Method for preparing seedling substrate from aquatic plant residues

Abstract

The invention discloses a method for preparing a seedling substrate by using aquatic plant residues, and belongs to the crossing field of agricultural waste recycling and environmental protection technologies. According to the method, aquatic plant residues are innovatively separated into two independent material flows, namely solid matters and squeezed liquid, through mechanical squeezing; then, according to the fundamental difference of physical and chemical characteristics of the two, two optimal conversion paths of'oxygen-limited catalytic carbonization 'and'complex microbial inoculant directional fermentation' are respectively designed; finally, functional products (biochar and organic liquid fertilizer) obtained through conversion are integrated in a granulation link, and a uniform and high-performance seedling culture substrate product is created. The core value of the invention lies in that full-quantization and high-value utilization of wastes is realized, and a complete technical closed loop without secondary pollution and with recyclable resources is formed.

Description

Technical Field

[0001] This invention relates to the intersection of agricultural waste resource utilization and environmental protection technology, specifically to a recycling method that simultaneously transforms aquatic plant residues generated from eutrophic water bodies into high-value-added biochar and specialized seedling substrate through an innovative process. Background Technology

[0002] Biochar, as a stable carbon-rich material, has great potential in soil improvement and carbon sequestration. Seedling substrates are the foundation of modern agricultural seedling cultivation, and their quality directly affects the robustness of seedlings. Currently, high-quality seedling substrates largely rely on peat moss, but peat moss extraction severely damages wetland ecosystems.

[0003] While there are reports on the preparation of biochar or substrates using crop straw in existing technologies, there is limited research on aquatic plant residues with high water content, high fiber, and rich in nutrients such as nitrogen, phosphorus, and potassium, and these studies generally suffer from the following shortcomings: (1) High energy consumption for drying: Aquatic plants usually have a water content of over 90%, and the energy consumption for direct carbonization or incineration is huge.

[0004] (2) Incomplete utilization of components: Existing methods often only focus on the utilization of solid parts (such as charcoal production), while ignoring the large amount of nitrogen, phosphorus, potassium and organic matter contained in the pressing liquid. If these liquids are discharged directly, they will cause secondary pollution of water bodies.

[0005] (3) Single product function: Usually only biochar or only substrate is produced, failing to maximize value.

[0006] (4) Low process coupling: lack of systematic and closed-loop process design that synergistically transforms the solid and liquid parts into two high-value products.

[0007] Floating aquatic plants (such as water hyacinth, water hyacinth, duckweed, and azolla) have the following advantages in preparing seedling substrates compared to traditional crop straw, emergent, floating-leaved, or submerged plant residues: (1) High mineral-organic ratio and fast nutrient availability: Floating plants grow rapidly and can absorb 1.5–3 times more nitrogen, phosphorus and potassium per unit time than emergent plants; dry nitrogen 2.5–4.2%, potassium oxide 3–5%, ash yield 15–25%, which is significantly higher than that of reeds, cattails and other straws.

[0008] (2) Low degree of lignification, low energy consumption for granulation and high molding rate: The cellulose / lignin ratio is about 1.2–1.8. After crushing, the fibers are flexible and micropores are easily formed inside the particles.

[0009] (3) Natural spongy aerenchyma: The petiole or the underside of the leaf has air sacs, and the dry matter volume density is only 60–90 kg m³.-3 By producing 3–5 mm particles, a “lightweight aggregate” structure with a total porosity of 65–75% and an air porosity of 15–20% can be obtained, which can directly improve the weaknesses of wetland clay soils such as easy compaction and lack of oxygen.

[0010] (4) Rich in organic acids and plant hormones, promoting root growth and inhibiting disease: duckweed, azolla, etc. contain free amino acids, gibberellins and auxin-like substances.

[0011] (5) Heavy metals have been “absorbed first and then fixed”, reducing the risk of secondary release from wetlands: floating plants have high enrichment coefficients for Cd, Pb and Zn, but low-temperature carbonization (350–400 ℃) can convert 70–85% of heavy metals into residues; the heavy metal concentration in the leachate of granular matrix is ​​lower than the limit of the “Standard for Pollutant Control of Agricultural Sludge”, while reed-cattail matrix still requires additional passivating agents.

[0012] (6) Raw materials are concentrated and easy to harvest, and can be supplied continuously throughout the year: The cost of harvesting 1 ton of fresh material by mechanized water surface is approximately RMB 60–80, and it can avoid the seasonal gap problem of emergent plants withering in winter and submerged plants being difficult to harvest, thus providing stable raw materials for large-scale substrate plants.

[0013] (7) Ecological and engineering benefits: For every 1 t of floating plant particle substrate produced, approximately 4–6 kg N and 0.4–0.7 kg P can be removed from the water body simultaneously, realizing a closed loop of "water purification - substrate products - wetland reuse", while traditional plant residues often need to be piled up externally or treated additionally.

[0014] Furthermore, with the increasing severity of eutrophication, aquatic plants such as water hyacinth and algae have proliferated uncontrollably, making the removal and disposal of these plant remains a challenging environmental task. Currently, the main disposal methods include landfilling, composting, and direct incineration, which suffer from problems such as land occupation, secondary pollution, low resource utilization efficiency, and high costs. Therefore, developing a new method for the simultaneous, comprehensive, and high-value utilization of floating aquatic plant remains is an urgent practical need with broad application prospects. Summary of the Invention

[0015] To achieve the above-mentioned technical objectives, the present invention provides a method for preparing seedling substrate using aquatic plant residues, comprising the following steps: (1) Raw material pretreatment and component separation: The aquatic plant residues are separated into solids and liquids by mechanical pressing to obtain solids and pressing liquid; (2) Preparation of biochar: The solid is heated to 350-450°C at a heating rate of 5-15°C / min under inert gas protection, carbonized for 30-90 minutes and then cooled to obtain biochar; (3) Directional fermentation of press liquid: Add compound microbial agent to the press liquid at an inoculation rate of 1% to 3%, and aerobic ferment for 5 to 7 days at 30 to 37°C and an aeration rate of 0.2 to 0.5 L / (L·min) to obtain organic liquid fertilizer; (4) Integrated preparation of seedling substrate: After the primary biochar is crushed and sieved, it is mixed with the organic liquid fertilizer, binder, water-retaining agent, mineral nutrient agent and physical regulator, and finally granulated and dried to obtain granular seedling substrate.

[0016] Furthermore, the moisture content of the solids is 50%-65%.

[0017] The inert gas mentioned in step (2) is nitrogen; the specific surface area of ​​the biochar is 250~500 m². 2 / g; The biochar preparation method further includes adding ferric chloride metal salt as a catalyst at a mass ratio of 1% to 5% before carbonization to adjust the pore structure of the biochar.

[0018] Furthermore, the compound microbial agent described in step (3) includes photosynthetic bacteria, lactic acid bacteria, and yeast.

[0019] Furthermore, the compound microbial agent comprises photosynthetic bacteria: lactic acid bacteria: yeast = 2:1:1.

[0020] Further, the method for preparing the seedling substrate in step (4) is as follows: according to the dry basis mass fraction, take 30-50 parts of the biochar powder, 20-40 parts of the organic liquid fertilizer, 5-10 parts of binder, 1-3 parts of water-retaining agent and 5-15 parts of mineral nutrients and physical regulators and place them in a mixer to mix thoroughly. Then, send the uniformly mixed wet material into an extrusion granulator to make spherical particles. Finally, dry the particles at a low temperature of 60-80℃ to obtain the seedling substrate.

[0021] Furthermore, the aquatic plant is a type of floating aquatic plant, preferably one of water hyacinth, algae, duckweed, azolla, water hyacinth, water chestnut, or water caltrop.

[0022] Furthermore, the binder is one or more of sodium carboxymethyl cellulose, modified starch, dextrin, polyvinyl alcohol, polylactic acid, or bentonite; the water-retaining agent is one or more of potassium polyacrylate or sodium polyacrylate; and the mineral nutrients and physical regulators are one or more of vermiculite and perlite mixture, zeolite, ceramsite, volcanic rock, fine sand, akadama clay, or rock wool particles.

[0023] Another object of the present invention is to provide a granular seedling substrate comprising the biochar, organic nutrients from the organic liquid fertilizer, and compound beneficial microorganisms.

[0024] Furthermore, the moisture content of the seedling substrate particles is <12%; the particle size of the seedling substrate particles is 5~10mm.

[0025] The substrate provided by this invention has the inherent ability to slow-release nutrients, promote growth and disease resistance, and improve the rhizosphere environment, and can be applied in wetland planting soil layers.

[0026] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) True closed-loop recycling and full utilization: This invention innovatively transforms the solid and liquid phases generated during the treatment process into high-value products, realizing the "complete utilization" of aquatic plant residues, with no secondary waste generated, forming a perfect environmental closed loop.

[0027] (2) Significant energy and cost benefits: By mechanically dehydrating the raw material, the moisture content is reduced to a suitable range for direct carbonization, avoiding the high-energy-consuming drying step in the traditional process and greatly reducing production costs.

[0028] (3) Product synergistic effect: The seedling substrate prepared by this invention is not a simple physical mixture. Its innovation lies in: using biochar with rich pore structure as "skeleton" and "micro warehouse", the active nutrients and beneficial microorganisms in the fermented liquid fertilizer are loaded into the pores of the carbon through granulation process, realizing the slow release of nutrients and regulation of rhizosphere microecology. Its growth promotion and disease resistance effects are far superior to ordinary substrates.

[0029] (4) Strong process innovation: The two technical paths of "oxygen-limited carbonization" and "directional fermentation" are organically combined and ultimately integrated into one product. The process design is unique and highly coupled, forming a complete and creative technical solution.

[0030] (5) Dual environmental benefits: It not only absorbs water pollution sources (aquatic plants), but also produces an environmentally friendly seedling substrate that can replace peat moss, thus protecting wetland resources. At the same time, biochar itself has the far-reaching significance of carbon sequestration and emission reduction. Attached Figure Description

[0031] Figure 1 Flowchart of a method for preparing seedling substrate using aquatic plant residues. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. The specific embodiments described herein are for illustrative purposes only and are not intended to limit the invention.

[0033] Example 1 This example provides a method for preparing seedling substrate using water hyacinth.

[0034] (1) Raw material pretreatment and component separation: Freshly harvested aquatic plant remains, such as water hyacinth, are mechanically dehydrated using a twin-screw press or a plate and frame press. The pressing pressure is controlled to maintain a moisture content of 50%-65% in the solids after pressing. This step achieves solid-liquid separation, yielding solids easily charred and a pressing liquor rich in soluble nutrients.

[0035] (2) Biochar preparation: The solid obtained in step (1) was directly fed into a continuous carbonization furnace. Under nitrogen protection, the temperature was programmed to rise to a lower carbonization temperature of 400℃ at a heating rate of 10℃ / min and held for 60 minutes. This low-temperature, slow carbonization process helps to form a rich mesoporous structure and retains the potassium, calcium, and other mineral components in the plant to the greatest extent. To further regulate the pore structure, ferric chloride and other metal salts can be added as catalysts at a mass ratio of 2% before carbonization. After carbonization, the material was cooled to room temperature under anaerobic conditions to obtain primary biochar with a high specific surface area and rich mineral nutrients. The physical structure characteristics are shown in Table 1. The main mineral elements detected by X-ray fluorescence spectroscopy (XRF analysis) are shown in Table 2. The available nutrients detected by inductively coupled plasma optical emission spectroscopy (ICP-OES analysis) are shown in Table 3.

[0036] Table 1 Physical Structure As can be seen from Table 1, the primary biochar prepared from the solids after pressing water hyacinth has a well-developed pore structure, which is conducive to adsorption and microbial attachment; the pore volume is large, which has a strong water and fertilizer retention capacity; and the pores are mainly mesoporous (2-50nm), which is suitable for nutrient transport and maintaining ideal enzyme activity.

[0037] Table 2 Major Mineral Elements As shown in Table 2, the primary biochar prepared from the solids after pressing water hyacinth is highly enriched in potassium, making it a good potassium source; it also contains a relatively high amount of calcium, which is beneficial for plant cell wall formation, and phosphorus, which is essential for plants; in addition, it contains iron from the raw materials and FeCl3 catalyst, as well as magnesium, a core element of chlorophyll.

[0038] Table 3 Available Nutrients As can be seen from Table 3, the primary biochar prepared from the solids after pressing water hyacinth has an extremely high content of available potassium, which is easily utilized by plants, and is rich in exchangeable calcium and has good availability of the trace element iron.

[0039] (3) Directional fermentation of press liquor: In the press liquor collected in step (1), a compound microbial agent (preferably a compound microbial community of photosynthetic bacteria: lactic acid bacteria: yeast = 2:1:1) is added at an inoculation rate of 2%. Aerobic fermentation is carried out at 35°C with an aeration rate of 0.3 L / (L•min) for 6 days. This process rapidly converts small-molecule sugars and proteins in the press liquor into active substances such as amino acids, organic acids, vitamins, and plant hormones (e.g., IAA), while simultaneously inhibiting the growth of putrefactive bacteria, eliminating odor, and yielding a highly active organic liquid fertilizer.

[0040] (4) Integrated preparation of seedling substrate: The primary biochar obtained in step (1) is crushed and passed through a 20-mesh sieve. Then, based on dry weight, 45 parts of biochar powder, 35 parts of organic liquid fertilizer obtained in step (3) (converted to dry matter), 8 parts of sodium carboxymethyl cellulose (binder), 2 parts of potassium polyacrylate (water-retaining agent), and 10 parts of a mixture of vermiculite and perlite (mineral nutrients and physical regulators) are placed in a mixer and thoroughly mixed. The uniformly mixed wet material is fed into an extrusion granulator to produce spherical particles with a diameter of 5-10 mm. Finally, the particles are dried at a low temperature of 60-80°C until the moisture content is below 12%, thus obtaining the final product of this invention—a granular seedling substrate rich in biochar, organic nutrients, and beneficial microorganisms, which is then applied to the wetland planting soil layer.

[0041] Example 2 This example provides a method for preparing seedling substrate using macroalgae.

[0042] (1) Raw material pretreatment and component separation: Freshly harvested aquatic plant remains, including large algae, are mechanically dehydrated using a twin-screw press or a plate and frame press. The pressing pressure is controlled to maintain a solids content of 50%-65%. This step achieves solid-liquid separation, yielding a solids product easily charred and a pressing liquor rich in soluble nutrients.

[0043] (2) Biochar preparation: The solid obtained in step (1) was directly fed into a continuous carbonization furnace. Under nitrogen protection, the temperature was programmed to rise to a lower carbonization temperature of 350°C at a heating rate of 5°C / min and held for 30 minutes. This low-temperature, slow carbonization process helps to form a rich mesoporous structure and retains the potassium, calcium, and other mineral components in the plant to the greatest extent. To further regulate the pore structure, ferric chloride and other metal salts can be added as catalysts at a mass ratio of 5% before carbonization. After carbonization, the material was cooled to room temperature under anaerobic conditions to obtain primary biochar with a high specific surface area and rich mineral nutrients. The physical structure characteristics are shown in Table 4. The main mineral elements detected by X-ray fluorescence spectroscopy (XRF analysis) are shown in Table 5. The available nutrients detected by inductively coupled plasma optical emission spectroscopy (ICP-OES analysis) are shown in Table 6.

[0044] Table 4 Physical Structure As can be seen from Table 4, the primary biochar prepared from the solids after pressing of algae has a larger specific surface area and pore volume compared with the water hyacinth biochar in Example 1. This is beneficial for adsorption and microbial attachment and has a stronger water and fertilizer retention capacity. This is due to the milder pyrolysis conditions and the structure of algae itself. The pore size is more concentrated at the small pore end of the mesopores, and the proportion of micropores is increased, which is beneficial for the adsorption of small molecule pollutants.

[0045] Table 5 Major Mineral Elements As shown in Table 5, the primary biochar prepared from the solids after pressing of algae is extremely rich in potassium, moderate in calcium, and high in phosphorus, indicating that algae can efficiently enrich potassium and phosphorus in water. Furthermore, the biochar also contains high levels of iron and magnesium. The iron mainly originates from magnetic iron oxide generated by the high-proportion addition of FeCl3 catalyst, endowing the biochar with potential magnetic separation and recovery or catalytic properties.

[0046] Table 6. Available Nutrients As can be seen from Table 6, the contents of available potassium, phosphorus and iron are all high, indicating that the primary biochar prepared from the solids after pressing algae has a large potential for potassium release. The available iron can not only be used as a nutrient, but its catalytic properties may also affect the rhizosphere microenvironment.

[0047] (3) Directional fermentation of press liquor: In the press liquor collected in step (1), a compound microbial agent (preferably a compound microbial community of photosynthetic bacteria: lactic acid bacteria: yeast = 2:1:1) is added at an inoculation rate of 3%. Aerobic fermentation is carried out at 37°C with an aeration rate of 0.2 L / (L•min) for 7 days. This process rapidly converts small-molecule sugars and proteins in the press liquor into active substances such as amino acids, organic acids, vitamins, and plant hormones (such as IAA), while simultaneously inhibiting the growth of putrefactive bacteria, eliminating odor, and yielding a highly active organic liquid fertilizer.

[0048] (4) Integrated preparation of seedling substrate: The primary biochar obtained in step (1) is crushed and passed through a 20-mesh sieve. Then, based on dry weight, 40 parts of biochar powder, 40 parts of organic liquid fertilizer obtained in step (3) (converted to dry matter), 5 parts of sodium carboxymethyl cellulose (binder), 3 parts of potassium polyacrylate (water-retaining agent), and 12 parts of a mixture of vermiculite and perlite (mineral nutrients and physical regulators) are placed in a mixer and thoroughly mixed. The uniformly mixed wet material is fed into an extrusion granulator to produce spherical particles with a diameter of 5-10 mm. Finally, the particles are dried at a low temperature of 60-80°C until the moisture content is below 12%, thus obtaining the final product of this invention—a granular seedling substrate rich in biochar, organic nutrients, and beneficial microorganisms, which is then applied to the wetland planting soil layer.

[0049] Example 3 This example provides a method for preparing seedling substrate using Azolla annua.

[0050] (1) Raw material pretreatment and component separation: Freshly harvested aquatic plant remains (Azolla) are fed into a twin-screw press or plate and frame press for mechanical dehydration. The pressing pressure is controlled to maintain a moisture content of 50%-65% in the solids after pressing. This step achieves solid-liquid separation, yielding solids easily charred and a pressing liquor rich in soluble nutrients.

[0051] (2) Biochar preparation: The solid obtained in step (1) was directly fed into a continuous carbonization furnace. Under nitrogen protection, the temperature was programmed to rise to a lower carbonization temperature of 450°C at a heating rate of 15°C / min and held for 90 minutes. This low-temperature, slow carbonization process helps to form a rich mesoporous structure and retains potassium, calcium, and other mineral components in the plant to the greatest extent. To further regulate the pore structure, ferric chloride and other metal salts can be added as catalysts at a mass ratio of 1% to 5% before carbonization. After carbonization, the material was cooled to room temperature under anaerobic conditions to obtain primary biochar with a high specific surface area and rich mineral nutrients. The physical structure characteristics are shown in Table 7. The main mineral elements detected by X-ray fluorescence spectroscopy (XRF analysis) are shown in Table 8. The available nutrients detected by inductively coupled plasma optical emission spectroscopy (ICP-OES analysis) are shown in Table 9.

[0052] Table 7 Physical Structure As shown in Table 7, due to the dense plant structure and high pyrolysis temperature of Azolla oblongata, the primary biochar prepared from its pressed solids has a suitable specific surface area and pore volume, meeting the basic requirements for substrate aeration and water retention. Furthermore, the pore size distribution is biased towards the larger pore ends of the mesopores, which is beneficial for the rapid transport of water and nutrients.

[0053] Table 8 Major Mineral Elements As shown in Table 8, this biochar is rich in potassium, making it a good potassium source, and has a high calcium content, which helps stabilize the substrate structure and facilitate plant utilization. Furthermore, due to the highly efficient absorption and enrichment of phosphorus in water by Azolla, its phosphorus content is very high. The addition of catalysts and the enrichment of raw materials also result in a high iron content. Iron, as a key component of nitrogenase, may affect the rhizosphere nitrogen cycle.

[0054] Table 9. Available Nutrients As shown in Table 9, the available potassium, phosphorus, and iron contents are all high, indicating that the primary biochar prepared from the solids after pressing of *Azolla officinalis* has a significant potassium release potential. The available iron can not only serve as a nutrient, but its catalytic properties may also influence the rhizosphere microenvironment. The content of alkaline-soluble nitrogen (slow-release nitrogen) is significant, which is its core value as "nitrogen-rich biochar," providing nitrogen slowly and sustainably.

[0055] (3) Directional fermentation of press liquor: In the press liquor collected in step (1), a compound microbial agent (preferably a compound microbial community of photosynthetic bacteria: lactic acid bacteria: yeast = 2:1:1) is added at an inoculation rate of 1%. Aerobic fermentation is carried out for 5 days at 30°C with an aeration rate of 0.5 L / (L•min). This process rapidly converts small-molecule sugars and proteins in the press liquor into active substances such as amino acids, organic acids, vitamins, and plant hormones (such as IAA), while simultaneously inhibiting the growth of putrefactive bacteria, eliminating odor, and yielding a highly active organic liquid fertilizer.

[0056] (4) Integrated preparation of seedling substrate: The primary biochar obtained in step (1) is crushed and passed through a 20-mesh sieve. Then, based on dry weight, 50 parts of biochar powder, 27 parts of organic liquid fertilizer obtained in step (3) (converted to dry matter), 10 parts of sodium carboxymethyl cellulose (binder), 3 parts of potassium polyacrylate (water-retaining agent), and 10 parts of a mixture of vermiculite and perlite (mineral nutrients and physical regulators) are placed in a mixer and thoroughly mixed. The uniformly mixed wet material is fed into an extrusion granulator to produce spherical particles with a diameter of 5-10 mm. Finally, the particles are dried at a low temperature of 60-80°C until the moisture content is below 12%, thus obtaining the final product of this invention—a granular seedling substrate rich in biochar, organic nutrients, and beneficial microorganisms, which is then applied to the wetland planting soil layer.

[0057] Table 10 Heavy metal analysis of particulate matrix leachates from Examples 1-3 Comparative Example 1 Based on Example 1, the compound microbial agent was replaced with (preferably photosynthetic bacteria), and the other steps were the same as in Example 1.

[0058] Comparative Example 2 Based on Example 1, the compound microbial agent was replaced with (preferably lactic acid bacteria), and the other steps were the same as in Example 1.

[0059] Comparative Example 3 Based on Example 1, the compound microbial agent was replaced with yeast (preferably), and the other steps were the same as in Example 1.

[0060] Comparative Example 4 Compared to Example 1, where the solids were not carbonized, the solids were crushed and passed through a 20-mesh sieve. Then, based on dry weight, 45 parts of the solids, 35 parts of the organic liquid fertilizer obtained in step (3) (converted to dry matter), 8 parts of sodium carboxymethyl cellulose (binder), 2 parts of potassium polyacrylate (water-retaining agent), and 10 parts of a mixture of vermiculite and perlite (mineral nutrients and physical regulators) were placed in a mixer and thoroughly mixed. The uniformly mixed wet material was fed into an extrusion granulator to produce spherical granules with a diameter of 5-10 mm. Finally, the granules were dried at a low temperature of 60-80°C until the moisture content was below 12%, thus obtaining granular seedling substrate, which was then applied to the wetland planting soil layer.

[0061] Table 11 Components of pre-fermentation pressing liquid and organic liquid fertilizer Table 12 shows the differences in germination rate, seedling height, root length, biomass, and survival rate when the organic liquid fertilizer and the pre-fermentation pressed liquid of Example 1, after being granulated with a mixture of biochar, binder, water-retaining agent, vermiculite, and perlite, are used as seedling substrates. As can be seen from the table, in Example 1, the seedling germination rate, seedling height, root length, aboveground fresh weight, and root fresh weight are all relatively high, and the survival rate is 100%, indicating that it has a very good application effect in wetland planting.

[0062] Table 12 Although the above embodiments have described the present invention and its implementation in detail, it should be noted that for those skilled in the art, any changes, modifications, substitutions, combinations, simplifications, etc., made to the corresponding conditions without departing from the technical principles of the present invention should be considered as equivalent substitutions, and these improvements should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a seedling substrate using aquatic plant residues, characterized by, The method comprises the following steps: (1) raw material pretreatment and component separation: solid-liquid separation of aquatic plant residues by mechanical pressing to obtain solid and pressed liquid; (2) preparation of biochar: heating the solid to 350-450 DEG C at a heating rate of 5-15 DEG C / min under inert gas protection, holding carbonization and cooling to obtain biochar; (3) directional fermentation of pressed liquid: adding a compound microbial inoculant to the pressed liquid at an inoculation amount of 1-3%, and carrying out aerobic fermentation at 30-37 DEG C and a ventilation amount of 0.2-0.5 L / (L·min) for 5-7 days to prepare an organic liquid fertilizer; (4) integrated preparation of seedling substrate: crushing and sieving the primary biochar, mixing the organic liquid fertilizer, adhesive, water-retaining agent, mineral nutrient agent and physical adjusting agent, and finally granulating and drying to obtain a granular seedling substrate.

2. The method of claim 1, wherein, The solid in step (1) has a moisture content of 50-65%.

3. The method of claim 1, wherein, The inert gas in step (2) is nitrogen; the specific surface area of the biochar is 250-500 m 2 / g; the biochar preparation method further comprises adding 1%-5% of iron chloride metal salt as a catalyst to adjust the pore structure of the biochar before carbonization.

4. The method of claim 1, wherein, The compound microbial inoculant in step (3) comprises photosynthetic bacteria, lactic acid bacteria and yeast.

5. The method of claim 1, wherein, The seedling substrate preparation method in step (4) is as follows: taking 30-50 parts of the biochar powder, 20-40 parts of the organic liquid fertilizer, 5-10 parts of adhesive, 1-3 parts of water-retaining agent and 5-15 parts of mineral nutrient agent and physical adjusting agent based on the dry mass, fully stirring and mixing in a mixer, then feeding the uniformly mixed wet material into an extrusion granulator to form spherical particles, and finally drying the particles at a low temperature of 60-80 DEG C to obtain the seedling substrate.

6. The method of claim 1, wherein, The aquatic plant is one of floating aquatic plants, preferably one of Eichhornia crassipes, macroalga, duckweed, Azolla filiculoides, Salvinia molesta, Trapo-natia dodecandra or Nymphoides peltatum.

7. The method of claim 1, wherein, The adhesive is one or more of sodium carboxymethyl cellulose, modified starch, dextrin, polyvinyl alcohol, polylactic acid or bentonite; the water-retaining agent is one or more of potassium polyacrylate or sodium polyacrylate; and the mineral nutrient agent and physical adjusting agent are one or more of a mixture of vermiculite and perlite, zeolite, ceramic ball, volcanic rock, fine sand, red soil or rock wool particles.

8. A granular nursery substrate, characterized in that, The substrate granules have a moisture content of <12%, and a particle size of 5-10 mm.

9. The substrate of claim 8, wherein, The substrate has the intrinsic abilities of slow-release nutrient, disease resistance and rhizosphere environment improvement, and can be applied in a wetland planting soil layer.

10. The substrate of claim 8, wherein, ​

Images