Efficient reduction repair method for cadmium pollution of rice field soil

Abstract

The invention provides an efficient reduction remediation method for cadmium pollution of rice field soil, and relates to the technical field of soil remediation. The efficient decrement remediation method for rice field soil cadmium pollution comprises the steps that high-cadmium-absorption-accumulation rice is planted in a target rice field; after the cadmium high-absorption accumulation rice turns green in the seedling stage, a deep water management process is conducted on the target rice field till the cadmium high-absorption accumulation rice is mature; the deep water management process comprises the step of repeatedly and periodically carrying out dry-wet alternate treatment and field drying on the target rice field; and harvesting the rice with high cadmium absorption and accumulation and separating from the field. According to the remediation method, on the premise that the structure and attributes of the rice field are not changed, according to the water requirement rule of the rice growth cycle, deep water fine management (water management cycle, frequency, strength and parameter control) is adopted, soil cadmium is activated, rice high absorption and accumulation of cadmium are enhanced, and efficient decrement remediation of soil cadmium pollution of the rice field is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of soil remediation, and in particular to a method for efficiently reducing and remediating cadmium pollution in paddy field soil. Background Art

[0002] Heavy metal pollution in soil is one of the environmental problems that need to be solved urgently worldwide. Especially in my country, heavy metal pollution in cultivated land is widespread, seriously affecting the sustainable development of agricultural production and ecological environment. As a typical type of heavy metal pollution, the restoration and management of soil cadmium pollution is of great significance to ensuring food security and ecological environment. Cadmium is a toxic heavy metal element with strong biological toxicity. It can enter the human body through the food chain and cause serious harm to human health. Therefore, the research on soil cadmium pollution remediation technology is of great practical significance for reducing the impact of cadmium pollution on agricultural production and ecological environment.

[0003] In the past 20 years, the technology for the safe utilization of cadmium-contaminated rice fields has made significant progress. In particular, in recent years, the cultivation and promotion of low-cadmium rice varieties have provided an effective solution for the safe production of rice in lightly and moderately cadmium-contaminated rice fields. However, for moderately and severely cadmium-contaminated rice fields, existing technologies still make it difficult for agricultural products to meet standards, and the cadmium in the soil has not been effectively repaired. This not only limits the sustainable use of these lands, but also poses risks for the cultivation of other crops and the migration of cadmium pollution. In addition, the development of paddy field soil cadmium reduction technology is relatively lagging, and it is difficult to meet the current urgent need for soil cadmium pollution remediation.

[0004] At present, phytoremediation technology is one of the commonly used methods for soil cadmium pollution remediation, which mainly absorbs and removes cadmium in the soil by planting cadmium hyperaccumulator plants. However, this method has poor applicability in most cadmium and arsenic contaminated rice fields in my country, and it is difficult to meet the needs of actual remediation and management. As one of the main food crops in my country, rice has a strong ability to absorb and accumulate cadmium. In addition, the special water management methods of rice fields, such as flooding and drying, will significantly affect the biological effectiveness of cadmium. Therefore, how to effectively utilize the characteristics of rice without changing the properties and structure of the rice field, combined with the key technologies to enhance rice's absorption and accumulation of cadmium, has become an important challenge facing the remediation and management of cadmium-contaminated rice fields.

[0005] In summary, the existing soil cadmium pollution remediation technology has many shortcomings when dealing with moderately and severely cadmium-contaminated rice fields. Although low-cadmium rice varieties can alleviate the agricultural product safety issues of lightly and moderately polluted rice fields to a certain extent, their effects on soil cadmium remediation are limited, and it is difficult to adapt to the remediation needs of moderately and severely polluted rice fields. Phytoremediation technology has limitations in applicability and is difficult to be widely used in most cadmium and arsenic-contaminated rice fields in my country. In addition, the development of paddy field soil cadmium reduction technology is lagging behind, and it is difficult to meet the current urgent needs for soil cadmium pollution remediation. The existence of these problems has brought many challenges to the research and application of soil cadmium pollution remediation technology, and it is urgent to develop more efficient and applicable remediation technologies to achieve effective control of soil cadmium pollution and sustainable land use.

[0006] In view of this, the present invention is proposed. Summary of the invention

[0007] The purpose of the present invention is to provide a highly efficient reduction and restoration method for cadmium pollution in paddy field soil. The restoration method can achieve the activation of soil cadmium and the enhancement of rice's high absorption and accumulation of cadmium, thereby achieving highly efficient reduction and restoration of soil cadmium pollution in paddy fields without changing the structure and properties of the paddy fields, according to the water demand law of the rice growth cycle, and adopting deep water fine management (water management cycle, water management frequency, irrigation depth).

[0008] In order to achieve the above-mentioned purpose of the present invention, the following technical solutions are particularly adopted:

[0009] In a first aspect, the present invention provides a method for efficiently reducing and repairing cadmium pollution in paddy soil, comprising:

[0010] For the target rice fields, plant rice with high cadmium absorption and accumulation;

[0011] After the cadmium high absorption and accumulation rice turns green at the seedling stage, the target rice field is subjected to a deep water management process until the cadmium high absorption and accumulation rice matures; wherein the deep water management process is to repeatedly perform periodic dry-wet alternating treatment and field sunning on the target rice field;

[0012] The rice with high cadmium absorption and accumulation is harvested and removed from the field.

[0013] In an optional embodiment, the deep moisture management process includes:

[0014] After the cadmium-high absorbing and accumulating rice in the target paddy field turns green, the wet-dry alternating treatment is repeatedly performed for multiple cycles until the middle of the grain filling period;

[0015] Drainage, drying and sunning of fields should be carried out from the middle filling stage to the maturity stage;

[0016] In an optional embodiment, the duration of a single cycle of the dry-wet alternating treatment is 3 to 5 days;

[0017] In an optional embodiment, the frequency of the dry-wet alternating treatment cycle is 15 to 45 times;

[0018] In an optional embodiment, during the dry-wet alternating treatment cycle, the soil Eh is controlled at 65mV to 350mV;

[0019] In an optional embodiment, the soil Eh during the drainage, drying and sun-drying treatment is controlled at 250mV to 400mV.

[0020] In an optional embodiment, a single cycle of the wet-dry alternating treatment includes:

[0021] When the soil is moist, it is allowed to dry naturally until the soil cracks and the rice leaves do not curl or wrinkle.

[0022] Water until the soil surface is moist or covered with water to a depth of 0 to 0.5 cm for 4 to 8 hours.

[0023] In an optional embodiment, the soil water content when cracks appear in the soil and the rice leaves do not show slight curling and wrinkles is 25% to 35%.

[0024] In an optional embodiment, when the soil surface is moistened or the soil surface is covered with 0 cm to 0.5 cm of water, the soil moisture content is controlled at 40% to 45%.

[0025] In an optional embodiment, when cracks appear in the soil, the crack size is 0.1 cm to 2 cm.

[0026] In an optional embodiment, when there is no rainfall, the dry-wet alternating treatment is directly performed;

[0027] When it rains, the target rice field is first drained until the soil cracks, and then the dry-wet alternating treatment is started.

[0028] In an optional embodiment, the step of harvesting the rice with high cadmium absorption and accumulation and removing it from the field comprises:

[0029] The above-ground part of the rice with high cadmium absorption and accumulation is harvested close to the ground and removed from the field; wherein the stubble height is controlled at 0 cm to 1 cm.

[0030] In an optional embodiment, the rice with high cadmium absorption and accumulation includes at least one of Yangdao No. 6, Yuzhenxiang and Pokkali.

[0031] In an optional embodiment, the soil of the target paddy field is at least moderately polluted or severely polluted; wherein the moderate pollution refers to the total cadmium content of the soil being C 镉 Meets: 3 times the soil cadmium pollution risk screening value < C 镉 ≤5 times the soil cadmium pollution risk screening value; severe pollution refers to the total cadmium content of the soil meeting the following requirements: C 镉 >5 times the risk screening value for soil cadmium pollution;

[0032] After the cadmium high absorption and accumulation rice is harvested and removed from the field, the method further comprises:

[0033] Obtaining the total cadmium content of the soil of the target paddy field;

[0034] If the total cadmium content is not higher than the soil cadmium pollution risk screening value, it is determined that the restoration of the target rice field is completed;

[0035] If the total cadmium content is not higher than the soil cadmium pollution risk screening value, it is determined that the restoration of the target rice field is incomplete, and the process returns to the step of planting rice with high cadmium absorption and accumulation in the target rice field.

[0036] Compared with the prior art, the present invention has the following beneficial effects:

[0037] (1) By planting rice with high cadmium absorption and accumulation, the bioaccumulation of plants can be effectively utilized to transfer cadmium from the soil into the plant body, thereby achieving cadmium removal. Rice with high cadmium absorption and accumulation has a strong cadmium absorption capacity and can enrich cadmium in the soil into the aboveground part of the plant, especially in the rice straw. When harvesting rice, removing the rice straw from the rice with high cadmium absorption and accumulation from the field can remove a large amount of cadmium from the soil, reduce the cadmium content in the soil, and achieve the purpose of reducing and repairing soil cadmium pollution.

[0038] (2) This method can repair soil cadmium pollution without changing the structure and properties of rice fields. Traditional soil remediation methods, such as chemical remediation and physical remediation, may have adverse effects on the soil structure and fertility of rice fields, and even require changes in the planting properties of rice fields, such as planting non-food crops. However, this method can repair cadmium-contaminated rice fields by planting rice with high cadmium absorption and accumulation, and combine it with deep water management. After the soil is repaired, rice can still be planted and harvested normally. It will not affect the planting properties of rice fields and farmers' planting habits. It has high practicality, operability and low cost.

[0039] (3) The operation process of this method is relatively simple, mainly involving the planting of high cadmium absorption and accumulation rice and deep water management. Deep water management mainly involves periodic alternating dry and wet treatments and sun drying of rice fields. These operations are common water management measures in the rice planting process, do not require complex equipment and technology, and farmers can master and implement them relatively easily.

[0040] (4) This method is an environmentally friendly soil cadmium pollution remediation technology. Planting rice with high cadmium absorption and accumulation and deep water management both use natural ecological processes to achieve cadmium removal and will not cause secondary pollution to the environment. Compared with chemical remediation and other methods, it does not introduce new chemicals and will not pollute the soil, water and other environments, meeting the requirements of sustainable development. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0042] Figure 1 This is a schematic flow chart of a highly efficient reduction and restoration method for cadmium pollution in paddy field soil in an embodiment of the present application;

[0043] Figure 2 This is a bar graph of soil DGT-Cd content under different water management methods in Example 1 of the present application;

[0044] Figure 3 This is a bar graph of Cd content in various parts of rice under different water management methods in Example 1 of the present application;

[0045] Figure 4 This is a bubble chart of the Cd accumulation in various parts of rice under different water management methods in Example 1 of the present application;

[0046] Figure 5 This is a bar graph showing the effects of different water management methods on cadmium accumulation of rice (Huang Huazhan) in field 1 in Example 2 of the present application;

[0047] Figure 6 This is a bar graph showing the effects of different water management methods on cadmium accumulation of rice (9311) in field 2 in Example 2 of the present application;

[0048] Figure 7 This is a bar graph showing the effects of different water management methods on cadmium accumulation in rice (Pokkali) in Plot 3 in Example 2 of the present application. DETAILED DESCRIPTION

[0049] The embodiments of the present invention will be described in detail below in conjunction with the examples, but it will be appreciated by those skilled in the art that the following examples are only used to illustrate the present invention and should not be considered as limiting the scope of the present invention. If no specific conditions are specified in the examples, the conditions are carried out according to normal conditions or the conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be obtained commercially.

[0050] refer to Figure 1 In the embodiment of the present application, a high-efficiency reduction and restoration method for cadmium pollution in paddy soil is provided, comprising:

[0051] Step S1, planting rice with high cadmium absorption and accumulation in the target rice field.

[0052] The target rice fields mentioned above may refer to rice fields that need to be remediated for cadmium pollution. These rice fields may have excessive cadmium content in the soil due to long-term industrial discharge, sewage irrigation, improper use of fertilizers and pesticides, etc., posing a threat to rice growth and agricultural product safety. Therefore, it is necessary to remediate cadmium pollution in these target rice fields to reduce the cadmium content in the soil and ensure the normal growth of rice and the safety of agricultural products.

[0053] The above-mentioned "Cadmium High Absorption and Accumulation Rice" refers to rice varieties or materials with strong cadmium absorption and accumulation capabilities. These rice varieties can absorb cadmium from the soil through their root systems during growth and enrich it in the aboveground parts of the plant, especially the rice straw. At harvest, by removing these cadmium-rich rice straws, the cadmium in the soil can be effectively removed, thereby achieving the purpose of repairing soil cadmium pollution. The selection and utilization of cadmium high absorption and accumulation rice is one of the keys to this remediation method, which can significantly improve the removal efficiency of soil cadmium.

[0054] The above-mentioned planting method for rice with high cadmium absorption and accumulation can adopt conventional fertilizer types and amounts according to the actual conditions of the target rice fields.

[0055] In this step, rice varieties with strong cadmium absorption and accumulation capabilities are planted in the target rice fields. Specifically, suitable rice varieties with high cadmium absorption and accumulation can be selected for sowing and planting, so that rice plants that can effectively absorb and accumulate cadmium grow in the rice fields.

[0056] Specifically, you can choose the appropriate planting time and method based on the local climate, soil conditions and the characteristics of the rice variety, and carry out conventional rice planting management measures such as sowing, fertilizing, and irrigation.

[0057] Step S2, after the cadmium high absorption and accumulation rice turns green in the seedling stage, the target rice field is subjected to a deep water management process until the cadmium high absorption and accumulation rice matures; wherein the deep water management process is to repeatedly perform periodic dry-wet alternating treatment and field sunning on the target rice field.

[0058] In this step, after the rice seedlings with high cadmium absorption and accumulation turn green, the rice fields are deeply water managed until the rice matures, including periodic alternating dry-wet treatment and field sunning of the target rice fields.

[0059] (1) Alternating dry-wet treatment: Alternating dry-wet treatment is implemented from the time when rice seedlings return to green to the late stage of heading and filling.

[0060] (2) Drying the fields: After the rice has begun to head and fill with grain, the fields are dried and sun-dried.

[0061] Through deep water management, the changes in soil cadmium forms are promoted and soil cadmium is activated, making it easier for rice to absorb and accumulate. Alternating wet and dry seasons and sunning the fields can change the redox conditions of the soil, changing the form of cadmium from insoluble to soluble, increasing the bioavailability of cadmium, and thus increasing the amount of cadmium absorbed by rice. Through repeated alternation of wet and dry seasons and sunning the fields, rice can absorb and accumulate more cadmium at different growth stages, improving the removal efficiency of cadmium.

[0062] Specifically, reasonable dry-wet alternation cycles and frequencies should be formulated according to the growth stage of rice and the moisture content of the soil. Also, after the rice has headed and filled with grain, the moisture in the rice field should be drained in time according to the drainage conditions of the soil and the growth needs of rice, so that the soil is kept dry until the rice matures.

[0063] Step S3, harvesting the rice with high cadmium absorption and accumulation and removing it from the field.

[0064] In this step, after the cadmium high absorption and accumulation rice matures, it is harvested and the harvested rice is removed from the field, that is, the mature cadmium high absorption and accumulation rice is harvested and the aboveground plant tissues such as rice straw are removed from the field. By removing the cadmium-rich rice straw, the cadmium in the soil is effectively removed, and the cadmium content in the soil is reduced.

[0065] The cadmium is transferred from the soil to the plant body and removed by removing the plant tissue, thus achieving the purpose of repairing the soil cadmium pollution. Since cadmium is mainly accumulated in rice straw and the cadmium content in rice is relatively low, it will not affect the safety of rice.

[0066] In summary, the paddy soil cadmium pollution repair method in the present embodiment, by planting cadmium high absorption accumulation rice, can effectively utilize the bioaccumulation of plants, transfer cadmium in the soil to the plant body, so as to achieve the removal of cadmium. Cadmium high absorption accumulation rice has a strong cadmium absorption capacity, can enrich cadmium in the soil to the aboveground part of the plant, especially in straw, when harvesting rice, the straw of cadmium high absorption accumulation rice is removed from the field, a large amount of cadmium can be removed from the soil, reduce the cadmium content in the soil, and achieve the purpose of repairing soil cadmium pollution. Secondly, the method repairs soil cadmium pollution without changing the structure and properties of the paddy field, and can still carry out normal planting and harvesting of rice, will not affect the planting properties of the paddy field and the planting habits of farmers, and has high practicality and operability. In addition, the operation process of the method is relatively simple, mainly involving planting cadmium high absorption accumulation rice and deep water management, does not require complex equipment and technology, farmers can be relatively easy to grasp and implement, and the cost is low, with good economy, can reduce the cost of soil cadmium pollution repair, improve the feasibility of repair. Finally, this method is an environmentally friendly soil cadmium pollution remediation technology that uses natural ecological processes to achieve cadmium removal without causing secondary pollution to the environment, meeting the requirements of sustainable development.

[0067] In summary, by adopting the paddy field soil cadmium pollution remediation method of this embodiment, by planting high-accumulation rice and using deep and fine water management methods to strengthen the high absorption and accumulation of rice cadmium, the rice cadmium accumulation is increased by more than 200%, the soil cadmium reduction and remediation efficiency is increased by more than 120%, and the soil remediation time is shortened by more than half, greatly improving the soil remediation efficiency.

[0068] Furthermore, in step S2, the deep moisture management process includes:

[0069] Step S21, after the cadmium high absorption and accumulation rice in the target paddy field turns green, to the middle of grain filling, repeatedly performing multiple cycles of alternating dry and wet treatments.

[0070] Step S22, draining, drying and sunning the field from the middle filling stage to the maturity stage.

[0071] As mentioned above, rice regreening refers to the process in which rice plants begin to resume growth, leaves turn from yellow to green, and plants gradually regain vitality after a period of adaptation and recovery after transplanting or transplanting. At this stage, the rice roots begin to take root in the soil and absorb nutrients and water. The growth rate of the plant gradually accelerates, the color of the leaves changes from yellow-green to bright green, and the plant as a whole presents a healthy growth state.

[0072] Greening is a critical stage in rice growth, marking the transition of rice from the adaptation period after transplanting or transplanting to the normal growth stage, laying the foundation for subsequent growth and development. Management during the greening period has an important impact on the growth and development of rice and the formation of yield.

[0073] As mentioned above, grain filling refers to the process in which the ovary begins to develop after rice flowers and pollinates, the endosperm gradually accumulates nutrients such as starch, and the rice grains gradually become full. At this stage, the vegetative growth of rice gradually weakens, and reproductive growth becomes dominant. The plant transports a large amount of nutrients and water to the ovary, the endosperm cells rapidly divide and expand, and nutrients such as starch gradually accumulate. The rice grains gradually change from small to large, the texture changes from soft to hard, and the color changes from light to dark.

[0074] Grain filling is a critical period for rice yield formation, which determines the grain weight and quality of rice. Management during the grain filling period is of great significance to improving rice yield and quality.

[0075] The mid-grain filling phase refers to the middle stage of the rice grain filling process, usually a period of time after the beginning of grain filling. During this phase, the rice grains fill up quickly, the starch and other nutrients in the endosperm accumulate rapidly, and the rice grains gradually become full. At this time, the volume and weight of the rice grains increase significantly, but have not yet reached their maximum value.

[0076] The mid-grain filling period is a critical stage in the rice filling process. The filling speed of rice and the accumulation of nutrients have an important impact on the final yield and quality. Reasonable management measures can promote the rapid filling of rice and the accumulation of nutrients, thereby improving the yield and quality of rice.

[0077] The maturity stage refers to the process when the rice grain filling is completed, the rice grains are fully mature, and the plants enter the harvest preparation stage. At this stage, the rice grain filling has been completed, the starch and other nutrients in the endosperm are fully accumulated, the volume and weight of the rice grains reach the maximum, the texture changes from soft to hard, the color changes from dark to yellow, the plant's vegetative growth basically stops, and the reproductive growth is also coming to an end. At this time, the rice leaves gradually turn yellow, the growth rate of the plant slows down, and preparations for harvesting begin. The maturity stage is the final stage of rice growth, marking the end of the growth and development process of rice and the time for harvesting is coming. Reasonable judgment of the maturity stage and timely harvesting are of great significance to ensuring the yield and quality of rice.

[0078] Draining and drying the rice fields refers to draining the water from the rice fields in the later stages of rice growth to dry the soil in order to promote rice maturity and harvesting. In this process, the water in the rice fields is gradually drained, the water content of the soil decreases, the soil surface becomes dry, and the water management of the rice fields changes from a wet state to a dry state. At this time, the growth rate of the rice slows down, the water metabolism and nutrient metabolism of the plants also weaken accordingly, and the maturity of the rice grains gradually increases.

[0079] Draining and drying the fields can promote the maturity and harvest of rice, reduce the moisture content of rice, and improve the quality and storage of rice. At the same time, it can also reduce the occurrence of pests and diseases in rice fields, reduce the risk of rice lodging, and create good conditions for rice harvesting and post-processing.

[0080] In step S21, it is necessary to repeat a plurality of cycles of wet-dry alternating treatment of water within a certain period.

[0081] The period is from the time when the rice with high cadmium absorption and accumulation in the target rice field turns green to the middle of grain filling period.

[0082] In this embodiment, it is necessary to repeat the dry-wet alternating treatment several times within the above period to execute step S22 again, that is, when the middle filling stage is reached, drainage, drying and sunning of the field are carried out from the middle filling stage to the mature stage.

[0083] Furthermore, the duration of a single cycle of the dry-wet alternating treatment is 3 to 5 days; for example, the duration of a single cycle may be 3 days, 4 days, or 5 days.

[0084] Furthermore, the frequency of the dry-wet alternating treatment cycle is 15 to 45 times. For example, the frequency of the cycle can be 15 times, 20 times, 25 times, 30 times, 35 times, 40 times, 45 times, etc.

[0085] For example, firstly, 25 times, i.e. 25 cycles of alternating wet and dry conditions are carried out, and then, when the crops reach the middle grain filling stage, drainage, drying and sunning of the fields are carried out from the middle grain filling stage to the maturity stage.

[0086] Furthermore, during the cycle of the dry-wet alternating treatment, the soil Eh is controlled at 65mV to 350mV; for example, the soil Eh can be controlled at 65mV, 80mV, 100mV, 150mV, 200mV, 250mV, 300mV, 350mV, and the like.

[0087] The soil Eh during the drainage, drying and sunning process is controlled at 250mV to 400mV. For example, the soil Eh can be controlled at 250mV, 300mV, 350mV, 400mV and the like.

[0088] Furthermore, in step S21, the dry-wet alternating treatment in a single cycle includes:

[0089] Step S211, when the soil is moist, allowing it to dry naturally until the soil cracks and the rice leaves do not curl or wrinkle.

[0090] In this step, when the soil in the target rice field is moist, stop irrigation and let the soil dry naturally until cracks appear on the soil surface, but the rice leaves have not yet shown micro-curling and wrinkling. It is necessary to stop irrigation and allow the rice field to drain and evaporate naturally, so that the soil moisture gradually decreases, the soil surface gradually dries, and cracks are formed. At the same time, observe the state of the rice leaves to ensure that the leaves do not show micro-curling and wrinkling.

[0091] The moisture content of the soil decreased and cracks appeared on the soil surface, but the rice plants remained healthy and the leaves showed no obvious symptoms of water shortage.

[0092] In this step, during the soil drying process, the soil redox conditions change, and the form of cadmium may change from insoluble to soluble, increasing the bioavailability of cadmium and facilitating the absorption of cadmium by rice. By controlling the degree of drying, the rice leaves are prevented from curling and wrinkling, ensuring the normal growth and physiological activities of rice, and creating conditions for the subsequent absorption and accumulation of cadmium.

[0093] Specifically, when the soil is moist, stop irrigation and allow the paddy field to drain and evaporate naturally. Regularly check the state of the soil surface and the condition of the rice leaves to ensure that the soil is cracked and the leaves are not slightly curled. You can judge whether the requirements are met by observing the dryness of the soil surface and the shape of the rice leaves.

[0094] Step S212, watering until the soil surface is moist, or the soil surface is covered with water to a depth of 0 cm to 0.5 cm, and maintaining this state for 4 to 8 hours.

[0095] As mentioned above, after the soil naturally dries up to the point of cracking, irrigation is performed to moisten the soil surface or to cover it with a water layer of 0 cm to 0.5 cm, and this state is maintained for 4 to 8 hours. Irrigation can be performed to introduce water into the paddy field to moisten the soil surface or to form a water layer of 0 cm to 0.5 cm. This state is maintained for a period of time, usually 4 to 8 hours.

[0096] The moisture content in the soil surface increases, and the soil is moist or covered with shallow water, providing suitable moisture conditions for rice growth and cadmium absorption.

[0097] A moist soil environment is conducive to the growth of rice roots and the absorption of cadmium. Moisture in the soil surface can promote the dissolution and migration of cadmium, making it easier for rice roots to absorb it. By controlling the irrigation time and water volume, maintaining the appropriate moisture state of the soil and avoiding excessive moisture or dryness, good conditions are created for the growth of rice and the repair of cadmium.

[0098] Specifically, after the soil dries up naturally, irrigation is carried out to introduce water into the paddy field so that the soil surface reaches a moist state or forms a water layer of 0 cm to 0.5 cm. This can be done through an irrigation system or artificial irrigation. After irrigation, this state is maintained for 4 to 8 hours, and the irrigation time and maintenance time can be controlled by timed irrigation or artificial observation.

[0099] As mentioned above, the state of water covering the soil surface can be, for example, 0 cm, 0.2 cm, 0.4 cm, 0.5 cm, etc.

[0100] As mentioned above, the holding time may be, for example, 4 hours, 6 hours, 8 hours, etc.

[0101] Furthermore, the soil water content when the soil cracks and the rice leaves do not have slight curling and wrinkles is 25% to 35%. For example, the soil water content can be 25%, 30%, 35%, and so on.

[0102] Furthermore, when the soil surface is moist or the soil surface is covered with 0 cm to 0.5 cm of water, the soil moisture content is controlled at 40% to 45%. For example, the soil moisture content can be 40%, 42%, 44%, 45%, etc.

[0103] Furthermore, when cracks appear in the soil, the size of the cracks is 0.1 cm to 2 cm, for example, 0.1 cm, 0.5 cm, 0.8 cm, 1 cm, 1.5 cm, 2 cm, etc.

[0104] Furthermore, there are two different treatments for whether there is rainfall:

[0105] (1) When there is no rainfall, the dry-wet alternating treatment is directly carried out.

[0106] Under the condition of no rainfall, irrigation and drainage are carried out according to the predetermined dry-wet alternation cycle and frequency to make the soil alternate between wet and dry. The soil can be alternately wet and dry by artificially controlling irrigation and drainage, which can promote the activation of cadmium and the absorption of cadmium by rice.

[0107] (2) When it rains, the target rice field is first drained until the soil cracks, and then the dry-wet alternating treatment is started.

[0108] In the case of rainfall, the target rice fields are first drained until the soil cracks, and then the dry-wet alternation treatment is carried out. After the rainfall, the accumulated water in the rice fields is drained using drainage facilities, and the soil is gradually dried until cracks appear on the soil surface. Then, irrigation and drainage are carried out according to the cycle and frequency of the dry-wet alternation. Through drainage and dry-wet alternation treatment, the impact of rainfall on the soil moisture state is eliminated, the soil is restored to a suitable dry-wet alternation state, and the activation of cadmium and the absorption of cadmium by rice are promoted.

[0109] It should be noted that rainfall will change the moisture state of the soil. Drainage can eliminate the impact of rainfall and ensure that the soil is alternately wet and dry at a predetermined cycle and frequency. Alternating wet and dry treatment after the soil cracks is beneficial to the activation of cadmium and the absorption of cadmium by rice, thus improving the restoration effect of soil cadmium pollution.

[0110] Furthermore, the step of harvesting the rice with high cadmium absorption and accumulation and removing it from the field comprises:

[0111] The aboveground part of the rice with high cadmium absorption and accumulation is harvested close to the ground and removed from the field, wherein the stubble height is controlled at 0 cm to 1 cm. For example, the stubble height can be 0 cm, 0.2 cm, 0.4 cm, 0.8 cm, 1 cm, etc.

[0112] Furthermore, the rice with high cadmium absorption and accumulation includes at least one of Yangdao No. 6, Yuzhenxiang and Pokkali.

[0113] Furthermore, the soil of the target paddy field is at least moderately polluted or severely polluted; wherein the moderate pollution refers to the total cadmium content of the soil C 镉 Meets: 3 times the soil cadmium pollution risk screening value < C 镉 ≤5 times the soil cadmium pollution risk screening value; severe pollution refers to the total cadmium content of the soil meeting the following requirements: C 镉 >5 times the soil cadmium pollution risk screening value. Further, the step S3, after harvesting the cadmium high absorption and accumulation rice and leaving the field, also includes:

[0114] Step S4-1, detecting the total cadmium content of the soil of the target rice field and determining whether the total cadmium content of the soil of the target rice field is not higher than the soil cadmium pollution risk screening value.

[0115] Step S4-2: If the total cadmium content is not higher than the soil cadmium pollution risk screening value, i.e., C 镉 ≤ soil cadmium pollution risk screening value, the restoration of the target rice field is determined to be completed.

[0116] Step S4-3, if the total cadmium content is higher than the soil cadmium pollution risk screening value, that is, C 镉>soil cadmium pollution risk screening value, it is determined that the restoration of the target rice field is not completed, and the process returns to the step of planting rice with high cadmium absorption and accumulation in the target rice field.

[0117] Among them, the soil cadmium pollution risk screening value refers to the definition of the pollutant cadmium project in the agricultural land soil pollution risk screening value in the standard GB15618-2018. Specifically include:

[0118] Table 1. Screening values ​​for soil pollution risk in agricultural land in GB15618-2018

[0119] project pH≤5.5 5.5<pH≤6.5 6.5<pH≤7.5 pH>7.5 paddy field 0.3 0.4 0.6 0.8

[0120] If the soil remediation of the target rice field is not completed, return and repeat the steps of planting high cadmium absorption and accumulation rice to carry out a new round of remediation. Replant high cadmium absorption and accumulation rice, wait for it to turn green in the seedling stage, and then carry out the deep water management process again until it matures, harvests and leaves the field, and recalculates the remediation efficiency until the remediation completion standard is reached. Through repeated remediation, the cadmium content in the soil is gradually reduced, and finally the remediation completion standard is reached.

[0121] Through repeated remediation, the cadmium content in the soil can be continuously reduced until the remediation target is reached, ensuring that soil cadmium pollution is effectively controlled. The remediation strategies and measures can be flexibly adjusted according to the results of the remediation efficiency and the actual situation of soil cadmium pollution to improve the success rate and efficiency of remediation.

[0122] The present invention is further described below by means of specific examples, but it should be understood that these examples are only used for more detailed description and should not be construed as limiting the present invention in any form.

[0123] Example 1

[0124] Experimental methods:

[0125] 1. Target paddy field: Select typical cadmium-contaminated paddy field soil as the test soil (target paddy field), the soil cadmium content is about 1.70 mg / kg, take 5 kg of soil and put it into a polyethylene barrel, and keep the water content of 60% outdoors for 1 month.

[0126] 2. Rice and planting: The rice variety selected was 9311. Three rice seedlings with similar growth were retained in each pot of direct seeding as test seedlings. 2.3 g of basal fertilizer was applied to each pot, and 1.0 g of topdressing was applied to each pot during the tillering period (compound fertilizer N:P2O5:K2O=25:10:16).

[0127] 3. Water management methods and grouping: alternate dry-wet irrigation, flooding irrigation, and moist irrigation. The treatments for enhancing rice Cd absorption and accumulation are shown in Table 1, and three parallel groups were set for each treatment.

[0128] Soil, plant and soil pore water samples were collected at the tillering stage, booting stage, filling stage and maturity stage. The effective state of soil Cd was extracted using a DGT device. Soil pore water was collected using a soil pore water sampler, and the Cd concentration of the samples was determined using ICP-OES. The roots of the rice samples were cleaned, dried to constant weight, and then manually disassembled into roots, stems, leaves and ears. The rice samples were wet digested on a graphite digester using a mixed acid (HClO4:HNO3=1:4). Three quality control samples and three blank samples were set as controls for each batch of digestion. Among them, the standard substance was green onion (GBW10049GSB-27), and the final recovery rate was 97% to 102%. The Cd concentration of the samples was determined using ICP-OES and the cumulative amount of each part was calculated.

[0129] 4. Specific measures for water management:

[0130] (1) Conventional water management group (conventional): The fields were dried and exposed to the sun during the peak tillering period and rice maturity period, and flooded at other times.

[0131] (2) Alternating dry and wet (alternating 1): After the seedling stage, the soil is allowed to dry naturally until cracks appear on the soil, then water is added until the soil moisture content reaches 40% to 45%, and this cycle is repeated until maturity.

[0132] (3) Alternating wet and dry once and then draining group (alternating wet and dry once and then draining): After the seedling stage, the soil is naturally drained until the soil just starts to crack, and then water is added until the soil reaches a moisture content of 40% to 45%. This process is repeated until the middle of the filling period. From the late filling period to the maturity period, the soil is drained and dried.

[0133] (4) Alternating dry and wet 2 groups (Alternating 2): After the seedling stage, the soil is naturally dried until the rice leaves begin to shrink slightly, and then water is added until the soil moisture content reaches 40%-45%, and this cycle is repeated until maturity.

[0134] Table 2. Pot experiment treatments for enhancing rice Cd absorption and accumulation

[0135] Treatment Group Name Water management methods Abbreviation CK group General Moisture Management conventional T1 Group Before the middle of heading and grain filling, dry and wet alternately for 1 hour, then dry and sun the field. Alternate front 1 back drop T2 Group Wet and dry alternation1 Alternate 1 T3 Group Wet and dry alternation 2 Alternate 2

[0136] 5. Calculation method of soil cadmium reduction and removal remediation efficiency:

[0137]

[0138] Wherein, E represents the repair efficiency; C r含量 represents the cadmium content in the aboveground part of the rice with high cadmium absorption and accumulation; B r represents the aboveground biomass of the rice with high cadmium absorption and accumulation; C s含量 represents the cadmium content in the tillage soil of the target paddy field; C screen represents the risk screening value of soil cadmium pollution; Ws Represents the weight of the topsoil of the target rice field.

[0139] Experimental results:

[0140] (1) At the rice maturity stage, the soil available cadmium (DGT-Cd) content in the CK group was 0.27 μg / kg, in the tillering stage, in the T1 group, it was 0.65 μg / kg, in the T2 group, it was 0.36 μg / kg, and in the T3 group, it was 0.33 μg / kg. Figure 2 There was no significant difference between the T2 and T3 groups and the conventional water management group. The tillering peak period of the T1 group was 140.74% higher than that of the conventional treatment.

[0141] (2) At the rice maturity stage, the Cd contents in the root, stem, leaf, and panicle of the CK group were 6.14, 1.01, 0.68, and 0.61 μg / kg, respectively ( Figure 3 );

[0142] (3) At the peak tillering stage, the Cd contents in the roots, stems, leaves and panicles of rice in the T1 group after the stem drop treatment were 33.26, 10.01, 6.31 and 6.26 μg / kg, respectively; the Cd contents in the roots, stems, leaves and panicles of rice in the T2 group were 26.39, 10.07, 6.78 and 5.97 μg / kg, respectively; the Cd contents in the roots, stems, leaves and panicles of rice in the T3 group were 25.93, 10.51, 6.93 and 5.56 μg / kg, respectively.

[0143] (4) In the rice root, the Cd content in the T1 group was significantly higher than that in the other treatments, and was 441.69% higher than that in the CK group. In the rice root, stem and leaf, although there was no difference in Cd content among the three water treatments, they were all significantly higher than those in the CK group. The Cd content in the stem, leaf and ear of the T1 group was 891.09% higher than that in the CK group, 827.94% higher than that in the CK group, and 926.23% higher than that in the CK group.

[0144] (5)Reference Figure 4 The difference between the accumulation of Cd in various parts of rice under water management and conventional water management is extremely significant, and over time, the accumulation of Cd in various parts of rice under water management is increasing. The accumulation of Cd in rice is root>stem>leaf>panicle. Among the comparison treatments, the accumulation of Cd in rice in the T1 group was the largest. When it reached maturity, the accumulation of each part of the treatment was 810.16 (root), 681.97 (stem), 241.20 (leaf), 119.28 (panicle) μg / stump, and the accumulation of cadmium in the aboveground part was 1042.45 μg / stump. The remediation efficiency of soil cadmium reduction and removal calculated by the above formula 1 is 14.89%, which is 9.56 times that of conventional treatment.

[0145] Example 2

[0146] Experimental methods:

[0147] 1. Target rice field: A rice field with cadmium and arsenic compound pollution located in Yonghe Town, Liuyang City, Hunan Province (113.87E, 28.29N):

[0148] (1) Field 1: soil pH 5.82, soil total Cd content about 1.23 mg / kg;

[0149] (2) Field 2: soil pH 5.68, soil total Cd content approximately 1.67 mg / kg;

[0150] (3) Field 3: soil pH 5.92, Cd content approximately 1.54 mg / kg.

[0151] The area has a typical subtropical monsoon climate, with an average temperature of 16.7℃ and an average annual precipitation of 1500mm. The irrigation and drainage conditions of the experimental fields are good. The field test will be carried out from June to October 2024.

[0152] 2. Rice: Plots 1, 2, and 3 were planted with rice varieties Huanghuazhan, 9311, and Pokkali (giant rice), respectively, and three types of water management (long-term flooding, conventional water management, and intermittent irrigation) were applied to them. The water management technology that enhanced the high absorption and accumulation of cadmium in rice was used to verify the remediation effect of cadmium-contaminated rice fields.

[0153] (1) Treatment settings for field 1 were: 1) long-term flooding + Huanghuazhan, 2) conventional water management + Huanghuazhan, 3) intermittent irrigation + Huanghuazhan;

[0154] (2) Treatment settings for field 2 were: 1) long-term flooding + 9311, 2) conventional water management + 9311; 3) intermittent irrigation + 9311;

[0155] (3) The treatment settings for field 3 were: 1) long-term flooding + Pokkali, 2) conventional water management + Pokkali, and 3) intermittent irrigation + Pokkali.

[0156] 3. Treatment method:

[0157] (1) Long-term flooding group: During the entire growth period of rice, the rice fields were flooded with 2-5 cm of water depending on the height of the rice.

[0158] (2) Conventional water management group: referring to local rice planting habits, flooding in the early stage of rice planting, flooding after drying the fields during the peak tillering period, and drying the fields from the late filling period to the maturity period.

[0159] (3) Intermittent irrigation group: After transplanting, the field begins to dry and irrigate after the rice turns green and survives. The field is then cycled between sunning and irrigation until the rice is filling with grain (sunning: the soil cracks greatly, but the rice grows normally; irrigation: irrigation is stopped when there is shallow water (0-1 cm) on the surface). The field is then dried and sunned from the late filling stage to the maturity stage.

[0160] Each treatment was replicated three times, for a total of 27 plots.

[0161] 4. The irrigation water is from the local river, and the cadmium and arsenic content is measured before each irrigation. At the same time, the atmospheric deposition of cadmium is monitored and the amount of deposition water is recorded each time the sample is taken.

[0162] Pesticide and fertilizer application followed local management practices, and all treatments remained consistent.

[0163] When rice was mature, it was harvested close to the ground. Rice and straw samples were taken, weighed (dry weight), and their cadmium content was determined. The accumulated cadmium content in rice and the cadmium removal efficiency in soil were calculated.

[0164] Experimental results:

[0165] Experimental data from three fields showed that intermittent irrigation greatly enhanced the absorption of cadmium by rice.

[0166] (1) Plot 1 ( Figure 5 ), the cadmium accumulation of rice straw in the upper part of the rice Huanghua area under the measures of long-term flooding group, conventional water management group and intermittent irrigation group in the community was 0.44mg, 0.50mg and 1.75mg respectively. Compared with the conventional water management group, the cadmium accumulation of rice straw in the upper part of the Huanghua area under the intermittent irrigation group increased by 348.21%, and the remediation efficiency of soil cadmium reduction and removal increased from 2.16% to 7.51%, an increase of 2.48 times.

[0167] (2) Plot 2 ( Figure 6 ), the cadmium accumulation in the aboveground straw of rice 9311 in the long-term flooding group, conventional water management group, and intermittent irrigation group was 0.36 mg, 0.65 mg, and 1.53 mg, respectively. Compared with conventional water management, the cadmium accumulation in the aboveground straw of Huanghua Land in the intermittent irrigation group increased by 235.96%, and the remediation efficiency of soil cadmium reduction and removal increased from 1.89% to 4.47%, an increase of 1.36 times.

[0168] (3) Experimental plot 3 ( Figure 7 ), the cadmium accumulation in the aboveground straw of rice Pokkali under the long-term flooding group, conventional water management group and intermittent irrigation group was 1.88mg, 2.65mg and 7.97mg respectively. Compared with the conventional water management, the cadmium accumulation in the aboveground straw of Huanghua land under the intermittent irrigation group increased by 300.90%, and the remediation efficiency of soil cadmium reduction and removal increased from 8.15% to 25.72%, an increase of 2.01 times.

[0169] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein by equivalents. However, these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A highly efficient reduction and restoration method for cadmium pollution in paddy field soil, characterized in that: include: For the target rice fields, plant rice with high cadmium absorption and accumulation; After the cadmium high absorption and accumulation rice turns green at the seedling stage, the target rice field is subjected to a deep water management process until the cadmium high absorption and accumulation rice matures; wherein the deep water management process is to repeatedly perform periodic dry-wet alternating treatment and field sunning on the target rice field; The rice with high cadmium absorption and accumulation is harvested and removed from the field.

2. The high-efficiency reduction and restoration method for cadmium pollution in paddy soil according to claim 1, characterized in that: The in-depth moisture management process includes: After the cadmium-high absorbing and accumulating rice in the target paddy field turns green, the wet-dry alternating treatment is repeatedly performed for multiple cycles until the middle of the grain filling period; Drainage, drying and sunning of fields should be carried out from the middle of grain filling to maturity; Preferably, the duration of a single cycle of the dry-wet alternating treatment is 3 to 5 days; Preferably, the frequency of the dry-wet alternating treatment cycle is 15 to 45 times; Preferably, during the dry-wet alternating treatment cycle, the soil Eh is controlled at 65mV to 350mV; Preferably, the soil Eh during the drainage, drying and sun-drying treatment is controlled at 250mV to 400mV.

3. The high-efficiency reduction and restoration method for cadmium pollution in paddy field soil according to claim 2, characterized in that: The single cycle of the wet-dry alternating treatment includes: When the soil is moist, it is allowed to dry naturally until the soil cracks and the rice leaves do not curl or wrinkle. Water until the soil surface is moist or covered with water to a depth of 0 to 0.5 cm for 4 to 8 hours.

4. The high-efficiency reduction and restoration method for cadmium pollution in paddy soil according to claim 3, characterized in that: The soil water content when the soil cracks and the rice leaves do not have micro-curling wrinkles is 25% to 35%.

5. The high-efficiency reduction and restoration method for cadmium pollution in paddy field soil according to claim 3, characterized in that: When the soil surface is moist, or when the soil surface is covered with 0 cm to 0.5 cm of water, the soil moisture content is controlled at 40% to 45%.

6. The high-efficiency reduction and restoration method for cadmium pollution in paddy field soil according to claim 3, characterized in that: When cracks appear in the soil, the size of the cracks is 0.1 cm to 2 cm.

7. The high-efficiency reduction and restoration method for cadmium pollution in paddy soil according to claim 2, characterized in that: When there is no rainfall, the dry-wet alternating treatment is directly carried out; When it rains, the target rice field is first drained until the soil cracks, and then the dry-wet alternating treatment is started.

8. The high-efficiency reduction and restoration method for cadmium pollution in paddy field soil according to claim 1, characterized in that: The step of harvesting the rice with high cadmium absorption and accumulation and removing it from the field comprises: The above-ground part of the rice with high cadmium absorption and accumulation is harvested close to the ground and removed from the field; wherein the stubble height is controlled at 0 cm to 1 cm.

9. The high-efficiency reduction and restoration method for cadmium pollution in paddy soil according to claim 1, characterized in that: The rice with high cadmium absorption and accumulation includes at least one of Yangdao No. 6, Yuzhenxiang and Pokkali.

10. The high-efficiency reduction and restoration method for cadmium pollution in paddy field soil according to claim 1, characterized in that: The soil of the target paddy field is at least moderately polluted or severely polluted; wherein the moderate pollution refers to the total cadmium content of the soil C 镉 Meets: 3 times the soil cadmium pollution risk screening value < C 镉 ≤5 times the soil cadmium pollution risk screening value; severe pollution refers to the total cadmium content of the soil meeting the following requirements: C 镉 >5 times the risk screening value for soil cadmium pollution; After the cadmium high absorption and accumulation rice is harvested and removed from the field, the method further comprises: Detecting the total cadmium content of the soil of the target paddy field and determining whether the total cadmium content of the soil of the target paddy field is not higher than the soil cadmium pollution risk screening value; If the total cadmium content is not higher than the soil cadmium pollution risk screening value, it is determined that the restoration of the target rice field is completed; If the total cadmium content is higher than the soil cadmium pollution risk screening value, it is determined that the restoration of the target rice field is incomplete, and the process returns to the step of planting rice with high cadmium absorption and accumulation in the target rice field.

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