Low-cost high-stability urease inhibitor as well as preparation method and application thereof

Abstract

The invention relates to a low-cost high-stability urease inhibitor and a preparation method and application thereof.The preparation method includes the steps that montmorillonite is modified with inorganic acid to obtain inorganic acid modified montmorillonite, then hydrogen ions in the inorganic acid modified montmorillonite are exchanged with a cationic surface active agent to obtain quaternary ammonium salt surface active agent modified organic montmorillonite, and the quaternary ammonium salt surface active agent modified organic montmorillonite is used for preparing the urease inhibitor. After montmorillonite is subjected to organic modification, the hydrophobicity is greatly improved, and the organic modified montmorillonite has hydrophilicity and hydrophobicity. The organic modified montmorillonite interacts with amino acid residues in a urease flap region due to the hydrophobic effect, so that the amino acid residues are gathered in the organic modified montmorillonite due to the hydrophobic effect, urease conformational change is caused, catalytic activity on urea is lost, and the organic modified montmorillonite has a remarkable urease inhibition effect, is stable in chemical property and non-toxic in material, and can be used for preparing a novel urease inhibitor. The fertilizer is easy to disperse in fertilizer and soil and low in price.

Description

Technical Field

[0001] The invention relates to a low-cost and high-stability urease inhibitor and a preparation method and application thereof, belonging to the field of fertilizer synergists. Background Art

[0002] Urea is currently the most widely used solid nitrogen fertilizer in the world due to its high nitrogen content. Urease (EC3.5.1.5) is the only nickel-containing protein enzyme in the soil that can hydrolyze urea into ammonia and carbon dioxide. Only after urease hydrolysis can the amide nitrogen in urea be converted into ammonium nitrogen that can be absorbed by crops. Therefore, the presence of urease in the soil is the basis for the widespread use of urea as a high-efficiency nitrogen fertilizer. However, urease catalyzes the hydrolysis of urea very quickly, and the release rate of ammonia is 3×10 faster than that of the uncatalyzed reaction. 15 times, far exceeding the absorption rate of ammonium nitrogen by crops, resulting in a large amount of ammonia volatilization in the soil and nitrate leaching after oxidation of ammonium nitrogen. According to statistics, the annual loss of chemical nitrogen fertilizer in farmland around the world reaches 120 Tg, and more than 50% of nitrogen enters the atmosphere and water bodies, causing immeasurable economic losses and environmental impacts. Faced with the current contradictory and severe situation, preparing materials that can inhibit the catalytic activity of urease and solving the scientific problem of the mismatch between the excessive hydrolysis of urea under the action of urease and the nitrogen absorption rate of crops is an effective way to achieve simultaneous improvement of economic benefits and environmental protection. In addition, urease inhibitors are not only developed as drug targets for the treatment of gastric ulcers and nephritis, but are also widely used in the field of new fertilizer additives and feed additives.

[0003] Urease inhibitors widely used in agriculture mainly include NBPT (n-butyl thiophosphoric triamide) of American Cosmos Agriculture, NBPT and NPPT (n-propyl thiophosphoric triamide) of German BASF, stable fertilizer series products of Shi Kefeng, nano zinc oxide materials, and new urease inhibitors developed by the Shenyang Institute of Ecology of the Chinese Academy of Sciences, etc. These products effectively reduce the adverse effects of urease hydrolysis too fast. However, existing urease inhibitors have many disadvantages: NBPT series has high toxicity and side effects, high cost, and poor stability in acidic soil; nano zinc oxide materials have poor dispersibility in both soil and fertilizer due to their high surface energy, and low cost performance; the new urease inhibitor developed by the Shenyang Institute of Ecology of the Chinese Academy of Sciences has unstable performance.

[0004] Montmorillonite, the key raw material for organically modified montmorillonite, is derived from the soil mineral bentonite and is commonly used as an environmental material. It has no toxic or side effects on the soil. The quaternary ammonium salt surfactants used for modification are commonly used and have bactericidal effects. Also, due to the extremely small addition amount, they can be ignored. In addition, organically modified montmorillonite has both hydrophilic and lipophilic properties. Whether added to fertilizers or directly applied to the soil, it has a good dispersion effect. At the same time, the physical and chemical properties of organically modified montmorillonite are stable and will not lose its functionality due to decomposition by soil microorganisms or changes in acidity and alkalinity. Finally, China ranks first in the world in terms of the reserved amount of bentonite. Using it for large-scale production of urease inhibitors will not be restricted by insufficient raw materials, and the raw material cost is extremely low. Moreover, there are currently no relevant literature reports on the large-scale production of urease inhibitors using montmorillonite.

[0005] Therefore, there is an urgent need to develop a urease inhibitor that has no toxic effects on the soil and crops, is inexpensive, has good dispersibility during the preparation of soil and fertilizers, and has stable chemical properties and low cost. Summary of the Invention

[0006] Aiming at the deficiencies of existing urease inhibitors, the present invention provides a low-cost and highly stable urease inhibitor, its preparation method and application. Overview of the Invention:

[0008] The present invention first modifies montmorillonite with inorganic acid to obtain inorganic acid-modified montmorillonite, and then exchanges the hydrogen ions in the inorganic acid-modified montmorillonite with cationic surfactants to obtain organically modified montmorillonite (hereinafter referred to as organically modified montmorillonite) modified with quaternary ammonium salt surfactants, which has an obvious inhibitory effect on urease. After the organic modification of montmorillonite, its hydrophobicity is greatly increased. Urease, as a protein, two key parts of its structure dominate the catalytic hydrolysis of urea, namely the nickel ion active center and the flap region. Therefore, urease inhibitors are divided into two categories according to the mechanism of action: the first category is to interact with the nickel ion of the urease active center; the second category is to interact with the amino acid residues in the flap region. Due to the hydrophobic effect, the organically modified montmorillonite of the present invention interacts with the amino acid residues in the urease flap region, causing the amino acid residues to aggregate on the organically modified montmorillonite due to the hydrophobic effect, resulting in conformational changes of urease, and thus losing its catalytic activity for urea, and having urease inhibitory function. The key driving force for urease inhibition, the hydrophobic effect, is not easily affected by the soil pH value. Therefore, the urease inhibitor of the present invention can still maintain high chemical stability in acidic soil compared with NBPT. Detailed Description of the Invention:

[0010] A low-cost and highly stable urease inhibitor, which is prepared by modifying montmorillonite with inorganic acid and then exchanging the hydrogen ions in the inorganic acid-modified montmorillonite with cationic surfactants.

[0011] Preferably according to the present invention, the inorganic acid is concentrated sulfuric acid.

[0012] Preferably according to the present invention, the cationic surfactant is one or a mixture of two or more of an alkyltrimethylammonium salt type quaternary ammonium salt surfactant, an alkyldimethylammonium salt type quaternary ammonium salt surfactant, a double-chain or Gemini cationic quaternary ammonium salt surfactant.

[0013] Preferably according to the present invention, the montmorillonite is natural sodium-based montmorillonite or natural calcium-based montmorillonite.

[0014] The present invention also provides a preparation method of a low-cost and highly stable urease inhibitor.

[0015] The preparation method of the above-mentioned low-cost and highly stable urease inhibitor includes the following steps:

[0016] (1) Inorganic acid modification treatment: Excessive concentrated sulfuric acid is added to montmorillonite, and hydrothermal reaction is carried out for 2 - 3 hours. During the reaction process, impurity cations in montmorillonite are removed through ion exchange and completely replaced with hydrogen ions to obtain acid-modified montmorillonite with low thermal stability. After washing with water to remove the excess acid and the pH of the material is close to 7, it is dried to obtain inorganic acid-modified montmorillonite;

[0017] (2) Cationic surfactant exchange: The hydrogen ions in the inorganic acid-modified montmorillonite are exchanged with a cationic surfactant to modify the inorganic acid-modified montmorillonite obtained in step (1) to obtain an organic montmorillonite modified with a quaternary ammonium salt surfactant, which is the low-cost and highly stable urease inhibitor.

[0018] Preferably according to the present invention, in step (1), the concentration of the concentrated sulfuric acid is 0.5 - 2 mol / L.

[0019] Preferably according to the present invention, in step (1), the addition amount of the concentrated sulfuric acid makes the hydrogen ion content of the concentrated sulfuric acid greater than the cation exchange capacity CEC of natural montmorillonite.

[0020] Preferably according to the present invention, in step (1), the montmorillonite is natural sodium-based montmorillonite or natural calcium-based montmorillonite, and the particle size is less than 100 mesh. Due to the larger cation exchange capacity and swelling ratio, the particle size of the montmorillonite is less than 100 mesh.

[0021] Preferably according to the present invention, in step (1), the addition of excessive concentrated sulfuric acid adjusts the liquid-solid ratio L:kg to 1:5 - 1:20.

[0022] More preferably, in step (1), the addition of excessive concentrated sulfuric acid adjusts the liquid-solid ratio L:kg to 1:10.

[0023] Preferably according to the present invention, in step (1), the hydrothermal reaction temperature is 85 - 95 °C.

[0024] Preferably according to the present invention, in step (1), the drying is carried out by drying at 80-90°C.

[0025] Preferably according to the present invention, in step (2), the specific method of cationic surfactant exchange is as follows:

[0026] Prepare the cationic surfactant into an aqueous surfactant solution, add inorganic acid-modified montmorillonite to the aqueous surfactant solution, react by hydrothermal method for 2-3 hours, the cationic surfactant exchanges the hydrogen ions in the inorganic acid-modified montmorillonite, wash with water to remove the excess surfactant, the pH of the material is close to 7, dry at 90-105°C, pulverize and then sieve to obtain the organophilic montmorillonite modified by quaternary ammonium salt surfactant.

[0027] Preferably according to the present invention, in step (2), the cation content in the cationic surfactant is 0.5-4.0 times the cation exchange capacity CEC of montmorillonite.

[0028] Preferably according to the present invention, in step (2), adjust the liquid-solid ratio L:kg to 40:1-10:1 by adding inorganic acid-modified montmorillonite to the aqueous surfactant solution.

[0029] Most preferably, adjust the liquid-solid ratio L:kg to 20:1 by adding inorganic acid-modified montmorillonite to the aqueous surfactant solution. The effect is the best when the liquid-solid ratio L:kg is 20:1, but it should also be increased or decreased according to the solubility of different surfactants. Appropriately reduce the liquid-solid ratio for surfactants with high solubility and appropriately increase the liquid-solid ratio for surfactants with low solubility.

[0030] Preferably according to the present invention, in step (2), the alkyl chain of the cationic surfactant is an alkyl group containing 12-20 carbon chains.

[0031] Preferably according to the present invention, in step (2), when the cationic surfactant is a single-chain cationic surfactant, the cation content in the single-chain cationic surfactant is 1.2 times the cation exchange capacity CEC of montmorillonite.

[0032] Preferably according to the present invention, in step (2), when the cationic surfactant is a double-chain cationic surfactant, the cation content in the double-chain cationic surfactant is 0.6 times the cation exchange capacity CEC of montmorillonite.

[0033] Preferably according to the present invention, the cationic surfactant is one or a mixture of two or more of alkyltrimethylammonium salt type quaternary ammonium salt surfactants, alkyldimethylammonium salt type quaternary ammonium salt surfactants, double-chain or Gemini cationic quaternary ammonium salt surfactants.

[0034] Preferably according to the present invention, in step (2), the reaction temperature of the hydrothermal method is 85-95°C.

[0035] The application of the above-mentioned low-cost and high-stable urease inhibitor, when used as a urease inhibitor, the addition amount is 3-10% of the weight of urea. The addition method is internal or surface coating.

[0036] Preferably, the surface coating method is better, as it can contact urease earlier than urea.

[0037] Features and advantages of the present invention:

[0038] 1. First, the present invention modifies montmorillonite with inorganic acid to obtain inorganic acid-modified montmorillonite, and then exchanges hydrogen ions in the inorganic acid-modified montmorillonite with a cationic surfactant to obtain organo-montmorillonite modified with quaternary ammonium salt surfactant. After the organic modification of montmorillonite, its hydrophobicity is greatly increased, and the organo-montmorillonite has both hydrophilic and hydrophobic properties. Urease, as a protein, two key parts of its structure dominate the catalytic hydrolysis of urea, namely the nickel ion active center and the flap region. Therefore, urease inhibitors are divided into two categories according to their action mechanisms: the first category interacts with the nickel ion of the urease active center; the second category interacts with the amino acid residues in the flap region. Due to the hydrophobic effect, the organo-montmorillonite of the present invention interacts with the amino acid residues in the flap region of urease, causing the amino acid residues to aggregate on the organo-montmorillonite due to the hydrophobic effect, resulting in a conformational change of urease, thus losing its catalytic activity for urea and having a urease inhibitory function.

[0039] 2. The present invention organically modifies montmorillonite through cation exchange, and through the hydrophobic effect, causes the amino acid residues of urease to aggregate with the modified montmorillonite, resulting in a conformational change of urease, thereby inactivating urease, having a significant urease inhibitory effect, stable chemical properties, non-toxic materials, easy to disperse in fertilizers and soils, and low in price. Description of the Drawings

[0040] Figure 1 It is the infrared spectrum curves of montmorillonite before modification and montmorillonite modified with different modifiers. From bottom to top, the curves are: Ca-Mt: natural calcium-based montmorillonite, DTAB-Mt: organo-montmorillonite modified with dodecyltrimethylammonium bromide, TTAB-Mt: organo-montmorillonite modified with tetradecyltrimethylammonium bromide, CTAB-Mt: organo-montmorillonite modified with hexadecyltrimethylammonium bromide, OTAB-Mt: organo-montmorillonite modified with octadecyltrimethylammonium bromide, DDAB-Mt: organo-montmorillonite modified with didodecyldimethylammonium bromide.

[0041] Figure 2These are the XRD curves of montmorillonite before modification and after modification with different modifiers. The curves from bottom to top are: Ca-Mt: natural calcium-based montmorillonite, DTAB-Mt: organic montmorillonite modified with dodecyltrimethylammonium bromide, TTAB-Mt: organic montmorillonite modified with tetradecyltrimethylammonium bromide, CTAB-Mt: organic montmorillonite modified with hexadecyltrimethylammonium bromide, OTAB-Mt: organic montmorillonite modified with octadecyltrimethylammonium bromide, and DDAB-Mt: organic montmorillonite modified with didodecyldimethylammonium bromide.

[0042] Figure 3 The contact angle changes of montmorillonite before modification and after modification with different modifiers are as follows: Ca-Mt: natural calcium-based montmorillonite, DTAB-Mt: organic montmorillonite modified with dodecyltrimethylammonium bromide, TTAB-Mt: organic montmorillonite modified with tetradecyltrimethylammonium bromide, CTAB-Mt: organic montmorillonite modified with hexadecyltrimethylammonium bromide, OTAB-Mt: organic montmorillonite modified with octadecyltrimethylammonium bromide, DDAB-Mt: organic montmorillonite modified with didodecyldimethylammonium bromide.

[0043] Figure 4 This is the Michaelis-Menten fitting curve of the enzymatic reaction of organic montmorillonite modified with different contents of hexadecyltrimethylammonium bromide. The lower the ammonia nitrogen reaction rate, the better the inhibition effect.

[0044] Figure 5 Changes of urease activity in soil under different treatments over time. DETAILED DESCRIPTION

[0045] The present invention is further described below in conjunction with embodiments. It should be understood that the embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0046] Raw materials used in the examples:

[0047] Natural montmorillonite, available at Lingshou County Hengchang Mineral Products Processing Plant;

[0048] Concentrated sulfuric acid: Sinopharm Reagent;

[0049] Cationic surfactant: Sigma-Aldrich, J&K;

[0050] Urease: Macklin's reagent

[0051] Urea for aqueous solution: Sinopharm Reagent;

[0052] Granular urea for soil culture and addition experiments: Stanley Fertilizer Co., Ltd.

[0053] Example 1

[0054] Preparation method of low-cost and high-stability urease inhibitor, the steps are as follows:

[0055] (1): Take 1 kg of natural calcium-based montmorillonite, and measure the cation exchange capacity of natural calcium-based montmorillonite (CEC = 855 mmol / kg) through the national standard GB 20973-2020. Take 5 L of 1 mol / L concentrated sulfuric acid, add natural montmorillonite to concentrated sulfuric acid, and adjust the liquid-solid ratio to 1:5; Use the hydrothermal method to stir and react in a high-boron glass reaction kettle for 3 hours, the reaction temperature is 90 °C, remove the impurity cations in natural montmorillonite, and replace them all with hydrogen ions to obtain inorganic acid-modified montmorillonite. After washing with water to remove the excess acid, the pH of the material is close to 7, and it is dried at 85 °C for 2 hours and pulverized to obtain the intermediate product inorganic acid-modified montmorillonite;

[0056] (2): Prepare 10 L of 0.1 mol / L cetyltrimethylammonium bromide aqueous solution, and the cation content of the cetyltrimethylammonium bromide solution is 1.17 times the CEC of natural montmorillonite. Mix the cetyltrimethylammonium bromide aqueous solution with the inorganic acid-modified montmorillonite in a reaction kettle, adjust the liquid-solid ratio to 10:1, use the hydrothermal method, the reaction temperature is 90 °C, stir and react for 2 hours, modify the intermediate product obtained in step (1), wash with water to remove the excess surfactant, and dry after the pH of the material is close to 7, and it is dried at 100 °C to obtain organophilic montmorillonite modified by quaternary ammonium salt surfactant. After pulverization and sieving for use, obtain cetyltrimethylammonium bromide modified organophilic montmorillonite, denoted as: CTAB-Mt.

[0057] When the organophilic montmorillonite modified by quaternary ammonium salt surfactant is used together with urea as a urease inhibitor, the addition amount is 5% of the weight of urea. Addition method: surface coating.

[0058] Example 2

[0059] Preparation method of low-cost and high-stability urease inhibitor, the steps are as follows:

[0060] (1): Take 1 kg of natural calcium-based montmorillonite, and measure the cation exchange capacity of natural calcium-based montmorillonite (CEC = 855 mmol / kg) through the national standard GB 20973-2020. Take 5 L of 1 mol / L concentrated sulfuric acid, add natural montmorillonite to concentrated sulfuric acid, and adjust the liquid-solid ratio to 1:5; Use the hydrothermal method to stir and react in a high-boron glass reaction kettle for 3 hours, the reaction temperature is 90 °C, remove the impurity cations in natural montmorillonite, and replace them all with hydrogen ions to obtain inorganic acid-modified montmorillonite. After washing with water to remove the excess acid, the pH of the material is close to 7, and it is dried at 90 °C for 2 hours and pulverized to obtain the intermediate product inorganic acid-modified montmorillonite;

[0061] (2): Prepare 20 L of an aqueous solution of tetradecyltrimethylethylammonium bromide with a concentration of 0.1 mol / L. The cation content of tetradecyltrimethylethylammonium bromide is 2.33 times the CEC of natural montmorillonite. Mix the aqueous solution of tetradecyltrimethylethylammonium bromide with the inorganic acid-modified montmorillonite in a reaction kettle, adjust the liquid-solid ratio to 20:1, and use the hydrothermal method at a reaction temperature of 90 °C. Stir and react for 2.5 hours to modify the intermediate product obtained in step (1). Wash with water to remove the excess surfactant. When the pH of the material is close to 7, dry it at 95 °C to obtain organophilic montmorillonite modified with quaternary ammonium salt surfactant. After pulverization and sieving for use, obtain tetradecyltrimethylammonium bromide-modified organophilic montmorillonite, denoted as TTAB-Mt.

[0062] When the organophilic montmorillonite modified with quaternary ammonium salt surfactant is used in combination with urea as a urease inhibitor, the addition amount is 7% of the weight of urea. Addition method: surface coating.

[0063] Example 3

[0064] Preparation method of a low-cost and highly stable urease inhibitor, the steps are as follows:

[0065] (1): Take 1 kg of natural sodium-based montmorillonite, and measure the cation exchange capacity (CEC = 1255 mmol / kg) of natural sodium-based montmorillonite through the national standard GB 20973-2020. Take 8 L of 1 mol / L concentrated sulfuric acid, add the natural montmorillonite to the concentrated sulfuric acid, and adjust the liquid-solid ratio to 1:8; use the hydrothermal method to stir and react in a high-boron glass reaction kettle for 3 hours at a reaction temperature of 90 °C to remove the impurity cations in the natural montmorillonite and replace them all with hydrogen ions to obtain inorganic acid-modified montmorillonite. After washing with water to remove the excess acid, when the pH of the material is close to 7, dry it at 90 °C for 2 hours, pulverize it to obtain the intermediate product inorganic acid-modified montmorillonite;

[0066] (2): Prepare 30 L of an aqueous solution of didodecyldimethylammonium bromide with a concentration of 0.025 mol / L. The cation content of didodecyldimethylammonium bromide is 0.6 times the CEC of natural montmorillonite. Mix the aqueous solution of didodecyldimethylammonium bromide with the inorganic acid-modified montmorillonite in a reaction kettle, adjust the liquid-solid ratio to 30:1, and use the hydrothermal method at a reaction temperature of 90 °C. Stir and react for 2.5 hours to modify the intermediate product obtained in step (1). Wash with water to remove the excess surfactant. When the pH of the material is close to 7, dry it at 95 °C to obtain organophilic montmorillonite modified with quaternary ammonium salt surfactant. After pulverization and sieving for use, obtain didodecyldimethylammonium bromide-modified organophilic montmorillonite, denoted as DDAB-Mt.

[0067] When the organophilic montmorillonite modified with quaternary ammonium salt surfactant is used in combination with urea as a urease inhibitor, the addition amount is 3% of the weight of urea. Addition method: surface coating.

[0068] Example 4

[0069] The preparation method is the same as that described in Example 1, except that:

[0070] Cetyltrimethylammonium bromide in step (2) was replaced with dodecyltrimethylammonium bromide, and the others were carried out according to Example 1 to obtain the final product dodecyltrimethylammonium bromide modified organic montmorillonite, denoted as: DTAB-Mt.

[0071] Example 5

[0072] The preparation method is the same as that described in Example 1, except that:

[0073] Cetyltrimethylammonium bromide in step (2) was replaced with octadecyltrimethylammonium bromide, and the others were carried out according to Example 1 to obtain the final product octadecyltrimethylammonium bromide modified organic montmorillonite, denoted as: OTAB-Mt.

[0074] Experimental Example 1

[0075] 1. The infrared spectra of montmorillonite before modification and montmorillonite modified by different modifiers in Examples 1-5 are shown in Figure 1 , Figure 1 Among them, after organic modification of montmorillonite in Examples 1-5, the absorption peak of the hydration layer disappeared, and the absorption peak of the C-H chain of the surfactant appeared, proving that the hydrophobicity of the organic montmorillonite increased.

[0076] 2. The XRD curves of montmorillonite before modification and montmorillonite modified by different modifiers in Examples 1-5 are shown in Figure 2 , Figure 2 It shows that the smaller the position of the first peak appears, the larger the layer spacing. The surfactant enters the intercalation structure of montmorillonite, increasing the layer spacing of montmorillonite, which is filled by the surfactant chain. The longer the chain length, the larger the layer spacing, and the higher the amount of urease that the organic modified montmorillonite can inhibit.

[0077] 3. The contact angle curves of montmorillonite before modification and montmorillonite modified by different modifiers in Examples 1-5 are shown in Figure 3 , Figure 3 It shows that the larger the contact angle, the stronger the hydrophobicity of the material surface and the better the inhibitory effect on urease. For montmorillonite modified by surfactants with different chain lengths, the larger the contact angle, the stronger the hydrophobic interaction.

[0078] Indoor Experimental Example 1: Inhibitory effect of organic modified montmorillonite on urease in aqueous solution

[0079] Principle for detecting urease inhibition: Using a series of urea with different concentrations as substrates and phenol red as an indicator, under the action of urease, urea decomposes to produce ammonia, the pH value rises, and under the action of phenol red indicator, the color of the system becomes darker and the absorbance increases. According to the increment of absorbance value, the ammonium nitrogen content produced by urea hydrolysis can be calculated. The lower the ammonium nitrogen content, the better the urease inhibition effect.

[0080] The urea concentration is 2 g / L, which is 30 times that of urease, and the content of urease inhibitor accounts for 10% of urea. The urease selected is commercial jack bean urease. The chromogenic agent is phenol red. The test is set with 5 treatments: no nitrogen (NO), urea (U), urea added with urease (U + urease), urea added with urease and NBPT (U + NBPT + urease), urea added with urease and the organically modified montmorillonite of Example 1 (U + organically modified montmorillonite + urease). The addition amount of urea is 30 times that of urease, and the content of urease inhibitor accounts for 10% of urea. The reaction time is 1 hour.

[0081] The ammonia nitrogen content produced by urea hydrolysis is shown in Table 1 below. In the presence of both urease and urea, urea is rapidly hydrolyzed to generate ammonium nitrogen. The addition of NBPT and organically modified montmorillonite can both reduce the ammonium nitrogen content. Among them, the ammonium nitrogen content in the U + urea + organically modified montmorillonite solution is the lowest, indicating that its urease inhibition effect is better than that of NBPT.

[0082] Table 1. Ammonium nitrogen content in aqueous solution

[0083]

[0084] Indoor Experimental Example 2: Inhibitory effect of combined application of organically modified montmorillonite and urea on urease in soil (soil culture, without crops)

[0085] Put the air-dried soil samples (200 g each) into 300 mL plastic bottles respectively, and mix them with deionized water to make the soil water holding rate reach 40%. All containers are covered with plastic films with 10 holes to allow gas exchange while minimizing water loss. These samples are pre-cultured at 25 °C for 1 week to reduce the change in microbial activity caused by the rewetting of dry soil at the beginning of the test. After the end of the equilibrium period, the soil samples are divided into five treatment groups: no nitrogen fertilizer application (NO), urea (U), urea applied with natural montmorillonite (U + Ca-Mt), urea applied with NBPT (U + NBPT), urea applied with the organically modified montmorillonite of Example 1 (U + CTAB-Mt). Except for the NO treatment, the pure nitrogen application rate for all treatments is 28 kg N / acre, and the added materials account for 5% of urea. All nitrogen application treatments are in the same concentration of 500 μg Ng -1 In the soil. During the whole test process, water is irrigated through the holes every 4 days to keep the soil water content at about 60% of the soil water holding capacity. Compare the urease activities in the soil of different treatments at 0 - 60 days.

[0086] Depend on Figure 5 It can be seen that the urease activity in the soil of the urea combined with organically modified montmorillonite treatment was the lowest from the 3rd to the 60th day of cultivation compared with other treatments. The urease activity in the soil of the urea combined with NBPT treatment was relatively low before 30 days, but it was still slightly higher than that of the organically modified montmorillonite treatment, and the urease activity of the NBPT treatment began to increase after 30 days. Therefore, compared with the mainstream urease inhibitor NBPT treatment on the market, organically modified montmorillonite is better than NBPT in terms of effect and duration.

[0087] Field experiment example 1: Effects of organically modified montmorillonite as a urease inhibitor combined with urea on corn yield composition and soil nitrogen residue

[0088] The soil for the corn plot field test is typical brown soil in Tai'an, where there is a long tradition of wheat and corn rotation. The plot area is 50m 2 The experiment set up five nitrogen fertilizer application treatments, each with 3 replicates, namely no nitrogen fertilizer (N0), urea (U), urea plus natural montmorillonite (U+Ca-Mt), urea plus NBPT (U+NBPT), urea plus organic modified montmorillonite of Example 1 (U+CTAB-Mt). Except for the N0 treatment, the pure nitrogen application rate of all treatments was 14kg N / mu, the added material accounted for 5% of urea, the phosphorus and potassium application rates of all treatments were the same, all fertilizers were applied once, and no topdressing was performed. The results are shown in Tables 2 and 3.

[0089] Table 2 Corn yield composition and yield

[0090]

[0091] Table 3 Residual nitrogen content in soil after corn harvest

[0092]

[0093] From the data in Table 2, it can be seen that the corn yield and yield composition of the treatments of urea combined with organic modified montmorillonite and urea combined with NBPT were significantly higher than those of other treatments. The yield of urea combined with organic modified montmorillonite was the highest, but there was no significant difference compared with the NBPT treatment. Further, from the data in Table 3, it can be seen that the nitrate nitrogen in the soil of the treatment of urea combined with organic modified montmorillonite was 15.47 mg kg -1 The content is significantly higher than that of other inhibitor treatments and can be absorbed and utilized by wheat in the next season. Therefore, the nitrogen inhibition effect of urea combined with organically modified montmorillonite is more significant.

Claims

1. A low-cost and highly stable urease inhibitor, which is prepared by modifying montmorillonite with an inorganic acid and then exchanging hydrogen ions in the inorganic acid-modified montmorillonite with a cationic surfactant.

2. The low-cost and highly stable urease inhibitor according to claim 1, characterized in that: The inorganic acid is concentrated sulfuric acid, the cationic surfactant is one or a mixture of two or more of alkyl trimethyl ammonium salt type quaternary ammonium salt surfactant, alkyl dimethyl ammonium salt type quaternary ammonium salt surfactant, double chain or Gemini cationic quaternary ammonium salt surfactant, and the montmorillonite is natural sodium montmorillonite or natural calcium montmorillonite.

3. The method for preparing the low-cost and highly stable urease inhibitor according to claim 1 comprises the following steps: (1) Inorganic acid modification: add excess concentrated sulfuric acid to montmorillonite and react it by hydrothermal method for 2-3 hours. During the reaction, the impurity cations in the montmorillonite are removed by ion exchange and replaced with hydrogen ions to obtain acid-modified montmorillonite with low thermal stability. The excess acid is removed by water washing. The pH of the material is close to 7 and dried to obtain inorganic acid-modified montmorillonite. (2) Cationic surfactant exchange: The inorganic acid-modified montmorillonite obtained in step (1) is modified by exchanging hydrogen ions in the inorganic acid-modified montmorillonite with a cationic surfactant to obtain an organic montmorillonite modified with a quaternary ammonium salt surfactant, which is a low-cost and highly stable urease inhibitor.

4. The preparation method according to claim 3, characterized in that: In step (1), the concentration of concentrated sulfuric acid is 0.5-2 mol / L, and the amount of concentrated sulfuric acid added is such that the content of concentrated hydrogen sulfate ions is greater than the cation exchange capacity CEC of natural montmorillonite.

5. The preparation method according to claim 3, characterized in that: In step (1), the montmorillonite is natural sodium montmorillonite or natural calcium montmorillonite, with a particle size of less than 100 mesh, and an excess of concentrated sulfuric acid is added to adjust the liquid-to-solid ratio L:kg to 1:5-1:

20.

6. The preparation method according to claim 3, characterized in that: In step (1), the hydrothermal reaction temperature is 85-95°C, and the drying is carried out at 80-90°C.

7. The preparation method according to claim 3, characterized in that: In step (2), the specific method of exchanging the cationic surfactant is as follows: The cationic surfactant is prepared into a surfactant aqueous solution, and the inorganic acid-modified montmorillonite is added to the surfactant aqueous solution. The reaction is carried out by a hydrothermal method for 2-3 hours, and the cationic surfactant exchanges hydrogen ions in the inorganic acid-modified montmorillonite. The excess surfactant is removed by washing with water, and the pH value of the material is close to 7. The material is dried at 90-105° C., crushed and sieved to obtain an organic montmorillonite modified with a quaternary ammonium salt surfactant.

8. The preparation method according to claim 7, characterized in that: In step (2), the cation content of the cationic surfactant is 0.5-4.0 times the cation exchange capacity CEC of montmorillonite, and inorganic acid-modified montmorillonite is added to the surfactant aqueous solution to adjust the liquid-to-solid ratio L:kg to 40:1-10:

1.

9. The preparation method according to claim 3, characterized in that: In step (2), the alkyl chain of the cationic surfactant is an alkyl chain containing 12-20 carbon chains. When the cationic surfactant is a single-chain cationic surfactant, the cation content in the single-chain cationic surfactant is 1.2 times the cation exchange capacity CEC of montmorillonite. When the cationic surfactant is a double-chain cationic surfactant, the cation content in the double-chain cationic surfactant is 0.6 times the cation exchange capacity CEC of montmorillonite. The hydrothermal reaction temperature is 85-95°C.

10. Use of the low-cost and high-stability urease inhibitor according to claim 1 as a urease inhibitor, the addition amount is 3-10% of the weight of urea, and the addition method is internal or surface coating.

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