Self-protective secondary salinization soil remediation microbial agent, its preparation method and application

Abstract

This invention relates to a self-protective secondary salinization soil remediation microbial agent, its preparation method, and its application. The agent comprises the following raw materials by weight percentage: 5%–15% *Bacillus megaterium* fermentation broth, 30%–45% nitrate-containing industrial wastewater, 30%–40% organic carbon source, and the balance being water; wherein the nitrate concentration in the nitrate-containing industrial wastewater is greater than 30%; and the effective viable bacteria count is ≥200 million / mL. The preparation method involves adding the organic carbon source to the treated nitrate-containing industrial wastewater in a specific ratio and mixing thoroughly. Then, *Bacillus megaterium* fermentation broth is added in a specific ratio, and water is added to bring the total to 100%. After mixing thoroughly, the mixture is allowed to stand for at least 12 hours. For application, the soil remediation microbial agent is first prepared by fertilization, then diluted and applied as a base fertilizer or top dressing to the secondary salinization soil requiring remediation. The soil remediation microbial agent of this invention is in liquid form and can be stored for up to 3 years in a high-salt environment, exhibiting good self-protection and salt tolerance.

Description

Technical Field

[0001] This invention relates to the field of secondary salinization soil remediation technology, specifically to a self-protective secondary salinization soil remediation microbial agent, its preparation method, and its application. Background Technology

[0002] Facility agriculture, due to its unique ecological environment and unreasonable water and fertilizer management practices, has led to numerous production problems such as secondary soil salinization, nutrient imbalance, and soil acidification, with secondary soil salinization being the most prominent. Secondary soil salinization severely affects crop nutrient absorption, causes physiological drought, and results in reduced crop yields. This reduced yield forces farmers to increase fertilizer input, which further exacerbates secondary soil salinization, creating a vicious cycle that seriously impacts farmers' economic returns.

[0003] Microbial methods have become the preferred approach for remediating secondary salinized soils due to their advantages such as low cost, ease of operation, and lack of secondary pollution. Liquid soil remediation microbial agents can be precisely formulated according to actual needs, allowing for the selection of fertilization methods, thereby saving fertilizer costs and improving fertilizer utilization. They are widely used in the cultivation of cash crops. With the increasing prominence of secondary salinization in my country and the widespread improvement of integrated water and fertilizer facilities, research on liquid microbial methods for treating nitrate nitrogen has broad prospects. However, the main problems in the current process of microbial remediation of secondary salinized soils are: the shelf life of liquid soil remediation microbial agents is only about 6 months even with the addition of protectants, which is very short. They are easily contaminated by other microorganisms during transportation, have short storage time, high repackaging risks, and high protectant costs. Most protectants function to inhibit bacterial growth, which, while maintaining the stability of the bacterial count in the solution, weakens the efficacy of the agent to some extent. Some protectants can also cause secondary pollution. These problems seriously limit the application of microbial remediation in the remediation of secondary salinized soils.

[0004] Wastewater containing high concentrations of nitrates is widely distributed in industries such as metal processing, electroplating, nuclear power, and food processing. It is characterized by high salinity, small volume, and strict discharge standards. However, direct discharge of high-concentration nitrate wastewater can cause excessive salinity, eutrophication, and foul odors in water bodies. Therefore, wastewater treatment is necessary. Nitrate treatment methods are typically biological, including traditional anoxic-aerobic processes, short-cut nitrification-denitrification, and anaerobic ammonium oxidation. These methods utilize the reduction action of microorganisms to convert nitrates into nitrites, which are further reduced to nitrogen gas. Related denitrification technologies include microbial fuel cells and constructed wetlands. However, these methods, on the one hand, produce greenhouse gases that harm the atmospheric environment; on the other hand, the high salinity of the wastewater means that some industrial wastewater lacks sufficient organic matter as a carbon source, significantly inhibiting microbial reproduction and thus hindering biological denitrification. Moreover, wastewater with high nitrate concentration has a high osmotic pressure, which can kill most bacteria that are intolerant to salt, making it unsuitable for the production of microbial fertilizers. Therefore, wastewater with high nitrate concentration is not suitable for biological treatment. In the treatment of high-concentration nitrate wastewater, physicochemical methods are also common, which mainly include the following categories: (1) Adding metal particles, metal salts or metal oxides to high-concentration nitrate wastewater, and under the assistance of light or electricity, rapidly removing nitrate concentration in the wastewater through catalytic reduction. Zero-valent nano iron and divalent iron salts are more commonly used; (2) Using reverse osmosis technology to obtain clean water from nitrate-containing wastewater, but leaving wastewater with higher residual nitrate concentration; (3) Using ion exchange resin to recover nitrate in wastewater, but requiring clean wastewater with few interfering ions. Therefore, how to directly utilize wastewater with high nitrate concentration without denitrification is a problem that needs to be solved. Summary of the Invention

[0005] To address the technical problem of short shelf life in existing liquid soil remediation microbial agents when protective agents are added, and to explore how to directly apply high-concentration nitrate wastewater to liquid soil remediation microbial agents without denitrification, this invention provides a self-protective secondary salinization soil remediation microbial agent, its preparation method, and its application. The soil remediation microbial agent of this invention is liquid and can survive for at least one year in high-concentration salt environments without the addition of conventional protective agents, exhibiting excellent self-protection and high salt tolerance. It requires pre-fertilization before application to remediate secondary soil salinization, demonstrating good application results.

[0006] The first aspect of this invention provides a self-protective secondary salinization soil remediation bacterial agent, comprising the following raw materials by weight percentage: 5%–15% Bacillus megaterium fermentation broth, 30%–45% nitrate-containing industrial wastewater, 30%–40% organic carbon source, and the balance being water; wherein the nitrate-containing industrial wastewater has a nitrate concentration greater than 30%.

[0007] Furthermore, the self-protective secondary salinization soil remediation microbial agent contains ≥200 million viable bacteria / mL, ≥15 wt% total organic matter content, and ≥5 wt% total nutrient content calculated as N+P2O5+K2O.

[0008] Furthermore, the Bacillus megaterium fermentation broth is obtained by fermenting Bacillus megaterium, and the effective viable count in the Bacillus megaterium fermentation broth is 40 to 100 billion / mL; the Bacillus megaterium is NCT-2.

[0009] Furthermore, the source of the nitrate-containing industrial wastewater is one of the following: metal processing industry, electroplating industry, food processing industry, or fertilizer processing industry.

[0010] Furthermore, the organic carbon source is one or a combination of several of molasses, soluble starch, glucose, potassium humate, potassium humate, and yeast waste liquid, and the organic matter content of the organic carbon source is at least 40 wt%.

[0011] A second aspect of this invention provides a method for preparing the above-mentioned self-protective secondary salinization soil remediation microbial agent, comprising the following steps:

[0012] (1) Industrial wastewater containing nitrates from the food processing industry and fertilizer industry can be used directly, or industrial wastewater containing nitrates from the metal processing industry and electroplating industry can be treated by chelation precipitation to remove heavy metal ions until no precipitation is produced, which can be considered as heavy metal ions being removed.

[0013] (2) Add an organic carbon source to the nitrate-containing industrial wastewater after step (1) in proportion and mix well. Then add Bacillus megaterium fermentation broth in proportion and make up to 100% with water. After mixing well, let stand for at least 12 hours to obtain a self-protective secondary salinization soil remediation agent.

[0014] The third aspect of the present invention provides the application of the above-mentioned self-protective secondary salinization soil remediation microbial agent, wherein the application method is as follows: first, the self-protective secondary salinization soil remediation microbial agent is fertilized and then applied to the secondary salinization soil that needs to be remediated.

[0015] Furthermore, the process of "awakening fertilizer" involves preparing a diluted solution of the self-protective secondary salinization soil remediation microbial agent and water at a mass ratio of 1:(500-2000), and allowing it to stand for one day before application. Bacillus megaterium can reduce nitrates and nitrites, and in the absence of growth factors, it can proliferate using inorganic nitrogen sources and organic carbon sources. Therefore, after standing for one day, the dormant spores in the Bacillus megaterium in the microbial agent of this invention can germinate, thereby converting nitrates into organic nitrogen, which can then be used as nitrogen fertilizer in the soil, avoiding nitrate pollution.

[0016] Furthermore, the method for remediating secondary salinized soil is to apply the diluted solution as a base fertilizer or top dressing at a rate of 500-5000 mL / mu to the soil to be remediated via irrigation, drip irrigation, or subsurface irrigation. The diluted solution contains more than 200 million viable bacteria of the Bacillus megaterium.

[0017] Beneficial technical effects:

[0018] 1. The self-protective secondary salinization soil remediation bacterial agent provided by this invention uses high-concentration nitrate industrial wastewater as raw material and performs efficient and harmless treatment to make it suitable for use in microbial agents. This breaks through the technical barrier of microbial treatment in the field of high-salinity waste nitrate nitrogen and solves the problem of greenhouse gas generation from biological treatment of waste nitrate nitrogen.

[0019] 2. The self-protective secondary salinization soil remediation agent provided by this invention is in liquid form. It is prepared using high-concentration nitrate industrial wastewater as raw material, with NCT-2 Bacillus megaterium as the main secondary salinization soil remediation bacterium, and with the addition of an organic carbon source. NCT-2 Bacillus megaterium not only possesses the soil remediation functions of conventional Bacillus megaterium (it can reduce secondary salinization and salt damage in the soil, and also increase the organic matter content in the soil, improving crop yield and quality), but also exhibits tolerance to high-salt environments. It can survive in liquid nitrate environments with a mass concentration of over 10% in the form of spores, demonstrating excellent tolerance to high-concentration salt environments. The significance of the so-called self-protective nature lies in the fact that the liquid bacterial agent of this invention can, without the addition of conventional protective agents, utilize the high-salt bactericidal properties of the high-salt environment provided by industrial wastewater containing high concentrations of nitrates in the liquid bacterial agent, as well as the high-salt environment tolerance of the NCT-2 Bacillus megaterium strain. These two elements form a self-protective mechanism: on the one hand, it can prevent contamination by other microorganisms under high-salt conditions, exhibiting good performance in killing other microorganisms; on the other hand, the high-salt environment has no effect on the NCT-2 Bacillus megaterium itself. Therefore, the bacterial agent of this invention has a shelf life of up to 3 years. The production of the self-protective secondary salinization soil remediation bacterial agent of this invention meets national standards, has a long shelf life, does not require the addition of additional protective agents, reduces production costs, and also prevents secondary pollution caused by protective agents.

[0020] 3. The high-salt environment in the self-protective secondary salinization soil remediation microbial agent of the present invention can greatly inhibit the reproduction of conventional salt-intolerant microorganisms, making it easy to package and transport. It is also rich in nutrients, which is beneficial for later application. It can provide some nutrients, significantly reduce the nitrate nitrogen content in the soil, reduce the soil EC value, increase the soil organic matter content, promote rhizosphere microbial diversity, reduce the emission of gases such as nitrous oxide, and help increase crop yield.

[0021] 4. The self-protective secondary salinization soil remediation microbial agent of the present invention can be applied to facility agriculture, which can improve the efficiency of secondary salinization remediation of soil and reduce labor costs; the microbial agent of the present invention can also be applied to the field of topdressing, improving the flexibility of soil remediation. Detailed Implementation

[0022] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the present invention or its application or use. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0023] Unless otherwise specifically stated, the numerical values ​​set forth in these embodiments do not limit the scope of the invention. Techniques and methods known to those skilled in the art may not be discussed in detail, but where appropriate, such techniques and methods should be considered part of the specification. In all examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not as limitations. Therefore, other examples of exemplary embodiments may have different values.

[0024] Experimental methods not specifically described in the following examples are generally determined according to national standards; if no corresponding national standard exists, they are performed according to generally accepted international standards or the standards proposed by relevant enterprises. Unless otherwise stated, all parts are parts by weight, and all percentages are weight percentages.

[0025] The nitrate-containing industrial wastewater used in the following examples from the food and fertilizer industries is the production waste liquid from the production of calcium ammonium nitrate and ammonium nitrate, wherein the nitrate content is greater than 30 wt%; the nitrate-containing industrial wastewater from the metal processing industry is the waste liquid from mechanical, photovoltaic, and other stretching agents, lubricants, and cleaning agents, wherein the nitrate content is greater than 30 wt%; the nitrate-containing industrial wastewater from the electroplating industry is the waste liquid generated after pickling, stripping, and etching during the production process, wherein the nitrate content is greater than 30 wt%.

[0026] The *Bacillus megaterium* used in the following examples is NCT-2, deposited at the China General Microbiological Culture Collection Center (CGMCC), with accession number CGMCC No. 4698. The *Bacillus megaterium* fermentation broth used in the following examples was obtained by fermenting *Bacillus megaterium* NCT-2 (using conventional fermentation; the optimal fermentation parameters were determined to be: pH = 8, temperature 30℃, inoculum size 4%, and rotation speed 200 rpm. Combined with the above fermentation parameters, the fermenter was controlled under the following conditions: aeration ratio of 1:1, and a tank pressure of 0.03–0.05 MPa for 48 hours, resulting in the highest bacterial content and a sporulation rate of over 90%). The effective viable count in the *Bacillus megaterium* fermentation broth was 40–100 billion / mL.

[0027] Example 1

[0028] Self-protective secondary salinization soil remediation microbial agent includes the following raw materials by weight percentage: Bacillus megaterium fermentation broth (4 billion / mL) 25kg (5.03%), industrial wastewater containing nitrates from the fertilizer processing industry 200kg (40.24%), potassium humate 200kg (40.24%), and tap water 72kg (14.49%).

[0029] The preparation method of the above-mentioned self-protective secondary salinization soil remediation microbial agent includes the following steps: potassium humate is added to industrial wastewater containing nitrates in the food processing industry in a certain proportion and mixed well. Then, Bacillus megaterium fermentation broth is added in a certain proportion and water is added to make up to 100%. After mixing well, the mixture is allowed to stand for at least 12 hours to obtain the self-protective secondary salinization soil remediation microbial agent of this embodiment.

[0030] The self-protective secondary salinization soil remediation microbial agent of this embodiment has an effective viable bacteria count of 500 million / mL, a total organic matter content of 20wt%, and a total nutrient content (calculated as N+P2O5+K2O) of 20wt%.

[0031] Example 2

[0032] Self-protective secondary salinization soil remediation microbial agent includes the following raw materials by weight percentage: 50 kg (10%) of Bacillus megaterium fermentation broth (4 billion / mL), 200 kg (40%) of industrial wastewater containing nitrates from the fertilizer processing industry, 180 kg (36%) of potassium humate, and 70 kg (14%) of tap water.

[0033] The preparation method of the self-protective secondary salinization soil remediation microbial agent is the same as that in Example 1.

[0034] The self-protective secondary salinization soil remediation microbial agent of this embodiment has an effective live bacteria count of 1 billion / mL, a total organic matter content of 20wt%, and a total nutrient content (calculated as N+P2O5+K2O) of 18wt%.

[0035] Example 3

[0036] The self-protective secondary salinization soil remediation agent comprises the following raw materials by weight percentage: Bacillus megaterium fermentation broth (4 billion / mL) 75kg (15%), industrial wastewater containing nitrates from the fertilizer processing industry 150kg (30%), potassium humate 150kg (30%), and tap water 125kg (25%).

[0037] The preparation method of the self-protective secondary salinization soil remediation microbial agent is the same as that in Example 1.

[0038] The self-protective secondary salinization soil remediation microbial agent of this embodiment has an effective live bacteria count of 1.5 billion / mL, a total organic matter content of 15wt%, and a total nutrient content (calculated as N+P2O5+K2O) of 15wt%.

[0039] Comparative Example 1

[0040] The soil remediation agent in this comparative example is Bacillus subtilis soil remediation agent, which includes the following raw materials by weight percentage: Bacillus subtilis fermentation broth (4 billion / mL) 25kg (5.03%), industrial wastewater containing nitrates from the fertilizer processing industry 200kg (40.24%), potassium humate 200kg (40.24%), and tap water 72kg (14.49%).

[0041] The preparation method of the soil remediation microbial agent is the same as that in Example 1.

[0042] The effective viable bacteria count of Bacillus subtilis soil remediation agent obtained in this comparative example was only 0.2 billion / mL, the total organic matter content was 20wt%, and the total nutrient content (calculated as N+P2O5+K2O) was 20wt%.

[0043] Comparing the viable bacterial counts of the soil remediation microbial agents prepared in Comparative Example 1 and Example 1 indirectly reflects that Bacillus subtilis is less salt-tolerant than Bacillus megaterium NCT-2. That is, in the presence of high concentrations of nitrate (nitrate concentration greater than 10%), Bacillus megaterium NCT-2 exhibits better salt tolerance.

[0044] Comparative Example 2

[0045] The soil remediation microbial agent in this comparative example comprises the following raw materials by weight percentage: 25 kg of Bacillus megaterium fermentation broth (4 billion / mL), and protectants: 10 kg of sorbitol, 20 kg of monosodium glutamate (MSG), 10 kg of Twen80, 200 kg of potassium humate, and 195 kg of tap water. This comparative example uses conventional protectants.

[0046] The preparation method of the soil remediation microbial agent in this comparative example is the same as that in Example 1.

[0047] The soil remediation microbial agent in this comparative example has a viable bacteria count of 500 million / mL, a total organic matter content of 20wt%, and a total nutrient content (calculated as N+P2O5+K2O) of 5wt%.

[0048] The soil remediation microbial agents obtained in the above examples and comparative examples were subjected to a shelf-life test. After a period of time, the number of viable bacteria in the microbial agents was tested, and the data are shown in Table 1. The viable bacteria test method refers to the current GB-20287.

[0049] Table 1. Number of viable bacteria during storage time

[0050]

[0051]

[0052] As shown in Table 1, Bacillus subtilis in Comparative Example 1 has difficulty surviving under high-concentration nitrate formulations. In Comparative Example 2, the survival period of viable bacteria using conventional preservatives is no more than 6 months (the viable bacterial count decreased by more than 58% after 180 days and by about 78% after 720 days), meaning the protection period using conventional preservatives is no more than 6 months. However, this invention uses industrial wastewater with a nitrate concentration of over 30% and NCT-2 Bacillus megaterium to prepare a bacterial agent (the nitrate content in the product bacterial agent is greater than 10%). After storage for 180 days, the viable bacterial count decreased by about 30%, and after storage for 720 days (1 year), the viable bacterial count decreased by about 60%. This invention utilizes a soil remediation microbial agent made from industrial wastewater with high nitrate concentrations. This agent offers superior protection compared to conventional preservatives because *Bacillus megaterium* NCT-2 can survive in spore form in a liquid nitrate environment with a concentration exceeding 10%, demonstrating excellent tolerance to high-salt conditions. It is a self-protective secondary salinization soil remediation microbial agent. The self-protective nature of this agent lies in its ability to utilize the high-salt bactericidal properties of the industrial wastewater containing high nitrates, combined with the high-salt tolerance of the *Bacillus megaterium* strain NCT-2, to create a self-protective mechanism. This mechanism prevents contamination by other microorganisms in the high-salt environment, effectively killing them, while the high-salt environment has no effect on *Bacillus megaterium* NCT-2 itself. The agent's shelf life can reach up to 3 years, and it remains a qualified product even after 3 years.

[0053] Application Example 1

[0054] The self-protective secondary salinization soil remediation microbial agent of Example 1 above was used in a field trial.

[0055] The experiment included four treatments, the details of which are as follows:

[0056] CK: Blank processing;

[0057] Treatment 1: Conventional fertilization;

[0058] Treatment 2: Conventional fertilization + 5000mL of substrate dilution per acre. The composition of this substrate is the same as that of Example 1, except that it does not contain NCT-2 Bacillus megaterium and is an inactivated substrate that has been sterilized by high temperature. The dilution concentration is the same as that of Treatment 3.

[0059] Treatment 3: Conventional fertilization + 5000 mL / mu of diluted self-protective secondary salinization soil remediation microbial agent from Example 1 (the preparation process of this diluted agent is as follows: the self-protective secondary salinization soil remediation microbial agent is mixed with water at a mass ratio of 1:2000 to prepare a diluted solution, which can be applied after standing for 1 day. When applying, it is used as a base fertilizer and irrigated into the soil).

[0060] The area of ​​each residential community is 15 square meters. 2 Each treatment was repeated three times in a randomized block arrangement.

[0061] CK refers to the absence of amendments and fertilizers, used to determine the absolute value of the effect of microbial agents.

[0062] Technical specifications for self-protective secondary salinization soil remediation microbial agent: effective live bacteria count ≥ 200 million / mL, total organic matter content ≥ 15wt%, and total nutrient content calculated as N+P2O5+K2O ≥ 5wt%.

[0063] (I) Analysis of the effects of different treatments on soil nitrate content

[0064] 1. Jiading Green Hope Cooperative

[0065] The effects of the above three treatments on the soil nitrate content of Jiading Lvwang Cooperative are shown in Table 2.

[0066] Table 2. Effects of different treatments on soil nitrate content at Lvwang Cooperative

[0067]

[0068] As shown in Table 2, treatment 3 effectively reduced the nitrate content in the soil, with a decrease of 55.6% compared to before treatment. Compared to treatment 2, treatment 3 showed a 42.11% increase in the reduction rate, demonstrating a significant reduction effect. Treatment 1 showed no significant decrease compared to before treatment. This indicates that the addition of the self-protective secondary salinization soil remediation microbial agent of the present invention (treatment 3) has a better effect on improving secondary salinization soil dominated by nitrate.

[0069] 2. Hongqiao Horticulture Farm

[0070] The effects of the above three treatments on the nitrate content of the soil in Hongqiao Horticulture Farm are shown in Table 3.

[0071] Table 3. Effects of different treatments on soil nitrate content in Hongqiao Horticulture Farm

[0072]

[0073] As shown in Table 3, the nitrate content after treatment was lower than before treatment, but the degree of reduction varied. Treatment 3, which incorporated the self-protective secondary salinization soil remediation microbial agent of the present invention, showed the highest reduction in nitrate content, decreasing by 38.6%. Compared with treatment 2, which was treated with the substrate, treatment 3 reduced nitrate content by 21.49%, while the blank control group showed a reduction of 16.1%. In contrast, treatment 1, which involved conventional fertilization, showed a reduction of only 0.54% in nitrate content, essentially no reduction. This indicates that the self-protective secondary salinization soil remediation microbial agent of the present invention can effectively reduce the nitrate content in the soil.

[0074] 3. Qixin Horticulture Farm

[0075] The effects of the above three treatments on the nitrate content of the soil in Qixin Horticulture Farm are shown in Table 4.

[0076] Table 4. Effects of different treatments on soil nitrate content in Qixin Horticulture Farm

[0077]

[0078] As shown in Table 4, the nitrate content in the soil decreased by 54.83% after treatment with the self-protective secondary salinization soil remediation microbial agent of the present invention (treatment 3), the nitrate content in the soil of the blank control treatment decreased by 14%, the nitrate content in the substrate treatment of treatment 2 decreased by 15.14%, and the nitrate content of the conventional fertilization treatment was not significantly different. Compared with the other two treatments, the self-protective secondary salinization soil remediation microbial agent of the present invention can reduce the nitrate content to a greater extent (54.83%).

[0079] (II) Analysis of the effects of different treatments on soil EC value and total salinity

[0080] On the harvest day of Shanghai bok choy at Jiading Lvwang Cooperative, the EC value and total salinity of soil under different treatments were measured, and the results are shown in Table 5 below.

[0081] Table 5 Effects of different treatments on soil EC value and total salt content

[0082]

[0083] Table 5 shows that the EC value of treatment 3 decreased by 41.3% compared to the CK treatment and by 13% compared to treatment 2; the change trend of total salt content showed a significant linear relationship with the EC value (R0). 2=0.9992), the total salt content was the lowest under treatment 3, which was reduced by 35.3% compared with the CK treatment. It was reduced by 12.3% compared with treatment 2. The above results show that the treatment (treatment 3) with the addition of the self-protective secondary salinization soil remediation microbial agent of the present invention can significantly reduce the soil EC value and total salt content, which is beneficial to the improvement of secondary salinization soil.

[0084] On the harvest day of *Gnaphalium affine* at Hongqiao Horticulture Farm and Qixin Horticulture Farm, soil EC values ​​and total salt content were also measured, showing the same trend. Treatment 3 showed EC values ​​that were 45.1% and 45.6% lower than the control (CK), and 10% and 8.5% lower than treatment 2, respectively. Total salt content decreased by 34.7% and 42.0% compared to the CK, and by 9.8% and 15.7% compared to treatment 2, respectively. Treatments with the self-protective secondary salinization soil remediation microbial agent of this invention significantly reduced soil EC values ​​and total salt content, thus improving the soil.

[0085] (III) Analysis of the impact of different treatments on crop yield

[0086] 1. Jiading Green Hope Cooperative

[0087] The impact of the above three treatments on the yield of Shanghai bok choy in Jiading Lvwang is shown in Table 6.

[0088] Table 6. Effects of different treatments on Shanghai bok choy yield indicators

[0089]

[0090] As shown in Table 6, the total yield of Shanghai bok choy in treatment 3 was significantly higher than that in treatments CK, 1, and 2, with increases of 32.7%, 63.5%, and 15.3%, respectively. Analysis of variance showed that the self-protective secondary salinization soil remediation microbial agent of this invention (treatment 3) significantly improved crop yield. The inactivated substrate treatment (treatment 2), due to its main component being potassium humate, provided a large amount of carbon source to the soil, balancing the carbon-nitrogen ratio and promoting microbial fermentation and decomposition, thus also increasing crop yield to some extent. The yield of treatment CK was 23.2% higher than that of treatment 1, indicating that in secondary salinized soils, applying more fertilizer may actually negatively impact crop yield.

[0091] 2. Hongqiao Horticulture Farm

[0092] The effects of the above three treatments on the yield of Chinese cabbage at Hongqiao Horticulture Farm are shown in Table 7.

[0093] Table 7. Effects of different treatments on the yield of Chinese cabbage at Hongqiao Horticulture Farm

[0094]

[0095] As shown in Table 7, the total yield of Chinese cabbage in treatment 3 was significantly higher than that in treatments CK, 1, and 2, with increases of 21.7%, 39.1%, and 4.5%, respectively. Similar to the trend observed at the Green Hope Cooperative, the addition of the self-protective secondary salinization soil remediation microbial agent of this invention balances the soil's carbon-nitrogen ratio, thus increasing crop yield.

[0096] 3. Qixin Horticulture Farm

[0097] The effects of the above three treatments on the yield of Chinese cabbage at Qixin Horticulture Farm are shown in Table 8.

[0098] Table 8. Effects of different treatments on the yield of Chinese cabbage at Qixin Horticulture Farm

[0099]

[0100] As shown in Table 8, in terms of yield, treatment 3 increased by 34.4%, 58.5%, and 6.9% compared to CK, treatments 1, and 2, respectively, all reaching a significant level, showing the same trend as the two experimental sites mentioned above. The application of the self-protective secondary salinization soil remediation microbial agent of this invention significantly increased the number of leaves, fresh weight, and yield of *Chenopodium album*. In greenhouses where the self-protective secondary salinization soil remediation microbial agent of this invention was applied, the number of leaves and yield of *Chenopodium album* were higher than in other treatments; the plant height of the treatments using the self-protective secondary salinization soil remediation microbial agent of this invention and the control group were both higher than those treated with bio-organic fertilizer.

[0101] (IV) Analysis of the impact of different treatments on crop quality

[0102] The nitrate content in vegetables is one of the important indicators for evaluating the safety and quality standards of vegetables, as shown in Table 9. In Table 9, the nitrate content in Shanghai bok choy from the Lvwang Cooperative was significantly lower in treatment 3 compared to the control (CK), treatments 1 and 2, with reductions of 37.4%, 27.5%, and 51.2%, respectively. This indicates that the application of the self-protective secondary salinization soil remediation microbial agent (treatment 3) of this invention can significantly reduce the nitrate content in Shanghai bok choy in greenhouses. The same trend was observed in Hongqiao Horticulture Farm and Qixin Horticulture Farm. In Hongqiao Horticulture Farm, treatment 3 reduced the nitrate content by 41.4%, 57.0%, and 34.9% compared to CK, treatments 1 and 2, respectively; in Qixin Horticulture Farm, treatment 3 reduced the nitrate content by 28.8%, 50.8%, and 27.1% compared to CK, treatments 1 and 2, respectively. Analysis of variance showed that all these reductions were statistically significant.

[0103] Table 9. Effects of different treatments on nitrate content in crops (g / kg)

[0104] deal with Green Hope Hongqiao Qi Xin CK 0.227±0.013 0.268±0.011 0.212±0.018 1 0.323±0.015 0.365±0.014 0.307±0.022 2 0.291±0.019 0.241±0.025 0.207±0.015 3 0.142±0.022 0.157±0.019 0.151±0.020

[0105] In summary:

[0106] 1. The self-protective secondary salinization soil remediation microbial agent of the present invention can significantly reduce the nitrate content in the soil. Compared with the control (CK) treatment, treatment 3 reduced the nitrate content in the soil by 55.6%, 38.6%, and 54.83%, respectively. This demonstrates that the self-protective secondary salinization soil remediation microbial agent of the present invention can significantly reduce the nitrate content in the soil and improve soil quality.

[0107] 2. Compared with conventional fertilization, the soil EC value decreased by 28.3%–45.6% and the total salt content decreased by 26.3%–42.0% when using the self-protective secondary salinization soil remediation microbial agent of the present invention. This indicates that the self-protective secondary salinization soil remediation microbial agent of the present invention has a significant effect on improving the soil environment, reducing nitrate nitrogen content, and reducing soil salt content, thus mitigating the adverse effects caused by secondary soil salinization.

[0108] 3. The use of the self-protective secondary salinization soil remediation microbial agent of the present invention can increase crop yield. The crop yield of treatment 3 at the three test sites increased by 65.3%, 39.1%, and 58.5% respectively compared with the conventional fertilization treatment. This shows that the application of the self-protective secondary salinization soil remediation microbial agent of the present invention can significantly increase crop yield.

[0109] 4. The application of the self-protective secondary salinization soil remediation microbial agent of the present invention can significantly reduce the nitrate content in crops. At the three test sites, the nitrate content in treatment 3 crops was reduced by 27.5%, 57.0%, and 50.8% respectively compared to the conventional fertilization treatment, demonstrating a significant improvement in crop quality. This indicates that the self-protective secondary salinization soil remediation microbial agent of the present invention can significantly reduce the nitrate content in crops and improve crop quality.

[0110] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A self-protective microbial agent for remediating secondary salinized soil, characterized in that, The raw materials include the following weight percentages: 5%–15% Bacillus megaterium fermentation broth, 30%–45% nitrate-containing industrial wastewater, 30%–40% organic carbon source, and the balance being water; wherein the nitrate-containing industrial wastewater has a nitrate concentration greater than 30%. The self-protective secondary salinization soil remediation microbial agent has an effective live bacteria count of ≥200 million / mL, a total organic matter content of ≥15wt%, and a total nutrient content of ≥5wt% calculated as N+P2O5+K2O. The Bacillus megaterium is NCT-2; The organic carbon source is one or a combination of several of the following: molasses, soluble starch, glucose, potassium humate, potassium humate, and yeast waste liquid, and the organic matter content of the organic carbon source is at least 40 wt%.

2. The self-protective secondary salinization soil remediation microbial agent according to claim 1, characterized in that, The fermentation broth of Bacillus megaterium is obtained by fermentation of Bacillus megaterium, and the effective viable count in the fermentation broth of Bacillus megaterium is 40 to 100 billion / mL.

3. The self-protective secondary salinization soil remediation microbial agent according to claim 1, characterized in that, The nitrate-containing industrial wastewater originates from one of the following industries: metal processing, electroplating, food processing, or fertilizer processing.

4. The preparation method of the self-protective secondary salinization soil remediation microbial agent according to any one of claims 1-3, characterized in that, Includes the following steps: (1) Industrial wastewater containing nitrates from the food processing industry and fertilizer industry can be used directly, or industrial wastewater containing nitrates from the metal processing industry and electroplating industry can be treated by chelation precipitation to remove heavy metal ions until no precipitation is produced, which can be considered as heavy metal ions being removed. (2) Add an organic carbon source to the nitrate-containing industrial wastewater after step (1) in proportion and mix well. Then add Bacillus megaterium fermentation broth in proportion and make up to 100% with water. After mixing well, let stand for at least 12 hours to obtain a self-protective secondary salinization soil remediation agent.

5. The application of the self-protective secondary salinization soil remediation microbial agent according to any one of claims 1-3, characterized in that, The application method is as follows: first, the self-protective secondary salinization soil remediation microbial agent is fertilized, and then applied to the secondary salinization soil that needs to be remediated.

6. The application according to claim 5, characterized in that, The process of preparing the fertilizer involves mixing the self-protective secondary salinization soil remediation bacteria with water at a mass ratio of 1:(500-2000) to form a diluted solution, which is then left to stand for 1 day before application.

7. The application according to claim 6, characterized in that, The method for remediating secondary salinized soil is to apply the diluted solution as a base fertilizer or top dressing at a rate of 500-5000 mL / mu to the soil to be remediated via irrigation, drip irrigation, or subsurface irrigation. The diluted solution contains more than 200 million viable bacteria of the Bacillus megaterium.

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