Organic acid liquid fertilizer for enhancing extraction of soil cadmium from rape as well as preparation method and application of organic acid liquid fertilizer

Abstract

The invention belongs to the technical field of fertilizers, and particularly relates to an organic acid liquid fertilizer for enhancing extraction of soil cadmium from oilseed rape, and a preparation method and application thereof. The organic acid liquid fertilizer for strengthening the extraction of soil cadmium from rape is prepared by taking aspergillus niger fermentation liquor as a matrix, so that the diversity and activity of soil microbial communities can be remarkably improved, the activation effect on soil cadmium is stronger, and the extraction effect of the rape on the cadmium in the soil is strengthened; on one hand, brassinolide-biomass ash performs physiological regulation on the rape, increases the aboveground biomass of the rape, and strengthens the capture ability of the rape on activated cadmium; the photosynthesis of the rape is enhanced, the resistance is improved, and the tolerance of the rape to metal cadmium is improved; on the other hand, strong acidity brought by part of aspergillus niger fermentation liquor can be neutralized, direct damage to rape root systems or damage to soil structures caused by too low soil pH is avoided, and the organic acid liquid fertilizer for extracting soil cadmium from rape can play a reinforcing role in extracting cadmium from soil from rape.

Description

Technical Field

[0001] This invention belongs to the field of fertilizer technology, specifically relating to an organic acid liquid fertilizer for enhancing the extraction of cadmium from soil by rapeseed, its preparation method, and its application. Background Technology

[0002] Unreasonable development and utilization of mineral resources and extensive discharge of wastewater containing heavy metals often lead to heavy metal pollution in farmland downstream of pollution sources. Among them, cadmium pollution in farmland is the most serious problem. Soil cadmium pollution can not only lead to crop yield reduction, but cadmium can also enter the human body through the food chain and easily induce cancer.

[0003] Phytoremediation, as a novel soil heavy metal remediation technology, has been widely used due to its advantages such as low cost and environmental friendliness. Rapeseed has strong resistance to cadmium stress and exhibits a high cadmium bioaccumulation coefficient in its aboveground parts and low translocation capacity to grains. Using rapeseed to replace wheat cultivation can extract cadmium from contaminated soil, reduce soil cadmium content, and remediate cadmium-contaminated soil, enabling safe wheat production in moderately to severely cadmium-contaminated arable land. However, without any auxiliary enhancement measures, rapeseed suffers from problems such as low biomass and weak absorption capacity in soils with low heavy metal mobility. Summary of the Invention

[0004] The purpose of this invention is to provide an organic acid liquid fertilizer for enhancing the extraction of cadmium from soil by rapeseed, its preparation method, and its application, so as to solve the above-mentioned technical problems.

[0005] To achieve the above-mentioned technical objectives, the technical solution of the present invention is as follows: A method for preparing an organic acid liquid fertilizer for enhancing cadmium extraction from soil using rapeseed, characterized by comprising the following steps: S1. Inoculate Aspergillus niger spores into concentrated mash, adjust the pH to 5-6 using sterile calcium carbonate, and ferment for 64 hours. Sterile air is introduced at the beginning, middle and end of the fermentation process, with flow rates of 0.7 vvm, 1-1.2 vvm and 0.25 vvm, respectively. After fermentation, the mixture is filtered through a membrane, separated by chromatography and concentrated to obtain the Aspergillus niger fermentation broth. S2. Add brassinolide-biomass ash to the Aspergillus niger fermentation liquid and stir at 35℃ and 300rpm for 30min. After mixing, the organic acid liquid fertilizer for extracting cadmium from soil from rapeseed is obtained. The mass ratio of brassinolide-biomass ash to Aspergillus niger fermentation liquid is 5~7:3.

[0006] As a further improvement, in step S2, the preparation method of brassinolide-biomass ash is as follows: soak the biomass ash in 1 mol / L citric acid at a solid-liquid ratio of 1:5, then wash it with water until neutral. After washing, dry and pulverize it at 80~85℃ and pass it through a 200-mesh sieve. Under a nitrogen atmosphere, immerse the biomass ash that has passed through the sieve into a brassinolide buffer solution, ultrasonically disperse it for 30 min, stir it at 80℃ for 4 h, and then dry it to obtain brassinolide-biomass ash, wherein the mass ratio of brassinolide to biomass ash is 0.02~0.05:1.

[0007] As a further improvement, the preparation method of the brassinolide buffer is as follows: potassium dihydrogen phosphate trihydrate, citric acid and sucrose are mixed evenly, and water is added to make up to 1000 mL to obtain a buffer dilution. Brassinolide is added to the buffer dilution to prepare a 100~120 μmol / L brassinolide buffer.

[0008] As a further improvement, the buffer diluent comprises, by weight, the following components: 2-6 parts potassium dihydrogen phosphate trihydrate, 1-3 parts citric acid, and 20-25 parts sucrose.

[0009] As a further improvement, in step S1, the preparation method of the concentrated mash is as follows: using corn flour as raw material, the corn flour is adjusted to a slurry temperature of 17~20℃, the pH is adjusted to 6.4~7.0, 2 / 3 of the required amount of α-amylase is added, high-temperature steam is introduced, and when the temperature of the slurry reaches 90℃, the initial slurry is obtained; the initial slurry is liquefied, and after liquefaction, 1 / 3 of the required amount of α-amylase is added, and the mixture is kept at 90℃ for 30 minutes. The pH is adjusted to 4.8~5.2 using 0.1mol / L dilute hydrochloric acid, filtered, and after continuous and actual sterilization, and cooled to 33~37℃, concentrated mash is obtained.

[0010] As a further improvement, the amount of α-amylase required for the corn flour is 6~9 U / g; the liquefaction step of the initial slurry is as follows: the initial slurry is pumped into the ejector for liquefaction. When the outlet material temperature reaches 95~97℃, the reflux valve is closed to allow the liquid to enter the laminar flow tank. When the material temperature reaches 140~145℃, it is maintained for 3~5 minutes and then flash-cooled to 20~25℃.

[0011] As a further improvement, in step S1, the inoculation amount of Aspergillus niger spores is 10-15 wt% of the concentrated mash; the early, middle and late stages are the 12th hour, 48th hour and 60th hour after inoculation with Aspergillus niger spores, respectively.

[0012] As a further improvement, in step S1, the membrane filtration and chromatographic separation are performed as follows: at room temperature, a reverse osmosis membrane is used for filtration at 25~45℃ and 2.0~5.0MPa. After filtration, a strongly basic anion exchange resin is used for chromatographic separation, and 0.05~0.08mol / L dilute sulfuric acid is used for elution at a flow rate of 1~5BV / h.

[0013] This invention also provides an organic acid liquid fertilizer for enhancing the extraction of cadmium from soil using rapeseed.

[0014] This invention also provides an application of an enhanced organic acid liquid fertilizer for extracting cadmium from rapeseed soil, characterized by the following method: During the budding and flowering stages of rapeseed, one day before or after rainfall, when the relative soil moisture content is 30-60%, the enhanced organic acid liquid fertilizer for extracting cadmium from rapeseed soil, diluted 10 times, is applied to the soil via root irrigation at a rate of 10-13 kg / mu each time. The relative soil moisture content is maintained at 30-60% for one week after application. If there is no rainfall during fertilization, the enhanced organic acid liquid fertilizer for extracting cadmium from rapeseed soil is diluted 20 times before application, and watered again after 3 days to ensure the relative soil moisture content reaches 30-60%.

[0015] Due to the adoption of the above technical solution, the beneficial effects of the present invention are as follows: (1) An organic acid liquid fertilizer for enhancing rapeseed's ability to extract cadmium from soil was prepared by combining Aspergillus niger fermentation broth with brassinolide-biomass ash. Compared with the application of a single organic acid, the organic acid liquid fertilizer based on Aspergillus niger fermentation broth can significantly increase the diversity and activity of soil microbial communities, has a stronger activating effect on soil cadmium, provides a stronger ability to dissolve and chelate cadmium, and enhances the extraction effect of cadmium from soil by rapeseed.

[0016] (2) Brassinolide-biomass ash can regulate the physiological function of rapeseed, increase the aboveground biomass of rapeseed, and enhance the rapeseed’s ability to capture activated cadmium; improve the rapeseed’s photosynthesis, enhance its resistance, and enhance its tolerance to cadmium; on the other hand, it can neutralize some of the strong acidity brought by Aspergillus niger fermentation liquid, avoid the soil pH being too low and causing direct damage to the rapeseed roots or destroying the soil structure, and make it more conducive to the Aspergillus niger fermentation liquid-based organic acid liquid fertilizer to play a strengthening role in the rapeseed’s extraction of cadmium from the soil. Detailed Implementation

[0017] The technical solution of the present invention will be clearly and completely described below with reference to specific embodiments. However, those skilled in the art will understand that the embodiments described below are some embodiments of the present invention, but not all embodiments, and are only used to illustrate the present invention, and should not be regarded as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall be followed. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially. The biomass ash used was purchased from Anhui Yingtianqing Biotechnology Co., Ltd.

[0018] Example 1: A method for preparing an organic acid liquid fertilizer for enhancing cadmium extraction from soil using rapeseed, specifically including the following steps: S1. Using corn flour as raw material, the corn flour is prepared into a slurry at 17°C. The pH is adjusted to 6.4 using 1% diluted lime water. Two-thirds of the amount of α-amylase required for the corn flour is added. High-temperature steam is introduced. When the temperature of the slurry reaches 90°C, the initial slurry is obtained. The amount of α-amylase required for the corn flour is 6 U / g. S2. Pump the initial slurry into the ejector for liquefaction. When the outlet temperature reaches 95°C, close the reflux valve to allow the liquid to enter the laminar flow tank. When the temperature reaches 140°C, maintain it for 3 minutes. After flash cooling to 20°C, add 1 / 3 of the amount of α-amylase required for corn flour. Maintain the temperature at 90°C for 30 minutes. Adjust the pH to 4.8 using 0.1 mol / L dilute hydrochloric acid. Filter the mixture. After continuous sterilization at 121°C for 30 minutes and actual sterilization at 135°C for 5 minutes, cool it down to 33°C to obtain concentrated mash. S3. Inoculate the concentrated mash with Aspergillus niger spores, adjust the pH to 5 using sterile calcium carbonate, and maintain the fermentation temperature at 37℃ and the fermenter rotation speed at 90 rpm. Sterile air is introduced at three stages: the first (12 hours after inoculation), the second (48 hours after inoculation), and the third (60 hours after inoculation), with flow rates of 0.7 vvm, 1.0 vvm, and 0.25 vvm respectively, for a total of 64 hours of fermentation. After fermentation, filter the mash at room temperature using a cellulose acetate membrane with a molecular weight cutoff of 200 Da at 25℃ and 2.0 MPa. After filtration, use a 201×7... Chromatographic separation was performed using a strongly basic styrene-based anion exchange resin, followed by elution with 0.05 mol / L dilute sulfuric acid at a flow rate of 1 BV / h. The mixture was then concentrated under reduced pressure at 0.09 MPa and 60 °C for 2 h to obtain the Aspergillus niger fermentation broth; the inoculum amount of Aspergillus niger spores was 10 wt% of the concentrated mash. S4. By weight, take 2 parts potassium dihydrogen phosphate trihydrate, 1 part citric acid, and 20 parts sucrose. Mix the potassium dihydrogen phosphate trihydrate, citric acid, and sucrose evenly, and add water to make up to 1000 mL to obtain a buffer dilution. Add brassinolide to the buffer dilution to prepare a 100 μmol / L brassinolide buffer solution. S5. Soak the biomass ash in 1 mol / L citric acid at a solid-liquid ratio of 1:5 to remove soluble heavy metals. Then wash with water until neutral. After washing, dry and pulverize at 80℃ and pass through a 200-mesh sieve. Under a nitrogen atmosphere, immerse the biomass ash that has passed through the sieve in brassinolide buffer solution, sonicate at 40 kHz for 30 min, stir at 80℃ and 200 rpm for 4 h, and dry at 85℃ to obtain brassinolide-biomass ash. The mass ratio of brassinolide to biomass ash is 0.02:1. S6. Add brassinolide-biomass ash to the Aspergillus niger fermentation liquid at a mass ratio of 5:3, stirring at 25℃ and 50 rpm. Stir and mix at 35℃ and 300 rpm for 30 minutes. After mixing, you will get an organic acid liquid fertilizer for extracting cadmium from soil from rapeseed.

[0019] Example 2: A method for preparing an organic acid liquid fertilizer for enhancing cadmium extraction from soil using rapeseed, specifically including the following steps: S1. Using corn flour as raw material, the corn flour is prepared into a slurry at 18°C. The pH is adjusted to 6.8 using 1% diluted lime water. Two-thirds of the amount of α-amylase required for the corn flour is added. High-temperature steam is introduced. When the temperature of the slurry reaches 90°C, the initial slurry is obtained. The amount of α-amylase required for the corn flour is 7 U / g. S2. Pump the initial slurry into the ejector for liquefaction. When the outlet temperature reaches 96°C, close the reflux valve to allow the liquid to enter the laminar flow tank. When the temperature reaches 143°C, maintain it for 4 minutes. After flash cooling, the temperature is reduced to 23°C. After liquefaction, add 1 / 3 of the amount of α-amylase required for corn flour. Maintain the temperature at 90°C for 30 minutes. Adjust the pH to 5.0 using 0.1 mol / L dilute hydrochloric acid. Filter the mixture. After continuous sterilization at 121°C for 30 minutes and actual sterilization at 135°C for 5 minutes, cool the mixture to 35°C to obtain concentrated mash. S3. Inoculate the concentrated mash with Aspergillus niger spores, adjust the pH to 6 using sterile calcium carbonate, and maintain the fermentation temperature at 39℃ and the fermenter rotation speed at 100 rpm. Sterile air is introduced at flow rates of 0.7 vvm, 1.1 vvm, and 0.25 vvm respectively during the initial (12 hours after inoculation), middle (48 hours after inoculation), and final (60 hours after inoculation) stages, and fermentation is carried out for 64 hours. After fermentation, the mash is filtered at 35℃ and 3.0 MPa using a cellulose acetate membrane with a molecular weight cutoff of 200 Da at room temperature. After filtration, a 201×7 filter is used. Chromatographic separation was performed using a strongly basic styrene-based anion exchange resin, eluted with 0.07 mol / L dilute sulfuric acid at a flow rate of 3 BV / h, and finally concentrated under reduced pressure at 0.09 MPa and 60 °C for 2 h to obtain the Aspergillus niger fermentation broth; wherein the inoculum amount of Aspergillus niger spores was 13 wt% of the concentrated mash. S4. By weight, take 4 parts potassium dihydrogen phosphate trihydrate, 2 parts citric acid, and 23 parts sucrose. Mix the potassium dihydrogen phosphate trihydrate, citric acid, and sucrose evenly, and add water to make up to 1000 mL to obtain a buffer dilution. Add brassinolide to the buffer dilution to prepare a 110 μmol / L brassinolide buffer solution. S5. Soak the biomass ash in 1 mol / L citric acid at a solid-liquid ratio of 1:5 to remove soluble heavy metals. Then wash with water until neutral. After washing, dry and pulverize at 83℃ and pass through a 200-mesh sieve. Under a nitrogen atmosphere, immerse the biomass ash that has passed through the sieve into brassinolide buffer solution, sonicate at 40 kHz for 30 min, stir at 80℃ and 200 rpm for 4 h, and dry at 85℃ to obtain brassinolide-biomass ash; wherein the mass ratio of brassinolide to biomass ash is 0.03:1. S6. Add brassinolide-biomass ash to the Aspergillus niger fermentation liquid at a mass ratio of 6:3, stirring at 26℃ and 60rpm. Stir and mix at 35℃ and 300rpm for 30 minutes. After mixing, you will get an organic acid liquid fertilizer for extracting cadmium from soil from rapeseed.

[0020] Example 3: A method for preparing an organic acid liquid fertilizer for enhancing cadmium extraction from soil using rapeseed, specifically including the following steps: S1. Using corn flour as raw material, the corn flour is prepared into a slurry at 20°C. The pH is adjusted to 7.0 using 1% diluted lime water. Two-thirds of the amount of α-amylase required for the corn flour is added. High-temperature steam is introduced. When the temperature of the slurry reaches 90°C, the initial slurry is obtained. The amount of α-amylase required for the corn flour is 8 U / g. S2. Pump the initial slurry into the ejector for liquefaction. When the outlet temperature reaches 97°C, close the reflux valve to allow the liquid to enter the laminar flow tank. When the temperature reaches 145°C, maintain it for 5 minutes. After flash cooling to 25°C, add 1 / 3 of the amount of α-amylase required for corn flour. Maintain the temperature at 90°C for 30 minutes. Adjust the pH to 5.2 using 0.1 mol / L dilute hydrochloric acid. Filter the mixture. After continuous sterilization at 121°C for 30 minutes and actual sterilization at 135°C for 5 minutes, cool it to 37°C to obtain concentrated mash. S3. Inoculate the concentrated mash with Aspergillus niger spores, adjust the pH to 6 using sterile calcium carbonate, and maintain the fermentation temperature at 40℃. The fermenter speed is 105 rpm. Sterile air is introduced at three stages: 12 hours after inoculation (early stage), 48 hours after inoculation (middle stage), and 60 hours after inoculation (late stage), with flow rates of 0.7 vvm, 1.2 vvm, and 0.25 vvm respectively, for a total of 64 hours of fermentation. After fermentation, filter the mash at room temperature using a cellulose acetate membrane with a molecular weight cutoff of 200 Da at 45℃ and 5.0 MPa. After filtration, use a 201×7... Chromatographic separation was performed using a strongly basic styrene-based anion exchange resin, followed by elution with 0.08 mol / L dilute sulfuric acid at a flow rate of 5 BV / h. The mixture was then concentrated under reduced pressure at 0.09 MPa and 60 °C for 2 h to obtain the Aspergillus niger fermentation broth; the inoculum amount of Aspergillus niger spores was 15 wt% of the concentrated mash. S4. By weight, take 6 parts potassium dihydrogen phosphate trihydrate, 3 parts citric acid, and 25 parts sucrose. Mix the potassium dihydrogen phosphate trihydrate, citric acid, and sucrose evenly, and add water to make up to 1000 mL to obtain a buffer dilution. Add brassinolide to the buffer dilution to prepare a 120 μmol / L brassinolide buffer solution. S5. Soak the biomass ash in 1 mol / L citric acid at a solid-liquid ratio of 1:5 to remove soluble heavy metals. Then wash with water until neutral. After washing, dry and pulverize at 85℃ and pass through a 200-mesh sieve. Under a nitrogen atmosphere, immerse the biomass ash that has passed through the sieve into brassinolide buffer solution, sonicate at 40 kHz for 30 min, stir at 80℃ and 200 rpm for 4 h, and dry at 85℃ to obtain brassinolide-biomass ash; wherein the mass ratio of brassinolide to biomass ash is 0.05:1. S6. At a mass ratio of 7:3, brassinolide-biomass ash is added to the Aspergillus niger fermentation liquid at 28℃ and 70rpm. The mixture is stirred at 35℃ and 300rpm for 30 minutes. After the reaction is complete, an organic acid liquid fertilizer for extracting cadmium from soil using rapeseed is obtained.

[0021] Comparative Example 1: A method for preparing an organic acid liquid fertilizer for enhancing cadmium extraction from soil using rapeseed, differing from Example 1 in that it does not include biomass ash components, and specifically includes the following steps: S1. Using corn flour as raw material, the corn flour is prepared into a slurry at 17°C. The pH is adjusted to 6.4 using 1% diluted lime water. Two-thirds of the amount of α-amylase required for the corn flour is added. High-temperature steam is introduced. When the temperature of the slurry reaches 90°C, the initial slurry is obtained. The amount of α-amylase required for the corn flour is 6 U / g. S2. Pump the initial slurry into the ejector for liquefaction. When the outlet temperature reaches 95°C, close the reflux valve to allow the liquid to enter the laminar flow tank. When the temperature reaches 140°C, maintain it for 3 minutes. After flash cooling to 20°C, add 1 / 3 of the amount of α-amylase required for corn flour. Maintain the temperature at 90°C for 30 minutes. Adjust the pH to 4.8 using 0.1 mol / L dilute hydrochloric acid. Filter the mixture. After continuous sterilization at 121°C for 30 minutes and actual sterilization at 135°C for 5 minutes, cool it to 33°C to obtain concentrated mash. S3. Inoculate the concentrated mash with Aspergillus niger spores, adjust the pH to 5 using sterile calcium carbonate, and maintain the fermentation temperature at 37℃ and the fermenter rotation speed at 90 rpm. Sterile air is introduced at three stages: the first (12 hours after inoculation), the second (48 hours after inoculation), and the third (60 hours after inoculation), with flow rates of 0.7 vvm, 1.0 vvm, and 0.25 vvm respectively, for a total of 64 hours of fermentation. After fermentation, filter the mash at room temperature using a cellulose acetate membrane with a molecular weight cutoff of 200 Da at 25℃ and 2.0 MPa. After filtration, use a 201×7... Chromatographic separation was performed using a strongly basic styrene-based anion exchange resin, eluted with 0.05 mol / L dilute sulfuric acid at a flow rate of 1 BV / h, and finally concentrated under reduced pressure at 0.09 MPa and 60 °C for 2 h to obtain the Aspergillus niger fermentation broth; wherein the inoculum amount of Aspergillus niger spores was 10 wt% of the concentrated mash. S4. By weight, take 2 parts potassium dihydrogen phosphate trihydrate, 1 part citric acid, and 20 parts sucrose. Mix the potassium dihydrogen phosphate trihydrate, citric acid, and sucrose evenly, and add water to make up to 1000 mL to obtain a buffer dilution. Add brassinolide to the buffer dilution to prepare a 100 μmol / L brassinolide buffer solution. S5. Add brassinolide to the Aspergillus niger fermentation liquid at a mass ratio of 5:3, stirring at 25℃ and 50 rpm. Stir and mix at 35℃ and 300 rpm for 30 minutes. After mixing, you will get an organic acid liquid fertilizer for extracting cadmium from soil from rapeseed.

[0022] Comparative Example 2: A method for preparing an organic acid liquid fertilizer for enhancing cadmium extraction from soil using rapeseed, differing from Example 1 in that it does not contain brassinolide components, and specifically includes the following steps: S1. Using corn flour as raw material, the corn flour is prepared into a slurry at 17°C. The pH is adjusted to 6.4 using 1% diluted lime water. Two-thirds of the amount of α-amylase required for the corn flour is added. High-temperature steam is introduced. When the temperature of the slurry reaches 90°C, the initial slurry is obtained. The amount of α-amylase required for the corn flour is 6 U / g. S2. Pump the initial slurry into the ejector for liquefaction. When the outlet temperature reaches 95°C, close the reflux valve to allow the liquid to enter the laminar flow tank. When the temperature reaches 140°C, maintain it for 3 minutes. After flash cooling to 20°C, add 1 / 3 of the amount of α-amylase required for corn flour. Maintain the temperature at 90°C for 30 minutes. Adjust the pH to 4.8 using 0.1 mol / L dilute hydrochloric acid. Filter the mixture. After continuous sterilization at 121°C for 30 minutes and actual sterilization at 135°C for 5 minutes, cool it down to 33°C to obtain concentrated mash. S3. Inoculate the concentrated mash with Aspergillus niger spores, adjust the pH to 5 using sterile calcium carbonate, and maintain the fermentation temperature at 37℃ and the fermenter rotation speed at 90 rpm. Sterile air is introduced at three stages: the first (12 hours after inoculation), the second (48 hours after inoculation), and the third (60 hours after inoculation), with flow rates of 0.7 vvm, 1.0 vvm, and 0.25 vvm respectively, for a total of 64 hours of fermentation. After fermentation, filter the mash at room temperature using a cellulose acetate membrane with a molecular weight cutoff of 200 Da at 25℃ and 2.0 MPa. After filtration, use a 201×7... Chromatographic separation was performed using a strongly basic styrene-based anion exchange resin, eluted with 0.05 mol / L dilute sulfuric acid at a flow rate of 1 BV / h, and finally concentrated under reduced pressure at 0.09 MPa and 60 °C for 2 h to obtain the Aspergillus niger fermentation broth; wherein the inoculum amount of Aspergillus niger spores was 10 wt% of the concentrated mash. S4. Soak the biomass ash in 1 mol / L citric acid at a solid-liquid ratio of 1:5 to remove soluble heavy metals. Then wash it with water until neutral. After washing, dry and pulverize it at 80℃ and pass it through a 200-mesh sieve. Add the treated biomass ash to the Aspergillus niger fermentation liquid at a mass ratio of 5:3 at 25℃ and 50 rpm. Stir and mix at 45℃ and 300 rpm for 60 minutes. After mixing, you will get an organic acid liquid fertilizer for extracting cadmium from soil from rapeseed.

[0023] Comparative Example 3: A method for preparing an organic acid liquid fertilizer for enhancing cadmium extraction from soil using rapeseed. The difference from Example 1 is that it does not use Aspergillus niger fermentation broth, but instead uses a combination of citric acid and brassinolide-biomass ash. The specific steps include: S1. By weight, take 2 parts potassium dihydrogen phosphate trihydrate, 1 part citric acid, and 20 parts sucrose. Mix the potassium dihydrogen phosphate trihydrate, citric acid, and sucrose evenly, and add water to make up to 1000 mL to obtain a buffer dilution. Add brassinolide to the buffer dilution to prepare a 100 μmol / L brassinolide buffer solution. S2. Soak the biomass ash in 1 mol / L citric acid at a solid-liquid ratio of 1:5 to remove soluble heavy metals. Then wash with water until neutral. After washing, dry and pulverize at 80℃ and pass through a 200-mesh sieve. Under a nitrogen atmosphere, immerse the biomass ash that has passed through the sieve in brassinolide buffer solution, sonicate at 40kHz for 30 min, stir at 80℃ and 200rpm for 4 h, and dry at 85℃ to obtain brassinolide-biomass ash. The mass ratio of brassinolide to biomass ash is 0.02:1. S3. Add brassinolide-biomass ash to citric acid at a mass ratio of 5:3, stirring at 25℃ and 50 rpm. Stir and mix at 45℃ and 300 rpm for 60 minutes. After mixing, organic acid liquid fertilizer is obtained.

[0024] Comparative Example 4: Citric acid alone was used to enhance the extraction of cadmium from soil.

[0025] Comparative Example 5: No soil treatment was performed.

[0026] The organic acid liquid fertilizers obtained in each embodiment and comparative example were applied to moderately to severely cadmium-contaminated arable land suitable for safe utilization when growing rapeseed. S1. During the budding and full bloom stages of rapeseed, apply a 10-fold diluted organic acid liquid fertilizer for extracting cadmium from the soil to the soil via root irrigation. The application rate is 10 kg / mu each time. To ensure the effectiveness of the organic acid liquid fertilizer for extracting cadmium from the soil in activating cadmium in the soil and promoting plant growth, the relative soil moisture content should be maintained at 40% within one week after application. Therefore, it is best to spray the fertilizer one day before or after rainfall when the relative soil moisture content is 40%. If there is no significant rainfall during the spraying period, the organic acid liquid fertilizer for extracting cadmium from the soil should be diluted 20 times before application, and watered again after 3 days to ensure that the relative soil moisture content reaches 40% and to ensure the effectiveness of the organic acid liquid fertilizer for extracting cadmium from the soil. S2. When 2 / 3 of the rapeseed pods turn yellow or the seed coat inside the pods in the middle of the main axis begins to change color, harvest manually or mechanically. Harvest all the above-ground parts, transport them to the drying yard and spread them out to dry for 6 days, then thresh manually or mechanically. After threshing, the straw is centrally processed.

[0027] 1. The microbial community diversity and activity, as well as the available cadmium content in the soil, were tested on soils treated with organic acid liquid fertilizer and untreated soils obtained from different embodiments and comparative examples for enhanced rapeseed cadmium extraction.

[0028] (1) Analysis of microbial community diversity and structure Community composition was analyzed for each soil sample at the phylum and genus levels, and alpha diversity analysis was performed on the community composition. The results are shown in Table 1.

[0029] Table 1 shows that, based on the bacterial alpha diversity index analysis, the bacterial and fungal diversity indices of Comparative Examples 1-5 were all lower than those of Examples 1-3, indicating that the rhizosphere microbial diversity of Examples 1-3 was higher than that of Comparative Examples 1-5. Organic acid liquid fertilizer based on Aspergillus niger fermentation broth can significantly increase the diversity and activity of soil microbial communities, better activate cadmium in the soil, and enhance the extraction effect of cadmium from the soil by rapeseed. Comparative Example 1 did not add biomass ash, which could not neutralize some of the acidity from the Aspergillus niger fermentation broth, potentially leading to excessively low soil pH and affecting the diversity of soil microbial communities. Comparative Example 2 did not add brassinolide, which could not neutralize the alkalinity of the biomass ash together with the Aspergillus niger fermentation broth, preventing the soil pH from falling within a range conducive to microbial community diversity. Comparative Examples 3-5 did not add Aspergillus niger fermentation broth, resulting in a significant decrease in soil microbial community diversity.

[0030] (2) Determination of available cadmium content in soil: DTPA extractant (0.005 mol·L⁻¹) was used. -1 DTPA + 0.1 mol·L -1 TEA + 0.01 mol·L -1 CaCl2) extraction, filtration, and atomic absorption spectrometry determination. 25.00 g of air-dried soil sample (passed through a 2 mm sieve) was placed in a 100 ml plastic bottle, and 50.00 ml of DTPA extraction reagent was added. The sample was incubated at (25±2)℃ for 180±20 times per minute. -1 After shaking for 2 hours, the solution was filtered to obtain a clear liquid. The Cd concentration in the filtrate was determined using a Shimadzu AA-6300 graphite furnace atomic absorption spectrometer (AAS). The test results are shown in Table 2.

[0031] As shown in Table 2, the activation rates of cadmium in soil obtained from enhanced rapeseed cadmium extraction in Examples 1-3 were higher than those in Comparative Examples 1-5. On one hand, the Aspergillus niger fermentation broth enhanced its strong dissolving and chelating abilities, resulting in a stronger activation effect on cadmium in the soil. On the other hand, brassinolide-biomass ash, through its synergistic effect with the Aspergillus niger fermentation broth, further stabilized the cadmium activated by the fermentation broth in the soil with the cations released from the biomass ash, preventing rapid refixation. This also avoided the excessive acidification problem caused by using only the Aspergillus niger fermentation broth, as well as the cadmium fixation problem caused by using only brassinolide-biomass ash, thus improving the bioavailability of cadmium in the soil more persistently and efficiently. In Comparative Example 2, no brassinolide was added, and the Aspergillus niger fermentation broth could not neutralize or reverse the passivation effect of biomass ash on cadmium, leading to a decrease in the effective cadmium content in the soil. In Comparative Examples 3-4, no Aspergillus niger fermentation broth was added, only citric acid, further significantly reducing the effective cadmium content in the soil.

[0032] 2. The aboveground biomass of rapeseed, the cadmium content in rapeseed grains, the cadmium content in rapeseed straw, and the soil MADC content were tested separately. The test results are shown in Table 3.

[0033] As shown in Table 3, the organic acid liquid fertilizer for enhancing rapeseed cadmium extraction from soil obtained in Examples 1-3 not only increases the aboveground biomass of rapeseed but also improves the translocation capacity of cadmium to straw while ensuring that the cadmium content in the grains meets the standards. Brassinolide-biomass ash can regulate plant physiology, enhance rapeseed photosynthesis, increase aboveground biomass, improve its resistance, and strengthen rapeseed's ability to capture activated cadmium. When biomass ash is used alone, cadmium in the soil is fixed. By combining brassinolide-biomass ash with Aspergillus niger fermentation liquid, cadmium fixation is avoided. The organic acid produced by Aspergillus niger chelates cadmium to form an absorbable complex, which, combined with the enhanced rapeseed's ability to capture activated cadmium, improves the translocation capacity of metallic cadmium to the aboveground parts of rapeseed.

[0034] The specific embodiments of the present invention described above do not constitute a limitation on the scope of protection of the present invention. Any other corresponding changes and modifications made in accordance with the technical concept of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing an organic acid liquid fertilizer for enhancing cadmium extraction from soil using rapeseed, characterized in that, Includes the following steps: S1. Inoculate Aspergillus niger spores into concentrated mash, adjust the pH to 5-6 using sterile calcium carbonate, and ferment for 64 hours. Sterile air is introduced at the beginning, middle and end of the fermentation process, with flow rates of 0.7 vvm, 1-1.2 vvm and 0.25 vvm, respectively. After fermentation, the mixture is filtered through a membrane, separated by chromatography and concentrated to obtain the Aspergillus niger fermentation broth. S2. Add brassinolide-biomass ash to the Aspergillus niger fermentation liquid and stir at 35℃ and 300rpm for 30min. After mixing, the organic acid liquid fertilizer for extracting cadmium from soil from rapeseed is obtained. The mass ratio of brassinolide-biomass ash to Aspergillus niger fermentation liquid is 5~7:

3.

2. The method for preparing organic acid liquid fertilizer for enhancing cadmium extraction from soil using rapeseed according to claim 1, characterized in that, In step S2, the preparation method of brassinolide-biomass ash is as follows: soak the biomass ash in 1 mol / L citric acid at a solid-liquid ratio of 1:5, then wash it with water until neutral, dry and pulverize it at 80~85℃ after washing, and pass it through a 200-mesh sieve. Under a nitrogen atmosphere, the sieved biomass ash was immersed in brassinolide buffer solution, ultrasonically dispersed for 30 min, stirred at 80℃ for 4 h, and dried to obtain brassinolide-biomass ash, wherein the mass ratio of brassinolide to biomass ash was 0.02~0.05:

1.

3. The method for preparing organic acid liquid fertilizer for enhancing cadmium extraction from soil using rapeseed according to claim 2, characterized in that, The method for preparing the brassinolide buffer solution is as follows: potassium dihydrogen phosphate trihydrate, citric acid and sucrose are mixed evenly, and water is added to make up to 1000 mL to obtain a buffer dilution. Brassinolide is then added to the buffer dilution to prepare a 100~120 μmol / L brassinolide buffer solution.

4. The method for preparing organic acid liquid fertilizer for enhancing cadmium extraction from soil using rapeseed according to claim 3, characterized in that, The buffer diluent comprises, by weight, the following components: 2-6 parts potassium dihydrogen phosphate trihydrate, 1-3 parts citric acid, and 20-25 parts sucrose.

5. The method for preparing organic acid liquid fertilizer for enhancing cadmium extraction from soil using rapeseed according to claim 1, characterized in that, In step S1, the preparation method of the concentrated mash is as follows: using corn flour as raw material, the corn flour is adjusted to a slurry temperature of 17~20℃, the pH is adjusted to 6.4~7.0, 2 / 3 of the required amount of α-amylase is added, high-temperature steam is introduced, and when the temperature of the slurry reaches 90℃, the initial slurry is obtained; the initial slurry is liquefied, and after liquefaction, 1 / 3 of the required amount of α-amylase is added, and the mixture is kept at 90℃ for 30 minutes. The pH is adjusted to 4.8~5.2 using 0.1mol / L dilute hydrochloric acid, filtered, and after continuous and actual sterilization, and cooled to 33~37℃, concentrated mash is obtained.

6. The method for preparing organic acid liquid fertilizer for enhancing rapeseed cadmium extraction from soil according to claim 5, characterized in that, The required amount of α-amylase added to the corn flour is 6~9 U / g; the liquefaction step of the initial slurry is as follows: the initial slurry is pumped into the ejector for liquefaction. When the outlet material temperature reaches 95~97℃, the reflux valve is closed to allow the liquid to enter the laminar flow tank. When the material temperature reaches 140~145℃, it is maintained for 3~5 minutes and then flash-cooled to 20~25℃.

7. The method for preparing organic acid liquid fertilizer for enhancing cadmium extraction from soil using rapeseed according to claim 1, characterized in that, In step S1, the inoculation amount of Aspergillus niger spores is 10-15 wt% of the concentrated mash; the early, middle and late stages are the 12th hour, 48th hour and 60th hour after inoculation with Aspergillus niger spores, respectively.

8. The method for preparing organic acid liquid fertilizer for enhancing cadmium extraction from soil using rapeseed according to claim 1, characterized in that, In step S1, the membrane filtration and chromatographic separation are performed as follows: at room temperature, a reverse osmosis membrane is used for filtration at 25~45℃ and 2.0~5.0MPa. After filtration, a strongly basic anion exchange resin is used for chromatographic separation, and 0.05~0.08mol / L dilute sulfuric acid is used for elution at a flow rate of 1~5BV / h.

9. The organic acid liquid fertilizer for extracting cadmium from soil from rapeseed prepared by the method of claim 1.

10. The application of the organic acid liquid fertilizer for enhancing cadmium extraction from soil using rapeseed as described in claim 9, characterized in that, The method is as follows: During the budding and full bloom stages of rapeseed, one day before or after rainfall, when the relative soil moisture content is 30-60%, apply a 10-fold diluted organic acid liquid fertilizer for cadmium extraction from rapeseed to the soil through root irrigation. The application rate is 10-13 kg / mu each time, and the relative soil moisture content should be maintained at 30-60% for one week after application. If there is no rainfall when fertilizing, dilute the organic acid liquid fertilizer for cadmium extraction from rapeseed to the soil 20 times before application, and water again after 3 days to ensure that the relative soil moisture content reaches 30-60%.

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