Synchronous improvement method for saline-alkali soil based on low-temperature stable acidic water-soluble fertilizer

Abstract

The invention relates to the technical field of saline-alkali soil improvement, in particular to a saline-alkali soil synchronous improvement method based on a low-temperature stable acidic water-soluble fertilizer, which comprises the following steps: step 1, dynamically partitioning a soil profile, excavating the soil profile according to a grid method, and collecting soil samples in layers; 2, in-situ synthesis of a water-soluble fertilizer, wherein ammonium dihydrogen phosphate, citric acid and the hydroxylated humic acid nano colloid react to form an acidic mother solution; coating calcium nitrate with a rosin glyceride-polyvinyl alcohol copolymer to form calcium source microcapsule particles; and compounding the acidic mother liquor, the calcium source microcapsule particles and the phase change regulator to obtain the low-temperature stable final fertilizer. And step 3, performing regional dynamic improvement, spraying a fertilizer solution dominated by an acid mother solution to the rapid salt return region, and burying a conductivity sensor. Through precise soil zoning, synthesis of the low-temperature stable fertilizer and dynamic regulation and control, targeted and efficient soil improvement can be achieved, and the soil quality of a plough layer of the saline-alkali area is remarkably improved.

Description

Technical Field

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

[0002] Due to the enrichment of high-concentration sodium ions (Na⁺), strong alkalinity (pH > 8.5) and compact structure in saline-alkali soil, osmotic pressure imbalance and nutrient fixation occur, seriously inhibiting crop root development and ion absorption capacity. Especially during the seasonal salt return period (such as the spring warming period), the groundwater salt moves to the tillage layer along the capillary water, forming a surface salt frost, resulting in a 40%-70% decrease in crop emergence rate. According to investigations, the area of saline-alkali land in China reaches 99 million hectares. In the northeast, northwest and coastal areas, due to the long low-temperature period (the number of days with an average annual temperature < 5°C > 150 days) and water resource scarcity, conventional improvement technologies are difficult to implement. In such regions, the improvement of saline-alkali soil needs to simultaneously meet three core requirements: low-temperature adaptability, synchronous removal of salinity and alkalinity, and dynamic precise regulation. However, the existing technologies have not effectively solved these contradictions, including the following specific problems:

[0003] Problem of blocked ion release: The solubility of traditional acidic water-soluble fertilizers (such as the ammonium sulfate-citric acid compound system) decreases significantly at low temperatures (< 5°C), resulting in a hydrogen ion (H⁺) and calcium ion (Ca²⁺) release rate of less than 30% of that at room temperature. For example, conventional liquid silicon fertilizers crystallize at 0°C and cannot be applied through a drip irrigation system. This causes the inability to neutralize soil OH⁻ in a timely manner during the peak salt return period in spring, leading to a continuous increase in sodium ion activity.

[0004] Inhibition of microbial activity: The metabolism of bacteria-containing improvers (such as the preparation of Bacillus velezensis) stagnates at low temperatures, and their salt-dissolving and growth-promoting effects drop sharply. Experiments show that the colonization rate of the bacterial agent at 5°C is only 18% of that at 25°C, and the phosphorus-dissolving and nitrogen-fixing functions are delayed by more than 15 days.

[0005] Limitations of physical salt inhibition: Although existing physical salt inhibition technologies (such as "plastic film on top and straw below") can block the upward movement of salts, the buried depth of the straw layer > 30 cm requires large-scale mechanical operations and cannot be implemented when the spring frozen soil has not thawed. In addition, plastic film covering will exacerbate the lag in soil temperature rise and delay the sowing period by 20-30 days.

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

[0007] Based on the above purpose, the present invention provides a method for synchronous improvement of saline-alkali soil based on a low-temperature stable acidic water-soluble fertilizer, including:

[0008] Step 1: Dynamic zoning of soil profiles, excavating soil profiles by grid method and collecting soil samples in layers;

[0009] Under simulated low-temperature field conditions, measure the active sodium ion concentration, exchangeable calcium and magnesium ion saturation, and buffer pH value;

[0010] Divide the rapid salt return area, stable salt accumulation area, and potential alkalization area according to the salt migration rate and the alkalization degree mutation threshold. The salt migration rate is calculated by the continuous daily increase in surface soil conductivity, and the alkalization degree mutation threshold is determined by the change rate of buffer pH value between adjacent soil layers;

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

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

[0013] Compound the acidic mother liquor, calcium source microcapsule particles with a phase change regulator to obtain a low-temperature stable final fertilizer;

[0014] Step 3: Dynamic improvement by zoning, spraying a fertilizer solution dominated by acidic mother liquor, that is, a fertilizer solution with the mass ratio of acidic mother liquor greater than or equal to 60% in the rapid salt return area, and burying a conductivity sensor;

[0015] When the conductivity increase drops to the set threshold, deeply loosen and inject a fertilizer solution dominated by calcium source microcapsules into the stable salt accumulation area;

[0016] Dynamically adjust the component ratio of the fertilizer solution according to the calcium and magnesium ion exchange efficiency, where the calcium and magnesium ion exchange efficiency is calculated by the molar ratio of calcium and sodium ions in the leaching solution.

[0017] Preferably, the method for determining the alkalization degree mutation threshold in Step 1 includes:

[0018] Collect soil samples at a fixed depth interval in the 40 - 60 cm soil layer and measure the buffer pH value of each soil sample;

[0019] Calculate the change rate of buffer pH value between adjacent soil layer depths. The change rate is the difference between the buffer pH value of the upper layer minus 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 the preset critical value, mark this depth interval as the alkalization mutation interface;

[0021] Designate the continuous soil layer containing the alkalization mutation interface as the potential alkalization area. 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 nanocolloid in Step 2 includes:

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

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

[0025] Collect the precipitate by centrifugation, and use ultrasonic fragmentation technology to process the precipitate into a colloidal dispersion system;

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

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

[0028] Dissolve rosin glyceride and polyvinyl alcohol in a mixed solvent to form a coating solution, and the ratio of the mixed solvent is optimized according to the test results of the elongation at break of the coating film at low temperature;

[0029] Place calcium nitrate powder in a fluidized bed, and control the air flow velocity to make the powder in a fluidized state;

[0030] Spray and inject the coating solution into the fluidized powder, and simultaneously introduce hot air to crosslink and cure the coating film;

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

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

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

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

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

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

[0037] Use a deep loosening device equipped with a fertilizer solution injection device, and the injection device consists of injection needles arranged in parallel;

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

[0039] Control the output pressure of the fertilizer hydraulic delivery system to enable the fertilizer solution to penetrate to the target soil layer depth;

[0040] The pitching angle is determined according to the soil compactness test data. When the soil compactness is higher than the critical value, increase the angle to enhance the shear disturbance;

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

[0042] Preferably, in step 3, the fertilizer solution components are dynamically adjusted, specifically including the following methods:

[0043] Collect the soil extract of each sub-region every week and measure the molar concentration ratio of calcium ions to sodium ions;

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

[0045] When the buffered pH value rises by more than the allowable range compared with the initial stage of improvement, add an acidic mother liquor by topdressing;

[0046] The preset target value and the allowable range are determined by the growth state of crop roots in the pot experiment.

[0047] Preferably, the control method for the dropping rate of the etherifying agent includes:

[0048] Monitor the light transmittance of the reaction system in real time. When the light transmittance is lower than the safety threshold, suspend the dropping;

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

[0050] After the light transmittance rises back to the safe range, resume the dropping operation at a rate that decreases in a gradient;

[0051] The rate change function of the gradient decrease is dynamically adjusted according to the peak temperature of the reaction heat release.

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

[0053] Take the coated microcapsule particles and soak them in the simulated soil solution;

[0054] Take out the particles at different time points and observe the surface cracking situation by using microscopic imaging technology;

[0055] Statistically calculate the duration when the proportion of the cracking area reaches the critical value of damage;

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

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

[0058] Preferably, the evaluation method for ensuring the formation of a continuous diffusion zone of the fertilizer solution in the target soil layer includes:

[0059] Excavate the profile 24 hours after fertilizer injection, and measure the horizontal and vertical extension distances of the wetting front of the fertilizer solution;

[0060] When the extension distance does not cover the target area, increase the output pressure or the fertilizer injection amount proportionally;

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

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

[0063] Advantages of the present invention:

[0064] 1. By adopting a low - temperature - stable acidic water - soluble fertilizer, especially by using the compounding method of hydroxylated humic acid nanocolloid and calcium - source microcapsule particles, the present invention can effectively improve the ion solubility and release rate in a low - temperature environment.

[0065] 2. By precisely controlling the molar concentration ratio of calcium ions and sodium ions in the fertilizer solution, the present invention makes the adjustment effect of the fertilizer solution on saline - alkali soil more direct and stable. By dynamically adjusting the components of the fertilizer solution, the problem of low temperature where traditional microbial agents cannot play their roles is avoided, ensuring the continuous improvement effect of saline - alkali soil.

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

[0067] 4. The low - temperature - stable acidic water - soluble fertilizer of the present invention ensures that the fertilizer solution can remain stable at low temperatures through the coating technology of calcium - source microcapsule particles, and will not precipitate crystals or become ineffective due to temperature changes. In addition, by dynamically adjusting the composition ratio of the fertilizer solution, especially the monitoring and optimization of the calcium - magnesium ion exchange efficiency, the formula and application amount of the fertilizer solution can be adjusted in real time with the changes in the salinization degree and salt - return rate of the soil, thereby ensuring that the improvement effect of saline - alkali soil can be continuously and accurately regulated in a low - temperature environment. Description of the Drawings

[0068] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, for those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

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

[0070] Figure 2 is the process flow chart of the method for determining the alkalinity mutation threshold of the method of the present invention;

[0071] Figure 3 is the process flow chart of the method for preparing hydroxy humic acid nano colloid of the method of the present invention. Detailed implementation manners

[0072] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. It should be noted here that in order to make the embodiments more detailed, the following embodiments are the best and preferred embodiments. For some well-known technologies, those skilled in the art can also adopt other alternative methods for implementation; moreover, the accompanying drawings are only for more specific description of the embodiments, and are not intended to specifically limit the present invention.

[0073] Please refer to Figures 1 - 3 , the embodiment of the present invention provides a method for synchronous improvement of saline-alkali soil based on a low-temperature stable acidic water-soluble fertilizer. The soil profile is excavated by the grid method, and soil samples are collected layer by layer to ensure a detailed analysis of each soil layer. The soil characteristics of each sampling point are recorded respectively, including salt content, pH value and other relevant physical and chemical properties.

[0074] Under simulated low-temperature conditions (such as below 5°C), the concentration of active sodium ions, the saturation of exchangeable calcium and magnesium ions and the buffer pH value in the soil are measured. These parameters are crucial for the treatment of saline-alkali soil and can help evaluate the dynamic migration of salt and its impact on soil fertility.

[0075] According to the salt migration rate of the soil and the mutation threshold of alkalinity, by analyzing the daily increase of surface soil conductivity and the change rate of buffer pH value, the rapid salt return area, the stable salt accumulation area and the potential alkalization area are divided. Through this precise zoning, it is helpful to reasonably arrange subsequent fertilization and soil improvement strategies to ensure that each area receives the most suitable treatment.

[0076] This step can effectively evaluate the degree of salinization of different regions and implement differential management according to the actual conditions of the soil. Through precise soil zoning, targeted improvement measures can be applied, avoiding waste of resources and unnecessary repeated fertilization, and improving the efficiency and effect of soil improvement.

[0077] Ammonium dihydrogen phosphate and citric acid are mixed, reacted and combined with hydroxy humic acid nano colloid to generate an acidic mother liquor with low-temperature stability. The mother liquor is rich in hydrogen ions and calcium ions, and can effectively adjust the pH value of the soil and improve the soil structure.

[0078] Calcium nitrate is coated with a rosin glyceride - polyvinyl alcohol copolymer to form calcium source microcapsule particles. These microcapsule particles can slowly release calcium ions in the soil, reduce the loss of calcium ions, and at the same time improve the dissolution stability of calcium ions at low temperatures.

[0079] An acidic mother liquor, calcium source microcapsule particles and a phase change regulator are compounded to obtain a low - temperature stable final fertilizer. The phase change regulator is sodium dodecyl sulfate or a polyoxyethylene ether surfactant, and the addition amount is 0.5% - 1.2% of the total mass of the final fertilizer. The phase change regulator can regulate the state change of the fertilizer at different temperatures, ensure that the fertilizer remains stable in a low - temperature environment, and avoid crystallization and precipitation. The fertilizer solution dominated by calcium source microcapsules means that the mass ratio of calcium source microcapsule particles in the fertilizer solution is ≥50%, and the remaining components are the acidic mother liquor and the phase change regulator.

[0080] This step realizes the stability and high efficiency of the fertilizer in a low - temperature environment. The low - temperature stable acidic water - soluble fertilizer can ensure that in the cold season, especially during the spring salt - return period, it can stably release hydrogen ions and calcium ions, avoid the decline in the efficiency of traditional fertilizers due to low temperatures, timely neutralize OH⁻ in the soil, and reduce the inhibitory effect of salts on crops.

[0081] In the rapid salt - return area, a fertilizer solution dominated by the acidic mother liquor is sprayed. Through the acidic action of this fertilizer solution, the alkaline ions in the soil are neutralized, and the nutrients required by the crops are provided. An electrical conductivity sensor is buried to monitor the change of soil electrical conductivity in real time and judge the dynamic change of salts.

[0082] When the increase rate of electrical conductivity drops to the set threshold, deep - loosening and injecting the fertilizer solution dominated by calcium source microcapsules into the stable salt - accumulation area is changed. This fertilizer solution can gradually release calcium ions, promote the exchange and release of sodium ions, and at the same time improve the physical structure of the soil.

[0083] According to the change of the calcium - sodium ion molar ratio in the leaching solution, the calcium - magnesium ion exchange efficiency in the fertilizer solution is dynamically adjusted to ensure that the formula of the fertilizer solution can be adaptively adjusted with the change of soil salinization degree. According to different calcium - magnesium ion exchange rates, the ratio of calcium source and sodium source is adjusted to ensure that the fertilizer solution can effectively remove the sodium ion accumulation in the soil.

[0084] Through zonal dynamic improvement, targeted fertilization and precise regulation can be realized, and the waste of resources caused by large - scale fertilization can be avoided. By real - time monitoring of electrical conductivity and dynamically adjusting the fertilizer solution formula, it is ensured that the fertilizer solution can play the best effect at different stages. Especially under low - temperature conditions, this method can ensure the effectiveness of the fertilizer solution in different soil areas and improve the stability and sustainability of soil improvement.

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

[0086] In a possible implementation, soil samples are collected at fixed depth intervals within the depth range of 40 - 60 cm. This depth range generally corresponds to the main acid-base change layer of saline-alkali soil and can represent an important area of soil alkalization. By collecting soil samples in this depth interval, soil buffer pH value data at different depth levels can be obtained.

[0087] The buffer pH value of each collected soil sample is measured. The buffer pH value is an important indicator for measuring the stability of soil acidity and alkalinity and can reflect the acid-base buffering capacity of the soil. When the soil acidity and alkalinity change significantly, the buffer pH value will show obvious changes, so it can be used as an important basis for judging the degree of soil alkalization.

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

[0089] When the absolute value of the change rate of the buffer pH value between adjacent soil layers reaches a preset critical value, this depth interval is marked as the alkalization mutation interface. The preset critical value is obtained through statistical analysis of historical saline-alkali disaster data. Historical data can provide empirical support for the mutation characteristics of saline-alkali soil, making the preset critical value have a certain degree of predictability and scientificity.

[0090] The continuous soil layer containing the alkalization mutation interface is delimited as the potential alkalization area. This process provides a clear regional division for subsequent soil improvement, enabling more precise fertilizer application and improvement measures for different regions. The identification of the potential alkalization area helps to determine which areas need to be treated preferentially to prevent the exacerbation of the alkalization phenomenon.

[0091] Through scientific analysis and precise identification of the alkalization mutation interface, a more targeted and operable solution can be provided for the improvement of saline-alkali soil. Especially in low-temperature environments, precise fertilization with low-temperature stable fertilizers makes the improvement of saline-alkali soil more efficient, avoiding excessive fertilization and resource waste. At the same time, the preset critical value obtained through historical data analysis also enhances the practical application value of this method, enabling it to be widely applicable to the improvement of different types of saline-alkali soil.

[0092] In a possible implementation, first, humic acid is dissolved in an alkaline solution to form a suspension of humic acid. The alkaline environment helps the full dissolution of humic acid and improves its reaction activity. Humic acid can better unfold in the alkaline solution, facilitating subsequent chemical modification reactions.

[0093] Under the condition of constant-temperature stirring, an etherifying agent is slowly added dropwise. In this embodiment, the etherifying agent is propylene oxide or chloroacetic acid. The role of the etherifying agent is to change the structure of humic acid molecules, promote the modification and modification of its surface functional groups, thereby enhancing its effect in soil improvement. The control of the dropping process is very important, and it is necessary to ensure the gentle progress of the reaction to avoid the formation of by-products or the degradation of humic acid caused by too fast a reaction.

[0094] After the addition of the etherifying agent is completed, the reaction system needs to be adjusted to an acidic environment. The acidic condition can promote the precipitation of the modified humic acid to form a solid precipitate. This step controls the reaction process by adjusting the pH value and causes the modified humic acid to precipitate from the solution, facilitating subsequent separation and treatment.

[0095] After the reaction is completed, the modified humic acid is separated from the reaction solution by centrifugation, and the precipitate is collected. Through centrifugation, unreacted impurities and other components in the solution can be effectively removed to obtain a relatively pure modified humic acid precipitate.

[0096] The collected precipitate is treated by ultrasonic fragmentation technology until a colloidal dispersion system is formed. The role of ultrasonic waves can physically break large particles in the precipitate, disperse them into small particles, and finally obtain a hydroxylated humic acid colloid with a nanoscale particle size. The ultrasonic fragmentation power and time in this process need to be dynamically adjusted according to the detection results of the colloidal particle size to ensure that the particle size of the colloid is stably within the nanoscale range. In this embodiment, the dynamic adjustment includes: when the laser particle size analyzer detects that the particle size is greater than 200 nm, the ultrasonic power is increased from 300 W to 500 W and the treatment is extended for 10 minutes, and when the particle size is less than 100 nm, the initial parameters are restored. The nanoscale colloid has a large specific surface area and good dispersibility, which can significantly improve its activity in the soil.

[0097] By combining chemical modification and physical treatment, a low-temperature stable hydroxylated humic acid nanocolloid can be prepared efficiently and precisely. This colloid not only enhances the soil improvement effect but also has strong adaptability and can play a role for a long time under low-temperature conditions. Its high efficiency, environmental protection, and the expansion of the applicable range make it an important technical means in saline-alkali soil improvement.

[0098] In a possible implementation, first, ester gum and polyvinyl alcohol (PVA) are dissolved in an optimally designed mixed solvent in proportion to form a coating solution. The mixed solvent consists of polar solvents such as water-ethanol, and its proportion is optimized through the test of the elongation at break of the coating film under low-temperature conditions, so as to ensure that the film material still has good flexibility and ductility at low temperature (such as 5°C), avoiding brittle failure. In this embodiment, the optimization method is as follows: when the elongation at break at -5°C is less than 80%, increase the proportion of ethanol; when it is greater than 120%, increase the proportion of water.

[0099] Calcium nitrate powder is added to a fluidized bed reactor, and by adjusting the gas flow rate, the powder is in a good fluidized state. This state is conducive to the uniform spraying of the coating solution on the surface of the particles, preventing agglomeration and uneven coating.

[0100] In the fluidized bed operation, the coating solution is spray-injected into the fluidized calcium nitrate particles, and at the same time, an appropriate amount of hot air is introduced to assist the film-forming, cross-linking and drying and curing of the film material in the coating solution. The key to this step is to control the spray particle size, droplet viscosity and hot air temperature to form a uniform and unbroken dense film layer.

[0101] The hot air temperature used needs to be determined according to the results of the swelling degree experiment of the film material. The swelling degree experiment simulates the water absorption and swelling in the soil at 5°C, and by comparing the structural stability of the film-forming material under different temperature conditions, the optimal hot air temperature is determined to ensure that the film material maintains its structural integrity in a 5°C low-temperature environment for at least 24 hours or more, thus ensuring the timeliness and reliability of the calcium source slow-release effect.

[0102] By scientifically selecting coating materials and precisely controlling process parameters, the calcium fertilizer has good slow-release performance and stability in low-temperature and saline-alkali environments. Its technology integrates chemical modification, fluid coating and physical property regulation, and is an innovative solution for saline-alkali soil improvement and efficient calcium supplementation for crops. This method can significantly improve the utilization rate of calcium fertilizer and reduce the environmental burden, and has good prospects for popularization and application.

[0103] In a possible implementation, before fertilization, the current situation of soil salinity is evaluated by continuously monitoring the soil electrical conductivity at the target soil layer depth. Electrical conductivity (EC), as an important indicator to measure the soil salt concentration, can reflect the accumulation of salt in real time. The monitoring time span should be long enough to comprehensively record the basic fluctuation range, that is, the fluctuation range of soil electrical conductivity without fertilization. This fluctuation range is usually affected by seasons, climate and soil types.

[0104] Based on the maximum value of the recorded basic fluctuation range, a conductivity increase threshold is set. Usually, this threshold is a certain proportion of the maximum value. This proportion is usually adjusted according to the saline-alkali characteristics of different soils and the growth requirements of crops. In this embodiment, 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 reference value.

[0105] The salt migration rate directly affects the distribution and accumulation rate of soil salt. If the soil salt migration rate is relatively fast, it may lead to rapid salt accumulation, exceeding the crop's salt tolerance threshold. Therefore, when setting the increase threshold, the corresponding relationship between the salt migration rate and the crop salt tolerance threshold needs to be referred to. When it is monitored that the salt migration rate is high, resulting in salt accumulation that may exceed the crop's tolerance threshold, the operation of deep loosening and injecting the fertilizer solution dominated by calcium source microcapsules should be triggered in advance. For this purpose, the increase threshold needs to be lowered proportionally to detect salt problems in advance and prevent the harm of salt damage to crops.

[0106] When the increase in soil conductivity exceeds the set threshold, the operation of deep loosening and injecting the fertilizer solution dominated by calcium source microcapsules is immediately triggered. This operation aims to promote the deep movement of salt through deep soil loosening and improve the soil structure and increase water absorption by applying an appropriate amount of fertilizer, thereby effectively alleviating the soil salinization problem.

[0107] Through the setting and dynamic adjustment of the increase threshold based on conductivity monitoring, early warning and precise response to soil salt problems are ensured. It can effectively avoid the harm of excessive salt accumulation in saline-alkali soil to crops, optimize the fertilization operation, and promote soil health and crop growth. This method has significant practical value and promotion prospects for improving the production capacity of saline-alkali soil and enhancing the salt tolerance of crops.

[0108] In a possible implementation manner, when implementing the operation of deep loosening and injecting the fertilizer solution dominated by calcium source microcapsules, first, a specially designed deep loosening device is required. This device is equipped with a fertilizer solution injection device that can accurately inject the fertilizer solution into the deep soil. The fertilizer solution injection device consists of multiple injection needles arranged in parallel. The injection needles can achieve uniform and precise fertilizer solution distribution, thereby effectively improving the soil fertility.

[0109] In order to enhance the permeability and diffusion effect of the fertilizer solution, the pitch angle of the injection needles needs to be adjusted. By setting an acute angle between the injection needles and the forward direction of the device, the fertilizer solution can be sprayed into the soil at a certain angle, thereby improving the penetration power and distribution depth of the fertilizer solution. A reasonable spraying angle helps the fertilizer solution form an effective diffusion zone in the deep soil, avoiding the excessive concentration of the fertilizer solution on the surface layer and affecting the improvement effect of the deep soil.

[0110] The pressure delivery system of the fertilizer solution adjusts the spraying effect of the fertilizer solution by controlling the output pressure. Appropriate pressure can ensure that the fertilizer solution can penetrate to the target soil layer depth, achieving the purpose of effectively improving saline-alkali soil. The pressure of the fertilizer solution delivery system needs to be dynamically adjusted according to the actual situation of the soil (such as soil compactness, porosity, etc.) to ensure that the fertilizer solution can penetrate to an appropriate depth and fully contact the soil;

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

[0112] ;

[0113] Wherein, is the output pressure (unit: MPa), is the soil compactness (unit: MPa) measured at the target soil layer depth, is the clay content, and the proportion of particles less than 0.002 mm is measured by a laser particle size analyzer;

[0114] The applicable range of the above empirical formula is saline-alkali soil (electrical conductivity EC ≤ 8 dS / m), soil compactness is between 1.5 - 3.0 MPa, and the clay content is between 10% - 40%;

[0115] The adjustment of the pitching angle is directly related to the soil compactness. When the soil compactness is higher than the critical value, it is necessary to increase the pitching angle of the injection needle to enhance the shear disturbance effect of the fertilizer solution, help the fertilizer solution break through the compact soil layer, and penetrate to deeper soil layers. This can effectively solve the obstacle of soil denseness to the penetration of the fertilizer solution, enabling the fertilizer solution to uniformly diffuse at the target depth.

[0116] To ensure that the fertilizer solution can penetrate deep into the target soil layer and form a continuous diffusion zone, the setting of the output pressure needs to be accurately calculated according to the soil porosity and clay content. The soil porosity is closely related to the permeability of the fertilizer solution, while the clay content affects the soil compactness and the diffusion degree of the fertilizer solution. Through reasonable pressure adjustment, it can ensure that the fertilizer solution forms a uniform diffusion zone in the soil, effectively improving soil fertility and solving the salinization problem.

[0117] Through precise equipment configuration and technical adjustment, it can effectively improve saline-alkali soil, enhance soil fertility and structure, and ensure that the fertilizer solution can penetrate deep and uniformly diffuse to the target soil layer. This technology can not only solve the salt problem of saline-alkali soil, but also improve soil compactness and enhance soil tillability, providing a more stable and efficient soil management solution for agricultural production.

[0118] In a possible implementation, during the process of soil improvement, it is necessary to regularly collect soil extracts from each partition and monitor the changes in the soil through the ion concentrations in the extracts. This step is carried out once a week, and the main purpose is to track the molar concentration ratio of calcium ions to sodium ions in the soil. By analyzing the calcium and sodium ion concentrations in the extract, the degree of soil salinization and the progress of soil improvement can be effectively understood.

[0119] Calcium ions and sodium ions play important roles in saline-alkali soil. The presence of calcium ions helps to improve the soil structure, while sodium ions are the main components of salinization. The molar concentration ratio of calcium ions to sodium ions is a key indicator for evaluating the effect of soil improvement. When this ratio is too low, it indicates an excessive amount of sodium ions, a strong soil salinity, and an insignificant soil improvement effect.

[0120] When the measured molar concentration ratio of calcium ions to sodium ions is lower than the preset target value, it means that there is a deficiency of calcium ions in the soil, and it may be necessary to increase the calcium source to alleviate the salinization problem. At this time, increase the mass ratio of calcium source microcapsule particles in the fertilizer solution to promote the effective supplementation of calcium ions, improve the calcium ion content in the soil, and enhance the soil's anti-salinization ability.

[0121] During the soil improvement process, the change in soil pH value is an important indicator. Usually, at the initial stage of improvement, the soil pH value will decrease, but over time, it may rise. If the buffered pH value rises by more than the allowable range compared to the initial stage of improvement, it is necessary to further adjust the fertilizer solution formula and additionally spray the acidic mother liquor. The acidic mother liquor can help inhibit the rise of soil pH value, maintain the acidic environment of the soil, and thus avoid the rebound of saline-alkali problems.

[0122] To ensure the effectiveness of dynamically adjusting the fertilizer solution components, it is necessary to determine appropriate target values and ranges through potting pre-tests. In the pre-tests, monitor the growth status of crop roots, and based on the experimental data, determine the appropriate molar concentration ratio of calcium ions to sodium ions and the allowable range of pH value rise. These values provide reference standards for subsequent soil improvement operations, making the soil improvement process more precise and controllable.

[0123] By dynamically adjusting the fertilizer solution components, especially the ratio of calcium source microcapsule particles and the spraying amount of acidic mother liquor, the composition of the fertilizer solution can be precisely controlled according to the molar concentration ratio of calcium ions to sodium ions in the soil and the change in soil pH value. This method can effectively improve the structure and fertility of saline-alkali soil, optimize the growth environment of crops, reduce fertilizer waste, and improve the effect and sustainability of soil improvement.

[0124] In a possible implementation, during the reaction process, an optical sensor is used to monitor the light transmittance of the reaction system in real time. The change in light transmittance can reflect the concentration of suspended substances in the reaction system, and thus reflect whether the reaction proceeds smoothly. Generally, in the etherification reaction, the formation of by-products will cause the reaction system to become turbid and reduce the light transmittance. Therefore, judging the reaction state by light transmittance helps to timely adjust the dropping rate.

[0125] Through experimental research, an association model between the light transmittance and the generation rate of reaction by-products is established to determine a safety threshold.

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

[0127] ;

[0128] where, is the generation rate of by-products, with the unit of mg / min;

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

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

[0131] When the light transmittance of the reaction system is lower than this safety threshold, it indicates that the generation rate of reaction by-products is too fast or an abnormality has occurred in the reaction process. At this time, the dropping of the etherifying agent needs to be paused to prevent the reaction from generating too many by-products or the reaction system from getting out of control.

[0132] After the light transmittance of the reaction system rises back to the safe range, it indicates that the generation of by-products has tended to be stable and the reaction can continue. At this time, resume the dropping operation of the etherifying agent and gradually resume the dropping at a rate that decreases in a gradient. The rate that decreases in a gradient makes the reaction smoother and avoids violent fluctuations in the reaction caused by too fast dropping rate.

[0133] The function of the rate change that decreases in a gradient in this control method is dynamically adjusted according to the peak temperature of the reaction heat release. In the etherification reaction, the reaction heat release may affect the reaction rate. Therefore, the peak temperature of the heat release becomes a key factor for adjusting the dropping rate. When the reaction heat release is too fast or the temperature reaches a certain peak value, it is necessary to timely adjust the dropping rate to avoid adverse effects on the reaction caused by too high temperature. According to the change in the peak temperature of the reaction heat release, the dropping rate is adjusted in real time to make the reaction proceed within the controllable range.

[0134] By real-time monitoring the light transmittance of the reaction system and establishing a correlation model with the generation rate of reaction by-products, the dropping operation of the etherification reaction can be ensured to be more accurate, avoiding the problems of too fast generation of by-products or out-of-control reaction. By dynamically adjusting the dropping rate and gradually decreasing it according to the peak temperature of the reaction heat release, the stability and efficiency of the reaction can be ensured. This control method not only improves the safety of the reaction, but also optimizes the production process, reduces by-products, enhances the controllability and economy of the reaction, and has significant technical advantages.

[0135] In a possible implementation, first, the coated microcapsule particles are placed in a simulated soil solution to simulate the soaking situation of the microcapsule particles in the actual environment. The composition of the simulated soil solution should be as close as possible to the aqueous solution characteristics of the actual soil, including different pH values, salt concentrations, etc., to more realistically reflect the performance of the coating film in actual applications.

[0136] At different time points, the soaked microcapsule particles are taken out, and microscopy imaging technology is used to observe whether cracks appear on the surface of the coating film. Microscopy imaging technology can clearly show the microscopic structure of the film surface, helping to accurately locate the position and degree of the cracks. Usually during the observation process, over time, the coating film may develop cracks due to swelling or the action of external factors, affecting the stability of the coating.

[0137] Through microscopy imaging image analysis, the proportion of the cracked area on the surface of the coating film is statistically analyzed, and the duration until it reaches the critical damage value is measured. When the proportion of the cracked area reaches the set critical value, record the duration, and evaluate the durability and stability of the coating film. This process helps to understand the performance of the coating film in a specific environment and its feasibility for long-term use.

[0138] If the statistically analyzed proportion of the cracked area and the duration do not meet the design requirements, it indicates that there are problems with the integrity of the coating film, and the formulation of the coating solution needs to be adjusted. Specifically, adjust the ratio of rosin glyceride to polyvinyl alcohol in the coating solution to optimize the physical properties of the film material and enhance the durability of the coating film. Adjusting the ratio of rosin glyceride to polyvinyl alcohol helps to control the flexibility, swelling degree, and brittleness of the film, and improves the crack resistance of the film.

[0139] The direction of ratio adjustment depends on the swelling degree - brittleness balance curve of the film material. This curve can guide the material selection and ratio, thereby optimizing the balance between the swelling characteristics and brittleness of the film. The balance between the swelling degree and brittleness is crucial because too high a swelling degree may lead to the fragility of the film, while too high a brittleness may reduce the elasticity and crack resistance of the film. By adjusting the ratio, the coating film has the optimal swelling degree and brittleness, thereby improving the durability of the film and ensuring that it is not easily broken during long-term use.

[0140] By adopting means such as microscopic imaging technology, crack area ratio statistics, and formulation adjustment, the integrity of the coating film is effectively verified and optimized. This method can ensure the stability of the coating film, reduce the cracking phenomenon, improve the long-term effect of soil improvement fertilizers, thereby enhancing the effect persistence and fertilizer utilization rate during the soil improvement process.

[0141] In a possible implementation, first, within 24 hours after fertilization, an excavation operation of the soil profile is carried out to observe and measure the diffusion of the fertilizer solution. The location of the excavated profile should be selected near the fertilizer application area to observe the wetting front of the fertilizer solution (i.e., the farthest boundary of the fertilizer solution diffusion in the soil). In the profile, measure the horizontal and vertical extension distances of the wetting front of the fertilizer solution to understand the diffusion depth and lateral expansion of the fertilizer solution in the soil. This measurement helps to evaluate whether the fertilizer uniformly penetrates into the target soil layer and confirm whether the fertilizer distribution meets the expectations.

[0142] If the measurement results show that the wetting front of the fertilizer solution fails to reach the predetermined target soil layer, indicating that the fertilizer solution fails to fully cover the target area of the soil, the fertilization parameters need to be adjusted at this time. According to the gap between the measured extension distance and the target soil layer, appropriately increase the output pressure of the fertilizer solution or the injection amount of fertilizer to ensure that the fertilizer solution can fully penetrate into the target soil layer and form a continuous diffusion zone. Increasing the injection amount of fertilizer or the output pressure helps to enhance the penetration ability of the fertilizer solution in the soil, thereby ensuring the uniform distribution of fertilizer in the target area.

[0143] The ratio of adjusting the fertilization parameters (such as output pressure or injection amount of fertilizer) is mainly calculated based on the ratio of the hydraulic conductivity of the soil to the viscosity of the solution. The hydraulic conductivity is the ability of soil water to flow, while the viscosity of the solution affects the fluidity of the fertilizer solution. A lower hydraulic conductivity or a higher solution viscosity will result in a slower penetration rate of the fertilizer solution in the soil. Therefore, it is necessary to appropriately increase the output pressure or the amount of fertilizer solution to compensate for the insufficient penetration. Through the calculation of this ratio, precise adjustment can be achieved to ensure that the fertilizer solution can uniformly diffuse under different soil conditions.

[0144] During this process, the double-ring infiltrometer test is used to measure the hydraulic conductivity. This test method sets two concentric rings on the soil surface, applies water flow to the inner ring and the outer ring respectively, and then calculates the hydraulic conductivity of the soil by observing the penetration of water in the soil. This test can provide data on the infiltration characteristics of the soil, help evaluate the water mobility of the soil, and provide a basis for adjusting the fertilization parameters.

[0145] By measuring the extension distance of the wetting front of the fertilizer solution, adjusting the fertilization parameters according to the ratio of soil hydraulic conductivity to solution viscosity, and obtaining accurate hydraulic conductivity through a double-ring infiltrometer test, the infiltration effect of the fertilizer can be optimized to ensure uniform distribution of the fertilizer. This method improves the efficiency of soil improvement, avoids fertilizer waste, and enhances the long-term soil improvement effect. It is an effective method for improving saline-alkali soil.

[0146] To verify the effectiveness of the saline-alkali soil synchronous improvement method based on the low-temperature stable acidic water-soluble fertilizer described in the present invention, a 90-day field experiment was conducted in a typical saline-alkali area. The test settings are as follows:

[0147] Experimental design:

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

[0149] Control group 1: Uniform spreading at the same frequency using a conventional acidic water-soluble fertilizer (ammonium sulfate-citric acid compound).

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

[0151] Three replicated plots are set in each group, and the area of each plot is 20 m².

[0152] Initial basic physical and chemical properties of the soil: 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 compactness (0-30 cm) > 2.0 MPa.

[0153] Key index monitoring:

[0154] Soil physical and chemical properties: Soil samples are collected by layer at 0-20 cm (tillage layer) and 20-40 cm (subsurface layer) before treatment (day 0), 30 days, 60 days, and 90 days after treatment to measure EC, buffer pH, ESP, calcium-sodium ion molar ratio (Ca²⁺ / Na⁺), and soil compactness.

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

[0156] Crop response (optional): Salt-tolerant pioneer crops (such as Suaeda glauca) are planted in the later stage of the experiment, and the emergence rate and biomass (fresh weight) are recorded.

[0157] Experimental result data:

[0158] Table 1: Changes in Key Soil Indexes in the Plough Layer (0 - 20 cm) (Mean ± Standard Deviation)

[0159] Treatment group Time (days) EC (dS / m) Buffered pH ESP (%) Ca²⁺ / Na⁺ (molar ratio) Soil compactness (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 a significant difference (p < 0.05) compared with the value at 0 days in the same group and is worse than the initial state.

[0161] Table 2: Changes in Key Soil Indexes in the Sub - surface Layer (20 - 40 cm) (at 90 days, Mean ± Standard Deviation)

[0162] Treatment group EC (dS / m) Buffered 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°C to 10°C for 48 hours)

[0165] Temperature (°C) Final fertilizer state of the experimental group Effective calcium dissolution rate of the experimental group (%) State of control group 1 (conventional fertilizer) Effective calcium dissolution rate of control group 1 (%) 10 Clear solution 98.5 ± 1.2 Slightly turbid, with a small amount of precipitate 85.3 ± 3.5 5 Clear solution 97.0 ± 1.5 Significantly turbid, with more precipitate 62.1 ± 4.8 0 Slightly turbid, without precipitate 92.5 ± 2.0 A large amount of precipitate, with stratification 28.7 ± 5.2 -5 Turbid, with trace precipitate 88.3 ± 2.8 Completely solidified, with crystal precipitation <5.0

[0166] Table 4: Growth Response of Crops (Suaeda glauca) (at 90 days)

[0167] Treatment group Emergence 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 is significant: In the experimental group within 90 days, the EC value in the plough layer decreased significantly from 5.8 dS / m to 2.3 dS / m (a decrease of 60.3%), the buffer pH value decreased significantly from 9.2 to 7.6 (a decrease of 1.6 units), the ESP decreased significantly from 28.7% to 8.4% (a decrease of 70.7%), the Ca²⁺ / Na⁺ molar ratio increased significantly from 0.15 to 0.92 (an increase of 513%), and the soil compactness decreased significantly from 2.15 MPa to 1.35 MPa (a decrease of 37.2%). The saline - alkali indexes in the sub - surface layer (20 - 40 cm) were also significantly improved synchronously, indicating that the zoned dynamic improvement effectively acts on soil layers at different depths. For Control Group 1 (conventional fertilizer), there was no significant improvement in various indexes and even a slight deterioration (increase in EC and ESP), and for Control Group 2 (blank), the continuous salinization became more serious.

[0170] Excellent low-temperature stability: As shown in Table 3, the low-temperature stable final fertilizer prepared by the present invention can still maintain a high solubility and an effective calcium ion dissolution rate (92.5%) at 0 °C, with only slight turbidity and no precipitation; at -5 °C, the effective calcium dissolution rate is still 88.3%, and there is only a trace amount of precipitation. While the conventional acidic water-soluble fertilizer is significantly turbid and precipitated at 5 °C, and the effective calcium dissolution rate drops sharply to 62.1%, and it is almost ineffective at 0 °C (dissolution rate < 30%, completely solidified). This fully demonstrates the key role of the coating technology and the phase change regulator in maintaining the fertilizer efficiency stability at low temperatures.

[0171] Promote crop growth: Suaeda salsa was planted on the improved experimental group soil, and the emergence rate was as high as 85.7%, and the fresh weight reached 1250 g / m², which was significantly better than that of Control Group 1 (emergence rate 42.3%, fresh weight 580 g / m²) and Control Group 2 (emergence rate 18.6%, fresh weight 220 g / m²), intuitively reflecting a 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 enhance the soil quality of the tillage layer and subsurface layer.

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

[0175] The zoning dynamic improvement strategy (based on the feedback of the conductivity sensor) realizes precise regulation and has high resource utilization efficiency.

[0176] Finally, it significantly improves the soil environment, provides good growth conditions for crops (such as Suaeda salsa), and increases the emergence rate and biomass.

[0177] The present invention covers any substitutions, modifications, equivalent methods, and solutions made on the essence and scope of the present invention. For the public to have a thorough understanding of the present invention, specific details are described in detail in the following preferred embodiments of the present invention, and those skilled in the art can fully understand the present invention without these detailed descriptions. In addition, well-known methods, processes, procedures, components, and circuits are not described in detail to avoid unnecessary confusion to the essence of the present invention.

[0178] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A method for simultaneous improvement of saline-alkali soil based on a low-temperature stable acidic water-soluble fertilizer, characterized in that, Including: Step 1: Dynamic zoning of soil profiles. Excavate soil profiles by the grid method and collect soil samples in layers; Under simulated low-temperature field conditions, measure the active sodium ion concentration, exchangeable calcium and magnesium ion saturation, and buffer pH value; Divide the rapid salt return area, stable salt accumulation area, and potential alkalization area according to the salt migration rate and the alkalization degree mutation threshold. The salt migration rate is calculated by the continuous daily increase in surface soil conductivity, and the alkalization degree mutation threshold is determined by the change rate of buffer pH value between adjacent soil layers; Step 2: In-situ synthesis of water-soluble fertilizer. React ammonium dihydrogen phosphate, citric acid with hydroxylated humic acid nanocolloid to form an acidic mother liquor; Coat calcium nitrate with rosin glyceride-polyvinyl alcohol copolymer to form calcium source microcapsule particles; Compound the acidic mother liquor, calcium source microcapsule particles with a phase change regulator to obtain a low-temperature stable final fertilizer; Step 3: Zoning dynamic improvement. Spray the fertilizer solution dominated by the acidic mother liquor into the rapid salt return area and bury conductivity sensors; When the conductivity increase rate drops to the set threshold, deep tillage and inject the fertilizer solution dominated by calcium source microcapsules into the stable salt accumulation area; Dynamically adjust the component ratio of the fertilizer solution according to the calcium and magnesium ion exchange efficiency, where the calcium and magnesium ion exchange efficiency is calculated by the calcium-sodium ion molar ratio of the leaching solution.

2. The method for simultaneously improving saline-alkali soil based on a low-temperature stable acidic water-soluble fertilizer according to claim 1, wherein: The method for determining the alkalization degree mutation threshold in the above Step 1 includes: Collect soil samples at fixed depth intervals in the 40 - 60 cm soil layer and measure the buffer pH value of each soil sample; Calculate the change rate of buffer pH value between adjacent soil layer depths. The change rate is the difference between the buffer pH value of the upper layer minus 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 the preset critical value, mark this depth interval as the alkalization mutation interface; Designate the continuous soil layer containing the alkalization mutation interface as the potential alkalization area. The preset critical value is obtained through statistical analysis of historical saline-alkali disaster data.

3. A method for simultaneously improving saline-alkali soil based on a low-temperature stable acidic water-soluble fertilizer according to claim 1, characterized in that: The preparation method of the hydroxylated humic acid nanocolloid in the above Step 2 includes: Dissolve humic acid in an alkaline solution to form a suspension, and slowly drop the etherifying agent under constant temperature stirring conditions; After dropping, adjust the reaction system to an acidic environment to precipitate the modified humic acid; Collect the precipitate by centrifugation and treat the precipitate with ultrasonic fragmentation technology to a colloidal dispersion system; The power and duration of the ultrasonic fragmentation are dynamically adjusted according to the detection results of the colloidal particle size until the colloidal particle size is stabilized in the nanometer range.

4. A method for simultaneous improvement of saline-alkali soil based on a low-temperature stable acidic water-soluble fertilizer according to claim 1, characterized in that: The coating method of the calcium source microcapsule particles in the above Step 2 includes: Dissolve rosin glyceride and polyvinyl alcohol in a mixed solvent to form a coating solution. The proportion of the mixed solvent is optimized according to the test results of the elongation at break of the coating film at low temperature; Place calcium nitrate powder in a fluidized bed and control the air flow rate to make the powder in a fluidized state; Spray and inject the coating solution into the fluidized powder, and simultaneously introduce hot air to crosslink and cure the coating film; The hot air temperature is determined according to the swelling degree experiment of the coating film to ensure that the film material maintains a complete structure in a 5℃ soil environment for at least 24 hours.

5. A method for simultaneously improving saline-alkali soil based on a low-temperature stable acidic water-soluble fertilizer according to claim 1, characterized in that: The method for determining the set threshold of the conductivity increase rate in the above Step 3 includes: Continuously monitor the soil conductivity at the target soil layer depth before fertilization and record the basic fluctuation range; Based on the maximum value of the basic fluctuation range, set the increase rate threshold in proportion; 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 tolerance value of the crop, the threshold is lowered proportionally to trigger the operation of subsoiling and injecting the calcium source microcapsule-dominated fertilizer solution in advance.

6. The synchronous improvement method for saline-alkali soil based on a low-temperature stable acidic water-soluble fertilizer according to claim 1, wherein: The operation method of subsoiling and injecting in step 3 includes: Using a subsoiling device equipped with a fertilizer solution injection device, and the injection device consists of injection needles arranged in parallel; Adjusting the pitch angle of the injection needles so that the fertilizer solution injection direction forms an acute angle with the forward direction of the device; Controlling the output pressure of the fertilizer solution delivery system so that the fertilizer solution penetrates to the target soil layer depth; The pitch angle is determined according to the soil compactness test data. When the soil compactness is higher than the critical value, the angle is increased to enhance the shear disturbance; The output pressure is calculated based on the soil porosity and clay content to ensure that the fertilizer solution forms a continuous diffusion zone in the target soil layer.

7. A method for simultaneous improvement of saline-alkali soil based on a low-temperature stable acidic water-soluble fertilizer according to claim 1, characterized in that: In step 3, the fertilizer solution components are dynamically adjusted, specifically including the following methods: Collecting soil extracts from each partition every week and measuring the molar concentration ratio of calcium ions to sodium ions; When the molar concentration ratio is lower than the preset target value, increasing the mass proportion of calcium source microcapsule particles in the fertilizer solution; When the buffered pH value rises by more than the allowable range compared with the initial stage of improvement, additionally spraying the acidic mother liquor; The preset target value and the allowable range are determined by the growth state of crop roots in the pot experiment.

8. A method for simultaneously improving saline-alkali soil based on a low-temperature stable acidic water-soluble fertilizer according to claim 3, characterized in that: The control method of the dropping rate of the etherifying agent includes: Real-time monitoring of the light transmittance of the reaction system, and suspending the dropping when the light transmittance is lower than the safety threshold; The safety threshold is determined by the correlation model between the reaction by-product generation rate and the light transmittance; After the light transmittance rises to the safe range, resuming the dropping operation at a rate that decreases in a gradient; The rate change function of the gradient decrease is dynamically adjusted according to the reaction exothermic peak temperature.

9. A method for simultaneously improving saline-alkali soil based on a low-temperature stable acidic water-soluble fertilizer according to claim 4, characterized in that: The verification method of the integrity of the coating film includes: Taking the coated microcapsule particles and soaking them in the simulated soil solution; Taking out the particles at different time points and observing the surface cracking situation by using microscopic imaging technology; Statistical duration of the cracking area ratio reaching the damage critical value; When the duration does not meet the design requirements, adjusting the ratio of rosin glyceride to polyvinyl alcohol in the coating solution; The adjustment direction of the ratio is determined according to the swelling-brittle balance curve of the film material.

10. A method for simultaneously improving saline-alkali soil based on a low-temperature stable acidic water-soluble fertilizer according to claim 6, characterized in that: The evaluation method for ensuring that the fertilizer solution forms a continuous diffusion zone in the target soil layer includes: Excavating the profile 24 hours after fertilizer injection and measuring the horizontal and vertical extension distances of the fertilizer solution wetting front; When the extension distance does not cover the target area, increasing the output pressure or the fertilizer injection amount proportionally; The ratio is calculated based on the ratio of the soil hydraulic conductivity to the solution viscosity; The hydraulic conductivity is obtained through the double-ring infiltration test.

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