A slow-release composite biochar-based fertilizer containing waste straw and a preparation method thereof

Abstract

The application discloses a slow-release composite biochar-based fertilizer containing waste straw and a preparation method thereof, and belongs to the technical field of biochar-based fertilizers, and comprises the following raw materials in parts by weight: 15-25 parts of straw biochar, 20-35 parts of a nitrogen source, 15-25 parts of a phosphorus source, 5-10 parts of a potassium source, 10-15 parts of humic acid, 5-10 parts of zeolite powder, 0.5-1 part of beneficial microbial agent and 3-5 parts of a binder, and 1-5 parts of modified zirconium phosphate ester; the scheme uses biochar made of waste straw as a carrier, innovatively introduces modified zirconium phosphate ester, combines the nitrogen source, the phosphorus source, the potassium source, the humic acid, the zeolite powder, the beneficial microbial agent and the binder, and is prepared through the steps of raw material mixing, granulation, drying and cooling; the application effectively solves the problems of traditional fertilizers, such as fast nutrient release and low utilization rate, realizes slow release of nutrients, improves the microenvironment of soil, and enhances microbial activity and the stability of aggregates.

Description

Technical Field

[0001] This invention belongs to the field of biochar-based fertilizer technology, specifically referring to a slow-release composite biochar-based fertilizer containing waste straw and its preparation method. Background Technology

[0002] The overuse of chemical fertilizers is a major problem in current agricultural production, leading to low nutrient utilization and non-point source pollution. At the same time, the disposal of large amounts of waste straw also puts pressure on the environment.

[0003] Biochar is a carbon-rich porous material produced by high-temperature pyrolysis of agricultural and forestry waste (such as straw and rice husks) under oxygen-limited conditions. It possesses characteristics such as large specific surface area, rich pore structure, and diverse surface functional groups. Using biochar as a carrier and compounding it with chemical fertilizers to prepare biochar-based fertilizers can delay nutrient release through the adsorption effect of biochar, improving fertilizer utilization efficiency while simultaneously improving soil physicochemical properties and the micro-ecological environment. Currently, research has explored the use of biochar as a fertilizer carrier to achieve slow nutrient release; however, the high-value utilization of agricultural waste such as straw using traditional biochar fertilizers is still insufficient, and there is room for improvement in its slow-release performance and the stability of nutrient supply. Developing biochar-based fertilizers that integrate the functions of "waste resource utilization + efficient slow-release fertilizer + soil improvement" has become an important direction for green agricultural development.

[0004] However, existing biochar-based fertilizers still face bottlenecks in achieving the synergistic effect of high-value utilization of straw and efficient slow-release performance. Traditional biochar carriers primarily rely on physical adsorption for nutrient loading, resulting in weak binding forces. Although some studies have modified biochar with phosphoric acid to enhance adsorption capacity, these modifications are limited and lack sufficient controlled-release capabilities. Nutrient release is too rapid, leading to a mismatch between nutrient release rate and crop requirements. Furthermore, biochar is easily lost from the soil, polluting the environment and limiting its effectiveness in improving soil conditions. Biochar itself is lightweight and porous; current granulation techniques result in insufficient particle strength and stability, making it prone to breakage and pulverization during storage, transportation, and application. This hinders mechanization and affects application efficiency. Existing biochar-based fertilizers focus primarily on nitrogen, phosphorus, and potassium supply, neglecting functions such as regulating soil microbial activity and improving soil aggregate structure. This makes it difficult to achieve a synergistic effect of "fertilization + soil improvement," resulting in low functional integration. Summary of the Invention

[0005] In response to the above situation and to overcome the shortcomings of the existing technology, this invention provides a slow-release composite biochar-based fertilizer containing waste straw and its preparation method, which realizes the synergistic function of "waste resource utilization, efficient slow-release fertilizer, and soil improvement", effectively solving the problems of excessively rapid nutrient release, low fertilizer utilization rate, easy environmental pollution, and single function of biochar fertilizers on the market.

[0006] The technical solution adopted in this invention is as follows: This invention proposes a slow-release composite biochar-based fertilizer containing waste straw and its preparation method, comprising the following raw materials in parts by weight: 15-25 parts of straw biochar, 20-35 parts of nitrogen source, 15-25 parts of phosphorus source, 5-10 parts of potassium source, 10-15 parts of humic acid, 5-10 parts of zeolite powder, 0.5-1 parts of beneficial microbial agent, 3-5 parts of binder, and 1-5 parts of modified zirconium phosphate.

[0007] Furthermore, the preparation method of the modified zirconium phosphate includes the following steps:

[0008] S1: Zirconium oxychloride octahydrate was dissolved in deionized water to prepare a zirconium oxychloride solution. Phosphoric acid solution was added dropwise at a constant rate under continuous stirring, followed by reflux reaction. After the reaction was completed, the solution was cooled, centrifuged, washed and dried to obtain a white powdery α-zirconium phosphate precursor.

[0009] S2: The α-zirconium phosphate precursor obtained in step S1 is dispersed together with an organic alcohol source in an anhydrous organic solvent to form a mixed suspension;

[0010] S3: Under an inert atmosphere, the mixed suspension obtained in step S2 is heated and refluxed. After the reaction is completed, it is filtered, washed and vacuum dried to obtain the zirconium phosphate.

[0011] Further, in step S1, the molar concentration of the zirconium oxychloride solution is 0.1-0.3 mol / L.

[0012] Furthermore, in step S1, the reflux reaction temperature is 95-105℃, and the reaction time is 10-14h.

[0013] Further, in step S2, the mass ratio of the α-zirconium phosphate precursor to the organic alcohol source is 1:(1.2-1.8).

[0014] Further, in step S2, the organic alcohol source is one of 3,5-di-tert-butylsalicyl alcohol, n-octanol, and lauryl alcohol.

[0015] Further, in step S2, the anhydrous organic solvent is one of xylene, toluene, and chlorobenzene.

[0016] Furthermore, in step S3, the heating temperature of the reflux reaction is 140-160°C, and the duration is 5-7 hours.

[0017] Furthermore, the preparation method includes the following steps: the modified zirconium phosphate is mixed evenly with straw biochar, nitrogen source, phosphorus source, potassium source, humic acid, zeolite powder and binder, then granulated, dried and cooled, and finally beneficial microbial agents are added under low temperature conditions, and the finished product is obtained after being mixed evenly.

[0018] Furthermore, the amount of water sprayed during the granulation process is 15-25% of the total weight of the mixture.

[0019] The beneficial effects achieved by the present invention using the above structure are as follows:

[0020] This paper proposes a slow-release composite biochar-based fertilizer containing waste straw and its preparation method. Modified zirconium phosphate forms a regular layered structure through alternating bonds of zirconium-oxygen octahedra and phosphate groups. Phospho-oxygen groups and zirconium-oxygen groups can exchange ions, allowing nutrient ions in the fertilizer to be adsorbed onto the negatively charged regions on the surface of the layers via electrostatic interactions and diffuse. These ions then undergo a displacement reaction with exchangeable cations between the layers, becoming fixed and stored within the layers. Simultaneously, the fertilizer exhibits hydrophobic properties, effectively preventing rapid water penetration and erosion, thus slowing the release rate of nutrients from the fertilizer granules into the soil. This makes the nutrient release rate more closely match the crop's growth needs, thereby achieving a sustained and stable fertilizer effect.

[0021] By using modified zirconium phosphate to fix nutrients, nutrients can be slowly released and absorbed by crop roots through exudates and as they grow. This targeted supply model allows more nutrients to be effectively utilized by crops, preventing them from being lost into the surrounding environment. This reduces the free flow and rapid dissolution of nutrients in the soil, and minimizes nutrient losses through volatilization and leaching. This not only reduces agricultural production costs but also helps to mitigate agricultural non-point source pollution at its source and protect the ecological environment.

[0022] The combination of modified zirconium phosphate and biochar carrier allows the porous structure of biochar to provide habitat for microorganisms. After the fertilizer granules are applied to the soil, the modified zirconium phosphate can undergo an exchange reaction with cations in the soil environment, releasing the loaded nutrient ions and adsorbing cations in the soil that may have toxic effects on crops, thereby optimizing the distribution of soil nutrients around plant roots. Modified zirconium phosphate can also electrostatically attract and cement clay minerals and organic matter in the soil through its surface charge, aggregating soil particles and forming more stable micro-aggregates, improving soil structure, and thus creating an environment suitable for microbial reproduction, promoting the health and balance of the soil ecosystem, and providing continuous favorable conditions for crop growth.

[0023] Modified zirconium phosphate itself contains phosphorus and is a slow-release phosphorus source that supplements and prolongs the supply of phosphorus; its functional binder-slow-release dual-effect component participates in the granulation process and can improve the structural stability of fertilizer granules. Attached Figure Description

[0024] Figure 1 This is a scanning electron microscope (SEM) image of a slow-release composite biochar-based fertilizer containing waste straw proposed in this invention.

[0025] Figure 2 This is a SEM image of a slow-release composite biochar-based fertilizer containing waste straw before and after nutrient release, as proposed in this invention.

[0026] Figure 3 The figure shows the experimental results of the nutrient release delay effect of a slow-release composite biochar-based fertilizer containing waste straw proposed in this invention.

[0027] Figure 4 The figure shows the experimental results of nutrient utilization rate and loss reduction effect of a slow-release composite biochar-based fertilizer containing waste straw proposed in this invention;

[0028] Figure 5 The figure shows the experimental results of the soil environment improvement effect of a slow-release composite biochar-based fertilizer containing waste straw proposed in this invention.

[0029] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used together with the embodiments of the invention to explain the invention and do not constitute a limitation thereof. Detailed Implementation

[0030] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0031] It should be noted that, unless otherwise specified, all chemical reagents involved in this invention were purchased through commercial channels.

[0032] The nitrogen source (granular, N≥46%) used in this invention was purchased from Kingenta Ecological Engineering Group Co., Ltd.; the phosphorus source (powder, P2O5≥16%) was purchased from Yunnan Yuntianhua Co., Ltd.; the potassium source (crystalline, K2O≥60%) was purchased from Qinghai Salt Lake Industry Co., Ltd.; the humic acid (powder, organic matter≥70%) was purchased from Xinjiang Xinlianxin Energy Chemical Co., Ltd.; the zeolite powder (200 mesh grayish-white powder) was purchased from Lingshou County Huayuan Mineral Products Processing Plant; the beneficial microbial agent (live bacteria count≥2 billion / g, liquid dosage form) was purchased from Shandong Baolai Lailai Biotechnology Co., Ltd.; and the binder (purity≥99%) was purchased from Shandong Heda Co., Ltd.

[0033] Example 1:

[0034] A slow-release compound biochar-based fertilizer containing waste straw and its preparation method

[0035] First, modified zirconium phosphate was prepared. 3.22 g of zirconium oxychloride octahydrate was weighed and placed in a beaker. 100 mL of deionized water was added, and the mixture was magnetically stirred until completely dissolved to obtain a clear, transparent solution. The solution was transferred to a flask and placed in an oil bath, heated to 100 °C, and magnetic stirring was started. 4 g of 85% phosphoric acid was slowly and uniformly added dropwise using a constant-pressure dropping funnel. After the addition was complete, the mixture was refluxed at 95 °C for 14 h. After the reaction was complete, heating was stopped, and the mixture was allowed to cool naturally to room temperature. The mixture was centrifuged at 8000 rpm for 5 min, the supernatant was discarded, and the precipitate was repeatedly washed with deionized water until the pH was neutral. The resulting white precipitate was dried for 12 h, ground, and sieved. A white powdery α-zirconium phosphate precursor was obtained. 1.0 g of the α-zirconium phosphate precursor, 1.2 g of n-octanol, and 100 mL of toluene solution were added to a flask. The flask was placed in an oil bath and nitrogen gas was continuously purged for 10 min to remove air and create an inert environment. Stirring and heating were started to slowly raise the oil bath temperature to 140 °C. The solvent was kept under vigorous reflux and the reaction was continued for 7 h. The water generated in the esterification reaction azeotropically with xylene was separated by a water separator. After the reaction was completed, heating was stopped and the mixture was cooled to below 60 °C. The reaction mixture was filtered and the solid product was washed three times with anhydrous ethanol. Then it was dried in a vacuum drying oven at 60 °C for 8 h to obtain modified zirconium phosphate ester.

[0036] Waste straw was cut, washed, dried, crushed, and sieved to obtain uniform straw powder. This powder was then placed in a pyrolysis furnace for high-temperature pyrolysis for 5 hours. After pyrolysis, the powder was allowed to cool naturally to room temperature, ground, and sieved to obtain straw biochar. The biochar was mixed with nitrogen fertilizer and heated to melt the nitrogen fertilizer. The mixture was then held at 0.36 MPa pressure for a period of time to allow nutrients to penetrate the pores. Modified zirconium phosphate powder was dispersed in deionized water at a mass ratio of 1-3% and ultrasonically treated with 300W power for 30 minutes to form a nanosheet dispersion. Basic nutrients were then loaded onto the biochar and impregnated with the nanosheet dispersion. The process involves slow stirring at 50℃ for 4 hours, filtering to separate the solids, gently rinsing with deionized water, and then vacuum drying at 80℃ to obtain zirconium phosphate modified biochar. Beneficial microbial agents such as phosphate-solubilizing bacteria and nitrogen-fixing bacteria are mixed with the zirconium phosphate modified biochar and fermented for 3 days to form a biochar-microbial complex. The immobilized biochar is then mixed thoroughly with phosphorus source, potassium source, humic acid, zeolite powder, etc., according to the specified ratio in a mixer. Microbial agents are added at low temperature, and after thorough mixing, the mixture is granulated. During this process, approximately 15% of the weight of distilled water is sprayed in to assist in the granulation. Finally, the mixture is dried and sieved to obtain the final product.

[0037] Example 2:

[0038] A slow-release compound biochar-based fertilizer containing waste straw and its preparation method

[0039] First, modified zirconium phosphate was prepared. 6.44 g of zirconium oxychloride octahydrate was weighed and placed in a beaker. 100 mL of deionized water was added, and the mixture was magnetically stirred until completely dissolved to obtain a clear, transparent solution. The solution was transferred to a flask and placed in an oil bath, heated to 100°C, and magnetic stirring was started. 4 g of 85% phosphoric acid was slowly and uniformly added dropwise using a constant-pressure dropping funnel. After the addition was complete, the mixture was refluxed at 100°C for 12 hours. After the reaction was complete, heating was stopped, and the mixture was allowed to cool naturally to room temperature. The mixture was centrifuged at 8000 rpm for 5 minutes, the supernatant was discarded, and the precipitate was repeatedly washed with deionized water until the pH was neutral. The resulting white precipitate was dried for 12 hours, ground, and sieved to obtain a white... Powdered α-zirconium phosphate precursor; 1.0 g of α-zirconium phosphate precursor, 1.5 g of 3,5-di-tert-butylsalicyl alcohol and 100 mL of anhydrous xylene were added to a flask. The flask was placed in an oil bath and nitrogen gas was continuously purged for 10 min to remove air and create an inert environment. Stirring and heating were started to slowly raise the oil bath temperature to 150 °C. The solvent was kept under vigorous reflux and the reaction was continued for 6 h. The water generated in the esterification reaction azeotropically with xylene was separated by a water separator. After the reaction was completed, heating was stopped and the mixture was cooled to below 60 °C. The reaction mixture was filtered and the solid product was washed three times with anhydrous ethanol. Then it was dried in a vacuum drying oven at 60 °C for 8 h to obtain modified zirconium phosphate ester.

[0040] Waste straw was cut, washed, dried, crushed, and sieved to obtain uniform straw powder. This powder was then placed in a pyrolysis furnace for high-temperature pyrolysis for 5 hours. After pyrolysis, the powder was allowed to cool naturally to room temperature, ground, and sieved to obtain straw biochar. The biochar was mixed with nitrogen fertilizer and heated to melt the nitrogen fertilizer. The mixture was then held at 0.36 MPa pressure for a period of time to allow nutrients to penetrate the pores. Modified zirconium phosphate powder was dispersed in deionized water at a mass ratio of 1-3% and ultrasonically treated with 300W power for 30 minutes to form a nanosheet dispersion. Basic nutrients were then loaded onto the biochar and impregnated with the nanosheet dispersion. The process involves slow stirring at 50℃ for 4 hours, filtering to separate the solids, gently rinsing with deionized water, and then vacuum drying at 80℃ to obtain zirconium phosphate modified biochar. Beneficial microbial agents such as phosphate-solubilizing bacteria and nitrogen-fixing bacteria are mixed with the zirconium phosphate modified biochar and fermented for 3 days to form a biochar-microbial complex. The immobilized biochar is then mixed thoroughly with phosphorus source, potassium source, humic acid, zeolite powder, etc., according to the specified ratio in a mixer. Microbial agents are added at low temperature, and after thorough mixing, the mixture is granulated. During this process, approximately 20% of the weight of distilled water is sprayed in to assist in the granulation. Finally, the mixture is dried and sieved to obtain the final product.

[0041] Example 3:

[0042] A slow-release compound biochar-based fertilizer containing waste straw and its preparation method

[0043] First, modified zirconium phosphate was prepared. 9.67 g of zirconium oxychloride octahydrate was weighed and placed in a beaker. 100 mL of deionized water was added, and the mixture was magnetically stirred until completely dissolved to obtain a clear, transparent solution. The solution was transferred to a flask and placed in an oil bath, heated to 100 °C, and magnetic stirring was started. 4 g of 85% phosphoric acid was slowly and uniformly added dropwise using a constant-pressure dropping funnel. After the addition was complete, the mixture was refluxed at 105 °C for 10 h. After the reaction was complete, heating was stopped, and the mixture was allowed to cool naturally to room temperature. The mixture was centrifuged at 8000 rpm for 5 min, the supernatant was discarded, and the precipitate was repeatedly washed with deionized water until the pH was neutral. The resulting white precipitate was dried for 12 h, ground, and sieved. A white powdery α-zirconium phosphate precursor was obtained. 1.0 g of the α-zirconium phosphate precursor, 1.8 g of lauryl alcohol and 100 mL of chlorobenzene solution were added to a flask. The flask was placed in an oil bath and nitrogen gas was continuously introduced for 10 min to remove air and create an inert environment. Stirring and heating were started to slowly raise the oil bath temperature to 160 °C. The solvent was kept under vigorous reflux and the reaction was continued for 5 h. The water generated in the esterification reaction azeotropically with xylene was separated by a water separator. After the reaction was completed, heating was stopped and the mixture was cooled to below 60 °C. The reaction mixture was filtered and the solid product was washed three times with anhydrous ethanol. Then it was placed in a vacuum drying oven at 60 °C and dried for 8 h to obtain modified zirconium phosphate ester.

[0044] Waste straw was cut, washed, dried, crushed, and sieved to obtain uniform straw powder. This powder was then placed in a pyrolysis furnace for high-temperature pyrolysis for 5 hours. After pyrolysis, the powder was allowed to cool naturally to room temperature, ground, and sieved to obtain straw biochar. The biochar was mixed with nitrogen fertilizer and heated to melt the nitrogen fertilizer. The mixture was then held at 0.36 MPa pressure for a period of time to allow nutrients to penetrate the pores. Modified zirconium phosphate powder was dispersed in deionized water at a mass ratio of 1-3% and ultrasonically treated with 300W power for 30 minutes to form a nanosheet dispersion. Basic nutrients were then loaded onto the biochar and impregnated with the nanosheet dispersion. The process involves slow stirring at 50℃ for 4 hours, filtering to separate the solids, gently rinsing with deionized water, and then vacuum drying at 80℃ to obtain zirconium phosphate modified biochar. Beneficial microbial agents such as phosphate-solubilizing bacteria and nitrogen-fixing bacteria are mixed with the zirconium phosphate modified biochar and fermented for 3 days to form a biochar-microbial complex. The immobilized biochar is then mixed thoroughly with phosphorus source, potassium source, humic acid, zeolite powder, etc., according to the specified ratio in a mixer. Microbial agents are added at low temperature, and after thorough mixing, the mixture is granulated. During this process, approximately 25% of the weight of distilled water is sprayed in to assist in the granulation. Finally, the mixture is dried and sieved to obtain the final product.

[0045] Comparative Example 1:

[0046] Waste straw is cut, washed, dried, crushed, and sieved to obtain uniform straw powder. The pretreated straw powder is placed in a pyrolysis furnace and pyrolyzed at 700℃ for 5 hours under limited oxygen conditions. After pyrolysis, it is naturally cooled to room temperature, ground, and sieved to obtain straw biochar with a rich porous structure. The biochar is mixed with nitrogen fertilizer and heated to melt the nitrogen fertilizer, and then maintained at a pressure of 0.36 MPa for a period of time to allow nutrients to penetrate into the pores. For microbial immobilization, beneficial microbial agents such as phosphate-solubilizing bacteria and nitrogen-fixing bacteria are mixed with biochar loaded with basic nutrients and fermented at a suitable temperature for 3 days to form a biochar-microbial complex. The concentration of the microbial agent is controlled at 10¹. 0 CFU / mL. During mixing, the immobilized biochar, phosphorus source, potassium source, humic acid, zeolite powder, etc., are added to the mixer according to the specified ratio and stirred thoroughly. If microbial agents need to be added, they are added at low temperature. During granulation, the uniformly mixed material is fed into the granulator, and distilled water of about 20% of the weight of the mixture is sprayed in to assist in the molding. The rotation speed of the turntable is controlled at 40 r / min and the tilt angle is 50º. In the drying and packaging stage, the granulated fertilizer granules are placed in an oven at 40-50℃ and dried to constant weight. After cooling, the granules with uniform particle size are screened and sealed for packaging to prevent moisture absorption.

[0047] Comparative Example 2:

[0048] First, fertilizer A is prepared by mixing 0.4 parts of binder to form a 5%-10% binder solution. Under anaerobic conditions at 300-500℃, straw is pyrolyzed to obtain biochar. Then, 32 parts of biochar, 30 parts of urea, 40 parts of potassium dihydrogen phosphate, 7 parts of potassium sulfate, and 0.2 parts of trace elements are mixed with the binder solution and pressed to form the final product. The trace elements include 0.02 parts of iron, 0.02 parts of boron, 0.02 parts of zinc, 0.02 parts of manganese, and 0.02 parts of... Copper and 0.02 parts molybdenum; to make fertilizer B, 0.2 parts of binder are made into a binder solution with a mass fraction of 5%-10%, and then 25 parts of straw, 30 parts of urea, 40 parts of potassium dihydrogen phosphate, and 15 parts of potassium sulfate are mixed with the binder solution and pressed together; the method of using this biochar fertilizer is to insert fertilizer A into the soil. During the period from seedling to maturity before flowering, the area where fertilizer A is located needs to be watered, while during the period of plant growth, flowering and fruiting, the area where fertilizer B is located needs to be watered.

[0049] Comparative Example 3:

[0050] The preparation method includes the following steps: slightly carbonizing straw raw material to obtain carbonized straw; mixing the carbonized straw with a metal complexing agent to obtain pretreated carbonized straw; wherein the metal complexing agent is composed of a complex formed by natural plant extracts and metal salts; modifying the pretreated carbonized straw with a surfactant to obtain modified straw; after mixing the modified straw with water and adding protease for degradation, extracting fulvic acid enriched solution by hydrothermal method; mixing the fulvic acid enriched solution, modified straw and bio-based polymer, extruding and drying to obtain the fulvic acid fertilizer based on straw biocarbonization.

[0051] Experimental Example 1:

[0052] This experiment set up fertilizer samples from Examples 1-3 as the experimental group and fertilizer samples from Comparative Examples 1-3 as the control group. First, the microstructure of the waste samples was observed using a scanning electron microscope (SEM). Then, 500g of typical farmland soil was air-dried, passed through a 2mm sieve, and the moisture content was adjusted to 60% field capacity. The soil was then layered and filled into the experimental apparatus and compacted to a density of 1.2g / cm³ to form a 25cm high soil column. Each treatment was repeated three times. After applying 10g of fertilizer sample to the soil surface and mixing it with the top 2cm of soil, a leaching process was carried out. 200mL of deionized water was added daily at a controlled flow rate of 5mL / min, and the volume of the leaching solution was collected and recorded. The nitrogen, phosphorus, and potassium concentrations in the leaching solution were measured periodically on days 1, 3, 7, 14, 21, and 28. The average value was taken for each sample after three measurements. The cumulative release amount and percentage were calculated, and the release curve was plotted. Finally, a first-order kinetic model was used to fit and compare the release rate constant k value to evaluate the delay effect.

[0053] Experimental results are as follows Figure 1 , Figure 3 As shown, the straw fragments in the example samples contain layered wrapping and a porous structure, which is beneficial for delaying nutrient release. All example samples containing modified zirconium phosphate exhibited slow and continuous nutrient release, with their cumulative release curves being significantly flat. In contrast, the nutrient release of the Comparative Example 1 sample without any slow-release material was relatively rapid, and the release rates of other control fertilizer samples were also relatively fast. These experimental results indicate that modified zirconium phosphate can effectively delay the release rate of fertilizer nutrients, demonstrating a superior controlled-release effect.

[0054] Experimental Example 2:

[0055] The experiment was conducted using fertilizer samples from Examples 1-3 as the experimental group, fertilizer samples from Comparative Examples 1-3 as the control group, and a control without fertilizer. Each treatment had five replicates. During fertilization, equal amounts of nitrogen, phosphorus, and potassium were applied to each pot according to the nutrient content. The fertilizer was mixed thoroughly with the soil, and then corn seeds were planted. After disinfection, three seeds were sown per pot. After emergence, the seedlings were thinned to two plants per pot. The field water holding capacity was maintained at 70%, and watering was maintained normally. Plant height, leaf area, and chlorophyll content were recorded weekly. After a 60-day growth cycle, the plants were harvested. The aboveground parts and roots were separated, blanched at 105℃ for 30 minutes, dried at 80℃, and weighed. After pulverization, the nitrogen, phosphorus, and potassium contents were measured. Soil samples were collected to measure available nitrogen, available phosphorus, and available potassium. Seepage water was collected weekly using a pot bottom seepage collection device to measure nutrient concentration and calculate leaching loss. Ammonia volatilization loss was monitored using the static chamber method. Finally, nutrient utilization rate and loss rate were calculated, and ANOVA and Duncan multiple comparisons were used for data analysis.

[0056] Experimental results are as follows Figure 2 , Figure 4 As shown, in the sample examples, Figures A and B show that the pores and cracks are partially filled by the adhesion of nitrogen, phosphorus, and potassium molecules, and the surface is relatively smooth. Figures C and D after slow release show a porous structure and cracks, and the surface is rough. Compared with the comparative examples, the dry weight of the plant samples of Examples 1-3 with modified zirconium phosphate fertilizer increased significantly, the utilization rate of nitrogen, phosphorus, and potassium nutrients was significantly improved, and the total nutrient loss rate was significantly reduced. The content of available nitrogen, available phosphorus, and available potassium in the soil after harvest was also higher than that of the comparative examples. The treatment effect of Example 3 was the most outstanding, effectively demonstrating that the fertilizer of this scheme has a positive effect on promoting plant growth, improving fertilizer utilization efficiency, and reducing nutrient loss.

[0057] Experimental Example 3:

[0058] The experiment included a soil incubation experiment. 500g of soil was weighed and mixed with 1% fertilizer sample by weight. The moisture content was adjusted to 60% of field capacity and incubated in the dark at 25℃. Weighing and replenishing water were done every 3 days. Samples were taken at 0, 15, 30, and 60 days of incubation, with three replicates for each treatment. Subsequently, microbial abundance was determined. 10g of fresh soil was added to 90mL of sterile water, shaken for 30min, and a series of dilutions were prepared. These dilutions were spread on bacterial, fungal, and actinomycete culture media and incubated, with colony-forming units (CFU) per gram of soil counted. Soil enzyme activity was measured using the indophenol blue method for urease activity and the disodium phenyl phosphate method for phosphatase activity. Soil aggregate analysis employed a wet sieving method. 50g of air-dried soil was soaked for 10min and then wet-sieved to separate aggregates of different sizes. The proportion and average weight diameter of water-stable aggregates larger than 0.25mm were calculated. Finally, soil pH and cation exchange capacity were determined.

[0059] Table 1 Results of the Soil Microenvironment Improvement Experiment

[0060]

[0061] The experimental results are shown in Table 1. Figure 5 As shown, the soils treated in all examples were superior to the comparative examples in terms of microbial quantity, enzyme activity, and aggregate stability, with Example 1 exhibiting the best results. Compared with the comparative examples, the examples effectively promoted the reproduction of bacteria, fungi, and actinomycetes, enhanced urease and phosphatase activities, and significantly increased the proportion and average weight diameter of water-stable aggregates larger than 0.25 mm. At the same time, the soil cation exchange capacity was improved. These results fully demonstrate that the compound fertilizer containing modified zirconium phosphate and biochar can effectively optimize the soil microenvironment and enhance soil biological activity and structural stability.

[0062] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus.

[0063] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

[0064] The present invention and its embodiments have been described above. This description is not restrictive, and the accompanying drawings are only one embodiment of the present invention; the actual structure is not limited thereto. In conclusion, if those skilled in the art are inspired by this description and design similar structures and embodiments without departing from the spirit of the invention, such designs should fall within the protection scope of the present invention.

Claims

1. A slow-release compound biochar-based fertilizer containing waste straw, characterized in that: The raw materials include the following parts by weight: 15-25 parts straw biochar, 20-35 parts nitrogen source, 15-25 parts phosphorus source, 5-10 parts potassium source, 10-15 parts humic acid, 5-10 parts zeolite powder, 0.5-1 parts beneficial microbial agent, 3-5 parts binder, and 1-5 parts modified zirconium phosphate.

2. The slow-release compound biochar-based fertilizer containing waste straw according to claim 1, characterized in that: The preparation method of the modified zirconium phosphate includes the following steps: S1: Zirconium oxychloride octahydrate was dissolved in deionized water to prepare a zirconium oxychloride solution. Phosphoric acid solution was added dropwise at a constant rate under continuous stirring, followed by reflux reaction. After the reaction was completed, the solution was cooled, centrifuged, washed and dried to obtain a white powdery α-zirconium phosphate precursor. S2: The α-zirconium phosphate precursor obtained in step S1 is dispersed together with an organic alcohol source in an anhydrous organic solvent to form a mixed suspension; S3: Under an inert atmosphere, the mixed suspension obtained in step S2 is heated and refluxed. After the reaction is completed, it is filtered, washed and vacuum dried to obtain the zirconium phosphate.

3. The slow-release compound biochar-based fertilizer containing waste straw according to claim 2, characterized in that: In step S1, the molar concentration of the zirconium oxychloride solution is 0.1-0.3 mol / L.

4. The slow-release compound biochar-based fertilizer containing waste straw according to claim 3, characterized in that: In step S1, the reflux reaction temperature is 95-105℃ and the reaction time is 10-14h.

5. The slow-release compound biochar-based fertilizer containing waste straw according to claim 4, characterized in that: In step S2, the mass ratio of the α-zirconium phosphate precursor to the organic alcohol source is 1:(1.2-1.8).

6. The slow-release compound biochar-based fertilizer containing waste straw according to claim 5, characterized in that: In step S2, the organic alcohol source is one of 3,5-di-tert-butylsalicyl alcohol, n-octanol, and lauryl alcohol.

7. A slow-release compound biochar-based fertilizer containing waste straw according to claim 6, characterized in that: In step S2, the anhydrous organic solvent is one of xylene, toluene, and chlorobenzene.

8. A slow-release compound biochar-based fertilizer containing waste straw according to claim 7, characterized in that: In step S3, the heating temperature of the reflux reaction is 140-160℃, and the duration is 5-7h.

9. A method for preparing a slow-release compound biochar-based fertilizer containing waste straw according to any one of claims 1-8, characterized in that: The preparation method includes the following steps: the modified zirconium phosphate is mixed evenly with straw biochar, nitrogen source, phosphorus source, potassium source, humic acid, zeolite powder and binder, then granulated, dried and cooled, and finally beneficial microbial agents are added under low temperature conditions. After mixing evenly, the finished product is obtained.

10. The method for preparing a slow-release compound biochar-based fertilizer containing waste straw according to claim 9, characterized in that: The amount of water sprayed during the granulation process is 15-25% of the total weight of the mixture.

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