Forest waste biochar base fertilizer for coastal low-lying land soil improvement

Abstract

The invention provides a forest waste biochar base fertilizer for coastal low-lying land soil improvement, which is characterized in that biochar with different characteristics is prepared through a directional carbonization process by utilizing the difference of tree wastes such as leaves, barks and branches in fiber density and chemical composition, and pseudomonas putida and montmorillonite are respectively loaded according to the porosity difference. Layered matching is carried out according to requirements of soil layers, the physical structure of soil is effectively improved, hardening and salt stress are relieved, meanwhile, the long-acting slow-release characteristic is achieved, the nutritional requirements of taxodium orientalis seedlings in the whole growing season can be continuously met, overground part growth and root development of taxodium orientalis can be effectively promoted, and the survival rate of taxodium orientalis seedlings is increased. And a green, economic and sustainable technical approach is provided for ecological restoration and vegetation reconstruction of the coastal saline-alkali land.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of soil improvement, and particularly relates to a forest waste biochar-based fertilizer for soil improvement in coastal low-lying land. BACKGROUND

[0002] Coastal beach land is an important land reserve resource available at present, but in coastal areas, due to the effects of tides, seawater immersion, high groundwater salinity, and strong evaporation, salt accumulates in large quantities in the surface layer of soil, resulting in high soil salt content and pH value, serious compaction, poor structure, poor air permeability, low organic matter content, low fertility, and poor water retention. At present, soil salinization is still on the rise worldwide, which seriously restricts local land use efficiency and agricultural production, causing serious economic losses and ecological and environmental safety problems.

[0003] Traditional methods for improving saline-alkali soil include physical measures (replacement of guest soil, underground pipe salt drainage), water conservancy projects (such as leaching drainage), and chemical improvement (such as gypsum, humic acid, etc.), but these methods generally have limitations such as high cost, short time efficiency, easy secondary pollution, or difficulty in large-scale promotion. Biochar is a carbon-rich solid product obtained by thermal chemical reaction of biomass materials under anaerobic or anoxic conditions. Due to its porous structure, high specific surface area, and rich functional groups on the surface, it has shown significant advantages in improving soil physical properties, regulating salt-alkali balance, fixing pollutants, and promoting microbial activity. At the same time, biochar raw materials are widely available (such as agricultural waste, algae, etc.), and it has dual environmental benefits of carbon sequestration and emission reduction and resource recycling.

[0004] In recent years, the global planting scale of forest resources has significantly expanded, mainly due to the need to address climate change and ecological restoration, urban forestry and landscape greening development, and large-scale management of economic forests and plantations. Large-scale planting of economic forests to meet the demand for wood, paper pulp, and other industries generates a large amount of waste such as branches and tree bark during felling and renewal. Intensive management of plantations further increases the short-term output of forest biomass. Traditional disposal methods such as landfilling and incineration not only occupy land resources but also release greenhouse gases and harmful substances, exacerbating environmental pollution. In addition, the organic matter and nutrients contained in the waste will be wasted if not recycled.

[0005] Therefore, the present application provides a forest waste biochar-based fertilizer for soil improvement in coastal low-lying land, which not only realizes resource utilization of waste but also improves coastal saline-alkali soil, and is a comprehensive solution with ecological and economic feasibility, having broad application prospects and promotional value. SUMMARY

[0006] In view of the above technical problems, the first object of the present application is to provide a forest waste biochar-based fertilizer.

[0007] A second object of the present application is to provide a preparation method of the forest waste biochar-based fertilizer.

[0008] A third object of the present application is to provide an application of the forest waste biochar-based fertilizer in soil improvement of coastal low-lying land.

[0009] Technical solution: A preparation method of a forest waste biochar-based fertilizer, characterized in that the method comprises the following steps:

[0010] S1. Collecting forest wastes of Cinnamomum camphora, Prunus cerasifera, Ligustrum lucidum and Magnolia grandiflora, including leaves, barks and branches, combining the same type of wastes of different tree species respectively, airing, and pyrolyzing and carbonizing in an oxygen-deficient environment to prepare leaf carbon, bark carbon and branch carbon;

[0011] S2. Activating and culturing Pseudomonas putida on a nutrient agar slant culture medium, picking colonies in a LB liquid culture medium for shaking culture, centrifuging the bacterial suspension, discarding the supernatant, washing twice with sterile PBS buffer and resuspending;

[0012] S3. Soaking the leaf carbon in a dilute nitric acid solution and washing to neutral, adding the resuspended Pseudomonas putida, shaking and adsorbing, drying after adsorption, and preparing a leaf carbon compound;

[0013] S4. Crushing and sieving montmorillonite, adding industrial alcohol, stirring, filtering to collect the solid, repeating 3 times, adding a dilute hydrochloric acid solution, stirring at room temperature, filtering to collect the solid, adding water for stirring, coarse filtering, fine filtering to collect the solid, drying to prepare nano-montmorillonite, mixing the nano-montmorillonite with the bark carbon, and pyrolyzing to prepare a bark carbon compound;

[0014] S5. Compounding the branch carbon in S1, the leaf carbon compound in S3 and the bark carbon compound in S4 with functional fertilizers in different proportions to prepare a forest waste biochar-based fertilizer.

[0015] Preferably, the temperature for pyrolyzing and carbonizing the leaves in step S1 is 350-400℃, and the time for pyrolyzing and carbonizing is 0.5-2 h.

[0016] Preferably, the temperature for pyrolyzing and carbonizing the barks in step S1 is 400-500℃, and the time for pyrolyzing and carbonizing is 1-3 h.

[0017] Preferably, the temperature for pyrolyzing and carbonizing the branches in step S1 is 500-600℃, and the time for pyrolyzing and carbonizing is 2-4 h.

[0018] Preferably, the temperature for activating and culturing Pseudomonas putida in step S2 is 26-28℃, and the time for activating and culturing is 24-40 h.

[0019] Preferably, in step S2, the temperature for shaking culture of *Pseudomonas putida* is 26-28°C, the shaking speed is 150-200 rpm, and the shaking culture time is 24-36 h.

[0020] Preferably, in step S2, the temperature for oscillation culture is 26~28℃, the rotation speed is 150~200rpm, and the oscillation culture time is 24~36h.

[0021] Preferably, the OD of the *Pseudomonas putida* suspension in step S2 is... 600 It ranges from 0.6 to 0.8.

[0022] Preferably, the viable count of *Pseudomonas putida* after resuspension in step S2 is 4.9~7.2×10⁻⁶. 9 CFU / mL.

[0023] Preferably, in step S3, the mass-to-volume ratio of leaf charcoal to resuspended *Pseudomonas putida* is 1-3:15-30.

[0024] Preferably, in step S3, the temperature for oscillation adsorption is 25~28℃, the rotation speed for oscillation adsorption is 120~180rpm, and the oscillation adsorption time is 1.5~4.5h.

[0025] Preferably, the drying temperature in step S3 is 30~35℃ and the drying time is 20~26 h.

[0026] Preferably, the mass ratio of bark charcoal to nano-montmorillonite in step S4 is 2~5:1~3.

[0027] Preferably, the pyrolysis temperature in step S4 is 350~500℃ and the pyrolysis time is 30~60 min.

[0028] Preferably, the heat treatment temperature in step S4 is 300~350℃, and the heat treatment time is 1~2 h.

[0029] Preferably, in step S5, the biochar-based fertilizer from forest waste is applied to the surface, middle, and lower layers of the soil in coastal low-lying areas in different proportions.

[0030] Furthermore, the surface forest waste biochar-based fertilizer comprises the following raw materials in parts by weight: 38-45 parts of leaf char complex, 20-28 parts of bark char complex, 10-17 parts of branch char, 10-15 parts of decomposed seaweed fertilizer, 3-8 parts of resin-coated urea, and 3-5 parts of calcium humate.

[0031] Furthermore, the intermediate layer of forest waste biochar-based fertilizer includes the following raw materials in parts by weight: 40-50 parts of bark char complex, 15-30 parts of leaf char complex, 10-20 parts of branch char, 5-10 parts of magnesium ammonium phosphate, and 2-6 parts of ferrous sulfate.

[0032] Furthermore, the lower layer of forest waste biochar-based fertilizer includes the following raw materials in parts by weight: 35-48 parts of branch charcoal, 30-36 parts of bark charcoal complex, 9-16 parts of leaf charcoal complex, 5-8 parts of lignin sulfonate, and 3-5 parts of sulfur powder.

[0033] The application of the above-mentioned forest waste biochar-based fertilizer in the improvement of soil in coastal low-lying areas.

[0034] Furthermore, in the application of topsoil biochar-based fertilizer for improving coastal low-lying areas, the application rate is 0.3~0.7 kg / m³. 2 The application rate of the biochar-based fertilizer from the middle-layer forest waste is 0.1~0.3 kg / m², and the application rate of the biochar-based fertilizer from the lower-layer forest waste is 0.2~0.5 kg / m². 2 .

[0035] Beneficial effects:

[0036] 1. This invention precisely matches the carbonization process to prepare forest waste biochar based on the differences in fiber density and chemical composition of forest waste (leaves, branches, and bark). Utilizing its different physical properties, it matches the needs of different soil layers (loose / stable / salt-inhibiting) in low-lying coastal saline-alkali land, improving soil structure and optimizing the plant growth environment. Leaf biochar is used for surface soil control; its loose and porous nature effectively reduces soil bulk density, increases porosity, alleviates compaction, enhances water infiltration, and reduces evaporation. This not only improves aeration but also creates a good channel for water infiltration, preventing surface runoff. The loaded *Pseudomonas malodorosa* promotes aggregate formation through biological action, indirectly fixing salts and creating an optimal physical environment for plant growth. Bark biochar plays a transitional, supporting, and regulating role in the middle layer, both absorbing surface infiltrating water and allowing the loaded montmorillonite to adsorb sodium through ion exchange. + The presence of salt ions effectively purifies infiltrated water. Placed at the bottom layer, the charcoal enhances the aeration and permeability of deep soil, effectively retains moisture, and traps salts, preventing them from returning to the upper layers.

[0037] 2. This invention achieves a salt control mechanism of "surface interception - middle layer adsorption - bottom layer retention" through stratified synergy. The surface layer of tree bark charcoal preferentially adsorbs and fixes the upward-moving salts due to its high specific surface area, alleviating salt surface accumulation. The loaded *Pseudomonas malodorosa* promotes the formation of soil aggregates through biological action, further enhancing the physical fixation of salts and providing protection for plant growth. The middle layer of bark charcoal loaded with montmorillonite efficiently captures Na+ through ion exchange and specific adsorption. + The presence of salt ions continuously purifies the infiltrated water, preventing secondary accumulation of salt during downward migration. The lower layer of dendritic charcoal physically intercepts leached salt, preventing its rapid entry into groundwater. This avoids salt returning to the upper soil layers via capillary water during dry seasons, achieving long-term salt control. This design not only effectively improves the typical "high density, low porosity" physical structure and "salt surface accumulation" phenomenon of coastal saline-alkali lands, but also creates a low-salt environment from the surface to the depths for plant roots, providing favorable soil conditions for plant growth.

[0038] 3. The forest waste biochar-based fertilizer provided by this invention also has slow-release characteristics. The cumulative release rates of alkaline nitrogen, available phosphorus, and available potassium are only 68.9%, 74.2%, and 63.5% respectively over 360 days. This can provide stable and sufficient nutrition for seedlings throughout their growth period, reduce the number of fertilizations, significantly reduce labor and maintenance costs, and at the same time reduce the risk of groundwater pollution and greenhouse gas emissions caused by fertilizer leaching from the source, which meets the development requirements of green and low-carbon agriculture. Attached Figure Description

[0039] Figure 1 A schematic diagram showing the morphology and stratification of biochar from forest waste;

[0040] Figure 2 The cumulative release rate of nitrogen from alkaline hydrolysis in forest waste biochar fertilizer;

[0041] Figure 3 The cumulative release rate of available phosphorus in biochar fertilizer made from forest waste;

[0042] Figure 4 The cumulative release rate of available potassium from forest waste biochar fertilizer. Detailed Implementation

[0043] The present invention will be further described below with reference to embodiments. These embodiments are illustrative of the present invention, but the present invention is not limited to these embodiments:

[0044] The *Pseudomonas putida* ATCC49128 used in the following examples, test cases and comparative examples was purchased from Shanghai Shifeng Biotechnology Co., Ltd., catalog number SJ01196.

[0045] Example 1

[0046] This embodiment describes the preparation of biochar-based fertilizer from forest waste, including the following steps:

[0047] S1. Collect forest waste from camphor trees, red-leaf plum trees, privet trees, and magnolia trees in the forest system of Chongming District, Shanghai, including leaves, bark, and branches (diameter ≤ 5 cm). Combine the same type of waste from different tree species and dry them to adjust the moisture content to below 30%.

[0048] S2. Different types of forest waste, such as leaves, branches, and bark, are placed in a skid-mounted "zero-energy" carbonization pyrolysis furnace and carbonized in an oxygen-deficient environment. The heating rate is 10℃ / min. Leaves are pyrolyzed at 400℃ for 1.5 h to obtain leaf charcoal; bark is pyrolyzed at 500℃ for 2 h to obtain bark charcoal; and branches are pyrolyzed at 580℃ for 3.5 h to obtain branch charcoal.

[0049] S3. Under aseptic conditions, *Pseudomonas putida* ATCC49128 was picked from a slant culture medium using a sterile inoculation loop and inoculated onto nutrient agar slant medium. The culture was incubated at 26°C for 36 h. Colonies were then picked and cultured in LB broth at 26°C with shaking at 180 rpm for 30 h until OD500 was reached. 600 The concentration was 0.8. The bacterial suspension was centrifuged at 12,000 rpm for 10 min at 4°C, the supernatant was discarded, and the suspension was washed twice with sterile PBS buffer (pH 7.4) and resuspended until the viable count was 6.7 × 10⁸. 9 CFU / mL;

[0050] S4. After crushing the leaf charcoal in S2, soak it in 1% HNO3 for 24 h and wash it until neutral. Mix the leaf charcoal and the Pseudomonas putida suspension at a ratio of 1:15 (v / w) and shake at 25℃ and 150 rpm for 2 h for adsorption. After adsorption is complete, dry it at 30℃ for 24 h until the water content is <5% to obtain the leaf charcoal complex. Store it in a sealed container away from light.

[0051] S5. After pulverizing montmorillonite, pass it through a 150-mesh sieve. Add industrial alcohol at a mass-to-volume ratio of 1:15, stir at 500 rpm for 24 h, filter and collect the solids. Repeat the above steps 3 times. Add 1 mol / L HCl solution at a mass-to-volume ratio of 1:15, stir at 300 rpm for 1 h at room temperature, filter and collect the solids. Add water at a mass-to-volume ratio of 1:30, stir at 1200 rpm for 2 h, coarsely filter and collect the solids. Finely filter the filtrate again, collect the solids, and dry at 100℃ for 14 h to obtain nano-montmorillonite. Pulverize the bark charcoal from S2 and mix it with the nano-montmorillonite at a mass ratio of 4:1, mix at 30 rpm for 30 min, and feed it into the feed end of a rotary kiln for pyrolysis at 400℃ for 45 minutes. At the same time, high-purity N2 (99.999% purity) is introduced and a slight positive pressure is maintained in the kiln. After pyrolysis, the material is discharged and enters a closed spiral cooling conveyor with a water-cooled jacket. Under the condition of continuous nitrogen protection, it is cooled to room temperature to obtain bark char composite.

[0052] S6. As shown in Table 1, by weight, the tree branch char in S2, the tree leaf char complex in S4, and the bark char complex in S5 are compounded with functional fertilizers in different proportions to prepare forest waste biochar base fertilizer.

[0053] Table 1. Composition and ratio of forest waste biochar-based fertilizer in Example 1

[0054]

[0055] Example 2

[0056] This embodiment describes the preparation of biochar-based fertilizer from forest waste, including the following steps:

[0057] S1. Collect forest waste from camphor trees, red-leaf plum trees, privet trees, and magnolia trees in the forest system of Chongming District, Shanghai, including leaves, bark, and branches (diameter ≤ 5 cm). Combine the same type of waste from different tree species and dry them to adjust the moisture content to below 30%.

[0058] S2. Different types of forest waste, such as leaves, branches, and bark, are placed in a skid-mounted "zero-energy" carbonization pyrolysis furnace. The heating rate is 10℃ / min. Leaves are pyrolyzed at 370℃ for 1.8 h to obtain leaf charcoal; bark is pyrolyzed at 450℃ for 2.4 h to obtain bark charcoal; and branches are pyrolyzed at 550℃ for 3 h to obtain branch charcoal.

[0059] S3. Under aseptic conditions, *Pseudomonas putida* ATCC49128 was inoculated onto nutrient agar slant culture medium using a sterile inoculation loop. The culture was incubated at 28°C for 30 h. Colonies were then transferred to LB broth and incubated at 28°C with shaking at 150 rpm for 25 h until OD500 was reached.600 The concentration was 0.7. The bacterial suspension was centrifuged at 12,000 rpm for 10 min at 4°C, the supernatant was discarded, and the suspension was washed twice with sterile PBS buffer (pH 7.4) and resuspended until the viable count was 5.5 × 10⁻⁶. 9 CFU / mL;

[0060] S4. After crushing the leaf charcoal in S2, soak it in 1% HNO3 for 24 h and wash it until neutral. Mix the leaf charcoal and the Pseudomonas putida suspension at a ratio of 2:17 (v / w), and adsorb it by shaking at 27℃ and 130 rpm for 3.5 h. After the adsorption is complete, dry it at 30℃ for 24 h until the water content is <5% to obtain the leaf charcoal complex. Store it in a sealed container away from light.

[0061] S5. After pulverizing montmorillonite, pass it through a 150-mesh sieve. Add industrial alcohol at a mass-to-volume ratio of 1:15, stir at 500 rpm for 24 h, filter and collect the solids. Repeat the above steps 3 times. Add 1 mol / L HCl solution at a mass-to-volume ratio of 1:15, stir at 300 rpm for 1 h at room temperature, filter and collect the solids. Add water at a mass-to-volume ratio of 1:30, stir at 1200 rpm for 2 h, coarsely filter and collect the solids. Finely filter the filtrate again, collect the solids, and dry at 100℃ for 14 h to obtain nano-montmorillonite. Pulverize the bark charcoal from S2 and mix it with the nano-montmorillonite at a mass ratio of 2:1, mix at 30 rpm for 30 min, and feed it into the feed end of a rotary kiln for pyrolysis at 320℃ for 30 minutes. At the same time, high-purity N2 (99.999% purity) is introduced and a slight positive pressure is maintained in the kiln. After pyrolysis, the material is discharged and enters a closed spiral cooling conveyor with a water-cooled jacket. Under the condition of continuous nitrogen protection, it is cooled to room temperature to obtain bark char composite.

[0062] S6. As shown in Table 2, by weight, the tree branch char in S2, the tree leaf char complex in S4, and the bark char complex in S5 are compounded with functional fertilizers in different proportions to prepare forest waste biochar base fertilizer.

[0063] Table 2 Composition and Proportioning of Forest Waste Biochar-Based Fertilizer in Example 2

[0064] Example 3

[0065] This embodiment describes the preparation of biochar-based fertilizer from forest waste, including the following steps:

[0066] S1. Collect forest waste from camphor trees, red-leaf plum trees, privet trees, and magnolia trees in the forest system of Chongming District, Shanghai, including leaves, bark, and branches (diameter ≤ 5 cm). Combine the same type of waste from different tree species and dry them to adjust the moisture content to below 30%.

[0067] S2. Different types of forest waste, such as leaves, branches, and bark, are placed in a skid-mounted "zero-energy" carbonization pyrolysis furnace and carbonized in an oxygen-deficient environment. The heating rate is 10℃ / min. Leaves are pyrolyzed at 350℃ for 2 hours to obtain leaf charcoal; bark is pyrolyzed at 420℃ for 1.5 hours to obtain bark charcoal; and branches are pyrolyzed at 520℃ for 3.5 hours to obtain branch charcoal.

[0068] S3. Under aseptic conditions, *Pseudomonas putida* ATCC49128 was inoculated onto nutrient agar slant culture medium using a sterile inoculation loop. The culture was incubated at 28°C for 36 h. Colonies were then transferred to LB broth and incubated at 28°C with shaking at 200 rpm for 28 h until OD500 was reached. 600 The concentration was 0.8. The bacterial suspension was centrifuged at 12,000 rpm for 10 min at 4°C, the supernatant was discarded, and the suspension was washed twice with sterile PBS buffer (pH 7.4) and resuspended until the viable count was 6.1 × 10⁸. 9 CFU / mL;

[0069] S4. The leaf charcoal in S2 was soaked in 1% HNO3 for 24 h and washed until neutral. The leaf charcoal and Pseudomonas putida suspension were mixed at a ratio of 3:15 (v / w) and adsorbed by shaking at 28℃ and 180 rpm for 4 h. After adsorption was completed, the leaf charcoal complex was dried at 35℃ for 24 h until the water content was <5% to obtain the leaf charcoal complex. It was then sealed and stored in the dark.

[0070] S5. After pulverizing montmorillonite, pass it through a 150-mesh sieve. Add industrial alcohol at a mass-to-volume ratio of 1:15, stir at 500 rpm for 24 h, filter and collect the solids. Repeat the above steps 3 times. Add 1 mol / L HCl solution at a mass-to-volume ratio of 1:15, stir at 300 rpm for 1 h at room temperature, filter and collect the solids. Add water at a mass-to-volume ratio of 1:30, stir at 1200 rpm for 2 h, coarsely filter and collect the solids. Finely filter the filtrate again, collect the solids, and dry at 100℃ for 14 h to obtain nano-montmorillonite. Mix the bark charcoal and nano-montmorillonite from S2 at a mass ratio of 5:2, mix at 30 rpm for 30 min, and feed into the feed end of a rotary kiln for pyrolysis at 450℃ for 50 minutes. At the same time, high-purity N2 (99.999% purity) is introduced and a slight positive pressure is maintained in the kiln. After pyrolysis, the material is discharged and enters a closed spiral cooling conveyor with a water-cooled jacket. Under the condition of continuous nitrogen protection, it is cooled to room temperature to obtain bark char composite.

[0071] S6. As shown in Table 3, by weight, the tree branch char in S2, the tree leaf char complex in S4, and the bark char complex in S5 are compounded with functional fertilizers in different proportions to prepare forest waste biochar base fertilizer.

[0072] Table 3. Composition and ratio of forest waste biochar-based fertilizer in Example 3

[0073]

[0074] Table 4. Characteristics of biochar from various forest wastes in Examples 1-3

[0075]

[0076] As shown in Table 4, there is a negative correlation between the fiber density of leaves, bark, and branches and various properties of forest waste biochar. The leaf char of Examples 1-3 has significant advantages in terms of specific surface area, pore size, and total pore volume. This is because the low fiber density leaf raw material has a loose physical structure and a high content of volatile components, which is more conducive to the violent release of volatile components and effective pore formation during pyrolysis, thereby forming a well-developed porous structure and making it easier to generate slightly larger mesopores. On the other hand, the high fiber density branches restrict pore development due to their dense structure, making it easier to form smaller micropores.

[0077] Test Example 1

[0078] This test case examines the effect of the forest waste biochar-based fertilizer prepared in Example 1 on the remediation of coastal low-lying soil, and includes the following steps:

[0079] S1. Within the planned planting area of ​​saline-alkali soil sample plots in Gangyan Town, Chongming District, Shanghai, experimental plots were delineated, and a completely randomized block design was adopted, with each sample plot having an area of ​​4×5 m². 2 Four biological replicates were constructed, with isolation rows at least 1 m wide between quadrats. Large stones and weeds were removed from the ground, and the entire area was initially leveled.

[0080] S2. Deeply till the soil within the sample plot to a depth of 50-60 cm. Immediately after tilling, apply the soil in layers as shown in Table 1 to prevent soil compaction.

[0081] (1) Lower layer (20~50 cm depth): Spread the forest waste biochar base fertilizer evenly on the tilled subsoil, and then use a rotary tiller to mix it thoroughly with the soil layer at a depth of 20~50 cm;

[0082] (2) Middle layer (10~20 cm depth): Spread the forest waste biochar base fertilizer evenly on the tilled subsoil, and then use a rotary tiller to mix it thoroughly with the soil layer at a depth of 10~20 cm;

[0083] (3) Surface layer (0~10 cm depth): Spread the forest waste biochar base fertilizer evenly on the tilled subsoil, and then use a rotary tiller to mix it thoroughly with the soil layer at a depth of 0~10 cm;

[0084] S3. Plant 60-80 cm tall Oriental pine cuttings at a density of 1 tree / m². 2 Immediately after planting, the soil was thoroughly watered. Soil samples were collected at 30, 60, 120, 180, 240, 300, and 360 days after planting to determine and calculate the cumulative release rates of available nitrogen, available phosphorus, and available potassium. The water content, salinity, bulk density, and porosity of the soil samples at 180 days were measured. Various growth indicators of Oriental pine were measured at 360 days after planting.

[0085] Test Example 2

[0086] This test case is a test of the effect of forest waste biochar-based fertilizer prepared in Example 2 on the soil remediation of coastal low-lying areas. The specific steps are the same as those in Test Case 1, and the application is carried out in layers according to Table 2.

[0087] Test Example 3

[0088] This test case is a test of the effect of forest waste biochar-based fertilizer prepared in Example 3 on the remediation of coastal low-lying soil. The specific steps are the same as those in Test Case 1, and the application is carried out in layers according to Table 3.

[0089] To further illustrate the technical effects of the present invention, a comparative example is also provided, as follows:

[0090] Comparative Example 1

[0091] This comparative example serves as the control group, receiving no treatment. The steps include:

[0092] S1. Within the planned planting area of ​​saline-alkali soil sample plots in Gangyan Town, Chongming District, Shanghai, experimental plots were delineated, and a completely randomized block design was adopted, with each sample plot having an area of ​​4×5 m². 2 Four biological replicates were constructed, with isolation rows at least 1 m wide between quadrats. Large stones and weeds were removed from the ground, and the entire area was initially leveled.

[0093] S2. Deeply till the soil within the sample plot to a depth of 10-30 cm. After tilling, plant 60-80 cm tall Oriental fir cuttings at a density of 1 cutting / m². 2 Immediately after planting, the soil was thoroughly watered. Soil samples were collected at 30, 60, 120, 180, 240, 300, and 360 days after planting to determine and calculate the cumulative release rates of available nitrogen, available phosphorus, and available potassium. The water content, salinity, bulk density, and porosity of the soil samples at 180 days were measured. Various growth indicators of Oriental pine were measured at 360 days after planting.

[0094] Comparative Example 2

[0095] The difference between this comparative example and Test Example 1 is that the leaf charcoal complex is replaced with leaf charcoal in this comparative example, while the other components remain unchanged. The specific process is the same as in Test Example 1, and the application is carried out according to Table 5.

[0096] Table 5. Composition and Proportioning of Forest Waste Biochar-Based Fertilizer (Comparative Example 2)

[0097]

[0098] Comparative Example 3

[0099] The difference between this comparative example and Test Example 1 is that the bark charcoal complex is replaced with bark charcoal in this comparative example, while the other components remain unchanged. The specific process is the same as in Test Example 1, and the application is carried out according to Table 6.

[0100] Table 6. Composition and Proportioning of Forest Waste Biochar-Based Fertilizer (Comparative Example 3)

[0101]

[0102] Comparative Example 4

[0103] The difference between this comparative example and Test Example 1 is that the bark charcoal composite is replaced with a bark charcoal-montmorillonite mixture in this comparative example. The preparation of the bark charcoal-montmorillonite mixture is as follows, and the specific process is the same as in Test Example 1. The application is carried out according to Table 7.

[0104] Preparation of bark charcoal-montmorillonite mixture: Montmorillonite was pulverized and passed through a 150-mesh sieve to obtain montmorillonite powder. The bark charcoal and montmorillonite powder from Example 1 S2 were mixed evenly at a mass ratio of 1:2 to obtain the bark charcoal-montmorillonite mixture.

[0105] Table 7. Composition and Proportioning of Forest Waste Biochar-Based Fertilizer (Comparative Example 4)

[0106]

[0107] Comparative Example 5

[0108] The difference between this comparative example and Test Example 1 is that no bark charcoal complex and twig charcoal are added in this comparative example. The specific process is the same as in Test Example 1, and the application is carried out according to Table 8.

[0109] Table 8. Composition and Proportioning of Forest Waste Biochar-Based Fertilizer (Comparative Example 5)

[0110]

[0111] Comparative Example 6

[0112] The difference between this comparative example and Test Example 1 is that no leaf charcoal complex and twig charcoal are added in this comparative example. The specific process is the same as in Test Example 1, and the application is carried out according to Table 9.

[0113] Table 9. Composition and Proportioning of Forest Waste Biochar-Based Fertilizer (Comparative Example 6)

[0114]

[0115] Comparative Example 7

[0116] The difference between this comparative example and Test Example 1 is that no bark charcoal complex and leaf charcoal complex are added in this comparative example. The specific process is the same as in Test Example 1, and the application is carried out according to Table 10.

[0117] Table 10 Composition and Proportioning of Forest Waste Biochar-Based Fertilizer (Comparative Example 7)

[0118]

[0119] Comparative Example 8

[0120] The difference between this comparative example and Test Example 1 is that the forest waste biochar-based fertilizer used in Test Example 1 in this comparative example has disrupted its original layered application method. The surface, middle and lower layers of forest waste biochar-based fertilizer in Test Example 1 are applied to the middle layer, lower layer and surface layer respectively. The specific process is the same as that in Test Example 1, and the application operation is carried out according to Table 11.

[0121] Table 11 Composition and Proportioning of Forest Waste Biochar-Based Fertilizer (Comparative Example 8)

[0122]

[0123] Comparative Example 9

[0124] The difference between this comparative example and Test Example 1 is that the application method of the forest waste biochar-based fertilizer used in Test Example 1 in this comparative example is changed to direct mixing without stratification, including the following steps:

[0125] S1. The forest waste biochar-based fertilizer in this comparative example comprises the following raw materials in parts by weight: 55 parts leaf char complex, 40 parts bark char complex, 40 parts branch char, 12 parts decomposed seaweed fertilizer, 5 parts resin-coated urea, 5 parts calcium humate, 7 parts magnesium ammonium phosphate, 5 parts ferrous sulfate, 7 parts lignin sulfonate, and 5 parts sulfur powder, with an application rate of 1.5 kg / m³. 2 .

[0126] S2. Within the planned planting area of ​​saline-alkali soil sample plots in Gangyan Town, Chongming District, Shanghai, experimental plots were delineated, and a completely randomized block design was adopted, with each sample plot having an area of ​​4×5 m². 2 Four biological replicates were constructed, with isolation rows at least 1 m wide between quadrats. Large stones and weeds were removed from the ground, and the entire area was initially leveled.

[0127] S3. Deeply till the soil in the sample plot to a depth of 10-30 cm. Apply the treatment immediately after tilling to avoid soil compaction.

[0128] S4. Plant 60-80 cm tall Oriental pine cuttings at a density of 1 tree / m². 2 Immediately after planting, the soil was thoroughly watered. Soil samples were collected at 30, 60, 120, 180, 240, 300, and 360 days after planting to determine and calculate the cumulative release rates of available nitrogen, available phosphorus, and available potassium. The water content, salinity, bulk density, and porosity of the soil samples at 180 days were measured. Various growth indicators of Oriental pine were measured at 360 days after planting.

[0129] Table 12. Effects of forest waste biochar-based fertilizer on soil moisture and salinity in coastal low-lying areas.

[0130]

[0131] As shown in Table 12, Test Examples 1-3 were used to treat coastal saline-alkali soil with the forest waste biochar-based fertilizer prepared in Examples 1-3, respectively. Test Examples 1-3 (complete layered formulation) showed the best improvement effect. The water content of each soil layer (0-50cm) was higher than that of the comparative examples, while the salt content was significantly lower than that of the comparative examples. This indicates that layered application of forest waste biochar-based fertilizer can effectively promote water retention, effectively inhibit salt surface accumulation, and inhibit salt upward migration. Although the indicators of Comparative Example 2 (leaf char without loading of Pseudomonas malodorosa) and Comparative Example 3 (bark char without loading of montmorillonite) were better than those of the control group, they were still significantly worse than those of Test Example 1, indicating that the functional loading process plays a key role in improving the performance of biochar. Comparative Example 4 (physical mixture of bark char and montmorillonite) was better than Comparative Example 3 in terms of water retention and salt inhibition, but not as good as Test Example 1, further indicating that the "loaded" composite material is better than simple mixing in terms of functional synergy. The improvement effects of Comparative Examples 5-7 were relatively poor. Compared with Test Example 1, the water content decreased and the salinity increased. The effects of Comparative Examples 5 (without bark charcoal complex and branch charcoal) and 6 (without leaf charcoal complex and branch charcoal) were extremely poor. The fundamental reason is that both removed the core framework material of branch charcoal, which forms the lower pore channels. The collapse of the lower structure prevented water from effectively infiltrating and retaining, and salt could not be blocked from leaching. The effect of Comparative Example 7 (without leaf charcoal complex and bark charcoal complex) was the worst because it lacked both "leaf charcoal loaded with Pseudomonas putida" and "bark charcoal loaded with montmorillonite," thus lacking biochemical improvement function. Comparative Example 9 (mixed application) destroyed the stratified structure, and its soil water content and salinity were worse than those of Test Example 1, further demonstrating the importance of physical stratification for salt retention and water conservation. Although Comparative Example 8 (layer misalignment) retained the layered form, its improvement effect was better than that of Comparative Example 9 due to the incorrect layer order, but still lower than that of Test Example 1, indicating that the water retention and salt barrier function is highly dependent on the physical layered structure.

[0132] Table 13 Effects of forest waste biochar-based fertilizer on soil bulk density and porosity in coastal low-lying areas

[0133]

[0134] As shown in Table 13, Test Examples 1-3 exhibited the best soil physical improvement effect. The bulk density of each soil layer (0-50 cm) was lower than that of the comparative example, while the porosity was higher. This indicates that the forest waste biochar-based fertilizer provided by this invention can effectively improve soil structure, enhance permeability, and provide a good channel for water transport and salt leaching. In contrast, Comparative Example 1 (control group) had the highest bulk density and the lowest porosity, indicating severe soil compaction and poor structural performance. Comparative Example 2 (leaf char without loading *Pseudomonas malodorosa*) and Comparative Example 3 (bark char without loading montmorillonite) had higher soil bulk density and lower porosity, which were better than the control group but still lower than Test Example 1, indicating that the functional loading process helps improve the ability of biochar to regulate soil structure. Comparative Example 4 (physical mixture of bark char and montmorillonite) was better than Comparative Example 3 but lower than Test Example 1, further demonstrating that the "loaded" composite material has a greater advantage in synergistically improving soil physical properties. Comparative Example 5 (without bark char compound and branch char) and Comparative Example 6 (without leaf char compound and branch char) showed a lack of skeletal support in the lower layers due to the absence of biochar-based fertilizer components. This resulted in increased soil bulk density and decreased porosity, particularly in the 20-50 cm soil layer, where the structure deteriorated significantly, hindering water infiltration and reducing salt leaching capacity. Comparative Example 7, lacking both leaf char compound and bark char compound, experienced further increases in bulk density and a sharp deterioration in pore structure, leading to a comprehensive decline in soil physical and chemical properties. These results clearly demonstrate that each component in forest waste biochar-based fertilizer plays an irreplaceable functional and structural role, and the absence of any key component significantly affects its comprehensive improvement effect on coastal saline-alkali land. Comparative Example 9 (mixed application) exhibited higher soil bulk density and lower porosity due to disruption of the stratified structure, resulting in poor overall structural performance. Although Comparative Example 8 (stratified misalignment) had a lower bulk density and slightly higher porosity than Comparative Example 9, it was still significantly worse than Test Example 1, indicating that not only the stratified structure itself but also the order of stratification plays a crucial role in improving soil physical properties.

[0135] Table 14. Effects of forest waste biochar-based fertilizer on the growth of Oriental fir seedlings

[0136]

[0137] As shown in Table 14, the Oriental pine in Test Examples 1-3 performed best in all growth indicators. Their tree height, diameter at ground level, crown width, and total root length were all superior to all comparative examples. This is directly related to the fact that the soils of Test Examples 1-3, after being improved with forest waste biochar-based fertilizer, had the best moisture conditions, the lowest salt stress, and the best soil physical structure. The superior soil environment provided the Oriental pine root system with lower mechanical resistance, better aeration and water permeability, and more abundant effective water and nutrients, thereby promoting the growth of all parts of the Oriental pine seedlings.

[0138] In addition, such as Figures 1-3As shown, compared with the control group, by the end of the 360-day experiment, the cumulative release rates of alkaline nitrogen, available phosphorus, and available potassium of the forest waste biochar-based fertilizer in Test Example 1 were 68.9%, 74.2%, and 63.5%, respectively. In contrast, the control group had almost completely released nutrients by 300 days. This indicates that the forest waste biochar-based fertilizer of the present invention has ultra-long-term slow-release potential, with a nutrient release period expected to be more than one year. It provides stable and sufficient nutrition for Oriental fir seedlings throughout their growth period, and can meet the nutrient needs of perennial trees throughout the entire growing season or even across years, greatly reducing the number of fertilizations and labor costs.

[0139] In summary, the layered application of functionalized biochar-based fertilizer can significantly improve soil structure, enhance water permeability and retention, and promote salt leaching by optimizing the bulk density and porosity of each soil layer, thereby comprehensively improving the physical environment of coastal saline-alkali land. This improvement measure effectively promotes the resource-based utilization of forest waste, creating favorable soil conditions for the growth of Oriental fir seedlings and continuously supplying the plants with the necessary nutrients through slow-release action, significantly promoting the development of tree height, diameter at breast height, crown width, and root system. The synergistic effect of the forest waste biochar-based fertilizer of this invention in reducing salinity and improving fertility provides an effective and feasible technical approach for vegetation restoration and ecological reconstruction in coastal saline-alkali land.

[0140] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any person skilled in the art can make many possible variations and modifications to the technical solutions of the present invention, or modify them into equivalent embodiments, without departing from the spirit and technical essence of the present invention. Therefore, any simple modifications, equivalent substitutions, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention, without departing from the content of the technical solutions of the present invention, shall still fall within the scope of protection of the present invention.

Claims

1. A method for preparing a biochar-based fertilizer from forest waste, characterized in that, Includes the following steps: S1. Collect forest waste from camphor trees, red-leaf plum trees, privet trees, and magnolia trees, including leaves, bark, and branches. Combine the same type of waste from different tree species, dry them, and then pyrolyze and carbonize them separately in an oxygen-deficient environment to obtain leaf charcoal, bark charcoal, and branch charcoal. S2. Inoculate *Pseudomonas putida* onto nutrient agar slant medium for activation culture, pick colonies and culture them in LB liquid medium with shaking, centrifuge the bacterial suspension and discard the supernatant, wash twice with sterile PBS buffer and resuspend; S3. Leaf charcoal was soaked in dilute nitric acid solution and washed until neutral. Resuspended Pseudomonas malodorosa was added, and the mixture was shaken to adsorb. After adsorption was completed, the mixture was dried to obtain the leaf charcoal complex. S4. After pulverizing montmorillonite, sieve it, add industrial alcohol, stir and filter to collect the solids. Repeat 3 times, add dilute hydrochloric acid solution, stir at room temperature and filter to collect the solids. Add water and stir, then coarsely filter and finely filter to collect the solids. After drying, nano-montmorillonite is obtained. After mixing bark charcoal and nano-montmorillonite, pyrolyze to obtain bark charcoal composite. S5. The tree branch char in S1, the tree leaf char complex in S3, and the bark char complex in S4 are compounded with functional fertilizers in different proportions to prepare forest waste biochar base fertilizer.

2. The preparation method according to claim 1, characterized in that: In step S1, the temperature for pyrolysis and carbonization of the leaves is 350~400℃, and the time for pyrolysis and carbonization is 0.5~2 h; the temperature for pyrolysis and carbonization of the bark is 400~500℃, and the time for pyrolysis and carbonization is 1~3 h; and the temperature for pyrolysis and carbonization of the branches is 500~600℃, and the time for pyrolysis and carbonization is 2~4 h.

3. The preparation method according to claim 1, characterized in that: In step S2, the activation culture temperature of *Pseudomonas putida* is 26-28℃, and the activation culture time is 24-40 h; the shaking culture temperature is 26-28℃, the shaking speed is 150-200 rpm, and the shaking culture time is 24-36 h; the OD of the bacterial suspension... 600 The concentration was 0.6–0.8; the viable count of the resuspended *Pseudomonas putida* was 4.9–7.2 × 10⁻⁶. 9 CFU / mL.

4. The preparation method according to claim 1, characterized in that: In step S3, the mass-to-volume ratio of leaf charcoal to resuspended *Pseudomonas putida* is 1-3:15-30; the temperature for oscillation adsorption is 25-28°C, the rotation speed for oscillation adsorption is 120-180 rpm, and the oscillation adsorption time is 1.5-4.5 h; the temperature for drying is 30-35°C, and the drying time is 20-26 h.

5. The preparation method according to claim 1, characterized in that: In step S4, the mass ratio of bark charcoal to nano-montmorillonite is 2~5:1~3; the pyrolysis temperature is 350~500℃, and the pyrolysis time is 30~60 min.

6. The preparation method according to claim 1, characterized in that: In step S5, the forest waste biochar-based fertilizer is applied to the surface, middle, and lower layers of the coastal low-lying soil in different proportions. The surface layer of forest waste biochar-based fertilizer includes the following raw materials in parts by weight: 38-45 parts of leaf char complex, 20-28 parts of bark char complex, 10-17 parts of branch char, 10-15 parts of decomposed seaweed fertilizer, 3-8 parts of resin-coated urea, and 3-5 parts of calcium humate. The middle layer of forest waste biochar-based fertilizer includes the following raw materials in parts by weight: 40-50 parts of bark char complex, 15-30 parts of leaf char complex, 10-20 parts of branch char, 5-10 parts of magnesium ammonium phosphate, and 2-6 parts of ferrous sulfate. The lower layer of forest waste biochar-based fertilizer includes the following raw materials in parts by weight: 35-48 parts of branch char, 30-36 parts of bark char complex, 9-16 parts of leaf char complex, 5-8 parts of lignin sulfonate, and 3-5 parts of sulfur powder.

7. The application of the forest waste biochar-based fertilizer prepared by the preparation method according to any one of claims 1 to 6 in the improvement of coastal low-lying soil.

8. The application according to claim 7, characterized in that: The application rate of the biochar-based fertilizer made from topsoil forest waste is 0.3~0.7 kg / m³. 2 The application rate of the biochar-based fertilizer from the middle-layer forest waste is 0.1~0.3 kg / m², and the application rate of the biochar-based fertilizer from the lower-layer forest waste is 0.2~0.5 kg / m². 2 .

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