Preparation of hydrothermal straw carbon-based fertilizer and application of hydrothermal straw carbon-based fertilizer in corn cultivation

Abstract

The invention relates to the technical field of plant cultivation, and provides preparation of a hydrothermal straw carbon-based fertilizer and application of the hydrothermal straw carbon-based fertilizer in corn cultivation, and the hydrothermal straw carbon-based fertilizer comprises hydrothermal straw biochar and a fertilizer; the hydrothermal straw biochar is prepared by taking rice straw as a raw material and carrying out hydrothermal carbonization reaction. On one hand, the pore structure of the straw charcoal is optimized by adjusting process conditions of a hydrothermal carbonization method and the like, so that the hydrothermal straw charcoal-based fertilizer plays a role in promoting growth of corn, or the pore structure and surface groups of the straw charcoal are adjusted by a post-treatment oxidation process, so that the slow release effect of the hydrothermal straw charcoal-based fertilizer is improved.

Description

Technical Field

[0001] This invention relates to the field of plant cultivation technology, and in particular to the preparation of a hydrothermal straw charcoal-based fertilizer and its application in corn cultivation. Background Technology

[0002] Corn is one of the world's most important food, feed, and industrial raw material crops, and its stable and high yields are crucial for ensuring national food security. Scientific fertilization is a core element in ensuring healthy growth and high yields for corn. Currently, chemical fertilizers, such as urea, ammonium phosphate, and potassium sulfate, are widely used in agricultural production. These chemical fertilizers can quickly replenish essential macronutrients such as nitrogen, phosphorus, and potassium, significantly increasing crop yields in the short term. However, long-term or excessive use of chemical fertilizers has revealed many problems, such as: low nutrient utilization rate, serious environmental pollution; damage to soil structure, leading to decreased soil fertility; and unbalanced nutrient supply, affecting healthy crop growth.

[0003] Traditional fertilizers provide nutrients in a single form, and their release rate is difficult to match with the nutrient requirements of corn at different growth stages (especially the seedling stage). For example, corn seedlings prefer nitrate nitrogen, and their root development is highly sensitive to the supply of available phosphorus. Traditional fertilization methods cannot accurately meet these specific needs, which may lead to slow growth and poor root development in corn seedlings, ultimately affecting the overall biomass and stress resistance of the plant. Commercial slow-release fertilizers also have limitations in their effectiveness due to the difficulty in degrading the coating materials (polyolefins, polyurethane) in the soil, which can cause microplastic pollution; and the high cost of bio-based materials (chitosan, lignin).

[0004] To overcome these shortcomings, researchers have begun exploring new fertilizers and soil amendment technologies. Among them, biochar, as a soil amendment, has received widespread attention. Biochar has a huge specific surface area, abundant pore structure, and stable chemical properties. When applied to the soil, it can effectively improve soil physical properties, enhance soil water and fertilizer retention capacity, and adsorb harmful substances in the soil.

[0005] Despite its numerous advantages, biochar has extremely low nutrient content, making it unsuitable for use as a standalone fertilizer. Currently, mixing biochar with fertilizers is a common application method, but nutrient release is uncontrollable, particularly in matching the specific nutrient requirements of crop seedlings (such as nitrate-to-nitrogen ratio and available phosphorus supply). Furthermore, developing a compound biochar-based fertilizer that can simultaneously optimize the soil microenvironment (such as pH and electrical conductivity EC) and synergistically promote root and aboveground growth in maize seedlings remains a pressing technical challenge in this field. Summary of the Invention

[0006] Currently, straw carbonization, as a technology for the resource utilization of agricultural waste, is of great significance for soil carbon sequestration and air quality improvement. However, research on the preparation of slow-release fertilizers using the porous structure and adsorption properties of carbon materials is still limited. To at least partially solve the above-mentioned technical problems, this invention provides a hydrothermal preparation method for straw-based carbon fertilizer and its application in maize cultivation.

[0007] In a first aspect, the present invention provides a hydrothermal straw biochar-based fertilizer, comprising: hydrothermal straw biochar and fertilizer; the preparation of the hydrothermal straw biochar comprises: obtaining it from rice straw as raw material through a hydrothermal carbonization reaction.

[0008] According to the hydrothermal straw biochar-based fertilizer provided by the present invention, the total specific surface area of ​​the hydrothermal straw biochar is 5-16 m². 2 / g, with an average pore size of 15~35nm and a mesopore volume of 0.03~0.1cm³. 3 / g, with a mesopore ratio of over 99%.

[0009] Preferably, the mesopore area of ​​the hydrothermal straw biochar is 5-20 m². 2 / g.

[0010] According to the hydrothermal straw biochar-based fertilizer provided by the present invention, the preparation of the hydrothermal straw biochar includes: Mix rice straw with water, heat to 200-280℃ under a nitrogen atmosphere, keep warm for 1-3 hours while stirring, and maintain the pressure inside the reactor at 1-6 MPa. After the hydrothermal carbonization reaction is complete, wash and dry to obtain the final product.

[0011] According to the hydrothermal straw biochar fertilizer provided by the present invention, the preparation of the hydrothermal straw biochar further includes an oxidation treatment; the oxidation treatment includes: washing and drying the product of the hydrothermal carbonization reaction, and then oxidizing it with H2O2.

[0012] Preferably, the oxidation treatment includes: washing and drying the product of the hydrothermal carbonization reaction, mixing it with an aqueous H2O2 solution for 1-3 hours, washing and drying it again to obtain the final product.

[0013] More preferably, the concentration of the H2O2 aqueous solution is 20-40%.

[0014] According to the hydrothermal straw biochar-based fertilizer provided by the present invention, the mass ratio of hydrothermal straw biochar to fertilizer is 1:0.5~1.5. Preferably, the fertilizer includes nitrogen fertilizer and phosphorus fertilizer; more preferably, the fertilizer includes urea and potassium dihydrogen phosphate.

[0015] More preferably, the mass ratio of urea to potassium dihydrogen phosphate is 1:0.5~1.5.

[0016] Preferably, the hydrothermal straw charcoal-based fertilizer further includes water, and the amount of water used is within 20% of the solid dry weight.

[0017] Secondly, the present invention also provides a method for preparing hydrothermal straw biochar fertilizer as described above, comprising: preparing hydrothermal straw biochar by hydrothermal carbonization reaction using rice straw as raw material, wherein the hydrothermal straw biochar is mixed with fertilizer.

[0018] Preferably, the hydrothermal straw biochar and fertilizer are mixed to form granular hydrothermal straw biochar-based fertilizer, which is then dried or air-dried at below 40°C until constant weight.

[0019] More preferably, the fertilizer is obtained by mixing urea and potassium dihydrogen phosphate and then passing it through a 40-mesh sieve.

[0020] Thirdly, the present invention also provides the application of the hydrothermal straw char-based fertilizer as described above or the hydrothermal straw char-based fertilizer prepared by the method described above in corn cultivation.

[0021] Preferably, the corn cultivation includes corn seedling cultivation.

[0022] According to the application provided by the present invention, the fertilization rate for cultivating maize seedlings is 500-750 kg / hm of biochar. 2 ; According to the application provided by the present invention, the fertilization rate for cultivating corn seedlings is 50-80 kg / hm² of nitrogen. 2 Phosphorus 50~80 kg / hm 2 .

[0023] According to the application provided by the present invention, the corn cultivation includes: sowing corn seeds 1.5-2.5 cm below the topsoil and applying fertilizer in a layer 0.8-1.2 cm below the topsoil.

[0024] According to the application provided by the present invention, the soil used for corn cultivation has a pH value of 6-8, an EC value of 100-600 μS / cm, an organic matter content of 20-160 g / kg, a total nitrogen content of 300-1500 mg / kg, and a total phosphorus content of 200-1000 mg / kg.

[0025] This invention provides a hydrothermal straw biochar-based fertilizer preparation method and its application in corn cultivation. The hydrothermal straw biochar-based fertilizer is prepared by converting rice straw into straw biochar using a hydrothermal carbonization method, which is then mixed with fertilizer. On the one hand, the pore structure of the straw biochar is optimized by adjusting the process conditions of the hydrothermal carbonization method to improve its adsorption effect on fertilizer and promote the growth of corn seedlings. On the other hand, the pore structure and surface groups of the straw biochar are adjusted through an oxidation modification process to improve the slow-release effect of the hydrothermal straw biochar-based fertilizer application. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0027] Figure 1 The dry and fresh weight of the potted crop plants in Test Example 2 was measured.

[0028] Figure 2 To test the effect of different treatments on the root-to-shoot ratio of maize seedlings in Example 2.

[0029] Figure 3 This is a schematic diagram illustrating the processing of the root system image in Test Example 2.

[0030] Figure 4 The standard curve for total phosphorus in soil in test example 2.

[0031] Figure 5 This is the standard curve for soil ammonium nitrogen in Test Example 2.

[0032] Figure 6 The standard curve for soil nitrate nitrogen in test example 2.

[0033] Figure 7 To test the significant effects of different treatments on soil ammonium nitrogen concentration in Example 2.

[0034] Figure 8 To test the significant effects of different treatments on soil nitrate nitrogen concentration in Example 2.

[0035] Figure 9 To test the content of different forms of phosphorus in the soil of potted corn seedlings under different treatments in Example 2.

[0036] Figure 10 The leaching apparatus used in Test Example 3.

[0037] Figure 11 This is the total nitrogen standard curve from test example 3.

[0038] Figure 12 This is the total phosphorus standard curve for test example 3.

[0039] Figure 13 This is one of the test results for Test Example 3, where a and c represent the cumulative dissolution rates of total nitrogen and total phosphorus, and b and d represent the single dissolution rates of total nitrogen and total phosphorus.

[0040] Figure 14 This is the second test result in Test Example 3, where a and c represent the cumulative dissolution rates of total nitrogen and total phosphorus, and b and d represent the single dissolution rates of total nitrogen and total phosphorus.

[0041] Figure 15 This is the third test result in Test Example 3, where a and c represent the cumulative dissolution rates of total nitrogen and total phosphorus, and b and d represent the single dissolution rates of total nitrogen and total phosphorus.

[0042] Figure 16 This is one of the results of test example 4.

[0043] Figure 17 This is the second result of test example 4.

[0044] Figure 18 This is the third result of test example 4. Detailed Implementation

[0045] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0046] The following is combined Figures 1-18 This invention describes the preparation of a hydrothermal straw-based charcoal fertilizer and its application in maize cultivation.

[0047] Where specific techniques or conditions are not specified in the examples, they shall be performed in accordance with the techniques or conditions described in the literature in this field, or in accordance with the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased through legitimate channels.

[0048] Preparation Example 1A: Hydrothermal Straw Biochar A method for preparing hydrothermal straw biochar, comprising the following steps: (1) Cut the rice straw into 2-3cm pieces, weigh 50g of rice straw raw material, and transfer it to a hydrothermal reactor with 500mL of deionized water. Seal the reactor and install it. Pour in nitrogen gas at 200mL / min for 10min. Remove the air from the reactor. Heat to 200℃ and keep warm for 2h (stirring speed is 100r / min). The pressure inside the reactor is 1MPa. After the hydrothermal carbonization reaction is completed, let the reactor cool naturally to room temperature.

[0049] (2) The hydrothermal products were filtered using a vacuum pump to achieve solid-liquid separation. Then, the solid products were repeatedly filtered and washed with deionized water and ethanol until the filtered ethanol was nearly colorless. After drying at 105°C to constant weight, solid rice straw hydrothermal char was obtained.

[0050] Preparation Example 2A: Hydrothermal Straw Biochar The preparation method is basically the same as that in Example 1A, except that the heating temperature is changed from 200°C to 220°C and the pressure inside the vessel is 2 MPa.

[0051] Preparation Example 3A: Hydrothermal Straw Biochar The preparation method is basically the same as that in Example 1A, except that the heating temperature is changed from 200°C to 240°C and the pressure inside the vessel is 3 MPa.

[0052] Preparation Example 4A: Hydrothermal Straw Biochar The preparation method is basically the same as that in Example 1A, except that the heating temperature is changed from 200°C to 260°C and the pressure inside the vessel is 4 MPa.

[0053] Preparation Example 5A: Hydrothermal Straw Biochar The preparation method is basically the same as that in Example 1A, except that the heating temperature is changed from 200°C to 280°C and the pressure inside the vessel is 6 MPa.

[0054] The hydrothermal straw biochar prepared in Examples 1A to 5A is numbered as follows: Table 1

[0055] Preparation Example 1B: Hydrogen peroxide-modified hydrothermal char of rice straw A method for preparing hydrothermal char of rice straw modified with hydrogen peroxide and oxygen, the specific process is as follows: take 3g of biochar prepared in Preparation Example 3A, mix it evenly with 12mL of 30% H2O2, shake it in a shaker at a speed of 100r / min for 2h, wash away the residual H2O2 of biochar with deionized water after shaking, and dry it at 105℃ to constant weight to obtain hydrothermal char of rice straw modified with hydrogen peroxide and oxygen.

[0056] Preparation Example 2B: Hydrogen peroxide-modified hydrothermal char of rice straw It is basically the same as Example 1B, except that the oscillation time of 2 hours is changed to 4 hours.

[0057] Preparation Example 3B: Hydrogen peroxide-modified hydrothermal char of rice straw It is basically the same as Example 1B, except that the oscillation time of 2 hours is changed to 6 hours.

[0058] Preparation Example 4B: Hydrogen peroxide-modified hydrothermal char of rice straw It is basically the same as Example 1B, except that the oscillation time of 2 hours is changed to 8 hours.

[0059] The hydrothermal straw biochar prepared in Examples 1B to 4B is numbered as follows: Table 2

[0060] Example 1C: Carbon-based fertilizer, numbered BF-260 A method for preparing straw-based biochar fertilizer includes the following steps: Hydrothermal char (product number B-260), fertilizer, and deionized water are mixed and filled into a metal mold at a loading rate of 0.9000g. The mold has 9 holes, each 6mm in diameter and 3mm in depth. The mixture is then pressurized using an infrared press (5MPa pressure maintained for 5 minutes) to produce columnar biochar-based fertilizer (product number BF-200). The fertilizer is then dried at 80℃ to constant weight, meeting the Type II standard in the standard NY / T3041-2016 Biochar-based Fertilizer. The mass ratio of hydrothermal char to fertilizer is 1:1, and the amount of deionized water is 10% of the solid dry weight. The fertilizer is obtained by mixing urea and potassium dihydrogen phosphate in a 1:1 mass ratio and passing the mixture through a 40-mesh sieve.

[0061] Example 2C: Carbon-based fertilizer, numbered BF-240 It is basically the same as Example 1C, except that the mass of hydrothermal char B-260 is replaced with hydrothermal char B-240.

[0062] Example 3C: Carbon-based fertilizer, numbered BF-6h It is basically the same as Example 1C, except that the mass of hydrothermal carbon numbered B-260 is replaced with hydrothermal carbon numbered B-6h.

[0063] Comparative Example 1: Carbon-based fertilizer, numbered BF-600 This is essentially the same as Example 1C, except that the hydrothermal char (numbered B-260) is replaced by pyrolytic char prepared by the following method: Rice straw is chopped into 2-3 cm pieces. 50 g of rice straw raw material is weighed and transferred into a pyrolysis furnace. Nitrogen gas is introduced at a flow rate of 200 mL / min for 10 min. The air in the furnace is then purged. The temperature is increased to 600℃ at a rate of 4℃ / min and held for 2 hours. The material is then allowed to stand at room temperature before being removed to obtain pyrolytic char.

[0064] Test Example 1: Pore Structure of Hydrothermal Carbon The testing method was as follows: A pore structure analyzer was used to characterize the straw charcoal samples. Data processing and analysis yielded various pore data for pyrolytic and hydrothermal charcoal, including: specific surface area, total pore volume, micropore specific surface area, micropore volume, mesopore specific surface area, mesopore volume, and average pore diameter.

[0065] The test results are as follows: Table 3

[0066] It can be seen that the effect of temperature increase on the pore structure of hydrothermal carbon exhibits a trend of first increasing and then decreasing. Within the temperature range of 220℃ to 240℃, the pore structure becomes more developed, with increased total specific surface area and total pore volume, larger pore size, and a higher proportion of micropores. When the temperature exceeds 240℃, the pore structure begins to deteriorate, with decreased total specific surface area and total pore volume, smaller pore size, a decreased proportion of micropores, and an increased proportion of mesopores. This may be because excessively high temperatures lead to more vigorous reactions, and the increased products cause the pore structures formed during the low-temperature reaction to become blocked.

[0067] Hydrogen peroxide modification affects the pore structure of hydrothermal biochar: the total specific surface area decreases compared to before oxidation, but increases with oxidation time, although 8 hours of oxidation time is insufficient to increase it back to the total specific surface area before oxidation; the micropore structure increases compared to before oxidation, and the number of micropores increases with oxidation time; the mesopore area decreases compared to before oxidation, but first increases and then decreases with oxidation time.

[0068] Test Example 2: Pot Experiment (1) Test methods Group setup: A pot experiment using maize seedlings was conducted with 10 treatments, each replicated 5 times. The soil used was horticultural potting mix. The corresponding relationships are as follows: CK represents the treatment without fertilizer; CF represents the single-fertilizer treatment (urea: potassium dihydrogen phosphate = 1:1). B-600 is a single application of carbon treatment with the number B-600; B-260 refers to a single application of carbon treatment numbered B-260; B-240 refers to the carbon treatment with the designation B-240. B-6h refers to a single carbon treatment with the application number B-6h. BF-600 is the carbon-based fertilizer treatment group numbered BF-600; BF-260 is the carbon-based fertilizer treatment group numbered BF-260; BF-240 is the carbon-based fertilizer treatment group numbered BF-240; BF-6h is the carbon-based fertilizer treatment group numbered BF-6h; The specific experimental design details are shown in the table below.

[0069] Table 4 Fertilizer application rates for each treatment

[0070] (2) Planting method The pot experiment was conducted in a greenhouse with consistent temperature and sufficient light for all groups. The pots used in the experiment had an inner diameter of 100mm×100mm×80mm. The maize seeds (variety Nongke Nuo 336) were soaked in deionized water for 24 hours beforehand and sown on September 28, 2024, with one plant per pot and a soil weight of 450±10g. The maize seeds were planted 2cm below the topsoil, and fertilizer was applied evenly in the 1cm layer below the soil surface. The fertilizer application rates for each treatment were as shown in Table 4. The plants were irrigated with 100mL of deionized water daily, and the biological characteristics of the crops were recorded every 7 days. The maize plants were harvested after 28 days, and the effects of biochar-based fertilizer on the crops and the crop soil were determined.

[0071] (3) Test results (3.1) Plant height and stem diameter The plant height was measured with a ruler, taking the distance from the soil surface to the top of the plant in a direction perpendicular to the soil surface. Each measurement was taken three times and the average value was recorded. The stem diameter of the plant was measured with vernier calipers. The stem diameter was taken 1 cm above the soil surface. The average value of the stem diameter was recorded for each measurement from three different directions.

[0072] The test results are as follows: Table 5. Plant height of maize plants

[0073] Note: Different lowercase letters such as abc indicate that the differences between treatments are significant at the P<0.05 level. For example, a>ab>b>c.

[0074] Table 6. Stem diameter of maize plants

[0075] Note: Different lowercase letters such as abc indicate that the differences between treatments are significant at the P<0.05 level. For example, a>ab>b>c.

[0076] It can be seen that the biochar-based fertilizer (BF series) exhibits a rapid initial effect on promoting stem diameter in maize seedlings, followed by a sustained increase in the later stages. On day 7, the stem diameter of the BF-240 group (1.56 mm) was significantly higher than that of the conventional fertilization group CF (1.30 mm), indicating that the hydrothermal carbonization temperature (240℃) optimized the physicochemical properties of the carbon carrier, promoting maize seedling development. By day 28, the stem diameter of the BF-240 group reached 5.06 mm, a 22.8% increase compared to the CF group (4.12 mm), and significantly higher than all pure biochar treatments (B series). Furthermore, on day 7, compared to BF-240 (1.56 mm), BF-6h inhibited stem diameter development (1.20 mm), but on day 28, there was no significant difference compared to the BF-240 group (4.64 mm, 5.06 mm), indicating that the regulatory effect of oxidation has a developmental stage-specific effect.

[0077] (3.2) Fresh weight and dry weight of the plant The fresh weight of the plants was measured when the plants were harvested 28 days after planting, using a 1 / 2000 balance. After weighing the fresh plants, they were blanched in a 105℃ forced-air drying oven for 30 minutes, then cooled to 60℃ and dried for 24 hours to remove the remaining moisture. After cooling to room temperature, the plants were weighed using a balance to obtain their dry weight.

[0078] Test results are as follows Figures 1-2 As shown.

[0079] It can be seen that the aboveground fresh weight (3.67g), aboveground dry weight (0.31g), and underground dry weight (0.70g) of the BF-240 group were significantly higher than those of other treatments, indicating that its carbon-based fertilizer had a comprehensive synergistic effect on the accumulation of biomass throughout the plant. While the underground dry weight (0.63g) of the BF-6h group was not significantly different from that of the BF-240 group, its aboveground fresh weight (2.84g) was significantly lower, reflecting that oxidation treatment may have inhibited water absorption by the aboveground parts.

[0080] The root-to-shoot ratio is an important indicator for measuring the biomass distribution between the underground and aboveground parts of a plant. It is the ratio of the biomass (dry weight) of the underground parts to the aboveground parts, reflecting the plant's adaptability and resource utilization efficiency under different growth environments. For maize seedlings, changes in the root-to-shoot ratio have a significant impact on plant growth and development. Studies have shown that an increase in the root-to-shoot ratio is generally associated with enhanced root activity and root biomass accumulation, which helps maize seedlings better absorb water and nutrients from the soil, thereby promoting their growth. Figure 2 Bubble charts showing the root-to-shoot ratio of maize seedlings under different treatments reveal that the BF-260 group achieved the highest root-to-shoot ratio of 3.40, significantly higher than the BF-240 group (2.26), indicating a greater tendency to allocate resources to the root system. This may be related to the nutrient release pattern regulated by the carbonization temperature (260℃). The root-to-shoot ratio of the CF group was only 0.71, reflecting an imbalance in resource allocation caused by conventional fertilization, where resources are heavily allocated to the above-ground parts and neglected in the underground parts.

[0081] (3.3) Analysis of Crop Plant Root System Characteristics Root data collection: Roots from each treatment were washed with clean water. Images of the corn seedling roots were scanned using a camera and stored in a computer. Pre-processing was performed using Adobe Photoshop CS6, followed by analysis of the root images using WinRHI 2.0 root analysis software to obtain root data such as root length and volume. The actual size of the root images was 23cm × 23cm. Original and processed images of the potted corn seedling roots are shown below. Figure 3 As shown.

[0082] The test results are as follows: Table 7

[0083] Note: Different lowercase letters such as abc indicate that the differences between treatments are significant at the P<0.05 level. For example, a>ab>b>c.

[0084] It can be seen that BF-240 showed the most outstanding performance in root length, reaching 34.16±8.43cm, while there was no significant difference in total root length among the five groups CK, CF, B-600, B-6h and BF-600. This indicates that conventional fertilizers, hydrothermal oxidized carbon, pyrolytic carbon and their carbon-based fertilizers cannot effectively promote root growth.

[0085] BF-240 also showed a significant advantage in root volume, followed by CF, with the CK group performing the worst; the other groups showed no significant difference. In terms of root surface area, BF-240 achieved the highest at 2.75±0.76 cm². 2 The surface area was the worst performing group, CK and B-600.

[0086] In terms of average root diameter, B-260 had the thickest root (0.31±0.07 mm), while B-240 had the thinnest (0.24±0.01 mm). Overall, the best performing group was BF-240, which had significantly higher total root length, root surface area, and root volume; the B-260 group had the largest average root diameter (0.31 mm, labeled a).

[0087] The worst performance was seen in the CK (control group): total root length, root surface area, and root volume were all the lowest. This indicates that the BF-240 group effectively promoted the development of corn seedling roots and was more effective than conventional fertilization in meeting the plant's nutritional needs. It also suggests that the pyrolytic carbon-based fertilizer did not promote root development sufficiently, and that oxidation was actually detrimental to better root development.

[0088] (3.4) Nitrogen and phosphorus uptake indicators of plants The determination of nitrogen and phosphorus in plants is based on the industry standard NY / T2017-2011 "Determination of Nitrogen, Phosphorus and Potassium in Plants".

[0089] The test results are as follows: Table 8

[0090] Note: Different lowercase letters such as abc indicate that the differences between treatments are significant at the P<0.05 level. For example, a>ab>b>c.

[0091] It can be seen that the series of carbon-based fertilizers significantly affect the nutrient absorption and distribution patterns of plants. Among them, the hydrothermal carbon-based fertilizer (BF-240, hydrothermal carbonization temperature 240℃) performed the best, with total nitrogen and total phosphorus accumulation in the aboveground and underground parts reaching 89.7 mg and 5.54 mg, respectively, which are 85.2% and 89.1% higher than conventional fertilization (CF). This is attributed to the moderate pore structure and abundant oxygen-containing functional groups (such as carboxyl and hydroxyl groups) of hydrothermal carbon, which synergistically delay nitrogen and phosphorus release through physical adsorption and chemical bonding, matching the dynamic nutrient requirements of maize seedlings.

[0092] Although oxidation treatment (BF-6h) further increased the aboveground nitrogen accumulation to 106.9 mg (19.2% higher than BF-240), the underground phosphorus accumulation decreased by 10.0% (0.63 mg, 0.70 mg), indicating that oxidation modification may preferentially promote nitrogen retention by enhancing polar groups (such as quinone groups) on the carbon surface, while excessive oxidation will weaken the slow release efficiency of phosphorus.

[0093] Although high-temperature pyrolysis char (B-600) has good pore connectivity, it lacks functional groups, and its total nitrogen accumulation (49.3 mg) is significantly lower than that of hydrothermal char, which verifies the advantages of hydrothermal carbonization process in optimizing the function of nutrient carrier.

[0094] In summary, the 240℃ hydrothermal carbon-based fertilizer (BF-240) achieves efficient and synergistic absorption of nitrogen and phosphorus by corn by balancing the carbon structure characteristics and nutrient slow-release kinetics.

[0095] (3.5) Crop soil property testing (3.5.1) Soil pH value Weigh 10g of air-dried soil sample that has passed through a 2mm sieve and transfer it together with 25mL of deionized water into a 250mL Erlenmeyer flask. Shake for 2 minutes and let stand for 30 minutes. Zero and calibrate the pH meter, and measure the pH value of the supernatant.

[0096] (3.5.2) Determination of soil electrical conductivity EC value Weigh 50.0 g of air-dried soil sample that has passed through a 2 mm sieve and transfer it to a 250 mL Erlenmeyer flask along with 25 mL of deionized water. Shake for 3 min. Filter the soil suspension through filter paper and determine the EC value of the filtrate.

[0097] (3.5.3) Determination of soil organic matter ①Preliminary preparations Weigh 0.1-0.5 g (accurate to 0.0001 g) of a 100-mesh soil sample. Transfer the entire sample to a dried test tube. Add potassium dichromate standard solution (0.8 M, 1 / 6 K₂Cr₂O₇) and 5 ml of concentrated sulfuric acid, and shake well. Cap the test tube. Simultaneously perform a blank test using powdered silica instead of the sample, following the same procedure.

[0098] ② Dissolve Preheat the infrared digestion furnace to 185-190℃, place the test tubes in the test tube rack (each rack contains 1-2 blank samples), place the test tube rack on the digestion furnace, and heat within the temperature range of 175±5℃ until the liquid in the test tube boils for 5 minutes. Remove the test tubes and let them stand to cool.

[0099] ③ Titration Wash the contents of the test tube into the conical flask with deionized water until the total volume is 60-70 ml. Then add 3-4 drops of o-phenanthroline indicator and titrate to the endpoint with standard 0.2 mol / L ferrous sulfate solution. Record the titration volume of ferrous sulfate.

[0100] ④ Result Calculation: Where: c—0.8000mol·L -1 (1 / 6) concentration of the K2Cr2O7 standard solution; 5-Volume (mL) of potassium dichromate standard solution added; V0 — Volume of FeSO4 used in blank titration (mL); V—Sample titration volume (mL); 3.0–1 / 4 molar mass of carbon atoms (g·mol⁻¹) -1 ); 10 -3 —Convert mL to L; 1.1 — Oxidation correction factor; m — Mass of air-dried soil sample (g); k—the coefficient for converting air-dried soil to oven-dried soil; Soil organic matter (g·kg) -1 = Soil organic carbon × 1.724 (average conversion factor).

[0101] (3.5.4) Determination of total nitrogen and total phosphorus in soil ① Soil sample decomposition Weigh 1g of air-dried soil sample (accurate to 0.0001g) that has passed through a 100-mesh sieve and place it in a Kjeldahl flask. Moisten the soil sample with a small amount of deionized water, add 2g of accelerator (potassium sulfate:copper sulfate:selenium = 100:10:1) and 5ml of concentrated sulfuric acid, and shake well. Prepare two blank samples without soil sample, following the same procedure. Place the Kjeldahl flasks containing the soil sample and reagents, as well as the blank samples, on a digestion furnace and digest at 280℃ for 1.5 hours.

[0102] ② Total nitrogen determination After the digestion solution cools, it is distilled using a semi-automatic nitrogen analyzer. After complete distillation, it is titrated with 0.01 mol / L (1 / 2) sulfuric acid standard solution (2.83 mL of concentrated sulfuric acid diluted with distilled water to a final volume of 10 L). The endpoint is reached when the solution changes from blue-green to purple-red. Record the volume of standard acid consumed. Calculate the nitrogen content of the sample using the following formula.

[0103] V — the number of milliliters of standard acid consumed during titration; V0 — The number of milliliters of standard acid consumed during blank titration; N—molar concentration of the standard acid; 0.014 — millimolecular mass of nitrogen atoms (g / mmol); 10 6 —Convert to mg·kg -1 .

[0104] ③ Total phosphorus determination After the digestion solution has cooled, rinse the Kjeldahl flask with water and bring it to volume. Using a drying funnel and phosphorus-free quantitative filter paper, filter the solution into a dry 100ml Erlenmeyer flask, and simultaneously perform a blank test.

[0105] The determination of total phosphorus content in the digestion solution referenced the molybdenum-antimony spectrophotometric method in Agricultural Standard NY / T 2017-2011 "Determination of Nitrogen, Phosphorus, and Potassium in Plants". The total phosphorus standard curve was plotted as follows: Figure 4 As shown.

[0106] (3.5.5) Determination of different nitrogen forms in soil Determination of ammonium nitrogen: The determination of nitrate nitrogen in soil follows the standard QX / T 217-2013 "Determination of Ammonia (Ammonium) in Atmosphere - Indophenol Blue Spectrophotometric Method". A standard curve can be plotted using standard samples to obtain... Figure 5 The corresponding amount of ammonium nitrogen can be found from the standard curve.

[0107] Determination of nitrate nitrogen: The determination of nitrate nitrogen in soil follows the industry standard HJ / T 346-2007 "Determination of Nitrate Nitrogen in Water - Ultraviolet Spectrophotometry". A standard curve is plotted using standard samples to obtain the desired nitrate nitrogen content. Figure 6 The corresponding amount of nitrate nitrogen can be found from the standard curve.

[0108] Specific results are as follows Figures 7-8 As shown.

[0109] (3.5.6) Determination of different phosphorus forms in soil The extraction methods for various phosphorus forms in soil were based on those described by Bornø M, Joseph O, Müller-Stöver D, et al. Effect of different biochars on phosphorus (P) dynamics in therhizosphere of Zea mays L. (maize)[J]. Plant and Soil, 2018, 431: 257-272. Specific results are as follows: Figure 9 As shown.

[0110] The results are as follows: Table 9

[0111] Note: Different lowercase letters such as abc indicate that the differences between treatments are significant at the P<0.05 level. For example, a>ab>b>c.

[0112] In summary, it can be seen that: (1) BF-240 significantly increased the biomass of maize seedlings, significantly increasing fresh weight (4.80 g), dry weight (0.51 g), and total phosphorus accumulation (5.54 mg). Total nitrogen accumulation was highest in the BF-6h group (106.9 mg). Plant height was the highest among all groups (42.20 cm), and stem diameter reached 5.06 mm, a 22.8% increase compared to the CF group (4.12 mm), and significantly higher than all other treatments. The total root length (34.16 cm) and root volume (0.017 cm³) in the BF-240 group were also significantly higher. 3 ) and root surface area (2.75cm²) 2 The values ​​were all extremely significant and highest. This indicates that hydrothermal carbon-based fertilizer has a good promoting effect on both maize seedling biomass and root development.

[0113] (2) The application of BF-240 will lower the soil pH (pH=5.92), increase the EC value appropriately (275μS / cm), and significantly increase organic matter, total nitrogen and total phosphorus (151.10g / kg, 1324.80mg / kg, 1158.59mg / kg).

[0114] (3) BF-240 group (0.286 mg / L NH 4+ and 5.31mg / LNO 3- It is more suitable for soils with active nitrification, matching the characteristic of maize seedlings that prefer nitrate nitrogen absorption. BF-240 has the highest available phosphorus content (879.36 mg / kg), while the residual phosphorus content is relatively low (150.07 mg / kg).

[0115] Test Example 3: Slow-release behavior of carbon-based fertilizers in sandy environments Adopting such Figure 10 The leaching device shown simulates an actual sandy environment. The specific operation is as follows: (1) Preparation of fertilizer packs: 0.1g of carbon-based fertilizer and conventional fertilizer were placed into nylon mesh with a mesh size of 150μm (200 mesh) as test samples, and the packs were sealed to make 2cm×2cm×0.5cm fertilizer packs. Among them, the CF group corresponds to conventional fertilizer, which is obtained by mixing urea and potassium dihydrogen phosphate in a mass ratio of 1:1 and passing it through a 40-mesh sieve.

[0116] (2) Filling the sand column: Simulate a sandy environment, take 270g of quartz sand to fill and compact to a height of 20cm, lay the fertilizer bag flat on it, then take 50g of quartz sand to fill and compact to a height of 25cm, and cover the top with cotton weighing 1.5g and 2cm high to prevent distilled water from interfering with the quartz sand column.

[0117] (3) Collection of leachate: On the first day of the experiment, add 150 mL of distilled water to the top of the apparatus (an additional 50 mL is needed to wet the sand column). Add 100 mL of distilled water every 24 hours and collect the leachate in an Erlenmeyer flask. Collect the leachate at the set time.

[0118] (4) Nutrient determination: Nitrogen and phosphorus elements in the leachate were determined using the following methods: (4.1) The determination of total nitrogen in aqueous solution was performed according to the national standard HJ636-2012 "Determination of Total Nitrogen in Water - Alkaline Potassium Persulfate Digestion Ultraviolet Spectrophotometric Method". The total nitrogen standard curve is shown below. Figure 11 As shown.

[0119] (4.2) The determination of total phosphorus in aqueous solution was performed according to the national standard GB11893-1989 "Determination of Total Phosphorus in Water - Ammonium Molybdate Spectrophotometric Method". The total phosphorus standard curve is shown below. Figure 12 As shown.

[0120] Test results are as follows Figures 13-15 As shown in the figure. Among them, group CF corresponds to conventional fertilizer, which is obtained by mixing urea and potassium dihydrogen phosphate in a mass ratio of 1:1 and then passing it through a 40-mesh sieve.

[0121] As can be seen from the table above: From a temperature perspective, the total nitrogen dissolution rate of BF-240 was the lowest at all time points. In the early leaching stage (days 1-4), BF-240 showed less total nitrogen dissolution, while the later stage showed more, indicating its superior slow-release effect on total nitrogen in sandy environments. In the first two days of leaching, except for the CF group, the total phosphorus dissolution rates of the carbon-based fertilizers in each group were relatively similar, while in the middle stage (days 2-5), the dissolution rate of BF-260 was relatively low.

[0122] From the perspective of oxidation time, BF-6h had the lowest total nitrogen dissolution rate after the first day. In the early leaching stage (days 1-4), BF-6h showed lower total nitrogen dissolution, but higher dissolution in the later stages, indicating its superior slow-release effect on total nitrogen in sandy environments. The overall dissolution rates of the oxidized hydrothermal char-based fertilizers were relatively similar across all groups. Compared to before oxidation, the oxidized hydrothermal char-based fertilizers showed a lower total phosphorus dissolution rate. The dissolution rates of the oxidized hydrothermal char fertilizers were very similar across groups. In the first two days of leaching, BF-6h showed a lower total phosphorus dissolution rate, while BF-4h showed a relatively low dissolution rate in the third to seventh days. BF-6h showed lower dissolution on the first and third days, but increased dissolution thereafter. The dissolution amounts of BF-4h and BF-6h were similar, indicating that BF-4h and BF-6h had better slow-release effects on phosphorus in sandy environments.

[0123] Test Example 4: Slow-release behavior of carbon-based fertilizers in aquatic environments The testing method is as follows: a conical flask is used to simulate a water environment, and the specific operation is as follows: (1) Fertilizer pack preparation: Same as in test example 3.

[0124] (2) Collect the extract: Take 6 100mL Erlenmeyer flasks, put 100mL of deionized water and 1 fertilizer pack into each flask, cover the mouth of the flask with plastic wrap and seal it. Set the soaking time to 1h, 3h, 5h, 10h, 24h and 48h respectively. Place the Erlenmeyer flasks in a constant temperature incubator at 25℃ and take them out in the order of time to determine the nutrient content released by the sample in water.

[0125] Test results are as follows Figures 16-18 As shown.

[0126] From a temperature perspective, the cumulative dissolution rates of total nitrogen and total phosphorus of all carbon-based fertilizers increased with soaking time. Among them, CF had a higher initial dissolution rate, increased rapidly in the early stage, and then stabilized. BF-260 and BF-280 showed a more obvious upward trend, and some even exceeded CF, indicating that their nutrient release rate was faster. BF-200, BF-220, and BF-240 had similar effects.

[0127] In general, CF-based charcoal fertilizers release nitrogen and phosphorus rapidly in the initial stage of immersion, but their release capacity weakens in the later stages. BF-260 and BF-280 charcoal fertilizers release nitrogen and phosphorus more slowly in the early stages, but their release capacity is strong in the later stages, continuously releasing a significant amount of nitrogen and phosphorus. BF-200, BF-220, and BF-240 charcoal fertilizers release nitrogen and phosphorus relatively gradually throughout the immersion process, with a relatively low overall release amount. Specifically, BF-260 exhibits better slow-release effect on phosphorus in sandy environments, while BF-240's slow-release effect is slightly less effective. BF-240 shows better slow-release effect on nitrogen in sandy environments, but its slow-release effect on phosphorus is not as good.

[0128] From the perspective of oxidation time, during the first 24 hours of immersion, the total nitrogen dissolution rate, ranked from highest to lowest, was: pure fertilizer > BF-0h > BF-2h > BF-8h > BF-4h > BF-6h, indicating that BF-6h had a better slow-release effect on nitrogen in the aquatic environment. In the first 3 hours, the total phosphorus dissolution rates of the various hydrothermal carbon-based fertilizers were relatively similar, but BF-6h had a slightly lower dissolution rate. In the subsequent 3-24 hours, the total phosphorus dissolution rates of BF-4h and BF-6h were similar, but lower than those of other oxidizing hydrothermal carbon-based fertilizers. During the 24-48 hour period, the total phosphorus in all groups of oxidizing hydrothermal carbon-based fertilizers was almost completely dissolved, with a dissolution rate approaching 100%.

[0129] Overall, in aquatic environments, BF-6h showed better slow-release effects on nitrogen and phosphorus, but its dominance in phosphorus release was not significant. In sandy environments, BF-6h showed better slow-release effects on nitrogen, while BF-4h and BF-6h showed better slow-release effects on phosphorus.

[0130] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A hydrothermal straw-based charcoal fertilizer, characterized in that, include: Hydrothermal straw biochar and fertilizer; The preparation of the hydrothermal straw biochar includes: obtaining it from rice straw through a hydrothermal carbonization reaction.

2. The hydrothermal straw charcoal-based fertilizer according to claim 1, characterized in that, The total specific surface area of ​​the hydrothermal straw biochar is 5-16 m². 2 / g, with an average pore size of 15~35nm and a mesopore ratio of over 99%.

3. The hydrothermal straw charcoal-based fertilizer according to claim 1 or 2, characterized in that, The preparation of the hydrothermal straw biochar includes: Mix rice straw with water, heat to 200-280℃ under a nitrogen atmosphere, keep warm for 1-3 hours while stirring, and maintain the pressure inside the reactor at 1-6 MPa. After the hydrothermal carbonization reaction is complete, wash and dry to obtain the final product.

4. The hydrothermal straw charcoal-based fertilizer according to any one of claims 1 to 3, characterized in that, The preparation of the hydrothermal straw biochar also includes an oxidation treatment; the oxidation treatment includes: washing and drying the product of the hydrothermal carbonization reaction, and then oxidizing it with H2O2.

5. The hydrothermal straw charcoal-based fertilizer according to any one of claims 1 to 4, characterized in that, The mass ratio of hydrothermal straw biochar to fertilizer is 1:0.5~1.

5. Preferably, the fertilizer includes nitrogen fertilizer and phosphorus fertilizer; more preferably, the fertilizer includes urea and potassium dihydrogen phosphate.

6. The method for preparing hydrothermal straw charcoal-based fertilizer according to any one of claims 1 to 5, characterized in that, include: Hydrothermal straw biochar is prepared by hydrothermal carbonization of rice straw as raw material, and the hydrothermal straw biochar is mixed with fertilizer.

7. The method for preparing hydrothermal straw charcoal-based fertilizer according to claim 6, characterized in that, include: Rice straw is mixed with water and heated to 200-280°C under a nitrogen atmosphere. The mixture is kept at this temperature for 1-3 hours with stirring and the pressure inside the reactor is 1-6 MPa. The hydrothermal carbonization reaction is then completed. The product of the hydrothermal carbonization reaction is obtained by washing and drying. The product of the hydrothermal carbonization reaction is washed and dried, then mixed with an aqueous H2O2 solution for 1-3 hours, washed and dried to obtain the hydrothermal straw biochar.

8. The application of the hydrothermal straw charcoal-based fertilizer according to any one of claims 1 to 5 or the hydrothermal straw charcoal-based fertilizer prepared by the preparation method according to claim 6 or 7 in corn cultivation.

9. The application according to claim 8, characterized in that the fertilizer application rate for corn cultivation is 500-750 kg / hm² of biochar. 2 .

10. The application according to claim 8 or 9, characterized in that the maize cultivation comprises: Sow corn seeds 1.5-2.5 cm below the topsoil and apply fertilizer 0.8-1.2 cm below the topsoil.

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