Value-added urea for rice topdressing and preparation method thereof

Abstract

The invention relates to value-added urea for rice topdressing and a preparation method thereof. The preparation method comprises the following steps: adding an acetate buffer solution into urea liquid between first-stage evaporation and second-stage evaporation of urea production; the method comprises the following steps: adding a composite reducing material into urea liquid after two-stage evaporation in urea production and before granulation; the value-added urea for rice topdressing is obtained. The invention aims to solve the problem that the value-added urea for rice topdressing and a urea device are combined and integrally produced by sequentially adding an acetate buffer solution and a composite reducing material into a urea liquid, and secondary processing is not needed.

Description

Technical Field

[0001] The invention relates to the technical field of fertilizers, and in particular to value-added urea for rice topdressing and a preparation method thereof. Background Art

[0002] Ammonium nitrogen and nitrate nitrogen are the main forms of nitrogen fertilizer directly absorbed by plants, and rice is an ammonium-loving crop. When urea is used as a topdressing fertilizer for rice, after urea is hydrolyzed into ammonium nitrogen, the ammonium nitrogen is volatilized and lost in the form of ammonia gas on the one hand, and converted into nitrate nitrogen on the other hand. At present, the main methods to reduce the ammonia volatilization loss of rice topdressing are to apply urease inhibitors, and to reduce the conversion of ammonium nitrogen to nitrate nitrogen by applying nitrification inhibitors. There are two problems. First, urease inhibitors slow down the conversion of urea to ammonium nitrogen, which may lead to insufficient supply of ammonium nitrogen; second, nitrification inhibitors slow down the conversion of ammonium nitrogen to nitrate nitrogen, which ensures sufficient ammonium nitrogen and is also prone to cause a large amount of ammonia volatilization loss. Therefore, urea used for rice topdressing should have two characteristics. One is to appropriately promote the conversion of urea to ammonium nitrogen while reducing ammonia volatilization loss, and the other is to slow down the conversion of ammonium nitrogen to nitrate nitrogen. At present, there is no value-added urea product that is specially used for rice topdressing and is produced in an integrated manner on a large urea device. Summary of the invention

[0003] In view of this, the main purpose of the present invention is to provide a value-added urea for rice topdressing and a preparation method thereof. The problem to be solved is to realize the integrated production of value-added urea for rice topdressing and a urea device by adding acetate buffer and a composite reducing material into urea liquid in sequence without the need for secondary processing.

[0004] The purpose of the present invention and the technical problem to be solved are achieved by adopting the following technical scheme. The present invention proposes a method for preparing value-added urea for rice topdressing, comprising the following steps:

[0005] Between the first and second evaporation stages of urea production, acetate buffer is added to the urea liquid;

[0006] After the second stage evaporation and before granulation in urea production, the composite reducing material is added into the urea liquid to obtain the value-added urea for rice topdressing.

[0007] The purpose of the present invention and the solution to its technical problems can be further achieved by adopting the following technical measures.

[0008] Preferably, in the aforementioned method for preparing value-added urea for rice topdressing, the method for preparing the acetate buffer comprises the following steps:

[0009] The sodium acetate trihydrate solution and the acetic acid aqueous solution are mixed evenly to obtain an acetate buffer solution with a pH value of 4.8 to 5.8.

[0010] The purpose of the present invention and the solution to its technical problems can be further achieved by adopting the following technical measures.

[0011] Preferably, in the aforementioned method for preparing value-added urea for rice topdressing, the concentration of the sodium acetate trihydrate solution is 0.3-0.5 mol / L; and the concentration of the acetic acid aqueous solution is 0.45-0.75 mol / L.

[0012] Preferably, in the aforementioned method for preparing value-added urea for rice topdressing, the volume ratio of the sodium acetate trihydrate solution to the acetic acid aqueous solution is 1.5:1 to 15:1.

[0013] Preferably, in the aforementioned method for preparing the value-added urea for rice topdressing, the method for preparing the composite reducing material comprises the following steps:

[0014] 1) mixing sulfur powder, ammonium thiosulfate and ferrous sulfate uniformly to obtain a mixture;

[0015] 2) uniformly mixing the mixture obtained in step 1) with glycerol to obtain a glycerol suspension;

[0016] 3) The glycerol suspension obtained in step 2) is mixed evenly with the gum arabic solution to obtain a composite reducing material.

[0017] Preferably, in the aforementioned method for preparing value-added urea for rice topdressing, in step 1), the particle size of the sulfur powder is >300 mesh.

[0018] Preferably, in the aforementioned method for preparing value-added urea for rice topdressing, in step 1), the mass ratio of the sulfur powder, ammonium thiosulfate and ferrous sulfate is 1:2-3:0.5-1.

[0019] Preferably, in the aforementioned method for preparing value-added urea for rice topdressing, in step 2), the mass ratio of the mixture to glycerol is 1:2-5.

[0020] Preferably, in the aforementioned method for preparing value-added urea for rice topdressing, in step 3), the volume ratio of the glycerol suspension to the gum arabic solution is 1:1-2.

[0021] Preferably, in the aforementioned method for preparing value-added urea for rice topdressing, in step 3), the concentration of the gum arabic solution is 0.5-1.5%.

[0022] The purpose of the present invention and the technical problem solved are achieved by adopting the following technical scheme. The present invention proposes a value-added urea for rice topdressing, which comprises an acetate buffer and a composite reducing material, and the volume ratio of the two is (10-50): (5-10); the value-added urea for rice topdressing is prepared by the above method.

[0023] By means of the above technical scheme, the present invention provides a value-added urea for rice topdressing and a preparation method thereof, which has at least the following advantages:

[0024] 1. The acetate buffer of the present invention can promote the conversion of urea into ammonium nitrogen while reducing ammonia volatilization loss, thereby better ensuring the supply of ammonium nitrogen fertilizer for rice;

[0025] 2. The composite reducing material of the present invention can slow down the process of ammonium nitrogen being oxidized to nitrate nitrogen to a certain extent, and the existence time of ammonium nitrogen is prolonged, which is more in line with the demand of rice for nitrogen fertilizer form;

[0026] 3. The present invention can realize the integrated production of value-added urea for rice topdressing and urea device, without the need for secondary processing, thus reducing manpower and production costs.

[0027] The above description is only an overview of the technical solution of the present invention. In order to more clearly understand the technical means of the present invention and implement it according to the contents of the specification, the preferred embodiments of the present invention are described in detail as follows. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a characteristic diagram of urea nitrogen residue in soil of the value-added urea (ZU) for rice topdressing of the present invention;

[0029] Figure 2 This is a graph showing the change in soil ammonium nitrogen content of the value-added urea (ZU) for rice topdressing of the present invention;

[0030] Figure 3 This is a characteristic diagram of ammonia volatilization of the value-added urea for rice topdressing of the present invention. DETAILED DESCRIPTION

[0031] To further explain the technical means and effects adopted by the present invention to achieve the predetermined invention purpose, the following is a detailed description of the specific implementation, structure, characteristics and effects of a rice topdressing value-added urea and a preparation method thereof proposed according to the present invention in conjunction with the preferred embodiments. In the following description, different "one embodiment" or "embodiment" do not necessarily refer to the same embodiment. In addition, the specific features, structures or characteristics in one or more embodiments can be combined in any suitable form.

[0032] The following materials or reagents, unless otherwise specified, were commercially available.

[0033] Some embodiments of the present invention provide a method for preparing value-added urea for rice topdressing, comprising the following steps:

[0034] Between the first stage and the second stage of evaporation in urea production, an acetate buffer is added to the urea liquid; after the second stage of evaporation in urea production and before granulation, a composite reducing material is added to the urea liquid; and the value-added urea for rice topdressing is obtained. The acetate buffer includes sodium acetate trihydrate and acetic acid, and the purpose is to provide acidic conditions, promote the hydrolysis of urea into ammonium nitrogen, and reduce the loss of ammonia volatilization; the composite reducing material includes ammonium thiosulfate, ferrous sulfate, sulfur powder, glycerin, and gum arabic, and the purpose is to create certain reducing conditions and slow down the conversion of ammonium nitrogen into nitrate nitrogen.

[0035] In specific implementation, the preparation method may include:

[0036] (1) Between the first and second evaporation stages of urea production, buffer C is added to the urea liquid pipeline using a metering pump, with the addition amount being 10 to 50 L per ton of urea;

[0037] (2) After the second stage evaporation of urea production and before granulation, the composite reducing material F is added into the urea liquid pipeline by a metering pump, and the addition amount is 5 to 10 L per ton of urea;

[0038] (3) Since both synergistic materials are liquid, their flow rates need to be calculated based on the capacity of the urea production unit. The hourly urea output is set to Y, in units of t / h; the amount of synergistic material added is set to X, in units of L / t urea; the synergistic material addition flow rate is set to W, in units of L / h; and the concentration of urea liquid is set to C, in units of %.

[0039] W(buffer)=X×Y=10~50L×Y;

[0040] W(reduced)=X×Y=5~10L×Y.

[0041] For example: if the urea production capacity is 10t / h and the amount of enhancement material added per ton of urea is 20L, then W = 10×20 = 200L / h.

[0042] The above-mentioned preparation method can also be called "two-point addition continuous method", that is, buffer solution C and composite reducing material F are added to urea solution at two locations in different working sections at the same time, and then enter the urea granulation system to meet the needs of rice production for accelerating the conversion of urea into ammonium nitrogen, reducing ammonia volatilization, and slowing down the nitrification process, and realize the one-time production of value-added urea for rice topdressing on the urea production device without secondary processing.

[0043] In some optional embodiments, the volume ratio of the acetate buffer and the composite reducing material can be set to (10-50): (5-10). This setting can reduce the ammonia volatilization of ammonium nitrogen in the soil on the one hand, and reduce the oxidation of ammonium nitrogen to nitrate nitrogen on the other hand, thereby better ensuring the supply of ammonium nitrogen.

[0044] In some optional embodiments, the method for preparing the acetate buffer comprises the following steps:

[0045] The sodium acetate trihydrate solution and the acetic acid aqueous solution are mixed evenly to obtain an acetate buffer solution with a pH value of 4.8 to 5.8. If the pH value is lower than 4.8, the addition process may corrode stainless steel; if the pH value is higher than 5.8, the effect of reducing ammonia volatilization loss is affected.

[0046] In some optional embodiments, the concentration of the sodium acetate trihydrate solution can be set to 0.3-0.5 mol / L; if the concentration of the sodium acetate trihydrate solution is less than 0.3 mol / L, the concentration is too low, which may lead to excessively high water content in urea; if the concentration is greater than 0.5 mol / L, the concentration is too high, which may affect the stability of the solution (such as low-temperature crystallization, etc.), and may be inconvenient to use. The concentration of the acetic acid aqueous solution can be set to 0.45-0.75 mol / L. If the concentration of the acetic acid aqueous solution is less than 0.45 mol / L, the concentration is too low, which may lead to excessively high water content in urea; if the concentration is greater than 0.75 mol / L, the concentration is too high, which may affect the stability of the solution (such as low-temperature crystallization, etc.), and may be inconvenient to use.

[0047] In some optional embodiments, the volume ratio of the sodium acetate trihydrate solution to the acetic acid aqueous solution can be set to 1.5: 1 to 15: 1. This is closely related to the adjustment of the pH value, and these ratios are selected to maintain the pH value between 4.8 and 5.8.

[0048] In some optional embodiments, the method for preparing the composite reducing material comprises the following steps:

[0049] 1) mixing sulfur powder, ammonium thiosulfate and ferrous sulfate uniformly to obtain a mixture;

[0050] 2) uniformly mixing the mixture obtained in step 1) with glycerol to obtain a glycerol suspension;

[0051] 3) The glycerol suspension obtained in step 2) is mixed evenly with the gum arabic solution to obtain a composite reducing material.

[0052] In some optional embodiments, in step 1), the particle size of the sulfur powder is greater than 300 meshes. This is to make the sulfur powder easier to suspend and keep the suspension stable.

[0053] In some optional embodiments, in step 1), the mass ratio of the sulfur powder, ammonium thiosulfate and ferrous sulfate can be set to 1:2-3:0.5-1. This setting is to solve the problem of reducing ions that quickly dissolve in the soil solution to solve the shortage reduction problem, while sulfur can solve the reduction problem for a longer time.

[0054] In some optional embodiments, in step 2), the mass ratio of the mixture to glycerol can be set to 1:2 to 5. If the mass ratio of the mixture to glycerol is less than 1:5, the ratio is too low, affecting the reduction effect; if the mass ratio of the mixture to glycerol is greater than 1:2, the ratio is too high, the dispersibility decreases, and it is inconvenient to add to urea later.

[0055] In some optional embodiments, in step 3), the volume ratio of the glycerol suspension to the gum arabic solution can be set to 1:1-2. This setting is to further enhance the suspension performance of the liquid.

[0056] In some optional embodiments, in step 3), considering the ease of operation, the concentration of the gum arabic solution can be set to 0.5-1.5%.

[0057] Some embodiments of the present invention also provide a value-added urea for rice topdressing, wherein the value-added urea for rice topdressing comprises an acetate buffer and a composite reducing material, and the volume ratio of the two is (10-50): (5-10); the value-added urea for rice topdressing is prepared by the above method.

[0058] In the above technical scheme, the present invention adds acetate buffer and composite reducing material into urea liquid in sequence, thereby realizing integrated production of value-added urea for rice topdressing and urea device without secondary processing.

[0059] The specific implementation methods of the present invention are further described in detail below in conjunction with the embodiments, but it should not be understood as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made to the present invention by technicians in this field based on the above-mentioned contents of the present invention still fall within the scope of protection of the present invention.

[0060] Unless otherwise specified, the materials, reagents, etc. involved below are all commercially available products well known to those skilled in the art; unless otherwise specified, the methods described are all methods well known in the art. Unless otherwise defined, the technical terms or scientific terms used should have the common meanings understood by ordinary technicians in the field to which the present invention belongs.

[0061] Example 1

[0062] This embodiment provides a method for preparing value-added urea for rice topdressing, comprising the following steps:

[0063] 1. Preparation of synergistic materials

[0064] (1) preparing 0.3 mol / L sodium acetate trihydrate aqueous solution A and 0.45 mol / L acetic acid aqueous solution B respectively;

[0065] (2) mixing sodium acetate trihydrate solution A and acetic acid solution B in a volume ratio of 1.5:1 to obtain acetate buffer solution C with a pH of 4.8;

[0066] (3) mixing sulfur powder (300 mesh), ammonium thiosulfate, and ferrous sulfate in a mass ratio of 1:2:0.5 to obtain a mixture D;

[0067] (4) mixing the mixture D and glycerol in a mass ratio of 1:2 to obtain a glycerol suspension E;

[0068] (5) The glycerol suspension E and a 1% by mass percent gum arabic solution were mixed uniformly in a volume ratio of 1:1 to obtain a composite reducing material F.

[0069] 2. Value-added urea production

[0070] (1) Between the first and second evaporation stages of urea production, buffer C is added to the urea liquid pipeline using a metering pump, with the addition amount being 10 L per ton of urea;

[0071] (2) After the second stage evaporation and before granulation in urea production, the composite reducing material F is added into the urea liquid pipeline by a metering pump, and the addition amount is 5L per ton of urea;

[0072] (3) The hourly output of the urea plant is 5 tons. The addition flow rate of the synergistic material is set to W, in L / h. W (buffer) = 10 × 5 = 50 L / h; W (reduction) = 5 × 5 = 25 L / h.

[0073] Example 2

[0074] This embodiment provides a method for preparing value-added urea for rice topdressing, comprising the following steps:

[0075] 1. Preparation of synergistic materials

[0076] (1) preparing 0.4 mol / L sodium acetate trihydrate aqueous solution A and 0.6 mol / L acetic acid aqueous solution B respectively;

[0077] (2) mixing sodium acetate trihydrate solution A and acetic acid solution B in a volume ratio of 6:1 to obtain acetate buffer solution C with a pH of 5.4;

[0078] (3) sulfur powder (400 mesh), ammonium thiosulfate, and ferrous sulfate were uniformly mixed in a mass ratio of 1:2.5:0.75 to obtain a mixture D;

[0079] (4) mixing the mixture D and glycerol in a mass ratio of 1:3 to obtain a glycerol suspension E;

[0080] (5) The glycerol suspension E and a 1% by mass concentration gum arabic solution were mixed uniformly in a volume ratio of 1:1.5 to obtain a composite reducing material F.

[0081] 2. Value-added urea production

[0082] (1) Between the first and second evaporation stages of urea production, buffer C is added to the urea liquid pipeline using a metering pump, with the addition amount being 30 L per ton of urea;

[0083] (2) After the second stage evaporation and before granulation in urea production, the composite reducing material F is added into the urea liquid pipeline by a metering pump, and the addition amount is 7L per ton of urea;

[0084] (3) The hourly output of the urea plant is 6 tons. The addition flow rate of the synergistic material is set to W, in L / h. W (buffer) = 30 × 6 = 180 L / h; W (reduction) = 7 × 6 = 42 L / h.

[0085] Example 3

[0086] This embodiment provides a method for preparing value-added urea for rice topdressing, comprising the following steps:

[0087] 1. Preparation of synergistic materials

[0088] (1) preparing 0.5 mol / L sodium acetate trihydrate aqueous solution A and 0.75 mol / L acetic acid aqueous solution B respectively;

[0089] (2) mixing sodium acetate trihydrate solution A and acetic acid solution B in a volume ratio of 15:1 to obtain acetate buffer solution C with a pH of 5.8;

[0090] (3) sulfur powder (500 mesh), ammonium thiosulfate, and ferrous sulfate were mixed in a mass ratio of 1:2:0.5 to obtain a mixture D;

[0091] (4) mixing the mixture D and glycerol in a mass ratio of 1:5 to obtain a glycerol suspension E;

[0092] (5) The glycerol suspension E and a 1% by mass percent gum arabic solution were mixed uniformly in a volume ratio of 1:2 to obtain a composite reducing material F.

[0093] 2. Value-added urea production

[0094] (1) Between the first and second evaporation stages of urea production, buffer C is added to the urea liquid pipeline using a metering pump, with the addition amount being 50 L per ton of urea;

[0095] (2) After the second stage evaporation and before granulation in urea production, the composite reducing material F is added into the urea liquid pipeline by a metering pump, and the addition amount is 10L per ton of urea;

[0096] (3) The hourly output of the urea plant is 10 tons; the addition flow rate of the synergistic material is set to W, in L / h. W (buffer) = 50 × 10 = 500 L / h; W (reduction) = 10 × 10 = 100 L / h.

[0097] Application Examples

[0098] The performance of the value-added urea prepared in the three embodiments of the present invention is similar. The value-added urea prepared in Example 2 is used for rice topdressing to perform a performance test.

[0099] 1. Conversion characteristics of value-added urea for rice topdressing in soil

[0100] (1) Test method:

[0101] The experiment set up three treatments: (1) a control (CK) without nitrogen fertilizer; (2) ordinary urea (U); (3) the value-added urea for rice topdressing described in Example 2 (RU). The amount of nitrogen applied in treatments (2) and (3) was 0.3 g / kg dry soil. Each treatment was repeated 3 times. Weigh 100 g of air-dried soil that passed through a 2 mm sieve, mix it evenly with the test urea, put it into a 250 mL plastic culture bottle, adjust the soil moisture content to 20% with pure water, seal it with plastic wrap, and culture it continuously in a culture room at 25°C. Collect fresh soil samples on the 0.25, 0.5, 1, 2, 3, 5, 7, 10, 14 and 28 days of culture to determine the content of urea nitrogen and ammonium nitrogen.

[0102] (2) Test results

[0103] 1) Changes in soil urea residual rate of value-added urea

[0104] The urea residue after soil culture test can reflect the conversion rate of urea in soil. Figure 1 It can be seen that with the extension of the cultivation time, the urea nitrogen content of the soil treated with U and RU showed a continuous downward trend; the urea conversion rate of the RU treatment was significantly faster than that of the U treatment. The urea of ​​the RU treatment was completely converted on the 10th day of cultivation, while the urea of ​​the U treatment was completely converted after 14 days. Within 28 days, the urea nitrogen content of the soil treated with RU was 15.2% lower than that of the U treatment on average; from the urea nitrogen content of the 2nd to the 10th day of cultivation, the reduction of RU compared with the U treatment reached 28.0%. This shows that the value-added urea for rice topdressing in Example 2 of the present invention can promote the hydrolysis of urea to a certain extent.

[0105] 2) Changes in soil ammonium nitrogen with added urea

[0106] The ammonium nitrogen content in the soil can better illustrate the advantage of using value-added urea as rice topdressing in increasing the ammonium nitrogen in the soil. Figure 2 It can be seen that within one day of soil cultivation, the ammonium nitrogen content of the soil in the RU treatment was 11.7% higher than that in the U treatment; from the 2nd to the 28th day of cultivation, the ammonium nitrogen content of the soil in the RU treatment was 80.3% higher than that in the U treatment; from the 10th to the 28th day of cultivation, the ammonium nitrogen content of the soil in the RU treatment was 4.1 times that in the U treatment on average. It can be seen that the value-added urea for rice topdressing in Example 2 of the present invention can significantly improve the ammonium nitrogen supply capacity within one month after fertilization, which is related to the buffer reducing ammonia volatilization loss and may also be related to the composite reducing material reducing the conversion of ammonium nitrogen to nitrate nitrogen.

[0107] 3. Ammonia volatilization characteristics of value-added urea used as rice topdressing in soil

[0108] Two treatments were set up: ordinary urea U and value-added urea RU for rice topdressing, and each treatment was repeated 3 times. Weigh 100g of air-dried soil that passed through a 2mm sieve and place it in a 1000mL culture bottle with a small hole of about 2mm drilled on the lid. The soil moisture content was adjusted to 18wt%, and pre-cultured in a constant temperature incubator at 25℃ for 3 days to enhance the microbial activity of the soil so that the ammonia volatilization loss of each treatment can be evaluated in a shorter time. After the pre-culture is completed, the test urea is thoroughly mixed with the soil, and the nitrogen application rate is 0.3g / kg dry soil. Culture in a climate chamber at 25℃ in the dark, and samples are taken on the 1st, 2nd and 3rd days of culture. The "ventilation-sponge absorption method" is used to collect NH3, and the ammonium nitrogen absorbed by the sponge is extracted with 1mol / L KCl solution, which is the ammonia volatilization nitrogen, and the unit is g / m 2 .

[0109] The comparison of ammonia volatilization losses between RU and U can further explain and illustrate why the soil ammonium nitrogen in RU treatment is higher. Figure 3 It can be seen that on the 1st, 2nd and 3rd day of cultivation, the ammonia volatilization of the RU treatment was reduced by 12.7%, 55.1% and 39.1% respectively compared with the U treatment, and the average reduction in three days was 42.3%. RU can ensure the supply of ammonium nitrogen in the soil to rice by reducing the loss of ammonia volatilization.

[0110] In the above embodiments, the description of each embodiment has its own emphasis. For parts that are not described in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0111] The numerical range described in the present invention includes all the numerical values ​​within the range, and includes the range value formed by any two numerical values ​​within the range. Different numerical values ​​of the same indicator appearing in all embodiments of the present invention can be arbitrarily combined to form a range value.

[0112] The technical features in the claims and / or the specification of the present invention may be combined, and the combination is not limited to the combination obtained by reference in the claims. The technical solution obtained by combining the technical features in the claims and / or the specification is also within the protection scope of the present invention.

[0113] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Any simple modification, equivalent change and modification made to the above embodiment according to the technical essence of the present invention still falls within the scope of the technical solution of the present invention.

Claims

1. A method for preparing value-added urea for rice topdressing, characterized in that: The following steps are involved: Between the first and second evaporation stages of urea production, acetate buffer is added to the urea liquid; After the second stage evaporation and before granulation in urea production, the composite reducing material is added into the urea liquid to obtain the value-added urea for rice topdressing.

2. The method for preparing the value-added urea for rice topdressing according to claim 1, characterized in that: The preparation method of the acetate buffer comprises the following steps: The sodium acetate trihydrate solution and the acetic acid aqueous solution are mixed evenly to obtain an acetate buffer solution with a pH value of 4.8 to 5.

8.

3. The method for preparing the value-added urea for rice topdressing according to claim 2, characterized in that: The concentration of the sodium acetate trihydrate solution is 0.3-0.5 mol / L; the concentration of the acetic acid aqueous solution is 0.45-0.75 mol / L.

4. The method for preparing the value-added urea for rice topdressing according to claim 2, characterized in that: The volume ratio of the sodium acetate trihydrate solution to the acetic acid aqueous solution is 1.5:1 to 15:

1.

5. The method for preparing the value-added urea for rice topdressing according to claim 1, characterized in that: The preparation method of the composite reducing material comprises the following steps: 1) mixing sulfur powder, ammonium thiosulfate and ferrous sulfate uniformly to obtain a mixture; 2) uniformly mixing the mixture obtained in step 1) with glycerol to obtain a glycerol suspension; 3) The glycerol suspension obtained in step 2) is mixed evenly with the gum arabic solution to obtain a composite reducing material.

6. The method for preparing the value-added urea for rice topdressing according to claim 5, characterized in that: In step 1), the particle size of the sulfur powder is greater than 300 meshes.

7. The method for preparing the value-added urea for rice topdressing according to claim 5, characterized in that: In step 1), the mass ratio of the sulfur powder, ammonium thiosulfate and ferrous sulfate is 1:2-3:0.5-1.

8. The method for preparing the value-added urea for rice topdressing according to claim 5, characterized in that: In step 2), the mass ratio of the mixture to glycerol is 1:2-5.

9. The method for preparing value-added urea for rice topdressing according to claim 5, characterized in that: In step 3), the volume ratio of the glycerol suspension to the gum arabic solution is 1:1-2; and the concentration of the gum arabic solution is 0.5-1.5%.

10. A value-added urea for rice topdressing, characterized in that: The value-added urea for rice topdressing comprises acetate buffer and composite reducing material, and the volume ratio of the two is (10-50):(5-10); the value-added urea for rice topdressing is prepared by the method described in any one of claims 1-9.

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