Compound microbial liquid for saline soil improvement and crop growth promotion and application thereof

Abstract

The application provides a composite microbial liquid for saline soil improvement and crop growth promotion and application thereof, and the composite microbial liquid comprises Bacillus amyloliquefaciens S1-13 liquid, Bacillus thuringiensis SP1-14 liquid, Pseudomonas putida SE1-6 liquid and Bacillus pacificus RC3-7 liquid. Each strain in the composite microbial liquid has specific functions, and after reasonable compounding, the composite microbial liquid can significantly reduce the pH of the soil, improve the soil microbial activity and increase the crop yield.

Description

Technical Field

[0001] This invention belongs to the field of agricultural microbial application technology, specifically relating to a compound microbial inoculum for improving saline soil and promoting crop growth, and its application. Background Technology

[0002] Saline soil is a serious ecological and environmental problem. Coastal saline-alkali lands, directly or indirectly affected by seawater or tides, experience particularly severe salinization. Excessively high levels of basic ions and high pH pressure in saline-alkali soils lead to decreased soil fertility, affecting crop root growth, hindering the absorption and utilization of water and nutrients, suppressing crop growth and development, and ultimately reducing crop yields. Therefore, alleviating soil salinization and increasing crop yields are of great significance for high-quality agricultural development.

[0003] Saline-alkali land is widely distributed and has low soil carbon and nitrogen content, thus possessing enormous potential for nitrogen and carbon sequestration. Studies have shown that adding organic matter can increase soil carbon and nitrogen reserves, but different organic materials exhibit varying effects in improving saline-alkali land and also present some challenges. For example, the types, sources, and nutrient contents of organic fertilizers vary considerably, making it difficult to control the application rate, and their slow release of nutrients makes it difficult to meet the needs of rapid crop growth. The planting and management of green manure crops require specific techniques and experience, are difficult to manage, and have long growth cycles. Biochar production costs are high, making large-scale application difficult, and as an alkaline substance, its application technology in saline-alkali land improvement is not yet mature and requires further research and improvement. Research by Zhao Huili et al. found that applying desulfurized gypsum + straw can significantly increase the proportion of microbial biomass nitrogen and large aggregates; however, desulfurized gypsum contains sulfates, which may exacerbate the inhibition of nitrification, and the addition of straw increases CO2 emissions. Microorganisms in microbial agents can multiply in the soil, thereby improving soil nutrient status, increasing soil enzyme activity, and enhancing microbial diversity, providing a favorable living environment for crop growth. CN 118308114A discloses a biological soil conditioner for improving saline-alkali land and its preparation method. This patent uses citric acid-modified chitosan, biomass carbon nanotubes, mixed straw powder, humic acid, urea, microbial agents, and calcium dihydrogen phosphate to prepare the conditioner, which can effectively regulate soil pH, improve soil microbial activity, and promote the recovery of organic matter. However, the high salt content of saline-alkali soil poses a challenge to the survival and reproduction of microorganisms. Some microbial agents may not be able to survive or function effectively in high-salt environments, thus affecting the improvement effect. Furthermore, the low organic matter content is detrimental to microbial growth and reproduction. Although microbial agents can supplement beneficial bacteria, their effectiveness may be limited in environments lacking organic matter.

[0004] Sweet potato, as an important global food, feed, and industrial raw material crop, is drought-resistant, tolerant of poor soil, and has high biomass, making it one of the preferred crops for adjusting agricultural planting structures in saline-alkali soil areas. However, sweet potato has a threshold for tolerance to salt stress. When the soil salinity exceeds 0.3%, its root development is significantly inhibited, tuber enlargement is hindered, and the content of nutrients such as starch and vitamins in the tubers decreases, resulting in reduced quality. Existing technical solutions for sweet potato cultivation in saline-alkali soils mostly focus on screening salt-tolerant varieties or optimizing cultivation management (such as mulching to control salt and precision irrigation), and have not yet formed an integrated biological solution of "soil improvement-crop growth promotion": on the one hand, the breeding cycle of existing salt-tolerant sweet potato varieties is as long as 5-8 years, and the improvement in salt tolerance is limited, making it difficult to adapt to the stress environment of different types of saline-alkali soils; on the other hand, traditional cultivation management techniques can only alleviate the effects of salt stress and cannot fundamentally repair the soil function of saline-alkali soils. Long-term application will still lead to continuous cropping obstacles and yield fluctuations in sweet potatoes.

[0005] To address the aforementioned issues, while there is some existing research on the synergistic improvement of saline soil by "microorganisms-crops," the relevant microbial communities are mostly broad-spectrum combinations, and there has been no targeted strain screening and functional optimization based on the physiological characteristics of sweet potato and the stress mechanisms of saline soil.

[0006] Therefore, developing a novel composite microbial inoculum with strong salt tolerance, synergistic functions, and high targeting is crucial to effectively reduce salinity in saline soil, improve soil physicochemical and microbial environments, and promote sweet potato root development, tuber formation, and nutrient accumulation. This synergistic effect of saline soil improvement and sweet potato yield increase is a key requirement for addressing the bottleneck in the development of the sweet potato industry in saline soil areas and aligns with the trend of green and sustainable agricultural development. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the present invention aims to provide a compound microbial inoculum for saline soil improvement and crop growth promotion, and its application. Each microbial species in the compound microbial inoculum provided by the present invention has a specific function; through rational compounding, the compound microbial inoculum significantly reduces soil pH, improves soil microbial activity, and increases crop yield.

[0008] To achieve this objective, the present invention adopts the following technical solution:

[0009] In a first aspect, the present invention provides a compound microbial inoculum for improving saline soil and promoting crop growth, the compound microbial inoculum comprising Bacillus amyloliquefaciens S1-13 inoculum, Bacillus thuringiensis SP1-14 inoculum, Pseudomonas putida SE1-6 inoculum and Bacillus paclitaxel RC3-7 inoculum.

[0010] In this invention, Bacillus amyloliquefaciens S1-13 in the composite microbial culture is the core strain, which has the ability to produce ACC deaminase, and can significantly reduce the Na+ level in plants after inoculation. + / K + The Bacillus thuringiensis SP1-14 can significantly enhance the activity of soil N-acetylglucosidase and alkaline phosphatase; the Pseudomonas putida SE1-6 has a certain promoting effect on the activity of soil N-acetylglucosidase and alkaline phosphatase, and has a strong IAA production capacity; the Bacillus paclitaxel RC3-7 has excellent salt tolerance.

[0011] Therefore, each microbial species in the compound microbial solution has a specific function. Through reasonable compounding, the compound microbial solution can reduce soil pH, improve soil microbial activity, and increase crop yield.

[0012] As a preferred technical solution of the present invention, the Bacillus amylolyticus S1-13 is classified as Paenibacillus amylolyticus, deposited at the China General Microbiological Culture Collection Center with accession number CGMCCNo.36206 and deposit date of October 9, 2025.

[0013] Preferably, the Bacillus thuringiensis SP1-14 is classified as Bacillus thuringiensis, deposited at the China General Microbiological Culture Collection Center with accession number CGMCC No. 36207 and deposit date of October 9, 2025;

[0014] Preferably, the *Pseudomonas putida* SE1-6 is classified as *Pseudomonas putida*, deposited at the China General Microbiological Culture Collection Center (CGMCC) with accession number CGMCC No. 36201 and deposit date of October 9, 2025.

[0015] Preferably, the Pacific Bacillus RC3-7 is classified as Bacillus pacificus, deposited at the China General Microbiological Culture Collection Center with accession number CGMCC No. 36202 and deposit date of October 9, 2025.

[0016] The Bacillus amyloliquefaciens S1-13 culture, Bacillus thuringiensis SP1-14 culture, Pseudomonas putida SE1-6 culture, and Bacillus paclitaxel RC3-7 culture described in this invention are all deposited at the China General Microbiological Culture Collection Center, located at No. 3, Courtyard 1, Beichen West Road, Chaoyang District, Beijing, Institute of Microbiology, Chinese Academy of Sciences.

[0017] As a preferred embodiment of the present invention, the volume ratio of the Bacillus amyloliquefaciens S1-13 bacterial suspension, Bacillus thuringiensis SP1-14 bacterial suspension, Pseudomonas putida SE1-6 bacterial suspension, and Bacillus paclitaxel RC3-7 bacterial suspension is 1:1~2:0.8~1.5:0.8~1.5, for example, it can be 1:1:1:1, 1:2:1.2:1.2, 1:1.5:0.8:0.8, 1:1:0.8:1.2, or 1:1:1.5:0.8, etc., but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0018] As a preferred embodiment of the present invention, the effective viable counts of the *Bacillus amyloliquefaciens* S1-13 bacterial suspension, *Bacillus thuringiensis* SP1-14 bacterial suspension, *Pseudomonas putida* SE1-6 bacterial suspension, and *Bacillus paclitaxel* RC3-7 bacterial suspension are all ≥10. 7 cfu / mL.

[0019] As a preferred embodiment of the present invention, the method for preparing the composite microbial culture includes:

[0020] (1) Bacillus amyloliquefaciens S1-13, Bacillus thuringiensis SP1-14, Pseudomonas putida SE1-6 and Bacillus paclitaxel RC3-7 were inoculated into 25 mL of LB liquid medium and cultured at 30 °C and 150 r / min for 24 h to obtain activated seed liquids.

[0021] (2) The activated seed liquid was inoculated into new LB liquid medium at an inoculation rate of 1% and cultured for 24 hours to obtain Bacillus amyloliquefaciens S1-13, Bacillus thuringiensis SP1-14, Pseudomonas putida SE1-6 and Bacillus paclitaxel RC3-7 bacterial solutions, respectively.

[0022] (3) Mix the Bacillus amyloliquefaciens S1-13 bacterial solution, Bacillus thuringiensis SP1-14 bacterial solution, Pseudomonas putida SE1-6 bacterial solution and Bacillus paclitaxel RC3-7 bacterial solution obtained in step (2) evenly to obtain the composite microbial bacterial solution.

[0023] Preferably, the number of viable bacteria in the seed solution in step (1) is not higher than 10. 7 cfu / mL, for example, could be 9 × 10⁻⁶ 6 cfu / mL, 8×10 6 cfu / mL, 7×10 6 cfu / mL, 6×10 6 cfu / mL or 5×10 6 cfu / mL, etc., but not limited to the listed values; other unlisted values ​​within the range also apply.

[0024] Secondly, the present invention provides an application of the composite microbial liquid as provided in the first aspect, wherein the microbial liquid is used to improve saline soil and promote crop growth.

[0025] As a preferred embodiment of the present invention, the application includes: irrigating the compound microbial solution into saline soil in which crops are being propagated.

[0026] Preferably, the procedure before cutting includes: uniformly mixing base fertilizer and saline soil.

[0027] Preferably, the base fertilizer includes urea and potassium sulfate.

[0028] In this invention, the nitrogen content in the urea is 46%, and the potassium sulfate content in the potassium sulfate is 50%.

[0029] Preferably, the molar ratio of N to K2O in the urea and potassium sulfate is 1:0.5 to 1, for example, it can be 1:0.5, 1:0.6, 1:0.7, 1:0.8, 1:0.9 or 1:1, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0030] Preferably, the mass ratio of the base fertilizer to the saline soil is 0.1~0.5:1000.

[0031] Preferably, the irrigation includes irrigating the compound microbial solution at least 5 times after the crop has grown normally for 5 to 7 days.

[0032] Preferably, the interval between two consecutive irrigations is 12 to 16 days, for example, 12, 13, 14, 14, 15 or 16 days.

[0033] Preferably, the amount of compound microbial inoculant solution used for irrigation per crop is 45-55 mL, such as 45 mL, 47 mL, 49 mL, 51 mL, 53 mL or 55 mL, but not limited to the listed values. Other values ​​not listed within the range are also used.

[0034] As a preferred embodiment of the present invention, the process of applying the composite microbial inoculum solution described in the first aspect to saline soil includes the following steps:

[0035] (a) After the saline soil is air-dried and sieved, it is mixed with base fertilizer and then filled into a rectangular plastic pot with a length of 51.5cm, a width of 21.4cm and a height of 25cm. After watering it thoroughly and leaving it for 48 hours, the crop is planted.

[0036] Each pot contains 18 kg of soil and two cuttings of the same size and growth in each pot.

[0037] (b) After the crops have grown normally for 5 to 7 days, irrigate each crop with compound microbial solution at least 5 times;

[0038] The interval between two consecutive irrigations is 12 to 16 days. During this period, water and weed on time, and the plants are placed in a greenhouse for growth. In the later stages, water in a timely and appropriate amount to maintain soil moisture at 60% field capacity.

[0039] As a preferred embodiment of the present invention, the composite microbial solution is used to reduce the pH value of saline soil, increase the nutrient content and microbial activity in saline soil.

[0040] Preferably, the nutrients include organic matter, available nitrogen, available phosphorus, and available potassium.

[0041] Preferably, the microorganisms include β-glucosidase, N-acetylglucosidase, and alkaline phosphatase.

[0042] As a preferred technical solution of the present invention, the compound microbial liquid is used to increase the fresh weight of the aboveground parts, the fresh weight of the underground parts, the vine length and the stem diameter of crops.

[0043] Preferably, the compound microbial inoculum is used to increase the K, P, and N content in crops.

[0044] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0045] Compared with the prior art, the present invention has the following beneficial effects:

[0046] (1) The composite microbial liquid provided by the present invention has the functions of reducing the pH of saline soil, increasing soil nutrient content and microbial activity, and promoting crop growth.

[0047] (2) The compound microbial liquid provided by the present invention has a reasonable combination of various microbial species, each of which has a specific function. Only through the synergistic effect of various microbial species can the improvement of saline soil and the promotion of crop growth be achieved.

[0048] (3) The method of field application of the compound microbial liquid provided by the present invention is simple and is a farmer-friendly microbial fertilizer. Detailed Implementation

[0049] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0050] Example 1

[0051] This embodiment provides a composite microbial culture solution, which includes Bacillus amyloliquefaciens S1-13 culture solution, Bacillus thuringiensis SP1-14 culture solution, Pseudomonas putida SE1-6 culture solution, and Bacillus paclitaxel RC3-7 culture solution.

[0052] The volume ratio of the Bacillus amyloliquefaciens S1-13 bacterial suspension, Bacillus thuringiensis SP1-14 bacterial suspension, Pseudomonas putida SE1-6 bacterial suspension, and Bacillus paclitaxel RC3-7 bacterial suspension is 1:1:1:1.

[0053] The effective viable counts of the Bacillus amyloliquefaciens S1-13 bacterial suspension, Bacillus thuringiensis SP1-14 bacterial suspension, Pseudomonas putida SE1-6 bacterial suspension, and Bacillus paclitaxel RC3-7 bacterial suspension were all 10. 7 cfu / mL.

[0054] The amylolyticus S1-13 is classified as Paenibacillus amylolyticus and is deposited at the China General Microbiological Culture Collection Center (CGMCC) with accession number CGMCC No. 36206 and deposit date of October 9, 2025.

[0055] The Bacillus thuringiensis SP1-14 is classified as Bacillus thuringiensis and is deposited at the China General Microbiological Culture Collection Center (CGMCC) with accession number CGMCC No. 36207 and deposit date of October 9, 2025.

[0056] The *Pseudomonas putida* SE1-6 strain is classified as *Pseudomonas putida* and is deposited at the China General Microbiological Culture Collection Center (CGMCC) with accession number CGMCC No. 36201 on October 9, 2025.

[0057] The Pacific Bacillus RC3-7 is classified as Bacillus pacificus and is deposited at the China General Microbiological Culture Collection Center (CGMCC) with accession number CGMCC No. 36202 on October 9, 2025.

[0058] Example 2

[0059] This embodiment provides a composite microbial culture solution, which includes Bacillus amyloliquefaciens S1-13 culture solution, Bacillus thuringiensis SP1-14 culture solution, Pseudomonas putida SE1-6 culture solution, and Bacillus paclitaxel RC3-7 culture solution.

[0060] The volume ratio of the Bacillus amyloliquefaciens S1-13 bacterial suspension, Bacillus thuringiensis SP1-14 bacterial suspension, Pseudomonas putida SE1-6 bacterial suspension, and Bacillus paclitaxel RC3-7 bacterial suspension is 1:1:0.8:1.5.

[0061] The effective viable counts of the Bacillus amyloliquefaciens S1-13 bacterial suspension, Bacillus thuringiensis SP1-14 bacterial suspension, Pseudomonas putida SE1-6 bacterial suspension, and Bacillus paclitaxel RC3-7 bacterial suspension were all 10. 7 cfu / mL.

[0062] Example 3

[0063] This embodiment provides a composite microbial culture solution, which includes Bacillus amyloliquefaciens S1-13 culture solution, Bacillus thuringiensis SP1-14 culture solution, Pseudomonas putida SE1-6 culture solution, and Bacillus paclitaxel RC3-7 culture solution.

[0064] The volume ratio of the Bacillus amyloliquefaciens S1-13 bacterial suspension, Bacillus thuringiensis SP1-14 bacterial suspension, Pseudomonas putida SE1-6 bacterial suspension, and Bacillus paclitaxel RC3-7 bacterial suspension is 1:2:1.5:0.8.

[0065] The effective viable counts of the Bacillus amyloliquefaciens S1-13 bacterial suspension, Bacillus thuringiensis SP1-14 bacterial suspension, Pseudomonas putida SE1-6 bacterial suspension, and Bacillus paclitaxel RC3-7 bacterial suspension were all 10. 7 cfu / mL.

[0066] Example 4

[0067] This embodiment provides a composite microbial culture solution, which differs from that of Embodiment 1 only in that:

[0068] In this embodiment, the volume ratio of the Bacillus amyloliquefaciens S1-13 bacterial solution, Bacillus thuringiensis SP1-14 bacterial solution, Pseudomonas putida SE1-6 bacterial solution, and Bacillus paclitaxel RC3-7 bacterial solution is adjusted to 1:0.5:0.5:0.5.

[0069] Example 5

[0070] This embodiment provides a composite microbial culture solution, which differs from that of Embodiment 1 only in that:

[0071] In this embodiment, the volume ratio of the Bacillus amyloliquefaciens S1-13 bacterial suspension, Bacillus thuringiensis SP1-14 bacterial suspension, Pseudomonas putida SE1-6 bacterial suspension, and Bacillus paclitaxel RC3-7 bacterial suspension is adjusted to 0.5:1:1:1.

[0072] Example 6

[0073] This embodiment provides a composite microbial culture solution, which differs from that of Embodiment 1 only in that:

[0074] In this embodiment, the volume ratio of the Bacillus amyloliquefaciens S1-13 bacterial solution, Bacillus thuringiensis SP1-14 bacterial solution, Pseudomonas putida SE1-6 bacterial solution, and Bacillus paclitaxel RC3-7 bacterial solution is adjusted to 1:1:2:2.

[0075] Comparative Example 1

[0076] This comparative example provides a composite microbial culture solution, which differs from Example 1 only in that:

[0077] The Bacillus amyloliquefaciens S1-13 bacterial culture was omitted in this comparative example.

[0078] Comparative Example 2

[0079] This comparative example provides a composite microbial culture solution, which differs from Example 1 only in that:

[0080] The Bacillus thuringiensis SP1-14 bacterial culture was omitted in this comparative example.

[0081] Comparative Example 3

[0082] This comparative example provides a composite microbial culture solution, which differs from Example 1 only in that:

[0083] The bacterial suspension of *Pseudomonas putida* SE1-6 was omitted in this comparative example.

[0084] Comparative Example 4

[0085] This comparative example provides a composite microbial culture solution, which differs from Example 1 only in that:

[0086] The *Bacillus paclitaxel* RC3-7 bacterial culture is omitted in this comparative example.

[0087] Application examples

[0088] Pot experiments were conducted using the composite microbial inoculum provided in the above embodiments and comparative examples.

[0089] The saline soil used in the pot experiment was Dongtai Tiaozi soil from Yancheng City, Jiangsu Province (120.937°E, 32.770°N). The soil type was coastal saline soil, with a pH of 9.10, a salt content of 3.16 g / kg, an organic matter content of 2.86 g / kg, a total nitrogen content of 48 mg / kg, an available phosphorus content of 8.55 mg / kg, and a available potassium content of 216 mg / kg.

[0090] The tested plants were salt-tolerant Xushu 51 and sensitive Xushu 32.

[0091] The specific experimental method includes the following steps:

[0092] (a) After the saline soil is air-dried and sieved, it is mixed with base fertilizer and then filled into a rectangular plastic pot with a length of 51.5cm, a width of 21.4cm and a height of 25cm. After watering it thoroughly and leaving it for 48 hours, the crop is planted.

[0093] Each pot contains 18 kg of soil; each pot contains two cuttings of the salt-tolerant Xushu 51 and the sensitive Xushu 32, both of similar growth and size.

[0094] (b) Five days after the crops have grown normally, irrigate each crop with compound microbial solution six times;

[0095] The interval between two consecutive irrigations is 14 days, and the amount of irrigation per crop is 50mL each time. During this period, watering and weeding are carried out on time, and the crops are grown in the greenhouse of the Institute of Agricultural Resources and Environment of Jiangsu Academy of Agricultural Sciences. In the later stage, watering is carried out in a timely and appropriate amount to maintain soil moisture at 60% field capacity.

[0096] In this application example, the blank control group, CK, is defined as the irrigation volume of the compound microbial inoculum solution being 0 mL.

[0097] After 98 days of crop growth, destructive sampling was conducted for soil and crop analysis.

[0098] When the crop is the salt-tolerant Xushu 51, the results of saline soil testing and crop growth testing are shown in Table 1 and Table 2, respectively.

[0099] When the crop is the sensitive Xushu 32, the results of saline soil detection and crop growth detection are shown in Table 3 and Table 4, respectively.

[0100] The saline soil testing items include: soil pH value, organic matter, available nitrogen, available phosphorus and available potassium content, and the activities of β-glucosidase, N-acetylglucosidase and alkaline phosphatase.

[0101] Soil pH was measured using a pH meter after mixing soil and water at a 1:5 ratio; organic matter was determined using the potassium dichromate-external heating method; nitrate nitrogen and ammonium nitrogen were extracted with 2 mol / L potassium chloride solution and then measured using a flow analyzer, with the sum of nitrate nitrogen and ammonium nitrogen being taken as available nitrogen; available phosphorus was determined using the sodium bicarbonate-molybdenum antimony colorimetric method; available potassium was extracted with 1 mol / L ammonium acetate solution and its content was determined using a flame photometer; the activities of β-glucosidase, N-acetylglucosidase, and alkaline phosphatase were determined using different substrates, namely p-nitrobenzene-β-D-glucopyranoside, p-nitrobenzeneacetylglucosidase, and p-nitrobenzene phosphate disodium salt;

[0102] The crop growth monitoring included the determination of aboveground and underground fresh weight, vine length, stem diameter, and K, P, and N content. After washing the plants and blotting off surface moisture with filter paper, they were placed in an oven and blanched at 105℃ for 30 minutes, then dried at 75℃ to constant weight, and the biomass dry weight was measured. Vine length and stem diameter were measured using a ruler and vernier calipers, respectively. The dried aboveground plant samples were pulverized, and total nitrogen, total phosphorus, and total potassium were determined using the H2SO4-H2O2 digestion method.

[0103] Table 1

[0104]

[0105] Table 2

[0106]

[0107] Table 3

[0108]

[0109] Table 4

[0110]

[0111] Based on the data in Tables 1-4, the following points can be observed:

[0112] (1) Comprehensive analysis of Examples 1-3 shows that the compound microbial inoculum provided by the present invention can significantly improve saline soil while promoting crop growth;

[0113] However, compared to the sensitive sweet potato 32, the salt-tolerant sweet potato 51 produced by the compound microbial inoculum provided in this invention is more effective. This is because the ACC deaminase produced by the compound microbial inoculum provided in this invention can enhance the stress resistance of sweet potato cells, improve the osmotic regulation of sweet potatoes, and has the most significant enhancing effect on soluble sugars and soluble proteins, while also improving the resistance to Na+. + / K +It also significantly reduced malondialdehyde and promoted the root growth of crops, thus significantly increasing the root volume and root surface area of ​​salt-tolerant sweet potatoes, affecting the nutrient absorption efficiency of crops, and thus making the dry weight and total nitrogen, phosphorus and potassium accumulation of crops most significant.

[0114] For different crops (salt-tolerant Xushu 51 and sensitive Xushu 32), the compound microbial inoculum provided by this invention has different effects on improving saline soil and promoting crop growth, which further illustrates the specificity of the compound microbial inoculum provided by this invention.

[0115] (2) Comprehensive analysis of Examples 1 and 4-6 shows that if the content of any one of the microbial species in the compound microbial inoculum of the present invention is too high or too low, it will affect the improvement effect of saline soil and the growth promotion ability of crops. This further proves that the content ratio of each microbial species in the compound microbial inoculum is one of the key factors affecting the ability of the microbial community.

[0116] (3) Comprehensive analysis of Example 1 and Comparative Examples 1-4 shows that the lack of any one of the bacterial species in the compound microbial solution cannot achieve the improvement of saline soil, which further illustrates the synergistic effect of each bacterial species in the compound microbial solution of the present invention.

[0117] Furthermore, omitting the solution of Bacillus amyloliquefaciens S1-13 will result in the loss of ACC deaminase production, insufficient decrease in soil pH, weakened crop root resistance, significantly lower increase in aboveground fresh weight, belowground fresh weight and vine length compared to Example 1, and a significant reduction in soil available nitrogen accumulation.

[0118] Omitting the Bacillus thuringiensis SP1-14 bacterial solution will result in limited improvement of soil N-acetylglucosidase and alkaline phosphatase activity, slow growth of organic matter and available phosphorus content, insufficient improvement of crop stem diameter and P content, and overall impact on soil microbial activity activation.

[0119] Omitting the *Pseudomonas putida* SE1-6 bacterial solution will result in a lack of IAA production capacity, leading to a weakened crop growth-promoting effect, sluggish growth of underground fresh weight, insignificant increase in soil available phosphorus content, low β-glucosidase activity, and decreased crop nutrient absorption efficiency.

[0120] Omitting the Bacillus RC3-7 bacterial solution will result in insufficient salt tolerance, inability to adapt to high-salt soil environments, poor effect on reducing soil pH, low accumulation of available potassium, significantly low K content in crops, decreased resistance to salt stress, and limited growth of vines and stems.

[0121] In summary, each microbial species in the compound microbial inoculum provided by this invention has a specific function. Through reasonable compounding, the compound microbial inoculum can significantly reduce soil pH, improve soil microbial activity, and increase crop yield.

[0122] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A compound microbial inoculum for improving saline soil and promoting crop growth, characterized in that, The composite microbial culture includes Bacillus amyloliquefaciens S1-13 culture, Bacillus thuringiensis SP1-14 culture, Pseudomonas putida SE1-6 culture, and Bacillus paclitaxel RC3-7 culture in a volume ratio of 1:1~2:0.8~1.5:0.8~1.

5. The amylolyticus S1-13 is classified as Paenibacillus amylolyticus and is deposited at the China General Microbiological Culture Collection Center (CGMCC) with accession number CGMCC No. 36206 and deposit date of October 9, 2025. The Bacillus thuringiensis SP1-14 is classified as Bacillus thuringiensis and is deposited at the China General Microbiological Culture Collection Center (CGMCC) with accession number CGMCC No. 36207 and deposit date of October 9, 2025. The *Pseudomonas putida* SE1-6 strain is classified as *Pseudomonas putida* and is deposited at the China General Microbiological Culture Collection Center (CGMCC) with accession number CGMCC No. 36201 on October 9, 2025. The Pacific Bacillus RC3-7 is classified as Bacillus pacificus and is deposited at the China General Microbiological Culture Collection Center (CGMCC) with accession number CGMCC No. 36202 and deposit date of October 9, 2025. The effective viable counts of the *Bacillus amyloliquefaciens* S1-13 bacterial suspension, *Bacillus thuringiensis* SP1-14 bacterial suspension, *Pseudomonas putida* SE1-6 bacterial suspension, and *Bacillus paclitaxel* RC3-7 bacterial suspension were all ≥10. 7 cfu / mL.

2. An application of the composite microbial inoculum as described in claim 1, characterized in that, The microbial inoculum is used to improve saline soil and promote crop growth; the crop is sweet potato.

3. The application according to claim 2, characterized in that, The application includes: irrigating the compound microbial inoculum into saline soil in which crops are being propagated; The process before cutting also includes: uniformly mixing base fertilizer and saline soil; The base fertilizer includes urea and potassium sulfate; The molar ratio of N to K2O in the urea and potassium sulfate is 1:0.5~1; The mass ratio of the base fertilizer to the saline soil is 0.1~0.5:1000.

4. The application according to claim 3, characterized in that, The irrigation includes: irrigating the compound microbial solution at least 5 times after the crop has grown normally for 5-7 days; The interval between two consecutive irrigations should be 12 to 16 days. The amount of compound microbial inoculum solution used for irrigation per crop is 45-55 mL.

5. The application according to claim 2, characterized in that, The compound microbial inoculum is used to lower the pH value of saline soil and increase the nutrient content and enzyme activity in saline soil.

6. The application according to claim 5, characterized in that, The nutrients include organic matter, available nitrogen, available phosphorus, and available potassium; The enzymes include β-glucosidase, N-acetylglucosidase, and alkaline phosphatase.

7. The application according to claim 2, characterized in that, The compound microbial inoculum is used to increase the fresh weight of the aboveground parts and the underground parts of the crop, as well as the vine length and stem diameter. The compound microbial inoculum is used to increase the K, P, and N content in crops.

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