Multifunctional high-efficiency carbon sequestration fertilizer based on iron-based nanoparticles addition and preparation method thereof

Abstract

The application provides a multifunctional high-efficiency carbon fixation fertilizer based on iron-based nanoparticle addition and a preparation method thereof, and belongs to the technical field of agricultural fertilizers.The application realizes the organic combination of organic fertilizer and inorganic fertilizer through the multi-element compounding of raw materials, can effectively promote the conversion of organic matter in the organic fertilizer into soil organic matter by adding iron-based nanoparticles such as nano-Fe3O4 or nano-zero-valent iron as the main representative under the condition of ensuring sufficient supply of crop nutrients, and significantly improves the soil carbon fixation capacity.The application does not reduce the efficacy of microbial agents and humic acid, can improve soil microbial activity, is environmentally friendly, can promote plant growth and development, and improves crop yield and quality.The multifunctional fertilizer prepared by the application has good fertilizer slow-release effect, long slow-release time, simple preparation method, low cost, and good popularization and application value.

Description

Technical Field

[0001] This invention relates to the field of agricultural fertilizer technology, and in particular to a multifunctional and efficient carbon-fixing fertilizer based on the addition of iron-based nanoparticles and its preparation method. Background Technology

[0002] Traditional fertilizers face the problem of low nutrient utilization efficiency in agricultural production, especially for key nutrients such as nitrogen and phosphorus. Due to factors such as soil adsorption, leaching, or volatilization, the actual proportion absorbed by crops is insufficient. This not only increases fertilization costs but may also lead to environmental risks such as soil compaction and eutrophication of water bodies. To improve nutrient utilization efficiency, some studies have attempted to extend the fertilizer's action time by adding slow-release agents or coating materials. However, these methods have limited effects on improving carbon fixation capacity and may affect fertilizer efficacy stability due to a mismatch between the material's degradation rate and crop requirements.

[0003] In recent years, integrating carbon fixation into fertilizer systems has become a research hotspot, such as using biochar or organic materials as carriers to adsorb carbon dioxide. However, conventional carbon fixation materials generally suffer from rapid mineralization rates and short-lived effects, and are easily decomposed by microorganisms in the soil, making it difficult to achieve long-term carbon fixation goals. Furthermore, some materials have a single mode of binding with fertilizer nutrients, failing to effectively coordinate the dynamic balance between carbon fixation and nutrient release, leading to insufficient nutrient supply during critical crop growth periods and limiting further improvements in fertilizer efficiency.

[0004] Iron-based materials have attracted attention in soil improvement due to their environmental friendliness and redox activity. Previous studies have used iron oxides for passivation of heavy metals or adjustment of soil pH; however, traditional iron-based materials have small specific surface areas and insufficient reaction sites, resulting in weak synergistic effects with fertilizer components. Although nanotechnology provides new avenues for optimizing material performance, the application of iron-based nanoparticles in fertilizers still faces technical bottlenecks: on the one hand, nanoparticles are prone to aggregation due to excessively high surface energy, reducing dispersion uniformity and nutrient binding efficiency; on the other hand, existing preparation processes struggle to precisely control the crystal structure and surface modification of nanoparticles, leading to suboptimal migration, stability, and nutrient slow-release effects in soil. These issues prevent the full realization of the potential of iron-based nanomaterials in enhancing fertilizer efficiency, thus limiting the practical application of multifunctional carbon-fixing fertilizers. Summary of the Invention

[0005] The purpose of this invention is to provide a multifunctional and efficient carbon-fixing fertilizer based on the addition of iron-based nanoparticles and its preparation method, which has excellent fertilizer effect.

[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0007] This invention provides a carbon-fixing multi-element fertilizer, the raw materials of which, by mass parts, comprise:

[0008] The ingredients are: 35-40 parts corn stalk pellets, 20-25 parts well-rotted pig manure pellets, 0.1-0.15 parts nano-ferric oxide, 0.08-0.12 parts nano-zero ferric oxide, 5-6 parts humic acid, 0.5-0.7 parts compound microbial agent, 12-15 parts urea, 6-8 parts potassium dihydrogen phosphate, 5-6 parts potassium chloride, 0.3-0.4 parts boric acid, 0.4-0.6 parts potassium hydroxide, and 2.5-3 parts liquid-modified hydrophilic polyurethane resin.

[0009] Preferably, the organic matter content of the decomposed pig manure pellets is ≥45%.

[0010] Preferably, the composite microbial agent contains Bacillus subtilis and Bacillus mucilaginosus in a live bacteria ratio of 2:1.

[0011] Preferably, the specific surface area of ​​the nano-tetraoxide or nano-zero-valent iron nanoparticles is ≥50m². 2 / g.

[0012] The present invention also provides a method for preparing the above-mentioned carbon-fixing multi-element fertilizer, comprising the following steps:

[0013] (1) Mix corn stalks with well-rotted pig manure and then crush them to form a mixed base;

[0014] (2) Mix the compound microbial agent, urea, nano iron tetroxide, nano zero-valent iron, humic acid, potassium dihydrogen phosphate and potassium chloride, heat to 75-85℃ and stir continuously at 180-220 rpm for 30-50 minutes to obtain a suspension.

[0015] (3) Dilute the suspension obtained in step (2) with water and spray it onto the mixed substrate to obtain a wetted material;

[0016] (4) The wet material is rolled and granulated in a drum granulator. Liquid modified hydrophilic polyurethane resin is added in batches during the granulation process, with the total amount added being 2.5% to 3% of the total mass of the material.

[0017] (5) The obtained granules are dried at 35-45℃ until the moisture content is ≤8% to obtain the carbon-fixing multi-element fertilizer.

[0018] Preferably, in step (1), the particles that are crushed to a size of less than 1 cm account for more than 90% of the total particles.

[0019] Preferably, the heating rate in step (2) is 2-3 °C / min, and the oxygen content of the system is kept ≤5% during stirring.

[0020] Preferably, the granulation temperature in step (4) is controlled at 45-55℃, the particle diameter is controlled at 2.5-4.5mm, and the roundness is ≥85%.

[0021] The present invention also provides the application of the above-mentioned carbon-fixing multi-element fertilizer in crop cultivation, wherein the crop includes rice, tomato or corn, and the application method includes basal application and topdressing combined application.

[0022] Preferably, for rice, the total application rate is 750-850 kg / ha, of which 70-80% is applied as basal fertilizer; for tomatoes, the total application rate is 900-1100 kg / ha; and for corn, the total application rate is 800-1000 kg / ha.

[0023] The technical effects and advantages of this invention are as follows:

[0024] This invention achieves the organic combination of organic and inorganic fertilizers through the multi-component compounding of raw materials. While ensuring sufficient nutrient supply to crops, the addition of iron-based nanoparticles, primarily nano-ferric oxide or nano-zero-valent iron, effectively promotes the conversion of organic matter in organic fertilizers into soil organic matter, significantly improving soil carbon sequestration capacity. This invention does not reduce the efficacy of microbial agents and humic acid, and can enhance soil microbial activity. It is environmentally friendly and can also promote plant growth and development, increasing crop yield and quality. The multi-component fertilizer prepared by this invention has good slow-release effect, long slow-release time, simple preparation method, and low cost, making it highly valuable for widespread application.

[0025] This invention's fertilizer has demonstrated significant dual advantages in field trials: enhanced carbon sequestration and increased yield. By optimizing the synergistic release pattern of carbon and nitrogen, it maintains a more stable soil carbon pool level throughout the entire crop growth cycle, while extending the effective nitrogen nutrient supply period. This allows for precise matching of nutrient requirements during key growth stages of crops such as rice and corn, ultimately achieving simultaneous increases in yield and fruit nutritional quality, while significantly reducing environmental emissions. This innovative technical solution couples the function of iron-based materials with agronomic requirements, resolving the core contradiction of the mismatch between mineralization rate and nutrient release in traditional carbon sequestration fertilizers. Through the synergistic design of the material-soil-crop system, it achieves simultaneous optimization of soil carbon sequestration intensity and fertilizer utilization efficiency without relying on exogenous additives, providing a novel technological carrier for green agricultural production that combines carbon reduction and yield increase potential. Detailed Implementation

[0026] This invention provides a carbon-fixing multi-element fertilizer, comprising, by weight parts: 35-40 parts corn stalk granules, 20-25 parts well-rotted pig manure granules, 0.1-0.15 parts nano-ferric oxide, 0.08-0.12 parts nano-zero-valent iron, 5-6 parts humic acid, 0.5-0.7 parts compound microbial agent, 12-15 parts urea, 6-8 parts potassium dihydrogen phosphate, 5-6 parts potassium chloride, 0.3-0.4 parts boric acid, 0.4-0.6 parts potassium hydroxide, and 2.5-3 parts liquid-modified hydrophilic polyurethane resin. Preferably, the organic matter content of the well-rotted pig manure granules is ≥45%. Preferably, the compound microbial agent comprises Bacillus subtilis and Bacillus mucilaginosa in a live bacteria ratio of 2:1. Preferably, the specific surface area of ​​the nano-ferric oxide or nano-zero-valent iron nanoparticles is ≥50 m². 2 / g.

[0027] The present invention also provides a method for preparing the above-mentioned carbon-fixing multi-element fertilizer, comprising the following steps: (1) mixing corn stalks with well-rotted pig manure and then crushing them to form a mixed base; (2) mixing compound microbial agent, urea, nano-iron tetroxide, nano-zero-valent iron, humic acid, potassium dihydrogen phosphate and potassium chloride, heating to 75-85°C and stirring continuously at 180-220 rpm for 30-50 minutes to obtain a suspension; (3) diluting the suspension obtained in step (2) with water and spraying it onto the mixed base to obtain a moist material; (4) granulating the moist material in a roller granulator, adding liquid modified hydrophilic polyurethane resin in batches during the granulation process, the total amount added being 2.5%-3% of the total mass of the material; (5) drying the obtained granules at 35-45°C until the moisture content is ≤8% to obtain the carbon-fixing multi-element fertilizer.

[0028] Preferably, in step (1), more than 90% of the pulverized particles have a particle size of less than 1 cm. Preferably, in step (2), the heating rate is 2-3℃ / min, and the oxygen content of the system is kept ≤5% during stirring. Preferably, in step (4), the granulation temperature is controlled at 45-55℃, the particle diameter is controlled at 2.5-4.5 mm, and the roundness is ≥85%. The present invention also provides the application of the above-mentioned carbon-fixing multi-element fertilizer in crop planting, wherein the crops include rice, tomato, or corn, and the application method includes a combination of basal application and topdressing. Preferably, for rice, the total application rate is 750-850 kg / ha, of which 70-80% is basal application; for tomatoes, the total application rate is 900-1100 kg / ha; and for corn, the total application rate is 800-1000 kg / ha.

[0029] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0030] Example 1

[0031] This embodiment provides a carbon-fixing multi-element fertilizer based on iron-based nanoparticles and its preparation method. The raw material composition, by mass parts, is as follows: 38 parts corn stalk granules, 22 parts well-rotted pig manure granules, 0.12 parts nano-ferric oxide, 0.09 parts nano-zero-valent iron, 5.5 parts humic acid, 0.6 parts composite microbial agent (the ratio of viable Bacillus subtilis to Bacillus mucilaginosus is 2:1), 13.5 parts urea, 7.2 parts potassium dihydrogen phosphate, 5.8 parts potassium chloride, 0.35 parts boric acid, 0.5 parts potassium hydroxide, and 2.8 parts liquid-modified hydrophilic polyurethane resin. The organic matter content of the well-rotted pig manure granules is ≥45%.

[0032] The preparation method is carried out according to the following steps: Corn stalks are mixed with well-rotted pig manure and then mechanically crushed until over 90% of the particles are less than 1 cm in diameter to form a mixed substrate; a compound microbial agent and urea are stirred at 180 rpm for 20 minutes at 28±2℃ to form a homogeneous mixture; nano-ferric oxide, nano-zero-valent iron, humic acid, potassium dihydrogen phosphate, and potassium chloride are added sequentially to the mixture, and the mixture is heated to 80℃ and stirred continuously at 200 rpm for 40 minutes to obtain a viscous suspension; the suspension is diluted with water at a mass ratio of 1:1000 and then evenly sprayed onto the mixed substrate, controlling the material moisture content within the range of 28%–32%; finally, the moistened material is granulated in a drum granulator at a speed of 12 rpm, with liquid-modified hydrophilic polyurethane resin added evenly in three batches at 2.8% of the total material mass during granulation to form regular particles with a diameter of 3–4 mm. The finished product is dried with hot air at 40℃ until the particle moisture content is ≤8%.

[0033] Example 2

[0034] This embodiment provides a carbon-fixing multi-element fertilizer based on iron-based nanoparticles and its preparation method. The raw material composition, by mass parts, is as follows: 35 parts corn stalk granules, 25 parts well-rotted pig manure granules, 0.15 parts nano-ferric oxide, 0.12 parts nano-zero-valent iron, 6.0 parts humic acid, 0.8 parts compound microbial agent (the ratio of viable bacteria of Bacillus subtilis to Bacillus mucilaginosus is 2:1), 15 parts urea, 6.8 parts potassium dihydrogen phosphate, 6.2 parts potassium chloride, 0.40 parts boric acid, 0.6 parts potassium hydroxide, and 3.0 parts liquid-modified hydrophilic polyurethane resin. The organic matter content of the well-rotted pig manure granules is ≥45%.

[0035] The preparation method is carried out according to the following steps: Corn stalks are mixed with well-rotted pig manure and then mechanically crushed until over 90% of the particles are less than 1 cm in diameter to form a mixed substrate; a compound microbial agent and urea are stirred at 200 rpm for 25 minutes at 30±2℃ to form a homogeneous mixture; nano-ferric oxide, nano-zero-valent iron, humic acid, potassium dihydrogen phosphate, and potassium chloride are added sequentially to the mixture, and the mixture is heated to 85℃ and continuously stirred at 220 rpm for 45 minutes to obtain a viscous suspension; the suspension is diluted with water at a mass ratio of 1:1200 and then evenly sprayed onto the mixed substrate, controlling the material moisture content within the range of 30%–34%; finally, the moistened material is granulated in a drum granulator at a speed of 15 rpm, with liquid-modified hydrophilic polyurethane resin added evenly in three batches at 3.0% of the total material mass during granulation to form regular particles with a diameter of 3–5 mm. The finished product is dried with hot air at 45℃ until the particle moisture content is ≤8%.

[0036] Example 3

[0037] This embodiment provides a carbon-fixing multi-element fertilizer based on iron-based nanoparticles and its preparation method. The raw material composition, by mass parts, is as follows: 40 parts corn stalk granules, 20 parts well-rotted pig manure granules, 0.10 parts nano-ferric oxide, 0.08 parts nano-zero-valent iron, 5.0 parts humic acid, 0.5 parts compound microbial agent (the ratio of viable bacteria of Bacillus subtilis to Bacillus mucilaginosus is 2:1), 12 parts urea, 7.5 parts potassium dihydrogen phosphate, 5.5 parts potassium chloride, 0.30 parts boric acid, 0.4 parts potassium hydroxide, and 2.5 parts liquid-modified hydrophilic polyurethane resin. The organic matter content of the well-rotted pig manure granules is ≥45%.

[0038] The preparation method is carried out according to the following steps: Corn stalks are mixed with well-rotted pig manure and then mechanically crushed until more than 90% of the particles are less than 1 cm in diameter, forming a mixed substrate. A compound microbial agent and urea are stirred at 150 rpm for 15 minutes at 25±2℃ to form a homogeneous mixture. Nano-ferric oxide, nano-zero-valent iron, humic acid, potassium dihydrogen phosphate, and potassium chloride are added sequentially to the mixture. The mixture is heated to 75℃ and stirred continuously at 180 rpm for 35 minutes to obtain a viscous suspension. The suspension is diluted with water at a mass ratio of 1:800 and then evenly sprayed onto the mixed substrate, controlling the material moisture content within the range of 26%–30%. Finally, the moistened material is granulated in a drum granulator at a speed of 10 rpm. During granulation, liquid-modified hydrophilic polyurethane resin is added three times at 2.5% of the total material mass to form regular particles with a diameter of 2–3 mm. The finished product is dried with hot air at 35℃ until the particle moisture content is ≤8%.

[0039] Example 4

[0040] This embodiment provides a carbon-fixing multi-element fertilizer based on iron-based nanoparticles and its preparation method. The raw material composition, by mass parts, is as follows: 36 parts corn stalk granules, 24 parts well-rotted pig manure granules, 0.14 parts nano-ferric oxide, 0.10 parts nano-zero-valent iron, 5.8 parts humic acid, 0.7 parts compound microbial agent (the ratio of viable Bacillus subtilis to Bacillus mucilaginosus is 2:1), 14 parts urea, 7.0 parts potassium dihydrogen phosphate, 6.0 parts potassium chloride, 0.38 parts boric acid, 0.55 parts potassium hydroxide, and 2.9 parts liquid-modified hydrophilic polyurethane resin. The organic matter content of the well-rotted pig manure granules is ≥45%.

[0041] The preparation method is carried out according to the following steps: Corn stalks are mixed with well-rotted pig manure and then mechanically crushed until over 90% of the particles are less than 1 cm in diameter to form a mixed substrate; a compound microbial agent and urea are stirred at 190 rpm for 22 minutes at 29±2℃ to form a homogeneous mixture; nano-ferric oxide, nano-zero-valent iron, humic acid, potassium dihydrogen phosphate, and potassium chloride are added sequentially to the mixture, and the mixture is heated to 82℃ and continuously stirred at 210 rpm for 42 minutes to obtain a viscous suspension; the suspension is diluted with water at a mass ratio of 1:1100 and then evenly sprayed onto the mixed substrate, controlling the material moisture content within the range of 29%–31%; finally, the moistened material is granulated in a drum granulator at a speed of 13 rpm, with liquid-modified hydrophilic polyurethane resin added evenly in three batches at 2.9% of the total material mass during granulation to form regular particles with a diameter of 3.5–4.5 mm. The finished product is dried with hot air at 42℃ until the particle moisture content is ≤8%.

[0042] Example 5

[0043] This embodiment provides a carbon-fixing multi-element fertilizer based on iron-based nanoparticles and its preparation method. The raw material composition, by mass parts, is as follows: 37 parts corn stalk granules, 23 parts well-rotted pig manure granules, 0.13 parts nano-ferric oxide, 0.09 parts nano-zero-valent iron, 5.6 parts humic acid, 0.65 parts composite microbial agent (the ratio of viable Bacillus subtilis to Bacillus mucilaginosus is 2:1), 13.8 parts urea, 7.3 parts potassium dihydrogen phosphate, 5.9 parts potassium chloride, 0.36 parts boric acid, 0.52 parts potassium hydroxide, and 2.85 parts liquid-modified hydrophilic polyurethane resin. The organic matter content of the well-rotted pig manure granules is ≥45%.

[0044] The preparation method is carried out according to the following steps: Corn stalks are mixed with well-rotted pig manure and then mechanically crushed until over 90% of the particles are less than 1 cm in diameter to form a mixed substrate; a compound microbial agent and urea are stirred at 175 rpm for 18 minutes at 27±2℃ to form a homogeneous mixture; nano-ferric oxide, nano-zero-valent iron, humic acid, potassium dihydrogen phosphate, and potassium chloride are added sequentially to the mixture, and the mixture is heated to 78℃ and continuously stirred at 195 rpm for 38 minutes to obtain a viscous suspension; the suspension is diluted with water at a mass ratio of 1:950 and then evenly sprayed onto the mixed substrate, controlling the material moisture content within the range of 27%–29%; finally, the moistened material is granulated in a drum granulator at a speed of 11 rpm, with liquid-modified hydrophilic polyurethane resin added evenly in three batches at 2.7% of the total material mass during granulation to form regular particles with a diameter of 3.2–3.8 mm. The finished product is dried with hot air at 38℃ until the particle moisture content is ≤8%.

[0045] Comparative Example 1

[0046] This comparative example provides a carbon-fixing multi-element fertilizer based on iron-based nanoparticles and its preparation method. The raw material composition, by mass parts, is as follows: 38 parts corn stalk granules, 22 parts well-rotted pig manure granules, 5.5 parts humic acid, 0.6 parts compound microbial agent (the ratio of viable Bacillus subtilis to Bacillus mucilaginosus is 2:1), 13.5 parts urea, 7.2 parts potassium dihydrogen phosphate, 5.8 parts potassium chloride, 0.35 parts boric acid, 0.5 parts potassium hydroxide, and 2.8 parts liquid-modified hydrophilic polyurethane resin. The organic matter content of the well-rotted pig manure granules is ≥45%.

[0047] The preparation method is carried out according to the following steps: Corn stalks are mixed with well-rotted pig manure and then mechanically crushed until over 90% of the particles are less than 1 cm in diameter, forming a mixed substrate. The compound microbial agent and urea are stirred at 180 rpm for 20 minutes at 28±2℃ to form a homogeneous mixture. Humic acid, potassium dihydrogen phosphate, and potassium chloride are added to the mixture sequentially, and the mixture is heated to 80℃ and stirred continuously at 200 rpm for 40 minutes to obtain a viscous suspension. The suspension is diluted with water at a mass ratio of 1:1000 and then evenly sprayed onto the mixed substrate, controlling the material moisture content within the range of 28%–32%. Finally, the moistened material is granulated in a drum granulator at a speed of 12 rpm. During granulation, liquid-modified hydrophilic polyurethane resin is added three times at 2.8% of the total material mass to form regular particles with a diameter of 3–4 mm. The finished product is dried with hot air at 40℃ until the particle moisture content is ≤8%.

[0048] Experimental Example

[0049] I. Experimental Design and Implementation

[0050] To systematically verify the comprehensive effects of this fertilizer on soil improvement, slow-release of nutrients, and increased crop yield and quality, field trials were conducted on three representative crops: rice, tomato, and corn. The experimental field was located in the warm temperate monsoon climate zone at 32°18′N, with an average annual temperature of 14.6℃ and an annual precipitation of 920 mm. Three treatment groups were set up: Group T1 received the carbon-fixing multi-element fertilizer prepared in Example 1; Group T2 received the control fertilizer (Comparative Example 1) with iron-based nanoparticles removed; and Group CK received commercially available 15-15-15 compound fertilizer. All treatment groups were adjusted for nitrogen content based on the iso-nitrogen principle (total nitrogen content difference ≤ 2.5%). Each treatment was replicated four times using a randomized block design with a plot area of ​​30 m². 2 The experimental field had uniform basic fertility (coefficient of variation <8%). Before sowing, 15t / ha of well-rotted cow manure was applied uniformly and the soil was plowed to a depth of 25cm.

[0051] II. Crop Planting and Management Plan

[0052] (I) Rice Field Trials

[0053] The japonica rice variety Ningjing 7 was selected. Seedlings were raised in dry conditions on April 10th and mechanically transplanted on May 20th, with a row spacing of 25cm × 13cm. The T1 group received 600kg / ha of basal fertilizer and 150kg / ha of topdressing during tillering; the CK group received 480kg / ha of compound fertilizer as basal fertilizer and 75kg / ha of urea as topdressing during tillering. Shallow water management (3-5cm) was implemented throughout the growth period, and the field was dried for 7 days at the end of tillering to control tillering. Tiller number, plant height, and SPAD value of the second leaf from the top were measured at 30, 60, and 90 days after transplanting. Rhizosphere soil samples were collected at harvest, and the organic carbon content of the 0-20cm soil layer was measured.

[0054] (II) Experiment on greenhouse cultivation of tomatoes

[0055] The Jinpeng No. 8 tomato variety was selected. Seedlings were raised in plug trays on February 15th and transplanted into a greenhouse on March 25th, using double-row raised bed cultivation (plant spacing 45cm, row spacing 60cm). The T1 group received 800kg / ha of basal fertilizer and 200kg / ha of topdressing at the initial flowering stage; the CK group received 640kg / ha of compound fertilizer as basal fertilizer and 90kg / ha of urea as topdressing. Soil moisture content was monitored using a tensiometer to maintain field water holding capacity at 70%-80%. Rhizosphere soil samples were collected at the fruit setting and color-changing stages to determine microbial biomass carbon and phosphatase activity. Soluble solids and vitamin C content in the fruit were measured at maturity.

[0056] (III) Field Trials of Maize

[0057] Planting variety: Fumin 985, mechanical precision sowing on April 25 (density 67,500 plants / ha). Group T1 received 700 kg / ha of basal fertilizer and 200 kg / ha of topdressing at the large trumpet stage; Group CK received 560 kg / ha of compound fertilizer as basal fertilizer and 105 kg / ha of urea as topdressing. Plant height, stem diameter, and leaf area index were measured at the jointing, tasseling, and grain-filling stages. Simultaneously, leachate samples were collected at a depth of 20 cm to analyze the dynamic changes in ammonium nitrogen. Crude protein content of the grains was measured after harvest.

[0058] III. Dynamic Monitoring and Analysis Methods

[0059] (I) Soil Parameter Testing

[0060] Organic carbon content: The potassium dichromate external heating method was used. Mixed soil samples of 0-20cm were collected from each plot using the five-point sampling method. After drying at 105℃, the samples were passed through a 0.25mm sieve. The average value was obtained after three repeated measurements.

[0061] Microbial activity: Microbial biomass carbon was determined by chloroform fumigation-K2SO4 extraction, phosphatase activity was determined by p-nitrophenyl phosphate method, and urease activity was determined by NH4+ after 24 h of incubation. + -N generation quantity characterization.

[0062] Nutrient release dynamics: Clay head percolators were buried at a depth of 20cm in each plot, and leachate was collected weekly. Ammonium nitrogen was determined by Nessler's reagent colorimetric method, nitrate nitrogen was determined by ultraviolet spectrophotometry (dual wavelength correction), and available phosphorus was determined by molybdenum antimony colorimetric method.

[0063] (II) Crop Indicator Measurement

[0064] Yield composition: Rice is calculated at 5m 2 Actual yield measurement includes determining the number of effective ears, the number of grains per ear, and the weight of 1000 grains; for tomatoes, the number of fruits per plant and the weight of a single fruit are counted when harvesting the middle two rows; for corn, the ear length, tip barrenness length, and weight of 100 grains are measured when harvesting the middle four rows.

[0065] Quality analysis: The amylose content of rice was determined according to GB / T 15683; the soluble solids content of tomatoes was determined using a digital refractometer; and the crude protein content of corn was determined by the Kjeldahl method (conversion factor 6.25).

[0066] IV. Experimental Results and Data Analysis

[0067] Table 1. Dynamic changes in soil improvement effects (paddy field)

[0068]

[0069]

[0070] Table 2 Correlation between tomato quality and rhizosphere microenvironment

[0071] index Group T1 Group T2 CK group Soluble solids (°Brix) 5.82±0.26a 5.17±0.29b 4.88±0.23c Vitamin C (mg / 100g) 22.3±1.7a 19.5±1.5b 17.1±1.3c <![CDATA[Actinomycetes (×10 4 CFU / g)]]> 8.6±0.5a 6.2±0.4b 4.8±0.3c Phosphatase activity (μmol / g / h) 4.08±0.27a 3.53±0.23b 2.95±0.20c

[0072] Table 3. Nutrient release characteristics during maize growth period

[0073]

[0074] Table 4 Effects of Crop Yield and Quality Improvement

[0075]

[0076]

[0077] V. Conclusion Verification and Mechanism of Action

[0078] Enhancing soil carbon sequestration: After rice harvest, the soil organic carbon content in group T1 reached 16.8 g / kg, an increase of 33.3% compared to group CK (p<0.01), and differences were already evident during the tillering peak stage (14.7 vs 12.8 g / kg), indicating that iron-based nanoparticles can accelerate organic matter transformation. Microbial biomass carbon and urease activity increased by 46.4% and 30.6%, respectively, verifying its biological pathway for promoting carbon fixation.

[0079] Nutrient slow-release characteristics: The soil ammonium nitrogen concentration in group T1 (8.4 mg / L) during the maize jointing stage was 51.4% lower than that in group CK, and remained at 6.9 mg / L during the grain-filling stage, indicating that the fertilizer release cycle was extended by 35-40 days. Nitrogen use efficiency increased to 61.2%, reducing nitrogen loss by 28.6% compared with conventional fertilization.

[0080] Mechanism of crop quality improvement: The number of rhizosphere actinomycetes in tomatoes was significantly positively correlated with vitamin C content (r = 0.796, p < 0.05). The phosphatase activity in the T1 group was 38.3% higher than that in the CK group, which confirmed that iron-based nanoparticles promote nutrient activation by regulating the microbial community, thereby improving the nutritional quality of fruits.

[0081] Overall yield increase: The yield of the three types of crops increased by 9.2%-11.5%, with the number of effective panicles of rice increasing by 14.2% (T1: 325 panicles / m²). 2 vs CK: 285 ears / m 2 The 100-kernel weight of corn increased by 6.8% (T1: 36.4g vs CK: 34.1g), and all quality indicators showed significant differences (p<0.05).

[0082] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A carbon-fixing multi-element fertilizer specifically for rice, tomatoes, or corn, characterized in that, Raw materials, by weight, include: The ingredients are: 35-40 parts corn stalk pellets, 20-25 parts well-rotted pig manure pellets, 0.1-0.15 parts nano-ferric oxide, 0.08-0.12 parts nano-zero ferric oxide, 5-6 parts humic acid, 0.5-0.7 parts compound microbial agent, 12-15 parts urea, 6-8 parts potassium dihydrogen phosphate, 5-6 parts potassium chloride, 0.3-0.4 parts boric acid, 0.4-0.6 parts potassium hydroxide, and 2.5-3 parts liquid-modified hydrophilic polyurethane resin. The compound microbial agent contains Bacillus subtilis and Bacillus mucilaginosus in a live bacteria ratio of 2:

1. The preparation method of the carbon-fixing multi-element fertilizer includes the following steps: (1) Mix corn stalks with well-rotted pig manure and then crush them to form a mixed base; (2) Mix the compound microbial agent, urea, nano iron tetroxide, nano zero-valent iron, humic acid, potassium dihydrogen phosphate and potassium chloride, heat to 75~85℃ and stir continuously at 180~220 rpm for 30~50 minutes to obtain a suspension. (3) Dilute the suspension obtained in step (2) with water and spray it onto the mixed substrate to obtain a wetted material; (4) The wet material is rolled and granulated in a drum granulator. During the granulation process, liquid modified hydrophilic polyurethane resin is added in several batches, with the total amount added being 2.5% to 3% of the total mass of the material. (5) The obtained granules are dried at 35~45℃ until the moisture content is ≤8% to obtain the carbon-fixing multi-element fertilizer; The organic matter content of the decomposed pig manure pellets is ≥45%; The specific surface area of ​​the nano-tetraoxide or nano-zero ferric oxide nanoparticles is ≥50 m² / g; The heating rate in step (2) is 2~3℃ / min, and the oxygen content of the system is kept ≤5% during stirring; The granulation temperature in step (4) is controlled at 45~55℃, the particle diameter is controlled at 2.5~4.5mm, and the roundness is ≥85%.

2. A method for preparing the carbon-fixing multi-element fertilizer as described in claim 1, characterized in that, Includes the following steps: (1) Mix corn stalks with well-rotted pig manure and then crush them to form a mixed base; (2) Mix the compound microbial agent, urea, nano iron tetroxide, nano zero-valent iron, humic acid, potassium dihydrogen phosphate and potassium chloride, heat to 75~85℃ and stir continuously at 180~220 rpm for 30~50 minutes to obtain a suspension. (3) Dilute the suspension obtained in step (2) with water and spray it onto the mixed substrate to obtain a wetted material; (4) The wet material is rolled and granulated in a drum granulator. During the granulation process, liquid modified hydrophilic polyurethane resin is added in several batches, with the total amount added being 2.5% to 3% of the total mass of the material. (5) The obtained granules are dried at 35~45℃ until the moisture content is ≤8% to obtain the carbon-fixing multi-element fertilizer; The heating rate in step (2) is 2~3℃ / min, and the oxygen content of the system is kept ≤5% during stirring; The granulation temperature in step (4) is controlled at 45~55℃, the particle diameter is controlled at 2.5~4.5mm, and the roundness is ≥85%.

3. The preparation method according to claim 2, characterized in that, In step (1), the particles are crushed to a size of less than 1 cm in more than 90% of the particles.

4. The application of the carbon-fixing multi-element fertilizer according to claim 1 in crop cultivation, characterized in that, The crop is rice, tomato, or corn, and the application method includes a combination of basal application and topdressing.

5. The application according to claim 4, characterized in that, For rice, the total application rate is 750-850 kg / ha, of which 70-80% is applied as basal fertilizer; for tomatoes, the total application rate is 900-1100 kg / ha. When applying to corn, the total application rate is 800-1000 kg / ha.

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