soaked in KOH solution for 24 h for activation. After filtration, it was washed with water and dried to obtain KOH activated bacterial residue. 3) Biochar preparation: KOH-activated bacterial bran was pyrolyzed under a nitrogen atmosphere, then soaked in hydrochloric acid solution for 24 h, and then filtered, washed, dried, pulverized and sieved to obtain bacterial bran-based biochar; 4) Modified material loading: The bacterial bran-based biochar is mixed with humic acid, sodium ion replacement material and purified water in a certain mass ratio, and stirred evenly to form a modified material mixture. 5) Modification material fixation: The modified material mixture is dried in an oven to fix the effective components, cooled, crushed and sieved to obtain humic acid biochar saline-alkali soil conditioner.

[0007] Preferred: Step 1) During the pretreatment of mushroom residue, the waste mushroom residue of edible fungi can be at least one of shiitake mushroom residue, wood ear mushroom residue, Ganoderma lucidum mushroom residue, oyster mushroom residue, enoki mushroom residue or button mushroom residue; The cleaning process involves using water washing to remove dust, impurities, and plastic residues adhering to the surface of the mushroom substrate. The drying temperature can be 50℃~100℃; The crushing process involves using a pulverizer to crush the mushroom residue to a particle size of 30-100 mesh.

[0008] Preferred: Step 2) During the activation of the bacterial substrate, the KOH solution is added to the pretreated bacterial substrate at a solid-liquid mass ratio of 1:(10-15). The concentration of the KOH solution can be 2–10 mol·L⁻¹ -1 ; The washing method involves slowly rinsing 2 to 4 times with 10 times the volume of KOH solution in deionized water. The temperature of the drying step can be controlled between 80℃ and 100℃, and the drying time can be 8 to 12 hours.

[0009] Preferred: Step 3) In the biochar preparation process, the pyrolysis process is carried out under a nitrogen protective atmosphere at 5°C·min. -1 The sample was heated from room temperature to 500–700°C at a heating rate of 1–3 h for pyrolysis. The concentration of the hydrochloric acid solution can be 1–3 mol·L⁻¹. -1 The hydrochloric acid solution is added to the KOH-activated bacterial substrate at a solid-liquid mass ratio of 1:(10-15). The washing operation involves rinsing with deionized water until the pH of the filtrate is close to neutral. The temperature of the drying step can be controlled between 80℃ and 100℃, and the drying time can be 8 to 12 hours.

[0010] The crushing and sieving process involves grinding and crushing the dried carbon material and passing it through a 50-100 mesh sieve.

[0011] Preferred: Step 4) During the loading of modified materials, the mass ratio of biochar, humic acid, sodium ion replacement material and pure water can be 1:(1-2):(3-5):(60-100). The sodium ion replacement material is selected from at least one of desulfurized gypsum powder and calcium chloride; The stirring method is magnetic stirring, with the speed controlled at 300–600 rpm and the stirring time at 2–3 hours to ensure that the components are fully dispersed.

[0012] Further optimization: Step 4) During the loading of modified materials, the mass ratio of biochar, humic acid, sodium ion replacement material and pure water can be 1:(1.5~2):4:80.

[0013] Preferred: Step 5) During the material fixing process, the drying temperature can be 120-140℃; The pulverization and sieving process involves grinding and pulverizing the cooled modified material and passing it through a 50-100 mesh sieve to obtain phytic acid-supported porous carbon material with uniform particle size.

[0014] Secondly, the present invention provides a humic acid biochar saline-alkali soil conditioner, which is prepared by the above-mentioned method for preparing humic acid biochar saline-alkali soil conditioners.

[0015] Preferred: The humic acid biochar soil conditioner is suitable for the improvement and treatment of saline-alkali soils where sodium ions account for more than 10% of the total exchangeable cations.

[0016] Compared with the prior art, the beneficial effects of the present invention are: The soil conditioner for saline-alkali land prepared in this invention mainly uses natural or renewable resources, such as humic acid, waste mushroom substrate, and desulfurized gypsum powder, as raw materials, which have the advantages of wide availability and low cost. By utilizing the mushroom substrate as a resource, not only is the land occupation and environmental pollution caused by its accumulation effectively reduced, but the ecological governance goal of "treating waste with waste" is also achieved, aligning with the needs of green agricultural development. The conditioner is rich in various nutrients such as calcium, nitrogen, and phosphorus, which can directly replenish soil nutrients, improve the basic fertility of saline-alkali land, improve crop growth conditions, and achieve the dual functions of nutrient supply and soil remediation.

[0017] This invention utilizes a combined process of KOH activation, pyrolysis, and acid washing to treat bacterial residue, promoting the reaction of lignin and cellulose with KOH at high temperatures to generate potassium carbonate, thereby forming a porous biochar material with a high specific surface area. This structure significantly improves the adsorption capacity and loading performance of the biochar, providing an excellent immobilization carrier for humic acid and sodium ion exchange materials. The humic acid in the amendment contains abundant acidic functional groups, which can regulate soil pH and form complexes with sodium ions. Simultaneously, the desulfurized gypsum and calcium chloride (CaCl2) in the sodium ion exchange material can release calcium ions, exchanging with sodium ions on soil colloids to generate relatively stable calcium compounds, thereby effectively reducing soil alkalinity and sodium adsorption ratio (SAR), and improving nutrient utilization. The synergistic effect of humic acid and bacterial residue-based biochar promotes soil aggregate formation, increases the looseness of the topsoil, effectively breaks up compacted layers, improves aeration and water retention, enhances soil buffering capacity, and provides a better physicochemical environment for plant root growth.

[0018] This invention provides a soil conditioner for saline-alkali land, rich in elements such as calcium, nitrogen, and phosphorus, which can replenish soil nutrients and improve the fertility of saline-alkali land. During the biochar preparation process, the inoculum residue is activated by KOH, calcined at high temperature, and acid-washed. KOH reacts with the lignin and cellulose in the inoculum residue to generate potassium carbonate, which, after acid washing, forms a porous biochar material, increasing its specific surface area and thus its adsorption and loading capacity. The components of the conditioner exhibit significant synergistic effects. Humic acid, with its acidic functional groups, works synergistically with desulfurized gypsum powder and calcium chloride in the sodium ion replacement material to effectively reduce soil pH and alleviate soil alkalinity. Furthermore, the calcium ion compounds and other components in the sodium ion replacement material can also undergo replacement reactions with other ions in the soil, such as sodium ions, to form stable compounds, further improving nutrient utilization efficiency. Humic acid and inoculum biochar components can improve soil aggregate structure, loosen the topsoil, and effectively break up soil compaction. This not only improves soil permeability and water and fertilizer retention capacity, but also promotes the growth and development of plant systems, providing a more favorable soil environment for crop growth. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the soil conditioner preparation method in this embodiment. Detailed Implementation

[0020] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that, unless otherwise specified, the following embodiments and features described therein can be combined with each other.

[0021] Example 1

[0022] This embodiment provides a method for preparing a humic acid biochar soil conditioner for saline-alkali land, and the specific steps are as follows: Step 1: Take waste shiitake mushroom substrate, rinse it with purified water to remove surface dust, plastic particles and other impurities, and dry it in an 80℃ oven for 12 hours; after drying, take it out and crush it with a pulverizer until the particle size is less than 0.3 mm to obtain pretreated substrate. The waste shiitake mushroom substrate comes from Xinjiang Chentian Agricultural Technology Co., Ltd.

[0023] Step 2: Weigh 5 g of pretreated bacterial residue and place it in a 100 mL beaker. Add 60 mL of 5 mol·L⁻¹ KOH solution, stir well, and let it stand for 24 h to activate. After activation, filter and slowly rinse three times with 600 mL of deionized water to remove residual KOH on the surface of the bacterial residue while retaining some KOH in the pores. Then dry in an oven at 80℃ for 12 h to obtain KOH-activated bacterial residue.

[0024] Step 3: The KOH-activated biochar residue was placed in a tube furnace and heated from room temperature to 600℃ at a rate of 5℃·min⁻¹ under a nitrogen atmosphere, and held at this temperature for 2 h for pyrolysis. After naturally cooling to room temperature, the carbonized material was removed and soaked in 2 mol·L⁻¹ hydrochloric acid solution for 24 h to remove residual K₂CO₃ and other impurities. After thorough filtration, it was washed with deionized water until neutral, dried in an oven at 80℃ for 12 h, ground, and passed through an 80-mesh sieve to obtain biochar residue-based biochar.

[0025] Step 4: Mix the bacterial bran-based biochar, humic acid, desulfurized gypsum powder, and purified water at a mass ratio of 1:1.5:4:80, and magnetically stir at 500 rpm for 3 hours to ensure uniform dispersion of the components, thus obtaining the modified material mixture. The humic acid was purchased from Shanghai Maclean Biochemical Technology Co., Ltd.

[0026] Step 5: Place the modified material mixture in an oven and dry it at 130℃ until stable. After cooling, grind and crush it and pass it through an 80-mesh sieve to obtain the target humic acid biochar saline-alkali soil conditioner.

[0027] Example 2

[0028] This embodiment provides a method for preparing a humic acid biochar soil conditioner for saline-alkali land, and the specific steps are as follows: Step 1: Take waste shiitake mushroom substrate, rinse it with purified water to remove surface dust, plastic particles and other impurities, and dry it in an 80℃ oven for 12 hours; after drying, take it out and crush it with a pulverizer until the particle size is less than 0.3 mm to obtain pretreated substrate.

[0029] Step 2: Weigh 5 g of pretreated bacterial residue and place it in a 100 mL beaker. Add 60 mL of 5 mol·L⁻¹ KOH solution, stir well, and let it stand for 24 h to activate. After activation, filter and slowly rinse three times with 600 mL of deionized water to remove residual KOH on the surface of the bacterial residue while retaining some KOH in the pores. Then dry in an oven at 80℃ for 12 h to obtain KOH-activated bacterial residue.

[0030] Step 3: The KOH-activated biochar residue was placed in a tube furnace and heated from room temperature to 600℃ at a rate of 5℃·min⁻¹ under a nitrogen atmosphere, and held at this temperature for 2 h for pyrolysis. After naturally cooling to room temperature, the carbonized material was removed and soaked in 2 mol·L⁻¹ hydrochloric acid solution for 24 h to remove residual K₂CO₃ and other impurities. After thorough filtration, it was washed with deionized water until neutral, dried in an oven at 80℃ for 12 h, ground, and passed through an 80-mesh sieve to obtain biochar residue-based biochar.

[0031] Step 4: Mix the bacterial bran-based biochar, humic acid, calcium chloride and purified water at a mass ratio of 1:1.8:4:80, and magnetically stir at 500 rpm for 3 hours to ensure uniform dispersion of the components and obtain the modified material mixture.

[0032] Step 5: Place the modified material mixture in an oven and dry it at 130℃ until stable. After cooling, grind and crush it and pass it through an 80-mesh sieve to obtain the target humic acid biochar saline-alkali soil conditioner.

[0033] Example 3

[0034] This embodiment provides a method for preparing a humic acid biochar soil conditioner for saline-alkali land, and the specific steps are as follows: Step 1: Take waste shiitake mushroom substrate, rinse it with purified water to remove surface dust, plastic particles and other impurities, and dry it in an 80℃ oven for 12 hours; after drying, take it out and crush it with a pulverizer until the particle size is less than 0.3 mm to obtain pretreated substrate.

[0035] Step 2: Weigh 5 g of pretreated bacterial residue and place it in a 100 mL beaker. Add 60 mL of 5 mol·L⁻¹ KOH solution, stir well, and let it stand for 24 h to activate. After activation, filter and slowly rinse three times with 600 mL of deionized water to remove residual KOH on the surface of the bacterial residue while retaining some KOH in the pores. Then dry in an oven at 80℃ for 12 h to obtain KOH-activated bacterial residue.

[0036] Step 3: The KOH-activated biochar residue was placed in a tube furnace and heated from room temperature to 700℃ at a rate of 5℃·min⁻¹ under a nitrogen atmosphere, and held at this temperature for 2 h for pyrolysis. After naturally cooling to room temperature, the carbonized material was removed and soaked in 2 mol·L⁻¹ hydrochloric acid solution for 24 h to remove residual K₂CO₃ and other impurities. After thorough filtration, it was washed with deionized water until neutral, dried in an oven at 80℃ for 12 h, ground, and passed through an 80-mesh sieve to obtain biochar residue-based biochar.

[0037] Step 4: Mix the bacterial bran-based biochar, humic acid, desulfurized gypsum powder, calcium chloride and purified water in a mass ratio of 1:2:2:2:80, and magnetically stir at 500 rpm for 3 hours to ensure uniform dispersion of the components and obtain the modified material mixture.

[0038] Step 5: Place the modified material mixture in an oven and dry it at 130℃ until stable. After cooling, grind and crush it and pass it through an 80-mesh sieve to obtain the target humic acid biochar saline-alkali soil conditioner.

[0039] Comparative Example 1 To compare the effect of KOH activation, the preparation process of this comparative example is the same as that of Example 3, except that the bacterial substrate was not treated with KOH activation, while the other steps are the same.

[0040] Comparative Example 2 To compare the effects of adding humic acid, the preparation process of this comparative example is the same as that of Example 3, except that no humic acid is added, while the other process steps are the same.

[0041] Comparative Example 3 To compare the effect of sodium ion replacement materials, the preparation process of this comparative example is the same as that of Example 3, except that desulfurized gypsum powder and calcium chloride are not added, while the other steps remain the same.

[0042] Experimental conditions and results To verify the actual effect of the soil conditioner of this invention, a pot experiment was conducted. The test site was a severely saline-alkali farmland in a test base in Xinjiang Uygur Autonomous Region. The original soil pH was 8.82–9.05, and the salt content was 7.81–8.13 g / kg. Soil samples were sieved through a 2 mm sieve and then air-dried for later use. Plastic flower pots with a diameter of 11 cm and a height of 10 cm were used as potting containers, and 1 kg of saline-alkali soil was filled in each pot. The amount of conditioner applied was 2% of the soil mass. The conditioners obtained in Examples 1–3 and Comparative Examples 1–3 were added to the soil and mixed evenly. After application, the soil was watered and pre-cultured for 3 days. Then, 10 wheat seeds (same size) were sown in each pot and cultivated under normal temperature conditions. The seed germination rate was measured on the 7th day after sowing, and the plant height and disease incidence were measured on the 30th day. Soil samples were also collected to measure pH, salt content, and sodium adsorption ratio (SAR).

[0043] Plant growth index determination: Germination status was investigated and germination rate was calculated on the 7th day after sowing (germination rate (%) = (number of germinated seeds / total number of seeds tested) × 100%); on the 30th day, the plant height of all surviving plants was measured with a tape measure and the disease incidence rate was calculated (disease incidence rate (%) = (number of diseased plants / total number of plants investigated) × 100%).

[0044] Soil physicochemical properties were determined: Soil samples were collected during the same period, air-dried, sieved, and then tested. Soil pH was determined using the potentiometric method (soil-water ratio 2.5:1); soil salinity was determined using the residue drying-mass method (soil-water ratio 1:5).

[0045] Sodium adsorption ratio (SAR):

[0046] Na + The content was determined by flame photometry, Ca 2+ Mg 2+ The content was determined using atomic absorption spectrometry; Each treatment was performed in 5 parallel replicates, and the average value was used to evaluate the effect.

[0047] Results are shown in Table 1: Changes in pH of saline-alkali soil. Table 1 shows that the effects of different treatment groups on soil pH regulation varied significantly. The blank control group maintained a pH of 8.94, exhibiting typical strong alkalinity characteristics and showing no improvement. Comparative Example 1, due to the lack of KOH activation, produced biochar with a dense structure and poor adsorption performance, resulting in limited buffering effect on soil pH, with a pH of 8.52. Comparative Example 2, although containing biochar and sodium ion exchanger, lacked humic acid and thus lacked acidic functional groups to regulate pH, causing a slight decrease in pH to 8.73. Comparative Example 3 lacked calcium source material, failing to achieve effective Na⁺ replacement, resulting in a high residual sodium salt and a pH still as high as 8.38. In contrast, Examples 1-3 all incorporated KOH-activated biochar, humic acid, and sodium ion exchange material. The synergistic effect of these three ingredients significantly reduced soil alkalinity, with pH values ​​decreasing to 7.82, 8.03, and 7.64, respectively. Example 3, which used gypsum and calcium chloride simultaneously, exhibited the strongest alkalinity-reducing ability and the largest pH reduction. This demonstrates that the soil conditioner prepared in this invention can effectively regulate soil pH, making it more neutral and suitable for plant root growth.

[0048] Table 1: Changes in pH of saline-alkali soil

[0049] Results 2 are shown in Table 2: Changes in salinity and sodium adsorption ratio in saline-alkali soil. Table 2 shows that the soil salinity in the blank control group was the highest, reaching 8.04 g / kg, with a SAR of 12.21, indicating severe soil salinity accumulation and sodium ion dominance. Comparative Example 1, without KOH activation treatment, had limited specific surface area and adsorption capacity of the resulting biochar, leading to only a slight decrease in salinity and SAR, at 6.43 g / kg and 8.33, respectively. Comparative Example 2, without humic acid, lacked aggregate structure and acidity regulation function, limiting sodium salt migration, and its SAR remained at 8.65. Comparative Example 3, without sodium ion exchanger, could not achieve effective Na⁺ exchange; despite containing humic acid and biochar, its SAR still rose to 9.18, close to the blank group, demonstrating the crucial role of calcium source materials in sodium removal. In contrast, Examples 1-3 all incorporated KOH-activated biochar, humic acid, and a sodium ion exchanger, exhibiting a significant synergistic effect in desalination and sodium removal. Soil salinity decreased to 5.24, 5.50, and 4.93 g / kg, respectively, and SAR decreased to 7.03, 7.55, and 6.86, respectively. Example 3, in particular, demonstrated the strongest sodium removal capacity under the action of a dual calcium source. These results indicate that the composite soil conditioner prepared in this invention can effectively reduce soil salinity and sodium load, and improve the structure and ion balance of saline-alkali soils.

[0050] Table 2: Changes in salinity and sodium ion content in saline-alkali soils

[0051] Result 3: Effects on wheat germination rate, plant height, and disease incidence Table 3 shows that, from the perspective of crop growth, each treatment group had a significant impact on the germination rate, plant height, and disease incidence of wheat. The blank control group, due to high soil salinity, dense structure, and severe ion toxicity, had a germination rate of only 68.32%, an average plant height of 12.66 cm, and a disease incidence rate as high as 20.43%, indicating that salt-alkali stress significantly inhibited crop germination and growth. Comparative Example 1 lacked the KOH activation process, resulting in limited adsorption and slow-release capacity of the soil conditioner; the germination rate and plant height were 75.42% and 13.77 cm, respectively, and the disease incidence rate remained high at 15.47%. Comparative Example 2, without the addition of humic acid, resulted in poor soil aggregate structure and insufficient aeration, leading to a disease incidence rate of 13.14%. Comparative Example 3, although containing humic acid and activated carbon, lacked a sodium ion exchange agent, resulting in poor sodium toxicity mitigation; the germination rate and plant height did not significantly improve, and the disease incidence rate remained at 15.84%. In comparison, Examples 1-3 showed superior improvement effects. Example 3 achieved a germination rate of 94.25%, a plant height of 18.12 cm, and a disease rate reduced to only 5.40%. Examples 1 and 2 also achieved germination rates exceeding 90%, significantly increased plant height, and disease rates below 8%. The results indicate that the composite amendment of this invention can effectively alleviate salt-alkali stress, improve the rhizosphere environment, inhibit disease occurrence, and significantly promote early crop growth and healthy development.

[0052] Table 3: Changes in wheat germination rate, plant height, and disease incidence

[0053] In summary, the three embodiments of this invention significantly outperformed the comparative treatments in terms of plant growth performance, soil salinity regulation, and improvement of physicochemical properties, fully verifying the scientific validity and effectiveness of the technical solution of this invention. Specifically, the KOH activation process endows biochar with a higher specific surface area and pore structure, significantly enhancing its adsorption and slow release capacity for salts and harmful ions; the introduction of humic acid not only regulates soil pH and improves aggregate structure but also enhances the soil's cation exchange capacity and microbial activity; calcium source materials (such as desulfurized gypsum and calcium chloride) act as highly efficient sodium ion exchangers, exchanging ions with Na+ in soil colloids to promote sodium ion migration out of the rhizosphere, thereby effectively reducing the soil sodium adsorption ratio (SAR). The synergistic effect of these three components constructs a functionally complementary and clearly defined saline-alkali land remediation system, particularly suitable for the ecological management and farmland improvement of moderately to severely saline-alkali land with sodium ion enrichment.

[0054] The humic acid biochar soil conditioner prepared by this invention has a simple preparation process and uses green and renewable raw materials. It not only realizes the high-value utilization of agricultural waste but also significantly improves the agricultural productivity of saline-alkali soils. Therefore, this technology has broad application prospects in saline-alkali land management, crop quality improvement and yield enhancement, and arable land expansion, and can provide a practical solution for achieving ecological restoration of saline-alkali land and sustainable agricultural development.

[0055] The embodiments described above are merely illustrative of specific implementations of the present invention, and while the descriptions are detailed, they should not be construed as limiting the scope of protection of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention.

Claims

1. A method for preparing a humic acid biochar soil conditioner for saline-alkali land, characterized in that, Includes the following steps: 1) Pretreatment of mushroom residue: Take waste mushroom residue from edible fungi, and wash, dry and crush it in sequence to obtain pretreated mushroom residue; 2) Activation of bacterial residue: The pretreated bacterial residue was soaked in KOH solution for 24 h for activation. After filtration, it was washed with water and dried to obtain KOH activated bacterial residue. 3) Biochar preparation: KOH-activated bacterial bran was pyrolyzed under a nitrogen atmosphere, then immersed in hydrochloric acid solution for 24 h, and after filtration, washing, drying, pulverizing and sieving, bacterial bran-based biochar was obtained. 4) Modified material loading: The bacterial bran-based biochar is mixed with humic acid, sodium ion replacement material and pure water in a certain mass ratio, and then uniformly dispersed under stirring conditions to form a modified material mixture. 5) Modification material fixation: The modified material mixture is dried and fixed in an oven to fix the effective components. After cooling, it is crushed and sieved to obtain humic acid biochar saline-alkali soil conditioner.

2. The preparation method according to claim 1, characterized in that, The edible fungus waste substrate mentioned in step 1) is at least one of the following: shiitake mushroom substrate, wood ear mushroom substrate, reishi mushroom substrate, oyster mushroom substrate, enoki mushroom substrate, and button mushroom substrate.

3. The preparation method according to claim 1, characterized in that, Step 2) The activation of the bacterial substrate specifically includes: adding KOH solution to the pretreated bacterial substrate at a solid-liquid mass ratio of 1:(10-15), stirring evenly, and letting it stand for 24 h for activation. After filtration, it is slowly rinsed 2-4 times with 10 times the volume of deionized water containing KOH solution, and then dried at 80-100℃ for 8-12 h to obtain KOH-activated bacterial substrate.

4. The preparation method according to claim 3, characterized in that, The concentration of the KOH solution is 2–10 mol·L⁻¹ -1 .

5. The preparation method according to claim 1, characterized in that, Step 3) involves the preparation of biochar as follows: KOH-activated bacterial residue is placed in a tube furnace and heated at 5°C / min under a nitrogen atmosphere. -1 The heating rate was increased from room temperature to 500–700℃, and the temperature was maintained for 1–3 h for pyrolysis. After pyrolysis, the material was naturally cooled to room temperature. The cooled char material was soaked in hydrochloric acid solution for 24 h, filtered, washed with deionized water until neutral, dried at 80–100℃ for 8–12 h, ground and pulverized and passed through a 50–100 mesh sieve to obtain bran-based biochar.

6. The preparation method according to claim 5, characterized in that, The concentration of the hydrochloric acid solution is 1–3 mol·L⁻¹. -1 .

7. The preparation method according to claim 1, characterized in that, In step 4), the loading of modified materials is specifically as follows: the bacterial bran-based biochar, humic acid, sodium ion replacement material and pure water are mixed at a mass ratio of 1:(1-2):(3-5):(60-100), and magnetically stirred at 300-600 rpm for 2-3 hours to form a modified material mixture.

8. The preparation method according to claim 7, characterized in that, The sodium ion replacement material is desulfurized gypsum powder and / or calcium chloride.

9. The preparation method according to claim 1, characterized in that, Step 5) involves fixing the modified material as follows: placing the modified material mixture in an oven and drying it at 120-140℃ until the quality is stable. After cooling, the mixture is ground and pulverized and passed through a 50-100 mesh sieve to obtain the humic acid biochar saline-alkali soil conditioner.

10. The humic acid biochar soil conditioner for saline-alkali land prepared by the method according to any one of claims 1 to 9, characterized in that, It is suitable for the improvement and treatment of saline-alkali soils where sodium ions account for more than 10% of the total exchangeable cations.

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