Simplified preparation process and application method of double-control nitrogen release suspension type urea formaldehyde multi-nutrient-element liquid fertilizer

Abstract

The invention belongs to the technical field of slow / controlled release fertilizers, and particularly relates to a simplified preparation process and an application method of a double-control nitrogen release suspension type urea formaldehyde multi-nutrient-element liquid fertilizer. After the reaction, adding a urea formaldehyde particle stabilizer, uniformly mixing, and continuing the reaction; the preparation method comprises the following steps: adding a fertilizer system containing at least one nutrient element except nitrogen and a nutrient synergist, and uniformly stirring to obtain a double-control nitrogen release suspension type urea formaldehyde multi-nutrient element liquid fertilizer prepolymer; and reacting the double-controlled nitrogen release suspension type urea formaldehyde multi-nutrient element liquid fertilizer prepolymer in high-speed shearing dispersion equipment to obtain the double-controlled nitrogen release suspension type urea formaldehyde multi-nutrient element liquid fertilizer. The flowability of the liquid fertilizer is remarkably improved by controlling the structure of dispersoid particles mainly containing urea formaldehyde in the liquid fertilizer, and the liquid fertilizer does not cake after being placed for a long time.

Description

Technical Field

[0001] The invention belongs to the technical field of slow / controlled release fertilizers, and in particular relates to a simplified preparation process and an application method of a double-controlled nitrogen release suspended urea-formaldehyde multi-nutrient element liquid fertilizer. Background Art

[0002] The low nutrient utilization efficiency of traditional fertilizers leads to resource waste and environmental pollution, so slow / controlled-release fertilizers came into being. Urea-formaldehyde-based slow-release nitrogen fertilizers have become a popular variety in the field of slow / controlled-release fertilizers due to their advantages such as good slow-release effect and lasting fertilizer effect. They are of great significance in promoting the upgrading of the nitrogen fertilizer industry and alleviating environmental pressure.

[0003] Liquid fertilizers have attracted widespread attention due to their advantages such as fast absorption, flexible formulation, and environmental protection, especially in today's era of rapid development of water / fertilizer integrated technology. Urea-formaldehyde liquid fertilizers are mainly divided into two types: clear liquid type and suspended type. Clear liquid urea-formaldehyde liquid fertilizers have limited nitrogen slow-release effect and poor storage stability; suspended urea-formaldehyde liquid fertilizers have problems such as complicated preparation process and difficult to control product quality.

[0004] Nitrogen, which ranks first among the mineral nutrients required by plants, is an essential nutrient for crop growth and has a decisive influence on the growth and yield of crops. However, traditional nitrogen fertilizers, such as urea, have low nitrogen utilization rates due to volatilization, leaching and nitrification during use. Currently, the utilization rate in the season is only 30%-50%, which not only increases production costs, but also poses a serious threat to the environment. Therefore, improving the utilization rate of nitrogen fertilizers and reducing nitrogen loss and the resulting environmental pollution have become one of the focuses of agricultural research.

[0005] Fertilizer enhancers refer to a class of substances that are produced through biological, physical, and chemical processes and added to fertilizers to stimulate plant nutrient absorption, increase nutrient effectiveness, or improve nutrient utilization efficiency. They are mainly divided into two categories: biological fertilizer enhancers and chemical fertilizer enhancers. Among them, chemical fertilizer enhancers are mainly divided into urease inhibitors and nitrification inhibitors. Urease inhibitors inhibit the activity of urease in the soil, delay the hydrolysis of urea, thereby reducing ammonia volatilization in the soil and improving the utilization efficiency of nitrogen fertilizers. Nitrification inhibitors can inhibit the nitrification rate of nitrogen in the soil and reduce NO3 - The accumulation, leaching and emission losses of N2O can be reduced, thereby improving the nitrogen use efficiency of fertilizers. Summary of the invention

[0006] In order to solve the problems that the preparation process of existing urea-formaldehyde liquid fertilizer is complicated, the product quality is difficult to control, the nitrogen slow-release effect is limited and the storage stability is poor, the present invention provides a simplified preparation process and application method of a double-controlled nitrogen release suspended urea-formaldehyde multi-nutrient element liquid fertilizer.

[0007] The present invention is achieved through the following technical scheme: a simplified preparation process of a dual-controlled nitrogen release suspended urea-formaldehyde multi-nutrient element liquid fertilizer, comprising the following steps: (1) Add a certain amount of urea, formaldehyde, cellulose and water into reactor A, wherein the molar ratio of urea to formaldehyde is 0.1-1:1, the mass ratio of cellulose to the total mass of urea and formaldehyde is 1-10:1, and the amount of water added is 10-80% of the total mass of urea, formaldehyde and cellulose; react at 50-90°C for 0.5-3h, dry the obtained reaction product at 80-120°C to constant weight, and grind it to obtain urea-formaldehyde grafted cellulose, which is a urea-formaldehyde particle stabilizer; (2) adding a certain amount of urea, formaldehyde and water into the reactor B, wherein the molar ratio of urea to formaldehyde is 10-20:1, and the amount of water added is 10-50% of the total mass of urea and formaldehyde; reacting at 30-60° C. for 0.5-3 h, adding the urea-formaldehyde granule stabilizer obtained in step (1) and mixing evenly, and continuing the reaction for 0.5-3 h; adding a fertilizer system containing at least one nutrient element other than nitrogen and a nutrient synergist, stirring evenly to obtain a dual-controlled nitrogen release suspended urea-formaldehyde multi-nutrient element liquid fertilizer prepolymer; (3) The dual-nitrogen-release suspended urea-formaldehyde multi-nutrient element liquid fertilizer prepolymer is reacted in a high-speed shear dispersion device for 15 to 30 minutes to obtain a dual-nitrogen-release suspended urea-formaldehyde multi-nutrient element liquid fertilizer.

[0008] As a further improvement of the process technology scheme of the present invention, in step (1) and step (2), the formaldehyde is at least one of formaldehyde aqueous solution, solid paraformaldehyde, and gaseous formaldehyde.

[0009] As a further improvement of the process technology scheme of the present invention, in step (1), the cellulose is selected from at least one of carboxymethyl cellulose, methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose and polyanionic cellulose.

[0010] As a further improvement of the process technology scheme of the present invention, in step (2), the amount of the urea-formaldehyde particle stabilizer added is 0-10% of the total mass of urea and formaldehyde in step (2) and is not 0.

[0011] As a further improvement of the process technology scheme of the present invention, in step (2), the fertilizer system containing at least one nutrient element other than nitrogen is selected from at least one of phosphate fertilizers, potassium salt fertilizers, medium element fertilizers and trace element fertilizers.

[0012] As a further improvement of the process technology scheme of the present invention, the phosphate fertilizer is selected from at least one of hydroxyapatite, diammonium phosphate, superphosphate, potassium tripolyphosphate and potassium dihydrogen phosphate; the potassium salt fertilizer is selected from at least one of potassium sulfate, potassium chloride, potassium nitrate and potassium carbonate.

[0013] As a further improvement of the process technology scheme of the present invention, in step (2), the nutrient enhancer is a chemical nutrient enhancer; the chemical nutrient enhancer is selected from at least one of a urease inhibitor and a nitrification inhibitor.

[0014] As a further improvement of the process technology scheme of the present invention, in step (2), the mass ratio of the added amount of the fertilizer system containing at least one nutrient element other than nitrogen to the urea in step (2) is 0-5:1 and is not 0; the added amount of the nutrient enhancer is 0-5% of the mass of the urea in step (2) and is not 0.

[0015] As a further improvement of the process technology scheme of the present invention, in step (3), the high-speed shearing and dispersing equipment is selected from one of a high-speed dispersing emulsifier, a colloid mill and a sand mill.

[0016] On the other hand, the present invention provides a method for applying a dual-controlled nitrogen-releasing suspended urea-formaldehyde multi-nutrient liquid fertilizer, including foliar spraying, seed soaking, root dipping, injection, drench application, pouring, sprinkler irrigation or drip irrigation; the application amount is 8 to 15 kg nitrogen / mu.

[0017] The simplified preparation process of the dual-controlled nitrogen-releasing suspended urea-formaldehyde multi-nutrient element liquid fertilizer provided by the present invention has the following advantages compared with the prior art: (1) The suspended urea-formaldehyde liquid fertilizer produced by the process of the present invention significantly improves the fluidity of the liquid fertilizer by controlling the structure of the dispersed particles mainly composed of urea-formaldehyde, and does not agglomerate when placed for a long time. In addition, the liquid fertilizer has excellent dispersibility and can be mixed with irrigation water in any proportion. The mixed system has good stability and low sedimentation rate when placed for a long time, and will not clog the application system during use.

[0018] (2) The suspended urea-formaldehyde liquid fertilizer produced by the process of the present invention can flexibly adjust the content of macro-, medium- and trace nutrients according to the soil characteristics of different regions and the nutrient requirements of crops at different growth stages, and accurately meet the requirements of crops in different regions for various nutrients throughout the growth cycle.

[0019] (3) The process of the present invention improves the slow-release effect and stability of liquid fertilizer by optimizing the structure of dispersed particles mainly composed of urea-formaldehyde. In addition, after application, the urea-formaldehyde particles in the liquid fertilizer form a stable network structure in the soil, which can slowly release nutrients, prolong the effective action time of the fertilizer, reduce nutrient loss, and improve fertilizer utilization efficiency.

[0020] (4) Using dual control technology to improve nitrogen utilization efficiency. The present invention effectively combines urea-formaldehyde slow-release technology with chemical nutrient inhibition technology, using urea-formaldehyde slow-release fertilizer to control the nitrogen release rate, while using urease inhibitors to inhibit the hydrolysis of urea in the soil, or using nitrification inhibitors to inhibit the nitrification of ammonium nitrogen in the soil, to achieve dual controlled release of nitrogen, thereby significantly improving the utilization efficiency of nitrogen fertilizers and effectively reducing nitrogen loss and the resulting environmental pollution. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.

[0022] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0023] Figure 1 The appearance effects of the dual-nitrogen-release suspended urea-formaldehyde multi-nutrient liquid fertilizer prepared in Example 2 on the 0th day and the 30th day and the analysis results of the laser pen Tyndall effect.

[0024] Figure 2 This is a curve showing the change of dispersed phase particle size over time of the dual-nitrogen-release suspended urea-formaldehyde multi-nutrient liquid fertilizer prepared in Example 2.

[0025] Figure 3 This is the static water nitrogen release curve of the dual-controlled nitrogen release suspended urea-formaldehyde multi-nutrient element liquid fertilizer prepared in Example 2. DETAILED DESCRIPTION

[0026] In order to more clearly understand the above-mentioned objectives, features and advantages of the present invention, the scheme of the present invention will be further described below. It should be noted that the embodiments of the present invention and the features in the embodiments can be combined with each other without conflict.

[0027] In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention may also be implemented in other ways different from those described herein; it is obvious that the embodiments in the specification are only part of the embodiments of the present invention, rather than all of the embodiments.

[0028] The present invention provides a specific embodiment of a simplified preparation process of a dual-controlled nitrogen-releasing suspended urea-formaldehyde multi-nutrient element liquid fertilizer, comprising the following steps: (1) Add a certain amount of urea, formaldehyde, cellulose and water into reactor A, wherein the molar ratio of urea to formaldehyde is 0.1-1:1, the mass ratio of cellulose to the total mass of urea and formaldehyde is 1-10:1, and the amount of water added is 10-80% of the total mass of urea, formaldehyde and cellulose; react at 50-90°C for 0.5-3h, dry the obtained reaction product at 80-120°C to constant weight, and grind it to obtain urea-formaldehyde grafted cellulose, which is a urea-formaldehyde particle stabilizer; (2) adding a certain amount of urea, formaldehyde and water into the reactor B, wherein the molar ratio of urea to formaldehyde is 10-20:1, and the amount of water added is 10-50% of the total mass of urea and formaldehyde; reacting at 30-60° C. for 0.5-3 h, adding the urea-formaldehyde granule stabilizer obtained in step (1) and mixing evenly, and continuing the reaction for 0.5-3 h; adding a fertilizer system containing at least one nutrient element other than nitrogen and a nutrient synergist, stirring evenly to obtain a dual-controlled nitrogen release suspended urea-formaldehyde multi-nutrient element liquid fertilizer prepolymer; (3) The dual-nitrogen-release suspended urea-formaldehyde multi-nutrient element liquid fertilizer prepolymer is reacted in a high-speed shear dispersion device for 15 to 30 minutes to obtain a dual-nitrogen-release suspended urea-formaldehyde multi-nutrient element liquid fertilizer.

[0029] Preferably, the mass ratio of the added amount of the fertilizer system containing at least one nutrient element other than nitrogen to the urea in step (2) is 0-5:1 and is not 0; the added amount of the nutrient enhancer is 0-5% of the mass of the urea in step (2) and is not 0.

[0030] In one embodiment provided by the present invention, in step (1) and step (2), the formaldehyde is at least one of a formaldehyde aqueous solution, solid paraformaldehyde, and gaseous formaldehyde.

[0031] In another embodiment provided by the present invention, in step (1), the cellulose is selected from at least one of carboxymethyl cellulose, methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose and polyanionic cellulose.

[0032] In one embodiment provided by the present invention, in step (2), the amount of the urea-formaldehyde particle stabilizer added is 0-10% of the total mass of urea and formaldehyde in step (2) and is not 0.

[0033] In another embodiment provided by the present invention, in step (2), the fertilizer system containing at least one nutrient element other than nitrogen is selected from at least one of phosphate fertilizers, potassium salt fertilizers, medium element fertilizers and trace element fertilizers.

[0034] In one embodiment provided by the present invention, the phosphate fertilizer is selected from at least one of hydroxyapatite, diammonium phosphate, superphosphate, potassium tripolyphosphate and potassium dihydrogen phosphate; the potassium salt fertilizer is selected from at least one of potassium sulfate, potassium chloride, potassium nitrate and potassium carbonate.

[0035] In another embodiment provided by the present invention, in step (2), the nutrient enhancer is a chemical nutrient enhancer; the chemical nutrient enhancer is selected from at least one of a urease inhibitor and a nitrification inhibitor. The urease inhibitor can be any one of an organic urease inhibitor, an inorganic urease inhibitor, a natural product urease inhibitor, and an artificially synthesized compound urease inhibitor; the nitrification inhibitor can be any one of a heterocyclic compound nitrification inhibitor, a thiourea compound nitrification inhibitor, and a biologically derived nitrification inhibitor.

[0036] In one embodiment provided by the present invention, in step (3), the high-speed shearing and dispersing equipment is selected from a high-speed dispersing emulsifier, a colloid mill and a sand mill.

[0037] On the other hand, the present invention provides a method for applying a dual-controlled nitrogen-releasing suspended urea-formaldehyde multi-nutrient liquid fertilizer, including foliar spraying, seed soaking, root dipping, injection, drench application, pouring, sprinkler irrigation or drip irrigation; the application amount is 8 to 15 kg nitrogen / mu.

[0038] The performance test of the present invention adopts the following standards: 1) Laser pen Tyndall effect test: Take an appropriate amount of liquid fertilizer and dilute it according to the mass ratio of liquid fertilizer to deionized water of 1:10. Place the diluted uniform liquid fertilizer at room temperature and let it stand for 30 minutes. Then use a laser pen to illuminate it in a dark room to observe whether a clear light path appears and record whether the Tyndall effect occurs.

[0039] 2) Test of dispersed phase particle size in suspended liquid fertilizer: Use a scraper fineness meter with a range of 0-50μm. Drop 2-3 drops of sample into the deep groove of the scraper fineness meter, scrape it from top to bottom at a constant speed within 3 seconds, make the viewing angle and the groove plane form an angle of 15-30° within 5 seconds, quickly observe the distribution of particles in the scratches against the light, and read the particle size value according to the scale line.

[0040] 3) Test for water-insoluble matter in suspended liquid fertilizer: At room temperature (25±5)℃, weigh 1g of liquid fertilizer (accurate to 0.001g), place it in a beaker, add 250mL of water, stir thoroughly for 3min, let stand for (15±3)min, and then filter with a glass crucible filter that has been dried to constant weight in a drying oven at (110±2)℃. Place the filter after filtration in a drying oven at (110±2)℃ for 1h, take it out, cool it to room temperature, and weigh it. The blank test is exactly the same except that no sample is added.

[0041] 4) Liquid fertilizer slow-release performance test: Characterize the nitrogen nutrient release performance and initial release rate through static water release test. Add 5mL of liquid fertilizer directly into a bottle containing 100mL of deionized water, incubate in a constant temperature water bath at 25℃, and take samples at 1, 3, 5, 7, 10, 14 and 28 days. Digest the solution with sulfuric acid-hydrogen peroxide method, determine the nitrogen content with Kjeldahl method, calculate the cumulative nutrient release rate, and the test result on the first day is the initial release rate.

[0042] The specific embodiments of the present invention are described in detail below. Example 1

[0043] A simplified preparation process of a dual-nitrogen-controlled release suspended urea-formaldehyde multi-nutrient element liquid fertilizer comprises the following steps: (S1) Add a certain amount of urea, a 37wt% formaldehyde aqueous solution, carboxymethyl cellulose and water into a reactor A, wherein the molar ratio of urea to formaldehyde in the formaldehyde aqueous solution is 0.8:1, the mass ratio of carboxymethyl cellulose to the total mass of formaldehyde in the urea and formaldehyde aqueous solution is 10:1, and the amount of water added is 40% of the total mass of formaldehyde and carboxymethyl cellulose in the urea and formaldehyde aqueous solution; after reacting at 50°C for 3h, the reaction product is dried at 120°C to constant weight, and pulverized to obtain urea-formaldehyde grafted carboxymethyl cellulose, which is a urea-formaldehyde particle stabilizer.

[0044] (S2) adding a certain amount of urea, a 37wt% formaldehyde aqueous solution and water into the reactor B, wherein the molar ratio of urea to formaldehyde contained in the formaldehyde aqueous solution is 10:1, and the amount of water added is 50% of the total mass of formaldehyde contained in the urea and formaldehyde aqueous solution. After reacting at 50°C for 2h, the urea-formaldehyde granule stabilizer obtained in step (S1) is added and mixed evenly, wherein the amount of urea-formaldehyde granule stabilizer added is 1% of the total mass of formaldehyde contained in the urea and formaldehyde aqueous solution in step (S2), and the reaction is continued for 2h; adding ammonium dihydrogen phosphate and urease inhibitor N-butylthiophosphoric triamide and mixing evenly, wherein the mass ratio of ammonium dihydrogen phosphate to urea in step (S2) is 1:2, and the mass ratio of N-butylthiophosphoric triamide to urea in step (S2) is 0.01:1; and obtaining a dual-nitrogen-controlled-release suspended urea-formaldehyde multi-nutrient element liquid fertilizer prepolymer.

[0045] (S3) reacting the double-controlled nitrogen-releasing suspended urea-formaldehyde multi-nutrient element liquid fertilizer prepolymer in a high-speed dispersing emulsifier for 15 minutes to obtain a double-controlled nitrogen-releasing suspended urea-formaldehyde multi-nutrient element liquid fertilizer.

[0046] The prepared double-controlled nitrogen release suspended urea-formaldehyde multi-nutrient element liquid fertilizer has a nutrient element N content of 157 g / L, a P2O5 content of 126 g / L, a water-insoluble content of 9.2 g / L, and an initial nitrogen nutrient release rate of 24.4%. When planting corn, the liquid fertilizer sprayer applies fertilizer at a rate of 80 L / mu. Example 2

[0047] A simplified preparation process of a dual-nitrogen-controlled release suspended urea-formaldehyde multi-nutrient element liquid fertilizer comprises the following steps: (S1) Add a certain amount of urea, solid paraformaldehyde, methyl cellulose and water into reactor A, wherein the molar ratio of urea to the formaldehyde structural unit contained in paraformaldehyde is 0.5:1, the mass ratio of methyl cellulose to the total mass of urea and paraformaldehyde is 10:1, and the amount of water added is 20% of the total mass of urea, paraformaldehyde and methyl cellulose; react at 80°C for 2h, dry the reaction product at 100°C to constant weight, and grind it to obtain urea-formaldehyde grafted methyl cellulose, which is a urea-formaldehyde particle stabilizer.

[0048] (S2) adding a certain amount of urea, solid polyformaldehyde and water into the reactor B, wherein the molar ratio of the formaldehyde structural unit contained in the urea to the polyformaldehyde is 15:1, and the amount of water added is 50% of the total mass of the urea and the polyformaldehyde. After reacting at 40°C for 3 hours, the urea-formaldehyde granule stabilizer obtained in step (S1) is added and mixed evenly, wherein the amount of the urea-formaldehyde granule stabilizer added is 0.5% of the total mass of the urea and the polyformaldehyde in step (S2), and the reaction is continued for 3 hours; adding ammonium dihydrogen phosphate, potassium sulfate and nitrification inhibitor dicyandiamide and mixing evenly, wherein the mass ratio of ammonium dihydrogen phosphate to the urea in step (S2) is 1:5, the mass ratio of potassium sulfate to ammonium dihydrogen phosphate is 1:3, and the mass ratio of dicyandiamide to the urea in step (S2) is 0.005:1; and obtaining a double-nitrogen-controlled-release suspended urea-formaldehyde multi-nutrient element liquid fertilizer prepolymer.

[0049] (S3) Adding the double-controlled nitrogen-releasing suspended urea-formaldehyde multi-nutrient element liquid fertilizer prepolymer into a colloid mill and reacting for 10 minutes to obtain the double-controlled nitrogen-releasing suspended urea-formaldehyde multi-nutrient element liquid fertilizer.

[0050] The prepared double-controlled nitrogen release suspended urea-formaldehyde multi-nutrient element liquid fertilizer has 185g / L nutrient element N, 109g / L P2O5, 79g / L K2O, 8.0g / L water insoluble matter, and an initial nitrogen nutrient release rate of 27.5%. When planting corn, the liquid fertilizer sprayer applies fertilizer at a rate of 60L / mu.

[0051] Figure 1In the embodiment of the present invention, the double-controlled nitrogen release suspension type urea-formaldehyde multi-nutrient element liquid fertilizer of embodiment 2 has excellent stability within 30 days of placement, no stratification occurs, and there is no precipitation at the bottom, indicating that the preparation method of the present invention can ensure the uniform dispersion of liquid fertilizer for a long time. In addition, an obvious Tyndall effect is produced during the test process, which not only intuitively proves the existence of particles in the liquid fertilizer, but also reflects its good dispersibility and stability. Because the dispersed material particles based on urea-formaldehyde in the liquid fertilizer are tightly coated by urea-formaldehyde particle stabilizers and form a stable suspension system, it is possible to effectively avoid the aggregation and sedimentation of particles. This stable dispersed material particle structure can maintain uniformity during long-term storage and use, ensuring that the storage stability and convenient use of liquid fertilizer products.

[0052] Figure 2 In the double-controlled nitrogen release suspended urea-formaldehyde multi-nutrient element liquid fertilizer, the particle size of the dispersed substance mainly composed of urea-formaldehyde remained at 2.5~2.6μm within 30 days, indicating that the liquid fertilizer has excellent stability. This stability is mainly due to the fact that the urea-formaldehyde particle stabilizer forms a protective film by tightly coating the dispersed substance particles mainly composed of urea-formaldehyde, which can effectively prevent direct contact between particles and aggregation caused by van der Waals forces or electrostatic effects. This dual mechanism ensures that the dispersed substance particles in the liquid fertilizer remain in a uniform dispersion state for a long time, significantly improving the stability and dispersibility of the liquid fertilizer.

[0053] Figure 3 In the experiment, the nitrogen cumulative release rate of the double-controlled nitrogen release suspended urea-formaldehyde multi-nutrient element liquid fertilizer gradually increased from 27.5% on the first day to 43.7% on the 28th day. This result shows that the liquid fertilizer has good slow-release performance and can continuously release nitrogen over a long period of time, meeting the continuous demand for nitrogen during crop growth, and is suitable for cash crops or field crops. Example 3

[0054] A simplified preparation process of a dual-nitrogen-controlled release suspended urea-formaldehyde multi-nutrient element liquid fertilizer comprises the following steps: (S1) Add a certain amount of urea, solid polyformaldehyde, polyanionic cellulose and water into reactor A, wherein the molar ratio of urea to the formaldehyde structural unit contained in polyformaldehyde is 1:1, the mass ratio of polyanionic cellulose to the total mass of urea and polyformaldehyde is 5:1, and the amount of water added is 40% of the total mass of urea, polyformaldehyde and polyanionic cellulose; react at 90°C for 1h, dry the reaction product at 80°C to constant weight, and grind it to obtain urea-formaldehyde grafted polyanionic cellulose, which is a urea-formaldehyde particle stabilizer.

[0055] (S2) adding a certain amount of urea, solid polyformaldehyde and water into the reactor B, wherein the molar ratio of the formaldehyde structural unit contained in the urea to the polyformaldehyde is 20:1, and the amount of water added is 40% of the total mass of the urea and the polyformaldehyde. After reacting at 60°C for 1 hour, the urea-formaldehyde granule stabilizer obtained in step (S1) is added and mixed evenly, wherein the amount of the urea-formaldehyde granule stabilizer added is 2% of the total mass of the urea and the polyformaldehyde in step (S2), and the reaction is continued for 1 hour; adding ammonium dihydrogen phosphate, potassium chloride and nitrification inhibitor 3,4-dimethylpyrazole phosphate and mixing evenly, wherein the mass ratio of ammonium dihydrogen phosphate to the urea in step (S2) is 1:4, the mass ratio of potassium chloride to ammonium dihydrogen phosphate is 1:2, and the mass ratio of 3,4-dimethylpyrazole phosphate to the urea in step (S2) is 0.01:1; and obtaining a double-controlled nitrogen release suspended urea-formaldehyde multi-nutrient element liquid fertilizer prepolymer.

[0056] (S3) Adding the double-controlled nitrogen-releasing suspended urea-formaldehyde multi-nutrient element liquid fertilizer prepolymer into a colloid mill and reacting for 10 minutes to obtain the double-controlled nitrogen-releasing suspended urea-formaldehyde multi-nutrient element liquid fertilizer.

[0057] The prepared double-controlled nitrogen release suspended urea-formaldehyde multi-nutrient element liquid fertilizer has 180g / L N, 127g / L P2O5, 90g / L K2O, 7.8g / L water-insoluble matter, and an initial nitrogen nutrient release rate of 30.1%. When planting corn, the liquid fertilizer sprayer applies fertilizer at a rate of 65L / mu.

[0058] The above is only a specific implementation of the present invention, which enables those skilled in the art to understand or implement the present invention. Although detailed descriptions are given with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions recorded in the aforementioned embodiments, or replace some or all of the technical features therein by equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments, and they should all be covered by the protection scope of the claims.

Claims

1. A simplified preparation process for a dual-controlled nitrogen-releasing suspended urea-formaldehyde multi-nutrient element liquid fertilizer, characterized in that: The following steps are involved: (1) Add a certain amount of urea, formaldehyde, cellulose and water into reactor A, wherein the molar ratio of urea to formaldehyde is 0.1-1:1, the mass ratio of cellulose to the total mass of urea and formaldehyde is 1-10:1, and the amount of water added is 10-80% of the total mass of urea, formaldehyde and cellulose; react at 50-90°C for 0.5-3h, dry the obtained reaction product at 80-120°C to constant weight, and grind it to obtain urea-formaldehyde grafted cellulose, which is a urea-formaldehyde particle stabilizer; (2) adding a certain amount of urea, formaldehyde and water into the reactor B, wherein the molar ratio of urea to formaldehyde is 10-20:1, and the amount of water added is 10-50% of the total mass of urea and formaldehyde; reacting at 30-60° C. for 0.5-3 h, adding the urea-formaldehyde granule stabilizer obtained in step (1) and mixing evenly, and continuing the reaction for 0.5-3 h; adding a fertilizer system containing at least one nutrient element other than nitrogen and a nutrient synergist, stirring evenly to obtain a dual-controlled nitrogen release suspended urea-formaldehyde multi-nutrient element liquid fertilizer prepolymer; (3) The dual-nitrogen-release suspended urea-formaldehyde multi-nutrient element liquid fertilizer prepolymer is reacted in a high-speed shear dispersion device for 15 to 30 minutes to obtain a dual-nitrogen-release suspended urea-formaldehyde multi-nutrient element liquid fertilizer.

2. The simplified preparation process of a dual-controlled nitrogen release suspended urea-formaldehyde multi-nutrient element liquid fertilizer according to claim 1, characterized in that: In step (1) and step (2), the formaldehyde is at least one of a formaldehyde aqueous solution, solid paraformaldehyde, and gaseous formaldehyde.

3. The simplified preparation process of a dual-controlled nitrogen release suspended urea-formaldehyde multi-nutrient element liquid fertilizer according to claim 1, characterized in that: In step (1), the cellulose is selected from at least one of carboxymethyl cellulose, methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose and polyanionic cellulose.

4. The simplified preparation process of a dual-controlled nitrogen release suspended urea-formaldehyde multi-nutrient element liquid fertilizer according to claim 1, characterized in that: In step (2), the amount of the urea-formaldehyde particle stabilizer added is 0-10% of the total mass of urea and formaldehyde in step (2) and is not 0.

5. The simplified preparation process of a dual-controlled nitrogen release suspended urea-formaldehyde multi-nutrient element liquid fertilizer according to claim 1, characterized in that: In step (2), the fertilizer system containing at least one nutrient element other than nitrogen is selected from at least one of phosphate fertilizers, potash fertilizers, medium element fertilizers and trace element fertilizers.

6. The simplified preparation process of a dual-controlled nitrogen release suspended urea-formaldehyde multi-nutrient element liquid fertilizer according to claim 5, characterized in that: The phosphate fertilizer is selected from at least one of hydroxyapatite, ammonium dihydrogen phosphate, superphosphate, potassium tripolyphosphate and potassium dihydrogen phosphate; the potassium salt fertilizer is selected from at least one of potassium sulfate, potassium chloride, potassium nitrate and potassium carbonate.

7. The simplified preparation process of a dual-controlled nitrogen release suspended urea-formaldehyde multi-nutrient element liquid fertilizer according to claim 1, characterized in that: In step (2), the nutrient enhancer is a chemical nutrient enhancer; the chemical nutrient enhancer is selected from at least one of a urease inhibitor and a nitrification inhibitor.

8. The simplified preparation process of a dual-controlled nitrogen release suspended urea-formaldehyde multi-nutrient element liquid fertilizer according to claim 1, characterized in that: In step (2), the mass ratio of the added amount of the fertilizer system containing at least one nutrient element other than nitrogen to the urea in step (2) is 0-5:1 and is not 0; the added amount of the nutrient enhancer is 0-5% of the mass of the urea in step (2) and is not 0.

9. The simplified preparation process of a dual-controlled nitrogen release suspended urea-formaldehyde multi-nutrient element liquid fertilizer according to claim 1, characterized in that: In step (3), the high-speed shearing and dispersing equipment is selected from a high-speed dispersing emulsifier, a colloid mill and a sand mill.

10. The method for applying the dual-controlled nitrogen-releasing suspended urea-formaldehyde multi-nutrient liquid fertilizer prepared as claimed in claims 1-9 comprises foliar spraying, seed soaking, root dipping, injection application, drench application, pouring application, sprinkler irrigation application or drip irrigation application; the application amount is 8-15 kg nitrogen / mu.

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