Method for repairing cadmium contaminated soil by using giant rice regeneration and dry planting

Abstract

The application provides a method for repairing Cd-polluted soil by using a giant rice regeneration dry planting method, and belongs to the technical field of soil pollution treatment. The repairing method comprises the following steps: in the first half of the natural year, a giant rice is planted in a rice field polluted by Cd according to a conventional method; after the giant rice is harvested, a stubble with a height of 7cm-20cm is left, and then water and fertilizer are applied for regeneration; after a tillering period, water in the rice field is drained, and dry planting is implemented without water irrigation; the regenerated giant rice is harvested when it is mature, and rice straw is removed from the field. The method selects the giant rice with large biomass, and improves the Cd concentration of the giant rice through dry planting, so as to overcome the defect that the Cd concentration of a plant with large biomass is generally low, realize efficient and low-cost plant extraction of soil Cd in a farmland, and realize low-cost and efficient repair of Cd-polluted soil.

Description

Technical Field

[0001] The present invention relates to the technical field of soil pollution control, and in particular to a method for repairing Cd-contaminated soil by cultivating giant rice regeneration and fallen stems. Background Art

[0002] Cadmium (Cd), a widespread heavy metal pollutant, easily accumulates in organisms, causing serious pollution to soil, water, and crops, posing a potential threat to human health through the food chain. Cd contamination in farmland soil has become an urgent environmental issue.

[0003] Existing remediation technologies for soil Cd contamination primarily fall into three categories: physical, chemical, and biological. While physical methods, such as soil removal and soil turning, can effectively reduce Cd content in the soil surface, they are labor-intensive, costly, and can potentially cause secondary pollution. Chemical methods, such as in-situ passivation remediation and soil leaching remediation, while effective in the short term, often only address the symptoms rather than the root cause, and residual chemical reagents can pose new environmental hazards. Biological methods, particularly phytoremediation, have attracted significant attention due to their environmental friendliness and relatively low cost. However, existing hyperaccumulators, such as Sedum alfredii, suffer from low biomass, long growth cycles, low remediation efficiency, and high overall costs, making them difficult to promote and apply in large-scale contaminated soil remediation.

[0004] Conventional regenerated rice is a new crop of rice formed by re-tillering and regenerating from the rice stumps left after the first crop of rice is harvested. Conventional regenerated rice can increase the frequency of rice harvests, has a short growth cycle, low production costs, and saves labor and effort. It is an economically feasible and environmentally friendly production method. At present, research on regenerated rice food production issues mainly focuses on how to increase yield and economic benefits, such as variety screening, yield-increasing methods, and the combination of planting and breeding. Research on regenerated rice food security issues mainly focuses on the heavy metal transport characteristics of conventional regenerated rice and measures to reduce heavy metal accumulation in regenerated rice. However, researchers have not yet conducted research on the use of regenerated rice for the extraction and remediation of heavy metal contaminated soil.

[0005] Giant rice, with its strong regeneration capacity, has been successfully used in vertical cultivation. In Guangdong, both early and late rice varieties are cultivated. Leveraging the advantages of giant rice's large biomass and the increased Cd concentrations achieved through stem-drop cultivation could potentially enable efficient plant-based Cd extraction, creating an innovative model for remediating contaminated soils. Because giant rice production is more readily accepted and implemented by farmers than hyperaccumulators, it could simultaneously achieve environmental, social, and economic benefits. Summary of the Invention

[0006] To overcome the problems existing in the related art, the purpose of the present invention is to provide a method for remediating Cd-contaminated soil by regenerating and dropping stem cultivation of giant rice. This method selects giant rice with a large biomass and increases the Cd concentration of the giant rice through dropping stem cultivation, thereby overcoming the defect that large-biomass plants generally have low Cd concentrations, achieving efficient and low-cost plant extraction of Cd from farmland soil, thereby achieving low-cost and efficient soil Cd contamination remediation.

[0007] A method for remediating Cd-contaminated soil by cultivating giant rice regeneration and dropping stems, comprising:

[0008] In the first half of the natural year, giant rice was cultivated in the Cd-contaminated paddy fields according to conventional methods;

[0009] After the giant rice matures and is harvested, a 7cm-20cm stubble is left, and then watered and fertilized for regeneration;

[0010] When the rice stubble of giant rice starts tillering again and the tillers and plants begin to joint, drain the rice fields and practice dry cultivation without irrigation.

[0011] The regenerated giant rice is harvested when it is mature, and the rice straw is taken away and not returned to the field.

[0012] In a preferred technical solution of the present invention, when cultivating giant rice, the cultivation is carried out under the moisture conditions of full flooding or moist soil; wherein, the moisture condition of moist soil is that there are no cracks on the rice field surface and the soil surface is in an anaerobic state.

[0013] In a preferred technical solution of the present invention, after the giant rice matures, the height of the rice plant is 160 cm to 220 cm.

[0014] In a preferred technical solution of the present invention, the conventional method of cultivating giant rice comprises:

[0015] Transplant the seedlings to the field, planting about 4,000-6,500 holes per mu and 12,000-19,500 basic seedlings.

[0016] In a preferred technical solution of the present invention, during the cultivation of giant rice, the giant rice is fertilized according to conventional rice cultivation methods.

[0017] In a preferred technical solution of the present invention, the regenerated giant rice is harvested when mature, and the regenerated giant rice is harvested at a low stubble height of less than 5 cm when mature.

[0018] In a preferred technical solution of the present invention, the non-irrigation and drying cultivation method includes:

[0019] The groundwater in the paddy field is 15cm-50cm below the paddy field surface to keep the soil surface in an aerobic state.

[0020] In a preferred technical solution of the present invention, after the giant rice is mature and harvested, a stubble of 7 cm to 20 cm is left, and then watering and fertilizing are applied for regeneration, comprising:

[0021] Before irrigation and fertilization for regeneration, dry the field for 2-5 days, then rewater to a water depth of 2cm-3cm.

[0022] The beneficial effects of the present invention are:

[0023] The present invention provides a method for remediating Cd-contaminated soil by regenerating giant rice and cultivating it dry. The method comprises: cultivating giant rice in a Cd-contaminated paddy field according to conventional methods in the first half of a natural year; after the giant rice is mature and harvested, leaving a stubble of 7-20 cm, followed by irrigation and fertilization for regeneration; draining the paddy field and practicing dry cultivation without irrigation when the giant rice stubble re-tillers and the tillers and plants begin to joint; harvesting the regenerated giant rice when mature, and removing the rice straw without returning it to the field. This method overcomes the generally low Cd concentration of large-biomass plants by selecting giant rice and cultivating it dry, thereby achieving efficient and low-cost plant-based extraction of Cd from farmland soil, thereby achieving low-cost and efficient remediation of Cd contaminated soil. This method is mainly divided into two stages: conventional cultivation of giant rice and dry cultivation without irrigation. In the conventional cultivation stage, flooding is used to ensure safe rice production and compliance with food safety standards. In the dry cultivation stage, dry cultivation is used to efficiently extract Cd, achieving the goal of simultaneous production and restoration, improving land utilization and economic benefits. In addition, by utilizing the large biomass characteristics of giant rice, dry cultivation significantly improves its ability to absorb and accumulate Cd in the soil, overcoming the low Cd concentration of traditional large-biomass plants and achieving efficient and low-cost plant extraction and restoration. Compared with traditional restoration methods, the present invention does not require expensive equipment and chemicals, reducing restoration costs. At the same time, by controlling soil moisture and straw treatment, the risk of environmental pollution is reduced, meeting the requirements of sustainable development, and has broad application prospects and promotion value. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a flow chart of the method for repairing Cd-contaminated soil by giant rice regeneration and stem cultivation provided by the present invention. DETAILED DESCRIPTION

[0025] The preferred embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. Although preferred embodiments of the present invention are shown in the accompanying drawings, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments described herein. Rather, these embodiments are provided to make the present invention more thorough and complete and to fully convey the scope of the present invention to those skilled in the art.

[0026] Example 1

[0027] Reference method for repairing Cd-contaminated soil by giant rice regeneration and stem cultivation Figure 1 The present application claims protection for a method for remediating Cd-contaminated soil by cultivating giant rice regeneration and drop stems, comprising:

[0028] S100: Giant rice was cultivated in Cd-contaminated paddies using conventional methods in the first half of the natural year.

[0029] Specifically, when cultivating giant rice, full flooding or moist soil conditions are adopted for cultivation; wherein, moist soil conditions are that there are no cracks on the rice field surface and the soil surface is in an anaerobic state.

[0030] During the cultivation process of full flooding or moist soil, keep the field surface free of cracks to prevent air from entering, so as to maintain the anaerobic state of the soil surface and reduce the Cd content in the native giant rice.

[0031] After the S200 and giant rice are harvested, a stubble of 7cm-20cm is left, and then irrigation and fertilization are applied for regeneration; more specifically, before irrigation and fertilization, the fields are first dried for 2-5 days, and then rewatered to a water depth of 2cm-3cm. A stubble of 7cm-20cm can retain more tillering nodes close to the surface, which are important parts for the germination of regenerated rice. The stubble height of this application can protect these growing points to the greatest extent possible, avoiding damage during the harvesting process, thereby ensuring the smooth germination of regenerated rice. However, if the stubble is too high, it will cause high-node regeneration, easy lodging and precociousness, and low biomass.

[0032] S300: When the rice stubbles of the giant rice begin to tiller again and after the tillering period, the rice fields are drained and dry cultivation without irrigation is implemented.

[0033] In actual application, when the rice tillers reach about 80% of the expected yield requirement, the field is dried and the water is drained in time to gradually expose the field surface.

[0034] Dry cultivation affects the redox potential and bioavailability of Cd in the soil by changing the moisture conditions of the rice fields. Under dry conditions, Cd in the soil is more easily absorbed by the giant rice roots, thereby improving the giant rice's efficiency in extracting Cd. As the giant rice grows, especially during the dry cultivation stage, the accumulation of Cd in the plant increases, which helps to remove Cd from the soil through subsequent methods such as harvesting rice straw. Dry cultivation helps the growth and development of the giant rice root system, making the root system more developed and able to absorb water and nutrients from the soil more deeply, while also improving its ability to absorb Cd. The developed root system enhances the giant rice's stress resistance, including drought resistance and lodging resistance, allowing it to maintain a good growth state under adverse environmental conditions.

[0035] S400: Regenerated giant rice is harvested when mature, and the rice straw is taken away and not returned to the field.

[0036] Retaining rice straw after harvesting can reduce secondary soil contamination from Cd in the straw. Furthermore, rice straw can be processed as a biomass resource and used as non-agricultural fiber material or biomass fuel.

[0037] The above-mentioned method for regenerating giant rice and cultivating it on the dry land to repair Cd-contaminated soil is to select giant rice with a large biomass and increase the Cd concentration of the giant rice through dry land cultivation, thereby overcoming the generally low Cd concentration of large-biomass plants and achieving efficient and low-cost plant extraction of Cd from farmland soil, thereby achieving low-cost and efficient remediation of Cd-contaminated soil. The method is mainly divided into two stages: conventional cultivation of giant rice and dry land cultivation without irrigation. In the conventional cultivation stage, flooding is adopted to ensure the safe production of rice and meet food safety standards; in the dry land cultivation stage without irrigation, dry land cultivation is used to efficiently extract Cd, achieving the goal of remediation while producing, improving land utilization and economic benefits. In addition, by utilizing the large biomass characteristics of giant rice, dry land cultivation significantly improves its ability to absorb and accumulate Cd in the soil, overcoming the low Cd concentration of traditional large-biomass plants and achieving efficient and low-cost plant extraction and remediation. Compared with traditional remediation methods, the present invention does not require expensive equipment and reagents, reducing remediation costs. At the same time, by controlling soil moisture and straw processing, the risk of environmental pollution is reduced, which meets the requirements of sustainable development and has broad application prospects and promotion value.

[0038] Furthermore, after the giant rice matures, the height of the rice plant is 160 cm to 220 cm.

[0039] Giant rice has a strong regeneration ability and has been successfully used in three-dimensional cultivation and breeding. It has the characteristics of significantly high yield, lodging resistance, disease and pest resistance, and flooding resistance. In southern my country, giant rice can be planted in both early and late rice. This application coordinates the advantages of giant rice's large biomass and dry cultivation to increase Cd concentration, achieves efficient plant extraction of Cd, and forms an innovative remediation model for contaminated soil. Since giant rice production is easier for farmers to accept and implement than hyperaccumulator plants, it can achieve environmental, social, and economic benefits at the same time. Due to its strong tillering ability and large number of grains per ear, the single-season yield of giant rice can exceed 800 kg / mu.

[0040] Furthermore, the cultivation of giant rice according to a conventional method comprises:

[0041] Transplant the seedlings to the field, planting about 4,000-6,500 holes per mu and 12,000-19,500 basic seedlings.

[0042] Furthermore, during the process of cultivating giant rice, fertilizer is applied to the giant rice regularly.

[0043] The regenerated giant rice is harvested when mature, and the regenerated giant rice is harvested at a low stubble height of less than 5 cm. The surface of the rice field after the low stubble harvest is relatively flat, which is convenient for subsequent field management operations. Furthermore, the non-irrigation and drying cultivation includes:

[0044] The groundwater in the paddy field is 15cm-50cm below the paddy field surface to keep the soil surface in an aerobic state.

[0045] In dry cultivation, maintaining groundwater in the paddy field at a depth of 15cm-50cm below the paddy field surface can keep the soil surface in a relatively dry aerobic state, which helps giant rice to better absorb Cd in the soil.

[0046] Example 2

[0047] This example uses experiments to verify the Cd contaminated soil remediation method of the present application, as follows:

[0048] The pH of the contaminated soil used in the experiment was 5.27; organic matter: 33.51 g / kg; total N: 1.68 g / kg; total P: 0.70 g / kg; total K: 15.58 g / kg; and total Cd: 1.186 mg / kg.

[0049] This study was conducted in a ventilated and lighted net room. Before the experiment began, the soil was sieved through a 2 cm sieve and placed in planting pots. Each pot was filled with 2 kg of air-dried soil. The planting pots were then moved into plastic baskets (80 cm × 60 cm × 40 cm) and the soil was saturated with tap water. Giant rice seedlings were cultivated in plastic incubators in advance and transplanted after 4 weeks. The first crop of giant rice was planted under flooded conditions with a 1-2 cm water layer on the soil surface. The planting density was 1 plant / pot, and each plant had 3 seedlings. Harvest when mature, leave about 20 cm of stubble, regenerate, and continue cultivation during the winter idle field period. Three different treatments were set up: (1) flooded cultivation, (2) flooded cultivation + acetic acid, and (3) dry cultivation. The specific experimental settings are shown in Table 1, and each treatment was repeated three times. The above-mentioned flooding means: keeping the water level 1-2 cm above the soil surface; the drying means: growing under moist moisture conditions in the early stage, and draining after the tillering period to make the water level 10-15 cm below the soil surface; the amount of acetic acid added: adding 20 ml of glacial acetic acid to each pot (2 kg of soil).

[0050] Table 1 Design of implementation plan for potted plant experiment

[0051]

[0052] The seeds and stalks of primary and regenerated giant rice were collected separately to measure their biomass and moisture content. After the rice was harvested, the topsoil was collected using a soil sampler and allowed to air dry in a contaminant-free location.

[0053] Plant samples from different parts were killed in an oven at 70°C for 30 min, dried at 55°C to constant weight, ground with a grinder, and passed through a 100-mesh sieve before being placed in sealed plastic bags. The soil was sampled by quartering and the visible root system was picked out, ground with an electric agate mortar, and passed through 20-mesh and 100-mesh sieves before being stored in sealed bags.

[0054] The total Cd in plants and soil was determined by microwave digestion-flame or graphite furnace atomic absorption spectrophotometry (HITACHI, Z-2700 / Z-2300) according to the national standard method (GB5009.15-2014) and the environmental standard method (HJ832-2017), respectively, and the determination results were verified by using the national standard materials (GBW(E)100348a) and (GBW07405a), respectively. The concentration of Cd in the extraction solution was determined by a graphite furnace atomic absorption spectrophotometer. The pH of the soil was determined by a pH meter, and the water-soil ratio was 2.5:1. -1 The available Cd in the soil was extracted by calcium chloride (DB35 / T860-2008), and the concentration of Cd in the extraction solution was determined by a graphite furnace atomic absorption spectrophotometer. The pH of the soil was determined by a pH meter, and the water-soil ratio was 2.5:1.

[0055] The biomass and Cd content of the giant rice under different treatments are shown in Table 2. Compared with the primary rice, the biomass of the winter regenerated giant rice decreased under the blank group (decreased by 39% under the flooding condition). In the regenerated rice, the addition of acetic acid reduced the biomass of the giant rice straw compared with the blank group, and the dry fall condition had no significant effect on the biomass of the giant rice. The Cd content of the grain and straw of the primary giant rice was low under the flooding condition, being 0.030 and 0.274 mg·kg -1 , respectively, and the rice was within the safety standard (≤0.2 mg·kg -1 ). In the regenerated rice, the Cd concentration of the giant rice straw was low under the flooding condition, being 0.362 mg·kg -1 . After the addition of acetic acid, the Cd concentration of the regenerated giant rice straw increased significantly, being 3.86 mg·kg -1 . Under the dry fall condition, the Cd concentration of the regenerated giant rice straw was the highest, being 12.54 mg·kg -1 .

[0056] Table 2 Biomass and Cd content of giant rice under different treatments

[0057]

[0058] Note: T1 is flooding, T2 is flooding + acetic acid, and T3 is dry fall in the second crop of giant rice. The data are represented as mean ± standard deviation (n = 3). Since the primary giant rice under different treatments was completely the same, the Cd content shared a set of data.

[0059] These results indicate that flooding the first-crop giant rice can produce Cd-safe rice. Adding acetic acid to the second-crop ratoon rice straw did not significantly increase Cd concentrations. However, using dry-drying conditions significantly increased Cd concentrations in the straw, facilitating the extraction of soil Cd using ratoon giant rice.

[0060] In terms of the amount of Cd extracted by giant rice (Table 3), the amount of Cd extracted from soil by regenerated giant rice straw under flooding conditions was extremely low, at 0.0123 mg·plant- 1 Adding acetic acid or maintaining dry conditions significantly increased Cd extraction from regenerated giant rice straw, with extractions per plant reaching 0.1099 and 0.4382 mg, respectively. Drying significantly increased the Cd extraction efficiency of regenerated giant rice from soil, reaching 5.36% and 19.20%, respectively, compared to adding acetic acid. This suggests that drying is more effective than adding acetic acid in enhancing Cd extraction from regenerated giant rice. Soil Cd removal efficiencies of T2 and T3, measured in soil, were 11.01% and 18.14%, respectively. These results indicate that drying is superior to adding acetic acid (flooding) in removing Cd from soil.

[0061] Table 3 Cd extraction amount of giant rice and soil Cd removal rate under different treatments

[0062]

[0063] Note: For each treatment of the second giant rice crop, T1 was flooding, T2 was flooding + acetic acid, and T3 was drying. Extraction rate = plant extractable amount / initial soil content; removal rate = soil reduction / initial soil content.

[0064] Example 3

[0065] This example uses three test products, namely Zengcheng silk seedlings, giant rice, and Miscanthus sinensis seed stems, to verify the Cd-contaminated soil remediation method of the present application, as follows:

[0066] The test soil properties are shown in Table 4.

[0067] Table 4 Chemical properties and Cd content of the tested soils

[0068]

[0069] Note: Data are expressed as mean ± standard deviation (n = 3).

[0070] The experiment included four treatments, each replicated three times, with randomized placement. Specifically, as shown in Table 5, T1: Silk seedlings were planted in both the first and second half of the year as a control for conventional rice, with the first half of the year flooded and the second half dry. T2: Giant rice was planted in the first half of the year and replanted in the second half, with the same water management. T3: Giant rice was planted in the first half of the year and replanted in the second half, with the same water management. T4: Giant rice was planted in the first half of the year and King bamboo grass was planted in the second half, with the same water management.

[0071] The soil column (PVC tube) had an inner diameter of 15 cm and a height of 50 cm. From bottom to top, the structure consisted of: quartz sand (5 cm), uncontaminated soil (20 cm), and Cd-contaminated soil (20 cm). Before the experiment began, the soil was sieved through a 2 cm sieve and then placed into the soil column. The soil bulk density was 1.25 g·cm -3 Each layer of soil was 4.5 kg. The soil column was moved into a large plastic water tank (800 L, 150 cm × 120 cm × 60 cm) and saturated with tap water.

[0072] After four weeks of growth in a plastic incubator, rice seedlings are transplanted. Plant one seedling per soil column, yielding three seedlings per column. Cut 5cm-long stalks of Pennisetum stalks for seedling cultivation and transplant them simultaneously with the rice. During the first half of the year, maintain 1-2cm of water throughout the planting process. During the early stages of the second half of the year, maintain 1-2cm of water during the planting period. After the tillering stage, dry the soil (keeping the water level 15-20cm below the soil surface).

[0073] Table 5 Design of soil column test implementation plan

[0074]

[0075] When harvesting Pennisetum, measure its aboveground biomass and moisture content. For primary and regenerated rice, collect the seeds and stalks separately and measure their biomass and moisture content. After planting, collect the topsoil using a soil sampler and air-dry it in a contaminant-free location.

[0076] The results are shown in Table 6. Under the condition of late rice drying, the grain biomass of regenerated giant rice decreased compared with the new rice (early rice and late rice), the straw yield did not change significantly, and the grass with the largest biomass was King bamboo grass.

[0077] Table 6 Biomass and Cd concentration of plants under different treatments

[0078]

[0079]

[0080] Note: Data are presented as mean ± standard deviation (n = 3). Cd concentrations in the second half of the year are weight-weighted averages of two results. Duncan's test was used; different letters in the same row indicate significant differences (P < 0.05).

[0081] Under flooding conditions of early rice, the Cd concentrations in the grains of giant rice and silk seedlings were relatively low, at 0.008 and 0.006 mg·kg, respectively. -1 The rice meets food safety standards. Under the drying conditions of late rice, the Cd concentrations in the grains of giant rice (new or regenerated) and silk seedlings were high, making them unsuitable for food. Under the drying conditions, the Cd concentration in the regenerated giant rice straw was 16.03 mg kg -1 , significantly higher than those in newly grown giant rice, silk seedlings, and Pennisetum. These results suggest that growing the first crop of newly grown giant rice in flooded conditions can produce Cd-safe rice. The Cd concentration in the straw of regenerated giant rice grown on dry land was significantly higher than that in silk seedlings and Pennisetum.

[0082] Table 7 shows that under flooded early rice conditions, giant rice and silk seedling straw extracted very low amounts of soil Cd. Under dry late rice conditions, soil Cd extraction by the different straw treatments increased significantly, with significant differences. Pennisetum and silk seedling straw extracted significantly less Cd than giant rice, at 0.5336 and 0.3521 mg / pot, respectively. For giant rice, ratooning extracted 1.98 times more Cd than native rice, at 1.168 and 0.589 mg / pot, respectively.

[0083] Table 7 Cd extraction amount of plants under different treatments (mg / pot)

[0084]

[0085] Note: Data are expressed as mean ± standard deviation (n = 3). Duncan's test was used. Different letters in the same row indicate significant differences (P < 0.05). Extraction rate = plant extract amount / total soil content.

[0086] The Cd extraction rates for plants during T1, T2, T3, and T4 were 8.55%, 13.08%, 23.17%, and 9.60%, respectively. This indicates that the order of plant Cd extraction efficiency from soil was: regenerated giant rice > giant rice > Pennisetum scabra > silk seedlings. These results indicate that regenerated giant rice plants with fallen stems are more effective in extracting Cd than those planted with newly grown giant rice plants, and significantly outperform Pennisetum scabra, which has a larger biomass. The extraction rate for regenerated giant rice plants reached 23%, which is also higher than most reported results for potted Sedum alfredii, indicating that regenerated giant rice plants have a superior ability to extract Cd from soil.

[0087] The Cd pollution concentration in the experimental surface soil used in this study was 1.186 mg kg -1, which is a moderately Cd-contaminated soil. As shown in Table 8, after remediation, the soil Cd removal efficiencies of T1, T2, T3, and T4 were 14.04%, 20.96%, 30.50%, and 21.66%, respectively. The removal efficiency of T2 for soil Cd was better than that of T1, indicating that the removal efficiency of giant rice for soil Cd was significantly better than that of ordinary rice (silk seedlings). Comparing T2 / T3 / T4, the removal efficiency of plants for soil Cd was: regenerated giant rice > giant rice ≈ king bamboo grass. The results show that under dry conditions, the remediation effect of regenerated giant rice on soil Cd was significantly better than that of new giant rice and king bamboo grass. Therefore, the dry growth of regenerated giant rice has a good removal effect on soil Cd.

[0088] Table 8 Effects of different plant treatments on soil Cd and its removal rate (mg·kg -1 )

[0089]

[0090] Note: Data are presented as mean ± standard deviation (n = 3). The first half of T2, T3, and T4 were identical and shared a single set of data. Removal rate = soil reduction / initial soil content.

[0091] Ratoon rice requires no plowing, sowing, or transplanting. It is less susceptible to pests and diseases, and generally does not require pesticides. A topdressing of fertilizer is sufficient, 7-10 days before the first harvest and 2-3 days after. Therefore, the production cost of ratooning giant rice is low, labor-saving, and an economically viable restoration method.

[0092] In summary, this application innovatively proposes a safe utilization and phytoremediation model for giant rice, utilizing "submerged primary rice cultivation followed by dry-cultivation of regenerated rice," to achieve the goals of "safe rice production in the first stage and efficient Cd extraction in the second stage." This method enables cost-effective and efficient extraction and remediation of Cd in soils, enabling simultaneous production and remediation. This provides new insights and approaches for the remediation of Cd-contaminated soils and holds significant potential for widespread adoption.

[0093] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A method for remediating Cd-contaminated soil by cultivating giant rice regeneration stems, characterized in that: include: In the first half of a natural year, giant rice was cultivated in a paddy field contaminated with Cd according to conventional methods; after the giant rice matured, the height of the rice plant was 160 cm to 220 cm; After the giant rice is harvested, a stubble of 7cm-20cm is left, and then watering and fertilizing are carried out for regeneration. Before watering and fertilizing for regeneration, the field is first dried for 2-5 days, and then re-watered to a water depth of 2cm-3cm; When giant rice starts tillering again and after the tillering period, drain the paddy field and practice dry cultivation without irrigation; The regenerated giant rice is harvested when it is mature, and the rice straw is taken away and not returned to the field; the regenerated giant rice is harvested when it is mature, and the regenerated giant rice is harvested at a low stubble height of less than 5 cm.

2. The method for remediating Cd-contaminated soil by giant rice regeneration and stem cultivation according to claim 1, characterized in that: When cultivating giant rice, full flooding or moist soil conditions are used for cultivation; among them, moist soil conditions are that there are no cracks on the rice field surface and the soil surface is in an anaerobic state.

3. The method for remediating Cd-contaminated soil by giant rice regeneration and stem cultivation according to claim 1, characterized in that: The method of cultivating giant rice according to a conventional method comprises: Transplant the seedlings to the field, planting 4,000-6,500 holes per mu and 12,000-19,500 basic seedlings.

4. The method for remediating Cd-contaminated soil by giant rice regeneration and stem cultivation according to claim 1, characterized in that: The non-irrigation and drying cultivation method comprises: The groundwater in the paddy field is 15cm-50cm below the paddy field surface to keep the soil surface in an aerobic state.

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