Organic stable fertilizer for rice as well as preparation method and application of organic stable fertilizer

Abstract

The invention belongs to the technical field of organic fertilizers, and particularly relates to an organic stable fertilizer for rice as well as a preparation method and application thereof. The organic stable fertilizer for rice is obtained by taking the modified biomass charcoal as a carrier, loading a tannic acid double-effect inhibitor and combining with a composite organic carbon source. Wherein the modified biomass charcoal is used for stably loading and slowly releasing the inhibitor through physical adsorption and weak hydrogen-bond interaction, and meanwhile, carboxyl on the surface of the modified biomass charcoal can be reversibly combined with soil ammonium nitrogen to realize nitrogen fixation; the tannic acid double-effect inhibitor can achieve double-effect inhibition of urease and nitration through coordination complexation, ammonia volatilization and nitrate nitrogen leaching loss are reduced, and the tannic acid double-effect inhibitor can be naturally degraded without residues; besides, the composite organic carbon source is obtained by compounding lignite humic acid, alkali lignin and rice straw powder, a gradient carbon supply mode is formed by virtue of degradation rate differences of the lignite humic acid, the alkali lignin and the rice straw powder, the carbon supply requirements of the rice in the tillering stage, the booting stage and the pustulation stage are met respectively, the nitrogen utilization rate is effectively improved, the nitrogen supply period is prolonged, and environment friendliness and large-scale cultivation suitability are both considered.

Description

Technical Field

[0001] This invention relates to the field of organic fertilizer technology, and in particular to an organic stable fertilizer for rice, its preparation method and application. Background Technology

[0002] As a major food crop, rice's high and stable yields are crucial for ensuring food security. Nitrogen fertilizer is the core nutrient for regulating rice growth and increasing yield. However, the unique flooded cultivation method of rice presents a severe nitrogen loss problem after traditional fast-acting nitrogen fertilizers such as urea are applied to the soil. Flooded paddy fields are in an anaerobic environment for a long time, with significant pH fluctuations between the surface water film and the rhizosphere. After urea is applied, it is rapidly catalyzed and hydrolyzed into ammonium nitrogen by soil urease. Some of the ammonium nitrogen is easily converted into free ammonia and volatilized from the water surface in a weakly alkaline environment. Another part is converted into nitrate nitrogen by nitrifying bacteria. Nitrate nitrogen cannot be adsorbed by soil colloids and is easily leached away by seepage water in the paddy field. At the same time, under anaerobic conditions, it will be converted into nitrogen gas, nitrous oxide and other gaseous substances through denitrification and escape. As a result, the nitrogen utilization rate of paddy fields is generally only 30%-40%, which not only causes serious waste of resources and economic burden, but also leads to a series of environmental problems such as eutrophication of water bodies and greenhouse gas emissions. Therefore, current technologies mainly focus on adding inhibitors to delay nitrogen conversion and prepare stable fertilizers. Currently, almost all commercially available stable fertilizers for rice rely on synthetic chemical inhibitors, primarily N-butylthiophosphoric triamine (NBPT), dicyandiamide (DCD), and their compound systems. While these chemical inhibitors can delay nitrogen loss and improve fertilizer efficiency in the short term, they have limitations such as high cost, poor environmental compatibility, and potential long-term impacts on soil microecology. Furthermore, current research focuses primarily on the single dimension of chemical inhibition, failing to synergistically achieve long-term nutrient supply and match crop needs, thus hindering further improvements in overall fertilizer efficiency and meeting the development needs of green agriculture. Summary of the Invention

[0003] To address the shortcomings of existing technologies, the present invention aims to provide an organic stable fertilizer for rice, its preparation method, and its application. Modified biochar serves as a carrier, loaded with a dual-effect tannic acid inhibitor, and combined with a composite organic carbon source to obtain the organic stable fertilizer for rice. Specifically, the modified biochar stabilizes the loaded inhibitor through physical adsorption and weak hydrogen bonding, while its surface carboxyl groups reversibly bind to soil ammonium nitrogen for nitrogen fixation. The dual-effect tannic acid inhibitor achieves dual inhibition of urease and nitrification through coordination complexation, reducing ammonia volatilization and nitrate leaching losses, and is naturally degradable without residue. Furthermore, the composite organic carbon source is obtained by compounding lignite humic acid, alkali lignin, and rice straw powder. Based on the differences in their degradation rates, a gradient carbon supply mode is formed, meeting the carbon supply needs of rice during the tillering, booting, and grain-filling stages, effectively improving nitrogen utilization and extending the nitrogen supply period, while also considering environmental friendliness and suitability for large-scale cultivation.

[0004] To achieve the above objectives, the present invention employs the following technical solution:

[0005] In a first aspect, the present invention provides an organic stable fertilizer for rice, comprising a modified biochar-supported tannic acid dual-effect inhibitor, a compound organic carbon source, nutrients, and adjuvants;

[0006] The modified biochar loaded with tannic acid dual-effect inhibitor is obtained by dissolving the tannic acid dual-effect inhibitor in an ethanol-deionized aqueous solution and spraying it onto the modified biochar through atomization; the modified biochar is obtained by modifying biochar with nitric acid; the tannic acid dual-effect inhibitor is obtained by alkaline hydrolysis and oxidative modification of tannic acid powder.

[0007] The composite organic carbon source includes lignite humic acid, alkali lignin, rice straw powder, and modified bentonite; the modified bentonite is obtained by modifying bentonite with a silane coupling agent.

[0008] The nutrients include organic and inorganic nutrients; the organic nutrients are well-rotted livestock and poultry manure; the inorganic nutrients include urea, monoammonium phosphate, potassium chloride, and zinc sulfate heptahydrate.

[0009] The additives include sodium silicate and hydroxypropyl starch.

[0010] Further, the mass ratio of the modified biochar, tannic acid dual-effect inhibitor, composite organic carbon source, nutrients and adjuvants is (60-100):(50-80):(347-398):(403-535):(15-23); the mass ratio of the lignite humic acid, alkali lignin, rice straw powder and modified bentonite is (150-175):(115-130):(75-85):(7-8); the mass ratio of the decomposed livestock and poultry manure, urea, monoammonium phosphate, potassium chloride and zinc sulfate heptahydrate is (100-150):(180-220):(80-100):(40-60):(3-5); and the mass ratio of sodium silicate and hydroxypropyl starch is (10-15):(5-8).

[0011] Further, the silane coupling agent is KH-550; the tannic acid powder has a tannic acid content ≥80% and a particle size of 60-100 mesh; the biochar is agricultural straw-based biochar with a particle size of 0.1-0.3 mm; the modified biochar has a carboxyl content ≥3.5 mmol / g; the lignite humic acid has a humic acid content ≥60% and a particle size of 0.1-0.5 mm; the alkali lignin has a lignin content ≥90% and a particle size of 0.1-0.5 mm; and the rice straw powder has a particle size of 0.6-0.8 mm.

[0012] Secondly, the present invention provides a method for preparing an organic stable fertilizer for rice, comprising the following steps:

[0013] S1. Mix tannic acid powder, sodium hydroxide and deionized water, add hydrogen peroxide solution dropwise, react, adjust pH with dilute hydrochloric acid, vacuum dry and pulverize, add trisodium citrate and mix to obtain a dual-effect tannic acid inhibitor.

[0014] S2. Mix bentonite with an aqueous solution of silane coupling agent, stir, dry and pulverize to obtain modified bentonite; mix lignite humic acid, alkali lignin and rice straw powder, add modified bentonite to obtain a composite organic carbon source;

[0015] S3. Mix biochar and nitric acid, reflux the reaction, filter, wash with water and dry to obtain modified biochar; dissolve the tannic acid dual-effect inhibitor in ethanol-deionized water solution and spray it onto the modified biochar by atomization to obtain modified biochar loaded with tannic acid dual-effect inhibitor.

[0016] S4. Dissolve sodium silicate in deionized water and adjust the pH with hydrochloric acid to obtain a sodium silicate solution; mix modified biochar loaded with tannic acid dual-effect inhibitor, composite organic carbon source, and decomposed livestock and poultry manure to obtain a premix; add urea, monoammonium phosphate, potassium chloride, and zinc sulfate heptahydrate to the premix and mix; spray with sodium silicate solution to obtain a fertilizer mixture.

[0017] S5. Mix hydroxypropyl starch with deionized water, add it to the fertilizer mixture, adjust the moisture content of the mixture, and then granulate, dry, and sieve to obtain organic stable fertilizer for rice.

[0018] In one feasible implementation, in S1, the mass-to-volume ratio of the tannic acid powder, sodium hydroxide, deionized water, and hydrogen peroxide solution is (50-80) kg : (5-8) kg : (283-453) L : (1.4-2.3) L; the mass fraction of the hydrogen peroxide solution is 30%; the dropping rate is 31-51 mL / min; the reaction temperature is 55-65℃, and the reaction time is 40-50 min; the mass fraction of the dilute hydrochloric acid is 10%; the pH value is adjusted to 6.8-7.2; the vacuum drying temperature is 55-65℃, and the vacuum drying time is 3.5-4.5 h; the particle size of the pulverized material is 70-90 mesh; and the mass ratio of the tannic acid powder to trisodium citrate is (50-80) : (0.25-0.64).

[0019] Tannic acid is modified in two steps to impart dual inhibition functions of urease and nitration, while ensuring its stability and environmental compatibility. First, alkaline hydrolysis is performed, utilizing an alkaline environment to break and hydrolyze the ester bonds in the tannic acid macromolecule, depolymerizing the originally highly polymerized tannic acid into smaller phenolic fragments. This process breaks down the steric hindrance within the tannic acid molecule, fully exposing its latent phenolic hydroxyl active sites, laying the foundation for subsequent inhibition. Next, oxidative modification is carried out, using an oxidant to further introduce active oxygen-containing functional groups such as carboxyl and quinone groups onto the smaller tannic acid fragments, enriching the types of active sites for the inhibitor. After modification, the inhibitor system is brought to a neutral and stable state by pH adjustment. After drying and pulverizing, it is compounded with trisodium citrate, which, as a functional excipient, plays multiple roles: chelating trace metal impurities in the system to protect active sites, constructing a pH buffer system to maintain system stability, improving powder dispersion and flowability to prevent agglomeration, and simultaneously enhancing the subsequent binding force with the carrier, ensuring the inhibitor's stability and effectiveness during subsequent loading.

[0020] The phenolic hydroxyl group of the tannic acid dual-effect inhibitor can react with Ni in the active site of urease in the soil. 2+When tannic acid forms stable coordination complexes with metal ions, it competitively occupies the catalytic active site of urease, thereby slowing down the rate of urea hydrolysis into ammonia nitrogen. This reduces the volatilization loss of ammonia nitrogen during paddy field flooding at the source, achieving highly efficient urease inhibition. Simultaneously, the carboxyl and quinone functional groups in its molecular structure can coordinate with metal ions such as Cu and Fe at the active site of ammonia monooxygenase during nitrification, blocking the conversion of ammonia nitrogen to nitrate nitrogen and reducing the gaseous loss of nitrate nitrogen due to leaching and denitrification, thus achieving nitrification inhibition. Furthermore, since tannic acid itself originates from natural plants, it retains its biodegradable properties after modification. It can gradually decompose into harmless substances in the soil, leaving no residue or pollution. This effectively regulates nitrogen loss, extends the nitrogen supply cycle, and improves nitrogen utilization efficiency, while avoiding the environmental risks associated with chemical inhibitors, fully ensuring the environmental friendliness of the fertilizer.

[0021] In one feasible implementation, in step S2, the mass-to-volume ratio of bentonite to the silane coupling agent aqueous solution is (7-8) kg:(35-40) L; the mass fraction of the silane coupling agent in the silane coupling agent aqueous solution is 3%; the stirring temperature is 20-30℃, the stirring speed is 180-220 r / min, and the stirring time is 1.5-2.5 h; the drying temperature is 60-70℃, and the drying time is 2-3 h; the particle size of the pulverized material is 70-90 mesh.

[0022] Bentonite, with montmorillonite as its main active ingredient, is a layered silicate mineral. Its surface naturally contains a large number of highly active adsorption sites, including exchangeable metal cations between layers, densely distributed silanol and aluminol polar groups on the surface, and unsaturated active sites formed by bond breaking at the mineral edges. These sites are extremely polar and have a prominent adsorption effect. If used directly, they will over-adsorb tannic acid dual-effect inhibitors in the subsequent system, causing the inhibitor active sites to be blocked and unable to be released and exert their effects in the soil. At the same time, its strong polarity makes it less compatible with organic carbon sources such as lignite humic acid, alkali lignin, and rice straw powder, and it is easy for components to stratify and aggregate.

[0023] Therefore, KH-550 silane coupling agent was used to modify bentonite. The silane coupling agent undergoes a hydrolysis reaction in aqueous solution, generating hydrolysis products containing silanol groups. These hydrolysis products can undergo dehydration condensation reactions with the silanol and aluminol groups on the surface of bentonite particles, causing the silane coupling agent to be firmly bonded to the bentonite surface by covalent bonds. Simultaneously, the organic long-chain segments of the coupling agent are orderly arranged on the bentonite surface, forming a continuous and uniform organic modification layer. This organic modification layer can physically cover and shield the polar hydroxyl groups and edge unsaturated sites on the bentonite surface, reducing the surface polarity of the bentonite. The strong electrostatic adsorption of exchangeable metal cations between the shielding layers effectively passivates and seals the highly active adsorption sites of bentonite itself, completely solving the problem of excessive adsorption of inhibitors. It also significantly improves the compatibility with components such as organic carbon sources and modified biochar, preventing the layering and aggregation between components. At the same time, the modified bentonite has better adhesion and dispersibility, and can be uniformly dispersed in the composite organic carbon source as a structural aid, improving the subsequent fertilizer granule forming effect and mechanical strength, reducing wear and breakage of fertilizer during transportation and application, and ensuring the stability of fertilizer granules.

[0024] Three organic carbon sources with different degradation rates—lignite humic acid, alkali lignin, and rice straw powder—were selected and compounded. These three sources exhibit naturally different degradation characteristics: lignite humic acid is a small-molecule organic carbon with good water solubility and is easily decomposed and utilized by soil microorganisms, enabling rapid degradation and carbon supply; alkali lignin is a medium-molecular-weight organic carbon with a slow degradation rate, enabling medium-speed degradation and carbon supply; and rice straw powder contains macromolecules such as cellulose and hemicellulose, resulting in a slow degradation rate and enabling slow and sustained carbon supply. After mixing the three sources in a specific ratio, modified bentonite was added. The modified bentonite acts as a binder and support, enhancing the bonding stability between the three organic carbon sources and improving the structural strength of the subsequent fertilizer granules, preventing easy wear and breakage during transportation or application.

[0025] The composite organic carbon source utilizes the differences in degradation rates of its three components to create a gradient carbon supply model adapted to the entire growth period of rice. The rapidly degrading lignite humic acid can meet the rapid carbon demand of rice during the tillering stage, while its functional groups such as carboxyl and hydroxyl groups can chelate mineral nutrients such as phosphorus, potassium, and zinc in the soil, reducing nutrient fixation by soil colloids and improving nutrient availability. The moderately degrading alkali lignin can meet the peak carbon demand of rice during the booting stage, while also enhancing the stability of fertilizer particles. The slowly degrading rice straw powder can ensure a continuous carbon supply during the grain-filling stage, supporting the fullness of rice grains. The three components work synergistically to achieve carbon supply throughout the entire growth period, while improving soil organic matter content and optimizing the soil micro-ecological environment.

[0026] In one feasible implementation, in step S3, the mass-to-volume ratio of biochar to nitric acid is (60-100) kg:(480-800) L; the mass fraction of nitric acid is 10%; the reflux reaction temperature is 65-75℃, and the reflux reaction time is 2.5-3.5 h; the water washing step is: repeatedly washing with deionized water until the pH is 6.5-7.0; the drying temperature is 100-110℃, and the drying time is 2-3 h; the mass-to-volume ratio of the tannic acid dual-effect inhibitor to the ethanol-deionized aqueous solution is (50-80) kg:(250-400) L; the volume ratio of ethanol to deionized water in the ethanol-deionized aqueous solution is (12.5-20):(237.5-380); the atomization spraying conditions are: atomization pressure 0.4-0.5 MPa, flow rate 7-9 mL / min.

[0027] Biochar was modified by nitric acid etching. Nitric acid, as a strong oxidant, can oxidize and etch the surface of biochar. The original biochar surface is covered with a relatively dense carbonaceous layer, with a tightly connected internal carbon skeleton and only a few scattered micropores. The strong oxidizing property of nitric acid preferentially acts on weak areas such as amorphous carbon and carbon defect sites on the biochar surface, causing the carbon-carbon bonds in these areas to oxidize and break. Some carbon elements are oxidized and decomposed into small molecule gaseous products that escape. At the same time, the dense surface carbon layer is gradually etched away, initially forming shallow micropores. As the etching reaction continues, nitric acid... The ions penetrate into the biochar through the initially formed micropores, further selectively oxidizing the internal carbon skeleton, breaking down the dense carbon connection structure, and promoting the formation of more and richer mesopores and macropores. At the same time, the gaseous products generated by oxidation and decomposition will slightly impact the internal carbon skeleton of the biochar during the escape process, promoting the interconnection of various pores, and finally forming a multi-level porous structure with interconnected micropores, mesopores and macropores. This significantly increases the specific surface area and porosity of the biochar, providing ample space for subsequent physical adsorption inhibitors and significantly enhancing its physical adsorption capacity.

[0028] Furthermore, during the biochar modification process, the oxidation of carbon on the biochar surface by nitric acid causes an oxidation reaction, generating a large number of carboxyl functional groups. This transforms the biochar from an inert carrier into a functional carrier with high surface activity. In a water-rich soil environment, carboxyl groups can dissociate to form negatively charged carboxylate ions. On one hand, these ions can form stable weak hydrogen bonds with the hydroxyl and phenolic hydroxyl groups in the tannic acid dual-effect inhibitor molecules. This ensures stable loading of the inhibitor on the carrier without irreversible strong adsorption or microporous locking, enabling smooth release of the inhibitor and ensuring its continuous and stable dual-inhibitory effect. On the other hand, they can form reversible ionic bonds with positively charged ammonium nitrogen in the soil, temporarily fixing the ammonium nitrogen on the carrier surface through electrostatic interactions. Adsorption and fixation are completed when soil nitrogen is sufficient, and the nitrogen is gradually dissociated and released when rice requires nitrogen. This reduces ammonia volatilization and nitrate nitrogen leaching losses, enabling on-demand nitrogen supply and further improving nitrogen utilization. This forms a synergistic nitrogen regulation system with the tannic acid dual-effect inhibitor.

[0029] In one feasible implementation, in step S4, the mass-to-volume ratio of sodium silicate to deionized water is (10-15) kg:(100-150) L; the mass fraction of hydrochloric acid is 10%; the pH value is adjusted to 8.0-9.0; and the spraying rate is 5-8 mL / min.

[0030] By adjusting the pH of the sodium silicate solution to a suitable range, sodium silicate molecules undergo moderate hydrolysis and polymerization reactions to form a siloxane network structure with good binding properties. This binding system can act as a bridge in the subsequent granulation process, tightly binding the fertilizer components and improving the granulation effect and structural stability.

[0031] Among these, well-rotted livestock and poultry manure not only replenishes soil organic matter and improves soil physicochemical properties and microbial community structure, but also provides some organic nutrients, synergistically enhancing soil fertility with compound organic carbon sources. Compound organic carbon sources provide a gradient of carbon sources for rice growth, while their active functional groups help retain nitrogen, synergistically reducing nitrogen loss with inhibitors. Modified biochar-loaded inhibitors continuously exert a dual inhibitory effect, regulating the nitrogen conversion process. Based on this, compounding with inorganic macronutrient fertilizers such as urea, monoammonium phosphate, and potassium chloride can supplement the core nutrients of nitrogen, phosphorus, and potassium required by rice throughout its entire growth period. Combined with micronutrient fertilizers such as zinc sulfate heptahydrate, it can compensate for the lack of micronutrients in the soil, preventing poor growth and yield reduction in rice due to nutrient deficiencies, and comprehensively meeting the needs of large-scale rice cultivation for nutrient and nitrogen regulation.

[0032] In one feasible implementation, in step S5, the mass-to-volume ratio of hydroxypropyl starch to deionized water is (5-8) kg:(10-16) L; the method for adjusting the moisture content of the mixture is to supplement with deionized water, and the range of the moisture content of the mixture is 18%-20%; the granulation step is to granulate under the conditions of a feed rate of 100-120 kg / h, a rotation speed of 30-40 r / min, and a disc tilt angle of 40-50°, and control the particle size to be 2-4 mm; the drying temperature is 75-85℃, and the drying time is 25-35 min; the sieving step is to sieve the mixture sequentially through 2 mm and 4 mm sieves.

[0033] Hydroxypropyl starch, as an environmentally friendly binder, contains a large number of hydrophilic groups in its molecules. It can combine with the moisture in the mixture to form a viscous binding network, which tightly connects the modified biochar, organic carbon source, inorganic nutrients, inhibitors and other components together, improving the binding and plasticity of the mixture and providing a guarantee for pellet formation. At the same time, its biodegradable properties will not cause pollution to the environment, which is in line with the environmentally friendly requirements of fertilizers.

[0034] Low-temperature drying process is used to dry wet granules. The low-temperature environment can effectively remove excess moisture inside the granules, improve the mechanical strength and storage stability of the granules. At the same time, the key is to avoid the oxidation and inactivation of tannic acid dual-effect inhibitors caused by high temperature. Since plant-derived inhibitors are sensitive to high temperature, low-temperature drying can retain their dual-inhibition activity to the greatest extent and ensure that the core function of fertilizer is not affected.

[0035] Thirdly, this invention provides an application of an organic stable fertilizer for rice in the process of increasing rice yield and improving rice quality.

[0036] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0037] This scheme uses modified biochar as a carrier to load a dual-effect tannic acid inhibitor, combined with a composite organic carbon source, to obtain an organic stable fertilizer for rice that combines high nitrogen utilization and environmental friendliness. Specifically, the modified biochar is etched with nitric acid to form a multi-level porous structure and introduce carboxyl groups. The inhibitor is stabilized and slowly released through physical adsorption and weak hydrogen bonding, ensuring its continuous and stable effect. Simultaneously, the carboxyl groups can form reversible ionic bonds with soil ammonium nitrogen for synergistic nitrogen fixation. The dual-effect tannic acid inhibitor is produced by alkaline hydrolysis of tannic acid to hydrolyze and depolymerize ester bonds into small phenolic fragments, exposing internal phenolic hydroxyl groups. Further oxidation modification introduces active oxygen-containing functional groups such as carboxyl groups. On one hand, the phenolic hydroxyl groups can bind with Ni in the active center of soil urease. 2+The inhibitor can coordinate with metal ions to competitively occupy the catalytic site of urease, slowing down the rate of urea hydrolysis to ammonia nitrogen and reducing ammonia volatilization loss during paddy field flooding, thus inhibiting urease. On the other hand, active oxygen-containing functional groups such as carboxyl and quinone groups can coordinate with Cu and Fe metal ions in the active center of ammonia monooxygenase to block the nitrification conversion of ammonia nitrogen to nitrate nitrogen, reduce nitrate nitrogen leaching and denitrification gaseous loss, and achieve nitrification inhibition. Moreover, this inhibitor is derived from natural plants and can be naturally degraded without residue, thus improving nitrogen utilization and extending the nitrogen supply cycle while ensuring environmental friendliness.

[0038] In addition, the compound organic carbon source is obtained by combining lignite humic acid, alkali lignin and rice straw powder. It forms a carbon supply gradient based on the difference in degradation rate of the three components: lignite humic acid degrades rapidly to meet the carbon supply needs of rice during the tillering stage and chelates nutrients such as phosphorus, potassium and zinc to reduce soil fixation; alkali lignin degrades at a medium rate to meet the peak carbon demand during the booting stage and enhance the stability of fertilizer particles; and straw powder degrades slowly to ensure continuous carbon supply during the grain filling stage, so as to realize the gradient supply of carbon source throughout the growth period and meet the needs of large-scale rice cultivation of various types. Attached Figure Description

[0039] Figure 1 This is a schematic diagram of the preparation process of an organic stable fertilizer for rice according to the present invention. Detailed Implementation

[0040] To make the technical problems, technical solutions, and beneficial effects to be solved by this application clearer, the application will be further described in detail below with reference to embodiments. However, this should not be construed as limiting the scope of this application to the following examples. All other embodiments obtained by those skilled in the art without creative effort without departing from the above-described methodological spirit of this application are within the scope of protection of this application.

[0041] The singular forms “for,” “or,” “a,” “any,” and “described” used in this application are intended to include the plural forms unless the context clearly indicates otherwise. Furthermore, the terms “first” and “second” are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0042] Example 1

[0043] like Figure 1 As shown, a method for preparing an organic stable fertilizer for rice includes the following steps:

[0044] S1. Mix 65 kg of tannic acid powder with a tannic acid content ≥80% and a particle size of 80 mesh, 6.5 kg of sodium hydroxide, and 374 L of deionized water. Stir at 55℃ and 350 r / min for 2 h. Add 1.88 L of hydrogen peroxide solution at a rate of 42 mL / min, wherein the mass fraction of hydrogen peroxide in the hydrogen peroxide solution is 30%. Maintain the system temperature at 60℃ and the stirring speed at 200 r / min during the addition process. After the addition, continue to react at 60℃ and 200 r / min for 45 min. Allow to cool naturally to room temperature. Adjust the pH of the system to 7.0 by adding 10% dilute hydrochloric acid at a rate of 4 mL / min. Let stand for 10 min, place in a vacuum drying oven at 60℃ and dry for 4 h. After pulverizing to 80 mesh, add 0.45 kg of trisodium citrate and put into a mixer. Stir at 200 r / min at room temperature for 10 min to obtain a dual-effect tannic acid inhibitor.

[0045] S2. Mix 7.5 kg of bentonite with 37.5 L of KH-550 aqueous solution, wherein the mass fraction of KH-550 in the KH-550 aqueous solution is 3%, stir at 25℃ and 200 r / min for 2 h (stop stirring for 5 min every 30 min), place in a constant temperature drying oven at 65℃ and dry for 2.5 h, pulverize to 80 mesh to obtain modified bentonite; mix 160 kg of lignite humic acid with a content ≥60% and a particle size of 0.3 mm, 122 kg of alkali lignin with a content ≥90 wt% and a particle size of 0.3 mm, and 80 kg of rice straw powder with a particle size of 0.7 mm at room temperature at 200 r / min for 15 min, then add 7.5 kg of modified bentonite, and continue mixing for 10 min to obtain a composite organic carbon source.

[0046] S3. 80 kg of agricultural straw-based biochar with a particle size of 0.2 mm was refluxed with 640 L of 10% nitric acid at 70 °C for 3 h. After the reaction, the mixture was filtered while hot, and the filter cake was repeatedly washed with deionized water until the pH of the washing liquid reached 6.5. The washed filter cake was then dried at 105 °C for 2.5 h to obtain modified biochar with a carboxyl content ≥3.5 mmol / g. 80 kg of modified biochar was put into a horizontal mixer, and 65 kg of tannic acid dual-effect inhibitor was dissolved in 325 L of ethanol-deionized water solution with a volume ratio of ethanol to deionized water of 16:309. Under the conditions of compressed air pressure of 0.45 MPa and liquid flow rate of 8 mL / min, the inhibitor solution was atomized and sprayed onto the carboxylated modified biochar. The stirring speed was maintained at 200 r / min during spraying, and stirring was continued for 15 min after spraying to obtain modified biochar loaded with tannic acid dual-effect inhibitor.

[0047] S4. Dissolve 12.5 kg of sodium silicate in 125 L of deionized water, adjust the pH to 8.5 with 10% hydrochloric acid, and prepare a sodium silicate solution. Add 370 kg of composite organic carbon source and 125 kg of decomposed livestock and poultry manure to the modified biochar-supported tannic acid dual-effect inhibitor, and mix at 200 r / min for 15 min to obtain a premix. Add 200 kg of urea, 90 kg of monoammonium phosphate, 50 kg of potassium chloride, and 4 kg of zinc sulfate heptahydrate to the premix, mix at 250 r / min for 10 min, and then spray the sodium silicate solution at a rate of 6.5 mL / min. Continue stirring for 10 min to obtain a fertilizer mixture.

[0048] S5. Mix 6.5 kg of hydroxypropyl starch with 13 L of deionized water and add it to the fertilizer mixture. While stirring, add more deionized water to adjust the moisture content of the mixture to 19%. Feed the mixture into a disc granulator at a feed rate of 110 kg / h and granulate it at a rotation speed of 35 r / min and a disc inclination angle of 45°. Control the particle size to 3 mm. Dry the wet granules at a constant temperature of 80°C for 30 min, and then let them cool naturally to room temperature. Sieve them through 2 mm and 4 mm sieves to obtain organic stable fertilizer for rice.

[0049] Example 2

[0050] like Figure 1 As shown, a method for preparing an organic stable fertilizer for rice includes the following steps:

[0051] S1. Mix 50 kg of tannic acid powder with a tannic acid content ≥80% and a particle size of 60 mesh, 5 kg of sodium hydroxide, and 283 L of deionized water. Stir at 55℃ and 350 r / min for 2 h. Add 1.4 L of hydrogen peroxide solution at a rate of 31 mL / min, wherein the mass fraction of hydrogen peroxide in the hydrogen peroxide solution is 30%. Maintain the system temperature at 55℃ and the stirring speed at 200 r / min during the addition process. After the addition, continue to react at 55℃ and 200 r / min for 40 min. Allow to cool naturally to room temperature. Adjust the pH of the system to 6.8 by adding 10% dilute hydrochloric acid at a rate of 4 mL / min. Let stand for 10 min, then dry in a vacuum drying oven at 55℃ for 3.5 h. After pulverizing to 70 mesh, add 0.25 kg of trisodium citrate and stir at 200 r / min at room temperature for 10 min to obtain a dual-effect tannic acid inhibitor.

[0052] S2. Mix 7 kg of bentonite with 35 L of KH-550 aqueous solution, wherein the mass fraction of KH-550 in the KH-550 aqueous solution is 3%. Stir for 1.5 h at 20℃ and 180 r / min (stop stirring for 5 min every 30 min), place in a 60℃ constant temperature drying oven to dry for 2 h, and pulverize to 70 mesh to obtain modified bentonite; Mix 150 kg of lignite humic acid with a content ≥60% and a particle size of 0.1 mm, 115 kg of alkali lignin with a content ≥90 wt% and a particle size of 0.1 mm, and 75 kg of rice straw powder with a particle size of 0.6 mm at 200 r / min at room temperature for 15 min, then add 7 kg of modified bentonite and continue mixing for 10 min to obtain a composite organic carbon source.

[0053] S3. 60 kg of agricultural straw-based biochar with a particle size of 0.1 mm was refluxed with 480 L of 10% nitric acid at 65 °C for 2.5 h. After the reaction, the mixture was filtered while hot, and the filter cake was repeatedly washed with deionized water until the pH of the washing solution was 6.5. The washed filter cake was then dried at 100 °C for 2 h to obtain modified biochar with a carboxyl content ≥3.5 mmol / g. 60 kg of modified biochar was put into a horizontal mixer, and 50 kg of tannic acid dual-effect inhibitor was dissolved in 250 L of ethanol-deionized water solution with a volume ratio of ethanol to deionized water of 12.5:237.5. Under the conditions of compressed air pressure of 0.4 MPa and liquid flow rate of 7 mL / min, the inhibitor solution was atomized and sprayed onto the carboxylated modified biochar. The stirring speed was maintained at 200 r / min during spraying, and stirring was continued for 15 min after spraying to obtain modified biochar loaded with tannic acid dual-effect inhibitor.

[0054] S4. Dissolve 10 kg of sodium silicate in 100 L of deionized water, adjust the pH to 8.0 with 10% dilute hydrochloric acid, and prepare a sodium silicate solution. Add 347 kg of composite organic carbon source and 100 kg of decomposed livestock and poultry manure to the modified biochar-supported tannic acid dual-effect inhibitor, mix at 200 r / min for 15 min to obtain a premix. Add 180 kg of urea, 80 kg of monoammonium phosphate, 40 kg of potassium chloride, and 3 kg of zinc sulfate heptahydrate to the premix, mix at 250 r / min for 10 min, then spray the sodium silicate solution at a rate of 5 mL / min, and continue stirring for 10 min to obtain a fertilizer mixture.

[0055] S5. Mix 5 kg of hydroxypropyl starch with 10 L of deionized water and add it to the fertilizer mixture. While stirring, add more deionized water to adjust the moisture content of the mixture to 18%. Feed the mixture into a disc granulator at a feed rate of 100 kg / h. Granulate the mixture at a speed of 30 r / min and a disc inclination angle of 40°. Control the particle size to 2 mm. Dry the wet granules at a constant temperature of 75°C for 25 min. Then, let them cool naturally to room temperature. Sieve them through 2 mm and 4 mm sieves to obtain organic stable fertilizer for rice.

[0056] Example 3

[0057] like Figure 1 As shown, a method for preparing an organic stable fertilizer for rice includes the following steps:

[0058] S1. Mix 80 kg of tannic acid powder with a tannic acid content ≥80% and a particle size of 100 mesh, 8 kg of sodium hydroxide, and 453 L of deionized water. Stir at 55℃ and 350 r / min for 2 h. Add 2.3 L of hydrogen peroxide solution at a rate of 51 mL / min, wherein the mass fraction of hydrogen peroxide in the hydrogen peroxide solution is 30%. Maintain the system temperature at 65℃ and the stirring speed at 200 r / min during the addition process. After the addition, continue to react at 65℃ and 200 r / min for 50 min. Allow to cool naturally to room temperature. Adjust the pH of the system to 7.2 by adding 10% dilute hydrochloric acid at a rate of 4 mL / min. Let stand for 10 min, then dry in a vacuum drying oven at 65℃ for 4.5 h. After pulverizing to 90 mesh, add 0.64 kg of trisodium citrate and stir at 200 r / min at room temperature for 10 min to obtain a dual-effect tannic acid inhibitor.

[0059] S2. Mix 8 kg of bentonite with 40 L of KH-550 aqueous solution, wherein the mass fraction of KH-550 in the KH-550 aqueous solution is 3%. Stir at 30℃ and 220 r / min for 2.5 h (stop stirring for 5 min every 30 min). Dry in a constant temperature drying oven at 70℃ for 3 h. Crush to 90 mesh to obtain modified bentonite. Mix 175 kg of lignite humic acid with a content ≥60% and a particle size of 0.5 mm, 130 kg of alkali lignin with a content ≥90 wt% and a particle size of 0.5 mm, and 85 kg of rice straw powder with a particle size of 0.8 mm at 200 r / min at room temperature for 15 min. Then add 8 kg of modified bentonite and continue mixing for 10 min to obtain a composite organic carbon source.

[0060] S3. 100 kg of agricultural straw-based biochar with a particle size of 0.3 mm was refluxed with 800 L of 10% nitric acid at 75℃ for 3.5 h. After the reaction, the mixture was filtered while hot, and the filter cake was repeatedly washed with deionized water until the pH of the washing solution reached 7.0. The washed filter cake was then dried at 110℃ for 3 h to obtain modified biochar with a carboxyl content ≥3.5 mmol / g. 100 kg of modified biochar was put into a horizontal mixer, and 80 kg of tannic acid dual-effect inhibitor was dissolved in 400 L of ethanol-deionized water solution with a volume ratio of ethanol to deionized water of 20:380. Under the conditions of compressed air pressure of 0.5 MPa and liquid flow rate of 9 mL / min, the inhibitor solution was atomized and sprayed onto the carboxylated modified biochar. The stirring speed was maintained at 200 r / min during spraying, and stirring was continued for 15 min after spraying to obtain modified biochar loaded with tannic acid dual-effect inhibitor.

[0061] S4. Dissolve 15 kg of sodium silicate in 150 L of deionized water, adjust the pH to 9.0 with 10% hydrochloric acid, and prepare a sodium silicate solution. Add 398 kg of composite organic carbon source and 150 kg of decomposed livestock and poultry manure to the modified biochar-supported tannic acid dual-effect inhibitor, mix at 200 r / min for 15 min to obtain a premix. Add 220 kg of urea, 100 kg of monoammonium phosphate, 60 kg of potassium chloride, and 5 kg of zinc sulfate heptahydrate to the premix, mix at 250 r / min for 10 min, then spray the sodium silicate solution at a rate of 8 mL / min, and continue stirring for 10 min to obtain a fertilizer mixture.

[0062] S5. Mix 8 kg of hydroxypropyl starch with 16 L of deionized water and add it to the fertilizer mixture. While stirring, add more deionized water to adjust the moisture content of the mixture to 20%. Feed the mixture into a disc granulator at a feed rate of 120 kg / h. Granulate the mixture at a speed of 40 r / min and a disc inclination angle of 50°. Control the particle size to 4 mm. Dry the wet granules at a constant temperature of 85°C for 35 min, and then let them cool naturally to room temperature. Sieve the mixture through 2 mm and 4 mm sieves to obtain organic stable fertilizer for rice.

[0063] Comparative Example 1

[0064] A method for preparing an organic stable fertilizer for rice differs from Example 1 in that the biochar in step S3 is not modified, while the remaining steps and parameters are the same.

[0065] Comparative Example 2

[0066] A method for preparing an organic stable fertilizer for rice differs from Example 1 in that step S1 does not involve preparing a tannic acid dual-effect inhibitor; instead, tannic acid powder is used directly to replace the tannic acid dual-effect inhibitor. The remaining steps and parameters are the same.

[0067] Comparative Example 3

[0068] A method for preparing an organic stable fertilizer for rice differs from Example 1 in that the composite organic carbon source is not prepared in step S2; that is, lignite humic acid is directly used to replace the composite organic carbon source. The remaining steps and parameters are the same.

[0069] Performance testing:

[0070] Urease inhibition rate test: 0.1g of fertilizer samples prepared in Examples 1-3 and Comparative Examples 1-3 and 5g of air-dried and sieved paddy field surface soil were placed in centrifuge tubes, and 10mL of urea aqueous solution with a concentration of 10mg / mL was added. At the same time, a blank control group was set up with no fertilizer sample and only an equal amount of urea aqueous solution added. All samples were placed in a constant temperature incubator at 25℃ and incubated in the dark for 24h. After the incubation, 25mL of potassium chloride solution with a concentration of 1mol / L was added, and the mixture was shaken and extracted for 30min. After filtration, the filtrate was used to determine the ammonia nitrogen content in the system using the phenol-sodium hypochlorite colorimetric method. Soil urease activity was calculated based on the ammonia nitrogen production of the blank control group and the treatment group. The calculation formula is: urease inhibition rate (%) = (urease activity of blank control group - urease activity of treatment group) / urease activity of blank control group × 100%. Three parallel determinations were set for each group, and the results are expressed as mean ± standard deviation.

[0071] Nitrification inhibition rate test: 0.1g of fertilizer samples prepared in Examples 1-3 and Comparative Examples 1-3 and 10g of air-dried and sieved paddy soil were placed in sealed culture bottles. 5mL of 5mg / mL ammonium sulfate aqueous solution was added to adjust the water content of the system to 60% of the soil field capacity. A blank control group was set up with no fertilizer sample and only an equal amount of ammonium sulfate aqueous solution added. All samples were placed in a constant temperature incubator at 25℃ and cultured in the dark for 7 days. After the culture was completed, 50mL of 1mol / L potassium chloride solution was added, and the mixture was shaken and extracted. After filtration, the nitrate nitrogen content in the filtrate was determined by ultraviolet spectrophotometry. The soil nitrification intensity was calculated based on the nitrate nitrogen production of the blank control group and the treatment group. The calculation formula is: nitrification inhibition rate (%) = (nitrification intensity of blank control group - nitrification intensity of treatment group) / nitrification intensity of blank control group × 100%. Three parallel determinations were set for each group. The results are expressed as mean ± standard deviation.

[0072] Soil ammonia volatilization loss rate test: The closed absorption method was used for testing. 0.2g of fertilizer samples prepared in Examples 1-3 and Comparative Examples 1-3 were mixed with 20g of air-dried and sieved paddy soil in a desiccator. The soil moisture content was adjusted to 60% of field capacity. 20mL of boric acid absorbent solution was placed inside the desiccator to capture volatilized ammonia. The desiccator was sealed and incubated at a constant temperature of 25℃ for 7 days. After incubation, the boric acid absorbent solution was titrated with a 0.1mol / L hydrochloric acid standard solution. The total ammonia volatilization was calculated based on the titration results. The calculation formula is: ammonia volatilization loss rate (%) = ammonia volatilization amount / total nitrogen input in fertilizer × 100%. Three parallel determinations were set for each group. The results are expressed as mean ± standard deviation.

[0073] Soil nitrate nitrogen leaching loss rate test: The soil column leaching method was used to simulate paddy field flooding conditions. 0.2g of fertilizer samples prepared in Examples 1-3 and Comparative Examples 1-3 were mixed evenly with 50g of air-dried and sieved paddy field soil and placed into a glass leaching soil column with an inner diameter of 5cm and a height of 20cm. 20mL of deionized water was added to the soil column at a uniform rate every day to simulate paddy field irrigation leaching. The leaching treatment was continued for 7 days. All leachate was collected and diluted to a fixed volume. The total nitrate nitrogen content in the leachate was determined by ultraviolet spectrophotometry. The calculation formula was: Nitrate nitrogen leaching loss rate (%) = Total nitrate nitrogen leaching amount / Total nitrogen input in fertilizer × 100%. Three parallel determinations were set up for each group. The results are expressed as mean ± standard deviation.

[0074] Organic carbon mineralization test: 0.10 g of fertilizer samples prepared in Examples 1-3 and Comparative Examples 1-3 were mixed evenly with 10 g of air-dried paddy field soil that had passed through a 2 mm sieve. The mixture was placed in a 100 mL culture bottle to simulate the flooding conditions during the rice tillering stage. The soil moisture content was adjusted to 100% of field capacity and cultured at 25°C in the dark until day 7. Subsequently, the soil moisture content was adjusted to 85% of field capacity to simulate wet irrigation during the booting stage and cultured for day 15. Finally, the soil moisture content was adjusted to 75% of field capacity to simulate alternating wet and dry conditions during the grain-filling stage and cultured for day 30. The amount of CO2 released from soil organic carbon mineralization was measured by alkaline absorption method on days 7, 15, and 30 and converted into the cumulative amount of mineralized carbon (calculated as C, mg). A blank control group without fertilizer was also set up. Each group was tested in triplicate. The results are expressed as mean ± standard deviation.

[0075] Table 1. Performance test results of fertilizers prepared in Examples 1-3 and Comparative Examples 1-3

[0076]

[0077] Table 2. Results of organic carbon mineralization at different time points for fertilizers prepared in Examples 1-3 and Comparative Examples 1-3.

[0078]

[0079] As shown in Table 1, the fertilizers of Examples 1-3 have higher urease inhibition rate, nitrification inhibition rate, and organic carbon mineralization at different time points than Comparative Examples 1-3. Furthermore, the ammonia volatilization loss rate and nitrate nitrogen leaching loss rate are lower than those of Comparative Examples 1-3. This indicates that the fertilizers prepared in Examples 1-3 have better dual-effect inhibition performance, nitrogen retention performance, and gradient carbon supply performance than Comparative Examples 1-3.

[0080] Comparative Example 1, lacking nitrate carboxylation modification, directly used unmodified biochar. This unmodified biochar lacks a multi-level porous structure and sufficient carboxyl active sites, failing to form a stable load and slow-release regulation for the dual-effect tannic acid inhibitor. Consequently, the inhibitor rapidly dissipates in the soil, significantly reducing its duration of action. This leads to a substantial weakening of the dual inhibition of urease and nitrification, making it difficult to effectively control nitrogen conversion and loss in paddy soil. Furthermore, the unmodified biochar exhibits weak compatibility and synergistic effect with organic carbon sources. It cannot assist in regulating the degradation rate of carbon sources through carrier structure, and it also reduces the overall mineralization efficiency of organic carbon sources, failing to provide a stable carbon source supply for rice growth, further weakening the overall application performance of the fertilizer.

[0081] Comparative Example 2 used unmodified tannic acid, which had not undergone alkaline hydrolysis and oxidation. Its molecular structure remained undepolymerized, and its internal active phenolic hydroxyl and carboxyl groups were not fully exposed. This made it difficult to form stable coordination complexes with the metal active centers of soil urease and nitrification-related enzymes, resulting in significantly weakened urease inhibition and nitrification inhibition effects. Consequently, it failed to effectively slow down the hydrolysis of urea and the nitrification conversion of ammonia nitrogen, thus exacerbating nitrogen losses in paddy soil, such as ammonia volatilization and nitrate leaching. Furthermore, the binding capacity of unmodified tannic acid to the modified biochar carrier was weak, making it difficult to form a stable slow-release system. This not only failed to achieve a continuous supply of inhibitors but also indirectly affected the degradation and release rhythm of organic carbon sources, reducing the overall synergistic effect of fertilizer in carbon supply and nitrogen retention.

[0082] Comparative Example 3, which used a single lignite humic acid source instead of a composite organic carbon source, lacked the synergistic effect of alkali lignin and rice straw powder. It could only achieve rapid carbon supply in the early stages, failing to form a gradient degradation carbon supply mode suitable for the entire rice growth cycle. In the later stages, insufficient carbon source supply made it difficult to meet the rice's growth needs. Furthermore, the single organic carbon source could not form a complete synergistic effect system with modified biochar and tannic acid dual-effect inhibitors. This weakened the supporting effect on fertilizer particle structure and reduced the chelation and retention capacity of soil nitrogen, indirectly leading to a decrease in the inhibition effects of urease and nitrification, and a corresponding increase in nitrogen loss. It could not achieve coordinated regulation of carbon supply and nitrogen retention, making it difficult to meet the long-term nutrient requirements of large-scale rice cultivation.

[0083] Comparative Examples 1-3, due to the lack of nitrate-modified biochar carrier, tannic acid dual-effect inhibitor, and core components of the composite organic carbon source, significantly reduced the dual-effect inhibition of soil urease and nitrification by fertilizer, significantly weakened nitrogen retention and storage capacity, and exacerbated nitrogen loss problems. At the same time, the organic carbon source could not form a gradient degradation carbon supply mode suitable for the rice growth period, resulting in a comprehensive deterioration of dual-effect inhibition performance, nitrogen retention performance, and gradient carbon supply performance.

[0084] The above results demonstrate and describe the basic principles and main features of this application, as well as its advantages.

[0085] The embodiments of the present invention have been described above with reference to the accompanying drawings. However, the present invention is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of the present invention without departing from the spirit and scope of the claims. All of these forms are within the protection scope of the present invention.

Claims

1. A stable organic fertilizer for rice, characterized in that, It includes modified biochar-supported tannic acid dual-effect inhibitors, composite organic carbon sources, nutrients, and adjuvants; The modified biochar loaded with tannic acid dual-effect inhibitor is obtained by dissolving the tannic acid dual-effect inhibitor in an ethanol-deionized aqueous solution and spraying it onto the modified biochar through atomization. The modified biochar is obtained by modifying biochar with nitric acid; The tannic acid dual-effect inhibitor is obtained by alkaline hydrolysis and oxidative modification of tannic acid powder; The composite organic carbon source includes lignite humic acid, alkali lignin, rice straw powder, and modified bentonite. The modified bentonite is obtained by modifying bentonite with a silane coupling agent; The nutrients include organic and inorganic nutrients; the organic nutrients are well-rotted livestock and poultry manure; the inorganic nutrients include urea, monoammonium phosphate, potassium chloride, and zinc sulfate heptahydrate. The additives include sodium silicate and hydroxypropyl starch.

2. The organic stabilized fertilizer for rice according to claim 1, characterized in that, The mass ratio of the modified biochar, tannic acid dual-effect inhibitor, composite organic carbon source, nutrients and adjuvants is (60-100):(50-80):(347-398):(403-535):(15-23); the mass ratio of the lignite humic acid, alkali lignin, rice straw powder and modified bentonite is (150-175):(115-130):(75-85):(7-8); the mass ratio of the decomposed livestock and poultry manure, urea, monoammonium phosphate, potassium chloride and zinc sulfate heptahydrate is (100-150):(180-220):(80-100):(40-60):(3-5); the mass ratio of the sodium silicate and hydroxypropyl starch is (10-15):(5-8).

3. The organic stabilized fertilizer for rice according to claim 1, characterized in that, The silane coupling agent is KH-550; the tannic acid powder has a tannic acid content ≥80% and a particle size of 60-100 mesh; the biochar is agricultural straw-based biochar with a particle size of 0.1-0.3 mm; the modified biochar has a carboxyl content ≥3.5 mmol / g; the lignite humic acid has a humic acid content ≥60% and a particle size of 0.1-0.5 mm; the alkali lignin has a lignin content ≥90% and a particle size of 0.1-0.5 mm; and the rice straw powder has a particle size of 0.6-0.8 mm.

4. A method for preparing an organic stable fertilizer for rice as described in any one of claims 1-3, characterized in that, include: S1. Mix tannic acid powder, sodium hydroxide and deionized water, add hydrogen peroxide solution dropwise, react, adjust pH with dilute hydrochloric acid, vacuum dry and pulverize, add trisodium citrate and mix to obtain a dual-effect tannic acid inhibitor. S2. Mix bentonite with an aqueous solution of silane coupling agent, stir, dry and pulverize to obtain modified bentonite; mix lignite humic acid, alkali lignin and rice straw powder, add modified bentonite to obtain a composite organic carbon source; S3. Mix biochar and nitric acid, reflux the reaction, filter, wash with water and dry to obtain modified biochar; dissolve the tannic acid dual-effect inhibitor in ethanol-deionized water solution and spray it onto the modified biochar by atomization to obtain modified biochar loaded with tannic acid dual-effect inhibitor. S4. Dissolve sodium silicate in deionized water and adjust the pH with hydrochloric acid to obtain a sodium silicate solution; mix modified biochar loaded with tannic acid dual-effect inhibitor, composite organic carbon source, and decomposed livestock and poultry manure to obtain a premix; add urea, monoammonium phosphate, potassium chloride, and zinc sulfate heptahydrate to the premix and mix; spray with sodium silicate solution to obtain a fertilizer mixture. S5. Mix hydroxypropyl starch with deionized water, add it to the fertilizer mixture, adjust the moisture content of the mixture, and then granulate, dry, and sieve to obtain organic stable fertilizer for rice.

5. The method for preparing an organic stable fertilizer for rice according to claim 4, characterized in that, In step S1, the mass-to-volume ratio of tannic acid powder, sodium hydroxide, deionized water, and hydrogen peroxide solution is (50-80) kg : (5-8) kg : (283-453) L : (1.4-2.3) L; the mass fraction of the hydrogen peroxide solution is 30%; the dropping rate is 31-51 mL / min; the reaction temperature is 55-65℃, and the reaction time is 40-50 min; the mass fraction of the dilute hydrochloric acid is 10%; the pH value is adjusted to 6.8-7.2; the vacuum drying temperature is 55-65℃, and the vacuum drying time is 3.5-4.5 h; the particle size of the pulverized material is 70-90 mesh; and the mass ratio of tannic acid powder to trisodium citrate is (50-80) : (0.25-0.64).

6. The method for preparing an organic stable fertilizer for rice according to claim 4, characterized in that, In step S2, the mass-to-volume ratio of bentonite to the silane coupling agent aqueous solution is (7-8) kg:(35-40) L; the mass fraction of the silane coupling agent in the aqueous solution is 3%; the stirring temperature is 20-30℃, the stirring speed is 180-220 r / min, and the stirring time is 1.5-2.5 h; the drying temperature is 60-70℃, and the drying time is 2-3 h; the particle size of the pulverized material is 70-90 mesh.

7. The method for preparing an organic stable fertilizer for rice according to claim 4, characterized in that, In step S3, the mass-to-volume ratio of biochar to nitric acid is (60-100) kg:(480-800) L; the mass fraction of nitric acid is 10%; the reflux reaction temperature is 65-75℃, and the reflux reaction time is 2.5-3.5 h; the water washing step is: repeatedly washing with deionized water until the pH is 6.5-7.0; the drying temperature is 100-110℃, and the drying time is 2-3 h; the mass-to-volume ratio of the tannic acid dual-effect inhibitor to the ethanol-deionized aqueous solution is (50-80) kg:(250-400) L; the volume ratio of ethanol to deionized water in the ethanol-deionized aqueous solution is (12.5-20):(237.5-380); the atomization spraying conditions are: atomization pressure 0.4-0.5 MPa, flow rate 7-9 mL / min.

8. The method for preparing an organic stable fertilizer for rice according to claim 4, characterized in that, In step S4, the mass-to-volume ratio of sodium silicate to deionized water is (10-15) kg:(100-150) L; the mass fraction of hydrochloric acid is 10%; the pH value is adjusted to 8.0-9.0; and the spraying rate is 5-8 mL / min.

9. The method for preparing an organic stable fertilizer for rice according to claim 4, characterized in that, In step S5, the mass-to-volume ratio of hydroxypropyl starch to deionized water is (5-8) kg:(10-16) L; the method for adjusting the moisture content of the mixture is to supplement with deionized water, and the range of the moisture content of the mixture is 18%-20%; the granulation step is to granulate under the conditions of a feeding rate of 100-120 kg / h, a rotation speed of 30-40 r / min, and a disc tilt angle of 40-50°, and control the particle size to be 2-4 mm; the drying temperature is 75-85℃, and the drying time is 25-35 min; the sieving step is to sieve the mixture sequentially through 2 mm and 4 mm sieves.

10. The application of an organic stable fertilizer for rice as described in any one of claims 1-3 in the process of increasing rice yield and improving rice quality.

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