Water-retaining agent with salt resistance and urease inhibition effects as well as preparation method and application of water-retaining agent

Abstract

The invention discloses a water-retaining agent with salt resistance and urease inhibition effects as well as a preparation method and application of the water-retaining agent, and belongs to the technical field of agriculture and forestry water retention. The water-retaining agent provided by the invention is prepared from the following raw materials in parts by mass: 100 parts of a monomer, 3-10 parts of an anionic natural polymer derivative, 0.1-0.5 part of a cross-linking agent, 5-15 parts of modified hectorite or modified bentonite and 0.1-1 part of an initiator, wherein the monomer is one or more of acrylic acid, acrylate or acrylamide; the modified hectorite or the modified bentonite is obtained by modifying hectorite or bentonite with a quaternary ammonium salt natural polymer derivative. The water-retaining agent provided by the invention has relatively high water absorption rate and saline water absorption rate, can keep stable water absorption and water retention performance in a high-salt environment, can delay the urea hydrolysis rate and reduce nitrogen loss, can realize synchronous application of the water-retaining agent and a fertilizer, and simplifies farming operation.

Description

Technical Field

[0001] The present invention relates to the technical field of water conservation in agriculture and forestry, and in particular to a water-retaining agent with both salt resistance and urease inhibition effects, and a preparation method and application thereof. Background Art

[0002] The information disclosed in the background of the invention is only intended to enhance understanding of the overall background of the invention and is not necessarily regarded as an admission or any form of suggestion that the information constitutes the prior art already known to a person skilled in the art.

[0003] As a high-molecular polymer with super water absorption and water retention capabilities, water retaining agents can significantly improve the physical and chemical properties of the soil, enhance the soil's ability to retain water and fertilizer, and slowly release water according to plant needs, providing a continuous water supply for crop growth. It plays an important role in ensuring the normal growth and development of crops in arid and semi-arid areas. However, existing agricultural and forestry water retaining agents mainly achieve water absorption and water retention functions based on the principle of osmotic pressure difference. When in a high-salt fertilizer environment, the sharp increase in external osmotic pressure will cause its water absorption performance to decrease significantly and even cause water reverse osmosis, which makes it impossible to apply water retaining agents and fertilizers simultaneously. In actual agricultural production, farmers have to adopt a step-by-step operation, that is, apply water retaining agents first and then fertilizers, or apply fertilizers first and then water retaining agents. This not only increases labor intensity, but also reduces the efficiency of agricultural operations.

[0004] Urea, a solid nitrogen fertilizer with a high nitrogen content, dominates the global nitrogen fertilizer market. The effective utilization of urea relies on the catalytic action of soil urease, a nickel-containing metalloenzyme that hydrolyzes urea into ammonia and carbon dioxide, converting amide nitrogen into ammonium nitrogen that can be absorbed by crops. However, urease's extremely high catalytic efficiency causes ammonia release rates far exceeding crop absorption capacity, resulting in significant nitrogen losses. This not only results in significant economic losses but also causes serious ecological and environmental problems.

[0005] In agricultural production, water-retaining agents (SAAs) are difficult to apply with fertilizers due to their lack of salt tolerance. Urea, on the other hand, causes nitrogen loss due to the rapid urease catalysis. Maintaining high soil moisture with SAAs further accelerates urease catalysis, exacerbating nitrogen loss. Commercially available SAAs struggle to stably absorb water in high-salt environments and are unable to inhibit urease activity, resulting in cumbersome operation and significant nitrogen waste. Therefore, there is an urgent need to develop a SA that combines salt tolerance with urease inhibition to achieve the dual goals of co-applying water and fertilizer while minimizing nitrogen loss. Summary of the Invention

[0006] In view of this, the present invention provides a water-retaining agent with both salt resistance and urease inhibition effects, as well as a preparation method and application thereof. The water-retaining agent provided by the present invention can maintain stable water absorption and retention properties in a high-salt environment, and can effectively regulate urease activity to slow down the urea hydrolysis rate. It can achieve the simultaneous application of the water-retaining agent and fertilizer, thereby simplifying agricultural operations and having good application value.

[0007] In a first aspect, the present invention provides a water-retaining agent having both salt resistance and urease inhibition effects, which is prepared from the following raw materials in parts by weight: 100 parts of monomer, 3-10 parts of anionic natural polymer derivative, 0.1-0.5 parts of cross-linking agent, 5-15 parts of modified hectorite or modified bentonite, 0.1-1 parts of initiator; The monomer is one or more of acrylic acid, acrylate or acrylamide; and the modified hectorite or modified bentonite is obtained by modifying hectorite or bentonite with a quaternary ammonium salt natural polymer derivative.

[0008] Preferably, the anionic natural polymer derivative is selected from one or both of low-ester pectin and sulfonated sodium alginate.

[0009] Preferably, the crosslinking agent is selected from one or more of divinylbenzene, propylene glycol, N,N'-methylenebisacrylamide or zinc oxide; and the initiator is selected from one or more of potassium persulfate, ammonium persulfate or sodium persulfate.

[0010] Preferably, the quaternized natural polymer derivative is selected from one or both of chitosan quaternary ammonium salt or cellulose quaternary ammonium salt; in the modified hectorite or modified bentonite, the ratio of the molar number of cationic groups provided by the quaternized natural polymer derivative to the molar number of cation exchange capacity of the hectorite or bentonite is (1.1~1.5):1.

[0011] In a second aspect, the present invention provides a method for preparing the water-retaining agent having both salt resistance and urease inhibition effects, comprising the following steps: The monomer and the anionic natural polymer derivative are mixed in water, modified hectorite or modified bentonite, a crosslinking agent and an initiator are added, and the temperature is raised to react to obtain a gel. The gel is soaked, washed with water and dried to obtain a water-retaining agent with both salt resistance and urease inhibition effects.

[0012] Preferably, the preparation method of the modified hectorite or modified bentonite is as follows: The quaternary ammonium salt natural polymer derivative and hectorite or bentonite are mixed in water, subjected to hydrothermal reaction, washed with water and dried to obtain the product.

[0013] Furthermore, the temperature of the hydrothermal reaction is 70-90° C., and the reaction time is 1-5 hours.

[0014] Preferably, the reaction temperature of the temperature-raising reaction is 60-80° C., and the reaction time is 0.4-3 h.

[0015] Preferably, the solvent used for the soaking is an ethanol-water solution; and the soaking time is 0.4 to 3 hours.

[0016] In a third aspect, the present invention provides the use of the water-retaining agent having both salt resistance and urease inhibition effects or the water-retaining agent having both salt resistance and urease inhibition effects prepared by the above preparation method in agricultural and forestry planting.

[0017] Compared with the prior art, the present invention has achieved the following beneficial effects: (1) The water-retaining agent provided by the present invention has a high water absorption rate and salt water absorption rate, the water absorption rate can reach more than 450g / g, and the salt water absorption rate can reach more than 80g / g. Through the synergistic effect of the modified hectorite or modified bentonite in the raw materials and the monomer and anionic natural polymer derivatives, it can maintain stable water absorption and water retention performance in a high-salt environment, effectively solving the problem that the existing water-retaining agent cannot be applied synchronously with fertilizers due to insufficient salt tolerance. At the same time, through the regulation of urease activity by the quaternary ammonium salt natural polymer derivatives in the modified hectorite or modified bentonite, the urea hydrolysis rate is delayed, and the nitrogen loss is reduced, the water-retaining agent and fertilizer can be applied synchronously, simplifying agricultural operations.

[0018] (2) The present invention introduces modified hectorite or modified bentonite, which not only utilizes its layered structure to enhance the network structure rigidity of the water retaining agent, restricts the movement of polymer chains, further reduces the damage of salt ions to the network structure of the water retaining agent, and improves the stability of water retention performance, but also synergistically enhances the salt resistance effect through the amphoteric polymer system formed by quaternary ammonium salt natural polymer derivatives and anionic groups, so that the water retaining agent can continue to play a role in water and fertilizer retention in complex soil environments, providing a stable supply of water and nutrients for crop growth.

[0019] (3) The anionic natural polymer derivatives used in the present invention are selected from natural source materials such as low-ester pectin and sulfonated sodium alginate. The quaternized natural polymer derivatives used in the modified hectorite or modified bentonite are natural polymer derivatives such as chitosan quaternary ammonium salt or cellulose quaternary ammonium salt. The overall raw materials have good biocompatibility and degradability. After use, they are friendly to the soil environment, meet environmental protection requirements, and avoid secondary pollution that may be caused by traditional chemical synthetic materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The drawings, which constitute part of the present invention, are intended to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are intended to explain the present invention and do not constitute undue limitations thereon. It is obvious that one of ordinary skill in the art could derive other drawings based on these drawings without inventive effort.

[0021] Figure 1 This is a graph showing changes in ammonia nitrogen concentration versus reaction time in the urease inhibition effect test of the experimental example of the present invention, in the CK group, the NBPT group, and the SAP4 group. DETAILED DESCRIPTION

[0022] It should be noted that the following detailed descriptions are exemplary and intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the present invention belongs.

[0023] The present invention provides a water-retaining agent having both salt resistance and urease inhibition effects, which is prepared from the following raw materials in parts by weight: 100 parts of monomer, 3-10 parts of anionic natural polymer derivative, 0.1-0.5 parts of cross-linking agent, 5-15 parts of modified hectorite or modified bentonite, 0.1-1 parts of initiator; The monomer is one or more of acrylic acid, acrylate or acrylamide; and the modified hectorite or modified bentonite is obtained by modifying hectorite or bentonite with a quaternary ammonium salt natural polymer derivative.

[0024] The water-retaining agent provided by the present invention achieves both urease inhibition and salt resistance through the synergistic effect of its raw material components. The monomers (acrylic acid, acrylate, or acrylamide) serving as the basic skeleton undergo polymerization under the action of an initiator, forming polymer chains with hydrophilic groups (carboxyl and amide groups). These hydrophilic groups bind to water molecules through hydrogen bonds and hydration, forming the basic structure of the water-retaining agent for water absorption and retention. Furthermore, anionic natural polymer derivatives interact with the hydrophilic polymer chains through intermolecular forces (hydrogen bonds and electrostatic attraction), helping to construct an interpenetrating network of composite polymers and enhancing the stability of the polymer network. Furthermore, the anionic groups carried by the derivatives further enhance the system's water-binding capacity. The crosslinker chemically connects the different polymer chains to form a three-dimensional network structure, limiting excessive swelling of the polymer chains and ensuring that the water-retaining agent remains in a gel state after absorbing water, preventing dissolution and loss, thereby stabilizing water retention.

[0025] Modified hectorite or modified bentonite is a modified mineral obtained by modifying quaternary ammonium salt natural polymer derivatives. The cationic groups of the quaternary ammonium salt natural polymer derivatives are combined with the layered silicate structure of the hectorite or bentonite through ion exchange. On the one hand, the modified hectorite or bentonite forms a rigid support with the polymer network through physical filling, restricting the shrinkage movement of the polymer chain in the salt solution and reducing the damage of the salt ions to the network structure; on the other hand, the positively charged groups of the quaternary ammonium salt natural polymer derivatives form a "positive and negative charge synergistic" system with the anionic groups (such as carboxyl groups) in the hydrophilic polymer chain and the anionic natural polymer derivatives. In a high-salt environment, this amphoteric charge distribution can weaken the charge neutralization effect of salt ions on the polymer network through the electrostatic shielding effect, maintain the swelling stability of the network structure, and thus significantly improve the salt resistance of the water-retaining agent. At the same time, the quaternary ammonium groups and long polymer chains of the quaternized natural polymer derivatives can bind to the urease protein molecules through electrostatic interactions and other intermolecular forces, changing the spatial conformation of urease and inhibiting its catalytic activity, thereby slowing the rate of urea hydrolysis and achieving urease inhibition. Through the above-mentioned synergistic effect, the various components give the water retaining agent the dual properties of salt resistance, water retention, and urease inhibition.

[0026] In an optional embodiment of the present invention, the anionic natural polymer derivative is more preferably 3 to 8 parts, ensuring that the anionic group fully matches the positive charge of the modified mineral, while enhancing salt resistance, maintaining the integrity and degradability of the network structure. The cross-linking agent is more preferably 0.1 to 0.3 parts, and a suitable amount can form a moderately cross-linked network structure, which can support the physical filling of the modified mineral and retain enough water absorption channels to ensure the long-term stability of water retention. Modified hectorite or modified bentonite is more preferably 8 to 13 parts, and its excessive amount easily leads to agglomeration of mineral particles and uneven dispersion, which may cause local network structure fracture, and both water retention and mechanical properties decrease; When the amount is too low, the polymer network lacks rigid support in a high salt environment, and the chain segment is easily compressed and shrunk by salt ions, and the salt resistance is not significantly improved; At the same time, the number of quaternary ammonium groups is insufficient, and the urease inhibition site is small, making it difficult to effectively regulate the urea hydrolysis rate. The appropriate dosage allows for uniform dispersion of the minerals. Its layered structure not only physically enhances network stability but also synergizes with anionic natural polymer derivatives through quaternary ammonium groups, maximizing salt resistance and urease inhibition. The initiator content is more preferably 0.1-0.4 parts to ensure full polymerization of the monomers, forming polymer chains with moderate molecular weight and uniform distribution.

[0027] In an optional embodiment of the present invention, the anionic natural polymer derivative is selected from one or both of low-ester pectin or sulfonated sodium alginate. This type of natural material not only carries anionic groups such as carboxyl groups and sulfonic acid groups, but can also form a network interpenetrating structure with hydrophilic polymer chains through hydrogen bonds or electrostatic interactions to enhance the stability of the polymer network. It can also cooperate with the positive charge groups of subsequent modified minerals through anionic groups to improve the charge balance ability of the system in a high-salt environment, further enhance the salt resistance, and at the same time, the natural source gives the material degradability, reducing the risk of soil residues. The present invention does not impose any special restrictions on the sources of low-ester pectin and sulfonated sodium alginate, which can be purchased or homemade; for example, low-ester pectin can be obtained by extraction and deesterification of plant raw materials, and its degree of esterification is less than 50%, and more than half of the carboxyl groups are in the form of free acid (-COOH) or salt (-COO - ) exists in the form of; sulfonated sodium alginate can be obtained by sulfonation reaction of sodium alginate.

[0028] In an optional embodiment of the present invention, the cross-linking agent is selected from one or more of divinylbenzene, propylene glycol, N,N'-methylenebisacrylamide or zinc oxide, more preferably N,N'-methylenebisacrylamide; the initiator is selected from one or more of potassium persulfate, ammonium persulfate or sodium persulfate, which can decompose under elevated temperature conditions to generate free radicals, thereby efficiently initiating monomer polymerization reactions.

[0029] In an optional embodiment of the present invention, the quaternized natural polymer derivative is selected from one or both of chitosan quaternary ammonium salts or cellulose quaternary ammonium salts; in the modified hectorite or modified bentonite, the ratio of the molar number of cationic groups provided by the quaternized natural polymer derivative to the molar number of cation exchange capacity of the hectorite or bentonite is (1.1-1.5):1, more preferably (1.2-1.4):1. The cationic groups (quaternary ammonium-N + (CH3)3) replaces the exchangeable cations between the layers of hectorite or bentonite through ion exchange to stably load the mineral layers and achieve modification. The above ratio ensures that the exchangeable cations between the mineral layers are fully replaced. Hectorite and bentonite have a typical "sheet-interlayer" structure, with exchangeable cations (such as Na + , Ca 2+), with large interlayer spacing and high specific surface area, providing ample active sites for loading quaternized natural polymer derivatives. The layered structures of hectorite and bentonite inherently exhibit excellent expandability and dispersibility, allowing them to disperse evenly in water as nanoscale sheets. These sheets tightly integrate with the polymer network and resist aggregation. Furthermore, as natural mineral materials, hectorite and bentonite are widely available, low-cost, and possess excellent chemical stability and environmental compatibility. Synergistically, these materials, when used in conjunction with the natural polymer derivatives in water-retaining agents, can enhance the biodegradability of the overall material and reduce the risk of soil residues.

[0030] The present invention also provides a method for preparing the water-retaining agent having both salt resistance and urease inhibition effects, comprising the following steps: The monomer and the anionic natural polymer derivative are mixed in water, modified hectorite or modified bentonite, a crosslinking agent and an initiator are added, and the temperature is raised to react to obtain a gel. The gel is soaked, washed with water and dried to obtain a water-retaining agent with both salt resistance and urease inhibition effects.

[0031] In the above technical solution of the present invention, the monomer and the anionic natural polymer derivative are first mixed in water, so that the two are pre-assembled through intermolecular forces, and then modified hectorite or modified bentonite, a crosslinker and an initiator are added. At this time, the positively charged groups of the modified minerals are initially combined with the anionic groups of the pre-assembled system to avoid mineral agglomeration and ensure that they are evenly dispersed in the polymer network; the initiator is decomposed by a temperature reaction, thereby initiating monomer polymerization, and a three-dimensional network gel is formed under the action of the crosslinker.

[0032] After mixing the monomers and the anionic natural polymer derivative in water, the present invention also includes a deoxygenation step to prevent oxygen from adversely affecting the subsequent polymerization process. The present invention does not impose any particular limitation on the deoxygenation process; for example, nitrogen bubbling deoxygenation, vacuum deoxygenation followed by nitrogen replacement, and other methods may be employed.

[0033] In an optional embodiment of the present invention, the preparation method of the modified hectorite or modified bentonite is as follows: The quaternized natural polymer derivative and hectorite or bentonite are mixed in water, subjected to a hydrothermal reaction, washed with water, and dried to obtain the product. Furthermore, the hydrothermal reaction temperature is 70-90°C, and the reaction time is 1-5 hours. The hydrothermal reaction allows for more complete interlayer ion exchange between the quaternized natural polymer derivative and the hectorite or bentonite, evenly distributing the quaternary ammonium groups between the mineral layers, thus avoiding the uneven distribution of groups encountered in traditional modification.

[0034] In an optional embodiment of the present invention, the temperature of the temperature-elevated reaction is 60-80° C., more preferably 65-75° C., and the reaction time is 0.4-3 hours, more preferably 0.5-1 hour. During the temperature-elevated reaction, the initiator decomposes to generate free radicals, thereby initiating monomer polymerization and crosslinking of the polymer chains.

[0035] In an optional embodiment of the present invention, the solvent used for the soaking is an ethanol-water solution; the soaking time is 0.4 to 3 hours, more preferably 0.5 to 1 hour. The ethanol-water soaking treatment effectively dissolves unreacted monomers, small molecule impurities, and residual initiator, while simultaneously promoting shrinkage and shaping of the gel network, thereby enhancing the mechanical strength of the water-retaining agent. The product is further purified by washing with water, and then dried to obtain a solid water-retaining agent for convenient storage and application. The present invention does not impose any particular limitation on the specific drying method, and examples thereof include freeze drying, conventional drying, vacuum drying, supercritical drying, and the like.

[0036] The present invention also provides the use of the water-retaining agent having both salt resistance and urease inhibition effects or the water-retaining agent having both salt resistance and urease inhibition effects prepared by the above preparation method in agricultural and forestry planting.

[0037] The salt-tolerance properties of the water-retaining agent of the present invention allow it to be applied directly and simultaneously with high-salt fertilizers, eliminating the need for step-by-step application and simplifying agricultural processes. In the soil, the water-retaining agent continuously absorbs and retains water through a stable three-dimensional network, providing a long-term water supply for crops and making it particularly suitable for use in arid and semi-arid regions. Simultaneously, the urease-inhibiting function, through the regulation of urease activity by the quaternized natural polymer derivatives in the modified minerals, slows the rate of urea hydrolysis, aligns nitrogen release with the rhythm of crop absorption, reduces nitrogen loss due to ammonia volatilization and nitrate leaching, and improves fertilizer utilization. Furthermore, the degradability of the natural polymer derivatives and modified minerals in the raw materials prevents damage to soil structure with long-term application, achieving a balance between environmental protection and agricultural benefits.

[0038] The technical solution of the present invention is further described below with reference to specific examples. The present invention has no particular limitation on the sources of the reagents used in the following examples, and commercially available products known to those skilled in the art can be used.

[0039] In the following examples, cellulose quaternary ammonium salt was purchased from Celuna Technology Co., Ltd.; low-ester pectin was purchased from Xi'an Yuhua Biotechnology Co., Ltd.; and chitosan quaternary ammonium salt was purchased from J&K Technology Co., Ltd., with a degree of substitution of 98%. In the following examples, references to 50% ethanol aqueous solution refer to volume fractions.

[0040] Example 1 This embodiment provides a water-retaining agent having both salt resistance and urease inhibition effects and a preparation method thereof.

[0041] The raw materials of the water-retaining agent of this embodiment are composed of the following components in parts by mass: 100 parts of acrylamide monomer, 5 parts of sulfonated sodium alginate, 0.2 parts of N,N'-methylenebisacrylamide, 0.2 parts of potassium persulfate, and 10 parts of modified hectorite.

[0042] The preparation method of sulfonated sodium alginate is as follows: 10g of dry sodium alginate is dissolved in 200mL of formamide, 12mL of chlorosulfonic acid is slowly added dropwise in an ice-salt bath at 0-4°C with stirring, the temperature is raised to 65°C and the reaction is carried out for 3 hours, the reaction solution is then poured into 2L of ice acetone for precipitation, and the product is collected and freeze-dried to obtain sulfonated sodium alginate.

[0043] The preparation method of the modified hectorite is as follows: in a glass reactor, chitosan quaternary ammonium salt is dissolved in water, and then hectorite is added, the ratio of the molar number of quaternary ammonium groups in the chitosan quaternary ammonium salt to the molar number of cation exchange capacity of the hectorite is controlled to be 1.3:1, and the mass ratio of hectorite to water is 1:10, the temperature is raised to 80°C for a hydrothermal reaction for 2 hours, and after the reaction is completed, the reaction is filtered, and the solid product is washed 3 times with deionized water, dried at 90°C to constant weight, crushed, and passed through a 100-mesh sieve to obtain the modified hectorite.

[0044] The preparation method of the water-retaining agent in this example is as follows: sulfonated sodium alginate is dissolved in water, followed by the addition of acrylamide monomer, with the ratio of acrylamide monomer to water being controlled at 3 g:50 mL. After dissolution, nitrogen is introduced to deoxygenate the mixture for 30 minutes. N,N'-methylenebisacrylamide, modified hectorite, and potassium persulfate are then added in sequence. The mixture is heated to 70°C with stirring. After approximately 0.5 hours of reaction, stirring becomes impaired, forming a hydrogel. The hydrogel is removed and cut into approximately 5 mm slices. The slices are then soaked in a 50% ethanol-water solution for 0.5 hours and washed three times with deionized water. The mixture is then oven-dried at 80°C to constant weight, yielding a water-retaining agent with both salt-resistance and urease-inhibiting properties.

[0045] Example 2 This embodiment provides a water-retaining agent having both salt resistance and urease inhibition effects and a preparation method thereof.

[0046] The raw materials of the water-retaining agent of this embodiment are composed of the following components in parts by mass: 100 parts of acrylamide monomer, 6 parts of low-ester pectin, 0.2 parts of N,N'-methylenebisacrylamide, 0.2 parts of ammonium persulfate, and 10 parts of modified hectorite.

[0047] The preparation method of the modified hectorite is as follows: in a glass reactor, cellulose quaternary ammonium salt is dissolved in water, and then hectorite is added, the ratio of the molar number of quaternary ammonium groups in the cellulose quaternary ammonium salt to the molar number of cation exchange capacity of the hectorite is controlled to be 1.3:1, and the mass ratio of hectorite to water is 1:10, the temperature is raised to 80°C for a hydrothermal reaction for 2 hours, and after the reaction is completed, the reaction is filtered, and the solid product is washed 3 times with deionized water, dried at 90°C to constant weight, crushed, and passed through a 100-mesh sieve to obtain the modified hectorite.

[0048] The preparation method of the water-retaining agent in this example is as follows: low-ester pectin is dissolved in water, followed by the addition of acrylamide monomer, with the ratio of acrylamide monomer to water being controlled at 3 g:50 mL. After dissolution, nitrogen is introduced for 30 minutes to deoxygenate the mixture. N,N'-methylenebisacrylamide, modified hectorite, and ammonium persulfate are then added in sequence. The mixture is stirred and heated to 70°C. After approximately 0.5 hours of reaction, stirring becomes impaired, forming a hydrogel. The hydrogel is removed and cut into approximately 5 mm slices. The slices are then soaked in a 50% ethanol-water solution for 0.5 hours and washed three times with deionized water. The mixture is then oven-dried at 80°C to constant weight, yielding a water-retaining agent with both salt-resistance and urease-inhibiting properties.

[0049] Example 3 This embodiment provides a water-retaining agent having both salt resistance and urease inhibition effects and a preparation method thereof.

[0050] The raw materials of the water-retaining agent of this embodiment are composed of the following components in parts by mass: 100 parts of acrylic acid monomer, 7 parts of sulfonated sodium alginate, 0.2 parts of N,N'-methylenebisacrylamide, 0.2 parts of potassium persulfate, and 12 parts of modified bentonite.

[0051] The preparation method of sulfonated sodium alginate is the same as that in Example 1.

[0052] The preparation method of modified bentonite is as follows: in a glass reactor, chitosan quaternary ammonium salt is dissolved in water, and then bentonite is added, the ratio of the molar number of quaternary ammonium groups in the chitosan quaternary ammonium salt to the molar number of cation exchange capacity of the bentonite is controlled to be 1.3:1, the mass ratio of bentonite to water is 1:10, the temperature is raised to 80°C for a hydrothermal reaction for 2 hours, and after the reaction is completed, the reaction is filtered, and the solid product is washed 3 times with deionized water, dried at 90°C to constant weight, crushed, and passed through a 100-mesh sieve to obtain modified bentonite.

[0053] The preparation method of the water-retaining agent of this embodiment is as follows: Acrylic acid monomer was neutralized and titrated with a 20% aqueous KOH solution in an ice-water bath. Titration was stopped at pH 6 to obtain a potassium acrylate solution with a neutralization degree of approximately 70%. Sulfonated sodium alginate was dissolved in water, and then the potassium acrylate solution was added, with the monomer:water ratio controlled at 3 g:50 mL. After dissolution, nitrogen was introduced to deoxygenate the mixture for 30 minutes. N,N'-methylenebisacrylamide, modified bentonite, and potassium persulfate were then added sequentially. The mixture was heated to 70°C with stirring. After approximately 1 hour of reaction, stirring became impeded, and a hydrogel was formed. The hydrogel was removed and cut into approximately 5 mm slices. The slices were then soaked in a 50% aqueous ethanol solution for 1 hour and washed three times with deionized water. The mixture was then oven-dried at 80°C to constant weight, yielding a water-retaining agent with both salt-resistance and urease-inhibiting properties.

[0054] Example 4 This embodiment provides a water-retaining agent having both salt resistance and urease inhibition effects and a preparation method thereof.

[0055] The raw materials of the water-retaining agent of this embodiment are composed of the following components in parts by mass: 100 parts of acrylic acid monomer, 8 parts of low-ester pectin, 0.2 parts of N,N'-methylenebisacrylamide, 0.2 parts of ammonium persulfate, and 13 parts of modified hectorite.

[0056] The preparation method of the modified hectorite is as follows: in a glass reactor, chitosan quaternary ammonium salt is dissolved in water, and then hectorite is added, the ratio of the molar number of quaternary ammonium groups in the chitosan quaternary ammonium salt to the molar number of cation exchange capacity of the hectorite is controlled to be 1.3:1, and the mass ratio of hectorite to water is 1:10, the temperature is raised to 80°C for a hydrothermal reaction for 2 hours, and after the reaction is completed, the reaction is filtered, and the solid product is washed 3 times with deionized water, dried at 90°C to constant weight, crushed, and passed through a 100-mesh sieve to obtain the modified hectorite.

[0057] The preparation method of the water-retaining agent of this embodiment is as follows: Acrylic acid monomer was neutralized and titrated with 20% aqueous KOH in an ice-water bath. Titration was stopped at pH 6 to obtain a potassium acrylate solution with a neutralization degree of approximately 70%. Low-ester pectin was dissolved in water, and then the potassium acrylate solution was added, with the monomer:water ratio controlled at 3 g:50 mL. After dissolution, nitrogen was introduced for deoxygenation for 30 minutes. N,N'-methylenebisacrylamide, modified hectorite, and ammonium persulfate were then added sequentially. The mixture was heated to 70°C with stirring. After approximately 1 hour of reaction, stirring became impeded, and a hydrogel was formed. The hydrogel was removed and cut into approximately 5 mm slices. The slices were then soaked in 50% aqueous ethanol for 1 hour and washed three times with deionized water. The resulting water-retaining agent exhibited both salt-resistance and urease-inhibiting properties.

[0058] Comparative Example 1 The difference between this comparative example and Example 1 is that sulfonated sodium alginate and modified hectorite are not added in this comparative example.

[0059] The water-retaining agent of this comparative example was prepared as follows: acrylamide monomer was dissolved in water, with the ratio of acrylamide monomer to water being 3 g:50 mL. Nitrogen was introduced to deoxygenate the mixture for 30 minutes. N,N'-methylenebisacrylamide and potassium persulfate were then added sequentially. The mixture was heated to 70°C with stirring. After approximately 0.5 hours of reaction, stirring became discontinued, resulting in the formation of a hydrogel. The hydrogel was removed and cut into approximately 5 mm slices. The slices were then soaked in a 50% ethanol-water solution for 0.5 hours and washed three times with deionized water. The mixture was then oven-dried at 80°C to constant weight to obtain the water-retaining agent.

[0060] Comparative Example 2 The difference between this comparative example and Example 4 is that low-ester pectin and modified hectorite are not added in this comparative example.

[0061] The water-retaining agent of this comparative example was prepared as follows: acrylic acid monomer was neutralized and titrated with a 20% aqueous KOH solution. Titration was stopped at pH 6 to obtain a potassium acrylate solution with a neutralization degree of approximately 70%. Water was then added to achieve a ratio of 3 g acrylic acid monomer to 50 mL of water. Nitrogen was introduced for 30 minutes to deoxygenate the solution. N,N'-methylenebisacrylamide and ammonium persulfate were then added sequentially. The solution was heated to 70°C with stirring. After approximately one hour of reaction, stirring became impaired, resulting in the formation of a hydrogel. The hydrogel was removed and cut into approximately 5 mm slices. The slices were then soaked in a 50% aqueous ethanol solution for one hour and washed three times with deionized water. The solution was then oven-dried at 80°C to a constant weight to obtain the water-retaining agent.

[0062] Comparative Example 3 The difference between this comparative example and Example 1 is that no modified hectorite is added in this comparative example.

[0063] The water-retaining agent of this comparative example was prepared as follows: sulfonated sodium alginate was dissolved in water, followed by the addition of acrylamide monomer, with the ratio of acrylamide monomer to water being 3 g:50 mL. After dissolution, nitrogen was introduced to deoxygenate the mixture for 30 minutes. N,N'-methylenebisacrylamide and potassium persulfate were then added sequentially. The mixture was heated to 70°C with stirring. After approximately 0.5 hours of reaction, stirring became impeded, resulting in the formation of a hydrogel. The hydrogel was removed and cut into approximately 5 mm slices, which were then soaked in a 50% ethanol-water solution for 0.5 hours and washed three times with deionized water. The mixture was then oven-dried at 80°C to constant weight to obtain the water-retaining agent.

[0064] Comparative Example 4 The difference between this comparative example and Example 1 is that no sulfonated sodium alginate is added in this comparative example.

[0065] The water-retaining agent of this comparative example was prepared as follows: acrylamide monomer was dissolved in water, with the ratio of acrylamide monomer to water being 3 g:50 mL. After dissolution, nitrogen was introduced to deoxygenate the mixture for 30 minutes. N,N'-methylenebisacrylamide, modified hectorite, and potassium persulfate were then added sequentially. The mixture was heated to 70°C with stirring. After approximately 0.5 hours of reaction, stirring became impeded, resulting in the formation of a hydrogel. The hydrogel was removed and cut into approximately 5 mm slices. The slices were then soaked in a 50% ethanol-water solution for 0.5 hours and washed three times with deionized water. The mixture was then oven-dried at 80°C to constant weight to obtain the water-retaining agent.

[0066] Comparative Example 5 The difference between this comparative example and Example 1 is that the modified hectorite is replaced by unmodified hectorite in this comparative example.

[0067] The water-retaining agent of this comparative example was prepared as follows: sulfonated sodium alginate was dissolved in water, followed by the addition of acrylamide monomer, with the ratio of acrylamide monomer to water being 3 g:50 mL. After dissolution, nitrogen was introduced for 30 minutes to deoxygenate the mixture. N,N'-methylenebisacrylamide, laponite, and potassium persulfate were then added in sequence. The mixture was heated to 70°C with stirring. After approximately 0.5 hours of reaction, stirring became impeded, forming a hydrogel. The hydrogel was removed and cut into approximately 5 mm slices. The slices were then soaked in a 50% ethanol-water solution for 0.5 hours and washed three times with deionized water. The mixture was then oven-dried at 80°C to constant weight to obtain the water-retaining agent.

[0068] Comparative Example 6 The difference between this comparative example and Example 1 is that the added amount of the modified hectorite in this comparative example is 20 parts.

[0069] Test example 1. Determination of water absorption rate and salt water absorption rate The test method is as follows: Weigh 1g of a water-retaining agent sample (accurate to 0.001g) and place it in a nylon mesh bag. Immerse the bag in deionized water or a 0.9% NaCl solution, respectively. Allow the bag to soak at room temperature (25±2°C) until swelling equilibrium (approximately 30 minutes). Remove the bag and hang it to drain for 10 minutes until no water drips. Weigh the mass of the swollen gel. Calculate the ratio of the mass before and after swelling to obtain the water absorption rate (g / g) and the salt water absorption rate (g / g). The water absorption rate and salt water absorption rate of the water-retaining agents of Examples 1-4 and Comparative Examples 1-6 are shown in Table 1.

[0070] Table 1 Water absorption rate and salt water absorption rate of the water retaining agents of Examples 1 to 4 and Comparative Examples 1 to 6

[0071] The water absorption rates of the water-retaining agents in the Examples and Comparative Examples are primarily derived from polyacrylamide, polyacrylic acid, and potassium polyacrylate. A comparison of Comparative Example 3 with Comparative Example 1 shows that the addition of an anionic natural polymer derivative (sulfonated sodium alginate) further increases the material's water absorption rate, slightly improving its salt water absorption rate. A comparison of Comparative Examples 1, 3, and 4 with Example 1, as well as a comparison of Comparative Example 2 with Example 4, shows that the anionic natural polymer derivative and modified hectorite act synergistically, significantly improving the water absorption and salt water absorption rates of the water-retaining agent. The hectorite in Comparative Example 5, which was not cationically modified, failed to effectively improve the material's salt water absorption rate. In Comparative Example 6, where an excess of modified hectorite was used, the water and salt absorption rates of the water-retaining agent were significantly reduced, even falling below industry standards, demonstrating that the amount of modified hectorite added significantly impacts the performance of the water-retaining agent.

[0072] 2. Urease inhibition effect test Using a series of different urea concentrations as the substrate and phenol red as the indicator, urea decomposes to produce ammonia under the action of urease, increasing the pH. The color of the system darkens under the action of the phenol red indicator, and the absorbance increase is monitored using a Tecan microplate reader. The increase in absorbance can be used to calculate the ammonium nitrogen content produced by urea hydrolysis. The lower the ammonium nitrogen content, the better the urease inhibition.

[0073] Three treatment groups were set up: (1) urea and urease were added, denoted as the CK group; (2) urea, urease and the urease inhibitor n-butylthiophosphoric triamide (NBPT) were added, denoted as the NBPT group; (3) urea, urease and the water-retaining agent of Example 4 were added, denoted as the SAP4 group. In each treatment group, the mass of urea was 30 times the mass of urease, the urea concentration was 200 mmol / L, and the contents of NBPT and the water-retaining agent of Example 4 were both 10 wt % of the urea. The reaction time was 360 minutes. Commercial giant soybean urease was used as the urease, and phenol red was used as the color developer. The results are shown in Figure 4. Figure 1 shown.

[0074] from Figure 1 It can be seen that both the water-retaining agent of Example 4 and NBPT have urease inhibition effects. Although the urease inhibition effect of the water-retaining agent of Example 4 is slightly worse than that of NBPT, it still has a water-retaining effect that NBPT does not have.

[0075] The same treatment method as that of the water-retaining agent in Example 4 was used to test the urease inhibition of the water-retaining agents in Example 1, Comparative Example 1, Comparative Example 3, and Comparative Example 5. The ammonia nitrogen concentration after 150 minutes of reaction was recorded. The results are summarized in Table 2.

[0076] Table 2 Ammonia nitrogen concentrations in different treatment groups at 150 min

[0077] As can be seen from Table 2, only when hectorite modified with quaternary ammonium salt natural polymer derivatives is added to the water retaining agent can it produce a significant inhibitory effect on urease.

[0078] 3. Mechanical properties test Five water-retention agents of the same particle size (Example 1, Example 2, Comparative Example 1, Comparative Example 2, and Comparative Example 6) were fully swelled in aqueous solution. The elastic modulus G' (i.e., storage modulus G') of the materials was measured using a HAAKE rheometer, reflecting the material's rigidity. A higher G' indicates greater rigidity. The swollen hydrogel samples were placed in a cone-plate fixture and subjected to a fixed stress of 1 Pa. Frequency sweeps (0.01-100 Hz) were performed to generate a curve of the material's elastic modulus versus stress. The elastic modulus G' within the linear viscoelastic region was recorded. The results are shown in Table 3.

[0079] Table 3 Elastic modulus data of hydrogel samples after swelling in different examples and comparative examples

[0080] As can be seen from Table 3, the hydrogels of Examples 1 and 4, after swelling with the water-retaining agents, have the highest elastic modulus, indicating greater rigidity and structural stability. In Comparative Example 6, the excessive addition of modified hectorite adversely affects the rigidity of the hydrogel.

[0081] 4. Wheat drought stress alleviation experiment Potting Setup: Each pot was filled with 8 kg of soil. A water-retaining agent (SAA) was added at a rate of 3 g per kg of soil. Mix thoroughly before potting. Drought Stress Treatment: Drought stress was simulated by controlling irrigation during the wheat jointing stage. During the drought stress period, soil moisture content was regularly monitored using a moisture meter to ensure consistent treatment conditions. Treatment group settings are shown in Table 4. Three replicates were run for each treatment group, with 10 seedlings planted per pot, for a total of 18 pots.

[0082] Table 4 Experimental treatment group design

[0083] Note: In Table 4, the relative soil moisture range refers to the percentage of soil moisture relative to field capacity.

[0084] After drought stress at the jointing stage of wheat, the leaves of the above treatment groups were taken for physiological characteristics testing. - ) content was determined according to the hydroxylamine hydrochloride method, the H2O2 content was determined according to the titanium sulfate method, and the malondialdehyde content was determined according to the thiobarbituric acid reactant method (TBA method); the test results are shown in Table 5.

[0085] Table 5 Effects of different treatments on the stress level of wheat leaves at the jointing stage under drought stress

[0086] Note: In Table 5, a~f represent the values ​​of different treatment groups ranked from high to low. For example, 21.73±0.83a in the MS group indicates that it has the highest amount of H2O2 among the six treatment groups. The same letter means that there is no significant difference between the two groups.

[0087] Table 5 shows that compared with the control (CK) group, moderate drought stress (MS) significantly increased the H₂O₂ content in wheat leaves by 114.09%, exacerbating oxidative stress. Compared with the MS group, the addition of different water-retaining agents alleviated the effects of stress to some extent, resulting in varying degrees of reduction in H₂O₂ content in wheat leaves. The MS-PAM treatment group saw a decrease of 18.41%, the MS-K-PAA group saw a decrease of 4.28%, the MS-SAP1 group saw a decrease of 18.55%, and the MS-SAP4 group saw a significant decrease of 41.42%. The MS-SAP4 treatment group demonstrated the best results, effectively reducing oxidative stress and alleviating drought stress most significantly.

[0088] Compared with the control group (CK treatment group), the MS treatment group significantly increased the superoxide anion (O2 - ) content increased by 277.82%, and the membrane system damage was aggravated. - ) content data, compared with the MS treatment group, the MS-PAM treatment group significantly reduced it by 40.56%; the MS-K-PAA treatment group reduced it by 45.49%; the MS-SAP1 treatment group reduced it by 56.82%; and the MS-SAP4 treatment group significantly reduced it by 61.76%, which was the best treatment group.

[0089] Compared with the control (CK) group, the MS treatment significantly increased malondialdehyde (MDA) levels in wheat leaves, increasing by 151.64%, indicating that stress-induced cell membrane damage was enhanced and membrane lipid peroxidation was severe. Compared with the MS treatment, the treatments with different water-retaining agents reduced MDA levels by 41.00%, 44.43%, 48.15%, and 49.00%, respectively, effectively alleviating the effects of stress. The MS-SAP4 treatment was the most effective in reducing cell membrane damage and alleviating stress levels.

[0090] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A water-retaining agent having both salt resistance and urease inhibition effects, characterized in that: Made from the following raw materials in parts by mass: 100 parts of monomer, 3-10 parts of anionic natural polymer derivative, 0.1-0.5 parts of cross-linking agent, 5-15 parts of modified hectorite or modified bentonite, 0.1-1 parts of initiator; The monomer is one or more of acrylic acid, acrylate or acrylamide; and the modified hectorite or modified bentonite is obtained by modifying hectorite or bentonite with a quaternary ammonium salt natural polymer derivative.

2. The water-retaining agent having both salt resistance and urease inhibition effects as claimed in claim 1, characterized in that: The anionic natural polymer derivative is selected from one or both of low-ester pectin and sulfonated sodium alginate.

3. The water-retaining agent having both salt resistance and urease inhibition effects as claimed in claim 1, characterized in that: The crosslinking agent is selected from one or more of divinylbenzene, propylene glycol, N,N'-methylenebisacrylamide or zinc oxide; the initiator is selected from one or more of potassium persulfate, ammonium persulfate or sodium persulfate.

4. The water-retaining agent having both salt resistance and urease inhibition effects according to claim 1, wherein The quaternized natural polymer derivative is selected from one or both of chitosan quaternary ammonium salts or cellulose quaternary ammonium salts; in the modified hectorite or modified bentonite, the ratio of the molar number of cationic groups provided by the quaternized natural polymer derivative to the molar number of cation exchange capacity of the hectorite or bentonite is (1.1~1.5):

1.

5. The method for preparing the water-retaining agent having both salt resistance and urease inhibition according to any one of claims 1 to 4, characterized in that: The steps include: The monomer and the anionic natural polymer derivative are mixed in water, modified hectorite or modified bentonite, a crosslinking agent and an initiator are added, and the temperature is raised to react to obtain a gel. The gel is soaked, washed with water and dried to obtain a water-retaining agent with both salt resistance and urease inhibition effects.

6. The preparation method according to claim 5, wherein The preparation method of the modified hectorite or modified bentonite is as follows: The quaternary ammonium salt natural polymer derivative and hectorite or bentonite are mixed in water, subjected to hydrothermal reaction, washed with water and dried to obtain the product.

7. The preparation method according to claim 6, wherein The temperature of the hydrothermal reaction is 70-90° C., and the reaction time is 1-5 hours.

8. The preparation method according to claim 5, wherein The reaction temperature of the temperature-raising reaction is 60-80° C., and the reaction time is 0.4-3 h.

9. The preparation method according to claim 5, wherein The solvent used for the soaking is ethanol-water solution; the soaking time is 0.4 to 3 hours.

10. Use of the water-retaining agent having both salt resistance and urease inhibition effects according to any one of claims 1 to 4 or the water-retaining agent having both salt resistance and urease inhibition effects prepared by the preparation method according to any one of claims 5 to 9 in agriculture and forestry planting.

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