PH response type intelligent slow-release fertilizer based on magnesium slag carrier as well as preparation method and application of pH response type intelligent slow-release fertilizer

Abstract

The invention relates to the field of agricultural fertilizers, in particular to a magnesium slag carrier-based pH-responsive intelligent slow-release fertilizer as well as a preparation method and application thereof, which are suitable for rice alternative wetting and drying AWD irrigation mode, and regulate nutrient release kinetics through reversible protonation / deprotonation of carboxylic acid groups-COOH / -COO-. The fertilizer has the advantages that the alkaline characteristic of the magnesium slag is utilized, slow release can be achieved according to the change of the pH value of soil, the long-term effective adjusting function is provided for acid soil, and meanwhile nutrient elements such as calcium, silicon, magnesium and iron needed by rice are released. The fertilizer not only can effectively recycle magnesium slag and reduce environmental pollution, but also can improve the growth efficiency of rice. During application, the fertilizer is buried in the soil of the rice field, can release alkalinity and nutrient elements according to the change of the pH value of the soil, improves the utilization rate of the magnesium slag, and has good economic benefits and social benefits.

Description

Technical Field

[0001] The present invention relates to the field of agricultural fertilizers, and particularly to a pH-responsive intelligent slow-release fertilizer based on a magnesium slag carrier, and a preparation method and application thereof. Background Art

[0002] Magnesium slag is an industrial waste residue generated in the Pidgeon process for producing magnesium. According to statistics, 8.0 - 10.0t of magnesium slag is generated during the production of 1t of metallic magnesium. At present, the magnesium treatment slag of enterprises mainly relies on landfill and stacking, polluting the land, hindering the growth of crops, and causing waste of resources and damage to the ecological environment. The rational utilization of magnesium slag is related to the development of enterprises and the improvement of the environment. Magnesium slag has alkalinity and can be used for the improvement of acidic soil. However, the alkalinity of magnesium slag is too strong, and the required amount for acidic soil is small. Therefore, the soil will turn acidic again over time. At the same time, magnesium slag contains a large amount of mineral elements such as Ca, Si, Mg, and Fe required for plant growth. Therefore, preparing magnesium slag into an acidic soil fertilizer with slow-release ability can not only effectively utilize magnesium slag but also increase soil fertility.

[0003] Rice is one of the most important food crops in the world and is the staple food for more than half of the population in China. Moreover, rice production is the largest consumer of agricultural water. The irrigation water volume of paddy fields is about 2.5 times that of other crops such as corn and wheat, and its irrigation water use efficiency is only about 1kg / m 3 or so. Alternate wetting and drying (AWD) irrigation, as one of the most effective water-saving irrigation techniques in rice production, has been popularized and applied in major rice-producing countries in Asia (such as China, Bangladesh, India, and Vietnam, etc.). AWD irrigation has an important regulatory effect on rice yield, water and nitrogen use efficiency, and rice quality, and is one of the most potential cultivation measures to achieve high-yield, high-efficiency, and high-quality rice production at present. However, the soil pH value of the land under AWD irrigation will change periodically with the change of soil moisture; there is currently no fertilizer specifically designed for the change of pH value. Summary of the Invention

[0004] The purpose of the present invention is to overcome the deficiencies in the prior art and provide a pH-responsive intelligent slow-release fertilizer based on a magnesium slag carrier, and a preparation method and application thereof. This intelligent slow-release fertilizer can not only make the solid waste magnesium slag be resourcefully utilized and alleviate its pollution problem, but also effectively improve the soil pH value while providing nutrients for rice.

[0005] The present invention is achieved through the following technical solutions: On the one hand, a pH-responsive intelligent slow-release fertilizer based on a magnesium slag carrier is provided, which is applicable to the alternate wetting and drying (AWD) irrigation mode of rice, and regulates the nutrient release kinetics through the reversible protonation / deprotonation of carboxylic acid groups -COOH / -COO - -.

[0006] Further, when the soil pH = 5.5, the release rate of magnesium slag in the soil is 2.69 mg·day -1 ; when the soil pH = 7.4, the release rate of magnesium slag in the soil is 0.55 mg·day -1 .

[0007] Further, the carrier of the intelligent slow-release fertilizer is a carboxylated cellulose-magnesium slag composite hydrogel, and the carboxyl density of the carboxylated cellulose-magnesium slag composite hydrogel is 0.1-1.255 mmol / g.

[0008] Further, the swelling ratio of the carboxylated cellulose-magnesium slag composite hydrogel is 1.8-3.2 within the pH range of 5-8, and the nutrient slow-release period is 30-90 days.

[0009] A method for preparing the above-mentioned magnesium slag-based pH-responsive intelligent slow-release fertilizer is also provided, including the following steps:

[0010] Step 1) Straw pretreatment;

[0011] Step 2) Oxidation: Dissolve the product obtained in Step 1) in a buffer system containing TEMPO and sodium bromide, add sodium hypochlorite to initiate the oxidation reaction, and add sodium hydroxide dropwise to maintain pH = 10 until the reaction reaches equilibrium to obtain an oxidized product;

[0012] Step 3) Nanometerization: Shear-treat the oxidized product obtained in Step 2) with a rotor-stator mixer at 10,000-20,000 rpm to obtain a translucent nanocellulose gel with a flow rate of 0.3 kg / s;

[0013] Step 4) Modification: Add MES buffer solution to the translucent nanocellulose gel obtained in Step 3), ultrasonically disperse it, and then sequentially add EDC, NHS and 1,4-diaminobutane, stir at room temperature for 15-30 min and then continue the reaction for 24 h; Dialyze the grafted product with saturated NaCl solution and deionized water until the conductivity is constant, and freeze-dry to obtain a modified cellulose carrier;

[0014] Step 5) Polymerization: Mix the modified cellulose carrier obtained in Step 4) with acrylamide, N,N'-methylenebisacrylamide and magnesium slag in a mass ratio of 1:5:0.1:2, and use potassium persulfate-TMEDA as an initiation system under nitrogen protection, and polymerize at 25 °C for 3 h to obtain a polymerization product;

[0015] Step 6) Molding: Inject the polymerization product obtained in Step 5) into a PVC mold for molding, and immerse it in deionized water at room temperature for 3 days, and then centrifuge to remove unreacted monomers.

[0016] Further, in Step 1), the treatment steps of the straw pretreatment are as follows:

[0017] Step a): Crush wheat straw into sections of 1 - 8 cm in length and sieve through a 20 - 100 mesh sieve;

[0018] Step b): Perform Soxhlet extraction on the sieved straw with an ethanol - water mixture in a volume ratio of 1 - 5:1 - 5; Step c): Conduct air plasma activation treatment on the extraction product, with a voltage of 50 V, a frequency of 20 - 25 kHz, a current of 0.11 A, an air flow rate of 1 L / min, and a single - treatment time of 30 - 300 s;

[0019] Step d): Pretreat the activated sample with a 5 wt% sodium hydroxide solution at 20 - 100 °C for 15 - 60 min, and then bleach it with a 3 wt% hydrogen peroxide solution at 25 - 60 °C for 10 - 30 min.

[0020] Furthermore, in step 4), the molar ratio of EDC to NHS is 1:1.2.

[0021] Furthermore, in step 6), the PVC mold is a circular mold with an inner diameter of 1 - 5 cm.

[0022] There is also provided a method for applying the pH - responsive intelligent slow - release fertilizer as described above in the AWD irrigation mode for rice, including:

[0023] The first step: Monitor the pH value of the soil during the drought period and adjust the rhizosphere pH to 6.5 - 7.5 by applying magnesium slag;

[0024] The second step: Bury the fertilizer at a depth of 10 - 30 cm in the soil layer, with a fertilization rate of 100 - 300 kg / ha;

[0025] The third step: Irrigate according to the AWD mode with a water depth of 5 - 15 cm during the wet period and a soil water content of 40 - 80% during the drought period.

[0026] Even further, the application amount of magnesium slag is 50 - 100 kg / ha.

[0027] Beneficial effects

[0028] The advantages of the present invention are that this fertilizer utilizes the alkaline properties of magnesium slag, can achieve slow release according to the change of soil pH value, provides a long - term and effective regulation function for acidic soil, and simultaneously releases the nutrient elements required by rice, such as calcium, silicon, magnesium, and iron. This fertilizer can not only effectively recycle magnesium slag and reduce environmental pollution, but also improve the growth efficiency of rice. The preparation process includes steps such as straw treatment, plasma activation, chemical modification, mechanical grinding, and copolymerization molding. During application, the fertilizer is buried in paddy soil and can release alkalinity and nutrient elements according to the change of soil pH value, improving the utilization rate of magnesium slag and having good economic and social benefits. Brief description of the drawings

[0029] Figure 1 is the nutrient release curve embodied by the present invention. Detailed implementation manners

[0030] In order to make the objectives, technical solutions and advantages of the present invention more clear and understandable, the present invention will be further described in detail below in conjunction with specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0031] Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the scope of protection of the present invention. The experimental methods without specific conditions noted in the following embodiments are usually carried out under conventional conditions or according to the conditions recommended by the manufacturers. Unless otherwise specified, all percentages, ratios, proportions or parts are by weight.

[0032] The reagents and raw materials used in the embodiments and comparative examples of the present invention can be obtained through commercial channels without special instructions.

[0033] Example 1

[0034] The wheat straw is broken up, and after screening, the straw with a length of 5 cm is selected and extracted with a mixed solution of ethanol and water. The volume ratio of the extract is 5:2 (ethanol: water). After extraction, solid-liquid separation is carried out and the solid material is retained. The treated material is subjected to air plasma activation. The treatment conditions are a voltage of 50 V, a frequency of 20 kHz, an air flow rate of 1 L / min, a current of 0.15 A, and a treatment time of 200 s. After the surface of the material is activated by plasma activation, it is washed with a 2% sodium hydroxide solution at 20 °C for 15 minutes. After washing, the bleaching process is carried out at 60 °C, and a 3% hydrogen peroxide solution is used for bleaching. The bleaching time is controlled at 10 min. The obtained solid material is dissolved in a solution containing 0.075 g of 2,2,6,6-tetramethylpiperidine oxide and 0.50 g of sodium bromide; and an oxidation reaction is initiated by adding sodium hypochlorite, and at the same time, a sodium hydroxide solution is added until it is observed that the pH value remains at 10 and no longer changes; after reacting for 2 h, the obtained material is placed in a rotor-stator mixer for mechanical pulverization, and the operating speed is controlled at 18,000 rpm until a translucent gel-like substance with a flow rate of 0.5 kg / s is obtained; 2-(N-morpholino)-ethanesulfonic acid buffer solution is added to the obtained gel, and the pH value is maintained at 7.4. Subsequently, after ultrasonic treatment, N'-(3-dimethylaminopropyl)-N-ethylcarbodiimide hydrochloride and N-hydroxysuccinimide (1:2) are added. After mixing and stirring at room temperature for 18 minutes, 1,4-diaminobutane is added for covalent crosslinking, and the reaction time is 24 hours. The obtained crosslinked material is dialyzed successively with a saturated sodium chloride solution and then with distilled water until no free diamine is contained in the dialysis solution. After dialysis is completed, the material is freeze-dried for 48 hours to obtain a powdery substance, which is used for the next fertilizer copolymerization reaction. The obtained material is co-dissolved with 5.5% magnesium slag, 4.2% acrylamide (AM), and 0.18% N,N'-methylenebisacrylamide (MBA) in a stirrer. The reaction temperature is controlled at 25 °C, and it is purged with nitrogen and continuously stirred for 3 hours; then 0.51% potassium persulfate and 0.52% tetramethylethylenediamine are added as promoters to initiate the copolymerization reaction. The reaction temperature is controlled at 25 °C, and the reaction time is 4 hours. The obtained copolymer is poured into a PVC circular mold with a diameter of 3 cm and left to set at room temperature. After setting, the material is soaked in distilled water for 3 days, and the water temperature is maintained at 25 °C. After soaking, the residual substances are removed by centrifugation to obtain a shaped fertilizer sample. 8 g of the shaped fertilizer sample is applied to 10.1 kg of soil with a pH value of 7.4, and normal watering is carried out every day to ensure wet and dry alternation. The release rate of magnesium slag is further judged by sampling and measuring the calcium ion concentration in the soil every day.

[0035] Example 2

[0036] The wheat straw was broken up and straws with a length of 5 cm were selected after screening. It was extracted with a mixed solution of ethanol and water. The volume ratio of the extraction solution was 5:1.8 (ethanol: water). After extraction, solid-liquid separation was carried out and the solid material was retained. The treated material was subjected to air plasma activation under the conditions of 50 V voltage, 20 kHz frequency, an air flow rate of 1 L / min, a current of 0.15 A, and a treatment time of 200 s. After the surface of the material was activated by plasma activation, it was washed with a 2% sodium hydroxide solution at 22 °C for 15 minutes. After washing, the bleaching process was carried out at 59.4 °C, and it was bleached with a 3% hydrogen peroxide solution, and the bleaching time was controlled at 10 min. The obtained solid material was dissolved in a solution containing 0.05 g of 2,2,6,6-tetramethylpiperidine oxide and 0.51 g of sodium bromide. And the oxidation reaction was initiated by adding sodium hypochlorite. At the same time, a sodium hydroxide solution was added until it was observed that the pH value remained unchanged at 9.4. After reacting for 2 h, the obtained material was put into a rotor-stator mixer for mechanical crushing, and the operating speed was controlled at 18,000 rpm until a translucent gel-like substance with a flow rate of 0.49 kg / s was obtained. 2-(N-morpholino)-ethanesulfonic acid buffer solution was added to the obtained gel, and the pH value was kept at 7.4. Then, after ultrasonic treatment, N'-(3-dimethylaminopropyl)-N-ethylcarbodiimide hydrochloride and N-hydroxysuccinimide (1:2) were added. After mixing and stirring at room temperature for 18 minutes, 1,4-diaminobutane was added for covalent crosslinking, and the reaction time was 24 hours. The obtained crosslinked material was dialyzed successively with a saturated sodium chloride solution and then with distilled water until no free diamine was contained in the dialysis solution. After dialysis was completed, the material was freeze-dried for 48 hours to obtain a powdery substance, which was used for the next fertilizer copolymerization reaction. The obtained material was co-dissolved with 5.1% magnesium slag, 4.6% acrylamide (AM), and 0.26% N,N-methylenebisacrylamide (MBA) in a stirrer. The reaction temperature was controlled at 25 °C, and it was purged with nitrogen and continuously stirred for 3 hours. Then, 0.52% potassium persulfate and 0.51% tetramethylethylenediamine were added as promoters to initiate the copolymerization reaction. The reaction temperature was controlled at 25 °C, and the reaction time was 4 hours. The copolymer was obtained. It was poured into a PVC circular mold with a diameter of 3 cm and set at room temperature. After setting, the material was soaked in distilled water for 3 days, and the water temperature was kept at 25 °C. After soaking, the residual substances were removed by centrifugation. 8 g of the set fertilizer sample was applied to 10.5 kg of soil with a pH value of 7.4, and normal watering was carried out every day to ensure wet and dry alternation. The release rate of magnesium slag was further judged by measuring the calcium ion concentration in the soil by sampling every day.

[0037] Example 3

[0038] The wheat straw is crushed and straw with a length of 5 cm is selected after screening. It is extracted with a mixed solution of ethanol and water. The volume ratio of the extraction solution is 5:2 (ethanol: water). After extraction, solid-liquid separation is carried out and the solid material is retained. The treated material is subjected to air plasma activation under the treatment conditions of 50 V voltage, 20 kHz frequency, an air flow rate of 1 L / min, a current of 0.15 A, and a treatment time of 200 s. After the surface of the material is activated by plasma activation, it is washed with a 2% sodium hydroxide solution at 21 °C for 15 minutes. After washing, the bleaching process is carried out at 62 °C using a 3% hydrogen peroxide solution for bleaching, and the bleaching time is controlled at 10 min. The obtained solid material is dissolved in a solution containing 0.02 g of 2,2,6,6-tetramethylpiperidine oxide and 0.48 g of sodium bromide. And an oxidation reaction is initiated by adding sodium hypochlorite. At the same time, a sodium hydroxide solution is added until it is observed that the pH value remains unchanged at 10.2. After reacting for 2 h, the obtained material is put into a rotor-stator mixer for mechanical crushing, and the operating speed is controlled at 18,000 rpm until a translucent gel-like substance with a flow rate of 0.5 kg / s is obtained. 2-(N-morpholino)-ethanesulfonic acid buffer solution is added to the obtained gel, and the pH value is maintained at 7.4. Then, after ultrasonic treatment, N'-(3-dimethylaminopropyl)-N-ethylcarbodiimide hydrochloride and N-hydroxysuccinimide (1:2) are added. After mixing and stirring at room temperature for 17 minutes, 1,4-diaminobutane is added for covalent cross-linking, and the reaction time is 24 hours. The obtained cross-linked material is dialyzed successively with a saturated sodium chloride solution and then with distilled water until no free diamine is contained in the dialysis solution. After dialysis is completed, the material is freeze-dried for 48 hours to obtain a powdery substance for the next fertilizer copolymerization reaction. The obtained material is co-dissolved with 5.3% magnesium slag, 3.6% acrylamide (AM), and 0.22% N,N-methylenebisacrylamide (MBA) in a stirrer. The reaction temperature is controlled at 24 °C, and it is purged with nitrogen and continuously stirred for 3 hours. Then, 0.57% potassium persulfate and 0.55% tetramethylethylenediamine are added as promoters to initiate the copolymerization reaction. The reaction temperature is controlled at 25 °C, and the reaction time is 4 hours. A copolymer is obtained. It is poured into a PVC circular mold with a diameter of 3 cm and set at room temperature. After setting, the material is soaked in distilled water for 3 days, and the water temperature is maintained at 24 °C. After soaking, the residual substances are removed by centrifugation. 8 g of the set fertilizer sample is applied to 10.4 kg of soil with a pH value of 7.4, and normal watering is carried out every day to ensure wet and dry alternation. The release rate of magnesium slag is further judged by measuring the calcium ion concentration in the soil by sampling every day.

[0039] Example 4

[0040] The wheat straw was crushed, and the obtained solid material was dissolved in a solution containing 0.074 g of 2,2,6,6-tetramethylpiperidine oxide and 0.51 g of sodium bromide. The oxidation reaction was initiated by adding sodium hypochlorite. At the same time, sodium hydroxide solution was added until it was observed that the pH value remained unchanged at 10.1. After reacting for 2 h, the obtained material was mechanically crushed in a rotor-stator mixer with the operating speed controlled at 18,000 rpm until a translucent gel-like substance with a flow rate of 0.5 kg / s was obtained. 2-(N-Morpholino)-ethanesulfonic acid buffer solution was added to the obtained gel, and the pH value was maintained at 7.4. Subsequently, N'-(3-dimethylaminopropyl)-N-ethylcarbodiimide hydrochloride and N-hydroxysuccinimide (1:2) were added after ultrasonic treatment. After mixing and stirring at room temperature for 18 minutes, 1,4-diaminobutane was added for covalent cross-linking, and the reaction time was 24 hours. The obtained cross-linked material was dialyzed successively with saturated sodium chloride solution and then with distilled water until no free diamine was contained in the dialysis solution. After dialysis was completed, the material was freeze-dried for 48 hours to obtain a powdery substance for the next fertilizer copolymerization reaction. The obtained material was co-dissolved with 5.6% magnesium slag, 4.3% acrylamide (AM), and 0.18% N,N'-methylenebisacrylamide (MBA) in a stirrer. The reaction temperature was controlled at 25 °C, and it was purged with nitrogen while continuously stirring for 3 hours. Then, 0.52% potassium persulfate and 0.52% tetramethylethylenediamine were added as promoters to initiate the copolymerization reaction. The reaction temperature was controlled at 26 °C, and the reaction time was 4 hours. A copolymer was obtained. It was poured into a PVC circular mold with a diameter of 3 cm and set at room temperature. After setting, the material was soaked in distilled water for 3 days with the water temperature maintained at 23 °C. After soaking, the residual substances were removed by centrifugation to obtain a set fertilizer sample. 8.5 g of the set fertilizer sample was applied to 10.7 kg of soil with a pH value of 7.4, and normal watering was carried out every day to ensure wet-dry alternation. The release rate of magnesium slag was further judged by sampling and measuring the calcium ion concentration in the soil every day.

[0041] Example 5

[0042] The wheat straw was broken up, and straw with a length of 5 cm was selected after screening. It was extracted with a mixed solution of ethanol and water. The volume ratio of the extraction solution was 5:2 (ethanol: water). After extraction, solid-liquid separation was carried out and the solid material was retained. The treated material was subjected to air plasma activation under the treatment conditions of 50 V voltage, 20 kHz frequency, an air flow rate of 1 L / min, a current of 0.15 A, and a treatment time of 200 s. After the surface of the material was activated by plasma activation, it was washed with a 2% sodium hydroxide solution at 20 °C for 15 minutes. The bleaching process after washing was carried out at 60 °C, and it was bleached with a 3% hydrogen peroxide solution, and the bleaching time was controlled at 10 min. The obtained material was put into a rotor-stator mixer for mechanical crushing, and the operating speed was controlled at 18,000 rpm until a translucent gel-like substance with a flow rate of 0.5 kg / s was obtained. 2-(N-morpholino)-ethanesulfonic acid buffer solution was added to the obtained gel, and the pH value was maintained at 7.4. Subsequently, after ultrasonic treatment, N'-(3-dimethylaminopropyl)-N-ethylcarbodiimide hydrochloride and N-hydroxysuccinimide (1:2) were added. After mixing and stirring at room temperature for 18 minutes, 1,4-diaminobutane was added for covalent crosslinking, and the reaction time was 24 hours. The obtained crosslinked material was dialyzed successively with saturated sodium chloride solution and then with distilled water until no free diamine was contained in the dialysis solution. After dialysis was completed, the material was freeze-dried for 48 hours to obtain a powdery substance for the next fertilizer copolymerization reaction. The obtained material was co-dissolved with 5% magnesium slag, 4% acrylamide (AM), and 0.2% N,N-methylenebisacrylamide (MBA) in a stirrer. The reaction temperature was controlled at 25 °C, and it was purged with nitrogen and continuously stirred for 3 hours. Then 0.5% potassium persulfate and 0.5% tetramethylethylenediamine were added as promoters to initiate the copolymerization reaction. The reaction temperature was controlled at 25 °C, and the reaction time was 4 hours. The obtained copolymer was poured into a PVC circular mold with a diameter of 3 cm and set at room temperature. After setting, the material was soaked in distilled water for 3 days, and the water temperature was maintained at 25 °C. After soaking, the residual substances were removed by centrifugation to obtain a shaped fertilizer sample. 8 g of the shaped fertilizer sample was applied to 10 kg of soil with a pH value of 7.4, and normal watering was carried out every day to ensure wet and dry alternation. The release rate of magnesium slag was further judged by sampling and measuring the calcium ion concentration in the soil every day.

[0043] Example 6

[0044] The wheat straw is broken up, and the straw with a length of 5 cm is selected after screening. It is extracted with a mixed solution of ethanol and water. The volume ratio of the extraction solution is 5:2 (ethanol: water). After extraction, solid-liquid separation is carried out and the solid material is retained. The treated material is subjected to air plasma activation. The treatment conditions are a voltage of 50 V, a frequency of 20 kHz, an air flow rate of 1 L / min, a current of 0.15 A, and a treatment time of 200 s. After the surface of the material is activated by plasma activation, it is washed with a 2% sodium hydroxide solution at 19 °C for 15 minutes. After washing, the bleaching process is carried out at 62 °C, and it is bleached with a 3% hydrogen peroxide solution. The bleaching time is controlled at 10 min. The obtained solid material is dissolved in a solution containing 0.03 g of 2,2,6,6-tetramethylpiperidine oxide and 0.53 g of sodium bromide. And the oxidation reaction is initiated by adding sodium hypochlorite. At the same time, a sodium hydroxide solution is added until it is observed that the pH value remains unchanged at 10.1. After reacting for 2 h, 2-(N-morpholino)-ethanesulfonic acid buffer solution is added to the obtained gel, and the pH value is maintained at 7.4. Then, after ultrasonic treatment, N'-(3-dimethylaminopropyl)-N-ethylcarbodiimide hydrochloride and N-hydroxysuccinimide (1:2) are added. After mixing and stirring at room temperature for 18 minutes, 1,4-diaminobutane is added for covalent crosslinking, and the reaction time is 24 hours. The obtained crosslinked material is dialyzed successively with a saturated sodium chloride solution and then with distilled water until no free diamine is contained in the dialysis solution. After dialysis is completed, the material is freeze-dried for 48 hours to obtain a powdery substance for the next fertilizer copolymerization reaction. The obtained material is co-dissolved with 5.4% magnesium slag, 4.5% acrylamide (AM), and 0.35% N,N'-methylenebisacrylamide (MBA) in a stirrer. The reaction temperature is controlled at 26 °C, and it is purged with nitrogen and continuously stirred for 3 hours. Then, 0.53% potassium persulfate and 0.45% tetramethylethylenediamine are added as promoters to initiate the copolymerization reaction. The reaction temperature is controlled at 25 °C, and the reaction time is 4 hours. The obtained copolymer is poured into a PVC circular mold with a diameter of 3 cm and set at room temperature. After setting, the material is immersed in distilled water for 3 days, and the water temperature is maintained at 25 °C. After immersion, the residual substances are removed by centrifugation to obtain a shaped fertilizer sample. 8 g of the shaped fertilizer sample is applied to 10.3 kg of soil with a pH value of 7.4, and water is normally watered every day to ensure wet-dry alternation. The release rate of magnesium slag is further judged by measuring the calcium ion concentration in the soil by sampling every day.

[0045] Example 7

[0046] The wheat straw is broken up and the straw with a length of 5 cm is selected after screening. It is extracted with a mixed solution of ethanol and water. The volume ratio of the extraction solution is 5:2 (ethanol: water). After extraction, solid-liquid separation is carried out and the solid material is retained. The treated material is subjected to air plasma activation. The treatment conditions are a voltage of 50 V, a frequency of 20 kHz, an air flow rate of 1 L / min, a current of 0.15 A, and a treatment time of 200 s. After the surface of the material is activated by plasma activation, it is washed with a 2% sodium hydroxide solution at 20 °C for 15 minutes. The bleaching process after washing is carried out at 59 °C, and it is bleached with a 3% hydrogen peroxide solution. The bleaching time is controlled at 10 min. The obtained solid material is dissolved in a solution containing 0.074 g of 2,2,6,6-tetramethylpiperidine oxide and 0.47 g of sodium bromide. And an oxidation reaction is initiated by adding sodium hypochlorite. At the same time, a sodium hydroxide solution is added until it is observed that the pH value remains unchanged at 9.87. After reacting for 2 h, the obtained material is put into a rotor-stator mixer for mechanical crushing. The operating rotation speed is controlled at 18,000 rpm until a translucent gel-like substance with a flow rate of 0.5 kg / s is obtained. The obtained material is co-dissolved with 5.2% magnesium slag, 3.8% acrylamide (AM), and 0.26% N,N'-methylenebisacrylamide (MBA) in a stirrer. The reaction temperature is controlled at 25 °C, and it is purged with nitrogen and continuously stirred for 3 hours. Then 0.48% potassium persulfate and 0.52% tetramethylethylenediamine are added as promoters to initiate a copolymerization reaction. The reaction temperature is controlled at 26 °C, and the reaction time is 4 hours. A copolymer is obtained. It is poured into a PVC circular mold with a diameter of 3 cm and set at room temperature. After setting, the material is immersed in distilled water for 3 days. The water temperature is kept at 25 °C. After immersion, the residual substances are removed by centrifugation to obtain a shaped fertilizer sample. 8 g of the shaped fertilizer sample is applied to 10.2 kg of soil with a pH value of 7.4. Water is normally poured every day to ensure wet-dry alternation. The release rate of magnesium slag is further judged by measuring the calcium ion concentration in the soil by sampling every day.

[0047] Example 8

[0048] The wheat straw is broken up, and after screening, the straw with a length of 5 cm is selected. It is extracted with a mixed solution of ethanol and water. The volume ratio of the extraction solution is 5:2 (ethanol: water). After extraction, solid-liquid separation is carried out and the solid material is retained. The treated material is subjected to air plasma activation. The treatment conditions are a voltage of 50 V, a frequency of 20 kHz, an air flow rate of 1 L / min, a current of 0.15 A, and a treatment time of 200 s. After the surface of the material is activated by plasma, it is washed with a 2% sodium hydroxide solution at 19 °C for 15 minutes. After washing, the bleaching process is carried out at 60 °C, and a 3% hydrogen peroxide solution is used for bleaching. The bleaching time is controlled at 10 min. The obtained solid material is dissolved in a solution containing 0.072 g of 2,2,6,6-tetramethylpiperidine oxide and 0.57 g of sodium bromide. And the oxidation reaction is initiated by adding sodium hypochlorite. At the same time, a sodium hydroxide solution is added until it is observed that the pH value remains unchanged at 10.2. After reacting for 2 h, the obtained material is put into a rotor-stator mixer for mechanical pulverization, and the operating speed is controlled at 18,000 rpm until a translucent gel-like substance with a flow rate of 0.5 kg / s is obtained. 2-(N-morpholino)-ethanesulfonic acid buffer solution is added to the obtained gel, and the pH value is maintained at 7.4. Subsequently, after ultrasonic treatment, N'-(3-dimethylaminopropyl)-N-ethylcarbodiimide hydrochloride and N-hydroxysuccinimide (1:2) are added. After mixing and stirring at room temperature for 18 minutes, 1,4-diaminobutane is added for covalent crosslinking, and the reaction time is 24 hours. The obtained crosslinked material is dialyzed successively with a saturated sodium chloride solution and then with distilled water until no free diamine is contained in the dialysis solution. After dialysis is completed, the material is freeze-dried for 48 hours to obtain a powdery substance, which is used for the next fertilizer copolymerization reaction. The obtained material is co-dissolved with 4.7% magnesium slag, 4.9% acrylamide (AM), and 0.19% N,N-methylenebisacrylamide (MBA) in a stirrer. The reaction temperature is controlled at 25 °C, and it is purged with nitrogen and continuously stirred for 3 hours. Then the obtained material is poured into a PVC circular mold with a diameter of 3 cm and set at room temperature. After setting, the material is soaked in distilled water for 3 days, and the water temperature is maintained at 24 °C. After soaking, the residual substances are removed by centrifugation to obtain a shaped fertilizer sample. 8.3 g of the shaped fertilizer sample is applied to 10.1 kg of soil with a pH value of 7.4, and normal watering is carried out every day to ensure wet and dry alternation. The release rate of magnesium slag is further judged by sampling and measuring the calcium ion concentration in the soil every day.

[0049] Example 9

[0050] The wheat straw is broken up, and the straw with a length of 5 cm is selected after screening. It is extracted with a mixed solution of ethanol and water. The volume ratio of the extract is 5:2 (ethanol: water). After extraction, solid-liquid separation is carried out and the solid material is retained. The treated material is subjected to air plasma activation under the treatment conditions of a voltage of 50 V, a frequency of 20 kHz, an air flow rate of 1 L / min, a current of 0.15 A, and a treatment time of 200 s. After the surface of the material is activated by plasma activation, it is washed with a 2% sodium hydroxide solution at 19 °C for 15 minutes. After washing, the bleaching process is carried out at 58.9 °C, and it is bleached with a 3% hydrogen peroxide solution, and the bleaching time is controlled at 10 min. The obtained solid material is dissolved in a solution containing 0.073 g of 2,2,6,6-tetramethylpiperidine oxide and 0.48 g of sodium bromide. And the oxidation reaction is initiated by adding sodium hypochlorite. At the same time, a sodium hydroxide solution is added until it is observed that the pH value remains at 10 and no longer changes. After reacting for 2 h, the obtained material is put into a rotor-stator mixer for mechanical grinding, and the operating speed is controlled at 18,000 rpm until a translucent gel-like substance with a flow rate of 0.5 kg / s is obtained. 2-(N-morpholino)-ethanesulfonic acid buffer solution is added to the obtained gel, and the pH value is maintained at 7.4. Then, after ultrasonic treatment, N'-(3-dimethylaminopropyl)-N-ethylcarbodiimide hydrochloride and N-hydroxysuccinimide (1:2) are added. After mixing and stirring at room temperature for 18 minutes, 1,4-diaminobutane is added for covalent crosslinking, and the reaction time is 24 hours. The obtained crosslinked material is dialyzed successively with a saturated sodium chloride solution and then with distilled water until no free diamine is contained in the dialysis solution. After dialysis is completed, the material is freeze-dried for 48 hours to obtain a powdery substance, which is used for the next fertilizer copolymerization reaction. The obtained material is co-dissolved with 5.4% magnesium slag, 4.2% acrylamide (AM), and 0.25% N,N-methylenebisacrylamide (MBA) in a stirrer. The reaction temperature is controlled at 26 °C, and it is purged with nitrogen and continuously stirred for 3 hours. Then 0.53% potassium persulfate and 0.64% tetramethylethylenediamine are added as promoters to initiate the copolymerization reaction. The reaction temperature is controlled at 24 °C, and the reaction time is 4 hours. A copolymer is obtained. It is shaped at room temperature. After shaping, the material is soaked in distilled water for 3 days, and the water temperature is maintained at 25 °C. After soaking, the residual substances are removed by centrifugation to obtain a shaped fertilizer sample. 7.3 g of the shaped fertilizer sample is applied to 10 kg of soil with a pH value of 7.4, and normal watering is carried out every day to ensure wet-dry alternation. The release rate of magnesium slag is further judged by measuring the calcium ion concentration in the soil by sampling every day.

[0051] Example 10

[0052] The wheat straw was broken up, and the straw with a length of 5 cm was selected after screening. It was extracted with a mixed solution of ethanol and water. The volume ratio of the extraction solution was 5:2 (ethanol: water). After extraction, solid-liquid separation was carried out and the solid material was retained. The treated material was subjected to air plasma activation under the conditions of a voltage of 50 V, a frequency of 20 kHz, an air flow rate of 1 L / min, a current of 0.15 A, and a treatment time of 200 s. After the surface of the material was activated by plasma activation, it was washed with a 2% sodium hydroxide solution at 20 °C for 15 minutes. After washing, the bleaching process was carried out at 58 °C, and a 3% hydrogen peroxide solution was used for bleaching, and the bleaching time was controlled at 10 min. The obtained solid material was dissolved in a solution containing 0.072 g of 2,2,6,6-tetramethylpiperidine oxide and 0.53 g of sodium bromide. And the oxidation reaction was initiated by adding sodium hypochlorite. At the same time, a sodium hydroxide solution was added until it was observed that the pH value remained at 10 without further change. After reacting for 2 h, the obtained material was put into a rotor-stator mixer for mechanical crushing, and the operating speed was controlled at 18,000 rpm until a translucent gel-like substance with a flow rate of 0.5 kg / s was obtained. 2-(N-morpholino)-ethanesulfonic acid buffer solution was added to the obtained gel, and the pH value was maintained at 7.4. Subsequently, after ultrasonic treatment, N'-(3-dimethylaminopropyl)-N-ethylcarbodiimide hydrochloride and N-hydroxysuccinimide (1:1) were added. After mixing and stirring at room temperature for 18 minutes, 1,4-diaminobutane was added for covalent crosslinking, and the reaction time was 24 hours. The obtained crosslinked material was dialyzed successively with saturated sodium chloride solution and then with distilled water until no free diamine was contained in the dialysis solution. After dialysis was completed, the material was freeze-dried for 48 hours to obtain a powdery substance for the next fertilizer copolymerization reaction. The obtained material was co-dissolved with 4.98% magnesium slag, 4.2% acrylamide (AM), and 0.39% N,N-methylenebisacrylamide (MBA) in a stirrer. The reaction temperature was controlled at 25 °C, and it was purged with nitrogen and continuously stirred for 3 hours. Then 0.57% potassium persulfate and 0.59% tetramethylethylenediamine were added as promoters to initiate the copolymerization reaction. The reaction temperature was controlled at 24.8 °C, and the reaction time was 4 hours. A copolymer was obtained. It was poured into a PVC circular mold with a diameter of 3 cm and set at room temperature. After setting, the material was soaked in distilled water for 3 days, and the water temperature was maintained at 25 °C. After soaking, the residual substances were removed by centrifugation to obtain a shaped fertilizer sample. 8.5 g of the shaped fertilizer sample was applied to 9.98 kg of soil with a pH value of 7.4, and normal watering was carried out every day to ensure wet and dry alternation. The release rate of magnesium slag was further judged by measuring the calcium ion concentration in the soil by sampling every day.

[0053] Example 11

[0054] The wheat straw is broken up, and after screening, the straw with a length of 5 cm is selected. It is extracted with a mixed solution of ethanol and water. The volume ratio of the extraction solution is 5:2 (ethanol: water). After extraction, solid-liquid separation is carried out and the solid material is retained. The treated material is subjected to air plasma activation under the treatment conditions of a voltage of 50 V, a frequency of 20 kHz, an air flow rate of 1 L / min, a current of 0.15 A, and a treatment time of 200 s. After the surface of the material is activated by plasma activation, it is washed with a 2% sodium hydroxide solution at 21 °C for 15 minutes. After washing, the bleaching process is carried out at 60 °C, and a 3% hydrogen peroxide solution is used for bleaching, and the bleaching time is controlled at 10 min. The obtained solid material is dissolved in a solution containing 0.072 g of 2,2,6,6-tetramethylpiperidine oxide and 0.54 g of sodium bromide. And the oxidation reaction is initiated by adding sodium hypochlorite. At the same time, a sodium hydroxide solution is added until it is observed that the pH value remains unchanged at 9.93. After reacting for 2 h, the obtained material is put into a rotor-stator mixer for mechanical grinding, and the operating speed is controlled at 18,000 rpm until a translucent gel-like substance with a flow rate of 0.5 kg / s is obtained. 2-(N-morpholino)-ethanesulfonic acid buffer solution is added to the obtained gel, and the pH value is maintained at 7.4. Subsequently, after ultrasonic treatment, N'-(3-dimethylaminopropyl)-N-ethylcarbodiimide hydrochloride and N-hydroxysuccinimide (0.7:1.2) are added. After mixing and stirring at room temperature for 18 minutes, 1,4-diaminobutane is added for covalent crosslinking, and the reaction time is 24 hours. The obtained crosslinked material is dialyzed successively with a saturated sodium chloride solution and then with distilled water until no free diamine is contained in the dialysis solution. After dialysis is completed, the material is freeze-dried for 48 hours to obtain a powdery substance, which is used for the next fertilizer copolymerization reaction. The obtained material is co-dissolved with 5.1% magnesium slag, 3.8% acrylamide (AM), and 0.27% N,N'-methylenebisacrylamide (MBA) in a stirrer. The reaction temperature is controlled at 25 °C, and it is purged with nitrogen and continuously stirred for 3 hours. Then 0.49% potassium persulfate and 0.52% tetramethylethylenediamine are added as promoters to initiate the copolymerization reaction. The reaction temperature is controlled at 24 °C, and the reaction time is 4 hours. The obtained copolymer is poured into a PVC circular mold with a diameter of 3 cm and set at room temperature. After setting, the material is immersed in distilled water for 3 days, and the water temperature is maintained at 24.3 °C. After immersion, the residual substances are removed by centrifugation to obtain a set fertilizer sample. 8.4 g of the set fertilizer sample is applied to 10.2 kg of soil with a pH value of 7.4, and normal watering is carried out every day to ensure wet-dry alternation. The release rate of magnesium slag is further judged by sampling and measuring the calcium ion concentration in the soil every day.

[0055] In summary, as Figure 1As shown, the effects of Example 1 are different from those of Examples 2 and 3 in terms of the addition amount of 2,6,6 - trimethylpiperidine 1 - oxide. Different addition amounts of 2,6,6 - trimethylpiperidine 1 - oxide will result in differences in the carboxyl density of the carboxylated cellulose - magnesium slag composite hydrogel. When the carboxylated cellulose - magnesium slag composite hydrogel contains different carboxyl densities, it will affect the reversible protonation / deprotonation rate of - COOH / -COO - in the carboxylated cellulose - magnesium slag composite hydrogel, thereby affecting the release rate of magnesium slag by the carboxylated cellulose - magnesium slag composite hydrogel. Example 1 can slowly release magnesium slag and nutrient elements in 1600 h, while Examples 2 and 3 still have the ability of slow release but the initial release rate is faster, and 20% of the magnesium slag is released within the first 100 h, compared with 10% in Example 1, the magnesium slag loss rate is faster.

[0056] In Example 4, no pretreatment was carried out, resulting in the lignin in wheat straw not being removed, uneven fiber structure, difficulty in nanosizing, and insufficient exposure of hydroxyl groups. TEMPO oxidation could not occur uniformly, so that the characteristics of pH - responsive intelligent fertilizer were lost. Example 4 did not show the ability to slowly release magnesium slag under the AWD irrigation mode, but had irregular fluctuating release. It released 40% of the magnesium slag in the first few hours after application. After 800 h of application, the magnesium slag release rate had reached more than 87%, proving that the oxidation of TEMPO is a key step in the preparation of pH - responsive fertilizers.

[0057] In Example 5, the oxidation step was missing. The next - prepared material had no carboxyl (-COOH) functional groups, and the amination modification failed. At the same time, it would cause the fertilizer precursor to lack cross - linking sites and the hydrogel could not be formed. Example 5 completely dissolved in the soil after being applied to the soil, with a release rate of 100%, further proving that it did not form a hydrogel shell and could not effectively release magnesium slag slowly into the soil.

[0058] In Example 6, no nanosizing treatment was carried out, and the fiber size was too large (>100 nm), which affected the uniformity of the hydrogel, the formed hydrogel structure was unstable, and the water absorption capacity decreased. Therefore, the pH - dependence and slow - release performance of the fertilizer were affected. Compared with Examples 1, 2, and 3, the release rate of Example 6 was further accelerated on this basis. It could maintain a magnesium slag release rate of 40% within 1600 h and still maintain the trend of slow release, but due to the too - large fiber size, its release cycle would be shortened.

[0059] In Example 7, without modification treatment, pH-responsive amino groups (-NH2) cannot be formed, and the hydrogel cannot regulate the swelling property with pH changes, resulting in uncontrolled nutrient release and loss of intelligent slow-release characteristics. The release rate of Example 7 is similar to that of Example 5. After being applied to the soil, the release rate of magnesium slag reaches 100%, proving that the modification treatment is also an essential step in the preparation of pH-responsive intelligent fertilizers.

[0060] In Example 8, there is no polymerization step and cross-linked structure, so the hydrogel network cannot be formed and the magnesium slag cannot be fixed, and it directly dissolves and is lost when encountering water. The release rate of Example 8 is the same as that of Examples 5 and 7, which proves that the polymerization step is also an essential step in the process of preparing the gel. The unsuccessful preparation of the gel will cause the magnesium slag to be completely exposed in the soil and then completely released in the soil.

[0061] In Example 9, no shaping is carried out, and the sizes and shapes of the fertilizers are inconsistent, which causes certain difficulties in use and affects the release performance of the fertilizers at the same time. It can be seen from the release curve of magnesium slag that the inconsistent sizes of the fertilizers will affect the release rate of magnesium slag and the pH sensing performance. In the later stage of application of Example 6, the release rule shows unstable slow release, but it can still maintain 85% release in 1600 h. The reason for this phenomenon is related to the specific surface area of the fertilizer to a certain extent. When the fertilizer particles are too small, the specific surface area increases, and there is more release space for the fertilizer, which strengthens its release ability and thus increases the release rate.

[0062] In Example 10, compared with Example 1, EDC is in excess relative to NHS, and the carboxyl groups will be over-activated. However, since the activated acyl isourea intermediate is not stable enough, it is prone to hydrolysis reaction and inactivation, resulting in insufficient amount of NHS ester generated and reducing the reaction efficiency with 1,4-diaminobutane, thereby affecting the slow-release performance of the fertilizer. In the reaction process of Example 10, the carboxyl groups will be over-activated, which will accelerate the release rate during the reaction process. After 400 h of reaction, 37% of the magnesium slag can be released, compared with only 15% released by Example 1 after 400 h, and it cannot achieve the ability of slow release in terms of the release rate of magnesium slag.

[0063] In Example 11, compared with Example 1, the excess of NHS will introduce competitive side reactions, change the reaction equilibrium, and the structure of the final product will deviate. After the structure deviates, the release rate of magnesium slag is increased. In the first 300 hours of the reaction, compared with Example 1, it still has a certain slow-release ability, with only a difference of 7-8% in the release rate of magnesium slag. However, after the reaction reaches 400 h, due to the deviation of the structure, under the slow action of the soil, the structure will be further damaged, and the slow-release performance will be further damaged, resulting in an accelerated release rate.

[0064] Effect Example 1

[0065] Apply the pH-responsive intelligent slow-release fertilizer prepared in Example 1 to a paddy field with a pH value of 6.5. First, apply magnesium slag (the application rate is 100 kg per hectare) to adjust the soil pH value to 7.4. Then bury the prepared intelligent fertilizer at a depth of 20 cm below the paddy field soil at a rate of 200 kg / ha. Conduct normal wet-dry alternate irrigation, monitor the periodic changes in soil pH value, and ensure that the slow-release effect of the fertilizer reaches the best.

[0066] Effect Example 2

[0067] Apply the pH-responsive intelligent slow-release fertilizer prepared in Example 1 to a paddy field with a pH value of 6.5. First, apply magnesium slag (the application rate is 100 kg per hectare) to adjust the soil pH value to 7.4. Then bury the prepared intelligent fertilizer at a depth of 20 cm below the paddy field soil at a rate of 100 kg / ha. Conduct normal wet-dry alternate irrigation, monitor the periodic changes in soil pH value, and ensure that the slow-release effect of the fertilizer reaches the best.

[0068] Effect Example 3

[0069] Apply the pH-responsive intelligent slow-release fertilizer prepared in Example 1 to a paddy field with a pH value of 6.5. First, apply magnesium slag (the application rate is 100 kg per hectare) to adjust the soil pH value to 7.4. Then bury the prepared intelligent fertilizer at a depth of 20 cm below the paddy field soil at a rate of 300 kg / ha. Conduct normal wet-dry alternate irrigation, monitor the periodic changes in soil pH value, and ensure that the slow-release effect of the fertilizer reaches the best.

[0070] Effect Example 4

[0071] For a paddy field with a pH value of 6.5, apply magnesium slag (the application rate is 100 kg per hectare) to adjust the soil pH value to 7.4. Plant rice without any treatment.

[0072] Table 2 Growth indicators of rice under different treatments

[0073] Serial number Plant height (cm) Root length (cm) Dry weight of leaves (g) Effect Example 1 49.96 21.54 0.35 Effect Example 2 49.23 19.34 0.27 Effect Example 3 46.45 17,76 0.30 Effect Example 4 43.87 16.23 0.24

[0074] Effect Examples 1, 2, 3 and Effect Example 4 The pH-responsive intelligent fertilizer prepared by the present invention can effectively adapt to the pH value change of the soil during the wet-dry alternate rice planting process after being applied to the soil, compared with the land without applying fertilizer. At the same time, the application rate of 200 kg / ha is more conducive to plant growth. The pH-responsive intelligent fertilizer of the present invention contains nitrogen element, which can effectively increase the nitrogen element content in the soil and effectively promote plant growth. As can be seen from Table 1, the plant height, root length and leaf dry weight have been significantly improved after applying the pH-responsive intelligent fertilizer. Therefore, the pH-responsive intelligent fertilizer of the present invention can effectively meet the growth of rice under the wet-dry alternate planting mode and promote plant growth at the same time.

[0075] Finally, it should be noted that the above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some of the technical features. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A pH-responsive intelligent slow-release fertilizer based on magnesium slag carrier, suitable for rice alternating wetting and drying AWD irrigation mode, through the carboxylic acid group -COOH / -COO - The reversible protonation / deprotonation of nutrient molecules regulates the nutrient release kinetics.

2. The pH-responsive intelligent slow-release fertilizer based on magnesium slag carrier according to claim 1, characterized in that: When soil pH = 5.5, the release rate of magnesium slag in soil is 2.69 mg·day -1 ; When soil pH = 7.4, the release rate of magnesium slag in the soil is 0.55 mg·day -1 .

3. The pH-responsive intelligent slow-release fertilizer based on magnesium slag carrier according to claim 1, characterized in that: The carrier of the intelligent slow-release fertilizer is a carboxylated cellulose-magnesium slag composite hydrogel, and the carboxyl density of the carboxylated cellulose-magnesium slag composite hydrogel is 0.1-1.255 mmol / g.

4. The pH-responsive intelligent slow-release fertilizer based on magnesium slag carrier according to claim 3, characterized in that: The carboxylated cellulose-magnesium slag composite hydrogel has a swelling ratio of 1.8-3.2 within a pH range of 5-8, and a nutrient sustained release period of 30-90 days.

5. A method for preparing the pH-responsive intelligent slow-release fertilizer based on magnesium slag carrier according to any one of claims 1 to 4, characterized in that: The following steps are involved: Step 1) pretreatment of straw; Step 2) Oxidation: dissolving the product obtained in step 1) in a buffer system containing TEMPO and sodium bromide, adding sodium hypochlorite to initiate an oxidation reaction, and adding sodium hydroxide dropwise to maintain pH=10 until the reaction is in equilibrium, to obtain an oxidation product; Step 3) Nano-crystallization: The oxidation product obtained in step 2) is sheared by a rotor-stator mixer at 10,000-20,000 rpm to obtain a translucent nanocellulose gel with a flow rate of 0.3 kg / s; Step 4) modification: adding MES buffer to the translucent nanocellulose gel obtained in step 3), adding EDC, NHS and 1,4-diaminobutane in sequence after ultrasonic dispersion, stirring at room temperature for 15-30 minutes and then continuing the reaction for 24 hours; dialyzing the grafted product with saturated NaCl solution and deionized water until the conductivity is constant, and freeze-drying to obtain a modified cellulose carrier; Step 5) polymerization: the modified cellulose carrier obtained in step 4) is mixed with acrylamide, N,N'-methylenebisacrylamide and magnesium slag in a mass ratio of 1:5:0.1:2, and the mixture is polymerized at 25°C for 3 hours under nitrogen protection with potassium persulfate-TMEDA as the initiation system to obtain a polymer product; Step 6) Molding: The polymer product obtained in step 5) is injected into a PVC mold for molding, immersed in deionized water at room temperature for 3 days, and then centrifuged to remove unreacted monomers.

6. The method for preparing a pH-responsive intelligent slow-release fertilizer based on a magnesium slag carrier according to claim 5, characterized in that: In step 1), the straw pretreatment process is as follows: Step a) crushing the wheat straw into 1-8 cm segments and passing through a 20-100 mesh sieve; Step b) performing Soxhlet extraction on the screened straw and an ethanol-water mixture with a volume ratio of 1-5:1-5; Step c) performing air plasma activation treatment on the extracted product, with a voltage of 50 V, a frequency of 20-25 kHz, a current of 0.11 A, an air flow rate of 1 L / min, and a single treatment time of 30-300 s; Step d) pre-treating the activated sample with a 5 wt % sodium hydroxide solution at 20-100° C. for 15-60 min, and then bleaching with 3 wt % hydrogen peroxide at 25-60° C. for 10-30 min.

7. The method for preparing a pH-responsive intelligent slow-release fertilizer based on a magnesium slag carrier according to claim 5, characterized in that: In step 4), the molar ratio of EDC to NHS is 1:1.

2.

8. The method for preparing a pH-responsive intelligent slow-release fertilizer based on a magnesium slag carrier according to claim 5, characterized in that: In step 6), the PVC mold is a circular mold with an inner diameter of 1-5 cm.

9. A method for applying the pH-responsive intelligent slow-release fertilizer according to any one of claims 1 to 4 in a rice AWD irrigation mode, characterized in that: include: Step 1: Monitor soil pH during drought and adjust rhizosphere pH to 6.5-7.5 by applying magnesium slag; Step 2: bury the fertilizer in the soil layer at a depth of 10-30cm, with a fertilizer application rate of 100-300kg / ha; Step 3: Irrigate according to the AWD mode with a water depth of 5-15cm in the wet period and a soil moisture content of 40-80% in the dry period.

10. The application method according to claim 9, characterized in that: The application rate of magnesium slag is 50-100kg / ha.

Images