A safe utilization method for heavily cadmium-contaminated rice fields

Abstract

The present invention provides a safe utilization method of a severely cadmium-contaminated paddy field, and relates to the technical field of rice cultivation in cadmium-contaminated paddy fields. The method comprises: measuring and selecting a field with a cultivable soil layer thickness of not less than 70 cm; transforming, swapping, isolating and backfilling the 0-30 cm surface soil and the 30-60 cm deep soil of the selected field, and maturing the deep soil after backfilling; then planting green manure and rotary tilling and breaking it during the vigorous growth period and mixing it with the deep soil; planting low cadmium accumulation rice varieties on the treated soil, spraying foliar control agents during the tillering stage and the booting stage of rice growth, respectively, and safely producing rice that meets the cadmium standard. The present invention can significantly reduce the cadmium content of heavily polluted paddy soil by adopting technologies such as soil layer swapping, isolation, and fertile surface construction under the premise of low cost, and the repair cycle is short and the repair effect is stable; at the same time, in conjunction with improved rice planting technology, it can ensure that the rice produced in heavily cadmium-contaminated paddy fields meets the cadmium standard.

Description

Technical Field

[0001] The invention relates to the technical field of rice cultivation in cadmium-contaminated paddy fields, and in particular to a method for safely utilizing heavily cadmium-contaminated paddy fields. Background Art

[0002] In the classification of cultivated land soil environmental quality, according to the standard GB15618-2018, combined with soil cadmium content, pH and other indicators, cultivated land is divided into three categories: priority protection, safe use, and strict control. Among them, the strict control category belongs to the heavy pollution type. Due to the extremely high risk of heavy metals in this type of cultivated land, it is strictly prohibited to grow edible crops.

[0003] At present, the mainstream technologies for the treatment of heavily cadmium-contaminated soil mainly include leaching, high-efficiency passivation, super-enrichment phytoremediation, imported soil or a combination of multiple technologies. For example, the existing Chinese patent document CN104041362A discloses a method for safe rice production on heavily cadmium-contaminated cultivated land, which includes the following steps: before plowing and fertilizing the heavily cadmium-contaminated cultivated land, evenly spread the composite passivation material on the soil surface, plow and mix well, mix the composite passivation material with the cultivated land soil, balance for 30 days, and then transplant rice varieties with low cadmium absorption, and use conventional water and fertilizer management during the growth of rice. CN117204288A discloses a method for safely utilizing rice fields contaminated by mercury / cadmium complex, the method comprising plowing the soil of the rice fields according to the soil pollution characteristics of the rice fields; conditioning the soil after plowing; selecting low-accumulation rice varieties and planting them in the conditioned rice fields; managing the water content of the rice fields during the rice planting process; managing the fertilization of the rice fields during the rice planting process; controlling the leaf surface from the 8th to 12th day of the rice tillering period to the beginning of the jointing period, the booting period and the filling period; harvesting the rice to obtain rice. CN115055510A discloses a method for repairing heavy metal contaminated soil, the method comprising the following steps: mixing hydrofluoric acid and the soil to be treated and reacting; performing solid-liquid separation on the treated soil and collecting the solid components; eluting the collected solid components with an eluent to obtain the repaired soil. CN108114977A discloses a method for rapidly repairing cadmium-contaminated farmland by rotating the planting of hyperaccumulators and energy plants. The method comprises the following steps: planting cadmium hyperaccumulator plants and energy plants in cadmium-contaminated farmland soil according to their natural growth period, carrying out conventional cultivation, and achieving the purpose of repairing cadmium-contaminated farmland through the absorption and enrichment capabilities of the cadmium hyperaccumulator plants and the energy plants for cadmium; the cadmium hyperaccumulator plants are Sedum serrata; and the energy plants are sorghum or rapeseed.

[0004] However, the above-mentioned existing technical solutions generally have the following problems: (1) The cost is high and difficult to promote and replicate. For example, the cost of three technical restoration and treatment methods such as leaching, super-enrichment plant restoration, and imported soil is as high as 20,000 yuan per mu. (2) The cycle is long and has a great impact on normal agricultural production. For example, the cycle of super-enrichment plant restoration is at least 8 to 10 years. (3) The effect is unstable. For example, in super-enrichment plant restoration technology, factors such as plant varieties and climate have a great impact on the restoration efficiency; high-efficiency passivation technology does not reduce the total cadmium in the soil, and the passivated cadmium has the potential to reactivate. Therefore, it is urgent to develop a safe utilization method for heavily cadmium-contaminated rice fields with low cost, short restoration cycle and stable restoration effect. Summary of the invention

[0005] The technical problem to be solved by the present invention is: in view of the defects of the prior art, a method for safely utilizing heavily cadmium-contaminated rice fields is provided. The method of the present invention can significantly reduce the cadmium content of the surface soil of heavily contaminated rice fields by adopting techniques such as soil layer swapping, isolation, and fertile surface layer construction at a low cost, and at the same time cooperate with improved rice planting techniques, thereby ensuring that the cadmium content of rice produced in heavily cadmium-contaminated rice fields meets the standards.

[0006] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0007] The present invention provides a method for safely utilizing a paddy field that is severely polluted by cadmium, comprising the following steps:

[0008] S1. Measure and select fields: Measure and select fields with arable soil thickness of not less than 70cm;

[0009] S2. The topsoil and deep soil of the field selected in S1 are transformed, exchanged, isolated and backfilled as follows:

[0010] (1) Excavation of topsoil: excavate the topsoil 0 to 30 cm from the ground surface and move it to the adjacent field;

[0011] (2) Deep soil excavation: excavate the deep soil 30 to 60 cm below the surface and move it to the adjacent field, and pile it separately from the surface soil;

[0012] (3) Backfilling of topsoil: backfilling the topsoil excavated in (1) into the excavated field;

[0013] (4) Passivation of topsoil: Apply calcium-silicon-based soil passivator to the backfilled topsoil, harrow it thoroughly, and then water it with an appropriate amount of water to make the soil moisture reach 60%~80% and maintain it for 2~3 days;

[0014] (5) Bentonite isolation: A layer of sodium-based bentonite is laid on the surface soil transformed in (4) to isolate the surface soil from the deep soil to be backfilled;

[0015] (6) Deep soil transformation: add humic acid, soil conditioner, and microbial agent to the deep soil excavated in (2) and mix thoroughly for transformation;

[0016] (7) Backfilling of deep soil: Backfill the transformed deep soil from (6) onto the sodium-based bentonite layer from (5) to a depth of 30 to 35 cm;

[0017] (8) Deep soil maturation: Add appropriate amount of water to the deep soil backfilled in (7) to make the field soil moisture reach 60%~80% and maintain it for 5~10 days;

[0018] S3. Deep soil pioneer planting: Plant green manure on mature soil, and when the green manure is in its vigorous growth period, grind it into pieces and mix it with the deep soil;

[0019] S4. Rice planting and management: Plant low cadmium-accumulating rice varieties on the soil treated with S3, spray foliar inhibitors during the tillering and heading stages of rice growth, and you can safely produce rice that meets cadmium standards.

[0020] Furthermore, in step S1, the thickness of the arable soil layer is usually measured by drilling or excavating a profile, and the arable soil layer includes an eluvial layer and an alluvial layer.

[0021] Furthermore, the application amount of the silicon-calcium based soil passivator in step S2 (4) is 4500-7500 kg / hm 2 .

[0022] Furthermore, the effective CaO in the silicon-calcium based soil passivator is ≥30%, the effective SiO2 is ≥10%, and the pH is 11~13.

[0023] Furthermore, the silicon-calcium-based soil passivator is a powder with a fineness of ≥95% and a particle size of ≤250 μm.

[0024] Furthermore, step S2 (5) further includes compacting the sodium-based bentonite layer, wherein the compaction degree is ≥ 95%, and the thickness of the compacted sodium-based bentonite layer is 3-5 cm.

[0025] Furthermore, the montmorillonite content in the sodium bentonite is ≥90%, the pH is 7-10, and the expansion multiple is 20-30.

[0026] Furthermore, the sodium bentonite powder has a fineness of ≥98% and a particle size of ≤100μm.

[0027] Furthermore, in step S2 (6), the amount of humic acid added is 0.5-1% of the dry weight of the deep soil.

[0028] Furthermore, the organic matter drying basis in humic acid is ≥55%, the pH is 5.5~7.0, and the nutrients are ≥6%.

[0029] Furthermore, the humic acid is a mineral source powder with a fineness of ≥95% and a particle size of ≤250 μm.

[0030] Furthermore, in step S2 (6), the amount of soil conditioner added is 0.1-0.2% of the dry weight of deep soil.

[0031] Furthermore, the soil conditioner contains effective CaO ≥ 30%, effective SiO2 ≥ 10%, effective MgO ≥ 5%, and a pH of 8~10.

[0032] Furthermore, the soil conditioner is a powder with a fineness of ≥95% and a particle size of ≤250 μm.

[0033] Furthermore, in step S2 (6), the amount of microbial agent added is 20-30 g / t soil (dry weight).

[0034] Furthermore, the microbial agent includes a mixture of nitrogen-fixing bacteria, rhizobia, Bacillus megaterium, actinomycetes, and Bacillus pumilus.

[0035] Furthermore, the effective viable count of nitrogen-fixing bacteria is ≥ 200 million / g; the effective viable count of rhizobia is ≥ 150 million / g; the effective viable count of Bacillus megaterium is ≥ 100 million / g; the effective viable count of actinomycetes is ≥ 120 million / g; and the effective viable count of Bacillus pumilus is ≥ 180 million / g.

[0036] Furthermore, the green manure planted in S3 is one or more of Chinese milk vetch, rapeseed, and radish.

[0037] The vigorous growth period of green manure usually refers to a planting period of ≥90 days; the fresh weight of green manure biomass produced per hectare is ≥7500kg.

[0038] Preferably, in step S4, the low accumulation rice variety is selected from indica hybrid rice, and the planting density is 350,000 to 400,000 plants / hm2. 2 , basic seedlings 1.35 million to 1.5 million / hm 2 .

[0039] Furthermore, the method for spraying the foliar barrier agent in step S4 is: 3-5 kg / hm2 of the foliar barrier agent is applied at the tillering stage and the booting stage of rice growth. 2 Dilute with 10 to 30 times of clean water and spray evenly on the front and back of rice leaves.

[0040] Furthermore, the foliar barrier agent contains Mn ≥ 3%, Zn ≥ 7%, Se ≥ 0.2%, water insoluble matter ≤ 2%, and pH 5.5 ~ 8.5.

[0041] Principle of the scheme of the present invention:

[0042] The leaching layer of the soil is located at the top of the soil and is the first place where pollutants come into contact and accumulate. For example, atmospheric deposition, sewage irrigation, and the application of chemical fertilizers and pesticides make cadmium mainly in the soil surface, so the cadmium content in the leaching layer will be at a relatively high level. Leaching causes some cadmium to migrate to the lower soil layer with water flow, but during the migration process, cadmium will react with soil particles such as adsorption and precipitation, resulting in a reduction in the amount of cadmium reaching the deposition layer. Generally, the cadmium content of the leaching layer soil is 3 to 5 times that of the deposition layer. That is, when the cadmium content of the leaching layer soil is at a severe pollution level, the cadmium content of the deposition layer soil is only at a medium-to-light or slightly polluted level. Generally, the roots of crops only touch the 0-30 cm tillage layer, and normal arable land environmental quality assessment sampling only needs to collect 0-30 cm tillage layer soil.

[0043] Therefore, in the scheme of the present invention, the surface 0-30cm soil and the deep 30-60cm soil are selected for transformation and exchange respectively, and a bentonite layer is used to isolate the two. On the one hand, the cadmium in the surface cadmium-contaminated soil can be passivated, and on the other hand, the fertility of the deep soil can meet the requirements of rice planting. Bentonite isolation can also reduce the mutual influence between the two soil layers. In addition, during the rice planting period, the ternary composite foliar barrier control agent of manganese, zinc and selenium is sprayed to coordinately regulate and inhibit the transport of cadmium in rice plants. Finally, safe production is achieved to obtain rice with cadmium standards.

[0044] The present invention has the following beneficial effects:

[0045] (1) The method of the present invention can effectively reduce the content of soil in the topsoil of heavily polluted rice fields and increase the area of ​​arable land available for grain production. According to relevant technical specifications, heavily polluted arable land must be included in the strictly controlled category and can only be used for the cultivation of non-food crops in principle. It is strictly prohibited to plant grain crops. After the implementation of this technology, the total Cd reduction rate of the new surface layer compared with the old surface layer is ≥70%, which can reduce the pollution level of most strictly controlled arable land to medium-light or mild, so that it can be included in the safe utilization category or priority protection category, allowing grain production, and the cadmium content of the produced grain is low, which meets the national standards. This is of great significance for ensuring my country's food security.

[0046] (2) The method of the present invention has low application cost, low soil fertility loss rate, and is easy to replicate and promote. The technology of the present invention uses in-situ heterogeneous soil as the cultivated soil after treatment, without the need to take soil from other places, which can avoid damage to other cultivated land and save a lot of treatment costs. Based on the deep soil, a fertile arable layer is constructed as a new arable layer of soil, so that the main indicators such as organic matter, nutrients, and structure meet the needs of rice planting, which can ensure that there is basically no reduction in production.

[0047] (3) The contaminated soil is disposed of in situ without secondary pollution. The technology of the present invention uses the heavily polluted surface soil as the underlying layer of the arable soil layer, which can solve the problem of disposal of contaminated soil after stripping at a low cost.

[0048] (4) The effect is long-lasting. First, the technology of the present invention has passivated the new bottom soil (original surface soil), and the cadmium activity therein has been greatly reduced; second, for rice fields, the movement of soil moisture has been in the direction of top to bottom for a long time, and the cadmium in the new bottom soil (original surface soil) is difficult to transfer to the new surface soil (original deep soil) with the movement of moisture; third, the technology of the present invention sets a sodium-based bentonite layer between the original surface soil and the original deep soil. The sodium-based bentonite layer has good impermeability and adsorption, which can effectively isolate the cadmium in the new bottom soil (original surface soil) from entering the new surface soil (original deep soil). The repair cycle of the present invention is short and the repair effect is relatively stable. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 A schematic flow chart of the method for safely utilizing heavily cadmium-contaminated rice fields provided by the present invention. DETAILED DESCRIPTION

[0050] like Figure 1 As shown, the present invention provides a method for safely utilizing a paddy field that is heavily contaminated by cadmium, comprising the following steps:

[0051] S1. Measurement and field selection: Measure the thickness of the arable soil layer by drilling or excavating profiles. The arable soil layer includes the eluvial layer and the sedimentary layer. Select fields with arable soil layer thickness of not less than 70cm.

[0052] S2. The surface soil and deep soil of the field selected in S1 are transformed, exchanged, isolated and backfilled as follows:

[0053] (1) Excavation of topsoil: excavate the topsoil 0 to 30 cm from the ground surface and move it to the adjacent field;

[0054] (2) Deep soil excavation: excavate the deep soil 30 to 60 cm below the surface and move it to the adjacent field, and pile it separately from the surface soil;

[0055] (3) Backfilling of topsoil: Backfilling the topsoil excavated in (1) into the excavated field.

[0056] (4) Passivation of topsoil: Apply silicon-calcium-based soil passivator to the backfilled topsoil, harrow it thoroughly, and then water it with an appropriate amount of water to make the soil moisture reach 60%~80% and maintain it for 2~3 days. In a preferred embodiment, the effective CaO of the silicon-calcium-based soil passivator is ≥30%, the effective SiO2 is ≥10%, and the pH is 11~13; the silicon-calcium-based soil passivator is a powder with a fineness of ≥95% and a particle size of ≤250μm; the application rate of the silicon-calcium-based soil passivator is 4500~7500kg / hm 2 .

[0057] (5) Bentonite isolation: A layer of sodium bentonite is laid on the surface soil after the transformation in (4) to isolate the surface soil from the deep soil to be backfilled; the sodium bentonite layer is compacted to a compaction degree of ≥95%, and the thickness of the compacted sodium bentonite layer is 3-5 cm. In a preferred embodiment, the montmorillonite content in the sodium bentonite is ≥90%, the pH is 7-10, and the expansion multiple is 20-30; the fineness of the sodium bentonite is ≥98%, and the particle size is ≤100 μm.

[0058] (6) Deep soil modification: Humic acid, soil conditioner, and microbial agent are added to the deep soil excavated in (2) and mixed thoroughly. In a preferred embodiment, the amount of humic acid added is 0.5-1% of the dry weight of the deep soil; the organic matter in the humic acid is ≥55% on a dry basis, the pH is 5.5-7.0, and the nutrients are ≥6%; the humic acid is a mineral source powder with a fineness of ≥95% and a particle size of ≤250μm. The amount of soil conditioner added is 0.1-0.2% of the dry weight of the deep soil; the effective CaO in the soil conditioner is ≥30%, the effective SiO2 is ≥10%, and the effective MgO is ≥5%, and the pH is 8-10; the soil conditioner is a powder with a fineness of ≥95% and a particle size of ≤250μm. The amount of microbial agent added is 20-30g / t soil (dry weight); the microbial agent includes a mixture of nitrogen-fixing bacteria, rhizobia, Bacillus megaterium, actinomycetes, and Bacillus pumilus. The effective live bacteria count of nitrogen-fixing bacteria is ≥ 200 million / g; the effective live bacteria count of rhizobia is ≥ 150 million / g; the effective live bacteria count of Bacillus megaterium is ≥ 100 million / g; the effective live bacteria count of actinomycetes is ≥ 120 million / g; the effective live bacteria count of Bacillus pumilus is ≥ 180 million / g.

[0059] (7) Backfilling of deep soil: Backfill the transformed deep soil from (6) onto the sodium bentonite layer from (5) to a depth of 30 to 35 cm.

[0060] (8) Deep soil maturation: Add appropriate amount of water to the deep soil backfilled in (7) to make the field soil moisture reach 60%~80% and maintain it for 5~10 days.

[0061] S3. Deep soil pioneer planting: Plant green manure on the matured soil, and till it to pieces and mix it with the deep soil during the vigorous growth period of the green manure. In a preferred embodiment, the green manure is one or more of Chinese milk vetch, rapeseed, and radish; the vigorous growth period of green manure usually refers to a planting period of ≥90 days; the fresh weight of green manure biomass produced per hectare is ≥7500kg.

[0062] S4. Rice planting and management: Plant low cadmium accumulation rice varieties on the soil treated with S3. Apply 3-5 kg / hm2 of foliar inhibitors at the tillering and booting stages of rice growth. 2 Dilute with 10-30 times of clean water and spray evenly on the front and back of rice leaves to safely produce rice that meets the cadmium standards. Low-accumulation rice varieties are preferably indica hybrid rice, with a planting density of 350,000-400,000 plants / hm2. 2 , basic seedlings 1.35 million to 1.5 million / hm 2 In a preferred embodiment, the foliar barrier agent contains Mn≥3%, Zn≥7%, Se≥0.2%, water-insoluble matter≤2%, and a pH of 5.5-8.5.

[0063] For ease of understanding of the present invention, preferred embodiments of the present invention are provided below. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the understanding of the disclosure of the present invention more thorough and comprehensive.

[0064] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in the specification of the present invention herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0065] The raw materials and their sources used in the following examples are as follows:

[0066] Calcium silicon-based soil passivator: Model JG-F-2 product provided by Environmental Bridge (Hunan) Ecological Environment Engineering Co., Ltd., powder, fineness (particle size ≤ 250μm) 96.2%, effective CaO content 33.5%, effective content SiO2 15.7%, pH 11.9.

[0067] Sodium bentonite: provided by Hunan Hongcheng Ore Powder Co., Ltd., powder, fineness (particle size ≤ 100μm) 99.8%, montmorillonite content 96.1%, pH 8.24, expansion multiple 27.

[0068] Humic acid: provided by Hunan Wanmufeng Agricultural Technology Co., Ltd., powder, fineness (particle size ≤ 250μm) 99.2%, organic matter (drying basis) 57%, pH 6.81, nutrients 6.9%.

[0069] Soil conditioner: Model GL-F-3 product provided by Environmental Bridge (Hunan) Ecological Environment Engineering Co., Ltd., powder, fineness (particle size ≤ 250μm) 98.3%, effective CaO content 35.1%, effective SiO2 content 13.9%, effective MgO content 7.5%, pH 9.1.

[0070] Microbial agent: provided by Cangzhou Kang Microbiological Technology Co., Ltd., including 253 million nitrogen-fixing bacteria / g, 156 million rhizobia / g, 180 million Bacillus megaterium / g, 213 million actinomycetes / g, and 217 million Bacillus pumilus / g.

[0071] Parameter requirements for foliar barrier agents: Model GL-F-9 product provided by Environmental Bridge (Hunan) Ecological Environment Engineering Co., Ltd., powder, Mn content 4.2%, Zn content 8.1%, Se content 0.37%, water-insoluble matter 0.2%, pH 6.3.

[0072] If the specific conditions are not specified in the examples, the experiments were carried out under conventional conditions or conditions recommended by the manufacturer. If the manufacturers of the reagents or instruments are not specified, they are all conventional products that can be purchased commercially.

[0073] Example 1 A governance project in Sichuan

[0074] In a severely cadmium-polluted area in Sichuan, a rice field was selected for the experiment. The total cadmium content of the initial surface soil of the rice field was 2.16 mg / kg, the effective cadmium content was 0.83 mg / kg, the pH was 5.01, the organic matter content was 13 g / kg, the total nitrogen content was 1.14 g / kg, the alkaline nitrogen content was 76.7 mg / kg, the effective phosphorus content was 11.8 mg / kg, and the available potassium content was 50.0 mg / kg. The rice field was divided into two parts, and a ridge (30 cm wide and 30 cm high) was made to separate them. Each field was 600 m 2 One treatment was set in each field, for a total of two treatments:

[0075] Treatment 1 (CK): control, conventional rice cultivation;

[0076] Treatment 2: Rice was planted using the technology of the present invention (details as follows).

[0077] Process 2 The specific steps of adopting the technology of the present invention are as follows:

[0078] (1) Measurement and field selection: The thickness of the arable soil layer (elution layer + sedimentation layer) was measured by drilling. The thickness of the arable soil layer in the field was 92 cm.

[0079] (2) Excavation of topsoil: Excavate the topsoil 0 to 30 cm from the ground surface and move it to the adjacent field.

[0080] (3) Deep soil excavation: Excavate the deep soil 30 to 60 cm below the ground surface to the adjacent field and pile it separately from the surface soil.

[0081] (4) Backfilling of topsoil: Backfill the topsoil into the excavated fields.

[0082] (5) Topsoil passivation: Apply calcium-silicon-based soil passivator to the backfilled topsoil at a rate of 4500 kg / hm2. 2 , rake it thoroughly, and irrigate it with appropriate amount of water to make the soil moisture reach 60% and maintain it for 2 days.

[0083] (5) Bentonite isolation: A layer of sodium-based bentonite is laid on the modified topsoil. The thickness of the sodium-based bentonite layer after compaction (compaction degree 96.8%) is 3 cm.

[0084] (6) Deep soil improvement: Humic acid, soil conditioner and microbial agent were added to the excavated deep soil and mixed thoroughly. The amount of humic acid added was 0.5% of the dry weight of the deep soil, the amount of soil conditioner added was 0.1% of the dry weight of the deep soil, and the amount of microbial agent added was 20 g / t soil (dry weight).

[0085] (7) Backfilling of deep soil: Backfill the transformed deep soil to the surface layer with a backfill depth of 30 cm.

[0086] (8) Deep soil maturation: Add appropriate amount of water to the backfilled deep soil to make the field soil moisture reach 60% and maintain it for 5 days.

[0087] (9) Deep soil pioneer planting: Green manure is planted on mature soil. Milk vetch and fat radish are mixed and planted. During the vigorous growth period of green manure (planting time is 98 days), it is rotary tilled and broken up and mixed with deep soil. The green manure biomass (fresh weight) per hectare is 10,227 kg.

[0088] (10) Rice planting: Planting low cadmium accumulation rice variety Yixiangyou 2115, with a planting density of 350,000 plants / hm2 2 , basic seedlings 1.35 million / hm 2 .

[0089] (11) Foliar control: When rice grows to the tillering stage and the booting stage, apply 3kg / hm2 of foliar control agent at each stage. 2 Dilute with 10 times the amount of clean water and spray evenly on the front and back of rice leaves.

[0090] The rice planting time of treatment 2 was the same as that of treatment 1, and the rice variety was Yixiangyou 2115. During the application of the technical steps (1) to (9) of treatment 2, treatment 1 was left fallow without interference. During the rice planting period, the field measures such as fertilization, pest and weed management, etc. of the two treatments remained completely consistent.

[0091] During the rice maturity period, yields were measured in different plots, and soil and rice samples were collected. Soil samples were tested for total cadmium, effective cadmium, and pH, and rice samples were tested for rice cadmium.

[0092] 1. Effects of different treatments on total cadmium, available cadmium and pH in soil

[0093] The total cadmium, effective cadmium and pH of soils treated in different ways are shown in Table 1. The total cadmium in treatment 1 (CK) was 2.11 mg / kg, which exceeded the risk control value (1.5 mg / kg) according to GB15618-2018, and the risk of exceeding the standard for crops grown was high. The total cadmium in treatment 2 was reduced to 0.28 mg / kg, which was 86.7% lower than that in treatment 1 (CK). According to GB 15618-2018, the total cadmium level risk in treatment 2 is low and can generally be ignored. Compared with treatment 1 (CK), the effective cadmium in treatment 2 was reduced by 82.9% and the pH was increased by 0.37 units. This shows that the technology of the present invention can significantly reduce the risk level of cadmium in heavily polluted paddy soil.

[0094]

[0095] 2. Effects of different treatments on cadmium content in rice and rice yield

[0096] The cadmium content and rice yield of different treatments are shown in Table 2. The cadmium content of rice in treatment 1 (CK) was 1.66 mg / kg, which was 7.3 times higher than the limit value (0.2 mg / kg) specified in GB2762-2022. The total cadmium content in treatment 2 was reduced to 0.07 mg / kg, which was 95.8% lower than that in treatment 1 (CK) and far lower than the limit value (0.2 mg / kg) specified in GB 2762-2022. Compared with treatment 1 (CK), the rice yield in treatment 2 was reduced by 3.1%, which was far lower than the limit value (10%) specified in NY / T 3499-2019. This shows that the technology of the present invention can effectively reduce the cadmium content of rice without causing a significant reduction in rice yield.

[0097]

[0098] Example 2 A governance project in Hunan

[0099] In a severely cadmium-polluted area in Hunan, a rice field was selected for the experiment. The total cadmium in the initial surface soil of the rice field was 4.32 mg / kg, the effective cadmium was 3.13 mg / kg, the pH was 5.34, the organic matter was 25.6 g / kg, the total nitrogen was 2.81 g / kg, the alkaline nitrogen was 172.1 mg / kg, the effective phosphorus was 13.6 mg / kg, and the available potassium was 151.3 mg / kg. The rice field was divided into two parts, and the ridge (30 cm wide and 30 cm high) for laying agricultural film was made to separate them. Each field was 963 m 2One treatment was set in each field, for a total of two treatments:

[0100] Treatment 1 (CK): control, conventional rice cultivation;

[0101] Treatment 2: Rice was planted using the technology of the present invention (details as follows).

[0102] Process 2 The specific steps of adopting the technology of the present invention are as follows:

[0103] (1) Measurement and field selection: The thickness of the arable soil layer (elution layer + sedimentation layer) is measured by drilling. The thickness of the arable soil layer in the field is 76 cm.

[0104] (2) Excavation of topsoil: Excavate the topsoil 0 to 30 cm from the ground surface and move it to the adjacent field.

[0105] (3) Deep soil excavation: Excavate the deep soil 30 to 60 cm below the ground surface to the adjacent field and pile it separately from the surface soil.

[0106] (4) Backfilling of topsoil: Backfill the topsoil into the excavated fields.

[0107] (5) Topsoil passivation: Apply calcium-silicon-based soil passivator to the backfilled topsoil at a rate of 7500 kg / hm2. 2 , and rake it thoroughly, and irrigate it with appropriate amount of water to make the soil moisture reach 60% and maintain it for 3 days.

[0108] (5) Bentonite isolation: A layer of sodium-based bentonite is laid on the modified topsoil. The thickness of the sodium-based bentonite layer after compaction (compaction degree 98.1%) is 5 cm.

[0109] (6) Deep soil improvement: Humic acid, soil conditioner and microbial agent were added to the excavated deep soil and mixed thoroughly. The amount of humic acid added was 1% of the dry weight of the deep soil, the amount of soil conditioner added was 0.2% of the dry weight of the deep soil, and the amount of microbial agent added was 30 g / t soil (dry weight).

[0110] (7) Backfilling of deep soil: Backfill the transformed deep soil to the surface layer with a backfill depth of 35 cm.

[0111] (8) Deep soil maturation: Add appropriate amount of water to the backfilled deep soil to make the field soil moisture reach 80% and maintain it for 10 days.

[0112] (9) Deep soil pioneer planting: Plant green manure on mature soil, plant only astragalus, and during the vigorous growth period of green manure (planting time 90 days), till it and break it up and mix it with the deep soil. The green manure biomass (fresh weight) per hectare is 9430 kg.

[0113] (10) Rice planting: Planting the low cadmium accumulation rice variety Zhuliangyou 15, with a planting density of 400,000 plants / hm2 2 , basic seedlings 1.5 million / hm 2 .

[0114] (11) Foliar control: When rice grows to the tillering stage and the booting stage, apply 5kg / hm2 of foliar control agent at each stage. 2 Dilute with 30 times of clean water and spray evenly on the front and back of rice leaves.

[0115] The rice planting time of treatment 2 was the same as that of treatment 1, and the rice variety was also Zhuliangyou 15. During the application of the technical steps (1) to (9) of treatment 2, treatment 1 was left fallow without interference. During the rice planting period, the field measures such as fertilization, pest and weed management, etc. of the two treatments remained completely consistent.

[0116] During the rice maturity period, yields were measured in different plots, and soil and rice samples were collected. Soil samples were tested for total cadmium, effective cadmium, and pH, and rice samples were tested for rice cadmium.

[0117] 1. Effects of different treatments on total cadmium, available cadmium and pH in soil

[0118] The total cadmium, effective cadmium and pH of soils treated in different ways are shown in Table 3. The total cadmium in treatment 1 (CK) was 4.36 mg / kg, which exceeded the risk control value (1.5 mg / kg) according to GB15618-2018, and the risk of excessive cadmium in crops planted was high. The total cadmium in treatment 2 was reduced to 0.95 mg / kg, a decrease of 78.2% compared with treatment 1 (CK). According to GB 15618-2018, the total cadmium level in treatment 2 was lower than the risk control value. Compared with treatment 1 (CK), the effective cadmium in treatment 2 was reduced by 83.3% and the pH was increased by 0.13 units. This shows that the technology of the present invention can significantly reduce the risk level of cadmium in heavily polluted paddy soil.

[0119]

[0120] 2. Effects of different treatments on cadmium content in rice and rice yield

[0121] The cadmium content and rice yield of different treatments are shown in Table 4. The cadmium content of rice in treatment 1 (CK) was 2.21 mg / kg, which was 10.05 times higher than the limit value (0.2 mg / kg) specified in GB2762-2022. The total cadmium content in treatment 2 was reduced to 0.18 mg / kg, which was 91.9% lower than that in treatment 1 (CK) and lower than the limit value (0.2 mg / kg) specified in GB 2762-2022. Compared with treatment 1 (CK), the rice yield in treatment 2 increased by 5%. This shows that the technology of the present invention can effectively reduce the cadmium content of rice and slightly increase the rice yield.

[0122]

[0123] In summary, the indicators that can be achieved by the technology of the present invention are: the reduction rate of total Cd in the new surface layer compared with the old surface layer is ≥70%; the reduction rate of Cd in rice compared with the control (not using this technology) is ≥90%; the reduction rate of rice yield compared with the control (not using this technology) is ≤5%. Applicable conditions: heavily cadmium-contaminated rice fields, arable soil layer (eluvial layer + sedimentation layer) thickness ≥70cm.

[0124] The safe utilization method of the heavily cadmium-contaminated rice fields provided by the present invention can significantly reduce the cadmium content of the surface soil of the heavily contaminated rice fields by adopting technologies such as soil layer swapping, isolation, and fertile surface construction at a low cost. At the same time, it cooperates with improved rice planting technology to ensure that the cadmium content of rice produced in the heavily cadmium-contaminated rice fields meets the standards, and the restoration period is short and the restoration effect is stable.

[0125] The above descriptions are only some preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for safely utilizing heavily cadmium-contaminated rice fields, characterized in that: The steps include: S1. Field measurement and selection: Measure and select fields with arable soil thickness of not less than 70cm; S2. The surface soil and deep soil of the field selected in S1 are transformed, exchanged, isolated and backfilled as follows: (1) Excavation of topsoil: excavate the topsoil 0 to 30 cm from the ground surface and move it to the adjacent field; (2) Deep soil excavation: excavate the deep soil 30 to 60 cm below the surface and move it to the adjacent field, and pile it separately from the surface soil; (3) Backfilling of topsoil: backfilling the topsoil excavated in (1) into the excavated field; (4) Passivation of topsoil: Apply calcium-silicon-based soil passivator to the backfilled topsoil, harrow it thoroughly, and then water it with an appropriate amount of water to make the soil moisture reach 60%~80% and maintain it for 2~3 days; (5) Bentonite isolation: A layer of sodium-based bentonite is laid on the surface soil transformed by (4) to isolate the surface soil from the deep soil to be backfilled; The sodium-based bentonite layer is compacted, with a compaction degree of ≥95%. The thickness of the compacted sodium-based bentonite layer is 3~5cm; the montmorillonite content in the sodium-based bentonite is ≥90%, the pH is 7~10, and the expansion multiple is 20~30; (6) Deep soil transformation: add humic acid, soil conditioner, and microbial agent to the deep soil excavated in (2) and mix thoroughly for transformation; (7) Deep soil backfill: backfill the transformed deep soil from (6) onto the sodium-based bentonite layer from (5) to a depth of 30 to 35 cm; (8) Deep soil maturation: Add appropriate amount of water to the deep soil backfilled in (7) to make the field soil moisture reach 60%~80% and maintain it for 5~10 days; S3. Deep soil pioneer planting: Plant green manure on mature soil, and when the green manure is in its vigorous growth period, grind it into pieces and mix it with the deep soil; S4. Rice planting and management: Plant low cadmium-accumulating rice varieties on the soil treated with S3, and spray manganese, zinc and selenium ternary composite foliar inhibitors during the tillering and booting stages of rice growth. The manganese, zinc and selenium ternary composite foliar inhibitor contains Mn ≥ 3%, Zn ≥ 7%, Se ≥ 0.2%, water-insoluble matter ≤ 2%, and pH 5.5-8.5, so that rice that meets cadmium standards can be safely produced.

2. The method for safe utilization of heavily cadmium-contaminated rice fields according to claim 1, characterized in that: The effective CaO in the calcium-silicon-based soil passivator in step S2 (4) is ≥30%, the effective SiO2 is ≥10%, and the pH is 11-13; the application rate is 4500-7500 kg / hm 2 .

3. The safe utilization method of severely cadmium-contaminated rice fields according to claim 1, characterized in that: In step S2 (6), the organic matter drying basis of the humic acid is ≥55%, the pH is 5.5-7.0, and the nutrients are ≥6%; the amount of humic acid added is 0.5-1% of the dry weight of the deep soil.

4. The method for safe utilization of heavily cadmium-contaminated rice fields according to claim 1, characterized in that: In step S2 (6), the effective CaO in the soil conditioner is ≥30%, the effective SiO2 is ≥10%, the effective MgO is ≥5%, and the pH is 8-10; the amount of the soil conditioner added is 0.1-0.2% of the dry weight of the deep soil.

5. The method for safe utilization of heavily cadmium-contaminated rice fields according to claim 1, characterized in that: In step S2 (6), the microbial agent includes a mixture of nitrogen-fixing bacteria, rhizobia, Bacillus megaterium, actinomycetes, and Bacillus pumilus; The amount of microbial agent added is 20~30g / t soil.

6. The method for safe utilization of heavily cadmium-contaminated rice fields according to claim 1, characterized in that: The green manure planted in S3 is one or more of Chinese milk vetch, rapeseed, and fertilizer radish.

7. The method for safe utilization of heavily cadmium-contaminated rice fields according to claim 1, characterized in that: In step S4, the low accumulation rice variety is selected as indica hybrid rice, and the planting density is 350,000 to 400,000 plants / hm2. 2 , basic seedlings 1.35 million to 1.5 million / hm 2 .

8. The method for safe utilization of heavily cadmium-contaminated rice fields according to claim 1, characterized in that: The method for spraying the foliar barrier agent in step S4 is: 3-5 kg / hm2 of the foliar barrier agent is applied at the tillering stage and the booting stage of rice growth. 2 Dilute with 10 to 30 times of clean water and spray evenly on the front and back of rice leaves.

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