A method for synchronously improving saline-alkali soil based on low-temperature stable acidic water-soluble fertilizer

Abstract

The present invention relates to the technical field of saline-alkali soil improvement, and in particular to a saline-alkali soil synchronous improvement method based on low-temperature stable acidic water-soluble fertilizer, comprising: step 1: dynamic zoning of soil profile, excavation of soil profile by grid method and collection of soil samples in layers; step 2: in-situ synthesis of water-soluble fertilizer, reaction of ammonium dihydrogen phosphate, citric acid and hydroxylated humic acid nano-colloid to form acidic mother liquor; coating calcium nitrate with rosin glycerol ester-polyvinyl alcohol copolymer to form calcium source microcapsule particles; compounding the acidic mother liquor, calcium source microcapsule particles and phase change regulator to obtain low-temperature stable final fertilizer; step 3: dynamic improvement of zoning, spraying fertilizer solution dominated by acidic mother liquor to fast salt return area, and burying conductivity sensor. Through precise soil zoning, synthesis and dynamic regulation of low-temperature stable fertilizer, targeted and efficient soil improvement can be achieved, and the quality of cultivated layer soil in saline-alkali areas can be significantly improved.

Description

Technical Field

[0001] The present invention relates to the technical field of saline-alkali soil improvement, and in particular to a saline-alkali soil synchronous improvement method based on low-temperature stable acidic water-soluble fertilizer. Background Art

[0002] Saline-alkali soils, due to their high concentrations of sodium ions (Na⁺), strong alkalinity (pH > 8.5), and compacted structure, lead to osmotic imbalance and nutrient fixation, severely inhibiting crop root development and ion absorption. Especially during seasonal salinity reversion periods (such as the spring warming period), groundwater salt migrates with capillary water into the cultivated layer, forming surface salt frost, which reduces crop emergence by 40%-70%. According to surveys, saline-alkali lands cover 99 million hectares in my country. Conventional soil improvement techniques are difficult to implement in the Northeast, Northwest, and coastal regions due to prolonged low-temperature periods (average annual temperatures below 5°C for >150 days) and water scarcity. In these areas, saline-alkali soil improvement requires simultaneously addressing three core requirements: adaptability to low temperatures, simultaneous salinization and alkali removal, and dynamic, precise control. Existing technologies have yet to effectively address these challenges, specifically the following:

[0003] Ion release is hindered: Traditional acidic water-soluble fertilizers (such as ammonium sulfate-citric acid mixtures) significantly reduce their solubility at low temperatures (<5°C), resulting in hydrogen ion (H⁺) and calcium ion (Ca²⁺) release rates less than 30% of those at room temperature. For example, conventional liquid silicon fertilizers crystallize at 0°C, making them impractical for application through drip irrigation systems. This prevents timely neutralization of soil OH⁻ during the peak spring salinity period, leading to a persistent increase in sodium ion activity.

[0004] Inhibition of microbial activity: Bacterial amendments (such as Bacillus velezensis) experience metabolic stagnation at low temperatures, significantly reducing their salt-solubilizing and growth-promoting effects. Experiments have shown that the colonization rate of bacterial agents at 5°C is only 18% of that at 25°C, and the onset of phosphorus and nitrogen fixation is delayed by over 15 days.

[0005] Limitations of physical salt control: While existing physical salt control technologies (such as "mulch covering and straw covering") can prevent salt from rising, burying the straw layer at a depth of >30 cm requires large-scale machinery and cannot be implemented in the spring when the frozen ground has not yet thawed. Furthermore, mulching can exacerbate the lag in soil temperature recovery, delaying sowing by 20-30 days.

[0006] The contradiction between the shortage of arable land and food security in severely saline-alkali areas is becoming increasingly acute. The defects of existing technologies have seriously restricted the improvement of saline-alkali arable land productivity. There is an urgent need for a method for synchronous improvement of saline-alkali soil based on low-temperature stable acidic water-soluble fertilizer to solve the above problems. Summary of the Invention

[0007] Based on the above objectives, the present invention provides a method for simultaneously improving saline-alkali soil based on low-temperature stable acidic water-soluble fertilizer, comprising:

[0008] Step 1: Dynamically partition the soil profile, excavate the soil profile according to the grid method and collect soil samples in layers;

[0009] Active sodium ion concentration, exchangeable calcium and magnesium ion saturation, and buffer pH were measured under simulated field low temperature conditions;

[0010] The rapid salinization zone, stable salinization zone, and potential salinization zone were divided according to the salt migration rate and alkalinity mutation threshold. The salt migration rate was calculated by the daily increase in surface soil electrical conductivity, and the alkalinity mutation threshold was determined by the change rate of the buffer pH value of the adjacent soil layer.

[0011] Step 2: In-situ synthesis of water-soluble fertilizer: reacting ammonium dihydrogen phosphate, citric acid and hydroxylated humic acid nanocolloid to form an acidic mother liquor;

[0012] Calcium nitrate is coated with rosin glycerol ester-polyvinyl alcohol copolymer to form calcium source microcapsule particles;

[0013] The acidic mother solution, calcium source microcapsule particles and phase change regulator are compounded to obtain a low-temperature stable final fertilizer;

[0014] Step 3: Dynamically improve the area by spraying a fertilizer solution dominated by acidic mother liquor (i.e., a fertilizer solution with an acidic mother liquor weight ratio of 60% or more) to the rapid salt return area, and bury a conductivity sensor;

[0015] When the increase in electrical conductivity drops to the set threshold, a fertilizer solution dominated by calcium source microcapsules is injected into the stable salt accumulation area for deep loosening;

[0016] The proportion of fertilizer solution components is dynamically adjusted according to the calcium and magnesium ion exchange efficiency, wherein the calcium and magnesium ion exchange efficiency is calculated by the molar ratio of calcium and sodium ions in the extract.

[0017] Preferably, the method for determining the alkalinity mutation threshold in step 1 includes:

[0018] Soil samples were collected at fixed depth intervals in the 40-60 cm soil layer, and the buffer pH value of each soil sample was measured;

[0019] Calculate the rate of change of buffer pH values ​​at adjacent soil layers, where the rate of change is the difference between the buffer pH value of the upper layer and the buffer pH value of the lower layer, divided by the distance between the upper and lower layers;

[0020] When the absolute value of the change rate reaches a preset critical value, the depth interval is marked as an alkalinization mutation interface;

[0021] The continuous soil layer containing the alkaline mutation interface is delineated as a potential alkalinization zone, and the preset critical value is obtained through statistical analysis of historical saline-alkali disaster data.

[0022] Preferably, the preparation method of the hydroxylated humic acid nano-colloid in step 2 comprises:

[0023] Dissolve humic acid in alkaline solution to form a suspension, and slowly add the etherifying agent dropwise under constant temperature and stirring conditions;

[0024] After the addition is completed, the reaction system is adjusted to an acidic environment to precipitate the modified humic acid;

[0025] The precipitate is collected by centrifugation and is processed into a colloidal dispersion system by ultrasonication;

[0026] The power and duration of the ultrasonic crushing are dynamically adjusted according to the colloid particle size detection result until the colloid particle size is stabilized in the nanometer range.

[0027] Preferably, the coating method of the calcium source microcapsule particles in step 2 includes:

[0028] dissolving rosin glycerol ester and polyvinyl alcohol in a mixed solvent to form a coating solution, wherein the ratio of the mixed solvent is optimized based on the elongation at break test result of the coating film at low temperature;

[0029] Placing calcium nitrate powder in a fluidized bed and controlling the air flow velocity to fluidize the powder;

[0030] The coating liquid is injected into the fluidized powder spray, and hot air is introduced simultaneously to crosslink and solidify the coating film;

[0031] The hot air temperature is determined based on a coating film swelling experiment to ensure that the film material maintains its intact structure in a 5° C. soil environment for at least 24 hours.

[0032] Preferably, the method for determining the conductivity increase threshold in step 3 includes:

[0033] Continuously monitor soil conductivity at the target soil depth before fertilization and record the basic fluctuation range;

[0034] Based on the maximum value of the basic fluctuation range, the increase threshold is set proportionally;

[0035] The ratio is adjusted according to the correspondence between the salt migration rate and the salt tolerance threshold of the crop. When the salt migration rate exceeds the critical value of crop tolerance, the threshold is proportionally lowered to trigger the operation of deep plowing and injecting calcium source microcapsule-dominated fertilizer solution in advance.

[0036] Preferably, the operation method of deep loosening and injection in step 3 includes:

[0037] Use deep loosening equipment equipped with a fertilizer injection device consisting of parallel arranged injection needles;

[0038] Adjust the pitch angle of the injection needle so that the fertilizer liquid injection direction forms an acute angle with the forward direction of the equipment;

[0039] Control the output pressure of the fertilizer liquid delivery system to ensure that the fertilizer liquid penetrates to the target soil depth;

[0040] The pitch angle is determined based on soil compaction test data, and when the soil compaction is higher than a critical value, the angle is increased to enhance shear disturbance;

[0041] The output pressure is calculated based on the soil porosity and clay content to ensure that the fertilizer liquid forms a continuous diffusion zone in the target soil layer.

[0042] Preferably, the dynamic adjustment of the fertilizer solution components in step 3 specifically includes the following methods:

[0043] Soil extracts from each partition were collected weekly to determine the molar concentration ratio of calcium ions to sodium ions;

[0044] When the molar concentration ratio is lower than the preset target value, the mass proportion of the calcium source microcapsule particles in the fertilizer solution is increased;

[0045] When the buffer pH value rises beyond the allowable range compared to the initial stage of improvement, additional acid mother solution should be sprayed;

[0046] The preset target value and the allowable range are determined by the growth status of the crop root system in a potted plant preliminary test.

[0047] Preferably, the method for controlling the dripping rate of the etherifying agent includes:

[0048] Monitor the transmittance of the reaction system in real time and suspend the addition when the transmittance is lower than the safety threshold;

[0049] The safety threshold is determined by a correlation model between the reaction by-product generation rate and the transmittance;

[0050] After the transmittance returns to a safe range, the dripping operation is resumed at a gradually decreasing rate;

[0051] The rate change function of the gradient reduction is dynamically adjusted according to the reaction exothermic peak temperature.

[0052] Preferably, the method for verifying the integrity of the coating film includes:

[0053] The coated microcapsule particles were immersed in a simulated soil solution;

[0054] The particles were taken out at different time points and the surface cracking was observed using microscopic imaging technology;

[0055] Calculate the duration of time when the crack area ratio reaches the critical value of damage;

[0056] When the duration does not meet the design requirements, adjust the ratio of rosin glycerol ester to polyvinyl alcohol in the coating solution;

[0057] The ratio adjustment direction is determined according to the membrane material swelling degree-brittleness balance curve.

[0058] Preferably, the evaluation method for ensuring that the fertilizer liquid forms a continuous diffusion zone in the target soil layer includes:

[0059] Excavate the section 24 hours after fertilizer injection and measure the horizontal and vertical extension of the fertilizer liquid wetting front;

[0060] When the extended distance does not cover the target area, increase the output pressure or the amount of fertilizer injected in proportion;

[0061] The ratio is calculated based on the ratio of soil hydraulic conductivity to solution viscosity;

[0062] The hydraulic conductivity coefficient is obtained through a double-ring infiltration test.

[0063] Beneficial effects of the present invention:

[0064] 1. The present invention adopts a low-temperature stable acidic water-soluble fertilizer, especially a compound of hydroxylated humic acid nano-colloid and calcium source microcapsule particles, which can effectively improve the ion solubility and release rate in a low-temperature environment.

[0065] 2. By precisely controlling the molar ratio of calcium ions to sodium ions in the fertilizer solution, this method makes its conditioning effect on saline-alkali soils more direct and stable. By dynamically adjusting the fertilizer solution composition, it avoids the low-temperature effects that hinder the effectiveness of traditional microbial preparations, ensuring a sustained improvement of saline-alkali soils.

[0066] 3. The present invention adopts deep loosening and injection of fertilizer liquid dominated by calcium source microcapsules. By configuring a special fertilizer liquid injection device, it can accurately apply fertilizer in a low-temperature environment, overcoming the problems faced by traditional physical salt barrier technology such as inconvenient mechanical operation and difficulty in low-temperature operation.

[0067] 4. The low-temperature stable acidic water-soluble fertilizer of the present invention utilizes calcium source microcapsule particle coating technology to ensure that the fertilizer solution remains stable at low temperatures and does not precipitate crystals or lose effectiveness due to temperature fluctuations. Furthermore, by dynamically adjusting the composition ratio of the fertilizer solution, particularly by monitoring and optimizing the calcium and magnesium ion exchange efficiency, the fertilizer solution formulation and application rate can be adjusted in real time as the degree of soil salinization and salt return rate change, thereby ensuring that the improvement effect of saline-alkali soil can be continuously and precisely regulated in low-temperature environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0068] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0069] Figure 1 is a flow chart of the steps of the method of the present invention;

[0070] Figure 2 Flow chart of the steps of the method for determining the alkalinity mutation threshold value according to the method of the present invention;

[0071] Figure 3 The figure is a flow chart of the steps of the preparation method of hydroxylated humic acid nano-colloid according to the present invention. DETAILED DESCRIPTION

[0072] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments. It is also noted that, to provide a more detailed description, the following embodiments are best and preferred embodiments, and those skilled in the art may employ alternative methods for implementing certain known technologies. Furthermore, the accompanying drawings are intended only to provide a more detailed description of the embodiments and are not intended to limit the present invention.

[0073] See Figure 1-Figure 3 The present invention provides a method for simultaneously improving saline-alkali soil using a low-temperature stable acidic water-soluble fertilizer. This method uses a grid-based method to excavate the soil profile and collect soil samples in layers, ensuring detailed analysis of each soil layer. Soil characteristics, including salinity, pH, and other relevant physical and chemical properties, are recorded at each sampling point.

[0074] Under simulated low-temperature conditions (e.g., below 5°C), soil active sodium ion concentration, exchangeable calcium and magnesium ion saturation, and buffer pH are measured. These parameters are crucial for the management of saline-alkali soils and can help assess the dynamic migration of salt and its impact on soil fertility.

[0075] Based on the soil's salt migration rate and alkalinity threshold, and by analyzing the daily increase in surface soil electrical conductivity and the rate of change in buffer pH, we can delineate areas of rapid salinization, stable salt accumulation, and potential alkalinization. This precise zoning facilitates the rational planning of subsequent fertilization and soil improvement strategies, ensuring that each area receives the most appropriate treatment.

[0076] This step effectively assesses the degree of salinization in different areas and implements differentiated management based on the actual soil conditions. Precise soil zoning allows for targeted improvement measures, avoiding wasteful resource use and unnecessary repeated fertilization, and improving the efficiency and effectiveness of soil improvement.

[0077] Ammonium dihydrogen phosphate is mixed with citric acid and reacted with hydroxylated humic acid nanocolloids to produce a low-temperature stable acidic mother liquor. This mother liquor is rich in hydrogen and calcium ions and can effectively adjust the soil pH and improve soil structure.

[0078] Calcium nitrate is coated with rosin glycerol ester-polyvinyl alcohol copolymer to form calcium source microcapsules. These microcapsules can slowly release calcium ions in the soil, reducing calcium ion loss and improving the solubility stability of calcium ions at low temperatures.

[0079] A low-temperature stable final fertilizer is obtained by combining an acidic mother liquor, calcium source microcapsule particles, and a phase change modifier. The phase change modifier is sodium lauryl sulfate or a polyoxyethylene ether surfactant, added at a level of 0.5%-1.2% of the total weight of the final fertilizer. The phase change modifier regulates the fertilizer's state changes at different temperatures, ensuring stability in low-temperature environments and preventing crystallization. A calcium source microcapsule-dominated fertilizer solution refers to a fertilizer solution in which the calcium source microcapsule particles account for ≥50% by weight, with the remaining components being the acidic mother liquor and the phase change modifier.

[0080] This step ensures fertilizer stability and efficiency in low-temperature environments. Low-temperature stable acidic water-soluble fertilizers ensure stable release of hydrogen and calcium ions during cold seasons, especially during the spring salt return period. This prevents the loss of efficiency of traditional fertilizers due to low temperatures, neutralizes OH⁻ in the soil, and reduces the inhibitory effect of salt on crops.

[0081] In areas with rapid salinization, a fertilizer solution dominated by an acidic mother liquor is sprayed. The acidity of this fertilizer solution neutralizes alkaline ions in the soil and provides nutrients for crops. Conductivity sensors are also embedded to monitor changes in soil conductivity in real time and determine the dynamic changes in salinity.

[0082] When the conductivity increase drops below a set threshold, deep loosening is performed in the stable salt accumulation area, followed by injection of a fertilizer solution containing calcium-source microcapsules. This fertilizer solution gradually releases calcium ions, promoting the exchange and release of sodium ions while also improving the soil's physical structure.

[0083] Dynamically adjust the calcium and magnesium ion exchange efficiency in the fertilizer solution based on the changes in the calcium-sodium ion molar ratio of the extract, ensuring that the fertilizer formula can be adaptively adjusted as the degree of soil salinization changes. Adjust the ratio of calcium and sodium sources based on different calcium and magnesium ion exchange rates to ensure that the fertilizer solution can effectively remove sodium ion accumulation in the soil.

[0084] Dynamic zoning-based improvement allows for targeted fertilization and precise control, avoiding the resource waste associated with large-scale fertilization. Real-time conductivity monitoring and dynamic adjustment of fertilizer formulations ensure optimal fertilizer effectiveness at each stage. Especially in low-temperature conditions, this method ensures fertilizer effectiveness across different soil zones, improving the stability and sustainability of soil improvement.

[0085] The present invention solves the problems of reduced fertilizer efficiency and unclear soil stratification in saline-alkali soil improvement under low temperature environments through precise soil zoning, synthesis of low-temperature stable fertilizers and dynamic regulation. It can achieve targeted and efficient soil improvement, significantly improve the quality of the cultivated layer soil in saline-alkali areas, and provide an innovative solution for agricultural production.

[0086] In one possible implementation, soil samples are collected at fixed depth intervals within a range of 40-60 cm. This depth range typically corresponds to the primary acid-base transition layer in saline-alkali soils and can represent significant areas of soil alkalinization. By collecting soil samples within this depth range, soil buffer pH data at different depth levels can be obtained.

[0087] The buffered pH value of each collected soil sample was measured. The buffered pH value is an important indicator of soil pH stability and reflects the soil's acid-base buffering capacity. When soil pH fluctuates significantly, the buffered pH value will show significant changes, making it an important indicator for determining soil alkalinity.

[0088] Calculate the buffer pH change rate between adjacent soil layers. Specifically, subtract the buffer pH value of the lower soil layer from the buffer pH value of the upper soil layer, and divide the result by the depth difference between the upper and lower layers. The buffer pH change rate reflects the sudden change trend of soil pH and can reveal the key change levels during salinization.

[0089] When the absolute value of the buffer pH change rate of adjacent soil layers reaches a preset critical value, the depth interval is marked as an alkalinization mutation interface. The preset critical value is obtained through statistical analysis of historical saline-alkali disaster data. Historical data provides empirical support for the characteristics of saline-alkali soil mutations, making the preset critical value predictive and scientific.

[0090] Continuous soil layers containing alkalinity mutation interfaces are delineated as potential alkalinity zones. This process provides clear regional demarcation for subsequent soil improvement, allowing for more precise fertilizer application and improvement measures in different areas. Identification of potential alkalinity zones helps prioritize areas for treatment to prevent further alkalinization.

[0091] Scientific analysis and precise identification of alkalinization mutation interfaces can provide more targeted and actionable solutions for saline-alkali soil improvement. In particular, precise fertilization with low-temperature-stable fertilizers in low-temperature environments makes saline-alkali soil improvement more efficient, avoiding over-fertilization and resource waste. Furthermore, preset critical values ​​derived from historical data analysis enhance the practical application of this method, making it widely applicable to different types of saline-alkali soil improvement.

[0092] In one possible embodiment, humic acid is first dissolved in an alkaline solution to form a humic acid suspension. An alkaline environment facilitates the full dissolution of the humic acid and increases its reactivity. Humic acid can be better expanded in an alkaline solution, facilitating subsequent chemical modification reactions.

[0093] Under constant temperature and stirring conditions, an etherifying agent, in this embodiment, propylene oxide or chloroacetic acid, is slowly added dropwise. The etherifying agent functions to modify the structure of the humic acid molecules, promoting the modification and modification of their surface functional groups, thereby enhancing their effectiveness in soil improvement. Control of the addition process is very important to ensure a gentle reaction to avoid excessively rapid reaction that leads to the formation of byproducts or degradation of the humic acid.

[0094] After the etherifying agent is added, the reaction system needs to be adjusted to an acidic environment. Acidic conditions promote the precipitation of the modified humic acid, forming a solid precipitate. This step controls the reaction progress by adjusting the pH value and allows the modified humic acid to precipitate from the solution, facilitating subsequent separation and processing.

[0095] After the reaction is complete, the modified humic acid is separated from the reaction solution by centrifugation and the precipitate is collected. Centrifugation can effectively remove unreacted impurities and other components in the solution, resulting in a relatively pure modified humic acid precipitate.

[0096] The collected precipitate is treated with ultrasonic crushing technology until a colloidal dispersion is formed. The effect of ultrasound can physically break down large particles in the precipitate, causing them to disperse into small particles, ultimately obtaining a hydroxylated humic acid colloid with a nanometer particle size. The ultrasonic crushing power and time in this process need to be dynamically adjusted according to the detection results of the colloid particle size to ensure that the colloid particle size is stable within the nanometer range. In this embodiment, the dynamic adjustment includes: when the laser particle size analyzer detects that the particle size is greater than 200nm, the ultrasonic power is increased from 300W to 500W and the treatment is extended for 10 minutes. When the particle size is less than 100nm, the initial parameters are restored. Nanoscale colloids have a large specific surface area and good dispersibility, which can significantly improve their activity in soil.

[0097] By combining chemical modification with physical treatment, low-temperature-stable hydroxylated humic acid nanocolloids can be efficiently and precisely prepared. This colloid not only enhances soil improvement but also exhibits strong adaptability, enabling it to function long-term under low-temperature conditions. Its high efficiency, environmental friendliness, and expanded scope of application make it an important technical tool for saline-alkali soil improvement.

[0098] In one possible implementation, rosin glycerol ester and polyvinyl alcohol (PVA) are first dissolved in an optimized mixed solvent in a proportioned mixture to form a coating solution. This mixed solvent consists of polar solvents such as water and ethanol. The ratio of these solvents is optimized by testing the elongation at break of the coating film at low temperatures to ensure that the film retains good flexibility and ductility at low temperatures (e.g., 5°C) and avoid brittle failure. In this embodiment, the optimization method is as follows: when the elongation at break at -5°C is less than 80%, the ethanol content is increased; when the elongation is greater than 120%, the water content is increased.

[0099] Calcium nitrate powder is added to the fluidized bed reactor and the air flow rate is adjusted to keep the powder in a well-fluidized state. This state facilitates the uniform spraying of the coating liquid on the particle surface, preventing agglomeration and uneven coating.

[0100] During fluidized bed operation, the coating solution is sprayed onto the fluidized calcium nitrate particles. Simultaneously, an appropriate amount of hot air is introduced to assist in film formation, crosslinking, and drying of the coating material in the solution. The key to this step is controlling the spray particle size, droplet viscosity, and hot air temperature to achieve a uniform, crack-free, and dense coating.

[0101] The hot air temperature used must be determined based on the membrane material's swelling test results. This test simulates soil water absorption and expansion at 5°C. By comparing the structural stability of the membrane material at different temperatures, the optimal hot air temperature is determined to ensure the membrane maintains structural integrity for at least 24 hours at 5°C, thereby ensuring the timeliness and reliability of the calcium source's slow-release effect.

[0102] By scientifically selecting coating materials and precisely controlling process parameters, calcium fertilizers exhibit excellent slow-release properties and stability in low-temperature, saline-alkali environments. This technology integrates chemical modification, fluid coating, and physical property control, offering an innovative solution for improving saline-alkali soils and efficiently supplementing calcium for crops. This method significantly improves calcium fertilizer utilization, reduces environmental impact, and holds great promise for widespread application.

[0103] In one possible implementation, soil salinity can be assessed by continuously monitoring soil electrical conductivity at a target depth before fertilization. Electrical conductivity (EC), as a key indicator of soil salt concentration, can provide a real-time snapshot of salt accumulation. The monitoring period should be long enough to fully capture the baseline fluctuation range—the range of soil EC fluctuations in the absence of fertilization. This fluctuation range is typically affected by season, climate, and soil type.

[0104] Based on the maximum value of the recorded baseline fluctuation range, a conductivity increase threshold is set. This threshold is typically a percentage of the maximum value. This percentage is typically adjusted based on the salinity and alkalinity of the soil and the growth requirements of the crop. In this example, when the salt migration rate is greater than 5 cm / day or the crop salt tolerance threshold is less than 2 dS / m, the increase threshold is lowered to 110% of the baseline value.

[0105] The salt migration rate directly affects the distribution and accumulation rate of soil salt. If the soil salt migration rate is fast, it may cause salt to accumulate rapidly and exceed the salt tolerance threshold of crops. Therefore, when setting the increase threshold, it is necessary to refer to the correspondence between the salt migration rate and the salt tolerance threshold of crops. When monitoring finds that the salt migration rate is high, causing salt accumulation to exceed the tolerance threshold of crops, deep loosening and injection of fertilizer solution dominated by calcium source microcapsules should be triggered in advance. To this end, it is necessary to proportionally lower the increase threshold so that salt problems can be detected in advance and salt damage to crops can be prevented.

[0106] When the increase in soil electrical conductivity exceeds a set threshold, deep loosening and the injection of fertilizer solution, led by calcium-source microcapsules, are immediately triggered. This operation aims to promote the deep movement of salts through deep loosening, and through the appropriate application of fertilizer, improve soil structure and increase water absorption, thereby effectively alleviating soil salinization.

[0107] By setting and dynamically adjusting the increase threshold based on conductivity monitoring, early warning and precise response to soil salinity issues are ensured. This method effectively prevents the damage to crops caused by excessive salt accumulation in saline-alkali soils, optimizes fertilization practices, and promotes soil health and crop growth. This method has significant practical value and potential for expansion in improving the productivity of saline-alkali soils and enhancing crop salt tolerance.

[0108] In one possible implementation, deep tillage and calcium-source microcapsule-based fertilizer injection requires the use of specially designed deep tillage equipment equipped with a fertilizer injection device that accurately injects the fertilizer deep into the soil. This device consists of multiple parallel injection needles that evenly and precisely distribute the fertilizer, effectively improving soil fertility.

[0109] To enhance the permeability and diffusion of liquid fertilizer, the pitch angle of the spray needle needs to be adjusted. By setting the acute angle between the spray needle and the forward direction of the device, the fertilizer can be injected into the soil at a specific angle, thereby improving its penetration and distribution depth. A reasonable spray angle helps the fertilizer form an effective diffusion zone deep in the soil, preventing excessive concentration of fertilizer in the surface layer, which can affect soil improvement in deeper layers.

[0110] The fertilizer delivery system regulates the spraying effect of the liquid fertilizer by controlling the output pressure. Appropriate pressure ensures that the fertilizer liquid penetrates to the target soil depth, effectively improving saline-alkali soils. The pressure of the fertilizer delivery system needs to be dynamically adjusted based on the actual soil conditions (such as soil compaction and porosity) to ensure that the fertilizer liquid penetrates to the appropriate depth and fully contacts the soil.

[0111] In this embodiment, the output pressure of the fertilizer delivery system is dynamically adjusted according to the following empirical formula:

[0112] ;

[0113] in, is the output pressure (unit: MPa), is the soil compaction (unit: MPa) measured at the target soil depth. The clay content is measured by a laser particle size analyzer to determine the proportion of particles smaller than 0.002 mm.

[0114] The above empirical formula is applicable to saline-alkali soil (electrical conductivity EC≤8 dS / m), soil compaction At 1.5-3.0MPa, clay content Between 10% and 40%;

[0115] Adjusting the pitch angle is directly related to soil compaction. When soil compaction exceeds a critical value, the pitch angle of the jet needle needs to be increased to enhance the shearing effect of the fertilizer liquid, helping it to break through the compacted soil layer and penetrate deeper into the soil. This effectively overcomes the barrier to fertilizer penetration caused by soil compaction, ensuring even distribution of the fertilizer liquid at the target depth.

[0116] To ensure that the fertilizer solution penetrates the target soil layer and forms a continuous diffusion zone, the output pressure must be precisely calculated based on the soil's porosity and clay content. Soil porosity is closely related to the permeability of the fertilizer solution, while clay content affects soil compactness and the degree of fertilizer diffusion. Proper pressure regulation ensures that the fertilizer solution forms a uniform diffusion zone in the soil, effectively improving soil fertility and alleviating salinization.

[0117] Through precise equipment configuration and technical adjustments, saline-alkali soils can be effectively improved, enhancing their fertility and structure, and ensuring that liquid fertilizer is distributed deeply and evenly throughout the target soil layer. This technology not only addresses the salinity issue in saline-alkali soils, but also improves soil compaction and enhances soil arability, providing a more stable and efficient soil management solution for agricultural production.

[0118] In one possible implementation, soil extracts from each zone are regularly collected during soil improvement, and changes in the soil are monitored by measuring the ion concentrations in the extracts. This step is performed weekly to track the molar ratio of calcium ions to sodium ions in the soil. Analyzing the calcium and sodium ion concentrations in the extracts can effectively assess the degree of soil salinization and the progress of soil improvement.

[0119] Calcium and sodium ions play a crucial role in saline-alkali soils. Calcium ions improve soil structure, while sodium ions contribute primarily to salinization. The molar ratio of calcium ions to sodium ions is a key indicator for evaluating soil improvement effectiveness. A low ratio indicates an excess of sodium ions, resulting in a more saline-alkaline soil and ineffective soil improvement.

[0120] When the measured molar concentration ratio of calcium ions to sodium ions is lower than the preset target value, it indicates that the soil is calcium deficient and may require additional calcium source to alleviate salinization. In this case, increasing the mass percentage of calcium source microcapsules in the fertilizer solution promotes effective calcium supplementation, improves the calcium ion content in the soil, and enhances the soil's resistance to salinization and alkali.

[0121] During the soil improvement process, changes in soil pH are a key indicator. Typically, soil pH will drop initially, but may rebound over time. If the buffer pH rises beyond the acceptable range compared to the initial improvement period, the fertilizer formulation should be adjusted, and additional application of an acidified mother solution should be applied. This acidified mother solution can help suppress the rise in soil pH, maintaining an acidic environment and preventing a rebound in salinity.

[0122] To ensure the effectiveness of dynamically adjusting fertilizer composition, preliminary potted plant tests are necessary to determine appropriate target values ​​and ranges. During these tests, the growth of crop roots is monitored and, combined with experimental data, the appropriate molar ratio of calcium ions to sodium ions, as well as the allowable pH rise, are determined. These values ​​provide a reference standard for subsequent soil improvement operations, making the soil improvement process more precise and controllable.

[0123] By dynamically adjusting the composition of the fertilizer solution, particularly the ratio of calcium-source microcapsules and the amount of acidic mother solution applied, the composition of the fertilizer solution can be precisely controlled based on the molar ratio of calcium ions to sodium ions in the soil and changes in soil pH. This approach can effectively improve the structure and fertility of saline-alkali soils, optimize the growing environment for crops, reduce fertilizer waste, and enhance the effectiveness and sustainability of soil improvement.

[0124] In one possible embodiment, an optical sensor is used to monitor the light transmittance of the reaction system in real time during the reaction. Changes in light transmittance can reflect the concentration of suspended matter in the reaction system and, therefore, indicate whether the reaction is proceeding smoothly. Typically, during etherification reactions, the formation of byproducts can cause turbidity in the reaction system, reducing light transmittance. Therefore, using light transmittance to determine the reaction status facilitates timely control of the addition rate.

[0125] Through experimental research, a correlation model between transmittance and the rate of reaction by-product generation was established to determine a safety threshold.

[0126] In this embodiment, the correlation model between light transmittance and reaction by-product generation rate is expressed by the following formula:

[0127] ;

[0128] in, is the by-product generation rate, in mg / min;

[0129] It is the real-time light transmittance, measured by spectrophotometer at a wavelength of 600 nm;

[0130] is an empirical constant with a value of 0.15.

[0131] When the transmittance of the reaction system is lower than this safety threshold, it means that the reaction by-product generation rate is too fast or the reaction process is abnormal. At this time, the addition of the etherifying agent needs to be suspended to prevent the reaction from producing too many by-products or the reaction system from getting out of control.

[0132] Once the transmittance of the reaction system returns to a safe range, byproduct formation has stabilized and the reaction can continue. At this point, resume the dropwise addition of the etherifying agent, gradually adding it at a decreasing rate. This gradual decrease in rate ensures a more stable reaction and avoids drastic fluctuations caused by excessively rapid additions.

[0133] The gradient reduction rate function in this control method is dynamically adjusted based on the peak exothermic temperature. In etherification reactions, the exothermic heat can affect the reaction rate, making the peak exothermic temperature a key factor in regulating the addition rate. When the reaction exotherm is too rapid or the temperature reaches a certain peak, the addition rate needs to be adjusted appropriately to prevent the adverse effects of excessive temperature on the reaction. The addition rate is adjusted in real time based on the peak exothermic temperature to ensure the reaction proceeds within the control range.

[0134] By monitoring the transmittance of the reaction system in real time and establishing a correlation model with the rate of reaction byproduct formation, the droplet addition process in the etherification reaction can be more precise, avoiding issues such as rapid byproduct formation or runaway reaction control. By dynamically adjusting the droplet addition rate and gradually reducing it based on the peak exothermic temperature of the reaction, the stability and efficiency of the reaction can be ensured. This control method not only improves reaction safety but also optimizes the production process, reduces byproducts, and enhances the controllability and cost-effectiveness of the reaction, offering significant technical advantages.

[0135] In one possible implementation, the coated microcapsules are first placed in a simulated soil solution to simulate the immersion of the microcapsules in a real-world environment. The composition of the simulated soil solution should be as close as possible to the aqueous solution properties of actual soil, including varying pH values ​​and salt concentrations, to more realistically reflect the performance of the coating in real-world applications.

[0136] At different time points, the soaked microcapsules were removed and the coating film surface was observed using microscopic imaging technology to see if any cracks appeared. Microscopic imaging technology can clearly display the microstructure of the film surface, helping to accurately locate the location and extent of any cracks. Often, during observation, cracks may develop in the coating film over time due to swelling or external factors, affecting the stability of the coating.

[0137] Through microscopic image analysis, the coating film surface crack area percentage is calculated and the duration of cracks reaching the critical damage threshold is measured. When the crack area percentage reaches the set critical value, the duration of cracks is recorded to evaluate the durability and stability of the coating film. This process helps to understand the performance of the coating film in specific environments and its long-term feasibility.

[0138] If the calculated crack area percentage and duration do not meet design requirements, it indicates a problem with the coating film's integrity and requires adjustments to the coating solution formulation. Specifically, the ratio of rosin glycerol ester to polyvinyl alcohol in the coating solution should be adjusted to optimize the film's physical properties and enhance its durability. Adjusting the ratio of rosin glycerol ester to polyvinyl alcohol helps control the film's flexibility, swelling, and brittleness, improving its crack resistance.

[0139] The direction of adjusting the ratio depends on the film material's swelling-brittleness balance curve. This curve guides material selection and ratio, thereby optimizing the balance between the film's swelling characteristics and brittleness. This balance is crucial, as excessive swelling can lead to film susceptibility to cracking, while excessive brittleness can reduce the film's elasticity and crack resistance. By adjusting the ratio, the coating film achieves optimal swelling and brittleness, thereby improving the film's durability and ensuring it resists cracking during extended use.

[0140] By employing microscopic imaging, crack area analysis, and fertilizer ratio adjustments, we effectively verify and optimize the integrity of the coating. This approach ensures coating stability, reduces cracking, and enhances the long-term effectiveness of soil-improving fertilizers, thereby increasing the sustainability of the soil-improving effect and fertilizer utilization.

[0141] In one possible implementation, a soil profile is first excavated within 24 hours of fertilization to observe and measure fertilizer diffusion. The excavation should be located near the fertilizer application area to observe the fertilizer wetting front (i.e., the farthest boundary of fertilizer diffusion in the soil). The horizontal and vertical extension of the fertilizer wetting front is measured within the profile to understand the depth and lateral spread of the fertilizer in the soil. This measurement helps assess whether the fertilizer has evenly penetrated the target soil layer and confirms that the fertilizer distribution is as expected.

[0142] If the measurement results show that the fertilizer's wetting front has not reached the target soil layer, indicating that the fertilizer has not fully covered the target area, the fertilization parameters need to be adjusted. Based on the difference between the measured extension distance and the target soil layer, the fertilizer output pressure or injection volume should be appropriately increased to ensure that the fertilizer fully penetrates the target soil layer and forms a continuous diffusion zone. Increasing the injection volume or output pressure helps enhance the fertilizer's ability to penetrate the soil, thereby ensuring even distribution of the fertilizer in the target area.

[0143] The ratio for adjusting fertilization parameters (such as output pressure or injection volume) is primarily calculated based on the ratio of the soil's hydraulic conductivity to the solution's viscosity. Hydraulic conductivity measures the soil's ability to move water, while solution viscosity influences the fluidity of the fertilizer solution. Low hydraulic conductivity or high solution viscosity results in slower soil penetration, necessitating an appropriate increase in output pressure or fertilizer volume to compensate for insufficient penetration. This ratio allows for precise adjustments, ensuring even fertilizer distribution across varying soil conditions.

[0144] During this process, the hydraulic conductivity is determined using the double-ring infiltration test. This test involves placing two concentric rings on the soil surface and applying water flow to the inner and outer rings, respectively. The hydraulic conductivity of the soil is estimated by observing how water penetrates the soil. This test provides data on soil permeability, helping to assess soil water mobility and providing a basis for adjusting fertilization parameters.

[0145] By measuring the extension of the fertilizer wetting front, adjusting fertilization parameters based on the ratio of soil hydraulic conductivity to solution viscosity, and obtaining an accurate hydraulic conductivity through a double-ring infiltration test, fertilizer penetration can be optimized and evenly distributed. This method improves soil improvement efficiency, avoids fertilizer waste, and enhances long-term soil improvement, making it an effective method for improving saline-alkali soils.

[0146] To verify the effectiveness of the method for simultaneously improving saline-alkali soils using a low-temperature stable acidic water-soluble fertilizer, a 90-day field trial was conducted in a typical saline-alkali region. The experimental setup is as follows:

[0147] Experimental Design:

[0148] Experimental group: The method of the present invention (low-temperature stable acidic water-soluble fertilizer + zoned dynamic improvement) was adopted.

[0149] Control group 1: Conventional acidic water-soluble fertilizer (ammonium sulfate-citric acid compound) was evenly applied at the same frequency.

[0150] Control group 2: No improvement treatment was performed (blank control).

[0151] Three replicate plots were set up in each group, and each plot had an area of ​​20 m².

[0152] Initial soil basic physical and chemical properties: surface layer (0-20 cm) electrical conductivity (EC) = 5.8±0.3 dS / m, buffer pH = 9.2±0.1, exchangeable sodium percentage (ESP) = 28.7±2.5%, soil compaction (0-30 cm) >2.0 MPa.

[0153] Key indicator monitoring:

[0154] Soil physical and chemical properties: Soil samples were collected from 0-20 cm (cultivated layer) and 20-40 cm (subsurface layer) before treatment (day 0), 30 days, 60 days, and 90 days after treatment, and the EC, buffer pH, ESP, calcium-sodium ion molar ratio (Ca²⁺ / Na⁺), and soil compaction were measured.

[0155] Fertilizer efficiency performance: Monitor the low-temperature solubility stability of low-temperature stable fertilizers (observe the crystallization and measure the effective calcium dissolution rate after placing at -5°C to 10°C for 48 hours).

[0156] Crop response (optional): Plant salt-tolerant pioneer crops (such as Suaeda salsa) in the later stage of the experiment and record the emergence rate and biomass (fresh weight).

[0157] Experimental results data:

[0158] Table 1: Changes in key soil indicators in the cultivated layer (0-20 cm) (mean ± standard deviation)

[0159] Treatment group Time (days) EC (dS / m) Buffer pH ESP (%) Ca²⁺ / Na⁺ (molar ratio) Soil compaction (MPa) Experimental group 0 5.8 ± 0.3 9.2 ± 0.1 28.7±2.5 0.15 ± 0.03 2.15 ± 0.20 30 4.1 ± 0.2* 8.3 ± 0.1* 19.2±1.8* 0.38 ± 0.05* 1.80 ± 0.15* 60 3.0 ± 0.2* 7.9 ± 0.1* 12.5±1.2* 0.65 ± 0.08* 1.55 ± 0.10* 90 2.3 ± 0.1* 7.6 ± 0.1* 8.4 ± 1.0* 0.92 ± 0.10* 1.35 ± 0.08* Control group 1 0 5.7 ± 0.4 9.1 ± 0.1 29.0±2.3 0.14 ± 0.03 2.18 ± 0.18 30 5.5 ± 0.3 8.9 ± 0.2 27.5±2.0 0.18 ± 0.04 2.10 ± 0.17 60 5.8 ± 0.4 9.0 ± 0.2 28.8±1.9 0.16 ± 0.03 2.05 ± 0.16 90 6.0 ± 0.3^ 9.1 ± 0.1 30.2±2.1^ 0.13 ± 0.02 2.00 ± 0.15 Control group 2 0 5.9 ± 0.3 9.3 ± 0.1 29.5±2.6 0.13 ± 0.02 2.20 ± 0.22 30 6.5 ± 0.4^ 9.4 ± 0.1 32.0±2.8^ 0.10 ± 0.02 2.25 ± 0.20 60 7.2 ± 0.5^ 9.5 ± 0.1 35.8±3.0^ 0.08 ± 0.01 2.30 ± 0.22 90 8.0 ± 0.6^ 9.6 ± 0.1 40.5±3.5^ 0.06 ± 0.01 2.35 ± 0.25

[0160] Note: “^” indicates significant difference compared with the value on day 0 of the same group (p<0.05) and worse than the initial state.

[0161] Table 2: Changes in key soil indicators in the subsurface layer (20-40 cm) (mean ± SD at 90 days)

[0162] Treatment group EC (dS / m) Buffer pH ESP (%) Ca²⁺ / Na⁺ (molar ratio) Experimental group 3.5 ± 0.2* 7.8 ± 0.1* 10.8±1.5* 0.85 ± 0.09* Control group 1 5.2 ± 0.3 8.8 ± 0.1 26.0±2.1 0.17 ± 0.03 Control group 2 7.5 ± 0.5^ 9.3 ± 0.1 38.2±3.2^ 0.07 ± 0.01

[0163] Note: “^” indicates significantly worse than the initial state (p<0.05).

[0164] Table 3: Performance test of low temperature stable fertilizer (placed at -5℃ to 10℃ for 48 hours)

[0165] Temperature (°C) Final fat status of the experimental group Effective calcium dissolution rate of the experimental group (%) Control group 1 (conventional fertilizer) status Effective calcium dissolution rate of control group 1 (%) 10 clear solution 98.5 ± 1.2 Slightly turbid, with a small amount of precipitation 85.3 ± 3.5 5 clear solution 97.0 ± 1.5 Obvious turbidity, more precipitation 62.1 ± 4.8 0 Slightly turbid, no precipitation 92.5 ± 2.0 Large amount of precipitation, stratification 28.7 ± 5.2 -5 Turbid, trace precipitation 88.3 ± 2.8 Complete solidification, crystal precipitation <5.0

[0166] Table 4: Crop (Suaeda salsa) growth response (at 90 days)

[0167] Treatment group Seedling rate (%) Fresh weight (g / m²) Experimental group 85.7 ± 5.3* 1250 ± 85* Control group 1 42.3 ± 7.1 580 ± 65 Control group 2 18.6 ± 4.5 220 ± 45

[0168] Result analysis:

[0169] The soil improvement effect was significant: within 90 days, the EC value of the cultivated layer in the experimental group significantly decreased from 5.8 dS / m to 2.3 dS / m (a 60.3% decrease), the buffer pH decreased significantly from 9.2 to 7.6 (a 1.6-unit decrease), the ESP decreased significantly from 28.7% to 8.4% (a 70.7% decrease), the Ca²⁺ / Na⁺ molar ratio increased significantly from 0.15 to 0.92 (a 513% increase), and the soil compaction decreased significantly from 2.15 MPa to 1.35 MPa (a 37.2% decrease). Salinity and alkalinity indicators in the subsurface layer (20-40 cm) also significantly improved, demonstrating that the zoned dynamic improvement was effective at different soil depths. In contrast, control group 1 (conventional fertilizer) showed no significant improvement in any of these indicators, and even saw a slight deterioration (increased EC and ESP), while control group 2 (no fertilizer) continued to experience worsening salinization.

[0170] Excellent low-temperature stability: As shown in Table 3, the low-temperature stable final fertilizer prepared by the present invention maintains high solubility and an effective calcium ion dissolution rate (92.5%) at 0°C, with only slight turbidity and no precipitation. At -5°C, it still has an effective calcium dissolution rate of 88.3%, with only trace precipitation. Conventional acidic water-soluble fertilizers, on the other hand, show significant turbidity and precipitation at 5°C, with an effective calcium dissolution rate plummeting to 62.1%. At 0°C, they are virtually ineffective (dissolution rate <30%, completely solidified). This fully demonstrates the critical role of coating technology and phase change modifiers in maintaining fertilizer stability at low temperatures.

[0171] Promoting crop growth: When Suaeda salsa was planted on the improved soil in the experimental group, the germination rate reached 85.7%, and the fresh weight reached 1250 g / m², which was significantly better than the control group 1 (germination rate 42.3%, fresh weight 580 g / m²) and the control group 2 (germination rate 18.6%, fresh weight 220 g / m²), directly reflecting the substantial improvement in soil quality.

[0172] Conclusion: The above experimental data strongly prove the superiority of the method of the present invention:

[0173] It can effectively and synchronously reduce the salinity (EC) and alkalinity (pH, ESP) of saline-alkali soil, significantly improve the soil physical structure (compactness), and improve the quality of the cultivated layer and subsurface soil.

[0174] The synthesized low-temperature stable acidic water-soluble fertilizer can still maintain high solubility and ion release capacity in a low temperature environment (0℃ to -5℃), solving the problem of conventional fertilizer failure at low temperatures.

[0175] The dynamic improvement strategy of partitioning (based on conductivity sensor feedback) achieves precise control and high resource utilization efficiency.

[0176] Ultimately, the soil environment was significantly improved, providing good growth conditions for crops (such as Suaeda salsa), and increasing the emergence rate and biomass.

[0177] The present invention encompasses any alternatives, modifications, equivalents, and solutions that fall within the spirit and scope of the present invention. To provide a thorough understanding of the present invention, specific details are described in detail below in connection with the preferred embodiments of the present invention, but those skilled in the art will be able to fully understand the present invention without these detailed descriptions. Furthermore, to avoid unnecessary confusion regarding the essence of the present invention, well-known methods, processes, procedures, components, and circuits have not been described in detail.

[0178] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A method for synchronously improving saline-alkali soil based on low-temperature stable acidic water-soluble fertilizer, characterized in that: include: Step 1: Dynamically partition the soil profile, excavate the soil profile according to the grid method and collect soil samples in layers; Active sodium ion concentration, exchangeable calcium and magnesium ion saturation, and buffer pH were measured under simulated field low temperature conditions; The rapid salinization zone, stable salinization zone, and potential salinization zone were divided according to the salt migration rate and alkalinity mutation threshold. The salt migration rate was calculated by the daily increase in surface soil electrical conductivity, and the alkalinity mutation threshold was determined by the change rate of the buffer pH value of the adjacent soil layer. Step 2: In-situ synthesis of water-soluble fertilizer: reacting ammonium dihydrogen phosphate, citric acid and hydroxylated humic acid nanocolloid to form an acidic mother liquor; Calcium nitrate is coated with rosin glycerol ester-polyvinyl alcohol copolymer to form calcium source microcapsule particles; The acidic mother solution, calcium source microcapsule particles and phase change regulator are compounded to obtain a low-temperature stable final fertilizer; Step 3: Dynamic improvement of the zones, spraying fertilizer solution dominated by acidic mother liquor to the rapid salt return areas and burying conductivity sensors; When the increase in electrical conductivity drops to the set threshold, a fertilizer solution dominated by calcium source microcapsules is injected into the stable salt accumulation area for deep loosening; The proportion of fertilizer solution components is dynamically adjusted according to the calcium and magnesium ion exchange efficiency, wherein the calcium and magnesium ion exchange efficiency is calculated by the molar ratio of calcium and sodium ions in the extract.

2. The method for synchronously improving saline-alkali soil based on low-temperature stable acidic water-soluble fertilizer according to claim 1, characterized in that: The method for determining the alkalinity mutation threshold in step 1 includes: Soil samples were collected at fixed depth intervals in the 40-60 cm soil layer and the buffer pH value of each soil sample was measured; Calculate the rate of change of buffer pH values ​​at adjacent soil layers, where the rate of change is the difference between the buffer pH value of the upper layer and the buffer pH value of the lower layer, divided by the distance between the upper and lower layers; When the absolute value of the change rate reaches a preset critical value, the depth interval is marked as an alkalinization mutation interface; The continuous soil layer containing the alkaline mutation interface is delineated as a potential alkalinization zone, and the preset critical value is obtained through statistical analysis of historical saline-alkali disaster data.

3. The method for synchronously improving saline-alkali soil based on low-temperature stable acidic water-soluble fertilizer according to claim 1, characterized in that: The preparation method of the hydroxylated humic acid nano-colloid in step 2 comprises: Dissolve humic acid in alkaline solution to form a suspension, and slowly add the etherifying agent dropwise under constant temperature and stirring conditions; After the addition is completed, the reaction system is adjusted to an acidic environment to precipitate the modified humic acid; The precipitate is collected by centrifugation and is processed into a colloidal dispersion system by ultrasonication; The power and duration of the ultrasonic crushing are dynamically adjusted according to the colloid particle size detection result until the colloid particle size is stabilized in the nanometer range.

4. The method for synchronously improving saline-alkali soil based on low-temperature stable acidic water-soluble fertilizer according to claim 1, characterized in that: The coating method of the calcium source microcapsule particles in step 2 includes: dissolving rosin glycerol ester and polyvinyl alcohol in a mixed solvent to form a coating solution, wherein the ratio of the mixed solvent is optimized based on the elongation at break test result of the coating film at low temperature; Placing calcium nitrate powder in a fluidized bed and controlling the air flow velocity to fluidize the powder; The coating liquid is injected into the fluidized powder spray, and hot air is introduced simultaneously to crosslink and solidify the coating film; The hot air temperature is determined based on a coating film swelling experiment to ensure that the film material maintains its intact structure in a 5° C. soil environment for at least 24 hours.

5. The method for synchronously improving saline-alkali soil based on low-temperature stable acidic water-soluble fertilizer according to claim 1, characterized in that: The method for determining the conductivity increase threshold value in step 3 includes: Continuously monitor soil conductivity at the target soil depth before fertilization and record the basic fluctuation range; Based on the maximum value of the basic fluctuation range, the increase threshold is set proportionally; The ratio is adjusted according to the correspondence between the salt migration rate and the salt tolerance threshold of the crop. When the salt migration rate exceeds the critical value of crop tolerance, the threshold is proportionally lowered to trigger the operation of deep plowing and injecting calcium source microcapsule-dominated fertilizer solution in advance.

6. The method for synchronously improving saline-alkali soil based on low-temperature stable acidic water-soluble fertilizer according to claim 1, characterized in that: The operation method of deep loosening and injection in step 3 includes: Use deep loosening equipment equipped with a fertilizer injection device consisting of parallel arranged injection needles; Adjust the pitch angle of the injection needle so that the fertilizer liquid injection direction forms an acute angle with the forward direction of the equipment; Control the output pressure of the fertilizer liquid delivery system to ensure that the fertilizer liquid penetrates to the target soil depth; The pitch angle is determined based on soil compaction test data, and when the soil compaction is higher than a critical value, the angle is increased to enhance shear disturbance; The output pressure is calculated based on the soil porosity and clay content to ensure that the fertilizer liquid forms a continuous diffusion zone in the target soil layer.

7. The method for synchronously improving saline-alkali soil based on low-temperature stable acidic water-soluble fertilizer according to claim 1, characterized in that: The dynamic adjustment of the fertilizer solution components in step 3 specifically includes the following methods: Soil extracts from each partition were collected weekly to determine the molar concentration ratio of calcium ions to sodium ions; When the molar concentration ratio is lower than the preset target value, the mass proportion of the calcium source microcapsule particles in the fertilizer solution is increased; When the buffer pH value rises above the allowable range compared to the initial stage of improvement, additional acid mother solution should be sprayed; The preset target value and the allowable range are determined by the growth status of the crop root system in a potted plant preliminary test.

8. The method for synchronously improving saline-alkali soil based on low-temperature stable acidic water-soluble fertilizer according to claim 3, characterized in that: The method for controlling the dripping rate of the etherifying agent comprises: Monitor the transmittance of the reaction system in real time and suspend the addition when the transmittance is lower than the safety threshold; The safety threshold is determined by a correlation model between the reaction by-product generation rate and the transmittance; After the transmittance returns to a safe range, the dripping operation is resumed at a gradually decreasing rate; The rate change function of the gradient reduction is dynamically adjusted according to the reaction exothermic peak temperature.

9. The method for synchronously improving saline-alkali soil based on low-temperature stable acidic water-soluble fertilizer according to claim 4, characterized in that: Methods for verifying the integrity of the coating film include: The coated microcapsule particles were immersed in a simulated soil solution; The particles were taken out at different time points and the surface cracking was observed using microscopic imaging technology; Calculate the duration of time when the crack area ratio reaches the critical value of damage; When the duration does not meet the design requirements, adjust the ratio of rosin glycerol ester to polyvinyl alcohol in the coating solution; The ratio adjustment direction is determined according to the membrane material swelling degree-brittleness balance curve.

10. The method for synchronously improving saline-alkali soil based on low-temperature stable acidic water-soluble fertilizer according to claim 6, characterized in that: Evaluation methods to ensure a continuous spread of fertilizer solution in the target soil layer include: Excavate the section 24 hours after fertilizer injection and measure the horizontal and vertical extension of the fertilizer liquid wetting front; When the extended distance does not cover the target area, increase the output pressure or the amount of fertilizer injected in proportion; The ratio is calculated based on the ratio of soil hydraulic conductivity to solution viscosity; The hydraulic conductivity coefficient is obtained through a double-ring infiltration test.

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