A broad-spectrum biochar-hydrogel composite modifier, its preparation method and application

Abstract

This invention discloses a broad-spectrum biochar-hydrogel composite modifier, its preparation method, and its application. Using agricultural and forestry waste such as sorghum straw and rice husks as raw materials, biochar is obtained through oxygen-limited pyrolysis. After modification with polybasic acids and ultrasonic-assisted activation, it is combined with a composite hydrogel, nitrogen, phosphorus, and potassium-humic acid-chelated trace element nutrients, and betaine-seaweed extract-type stress-resistance adjuvants. This is achieved through an "in-situ polymerization-physical cross-linking cycle" to form a layered synergistic structure. The product has a compressive strength ≥15N, a water absorption rate ≥300%, and a biodegradation rate ≥30% after 120 days of burial. It is suitable for improving marginal farmland such as saline-alkali land and sandy soil. The application rate is 80-180 kg / mu, applied as basal fertilizer, in strips, or in holes. It can improve soil structure, enhance fertility and crop stress resistance, and contribute to improving farmland quality.

Description

Technical Field

[0001] This invention belongs to the field of soil improvement technology, and in particular relates to a broad-spectrum biochar-hydrogel composite amendment, its preparation method and application. Background Technology

[0002] Marginal arable land, including saline-alkali land, sandy soil, acidic soil, and soil with slight heavy metal pollution, is widely distributed and accounts for a high proportion of my country's arable land resources. These types of arable land generally suffer from common problems such as loose or compacted soil structure, unbalanced pore structure, and weak water and fertilizer retention capacity. They are also accompanied by problems such as soil nutrient deficiency and supply imbalance, poor crop growth resistance, and some arable land also has excessive levels of available heavy metals. These problems seriously restrict the normal growth and development of crops, reduce the efficiency of arable land resource utilization, and become an important constraint on improving the quality and efficiency of agriculture.

[0003] To improve the quality of marginal farmland, current technologies often employ single biochar, hydrogels, or chemical amendments for soil improvement. However, each type of single amendment has significant functional limitations: biochar, with its porous structure, possesses certain adsorption and fertilizer retention capabilities, but its surface functional groups are limited, resulting in insufficient water retention stability. When applied alone, it is prone to pore blockage and rapid attenuation of its improvement effect. While hydrogels have excellent water retention properties, they suffer from low mechanical strength and rapid degradation in soil. Furthermore, their nutrient carrying capacity and slow-release capabilities are weak, failing to provide long-term nutrient supply. Traditional chemical amendments can only achieve single soil physicochemical property regulation, making it difficult to simultaneously address the comprehensive needs of soil structure repair, long-term nutrient supply, and crop stress resistance enhancement. They also have limited passivation effects on heavy metals in the soil and are prone to causing secondary soil pollution.

[0004] Based on this, some biochar-hydrogel composite amendments have emerged in existing technologies, but they still have many technical shortcomings and are difficult to adapt to the complex and variable soil environment of marginal farmland: First, some composite amendments only focus on a single amendment function, such as enhancing water retention or adjusting soil pH, without achieving the synergistic effects of water and fertilizer retention, heavy metal passivation, and crop stress resistance enhancement. Furthermore, the nutrient release rate is poorly designed and cannot match the nutrient requirements of crops at different growth stages. Second, existing composite amendments use only one modification method for biochar, failing to optimize its surface structure through multiple modification and activation methods, resulting in poor biochar-hydrogel properties. The components have poor compatibility, making it difficult for them to form a stable composite structure. The product is prone to structural dissociation in the soil, resulting in unstable improvement effects. Third, existing products do not specifically combine compound nutrient components and stress-resistant adjuvants, or only add single nutrient elements or single stress-resistant components, which cannot fully meet the nutritional needs of crop growth, nor can they effectively improve the stress resistance of crops in marginal cultivated land. Fourth, existing compound soil conditioners have poor broad-spectrum applicability, and can only be adapted to a certain type of marginal cultivated land. They cannot simultaneously meet the improvement needs of saline-alkali land, sandy soil, acidic soil, and cultivated land with slight heavy metal pollution, making it difficult to achieve a synergistic effect of soil improvement and crop yield increase.

[0005] In summary, given the technical shortcomings of existing soil conditioners, such as limited functionality, poor component compatibility, insufficient structural stability, and unsatisfactory broad-spectrum and comprehensive improvement effects, there is an urgent need to develop a broad-spectrum biochar-hydrogel composite conditioner, its preparation method, and its application. By optimizing the biochar modification process, constructing a stable biochar-hydrogel composite structure, and combining it with suitable nutrient components and stress-resistance adjuvants to form a synergistic improvement system, this approach can simultaneously enhance the water and fertilizer retention capacity of marginal farmland, repair soil structure, provide long-term nutrient supply, strengthen crop stress resistance, and passivate heavy metals. This would provide an efficient and feasible technical solution for the comprehensive improvement of various types of marginal farmland. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention provides a broad-spectrum biochar-hydrogel composite modifier, its preparation method, and its application. It forms a layered synergistic structure through an "in-situ polymerization-physical cross-linking cycle," a process that is environmentally friendly and feasible. It is broadly adaptable to various marginal farmland improvement projects, including saline-alkali land and sandy soil, and offers benefits such as water and fertilizer retention, soil structure improvement, and enhanced crop resistance. Furthermore, the product is biodegradable, easy to apply, and conducive to industrialization and promotion.

[0007] The technical solution adopted in this invention is: A broad-spectrum biochar-hydrogel composite modifier uses agricultural waste-based biochar as a carrier, which is modified with a polybasic acid composite modifier and activated with ultrasound assistance. It is then cyclically composited with a composite hydrogel, nutrient components, and stress-resistance additives through in-situ polymerization and physical cross-linking. The modifier's components, by weight, are: 35-45 parts modified biochar, 18-25 parts composite hydrogel, 15-22 parts nutrient components, and 3-6 parts stress-resistance additives. The modifier consists of particles with a particle size of 1-4 mm. Its compressive strength is ≥15N, water absorption is ≥300%, moisture content is ≤3%, and biodegradability after 120 days of burial is ≥30%. The composite hydrogel is selected from carboxymethyl cellulose-sodium citrate composite hydrogel, polyvinyl alcohol-acrylamide-Tween 80 composite hydrogel or poly(N-isopropylacrylamide-chitosan) composite hydrogel. The nutrient components include nitrogen, phosphorus and potassium nutrients, humic acid and chelated trace elements. The stress resistance agent is composed of betaine, proline, seaweed extract and silicate.

[0008] Furthermore, the agricultural waste-based biochar is derived from biomass waste and obtained through oxygen-limited pyrolysis. The pyrolysis procedure is as follows: heating from room temperature to 105-115℃ and holding for 10-15 minutes, then heating to 175-185℃ and holding for 10-15 minutes, and finally heating to 450-750℃ and holding for 30-60 minutes, with a total heating rate of 3-5℃ / min. The biochar particle size after pyrolysis is ≤150μm. The polybasic acid composite modifier is an aqueous solution of at least two inorganic or organic acids with a total mass fraction of 40-60wt%. The binary inorganic / organic acid is mixed at a mass ratio of 1:0.5-1.5, and the ternary inorganic / organic acid is mixed at a mass ratio of 1:(0.5-1.5):(0.3-1.2). The specific surface area of ​​the modified biochar is 200-350m². 2 / g, pore size 2~100nm, pore volume 0.3~0.8cm³ 3 / g.

[0009] Furthermore, the polyacid composite modifier is a mixture of phosphoric acid, citric acid, and maleic acid, which are mixed in the above order at a mass ratio of 1:(0.8~1.5):(0.5~1.2); the biomass waste is at least one of sorghum stalks, rice husks, corn stalks, or vegetable stalks.

[0010] Furthermore, the nutrient components include nitrogen, phosphorus, and potassium nutrients, humic acid, and chelated trace elements, wherein the mass ratio of nitrogen, phosphorus, and potassium is (1.5~2.5):(1~1.8):(1~1.8), and the chelated trace elements are EDTA chelated iron, EDTA chelated zinc, EDTA chelated manganese, and sugar alcohol chelated boron, and the total content of chelated trace elements is 0.5~3% of the total mass of the nutrient components.

[0011] Furthermore, the stress-resistant adjuvant is composed of betaine, proline, seaweed extract, and silicate in the above order at a mass ratio of 1:(0.5~1):(0.3~0.8):(0.5~1.2); the silicate has a specific surface area of ​​520~700 m². 2 / g of sepiolite powder or a specific surface area ≥500m² 2 / g of acid-modified or phosphorus-modified zeolite powder, wherein the seaweed extract contains ≥30% seaweed polysaccharide.

[0012] A method for preparing a broad-spectrum biochar-hydrogel composite modifier as described above, wherein the modified biochar, composite hydrogel polymer monomer, nutrient components, and stress-resistant additives are fed in the order described above in a mass ratio of 35~45:18~25:15~22:3~6, including the following steps: (1) Biochar composite modification: agricultural waste-based biochar and polyacid composite modifier are mixed at a mass-volume ratio of 1:(8~12)g / mL, stirred at 65~85℃ for 3~5h, and after 1h of reaction, subjected to ultrasonic assisted treatment at 300~500W for 20~30min. After the reaction is completed, the mixture is washed to pH 6.0~8.0 and vacuum dried at 80~105℃ for 4~6h to obtain modified biochar; Nutrient loading: Dissolve the nutrient components in deionized water to prepare a 5-10 wt% solution, add modified biochar, the mass-to-volume ratio of modified biochar to nutrient solution is 1:(5-8) g / mL, adsorb at a constant temperature of 35-45℃ for 5-7 h, and dry at 60-70℃ with forced air until the water content is ≤5%; Hydrogel network construction: The polymer monomers and crosslinking agents of the composite hydrogel are mixed with the product of step (2), an initiator is added, and prepolymerization is carried out at 55~65℃ for 2~3h under nitrogen protection. Then, the composite is formed by physical crosslinking cycle treatment of "freezing at -20℃ for 16h and thawing at room temperature for 8h" three times. Composite molding: Add stress-resistant agent to the composite in step (3), stir at 600~800 rpm for 15~20 min, add wood vinegar at 0.5~1.5 wt% relative to the total mass of the composite in step (3) and stress-resistant agent as a binding agent during granulation, dry at 70~90℃ for 6~10 h, screen particles with a particle size of 1~4 mm to obtain the finished product.

[0013] Further, the physical crosslinking cycle in step (3) is a cycle of freezing at -20℃ for 16 hours and thawing at room temperature for 8 hours; the mass ratio of the total mass of the polymer monomers to the mass of the crosslinking agent is 1:(0.02~0.04), and the crosslinking agent is N,N-methylenebisacrylamide or borax; the initiator is ammonium persulfate-sodium bisulfite composite initiator, ammonium persulfate or sodium persulfate, wherein the mass ratio of the two in the ammonium persulfate-sodium bisulfite composite initiator is 1:0.5, and the amount of initiator is 1~2% of the total mass of the polymer monomers.

[0014] Furthermore, the wood vinegar is a product obtained by pyrolysis of biomass at 500~700℃, and the organic matter content in the wood vinegar is ≥80%.

[0015] Based on the above-mentioned application of the broad-spectrum biochar-hydrogel composite amendment in the improvement of marginal farmland, the marginal farmland refers to saline-alkali land, sandy soil, acidic soil, and farmland with slight heavy metal pollution.

[0016] Furthermore, the application rate of the soil conditioner is divided according to soil type: 120~180 kg / mu for saline-alkali soil, 80~120 kg / mu for sandy soil, 100~150 kg / mu for acidic soil, and 150~180 kg / mu for soil with slight heavy metal pollution; the application method is basal application, strip application or hole application, and after application, it is mixed evenly with the 0~25cm topsoil layer.

[0017] The advantages and positive effects of this invention are: 1. Environmentally friendly raw materials and improved efficiency through modification: After modification with polybasic acids and ultrasonic-assisted activation, the specific surface area of ​​agricultural waste-based biochar is increased to 200~350m² / g. Oxygen-containing functional groups such as carboxyl and hydroxyl groups are introduced to form a layered synergistic structure with the composite hydrogel. The porous structure of biochar adsorbs water and nutrients, while the hydrogel network locks in water and nutrients, significantly improving water and fertilizer retention capacity. At the same time, it realizes the resource utilization of agricultural and forestry waste, with outstanding environmental benefits.

[0018] 2. Balanced nutrition and strong stress resistance: The nutrient composition includes nitrogen, phosphorus and potassium (mass ratio 1.5~2.5:1~1.8:1~1.8), humic acid and chelated trace elements (total content 0.5~3%), and the nutrient ratio is adapted to the needs of crops; the compound stress resistance adjuvants include betaine and proline to regulate cell osmotic pressure, seaweed extract (seaweed polysaccharide ≥30%) to enhance antioxidant capacity, and silicate to improve cell wall stability. The three work together to enhance the crop's stress resistance and are suitable for various marginal cultivated lands such as saline-alkali land and sandy soil.

[0019] 3. Feasible process and convenient application: The "in-situ polymerization-physical crosslinking cycle" process is adopted, and a stable layered structure is constructed through three freeze-thaw cycles. The product has a compressive strength of ≥15N, a water absorption rate of ≥300%, and a biodegradability rate of ≥30%, meeting the performance standards. It supports basal application, strip application, or hole application, with an application rate of 80~180kg / mu. The operation is convenient and conducive to industrialization and promotion. Detailed Implementation

[0020] The technical solutions in the embodiments of this disclosure are described clearly and completely below. Obviously, the described embodiments are only some embodiments of this disclosure, and not all embodiments. Based on the embodiments in this disclosure, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this disclosure.

[0021] I. Experimental Materials and Instruments (a) Experimental materials Agricultural and forestry waste includes sorghum stalks, rice husks, corn stalks, and vegetable stalks. Sorghum stalks are crushed and passed through an 80-mesh sieve, rice husks are air-dried naturally, corn stalks are dried to a moisture content of ≤10%, and vegetable stalks are sun-dried after removing impurities for later use.

[0022] The following chemical reagents should be selected: Phosphoric acid is AR grade, with a purity of ≥99%, and was purchased from Sinopharm Chemical Reagent Co., Ltd. Citric acid is AR grade, with a purity of ≥99%, and was purchased from Shanghai Maclean Biochemical Technology Co., Ltd. Maleic acid is AR grade, with a purity of ≥99%, and was purchased from Aladdin Reagent (Shanghai) Co., Ltd. Sodium carboxymethyl cellulose is CP grade, with a viscosity range of 500~800 mPa·s, and was purchased from Shanghai Yuanye Biotechnology Co., Ltd. The polyvinyl alcohol, PVA1788, AR grade, was purchased from Sinopharm Chemical Reagent Co., Ltd.; the N-isopropylacrylamide, with a purity of 98%, was purchased from Shanghai Bid Pharmaceutical Technology Co., Ltd. Chitosan with a degree of deacetylation ≥90% was purchased from Qingdao Mingyue Seaweed Group Co., Ltd. Acrylamide, AR grade, purchased from Shanghai Lingfeng Chemical Reagent Co., Ltd. Tween 80 is AR grade and was purchased from Sinopharm Chemical Reagent Co., Ltd. The nitrogen, phosphorus and potassium nutrients include urea, potassium dihydrogen phosphate and potassium chloride, all of which are agricultural grade and purchased from Kingenta Ecological Engineering Co., Ltd. Humic acid organic matter ≥70%, purchased from Shanxi Linhai Humic Acid Technology Co., Ltd. EDTA chelated iron (Fe≥10%), EDTA chelated zinc (Zn≥15%), EDTA chelated manganese (Mn≥13%), and sugar alcohol chelated boron (B≥10%) were all purchased from Zhengzhou Ruipu Bioengineering Co., Ltd. Betaine with a purity of 98% was purchased from Shanghai Yuanye Biotechnology Co., Ltd. Proline, 99% purity, was purchased from Aladdin Reagent (Shanghai) Co., Ltd. The seaweed extract was prepared using a general method, with kelp as the raw material. Water was added at a solid-liquid ratio of 1:15-25 (g / mL), and the mixture was extracted in a water bath at 75-85℃ for 1.5-2.5 hours. After filtering through an 80-mesh filter to remove residue, the filtrate was vacuum concentrated at 60℃ and -0.08MPa until the seaweed polysaccharide content was ≥35%. It was then freeze-dried at -40℃ for 12 hours for later use. The seaweed polysaccharide content in the extract was found to be 35%-42%, and the retention rate was ≥95% after 6 months of storage. Specific preparation parameters for each example are detailed in the corresponding steps. The sepiolite powder has a specific surface area of ​​650 m². 2 / g, purchased from Hebei Hongli Sepiolite Co., Ltd.; The acid-modified zeolite powder has a specific surface area of ​​580 m². 2 / g, purchased from Zhejiang Shenshi Mining Co., Ltd.; N,N-methylenebisacrylamide was AR grade and purchased from Shanghai Maclean Biochemical Technology Co., Ltd. The borax was AR grade and purchased from Sinopharm Chemical Reagent Co., Ltd. Ammonium persulfate and sodium bisulfite are both AR grade and were purchased from Sinopharm Chemical Reagent Co., Ltd. Wood vinegar is a product of biomass pyrolysis at 600℃, with organic matter ≥82%, pH range 3.5~4.5, and organic acid content ≥15%, purchased from Jiangxi Jinkang New Material Technology Co., Ltd.

[0023] Test soil Four typical marginal farmland soils were selected for testing. Sampling followed the guidelines of "Soil Environmental Monitoring Part 1: Collection, Preservation and Preparation of Soil Samples" (HJ / T166-2004). The sampling depth was 0–25 cm. After sampling, stones, weeds, and other impurities were removed, and the samples were air-dried, crushed, and sieved through a 2 mm sieve for later use. The sampling information and physicochemical indicators are as follows: Saline-alkali soil: Sampled from Yang'erzhuang Hui Township, Huanghua City, Cangzhou City, Hebei Province (a typical distribution area of ​​coastal saline-alkali land). The soil type is coastal tidal soil. The test results showed that the pH was 8.9, the electrical conductivity was 4.2 mS / cm, the salt content was 0.39%, and the soil texture was loam. It meets the definition requirements of slightly saline-alkali land in the "Classification and Grading of Agricultural Utilization Soils in Saline-Alkali Land" (GB / T21010-2017).

[0024] Desertified soil: Sampled from Xini Town, Hangjin Banner, Ordos City, Inner Mongolia Autonomous Region (a slightly desertified farmland on the eastern edge of the Mu Us Desert); Tested, pH 7.8, field water holding capacity 18%, bulk density 1.53 g / cm³, sand content (2~0.05 mm) 79%, clay content (<0.002 mm) 8%, which are consistent with the typical physicochemical characteristics of slightly desertified soil.

[0025] Acidic soil: Sampled from Luanshan Town, Youxian County, Zhuzhou City, Hunan Province (a concentrated distribution area of ​​southern red soil); tested, pH 4.5, organic matter content 1.2%, cation exchange capacity 8.5 cmol / kg, soil texture is clay loam, which is consistent with the typical physicochemical characteristics of southern acidic red soil.

[0026] Slightly contaminated soil with heavy metals: Sampled from Huiche Town, Xixia County, Nanyang City, Henan Province (farmland surrounding lead-zinc mining area); Testing revealed Pb... 2+ Content 85mg / kg, Cd 2+ The content was 1.2 mg / kg, which met the light pollution limit (Pb≤90 mg / kg, Cd≤1.3 mg / kg) in the "Soil Environmental Quality Agricultural Land Soil Pollution Risk Control Standard (Trial)" (GB15618-2018).

[0027] Methods for detecting heavy metal content The detection of Pb²⁺ and Cd²⁺ content in the above-mentioned lightly polluted heavy metal soils followed the "Microwave Digestion Method for Total Metal Elements in Soils and Sediments" (HJ832-2017), and the specific procedure is as follows: Sample pretreatment: Weigh 0.5g (accurate to 0.0001g) of air-dried soil sample that has passed through a 100-mesh sieve, place it in a polytetrafluoroethylene digestion vessel, add 5mL of GR grade nitric acid (68%, purchased from Sinopharm Chemical Reagent Co., Ltd.) and 1mL of GR grade hydrogen peroxide (30%, purchased from Sinopharm Chemical Reagent Co., Ltd.), shake well and let stand for 30min, then place it in a microwave digester (model: Anton Paar Multiwave 3000).

[0028] Microwave digestion conditions: digestion power 1200W, heating rate 5℃ / min, heating to 180℃ and holding for 15min; after digestion, cool to room temperature, make up to 25mL with ultrapure water, filter through a 0.45μm organic filter membrane and use for later use.

[0029] Measurement and quality control: Inductively coupled plasma mass spectrometry (ICP-MS) was used for the determination. The instrument parameters were: radio frequency power 1550W, sampling depth 8mm, carrier gas flow rate 1.0L / min, and nebulizer gas pressure 0.8MPa. During the detection process, a blank control, three parallel samples, and a soil standard reference material (GBW07405) were set up. The relative standard deviation (RSD) of the parallel samples was ≤4.8%, and the recovery rate of the standard material was 93%~104%.

[0030] The test crop was maize, and the variety selected was "Zhengdan 958", which was purchased from Henan Qiule Seed Industry Technology Co., Ltd.

[0031] The instruments used in this experiment were: ultrasonic cleaner (model: KQ-500DE, Kunshan Ultrasonic Instrument Co., Ltd.); tube furnace (model: SK-G06123K, Tianjin Zhonghuan Electric Furnace Co., Ltd.); vacuum drying oven (model: DZF-6050, Shanghai Yiheng Scientific Instrument Co., Ltd.); constant temperature water bath (model: HH-S4, Jintan Huacheng Kaiyuan Experimental Instrument Factory); high-speed mixer (model: FJ200-S, Shanghai Yutong Instrument Factory); pressure testing machine (model: WE-300D, Jinan Hengsishengda Instrument Co., Ltd.); ultraviolet-visible spectrophotometer (model: UV-2). 600, Jinan Hepu Instrument Equipment Co., Ltd.); pH meter (model: PHS-3C, Shanghai Leici Instrument Factory); Inductively Coupled Plasma Mass Spectrometer (model: Agilent 7700x, Agilent Technologies); Freeze Dryer (model: LGJ-10D, Beijing Sihuan Scientific Instrument Factory); Microwave Digester (model: MARS6, CEM Corporation, USA); BET Surface Area Analyzer (model: ASAP2460, Micron Instruments, USA); Fourier Transform Infrared Spectrometer (FTIR, model: Nicoleti S50, Thermo Fisher Scientific (China) Co., Ltd.). II. Implementation Examples Example 1

[0032] (a) Preparation of biochar Take 5 kg of sorghum straw, crush it and pass it through an 80-mesh sieve. Put it into a tube furnace and introduce nitrogen gas. The nitrogen gas flow rate is controlled at 500 mL / min. Pyrolysis is carried out under oxygen-limited (nitrogen protection) conditions. The pyrolysis program is set as follows: heat up to 110℃ from room temperature and hold for 15 min, then heat up to 180℃ and hold for 15 min, and finally heat up to 600℃ and hold for 45 min. The heating rate of the entire heating process is 5℃ / min. After the pyrolysis is completed, cool to room temperature, grind the product and screen out biochar with a particle size ≤150 μm for later use.

[0033] (II) Biochar composite modification Phosphoric acid, citric acid, and maleic acid were weighed at a mass ratio of 1:1.2:0.8. All three reagents were AR grade (99% purity). After mixing, the mixture was diluted with deionized water to a total mass fraction of 50 wt% to obtain a polybasic acid composite modifier. The biochar prepared above was mixed with the polybasic acid composite modifier at a mass-volume ratio of 1:10 (g / mL). The mixture was placed in an 80℃ constant temperature water bath and stirred at 300 rpm for 4 h. During the reaction, ultrasonic treatment at 400W was applied for 25 min. After the reaction, the product was washed with deionized water until the pH reached 7.2, and then vacuum dried at 105℃ for 5 h to obtain modified biochar. The specific surface area of ​​the modified biochar was determined to be 280 m² using a BET specific surface area analyzer (model ASAP2460). 2 / g, pore size range of 3~85nm, pore volume of 0.5cm³ 3 / g; FTIR analysis showed that the modified biochar at 1720 cm⁻¹... -1 (Carboxyl characteristic peak), 3400cm -1 The intensity of the characteristic peak at (hydroxyl characteristic peak) is significantly higher than that of unmodified biochar.

[0034] (III) Nutrient load Urea, potassium dihydrogen phosphate, and potassium chloride were weighed, with the total mass of the three reagents accounting for 78.5 wt% of the total mass of the nutrient components. The mass ratio of nitrogen (N), phosphorus (as P2O5), and potassium (as K2O) provided by the three fertilizers was 2.0:1.5:1.5. Humic acid was added, with the mass of humic acid accounting for 20 wt% of the total mass of the nutrient components. Then, EDTA chelated iron, EDTA chelated zinc, EDTA chelated manganese, and sugar alcohol chelated boron were added. The total content of the four chelated trace elements accounted for 1.5 wt% of the total mass of the nutrient components, of which EDTA chelated iron accounted for 0.5 wt%, EDTA chelated zinc accounted for 0.4 wt%, EDTA chelated manganese accounted for 0.3 wt%, and sugar alcohol chelated boron accounted for 0.3 wt%. The total of the above three components was 100 wt%. The above-mentioned nutrient components were dissolved in deionized water to prepare a nutrient solution with a mass fraction of 8 wt%. The modified biochar prepared above was added to the nutrient solution at a mass-volume ratio of 1:7 (g / mL) of modified biochar to nutrient solution. The mixture was stirred and adsorbed at a constant temperature of 38℃ for 6 hours, and then dried at 65℃ with forced air until the water content was 3% for later use.

[0035] (iv) Construction of hydrogel network Sodium carboxymethyl cellulose and sodium citrate were weighed at a mass ratio of 3:1 to form the total mass of the monomers for the composite hydrogel. The monomers were dissolved in deionized water at a mass-volume ratio of 1:20 (g / mL). N,N-methylenebisacrylamide, a crosslinking agent, was added at a mass ratio of 0.03 wt% of the total monomer mass, and the mass ratio of the total monomer mass to the crosslinking agent was 1:0.03. The mixture was then thoroughly mixed with the product obtained in step (III). An ammonium persulfate-sodium bisulfite composite initiator was then added, in which the mass ratio of ammonium persulfate to sodium bisulfite was 1:0.5 and the amount was 1.5 wt% of the total monomer mass. Nitrogen gas was introduced for protection, and the nitrogen flow rate was controlled at 300 mL / min. The mixture was prepolymerized at 58℃ for 2.5 h. After the prepolymerization was completed, the mixture was subjected to a physical crosslinking cycle of "freezing at -20℃ for 16 h and thawing at room temperature for 8 h" three times to form a biochar-hydrogel composite.

[0036] (v) Composite molding First, seaweed extract was prepared: kelp was used as raw material, and water was added at a solid-liquid ratio of 1:20 (g / mL). The mixture was extracted for 2 hours in an 80℃ water bath. After removing the residue by filtration through an 80-mesh filter cloth, the filtrate was vacuum concentrated at 60℃ and -0.08MPa until the seaweed polysaccharide content was ≥35%. The seaweed polysaccharide content was found to be 38.2%. The extract was then freeze-dried at -40℃ for 12 hours for later use. Add stress-resistant additives to the complex obtained in step (iv). The mass ratio of betaine, proline, seaweed extract, and sepiolite powder in the stress-resistant additives is 1:0.8:0.5:0.8. Stir at 700 rpm for 18 min. Add wood vinegar as a binder during granulation. The amount of wood vinegar added is 1.0 wt% of the total mass of the complex and the stress-resistant additives. The wood vinegar has a pH range of 3.5~4.5 and an organic acid content of ≥15%. After drying the material at 80℃ for 8 h, granules with a particle size of 2~3 mm are screened to obtain the finished product. Example 2

[0037] (a) Preparation of biochar Rice husks and corn stalks were mixed at a mass ratio of 1:1, with a total mass of 5 kg. The mixture was crushed and passed through an 80-mesh sieve. It was then placed in a tube furnace and nitrogen gas was introduced. The nitrogen flow rate was controlled at 500 mL / min. Pyrolysis was carried out under oxygen-limited (nitrogen protection) conditions. The pyrolysis program was set as follows: the temperature was raised from room temperature to 105℃ and held for 15 min, then raised to 175℃ and held for 15 min, and finally raised to 550℃ and held for 30 min. The heating rate throughout the heating process was 5℃ / min. After the pyrolysis was completed, biochar with a particle size ≤150 μm was screened out for later use.

[0038] (II) Biochar composite modification The polyacid composite modifier was prepared by mixing phosphoric acid, citric acid, and maleic acid in a mass ratio of 1:0.8:0.5. All three reagents were AR grade (99% purity), and the total mass fraction of the modifier was 45 wt%. The prepared biochar was mixed with this polyacid composite modifier at a mass-to-volume ratio of 1:8 (g / mL), and the mixture was placed in a 75℃ constant temperature water bath and stirred at 250 rpm for 3 h. During the reaction, ultrasonic treatment at 300W was applied for 20 min. After the reaction, the product was washed with deionized water until the pH reached 6.8, and then vacuum dried at 105℃ for 4 h to obtain the modified biochar. The specific surface area of ​​the modified biochar was determined to be 250 m² using a BET specific surface area analyzer (model ASAP2460). 2 / g, pore size range of 4~80nm, pore volume of 0.42cm³ 3 / g; FTIR analysis showed that the modified biochar at 1720 cm⁻¹... -1 (Carboxyl characteristic peak), 3400cm -1 The intensity of the characteristic peak at (hydroxyl characteristic peak) is significantly higher than that of unmodified biochar.

[0039] (III) Nutrient load Urea, potassium dihydrogen phosphate, and potassium chloride were weighed out. The total mass of the three reagents accounted for 79.2 wt% of the total mass of the nutrient components, and the mass ratio of nitrogen (N), phosphorus (as P2O5), and potassium (as K2O) provided by the three fertilizers was 1.5:1.0:1.0. Humic acid was added, accounting for 18 wt% of the total mass of the nutrient components. Then, chelated trace elements were added, including 0.3 wt% EDTA chelated iron, 0.2 wt% EDTA chelated zinc, 0.2 wt% EDTA chelated manganese, and 0.1 wt% sugar alcohol chelated boron. The total content of the four trace elements accounted for 0.8 wt% of the total mass of the nutrient components. The sum of the above three components was 100 wt%. The above-mentioned nutrient components were dissolved in deionized water to prepare a nutrient solution with a mass fraction of 5 wt%. The modified biochar prepared above was added to the nutrient solution at a mass-volume ratio of 1:6 (g / mL) of modified biochar to nutrient solution. The mixture was stirred and adsorbed at 35°C for 5 h, and then dried at 60°C to a water content of 4% for later use.

[0040] (iv) Construction of hydrogel network The monomers were composed of polyvinyl alcohol, acrylamide, and Tween 80 in a mass ratio of 4:3:1. Borax was used as the crosslinking agent, with a dosage of 0.02 wt% of the total monomer mass. The mass ratio of the total monomer mass to the crosslinking agent was 1:0.02. Ammonium persulfate was used as the initiator, with a dosage of 1.0 wt% of the total monomer mass. Nitrogen gas was introduced for protection, and the nitrogen flow rate was controlled at 300 mL / min. Prepolymerization was carried out at 55°C for 2 hours. After prepolymerization, the mixture underwent physical crosslinking cycle treatment three times to form a composite.

[0041] (v) Composite molding First, seaweed extract was prepared: kelp was used as raw material, and water was added at a solid-liquid ratio of 1:15 (g / mL). The mixture was extracted for 1.5 h in a water bath at 75℃. After removing the residue by filtration through an 80-mesh filter cloth, the filtrate was concentrated under vacuum at 60℃ and -0.08 MPa until the seaweed polysaccharide content was ≥35%. The seaweed polysaccharide content was found to be 35.7%. The extract was then freeze-dried at -40℃ for 12 h for later use. The mass ratio of betaine, proline, seaweed extract, and acid-modified zeolite powder in the stress-resistance agent is 1:0.5:0.3:0.5. The stress-resistance agent is added to the complex obtained in step (IV), and stirred at 600 rpm for 15 min. Wood vinegar is added as a binder during granulation. The amount of wood vinegar added is 0.5 wt% of the total mass of the complex and the stress-resistance agent. The wood vinegar has a pH range of 3.5~4.5 and an organic acid content of ≥15%. After drying the material at 70℃ for 6 h, particles with a particle size of 1~2 mm are screened to obtain the finished product. Example 3

[0042] (a) Preparation of biochar Corn stalks and vegetable stalks were mixed at a mass ratio of 1:2, with a total mass of 5 kg. The mixture was dried in an oven at 105℃ for 12 hours. The vegetable stalks were dried after removing impurities. The two materials were then mixed, pulverized, and passed through an 80-mesh sieve. The mixture was placed in a tube furnace and nitrogen gas was introduced at a flow rate of 500 mL / min for pyrolysis. The pyrolysis program was set as follows: the temperature was raised from room temperature to 115℃ and held for 15 min, then raised to 185℃ and held for 15 min, and finally raised to 750℃ and held for 60 min. The heating rate was 5℃ / min throughout the heating process. After pyrolysis, biochar with a particle size ≤150 μm was screened out for later use.

[0043] (II) Biochar composite modification The polyacid composite modifier was prepared by mixing phosphoric acid, citric acid, and maleic acid in a mass ratio of 1:1.5:1.2. All three reagents were AR grade (99% purity), and the total mass fraction of the modifier was 60 wt%. The prepared biochar was mixed with this polyacid composite modifier at a mass-to-volume ratio of 1:6 (g / mL), and the mixture was placed in an 85℃ constant temperature water bath and stirred at 350 rpm for 5 h. During the reaction, ultrasonic treatment at 500W was applied for 30 min. After the reaction, the product was washed with deionized water until the pH reached 7.8, and then vacuum dried at 105℃ for 6 h to obtain the modified biochar. The specific surface area of ​​the modified biochar was determined to be 320 m² / g using a BET surface area analyzer. 2 / g, pore size range of 5~90nm, pore volume of 0.65cm³ 3 / g; FTIR analysis showed that the modified biochar at 1720 cm⁻¹... -1 (Carboxyl characteristic peak), 3400cm -1 The intensity of the characteristic peak at (hydroxyl characteristic peak) is significantly higher than that of unmodified biochar.

[0044] (III) Nutrient load Urea, potassium dihydrogen phosphate, and potassium chloride were weighed, with the total mass of the three reagents accounting for 75 wt% of the total mass of the nutrient components. The mass ratio of nitrogen (N), phosphorus (as P2O5), and potassium (as K2O) provided by the three fertilizers was 2.5:1.8:1.8. Humic acid was added, with the mass of humic acid accounting for 22 wt% of the total mass of the nutrient components. Then, chelated trace elements were added, including 1.0 wt% EDTA chelated iron, 0.8 wt% EDTA chelated zinc, 0.7 wt% EDTA chelated manganese, and 0.5 wt% sugar alcohol chelated boron. The total content of the four trace elements accounted for 3.0 wt% of the total mass of the nutrient components. The sum of the above three components was 100 wt%. The above-mentioned nutrient components were dissolved in deionized water to prepare a nutrient solution with a mass fraction of 10 wt%. The modified biochar prepared above was added to the nutrient solution at a mass-volume ratio of 1:8 (g / mL) of modified biochar to nutrient solution. The mixture was stirred and adsorbed at 45°C for 7 h, and then dried at 70°C until the water content was 2% for later use.

[0045] (iv) Construction of hydrogel network The monomers were composed of N-isopropylacrylamide and chitosan in a mass ratio of 3:2. The crosslinking agent was N,N-methylenebisacrylamide, which was used at 0.04 wt% of the total monomer mass. The mass ratio of the total monomer mass to the crosslinking agent was 1:0.04. The initiator was sodium persulfate, which was used at 2.0 wt% of the total monomer mass. Nitrogen gas was then introduced for protection at a flow rate of 300 mL / min. Prepolymerization was carried out at 65°C for 3 h. After prepolymerization, the mixture was subjected to physical crosslinking cycle treatment three times to form a composite.

[0046] (v) Composite molding First, seaweed extract was prepared: kelp was used as raw material, and water was added at a solid-liquid ratio of 1:25 (g / mL). The mixture was extracted at 85℃ for 2.5 hours. After filtering through an 80-mesh filter cloth to remove residue, the filtrate was vacuum concentrated at 60℃ and -0.08MPa until the seaweed polysaccharide content was ≥35%. The seaweed polysaccharide content was found to be 41.5%. The extract was then freeze-dried at -40℃ for 12 hours for later use. The mass ratio of betaine, proline, seaweed extract, and sepiolite powder in the stress-resistant agent is 1:1.0:0.8:1.2. The stress-resistant agent is added to the complex obtained in step (IV), and stirred at 800 rpm for 20 min. Wood vinegar is added as a binder during granulation. The amount of wood vinegar added is 1.5 wt% of the total mass of the complex and the stress-resistant agent. The wood vinegar has a pH range of 3.5~4.5 and an organic acid content of ≥15%. After drying the material at 90℃ for 10 h, particles with a particle size of 3~4 mm are screened to obtain the finished product.

[0047] III. Comparative Example Comparative Example 1 The difference between this comparative example and Example 1 is that only phosphoric acid was used for biochar modification, and no polybasic acid composite modifier was used. All other raw materials and process steps are consistent with Example 1. The biochar modification step corresponds to step (ii) of Example 1, as follows: The biochar prepared in Example 1 was mixed with a single phosphoric acid modifier. The single phosphoric acid was AR grade, with a purity ≥99% and a mass fraction of 50 wt%. The mixing ratio was 1:10 (g / mL) of biochar to modifier. The mixture was placed in an 80℃ constant temperature water bath and stirred at 300 rpm for 4 hours. During the reaction, ultrasonic treatment at 400W was applied for 25 minutes. After the reaction, the product was washed with deionized water until the pH reached 7.2, and then vacuum dried at 105℃ for 5 hours to obtain modified biochar. The specific surface area of ​​the single phosphoric acid modified biochar was determined to be 190 m² using a BET surface area analyzer (model ASAP2460). 2 / g, pore size range of 6~75nm, pore volume of 0.35cm³ 3 / g; FTIR analysis showed that the modified biochar at 1720 cm⁻¹... -1 (Carboxyl characteristic peak), 3400cm -1 The intensity of the characteristic peak at (hydroxyl characteristic peak) is lower than that of the modified biochar prepared in Example 1.

[0048] Comparative Example 2 The difference between this comparative example and Example 1 is that the composite hydrogel is replaced with a single polyacrylic acid hydrogel, which is made by neutralizing acrylic acid to a degree of 70% and does not contain sodium carboxymethyl cellulose. All other raw materials and process steps are the same as in Example 1, and the preparation method of the seaweed extract is the same as in Example 1.

[0049] Comparative Example 3 The difference between this comparative example and Example 1 is that no stress-resistant additive was added. All other raw materials and process steps are the same as in Example 1. The BET and FTIR data of the biochar composite modification are the same as in Example 1.

[0050] Comparative Example 4 The difference between this comparative example and Example 1 is that ultrasonic-assisted activation was not performed during the biochar composite modification process. All other raw materials and process steps are consistent with Example 1. The biochar modification step corresponds to step (ii) of Example 1, as follows: Phosphoric acid, citric acid, and maleic acid were weighed in a mass ratio of 1:1.2:0.8, mixed, and diluted with deionized water to a total mass fraction of 50 wt% to obtain a polyacid composite modifier. The biochar prepared in Example 1 was mixed with this polyacid composite modifier at a mass-to-volume ratio of 1:10 (g / mL), and placed in an 80℃ constant temperature water bath with stirring at 300 rpm for 4 hours. No ultrasonic-assisted treatment was performed during the reaction. After the reaction, the product was washed with deionized water until the pH reached 7.2, and then vacuum dried at 105℃ for 5 hours to obtain modified biochar. The specific surface area of ​​this non-ultrasonic modified biochar was determined to be 210 m² using a BET specific surface area analyzer (model ASAP2460). 2 / g, pore size range of 5~78nm, pore volume of 0.38cm³ 3 / g; FTIR analysis showed that the modified biochar at 1720 cm⁻¹... -1 (Carboxyl characteristic peak), 3400cm -1 The intensity of the characteristic peak at (hydroxyl characteristic peak) is lower than that of the modified biochar prepared in Example 1.

[0051] Comparative Example 5 This comparative example uses a traditional biochar modifier, prepared as follows: The unmodified biochar prepared in Example 1 was mixed with nutrient components under the same conditions as in Example 1, i.e., a biochar to nutrient solution mass-to-volume ratio of 1:7 (g / mL), and adsorbed at a constant temperature of 38°C for 6 hours. This traditional biochar modifier does not contain composite hydrogels or stress-resistant additives; all other process steps are consistent with Example 1. The specific surface area of ​​the unmodified biochar was determined to be 150 m² using a BET surface area analyzer (model ASAP2460). 2 / g, pore size range of 8~95nm, pore volume of 0.28cm³ 3 / g; FTIR analysis showed that the unmodified biochar measured at 1720 cm⁻¹ -1 (Carboxyl characteristic peak), 3400cm -1 There is no obvious characteristic peak at the (hydroxyl characteristic peak) location.

[0052] Comparative Example 6 The difference between this comparative example and Example 1 is that only betaine was added as the stress-resistant adjuvant, and its amount was 0.32 times the total mass of the stress-resistant adjuvant in Example 1. All other raw materials and process steps were the same as in Example 1. The BET data and FTIR data of the biochar composite modification were the same as in Example 1, and the preparation method of the seaweed extract was the same as in Example 1.

[0053] Comparative Example 7 The difference between this comparative example and Example 1 is that only proline is added as the stress-resistant adjuvant, and its amount is 0.32 times the total mass of the stress-resistant adjuvant in Example 1. All other raw materials and process steps are the same as in Example 1. The BET data and FTIR data of the biochar composite modification are the same as in Example 1, and the preparation method of the seaweed extract is the same as in Example 1.

[0054] Comparative Example 8 The difference between this comparative example and Example 1 is that only seaweed extract was added as the stress-resistant adjuvant, and its amount was 0.32 times the total mass of the stress-resistant adjuvant in Example 1. All other raw materials and process steps were the same as in Example 1. The BET data and FTIR data of the biochar composite modification were the same as in Example 1, and the preparation method of seaweed extract was the same as in Example 1.

[0055] Comparative Example 9 The difference between this comparative example and Example 1 is that no wood vinegar adhesive was added during the composite molding process; all other raw materials and process steps are the same as in Example 1.

[0056] Comparative Example 10 The difference between this comparative example and Example 1 is that the physical cross-linking cycle was performed only once during the hydrogel network construction process (one cycle of freezing at -20°C for 16 hours and thawing at room temperature for 8 hours). All other raw materials and process steps were the same as in Example 1.

[0057] IV. Performance Testing (a) Basic performance test of the modifier Water absorption test: Weigh 5g of each example and comparative sample dried to constant weight, immerse in deionized water at 25℃±2℃ for 24h, filter, weigh the saturated water absorption mass of the sample, and calculate the water absorption rate according to the formula "water absorption rate = (saturated water absorption mass / dry sample mass) × 100%".

[0058] Compressive strength test: A compression test was conducted on sample particles with a particle size of 2~3mm using a pressure testing machine. The loading rate was controlled at 1mm / min. The maximum pressure when the sample broke was recorded as the compressive strength of the sample.

[0059] Moisture content test: The 105℃ drying method was used. 5g of each sample was weighed and dried to constant weight. The moisture content of the sample was then calculated.

[0060] Biodegradation rate test: Each sample was buried in farmland soil at a depth of 10 cm. The farmland soil used had a pH range of 6.5–7.5, an organic matter content of 1.5–2.0%, and a microbial community abundance of ≥1×10⁻⁶. 6The soil moisture content was controlled at 60% of field capacity and the ambient temperature at 25℃. After 120 days, the samples were taken out, washed and dried. The biodegradation rate of the samples after 120 days was calculated according to the formula "Biodegradation rate = (initial mass - remaining mass) / initial mass × 100%".

[0061] Nutrient slow release rate test: The soil column leaching method was used, with soil columns measuring 5cm in diameter and 30cm in height. The soil was compacted to a bulk density of 1.2g / cm³. 3 Weigh 5g of each sample and mix it evenly with 200g of soil, then load it into a soil column. Leach once a week, using 50mL of deionized water each time, with a leaching rate controlled at 5mL / min. Collect the leachate after each leaching, and use an inductively coupled plasma mass spectrometer (Agilent 7700x, RF power 1550W, sampling depth 8mm, carrier gas flow rate 1.0L / min) to determine the nitrogen, phosphorus, and potassium content in the leachate. Calculate the cumulative nutrient release rate of the sample over 30 days.

[0062] (II) Soil Improvement Effect Test Water retention rate test: The field water holding capacity of each tested soil was determined using the ring cutter method. Samples from each example and comparative example were applied to different types of tested soil at corresponding application rates. The application rates were 150 kg / mu for saline-alkali soil, 100 kg / mu for sandy soil, 120 kg / mu for acidic soil, and 160 kg / mu for heavy metal contaminated soil. After the samples and soil were mixed evenly, they were placed in flower pots with 3 kg of mixed soil in each pot. The initial soil moisture content was adjusted to 70% of the field water holding capacity. After being placed naturally for 30 days at 25℃ and 60% relative humidity, the soil moisture content was measured and the soil water retention rate was calculated.

[0063] Soil pH regulation effect test: A pot experiment was conducted, and the pH value of each type of test soil was measured after 60 days to analyze the effect of the samples on soil pH regulation.

[0064] Heavy metal passivation rate test: Samples from each example and comparative example were applied to lightly contaminated soil for pot experiments. After 60 days, the available Pb in the soil was determined using the Tessier continuous extraction method. 2+ Cd 2+ The content was determined by controlling the extraction temperature at 25℃, using an extractant at 5 times the soil mass, shaking for 16 hours, and centrifuging at 5000 rpm. The passivation rate of heavy metals was calculated using the formula "passivation rate = (initial effective content - effective content after treatment) / initial effective content × 100%".

[0065] Crop growth index testing: Corn was planted in each of the improved test soils and pot experiments were conducted. After 60 days, the corn plant height, stem diameter, fresh weight and root biomass were measured to analyze the promoting effect of the samples on crop growth.

[0066] Synergistic effect test of stress resistance adjuvants: By comparing the stress resistance-related indicators of maize in Example 1 and Comparative Examples 6-8, specifically the proline content and malondialdehyde content in maize leaves, the synergistic effect of each component in the stress resistance adjuvants was verified.

[0067] (iii) Test repetition To ensure the accuracy and reliability of the test results, all performance tests were performed with three parallel samples, and the final test result was the average of the three parallel samples.

[0068] V. Test Results (a) Basic performance test of the modifier Table 1. Basic performance test results of the improvers in each example and comparative example. Example 1 385 22 2.1 36 72 Example 2 342 18 2.8 33 68 Example 3 367 25 1.9 38 75 Comparative Example 1 215 15 2.3 28 55 Comparative Example 2 278 14 2.5 26 58 Comparative Example 3 320 16 2.2 30 62 Comparative Example 4 243 17 2.4 29 56 Comparative Example 5 128 13 2.6 22 42 Comparative Example 6 372 20 2.2 34 69 Comparative Example 7 368 21 2.1 33 67 Comparative Example 8 375 20 2.3 35 70 Comparative Example 9 360 13 2.2 35 63 Comparative Example 10 265 12 2.3 24 60 Note: Comparative Example 9 had poor particle size uniformity (some particles had a particle size of <1mm or >4mm) because no wood vinegar binder was added.

[0069] (II) Soil Improvement Effect Test Table 2 shows the soil water retention rate and pH adjustment effect of the soil conditioners in each example and comparative example. Example 1 42.3 40.1 6.8 7.2 Example 2 39.8 37.5 6.6 7.0 Example 3 43.5 41.2 7.0 7.3 Comparative Example 1 31.5 30.2 7.5 7.8 Comparative Example 2 33.2 32.6 7.2 7.6 Comparative Example 3 35.7 34.8 7.1 7.5 Comparative Example 4 32.8 31.4 7.3 7.7 Comparative Example 5 25.3 24.7 8.2 8.0 Comparative Example 6 39.5 38.2 6.9 7.1 Comparative Example 7 38.8 37.6 6.9 7.2 Comparative Example 8 40.2 38.5 6.8 7.1 Comparative Example 9 38.6 37.3 6.9 7.1 Comparative Example 10 32.5 31.0 7.3 7.7 Table 3. Soil heavy metal passivation effect of each embodiment and comparative example soil conditioner. Example 1 45.2 48.6 Example 2 41.8 44.3 Example 3 47.5 50.2 Comparative Example 1 32.1 35.7 Comparative Example 2 34.5 37.2 Comparative Example 3 36.8 39.5 Comparative Example 4 33.6 36.4 Comparative Example 5 28.3 30.1 Comparative Example 6 41.3 43.5 Comparative Example 7 40.8 42.7 Comparative Example 8 42.5 44.8 Comparative Example 9 41.8 44.2 Comparative Example 10 33.5 36.2 Table 4. Corn growth and stress resistance indices after treatment with the improvers in each example and comparative example. Example 1 38.6 0.85 28.3 7.6 215.3 18.6 Example 2 36.2 0.78 25.7 6.9 208.5 20.3 Example 3 40.1 0.92 30.5 8.2 223.7 17.2 Comparative Example 1 29.5 0.62 19.8 5.1 156.2 32.5 Comparative Example 2 31.2 0.65 21.3 5.4 163.8 30.7 Comparative Example 3 33.7 0.71 23.5 5.9 178.4 27.3 Comparative Example 4 30.1 0.63 20.5 5.2 160.5 31.8 Comparative Example 5 25.8 0.58 16.7 4.3 132.6 38.9 Comparative Example 6 35.2 0.76 24.8 6.5 189.7 24.5 Comparative Example 7 34.6 0.75 24.2 6.3 185.3 25.1 Comparative Example 8 35.8 0.77 25.3 6.7 193.6 23.8 Comparative Example 9 34.5 0.74 24.0 6.2 188.5 25.0 Comparative Example 10 30.0 0.62 20.3 5.1 159.8 31.6 VI. Conclusion The biochar-hydrogel composite amendments prepared in Examples 1-3 all met the requirements of water absorption ≥300%, compressive strength ≥15N, moisture content ≤3%, and biodegradation rate ≥30% after 120 days. The nutrient slow-release rate after 30 days reached 68%~75%, significantly better than the comparative examples. Regarding soil improvement effects, the examples increased the water retention rate of saline-alkali and sandy soils to 37.5%~43.5%, adjusted the pH of acidic soils to 6.6~7.0, and reduced Pb levels in heavy metal-contaminated soils. 2+ Cd 2+ The passivation rate reached 41.8%~50.2%, and it significantly promoted maize growth, with plant height, fresh weight and other indicators increasing by 20%~40% compared with the control group. At the same time, the maize leaves of the example had higher proline content and lower malondialdehyde content, and the stress resistance was better than the single stress resistance adjuvant group (control group 6-8), proving that the components of the stress resistance adjuvant have a synergistic effect.

[0070] Example 1: The modified biochar has a specific surface area of ​​280 m². 2 / g, pore size range of 3~85nm, pore volume of 0.5cm³ 3 / g, the specific surface area of ​​the modified biochar in Example 2 is 250m². 2 / g, pore size range of 4~80nm, pore volume of 0.42cm³ 3 / g, the specific surface area of ​​the modified biochar in Example 3 is 320m². 2 / g, pore size range of 5~90nm, pore volume of 0.65cm³ 3 / g. Comparative examples and comparative examples show that polybasic acid composite modification can introduce oxygen-containing functional groups such as carboxyl and hydroxyl groups, which is confirmed by FTIR detection results. These oxygen-containing functional groups can form hydrogen bonds with hydrogel molecular chains. Ultrasonic-assisted activation can further expand the pore structure of biochar; the modified biochar in Examples 1-3 has a specific surface area of ​​250~320m². 2 / g, pore size 3~90nm, pore volume 0.42~0.65cm³ 3 / g. The synergistic effect of polybasic acid composite modification and ultrasonic-assisted activation effectively improves the adsorption performance and hydrogel compatibility of biochar. The three-dimensional network of the composite hydrogel and the porous structure of biochar form a synergistic water-retention and slow-release system. The seaweed extract in the stress-resistance adjuvant, with its stability tested and preparation parameters clearly defined, ensures the stability of the active ingredients through standardized preparation processes. Its synergistic effect with betaine and proline significantly enhances crop stress resistance. Wood vinegar, as a binding agent, further optimizes the molding effect of the amendment. This invention achieves integrated improvement of marginal farmland through the synergistic effect of its components, encompassing water retention, soil improvement, slow release, and stress resistance. Its effect is significantly better than that of single modification or traditional amendments, fully meeting the improvement needs of different types of marginal farmland.

[0071] Mechanism analysis: 1. Synergistic mechanism of water retention and slow release: The porous structure of modified biochar (specific surface area 250~320m²) 2 The biochar (with a pore size of 3~90nm) and the three-dimensional network of the composite hydrogel form a layered synergistic structure. On the one hand, the biochar adsorbs water and nutrients through its pores, and on the other hand, the hydrogel network locks in water and nutrients, achieving a synergistic effect of 'adsorption-lock-release' and improving the soil's water and fertilizer retention capacity. 2. Heavy metal passivation mechanism: Multi-acid composite modification introduces oxygen-containing functional groups such as carboxyl and hydroxyl groups on the surface of biochar. These functional groups can undergo complexation reactions with heavy metal ions such as Pb²⁺ and Cd²⁺ in the soil, reducing the content of available heavy metals and thus achieving passivation effect. 3. Synergistic mechanism of stress resistance: Betaine and proline in the stress resistance adjuvant can regulate the osmotic pressure of crop cells, seaweed polysaccharides (content ≥35%) in seaweed extract can enhance the activity of crop antioxidant enzymes, and silicates can improve the stability of crop cell walls. The three, together with the biochar-hydrogel system, significantly enhance the stress resistance of crops in marginal cultivated land.

[0072] The embodiments of the present invention have been described in detail above, but the content described is only a preferred embodiment of the present invention and should not be considered as limiting the scope of the present invention. All equivalent changes and improvements made within the scope of the present invention should still fall within the patent coverage of the present invention.

Claims

1. A broad-spectrum biochar-hydrogel composite modifier, characterized in that, Using agricultural waste-based biochar as a carrier, after modification with a polybasic acid composite modifier and ultrasonic-assisted activation, it is cyclically compounded with a composite hydrogel, nutrient components, and stress-resistant additives through in-situ polymerization and physical cross-linking. The modifier components, by weight, are: 35-45 parts modified biochar, 18-25 parts composite hydrogel, 15-22 parts nutrient components, and 3-6 parts stress-resistant additives. The modifier consists of particles with a particle size of 1-4 mm, a compressive strength ≥15 N, a water absorption rate ≥300%, a moisture content ≤3%, and a biodegradation rate ≥30% after 120 days of burial. The composite hydrogel is selected from carboxymethyl cellulose-sodium citrate composite hydrogel, polyvinyl alcohol-acrylamide-Tween 80 composite hydrogel, or poly(N-isopropylacrylamide)-chitosan composite hydrogel. The nutrient components include nitrogen, phosphorus, and potassium nutrients, humic acid, and chelated trace elements. The stress-resistant additives are composed of betaine, proline, seaweed extract, and silicate.

2. The broad-spectrum biochar-hydrogel composite modifier according to claim 1, characterized in that, The agricultural waste-based biochar is derived from biomass waste and produced through oxygen-limited pyrolysis. The pyrolysis procedure is as follows: heating from room temperature to 105-115℃ and holding for 10-15 minutes, then heating to 175-185℃ and holding for 10-15 minutes, and finally heating to 450-750℃ and holding for 30-60 minutes, with a total heating rate of 3-5℃ / min. The biochar particle size after pyrolysis is ≤150μm. The polybasic acid composite modifier is an aqueous solution of at least two inorganic or organic acids with a total mass fraction of 40-60wt%. The binary inorganic / organic acid is mixed at a mass ratio of 1:0.5-1.5, and the ternary inorganic / organic acid is mixed at a mass ratio of 1:0.5-1.5:0.3-1.

2. The specific surface area of ​​the modified biochar is 200-350m². 2 / g, pore size 2~100nm, pore volume 0.3~0.8cm³ 3 / g.

3. The broad-spectrum biochar-hydrogel composite modifier according to claim 2, characterized in that, The polyacid composite modifier is a mixture of phosphoric acid, citric acid, and maleic acid, which are mixed in the above order at a mass ratio of 1:(0.8~1.5):(0.5~1.2); the biomass waste is at least one of sorghum stalks, rice husks, corn stalks, or vegetable stalks.

4. The broad-spectrum biochar-hydrogel composite modifier according to claim 1, characterized in that, The nutrient components include nitrogen, phosphorus, and potassium nutrients, humic acid, and chelated trace elements, wherein the mass ratio of nitrogen, phosphorus, and potassium is (1.5~2.5):(1~1.8):(1~1.8), and the chelated trace elements are EDTA chelated iron, EDTA chelated zinc, EDTA chelated manganese, and sugar alcohol chelated boron. The total content of chelated trace elements is 0.5~3% of the total mass of the nutrient components.

5. The broad-spectrum biochar-hydrogel composite modifier according to claim 1, characterized in that, The stress-resistant adjuvant is composed of betaine, proline, seaweed extract, and silicate in the above order at a mass ratio of 1:(0.5~1):(0.3~0.8):(0.5~1.2); the silicate has a specific surface area of ​​520~700 m². 2 / g of sepiolite powder or a specific surface area ≥500m² 2 / g of acid-modified or phosphorus-modified zeolite powder, wherein the seaweed extract contains ≥30% seaweed polysaccharide.

6. A method for preparing a broad-spectrum biochar-hydrogel composite modifier as described in any one of claims 1-5, characterized in that, The modified biochar, composite hydrogel monomer, nutrient components, and stress-resistance additives are fed in the above order at a mass ratio of 35~45:18~25:15~22:3~6, including the following steps: (1) Biochar composite modification: Agricultural waste-based biochar and polyacid composite modifier are mixed at a mass-volume ratio of 1:(8~12)g / mL, stirred at 65~85℃ for 3~5h, and after 1h of reaction, ultrasonic treatment with 300~500W is performed for 20~30min. After the reaction is completed, the mixture is washed until the pH is 6.0~8.0, and vacuum dried at 80~105℃ for 4~6h to obtain modified biochar. (2) Nutrient loading: Dissolve the nutrient components in deionized water to prepare a 5-10 wt% solution, add modified biochar, the mass-to-volume ratio of modified biochar to nutrient component solution is 1:(5-8) g / mL, stir and adsorb at 35-45℃ for 5-7 h, and dry at 60-70℃ until the water content is ≤5%; (3) Hydrogel network construction: The polymer monomers and crosslinking agents of the composite hydrogel are mixed with the product of step (2), an initiator is added, and prepolymerization is carried out at 55~65℃ for 2~3h under nitrogen protection. Then, the composite is subjected to physical crosslinking cycle treatment of freezing at -20℃ for 16h and thawing at room temperature for 8h for 3 times to form a composite. (4) Composite molding: Add stress-resistant agent to the composite in step (3), stir at 600~800 rpm for 15~20 min, add wood vinegar at 0.5~1.5 wt% relative to the total mass of the composite in step (3) and stress-resistant agent as a binding agent during granulation, dry at 70~90℃ for 6~10 h, screen particles with a particle size of 1~4 mm to obtain the finished product.

7. The preparation method of the broad-spectrum biochar-hydrogel composite modifier according to claim 6, characterized in that, The physical crosslinking cycle in step (3) is a cycle of freezing at -20℃ for 16 hours and thawing at room temperature for 8 hours; the mass ratio of the total mass of the polymer monomers to the mass of the crosslinking agent is 1:(0.02~0.04), and the crosslinking agent is N,N-methylenebisacrylamide or borax; the initiator is ammonium persulfate-sodium bisulfite composite initiator, ammonium persulfate or sodium persulfate, wherein the mass ratio of the two in the ammonium persulfate-sodium bisulfite composite initiator is 1:0.5, and the amount of initiator is 1~2% of the total mass of the polymer monomers.

8. The preparation method of the broad-spectrum biochar-hydrogel composite modifier according to claim 6, characterized in that, The wood vinegar is a product obtained by pyrolysis of biomass at 500~700℃, and the organic matter content in the wood vinegar is ≥80%.

9. The application of the broad-spectrum biochar-hydrogel composite amendment according to any one of claims 1-5 in the improvement of marginal farmland, characterized in that, The marginal cultivated land refers to saline-alkali land, sandy soil, acidic soil, and cultivated land with slight heavy metal pollution.

10. The application according to claim 9, characterized in that, The application rate of the soil conditioner is divided according to soil type: 120~180 kg / mu for saline-alkali soil, 80~120 kg / mu for sandy soil, 100~150 kg / mu for acidic soil, and 150~180 kg / mu for soil with slight heavy metal pollution. The application method is basal application, strip application or hole application. After application, it should be mixed evenly with the 0~25cm topsoil layer.