Saline-alkali soil salt-reducing, plate-changing and quality-improving method

Abstract

The invention relates to the technical field of soil improvement, in particular to a saline-alkali soil salt reducing, plate modifying and quality improving method which comprises the following steps that a, a clay immobilization layer is constructed at the position 30-40 cm below the earth surface, the clay immobilization layer is composed of modified zeolite powder, nanometer biochar, attapulgite clay, a microorganism immobilizing agent and a slow-release calcium source, and the filling and compacting thickness is 3-5 cm; b, modified water is used for irrigation so as to reduce the content of salt, alkali and clay on the surface layer, citric acid, a biological surfactant compound, electrolytic activated water and sodium humate are added into irrigation water, the irrigation amount is 60-100 cubic meters per mu, and irrigation is conducted twice; c) uniformly spreading a plough layer improvement material to the earth surface to reconstruct a plough layer structure, the plough layer improvement material comprises a modified organic fertilizer matrix, a ferrous sulfate complex, a calcium magnesium phosphate mineral compound, a saline alkali soil microbial agent and a biological enzyme activator, the dosage is 1.5-2 tons / mu, rotary tillage is uniform, and the depth is 18-22 cm.

Description

Technical Field

[0001] The present invention relates to the technical field of soil improvement, and specifically relates to a method for reducing salt, improving soil texture and enhancing quality in saline-alkali land, which can be used for the comprehensive management and improvement of saline-alkali soil and improve the agricultural production capacity of saline-alkali land. Background Art

[0002] Carrying out the comprehensive utilization of saline-alkali land is an important way to supplement the reserve resources of cultivated land, protect the existing cultivated land and improve the comprehensive agricultural production capacity, and is of strategic significance for ensuring national food security and firmly holding the Chinese rice bowl.

[0003] At present, the methods for improving saline-alkali soil mainly include various measures such as physical improvement, chemical improvement, and biological improvement. The research published by Zhang, L., Zhang, G., Wang, Y., et al. (2023), "Combining chemical and organic treatments enhances remediation performance and soil health in saline-sodic soils. Communications Earth & Environment, 4(1), 119-133" shows that the combined chemical and organic treatment can significantly improve the remediation effect and soil health of saline-alkali soils, but the effect of single measures is limited and the persistence is poor. The six-year long-term experimental study by Li, X., Chen, W., Wu, J., et al. (2024), "Long-term effects of biochar one-off application on soil physicochemical properties, salt concentration, nutrient availability, enzyme activity, and rice yield of highly saline-alkali paddy soils: based on a 6-year field experiment. Biochar, 6(2), 112-128" confirms that the application of biochar has a lasting improvement effect on the physicochemical properties, salt concentration, and microbial activity of saline-alkali soils, but the cost is high and other measures need to be combined to obtain the best effect.The research of "Wang, H., Liu, S., Zhang, Y., et al. (2024), 'Synthetic microbial communities: Sandbox and blueprint for soil health enhancement. iMeta, 3(1), 172 - 196'" shows that synthetic microbial communities have good application prospects as a blueprint for soil health enhancement, but still face challenges in stability and environmental adaptability in large-scale applications. The global meta-analysis of "Leng, P., Xiao, C., Zhao, Y., et al. (2023), 'Drip irrigation in agricultural saline-alkali land controls soil salinity and improves crop yield: Evidence from a global meta-analysis. Science of The Total Environment, 868(1), 18454 - 18472'" shows that drip irrigation technology can effectively control soil salinity in agricultural saline-alkali land and improve crop yield, but it needs to be applied in coordination with other improvement measures to achieve long-term effects.

[0004] The following problems generally exist in the prior art: First, the problems of soil salinization and hardening are often treated separately, lacking a systematic solution; second, the research on the synergistic mechanism of physical, chemical, and biological measures is insufficient, making it difficult to exert a comprehensive effect; third, the durability of the improvement effect is insufficient, and frequent repeated treatments are required; fourth, there is a lack of a hierarchical implementation plan for different salinization degrees, making it difficult to meet the complex and changeable soil conditions.

[0005] Therefore, there is an urgent need to develop a method for treating saline-alkali land that can synchronously solve the problems of salinization and hardening, physical-chemical-biological synergy, has a long-lasting effect, and wide applicability, so as to achieve the goals of rapid salt reduction, soil hardening improvement, and quality improvement in saline-alkali land. Summary of the Invention

[0006] The purpose of the present invention is to provide a method for reducing salt, improving soil hardening, and enhancing soil quality in saline-alkali land, aiming to solve the technical problems of poor treatment effect, poor persistence, and inability to synchronously solve the problems of soil salinization and hardening in the prior art, and achieve the goals of rapid salt reduction, improvement of soil structure, and enhancement of soil fertility in saline-alkali cultivated land, providing a technical approach for the comprehensive management and efficient utilization of saline-alkali land.

[0007] To achieve the above purpose, the present invention provides a method for reducing salt, improving soil hardening, and enhancing soil quality in saline-alkali land, including the following steps:

[0008] a) Construct a clay retention layer at a depth of 30 - 40 cm below the ground surface. The clay retention layer is composed of modified zeolite powder, nano biochar, attapulgite clay, microbial fixative, and slow-release calcium source, and is filled and compacted to a thickness of 3 - 5 cm.

[0009] b) Use modified water for irrigation to reduce the surface salinity and clay content. The modified water is obtained by adding citric acid, bio-surfactant complex, electrolyzed activated water, and sodium humate to the irrigation water. The irrigation volume is 60 - 100 cubic meters per mu, and irrigation is carried out 2 times.

[0010] c) Uniformly spread tillage layer improvement materials on the ground surface to reconstruct the tillage layer structure. The tillage layer improvement materials include modified organic fertilizer matrix, ferrous sulfate complex, calcium magnesium phosphate mineral complex, saline-alkali soil microbial inoculant, and bio-enzymatic activator, with a dosage of 1.5 - 2 tons per mu, and are evenly rotary tilled to a depth of 18 - 22 cm.

[0011] Preferably, in the clay retention layer, the modified zeolite powder is 10 - 30 parts by weight, the nano biochar is 15 - 40 parts by weight, the attapulgite clay is 5 - 20 parts by weight, the microbial fixative is 5 - 25 parts by weight, and the slow-release calcium source is 5 - 15 parts by weight.

[0012] Preferably, the modified zeolite powder is obtained by modifying natrolite with quaternary ammonium salt surfactant. The nano biochar is prepared from rice husk as raw material by pyrolysis at a temperature of 350 - 450 °C for 2 - 4 hours. The microbial fixative is sodium alginate-chitosan complex, and the slow-release calcium source is calcium lactate pentahydrate.

[0013] Preferably, in the modified water, the citric acid is 0.05 - 0.15 parts by weight, the bio-surfactant complex is 0.1 - 0.25 parts by weight, the electrolyzed activated water is 80 - 95 parts by weight, and the sodium humate is 0.05 - 0.2 parts by weight.

[0014] Preferably, the bio-surfactant complex includes rhamnolipid and lipopeptide. The electrolyzed activated water is prepared by electrolyzing an aqueous solution containing 0.1% - 0.3% sodium chloride, with a pH value of 5.8 - 6.5 and an oxidation-reduction potential of +500 to +700 mV.

[0015] Preferably, in the tillage layer improvement materials, the modified organic fertilizer matrix is 70 - 85 parts by weight, the ferrous sulfate complex is 8 - 15 parts by weight, the calcium magnesium phosphate mineral complex is 5 - 10 parts by weight, the saline-alkali soil microbial inoculant is 3 - 8 parts by weight, and the bio-enzymatic activator is 1 - 3 parts by weight.

[0016] Preferably, the modified organic fertilizer substrate comprises 40%-50% of livestock and poultry manure compost, 20%-30% of straw biochar, and 20%-30% of plant residue compost. The ferrous sulfate complex is a complex of ferrous sulfate heptahydrate and amino acids. The saline-alkali soil microbial inoculant comprises salt-tolerant rhizobium flora, halophilic bacillus, pseudomonas secreting extracellular polysaccharides, and salt-tolerant micrococcus producing ACC deaminase. The bio-enzymatic activator comprises β-glucosidase, urease, alkaline phosphatase, and sucrase.

[0017] Preferably, after the construction of the clay retention layer, an activation solution containing highly efficient microbial strains for saline-alkali environments is sprayed, with a dosage of 50-100 mL / m 2 , and the microbial strain is Pseudomonas halophila, with a concentration of 1×108 CFU / mL.

[0018] Preferably, the interval between the two modified water irrigations is 7-10 days. The irrigation timing is controlled by monitoring the soil water content through a soil moisture sensor. The dosage of the first irrigation is 40-50 m³ / acre, and the dosage of the second irrigation is 30-40 m³ / acre.

[0019] Preferably, a hierarchical implementation plan is adopted according to the degree of salinization: for slightly saline soil (EC < 4 dS / m, ESP < 15%), the thickness of the clay retention layer is 3 cm, the total amount of modified water irrigation is 60-70 m³ / acre, and the dosage of the tillage layer improvement material is 1.5 tons / acre; for moderately saline soil (EC is 4-8 dS / m, ESP is 15%-25%), the thickness of the clay retention layer is 4 cm, the total amount of modified water irrigation is 80-90 m³ / acre, and the dosage of the tillage layer improvement material is 1.7 tons / acre; for severely saline soil (EC > 8 dS / m, ESP > 25%), the thickness of the clay retention layer is 5 cm, the total amount of modified water irrigation is 90-100 m³ / acre, and the dosage of the tillage layer improvement material is 2.0 tons / acre, and an additional 1-2 times of conventional water leaching is added in the early stage, with each time being 50-60 m³ / acre.

[0020] The method for reducing salt, improving soil compaction and enhancing soil quality in saline-alkali land provided by the present invention has the following beneficial effects:

[0021] (1) Systematically solve the dual problems of salinity and soil compaction: The present invention realizes the synchronous solution of salinity and soil compaction problems and forms a complete soil optimization system through the three-step coordinated action of constructing a clay retention layer, reducing the surface salinity and clay content, and reconstructing the tillage layer structure.

[0022] (2) Multi-component synergistic action mechanism: A physical-chemical-biological synergistic action network is formed among the components of the present invention. The clay retention layer physically intercepts and chemically adsorbs the downward-moving clay; the modified water promotes the dissolution and migration of salts and the dispersion and downward movement of clay; the tillage layer improvement material reconstructs the soil aggregate structure, adjusts the pH value, and restores the microbial activity. Each link is interconnected, and the effect is significantly improved.

[0023] (3) Sustained improvement effect: Through the long-term stabilization of the clay holding layer and the reconstruction of the microbial ecosystem in the tillage layer, the method of the present invention can achieve long-term sustainability of the improvement effect, avoiding the problem of frequent repeated treatment required by traditional methods.

[0024] (4) The graded implementation plan has strong adaptability: Differentiated implementation strategies are adopted according to the degree of salinity, which is suitable for saline-alkali land of different degrees, has strong practicality and a wide range of applications.

[0025] (5) Significantly improve soil quality and crop yield: Experimental verification shows that this method can reduce the electrical conductivity of surface soil by 65% ​​to 80%, reduce the percentage of exchangeable sodium by 55% to 70%, increase the soil organic matter content by 80% to 120%, and increase crop yield by 30% to 60%, with significant comprehensive benefits. DETAILED DESCRIPTION

[0026] The present invention is further illustrated by the following detailed scheme, but is not intended to limit the present invention in any way.

[0027] 1. Raw material components and preparation methods

[0028] 1. Clay holding layer material

[0029] 1.1 Modified zeolite powder

[0030] The modified zeolite powder is prepared by modifying sodium clinoptilolite with a quaternary ammonium surfactant. The specific preparation method is as follows: sodium clinoptilolite powder (particle size <10 μm, specific surface area 400-600 m 2 / g, cation exchange capacity 140-180meq / 100g) is placed in a reaction container, hexadecyltrimethylammonium bromide aqueous solution (concentration 5% to 10%) is added, stirred and reacted at 60-70°C for 2-4 hours, filtered and washed with distilled water 3-5 times until no bromide ions are detected in the filtrate, dried at 60-80°C for 10-12 hours, ground to a particle size of 1-10μm, and a modified zeolite powder is obtained. The surface of the modified zeolite powder has quaternary ammonium groups, which can adsorb negatively charged clay particles through electrostatic action, thereby improving the adsorption capacity of the holding layer for clay particles.

[0031] 1.2 Nanobiochar

[0032] The nano biochar is prepared from rice husks through low-temperature pyrolysis and physical activation. The specific preparation method is as follows: Wash and dry the rice husks (at 105 - 110 °C for 3 - 4 hours), introduce nitrogen (flow rate 2 - 3 L / min) into a closed pyrolysis furnace, heat at a heating rate of 5 - 10 °C / min to 350 - 450 °C, hold at this temperature for 2 - 4 hours, take out after cooling to room temperature, grind to a particle size < 1 mm, then use the ball milling method to crush the biochar to 50 - 200 nm, wash with deionized water 3 - 5 times, and dry at 80 - 90 °C for 12 - 24 hours to obtain the nano biochar. The nano biochar has a high specific surface area (800 - 1200 m 2 / g) and a rich pore structure, can provide a large number of micropores and mesopores, enhance the physical interception ability of the retention layer, and at the same time, the oxygen-containing functional groups on the surface can form coordination bonds with metal ions in the clay particles to improve the chemical adsorption ability.

[0033] 1.3 Attapulgite clay

[0034] Attapulgite clay is a natural magnesium-aluminum silicate clay mineral with a special needle-like fiber structure and high adsorption performance. The attapulgite clay used in this invention has the trade name AttagelTM 50, with a particle size of 0.5 - 2 μm, a specific surface area of 150 - 200 m 2 / g, and a pH value of 7.5 - 8.5. Attapulgite clay in the retention layer can enhance the stability and continuity of the network structure and improve the interception efficiency of clay particles.

[0035] 1.4 Microbial fixative

[0036] The microbial fixative is a sodium alginate-chitosan complex, in which sodium alginate and chitosan form a stable complex through electrostatic interaction. The preparation method is as follows: Dissolve sodium alginate in deionized water to make a 2% aqueous solution, dissolve chitosan in a 1% acetic acid solution to make a 1% solution, mix the two solutions according to a mass ratio of 3:2, and stir evenly to obtain a microbial fixative with a viscosity of 300 - 500 mPa·s. This fixative can form a three-dimensional network structure in the retention layer to entrap and fix microorganisms and clay particles, enhancing the stability and persistence of the retention layer.

[0037] 1.5 Sustained-release calcium source

[0038] The sustained-release calcium source uses calcium lactate pentahydrate, with a solubility of 9 g / 100 mL (25 °C) and a pH value of 6.0 - 7.0 (10% solution). As an organic calcium source, calcium lactate can slowly release Ca 2 + ions during hydrolysis, promote the flocculation of clay particles and replace Na + on the surface of clay particles. At the same time, lactate can serve as a carbon source for microorganisms, promoting microbial growth and metabolic activities.

[0039] 2. Modified water component

[0040] 2.1 Citric acid

[0041] Citric acid, with the chemical name of 2-hydroxy-1,2,3-propanetricarboxylic acid, is a natural organic acid that can provide H in the modified water + to replace Na on the surface of soil colloids + , reduce the electrostatic repulsion between clay particles, and at the same time can act as a complexing agent to form soluble complexes with metal ions in the soil, promoting the dissolution and migration of salts.

[0042] 2.2 Biosurfactant complex

[0043] The biosurfactant complex is composed of rhamnolipid and lipopeptide, with a critical micelle concentration of 10-15 mg / L and a surface tension of 27-30 mN / m. These bio-based surfactants have good biodegradability and environmentally friendly characteristics, can significantly reduce the surface tension of water, enhance the permeability and uniform distribution of water in the soil, and at the same time act on the soil colloid interface, reduce the adhesion force between clay particles, and promote the dispersion and downward movement of clay particles.

[0044] 2.3 Electrolytically activated water

[0045] Electrolytically activated water is prepared by electrolyzing an aqueous solution containing sodium chloride. The specific preparation method is as follows: Add clean water to the water tank, adjust the water temperature to 20-25 °C, add high-purity sodium chloride (purity ≥ 99.5%), control the concentration at 0.1% - 0.3%, and treat it through an electrolysis device. Control the current at 10-15 A, maintain the voltage at 12-24 V, and the treatment time is 20-30 minutes to obtain electrolytically activated water. Electrolytically activated water has special physical and chemical properties, including low surface tension, high permeability, and appropriate redox potential (+500 to +700 mV), which can enhance the ability of water to dissolve salts, and at the same time promote the activity of aerobic microorganisms and accelerate the decomposition of organic matter.

[0046] 2.4 Sodium humate

[0047] Sodium humate is a water-soluble salt formed by humic acid and sodium ions, with a total humic acid content of ≥ 60%, a solubility of > 98%, and a pH value of 8.0-9.0 (1% solution). Sodium humate can complex with metal ions in the soil in the modified water, promote the dispersion of clay particles, and at the same time provide a carbon source to stimulate the activities of soil microorganisms, produce more organic acids, and enhance the formation of soil aggregate structure.

[0048] 3. Plough layer improvement materials

[0049] 3.1 Modified organic fertilizer matrix

[0050] The modified organic fertilizer substrate is made by fermenting livestock and poultry manure compost (40% - 50%), straw biochar (20% - 30%) and plant residue compost (20% - 30%). The specific preparation method is as follows: Mix the above raw materials in proportion, add EM bacterial liquid (effective microbial group, concentration ≥ 1×10 9 CFU / mL) and mix in a ratio of 1:100, adjust the water content to 50% - 60%, stack and ferment, control the temperature at 45 - 55°C, for 30 - 45 days, turn the pile 2 - 3 times during this period, with an interval of 10 - 15 days each time. After fermentation is completed, air-dry to a water content < 25%, and screen to a particle size < 5mm to obtain the modified organic fertilizer substrate. The organic matter content of this substrate is ≥ 45%, total nitrogen ≥ 2.0%, total phosphorus ≥ 1.0%, total potassium ≥ 1.5%, and the pH value is 6.5 - 7.5, which can provide rich organic matter and nutrients for the soil and promote the formation of aggregate structure.

[0051] 3.2 Ferrous sulfate complex

[0052] The ferrous sulfate complex is prepared by compounding ferrous sulfate heptahydrate with amino acids. The specific method is: Dissolve ferrous sulfate heptahydrate in deionized water, add an amino acid mixture (glycine, glutamic acid, alanine, and the weight ratio of glycine, glutamic acid, alanine is 1:1:1), stir and react at a pH value of 3.0 - 4.0 and a temperature of 40 - 50°C for 2 - 3 hours, and dry using spray drying technology (inlet temperature 160 - 180°C, outlet temperature 70 - 90°C), and grind to a particle size < 0.2mm to obtain a ferrous sulfate complex with an iron content of 12% - 14%. This complex hydrolyzes in the soil to produce an acidic environment, neutralizes the soil alkalinity, reduces the pH value, and at the same time Fe 2+ forms iron bridge bonds with soil colloids to enhance the stability of aggregates.

[0053] 3.3 Calcium magnesium phosphate mineral complex

[0054] The calcium magnesium phosphate mineral complex is mainly composed of dicalcium phosphate and calcium magnesium carbonate, with a weight ratio of 1:1 - 1.2, a total phosphorus content of 18% - 20%, a calcium content of 22% - 25%, a magnesium content of 3% - 5%, and a particle size of 0.3 - 0.8mm. This complex can provide medium elements such as calcium, magnesium, and phosphorus necessary for plant growth. At the same time, polyvalent cations such as calcium and magnesium can promote the flocculation of clay particles and form a stable soil aggregate structure.

[0055] 3.4 Microbial inoculant for saline-alkali soil

[0056] The microbial inoculant for saline-alkali soil is composed of various salt-tolerant microorganisms, including:

[0057] Salt-tolerant rhizobial community (ATCC BAA-2049, concentration ≥ 2×109 CFU / g): It can grow in saline-alkali environments and form a symbiotic relationship with leguminous plants to fix nitrogen in the atmosphere.

[0058] Halophilic Bacillus (ATCC 700290, concentration ≥ 3×109 CFU / g): It produces a variety of hydrolases to promote the decomposition of organic matter and the release of nutrients.

[0059] Pseudomonas sp. secreting exopolysaccharides (ATCC 27853, concentration ≥ 2×109 CFU / g): It produces exopolysaccharides to form a biofilm and improve soil structure.

[0060] Salt-tolerant Micrococcus producing ACC deaminase (ATCC 49732, concentration ≥ 2×109 CFU / g): It produces ACC deaminase to reduce the ethylene level in plants and relieve salt stress.

[0061] These microorganisms are preserved by lyophilization, and the preservation conditions are sealed preservation at 4 - 10°C with a validity period of 12 months. In the soil, these microorganisms can establish a multifunctional microbial community, form a healthy soil food web, and promote the restoration of the soil ecosystem.

[0062] 3.5 Biological enzyme activator

[0063] The biological enzyme activator is composed of a variety of enzymes tolerant to saline-alkali environments, including:

[0064] β-Glucosidase (EC 3.2.1.21, activity ≥ 200 U / g): It catalyzes the hydrolysis of β-glucosidic bonds to release glucose.

[0065] Urease (EC 3.5.1.5, activity ≥ 150 U / g): It catalyzes the hydrolysis of urea to release ammonia and carbon dioxide.

[0066] Alkaline phosphatase (EC 3.1.3.1, activity ≥ 250 U / g): It catalyzes the hydrolysis of organic phosphates to release inorganic phosphorus.

[0067] Sucrase (EC 3.2.1.26, activity ≥ 180 U / g): It catalyzes the hydrolysis of sucrose to release glucose and fructose.

[0068] These enzymes are prepared by low-temperature spray drying technology, and the preservation conditions are -5 to -20°C with a validity period of 18 months. In the soil, these enzymes can directly participate in the transformation of organic substances, initiate the nutrient cycle before the reproduction of microorganisms, and accelerate the process of soil improvement.

[0069] II. Specific implementation steps of the technical solution

[0070] The method for reducing salt, improving soil texture and enhancing quality of saline-alkali land in the present invention mainly includes the following three key steps:

[0071] 1. Construction of Clay Retention Layer

[0072] First, mix modified zeolite powder (10 - 30 parts by weight), nano biochar (15 - 40 parts by weight), attapulgite clay (5 - 20 parts by weight) according to the formula, add microbial immobilizer solution (5 - 25 parts by weight, concentration 2% - 5%) and slow-release calcium source (5 - 15 parts by weight), stir evenly to form a moist mixture, and pre-cure it for 12 - 24 hours under the conditions of temperature 5 - 35°C and relative humidity 60% - 80% to preliminarily stabilize the material.

[0073] Then, plow the surface soil of the cultivated land to a depth of 30 - 40 cm, form a flat surface at 30 - 40 cm below the ground surface, evenly lay the prepared clay retention layer material mixture, control the thickness at 3 - 5 cm, and compact the material to a bulk density of 1.2 - 1.4 g / cm 3 , ensuring that the retention layer has appropriate strength and stability.

[0074] Next, spray the activation solution containing highly efficient microbial strains for saline-alkali environment (Pseudomonas halophila ATCC 27853, concentration 1×10 8 CFU / mL), with a dosage of 50 - 100 mL / m 2 , to promote the rapid establishment of the microbial community in the retention layer. Finally, cover the original surface soil and let it stand for 24 - 48 hours to stabilize the structure of the retention layer and establish a preliminary ecosystem for the microbial flora.

[0075] During this process, the clay retention layer acts on the downward-moving clay through three mechanisms: physical interception, chemical adsorption, and biological fixation. The quaternary ammonium groups on the surface of the modified zeolite powder adsorb the negatively charged clay through electrostatic interaction; the nano biochar provides a large number of micropores and mesopores, enhancing the physical interception ability, and at the same time, the oxygen-containing functional groups on the surface form coordination bonds with metal ions in the clay; the needle-like structure of the attapulgite clay forms a network, enhancing the interception efficiency; the microbial immobilizer forms a three-dimensional network structure to embed and fix the clay; the slow-release calcium source releases Ca 2 + to promote the flocculation of clay and stabilize the structure. The multi-component synergistic effect forms an efficient and stable clay retention system.

[0076] 2. Reducing Surface Salinity and Clay Content by Modified Water Irrigation

[0077] The preparation method of the modified water is as follows: Place the electrolytic activated water (80 - 95 parts by weight) in a stirring container, add citric acid (0.05 - 0.15 parts by weight), and stir until completely dissolved. Then add the biosurfactant complex (0.1 - 0.25 parts by weight) and sodium humate (0.05 - 0.2 parts by weight), and stir for 15 - 20 minutes until uniform. Test the pH value to ensure it is within the range of 5.8 - 6.5, and adjust with potassium hydroxide (0.1mol / L) if necessary. The modified water should be prepared within 24 hours before use to avoid affecting the effect due to long-term storage.

[0078] Irrigation is carried out in a precise control manner. The amount of the first irrigation is controlled at 40 - 50 cubic meters per mu and is evenly distributed on the surface of the cultivated land. When the soil moisture drops to 60% - 70% of the field water holding capacity (usually taking 7 - 10 days), the second irrigation is carried out, and the amount is controlled at 30 - 40 cubic meters per mu. Throughout the irrigation process, a soil moisture sensor (TDR technology) is used to monitor the soil water content to ensure the irrigation effect.

[0079] The modified water reduces the surface salinity and clay content through multiple mechanisms: The H provided by citric acid + replaces Na on the surface of soil colloids + , reducing the electrostatic repulsion between clay particles; The low surface tension and high permeability of the electrolytic activated water enhance the dissolving ability of water for salts; The biosurfactant reduces the surface tension, enhances the uniform distribution of water in the soil, and at the same time acts on the soil colloid interface to reduce the adhesion force between clay particles; Sodium humate complexes with metal ions in the soil to further promote the dispersion of clay particles. These factors work together to promote the dissolution of salts and their downward migration with water, and at the same time disperse and move the clay particles down to the retention layer, realizing the desalination and deflocculation of the surface soil.

[0080] 3. Reconstruction of the plough layer structure

[0081] The preparation of the plough layer improvement materials is as follows: Place the modified organic fertilizer matrix (70 - 85 parts by weight) in a mixing device, add ferrous sulfate complex (8 - 15 parts by weight) and calcium magnesium phosphate mineral complex (5 - 10 parts by weight). After mixing evenly, add the saline-alkali soil microbial inoculant (3 - 8 parts by weight) and the biological enzyme activator (1 - 3 parts by weight). The rotation speed of the mixing device is controlled at 20 - 30 r / min, and the mixing time is 15 - 20 minutes. The product is bagged and sealed, and stored in a dark place at 10 - 25 °C.

[0082] The application method is as follows: evenly spread the plough layer improvement materials on the soil surface after the construction of the clay retention layer and treatment with modified water irrigation, with the dosage controlled at 1.5 - 2 tons per mu. Use a rotary tiller to turn and mix, with the depth controlled at 18 - 22 cm, the rotary tiller speed controlled at 180 - 220 r / min, and the traveling speed at 2 - 3 km / h. After leveling the land, let it stand for 3 - 5 days, and conduct shallow irrigation (15 - 20 cubic meters per mu) to activate the microbial activity.

[0083] The plough layer improvement materials reconstruct the soil structure through multiple synergistic mechanisms: the organic matter provided by the modified organic fertilizer and the ferrous sulfate complex act synergistically to promote the formation of aggregate structures; Fe in the ferrous sulfate complex 2+ forms iron bridge bonds with soil colloids, enhancing the stability of aggregates. At the same time, the acidic environment generated by hydrolysis neutralizes the soil alkalinity; the multivalent cations provided by calcium magnesium phosphate minerals promote the flocculation of clay particles to form a stable micro-structure; the saline-alkali soil microbial inoculant establishes a multi-functional microbial community to promote the restoration of the soil ecosystem; the bio-enzymatic activator directly participates in the transformation of organic matter and initiates the nutrient cycle. These factors act together to achieve the reconstruction of the plough layer soil structure and improve the soil quality.

[0084] The following specifically illustrates the present invention through specific embodiments, but does not limit the present invention in any way.

[0085] Example 1: Treatment plan for slightly saline-alkali land

[0086] This example is for the treatment of slightly saline-alkali land (EC = 3.5 dS / m, ESP = 12%).

[0087] (1) Construction of the clay retention layer:

[0088] Mix 10 parts by weight of modified zeolite powder (sodium clinoptilolite is modified with cetyltrimethylammonium bromide, the dosage of quaternary ammonium salt is 5% of the zeolite weight, and the reaction is carried out at 60 °C for 3 hours), 15 parts by weight of nano-biochar (prepared by pyrolyzing rice husks at 350 °C for 2 hours and ball-milling to a particle size of 150 nm), 5 parts by weight of attapulgite clay, 5 parts by weight of microbial fixative (sodium alginate and chitosan are mixed in a mass ratio of 3:2), and 5 parts by weight of slow-release calcium source (calcium lactate pentahydrate), add an appropriate amount of water to adjust the water content to 30%, stir evenly, and pre-cure for 18 hours. Construct a 3-cm-thick retention layer at 35 cm below the ground surface and compact it to a bulk density of 1.3 g / cm 3 , spray the activated solution of Pseudomonas halophila (concentration 1×108 CFU / mL), with a dosage of 50 mL / m 2 .

[0089] (2) Modified water irrigation:

[0090] Preparation of modified water: 95 parts by weight of electrolytic activated water (0.1% sodium chloride solution, current 12 A, voltage 18 V, treated for 25 minutes, pH = 6.2, redox potential +550 mV), 0.05 parts by weight of citric acid, 0.1 part by weight of biosurfactant complex (rhamnolipid and lipopeptide mixed in a mass ratio of 3:1), 0.05 part by weight of sodium humate, and stir evenly. The dosage for the first irrigation is 40 m³ / acre, the second irrigation is carried out after 7 days with a dosage of 30 m³ / acre, and the total irrigation amount is 70 m³ / acre.

[0091] (3) Reconstruction of the plough layer structure:

[0092] Preparation of plough layer improvement materials: 85 parts by weight of modified organic fertilizer matrix (40% livestock and poultry manure compost, 30% straw biochar, 30% plant residue compost, fermented for 40 days, organic matter content 46%), 8 parts by weight of ferrous sulfate complex (ferrous sulfate heptahydrate and amino acid compounded in a mass ratio of 4:1, reacted at 45 °C for 2.5 hours), 5 parts by weight of calcium magnesium phosphate mineral complex, 3 parts by weight of saline-alkali soil microbial inoculant (mass ratio of 1:1:1:1, each strain concentration is 2×10⁹ CFU / g), 1 part by weight of bio-enzymatic activator (mass ratio of 1:1:1:1, each enzyme activity is the minimum specified value). Evenly spread on the soil surface, with a dosage of 1.5 tons / acre, rotary tillage depth of 20 cm, leveled and left standing for 4 days, and shallow irrigation of 15 m³ / acre to activate microorganisms.

[0093] Test results after 120 days of treatment: Soil EC decreased to 1.2 dS / m (decreased by 65.7%), ESP decreased to 5.3% (decreased by 55.8%), pH value decreased from 9.2 to 7.8, organic matter content increased from 0.8% to 1.5% (increased by 87.5%), the proportion of aggregate structure (>0.25 mm) increased from 18% to 42% (increased by 133.3%), and wheat yield increased by 35%.

[0094] Example 2: Moderate saline-alkali land treatment plan

[0095] This example is for the treatment of moderately saline-alkali land (EC = 6.8 dS / m, ESP = 22%).

[0096] (1) Construction of clay retention layer:

[0097] Mix 20 parts by weight of modified zeolite powder (the dosage of quaternary ammonium salt is 8% of the weight of zeolite, reacted at 65 °C for 3.5 hours), 25 parts by weight of nano biochar (prepared by pyrolyzing rice husk at 400 °C for 3 hours and ball-milled to a particle size of 100 nm), 10 parts by weight of attapulgite clay, 15 parts by weight of microbial immobilizer (sodium alginate and chitosan are mixed in a mass ratio of 2:1), and 10 parts by weight of slow-release calcium source (calcium lactate pentahydrate). Add an appropriate amount of water to adjust the water content to 35%, stir evenly, and pre-cure for 20 hours. Construct a holding layer with a thickness of 4 cm at 32 cm below the ground surface and compact it to a bulk density of 1.35 g / cm 3 , spray the activated solution of Pseudomonas halophila (concentration 1×10 8 CFU / mL), with a dosage of 75 mL / m 2 .

[0098] (2) Modified water irrigation:

[0099] Prepare modified water: 90 parts by weight of electrolyzed activated water (0.2% sodium chloride solution, current 13 A, voltage 20 V, treated for 28 minutes, pH = 6.0, redox potential +600 mV), 0.1 part by weight of citric acid, 0.15 part by weight of biosurfactant complex (rhamnolipid and lipopeptide are mixed in a mass ratio of 2:1), 0.1 part by weight of sodium humate, and stir evenly. The dosage for the first irrigation is 45 m³ / acre, the second irrigation is carried out 8 days later with a dosage of 35 m³ / acre, and the total irrigation amount is 80 m³ / acre.

[0100] (3) Reconstruction of plough layer structure:

[0101] Prepare plough layer improvement materials: 80 parts by weight of modified organic fertilizer matrix (45% livestock manure compost, 25% straw biochar, 30% plant residue compost, fermented for 35 days, organic matter content 48%), 12 parts by weight of ferrous sulfate complex (ferrous sulfate heptahydrate and amino acid are compounded in a mass ratio of 3:1, reacted at 50 °C for 3 hours), 7 parts by weight of calcium magnesium phosphate mineral complex, 5 parts by weight of saline-alkali soil microbial inoculant (mass ratio 1:1:1:1, each strain concentration is 2.5×10 9 CFU / g), 2 parts by weight of bio-enzymatic activator (mass ratio 1:1:1:1, each enzyme activity is the average specified value). Evenly spread it on the soil surface with a dosage of 1.7 tons / acre, rototill to a depth of 20 cm, level it and let it stand for 5 days, and lightly irrigate 18 m³ / acre to activate microorganisms.

[0102] Test results after 120 days of treatment: The soil EC decreased to 1.8 dS / m (a 73.5% reduction), the ESP decreased to 7.2% (a 67.3% reduction), the pH value decreased from 9.8 to 7.9, the organic matter content increased from 0.6% to 1.4% (a 133.3% increase), the proportion of aggregate structure (>0.25 mm) increased from 15% to 40% (a 166.7% increase), and the corn yield increased by 45%.

[0103] Example 3: Treatment plan for severely saline-alkali land

[0104] This example treats severely saline-alkali land (EC = 10.5 dS / m, ESP = 30%).

[0105] (1) Preliminary leaching treatment:

[0106] Conventional water is used for preliminary leaching, with a dosage of 55 m³ / mu, leaching twice at an interval of 10 days, and a total leaching volume of 110 m³ / mu.

[0107] (2) Construction of clay retention layer:

[0108] Mix 30 parts by weight of modified zeolite powder (the dosage of quaternary ammonium salt is 10% of the weight of zeolite, reacting at 70 °C for 4 hours), 40 parts by weight of nano biochar (prepared by pyrolyzing rice husk at 450 °C for 4 hours and ball-milling to a particle size of 80 nm), 20 parts by weight of attapulgite clay, 25 parts by weight of microbial immobilizer (sodium alginate and chitosan are mixed in a mass ratio of 1:1), and 15 parts by weight of slow-release calcium source (calcium lactate pentahydrate), add an appropriate amount of water to adjust the water content to 40%, stir evenly, and pre-cure for 24 hours. Construct a 5-cm-thick retention layer at 30 cm below the ground surface and compact it to a bulk density of 1.4 g / cm 3 , spray the activated solution of Pseudomonas halophila (concentration 1×10 8 CFU / mL), with a dosage of 100 mL / m 2 .

[0109] (3) Modified water irrigation:

[0110] Prepare modified water: 80 parts by weight of electrolyzed activated water (0.3% sodium chloride solution, current 15 A, voltage 24 V, treated for 30 minutes, pH = 5.8, redox potential +700 mV), 0.15 parts by weight of citric acid, 0.25 parts by weight of biosurfactant complex (rhamnolipid and lipopeptide are mixed in a mass ratio of 1:1), 0.2 parts by weight of sodium humate, and stir evenly. The dosage of the first irrigation is 50 m³ / mu, the second irrigation is carried out 10 days later with a dosage of 40 m³ / mu, and the total irrigation volume is 90 m³ / mu.

[0111] (4) Reconstruction of plough layer structure:

[0112] Preparation of plough layer improvement materials: 70 parts by weight of modified organic fertilizer matrix (50% livestock manure compost, 20% straw biochar, 30% plant residue compost, fermented for 45 days, organic matter content 50%), 15 parts by weight of ferrous sulfate complex (compounded from ferrous sulfate heptahydrate and amino acids at a mass ratio of 2:1, reacted at 50°C for 3.5 hours), 10 parts by weight of calcium magnesium phosphate mineral complex, 8 parts by weight of saline-alkali soil microbial inoculant (mass ratio 1:1:1:1, each strain concentration 3×109 CFU / g), 3 parts by weight of bio-enzymatic activator (mass ratio 1:1:1:1, each enzyme activity at the highest specified value). Uniformly spread on the soil surface, with a dosage of 2.0 tons per mu, rotary tillage depth of 22 cm, leveled and left standing for 5 days, shallow irrigation of 20 cubic meters per mu to activate microorganisms.

[0113] Test results after 150 days of treatment: Soil EC decreased to 2.1 dS / m (80% reduction), ESP decreased to 9.0% (70% reduction), pH value decreased from 10.2 to 8.0, organic matter content increased from 0.5% to 1.2% (140% increase), the proportion of aggregate structure (>0.25 mm) increased from 12% to 35% (191.7% increase), and rice yield increased by 40%.

[0114] Example 4: Optimization experiment on the proportion of clay retention layer materials

[0115] This example explores the influence of different proportions of clay retention layer materials on the retention effect.

[0116] Formula A: 15 parts by weight of modified zeolite powder, 30 parts by weight of nano-biochar, 10 parts by weight of attapulgite clay, 10 parts by weight of microbial fixative, 8 parts by weight of slow-release calcium source

[0117] Formula B: 25 parts by weight of modified zeolite powder, 20 parts by weight of nano-biochar, 15 parts by weight of attapulgite clay, 20 parts by weight of microbial fixative, 12 parts by weight of slow-release calcium source

[0118] An experiment was carried out using moderately saline-alkali soil (EC = 7.2 dS / m, ESP = 23%), with other conditions the same as in Example 2. The experimental results showed that the clay interception rate of Formula B reached 92%, significantly higher than 85% of Formula A, indicating that increasing the proportion of modified zeolite powder and microbial fixative can improve the interception efficiency of the retention layer for clay. At the same time, the stability of Formula B is also better. In the simulated rainfall erosion experiment, the structural integrity retention rate of Formula B was 96%, while that of Formula A was 90%.

[0119] Example 5: Optimization experiment on the proportion of modified water components

[0120] This example explores the influence of different proportions of modified water components on the salt reduction and deflocculation effects.

[0121] Formula C: 90 parts by weight of electrolytically activated water, 0.08 parts by weight of citric acid, 0.12 parts by weight of biosurfactant complex, 0.08 parts by weight of sodium humate

[0122] Formula D: 85 parts by weight of electrolytically activated water, 0.12 parts by weight of citric acid, 0.20 parts by weight of biosurfactant complex, 0.15 parts by weight of sodium humate

[0123] Experiments were carried out using moderately saline-alkali soil (EC = 7.0 dS / m, ESP = 21%). Other conditions were the same as in Example 2. The experimental results showed that the salt dissolution rate of Formula D reached 75%, significantly higher than 65% of Formula C; the clay dispersion degree reached 80%, higher than 70% of Formula C. This indicates that increasing the proportions of citric acid, biosurfactant, and sodium humate can significantly improve the salt reduction and flocculation-deflocculation effects of the modified water.

[0124] Example 6: Optimization experiment on the component ratio of the plough layer improvement material

[0125] This example explores the influence of different proportions of plough layer improvement materials on the effect of soil structure reconstruction.

[0126] Formula E: 80 parts by weight of modified organic fertilizer matrix, 10 parts by weight of ferrous sulfate complex, 6 parts by weight of calcium magnesium phosphate mineral complex, 4 parts by weight of saline-alkali soil microbial agent, 2 parts by weight of bio-enzymatic activator

[0127] Formula F: 75 parts by weight of modified organic fertilizer matrix, 13 parts by weight of ferrous sulfate complex, 8 parts by weight of calcium magnesium phosphate mineral complex, 6 parts by weight of saline-alkali soil microbial agent, 2.5 parts by weight of bio-enzymatic activator

[0128] Experiments were carried out using moderately saline-alkali soil (EC = 6.9 dS / m, ESP = 22%). Other conditions were the same as in Example 2. The experimental results showed that after 60 days of treatment with Formula F, the proportion of soil aggregate structure (>0.25 mm) reached 35%, significantly higher than 28% of Formula E; the soil microbial biomass carbon reached 250 mg / kg, higher than 180 mg / kg of Formula E; the soil enzyme activity index (comprehensively evaluating the activities of urease, β-glucosidase, and alkaline phosphatase) reached 3.8, higher than 2.9 of Formula E. This indicates that increasing the proportions of ferrous sulfate complex, calcium magnesium phosphate mineral complex, and microbial agent can significantly improve the effect of soil structure reconstruction.

[0129] Comparative Example 1: Experiment without clay retention layer

[0130] In this comparative example, the construction step of the clay retention layer was omitted, and only modified water irrigation and plough layer improvement were carried out. Other conditions were the same as in Example 2.

[0131] The results showed that after 120 days of treatment, the soil EC decreased to 3.2 dS / m (a 52.9% decrease, 20.6 percentage points lower than that of Example 2), the ESP decreased to 12.8% (a 41.8% decrease, 25.5 percentage points lower than that of Example 2), and the pH value decreased from 9.8 to 8.5 (0.6 units higher than that of Example 2). More importantly, the clay content in the topsoil (0 - 20 cm) only decreased by 12%, far lower than 45% of Example 2, resulting in the soil bulk density still remaining at 1.55 g / cm 3 at a high level, and the soil structure was significantly worse than that of Example 2. In addition, since the clay was not effectively fixed, after 3 heavy rainfalls, the soil EC and ESP began to rise, indicating that the improvement effect was unstable and lacked persistence.

[0132] Comparative Example 2: Conventional water irrigation experiment

[0133] In this comparative example, conventional water was used instead of modified water for irrigation, and the irrigation amount was the same as that of Example 2, with other conditions unchanged.

[0134] The results showed that after 120 days of treatment, the soil EC decreased to 4.1 dS / m (a 39.7% decrease, 33.8 percentage points lower than that of Example 2), the ESP decreased to 14.5% (a 34.1% decrease, 33.2 percentage points lower than that of Example 2), and the pH value decreased from 9.8 to 8.8 (0.9 units higher than that of Example 2). Due to the lack of the multiple action mechanisms of modified water, the efficiency of salt dissolution and migration was low, and the effect of clay dispersion was poor, resulting in an obvious insufficient improvement effect. At the same time, conventional water irrigation required more times (4 - 5 times) to achieve a similar salt reduction effect, with low water resource utilization efficiency.

[0135] Comparative Example 3: Experiment without biological components

[0136] In this comparative example, all biological components in the technical solution were removed, including the microbial fixative, saline-alkali soil microbial inoculum, and bio-enzymatic activator, with other conditions the same as those of Example 2.

[0137] The results showed that after 120 days of treatment, the soil EC decreased to 2.5 dS / m (a 63.2% decrease, 10.3 percentage points lower than that in Example 2), the ESP decreased to 9.8% (a 55.5% decrease, 11.8 percentage points lower than that in Example 2), and the pH value decreased from 9.8 to 8.2 (0.3 units higher than that in Example 2). Although the physical-chemical treatment could still achieve a certain effect of salt reduction and soil improvement, the soil biological activity indicators were significantly insufficient. The soil respiration intensity was only 40% of that in Example 2, the microbial diversity index (Shannon index) was only 55% of that in Example 2, and the overall level of soil enzyme activity was only 45% of that in Example 2. Long-term monitoring showed that due to the lack of an active microbial community to maintain the soil ecosystem function, the durability of the improvement effect was poor, and soil structure degradation began to occur 180 days after the treatment.

[0138] III. Test data analysis

[0139] Based on the test data of the above examples and comparative examples, a comprehensive analysis is as follows:

[0140] Table 1: Improvement effects of different treatment methods on the main indicators of saline-alkali soil (after 120 days of treatment)

[0141]

[0142] Table 2: Effects of different treatment methods on soil biological activity indicators (after 120 days of treatment)

[0143]

[0144] Table 3: Effects of different treatment methods on crop yields (compared with before treatment)

[0145]

[0146] The following conclusions can be drawn from the test data:

[0147] 1. The comprehensive effect of the three-step collaborative treatment is significant: The three-step collaborative treatment method of clay fixation layer construction, modified water irrigation, and tillage layer structure reconstruction adopted in Examples 1-3 is significantly superior to the simplified treatment methods of Comparative Examples 1-3 in various saline-alkali soil improvement indicators. Especially for the severely saline-alkali land (Example 3), the improvement effect is the most obvious, with an EC reduction rate of 80% and an ESP reduction rate of 70%, indicating that the present invention has better applicability to severely saline-alkali soils.

[0148] 2. The key role of the clay fixation layer: Compared with Example 2, all indicators in Comparative Example 1 (without a clay fixation layer) decreased significantly. Especially, the reduction effect of the clay content in the surface soil was poor, the soil structure improvement was not significant, and the durability of the improvement effect was poor. This fully proves the key role of the clay fixation layer in fixing the downward-moving clay and preventing salt back-migration.

[0149] 3. Special effects of the modified water: Compared with Example 2, Comparative Example 2 (irrigation with conventional water) has a lower salt reduction efficiency and a poor water resource utilization efficiency. Through its unique physical-chemical properties, the modified water significantly improves the salt dissolution and migration efficiency, and at the same time promotes the dispersion and downward movement of clay particles, which is an important part of the entire technical solution.

[0150] 4. Synergistic effect of biological components: Compared with Example 2, Comparative Example 3 (without biological components) can still achieve certain effects in the short term by physical-chemical treatment, but the soil biological activity index is significantly insufficient and the long-term improvement effect has poor persistence. This indicates that the microbial and enzyme systems play an irreplaceable role in maintaining soil ecological functions, promoting nutrient cycling, and improving the persistence of the improvement effect.

[0151] 5. Necessity of graded treatment for saline-alkali degree: Examples 1-3 adopt differential treatment schemes for saline-alkali lands with different degrees, and the dosages of each component and treatment parameters increase with the increase of the saline-alkali degree, achieving good results, which proves the necessity and rationality of graded treatment.

[0152] 6. Significant increase in crop yield: After the treatments in Examples 1-3, the yields of various crops increase by 30% - 55%, which is significantly higher than 15% - 35% of the comparative examples, fully proving the significant effect of the present invention in improving the agricultural production capacity of saline-alkali lands.

[0153] In summary, the method for reducing salt, improving soil compaction and enhancing quality of saline-alkali lands provided by the present invention forms an overall solution with multiple physical-chemical-biological mechanisms through the synergistic effects of constructing a clay retention layer, irrigating with modified water, and reconstructing the plow layer structure, achieving the synchronous solution of saline-alkali and soil compaction problems, having significant improvement effects and persistence, and providing a new technical approach for the comprehensive management and efficient utilization of saline-alkali lands.

[0154] The method for reducing salt, improving soil compaction and enhancing quality of saline-alkali lands of the present invention has the following industrial application advantages:

[0155] 1. Wide application scope: Through the graded implementation scheme, this method is applicable to the comprehensive management of lightly, moderately and severely saline-alkali lands, adapts to different soil conditions and regional characteristics, and has a wide application range.

[0156] 2. Convenient access to materials: The main raw materials used in this method can be industrially produced or obtained from the market, such as zeolite, biochar, attapulgite clay, ferrous sulfate, etc., ensuring the feasibility and promotion of the method.

[0157] 3. Simple operation and implementation: The implementation steps of this method are clear, and the technical key points are distinct. It can be implemented by ordinary agricultural technicians under guidance, without the need for complex professional skills and equipment.

[0158] 4. Significant economic benefits: Although the initial investment is slightly higher than the conventional method, due to the long-lasting improvement effect and significant increase in crop yield, the long-term economic benefits far exceed the traditional method. Preliminary calculations show that the input-output ratio of this method can reach more than 1:3.5, and the investment recovery period is 1-2 years.

[0159] 5. Environmentally friendly: This method uses a variety of environmentally friendly materials and biological agents, avoiding the potential harm of traditional chemical modifiers to the environment, and meeting the requirements of sustainable development and ecological civilization construction.

[0160] 6. Great potential for popularization and application: Considering that there are more than 100 million mu of saline-alkali land resources in China, this method has broad application prospects in severely saline-alkali areas such as the Yellow River Delta, Songnen Plain, and Xinjiang inland basin, and can make important contributions to national food security and the improvement of cultivated land quality.

[0161] In addition, the method of the present invention can be combined with other saline-alkali land utilization technologies such as the cultivation of salt-tolerant crops and the development of halophytes to form a more perfect comprehensive utilization system for saline-alkali land, further improving the comprehensive utilization efficiency and economic value of saline-alkali land resources.

Claims

1. A method for reducing salt and improving the quality of saline-alkali land, characterized in that: The following steps are involved: a) constructing a clay-retaining layer 30-40 cm below the ground surface, wherein the clay-retaining layer is composed of modified zeolite powder, nano-biochar, attapulgite clay, microbial fixative and slow-release calcium source, and the filling and compaction thickness is 3-5 cm; b) using modified water for irrigation to reduce the content of surface salt and clay, wherein the modified water is citric acid, biosurfactant complex, electrolytic activated water and sodium humate added to the irrigation water, the irrigation amount is 60-100 cubic meters per mu, and the irrigation is repeated twice; c) Evenly spread tillage layer improvement materials on the ground surface to rebuild the tillage layer structure. The tillage layer improvement materials include modified organic fertilizer matrix, ferrous sulfate complex, calcium magnesium phosphate mineral complex, saline-alkali soil microbial agent and biological enzyme activator. The dosage is 1.5-2 tons / mu, and the tillage is uniform to a depth of 18-22cm.

2. The method for reducing salt in saline-alkali land and improving its quality according to claim 1, characterized in that: In the clay particle holding layer, the modified zeolite powder is 10-30 parts by weight, the nano biochar is 15-40 parts by weight, the attapulgite clay is 5-20 parts by weight, the microbial fixative is 5-25 parts by weight, and the slow-release calcium source is 5-15 parts by weight.

3. The method for reducing salt in saline-alkali land and improving its quality according to claim 1, characterized in that: The modified zeolite powder is prepared by modifying sodium clinoptilolite with a quaternary ammonium surfactant, the nano biochar is prepared by pyrolysis of rice husk at 350-450°C for 2-4 hours, the microbial fixative is a sodium alginate-chitosan complex, and the slow-release calcium source is calcium lactate pentahydrate.

4. The method for reducing salt in saline-alkali land and improving its quality according to claim 1, characterized in that: In the modified water, the citric acid is 0.05-0.15 parts by weight, the biosurfactant complex is 0.1-0.25 parts by weight, the electrolytic activated water is 80-95 parts by weight, and the sodium humate is 0.05-0.2 parts by weight.

5. The method for reducing salt in saline-alkali land and improving its quality according to claim 4, characterized in that: The biosurfactant complex comprises rhamnolipid and lipopeptide, and the electrolytic activated water is prepared by electrolyzing an aqueous solution containing 0.1% to 0.3% sodium chloride, with a pH value of 5.8-6.5 and an oxidation-reduction potential of +500 to +700 mV.

6. The method for reducing salt in saline-alkali land and improving its quality according to claim 1, characterized in that: In the tillage layer improvement material, the modified organic fertilizer matrix is ​​70-85 parts by weight, the ferrous sulfate complex is 8-15 parts by weight, the calcium magnesium phosphate mineral complex is 5-10 parts by weight, the saline-alkali soil microbial agent is 3-8 parts by weight, and the biological enzyme activator is 1-3 parts by weight.

7. The method for reducing salt in saline-alkali land and improving its quality according to claim 6, characterized in that: The modified organic fertilizer matrix comprises 40% to 50% of livestock and poultry manure compost, 20% to 30% of straw biochar and 20% to 30% of plant residue compost; the ferrous sulfate complex is a complex of ferrous sulfate heptahydrate and amino acids; the saline-alkali soil microbial agent comprises salt-alkali tolerant rhizobia, halophilic bacillus, Pseudomonas secreting extracellular polysaccharides and salt-tolerant micrococcus producing ACC deaminase; and the biological enzyme activator comprises beta-glucosidase, urease, alkaline phosphatase and sucrase.

8. The method for reducing salt in saline-alkali land and improving its quality according to claim 1, characterized in that: After the clay holding layer is constructed, an activation solution containing highly efficient microbial strains for saline-alkali environments is sprayed at a dosage of 50-100 mL / m 2 The microbial strain is salt-tolerant Pseudomonas, with a concentration of 1×10 8 CFU / mL.

9. The method for reducing salt in saline-alkali land and improving its quality according to claim 1, characterized in that: The interval between the two modified water irrigations is 7-10 days, and the irrigation timing is controlled by monitoring the soil moisture content through a soil moisture sensor. The first irrigation amount is 40-50 cubic meters per mu, and the second irrigation amount is 30-40 cubic meters per mu.

10. The method for reducing salt in saline-alkali land and improving its quality according to claim 1, characterized in that: A graded implementation plan is adopted according to the degree of salinization: for slightly saline-alkali land (EC<4dS / m, ESP<15%), the thickness of the clay retaining layer is 3cm, the total amount of modified water irrigation is 60-70 cubic meters / mu, and the amount of tillage layer improvement materials is 1.5 tons / mu; for moderately saline-alkali land (EC is 4-8dS / m, ESP is 15%-25%), the thickness of the clay retaining layer is 4cm, the total amount of modified water irrigation is 80-90 cubic meters / mu, and the amount of tillage layer improvement materials is 1.7 tons / mu; for severely saline-alkali land (EC>8dS / m, ESP>25%), the thickness of the clay retaining layer is 5cm, the total amount of modified water irrigation is 90-100 cubic meters / mu, and the amount of tillage layer improvement materials is 2.0 tons / mu, and 1-2 times of conventional water leaching in the early stage are added, each time 50-60 cubic meters / mu.

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