Method for planting crops in hardened soil and soil remediation material

Abstract

The invention provides a method for planting crops in hardened soil and a soil remediation material.The method comprises the following steps that agricultural waste is subjected to alkali washing to remove lignin and then subjected to carbonization treatment, then the carbonized agricultural waste is mixed with egg shell powder, and calcium modified biochar powder is prepared after firing; humic acid and the calcium modified charcoal powder are mixed, filtered and dried, and the soil remediation material is obtained. Wherein the mass ratio of the humic acid to the calcium modified charcoal powder is 1: (4-16). The soil remediation material and hardened soil are mixed according to the mass ratio of 1: (3-17), crops are planted after incubation, water is watered once every other day before seed germination, water is watered once every day after seed germination, and it is ensured that the soil is kept moist. The method for planting the crops in the hardened soil can improve the yield and quality of the crops planted in the hardened soil and increase the fertilizer efficiency and organic matter content of the soil.

Description

Technical Field

[0001] The present invention relates to the field of soil remediation. Specifically, it relates to a method for growing crops in compacted soil and a soil remediation material. Background Art

[0002] Soil is the material basis for human survival, and soil health is crucial for the sustainable development of agriculture and the ecosystem. However, due to the increase in waste in the agricultural production process in the soil, as well as the excessive application of pesticides and fertilizers, the properties of farmland soil have degraded, and problems such as soil compaction, acidification, and secondary salinization have even occurred. In addition, the application of agricultural machinery is more popular, and the soil is crushed by agricultural machinery, which destroys the original loose soil aggregate structure in the farmland. And shallow tillage all year round will cause the cultivated land to become more and more solid; deep tillage all year round can damage the capillary tubes of the cultivated land, thereby increasing the capillary effect of the soil, resulting in a sharp decline in the water retention and ventilation capacity of the soil, and thus leading to a decline in soil fertility and crop yields to varying degrees.

[0003] The invention patent application with the authorization announcement number CN114891512B discloses a composite material of calcium chloride-modified biochar for saline-alkali soil improvement and its preparation method, including the following steps: collecting plant raw materials, thoroughly drying them after rinsing with deionized water, and then performing oxygen-limited pyrolysis at 450°C for 1 h. After cooling, the biochar is crushed and sieved with a pulverizer to obtain the original biochar; mixing the original biochar with a calcium chloride solution with a concentration of 0.5 mol / L according to a solid-liquid ratio of 1:15 (g:mL); then fully stirring under a constant temperature oscillator, filtering and washing with ultrapure water until the pH and conductivity of the washing liquid are stable; completely drying at a certain temperature and then performing oxygen-limited pyrolysis at 200°C for 1 h, and the obtained product is marked as a composite material of biochar loaded with calcium chloride-modified biochar. This composite material of calcium chloride-modified biochar for saline-alkali soil improvement and its preparation method can effectively reduce the pH in saline-alkali soil, improve the physical and chemical properties of the soil, increase the germination rate of plants, have low cost, and will not cause secondary pollution, which is beneficial to the development and utilization of saline-alkali soil, maintaining the stability of existing cultivated land, and protecting the ecological environment. However, this method only modifies the biochar with calcium to reduce the pH in saline-alkali soil, and does not significantly improve the fertilizer efficiency and organic matter content of the soil, and is not suitable for growing crops in compacted soil. Summary of the Invention

[0004] In order to increase the yield and quality of crops grown in compacted soil and increase the fertilizer efficiency and organic matter content of the soil, the technical solution adopted by the present invention is: a method for growing crops in compacted soil, including the following steps:

[0005] Step 1. Alkaline wash agricultural waste to remove lignin and then carbonize it to obtain biochar. Then mix the biochar with eggshell powder, burn it, and obtain calcium-modified biochar powder. Mix humic acid with the calcium-modified biochar powder, filter and dry it to obtain a soil remediation material, namely humic acid-modified calcium-modified biochar. Among them, the mass ratio of the humic acid to the calcium-modified biochar powder is 1:(4 - 16);

[0006] Step 2. Mix the soil remediation material with compacted soil in a mass ratio of 1:(3 - 17), incubate it, and then plant crops. Before the seeds germinate, water once every 1 day, and after the seeds germinate, water once a day to ensure that the soil remains moist.

[0007] Based on the above, in Step 2, the incubation time after mixing the soil remediation material with compacted soil is 60 days to 120 days. Preferably, the incubation time is 90 days.

[0008] Based on the above, the agricultural waste is mushroom stick residue, peanut shell or wood chip.

[0009] Based on the above, in Step 1, the calcium-modified biochar powder is obtained through the following steps:

[0010] Wash agricultural waste with deionized water, dry it, crush and screen it. Stir the obtained agricultural waste powder in NaOH solution for 3h - 8h to remove lignin in the components of the agricultural waste powder. Filter it, then wash the filter residue with deionized water until neutral, and after drying, grinding and screening, carry out carbonization treatment for 1h - 3h under the conditions of N2 atmosphere, carbonization temperature of 400°C - 800°C, and heating rate of 3°C / min - 10°C / min to obtain biochar powder. The specific surface area of the biochar powder is 35m 2 / g - 43m 2 / g, and the pore volume is 0.045cm 3 / g - 0.090cm 3 / g;

[0011] Wash, air-dry, crush and sieve eggshells, and then carry out carbonization treatment for 1h - 3h under the conditions of carbonization temperature of 400°C - 800°C and heating rate of 3°C / min - 10°C / min to obtain carbonized eggshell powder;

[0012] Finally, mix and ball-mill the carbonized eggshell powder and the biochar powder in a mass ratio of (2 - 8):1, and place the dried solid powder under the conditions of 500°C - 900°C, N2 atmosphere and heating rate of 15°C / min - 25°C / min for burning for 1h - 2h; obtain the calcium-modified biochar powder.

[0013] The present invention also provides a soil remediation material, which is prepared through the following steps: alkali-washing agricultural waste to remove lignin, followed by carbonization treatment, and then mixing with eggshell powder and burning to obtain calcium-modified biochar powder; mixing humic acid with the calcium-modified biochar powder, and obtaining the soil remediation material after filtration and drying; wherein, the mass ratio of the humic acid to the calcium-modified biochar powder is 1:(4-16).

[0014] Specifically, the specific surface area range of the soil remediation material is 69.28 m 2 / g to 92.62 m 2 / g, and the pore volume is 0.112 cm 3 / g to 0.226 cm 3 / g.

[0015] The present invention has outstanding substantial features and remarkable progress compared with the prior art. Specifically, a method for growing crops in compacted soil and a soil remediation material provided by the present invention, by applying humic acid-modified calcium-modified biochar to farmland suffering from soil compaction and heavy metal pollution, the biochar-based composite material enters the heavy metal-polluted soil, and the negative charges and polar oxygen-containing functional groups on its surface respectively have electrostatic adsorption effects with lead ions and cadmium ions carrying positive charges.

[0016] Moreover, the surface of the calcium-modified biochar contains a large number of inorganic mineral ions (such as Ca 2+ ) and oxygen-containing anions, which can all undergo ion exchange reactions with heavy metal ions (such as lead and cadmium) in the soil, thereby inhibiting the migration and transfer of heavy metal ions in the soil.

[0017] At the same time, the surface of the humic acid-modified biochar contains a large number of polar oxygen-containing groups (such as hydroxyl groups, carboxyl groups, carbonyl groups, etc.), which can achieve the purpose of immobilization by oxidizing reactions with heavy metals lead and cadmium. In addition, the biochar with a high specific surface area and a developed pore structure has more adsorption sites on its surface or in the pores, and can fix heavy metals on the surface or inside the pores of the biochar through intermolecular forces, thereby achieving the effect of passivating heavy metals.

[0018] Applying humic acid-modified calcium-modified biochar to compacted soil, the abundant oxygen-containing groups on its surface increase the soil pH value, while also increasing the organic matter content and decreasing the electrical conductivity in the soil. The introduction of biochar changes the microbial community structure in the soil, increasing the activities of urease, sucrase, and alkaline phosphatase in the soil, thereby achieving the purpose of soil carbon sequestration and stabilizing nitrogen and phosphorus contents. In addition, the surface of the biochar prepared from waste mushroom stick residues contains a large amount of inorganic mineral ions. When it enters the soil, it improves the cation exchange capacity in the soil and enhances the soil water-holding capacity, reducing the degree of soil compaction. The test results show that the pakchoi plants grown in the repaired compacted soil have good growth, and their germination rate, plant height, dry weight, and fresh weight are all high. The chlorophyll content and soluble protein content in the pakchoi plants are both relatively high. Moreover, it can effectively passivate the heavy metal ions in the soil, resulting in little difference in the content and morphological distribution of available lead in the soil before pakchoi planting and after pakchoi harvest, and the same phenomenon is also shown in the content and morphological distribution of available cadmium in the soil before and after pakchoi planting.

[0019] Therefore, the method for planting crops in compacted soil and the soil remediation material provided by the present invention can improve the yield and quality of crops planted in compacted soil, increase the fertilizer efficiency and organic matter content of the soil, and effectively solve problems such as soil compaction and heavy metal pollution. Description of the Drawings

[0020] Figure 1 SEM photos of soil remediation materials prepared from different biomass raw materials and their matrices. Among them, Figure 1 A, D, and G respectively refer to biochar prepared from mushroom stick residues, calcium-modified biochar powder, and humic acid-modified calcium-modified biochar; B, E, and H respectively refer to biochar prepared from peanut shells, calcium-modified biochar powder, and humic acid-modified calcium-modified biochar; C, F, and I respectively refer to biochar prepared from wood chips, calcium-modified biochar powder, and humic acid-modified calcium-modified biochar; J-L respectively refer to three kinds of humic acid-modified calcium-modified biochars prepared by ball milling method.

[0021] Figure 2 SEM photos of calcium-modified biochar modified with different concentrations of humic acid. Among them, Figure 2 A refers to mushroom stick residue biochar; B-D are humic acid-modified calcium-modified biochars, and the mass ratio of biochar to humic acid is 15:1, 10:1, and 5:1 respectively.

[0022] Figure 3 Infrared spectra of soil remediation materials and their matrices.

[0023] Figure 4 Infrared spectra of calcium-modified biochar modified with different concentrations of humic acid.

[0024] Figure 5 Soil pH change diagrams for different repair times.

[0025] Figure 6 Soil electrical conductivity change diagrams for different repair times.

[0026] Figure 7 Soil organic matter content change diagrams for different repair times.

[0027] Figure 8 Soil urease activity change diagrams for different repair times.

[0028] Figure 9 Soil sucrase activity change diagrams for different repair times.

[0029] Figure 10 Soil alkaline phosphatase activity change diagrams for different repair times.

[0030] Figure 11 Soil catalase activity change diagrams for different repair times.

[0031] Among them, Figures 5 to 11 in which A, B, C, and D respectively refer to the soil pH values at the 15th d, 30th d, 45th d, and 60th d of repair; 1-1, 1-3, and 1-5 respectively represent adding soil remediation agent QCa@PSC-600@HA-1 to the soil sample at ratios of 1%, 3%, and 5%; 2-1, 2-3, and 2-5 respectively represent adding soil remediation agent QCa@PSC-600@HA-2 to the soil sample at ratios of 1%, 3%, and 5%; 3-1, 3-3, and 3-5 respectively represent adding soil remediation agent QCa@PSC-600@HA-3 to the soil sample at ratios of 1%, 3%, and 5%; 4-1, 4-3, and 4-5 respectively represent adding soil remediation agent QCa@MDC-600@HA-2 to the soil sample at ratios of 1%, 3%, and 5%; the control represents that no soil remediation agent is added to the soil sample.

[0032] Figure 12 Morphological distribution diagrams of Pb and Cd elements in improved soil sample No. 1 at different time periods.

[0033] Figure 13 Morphological distribution diagrams of Pb and Cd elements in improved soil sample No. 2 at different time periods.

[0034] Among them, Figure 12 and Figure 131-1, 2-1, 3-1, and 4-1 respectively refer to the soils of Specimen No. 1 or No. 2 with the remediation agents QCa@PSC-600@HA-1, QCa@PSC-600@HA-2, QCa@PSC-600@HA-3, and QCa@MDC-600@HA-2 added at a dose of 1% respectively; 1-3, 2-3, 3-3, and 4-3 respectively refer to the soils of Specimen No. 1 or No. 2 with the remediation agents QCa@PSC-600@HA-1, QCa@PSC-600@HA-2, QCa@PSC-600@HA-3, and QCa@MDC-600@HA-2 added at a dose of 3% respectively; 1-5, 2-5, 3-5, and 4-5 respectively refer to the soils of Specimen No. 1 or No. 2 with the soil remediation agents QCa@PSC-600@HA-1, QCa@PSC-600@HA-2, QCa@PSC-600@HA-3, and QCa@MDC-600@HA-2 added at a dose of 5% respectively.

[0035] Figure 14 It is a comparison chart of the growth of pakchoi. Among them, from left to right in the first row are the control and the soils added with different types of biochar-based composites; the second row is the pakchoi potted plants planted in the flowerpots corresponding to the first row; the third row is the pakchoi plants (36d) in the flowerpots corresponding to the first row; the fourth row is the pakchoi (30d) planted in large quantities in the greenhouse simulating the soil collected from the outside.

[0036] Figure 15 It is a diagram showing the effect of soil remediation materials on the chlorophyll content in pakchoi.

[0037] Figure 16 It is a diagram showing the effect of soil remediation materials on the soluble protein content in pakchoi.

[0038] Figure 17 It is a diagram showing the effect of soil remediation materials on the soluble sugar content in pakchoi.

[0039] Among them, Figures 15 to 17 1-1, 1-2, and 1-3 respectively refer to the soil samples with the soil remediation agent QCa@PSC-600@HA-1 added at ratios of 1%, 3%, and 5%; 2-1, 2-2, and 2-3 respectively refer to the soil samples with the soil remediation agent QCa@PSC-600@HA-2 added at ratios of 1%, 3%, and 5%; 2-1, 2-2, and 2-3 respectively refer to the soil samples with the soil remediation agent QCa@PSC-600@HA-3 added at ratios of 1%, 3%, and 5%; control - the soil without the soil remediation agent.

[0040] Figure 18 It is a morphological distribution diagram of Pb and Cd in the soil before and after harvesting pakchoi. Detailed implementation method

[0041] The technical solution of the present invention will be further described in detail below through specific embodiments.

[0042] Embodiment

[0043] This embodiment provides a soil remediation material, which is prepared through the following steps:

[0044] Preparation of biochar powder: First, agricultural waste is washed and dried with deionized water, and then crushed and screened (through a 60-mesh steel sieve) with a pulverizer. The obtained agricultural waste powder is stirred in a hot alkali solution (5% NaOH solution) for 6 hours to remove part of the lignin in its components. Finally, the filter residue is washed with deionized water until neutral, dried, ground, and screened to obtain a biomass pretreatment sample. The agricultural wastes used in the experiment are respectively the waste mushroom stick residues (MD) from a mushroom planting base in Biyang County, Zhumadian, the peanut shells (PS) locally planted and with kernels removed, and the sawdust (SD) from the woodworking workshop of the School-Enterprise Innovation and Entrepreneurship Park on the campus of Huanghuai University.

[0045] The pretreated agricultural waste powder is placed in a tube furnace under a N2 atmosphere for carbonization treatment. The carbonization temperatures are respectively set at 400 °C, 600 °C, and 800 °C, and the heating rate and carbonization time are 5 °C / min and 2 h respectively. After the reaction is completed, the obtained black solid is the biochar product. According to the yields and infrared spectra of the biochars obtained from the same biomass raw material at different carbonization temperatures, biochar products with higher carbonization yields and rich surface groups are selected, and their naming numbers are respectively MDC-600, PSC-600, and SDC-600.

[0046] Preparation of calcium-modified biochar powder: Method 1, using calcium chloride as the calcium source. Weigh 5 g of biochar powder and transfer it to 250 mL of 1 mol / L calcium chloride solution. Stir the solution at room temperature for 24 h. After the reaction is completed, filter the reaction solution by suction. The obtained filter residue is washed with deionized water and then placed in an oven at 105 °C for drying. The obtained black solid is ground and screened to obtain calcium-modified biochar powder, and its names and numbers are respectively: HCa@PSC-600, HCa@MDC-600, and HCa@SDC-600.

[0047] Method 2: The eggshells were carbonized at 600 °C for 2 h, and the heating rate was set at 5 °C / min. Before carbonizing the eggshells, operations such as cleaning, air-drying, crushing, and sieving (100 mesh) were required. Then, the eggshell powder and biochar powder were mixed at a mass ratio of 5:1, and ball milling was carried out under the action of an ethanol solvent. The temperature and rotation speed of ball milling were set at 70 °C and 30 r / min, respectively. After 4 h, the solid was separated, and the dried solid powder was placed in a tubular heating furnace at 800 °C under a nitrogen atmosphere for calcination, and the heating rate of the furnace was adjusted to 20 °C / min. After 1.5 h, the calcium-modified biochar samples were obtained, and their name numbers were: QCa@PSC-600, QCa@MDC-600, and QCa@SDC-600.

[0048] Preparation of soil remediation material, i.e., calcium-modified biochar modified by humic acid: The calcium-modified biochar powder and humic acid were mixed according to the set ratio, transferred to 50 mL of deionized water, and the reaction solution was stirred at room temperature. After 8 h, the reaction solution was filtered, and the obtained filter residue was naturally air-dried to obtain the soil remediation material. Among them, the mixing ratios of calcium-modified biochar powder and humic acid were set to 15:1 (w / w), 10:1 (w / w), and 5:1 (w / w), respectively, and the corresponding product numbers were: HCa@PSC-600@HA-1, HCa@MDC-600@HA-1, HCa@SDC-600@HA-1, QCa@PSC-600@HA-1, QCa@MDC-600@HA-1, QCa@SDC-600@HA-1, HCa@PSC-600@HA-2, HCa@MDC-600@HA-2, HCa@SDC-600@HA-2, QCa@PSC-600@HA-2, QCa@MDC-600@HA-2, QCa@SDC-600@HA-2, HCa@PSC-600@HA-3, HCa@MDC-600@HA-3, HCa@SDC-600@HA-3, QCa@PSC-600@HA-3, QCa@MDC-600@HA-3, and QCa@SDC-600@HA-3. The experiment tested the physicochemical properties of a series of soil remediation materials obtained by modifying with different calcium sources and modifying with different concentrations of humic acid, and the relevant results are shown in Table 1.

[0049] Table 1 Basic physicochemical properties of soil remediation materials

[0050]

[0051] As can be seen from Table 1: Before the carbonization of the three agricultural wastes, they need to be pretreated with alkali in advance, and the resulting biochars are all alkaline. Compared with the modified biochars, the three unmodified biochars all show lower ash content and pore volume, higher yield and specific surface area. Among the three unmodified biochars, the biochar prepared from the spent mushroom substrate shows the characteristics of less ash, high yield, large specific surface area and low pore volume. During the preparation of the modified biochar, as the dosage of humic acid increases, the pH value of the prepared soil remediation material decreases more significantly.

[0052] The reason for this phenomenon is that the humic acid solution shows a certain acidity. In addition, there is about 8% ash content in the newly prepared humic acid-modified calcium modified biochar, and as the dosage of humic acid increases, the ash content in the biochar composite gradually decreases.

[0053] Comparing the specific surface area and pore volume of the calcium modified biochars modified by different concentrations of humic acid, it is found that for the biochars prepared from the same biomass carbonization, when the mass ratio of humic acid to calcium modified biochar is 1:10, the specific surface area and pore volume of the prepared humic acid-modified calcium modified biochar are both large. Different types of biochar raw materials are modified with the same concentration of humic acid solution, and the specific surface area and porosity of the obtained humic acid-modified calcium modified biochars are also different. However, the influence of the difference in the types of biochar raw materials on the specific surface area and pore volume of the modified biochar is relatively small.

[0054] This embodiment also provides a method for planting crops in compacted soil, including the following steps:

[0055] Step 1: After alkali washing the agricultural waste to remove lignin, carry out carbonization treatment, and then mix it with eggshell powder, and obtain calcium modified biochar powder after calcination; mix humic acid with the calcium modified biochar powder, and obtain a soil remediation material after filtration and drying; wherein, the mass ratio of the humic acid to the calcium modified biochar powder is 1:(4-16).

[0056] Step 2: Mix the soil remediation material with the compacted soil according to a mass ratio of 1:(3-17), incubate and then plant crops. Before the seeds germinate, water once every 1 day, and after the seeds germinate, water once a day to ensure that the soil remains moist.

[0057] Structure Characterization

[0058] The apparent morphological characteristics of the soil remediation materials, namely humic acid-modified calcium modified biochars and their matrices, prepared from spent mushroom substrates, peanut shells and wood chips as raw materials are shown in Figure 1As shown. It can be seen from the figure that for the mushroom stick residue biochar, its surface presents a hollow tubular fiber structure, and the tube wall is relatively smooth. After modification treatment, the mushroom stick residue-based biochar presents a fragmented structure, with a smaller particle size. Obvious pores appear on some surfaces of its particles, and some fine pores also appear, indicating that the humic acid modification and calcium modification treatments have changed the surface morphology structure of the mushroom stick biochar. At the same time, there are some irregular ellipsoidal substances on the surface of the modified biochar, indicating that part of the calcium (calcium chloride or carbonized eggshell) element is doped on the biochar surface.

[0059] For the peanut shell-based biochar, after carbonization, the original fiber structure of the biomass is still retained on the surface of the biochar. There are micropores of different sizes distributed on its surface, and there are many surface wrinkles. Compared with the unmodified biochar, in addition to being covered with more pores and wrinkles, the surface of the modified biochar also shows more fine particles, its structure is more fluffy, and the layered structure is more obvious. For the wood chip-based biochar, after the wood chips are carbonized, the surface of the wood chip biochar presents a rough surface morphology, and there are many impurities attached, and the pores are relatively few. After modification treatment, the impurity residues and ash on the surface of the sawdust biochar are removed and it becomes smooth. At the same time, after modification treatment, the pore structure on the surface of the wood chip-based biochar increases, and its structure is more fluffy.

[0060] The apparent morphological characteristics of the humic acid-modified calcium-modified biochar prepared from different concentrations of humic acid are shown in Figure 2 as shown. From Figure 2 it can be seen that as the concentration of the humic acid modifier increases, the fine pores on the surface of the modified biochar become more, indicating that humic acid can destroy the microscopic structure of the biochar surface. However, as the amount of humic acid used further increases, some pores on the biochar surface are blocked. To sum up, when using humic acid to modify calcium-modified biochar, in order to ensure the high specific surface area and well-developed pore structure of the modified biochar, soil remediation materials with relatively strong remediation ability for problem soils are screened out, which are QCa@PSC-600@HA-1, HCa@PSC-600@HA-2, HCa@MDC-600@HA-2, QCa@PSC-600@HA-2, QCa@MDC-600@HA-2, HCa@PSC-600@HA-3 and QCa@PSC-600@HA-3 respectively.

[0061] Infrared spectrum analysis

[0062] The infrared spectra of the calcium humic acid-modified biochar composite material and its matrix prepared from waste mushroom stick residues are shown in Figure 3 as shown. From Figure 3 it can be seen that for the infrared spectrum of the unmodified mushroom stick residue biochar, at 3422 cm -1The strong and broad vibration absorption peak at the wavenumber belongs to the stretching vibration of hydroxyl groups, 2834 cm -1 The vibration absorption peak at the wavenumber is caused by the C-H stretching vibration on -CH2, 1365 cm -1 The absorption peak at the wavenumber is caused by the skeletal bending vibration of the benzene ring, 1628 cm -1 The absorption peak at the wavenumber is caused by the C=O stretching vibration, while at 1147 cm -1 The characteristic absorption peak at the wavenumber is caused by the C-O stretching vibration. Compared with the unmodified mushroom stick residue biochar, the overall change in the functional group composition of the mushroom stick biochar after modification with calcium chloride and humic acid is not significant. However, the intensity of the absorption peaks of the mushroom stick biochar after modification with calcium chloride and humic acid has increased. At the same time, the positions and intensities of the vibration absorptions on the spectra of HCa@PSC-600@HA-2 and QCa@PSC-600@HA-2 are almost the same, indicating that the differences in the functional group composition and content on the surfaces of these two modified biochars are not obvious.

[0063] In addition, new absorption peaks appear at 775 cm -1 and 776 cm -1 on the spectra of HCa@PSC-600@HA-2 and QCa@PSC-600@HA-2 respectively. This is attributed to the action of C-Ca bonds on the surface of the modified biochar. At the same time, humic acid is modified on the surface of the biochar, and a large number of oxygen-containing functional groups are introduced onto the biochar surface during this process, resulting in the enhancement of the vibration absorptions at 3422 cm -1 and 1628 cm -1 on the spectra of HCa@PSC-600@HA-2 and QCa@PSC-600@HA-2 respectively, indicating an increase in the content of acidic groups on the surface of the humic acid-modified calcium-modified biochar.

[0064] The infrared spectra of the calcium-modified biochar modified with different concentrations of humic acid are shown in Figure 4 as follows. It can be seen from Figure 4 that changing the concentration of humic acid has little effect on the chemical composition of the humic acid-modified calcium-modified biochar, indicating that the changes in the oxygen-containing polar groups, organic matter composition and content on the surface of the humic acid-modified calcium-modified biochar prepared by modifying the calcium-modified biochar with different concentrations of humic acid modifiers are not reflected in the infrared spectra. However, precisely due to the abundant polar groups on the surface of the modified biochar, when it is applied to farmland with problems of soil compaction and heavy metal pollution, it can improve the air permeability and water retention capacity of the soil by changing the soil aggregate structure, and can also adsorb heavy metal ions in the soil through ion exchange, surface complexation and other methods.

[0065] Meanwhile, there is no difference in the morphological characteristics between the modified biochar prepared by ball milling and that prepared by chemical impregnation. Given that the calcium-modified biochar prepared by ball milling can reduce the types and amounts of chemical reagents, subsequent experiments will be carried out using QCa@PSC-600@HA-1, QCa@PSC-600@HA-2, QCa@PSC-600@HA-3 and QCa@MDC-600@HA-2 as raw materials.

[0066] Elemental analysis

[0067] The percentage contents of C, H, N and S elements in the biochar samples were determined using an elemental analyzer, and the content of O element was calculated by the subtraction method. The organic elemental compositions and contents of the soil remediation materials and their precursors are shown in Table 2.

[0068] Table 2 Elemental analysis of soil remediation materials and their precursors

[0069]

[0070] Specifically, the H / C molar ratio of the soil remediation material can be used as an index to measure its degree of aromatization, while the O / C molar ratio is positively correlated with the oxygen-containing functional groups on its surface. At the same time, it can also be used as a basis for judging the hydrophilicity of the biochar material. Moreover, the larger the O / C molar ratio of the biochar, the better its hydrophilicity. In addition, the (O+N) / C molar ratio of the carbon-rich material can reflect the polarity of the material. The larger the (O+N) / C molar ratio of the biochar, the greater its polarity.

[0071] It can be seen from Table 2 that for the unmodified biochar, although the types of agricultural waste used to make the biochar are different, when carbonized at the same temperature, the aromatization degrees of the obtained biochars are not different, and their hydrophilicities and polarities are also similar. Compared with the unmodified biochar, the biochars modified by humic acid and calcium modification have higher aromaticity, hydrophilicity and polarity, indicating that the content of polar functional groups on the surface of the modified biochar is higher, and it also indicates that humic acid has been successfully grafted onto the surface of the calcium-modified biochar. This conclusion is consistent with the analysis results of the infrared spectrum of the humic acid-modified calcium-modified biochar in the previous text. Regarding the concentration of the modifier humic acid, as the amount of humic acid used increases, the aromaticity of the obtained modified biochar increases, while its hydrophilicity and polarity do not change significantly, indicating that an appropriate addition amount of humic acid is a necessary condition for increasing the organic matter content in the modified biochar.

[0072] Soil saturation experiment

[0073] Soil remediation materials labeled QCa@PSC-600@HA-1, QCa@PSC-600@HA-2, QCa@PSC-600@HA-3 and QCa@MDC-600@HA-2 were selected for soil remediation experiments. The specific steps include: mixing the soil samples with the above four soil remediation materials in proportion and placing them in pots, watering them, and leaving them for 12 hours after water seeps from the water holes at the bottom of the pots. Then watering them again until water comes out from the bottom of the pots, and then placing the flower pots in a greenhouse and watering them thoroughly once a week. When the soil body has no obvious drop, it is in equilibrium. After reaching equilibrium, it is placed for 15 days. Thereafter, soil samples are taken every 15 days and sieved through an 18-mesh sieve for the determination of soil physical and chemical properties. The sampling interval for the determination of heavy metal ion content in the soil is 30 days.

[0074] The experiment took four kinds of soil remediation materials as the research objects, and adopted the indoor simulation test method. The soil remediation agent was added at 0%, 1.0%, 3.0% and 5.0% of the soil mass at one time, and soil samples were collected on the 15th, 30th, 45th and 60th days. Thirteen groups of soil samples were designed for each soil type, and each group of experimental operations was repeated 3 times. The soil samples without any amendments were used as the blank control group.

[0075] Changes in soil pH: During soil remediation, the changes in soil pH in different treatment groups are shown in Figure 5 As shown. Figure 5 It can be seen that, in general, the pH value of the soil after the application of soil remediation materials showed an overall increasing trend. However, the pH value of the soil without soil remediation materials did not change much during the entire incubation period and remained weakly acidic. After adding soil remediation materials to the problematic soil, its pH value increased with the increase of soil incubation time, and the pH value of the soil reached its maximum value after 45 days of soil incubation. In addition, from Figure 5 It can also be seen that in terms of the types of soil remediation materials, compared with other types of soil remediation materials, the soil remediation material QCa@PSC-600@HA-3 has a good effect on improving the pH value of the three soils, and increasing the amount of soil remediation materials used will increase the pH value of the soil. The above analysis shows that adding soil conditioners can increase the pH value of the soil to a certain extent, among which the soil remediation agent QCa@PSC-600@HA-3 has the most significant effect on the treatment of pantothenic farmland.

[0076] Changes in soil conductivity: During the restoration process, the change trends of soil conductivity in different treatment groups are shown in Figure 6 As shown. Figure 6It can be seen that, compared with the soil without the addition of soil remediation materials, the electrical conductivity of the soil in the farmland with the addition of soil remediation materials has decreased. For different types of soil remediation materials, the decrease in the electrical conductivity value in the soil with the addition of QCa@PSC-600@HA-2 is the most significant, followed by QCa@MDC-600@HA-2, indicating that although the raw materials for preparing the soil remediation materials are different, the trend of their influence on the change of electrical conductivity in the soil is the same.

[0077] Take the soil remediation material QCa@PSC-600@HA-2 as an example. Its mixing dosage with the sample soil is different, and the electrical conductivity of the soil after remediation is also different. As the dosage of the soil remediation material increases, the decrease in the electrical conductivity value in the affected soil is more obvious. When the mass ratio of the soil remediation material to the sample soil is 1:10, the electrical conductivity value in the affected soil is the lowest, and this research result is valid for both soil samples. Applying QCa@PSC-600@HA-2 to the sample soil at a ratio of 1:10 (w / w), its electrical conductivity value decreases significantly within 0 - 45 days, while the change in the electrical conductivity value is not obvious after more than 45 days, indicating that the soil remediation material can improve the fertility of degraded soil in a short time.

[0078] Change in soil organic matter content: The change trend of the organic matter content in the remediated soil of different treatment groups is shown in Figure 7 as follows. It can be seen from Figure 7 that, compared with the soil without the addition of soil remediation materials, the organic matter content in the soil with the addition of soil remediation materials has increased. For different types of soil remediation materials, the increase in the organic matter content in the soil with the addition of QCa@PSC-600@HA-2 is the largest, followed by QCa@MDC-600@HA-2, indicating that although the raw materials for preparing the soil remediation materials are different, the trend of their influence on the change of organic matter content in the soil is the same. For the soil remediation material QCa@PSC-600@HA-2, its mixing dosage with the soil sample is different, and the organic matter content in the soil after remediation is also different.

[0079] With the increase in the dosage of carbon-based composite materials, the increase in the organic matter content in the affected soil becomes more obvious. When the mass ratio of the soil remediation material to the sample soil is 1:10, the organic matter content in the affected soil is the highest, and this research result is valid for both soil samples. When QCa@PSC-600@HA-2 is applied to the sample soil at a ratio of 1:10 (w / w), the organic matter content in the soil increases significantly within 30 days of soil incubation. After more than 45 days, the change trend of the organic matter content in the soil is not obvious. Since the organic matter content in the soil is an important indicator to measure the soil fertility, the soil remediation material can greatly increase the organic matter content in the soil in a short time, indirectly indicating that when the modified biochar is applied to the soil with degraded fertility, the improvement and remediation effects can be gradually achieved in a short time.

[0080] Changes in soil urease activity: The change rules of urease activity in the soil after remediation in different groups are shown in Figure 8 the figure. It can be seen from Figure 8 the figure that as the soil incubation time is extended, the change in urease activity in the control group is not obvious, while the urease activity in the soil of other groups increases with the increase in the remediation time. However, the increase amplitudes of urease activity in different groups are different at the same time period. In the initial stage of soil incubation (0 - 30 days), the urease activity in the soil of groups 1-1 and 3-1 increases slowly. However, when the incubation time exceeds 30 days, the increase rate of urease activity in the soil of groups 2-5 and 4-5 speeds up, while the increase of urease activity in the soil of group 3-3 is the slowest. During the whole remediation process, the urease activity in the soil of groups 2-3 and 4-3 has been showing a stable upward trend, and the increase rate of the value is the fastest.

[0081] Since the urease activity in the soil is closely related to the number of microorganisms in it. When the soil remediation material is applied to the soil, the biochar interacts with the microbial community in the soil, resulting in an accelerated increase rate of urease activity. Therefore, applying the soil remediation materials QCa@PSC-600@HA-2 and QCa@PSC-600@HA-2 to the problematic soil can significantly increase the number of microorganisms, and then cause an accelerated increase rate of urease activity in the soil.

[0082] Changes in soil invertase activity: During the soil incubation process, the change rules of invertase activity in the soil of different groups are as shown in Figure 9 the figure. As shown in Figure 9It can be seen that when the soil incubation time is extended, the change in the sucrase activity in the control group is not obvious. The sucrase activities in the repaired soils of other groups all increase with the increase in the repair time. However, the increase amplitudes of the sucrase activities in different groups are different during the same time period. In the initial stage of soil incubation (0 - 30 d), the increase in the sucrase activities in groups 1 - 1 and 3 - 1 is slow. However, when the incubation time exceeds 30 d, the increase rate of the sucrase activity in the repaired soils of groups 2 - 5 and 4 - 5 speeds up, while the increase rate of the sucrase activity in the repaired soil of group 3 - 3 is the slowest. During the entire repair process, the sucrase activities in the repaired soils of groups 2 - 3 and 4 - 3 are always in a stable upward trend, and the numerical increase rate is the fastest. Since the sucrase activity in the soil is closely related to the number of microorganisms in it. When the biochar-based composite material is applied to the soil, the modified biochar interacts with the microbial community in the soil, resulting in an accelerated increase rate of the sucrase activity. Therefore, applying the soil repair materials QCa@PSC-600@HA-2 and QCa@PSC-600@HA-2 to the problematic soil can significantly increase the number of microorganisms, and further cause the increase rate of the sucrase activity in the soil to reach the fastest.

[0083] Changes in soil alkaline phosphatase activity: The change rules of the alkaline phosphatase activities in the repaired soils of different groups are as Figure 10 shown. As can be seen from Figure 10 , the change trends of the alkaline phosphatase activities in the repaired soils of different groups are different. Regarding the soils repaired with the soil repair materials, with the increase in the soil incubation time, the alkaline phosphatase activities in the repaired soils of all groups increase with the increase in the repair time. However, the increase amplitudes of the alkaline phosphatase activities in the repaired soils of different groups are different during the same time period. In the initial stage of soil incubation (0 - 30 d), the increase in the alkaline phosphatase activities in the repaired soils of groups 1 - 1 and 3 - 1 is slow. However, when the incubation time exceeds 30 d, the increase rate of the alkaline phosphatase activity in the repaired soils of groups 2 - 5 and 4 - 5 speeds up, while the increase in the alkaline phosphatase activity in the repaired soil of group 3 - 3 is the slowest. During the entire repair process, the alkaline phosphatase activities in the soils of groups 2 - 3 and 4 - 3 are always in a steady upward trend, and the numerical increase rate is the fastest.

[0084] Since the alkaline phosphatase activity in the soil is closely related to the number of its microorganisms. When the soil repair material is applied to the test soil, the modified biochar interacts with the microbial community in the soil, resulting in an accelerated increase rate of its alkaline phosphatase activity. Therefore, applying the soil repair materials QCa@PSC-600@HA-2 and QCa@PSC-600@HA-2 to the problematic soil can cause the alkaline phosphatase activity in the soil to reach the maximum.

[0085] Changes in soil catalase activity: Different types and dosages of soil remediation materials were applied to the test soil. The changing trends of the catalase activity in the soil at different incubation stages after incubation are shown in Figure 11 the following. It can be seen from Figure 11 that the changing rules of the catalase activity in the remediated soil of each treatment group are different from those of urease, sucrase, and alkaline phosphatase activities in the soil. The catalase activity in the remediated soil of the control group is higher than that of other groups, and its enzyme activity basically does not change with the increase of soil incubation time. However, the catalase activity in the remediated soil of other groups shows a decreasing trend with the increase of time. In the initial stage of soil incubation (0 - 45 d), the catalase activity in the remediated soil of groups 2 - 5 and 4 - 5 decreases the fastest. After more than 45 d, the decrease in its catalase activity is not obvious, indicating that the soil remediation material can reduce the catalase activity in the soil, and its reduction rate will change with the incubation time of the soil sample. Based on the above analysis, it can be known that the pH value, organic matter content, conductivity, and enzyme activity in the soil are related to the types and dosages of the added soil remediation materials, and have nothing to do with the types of biomass used to prepare biochar.

[0086] Content of available lead and cadmium in the soil after remediation of problem soil: Using soil samples No. 1 and No. 2 collected in the laboratory as research objects respectively, the effects of the types and dosages of soil remediation materials on the existing effective forms and contents of lead and cadmium elements in problem soil at different incubation time periods were studied. When the soil remediation material was applied to soil sample No. 1, the available contents and morphological distributions of Pb and Cd elements at different time periods are shown in Table 3 and Figure 12 the following.

[0087] Table 3 Available contents of Pb and Cd elements in remediated soil sample No. 1 at different time periods

[0088]

[0089] Note: 1 - 1, 1 - 3, and 1 - 5 respectively refer to the soil samples added with soil remediation agent QCa@PSC - 600@HA - 1 at the ratios of 1%, 3%, and 5%. 2 - 1, 2 - 3, and 2 - 5 respectively refer to the soil samples added with soil remediation agent QCa@PSC - 600@HA - 2 at the ratios of 1%, 3%, and 5%. 3 - 1, 3 - 3, and 3 - 5 respectively refer to the soil samples added with soil remediation agent QCa@PSC - 600@HA - 3 at the ratios of 1%, 3%, and 5%. 4 - 1, 4 - 3, and 4 - 5 respectively represent the soil samples added with soil remediation agent QCa@MDC - 600@HA - 2 at the ratios of 1%, 3%, and 5%.

[0090] As can be seen from the table, compared with the soil without the application of soil remediation materials, after 60 days of soil incubation experiment on Soil Sample No. 1, the content of available Pb in it decreased significantly, and its content reached the lowest after 90 days of soil incubation. At the same time, the change trend of the content of available cadmium in Soil No. 1 was basically the same as that of available lead during different incubation periods. Regarding different types of soil remediation materials, when QCa@PSC-600@HA-2 and QCa@MDC-600@HA-2 were respectively applied to the soil samples, their passivation effects on available Pb and Cd in the soil were better than those of other types of soil remediation materials. Regarding the addition amount of the soil remediation materials, increasing the dosage of the soil remediation materials, the contents of available Pb and Cd in the sample soil decreased. When the addition amount of the soil remediation materials reached 5% (percentage with respect to the sample soil), the contents of available Pb and Cd in it reached the lowest, basically reaching the level of the control soil sample (Soil Sample No. 3) in this study.

[0091] Content of available lead and cadmium in the soil after the problem soil is remediated: At the end of the soil incubation, the present invention analyzed the morphological distributions of Pb and Cd in the experimental soil respectively. From Figure 12 it can be seen that when different types and different proportions of soil remediation materials are applied to Soil Sample No. 1, the morphological distributions of Pb and Cd in it are different.

[0092] Generally speaking, compared with the soil without the application of soil remediation materials, the content of fixed Pb in the improved sample soil number increased significantly, while the content of acid-soluble and exchangeable Pb in it decreased significantly. Regarding different types of soil remediation materials, QCa@MDC-600@HA-2 and QCa@MDC-600@HA-2 were respectively used to adsorb and immobilize the available lead Pb in the repaired sample soil, and their passivation abilities for Pb were almost equivalent.

[0093] Regarding different dosages of the same soil remediation material, during the soil incubation process, as the dosage of the soil remediation material increased, the content of acid-soluble and exchangeable Pb in the repaired soil decreased, while the content of fixed Pb increased. When the ratio of the soil remediation material to the sample soil was 1:10, the contents of acid-soluble and exchangeable Pb and fixed Pb in the repaired soil were 18.59% and 46.83% respectively. Compared with the corresponding values of the soil repaired without using soil remediation materials, the two decreased by 25.87% and increased by 25.97% respectively. In addition, the influence of the soil remediation material on the Cd morphology in the repaired soil was similar to that of the Pb morphology. Therefore, for the soil sample repaired by the soil remediation material, the content of fixed Cd in it increased by 21.89% compared with the soil before repair. When the soil remediation material was applied to Soil Sample No. 2, the available content and morphological distributions of Pb and Cd elements at different time periods are shown in Table 4 and Figure 13 as shown.

[0094] As can be seen from Table 4, in the initial stage of soil incubation, the change trend of the available Pb content in the soil was relatively similar to that of the available Cd content, and both decreased to varying degrees. However, when the soil incubation time exceeded 60 days, the decreasing trends of the available Pb content and the available Cd content in the soil were not obvious, and this value reached the lowest after 90 days of soil incubation. The reason for this phenomenon is that when the soil remediation material acts on the lead- and cadmium-polluted soil, the adsorption sites on the surface of the modified biochar are basically all occupied by lead and cadmium. In addition, when the soil remediation material acts on Soil Sample No. 2, the impact on the available lead and cadmium contents in the soil is similar to that of Soil Sample No. 1, and this result is also consistent with the research conclusions on the pH value, organic matter content, conductivity, and various enzyme activities in the remediated soil, which further confirms that the soil remediation material developed in this study has potential market promotion prospects for treating farmland suffering from soil compaction and lead and cadmium pollution.

[0095] Table 4 Available state contents of Pb and Cd elements in the improved Soil Sample No. 2 at different time periods

[0096]

[0097] Note: 1-1, 1-3, and 1-5 respectively refer to the soil samples added with the soil remediation agent QCa@PSC-600@HA-1 at ratios of 1%, 3%, and 5%; 2-1, 2-3, and 2-5 respectively refer to the soil samples added with the soil remediation agent QCa@PSC-600@HA-2 at ratios of 1%, 3%, and 5%; 3-1, 3-3, and 3-5 respectively refer to the soil samples added with the soil remediation agent QCa@PSC-600@HA-3 at ratios of 1%, 3%, and 5%; 4-1, 4-3, and 4-5 respectively represent the soil samples added with the soil remediation agent QCa@MDC-600@HA-2 at ratios of 1%, 3%, and 5%.

[0098] Figure 13 It shows the morphological distribution and content change law of cadmium element at the end of soil incubation. By comparing the contents of fixed Pb and fixed Cd in the remediated soils of different groups, it can be seen that the content of fixed Cd is slightly lower than that of fixed Pb, indicating that the passivation effect of the soil remediation material on the available lead in the soil is better than that on the available cadmium. This may be due to the hydrolysis constant of Pb(II) being lower than that of Cd(II), and it is easier to be fixed by the modified biochar through ion exchange.

[0099] It can also be seen from the figure that when different types and proportions of soil remediation materials are applied to the test soil No. 2, there are slight differences in the contents of various forms of Pb and various forms of Cd. Generally speaking, compared with the soil without the application of soil remediation materials, the content of fixed Cd in the improved test soil No. 2 increases significantly, while the content of acid-soluble and exchangeable Cd decreases significantly. In terms of different types of soil remediation materials, QCa@PSC-600@HA-2 and QCa@MDC-600@HA-2 are respectively used to adsorb and immobilize the available Cd in the repaired test soil, and their passivation abilities for Cd are almost the same.

[0100] In terms of different dosages of the same soil remediation material, during the soil incubation process, as the dosage of the soil remediation material increases, the content of acid-soluble and exchangeable Cd in the repaired soil decreases, while the content of fixed Cd increases. When the ratio of the soil remediation material to the test soil is set at 1:10 (w / w), the contents of acid-soluble and exchangeable Cd and fixed Cd in the repaired soil are 11.23% and 38.82% respectively. Compared with the corresponding values of the soil without the application of soil remediation materials, the two decrease by 18.63% and increase by 21.48% respectively.

[0101] Based on the above analysis, it can be seen that there are obvious differences in the contents of various forms of Pb and various forms of Cd in the two tested soil samples. This may be related to the differences in the initial concentrations of lead and cadmium in the test soil and the competitive adsorption between heavy metal elements on the surface of the modified biochar. Since the influence laws of the soil remediation materials QCa@PSC-600@HA-2 and QCa@MDC-600@HA-2 on the physical and chemical properties, available lead and cadmium contents and their morphological distributions of the repaired soil are the same, in order to avoid a large amount of useless work and simplify the workload, it is determined to use the soil remediation materials QCa@PSC-600@HA-1, QCa@PSC-600@HA-2 and QCa@PSC-600@HA-3 as the soil remediation agents for the subsequent bioavailability experiments of soil samples.

[0102] Bioavailability evaluation of improved soil

[0103] According to the conclusions drawn from the aforementioned experiments, applying soil remediation materials to problem soils can not only increase the pH value, organic matter content and conductivity of the acidified soil, but also improve the activities of urease, sucrase and alkaline phosphatase in the soil. In order to further evaluate the production quality of the soil remediation materials for repairing test soils, the present invention carried out an experiment on the variety of pakchoi in the school greenhouse.

[0104] Three different soil remediation materials (QCa@PSC-600@HA-1, QCa@PSC-600@HA-2 and QCa@PSC-600@HA-3) were used in the experiment. Their mixing mass ratios with the sample soil were 1:5, 1:10 and 1:15 respectively, and soil without adding soil remediation materials was selected for comparison. Based on the growth trend and quality index evaluation of pakchoi in the pot experiment, the remediation ability of the prepared soil remediation materials for the selected problem soil was evaluated, and the contents and morphological distributions of available Pb and available Cd in the sample soil and pakchoi plants were studied respectively.

[0105] In the experiment, two kinds of problem soils collected were used as research objects. By applying different types and concentrations of soil remediation materials to them and planting pakchoi on them, the growth of pakchoi, the physical and chemical properties of the soil, and the heavy metal content in them were observed. The detailed experimental steps are described as follows:

[0106] The soil remediation materials were mixed with the sample soil according to the ratios of 1:5 (w / w), 1:10 (w / w) and 1:15 (w / w) respectively, and then they were filled into flower pots respectively. Then, the carefully screened pakchoi seeds were evenly sown into each flower pot, and 18 pakchoi seeds were sown in each pot experiment. Before the seeds germinated, water was poured once every other day. After the seeds germinated, water was poured once a day, and it was ensured that the soil in the pakchoi pots remained moist, and the germination rate of the pakchoi seeds was observed regularly. Thinning of pakchoi was started 16 days after sowing. After the pakchoi grew for 36 days, the pakchoi was pulled out from the planted pakchoi pots, and the growth trend indexes of the pakchoi plants in each group of pots were observed.

[0107] Two small plots of land were found in the on-campus greenhouse. The outer-sampled sample soils were simulated respectively, and the soil remediation agent QCa@PSC-600@HA-2 was used. It was mixed and incubated with the two simulated soils (soil sample No. 1 and soil sample No. 2) according to the mass ratio of 1:10 respectively. After 90 days, pakchoi was planted on them respectively. After the pakchoi grew for 30 days, the growth status of the pakchoi was observed and the heavy metal content in the soil and pakchoi plants was measured.

[0108] By carrying out the pakchoi planting experiment in the greenhouse and dynamically monitoring the growth trend indexes (germination rate, fresh weight and dry weight of plants, plant height) and quality indexes (chlorophyll, soluble protein and soluble sugar) of pakchoi planted in the soil incubated with the soil remediation materials, the influence of the soil remediation agent on the growth status of pakchoi was studied.

[0109] Influence on the growth trend of pakchoi: Figure 14 are the physical pictures of pakchoi planted in the soil before and after being repaired by the soil remediation materials screened out. By Figure 14It can be seen that overall, compared with the Chinese cabbage plants grown in the soil without the application of soil remediation materials, the Chinese cabbage plants in the soil with the application of soil remediation materials grow better; moreover, when the same type and concentration of soil remediation materials are applied to Soil Sample No. 1 and Soil Sample No. 2 respectively, the growth of the Chinese cabbage plants planted is also good. Regarding different types of soil remediation materials, QCa@PSC-600@HA-2 as a soil remediation agent is superior to QCa@PSC-600@HA-1 and QCa@PSC-600@HA-3 in terms of the plant height and leaf greenness of Chinese cabbage.

[0110] This shows that during the preparation of modified biochar, an appropriate amount of humic acid is beneficial for more oxygen-containing groups to be immobilized on the biochar surface; moreover, as the dosage of the soil remediation agent increases, the plant height of Chinese cabbage plants in the remediated Soil Sample No. 1 and Soil Sample No. 2 increases. This indicates that in the soil with the application of soil remediation materials, the modified biochar and its surface humic acid both contribute to improving the soil permeability, electrical conductivity, and organic matter content, thereby alleviating the soil compaction degree and promoting the growth of Chinese cabbage.

[0111] The biological trait parameters of Chinese cabbage (such as germination rate, plant fresh weight, plant dry weight, plant height, etc.) can reflect its growth situation. Table 5 lists the biological trait parameters of Chinese cabbage in the soil remediated by different soil remediation agents.

[0112] The changes in the soil environment can directly affect plant growth. Table 6 lists the biological trait parameters of Chinese cabbage after 36 days of planting. It can be seen from the table that compared with the soil without the application of soil remediation materials, the germination rate of Chinese cabbage in the soil remediated by soil remediation materials has increased significantly. Regarding different types of soil remediation materials, when QCa@PSC-600@HA-2 is added to the test soil at a ratio of 1:10 (w / w), the germination rate of Chinese cabbage planted on it is relatively high, followed by the Chinese cabbage planted in the soil treated with QCa@PSC-600@HA-3 at the same ratio. Regarding the dosage of the same type of soil remediation material, when the soil remediation material is applied to the test sample at a mass ratio of 1:10, the germination rate of Chinese cabbage is relatively high; when the mass ratio of the two decreases to 1:15, the germination rate of Chinese cabbage in the remediated soil is relatively low, indicating that the dosage of the soil remediation agent has a significant impact on improving the fertility of degraded soil.

[0113] Table 5 Biological Trait Parameters of Chinese Cabbage

[0114]

[0115] Note: 1-1, 2-1, and 3-1 were obtained by adding QCa@PSC-600@HA-1, QCa@PSC-600@HA-2, and QCa@PSC-600@HA-3 to the test soil No. 1 at a ratio of 1:5 (w / w), respectively; 2-1, 2-2, and 2-3 were obtained by adding QCa@PSC-600@HA-1, QCa@PSC-600@HA-2, and QCa@PSC-600@HA-3 to the test soil No. 1 at a ratio of 1:10 (w / w), respectively; 3-1, 3-2, and 3-3 were obtained by adding QCa@PSC-600@HA-1, QCa@PSC-600@HA-2, and QCa@PSC-600@HA-3 to the test soil No. 1 at a ratio of 1:15 (w / w), respectively.

[0116] In addition, compared with the un-repaired test soil, the fresh weight, dry weight, and plant height of pakchoi planted in the improved test soil increased. For different types of soil remediation materials, when QCa@PSC-600@HA-2 was added to the test soil at a ratio of 1:10 (w / w), the increases in the fresh weight, dry weight, and plant height of pakchoi planted on it reached 99.6%, 113.8%, and 146.1%, respectively. The increases in the fresh weight, dry weight, and plant height of pakchoi in the soil treated with QCa@PSC-600@HA-1 were relatively small. Regarding the dosage of the same soil remediation material, the highest increases in the fresh weight, dry weight, and plant height of pakchoi were observed in the soil where the soil remediation material was applied at a mass ratio of 1:10 to the test sample, while the smallest increases in the fresh weight, dry weight, and plant height of pakchoi were found in the soil where the remediation agent was applied at a mass ratio of 1:5 to the test sample. This result was the same as the germination rate of pakchoi.

[0117] In addition, the ability of the soil remediation material to improve the test soil No. 2 was almost the same as that of the test soil No. 1, indicating the universality of the ability of the soil remediation material to improve problematic soils.

[0118] Effect on the quality of pakchoi: To further explore the remediation effect of soil remediation materials on compacted and heavy metal-polluted soils, the physiological and biochemical indexes of pakchoi in the repaired soil (such as chlorophyll, soluble sugar, and protein) were measured to indirectly reflect the ability of soil remediation materials to improve problematic soils. The relevant test results are shown in Figure 15 、 Figure 16 and Figure 17 as shown. The chlorophyll content of pakchoi in the soil repaired with different concentrations and different types of soil remediation materials is shown in Figure 15 as shown. It can be seen from the figure that in the pakchoi planting experiment in soil sample No. 1, compared with pakchoi planted in the soil without applying soil remediation materials, the chlorophyll content in the leaves of pakchoi in the improved soil increased, and the increase amplitude was as high as 124.68%.

[0119] For different types of soil remediation materials, the chlorophyll content in pakchoi grown in the soil modified by QCa@PSC-600@HA-2 is higher than that of other types. By comparing the chlorophyll content of pakchoi in the soil treated with the same type of soil remediation material at different dosages, it is found that the chlorophyll content increases with the increase in the dosage of modified biochar. The variation law of the chlorophyll content obtained from the pakchoi planting experiment in soil sample No. 1 is consistent with that in the pakchoi planting experiment in soil sample No. 2. Of course, during the soil remediation process, the dosage of biochar is not the more the better, and this phenomenon has been verified in the determination of the chlorophyll content of pakchoi in both soil samples. When the mass ratio of the soil remediation material to the sample soil is 1:10, the chlorophyll content of pakchoi in the modified soil reaches the maximum, and the chlorophyll contents of pakchoi in soil sample No. 1 and soil sample No. 2 are 2.53 mg / g and 2.62 mg / g respectively.

[0120] Effect on the soluble protein content in pakchoi plants: Among them, the soluble protein content of pakchoi in the soil treated with different concentrations and different types of soil remediation materials is shown in Figure 16 as follows. It can be seen from Figure 16 that in the pakchoi planting experiment in soil sample No. 1, compared with pakchoi in the soil without applying soil remediation materials, the soluble protein content in the leaves of pakchoi in the modified soil has increased, and the increase amplitude is as high as 32.87%. For different types of soil remediation materials, the soluble protein content of pakchoi in the soil modified by QCa@PSC-600@HA-2 is higher than that of other types. By comparing the soluble protein content of pakchoi in the repaired soil with the same type of soil remediation material at different dosages, it is found that the soluble protein content can increase with the increase in the dosage of modified biochar. The variation law of the soluble protein content obtained from the pakchoi planting experiment in soil sample No. 1 is consistent with that in the pakchoi planting experiment in soil sample No. 2. Of course, during the soil remediation process, the dosage of the soil remediation material is not the more the better, and this phenomenon has been verified in the determination of the soluble protein content of pakchoi in both soil samples. When the mass ratio of the soil remediation material to the sample soil is 1:10, the soluble protein content of pakchoi grown in the modified soil is the highest, and the chlorophyll contents of pakchoi in soil sample No. 1 and No. 2 are 27.69 mg / g and 28.92 mg / g respectively.

[0121] Effect on the soluble sugar content in pakchoi plants: The soluble sugar content of pakchoi in the soil repaired by different concentrations and different types of soil remediation materials is shown in Figure 17 as follows. As can be seen from Figure 17It can be seen that overall, in the pakchoi planting experiment of soil sample No. 1, the soil remediation material has little correlation with the soluble sugar content of pakchoi in the remediated soil. For the test soils treated with soil remediation materials of the same dose but different types, there is no regularity in the soluble sugar content of pakchoi grown on them. However, when comparing the test soils treated with soil remediation materials of the same type but different dosages, the changes in the soluble sugar content of the harvested pakchoi leaves basically do not show regularity. Moreover, in soil sample No. 1 and soil sample No. 2 treated with soil remediation materials of the same type and the same dose respectively, the soluble sugar content of the grown pakchoi is not very different, indicating that the soluble sugar content in plants is not only affected by the nutrients in the soil, but also the growth environment has a great impact on its soluble sugar content.

[0122] Content and morphological distribution of available lead and cadmium in the soil after pakchoi maturation: Given that no heavy metals were detected in the pakchoi grown in two small experimental fields simulating the externally collected soil in the school greenhouse, the experiment also measured the content and morphological distribution of available lead and cadmium in the soil of the simulated plots before and after applying the soil remediation agent. The relevant test results are shown in Table 7 and Figure 18 as follows. The content of available lead and cadmium in the soil of the simulated plot after 90 days of remediation with the soil remediation material QCa@PSC-600@HA-2 is listed in Table 6 before and after pakchoi planting.

[0123] Table 6 Content of available Pb and available Cd in the soil before and after pakchoi planting

[0124]

[0125] As can be seen from Table 6, when pakchoi was planted in soil sample No. 1 after being remediated with the soil remediation material, by comparing the content of available Pb in the soil before and after pakchoi planting, it was found that the numerical changes were not obvious, indicating that the available lead in the soil did not transfer to the pakchoi plants. The reason for this phenomenon is that when the soil remediation material is applied to the test soil, the polar oxygen-containing groups on the surface of the biochar may adsorb and complex with some heavy metals in the soil, thereby achieving the purpose of passivating the heavy metals. Moreover, oxygen-containing acid root ions such as PO4 3- and CO3 2- in the soil may also react with lead and cadmium ions to form precipitates.

[0126] In addition, before and after the planting of pakchoi, the difference in the available Cd content in the soil was not significant, indicating that the available Cd in the soil was not transferred to the pakchoi plants. In addition, pakchoi was planted in soil samples No. 1 and No. 2 that had been repaired with soil remediation materials, and the difference in the available lead content in the soil before and after harvesting was also not significant. Since no available lead and available cadmium were detected in the harvested pakchoi plants in this study, the accuracy of the experimental results was verified. Pakchoi was planted in soil sample No. 1 that had been repaired with soil remediation materials, and the morphological distributions of Pb (or / and Cd) in the soil before and after the planting of pakchoi were measured respectively. The relevant results are shown in Figure 18 as follows. As can be seen from Figure 18 , for soil sample No. 1 that had been repaired with soil remediation materials, comparing the content of fixed Pb in the soil before and after the planting of pakchoi, it was found that the changes were not significant, and the differences in the contents of other forms of Pb (such as acid-soluble and exchangeable Pb, oxidized Pb, and reduced Pb) were also not obvious. At the same time, the differences in the contents of various forms of Cd in the soil before and after the planting of pakchoi were not significant. In summary, during the growth of pakchoi, neither the available lead nor the available cadmium in the soil was transferred to the pakchoi plants. In addition, pakchoi was planted in soil sample No. 2 that had been repaired with soil remediation materials, and the contents of available lead and cadmium in the soil before and after the planting of pakchoi did not change significantly.

[0127] Analysis of the mechanism of soil remediation materials in repairing compacted and heavy metal-contaminated soils: When soil remediation materials are applied to farmland suffering from soil compaction and heavy metal pollution, there are interactions between biochar and anions, cations, heavy metals, microorganisms, etc. in the soil. When the soil remediation materials enter the heavy metal-contaminated soil, the negative charges and polar oxygen-containing functional groups on their surfaces respectively have electrostatic adsorption effects on the positively charged lead ions and cadmium ions. Moreover, the surface of calcium-modified biochar contains a large number of inorganic mineral ions (such as Ca 2+ ) and oxygen-containing anions, all of which can undergo ion exchange reactions with heavy metal ions (such as lead and cadmium) in the soil, thereby inhibiting the migration and transfer of heavy metal ions in the soil.

[0128] Meanwhile, the surface of humic acid-modified biochar contains a large number of polar oxygen-containing groups (such as hydroxyl groups, carboxyl groups, carbonyl groups, etc.), which can achieve the purpose of immobilization by oxidizing heavy metals such as lead and cadmium. In addition, biochar with a high specific surface area and a developed pore structure has more adsorption sites on its surface or in its pores, and can immobilize heavy metals on the surface or inside the pores of biochar through intermolecular forces, thereby achieving the effect of passivating heavy metals. When humic acid-modified calcium-modified biochar acts on compacted soil, the abundant oxygen-containing groups on its surface increase the soil pH value, while also increasing the organic matter content and decreasing the electrical conductivity in the soil. The introduction of biochar changes the microbial community structure in the soil, increasing the activities of urease, sucrase, and alkaline phosphatase in the soil, and thus achieving the purpose of soil carbon sequestration and stabilizing nitrogen and phosphorus contents. In addition, the surface of biochar prepared from waste mushroom stick residues contains a large number of inorganic mineral ions. When it enters the soil, it improves the cation exchange capacity in the soil and enhances the soil water holding capacity, reducing the soil compactness.

[0129] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them; although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that: it is still possible to modify the specific implementation manners of the present invention or perform equivalent replacements for some technical features; without departing from the spirit of the technical solutions of the present invention, they should all be covered within the scope of the technical solutions claimed by the present invention.

Claims

1. A method for growing crops in compacted soil, comprising the following steps: Step 1: Alkaline wash agricultural waste to remove lignin, then carbonize it, and then mix it with eggshell powder, burn it to obtain calcium-modified biochar powder; mix humic acid with the calcium-modified biochar powder, filter and dry it to obtain a soil remediation material; wherein, the mass ratio of the humic acid to the calcium-modified biochar powder is 1:(4 - 16); Step 2: Mix the soil remediation material with the compacted soil in a mass ratio of 1:(3 - 17), incubate it and then grow crops. Before the seeds germinate, water once every 1 day, and after the seeds germinate, water once a day to ensure that the soil remains moist.

2. The method for growing crops in compacted soil according to claim 1, wherein: In Step 2, the incubation time after mixing the soil remediation material with the compacted soil is 60 days to 120 days.

3. A method for growing crops in compacted soil according to claim 1 or 2, characterized in that: The agricultural waste is mushroom stick residue, peanut shell or wood chip.

4. A method for growing crops in compacted soil according to claim 1, characterized in that: In Step 1, the calcium-modified biochar powder is obtained through the following steps: Wash agricultural waste with deionized water, dry it, and then perform crushing and screening. The obtained agricultural waste powder is stirred in a NaOH solution for 3 h to 8 h to remove lignin in the components of the agricultural waste powder. After filtration, the filter residue is washed with deionized water until neutral, and then dried, ground, and screened. Then, under the conditions of a N2 atmosphere, a carbonization temperature of 400 °C to 800 °C, and a heating rate of 3 °C / min to 10 °C / min, carbonization treatment is carried out for 1 h to 3 h to obtain biochar powder. The specific surface area of the biochar powder is 35 m 2 / g to 43 m 2 / g, and the pore volume is 0.045 cm 3 / g to 0.090 cm 3 / g; Wash, air-dry, crush and screen the eggshells, and then carbonize them for 1 h - 3 h under the conditions of a carbonization temperature of 400 °C - 800 °C and a heating rate of 3 °C / min - 10 °C / min to obtain carbonized eggshell powder; Finally, mix and ball-mill the carbonized eggshell powder and the biochar powder in a mass ratio of (2 - 8):1, and place the dried solid powder under the conditions of 500 °C - 900 °C and a heating rate of 15 °C / min - 25 °C / min in an N2 atmosphere and burn it for 1 h - 2 h; obtain the calcium-modified biochar powder.

5. A soil remediation material, characterized in that, The soil remediation material is prepared through the following steps: Alkaline wash agricultural waste to remove lignin, then carbonize it, and then mix it with eggshell powder, burn it to obtain calcium-modified biochar powder; mix humic acid with the calcium-modified biochar powder, filter and dry it to obtain a soil remediation material; wherein, the mass ratio of the humic acid to the calcium-modified biochar powder is 1:(4 - 16).

Images