Wormcast-based hydrogel as well as preparation method and application thereof

Abstract

The invention provides wormcast-based hydrogel and a preparation method and application thereof, and the preparation method comprises the following steps: (1) dissolving sodium alginate in a buffer solution to obtain a sodium alginate solution; (2) dissolving chitosan in a solvent, stirring until the chitosan is completely dissolved, and adjusting the pH value of the solution to be below 5.5 to obtain a chitosan solution; (3) uniformly mixing the chitosan solution and the sodium alginate solution to obtain a polyelectrolyte composite emulsion; (4) dissolving wormcast in water to obtain wormcast turbid liquid with the concentration of 20-40wt%; and (5) adding the wormcast turbid liquid into the polyelectrolyte composite emulsion, and stirring to fully crosslink the wormcast turbid liquid. The preparation method can effectively promote crosslinking among sodium alginate, chitosan and wormcast, effectively improve the mechanical strength and salt resistance of the gel, enhance the soil improvement effect of the saline-alkali soil, improve the retention rate of nitrogen in the saline-alkali soil, and promote the growth of crops in the saline-alkali soil.

Description

Technical Field

[0001] This invention relates to the field of land improvement technology, and in particular to an earthworm castings-based hydrogel, its preparation method, and its application. Background Technology

[0002] Globally, soil salinization has become a major threat to agricultural production, food security, and sustainable development in arid and semi-arid regions. Statistics show that, to date, due to topographical and human factors, over 424 million hectares of topsoil (0-30 cm) and 833 million hectares of subsoil (30-100 cm) have suffered from salinization. High concentrations of sodium ions (Na₂O₃) are a significant contributing factor. + This damages soil aggregate structure, reduces soil microbial activity, and consequently leads to a significant decrease in soil water retention capacity and nutrient availability, severely negatively impacting crop productivity in saline-alkali soils. Therefore, adopting environmentally friendly, efficient, and sustainable methods to improve soil properties is particularly important.

[0003] Hydrogels are functional polymer materials with a three-dimensional network structure formed by the physical or chemical cross-linking of hydrophilic polymer chains. Their unique structural characteristics make them valuable for applications in agriculture. The porous structure formed by the cross-linking of polymer chains and the abundance of surface functional groups endow the material with excellent water retention properties and provide an ideal carrier platform for the controlled release of nutrients, thereby achieving the synergistic regulation of water and nutrients.

[0004] However, hydrogels synthesized from artificial polymers such as acrylic acid and acrylamide have drawbacks such as high environmental risk (containing Group 2A carcinogens) and difficulty in degradation (half-life > 5 years). In contrast, natural polymer hydrogels (such as sodium alginate / chitosan), while possessing biocompatibility, have drawbacks such as high calcium content. 2+ Cross-linked gel systems can only provide ion exchange and water retention capabilities to the soil, exhibiting relatively limited functionality and poor salt resistance. In contrast, systems constructed using natural substances rich in various nutrients as cross-linking agents demonstrate significant advantages in saline-alkali soil applications. Earthworm castings are the excrement of organic waste products from the digestion and metabolism of earthworms, rich in nutrients and beneficial microorganisms.

[0005] Therefore, how to effectively utilize earthworm castings as organic waste to construct a multifunctional hydrogel system that combines water retention, slow nitrogen release, and soil structure improvement has become a key technical challenge that urgently needs to be addressed. Summary of the Invention

[0006] This invention provides an earthworm castings-based hydrogel, its preparation method, and its application. The preparation method can effectively promote the cross-linking among sodium alginate, chitosan, and earthworm castings, effectively improving the mechanical strength and salt resistance of the gel, and realizing the improvement of saline-alkali soil.

[0007] This invention provides a method for preparing earthworm castings-based hydrogels, comprising the following steps: (1) Dissolve sodium alginate in a buffer solution to obtain sodium alginate solution; (2) Dissolve chitosan in a solvent and stir until completely dissolved. Adjust the pH of the solution to below 5.5 to obtain a chitosan solution. When the pH is greater than 5.5, chitosan will precipitate out when a polyelectrolyte complex emulsion is formed in the future, and it will not be able to effectively bind with sodium alginate, thus reducing the cross-linking effect. (3) Mix the chitosan solution and the sodium alginate solution evenly to obtain a polyelectrolyte composite emulsion; (4) Dissolve earthworm castings in water to obtain an earthworm castings suspension with a concentration of 20-40wt%. When the concentration of earthworm castings is less than 20wt%, the system cannot form a solidified gel. When the concentration is greater than 40wt%, the gel system becomes uneven and the water absorption performance decreases.

[0008] (5) Add the earthworm castings suspension to the polyelectrolyte composite emulsion at a volume ratio of 1:4-6, and stir to ensure full cross-linking. Controlling the volume ratio of the polyelectrolyte composite emulsion to the earthworm castings suspension within this range can effectively promote the formation of a structurally stable composite gel system with a three-dimensional network structure, thereby improving the mechanical strength and sustained-release performance of the material.

[0009] In the preparation of the hydrogel of this invention, sodium alginate, a natural polymer, is used as an encapsulating agent. Through electrostatic attraction, it forms a dense network of polyelectrolyte complexes with chitosan, enhancing the mechanical strength and toughness of the hydrogel. Furthermore, earthworm castings suspension is used instead of traditional calcium ion solution as a crosslinking agent, eliminating the need for any additional crosslinking agents. This not only further promotes the crosslinking and compounding of sodium alginate and chitosan, but also utilizes the various polyvalent cations (such as Ca2+) abundant in the alginate itself. 2+ Mg 2+ Fe 3+ (etc.) can also react with the carboxyl group (-COO) on the sodium alginate molecular chain. - Ionic cross-linking occurs, forming an "egg box" structure, which further improves the mechanical strength and salt resistance of the hydrogel; and earthworm castings endow the hydrogel with multiple improvement functions. The humic acid, active microorganisms and trace elements contained therein synergistically enhance the improvement effect of saline-alkali soil, forming a multifunctional hydrogel.

[0010] The inventors also discovered that when earthworm castings are added directly to the polyelectrolyte composite emulsion in solid form, the cross-linking substances in the earthworm castings react directly with sodium alginate to form a jelly-like encapsulation. This encapsulates the earthworm castings, preventing them from being evenly dispersed in the polyelectrolyte composite emulsion system and effectively cross-linking with sodium alginate, thus preventing the formation of a gel. However, when earthworm castings are added to the polyelectrolyte composite emulsion in the form of an earthworm castings suspension prepared by dissolving earthworm castings in water, the earthworm castings are effectively dispersed, promoting the cross-linking of sodium alginate with chitosan and the effective cross-linking of the earthworm castings themselves with sodium alginate, forming a stable hydrogel.

[0011] Preferably, the volume ratio of the polyelectrolyte composite emulsion to the earthworm castings suspension is 1:6.

[0012] According to the preparation method of the earthworm castings-based hydrogel provided by the present invention, the volume ratio of the chitosan solution to the sodium alginate solution is 1:4-6. Controlling the volume ratio of the chitosan solution to the sodium alginate solution within this range can effectively promote electrostatic interactions between polyelectrolyte molecular chains with opposite charges, forming a stable composite condensation system, thereby optimizing the stability, encapsulation efficiency, and controlled release performance of the emulsion.

[0013] Preferably, the volume ratio of the chitosan solution to the sodium alginate solution is 1:4.

[0014] The method for preparing the earthworm castings-based hydrogel provided by this invention further includes step (2) of adding urea to the sodium alginate solution, wherein the mass-to-volume ratio of urea to the sodium alginate solution is 1:20-25. Urea is relatively stable in neutral aqueous solution and its hydrolysis rate is very slow. This ensures that urea exists in its complete molecular form before mixing and crosslinking. If added to a chitosan solution, it will cause the urea to hydrolyze.

[0015] This invention involves adding urea to a sodium alginate solution. Through the chemical interaction between the organic matter in earthworm castings and nitrogen, urea can be stably loaded onto a hydrogel carrier, thereby achieving the slow-release function of nitrogen and other nutrients in earthworm castings.

[0016] Preferably, the mass-to-volume ratio of the urea to the sodium alginate solution is 1:25.

[0017] According to the preparation method of the earthworm castings-based hydrogel provided by the present invention, the concentration of the sodium alginate solution is 2-4%, and its pH is greater than 5.5 and less than or equal to 7, and / or the concentration of the chitosan solution is 1-3%. When the pH of the sodium alginate solution is greater than 7 and the pH of the chitosan solution is greater than 5.5, the chitosan is easily precipitated when the two are mixed, and cannot crosslink with the sodium alginate to form a polyelectrolyte complex with a dense network.

[0018] According to the preparation method of the earthworm feces-based hydrogel provided by the present invention, the pH of the buffer solution is 6-7; controlling the pH of the buffer solution within this range can be used to provide pH stability in the polyelectrolyte composite emulsion, and to provide a more suitable cross-linking environment for the combination of chitosan and sodium alginate.

[0019] More preferably, the phosphate buffer solution is a mixed solution of phosphate and sodium chloride, wherein the concentration of phosphate in the phosphate buffer solution is 10 mM and the concentration of sodium chloride is 140 mM.

[0020] Preferably, the solvent is a glacial acetic acid solution with a concentration of 1%.

[0021] The method for preparing the earthworm castings-based hydrogel provided by this invention includes a polyelectrolyte composite emulsion with a pH of 5-6. Controlling the pH of the polyelectrolyte composite emulsion within this range provides a more suitable environment for the subsequent cross-linking reaction with earthworm castings. This also provides a more suitable cross-linking environment for the combination of chitosan and sodium alginate, promoting not only the cross-linking of sodium alginate and chitosan but also the cross-linking effect between chitosan and sodium alginate, further improving the mechanical strength and salt resistance of the hydrogel.

[0022] The method for preparing the earthworm feces-based hydrogel provided by the present invention includes sodium alginate with CAS number 9005-38-3 and / or chitosan with CAS number 9012-76-4.

[0023] In the preparation method of the earthworm castings-based hydrogel provided by the present invention, the stirring time in step (5) is 2-5 min.

[0024] Preferably, in step (5), the product after the polyelectrolyte composite emulsion and the earthworm castings suspension are fully cross-linked is subjected to aging treatment, and the aging temperature is room temperature and the aging time is 12-24h.

[0025] Preferably, the aging treatment further includes a drying step, wherein the drying time is 40-48 hours and the drying temperature is 40-45°C.

[0026] The present invention also provides an earthworm castings-based hydrogel, which is prepared by the preparation method described above.

[0027] This invention also provides a method for preparing earthworm castings-based hydrogels as described above, wherein the earthworm castings-based hydrogel obtained by the method described above, or the earthworm castings-based hydrogel described above, has any of the following applications, including: (1) Application in improving soil salinization; (2) Application in promoting plant growth; Its preferred application is in promoting maize growth.

[0028] The inventors discovered that when this hydrogel is used to promote plant growth, especially corn growth, the slow-release system of the hydrogel makes the nitrogen release pattern match the needs of corn during the jointing stage, which can significantly promote corn growth.

[0029] The beneficial effects of the earthworm castings-based hydrogel, its preparation method, and its application provided by this invention are as follows: (1) This invention uses only three main materials: sodium alginate, chitosan and earthworm castings. In addition to the mixing step, the preparation mainly involves simply preparing a solution of the three main materials to obtain a multifunctional hydrogel with high salt resistance and slow-release nitrogen. Its preparation process and raw materials are simple and inexpensive, and it is suitable for large-scale production. (2) The hydrogel formed by earthworm castings suspension as crosslinking agent in this invention not only realizes the transformation of earthworm castings from agricultural waste to high-value-added environmental functional materials, but also endows the hydrogel with multiple improvement functions. The humic acid, active microorganisms and trace elements contained therein synergistically enhance the improvement effect of saline-alkali soil, and also improve the mechanical strength and salt resistance of the hydrogel. (3) The hydrogel, as a nitrogen carrier, improves the retention rate of nitrogen in saline-alkali soil through earthworm castings-urea complexation, and promotes the growth of crops in saline-alkali land. Attached Figure Description

[0030] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0031] Figure 1 It is the swelling rate of SA-VC-2, SA-VC-3, and SA-VC-4 in Experiment Example 1.

[0032] Figure 2 These are the swelling rate and water retention rate of SA-VC-3 and SA-VC-3N in Experiment Example 1.

[0033] Figure 3This is the change in the cumulative release rate of SA-VC-3N urea over time in Experiment Example 1.

[0034] Figure 4 This is the effect of different treatments on the total salt content of the soil in Experiment Example 2.

[0035] Figure 5 This is the effect of different treatments on the total salt content of the soil in Experiment Example 2.

[0036] Figure 6 This is the effect of different treatments on soil organic matter content in Experiment Example 2.

[0037] Figure 7 This is the effect of different treatments on the available potassium content in the soil in Experiment Example 2.

[0038] Figure 8 This is the effect of different treatments on the available phosphorus content in the soil in Experiment Example 2.

[0039] Figure 9 This is the effect of different treatments on the inorganic nitrogen content of the soil in Experiment Example 2.

[0040] Figure 10 This is the effect of different treatments on plant height in Experiment Example 2.

[0041] Figure 11 This refers to the effect of different treatments on plant biomass. Detailed Implementation

[0042] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0043] The following is combined with Figures 1-11 This invention describes an earthworm castings-based hydrogel, its preparation method, and its applications.

[0044] Where specific techniques or conditions are not specified in the examples, they shall be performed in accordance with the techniques or conditions described in the literature in this field, or in accordance with the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased through legitimate channels.

[0045] The “parts” used in the following examples and comparative examples refer to parts by weight.

[0046] The solution preparation methods used in the following examples and comparative examples are as follows: Preparation of phosphate buffer solution: The phosphate buffer solution is a mixed solution of phosphate and sodium chloride, wherein the concentration of phosphate in the phosphate buffer solution is 10 mM and the concentration of sodium chloride is 140 mM; the pH of the phosphate buffer solution is adjusted to 6 using 1% glacial acetic acid.

[0047] Example 1 A method for preparing an earthworm castings-based hydrogel includes the following steps: (1) Add 1.2 parts of sodium alginate (SA) to 30 parts of phosphate buffer solution with pH 6 and stir mechanically for 1 hour at room temperature to prepare an SA solution (chitosan solution) with a concentration of 4wt%. The higher the SA content, the higher the water absorption. However, under stirring conditions at room temperature, after exceeding 4wt%, some of the SA is insoluble in the phosphate buffer solution. (2) Dissolve 0.15 parts of chitosan (CS) in 7.5 parts of 1% acetic acid solution and stir continuously with magnetic force. After the CS is completely dissolved, adjust the pH of the solution to 5.5 to obtain chitosan solution (CS solution). (3) The CS solution is slowly added dropwise to the SA solution at a volume ratio of 1:4, and the mixture is stirred thoroughly to form a polyelectrolyte composite emulsion of SA and CS. The emulsion is milky white and the pH of the polyelectrolyte composite emulsion is 6. (4) Pass earthworm castings through a 100-mesh sieve, take 1.8 parts and dissolve them in 6 parts of deionized water to obtain an earthworm castings suspension with a concentration of 30wt%; (5) Add earthworm castings suspension to the polyelectrolyte composite emulsion at a volume ratio of 1:6, stir for 3 min to allow it to fully crosslink, age at room temperature for 12 h, and then dry at 45 degrees for 48 h to obtain earthworm castings-based hydrogel, denoted as SA-VC-3.

[0048] The raw material information used in this embodiment is as follows: Sodium alginate: CAS No. 9005-38-3, Model No. S817374, purchased from Maclean; Chitosan: CAS No. 9012-76-4, purchased from Maclean's; Earthworm castings: purchased from Binzhou.

[0049] Example 2 The steps in this embodiment are basically the same as those in embodiment 1, except that: in step (4), earthworm castings are passed through a 100-mesh sieve, and 1.2 parts are dissolved in 6 parts of deionized water to obtain an earthworm castings suspension with a concentration of 20wt%.

[0050] The earthworm castings-based hydrogel obtained in this embodiment is denoted as SA-VC-2.

[0051] Example 3 The steps in this embodiment are basically the same as those in embodiment 1, except that: in step (4), earthworm castings are passed through a 100-mesh sieve, and 2.4 parts are dissolved in 6 parts of deionized water to obtain an earthworm castings suspension with a concentration of 40wt%.

[0052] The earthworm castings-based hydrogel obtained in this embodiment is denoted as SA-VC-4.

[0053] Example 4 The steps in this embodiment are basically the same as those in Embodiment 1, except that: urea is added to the SA solution prepared in step (1), with a mass-to-volume ratio of urea to sodium alginate solution of 1:25, to ensure complete dissolution; in step (3), the SA solution is replaced with an SA solution containing urea. The earthworm castings-based hydrogel obtained in this embodiment is designated as SA-VC-3N.

[0054] Comparative Example 1 The steps in this embodiment are basically the same as those in embodiment 1, except that: in step (4), earthworm castings are passed through a 100-mesh sieve, and 0.6 parts are dissolved in 6 parts of deionized water to obtain an earthworm castings suspension with a concentration of 10wt%.

[0055] The earthworm castings-based hydrogel obtained in this embodiment is denoted as SA-VC-1.

[0056] Comparative Example 2 The steps of this comparative example are basically the same as those of Example 1, except that the earthworm castings suspension in step (4) is replaced with a 2.5% calcium chloride solution.

[0057] The earthworm castings-based hydrogel obtained in this comparative example is denoted as SA-Ca.

[0058] Experiment Example 1: Effect of different concentrations of earthworm castings suspension on hydrogel properties This experiment tested the properties of the hydrogels prepared in Example 1 (SA-VC-3), Example 2 (SA-VC-2), Example 3 (SA-VC-4), and Comparative Example 1 (SA-VC-1) and Comparative Example 2 (SA-Ca). The experimental methods are as follows: 1. Swelling properties of different earthworm castings-based hydrogels and calcium-based hydrogels (SA-VC-1, SA-VC-2, SA-VC-3, SA-VC-4, SA-Ca) in pure water. Immerse 0.5g of different samples in 50ml of deionized water. The samples will absorb water and swell. After the samples reach swelling equilibrium, dry the surface of the material and weigh it.

[0059] The hydrogel formed by cross-linking sodium alginate / chitosan with earthworm castings possesses a highly porous structure. Through adsorption, capillary action, and osmosis, the hydrogel can act as a small water reservoir. When the soil is irrigated, the hydrogel swells; when the soil dries, it slowly releases water into the environment. Experiments showed that when the concentration of the earthworm castings suspension was 10% (Comparative Example 1, SA-VC-1), the system could not form a solidified gel; however, the gel with the best texture was obtained at a concentration of 30%. The swelling results of SA-VC-2, SA-VC-3, SA-VC-4, and SA-Ca hydrogels in deionized water are shown below. Figure 1 As shown, the water absorption ratio of the 30% earthworm castings suspension hydrogel (Example 1, SA-VC-3) was significantly higher than that of the other three materials, reaching 2380%. Furthermore, the water absorption ratios at concentrations of 20% (Example 2, SA-VC-2) and 40% (Example 3, SA-VC-4) were significantly higher than those of the calcium-based hydrogel SA-Ca (Comparative Example 1). The results indicate that hydrogels can be synthesized with earthworm castings suspensions at concentrations ranging from 20% to 40%, and that 30% is the optimal concentration for hydrogel synthesis; therefore, this concentration was selected for subsequent experiments.

[0060] 2. Swelling test of earthworm castings-based bifunctional hydrogels (SA-VC-3, SA-VC-3N) in different solutions 0.5g of different samples were immersed in a pre-prepared 0.9% NaCl solution and an extract of moderately saline-alkali soil, respectively. The samples absorbed water and swelled. After the samples reached swelling equilibrium, the surface moisture of the materials was dried and weighed.

[0061] The swelling experiment (Figure 2a) showed that the swelling rates of both hydrogels in pure sodium chloride solution were higher than those in the soil extract, at 1325% and 1073%, respectively. This is because various ions in the soil extract compete with water molecules for adsorption sites, leading to a decrease in the swelling rate.

[0062] 3. The variation of water retention rate of earthworm castings-based bifunctional hydrogels (SA-VC-3, SA-VC-3N) over time. Earthworm castings-based hydrogels that have reached swelling equilibrium under different systems of the same mass are placed in dry petri dishes. At room temperature, the weight of the earthworm castings-based hydrogels is weighed at regular intervals, and the weight loss of the earthworm castings-based hydrogels at different times is calculated to evaluate its water retention performance.

[0063] Figure 2b shows the change in water retention rate of earthworm castings-based hydrogels over time. With increasing time, the water retention rates of SA-VC-3 and SA-VC-3N showed a relatively uniform decreasing trend, with a retention time of approximately 40 hours. The water retention effect of the hydrogel containing urea was slightly worse than that of the hydrogel without urea. The addition of urea increased the crosslinking density of the hydrogel, resulting in lower swelling properties of SA-VC-3N compared to SA-VC-3.

[0064] 4. Investigation into the sustained-release properties of urea 0.5 g of earthworm castings-based hydrogel (SA-VC-3, SA-VC-3N) was added to 200 mL of deionized water for a urea release experiment. Then, at regular intervals, 5.0 mL of the supernatant was taken and the urea concentration in the surrounding medium was measured using a UV-Vis spectrophotometer at a wavelength of 420 nm. To maintain a constant total solution volume, an equal volume of fresh deionized water (5.0 mL) was added after each sample.

[0065] Figure 3 The graph shows the cumulative release rate of SA-VC-3N urea over time. In the initial 0.5–6 hours, the urea release rate is relatively fast. At 6 h, the cumulative release rates of SA-VC-3N in pure sodium chloride solution and saline-alkali soil leachate are 61.78% and 54.93%, respectively. The release rate decreases significantly from 6 to 24 h, reaching 72.97% and 62.56% at 24 h, respectively. At 48 h, the urea release rates are 79.00% and 74.13%, respectively. The urea release rate of SA-VC-3N in salt solution is higher than that in saline-alkali soil leachate. The high salinity of Na+ in the high-salt environment... + Crosslinking ions (such as Ca) in competing gels 2+ This leads to a loosening of the network structure, which in turn accelerates urea diffusion.

[0066] Experimental Example 2: Effects of the hydrogels prepared in Examples 1 and 4 on soil and plant growth A pot experiment was conducted using earthworm castings-based hydrogels prepared in Example 1 (SA-VC-3) and Example 4 (SA-VC-3N), as well as Control Example 1 (urea) and Control Example 2 (no exogenous substances added). The experiment included the following steps: The experiment employed a randomized experimental design, including: a control group (no exogenous substances added, CK), treatment group 1 (SA-VC-3, A1), treatment group 2 (commercially available urea, A2), and treatment group 3 (SA-VC-3N, A3), with 5 replicates in each group. For each replicate, 600g of air-dried soil (passed through a 2mm sieve) was weighed. 400g of soil was first weighed, and earthworm castings-based hydrogel and urea were evenly spread on the soil surface. The remaining soil was then evenly covered on the surface and allowed to stabilize for 3 days. For breeding: Zhengdan 958 seeds were surface-sterilized with a 10% H2O2 solution for 10 min and incubated at 25℃ for 24 h. After soil stabilization, three germinated maize seeds were sown in each pot. After germination, seedlings were thinned, and all plastic pots were arranged completely randomly. Throughout the experiment, the soil moisture content was maintained at 60% of field capacity. After 30 days, plant and soil samples were collected for relevant physicochemical index determination.

[0067] Test results 1. Effects of different treatments on total salt content in saline soils Changes in total soil salt content under different treatments, such as Figure 4 As shown, the total salt content of each treatment ranged from 1.59 to 2.64 g / kg. -1 Compared to the control (CK), the total soil salt content was significantly lower in treatments A1, A2, and A3. Specifically, the salt content in treatment A1 was 1.59 g / kg. -1 The salt content of the A3 treatment was 1.78 g / kg. -1 All were lower than the salt content of the A2 treatment (2.02 g / kg). -1 This indicates that after the hydrogel absorbs water and swells, the osmotic pressure causes salt in the saline-alkali soil to permeate into the gel until osmotic pressure equilibrium is reached, thereby reducing the salt content.

[0068] 2. Effects of different treatments on soil pH The effects of different treatments on soil pH are as follows: Figure 5 As shown in the figure, the soil pH values ​​of different treatments ranged from 7.43 to 7.68. Compared with the control group, the soil pH values ​​of SA-VC-3 (A1), urea (A2), and SA-VC-3N (A3) generally showed a decreasing trend, with pH values ​​decreasing by 0.90%, 0.85%, and 3.28%, respectively. Except for the A3 treatment group, which showed significant differences, there were no significant differences among the other treatments.

[0069] 3. Effects of different treatments on soil organic matter content Changes in soil organic matter content under different treatments, such as Figure 6As shown, the addition of SA-VC-3 (A1) and SA-VC-3N (A3) effectively improved soil organic matter content, with A3 treatment showing a significant effect, increasing organic matter content by 15.70% compared to the control group. In contrast, the organic matter content in the urea (A2) treatment group decreased by 1.60% compared to the control group. Earthworm castings are the excrement of earthworms after they have digested and metabolized livestock manure or other organic waste. They contain a large amount of organic matter and nutrients. During the swelling process of the hydrogel, the nutrients in the earthworm castings are gradually released, thereby increasing the organic matter content in the soil.

[0070] 4. Effects of different treatments on soil available potassium content Changes in available potassium content in soil under different treatments, such as Figure 7 As shown, compared with the control group, the addition of SA-VC-3, urea, and SA-VC-3N significantly increased the content of available potassium in the soil. Compared with the control group, the available potassium content in the soil treated with SA-VC-3N (A3) increased by 44.20%. Earthworm castings contain abundant soluble potassium, which is encapsulated in hydrogels through cross-linking. Therefore, the addition of SA-VC-3 and SA-VC-3N can effectively increase the content of available potassium in the soil. The addition of nitrogen, on the other hand, provides a nitrogen source for microorganisms, promotes their metabolism, accelerates the bioweathering of soil minerals, and releases potassium. + Loading nitrogen (SA-VC-3N) into the earthworm castings-based hydrogel prolonged the nitrogen's action time and maintained the long-term potassium solubilization by microorganisms. As a result, the available potassium content in the soil of the A3 treatment group was significantly increased under the synergistic effect of earthworm castings hydrogel and nitrogen.

[0071] 5. Effects of different treatments on available phosphorus content in soil Changes in available phosphorus content in soil under different treatments, such as Figure 8 As shown, compared with the control group, the available phosphorus in the soil of treatments A1, A2, and A3 showed an increasing trend, with treatment A3 having the highest available phosphorus content at 15.29 mg / kg. This is because phosphorus in the soil readily combines with Fe. 3+ Al 3+ or Ca 2+ These substances form insoluble compounds that are difficult for plants to absorb. Therefore, although nitrogen addition and earthworm castings hydrogel can increase the available phosphorus content through earthworm castings release and microbial activation, the effect of adding exogenous substances on increasing soil phosphorus is not significant due to the stubborn nature of soil phosphorus fixation.

[0072] 6. Effects of different treatments on soil inorganic nitrogen content The effects of different treatments on soil inorganic nitrogen, such as Figure 9 As shown in the results, soil nitrate nitrogen ( Figure 9 a) The addition of SA-VC-3N can significantly increase the soil ammonia nitrogen content, and from the soil nitrate nitrogen results ( Figure 9 (b) The addition of urea and SA-VC-3N both increased the NO3-N content in the soil, with increases of 1.08 and 5.26 times, respectively. This indicates that the earthworm castings-based hydrogel controls the slow release of urea, thus preventing the absorption of NH4+. + High concentrations of urea in the short term inhibit the activity of nitrifying bacteria, thereby promoting continuous nitrification. In contrast, ordinary urea is difficult to accumulate NH4 due to rapid conversion and loss. + This leads to a weakening of digestive function.

[0073] 7. Effects of different treatments on plant height The effects of different treatments on maize plants, such as Figure 10 As shown, the plant height of the SA-VC-3N treatment group was significantly higher than that of the SA-VC-3 treatment and the N treatment. This is because the hydrogel slow-release system makes the nitrogen release pattern match the needs of maize during the jointing stage, thus promoting maize growth.

[0074] 8. Effects of different treatments on plant biomass The effects of different treatments on the aboveground and underground biomass of maize, such as Figure 11 As shown, except for the dry weight of the underground parts, the fresh weight and dry weight of the aboveground parts in the A2(N) and A3(SA-VC-3N) treatments were significantly higher than those in the control group. The fresh weight of maize plants in the SA-VC-3N-added group was 111.65% higher than that in the control group and 5.92% higher than that in the urea-added group. Compared with the urea-added group, the slow-release effect of SA-VC-3N on urea can effectively reduce nitrogen loss and improve nitrogen use efficiency. In addition, the nutrients in earthworm castings can exert a synergistic effect with urea, significantly promoting maize growth.

[0075] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing an earthworm castings-based hydrogel, characterized in that, Includes the following steps: (1) Dissolve sodium alginate in a buffer solution to obtain sodium alginate solution; (2) Dissolve chitosan in a solvent and adjust the pH of the solution to below 5.5 to obtain a chitosan solution; (3) Mix the chitosan solution and the sodium alginate solution evenly to obtain a polyelectrolyte composite emulsion; (4) Dissolve earthworm castings in water to obtain an earthworm castings suspension with a concentration of 20-40 wt%; (5) Add earthworm castings suspension to the polyelectrolyte composite emulsion at a volume ratio of 1:4-6 and stir to ensure full cross-linking.

2. The method for preparing earthworm castings-based hydrogel according to claim 1, characterized in that, The volume ratio of the chitosan solution to the sodium alginate solution is 1:4-6.

3. The method for preparing earthworm castings-based hydrogel according to claim 1, characterized in that, Step (2) also includes the step of adding urea to the sodium alginate solution; Preferably, the mass-to-volume ratio of urea to sodium alginate solution is 1:20-25.

4. The method for preparing earthworm castings-based hydrogel according to any one of claims 1-3, characterized in that, The concentration of the sodium alginate solution is 2-4%, and its pH is greater than 5.5 and less than or equal to 7, and / or the concentration of the chitosan solution is 1-3%.

5. The method for preparing earthworm castings-based hydrogel according to any one of claims 1-3, characterized in that, The pH of the buffer solution is 6-7; Preferably, the buffer solution is a phosphate buffer solution.

6. The method for preparing earthworm castings-based hydrogel according to any one of claims 1-3, characterized in that, The pH of the polyelectrolyte composite emulsion is 5-6.

7. The method for preparing earthworm castings-based hydrogel according to any one of claims 1-3, characterized in that, The CAS number of the sodium alginate is 9005-38-3, and / or the CAS number of the chitosan is 9012-76-4.

8. The method for preparing earthworm castings-based hydrogel according to any one of claims 1-7, characterized in that, The stirring time is 2-5 minutes; Preferably, in step (5), the cross-linked product is subjected to an aging treatment, wherein the aging temperature is room temperature and the aging time is 12-24 hours. Preferably, the aging treatment further includes a drying step, wherein the drying time is 40-48 hours and the drying temperature is 40-45°C.

9. A vermicompost-based hydrogel, characterized in that, It is prepared by the preparation method described in any one of claims 1-8.

10. An earthworm castings-based hydrogel prepared by the method of any one of claims 1-8, or an earthworm castings-based hydrogel as described in claim 9, having any one of the following applications, characterized in that: include: (1) Application in improving soil salinization; (2) Application in promoting plant growth; Its preferred application is in promoting maize growth.

Images