Preparation method and application of an iron-based coastal saline-alkali land composite improver

Abstract

The invention discloses a preparation method and application of an iron-based coastal saline-alkali land composite improver, wherein the composite improver is composed of the following raw materials by weight: 50-150 parts of ferrous sulfate, 5-50 parts of humic acid, and 0.01-0.02 parts of immobilized beneficial bacteria. The ferrous sulfate is granular or powdery, and the content of ferrous sulfate heptahydrate is ≥90wt.%, and the pH is 4-5. The humic acid is powdery after passing through a 100-mesh sieve, and the dry weight content of humic acid is ≥60 wt.%, the organic content is ≥70 wt.%, and the moisture is ≤10 wt.%, and the pH is 4-5. The immobilized beneficial bacteria is a composite bacteria prepared by immobilizing a variety of microbial agents with mesoporous zinc oxide. The improver of the present invention has a simple application method and a short improvement cycle. After one month of application, the salt content of coastal saline-alkali land soil can be significantly reduced, and the aggregate content and organic matter content can be increased.

Description

Technical Field

[0001] The invention belongs to the technical field of saline-alkali land improvement, and in particular relates to the preparation and application of a coastal saline-alkali land improver suitable for coastal saline-alkali land and capable of changing soil structure, reducing salinity and increasing soil organic matter content. Background Art

[0002] The total area of ​​saline-alkali soil in my country is about 36 million hectares, accounting for 4.88% of the country's available land area. As an important type, coastal saline-alkali soil has a total area of ​​about 1 million hectares, mainly distributed in coastal provinces such as Jiangsu, Shandong, and Zhejiang. With the acceleration of coastal reclamation in recent years, the area of ​​newly reclaimed tidal flat saline-alkali land has continued to increase. As food security has been elevated to a strategic level in my country in recent years, the quantity and quality of cultivated land have become the top priority for ensuring food security. As an important reserve cultivated land resource, it is of great practical significance to quickly and high-quality improve the quality of this type of land.

[0003] Coastal saline-alkali soil is a soil developed on saline silt. The salt mainly comes from seawater. The soil has high salt content, low organic carbon content and is difficult to form a stable aggregate structure. Soil aggregates are the basic units of soil structure and the material basis for determining soil fertility and quality. The size, distribution and stability of aggregates play an important role in maintaining soil permeability, improving fertility, promoting carbon fixation and preventing soil erosion and degradation. Therefore, the unstable structure of coastal saline-alkali soil aggregates makes coastal saline-alkali soil easy to compact, poor in water and fertilizer retention, and difficult for crops to grow. In the past, saline-alkali land improvement mainly used engineering measures to reduce groundwater levels and salt content, and applied organic fertilizers to increase organic carbon content. However, this method is subject to great environmental constraints, serious organic matter loss and easy to return to salt. In recent years, with the acceleration of the development of coastal saline-alkali land in my country, a large number of experiments and research have been carried out on saline-alkali soil conditioners, such as a humic acid salt alkali soil conditioner and its preparation method (201310546681.7), biochar-based coastal saline-alkali soil conditioner and its preparation method and application (201510800972.3), etc. These conditioners are mainly simple organic fertilizers, artificial synthetic polymer compounds or beneficial bacteria microbial preparations, etc., which can provide certain nutrients to the soil, but ignore the salt reduction, air permeability and carbon fixation brought about by changing the soil structure, resulting in nutrients not being released and crops difficult to grow. Pure beneficial bacteria and microorganisms are difficult to survive in the saline-alkali soil environment and their reproduction is also restricted, and the effect is general. Summary of the invention

[0004] The technical problem to be solved by the present invention is to use Fe 2+The basic principle is that the cementation during the oxidation process forms the mineral skeleton of soil aggregates and uses beneficial bacteria to activate humic acid to provide nutrients. A preparation and application method of a saline-alkali land composite improver is provided, which can improve soil structure, reduce salinity and increase soil organic carbon content.

[0005] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0006] An iron-based coastal saline-alkali land composite improver, wherein the total salt content of the iron-based coastal saline-alkali land composite improver is in the range of 3‰-25‰, and is characterized in that, by weight, it contains: 50-150 parts of ferrous sulfate, 5-50 parts of humic acid, and 0.01-0.02 parts of immobilized beneficial bacteria.

[0007] According to a specific and preferred aspect of the present invention, the composition is composed of the following raw materials in parts by weight: 110-140 parts of ferrous sulfate, 30-45 parts of humic acid sulfuric acid, and 0.01 part of immobilized beneficial bacteria.

[0008] Preferably, when the total salt content of the coastal saline-alkali land is 3‰-15‰, the improver is composed of the following raw materials in weight fractions: 110 parts of ferrous sulfate, 30 parts of humic acid, and 0.01 parts of immobilized beneficial bacteria.

[0009] Preferably, when the total salt content of the coastal saline-alkali land is 15‰-25‰, the improver is composed of the following raw materials in weight fractions: 140 parts of ferrous sulfate, 45 parts of humic acid, and 0.01 parts of immobilized beneficial bacteria.

[0010] The ferrous sulfate is in granular or powdery form, and is crushed through a 10-mesh sieve to form a powdery form. The content of ferrous sulfate heptahydrate is ≥90wt.%, and the pH is 4-5. Ferrous sulfate forms trivalent iron oxide in the soil, forming a mineral skeleton of soil aggregates.

[0011] The humic acid is powdered after passing through a 100-mesh sieve, the humic acid dry weight content is ≥60wt.%, the organic matter content is ≥70wt.%, the moisture content is ≤10wt.%, and the pH value is 4-5.

[0012] The beneficial bacteria agent can be a microbial agent or a combination thereof that has been reported or industrially applied in saline-alkali land improvement. As a preferred embodiment of the present invention, the beneficial bacteria agent is a composite agent prepared by immobilizing multiple microbial agents with mesoporous zinc oxide, wherein at least one of Bacillus megaterium and Bacillus subtilis is included, and the others are nitrogen-fixing bacteria, phosphate-dissolving bacteria and potassium-dissolving bacteria, with a total effective live bacteria count of ≥100 billion / g, and the number of each effective bacteria count of ≥3 billion / g. These beneficial bacteria coordinate and interact with each other to promote the decomposition of humic acid and the absorption of nutrients by crops, and at the same time secrete multiple enzymes, which combine with iron oxides to promote the formation of large agglomeration structures in the soil.

[0013] The present invention also provides a method for preparing the iron-based coastal saline-alkali land mixed improver described in the above technical solution, comprising the following steps:

[0014] (1) drying, grinding, and sieving ferrous sulfate and humic acid respectively to obtain powdered ferrous sulfate and humic acid;

[0015] (2) fully mixing and stirring the powder obtained in (1) to obtain a mixed material;

[0016] (3) activating and expanding the beneficial bacteria powder, inoculating it into a liquid culture medium for fermentation, mixing different bacterial liquids according to a mass ratio to obtain a mixed bacterial suspension, then adding mesoporous zinc oxide to the mixed bacterial suspension for microbial adsorption and immobilization, and then centrifuging and low-temperature drying to obtain the immobilized beneficial bacteria agent;

[0017] (4) The mixture prepared in (2) and the immobilized beneficial bacteria agent prepared in (3) are mixed and granulated using a disc granulator, starch is added as a binder, the particle diameter is 2-3 mm, and the amount of starch is 0.05 times the total weight of ferrous sulfate, humic acid, and immobilized beneficial bacteria agent.

[0018] The invention has simple ingredients and only three raw materials. The raw materials are easy to obtain and are low in price. A large number of tests and application examples have proved that the average cost of the reagent per mu is 400-1000 yuan. After 1-3 months of application, the salt content of saline-alkali land is reduced by 20%-30%, large aggregates are increased by 30%-50%, organic matter is increased by 10%-30%, and the crop survival rate is more than 70%.

[0019] The present invention also provides a method for using the coastal saline-alkali land improver to improve saline-alkali land: when the total salt content in the 0-20 cm tillage layer soil is 3‰-15‰, the amount of the improver used is 400-500 kg / mu; when the total salt content in the 0-20 cm tillage layer soil is 15‰-25‰, the amount of the improver used is 700-900 kg / mu. Preferably, the 0-40 cm soil is first loosened with a rotary tiller, and then the improver is evenly sprinkled into the soil, and the improver is evenly mixed with the 0-20 cm soil with a rotary tiller, and left for more than 30 days.

[0020] Preferably, after spreading the improver, a ditch more than 30 cm deep and more than 30 cm wide is dug every 5 meters in the improved area for drainage on rainy days.

[0021] The present invention is mainly a composite improver of ferrous sulfate, humic acid and mesoporous zinc oxide to immobilize beneficial bacteria nutrients. Iron oxide is the basis for the formation of soil aggregate skeleton. Humic acid provides organic matter to form soil organic-mineral aggregates, and at the same time provides a growth and reproduction environment for beneficial bacteria. Humic acid interacts with ferrous sulfate to further promote the formation of soil aggregate structure. Beneficial bacteria agent can effectively increase the content of soil organic matter. At the same time, the enzymes secreted by it are combined with the aggregate particles formed by ferrous sulfate and humic acid to further increase the content of large aggregates, reduce salt content, and increase crop yield. Humic acid has a wide source, low price, and will not cause secondary pollution to the environment. In addition, the mesoporous zinc oxide immobilization of microorganisms combines the advantages of nanomaterials and biotechnology. Mesoporous zinc oxide has a high specific surface area and a unique pore structure. Due to its high specific surface area, rich pore structure and good biocompatibility, it provides a large number of attachment sites and nutrient channels for beneficial bacteria, which helps to improve the activity and metabolic efficiency of beneficial bacteria. The beneficial bacteria immobilized on mesoporous zinc oxide have higher stability and environmental adaptability, and can maintain activity under different environmental conditions. The difference between the present invention and the previous saline-alkali land composite improvers is that the previous ones mainly focus on improving soil nutrients, and there is no composite improver suitable for coastal saline-alkali land that uses ferrous sulfate, humic acid and mesoporous zinc oxide to immobilize beneficial bacteria nutrients. Beneficial effects: Compared with the prior art, the present invention has the following advantages:

[0022] (1) The ferrous sulfate described in the present invention is an important factor in the formation of soil aggregate skeletons, which can effectively increase the number of soil aggregates and the content of large aggregates, and can significantly reduce the increase of soil salt due to capillary force migration, thereby reducing the soil salt content; humic acid can quickly increase the organic matter content of the soil, and at the same time interact with ferrous sulfate to further promote the formation of soil aggregate structure; the beneficial bacteria agent immobilized by mesoporous zinc oxide effectively maintains biological activity and metabolic efficiency, which is more conducive to stabilizing and increasing the soil organic matter content. At the same time, the enzymes secreted by the bacteria combine with the aggregate particles formed by ferrous sulfate and humic acid, further increasing the content of large aggregates, reducing the salt content, and increasing crop yields.

[0023] (2) The improver of the present invention utilizes the combined effects of physics, chemistry and biology to improve the soil, and has high efficiency and significant effect. The ferrous sulfate, humic acid and beneficial bacteria used in the present invention are widely available, low in price and will not cause secondary pollution to the environment.

[0024] (3) The present invention has conducted a large number of laboratory and field tests on the selection and dosage of the three materials, and has conducted rigorous analysis on the test results, on which basis the component contents of the materials in soils with different salt contents are finally determined.

[0025] (4) The improver of the present invention has a simple application method and a short improvement period. After one month of application, the salt content of coastal saline-alkali land soil can be significantly reduced, and the aggregate content and organic matter content can be increased. DETAILED DESCRIPTION

[0026] The following specific embodiments are further explanations of the present invention, but the described embodiments are only a part of the embodiments of the present invention, and do not mean that the content of the present invention is limited to the scope of the examples given.

[0027] Unless otherwise specified, the materials used in the following examples can be obtained from the market.

[0028] In the present invention, Bacillus subtilis, Bacillus megaterium, nitrogen-fixing bacteria, phosphate-solubilizing bacteria and potassium-solubilizing bacteria can all be purchased from the market. The following are the strains used in the embodiments:

[0029]

[0030]

[0031] The strain can grow in the range of 20-35°C on a beef extract medium containing 2% NaCl, and the activation and expansion culture methods can be carried out according to conventional methods in the art or the manufacturer's instructions.

[0032] The mesoporous zinc oxide material used in the present invention refers to Liu Wenkui's "Preparation, Characterization and Performance Research of Zinc Oxide Nanostructures", Master's thesis, 2013. The specific preparation method is as follows:

[0033] (1) Use a balance to weigh 1.5 mmol (0.4464 g) of zinc nitrate hexahydrate, 7.5 mmol (0.45 g) of urea, and 0.3 mmol (0.045 g) of tartaric acid, pour into a 100 ml beaker, add 30 ml of deionized water to the beaker, and stir magnetically for 1 min to obtain a clear and transparent solution.

[0034] (2) The solution was poured into a 50 ml polytetrafluoroethylene-lined stainless steel reactor, sealed, and reacted in an oven at 150° C. for 6 h. After the reaction was completed, the reaction was naturally cooled to room temperature.

[0035] (3) The obtained white precipitate was washed several times with deionized water and anhydrous ethanol, centrifuged, and dried at 60° C. for 10 h until completely dry to obtain a basic zinc carbonate microsphere precursor.

[0036] (4) The basic zinc carbonate microsphere precursor is placed in a clean and dried porcelain boat, placed in a box-type resistance furnace, heated to 300°C within 1 hour, kept constant for 2 hours, and naturally cooled to room temperature, and finally a white powder, namely the prepared zinc oxide mesoporous microspheres, is obtained.

[0037] Example 1

[0038] The iron-based coastal saline-alkali land composite improver of this embodiment includes the following components by weight: 110 parts of ferrous sulfate, 30 parts of humic acid, and 0.01 parts of immobilized beneficial bacteria.

[0039] The ferrous sulfate is particles or powders with a ferrous sulfate heptahydrate content of ≥90wt.%.

[0040] The humic acid is coal humic acid, wherein the humic acid content is ≥65wt.%, and the organic matter content is ≥75wt.%.

[0041] The beneficial bacteria are Bacillus subtilis, nitrogen-fixing bacteria, phosphate-solubilizing bacteria, and potassium-solubilizing bacteria, the total effective live bacteria count is ≥100 billion / g, the number of each effective bacteria in the beneficial bacteria agent is ≥3 billion / g, and the weight ratio is 2:1:1:1.

[0042] The preparation of the improver includes the following steps:

[0043] (1) After drying ferrous sulfate, grind it with a pair of rollers and then pass it through a 10-mesh sieve. Humic acid is dried to a moisture content of ≤10 wt.%, grind it with a ball mill and then pass it through a 100-mesh sieve.

[0044] (2) Add ferrous sulfate powder and humic acid powder into a blender and mix well.

[0045] (3) Activating the beneficial bacteria powder and expanding the culture, inoculating it into a liquid culture medium for fermentation, mixing different bacterial liquids according to a mass ratio to obtain a mixed bacterial suspension, then adding mesoporous zinc oxide to the mixed bacterial suspension for microbial adsorption and immobilization, and then centrifuging and low-temperature drying to obtain an immobilized beneficial bacteria agent.

[0046] (4) Add the powder obtained in (2) into a disc granulator, add starch as a binder, and slowly add the immobilized beneficial bacteria obtained in (3) to make granules with a particle size of 2-3 mm. After drying, seal and package them for later use.

[0047] Example 2

[0048] The iron-based coastal saline-alkali land composite improver of this embodiment is the same as that of Example 1, except that the beneficial bacteria composition is: Bacillus megaterium, nitrogen-fixing bacteria, phosphate-solubilizing bacteria, and potassium-solubilizing bacteria, and the weight ratio thereof is 2:1:1:1.

[0049] Example 3

[0050] The iron-based coastal saline-alkali land composite improver of this embodiment is the same as that of Example 1, except that the beneficial bacteria composition is: Bacillus subtilis, Bacillus megaterium, nitrogen-fixing bacteria, phosphate-solubilizing bacteria, and potassium-solubilizing bacteria, and the weight ratio thereof is 1:1:1:1:1:1.

[0051] Example 4

[0052] The type of the iron-based coastal saline-alkali land composite improver of this embodiment is the same as that of Example 1, except that it contains 140 parts of ferrous sulfate, 45 parts of humic acid, and 0.01 parts of immobilized beneficial bacteria.

[0053] The ferrous sulfate is particles or powders with a ferrous sulfate heptahydrate content of ≥90wt.%.

[0054] The humic acid is coal humic acid, wherein the humic acid content is ≥65wt.%, and the organic matter content is ≥75wt.%.

[0055] The beneficial bacteria are Bacillus subtilis, nitrogen-fixing bacteria, phosphate-solubilizing bacteria, and potassium-solubilizing bacteria, the total effective live bacteria count is ≥100 billion / g, the number of each effective bacteria in the beneficial bacteria agent is ≥3 billion / g, and the weight ratio is 2:1:1:1.

[0056] Comparative Example 1

[0057] The iron-based coastal saline-alkali land composite improver of this comparative example is the same as that of Example 1, except that the humic acid is provided by mineral potassium humate, wherein the humic acid content is ≥60wt.%, and the organic matter content is ≥70wt.%.

[0058] Comparative Example 2

[0059] The proportion of the iron-based coastal saline-alkali land composite improver in this comparative example is the same as that in Example 1, except that there is no ferrous sulfate.

[0060] Comparative Example 3

[0061] The proportion of the iron-based coastal saline-alkali land composite improver in this comparative example is the same as that in Example 1, except that there is no humic acid.

[0062] Comparative Example 4

[0063] The proportion of the iron-based coastal saline-alkali land composite modifier in this comparative example is the same as that in Example 1, except that the preparation of the modifier comprises the following steps:

[0064] (1) After drying ferrous sulfate, grind it with a pair of rollers and then pass it through a 10-mesh sieve. Humic acid is dried to a moisture content of ≤10 wt.%, grind it with a ball mill and then pass it through a 100-mesh sieve.

[0065] (2) Add ferrous sulfate powder and humic acid powder into a blender and mix well.

[0066] (3) Activating the beneficial bacteria powder and expanding the culture, inoculating it into a liquid culture medium for fermentation, and then mixing different bacterial liquids according to a mass ratio to obtain a mixed bacterial suspension.

[0067] (4) Add the powder obtained in (2) into a disc granulator, add starch as a binder, and slowly add the mixed bacterial suspension obtained in (3) to make granules with a particle size of 2-3 mm. After drying, seal and package for later use.

[0068] The improvers of Examples 1-4 and Comparative Examples 1-4 were used to carry out improvement tests on moderate saline-alkali barrier farmland on coastal tidal flats, as follows:

[0069] (1) Basic information of the test site: The test site is located in Juju Reclamation Area, Rudong County, Nantong City, Jiangsu Province. The soil of the test site is sandy loam. The total salt content of the soil in the 0-20cm topsoil layer of the test site is 4.17-6.85‰, with an average content of 5.9‰, an average pH value of 8.52, an average organic matter of 7.36g / kg, a total nitrogen of 0.52g / kg, an available potassium of 330mg / kg, and an available phosphorus of 75.3mg / kg. The average content of soil macroaggregates with a diameter of ≥0.25mm is 1.42%. The test site was divided into 8 areas of equal size, each with a size of 5mX5m, and each area was separated by a 40cm deep and 30cm wide ditch.

[0070] (2) Test method: First, improve 8 areas, and use another area as the original soil control. Plow the soil 40 cm deep, then spread the improvers prepared by the methods of Examples 1-4 and Comparative Examples 1-4 at a dosage of 400 kg per mu, plow 20 cm, and keep it for 30 days after spreading. During the process, keep the drainage of the intermediate isolation ditch normal. After the specified time, test the various soil indicators. The specific results are shown in Table 1. The 9th saline-alkali land was used as a blank control, and no improver was added.

[0071] Table 1 Various indicators of soil after improvement

[0072]

[0073]

[0074] (3) Planting test: A planting test was conducted on the test plot and the control plot 30 days after the amendment was applied. The planting started in June 2022. The crop was soybean (purchased from the market). One hole was planted every 20 cm, and 3 soybean seeds were planted in each hole. Watering was done every 3 days (delayed on rainy days), and the germination was counted every other day until no more germination occurred. Normal field and water and fertilizer management work was carried out in the later stage. After the soybean matured, the yield and soil organic matter and aggregate content indicators were counted. The yield was mainly counted as the total soybean quality of each plot.

[0075] Table 2 Germination rate, yield, organic matter and aggregate content of soybean after planting

[0076]

[0077] From the above test results, it can be seen that the use of the improver and the improvement method of the present invention can increase soil organic matter, increase aggregate content, and improve soil components. At the same time, it can also reduce soil salt content and increase crop germination rate and yield, with significant effects.

[0078] Example 5

[0079] The iron-based coastal saline-alkali land composite improver of this embodiment includes the following components by weight: 140 parts of ferrous sulfate, 45 parts of humic acid, and 0.01 parts of immobilized beneficial bacteria.

[0080] The ferrous sulfate is particles or powders with a ferrous sulfate heptahydrate content of ≥90wt.%.

[0081] The humic acid is coal humic acid, wherein the humic acid content is ≥65wt.%, and the organic matter content is ≥75wt.%.

[0082] The beneficial bacteria are Bacillus subtilis, nitrogen-fixing bacteria, phosphate-solubilizing bacteria, and potassium-solubilizing bacteria, the total effective live bacteria count is ≥100 billion / g, the number of each effective bacteria in the beneficial bacteria agent is ≥3 billion / g, and the weight ratio is 2:1:1:1.

[0083] The preparation of the improver is the same as in Example 1.

[0084] Example 6

[0085] The iron-based coastal saline-alkali land composite improver of this embodiment is the same as that of Example 5, except that the beneficial bacteria composition is: Bacillus megaterium, nitrogen-fixing bacteria, phosphate-solubilizing bacteria, and potassium-solubilizing bacteria, and the weight ratio thereof is 2:1:1:1.

[0086] Example 7

[0087] The iron-based coastal saline-alkali land composite improver of this embodiment is the same as that of Example 5, except that the beneficial bacteria composition is: Bacillus subtilis, Bacillus megaterium, nitrogen-fixing bacteria, phosphate-solubilizing bacteria, and potassium-solubilizing bacteria, and the weight ratio thereof is 1:1:1:1:1:1.

[0088] Example 8

[0089] The type of iron-based coastal saline-alkali land composite improver in this embodiment is the same as that in Example 5, except that 110 parts of ferrous sulfate, 30 parts of humic acid, and 0.01 parts of immobilized beneficial bacteria are used.

[0090] Comparative Example 5

[0091] The iron-based coastal saline-alkali land composite improver of this comparative example is the same as that of Example 5, except that the humic acid is provided by mineral source potassium humate, wherein the humic acid content is ≥60wt.%, and the organic matter content is ≥70wt.%.

[0092] Comparative Example 6

[0093] The proportion of the iron-based coastal saline-alkali land composite improver in this comparative example is the same as that in Example 5, except that there is no ferrous sulfate.

[0094] Comparative Example 7

[0095] The proportion of the iron-based coastal saline-alkali land composite improver in this comparative example is the same as that in Example 5, except that there is no humic acid.

[0096] Comparative Example 8

[0097] The proportion of the iron-based coastal saline-alkali land composite modifier in this comparative example is the same as that in Example 5, except that the preparation of the modifier comprises the following steps:

[0098] (1) After drying ferrous sulfate, grind it with a pair of rollers and then pass it through a 10-mesh sieve. Humic acid is dried to a moisture content of ≤10 wt.%, grind it with a ball mill and then pass it through a 100-mesh sieve.

[0099] (2) Add ferrous sulfate powder and humic acid powder into a blender and mix well.

[0100] (3) Activating the beneficial bacteria powder and expanding the culture, inoculating it into a liquid culture medium for fermentation, and then mixing different bacterial liquids according to a mass ratio to obtain a mixed bacterial suspension.

[0101] (4) Add the powder obtained in (2) into a disc granulator, add starch as a binder, and slowly add the mixed bacterial suspension obtained in (3) to make granules with a particle size of 2-3 mm. After drying, seal and package for later use.

[0102] The improvers of Examples 5-8 and Comparative Examples 5-8 were used to carry out improvement tests on severely saline-alkali barrier farmland on coastal tidal flats, as follows:

[0103] (1) Basic information of the test site: The test site is located in Tongzhou Bay Reclamation Area, Nantong City, Jiangsu Province. The soil of the test site is sandy loam. The total salt content of the soil in the 0-20 cm topsoil layer of the test site is 15.86-23.47‰, with an average content of 18.63‰, an average pH value of 8.40, an average organic matter of 3.33 g / kg, a total nitrogen of 0.293 g / kg, an available potassium of 226 mg / kg, and an available phosphorus of 3.70 mg / kg. The average content of soil macroaggregates with a diameter of ≥ 0.25 mm is 0.84%. The test site was divided into 5 areas of equal size, each with a size of 5 mX5 m, and each area was separated by a 40 cm deep and 30 cm wide ditch.

[0104] (2) Test method: First, improve 8 areas, and use another area as the original soil control. Plow the soil 40 cm deep once, then apply the improvers prepared by the methods of Examples 5-8 and Comparative Examples 5-8 at a dosage of 800 kg per mu, plow 20 cm, and water thoroughly once and keep it for 30 days. During the process, keep the drainage of the intermediate isolation ditch normal. After the specified time, test the various soil indicators. The 9th saline-alkali land was used as a blank control, and no improver was added.

[0105] The experiment shows that, compared with the single use of humic acid or ferrous sulfate, or the use of beneficial bacteria without mesoporous zinc oxide immobilization, the use of the improver and improvement method of the present invention can significantly increase soil organic matter, increase aggregate content, and improve soil components, while also reducing soil salt content, which is consistent with the goal of improving coastal saline-alkali land.

Claims

1. An iron-based coastal saline-alkali land composite improver, characterized in that: The composite improver is composed of the following raw materials in parts by weight: 50-150 parts of ferrous sulfate, 5-50 parts of humic acid, and 0.01-0.02 parts of immobilized beneficial bacteria; The immobilized beneficial bacteria agent is a composite bacteria agent prepared by immobilizing a variety of microbial bacteria agents through mesoporous zinc oxide; The humic acid is coal humic acid; The composite bacterial agent contains at least one of Bacillus megaterium and Bacillus subtilis, and the others are nitrogen-fixing bacteria, phosphate-dissolving bacteria and potassium-dissolving bacteria.

2. The iron-based coastal saline-alkali land composite improver according to claim 1, characterized in that: The ferrous sulfate is a particle or powder with a ferrous sulfate heptahydrate content of ≥90wt.%, and a pH of 4-5.

3. The iron-based coastal saline-alkali land composite improver according to claim 1, characterized in that: The humic acid is in powder form after passing through a 100-mesh sieve, the humic acid dry weight content is ≥60 wt.%, the organic matter content is ≥70 wt.%, the moisture content is ≤10 wt.%, and the pH is 4-5.

4. The iron-based coastal saline-alkali land composite improver according to claim 1, characterized in that: The invention is composed of the following raw materials in parts by weight: 110-140 parts of ferrous sulfate, 30-45 parts of humic acid and 0.01 part of immobilized beneficial bacteria.

5. The iron-based coastal saline-alkali land composite improver according to claim 1, characterized in that: The total salt content of the iron-based coastal saline-alkali land composite improver used ranges from 3‰ to 25‰.

6. The iron-based coastal saline-alkali land composite improver according to claim 5, characterized in that: When the total salt content of the coastal saline-alkali land is 3‰-15‰, the improver is composed of the following raw materials in weight fractions: 110 parts of ferrous sulfate, 30 parts of humic acid, and 0.01 parts of immobilized beneficial bacteria.

7. The iron-based coastal saline-alkali land composite improver according to claim 5, characterized in that: When the total salt content of the coastal saline-alkali land is 15‰-25‰, the improver is composed of the following raw materials in weight fractions: 140 parts of ferrous sulfate, 45 parts of humic acid, and 0.01 parts of immobilized beneficial bacteria.

8. The method for preparing the iron-based coastal saline-alkali land composite improver according to any one of claims 1 to 5, characterized in that: The steps are: (1) Drying, grinding, and sieving ferrous sulfate and humic acid respectively to obtain powdered ferrous sulfate and humic acid; (2) The powder obtained in (1) is thoroughly mixed and stirred to obtain a mixture; (3) activating and expanding the culture of multiple microbial agents, inoculating them into a liquid culture medium for fermentation, mixing different bacterial suspensions according to a mass ratio to obtain a mixed bacterial suspension, then adding mesoporous zinc oxide to the mixed bacterial suspension for microbial adsorption and immobilization, and then centrifuging and low-temperature drying to obtain the immobilized beneficial bacterial agent; (4) The mixture prepared in (2) and the immobilized beneficial bacteria prepared in (3) are mixed and granulated using a disc granulator. Starch is added as a binder. The particle diameter is 2-3 mm. The amount of starch is 0.05 times the total weight of ferrous sulfate, humic acid, and immobilized beneficial bacteria.

9. The method for using the iron-based coastal saline-alkali land composite improver according to any one of claims 1 to 5 for improving saline-alkali land, characterized in that: When the total salt content in the 0-20cm tillage layer of soil is 3‰-15‰, the amount of improver used is 400-500kg / mu; when the total salt content in the 0-20cm tillage layer of soil is 15‰-25‰, the amount of improver used is 700-900kg / mu.

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