Method for improving water retention capacity and greening level of sandy land

Abstract

The present application belongs to the technical field of soil improvement, and particularly relates to a method for improving water retention capacity and greening level of sandy land, which comprises paper paving, primary backfilling, secondary backfilling, injection of bacterial agent, tertiary backfilling and quaternary backfilling. The present application sets up different 5-layer structures, and simultaneously realizes good water retention and ecological benefits through cooperation and synergistic effect among the layers. By introducing Bacillus mucilaginosus, the effectiveness of phosphorus and potassium elements in the sandy land soil is improved on the basis of the cooperation between Bacillus mucilaginosus and Bacillus pasteurii. Meanwhile, the introduction of biochar as a carrier helps to further improve the survival rate and activity of the bacterial agent and improve the application effect. The preparation of biochar innovatively uses the method of sand bath heating, and the sand soil is reused as sand bath material, which has good reusability and is also conducive to cost reduction. The present application organically combines the functions of water retention, sand fixation and growth promotion, and is helpful to realize the overall restoration and improvement of the sandy land ecology.

Description

Technical Field

[0001] This invention belongs to the field of soil improvement technology, specifically relating to a method for improving the water retention capacity and greening level of sandy land. Background Technology

[0002] With global climate change and the continuous expansion of human activities, desertification has become an increasingly serious environmental problem. Desertified land not only loses its original soil fertility and water retention capacity, but also leads to vegetation degradation and biodiversity loss, further exacerbating the vulnerability of the ecosystem. Against this backdrop, how to effectively improve the ecological environment of desertified land, promote vegetation restoration, and stabilize the soil has become an urgent problem to be solved. The management of desertified land is a complex and arduous task. Due to the special properties of sandy soil, its water retention capacity is extremely poor, making it difficult to effectively retain water in the soil, thus hindering vegetation growth. At the same time, the loose structure of sandy soil also makes sowing grass seeds exceptionally difficult, often resulting in poor rooting and extremely low survival rates. Therefore, developing a technology that can achieve water retention and efficient sowing on desertified land is of vital importance for improving the ecological environment of desertified land.

[0003] Currently, some preliminary explorations and practices have been conducted regarding the management of desertified land. For example, Chinese patent CN102535426A discloses a three-dimensional plastic mulch technology for water retention, seepage prevention, and evaporation prevention in desert management. This technology is a three-dimensional plastic mulch technology for large-scale mechanized and manual desert management. Its technical principle is as follows: Plastic is used to create a grid strip approximately 4.5 meters wide and 45 meters long. The grid is composed of thin, flexible, and interconnected individual units, completely closed except for the top opening, formed by regular triangular prisms with sides of 30cm and a height of 40cm. Two sides of the plastic mulch are made into adhesive, raised, thin sheets (flat), while the other two sides have recessed pits at the bottom of the grid, approximately 50cm wide. Several water-passing holes are left at 2 / 3 or 1 / 2 of the height of the mulch grid. The top opening of the mulch has longitudinal and transverse ribs; the transverse ribs are approximately 1cm high and 3mm thick, while the longitudinal ribs are integrated with the transverse ribs and extend 2cm higher than the transverse ribs, forming a T-shape. The top is arranged with longitudinal and transverse reinforcing bars connected to the main reinforcing bars, and plastic film with openings on both sides of the reinforcing bars. Although this method solves the most difficult water retention problem for vegetation survival in desertification control, the plastic applied to the soil is difficult to degrade and may cause subsequent soil pollution problems. At the same time, the mulch film may affect the local water cycle, which has a negative effect on subsequent plant growth and microhabitat modification.

[0004] For example, Chinese patent CN 106069271A discloses a method for desert greening, including the following steps:

[0005] Step 1: Dig a filling trench and lay a water-blocking and seepage-proof layer on the surface of the trench; Step 2: Lay a sand layer on the water-blocking and seepage-proof layer, and then lay a plant growth layer on the sand layer; Step 3: Lay a grass mesh on the plant growth layer, connect the grass mat on the winch to the hook of the mountain bike, start the mountain bike and move forward at a constant speed until all the grass mats on the winch are laid; Step 4: Sow plant seeds in the grass mesh and then spray water. Although the method of this invention for greening deserts can green deserts with suitable conditions, has a wide range of applications, facilitates standardized construction, increases desert vegetation coverage, and can improve the local ecological environment of deserts, grass seeds directly sown on sandy land still face a relatively harsh survival environment and may have a low subsequent survival rate; at the same time, only laying a water-blocking layer means that the grass seeds lack the nutrient and water retention environment to grow on sandy land, which is not conducive to the subsequent growth of grass seeds.

[0006] It is evident that existing technologies suffer from several drawbacks: the materials used have poor biodegradability, which is detrimental to environmental protection; they fail to balance soil moisture retention and nutrient supply; their water retention efficiency is low; and their support for subsequent growth of sandy vegetation is weak. In other words, while current sand-fixing technologies such as MIP have developed rapidly, they have only addressed the problem of sand consolidation, without solving the problem of low element availability in the soil and weak support for sandy vegetation. Summary of the Invention

[0007] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a method for improving the water retention capacity and greening level of sandy land. This objective is achieved through the following technical solution: A method for improving the water retention capacity and greening level of sandy land, comprising the following steps:

[0008] S1. Laying paper: Dig a trench to a depth of 630-680mm on the surface of the target sandy land, and lay a layer of kraft paper after leveling the bottom of the trench.

[0009] S2. First backfill: Take a portion of the excavated sand and mix it evenly with sodium polyacrylate, then fill it into the groove lined with kraft paper to a depth of 130-150mm;

[0010] S3. Secondary backfilling: Take another portion of excavated sand and mix it with the external soil in a 1:1 weight ratio. Then add super absorbent resin, mix evenly, fill the groove and make holes. The filling depth is 180-220mm.

[0011] S4. Injection of bacterial agent: Mix Bacillus pasteurellium bacterial solution with urea to form mixture 1. After mixing mixture 1 evenly, inject it into the hole and cure for ≥144h; then mix biochar with Bacillus mucilaginosus bacterial solution to form mixture 2 and inject it into the hole;

[0012] S5. Third backfilling: Take another portion of the excavated sand and mix it with the external soil in a 1:1 weight ratio. Continue to fill the groove to a depth of 140-160mm. After leveling the top, sprinkle grass seeds and water until the surface is moist.

[0013] S6. Fourth backfilling: Finally, take some of the excavated sand and fill it into the groove sprinkled with grass seeds. After filling the groove, spray it with lignin sulfonate solution.

[0014] As a preferred technical solution, the amount of sodium polyacrylate added in step S2 is 3 to 4% of the mass of the sand.

[0015] As a preferred technical solution, the number of holes drilled in step S3 is 18-22 holes / m. 2 The amount of superabsorbent polymer added is 2-4% of the total mass of sand and foreign soil.

[0016] As a preferred technical solution, the superabsorbent resin in step S3 is prepared by the following method: 40 ml of 0.067 mol / L sodium hydroxide solution and 1.2 g of guar gum are mixed and stirred evenly, then heated to 60-80℃ and reacted at a constant temperature for 50-70 min. Then, 4 ml of aqueous solution containing 0.1008 g of APS (ammonium sulfate) is added dropwise and reacted for 15-25 min. The reactant is cooled to 45-55℃, and a solution containing 7.2 g of acrylic acid, 0.0216 g of N,N'-methylenebisacrylamide, and 8.5 ml of 8 mol / L sodium hydroxide solution is added dropwise. After the addition is completed, the temperature is slowly raised to 65-75℃ and reacted at a constant temperature for 2.5-3.5 h. The entire reaction is carried out under a nitrogen atmosphere. After the reaction is completed, the resin is dried at 65-75℃ to constant weight and then pulverized to a size of 50 mesh.

[0017] As a preferred technical solution, the concentration of Bacillus pasteurellii in the mixture 1 in step S4 is 0.8–1.2 × 10⁻⁶. 8 The concentration of urea is 10–20 g / L, and the injection volume of mixture 1 is 80–120 ml / well.

[0018] As a preferred technical solution, in step S4, the concentration of biochar in the mixture 2 is 45–55 g / L, and the concentration of Bacillus mucilaginosus is 0.8–1.2 × 10⁻⁶ g / L. 5 The volume of mixed solution 2 is 140–160 ml / well, with a cell / L ratio.

[0019] As a preferred technical solution, the biochar in step S4 is prepared by the following method: Pine wood chips and straw are mixed evenly at a mass ratio of 1.5–2.5:1, washed, dried, and passed through an 80-mesh sieve. The mixture is then heated in a sand bath at 450–550°C under vacuum for 1.3–1.8 hours. The resulting product is primary biochar. The primary biochar is then soaked in a 1.5–2.5 mol / L citric acid solution for 45–50 hours, rinsed thoroughly with ultrapure water, and then soaked in a 0.4–0.6 mol / L calcium fluoride solution for 10–14 hours. After rinsing thoroughly with ultrapure water and drying, the biochar is obtained. The straw is preferably a mixture of corn straw and rice straw, with a mass ratio of corn straw to rice straw of 2:1.

[0020] Furthermore, the heating material for the sand bath is prepared by the following method: sand with a particle size of 1-3 mm is mixed evenly with graphene at a mass ratio of 45-55:1. The sand is preferably sourced locally from sandy areas.

[0021] As a preferred technical solution, the grass species mentioned in step S5 are sea buckthorn, caragana, sand fern, ice grass and red bean grass.

[0022] As a preferred technical solution, the concentration of the lignin sulfonate solution in step S6 is 25-35 wt%, and the spraying rate is 3-4 L / m³. 2 .

[0023] In this invention:

[0024] (1) Through the cooperation and synergistic effect between different layers, a good water retention function and ecological benefits can be achieved at the same time.

[0025] (2) By combining the application of external soil and water-retaining agents, the growth of grass seeds can be supported by both nutrition and water.

[0026] (3) Based on the existing urea + Bacillus pasteurization technology for achieving MIP sand fixation, Bacillus mucilaginosus is added. On the one hand, the calcium carbonate crystals produced by MIP during sand fixation can provide better attachment conditions for Bacillus mucilaginosus, enabling the growth of the bacteria; on the other hand, the addition of Bacillus mucilaginosus helps to improve the availability of phosphorus and potassium elements in the soil, and helps Bacillus pasteurization and the above-ground plants to absorb and utilize them, thus forming a positive cycle.

[0027] (4) While ensuring basic water retention and nutrient supply, the system can improve water retention capacity in the early stage of application by laying thick kraft paper in the lower layer. In the later stage of plant growth, it reduces the obstruction to the root system and reduces the amount of subsequent construction.

[0028] (5) Mixing sandy soil with imported soil helps improve the physical and chemical properties of the original soil to a certain extent, while also preventing the rapid diffusion of soil moisture to the surrounding sandy soil due to significant differences in properties. Combining sodium polyacrylate with the above-mentioned mixed soil helps to further improve the water retention capacity of the mixed soil. The mixing effect of urea and Bacillus pasteurellii helps to increase the nitrogen content of the soil, and calcium carbonate crystals can be produced during the hydrolysis of urea by Bacillus pasteurellii, which plays a role in further consolidating the soil. Bacillus mucilaginosus helps to promote plant growth and development, and has a positive effect on improving the availability of phosphorus and potassium in the soil. At the same time, the calcium carbonate crystals produced by the hydrolysis of urea by Bacillus pasteurellii also help to provide a high-quality habitat for Bacillus mucilaginosus, helping its growth. Through attachment to calcium carbonate crystals and the water supply from sodium polyacrylate, Bacillus mucilaginosus can continuously grow and develop in the mixed soil, promoting the improvement of phosphorus and potassium availability in the soil. Therefore, the three major plant growth elements in this layer, namely nitrogen, phosphorus, and potassium, have high availability and have a good promoting effect on plant growth.

[0029] (6) The superabsorbent resin used has good water absorption and retention properties, and the material cost is low, which helps to reduce application costs and expand the scope of application; at the same time, it is environmentally friendly and will not cause secondary pollution.

[0030] (7) The biochar formulation used incorporates more woody materials, resulting in a higher carbon content compared to commercially available single-component biochar, thus providing better nutritional conditions for the microorganisms it supports. Furthermore, the use of a higher-temperature carbonization method helps to increase the surface area, stability, and pore size of the biochar, making it more suitable for the survival and efficacy of Bacillus mucilage. The citric acid and calcium fluoride soaking process during biochar preparation further enhances the specific surface area and pore volume of the finished biochar product.

[0031] (8) The biochar carbonization process innovatively utilizes a sand bath heating method, where the sand bath material is sourced directly from the sandy land, facilitating the reuse of sandy land resources. Compared to traditional muffle furnace carbonization, sand bath heating significantly improves heating uniformity and maintains the temperature for a longer period, allowing the heat source to be removed at the end of the reaction and the residual heat to continue the carbonization process, thus saving energy and reducing costs. Furthermore, the stability of sand bath heating helps create uniform pores conducive to the growth of beneficial microorganisms during the subsequent etching process, and also facilitates the full release of nutrients from the biochar, promoting the restoration of sandy land nutrients and the effective utilization of microbial agents.

[0032] This invention offers the following advantages: It discloses a method for enhancing the water retention capacity and greening level of sandy land. By employing a five-layer structure with different layers, the method achieves both effective water retention and ecological benefits through the synergistic effect of these layers. The invention introduces *Bacillus mucilaginosus*, enhancing the availability of phosphorus and potassium in sandy soil through synergistic effects with *Bacillus pasteurellii*. Furthermore, the use of biochar as a carrier during construction further improves the survival rate and activity of the microbial agent, enhancing its application effect. The innovative use of sand bath heating in biochar preparation facilitates the reuse of sand in sand bath materials, which possess excellent reusability, improving the usability of sandy soil and reducing material costs. This invention organically combines water retention, sand fixation, and vegetation promotion, contributing to the overall restoration and improvement of sandy land ecosystems. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of the structure of the target sandy land after improvement using the method of the present invention. In the diagram, 1 is sand layer + lignin sulfonate, 2 is foreign soil + grass seed, 3 is sand + foreign soil + superabsorbent resin + urea + biochar + Bacillus pasteurellii + Bacillus mucilaginosus, 4 is sand + sodium polyacrylate, and 5 is kraft paper. Detailed Implementation

[0034] The present invention will be further described below with reference to the accompanying drawings and embodiments. The scope of protection of the present invention is not limited to the following: Embodiment 1: A method for improving the water retention capacity and greening level of sandy land, comprising the following steps:

[0035] S1. Laying paper: Dig a trench to a depth of 630mm on the surface of the target sandy land, and lay a layer of kraft paper after leveling the bottom of the trench;

[0036] S2. First backfill: Take a portion of the excavated sand and mix it evenly with sodium polyacrylate and fill it into the groove lined with kraft paper. The amount of sodium polyacrylate added is 3% of the mass of the sand and the filling depth is 130mm.

[0037] S3. Secondary backfilling: Take another portion of excavated sand and mix it with the external soil at a weight ratio of 1:1. Then add superabsorbent resin, mix evenly, fill the grooves, and drill holes; wherein, the filling depth is 180mm, and the number of holes is 18 holes / m. 2 The amount of superabsorbent polymer added is 2% of the total mass of sand and foreign soil.

[0038] The superabsorbent resin was prepared by the following method: 40 ml of 0.067 mol / L sodium hydroxide solution and 1.2 g of guar gum were mixed and stirred evenly, and then heated to 60 °C and reacted at a constant temperature for 50 min. Then, 4 ml of aqueous solution containing 0.1008 g of APS was added dropwise and reacted for 15 min. The reactant was cooled to 45 °C, and 7.2 g of acrylic acid, 0.0216 g of N,N'-methylenebisacrylamide and 8.5 ml of 8 mol / L sodium hydroxide solution were added dropwise. After the addition was completed, the temperature was slowly raised to 65 °C and reacted at a constant temperature for 2.5 h. The entire reaction was carried out under a nitrogen atmosphere. After the reaction was completed, the resin was dried at 65 °C to constant weight and then pulverized to a size of 50 mesh.

[0039] S4. Injection of bacterial agent: Mix Bacillus pasteurellium bacterial solution with urea to form mixture 1. After mixing mixture 1 evenly, inject it into the well and cure for 144 hours; then mix biochar with Bacillus mucilaginosus bacterial solution to form mixture 2 and inject it into the well; wherein, the concentration of Bacillus pasteurellium in mixture 1 is 0.8 × 10⁻⁶. 8 The concentration of urea was 10 g / L, and the injection volume of mixture 1 was 80 ml / well; the concentration of biochar in mixture 2 was 45 g / L, and the concentration of Bacillus subtilis was 0.8 × 10⁻⁶ cells / L. 5 cells / L, the injection volume of mixture 2 is 140 ml / well;

[0040] The biochar was prepared by the following method: pine wood chips, corn stalks, and rice stalks were mixed evenly in a mass ratio of 1.5:0.6:0.3, washed, dried, and passed through an 80-mesh sieve; sand with a particle size of 1-3 mm was taken locally and mixed evenly with graphene in a mass ratio of 45:1 to prepare a sand bath; the sand bath was heated for 1.3 h under vacuum and 450℃ conditions, and the resulting product was primary biochar. The primary biochar was soaked in a 1.5 mol / L citric acid solution for 45 h, rinsed with ultrapure water, and then soaked in a 0.4 mol / L calcium fluoride solution for 10 h, rinsed with ultrapure water, and dried to obtain biochar.

[0041] S5. Third backfilling: Take another portion of the excavated sand and mix it with the external soil at a weight ratio of 1:1. Continue to fill the groove to a depth of 140mm. After leveling the top, sprinkle grass seeds and water until the surface is moist. The grass seeds are Ganzi sea buckthorn, Caragana korshinskii, Alternanthera philoxeroides, Ice grass and red bean grass.

[0042] S6. Fourth backfilling: Finally, take a portion of the excavated sand and fill it into the trenches sprinkled with grass seeds. After leveling the trenches, spray with a 25wt% lignin sulfonate solution at a rate of 3L / m². 2 ;

[0043] After laying paper, first backfilling, second backfilling, injection of fungicide, third backfilling, and fourth backfilling, the target sandy land was formed as follows: Figure 1 The layered structure shown.

[0044] Example 2: A method for improving the water retention capacity and greening level of sandy land, comprising the following steps:

[0045] S1. Laying paper: Dig a trench to a depth of 680mm on the surface of the target sandy land, and lay a layer of kraft paper after leveling the bottom of the trench;

[0046] S2. One-time backfilling: Take a portion of the excavated sand and mix it evenly with sodium polyacrylate and fill it into the groove lined with kraft paper. The amount of sodium polyacrylate added is 4% of the mass of the sand and the filling depth is 150mm.

[0047] S3. Secondary backfilling: Take another portion of excavated sand and mix it with the external soil at a weight ratio of 1:1. Then add superabsorbent resin, mix evenly, fill the grooves, and drill holes; wherein, the filling depth is 220mm, and the number of holes is 22 holes / m. 2 The amount of superabsorbent polymer added is 4% of the total mass of sand and foreign soil.

[0048] The superabsorbent resin was prepared by the following method: 40 ml of 0.067 mol / L sodium hydroxide solution and 1.2 g of guar gum were mixed and stirred evenly, and then heated to 80 °C and reacted at a constant temperature for 70 min. Then, 4 ml of aqueous solution containing 0.1008 g of APS was added dropwise and reacted for 25 min. The reactant was cooled to 55 °C, and 7.2 g of acrylic acid, 0.0216 g of N,N'-methylenebisacrylamide and 8.5 ml of 8 mol / L sodium hydroxide solution were added dropwise. After the addition was completed, the temperature was slowly raised to 75 °C and reacted at a constant temperature for 3.5 h. The entire reaction was carried out under a nitrogen atmosphere. After the reaction was completed, the resin was dried at 75 °C to constant weight and then pulverized to a size of 50 mesh.

[0049] S4. Injection of bacterial agent: Mix Bacillus pasteurellii bacterial solution with urea to form mixture 1. After mixing mixture 1 evenly, inject it into the well and cure for 145 hours; then mix biochar with Bacillus mucilaginosus bacterial solution to form mixture 2 and inject it into the well; wherein, the concentration of Bacillus pasteurellii in mixture 1 is 1.2 × 10⁻⁶. 8 The concentration of urea was 20 g / L, and the injection volume of mixture 1 was 120 ml / well; the concentration of biochar in mixture 2 was 55 g / L, and the concentration of Bacillus subtilis was 1.2 × 10⁻⁶ cells / L. 5 cells / L, the injection volume of mixture 2 is 160 ml / well;

[0050] The biochar was prepared by the following method: pine wood chips, corn stalks, and rice straw were mixed evenly in a mass ratio of 2.5:0.6:0.3, washed, dried, and passed through an 80-mesh sieve; sand with a particle size of 1-3 mm was taken locally and mixed evenly with graphene in a mass ratio of 55:1 to prepare a sand bath. The sand bath was heated for 1.8 h under vacuum and 550℃ conditions. The product obtained was primary biochar. The primary biochar was soaked in a 2.5 mol / L citric acid solution for 50 h, rinsed with ultrapure water, and then soaked in a 0.6 mol / L calcium fluoride solution for 14 h, rinsed with ultrapure water, and dried to obtain biochar.

[0051] S5. Third backfilling: Take another portion of the excavated sand and mix it with the external soil at a weight ratio of 1:1. Continue to fill the groove to a depth of 160mm. After leveling the top, sprinkle grass seeds and water until the surface is moist. The grass seeds are Ganzi sea buckthorn, Caragana korshinskii, Alternanthera philoxeroides, Ice grass and red bean grass.

[0052] S6. Fourth backfilling: Finally, take a portion of the excavated sand and fill it into the trenches sprinkled with grass seeds. After leveling the trenches, spray with a 25-35 wt% lignin sulfonate solution at a rate of 4 L / m². 2 .

[0053] Example 3: A method for improving the water retention capacity and greening level of sandy land, comprising the following steps:

[0054] S1. Laying paper: Dig a trench to a depth of 650mm on the surface of the target sandy land, and lay a layer of kraft paper after leveling the bottom of the trench;

[0055] S2. First backfill: Take a portion of the excavated sand and mix it evenly with sodium polyacrylate and fill it into the groove lined with kraft paper. The amount of sodium polyacrylate added is 3.5% of the mass of the sand and the filling depth is 140mm.

[0056] S3. Secondary backfilling: Take another portion of excavated sand and mix it with the external soil at a weight ratio of 1:1. Then add superabsorbent resin, mix thoroughly, fill the grooves, and drill holes; wherein, the filling depth is 200mm, and the number of holes is 20 holes / m. 2 The amount of superabsorbent polymer added is 3% of the total mass of sand and foreign soil.

[0057] The superabsorbent resin was prepared by the following method: 40 ml of 0.067 mol / L sodium hydroxide solution and 1.2 g of guar gum were mixed and stirred evenly, and then heated to 70 °C and reacted at a constant temperature for 60 min. Then, 4 ml of aqueous solution containing 0.1008 g of APS was added dropwise and reacted for 20 min. The reactant was cooled to 50 °C, and 7.2 g of acrylic acid, 0.0216 g of N,N'-methylenebisacrylamide and 8.5 ml of 8 mol / L sodium hydroxide solution were added dropwise. After the addition was completed, the temperature was slowly raised to 70 °C and reacted at a constant temperature for 3 h. The entire reaction was carried out under a nitrogen atmosphere. After the reaction was completed, the resin was dried at 70 °C to constant weight and then pulverized to a size of 50 mesh.

[0058] S4. Injection of bacterial agent: Mix Bacillus pasteurellium bacterial solution with urea to form mixture 1. After mixing mixture 1 evenly, inject it into the well and cure for 150 hours; then mix biochar with Bacillus mucilaginosus bacterial solution to form mixture 2 and inject it into the well; wherein, the concentration of Bacillus pasteurellium in mixture 1 is 1×10⁻⁶. 8 The concentration of urea was 16 g / L, and the injection volume of mixture 1 was 100 ml / well; the concentration of biochar in mixture 2 was 50 g / L, and the concentration of Bacillus subtilis was 1 × 10⁻⁶ cells / L. 5 cells / L, the injection volume of mixture 2 is 150 ml / well;

[0059] The biochar was prepared by the following method: pine wood chips, corn stalks, and rice stalks were mixed evenly in a mass ratio of 2:0.6:0.3, washed, dried, and passed through an 80-mesh sieve; sand with a particle size of 1-3 mm was taken locally and mixed evenly with graphene in a mass ratio of 50:1 to prepare a sand bath. The sand bath was heated for 1.5 h under vacuum and 500°C. The product obtained was primary biochar. The primary biochar was soaked in a 2 mol / L citric acid solution for 48 h, rinsed with ultrapure water, soaked in a 0.5 mol / L calcium fluoride solution for 12 h, rinsed with ultrapure water, and dried to obtain biochar.

[0060] S5. Third backfilling: Take another portion of the excavated sand and mix it with the external soil at a weight ratio of 1:1. Continue to fill the groove to a depth of 150mm. After leveling the top, sprinkle grass seeds and water until the surface is moist. The grass seeds are Ganzi sea buckthorn, Caragana korshinskii, Alternanthera philoxeroides, Ice grass and red bean grass.

[0061] S6. Fourth backfilling: Finally, take a portion of the excavated sand and fill it into the trenches sprinkled with grass seeds. After leveling the trenches, spray with a 30wt% lignin sulfonate solution at a rate of 3.5L / m². 2 .

[0062] The following experiments illustrate the beneficial effects of this invention:

[0063] Experimental site: Zhanang County, Shannan City, Tibet Autonomous Region

[0064] Experiment period: June 2023 to present

[0065] Experimental methods: The experimental site was tested using the method described in Example 3. The indicators of sand fixation, water conservation, and vegetation promotion were investigated and measured.

[0066] Experimental results:

[0067] (1) In terms of sand fixation: After improvement, the percentage of clay (<2μm) in the sandy soil increased from 0.60% to 1.85%; the percentage of fine silt (2-10μm) increased from 0.28% to 4.68%; the percentage of silt (10-50μm) increased from 2.27% to 12.20%; the percentage of fine sand (50-250μm) decreased from 76.62% to 64.07%; and the percentage of coarse sand (250-2000μm) decreased from 20.22% to 17.11%. Overall, the particle size composition of the improved sandy soil was improved, and the sandy soil showed a trend of clayification.

[0068] (2) Regarding water retention: The soil moisture at a depth of 10cm decreased from 11.16±4.56 to 7.70±0.27, a decrease of 29.01%; the soil moisture at a depth of 20cm decreased from 13.98±4.98 to 12.68±2.46, a decrease of 9.27%; the soil moisture at a depth of 30cm decreased from 13.92±5.27 to 12.79±2.02, a decrease of 8.12%; and the soil moisture at a depth of 40cm increased from 11.81±3.89 to 12.02±2.44, an increase of 1.76%. In general, the improvement method had a certain inhibitory effect on the increase of soil moisture in all layers of sandy land. The decrease in moisture in the upper layer of sandy land was more significant, while the moisture in the lower layer of sandy land remained stable with a slight increase. This may be closely related to the addition of water-retaining materials. The transfer of water from the soil to the superabsorbent resin in the sand helps to reduce the natural infiltration and loss of water in the sand, and also provides positive water supply conditions for the growth of sand plants.

[0069] (3) In terms of growth promotion: the one-year overall survival rate of grass and shrubs increased from 70.4% to 88.9%.

[0070] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, are covered within the scope of protection of the present invention.

Claims

1. A method for improving the water retention capacity and greening level of sandy land, characterized in that, It includes the following steps: S1. Laying paper: Dig a trench to a depth of 630-680mm on the surface of the target sandy land, and lay a layer of kraft paper after leveling the bottom of the trench; S2. One-time backfilling: Take a portion of the excavated sand and mix it evenly with sodium polyacrylate, then fill it into the groove lined with kraft paper to a depth of 130-150mm; S3. Secondary backfilling: Take another portion of excavated sand and mix it with the external soil in a 1:1 weight ratio. Then add super absorbent resin, mix evenly, fill the groove and make holes. The filling depth is 180-220mm. S4. Injection of bacterial agent: Mix Bacillus pasteurellium bacterial solution with urea to form mixture 1. After mixing mixture 1 evenly, inject it into the hole and cure for ≥144h; then mix biochar with Bacillus mucilaginosus bacterial solution to form mixture 2 and inject it into the hole; S5. Third backfilling: Take another portion of the excavated sand and mix it with the external soil in a 1:1 weight ratio. Continue to fill the groove to a depth of 140-160mm. After leveling the top, sprinkle grass seeds and water until the surface is moist. S6. Four backfilling stages: Finally, take some of the excavated sand and fill it into the grooves sprinkled with grass seeds. After leveling the grooves, spray with lignin sulfonate solution.

2. The method for improving the water retention capacity and greening level of sandy land according to claim 1, characterized in that, The amount of sodium polyacrylate added in step S2 is 3 to 4% of the mass of the sand.

3. The method for improving the water retention capacity and greening level of sandy land according to claim 1, characterized in that, In step S3, the number of holes drilled is 18-22 per meter. 2 The amount of superabsorbent resin added is 2 to 4% of the total mass of sand and foreign soil.

4. A method for improving the water retention capacity and greening level of sandy land according to claim 1, characterized in that, The superabsorbent resin described in step S3 is prepared by the following method: 40 ml of 0.067 mol / L sodium hydroxide solution and 1.2 g of guar gum are mixed and stirred evenly, then heated to 60-80℃ and reacted at a constant temperature for 50-70 min. Then, 4 ml of aqueous solution containing 0.1008 g of APS is added dropwise and reacted for 15-25 min. The reactant is cooled to 45-55℃, and 7.2 g of acrylic acid, 0.0216 g of N,N'-methylenebisacrylamide, and 8.5 ml of 8 mol / L sodium hydroxide solution are added dropwise. After the addition is completed, the temperature is slowly raised to 65-75℃ and reacted at a constant temperature for 2.5-3.5 h. The entire reaction is carried out under a nitrogen atmosphere. After the reaction is completed, the resin is dried at 65-75℃ to constant weight and then pulverized to a size of 50 mesh.

5. A method for improving the water retention capacity and greening level of sandy land according to claim 1, characterized in that, The concentration of Bacillus pasteurellii in the mixture 1 described in step S4 is 0.8–1.2 × 10⁻⁶. 8 The concentration of urea is 10–20 g / L, and the injection volume of mixture 1 is 80–120 ml / well.

6. A method for improving the water retention capacity and greening level of sandy land according to claim 1, characterized in that, In step S4, the concentration of biochar in the mixture 2 is 45–55 g / L, and the concentration of Bacillus mucilaginosus is 0.8–1.2 × 10⁻⁶ g / L. 5 The volume of mixed solution 2 is 140–160 ml / well, with a cell / L ratio.

7. The method for improving the water retention capacity and greening level of sandy land according to claim 1, characterized in that, The biochar in step S4 is prepared by the following method: Pine wood chips and straw are mixed evenly in a mass ratio of 1.5 to 2.5:1, washed and dried, and then passed through an 80-mesh sieve. The mixture is heated in a sand bath at 450 to 550°C under vacuum for 1.3 to 1.8 hours. The resulting product is primary biochar. The primary biochar is soaked in a 1.5 to 2.5 mol / L citric acid solution for 45 to 50 hours, rinsed with ultrapure water, and then soaked in a 0.4 to 0.6 mol / L calcium fluoride solution for 10 to 14 hours. After rinsing with ultrapure water and drying, the biochar is obtained.

8. The method for improving the water retention capacity and greening level of sandy land according to claim 7, characterized in that, The heating material for the sand bath is prepared by the following method: sand with a particle size of 1-3 mm is mixed evenly with graphene at a mass ratio of 45-55:

1.

9. The method for improving the water retention capacity and greening level of sandy land according to claim 1, characterized in that, The grass species mentioned in step S5 are sea buckthorn, caragana, sand fern, ice grass and red bean grass.

10. A method for improving the water retention capacity and greening level of sandy land according to claim 1, characterized in that, The concentration of the lignin sulfonate solution in step S6 is 25-35 wt%, and the spraying rate is 3-4 L / m³. 2 .

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