A soil conditioner of modified lignin for improving soil and promoting growth and a preparation method thereof

Abstract

This invention discloses a soil-improving and growth-promoting modified lignin soil conditioner and its preparation method, belonging to the fields of polymer materials and soil improvement technology. The modified lignin soil conditioner of this invention includes agent A, agent B, and agent C; agent A is a cationic modified lignin polymer, prepared by graft copolymerization of lignin sulfonate and cationic monomers via free radical initiation; agent B is lignin controlled-release particles, prepared by electrostatic intercalation self-assembly of the cationic modified lignin polymer and another negatively charged natural polymer to encapsulate an amino acid amphoteric regulator; agent C is at least one selected from citric acid, lactic acid, itaconic acid, fulvic acid, wood vinegar, maleic acid, maleic anhydride, and polyacrylic acid. The soil conditioner of this invention combines low cost, environmental friendliness, and high remediation performance, providing an innovative solution for agricultural soil improvement.

Description

Technical Field

[0001] This invention relates to the fields of polymer materials and soil improvement technology, specifically to a soil-improving and growth-promoting modified lignin soil conditioner and its preparation method. Background Technology

[0002] With the increasing severity of global farmland degradation and salinization, soil conditioners have become an important research direction for sustainable agricultural development. While traditional conditioners (such as gypsum and humic acid) can regulate soil pH or ion balance in the short term, they generally suffer from problems such as limited functionality, high cost, and poor environmental compatibility. For example, gypsum-based conditioners require large application amounts and have limited effect on improving soil aggregate structure; synthetic polymeric conditioners (such as polyacrylamide) can enhance soil water retention, but their non-degradable nature easily causes secondary pollution. Furthermore, existing conditioners for saline-alkali land mostly focus on single functions (such as reducing salinity, adjusting acidity, or promoting growth), making it difficult to synergistically address complex problems such as soil structure damage, nutrient loss, and weak plant resistance.

[0003] Lignosulfonates, a major byproduct of the papermaking industry, are considered highly promising soil amendment materials due to their abundant aromatic ring structures and active functional groups. However, natural lignin sulfonates suffer from drawbacks such as low charge density, poor water solubility, and functional inertness, resulting in poor and unstable amendment effects when applied directly. In recent years, researchers have conducted extensive research on the chemical modification of lignin, aiming to enhance its functional properties. However, existing lignin-modified products used for soil amendment mainly rely on providing nutrients such as nitrogen and potassium after mineralization, or on preparing water-retaining materials through high cross-linking with other polymers. These methods fail to fully utilize the multifunctional potential of lignin, and the prepared products lack synergistic regulation of structural modification, nutrient controlled release, and plant growth promotion. Furthermore, the modification processes are complex and costly, hindering their large-scale application. Summary of the Invention

[0004] The purpose of this invention is to provide a soil conditioner with modified lignin that promotes soil growth and its preparation method. This invention innovatively develops a multifunctional soil conditioner system based on lignin sulfonate, overcoming the limitations of traditional conditioners. The cationic modified lignin polymer (LS-g-QAS) in Agent A is copolymerized using lignin sulfonate grafted cationic monomers, endowing it with high charge density and anionic / cationic polyelectrolyte properties. It can not only rapidly reconstruct soil aggregates through colloidal flocculation, but also react with excess Na+ in saline-alkali soils. +Ion exchange occurs, reducing the percentage of exchangeable sodium (ESP). The lignin-controlled-release particles in Agent B utilize electrostatic intercalation self-assembly technology to encapsulate the amino acid amphoteric plant regulator within a structure constructed from cationic lignin and negatively charged natural polymers, achieving targeted and sustained release of the plant regulator. Agent C is an acidic functional component that, on one hand, neutralizes soil alkalinity through protonation, and on the other hand, dynamically disrupts the electrostatic interactions of the controlled-release particles to intelligently release the regulator, thereby activating plant stress resistance signaling pathways, promoting root development and nutrient absorption. Simultaneously, its material cost is significantly reduced, and it is biodegradable.

[0005] This invention first provides a modified lignin soil conditioner, which includes agent A, agent B and agent C; Agent A is a cationic modified lignin polymer, which is prepared by graft copolymerization of lignin sulfonate and cationic monomer through free radical initiation. The agent B is a lignin controlled-release particle, which is prepared by electrostatic intercalation self-assembly of the cationic modified lignin polymer and another negatively charged natural polymer to encapsulate an amino acid amphoteric regulator. Agent C is at least one of citric acid, lactic acid, itaconic acid, fulvic acid, wood vinegar, maleic acid, maleic anhydride, and polyacrylic acid.

[0006] In the above-mentioned modified lignin soil conditioner, the lignin sulfonate is at least one of calcium lignin sulfonate, magnesium lignin sulfonate, sodium lignin sulfonate, and potassium lignin sulfonate. The cationic monomer is at least one of methacryloyloxyethyltrimethylammonium chloride and acryloyloxyethyltrimethylammonium chloride; The negatively charged natural polymer is at least one of sodium carboxymethyl cellulose, hydroxyethyl cellulose, sodium alginate, pectin, gelatin, gum arabic, and xanthan gum. The amino acid amphoteric regulator is at least one of proline, γ-aminobutyric acid, aspartic acid, and arginine.

[0007] In the above-mentioned modified lignin soil conditioner, by mass percentage, agent A accounts for 50%-70%, agent B accounts for 25%-45%, and agent C accounts for 5%-10%.

[0008] In the above-mentioned modified lignin soil conditioner, the preparation method of agent A includes the following steps: mixing the lignin sulfonate, cationic monomer, initiator and water, and reacting to obtain agent A.

[0009] In the above-mentioned modified lignin soil conditioner, the initiator is a low-temperature initiation system or a thermal initiation system; The low-temperature initiation system is ammonium persulfate-ascorbic acid and / or Fe. 2+ - Hydrogen peroxide; the thermal initiation system is ammonium persulfate and / or potassium persulfate; The initiator is 0.5%-10% of the total mass of lignin sulfonate and cationic monomer; The mass ratio of the lignin sulfonate to the cationic monomer is 1:1-1:10; preferably 1:2-1:7. The reaction temperature is 40-90℃, specifically 70℃, 75℃ or 80℃; the reaction time is 2-6 hours; preferably 3 hours or 4 hours. The reaction is carried out in an inert atmosphere, specifically a nitrogen or argon atmosphere.

[0010] In the above-mentioned modified lignin soil conditioner, the preparation method of agent A includes the following steps: adding an initiator aqueous solution to a lignin sulfonate aqueous solution for reaction, and then adding a cationic monomer solution for reaction to obtain agent A.

[0011] In the lignin sulfonate aqueous solution, the mass ratio of lignin sulfonate to water is 1:10-1:50; in the initiator aqueous solution, the mass ratio of initiator to water is 1:15-1:30.

[0012] The mass percentage concentration of the cationic monomer solution is 50%-80%; specifically, it can be 60% or 75%.

[0013] The reaction temperature is 40-90℃, specifically 70℃, 75℃ or 80℃, when the initiator aqueous solution is added dropwise to the lignin sulfonate aqueous solution; the reaction time is 15-30 min, specifically 20 min.

[0014] The preparation method of Agent A includes a step of cooling to room temperature after the reaction is completed, precipitating the solid with ethanol, and drying.

[0015] The preparation method of Agent B in the above-mentioned modified lignin soil conditioner includes the following steps: mixing the cationic modified lignin polymer, amino acid amphoteric regulator, negatively charged natural polymer and water, stirring to gradually form colloidal particles of the complex, and then collecting and drying the precipitate to obtain Agent B.

[0016] In the above-mentioned modified lignin soil conditioner, the mass ratio of the cationic modified lignin polymer to the negatively charged natural polymer is 1:0.5-1:3.5; specifically, it can be 1:1 or 3:2. The mass ratio of the amino acid amphoteric regulator to the total mass of the cationic modified lignin polymer and the negatively charged natural polymer is 1:3-1:8; specifically, it can be 1:4 or 1:5. The stirring speed is 600-1200 rpm.

[0017] The preparation method of Agent B in the above-mentioned modified lignin soil conditioner includes the following steps: dissolving the cationic modified lignin polymer and the amino acid amphoteric regulator in water to obtain a mixed solution; then slowly adding the aqueous solution of the negatively charged natural polymer dropwise to the above mixed solution, stirring to gradually form colloidal particles of the complex, and then collecting and drying the precipitate to obtain Agent B.

[0018] Specifically, in the mixed solution, the mass ratio of the cationic modified lignin polymer to water is 1:5-1:30; In the aqueous solution of the negatively charged natural polymer, the mass ratio of the negatively charged natural polymer to water is 1:10 to 1:50.

[0019] In agent B, the encapsulation rate of the amino acid amphoteric regulator is 60%-90%.

[0020] This invention also provides the application of the above-mentioned modified lignin soil conditioner in improving saline-alkali soil.

[0021] Furthermore, the present invention provides a method for improving saline-alkali soil, comprising the following steps: mixing the A agent and B agent with air-dried soil and spreading it evenly on the surface of saline-alkali land, turning the soil over and making it uniform, and applying the C agent after 4-24 h (specifically 6 h); the application rate of the modified lignin soil conditioner is 150-200 kg / mu.

[0022] In this invention, LS-g-QAS has an acidic group (SO3). - ) and a large number of cationic groups (-N) + (CH3)2) can interact electrostatically with the positive and negative charges on the edges and surfaces of clay particles, thereby neutralizing the surface charge and compressing the electric double layer, reducing the distance between clay mineral particles; at the same time, its high molecular weight characteristics enable it to act as a "flexible bridge" between particles: on the one hand, it adsorbs multiple particles through hydrogen bonding and hydrophobic interactions, and on the other hand, it forms a three-dimensional network structure by means of long chain conformation entanglement, promoting soil particle flocculation and co-deposition.

[0023] In this invention, the amino acid amphoteric regulator encapsulated in the lignin controlled-release particles has both amino and carboxyl groups. The quaternary ammonium salt groups in the cationic modified lignin polymer can interact electrostatically with the carboxyl groups in the amino acids, while the anionic groups in the negatively charged natural polymer can interact electrostatically with the amino groups in the amino acids, thereby enhancing the loading stability of the regulator.

[0024] The negatively charged natural polymer is one or more of sodium carboxymethyl cellulose, hydroxyethyl cellulose, sodium alginate, pectin, gelatin, gum arabic, and xanthan gum, preferably sodium carboxymethyl cellulose; the amino acid amphoteric regulator includes one or more of proline and γ-aminobutyric acid, preferably proline.

[0025] Specifically, encapsulating amino acid amphoteric plant regulators in an electrostatic intercalation structure constructed from cationic lignin and negatively charged natural polymers can significantly prolong the release cycle, avoid the impact of sudden concentration changes on plants, and form a protective layer on the surface of the regulators, reducing photosynthesis and leaching losses.

[0026] Specifically, acidic substances in agent C undergo a protonation reaction (H+). + Release) to neutralize alkaline substances in the soil (such as OH) - On the one hand, it can be a smart release regulator that can dynamically disrupt the electrostatic interactions of controlled-release particles (Na2CO3).

[0027] Compared with traditional soil conditioners, the present invention has the following advantages: (1) A lignin sulfonate-cationic monomer graft copolymer (LS-g-QAS) was developed through a free radical grafting process. It has both high cation exchange rate and bridging flocculation function, which can effectively improve the soil aggregate structure, increase soil water holding capacity, and reduce the concentration of exchangeable sodium ions in the soil.

[0028] (2) Using the electrostatic intercalation self-assembly technology of cation / anion natural polymers, lignin controlled-release particles are constructed. Amino acid amphoteric regulators are enhanced by charge interaction to improve the stability of the carrier loading. After release, they form a rhizosphere pH buffer system, simultaneously achieving dual-pathway enhancement of osmotic protection and metabolic signal transduction.

[0029] (3) By using the synergistic mechanism of A / B / C agents, functional dissociation and application synergy are achieved through physical isolation; the acidic component of agent C triggers the release of amino acid amphoteric regulators by destroying the electrostatic intercalation structure of lignin controlled-release particles in agent B, thereby achieving precise regulation of soil structure improvement and plant growth promotion.

[0030] (4) This invention uses natural polymer material lignin sulfonate as the matrix to realize the comprehensive utilization of lignin materials such as wood pulp and paper waste liquid. At the same time, this soil conditioner has the characteristics of being non-toxic, biodegradable and environmentally friendly. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of the preparation process of the modified lignin soil conditioner of the present invention.

[0032] Figure 2 This is a diagram illustrating the graft copolymerization mechanism of DMC-modified calcium lignosulfonate.

[0033] Figure 3 SEM, FT-IR plots, and zeta potential plots for CLS and CLS-g-DMC; among them, Figure 3 In the diagram, a is the SEM image of CLS; b is the SEM image of CLS-g-DMC; c is the FT-IR image of CLS, DMC and CLS-g-DMC; and d is the zeta potential image of CLS and CLS-g-DMC (the concentration of CLS and CLS-g-DMC is 0.02 mg / mL).

[0034] Figure 4 Infrared image of CLS-g-DMC / CMC@Pro.

[0035] Figure 5 This is a diagram showing the soil flocculation effect of CLS-g-DMC.

[0036] Figure 6 This is a diagram showing the effect of citric acid on the controlled release of proline in lignin controlled-release granules (CLS-g-DMC / CMC@Pro).

[0037] Figure 7 This is a diagram showing the growth status of potted corn.

[0038] Figure 8 This is a graph showing the percentage content of soil aggregates of different particle sizes under different conditioner treatments in a pot experiment.

[0039] Figure 9 A comparison chart of leachate volume and immersion time for soil columns under different treatment methods. Detailed Implementation

[0040] The present invention will be further described in detail below with reference to specific embodiments. The embodiments given are only for illustrating the present invention and are not intended to limit the scope of the present invention.

[0041] Unless otherwise specified, the experimental methods described in the following examples are conventional methods.

[0042] Unless otherwise specified, the quantitative experiments in the following examples are all repeated three times, and the results are averaged.

[0043] Unless otherwise specified, all materials and reagents used in the following examples are commercially available.

[0044] Example 1: Preparation of Modified Lignin Soil Conditioner A schematic diagram of the preparation process of the soil-improving and growth-promoting modified lignin soil conditioner of the present invention is shown below. Figure 1 As shown, it is mainly divided into three parts: preparation of cationic modified lignin polymer A, preparation of lignin controlled-release granules B, and mixing and application with agent C.

[0045] The specific preparation method of the modified lignin soil conditioner in this embodiment is as follows: (1) Agent A: Preparation of cationic modified lignin polymer Weigh 5 g of calcium lignosulfonate (CLS) and dissolve it in 100 mL of deionized water. Stir until fully dissolved, then transfer the solution to a 250 mL three-necked flask. Place the flask in an oil bath and heat to 70 °C. During this process, continuously purge the flask with high-purity nitrogen to remove air. Dissolve 0.6 g of ammonium persulfate (APS) in 15 mL of deionized water. Add the APS solution dropwise to the three-necked flask and react for 20 min. Then, add 20 g of DMC solution (methacryloyloxyethyltrimethylammonium chloride, 75 wt% dissolved in water) dropwise to the above mixture and stir continuously for 4 h. The synthesis process needs to be carried out under nitrogen protection. After the reaction is complete, cool the mixture to room temperature, then precipitate the solid with ethanol. Dry the solid product in an oven at 70 °C, grind it, and obtain the cationic modified lignin polymer (CLS-g-DMC).

[0046] (2) Agent B: Preparation of lignin controlled-release granules 2 g of CLS-g-DMC powder was dissolved in 50 mL of deionized water and stirred for 10 min to obtain a CLS-g-DMC solution. 1 g of proline was dissolved in the CLS-g-DMC solution, stirred, and sonicated for 15 min. 2 g of sodium carboxymethyl cellulose was dissolved in 60 mL of water and slowly added dropwise to the above mixed solution while controlling the stirring speed at 1000 rpm to allow the complex to gradually form colloidal particles. The precipitate was then collected by centrifugation and vacuum dried at 50 °C to obtain lignin controlled-release particles (CLS-g-DMC / CMC@Pro).

[0047] The acidic substance in agent C is citric acid. Agent A CLS-g-DMC, agent B CLS-g-DMC / CMC@Pro and agent C citric acid are prepared in proportions of 65wt%, 25wt% and 10wt% respectively, and packaged separately to obtain modified lignin soil conditioner.

[0048] Figure 2 This diagram illustrates the graft copolymerization mechanism of DMC-modified calcium lignosulfonate. The graft copolymerization of calcium lignosulfonate and DMC occurs in an aqueous system initiated by persulfate. First, ammonium persulfate undergoes pyrolysis at high temperature, generating two active free radicals, SO42-. - SO4 -Free radicals react with monomer molecules to generate lignin free radicals. Upon the addition of DMC, its alkenyl groups will be attacked by free radicals, thereby generating DMC free radicals. CLS-g-DMC can be obtained through copolymerization of lignin phenoloxy free radicals and DMC free radicals.

[0049] The basic properties of CLS-g-DMC directly affect the soil flocculation characteristics in practical applications, such as the molecular weight, cationicity, and elemental content of the copolymer. The basic parameters of CLS-g-DMC were determined in this invention and are shown in Table 1 below.

[0050] Table 1. Basic parameters of CLS-g-DMC prepared in Example 1

[0051] a PDI: Polydispersity Index, Mw / Mn b CD: Cationicity Table 2 shows a comparison of the basic properties of lignin polymers modified with different cationic monomers. The preparation methods of lignin polymers modified with acryloyloxyethyltrimethylammonium chloride (DAC) and dimethylallylammonium chloride (DMDAAC) are the same as those of Agent A above, except that DMC is replaced with DAC or DMDAAC.

[0052] As shown in Table 2, three common cationic monomers with unsaturated double bonds, methacryloyloxyethyltrimethylammonium chloride (DMC), acryloyloxyethyltrimethylammonium chloride (DAC), and dimethylallylammonium chloride (DMDAAC), were selected for graft polymerization with calcium lignosulfonate. The low reactivity and easy chain transfer characteristics caused by the allyl structure of DMDAAC may be the main reason for its low grafting rate and poor polymerization effect with calcium lignosulfonate. On the other hand, the methacrylic acid of DMC and the acrylate of DAC are conducive to free radical addition reaction, so DMC and DAC were selected as cationic monomers.

[0053] Table 2. Comparison of basic properties of lignin polymers modified with different cationic monomers

[0054] Figure 3 The images show SEM, Fourier transform infrared, and zeta potential images of CLS and CLS-g-DMC. CLS-g-DMC has a loose porous structure and a large specific surface area. Figure 3 (b) This may be due to the high positive charge density of DMC grafted onto lignin, which dramatically increases the electrostatic repulsion within the copolymer, resulting in a rough, porous structure. Fourier transform infrared spectroscopy analysis determined the functional groups of CLS, DMC, and CLS-g-DMC ( Figure 3 (c) Compared with the Fourier transform infrared spectrum of CLS, CLS-g-DMC shows differences at 1726, 1480, and 950 cm⁻¹. -1 A new peak appeared at 1726 cm. -1 The stretching vibration peaks at 1480 and 950 cm⁻¹ are due to the introduction of a carbonyl group (C=O) into DMC. -1 The characteristic absorption peak at that location corresponds to the bending vibration of the -CN group adjacent to the quaternary ammonium group in the DMC monomer and the -CH2 group. - N + The stretching vibration of (CH3)3 and the new peak of the quaternary ammonium group confirmed the success of the copolymerization. Furthermore, due to the presence of sulfonic acid groups and phenolic hydroxyl groups, CLS exhibits a negative zeta potential in water with pH values ​​of 2-12. Figure 3 (d) in the text, while the zeta potential of the cationic modified calcium lignin sulfonate is positive at pH 2-12.

[0055] Measurement of CLS-g-DMC / CMC@Pro encapsulation efficiency: The prepared lignin microparticles were added to a 50 mL centrifuge tube, and 40 mL of deionized water was added. The mixture was stirred to disperse the particles in the centrifuge tube. The mixture was centrifuged at 8000 rpm for 10 min. The supernatant was carefully aspirated while avoiding disturbing the precipitate. The volume V of the supernatant was recorded, and the concentration c of proline in the supernatant was determined by the ninhydrin colorimetric method.

[0056] Proline encapsulation efficiency =

[0057] m represents the initial amount of proline added (g).

[0058] The encapsulation efficiency of proline was measured to be 75%.

[0059] Figure 4 Infrared image of CLS-g-DMC / CMC@Pro. Figure 4 This indicates that CLS-g-DMC / CMC@Pro at 1630 cm -1 A distinct peak appears at this point, due to the carboxyl group (-COO) of sodium carboxymethyl cellulose. - Antisymmetric stretching vibration at 1430 cm -1 The absorption peak at the point is related to the bending vibration of NH or OH in the amino and carboxyl groups of proline, indicating that the lignin controlled-release particles were successfully prepared.

[0060] The soil flocculation effect diagram of CLS-g-DMC in a small test tube is shown below. Figure 5As shown. 5 g of saline-alkali soil (topsoil (0-15 cm) from Kenli County, Dongying City, Shandong Province (37°70'N, 118°85'E), sieved to 2 mm, air-dried, pH 8.2, EC 1627 μS / cm) was added to a 50 mL test tube. Three treatments were set up: CK (no conditioning agent), unmodified calcium lignin sulfonate with 0.01 wt% saline-alkali soil, and CLS-g-DMC with 0.01 wt% saline-alkali soil. Then, 45 mL of deionized water was added, and the mixture was vigorously shaken for 90 s and allowed to stand. Every 1, 3, 5, 7, and 9 min, 1 mL of liquid was extracted from the 35-40 mL mark of the test tube and placed in a glass bottle. Subsequently, 9 mL of deionized water was added to adjust the volume to 10 mL. The sample bottle was then placed on a turbidimeter for measurement, and the reading was recorded after the turbidity stabilized.

[0061] Depend on Figure 5 It can be seen that CLS-g-DMC can improve the flocculation of soil colloids when applied to saline-alkali soil. After 1 min of flocculation and sedimentation, the residual turbidity of CLS-g-DMC decreased by 96.49% compared with CK and by 95.8% compared with soil containing calcium lignosulfonate. After 9 min, the residual turbidity of CLS-g-DMC decreased by 95.43% compared with CK and by 93.27% compared with calcium lignosulfonate.

[0062] The controlled-release experiment of lignin-based granules (CLS-g-DMC / CMC@Pro) in saline with citric acid involved three treatments. T1 was the controlled-release experiment of CLS-g-DMC / CMC@Pro in saline without acidic substances. The experimental procedure was as follows: 2 g of CLS-g-DMC / CMC@Pro was placed in a dialysis bag (1000 Da), both ends were sealed with a sealing clip, and it was placed in 50 mL of 25 mmol / L NaCl aqueous solution. The experiment was carried out under magnetic stirring. 5 mL of supernatant was taken at 2 h, 5 h, 8 h, 12 h, 24 h, 36 h, 48 h, and 72 h, and the volume was made up to 50 mL with deionized water. The concentration of proline solution was determined by ninhydrin colorimetry-spectrophotometry. T2 was the combined application of acidic substances B and C. 0.2 g of citric acid C was added at 6 h, and the other steps were the same as T1. The control group (CK) was 50 mL of deionized water with 0.1 g of proline added. The results are as follows Figure 6 As shown, after the addition of agent C (citric acid), the release of proline increased significantly at 8 h compared to the case without agent C, indicating that agent C (citric acid) has a controlling effect on lignin particles.

[0063] Example 2: Comparison of Agent A of the present invention with other lignin-based soil conditioners This experiment used containers with a diameter of 11 cm, a height of 40 cm, and perforated bottoms to simulate soil columns. The bottom of each container was lined with two layers of gauze and a 1 cm thick layer of quartz sand to prevent soil leakage. The treatment is shown in Table 3, with an addition amount of 0.1% of the soil mass. Air-dried soil (topsoil (0-15 cm) from Kenli County, Dongying City, Shandong Province, 37°70'N, 118°85'E, EC=2575.33, pH=8.51) was sieved through a 2 mm sieve and thoroughly mixed with the soil conditioner. Then, 1200 g of the mixed soil sample was layered into the containers and naturally compacted to ensure a uniform soil height (11 cm) in each column. Initially, the soil was irrigated with 350 mL of deionized water until it reached saturation water holding capacity. The soil was incubated at room temperature for 14 days to allow complete reaction with the conditioner. Soil bulk density was measured using the ring cutter method. Afterward, the soil was removed, air-dried, and its water-stable aggregates were measured. The results are shown in Table 3. As shown in Table 3, the soil with added CLS-g-DMC (calcium lignosulfonate to DMC in a mass ratio of 1:3) showed significant improvements in soil bulk density and the proportion of water-stable aggregates compared to CK and the other three soil conditioners. The soil bulk density decreased from 1.32 to 1.18 compared to CK, and the proportion of water-stable aggregates >0.25mm increased by 164.92% compared to CK.

[0064] A3: In a 150 mL three-necked flask, add 50 mL of deionized water, 3 g of sodium lignosulfonate, and 50 mg of EDTA. Purge with nitrogen and start the reaction at 50 °C with stirring at 300 r / min. After the lignosulfonate is fully activated, add potassium persulfate (0.3 g) and DMDAAC (4.5 g) as initiators. Stir at 50 °C for 4 h to obtain the amphoteric polymerization product of aminated lignosulfonate. Weigh polyvinyl alcohol (PVA) and place it in a three-necked flask. Add an appropriate amount of distilled water and stir at 90 °C for 2 h to obtain a 5% PVA solution. Add 10 mL of 5% PVA to 50 mL of the prepared aminated lignin solution. The crosslinking agent is 1 mL of 25% glutaraldehyde. React at 70 °C for 4 h, adjust the pH of the solution to 6.5, and finally obtain an ASL / PVA emulsion (6% ASL, 1% PVA).

[0065] A4: Add 1.5 g of sodium lignosulfonate and 20 g of acrylic acid to 78.5 g of deionized water and stir until completely dissolved. Then add 20 g of humic acid, 10 g of wood vinegar, 2 g of tannic acid, and 1 g of ferric sulfate and mix well. Purge with nitrogen for 30 min, then heat to 50°C and react for 2 h to obtain the resin. Remove the resin and dry it in a 70°C oven until the mass is constant to obtain the lignin biomass resin-based saline-alkali land conditioner.

[0066] Table 3. Comparison of the soil conditioner of this invention with other lignin-based soil amendments.

[0067] References: Patent 1 A soil conditioner and its preparation method CN115772267A Patent 2 A method for preparing a lignin biomass resin-based saline-alkali land conditioner CN112537989A.

[0068] Example 3: Pot Culture Experiment of Maize with Modified Lignin Soil Conditioner Soil samples (0-15 cm) from Kenli County, Dongying City, Shandong Province (37°70'N, 118°85'E) were collected, sieved to 2 mm, air-dried, with a pH of 8.2 and an EC value of 1627 μS / cm. Pot experiments were conducted in a glass greenhouse at the China Agricultural University Experimental Station. The experiment included three treatments: a control group (CK, no soil treatment); TB0 treated with agents A and B (mass ratio 13:5) of the modified lignin soil conditioner from Example 1, but without agent C; and TB1 treated with agents A + B + C (65wt% + 25wt% + 10wt%) of the modified lignin soil conditioner from Example 1. The conditioner dosage was 0.1% of the soil mass. Agents A and B were evenly mixed into the soil and then potted (1.2 kg of dry soil per pot). Agent C was added 6 h later. 480 mL of deionized water was added to each pot before planting to balance the soil. Two days later, three corn seeds (variety "Zhengdan 958", Hebei Maohua Seed Industry Co., Ltd.) were planted in each pot. After seven days of growth, one seedling with the most representative growth status was retained from each pot (selected based on the principle that the plant height, number of leaves, and stem diameter were closest to the average of the three plants in the same pot). After seed germination, 300 mL of water was added every three days, and no fertilizer was applied throughout the entire growth period. Each treatment was repeated three times, and the seedlings were harvested 21 days after transplanting, and relevant indicators were measured.

[0069] The results are shown in Figure 7 ,Depend on Figure 7 It can be seen that compared with the control (CK) corn, TB0 corn showed increases in fresh weight, dry weight, seedling height, stem width, and root length by 58.53%, 42.15%, 31.05%, 1.48%, and 31.14%, respectively. Compared with the control (CK) corn without agent C, TB1 corn showed increases in fresh weight, dry weight, seedling height, stem width, and root length by 33.25%, 51.6%, 27.08%, 21.3%, and 32.11%, respectively. This indicates that the combined use of agents A, B, and C can more effectively promote the growth of corn seedlings.

[0070] Soil aggregates were measured after the corn seedlings were harvested 21 days later. The soil in the pots was air-dried, and 50 g of soil was taken and the aggregates were measured using the wet sieving method. The results are shown below. Figure 8 . Figure 8The results showed that, compared with the control (CK), the proportion of aggregates larger than 0.25 mm in soils TB0 and TB1 increased significantly, by 86.67% and 138.9%, respectively. The mean weight diameter (MWD) and geometric mean diameter (GMD) of the soil were used to describe the distribution of soil aggregate structure. Table 4 shows that agents A and B in the conditioner promoted soil aggregate structure, and by comparing TB1 and TB0, the improvement effect was more significant after adding agent C; MWD increased from 0.18 to 0.32, GMD increased from 0.1 to 0.17, and the soil fractal dimension Dm decreased from 2.72 to 2.51, indicating that the higher the degree of particle size aggregation, the stronger the erosion resistance and the better the stability.

[0071] Table 4. Effects of modified lignin soil conditioner on soil aggregate stability

[0072] Example 4: Effects of modified lignin soil conditioner on seed germination I. Preparation of Modified Lignin Soil Conditioner (1) Agent A: Preparation of cationic modified lignin polymer Weigh 5 g of sodium lignosulfonate (NLS) and dissolve it in 100 mL of deionized water. After stirring until fully dissolved, transfer the solution to a 250 mL three-necked flask. Place the flask in an oil bath and heat to 75 °C. During this process, continuously purge the flask with high-purity nitrogen to remove air. Dissolve 0.8 g of potassium persulfate (KPS) in 15 mL of deionized water. Add the KPS solution dropwise to the three-necked flask and react for 20 min. Then, add 30 mL of DAC solution (acryloyloxyethyltrimethylammonium chloride solution, 80 wt% dissolved in water) dropwise to the above mixture and stir continuously for 4 h. The synthesis process needs to be carried out under nitrogen protection. After the reaction is complete, cool the mixture to room temperature and precipitate the solid with ethanol. Dry the solid product in an oven at 75 °C and grind it to obtain the cationic modified lignin polymer (NLS-g-DAC).

[0073] (2) Agent B: Preparation of lignin controlled-release granules 2 g of NLS-g-DAC powder was dissolved in 50 mL of deionized water and stirred for 10 min to obtain an NLS-g-DAC solution. 1 g of proline was dissolved in the NLS-g-DAC solution, stirred, and sonicated for 15 min. 2 g of sodium alginate (SA) was dissolved in 50 mL of water and slowly added dropwise to the above mixed solution while maintaining a stirring speed of 1000 rpm. The mixture was then centrifuged to collect the precipitate, which was then vacuum dried to obtain lignin controlled-release particles (NLS-g-DAC / SA@Pro).

[0074] The acidic substance in agent C is fulvic acid. NLS-g-DAC, NLS-g-DAC / SA@Pro and fulvic acid are prepared in proportions of 60wt%, 35wt% and 5wt%, respectively, and packaged separately to obtain modified lignin soil conditioner.

[0075] Seed germination experiments were conducted according to the standard "Organic Fertilizer" NY525-2021, with slight modifications. In the germination experiment, cucumber seeds were disinfected with sodium hypochlorite for 10 min, and a 25 mmol / L NaCl solution (T0) was used to simulate salt stress. Solutions of the modified lignin soil conditioner (T1-T3) and polyacrylamide (cationic, molecular weight 8 million-1 million, PAM) at concentrations of 0.5 wt%, 1.25 wt%, and 2.5 wt% (T4-T6) were prepared, and 10 mL of each solution was transferred onto filter paper.

[0076] During the experiment, the germination rate (GR), average shoot length (ABL), and germination index (GI) of the seeds were evaluated, and the results are shown in Table 5. As can be seen from Table 5, the modified lignin soil conditioner has a significant promoting effect on seed germination.

[0077] Table 5 Seed germination status of modified lignin soil conditioner

[0078] Example 5: Field application of modified lignin soil conditioner The modified lignin soil conditioner prepared in Examples 1 and 3 above was applied to saline-alkali land. The experimental field was located in Kenli County, Dongying City, Shandong Province (37°70'N, 118°85'E). The application method is as follows: Agents A, B, and C are applied in combination. The air-dried soil is taken from the top 0-15cm of the saline-alkali land, air-dried, ground, and set aside. Agents A and B of the modified lignin soil conditioner are mixed with the air-dried soil and then evenly spread on the surface of the saline-alkali land. The mass ratio of air-dried soil to soil conditioner is 10:1. The soil is then deeply tilled to a depth of 30cm and shaped evenly. Agent C is applied 6 hours later. The application rate of the modified lignin soil conditioner is 150 kg / mu. After emergence, the rhizosphere soil is removed to test the exchangeable sodium content, soil pH, and soil EC value. Three parallel samples are tested for each group of samples, and the average value is taken. Untreated saline-alkali land is used as the control group CK. The test results are shown in Table 6 below.

[0079] Table 6 Soil Physicochemical Indicators

[0080] Table 6 shows that pH, EC, and exchangeable sodium were significantly lower than in the control group (CK). pH decreased from 8.18 to 7.15, EC decreased from 967.67 uS / cm to 411.33 uS / cm, and exchangeable sodium... + The concentration decreased from 650 mg / L to 400.43 mg / L, indicating that the conditioner can reduce soil salinity and soil alkalinity.

[0081] The actual yields were as follows: the fresh corn ear yield of the CK control group was 1100.2 kg / mu, the fresh corn ear yield of the conditioner in Example 1 was 1375.4 kg / mu, and the fresh corn ear yield of the conditioner in Example 3 was 1452.89 kg / mu.

[0082] Example 6: Modified lignin soil conditioner and soil column leaching simulation experiment The specific preparation method of the modified lignin soil conditioner in this embodiment is as follows: (1) Agent A: Preparation of cationic modified lignin polymer Weigh 7 g of potassium lignosulfonate (KLS) and dissolve it in 100 mL of deionized water. After stirring until fully dissolved, transfer the solution to a 250 mL three-necked flask. Place the flask in an oil bath and heat to 80 °C. During this process, continuously purge the flask with high-purity nitrogen to remove air. Dissolve 0.8 g of ammonium persulfate (APS) in 15 mL of deionized water and add the APS solution dropwise to the flask. React for 20 min. Then, add 35 mL of DMC solution (methacryloyloxyethyltrimethylammonium chloride, 75 wt% dissolved in water) dropwise to the above mixture and stir continuously for 3 h. The synthesis process needs to be carried out under nitrogen protection. After the reaction is complete, cool the mixture to room temperature and precipitate the solid with ethanol. Dry the solid product in an oven at 80 °C and grind it to obtain the cationic modified lignin polymer (KLS-g-DMC).

[0083] (2) Agent B: Preparation of lignin controlled-release granules Dissolve 3 g of KLS-g-DMC powder in 50 mL of deionized water and stir for 10 min to ensure complete dissolution, obtaining a KLS-g-DMC solution. Dissolve 1 g of γ-proline in the KLS-g-DMC solution, stir, and sonicate for 15 min. Dissolve 2 g of pectin (Pec) in 50 mL of water and slowly add it dropwise to the above mixed solution while controlling the stirring speed at 1000 rpm. Then centrifuge to collect the precipitate, and dry it under vacuum at 70 °C to obtain lignin controlled-release particles (KLS-g-DMC / Pec@Pro).

[0084] The acidic substance in agent C is polyacrylic acid (molecular weight Mw is 200). KLS-g-DMC, KLS-g-DMC / Pec@Pro and polyacrylic acid are prepared in proportions of 70wt%, 25wt% and 5wt%, respectively, and packaged separately to obtain the modified lignin soil conditioner.

[0085] This experiment used containers with a diameter of 11 cm, a height of 40 cm, and a perforated bottom to simulate soil columns. The bottom of each container was lined with two layers of gauze and a 1 cm thick layer of quartz sand to prevent soil leakage. A 500 mL beaker was placed underneath to collect the leachate. Treatments included a control group (CK), TB1 treated with 0.6 g of the modified lignin soil conditioner (0.05% of soil mass), and TB2 treated with 1.2 g of the modified lignin soil conditioner (0.1% of soil mass). Each treatment was repeated three times. Air-dried soil (topsoil (0-15 cm) from Kenli County, Dongying City, Shandong Province (37°70'N, 118°85'E), sieved to 2 mm, air-dried, pH 8.2, EC 1627 μS / cm) was passed through a 2 mm sieve and thoroughly mixed with the soil conditioner. Then, 1200 g of the mixed soil sample was layered into containers and naturally compacted. The soil was initially irrigated with 350 mL of deionized water until it reached saturation water holding capacity. It was then left at room temperature for two days to allow the soil and conditioner to fully react. The leaching process was then initiated with 400 mL of deionized water. Leaching was complete when no liquid flowed out from the bottom of the soil column within 10 minutes; the volume of the leachate was measured directly using a graduated cylinder. After thorough mixing, 100 mL of the leachate was collected and stored in a refrigerator for further analysis. After leaching and soil air-drying, the soil was removed from the soil column, and its physicochemical properties were measured.

[0086] like Figure 9 As shown in Table 7, compared with the control (CK), TB1 and TB2 significantly shortened the soil infiltration time, reducing it by 32.16% and 31.66% respectively, and reduced the leachate volume (by 8.77%-9.82%), thus increasing the soil's water retention capacity. Meanwhile, as shown in Table 8, both TB1 and TB2 significantly reduced soil pH and electrical conductivity. When the conditioner dosage was 1 / 1000 of the soil mass, the soil pH decreased from 8.18 to 6.82, and the EC value decreased by 42.8% compared to CK. As shown in Table 8, the sodium ion concentration in the leachate from TB1 and TB2 decreased by 28.65% and 39.18% respectively compared to CK.

[0087] Table 7. Changes in soil pH and electrical conductivity (EC value)

[0088] Table 8 Sodium ion concentration in the eluent .

Claims

1. A modified lignin soil conditioner, characterized in that: The modified lignin soil conditioner includes Agent A, Agent B, and Agent C; Agent A is a cationic modified lignin polymer, which is prepared by graft copolymerization of lignin sulfonate and cationic monomer through free radical initiation. The agent B is a lignin controlled-release particle, which is prepared by electrostatic intercalation self-assembly of the cationic modified lignin polymer and another negatively charged natural polymer to encapsulate an amino acid amphoteric regulator. The agent C is at least one of citric acid, lactic acid, itaconic acid, fulvic acid, wood vinegar, maleic acid, maleic anhydride and polyacrylic acid; The lignin sulfonate is at least one of calcium lignin sulfonate, magnesium lignin sulfonate, sodium lignin sulfonate, and potassium lignin sulfonate. The cationic monomer is at least one of methacryloyloxyethyltrimethylammonium chloride and acryloyloxyethyltrimethylammonium chloride; The negatively charged natural polymer is at least one of sodium carboxymethyl cellulose, sodium alginate, and pectin; The amino acid amphoteric regulator is at least one of proline, γ-aminobutyric acid, aspartic acid, and arginine.

2. The modified lignin soil conditioner of claim 1, wherein: By mass percentage, the modified lignin soil conditioner contains 50%-70% of agent A, 25%-45% of agent B, and 5%-10% of agent C.

3. The modified lignin soil conditioner of claim 1, wherein: The preparation method of Agent A includes the following steps: mixing the lignin sulfonate, cationic monomer, initiator and water, and reacting to obtain Agent A.

4. The modified lignin soil conditioner of claim 3, wherein: The initiator is a low-temperature initiation system or a thermal initiation system; The low temperature initiation system is ammonium persulfate - ascorbic acid and / or Fe 2+ - hydrogen peroxide; the thermal initiation system is ammonium persulfate and / or potassium persulfate; The initiator is 0.5%-10% of the total mass of lignin sulfonate and cationic monomer; The mass ratio of the lignin sulfonate to the cationic monomer is 1:1 to 1:10; The reaction temperature is 40-90℃; the reaction time is 2-6 h; The reaction is carried out in an inert atmosphere.

5. The modified lignin soil conditioner of claim 1, wherein: The preparation method of Agent B includes the following steps: mixing the cationic modified lignin polymer, amino acid amphoteric regulator, negatively charged natural polymer and water, stirring to gradually form colloidal particles of the complex, and then collecting and drying the precipitate to obtain Agent B.

6. The modified lignin soil conditioner of claim 5, wherein: The mass ratio of the cationic modified lignin polymer to the negatively charged natural polymer is 1:0.5-1:3.5; The mass ratio of the amino acid amphoteric regulator to the total mass of the cationic modified lignin polymer and the negatively charged natural polymer is 1:3-1:

8. The stirring speed is 600-1200 rpm.

7. The modified lignin soil conditioner according to claim 5 or 6, characterized in that: The preparation method of Agent B includes the following steps: dissolving the cationic modified lignin polymer and the amino acid amphoteric regulator in water to obtain a mixed solution; then slowly adding an aqueous solution of the negatively charged natural polymer dropwise to the above mixed solution, stirring to gradually form colloidal particles of the complex, and then collecting and drying the precipitate to obtain Agent B.

8. The application of the modified lignin soil conditioner according to any one of claims 1-7 in improving saline-alkali soil.

9. A method of improving saline soil, characterized by: The method includes the following steps: mixing Agent A and Agent B of the modified lignin soil conditioner according to any one of claims 1-7 with air-dried soil, spreading the mixture evenly on the surface of saline-alkali land, turning over the soil to make it uniform, and applying Agent C of the modified lignin soil conditioner according to any one of claims 1-7 after 4-24 hours; the application rate of the modified lignin soil conditioner is 150-200 kg / mu.

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