Multi-vitamin improved organic fertilizer for saline-alkali soil and gradient preparation process thereof

Abstract

The invention relates to the field of soil improvement, and discloses a multi-dimensional improved organic fertilizer for saline-alkali soil and a gradient preparation process thereof, the fertilizer is prepared from an organic fermentation substrate, first lignin sulfonate, second lignin sulfonate, elemental sulfur powder, a sulfur autotrophic oxidizing bacterial agent and humic acid; the preparation method adopts a gradient acidification and synergistic fermentation process and comprises the following steps: carrying out thermophilic pre-decomposition on an organic fermentation substrate; adding first sulfonated lignin with low molecular weight and high sulfonation degree to carry out chemical start acidification; and then adding high-molecular-weight second sulfonated lignin, elemental sulfur powder, a sulfur autotrophic oxidizing bacterial agent and humic acid for biological synergistic fermentation to obtain a final product. After the fertilizer is applied to soil, the pH value of the soil and the content of water-soluble sodium ions can be continuously reduced, meanwhile, formation of water-stable aggregates of the soil is promoted through a high-molecular polymer, chemical and physical multi-dimensional improvement on the saline-alkali soil is synchronously achieved, and the effect is remarkable.

Description

Technical Field

[0001] The present invention relates to the technical field of soil improvement, in particular to a multi-dimensional improved organic fertilizer for saline-alkali land and a gradient preparation process thereof. Background Art

[0002] Saline-alkali soils, due to their high pH and high soluble salt content, lead to soil compaction and low nutrient availability, severely inhibiting plant growth. Currently, improvements to saline-alkali soils typically rely on chemical, physical, or conventional biological methods.

[0003] Chemical methods often neutralize soil alkalinity by applying chemical amendments such as gypsum, desulfurized gypsum, or acidic industrial waste. While these methods can lower soil pH in the short term, their effects are typically temporary and fail to provide a sustained acidic environment. They also have no effect on physical and fertility indicators such as soil aggregate structure and organic matter content. Physical methods, such as deep tillage, soil addition, or sand incorporation, are labor-intensive and costly, and fail to fundamentally address the underlying chemical properties of the soil.

[0004] Conventional biological improvement measures, such as the application of ordinary organic fertilizers, are mainly aimed at increasing the organic matter content of the soil and improving its physical structure. However, the pH value of traditional organic fertilizers themselves is mostly neutral or alkaline, and their direct neutralization ability for highly alkaline soils is very limited. The acidic substances produced by their decomposition in the soil are slow and have low acid production efficiency, making it difficult to achieve the goal of effectively improving alkaline soils in a short period of time. Therefore, there is a clear technical gap in the existing technology in achieving rapid and continuous improvement of the chemical properties and reconstruction of the physical structure of saline-alkali soils. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide an organic fertilizer and a preparation method thereof that can effectively improve the physical and chemical properties of saline-alkali soil, so as to overcome the problems in the prior art of slow improvement of organic fertilizers, the risk of secondary damage of chemical improvers, and insufficient synergy of the components of compound fertilizers.

[0006] In order to solve the above technical problems, the present invention is implemented through the following technical solutions: The first aspect of the present invention provides a multi-dimensional improved organic fertilizer for saline-alkali land, which is made from the following raw materials in parts by weight: Organic fermentation matrix: 50-70 parts; First sulfonated lignin: 5-10 parts, with a molecular weight range of 1,000-3,000 g / mol and a degree of sulfonation of 1.5-2.5 mmol / g; Second sulfonated lignin: 5-10 parts, with a molecular weight range of 20,000-40,000 g / mol and a degree of sulfonation of 0.8-1.4 mmol / g; Elemental sulfur powder: 1-5 parts; Sulfur autotrophic oxidizing bacteria agent: 0.5-1 part; Humic acid: 5-10 parts.

[0007] In one embodiment, the organic fermentation substrate is formed by mixing cow dung and corn straw powder in a dry weight ratio of 2:1 to 3:1.

[0008] In one embodiment, the sulfur autotrophic oxidizing bacteria agent comprises Acidithiobacillus thiooxidans and Acidithiobacillus ferrooxidans, and the total effective viable bacterial count thereof is not less than 1.0×10 9 CFU / g.

[0009] In a preferred embodiment, the strain number ratio of the acidithiobacillus and the ferrothiobacillus is (3-5):1.

[0010] In the technical solution provided by the present invention, the components are combined through a specific preparation process to achieve a preset technical effect.

[0011] The first sulfonated lignin, due to its low molecular weight and high degree of sulfonation, can quickly release hydrogen ions when mixed with a neutral or weakly alkaline organic fermentation matrix that has been thermophilically pre-decomposed, thereby reducing the pH value of the material system to a preset slightly acidic range before subsequent microbial action.

[0012] Under aerobic conditions, sulfur autotrophic oxidizing bacteria use elemental sulfur powder as energy and oxidize it to produce sulfuric acid through metabolic activities. This process is the main reason why the pH value of the fertilizer system continues to decrease and stabilize in the range of 3.0-5.0.

[0013] The initial pH drop caused by the first sulfonated lignin provides suitable environmental conditions for the rapid activation and reproduction of sulfur autotrophic oxidizing bacteria.

[0014] The final low pH environment formed by the sulfuric acid produced by the metabolism of sulfur autotrophic oxidizing bacteria enhances the ability of the functional groups in the second sulfonated lignin and humic acid to complex with metal cations.

[0015] The second sulfonated lignin, due to its high molecular weight, forms a macromolecular structural framework in the fertilizer. Its sulfonic acid groups can complex with cations such as sodium ions in the soil. The final fertilizer product has a final pH of 3.0-5.0.

[0016] A second aspect of the present invention provides a gradient preparation method for a multi-dimensional improved organic fertilizer for saline-alkali land, comprising the following steps: (1) Thermophilic pre-decomposition: The organic fermentation substrate is thermophilically fermented at a temperature range of 55°C to 70°C for 7-10 days at a water content of 55% to 60%, and then cooled to below 40°C; (2) Gradient acidification and synergistic fermentation: (2a) adding the first sulfonated lignin to the material obtained in step (1) and mixing them uniformly; (2b) Subsequently, the second sulfonated lignin, elemental sulfur powder, humic acid and sulfur autotrophic oxidizing bacteria are added to the material obtained in step (2a) and mixed evenly, and then aerobic fermentation is carried out at a temperature of 25° C. to 35° C. for 14 to 21 days until the pH value of the material is stabilized in the range of 3.0 to 5.0.

[0017] In a specific embodiment, the thermophilic pre-decomposition in step (1) adopts tank fermentation, and the material is turned over 1-2 times a day.

[0018] In a specific embodiment, in step (2a), after the first sulfonated lignin is added, it is stirred at a low speed for 15-20 minutes by a mechanical device to ensure that it is evenly dispersed in the material.

[0019] In a specific embodiment, the aerobic fermentation in step (2b) is performed by turning the material once every 24-48 hours to supply oxygen.

[0020] In a specific embodiment, in step (2b), the criterion for determining the end of fermentation is that the pH value of the material changes by less than 0.2 when monitored for three consecutive days.

[0021] In a specific embodiment, after step (2), the method further comprises a post-processing step: drying the fermented material until its final moisture content is less than 20%.

[0022] In the technical solution provided by the present invention, there is the following synergistic relationship: The first sulfonated lignin added in step (2a) functions to chemically initiate acidification. This step solves the technical problem that sulfur autotrophic bacteria have a growth hysteresis period or low activity in a neutral or alkaline environment. The pH value of the material is pre-adjusted to a slightly acidic range by chemical means, providing a favorable initial environment for the rapid proliferation and metabolic activity of the sulfur autotrophic bacteria in step (2b), thereby shortening the start-up time of the entire biological acid production process. The sulfur autotrophic bacteria in step (2b) use elemental sulfur powder as energy for biological relay acidification, and its continuous metabolic acid production activity is the main reason why the fertilizer system eventually reaches and stabilizes within the pH range of 3.0-5.0. This gradient acidification mode achieves a combination of rapid response and long-term acid production.

[0023] This scheme establishes a two-way synergistic relationship between multiple components. On the one hand, the low pH environment formed by the sulfuric acid produced by the metabolism of sulfur autotrophic bacteria promotes the full protonation of functional groups such as carboxyl and sulfonic acid groups in the second sulfonated lignin and humic acid, thereby significantly enhancing their interaction with Na in the soil. + On the other hand, the second sulfonated lignin and humic acid, as macromolecular organic carriers, provide physical attachment sites for sulfur autotrophic oxidizing bacteria in the material, helping them to form a uniform and stable microbial community. After the fertilizer is applied to the soil, it provides a certain physical microenvironment for them to maintain their survival and function.

[0024] In summary, the present invention includes at least one of the following beneficial technical effects: 1. The present invention solves the technical problem of achieving both rapid and long-term effectiveness in saline-alkali land improvement by incorporating a gradient acidification mode into the preparation method. During preparation, a first sulfonated lignin is first used to rapidly reduce the pH value of the material, creating favorable breeding conditions for sulfur autotrophic bacteria. The sulfur autotrophic bacteria are then used to continuously oxidize elemental sulfur to produce sulfuric acid, achieving deep acidification of the fertilizer system. The fertilizer produced by this method, when applied to the soil, can both rapidly neutralize alkalinity and maintain the soil's acidity through the continued action of microorganisms.

[0025] 2. Through a specific component formulation and preparation process, this invention establishes a bidirectional synergistic relationship between the components, enhancing the fertilizer's overall performance. The low pH environment generated by the metabolism of sulfur autotrophic bacteria enhances the ability of the second sulfonated lignin and humic acid to complex with sodium ions in the soil. Furthermore, the macromolecular structure of the second sulfonated lignin and humic acid provides a carrier for the sulfur autotrophic bacteria to attach. This synergistic relationship ensures that the final product combines multiple functions, including efficient chemical complexation, sustained bioacid production, and improved soil aggregate structure.

[0026] 3. The present invention provides a safe and controllable method for preparing acidic organic fertilizer. The entire preparation process does not directly add high-risk chemicals such as liquid strong acid. Instead, the acid is generated through in-situ biotransformation within the material system, improving the safety of production operations. Furthermore, by controlling process parameters such as fermentation temperature, time, and feeding sequence, the pH value of the final product can be precisely controlled, ensuring the stability and consistency of product quality.

[0027] 4. The fertilizer product provided by the present invention has components and structures that enable it to simultaneously achieve multi-dimensional improvements to saline-alkali soils. First, the product itself has a pH value of 3.0 to 5.0, and can directly neutralize the alkalinity of the soil after being applied to the soil; at the same time, the sulfur autotrophic oxidizing bacteria contained therein can continue to utilize elemental sulfur for metabolism, continuously produce acidic substances, and maintain the neutralization effect on the alkalinity of the soil. Secondly, the second sulfonated lignin and humic acid in the product, as high molecular weight organic polymers, can be used as binders in the soil to bond the dispersed soil particles into a water-stable aggregate structure, thereby improving the physical properties of the soil. Finally, nutrients such as nitrogen, phosphorus, and potassium in the fertilizer mainly exist in the organic fermentation matrix in an organic or complexed form, and their release depends on the mineralization of soil microorganisms. The process rate is relatively slow, thereby achieving a slow release of nutrients, reducing the risk of loss and extending the fertilizer supply cycle. DETAILED DESCRIPTION

[0028] To make the purpose, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with specific embodiments. It should be understood that the specific embodiments herein are only used to explain the present invention and are not used to limit the scope of protection of the present invention.

[0029] The sources and specifications of the main raw materials and reagents used in the following examples and comparative examples are as follows. Reagents not specifically specified are all commercially available products of analytical grade or higher.

[0030] Acidithiobacillus is a strain with the species number ATCC19377 preserved in the American Type Culture Collection.

[0031] Thiobacillus ferrooxidans is a strain numbered ATCC23270 preserved in the American Type Culture Collection.

[0032] Elemental sulfur powder is industrial grade elemental sulfur powder with a purity of ≥99.5%, a particle size passing through a 200-mesh sieve, and a CAS number of 7704-34-9.

[0033] Humic acid is mineral humic acid powder derived from weathered lignite, with a humic acid content of ≥70%.

[0034] The organic fermentation matrix is ​​made of a mixture of fully decomposed cow dung and crushed corn straw in a ratio of 1:1 by dry matter weight.

[0035] Example 1

[0036] This embodiment provides a gradient preparation method for a multi-dimensional improved organic fertilizer for saline-alkali land.

[0037] 1. Raw material preparation: Prepare the following raw materials by weight: Organic fermentation substrate: 60 kg, which was a mixture of cow dung and corn straw powder at a dry weight ratio of 2.5:1.

[0038] First sulfonated lignin: 7.5 kg, with a molecular weight of 2,000 g / mol and a degree of sulfonation of 2.0 mmol / g.

[0039] Second sulfonated lignin: 7.5 kg, with a molecular weight of 30,000 g / mol and a degree of sulfonation of 1.1 mmol / g.

[0040] Elemental sulfur powder: 3 kg, particle size less than 74 μm.

[0041] Sulfur autotrophic oxidizing bacteria: 0.8 kg, containing Acidithiobacillus and Ferrothiobacillus, with a strain ratio of 4:1 and a total effective viable count of not less than 1.0 × 10 9 CFU / g.

[0042] Humic acid: 8 kg, humic acid content not less than 70%.

[0043] 2. Preparation method: Step (1) Thermophilic pre-decomposition: 60 kg of organic fermentation substrate was placed in a trough fermentation tank, clean water was added and stirred, and the moisture content of the substrate was adjusted to 58%. The turning device was started and the substrate was turned twice a day. The substrate temperature was raised to 65°C within 3 days and the temperature was maintained in the range of 60°C-65°C for 8 days. The turning was then stopped and the substrate was allowed to cool naturally to 38°C.

[0044] Step (2) Gradient acidification and coordinated fermentation: (2a) Add 7.5 kg of the first sulfonated lignin to the material obtained in step (1), and stir at a low speed for 18 minutes by a mechanical device to mix the mixture evenly.

[0045] (2b) Subsequently, 7.5 kg of the second sulfonated lignin, 3 kg of elemental sulfur powder, 8 kg of humic acid, and 0.8 kg of sulfur autotrophic oxidizing bacteria were added to the material obtained in step (2a), and the mixture was stirred for 25 minutes by a mechanical device to mix them uniformly. The mixed material was piled up, and the ambient temperature was maintained at 30° C. by an environmental control system. The material was tossed every 36 hours. After fermentation was continued for 18 days, the final product was obtained.

[0046] Example 2

[0047] This embodiment provides a gradient preparation method for a multi-dimensional improved organic fertilizer for saline-alkali land.

[0048] 1. Raw material preparation: Prepare the following raw materials by weight: Organic fermentation substrate: 70 kg.

[0049] First sulfonated lignin: 5 kg, with a molecular weight of 1,000 g / mol and a degree of sulfonation of 1.5 mmol / g.

[0050] Second sulfonated lignin: 5 kg, with a molecular weight of 20,000 g / mol and a degree of sulfonation of 0.8 mmol / g.

[0051] Elemental sulfur powder: 1 kg.

[0052] Sulfur autotrophic oxidizing bacteria: 0.5 kg, containing Acidithiobacillus and Ferrothiobacillus, with a strain ratio of 3:1 and a total effective viable count of not less than 1.0 × 10 9 CFU / g.

[0053] Humic acid: 5 kg.

[0054] 2. Preparation method: The preparation method is the same as that of Example 1, and the process parameters are adjusted as follows: Step (1) Thermophilic pre-decomposition: Adjust the moisture content of the material to 55%. Maintain the temperature between 55°C and 60°C and continue fermentation for 7 days. Then cool to below 40°C.

[0055] Step (2) Gradient acidification and coordinated fermentation: In step (2b), the ambient temperature is maintained at 25° C., and the fermentation is continued for 14 days to obtain the final product.

[0056] Example 3

[0057] This embodiment provides a gradient preparation method for a multi-dimensional improved organic fertilizer for saline-alkali land.

[0058] 1. Raw material preparation: Prepare the following raw materials by weight: Organic fermentation substrate: 50 kg.

[0059] First sulfonated lignin: 10 kg, with a molecular weight of 3,000 g / mol and a degree of sulfonation of 2.5 mmol / g.

[0060] Second sulfonated lignin: 10 kg, having a molecular weight of 40,000 g / mol and a degree of sulfonation of 1.4 mmol / g.

[0061] Elemental sulfur powder: 5 kg.

[0062] Sulfur autotrophic oxidizing bacteria: 1 kg, containing Acidithiobacillus and Ferrothiobacillus, with a strain ratio of 5:1 and a total effective viable count of not less than 1.0 × 10 9 CFU / g.

[0063] Humic acid: 10 kg.

[0064] 2. Preparation method: The preparation method is the same as that of Example 1, and the process parameters are adjusted as follows: Step (1) Thermophilic pre-decomposition: Adjust the moisture content of the material to 60%. Maintain the temperature between 65°C and 70°C and continue fermentation for 10 days. Then cool to below 40°C.

[0065] Step (2) Gradient acidification and coordinated fermentation: In step (2b), the ambient temperature is maintained at 35° C., and the fermentation is continued for 21 days to obtain the final product.

[0066] Comparative Example 1: Compared with Example 1, the difference is that the raw materials used only contain 60 kg of organic fermentation substrate, and no first sulfonated lignin, second sulfonated lignin, elemental sulfur powder, sulfur autotrophic oxidizing bacteria agent and humic acid are added; the preparation method only performs step (1) of thermophilic pre-decomposition in Example 1, and the final product is obtained after fermentation is completed. All other aspects are the same.

[0067] Comparative Example 2: The difference from Example 1 lies in the preparation method: all the raw materials listed in Example 1 (I) were mixed uniformly at once, and then fermented at an ambient temperature of 30°C for 18 days. The stepwise addition of the gradient acidification process was not performed. All other processes were the same.

[0068] Comparative Example 3: Compared with Example 1, the difference lies in the preparation method: in step (2a), the first sulfonated lignin is not added, and the operation of step (2b) is directly performed after step (1). The rest are the same.

[0069] Comparative Example 4: Compared with Example 1, the difference lies in the preparation method: in step (2b), no sulfur autotrophic oxidizing bacteria agent is added. The rest are the same.

[0070] Test Example 1: Physical and Chemical Properties of Fertilizer Products 1. Test subjects: The final products prepared in Examples 1 to 3 and Comparative Examples 1 to 4.

[0071] 2. Test method: (1) Final pH determination: Step 1: Take the final product of each group, air-dry it, grind it, and pass it through a 2mm sieve.

[0072] Step 2: Accurately weigh 10.0 g of the sieved sample and place it in a 100 mL beaker.

[0073] Step 3: Add 50 mL of deionized water (material-water ratio is 1:5) to the beaker and stir with a glass rod for 5 minutes to fully disperse it.

[0074] Step 4: After the beaker has rested for 1 hour, use a pH meter calibrated with standard buffers (pH 4.00, 6.86, 9.18) to insert the electrode into the supernatant of the sample suspension. Once the reading stabilizes, record the pH value. Repeat the measurement three times for each sample and take the average value.

[0075] (2) Determination of organic matter content: Determined by potassium dichromate volumetric method (external heating method).

[0076] Step 1: Take the final product of each group, dry it in a 65℃ oven to constant weight, grind it and pass it through a 0.15mm sieve.

[0077] Step 2: Accurately weigh 0.2 g of the processed sample and place it in a hard digestive tube.

[0078] Step 3: Add 5.00 mL of 1.0 mol / L potassium dichromate-sulfuric acid solution and 20 mL of concentrated sulfuric acid.

[0079] Step 4: Place the digestion tube in a digestion apparatus preheated to 180°C and heat digestion for 5 minutes.

[0080] Step 5: After cooling, transfer all the digestion solution to a 250 mL Erlenmeyer flask, add water to about 100 mL, and add 3 drops of o-phenanthroline indicator.

[0081] Step 6: Titrate with 0.2 mol / L ferrous sulfate standard solution until the solution color changes from orange-yellow to blue-green and finally to brick red. This is the endpoint. Record the volume of ferrous sulfate standard solution consumed. Simultaneously perform a blank test.

[0082] Step 7: Calculate the organic matter content based on the titrated consumption.

[0083] 3. Test results: The test results of the physical and chemical properties of the products of each embodiment and comparative example are recorded in Table 1.

[0084] Table 1: Test results of physical and chemical properties of products in various examples and comparative examples sample Final pH Organic matter content (%) Example 1 4.21 47.3 Example 2 4.65 53.8 Example 3 3.88 41.2 Comparative Example 1 7.82 64.7 Comparative Example 2 5.63 46.8 Comparative Example 3 6.15 47.1 Comparative Example 4 5.17 47.5 Test result analysis: The test data in Table 1 show that the final pH values ​​of the products prepared by the methods of Examples 1, 2, and 3 are all within the acidic range of 3.0 to 5.0. This result is attributed to the gradient acidification and synergistic fermentation process adopted. In this process, the first sulfonated lignin added in step (2a), by virtue of its low molecular weight and high degree of sulfonation, first realizes chemical startup acidification in the material system, reducing the environmental pH value to a slightly acidic range suitable for microbial activity. This provides the necessary startup conditions for the sulfur autotrophic oxidizing bacteria added in step (2b), enabling it to be rapidly activated and metabolized with elemental sulfur as energy, and continuously generating sulfuric acid through biological oxidation, thereby further deeply reducing the pH value of the material system and stabilizing it in the target acidic range.

[0085] Comparing the results of Example 1 with those of Comparative Examples 3 and 4 confirms the functionality of the key components in the gradient acidification mechanism. Comparative Example 3, which did not add the first sulfonated lignin, achieved a final pH of 6.15, significantly higher than that of Example 1. This confirms the necessity of a chemically initiated acidification step for activating the subsequent bioacidification process. Comparative Example 4, which did not add the sulfur autotrophic oxidizing agent, achieved a final pH of 5.17, which, while acidic, fell outside the target range. This demonstrates that deep acidification cannot be achieved solely with sulfonated lignin, and that bioacidification by sulfur autotrophic bacteria is the decisive factor in achieving and stabilizing the pH range of 3.0-5.0.

[0086] By comparing the results of Example 1 with those of Comparative Example 2, the necessity of a specific preparation process sequence can be confirmed. In Comparative Example 2, all raw materials were mixed and fermented at one time, and the final pH value was 5.63, which failed to reach the same acidification level as in Example 1. This shows that the sequential feeding steps designed in this technical solution, i.e., the process flow of chemically starting acidification first and then conducting biological synergistic fermentation, is an indispensable technical feature for achieving efficient and deep acidification. As a conventional organic fertilizer, the pH value of Comparative Example 1 is neutral to alkaline, which further proves the uniqueness of the acidic fertilizer product prepared by this technical solution.

[0087] Test Example 2: Soil pH Improvement Effect Test 1. Experimental materials and equipment: Test soil: Surface soil (0-20 cm) from saline-alkali areas, air-dried, and then passed through a 2 mm sieve. The initial pH was determined to be 8.95.

[0088] Culture container: a plastic culture bowl with a capacity of 1 kg.

[0089] Test objects: the final products prepared in Examples 1 to 3 and Comparative Examples 1 to 4.

[0090] Others: deionized water, pH meter, constant temperature incubator.

[0091] 2. Experimental methods: Step 1: Divide the air-dried test soil into 800 g per pot.

[0092] Step 2: Set up 9 treatment groups, namely: blank control group (CK, no fertilizer applied), Example 1 treatment group, Example 2 treatment group, Example 3 treatment group, Comparative Example 1 treatment group, Comparative Example 2 treatment group, Comparative Example 3 treatment group, and Comparative Example 4 treatment group. Set up 3 replicates for each treatment group.

[0093] Step 3: Add each fertilizer sample to the culture pot of the corresponding treatment group at an application rate of 2.5 g / kg soil (equivalent to 2.0 g per pot) and mix thoroughly with the soil.

[0094] Step 4: Slowly add deionized water to each culture pot, adjust the soil moisture content to 60% of the maximum field water holding capacity, and weigh and record.

[0095] Step 5: Place all the culture pots in a constant temperature incubator at 25°C for cultivation. During the cultivation period, add deionized water by weighing every 3 days to maintain a constant soil moisture content.

[0096] Step 6: Collect representative soil samples from each pot on the 7th, 30th, and 60th day of incubation. Prepare a soil suspension at a 1:5 soil-to-water ratio (10.0 g soil sample to 50 mL deionized water). After stirring and allowing to stand, measure and record the pH using a calibrated pH meter.

[0097] 3. Test results: The effects of different treatments on the pH value of saline-alkali soil are recorded in Table 2.

[0098] Table 2: Effects of different treatments on pH value of saline-alkali soil sample Initial pH pH value on day 7 pH value on day 30 pH value on day 60 Blank control 8.95 8.91 8.87 8.85 Example 1 8.95 7.42 6.95 6.81 Example 2 8.95 7.63 7.21 7.14 Example 3 8.95 7.25 6.78 6.63 Comparative Example 1 8.95 8.82 8.71 8.66 Comparative Example 2 8.95 7.91 7.58 7.52 Comparative Example 3 8.95 8.24 7.72 7.63 Comparative Example 4 8.95 7.73 7.45 7.48 Test result analysis: The data in Table 2 show that compared to the blank control group and the comparative examples, the soil pH values ​​in the treatment groups treated with the products of Examples 1, 2, and 3 showed a sustained and significant decrease throughout the 60-day incubation period. By the 7th day of incubation, the soil pH value in the Example group had already dropped rapidly, which is attributed to the direct neutralization of soil alkalinity by the acidic substances contained in the fertilizer products. As the incubation time increased, the pH value further decreased and remained at a low level, indicating that the functional components in the fertilizers continued to function in the soil environment, providing a continuous source of acidic substances.

[0099] Comparison of Example 1 with Comparative Examples 3 and 4 reveals the role of the gradient acidification mechanism in soil applications. The rate of soil pH decline in the treatment group of Comparative Example 3 (without the addition of the first sulfonated lignin) lagged significantly behind that of Example 1, indicating that the presence of a chemically initiated acidification component in the fertilizer is essential for rapidly establishing an environment suitable for microbial activity in the soil. In the treatment group of Comparative Example 4 (without the addition of a sulfur autotrophic oxidizing agent), the pH initially declined but then stabilized and even rebounded slightly, failing to achieve a sustained decrease. This confirms that sulfur autotrophic bacteria, as the core of biological acid production, are the decisive factor in achieving long-term, stable soil acidification.

[0100] Comparison of Example 1 with Comparative Example 2 (all raw materials mixed at once) demonstrates the necessity of a specific preparation process. The soil pH in the Example 1 treatment group remained significantly lower than that in the Comparative Example 2 treatment group throughout the entire cycle. This indicates that the fertilizer product, prepared via the gradient acidification process, has its functional components in a synergistic, preparatory state, enabling it to exhibit more efficient and sustained acid production upon application to the soil. This result confirms the direct correlation between this preparation method and the soil-improving effects of the final product.

[0101] Test Example 3: Test on the effect of reducing the water-soluble sodium ion content in soil 1. Experimental materials and equipment: Test subjects: Soil samples from each treatment group in Test Example 2 after 60 days of cultivation.

[0102] Main equipment: flame photometer, reciprocating oscillator, centrifuge, analytical balance.

[0103] Main reagents: deionized water, sodium chloride standard stock solution.

[0104] 2. Experimental methods: Step 1: The soil samples from each group after incubation in Test Example 2 were air-dried, ground, and passed through a 2 mm sieve.

[0105] Step 2: Accurately weigh 20.0 g of sieved soil sample and place it in a 250 mL Erlenmeyer flask.

[0106] Step 3: Accurately add 100 mL of deionized water to the flask to form a soil-water ratio of 1:5.

[0107] Step 4: Place the Erlenmeyer flask on a reciprocating shaker and shake at 200 times / min for 30 minutes at 25°C.

[0108] Step 5: Centrifuge the shaken suspension at 4000 rpm for 10 minutes and collect the supernatant. If the supernatant is not clear, filter it through ash-free filter paper and collect the filtrate. This filtrate is the soil water extract.

[0109] Step 6: Use the sodium chloride standard stock solution to prepare a series of sodium ion solutions with standard concentrations for drawing a standard curve.

[0110] Step 7: Use a flame photometer to measure the sodium ion concentration in the soil water extract of each sample at a set wavelength.

[0111] Step 8: Calculate the mass content of water-soluble sodium ions in the soil (unit: mg / kg) based on the measured concentration and soil-water ratio.

[0112] 3. Test results: The effects of different treatments on soil water-soluble sodium ion content are recorded in Table 3.

[0113] Table 3: Effects of different treatments on soil water-soluble sodium ion content sample <![CDATA[Initial water-soluble Na + Content (mg / kg)]]> <![CDATA[Water-soluble Na on the 60th day + Content (mg / kg)]]> Blank control 2150 2135 Example 1 2150 987 Example 2 2150 1152 Example 3 2150 843 Comparative Example 1 2150 1956 Comparative Example 2 2150 1418 Comparative Example 3 2150 1633 Comparative Example 4 2150 1521 Test result analysis: The test data in Table 3 show that the water-soluble sodium ion content of the soil in the treatment groups treated with the products of Examples 1, 2, and 3 was significantly reduced compared to the blank control group and each comparative example group. This result is directly related to the reduction in soil pH in Test Example 2. The fertilizer product prepared by this technical solution reduces the pH value of the soil environment by in-situ acid production. The low pH environment promotes the full protonation of functional groups such as sulfonic acid groups and carboxyl groups carried by high molecular polymers such as the second sulfonated lignin and humic acid in the fertilizer. These functional groups fix the free water-soluble sodium ions in the soil solution through ion exchange and complexation, thereby reducing its effective concentration in the soil.

[0114] Comparing the results of Example 1 with those of Comparative Examples 3 and 4 validates the role of the different functional components in the product. The water-soluble sodium ion content of the soil in Comparative Example 4 (without the addition of the sulfur autotrophic oxidizing agent) was significantly higher than that in Example 1, indicating that the acid produced by the continuous metabolism of the sulfur autotrophic bacteria is key to maintaining a low pH environment and driving the complexation reaction. The results of Comparative Example 3 (without the addition of the first sulfonated lignin) were also inferior to those of Example 1, indicating that the chemically initiated acidification step is essential for rapidly establishing a microenvironment conducive to subsequent bioacid production and complexation reactions; its omission reduces the overall efficiency of the system.

[0115] Comparison of Example 1 with Comparative Example 2 (all raw materials mixed at once) confirms the necessity of a specific preparation process. The Example 1 treatment group demonstrated significantly superior water-soluble sodium ion removal compared to Comparative Example 2, demonstrating that the fertilizer produced using the gradient acidification process establishes an effective synergistic foundation among its internal functional components. This process ensures the timing and functional coupling of the three processes—chemically initiated acidification, biological relay acidification, and polymer complexation—enabling more efficient soil operation and achieving a greater reduction in water-soluble sodium ions. This demonstrates the contribution of this preparation method to achieving the ultimate technical effect.

[0116] Test Example 4: Test on the effect of increasing the content of water-stable aggregates in soil 1. Experimental materials and equipment: Test subjects: Soil samples from each treatment group in Test Example 2 after 60 days of cultivation.

[0117] Main equipment: water-stable aggregate analyzer (wet screening method), set sieves (apertures include 2mm, 1mm, 0.5mm, 0.25mm), drying oven, analytical balance.

[0118] 2. Experimental methods: Step 1: Air-dry the soil samples from each group after incubation in Test Example 2, remove visible plant residues, and break the soil into small pieces with a diameter of less than 10 mm along the natural structural surface.

[0119] Step 2: Accurately weigh 50.0 g of the treated soil sample and place it evenly on the top layer of a sieve with a pore size of 2 mm.

[0120] Step 3: Place the sieve set containing the soil sample into the sieve bucket of the water-stable aggregate analyzer and add deionized water until the soil sample is submerged. After soaking for 10 minutes, start the instrument and vibrate up and down at a frequency of 30 times / minute with an amplitude of 4 cm for 30 minutes.

[0121] Step 4: After the vibration is completed, carefully remove the sieve set and rinse the materials retained on each level of the sieve surface into aluminum boxes of known mass.

[0122] Step 5: Place the aluminum box containing aggregates of various levels in an oven at 105°C and dry to constant weight, weigh and record.

[0123] Step 6: Calculate the mass of water-stable aggregates at each particle size, and finally calculate the percentage of water-stable aggregates with a particle size greater than 0.25 mm in the total mass of the soil sample.

[0124] 3. Test results: The effects of different treatments on the content of soil water-stable aggregates (>0.25 mm) are recorded in Table 4.

[0125] Table 4: Effects of different treatments on the content of soil water-stable aggregates (>0.25 mm) sample Initial content (%) Content on the 60th day (%) Blank control 11.8 12.3 Example 1 11.8 26.7 Example 2 11.8 23.1 Example 3 11.8 30.4 Comparative Example 1 11.8 13.9 Comparative Example 2 11.8 19.5 Comparative Example 3 11.8 17.2 Comparative Example 4 11.8 18.3 Test result analysis: The data in Table 4 show that the treatment groups treated with the products of Examples 1, 2, and 3 had significantly higher levels of water-stable soil aggregates with a particle size greater than 0.25 mm than the blank control group and the comparative example groups. This result demonstrates that the fertilizer product prepared by this technical solution can improve the physical structure of the soil. This effect occurs because the second sulfonated lignin and humic acid in the product act as high-molecular-weight organic polymers, acting as binders in the soil. These polymers interact with the surface of soil particles through their functional groups, bonding the dispersed soil particles into larger aggregate structures, thereby improving the structural stability of the soil.

[0126] Comparing the results of Example 1 with Comparative Examples 1, 3, and 4 demonstrates the synergistic effect between the product components. Comparative Example 1 (conventional organic fertilizer) achieved limited improvement in aggregate content, demonstrating that relying solely on the organic fermentation matrix cannot effectively rebuild soil structure. The results of Comparative Examples 3 and 4 were both inferior to those of Example 1, which aligns with the results of Test Examples 2 and 3: the product's ability to lower soil pH through acid production and complex water-soluble sodium ions is a prerequisite for its structural improvement function. The lower pH and water-soluble sodium ion content reduce the dispersibility of soil colloids, creating a favorable chemical environment for the polymer to effectively perform its cementing function.

[0127] Comparison of Example 1 with Comparative Example 2 (all raw materials mixed at once) confirms the necessity of a specific preparation process. The Example 1 treatment significantly improved soil aggregate content compared to Comparative Example 2. This demonstrates that the gradient acidification process achieves functional coupling within the product—chemical activation, bioacidification, and polymer complexation and cementation—during the preparation stage. This allows for more efficient and simultaneous regulation of the soil's chemical environment and reconstruction of its physical structure upon application. This result confirms the contribution of this preparation method to achieving the ultimate soil structural improvement.

[0128] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A multi-dimensional improved organic fertilizer for saline-alkali land, characterized in that: The invention comprises the following raw materials in parts by weight: Organic fermentation matrix: 50-70 parts; First sulfonated lignin: 5-10 parts, with a molecular weight range of 1000-3000 g / mol and a sulfonation degree of 1.5-2.5 mmol / g; Second sulfonated lignin: 5-10 parts, with a molecular weight range of 20,000-40,000 g / mol and a sulfonation degree of 0.8-1.4 mmol / g; Elemental sulfur powder: 1-5 parts; Sulfur autotrophic oxidizing bacteria agent: 0.5-1 part, wherein the sulfur autotrophic oxidizing bacteria agent comprises acidithiobacillus and ferrooxidans; Humic acid: 5-10 parts.

2. The saline-alkali land multidimensional improved organic fertilizer according to claim 1, characterized in that The final pH value of the fertilizer is 3.0-5.

0.

3. The saline-alkali land multidimensional improved organic fertilizer according to claim 1, characterized in that The organic fermentation matrix is ​​prepared by mixing cow dung and corn straw powder in a dry weight ratio of 2:1 to 3:

1.

4. The saline-alkali land multidimensional improved organic fertilizer according to claim 1, characterized in that The effective viable bacteria count of Acidithiobacillus and Ferrothiobacillus is not less than 1.0×10 9 CFU / g.

5. A gradient preparation process for the multidimensional improved organic fertilizer for saline-alkali land according to any one of claims 1 to 4, characterized in that: The following steps are involved: (1) Thermophilic pre-decomposition: The organic fermentation substrate is thermophilically fermented at a temperature range of 55°C to 70°C for 7 to 10 days with a water content of 55% to 60%, and then cooled to below 40°C; (2) Gradient acidification and synergistic fermentation: (2a) adding the first sulfonated lignin to the material obtained in step (1) and mixing them uniformly; (2b) Subsequently, the second sulfonated lignin, elemental sulfur powder, humic acid and sulfur autotrophic oxidizing bacteria are added to the material obtained in step (2a) and mixed evenly, and then aerobic fermentation is carried out at a temperature of 25° C. to 35° C. for 14 to 21 days until the pH value of the material is stabilized in the range of 3.0 to 5.

0.

6. The gradient preparation process according to claim 5, characterized in that: The thermophilic pre-decomposition in step (1) adopts tank fermentation, and is turned over 1 to 2 times a day.

7. The gradient preparation process according to claim 5, characterized in that: In step (2a), after adding the first sulfonated lignin, stirring is carried out at a low speed for 15 to 20 minutes.

8. The gradient preparation process according to claim 5, characterized in that: The aerobic fermentation in step (2b) is achieved by turning the material once every 24 to 48 hours.

9. The gradient preparation process according to claim 5, characterized in that: In step (2b), the end of fermentation is marked by the pH value of the material changing by less than 0.2 for three consecutive days.

10. The gradient preparation process according to claim 5, characterized in that: After the fermentation is completed, the process also includes drying the material to a moisture content of less than 20%.