A molasses-biogas liquid special fertilizer for crops and a preparation method thereof

Abstract

The application discloses a molasses-biogas liquid crop special liquid water-soluble fertilizer and a preparation method thereof, and relates to the technical field of organic fertilizer. The molasses-biogas liquid crop special liquid water-soluble fertilizer comprises the following raw materials in parts by weight: 55-65 parts of clarified biogas liquid, 10-15 parts of sugarcane molasses, 2-3 parts of synergist, 3-5 parts of urea, 3-6 parts of potassium sulfate, 2-4 parts of potassium dihydrogen phosphate and 10-20 parts of deionized water. The molasses-biogas liquid crop special liquid water-soluble fertilizer prepared by the application has a high soluble phosphorus retention rate, a low long-term storage water-insoluble precipitation rate and a good yield-increasing effect.

Description

Technical Field

[0001] This invention relates to the field of organic fertilizer technology, specifically to a molasses-biogas slurry crop-specific liquid water-soluble fertilizer and its preparation method. Background Technology

[0002] With the increasing intensification of agricultural production, water-soluble fertilizers have been widely used due to their advantages such as rapid dissolution, convenient application, and suitability for drip irrigation and fertigation. Meanwhile, livestock and poultry farming and the anaerobic fermentation of organic waste generate large amounts of biogas slurry, which contains ammonium nitrogen, potassium, organic matter, and trace elements; molasses produced in the sugar industry contains sugars, organic acids, and various organic components. Using biogas slurry and molasses in the preparation of liquid water-soluble fertilizers can realize the resource utilization of organic byproducts and reduce the cost of some fertilizer raw materials. However, biogas slurry has a complex composition, typically containing polyvalent metal ions such as calcium, magnesium, and iron, as well as humic substances, fine inorganic particles, and organic colloids. When water-soluble phosphate fertilizers such as potassium dihydrogen phosphate are added to biogas slurry, polyvalent metal ions easily react with phosphate ions to form insoluble phosphates, leading to a decrease in soluble phosphorus content and precipitation and stratification of the product. The addition of molasses also increases the organic matter content and viscosity of the system, making fine particles and colloids more prone to aggregation, affecting the product's storage stability, filtration performance, and drip irrigation performance. Existing technologies typically improve the stability of water-soluble fertilizers by adding citric acid, lignin sulfonate, polycarboxylic acid, humic acid, or conventional chelating agents. However, small-molecule complexing agents have limited dispersing and protective effects on colloids and precipitated particles. Furthermore, conventional adjuvants often fail to simultaneously ensure metal ion stability, phosphorus nutrient retention, and colloidal dispersion performance in high-organic-matter, high-salt, and multi-colloid coexistence systems formed from molasses and biogas slurry. Therefore, it is necessary to develop a simple process that can effectively improve the nutrient stability of molasses-biogas slurry liquid water-soluble fertilizers and reduce precipitation and stratification during storage. Summary of the Invention

[0003] To address the shortcomings of existing technologies, the purpose of this invention is to provide a molasses-biogas slurry-specific liquid water-soluble fertilizer for crops and its preparation method.

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

[0005] A molasses-biogas slurry crop-specific liquid water-soluble fertilizer comprises the following raw materials in parts by weight: 55-65 parts clarified biogas slurry, 10-15 parts sugarcane molasses, 2-3 parts synergist, 3-5 parts urea, 3-6 parts potassium sulfate, 2-4 parts potassium dihydrogen phosphate, and 10-20 parts deionized water.

[0006] The synergist is prepared by the following method:

[0007] Corn dextrin was mixed with deionized water, and ammonium lignosulfonate was added and stirred. The pH was adjusted to obtain the basic reaction solution. Itaconic acid was dissolved in deionized water and neutralized with ammonia to obtain a neutralized itaconic acid solution. The neutralized itaconic acid solution, ammonium persulfate solution, and sodium bisulfite solution were added dropwise to the basic reaction solution to react and obtain the synergist.

[0008] The mass ratio of corn dextrin, ammonium lignin sulfonate, itaconic acid, ammonium persulfate, and sodium bisulfite is 100:50:10:0.6:0.3.

[0009] The ammonia solution has a mass concentration of 10 wt%, and the amount of ammonia solution used is 78% of the mass of itaconic acid.

[0010] The mass concentration of the ammonium persulfate aqueous solution is 30 g / L.

[0011] The sodium bisulfite aqueous solution has a mass concentration of 15 g / L.

[0012] The reaction conditions are as follows: first react at 60℃ for 2 hours, then keep warm at 75℃ for 30 minutes.

[0013] A method for preparing a molasses-biogas slurry-specific liquid water-soluble fertilizer for crops includes the following steps:

[0014] (1) Weigh out the following by weight: 55-65 parts of clarified biogas slurry, 10-15 parts of sugarcane molasses, 2-3 parts of synergist, 3-5 parts of urea, 3-6 parts of potassium sulfate, 2-4 parts of potassium dihydrogen phosphate, and 10-20 parts of deionized water.

[0015] (2) Mix the clarified biogas slurry and deionized water, add sugarcane molasses and stir, perform the first pH adjustment and then heat treatment; after cooling, add synergist and stir, add urea and stir, add potassium sulfate in batches and stir, add potassium dihydrogen phosphate in batches and stir, and after degassing, perform the second pH adjustment to obtain the final product.

[0016] The pH range for the first pH adjustment is 5.5-6.5.

[0017] The heat treatment operation is as follows: heat to 65-75℃ at a heating rate of 1-2℃ / min, and hold at that temperature for 25-35min.

[0018] The pH range for the second pH adjustment is 5.0-6.0.

[0019] Due to the adoption of the above technical solutions, the beneficial effects of the present invention include:

[0020] (1) The synergist prepared in this application has hydroxyl, carboxyl, sulfonic acid and lignin aromatic structures, wherein the carboxyl and sulfonic acid groups can react with Ca in biogas slurry. 2+ Mg2+ Fe 3+ The complexation and adsorption of polyvalent metal ions reduce the likelihood of them combining with phosphate to form insoluble phosphates, thereby improving the soluble phosphorus retention rate during the storage of liquid water-soluble fertilizer. Simultaneously, the ammonium lignin sulfonate structure can adsorb onto the surface of inorganic and colloidal particles in biogas slurry. The carboxyl and sulfonic acid groups enhance the hydrophilicity and electrostatic repulsion of the particle surface, while the corn dextrin segments inhibit particle aggregation through polyhydroxyl hydration and steric hindrance. The synergistic effect of these structures in the synergist results in a high soluble phosphorus retention rate and a low rate of water-insoluble precipitation during storage of the prepared liquid water-soluble fertilizer.

[0021] (2) In this application, after the clarified biogas slurry and sugarcane molasses are mixed and heat-treated, an synergist is added first to allow it to react with polyvalent metal ions and colloidal particles in advance, followed by the addition of urea, potassium sulfate, and finally potassium dihydrogen phosphate. This order of addition can form a stable complexing and dispersion environment before phosphate enters the system, reduce the initial nucleation of phosphate, and is more conducive to maintaining the soluble state of phosphorus.

[0022] (3) Clarified biogas slurry and sugarcane molasses can provide nitrogen, potassium, organic matter and a variety of micronutrients. Urea, potassium sulfate and potassium dihydrogen phosphate further supplement the macronutrients required by crops. Synergists improve the stability of phosphorus, reduce nutrient precipitation loss and improve fertilizer dispersibility, making nutrients easier for crop roots to absorb and utilize after application, thereby increasing crop yield. Attached Figure Description

[0023] Figure 1 Fourier transform infrared spectrum of the synergist.

[0024] Figure 2 The full X-ray photoelectron spectrum of the synergist. Detailed Implementation

[0025] The following description, in conjunction with specific embodiments, provides further details, but the present invention is not limited to these embodiments.

[0026] Example 1: Preparation of the synergist

[0027] S1: Add 400ml of deionized water and 100g of corn dextrin to the reaction flask and stir at 55℃ and 400rpm for 30min; add 50g of ammonium lignosulfonate and continue stirring at 55℃ and 400rpm for 30min; adjust the pH to 4.8 using 10wt% dilute sulfuric acid aqueous solution or 10wt% ammonia water to obtain the basic reaction solution; purge nitrogen gas into the reaction flask at a flow rate of 0.2L / min for 20min to reduce dissolved oxygen in the reaction system, then adjust the nitrogen flow rate to 0.05L / min and maintain nitrogen protection at atmospheric pressure during the subsequent reaction process.

[0028] S2: Mix 50ml of deionized water and 10g of itaconic acid at 35℃ and 300rpm, then slowly add 7.8g of 10wt% ammonia solution dropwise over 15min. Stir at 300rpm for 15min to obtain a neutralized itaconic acid solution. Dissolve 0.6g of ammonium persulfate in 20ml of deionized water to obtain an ammonium persulfate aqueous solution. Dissolve 0.3g of sodium bisulfite in 20ml of deionized water to obtain a sodium bisulfite aqueous solution.

[0029] S3: Heat all the basic reaction solution obtained in step S1 to 60℃, and simultaneously add all the itaconic acid neutralization solution, all the ammonium persulfate aqueous solution, and all the sodium bisulfite aqueous solution to the reaction flask at 400 rpm (controlling the reaction temperature at 60℃ during the addition, and maintaining the pH at 4.8 using 10wt% dilute sulfuric acid aqueous solution or 10wt% ammonia water). Add all three solutions dropwise over 60 minutes, and continue the reaction at 60℃ and 400 rpm for 2 hours. Then, increase the temperature to 75℃ at a rate of 1℃ / min and hold at 400 rpm for 30 minutes. Cool down to 55℃, and... The stirring speed was reduced to 300 rpm, and a vacuum was first drawn to a gauge pressure of -0.05 MPa and maintained for 10 min. Then the vacuum was increased to a gauge pressure of -0.09 MPa, and the system was concentrated under reduced pressure at 55°C until the solid content was 42.7 wt% (measured by vacuum drying). The vacuum was released and the system was restored to normal pressure. The concentrate was cooled to 40°C, and the pH of the system was adjusted to 4.8 using a 10 wt% dilute sulfuric acid aqueous solution or a 10 wt% ammonia solution. Deionized water was added to adjust the solid content to 40 wt%. The mixture was stirred for another 15 min, and the resulting concentrate was filtered through a 100 μm filter to obtain the synergist.

[0030] In the above preparation process, ammonium persulfate and sodium bisulfite form a redox initiation system, generating free radical active species that promote the formation of active sites in corn dextrin and ammonium lignin sulfonate, and then undergo addition with the itaconic acid double bond, thereby introducing carboxyl-containing itaconic acid units to form an itaconic acid-modified dextrin-lignin sulfonate composite synergist. After partial neutralization, the water solubility of itaconic acid can be improved, while retaining a certain amount of free carboxyl groups.

[0031] Figure 1 The Fourier transform infrared spectrum of the synergist is shown in the figure. As can be seen from the figure, at 3418 cm⁻¹... -1 A broad and strong absorption peak appeared nearby, which can be attributed to the stretching vibration of OH introduced into the carboxyl group by corn dextrin, ammonium lignin sulfonate, and the 2932 cm⁻¹. -1 and 2872cm -1 The nearby absorption peak corresponds to the aliphatic CH stretching vibration; 1718 cm⁻¹ -1 An absorption peak for the stretching vibration of the C=O group in the carboxyl group appeared nearby, at 1602 cm⁻¹. -1The nearby absorption peaks can be attributed to the carboxylate group COO. - The overlap absorption of asymmetric stretching vibrations and lignin aromatic skeleton vibrations, 1414 cm⁻¹ -1 Carboxylate ions (COO) appeared nearby. - Symmetric stretching vibration related absorption peak; 1512 cm⁻¹ -1 The nearby absorption peak corresponds to the vibration of the lignin aromatic ring skeleton, indicating that the synergist retains the lignin aromatic structure; 1184 cm⁻¹ -1 The nearby absorption peak is related to the S=O stretching vibration in the sulfonic acid group; 1153 cm⁻¹ -1 and 1078cm -1 The nearby absorption peak is related to the stretching vibrations of the polysaccharide glycosidic bond COC and CO; 1032 cm⁻¹ -1 Overlapping absorption peaks were observed in the vicinity of SO stretching vibration of sulfonic acid group and CO stretching vibration of polysaccharide.

[0032] Figure 2 The X-ray photoelectron spectroscopy (XPS) spectrum of the synergist is shown. As can be seen from the figure, characteristic peaks of C 1s, N 1s, O 1s, S 2p, and S 2s appear at approximately 284.8 eV, 401.4 eV, 532.6 eV, 168.5 eV, and 232.4 eV, respectively. The C 1s and O 1s peaks mainly originate from the carbon skeleton, hydroxyl groups, ether bonds, carboxyl groups, and sulfonic acid groups in corn dextrin, ammonium lignin sulfonate, and itaconic acid; the N 1s peak is mainly related to the ammonium ions in ammonium lignin sulfonate and the ammonium salt formed after partial neutralization by itaconic acid; the S 2p and S 2s peaks are attributed to the high-valence sulfur contained in the sulfonic acid groups of ammonium lignin sulfonate. The above infrared and XPS results together indicate that the prepared synergist simultaneously contains hydroxyl, carboxyl, sulfonic acid, and lignin aromatic structures.

[0033] Example 2: Preparation of Molasses-Biogas Slurry Crop-Specific Liquid Water-Soluble Fertilizer:

[0034] (1) Weigh out: 550g of clarified biogas slurry, 100g of sugarcane molasses, 20g of synergist (prepared in Example 1), 30g of urea, 30g of potassium sulfate, 20g of potassium dihydrogen phosphate, and 100g of deionized water;

[0035] (2) Mix clarified biogas slurry and deionized water, stir at 400 rpm for 10 min, add sugarcane molasses, continue stirring for 20 min, adjust pH to 5.5 with 10 wt% citric acid aqueous solution, heat to 65 ℃ at a heating rate of 1 ℃ / min, and keep warm at 400 rpm for 35 min; cool down to 45 ℃, add synergist at 400 rpm, continue stirring for 20 min, add urea and continue stirring for 15 min; add potassium sulfate in 3 equal batches (5 min interval between batches), and continue stirring for 20 min after all the potassium sulfate has been added; finally add potassium dihydrogen phosphate in 3 equal batches (5 min interval between batches), and continue stirring for 30 min after all the potassium dihydrogen phosphate has been added; cool to room temperature, degas under vacuum (25 ℃, -0.09 MPa) for 20 min, adjust pH to 5.0 with 10 wt% citric acid aqueous solution or 10 wt% ammonia water, and filter through a filter with a pore size of 100 μm to obtain molasses-biogas slurry crop-specific liquid water-soluble fertilizer.

[0036] Example 3: Preparation of Molasses-Biogas Slurry Crop-Specific Liquid Water-Soluble Fertilizer:

[0037] (1) Weigh out: 600g of clarified biogas slurry, 120g of sugarcane molasses, 25g of synergist (prepared in Example 1), 40g of urea, 45g of potassium sulfate, 30g of potassium dihydrogen phosphate, and 150g of deionized water;

[0038] (2) Mix clarified biogas slurry and deionized water, stir at 400 rpm for 10 min, add sugarcane molasses, continue stirring for 20 min, adjust pH to 6.0 with 10 wt% citric acid aqueous solution, heat to 70 ℃ at a heating rate of 1 ℃ / min, and keep warm at 400 rpm for 30 min; cool down to 45 ℃, add synergist at 400 rpm, continue stirring for 20 min, add urea and continue stirring for 15 min; add potassium sulfate in 3 equal batches (5 min interval between batches), and continue stirring for 20 min after all the potassium sulfate has been added; finally add potassium dihydrogen phosphate in 3 equal batches (5 min interval between batches), and continue stirring for 30 min after all the potassium dihydrogen phosphate has been added; cool to room temperature, degas under vacuum (25 ℃, -0.09 MPa) for 20 min, adjust pH to 5.5 with 10 wt% citric acid aqueous solution or 10 wt% ammonia water, and filter through a filter with a pore size of 100 μm to obtain molasses-biogas slurry crop-specific liquid water-soluble fertilizer.

[0039] Example 4: Preparation of Molasses-Biogas Slurry Crop-Specific Liquid Water-Soluble Fertilizer:

[0040] (1) Weigh out: 650g of clarified biogas slurry, 150g of sugarcane molasses, 30g of synergist (prepared in Example 1), 50g of urea, 60g of potassium sulfate, 40g of potassium dihydrogen phosphate, and 200g of deionized water;

[0041] (2) Mix clarified biogas slurry and deionized water, stir at 400 rpm for 10 min, add sugarcane molasses, continue stirring for 20 min, adjust pH to 6.5 with 10 wt% citric acid aqueous solution, heat to 75 ℃ at a heating rate of 2 ℃ / min, and keep warm at 400 rpm for 25 min; cool down to 45 ℃, add synergist at 400 rpm, continue stirring for 20 min, add urea and continue stirring for 15 min; add potassium sulfate in 3 equal batches (5 min interval between batches), and continue stirring for 20 min after all the potassium sulfate has been added; finally add potassium dihydrogen phosphate in 3 equal batches (5 min interval between batches), and continue stirring for 30 min after all the potassium dihydrogen phosphate has been added; cool to room temperature, degas under vacuum (25 ℃, -0.09 MPa) for 20 min, adjust pH to 6.0 with 10 wt% citric acid aqueous solution or 10 wt% ammonia water, and filter through a filter with a pore size of 100 μm to obtain molasses-biogas slurry crop-specific liquid water-soluble fertilizer.

[0042] Comparative Example 1

[0043] The raw material composition and preparation method of the molasses-biogas slurry crop-specific liquid water-soluble fertilizer are basically the same as those in Example 3. The difference is that the synergist is replaced with an equal weight of humic acid.

[0044] Comparative Example 2

[0045] The raw material composition and preparation method of the molasses-biogas slurry crop-specific liquid water-soluble fertilizer are basically the same as those in Example 3, except that the synergist is replaced with an equal weight of a physically mixed synergist prepared by the following method:

[0046] S1: Add 400ml of deionized water and 100g of corn dextrin to the reaction flask and stir at 55℃ and 400rpm for 30min; add 50g of ammonium lignosulfonate and continue stirring at 55℃ and 400rpm for 30min; adjust the pH to 4.8 using 10wt% dilute sulfuric acid aqueous solution or 10wt% ammonia water to obtain the basic reaction solution.

[0047] S2: Mix 50ml of deionized water and 10g of itaconic acid at 35℃ and 300rpm. Slowly add 7.8g of 10wt% ammonia water dropwise over 15min. Stir at 300rpm for 15min to obtain a neutralized itaconic acid solution.

[0048] S3: Heat all the basic reaction solution obtained in step S1 to 60℃, and add all the itaconic acid neutralization solution dropwise to the reaction flask at 400 rpm (control the reaction temperature at 60℃ during the dropwise addition, and maintain the pH at 4.8 using 10wt% dilute sulfuric acid aqueous solution or 10wt% ammonia water). After the dropwise addition is completed in 60 min, continue the reaction at 60℃ and 400 rpm for 2 h; then heat to 75℃ at a heating rate of 1℃ / min, and hold at 400 rpm for 30 min; cool to 55℃, reduce the stirring speed to 300 rpm, and first... The vacuum was evacuated to a gauge pressure of -0.05 MPa and maintained for 10 min. The vacuum was then increased to a gauge pressure of -0.09 MPa. The system was concentrated under reduced pressure at 55 °C until the solid content was 43.1 wt% (measured by vacuum drying). The vacuum was released and the system was brought back to normal pressure. The concentrate was cooled to 40 °C. The pH of the system was adjusted to 4.8 using a 10 wt% dilute sulfuric acid aqueous solution or a 10 wt% ammonia solution. Deionized water was added to adjust the solid content to 40 wt%. The mixture was stirred for another 15 min. The resulting concentrate was filtered through a 100 μm filter to obtain the synergist.

[0049] Comparative Example 3

[0050] The raw material composition and preparation method of the molasses-biogas slurry crop-specific liquid water-soluble fertilizer are basically the same as those in Example 3, except that the synergist is replaced with an equal weight of the synergist prepared by the following method:

[0051] S1: Add 400ml of deionized water and 100g of corn dextrin to the reaction flask, stir at 55℃ and 400rpm for 30min, adjust the pH to 4.8 with 10wt% dilute sulfuric acid solution or 10wt% ammonia solution to obtain corn dextrin dispersion; purge nitrogen gas into the reaction flask at a flow rate of 0.2L / min for 20min to reduce dissolved oxygen in the reaction system, then adjust the nitrogen flow rate to 0.05L / min, and maintain nitrogen protection at atmospheric pressure during the subsequent reaction process.

[0052] S2: Mix 50ml of deionized water and 10g of itaconic acid at 35℃ and 300rpm, then slowly add 7.8g of 10wt% ammonia solution dropwise over 15min. Stir at 300rpm for 15min to obtain a neutralized itaconic acid solution. Dissolve 0.6g of ammonium persulfate in 20ml of deionized water to obtain an ammonium persulfate aqueous solution. Dissolve 0.3g of sodium bisulfite in 20ml of deionized water to obtain a sodium bisulfite aqueous solution.

[0053] S3: Heat the corn dextrin dispersion obtained in step S1 to 60℃, and simultaneously add all the itaconic acid neutralization solution, all the ammonium persulfate aqueous solution, and all the sodium bisulfite aqueous solution to the reaction flask at 400 rpm (the reaction temperature is controlled at 60℃ during the addition, and the pH is maintained at 4.8 using 10wt% dilute sulfuric acid aqueous solution or 10wt% ammonia water). All three solutions are added dropwise over 60 min, and the reaction continues at 60℃ and 400 rpm for 2 h. Then, the temperature is increased to 75℃ at a rate of 1℃ / min and held at 400 rpm for 30 min. The temperature is then lowered to 55℃, and 50g of lignin is added. Ammonium sulfonate was stirred at 300 rpm for 30 min. A vacuum was first applied to a gauge pressure of -0.05 MPa and maintained for 10 min. The vacuum was then increased to a gauge pressure of -0.09 MPa. The mixture was concentrated under reduced pressure at 55 °C until the solid content of the system reached 42.3 wt% (measured by vacuum drying). The vacuum was released and the system was brought back to normal pressure. The concentrate was cooled to 40 °C. The pH of the system was adjusted to 4.8 using a 10 wt% dilute sulfuric acid aqueous solution or a 10 wt% ammonia solution. Deionized water was added to adjust the solid content to 40 wt%. Stirring was continued for 15 min. The resulting concentrate was filtered through a 100 μm filter to obtain the synergist.

[0054] Comparative Example 4

[0055] The raw material composition and preparation method of the molasses-biogas slurry crop-specific liquid water-soluble fertilizer are basically the same as those in Example 3, except that the synergist is replaced with an equal weight of the synergist prepared by the following method:

[0056] S1: Add 400ml of deionized water and 50g of ammonium lignosulfonate to the reaction flask, stir at 55℃ and 400rpm for 30min, adjust the pH to 4.8 with 10wt% dilute sulfuric acid solution or 10wt% ammonia solution to obtain ammonium lignosulfonate aqueous solution; introduce nitrogen gas into the reaction flask at a flow rate of 0.2L / min for 20min to reduce dissolved oxygen in the reaction system, then adjust the nitrogen flow rate to 0.05L / min, and maintain nitrogen protection at atmospheric pressure during the subsequent reaction process.

[0057] S2: Mix 50ml of deionized water and 10g of itaconic acid at 35℃ and 300rpm, then slowly add 7.8g of 10wt% ammonia solution dropwise over 15min. Stir at 300rpm for 15min to obtain a neutralized itaconic acid solution. Dissolve 0.6g of ammonium persulfate in 20ml of deionized water to obtain an ammonium persulfate aqueous solution. Dissolve 0.3g of sodium bisulfite in 20ml of deionized water to obtain a sodium bisulfite aqueous solution.

[0058] S3: Heat the ammonium lignosulfonate aqueous solution obtained in step S1 to 60℃, and simultaneously add all itaconic acid neutralization solution, all ammonium persulfate aqueous solution, and all sodium bisulfite aqueous solution to the reaction flask at 400 rpm (controlling the reaction temperature at 60℃ during the addition, and maintaining the pH at 4.8 using 10wt% dilute sulfuric acid aqueous solution or 10wt% ammonia water). All three solutions are added dropwise over 60 minutes. Continue the reaction at 60℃ and 400 rpm for 2 hours. Then, increase the temperature to 75℃ at a rate of 1℃ / min and maintain the temperature at 400 rpm for 30 minutes. Cool down to 55℃ and add 100... g of corn dextrin was stirred at 300 rpm for 30 min. First, a vacuum was drawn to a gauge pressure of -0.05 MPa and maintained for 10 min. Then, the vacuum was increased to a gauge pressure of -0.09 MPa. The mixture was concentrated under reduced pressure at 55 °C until the solid content of the system was 43.6 wt% (measured by vacuum drying). The vacuum was released and the system was brought back to normal pressure. The concentrate was cooled to 40 °C. The pH of the system was adjusted to 4.8 using a 10 wt% dilute sulfuric acid aqueous solution or a 10 wt% ammonia solution. Deionized water was added to adjust the solid content to 40 wt%. The mixture was stirred for another 15 min. The resulting concentrate was filtered through a 100 μm filter to obtain the synergist.

[0059] Comparative Example 5

[0060] The raw material composition and preparation method of the molasses-biogas slurry crop-specific liquid water-soluble fertilizer are basically the same as those in Example 3, except that the synergist is replaced with an equal weight of the synergist prepared by the following method:

[0061] The preparation method of the synergist is basically the same as that in Example 1, except that 10g itaconic acid in step S2 is replaced with 8.93g maleic acid.

[0062] Comparative Example 6

[0063] The raw material composition and preparation method of the molasses-biogas slurry crop-specific liquid water-soluble fertilizer are basically the same as those in Example 3, except that the synergist is replaced with an equal weight of the synergist prepared by the following method:

[0064] The preparation method of the synergist is basically the same as that in Example 1, except that the amount of 10wt% ammonia in step S2 is replaced with 13g.

[0065] Comparative Example 7

[0066] The preparation method of molasses-biogas slurry crop-specific liquid water-soluble fertilizer is as follows:

[0067] (1) Weigh out: 600g of clarified biogas slurry, 120g of sugarcane molasses, 25g of synergist (prepared in Example 1), 40g of urea, 45g of potassium sulfate, 30g of potassium dihydrogen phosphate, and 150g of deionized water;

[0068] (2) Mix clarified biogas slurry and deionized water, stir at 400 rpm for 10 min, add sugarcane molasses, continue stirring for 20 min, adjust pH to 6.0 with 10 wt% citric acid aqueous solution, heat to 70 ℃ at a heating rate of 1 ℃ / min, keep warm at 400 rpm for 30 min; cool to 45 ℃, add urea and continue stirring for 15 min; add potassium sulfate in 3 equal batches (5 min interval between batches), and continue stirring for 20 min after all additions; add potassium dihydrogen phosphate in 3 equal batches (5 min interval between batches), and continue stirring for 30 min after all additions; add synergist at 400 rpm and continue stirring for 20 min; cool to room temperature, degas under vacuum (25 ℃, -0.09 MPa) for 20 min, adjust pH to 5.5 with 10 wt% citric acid aqueous solution or 10 wt% ammonia water, filter through a filter with a pore size of 100 μm to obtain molasses-biogas slurry crop-specific liquid water-soluble fertilizer.

[0069] The corn dextrin used in the embodiments and comparative examples of this application is food-grade corn dextrin with a purity of 99% (on a dry basis) and a number-average molecular weight of 10,000, produced by Wuhan Pushida Biotechnology Co., Ltd.; the ammonium lignin sulfonate has a dry component content of 94.1 wt%, a moisture content of 5.9 wt%, a water-insoluble matter content of 1.4 wt%, and a lignin sulfonate content of 58.7 wt%, produced by Shenyang Xingzhenghe Chemical Co., Ltd.; the sugarcane molasses is produced by Guangxi Nanning Sugar Industry Co., Ltd. Mingyang Sugar Factory, and its main components and contents are as follows: Brix of 86.02°Bx, total sugar of 45.52 wt% (of which sucrose is 26%). The anaerobic digestate contained 0.58 wt% reducing sugar, 3.81% colloids, a pH of 5.19, and 9.85% ash. The clarified digestate was obtained by filtration of the supernatant from the anaerobic fermentation of cow dung, after standing for 12 hours, through filters with pore sizes of 200 μm and 50 μm. The urea contained 46.0 wt% total nitrogen, 0.5 wt% moisture, and 0.9 wt% biuret, and was produced by Henan Zhongyuan Dahua Group Co., Ltd. The potassium sulfate was "Lop Nur" brand water-soluble agricultural potassium sulfate, with a K2O content of 53.8 wt%, a S content of 18.0 wt%, and a Cl- content of 9.85%. - The content is 0.5wt%, produced by SDIC Xinjiang Lop Nur Potash Co., Ltd.; the potassium dihydrogen phosphate is industrial grade potassium dihydrogen phosphate, with KH2PO4 content of 99.2wt% and water-insoluble matter content of 0.09wt%, produced by Sichuan Shengfeng Phosphate Chemical Co., Ltd.

[0070] The molasses-biogas slurry crop-specific liquid water-soluble fertilizers prepared in the examples and comparative examples were tested for soluble phosphorus retention rate, storage water insoluble precipitation rate, and yield increase rate of Chinese cabbage. The test results are shown in Table 1.

[0071] Soluble phosphorus retention rate test: 200g of the liquid water-soluble fertilizer prepared in each example and comparative example was placed into a 300ml high-density polyethylene bottle, sealed, and stored at 25℃ in the dark for 90 days. Three parallel samples were set up for each group. A freshly prepared sample from the same batch was used as the pre-storage sample. During the test, the pre-storage sample and the sample after 90 days of storage were inverted and mixed 10 times, centrifuged at 3000rpm for 10min, and the supernatant was filtered through a 0.45μm filter membrane. 1g of the filtrate was weighed, 5ml of nitric acid and 2ml of 30wt% hydrogen peroxide were added, and the mixture was heated to 120℃ and digested for 50min in an electrothermal digester. After cooling to room temperature, the volume was adjusted to 50ml with deionized water. The phosphorus content in the filtrate was determined using inductively coupled plasma atomic emission spectrometry (ICP-AES). The soluble phosphorus retention rate was calculated according to the formula P=C. 90 / C0×100% (C0 is the soluble phosphorus content in the sample filtrate before storage; C 90 The soluble phosphorus content in the filtrate of the sample after 90 days of storage at 25℃ was calculated, and the average value of the results from 3 parallel samples was taken.

[0072] Test for insoluble precipitate rate during storage: 200g (denoted as m0) of the liquid water-soluble fertilizer prepared in each example and comparative example was placed into a 300ml high-density polyethylene bottle, sealed, and stored at 25℃ in the dark for 90 days. Three parallel samples were set up for each group. After storage, the supernatant was slowly poured out without shaking the sample. The bottom and walls of the bottle were rinsed three times with 30ml of deionized water. The precipitate and rinsing liquid were transferred to a glass centrifuge tube that had been dried to constant weight at 105℃ and weighed as m1. The tube was centrifuged at 2000rpm for 10min, the supernatant was discarded, and 30ml of deionized water was added to redisperse the precipitate. The tube was centrifuged at 2000rpm for 10min, and the supernatant was discarded to remove soluble salts entrained in the precipitate. The glass centrifuge tube and the obtained precipitate were dried to constant weight at 105℃, cooled to room temperature, and the total mass was weighed and recorded as m2. The insoluble precipitation rate of stored water is calculated according to the formula: R=[(m2-m1) / m0]×100%.

[0073] The liquid water-soluble fertilizers prepared in the examples and comparative examples were tested in Shalong Village, Yanxi Town, Liuyang City, Changsha City, Hunan Province. Basic soil physicochemical properties: pH 6.5, organic matter content 28.42 g / kg, available nitrogen content 108.34 mg / kg, available phosphorus content 8.95 mg / kg, and available potassium content 84.79 mg / kg.

[0074] A field trial was conducted on Chinese cabbage to investigate the effect of the liquid water-soluble fertilizer prepared in this invention on the yield of Chinese cabbage.

[0075] 1. Test materials

[0076] The tested crop was the heat-resistant 605 Chinese cabbage variety.

[0077] Fertilizers tested:

[0078] Base fertilizer: Commercially available Shikefeng compound fertilizer, in accordance with standard GB15063-2020, with a total nutrient content of 28wt% (N-P2O5-K2O mass ratio of 15:5:8), nitrate-sulfur based type.

[0079] Water-soluble fertilizer: The liquid water-soluble fertilizer prepared in the embodiments and comparative examples of this invention was stored for 90 days at 25±2℃, in the dark and sealed conditions after preparation, and then used in field fertilization trials of Chinese cabbage.

[0080] 2. Experimental Design

[0081] The experiment consisted of 10 groups (10 test plots, each plot being 12.95m long and 1.75m wide; with a 0.5m wide isolation strip between plots), and the treatment for each group was as follows:

[0082] Blank control group: Only basal fertilizer was applied.

[0083] Experimental group: Base fertilizer + liquid water-soluble fertilizer prepared in Examples 2-4 of this invention, applied separately.

[0084] Control group: Base fertilizer + liquid water-soluble fertilizer prepared by comparative examples 1-6 of this invention, applied by irrigation.

[0085] 3. Test methods

[0086] 3.1 Application of base fertilizer

[0087] Before planting bok choy, evenly spread 0.6 kg of compound fertilizer in each plot, then till the soil to mix the fertilizer thoroughly with the soil layer at a depth of 0-20 cm, and then rake it flat for later use.

[0088] 3.2 Planting methods and planting time

[0089] Planting Method: Bok choy will be planted using the hill-sowing method. Each plot will have 4 rows, with a row spacing of 0.35m and a hill spacing of 0.25m (the first and 50th columns will be 0.35m from the plot edge). Each row will have 50 hills, with 6 seeds sown per hill (the first, fourth, first, and 50th columns will be 0.35m from the plot edge). After sowing, cover with 1cm of soil and water thoroughly. Thin the seedlings when they have 2-3 true leaves, removing weak and diseased seedlings. When they have 4-5 true leaves, finalize the seedlings, retaining one healthy, uniformly sized seedling per hill, ultimately maintaining 200 bok choy plants per plot. Planting Date: August 20, 2025

[0090] 3.3 Application of water-soluble fertilizers

[0091] On the 20th day after sowing, both the experimental and control groups of pakchoi received water-soluble fertilizer in the evening. The application method was as follows: 200 mL of the corresponding water-soluble fertilizer for each group was measured and diluted with water at a volume ratio of 1:175 (i.e., 200 mL of fertilizer added to 35 L of water). After thorough mixing, the solution was evenly applied to the soil around the roots of the pakchoi using a handheld watering can. The control group received the same amount of water at the same time.

[0092] 3.4 Field Management

[0093] Throughout the entire growth period of the bok choy, apart from applying different water-soluble fertilizers according to the experimental design, all other field management practices remained consistent across the plots:

[0094] Watering was carried out 6 times, on the 1st, 8th, 14th, 28th, 36th and 45th days after sowing. Each time, 35L of water was used for each plot, and the water was sprayed evenly on the soil around the roots of the cabbage using a sprayer. Weeding was carried out 3 times, on the 15th, 25th and 40th days after sowing.

[0095] 3.5 Sample Collection and Measurement

[0096] Fifty days after the bok choy was sown, each plot was harvested in sections, and the actual yield was weighed and recorded.

[0097] The yield increase rate is calculated using the following formula: Yield increase rate = (Experimental group yield or control group yield - Blank control group yield) / Blank control group yield × 100%.

[0098] Table 1 Performance Test Data of Molasses-Biogas Slurry Crop-Specific Liquid Water-Soluble Fertilizer

[0099] project Soluble phosphorus retention rate / % Storage water insoluble precipitation rate / % Production increase rate / % Example 2 96.2 0.23 8.5 Example 3 97.0 0.17 9.4 Example 4 94.6 0.28 9.0 Comparative Example 1 86.5 0.76 4.6 Comparative Example 2 84.3 0.89 3.1 Comparative Example 3 89.7 0.64 5.7 Comparative Example 4 91.1 0.45 6.3 Comparative Example 5 93.4 0.31 7.9 Comparative Example 6 91.8 0.40 7.2 Comparative Example 7 83.9 0.62 5.8

[0100] As can be seen from Table 1, the molasses-biogas slurry crop-specific liquid water-soluble fertilizer prepared in the embodiments of this application has a high soluble phosphorus retention rate, a low long-term storage water-insoluble precipitation rate, and a good yield-increasing effect.

[0101] In Comparative Example 1, although humic acid contains carboxyl and phenolic hydroxyl groups and has a certain complexing ability, its water solubility and dispersion stability are weak, and it lacks the synergistic effect of carboxyl, sulfonic acid, and hydrophilic polymer segments in the synergist of this application. 2+ Mg 2 + Fe 2+ The plasma's complexing and dispersing ability is insufficient, resulting in a decrease in the retention rate of soluble phosphorus, an increase in the insoluble precipitation rate in stored water, and a decline in the yield-increasing effect.

[0102] In Comparative Example 2, corn dextrin, ammonium lignin sulfonate, and itaconic acid were only physically mixed. Although they still had certain hydration, dispersion, and complexation effects, the functional components did not form a stable composite structure. During long-term storage, they were prone to migration and redistribution and could not continuously and synergistically stabilize metal ions and colloidal particles, thus reducing their performance.

[0103] In Comparative Example 3, itaconic acid only modified corn dextrin. The resulting modified corn dextrin had certain carboxyl complexation and steric hindrance effects. However, the added ammonium lignin sulfonate did not participate in the reaction. Its particle adsorption effect and the steric protection effect of the modified corn dextrin could not be stably synergistic, resulting in a decline in the performance of water-soluble fertilizer.

[0104] In Comparative Example 4, itaconic acid only modified ammonium lignosulfonate. The resulting product had good metal ion binding and particle adsorption capabilities. However, the corn dextrin added later did not form a stable bond with it, making it difficult to continuously provide a sufficient hydration layer and steric hindrance on the particle surface. Therefore, the long-term storage stability and nutrient utilization rate were reduced.

[0105] In Comparative Example 5, although maleic acid can also introduce carboxyl groups and participate in free radical modification, the distribution of carboxyl groups after the reaction is more concentrated, the chain segment extension and the degree of effective utilization of some carboxyl groups are lower than those of itaconic acid modified structure, and the comprehensive stabilizing effect on polyvalent metal ions, phosphate crystal nuclei and colloidal particles is weaker, so the performance of water-soluble fertilizer is reduced.

[0106] In Comparative Example 6, increasing the amount of ammonia used during itaconic acid neutralization resulted in excessive itaconic acid neutralization, which increased the ionization degree and ionic strength of the system. This altered the free radical grafting reaction environment of itaconic acid with corn dextrin and ammonium lignin sulfonate, affecting the grafting degree and functional group distribution of the resulting synergist. Consequently, it weakened the complexing and dispersing stabilizing effect on polyvalent metal ions, leading to a decrease in soluble phosphorus retention rate and yield increase, and an increase in the insoluble precipitation rate in storage water.

[0107] In Comparative Example 7, when potassium dihydrogen phosphate was added followed by the synergist, the phosphate ions had already reacted with some of the Ca. 2+ Mg 2+ Fe 3+ The particles come into contact with each other and form primary crystal nuclei or precipitates. Although the added synergists can inhibit the continued growth and aggregation of particles, they are difficult to completely restore the phosphorus that has been converted into an insoluble state. As a result, the soluble phosphorus retention rate decreases, the insoluble precipitation rate in the stored water increases, and the yield increase effect decreases.

[0108] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. However, any modifications, alterations, and variations made by those skilled in the art without departing from the scope of the present invention based on the disclosed technical content are equivalent embodiments of the present invention. Furthermore, any modifications, alterations, and variations made to the above embodiments based on the essential technology of the present invention are still within the protection scope of the present invention.

Claims

1. A molasses-biogas slurry crop-specific liquid water-soluble fertilizer, characterized in that, The raw materials include the following parts by weight: 55-65 parts clarified biogas slurry, 10-15 parts sugarcane molasses, 2-3 parts synergist, 3-5 parts urea, 3-6 parts potassium sulfate, 2-4 parts potassium dihydrogen phosphate, and 10-20 parts deionized water. The synergist is prepared by the following method: Corn dextrin was mixed with deionized water, and ammonium lignosulfonate was added and stirred. The pH was adjusted to obtain the basic reaction solution. Itaconic acid was dissolved in deionized water and neutralized with ammonia to obtain a neutralized itaconic acid solution. The neutralized itaconic acid solution, ammonium persulfate solution, and sodium bisulfite solution were added dropwise to the basic reaction solution to react and obtain the synergist.

2. The molasses-biogas slurry crop-specific liquid water-soluble fertilizer according to claim 1, characterized in that, The mass ratio of corn dextrin, ammonium lignin sulfonate, itaconic acid, ammonium persulfate, and sodium bisulfite is 100:50:10:0.6:0.

3.

3. The molasses-biogas slurry crop-specific liquid water-soluble fertilizer according to claim 1, characterized in that, The ammonia solution has a mass concentration of 10 wt%, and the amount of ammonia solution used is 78% of the mass of itaconic acid.

4. The molasses-biogas slurry crop-specific liquid water-soluble fertilizer according to claim 1, characterized in that, The mass concentration of the ammonium persulfate aqueous solution is 30 g / L.

5. The molasses-biogas slurry crop-specific liquid water-soluble fertilizer according to claim 1, characterized in that, The sodium bisulfite aqueous solution has a mass concentration of 15 g / L.

6. The molasses-biogas slurry crop-specific liquid water-soluble fertilizer according to claim 1, characterized in that, The reaction conditions are as follows: first react at 60℃ for 2 hours, then keep warm at 75℃ for 30 minutes.

7. A method for preparing a molasses-biogas slurry crop-specific liquid water-soluble fertilizer according to any one of claims 1-6, characterized in that, Includes the following steps: (1) Weigh out the following by weight: 55-65 parts of clarified biogas slurry, 10-15 parts of sugarcane molasses, 2-3 parts of synergist, 3-5 parts of urea, 3-6 parts of potassium sulfate, 2-4 parts of potassium dihydrogen phosphate, and 10-20 parts of deionized water. (2) Mix the clarified biogas slurry and deionized water, add sugarcane molasses and stir, perform the first pH adjustment and then heat treatment; after cooling, add synergist and stir, add urea and stir, add potassium sulfate in batches and stir, add potassium dihydrogen phosphate in batches and stir, and after degassing, perform the second pH adjustment to obtain the final product.

8. The method for preparing a molasses-biogas slurry crop-specific liquid water-soluble fertilizer according to claim 7, characterized in that, The pH range for the first pH adjustment is 5.5-6.

5.

9. The method for preparing a molasses-biogas slurry crop-specific liquid water-soluble fertilizer according to claim 7, characterized in that, The heat treatment operation is as follows: heat to 65-75℃ at a heating rate of 1-2℃ / min, and hold at that temperature for 25-35min.

10. The method for preparing a molasses-biogas slurry crop-specific liquid water-soluble fertilizer according to claim 7, characterized in that, The pH range for the second pH adjustment is 5.0-6.0.

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