Compound microbial agent for promoting crop growth and improving soil and application thereof

Abstract

The invention discloses a compound microbial agent for promoting crop growth and improving soil and application thereof. The compound microbial agent comprises two functional strains and carriers and protective agents thereof. The functional bacterial strains comprise a functional bacterial strain of Bacillus sp. CCNWX2 and a functional bacterial strain of Sinorhizobium sp. CCNWCJ6, and the functional bacterial strain of Bacillus sp. CCNWX2 and the functional bacterial strain of Sinorhizobium sp. CCNWCJ6; the preservation number of the bacillus sp. CCNWX2 in the China General Microbiological Culture Collection Center (CGMCC) is CGMCC No: 19895, and the preservation number of the bacillus sp. CCNWX2 in the China General Microbiological Culture Collection Center (CGMCC) is CGMCC No: 19895. The preservation number of the Sinorhizobium sp. CCNWCJ6 in the China General Microbiological Culture Collection Center (CGMCC) is CGMCC No. 29694, and the preservation number of the Sinorhizobium sp. CCNWCJ6 is CGMCC No. 29694. A carrier and a protective agent of the Bacillus sp. CCNWX2 are respectively corn straw skin powder and egg white powder; a carrier of the Sinoorhizobium sp. CCNWCJ6 is zeolite powder, and a protective agent of the Sinoorhizobium sp. CCNWCJ6 is trehalose. The compound microbial agent is matched with straw returning for use, so that crop growth can be promoted, and soil can be improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of agricultural microorganism technology, and particularly relates to a compound microbial agent for promoting crop growth and improving soil and application thereof. BACKGROUND

[0002] Straw returning to field has shown certain potential in improving soil organic carbon pool, improving soil structure and optimizing nutrient cycling, and has been increasingly valued. At present, the resource utilization of straw and other agricultural wastes is gradually replacing the traditional straw burning treatment through straw returning to field, which not only reduces environmental pollution but also reduces nutrient loss.

[0003] However, in actual operation, there is still the problem of unstable yield increase effect after straw returning to field. Purely relying on straw returning to field often fails to achieve the expected effect, and the practical effect of single straw returning to field is significantly heterogeneous due to differences in crop types and soil environments. For example, the low carbon-nitrogen ratio (<30:1) of legume straw is more prone to decomposition and release of available nitrogen, while the high cellulose content (>40%) of corn straw may delay the decomposition process, resulting in a lag in nutrient release in the subsequent crop season. This difference is more complex in a rotation system - the type of straw buried before winter wheat planting directly affects the soil microenvironment of the summer maize / soybean intercropping system. Existing researches mostly focus on the local effect of a single season or a single crop, and lack of systematic analysis of the cross-crop, multi-crop synergistic process.

[0004] The introduction of plant growth-promoting rhizobacteria (PGPR) provides a new way to reduce the limitations of straw returning to field and the instability of yield increase effect. Cellulose-degrading bacteria can secrete endoglucanase and xylanase to accelerate the hydrolysis of recalcitrant polysaccharides in straw. At the same time, the symbiotic nitrogen fixation of Sinorhizobium meliloti with legume crops can supplement soil nitrogen. The combination of straw returning to field and microbial technology helps to build a more efficient soil improvement system. However, current microbial agent researches mostly use single strain or single functional bacterial line laboratory simulation, ignoring the microbial community interaction and functional synergy in complex field environment. For example, soil porosity, water infiltration rate and other physical properties can significantly affect the colonization efficiency of microbial agents at the straw-soil interface, and the regulation mechanism of different straw types (such as carbon-nitrogen ratio, lignin content) on microbial metabolic pathways has not been clearly defined.

[0005] In terms of planting patterns, corn / soybean intercropping has been proven to improve resource use efficiency through root complementarity and light energy utilization optimization, but its synergistic potential with straw inoculant has not been fully explored. Studies have shown that the dense root system of corn can form a physical barrier to slow down soil organic carbon mineralization, while the deep straight root system of soybean promotes the activation of deep nutrients, which may provide a differentiated niche for growth-promoting bacteria. However, existing field test designs are mostly limited to single-season crops or a single treatment factor, making it difficult to reveal the dynamic process of multi-factor interactions. For example, mixed straw return (corn + soybean) in the winter wheat season may change the soil microbial community structure (such as an increase in actinomycete abundance by 15%-22%), indirectly affecting the nodulation efficiency of Bradyrhizobium japonicum in the summer intercropping system.

[0006] In recent years, with the wide application of microbial technology in agricultural yield increase, soil remediation, and waste resource utilization, the efficient preparation, long-term stability, and easy storage and transportation of solid microbial inoculants have become the focus of research. Compared with liquid inoculants, solid inoculants significantly improve the survival rate of microorganisms under storage and environmental stress through the dual mechanisms of physical adsorption and chemical protection, while reducing the cost of transportation and application. In the method of microbial immobilization, adsorption is favored due to its simple operation, little effect on microbial activity, and easy scalability. This method fixes microorganisms in porous materials through physical adsorption or chemical bonding on the surface of the carrier, which not only preserves the metabolic activity of the bacterial cells but also enhances their tolerance to environmental stress. However, the adsorption performance of the carrier, the molecular mechanism of the protective agent, and the adaptability of the drying process are still the core factors that constrain the function of the inoculant. SUMMARY

[0007] The present application aims to address the technical bottlenecks of existing microbial inoculants in straw application, such as single function, poor strain synergy, and poor field stability. A composite microbial inoculant for promoting crop growth and improving soil is provided, which can fully exert the synergistic function of Bacillus sp. CCNWX2 and Sinorhizobium sp. CCNWCJ6. It achieves the synergistic promotion of efficient straw degradation, soil quality improvement, and crop yield increase, providing new technical support for sustainable agricultural development.

[0008] To achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows: A composite microbial inoculant for promoting crop growth and improving soil, characterized in that: the composite microbial inoculant comprises two functional strains and their carriers and protective agents; the functional strains include Bacillus sp. CCNWX2 and Sinorhizobium sp. CCNWCJ6. BacillusThe preservation number of Bacillus sp. CCNWX2 in the China General Microbiological Culture Collection Center (CGMCC) is CGMCC No: 19895; Sinorhizobium The preservation number of Bacillus sp. CCNWCJ6 in the China General Microbiological Culture Collection Center (CGMCC) is CGMCC No. 29694; Bacillus The carrier and protective agent of Bacillus sp. CCNWX2 are corn stalk skin powder and egg white powder, respectively; Sinorhizobium The carrier and protective agent of Bacillus sp. CCNWCJ6 are zeolite powder and trehalose, respectively.

[0009] The addition ratio of corn stalk skin powder and egg white powder is 12.6% (w / v) and 5.4% (w / v), and the addition ratio of zeolite powder and trehalose is 10.8% (w / v) and 4.7% (w / v).

[0010] The two bacteria are compounded, and the viable cell count ratio of Bacillus sp. CCNWX2 and Bacillus sp. CCNWCJ6 is 1:1. Bacillus The two bacteria are compounded, and the viable cell count ratio of Bacillus sp. CCNWX2 and Bacillus sp. CCNWCJ6 is 1:1. Sinorhizobium The two bacteria are compounded, and the viable cell count ratio of Bacillus sp. CCNWX2 and Bacillus sp. CCNWCJ6 is 1:1.

[0011] According to the application of any of the composite microbial agents, the composite microbial agents are used in combination with straw returning to promote crop growth and improve soil.

[0012] The composite microbial agents are applied to corn-soybean intercropping and straw returning systems, and compared with the control, the composite microbial agents increase the yield of corn and wheat in field tests, and improve the organic matter and nutrient level of soil. When the composite microbial agents are applied to corn-soybean intercropping and straw returning systems, the yield of wheat is increased by 17.2%, the yield of corn is increased by 13.3%, the pod number per plant of soybean is increased by 28%, and the organic carbon content of soil is increased by 29.5%.

[0013] The beneficial effects of the present application are: High specificity: the optimal carrier-protective agent combination for two different functional strains is found, solving the problem that it is difficult for each strain in the composite microbial agent to maintain high activity at the same time.

[0014] High survival rate of viable cells: through scientific optimization, the survival rate of the two strains after freeze-drying is as high as 85% or more, significantly improving the product quality of the microbial agent.

[0015] Good stability: the optimized solid microbial agent is convenient for storage and transportation, prolonging the shelf life and being conducive to industrial application.

[0016] Synergistic effect: Combining the compound microbial agent of this invention with straw return technology, field experiments have confirmed that it can significantly promote crop growth, increase yield and improve soil, achieving a highly efficient synergy of "microorganism-organic matter-planting model".

[0017] This invention, based on the principles of resource utilization and functional complementarity, screens a protection strategy that combines corn stalk outer husk powder (natural organic carrier), corn stalk biochar (biological carrier), and zeolite powder (inorganic carrier) with egg white powder (protein protectant), potato starch (polysaccharide protectant), and trehalose (sugar protectant). Combined with vacuum freeze-drying technology, the microbial agent formulation is systematically optimized to achieve a synergistic improvement in microbial activity and stability. Simultaneously, using a typical crop rotation area in the Guanzhong Plain (Lintong District, Xi'an City) as an experimental base, a wheat-corn / soybean year-round rotation system is constructed, integrating a three-factor split-plot design and process monitoring. This is achieved by setting up winter treatments involving the return of soybean straw, corn straw, and mixed straw to the field, and coordinating... Bacillus The application of sp. CCNWX2 inoculant was systematically analyzed to determine the effects of straw type and inoculant interaction on soil physicochemical properties; *Rhizobium sinense* was further introduced in summer. Sinorhizobium Treatments of sp. CCNWCJ6 alone and in combination with growth-promoting bacteria, combined with monoculture and intercropping planting patterns, elucidate the synergistic effect of bacterial agent compatibility and planting structure. Attached Figure Description

[0018] Figure 1 Different carrier-protectant combinations for cellulose-degrading bacteria Bacillus The effect of sp.CCNWX2 on the viable count of freeze-dried bacteria, the error bar represents the standard deviation (n=3), and different letters indicate significant differences between groups. p <0.05); Figure 2 For the type of carrier and the type of protective agent Bacillus The interaction of viable cell rate of sp. CCNWX2 was shown to be significant in two-way ANOVA. p =0.0038); Figure 3 Different carrier-protectant combinations for the effects of Rhizobium sinense Sinorhizobium The effect of sp. CCNWCJ6 on viable cell rate after freeze-drying: different letters in each group indicate significant differences between treatments. p <0.05); Figure 4 For the type of carrier and the type of protectant, the Chinese rhizobium Sinorhizobium The interaction of viability of sp. CCNWCJ6; Figure 5 The effect of adding corn husk powder and egg white powder on cellulose-degrading bacteria BacillusResponse surface (a) and contour (b) of viable cell density of sp. CCNWX2 Figure 6 Response surface (a) and contour (b) of viable cell density of sp. CCNWCJ6 Sinorhizobium Figure 7 Wheat yield index, (a) is wheat single ear weight (b) is wheat thousand seed weight, K is straw non-returning field without adding bacteria treatment, L is straw non-returning field with adding bacteria treatment, M is straw returning field without adding bacteria treatment, N is straw returning field with adding bacteria treatment. Different letters in each group of different treatments represent significant difference between treatments p <0.05 Figure 8 Maize seed yield, DK is straw non-returning field without adding bacteria treatment, DL is straw non-returning field with adding bacteria treatment, DM is straw returning field without adding bacteria treatment, DN is straw returning field with adding bacteria treatment. Different letters in each group of different treatments represent significant difference between treatments p <0.05 Figure 9 Soybean pod setting characteristics and grain yield, (a) is soybean effective pod number (b) is soybean hundred seed weight, DK is straw non-returning field without adding bacteria treatment, DL is straw non-returning field with adding bacteria treatment, DM is straw returning field without adding bacteria treatment, DN is straw returning field with adding bacteria treatment. Different letters in each group of different treatments represent significant difference between treatments p <0.05 DETAILED DESCRIPTION

[0019] The application will be described in detail below in combination with specific examples.

[0020] Example 1 Sinorhizobium Isolation, purification and screening of sp. CCNWCJ6 1. Sample collection: In early April 2009, soybean variety "Zhonghuang 13" was planted in a test field in Yangling District, Shaanxi Province (34° 16' N, 108° 4' E). In June of the same year, 3 healthy plants were selected and the complete root system was dug up and quickly taken back to the laboratory for treatment.

[0021] 2. Medium formula: 1) Beef extract peptone medium: beef extract 3.0 g, peptone 10.0 g, NaCl 5.0 g, agar 18-20 g, water 1000 mL, pH 7.2-7.4, 121°C sterilization for 20 min.

[0022] ​2) YMA medium: Mannitol 10.0 g, K2HPO4 0.5 g, MgSO4·7H2O 0.2 g, NaCl 0.1 g, 1% yeast extract 100 mL, CaCO3 3.0 g, agar 18-20 g, distilled water 900 mL, sterilized at 121°C for 20 min.

[0023] 3) YM medium: Mannitol 10.0 g, K2HPO4 0.5 g, MgSO4·7H2O 0.2 g, NaCl 0.1 g, 1% yeast extract 100 mL, CaCO3 3.0 g, distilled water 900 mL, sterilized at 121°C for 20 min.

[0024] 4) Nitrogen-free medium: K2HPO4 0.5 g, Ca3(PO4)2 2.0 g, MgSO4·7H2O 0.2 g, NaCl 0.1 g, FeCl3 0.01 g, distilled water 1000 mL.

[0025] 3. Isolation and purification of strains 1. Isolation of rhizosphere strains from nodule surface After shaking off the soil on the root, the full nodule was picked up with sterile forceps and washed with sterile water for 3 times (3 min each time) to remove the loosely attached bacteria on the surface. The nodule was placed in a flask containing glass beads and 0.7% NaCl solution and shaken at 150 rpm for 1 hour at 28°C. The suspension was diluted and spread on beef extract peptone agar medium and incubated at 28°C for 2-7 days. The rhizosphere strains on the nodule surface were picked up according to the colony morphology and purified.

[0026] 2. Isolation and purification of rhizobium The washed nodules were surface sterilized by 75% ethanol for 30 seconds and 1% sodium hypochlorite for 4 minutes, and washed with sterile water for 6 times. The 59 nodules were squeezed with sterile forceps and the squeezed liquid was spread on YMA medium and incubated at 28°C for 3-15 days. The rhizobium strains were preliminarily screened according to the colony morphology and single colonies were obtained by purification.

[0027] 3. Verification of re-inoculation nodulation Vermiculite and perlite were mixed at a ratio of 2:1 and sterilized at 121°C for 1.5 hours. The surface of soybean seeds was sterilized and placed on 1.2% water agar plates and germinated in the dark at 28°C for 3 days. Healthy germinated seeds were selected and transplanted into the planting bags (2 seeds per bag), irrigated with 150 mL of nitrogen-free nutrient solution, and grown in a culture room with 14 hours of light per day. One plant per bag was retained after the cotyledon unfolded.

[0028] The isolated strains were cultured in YM liquid medium at 28°C and 150 rpm for 3 days, centrifuged to collect the bacterial cells, resuspended in 0.7% NaCl to OD 600≈ 0.55 (about 10 8 -10 9 cfu / mL). Each plant was irrigated with 1 mL bacterial suspension, with 3 replicates, and sterile NaCl solution as control. 150 mL nitrogen-free nutrient solution was supplemented every 10 days after inoculation, and the nodule number was counted after 30 days. The strains with more nodules were purified again and stored.

[0029] 4. Strain identification and property analysis A total of 126 strains of rhizobium were isolated from root nodules, and strains with good nodule effect were screened by re-inoculation test (as shown in Table 1). Among them, strain L5-1 had a nodule number of 28 per plant, showing the best performance. Through 16S rRNA gene RFLP analysis and sequence alignment, the similarity of this strain with Sinorhizobium americanum CFNEI 156 (AF506513), S. fredii ATCC 35423 (D14516) and S. soyae CCBAU 05684 (GU593061) was 99.20%, 99.06% and 98.96 respectively, and it was identified as Sinorhizobium sp., named Sinorhizobium sp. CCNWCJ6, and the 16S rDNA sequence was submitted to GenBank (accession number KF735789).

[0030] Table 1. Nodule number of rhizobium re-inoculation

[0031] The values in the table are "mean ± standard error", n = 3.

[0032] The strain CCNWCJ6 was preserved in the China General Microbiological Culture Collection Center (CGMCC) on January 22, 2024, with the preservation number CGMCC No: 29694. The preservation address is: No. 3, Institute of Microbiology, Chinese Academy of Sciences, Beijing City, Chaoyang District, Beichen West Road 1st Courtyard 3rd.

[0033] Bacillus The isolation, purification and identification of sp. CCNWX2 are described in the patent CN202010807861.6; the strain was preserved in the China General Microbiological Culture Collection Center (CGMCC) on June 1, 2020, with the preservation number CGMCC No: 19895. The preservation address is: No. 3, Institute of Microbiology, Chinese Academy of Sciences, Beijing City, Chaoyang District, Beichen West Road 1st Courtyard 3rd.

[0034] Example 2: Screening of carrier and protective agent combination Material preparation: The carriers (corn stalk husk powder, corn stalk biochar, zeolite powder) and protectants (egg white powder, potato starch, trehalose) were dried, passed through a 100-mesh sieve, and sterilized for use.

[0035] Bacterial liquid preparation: Bacillus sp. CCNWX2 and Sinorhizobium sp. CCNWCJ6 were centrifuged after liquid fermentation, and the bacterial bodies were resuspended in sterile normal saline to OD 600 ≈0.55 (about 10 8 -10 9 CFU / mL).

[0036] Screening experiment: According to Table 2, 10% carriers and 5% protectants (w / v) were added to the bacterial suspensions of the two strains in nine combinations. After 4 hours of shaking adsorption at 28°C, samples were taken for viable cell counting (recorded as N0). The remaining samples were pre-frozen at -80°C and then vacuum freeze-dried (-40~-50°C, 0.02-0.04 mbar).

[0037] Table 2 Combination of bacterial agent carriers and protectants

[0038] Result calculation: After freeze-drying, the samples were reconstituted and viable cell counting was performed (recorded as N1). Freeze-drying survival rate (%) = (N1 / N0) x 100%.

[0039] Experimental results: Bacillus sp. CCNWX2: The best combination was corn husk powder + egg white powder, with a survival rate of 87.44±4.18% (see Table 3 / 2). Figure 1 / 2).

[0040] Sinorhizobium sp. CCNWCJ6: The best combination was zeolite powder + trehalose, with a survival rate of 85.67±2.86% (see Table 3 / 4). Figure 3 / 4).

[0041] Two-factor variance analysis confirmed that the effects of carriers, protectants, and their interactions were extremely significant (P<0.05). p <0.05).

[0042] Example 3: Optimization of the addition ratio of carriers and protectants (response surface method) Experimental design: Based on the results of Example 1, the cellulose-degrading bacteria Bacillus sp. CCNWX2 and rhizobium SinorhizobiumA two-factor three-level central composite design (CCD) experiment (Tables 3 and 4) was performed on sp. CCNWX2 and sp. CCNWCJ6. The experiment included 13 groups of treatments (including central point repeats), each repeated 3 times, and the protective effect was characterized by measuring the viable cell count, the non-linear relationship of synergistic effect was explored, and the addition amount of the two was optimized to obtain the highest viable cell rate.

[0043]

[0044] Model establishment and verification: The viable cell rate was used as the response value, and Design-Expert software was used for quadratic polynomial model fitting.

[0045] Bacillus sp. CCNWX2: The model equation is Y=87.26+2.17A+0.4525AB-5.49A 2 . The model is extremely significant ( p =0.0015), and the lack-of-fit term is not significant ( p =0.4298), R²=0.9099.

[0046] Sinorhizobium sp. CCNWCJ6: The model equation is Y=87.30-1.87B-6.16A 2 -8.99B 2 . The model is extremely significant ( p <0.0001), and the lack-of-fit term is not significant ( p =0.1428), R²=0.9664.

[0047] Optimal solution prediction: Bacillus sp. CCNWX2: The theoretical optimal point is corn husk powder 12.6%, egg white powder 5.4%, and the predicted viable cell rate is 89.70% (see Figure 5 ).

[0048] Sinorhizobium sp. CCNWCJ6: The theoretical optimal point is zeolite powder 10.8%, trehalose 4.7%, and the predicted viable cell rate is 88.94% (see Figure 6 ).

[0049] The above experimental results show that, through the specific formulation and preparation method provided by the present application, the activity of sp. CCNWX2 and sp. CCNWCJ6 can be efficiently immobilized and stably preserved for a long time, so that the solid bacterial agent prepared subsequently can maximize the functional activity of the original bacterial solution, and provides a fundamental guarantee for realizing an application effect equivalent to field bacterial solution testing. Bacillus sp. CCNWX2 and Sinorhizobium sp. CCNWCJ6 can be efficiently immobilized and stably preserved for a long time, so that the solid bacterial agent prepared subsequently can maximize the functional activity of the original bacterial solution, and provides a fundamental guarantee for realizing an application effect equivalent to field bacterial solution testing.

[0050] Example 4: Preparation and field application of complex microbial agent Complex microbial agent: The optimal carrier and protective agent in Example 3 were used: Bacillus sp. CCNWX2: Corn husk powder 12.6%, egg white powder 5.4%. Sinorhizobium sp. CCNWCJ6: Zeolite powder 10.8%, trehalose 4.7%. The bacterial solutions of the two strains were physically mixed at a ratio of 1:1 in terms of viable bacterial count to obtain the final complex microbial solid agent.

[0051] Field application: 1) Test area overview A one-year field test was conducted in Guanzhuang Village, Hezhai Street, Lintong District, Xi'an City, Shaanxi Province (34°30'19"N, 109°14'35"E) from October 2023 to September 2024. The region is in a warm temperate semi-humid monsoon climate, with an average annual temperature of 13.5°C, an annual precipitation of 580 mm, and a frost-free period of 216 days. The test site is a brown soil developed from loess parent material, with flat terrain and good irrigation conditions, meeting the requirements of dryland agricultural testing.

[0052] 2) Test design The test design covers a wheat-corn / soybean annual rotation system, with two seasons of field testing (2023-2024 winter wheat season and 2023 summer corn / soybean season). The split-plot design method was used to study the multi-factor interaction effects of straw type, microbial agent compatibility, and planting mode.

[0053] Winter wheat planting season test: The test used a three-factor split-plot design, with the main zone factor being straw type (A), the sub-zone factor being whether to return straw (B) and whether to apply microbial agent (C). Factor A (main treatment): 3 levels - full amount of soybean straw returned (dry weight 4.2 t / ha), full amount of corn straw returned (4.2 t / ha), and mixed corn + soybean straw returned (full amount of soybean + full amount of corn); Factor B (sub-treatment one): straw returned (buried to a depth of 20 cm) and not returned (removing surface straw); Factor C (sub-treatment two): applying Sinorhizobium sp. CCNWCJ6 + cellulose-degrading bacteria Sinorhizobium sp. CCNWCJ6 + cellulose-degrading bacteria Bacillussp. CCNWX21:1 inoculant (effective viable cell number ≥ 1 x 108 CFU / mL) and no inoculant. Each treatment was repeated 3 times, forming 3 block groups x 3 repetitions x 2 B treatments x 2 C treatments = 36 plots. The area of a single plot was 11 m x 10 m (110 m2). The total area of each test plot group was 110 x 2 x 2 x 3 = 1320 m2, and the total area of the test plot was 1320 x 3 = 3960 m2. Each plot was provided with a 1.6 m left and right protective row in the north-south direction, and a 2 m protective row in the east-west direction. The total area of the test plot was about 7.56 mu. The inoculant was diluted 50 times according to 0.5% of the straw weight, and then evenly sprayed on the surface of the straw. After rotary tillage, wheat was sown, and disease and pest control was carried out according to local conventional management measures.

[0054] Summer corn / soybean planting season test: The wheat season test was continued, and a three-factor split plot design was set up in the summer. The main zone factor was planting mode (A), the sub-zone factor was whether the straw was returned to the field (B) and the type of inoculant (C). Factor A (main treatment): single corn, single soybean, corn / soybean intercropping factor B (sub-treatment one): wheat season straw left in place, removed straw factor C (sub-treatment two): two kinds of inoculant treatment were set up - no inoculant (CK), mixed inoculant (Sinorhizobium sp. CCNWCJ6 + cellulose-degrading bacteria Sinorhizobium Sinorhizobium sp. CCNWCJ6 + cellulose-degrading bacteria Bacillus Sinorhizobium sp. CCNWX21:1). A total of 3 block groups x 3 repetitions x 2 B treatments x 2 C treatments = 36 plots were formed, and the area of a single plot was 11 m x 10 m (110 m2). The amount of inoculant spraying was the same as that of the wheat season.

[0055] In the wheat-corn / soybean annual rotation system, the composite inoculant was applied in combination with straw return. The results showed that the yield of wheat increased by 17.2% (see Figure 7 ), the yield of intercropped corn increased by 13.3% (see Figure 8 ), and the number of pods per plant of soybean increased by 28% (see Figure 9 ). Soil nutrient analysis showed that the organic carbon content increased by 29.5%, and the total nitrogen, available potassium and total phosphorus contents were significantly improved.

[0056] It should be understood that improvements and modifications can be made to the above specification by those of ordinary skill in the art without departing from the scope of the present application, and all such improvements and modifications shall fall within the scope of the appended claims of the present application.

Claims

1. A complex microbial inoculant for promoting crop growth and improving soil, characterized in that: The complex microbial agent comprises two functional strains and carriers and protective agents of the functional strains. Bacillus the functional strains of Bacillus sp. CCNWX2 and Sinorhizobium Bacillus sp. CCNWCJ6; Bacillus The preservation number of Bacillus sp. CCNWX2 in the China General Microbiological Culture Collection Center (CGMCC) is CGMCC No: 19895; Sinorhizobium The preservation number of Bacillus sp. CCNWCJ6 in the China General Microbiological Culture Collection Center (CGMCC) is CGMCC No. 29694; Bacillus The carrier and protective agent of Bacillus sp. CCNWX2 are corn straw skin powder and egg white powder respectively; Sinorhizobium The carrier and protective agent of Bacillus sp. CCNWCJ6 are zeolite powder and trehalose respectively.

2. The complex microbial agent according to claim 1, characterized by, The adding ratio of the corn stalk husk powder and egg white powder is 12.6% (w / v) and 5.4% (w / v), and the adding ratio of zeolite powder and trehalose is 10.8% (w / v) and 4.7% (w / v).

3. The complex microbial agent according to claim 1, characterized by, The two bacteria are compounded in a ratio of 1:1 of the viable cell number of Bacillus sp. CCNWX2 and Sinorhizobium sp. CCNWCJ6.

4. The use of the complex microbial agent according to any one of claims 1 to 3, characterized in that, The complex microbial agent is used in combination with straw returning to field to promote crop growth and improve soil.

5. Use according to claim 4, characterized in that, The complex microbial agent is applied to corn-soybean intercropping system and straw returning system.

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