Nutrient slow-release carrier based on microwave pyrolysis rice straw biochar as well as preparation method and application of nutrient slow-release carrier

Abstract

The invention relates to the technical field of agricultural waste resource utilization and functional materials, in particular to a nutrient slow-release carrier based on microwave pyrolysis of rice straw biochar and a preparation method and application of the nutrient slow-release carrier. The preparation method of the nutrient slow-release carrier based on microwave pyrolysis of the rice straw biochar comprises the following steps: pretreating rice straw so that the water content of the rice straw is less than or equal to 30% by mass; carrying out microwave pyrolysis on the pretreated rice straws; the power of the microwave pyrolysis is 1200 to 1400 W, the temperature is 300 to 600 DEG C, and the time is 45 to 60 minutes. According to the invention, the rice straw is successfully converted into the porous biochar with optimized specific surface area and pore size distribution through a microwave pyrolysis technology. The biochar is used as a nutrient slow-release carrier, so that the defect that the adsorption capacity is high but the release rate is too high in the prior art is remarkably overcome, and the adsorption and continuous release dynamic state of nutrients can be effectively regulated and controlled.

Description

Technical Field

[0001] This invention relates to the field of agricultural waste resource utilization and functional materials technology, and in particular to a nutrient slow-release carrier based on microwave pyrolysis of rice straw biochar, its preparation method and application. Background Technology

[0002] As a major agricultural producer, my country has abundant crop straw resources. However, traditional methods of straw disposal, such as direct burning and dumping, not only cause serious environmental pollution, such as air pollution and soil degradation, but also waste its potential resource value. Converting straw into biochar can realize the value-added utilization of solid waste and provide new materials for carbon sequestration and soil improvement, which has important environmental and economic significance.

[0003] Biochar, due to its porous structure, high specific surface area, and abundant functional groups, has been widely studied as an adsorbent, soil conditioner, and nutrient slow-release carrier. In the field of slow-release fertilizers, biochar can adsorb and fix nutrients in fertilizers, prolonging the release cycle of nutrients in the soil, thereby improving fertilizer utilization and reducing nutrient loss and environmental pollution.

[0004] Traditional biomass pyrolysis methods typically require long processing times and high temperatures, resulting in high energy consumption and low efficiency. The biochar produced by this method often suffers from difficulty in precisely controlling its pore structure, leading to insufficient nutrient slow-release performance when used as a nutrient carrier. For example, the rapid release of nutrients may fail to meet the crop's continuous nutrient supply needs, thus affecting fertilizer utilization efficiency. For instance, patent application CN115259920A discloses a method for improving albic soil using biochar-based slow-release fertilizer. It attempts to prepare biochar by prolonged pyrolysis of biomass such as corn stalks under anaerobic conditions at 400-500℃, and then uses this biochar-based slow-release fertilizer to improve the soil. However, such traditional pyrolysis processes have limitations in controlling the pore structure of biochar, making it difficult to effectively solve the problem of excessively rapid nutrient release.

[0005] In recent years, microwave pyrolysis technology has attracted widespread attention due to its unique heating mechanism. Compared with traditional pyrolysis, microwave pyrolysis has advantages such as fast heating speed, concentrated energy, high thermal utilization efficiency, and uniform heating, enabling the rapid conversion of biomass waste into high-value-added products in a short time. However, existing microwave pyrolysis processes still face bottlenecks in structural control, especially for specific biomass raw materials such as rice straw. How to achieve the synergistic construction of the micropore-mesopore-macropore hierarchical structure of biochar by precisely controlling parameters such as microwave power, pyrolysis temperature, and time, thereby significantly optimizing its performance as a nutrient slow-release carrier, remains a current technical challenge. The formation rules of the pore structure of biochar from different biomass sources by microwave pyrolysis parameters are not yet fully understood, which restricts the targeted preparation and application of high-performance slow-release carriers.

[0006] Therefore, developing a microwave pyrolysis process that can precisely control the pore structure of rice straw biochar to overcome the problems of uncontrollable pore structure, insufficient nutrient slow-release performance, high energy consumption, and complex process of traditional pyrolysis is a key technological direction for achieving efficient and green conversion of straw and developing high-performance green fertilizer carrier materials. Summary of the Invention

[0007] This invention provides a nutrient slow-release carrier based on microwave pyrolysis of rice straw biochar, its preparation method, and its application, in order to solve the above-mentioned problems existing in the prior art.

[0008] According to a first aspect of the present invention, the present invention provides a method for preparing a nutrient slow-release carrier based on microwave pyrolysis of rice straw biochar, comprising the following steps: The rice straw is pretreated to ensure that the water content of the rice straw is ≤30% (preferably 15~30%). The pretreated rice straw is subjected to microwave pyrolysis; wherein the power of the microwave pyrolysis is 1200~1400W, the temperature is 300~600℃, and the time is 45~60min.

[0009] This invention utilizes microwave pyrolysis technology with precisely controlled parameters (power 1200-1400W, temperature 300-600℃, time 45-60min) to pretreat rice straw, enabling efficient and rapid conversion of agricultural waste into biochar. The key to this optimized process lies in promoting the formation of biochar with a specific structure from rice straw in a microwave field, thereby significantly enhancing its performance as a nutrient slow-release carrier. This achieves efficient adsorption and long-term controllable nutrient release, effectively improving fertilizer utilization and reducing environmental pollution.

[0010] According to the method for preparing a nutrient slow-release carrier based on microwave pyrolysis of rice straw biochar of the present invention, the microwave pyrolysis is carried out under a nitrogen atmosphere. Providing an inert environment during the preparation process effectively inhibits the oxidation or combustion of biomass during pyrolysis, ensuring biochar formation and helping to control the composition and pore structure of the biochar.

[0011] Preferably, the nitrogen flow rate is 50~150 mL / min. This suitable nitrogen flow rate can promptly remove volatile substances produced by pyrolysis, preventing them from condensing or undergoing secondary reactions in the pores of biochar. This facilitates the formation of an open, abundant pore structure and a high specific surface area, thus optimizing the performance of biochar as a nutrient slow-release carrier.

[0012] Preferably, the microwave pyrolysis is carried out in a quartz glass reactor. Quartz glass has high transparency to microwave radiation, ensuring that microwave energy acts directly on the rice straw efficiently and without damage, thereby achieving rapid and uniform heating. Furthermore, quartz glass possesses excellent high-temperature resistance and chemical stability, preventing the reactor material from reacting with biomass or pyrolysis products at high temperatures. This ensures the purity of the biochar and the stability and controllability of the preparation process, which is crucial for obtaining a high-quality nutrient slow-release carrier.

[0013] According to the method for preparing a nutrient slow-release carrier based on microwave pyrolysis of rice straw biochar of the present invention, the rice straw is pretreated by first crushing and sieving the rice straw with a pulverizer to obtain fine powder; then washing the obtained fine powder with water and drying it.

[0014] Preferably, the particle size of the fine powder is 100-150 mesh.

[0015] According to a second aspect of the present invention, the present invention also provides a nutrient slow-release carrier based on microwave pyrolysis of rice straw biochar, which is prepared by the above-described method for preparing a nutrient slow-release carrier based on microwave pyrolysis of rice straw biochar.

[0016] The nutrient slow-release carrier obtained by the specific microwave pyrolysis method of this invention has a specific pore size distribution and surface chemical properties, which enables it to achieve efficient nutrient adsorption and precise slow-release function, which is superior to biochar prepared by traditional methods, thus providing a high-performance carrier material for slow-release fertilizers.

[0017] According to the nutrient slow-release carrier based on microwave pyrolysis of rice straw biochar of the present invention, the specific surface area of ​​the nutrient slow-release carrier is 50~135m². 2 / g, with a total pore volume of 0.05~0.15mL / g and an average pore size of 6~12nm.

[0018] These values, limited to a specific range, demonstrate that the nutrient slow-release carrier possesses an optimized microstructure that provides ample adsorption sites (high specific surface area, suitable pore volume) and regulates the diffusion pathways of nutrient molecules (suitable average pore size), thereby ensuring its efficient nutrient loading capacity and effective slow-release performance.

[0019] The nutrient slow-release carrier based on microwave pyrolysis of rice straw biochar according to the present invention generally exhibits a hierarchical pore feature with the synergistic presence of micropores, mesopores and macropores, with the following pore size distribution: micropores account for 15~45%, mesopores account for 38~60%, and macropores account for 11~30%.

[0020] The nutrient slow-release carrier of this invention possesses a unique "hierarchical pore structure." This multi-level pore synergy provides multi-scale transport pathways for nutrients, enabling precise control of the nutrient release rate: micropores may be used for strong adsorption and extremely slow release, mesopores for primary slow-release diffusion, and macropores may promote initial nutrient penetration and rapid pathways. This complex pore structure design significantly improves the sustainability and efficiency of nutrient slow release, better meeting the nutrient needs of crops at different growth stages.

[0021] According to a third aspect of the present invention, the present invention also provides the application of the above-mentioned nutrient slow-release carrier based on microwave pyrolysis rice straw biochar in slow-release fertilizers.

[0022] Applying the nutrient slow-release carrier of the present invention to slow-release fertilizers can effectively improve the nutrient utilization rate of fertilizers, reduce nutrient loss (such as leaching and volatilization), reduce agricultural non-point source pollution, and extend the effective supply time of nutrients in the soil, thereby achieving fertilizer saving, efficiency improvement and environmental friendliness in agricultural production.

[0023] According to a fourth aspect of the present invention, the present invention also provides a slow-release fertilizer, comprising the above-described nutrient slow-release carrier based on microwave pyrolysis of rice straw biochar.

[0024] By optimizing the combination of the nutrient slow-release carrier unique to this invention with specific components (such as nitrogen, phosphorus, potassium, and other nutrients, and other additives), this slow-release fertilizer can synergistically exert the effects of each component to achieve a stable and efficient supply of nutrients. The nutrient slow-release carrier not only provides slow-release functionality but may also positively influence the physical properties of the fertilizer, its dispersibility in the soil, and its interaction with the soil environment, thereby improving the overall performance of the fertilizer.

[0025] According to the present invention, the slow-release fertilizer is prepared as follows: the above-mentioned nutrient slow-release carrier is immersed in an ammonium chloride solution with a concentration of 50-150 mg / L, and after soaking at room temperature for 0.5-2 days, it is taken out. The content of the nutrient slow-release carrier in the suspension is 1-3 g / L, thus obtaining nitrogen-rich slow-release ammonium fertilizer.

[0026] According to the slow-release fertilizer of the present invention, the preparation method is as follows: the above-mentioned nutrient slow-release carrier is immersed in an ammonium chloride solution with a concentration of 100 mg / L, and after soaking at room temperature for 1 day, it is taken out. The content of the nutrient slow-release carrier in the suspension is 2 g / L, and nitrogen-rich slow-release ammonium fertilizer is obtained.

[0027] According to a fifth aspect of the present invention, the present invention also provides a method for improving soil using the above-mentioned slow-release fertilizer, comprising the following steps: applying the slow-release fertilizer into the topsoil and mixing it evenly with the topsoil at a depth of 5-15 cm; preferably, water management is carried out daily by irrigation with tap water, and the water layer is maintained at 3-5 cm.

[0028] By applying the slow-release fertilizer containing the nutrient slow-release carrier of this invention to the soil, not only can crops be provided with a continuous and stable supply of nutrients, but the porous structure and adsorption properties of biochar itself can also improve the physical and chemical properties of the soil, such as enhancing the soil's water and fertilizer retention capacity, increasing the soil's organic matter content, optimizing the soil's aggregate structure, and promoting the growth of beneficial microorganisms, thereby achieving long-term soil health and fertility improvement.

[0029] During the crop growth cycle, the slow-release fertilizer slowly releases nutrients to improve soil nutrient supply. The biochar component in the slow-release fertilizer increases soil organic matter content, improves soil aggregate structure, enhances soil water and fertilizer retention capacity, and retains and slowly releases ammonium nitrogen through its porous structure, thereby promoting crop nutrient absorption.

[0030] The method for improving soil with slow-release fertilizer according to the present invention is characterized in that the application rate of the slow-release fertilizer is 1000-1500 (preferably 1100-1300) kg / ha.

[0031] By limiting the application rate of slow-release fertilizer within the aforementioned reasonable range, optimal soil improvement and resource utilization efficiency can be achieved. This application rate was determined based on experimental optimization, ensuring sufficient nutrients are provided and soil improvement is achieved while avoiding waste and environmental burden caused by excessive application, thereby enhancing the practicality and economy of this soil improvement method.

[0032] The beneficial effects of this invention are: This invention utilizes efficient, simple, and low-energy-consumption microwave pyrolysis technology to successfully convert agricultural waste, rice straw, into porous biochar with optimized specific surface area and pore size distribution. This biochar, as a nutrient slow-release carrier, significantly overcomes the shortcomings of existing technologies, which suffer from high adsorption capacity but excessively rapid release rates. It effectively regulates the dynamics of nutrient adsorption and continuous release, greatly enhancing its practicality and stability in agricultural applications. Attached Figure Description

[0033] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0034] Figure 1 This is an electron microscope image of the dried rice straw during the preparation process provided in Example 6 of the present invention.

[0035] Figure 2 This is an electron microscope image of the nutrient slow-release carrier provided in Embodiment 6 of the present invention.

[0036] Figure 3 This is a nitrogen release trend diagram in water for the nutrient slow-release carriers provided in Examples 1 and 4-6 of the present invention. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0038] Example 1 This embodiment provides a method for preparing a nutrient slow-release carrier based on microwave pyrolysis of rice straw biochar, including the following steps: Take 100g of rice straw, crush it with a pulverizer, sieve it to obtain a fine powder sample of 100~120 mesh for later use; clean the impurities of the obtained fine powder sample with deionized water, dry the sample and keep the moisture content at 20%.

[0039] The pretreated rice straw was transferred to a quartz glass reactor and placed in a microwave pyrolysis furnace for microwave pyrolysis. The microwave pyrolysis power was 1200W, the temperature was 500℃, and the time was 60min. The entire reaction was carried out under a nitrogen atmosphere with a nitrogen flow rate of 150mL / min. After microwave pyrolysis, the mixture was cooled to room temperature to obtain a nutrient slow-release carrier.

[0040] This embodiment also provides a nitrogen-enriched slow-release ammonium fertilizer, which is prepared as follows: The nutrient slow-release carrier obtained in this embodiment is immersed in an ammonium chloride solution with a concentration of 100 mg / L, and after soaking at room temperature for 1 day, it is taken out. The content of the nutrient slow-release carrier in the suspension is 2 g / L, thus obtaining the nitrogen-enriched slow-release ammonium fertilizer.

[0041] Example 2 This embodiment provides a method for preparing a nutrient slow-release carrier based on microwave pyrolysis of rice straw biochar. The only difference from Embodiment 1 is that the microwave pyrolysis power is 1300W.

[0042] This embodiment also provides a nitrogen-enriched slow-release ammonium fertilizer, which is prepared as follows: The nutrient slow-release carrier obtained in this embodiment is immersed in an ammonium chloride solution with a concentration of 100 mg / L, and after soaking at room temperature for 1 day, it is taken out. The content of the nutrient slow-release carrier in the suspension is 2 g / L, thus obtaining the nitrogen-enriched slow-release ammonium fertilizer.

[0043] Example 3 This embodiment provides a method for preparing a nutrient slow-release carrier based on microwave pyrolysis of rice straw biochar. The only difference from Embodiment 1 is that the microwave pyrolysis power is 1400W.

[0044] This embodiment also provides a nitrogen-enriched slow-release ammonium fertilizer, which is prepared as follows: The nutrient slow-release carrier obtained in this embodiment is immersed in an ammonium chloride solution with a concentration of 100 mg / L, and after soaking at room temperature for 1 day, it is taken out. The content of the nutrient slow-release carrier in the suspension is 2 g / L, thus obtaining the nitrogen-enriched slow-release ammonium fertilizer.

[0045] Example 4 This embodiment provides a method for preparing a nutrient slow-release carrier based on microwave pyrolysis of rice straw biochar, which differs from Embodiment 1 only in that the microwave pyrolysis temperature is 300℃.

[0046] This embodiment also provides a nitrogen-enriched slow-release ammonium fertilizer, which is prepared as follows: The nutrient slow-release carrier obtained in this embodiment is immersed in an ammonium chloride solution with a concentration of 100 mg / L, and after soaking at room temperature for 1 day, it is taken out. The content of the nutrient slow-release carrier in the suspension is 2 g / L, thus obtaining the nitrogen-enriched slow-release ammonium fertilizer.

[0047] Example 5 This embodiment provides a method for preparing a nutrient slow-release carrier based on microwave pyrolysis of rice straw biochar, which differs from Embodiment 1 only in that the microwave pyrolysis temperature is 400℃.

[0048] This embodiment also provides a nitrogen-enriched slow-release ammonium fertilizer, which is prepared as follows: The nutrient slow-release carrier obtained in this embodiment is immersed in an ammonium chloride solution with a concentration of 100 mg / L, and after soaking at room temperature for 1 day, it is taken out. The content of the nutrient slow-release carrier in the suspension is 2 g / L, thus obtaining the nitrogen-enriched slow-release ammonium fertilizer.

[0049] Example 6 This embodiment provides a method for preparing a nutrient slow-release carrier based on microwave pyrolysis of rice straw biochar, which differs from Embodiment 1 only in that the microwave pyrolysis temperature is 600℃.

[0050] During the preparation process, the scanning electron microscope image of the dried rice straw is shown below. Figure 1 As shown, its surface structure is relatively smooth and lacks obvious porous structure, thus limiting its ability to retain and slowly release nutrients. In contrast, the scanning electron microscope image of the obtained nutrient slow-release carrier is shown below. Figure 2 As shown, after microwave pyrolysis treatment, a unique hierarchical pore structure is formed on the material surface. This hierarchical pore structure is composed of micropores, mesopores, and macropores working together, which can provide multi-scale transport channels, which is conducive to the effective adsorption and gradual release of nutrients, thereby achieving precise control of the nutrient release rate.

[0051] This embodiment also provides a nitrogen-enriched slow-release ammonium fertilizer, which is prepared as follows: The nutrient slow-release carrier obtained in this embodiment is immersed in an ammonium chloride solution with a concentration of 100 mg / L, and after soaking at room temperature for 1 day, it is taken out. The content of the nutrient slow-release carrier in the suspension is 2 g / L, thus obtaining the nitrogen-enriched slow-release ammonium fertilizer.

[0052] Comparative Example 1 This comparative example provides a method for preparing a nutrient slow-release carrier based on microwave pyrolysis of rice straw biochar. The only difference from Example 1 is that the pyrolysis method used is different. Specifically, it is conventional pyrolysis, that is, the rice straw is heated to 500°C and held for 30 minutes under an inert atmosphere to obtain biochar. The remaining preparation steps are the same as in Example 1.

[0053] Comparative Example 2 This comparative example provides a method for preparing a nutrient slow-release carrier based on microwave pyrolysis biochar, which differs from Example 1 only in that wood powder is used instead of rice straw.

[0054] The nutrient slow-release carriers provided in Examples 1-6 and Comparative Examples 1-2 were subjected to adsorption-release analysis and performance tests such as specific surface area. The test method was as follows: the nutrient slow-release carrier was immersed in a 100 mg / L ammonium chloride solution at room temperature for 7 days. After immersion, it was removed and placed in a glass bottle for shaking in a constant-temperature shaker at 160-180 rpm. After adsorption equilibration for 7 days, it was centrifuged at 4000-6000 rpm for 20 minutes, filtered through a 0.22 μm filter membrane, and then the NH4+ content was measured. + -N content. Subsequently, an equal volume of buffer solution (pH=7) was added to the original suspension to maintain a constant system volume. Under the same equilibrium conditions, the release process was performed continuously for three cycles, each cycle containing a 7-day equilibrium period, for a total desorption time of 21 days.

[0055] The performance indicators of the nutrient slow-release carriers obtained in Examples 1-6 and Comparative Examples 1-2 are shown in Table 1 below.

[0056] Table 1

[0057] Table 1 shows that there are significant differences between biochar prepared by microwave pyrolysis and biochar prepared by conventional pyrolysis in terms of pore structure characteristics and nutrient slow-release performance. Regarding specific surface area and pore volume distribution, microwave pyrolysis biochar generally exhibits a higher specific surface area (52.01–131.39 m² / g) and a moderate total pore volume (0.073–0.107 ml / g), while the specific surface area of ​​the conventionally pyrolyzed sample in Comparative Example 1, although large (324.2 m² / g), is significantly lower. 2The sample (g) has a pore size concentrated in micropores, with a low proportion of mesopores (only 25.65%), lacking a reasonable hierarchical pore distribution. Comparative Example 2, due to a change in raw materials, has a specific surface area of ​​only 5.63 m². 2 / g, with an extremely imperfect pore structure. In contrast, the samples of Examples 1-6 generally exhibited a hierarchical pore structure with micropores, mesopores, and macropores coexisting, with micropores accounting for 17.90-44.18%, mesopores accounting for 38.87-55.47%, and macropores accounting for 11.72-28.59%, which was significantly better than the comparative samples.

[0058] Experimental results show that under microwave pyrolysis conditions, the pyrolysis temperature has a significant regulatory effect on the mesoporous structure and surface properties of rice straw biochar, thereby affecting its nutrient adsorption capacity and sustained-release kinetics. The biochar prepared in Example 5 has a large specific surface area and abundant polar sites, resulting in the highest adsorption capacity (13.7 mg / g), but its initial release rate is rapid (approximately 74.2% release rate after 7 days), stabilizing after 14 days. In contrast, the nutrient sustained-release carriers prepared in Examples 1 and 6 have enlarged average pore size and a more favorable pore structure for delayed diffusion, and a reduction in surface polar functional groups, which suppresses initial release. However, they still maintain a high release increment (≥10%) from 14 to 21 days, achieving a longer-term sustained-release effect.

[0059] In summary, this invention successfully constructed a hierarchical pore system in which micropores, mesopores, and macropores coexist by regulating the pore structure of rice straw biochar through microwave pyrolysis. This hierarchical pore structure can effectively adsorb and retain nutrients while providing multi-scale transport channels, thereby achieving sustained and efficient nutrient release and utilization. The biochar prepared under optimal conditions of 1200 W microwave power and 400-500 °C pyrolysis temperature exhibits a high specific surface area, a reasonable pore size distribution, and excellent nutrient slow-release performance. The nutrient slow-release carrier prepared in Example 1 achieves the best balance between high-efficiency loading and long-term slow release, making it suitable as a preferred agricultural nutrient slow-release carrier.

[0060] Application examples Effects of nitrogen-enriched slow-release ammonium fertilizer prepared in Example 1 on growth indicators of potted rice.

[0061] Pot experiment setup: Example 1 and a control group were set up, with 3 pots for each treatment as replicates. Each pot was planted with three holes, and each hole contained three seedlings. Each soil column contained 35 kg of paddy soil, including 10 kg of topsoil, forming a 10 cm thick paddy soil column. The application rate of nitrogen-enriched slow-release ammonium fertilizer was 1200 kg / ha. Water management was carried out daily with tap water irrigation, maintaining a water level of 3-5 cm.

[0062] Rice growth indicators, including actual yield, total number of panicles, thousand-grain weight, fresh weight of panicles, and seed setting rate, were measured 134 days after planting. The test results are shown in Table 2.

[0063] Table 2

[0064] As can be seen from Table 2, the actual yield, total number of panicles, thousand-grain weight, fresh weight of rice panicles, and grain filling rate of Example 1 showed excellent results compared with the control group, indicating that the nitrogen-enriched slow-release ammonium fertilizer of the present invention releases nutrients slowly in rice cultivation, which is more in line with the growth pattern of crops and improves nutrient utilization efficiency.

[0065] The effect of nitrogen-rich slow-release ammonium fertilizer prepared in Example 1 on soil NH3 volatilization.

[0066] Soil NH3 volatilization was determined using a continuous gas flow method. The apparatus consisted of an 11 cm diameter glass cylinder, a vacuum pump, and a 2 m long exhaust pipe. An 80 mL 2% boric acid solution was connected as the absorbent for NH3 emissions, and the boric acid absorbent was titrated with 0.01 MH2SO4 solution. Soil ammonia volatilization was continuously monitored, with NH3 volatilization and absorbent sampling conducted between 8:00–10:00 am and 1:00–3:00 pm on monitoring days. The test results are shown in Table 3.

[0067] Table 3

[0068] Compared to conventional urea treatment, the treatment in Example 1 significantly reduced NH3 volatilization by 52.26% during the rice season. Its nutrient release process was more stable and slower, better matching the absorption pattern of compounds, thus greatly reducing nitrogen loss.

[0069] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a nutrient slow-release carrier based on microwave pyrolysis of rice straw biochar, characterized in that, Includes the following steps: The rice straw is pretreated to ensure that the water content of the rice straw is ≤30% by mass. The pretreated rice straw is subjected to microwave pyrolysis; wherein the power of the microwave pyrolysis is 1200~1400W, the temperature is 300~600℃, and the time is 45~60min.

2. The method for preparing a nutrient slow-release carrier based on microwave pyrolysis of rice straw biochar according to claim 1, characterized in that, The microwave pyrolysis was carried out under a nitrogen atmosphere. Preferably, the nitrogen flow rate is 50~150 mL / min; Preferably, the microwave pyrolysis is carried out in a quartz glass reactor.

3. The method for preparing a nutrient slow-release carrier based on microwave pyrolysis of rice straw biochar according to claim 1 or 2, characterized in that, The pretreatment of rice straw involves first crushing the rice straw with a crusher, sieving it to obtain fine powder; then washing the obtained fine powder with water and drying it. Preferably, the particle size of the fine powder is 100-150 mesh.

4. A nutrient slow-release carrier based on microwave pyrolysis of rice straw biochar, characterized in that, The nutrient slow-release carrier based on microwave pyrolysis of rice straw biochar was prepared using any one of claims 1-3.

5. The nutrient slow-release carrier based on microwave pyrolysis of rice straw biochar according to claim 4, characterized in that, The specific surface area of ​​the nutrient slow-release carrier is 50~135m². 2 / g, with a total pore volume of 0.05~0.15mL / g and an average pore size of 6~12nm.

6. The nutrient slow-release carrier based on microwave pyrolysis of rice straw biochar according to claim 4 or 5, characterized in that, The nutrient slow-release carrier comprises micropores, mesopores, and macropores; preferably, the proportion of micropores is 15-45%, the proportion of mesopores is 38-60%, and the proportion of macropores is 11-30%.

7. The application of the nutrient slow-release carrier based on microwave pyrolysis of rice straw biochar as described in any one of claims 4-6 in slow-release fertilizers.

8. A slow-release fertilizer, characterized in that, Includes the nutrient slow-release carrier based on microwave pyrolysis of rice straw biochar as described in any one of claims 4-6.

9. A method for improving soil using the slow-release fertilizer according to claim 8, characterized in that, The process includes the following steps: applying slow-release fertilizer into the topsoil and mixing it evenly with the topsoil at a depth of 5-15 cm; preferably, daily irrigation with tap water is used for water management, and the water level is maintained at 3-5 cm.

10. The method for improving soil with slow-release fertilizer according to claim 9, characterized in that, The application rate of the slow-release fertilizer is 1000-1500 kg / ha.

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