A composite microbial soil conditioner for saline-alkali soil, its preparation method and application

Abstract

This invention relates to a composite microbial saline-alkali soil conditioner, its preparation method, and its application, belonging to the field of saline-alkali soil improvement technology. The composite microbial saline-alkali soil conditioner of this invention comprises the following raw materials: tailings-based organic matter complex, microbial compound inoculant, and ammonium sulfate; the raw materials of the tailings-based organic matter complex include iron tailings and earthworm castings organic fertilizer; the raw materials of the microbial compound inoculant include rhizosphere Coccidioides and Bacillus subtilis. This invention prepares a composite microbial saline-alkali soil conditioner using tailings-based organic matter complex, microbial compound inoculant, and ammonium sulfate. This not only reduces the pH value and salinity of saline-alkali land, but also increases soil aggregates and improves soil structure through the cementing effect of microorganisms, organic fertilizer, and mineral particles, thus improving the compaction state of saline-alkali land, enhancing water and fertilizer retention capacity, and significantly improving the soil ecological environment.

Description

Technical Field

[0001] This invention relates to the field of saline-alkali soil improvement technology, specifically to a composite microbial saline-alkali soil conditioner, its preparation method, and its application. Background Technology

[0002] Currently, internationally recognized methods for improving saline-alkali soils include hydraulic engineering and agricultural remediation, as well as chemical and biological methods. However, these methods inevitably have some drawbacks. Drainage helps lower the water table, but it is costly. Using fresh water to suppress salts is beneficial for transferring salts from plant root zones to deeper soil layers, but it is difficult to implement in areas where fresh water is scarce. Chemical reagents can react with certain types of salts and remove them from the soil, but this method is expensive and may lead to other negative environmental consequences. Breeding and genetically modifying salt-tolerant plants in saline-alkali soils is time-consuming and technically costly. Therefore, there is a need for green improvement technologies that are widely available, inexpensive, easy to operate, and effective, tailored to local conditions, to improve the quality of saline-alkali soils.

[0003] In recent years, the main patents for improving saline-alkali land using iron tailings composite microorganisms include CN111057556A, CN111117639A, CN117050913A, CN111117638A, CN111117639A, CN118222292A, and CN119020198A. Most of them focus on single indicators of vegetation growth or soil, and do not fully consider the role of iron tailings trace elements in the improvement of saline-alkali soil and soil fertility, ignoring the synergistic effect of "amendant-soil-plant". Summary of the Invention

[0004] The technical problem to be solved by this invention is to provide a composite microbial saline-alkali soil conditioner, its preparation method, and its application. The composite microbial saline-alkali soil conditioner prepared by this invention can not only lower the pH value and salinity of saline-alkali land, but also increase soil aggregates through the cementing effect of microorganisms with organic fertilizers and mineral particles, improving soil structure, mitigating soil compaction, enhancing water and fertilizer retention capacity, and significantly improving the soil ecological environment.

[0005] The technical solution of the present invention to solve the above-mentioned technical problems is as follows:

[0006] The first objective of this invention is to provide a composite microbial saline-alkali soil conditioner, which comprises the following raw materials: tailings-based organic matter complex, microbial composite inoculant, and ammonium sulfate;

[0007] The raw materials for the tailings-based organic matter complex include iron tailings and earthworm castings organic fertilizer;

[0008] The raw materials for the microbial compound inoculant include rhizosphere cocci and Bacillus subtilis. The rhizosphere cocci is ACCC 60042, purchased from Beijing Dahonglihui Biotechnology Center; furthermore, the Bacillus subtilis is ACCC 19742, also purchased from Beijing Dahonglihui Biotechnology Center.

[0009] The beneficial effects of this invention are as follows: The raw materials of the compound microbial saline-alkali soil conditioner of this invention include iron tailings minerals, earthworm castings organic fertilizer, microbial compound inoculants, and ammonium sulfate. It can not only reduce the pH value of saline-alkali land and reduce its salinity, but also increase soil aggregates through the cementing effect of microorganisms, organic fertilizer, and mineral particles, improve soil structure, improve the compaction state of saline-alkali land, enhance water and fertilizer retention capacity, and greatly improve the soil ecological environment.

[0010] The beneficial effects of adopting the above-mentioned further scheme are as follows: Bacillus subtilis and rhizosphere cokrysii are beneficial plant microorganisms that can alleviate abiotic stresses such as drought and salinity, effectively inhibit various plant pathogens, and, through their metabolic activities, fully interact with the biochar and nitrogen fertilizers in the invention to improve soil structure and enhance soil fertility, thereby providing a better growth environment for plants. Furthermore, the rhizosphere cokrysii selected is ACCC 60042, isolated from high-salt and alkaline environments, which can promote the dissolution and precipitation of minerals such as Fe, Si, and K in iron tailings.

[0011] Furthermore, the ratio of the tailings-based organic matter complex, the microbial compound agent, and the ammonium sulfate is 15g~20g:3ml~5ml:2g~4g.

[0012] The beneficial effects of adopting the above-mentioned further scheme are as follows: through the reasonable ratio and proper treatment of iron tailings minerals, earthworm castings organic fertilizer, microbial compound inoculants, and ammonium sulfate, not only can the pH value of saline-alkali land be reduced and its salinity be decreased, but also the soil aggregates are increased through the cementing effect of microorganisms, organic fertilizer, and mineral particles, the soil structure is improved, the compaction of saline-alkali land is improved, the water and fertilizer retention capacity is enhanced, and the soil ecological environment is greatly improved.

[0013] Furthermore, the effective viable concentration of Bacillus subtilis in the microbial compound inoculant is 4 × 10⁻⁶. 7 ~9×10 7 CFU / mL; the effective viable concentration of *Coccobacillus rhizosphereus* in the microbial compound agent is 4 × 10⁻⁶ CFU / mL; 7 ~9×10 7 CFU / mL.

[0014] Furthermore, the volume ratio of the rhizosphere Cochlea to the Bacillus subtilis is 1~2:1~2.

[0015] Furthermore, the water content of the tailings-based organic matter complex is ≤8%.

[0016] Furthermore, the mass ratio of the iron tailings to the earthworm castings organic fertilizer is 15~20:2~3.

[0017] Furthermore, the raw materials of the earthworm casting organic fertilizer include earthworm castings and biochar; the mass ratio of the earthworm castings to the biochar is 6~7:3~4.

[0018] Furthermore, the volume ratio of the rhizosphere Cochlea to the Bacillus subtilis is 1~2:1~2.

[0019] The second objective of this invention is to provide a method for preparing a composite microbial saline-alkali soil conditioner, comprising the following steps: mixing tailings-based organic matter complex with microbial composite inoculants and ammonium sulfate to obtain the composite microbial saline-alkali soil conditioner.

[0020] The beneficial effects of this invention are as follows: Based on the fully aged treatment of readily available and low-cost mineral solid waste and biochar, this invention fully considers improving the dissociation of various minerals in iron tailings and the salt and alkali tolerance of vegetation. It combines Bacillus subtilis and rhizosphere Coccidia, and the process is simple. Starting from the synergistic approach of "amendrant optimization - soil improvement - plant growth", it improves the dissolution and precipitation of minerals such as Fe, Si, and K in iron tailings, increases soil aggregate structure, improves the ecological environment of saline-alkali land, and optimizes the conditions for plant colonization and growth, providing a new approach for the green recycling of bulk mining waste and the improvement of saline-alkali soil.

[0021] Furthermore, the preparation steps of the tailings-based organic matter complex are as follows:

[0022] Earthworm castings and biochar are mixed to obtain earthworm castings organic fertilizer; iron tailings and earthworm castings organic fertilizer are then mixed, composted, and aged to obtain tailings-based organic matter complex.

[0023] Furthermore, the temperature for mixed composting is 30~40℃, and the time is 2~3 days.

[0024] The third objective of this invention is to provide an application of a compound microbial saline-alkali soil conditioner, which is used in the improvement of saline-alkali soil.

[0025] The beneficial effects of this invention are: the compound microbial saline-alkali soil conditioner prepared by this invention improves saline-alkali soil, enhances its fertility, improves the saline-alkali land ecosystem, provides a good habitat for plant growth, and improves plant quality.

[0026] Furthermore, the saline-alkali soil includes at least one of coastal saline-alkali land, inland saline-alkali land, and secondary salinized soil. Attached Figure Description

[0027] Figure 1 These are spinach plants in each pot after 45 days of planting, as shown in Experiment 1 of this invention. Detailed Implementation

[0028] The principles and features of this invention are described below. The examples given are for illustrative purposes only and are not intended to limit the scope of the invention. Where specific techniques or conditions are not specified in the embodiments, they should be performed according to the techniques or conditions described in the literature in this field, or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased through legitimate channels.

[0029] The earthworm castings and biochar used in this invention are commercially available products with a biochar content of ≥45%, total nutrients (N+P2O5+K2O) ≥5%, and moisture content ≤30%, which meet the national organic fertilizer standard (NY 525-2021).

[0030] Biochar is produced by pyrolysis of agricultural waste under limited oxygen conditions. It has a carbon content of ≥60%, an ash content of ≤20%, a pH value of 7.0~9.0, and a particle size of 0.5~2.0 mm.

[0031] The iron tailings were provided by Hebei Iron and Steel Group Sijiaying Yanshan Iron Mine Co., Ltd. The major components of the iron tailings were analyzed by X-ray fluorescence spectrometry (XRF) using an X-ray fluorescence spectrometer (ZSX Primus II 03030429; Rigaku Corporation, Japan). Trace elements As and Hg were determined by inductively coupled plasma optical emission spectrometry (ICP-OES) using an ICAP-7400 (Thermo Fisher Scientific). Pb, Cd, and Cr were determined by atomic absorption spectrometry (AAS) using a graphite furnace atomizer (GFA-6880; Shimadzu Instruments (Suzhou) Co., Ltd.) and an atomic absorption spectrophotometer (AA-6880; Shimadzu). The particle size distribution of the iron tailings was determined by sieve analysis. The main components, toxic elements, and particle size distribution are shown in Tables 1, 2, and 3.

[0032] Table 1. Analysis results of major components of iron tailings

[0033]

[0034] The content of five heavy metals—cadmium, chromium, lead, arsenic, and mercury—generally meets the requirements of the Ministry of Agriculture and Rural Affairs' "Standards for Water-Soluble Fertilizers with Macro-elements" (NY / T1107-2020), and the content of radioactive elements meets the requirements of the "Soil Environmental Quality Standard" (GB 15618-2018).

[0035] Table 2. Toxic element analysis of iron tailings

[0036]

[0037] Table 3. Particle size composition analysis of iron tailings

[0038]

[0039] Example 1: Preparation of a compound microbial saline-alkali soil conditioner

[0040] In this embodiment, the preparation of the compound microbial saline-alkali soil conditioner requires the prior preparation of its raw materials: earthworm castings organic fertilizer, tailings-based organic matter complex, and microbial compound inoculant. The specific preparation steps are as follows:

[0041] a. Preparation of earthworm castings organic fertilizer:

[0042] Earthworm castings and biochar are mixed in a mass ratio of 7:3 to obtain earthworm castings organic fertilizer.

[0043] b. Preparation of tailings-based organic matter complexes:

[0044] The iron tailings were passed through a 200-mesh sieve. 17.5g of the iron tailings that passed through the sieve were mixed with 2.5g of earthworm castings organic fertilizer. The resulting mixture was composted for 2.5 days to fully age and obtain a tailings-based organic matter complex with a moisture content of ≤8%.

[0045] c. Preparation of microbial compound inoculants:

[0046] The effective viable bacteria concentration was 5.5 × 10⁻⁶. 7 ACCC 60042 rhizosphere cocci, with an effective viable bacterial concentration of 5.5 × 10⁻⁶ CFU / mL. 7 Bacillus subtilis CFU / mL of ACCC 19742 was mixed at a volume ratio of 1:1 to obtain a microbial compound inoculant.

[0047] d. Preparation of compound microbial saline-alkali soil conditioner:

[0048] Mix 15g of tailings-based organic matter complex with 3ml of microbial compound inoculant and 2g of ammonium sulfate, place them in a mixer and mix thoroughly. Control the mixing speed at 225 rpm and the mixing time at 13 minutes to obtain the compound microbial saline-alkali soil conditioner.

[0049] Example 2: Preparation of Compound Microbial Saline-Alkali Soil Conditioner

[0050] In this embodiment, the preparation of the compound microbial saline-alkali soil conditioner requires the prior preparation of its raw materials: earthworm castings organic fertilizer, tailings-based organic matter complex, and microbial compound inoculant. The specific preparation steps are as follows:

[0051] a. Preparation of earthworm castings organic fertilizer:

[0052] Earthworm castings and biochar are mixed in a mass ratio of 7:3 to obtain earthworm castings organic fertilizer.

[0053] b. Preparation of tailings-based organic matter complexes:

[0054] Iron tailings, a major waste from mining, are passed through a 200-mesh sieve. 15g of the iron tailings that pass through the sieve are mixed with 2g of earthworm castings organic fertilizer and composted for 2 days to fully age, resulting in a tailings-based organic matter complex with a moisture content of ≤8%.

[0055] c. Preparation of microbial compound inoculants:

[0056] The effective viable bacteria concentration is 4×10 7 ACCC 60042 rhizosphere cocci, with an effective viable bacterial concentration of 4 × 10⁻⁶ CFU / mL. 7 Bacillus subtilis CFU / mL of ACCC 19742 was mixed at a volume ratio of 1:1 to obtain a microbial compound inoculant.

[0057] d. Preparation of compound microbial saline-alkali soil conditioner:

[0058] Mix 15g of tailings-based organic matter complex with 4ml of microbial compound inoculant and 3g of ammonium sulfate, place them in a mixer and mix thoroughly. Control the mixing speed at 150 rpm and the mixing time at 15 minutes to obtain the compound microbial saline-alkali soil conditioner.

[0059] Example 3: Preparation of compound microbial saline-alkali soil conditioner.

[0060] In this embodiment, the preparation of the compound microbial saline-alkali soil conditioner requires the prior preparation of its raw materials: earthworm castings organic fertilizer, tailings-based organic matter complex, and microbial compound inoculant. The specific preparation steps are as follows:

[0061] a. Preparation of earthworm castings organic fertilizer:

[0062] Earthworm castings and biochar are mixed in a mass ratio of 7:3 to obtain earthworm castings organic fertilizer.

[0063] b. Preparation of tailings-based organic matter complexes:

[0064] The iron tailings were passed through a 200-mesh sieve. 20g of the iron tailings that passed through the sieve were mixed with 3g of earthworm castings organic fertilizer and composted for 3 days to fully age, resulting in a tailings-based organic matter complex with a moisture content of ≤8%.

[0065] c. Preparation of microbial compound inoculants:

[0066] The effective viable bacteria concentration is 9×10 7ACCC 60042 rhizosphere cocci, with an effective viable bacterial concentration of 9 × 10⁻⁶ CFU / mL. 7 Bacillus subtilis CFU / mL of ACCC 19742 was mixed at a volume ratio of 1:1 to obtain a microbial compound inoculant.

[0067] d. Preparation of compound microbial saline-alkali soil conditioner:

[0068] Mix 15g of tailings-based organic matter complex with 5ml of microbial compound inoculant and 4g of ammonium sulfate, place them in a mixer and mix thoroughly. Control the mixing speed at 300 rpm and the mixing time at 10 minutes to obtain the compound microbial saline-alkali soil conditioner.

[0069] Comparative Example 1: Preparation of Compound Microbial Saline-Alkali Soil Conditioner

[0070] This comparative example is the same as Example 1, except that no microbial compound inoculant is added when preparing the compound microbial saline-alkali soil conditioner. The specific preparation steps are as follows:

[0071] a. Preparation of earthworm castings organic fertilizer:

[0072] Earthworm castings and biochar are mixed in a mass ratio of 7:3 to obtain earthworm castings organic fertilizer.

[0073] b. Preparation of tailings-based organic matter complexes:

[0074] The iron tailings were passed through a 200-mesh sieve. 15g of the iron tailings that passed through the sieve were mixed with 2g of earthworm castings organic fertilizer and composted for 2 days to fully age, resulting in a tailings-based organic matter complex with a moisture content of ≤8%.

[0075] c. Preparation of compound saline-alkali soil conditioner:

[0076] Mix 15g of tailings-based organic matter complex with 3g of ammonium sulfate, place the mixture in a mixer and mix thoroughly. The mixing speed is controlled at 225 rpm and the mixing time is 13 minutes to obtain the compound microbial saline-alkali soil conditioner.

[0077] Comparative Example 2: Preparation of Compound Saline-Alkali Soil Conditioner

[0078] This comparative example is the same as Example 1, except that tailings-based organic matter complex is not added when preparing the composite microbial saline-alkali soil conditioner. The specific preparation steps are as follows:

[0079] a. Preparation of earthworm castings organic fertilizer:

[0080] Earthworm castings and biochar are mixed in a mass ratio of 7:3 to obtain earthworm castings organic fertilizer.

[0081] b. Preparation of microbial compound inoculants:

[0082] The effective viable bacteria concentration is 4×10 7 ACCC 60042 rhizosphere cocci, with an effective viable bacterial concentration of 4 × 10⁻⁶ CFU / mL. 7 Bacillus subtilis CFU / mL of ACCC 19742 was mixed at a volume ratio of 1:1 to obtain a microbial compound inoculant.

[0083] c. Preparation of compound microbial saline-alkali soil conditioner:

[0084] Mix 3 ml of microbial compound inoculant with 3 g of ammonium sulfate, place the mixture in a stirrer and stir thoroughly at a speed of 225 rpm for 13 minutes to obtain the compound microbial saline-alkali soil conditioner.

[0085] Experimental Example 1:

[0086] The experiment selected moderately saline-alkali soil from uncultivated wasteland in Caofeidian District, Tangshan City, Hebei Province. The soil was sieved through a 3mm sieve. The sieved soil was then mixed evenly with the compound microbial saline-alkali soil conditioner prepared in Example 1 (at 15% of the total mass of the sieved soil). The mixture was then watered to 70% of its maximum water holding capacity before being potted. The pots were 20cm in diameter and 25cm in height, with drainage holes at the bottom. Before filling with soil, a non-woven fabric was placed at the bottom, followed by approximately 2cm of gravel. Vaseline was applied to the sides of the pots to prevent edge effects with the soil. Watering was performed regularly using the weight method to maintain a maximum water holding capacity of 60-70%. The soil was loosened periodically. After 30 days of equilibration, spinach (Boza 10), a commonly used plant, was selected as the target for potted cultivation.

[0087] After 45 days of potted spinach cultivation, soil samples were collected and its physicochemical properties were measured, including: organic matter, available nitrogen, available phosphorus, available potassium, available silicon, available iron, bulk density, pH, soil salinity, and soil porosity. Spinach survival rate, maximum plant height, aboveground biomass, underground (root) biomass fresh weight, taproot length, root surface area, and maximum root diameter were also measured. Soil without the compound microbial saline-alkali soil conditioner served as the control (CK). Soil with the compound microbial saline-alkali soil conditioners prepared in Examples 1, 2, and 3 served as the experimental group, and soil with the compound saline-alkali soil conditioners prepared in Comparative Examples 1 and 2 served as the control group. The effects of this invention on the improvement of saline-alkali land and vegetation were verified. The results are as follows: Figure 1 As shown in Tables 4 and 5.

[0088] Table 4. Effects of soil conditioner on soil properties in saline-alkali land

[0089]

[0090] Table 5. Experimental Results and Ranking of Improvement Effects

[0091]

[0092] Depend on Figure 1 From Tables 4 and 5, we can obtain:

[0093] (1) The soil physicochemical and plant growth indicators of Examples 1, 2, and 3 were significantly better than those of the control group (CK group). The soil salinity, pH, porosity, bulk density, available silicon, available iron, available nitrogen, available potassium, available phosphorus, and organic matter in the Example groups all showed significant improvements. For example, in Example 1, the soil salinity decreased from 0.53 g / kg to 0.41 g / kg, the pH decreased from 8.4 to 8.3, and the organic matter increased from 22.4 g / kg to 42.3 g / kg. Regarding plant growth, the survival rate of spinach in Example 1 increased from 71.3% to 88.7%, and the maximum plant height increased from 17.2 cm to 28.5 cm. The results of Examples 2 and 3 also showed similar improvement trends. The compound microbial saline-alkali soil conditioner, through the rational ratio and synergistic effect of tailings minerals, organic matter, microorganisms and nitrogen fertilizer, not only effectively reduces the pH value and salinity of the soil, but also promotes the formation of soil aggregates, improves soil structure, and enhances water and fertilizer retention capacity through the interaction of microorganisms with organic fertilizer and mineral particles, thereby significantly improving the soil ecological environment and creating soil conditions conducive to plant growth.

[0094] (2) The improvement effects of Comparative Examples 1 and 2 were significantly lower than those of the Example Group. Comparative Example 1 used only tailings-based organic matter complex and lacked microbial compound inoculants. Although the soil physicochemical indicators were improved, the effect was significantly inferior to that of the Example Group. For example, the soil salinity of Comparative Example 1 was 0.49 g / kg, and the spinach survival rate was 75.2%, both lower than 0.41 g / kg and 88.7% of Example 1. Comparative Example 2 used only microbial compound inoculants and lacked tailings-based organic matter complex. The improvement of trace elements in the soil was limited, and the plant growth conditions were not fully optimized. The spinach survival rate was 78.5%, and the soil salinity was 0.50 g / kg, both lower than 0.41 g / kg and 88.7% of Example 1. This indicates that neither tailings-based organic matter complex nor microbial compound inoculants alone can achieve the effect of combined use. The synergistic effect of the two is crucial for the improvement of saline-alkali soil.

[0095] (3) In addition, the Bacillus subtilis and Coxella rhizosphere used in this invention are beneficial plant microorganisms that can alleviate abiotic stresses such as drought and salinity, effectively inhibit a variety of plant pathogens, and at the same time, through their metabolic activities, they can fully interact with the biochar and nitrogen fertilizer in the invention to improve soil structure and increase soil fertility, thereby providing a better growth environment for plants; Coxella rhizosphere can also promote the dissolution and precipitation of minerals such as Fe, Si and K in iron tailings.

[0096] In summary, the composite microbial saline-alkali soil conditioner of the present invention increases the mineral trace elements in saline-alkali land, promotes the formation of soil aggregates, improves the plant's tolerance to salinity and alkali, and provides optimized saline-alkali soil conditions for plant establishment.

[0097] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A compound microbial soil conditioner for saline-alkali soil, characterized in that, The composite microbial saline-alkali soil conditioner includes the following raw materials: tailings-based organic matter complex, microbial composite inoculant, and ammonium sulfate; The raw materials for the tailings-based organic matter complex include iron tailings and earthworm castings organic fertilizer; The raw materials for the microbial compound inoculant include rhizosphere Coccidioides and Bacillus subtilis; The ratio of the tailings-based organic matter complex, the microbial compound agent, and the ammonium sulfate is 15g~20g: 3ml~5ml: 2g~4g; The rhizosphere Cochlea is ACCC 60042 rhizosphere Cochlea, and the Bacillus subtilis is ACCC 19742 Bacillus subtilis.

2. The composite microbial saline-alkali soil conditioner according to claim 1, characterized in that, The effective viable concentration of Bacillus subtilis in the microbial compound agent is 4 × 10⁻⁶. 7 ~9×10 7 CFU / mL; the effective viable concentration of *Coccobacillus rhizosphereus* in the microbial compound agent is 4 × 10⁻⁶ CFU / mL; 7 ~9×10 7 CFU / mL.

3. The composite microbial saline-alkali soil conditioner according to claim 1, characterized in that, The water content of the tailings-based organic matter complex is ≤8%.

4. The composite microbial saline-alkali soil conditioner according to claim 3, characterized in that, The mass ratio of the iron tailings to the earthworm castings organic fertilizer is 15~20:2~3.

5. The composite microbial saline-alkali soil conditioner according to claim 4, characterized in that, The raw materials for the earthworm castings organic fertilizer include earthworm castings and biochar; the mass ratio of the earthworm castings to the biochar is 6~7:3~4.

6. A method for preparing a composite microbial saline-alkali soil conditioner according to any one of claims 1 to 5, characterized in that, The process includes the following steps: mixing tailings-based organic matter complex with microbial compound inoculants and ammonium sulfate to obtain a compound microbial saline-alkali soil conditioner.

7. The preparation method of a composite microbial saline-alkali soil conditioner according to claim 6, characterized in that, The preparation steps of the tailings-based organic matter complex are as follows: Earthworm castings and biochar are mixed to obtain earthworm castings organic fertilizer; iron tailings and earthworm castings organic fertilizer are then mixed, composted, and aged to obtain tailings-based organic matter complex.

8. The application of a compound microbial saline-alkali soil conditioner, characterized in that, The composite microbial saline-alkali soil conditioner according to any one of claims 1 to 5 is used in the improvement of saline-alkali soil.

9. The application of the composite microbial saline-alkali soil conditioner according to claim 8, characterized in that, The saline-alkali soil includes at least one of coastal saline-alkali land, inland saline-alkali land, and secondary salinized soil.

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