CN115772267B

CN115772267B - Soil conditioner and preparation method thereof

Info

Publication number: CN115772267B
Application number: CN202211450546.8A
Authority: CN
Inventors: 李�浩; 侯亚慧; 方静; 齐俊杰; 黎钢
Original assignee: Hebei University of Technology
Current assignee: Hebei University of Technology
Priority date: 2022-11-18
Filing date: 2022-11-18
Publication date: 2024-01-26
Anticipated expiration: 2042-11-18
Also published as: CN115772267A

Abstract

The invention discloses a soil conditioner and a preparation method thereof. The soil conditioner is prepared from SL, PVA and quaternary ammonium salt by graft copolymerizing to obtain amphoteric monomer ASL; and then ASL and PVA are crosslinked to prepare ASL/PVA copolymer emulsion. According to the invention, lignosulfonate is taken as a raw material, and is subjected to amination modification and cross-linking copolymerization with polyvinyl alcohol to prepare the zwitterionic emulsion, so that the novel soil conditioner is synthesized, the wind erosion resistance, the water retention performance and the salt resistance of soil can be improved, a certain protection effect on plant growth can be achieved, the physicochemical properties and the nutrients of sandy high-salt soil can be improved, the environment is protected, the degradation is realized, and the action time is long and the degradation is more resistant.

Description

Soil conditioner and preparation method thereof

Technical Field

The invention relates to the technical field of agriculture and soil treatment, in particular to a soil conditioner and a preparation method thereof.

Background

Soil degradation and grain problems have become a global problem, with saline-alkali soil problems being particularly pronounced. Saline-alkali soil is mostly distributed in arid and semiarid regions, and the soil in the regions is sandy soil, loose in soil particles, weak in capillary action, rapid in moisture permeation and poor in water and fertilizer retaining capacity. When the ambient temperature rises, the water evaporates rapidly, and the salt in the soil and groundwater is brought to the soil surface layer, where it accumulates for a long period of time to form saline-alkali soil. The salinity limits the fertility of the soil and the accumulation of excess soluble salts in the soil negatively affects the physical and chemical properties of the soil. The long-term saline-alkali environment can lead to poor soil nutrient, further forms more serious desertification, accelerates the soil degradation and can cause loss to crops and fertilizers. In addition, the problems of sand and dust weather, desertification, soil fertility reduction and the like caused by strong wind erosion in arid areas can also have great influence on the treatment of the saline-alkali soil. Salt stress, drought stress and wind erosion environments are, to some extent, co-occurring. Therefore, the treatment of saline-alkali soil needs to adopt salt-tolerant sand-fixing water-retaining measures at the same time, which is a key for solving the problem of agricultural sustainability in arid areas.

Organic high molecular polymer materials are commonly used as soil amendments for relieving and controlling drought stress, salt stress and wind and sand erosion, and after being sprayed on the surface of sandy soil or mixed with the sand, the polymer materials show the functions of gathering the sandy soil and forming crusts on the surface of a sand layer, and have good water absorption and retention, evaporation resistance and wind erosion resistance. The soil sand-fixing materials commonly used in the market at present mainly comprise polyacrylamide, polyvinyl alcohol, vinyl acetate-ethylene copolymer, polyurethane and the like. The polymerized sand fixing agent and the composite material are non-degradable, wherein non-degradable chemical components accumulate in soil for a long time to pollute the soil, simultaneously, the potentially toxic micromolecular monomers such as acrylamide and the like contained in the composite material can cause irreversible injury to human bodies, and most of polymers have high viscosity, and weak cohesive force among sand particles leads to lower stability of sand particles, surface crusting frequently occurs in the sand, and the sand is difficult to permeate into deeper sand layers to form a shell with high wind erosion resistance. In recent years, chemically modified and crosslinked natural biomass materials have been developed and applied in agriculture based on environmental requirements. Biomass materials such as cellulose, starch, chitosan, sodium alginate, pectin, polyaspartic acid, humic acid and the like are used as environment-friendly substitutes for traditional polyacrylic acid soil amendments and applied to agriculture and soil treatment, however, the degradation rate of the materials is high, and biodegradation begins within weeks to months after soil application.

The lignin is used as a second abundant natural biomass material, has low price and wide sources, and has natural environmental protection performance. Original lignin has great limitations in soil improvement, including low adhesion properties and surface activity. Functionalization and modification of lignin into composite materials is critical to improving their environmental suitability. The lignin is used as a sand fixing agent prepared by grafting and modifying urea resin or polyacrylamide which are traditional materials. However, the preparation method does not fully exert the environmental protection property of lignin. There have been studies on modifying lignin to treat soil, and oxyethylated lignin (OEL) is used as a sustainable water-retaining soil conditioner to remarkably improve physical and hydraulic properties of soil. The lignin (KSL) modified by ozone can improve acid soil, complex aluminum ions and effectively reduce aluminum toxicity. The prepared lignin hydrogel has good effect on soil improvement. The research above, the adsorption performance and degradation resistance of lignin are utilized for soil heavy metal treatment and improving the mechanical properties of soil conditioner.

In order to improve the physical and chemical properties of soil in arid high-salinity areas and solve the problems of salt stress and drought stress on plants, an environment-friendly soil conditioner with high performance, low cost and degradation resistance needs to be prepared.

Disclosure of Invention

In view of the above problems, the present invention provides a soil conditioner, wherein the raw materials for preparing the soil conditioner include SL (lignosulfonate), PVA (polyvinyl alcohol), and quaternary ammonium salt, and the amphoteric monomer ASL (quaternized lignin) is synthesized by graft copolymerization of SL and quaternary ammonium salt; and then ASL and PVA are subjected to crosslinking reaction to prepare ASL/PVA copolymer emulsion.

The mass ratio of SL to PVA in the raw materials is as follows: 3:1 to 12:1, preferably 4:1 to 10:1, more preferably 6:1. the mass ratio of SL to quaternary ammonium salt is 1:1-1:2.5, preferably 1:1,1:1.5,1:2,1:2.5.

The lignosulfonate can be sodium lignosulfonate and calcium lignosulfonate; or one or more of alkali lignin and lignosulfonate obtained by sulfonation of kraft lignin. Can be obtained by pulping by a sulfite method or by-product lignin in the biorefinery industry through sulfonation modification, and can also be purchased for commercial products.

The quaternary ammonium salt may be selected from dimethylallyl ammonium chloride, 3-chloro-2-hydroxypropyl trimethyl ammonium chloride, octadecyl trimethyl ammonium bromide, tetradecyl trimethyl ammonium bromide, dodecyl trimethyl ammonium bromide, dioctadecyl dimethyl ammonium chloride, dicetyl dimethyl ammonium chloride, octadecyl trimethyl ammonium chloride, hexadecyl trimethyl ammonium chloride, tetradecyl trimethyl ammonium chloride, dodecyl trimethyl ammonium chloride, preferably dimethylallyl ammonium chloride (DMDAAC).

The cross-linking agent in the cross-linking reaction can be aldehyde cross-linking agent, such as glutaraldehyde or glyoxal.

The invention further provides a preparation method of the soil conditioner. The preparation method comprises the following steps:

step one: SL and quaternary ammonium salt are synthesized into an amphoteric monomer ASL through graft copolymerization reaction;

step two: and (3) crosslinking the ASL and PVA obtained in the step one to obtain ASL/PVA copolymer emulsion.

The invention utilizes potential surface activity in lignin molecular structure to carry out functional modification to study the saline-alkali soil. In order to develop polyelectrolyte characteristics of lignin and develop potential salt resistance, lignosulfonate is subjected to amination modification, and meanwhile, polyvinyl alcohol which does not influence polyelectrolyte characteristics is crosslinked, so that viscosity of a solution is improved. The emulsion-based adhesive has lower cost and good adhesive force, can be infinitely diluted in water, and is convenient to prepare and apply.

The invention successfully synthesizes a novel ASL/PVA zwitterionic copolymer emulsion as a soil conditioner for high-salt wind erosion arid areas by adopting a graft copolymerization method, researches the water retention property, wind erosion resistance, salt resistance, heat aging and freeze thawing properties of emulsions with different lignin addition amounts, and tests the pH, salt content, total nitrogen, effective potassium, quick-acting phosphorus and organic matter content of soil after the ASL/PVA emulsion is applied. The result shows that the zwitterionic emulsion can obviously improve the water retention, wind erosion resistance and salt resistance of the high-salt sandy soil, has good heat stability and freeze thawing stability, and can bear the change of environmental temperature. The emulsion has great potential in improving the quality of saline-alkali soil, and lignin can adsorb alkali ions in soil and reduce the pH and conductivity of the saline-alkali soil. Lignin can also be degraded into humus to increase nutrient (e.g., N, P and K) and organic content. Potted experiments show that ASL/PVA provides a more suitable environment for plant growth to a certain extent compared with a control, so that the germination rate and plant growth of alfalfa are promoted.

Experimental results show that the emulsion is successfully synthesized and can be used as an ecological sand-fixation salt-resistant material. The reason for this is that: firstly, the emulsion can obviously improve the compressive strength and the water retention; secondly, the emulsion has good heat aging, freeze thawing stability and salt tolerance, and can bear the change of temperature and the concentration of the desert NaCl; third, the effect of the emulsion on plant growth and sandy soil microbial growth also showed reliable ecological effects.

The invention has the beneficial effects that:

according to the invention, lignosulfonate is taken as a raw material, and is subjected to amination modification and cross-linking copolymerization with polyvinyl alcohol to prepare the zwitterionic emulsion, so that the novel soil conditioner is synthesized, the wind erosion resistance, the water retention performance and the salt resistance of soil can be improved, a certain protection effect on plant growth can be achieved, the physicochemical properties and the nutrients of sandy high-salt soil can be improved, the environment is protected, the degradation is realized, and the action time is long and the degradation is more resistant.

Drawings

The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the invention.

In the drawings:

FIG. 1 is a schematic diagram of ASL preparation in accordance with the present invention.

FIG. 2 is a schematic diagram of the preparation of ASL/PVA emulsions of the present invention.

FIG. 3 is a schematic diagram of the salt tolerance mechanism (c) showing the effect of NaCl content on tensile strength and percent elongation (a), viscosity (b).

FIG. 4 is a graphical representation of biodegradation of microspheres in a soil burial test.

FIG. 5 shows the effect of ASL/PVA on plant growth (a, b), germination (c), plant height and root length (d) in coastal saline-alkali soil.

Detailed Description

Test description:

(1) Reagent source:

the sodium lignin sulfonate of the embodiment of the invention is a commercial finished product.

Diallyl dimethyl ammonium chloride (DMDAAC, 60% in water) and ammonium persulfate (APS, 98% purity) were purchased from shanghai alaa Ding Shenghua technologies limited.

Ethylenediamine tetraacetic acid disodium salt (EDTA, 99% pure) was purchased from the upper seafood tripod biotechnology company.

Polyvinyl alcohol (PVA, alcoholysis of 87.0-89.0, relative molecular mass mn= 130.06 mol/L) was produced from Shanghai flax technologies development limited.

Glutaraldehyde (GA, 25% in water) was purchased from the company, einkmi chemical reagent limited. Deionized water was used for all reactions and solution preparation.

The sandy soil sample is taken from the surface soil (0-30 cm) of the Buzhi desert in inner Mongolian, and is air-dried and sieved (< 0.02 mm) and stored at 25 ℃. The pH of the soil is 7.77, the EC is 1705 mu s/cm, the organic matter content is 7.308g/kg, the total nitrogen is 10.426g/kg, the quick-acting phosphorus is 5.181mg/kg, the quick-acting K is 55.276mg/kg, and the soil is typical sandy high-salt soil.

(2) Description of test instruments

The viscosity of the samples was measured using a digital rotary viscometer (Tuohe NDJ-5S, CN).

The zeta potential of the sample was determined with a zeta potential analyzer (Zetasizer Nano ZS, UK).

The particle size of the samples was determined using a particle size analyzer (Mastersizer 2000, uk).

Example 1 preparation method of soil conditioner

Amphoteric lignin is synthesized by introducing an amino amine through graft copolymerization, and the synthesized amphoteric monomer ASL is shown in figure 1. The reaction was carried out in a 150mL three-necked flask equipped with a mechanical stirrer, with a mass ratio of SL to DMDAAC of 2:3. Ionic water (50 ml), sodium lignin sulfonate (3 g) and EDTA (50 mg) were added to the flask, the reaction was started at 45-55℃with stirring at 300r/min, and after the lignin sulfonate was sufficiently activated, potassium persulfate (0.3 g) and DMDAAC (4.5 g) were added as initiators, and after the addition, the mixture was stirred at 50℃for 4-6 hours to obtain an amphoteric polymerization reaction product of aminated lignin sulfonate.

ASL and PVA are crosslinked to prepare the zwitterionic emulsion, and the synthesis process is shown in figure 2. Weighing polyvinyl alcohol (PVA) with certain mass, putting the PVA into a three-necked flask, adding a proper amount of distilled water, and stirring at 90 ℃ for 2 hours to obtain PVA with the concentration of 5%. 5% PVA with different capacities is added into 50mL of the prepared aminated lignin, and the cross-linking agent is glutaraldehyde with the mass concentration of 1mL of 25%. Reacting at 50-70 deg.c for 5-7 hr, preferably 4 hr, and regulating pH value to 6.0-6.5 to obtain ASL/PVA copolymer emulsion.

The above-mentioned 5% PVA solutions of 1mL,2mL,3mL,4mL and 5mL different capacities were added separately to obtain the optimum PVA addition by measuring the properties.

Example 2ASL/PVA emulsion Performance test

The basic properties of the emulsion can directly influence the sand fixation effect in practical application, such as emulsion particle size, viscosity, zeta potential and stability, and the basic parameters of ASL/PVA emulsion are measured. Particle size is a physical indicator of dispersion uniformity, and particle size and polydispersity index (PDI) data for ASL/PVA emulsions have been determined. The average particle diameter of the prepared emulsion is 446.6nm, the particle diameter of the emulsion is less than 1mm, and the emulsion can easily permeate into the pore space of sand grains and form crust on the surface layer of the sand sample. Furthermore, the average value of PDI is below 0.5, which is considered to be successful in polymerizing the emulsion, the particles of which are monodisperse. In general, the larger the absolute value of the zeta potential of the particles in the emulsion, the more repulsive the particles are, which makes the emulsion more stable. The measured zeta potential of the emulsion shows that the zeta potential of the emulsion after modified crosslinking is increased, so that the emulsion is more stable. Proper emulsion viscosity and emulsion dilution are key factors in sand fixation success. As can be seen from Table 1, the ASL/PVA (ASL/PVA mass ratio of 6:1) emulsion viscosity was in a lower viscosity range and exhibited very good permeability and consolidation properties at the same time during sand-like experiments, and the measured emulsion viscosity was suitable for sand fixation.

TABLE 1 Performance parameters of ASL/PVA emulsions

Sample	Particlesize(nm)	PDI	Viscosity(mpa.s)	Zetapotential(mV)
					SL	81.3	0.245	2.68	-20.9
ASL	338.1	0.404	7.32	-24.7
					ASL/PVA	446.6	0.378	17.56	-39.5

Example 3 selection of PVA typical experiments

1.2a: lignosulfonate (3 g), dimethylallylammonium chloride (4.5), initiator ammonium persulfate (0.3 g), PVA concentration 5% (10 mL), glutaraldehyde concentration 25% (1 mL)

1.2b. Lignosulfonate (3 g), dimethylallylammonium chloride (4.5), initiator ammonium persulfate (0.3 g), chitosan concentration 2% (10 mL), glutaraldehyde concentration 25% (1 mL)

1.2c. Lignosulfonate (3 g), dimethylallylammonium chloride (4.5), initiator ammonium persulfate (0.3 g), hydroxymethyl cellulose 5% (10 mL), glutaraldehyde 25% (1 mL)

1.2d. Lignosulfonate (3 g), dimethylallylammonium chloride (4.5), initiator ammonium persulfate (0.3 g), kaolin concentration 5% (10 mL), glutaraldehyde concentration 25% (1 mL)

TABLE 2 selection of PVA typical experiments

Sequence number	Material	Sand fixation performance	Water retention properties
				1.2a	PVA	0.24g/(m ² ·min)	66％
1.2b	Chitosan	0.19g/(m ² ·min)	47％
				1.2c	Cellulose	0.43g/(m ² ·min)	53％
1.2d	Kaolin clay	0.35g/(m ² ·min)	55％

From Table 2, PVA is found to be a more preferred choice.

The water retention performance test method shows that:

a quantity of sand was placed on a 6.5cm diameter petri dish. ASL/PVA emulsion is uniformly sprayed on the surface of the sand shell, and the dosage is 1L/m2. The wet sand samples were placed in an oven at a constant temperature of 50 c, and then the water retention rate of the sand samples was measured every 1 hour according to the weight loss condition, and each sand sample was repeated 3 times. The water retention rate calculation formula is as follows:

wherein M0 is the weight (g) before drying, M1 is the weight (g) after drying, and M is the mass of water added to the sample.

The sand stabilization performance test method is as follows:

the sand stabilization performance is mainly evaluated by measuring the wind erosion modulus, which mainly describes the level of the physical sand conveying process of wind sand blown away by air flow. Sand 80-100 mesh, glass culture dish diameter 6.5cm. The wind erosion resistance test was performed in a portable wind tunnel.

The wind speed of the air outlet is measured by adopting an anemometer (PM 6252A, shenzhen friendship instrument Co., ltd., china) and the wind speed is regulated by changing the gear of the fan. The sample model was dried at a temperature of 50℃and a humidity of 30% for 24 hours (vacuum oven, DNF-6020, shandong sea standard instruments Co., ltd.). Spraying ASL/PVA emulsion with a certain volume on the surface of the sand cone model, and performing an anti-wind erosion test under the condition of adjusting the wind speed (12 m/s). The emulsion was sprayed with a spray having a spray volume of 1L/m2 and each condition was repeated three times. The wind erosion modulus calculation formula is as follows:

wherein E is wind erosion modulus, g/(m2.min)); s is the area (m 2) of eroded soil in the wind tunnel; t is the erosion time (min); m0 is the weight before wind erosion, and M1 is the weight (g) after wind erosion.

Example 4 concentration selection of PVA typical experiments

When the concentration of the fixed ASL solution was 6%, namely, sodium lignin sulfonate SL (3 g) was dissolved in ionized water (50 ml) in example 1 to obtain an ASL solution having a concentration of 6%.

Table 3: concentration selection of PVA typical experiments

PVA	Sand fixation performance	Water retention properties	ASL：PVA
				0.5％	0.54g/(m ² ·min)	53％	12:1
1％	0.24g/(m ² ·min)	66％	6：1
				1.5％	0.26g/(m ² ·min)	57％	4:1
2％	0.17g/(m ² ·min)	51％	3:1
				2.5％	0.11g/(m ² ·min)	45％	2.4:1

From Table 3, it was found that the PVA concentration of 1% gave the best overall performance in terms of soil improvement. And (3) injection: the concentration of PVA in Table 3 of 1% means that 10mL of 5% PVA was added to 50mL of the aminated lignin prepared in example 1, i.e., 0.5g of PVA was added to a 50mL ASL solution at a concentration of 1%. The other PVA concentrations shown in Table 3 were calculated by analogy. The mass ratio of ASL/PVA in the invention is 6:1 refers to the ratio of ASL solution with a concentration of 6% to PVA with a concentration of 1%. And the other ratios are analogized.

Example 5ASL to PVA ratio A typical experiment is preferred

The following examples illustrate some typical conditions during the discovery of optimal amounts of ASL and PVA, and other reaction parameters are the same as those of example 1.

TABLE 4 selection of optimum proportions of ASL and PVA typical experiments

ASL:PVA	Sand fixation performance	Water retention properties
			2：1	0.49g/(m ² ·min)	38％
4：1	0.26g/(m ² ·min)	57％
			6：1	0.24g/(m ² ·min)	66％
8：1	0.19g/(m ² ·min)	61％
			10：1	0.21g/(m ² ·min)	53％

As can be seen from tables 3 and 4, the mass ratio of SL to PVA is 3:1 to 12:1, the sand fixing performance and the water retention performance can be basically ensured at the same time, and the method is an optional range; the mass ratio of SL to PVA is 4: 1-10:1, more preferably 6:1.

EXAMPLE 6 comparative experiments of soil conditioner of the present invention with other Sand-fixing Agents

TABLE 5 comparative experimental data for various sand fixing agents

Reference is made to:

[1]X.Meng,L.Liang,B.Liu,Synthesis and Sand-Fixing Properties of Cationic Poly(vinyl acetate-butyl acrylate-2-hydroxyethyl acrylate-DMC)Copolymer Emulsions,Journal of Polymers and the Environment 25(2)(2016)487-498.10.1007/s10924-016-0826-z.

[2] peng, lei, zhang Lidan, < Synthesis of Sand fixing agent P (VAc-BA) and application thereof-Peng Lei. Pdf >, application chemistry (2009)

[3] Liu, hui 1, wang Yuwei, jiying, <2020 New Environment protection sand fixing agent Performance research_ Liu Hui. Pdf >, jilin chemical academy of sciences (2020)

Example 7: the invention relates to a preparation method of a soil improvement mulch film

In example 1, the amount of PVA was increased by 2 times, and the prepared emulsion ASL/PVA was placed in an oven at 70℃for 8 hours to prepare a latex film.

Example 8: performance test of soil conditioner

Example 8.1: salt tolerance test

In order to improve the sand-fixing capability of the emulsion in high-salinized sand, the salt tolerance of an ASL/PVA emulsion film becomes an important parameter for the sand-fixing effect of salinized desert, and also becomes a standard for evaluating the sand-fixing effect. The emulsion was prepared at room temperature as a film. The prepared film has uniform area and thickness. NaCl is dissolved in deionized water, and the concentration is between 0.0 and 5.0 weight percent. These membranes were then immersed in saline for 72 hours and then dried under natural conditions.

To determine whether the latex film (latex film prepared in example 7) satisfies the requirement of sand fixation under different NaCl conditions, the influence of NaCl content on the mechanical properties of the latex film was evaluated by changing the concentration of NaCl solution, as shown in FIG. 3 (a). The experimental results show that as the NaCl concentration increases, the tensile strength of the latex film decreases, but the decrease trend is not great.

The viscosity has a great influence on the sand-fixing ability and salt tolerance of the polymer. FIG. 3 (b) shows the viscosity of the emulsion at different NaCl concentrations. At NaCl concentrations of 0wt% to 1wt%, the viscosity of the emulsion increases, and at NaCl concentrations greater than 1wt%, the viscosity of the emulsion decreases. These results indicate that the high salt environment does not have a large impact on the performance of the emulsion, and therefore, the amphoteric emulsion is a good material for remediation of high salt sandy soil.

Example 8.2: physical and chemical properties of soil

The emulsions with different ASL concentrations are sprayed into the soil according to a ratio of 1:100, so that the emulsions are uniformly mixed with the soil. And taking a certain amount of modified soil after 30d, drying and screening, and measuring soil nutrients.

And determining the influence of the ASL/PVA emulsion on the physicochemical properties of the soil by measuring the pH, the conductivity (EC), the organic matter content (SOM) and the content of soil nutrients (N, P, K) of the soil before and after the ASL/PVA treatment.

The pH of the soil treated with ASL/PVA emulsion was lower than that of the control group (pH=7.77), and when the pH of the soil was > 7.5, it was judged as alkaline soil, and as the addition amount of ASL in the ionic emulsion was increased, the tendency of the pH of the soil to decrease was greater. When the ASL addition was 6%, the soil pH had fallen below 7.5.

Conductivity (EC) is a very important indicator of the salt content of the soil, as measured by experimentation, as the ASL addition increases, the conductivity of the soil leachate decreases.

Organic Matter (SOM) in soil is a main source of soil nutrients, and as the amount of ASL added in emulsion increases, the content of organic matter in soil increases as measured by experiments.

N, P, K in the soil is an essential nutrient for plant growth, and as can be measured through experiments, N, P, K in the soil increases to different degrees with increasing ASL addition in the emulsion.

Example 8.3: degradation analysis

And naturally drying the emulsion to form a latex film. According to the requirement of the GB/T19275 material degradation test, the degradation performance of the soil modifier under natural conditions is tested by adopting a soil burying method. Preparing emulsion into emulsion film, placing into 80 mesh nylon mesh bag, and burying into 6-8cm soil. Samples were taken every 15 days, washed with deionized water, dried at 40 ℃ for 4 hours, and the degraded film was returned to the soil. The test period is 90d. This test was repeated three times.

Wherein eta is degradation rate (%), m0 (g) and m1 (g) are respectively the mass of the liquid mulch film before and after degradation.

Through experimental tests on the relation between the degradation rate and the degradation time of the emulsion, the degradation performance of the modifier is found to increase with the increase of ASL content. The degradation process of the soil conditioner is divided into three stages. The degradation rate was slightly faster in the first 30 days, due to the incorporation of ungrafted or uncrosslinked molecules into the soil. Around 30 days, the soil conditioner remained slow and degraded relatively slowly, probably due to the accumulation of microorganisms on the latex film surface. After 60 days, the degradation rate of the soil conditioner suddenly increases, possibly due to degradation of macromolecules or disruption of cross-links in the three-dimensional network. The moisture and humidity in the soil are critical to the degradation process, and the water can dissolve hydrophilic groups on the polymer molecular chain, so that the internal structure is changed, and the degradation process is accelerated. The lignosulfonate in the emulsion can be decomposed into humic acid small molecules in the soil so as to improve the physicochemical property of the soil and provide nutrition for the growth of microorganisms. The quality loss of the modifier with different ASL addition amounts is 16.46-24.91% in 90 days, and compared with other soil modifiers (such as soil modifiers prepared by other natural biomasses, for example sodium alginate, starch, polysaccharide chitosan, amino acids and the like), the degradation speed of ASL/PVA is slower, and the time of acting in soil is longer. The result shows that ASL/PVA is a biodegradable film with corrosion resistance and durability. In addition, the emulsion was cultured at 25℃in the medium. After a period of time, the medium was covered with white colonies (FIG. 4). This indicates that the emulsion preparation material is non-toxic to microorganisms and can be degraded by microorganisms.

Example 8.4: plant experiment

Potting experiments set different concentrations of ASL treatment and blank. 1 kg of the sand treated with the emulsion was put into a flowerpot. In the soil cultivation process, the soil moisture addition amount reaches 60%. 15 alfalfa seeds are planted in each pot, and plant analysis is carried out after 20 days of sowing. The collected plants were washed with water and divided into an overground part and an underground part, and germination rate, plant height and root length were measured, 3 replicates per group.

The growth condition of plants added with ASL/PVA with different concentrations is observed by planting alfalfa in saline-alkali sandy soil. The maize plants showed significant differences in growth between the different treatments (fig. 5a,5 b). Alfalfa plants in the soil of the control group cannot grow normally due to high salt content and lack of nutrients in the soil; however, the germination and growth of plants were significantly promoted after application of ASL/PVA soil conditioner, and the higher the content of aminated lignin added to the soil conditioner, the better the germination rate and growth of plants were as demonstrated from the height and root length of the plants (fig. 5b,5c,5 d). This shows that ASL/PVA soil conditioner has excellent effect of improving saline-alkali soil in arid area and promoting alfalfa growth. This was also confirmed by the positive correlation between plant length and root length, N, P, K, organic matter.

The foregoing is a further detailed description of the invention in connection with specific embodiments, and it is not intended that the invention be limited to such description. It will be apparent to those skilled in the art that several simple modifications and adaptations of the invention can be made without departing from the spirit of the invention and are intended to be within the scope of the invention.

Claims

1. The soil conditioner is characterized in that the soil conditioner is prepared from SL, PVA and quaternary ammonium salt, and is synthesized into amphoteric monomer ASL through graft copolymerization reaction of SL and quaternary ammonium salt; then ASL and PVA are subjected to crosslinking reaction to prepare ASL/PVA copolymer emulsion; the SL is one or more of sodium lignosulfonate, calcium lignosulfonate, lignin sulfonate obtained by sulfonation modification of alkali lignin and sulfate lignin; the quaternary ammonium salt is dimethyl allyl ammonium chloride, 3-chloro-2-hydroxypropyl trimethyl ammonium chloride, octadecyl trimethyl ammonium bromide, tetradecyl trimethyl ammonium bromide, dodecyl trimethyl ammonium bromide, dioctadecyl dimethyl ammonium chloride, dicetyl dimethyl ammonium chloride, octadecyl trimethyl ammonium chloride, hexadecyl trimethyl ammonium chloride, tetradecyl trimethyl ammonium chloride, dodecyl trimethyl ammonium chloride.

2. The soil conditioner according to claim 1, wherein the mass ratio of SL to PVA in the preparation raw material is: 3: 1-12: 1.

3. the soil conditioner according to claim 1, wherein the mass ratio of SL to PVA in the preparation raw material is: 4: 1-10:1.

4. The soil conditioner of claim 1, wherein the mass ratio of SL to quaternary ammonium salt in the raw material is 1:1-1:2.5.

5. The soil conditioner according to claim 1, wherein the crosslinking agent in the crosslinking reaction is an aldehyde crosslinking agent.

6. The soil amendment according to claim 5, wherein the cross-linking agent is glutaraldehyde or glyoxal.

7. The soil conditioner of claim 1, wherein the quaternary ammonium salt is dimethylallyl ammonium chloride.

8. The soil conditioner of claim 1, wherein the soil conditioner has a particle size of 300nm to 800nm and a viscosity of 10mpa.s to 100mpa.s.

9. A method for preparing the soil conditioner according to claim 1, which is characterized in that: the preparation method comprises the following steps:

10. The preparation method according to claim 9, wherein the mass ratio of the SL to the quaternary ammonium salt is 1:1-1:2.5; the mass ratio of SL to PVA is 3: 1-12: 1.

11. the preparation method according to claim 9, wherein the first step is carried out under nitrogen atmosphere at 45-55deg.C for 4-6h; the reaction temperature of the second step is 50-70 ℃ and the reaction time is 5-7h.