Remediation agent for secondary salinized soil and application

Abstract

The invention provides a repairing agent for secondary salinization soil and application, and solves the technical problem that in the prior art, secondary salinization of soil affects plant growth. The magnesium modified charcoal is applied to the salinized soil, so that the structure and the property of the salinized soil are effectively improved, the pH value and the organic matter content of the soil are increased, and the stress resistance of the soil is enhanced; meanwhile, the Mg-BC can also improve the soil fertility, increase the potassium content in the soil, reduce the sodium content, improve the enzyme activity of the soil and promote the nutrient conversion of the soil. When cucumbers are planted, Mg-BC can remarkably promote growth of the cucumbers, increase the biomass of root systems and overground parts of the cucumbers, increase the chlorophyll content and the photosynthetic rate of the cucumbers, enhance the stress resistance of plants, regulate ion balance in the plants and enable the Na / K content to tend to be normal. Besides, after the Mg-BC is added for treatment, the chlorophyll content and the plant growth condition of the cucumber are superior to those of a plant which is not subjected to salt stress, which indicates that the Mg-BC not only effectively relieves the adverse effect of the salt stress on the growth of the cucumber, but also remarkably promotes the growth and development of the cucumber on the basis.

Description

Technical Field

[0001] The present invention belongs to the technical field of soil remediation agents, and particularly relates to a remediation agent for secondary salinized soil and its application. Background Art

[0002] In recent years, the facility vegetable industry in China has developed rapidly. During the cultivation of facility vegetables, the soil is in cultivation environments such as greenhouses and sheds, lacking rain leaching. This special ecological environment and unreasonable water and fertilizer management measures are likely to cause secondary salinization of the soil, resulting in stunted growth of vegetables. Especially for cucumbers, their seedling roots are fragile and extremely sensitive to salt. The secondary salinization of the soil limits high-efficiency production and leads to a reduction in its yield. Summary of the Invention

[0003] The present invention provides a remediation agent for secondary salinized soil and its application, aiming to solve the technical problem that the secondary salinization of the soil in the prior art affects plant growth.

[0004] To solve the above technical problems, the technical solutions adopted in the present invention are as follows:

[0005] In a first aspect, the present invention provides a remediation agent for secondary salinized soil, which includes Mg-modified biochar.

[0006] In a preferred embodiment, the Mg content in the Mg-modified biochar is 7.0 - 7.5%.

[0007] Based on the above embodiment, the Mg-modified biochar with an Mg content of 7.0 - 7.5% can increase the magnesium content in the soil. Magnesium is one of the important nutrient elements for plant growth. Appropriate addition can supplement the magnesium element in the soil, promote the normal growth of plants, and improve the yield and quality of crops.

[0008] In a preferred embodiment, the preparation method of the Mg-modified biochar includes:

[0009] S1. Preparation of biochar: Using the leaves of Photinia serratifolia as raw materials, after drying, carbonization treatment is carried out at 450 - 550°C under anaerobic or oxygen-limited conditions for 1.5 - 2.5 h, and then washed and dried to obtain biochar;

[0010] S2. Modification by magnesium chloride impregnation method: Mix the prepared biochar with magnesium chloride solution, soak the magnesium chloride solution into the biochar, filter after stirring and sealed impregnation, wash to remove impurities, and then dry and perform anaerobic calcination to obtain Mg-modified biochar.

[0011] Based on the above scheme, using the leaves of Photinia × fraseri as raw materials, which are widely sourced and low in cost, the resource utilization of waste is realized. By preparing Mg-modified biochar through the magnesium chloride impregnation method, magnesium ions can be evenly loaded on the surface and internal pores of the biochar, increasing the active sites and oxygen-containing functional groups (such as hydroxyl, carboxyl, and carbonyl) on the biochar surface, thereby significantly improving the adsorption capacity of the biochar for heavy metal ions (such as copper, cadmium, lead, etc.).

[0012] In a second aspect, the present invention provides an application of the repair agent described in the first aspect in repairing secondary salinized soil.

[0013] In a third aspect, the present invention provides an application of the repair agent described in the first aspect in promoting the growth and development of cucumbers in secondary salinized soil.

[0014] In a fourth aspect, the present invention provides a method for promoting the growth and development of cucumbers under the condition of secondary salinized soil, including: under the condition of secondary salinized soil, planting cucumbers after adding the Mg-modified biochar in the repair agent for secondary salinized soil described in the first aspect;

[0015] In every 95 - 105 parts by mass of salinized soil, 0.8 - 1.2 parts by mass of Mg-modified biochar is added.

[0016] In a preferred scheme, in every 100 parts by mass of salinized soil, 1.0 part by mass of Mg-modified biochar is added.

[0017] Based on the above scheme, Mg-modified biochar can increase the pH value of the soil, improve the acid-base balance of the soil. Appropriate addition can effectively neutralize the alkalinity of salinized soil, making it more suitable for plant growth, and will not cause excessive changes in soil properties due to excessive addition, affecting the normal ecological functions of the soil.

[0018] In a preferred scheme, in every 95 parts by mass of salinized soil, 1.1 parts by mass of Mg-modified biochar is added.

[0019] In a preferred scheme, in every 105 parts by mass of salinized soil, 0.8 parts by mass of Mg-modified biochar is added.

[0020] The beneficial effects of the present invention are as follows:

[0021] The present invention provides a soil amendment for secondary salinized soil and its application. Mg-modified biochar can effectively improve the structure and properties of salinized soil, increase the soil pH value and organic matter content, and enhance the soil stress resistance. At the same time, it can also improve soil fertility, increase the potassium content in the soil and reduce the sodium content, enhance soil enzyme activity, and promote soil nutrient transformation. When planting cucumbers, Mg-BC can significantly promote cucumber growth, increase the biomass of its roots and shoots, increase chlorophyll content and photosynthetic rate, enhance plant stress resistance, regulate the ion balance in plants, and make the Na / K content tend to be normal, thus effectively alleviating the adverse effects of salt stress on cucumber growth and providing strong support for the healthy growth of cucumbers. Specifically as follows:

[0022] The present invention provides a soil amendment for secondary salinized soil and its application. By applying Mg-modified biochar (Mg-BC) to the soil, the soil structure and properties can be improved, soil fertility can be enhanced, and plant nutrient absorption can be promoted.

[0023] Experimental results have shown that Mg-BC can increase the pH value of salinized soil, increasing the soil pH by 0.17 and 1.33 respectively, effectively improving saline-alkali soil, improving the soil acid-base balance, and enhancing soil quality and productivity. It can also increase the soil organic matter content, with the increase rates being 16.86% and 28.21% respectively, further improving the soil stress resistance and making the soil more adaptable to environmental changes and external pressures.

[0024] After applying Mg-BC, the potassium (K) content in the soil increased by 35.92% and 77.84% compared with the NaCl group, while the sodium (Na) content decreased, which helps to improve the soil's ion adsorption capacity and cation exchange capacity, enhance the soil buffer capacity, and reduce the adverse effects of salinization on plants. In addition, Mg-BC can also significantly increase soil enzyme activity, such as soil urease and soil acid phosphatase activity, promote soil nitrogen and phosphorus transformation, and thus improve soil fertility.

[0025] In addition, under salt stress, adding Mg-BC can reduce the Na content in the shoots and roots of cucumbers and increase the K content, which is beneficial to the absorption of nutrient K, reduces the adverse effects of Na on plants, and provides more balanced nutrition for plants.

[0026] When the present invention applies Mg-modified biochar to cucumber planting, it has the effects of promoting cucumber growth, improving photosynthesis efficiency, enhancing the stress resistance of cucumber plants, and regulating the ion balance in cucumber plants.

[0027] Experimental results show that under salinization treatment, the plant height, root length and dry weight of cucumber decreased significantly, while the addition of Mg-BC significantly promoted plant growth and alleviated salt stress. The biomass of cucumber roots and shoots with BC and Mg-BC addition increased by 133.68%, 60.01% and 257.44%, 91.68% respectively. The plant height and root length of cucumber in the Mg-BC+NaCl group increased by 55.11% and 76.59% compared with the NaCl group, which was beneficial to improving the root growth of cucumber. Moreover, the root length and plant height of the plants grown after adding Mg-BC were higher than those of the plants not under salt stress, indicating that Mg-BC can not only effectively improve the adverse effects of salt stress on plants, but also further promote plant growth.

[0028] Compared with salt stress, the addition of BC and Mg-BC significantly increased the contents of chlorophyll a, chlorophyll b and total chlorophyll, and the effect of the Mg-BC treatment group was better. By increasing the chlorophyll content, Mg-BC improved the light energy utilization rate, which was beneficial to plant growth and development. In addition, NaCl treatment significantly decreased the Fv / Fm of cucumber leaves, while the Fv / Fm of the BC+NaCl and Mg-BC+NaCl treatments increased by 8.96% and 11.71% compared with the NaCl treatment, effectively improving the photosynthetic rate of plants under salt stress. Moreover, after adding Mg-BC, the chlorophyll content of the grown plants was higher than that of the plants not under salt stress, indicating that Mg-BC can not only alleviate the decrease in chlorophyll caused by salt stress, but also further increase the chlorophyll content on the basis of restoring the chlorophyll content, thus improving the light energy utilization rate and being more beneficial to plant growth and development.

[0029] Among them, after Mg-BC treatment, the antioxidant enzyme activity increased significantly compared with the NaCl group, triggering a series of physiological reactions, reducing the impact of salt stress on intracellular oxidative stress in cucumber cells, enhancing the plant's ability to scavenge excess ROS, and enabling it to better adapt to the salt stress environment.

[0030] In addition, under salt stress, when BC and Mg-BC were added, the Na content ratios of the cucumber shoots, roots and soil were significantly lower than those of the NaCl treatment, while the K content was significantly higher than that of the NaCl group. When Mg-BC was applied, the Na / K content tended to be normal, balancing the contents of Na, K, etc. in plants and soil, and improving soil fertility and potential oxygen supply levels. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention, and therefore should not be regarded as limiting the scope. For those of ordinary skill in the art, other related drawings can be obtained based on these drawings without creative efforts.

[0032] Figure 1 It is the characterization diagram of biochar in the present invention.

[0033] Figure 2 It is the result diagram of the effect of magnesium-modified biochar on cucumber growth and protective enzyme activity under salt stress in the experiment of the present invention.

[0034] Figure 3 It is the result diagram of the effect of magnesium-modified biochar on Na and K absorption of cucumber under salt stress in the experiment of the present invention.

[0035] Figure 4 It is the result diagram of the effect of magnesium-modified biochar on soil properties and enzyme activity under salt stress in the experiment of the present invention. Detailed implementation manners

[0036] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative labor fall within the protection scope of the present invention.

[0037] Embodiment 1:

[0038] This embodiment provides a repair agent for secondary salinized soil, including Mg-modified biochar.

[0039] Among them, the Mg content in the Mg-modified biochar is 7.0-7.5%.

[0040] Specifically, in the magnesium (Mg)-modified biochar, the content of magnesium accounts for 7.0% to 7.5% of the total mass of the biochar, and can be 7.2%, 7.3% or 7.5%, etc. A relatively optimal scheme: the content of magnesium accounts for 7.21% of the total mass of the biochar.

[0041] In addition, the preparation method of the Mg-modified biochar includes:

[0042] S1. Preparation of biochar: Using the leaves of Photinia serratifolia as raw materials, carbonization treatment is carried out under high temperature, anaerobic or oxygen-limited conditions to obtain biochar;

[0043] Specifically, wash the leaves of Photinia serratifolia, dry them, and then crush them into small particles, and use a tube furnace or a fixed-bed reactor for carbonization treatment. Put the crushed leaves into the reactor, introduce nitrogen to exclude oxygen and prevent oxidation, set the carbonization temperature to 600-1000 °C, keep the time for 45-90 minutes, and after carbonization is completed, naturally cool to room temperature to obtain biochar.

[0044] S2. Modification by magnesium chloride impregnation method: Mix the prepared biochar with magnesium chloride solution to impregnate the magnesium chloride solution into the biochar, and then dry and calcine the impregnated biochar to obtain Mg-modified biochar.

[0045] Specifically, mix the prepared biochar with magnesium chloride solution for 18 - 24 h, take out the impregnated biochar from the solution, filter off the excess solution, put the filtered biochar into an oven, set the temperature at 60 - 100 °C, and dry for 12 - 24 hours to remove moisture. Carry out calcination treatment with a tube furnace or a muffle furnace. Put the dried biochar into a reactor, introduce nitrogen to prevent oxidation, set the calcination temperature at 300 - 600 °C, and keep the time for 1 - 2 hours. The calcination process can remove excess organic impurities and improve the stability and adsorption performance of the biochar. After calcination, cool down to room temperature naturally to obtain Mg-modified biochar.

[0046] Example Two:

[0047] This example provides an application of the repair agent described in Example One in repairing secondary salinized soil.

[0048] Example Three:

[0049] This example provides an application of the repair agent described in Example One in promoting the growth and development of cucumbers in secondary salinized soil.

[0050] Example Four:

[0051] This example provides a method for promoting the growth and development of cucumbers under the conditions of secondary salinized soil, including: under the conditions of secondary salinized soil, plant cucumbers after adding the Mg-modified biochar in the repair agent for secondary salinized soil described in Example One;

[0052] In every 95 - 105 parts by mass of salinized soil, add 0.8 - 1.2 parts by mass of Mg-modified biochar.

[0053] Among them, in every 95 parts by mass of salinized soil, add 1.1 parts by mass of Mg-modified bio.

[0054] Or, in every 105 parts by mass of salinized soil, add 0.8 parts by mass of Mg-modified bio.

[0055] A better scheme: In every 100 parts by mass of salinized soil, add 1.0 parts by mass of Mg-modified bio.

[0056] The following further explains and illustrates the present invention in combination with specific tests:

[0057] 1. Materials and Methods

[0058] 1.1 Test Materials and Design

[0059] 1.1.1 Materials

[0060] Test seeds: Cucumber variety Zhongnong 49, produced by Zhongshu Seed Industry Science and Technology Co., Ltd., Beijing.

[0061] Salinized soil: Collected from Zhejiang Province, with geographical coordinates of 19°35'47″E and 29°5′46″N, being the 0 - 20 cm soil of a facility vegetable field.

[0062] Cultivation pots: With a specification of 15×15 cm, each pot filled with 1 kg of soil.

[0063] 1.1.2 Preparation of Biochar

[0064] A1. Preparation of biochar (BC): Take the leaves of Photinia serratifolia, a garden waste, and wash them repeatedly with tap water to remove impurities, then rinse them thoroughly with deionized water. Place the washed leaves in a drying oven at 65°C for 6 hours, crush them, and pass them through a 1 - mm sieve to obtain powder. Put the powder into a tubular furnace, and introduce nitrogen (N 2 ) for protection at a flow rate of 400 mL / min. Raise the temperature to 500°C at a heating rate of 10°C / min, keep it at a constant temperature for 120 minutes, then continue to introduce nitrogen and cool it to 25°C. Wash the fired biochar with deionized water, then dry it at 70°C for 6 hours, and finally store it sealed in a desiccator, labeled as BC.

[0065] A2. Preparation of magnesium - modified biochar (Mg - BC):

[0066] Accurately weigh 10 g of the crushed garden waste powder and immerse it in 100 mL of a 1 mol / L MgCl 2 ·6H 2 O solution. Oscillate it for 12 hours under magnetic stirring, and then seal the mixture for impregnation for 12 hours. After filtration, wash it alternately with deionized water and absolute ethanol 3 times to remove unreacted impurities and excess MgCl 2 ·6H 2 O solution. Place the washed solid in an oven at 105°C to dry and remove the residual moisture and organic solvents. Transfer the dried solid to a tubular furnace, and introduce nitrogen (N 2 ) for protection at a flow rate of 400 mL / min. Raise the temperature to 500°C at a heating rate of 10°C / min, keep it at a constant temperature for 120 minutes, then continue to introduce nitrogen and cool it to 25°C. Wash the fired biochar with deionized water, then dry it at 70°C for 6 hours, and finally store it sealed in a desiccator, labeled as Mg - BC.

[0067] 1.1.3 Test Design

[0068] CK: Normal soil, without salinization.

[0069] NaCl: Secondary salinized soil.

[0070] BC + NaCl: BC was added to the salinized soil at a ratio of 1% (w / w).

[0071] Mg - BC + NaCl: Mg - BC was added to the salinized soil at a ratio of 1% (w / w).

[0072] Cucumbers were grown in substrate seedlings. After growing one true leaf, they were transplanted into the soil, two plants per pot. After 50 days of planting, soil samples were taken to measure soil enzyme activities, pH, organic matter, and carbon-nitrogen ratio, and physiological indexes and biomass of cucumbers were determined.

[0073] 1.2 Determination methods

[0074] The morphology and particle size of BC were determined by scanning electron microscope (SEM, Zeiss, G300, Germany) and X-ray diffractometer (XRD). The functional groups of BC were identified by Fourier transform infrared spectroscopy (FT-IR, USA). The sodium and potassium contents of plants were determined by digestion method (Wang Duojia et al., 2023); the chlorophyll content was determined by ethanol extraction method; the chlorophyll fluorescence parameters were determined by PAM-2500 portable modulated chlorophyll fluorometer (WALZ, Germany); the sodium and potassium contents of soil were determined by atomic absorption method; the activity of soil urease (S-UE) was determined by indophenol blue colorimetric method; the activity of soil acid phosphatase (S-ACP) was determined by disodium phenyl phosphate colorimetric method; the content of soil organic matter was determined by potassium dichromate volumetric method.

[0075] 1.3 Data processing

[0076] The experimental data were sorted out by Microsoft Excel 2019, and the mean values and standard errors were calculated by one-way ANOVA and Least Significant Difference (LSD) using SPSS 25.0 to analyze the significant differences, and the graphs were plotted using Origin 2022.

[0077] 2. Results and analysis

[0078] 2.1 Characterization of magnesium-modified biochar

[0079] In Figure 1 a. SEM characterization of BC, b. SEM-EDX of BC, c. SEM characterization of Mg-BC, d. SEM-EDX map of Mg-BC, e. XRD patterns of BC and Mg-BC.

[0080] The SEM results of BC and Mg-BC showed that the surface of BC presented a porous and rod-like structure, while a large number of particles appeared on the surface of Mg-BC, which were MgCl particles formed during the Mg modification process. SEM-EDX indicated that the Mg content in Mg-BC was (7.21 wt%), indicating that BC had been successfully modified (a, b, c, d). XRD characterization showed that the characteristic peaks in BC corresponded to CaCO, while several new peaks appeared in Mg-BC relative to the BC sample, corresponding to MgCl, indicating that Mg had been successfully loaded on the biochar and MgCl was the main substance (e). 2 Particles. SEM-EDX showed that the Mg content in Mg-BC was (7.21 wt%), indicating that BC had been successfully modified ( Figure 1 a, b, c, d). XRD characterization showed that the characteristic peaks in BC corresponded to CaCO 3 , while several new peaks appeared in Mg-BC relative to the BC sample, corresponding to MgCl 2 , indicating that Mg had been successfully loaded on the biochar and MgCl 2 was the main substance ( Figure 1 e).

[0081] 2.2 Effects of magnesium-modified biochar on cucumber growth under salt stress

[0082] At Figure 2 , a. Plant height and root length, b. Dry weights of roots and shoots, c. Cucumber growth diagram, d. Root scanning, e. Leaf SOD activity, f. Leaf POD activity, g. Leaf CAT activity.

[0083] The growth indexes of plants can directly reflect the accumulation degree of photosynthetic organic matter and the growth trend of plants under different environments. Under salt stress treatment, the plant height, root length and dry weight of cucumbers decreased significantly. However, after adding Mg-BC, the situation improved greatly. It could not only significantly promote plant growth and relieve salt stress, but its growth performance even exceeded that of the non-salt-stress treatment group ( Figure 2 a, b, c, d). The biomass of roots and shoots of cucumbers with BC and Mg-BC added increased by 133.68%, 60.01% and 257.44%, 91.68% respectively. The plant height and root length of cucumbers in the Mg-BC + NaCl group increased by 55.11% and 76.59% compared with the NaCl group. The root length and plant height of the plants grown after adding Mg-BC were higher than those of the plants not under salt stress, which fully indicated that Mg-BC could not only effectively improve the adverse effects of salt stress on plants, but also further promote plant growth.

[0084] It can be seen that magnesium-modified biochar has a good effect on improving the growth of cucumber roots. Magnesium-modified biochar is beneficial to cucumber growth, significantly improving salt stress, especially for the growth of cucumber roots.

[0085] 2.3 Effects of magnesium-modified biochar on sodium and potassium uptake by cucumbers under salt stress

[0086] At Figure 3 : a. Na content in shoots and roots, b. K content in shoots and roots, c. Na / K in shoots and roots.

[0087] The available potassium nutrient content in saline soil is relatively low, and the high sodium content will increase the solubility of organic matter in the soil and exacerbate the loss of mineralized nutrients. As can be seen from Figure 3 (a, b, c), under salt stress, Na accumulates more in the above-ground parts and roots, while K accumulates less. After adding BC and Mg-BC under salt stress, the Na content in the roots and above-ground parts decreased by 16.83% and 24.36% respectively compared with that under salt stress, and the K content increased by 98.37% and 144.72% respectively.

[0088] Thus, both BC and Mg-BC can effectively reduce Na in the above-ground parts and roots of cucumbers and are beneficial to the absorption of nutrient K.

[0089] 2.4 Effects of magnesium-modified biochar on chlorophyll content and chlorophyll fluorescence of cucumbers under salt stress

[0090] 2.4.1 Effects of magnesium-modified biochar on chlorophyll content of cucumbers under salt stress

[0091] Chlorophyll is one of the main photosynthetic pigments in plant photosynthesis and is of great significance in the growth and development of plants. As can be seen from Table 1, compared with salt stress, adding BC and Mg-BC significantly increased the contents of chlorophyll a, chlorophyll b and total chlorophyll, and the effect of the Mg-BC treatment group was better. After adding Mg-BC, the chlorophyll content of the grown plants was higher than that of the plants without salt stress, indicating that Mg-BC can not only alleviate the decrease in chlorophyll caused by salt stress, but also further increase the chlorophyll content on the basis of restoring the chlorophyll content, thereby improving the light energy utilization rate and being more beneficial to the growth and development of plants.

[0092] 1 Effects of Mg-BC on chlorophyll content and chlorophyll fluorescence of cucumbers under salt stress

[0093]

[0094] Note: Different letters in the same column indicate significant differences (P<0.05).

[0095] 2.4.2 Effects of magnesium-modified biochar on the chlorophyll fluorescence parameter Fv / Fm of cucumbers under salt stress

[0096] Chlorophyll fluorescence parameters can directly reflect plant photosynthesis and are indicators of light energy utilization efficiency. Fv / Fm reflects the light energy conversion efficiency when the PS II reaction center is in a fully open state, and the change in the Fv / Fm fluorescence imaging intensity can be used as an internal parameter to detect the response of plant photosynthesis to adversity.

[0097] As shown in Table 1, the Fv / Fm of cucumber leaves was significantly decreased by NaCl treatment, while the Fv / Fm of BC+NaCl and Mg-BC+NaCl treatments increased by 8.96% and 11.71% compared with that of the NaCl treatment. The Fv / Fm value of normal plants is 0.7-0.8. The increase in Fv / Fm indicates that there are more open or oxidized electron acceptors in PS-II, which reduces the generation of active free radicals and effectively improves the photosynthetic rate of plants under salt stress.

[0098] 2.5 Improvement of magnesium-modified biochar on saline soil

[0099] 2.5.1 Improvement of sodium and potassium contents in saline soil by magnesium-modified biochar

[0100] In Figure 4 a. Soil Na and K contents, b. Soil urease activity, c. Soil acid phosphatase activity, d. Soil carbon-nitrogen ratio, e. Soil pH, f. Soil organic matter content.

[0101] Na has relatively little physiological effect on plants under normal growth conditions, but it may have an adverse effect on plants under special circumstances such as salt stress. K plays a more positive and extensive role in plant growth and is one of the key factors for plant growth, development and adaptation to the environment. As shown in Figure 4 (a), the application of BC and Mg-BC treatments can reduce the Na content in saline soil by 38.78% and 51.38% compared with the NaCl group, and increase the K content by 35.92% and 77.84% compared with the NaCl group. This indicates that the addition of BC improves the physical environment of saline soil, and the effect of Mg-BC is better. The increase in K content helps to improve the ion adsorption capacity of the soil and the cation exchange capacity, enhance the buffering capacity of the soil, while reducing the proportion of Na, maintaining soil fertility and reducing the adverse effects of salinization on plants.

[0102] 3.5.2 Enhancement of enzyme activities in saline soil by magnesium-modified biochar

[0103] Soil enzyme activity is an important indicator for characterizing soil nutrient cycling, microbial metabolic activity and soil fertility evaluation. As shown in Figure 4 (b, c), compared with salt stress, the addition of BC and Mg-BC significantly increased the activities of S-UE and S-ACP, and the enhancement of S-ACP activity by Mg-BC was better than that of BC.

[0104] 3.5.3 Improvement of physical and chemical properties of saline soil by magnesium-modified biochar

[0105] In most cases, a higher soil carbon-nitrogen ratio may be beneficial to the soil ecosystem and plant growth. As shown in Figure 4(d) It was found that the addition of BC and Mg-BC increased the carbon-nitrogen ratio of saline soil to 6.33 and 6.85, promoted the decomposition of organic matter, released nutrients, and thus improved soil fertility.

[0106] Soil pH is one of the important parameters determining the fertility characteristics of farmland soil. Soil acidification can lead to the destruction of soil structure, nutrient loss, and enhanced activity of soil heavy metals, thus directly or indirectly affecting the growth and development of crops. Through this, both BC and Mg-BC can increase the pH of saline-alkali soil, increasing it by 0.17 and 1.33 respectively, which can improve saline soil and enhance soil quality and productivity ( Figure 4 (e)).

[0107] The content of soil organic matter plays an important role in the physical, chemical, and biological characteristics of the soil. Analysis Figure 4 (f) showed that the addition of both BC and Mg-BC could effectively increase the content of organic matter in saline soil, with the increase rates being 16.86% and 28.21% respectively. The addition of Mg-BC increased soil organic matter, thus improving the stress resistance of the soil and enabling the soil to better adapt to environmental changes and cope with external pressures.

[0108] In this study, high-performance biochar was prepared by modifying red-leaf photinia biochar with magnesium chloride for the improvement of secondary saline soil. The growth of cucumbers growing in secondary saline soil was inhibited, and the dry weights of the above-ground parts and roots and the chlorophyll content were significantly reduced. After the addition of BC and Mg-BC, the inhibition of salt stress on cucumber growth and chlorophyll was reversed, and Mg-BC had a better alleviating effect on cucumbers under salt stress. Mg-BC could effectively provide Mg nutrition for the soil and cucumbers, reduce the damage of saline soil to chlorophyll and photosynthetic systems in leaves, thus improving the stability of the photosynthetic structure and the activity of reaction centers, maintaining the operation of photosynthesis, and contributing to the healthy growth of plants. After the Mg-BC treatment, the antioxidant enzyme activity increased significantly compared with the NaCl group, triggering a series of physiological reactions, reducing the impact of salt stress on intracellular oxidative stress in cucumbers, strengthening the plant's ability to scavenge excess ROS, and enabling it to better adapt to the salt stress environment.

[0109] Under salt stress conditions, the change trends of Na and K element contents in plants and soil are different. This experiment proved that under salt stress, after adding BC and Mg-BC, the Na content ratios in the above-ground parts, roots, and soil of cucumbers were significantly lower than those in the NaCl treatment, while the K contents were significantly higher than those in the NaCl group. This experiment proved that under salt stress, after adding BC and Mg-BC, the Na content ratios in the above-ground parts, roots, and soil of cucumbers were significantly lower than those in the NaCl treatment, while the K contents were significantly higher than those in the NaCl group.

[0110] In summary, Mg-BC can mitigate the adverse effects of salt stress on cucumber growth, increase the chlorophyll content, chlorophyll fluorescence, and antioxidant enzyme activity in cucumber leaves, and contribute to promoting cucumber growth. At the same time, BC can also improve the physical, chemical, and biochemical properties of the soil, increase nutrient absorption and utilization, and enhance soil enzyme activity, thereby promoting cucumber growth.

[0111] The present invention is not limited to the above-mentioned optional embodiments, and anyone can obtain other various forms of products under the inspiration of the present invention. However, no matter what changes are made in its shape or structure, as long as the technical solutions fall within the scope defined by the claims of the present invention, they are all within the protection scope of the present invention.

Claims

1. A remediation agent for secondary salinized soil, characterized in that: Including Mg-modified biochar.

2. The remediation agent for secondary salinized soil according to claim 1, characterized in that: The Mg content in the Mg-modified biochar is 7.0-7.5%.

3. The remediation agent for secondary salinized soil according to claim 1, characterized in that: The preparation method of the Mg-modified biochar comprises: S1. Preparation of biochar: using leaves of Photinia fraseri as raw material, drying them, and then carbonizing them under anaerobic or oxygen-limited conditions at 450-550° C. for 1.5-2.5 h, and washing and drying them to obtain biochar; S2. Modification by magnesium chloride impregnation method: The prepared biochar is mixed with magnesium chloride solution, and the magnesium chloride solution is impregnated into the biochar. After stirring and sealing, the biochar is filtered, washed to remove impurities, and then dried and calcined in an oxygen-free state to obtain Mg-modified biochar.

4. Use of the repair agent according to claim 1 in repairing secondary salinized soil.

5. Use of the repair agent according to claim 1 in promoting the growth and development of cucumber in secondary salinized soil.

6. A method for promoting the growth and development of cucumber under secondary salinized soil conditions, characterized in that: include: Under the condition of secondary salinized soil, cucumbers are planted after adding the Mg-modified biochar in the remediation agent for secondary salinized soil according to claim 1; 0.8-1.2 parts by mass of the Mg-modified biochar is added to every 95-105 parts by mass of salinized soil.

7. The method for promoting the growth and development of cucumber under secondary salinized soil conditions according to claim 6, characterized in that: 1.0 mass part of Mg-modified organisms was added to every 100 mass parts of salinized soil.

8. The method for promoting the growth and development of cucumber under secondary salinized soil conditions according to claim 6, characterized in that: 1.1 parts by mass of Mg-modified organisms were added to every 95 parts by mass of salinized soil.

9. The method for promoting the growth and development of cucumber under secondary salinized soil conditions according to claim 6, characterized in that: 0.8 parts by mass of Mg-modified organisms were added to every 105 parts by mass of salinized soil.

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