Magnesium salt modified charcoal soil conditioner and preparation method thereof

Abstract

The invention relates to a magnesium salt modified charcoal soil conditioner and a preparation method thereof, and belongs to the technical field of soil improvement. The invention provides a preparation method of a magnesium salt modified charcoal soil conditioner. The preparation method comprises the following steps: (1) preparing a reactant from crop straws and a magnesium chloride solution; (2) preparing a modified reactant from the reactant and a sodium hydroxide solution, and cracking to obtain magnesium salt modified biochar; and (3) mixing magnesium oxide with the magnesium salt modified biochar to obtain the magnesium salt modified biochar soil conditioner. The magnesium salt modified biochar soil conditioner prepared according to the method disclosed by the invention can remarkably improve nitrogen and phosphorus nutrient indexes such as quick-acting phosphorus, ammonia nitrogen and quick-acting nitrogen in soil, can effectively improve acid soil, and also can improve the growth traits and yield of crops.

Description

Technical Field

[0001] This invention relates to the field of soil improvement technology, and in particular to a magnesium salt modified biochar soil conditioner and its preparation method. Background Technology

[0002] Soil, as the foundation for plant growth, directly affects plant health and yield. Ideal soil provides plants with sufficient water and nutrients, possesses good aeration, and a suitable pH level. However, in reality, soil faces numerous problems that severely impact its performance and the plant's growth environment. With population growth and increasing agricultural production demands, large amounts of chemical fertilizers are being applied indiscriminately and excessively. Excessive fertilizers damage the original soil structure, impairing soil aggregates, reducing porosity, leading to soil compaction, and decreased aeration and permeability. This not only hinders the normal growth and respiration of plant roots but also affects the survival and activity of soil microorganisms, reducing soil biological activity. Simultaneously, long-term excessive application of single-nutrient fertilizers also causes deficiencies in other soil nutrients, disrupting the soil nutrient balance, resulting in poor crop growth, reduced yields, and compromised agricultural product quality, ultimately leading to a decline in the economic benefits of cash crops.

[0003] To address these soil problems, researchers both domestically and internationally have conducted extensive studies and developed various soil conditioners. Currently, soil conditioners developed in my country mainly include inorganic, organic, and inorganic-organic composite types. Inorganic soil conditioners include lime and perlite, while organic soil conditioners include biochar and humic acid, as well as their mixed application products. These conditioners can improve soil physicochemical properties to some extent, but they still have some limitations, such as high cost, unstable effects, and the potential for soil pollution with long-term application. Therefore, developing a highly efficient, environmentally friendly, widely adaptable soil conditioner that can comprehensively solve multiple soil problems is of significant practical importance and is crucial for improving soil quality, increasing crop yield and quality, and promoting sustainable agricultural development. Summary of the Invention

[0004] The purpose of this invention is to provide a magnesium salt modified biochar soil conditioner and its preparation method, so as to solve the problems of high cost, unstable effect and soil pollution caused by long-term application of existing soil conditioners.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0006] A method for preparing a magnesium salt-modified biochar soil conditioner includes the following steps:

[0007] (1) Mix crop straw with magnesium chloride solution, heat to 55-65℃ and keep for 1-3 hours to obtain a mixed solution, filter the mixed solution to obtain the filter residue, and dry to obtain the reactant;

[0008] (2) Mix the reactants with sodium hydroxide solution and react for 3.5 to 4.5 hours. Filter the residue and dry it to obtain the modified reactants. Heat the modified reactants to 600 to 700°C under nitrogen and maintain the temperature for 3 to 5 hours to obtain magnesium salt modified biochar.

[0009] (3) Magnesium oxide is mixed with magnesium salt modified biochar to obtain magnesium salt modified biochar soil conditioner.

[0010] Preferably, the particle size of the crop straw in step (1) is 1-3 mm;

[0011] The crop straw includes one or more of corn straw, wheat straw, and soybean straw.

[0012] Preferably, the mass-to-volume ratio of the crop straw to the magnesium chloride solution in step (1) is 1g: 45-55mL;

[0013] The initial concentration of the magnesium chloride solution is 1–2 mol / L.

[0014] Preferably, the mass-to-volume ratio of the reactant to the sodium hydroxide solution in step (2) is 1 g: 8-12 mL;

[0015] The initial concentration of the sodium hydroxide solution is 0.2–0.4 mol / L.

[0016] Preferably, the heating rate in step (2) is 12-14 °C / min.

[0017] Preferably, the mass ratio of magnesium oxide to magnesium salt modified biochar in step (3) is 0.2 to 0.4:1.

[0018] This invention provides a magnesium salt modified biochar soil conditioner prepared by the aforementioned preparation method.

[0019] This invention provides a magnesium salt modified biochar soil conditioner prepared by the aforementioned preparation method, or the application of the magnesium salt modified biochar soil conditioner in improving acidic soil.

[0020] This invention provides a magnesium salt modified biochar soil conditioner prepared by the aforementioned preparation method, or the application of the magnesium salt modified biochar soil conditioner in increasing crop yield.

[0021] The present invention has the following technical effects and advantages:

[0022] This invention aims to expand soil nutrient storage and improve soil fertility by providing a method for preparing a magnesium salt modified biochar soil conditioner. When the magnesium salt modified biochar soil conditioner prepared according to this invention is applied at a rate of not less than 100 kg / mu, its slow-release nitrogen and phosphorus effect can significantly improve nitrogen and phosphorus nutrient indicators such as available phosphorus, ammonia nitrogen, and available nitrogen in the soil, effectively improving acidic soils. At the same time, the magnesium salt modified biochar soil conditioner prepared by this invention can also improve crop growth and yield. Attached Figure Description

[0023] Figure 1 The results show the nitrogen and phosphorus retention capacity of magnesium salt modified biochar soil conditioners with different magnesium / carbon mass ratios.

[0024] Figure 2 Magnesium salt-modified biochar soil conditioner with magnesium / char mass ratios of 20% and 40% showed its effect on NH4+ in single and composite systems. 4+ and PO4 3- Isothermal adsorption curves illustrating the retention capacity;

[0025] Figure 3 The slow-release effect of phosphorus in soils treated with different amounts of magnesium salt-modified biochar soil conditioner;

[0026] Figure 4 The nitrogen slow-release effect of soils treated with different amounts of magnesium salt-modified biochar soil conditioner;

[0027] Figure 5 pH values ​​of soils treated with different amounts of magnesium salt-modified biochar soil conditioner;

[0028] Figure 6 Geographical location map of the field test site for magnesium salt modified biochar soil conditioner;

[0029] Figure 7 These are photos of the field test site. Detailed Implementation

[0030] This invention provides a method for preparing a magnesium salt-modified biochar soil conditioner, comprising the following steps:

[0031] (1) Mix crop straw with magnesium chloride solution, heat to 55-65℃ and keep for 1-3 hours to obtain a mixed solution, filter the mixed solution to obtain the filter residue, and dry to obtain the reactant;

[0032] The heating temperature is preferably 60°C; the holding time is preferably 2 hours.

[0033] (2) Mix the reactants with sodium hydroxide solution and react for 3.5 to 4.5 hours. Filter the residue and dry it to obtain the modified reactants. Heat the modified reactants to 600 to 700°C under nitrogen and maintain the temperature for 3 to 5 hours to obtain magnesium salt modified biochar.

[0034] The reaction time is preferably 4 hours; the heating temperature is preferably 650°C; and the holding time is preferably 4 hours.

[0035] (3) Magnesium oxide is mixed with magnesium salt-modified biochar to obtain magnesium salt-modified biochar soil conditioner. In this invention, the particle size of the crop straw in step (1) is 1-3 mm, preferably 2 mm;

[0036] The crop straw includes one or more of corn straw, wheat straw, and soybean straw.

[0037] In this invention, the mass-to-volume ratio of crop straw to magnesium chloride solution in step (1) is 1g:45-55mL, preferably 1g:50mL;

[0038] The initial concentration of the magnesium chloride solution is 1-2 mol / L, preferably 1.5 mol / L.

[0039] In this invention, the mass-to-volume ratio of the reactant to the sodium hydroxide solution in step (2) is 1g:8-12mL, preferably 1g:10mL;

[0040] The initial concentration of the sodium hydroxide solution is 0.2–0.4 mol / L, preferably 0.3 mol / L.

[0041] In this invention, the heating rate in step (2) is 12-14°C / min, preferably 13°C / min.

[0042] In this invention, the mass ratio of magnesium oxide to magnesium salt modified biochar in step (3) is 0.2 to 0.4:1, preferably 0.3:1.

[0043] This invention provides a magnesium salt modified biochar soil conditioner prepared by the aforementioned preparation method.

[0044] This invention provides a magnesium salt modified biochar soil conditioner prepared by the aforementioned preparation method, or the application of the magnesium salt modified biochar soil conditioner in improving acidic soil.

[0045] This invention provides a magnesium salt modified biochar soil conditioner prepared by the aforementioned preparation method, or the application of the magnesium salt modified biochar soil conditioner in increasing crop yield.

[0046] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0047] Example 1

[0048] A method for preparing a magnesium salt modified biochar soil conditioner, comprising the following steps:

[0049] (1) Crush corn stalks and wheat stalks to a particle size of 0.2 mm to obtain crushed crop stalks. Take 100 g of crop stalks and mix them with 5000 mL of magnesium chloride solution with a concentration of 1.5 mol / L. Heat the mixture to 60 °C and keep it for 2 h to obtain a mixed solution. Filter the mixed solution and dry the filter residue to obtain the reactant.

[0050] (2) The reactants were mixed with a sodium hydroxide solution with a concentration of 0.3 mol / L at a mass-volume ratio of 1 g: 10 mL and reacted for 4 h. The filter residue was dried to obtain the modified reactants. The reactants were placed in a muffle furnace, nitrogen gas was introduced, and the temperature was raised to 650 °C at a rate of 13 °C / min and held for 4 h to obtain magnesium salt modified biochar.

[0051] (3) Mix 20g of magnesium oxide with 100g of magnesium salt modified biochar to obtain magnesium salt modified biochar soil conditioner.

[0052] Example 2

[0053] A method for preparing a magnesium salt modified biochar soil conditioner, comprising the following steps:

[0054] (1) Crush corn stalks and soybean stalks to a particle size of 0.2 mm to obtain crushed crop stalks. Take 50 g of crop stalks and mix them with 2500 mL of magnesium chloride solution with a concentration of 1 mol / L. Heat the mixture to 64 °C and keep it for 2.5 h to obtain a mixed solution. Filter the mixed solution and dry the filter residue to obtain the reactant.

[0055] (2) The reactants were mixed with a sodium hydroxide solution with a concentration of 0.4 mol / L at a mass-volume ratio of 1 g: 12 mL and reacted for 4.5 h. The filter residue was dried to obtain the modified reactants. The reactants were placed in a muffle furnace, nitrogen gas was introduced, and the temperature was raised to 630 °C at a heating rate of 12 °C / min and held for 3.5 h to obtain magnesium salt modified biochar.

[0056] (3) Mix 30g of magnesium oxide with 100g of magnesium salt modified biochar to obtain magnesium salt modified biochar soil conditioner.

[0057] Example 3

[0058] A method for preparing a magnesium salt modified biochar soil conditioner, comprising the following steps:

[0059] (1) Crush corn stalks and soybean stalks to a particle size of 0.2 mm to obtain crushed crop stalks. Take 150 g of crop stalks and mix them with 7500 mL of magnesium chloride solution with a concentration of 3 mol / L. Heat the mixture to 55 °C and keep it for 1.5 h to obtain a mixed solution. Filter the mixed solution and dry the filter residue to obtain the reactant.

[0060] (2) The reactants were mixed with a sodium hydroxide solution with a concentration of 0.2 mol / L at a mass-volume ratio of 1 g: 9 mL and reacted for 3.5 h. The filter residue was dried to obtain the modified reactants. The reactants were placed in a muffle furnace, nitrogen gas was introduced, and the temperature was raised to 680 °C at a heating rate of 14 °C / min and held for 4.5 h to obtain magnesium salt modified biochar.

[0061] (3) Mix 40g of magnesium oxide with 100g of magnesium salt modified biochar to obtain magnesium salt modified biochar soil conditioner.

[0062] Experimental Example 1: Screening of Component Proportions for Magnesium Salt-Modified Biochar Soil Conditioner

[0063] Corn stalks and wheat stalks were crushed to a particle size of 0.2 mm to obtain crushed crop stalks. 100 g of crop stalks were mixed with 5000 mL of 1.5 mol / L magnesium chloride solution and heated to 60 °C for 2 h to obtain a mixed solution. The mixed solution was filtered, and the filter residue was dried to obtain the reactant. The reactant was mixed with 0.3 mol / L sodium hydroxide solution at a mass-volume ratio of 1 g: 10 mL and reacted for 4 h. The filter residue was filtered and dried to obtain the modified reactant. The reactant was placed in a muffle furnace, nitrogen gas was introduced, and the temperature was raised to 650 °C at a rate of 13 °C / min and held for 4 h to obtain magnesium salt modified biochar for later use.

[0064] 1. Nitrogen and phosphorus retention capacity of magnesium salt-modified biochar soil conditioners with different magnesium / carbon mass ratios

[0065] Experimental Groups: Magnesium oxide and magnesium salt modified biochar were mixed in different mass ratios to obtain magnesium salt modified biochar soil conditioners with different magnesium / carbon mass ratios. Five experimental groups were set up: 0% (without magnesium oxide), 10% (magnesium oxide: magnesium salt modified biochar = 10:100), 20% (magnesium oxide: magnesium salt modified biochar = 20:100), 40% (magnesium oxide: magnesium salt modified biochar = 40:100), and 60% (magnesium oxide: magnesium salt modified biochar = 60:100).

[0066] Batch adsorption tests were conducted to analyze the nitrogen and phosphorus retention capacity of magnesium salt-modified biochar soil conditioners with different magnesium / carbon mass ratios. The specific experimental scheme was as follows:

[0067] Experimental solutions with initial ammonia nitrogen concentrations of 4 mg / L and initial phosphate concentrations of 0.8 mg / L were prepared. 2 g of soil conditioner from different experimental groups were placed in 1 L of each solution for adsorption for 1 h. The nitrogen and phosphorus retention capacity of magnesium-modified biochar soil conditioners with different magnesium / carbon mass ratios was determined. The results are as follows: Figure 1 As shown in the figure, the horizontal axis represents different experimental groups, and the vertical axis represents the adsorption amount (mg / kg).

[0068] according to Figure 1 It was found that the adsorption capacities of magnesium salt-modified biochar soil conditioner with a magnesium / char mass ratio of 0% for ammonia nitrogen and phosphate were 1840 and 523.9 mg / kg, respectively. The adsorption capacities of magnesium salt-modified biochar soil conditioners with magnesium / char mass ratios of 10%–60% for ammonia nitrogen and phosphate were 4550–7860 mg / kg and 1702–1931 mg / kg, respectively. The retention capacities of magnesium salt-modified biochar soil conditioners for ammonia nitrogen and phosphate were significantly higher than those of magnesium salt-modified biochar. No significant difference was shown in the adsorption capacity of phosphate for magnesium salt-modified biochar soil conditioners with different magnesium / char mass ratios. The adsorption capacity for ammonia nitrogen reached a higher level at magnesium / char mass ratios of 20% and 40%.

[0069] 2. Magnesium salt-modified biochar soil conditioner with magnesium / char mass ratios of 20% and 40% showed its effect on NH4+ in single and composite systems. 4+ and PO4 3- Holding capacity

[0070] Experimental Groups: The experiment was divided into 4 groups, namely Experimental Group 1: NH 4+ Experimental solutions with initial concentrations of 0.5, 1, 2, 4, 6, and 8 mg / L; Experimental group 2: PO4 3- The initial concentration was kept constant at 0.8 mg / L, NH 4+ Experimental solutions with initial concentrations of 0.5, 1, 2, 4, 6, and 8 mg / L; Experimental group 3: PO4 3- Experimental solutions with initial concentrations of 0.1, 0.2, 0.4, 0.6, 0.8, and 1.0 mg / L; Experimental group 4: NH 4+ The initial concentration was kept constant at 4 mg / L, PO4 3- Experimental solutions with initial concentrations of 0.1, 0.2, 0.4, 0.6, 0.8 and 1.0 mg / L.

[0071] Isothermal adsorption experiments were used to further investigate the effects of magnesium salt-modified biochar soil conditioner on NH3 in single and composite systems at magnesium / char mass ratios of 20% and 40%. 4+ and PO4 3- The difference in retention capacity was determined by the following experimental design:

[0072] Two g of magnesium salt-modified biochar soil conditioner with magnesium / char mass ratios of 0%, 20%, and 40% were respectively placed into experimental solutions of different concentrations in experimental groups 1–4, each with a volume of 1 L, for adsorption for 1 h. The effects of magnesium salt-modified biochar soil conditioner on NH3 in single and composite systems were determined when the magnesium / char mass ratio was 20% and 40%. 4+ and PO4 3- The retention capacity was assessed by plotting isothermal adsorption curves, and the results are as follows: Figure 2 As shown in the figure, Figure a represents the isothermal adsorption curves of nitrogen and phosphorus adsorption capacity of magnesium salt modified biochar soil conditioners with magnesium / carbon mass ratios of 0%, 20%, and 40% in Experimental Group 1 solution; Figure b represents the isothermal adsorption curves of nitrogen and phosphorus adsorption capacity of magnesium salt modified biochar soil conditioners with magnesium / carbon mass ratios of 0%, 20%, and 40% in Experimental Group 2 solution; Figure c represents the isothermal adsorption curves of nitrogen and phosphorus adsorption capacity of magnesium salt modified biochar soil conditioners with magnesium / carbon mass ratios of 0%, 20%, and 40% in Experimental Group 3 solution; Figure d represents the isothermal adsorption curves of nitrogen and phosphorus adsorption capacity of magnesium salt modified biochar soil conditioners with magnesium / carbon mass ratios of 0%, 20%, and 40% in Experimental Group 4 solution.

[0073] according to Figure 2 It can be seen that in a container containing only NH 4+ In solutions, magnesium salt-modified biochar, magnesium salt-modified biochar soil conditioner with a magnesium / char mass ratio of 20%, and magnesium salt-modified biochar soil conditioner with a magnesium / char mass ratio of 40% showed effects on NH4+. 4+ The maximum adsorption capacities were 3324.4 mg / kg, 7876.1 mg / kg, and 7882.3 mg / kg, respectively; in the presence of only PO4 3- In the solution, magnesium salt modified biochar, magnesium salt modified biochar soil conditioner with a magnesium / char mass ratio of 20%, and magnesium salt modified biochar soil conditioner with a magnesium / char mass ratio of 40% showed effects on PO4. 3- The maximum adsorption capacities were 625.0 mg / kg, 3245.9 mg / kg, and 3626.3 mg / kg, respectively; while simultaneously containing NH4+... 4+ and PO4 3- In solutions, magnesium salt-modified biochar, magnesium salt-modified biochar soil conditioner with a magnesium / char mass ratio of 20%, and magnesium salt-modified biochar soil conditioner with a magnesium / char mass ratio of 40% showed effects on NH4+. 4+ The maximum adsorption capacities were 2321.2 mg / kg, 8051.9 mg / kg, and 7890.5 mg / kg, respectively, for PO4. 3-The maximum adsorption capacities were 4596.3 mg / kg, 4052.7 mg / kg, and 323.7 mg / kg, respectively. In summary, considering both cost and nitrogen and phosphorus retention effects, the magnesium / carbon mass ratio of the magnesium salt modified biochar soil conditioner was set at 20%, and this magnesium salt modified biochar soil conditioner was used for subsequent experiments.

[0074] Experimental Example 2: Nutrient and Alkalinity Slow-Release Capacity of Magnesium Salt Modified Biochar Soil Conditioner

[0075] Magnesium salt modified biochar soil conditioner with a magnesium / carbon mass ratio of 20% was applied to the soil. Different application rates of 0, 50, 150, 300, 450, 600 and 750 kg / mu were set to conduct intermittent leaching experiments to simulate the water infiltration process under natural conditions. Then, the nitrogen and phosphorus nutrient concentrations in the soil were continuously monitored.

[0076] 1. Slow-release effect on phosphorus in soil

[0077] The slow-release effect of phosphorus in soils treated with different amounts of magnesium salt-modified biochar soil conditioner was determined, and the results are as follows: Figure 3 As shown in the figure, a represents the total phosphorus concentration of soils treated with different amounts of magnesium salt modified biochar soil conditioner, with the horizontal axis representing the number of days and the vertical axis representing the total phosphorus concentration of the soil (g / kg); b represents the available phosphorus concentration of soils treated with different amounts of magnesium salt modified biochar soil conditioner, with the horizontal axis representing the number of days and the vertical axis representing the available phosphorus concentration of the soil (g / kg).

[0078] according to Figure 3 It can be seen that applying different amounts of magnesium salt modified biochar soil conditioner to the soil has basically no effect on the total phosphorus concentration, but it does affect the concentration of available phosphorus. When the field application rate of magnesium salt modified biochar soil conditioner is 0 kg / mu, the soil available phosphorus concentration gradually decreases from 30.0 mg / kg to 22.8 mg / kg. When the field application rate of magnesium salt modified biochar soil conditioner is 50 kg / mu, the soil available phosphorus concentration gradually increases from 44.4 mg / kg to 63.6 mg / kg. In the other treatments (150–750 kg / mu), the available phosphorus concentration is finally maintained in the range of 123.0–150.7 mg / kg.

[0079] 2. Slow-release effect on nitrogen in soil

[0080] The nitrogen slow-release effect of soils treated with different amounts of magnesium salt-modified biochar soil conditioner was determined, and the results are as follows: Figure 4As shown in the figure, Figure a represents the total nitrogen concentration of soils treated with different amounts of magnesium salt-modified biochar soil conditioner, with the horizontal axis representing the number of days and the vertical axis representing the total nitrogen concentration of the soil (g / kg); Figure b represents the ammonia nitrogen concentration of soils treated with different amounts of magnesium salt-modified biochar soil conditioner, with the horizontal axis representing the number of days and the vertical axis representing the ammonia nitrogen concentration of the soil (g / kg); Figure c represents the nitrate nitrogen concentration of soils treated with different amounts of magnesium salt-modified biochar soil conditioner, with the horizontal axis representing the number of days and the vertical axis representing the nitrate nitrogen concentration of the soil (g / kg); and the available nitrogen concentration of soils treated with different amounts of magnesium salt-modified biochar soil conditioner, with the horizontal axis representing the number of days and the vertical axis representing the ammonia nitrogen concentration of the soil (g / kg).

[0081] according to Figure 4 It was found that applying different amounts of magnesium salt-modified biochar soil conditioner had virtually no effect on the total nitrogen concentration, but did affect the ammonia nitrogen, nitrate nitrogen, and available nitrogen concentrations. When the application rate of magnesium salt-modified biochar soil conditioner was 0 kg / mu, the soil ammonia nitrogen concentration gradually decreased from 4.20 mg / kg to 3.20 mg / kg. At an application rate of 50 kg / mu, the soil ammonia nitrogen concentration first increased to 4.73 mg / kg and then gradually decreased to 3.65 mg / kg. In the other treatments (150–750 kg / mu), the soil ammonia nitrogen concentration slowly increased to the range of 7.40–8.98 mg / kg. Similarly, when the application rate of magnesium salt-modified biochar soil conditioner was 0 kg / mu, the soil nitrate nitrogen concentration gradually decreased from 2.00 mg / kg to 1.92 mg / kg. At an application rate of 50 kg / mu, the soil nitrate nitrogen concentration... The nitrate nitrogen concentration gradually decreased from 2.77 mg / kg to 2.45 mg / kg. In the other treatments (150–750 kg / mu), the soil nitrate nitrogen concentration ultimately remained in the range of 3.59–3.70 mg / kg. When the field application rate of magnesium salt modified biochar soil conditioner was 0 kg / mu, the soil available nitrogen concentration gradually decreased from 7.86 mg / kg to 6.00 mg / kg. When the application rate was 50 kg / mu, the soil available nitrogen concentration remained at around 8.30 mg / kg. In the other treatments (150–750 kg / mu), the soil available nitrogen concentration ultimately remained in the range of 11.90–14.92 mg / kg.

[0082] 3. Effects on soil pH

[0083] The pH values ​​of soils treated with different amounts of magnesium salt-modified biochar soil conditioner were measured, and the results are as follows: Figure 5 As shown in the figure, the horizontal axis represents the number of days, and the vertical axis represents the pH value of the soil.

[0084] according to Figure 5It was found that applying different amounts of magnesium salt-modified biochar soil conditioner altered the soil pH. When the application rate of magnesium salt-modified biochar soil conditioner was 0 kg / mu, the soil pH remained around 4.5. At an application rate of 50 kg / mu, the soil pH slowly increased from 4.61 to 5.03. At other application rates, the soil pH significantly increased to 6.12–6.20, demonstrating a good improvement effect on acidic soils.

[0085] In summary, when using magnesium salt modified biochar soil conditioner to improve soil, if the application rate is not less than 100 kg / mu, the slow-release effect of magnesium salt modified biochar soil conditioner can significantly improve nitrogen and phosphorus nutrient indicators such as available phosphorus, ammonia nitrogen, and available nitrogen in the soil, and can also effectively improve acidic soil.

[0086] Example 3: Effects of magnesium salt modified biochar soil conditioner on maize yield

[0087] A field experiment was conducted to investigate the effect of applying magnesium salt modified biochar soil conditioner on improving maize yield.

[0088] Maize was planted in the field using conventional methods, divided into four regions, with four different treatment levels: 0 kg / mu, 150 kg / mu, 300 kg / mu, and 600 kg / mu of magnesium-modified biochar soil conditioner. Three replicate plots were set up for each treatment to ensure the reliability and comparability of the data. At harvest, the plant height (cm), stem diameter (mm), above-ground fresh weight (g), and fresh ear weight (g) of maize were measured. The effects of different magnesium salt-modified biochar soil conditioner application rates on maize growth and yield were determined. The results are shown in Table 1, where different letters indicate significant differences.

[0089] Table 1. Effects of different magnesium salt modified biochar soil conditioner application rates on maize growth and yield.

[0090]

[0091] Table 1 shows that when the field application rate of magnesium salt-modified biochar soil conditioner was 0 kg / mu, the maize plant height was 202.1 cm, while the plant height significantly increased to 217.0–221.2 cm when the application rate was 150–600 kg / mu. Similarly, when the field application rate of magnesium salt-modified biochar soil conditioner was 0 kg / mu, the maize stalk diameter was 25.1 mm, while the plant height significantly increased to 26.8–27.6 mm when the application rate was 150–300 kg / mu. When the application rate of magnesium salt-modified biochar soil conditioner was 0 kg / mu, the above-ground fresh weight of maize was 524.1 g. With an application rate of 150–600 kg / mu, the above-ground fresh weight of maize significantly increased to 570.4–616.7 g. Similarly, when the application rate was 0 kg / mu, the fresh ear weight of maize was 295.6 g. With an application rate of 150–300 kg / mu, the above-ground fresh weight of maize significantly increased to 335.6–362.2 g. In conclusion, this indicates that the application rate of magnesium salt-modified biochar soil conditioner at 150–300 kg / mu can significantly improve the growth traits and yield of maize.

[0092] Example 4: Field trial of magnesium salt modified biochar soil conditioner

[0093] A field experiment was conducted to investigate the soil improvement effect of magnesium salt modified biochar soil conditioner one year after application under the wheat-maize rotation model.

[0094] Test location: Ciwu Town, Zhuji City, Shaoxing City, Zhejiang Province, address as follows Figure 6 As shown.

[0095] Experimental Design: Wheat sowing and fertilization were carried out on November 19, 2023, following traditional practices of local farmers. Specifically, 25 kg of compound fertilizer (NPK ratio of 20-10-15) was applied as basal fertilizer after sowing. The experimental design included four different treatment levels with magnesium-modified biochar soil conditioner application rates of 0 kg / mu, 150 kg / mu, 300 kg / mu, and 600 kg / mu. Three replicates were established for each treatment to ensure data reliability and comparability. Field photos are shown below. Figure 7 As shown.

[0096] 1. Changes in soil nutrient content one year after application of different magnesium salt-modified biochar.

[0097] One year later, the soil's available nitrogen (mg / kg), total nitrogen (g / kg), available phosphorus (mg / kg), total phosphorus (g / kg), organic matter (g / kg), total potassium (g / kg), available potassium (mg / kg), and pH value were measured under different application rates of magnesium salt modified biochar and soil conditioner. The results are shown in Table 2. Different letters in the table indicate significant differences.

[0098] Table 2 Soil nutrient indices under different magnesium salt modified biochar application rates and soil conditioner application rates.

[0099]

[0100]

[0101] Table 2 shows that, regarding the available nitrogen content in the soil, when the application rate of magnesium salt modified biochar soil conditioner was 0 kg / mu, the available nitrogen content in the soil was 36.72 mg / kg. At application rates of 150 and 300 kg / mu, the available nitrogen content increased by 0.81 and 3.15 kg / mu respectively compared to the 0 kg / mu application rate, but the increase was not significant. At an application rate of 600 kg / mu, the available nitrogen content increased significantly by 7.79 mg / kg compared to the 0 kg / mu application rate. Regarding the available phosphorus content in the soil, magnesium salt modified biochar… When the application rate of magnesium salt-modified biochar soil conditioner was 0 kg / mu, the available phosphorus content in the soil was 22.75 mg / kg. The available phosphorus content in the soil did not change significantly at application rates of 150 and 300 kg / mu. At an application rate of 600 kg / mu, the available phosphorus content in the soil was 27.30 mg / kg, a significant increase of 4.55 mg / kg compared to the 0 kg / mu application rate. Regarding total nitrogen, organic matter, total potassium, available potassium, and pH value in the soil, the total nitrogen content did not change significantly under different application rates of magnesium salt-modified biochar soil conditioner. In conclusion, under a wheat-maize rotation system, the application of magnesium salt-modified biochar soil conditioner (600 kg / mu) significantly increased the content of available nitrogen and phosphorus in the soil after one year.

[0102] 2. Effects of different application rates of magnesium salt-modified biochar soil conditioner on the growth and yield of wheat and maize.

[0103] Through field experiments, this study further explored the effects of magnesium salt modified biochar soil conditioner on wheat and corn growth and yield one year after the application of the soil conditioner under wheat-corn rotation. The plant height (cm), stem diameter (mm), thousand-grain weight (g), and yield (kg / mu) of wheat were measured at harvest. The effects of different magnesium salt modified biochar application rates on wheat growth and yield were also measured. The results are shown in Table 3, where different letters indicate significant differences.

[0104] Table 3. Effects of different magnesium salt modified biochar application rates on wheat growth and yield.

[0105]

[0106]

[0107] The plant height (cm), stem diameter (mm), above-ground fresh weight (g), and yield (kg / mu) of maize at harvest were measured. The effects of different application rates of magnesium salt modified biochar soil conditioner on maize growth and yield were also determined. The results are shown in Table 4, where different letters indicate significant differences.

[0108] Table 4. Effects of different magnesium salt modified biochar soil conditioner application rates on maize growth and yield.

[0109]

[0110] Tables 3 and 4 show that corn yield increased by 16.0%, while wheat plant height and yield increased by 4.78% and 3.12%, respectively. This indicates that magnesium salt-modified biochar soil conditioner can increase crop yield.

[0111] As can be seen from the above embodiments, the present invention provides a method for preparing a magnesium salt modified biochar soil conditioner, comprising the following steps: (1) preparing reactants using crop straw and magnesium chloride solution; (2) preparing modified reactants using sodium hydroxide solution and pyrolyzing them to obtain magnesium salt modified biochar; (3) mixing magnesium oxide and magnesium salt modified biochar to obtain a magnesium salt modified biochar soil conditioner. The magnesium salt modified biochar soil conditioner prepared according to the method of the present invention can significantly improve nitrogen and phosphorus nutrient indicators such as available phosphorus, ammonia nitrogen, and available nitrogen in the soil, effectively improve acidic soil, and also improve crop growth traits and yield.

[0112] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a magnesium salt-modified biochar soil conditioner, characterized in that, Includes the following steps: (1) Mix crop straw with magnesium chloride solution, heat to 55-65℃ and keep for 1-3 hours to obtain a mixed solution, filter the mixed solution to obtain the filter residue, and dry to obtain the reactant; (2) Mix the reactants with sodium hydroxide solution and react for 3.5 to 4.5 hours. Filter the residue and dry it to obtain the modified reactants. Heat the modified reactants to 600 to 700°C under nitrogen and maintain the temperature for 3 to 5 hours to obtain magnesium salt modified biochar. (3) Magnesium oxide is mixed with magnesium salt modified biochar to obtain magnesium salt modified biochar soil conditioner.

2. The preparation method according to claim 1, characterized in that, The particle size of the crop straw mentioned in step (1) is 1-3 mm; The crop straw includes one or more of corn straw, wheat straw, and soybean straw.

3. The preparation method according to claim 1, characterized in that, The mass-to-volume ratio of crop straw to magnesium chloride solution in step (1) is 1 g: 45-55 mL; The initial concentration of the magnesium chloride solution is 1–2 mol / L.

4. The preparation method according to claim 1, characterized in that, The mass-to-volume ratio of the reactant to the sodium hydroxide solution in step (2) is 1 g: 8-12 mL; The initial concentration of the sodium hydroxide solution is 0.2–0.4 mol / L.

5. The preparation method according to claim 1, characterized in that, The heating rate in step (2) is 12-14 °C / min.

6. The preparation method according to claim 1, characterized in that, The mass ratio of magnesium oxide to magnesium salt modified biochar in step (3) is 0.2 to 0.4:

1.

7. The magnesium salt modified biochar soil conditioner prepared by the preparation method according to any one of claims 1 to 6.

8. The application of the magnesium salt modified biochar soil conditioner prepared by the preparation method according to any one of claims 1 to 6 or the magnesium salt modified biochar soil conditioner according to claim 7 in improving acidic soil.

9. The application of the magnesium salt modified biochar soil conditioner prepared by the preparation method according to any one of claims 1 to 6 or the magnesium salt modified biochar soil conditioner according to claim 7 in improving crop yield.

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