A pH-responsive controlled-release iron fertilizer and preparation method thereof

Abstract

The present invention discloses a pH-responsive controlled-release iron fertilizer and a preparation method thereof. The pH-responsive controlled-release iron fertilizer provided by the present invention comprises an adsorption carrier and an iron-containing compound; the adsorption carrier is made of raw materials comprising the following components: 100 to 200 parts of organic polymer materials, 50 to 250 parts of organic acids, 5 to 200 parts of cross-linking agents, and 100 to 200 parts of colloidal stabilizers by mass. The pH-responsive controlled-release iron fertilizer of the present invention can control nutrient release according to changes in the soil pH environment, and crops can quickly absorb nutrients in acid-base adverse soils, thereby increasing the stress resistance level of crops in the seedling stage.

Description

Technical Field

[0001] The invention relates to the field of fertilizers, and in particular to a pH-responsive controlled-release iron fertilizer and a preparation method thereof. Background Art

[0002] Iron is a major redox system in plants and has been found to play important roles in plant growth and metabolism, such as chlorophyll synthesis, respiration, nitrogen fixation, reproduction and extended shelf life. Iron deficiency is a common micronutrient disorder in many crops, especially those grown in calcareous and high pH soil regions. Generally, soil application of inorganic iron sources (such as ferrous sulfate) is ineffective in treating this micronutrient deficiency because under these soil conditions, iron is rapidly converted to unavailable, insoluble forms such as iron oxides; however, hydroxide ions are formed especially in alkaline and calcareous soils through carbonate and bicarbonate ions, which are only soluble in strong acid (pH 2.25). For every unit increase in soil pH, the availability of iron to plants decreases by 1000-fold. Therefore, there is a need for a coating or carrier that can regulate the release of iron in response to different soil pH environments.

[0003] For micronutrients, adding nutrient sources to the coating of fertilizer particles is a well-known method. However, the coating materials of traditional fertilizers are mostly petroleum-based polymers, which delay the release of nutrients and prevent the loss of nutrients. However, the main disadvantage of this coating method is that the resistance of synthetic polymers to the action of biological systems leads to the accumulation of plastic residues in the soil after the fertilization process. Based on the above limitations, biodegradable polymers are often tested as plastic substitutes for such applications. The Chinese invention patent (CN 103626598A) applied by Zhou Li et al. of Stanley Fertilizer Co., Ltd. discloses a functional chitosan biological slow-release fertilizer, which is prepared by coating a chitosan coating agent on a core fertilizer particle, which significantly reduces the cost of coated slow-release fertilizers; the production of the membrane material does not use organic solvents, is pollution-free, is easily degraded in the soil, has no residue, and can significantly improve the soil. The Chinese invention patent (CN115093855A) applied by Liu Hanfa of Beijing Jinrong Agricultural Technology Co., Ltd. discloses a multi-element soil conditioner, which is prepared by mixing chitosan, polylactic acid, nutrient-rich polysaccharides and genipin, which can achieve nutrient fixation and achieve the effect of long-term release of nutrients. The Chinese invention patent (CN105532280A) applied by Qian Shanqin of Guangxi Science and Technology Normal University discloses a method for promoting the growth of green vegetables, using genipin as a yield-increasing agent, which promotes the chlorophyll content and chlorophyll light energy conversion efficiency of green vegetables, improves the accumulation of soluble sugars and proteins, and promotes the growth and yield of green vegetables. However, these traditional methods are limited in the amount of micronutrients they can carry, and because they fail to solve the problem of soil release environment, plants still lack micronutrients.

[0004] Therefore, the existing technology has begun to use bio-based carriers to absorb trace nutrients and directly apply them to the soil as trace element fertilizers. However, most of the research results on bio-based carriers are currently focused on drug transportation or pesticide formulations, and there is a lack of relevant research on trace element fertilizers. Therefore, it is necessary to develop a pH-responsive slow / controlled release iron fertilizer. Summary of the invention

[0005] The invention provides a pH-responsive controlled-release iron fertilizer and a preparation method thereof. The pH-responsive controlled-release iron fertilizer of the invention can control nutrient release according to changes in soil pH environment, so that crops can quickly absorb nutrients in acid-base adverse soils, thereby increasing the stress resistance level of crops at the seedling stage.

[0006] The present invention first provides a pH-responsive controlled-release iron fertilizer, comprising an adsorption carrier and an iron-containing compound;

[0007] The adsorption carrier is made of raw materials including the following components: 100 to 200 parts of organic polymer materials, 50 to 250 parts of organic acids, 5 to 200 parts of crosslinking agents and 100 to 200 parts of colloid stabilizers in parts by mass.

[0008] In the above-mentioned pH-responsive controlled-release iron fertilizer, the loading amount of the iron-containing compound is 150-350 mg / g; specifically, it can be 250-330 mg / g, and the loading amount is calculated based on the mass of iron in the iron-containing compound.

[0009] The iron-containing compound is adsorbed around the pore wall of the adsorption carrier in a flocculent state.

[0010] In the above-mentioned pH-responsive controlled-release iron fertilizer, the organic polymer material is chitosan and / or chitosan salt;

[0011] Specifically, the chitosan and chitosan salt are selected from at least one of chitosan, N-carboxymethyl chitosan, deacetylated chitosan and maleic acid chitosan.

[0012] In the above-mentioned pH-responsive controlled-release iron fertilizer, the organic acid is selected from at least one of acetic acid, malic acid, citric acid, salicylic acid, methanesulfonic acid and ascorbic acid;

[0013] The cross-linking agent is selected from at least one of glutaraldehyde, formaldehyde, succinaldehyde, genipin, sodium tripolyphosphate, polyol, N,N-dimethylacetyl, dialdehyde-terminated PEO, toluene diisocyanate, diphenylmethane diisocyanate and epichlorohydrin;

[0014] The iron-containing compound is selected from at least one of ferrous sulfate, ferrous sulfate, ferrous chloride, ferric chloride, ferrous acetate, ferrous carbonate, ferrous nitrate and ferrous sulfate heptahydrate;

[0015] The colloid stabilizer is at least one of glycerol, ethylene glycol, propylene glycol, isoprene glycol, hexylene glycol, polyethylene glycol, polyvinyl alcohol and pentaerythritol.

[0016] In the above-mentioned pH-responsive controlled-release iron fertilizer, the cross-linking agent is any one of the following:

[0017] 1) When the cross-linking agent is genipin, the weight fraction of the cross-linking agent is 8 to 40 parts, 8 parts, 12 parts, 16 parts, 20 parts or 40 parts;

[0018] 2) When the cross-linking agent is sodium tripolyphosphate, the weight fraction of the cross-linking agent is 20 to 160 parts, 20 parts, 40 parts, 80 parts, 120 parts or 160 parts;

[0019] 3) When the cross-linking agent is glutaraldehyde, the weight fraction of the cross-linking agent is 20-160 parts, 20 parts, 40 parts, 80 parts, 120 parts or 160 parts;

[0020] 4) When the cross-linking agent is succinaldehyde, the mass fraction of the cross-linking agent is 20-160 parts, 20 parts, 40 parts, 80 parts, 120 parts or 160 parts.

[0021] In the above-mentioned pH-responsive controlled-release iron fertilizer, the raw material of the adsorption carrier also includes water;

[0022] The adsorption carrier is aerogel.

[0023] The specific surface area of ​​the adsorption carrier is 0.5 to 50 m 2 / g, specifically 8~23m 2 / g effective pore volume is 0.003~0.5cm 3 / g, specifically 0.03~0.08cm 3 / g.

[0024] In the above-mentioned pH-responsive controlled-release iron fertilizer, the adsorption carrier is prepared by a method comprising the following steps:

[0025] 1) mixing the organic polymer material, organic acid and water to form an aqueous phase a;

[0026] 2) mixing the colloid stabilizer and the aqueous phase a to form an aqueous phase b;

[0027] 3) mixing the aqueous phase b and the crosslinking agent solution to obtain a wet gel;

[0028] 4) Aging, freezing and drying the wet gel to obtain the adsorption carrier.

[0029] In the above-mentioned pH-responsive controlled-release iron fertilizer, in step 1), the mass ratio of the organic polymer material to water is 1:25 to 1:50;

[0030] In step 3), in the cross-linking agent solution, the mass ratio of the cross-linking agent to water is 1:10 to 1:100, and can be specifically 1:50 to 1:100.

[0031] In step 4), the aging is placed at room temperature for 24 to 48 hours, specifically 24 hours;

[0032] The freezing is freezing at -20 to -50°C for 12 to 24 hours, specifically freezing at -20°C for 12 hours.

[0033] In the preparation method of the adsorption carrier, the wet gel is aged after washing; specifically, the washing is performed using ethanol and water.

[0034] The present invention also provides a method for preparing the pH-responsive controlled-release iron fertilizer, comprising the following steps: preparing the iron-containing compound into an aqueous solution of the iron-containing compound, immersing the adsorption carrier in the aqueous solution of the iron-containing compound, and removing the adsorption carrier to obtain the pH-responsive controlled-release iron fertilizer.

[0035] In the above preparation method, the mass ratio of the iron-containing compound to water is 1:5 to 1:15; specifically, it can be 1:8 to 1:15, and more specifically, it can be 1:10 to 1:13;

[0036] The mass ratio of the adsorption carrier to the iron-containing compound is 1:25 to 100;

[0037] The adsorption carrier is immersed in the iron-containing compound aqueous solution and stirred at a speed of 200 to 400 rpm for 12 to 24 hours.

[0038] In the above-mentioned preparation method, the preparation method also includes the steps of washing the adsorption carrier with water and drying after impregnation.

[0039] The room temperature mentioned in the present invention is well known to those skilled in the art, and is generally 15-35°C.

[0040] The present invention uses a network structure formed by chemical cross-linking of chitosan and a cross-linking agent to complex nutrient elements and organic acids, and the chitosan aerogel network structure chelates ferrous ions, and releases the iron element through the pH responsiveness of the release carrier, thereby enhancing the stress resistance of crops in acid-base adversity environments. The organic acid in the adsorption carrier material can promote the activation of the rhizosphere microenvironment, protect the released ferrous ions, and prevent them from being quickly fixed and oxidized by the soil, so that the plant can fully absorb the iron element; at the same time, the organic acid can activate nutrient elements such as phosphorus in the soil, and improve the absorption of nutrient elements by the crop root system. After being degraded in the soil, the chitosan aerogel will generate different types of glycoside substances, which are beneficial to the plant's stress resistance, rooting, budding, chlorophyll synthesis and biomass accumulation.

[0041] Compared with traditional iron fertilizers, the present invention cross-links and modifies chitosan polymer materials, uses chitosan as an adsorption carrier to carry trace elements, and prepares pH-responsive controlled-release iron fertilizer, which has the following advantages:

[0042] 1) The release carrier of the present invention is a green and environmentally friendly natural organic matter, the material is completely biodegradable and will not cause pollution to the soil and the environment;

[0043] 2) pH-sensitive materials are added, and the chitosan-based carrier dissolves under acidic conditions and breaks the coordination bond with iron under alkaline conditions. The released carrier can control the release of nutrients according to different soil pH environments. Crops can quickly absorb nutrients in acid-base stress soils, increasing the stress resistance level of crops in the seedling stage;

[0044] 3) The adsorption carrier material of the present invention generates various glycosides after degradation, which promote plant rooting, budding, biomass accumulation, chlorophyll synthesis and crop stress resistance;

[0045] 4) The organic acid in the adsorption carrier material of the present invention in a suitable proportion can promote the activation of the rhizosphere microenvironment, protect the ferrous ions to the maximum extent, prevent them from being quickly fixed and oxidized by the soil, and enable the plants to fully absorb the iron element; at the same time, the organic acid can activate nutrients such as phosphorus in the soil, and improve the absorption of nutrients by the crop roots;

[0046] 5) The multi-effect controlled-release linkage design of this fertilizer is particularly suitable for promoting root growth and seedling growth in adverse environments during the seedling stage of crops, thereby ensuring income and increasing production. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 This is the structure of the pH-responsive controlled-release iron fertilizer in Example 1.

[0048] Figure 2 This is the hydrolysis reaction of the genipin chitosan aerogel in Example 1.

[0049] Figure 3 The photos and SEM images of the genipin chitosan aerogel and the pH-responsive controlled-release iron fertilizer in Example 1 are shown; wherein, Figure 3 a-1 and a-2 are the surface and cross-sectional photos of genipin chitosan aerogel, respectively; b-1 and b-2 are SEM images of genipin chitosan aerogel; c-1 and c-2 are SEM images of pH-responsive controlled-release iron fertilizer.

[0050] Figure 4 FT-IR images of the genipin chitosan aerogel and the pH-responsive controlled-release iron fertilizer in Example 1; in the figure, (a) is chitosan; (b) is genipin chitosan aerogel; and (c) is the pH-responsive controlled-release iron fertilizer.

[0051] Figure 5The XRD diagram of the genipin chitosan aerogel and the pH-responsive controlled-release iron fertilizer in Example 1; in the figure, (a) is chitosan; (b) is genipin chitosan aerogel; and (c) is the pH-responsive controlled-release iron fertilizer.

[0052] Figure 6 This is the TGA graph of the genipin chitosan aerogel and the pH-responsive controlled-release iron fertilizer in Example 1; in the figure, a is chitosan; b is genipin chitosan aerogel; and c is the pH-responsive controlled-release iron fertilizer.

[0053] Figure 7 The iron release amount and swelling rate of the pH-responsive controlled-release iron fertilizer at different pH values ​​in Example 1.

[0054] Figure 8 The effect of the pH-responsive controlled-release iron fertilizer and ferrous sulfate prepared in Example 1 on the germination rate of wheat seeds.

[0055] Fig. 9 The effects of the pH-responsive controlled-release iron fertilizer prepared in Example 1 and ferrous sulfate at different application levels on the growth traits of tomato seedlings.

[0056] Fig.10 The effects of the pH-responsive controlled-release iron fertilizer and ferrous sulfate prepared in Example 1 on the nutrient content of tomato plants at the seedling stage at different application levels.

[0057] Fig.11 The effects of the pH-responsive controlled-release iron fertilizer and ferrous sulfate prepared in Example 1 on the element content of the matrix extract at the tomato seedling stage at different application levels. DETAILED DESCRIPTION

[0058] The present invention is further described in detail below in conjunction with specific embodiments. The given examples are only for illustrating the present invention, but not for limiting the scope of the present invention.

[0059] The experimental methods in the following examples are all conventional methods unless otherwise specified.

[0060] Unless otherwise specified, the materials and reagents used in the following examples can be obtained from commercial sources.

[0061] The "parts" described in the following examples are all "parts by mass".

[0062] In the following examples, low-viscosity deacetylated chitosan (100-200 mPa.s), N-carboxymethyl chitosan, high-viscosity deacetylated chitosan (viscosity>400 mPa.s), and maleic acid chitosan were purchased from Aladdin Biochemical Technology Co., Ltd. (Shanghai, China).

[0063] The following examples all evaluated the release performance and biosafety of the pH-responsive controlled-release iron fertilizer according to the following method:

[0064] The method recommended by GB / T23348-2009 is adopted. The specific operation is as follows: weigh about 10g (accurate to 0.01g) of the prepared controlled-release fertilizer and put it into a small bag made of 100-mesh nylon gauze. After sealing, put the small bag into a 250mL glass bottle or plastic bottle, add 200mL of water, cover and seal, and place it in a biochemical constant temperature incubator at 25°C. The sampling time is 1h, 2h, 4h, 24h, 48h, 72h, 96h, 120h, until the cumulative nutrient dissolution rate reaches more than 80%, which is considered to be completely released. When sampling, turn the bottle upside down three times to make the liquid concentration in the bottle consistent, transfer it to a 250mL volumetric flask, cool it to room temperature, and then adjust the volume to the scale for nutrient determination. Then, add 200mL of water to the bottle containing the sample bag, cover and seal it, and place it in a biochemical constant temperature incubator for continued cultivation. Among them, Fe 2+ Elements were determined using the o-phenanthroline spectrophotometric method of GB / T 223.70-2008.

[0065] Example 1

[0066] 1. Preparation of pH-responsive controlled-release iron fertilizer

[0067] Dissolve 100 parts of low-viscosity deacetylated chitosan (100-200 mPa.s) in deionized water (5000 parts) containing 250 parts of acetic acid to obtain a chitosan solution. Slowly add 100 parts of glycerol to the chitosan solution to obtain a chitosan / glycerol mixed solution. Dissolve 20 parts of genipin in deionized water (2000 parts) to obtain a genipin solution. Mix the chitosan / glycerol mixed solution with the genipin solution and stir evenly to obtain a genipin chitosan wet gel. Wash the genipin chitosan wet gel with ethanol and deionized water 3 times each, then place it at room temperature for aging for 24 hours, then freeze it at -20°C for 12 hours, and finally place it in a vacuum dryer for drying to obtain a genipin chitosan aerogel. 500 parts of ferrous sulfate were dissolved in deionized water (5000 parts), and then the genipin chitosan aerogel was added to the ferrous sulfate solution (the mass ratio of genipin chitosan aerogel and ferrous sulfate was 1:25), stirred at 400 rpm for 24 hours, and the fertilizer was washed 3 times with deionized water, and then dried to obtain a pH-responsive controlled-release iron fertilizer (the material dissolution pH was 2.6±0.5).

[0068] The pH-responsive controlled-release iron fertilizer prepared in Example 1 was subjected to SEM, FT-IR scanning, XRD test, and TGA test. Figure 1It is the structure of the pH-responsive controlled-release iron fertilizer in Example 1. Chitosan and genipin first undergo a chemical cross-linking reaction to produce amide bonds, form a gel, and present a network structure. After the network structure of genipin chitosan aerogel adsorbs iron, it coordinates with ferrous ions; at the same time, the amino, hydroxyl and ferrous ions in chitosan are combined with organic acids (acetic acid). The chitosan aerogel network structure chelates ferrous ions, and releases the pH-responsive controlled-release iron element of the release carrier, thereby enhancing the stress resistance of crops in acid-base adversity environments. The organic acid in the adsorption carrier material can promote the activation of the rhizosphere microenvironment, protect the released ferrous ions, prevent rapid fixation and oxidation by the soil, and enable plants to fully absorb iron elements; at the same time, organic acids can activate nutrients such as phosphorus in the soil, and improve the absorption of nutrients by crop roots. Figure 2 This is the hydrolysis reaction of the genipin chitosan aerogel in Example 1. Genipin chitosan aerogel is hydrolyzed under acidic and alkaline conditions to produce multiple types of glycosides, which are beneficial to the stress resistance, rooting, budding, chlorophyll synthesis and biomass accumulation of plants. Figure 3 The following are photos and SEM images of the genipin chitosan aerogel and the pH-responsive controlled-release iron fertilizer in Example 1. Figure 3 As shown in a-1, a-2, b-1, and b-2, chitosan exhibits a sequential pore structure after cross-linking modification, proving that chitosan cross-linking is successful. Figure 3 As shown in c-1 and c-2, after the genipin chitosan aerogel is loaded with iron, ferrous sulfate is adsorbed around the pore wall in the form of flocs.

[0069] Figure 4 FT-IR images of genipin chitosan aerogel and pH-responsive controlled-release iron fertilizer in Example 1. Figure 4 It can be seen that in (a), 3000-3500cm -1 The broad absorption peaks of -OH and -NH2 represent the stretching vibration absorption peaks of -OH and -NH2, which means that chitosan contains a large number of active amino and hydroxyl groups, which can easily form intramolecular and intermolecular hydrogen bonds. (b) It can be seen that the absorption peaks of -OH and -NH2 are weakened, and the 1410cm -1 The broad absorption peak represents the bending vibration absorption peak of -CO-NH, which means that a large number of amino groups and genipin undergo chemical cross-linking reactions to form amide bonds. The spectrum in (c) shows that SO4 2- The characteristic peaks are located at 606 and 1125 cm -1 ; The characteristic peak corresponding to -COC is 1100cm -1 The peak shifts to 989 cm due to coordination with Fe. -1 , which means that the iron loading of genipin aerogel was successful.

[0070] Figure 5The XRD diagram of the genipin chitosan aerogel and the pH-responsive controlled-release iron fertilizer in Example 1. Figure 5 It can be seen that in (a), broad diffraction peaks appear near 2θ=11.86° and 21.31°, indicating that CS has a relatively regular lattice, which is mainly caused by the presence of intramolecular or intermolecular hydrogen bonds between a large number of -NH2 and -OH on CS. The diffraction peak in (b) moves to the range of 2θ=19.56°-20.29°, indicating that the molecular chains are rearranged during the crosslinking process. The diffraction peak in (c) moves to 26.16° (corresponding to FeSO4).

[0071] The specific surface area and effective pore volume of pH-responsive controlled-release iron fertilizer were measured by N2 adsorption-desorption analysis using a Brunauer-Emmett-Teller (BET) surface area analyzer (AutosorbiQ2, quantachrome instrument), which were 20.6060 m 2 / g and 0.068722cm 3 / g.

[0072] The Fe content in the pH-responsive controlled-release iron fertilizer was determined by inductively coupled plasma atomic emission spectrometry (ICP-AES), which was 326.15 mg / g.

[0073] Thermosensitivity of genipin chitosan aerogel and pH-responsive controlled-release iron fertilizer was evaluated by thermogravimetric analysis. The samples were heated from 25°C to 900°C. TGA was performed in nitrogen using a Labsys Evo (Setaram, Lyon, France). The results are shown in Figure 2. Figure 6 As shown, the genipin crosslinker does not improve the thermal stability of chitosan much. After iron loading, the temperature at which the pH-responsive controlled-release iron fertilizer loses 50% of its mass rises due to the high melting point of ferrous sulfate.

[0074] The pH of the fertilizer solution was adjusted to 3, 5, 7 or 9 with 1 mol / L hydrochloric acid or 1 mol / L sodium hydroxide solution, and the release rate of pH-responsive controlled-release iron fertilizer under different pH environments was determined using the method recommended by GB / T23348-2009. In order to examine the swelling behavior of genipin chitosan aerogel, 100 mg of the sample was weighed and placed in a small Petri dish filled with 50 mL of swelling medium. PBS solution was used as the swelling medium, and it was adjusted to different pH using 1 mol / L hydrochloric acid or 1 mol / L sodium hydroxide solution. After a predetermined regular interval, the sample was removed from the plate and the excess water was tapped with the help of tissue paper.

[0075] Take the final weight of the sample and calculate the % swelling according to the following formula:

[0076] %Swelling=(W2-W1) / W1 x 100

[0077] Where W2 is the final weight of the sample and W1 is the initial weight of the sample.

[0078] Results Figure 7 , Figure 7 The iron release amount and swelling rate of the pH-responsive controlled-release iron fertilizer at different pH values ​​in Example 1. Figure 7 In (a), the release rate of pH-responsive controlled-release iron fertilizer in a strong acid environment is greater than that in a strong alkaline environment and greater than that in a neutral environment. Figure 7 (b) The swelling behavior of pH-responsive controlled-release iron fertilizer at different pH values ​​matches its release behavior.

[0079] 2. Application

[0080] 1. Biosafety evaluation

[0081] The experiment set up three treatments: CK: no fertilizer; GE: pH-responsive controlled-release iron fertilizer; Fe: ferrous sulfate; 1 mg each of pH-responsive controlled-release iron fertilizer and ferrous sulfate was added.

[0082] Twenty full, sterilized and selected wheat seeds were placed in each culture dish. After different treatments (three replicates for each treatment), sufficient water was added to keep the filter paper moist. The dishes were then placed in a constant temperature incubator at 25°C for culture, and water was added in time to keep the filter paper moist.

[0083] Germination rate (%) = (number of germinated seeds / total number of seeds) × 100%

[0084] Figure 8 The effect of pH-responsive controlled-release iron fertilizer and ferrous sulfate prepared in Example 1 on the emergence rate of wheat seeds. Figure 8 As shown, on the fifth day, the wheat seed emergence rate treated with pH-responsive controlled-release iron fertilizer was 10% higher than that of unfertilized (CK) and 7% higher than that of ferrous sulfate.

[0085] 2. Impact on tomatoes

[0086] The experiment set up three treatments: CK: no fertilizer; GE: application of pH-responsive controlled-release iron fertilizer; Fe: application of FeSO4. GE and Fe were set at four different application levels: 2.5 mg / plant, 5.0 mg / plant, 7.5 mg / plant and 10.0 mg / plant.

[0087] All potted plants were cultured with Hoagland complete nutrient solution (iron-free) and vermiculite. Hoagland complete nutrient solution (iron-free) was used for potted plants, and watering was carried out according to the nutrient requirements of normal growth of tomato (red dwarf) seedlings. Quantitative watering (100 mL / plant) was carried out at regular intervals (8:00-9:00) every 3 days, and the water content of vermiculite was maintained at about 60%. The pH value of the nutrient solution was maintained at 5.8±0.2.

[0088] Samples were taken from each treatment every 7 days (6 replicates for each treatment), for a total of 3 samples, and the total number of experimental days was 21 days.

[0089] (1) Tomato plant height, root length, stem diameter, leaf length and width: measured using a vernier caliper;

[0090] The SPAD value is measured five times on different leaves from the fifth leaf section from top to bottom using a handheld chlorophyll meter (SPAD-502PIU), and the average value is taken as the SPAD value of the tomato plant;

[0091] Fresh weight and dry weight of tomatoes: established using a ten-thousandth balance. For dry weight, the roots, stems and leaves of the aboveground parts of tomatoes were dried at 105°C for 30 minutes, and then dried at 65°C to constant weight, and the weights were weighed.

[0092] Leaf area: LA = 0.347 × (L × W) - 10.7

[0093] Among them, LA is the actual leaf area; L and W represent the leaf length and leaf width, respectively.

[0094] Results Fig. 9 , which is the effect of the pH-responsive controlled-release iron fertilizer (GE) prepared in Example 1 and ferrous sulfate at different application levels on the growth traits of tomato seedlings. Fig. 9 In (a), on the 21st day, when GE was used as the iron source, the GE-5.0 plant height was the highest, 37% higher than CK; when FeSO4 was used as the iron source, the Fe-5.0 plant height was the highest, 16% higher than CK. Fig. 9 In (b), on the 21st day, when GE was used as the iron source, the root length of GE-5.0 was the longest, 39% higher than that of CK; when FeSO4 was used as the iron source, the root length of Fe-5.0 was the longest, 10% higher than that of CK. Fig. 9 In (c), on the 21st day, the stem diameter of GE-5.0 was the largest, 38% higher than that of CK; when FeSO4 was used as the iron source, the stem diameter of Fe-5.0 was the largest, 22% higher than that of CK. Fig. 9 In (d), on the 21st day, the chlorophyll content of GE-5.0 was the highest, 25% higher than that of CK; when FeSO4 was used as the iron source, the chlorophyll content of Fe-5.0 was the highest, 12% higher than that of CK. Fig. 9In (e), on the 21st day, when GE was used as the iron source, the number of GE-5.0 leaves was the largest, 13% higher than that of CK; when FeSO4 was used as the iron source, the number of Fe-5.0 leaves was the largest, 2% higher than that of CK. Fig. 9 In (f), on the 21st day, when GE was used as the iron source, the leaf area of ​​GE-5.0 was the largest, 52% higher than that of CK; when FeSO4 was used as the iron source, the leaf area of ​​Fe-5.0 was the largest, 16% higher than that of CK. In summary, pH-responsive controlled-release iron fertilizer has a more significant effect on plant height, root length, stem diameter, chlorophyll content, leaf number, leaf area and fresh-dry weight than ferrous sulfate.

[0095] (2) Determination of plant nutrient content: Samples were taken on the 21st day of the experiment to determine the total nitrogen (N), P, K, Ca, Mg, Fe, Mn, and Zn content of the plants. The total nitrogen (N) content of the plants was determined by the Kjeldahl method; the content of P, K, Ca, Mg, Fe, Mn, and Zn was determined by inductively coupled plasma atomic emission spectrometry (ICP-AES). Fig.10 The effect of pH-responsive controlled-release iron fertilizer and ferrous sulfate prepared in Example 1 on the nutrient content of tomato seedlings at different application levels. Fig.10 As shown in the figure, pH-responsive controlled-release iron fertilizer has a more significant effect on improving plant nutrients than ferrous sulfate, among which N, P, K, Mg, Fe and other elements are significantly improved.

[0096] (3) The total nitrogen (N) content in the matrix extract was determined by the Kjeldahl method.

[0097] After the 21st day of the experiment, take the vermiculite and air dry it. Use a sampler to measure 5.00mL of air-dried vermiculite (passed through a 2mm nylon sieve), weigh and record its mass at the same time, add 50.0mL of M3 extractant with a liquid adder, and stir with a stirrer for 5 minutes. Then filter with dry filter paper and collect the filtrate in a 50mL plastic bottle. The entire extraction process should be carried out under constant temperature conditions, and the temperature should be controlled at 25±1℃.

[0098] M3 extractant: Use a 1000mL or 2000mL measuring cylinder to measure 2000mL of deionized water, add it into a 5000mL plastic bucket, weigh 100.0g of ammonium nitrate, dissolve it, add 20.0mL of M3 stock solution, then add 57.5mL of glacial acetic acid (i.e. 17.4mol / L) and 4.1mL of concentrated HNO3 (HNO3, 68%~70%, analytical grade), dilute to 5000mL with water using a measuring cylinder, mix thoroughly, the pH of this solution should be 2.5±0.1.

[0099] The P and K in the matrix extract were determined by molybdenum antimony colorimetry and flame spectrophotometry, respectively.

[0100] Inductively coupled plasma atomic emission spectrometry (ICP-AES) was used to determine the contents of Ca, Mg, Fe, Mn and Zn in the matrix extract.

[0101] Fig.11 The effect of pH-responsive controlled-release iron fertilizer and ferrous sulfate prepared in Example 1 on the element content of matrix extract at tomato seedling stage at different application levels. Fig.11 As shown in the figure, compared with ferrous sulfate, genipin chitosan aerogel iron fertilizer has a more obvious effect on improving the effective form of nutrients in the matrix. Among them, the dissolved elements such as N, P, Ca, Mg, Mn, and Zn are significantly improved.

[0102] Example 2

[0103] 200 parts of N-carboxymethyl chitosan were dissolved in deionized water (5000 parts) containing 50 parts of citric acid to obtain a chitosan solution. 150 parts of glycerol were slowly added to the chitosan solution to obtain a chitosan / glycerol mixed solution. 40 parts of sodium tripolyphosphate were dissolved in deionized water (2000 parts) to obtain a sodium tripolyphosphate solution. The chitosan / glycerol mixed solution was mixed with the sodium tripolyphosphate solution and stirred evenly to obtain a sodium tripolyphosphate chitosan wet gel, and the gel pH was adjusted to 6.0±0.5 using a sodium hydroxide solution. The sodium tripolyphosphate chitosan wet gel was washed with ethanol and deionized water for 3 times each, then aged at room temperature for 24 hours, then frozen at -20°C for 12 hours, and finally dried in a vacuum dryer to obtain a tripolyphosphate chitosan aerogel. 500 parts of ferrous sulfate were dissolved in deionized water (5000 parts), and then the tripolyphosphate chitosan aerogel was placed in the ferrous sulfate solution (the mass ratio of tripolyphosphate chitosan aerogel to ferrous sulfate was 1:50), stirred at 400 rpm for 24 hours, and the fertilizer was washed 3 times with deionized water and then dried to obtain a pH-responsive controlled-release iron fertilizer.

[0104] The pH-responsive controlled-release iron fertilizer prepared in Example 2 was subjected to the same physical characterization and fertilizer release experiments as in Example 1. The specific surface area and effective pore volume of the pH-responsive controlled-release iron fertilizer were measured to be 8.0390 m 2 / g and 0.034499cm 3 / g. The Fe content in the pH-responsive controlled-release iron fertilizer was measured to be 311.00 mg / g.

[0105] Example 3

[0106] 150 parts of high viscosity deacetylated chitosan (viscosity> 400mPa.s) were dissolved in deionized water (5000 parts) containing 100 parts of malic acid to obtain a chitosan solution. 200 parts of glycerol were slowly added to the chitosan solution to obtain a chitosan / glycerol mixed solution. 40 parts of glutaraldehyde were dissolved in deionized water (2000 parts) to obtain a glutaraldehyde solution. The chitosan / glycerol mixed solution was mixed with the glutaraldehyde solution, stirred evenly, and a glutaraldehyde chitosan wet gel was obtained. The glutaraldehyde chitosan wet gel was washed with ethanol and deionized water for 3 times each, then aged at room temperature for 24 hours, then frozen at -20°C for 12 hours, and finally dried in a vacuum dryer to obtain a glutaraldehyde chitosan aerogel. 400 parts of ferrous sulfate were dissolved in deionized water (5000 parts), and then glutaraldehyde chitosan aerogel was added to the ferrous sulfate solution (the mass ratio of glutaraldehyde chitosan aerogel to ferrous sulfate was 1:75), stirred at 400 rpm for 24 hours, and the fertilizer was washed 3 times with deionized water and then dried to obtain a pH-responsive controlled-release iron fertilizer.

[0107] The pH-responsive controlled-release iron fertilizer prepared in Example 3 was subjected to the same physical characterization and fertilizer release experiments as in Examples 1 and 2. The specific surface area and effective pore volume of the pH-responsive controlled-release iron fertilizer were measured to be 11.6148 m 2 / g and 0.036459cm 3 / g. The Fe content in the pH-responsive controlled-release iron fertilizer was measured to be 283.54 mg / g.

[0108] Example 4

[0109] 150 parts of maleic acid chitosan were dissolved in deionized water (5000 parts) containing 50 parts of salicylic acid to obtain a chitosan solution. 200 parts of glycerol were slowly added to the chitosan solution to obtain a chitosan / glycerol mixed solution. 40 parts of succinaldehyde were dissolved in deionized water (2000 parts) to obtain a succinaldehyde solution. The chitosan / glycerol mixed solution was mixed with the succinaldehyde solution and stirred to obtain a succinaldehyde chitosan wet gel. The succinaldehyde chitosan wet gel was washed with ethanol and deionized water for 3 times each, then aged at room temperature for 24 hours, then frozen at -20°C for 12 hours, and finally dried in a vacuum dryer to obtain a succinaldehyde chitosan aerogel. 450 parts of ferrous sulfate were dissolved in deionized water (5000 parts), and then succinaldehyde chitosan aerogel was added to the ferrous sulfate solution (the mass ratio of succinaldehyde chitosan aerogel to ferrous sulfate was 1:100), stirred at 400 rpm for 24 hours, and the fertilizer was washed 3 times with deionized water and then dried to obtain a pH-responsive controlled-release iron fertilizer.

[0110] The pH-responsive controlled-release iron fertilizer prepared in Example 4 was subjected to the same physical characterization and fertilizer release experiments as in Examples 1 and 2. The specific surface area and effective pore volume of the pH-responsive controlled-release iron fertilizer were measured to be 8.7542 m 2 / g and 0.030175cm 3 / g. The Fe content in the pH-responsive controlled-release iron fertilizer was measured to be 297.79 mg / g.

[0111] Example 5: Cross-linking agent concentration screening experiment

[0112] 1.1 The preparation method of pH responsive controlled-release iron fertilizer is the same as that in Example 1, except that the amount of genipin cross-linking agent is replaced. A total of five concentration gradients (0.4wt.%, 0.6wt.%, 0.8wt.%, 1.0wt.% and 2.0wt.%) are set, where percentage concentration refers to the mass percentage concentration of the cross-linking agent in deionized water, such as 20 parts of genipin are dissolved in 2000 parts of deionized water in Example 1, and the genipin concentration is 1.0wt.%). The iron loading of the pH responsive controlled-release iron fertilizer prepared under different cross-linking agent concentrations is determined by inductively coupled plasma atomic emission spectrometry (ICP-AES).

[0113] It can be seen from the concentration screening experiment that when genipin is selected as the cross-linking agent, the iron loading of the pH-responsive controlled-release iron fertilizer prepared by 0.4wt.%, 0.6wt.%, 0.8wt.%, 1.0wt.% and 2.0wt.% genipin is 281.22mg / g, 268.25mg / g, 310.97mg / g, 326.15mg / g and 289.62mg / g, respectively. Among them, the pH-responsive controlled-release iron fertilizer prepared by 1.0wt.% genipin has the highest iron loading.

[0114] 1.2 Using Example 1 Figure 8 The experimental method in the experiment was used to study the effect of pH-responsive controlled-release iron fertilizers prepared with different concentration gradients of genipin on wheat seed germination. The experiment found that on the 5th day, the germination rates of the pH-responsive controlled-release iron fertilizers prepared with 0.4wt.%, 0.6wt.%, 0.8wt.%, 1.0wt.% and 2.0wt.% genipin were 78.35%, 81.65%, 83.35%, 80.00% and 71.65%, respectively. Among them, the pH-responsive controlled-release iron fertilizer prepared with 0.8wt.% genipin had the highest germination rate of wheat seeds.

[0115] 2.1 The preparation method of pH responsive controlled-release iron fertilizer is the same as that in Example 2, except that the amount of sodium tripolyphosphate cross-linking agent is replaced. A total of five concentration gradients (1.0wt.%, 2.0wt.%, 4.0wt.%, 6.0wt.% and 8.0wt.%) are set, and the iron loading of pH responsive controlled-release iron fertilizers prepared at different cross-linking agent concentrations is determined by inductively coupled plasma atomic emission spectrometry (ICP-AES).

[0116] It can be seen from the concentration screening experiment that when sodium tripolyphosphate is selected as the cross-linking agent, the iron loading of the pH-responsive controlled-release iron fertilizer prepared by 1.0wt.%, 2.0wt.%, 4.0wt.%, 6.0wt.% and 8.0wt.% sodium tripolyphosphate is 264.17mg / g, 311.00mg / g, 253.18mg / g, 273.84mg / g and 214.10mg / g, respectively. Among them, the pH-responsive controlled-release iron fertilizer prepared by 2.0wt.% sodium tripolyphosphate has the highest iron loading.

[0117] 2.2 Using Example 1 Figure 8 The experimental method in the experiment was used to study the effect of pH-responsive controlled-release iron fertilizers prepared with different concentration gradients of sodium tripolyphosphate on wheat seed germination. The experiment found that on the 5th day, the germination rates of pH-responsive controlled-release iron fertilizers prepared with 1.0wt.%, 2.0wt.%, 4.0wt.%, 6.0wt.% and 8.0wt.% sodium tripolyphosphate were 73.35%, 81.65%, 78.35%, 90.00% and 70.00%, respectively. Among them, the pH-responsive controlled-release iron fertilizer prepared with 6.0wt.% sodium tripolyphosphate had the highest germination rate of wheat seeds.

[0118] 3.1 The preparation method of pH responsive controlled-release iron fertilizer is the same as that in Example 3, except that the amount of glutaraldehyde cross-linking agent is replaced. A total of five concentration gradients (1.0wt.%, 2.0wt.%, 4.0wt.%, 6.0wt.% and 8.0wt.%) are set, and the iron loading of pH responsive controlled-release iron fertilizer prepared under different cross-linking agent concentrations is determined by inductively coupled plasma atomic emission spectrometry (ICP-AES).

[0119] It can be seen from the concentration screening experiment that when glutaraldehyde is selected as the cross-linking agent, the iron loading of the pH-responsive controlled-release iron fertilizer prepared by 1.0wt.%, 2.0wt.%, 4.0wt.%, 6.0wt.% and 8.0wt.% glutaraldehyde is 192.75mg / g, 283.54mg / g, 244.96mg / g, 260.19mg / g and 227.26mg / g, respectively. Among them, the pH-responsive controlled-release iron fertilizer prepared by 2.0wt.% glutaraldehyde has the highest iron loading.

[0120] 3.2 Using Example 1 Figure 8 The experimental method in the experiment was used to study the effect of pH-responsive controlled-release iron fertilizers prepared with different concentration gradients of glutaraldehyde on wheat seed germination. The experiment found that on the 5th day, the germination rates of the pH-responsive controlled-release iron fertilizers prepared with 1.0wt.%, 2.0wt.%, 4.0wt.%, 6.0wt.% and 8.0wt.% glutaraldehyde were 71.65%, 78.35%, 81.65%, 80.00% and 83.35%, respectively. Among them, the pH-responsive controlled-release iron fertilizer prepared with 4.0wt.% glutaraldehyde had the highest germination rate of wheat seeds.

[0121] 4.1 The preparation method of pH responsive controlled-release iron fertilizer is the same as that in Example 4, except that the amount of succinaldehyde cross-linking agent is replaced. A total of five concentration gradients (1.0wt.%, 2.0wt.%, 4.0wt.%, 6.0wt.% and 8.0wt.%) are set, and the iron loading of pH responsive controlled-release iron fertilizer prepared at different cross-linking agent concentrations is determined by inductively coupled plasma atomic emission spectrometry (ICP-AES).

[0122] It can be seen from the concentration screening experiment that when succinaldehyde is selected as the cross-linking agent, the iron loading of the pH-responsive controlled-release iron fertilizer prepared by 1.0wt.%, 2.0wt.%, 4.0wt.%, 6.0wt.% and 8.0wt.% succinaldehyde is 205.47mg / g, 297.79mg / g, 261.65mg / g, 242.47mg / g and 229.38mg / g, respectively. Among them, the pH-responsive controlled-release iron fertilizer prepared by 2.0wt.% succinaldehyde has the highest iron loading.

[0123] 4.2 Using Example 1 Figure 8 The experimental method in the experiment was used to study the effect of pH-responsive controlled-release iron fertilizers prepared with different concentration gradients of succinic dialdehyde on wheat seed germination. The experiment found that on the 5th day, the germination rates of pH-responsive controlled-release iron fertilizers prepared with 1.0wt.%, 2.0wt.%, 4.0wt.%, 6.0wt.% and 8.0wt.% succinic dialdehyde were 73.15%, 83.35%, 80.00%, 78.15% and 75.35%, respectively. Among them, the germination rate of wheat seeds treated with pH-responsive controlled-release iron fertilizers prepared with 2.0wt.% succinic dialdehyde was the highest.

Claims

1. A pH-responsive controlled-release iron fertilizer comprising an adsorption carrier and an iron-containing compound; The adsorption carrier is made of raw materials including the following components: 100 to 200 parts by mass of organic polymer material, 50 to 250 parts by mass of organic acid, 5 to 200 parts by mass of cross-linking agent and 100 to 200 parts by mass of colloidal stabilizer; The organic polymer material is chitosan and / or chitosan salt; The organic acid is selected from at least one of acetic acid, malic acid, citric acid, salicylic acid methanesulfonic acid and ascorbic acid; The cross-linking agent is selected from at least one of glutaraldehyde, formaldehyde, succinaldehyde, genipin, sodium tripolyphosphate, N,N-dimethylacetyl and dialdehyde-terminated PEO; The colloidal stabilizer is at least one of glycerol, ethylene glycol, propylene glycol, isoprene glycol, polyethylene glycol, polyvinyl alcohol, hexylene glycol and pentaerythritol; The adsorption carrier is aerogel; In the pH-responsive controlled-release iron fertilizer, the loading amount of the iron-containing compound is 150-350 mg / g, and the loading amount is calculated based on the mass of iron in the iron-containing compound; The iron-containing compound is selected from at least one of ferrous sulfate, ferrous sulfate, ferrous chloride, ferric chloride, ferrous acetate, ferrous carbonate, ferrous nitrate and ferrous sulfate heptahydrate.

2. The pH-responsive controlled-release iron fertilizer according to claim 1, wherein: The chitosan and chitosan salt are selected from at least one of chitosan, N-carboxymethyl chitosan, deacetylated chitosan and maleic acid chitosan.

3. The pH-responsive controlled-release iron fertilizer according to claim 1 or 2, characterized in that: The raw material of the adsorption carrier also includes water.

4. The pH-responsive controlled-release iron fertilizer according to claim 1 or 2, characterized in that: The specific surface area of ​​the adsorption carrier is 0.5 to 50 m 2 / g, effective pore volume is 0.003~0.5cm 3 / g.

5. The pH-responsive controlled-release iron fertilizer according to claim 1 or 2, characterized in that: The preparation method of the adsorption carrier comprises the following steps: 1) mixing the organic polymer material, organic acid and water to form an aqueous phase a; 2) mixing the colloidal stabilizer and the aqueous phase a to form an aqueous phase b; 3) mixing the aqueous phase b and the cross-linking agent solution to obtain a wet gel; 4) Aging, freezing and drying the wet gel to obtain the adsorption carrier.

6. The pH-responsive controlled-release iron fertilizer according to claim 5, characterized in that: In step 1), the mass ratio of the organic polymer material to water is 1:25 to 1:50; In step 3), in the cross-linking agent solution, the mass ratio of the cross-linking agent to water is 1:10 to 1:100; In step 4), the aging is performed by placing the mixture at room temperature for 24 to 48 hours; and the freezing is performed by freezing the mixture at -20 to -50°C for 12 to 24 hours.

7. The method for preparing the pH-responsive controlled-release iron fertilizer according to any one of claims 1 to 6, comprising the steps of: preparing an iron-containing compound into an aqueous solution of the iron-containing compound, immersing the adsorption carrier in the aqueous solution of the iron-containing compound, and removing the adsorption carrier to obtain the pH-responsive controlled-release iron fertilizer.

8. The preparation method according to claim 7, characterized in that: The mass ratio of the iron-containing compound to water is 1:5 to 1:15; The adsorption carrier is immersed in the iron-containing compound aqueous solution and stirred at a speed of 200-400 rpm for 12-24 hours.

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