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

Abstract

The invention belongs to the technical field of soil improvement, and particularly relates to a method for improving the water retention capacity and greening level of sand land, and the method comprises the steps of paper laying, primary backfilling, secondary backfilling, microbial inoculum injection, tertiary backfilling and quartic backfilling. According to the invention, different five-layer structures are arranged, and good moisture retention effect and ecological benefit are realized through cooperation and synergistic effect among the layers. By introducing the bacillus mucilaginosus, the effectiveness of phosphorus and potassium elements in the sand soil is improved on the basis of synergism of the bacillus mucilaginosus and the bacillus pasteurii. Meanwhile, biochar is introduced as a carrier, so that the survival rate and activity of the microbial inoculum are further improved, and the application effect is improved. A sand bath heating method is innovatively used for preparation of the biochar, sand is reused as a sand bath material, good reusability is achieved, and cost reduction is facilitated. The three functions of water retention, sand stabilization and growth promotion are organically combined, and integral restoration and improvement of sand ecology can be achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of soil improvement, and in particular relates to a method for improving the water retention capacity and greening level of sandy land. Background Art

[0002] With the change of global climate and the continuous expansion of human activities, land 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 the degradation of vegetation and the loss of biodiversity, further exacerbating the fragility of the ecosystem. In this context, how to effectively improve the ecological environment of desertified land and promote the recovery of vegetation and the stability of soil has become an urgent problem to be solved. The governance of desertified land is a complex and arduous task. Due to the special properties of sandy soil, its water retention capacity is extremely poor, and it is difficult for water to be effectively retained in the soil, making it difficult for vegetation to grow. At the same time, the loose structure of sandy soil also makes it extremely difficult to sow grass seeds. Grass seeds are often difficult to take root and have a very low survival rate. Therefore, developing a technology that can achieve water retention and efficient sowing on desertified land is of vital significance to improving the ecological environment of desertified land.

[0003] At present, there have been some preliminary explorations and practices for the management of desertified land. For example, the Chinese patent with publication number CN102535426A discloses a three-dimensional plastic mulch film technology for water conservation, seepage prevention and evaporation prevention in desert management. This technology is a three-dimensional plastic mulch film technology for large-scale mechanization and artificial implementation of desert management. Its technical principle is as follows: plastic is used to make a grid strip about 4.5 meters wide and about 45 meters long. The grid is composed of a completely closed, thin, soft, and connected individual body with a side length of 30cm and a height of 40cm. The two sides of the plastic mulch are made into a convex sheet shape (plane) that can be bonded, and the other two sides are made into a pit shape at the bottom of the grid, about 50cm wide. A number of water holes are left at 2 / 3 or 1 / 2 of the height of the mulch grid body. There are ribs in the upper mouth of the mulch, and the horizontal ribs are about 1cm high and 3mm thick. The longitudinal ribs and the horizontal ribs form a whole, and are 2cm higher than the horizontal ribs, forming a T shape. The upper opening is connected to the main reinforcement with vertical and horizontal small ribs, and the small ribs have open plastic film fissures on both sides. Although this method solves the most difficult water conservation problem for vegetation survival in desert control, plastic is difficult to degrade in the soil and may cause subsequent soil pollution problems. At the same time, the coverage of the ground film may affect the local water cycle and have a negative effect on the subsequent plant growth and microhabitat transformation.

[0004] Another example is a Chinese patent with publication number CN 106069271A that discloses a method for desert greening, comprising the following steps:

[0005] Step 1, dig a filling groove, and lay a water-blocking and anti-seepage layer on the surface of the filling groove; Step 2, lay a sand layer on the water-blocking and anti-seepage layer, and lay a plant growth layer on the sand layer; Step 3, lay a straw grid on the plant growth layer, connect the grass mat on the winch to the hook of the mountain bike, start the mountain bike, drive forward, and keep running at a constant speed until all the grass mats on the winch are laid; Step 4, sprinkle plant seeds in the straw grid, and then spray water. Although the method of the present invention can green the desert, green the desert that is conditional and can be greened, has a wide application area, is convenient for standardized construction, increases the vegetation coverage rate of the desert, and can improve the local ecological environment of the desert, the grass seeds directly sown on the sand still face a harsh living environment, and there may be a problem of low subsequent survival rate; at the same time, only a water-blocking layer is laid, and the growth of grass seeds on the sand lacks nutrients and water to maintain the environment, which is not conducive to the subsequent growth of grass seeds.

[0006] It can be seen that the existing technologies have the following problems: the materials used are poorly degradable, which is not conducive to environmental protection; they do not take into account the soil moisture retention and nutrient supply capacity; the water retention efficiency is low; and the support for the subsequent growth of sandy plants is weak. That is, the current sand fixation technologies such as MICP have developed rapidly, but they have only solved the problem of consolidating sandy soil, and have not solved the problem of low effectiveness of elements in the soil and weak support for sandy plants. Summary of the invention

[0007] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a method for improving the water retention capacity and greening level of sandy land. The purpose of the present invention is achieved through the following technical scheme: A method for improving the water retention capacity and greening level of sandy land, which comprises the following steps:

[0008] S1. Paper laying: Dig a groove with a depth of 630-680mm on the target sand surface, and lay a layer of kraft paper after leveling the bottom of the groove;

[0009] S2. Primary backfill: Take part of the excavated sand and mix it with sodium polyacrylate and fill it into the groove covered with kraft paper. The filling depth is 130-150mm;

[0010] S3. Secondary backfill: Take another part of the excavated sand, mix it with the foreign soil at a weight ratio of 1:1, then add super absorbent resin, mix well and fill it into the groove and drill holes, filling the depth to 180 ~ 220mm;

[0011] S4. Injection of bacterial agent: Mix the Bacillus pasteurianus bacterial solution with urea to form a mixed solution 1, mix the mixed solution 1 evenly and inject it into the hole for solidification for ≥144h; then mix the biochar with the Bacillus colloids bacterial solution to form a mixed solution 2 and inject it into the hole;

[0012] S5. Three-time backfilling: Take some of the excavated sand and mix it with the external soil in a weight ratio of 1:1, and continue to fill it into the groove to a depth of 140-160mm. After leveling the top, sprinkle grass seeds and water until the surface is moistened;

[0013] S6. Four backfillings: Finally, some of the excavated sand is filled into the grooves sprinkled with grass seeds, and the grooves are filled and leveled and then sprayed with lignin sulfonate solution.

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

[0015] As a preferred technical solution, the amount of holes punched in step S3 is 18 to 22 holes / m 2 The amount of super absorbent resin added is 2-4% of the total mass of sand and foreign soil.

[0016] As a preferred technical solution, the super absorbent 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, and then the temperature is raised to 60-80° C. and the reaction is carried out at a constant temperature for 50-70 min. Then, 4 ml of an aqueous solution containing 0.1008 g of APS (ammonium sulfate) is added dropwise for reaction for 15-25 min. The reactant is cooled to 45-55° C., and 7.2 g of acrylic acid, 0.0216 g of N,N'-methylenebisacrylamide, and 8.5 ml of an 8 mol / L sodium hydroxide solution are added dropwise thereto. After the addition is completed, the temperature is slowly raised to 65-75° C. and the reaction is carried out 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, it is dried at 65-75° C. to constant weight and crushed to a size of 50 mesh.

[0017] As a preferred technical solution, the concentration of Bacillus pasteurianus in the mixed solution 1 in step S4 is 0.8-1.2×10 8 cells / L, the concentration of urea is 10-20 g / L, and the injection volume of the mixed solution 1 is 80-120 ml / well.

[0018] As a preferred technical solution, the concentration of biochar in the mixed solution 2 in step S4 is 45-55 g / L, and the concentration of Bacillus colloids is 0.8-1.2×10 5 cells / L, and the injection volume of mixed solution 2 was 140-160 ml / well.

[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 in a mass ratio of 1.5 to 2.5:1, and then washed and dried and passed through an 80-mesh sieve, and heated in a sand bath under vacuum and 450 to 550°C for 1.3 to 1.8 hours. The obtained product is primary biochar, and 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, rinsed with ultrapure water, and dried to obtain biochar. The straw is preferably a mixture of corn straw and rice straw, and the mass ratio of corn straw to rice straw is 2:1.

[0020] Furthermore, the heating material of the sand bath is prepared by the following method: sand with a particle size of 1 to 3 mm is mixed evenly with graphene in a mass ratio of 45 to 55:1. The sand is preferably obtained from local sand.

[0021] As a preferred technical solution, the grass species in step S5 are Hippophae rhamnoides L., Caragana spp., Astragalus membranaceus, Agropyron ovata, Wheatgrass and Sainfoin.

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

[0023] In the present invention:

[0024] (1) Through the coordination and synergy between different layers, better water retention and ecological benefits can be achieved simultaneously.

[0025] (2) The combined application of foreign soil and water retaining agent provides both nutritional support and water support for grass seed growth.

[0026] (3) On the basis of the existing urea + Bacillus pasteurianus MICP sand fixation technology, Bacillus pasteurianus was added. On the one hand, the calcium carbonate crystals produced by MICP during the sand fixation process can provide a better attachment condition for Bacillus pasteurianus and achieve the growth of the bacteria; on the other hand, the addition of Bacillus pasteurianus helps to increase the availability of phosphorus and potassium elements in the soil, helping Bacillus pasteurianus and upper layer plants to absorb and utilize them, thus forming a positive cycle.

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

[0028] (5) Mixing sand with foreign soil can help improve the physical and chemical properties of the original soil to a certain extent, and at the same time, it will not cause the water in the soil to diffuse rapidly to the surrounding sand due to the large difference in properties. Combining sodium polyacrylate with the above-mentioned mixed soil can help further improve the water retention capacity of the mixed soil. The mixing effect of urea and Bacillus pasteurianus can help increase the nitrogen content level of the soil, and calcium carbonate crystals can be produced in the process of Bacillus pasteurianus hydrolyzing urea, which plays a role in further fixing the soil. Bacillus pasteurianus helps promote the growth and development of plants, and has a positive effect on improving the effectiveness of phosphorus and potassium in the soil. At the same time, the calcium carbonate crystals produced by Bacillus pasteurianus hydrolyzing urea also help provide a high-quality habitat for Bacillus pasteurianus and help the growth of Bacillus pasteurianus. Through the attachment to calcium carbonate crystals and the water supply of sodium polyacrylate, Bacillus pasteurianus can continue to grow and develop in the mixed soil, promoting the improvement of the effectiveness of phosphorus and potassium in the soil. Therefore, the three major growth elements of plants in this layer, namely nitrogen, phosphorus and potassium, have high availability, which has a good promoting effect on plant growth.

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

[0030] (7) The biochar formula used uses more wood materials and has a higher carbon content than commercially available single-component biochar, which helps provide better nutritional conditions for the microorganisms contained. On this basis, the use of a higher temperature carbonization method for preparation helps to increase the surface area, stability and pore size of the biochar, making it more suitable for the survival and effectiveness of Bacillus subtilis. The citric acid and calcium fluoride soaking process during the biochar preparation process helps to further increase the specific surface area and pore volume of the biochar product.

[0031] (8) The biochar carbonization process innovatively uses a sand bath heating method, in which the sand bath material used is sand from the original sand field, which helps to reuse sand resources; at the same time, compared with the traditional muffle furnace heating carbonization process, sand bath heating can significantly improve the uniformity of heating; at the same time, the temperature can be maintained longer, and the heat source can be removed at the end of the reaction, and the residual heat can be used to continue the carbonization process, which helps to save energy and reduce costs. In addition, the stability of sand bath heating also helps the subsequent etching process to produce uniform pores that are conducive to the habitat of growth-promoting bacteria, and also helps to fully release the nutrients in the biochar, promote the recovery of sand nutrients and the effective use of bacterial agents.

[0032] The present invention has the following advantages: The present invention discloses a method for improving the water retention capacity and greening level of sandy land, and sets different 5-layer structures, so as to achieve good water retention and ecological benefits at the same time through the coordination and synergistic effect between different layers. The present invention introduces Bacillus mucilaginosus to improve the effectiveness of phosphorus and potassium elements in sandy soil on the basis of achieving the synergy between Bacillus mucilaginosus and Bacillus pasteurianus. At the same time, introducing biochar as a carrier into the construction process 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 sand bath heating method. The present invention helps to reuse sand as sand bath material, and the material has good reuse properties, which helps to improve the availability of sand and is also conducive to further reducing material costs. The present invention organically combines the three functions of water retention, sand fixation and growth promotion, which helps to achieve the overall restoration and improvement of the sand ecology. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 It is a schematic diagram of the structure after the target sandy land is improved by the method of the present invention, wherein 1 is sand layer + lignin sulfonate, 2 is foreign soil + grass seeds, 3 is sandy soil + foreign soil + highly absorbent resin + urea + biochar + Bacillus pasteurianus + Bacillus mucilaginosus, 4 is sandy soil + sodium polyacrylate, and 5 is kraft paper. DETAILED DESCRIPTION

[0034] The present invention is further described below in conjunction with the accompanying drawings and embodiments, and the protection scope 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. Paper laying: dig a 630mm deep trench on the target sand surface, and lay a layer of kraft paper after leveling the bottom of the trench;

[0036] S2. Backfill once: Take part of the excavated sand and mix it evenly with sodium polyacrylate and fill it into the groove covered 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 backfill: Take another part of the excavated sand and mix it with the external soil in a weight ratio of 1:1, then add super absorbent resin, mix well and fill it into the groove and punch holes; wherein the filling depth is 180mm and the punching amount is 18 holes / m 2 ; The amount of super absorbent resin added is 2% of the total mass of sand and foreign soil;

[0038] The highly absorbent 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 the temperature was raised to 60° C. and the mixture was reacted at a constant temperature for 50 min. Then, 4 ml of an aqueous solution containing 0.1008 g of APS was added dropwise to react 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 thereto. After the addition was completed, the temperature was slowly raised to 65° C. and the mixture was 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 mixture was dried at 65° C. to a constant weight and crushed to a size of 50 mesh.

[0039] S4. Injection of bacterial agent: Mix the Bacillus pasteurianus bacterial solution with urea to form a mixed solution 1, mix the mixed solution 1 evenly and inject it into the well for solidification for 144 hours; then mix the biochar with the Bacillus colloidus bacterial solution to form a mixed solution 2 and inject it into the well; wherein the concentration of Bacillus pasteurianus in the mixed solution 1 is 0.8×10 8 cells / L, the concentration of urea was 10 g / L, and the injection volume of the mixed solution 1 was 80 ml / well; the concentration of biochar in the mixed solution 2 was 45 g / L, and the concentration of Bacillus colloids was 0.8×10 5 cells / L, the injection volume of mixed solution 2 was 140 ml / well;

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

[0041] S5. Backfill three times: Take part of the excavated sand and mix it with foreign soil in a weight ratio of 1:1, and continue to fill the groove to a depth of 140mm. After leveling the top, sprinkle the grass seeds and water until the surface is moistened; the grass seeds are Ganzi seabuckthorn, Caragana, Astragalus, Ice grass and Sainfoin;

[0042] S6. Four backfilling: Finally, take part of the excavated sand and fill it into the groove sprinkled with grass seeds. After the groove is filled, spray a 25wt% lignin sulfonate solution at a spraying rate of 3L / m 2 ;

[0043] After paper laying, primary backfilling, secondary backfilling, bacterial injection, tertiary backfilling and quaternary backfilling, the target sand land is formed as follows: Figure 1 The hierarchical structure shown.

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

[0045] S1. Paper laying: dig a 680mm deep trench on the target sand surface, and lay a layer of kraft paper after leveling the bottom of the trench;

[0046] S2. Backfill once: Take part of the excavated sand and mix it evenly with sodium polyacrylate and fill it into the groove covered 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 backfill: Take another part of the excavated sand and mix it with the external soil in a weight ratio of 1:1, then add super absorbent resin, mix well and fill it into the groove and punch holes; wherein, the filling depth is 220mm and the punching amount is 22 holes / m 2 ; The amount of super absorbent resin added is 4% of the total mass of sand and foreign soil;

[0048] The highly absorbent 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, then heated to 80°C and reacted at a constant temperature for 70 min, then 4 ml of an aqueous solution containing 0.1008 g of APS was added dropwise for reaction for 25 min, the reactant was cooled to 55°C, 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 thereto, and 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, and after the reaction was completed, it was dried at 75°C to constant weight and crushed to a size of 50 mesh;

[0049] S4. Injection of bacterial agent: Mix the Bacillus pasteurianus bacterial solution with urea to form a mixed solution 1, mix the mixed solution 1 evenly and inject it into the well for solidification for 145 hours; then mix the biochar with the Bacillus colloidus bacterial solution to form a mixed solution 2 and inject it into the well; wherein the concentration of Bacillus pasteurianus in the mixed solution 1 is 1.2×10 8 cells / L, the concentration of urea was 20 g / L, and the injection volume of the mixed solution 1 was 120 ml / well; the concentration of biochar in the mixed solution 2 was 55 g / L, and the concentration of Bacillus colloids was 1.2×10 5 cells / L, the injection volume of mixed solution 2 was 160 ml / well;

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

[0051] S5. Backfill three times: Take part of the excavated sand and mix it with foreign soil in a weight ratio of 1:1, continue to fill the groove, fill it to a depth of 160mm, sprinkle grass seeds and water the top after leveling until the surface is moistened; the grass seeds are Ganzi seabuckthorn, Caragana, Astragalus, Ice grass and Sainfoin;

[0052] S6. Four backfilling: Finally, take part of the excavated sand and fill it into the groove sprinkled with grass seeds. After the groove is filled, spray it with a 25-35wt% lignin sulfonate solution at a spraying rate of 4L / m 2 .

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

[0054] S1.Paper laying: dig a 650mm deep trench on the target sand surface, level the bottom of the trench and lay a layer of kraft paper;

[0055] S2. Backfill once: Take part of the excavated sand and mix it evenly with sodium polyacrylate and fill it into the groove covered 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 backfill: Take another part of the excavated sand and mix it with the external soil in a weight ratio of 1:1, then add super absorbent resin, mix well and fill it into the groove and punch holes; wherein the filling depth is 200mm and the punching amount is 20 holes / m 2 ; The amount of super absorbent resin added is 3% of the total mass of sand and foreign soil;

[0057] The highly absorbent 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 the temperature was raised to 70°C for constant temperature reaction for 60 min, and then 4 ml of 0.1008 g of APS aqueous solution was added dropwise for reaction 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 thereto. After the addition was completed, the temperature was slowly raised to 70°C for constant temperature reaction for 3 h. The entire reaction was carried out under a nitrogen atmosphere. After the reaction was completed, it was dried at 70°C to constant weight and crushed to a size of 50 mesh.

[0058] S4. Injection of bacterial agent: Mix the Bacillus pasteurianus liquid with urea to form a mixed solution 1, mix the mixed solution 1 evenly and inject it into the hole to solidify for 150 hours; then mix the biochar with the Bacillus colloidus liquid to form a mixed solution 2 and inject it into the hole; wherein the concentration of Bacillus pasteurianus in the mixed solution 1 is 1×10 8 cells / L, the concentration of urea was 16 g / L, and the injection volume of the mixed solution 1 was 100 ml / well; the concentration of biochar in the mixed solution 2 was 50 g / L, and the concentration of Bacillus colloids was 1×10 5 cells / L, the injection volume of mixed solution 2 was 150 ml / well;

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

[0060] S5. Backfill three times: Take part of the excavated sand and mix it with foreign soil in a weight ratio of 1:1, continue to fill the groove, fill it to a depth of 150mm, sprinkle grass seeds and water the top after leveling until the surface is moistened; the grass seeds are Ganzi seabuckthorn, Caragana, Astragalus, Ice grass and Sainfoin;

[0061] S6. Four backfilling: Finally, take part of the excavated sand and fill it into the groove sprinkled with grass seeds. After the groove is filled, spray a 30wt% lignin sulfonate solution at a spraying rate of 3.5L / m 2 .

[0062] The beneficial effects of the present invention are described below by experiments:

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

[0064] Experimental period: June 2023 to present

[0065] Experimental method: The method of Example 3 was used to conduct experiments on the test site, and the test site was investigated and indicators were measured from the aspects of sand fixation, water conservation and growth promotion.

[0066] Test results:

[0067] (1) Sand fixation: the percentage of clay particles (<2μm) in the improved sand 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 particles (10-50μm) increased from 2.27% to 12.20%; the percentage of fine sand (50-250μm) decreased from 76.62% to 64.07%; the percentage of coarse sand (250-2000μm) decreased from 20.22% to 17.11%. In general, the particle size composition of the improved sandy soil has been improved, and the sandy soil has shown a trend of clayification.

[0068] (2) Water conservation: the soil moisture of the sandy land with a depth of 10 cm decreased from 11.16±4.56 to 7.70±0.27, a decrease of 29.01%; the soil moisture of the sandy land with a depth of 20 cm decreased from 13.98±4.98 to 12.68±2.46, a decrease of 9.27%; the soil moisture of the sandy land with a depth of 30 cm decreased from 13.92±5.27 to 12.79±2.02, a decrease of 8.12%; the soil moisture of the sandy land with a depth of 40 cm increased from 11.81±3.89 to 12.02±2.44, an increase of 1.76%. In general, the improvement method has a certain inhibitory effect on the increase of soil moisture in each layer of the sandy land. The humidity of the upper sandy land decreased more significantly, while the humidity of the lower sandy land increased steadily, which may be closely related to the addition of water-retaining materials. The water in the sand is transferred from the soil to the super absorbent resin, which 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) Growth promotion: The one-year comprehensive survival rate of grass seeds and shrubs increased from 70.4% to 88.9%.

[0070] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which are all covered by the protection scope 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.Paper laying: dig a groove with a depth of 630-680mm on the target sand surface, and lay a layer of kraft paper after leveling the bottom of the groove; S2. Primary backfilling: Take part of the excavated sand and mix it evenly with sodium polyacrylate and fill it into the groove covered with kraft paper. The filling depth is 130-150mm; S3. Secondary backfill: Take another part of the excavated sand, mix it with the foreign soil at a weight ratio of 1:1, then add super absorbent resin, mix well and fill it into the groove and drill holes, filling the depth to 180 ~ 220mm; S4. Injection of bacterial agent: Mix the Bacillus pasteurianus bacterial solution with urea to form a mixed solution 1, mix the mixed solution 1 evenly and inject it into the hole for solidification for ≥144h; then mix the biochar with the Bacillus colloids bacterial solution to form a mixed solution 2 and inject it into the hole; S5. Three-time backfilling: Take some of the excavated sand and mix it with the external soil in a weight ratio of 1:1, and continue to fill it into the groove to a depth of 140-160mm. After leveling the top, sprinkle grass seeds and water until the surface is moistened; S6. Four backfillings: Finally, some of the excavated sand is filled into the grooves sprinkled with grass seeds, and the grooves are filled and leveled and then sprayed with lignin sulfonate solution.

2. A 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 3-4% of the mass of the sand.

3. A method for improving the water retention capacity and greening level of sandy land according to claim 1, characterized in that: The punching amount in step S3 is 18 to 22 holes / m 2 The amount of super absorbent resin added is 2-4% 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 highly absorbent 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, and then the temperature is raised to 60-80 ° C. and the reaction is carried out at a constant temperature for 50-70 min, and then 4 ml of 0.1008 g of APS aqueous solution is added dropwise to react for 15-25 min. The reactant is cooled to 45-55 ° 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 are added dropwise thereto. After the addition is completed, the temperature is slowly raised to 65-75 ° C. and the reaction is carried out 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, it is dried at 65-75 ° C. to constant weight and crushed to a size of 50 mesh.

5. The method for improving the water retention capacity and greening level of sandy land according to claim 1, characterized in that: The concentration of Bacillus pasteurianus in the mixed solution 1 in step S4 is 0.8-1.2×10 8 cells / L, the concentration of urea is 10-20 g / L, and the injection volume of the mixed solution 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 mixed solution 2 is 45-55 g / L, and the concentration of Bacillus colloids is 0.8-1.2×10 5 cells / L, and the injection volume of mixed solution 2 was 140-160 ml / well.

7. The method for improving the water retention capacity and greening level of sandy land according to claim 1, characterized in that: The biochar described in step S4 is prepared by the following method: pine wood chips and straw are evenly mixed in a mass ratio of 1.5 to 2.5:1, and then washed and dried and passed through an 80-mesh sieve, and heated in a sand bath under vacuum and 450 to 550°C for 1.3 to 1.8 hours. The resulting product is primary biochar, which 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, rinsed with ultrapure water, and dried to obtain biochar.

8. A method for improving the water retention capacity and greening level of sandy land according to claim 7, characterized in that: The heating material of the sand bath is prepared by the following method: sand with a particle size of 1 to 3 mm is taken and mixed evenly with graphene in a mass ratio of 45 to 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 in step S5 are Hippophae rhamnoides L., Caragana spp., Astragalus membranaceus, Agropyron ovata, Wheatgrass and Sainfoin.

10. The 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 amount is 3-4 L / m 2 .

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