A saline-alkali soil improvement liquid fertilizer, a preparation method and application thereof

Abstract

The application discloses a saline-alkali soil improvement liquid fertilizer and a preparation method and application thereof, and relates to the technical field of liquid fertilizers.The saline-alkali soil improvement liquid fertilizer is prepared by taking acid pulping waste liquid rich in lignin sulfonate as a skeleton, taking fulvic acid and amino acid as functional monomers, preparing a terpolymer through a free radical graft copolymerization reaction, and then adding sodium sulfinate into the terpolymer to improve the content of sulfonic acid groups in the terpolymer.The liquid fertilizer has the structural improvement ability of lignin sulfonate, the buffer complexing ability of fulvic acid and the nutritional activity of amino acid, and can realize the synergistic improvement of saline-alkali soil from three dimensions of chemical alkali reduction, physical salt removal and structure improvement.

Description

Technical Field

[0001] This invention relates to the field of liquid fertilizer technology, and in particular to a liquid fertilizer for improving saline-alkali land, its preparation method, and its application. Background Technology

[0002] Acid pulping waste liquor is the cooking waste liquor generated during the sulfite pulping process. It includes organic matter such as lignin sulfonates, sugars, and organic acids, as well as inorganic matter such as calcium salts, magnesium salts, sulfates, and sulfites. Direct discharge or simple incineration would cause serious resource waste and environmental pollution. Therefore, the resource utilization of acid pulping waste liquor, and the reduction, resource recovery, and harmless treatment of waste, have become urgent environmental and resource challenges.

[0003] Saline-alkali land is one of the key obstacles restricting global agricultural production and food security. Excessive soluble salts and high pH levels in saline-alkali soils severely inhibit crop root growth and nutrient absorption, leading to reduced yields or even crop failure. Currently, saline-alkali land improvement relies heavily on chemical amendments, biological amendments, and organic fertilizers. While chemical amendments, such as phosphogypsum and superphosphate, can reduce alkali levels in the short term, their effects are limited and short-lived, and they may also pose secondary pollution problems. Biological amendments mainly rely on planting salt-tolerant plants, but these plants only function within certain salinity thresholds and are limited by factors such as climate, planting habits, supporting machinery, and economic viability, making large-scale application difficult. In contrast, organic fertilizers / water-soluble fertilizers are rich in various active substances, simultaneously performing multiple functions such as reducing alkali, removing salt, increasing fertility, and improving soil, with more lasting effects and less need for frequent application.

[0004] In the prior art, WO2021128403A1 discloses a fulvic acid compound fertilizer, comprising fulvic acid, amino acids, inorganic compound fertilizer, and a dispersant (lignin sulfonate). Although this patent discloses the preparation of compound fertilizer using fulvic acid, lignin sulfonate, and amino acids as raw materials, the components in the physically blended product are only bound by intermolecular forces, and the components cannot form a chemically bonded copolymer network. Therefore, it is easily leached and separated in the soil, resulting in poor soil improvement.

[0005] Therefore, developing a ternary copolymer liquid fertilizer based on acid pulping waste liquid, humic acid and amino acids to achieve chemical bonding and functional synergy of the three components is of great practical significance for the efficient improvement of saline-alkali land and the resource utilization of pulping waste liquid. Summary of the Invention

[0006] In view of the above-mentioned prior art, the purpose of this invention is to provide a liquid fertilizer for improving saline-alkali land, its preparation method and application.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a method for preparing a liquid fertilizer for improving saline-alkali land, comprising the following steps: (1) Add alkali solution to mineral fulvic acid solution to adjust pH to obtain activated fulvic acid solution; decolorize amino acid waste liquid to obtain amino acid solution; (2) Pre-treat the waste liquid from acid pulping to obtain lignin sulfonate solution; add activated humic acid solution and amino acid solution to the lignin sulfonate solution and mix well to obtain a mixed solution; add an initiator to the mixed solution and carry out the first reaction under heating; add sodium sulfite to the system after the reaction, raise the temperature and carry out the second reaction; after the reaction is completed, cool down and adjust the pH to obtain liquid fertilizer for improving saline-alkali land.

[0008] Preferably, in step (1), the mineral fulvic acid solution is prepared by mixing mineral fulvic acid and water in a mass ratio of 1:(2-3).

[0009] Preferably, in step (1), the alkaline solution is a KOH solution and / or a NaOH solution, and the mass fraction of the alkaline solution is 15%-25%.

[0010] Preferably, in step (1), the pH is adjusted to 7-8.

[0011] Preferably, in step (1), the pH of the amino acid waste liquid is 2-6 and the total amino acid content is ≥10%.

[0012] As a preferred option, in step (1), the specific operation for decolorizing the amino acid waste liquid is as follows: add activated carbon to the amino acid waste liquid, stir for 30-60 minutes to decolorize, filter after stirring, and collect the filtrate as an amino acid solution.

[0013] Furthermore, the amount of activated carbon added is 0.5%-1.5% of the mass of the amino acid waste liquid.

[0014] Preferably, in step (2), the pH of the acid pulping waste liquor is 2-4 and its solid content is 25%-40%.

[0015] Preferably, in step (2), the specific operation for pretreating the acid pulping waste liquor is as follows: Add 15%-25% alkali solution to the acid pulping waste liquid to adjust the pH to 6-7, filter and collect the supernatant.

[0016] Furthermore, the alkaline solution is a KOH solution and / or a NaOH solution.

[0017] Preferably, in step (2), the mass ratio of the pretreated acid pulping waste liquid, the activated humic acid solution and the amino acid solution is 100:(20-40):(10-20).

[0018] Preferably, in step (2), the initiator is ammonium persulfate and / or sodium persulfate.

[0019] Preferably, in step (2), the amount of initiator added is 0.5%-2.0% of the solid content in the mixture.

[0020] Preferably, in step (2), the heating temperature is 70-85℃ and the first reaction time is 2-4h.

[0021] Preferably, in step (2), the amount of sodium sulfite added is 5%-10% of the solid content in the system after the reaction.

[0022] Preferably, in step (2), the heating temperature is 80-90℃ and the second reaction time is 1-2h.

[0023] Preferably, in step (2), the temperature is lowered to 40-50℃.

[0024] As a preferred option, in step (2), the specific operation of adjusting pH is as follows: add 20%-30% citric acid solution to the system after reaction to adjust the pH to 4.5-5.5.

[0025] In a second aspect, the present invention provides a liquid fertilizer for improving saline-alkali land prepared by the above-described preparation method.

[0026] A third aspect of the present invention provides the application of the above-mentioned liquid fertilizer for improving saline-alkali land in the improvement of saline-alkali land.

[0027] The beneficial effects of this invention are: 1. This invention uses amino acid solution, activated fulvic acid solution and acid pulping waste liquid as raw materials. After mixing, an initiator is added to carry out a copolymerization reaction. Then, sodium sulfite is added to the reaction system to carry out the reaction and obtain a liquid fertilizer for improving saline-alkali land.

[0028] This invention uses acid pulping waste liquor (rich in lignin sulfonate) as a framework and fulvic acid and amino acids as functional monomers. A terpolymer is prepared through a free radical graft copolymerization reaction. Sodium sulfinate is then added to the terpolymer to increase the sulfonic acid group content, resulting in a liquid fertilizer for improving saline-alkali land. This liquid fertilizer combines the structural improvement capabilities of lignin sulfonate, the buffering and complexing capabilities of fulvic acid, and the nutritional activity of amino acids, synergistically improving saline-alkali land from three dimensions: chemical alkali reduction, physical salt removal, and structural improvement.

[0029] 2. Compared with the physical mixing of acid pulping waste liquid, humic acid and amino acids, the present invention improves the stability and salt-out resistance of liquid fertilizer, enhances soil improvement capacity and increases buffer capacity through free radical graft copolymerization reaction chemical bonding.

[0030] 3. The liquid fertilizer for improving saline-alkali land prepared in this invention improves saline-alkali land through direct acid neutralization, sulfonic acid group exchange, and network buffering in a synergistic manner. Specifically: Direct acid neutralization (rapid): The product has a pH of 4.5-5.5. After being applied to alkaline soil, the free H⁺ reacts immediately with OH⁻, rapidly reducing the rhizosphere pH within 1-3 days after application.

[0031] Sulfonate group exchange (continuous): The sulfonate groups in the copolymer exchange with sodium ions in the soil, generating H... + Continue to neutralize OH - The generated R-SO3Na is washed away with irrigation water. Network buffer (long-lasting): The carboxyl and phenolic hydroxyl groups in the copolymer network constitute a buffer system. When the soil pH increases: -COOH + OH⁻ → -COO⁻ + H2O (consuming OH⁻), when the soil pH decreases: -COO⁻ + H⁺ → -COOH (resisting acidification).

[0032] 4. The sulfonic acid and carboxyl groups in the copolymer interact with exchangeable Na+ groups on soil colloids. + A cation exchange reaction occurs, converting Na... + The Na+ is displaced into the soil solution. Simultaneously, the copolymer polymer chains form water-stable aggregates through bridging, constructing microporous channels, improving soil pore structure, enhancing irrigation water infiltration, and allowing the displaced Na+ to dissolve. + The salt is leached into deeper soil layers or discharged from the root zone, reducing soil alkalinity and salinity at the root. Furthermore, the polymer network structure formed by graft copolymerization plays multiple physical improvement roles in the soil: the polymer chains bind dispersed soil particles into water-stable aggregates through adsorption and bridging, enhancing the soil's resistance to erosion; the network structure creates interconnected micropores in the soil, increasing non-capillary porosity, promoting salt leaching while simultaneously cutting off capillary ascending channels, inhibiting the return of bottom salts to the surface with water evaporation; the flexibility of the polymer chains buffers the contraction and expansion of the soil during alternating wet and dry periods, preventing surface crusting and compaction, and maintaining loose, breathable soil. Detailed Implementation

[0033] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0034] To enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to specific embodiments.

[0035] The experimental materials used in the embodiments of this invention are all conventional experimental materials in the art and can be purchased through commercial channels.

[0036] In this invention, the mineral-derived fulvic acid was purchased from Shandong Agricultural University Fertilizer Technology Co., Ltd., and the product name is "Agricultural University Fulvic Acid Powder". The sodium sulfite is sodium methanesulfite, with CAS number 20277-69-4. The method for preparing amino acid waste liquid is as follows: using corn as raw material, the fermentation waste mother liquor generated during the fermentation process to produce amino acids. It appears as a dark brown, viscous liquid with a pH of 5-6, a total amino acid content ≥10%, an organic matter content of 35%-45%, and a water-insoluble matter content ≤5%.

[0037] Solid content refers to the percentage of the mass of non-volatile residues remaining after the mixture has been dried under specified drying conditions to remove moisture and other volatile components, relative to the total mass of the mixture. Non-volatile residues include lignin sulfonates and other organic / inorganic solids in acid pulping wastewater, humates in activated fulvic acid solutions, and amino acids and other soluble organic matter in amino acid solutions.

[0038] Acid pulping waste liquor is prepared by the following method: using wheat straw or wood chips as raw materials, the pulping waste liquor generated during the sulfite pulping process has a pH of 2-4 and a solid content of 8%-18%, and its main components are lignin sulfonates, sugars, organic acids and inorganic salts; then the pulping waste liquor is subjected to coarse filtration, microfiltration and concentration in sequence to obtain acid pulping waste liquor with a solid content of 25%-40%.

[0039] Example 1: (1) Mix mineral fulvic acid and water at a ratio of 1:2.5 to obtain a mineral fulvic acid solution; add 20% KOH solution to the mineral fulvic acid solution to adjust the pH to 7.5 to obtain an activated fulvic acid solution; Activated carbon was added to the amino acid waste liquid at a concentration of 1% of the waste liquid mass. The mixture was stirred at room temperature for 45 minutes for decolorization. After stirring, the mixture was filtered and the filtrate was collected to obtain an amino acid solution. (2) Add 20% KOH solution to acid pulping waste liquid to adjust pH to 6.5, filter to remove insoluble impurities and macromolecular colloids, collect the supernatant to obtain lignin sulfonate solution; A mixture of lignin sulfonate solution, activated humic acid solution, and clarified amino acid solution was prepared by mixing in a mass ratio of 100:30:15 and stirring until homogeneous. Ammonium persulfate was added to the mixture and reacted at 75°C for 3 hours, with the amount of ammonium persulfate being 1.5% of the solid content in the mixture. After the reaction was completed, sodium sulfite was added to the system, with the amount being 7.5% of the solid content in the system. The mixture was then reacted at 85°C for 1.5 hours. The reaction solution was then cooled to 45°C, and a 25% citric acid solution was added to adjust the pH to 5, yielding a liquid fertilizer for improving saline-alkali land.

[0040] Comparative Example 1: The difference between this comparative example and Example 1 is that only mineral-derived fulvic acid and acid pulping waste liquor were used for the free radical grafting reaction. Specifically: An activated fulvic acid solution and a lignin sulfonate solution were prepared according to the method in Example 1. The lignin sulfonate solution and the activated fulvic acid solution were mixed at a mass ratio of 100:30 and stirred evenly to obtain a mixed solution. Ammonium persulfate was added to the mixture and reacted at 75°C for 3 hours, with the amount of ammonium persulfate added being 1.5% of the solid content. After the reaction was completed, sodium sulfite was added to the system, with the amount added being 7.5% of the solid content of the system. The mixture was then reacted at 85°C for 1.5 hours. The reaction solution was then cooled to 45°C, and a 25% citric acid solution was added to adjust the pH to 5, thus obtaining a liquid fertilizer for improving saline-alkali land.

[0041] Comparative Example 2: The difference between this comparative example and Example 1 is that only amino acid waste liquid and acid pulping waste liquid are used for the free radical grafting reaction. The specific steps are as follows: A clear amino acid solution and a lignin sulfonate solution were prepared according to the method in Example 1. The lignin sulfonate solution and the clear amino acid solution were mixed at a mass ratio of 100:15 and stirred evenly to obtain a mixed solution. Ammonium persulfate was added to the mixture and reacted at 75°C for 3 hours. The amount of ammonium persulfate added was 1.5% of the solid content in the mixture. After the reaction was completed, sodium sulfite was added to the system and reacted at 85°C for 1.5 hours. The reaction solution was then cooled to 45°C, and a 25% citric acid solution was added to adjust the pH to 5 to obtain a liquid fertilizer for improving saline-alkali land.

[0042] Comparative Example 3: The difference between this comparative example and Example 1 is that, in step (2), the amount of sodium sulfite added is 4% of the solid content. The specific steps are as follows: A lignin sulfonate solution, an activated fulvic acid solution, and a clarified amino acid solution were prepared according to the method in Example 1. The lignin sulfonate solution, the activated fulvic acid solution, and the clarified amino acid solution were mixed at a mass ratio of 100:30:15 and stirred evenly to obtain a mixed solution. Ammonium persulfate was added to the mixture and reacted at 75°C for 3 hours, with the amount of ammonium persulfate added being 1.5% of the total solid content. After the reaction was completed, sodium sulfite was added to the system, with the amount added being 4% of the solid content of the system. The mixture was then reacted at 85°C for 1.5 hours. The reaction solution was then cooled to 45°C, and a 25% citric acid solution was added to adjust the pH to 5, thus obtaining a liquid fertilizer for improving saline-alkali land.

[0043] Comparative Example 4: The difference between this comparative example and Example 1 is that in step (2), the amount of sodium sulfite added is 11% of the total solid content. The specific steps are as follows: A lignin sulfonate solution, an activated fulvic acid solution, and a clarified amino acid solution were prepared according to the method in Example 1. The lignin sulfonate solution, the activated fulvic acid solution, and the clarified amino acid solution were mixed at a mass ratio of 100:30:15 and stirred evenly to obtain a mixed solution. Ammonium persulfate was added to the mixture and reacted at 75°C for 3 hours, with the amount of ammonium persulfate added being 1.5% of the total solid content. After the reaction was completed, sodium sulfite was added to the system, with the amount added being 11% of the solid content of the system. The mixture was then reacted at 85°C for 1.5 hours. The reaction solution was then cooled to 45°C, and a 25% citric acid solution was added to adjust the pH to 5, thus obtaining a liquid fertilizer for improving saline-alkali land.

[0044] Comparative Example 5: The difference between this comparative example and Example 1 is that the lignin sulfonate, mineral-derived humic acid, and amino acids did not undergo free radical graft copolymerization. Specifically: Lignosulfonate solution, activated fulvic acid solution and amino acid solution were prepared according to the method in Example 1; Lignosulfonate solution, activated humic acid solution and clarified amino acid solution were mixed in a mass ratio of 100:30:15 and stirred evenly to obtain a mixed solution. Sodium sulfinate was added to the mixed solution at an amount equal to 7.5% of the solid content of the mixed solution. The mixture was reacted at 85°C for 1.5 hours. The reaction solution was then cooled to 45°C, and a 25% citric acid solution was added to adjust the pH to 5 to obtain a liquid fertilizer for improving saline-alkali land.

[0045] Experimental Example 1: According to NY 1429-2020 "General Requirements for Amino Acid-Containing Trace Element Types", the free amino acids, humic acid, organic matter, pH, water-insoluble matter, and trace elements iron, boron, and zinc in the saline-alkali land improvement liquid fertilizer prepared in Example 1 were tested, and the results are shown in Table 1.

[0046] Table 1 Content of each component in water-soluble fertilizer According to NY 1429-2020 "General Requirements for Amino Acid-Containing Trace Element Types": free amino acids ≥100g / L, trace elements ≥20g / L, and water-insoluble matter ≤50g / L. As shown in Table 1, the free amino acid content in the saline-alkali land improvement liquid fertilizer prepared by this invention is 124.3 g / L (≥100 g / L), and the total content of trace elements (Fe, B, and Zn) is 22.5g / L, meeting the requirements of this standard for trace element-containing amino acid-containing water-soluble fertilizers.

[0047] Experiment Example 2: Pot Experiment Soil samples were collected from the 0-20 cm topsoil layer in saline-alkali areas of Xinjiang, air-dried, and sieved through a 2 mm sieve for later use. The physicochemical properties of the soil were tested and are as follows: pH 8.9, alkalinity (ESP) 28.6%, total salt content 4.2 g / kg, and organic matter content 8.5 g / kg.

[0048] The tested fertilizers were the liquid fertilizers for improving saline-alkali land prepared in Example 1 and Comparative Examples 1-5. A water control (CK) was also included.

[0049] The specific steps are as follows: (1) Use pots with a diameter of 25 cm, and fill each pot with 8 kg of sieved soil. Select 3 seedlings of the maize variety 'Ludan 510' with uniform growth in each pot and plant them in an equilateral triangle. Mix different test fertilizers and water at a volume ratio of 1 mL: 500 mL and dilute them. Apply the diluted test fertilizers to the roots before sowing, during the seedling stage and at the jointing stage. The amount of water applied to the roots each time is 250 mL. Each treatment is replicated 3 times, and the water and fertilizer management of each group is kept consistent until harvest. Soil samples are collected 15 days after the last fertilization for the determination of various indicators (soil pH, alkalinity, total salt content).

[0050] Specifically, soil pH was determined according to NY / T 1377-2007 "Determination of Soil pH", total salt content was determined by conductivity method according to NY / T 1121.16-2006 "Soil Testing Part 16 Determination of Total Water-Soluble Salts in Soil", soil cation exchange capacity was determined according to NY / T1121.5-2006 "Soil Testing Part 5 Determination of Cation Exchange Capacity in Calcareous Soils", and soil exchangeable sodium content was determined according to LY / T 1248-1999 "Determination of Exchangeable Sodium in Alkaline Soils". The formula for calculating alkalinity is: ESP (%) = (exchangeable sodium content / soil cation exchange capacity) × 100%.

[0051] (2) Place the collected soil samples on top of a sieve (pore sizes 2 mm, 1 mm, 0.5 mm, 0.25 mm) and shake in water at a rate of 30 times / minute for 10 minutes. Calculate the content of aggregates of each particle size. The content of water-stable aggregates >0.25 mm (WR) is used as the criterion. 0.25 The soil density, total porosity, and penetration resistance were used as evaluation indicators. Simultaneously, soil bulk density, total porosity, and penetration resistance were measured, and the results are shown in Table 3.

[0052] Among them, the soil bulk density was determined by the ring cutter method in NY / T 1121.4-2006 "Soil Testing Part 4: Determination of Soil Bulk Density"; and the penetration resistance of the 0-5cm soil layer was determined by NY / T 1121.25-2012 "Soil Testing Part 25: Determination of Soil Compactness". The formula for calculating total porosity is: Total porosity (%) = [1 - (soil bulk density / 2.65)] × 100%, where 2.65 is the soil specific gravity.

[0053] Among them, WR 0.25 The calculation formula for WR is: 0.25 (%) = (mass of water-stable aggregates > 0.25 mm / total mass of soil sample) × 100%.

[0054] Table 2. Improvement effects of each treatment on saline-alkali soil As shown in Table 2, after treatment with the liquid fertilizer for improving saline-alkali soil prepared according to this invention, the soil pH was 7.78, the alkalinity was 12.0%, and the total salt content was 2.05 g / kg. In contrast, after treatment with the liquid fertilizers for improving saline-alkali soil prepared in Comparative Examples 1-5, the soil pH was 7.85-8.45, the alkalinity was 13.1-22.1%, and the total salt content was 2.18-3.52 g / kg. Therefore, the liquid fertilizer for improving saline-alkali soil prepared according to this invention can significantly improve the condition of saline-alkali soils. Specifically, it reduces soil pH, alkalinity, and total salt content.

[0055] Furthermore, data from Example 1 and Comparative Examples 3-4 show that insufficient addition of sodium sulfite results in inadequate improvement, while excessive addition, although potentially reducing some salt-alkali indices, only slightly improves anti-salting properties or results in inferior overall performance compared to Example 1. Therefore, more sodium sulfite is not necessarily better; excessive amounts may introduce excessive side reactions or increase costs. 7.5% is the optimal dosage.

[0056] Table 3. Effects of each treatment on soil aggregates, bulk density, and porosity. After treatment in Example 1, the content of water-stable aggregates >0.25 mm in the soil reached 48.6%, which was much higher than that of CK (18.3%) and the physical mixture (28.6%), and about 38%~41% higher than that of Comparative Example 1 (35.2%) and Comparative Example 2 (34.5%). This indicates that the terpolymer binds dispersed soil particles into water-stable aggregates through the adsorption and bridging effect of polymer chains, and its effect is significantly better than that of binary copolymers.

[0057] Regarding soil bulk density, the bulk density of the treatment in Example 1 was reduced to 1.23 g / cm³, which was 0.29 g / cm³ lower than the control (CK) and 0.13 g / cm³ lower than the control (Comparative Example 1). Total porosity increased to 53.6%, an increase of 11 percentage points compared to the control (CK). The lower bulk density and higher porosity are beneficial for irrigation water infiltration and salt leaching.

[0058] Penetration resistance is an important indicator reflecting the degree of surface soil compaction. The penetration resistance after treatment in Example 1 was 86 kPa, significantly lower than that of the control (CK) (185 kPa) and the comparative proportions. Field observations also revealed that the surface soil treated in Example 1 was loose and free of crust, while the control (CK) and the physical mixture treatments showed obvious compaction and cracking. This is attributed to the fact that the microporous channels formed by the copolymer interrupted the capillary ascending channels, inhibiting the return of subsurface salts to the surface with water evaporation, while the flexibility of the polymer network buffered the shrinkage and expansion during soil wetting and drying processes.

[0059] Experimental Example 3: Take 10 mL of the saline-alkali land improvement liquid fertilizer prepared in Example 1 and Comparative Examples 1-5 respectively, and add solid salts (NaCl, CaCl2 and MgSO4) to the saline-alkali land improvement liquid fertilizer respectively, so that the salt concentrations in the solution are 0.5%, 1.0%, 1.5% and 2.0% (w / v) respectively. After adding solid salt, shake well and let stand at 25°C for 24 h. The lowest salt concentration at which obvious turbidity or precipitation occurs is taken as the critical salting-out concentration. Each concentration is repeated 3 times and the average value is taken.

[0060] Table 4 Salting-out resistance of liquid fertilizers in each treatment (critical salting-out concentration, unit: %) As shown in Table 4, the critical salt-out concentrations of Example 1 in NaCl, CaCl2, and MgSO4 solutions were 1.8%, 1.3%, and 1.5%, respectively, significantly higher than those of Comparative Examples 1-5. The higher critical salt-out concentrations mean that this liquid fertilizer is less prone to salt-out in irrigation water for saline-alkali land (typically containing 0.3%–1.0% salt), making it suitable for use in high-salt environments. The superior salt-out resistance of Example 1 compared to Comparative Example 4 (11% sodium sulfite) indicates that the appropriate introduction of sulfonic acid groups can improve salt-out resistance; however, excessive introduction may lead to increased salt sensitivity due to excessive charge concentration.

[0061] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for preparing a liquid fertilizer for improving saline-alkali land, characterized in that, Includes the following steps: (1) Add alkali solution to mineral fulvic acid solution to adjust pH to obtain activated fulvic acid solution; decolorize amino acid waste liquid to obtain amino acid solution; (2) The acid pulping waste liquid is pretreated to obtain a lignin sulfonate solution; Add activated fulvic acid solution and amino acid solution to lignin sulfonate solution and mix well to obtain a mixed solution; add an initiator to the mixed solution and carry out the first reaction under heating; add sodium sulfite to the system after the reaction, raise the temperature and carry out the second reaction; after the reaction is completed, cool down and adjust the pH to obtain liquid fertilizer for improving saline-alkali land.

2. The method for preparing liquid fertilizer for improving saline-alkali land as described in claim 1, characterized in that, In step (1), the mineral fulvic acid solution is prepared by mixing mineral fulvic acid and water at a mass ratio of 1:(2-3); the alkaline solution is KOH solution and / or NaOH solution, and the mass fraction of the alkaline solution is 15%-25%; the pH is adjusted to 7-8.

3. The method for preparing liquid fertilizer for improving saline-alkali land as described in claim 1, characterized in that, In step (1), the pH of the amino acid waste liquid is 2-6 and the total amino acid content is ≥10%; The specific operation for decolorizing amino acid waste liquid is as follows: add activated carbon to the amino acid waste liquid, stir for 30-60 minutes to decolorize, filter after stirring, and collect the filtrate as amino acid solution; wherein, the amount of activated carbon added is 0.5%-1.5% of the mass of amino acid waste liquid.

4. The method for preparing liquid fertilizer for improving saline-alkali land as described in claim 1, characterized in that, In step (2), the pH of the acid pulping waste liquor is 2-4, and its solid content is 25%-40%; The specific operation for pretreatment of acid pulping waste liquor is as follows: add 15%-25% (by mass) of alkaline solution to the acid pulping waste liquor to adjust the pH to 6-7, filter and collect the supernatant; wherein, the alkaline solution is KOH solution and / or NaOH solution.

5. The method for preparing liquid fertilizer for improving saline-alkali land as described in claim 1, characterized in that, In step (2), the mass ratio of the pretreated acid pulping waste liquor, activated humic acid solution and amino acid solution is 100:(20-40):(10-20).

6. The method for preparing liquid fertilizer for improving saline-alkali land as described in claim 1, characterized in that, In step (2), the initiator is ammonium persulfate and / or sodium persulfate; the amount of initiator added is 0.5%-2.0% of the solid content in the mixture; the heating temperature is 70-85℃; and the first reaction time is 2-4h.

7. The method for preparing liquid fertilizer for improving saline-alkali land as described in claim 1, characterized in that, In step (2), the amount of sodium sulfite added is 5%-10% of the solid content in the system after the reaction; the heating temperature is 80-90℃ and the second reaction time is 1-2h.

8. The method for preparing liquid fertilizer for improving saline-alkali land as described in claim 1, characterized in that, In step (2), the specific operation of adjusting pH is as follows: add 20%-30% citric acid solution to the system after reaction to adjust the pH to 4.5-5.

5.

9. The saline-alkali land improvement liquid fertilizer prepared by the preparation method according to any one of claims 1-8.

10. The application of the liquid fertilizer for improving saline-alkali land according to claim 9 in the improvement of saline-alkali land.

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