Water-retaining agent with both salt and urease inhibition effects, and preparation method and application thereof

Abstract

The application discloses a water-retaining agent with salt resistance and urease inhibition, and a preparation method and application thereof, and belongs to the technical field of water-retaining in agriculture and forestry. The water-retaining agent is prepared from the following raw materials in mass parts: 100 parts of monomers, 3-10 parts of anionic natural polymer derivatives, 0.1-0.5 parts of cross-linking agents, 5-15 parts of modified lithium saponite or modified bentonite, and 0.1-1 parts of initiators; wherein the monomers are one or more of acrylic acid, acrylic acid salt or acrylamide; and the modified lithium saponite or modified bentonite is obtained by modifying lithium saponite or bentonite by quaternary ammonium salt natural polymer derivatives. The water-retaining agent has high water absorption ratio and salt water absorption ratio, can maintain 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 fertilizer, and can simplify farm operations.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of agriculture and forestry water conservation, and particularly relates to a water-retaining agent with salt resistance and urease inhibition, and a preparation method and application thereof. BACKGROUND

[0002] The information disclosed in the background of the present application is only intended to increase the understanding of the overall background of the present application, and should not necessarily be regarded as acknowledging or implying in any form that the information constitutes prior art known to those skilled in the art.

[0003] As a kind of high molecular polymer with super water absorption and water retention capacity, water-retaining agent can significantly improve the physical and chemical properties of soil, enhance the water and fertilizer retention capacity of soil, and slowly release water according to the needs of plants, providing continuous water supply for crop growth, which plays an important role in ensuring normal growth and development of crops in arid and semi-arid areas. However, the existing agriculture and forestry water-retaining agent mainly realizes water absorption and retention function based on the principle of osmotic pressure difference. When in a high salt and fertilizer environment, the sharp rise of external osmotic pressure will cause the water absorption performance of the water-retaining agent to decrease significantly or even appear water reverse osmosis phenomenon, which makes the water-retaining agent unable to be applied synchronously with fertilizer. In actual agricultural production, farmers have to adopt step-by-step operation, i.e., applying water-retaining agent first and then applying fertilizer, or applying fertilizer first and then applying water-retaining agent, which not only increases the labor intensity, but also reduces the efficiency of agricultural operation.

[0004] Urea, as a solid nitrogen fertilizer with high nitrogen content, dominates the global nitrogen fertilizer market. The effective use of urea depends on the catalytic action of soil urease, which is a nickel-containing metal enzyme that can hydrolyze urea into ammonia and carbon dioxide, thereby converting amide nitrogen into ammonium nitrogen that can be absorbed by crops. However, the catalytic efficiency of urease is extremely high, resulting in a release speed of ammonia far exceeding the absorption capacity of crops, which in turn causes a large loss of nitrogen, not only causing significant economic losses, but also leading to serious ecological and environmental problems.

[0005] In agricultural production, water-retaining agent is difficult to be applied synchronously with fertilizer due to its insufficient salt tolerance, while urea leads to nitrogen loss due to the excessive catalysis of urease, which will further accelerate the catalysis of urease and exacerbate the loss of nitrogen in the environment with high soil moisture maintained by water-retaining agent. Commercially available water-retaining agents are difficult to stably absorb water in a high salt environment and cannot inhibit urease activity, resulting in complicated operation and serious nitrogen waste. Therefore, it is urgent to develop a water-retaining agent with salt tolerance and urease inhibition function to achieve the dual goals of water and fertilizer application and nitrogen loss reduction. SUMMARY

[0006] Therefore, the application provides a water-retaining agent with salt resistance and urease inhibition, a preparation method and application thereof.

[0007] In a first aspect, the application provides a water-retaining agent with salt resistance and urease inhibition, which is prepared from the following raw materials by mass:

[0008] 100 parts of monomer, 3-10 parts of anionic natural polymer derivative, 0.1-0.5 parts of crosslinking agent, 5-15 parts of modified hectorite or modified bentonite, and 0.1-1 parts of initiator.

[0009] The monomer is one or more of acrylic acid, acrylic acid salt or acrylamide; the modified hectorite or modified bentonite is obtained by modifying hectorite or bentonite with quaternary ammonium salt natural polymer derivative.

[0010] Preferably, the anionic natural polymer derivative is selected from one or both of low ester pectin and sulfonated sodium alginate.

[0011] Preferably, the crosslinking agent is selected from one or more of divinylbenzene, propylene glycol, N,N'-methylene bisacrylamide or zinc oxide; and the initiator is selected from one or more of potassium persulfate, ammonium persulfate or sodium persulfate.

[0012] Preferably, the quaternary ammonium salt natural polymer derivative is selected from one or both of chitosan quaternary ammonium salt or cellulose quaternary ammonium salt; and the ratio of the number of moles of cationic groups provided by the quaternary ammonium salt natural polymer derivative to the number of moles of cation exchange capacity of the hectorite or bentonite in the modified hectorite or modified bentonite is (1.1-1.5) : 1.

[0013] In a second aspect, the application provides a preparation method of the water-retaining agent with salt resistance and urease inhibition, which comprises the following steps:

[0014] The monomer and the anionic natural polymer derivative are mixed in water, the modified hectorite or modified bentonite, the crosslinking agent and the initiator are added, and the gel is obtained by heating reaction, and then the gel is soaked, washed with water and dried to obtain the water-retaining agent with salt resistance and urease inhibition.

[0015] Preferably, the preparation method of the modified hectorite or modified bentonite is as follows:

[0016] The quaternary ammonium salt natural polymer derivative and the hectorite or bentonite are mixed in water, and then the water is heated, washed and dried to obtain the modified hectorite or modified bentonite.

[0017] Further, the temperature of the hydrothermal reaction is 70-90 DEG C, and the reaction time is 1-5h.

[0018] Preferably, the reaction temperature of the temperature rising reaction is 60-80 DEG C, and the reaction time is 0.4-3h.

[0019] Preferably, the solvent used in the soaking is an ethanol aqueous solution, and the soaking time is 0.4-3h.

[0020] In a third aspect, the application provides application of the water-retaining agent with both salt resistance and urease inhibition effect or the water-retaining agent prepared by the preparation method in farming and forestry planting.

[0021] Compared with the prior art, the application has the following beneficial effects:

[0022] (1) The water-retaining agent provided by the application has high water absorption ratio and salt water absorption ratio, and the water absorption ratio can reach more than 450g / g, and the salt water absorption ratio can reach more than 80g / g. Through the synergistic effect of the modified hectorite or modified bentonite and the monomer and anionic natural polymer derivative in the raw material, the water-retaining agent 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 fertilizer due to insufficient salt resistance, and simultaneously delaying the urea hydrolysis rate and reducing nitrogen loss through the regulation of the urease activity of the quaternary ammonium saltified natural polymer derivative in the modified hectorite or modified bentonite, so that synchronous application of the water-retaining agent and the fertilizer can be realized, and the farming operation is simplified.

[0023] (2) The modified hectorite or modified bentonite is introduced in the application, not only the layered structure of the modified hectorite or modified bentonite enhances the rigidity of the network structure of the water-retaining agent, limits the movement of the polymer chain, further reduces the damage of salt ions to the network structure of the water-retaining agent, and improves the stability of the water-retaining performance, but also the amphoteric polymer system formed by the quaternary ammonium saltified natural polymer derivative and the anionic group synergistically improves the salt resistance effect, so that the water-retaining agent can still continuously play the water-retaining and fertilizer-retaining role in a complex soil environment, and provide stable water and nutrient supply for crop growth.

[0024] (3) The anionic natural polymer derivative used in the application is selected from natural source materials such as low-ester pectin and sulfonated sodium alginate, and the quaternary ammonium saltified natural polymer derivative used in the modified hectorite or modified bentonite is a natural polymer derivative such as chitosan quaternary ammonium salt or cellulose quaternary ammonium salt, and the whole raw material has good biocompatibility and degradability, is friendly to the soil environment after use, meets the environmental protection requirements, and avoids possible secondary pollution caused by traditional chemical synthetic materials. BRIEF DESCRIPTION OF DRAWINGS

[0025] The accompanying drawings, which form a part of this specification, are included to provide a further understanding of the application and are incorporated in and constitute a part of this specification. The embodiments of the application, and their

[0026] Figure 1 Figure 1 is a graph showing the change in ammonia nitrogen concentration over time for the CK group, the NBPT group, and the SAP4 group in the urease inhibition effect test of the present application. DETAILED DESCRIPTION

[0027] It should be noted that the following detailed description is exemplary in nature and is intended to provide further description of the application. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

[0028] The present application provides a water-retaining agent with both salt resistance and urease inhibition effects, which is made from the following raw materials by mass:

[0029] 100 parts of monomer, 3-10 parts of anionic natural polymer derivative, 0.1-0.5 parts of crosslinking agent, 5-15 parts of modified hectorite or modified bentonite, and 0.1-1 parts of initiator;

[0030] The monomer is one or more of acrylic acid, acrylic acid salt, or acrylamide; and the modified hectorite or modified bentonite is obtained by modifying hectorite or bentonite with a quaternary ammonium salt natural polymer derivative.

[0031] The water-retaining agent provided by the present application achieves the effects of both urease inhibition and salt resistance through the synergistic effect of the raw material components. The monomer (acrylic acid, acrylic acid salt, or acrylamide) as the basic skeleton undergoes a polymerization reaction under the action of the initiator to form a high molecular chain with hydrophilic groups (carboxyl, amide groups). These hydrophilic groups combine with water molecules through hydrogen bonds, hydration, etc., to form the basic structure of the water-retaining agent for water absorption and retention. On this basis, the anionic natural polymer derivative interacts with the hydrophilic polymer chain through intermolecular forces (hydrogen bonds and electrostatic attraction) to assist in building a network-interpenetrating composite polymer system, enhancing the stability of the polymer network, while the anionic groups carried by itself further improve the water binding capacity of the system. The crosslinking agent connects different polymer chains through chemical bonds to form a three-dimensional network structure, limiting the excessive swelling of the polymer chain, ensuring that the water-retaining agent remains in a gel state after absorbing water, avoiding dissolution and loss, and thus stabilizing the water retention performance.

[0032] The modified hectorite or modified bentonite is a modified mineral obtained by modifying a quaternary ammonium salt of a natural polymer derivative. The cationic group of the quaternary ammonium salt of the natural polymer derivative is combined in 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, limits the shrinkage movement of the polymer chain in the salt solution, and reduces the damage of the salt ion to the network structure. On the other hand, the positive charge group of the quaternary ammonium salt of the natural polymer derivative forms a "positive and negative charge synergistic" system with the hydrophilic polymer chain and the anion group (such as carboxyl) in the anionic natural polymer derivative. In a high salt environment, the amphoteric charge distribution can weaken the charge neutralization effect of the salt ion 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 group and the polymer long chain of the quaternary ammonium salt of the natural polymer derivative can be combined with the urease protein molecule through electrostatic interaction and other intermolecular forces, change the spatial conformation of the urease, inhibit the catalytic activity of the urease, and thus delay the urea hydrolysis rate, realizing the urease inhibition function. Through the above synergistic effect, the components give the water retaining agent the dual characteristics of salt resistance and urease inhibition.

[0033] In an alternative embodiment of the present application, the anionic natural polymer derivative is more preferably 3-8 parts, which ensures that the anion group is fully matched with the positive charge of the modified mineral, enhances the salt resistance, and maintains the integrity and degradability of the network structure. The crosslinking agent is more preferably 0.1-0.3 parts, and a suitable amount can form a moderately crosslinked network structure, which can support the physical filling of the modified mineral and retain sufficient water absorption channels, ensuring the long-term stability of the water retention performance. The modified hectorite or modified bentonite is more preferably 8-13 parts. If the amount is too high, the mineral particles are easy to agglomerate and disperse unevenly, which may cause local network structure to break, and the water retention performance and mechanical properties to decrease. If the amount is too low, the polymer network lacks rigid support in a high salt environment, the chain segments are easy to shrink under the compression of salt ions, the salt resistance is not obviously improved, and the number of quaternary ammonium groups is insufficient, the urease inhibition sites are few, and it is difficult to effectively control the urea hydrolysis rate. A suitable amount can realize uniform dispersion of the mineral, the layered structure of which can physically enhance the network stability and synergize with the anionic natural polymer derivative through the quaternary ammonium group to maximize the salt resistance and urease inhibition effect. The initiator is more preferably 0.1-0.4 parts, which ensures that the monomers are fully polymerized to form polymer chains with moderate molecular weight and uniform distribution.

[0034] In an alternative embodiment of the present application, the anionic natural polymer derivative is selected from one or both of low-ester pectin or sulfonated sodium alginate. Such natural materials not only carry anionic groups such as carboxyl groups, sulfonic acid groups, etc., but can form a network interpenetrating structure with the hydrophilic polymer chain through hydrogen bonding or electrostatic interaction, enhancing the stability of the polymer network, and can also coordinate with the positive charge groups of the subsequent modified minerals through the anionic groups, improving the charge balance ability of the system in a high-salt environment, further strengthening the salt resistance. Meanwhile, the natural origin endows the material with degradability, reducing the risk of soil residue. The present application does not make special restrictions on the source of low-ester pectin and sulfonated sodium alginate, which can be purchased or self-made. For example, low-ester pectin can be obtained by extracting and de-esterifying plant raw materials, and its esterification degree is less than 50%, and more than half of the carboxyl groups exist in the form of free acid (-COOH) or salt (-COO - ).

[0035] In an alternative embodiment of the present application, the crosslinking agent is selected from one or more of divinylbenzene, propylene glycol, N,N'-methylene bisacrylamide or zinc oxide, and more preferably N,N'-methylene bisacrylamide; and the initiator is selected from one or more of potassium persulfate, ammonium persulfate or sodium persulfate, which can decompose to generate free radicals under elevated temperature conditions, efficiently initiating the polymerization reaction of monomers.

[0036] In an alternative embodiment of the present application, the quaternary ammonium saltified natural polymer derivative is selected from one or both of chitosan quaternary ammonium salt or cellulose quaternary ammonium salt; and in the modified hectorite or modified bentonite, the ratio of the number of moles of cationic groups provided by the quaternary ammonium saltified natural polymer derivative to the number of moles of cation exchange capacity of the hectorite or bentonite is (1.1-1.5) : 1, and more preferably (1.2-1.4) : 1. The cationic groups (quaternary ammonium groups -N + (CH3)3) of the quaternary ammonium saltified natural polymer derivative replace the exchangeable cations in the interlayer of the hectorite or bentonite through ion exchange, to stabilize the loading in the interlayer of the mineral and achieve modification. The above ratio ensures that the exchangeable cations in the interlayer of the mineral are fully replaced. Hectorite and bentonite have a typical "sheet-layer" structure, and exchangeable cations (such as Na + , Ca 2+The layered structure of hectorite and bentonite has good swelling and dispersing properties, and can be uniformly dispersed into nanoscale layers in water, and can be tightly combined with the polymer network without easy aggregation. In addition, as a natural mineral material, hectorite and bentonite are widely available, low in cost, and have good chemical stability and environmental compatibility. In combination with the natural polymer derivatives in the water-retaining agent, the biodegradability of the overall material can be improved, and the risk of soil residue can be reduced.

[0037] The application also provides a preparation method of the above-mentioned water-retaining agent with both salt resistance and urease inhibition, comprising the following steps:

[0038] 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 gel is obtained by heating reaction. The gel is soaked, washed with water and dried to obtain the water-retaining agent with both salt resistance and urease inhibition.

[0039] In the above technical solution of the application, the monomer and the anionic natural polymer derivative are mixed in water to pre-assemble them through intermolecular forces, and then the modified hectorite or modified bentonite, the crosslinking agent and the initiator are added. At this time, the positive charge groups of the modified mineral are preliminarily combined with the anion groups of the pre-assembled system to avoid mineral aggregation and ensure uniform dispersion of the mineral in the polymer network. The initiator is decomposed by heating reaction to initiate polymerization of the monomer, and a three-dimensional network gel is formed under the action of the crosslinking agent.

[0040] After the monomer and the anionic natural polymer derivative are mixed in water, the application further includes a step of removing oxygen to avoid the adverse effects of oxygen on the subsequent polymerization process. The application does not make special limitations on the process of removing oxygen, for example, nitrogen bubbling, vacuum deoxygenation and nitrogen replacement can be used.

[0041] In an optional embodiment of the application, the preparation method of the modified hectorite or modified bentonite is as follows:

[0042] After the quaternary ammonium salt natural polymer derivative and the hectorite or bentonite are mixed in water, the hydrothermal reaction, water washing and drying are performed to obtain the modified hectorite or modified bentonite. Further, the temperature of the hydrothermal reaction is 70-90℃, and the reaction time is 1-5h. The hydrothermal reaction makes the ion exchange between the quaternary ammonium salt natural polymer derivative and the hectorite or bentonite more sufficient, and the quaternary ammonium groups are uniformly loaded in the interlayer of the mineral, avoiding the problem of uneven distribution of groups in the traditional modification.

[0043] In an alternative embodiment of the present application, the reaction temperature of the temperature-increasing reaction is 60-80℃, more preferably 65-75℃; and the reaction time is 0.4-3h, more preferably 0.5-1h. During the temperature-increasing reaction, the initiator decomposes to generate free radicals, thereby initiating the polymerization of monomers and the crosslinking of polymer chains.

[0044] In an alternative embodiment of the present application, the solvent used for the soaking is an aqueous ethanol solution; and the soaking time is 0.4-3h, more preferably 0.5-1h. The soaking treatment with the aqueous ethanol solution can effectively dissolve the unreacted monomers, small molecular impurities and residual initiators, and at the same time, promote the shrinkage and setting of the gel network, thereby improving 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, which is convenient for storage and application. The present application does not make special limitation to the specific drying method, for example, freeze-drying, ordinary drying, vacuum drying, supercritical drying, etc.

[0045] The present application also provides the use of the above-mentioned water-retaining agent with both salt resistance and urease inhibition effect or the above-mentioned water-retaining agent with both salt resistance and urease inhibition effect prepared by the preparation method in the farming and forestry planting.

[0046] The salt resistance of the water-retaining agent of the present application enables it to be directly applied synchronously with high-salt fertilizer without step-by-step operation, thereby simplifying the farming process. In the soil, the water-retaining agent continuously absorbs and retains water through the stable three-dimensional network, thereby providing long-acting water supply for crops, especially in arid and semi-arid areas. At the same time, the urease inhibition function regulates the urease activity through the modification of the quaternary ammonium salt of the natural high molecular weight derivative in the mineral, thereby delaying the urea hydrolysis rate, matching the nitrogen release with the crop absorption rhythm, reducing the nitrogen loss caused by ammonia volatilization and nitrate leaching, and improving the fertilizer utilization rate. In addition, the degradability of the natural high molecular weight derivative and the modified mineral in the raw material avoids the damage to the soil structure caused by long-term application, thereby realizing the unification of environmental protection and agricultural benefits.

[0047] The technical solutions of the present application are further described below in combination with specific examples. The present application does not make special limitation to the sources of the reagents used in the following examples, and the commercially available products known to those skilled in the art can be used.

[0048] In the following examples, the cellulose quaternary ammonium salt is purchased from Sailuna Technology Co., Ltd.; the low-ester pectin is purchased from Xi'an Yuhua Biological Technology Co., Ltd.; and the chitosan quaternary ammonium salt is purchased from Bailingwei Technology Co., Ltd., with a degree of substitution of 98%. In the following examples, the 50% aqueous ethanol solution refers to the volume fraction.

[0049] Example 1

[0050] The present example provides a water-retaining agent with both salt resistance and urease inhibition effect and a preparation method.

[0051] The raw materials of the water-retaining agent of the present embodiment are composed of the following components in mass parts: acrylamide monomer 100 parts, sulfonated sodium alginate 5 parts, N,N'-methylene bisacrylamide 0.2 parts, potassium persulfate 0.2 parts, and modified hectorite 10 parts.

[0052] The preparation method of the sulfonated sodium alginate is as follows: 10 g of dry sodium alginate is dissolved in 200 mL of formamide, and then 12 mL of chlorosulfonic acid is slowly added dropwise under the conditions of 0-4 ℃ ice salt bath and stirring, and the temperature is raised to 65 ℃ for 3 hours of reaction. Then, the reaction solution is poured into 2 L of ice acetone for precipitation, and the product is collected and freeze-dried to obtain the sulfonated sodium alginate.

[0053] The preparation method of the modified hectorite is as follows: in a glass reaction kettle, chitosan quaternary ammonium salt is dissolved in water, and then hectorite is added. The molar ratio of quaternary ammonium groups in the chitosan quaternary ammonium salt to the 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 ℃ for 2 hours of hydrothermal reaction. After the reaction is completed, the solid product is filtered and washed with deionized water for 3 times. The product is dried at 90 ℃ until the weight is constant, crushed, and then sieved through a 100 mesh sieve to obtain the modified hectorite.

[0054] The preparation method of the water-retaining agent of the present embodiment is as follows: the sulfonated sodium alginate is dissolved in water, and then the acrylamide monomer is added. The mass ratio of the acrylamide monomer to water is controlled to be 3 g: 50 mL. After dissolution, nitrogen is introduced to remove oxygen for 30 minutes. Then, N,N'-methylene bisacrylamide, modified hectorite, and potassium persulfate are added in sequence. The temperature is raised to 70 ℃ under stirring, and the stirring is blocked after about 0.5 hours of reaction to form a hydrogel. The hydrogel is taken out, cut into about 5 mm thin slices with a knife, soaked in 50% ethanol aqueous solution for 0.5 hours, washed with deionized water for 3 times, and dried in an 80 ℃ oven until the weight is constant to obtain the water-retaining agent with both salt resistance and urease inhibition effects.

[0055] Example 2

[0056] The present embodiment provides a water-retaining agent with both salt resistance and urease inhibition effects and a preparation method.

[0057] The raw materials of the water-retaining agent of the present embodiment are composed of the following components in mass parts: acrylamide monomer 100 parts, low-ester pectin 6 parts, N,N'-methylene bisacrylamide 0.2 parts, ammonium persulfate 0.2 parts, and modified hectorite 10 parts.

[0058] The preparation method of the modified hectorite is as follows: in a glass reaction kettle, the cellulose quaternary ammonium salt is dissolved in water, then the hectorite is added, the molar ratio of the quaternary ammonium group in the cellulose quaternary ammonium salt to the cation exchange capacity of the hectorite is controlled to be 1.3:1, the mass ratio of the hectorite to water is 1:10, the hydrothermal reaction is carried out at 80℃ for 2h, after the reaction is completed, the solid product is filtered, washed with deionized water for 3 times, dried at 90℃ to constant weight, crushed and sieved through a 100 mesh sieve, and the modified hectorite is obtained.

[0059] The preparation method of the water-retaining agent of the present embodiment is as follows: the low-ester pectin is dissolved in water, then the acrylamide monomer is added, the amount ratio of the acrylamide monomer to water is controlled to be 3g:50mL; after dissolution, nitrogen is introduced to remove oxygen for 30min, then N,N'-methylene bisacrylamide, modified hectorite and ammonium persulfate are added in sequence, the temperature is increased to 70℃ under stirring, and the stirring is blocked when the reaction is about 0.5h, and a hydrogel is formed. The hydrogel is taken out, cut into about 5mm thin slices with a knife, soaked in 50% ethanol aqueous solution for 0.5h, washed with deionized water for 3 times, and dried in an oven at 80℃ to constant weight, and the water-retaining agent with salt resistance and urease inhibition is obtained.

[0060] Example 3

[0061] The present embodiment provides a water-retaining agent with salt resistance and urease inhibition and a preparation method.

[0062] The raw materials of the water-retaining agent of the present embodiment are composed of the following components by mass fraction: 100 parts of acrylamide monomer, 7 parts of sulfonated sodium alginate, 0.2 parts of N,N'-methylene bisacrylamide, 0.2 parts of potassium persulfate, and 12 parts of modified bentonite.

[0063] The preparation method of the sulfonated sodium alginate is the same as that of Example 1.

[0064] The preparation method of the modified bentonite is as follows: in a glass reaction kettle, the chitosan quaternary ammonium salt is dissolved in water, then the bentonite is added, the molar ratio of the quaternary ammonium group in the chitosan quaternary ammonium salt to the cation exchange capacity of the bentonite is controlled to be 1.3:1, the mass ratio of the bentonite to water is 1:10, the hydrothermal reaction is carried out at 80℃ for 2h, after the reaction is completed, the solid product is filtered, washed with deionized water for 3 times, dried at 90℃ to constant weight, crushed and sieved through a 100 mesh sieve, and the modified bentonite is obtained.

[0065] The preparation method of the water-retaining agent of the present embodiment is as follows:

[0066] Under ice water bath condition, the acrylic acid monomer was neutralized and titrated with 20% KOH aqueous solution, and the titration was stopped at pH = 6 to obtain a potassium acrylate solution with a neutralization degree of about 70%. The sulfonated sodium alginate was dissolved in water, and then the potassium acrylate solution was added. The amount ratio of monomer to water was controlled to be 3 g: 50 mL. After dissolution, nitrogen was introduced to remove oxygen for 30 min. Then N,N'-methylene bisacrylamide, modified bentonite and potassium persulfate were added in sequence. The temperature was increased to 70°C under stirring. After about 1 h of reaction, the stirring was blocked and a hydrogel was formed. The hydrogel was taken out, cut into about 5 mm slices with a knife, soaked in 50% ethanol aqueous solution for 1 h, and washed with deionized water for 3 times. Drying was performed in an oven at 80°C until constant weight to obtain a water-retaining agent with both salt resistance and urease inhibition effects.

[0067] Example 4

[0068] The present example provides a water-retaining agent with both salt resistance and urease inhibition effects and a preparation method.

[0069] The raw materials of the water-retaining agent of the present example are composed of the following components by mass fraction: acrylic acid monomer 100 parts, low-ester pectin 8 parts, N,N'-methylene bisacrylamide 0.2 parts, ammonium persulfate 0.2 parts, and modified hectorite 13 parts.

[0070] The preparation method of the modified hectorite is as follows: in a glass reaction kettle, chitosan quaternary ammonium salt is dissolved in water, and then hectorite is added. The molar ratio of quaternary ammonium groups in the chitosan quaternary ammonium salt to the 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 increased to 80°C for 2 h of hydrothermal reaction. After completion, the solid product is filtered and washed with deionized water for 3 times. Drying is performed at 90°C until constant weight. After crushing, the product is sieved through a 100 mesh sieve to obtain the modified hectorite.

[0071] The preparation method of the water-retaining agent of the present example is as follows:

[0072] Under ice water bath condition, the acrylic acid monomer was neutralized and titrated with 20% KOH aqueous solution, and the titration was stopped at pH = 6 to obtain a potassium acrylate solution with a neutralization degree of about 70%. The sulfonated sodium alginate was dissolved in water, and then the potassium acrylate solution was added. The amount ratio of monomer to water was controlled to be 3 g: 50 mL. After dissolution, nitrogen was introduced to remove oxygen for 30 min. Then N,N'-methylene bisacrylamide, modified bentonite and potassium persulfate were added in sequence. The temperature was increased to 70°C under stirring. After about 1 h of reaction, the stirring was blocked and a hydrogel was formed. The hydrogel was taken out, cut into about 5 mm slices with a knife, soaked in 50% ethanol aqueous solution for 1 h, and washed with deionized water for 3 times. Drying was performed in an oven at 80°C until constant weight to obtain a water-retaining agent with both salt resistance and urease inhibition effects.

[0073] Comparative Example 1

[0074] The comparative example is compared with example 1, the difference is that the comparative example does not add sulfonated sodium alginate and modified hectorite.

[0075] The preparation method of the water retaining agent of the comparative example is as follows: the acrylamide monomer is dissolved in water, and the amount ratio of the acrylamide monomer and water is controlled to be 3g:50mL. Nitrogen is introduced to remove oxygen for 30min, then N,N'-methylene bisacrylamide and potassium persulfate are added in turn, and the temperature is stirred to 70℃. When the stirring is blocked after about 0.5h of reaction, a hydrogel is formed. The hydrogel is taken out, cut into about 5mm slices with a knife, soaked in 50% ethanol aqueous solution for 0.5h, and washed with deionized water for 3 times. Drying in an oven at 80℃ to constant weight to obtain the water retaining agent.

[0076] Comparative example 2

[0077] The comparative example is compared with example 4, the difference is that the comparative example does not add low ester pectin and modified hectorite.

[0078] The preparation method of the water retaining agent of the comparative example is as follows: the acrylamide monomer is neutralized and titrated with 20% KOH aqueous solution, and the titration is stopped when the pH is 6 to obtain a potassium acrylate solution with a neutralization degree of about 70%, and water is added to make the amount ratio of the acrylamide monomer and water to be 3g:50mL. Nitrogen is introduced to remove oxygen for 30min, then N,N'-methylene bisacrylamide and ammonium persulfate are added in turn, and the temperature is stirred to 70℃. When the stirring is blocked after about 1h of reaction, a hydrogel is formed. The hydrogel is taken out, cut into about 5mm slices with a knife, soaked in 50% ethanol aqueous solution for 1h, and washed with deionized water for 3 times. Drying in an oven at 80℃ to constant weight to obtain the water retaining agent.

[0079] Comparative example 3

[0080] The comparative example is compared with example 1, the difference is that the comparative example does not add modified hectorite.

[0081] The preparation method of the water retaining agent of the comparative example is as follows: the sulfonated sodium alginate is dissolved in water, then the acrylamide monomer is added, and the amount ratio of the acrylamide monomer and water is controlled to be 3g:50mL; after dissolution, nitrogen is introduced to remove oxygen for 30min, then N,N'-methylene bisacrylamide and potassium persulfate are added in turn, and the temperature is stirred to 70℃. When the stirring is blocked after about 0.5h of reaction, a hydrogel is formed. The hydrogel is taken out, cut into about 5mm slices with a knife, soaked in 50% ethanol aqueous solution for 0.5h, and washed with deionized water for 3 times. Drying in an oven at 80℃ to constant weight to obtain the water retaining agent.

[0082] Comparative example 4

[0083] The comparative example is compared with example 1, the difference is that the comparative example does not add sulfonated sodium alginate.

[0084] The preparation method of the water-retaining agent of the present comparative example is as follows: acrylamide monomer is dissolved in water, and the amount ratio of acrylamide monomer to water is controlled to be 3 g: 50 mL; after dissolution, nitrogen is introduced to remove oxygen for 30 min, then N,N'-methylenebisacrylamide, modified lithium soapstone and potassium persulfate are sequentially added, stirring is carried out to heat to 70°C, and when the stirring is blocked after about 0.5 h, a hydrogel is formed. The hydrogel is taken out, cut into about 5 mm slices with a knife, soaked in 50% ethanol aqueous solution for 0.5 h, washed with deionized water for 3 times. Drying in an oven at 80°C to constant weight to obtain the water-retaining agent.

[0085] Comparative Example 5

[0086] The present comparative example is different from Example 1 in that the modified lithium soapstone is replaced by unmodified lithium soapstone.

[0087] The preparation method of the water-retaining agent of the present comparative example is as follows: acrylamide monomer is dissolved in water, and the amount ratio of acrylamide monomer to water is controlled to be 3 g: 50 mL; after dissolution, nitrogen is introduced to remove oxygen for 30 min, then N,N'-methylenebisacrylamide, modified lithium soapstone and potassium persulfate are sequentially added, stirring is carried out to heat to 70°C, and when the stirring is blocked after about 0.5 h, a hydrogel is formed. The hydrogel is taken out, cut into about 5 mm slices with a knife, soaked in 50% ethanol aqueous solution for 0.5 h, washed with deionized water for 3 times. Drying in an oven at 80°C to constant weight to obtain the water-retaining agent.

[0088] Comparative Example 6

[0089] The present comparative example is different from Example 1 in that the amount of modified lithium soapstone added in the present comparative example is 20 parts.

[0090] Test Example

[0091] 1. Water absorption ratio and salt water absorption ratio determination

[0092] The test method is as follows: 1 g (accurate to 0.001 g) of the water-retaining agent sample is weighed and placed in a nylon mesh bag, and then immersed in deionized water or 0.9% NaCl solution, respectively, and soaked at room temperature (25±2°C) until swelling equilibrium (about 30 min). After taking out, it is hung to drip water for 10 min until no water drops, and then the mass of the swollen gel is weighed. The water absorption ratio (g / g) and the salt water absorption ratio (g / g) are obtained by calculating the mass ratio before and after swelling. The water absorption ratio and the salt water absorption ratio of the water-retaining agents of Examples 1-4 and Comparative Examples 1-6 are shown in Table 1.

[0093] Table 1 Water absorption ratio and salt water absorption ratio of water-retaining agents of Examples 1-4 and Comparative Examples 1-6

[0094]

[0095] The water absorption ratio of the water-retaining agent of the examples and the comparative examples mainly comes from polyacrylamide, polyacrylic acid and potassium polyacrylate. As can be seen from the comparison between Comparative Example 3 and Comparative Example 1, the addition of the anionic natural polymer derivative (sulfonated sodium alginate) can further improve the water absorption ratio of the material, and the salt water absorption ratio of the material is slightly improved. As can be seen from the comparison between Comparative Example 1, Comparative Example 3, Comparative Example 4 and Example 1, and the comparison between Comparative Example 2 and Example 4, the anionic natural polymer derivative and the modified hectorite play a synergistic role, significantly improving the water absorption ratio and the salt water absorption ratio of the water-retaining agent. The hectorite of Comparative Example 5 is not cationically modified, and cannot effectively improve the salt water absorption ratio of the material. In Comparative Example 6, the modified hectorite is excessive, and it can be seen that the water absorption and salt absorption ratio of the water-retaining agent are significantly reduced, even lower than the industry standard, indicating that the amount of the modified hectorite has a great influence on the performance of the water-retaining agent.

[0096] 2. Urease inhibition effect test

[0097] A series of urea with different concentrations were used as substrates, and phenol red was used as an indicator. Under the action of urease, urea was decomposed to produce ammonia, and the pH value rose. Under the action of the phenol red indicator, the color of the system became deeper. The increase in absorbance was monitored by a Tecan microplate reader. According to the increase in absorbance, the content of ammonium nitrogen produced by the hydrolysis of urea was calculated. The lower the content of ammonium nitrogen, the better the urease inhibition effect.

[0098] Three treatment groups were set: (1) adding urea and urease, denoted as CK group; (2) adding urea, urease and urease inhibitor n-butyl thiophosphoric triamide (NBPT), denoted as NBPT group; (3) adding urea, urease and the water-retaining agent of Example 4, denoted as SAP4 group. In each treatment group, the mass of urea was 30 times the mass of urease, the concentration of urea was 200 mmol / L, and the content of NBPT and the water-retaining agent of Example 4 accounted for 10wt% of urea. The reaction time was 360 minutes. Commercial giant soybean urease was used as urease, and phenol red was used as a color developing agent. The results are shown in Figure 1 .

[0099] As can be seen from Figure 1 , the water-retaining agent of Example 4 and NBPT both have urease inhibition effect. Although the urease inhibition effect of the water-retaining agent of Example 4 is slightly worse than that of NBPT, it also has the water-retaining effect that NBPT does not have.

[0100] The urease inhibition effect of the water-retaining agents of Example 1, Comparative Example 1, Comparative Example 3 and Comparative Example 5 was determined by using the same treatment method as the water-retaining agent of Example 4 described above. The ammonia nitrogen concentration at 150 min was recorded, and the results are summarized in Table 2.

[0101] Table 2 Ammonia nitrogen concentration at 150 min of different treatment groups

[0102]

[0103] As can be seen from Table 2, the urease can be significantly inhibited only when the quaternary ammonium salt modified natural polymer derivative modified hectorite is added in the water-retaining agent.

[0104] 3. Mechanical property test

[0105] The same particle size of 5 kinds of water-retaining agents (Example 1, Example 2, Comparative Example 1, Comparative Example 2 and Comparative Example 6) were fully water-swellable in an aqueous solution, and the elastic modulus G' (i.e. storage modulus G') of the material was measured by using a HAAKE rheometer to reflect the rigidity of the material. The higher the G', the stronger the rigidity of the material. The swelled hydrogel sample was placed in a cone-plate fixture, a stress of 1 Pa was fixed, and a frequency (0.01-100 Hz) scan was performed to obtain the curve of the elastic modulus of the material with the stress, and the elastic modulus G' in the linear viscoelastic region was recorded. The results are shown in Table 3.

[0106] Table 3 Elastic modulus data of swelled hydrogel samples of different examples and comparative examples

[0107]

[0108] As can be seen from Table 3, the swelled hydrogel of the water-retaining agent of Example 1 and Example 4 has the highest elastic modulus, indicating that it has stronger rigidity and better structural stability. The addition amount of the modified hectorite in Comparative Example 6 is too much, which has an adverse effect on the rigidity of the hydrogel.

[0109] 4. Wheat drought stress relief experiment

[0110] Potting setting: the soil amount in each pot was 8 kg, and the water-retaining agent was added at a proportion of 3 g per kg of soil, and then fully mixed and potted. Drought stress treatment: at the jointing stage of wheat, drought stress was simulated by controlling the irrigation amount. During the drought stress period, the soil moisture content was monitored by using a water detector to ensure the consistency of the treatment conditions. The treatment group setting is shown in Table 4, three parallel experiments were set for each treatment group, 10 seedlings were planted in each pot, and a total of 18 pots.

[0111] Table 4 Experimental treatment group design

[0112]

[0113] Note: In Table 4, the soil relative water content range refers to the percentage of the soil water content relative to the field water holding capacity.

[0114] After the above treatment groups were subjected to drought stress at the jointing stage of wheat, the physiological characteristics of the wheat leaves were detected, and the superoxide anion (O2 -The content of H2O2 was determined by hydroxylamine hydrochloride method, the content of H2O2 was determined by titanium sulfate method, and the content of malondialdehyde was determined by thiobarbituric acid reaction method (TBA method); the test results are shown in Table 5.

[0115] Table 5 Influence of different treatment groups on the stress degree of wheat leaf at the jointing stage under drought stress

[0116]

[0117] Note: In Table 5, a~f represent the numerical values of different treatment groups from high to low, for example, 21.73±0.83a in the MS group means that the amount of H2O2 is the highest among the 6 treatment groups, and the same letter means that there is no significant difference between the two groups.

[0118] As shown in Table 5, compared with the control group (CK treatment group), the content of H2O2 in the wheat leaf of the moderate drought stress (MS treatment group) was significantly increased by 114.09%, and the oxidative stress was aggravated. Compared with the MS treatment group, the addition of different water-retaining agents could alleviate the stress effect to a certain extent, and the content of H2O2 in the wheat leaf was reduced to different degrees. The MS-PAM treatment group was reduced by 18.41%, the MS-K-PAA treatment group was reduced by 4.28%, the MS-SAP1 treatment group was reduced by 18.55%, and the MS-SAP4 treatment group was significantly reduced by 41.42%. The MS-SAP4 treatment group showed the best effect, which could effectively reduce the oxidative stress and had the most significant effect on alleviating drought stress.

[0119] Compared with the control group (CK treatment group), the content of superoxide anion (O2 - ) in the wheat leaf of the MS treatment group was significantly increased by 277.82%, and the membrane system damage was aggravated. Compared with the MS treatment group, the content of superoxide anion (O2 - ) in the wheat leaf was reduced by 40.56% in the MS-PAM treatment group, by 45.49% in the MS-K-PAA treatment group, by 56.82% in the MS-SAP1 treatment group, and by 61.76% in the MS-SAP4 treatment group, which showed the best effect.

[0120] Compared with the control group (CK treatment group), the content of malondialdehyde in the wheat leaf of the MS treatment group was significantly increased by 151.64%, indicating that the damage degree of stress to the cell membrane was enhanced and the membrane lipid peroxidation was serious. Compared with the MS treatment group, the content of malondialdehyde was reduced by 41.00%, 44.43%, 48.15% and 49.00% in the treatment groups with different water-retaining agents, respectively, which effectively alleviated the stress effect. Among them, the MS-SAP4 treatment group showed the best effect on reducing the damage to the cell membrane and had the most significant effect on reducing the stress degree.

[0121] The above merely provides the preferred embodiments of the present application, and is not used to limit the present application. For those skilled in the art, the present application can have various modifications and changes. Any modifications, equivalent replacements, improvements, etc. made within the principles and technical scope of the present application shall fall into the scope of the present application.

Claims

1. A water-retaining agent possessing both salt resistance and urease inhibition properties, characterized in that, Made from the following parts by weight of raw materials: 100 parts monomer, 3-10 parts anionic natural polymer derivative, 0.1-0.5 parts crosslinking agent, 8-13 parts modified lithium saponite or modified bentonite, and 0.1-1 parts initiator; Wherein, the monomer is one or more of acrylic acid, acrylate or acrylamide; the modified lithium saponite or modified bentonite is obtained by modifying lithium saponite or bentonite with quaternized natural polymer derivatives. The anionic natural polymer derivative is selected from one or both of low-ester pectin or sulfonated sodium alginate. The quaternized natural polymer derivative is selected from one or two of chitosan quaternary ammonium salt or cellulose quaternary ammonium salt; in the modified lithium saponite or modified bentonite, the ratio of the number of moles of cationic groups provided by the quaternized natural polymer derivative to the number of moles of cation exchange capacity of lithium saponite or bentonite is (1.1~1.5):

1. Preparation method of modified lithium saponite or modified bentonite: After mixing quaternary ammonium salted natural polymer derivatives and lithium saponite or bentonite in water, the mixture is subjected to hydrothermal reaction, water washing, and drying to obtain the product.

2. The water-retaining agent with both salt resistance and urease inhibition effects as described 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.

3. The method for preparing the water-retaining agent with both salt resistance and urease inhibition effects as described in any one of claims 1 to 2, characterized in that, Includes the following steps: The monomer and anionic natural polymer derivative are mixed in water, and modified lithium saponite or modified bentonite, crosslinking agent and initiator are added. The reaction is heated 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. Preparation method of modified lithium saponite or modified bentonite: After mixing quaternary ammonium salted natural polymer derivatives and lithium saponite or bentonite in water, the mixture is subjected to hydrothermal reaction, water washing, and drying to obtain the product.

4. The preparation method according to claim 3, characterized in that, The hydrothermal reaction is carried out at a temperature of 70-90℃ for 1-5 hours.

5. The preparation method according to claim 3, characterized in that, The reaction temperature of the heating reaction is 60~80℃, and the reaction time is 0.4~3h.

6. The preparation method according to claim 3, characterized in that, The solvent used for soaking is an aqueous ethanol solution; the soaking time is 0.4 to 3 hours.

7. The application of the water-retaining agent with both salt resistance and urease inhibition as described in any one of claims 1 to 2, or the water-retaining agent with both salt resistance and urease inhibition prepared by the preparation method described in any one of claims 3 to 6, in agricultural and forestry planting.

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