Starch-based gel coated slow-release fertilizer with pH and temperature double responses

Abstract

The invention relates to the technical field of slow release fertilizer preparation, and discloses a pH temperature dual-response starch-based gel coated slow release fertilizer, which comprises: an amorphous starch matrix, which is prepared by treating common corn starch with ethanol and drying; the invention relates to a pH / temperature responsive starch-based gel coating material, which is formed by taking amorphous starch, N-isopropylacrylamide (NIPAM), acrylic acid (AA) and N, N '-methylenebisacrylamide (MBA) as cross-linking agents through a cross-linking reaction under the initiation of potassium persulfate (KPS), and has dual responsiveness to pH value and temperature change. The at least one fertilizer core substance is uniformly coated with the pH / temperature-responsive starch-based gel coating material to form a slow-release structure. The slow release fertilizer provided by the invention integrates a pH and temperature dual response mechanism, and can intelligently adjust the release rate of nutrients according to the actual change of the soil environment, thereby realizing accurate supply of nutrients.

Description

Technical Field

[0001] The invention relates to the technical field of slow-release fertilizer preparation, in particular to a pH-temperature dual-responsive starch-based gel-coated slow-release fertilizer. Background Art

[0002] Slow-release fertilizer, also known as long-acting fertilizer, is a type of fertilizer manufactured through specific production processes and technologies. Its main feature is that it can slowly release the nutrients in the fertilizer, thereby meeting the growth needs of plants over a longer period of time. Compared with traditional quick-acting fertilizers, the release rate of slow-release fertilizers is controlled, which can continuously provide plants with a stable supply of nutrients.

[0003] In the actual use process of modern agriculture, the growth of plants is not only related to soil moisture, soil nutrient types and contents, but also affected by environmental factors such as soil pH, ambient temperature, and microorganisms. Existing slow-release fertilizers can generally only respond to a single temperature or pH, that is, at a suitable temperature or pH, the best slow-release effect can be achieved. However, in real life, the temperature and pH of the environment often cannot reach the best at the same time, that is, the slow-release fertilizer is in an environment where temperature and pH act simultaneously, and there is a lack of research on fertilizers that are dual-responsive to pH and temperature, resulting in poor slow-release effects of existing fertilizers in actual operations. Based on this, the present invention designs a pH-temperature dual-responsive starch-based gel-coated slow-release fertilizer to solve the above problems. Summary of the invention

[0004] The purpose of the present invention is to provide a pH-temperature dual-responsive starch-based gel-coated slow-release fertilizer, which solves the problem of lack of pH-temperature dual-responsive research in the background technology.

[0005] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0006] A pH-temperature dual-responsive starch-based gel-coated slow-release fertilizer, comprising:

[0007] An amorphous starch matrix, which is prepared by treating ordinary corn starch with ethanol and drying it;

[0008] A pH / temperature responsive starch-based gel coating material, which is formed by a cross-linking reaction of the amorphous starch, N-isopropylacrylamide (NIPAM), acrylic acid (AA) and N,N'-methylenebisacrylamide (MBA) as cross-linking agents under the initiation of potassium persulfate (KPS) and has dual responsiveness to changes in pH and temperature;

[0009] At least one fertilizer core material, the fertilizer core material is uniformly coated by the pH / temperature responsive starch-based gel coating material to form a slow-release structure.

[0010] Preferably, the method for preparing the amorphous starch matrix comprises the following steps:

[0011] Step S101, mixing common corn starch with 50% by volume ethanol, and stirring in a water bath at 85° C. for 2 hours;

[0012] Step S102, filtering and separating the solid matter, washing with 50% by volume ethanol, drying at 50°C for 24 hours, and then crushing and sieving to obtain amorphous starch powder.

[0013] Preferably, the method for preparing the pH / temperature responsive starch-based gel comprises:

[0014] Step S201, dissolving amorphous starch in distilled water, adding NIPAM, AA and MBA as cross-linking agents, and performing a pre-cross-linking treatment at 55° C.;

[0015] Step S202, dissolving KPS in water, and adding it dropwise into the pre-crosslinking solution as an initiator, heating it to a suitable temperature to initiate a crosslinking reaction, thereby obtaining a gel, which is then dried and ground for later use.

[0016] Preferably, the core material of the fertilizer is urea, the surface of which is moistened with anhydrous ethanol and then uniformly coated with the pH / temperature responsive starch-based gel powder using a disc method to form a multi-layer coating structure.

[0017] Preferably, the method for preparing the pH / temperature dual-responsive starch-based gel-coated slow-release fertilizer comprises the following steps:

[0018] Step S301, preparing amorphous starch according to steps S101 and S102;

[0019] Step S302, preparing a pH / temperature responsive starch-based gel according to steps S201 and S202;

[0020] Step S303, after wetting the surface of the fertilizer core material, use the gel powder to perform multi-layer coating, and dry to obtain pH / temperature dual-responsive starch-based gel-coated slow-release fertilizer.

[0021] Preferably, during the coating process, the slow-release performance of the slow-release fertilizer can be optimized by adjusting the number of coating layers and drying conditions.

[0022] Preferably, the application of the pH-temperature dual-responsive starch-based gel-coated slow-release fertilizer is particularly suitable for improving fertilizer utilization, reducing nutrient loss, promoting plant growth and adapting to agricultural practices under different soil and climatic conditions.

[0023] Compared with the prior art, the beneficial effects achieved by the present invention are:

[0024] 1. The slow-release fertilizer of the present invention integrates a dual response mechanism of pH and temperature, and can intelligently adjust the release rate of nutrients according to the actual changes in the soil environment. Under suitable pH and temperature conditions, the fertilizer can efficiently release nutrients, while under non-optimal conditions, the release is slowed down, thereby achieving accurate nutrient supply and significantly improving the utilization rate of the fertilizer.

[0025] 2. In the present invention, traditional slow-release fertilizers can only respond to temperature or pH value, which limits their effect in practical applications. The dual-responsive slow-release fertilizer designed in the present invention can simultaneously respond to changes in soil pH and temperature, enhancing its adaptability under different soil and climatic conditions, and providing the possibility for its wide application in various farmland environments.

[0026] 3. The starch-based gel coating material of the present invention has good water holding and water retention properties, and can effectively reduce the evaporation and loss of soil moisture in arid and semi-arid areas. This property not only improves the water retention rate of the soil, but also improves the moisture condition of the soil, providing a more stable moisture environment for plant growth. By controlling the release rate of nutrients, the slow-release fertilizer of the present invention significantly reduces the loss and waste of nutrients and reduces the risk of environmental pollution. At the same time, its water holding and water retention properties also help to reduce nutrient loss caused by irrigation and rainwater erosion, further protecting the ecological environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 is a flow chart of the preparation method of the present invention;

[0028] Figure 2 The present invention is a flow chart for preparing the amorphous starch matrix and the pH / temperature responsive starch-based gel;

[0029] Figure 3 The formula table of the pH / temperature responsive starch-based gel (DNA) of the present invention;

[0030] Figure 4 FTIR spectra of amorphous starch (Aa), DNA (Ab), DNA starch-based gels with different NIPAM to AA molar ratios (B) and different St to monomer molar ratios (C) of the present invention;

[0031] Figure 5 XRD spectra of starch (a), amorphous starch (b) and DNA (c) of the present invention;

[0032] Figure 6 The SEM images of DNA gels with different NIPAM to AA molar ratios at different scales of the present invention;

[0033] Figure 7The SEM images of DNA gels with different molar ratios of St to monomer of the present invention at different scales;

[0034] Figure 8 The present invention is a trend diagram of the water absorption swelling rate (A, D), equilibrium swelling rate (B, E) and swelling equilibrium time (C, F) of the DNA gel with different NIPAM to AA molar ratios and different St to monomer molar ratios;

[0035] Fig. 9 The present invention is a trend diagram of the water absorption swelling rate (A, D, G, J, M), equilibrium swelling rate (B, E, H, K, N) and swelling equilibrium time (C, F, I, L, O) of the DNA gel with different NIPAM to AA molar ratios at different pH values;

[0036] Fig.10 It is the pH responsiveness trend diagram of DNA gel with different NIPAM and AA molar ratios;

[0037] Fig.11 Trend diagrams of water absorption swelling ratio (A, D, G, J, M), equilibrium swelling ratio (B, E, H, K, N) and swelling equilibrium time (C, F, I, L, O) of DNA gels with different St to monomer molar ratios at different pH values;

[0038] Fig.12 The pH response performance diagram of DNA gel with different molar ratios of St to monomer;

[0039] Fig.13 The trend graphs of water absorption swelling rate (A, D, G, J, M), equilibrium swelling rate (B, E, H, K, N) and swelling equilibrium time (C, F, I, L, O) of DNA gels with different NIPAM to AA molar ratios at different temperatures;

[0040] Fig.14 The trend diagram of temperature responsiveness of DNA gel with different NIPAM to AA molar ratios;

[0041] Fig.15 The graphs show the changing trends of water absorption swelling ratio (A, D, G, J, M), equilibrium swelling ratio (B, E, H, K, N) and swelling equilibrium time (C, F, I, L, O) of DNA gels with different molar ratios of St to monomer at different temperatures;

[0042] Fig.16 The temperature response performance diagram of DNA gel with different molar ratios of St to monomer;

[0043] Fig.17 This is the water holding capacity diagram of DNA-SRF in soils with different pH and different temperatures;

[0044] Fig.18This is the water retention performance diagram of DNA-SRF in soil environment with pH = 7 and 25℃;

[0045] Fig.19 The water retention performance diagram of DNA-SRF in soil environments with different pH (A, B, C) and different temperatures (D, E, F);

[0046] Fig. 20 This is the slow-release performance diagram of urea and DNF-SRF in a water environment of pH = 7 and 25°C;

[0047] Fig.21 The sustained release performance diagram of DNA-SRF in water environments with different pH (A, B, C) and different temperatures (D, E, F);

[0048] Fig. 22 This is the slow-release performance diagram of urea and DNF-SRF in soil environment with pH = 7 and 25°C;

[0049] Fig.23 This is a graph showing the slow-release performance of DNA-SRF in soil environments with different pH (A, B, C) and different temperatures (D, E, F). DETAILED DESCRIPTION

[0050] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0051] Embodiment 1;

[0052] In an embodiment of the present invention, a pH-temperature dual-responsive starch-based gel-coated slow-release fertilizer comprises:

[0053] An amorphous starch matrix, which is prepared by treating ordinary corn starch with ethanol and drying it;

[0054] A pH / temperature responsive starch-based gel coating material, which is formed by a cross-linking reaction of amorphous starch, N-isopropylacrylamide (NIPAM), acrylic acid (AA) and N,N'-methylenebisacrylamide (MBA) as cross-linking agents under the initiation of potassium persulfate (KPS) and has dual responsiveness to changes in pH and temperature;

[0055] At least one fertilizer core material, the fertilizer core material is uniformly coated by a pH / temperature responsive starch-based gel coating material to form a slow-release structure.

[0056] The preparation method of the amorphous starch matrix comprises the following steps:

[0057] Step S101, mixing common corn starch with 50% by volume ethanol, and stirring in a water bath at 85° C. for 2 hours;

[0058] Step S102, filtering and separating the solid matter, washing with 50% by volume ethanol, drying at 50°C for 24 hours, and then crushing and sieving to obtain amorphous starch powder.

[0059] The preparation method of pH / temperature responsive starch-based gel comprises:

[0060] Step S201, dissolving amorphous starch in distilled water, adding NIPAM, AA and MBA as cross-linking agents, and performing a pre-cross-linking treatment at 55° C.;

[0061] Step S202, dissolving KPS in water, and adding it dropwise into the pre-crosslinking solution as an initiator, heating it to a suitable temperature to initiate a crosslinking reaction, thereby obtaining a gel, which is then dried and ground for later use.

[0062] The core material of the fertilizer is urea. After its surface is moistened with anhydrous ethanol, the pH / temperature responsive starch-based gel powder is evenly coated using the disc method to form a multi-layer coating structure.

[0063] The preparation method of pH / temperature dual-responsive starch-based gel-coated slow-release fertilizer comprises the following steps:

[0064] Step S301, preparing amorphous starch according to steps S101 and S102;

[0065] Step S302, preparing a pH / temperature responsive starch-based gel according to steps S201 and S202;

[0066] Step S303, after wetting the surface of the fertilizer core material, it is coated with gel powder in multiple layers, and then dried to obtain a pH / temperature dual-responsive starch-based gel-coated slow-release fertilizer.

[0067] During the coating process, the slow-release performance of the slow-release fertilizer can be optimized by adjusting the number of coating layers and drying conditions.

[0068] The application of pH-temperature dual-responsive starch-based gel-coated slow-release fertilizer is particularly suitable for improving fertilizer utilization, reducing nutrient loss, promoting plant growth and adapting to different soil and climatic conditions in agricultural practice.

[0069] The working principle of the embodiment of the present invention is that the preparation of amorphous starch matrix is ​​the cornerstone of the entire slow-release fertilizer system. By treating corn starch with ethanol and drying it, the crystal structure of the starch is destroyed, and it is transformed into an amorphous state, which enhances the solubility and reactivity of the starch, and provides a good base material for the subsequent preparation of pH / temperature responsive gel coating materials.

[0070] The synthesis of pH / temperature responsive starch-based gel coating material is a key step. This material combines amorphous starch, N-isopropylacrylamide (NIPAM, which imparts temperature responsiveness), acrylic acid (AA, which imparts pH responsiveness) and N,N'-methylenebisacrylamide (MBA, as a cross-linking agent). Under the initiation of potassium persulfate (KPS), a gel with dual responsiveness is formed through a cross-linking reaction. This gel can swell or shrink according to changes in environmental pH and temperature, thereby adjusting the release rate of the fertilizer.

[0071] During the coating process of the fertilizer core material (such as urea), anhydrous ethanol is used to wet the fertilizer surface, and then the pH / temperature responsive starch-based gel powder is evenly coated by the disc method to form a multi-layer coating structure. This structure not only effectively protects the fertilizer core, but also gives the fertilizer the ability to respond to changes in the soil environment.

[0072] When the slow-release fertilizer is applied to the soil, its working principle is mainly reflected in two aspects: first, according to the change of soil pH value, the AA component will cause the gel capsule to swell or shrink, adjusting the release rate of the fertilizer; second, as the soil temperature changes, the NIPAM component will responsively change the hydrophilicity and permeability of the gel, further controlling the release of nutrients. This dual response mechanism enables the fertilizer to release nutrients in a more precise and efficient manner under specific soil and climate conditions, thereby improving the utilization rate of the fertilizer, reducing nutrient loss, and promoting plant growth.

[0073] Embodiment 2;

[0074] In the embodiment of the present invention,

[0075] 1. FTIR characterization and analysis of DNA

[0076] The FTIR analysis results of amorphous starch (Aa), SNA (Ab), NIPAM with AA molar ratio of 2:1 (Ba), 3:2 (Bb), 1:1 (Bc), 2:3 (Bd), 1:2 (Be) and SNA gel with St and monomer molar ratio of 2:1 (Ca), 3:1 (Cb), 4:1 (Cc), 5:1 (Cd), 6:1 (Ce) are shown in Figure 2. Figure 4 As shown. 3200~3400cm in curve Aa -1 It is the stretching vibration absorption peak of the hydroxyl (-OH) on the starch molecular chain, 2900cm-1 is the stretching vibration absorption peak of methylene (-CH2-) in starch, 1650cm -1 is the stretching vibration absorption peak of the carbonyl (C=O) in starch, 1400cm -1 It is the stretching vibration absorption peak of the carbon-hydrogen bond (CH) in starch. 2820cm in curve Ab -1 is the stretching vibration absorption peak of the hydroxyl group (-OH) in AA, 1650cm -1 The increase in the intensity of the peak at 1479 cm is due to the synergistic effect of the carbonyl (C=O) in AA, the carbonyl (C=O) in NIPAM and the carbonyl (C=O) in starch, while the peak at 1479 cm -1 The characteristic absorption peak at 2820cm is enhanced due to the antisymmetric and stretching vibration of the carboxyl C=O in AA. -1 、1650cm -1 and 1479cm -1 The presence of the peak at is sufficient to indicate that the DNA has been successfully prepared.

[0077] As the proportion of NIPAM increases, the 1650 cm -1 The characteristic absorption peaks of carbonyl (C=O) and 1120 cm -1 The ML in-plane rocking vibration absorption peak gradually increases ( Figure 4 B) As the proportion of starch increases, the 1650cm -1 The stretching vibration absorption peak of the carbonyl group (C=O) gradually weakens ( Figure 4 C).

[0078] 2. XRD characterization and analysis of DNA

[0079] XRD was used to characterize the crystal structure of starch (a), amorphous starch (b) and DNA (c) gel. In curve a, the diffraction peaks of starch appeared at 2θ of 18.2°, 22.6°, 34.2° and 81.3°. The baseline of the spectrum was not stable, the diffraction peaks were relatively thin and strong, and there were many sharp peaks between 10° and 25°, which may come from the impurities in the starch. In curve b, the diffraction peaks at 2θ of 18.2°, 22.6° and 34.2° were relatively wide and weak, indicating that the crystallinity of amorphous starch was lower than that of starch, and the gel prepared with amorphous starch as raw material would have a higher degree of cross-linking. Compared with the XRD spectrum of amorphous starch, the baseline of the DNA gel spectrum was stable, and there was only a wide and blunt single peak between 10° and 25°, and the impurities disappeared significantly.

[0080] 3. SEM characterization and analysis of DNA

[0081] Figure 6SEM images of DNA gels at different scales with NIPAM to AA molar ratios of 2:1 (a, b, c), 3:2 (d, e, f), 1:1 (g, h, i), 2:3 (j, k, l) and 1:2 (m, n, o) are shown. When the NIPAM to AA molar ratio is 2:1 and 3:2, the gel presents a dense three-dimensional network structure with uniform pore distribution, pore diameter between 10-20 μm, and gel skeleton width and thickness between 3-5 μm. When the NIPAM to AA molar ratio is 1:1, the pore diameter expands to between 15-30 μm, and the gel skeleton width is about 7 μm, providing a good structural basis for the water absorption and swelling properties of the gel. When the NIPAM to AA molar ratio is 2:3 and 1:2, the pore diameter is limited to less than 10 μm, the gel skeleton width is about 10 μm, and the structure of the gel becomes more compact. With the increase of NIPAM content, the pore diameter of DNA gel first increases and then decreases, reaching the maximum value when the molar ratio of NIPAM to AA is 1:1.

[0082] Figure 7 SEM images of DNA gels at different scales with St to monomer molar ratios of 2:1 (a, b), 3:1 (c, d), 4:1 (e, f), 5:1 (g, h) and 6:1 (i, j) are shown. When the molar ratio of St to monomer is 2:1, the three-dimensional network structure of the gel is intricate and densely arranged, but the "empty chamber" phenomenon occurs, and vacancies appear in some spaces without cross-linking. When the molar ratio of St to monomer is 3:1 and 4:1, the gel presents a dense three-dimensional network structure with pore diameters between 10-15μm and gel skeleton width and thickness between 3-5μm. When the molar ratio of St to monomer is 3:1 and 4:1, a large area of ​​wall appears, which will cause a greater obstacle to the release of nutrients. With the increase of St content, the width and thickness of the gel skeleton have been increasing. When a large area of ​​wall appears, its sustained release performance will be reduced.

[0083] 4. Effect of process conditions on DNA water absorption and swelling rate

[0084] The slow-release and water-retention properties of hydrogel slow-release fertilizers depend on the water absorption and swelling characteristics of the polymer network, and the swelling capacity depends on the strength and elasticity of the hydrogel network. If the network is weak, in this chapter, the swelling behavior was measured using a single factor experiment, and the molar ratio of NIPAM to AM and the molar ratio of St to monomer were optimized. All prepared SNA hydrogels were subjected to equilibrium swelling studies in a water environment at room temperature and pH = 7, and the water absorption and swelling rate of the samples were measured every 5 hours.

[0085] Figure 8The water absorption swelling rate (A, D), equilibrium swelling rate (B, E) and swelling equilibrium time (C, F) of DNA gels with NIPAM to AA molar ratios of 2: 1, 3: 2, 1: 1, 2: 3 and 1: 2 and St to monomer molar ratios of 2: 1, 3: 1, 4: 1, 5: 1 and 6: 1 are shown. The water absorption swelling rate of DNA gels with different NIPAM to AA molar ratios and different St to monomer molar ratios gradually increases with time and reaches swelling equilibrium after a certain period of time.

[0086] like Figure 8 As shown in Figure A, DNA gels with NIPAM to AA molar ratios of 2:1, 3:2 and 1:1 reached swelling equilibrium at the fastest speed at 40 h, and the equilibrium swelling rates were 12.77 g / g, 7.41 g / g and 12.66 g / g, respectively. Among them, the DNA gel with a NIPAM to AA molar ratio of 2:1 showed the highest equilibrium swelling rate. DNA gels with NIPAM to AA molar ratios of 5:1 and 6:1 reached swelling equilibrium at 85 h, and the equilibrium swelling rates were 9.14 g / g and 6.59 g / g, respectively. The water absorption swelling rate of DNA gels gradually decreased according to the following NIPAM to AA molar ratios: NIPAM:AA = 2:1 > NIPAM:AA = 1:1 > NIPAM:AA = 2:3 > NIPAM:AA = 3:2 > NIPAM:AA = 1:2.

[0087] like Figure 8 As shown in D, the DNA gel with a St to monomer molar ratio of 6:1 reached swelling equilibrium the fastest at 25 h, with an equilibrium swelling rate of 9.16 g / g. The DNA gel with a St to monomer molar ratio of 3:1 achieved the highest equilibrium swelling rate (12.66 g / g) at 40 h. The DNA gel with a St to monomer molar ratio of 3:1 showed the longest swelling equilibrium time (60 h) and a good equilibrium swelling rate (14.64 g / g). The water absorption swelling rate of the DNA gel gradually decreased according to the following St to monomer molar ratios: St:(NIPAM+AA)=3:1>St:(NIPAM+AA)=2:1>St:(NIPAM+AA)=4:1>St:(NIPAM+AA)=5:1>St:(NIPAM+AA)=6:1.

[0088] 5. Study on pH response properties of DNA

[0089] (1) Effect of different NIPAM to AA molar ratios on the pH response of DNA

[0090] Fig. 9The water absorption swelling rate, equilibrium swelling rate and swelling equilibrium time of DNA gels with NIPAM to AA molar ratio of 2:1 (A, B, C), 3:2 (D, E, F), 1:1 (G, H, I), 2:3 (J, K, L) and 1:2 (M, N, O) in water environments of pH = 3, pH = 5, pH = 7, pH = 9 and pH = 11 are shown. The DNA gel with NIPAM to AA molar ratio of 2:1 reached swelling equilibrium the fastest in water environment of pH = 11, with a swelling equilibrium time of 20h, and showed the highest equilibrium swelling rate (18.59g / g); it showed excellent swelling equilibrium time (45h) in water environments of pH = 7 and pH = 9, and its equilibrium swelling rate was 12.61g / g and 14.38g / g, respectively. SA gel with a NIPAM to AA molar ratio of 3:2 quickly reached swelling equilibrium in water environments of pH=3 and pH=5, with a swelling equilibrium time of 25h; it also showed the highest equilibrium swelling rate (14.69g / g) in water environments of pH=11; and it also showed the longest swelling equilibrium time (85h) in water environments of pH=7. DNA gel with a NIPAM to AA molar ratio of 1:1 reached swelling equilibrium most quickly in water environments of pH=7, with a swelling equilibrium time of 20h, and also showed a high equilibrium swelling rate (13.49g / g); it showed the highest equilibrium swelling rate (20.74g / g) and the longest swelling equilibrium time (30h) in water environments of pH=11. DNA gels with a NIPAM to AA molar ratio of 2:3 reached swelling equilibrium most quickly in a water environment of pH = 3, with a swelling equilibrium time of 30 h; they showed the highest equilibrium swelling rate (14.82 g / g) in a water environment of pH = 11; and they showed the longest swelling equilibrium time (65 h) in a water environment of pH = 7. DNA gels with a NIPAM to AA molar ratio of 1:2 showed the highest equilibrium swelling rate (15.59 g / g) and the longest swelling equilibrium time (90 h) in a water environment of pH = 11.

[0091] Fig.10 The pH responsiveness of DNA gels with NIPAM to AA molar ratios of 2:1, 3:2, 1:1, 2:3, and 1:2 is shown. Fig.10 As shown in Figure A, the equilibrium swelling rate of DNA gels with NIPAM and AA molar ratios of 2:1 and 1:1 basically shows an upward trend as the pH value gradually increases. In an alkaline water environment, it exhibits good water absorption and swelling properties. Fig.10 As shown in Figure B, the pH response curves of SA gels with NIPAM to AA molar ratios of 3:2, 2:3, and 1:2 have similar changing trends, showing an "N" type change. All DNA gels exhibited optimal water absorption and swelling properties in a water environment of pH = 11.

[0092] (2) Effects of different St to monomer molar ratios on the pH response of DNA

[0093] Fig.11 The water absorption swelling rate, equilibrium swelling rate and swelling equilibrium time of DNA gels with St to monomer molar ratios of 2:1 (A, B, C), 3:1 (D, E, F), 4:1 (G, H, I), 5:1 (J, K, L) and 6:1 (M, N, O) in water environments of pH=3, pH=5, pH=7, pH=9 and pH=11 are shown. The DNA gel with a St to monomer molar ratio of 2:1 showed the highest equilibrium swelling rate (29.27 g / g) in a water environment of pH=11 and reached the longest swelling equilibrium time (85 h) in a water environment of pH=9. The DNA gel with a St to monomer molar ratio of 3:1 showed the highest equilibrium swelling rate (34.75 g / g) in a water environment of pH=11. DNA gels with a molar ratio of St to monomer of 4:1 reached swelling equilibrium most quickly in a water environment with a pH of 7, with a swelling equilibrium time of 20 hours, and also showed a high equilibrium swelling rate (13.49 g / g); they showed the highest equilibrium swelling rate (20.74 g / g) and the longest swelling equilibrium time (30 hours) in a water environment with a pH of 11. DNA gels with a molar ratio of St to monomer of 5:1 and 6:1 also showed the highest equilibrium swelling rates in a water environment with a pH of 11, which were 23.73 g / g and 20.41 g / g, respectively.

[0094] Fig.12 The pH response properties of DNA gels with St to monomer molar ratios of 2:1, 3:1, 4:1, 5:1, and 6:1 were demonstrated. Fig.12 As shown in A, the DNA gels with St to monomer molar ratios of 2:1 and 3:1 show an "N" shape change with the increase of pH, and the highest equilibrium swelling rate is achieved at pH = 11. When the DNA gels with St to monomer molar ratios of 4:1, 5:1, and 6:1 are in a neutral to weakly alkaline environment, their equilibrium swelling rates will decrease slightly, and then continue to rise, and the highest equilibrium swelling rate is achieved at pH = 11.

[0095] 6. Study on the temperature response performance of DNA

[0096] (1) Effects of different NIPAM to AA molar ratios on the temperature response of DNA

[0097] Fig.13The water absorption swelling rate, equilibrium swelling rate and swelling equilibrium time of DNA gels with NIPAM to AA molar ratios of 2:1 (A, B, C), 3:2 (D, E, F), 1:1 (G, H, I), 2:3 (J, K, L) and 1:2 (M, N, O) in water environments of T = 0°C, T = 15°C, T = 25°C, T = 35°C and T = 45°C are shown. The DNA gel with a NIPAM to AA molar ratio of 2:1 reached swelling equilibrium the fastest (20h) in a water environment of T = 45°C, and showed the lowest equilibrium swelling rate (6.61g / g); it showed the highest equilibrium swelling rate (12.77g / g) and the longest swelling equilibrium time (40h) in a water environment of T = 25°C. The DNA gel with a molar ratio of NIPAM to AA of 3:2 also reached swelling equilibrium the fastest (25h) in a water environment at T = 45℃, and showed the lowest equilibrium swelling rate (5.20g / g); it showed the highest equilibrium swelling rate (9.77g / g) and the longest swelling (5.20g / g) in a water environment at T = 15℃; it showed the highest equilibrium swelling rate (9.77g / g) and the longest swelling equilibrium time (40h) in a water environment at T = 15℃. The DNA gel with a molar ratio of NIPAM to AA of 1:1 reached swelling equilibrium the fastest (30h) in a water environment at T = 35℃, and showed the lowest equilibrium swelling rate (5.48g / g); it showed the highest equilibrium swelling rate (13.28g / g) and the longest swelling equilibrium time (40h) in a water environment at T = 15℃. The DNA gel with a NIPAM to AA molar ratio of 2:3 showed the highest equilibrium swelling rate (9.14 g / g) and the longest swelling equilibrium time (85 h) in a water environment at T = 25 ° C. The DNA gel with a NIPAM to AA molar ratio of 1:2 also showed the longest swelling equilibrium time (85 h) and a higher equilibrium swelling rate (6.59 g / g) in a water environment at T = 25 ° C.

[0098] Fig.14 The temperature responsiveness of DNA gels with NIPAM to AA molar ratios of 2:1, 3:2, 1:1, 2:3, and 1:2 is shown. Fig.14 As shown in A, the temperature response curves of DNA gels with NIPAM to AA molar ratios of 2:1, 1:1, and 2:3 increase first, then decrease, and then increase again as the temperature rises, showing an "N"-shaped change pattern. They exhibit excellent water absorption and swelling properties in both room temperature and low temperature regions. Fig.14 As shown in Figure B, the temperature response curve of the DNA gel with a molar ratio of NIPAM to AA of 3:2 first increases and then decreases as the temperature increases, while the temperature response of the DNA gel with a molar ratio of NIPAM to AA of 1:2 is weaker, and its temperature response curve fluctuates slightly around 6.5 g / g as the temperature increases.

[0099] (2) Effects of different St to monomer molar ratios on the temperature response of DNA

[0100] Fig.15 The water absorption swelling rate, equilibrium swelling rate and swelling equilibrium time of DNA gels with St to monomer molar ratios of 2:1 (A, B, C), 3:1 (D, E, F), 4:1 (G, H, I), 5:1 (J, K, L) and 6:1 (M, N, O) in water environments of T=0℃, T=15℃, T=25℃, T=35℃ and T=45℃ are shown. The DNA gel with a St to monomer molar ratio of 2:1 reached swelling equilibrium the fastest (25h) in a water environment of T=45℃ and showed the highest equilibrium swelling rate (16.05g / g) in a water environment of T=15℃. The DNA gel with a St to monomer molar ratio of 3:1 showed the highest equilibrium swelling rate (16.41g / g) and the longest swelling equilibrium time (40h) in a water environment of T=25℃. DNA gels with a St to monomer molar ratio of 4:1 reached swelling equilibrium the fastest (30 h) in a water environment at T = 35 °C, and showed the lowest equilibrium swelling rate (5.48 g / g); they showed the highest equilibrium swelling rate (13.28 g / g) and the longest swelling equilibrium time (40 h) in a water environment at T = 15 °C. DNA gels with a St to monomer molar ratio of 5:1 showed the highest equilibrium swelling rate (11.87 g / g) and the longest swelling equilibrium time (35 h) in a water environment at T = 15 °C. DNA gels with a St to monomer molar ratio of 6:1 showed the highest equilibrium swelling rate (9.16 g / g) in a water environment at T = 25 °C.

[0101] Fig.16 The temperature responsiveness of DNA gels with St to monomer molar ratios of 2:1, 3:1, 4:1, 5:1 and 6:1 is shown. Except for the DNA gel with St to monomer molar ratio of 6:1, the temperature responsiveness curves of DNA gels with other molar ratios show an "N" shape change, first increasing, then decreasing, and then increasing again. The water absorption and swelling properties at 25℃ and 15℃ are higher than those at 0℃, 35℃ and 45℃.

[0102] Based on the results of DNA structural characterization, water absorption and swelling properties, pH response properties and temperature response properties, and taking the arid and cold climate and weakly alkaline soil in the northwest as the application environment, it is necessary to maintain good swelling properties under low temperature, normal temperature and weakly alkaline soil environment. This patent selects DNA gel with a molar ratio of NIPAM to AA of 1:1 and a molar ratio of St to monomer of 3:1 as the coating material of the fertilizer.

[0103] The working principle of the embodiment of the present invention is: through characterization methods such as FTIR, XRD and SEM, it is found that DNA gels with different ratios show significant differences in molecular structure and morphology. FTIR analysis reveals the synergistic effect of chemical bonds between different components, confirming the successful preparation of DNA. XRD analysis shows that DNA gel has lower crystallinity than amorphous starch, which is conducive to the formation of a gel network with a high degree of cross-linking. SEM images intuitively show the three-dimensional network structure of the gel and its pore distribution, providing a structural basis for understanding its swelling properties.

[0104] The study measured the water absorption and swelling behavior of DNA gels with different ratios through single-factor experiments and found that their swelling ability was significantly affected by the molar ratio of NIPAM to AA and the molar ratio of St to monomer. Specifically, when the molar ratio of NIPAM to AA was 1:1, the DNA gel showed the highest equilibrium swelling rate, while when the molar ratio of St to monomer was 3:1, a good balance was achieved between the swelling equilibrium time and the swelling rate. This shows that the water absorption and swelling properties of the gel can be optimized by properly adjusting the raw material ratio.

[0105] Water absorption and swelling experiments under different pH environments showed that DNA gels have obvious pH responsiveness. In alkaline environments, especially when pH = 11, DNA gels of various ratios showed optimal water absorption and swelling properties. This is because alkaline conditions promote the breaking of hydrogen bonds in the gel network, thereby enhancing its swelling capacity. In addition, DNA gels with different NIPAM to AA molar ratios and St to monomer molar ratios showed different trends in pH responsiveness, further verifying that the pH response behavior of the gel can be regulated by adjusting the ratio.

[0106] Temperature also has a significant effect on the water absorption and swelling properties of DNA gel. Studies have found that as the temperature increases, the swelling properties of DNA gel generally show a downward trend, but at certain specific temperature points (such as 15°C and 25°C), it shows better water absorption and swelling properties. This may be because temperature affects the interaction force between molecules in the gel network, thereby changing its swelling behavior. By adjusting the ratio of NIPAM to AA and St to monomer, the swelling properties of DNA gel at different temperatures can be optimized.

[0107] Based on the above performance analysis, this patent selected DNA gel with a molar ratio of NIPAM to AA of 1:1 and a molar ratio of St to monomer of 3:1 as the fertilizer coating material for the dry and cold climate and weak alkaline soil environment in the northwest. This selection is intended to ensure that the DNA gel can maintain good swelling properties under low temperature, room temperature and weak alkaline soil environments, thereby effectively improving the slow-release effect and water retention capacity of the fertilizer and adapting to the special climatic conditions in the northwest.

[0108] Embodiment 3;

[0109] In the embodiment of the present invention,

[0110] 1. Water holding and conservation performance of DNA-SRF in soil

[0111] (1) Water-holding capacity of DNA-SRF in soil

[0112] Fig.17 The water holding capacity of 200 g dry soil after adding 0 g and 1 g DNA-SRF in a soil environment at 25°C (A), the water holding capacity of 200 g dry soil after adding 1 g DNA-SRF in a soil environment at pH = 3, pH = 5, pH = 7, pH = 9 and pH = 11 (B), and the water holding capacity of 200 g dry soil after adding 1 g DNA-SRF in a soil environment at 0°C, 10°C, 25°C, 35°C and 45°C (C) are shown. Fig.17 As shown in A, at 25°C, after adding 0g and 1g DNA-SRF, the water holding rate of 200g dry soil was 46.70% and 54.07% respectively. The water holding rate of the blank group increased by 7.37% after adding 1g DNA-SRF. Fig.17 As shown in Figure B, in soil environments of pH = 3, pH = 5, pH = 7, pH = 9 and pH = 11, after adding 1g of DNA-SRF, the water holding rate of 200g of dry soil was 53.21%, 54.87%, 54.07%, 54.94% and 64.07% respectively. DNA-SRF showed good water holding capacity in weakly acidic, neutral and alkaline soil environments. Fig.17 As shown in Figure C, in the soil environments of 0℃, 10℃, 25℃, 35℃ and 45℃, after adding 1g DNA-SRF, the water holding rates of 200g dry soil were 53.27%, 53.84%, 54.90%, 50.68% and 50.59%, respectively. DNA-SRF showed good water holding capacity in both low temperature and normal temperature soil environments.

[0113] (2) Water retention performance of DNA-SRF in soil

[0114] Fig.18 The results show the water retention performance of 200g dry soil after adding 0g and 1g DNA-SRF in a soil environment of pH = 7 and 25°C. In a soil environment of pH = 7 and 25°C, the water retention rates of 200g dry soil after adding 0g and 1g DNA-SRF were 19.17% and 36.24% respectively, and the water retention rate of the blank group increased by 17.07% after adding 1g DNA-SRF.

[0115] Fig.19The water retention performance (A), water retention rate (B) and water retention balance time (C) of 200g dry soil after adding 1g DNA-SRF in soil environments at pH=3, pH=5, pH=7, pH=9 and pH=11, and the water retention performance (D), water retention rate (E) and water retention balance time (F) of 200g dry soil after adding 1g DNA-SRF in soil environments at 0℃, 10℃, 25℃, 35℃ and 45℃ are shown. Fig.19 As shown in A and D, the period from 0 to 30 days is a rapid water loss stage. After 30 days, the water retention rate curves at different temperatures gradually reach a plateau. Fig.19 As shown in B and C, in the soil environment of pH = 3, pH = 5, pH = 7, pH = 9 and pH = 11, after adding 1g DNA-SRF, the water retention rate of 200g dry soil was 30.84%, 36.73%, 34.49%, 37.96% and 53.64%, respectively, and the time to reach the plateau period was 30d, 50d, 45d, 40d and 50d, respectively. Fig.19 As shown in E and F, in the environments of 0℃, 10℃, 25℃, 35℃ and 45℃, after adding 1g DNA-SRF, the water retention rate of 200g dry soil was 32.67%, 34.33%, 36.24%, 27.94% and 26.07%, respectively, and the time to reach the plateau period was 40d, 50d, 45d, 35d and 30d, respectively. In the soil environment of 0℃ and 10℃, due to the low ambient temperature, the evaporation rate of water was slow, and a small amount of water condensed and remained in the soil, making it have a higher water retention rate. In the environment of 25℃, its water retention rate was 36.24%, and in the soil environment of pH=11, its water retention rate was 53.64%, which was mainly because the DNA gel improved the water holding capacity and interception capacity of the soil, reduced water evaporation, and effectively prevented water loss.

[0116] 2. Slow-release performance of DNA-SRF in water environment and soil

[0117] (1) Sustained release performance of DNA-SRF in water environments with different pH and temperatures

[0118] Fig. 20 The nitrogen release rates of urea and DNA-SRF in a water environment of pH 7 and 25°C are shown. Pure urea as the blank group is rapidly and completely released within 12 hours, and the cumulative nitrogen release rate is 100.00%. The cumulative nitrogen release of DNA-SRF reaches equilibrium at 132 hours, and the cumulative nitrogen release rate is 83.67%.

[0119] Fig.21The nitrogen release rate (A), nitrogen balance cumulative release rate (B) and nitrogen balance release time (C) of DNA-SRF in water environments at pH = 3, pH = 5, pH = 7, pH = 9 and pH = 11, as well as the nitrogen release rate (D), nitrogen balance cumulative release rate (E) and nitrogen balance release time (F) of DNA-SRF in water environments at 0°C, 10°C, 25°C, 35°C and 45°C are shown. Fig.21 As shown in A and D, the nitrogen release curve of DNA-SRF in water environment is a rapid release period from 0 to 48 hours, the nitrogen release rate gradually decreases from 48 to 84 hours, and the nitrogen release curve gradually enters a plateau period after 84 hours and reaches equilibrium. Fig.21 As shown in B and C, the nitrogen balance cumulative release rates of DNA-SRF in water environments of pH=3, pH=5, pH=7, pH=9 and pH=11 are 79.98%, 83.63%, 82.84%, 83.71% and 87.84% respectively, and the required time is 84h, 144h, 132h, 120h and 132h respectively. The sustained release performance of DNA-SRF in alkaline water environment is significantly better than that in acidic water environment. Fig.21 As shown in E and F, the nitrogen balance cumulative release rates of DNA-SRF in water environments at 0℃, 10℃, 25℃, 35℃ and 45℃ were 82.04%, 82.61%, 83.67%, 79.45% and 79.36%, respectively, and the required time was 108h, 132h, 132h, 84h and 72h, respectively. Compared with high temperature conditions, the sustained release performance of DNA-SRF at room temperature and low temperature is more outstanding.

[0120] (2) Slow-release performance of DNA-SRF in soil environments with different pH and temperature

[0121] Fig. 22 The nitrogen release rates of urea and DNA-SRF in a soil environment of pH 7 and 25°C are shown. Pure urea as the blank group is rapidly and completely released within 5 days, with a nitrogen balance cumulative release rate of 100.00%. The nitrogen cumulative release of DNA-SRF reaches equilibrium at 55 days, with a nitrogen balance cumulative release rate of 81.81%.

[0122] Fig.23 The nitrogen release rate (A), nitrogen balance cumulative release rate (B) and nitrogen balance release time (C) of DNA-SRF in soil environments at pH = 3, pH = 5, pH = 7, pH = 9 and pH = 11, as well as the nitrogen release rate (D), nitrogen balance cumulative release rate (E) and nitrogen balance release time (F) of DNA-SRF in soil environments at 0°C, 10°C, 25°C, 35°C and 45°C are shown. Fig.23As shown in A and D, the nitrogen release curve of DNA-SRF in the soil environment is a rapid release period from 0 to 25 days, and the nitrogen release rate gradually decreases from 25 to 35 days. After 35 days, the nitrogen release curve gradually enters a plateau period and reaches equilibrium. Fig.23 As shown in B and C, the nitrogen balance cumulative release rates of DNA-SRF in soil environments of pH = 3, pH = 5, pH = 7, pH = 9 and pH = 11 are 77.74%, 81.72%, 79.81%, 81.90%, 83.82%, respectively, and the required time is 35d, 55d, 132h, 50d, 60d, respectively. The results of the sustained release performance in soil environments at different pH are consistent with those in water environments. The sustained release performance of DNA-SRF in alkaline soil environments is significantly better than that in acidic soil environments. Fig.23 As shown in E and F, the nitrogen balance cumulative release rate of DNA-SRF in soil environments at 0℃, 10℃, 25℃, 35℃ and 45℃ is 77.89%, 79.26%, 81.81%, 71.69%, 71.47%, respectively, and the required time is 40d, 65d, 55d, 40d, 35d, respectively. Compared with the water environment, the nitrogen balance cumulative release rate of DNA-SRF in the soil environment is reduced to a certain extent, but it can still prove that the sustained release performance of DNA-SRF at room temperature and low temperature is better.

[0123] According to the FTIR and XRD characterization test results, this patent successfully prepared a starch-based hydrogel DNA with pH / temperature dual responsiveness using starch as the base material, AA as the monomer, and NIPAM as the thermosensitive group.

[0124] Based on the results of DNA structural characterization, water absorption and swelling properties, pH response properties and temperature response properties, and taking the arid and cold climate and weakly alkaline soil in the northwest as the application environment, it is necessary to maintain good swelling properties under low temperature, normal temperature and weakly alkaline soil environment. This patent selects DNA gel with a molar ratio of NIPAM to AA of 1:1 and a molar ratio of St to monomer of 3:1 as the coating material of the fertilizer.

[0125] According to the research results on the water holding and water conservation performance of SNA-SRF in soil, DNA-SRF exhibits good water holding and water conservation capabilities in neutral and alkaline, low temperature and normal temperature soil environments.

[0126] According to the results of the sustained-release performance of DNA-SRF in water and soil environments, the sustained-release performance of DNA-SRF under alkaline, normal temperature and low temperature conditions is significantly better than that under acidic and high temperature conditions, which is in line with the application environment of the arid, cold and weakly alkaline soils in the northwest.

[0127] The working principle of the embodiment of the present invention is that DNA-SRF exhibits excellent water holding capacity in the soil through its unique chemical structure and physical properties. The material is based on starch, combined with acrylic acid (AA) monomers and N-isopropylacrylamide (NIPAM) thermosensitive groups to form a starch-based hydrogel with pH / temperature dual responsiveness. This structure enables DNA-SRF to absorb and retain a large amount of water, and maintain a high water holding rate even in low and normal temperature soil environments. In particular, under neutral and alkaline soil conditions, the water holding performance of DNA-SRF is more prominent, which is mainly due to the effective retention of water and slowing of evaporation by its gel structure.

[0128] DNA-SRF also has significant water retention performance in the soil. Experimental results show that after adding DNA-SRF, the water retention rate of the soil is significantly improved, and a relatively stable water retention rate can be maintained for a long time (such as more than 30 days). This improvement in water retention performance helps to reduce the rapid loss of soil moisture, especially in arid and semi-arid areas, and is of great significance for improving soil water use efficiency and promoting plant growth. In addition, the water retention performance of DNA-SRF is stable under different pH values ​​and temperature conditions, further proving its environmental adaptability and practicality.

[0129] DNA-SRF also has excellent slow-release properties. In water and soil environments, DNA-SRF can control the release rate of nutrients and achieve continuous supply of nutrients. Compared with quick-release fertilizers such as pure urea, DNA-SRF can significantly prolong the release time of nutrients such as nitrogen and reduce nutrient loss and waste. Especially under alkaline, normal temperature and low temperature conditions, the slow-release performance of DNA-SRF is more superior, which meets the application environment requirements of the arid, cold and weakly alkaline soils in the northwest. By adjusting the composition and structure of DNA-SRF, its slow-release performance can be further optimized to meet the nutrient requirements under different crops and soil conditions.

[0130] DNA-SRF plays an important role in improving soil moisture conditions and increasing nutrient utilization efficiency through its unique water-holding, water-retention and slow-release properties. The development and application of this new material provides new solutions for agricultural production and ecological environmental protection.

[0131] Working principle: First, corn starch is treated with ethanol and dried to successfully destroy its crystal structure and form an amorphous starch matrix. This process not only enhances the solubility and reactivity of starch, but also provides an ideal base for the subsequent synthesis of dual-responsive gel materials. The amorphous structure weakens the interaction between starch molecules, making it easier to react with other monomers and cross-linking agents to form a stable gel network.

[0132] During the preparation process, amorphous starch undergoes cross-linking reaction with N-isopropylacrylamide (NIPAM, which gives temperature responsiveness), acrylic acid (AA, which gives pH responsiveness) and N,N'-methylenebisacrylamide (MBA, as a cross-linking agent) under the initiation of potassium persulfate (KPS) to generate a gel with dual responsiveness to pH and temperature. This gel can swell or shrink according to changes in environmental pH and temperature, thereby accurately regulating the release rate of the fertilizer.

[0133] After wetting the fertilizer surface with anhydrous ethanol, the pH / temperature responsive starch-based gel powder is evenly coated on the fertilizer core (such as urea) through the disc method to form a multi-layer coating structure. This structure not only effectively protects the fertilizer core and prevents it from being directly exposed to the soil environment and causing rapid decomposition, but also gives the fertilizer the ability to respond to changes in soil pH and temperature. Multi-layer coating further enhances the slow-release effect, ensuring that nutrients are slowly released under suitable conditions.

[0134] When the slow-release fertilizer is applied to the soil, its dual response mechanism begins to work. On the one hand, the AA component causes the gel capsule to swell or shrink according to the change in soil pH, adjusting the release rate of the fertilizer. Under alkaline soil conditions, the breaking of hydrogen bonds causes the gel to swell and accelerate the release of nutrients; while in acidic soils, the opposite is true. On the other hand, the NIPAM component changes the hydrophilicity and permeability of the gel according to changes in soil temperature, further controlling the release rate of nutrients. At low temperatures, the hydrophilicity of NIPAM is enhanced, which is conducive to the slow release of nutrients; at high temperatures, it promotes gel shrinkage and slows down nutrient release.

[0135] DNA-SRF not only regulates nutrient release through its dual responsiveness, but also exhibits excellent water holding and retention capabilities. Its unique gel structure can absorb and retain a large amount of water, and maintain a high water holding rate even in low-temperature and normal-temperature soil environments. This water-holding performance helps reduce the rapid loss of soil moisture and improve the water use efficiency of the soil. At the same time, the slow-release performance of DNA-SRF ensures the continuous supply of nutrients in the soil, reduces nutrient loss and waste, and promotes the healthy growth of plants.

[0136] In summary, the DNA-SRF slow-release fertilizer system achieves precise response and efficient regulation to changes in soil environment and climatic conditions through its unique amorphous starch matrix, pH / temperature dual-responsive gel coating, and the synergistic effects of water retention, water conservation and slow-release properties, providing strong support for improving fertilizer utilization, reducing nutrient loss and promoting sustainable agricultural development.

[0137] Although the embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit thereof, and the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A pH-temperature dual-responsive starch-based gel-coated slow-release fertilizer, characterized in that: include: An amorphous starch matrix, which is prepared by treating ordinary corn starch with ethanol and drying it; A pH / temperature responsive starch-based gel coating material, which is formed by a cross-linking reaction of the amorphous starch, N-isopropylacrylamide (NIPAM), acrylic acid (AA) and N,N'-methylenebisacrylamide (MBA) as cross-linking agents under the initiation of potassium persulfate (KPS) and has dual responsiveness to changes in pH and temperature; At least one fertilizer core material, the fertilizer core material is uniformly coated by the pH / temperature responsive starch-based gel coating material to form a slow-release structure.

2. A pH-temperature dual-responsive starch-based gel-coated slow-release fertilizer according to claim 1, characterized in that: The preparation method of the amorphous starch matrix comprises the following steps: Step S101, mixing common corn starch with 50% by volume ethanol, and stirring in a water bath at 85° C. for 2 hours; Step S102, filtering and separating the solid matter, washing with 50% by volume ethanol, drying at 50°C for 24 hours, and then crushing and sieving to obtain amorphous starch powder.

3. A pH-temperature dual-responsive starch-based gel-coated slow-release fertilizer according to claim 1, characterized in that: The preparation method of the pH / temperature responsive starch-based gel comprises: Step S201, dissolving amorphous starch in distilled water, adding NIPAM, AA and MBA as cross-linking agents, and performing a pre-cross-linking treatment at 55° C.; Step S202, dissolving KPS in water, and adding it dropwise into the pre-crosslinking solution as an initiator, heating it to a suitable temperature to initiate a crosslinking reaction, thereby obtaining a gel, which is then dried and ground for later use.

4. A pH-temperature dual-responsive starch-based gel-coated slow-release fertilizer according to claim 1, characterized in that: The core material of the fertilizer is urea, and after its surface is moistened with anhydrous ethanol, the pH / temperature responsive starch-based gel powder is evenly coated by a disc method to form a multi-layer coating structure.

5. A pH-temperature dual-responsive starch-based gel-coated slow-release fertilizer according to claim 1, characterized in that: The preparation method of the pH / temperature dual-responsive starch-based gel-coated slow-release fertilizer comprises the following steps: Step S301, preparing amorphous starch according to steps S101 and S102; Step S302, preparing a pH / temperature responsive starch-based gel according to steps S201 and S202; Step S303, after wetting the surface of the fertilizer core material, use the gel powder to perform multi-layer coating, and dry to obtain pH / temperature dual-responsive starch-based gel-coated slow-release fertilizer.

6. A pH-temperature dual-responsive starch-based gel-coated slow-release fertilizer according to claim 5, characterized in that: During the coating process, the slow-release performance of the slow-release fertilizer can be optimized by adjusting the number of coating layers and drying conditions.

7. The pH-temperature dual-responsive starch-based gel-coated slow-release fertilizer according to claim 1, characterized in that: The application of the pH-temperature dual-responsive starch-based gel-coated slow-release fertilizer is particularly suitable for improving fertilizer utilization, reducing nutrient loss, promoting plant growth, and adapting to agricultural practices under different soil and climate conditions.

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