High water-holding capacity sponge type garden soil and preparation method thereof

Abstract

The application discloses a kind of high water-holding spongy garden soil and preparation method thereof, it is related to the technical field of landscape engineering.The following components are included: modified biochar 20-25%, humus 25-30%, modified attapulgite-polyacrylamide composite hydrogel 6-9%, vermiculite 10-12%.The application forms integrated water storage, water diversion and water retention channels through the synergistic cooperation of the high porosity skeleton of modified biochar and the semi-interpenetrating network structure of modified attapulgite-polyacrylamide composite hydrogel.The surface of modified biochar is loaded with iron oxides after modification by ferric chloride, which enhances the adsorption and slow-release capacity of water.The composite hydrogel has high water absorption ratio, and the attapulgite nanorods act as reinforcing phase to prevent the structure from collapsing after repeated swelling and shrinking of the gel.The inorganic particles such as vermiculite and perlite jointly construct high total porosity, and the air porosity is kept within a suitable range, which solves the problem of the contradiction between water retention and air permeability of traditional materials.

Description

Technical Field

[0001] This invention belongs to the field of landscape engineering technology, and in particular relates to a high water-holding capacity sponge-type landscape soil and its preparation method. Background Technology

[0002] With the rapid advancement of urbanization in my country, the area of ​​urban green space continues to decrease. New greening methods such as rooftop greening and vertical greening are gradually becoming important ways to expand urban green space. However, traditional garden soil has many technical defects and cannot meet the needs of new greening scenarios.

[0003] First, traditional garden soils generally have low water-holding capacity, with a saturation water-holding capacity typically only 25%-35%. In shallow planting environments such as rooftop greening, soil moisture is rapidly lost due to limitations in soil cover thickness and wind evaporation, leading to frequent wilting and even death of plants, and a significant increase in irrigation water consumption. Studies have shown that rooftop greening in northern regions has extremely high daily irrigation volumes during the hot summer months, resulting in enormous water resource consumption.

[0004] Secondly, most existing water-retaining garden soils use a single superabsorbent polymer (SAP) as a water-retaining agent. Although this can improve water retention to some extent, it has obvious shortcomings: Sodium polyacrylate water-retaining agents are prone to degradation and failure after repeated water absorption and release cycles, resulting in a short water retention life; the compatibility of SAP particles with the soil matrix is ​​poor, and they are easily lost with irrigation water; after absorbing water and swelling, superabsorbent polymers significantly reduce soil aeration, causing root hypoxia.

[0005] Furthermore, some researchers have attempted to use biochar to improve soil, but the pore structure of ordinary biochar is mainly microporous. Although it has a certain adsorption capacity, its water retention capacity is limited, and it lacks effective slow-release function. In addition, existing preparation processes mostly use high-temperature drying, which leads to the inactivation of a large number of added functional microorganisms, making it difficult to form a stable rhizosphere micro-ecosystem. To address these issues, we provide a high water-holding capacity sponge-type garden soil and its preparation method. Summary of the Invention

[0006] The purpose of this invention is to provide a high water-holding capacity sponge-type garden soil and its preparation method, solving the following technical problems: insufficient water holding capacity and rapid water loss in traditional garden soils; short water retention life and poor soil compatibility of single water-absorbing resins; high inactivation rate of functional microorganisms in existing preparation processes; and the contradiction between water retention and aeration.

[0007] To solve the above-mentioned technical problems, the present invention is achieved through the following technical solution.

[0008] This invention relates to a high water-holding capacity, sponge-type garden soil, comprising the following components: 20%-25% modified biochar, 25%-30% humus, 6%-9% modified attapulgite-polyacrylamide composite hydrogel, 10%-12% vermiculite, 8%-10% perlite, 3%-5% zeolite powder, 5%-7% coconut coir, 0.6%-0.9% mycorrhizal fungi inoculant, 0.3%-0.4% nitrogen-fixing bacteria inoculant, and 0.1%-0% trace element mixture. 0.2%, with the remainder being water or inert filler up to 100%; wherein, the modified biochar is pyrolytic biochar of agricultural and forestry waste modified by impregnation with ferric chloride solution, with a particle size of 2mm-5mm and a porosity of 65%-75%; the modified attapulgite-polyacrylamide composite hydrogel is a semi-interpenetrating network structure hydrogel with attapulgite nanorods as the reinforcing phase and partially neutralized polyacrylamide as the matrix, with a water absorption ratio of 150g / g-250g / g.

[0009] The present invention further specifies that the modified biochar is prepared by: pyrolyzing agricultural and forestry waste at 400℃-500℃ under oxygen-limited conditions for 2-3 hours to obtain raw biochar; then impregnating it with a 0.5mol / L-1.0mol / L ferric chloride solution at a solid-liquid ratio of 1:5-1:8 for 12-24 hours; and then drying it at 80℃-100℃ and passing it through a 2mm-5mm sieve. Attapulgite nanorods are used as a physical cross-linking reinforcing phase and uniformly dispersed in an acrylamide monomer solution. The agricultural and forestry waste is pyrolyzed at 400-500℃ under oxygen-limited conditions to form raw biochar with a preliminary porous structure. Subsequently, it is modified by impregnation with ferric chloride solution, and iron ions are loaded onto the surface and pore walls of the biochar through electrostatic adsorption and complexation. After drying, the iron ions exist in the form of iron oxide or ferric hydroxide, forming a composite structure of biochar and iron oxide.

[0010] The present invention is further configured such that the preparation method of the modified attapulgite-polyacrylamide composite hydrogel includes: dispersing attapulgite in deionized water at a mass ratio of 1:20-1:30 and ultrasonically dispersing for 30 min; adding acrylamide monomer to a concentration of 1.5 mol / L-2.5 mol / L; adjusting the neutralization degree to 60%-70% with sodium hydroxide solution; adding a crosslinking agent and ammonium persulfate initiator; and polymerizing in a water bath at 50℃-60℃ for 2-4 h; the product is then crushed and passed through a 20-40 mesh sieve. Under the action of the initiator and crosslinking agent, acrylamide polymerizes to form a three-dimensional polyacrylamide network. A large number of hydroxyl groups on the surface of attapulgite form hydrogen bonds and partial chemical bonds with the polyacrylamide chains, constituting a semi-interpenetrating network structure. When water molecules enter, the network expands to form a highly hydrated gel; under external force or dehydration conditions, the network shrinks but still maintains structural integrity.

[0011] The present invention is further configured such that the trace element mixture comprises, by mass ratio: 30%-40% borax, 25%-35% zinc sulfate, 15%-20% sodium molybdate, 10%-15% manganese sulfate, and 5%-10% ferrous sulfate. The trace element mixture is pretreated with EDTA chelation, whereby EDTA acts as a chelating agent to form a stable chelate ring structure with the metal ions in borax, zinc sulfate, sodium molybdate, manganese sulfate, and ferrous sulfate, thereby preventing the trace elements from precipitating or becoming ineffective in alkaline or oxidizing environments.

[0012] The present invention further specifies that the soil is a porous granular body with a particle size of 3mm-8mm and a bulk density of 0.35g / cm³. 3 -0.50g / cm 3 The total porosity is 70%-85%, the saturated water holding capacity is 65%-80%, the pH value is 6.0-7.5, and the aeration porosity is 15%-25%.

[0013] The present invention is further configured such that the mycorrhizal fungal agent is a mixed agent of arbuscular mycorrhizal fungi and rhododendron mycorrhizal fungi, and the nitrogen-fixing fungal agent is brown nitrogen-fixing bacteria.

[0014] A method for preparing a high water-holding capacity sponge-type garden soil includes the following steps: S1: Agricultural and forestry waste is crushed to a particle size ≤5cm, pyrolyzed under oxygen-limited conditions at 400℃-500℃ for 2h-3h, modified by impregnation in 0.5mol / L-1.0mol / L ferric chloride solution at a solid-liquid ratio of 1:5-1:8 for 12h-24h, dried at 80℃-100℃ and passed through a 2mm-5mm sieve to obtain modified biochar; S2: Attapulgite is ultrasonically dispersed in deionized water at a mass ratio of 1:20-1:30 for 30 min. Acrylamide monomer is added to make the concentration 1.5 mol / L-2.5 mol / L. The neutralization degree of sodium hydroxide is adjusted to 60%-70%. Crosslinking agent and initiator ammonium persulfate are added. Polymerization reaction is carried out in a water bath at 50℃-60℃ for 2-4 h. The product is crushed and passed through a 20-40 mesh sieve to obtain modified attapulgite-polyacrylamide composite hydrogel. S3: Crush humus, vermiculite, perlite, zeolite powder, and coconut coir separately and pass them through a 2mm-5mm sieve. Measure them by mass percentage and add them to a horizontal mixer with the modified biochar obtained in step S1 for dry premixing. The stirring speed is 30r / min-50r / min and the time is 10min-15min to obtain a dry mixture. S4: Add the composite hydrogel obtained in step S2 to the dry mixture according to the ratio, and spray atomized water accounting for 15%-25% of the dry mixture mass. Wet mix in a twin-screw mixer at a speed of 20r / min-40r / min for 8min-12min to obtain the wet mixture. S5: Feed the wet mixture obtained in step S4 into a twin-screw extruder, control the extrusion orifice diameter to be 4mm-6mm, the pellet length to be 5mm-10mm, and the extrusion pressure to be 2MPa-4MPa to obtain pellet blanks. S6: Place the granular blank in a fluidized bed dryer, control the inlet air temperature to 40℃-50℃ and the material residence time to 15min-25min, and perform low-temperature curing and drying to the set moisture content to obtain dried granules; S7: Mix the mycorrhizal fungi agent and nitrogen-fixing bacteria agent according to the mass ratio, and spray them evenly onto the surface of the dried particles obtained in step S6. The inoculation amount should be such that the final mass percentage of the mycorrhizal fungi agent and nitrogen-fixing bacteria agent in the finished soil reaches the range described in claim 1. Then, air dry under sterile conditions to the set moisture content to obtain the finished sponge-type garden soil.

[0015] The present invention is further configured such that, during the low-temperature curing and drying process described in step S6, the outlet air temperature of the fluidized bed dryer is controlled at 35℃-45℃ and the air velocity is 1.5m / s-2.5m / s, so as to ensure that the internal moisture gradient of the particles diffuses outward, while avoiding the carbonization of organic matter in coconut coir and humus and the collapse of the composite hydrogel network structure caused by high temperature, thus ensuring the physical strength and porous structure of the particles.

[0016] The present invention is further configured such that, in step S7, the mycorrhizal fungal agent and nitrogen-fixing fungal agent are mixed with zeolite powder at a mass ratio of 1:3-1:5 and adsorbed for 10-15 minutes before inoculation, so as to improve the adhesion and survival rate of the agent on the particle surface.

[0017] The present invention is further configured such that, after step S7, the preparation method further includes: placing the finished sponge-type garden soil in a curing room with a temperature of 15℃-25℃ and a relative humidity of 50%-65% for 24h-48h to allow the microbial agent to form a stable biofilm layer on the surface of the particles, and then sealing and packaging it.

[0018] The present invention has the following beneficial effects.

[0019] 1. This invention utilizes the high porosity framework of modified biochar and the semi-interpenetrating network structure of modified attapulgite-polyacrylamide composite hydrogel to form an integrated channel for water storage, conduction, and retention. The modified biochar is modified with ferric chloride and loaded with iron oxides on its surface, which enhances its ability to adsorb and release water. The composite hydrogel has a high water absorption ratio, and the attapulgite nanorods act as a reinforcing phase to prevent structural collapse after repeated swelling and shrinkage of the gel. Together with inorganic particles such as vermiculite and perlite, they form a high total porosity, with the aeration porosity maintained within an appropriate range, thus solving the problem of the contradiction between water retention and aeration in traditional materials.

[0020] 2. This invention employs a low-temperature fluidized bed drying process combined with inoculation of microbial agents, avoiding the damage of high temperatures to organic matter and composite hydrogel networks in coconut coir and humus. Simultaneously, it enhances the survival rate of mycorrhizal fungi and nitrogen-fixing bacteria. Before inoculation, the microbial agent is adsorbed onto zeolite powder, increasing its adhesion to the particle surface. After further maintenance, a stable biofilm layer is formed, creating a long-lasting and active rhizosphere microecology. The microenvironment provided by modified biochar and zeolite powder is conducive to microbial colonization. Extracellular polysaccharides produced by microbial metabolism further promote soil particle aggregation and moisture retention, forming a dual mechanism of physical water retention and biological water fixation, thereby continuously improving soil structure and reducing fertilizer dependence. Attached Figure Description

[0021] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below.

[0022] Figure 1 This is a process flow diagram of modified biochar preparation in a high water-holding capacity sponge-type garden soil and its preparation method.

[0023] Figure 2 This is a flowchart illustrating the process of preparing composite hydrogels in a high water-holding capacity sponge-type garden soil and its preparation method.

[0024] Figure 3 This document describes the process flow for preparing a high water-holding capacity sponge-type garden soil and its preparation method. Figure 1 .

[0025] Figure 4 This document describes the process flow for preparing a high water-holding capacity sponge-type garden soil and its preparation method. Figure 2 .

[0026] Figure 5 This document describes the process flow for preparing a high water-holding capacity sponge-type garden soil and its preparation method. Figure 3 . Detailed Implementation

[0027] The technical solutions of the present invention will be described below with reference to the accompanying drawings. The described embodiments are only some embodiments of the present invention, and not all embodiments.

[0028] Example 1 This embodiment provides a high water-holding capacity sponge-type garden soil and its preparation method. By weight percentage, the soil comprises: 25% modified biochar, 30% humus, 8% modified attapulgite-polyacrylamide composite hydrogel, 12% vermiculite, 10% perlite, 4% zeolite powder, 7% coconut coir, 0.8% mycorrhizal fungal inoculant, 0.4% nitrogen-fixing bacteria inoculant, and 0.2% trace element mixture.

[0029] The preparation method includes the following steps: Step S1: Rice straw was crushed to a particle size ≤5cm and pyrolyzed at 450℃ for 2.5h under a nitrogen atmosphere to obtain raw biochar. The raw biochar was immersed in a 0.8mol / L ferric chloride solution and magnetically stirred at room temperature for 18h. Then it was dried in a 90℃ oven to constant weight and passed through a 3mm sieve to obtain modified biochar. The porosity of the modified biochar was measured to be 70%, and the average pore size was 85μm.

[0030] Step S2: Add attapulgite clay to deionized water at a mass ratio of 1:25 and ultrasonically disperse for 30 min to obtain a uniform suspension. Add acrylamide monomer to make the concentration 2.0 mol / L, adjust the neutralization degree to 65% with 1 mol / L sodium hydroxide solution, add 0.08% N,N'-methylenebisacrylamide and 0.2% ammonium persulfate, and polymerize in a 55℃ water bath for 3 h. Remove the product, crush it, and pass it through a 30-mesh sieve to obtain composite hydrogel particles.

[0031] Step S3: Pass the humus, vermiculite, perlite, zeolite powder and coconut coir through a 3mm sieve, measure them according to the formula ratio, and add them to the modified biochar obtained in step S1 into a horizontal ribbon mixer. Stir at 40r / min for 12min to obtain a uniform dry mixture.

[0032] Step S4: Add the composite hydrogel obtained in step S2 to the dry mix according to the formula ratio, and spray 20% of the dry mix mass of deionized water through an atomizing nozzle. Stir in a twin-screw mixer at 30 r / min for 10 min to make the hydrogel uniformly coat the surface of each component and form a wet mix with adhesive properties.

[0033] Step S5: Feed the wet mixture into a twin-screw extruder to obtain cylindrical granule preforms.

[0034] Step S6: Feed the granular material into a fluidized bed dryer, control the inlet air temperature to 45℃, the outlet air temperature to 40℃, the air velocity to 2.0m / s, and the material residence time to 20min, and dry to the set moisture content to obtain dried granules.

[0035] Step S7: Mix arbuscular mycorrhizal fungi inoculant and brown nitrogen-fixing bacteria inoculant at a mass ratio of 2:1, and then adsorb the mixture with zeolite powder at a ratio of 1:4 for 12 minutes. Spray the mixture evenly onto the surface of the dried granules, with an inoculum amount of 1.2% of the total soil mass. Air dry under sterile conditions until the moisture content reaches 12%, then place it in a curing room at 20℃ and 60% relative humidity for 36 hours. Finally, seal the mixture in aluminum foil bags to obtain the finished sponge-type garden soil.

[0036] Example 2 By weight percentage, this embodiment includes: 22% modified biochar, 32% humus, 6% modified attapulgite-polyacrylamide composite hydrogel, 13% vermiculite, 11% perlite, 4% zeolite powder, 8% coconut coir, 0.6% mycorrhizal fungi inoculant, 0.4% nitrogen-fixing bacteria inoculant, and 0.2% trace element mixture.

[0037] In step S1, the pyrolysis temperature was 400℃ and the ferric chloride concentration was 0.6 mol / L; in step S2, the acrylamide concentration was 1.8 mol / L and the neutralization degree was 60%. Testing showed that the resulting product had a saturated water retention rate of 68.5%, and after 50 cycles, the water absorption retention rate was within the set range, indicating good performance across all indicators.

[0038] Step S2: Add attapulgite clay to deionized water at a mass ratio of 1:25 and ultrasonically disperse for 30 min to obtain a uniform suspension. Add acrylamide monomer to make the concentration 2.0 mol / L, adjust the neutralization degree to 65% with 1 mol / L sodium hydroxide solution, add 0.08% N,N'-methylenebisacrylamide and 0.2% ammonium persulfate, and polymerize in a 55℃ water bath for 3 h. Remove the product, crush it, and pass it through a 30-mesh sieve to obtain composite hydrogel particles.

[0039] Step S3: Pass the humus, vermiculite, perlite, zeolite powder and coconut coir through a 3mm sieve, measure them according to the formula ratio, and add them to the modified biochar obtained in step S1 into a horizontal ribbon mixer. Stir at 40r / min for 12min to obtain a uniform dry mixture.

[0040] Step S4: Add the composite hydrogel obtained in step S2 to the dry mix according to the formula ratio, and spray 20% of the dry mix mass of deionized water through an atomizing nozzle. Stir in a twin-screw mixer at 30 r / min for 10 min to make the hydrogel uniformly coat the surface of each component and form a wet mix with adhesive properties.

[0041] Step S5: Feed the wet mixture into a twin-screw extruder to obtain cylindrical granule preforms.

[0042] Step S6: Feed the granular material into a fluidized bed dryer, control the inlet air temperature to 45℃, the outlet air temperature to 40℃, the air velocity to 2.0m / s, and the material residence time to 20min, and dry to the set moisture content to obtain dried granules.

[0043] Step S7: Mix arbuscular mycorrhizal fungi inoculant and brown nitrogen-fixing bacteria inoculant at a mass ratio of 2:1, and then adsorb the mixture with zeolite powder at a ratio of 1:4 for 12 minutes. Spray the mixture evenly onto the surface of the dried granules, with an inoculum amount of 1.2% of the total soil mass. Air dry under sterile conditions until the moisture content reaches 12%, then place it in a curing room at 20℃ and 60% relative humidity for 36 hours. Finally, seal the mixture in aluminum foil bags to obtain the finished sponge-type garden soil.

[0044] Example 3 By weight percentage, this embodiment includes: 28% modified biochar, 28% humus, 10% modified attapulgite-polyacrylamide composite hydrogel, 10% vermiculite, 9% perlite, 5% zeolite powder, 6% coconut coir, 1.0% mycorrhizal fungi inoculant, 0.5% nitrogen-fixing bacteria inoculant, and 0.3% trace element mixture.

[0045] In step S1, the pyrolysis temperature was 500℃ and the ferric chloride concentration was 1.0 mol / L; in step S2, the acrylamide concentration was 2.2 mol / L and the neutralization degree was 70%. Testing showed that the resulting product had a saturated water retention rate of 78.6%, and after 50 cycles, the water absorption retention rate was within the set range, indicating optimal water retention performance.

[0046] Step S2: Add attapulgite clay to deionized water at a mass ratio of 1:25 and ultrasonically disperse for 30 min to obtain a uniform suspension. Add acrylamide monomer to make the concentration 2.0 mol / L, adjust the neutralization degree to 65% with 1 mol / L sodium hydroxide solution, add 0.08% N,N'-methylenebisacrylamide and 0.2% ammonium persulfate, and polymerize in a 55℃ water bath for 3 h. Remove the product, crush it, and pass it through a 30-mesh sieve to obtain composite hydrogel particles.

[0047] Step S3: Pass the humus, vermiculite, perlite, zeolite powder and coconut coir through a 3mm sieve, measure them according to the formula ratio, and add them to the modified biochar obtained in step S1 into a horizontal ribbon mixer. Stir at 40r / min for 12min to obtain a uniform dry mixture.

[0048] Step S4: Add the composite hydrogel obtained in step S2 to the dry mix according to the formula ratio, and spray 20% of the dry mix mass of deionized water through an atomizing nozzle. Stir in a twin-screw mixer at 30 r / min for 10 min to make the hydrogel uniformly coat the surface of each component and form a wet mix with adhesive properties.

[0049] Step S5: Feed the wet mixture into a twin-screw extruder to obtain cylindrical granule preforms.

[0050] Step S6: Feed the granular material into a fluidized bed dryer, control the inlet air temperature to 45℃, the outlet air temperature to 40℃, the air velocity to 2.0m / s, and the material residence time to 20min, and dry to the set moisture content to obtain dried granules.

[0051] Step S7: Mix arbuscular mycorrhizal fungi inoculant and brown nitrogen-fixing bacteria inoculant at a mass ratio of 2:1, and then adsorb the mixture with zeolite powder at a ratio of 1:4 for 12 minutes. Spray the mixture evenly onto the surface of the dried granules, with an inoculum amount of 1.2% of the total soil mass. Air dry under sterile conditions until the moisture content reaches 12%, then place it in a curing room at 20℃ and 60% relative humidity for 36 hours. Finally, seal the mixture in aluminum foil bags to obtain the finished sponge-type garden soil.

Claims

1. A high water-holding capacity sponge-type garden soil, characterized in that: By weight percentage, it includes the following components: 20%-25% modified biochar, 25%-30% humus, 6%-9% modified attapulgite-polyacrylamide composite hydrogel, 10%-12% vermiculite, 8%-10% perlite, 3%-5% zeolite powder, 5%-7% coconut coir, 0.6%-0.9% mycorrhizal fungi inoculant, 0.3%-0.4% nitrogen-fixing bacteria inoculant, 0.1%-0.2% trace element mixture, with the balance being water or inert filler to 100%. The modified biochar is pyrolytic biochar of agricultural and forestry waste modified by impregnation with ferric chloride solution, with a particle size of 2mm-5mm and a porosity of 65%-75%; the modified attapulgite-polyacrylamide composite hydrogel is a semi-interpenetrating network structure hydrogel with attapulgite nanorods as the reinforcing phase and partially neutralized polyacrylamide as the matrix, with a water absorption ratio of 150g / g-250g / g.

2. The high water-holding capacity sponge-type garden soil according to claim 1, characterized in that: The modified biochar is prepared by pyrolyzing agricultural and forestry waste at 400℃-500℃ under oxygen-limited conditions for 2-3 hours to obtain raw biochar, then impregnating it with a 0.5mol / L-1.0mol / L ferric chloride solution at a solid-liquid ratio of 1:5-1:8 for 12-24 hours, and then drying it at 80℃-100℃ and passing it through a 2mm-5mm sieve.

3. The high water-holding capacity sponge-type garden soil according to claim 1, characterized in that: The preparation method of the modified attapulgite-polyacrylamide composite hydrogel includes: dispersing attapulgite in deionized water at a mass ratio of 1:20-1:30 and ultrasonically dispersing for 30 min; adding acrylamide monomer to make its concentration 1.5 mol / L-2.5 mol / L; adjusting the neutralization degree to 60%-70% with sodium hydroxide solution; adding crosslinking agent and ammonium persulfate initiator; and polymerizing in a water bath at 50℃-60℃ for 2-4 h; and obtaining the product by crushing and passing it through a 20-40 mesh sieve.

4. The high water-holding capacity sponge-type garden soil according to claim 1, characterized in that: The trace element mixture comprises, by mass ratio: 30%-40% borax, 25%-35% zinc sulfate, 15%-20% sodium molybdate, 10%-15% manganese sulfate, and 5%-10% ferrous sulfate. The trace element mixture is pretreated with EDTA chelation.

5. The high water-holding capacity sponge-type garden soil according to claim 1, characterized in that: The soil consists of porous particles with a particle size of 3mm-8mm and a bulk density of 0.35g / cm³. 3 -0.50g / cm 3 The total porosity is 70%-85%, the saturated water holding capacity is 65%-80%, the pH value is 6.0-7.5, and the aeration porosity is 15%-25%.

6. The high water-holding capacity sponge-type garden soil according to claim 1, characterized in that: The mycorrhizal fungal inoculant is a mixed inoculant of arbuscular mycorrhizal fungi and rhododendron mycorrhizal fungi, and the nitrogen-fixing fungal inoculant is brown nitrogen-fixing bacteria.

7. A method for preparing a high water-holding capacity sponge-type garden soil according to any one of claims 1-6, characterized in that: Includes the following steps: S1: Agricultural and forestry waste is crushed to a particle size ≤5cm, pyrolyzed under oxygen-limited conditions at 400℃-500℃ for 2h-3h, modified by impregnation in 0.5mol / L-1.0mol / L ferric chloride solution at a solid-liquid ratio of 1:5-1:8 for 12h-24h, dried at 80℃-100℃ and passed through a 2mm-5mm sieve to obtain modified biochar; S2: Attapulgite is ultrasonically dispersed in deionized water at a mass ratio of 1:20-1:30 for 30 min. Acrylamide monomer is added to make the concentration 1.5 mol / L-2.5 mol / L. The neutralization degree of sodium hydroxide is adjusted to 60%-70%. Crosslinking agent and initiator ammonium persulfate are added. Polymerization reaction is carried out in a water bath at 50℃-60℃ for 2-4 h. The product is crushed and passed through a 20-40 mesh sieve to obtain modified attapulgite-polyacrylamide composite hydrogel. S3: Crush humus, vermiculite, perlite, zeolite powder, and coconut coir separately and pass them through a 2mm-5mm sieve. Measure them by mass percentage and add them to a horizontal mixer with the modified biochar obtained in step S1 for dry premixing. The stirring speed is 30r / min-50r / min and the time is 10min-15min to obtain a dry mixture. S4: Add the composite hydrogel obtained in step S2 to the dry mixture according to the ratio, and spray atomized water accounting for 15%-25% of the dry mixture mass. Wet mix in a twin-screw mixer at a speed of 20r / min-40r / min for 8min-12min to obtain the wet mixture. S5: Feed the wet mixture obtained in step S4 into a twin-screw extruder, control the extrusion orifice diameter to be 4mm-6mm, the pellet length to be 5mm-10mm, and the extrusion pressure to be 2MPa-4MPa to obtain pellet blanks. S6: Place the granular blank in a fluidized bed dryer, control the inlet air temperature to 40℃-50℃ and the material residence time to 15min-25min, and perform low-temperature curing and drying to the set moisture content to obtain dried granules; S7: Mix the mycorrhizal fungi agent and nitrogen-fixing bacteria agent according to the mass ratio, and spray them evenly onto the surface of the dried particles obtained in step S6. The inoculation amount should be such that the final mass percentage of the mycorrhizal fungi agent and nitrogen-fixing bacteria agent in the finished soil reaches the range described in claim 1. Then, air dry under sterile conditions to the set moisture content to obtain the finished sponge-type garden soil.

8. The method for preparing a high water-holding capacity sponge-type garden soil according to claim 7, characterized in that: In the low-temperature curing and drying process described in step S6, the outlet air temperature of the fluidized bed dryer is controlled at 35℃-45℃, and the air velocity is 1.5m / s-2.5m / s, so as to ensure that the internal moisture gradient of the particles diffuses outward, while avoiding the carbonization of organic matter in coconut coir and humus and the collapse of the composite hydrogel network structure caused by high temperature, thus ensuring the physical strength and porous structure of the particles.

9. The method for preparing a high water-holding capacity sponge-type garden soil according to claim 7, characterized in that: Before inoculation, the mycorrhizal fungi agent and nitrogen-fixing bacteria agent described in step S7 are mixed with zeolite powder at a mass ratio of 1:3-1:5 and adsorbed for 10-15 minutes to improve the adhesion and survival rate of the agents on the particle surface.

10. The method for preparing a high water-holding capacity sponge-type garden soil according to claim 7, characterized in that: The preparation method further includes, after step S7: the finished sponge-type garden soil is left to stand in a curing room at a temperature of 15℃-25℃ and a relative humidity of 50%-65% for 24h-48h to allow the microbial agent to form a stable biofilm layer on the surface of the particles, and then sealed and packaged.

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