Gamma-aminobutyric acid modified urea-formaldehyde slow-release suspension fertilizer and preparation method thereof

Abstract

The application discloses a kind of gamma-aminobutyric acid modified urea formaldehyde slow-release suspending fertilizer and preparation method thereof, and it relates to the technical field of fertilizer.The suspending fertilizer is made of gamma-aminobutyric acid modified urea formaldehyde slow-release polymer, water-soluble nitrogen, phosphorus and potassium fertilizer, suspending agent, thickening agent and water by emulsification dispersion.The application regulates the polycondensation reaction condition, makes gamma-aminobutyric acid embed in the molecular skeleton of urea formaldehyde with covalent bond, on the one hand, utilizes the amino and carboxyl of gamma-aminobutyric acid to participate in polycondensation reaction, adjusts the molecular chain structure and release curve of urea formaldehyde, inhibits the initial burst release of oligomeric component, and promotes the steady release in middle and later period;On the other hand, makes gamma-aminobutyric acid gradually release with the degradation of urea formaldehyde, continuously plays the biological function of promoting plant nitrogen metabolism and enhancing stress resistance while releasing nitrogen.The suspending fertilizer of the application omits the granulation drying process, is convenient for water and fertilizer integration precision application, effectively improves the utilization rate of nitrogen, reduces environmental pollution, and is suitable for various fields and economic crops.

Description

Technical Field

[0001] This invention relates to the field of fertilizer technology, and in particular to a γ-aminobutyric acid modified urea-formaldehyde slow-release suspension fertilizer and its preparation method. Background Technology

[0002] Urea-formaldehyde is a mixture of methylene urea with different degrees of polymerization. Its nitrogen release depends on the gradual degradation by soil microorganisms, which can achieve slow release and improve utilization. However, the low-polymerization-degree component is released too quickly in the early stage of crop growth, exceeding the nitrogen requirement in the early stage; the high-polymerization-degree component is released too slowly in the later stage, making it difficult to meet the needs in the middle and later stages, which to some extent limits the application of urea-formaldehyde in field crops.

[0003] Gamma-aminobutyric acid (GABA) is a non-protein amino acid widely found in plant tissues, playing a crucial role in plant growth, development, and stress response. Exogenous GABA can significantly improve the absorption efficiency of nitrogen, phosphorus, potassium, and micronutrients by crops through mechanisms such as regulating ion channel activity, promoting root development, and enhancing the activity of nitrogen metabolism-related enzymes. However, current technologies for applying GABA in fertilizers mainly involve using GABA as an independent synergist in simple physical mixing with raw materials such as urea-formaldehyde, as exemplified by Chinese patent CN112723942A. In this patent, no chemical bond is formed between GABA and urea-formaldehyde, posing a risk of leaching and loss, and failing to achieve the molecular-level synergy between GABA's synergistic effect and urea-formaldehyde's slow-release function.

[0004] Furthermore, existing urea-formaldehyde fertilizers are mostly in solid granular form, requiring multiple processes such as polymerization, drying, and granulation during production, resulting in high energy consumption. Application mainly relies on manual spreading or mechanical application, making precise targeting difficult. Suspension fertilizer, on the other hand, is a high-concentration, easily flowing liquid fertilizer that requires no dehydration or granulation during preparation, resulting in low production energy consumption. It can also be used in conjunction with drip irrigation and sprinkler irrigation for precise, integrated water and fertilizer application, meeting the labor-saving and high-efficiency requirements of modern agriculture. Summary of the Invention

[0005] To address the above shortcomings, this invention provides a γ-aminobutyric acid (GABA)-modified urea-formaldehyde slow-release suspension fertilizer and its preparation method. By chemically copolymerizing GABA into the urea-formaldehyde molecular framework, it achieves long-term fixation of the release curve regulation and GABA's bio-enhancing function. This solves the problems of uneven nitrogen release rates in existing urea-formaldehyde fertilizers, which cannot match the nutritional needs of crops in the early and late stages of growth, and the easy loss of exogenous GABA through simple physical mixing, which fails to achieve synergistic functional effects at the molecular level. The specific technical solution is as follows: A γ-aminobutyric acid-modified urea-formaldehyde slow-release suspension fertilizer, by weight, mainly consists of the following raw materials: 10-25 parts of γ-aminobutyric acid-modified urea-formaldehyde slow-release polymer, 25-65 parts of water-soluble nitrogen, phosphorus, and potassium fertilizer, 0.2-2 parts of suspending agent, 0.1-1 parts of thickener, and water to make up to 100 parts; the γ-aminobutyric acid-modified urea-formaldehyde slow-release polymer is obtained by covalently embedding γ-aminobutyric acid into the molecular backbone of urea-formaldehyde.

[0006] Preferably, the water-soluble nitrogen, phosphorus, and potassium fertilizer is selected from one or more of urea, ammonium sulfate, ammonium nitrate, monoammonium phosphate, diammonium phosphate, polyphosphate, potassium dihydrogen phosphate, potassium chloride, potassium sulfate, and potassium nitrate.

[0007] Preferably, the suspending agent is selected from one or two of magnesium aluminum silicate and bentonite.

[0008] Preferably, the thickener is selected from one or more of xanthan gum, guar gum, sodium alginate, and sodium polyacrylate.

[0009] This invention also provides a method for preparing the above-mentioned slow-release suspension fertilizer, comprising the following steps: (1) Preparation of hydroxymethylurea solution: urea and formaldehyde are mixed and reacted to obtain hydroxymethylurea solution; (2) Preparation of γ-aminobutyric acid modified urea-formaldehyde slow-release polymer: γ-aminobutyric acid is added to the hydroxymethyl urea solution, the molar ratio of γ-aminobutyric acid to urea is (0.01-0.10):1.0, the pH is adjusted to 4.0-5.0, the temperature is raised to 60-80℃, and the polycondensation reaction is carried out for 1-3 hours to obtain γ-aminobutyric acid modified urea-formaldehyde slow-release polymer; (3) Preparation of suspension fertilizer: The γ-aminobutyric acid modified urea-formaldehyde slow-release polymer is mixed with water-soluble nitrogen, phosphorus and potassium fertilizer, suspending agent, thickener and water in proportion, and then sheared, emulsified and homogenized to obtain suspension fertilizer.

[0010] Preferably, in step (1), urea and formaldehyde are mixed in a molar ratio of 1.2-1.8:1, the pH is adjusted to 8.0-9.0, and the mixture is reacted at 75-85°C for 0.5-2 hours to obtain a hydroxymethylurea solution.

[0011] Preferably, in step (2), the preparation method of the γ-aminobutyric acid modified urea-formaldehyde slow-release polymer is as follows: First, gallic acid and γ-aminobutyric acid are added to water at a mass ratio of 3:(4-5). Under the catalysis of toluenesulfonic acid, the mixture is heated to 80-85℃ and reacted for 3-4 hours. Then, the temperature is lowered to 35-40℃, and the pH is adjusted to 7.0-7.5 to obtain intermediate 1. Then, intermediate 1 is added to the hydroxymethyl urea solution, with a molar ratio of γ-aminobutyric acid to urea of ​​(0.01-0.10):1.0. The pH is adjusted to 4.0-5.0, and the temperature is raised to 60-80℃. The polycondensation reaction is carried out for 1-3 hours to obtain the γ-aminobutyric acid modified urea-formaldehyde slow-release polymer. This preparation method is designed to enable the prepared suspension fertilizer to adapt to the acidic soil of karst areas. Guangxi is primarily characterized by karst topography, with generally acidic soils and high aluminum ion content, posing a significant toxic effect on crop growth. Urea-formaldehyde polymers prepared solely through GABA modification degrade rapidly in acidic environments. Furthermore, the low microbial activity in acidic soils hinders the achievement of slow release during the early stages of crop growth and rapid release in the later stages. To adapt to the acidic soils of karst regions, this preparation method introduces gallic acid during the preparation of γ-aminobutyric acid-modified urea-formaldehyde slow-release polymers. This results in a gallic acid-containing benzene ring, which makes the polymer less prone to degradation under acidic conditions. The gallic acid also provides phenolic hydroxyl groups, which can chelate aluminum ions in the soil, thus mitigating aluminum toxicity. Therefore, in karst acidic soils, the suspension fertilizer prepared according to this method can slow down the degradation rate and chelate aluminum ions in the early stage of application, thereby reducing soil aluminum toxicity. After the soil aluminum toxicity is reduced, the growth environment of microorganisms is improved, which promotes the activity and reproduction of soil microorganisms. When crops enter the middle and late stages of growth, nutrients are released rapidly with the help of microorganisms, thus achieving rapid fertilizer release.

[0012] Preferably, in step (3), the rotation speed of shear emulsification is 3000-7000 rpm, the dispersion time is 15-60 minutes, and the suspended particle size is controlled to be ≤80μm.

[0013] The γ-aminobutyric acid modified urea-formaldehyde slow-release suspension fertilizer prepared by this invention can be used in the planting of corn, wheat and sugarcane. It can be applied by drip irrigation, sprinkler irrigation or root application followed by soil covering.

[0014] Compared with the prior art, the beneficial effects of the present invention are: 1. In this invention, GABA is covalently embedded in the molecular skeleton of urea-formaldehyde, and its amino and carboxyl groups participate in the condensation reaction, which regulates the molecular chain length and cross-linking degree of urea-formaldehyde, moderately suppresses the initial burst release of low-polymerization components, and makes the release curve more stable, which is more matched with the nitrogen requirement sequence of various crops.

[0015] 2. In this invention, the GABA copolymer unit can be gradually released as the urea-formaldehyde skeleton is hydrolyzed, continuously promoting the activity of nitrogen metabolism-related enzymes in plants and promoting root development, thus overcoming the time mismatch problem of GABA being lost first and nitrogen being released later in physical mixing methods.

[0016] 3. This invention introduces gallic acid during polymer preparation. Its benzene ring structure enhances the polymer's chemical stability in acidic soils and slows down the early hydrolysis rate. Its phenolic hydroxyl groups can chelate aluminum ions in acidic soils, reducing aluminum toxicity and improving the microbial environment. This allows for accelerated nutrient release through microbial action in the later stages of crop growth, resulting in a nutrient supply rhythm of slow release in the early stages and accelerated release in the later stages, better matching the crop's nutrient requirements. This is particularly suitable for acidic red soils in karst regions. In contrast, the GABA-modified system without gallic acid is more suitable for neutral or alkaline soils.

[0017] 4. This invention directly combines modified urea-formaldehyde with water-soluble nitrogen, phosphorus, and potassium fertilizers and emulsifies and disperses them to form a suspension fertilizer, eliminating high-energy-consuming processes such as granulation and drying; the suspension fertilizer is easy to flow and can be pumped, and can be used with drip irrigation and sprinkler irrigation to achieve precise application of water and fertilizer, significantly reducing labor costs. Attached Figure Description

[0018] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 The infrared spectra of GABA-modified urea-formaldehyde, unmodified urea-formaldehyde, and pure GABA prepared in Example 2 are compared. Figure 2 The graph shows the results of the cumulative nitrogen release rate determination of fertilizers in neutral soil for Examples 2, 5, Comparative Examples 1, 3 and 4. Figure 3 The graph shows the cumulative nitrogen release rate of fertilizers from Examples 2, 5, 1, 3, and 4 in acidic soil. Detailed Implementation

[0020] The specific embodiments of the present invention are described in detail below, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments. Unless otherwise defined, all technical terms used below have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing specific embodiments only and are not intended to limit the scope of protection of the present invention. Unless otherwise specifically stated, all raw materials, reagents, instruments, and equipment used in the present invention are commercially available or can be prepared by existing methods.

[0021] Example 1 The preparation method of GABA-modified urea-formaldehyde slow-release suspension fertilizer in this embodiment is as follows: (1) Preparation of hydroxymethylurea solution: Take 90.0g of urea and 97.3g of 37% formaldehyde solution (i.e., the molar ratio of urea to formaldehyde is 1.25:1), add 20g of water, adjust the pH to 8.5 with 10% NaOH solution, heat to 80℃, stir and react for 1 hour to obtain hydroxymethylurea solution; (2) Preparation of GABA-modified urea-formaldehyde slow-release polymer: 0.015 mol (1.545 g) of γ-aminobutyric acid was added to the above solution, i.e., the molar ratio of GABA to urea was 0.01:1.0. The pH was adjusted to 4.5 with 10% H2SO4 solution, the temperature was raised to 70℃, and the reaction was maintained for 2 hours to obtain wet material of GABA-modified urea-formaldehyde slow-release polymer (solid content about 50%), denoted as GMP-1; (3) Preparation of suspension fertilizer: Take 20 parts of the above-mentioned GABA-modified urea-formaldehyde slow-release polymer, add 15 parts of potassium chloride, 24 parts of urea, 10 parts of monoammonium phosphate, 0.2 parts of xanthan gum, 0.3 parts of sodium polyacrylate, and 0.5 parts of magnesium aluminum silicate, add water to make up to 100 parts, disperse at 4000 rpm for 30 minutes using a high-shear emulsification pump to obtain suspension fertilizer F-1. The total nutrients of F-1 were determined to be N 16%, P2O5 6%, K2O 9%, viscosity at 25℃ 420 mPa·s, and particle size D95 approximately 70 μm.

[0022] Example 2 The preparation method of GABA-modified urea-formaldehyde slow-release suspension fertilizer in this embodiment is as follows: (1) Preparation of hydroxymethylurea solution: Take 60.0g of urea and 56.7g of 37% formaldehyde solution (i.e., the molar ratio of urea to formaldehyde is 1.43:1), add 15g of water, adjust the pH to 8.5 with 10% NaOH, heat to 80℃, and stir for 1.5 hours. (2) Preparation of GABA-modified urea-formaldehyde slow-release polymer: 0.05 mol (5.16 g) of γ-aminobutyric acid was added at a molar ratio of 0.05:1.0. The pH was adjusted to 4.5 with 10% H2SO4, the temperature was raised to 70℃, and the reaction was maintained for 2.5 hours to obtain GMP-2; (3) Preparation of suspension fertilizer: Take 10 parts of the above-mentioned GABA-modified urea-formaldehyde slow-release polymer, add 28 parts of urea, 10 parts of monoammonium phosphate, 15 parts of potassium chloride, 0.2 parts of xanthan gum, 0.3 parts of sodium polyacrylate, and 0.5 parts of magnesium aluminum silicate, add water to make up to 100 parts, disperse at 5000 rpm for 25 minutes using a high-shear emulsification pump to obtain suspension fertilizer F-2. Total nutrients: N 16%, P2O5 6%, K2O 9%, viscosity 445 mPa·s, particle size D95 approximately 63 μm.

[0023] The infrared spectra of GABA-modified urea-formaldehyde, unmodified urea-formaldehyde, and pure GABA prepared in this embodiment are shown in the figure below. Figure 1 As shown in the figure, in the infrared spectrum of urea-formaldehyde, 3327 cm⁻¹ represents the NH stretching of secondary amides, 3208 cm⁻¹ represents the NH stretching of primary amides, and 1550 cm⁻¹ represents the coupling of NH bending and CN stretching. After GABA grafting, the intensity of the 1550 cm⁻¹ absorption peak weakens because the number of NH bonds in the system decreases after GABA grafting; the NH peak at 3327 cm⁻¹ broadens with a blue shift, indicating that the number of carboxyl groups in the system increases after GABA introduction, forming a more complex and stronger hydrogen bond network; the weakening of the primary amide peak at 3208 cm⁻¹ is attributed to reaction consumption; the newly appearing absorption peak at 886 cm⁻¹ represents the CC skeletal vibration of the GABA molecule, providing direct evidence of GABA's introduction via chemical bonds. These changes in the infrared spectrum collectively indicate that GABA has been successfully grafted onto the urea-formaldehyde molecular chain.

[0024] Example 3 The preparation method of GABA-modified urea-formaldehyde slow-release suspension fertilizer in this embodiment is as follows: (1) Preparation of hydroxymethylurea solution: Take 96g of urea and 81g of 37% formaldehyde solution (i.e., the molar ratio of urea to formaldehyde is 1.60:1), add 30g of water, adjust the pH to 8.5 with 10% NaOH, heat to 80℃, and stir for 2 hours. (2) Preparation of GABA-modified urea-formaldehyde slow-release polymer: 0.16 mol (16.49 g) of γ-aminobutyric acid was added at a molar ratio of 0.10:1.0. The pH was adjusted to 4.5 with 10% H2SO4, the temperature was raised to 70℃, and the reaction was maintained for 3 hours to obtain GMP-3; (3) Preparation of suspension fertilizer: Take 25 parts of the above-mentioned GABA-modified urea-formaldehyde slow-release polymer, add 21 parts of urea, 10 parts of monoammonium phosphate, 15 parts of potassium chloride, 0.2 parts of xanthan gum, 0.3 parts of sodium polyacrylate, and 0.5 parts of magnesium aluminum silicate, add water to make up to 100 parts, disperse at 6000 rpm for 20 minutes using a high-shear emulsification pump to obtain F-3. Total nutrients: N 16%, P2O5 6%, K2O 9%, viscosity 468 mPa·s, particle size D95 approximately 71 μm.

[0025] Example 4 The preparation method of GABA-modified urea-formaldehyde slow-release suspension fertilizer in this embodiment is as follows: Using GMP-1 from Example 1, in step (3) the suspension compounding was changed to 12 parts diammonium phosphate and 21 parts urea, the other additives were the same as in Example 1, water was added to make up to 100 parts, and F-4 was obtained. The total nutrients were N 16%, P2O5 6%, K2O 9%, and the viscosity was 430 mPa·s.

[0026] Example 5 The preparation method of GABA-modified urea-formaldehyde slow-release suspension fertilizer in this embodiment is as follows: (1) The preparation of hydroxymethylurea solution is the same as in Example 1; (2) Preparation of GABA-modified urea-formaldehyde slow-release polymer: First, add 1.01g of gallic acid and 1.55g of γ-aminobutyric acid (GABA to urea molar ratio 0.01:1.0) to 100g of water. Under the catalysis of toluenesulfonic acid, heat to 80-85℃ and react for 3-4 hours. Then, cool down to 35-40℃ and adjust the pH to 7.0-7.5 to obtain intermediate 1. Then, add intermediate 1 to hydroxymethyl urea solution, adjust the pH to 4.5 with 10% H2SO4 solution, heat to 70℃, and keep the reaction for 2 hours to obtain wet material of GABA-modified urea-formaldehyde slow-release polymer. (3) Preparation of suspension fertilizer: Take 20 parts of the above-mentioned GABA-modified urea-formaldehyde slow-release polymer, add 26 parts of urea, 10 parts of monoammonium phosphate, 15 parts of potassium chloride, 0.2 parts of xanthan gum, 0.3 parts of sodium polyacrylate, and 0.5 parts of magnesium aluminum silicate, add water to make up to 100 parts, disperse at 5000 rpm for 30 minutes using a high-shear emulsification pump to obtain suspension fertilizer F-5. The total nutrients of F-5 were determined to be N 16%, P2O5 6%, K2O 9%, viscosity at 25℃ 433 mPa·s, and particle size D95 approximately 61 μm.

[0027] Comparative Example 1 In this comparative example, GABA was not used to modify urea-formaldehyde. Instead, unmodified urea-formaldehyde (N 18.5%) was used to replace GMP-1 in equal amounts, and the rest was the same as in Example 1, resulting in D-1.

[0028] Comparative Example 2 In this comparative example, GABA was not used to modify urea-formaldehyde. Unmodified urea-formaldehyde was used instead of GMP-1, and GABA was added in addition (the amount added was equivalent to the amount of GABA contained in GMP-2 in Example 2). The rest was the same as in Example 1, resulting in D-2.

[0029] Comparative Example 3 In this comparative example, arginine was used instead of GABA to modify urea-formaldehyde, and the remaining steps were the same as in Example 1, resulting in D-3.

[0030] Comparative Example 4 In this comparative example, glycine was used instead of GABA to modify urea-formaldehyde, and the remaining steps were the same as in Example 1, resulting in D-4.

[0031] Comparative Example 5 This comparative example did not use GABA to modify urea-formaldehyde. Instead of the GABA-modified urea-formaldehyde slow-release polymer in Example 2, 25 parts of unmodified wet urea-formaldehyde (N 18.5%) were used. One part of pure GABA was added (equivalent to the GABA content in GMP-2 in Example 2), along with 18 parts of urea, 8.5 parts of monoammonium phosphate, and 13 parts of potassium chloride. Kaolin and bentonite were added to bring the total to 100 parts. The mixture was then mixed, dried, and granulated to obtain granular fertilizer, D-5. The total nutrients in D-5 were determined to be N 16.2%, P2O5 6.0%, K2O 9.2%, and total nitrogen, phosphorus, and potassium 31.4%. The moisture content was ≤2%, and the granule strength met the requirements for agricultural use.

[0032] Suspension fertilizer storage stability test F-1, F-2, F-3, F-4, F-5 and D-1, D-2, D-3, D-4 were sealed in transparent PET bottles of the same size and stored at room temperature (25±2℃) for 90 days. Layering was determined by visually observing the color difference interface between the upper liquid and the lower suspension and the height of the clear liquid layer. Viscosity was measured using a rotational viscometer at 30 rpm and 25±0.5℃, and the viscosity change rate before and after storage was calculated. Particle size was measured using a laser particle size analyzer to determine the median particle size (D50), and the particle size growth rate before and after storage was calculated. pH was measured using a pH meter, and the pH change amplitude (ΔpH) before and after storage was recorded. The results are shown in Table 1. Table 1. Stability of fertilizers prepared in each example and comparative example. The stability indicators of the fluid fertilizer samples from each example and comparative example showed significant differences after 90 days of storage at room temperature. Regarding stratification, the γ-aminobutyric acid-modified urea-formaldehyde suspension fertilizer system (Examples 1-5) was homogeneous without stratification, the arginine (Comparative Example 3) and glycine (Comparative Example 4) modified samples showed slight stratification, while the unmodified samples (Comparative Example 1 and Comparative Example 2) showed obvious stratification. This indicates that γ-aminobutyric acid modification can effectively maintain the overall phase homogeneity of the system and inhibit solid-liquid phase separation.

[0033] In terms of quantitative indicators, the viscosity fluctuation rate, particle size growth rate, and pH fluctuation value of the γ-aminobutyric acid modified urea-formaldehyde suspension fertilizer were significantly better than those of other comparative samples. Although the arginine-modified sample was better than the glycine-modified sample, the difference between it and the γ-aminobutyric acid-modified sample was significant; the glycine-modified sample was only slightly better than the unmodified sample, while the unmodified urea-formaldehyde suspension fertilizer had the worst stability, with a viscosity fluctuation rate of about +26%, a particle size growth rate of about +20%, and a pH decrease of about -0.40.

[0034] In summary, amino acid modification, especially γ-aminobutyric acid modification, can effectively inhibit particle growth and aggregation of urea-formaldehyde in fluid fertilizer systems, as well as pH changes in the system, and significantly improve the overall stability of the suspension system.

[0035] Field fertilizer efficiency trial A sugarcane fertilizer efficacy trial was conducted in Bao'an Village, Suwei Town, Jiangnan District, Nanning City, Guangxi Province. The tested variety was Guitang 44, and the sugarcane was newly planted with a row spacing of 1.4 meters. The trial period was hilling and topdressing. The tested fertilizers were GABA-modified urea-formaldehyde suspension fertilizer prepared in Examples 2 and 5, Comparative Example 1 (pure urea-formaldehyde liquid fertilizer), Comparative Example 2 (unmodified urea-formaldehyde suspension fertilizer control group), and Comparative Example 5 (granular fertilizer). The application rate for each treatment was 100 kg per mu (approximately 667 square meters), and each treatment covered 10 mu. Application was carried out on June 8, 2025, using a manual backpack liquid fertilizer applicator, applying the suspension fertilizer strips approximately 15 cm to the side of the sugarcane row, followed by hilling and covering with soil. The number of effective stems per mu, average plant height, and average stem diameter were investigated at 60 days (August 7), 122 days (October 8), and 200 days (December 25) after topdressing, and the theoretical yield was calculated. The results are shown in Table 2. Table 2 Comparison of fertilizer effects among groups Sixty days after topdressing, the number of effective stems and plant height of the GABA-modified treatment groups (Examples 2 and 5) were lower than those of the control groups, and the theoretical yield was 0.05 to 0.60 tons lower than that of the control groups. Specifically, Example 5 was 0.05 tons, 0.10 tons, and 0.45 tons lower than Comparative Example 1 (pure urea-formaldehyde fluid fertilizer), Comparative Example 2 (physical mixed fluid fertilizer), and Comparative Example 5 (physical mixed granular fertilizer), respectively; Example 2 was 0.20 tons, 0.25 tons, and 0.60 tons lower than the above three control groups, respectively. This is not due to insufficient fertilizer efficiency, but rather because the initial release rate was effectively suppressed after modification, and the available nitrogen in the soil remained at a stable to low level, causing ineffective tillers to naturally die due to nutrient competition, thereby concentrating nutrients to supply the effective stems and laying the foundation for robust growth in the later stages.

[0036] 122 days after topdressing, the yield gap between the modified treatment group and the control group narrowed significantly. Specifically, the theoretical yield of Example 5 (4.68 tons) was slightly higher than that of the granular physical mixture group (Comparative Example 5, 4.54 tons), showing an initial trend of overtaking. While the theoretical yield of Example 2 (4.45 tons) was still slightly lower than that of Comparative Example 5, the gap had significantly narrowed from 0.60 tons at 60 days to 0.09 tons, indicating a clear catch-up trend in the modified group. This is because the modified urea-formaldehyde skeleton degraded more rapidly at this stage, resulting in sufficient nitrogen supply in the mid-term. Simultaneously, the gradually released GABA improved the plant's assimilation efficiency of water and nutrients by regulating root morphology and enhancing membrane transport activity, leading to good plant growth.

[0037] Two hundred days after topdressing, both GABA-modified treatment groups showed excellent performance. Specifically, Example 5 had a theoretical yield of 6.7 tons, representing increases of 30.4%, 14.7%, and 6.7% compared to pure urea-formaldehyde fluid fertilizer (Comparative Example 1), GABA physical mixed fluid fertilizer (Comparative Example 2), and GABA physical mixed granular fertilizer (Comparative Example 5), respectively. Example 2 had a theoretical yield of 6.57 tons, representing increases of 27.8%, 12.5%, and 4.6% compared to the three control groups, respectively, also showing significant yield increases. The final yields of both modified groups were significantly higher than those of the control groups, indicating that the slow-release system of GABA chemical modification highly matches the nutrient release rhythm of sugarcane's "stable in the early stage, sufficient in the middle stage, and supplemental in the later stage" nutrient requirements. In contrast, the physical mixed group, lacking chemical bond fixation, experienced a significant decrease in nitrogen mineralization rate in the later stages, failing to meet the nutritional needs during the elongation and sugar accumulation periods, resulting in insufficient yield growth in the later stages.

[0038] Regarding sugar accumulation, the sucrose content in both GABA-modified treatment groups was significantly higher than that in the control groups. Specifically, the sucrose content in Example 5 reached 15.62%, and in Example 2 it was 15.58%, while the sucrose content in the control groups ranged from 15.30% to 15.50%. This indicates that GABA chemical modification not only optimizes the nutrient release rhythm, but the gradually released γ-aminobutyric acid also effectively reduces carbon consumption under later environmental stress by strengthening root absorption and enhancing cell osmotic regulation, promoting the directional transport of photosynthetic products to sucrose, thus achieving a dual gain in yield and sugar content.

[0039] Nitrogen release rate determination (1) The nitrogen release rate of fertilizers from Examples 2 (GABA-modified urea-formaldehyde), 5 (gallic acid-GABA-modified urea-formaldehyde), 1 (unmodified urea-formaldehyde), 3 (arginine-modified urea-formaldehyde), and 4 (glycine-modified urea-formaldehyde) was determined using the soil culture-leaching method. The tested soil was alluvial soil with a pH of 6.7, air-dried, and passed through a 2 mm sieve. A sample equivalent to 200 mg N was weighed and mixed with 100 g of soil, then packed into a leaching column (3 cm inner diameter, 30 cm height), with quartz sand and glass wool at the bottom. The column was cultured at 25℃, leached weekly with 50 mL of deionized water, and the nitrogen content of the leached liquid was measured. The culture was continued for 120 days. Each group had three replicates. The results are shown in the table below. Figure 2 , Figure 2 show: From the perspective of cumulative nitrogen nutrient release rate, unmodified urea-formaldehyde released too quickly in the early stage (reaching 13% on day 1 and 39% on day 7), while the release was significantly insufficient in the later stage (only 72% after 75 days and 73% after 90 days), indicating a mismatch between nutrient supply and crop demand. After modification with γ-aminobutyric acid (GABA), the release rate in the early stage was significantly slowed down (only 3.7% on day 1 and 13.8% on day 7), effectively avoiding initial nutrient loss; at the same time, the release capacity in the later stage was continuously enhanced, with a cumulative release rate of 76.6% after 90 days. Example 5 showed similar performance to Example 2, both superior to unmodified urea-formaldehyde (73%) and other amino acid-modified samples (glycine 63.3%, arginine 69%). The above results indicate that GABA-modified urea-formaldehyde effectively solved the release defect of "too fast in the early stage and insufficient in the later stage" in unmodified urea-formaldehyde, achieving a stable and continuous supply of nutrients, and the modification effect was superior to glycine and arginine.

[0040] (2) The nitrogen release rate of fertilizers from Examples 2 (GABA-modified urea-formaldehyde), 5 (gallic acid-GABA-modified urea-formaldehyde), 1 (unmodified urea-formaldehyde), 3 (arginine-modified urea-formaldehyde), and 4 (glycine-modified urea-formaldehyde) was determined using the soil culture-leaching method. The tested soil was alluvial soil with a pH of 4.4, air-dried, and passed through a 2mm sieve. A sample equivalent to 200 mg N was weighed and mixed with 100 g of soil, then packed into a leaching column (3 cm inner diameter, 30 cm height), with quartz sand and glass wool at the bottom. The column was cultured at 25℃, leached weekly with 50 mL of deionized water, and the nitrogen content of the leached liquid was measured. The culture was continued for 120 days. Three replicates were performed for each group. Results are shown in […]. Figure 3 . Figure 3 The results show that in acidic soil (pH 4.4), the slowing effect of the GABA-modified fertilizer in Example 2 on the initial release rate was weaker than that in neutral soil, indicating that the acidic environment weakened the inhibitory effect of GABA modification on the initial release. In contrast, the gallic acid-GABA-modified fertilizer in Example 5 showed a significant slowing effect on the initial release rate, and its release capacity continued to increase in the later stages, outperforming the GABA-modified fertilizer. These results indicate that in acidic soil, the gallic acid-GABA-modified urea-formaldehyde fertilizer achieves a better effect of slow release in the early stages and accelerated release in the later stages than the GABA-modified urea-formaldehyde fertilizer, and is also superior to the effects of comparative examples 1, 3, and 4.

[0041] The foregoing description of specific exemplary embodiments of the invention is for illustrative and explanatory purposes. These descriptions are not intended to limit the invention to the precise forms disclosed, and it will be apparent that many changes and variations can be made in accordance with the foregoing teachings. The exemplary embodiments were chosen and described in order to explain the specific principles of the invention and its practical application, thereby enabling those skilled in the art to implement and utilize various different exemplary embodiments of the invention, as well as various different choices and variations. The scope of the invention is intended to be defined by the claims and their equivalents.

Claims

1. A γ-aminobutyric acid-modified urea-formaldehyde slow-release suspension fertilizer, characterized in that, Based on mass parts, it is mainly composed of the following raw materials: 10-25 parts of γ-aminobutyric acid modified urea-formaldehyde slow-release polymer, 25-65 parts of water-soluble nitrogen, phosphorus and potassium fertilizer, 0.2-2 parts of suspending agent, 0.1-1 parts of thickener, and water to make up to 100 parts; the γ-aminobutyric acid modified urea-formaldehyde slow-release polymer is obtained by embedding γ-aminobutyric acid into the molecular skeleton of urea-formaldehyde with covalent bonds.

2. The γ-aminobutyric acid modified urea-formaldehyde slow-release suspension fertilizer according to claim 1, characterized in that, The water-soluble nitrogen, phosphorus, and potassium fertilizer is selected from one or more of urea, ammonium sulfate, ammonium nitrate, monoammonium phosphate, diammonium phosphate, polyammonium phosphate, potassium dihydrogen phosphate, potassium chloride, potassium sulfate, and potassium nitrate.

3. The γ-aminobutyric acid modified urea-formaldehyde slow-release suspension fertilizer according to claim 1, characterized in that, The suspending agent is selected from one or two of magnesium aluminum silicate and bentonite.

4. The γ-aminobutyric acid modified urea-formaldehyde slow-release suspension fertilizer according to claim 1, characterized in that, The thickener is selected from one or more of xanthan gum, guar gum, sodium alginate, and sodium polyacrylate.

5. A method for preparing a slow-release suspension fertilizer as described in any one of claims 1-4, characterized in that, Includes the following steps: (1) Preparation of hydroxymethylurea solution: urea and formaldehyde are mixed and reacted to obtain hydroxymethylurea solution; (2) Preparation of γ-aminobutyric acid modified urea-formaldehyde slow-release polymer: γ-aminobutyric acid is added to the hydroxymethyl urea solution, the molar ratio of γ-aminobutyric acid to urea is (0.01-0.10):1.0, the pH is adjusted to 4.0-5.0, the temperature is raised to 60-80℃, and the polycondensation reaction is carried out for 1-3 hours to obtain γ-aminobutyric acid modified urea-formaldehyde slow-release polymer; (3) Preparation of suspension fertilizer: The γ-aminobutyric acid modified urea-formaldehyde slow-release polymer is mixed with water-soluble nitrogen, phosphorus and potassium fertilizer, suspending agent, thickener and water in proportion, and then sheared, emulsified and homogenized to obtain suspension fertilizer.

6. The method for preparing slow-release suspension fertilizer according to claim 5, characterized in that, In step (1), urea and formaldehyde are mixed in a molar ratio of 1.2-1.8:1, the pH is adjusted to 8.0-9.0, and the mixture is reacted at 75-85℃ for 0.5-2 hours to obtain a hydroxymethylurea solution.

7. The method for preparing slow-release suspension fertilizer according to claim 5, characterized in that, In step (2), the preparation method of γ-aminobutyric acid modified urea-formaldehyde slow-release polymer is as follows: First, gallic acid and γ-aminobutyric acid are added to water at a mass ratio of 3:(4-5). Under the catalysis of toluenesulfonic acid, the mixture is heated to 80-85℃ and reacted for 3-4 hours. Then, the temperature is lowered to 35-40℃ and the pH is adjusted to 7.0-7.5 to obtain intermediate 1. Then, intermediate 1 is added to the hydroxymethyl urea solution. The molar ratio of γ-aminobutyric acid to urea is (0.01-0.10):1.

0. The pH is adjusted to 4.0-5.0, the temperature is raised to 60-80℃, and the polycondensation reaction is carried out for 1-3 hours to obtain γ-aminobutyric acid modified urea-formaldehyde slow-release polymer.

8. In the method for preparing slow-release suspension fertilizer according to claim 5, in step (3), the rotation speed of shear emulsification is 3000-7000 rpm, the dispersion time is 15-60 minutes, and the suspended particle size is controlled to be ≤80μm.

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