Passivation culture solution for reducing cadmium in rice and preparation method of passivation culture solution

Abstract

The invention relates to the technical field of agricultural environment restoration and plant nutrition regulation and control, in particular to a passivation culture solution for rice cadmium reduction and a preparation method of the passivation culture solution. The culture solution is composed of a ferric citrate complexing solution, a sodium polyaspartate graft, potassium dihydrogen phosphate, a choline-stabilized orthosilicic acid mother solution and a zinc ethylenediamine tetraacetate disodium salt hydrate. In the preparation process, a stable system is cooperatively constructed through multi-coordination complexing, electrostatic regulation and an organic framework stabilization mechanism. The culture solution still keeps good dispersity and stability under acidic and hard water conditions, can form a weak-acid-to-neutral buffer area in rice rhizosphere, effectively reduces migration and absorption of cadmium ions, maintains availability of nutrient elements such as iron and zinc, remarkably reduces the cadmium content of rice grains, improves the nutritional quality and environmental adaptability of crops, and has a wide application prospect. The method is suitable for efficient and safe treatment of cadmium-polluted rice fields.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of agricultural environment remediation and plant nutrition regulation, and particularly relates to a passivation culture solution for reducing cadmium in rice and a preparation method thereof. BACKGROUND

[0002] The problem of cadmium (Cd) pollution in rice is particularly prominent in the acid paddy fields in southern China. High soil acidity causes cadmium to exist mainly in the forms of exchangeable and carbonate-bound states, which are easily absorbed by plants. To reduce cadmium accumulation in rice, existing researches mostly use passivation culture solutions, amendments or foliar spraying solutions to achieve chemical fixation or transport inhibition of cadmium bioavailability. Among them, phosphate and silicate passivation agents are widely used, which generate insoluble salts through coprecipitation to reduce the migration of cadmium. However, the phosphate and single silicon source system has multiple limitations in practical application.

[0003] Firstly, under hard water and acidic conditions, phosphate and Ca 2+ , Mg 2+ easily form precipitates such as Ca3(PO4)2 and MgHPO4, resulting in serious turbidity and sedimentation of the solution, and a decrease in nutrient availability; in the silicate system, orthosilicic acid rapidly polymerizes to form SiO2·nH2O gel at pH>7 or high electrolyte strength, which reduces the activity of silicon and makes it difficult for crops to absorb. This is particularly evident in hard water areas (calcium carbonate hardness > 250 mg / L), where silicates are quickly polymerized and precipitated after reacting with calcium and magnesium ions, causing problems such as clogging of the spray head and sedimentation after field spraying, which significantly reduces the operability and stability of the effect in the field.

[0004] Secondly, the existing phosphate or single silicon source passivation solution relies only on simple coprecipitation or physical adsorption to fix cadmium, which has poor selectivity for essential elements such as Fe and Zn, often reducing the availability of iron, zinc and other trace elements while reducing the availability of cadmium. In particular, in iron-deficient paddy fields, insufficient supply of Fe can induce plants to up-regulate metal transmembrane transporters, leading to enhanced competitive absorption of cadmium, thereby producing a negative feedback effect. Single chemical passivation cannot achieve both cadmium inhibition and iron and zinc preservation.

[0005] Thirdly, the traditional passivation solution system lacks interface compatibility design. The pH window of phosphate and silicon source is quite different, and it is difficult to be compatible in the same system; organic complexing agents (such as citrate, amino acid salt) can improve solubility, but they are easily complexed with Ca 2+ under hard water conditions, resulting in unstable system. Most existing products are single component or two-component mixture, without considering the construction of a multi-coordination network with matching electric properties, complexation and coprecipitation at the molecular level. Therefore, the system is easy to precipitate or lose effectiveness during storage and application, resulting in unstable field effect.

[0006] Fourthly, from the rhizosphere process, phosphate type passivation only improves soil pH and forms precipitate in a short time, and Cd is easily redissolved with the change of redox environment; silicate type passivation mainly relies on root surface silicification or down-regulation of transport, but a single silicon source is insufficient in stability in acidic paddy fields, and it is difficult to form a sustained silicification barrier. The silicate passivation agent lacking an organic skeleton support is difficult to maintain long-term existence in the rhizosphere, and it also does not have high affinity complexing ability for Cd 2+ .

[0007] In addition, the traditional system ignores the key factor of the dynamic microenvironment in the rhizosphere. Local pH fluctuation and redox alternation are caused by root respiration and microbial metabolism, and a single inorganic passivation system is difficult to cope with such changes, and is prone to fail after a short-term effect. Due to the lack of organic components with electric property regulation and coordination buffer capacity, the system has poor tolerance to environmental disturbance, and Cd may still be reactivated and migrated to the grain in the growth later period.

[0008] Finally, the existing technology also has the problem of poor compatibility with fertilizers, pesticides and the like. Most phosphate or silicate passivation agents immediately form white precipitate and increase turbidity after being mixed with fertilizers under hard water conditions, which cannot meet the dispersion requirements of field spraying or drip irrigation, and greatly limits the application range. The lack of intermediate components with electric property matching and colloidal stability makes the system difficult to maintain uniform dispersion and persistence in acidic, hard water and multi-component environments.

[0009] Therefore, there is an urgent need for a composite passivation culture solution that can still maintain stability under acidic and hard water conditions, has multi-coordination synergy and interface electric property regulation ability, in order to realize high selectivity fixation of cadmium and also consider crop nutrition and environmental adaptability. SUMMARY

[0010] Therefore, the purpose of the present application is to provide a passivation culture solution for reducing cadmium in rice and a preparation method thereof, in order to solve the problems that the existing phosphate or single silicon source type passivation solution is easy to precipitate under hard water / acidic conditions, and the poor Cd selectivity and negative effect on Fe / Zn nutrients caused by simple co-precipitation.

[0011] In order to achieve the above purpose, the present application provides a preparation method of a passivation culture solution for reducing cadmium in rice, comprising the following steps: Step 1: preparing polyaspartic acid sodium graft, dissolving poly-(α,β)-DL-aspartic acid sodium salt in deionized water, adjusting pH to 5.8, adding N-hydroxysuccinimide and 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride and reacting for 10-20 min, then adding cysteamine hydrochloride and 3-dimethylaminopropylamine and stirring for 3-5 h, adding iodomethane and stirring for 1.5-2.5 h, and then performing dialysis and vacuum drying to obtain polyaspartic acid sodium graft; Step 2: preparation of choline-stabilized orthosilicic acid mother liquor, mixing glycerol and deionized water, adding choline chloride to dissolve, adding hydrochloric acid dropwise, adding sodium silicate aqueous solution dropwise under continuous stirring, maintaining pH in the range of 2.0-2.5 with hydrochloric acid during the dropwise addition, and stirring for 20-40 min to obtain the choline-stabilized orthosilicic acid mother liquor; Step 3: preparation of iron citrate complex solution, dissolving citric acid monohydrate in deionized water, adding ferric chloride hexahydrate, adjusting pH to 4.0 with sodium hydroxide solution, and stirring for 20-40 min to obtain the iron citrate complex solution; Step 4: preparation of passivation culture solution, sequentially adding the iron citrate complex solution, polyaspartic acid sodium graft aqueous solution, potassium dihydrogen phosphate, choline-stabilized orthosilicic acid mother liquor, and zinc ethylenediaminetetraacetate disodium salt hydrate in deionized water, and controlling pH in the range of 5.6-6.2 during the process to obtain the passivation culture solution.

[0012] Preferably, the weight average molecular weight of the poly-(α,β)-DL-aspartic acid sodium salt in step 1 is 5000.

[0013] Preferably, the amount of N-hydroxysuccinimide used in step 1 is 900-1260 mg, and the amount of 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride used is 1500-2100 mg.

[0014] Preferably, the amount of cysteamine hydrochloride used in step 1 is 350-520 mg, the amount of 3-dimethylaminopropylamine used is 400-580 mg, and the amount of iodomethane used is 700-1100 mg.

[0015] Preferably, the dialysis in step 1 uses a dialysis bag with a molecular weight cutoff of 3.5 kDa, and the dialysis water is replaced 3 times during 24 h of dialysis, with an interval of 8 h each time.

[0016] Preferably, the amount of choline chloride used in step 2 is 8-12 g, the concentration of hydrochloric acid is 37 wt% and the amount used is 2.5-3.5 g, the solid content of the sodium silicate aqueous solution is 40%, the modulus is 3.4, and the amount used is 8-12 g.

[0017] Preferably, the amount of citric acid monohydrate used in step 3 is 850-1250 mg, and the amount of ferric chloride hexahydrate used is 1100-1600 mg.

[0018] Preferably, the amounts of the components used in step 4 are as follows: iron citrate complex solution 3-10 g, polyaspartic acid sodium graft aqueous solution 0.5-2.0 g, potassium dihydrogen phosphate 80-200 mg, choline-stabilized orthosilicic acid mother liquor 1-4 g, and zinc ethylenediaminetetraacetate disodium salt hydrate 20-60 mg.

[0019] Preferably, the concentration of the aqueous solution of the polyaspartic acid sodium grafting product in step 4 is 10 wt%.

[0020] The application also provides a passivation culture solution for reducing cadmium in rice, which is obtained by the preparation method of the passivation culture solution for reducing cadmium in rice.

[0021] The application has the following beneficial effects: The passivation culture solution provided by the application adopts an integrated technical solution of a silicon-containing component-iron-containing complex-multiple coordination organic framework, and can construct a stable and functionally coordinated microenvironment regulation system in the rhizosphere region of plants. The orthosilicic acid in the culture solution effectively maintains the long-term stability of its active silicon form through a double stabilization mechanism of choline and polyols. When it enters the root surface region, it can significantly promote the silicification process of plant cell walls and the densification modification of extracellular polymeric substance matrix, thereby effectively weakening the transmembrane migration flux of heavy metal cadmium ions under the dual action mechanisms of physical barrier and chemical passivation. The ferric citrate complex in the culture solution provides a high-bioavailability iron nutrient source for plant roots. The complex exhibits excellent solubility and migration performance in weakly acidic to neutral soil environments, and can significantly alleviate the competitive interference effect of divalent heavy metal ions at the root surface absorption sites, thereby avoiding the phenomenon of non-specific excess absorption of heavy metal ions by plants induced by iron nutrient deficiency.

[0022] The polyaspartic acid graft copolymer framework provides a high density of multifunctional coordination groups, in which the carboxyl groups are responsible for long-range electrostatic capture and primary complex fixation of heavy metal ions, and the thiol groups introduced through thiolation modification provide a highly selective soft acid-soft base strong coordination binding ability for cadmium ions, ensuring that cadmium ions are preferentially fixed to the binding sites of plant extracellular matrix and cell walls, significantly reducing the possibility of their migration and transport into the plant body. The permanent positive charge side chains introduced by quaternization modification can effectively improve the electrical compatibility between the culture solution and silicon-containing anions, citrate complexes, and various trace element chelates in the soil. In a hard water environment containing high concentrations of calcium and magnesium ions, the system can still maintain good dispersibility and spraying uniformity, effectively avoiding the adverse effects of secondary aggregation induced by calcium and magnesium ions on field application effects.

[0023] The comprehensive effect of the technical scheme is that: under the premise of not changing the existing crop cultivation management measures, high-selective passivation treatment of cadmium in the soil is realized, and the bioavailability of essential nutrients such as iron and zinc and their normal deposition and distribution in the grains of crops are effectively maintained or even improved, so that the safety of agricultural products for eating is ensured while the overall improvement of the nutritional quality of the agricultural products is taken into account. The culture solution has good environmental adaptability and stability of treatment effect in acidic to slightly acidic paddy soil, is suitable for being used in cooperation with conventional fertilization management, irrigation and drainage and other agricultural systems, and has good scalability from test plots to large-scale production conditions. BRIEF DESCRIPTION OF DRAWINGS

[0024] In order to more clearly illustrate the technical scheme in the application or the prior art, the drawings needed to be used in the following embodiment or prior art description will be briefly introduced.

[0025] Figure 1 The preparation flow chart of the passivation culture solution for reducing cadmium in rice in the application; Figure 2 The infrared spectrum of the polyaspartic acid sodium graft in Example 2 in the application. DETAILED DESCRIPTION

[0026] In order to make the purpose, technical scheme and advantages of the application more clear and obvious, the application will be further described in detail below in combination with specific examples.

[0027] Example 1 Step 1: Preparation of polyaspartic acid sodium graft In a 500ml glass beaker, 100g of deionized water, 5g of poly-(α,β)-DL-sodium aspartate (weight average molecular weight 5000) were added, stirred with a glass rod until completely dissolved, and the pH was adjusted to 5.8 with 0.1mol / L hydrochloric acid. Then 900mg of N-hydroxysuccinimide and 1500mg of 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride were added, and the reaction was stirred at room temperature for 10min. Then 350mg of cysteamine hydrochloride and 400mg of 3-dimethylaminopropylamine were added in turn, and the stirring was continued for 3h, during which the pH was maintained in the range of 5.8-6.2 with 0.1mol / L sodium hydroxide solution. Then 700mg of iodomethane was added, and the stirring was continued for 1.5h. Then the mixture was transferred into a dialysis bag with a molecular weight cutoff of 3.5kDa, and dialyzed in 2000g of deionized water for 24h, during which the dialysis water was replaced 3 times at intervals of 8h. After dialysis, the dialysis bag was taken out and vacuum dried to obtain the polyaspartic acid sodium graft; Step 2: Preparation of choline-stabilized orthosilicic acid mother liquor In a 250 ml glass beaker, 50 g of glycerol and 50 g of deionized water were added, stirred with a glass rod until uniform, then 8 g of choline chloride was added, and stirring was continued until complete dissolution. 2.5 g of hydrochloric acid (concentration 37 wt%) was slowly added dropwise, and 8 g of sodium silicate aqueous solution (solid content 40%, modulus 3.4) was slowly added dropwise under continuous stirring. During the dropwise addition, the pH was maintained at 2.0-2.5 with hydrochloric acid. After the dropwise addition was completed, stirring was continued for 20 min. A choline-stabilized orthosilicic acid mother liquor was obtained. Step 3: Preparation of iron citrate complex solution In a 250 ml glass beaker, 100 g of deionized water and 850 mg of citric acid monohydrate were added, stirred until completely dissolved, and then 1100 mg of iron chloride hexahydrate was added. The pH was adjusted to 4.0 with 0.1 mol / L sodium hydroxide solution, and stirring was continued for 20 min. An iron citrate complex solution was obtained. Step 4: Preparation of passivation culture solution In a 1000 ml polypropylene graduated cylinder, 1000 g of deionized water, 3 g of iron citrate complex solution, and 0.5 g of polyaspartic acid sodium graft aqueous solution (concentration 10 wt%) were added, stirred for 2 min, and then 80 mg of potassium dihydrogen phosphate was added. Stirring was continued for 10 min, and the pH was controlled at 5.6-6.2 with 0.1 mol / L sodium hydroxide solution. Then, 1 g of choline-stabilized orthosilicic acid mother liquor was added, and stirring was continued for 10 min. Then, 20 mg of zinc ethylenediaminetetraacetate disodium salt hydrate was added, and stirring was continued for 5 min. A passivation culture solution for rice cadmium reduction was obtained.

[0028] Example 2: Step 1: Preparation of polyaspartic acid sodium graft In a 500 ml glass beaker, 100 g of deionized water, 5 g of poly-(α,β)-DL-aspartic acid sodium salt (weight average molecular weight 5000) were added, and stirred with a glass rod until completely dissolved. The pH was adjusted to 5.8 with 0.1 mol / L hydrochloric acid, and then 1080 mg of N-hydroxysuccinimide and 1800 mg of 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride were added. Stirring was continued at room temperature for 15 min, and then 432 mg of cysteamine hydrochloride and 494 mg of 3-dimethylaminopropylamine were added in sequence. Stirring was continued for 4 h, and the pH was maintained at 5.8-6.2 with 0.1 mol / L sodium hydroxide solution. Then, 880 mg of iodomethane was added, and stirring was continued for 2 h. The mixture was transferred to a dialysis bag with a molecular weight cutoff of 3.5 kDa, and dialyzed in 2000 g of deionized water for 24 h. The dialysis water was replaced 3 times at intervals of 8 h. After dialysis was completed, the dialysis bag was removed, and vacuum drying was performed. Polyaspartic acid sodium graft was obtained. Step 2: Preparation of choline-stabilized orthosilicic acid mother liquor In a 250 ml glass beaker, 50 g of glycerol and 50 g of deionized water were added, stirred with a glass rod until uniform, then 10 g of choline chloride was added, and stirring was continued until completely dissolved, 3 g of hydrochloric acid (concentration 37 wt%) was slowly added dropwise, 10 g of sodium silicate aqueous solution (solid content 40%, modulus 3.4) was slowly added dropwise under continuous stirring, and the pH was maintained at 2.0-2.5 with hydrochloric acid during the dropwise addition, and stirring was continued for 30 min after the dropwise addition was completed, to obtain a choline-stabilized orthosilicic acid mother liquor; Step 3: Preparation of iron citrate complex solution In a 250 ml glass beaker, 100 g of deionized water and 1050 mg of citric acid monohydrate were added, stirred until completely dissolved, 1350 mg of iron chloride hexahydrate was added, the pH was adjusted to 4.0 with 0.1 mol / L sodium hydroxide solution, and stirring was continued for 30 min to obtain an iron citrate complex solution; Step 4: Preparation of passivation culture solution In a 1000 ml polypropylene graduated cylinder, 1000 g of deionized water, 5 g of iron citrate complex solution, and 1 g of polyaspartic acid sodium graft aqueous solution (concentration 10 wt%) were added, stirred for 2 min, then 130 mg of potassium dihydrogen phosphate was added, stirred for 10 min, and the pH was controlled at 5.6-6.2 with 0.1 mol / L sodium hydroxide solution during the stirring, then 2 g of choline-stabilized orthosilicic acid mother liquor was added, stirred for 10 min, then 40 mg of zinc ethylenediaminetetraacetate disodium salt hydrate was added, and stirred for 5 min to obtain a passivation culture solution for cadmium reduction in rice.

[0029] Example 3 Step 1: Preparation of polyaspartic acid sodium graft In a 500 ml glass beaker, 100 g of deionized water, 5 g of poly-(α,β)-DL-aspartic acid sodium salt (weight average molecular weight 5000) were added, stirred with a glass rod until completely dissolved, the pH was adjusted to 5.8 with 0.1 mol / L hydrochloric acid, then 1260 mg of N-hydroxysuccinimide and 2100 mg of 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride were added, and stirring was continued at room temperature for 20 min, then 520 mg of cysteamine hydrochloride and 580 mg of 3-dimethylaminopropylamine were added in sequence, and stirring was continued for 5 h, and the pH was maintained at 5.8-6.2 with 0.1 mol / L sodium hydroxide solution during the stirring, then 1100 mg of iodomethane was added, and stirring was continued for 2.5 h, then it was transferred to a dialysis bag with a molecular weight cutoff of 3.5 kDa, and dialyzed in 2000 g of deionized water for 24 h, and the dialysis water was replaced 3 times at intervals of 8 h, after the dialysis was completed, the dialysis bag was taken out, and vacuum drying was performed to obtain polyaspartic acid sodium graft; Step 2: Preparation of choline-stabilized orthosilicic acid mother liquor In a 250 ml glass beaker, 50 g of glycerol and 50 g of deionized water were added, stirred with a glass rod until mixed evenly, then 12 g of choline chloride was added, and stirring was continued until completely dissolved. 3.5 g of hydrochloric acid (concentration 37 wt%) was slowly added dropwise, and 12 g of sodium silicate aqueous solution (solid content 40%, modulus 3.4) was slowly added dropwise under continuous stirring. During the dropwise addition, hydrochloric acid was used to maintain the pH in the range of 2.0-2.5. After the dropwise addition was completed, stirring was continued for 40 min to obtain a choline-stabilized orthosilicic acid mother liquor. Step 3: Preparation of iron citrate complex solution In a 250 ml glass beaker, 100 g of deionized water and 1250 mg of citric acid monohydrate were added, stirred until completely dissolved, and then 1600 mg of iron chloride hexahydrate was added. The pH was adjusted to 4.0 with 0.1 mol / L sodium hydroxide solution, and stirring was continued for 40 min to obtain an iron citrate complex solution. Step 4: Preparation of passivation culture solution In a 1000 ml polypropylene graduated cylinder, 1000 g of deionized water, 10 g of iron citrate complex solution, and 2.0 g of polyaspartic acid sodium graft aqueous solution (concentration 10 wt%) were added and stirred for 2 min. Then 200 mg of potassium dihydrogen phosphate was added and stirred for 10 min, during which the pH was controlled in the range of 5.6-6.2 with 0.1 mol / L sodium hydroxide solution. Then 4 g of choline-stabilized orthosilicic acid mother liquor was added and stirred for 10 min. Then 60 mg of zinc ethylenediaminetetraacetate disodium salt hydrate was added and stirred for 5 min to obtain a passivation culture solution for rice cadmium reduction.

[0030] Comparative Example 1: The difference between Comparative Example 1 and Example 2 is that polyaspartic acid sodium graft is not added, and the rest of the conditions are consistent with Example 2.

[0031] Comparative Example 2: The difference between Comparative Example 2 and Example 2 is that choline-stabilized orthosilicic acid mother liquor is not added, and the rest of the conditions are consistent with Example 2.

[0032] Comparative Example 3: The difference between Comparative Example 3 and Example 2 is that iron citrate complex solution is not added, and the rest of the conditions are consistent with Example 2.

[0033] Comparative Example 4: The difference between Comparative Example 4 and Example 2 is that cysteamine hydrochloride is not added in the preparation step of polyaspartic acid sodium graft, and the rest of the conditions are consistent with Example 2.

[0034] Comparative Example 5: The difference between Comparative Example 5 and Example 2 is that iodomethane is not added in the preparation step of polyaspartic acid sodium graft, and the rest of the conditions are consistent with Example 2.

[0035] Comparative Example 6: Comparative Example 6 differs from Example 2 in that no choline chloride is added during preparation of the choline-stabilized orthosilicate mother liquor, and the rest of the conditions are consistent with Example 2.

[0036] Performance test: Pot experiment: The pot experiment adopts randomized block design, and the treatments are 8 groups: CK (no application), Examples 1-3, Comparative Examples 1-6, each treatment 5 pots for repetition; the flowerpot is 28 cm in diameter and 30 cm in height, and 8.0 kg of cadmium-contaminated paddy soil (pre-test pH ≈ 5.2) is placed in each pot, and the same batch of conventional rice is transplanted to 2 clumps × 2 plants per pot, and a 2-3 cm shallow water layer is maintained at all times; base fertilizer is added according to the pot, and pure N 0.80 g, P2O5 0.40 g, K2O 0.80 g (base application of P, K and 50% N, and the remaining 50% N is applied during the tillering stage); the passivation culture solution is slowly poured into the rhizosphere at 3d, 20d and 15d before heading, each time 200 mL, and a total of 600 mL / pot, and the CK is poured with an equal amount of deionized water; the rhizosphere soil is collected at 30d and the harvest stage to measure the aqua regia extraction Cd and pH, and polished rice is prepared after harvesting to measure Cd (GB 5009.15; the limit determination is according to GB 2762).

[0037] Infrared spectrum: Fourier transform infrared spectrometer was used for characterization, and KBr tablet was pressed.

[0038] Hard water compatibility stability (turbidity): According to “HJ 1075-2019”, the hard water has a calcium carbonate hardness of 300 mg / L, and the turbidity is measured at 1 min and 10 min after mixing the passivation culture solution with the hard water at a volume ratio of 1:9, and the results are shown in Table 1.

[0039] Table 1 Performance test results

[0040] Data analysis: From the analysis of examples 1-3 in Table 1, it can be found that the system forms a weakly acidic to neutral buffer zone environment in the rhizosphere, and can effectively inhibit the transport of cadmium to the grain by means of multi-ligand coordination mechanism, while maintaining the availability of essential elements. The selective complexation of carboxyl and reducible sulfhydryl sites in the system to cadmium, combined with the stability of choline and positive silicic acid, promotes the deposition of silicon in the cell wall and extracellular polymer, reduces the expression activity of transmembrane transporter. In addition, ferric citrate provides a matching and stable iron source for the root surface, reducing the antagonistic effect of cadmium and iron on the absorption site; zinc chelate helps to improve the accumulation of grain zinc without increasing the risk of cadmium absorption. Overall, the system not only significantly improves the safety of Cd, but also ensures that the nutritional elements such as iron and zinc are in a reasonable range, and maintains good dispersion stability even in hard water environment. The above results show that the system is suitable for cadmium medium and light pollution paddy fields, and can simultaneously ensure the quality and safety of rice under the condition of not changing the conventional irrigation and fertilization system.

[0041] From the data of Example 2 and Comparative Example 1 in Table 1, the absence of polyaspartic acid graft copolymer significantly reduces the system's ability to fix and transport cadmium, leading to an increase in grain cadmium risk. The mechanism is that the absence of multi-dentate carboxyl / thiol sites in the polymer hinders the formation of a dense complex barrier, making it easier for cadmium to enter the vascular system under the pull of transpiration; at the same time, the absence of quaternary ammonium segment weakens the electrostatic neutralization ability, causing the micro-flocculation and dispersion instability induced by calcium and magnesium in hard water to increase, ultimately increasing the volatility of the field effect.

[0042] From the comparison of data of Example 2 and Comparative Example 2 in Table 1, the removal of choline-stabilized orthosilicic acid leads to the increase of rhizosphere pH and the double weakening of silicon deposition effect, resulting in the undesirable performance of grain cadmium and solution turbidity. The fundamental reason is that orthosilicic acid is prone to polysiliconization without choline and polyol stabilization, resulting in the loss of available silicon form, which is difficult to inhibit cadmium transport through cell wall silicification and transporter regulation; at the same time, hard water environment is prone to silicon polymer flocculation, which increases the turbidity of the system.

[0043] As can be seen from the data of Example 2 and Comparative Example 3 in Table 1, the lack of ferric citrate significantly reduces the grain iron content and the cadmium inhibition is insufficient. Ferric citrate has high coordination stability under weakly acidic-neutral conditions, which can maintain the function of iron channels in the rhizosphere and reduce the competition between cadmium and iron; without this component, iron deficiency induces non-selective absorption of divalent metals, indirectly increasing the flux of cadmium.

[0044] Comparing Example 2 and Comparative Example 4 in Table 1, the absence of sulfhydryl modification weakens the cadmium inhibition effect. The main reason is that sulfhydryl as a soft-soft coordination site can capture cadmium with high affinity, and the absence of high-affinity complexing sites on the root surface makes it more difficult for cadmium to be fixed in the cell wall and extracellular matrix, and the proportion of entering the xylem increases.

[0045] Comparing Example 2 with Comparative Example 5 in Table 1, the static inhibition of Cd is acceptable without quaternary ammonium modification, but the compatibility in hard water environment deteriorates seriously. Since the polymer does not contain permanent positive charge, it is difficult to electrically neutralize and stabilize the complex of silicate anion and organic acid salt, resulting in enhanced secondary aggregation induced by calcium and magnesium, significantly increased system turbidity, and greatly reduced spray uniformity and field consistency.

[0046] Comparing Example 2 with Comparative Example 6 in Table 1, the hard water turbidity significantly increases after the absence of choline chloride in the silicon source solution, and the inhibition of grain Cd and the improvement of rhizosphere pH are both deteriorated. The main reason is that the active silicon supply decreases due to the rapid polysiliconization of orthosilicic acid under acidic and high ionic strength, and the cell wall silicification and transporter down-regulation effect is weakened; at the same time, the electric stability of the absence of quaternary ammonium type compatibility agent, the secondary flocculation of silicon polymer and calcium and magnesium salt occurs, resulting in poor application uniformity and insufficient effective dose in the rhizosphere. It can be seen that choline stabilization plays a key synergistic role in maintaining active silicon and compatibility stability, which embodies the interface stability gain of 1+1>2.

[0047] From Figure 2 It can be seen that the sample appears strong amide I at 1650 cm -1 The symmetric / asymmetric stretching of carboxylate coexists, 1542 cm -1 amide II is clear, 970 and 1170 cm -1 amide II is clear, 970 and 1170 cm -1 Quaternary ammonium characteristic peak is significant and 2550 cm -1 There is a weak S-H band, indicating that the carboxyl group has been partially amidated and the quaternization and thiol group introduction are successful.

[0048] It should be understood by those of ordinary skill in the art that the above discussion of any embodiment is only exemplary and is not intended to suggest that the scope of the present application is limited to these examples; under the idea of the present application, the technical features in the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other changes of different aspects of the present application as described above. In order to be brief, they are not provided in detail.

Claims

1. A method for preparing a passivation culture solution for cadmium reduction in rice, characterized by, The method comprises the following steps: Step 1: preparing poly-sodium aspartate graft, dissolving poly-(α,β)-DL-sodium aspartate in deionized water, adjusting pH to 5.8, adding N-hydroxysuccinimide and 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride and reacting for 10-20 min, then adding cysteamine hydrochloride and 3-dimethylaminopropylamine in sequence and stirring for 3-5 h, adding iodomethane and stirring for 1.5-2.5 h, and then performing dialysis and vacuum drying to obtain poly-sodium aspartate graft; Step 2: preparing choline-stabilized orthosilicic acid mother liquor, mixing glycerol and deionized water, adding choline chloride to dissolve, adding hydrochloric acid dropwise, adding sodium silicate aqueous solution dropwise while maintaining pH in the range of 2.0-2.5 by using hydrochloric acid, and stirring for 20-40 min to obtain choline-stabilized orthosilicic acid mother liquor; Step 3: preparing iron citrate complex solution, dissolving citric acid monohydrate in deionized water, adding iron chloride hexahydrate, adjusting pH to 4.0 by using sodium hydroxide solution, and stirring for 20-40 min to obtain iron citrate complex solution; Step 4: preparing passivation culture solution, adding iron citrate complex solution, poly-sodium aspartate graft aqueous solution, potassium dihydrogen phosphate, choline-stabilized orthosilicic acid mother liquor and zinc disodium ethylenediaminetetraacetate hydrate in deionized water in sequence while controlling pH in the range of 5.6-6.2 to obtain passivation culture solution.

2. The method for preparing the passivation culture solution for cadmium reduction in rice according to claim 1, characterized in that, The weight average molecular weight of the poly-(α,β)-DL-sodium aspartate in step 1 is 5000.

3. The method for preparing the passivation culture solution for cadmium reduction in rice according to claim 1, characterized in that, In step 1, the amount of N-hydroxysuccinimide is 900-1260 mg, the amount of 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride is 1500-2100 mg, the amount of cysteamine hydrochloride is 350-520 mg, the amount of 3-dimethylaminopropylamine is 400-580 mg, and the amount of iodomethane is 700-1100 mg.

4. The method for preparing a passivation culture solution for cadmium reduction in rice according to claim 1, characterized by, In step 1, the dialysis is performed by using a dialysis bag with a molecular weight cut-off of 3.5 kDa, and the dialysis water is replaced for 3 times at intervals of 8 h during dialysis for 24 h.

5. The method for preparing the passivation culture solution for cadmium reduction in rice according to claim 1, characterized in that, In step 2, the amount of choline chloride is 8-12 g, the concentration of hydrochloric acid is 37 wt%, and the amount of hydrochloric acid is 2.5-3.5 g.

6. The method for preparing a passivation culture solution for cadmium reduction in rice according to claim 1, characterized in that, In step 2, the solid content of the sodium silicate aqueous solution is 40%, the modulus is 3.4, and the amount is 8-12 g.

7. The method for preparing a passivation culture solution for cadmium reduction in rice according to claim 1, characterized by, In step 3, the amount of citric acid monohydrate is 850-1250 mg, and the amount of iron chloride hexahydrate is 1100-1600 mg.

8. The method for preparing the passivation culture solution for cadmium reduction in rice according to claim 1, characterized in that, In step 4, the amounts of the components are as follows: iron citrate complex solution 3-10 g, poly-sodium aspartate graft aqueous solution 0.5-2.0 g, potassium dihydrogen phosphate 80-200 mg, choline-stabilized orthosilicic acid mother liquor 1-4 g, and zinc disodium ethylenediaminetetraacetate hydrate 20-60 mg.

9. The method for preparing the passivation culture solution for cadmium reduction in rice according to claim 1, characterized in that, In step 4, the concentration of the poly-sodium aspartate graft aqueous solution is 10 wt%.

10. A passivation culture solution for cadmium reduction in rice, characterized by, The passivation culture solution is prepared by the method of any one of claims 1-9.

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