Preparation method of iron-modified biochar and application of iron-modified biochar in crop rotation planting of rice and wheat

Abstract

The invention relates to the technical field of agriculture, in particular to a preparation method of iron-modified biochar and application of the iron-modified biochar in crop rotation planting of rice and wheat. The preparation method of the iron modified biochar comprises the following steps: crushing rice straws, putting the crushed rice straws into a ferric sulfate solution, and dipping for 24-48 hours; the soaked rice straw is dried at the temperature of 60 DEG C to 80 DEG C; and pyrolyzing the dried rice straws at 500-600 DEG C for 1-3 hours to obtain the iron modified biochar. According to the invention, the iron-modified biochar is applied to the rice-wheat crop rotation system, so that greenhouse gas emission in the rice-wheat crop rotation system is effectively reduced, the crop yield is increased, heavy metal pollution of soil is avoided, and a win-win situation of economic, environmental and social benefits of agricultural production is realized.

Description

Technical Field

[0001] The present invention relates to the technical field of agriculture, and particularly relates to a preparation method of iron-modified biochar and its application in rice-wheat rotation planting. Background Art

[0002] The issue of greenhouse gas (GHG) emissions has become the focus of global attention. As an important source of greenhouse gas emissions, agriculture, especially the emissions of methane (CH4) and nitrous oxide (N2O), has a significant impact on global climate change. In China, rice-wheat rotation is a widely applied farming system. However, traditional rice-wheat rotation systems are often accompanied by relatively high GHG emissions, especially methane emissions during the rice planting stage and nitrous oxide emissions during the wheat growth period.

[0003] To address this challenge, researchers have started to explore reducing GHG emissions in the rice-wheat rotation system by applying biochar. Biochar is a carbon-rich solid material with a highly porous structure and a large specific surface area, which can improve the physical and chemical properties of the soil, thereby reducing methane production and reducing nitrous oxide emissions by improving nitrogen use efficiency. However, the emission reduction effect of ordinary biochar is uncertain, and its ability to adsorb nitrogen and regulate the microbial community is limited, which restricts its effect in practical applications. This urgently requires us to explore new methods to improve its emission reduction efficiency, and modifying biochar is considered a very promising regulation strategy and is receiving increasing attention. Summary of the Invention

[0004] The present invention provides a preparation method of iron-modified biochar and its application in rice-wheat rotation planting to solve the problem of greenhouse gas emissions in the rice-wheat rotation system, while overcoming the uncertainty of the emission reduction effect of ordinary biochar and avoiding the problem of soil heavy metal pollution risk caused by modification.

[0005] According to the first aspect of the present invention, the present invention provides a preparation method of iron-modified biochar, including the following steps: crushing rice straw and putting it into a ferric sulfate solution, impregnating for 24 - 48 h; drying the impregnated rice straw at 60 - 80 °C; pyrolyzing the dried rice straw at 500 - 600 °C for 1 - 3 h to obtain iron-modified biochar.

[0006] Experiments have found that the iron-modified biochar obtained by modifying rice straw with ferric sulfate exhibits good greenhouse gas emission reduction and soil improvement effects in rice-wheat rotation. By controlling parameters such as impregnation time, drying temperature, and pyrolysis time, iron-modified biochar that meets the requirements can be stably prepared, providing an operable preparation process for the practical application of this technical solution.

[0007] Further, the rice straw and Fe3+ The mass ratio is 1:(20 - 30); the concentration of the ferric sulfate solution is 0.4 - 0.6 mol / L -1 . The preparation conditions of the iron-modified biochar are further optimized. By limiting the mass ratio of rice straw to Fe 3+ and the concentration range of the ferric sulfate solution, the modification effect of the biochar can be better controlled, enabling it to exhibit better performance in greenhouse gas emission reduction and soil improvement.

[0008] Furthermore, the pH value of the iron-modified biochar is 5 - 6, the total carbon content is 420.37 - 500.35 g / kg -1 , the total nitrogen content is 0.98 - 1.16 g / kg -1 , the specific surface area is 96.78 - 111.06 m 2 / g -1 , the pore volume is 0.24 - 0.26 cm 3 / g -1 , and the pore diameter is 8.68 - 9.04 nm. These physical and chemical properties of the iron-modified biochar enable the biochar to better play its roles of adsorption, soil structure improvement, and microbial community regulation in the soil, thereby more effectively reducing greenhouse gas emissions and ensuring the safety of the soil environment.

[0009] Furthermore, in the iron-modified biochar, the mass percentage of C is 70 - 75%, the mass percentage of O is 20 - 25%, the mass percentage of N is 2.5 - 3%, the mass percentage of Fe is 2 - 2.5%, the mass percentage of Cd is 0.08 - 0.1%, and the mass percentage of As is 0.5 - 0.7%. The mass percentages of various elements in the iron-modified biochar are further clarified to ensure that while achieving the greenhouse gas emission reduction effect, it will not cause soil environmental pollution due to excessive contents of heavy metal elements (such as Cd and As), thus ensuring the environmental safety of this technical solution.

[0010] According to the second aspect of the present invention, the present invention also provides the application of the above-mentioned preparation method of the iron-modified biochar in rice-wheat rotation planting. The application method is as follows: after the rice is harvested, the collected rice straw is prepared into iron-modified biochar by using the above-mentioned preparation method of the iron-modified biochar; before sowing wheat, the obtained iron-modified biochar is applied to the soil at one time and mixed evenly; fertilizers are added during the rice-wheat rotation period.

[0011] A rice-wheat rotation planting method of the present invention can effectively reduce the emissions of greenhouse gases (CH4 and N2O) in the rice-wheat rotation system by applying the iron-modified biochar during the rice-wheat rotation, and will not bring exogenous heavy metal pollution to the soil. At the same time, it can improve soil fertility and crop yields, realizing the green and sustainable development of agriculture.

[0012] Furthermore, the application rate of the iron-modified biochar is 8 - 12 t hm -2 . By clarifying the application rate range of the iron-modified biochar, it is ensured that it can achieve the best greenhouse gas emission reduction and soil improvement effects in the rice-wheat rotation system, while avoiding negative impacts on the soil environment and crop growth due to improper application rates.

[0013] Furthermore, the application rate of the fertilizer is 240 kg hm of pure nitrogen -2 , 146 kg hm of P2O5 -2 and 52 kg hm of K2O -2 . By limiting the application rate of the fertilizer within a reasonable range value, it is ensured that while applying the iron-modified biochar, sufficient nutrients can be provided for the rice-wheat rotation, guaranteeing the normal growth and yield of crops, and achieving a balance between greenhouse gas emission reduction and crop production.

[0014] Furthermore, during the application process of the fertilizer, 40% of N and all P and K are applied as a compound fertilizer before wheat sowing or rice transplanting as basal fertilizers into the soil, and the remaining 60% of N is applied as urea in a ratio of 40%:20% as topdressing into the soil. By reasonably distributing the ratio of basal fertilizers and topdressing, it can better meet the nutrient requirements of crops at different growth stages, improve the fertilizer utilization efficiency, and combined with the application of the iron-modified biochar, further optimize the greenhouse gas emission reduction and crop yield effects of the rice-wheat rotation system.

[0015] Furthermore, in the compound fertilizer, it includes 15% by weight of N, 15% of P2O5 and 15% of K2O.

[0016] Furthermore, the variety of the rice is Yongyou 7850 or Yongyou 12; the variety of the wheat is Yangmai 34 or Zhenmai 18.

[0017] Furthermore, for rice planting, there are two seedlings per hill and two hills per pot; for wheat planting, there are 20 - 40 plants per pot.

[0018] Furthermore, the application method also includes field management measures: during the wheat planting process, level the land, loosen the soil, and control pests and weeds; for weed control, select one or more of the agents including mesosulfuron-methyl, MCPA, and florasulam before sowing or after emergence to conduct pre-emergence or post-emergence control against broad-leaved weeds and gramineous weeds; for pest and disease control, regularly inspect the wheat fields, pay attention to the occurrence of aphids, leaf rust, and sheath blight, and apply pesticides in a timely manner when the pest population or disease spots are found; at the same time, keep the fields clean, remove weeds and residues, and reduce the sources of pests and diseases; During the rice planting process, pest and weed control are carried out. 7 - 10 days after transplanting, at the tillering stage and the booting stage, agents including one or more of pymetrozine, lambda - cyhalothrin, and tricyclazole are used respectively to control planthoppers, leaf - rolling caterpillars, and rice blast. For weed control, herbicides including one or two of sulfometuron methyl or propisochlor are sprayed during the peak weed period. In terms of water management, the field is flooded in advance before transplanting, a water layer of 3 - 8 cm is maintained from the initial stage of transplanting to the late tillering stage, the field is drained and sunned for 3 - 4 days at the end of the tillering stage, and the water is drained one week before the yellow - ripening stage for convenient harvesting.

[0019] By reasonably optimizing the field management measures, it can ensure that during the rice - wheat rotation process, the application effects of iron - modified biochar and fertilizers are fully exerted, while protecting the growth environment of crops and soil quality, and achieving the coordinated optimization of greenhouse gas emission reduction, soil improvement, and crop production.

[0020] Advantages of the present invention: A rice - wheat rotation planting method provided by the present invention, through the application of iron - modified biochar, not only effectively reduces greenhouse gas emissions in the rice - wheat rotation system, improves crop yields, but also avoids soil heavy - metal pollution, achieving a win - win situation for the economic, environmental, and social benefits of agricultural production. Description of the Drawings

[0021] To more clearly illustrate the technical solutions in the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0022] Figure 1 It is a scanning electron microscope image of the iron - modified biochar Fe - BC provided in Example 1 of the present invention and the biochar BC of Comparative Example 2.

[0023] Figure 2 It is a Fourier spectrum image of the iron - modified biochar Fe - BC provided in Example 1 of the present invention and the biochar BC of Comparative Example 2.

[0024] Figure 3 It is a dynamic graph of greenhouse gas (CH4, N2O) emissions during two - year rice - wheat rotation provided by Example 1, Comparative Example 1, and Comparative Example 2 of the present invention.

[0025] Figure 4 It is a cumulative CH4 emission graph during two - year rice - wheat rotation provided by Example 1, Comparative Example 1, and Comparative Example 2 of the present invention.

[0026] Figure 5 It is a cumulative N2O emission graph during two - year rice - wheat rotation provided by Example 1, Comparative Example 1, and Comparative Example 2 of the present invention.

[0027] Figure 6 These are the two-year rice-wheat rotation yield graphs provided by Example 1, Comparative Example 1, and Comparative Example 2 of the present invention.

[0028] Figure 7 These are the two-year rice-wheat rotation global warming potential graphs provided by Example 1, Comparative Example 1, and Comparative Example 2 of the present invention.

[0029] Figure 8 These are the two-year rice-wheat rotation greenhouse gas emission intensity graphs provided by Example 1, Comparative Example 1, and Comparative Example 2 of the present invention.

[0030] Figure 9 These are the comparison graphs of soil heavy metal contents at the end of the experiment provided by Example 1, Comparative Example 1, and Comparative Example 2 of the present invention. Detailed implementation manners

[0031] To make the objectives, technical solutions, and advantages of the present invention clearer, the technical solutions in the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present invention without making creative efforts fall within the scope of protection of the present invention.

[0032] Example 1 This example provides a rice-wheat rotation planting method (abbreviated as Fe-BC treatment), with the rice variety being Yongyou 7850 and the wheat variety being Yangmai 34. Pot experiments were carried out, with a total of 3 treatments and 3 replicates for each treatment. The specific steps are as follows: After rice harvest, rice straw was collected for the preparation of iron-modified biochar Fe-BC. The preparation method of iron-modified biochar Fe-BC is as follows: 15 kg of straw was washed and reserved; a ferric sulfate solution of 0.5 mol L -1 was prepared, and the mass ratio of straw to Fe 3+ was controlled to be 1:25, that is, 2.2 kg of ferric sulfate powder was dissolved in 11 L of water; the crushed straw was put in and impregnated for 24 h, with intermittent stirring during this period; the crushed straw was filtered out and dried to constant weight at 70°C. The dried rice straw was pyrolyzed at 550°C for 2 h to obtain iron-modified biochar.

[0033] Before wheat sowing at the end of November 2022, the iron-modified biochar was applied to the soil at a one-time application rate of 10 t hm -2 and mixed evenly, and no more biochar was added subsequently.

[0034] Fertilizers were added during the rice-wheat rotation period, and the fertilizer application rates were 240 kg hm -2 for pure nitrogen, 146 kg hm for P2O5-2 and 52 kg hm of K₂O -2 Among them, 40% of N and all P and K are applied as compound fertilizers into the soil before wheat sowing or rice transplanting as base fertilizers, and the remaining N is applied as topdressing into the soil in a ratio of 40%:20% in the form of urea (two topdressings. For rice, tillering fertilizer and panicle fertilizer; for wheat, jointing fertilizer and panicle fertilizer).

[0035] Field management includes: In terms of wheat management measures, compound fertilizers (96 kg hm of N -2 , 146 kg hm of P₂O₅ -2 , and 52 kg hm of K₂O -2 ) should be applied before sowing, combined with deep plowing of 10 cm for land preparation, and then the soil should be finely harrowed and leveled. After sowing, 96 kg hm of nitrogen fertilizer should be topdressed during the green-recovery period -2 , and another 48 kg hm of nitrogen fertilizer should be topdressed at the end of the jointing stage -2 to promote tillering and grain filling. For weed control, before sowing or after emergence, drugs such as mesosulfuron-methyl, MCPA, and florasulam can be selected to conduct pre-emergence or post-emergence control against broad-leaved weeds and gramineous weeds. The drugs should be evenly sprayed with water according to the recommended dosage. For pest and disease control, the wheat field should be regularly inspected, and attention should be paid to the occurrence of aphids, leaf rust, and sheath blight. When the pest population or disease spots are found, drugs should be applied in time for prevention and control; at the same time, keep the field clean, remove weeds and stubbles to reduce the sources of pests and diseases.

[0036] In terms of rice management, compound fertilizers with the same ratio (96 kg hm of N -2 , 146 kg hm of P₂O₅ -2 , and 52 kg hm of K₂O -2 ) should be applied before transplanting, and the land should be deeply plowed and leveled. At 7 - 10 days after transplanting, during the tillering stage, and the booting stage, drugs such as pymetrozine, lambda-cyhalothrin, and tricyclazole are used respectively to control planthoppers, leaf rollers, and rice blast; for weed control, sulfentrazone or isoproturon herbicides are sprayed during the peak weed period. In terms of water management, keep a water layer of 3 - 8 cm from the initial transplanting stage to the late tillering stage, drain the field for sunning for 3 - 4 days at the end of the tillering stage, and let the water dry out one week before the yellow ripening stage for convenient harvesting. Combine shallow loosening (3 - 5 cm) during middle tillage to remove weeds and conserve soil moisture, and topdress 96 kg hm of urea -2 and 48 kg hm of urea -2 during the tillering and booting stages respectively. Through cleaning stubbles, reasonable crop rotation, and scientific management, comprehensively ensure the yield and quality of wheat and rice.

[0037] Comparative Example 1 This comparative example provides a rice-wheat rotation planting method (abbreviated as CF treatment), which is different from Example 1 in that: during the rice-wheat rotation period, only fertilizers are added, and iron-modified biochar is not added.

[0038] Comparative Example 2 This comparative example provides a rice-wheat rotation planting method (abbreviated as BC treatment). The difference from Example 1 is that biochar BC is used to replace iron-modified biochar.

[0039] The carbonization step of biochar BC is pyrolysis at 500 - 600 °C for 2 hours to obtain ordinary biochar (BC). When applying, it is sieved through a 100-mesh sieve to make it fully mixed with the soil evenly.

[0040] Comparative Example 3 This comparative example provides a rice-wheat rotation planting method (abbreviated as nZVI-BC treatment). The difference from Example 1 is that nano zero-valent iron biochar (nZVI-BC) is used to replace iron-modified biochar.

[0041] Nano zero-valent iron biochar (nZVI-BC) is prepared by dissolving 5.56 g of biochar (BC) in 100 ml of deionized water, then adding 2.78 g of nano-ferroferric oxide, and placing the mixture in a nitrogen-filled atmosphere and stirring for 60 min. Then it is washed three times with ethanol and deionized water respectively. Subsequently, the obtained solid is transferred to an oven to remove moisture, and the dried composite material is named nano biochar (nZVI-BC).

[0042] The obtained nano biochar (nZVI-BC) is applied to the soil, and a pot experiment is carried out with reference to the treatment Fe-BC group. The results show that the methane emission is reduced by about 16% on average compared with the treatment CF group, and the nitrous oxide emission is reduced by about 11% on average.

[0043] The scanning electron microscope images of the iron-modified biochar Fe-BC in Example 1 and the biochar BC in Comparative Example 2 are as Figure 1 shown. It can be seen that the SEM images of the two biochars at different magnification ratios show that the surface of BC presents rough, irregular, fragmented and porous particles, while Fe-BC shows a relatively rough granular structure with fine particles aggregated on the surface.

[0044] The Fourier spectra (FTIR) of the iron-modified biochar Fe-BC in Example 1 and the biochar BC in Comparative Example 2 are as Figure 2 shown. It can be seen that the infrared spectral characteristics of BC and Fe-BC reveal the changes in their functional groups. First, the absorption peak appearing at 802 cm -1 is related to the in-plane vibration of the C-H bond on aromatic carbon. Then, at 1106 cm -1 , the C-O stretching vibration absorption peak of Fe-BC is significantly enhanced compared with BC, while the absorption peak at 1388 cm -1 corresponding to C-N vibration weakens. At 1610 cm -1At this point, the intensity of the C=C absorption peak of Fe-BC is weaker than that of BC. At 2924 cm -1 For Fe-BC, a weaker absorption peak of C-H stretching vibration appears compared to BC. Finally, the absorption peak at 3432 cm -1 reflects the stretching vibration of the O-H bond, and this peak is stronger in BC than in Fe-BC.

[0045] The basic physical and chemical properties of the iron-modified biochar Fe-BC in Example 1 and the biochar BC in Comparative Example 2 are shown in Table 1 below.

[0046] Table 1

[0047] Table 1 shows the differences in the main physical and chemical characteristics between BC and Fe-BC. After Fe-BC was impregnated and modified with Fe2(SO4)3 solution, its pH decreased from 10 of BC to 5.73, and the total carbon (TC) and total nitrogen (TN) contents decreased by 20.3 g kg -1 and 2.44 g kg -1 . BET analysis shows that the specific surface area and pore volume of Fe-BC decreased, but the pore diameter increased slightly. The XPS analysis results show that the carbon (C) content in Fe-BC increased to 71.24%, while the contents of oxygen (O) and nitrogen (N) elements decreased. At the same time, the iron (Fe) content in Fe-BC increased significantly to 2.36%, while the contents of heavy metal elements such as cadmium (Cd) and arsenic (As) changed little, only increasing by 0.01% and 0.1% respectively.

[0048] Index determination: The static closed chamber-gas chromatography combined method was used to monitor the greenhouse gas emissions of rice-wheat rotation: Gas samples were extracted from the sealed chambers in the field using a static closed chamber, and the sampling frequency of gas samples was once a week, with sampling being densified after fertilization. After the samples were collected, an Agilent 7890A gas chromatograph was used to analyze the greenhouse gas emission flux, and then the cumulative emissions were calculated.

[0049] The following formula was used to calculate the emission fluxes of N2O and CH4: F = ρ×V / A×dc / dt×273 / (273 + T)×P / 1013 F represents the emission flux of CH4 (mg m -2 h -1 ) or N2O (μg m -2 h -1 ), ρ represents the density of CH4 (0.53 g L -1 ) or N2O (1.25 g L -1 ), V represents the volume of the sampling chamber (m 3), A represents the bottom frame coverage area (m 2 ), dc / dt represents the gas emission rate, T is the temperature in the sampling chamber (°C), and P is the local atmospheric pressure. Finally, the cumulative emissions of N2O (g pot -1 ) and CH4 (g pot -1 ) are calculated based on the emission flux and sampling date.

[0050] Taking into account the emissions of N2O and CH4, the greenhouse effect (GWP, g CO 2-eq pot -1 ) and greenhouse gas intensity (GHGI, g CO 2-eq g -1 ) are calculated: GWP = 273×N2O×44 / 28 + 27.2×CH4×16 / 12 GHGI = GWP / grain yield Among them, the numbers 273 and 27.2 represent the warming potentials of N2O and CH4 respectively.

[0051] Results of the pot experiment 1. Emission dynamics of greenhouse gases (CH4, N2O) during two-year rice-wheat rotation As Figure 3 shown, by observing the emission dynamics of greenhouse gases during two-year rice-wheat rotation after applying different biochars, it is found that there are higher CH4 emissions during the rice season, while the emissions are relatively low during the wheat season. CH4 emissions are higher under flooded conditions during the rice season, but there is almost no emission during the mid-season drainage and moist irrigation periods. The peak period of soil N2O emissions mainly exists within 7 to 10 days after fertilization during the wheat season, and obvious emission peaks are also observed during the mid-season drainage period of the rice season.

[0052] 2. Cumulative CH4 emissions during two-year rice-wheat rotation As Figure 4 shown, calculating the cumulative CH4 emissions for two years shows that the methane emissions of the CF treatment were the highest in 2023, and the methane emissions of the BC treatment decreased significantly. The methane emissions of the Fe-BC treatment further decreased, and the methane emissions of wheat increased slightly but were still relatively low overall. In 2024, the methane emissions of the CF treatment decreased compared with 2023 but were still higher than those of other treatments. The methane emissions of the BC treatment decreased significantly. The methane emissions of the Fe-BC treatment were the lowest.

[0053] 3. Cumulative N2O emissions during two-year rice-wheat rotation As Figure 5As shown, the N2O emissions during the rice season of the CF treatment in 2023 were relatively high, while those during the wheat season were relatively low. The N2O emissions during the rice season of the BC treatment decreased slightly. The N2O emissions of the Fe-BC treatment were similar to those of the BC treatment. The N2O emissions during the wheat season of the CF treatment in 2024 increased compared to 2023. The N2O emissions of the BC treatment were lower than those of the CF treatment. Similar to the BC treatment, the N2O emissions during both the rice and wheat seasons of the Fe-BC treatment were lower than those of the CF treatment.

[0054] 4. Yields of rice and wheat in the two-year rice-wheat rotation As Figure 6 shown, the rice yield of the CF treatment in 2023 was the highest, while the wheat yield was relatively low. After applying biochar in the BC treatment, the rice yield was slightly lower than that of the CF treatment. The rice yield of the Fe-BC treatment was slightly higher than those of the CF and BC treatments, and the wheat yield was similar to those of the CF and BC treatments. In 2024, the rice yield of the BC treatment increased significantly compared to the CF treatment, and the wheat yield increased slightly. The yields of both rice and wheat of the Fe-BC treatment were the highest.

[0055] 5. Global warming potential (GWP) of the two-year rice-wheat rotation As Figure 7 shown, after calculating the global warming potential of the two-year rice-wheat rotation, the GWP of the CF treatment in 2023 was the highest.

[0056] After applying biochar in the BC treatment, the GWP of rice decreased significantly, while the GWP of wheat changed little. Compared with the CF treatment, the GWP of the Fe-BC treatment also decreased, but was close to that of the BC treatment. In 2024, the GWP of rice in the BC treatment decreased, and the GWP of wheat was similar to that in 2023, indicating that biochar could still reduce GWP in the second year. The Fe-BC treatment had the largest reduction in GWP, and the GWPs of both rice and wheat were lower than those of other treatments.

[0057] 6. Greenhouse gas emission intensity (GHGI) of the two-year rice-wheat rotation As Figure 8 shown, the GHGI of the CF treatment in 2023 was the highest. The GHGI of the BC treatment decreased significantly. The GHGI of the Fe-BC treatment was lower than that of the CF treatment and equivalent to that of the BC treatment. In 2024, the GHGI of the CF treatment was still the highest, while the GHGI of the BC treatment decreased significantly, especially with a greater reduction in rice, indicating that biochar still maintained good emission reduction effects in the second year. The GHGI of the Fe-BC treatment further decreased to the lowest level, and the GHGIs of both rice and wheat were lower than those of other treatments, highlighting the more significant emission reduction advantage of Fe-BC in the second year.

[0058] 7. Heavy metal content in the soil at the end of the experiment As Figure 9As shown, there were no significant differences in the contents of the four main heavy metals (lead, arsenic, chromium, cadmium) in the soil treated with BC and Fe-BC compared with the CF treatment, indicating that the application of BC and Fe-BC did not significantly increase the heavy metal content in the soil and did not pose an additional heavy metal pollution risk.

[0059] 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 foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A preparation method of iron-modified biochar, characterized in that, It includes the following steps: pulverize rice straw and put it into a ferric sulfate solution, and soak for 24 - 48 h; dry the soaked rice straw at 60 - 80 °C; pyrolyze the dried rice straw at 500 - 600 °C for 1 - 3 h to obtain iron-modified biochar; The mass ratio of the rice straw to Fe 3+ is 1:(20 - 30); the concentration of the ferric sulfate solution is 0.4 - 0.6 mol / L -1 .

2. The preparation method of the iron-modified biochar according to claim 1, wherein The pH value of the iron-modified biochar is 5 - 6, and the total carbon content is 420.37 - 500.35 g kg -1 , the total nitrogen content is 0.98 - 1.16 g kg -1 , the specific surface area is 96.78 - 111.06 m 2 g -1 , the pore volume is 0.24 - 0.26 cm 3 g -1 , and the pore diameter is 8.68 - 9.04 nm.

3. The preparation method of the iron-modified biochar according to claim 1 or 2, characterized in that In the said iron-modified biochar, the mass percentage of C is 70 - 75%, the mass percentage of O is 20 - 25%, the mass percentage of N is 2.5 - 3%, the mass percentage of Fe is 2 - 2.5%, the mass percentage of Cd is 0.08 - 0.1%, and the mass percentage of As is 0.5 - 0.7%.

4. Use of the preparation method of the iron-modified biochar according to any one of claims 1-3 in rice-wheat rotation planting, characterized in that The application method is as follows: after rice harvest, prepare iron-modified biochar from the collected rice straw by using the preparation method of the said iron-modified biochar; Before wheat sowing, apply the obtained iron-modified biochar into the soil at one time and mix well; add fertilizers during the rice-wheat rotation period.

5. Use of the preparation method of iron-modified biochar according to claim 4 in rice-wheat rotation planting, characterized in that The application rate of the iron-modified biochar is 8 - 12 t / hm 2 .

6. Use of the method for preparing iron-modified biochar according to claim 4 or 5 in rice-wheat rotation planting, characterized in that, The application rate of the fertilizer is 240 kg N ha -2 , 146 kg P2O5 ha -2 and 52 kg K2O ha -2 .

7. Use of the preparation method of iron-modified biochar according to claim 6 in rice-wheat rotation planting, characterized in that, During the application of the said fertilizers, 40% of N and all P and K are applied into the soil as base fertilizers in the form of compound fertilizers before wheat sowing or rice transplanting, and the remaining 60% of N is applied into the soil as topdressing in the form of urea according to the ratio of 40%:20%.

8. Use of the preparation method of iron-modified biochar according to claim 4 in rice-wheat rotation planting, characterized in that The variety of the said rice is Yongyou 7850 or Yongyou 12; the variety of the said wheat is Yangmai 34 or Zhenmai 18; for rice planting, there are two seedlings per hill and two hills per pot; for wheat planting, there are 20 - 40 plants per pot.

9. Use of the preparation method of iron-modified biochar according to claim 4 in rice-wheat rotation planting, characterized in that, The said application method also includes field management measures: during wheat planting, level the land, loosen the soil, and control insects and weeds; for weed control, select one or more of the medicaments including mesosulfuron-methyl, MCPA, and florasulam before sowing or after emergence to conduct closed or post-emergence control against broad-leaved weeds and gramineous weeds; for pest and disease control, regularly inspect the wheat field, pay attention to the occurrence of aphids, leaf rust, and sheath blight, and apply pesticides in time when the pest population or disease spots are found; at the same time, keep the field clean, remove weeds and residues, and reduce the sources of pests and diseases; During rice planting, control insects and weeds; at 7 - 10 days after transplanting, at the tillering stage, and at the booting stage, use one or more of the medicaments including pymetrozine, lambda-cyhalothrin, and tricyclazole to control planthoppers, leaf rollers, and rice blast; for weed control, spray one or two of the herbicides including sulfentrazone or isoproturon at the high weed occurrence period; for water management, flood the field in advance before transplanting, keep a water layer of 3 - 8 cm from the initial stage of transplanting to the late tillering stage, drain the field and sun it for 3 - 4 days at the end of the tillering stage, and drain the water one week before the yellow ripening stage for convenient harvesting.

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