Standardized cultivation method for crops in moderate and severe saline-alkali soil based on gradient regulation

Abstract

The application relates to the technical field of agricultural soil improvement, and discloses a standardization cultivation method for crops in medium and severe saline-alkali soil based on gradient regulation, which comprises the following steps: sequentially applying liquid component A containing an anion polymer and a slow-release acid precursor and liquid component B containing a cation polymer and a double crosslinking system into the soil in the root zone of crops at preset time intervals; through the time-sequential application, the two components are in-situ reacted in the soil to form a three-dimensional network structure with rapid ionic crosslinking and slow covalent crosslinking; the network structure, in combination with the sustained acidolysis of the slow-release acid precursor, can build a vertical gradient of pH value and salt content with low surface layer and high deep layer in the soil profile in the root zone of crops and significantly improve the water retention performance of the soil; the functional gradient microenvironment formed by the application can effectively overcome the adverse effects of medium and severe saline-alkali stress on the growth of crops and significantly improve the survival rate, root activity and final biomass of the crops.

Description

Technical Field

[0001] This invention relates to the field of agricultural soil improvement technology, and in particular to a standardized cultivation method for crops in moderately to severely saline-alkali land based on gradient regulation. Background Technology

[0002] Soil salinization is one of the global challenges that restricts sustainable agricultural development. Moderate to severe saline-alkali soils, due to their excessively high pH and salt content, as well as the resulting problems such as soil compaction and reduced nutrient availability, pose a serious stress on crop growth, making it difficult to achieve ideal yields and economic benefits using conventional planting methods.

[0003] Currently, the main technologies for improving saline-alkali land include physical, chemical, and biological methods. Physical improvement measures, such as deep plowing, topsoil application, or large-scale water leaching, involve massive engineering projects, are costly, and difficult to implement in water-scarce areas. While chemical improvement methods are widely used, their limitations are also significant. For example, the application of amendments such as gypsum, due to their low solubility and slow reaction rate, usually results in slow and limited effects; while direct neutralization with acidic substances is a violent and difficult-to-control process, easily damaging the original soil aggregate structure, and its improvement effect lacks persistence, failing to provide a stable low-stress root zone environment for crops throughout their growth period.

[0004] In recent years, the application of polymer soil conditioners has provided new ideas for the improvement of saline-alkali land, showing potential in water retention, fertilization, and soil structure improvement. However, existing polymer improvement technologies still have significant shortcomings in dealing with moderate to severe saline-alkali stress. Most conditioners have a single function and cannot simultaneously address the dual stresses of high salt and high alkali. Some multi-component reactive conditioners, if pre-mixed or applied without a time interval, will cause the components to react rapidly before entering the soil or on the soil surface, forming a dense gel barrier layer. This not only fails to penetrate deep into the root zone to exert its effects but may also hinder soil permeability. Therefore, current technologies generally lack a technical solution that can construct, in situ and controllably, a microenvironment with structural stability and multiple regulatory functions in the crop root zone soil, creating a gradient-layered and continuously optimized microenvironment for the roots. Summary of the Invention

[0005] The technical problem to be solved by this application is to provide a standardized cultivation method that can locally and dynamically improve the crop root zone growth environment in moderately to severely saline-alkali land, so as to improve crop survival rate and resource utilization efficiency.

[0006] This application provides a standardized cultivation method for crops in moderately to severely saline-alkali land based on gradient regulation, employing the following technical solution:

[0007] A standardized cultivation method for crops in moderately to severely saline-alkali land based on gradient regulation includes the following steps:

[0008] (a) Apply a permeable liquid component A containing anionic polymers and slow-release acid precursors to the crop rhizosphere soil;

[0009] (b) After a preset time interval, a liquid component B comprising a cationic polymer and a crosslinking agent is applied to the soil in the root zone of the crop.

[0010] In this process, liquid component A and liquid component B react in situ in the soil to form a hydrogel network with a gradient structure, which is used to regulate the microenvironment of the crop root zone.

[0011] By employing the above-mentioned technical solution, two liquid components are applied sequentially. Utilizing the permeability of component A in the soil and the low mobility of component B, they react in situ at a predetermined soil depth. This reaction, through the electrostatic interaction of anionic and cationic polymers and the cross-linking of multivalent ions, forms a three-dimensional hydrogel network in the soil pores. The presence of this network achieves the following effects in a localized area: First, the functional groups in the network structure adsorb and fix sodium ions in the soil solution through ion exchange, reducing the concentration of free sodium ions in the root zone; second, the slow-release acid precursor slowly hydrolyzes within the network formation area, continuously releasing acidic substances to neutralize soil alkalinity; third, the network structure itself has water retention capacity, increasing the water content of the root zone soil; and finally, the nutrients loaded in the network are slowly released. In this way, a local microenvironment with gradient changes in multiple physicochemical indicators, significantly different from the external saline-alkali soil, is constructed around the crop roots.

[0012] Preferably, the gradient structure of the hydrogel network exhibits at least two gradient combinations selected from the following:

[0013] A salinity gradient decreasing from the inside out, a pH gradient decreasing from the surface to the depths, a gradient of highly available nutrient concentrations around the roots, or a water gradient decreasing from the inside out.

[0014] By adopting the above technical solution, the multi-gradient structure can simultaneously and synergistically regulate multiple limiting factors such as salt, alkali, water, and fertilizer that affect crop growth, providing a comprehensive suitable environment for crop roots.

[0015] Preferably, the anionic polymer is modified polyaspartic acid with end-capped groups that are sensitive to crop root exudates grafted onto its molecular chain.

[0016] By employing the above technical solution, the capping groups break upon contact with specific enzymes secreted by crop roots, exposing more active functional groups. This structure enhances the adsorption capacity of the hydrogel network for sodium ions at the root-soil interface, enabling precise control of desalination at the microscale.

[0017] Preferably, the modified polyaspartic acid is prepared by the following steps: L-aspartic acid is thermally polycondensed to obtain polysuccinimide; the polysuccinimide is subjected to an end-capping reaction with ethyl glycolate; and the end-capped product is obtained by ring-opening hydrolysis under alkaline conditions.

[0018] By adopting the above technical solution, a specific and reproducible preparation route is provided for obtaining the modified polyaspartic acid with specific responsive functional groups.

[0019] Preferably, the slow-release acid precursor is a polylactic acid oligomer or a polyglycolic acid oligomer.

[0020] By adopting the above technical solution and utilizing the slow hydrolysis characteristics of this type of ester oligomer, acidic substances can be continuously and stably released throughout the entire growth period of the crop, thereby achieving long-term regulation of the pH value in the root zone.

[0021] Preferably, the crosslinking agent is a dual crosslinking system comprising a fast ionic crosslinking agent and a slow covalent crosslinking agent. Specifically, the cationic polymer is chitosan oligosaccharide; the fast ionic crosslinking agent is calcium ions and / or magnesium ions; and the slow covalent crosslinking agent is an organosilane crosslinking agent.

[0022] By adopting the above technical solutions, rapid ionic cross-linking ensures that the hydrogel network forms quickly within a short period of time after application, and immediately exerts its salt-fixing and water-retaining functions; while slow covalent cross-linking gradually forms more stable chemical bonds, prolonging the structural stability and function period of the hydrogel network, so that its functional continuity matches the crop growth cycle.

[0023] Preferably, liquid component A is made from raw materials comprising the following weight percentages: 15-30% anionic polymer, 8-20% slow-release acid precursor, and the balance being water; liquid component B is made from raw materials comprising the following weight percentages: 8-18% cationic polymer, 6-17% crosslinking agent, 0.5-2.0% chelated trace elements, and the balance being water.

[0024] By adopting the above technical solution, the ratio range of each component can ensure that the liquid component has suitable fluidity and reactivity, and ensure that the hydrogel network formed in the soil has the expected structural strength and functional capacity.

[0025] Preferably, the preset time interval in step (b) is 1 to 3 hours; both liquid component A and liquid component B are applied through a drip irrigation system.

[0026] By employing the above technical solution, this time interval ensures that liquid component A has sufficient time to penetrate to the target soil depth, thereby allowing subsequent reactions to occur at the predetermined root zone location. Using a drip irrigation system allows for precise control of the application rate and location of the liquid component, saving materials and improving operational efficiency.

[0027] Preferably, liquid component A and / or liquid component B further contain plant growth regulators or soil microbial agents.

[0028] By adopting the above technical solutions, other components that are beneficial to plant growth or soil health can be integrated into the regulatory system to achieve multifunctional synergistic delivery.

[0029] In summary, the present invention has at least one of the following beneficial technical effects:

[0030] 1. This invention utilizes the sequential application of two liquid components with different chemical properties, leveraging their varying migration and reactivity in the soil, to construct an in-situ hydrogel network with a specific gradient structure in the crop root zone. This method departs from the traditional model of uniform material mixing in soil amendment, achieving structured and precise regulation of environmental factors such as salt, alkali, water, and fertilizer in the root zone at the microscale. It creates a suitable local micro-habitat for crop roots, significantly different from the field environment, thereby significantly improving the survival rate and growth robustness of crops in adverse environments such as saline-alkali soils.

[0031] 2. The anionic polymer used in this invention contains end-capped groups sensitive to crop root exudates, introducing a biofeedback mechanism. When crop roots come into contact with the gel network, the release of active functional groups is actively triggered, enhancing the desalination capacity of the root surface. This on-demand response regulation allows the improvement effect to more precisely match the growth needs of the root system, improving material utilization efficiency and providing more timely and effective protection for crop roots.

[0032] 3. This invention constructs a dual network with temporal deconstruction characteristics by combining a rapid ionic crosslinking agent and a slow covalent crosslinking agent in a crosslinking system. Rapid crosslinking ensures the rapid establishment of initial protective functions, while slow covalent crosslinking prolongs the structural stability and duration of action of the functional network. This programmed network degradation characteristic allows its functional release rhythm to better match the different needs of crops from the seedling stage to the growth stage, achieving long-term dynamic management of the rhizosphere environment from establishment and maintenance to orderly release. Attached Figure Description

[0033] Figure 1 This is a three-dimensional surface diagram of the pH distribution of the root zone soil profile after treatment in Example 1, Comparative Example 1 and Comparative Example 4 of the present invention.

[0034] Figure 2 This is a three-dimensional surface diagram of the distribution of electrical conductivity values ​​in the root zone soil profile after treatment in Example 1, Comparative Example 1, and Comparative Example 4 of Test Example 1 of the present invention.

[0035] Figure 3 This is a box plot showing the distribution of soil moisture content in all treatment groups on the 7th day after saturated irrigation in Test Example 2 of this invention. Detailed Implementation

[0036] To enable those skilled in the art to more clearly understand the technical solutions of the present invention, the present invention will be further described in detail below. Obviously, the described embodiments are merely some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0037] The main raw materials and reagents used in the following examples and comparative examples have the following sources and specifications. Reagents not specifically mentioned are all commercially available analytical grade or higher grade products.

[0038] L-Aspartic acid (CAS: 56-84-8), analytical grade.

[0039] Phosphoric acid (Orthophosphoric acid, 85%, CAS: 7664-38-2), analytical grade.

[0040] N,N'-Dicyclohexylcarbodiimide (DCC, CAS: 538-75-0), purity ≥99%.

[0041] 4-Dimethylaminopyridine (DMAP, CAS: 1122-58-3), purity ≥99%.

[0042] Ethyl glycolate (CAS: 623-50-7), purity ≥98%.

[0043] Dichloromethane (DCM, CAS: 75-09-2), analytical grade.

[0044] Sodium hydroxide (CAS: 1310-73-2), analytical grade.

[0045] L-lactic acid (CAS: 79-33-4), 88-92% aqueous solution.

[0046] Stannous octoate (Sn(Oct)2, CAS: 301-10-0), purity ≥95%.

[0047] Chitosan oligosaccharide, with a water solubility of ≥98%, a degree of deacetylation of ≥90%, and an average molecular weight of 1500-3000 Da.

[0048] Anhydrous calcium chloride (CAS: 10043-52-4), analytical grade.

[0049] Magnesium sulfate heptahydrate (CAS: 10034-99-8), analytical grade.

[0050] 3-Aminopropyltriethoxysilane (APTES, CAS: 919-30-2), purity ≥99%.

[0051] Glycolic acid (70% aqueous solution, CAS: 79-14-1), industrial grade.

[0052] Disodium zinc ethylenediaminetetraacetate (EDTA-Zn, CAS: 14025-21-9), with a chelated zinc content ≥14.5%.

[0053] Sodium iron ethylenediaminetetraacetate (EDTA-Fe, CAS: 15708-41-5), with chelated iron content ≥13.0%.

[0054] Disodium manganese ethylenediaminetetraacetate (EDTA-Mn, CAS: 15375-84-5), with chelated manganese content ≥12.5%.

[0055] Preparation Examples 1-6:

[0056] Preparation Example 1:

[0057] This preparation example provides a method for preparing enzyme-sensitive capped polyaspartic acid (ES-PASP), the steps of which are as follows:

[0058] 1. Add 133.1 g of L-aspartic acid and 1.5 g of phosphoric acid to a reaction vessel and mix thoroughly. Under nitrogen protection, the temperature is programmed to 190 °C and reacted under a vacuum of -0.095 MPa for 4 hours. After the reaction is complete, allow it to cool naturally to room temperature to obtain a pale yellow solid powder of polysuccinimide (PSI).

[0059] 2. Dissolve 97.1 g (equivalent to 1 mol monomer unit) of the PSI powder prepared in step 1 in 500 mL of dichloromethane. Under 0°C ice-water bath conditions, add 104.1 g (1.0 mol) of ethyl glycolate and 12.2 g (0.1 mol) of 4-dimethylaminopyridine sequentially. After stirring until homogeneous, slowly add 226.9 g (1.1 mol) of N,N'-dicyclohexylcarbodiimide dissolved in 100 mL of dichloromethane dropwise to the reaction system. After the addition is complete, remove the ice bath and stir the reaction at room temperature for 24 hours. After the reaction is complete, filter to remove byproducts, remove dichloromethane from the filtrate by rotary evaporation, and dry under vacuum to obtain end-capped polysuccinimide powder.

[0060] 3. Disperse the powder obtained in step 2 in deionized water. Under the conditions of heating and stirring in a 50°C water bath, add dropwise a 30% sodium hydroxide solution to adjust and maintain the pH of the reaction system at 10.0. Continue the reaction for 3 hours until the solid is completely dissolved, obtaining a brown transparent liquid of enzyme-sensitive terminal polyaspartic acid (ES-PASP) with a solid content of 30%.

[0061] Preparation Example 2:

[0062] This preparation example provides a method for preparing enzyme-sensitive capped polyaspartic acid (ES-PASP), the steps of which are as follows:

[0063] 1. Add 133.1 g of L-aspartic acid and 2.0 g of phosphoric acid to a reaction vessel and mix thoroughly. Under nitrogen protection, the temperature is programmed to 210 °C and reacted under a vacuum of -0.1 MPa for 3 hours. After the reaction is complete, allow it to cool naturally to room temperature to obtain a pale yellow solid powder of polysuccinimide (PSI).

[0064] 2. Dissolve 97.1 g (equivalent to 1 mol monomer unit) of the PSI powder prepared in step 1 in 500 mL of dichloromethane. Under 0°C ice-water bath conditions, add 124.9 g (1.2 mol) of ethyl glycolate and 24.4 g (0.2 mol) of 4-dimethylaminopyridine sequentially. After stirring until homogeneous, slowly add 268.3 g (1.3 mol) of N,N'-dicyclohexylcarbodiimide dissolved in 100 mL of dichloromethane dropwise to the reaction system. After the addition is complete, remove the ice bath and stir the reaction at room temperature for 18 hours. After the reaction is complete, filter to remove byproducts, remove dichloromethane from the filtrate by rotary evaporation, and dry under vacuum to obtain end-capped polysuccinimide powder.

[0065] 3. Disperse the powder obtained in step 2 in deionized water. Under the conditions of heating and stirring in a 60°C water bath, add dropwise a 30% sodium hydroxide solution to adjust and maintain the pH of the reaction system at 11.0. Continue the reaction for 2 hours until the solid is completely dissolved to obtain a brown transparent liquid of enzyme-sensitive terminal polyaspartic acid (ES-PASP) with a solid content of 35%.

[0066] Preparation Example 3:

[0067] This preparation example provides a method for preparing enzyme-sensitive capped polyaspartic acid (ES-PASP), the steps of which are as follows:

[0068] 1. Add 133.1 g of L-aspartic acid and 1.0 g of phosphoric acid to a reaction vessel and mix thoroughly. Under nitrogen protection, the temperature is programmed to 220 °C and reacted under a vacuum of -0.09 MPa for 2 hours. After the reaction is complete, allow it to cool naturally to room temperature to obtain a pale yellow solid powder of polysuccinimide (PSI).

[0069] 2. Dissolve 97.1 g (equivalent to 1 mol monomer unit) of the PSI powder prepared in step 1 in 500 mL of dichloromethane. Under 0°C ice-water bath conditions, add 114.5 g (1.1 mol) of ethyl glycolate and 18.3 g (0.15 mol) of 4-dimethylaminopyridine sequentially. After stirring until homogeneous, slowly add 247.6 g (1.2 mol) of N,N'-dicyclohexylcarbodiimide dissolved in 100 mL of dichloromethane dropwise to the reaction system. After the addition is complete, remove the ice bath and stir the reaction at room temperature for 20 hours. After the reaction is complete, filter to remove byproducts, remove dichloromethane from the filtrate by rotary evaporation, and dry under vacuum to obtain end-capped polysuccinimide powder.

[0070] 3. Disperse the powder obtained in step 2 in deionized water. Under the conditions of heating and stirring in a 40°C water bath, add dropwise a 30% sodium hydroxide solution to adjust and maintain the pH of the reaction system at 9.0. Continue the reaction for 4 hours until the solid is completely dissolved to obtain a brown transparent liquid of enzyme-sensitive terminal polyaspartic acid (ES-PASP) with a solid content of 25%.

[0071] Preparation Example 4:

[0072] This preparation example provides a method for preparing a polylactic acid (PLA) oligomer suspension, the steps of which are as follows:

[0073] 1. 1000 g of L-lactic acid aqueous solution and 3.0 g of stannous octoate catalyst were added to a reactor equipped with a water separator. Under nitrogen protection, the mixture was heated and stirred at 130 °C for 3 hours to remove water. Subsequently, the system vacuum was evacuated to 300 Pa, and the temperature was raised to 170 °C for melt polycondensation reaction for 2 hours to obtain polylactic acid (PLA) oligomers with an average molecular weight of approximately 1000 Da.

[0074] 2. The viscous PLA oligomer obtained in step 1 is slowly added to deionized water under the action of a high-speed shear emulsifier at 8000 rpm to prepare a stable suspension with a solid content of 25%.

[0075] Preparation Example 5:

[0076] This preparation example provides a method for preparing a polylactic acid (PLA) oligomer suspension, the steps of which are as follows:

[0077] 1. 1000 g of L-lactic acid aqueous solution and 5.0 g of stannous octoate catalyst were added to a reactor equipped with a water separator. Under nitrogen protection, the mixture was heated and stirred at 150 °C for 2 hours to remove water. Subsequently, the system vacuum was reduced to 100 Pa, and the temperature was raised to 190 °C for melt polycondensation reaction for 1.5 hours to obtain polylactic acid (PLA) oligomers with an average molecular weight of approximately 1800 Da.

[0078] 2. The viscous PLA oligomer obtained in step 1 is slowly added to deionized water under the action of a high-speed shear emulsifier at 10,000 rpm to prepare a stable suspension with a solid content of 30%.

[0079] Preparation Example 6:

[0080] This preparation example provides a method for preparing a polyglycolic acid (PGA) oligomer suspension, the steps of which are as follows:

[0081] 1. 1000g of a 70% aqueous glycolic acid solution and 4.0g of stannous octoate catalyst were added to a reactor equipped with a water separator. Under nitrogen protection, the mixture was heated and stirred at 120°C for 4 hours to remove water. Subsequently, the system vacuum was reduced to 200 Pa, and the temperature was raised to 180°C for melt polycondensation reaction for 2.5 hours to obtain polyglycolic acid (PGA) oligomers with an average molecular weight of approximately 1200 Da.

[0082] 2. The viscous PGA oligomer obtained in step 1 is slowly added to deionized water under the action of a high-speed shear emulsifier at 9000 rpm to prepare a stable suspension with a solid content of 25%.

[0083] Examples 1-3:

[0084] Example 1:

[0085] This embodiment provides a standardized cultivation method for crops in moderately to severely saline-alkali land with gradient regulation. The steps are as follows:

[0086] 1. Preparation of liquid component A:

[0087] The enzyme-sensitive capped polyaspartic acid (ES-PASP) liquid prepared in Preparation Example 1, the polylactic acid (PLA) oligomer suspension prepared in Preparation Example 4, and deionized water were mixed and stirred until homogeneous. The amounts of each component were adjusted so that the final liquid component A, by weight percentage of effective solids, was: 20% enzyme-sensitive capped polyaspartic acid, 10% polylactic acid oligomer, and the remainder being water.

[0088] Preparation of liquid component B:

[0089] By weight, 10.0 parts of chitosan oligosaccharide were dissolved in water, followed by the sequential addition of 6.0 parts of anhydrous calcium chloride, 3.0 parts of magnesium sulfate heptahydrate, 2.0 parts of 3-aminopropyltriethoxysilane, 1.5 parts of disodium zinc ethylenediaminetetraacetate, and 0.5 parts of sodium iron ethylenediaminetetraacetate. Finally, deionized water was added to bring the total weight to 100 parts, and the mixture was stirred continuously until all components were completely dissolved and the system became clear and transparent, yielding liquid component B.

[0090] 3. Field application:

[0091] In an experimental field with a soil surface layer (0–20 cm) pH of 8.8 and a total salt content of 0.65%, cotton was planted. During the cotton seedling stage, the following operations were performed using a drip irrigation system:

[0092] (a) The liquid component A prepared in step 1 is applied evenly to the crop root zone soil at a rate of 35 liters / hectare with 20 cubic meters / hectare of irrigation water.

[0093] (b) Two hours later, the liquid component B prepared in step 2 is applied evenly to the crop root zone soil at a rate of 35 liters / hectare with 20 cubic meters / hectare of irrigation water.

[0094] Example 2:

[0095] This embodiment provides a standardized cultivation method for crops in moderately to severely saline-alkali land with gradient regulation. The steps are as follows:

[0096] 1. Preparation of liquid component A:

[0097] The enzyme-sensitive capped polyaspartic acid (ES-PASP) liquid prepared in Preparation Example 2, the polylactic acid (PLA) oligomer suspension prepared in Preparation Example 5, and deionized water were mixed and stirred until homogeneous. The amounts of each component were adjusted so that the final liquid component A, by weight percentage of effective solids, was: 25% enzyme-sensitive capped polyaspartic acid, 15% polylactic acid oligomer, and the remainder being water.

[0098] 2. Preparation of liquid component B:

[0099] By weight, 15.0 parts of chitosan oligosaccharide were dissolved in 69.0 parts of deionized water and stirred until completely dissolved. Then, 10.0 parts of anhydrous calcium chloride and 4.0 parts of 3-aminopropyltriethoxysilane were added sequentially, and the mixture was stirred until the system was clear and transparent. Then, 1.0 part of disodium manganese ethylenediaminetetraacetate and 1.0 part of disodium zinc ethylenediaminetetraacetate were added and stirred until homogeneous to obtain liquid component B.

[0100] 3. Field application:

[0101] In an experimental field with a soil surface layer (0–20 cm) pH of 9.2 and a total salt content of 0.80%, tomatoes were planted. After the tomato seedlings had established themselves, the following procedures were performed using a drip irrigation system:

[0102] (a) The liquid component A prepared in step 1 is applied evenly to the crop root zone soil at a rate of 45 liters / hectare with 25 cubic meters / hectare of irrigation water.

[0103] (b) After a 3-hour interval, the liquid component B prepared in step 2 is applied evenly to the crop root zone soil at a rate of 45 liters / hectare along with 25 cubic meters / hectare of irrigation water.

[0104] Example 3:

[0105] This embodiment provides a standardized cultivation method for crops in moderately to severely saline-alkali land with gradient regulation. The steps are as follows:

[0106] 1. Preparation of liquid component A:

[0107] The enzyme-sensitive capped polyaspartic acid (ES-PASP) liquid prepared in Preparation Example 3, the polyglycolic acid (PGA) oligomer suspension prepared in Preparation Example 6, and deionized water were mixed and stirred until homogeneous. The amounts of each component were adjusted so that the final liquid component A, by weight percentage of effective solids, was: 15% enzyme-sensitive capped polyaspartic acid, 20% polyglycolic acid oligomer, and the remainder being water.

[0108] 2. Preparation of liquid component B:

[0109] By weight, 8.0 parts of chitosan oligosaccharide were dissolved in 78.5 parts of deionized water and stirred until completely dissolved. Then, 8.0 parts of magnesium sulfate heptahydrate and 1.0 part of 3-aminopropyltriethoxysilane were added sequentially, and the mixture was stirred until the system was clear and transparent. Then, 2.0 parts of ferric sodium ethylenediaminetetraacetate and 2.5 parts of plant growth regulator (sodium nitrophenolate) were added and stirred evenly to obtain liquid component B.

[0110] 3. Field application:

[0111] In an experimental field with a soil surface layer (0–20 cm) pH of 8.5 and a total salt content of 0.72%, sunflowers were planted. During the early budding stage of the sunflowers, the following operations were performed using a drip irrigation system:

[0112] (a) The liquid component A prepared in step 1 is applied evenly to the crop root zone soil at a rate of 30 liters / hectare with 15 cubic meters / hectare of irrigation water.

[0113] (b) After an interval of 1 hour, the liquid component B prepared in step 2 is applied evenly to the crop root zone soil at a rate of 30 liters / hectare with 15 cubic meters / hectare of irrigation water.

[0114] Comparative Examples 1-9:

[0115] Comparative Example 1:

[0116] Compared with Example 1, the difference is that liquid components A and B are not applied in the field application steps. Instead, the same volume of clean water as in Example 1 is applied through a drip irrigation system.

[0117] Comparative Example 2:

[0118] The difference from Example 1 is that in the field application step (b), liquid component B is replaced with the same volume of clean water as in Example 1.

[0119] Comparative Example 3:

[0120] The difference from Example 1 is that in the field application step (a), liquid component A is replaced with the same volume of clean water as in Example 1.

[0121] Comparative Example 4:

[0122] Compared with Example 1, the difference is that when applying it in the field, the liquid components A and B prepared in Example 1 are premixed evenly and then applied to the soil in one go through the drip irrigation system, with the total application volume being equivalent to that of Example 1.

[0123] Comparative Example 5:

[0124] The difference from Example 1 is that in the preparation of liquid component A, conventional sodium polyaspartate was used instead of enzyme-sensitive capped polyaspartic acid (ES-PASP). This conventional sodium polyaspartate was obtained directly from the polysuccinimide (PSI) obtained in step 1 of Preparation Example 1 by hydrolysis at pH=10, without the capping reaction in step 2.

[0125] Comparative Example 6:

[0126] Compared with Example 1, the difference is that 3-aminopropyltriethoxysilane (APTES) is not added during the preparation of liquid component B, and its weight is made up by deionized water.

[0127] Comparative Example 7:

[0128] Compared with Example 1, the difference is that anhydrous calcium chloride and magnesium sulfate heptahydrate are not added during the preparation of liquid component B, and its weight is made up by deionized water.

[0129] Comparative Example 8:

[0130] Compared with Example 1, the difference is that in the preparation of liquid component A, citric acid was used to replace polylactic acid (PLA) oligomer with an equal molar amount of effective acid.

[0131] Comparative Example 9:

[0132] Compared with Example 1, the difference is that in its field application steps, the time interval between steps (a) and (b) is 0, that is, liquid component B is applied immediately after liquid component A is applied.

[0133] Test Examples 1-3:

[0134] Test Example 1: Gradient Test of Soil Physicochemical Properties in the Root Zone

[0135] The experimental steps are as follows:

[0136] 1. Sampling:

[0137] Thirty days after the completion of field trials for each treatment group in Examples 1-3 and Comparative Examples 1-9, five test sites were randomly selected within each treatment group. Soil samples were drilled vertically downwards using a soil auger, centered on the base of the crop stem. Soil samples were collected in layers at depths of 0-10 cm, 10-20 cm, and 20-30 cm. The soil samples from the five test sites at the same depth and treatment group were uniformly mixed to form a composite soil sample for testing. All composite soil samples were then air-dried indoors in a dark, well-ventilated area.

[0138] 2. Sample preparation and determination:

[0139] After air-drying, remove stones and plant roots from the soil sample, crush it with a wooden stick, and then sieve it through a 2mm sieve. Accurately weigh 20.0g of the sieved, air-dried soil sample and place it in a 100mL beaker. Add 50mL of deionized water (soil-to-water ratio 1:2.5). Stir with a glass rod for 1 minute to fully mix the soil and water, and then let it stand for 30 minutes.

[0140] Using a pH meter calibrated with a standard buffer solution, insert the electrode into the clear liquid above the soil suspension to be tested, and record the pH value after the reading stabilizes.

[0141] Subsequently, using a conductivity meter calibrated with a standard potassium chloride solution, the conductivity electrode was inserted into the upper clear liquid of the same soil suspension. After the reading stabilized, the conductivity (EC) value was recorded in mS / cm. Each sample was measured three times, and the average value was taken.

[0142] The average pH and average EC values ​​of all treatment groups at different depths are recorded in Table 1.

[0143] Table 1. pH and electrical conductivity (EC) values ​​of soil at different depths in each treatment group:

[0144]

[0145] Figure 1 A three-dimensional surface plot shows the pH distribution of the root zone soil profile after treatment in Example 1, Comparative Example 1, and Comparative Example 4. In the figure, the X-axis represents the treatment group, the Y-axis represents the soil depth (in cm), and the Z-axis represents the measured soil pH value.

[0146] Figure 2 A three-dimensional surface plot shows the distribution of electrical conductivity (EC) values ​​in the root zone soil profile after treatment in Example 1, Comparative Example 1, and Comparative Example 4. In the figure, the X-axis represents the treatment group, the Y-axis represents the soil depth (in cm), and the Z-axis represents the measured soil electrical conductivity value (in mS / cm).

[0147] Table 1 Figure 1 and Figure 2 Data shows that, compared to the initial soil condition (reflected by Comparative Example 1), the treatments in Examples 1-3 generated structures with clearly hierarchical differences in physicochemical properties within the 0-30 cm soil profile. Specifically, in the 0-10 cm topsoil layer, pH and EC values ​​were reduced to their lowest levels; in the 10-20 cm and 20-30 cm subsurface and deep soil layers, pH and EC values ​​increased progressively. This result indicates that the slow-release acid precursor and anionic polymer in liquid component A, and the cationic polymer and crosslinking agent in liquid component B, react in situ in the soil through time-interval drip irrigation, forming a functional network structure. This structure plays a major role in reducing salinity and alkalinity in the surface layer and fixes or migrates most soluble salt ions to deeper soil layers.

[0148] The results of the comparative examples, in turn, verified the necessary conditions for the formation and realization of the aforementioned structure. Data from Comparative Examples 4 (mixed application) and 9 (application without intervals) showed that although the pH and EC values ​​decreased to some extent throughout the profile, their values ​​were uniformly distributed, failing to form a gradient structure, and their overall effect was significantly lower than that of the examples. This indicates that the time-sequential application of the two components is a prerequisite for the formation of a functionally gradient structure. The results of Comparative Examples 2 (application of A only) and 3 (application of B only) were close to those of Comparative Example 1 (blank control), indicating that the two liquid components must work synergistically. The results of Comparative Example 7 (without ionic crosslinking agent) also showed functional failure, demonstrating the necessity of rapid ionic crosslinking for the initial establishment of the network structure.

[0149] The functions of different components were confirmed by data from other comparative examples. In Comparative Example 8, the use of fast-acting citric acid to replace the slow-release acid precursor resulted in an excessive decrease in pH at the 0–10 cm surface layer, but no significant effect at deeper layers. This indicates that the sustained and mild acidolysis characteristics of the slow-release acid precursor are the basis for constructing a stable pH gradient. Compared to Example 1, Comparative Example 5 (without enzyme-sensitive end-capping) showed a weakened effect in controlling surface pH and EC, indicating that specific end-capping groups on the anionic polymer have a direct effect on enhancing the regulatory function of the root-surface interface. Compared to Example 1, Comparative Example 6 (without slow covalent crosslinking agent) showed a slight decrease in pH and EC gradient effects, indicating that slow covalent crosslinking contributes to maintaining the long-term stability of the network structure.

[0150] Test Example 2: Soil Water Holding Capacity Test

[0151] The experimental steps are as follows:

[0152] 1. Irrigation and Sampling:

[0153] Thirty days after the completion of field trials for each treatment group in Examples 1-3 and Comparative Examples 1-9, all treatment group experimental fields were saturated with water to ensure that the 0-30cm soil layer was completely moist. On the 3rd and 7th days after saturated irrigation, five test points were randomly selected within each treatment group. Soil samples were collected at a depth of 0-20cm using a soil auger. The soil samples from the five test points of the same treatment group and the same sampling time were uniformly mixed to form a composite soil sample to be tested, and immediately placed in a sealed bag for storage.

[0154] 2. Moisture content determination:

[0155] Soil moisture content was determined using the drying method. Immediately after opening the sealed bag, a sample was taken, and a known-mass aluminum box was accurately weighed. Approximately 30g of fresh soil sample was then placed into the aluminum box, and the total weight (aluminum box + moist soil) was measured and recorded as follows: Place the aluminum box containing the soil sample (with the lid open) in a 105℃ electric thermostatic drying oven and dry for 12 hours until constant weight. Transfer the dried aluminum box to a desiccator to cool to room temperature, and weigh the total weight (aluminum box + dry soil), recording it as _____. Soil moisture content (%) is calculated using the following formula:

[0156] ;

[0157] in, The mass of the aluminum box. Each composite soil sample was measured three times, and the average value was taken.

[0158] The average soil moisture content of all treatment groups at different time points is recorded in Table 2.

[0159] Table 2 Soil moisture content at different time points for each treatment group:

[0160]

[0161] Figure 3 This is a box plot showing the soil moisture content of all treatment groups on day 7 after saturated irrigation. The X-axis represents the treatment group number, and the Y-axis represents the soil moisture content (%). Each box indicates the distribution of data for its corresponding treatment group.

[0162] The data in Table 2 show that the soil treated in Examples 1-3 had significantly higher mass moisture content on the 3rd and 7th days after saturated irrigation than the soil treated in all comparative examples. Figure 3 The soil water-holding capacity of all treatment groups on day 7 was compared globally using box plots. The figures show that the data distribution intervals (including the median and interquartile range) of Examples 1-3 are generally above the data distribution intervals of all comparative examples, with the highest values. This indicates that after treatment with this technical solution, a three-dimensional network structure with high water-holding capacity is formed in situ between soil particles. This network structure can absorb and physically bind water, effectively reducing water loss due to gravity and surface evaporation, thereby extending the effective water supply time of the soil.

[0163] The results of the comparative examples provide evidence for the formation mechanism and stability of the aforementioned network structure. The soil water holding capacity of Comparative Example 7 (without ionic crosslinking agent) was not significantly different from that of Comparative Example 1 (blank control). While the water holding capacity of Comparative Example 6 (without slow covalent crosslinking agent) was higher than that of Comparative Example 7, the decrease in water content from day 3 to day 7 was greater than that of Example 1. This confirms that rapid ionic crosslinking is the initial step in forming the network framework, while slow covalent crosslinking further enhances the long-term structural stability of the network, enabling it to continuously and effectively bind water. The water holding capacities of Comparative Example 4 (mixed application) and Comparative Example 9 (application without intervals) were lower than those of the Examples, indicating that the sequential application of components is a necessary process condition to ensure the formation of an effective, homogeneous network in the soil pores rather than the formation of ineffective flocs in the solution.

[0164] The contributions of different components to water-holding capacity were also verified. Comparative Example 2 (A only) and Comparative Example 3 (B only) showed no significant improvement in water-holding capacity, indicating that a single component cannot form a network. The water-holding capacity of Comparative Example 8 (using small molecule citric acid) was close to the blank control, indicating that the slow-release acid precursor itself, as a polymer segment, participated in the physical entanglement and construction of the network structure, while the small molecule acid does not possess this structural function. Compared to Example 1, Comparative Example 5 (without enzyme-sensitive end-capping) showed a decrease in water-holding capacity, indicating that the presence of specific groups on the anionic polymer optimized the network's microstructure, enabling it to interact more effectively with water molecules.

[0165] Test Example 3: Crop Growth and Physiological Indicators Test

[0166] Sixty days after the completion of field trials for each treatment group in Examples 1-3 and Comparative Examples 1-9, the following indicators were measured:

[0167] (a) Survival rate statistics: In each treatment group area, the initial total number of plants and the current total number of surviving plants are counted, and the survival rate is calculated by the formula (number of surviving plants / initial total number of plants) × 100%.

[0168] (b) Morphological and Biomass Measurements: Five representative plants were randomly selected from each treatment group. The height of the plant from the ground surface to the apical meristem was measured using a ruler and recorded as plant height. The diameter of the stem at the base of the plant was measured using electronic vernier calipers and recorded as stem diameter. After measurement, the plant was cut off at the ground surface to separate the aboveground and underground parts. The underground root system was rinsed clean with water. The aboveground and underground parts were placed separately into labeled kraft paper bags and placed in an oven at 65°C for 30 minutes to blanch, and then dried at this temperature to constant weight. The dry weight of the aboveground and underground parts was weighed separately using an electronic balance with an accuracy of 0.001 g.

[0169] (c) Root activity assay: For biomass determination, approximately 0.2 g of active white root tips were cut from the underground root system of each sample. The TTC (triphenyltetrazolium chloride) reduction method was used for determination. The root tip sample was placed in a test tube, TTC solution and phosphate buffer were added, and the reaction was carried out at 37°C in the dark for 2 hours. After the reaction was completed, sulfuric acid was added to terminate the reaction, and then ethyl acetate was added to extract the reaction product, red A. The supernatant red extract was taken, and its absorbance (OD) value was measured at a wavelength of 485 nm using a spectrophotometer.

[0170] The average values ​​of all growth and physiological indicators measured for all treatment groups are recorded in Table 3.

[0171] Table 3. Crop growth and physiological indicators for each treatment group:

[0172]

[0173] The data in Table 3 show that, compared with all comparative examples, the crops treated in Examples 1-3 achieved the highest levels in six indicators: survival rate, plant height, stem diameter, aboveground and underground dry weight, and root activity. This result directly corresponds to the changes in soil physicochemical properties and water-holding capacity observed in Test Examples 1 and 2. The network structure formed in the rhizosphere soil, with pH and salinity gradients and high water-holding capacity, provides a low-stress growth environment for crop roots, thereby allocating more resources to biomass accumulation, which is manifested in the increase of various growth indicators.

[0174] The results of the comparative examples verified the structural and functional mechanisms of this technical solution from a crop physiological perspective. The crop growth indicators of Comparative Example 4 (mixed application) and Comparative Example 9 (application without intervals) were significantly lower than those of the Example, confirming the importance of time-sharing and sequential application for constructing an effective functional structure in situ in the soil; failure to effectively form this structure prevents the maximization of crop growth conditions. The crop growth indicators of Comparative Example 7 (without ionic crosslinking) and Comparative Example 6 (without covalent crosslinking) were both inferior to those of the Example, with Comparative Example 7 showing a more significant decline in performance. This indicates that the dual crosslinking network, rapidly formed by ionic crosslinking and then slowly stabilized by covalent crosslinking, is the foundation for maintaining long-term stability of the rhizosphere environment, and this stability is directly reflected in the final crop biomass.

[0175] The influence of the chemical structure of different components on the final physiological effects was also confirmed. Comparative Example 8 (using citric acid) showed no significant difference in crop growth indicators compared to the blank control (Comparative Example 1), indicating that the gradual pH regulation and structural occupation provided by the slow-release acid precursor polymer are key to maintaining root health and vigor, while the instantaneous and intense effects of small molecule acids failed to produce this effect. Comparative Example 5 (without enzyme-sensitive end-capping) showed better performance than the blank control in all indicators, but was lower than Example 1 across the board, especially in root vigor and underground dry weight. This indicates that the enzyme-sensitive end-capping groups on the anionic polymer undergo specific reactions in the rhizosphere microenvironment, further optimizing the root-soil interface, promoting root physiological activity and nutrient absorption, and ultimately resulting in an increase in overall plant biomass.

[0176] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A standardized cultivation method for crops in moderately to severely saline-alkali land based on gradient regulation, characterized in that, Includes the following steps: (a) Apply a permeable liquid component A containing anionic polymers and slow-release acid precursors to the crop rhizosphere soil; The anionic polymer is a modified polyaspartic acid with end-capped groups that are sensitive to crop root exudates grafted onto its molecular chain. (b) After a preset time interval, a liquid component B comprising a cationic polymer and a crosslinking agent is applied to the soil in the root zone of the crop; the cationic polymer is chitosan oligosaccharide. The liquid component A and the liquid component B react in situ in the soil to form a hydrogel network with a gradient structure, which is used to regulate the microenvironment of the crop root zone. The crosslinking agent in liquid component B is a dual crosslinking system comprising a fast ionic crosslinking agent and a slow covalent crosslinking agent; wherein the fast ionic crosslinking agent is calcium ions and / or magnesium ions; and the slow covalent crosslinking agent is an organosilane crosslinking agent.

2. The standardized cultivation method for crops in moderately to severely saline-alkali land based on gradient regulation according to claim 1, characterized in that, The gradient structure of the hydrogel network exhibits at least two gradient combinations selected from the following: A salinity gradient decreasing from the inside out, a pH gradient decreasing from the surface to the depths, a gradient of highly available nutrient concentrations around the roots, or a water gradient decreasing from the inside out.

3. The standardized cultivation method for crops in moderately to severely saline-alkali land based on gradient regulation according to claim 1, characterized in that, The modified polyaspartic acid is prepared through the following steps: L-Aspartic acid was thermally polycondensed to obtain polysuccinimide; The polysuccinimide is subjected to an end-capping reaction with ethyl glycolate; The end-capped product is obtained by ring-opening hydrolysis under alkaline conditions.

4. The standardized cultivation method for crops in moderately to severely saline-alkali land based on gradient regulation according to claim 1 or 2, characterized in that, The slow-release acid precursor is a polylactic acid oligomer or a polyglycolic acid oligomer.

5. The standardized cultivation method for crops in moderately to severely saline-alkali land based on gradient regulation according to claim 1, characterized in that, The liquid component A is made from raw materials comprising the following weight percentages: 15-30% anionic polymer, 8-20% slow-release acid precursor, and the balance being water; The liquid component B is made from raw materials comprising the following weight percentages: 8-18% cationic polymer, 6-17% crosslinking agent, 0.5-2.0% chelated trace elements, and the balance being water.

6. The standardized cultivation method for crops in moderately to severely saline-alkali land based on gradient regulation according to claim 1, characterized in that, The preset time interval is 1 to 3 hours; both liquid component A and liquid component B are applied through a drip irrigation system.

7. The standardized cultivation method for crops in moderately to severely saline-alkali land based on gradient regulation according to claim 1, characterized in that, The liquid component A and / or the liquid component B may further contain plant growth regulators or soil microbial agents.

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